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UNIVERSITY OF HAWAII LIBRARY
APPLICATION OF EMMC-BIOBARREL TECHNOLOGY FOR DOMESTIC WASTEWATER TREATMENT AND REUSE
A THESIS SUBMI'I"l'ED TO THE GRADUATE DMSION OF THE UNIVERSITY OF HAW AI'I IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCmNCE
IN
BIOENGINEERING
DECEMBER 2006
By
liaZhu
Thesis Committee:
Ping-Yi Yang, Chairperson Ping-Sun Leung
Eulsaeng Cho
We certify that we have read this thesis and that, in our opinion, it is satisfactory in scope,
and quality as a thesis for the degree of Master of Science in Bioengineering.
THESIS COMMITTEE
ii
ACKNOWLEDGMENT
The author would like to express my sincere gratitude to Dr. P.Y.Yang for his
guidance and advice during the development of this thesis. Gratitude is also extended to
Dr. P. Leung and Dr. E.Cho, turn for serving on the thesis committee.
The author expresses appreciation to Mr. Charles Nelson and Mr. Dan Paquin of
the Molecular Bioscience and Bioengineering Department who offered continuing help
for the entire program of the study.
Lastly, the author can not forget to thank her husband for his understanding and
moral support.
iii
ABSTRACT
The entrapped-mixed-microbial-cell-biobarrel (EMMC-biobarrel) processes with
both configurations of single-layer and double-layer were investigated for the removal of
carbon and nitrogen simultaneously from synthetic-domestic wastewater with a CODIN
ratio of 5 under various operational conditions. For the single-layer systems, the carrier
was employed at the packing ratios of 10% and 20% based on the bioreactor water
volume. In the double-layer system, carriers were separated into two layers which
occupied the top and bottom parts of the reactor with an overall packing ratio of 13%. At
the organic and nitrogen loading ofO.75kg COD/m3/day and 0.16kg NH3-N/m3/day, all
these systems achieved more than 96% ofSCOD removal and NH3-N removal
efficiencies under continuous aeration. The double-layer system achieved about 40% of
total nitrogen removal, which was comparable with the single-layer system with packing
ratio of20% but higher than the single-layer system with a packing ratio of 10%. The
SRT for the double-layer system and single-layer system with a packing ratio of20%
could be achieved to more than 200 days. Based on the economics analysis, in the
achievement of comparable performance, the capital cost for the double-layer
configuration was lower than that for the single-layer configuration. Therefore, double
layer configuration is recommended for the EMMC-biobarrel process design. EMMC
biobarrel process offers many advantages over the existing wastewater treatment
processes including small space requirement, simple operation and maintenance and .
improved nitrogen removal. It demonstrates great potential for onsite, small scale/land
iv
limited wastewater treatment applications. The installation cost for an EMMC-biobarrel
treatment unit with capacity of 400 gallons/day and 1,500 gallons/day are estimated as
$4,671 and $10,191, respectively, which are comparable or lower than those for the
existing commercial products which also involve the nitrogen removal technology. For
sma11 sca1e/land limited application, the total cost requirement is about $0.90 per 1000
gallons for treating settled domestic sewage per day.
v
CONTENTS
Acknowledgements.......................................................................... .... iii
Abstract... .. . . ...... . .. . . . . .. . .. . . . . .. ... . . . . ... . .. ... .. . . .. .. .. ... . . . . .. . . . . . . . .. .. . . . . . ....... .. iv
List of tables................................................................... .................. x
List of figures.................................................................................... xiv
List of abbreviations............................................................................ xvi
Chapter 1 Introduction and Objectives................................................... I
1.1 Introduction ................................................................................. I
1.2 Objectives............................... .... ............................................. .... 3
Chapter 2 Literature Review.. . . . .. . . . .. ... . .. .. .. . . . .. .. .. .. . . . . . .. .. . . . . . .. .. . .. ........ .. 4
2.1 General....................................................................................... 4
2.1.1 Composition of domestic wastewater.............................................. 4
2.1.2 Purposes of biological domestic wastewater treatment......................... 5
2.2 Domestic wastewater treatment system....... ...... ....... .................. ......... ... 5
2.3 Microbiology of biological nitrogen removal... ........... ......... ......... ...... ...... 6
2.3.1 Traditional concept ofBNR- nitrification and denitrification........ .......... 6
2.3.2 Some new concepts for biological nitrogen removal........................... 11
2.3.3 Simultaneous nitrification and denitrification (SND).......... ........ ..... ..... 13
2.4 BNR for large-scale wastewater treatment............................................. 14
2.5 Alternative BNR processes for land limited applications..... ..................... ... 17
2.5.1 Membrane Bioreactor (MBR) process.... . . . . . . . .... . . . .. .. .. . . . .. .. . . . . . .. ...... 18
2.5.2 Moving Bed Biofilm Reactor (MBBR)...................................... ..... 23
2.5.3 Integrated Fixed Film Activated Sludge Process (IF AS).................... ... 25
2.5.4 Application of Entrapped Mixed Microbial CelIs (EMMC) technology
vi
for nitrogen removal................................................................. 28
2.5.4.1 Technology description....................... ............................. 28
2.5.4.2 Factors affect EMMC performance...................................... 30
2.5.4.3 Application ofEMMC process for real domestic wastewater
treatment..................................................................... 33
2.5.4.4 Moving EMMC system............................................... .. ... 34
2.6 Biological nitrogen removal in onsite wastewater treatment application..... ........ 34
2.7 Bioreactor design- engineering concerns................ ................................. 37
2.7.1 CS1R (completely stirred tank reactor) design- single or in series............ 37
2.7.2 Application ofmuiti-layer design in biological wastewater treatment........ 37
2.8 SlImmary...................................................................................... 37
Chapter 3 Methodology....................................................................... 41
3.1 Experiment approach....................................................................... 41
3.1.1 Immobilization of entrapped cells...................................... ......... .. 41
3.1.2 Influent characteristics.......................................................... ..... 44
3.1.2.1 Composition of synthetic wastewater................................ ..... 44
3.1.2.2 Composition ofreal wastewater.......................................... 45
3.1.3 Fixed bed EMMC-biobarrel system set up........................................ 45
3.1.4 Operational condition................................................................ 49
3.2 Analysis.................................. .................................................... 49
3.2.1 Sample preparation. . ... . . .. .. ... . . .. . . . . .. ... . . .. . . .... . . . . . .. .. ..... . . .. . . . . . . . .. . . 49
3.2.2 Evaluation of process performance................ ................................ 49
3.2.3 Data Analysis.................................................................. ....... 51
3.2.4 Economic Analysis.. ............................................. ............... ..... 51
Chapter 4 Results and Disseussions........................................................ 52
4.1 Fixed bed single-layer EMMC-biobarrel processes.................................... 52
4.1.1 Process performance.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 52
4.1.2lmpact of operation condition on the performance characteristics............. 61
vii
4.1.3 Evaluation of SRT.... ................................. .............................. 65
4.1.4 Comparison ofEMMC-biobarrel and EMMC processes without biobarrel
frame........................... ........................ ........................... .... 69
4.1.4.1 Comparison of carrier characteristics.................................... 69
4.1.4.2 Comparison of performance............................................ ... 70
4.1.5 Summary of single layer EMMC-biobarrel processes for synthetic
wastewater treatment................................................................ 74
4.2 Fixed bed double-layer EMMC-biobarrel process........ .. ........................... 76
4.2.1 Process performance........................................................ ...... ... 77
4.2.2 Impact of operation condition on the process performance characteristics
...................................................................................... ... 79
4.2.3 Evaluation of SRT.................................................................. 82
4.3 Comparison of fixed bed single-layer and double-layer EMMC-biobarrel
process................................................................................... .... 83
4.3.1 Comparison of system configuration. .................. .................... ....... 83
4.3.2 Comparison of SRT accumulation rate........................................... 84
4.3.3 Comparison of performance....................... .............................. ... 86
4.3.4 Comparison of single-layer and double-layer configurations with
engineering concerns ......................................................... ........ 90
4.3.4.1 Technical concern.......................................................... 90
4.3.4.2 Economic concern......................................................... 92
4.4 Real domestic wastewater application by using EMMC-biobarrel process..... .... 94
4.5 Comparison with other compact biological treatment processes................. .... 96
4.5.1 Comparison with MBR process................................... ................ 97
4.5.2 Comparison with MBBR and IF AS processes.................................. 99
Chapter 5 Potential Applieations and Economics Analysis........................... 104
5.1 Application in aerobic treatment unit for onsite wastewater treatment............. 104
5.1.1 Technical potential..... .............................................................. 104
5.1.2 Design Criteria................ ........................................................ 105
viii
5.1.3 Economic evaluation for the aerobic EMMC-biobarrel units with capacities of
40000 and 150000..................................................................... 107
5.1.3.1 Evaluation of capital cost....... ............................................... 107
5.1.3.2 Evaluation of annual O&M cost .... .................. .......... .............. 112
5.2 Land limited! small scale application.................................................... 113
52.1 Technical potential................................................................... 113
5.2.2 Design Criteria................................................................. ........ 113
5.2.3 Economic analysis for the EMMC-biobarrel process with 0.1 MOD
capacity.............................................. ............................... 114
5.2.3.1 Evaluation of capital cost............................................... 114
5.2.3.2 Annual O&M cost....................................................... 118
5.2.3.3 Calculation ofNPW (net present worth)............................. 118
5.2.3.4 Sensitivity Analysis..................................................... 119
5.3 Combined with MBR...................................................................... 121
Chapter 6. Conclusions and Recommendations........ .................... ............ 124
6.1 Conclusions................................................................................. 124
6.2 Recommendations ............................................................................ 125
Reference ........ , .. .. . .. .... .. . .. . . .. .... . . . .. .. . . ...... . ...... .. . . . ..... . . . . . . .. .... .. . .. .. .. ... 127
ix
LIST OF TABLES
Table Page
2.1 Typical characteristics of untreated domestic wastewater........... ....... ... 4
2.2 General comparison ofBNR processes.... ............. .......... ........... .... 17
2.3 Operational conditions of gas permeable membrane bioreactor (Semmens et al., 2003).......... ......... ....... ........ .......... ....................................... 22
2.4 Typical values for effiuent quality parameters for septic tank and A TU (Adapted from Wallace et al., 2004)....... ... ........... ......... ........... .... 36
2.5 Several products that have completed the ETV process for nitrogen reduction in domestic wastewater from individual residential homes....... 37
3.1 Composition of synthetic wastewater............................................. 44
3.2 The characteristics of the real domestic wastewater............................ 45
3.3 Fixed bed EMMC-biobarrel systems description.............................. 46
3.4 Operational strategies.............. ............................................. .... 49
3.5 Analytical methods....... ......... .... ............. ........... ......... ......... .... 50
4.1 Single-layer EMMC-biobarrel processes performance at HRT of9h with intermittent aeration of Ih onl2h off................................... .......... 53
4.2 The test of the significant difference between the removal efficiencies of system I and system II at HRT of9h with intermittent aeration of Ih onl2h off. .... .. . . . . ... .. . . . . .. . .. . . . . .. . . . ...... . . .. . . . ..... . . . . . .... ... . . ..... .. . . ... 53
4.3 Single-layer EMMC-biobarrel processes performance at HRT of 9h with continuous aeration.............................................................. ... 54
4.4 The test of the significant difference between the removal efficiencies of system I and system II at HRT of9h with continuous aeration............... 55
4.5 Single-layer EMMC-biobarrel processes performance at HRT of 6h with continuous aeration.............. .. .............................................. .... 57
4.6 The test of significant difference between the removal efficiencies of system I and system II at HRT of 6h with continuous aeration........... .... 57
x
4.7 Performance of system II at HRT of 6h with continuous aeration for treating influent with a CODIN ratio of 8....................................... 58
4.8 Performance of system II at HRT of 3h with continuous aeration........ ... 59
4.9 The test of significant difference between the removal efficiencies of system I and system II at HRT of 6h and HRT of 9h with continuous aeration ........................................................................... .... 61
4.10 The test of the significant difference between the removal efficiencies of system I and system II under different aeration schedules................. .... 63
4.11 The test of the significant difference of the total nitrogen removal efficiencies of system II at HRT of 6h with continuous aeration using influent CODIN ratios of 5 and 8....... ............. ........... ....... ........... 65
4.12 Comparison ofEMMC-biobarrel carrier and previous EMMC carrier...... 70
4.13 Performance comparison among the medium EMMC carrier, large EMMC carrier and EMMC-biobarrel systems at HRT of 9h with intermittent aeration of Ih onl2h off.............................................. 71
4.14 Performance comparison ofEMMC and EMMC biobarrel processes at HRT of 6h with continuous aeration......................................... ..... 72
4.15 Summary of systems performances under different operational conditions.......................................................................... ... 76
4.16 Double-layer EMMC-biobarrel process performance at HRT of9h with intermittent aeration of Ih onl2h off.. . . ....... .. .. .. . . . ...... .. . . . .... . . . .. .... .. 77
4.17 Double-layer EMMC-biobarrel process performance at HRT of9h with continuous aeration. . . . .. . . .. . . . . . .. .. .. ..... .. .. ... . .. .. .. . . . .. .. .. .. . . . .... . .. . . ... 78
4.18 Double-layer EMMC-biobarrel process performance at HRT of6b with continuous aeration. . . . . .. . .... .. . . . .. . ....... . . .. . . . . . .. .. . . . . . ........ . .... . ... . ... 79
4.19 The test of significant difference of system ill under different aeration schedule.................................. ............................................. 80
4.20 The test of significant difference of system ill at different HRTs............ 81
4.21 Comparison of systems configuration..... ..... ........... ......... ....... ....... 83
xi
4.22 The test of significant differences between the removal efficiencies of single layer system and double layer system at HRT of9h with intermittent aeration of Ih onl2h off.............................................. 86
4.23 The test of significant differences between the removal efficiencies of single layer and double layer systems at HRT of9h with continuous aeration.... .. .. .. . .. ...... .. . . . .... . . . . .. . . . . . .. .. . . .. . . . .. .... .. . . .. . . . .. .. . .. ..... ... 88
4.24 The test of significant differences between the removal efficiencies of single layer system and double layer system at HRT of 6hwith continuous aeration............................ ................................................... 89
4.25 Unit cost for carrier materials.................................................. .... 93
4.26 Materials cost analysis.............................................................. 93
4.27 Process performance ofEMMC-biobarrel system II to treat real wastewater at HRT of9h with intermittent aeration of Ih onl2h off. .... ..... 94
4.28 Performances comparison of system II for treating synthetic wastewater and real wastewater at HRT of9h with intermittent aeration of Ih onl2h off. .. . . . . . .. .. . . . . . .. .. .... ... .. .... . . .... . . . .. .... . . . . . . . .. .... . . . . . . . . . .. . . . .. .... ... 96
4.29 Process performance ofMBR (Fan et al., 1996) compared with the EMMC-biobarrel process.............. ........................ .................... 98
4.30 Performance comparison between multi-stage MBR processes and EMMC-biobarrel process for domestic wastewater treatment................ 99
4.31 General comparison of compact biological wastewater treatment systems 103
5.1 NSF class I effluent performance limits...................................... .... 105
5.2 The characteristics of typical effluent from septic tank.................... ..... 106
5.3 Design criteria for aerobic EMMC-biobarrel unit.............................. 106
5.4 Information of EMMC-biobarrel reactors....................................... 108
5.5 Information of required instruments.............................................. 108
5.6 Materials cost evaluation........................................................... 109
5.7 Labor cost for carrier making........ ......... ..................................... 110
xii
5.8 Other cost estimation...................... ............. ............................ 110
5.9 Total capital costs analysis..................................................... ..... 111
5.10 Design criteria of the EMMC-biobarrel process for sma1I scale wastewater treatment plant..................................................... .... 114
5.11 The volume information for 0.1 MGD EMMC-biobarrel aeration tank..... 115
5.12 Information of required instruments.............................................. 115
5.13 Summary of capital costs for the 0.1 MGD EMMC-biobarrel process...... 117
5.14 Cost information for the 0.1 MGD EMMC-biobarrel process................ 118
5.15 Cost analysis for the 0.1 MGD EMMC-biobarrel process..................... 119
LIST OF FIGURES
Figure Page
2.1 Flow scheme of MLE process (Adapted from Metcalf and Eddy, 2003) 15
2.2 Postanoxic BNR processes (Adapted from Metcalf and Eddy, 2003)...... 16
2.3 Schematic diagram of the MABR (Casey et at., 1998)........................ 21
2.4 Basic MBBR process flow scheme (Adapted from Broch-Due et at., 1997)................................................................................. 25
2.5 MBBR biocarrier (Rusten et at., 1997)...................................... .... 25
2.6 Principle of the moving bed biofilm reactor (Rusten et at., 1997)........... 25
2.7 Typical flow diagram for IF AS processes (Adapted from Metcalf and Eddy, 2003). ............. ................. ......... ......... ............... ......... 26
2.8 An IF AS system can offer the same level of treatment as conventional treatment, while taking up much less space (Johnson et at., 2006).......... 27
2.9 SRT for EMMC carrier system using phenol as substrate (Adapted from Yang et at., 1988).................................................................. 29
2.10 Typical aerobic treatment unit.................................................... 35
3.1 Biobarrel ring and EMMC -biobarrel carrier................................... 42
3.2 EMMC-biobarrel carrier making procedure.... ................................ 43
3.3 Single-layer EMMC-biobarrel processes. .......... ............... ......... .... 47
3.4 Double-layer EMMC-biobarrel process............. ............. ....... ........ 48
4.1 Performance of system II at HRT of 3h with continuous aeration........ ... 60
4.2 SS concentration in effluent of system II at HRT of 3h with continuous aeration. ..... . . . . .... . . . . . . . .. .. .... ...... . .. .. . . . . . . . ..... . . .. .. .... .. .. . . . . . .. ... . . 60
4.3 SCOD and NH3-N removat efficiencies of system II vs. HRT.... ....... .... 62
xiv
4.4 Performance comparison of system I at different aeration schedules....... 63
4.5 Performance comparison of system II at different aeration schedules...... 64
4.6 Performance comparison of system II for treating influent with different CODIN retio........................................................................ 65
4.7 SRT accumulation in system I .................... ........................................ 68
4.8 SRT accumulation in system II............................................... .... 68
4.9 Performance comparison among previous EMMC systems and EMMCbiobarrel system at HRT of 9h with intermittent aeration of Ih onl2h off ........................................................................................ 71
4.10 Performance comparison ofEMMC (medium carrier) and EMMC-biobarrel processes at HRT of 6h with continuous aeration.................. 72
4.11 Performance comparison of system ill at different aeration schedule...... 80
4.12 Performance comparison of system ill at different HRTs..................... 81
4.13 SRT accumulation of system ill (double-layer EMMC-biobarrel processes).. .. . . . .... .. .. .. .. . .. . . . . . . .. .. . . . . . .... .. . . . .... .. . . . .... .. . . . . . . . ... . .. . 82
4.14 SRT accumulation retes of the three systems.................................. 85
4.15 Performance comparison among system I, II and ill at HRT of9h with intermittent aeration of Ih onl2h off......................................... ... 87
4.16 Performance comparison among system I, II and ill at HRT of9h with continuous aeration............................................................... 88
4.17 Performance of system I, II and ill atHRT of6h with continuous aeration.......................................................................... ..... 90
5.1 S ... th· ensltiVlty to e mterest rete .................................................... . 120
5.2 S ··· thl··har ensltiVlty to e e ectriclty c ge rete ........................................ . 121
5.3 Suggested EMMC-biobarrel and MBR integmtion .......................... . 123
xv
ATU
BODs
BNR
DO
ETV
HRT
MLSS
NIl/-N
NDJ--N
NOi-N
NPW
SCOD
SEM
SRT
STIN
SND
TCOD
TN
TSS
LIST OF ABBREVIATIONS
Aerobic treatment unit
5-day biological oxygen demand
Biological nitrogen removal
Dissolved oxygen
Environmental technology verification
Hydraulic retention time
Mixed-liquor suspended solids
Ammonia nitrogen
Nitrate nitrogen
Nitrite nitrogen
Net present worth
Soluble chemical oxygen demand
Scanning electrical microscopy
Solid retention time
Total soluble inorganic nitrogen
Simultaneous nitrification and denitrification
Total chemical oxygen demand
Total nitrogen
Total suspended solids
xvi
Chapter 1. Introduction and Objectives
1.1 Introduction
Oxygen demand and nitrogenous pollutants in wastewater are a potential threat to the
aquatic environment and hence to public health. The oxygen demand and NH/ -N can
result in a DO (dissolved oxygen) depletion of the receiving water body; N0)- and NOi
are considered as the main cause of eutrophication and infant methaemoglobinaemia
(Metcalf and Eddy, 1991). Therefore, biological oxidation including nitrogen removal
from wastewater became an essential treatment process to avoid organics and nitrogen
contamination to the environment.
Biological nitrogen removal involves two successive processes, i.e., nitrification and
denitrification. NH/ -N, the predominant form of nitrogen in untreated wastewater, can
be oxidized to NO)-- N and NOi- N by nitrification, which then converted to nitrogen gas
in the subsequent denitrification process (Kuenen and Robertson, 1988). The two
processes require different conditions: nitrification occurs under aerobic conditions while
denitrification prevails in the absence of oxygen (Sabalowsky, 1999). Therefore, for the
practical application, they are generally designed to occur in two or more reactors.
Current domestic wastewater treatment approaches, including conventional activated
sludge process, mainly serve to remove organics and ammonia from the wastewater, a
large amount of nitrate, however, still remain in the effluent. Two-stage and multi-stage
nitrogen removal were developed to achieve total nitrogen removal. All of these
approaches add to the complexity and the cost of wastewater treatment process and each
of them has limitations (Semmens et. ai, 2003).
I
A number of studies showed that both aerobic and anaerobic conditions can be
established into a single reactor like SND (simultaneous nitrification and denitrification),
which can simplify the conventional biological nitrogen removal process.
The EMMC (Entrapped Mixed Microbial Cell) process has been reported as an
effective technology to remove organics and nitrogen simultaneously from various
wastewaters (Yang et aI. 1994; Yang et aI.l997; Yang et aI. 2002). It has demonstrated
many advantages over conventional wastewater treatment processes such as short start-up
period, long SRT, toleration of shock load and capability of achieving total nitrogen
removal (Cao, 1998). However, according to the previous studies, the high carrier making
cost and low mass transfer efficiency can be two potential problems associated with
EMMC technology when sca1ing up (Cao, 1998; Zhang, 1995). In order to solve these
problems, modifications to the carrier making procedure and carrier distribution in the
reactor need to be made.
Currently, EMMC-biobarrel carrier, a modified EMMC carrier has been investigated
in order to simplify the carrier making procedure and reduce the cost of chemicals for the
carrier making. The EMMC-biobarrel is a plastic-framed media, that is, cellulose
triacetate coated bio-barrel. Compared to the original carrier, the new one may have
many advantages such as lower cost, easier preparation and longer contact time with the
substrate.
An effort for enhancing the mass transfer is to distribute the carrier in two layers by
introducing the plastic cage. The idea behind this approach is similar to the engineering
design concept so-called ''reactors in series".
2
Although these modifications are theoretically feasible, they need to be verified by
experiments. Therefore, this research attempts to evaluate the performances of the
EMMC-biobarrel process with both single- and double- layer configurations in order to
provide the validation for these modifications.
1.2 Objectives
The specific objectives for this study are listed as follows:
(1) Investigate the EMMC-biobarrel processes performance on carbon and nitrogen
removal in a single reactor;
(2) Compare the EMMC-biobarrel process with previous EMMC process;
(3) Compare the single-layer and double-layer EMMC-biobarrel processes;
(4) Compare the performance of the EMMC-biobarrel system with other compact
biological processes;
(5) Develop the optimum design criteria for the potential applications and conduct
economic analysis for the newly developed processes.
3
Chapter 2. Literature Review
2.1 General
2.1.1 Composition of domestic wastewater
Domestic wastewater is defined as the wastewater discharged from residential,
commercial, institutional and similar facilities (Metcalf and Eddy, 1991). It is generated
from our daily chores such as bathing, doing laundry, flushing toilets, preparing meals,
washing dishes, etc. Characteristics of domestic wastewater are shown in Table 2.1.
Table 2.1 Typical eharaeterlsties ofnntreated domestic wastewater· (UnIt: mglL) Concentration
Contaminants Weak Medium Strong
COD 250 500 1000
BODs 110 220 400
Organic-N 8 15 35
NH/-N 12 25 50
Total-N 20 40 85
TSS 100 220 350
TS 350 720 1200
Total-P 4 8 15
>1< From Metcalfand Eddy, Inc. (1991)
Oxygen demanding and nitrogenous pollutants in domestic wastewater are
considered as a potential threat to the aquatic environment and hence to public health.
CODIBODs and NH/ -N can result in a DO (dissolved oxygen) depletion of the receiving
water body; NH/-N can be toxic to fish; N03- and NOi are considered as the main cause
of eutrophication and infant methaemoglobinaemia (Metcalf and Eddy, 1991). Therefore,
domestic wastewater treatment, particularly biological oxidation including nitrogen
4
removal from wastewater became an essential treatment process to avoid organic and
nitrogen contamination to the environment.
2.1.2 Purposes of biological domestic wastewater treatment
Today there are approximately 15,000 wastewater treatment facilities in the United
States (Bitton, 1994). About 75% of them have the secondary treatment, i.e., biological
treatment (Ouellette, R.P. 1991).
The overall objectives of the biological treatment of domestic wastewater include: 1)
transform the dissolved and particulate biodegradable constituents into acceptable end
products; 2) capture and incorporate suspended and non-settleable colloidal solids into
biological floc or biofilm; 3) transform or remove nutrient, such as nitrogen phosphorus;
4) in some cases, remove specific trace organic constituents and compounds (Metcalf and
Eddy, 2003).
2.2 Domestic wastewater treatment system
In U.S., according to the treatment scale, domestic wastewater collection and
treatment system can be categorized into two groups: centralized system and
decentralized system.
Centralized wastewater treatment system refers to a wastewater collection and
treatment system that consists of collection sewers and a centralized treatment facility
(USEP A Glossary). In central systems, the wastewater is transported from the origin to
the central treatment plant, where it is treated and disposed of in compliance with state
and federal regulations. The most common processes used in central municipal
5
wastewater treatment are activated sludge processes and trickling filter processes. The
principals of these two processes will be discussed later in this chapter.
Centralized system mainly serves for heavily populated areas where the wastewater
generation is huge. However, in less populated or rural areas, the centralized system can
be cost prohibitive, therefore, in these areas, decentralized or so called "onsite" treatment
systems are commonly used to treat and dispose of the household wastewater.
Septic system, a natural method of treatment and disposal of household wastes, is
the most commonly used onsite wastewater treatment system. A typical septic system
consists of a septic tank and a drain field that allows treated effiuent to infiltrate into the
soil. Generally, septic system is cost effective and when functioning, it is effective at
removing pollutant before they enter the environment. However, it has been decided that
213 of the U.S. is unsuitable for septic systems due to the geological and hydrological
conditions. The improperly-sited septic tank may result in release of pollutant (USEP A,
2000). Fortunately, many alternative technologies/processes have been developed to
replace the failure of septic system. Among them, aerobic treatment unit (ATU) is
considered the most promising alternative to the conventional septic system. More
detailed information such as configuration, design concept and operation of ATUs will be
presented later in this chapter.
2.3 Microbiology of biological nitrogen removal (BNR)
2.3.1 Traditional concept of BNR - nitrification and denitrifieation
Biological nitrogen removal requires two successive processes: nitrification and
denitrification. Nitrification converts ~ + to more oxidized forms such as N0)- or NOi,
6
which is then reduced to nitrogen gas or N20, NO by the following denitrification
process (Kuene and Robertson, 1988).
Nrtrijication
Biological nitrification is generaI1y considered as a two-step process in which
ammonia is oxidized to nitrate with nitrite as an intermediate. Autotrophic
microorganisms Nitrosomonas and Nitrobacter are the most frequently identified genus
associated with these two steps respectively. The energy-yielding two-step oxidation
from ammonia to nitrate can be expressed as follows:
First step: Nl4'" +1.502 NiJrosoommos) NOz"+2W +H20 [aGo' -275kJ morl]
Second step: NOz"+ 0.502 -) N03" [[aGo' -74kJ morl]
OveraI1:
(Schmidt et al., 2003)
The above total oxidation reaction indicates that the oxygen required for complete
oxidation of ammonia is 4.57g Oz/g N. Alkalinity consumption is also suggested, about
7.l4g of alkalinity (as CaC03) are destroyed for removing 1 gram of ammonia nitrogen.
Denitrijication
Denitrification is termed as the reduction of oxidized nitrogen formation such as
nitrate or nitrite to gaseous nitrogen gas compounds (NO, N20, N2) (Schmidt, et al.,
2003). This process is carried out by a variety of facultative heterotrophic bacteria which
can utilize nitrate/nitrite as finial electron acceptor in the absence of oxygen. Unlike
nitrification, denitrification requires organic carbon as electron donor, these carbon
source may be from 1) biodegradable soluble COD in influent; 2) biodegradable soluble
7
COD release from endogenous decay; and 3) exogenous carbon source such as methanol
(Metcalf and Eddy, 2003).
Similar to nitrification, denitrification is generaI1y considered a two-step reaction.
The stoichiometric equations for denitrification using methanol as carbon source are
expressed as follows (McCarty et aI., 1969):
First step: NOi+0.33CH30H --> NOi+O.67H20
Second step: NOi + 0.5 CH30H-->O.5N2+O.5C~+O.5H20+0li
Overall: N03 ·+O.83CH30H-->O.5N2+O.833C~+ I . 1 67H20+0li
Note that the aIIcaiinity produced during the denitrification process result in a 50%
replacement of that consumed during nitrification. Therefore, the overaI1 theoretical
aIIcaiinity consumption is 3.57g (as CaCDJ) for removing 1 gram of ammonia nitrogen
from wastewater via a nitrification/denitrification process.
Environmentfll factors affect nitrljication and denitrification
00 concentration
The effect of DO concentration on nitrification has been widely studied. Dissolved
oxygen has been reported an "absolute requirement" for autotrophic nitrification (Barnes
and Bliss, 1983). A DO concentration of 2m gIL was considered as a cutoffvaIue for
achieving complete nitrification without oxygen transfer limitation (W"Ild et aI., 1971).
Note that the nitrification/denitrification efficiency may relate to the size of the floc or the
thickness of the biofilm due to diffusion limitations on the penetration of oxygen into the
8
interior of the floc or biofi1m (Barnes and Bliss, 1983; Sedlak, 1991). The operating DO,
therefore can be higher than 2mg/L. For certain processes which using larger-size media
(carrier), such as MBBR and EMMC process, a DO concentration of 4-6 mg/L is
recommended for achieving complete nitrification. (Rusten et al., 2006; Cao, 1998).
Denitrification can be occurred at DO is lower than Img/L, with optimum results
occurring at zero DO (Sedlak, 1991; Barnes and Bliss, 1983).
pH
pH can affect nitrification in a significant way. According to Sedlak (1991),
nitrification is pH-sensitive when pH is below 6.8 or above 8.6. Negligible nitrification
rate is observed at pH oflower than 6.0 at any temperature and the optimum pH value for
nitrification is reported at approximately 7.5-8.0 (painter and Loveless, 1983).
As with nitrification, the optimum pH for denitrification is in the range of7 to 8
(Metcalf and Eddy, 2003). In addition, since these two processes are complementary in
alkalinity consumption/generation, maintaining pH is generally enhanced using
biological denitrification (Metcalf and Eddy, 2003).
SRT (Sludge age)
Because nitrifiers grow much slower than heterotrophic bacteria, which comprises
the great portion of the biomass in both biofi1m and suspended growth systems, a long
sludge age (SR T), therefore, is required in order to have a sustainable nitrifier population
(Metcalf and Eddy, 1991 b). Although it has been suggested that denitrification rate can
be reduced at a higher SRT of over 15 days in extended activated sludge process (Barnes
and Bliss, 1983), a recent study (Sabalowsky, 1999) determined that the denitrification
rates were still adequate at an even longer SRT (over 24 days).
9
Temperature
Numerous studies have been conducted on the temperature effect on
nitrification/denitrification processes. An optimal temperature for nitrification bas been
reported approximately 35°C, with an overall range for growth between 4°C and 45°C to
50°C (Prakasam and Loehr, 1972; Barnes and Bliss, 1983). Denitrification may occur
between OOC and 50°C, with optimum reaction range at 35-50oC (Barnes and Bliss, 1983).
CODlNratio
CODIN ratio is an important parameter for both nitrification and denitrification
processes. For nitrification, CODIN ratio directly influences the growth of the
competition between autotrophic and heterotrophic microorganism populations (Cheng
and Chen, 1994). A high organic loading, therefore, can result in the nitrification
inbibitation. It bas been shown that BODs levels over 4Omg/L can cause a reduction of
nitrification efficiency up to 50% (Azevedo et al., 1995).
On the other hand, availability of carbon source is essential to denitrification since
the heterotrophic denitrifiers require organic carbon for the synthesis of new cells and for
respiration to obtain energy used to synthesize the cells. Generally, a CODIN ratio range
between 20/1-25/1 is considered to be ideal for "healthful" nitrogen content of biomass in
an aerobic treatment system (Gaudy and Gaudy, 1988). However, the CODIN ratio in
domestic wastewater is usually much lower (from 211-15/1).
A BODITKN ratio of 4/1 in the influent wastewater is generally considered to be
sufficient for effective nitrate reduction by preanoxic process (Metcalf and Eddy, 2003).
Furthermore, it has been concluded that the natore of carbon can have significantly
impact on denitrification rate, with the highest rate occurring at the availability of easily
10
biodegradable forms. Suitable carbon source for denitrification include methanol, acetic
acid, citric acid, acetone, with methanol being the most preferred carbon source due to
the low cost, high effectiveness and availability (USEP A 1975).
Cao (1998) investigated the impact of CODIN ratio on the nitrogen removal
performance ofEMMC process. SCODIN ratio of 15 was reported as the optimum
condition for medium carrier system, organic and nitrogen removals were 99% and 95%
respectively at hydraulic retention time of 12h, intermittent aeration of Ih onl2h off. It
has also been reported that SCODIN ratio of7 to 15 for higher removal efficiencies of
both organics and nitrogen, and SCODIN ratio of 4 is the mjnjmum requirement for the
nitrogen removal.
2.3.2 Some new concepts for biological nitrogen removal
Traditional concepts for 8NR have been used for the design of mainstream domestic
wastewater treatment for decades. In recent years, some new concepts in 8NR
microbiology have been developed, which may be a good complementary to the
traditional theory and lead to an increasing flextbility for wastewater treatment design
(Schmidt et al., 2005).
Heterotrophic nitrification and aerobic denitrification
Although autotrophic microorganisms are generally considered responsible for
nitrification, various groups of heterotrophic bacteria and fungi have been fouod to be
able to carry out nitrification (Robertson et aI., 1988). The theory of heterotrophic
nitrification explained the phenomena of complete nitrification at DO as low as 0.5 mgIL.
II
Compared to those of autotrophic nitrification, rates of heterotrophic nitrification are
much lower (Robertson et al., 1988). Therefore, heterotrophic nitrification was thought
to occur preferentially under conditions which are not favorable for autotrophic
nitrification. The favorable environmental conditions for heterotrophic nitrification were
summarized as 1) low DO concentration; 2) High CODIN ratios; 3) short SRT and 4)
acidic environment (Focht and Verstraete, 1977; van Neil, 1991).
Denitrification was originally considered to occur under strictly anoxic condition
(Knowles, 1982). However, certain species of organisms were found to be able to
denitrify aerobically (Meiberg et al., 1980; Robertson and Kuenen, 1995). Contrary to
anoxic denitrifiers, aerobic ones usually appear to 1) have slower denitrification rates, 2)
have an ecological advantage in niches with fluctuating aerobic/anoxic period and 3)
prefer certain organic substrates (Rovertson and Kuenen, 1995; Bang et al., 1995).
PartioJ Nitrification
According to traditional concepts, BNR is designed to follow the sequence as:
Nl4 + -+ N02--+N0)--+ N~--+N2.
A new path to achieve biological nitrogen removal, "partial nitrification" has been
suggested (Schmidt et al., 2005; Yeom et al., 1999). In partial nitrification, ammonia
nitrogen is oxidized to nitrite, but not to nitrate. The nitrogen removal sequence, therefore,
appears to be:
NH/ -+ N02--+ N2.
There are significant benefits in terms of resources consumptions (Hellinga et al.,
1998; Turk and Mavinic, 1989) if partial nitrification is applied. This process needs less
12
aeration and the subsequent denitrification consumes less COD. It is cost-effective
especially when the influent CODIN retio is low. Besides, this process has demonstmted
many advantages such as higher denitrification rete, lower biomass yield and less nitrite
toxicity effects can be achieved (Turk and Mavinic, 1989).
The key point of this process is to prevent the oxidation from nitrite to nitmte. To
achieve this goal, the following guidelines need to be followed: 1) use simultaneous
and/or alternating nitrification/denitrification process in the same reactor; 2) maintain low
DO during aeration; 3) keep the bacteria in direct contact with the influent in oxygen
deficient condition; 4) mise the pH; 5) add hydroxylamine to the reactor and 6) maintain
the reactor temperature near 25°C (Yeom et aI., 1998 citing various sources).
2.3.3 Simultaneous nitrification and denitrification (SND)
According to the traditional concepts ofBNR, it is impossible to achieve
nitrification and denitrification in the same reactor since the favomble conditions for
these two processes to occur are very different. However, a number of studies showed
that if both aerobic and anaerobic conditions can be established in a single reactor,
simultaneous nitrification and denitrification (SND) can be achieved (Yamagiwa et aI.,
1995; Yang et aI., 1992, 1997; Zhao, et aI., 1998). This theory can explain the phenomena
of partial total nitrogen removal in aerated activated sludge process (USEP A 1987).
The concept of SND has led to the development of various process including attach
growth (MABR) and cell-immobilization (EMMC) (Hibiya, et aI., 2003; Yang et aI.,
1992, 1995, 1997). Compared to the conventional separated stage BNR processes, SND
13
process offers the potential to save energy, carbon source and overall reactor volume
(Metcalf and Eddy, 2003; Munch et aI., 1996).
Numerous studies have been conducted to investigate the favorable conditions for
SND (Hibiya et aI., 2002; Yeom et aI., 1999; Yang et aI., 1997). Generally, the key
control parameters include: a proper oxygen transfer rate which must be sufficient for
organic oxidation and nitrification while low enough to satisfy denitrification; a spatial
distribution of bacteria which are responsible for nitrification and denitrification; a
suitable carbon source and CODIN ratio (Hibiya et aI., 2003; Watanable et aI., 1995).
2.4 BNR processes for Iarge-scale wastewater treatment
According to the design/operation concepts, processes for BNR can be basically
grouped into three categories: preanoxic, postanoxic and SND.
Preanoxic BNR
Preanoxic BNR refers to an anoxic-aerobic operation sequence. One of the most
commonly used BNR process is the modified Ludzack-Ettinger (MLE) process which is
presented in Figure 2.1. In MLE process, the nitrate fed to the anoxic zone is from
recycle activated sludge and internal recycle from aerobic tank. With proper operation
and sufficient carbon source in the influent, the average nitrate nitrogen concentration in
the effiuent is in the range from 4-7 mgIL when treating domestic wastewater (Metcalf
and Eddy, 2003).
14
I Influent - r--
Anoxic Aerobic
L,--J
Sludge rectrCUlatton
Figure 2.1 Flow seheme of MLE proeess (Adapted from Metea1f and Eddy, 2003)
Effluent
Many other BNR processes have been developed based on the preanoxic concept
such as eMLE, SBR, NitroxlM, BiodenitrolM (Metcalf and Eddy, 2003).
Postanoxic BNR
Postanoxic BNR process is characterized by an operating sequence in which an
anoxic zone following with aerobic zone. Nitrate/nitrite formed in aerobic zone can be
denitrified in the following anoxic zone. Since most of the BOD has been removed in the
previous step, organics which support the denitrification process are either from
endogenous or exogenous source. Typical postanoxic BNR processes are presented in
Figure 2.2.
Other postanoxic BNR processes include Bardenpho (4-stage), oxidation ditch
(Metcalf and Eddy, 2003).
15
( I I ) Oxidation ditch
Two-stage with an external carbon source
Figure 2.2 Postanoxic BNR processes (Adapted from Metealf and Eddy,
Simultaneous nitriftcation and denitriftcation (SND)
In SND process, nitrification and denitrification processes are designed to occur in
the same reactor. Oxidation ditch with sufficient volume is able to accommodate both
nitrification and denitrification at lower rates under low DO concentration (O.5mgIL).
Sym-Bio™ system is basically a low DO oxidation ditch system with appropriate control
of DO and bacteria content of coenzyme nicotinamide adenine dinucleotide (NADH).
With proper operation, effiuent nitrate nitrogen and ammonia nitrogen concentrations of
less than 3mgIL and ImgIL, respectively, have been achieved (Metcalf and Eddy, 2003).
A general comparison among the above BNR processes is listed in Table2.2.
16
T bl 22 Ge ral a e . De ariso fBNR rompi DO , .,rocesses Process Advantages Limitations
Saves energy DO control is required
BOD is removed before aerobic zone Compl"" operation is required in many
Preanoxic Alkalinity is prodw:ed before nitrification processes
Design includes an SVI selector Potential Nocardia growth problem
Resistant to load variations without Large reactor volume is required
Postanoxic without carbon affecting emuent quality significantly Skilled operation and control are required
addition Has good capacity for nitrogen removal;
Less than 10mg/L TN is possible
Postanoxic with carbon Capsble of achieving .muent nitrogen Higher operating cost due to purchase of
levels less than 3mgIL methanol addition
Methanol control required
Low emuent nitrogen level possible Large reactor volume; skilled operation
(3mgIL lower limit) also required
Significant energy savings possible Process control system required
SND Process may be incoJporated into existing
facilities without construction
SVI control enhanced
Produces Alkalinity
·(Adapted from Metcalf and Eddy, 2003)
2.5 Alternative BNR processes for land Umited appfieatioD
Conventional biological BNR processes usually require large space. However, they
may not be appropriate options for some cases due to the insufficient space availability.
In these cases, a compact biological has to be applied, particularly in the small
communities where land is strictly limited.
The compact systems include membrane bioreactor (MBR), moving bed biofilm
reactor (MBBR), entrapped mixed microbial cells (EMMC). Contrary to the conventional
processes, the design concepts for these systems are at least "double fold", i.e., the
17
combinations of various technologies such as attach growth, suspended growth, cell
immobilization and membrane separation technologies are presented in these systems.
2.5.1 Membrane bloreactor (MBR) process
General
Membrane bioreactor technology, a combination of activated sludge process and
membrane separation, has been investigated over 30 years and several generations of
MBR systems have evolved (Cicek et aI. 2005).
Compared to conventional biological process, MBR has demonstrated many
technical advantages, include:
(1) high quality effluent, ideal for post membrane treatment
(2) space savings enabling upgrading of plants without land expansion
(3) shorter start-up time
(4) low operating and maintenance manpower requirement
(Cicek et aI., 2005 citing various sources)
Despite the above benefits, MBR technology, however, is facing some research and
development challenges which limit its commercial application, such as membrane
fouling, pretreatment, membrane lifespan, costs, plant capacity, etc.
MBR design for nitrogen removal
Many researches (Cicek et a. 1998; Comerton et aI. 2005; Y oon et aI. 2004; Fan et aI.
1996) have been conducted for municipal and domestic wastewater treatment using MBR
technology. In general, MBR process is able to achieve high soluble COD removal
18
(>93%), and, because of the ultrafiltration membrane, the effluent did not contain any
suspended solid. Regarding to nitrogen removal, MBR process bas been shown to
provide completely nitrification (>99%) and partial denitrification of municipal
wastewater, resulting in low ammonia and organic nitrogen concentrations but high
nitrate concentrations. Modifications to basic MBR process therefore have been
developed for achieving further nitrogen removal.
MBR processes for nitrogen removal, based on the design concepts, can be grouped
into the following types.
Multl-slilge nitrogen removal
A number of studies have been conducted to use multi-stage MBR to enhance
nitrogen removal. Y oon et al. (2004) reported that RANT, a modified MBR system,
composed of anoxic/anaerobiC/oxic/anoxic stages with hollow fiber membrane, is able to
achieve over 70% of1N removal efficiency from municipal wastewater at HRT of 6h.
Another research on modified MBR system, (Qin, et al. 2005) shows that an anoxic/oxic
MBR system can remove about 60% of total nitrogen from domestic wastewater and the
organics and suspended solid removals are relatively high.
Similar to the situation of conventional activated sludge process, although multi
stage strategy does improve the nitrogen removal to a certain extent, this approach adds
to the complexity and the cost of the wastewater treatment process. Moreover, many
studies have shown that without carbon source addition, the multi-stage treatment can
only remove about 70% of total nitrogen. Addition of carbon source, however,
dramatically increases the costs related to the equipment, chemical and driving energy.
19
Intermittent aeration
Introducing intermittent aeration to conventional MBR process has been reported as
a possible approach to enhance biological nitrogen removal. Yamagiwa et aI. (1995)
investigated simultaneous removal of total organic carbon (TOC) and nitrogen (TN) by a
crossflow membrane reactor for small-scale treatment of domestic wastewater. Synthetic
wastewater with a BODfI'N ratio of 12 was employed as influent. At HRT of 6-12h, the
system achieved more than 90% TOC and 84% TN removal under intermittent aeration.
Ick-Tae et al., (1999) conducted a study to evaluate the impact of intermittent aeration on
nitrogen removal. In their studies, a submerged hollow fiber membrane was applied in
lab-scale to treat household wastewater including toilet flushing water. The results came
out that at HRT of8-lSh, 96% of TCOD and 100% SS could be removed; the average
TN removal was 83%. Besides, track study and denitrification batch study indicated that
the endogenous denitrification may playa significant role in total nitrogen removal,
particularly when influent BODfI'N ratio was low.
Membrane-aerated biofllm reactor (MABR)
MABR process, a combination ofbiofilm and MBR technology, was proposed to
achieve simultaneous carbon and nitrogen removal in a single reactor. A MABR is shown
schematically in Figure 2.3. In MABR processes, an oxygen concentration gradient is
created across aggregated microorganisms, so that both aerobic and anaerobic conditions
can be established inside a single reactor resulting in simultaneous carbon and nitrogen
removal.
20
Gas Phase Membrane
0,
Liquid
Biomass Co,.
Figure 2.3 Sehematle diagram of the MABR (Casey et aL, 1998)
IIlDiya et aI. (2003) reported that at HRT of 6h with continuous aeration, MABR
process was capable to remove more than 90% TOC and 1N from synthetic influent
(with a TOCIN ration of 10). By analyzing the bacteria activity in the vertical and
horizontal direction, it was concluded that the removal of carbon and nitrogen
compounds could be accomplished efficiently by using various kinds of bacteria
distributed vertically and horizontally in a single reactor.
Semmens et aI. (2003) investigated COD and nitrogen removals by biofilms
growing on a gas permeable membrane. In this research. an influent with CODIN of 5
was employed to simulate the actua1 domestic wastewater. The operating condition of the
experiment is summarized in Table 2.3.
21
Table 2.3 Operational conditions of gas permeable membrane bioreactor
HRT 6h-12h (in the end of experiment, the actual HRT
was reduced to 1.25h due to accumulation of sludge)
Aeration
Operation days
MLSS (by the end)
Thickness ofbiofilm
Starting-up period
continuous
190d
>2000Omgll
600J,lm
20d (nitrification)
The results illustrate the gas permeable membranes-biofilm process is capable to
remove the carbon and nitrogen efficiently. A short start-up period was also observed: the
COD removals rose to over 90% in about 40 days, nitrification was established within 20
days.
Also, this study provided sufficient evidence to show that the single-stage membrane
aerated bioreactor can effectively remove COD and nitrogen in a single reactor. However,
it also demonstrated the challenges for practicing this new technology, such as rapid
membrane clogging at the end of operation; optimized thickness ofbiofilm; scale-up
design etc.
Combination of MBR-RO process
Membrane bioreactor and reverse osmosis (MBR-RO) system is a newly developed
technology to assess potential reuse applications of municipal wastewater. In MBR-RO
process, the nitrate in the effiuent ofMBR system can be significantly reduced (>90%)
22
by RO, in the meantime, the concentrations ofTHMs (trihalomethanes), HAAs
(haloacetic acids),total cloliform, are also meeting the US EPA drinking water limitation.
Therefore, the MBR-RO process is a promising technology for producing high quality
water directly from the sewage (Comerton et al., 2005; Qin et al., 2005). However, the
costs related to membrane production, membrane fouling, especially to the high energy
requirement for the RO limits the application for this new technology.
These modified MBR processes demonstrate great potential to improve nitrogen
removal. However, most of these studies are still in research stage, a lot of factors such as
energy cost, fouling prevention need to be evaluated for scaling up.
2.5.2 Moving bed biofiIm reactor (MBBR)
MBBR is another compact design for wastewater treatment which is presented in
Fignre 2.4 (Broch-Due et al., 1997). This process utilizes the small carrier elements serve
as mobile carrier for biomass accumulation. The movement of carrier is normally caused
by air agitation or mixers. A sieve is arranged in the outlet of the reactor to prevent the
carrier to be ''washed out" (Metcalf and Eddy, 2003). The idea behind ofMBBR process
is to represent the best features of activated sludge process and biofilter processes,
without "including the worst". Contrary to activated sludge process, no sludge recycle is
required in MBBR process, resulting in a simple operation/maintenance and energy
saving. Contrary to conventional biofilm processes, MBBR utilizing the entire aeration
tank for biomass growth; it also has a very low head-loss (Rusten et al., 2005).
The freely-move carrier elements play the key role in MBBR process. The cylinder
shaped carriers (about IOmm in diameter and 7mm in height), are made of polyethylene
23
(density 0.96g1cm\ with a cross inside the cylinder and 10ngitudinaI fins on the outside
(Metcalf and Eddy, 2003). They are able to provide great specific area for biomass
growth. The packing may fill 25% to 70% of the tank volume. The specific area of the
packing is about 500m2/m3 of bulk volume and 300m2/m3 of 60% fill (Rusten et al., 2005).
Figure 2.5 presents the photo ofMBBR biofilm carriers.
MBBR offers flexibility for application. It may be used for aerobic, anoxic and
anaerobic processes, as illustrated in Fig.2.6.
Rusten et al. (1995) designed a MBBR process for nitrogen removal in which
nitrification and denitrification are design to occur separately in six reactors, three for
nitrification and three for denitrification. Raw municipal wastewater with TN
concentration of21l-2Smg/L was employed as influent. Both preanoxic and postanoxic
(using sodium acetate as external carbon source) processes were examined. With
preanoxic design, 500/.-70% of total nitrogen removal was achieved at a recirculation
ratio of approximately 2.0 and a total bed hydraulic residence time of 6 hours in the
MBBR. Wile with the postanoxic and external carbon source, the system could easily
achieve 800/.-90% total nitrogen removal at total empty bed hydraulic residence times
less than 3 hours.
According to Rusten et al. (2005), MBBR has become very popular in Europe. More
than 400 large-scale treatment plants adopted this process in operation. Additionally, in
Germany, MBBR is also applied for small scale or onsite wastewater treatment.
Moreover, an "ongoing" effort of applying MBBR in fish farm treatment is being made.
24
MBBR Secondary clarifier
~/
Figure 2.4.Basic MBBR process flow scheme (Adapted from Broch-Due et aI., 1997)
Figure 2.S MBBR biocarrier (Rusten et aI., 1997)
• • • ~ . I
Figure 2.6 Principle of the moving bed biotilm reactor (Rusten et aI., 1997)
2.S.3 Integrated fixed film activated sludge process (IF AS)
Integrated fixed fi lm activated sludge process (IF AS) provides the combination of
suspended culture growth and attached growth. In this hybrid system, small carriers,
25
usually made of polyurethane (density 0.95g/cm3) or other plastic material, are added in
the aeration tank of activated sludge process in a free-floating fashion and retained by an
effluent sieve (see Fig.2.7). The volume occupied by the carriers usually accounts for
20-30% of the total reactor volume (Metcalf and Eddy, 2003).
influent . . . . . . . . . . . . . . . . . . . . . ......... . . .
................. ......... . . . ... . ........... . .... . ......... .. . ... . ........... . .... . ......... . . .... . ................ .
eftluent
Figure 2.7 Typical Dow diagram for IF AS processes (Adapted from Metcalf and Eddy, 2003)
Similar to MBBR process, IF AS is also designed to offer the advantages of
suspended growth and attached growth without the drawbacks ofMBBR by the addition
of small media elements. The difference between these two processes is that in the
MBBR process, the contaminant removal is mostly achieved by the floating carriers and
suspended solid concentration is very low, sludge recycle therefore can be eliminated.
While in IF AS process, both suspend solid (provided by activated sludge process) and
floating carrier (attached growth) contribute to the pollutant removal, sludge recycling is
therefore required.
Compared to MBBR process, IF AS is more attractive to the wastewater treatment
plant owner for upgrading the existing treatment facility for increasing treatment capacity
and/or improving nitrogen removal (Campell and Schnell, 2001; Johnson et al., 2006).
The idea of using IFAS for upgrading existing facility is simply presented by Figure 2.8.
26
Since the small carrier is able to provide large specific surface area for microbial growth,
the addition of carriers therefore allows the bioreactor to be operated at 2-3 times greater
biomass concentration than conventional activated sludge process (Gilligan and Morper,
1999). The capacity of the existing system thus can be increased without physical
expansion. Moreover, nitrification efficiency can also be promoted due to the higher SRT
in IFAS system (Gilligan and Morper, 1999).
Conventional
Extended aenuion
IFAS
Figure 2.8 An IF AS system can offer the same level of treatment as conventional treatment, whHe taking up much less space (Johnson et aI., 2006)
IF AS is proposed as an inexpensive device for upgrading existing activated sludge
facility compared to the expansion of the conventional treatment process. It has been
reported that for expanding an activated sludge factory with existing capacity of
45,600m3/d (12 USMGD) to 60,65Om3/d (33% expansion), the capital cost of applying
27
IFAS process (adding ConoPac media) was about 54% of the cost for conventional
expansion (Water Technology International, 1998). The operating cost has been reported
to be same to that of conventional activated sludge process by many case studies
(www.brentwoodprocess.com).
In terms of nitrogen removal, performance of IF AS system varies depending on the
media material used. Plastic-media is normally only designed for improving nitrification
(Johnson et al., 2006). A full-scale case study in u.S. (White, 1997) for an IFAS
(AccuWeb) system demonstrated that adding AccuWeb media to conventional activated
sludge process improved nitrification by 24% during winter season. For achieving total
nitrogen removal in the plastic-media cases, second (anoxic) tank is required. Sponge
media can be used for simultaneous nitrification and denitrification. A pilot study in
Germany (Gilligan and Morper, 1999) reported that Linpor® -eN process, an IF AS with
certain necessary expansion using polyurethane as media, achieved 98% BODs removal,
100% nitrification and 60% 1N removal. The high nitrogen removal efficiency could
partially relate to the reactor expansion (i.e., higher HRT). In addition, it has been
reported that sponge media is more fragile compared to the plastic one.
2.5.4 Application of entrapped mixed microbial cells (EMMC) technology for
nitrogen removal
2.5.4.1 Technology description
Entrapped mixed microbial cells (EMMC) technology is a mixed microbial cell
entrapped technology developed by Yang and his coworkers (1988). Cellulose triacetate
(CTA), a water-permeable polymer, is used as gel material to confine the migration of
28
microorganisms. The advantages of employing CT A for carrier-making such as simpler
preparation and better mechanical strength have been demonstrated by Yang, et aI.,
(1988). Also, it is interested to note that CTA is also a widely used membrane material
(Gander, et aI., 1999).
The principle ofEMMC is to provide longer SRT for slow growing bacteria by the
innovative entrapment design. The highly porous inner structore ofEMMC carrier allows
the entrapped microorganisms to grow using the substrate in the influent, the biomass in
the bioreactor hence can be accumulated to a high concentration. Since most of the
biomass is entrapped inside the carrier and hardly to be washed out even when the low
HRT is applied, the SRT therefore can be prolonged dramatically. Moreover, the second
clarifier can be eliminated due to the low SS concentration in the effiuent (Yang, et aI.,
1988). Figure 2.9 presents the graph ofSRT accumulation in EMMC process.
130 [ 120 . 110 100 90
I 80 70 80
Iii 50 .. 40 30 20 10 0
-10 3 6 7 9 11 13 15 17 19 21 days of operation
Figure 2.9 SRT for EMMC carrier system using phenol as substrate (Adapted from Yang et aI., 1988)
29
The long SRT provided by EMMC system prevents the slow-growing nitrifiers from
being washed out. The nitrification therefore can be improved significantly. In addition,
EMMC system offers the potential to achieve total nitrogen removal via simultaneous
nitrification and denitrification (SND) process. As discussed previously, the key
requirements for SND include proper DO gradient, presence of responsible bacteria for
nitrification and denitrification, and favorable CODIN ratio. In EMMC system, co
current aerobic and anoxic can be well established due to the oxygen uptake and diffusion
limitation. With the presence of nitrifiers and denitrifiers and organics substrates from
influent, it is possible that nitrification can be occurred in the surface part of carrier while
denitrification can be occurred in the inside part (Cao, 1998). Simultaneous nitrification
and denitrification has been observed in a number ofEMMC studies (Yang, et al., 1997;
Zhang, 1995; Su, 1999; Song, 2003).
EMMC technology has been reported to successfully treat various wastewater
including synthetic wastewater, domestic wastewater, nitrate rich wastewater, pesticide
wastewater, piggy and milk parlor wastewater, etc. The main advantages ofEMMC
process over traditional activated sludge processes include: long SRT, short start-up
period, better nitrogen removal and toleration of shock load.
2.5.4.2 Factors affect EMMC performance
Numerous studies have been conducted to investigate the effects of various
conditions on the performance ofEMMC system using synthetic wastewater (Yang, et al.,
30
1988; Zhang, 1995; Cao, 1998; Suo 1999; Yang, et al., 2002). The factors which may
affect performance of EMMC are snmmarized as follows:
Temperature
Zhang (1995) investigated the effect of temperature on EMMC process performance.
Three different temperature, WOC, 25°C and 30°C were employed. It was concluded that
SCOD and TSS removal were not affected by the change of temperature. However,
nitrification and total nitrogen removal showed the response to the temperature change. It
was reported that nitrification and total nitrogen removal efficiencies decreased 30%
when the temperature decreased from 25°C to 10°C and total nitrogen removal increased
about 10% when temperature increased from 25°C to 30°C. This result can be explained
by the bacteria activity under different temperature conditions. It was also suggested that
optimum temperature condition for EMMC process was in the range of 20°C to 30°C.
pH and alkalinity
Influent pH of 7.5-8.5 is considered as the optimal condition for achieving total
nitrogen removal by EMMC processes, which is correspondent to the optimal condition
for nitrification and denitrification. However, the alkaHnity of influent (14Omg/L and
230mg/L as CaC~) showed less impact on the TN removal compared to other factors
such as CODIN ratio (Cao, 1998).
31
Influent CODIN ratio
EMMC process demonstrated the good potential to treat both readily biodegradable
substrates, such as glucose and sucrose, and some toxic substrates such as phenol (Yang,
et al., 1988).
CODIN ratio is a very important parameter for simultaneous nitrification and
denitrification. Cao (1998) investigated the effects of CODIN ratio on the total nitrogen
removal ofEMMC process. The highest total nitrogen reduction (>92%) was observed
when the influent CODIN ratio is IS. While with a CODIN ratio of 4, the total nitrogen
removal is about 45%. This result suggests that EMMC is able to achieve good nitrogen
removal even at low CODIN ratio compared to other processes.
Air supply
DO gradient is a key factor for achieving simultaneous nitrification a,nd
denitrification. In EMMC process, DO is controlled by applying various aeration
schedules. Both continuous aeration and intermittent aeration are employed for organics
and nitrogen removal. Intermittent aeration has been suggested as an efficient approach to
enhance the total nitrogen removal due to the sufficient time of the system combined
anoxic/anaerobic stages. Cao (1998) recommended a non-aeration/aeration time ratio of
3-4 for achieving higher TN reduction. The overall liquor DO range during intermittent
aeration is usually within 0-8 mgIL (Zhang, 1995; Cao, 1998), suggesting the air flow
rate should be high enough during the aeration time for achieving high nitrification
efficiency. Cao (1998) reported with the influent CODIN ratio of IS and intermittent
32
aeration of 0.5h on and 2h off, EMMC system achieved more than 92% of total nitrogen
removal.
Loading rate
Yang et al. (1988) investigated the effect ofTCOD loading rates on EMMC
performance by stepping increasing the loading from 1.2 to 12g1Ud After 92 days of
operation, it was found loading rate of about 4 to 6g1Ud could achieve the maximum
SCOD removal efficiency of98%. In Song's (2003) study, EMMC systems achieved
more than 95% of SCOD removal efficiencies and nitrification efficiency of more than
97% with SCOD loading rates ranging from 0.77-1.76 glUd and ammonia nitrogen
loading rate ofO.I6-0.368g1Ud
2.5.4.3 Application ofEMMC process for real domestic wastewater treatment
The performance ofEMMC for treating real domestic wastewater was thoroughly
investigated by many studies (Cao, 1998; Su, 1999 and Yang et al., 2002). In Cao's
research (1998), fix-bed EMMC system removed 94.6% of BOD, 97% ofNl4-N and
61 % of total nitrogen from the actual wastewater with a CODIN ratio of 4.6 at HRT of
13h and intermittent aeration of Ih on/2h off. Su (1999) reported EMMC achieved a 73%
of TN removal from real domestic wastewater at HRT of8.5h.
A pilot scale experiment result (Shimabukuro et al., 2001) showed that medium
EMMC system at HRT of9h with continuous aeration achieved 68% of COD removal
and 79% of STN removal.
33
All these results suggested that the EMMC system has great potential for treating
real domestic wastewater for simultaneous removal of COD and nitrogen and the
advantages ofEMMC over conventional AS process.
2.5.4.4 Moving carrier EMMC system
Based on the fixed bed EMMC studies, moving carrier system was developed for
years in order to reduce the carrier making cost and offer the flexibility for EMMC
system applications.
Similar to the IF AS process, moving carrier EMMC system can be considered as a
modified activated sludge process in which 5-10% of the liquid volume is occupied by
the highly porous EMMC carriers.
Presence of EMMC carriers allows the bioreactor to operate at 2 to 3 times greater
of total biomass concentration than a conventional aerobic activated sludge process. In
addition, total nitrogen removal can also be dramatically enhanced due to the innovative
inner structure ofEMMC carrier.
Su (1999) and Song (2003) reported that moving carrier EMMC systems provide
similar removal efficiencies for organics, nitrogen when compared with the fixed bed
EMMC system. In addition, it has also been reported that both fixed bed and moving
carrier systems could achieve higher nitrification ( 40% difference) and nitrogen removal
efficiencies (20% difference) than the conventional AS process which was operated
under same operation conditions.
2.6 Biologieal nitrogen removal in onsite wastewater treatment
34
As mentioned earlier in this chapter, centralized collection and treatment system
only solves ''half' of the wastewater problem. In the rural or less populated area, the
household, hotel and school wastewater treatment and disposal depends on the onsite
treatment systems. Compared to centralized system, it is more difficult to improve the
treatment level especially for nitrogen removal due to the technical and financial issues.
Septic system is the most commonly used onsite wastewater treatment system which
consists of a septic tank and a drain field that allows treated effluent to be infiltrated into
the soil. The effluent from septic tank contains high concentration ofNl4-N and organic
N, which is converts to nitrate in the following drain field This could result in a long
term consequence of ground water contamination due to the uneven distribution of the
effluent nitrogen in the soil (Health Department Report, W A, 2005). Moreover, for the
locations that the drain field is too shallow, it may also cause surface water contamination.
Aerobic treatment unit (ATU) is a promising alternative to upgrade existing onsite
wastewater treatment facility especially the improper sited septic tank (USEP A, 2000).
A ru, is basically a ''mini'' activated sludge process which is presented in Figure 2.10.
" Aerobic Tre2ltrnen t Unit (l\TU)
Figure 2.10 Typical aerobic treatment unit
35
As with its large scale counterpart, basic A TU is only designed to remove
organics and ammonia nitrogen, large amount of nitrate and nitrite which may cause
environmental contaminations, however, are still remained in the eft1uent Table 2.4 lists
the typical effiuent quality from septic tank and ATU.
Table 2.4 Typical values for effiuent quality parameters for septic tank and A TU (Adapted from Wallace et at.. 2004)
BOD N03"-N TSS N}4-N DO
(mg/L) (mg/L) (mg/L) (mg/L) (mg/L)
Septic tank 130-250 0-2 30-130 30-60 <1
ATU 33 25 22 7 3
Many designs have been focused on improving total nitrogen removal for onsite
wastewater treatment using the same principles as those used in the large scale design
such as preanoxic, postanoxic with external carbon source. Although these processes
have been proved effectively in improving nitrogen removal, the high capital and
maintenance cost may limit the wide spread application of those systems (Health
Department Report, W A, 2005). The information of some products that have completed
the ETV (environmental technology verification) program is listed in Table 2.5.
It has been decided that, for most onsite treatment devices including the nitrogen removal
units (with capacity of 400-1 ,500 USGD), the iDsta1lation cost ranges from
$15,000-$20,000. The annual O&M cost is estimated as $1,500. Since the cost is one of
the most significant concerns of the homeowner, the producer and designer, have aimed
in modifying current processes or developing new processes with lower cost
36
Table 2.5 Some products that have complete the ETV process for nitrogen reduction in domestic wastewater from individual residential homes* System Name Technology Performance Cost Waterloo Fixed film trickling filter It averaged 62% removal of total $13,000-17,000 Biofilter nitrogen with an average total for total system
nitrogen efl1uent of 14mgIL over installation. 13-month testing period with multi-pass configuration. With single pass mode, it could remove 2()-.4()% total nitrogen.
Amphidrome'M SBR in conjlUlction with It averaged 59"10 removal of tota1 The manufacturer Model an anoxic/equalization tank nitrogen with an average total estimated it could Single Family and a clesr well tank for nitrogen efl1uent of 15mgIL over cost System wastewater treatment the 13-month teating period. $12,000-15,000
for a total installation.
Sepitech'" Two stage fixed film Averaged 64% removal of total The manufacturer Model 400 trickling filter using a nitrogen with an average total estimated that a System patented highly permeable nitrogen efl1uent of 14 mgIl over total system with
hydrophobic media the 12-month teating period. pressure distribution drain field would cost approximately $20,000.
>Ie: Adapted from Health Department Report, W A, 2005.
2.7 Bioreaetor design - engineering concerns
2.7.1 CSTR (completely stirred tank reactor) deslgn- single or in series
CSTR is one of the most common designs in activated sludge process. Theoretically,
a sequence of CSTR can achieve higher removal efficiency than a single CSTR with the
same total volume. However, since the capital cost for several small reactors is greater
than one large reactor, an economics optimization need to be made for the number of
small reactors in series (Sundstorm, 1979).
2.7.2 AppHeation of multi-layer design in biologieal wastewater treatment
Similar to CSTR in series, multi-layer design is considered to be a proper approach
to improve the biological treatment efficiency for attached growth process (Yang et al.
2003). Yang (2003) investigated the performance of single-layer and multi-layer rotating
37
drums biofilters for VOC removal. It was found that the biofilter with 4 thin layer media
achieved more stable and higher removal efficiency for ether than the one with one thick
layer media. Also it was observed that the biomass distribution of multi-layer biofilter on
a concentric surface was more even than that on the single layer biofilter at the same
depth. The even biomass distribution resulted in a reduced possibility of gas stream short
circuiting and hence better performance.
2.8 Summary
Nitrogenous pollutant in domestic wastewater is a potential threat to environment
and public health. The problems caused by nitrogenous pollutant include eutrophication,
DO depletion, ''blue baby" syndrome, etc.
Biological nitrogen removal (BNR) is considered the most effective and economic
way to control the nitrogenous pollutant compared with other physical-chemical
processes (Sedlak, 1991). The kinetics of biological nitrogen removal was thoroughly
investigated. Biological nitrogen removal involves two successive steps: nitrification and
denitrification. These two processes required opposite environmental conditions.
Therefore, they are designed to occur in two or more reactors or, in the same reactor
where the DO gradient is presented.
According to the concepts of biological nitrogen removal, many processes have been
developed for carbon and nitrogen removal from domestic wastewater including
preanoxic, postanoxic and simultaneous nitrification and denitrification processes. Each
of them has advantages and disadvantages when the reliability, convenience and cost
issues are considered.
38
Biological nitrogen removal for land limited applications, however, can be quite
different from the large-scale treatment application in terms of the design concepts. MBR,
MBBR, IF AS and EMMC are the typical processes developed for land limited area like
the State of Hawaii. Contrary to their large-scale counterparts, these designs tend to be
combined multiple technology elements in order to offer the advantages of all the
technologies involved.
In MBR processes, the nitrogen removal is achieved by separated stages treatment.
Although the MBR processes offer many advantages such as reliable performance and
easy operation and maintenance, the relatively high cost related to the membrane
purchase/installation, membrane fouling, energy, and externaI carbon source may limit
the wide spread application of this process. Currently, the emphases on MBR research
include prevent membrane fouling, reducing cost, membrane lifespan, etc.
Compared to MBR, MBBR and IF AS are .less expensive altemative for land limited
application. Both of them can be considered as "hybrid" systems of suspended growth
and attached growth. The media (carrier) with certain packing ratio (200/ ..... 70%) in the
systems play the key role in pollutant removal. In these two processes, nitrogen removal
are also achieved by separated nitrification, denitrification stages in which certain space
and energy cost related to the circulation are required.
Based on the previous studies (Yang, et al., 1995; 1997; 2002), EMMC processes
have demonstrated many advantages compared to other compact designs as follows:
Firstly, EMMC process can be more space effective since the simultaneous nitrification
and denitrification can be achieved in the same reactor. Moreover, EMMC is designed to
solve the liquid-solid separation problem, the second clarifier, therefore, can be
39
eliminated. Secondly, EMMC process can be more cost effective. Since the carbon and
nitrogen removal can be achieved in the same reactor, the cost related to the recirculation
energy and reactor volume can be minimized. Also, Compared to the carrier in MBBR
and IF AS, EMMC carrier size is much larger resulting in the lower cost of both material
purchase and labor work. Thirdly, EMMC technology provides flexibility for the
application. It has been designed for different purposes such as simultaneous carbon and
nitrogen removal, nitrification and denitrification. Both fixed bed and moving carrier
processes were developed for different application situations.
All the advantages suggest many potential applications ofEMMC technology,
including upgrading existing activated sludge facility, upgrading aerobic treatment units
for onsite wastewater treatment and combining with MBR process for reducing the
membrane fouling.
According to the previous studies (Cao, 1998; Zhang, 1995), the high carrier making
cost and the low mass transfer efficiency when scaling up can be two potential problems
associated with EMMC technology. This study intends to explore the solutions of these
two problems by making modifications to the carrier making procedure and system
configurations.
40
Chapter 3. Methodology
3.1 Experiment Approach
EMMC-biobarrel process is a modification to the original EMMC process by
introducing biobarrel ring to the carrier making procedure. It is designed to reduce the
chemicals cost for carrier making, increase the substrate contact time and improve the
mass transfer efficiency.
In order to evaluate the potential ofEMMC-biobarrel system for domestic
wastewater treatment and reuse, processes performance of two types of configurations
including single-layer fixed bed systems (with packing ratio of 10% and 20%) and
double-layer fixed bed system (with packing ratio of 13%) were investigated.
3.1.1 Immobilization of entrapped ceUs
Mixed microbial cells were taken from East Honolulu Wastewater Treatment Plant
on the island of Oahu, Hawaii. EMMC-biobarrel carriers were prepared by using
cellulose triacetate to entrap microbial ceUs according to Yang and See (1994). The
EMMC-biobarrel carrier was introduced with plastic biobarrel ring as the "skeleton" in
order to eliminate the shape cutting step. Figure 3. 1 (a, b) present the images ofbiobarrel
ring and EMMC-biobarrel carrier, respectively; (c) presents the scanning electron
microscopy (SEM) image of EMMC-biobarrel carrier inner structure. The carrier making
procedure is shown in Figure 3.2.
41
a. Biobarrel ring
D=3 .8cm; H=3.8cm
b. EMMC-biobarrel carrier
D=3.8cm; H=3.8cm
c. SEM image of EMMC-biobarrel inner structure
Figure 3.1 Biobarrel ring and EMMC-biobarrel carrier
42
5L of lO%(w/v) 2L of dewatered sludge cellulose triacetate in (containing 90% water) methylene chloride
Complete mixing to emulsion
Mix with plastic biobarrel 1 Organic solvent
Well-coated biobarrel carrier formation in toluene solution
Flush with running water r Organic solvent recovery device I
Pack in the reactor Reuse organic solvent
Figure.3.2 EMMC-biobarrel carrier making procedure
43
3.1.2 Influent characteristics
Two types of wastewater, i.e., synthetic domestic wastewater and real domestic
wastewater were used for the experiment.
3.1.2.1 Composition of synthetic wastewater
In most experiments oftbis study, the synthetic wastewater with the following
composition (as shown in Table 3.1.) was used as influent.
Table 3.1 Composition of synthetic wastewater
Content Concentration (mgII)
Sucrose 177.75
(NH4)2S04 189.75
KH2P04 131.75
K2HP04 267.5
NaC~ 200.5
MgS04.7H20 20
MnS04.H2O 2.5
CaC12 1.87
FeCiJ.6H20 0.125
The COO and total inorganic nitrogen concentrations of the synthetic wastewater
were about 20Omg/L and 4Omg/L, respectively. Therefore, the COOIN ratio of the
synthetic influent was about 5. In order to see the impact of influent COOIN ratio on the
process performance, COOIN ratio.was increased to 8 by reducing the influent ammonia
concentration in Experiment 4.
As discussed in Chapter 2. COOIN ratio is an important parameter for biological
nitrogen removal. Generally, a COOIN ratio· ranging between 20-25 is considered to be
the appropriate nitrogen content of biomass in an aerobic treatment system (Gaudy and
44
Gaudy, 1988). Cao (1998) reported that the EMMC process achieved 92% of total
nitrogen removal when the influent CODIN ratio was maintained at 15. Many studies on
the other processes such as MBR also reported high TN removal (more than 80%) using
the influent with high CODIN ratio (10-15). However, the CODIN ratio in the real
wastewater can be varied, ranging from 2-15. In order to make this research more
realistic and applicable, lower CODIN ratios (5-8) were applied.
3.1.2.2 Composition of real wastewater
Real wastewater was taken from primary settling tank of East Honolulu Wastewater
Treatment Plant in Oahu, Hawaii. It was kept in a refrigerated room (5°C) after collection.
Chafacteristics of the real wastewater incorporated in this study are given in Table 3.2.
Table 3.2 Characteristics of the real domestic wastewater Item TCOD SCOD NH3-N pH
Cone. mg/L 212 120 18 6.6-7.0 pH
units
3.1.3 Fixed bed EMMC-biobarrel system set up
a. Single-layer fixed bed EMMC-biobarrel system
Single-layer fixed bed EMMC-biobarrel systems with different packing ratios (10%
and 20%) were investigated. The schematic diagram of the single-layer systems is
presented in Figure 3.3.
b. Double-layer fixed bed EMMC-biobarrel sYstem
Double-layer fixed bed reactor is designed to reduce the packing ratio, i.e., carrier
making cost and improve the mass transfer efficiency in the system. Another idea behind
double-layer design is that this design can be considered as the operation so-called
45
"EMMC reactor in series". It is known that for activated sludge process design. with
same total volume. several small reactors in series can achieve higher performance than
one large reactor (Sundstorm, 1979). Therefore. in the engineering stand point, double
layer EMMC-biobarrel reactor is expected to provide higher conversion than the single
layer reactor. EMMC-biobarrel carriers with an overa11 packing ratio of 13% were
separated into two layers with certain void volume in between. Figure 3.4 shows the
configuration of the system.
Table 3.3 Fixed bed EMMC-biobarrel systems deseription
System Design Packing Reactor volume Void volume
ratio (ml) (ml)
I Fixed bed single-layer 10% 4760 4284
II Fixed bed single-layer 20% 4965 3972
III Fixed bed double-layer 13% 18900 16440
46
Effluent Tank
Pump
Packing ratio=10 %
Packing ratio=20 %
Aerator
Influent Reservior
Figure 3.3 Single-layer EMMC-biobarrel processes (packing ratio "'10%; 20%)
47
Overall Packing Ratio =13%
Influent Reservoir
EffiuentTank
Aerator
Figure 3.4 Double-layer EMMC-biobarrel process (packing ratio =13%)
48
3.1.4 Operational condition
'The performances of EMMC-biobarrel processes under various operational
conditious were investigated. 'The operational strategies were summarized in Table 3.4.
Similar to the previous studies (Zhang, 1995; Cao, 1998), the air flow rate was controlled
at about 1-1.2UL void volume/min during the scheduled aeration. 'The temperature of
operation was controlled at room temperature with 20°C±2°C.
Table 3.4 Operational strategies
System Influent wastewater HRT(hr) Aeration Schedule
I Synthetic wastewater 6; 9 Continuous aeration;
Ih air onl2h air off
11 Synthetic wastewater; 3;6;9 Continuous aeration;
Real wastewater I h air onl2h air off
ill Synthetic wastewater 6;9 Continuous aeration;
lh air onl2h air off
3.2 Analysis
3.2.1 Sample preparation
Samples were collected from the effluent reservoir of each reactor every 48 hours.
All the effluent samples were filtered through a GF/C with 47 diameter glass microfiber
and 1.5f.!m of pore size.
3.2.2 Evaluation of process performance
'The influent and effluent samples were analyzed for total chemical oxygen demand
(TCOD), soluble COD (SCOD), NH3-N, N03--N, NOi-N, TSS (total suspended solid)
and pH. 'The analytical methods and reference are listed in Table 3.5.
49
For the synthetic wastewater experiments, the results were expressed by the removal
efficiency of SCOD, SNH3-N (nitrification), and total soluble inorganic nitrogen (STIN)
as listed in the following equations:
Removal of SCOD:
Removal ofNH3-N:
Removal ofSTIN:
REo/a- (SCODmr - SCOD.,q ) xl 00% SCODmr
(SNH - N) - (SNH - N) REo/a- 3 mr 3.,q x 100% (SNH3 -N)mr
Table 3.5 Analytical Methods
Analytical Parameters Method Reference
COD Colorimetric Determination Hach DRl4000
Spectrophotometer Manual
NH3-N Nessler Hach DRl4000
Spectrophotometer Manual
N~--N Cadmium Reduction Hach DRl4000
(powder pillow) Spectrophotometer Manual
NOi-N Diazotization Hach DRl4000
(powder pillow) Spectrophotometer Manual
pH OAKION 510 pH/mY OAKION 510 pH/mY
meter meter Manual
TSS Wet-dilution Standard Method
50
3.2.3 Data Analysis
A student's t test was performed to test the significant difference between the results
of two operating conditions based on independent random samples using the Excel
spreadsheet. A significance of 0.05 (a=O.05) is chosen for the test.
3.2.4 Economic Analysis
Economic analysis for the potential applications ofEMMC-biobarrel processes
including an aerobic EMMC-biobarrel treatment unit and a O.IMGD domestic
wastewater treatment system were conducted. For the aerobic EMMC-biobarrel treatment
unit, the installation cost and annual O&M cost were evaluated. For the 0.1 MGD
domestic wastewater treatment system, the analysis was conducted based on the net
present worth (NPW) and the unit volume treatment cost ($/1,000 gallons/day). The
sensitivity analysis of the annual worth (A W) to the electricity charge rete and the annual
interest rete were also conducted.
51
Chapter 4. Results and Discussions
4.1 Fixed bed single-layer EMMC-biobarrel processes
4.1.1 Processes performance
a. Processes performance at HRT of 9h and intermittent aeration of Ih onl2h off (Experiment I)
Intermittent aeration of 1 h air onl2h air off was recommended for improving total
nitrogen removal by previous studies (Zhang, 1995; Cao, 1998; Su, 1999). Therefore, this
aeration schedule was applied as the start point of investigating the performance of
EMMC-biobarrel process. The experiment data are summarized in Table 4.1.
As shown in Table 4.1, fixed bed single-layer EMMC-biobarrel processes removed
about 90% of COD at HRT of 9h and intermittent aeration of Ih onl2h off. However, the
nitrification was not well accomplished, i.e., the ammonia nitrogen removals were only
46.7% and 69.3% for system I and system II, respectively. This could be mainly due to
the insufficient oxygen supply. Total nitrogen removal, consequently, was further
inhibited.
Effect of packing ratio
As shown in Table 4.2, the student's t-test for the performance of system I and
system II is presented. There was insignificant difference of the SCOD removal between
system I and system II. However, system II achieved much higher nitrification efficiency
(25% difference) than system 1. This result is reasonable since EMMC-biobarrel system
with higher packing ratio can provide larger specific surface for nitrifiers accumulation.
In terms of denitrification, although system II achieves higher nitrification efficiency, the
52
total nitrogen removal was similar to that achieved from system I. The low nitrogen
removal efficiency could be mostly due to the poorly developed nitrification in both
systems.
Table 4.1 Single-layer EMMC-biobarrel processes performance at HRT of 9h witb intermittent aeration of 1h air onl2h air otT
Parameters Influent System I (10%) System II (20%)
SCOD(mg/L) 184±22 20.0±4.4 19.5±4.0
SCODre% 89.0±3.5 89.0±3.8
SNH3-N(mg/l) 42±4.1 21.2±2.3 11.4±2.9
SNH3-Nre% 46.7±6.2 69.3±5.8
SN~·-N (mg/l) 7.4±2.4 13.8±1.8
SNOi-N (mg/l) 2.9±1.0 4.2±O.8
STIN (mg/L) 42±4.1 31.6±1.6 29.4±4.0
STlNre% 20.8±3.8 21.3±4.5
pH 7.3-7.8 6.8-7.5 6.7-7.3
TSS 18.8±12.6 15.6±8.5
Table 4.2 The test oftbe significant difference between tbe removal efficiencies (%) f I d IT HRT f9h witb in rmi ti f 1h n12h tT o ··system an . system at 0 te ttent aera on 0 0 0
Parameters System I System II t-value Critical t value·
n=10 n=lO (nrtn:z-2)= 18
SCODre% 89.0±3.5 89.0±3.8 -0.1166 ±2.1098
NH3-Nre% 46.7±6.2 69.3±5.8 -8.4407 ±2.1098
STlNre% 20.8±3.8 21.3±4.5 -0.2721 ±2.1098
• 95% confidence
b. Processes performance at HRT of 9h witb continuous aeration (Experiment 2)
53
Because the insufficient oxygen supply inhibited the development of nitrification in the
EMMC-biobarrel systems, the aeration schedule was then switched to continuous
aeration in order to enhance the oxidation of organics and nitrogen. Also, since the liquid
in the system could be mixed constantly by the continuous aeration, it is expected that the
mass transfer efficiency can be improved. Table 4.3 presents the processes performance
at HRT of9h with continuous aeration.
Table 4.3 Single-layer EMMC-biobarrel proeesses performance at HRT of 9h with continuous aeration
Parameters Influent System I System II
SCOD(mgIL) I 97.0±16.7 8.0±4.6 7.6±4.6
SCODre% 96.0±2.1 96.2±2.2
SNH3-N(mg/l) 41.2±2.6 O.4±O.4 O.l±O.l
SNH3-Nre% 99.0±1.0 99.7±O.1
SN03·-N (mg/l) 25.6±3.1 20.4±2.5
SNOi-N (mg/l) 0.4±O.3 O.l±O.l
SNOx-Nre% 36.5±6.6 50.3±5.1
STIN(mgIL) 41.2±2.6 26.7±3.1 20.5±2.5
STINre% 36.1±6.7 50.1±5.7
pH 7.3-7.8 6.2-7.0 6.4-7.1
TSS 31.1±15.0 19.3±13.8
With continuous aeration, near 100% of ammonia oxidation is achieved from both
systems. The SCOD removal efficiencies are also achieved to about 96%. The high
nitrification and high SCOD removal efficiencies apparently resulted from the sufficient
oxygen supply and the improved mass transfer in both of these two systems. Additionally,
the total nitrogen removal efficiencies of both systems were also promoted to 36%
54
(system I) and 50% (system II) respectively, which could mostly be due to the improved
nitrification in the systems. Also, it indicates that the concurrent anoxic/aerobic
conditions can be well developed in the EMMC-biobarrel systems even under continuous
aeration in the presence ofEMMC-biobarrel carrier.
As shown in Table 4.4, under continuous aeration, system I and II achieved
comparable SCOD removal efficiencies (about 96%) and nitrification efficiencies (99%),
indicating EMMC-biobarrel system is able to achieve satisfied carbon and ammonia
removal efficiencies even at packing mtio of 10%. In terms of total nitrogen removal, the
system II achieves about 15% higher performance than the system 1. It is suggested that
the higher packing mtio is required for achieving better total nitrogen removal.
Theoretically, this difference could be due to two reasons. Firstly, the denitrifier
concentmtion could be higher in 20% system due to the greater specific surface area.
Secondly, the carrier distribution in the system with higher packing mtio could be more
"compact" than that in the system with lower packing mtio, which could favor the
establishment of co-existing aerobic/anoxic environments.
Table 4.4 The test of the significant difference between the removal efficiencies (%) f d n T f9 with o c system I an IYStem atHR 0 h continuous aeration
Pammeters 10% system 20% system t-value Critical t value*
n=9 n=9 (n.+n2-2)= 16
SCODre% 96.O:t2.1 96.1±2.2 0.8085 ±2.2281
NH3-Nre% 99.O:t1.0 99.7±O.l -1.9858 ±2.3060
STINre% 36.1±6.7 50.1±5.7 -4.8226 ±2.1199
* 95% confidence
Co Processes performance at HRT of 6h with continuous aeration (Experiment 3)
55
The results of experiment 2 suggested that the EMMC-biobarrel systems are able to
achieve high SCOD removal and nitrification efficiencies under the condition of HRT of
9h with continuous aeration. In order to observe the impact of the reduction ofHRT on
the treatment efficiency, HRT of 6h was applied to both of the systems. Table 4.5
presents the experimental results.
At HRT of 6h with continuous aeration, the EMMC-biobarrel processes still
achieved high SCOD removal and ammonia oxidation efficiencies, which were about
97% and 99%, respectively. These results indicate that HRT of 6h is enough for the fixed
bed EMMC-biobarrel systems to remove carbon and ammonia nitrogen from low to
medium strength domestic wastewater. At the operation ofHRT of6h, the COD loading
rate is 0.75g/Ud, which is comparable or higher than that of the conventional activated
sludge process, which is about 0.6g/Ud (Rittiman & McCarty, 2001). Therefore, the
EMMC-biobarrel system demonstrates great potential of replacing the existing activated
sludge process for not only carbon removal but also a high nitrogen removal via
nitrification process.
For total nitrogen removal, the systems also demonstrate good performance. System
I and system II achieved 34.5% and 42.2% of total nitrogen removal, respectively which
are relatively high considering the low influent CODIN ratio applied.
Table 4.6 presents the student's test for the performance of systems with different
packing ratios. There was no difference of removals of SCOD and NH3-N, but the
difference occurred for the TIN removal, i.e., system II (packing ratio 20%) is higher than
system I (packing ratio 10%).
56
Table 4.5 Single-layer EMMC-biobarrel processes performance at HRT of 6h with continuons aeration
Parameters Influent System I System II
SCOD(mg/L) 195.0±20.5 5.9±4.7 5.2±3.4
SCODre% 96.9±2.6 97.5±1.8
SNH4-N(mgll) 41.2±.2.1 0.2±<J.4 0.2±<J.2
SNH4-Nre% 99.4±1.0 99.5±<J.5
SNOi-N (mgll) 25.1±3.9 25.1±5.1
SNOi-N (mgll) 0.4±<J.2 0.3±<J.2
SNOx-Nre% 34.8±5.2 42.3±7.7
STIN (mg/L) 41.2±2.1 26.3±1.8 23.6;t3.9
STINre% 34.5±5.2 42.2±7.6
pH 7.0-7.5 6.2-7.1 6.4-7.1
TSS 34.7±19.0 18.6;t14.2
Table 4.6 The test of the significant difference between the removal efficiencies (%) f tId t IT tHRT f6hwith tin ti osYs em an iYS em a 0 con uous aera on
Parameters 10% system 20% system t-value Critical t value*
n=10 n=1O (n\+nr-2)= 18
SCODre% 96.9±2.6 97.5±1.8 0.8085 ±2.2281
NH3-Nre% 99.4±1.0 99.5±0.5 -1.9858 ±2.3060
STINre% 34.5±5.2 42.3±7.7 -3.001 ±.2.1010
d. Process performance at HRT of 6h with continuons aeration using intluent with CODIN ratio of 8 (Experiment 4)
As discussed previously, CODIN ratio is important for total nitrogen removal. In a
certain extent, higher CODIN ratio results in higher denitrification efficiency, total
nitrogen removal, consequently, is high. In order to observe the effect of CODIN ratio on
the system performance, CODIN ratio of influent was slightly elevated from 5 to 8 in
Experiment 4. The results are listed in Table 4.7.
57
With influent CODIN ratio of 8, the SCOD, ammonia nitrogen and total nitrogen
removal of system II are 97.9%, 99.7% and 47.0% respectively. Compared to the
achievement at influent CODIN ratio of 5, total nitrogen removal efficiency improved
about 5%. This suggested that the EMMC-biobarrel process has the potential to achieve
higher total nitrogen removal when the high influent CODIN ratio is applied.
Table 4.7 Performance of system II at HRT of 6h with continuous aeration for tin intl 0 IN ti f8 trea II!: uentwithaC D ra 00
P=eters Influent Effluent f-bed 20%
SCOD(mgIL) 212.8±8.8 4.4±1
SCODre% 97.9±0.5
SNl:4-N(mgll) 26.5±O.9 O.I±O.I
SNl:4-Nre% 99.7±O.2
SNDJ·-N (mgll) 13.7±2.1
SNOi-N (mgll) 0.2±0.1
SNOx-Nre% 47.1±8.3
STIN (mgIL) 26.5±O.9 14.0±2.1
STINre% 47.0±8.3
pH 7.0-7.5 6.8-7.2
TSS 19.6±14.0
e. Process performance at HRT of 3h with continuous aeration (Experiment
S)
In the Experiment 5, HRT of 20% EMMC-biobarrel systenl was further reduced to
3h in order to investigate the SYstenl performance at low HRT. The results are shown in
Table 4.8, Figure 4.1 and 4.2.
58
T bl 4.8 P rfi f tnt HRT f3h with tin ti a e e onnaneeo s sem a 0 eon nons aera on Parameters Influent Eftluent f-bed 20%
SCOD(mgIL) l73.6±10.9 17.9±2.3
SCODre% 89.7±0.8
S~-N(mg/l) 34.0±5.0 15.2±1.8
S~-Nre% 55.8±7.2
SNOi-N (mg/l) 16.9±5.4
SN02--N (mg/l) 3.4±1.4 I
STIN (mgIL) 34.0±5.0 35.1±1.7
STINre% -3.5±35.5
pH 7.5 -8.5 7.3-7.6
TSS 4O.0±12.0
At HRT of3h With continuous aeration, the system II stably achieved about 90% of
SCOD removal while the nitrification efficiency was only 55.8%. This suggests that the
nitrification can not be well developed in the EMMC-biobarrel process under the HRT as
low as 3h. Accordingly, the further denitrification process can be inhibited.
Another problem caused by the low HRT, as shown in Fig.4.11, is the increasing of
SS concentration in the eftluent. This phenomenon could be explained by the following.
At HRT of3h, the mass transfer of the substrate from the influent liquor to the entrapped
microorganisms can be inhibited by the short contact time. A large portion of the
substrate, therefore, can only be utilized by the suspended microorganisms, i.e., the
biomass outside of the carriers. At HRT of 3h, the loading rate was as high as
1.5g!Uday; the suspended microorganisms therefore can grow very fast, leading to an
increase of the SS concentration in the eftluent. The decay of the biomass can release
organic/inorganic nitrogen, which caused the total nitrogen concentration increasing in
the eftluent.
59
Figore.4.1 Performance of system II at HRT of 3h with continuous aeration
70.00 -" .. 60.00 • .. • E .. 50.00 • • ..
-5 .5~40.00 ,,-0'" • g-S30.00 • • " 20.00 .. .. " 0
10.00 .. CD CD
0.00 0 2 4 6 8 10 12 14 16
cia", vi operation
Figure 4.2 SS concentration in effluent ofsystem II (20%) at HRT of 3h with continuous aeration
All these suggest that, for EMMC-biobarrel process, HRTof3h can be too short to
achieve satisfied performance. Therefore, low HRT such as 3h may not be suitable for
EMMC-biobarrel systems.
60
4.1.2 Impact of operational condition on the performance characteristics
a. Effect of HRT
In this study, two HRTs (6h and 9h) were investigated for system I (10%) and
system IT (20%). Table 4.8 presents the student's test for the significance difference
between the removal efficiencies of these two systems at HRT of 6h and HRT of9h with
continuous aeration.
Table 4.9 The test of the significant difference between the removal efficiencies (%) f I d II HRT f 6h d HRT f 9h with tin ti o system an . system at 0 an 0 eon uonsaera on
System Parameters HRT=9h HRT=6h t-value Critical t
nl=9 nr12 value*
(nl+nr
2=17)
SCODre% 96.0±2.1 96.9;t2.6 0.8282 ±2.1009
System I NH3-Nre% 99.0±1.0 99.4±1.0 0.9123 ±2.1009
(10%) STINre% 36.1±6.7 34.5±5.2 0.6018 ±2.2281
SCODre% 96.2±2.2 97.5±1.8 -1.5390 ±2.1199
System IT NH3-Nre% 99.7±.O.1 99.5±.O.5 1.5389 ±2.1604
(20%) STINre% 50.1±5.7 42.2±7.6 2.8852 ±2.1199
*95% confidence
As shown in Table 4.8, the reduction ofHRT from 9h to 6h had little impact on the
SCOD and ammonia nitrogen removal efficiencies. The denitrification efficiency,
however, was influenced by the HRT for system IT (20%). The total nitrogen removal
efficiency at HRT of 6h was about 10% lower than that at HRT of 9h. This indicates that
longer HRT, i.e., longer reaction time favors the denitrification process.
As shown in Figure 4.3, the removal efficiency for organics at an HRT of3h
slightly decreasesd compared to those at HRT of 6h and 9h. However, the nitrification
61
efficiency was dramatically reduced when HRT of 3h was applied. The decreased
nitrification efficiency may result mainly from the lack development of the nitrification at
the lower HRT applied.
I
. --
120
~ 100 7'- =t OJ .!!
80 I! .!! __ SCODre
~ 60 ....... NH3·Nre
'iii ~ 40
E &! 20
0 ~ , , ,
0 3 6 9 12
HRT(h)
Figure 4.3 SCOD and NHrN removal efficiencies of system n vs. HRTs
b. Effect of aeration schedule
At a HRT of 9h, the processes performance was tested under two different aeration
schedules, i.e., continuous aeration and intermittent aeration of Ih air onl2h air off. Table
4.10, Fig 4.4 and 4.5 present the comparison of the performances under the different
aeration schedules.
As shown, compared to Ih air onl2h air off, the EMMC-biobarrel systems achieved
higher nitrification efficiencies (nearly 100%) and SCOD removal efficiencies under
continuous aeration condition. The high nitrification and SCOD removal efficiencies can
be achieved from the sufficient oxygen supply and better mass transfer in both systems.
Additionally, the total nitrogen removal efficiencies of both systems were also achieved
to 36% (system I) and 50% (system II) respectively under continuous aeration, which
62
were much higher than those achieved under intermittent aeration. This result could
mostly be due to the improved nitrification in the systems with continuous aeration. Also,
the concurrent anoxic/aerobic conditions can be well developed in EMMC-biobarrel
systems even under continuous aeration.
Table 4.10 The test oftbe significant difference between tbe removal efficiencies (%) f Id Dddifti d edul o 'system an. system un er erent aera on sch es
System Parameters Intermittent Continuous t-value Critical t
aeration (I h aeration value'"
air onl2h air (nl+n2-
oft) nl=IO nr9 2=17)
SCODre% 89.0±3.5 96.0±2.1 -5.11l2 ±2.1448
System! NH3-Nre% 46.7±6.2 99.0±1.0 -26.2546 ±2.2281
(10%) STINre% 20.8±3.8 36.1±6.7 -6.0380 ±2.1064
SCODre% 89.0±3.8 96.2±2.2 -4.4264 ±2.1448
System II NH3-Nre% 69.3±5.8 99.7±0.1 -11.5684 ±2.2621
(20%) STINre% 21.3±8 50.1±5.7 -7.3154 ±2.1448
"'95% confidence
100
90
80 lit II 70
1 60 13
80 'Ii 1 40
~ 30
20
10
0 SCOO",% NJi3.N re% SllNre%
Figure 4.4 Performance comparison of system I at different aeration schedules
63
50
40
30
20
10
o SCODra% NH3-N re% S11N ra%
1-1nIenn1llenl_1h an/2h 0111 tl continuous _on
Figure 4.5 Performance comparison of system IT at different aeration schedules
Co Effect ofintluent CODIN ratio
As discussed previously, higher CODIN ratio can result in higher total nitrogen
removal since the denitrification process requires additional carbon source (Cao, 1998).
In this study, synthetic wastewater influent with CODIN ratios of 5 and 8 were
experimented. Fig. 4.6 shows the performance comparison and Table 4.11 presents the
significant difference of the system performance using the influent with different CODIN
ratio.
The t-test result (Table 4.11) shows that the total nitrogen removal efficiency of
20% system with COOIN ratio of 8 was slightly higher than that with CODIN ratio of 5.
However, at a CODIN ratio of 8, the system's total nitrogen removal efficiency was still
less than 50%, which suggests that in achievement of higher nitrogen removal, the higher
influent CODIN ratio is required.
64
Table 4.11 The test of significant difference of the total nitrogen removal efficiencies of 20% system at HRT of 6h with continuons aeration using influent CODIN ratios ofS and 8 Parameters Influent Influent t-value Critical t value'"
COD/N=5 COD/N=8 (n.+n2-2=15)
nr=10 nr=7
STINre% 42.2±7.6 47.0±8.3 1.7611 ±1.7459
'" 95% confidence.
100
90
!! 80
II 70
1 80
I_ CODffi=61 'II 60 Ii [)CODIN=8
1 40
! 30
20
10
0 SCODre NH3-N re SllN re
Figure 4.6 Performance comparison of system n for treating influent with dlfferent CODlNratio
4.1.3 Evaluation of SRT
Solid retention time (SRT) is a very important parameter in the biological
wastewater treatment process. The long SRT ensures the high biomass concentrations in
the system, especially for development of slow growing bacteria such as nitrifiers. A
system with long SRT is capable of handling the shock load. The typical SRT for
conventional activated sludge process is 4-14 days while for extended aeration process is
15-30 days (Rittiman & McCarty, 2001).
65
The accumulative SRT ofEMMC-biobarrel system can be evaluated by the following
equation:
SRT= L d(COD)xQDxYobs (4.1) CODssxQ
where:
d(COD)=the difference between the SCOD in the influent and the eIDuent( i.e. total
SCOD consumption), mg/L
CODss=the COD of SS with the value of (1.42mg/Lxss)
Y obs= the observed cell yield expressed as the ratio of the organic carbon source that is
converted to the cells (g MLSS/g COD).
Q= the flow rate of fluid IJd.
D= the days of operation, d.
(Adapted from Yang and Qian, 2000)
As shown in Equation 4.1, the accumulation of SRT results from the biomass
growth in the system. The Yobs indicates the ratio of the organic carbon source that is
converted to the cells. The Yobs can be affected by many parameters such as type of
substrate, original biomass concentration, etc. (Metcalf and Eddy, 2003). In the EMMC-
biobarrel process, the original biomass concentration, i.e., the concentration of entrapped
microorganisms is evaluated from 5,00()""10,000 mg/L, which is similar to that of the
MBR process. For MBR process, the typical Yobs ranges from 0.2....().25 when treating the
municipal wastewater (Visvanathan, 2000). Thus, in this evaluation, the Yobs was
assumed as 0.25.
66
According to Equation 4.1, the SRTs of system I and system II were evaluated and
plotted in Figure 4.7 and 4.8. As shown, an SRT of 85 days was achieved in system I
after 50 days of operation; in system II, SRT reached to 200 days after 58 days of
operation. From Figure 4.8, the SRT accumulation rate for system II showed a significant
increase during the operation days of 36-42. This could be related to the switch of
operational conditions. The aeration schedule was changed from intermittent aeration to
continuous aeration at the 36th day. As discussed previously, the continuous aeration
leads to a higher SCOD removal efficiency, which broke the equilibrium of system
achieved under the previous conditions at the beginning days of the new stage. The SRT
accumulation rate, therefore, can be accelerated during this short period. After several
days of the adjustment (days of36-42), the system reached to a new equilibrium of the
biomass growth and washout, the SRT accumulation rate, consequently were slowed
down.
The SRTs achieved by EMMC-biobarrel processes are approximately 5-10 times longer
than that of the extended aeration activated sludge process, which has been observed to
be the best possible to withstand shock loads (Gaudy and Gaudy, 1978). Therefore, it can
be concluded that the high SCOD and nitrogen removals in the EMMC-biobarrel systems
are mainly due to the high concentrations of various microorganisms which are easily
washed out in the conventional suspended culture systems.
According to Equation 4.1, SRT accumulation is strongly related to the suspended
solid (SS) concentration in the effluent The results of experiment 1-3 show that the SS
concentration in system I (10%) effluent was always higher than that in system II (20%).
67
Therefore, the system with higher packing ratio achieves higher SRT and consequently,
provides better performance.
100.00 90.00 80.00
i 70.00 80.00
:!!. 50.00 Ii: 40.00 II)
30.00 20.00 10.00 0.00
0 10 20 30 40
days of operation
Figure 4.7 SRT accumulations in system I
250 r 200
~150 ~ 100
50 60
~l.~~~~~~~:==:~==~~----~--~ o 10 20 30 40 50 80
Days of operation
Figure 4.8 SRT accumulations in system n
4.1.4 Comparison ofEMMC-biobarrel and EMMC processes without biobarrel frame
4.1.4.1 Comparison of carrier characteristics
As discussed in chapter 2, EMMC technology is designed to offer the potential to
provide longer SRT for slow growing bacteria, solve liquid-solid separation and sludge
68
recycling problems (Yang, et.a!, 2002). This was achieved by utilizing the small carrier
elements (made of CTA) to serve for biomass entrapment and accumulation. Therefore,
the carrier element plays a key role in the EMMC process. Previous EMMC carrier is a
cube with dimension of 1 ern or 2cm. Since the density ofEMMC carrier is much higher
than that of water, it tends to settle down in the reactor. For fixed bed EMMC system, the
packing ratio, i.e., the percentage of the liquid volume occupied by the carrier is usually
in the range of 300/0-40% depending on the shape and size of the reactor.
The small carrier element has been proved to be able to provide large specific area
for biomass growth. However, it has several disadvantages including higher chemicals
cost for the carrier making, complicate making procedure for the shape cutting and lower
mass transfer efficiency because of the high density.
EMMC-biobarrel technology is designed to overcome these disadvantages by
introducing biobarrel to the carrier making procedure. Compared to the previous EMMC
carrier, the biobarrel carrier has larger size and lower density. Accordingly, packing ratio
of applying biobarrel carrier is much lower. The main differences between previous
EMMC and biobarrel carrier are listed in Table 4.12.
69
Table 4.12 Comparison ofEMMC-biobarrel carrier and pervious EMMC carrier
Previous Carrier Biobarrel Carrier
Shape Cube Cylinder
Size D=lcm;2cm D=H=3.8cm
Frame No Plastic bioarrel ring
Max. 30o/r40% 15%-20%
Packing Ratio
4.1.4.2 Comparison of performance
a. Comparison of performance at HRT of 9h with intermittent aeration of Ih air onl2h air otT
Table 4.13 and Figure 4.9 present the performance comparison among the medium
EMMC carrier, large EMMC carrier and EMMC-biobarrel systems at HRT of9h with
intermittent aeration of 1 h air onl2h air otT.
As shown in Table 4.13 and Figure 4.9, EMMC-biobarrel system achieved
comparable SCOD removal with EMMC system at SCOD loading rate of 0.49g!L1c1.
Nitrification efficiency achieved by EMMC-biobarrel system is higher than that in the
large carrier EMMC system but lower than that in the medium carrier EMMC system. It
should be noted that the loading rate ofEMMC-biobarrel system was 0.1 12g!L1d, which
was about 50% higher than the previous EMMC systems. It could be postulated that
EMMC-biobarrel system has the potential to achieve comparable nitrification efficiency
with medium carrier system if same nitrogen loading rate are applied. In terms of total
nitrogen removal efficiency, EMMC-bioharrel system was lower than those ofEMMC
systems. This could be partially explained by 1) the higher influent CODIN ratio and
lower loading rate used in previous studies and 2) better development of anoxic
70
environment for denitrification due to more "compact" distribution of the smaller carriers
in the previous EMMC systems.
Table 4.13 Performance comparison among the medium EMMC carrier, large EMMC carrier and EMMC-biobarrel systems at HRT of9h with intermittent aeration of Ih on!2h oft'"
Parameters Medium carrier Large carrier
(D=lcm) (D=2cm)
Packing ratio % 31.8 31.8
SCOD loading rate 0.49 0.49
(WUd)
N loading rate 0.075 0.075
WUd
SCODIN ratio 7 7
HRT 9 9
SRT N/A·· N/A··
SCODre% 89.Q±4.3 88.5±1.5
SNH4-Nre% 86.0 54.7
STlNre% 57.7± 14.5 44.2±6.7
.: EMMC data IS from Cao (1998) Master ThesIS • •• : Not available .
EMMC-biobarrel
(D=H=3.8cm)
20
0.49
0.112
5
9
75···
89.Q±3.5
69.3
21.3±4.5
••• : SRT accumulation during the intermittent aeration period.
100
90
80 "If. 70
I 60
60
J 40
30
20
10
0 SCODre% NH3-Nre% STlNra%
m EMMC medfum carrier • EMMC large carrier C EMMC blobarrel cartier
Figure 4.9 Performance comparison among previous EMMC systems and EMMCbiobarrel system at HRT of 9h with intermittent aeration of Ih air on! 2h air off
71
b. Comparison of performance at HRT of 6h with continuous aeration
Song (2003) investigated a fixed bed EMMC process with packing ratio of39.8%
under various operation conditions. Table 4.14 and Figure 4.10 show the performance
comparison between medium carrier EMMC system and EMMC-biobarrel system.
Table 4.14 Performance comparison ofEMMC and EMMC biobarrel processes at HRT of 6h with continuous aeration*
Parameters Medium carrier
(O=lem)
Packing ratio % 39.8
SCOD loading rate 0.75
(glLld)
SCODre% 95.9±4.4
N loading rate 0.Q75
gILId
S~-Nre% 98.9±O.1
STlNre% 51.7±3.6
"': EMMC data 18 from Song's (2003) Master's Thesis
100
90
80
H j :
20
10
o "---'JJ.LLJ.J.L
seOOre% SNH3-Nre%
EMMC-biobarrel carrier
STlNre%
(0=3.8 em)
20
0.75
97.5±1.5
0.Q75
99.5:tO.5
42.2±7.6
[J EMtoIC medium • EM\IC b10barrel
Figure 4.10 Performance comparison ofEMMC (medium carrier) and EMMCbiobarrel processes at HRT of 6h with continuous aeration
72
As shown in Table 4.13 and Figure 4.10, although the packing ratio ofEMMC
(medium carrier) process was about two times higher than that ofEMMC-biobarrel
process, these two systems achieved comparable SCOD and ammonia nitrogen removals
and the total nitrogen removal efficiency of EMMC-biobarrel process was about 10%
lower than that of the EMMC (medium carrier) process.
Theoretically, with certain total volume, the small carrier system is more efficient
for the wastewater treatment since the smaIIer carrier can provide larger specific area for
the microbial growth. Cao (1998) reported the smaller EMMC carrier provides less
resistance to the mass transfer. However, the comparison among the EMMC and EMMC
biobarrel systems indicates that EMMC-biobarrel carrier can achieve at least comparable
performance for COD and ammonia removals with the systems using smaIIer carriers.
This phenomenon may be explained as follows:
1) Although the EMMC-biobarrel carrier is much larger than the previous EMMC
carriers in total diameter, the innovative structure ofbiobarrel rings, which is
presented in Figure 3.1 can divide the CTA matrix into small parts. Therefore, an
EMMC-biobarrel carrier is actually a combination of several smaller carrier
elements.
2) Unlike the smaller carriers which tend to settle in the bottom of the reactors, the
EMMC-biobarrel carriers occupy more space due to its bigger size. Therefore, the
distribution of carriers in EMMC-biobarrel system is more "loosen" than those in
the previous EMMC systems. On one hand, the "loosen" distribution suggests that
the biobarrel carriers occupy more space in the reactor, which prolongs the actual
contact time, i.e., biological reaction time of carriers with incoming substrate. On
73
the other hand, the "loosen" distribution could be negative to the development of
anoxic zones in the reactor, which may inhibit the denitrification process. This
also could partia11y contribute to the lower total nitrogen removal efficiency
achieved by the EMMC-biobarrel system.
4.1.5 Summary of single-layer EMMC-biobarrel processes for synthetic wastewater treatment
The single-layer EMMC-biobarrel processes with packing ratio of 10% and 20%
were studied for the simultaneous removal of carbon and nitrogen in one single reactor to
treat synthetic wastewater under various operational conditions. EMMC-biobarrel
process demonstrates good performance in carbon and nitrogen removals. The
conclusions resulting from this study are summarized as follows:
1) Packing ratio has little impact on system performance of SCOD removal and
nitrification removal under continuous aeration. Both systems achieve high SCOD
removal (96%) and ammonia nitrogen removal (>99%) efficiencies at COD
loading rate ofO.7SglUd and nitrogen loading rate of0.16g1Ud. However, system
II (20%) presents higher total nitrogen removal due to the greater specific surface
area and the potentially better development of anoxic enviromnents.
2) System performance of total nitrogen removal showed strong response to the
influent CODIN ratio. System II is able to remove SO% of total nitrogen at HRT of
9h and continuous aeration when the influent CODIN ratio is S. Under same
operational conditions, the total nitrogen removal efficiency at CODIN ratio of 8
was higher than that at CODIN ratio ofS.
74
3) Air supply influences the system performance in a significant way. At HRT of9h,
with intermittent aeration of lh air on and 2h air off, both systems achieves 89%
of SCOD removal; the nitrification efficiencies of system I and IT were only 46%
and 69% respectively. When the continuous aeration is applied, the SCOD
removal efficiencies are improved to 96% of SCOD removal and almost complete
nitrification were achieved by both systems; total nitrogen removal efficiencies of
20% and 10% system are 50% and 36%, respectively. These results suggest that
EMMC-biobarrel system requires higher oxygen input to achieve complete carbon
and nitrogen oxidation. Also, the concurrent anoxic-aerobic conditions can be
well-developed under continuous aeration due to the presence of the EMMC
biobarrel carriers.
4) For the continuous aeration, reducing HRT from 9h to 6h had little impact on
SCOD removal and nitrification for system IT; however, the total nitrogen removal
efficiency decreased from 50% to 42%. HRT of 3h is not recommended for
EMMC-biobarrel process since the nitrifiers can not be developed for better
nitrification process.
5) The suggested systems performances under different operational conditions are
listed in Table 4.15.
6) Both systems achieved much higher SRTs than that achieved by conventional
activated sludge process. After 50 days of operation, the SRTs in system I and
systems IT were 85 days and 220 days, respectively. The high SRT ensures the
concentration of slow-growing bacteria such as nitrifers, resulting in the high COD
removal and nitrification efficiencies.
75
Table 4.15 SummaJ~ of systems performanees under various 0 !Jera 0 eon ODS ti naI dlti Packing Intluent Operation Conditions SCOD NH3-N TIN
Ratio CODIN Removal Removal % Removal
Ratio HRT(h) Aeration schedule % %
10% 5 9 Ih air onl2h air off 89.0 46.7 20.8
9 Continuous air 96.0 99.0 36.1
6 Continuous air 96.9 99.4 37.6
20% 5 9 lh air onl2h air off 89.0 69.3 21.3
9 Continuous air 96.2 99.7 50.1
6 Continuous air 97.5 99.5 42.2
3 Continuous air 89.7 55.8 -3.5
8 6 Continuous air 97.9 99.7 47.3
7) System II 20% EMMC-blObarrel system IS able to achieve comparable
performance for SCOD and ammonia nitrogen removal but slightly lower total
nitrogen removal efficiencies with previous EMMC systems with packing ratio of
32% and 39.8%. This suggests that EMMC-biobarrel process is technically
feasible to be used for replacing the previous EMMC process.
4.2 Fixed bed double-layer EMMC-biobarrel process
Double-layer fixed bed EMMC-biobarrel process is designed for improving the
system mass transfer efficiency and reducing the chemicals cost for the carrier making.
Also, it introduced the engineering design concept so-called "reactors in series" to
EMMC process in order to improve the system performance. In double-layer system,
EMMC-biobarrel carriers with packing ratio of 13% (system III) were separated into two
layers which occupy certain volume of the bottom and top parts of the reactor. The same
operational conditions were controlled as those for the single-layer system.
76
4.2.1 Process performance
a. Process performance at HRT of 9h and intermittent aeration of Ih onl2h off (Experiment 6)
The process performance of double-layer EMMC-biobarrel system operated at
HRT of 9h with intermittent aeration of Ih air onl2h air off is presented in Table 4.16.
As shown in Table 4.16, at HRT of9h and intermittent aeration Ih on/2h off,
system ill achieved a good perfonnance on SCOD removal (95.6%). However, the
nitrification efficiency was only 71.4% and the total nitrogen removal was 29.8%.
Similar to the situation of single-layer system, the poor nitrification performance resulted
from the lack of oxygen supply and the carrier resistance to the mass transfer. The
relatively low total nitrogen removal could be due to 1) the poorly developed nitrification
and 2) short of carbon source.
Table 4.16 Double-layer EMMC-biobarrel process performance at HRT of9h with intermittent aeration of Ih onl2h off
Parameters Influent System ill
SCOD(mg/L) 219:±37 9.6S±4.2
SCODre% 9S.6±1.7
S~-N(mg/l) 43.S±7.7 13.9±4.8
S~-Nre% 71.4±IO.1
SNDJ"-N (mg/l) 13.4±2.3
SNOi-N (mg/l) 4.3±O.6
SNOx-Nre% 41.8±9.2
STIN (mg/L) 43.S±7.7 30.3j:4.5
STlNre% 29.8±7.2
pH 7.3-7.8 7.2-7.6
TSS 6.8±6.3
77
b. Process performance at HRT of 9h with continuous aeration (Experiment 7)
The process performances of fixed bed double-layer EMMC-biobarrel process at
HRT of9h with continuous aeration is presented in Table 4.17.
As shown, under continuous aeration, system achieved 96.4% ofSCOD removal
efficiency. Additionally, since sufficient oxygen was provided for nitrifiers growth, the
nitrification efficiency was dramatically increased to 98.2%. The total nitrogen removal
efficiency was 42%, suggesting the concurrent aerobic/anoxic environments can be
developed in the system.
Table 4.17 Double-layer EMMC-biobarrel process performance at HRT of 9h with continuous aeration
Parameters Influent Double layer (13%)
SCOD(mg/L) 208±6.5 7.4±1.5
SCODre% 96.4±O.8
SNFJ4-N(mgll) 37.6±1.2 O.7±O.2
SNH4-Nre% 98.2±2.0
SNOi-N (mgll) 18.4±.4.4
SNO£-N (mgll) 1.4±O.8
STIN (mg/L) 37.6±1.2 21.8±1.5
STINre% 42.0±2.7
pH 7.5-8.3 6.8-7.2
TSS 11.7±3.7
Co Process performance at HRT of 6h and continuous aeration (Experiment 8)
Double-layer system (system Ill) demonstrated good performance at HRT of 9h
with continuous aeration. In this experiment, the system HRT was further reduced to 6h
to test the system performance at higher loading rate. The results are presented in Table
4.18. 78
As shown in Table4.1S, at HRT of6h with continuous aeration, system ill showed
good performance on both SCOD and ammonia nitrogen removals. This suggests that
HRT of 6h is enough for the double layer system for the removal of organics and
ammonia. The tota1 nitrogen removal efficiency was about 40%, which is relatively high
considering the low CODIN ratio and low HRT applied.
Table 4.18 Double layer EMMC-biobarrel process performance at HRT of 6h with continuous aeration
Parameters Influent System ill
SCOD(mg/L) 215.0±17.S 7.2±2.5
SCODre% 96.6±1.1
SNJ4-N(mgll) 3S.2±2.5 1.3±O.4
SNJ4-Nre% 96.6±1.2
SN03"-N (mgll) 20.5±2.3
SNOi-N (mgll) 1.3±O.S
STIN (mg/L) 3S.2±2.5 23.1±2.1
STINre% 39.6±2.7
pH 7.S-S.5 7.2-7.6
TSS 13.S±3.5
4.2.2 Impact of operation condition on the process performance characteristics
Similar to the single-layer system, double-layer EMMC-biobarrel system shows
response to the change of operational conditions such as aeration schedule and HRT.
a. Effect of aeration schedule
The performance comparison of system ill at different aeration schedule is
presented in Table 4.19 and Figure. 4.11.
79
Table 4.19 The test of significant difference of system m under different aeration
schedule
Parameters HRT=9h HRT=9h t-value Criticalt
Continuous value·
Ih air onl2h aeration (n1+02-2)=13
air off n2=7
n1=8
SCODre% 95.6±1.7 96.4±0.8 -1.1458 ±2.2281
NH3-Nre% 71.4±10.1 98.2±2.4 -4.0695 ±2.3060
STINre% 29.8±7.2 42.0±2.7 -4.7682 ±2.2621
100
90
~ 80
II 70 U 60
~ • lh air on/2h air off 50
Iii 1:1 Omtinuous aeration
-= 40
a 30 E
20 &! 10
0 SOOOre NH3-Nre SllNre
Figure 4.11 Performance comparison of system m at different aeration schedule
At HRT of9h, the change of aeration schedule from Ih air onl2h air off to
continuous aeration has little impact on organics removal. The system achieved about
96% of SCOD removal efficiency under both aeration schedules. However, the
nitrification efficiency increased from 71.4% to 98.2% when switching the aeration
schedule from Ih air onl2h air off to the continuous aeration. Apparently, sufficient
oxygen supply is required for EMMC-biobarrel system to remove ammonia-nitrogen. In
80
addition, compared to the intennittent aeration, the total nitrogen removal at continuous
aeration is increased about 12%. This suggests the double-layer EMMC-biobarrel system
is able to achieve simultaneous carbon and nitrogen removal for the operation of
continuous aeration.
b. Effect ofHRT
Table 4.20 The test of sil!Ilificant difference of s' stem m at different HRTs Parameters HRT=9h HRT~6h t-value Critical t
Continuous Continuous value*
aeration aeration (nl+n2-2)=13
nl=7 nr9
SCODre% 96.4±0.8 96.6±1.l -0.471 ±2.1448
NH3-Nre% 98.2±2.0 96.6±1.2 1.9038 ±2.2622
STlNre% 42.0±2.7 39.6±2.7 1.7682 ±2.1604
100
90 -~ 80
III 70 "ll
60 Iii l-tRT=9h1 "ll 50 Ii 40
IJtRT=I!h ~ 30
! 20
10
0 SCODre NlG-Nre SllNre
Figure 4.12 Performance comparison of system m at different HRTs
AB shown in Table 4.20 and Figure 4.12, the reduction ofHRT from 9h to 6h
almost has no impact on the system's performance. This suggests that the double-layer
system is able to handle the shock load in certain extent. The good performance at lower
81
HRT (Le. higher loading rate) could be due to the double-layer design and the biomass
concentration increasing inside the carrier with the increasing of operation days. Note
that the suspended biomass concentration at HRT of 6h was still relatively low.
4.2.3 Evaluation of SRT
Based on the Equation 4.1, SRT of double-layer EMMC-biobarrel process was
estimated as following and is presented in Fig.4.13.
As presented in Fig.4.13, the SRT of double-layer EMMC-biobarrel process can
reach about 200 days after 33 days of operation. The high SRT responds to the good
performance of the system used.
200.00
180.00 180.00 140.00
i 120.00 - 100.00 Iii 80.00
'" 80.00 40.00 20.00
0.00 0 5 10 15 20 25 30 35
08". of opemllan
Figure 4.13 SRT accumulation of system m (double-layer EMMC-biobarrel process)
82
4.3 Comparison of fixed bed single-layer and double-layer EMMC-biobarrel processes
4.3.1 Comparison of system configuration
The descriptions for the system I, II, ill are presented in Table 4.21.
Table 4.21 Comparison of systems co tion Parameters System I Systemn System ill
Total volume (ml) 4760 4965 189000
Void volume (ml) 4284 3972 16440
Packing ratio (%) 10% 20% 13%
Packing density 12.1 12.5 11.4
(numberlL)*
Carrier supporting No No PE plastic cage
Air flow rate 5 5 19.5
(Umin) . . .
*: Packing denslty= number of carner/space volume occuPied by carner
In the single-layer system, all the carriers were randomly packed, forming one
layer by the gravity. While for the double-layer system, the carriers were separated into
two layers by introducing the plastic cages. In system n, the carriers occupied the space
from the bottom to the top of the reactor. In system I, only half of the reactor space was
occupied by the carriers. Therefore, althougli the packing ratio (the costs for carrier
making) was reduced to half, the actual reaction time was also reduced. Therefore, the
idea behind double-layer design is to utilize the space in the reactor more efficiently with
lower packing ratio applied.
The same packing density of system I and system II were made, which is slightly
higher than system ill. This is because the cage shape and size influences the carrier
distribution within each layer in certain extent. 83
4.3.2 Comparison of SRT accumnlation rate
Figure 4.14 (a, b, c) present the SRT accumulation rate during the operation of
HRT of9h with intermittent aeration of Ih onl2h off. As shown, the SRT accumulation
rate of system ill was estimated as 10.6 days/day of operation, which was much higher
than those of the single-layer systems. This was partially due to the higher COD removal
performance of double-layer system as mentioned previously. Besides, according to
Equation 4.1, the SS concentration in the effiuent is another important factor which
affects the SRT accumnlation rate. The mean SS concentration in the effiuent of the three
systems during the operation ofHRT of9h with intermittent aeration was 18.8 mg/L,
15.6mg/L and 6.8 mg/L, respectively. The lower effiuent SS concentration in the effiuent
of system ill suggests that the biomass could be "held" more effectively by the double
layer structure. Another factor which may contribute to the low SS concentration is that
the carrier supporter, i.e., the plastic cage can also serve as "sludge holder" by attsching
the biomass.
84
60.00
60.00 _ 40.00
I: 30.00
I;: 20.00
til 10.00
0.00 I----"~~-~--~--~-~--~
-10.00 5 10 15 20 25 30
Days of operation
a. SRT accumulation in system n dnrlng the operation ofHRT of9h with intermittent aeration of Ih onl2h otT
60
70
60
160 _40
1;:30 til
20
10 0
0 6 10 15 20 25 30 35 40
Days of operallon
b. SRT accumulation in system n dnrlng the operation of HRT of 9h with intermittent aeration of Ih onl2h otT
200.00
150.00
i 100.00
Ii 50.00
0.00 f-----~~~~'---~--~--~ 5 10 15 20
-50.00
Days of operation
Co SRT accumulation in system n during the operation ofHRT of9h with intermittent aeration of Ih onl2h otT
Figure 4.14 SRT accumulation rates of the three systems
85
4.3.3 Comparison of performance
The operational conditions for these three systems were operated under similar
conditions in order to compare the system performances.
a. Performance comparison at HRT of 9h and intermittent aeration of Ih air onl2h air off
The performance comparisons of single-layer and double-layer systems are
presented in Table 4.22 and Fig.4.15.
Table 4.22 The test of significant differences betwcen the removal efficiencies (%) of single-layer system and double-layer system at HRT of 9h with intermittent aeration of Ih onl2h off Parameters System Criticalt
System I SystemD systemm t-value value'"
n=lO n=lO n=9 n\+n2-2=15
SCOD 89.0±3.5 95.6j).7 -5.28915 ±2.2001
89.0±3.8 95.6±1.7 -7.4380 ±2.0860
NH3-N 46.7±6.2 71.4±10.I -5.7803 ±2.2622
69.3±5.8 71.4±10.1 -0.2412 ±2.3060
STIN 20.8±3.8 29.8±7.2 -3.0139 ±2.3060
21.3±4.5 29.8±7.2 -1.9112 ±2.1604
"':95% confidence
As shown in Table 4.22 and Figure 4.17, the SCOD removal and NH3-N removal
efficiencies achieved by double-layer system were much higher than those achieved by
10% single-layer system, although the packing ratio difference was only 3%. With lower
packing ratio, double-layer system (13%) achieved comparable nitrification and total
86
nitrogen removal efficiencies with single layer system (20%). Additionally, the SCOD
removal of double layer system was even higher. These results suggest that double layer
design can improve the pollutant removal efficiencies by enhancing the oxygen mass
transfer.
100
90
II 80
"l3 70 c -tl 80 • single layer 10"k
'Ill 50 IJ single layer 20%
~ 40 D double layer 13%
~ 30
20
10
0 SCX)[)re NJ-B.Nre STNre
Figure 4.15 Performance comparisons among system I. II and m at HRT of9h with intermittent aeration of Ih onl2h off
b. Performance comparison at HRT of9h and continuons aeration
Table 4.22 and Fig.4.16 gives the performance comparison of single-layer and
double-layer systems at HRT of 9h with continuous aeration.
At HRT of9h and continuous aeration, all systems achieve comparable SCOD
removal and nitrification efficiencies. For total nitrogen removal, system 11 achieved the
highest (50.1 %) among these three systems, following with system ill (42.1 %) and
system I (36.1%).
87
Table 4.23 The test of significant differences between tbe removal efficiencies (%) of smlde-layer ystem and double-layer system at HRT=9h witb continuous aeration Parameters System Critical t value*
System! System II System III t-value n)+n2-2=14
n=9 n=9 n=9
SCOD 96.0±2.1 96.4±.O.8 0.9093 ±2.2622
96.2±2.2 96.4±.O.8 -1.1496 ±2.3060
NH3-N 99.0±1.0 98.2±2.4 -0.9655 ±2.3060
99.7±0.1 98.2±2.4 1.9481 ±2.4469
STIN 36.1±6.7 42.1±2.7 2.2363 ±2.2281
50.1±5.7 42.1±2.7 4.2330 ±2.2001
*:95% confidence
100
!! 90 so
I 70
~ so • System)
50 C System 0 Ii 40 cSystemm
! 30
i 20 10 0
SOODre N-B-Nre SilNre
Figure 4.16 Performance comparisons among system I, n and m at HRT of 9h witb continuous aeration
The higher total nitrogen removal efficiency in system II can be explained by I) the
higher biomass concentration resulted from the higher packing ratio; and 2) the better
developed anoxic environments due to the more "compact" distribution of carriers in the
system.
88
c. Performance comparison at HRT of 6h with continuous aeration
The performance comparison of system I, II, m are presented in Table 4.24 and
Fig.4.17.
At HRT of 6h, all the systems achieved comparable organics removal. Although the
nitrification efficiency of system m was slightly lower than the other systems, the total
nitrogen removal of system m was higher than system I and comparable with system II.
Table 4.24 The test of significant differences between the removal efficiencies (%) of sinlde layer s /Stem and double layer system at HRT of 6h with continuous aeration Parameters System Critical t
System I System II systemm t-value value*
n=1O n=1O n=9 n1+n2-2=17
SCOD 96.9.±2.6 96.6i:1.1 0.6190 ±2.1603
97.5±1.8 96.6i:1.1 1.1069 ±2.1315
NH3-N 99.4±1.0 96.6i:1.2 5.2712 ±2.1098
99.5±O.5 96.6i:1.2 6.8231 ±2.2281
STIN 34.5±5.2 39.6±2.7 -4.1209 ±2.1098
42.2±7.6 39.6i:2.7 0.9804 ±2.2001
*:95% confidence
89
100 - 90 ~ SO
I 70 c SO • System! " 13 50 &1 System 0 Iii 40 cSystemm
1 30
! 20 10 0
SCODre NfIl-N SlIN
Figure 4.17 Performance comparison of the system I, II and m at HRT of 6b with continuous aeration
4.3.4 Comparison of single-layer and double-layer configurations with engineering
concerns
Based on the experimental results, both the single-layer and double-layer EMMC-
biobarrel processes are able to achieve good performance in the pollutant removal.
However, in engineering stand point, it is necessary to compare these two configurations
in order to optimize the process design both technically and economically.
4.3.4.1 Technical concern
a. Oxygen mass transfer efficiency
Dissolved oxygen is one of the critical parameters for aerobic biological treatment
since well developed aerobic condition is required for both organics and ammonia
oxidation (Metcalf and Eddy, 2003). A system with better oxygen mass transfer
efficiency, therefore, is expected to achieve higher COD and ammonia removals.
Introducing double layer design to EMMC-biobarrel process is considered as an
approach to improve system mass transfer. One of the most important factors affect mass
90
transfer efficiency is the interfacial surface area. For a packed-bed system, in a certain
extent, reducing packing density (the number of the media in unit volume) can result in
higher mass transfer efficiency because lower packing density can avoid the surface
overlapping, i.e., the waste of specific area. With similar concept, EMMC carriers were
split to double-layer in order to improve the interfacial area between carrier and incoming
oxygen and substrate, and consequently, the treatment efficiency.
This approach was verified by the experiment result. Under the operation of HRT of
9h with intermittent aeration of Ih onl2h off. double-layer system achieved higher COD
and ammonia nitrogen removal efficiencies than single-layer systems, suggesting a better
mass transfer developed in the double-layer system.
b. System performance
"Reactors in series" design has been proved as an effective approach to improve
system performance (Sundstorm, 1979). Double-layer EMMC-biobarrel system can be
considered as EMMC reactors in series in the system.
Based on the experiment results, double-layer system (13%) achieves higher
performance than single-layer system with lower packing ratio (10%) at all the
operational conditions. Compared to the single-layer system with higher packing ratio
(20%), the performances of double-layer system are comparable or slightly lower,
suggesting double-layer design is technically feasible to be applied in EMMC-biobarrel
process.
Another potential advantage of double layer system is the capability of toleration to
the shock load. Experiment data suggested that when the HRT was reduced from 9h to 6h,
91
there was almost no impact on the system perfonnance. This feature ensures the
reliability of double-layer system for absorbing the potential shock loading condition.
4.3.4.2. Economic concern
The differences between the single-layer and double-layer system configurations
include the carrier packing ratio and the employment of layer support, i.e., the plastic
cage.
A cost analysis was made in order to evaluate the economics feasibility of applying
double-layer design in the EMMC-biobarrel system. Table 4.25 gives the unit cost for the
carrier making materials. A carrier making cost comparison is presented in Table 4.26.
For the double-layer system, although adopting the plastic cages adds the costs for
material purchasing, the chemicals cost saving due to the lower packing ratio lead to a
lower total materials cost. As shown in Table 4.25, for a lab scale (5L) system, the
materials cost difference between single-layer (20%) and double-layer (13%) was $0.33.
It is expected that this materials cost difference will be enlarged with the increasing of the
process scale. Additionally, because the required labor for the plastic cage making is less
than that for the carrier making, the total labor cost for double-layer configuration can be
lower than that for single layer configuration.
Besides material and labor cost, double-layer design also has the potential to save
the energy cost in the large scale application due to the more efficient oxygen and
substrate mass transfer. Therefore, it is more economically sound to adopt the double
layer configuration than the single layer one.
92
Table 4.25 Unit cost for carrier materlals Item Unit cost
Chemicals Cellulose Triacetate $2.081lb
Methylene Chloride $O.861lb
Toluene $O.601lb
Biobmel Biobmel media $17.6/cu ft ($621.5/cu m)
Biomass Biomass $OIL
Plastic cage Plastic sheet $0.43/s ft
T bl 4.26 Mat rlals t anal Is" a e e cos ilYS Item Single layer (20%) Double layer (13%)
Cellulose Triacetate $0.46 $0.30
Methylene Chloride $2.51 $1.63
Toluene $1.38 $0.90
Biomass $0.00 $0.00
Biobmel Ring** $2.45 $1.60
Plastic Cage··· $0.88
Total···· $3.49 $3.16
. *: Evaluation based on reactor With total volume of 5L **: Assume Biobarrel rings actual volume are 75% ,37% and 49% of the total reactor space for the 20%, I 0% and 13% systems, respectively ***: Cost calculation based on the surface area of the plastic cage with a safety factor of 1.5 ****: Assume methylene chloride and toluene bave 85% recoverymtes (Zhang, 1995)
93
4.4 Real domestic wastewater application by using EMMC-biobarrel process
The performance ofEMMC-biobarrel process (system II) for real domestic
wastewater treatment was investigated. Real domestic wastewater was taken from
primary settling tank of East Honolulu Wastewater Treatment Plant in Oahu, Hawaii
(EHWWTP).
According to the previous studies results (Cao, 1998) and preliminary conclusions
of this study, the operation conditions for the real wastewater treatment was set as HRT
of 9h with intermittent aeration of Ih onl2h off. The process performance is snmmarized
in Table 4.27.
Table 4.27 Process performance ofEMMC-biobarrel system II to treat real wastewater at HRT of 9h with Ih air onl2h air off
Parameters Influent System II
TCOD(mgIL) 212±74 44.1±10.2
TCODre% 77.5±7.9
SCOD(mgIL) 119.3±30.4 36.6±5.3
SCODre% 67.6±8.9
SNH3-N(mg/l) 17.9±3.7 l.5±1.3
SNH3-Nre% 92.1±4.9
SN03-·N (mg/l) 5.7±2.0
SN~-·N (mg/l) 1.6±O.9
STIN (mgIL) 17.9±3.7 7.9±4.4
STINre% 52.6±12.0
pH 6.6-7.0 7.3-7.7
TSS 85.8±13.8 30.2±7.4
In real domestic wastewater, not all the organics or COD can be used by
microorganisms, i.e., certain portion of organics in will remain in the effluent as residual
94
COD. A biodegradability measurement (using batch reactor) is usually conducted to
determine the amount of carbon source in the wastewater that can be utilized as food for
microbial population. The biodegradability of wastewater is calculated by the following
equation:
Biodegradability (%) _S_C_o_'/J.::IlI_-_S_C_o_'/J-'!'!If,-x 100% SCODIlI
According to Cao (1998), the biodegradability ofEHWWTP wastewater is about
73.8%. EMMC-biobarrel process achieved about 67.6% of total SCaD removal;
therefore, the removal efficiency for the biodegradable SCaD was calculated as
67.6173.8* 1000/0=92%.
Based on the biodegradability measurement, the mean ratio of usable SCODINH3-
N ofEHWWTP wastewater was estimated as 5. EMMC-biobarrel system achieved 92%
of nitrification and 52.6% of total soluble inorganic nitrogen removal efficiency in
average. It was also found that the STIN removal performance was varied to certain
extent during test period due to the variation of influent CODIN ratio.
It is found that even though the same operational conditions were applied, the
performance demonstrated by the system could be different in certain extent depending
on other parameters such as substrate type and loading rates. Table 4.28 presents the
performances comparison of using synthetic wastewater and real wastewater as influent
at same operational conditions.
95
As shown in Table 4.28, although the operational conditions for synthetic
wastewater and EHWWfP wastewater treatment were almost same, the system achieved
better performances in treating EHWWfP wastewater because the pollutants
concentration in actua1 wastewater was much lower. This suggests that for optimizing the
design criteria for application ofEMMC-biobarrel process in real wastewater treatment,
many factors including substrate type, concentration, biodegradability need to be
seriously considered.
Table 4.28 Performances comparison of system II for treating synthetic wastewater and real wastewater at HRT of 9h with Intermittent aeration Ih onl2h off Parameter Synthetic wastewater EHWWPT wastewater
SCOD(mgIL) 184.0 88.6*
SCOD loading rate 0.49 0.24
(glUd)
SNH3-N (mgIL) 41.2 17.9
STIN loading rate (gIUd) 0.11 0.05
SCOD/SNH3-N 5 5
SCOD removal (%) 89 92.0
SNH3-N removal (%) 69.3 92.1
STIN removal (%) 21.3 52.6
"': Usable SCOD concentration m the EHWWPT.
4.5 Comparison with other compact biological wastewater treatment processes
Compact biological wastewater treatment processes are designed for sma11 scale or
land limited applications. The main compact biological wastewater treatment processes
include membrane bioreactor (MBR), moving bed bioreactor (MBBR), and integrated
96
fixed bed activated sludge (IF AS). In this section, the perfonnance ofEMMC-biobarrel
process will be compared with those of above processes in order to evaluate the potential
ofEMMC-biobarrel process for actual applications.
4.5.1 Comparison with MBR process
a. Comparison with single-stage MBR process
Perfonnance of single-stage MBR processes for domestic wastewater treatment has
been investigated for decades. In general, single-stage MBR process is able to achieve
high organics and SS removal efficiencies. Regarding to nitrogen removal, MBR process
has been shown to provide completely nitrification (>99%) and partial denitrification of
municipal wastewater, resulting in low ammonia and organic nitrogen concentrations but
high nitrate concentration (Fan et al. 1996). Table 4.29 shows the perfonnance
comparison between a typical single-stage MBR and EMMC-biobarrel processes.
As shown in Table 4.29, both of the single stage MBR and the EMMC-biobarrel
processes demonstrate the advantages and disadvantages. On one hand, the single-stage
MBR achieved about 10% higher TCOD removal efficiency than that ofEMMC
biobarrel process. This is because the ultrafiltration (UF) membrane is able to completely
prevent the suspended solid from being washed out, and consequently, leads to a lower
TCOD concentration. On the other hand, because the concurrent aerobic/anoxic
conditions can be well developed in the EMMC-biobarrel process due to the presence of
the carrier, EMMC-biobarrel process achieved about 23% higher total nitrogen removal
efficiency than that of single stage MBR even at a lower influent CODIN mtio.
MBR process requires high cost related to the membrane purchasing, fouling
remediation and energy consumption. Therefore, it seems that EMMC-biobarrel is more
97
t
cost effective than MBR due to the simple configuration and easy operation and
maintenance.
Table 4.29 Process performance ofMBR (Fan et aI. 1996) compared with the EMMCbi b I - 0 arre rocess Parameters Unit Single stage MBR Double-layer
EMMC-biobarrel'l'
TCOD loading rate kg/m'/day 1.32 0.86
IN loading rate kg/m'/day 0.17 0.15
TCODIN . 7.7 5.7
TCOD reduction % 96 86
NH3-N reduction % >99 96.6
IN reduction % 17 39.6
TSS reduction % >99 --Aeration schedule Continuous Continuous
>to: Data are based on the synthetic wastewater treatment by usmg the double layer EMMC-biobarrel process at HRT of 6h.
b. Comparison with multi-stage MBR process
Many modifications to single stage MBR process has been made for improving total
nitrogen removal. Among the various alternatives, multi-stage MBR process is
considered the most reliable and practical one. The biological nitrogen removal
performance comparison between typical multi-stage MBR processes and EMMC-
biobarrel processes is snmmarized in Table 4.30.
As shown, multi-stage nitrogen removal strategy is able to improve the total
nitrogen removal. Similar to the conventional activated sludge processes, more stages
design leads to higher performance. However, in economics concern, the multi-stage
approach adds to the complexity and the cost of the wastewater treatment process
98
Table 4.30 Performance comparison between multi-stage MBR processes and EMMC bi b I Ii d ti - o arre I process or omes c wastewater treatment Parameter Unit MBRI· MBR2·· Double layer
Two stages Four stages EMMC-
biobarrel
TCOD loading rate kglm'/day 1.06 0.38-5.08 0.86
TN loading rate kglm'/day 0.18 0.06-0.24 0.15
TCODIN 5.9 6-20 5.7
NH3-N reduction % >99 99 96.6
TN reduction % 50-60 72-80 39.6
.: Two stage MBR design: anOluc/OluC. Qin et at. 2005 . •• : Four stage MBR design: anoxic/anaerobicloxiclanoxic. Yoon et at. 2004
EMMC-biobarrel process achieved about 100/tr" 30% lower total nitrogen removals
than multi-stage MBR process at similar operational conditions. Based on the previous
studies on EMMC process (Cao, 1998; Zhang, 1995), the system performance can be
improved by increasing the HRT and applying proper aeration schedule. In other words,
the optimization of design and operation criteria is expected to minimize the difference of
these two processes. Additionally, the cost for EMMC-biobarrel process can be much
lower than that of multi stage MBR process. All these suggest that EMMC-biobarrel
process may be a more suitable technology than MBR for certain application scenarios.
4.5.2 Comparison with MBBR and IF AS processes
EMMC-biobarrel process, MBBR and IF AS processes can be grouped into cell-
immobilization technology, in which small media elements are utilized to immobilize the
microorganisms in order to achieve high biomass concentration. However, there are
differences among theses three processes in design concepts and system performance.
The general comparisons of the three processes are discussed as following:
99
Design concept
a. Cell-immobilization strategies
Although these tbree processes can be categorized to cell-immobilization
technology, their strategies for immobi1izing cell are different. Generally, the media
elements in IF AS and MBBR immobilize microorganisms by the "attachment" of the
biomass onto the surface of the carrier; while for EMMC-biobarrel, most of the biomass
are "entrapped" inside the carrier.
b. Carrier element
The carrier size for MBBR and IFAS is usually sma11 (D= lcm). For MBBR
process the packing ratio is relatively high (500/ .... 70%) and for IF AS is about 200/ .... 30%
because in IF AS process the media is designed to be combined with suspended culture.
Although the overall size ofEMMC-biobarrel carrier (D=3.8cm; H=3.8cm) is
much larger compared to those ofMBBR and IF AS, the innovative structure ofbiobarrel
ring divides the matrix into several small parts inside of the carrier, which results in an
actua11y great specific area for biomass accumu1ation.
Co System confignration
As discussed previously, one of the advantages ofEMMC-biobarrel process is the
simple configuration. Because most of the biomass is entrapped inside the carriers and
hardly to be washed out, the secondary clarifier can be eliminated. Therefore, the
EMMC-biobarrel process norma11y only involves the primary settling tank and aeration
tank.
For MBBR process, although the carriers posses the capability to maintain the
biomass concentration in certain level, the excessive sludge is still tended to be washed
100
out from the aeration tank. Therefore, secondary clarifier is required for the MBBR
process integration. Because the washed out sludge is in smaller amount compared to the
conventional activated sludge process, no biomass recirculation is required.
IF AS is a modification to conventional activated sludge process by adding media
elements into the aeration tank, which means the integration of the IFAS process, is
almost same with that of conventional ASP process, which include primary settling,
aeration tank, secondary settling tank, and, of course, sludge recycle facility. Because the
IF AS process is able to improve the capacity of existing activated sludge process with
simple modification, it has become an attractive technology to the wastewater treatment
plant owners.
System performance
a. Mass transfer efficiency
For MBBR and IF AS processes, the carrier elements are suspended in the aeration
tank while for EMMC-biobarrel process, the carriers are packed and fixed. As a result,
theoretically, the mass transfer efficiency in MBBR and IF AS process can be higher than
that in EMMC-biobarrel process. However, the mass transfer efficiency for EMMC
biobarrel is expected to be improved by modifying the carrier distribution design. In the
present study, it has been proved that double-layer design is able to improve the mass
transfer to certain level.
b. Pollutant removal efficiency
101
Generally, all the processes are able to achieve high COD removal and nitrification
efficiencies at proper operational conditions but the capabilities of removing total
nitrogen are different.
MBBR can hardly achieve simultaneous nitrification and denitrification (SND) due
to the relatively high operational DO concentration (norma11y 4-7mg/L). Therefore,
multi-stage nitrogen removal strategy is usually employed in MBBR process.
Most types of carrier for IF AS process are only designed for improving organics
removal and nitrification efficiencies, which mean that it is difficult to achieve total
nitrogen removal in most of single-stage IF AS processes. Although some types sponge
carrier is reported to guarantee 40% total nitrogen removal, their useful lives are
relatively short due to the damage of the carriers.
EMMC-biobarrel process is able to achieve simultaneous carbon and nitrogen
removal in the presence of the concurrent aerobic/anoxic conditions. Based on the
experiment data, at HRT of 6h, the system is able to remove about 40% oftota1 nitrogen
from influent with a CODIN ratio of 5. As discussed in Chapter 2, since the influent
CODIN ratio can significantly affect the nitrogen removal performance, it is expected the
EMMC-biobarrel process can achieve higher nitrogen removal efficiency for treating
wastewater with higher CODIN ratio.
A general comparison among the compact biological treatment processes is
presented in Table 4.31.
102
Table 4.31 General comparison of compact biological wastewater treatment systems Process Double-1ayer MBR
EMMC-biobmrel Process The mixed microbial A combined system Description were entmpped inside of includes a bioreactor
the biobmrel-ce\lulose and filtration UDit. triacetate carrier which were packed in two separate layers in the upflow reru:tor.
Technologies Coll-immobilized Suspended growth involved technology Membrane filtration
(Entrapment)
Carrier size 0=3.8cm; H~3.8cm
Carrier packing 13% ratio Advantages Simultaneons High effluent
nitrification and quality; denitrification; LowSS Low sludge production; concentmtion in No secondary clarifier; efiluent; No sludge recycle; Low sludge Easy operation and production; maintenance. Operation reIiabi1ity
andatability Nosecondmy clarifier; No sl. recycle
Drawbacks Limited mass transfer High oxygen efficiency; consumption; Back washing is High operation required. consumption;
Metnimme fou\ing; Low nitrogen removaI in aingie reru:tor.
': Carrier size for Kaldnes® process (Metcalf and Eddy. 2003). '0: Carrier size for Linpor® process (Metcalf and Eddy. 2003).
103
MBBR IFAS
Small floating carriers A modification to which can provide the conventional AS 1arge surface area are process by adding 1lIilized for carrier elements to microorganisms' aeration tank. growth and kept in circulaIion by the air introdnced at the bottom of the reru:tor. Auached growth Attached growth Suspended growth Suspended growth
0=1cm; 0=1-1.3 em" HcO.7em* 50% ... 70"10 20%-30"10
No back washing; Easy to be integrated Low head loss; with AS process; No clogging; Improved catbon Low manpowOl romovaland requirement nitrification
efficiencies; Flexible design
High fil1ing ratio; Sludge recycle is Low nitrogen removal required; in aingIe reactor; Low nitrogen Air distributor removal washing is required.
Chapter 5. Potential Applications and Economics Analysis
According to the experiment results, EMMC-biobarrel processes have been proved
to be able to 1) maintain a high concentration of biomass (Le., long SRT), which ensures
the high pollutants removal performances and 2) accommodate nitrification,
denitrification and biological oxidation in a single reactor. Additionally, since most of the
biomass is entrapped inside the carriers, the sludge loading to the secondary clarifier can
be minimized and no sludge recycle is required, which leads to a significant saving of
space and energy. All these features make EMMC-biobarrel a promising technology in
many applications.
5.1 Application in aerobic treatment unit for onsite treatment
5.1.1 Technical Potential
According to EPA decentralized treatment technology fact sheet (2000), aerobic
treatment units (ATUs) are considered as the most promising alternative to the failing
septic tank and have been widely applied in mainland U.S. However, it is found that one
of the main disadvantages of this technology is that it may release more nitrate to the
environment due to the incomplete nitrogen removal, which can cause the contamination
of surface and ground water, hence becoming a threat to environment and public health.
Since EMMC-biobarrel posses the capability of achieving simultaneous carbon and
nitrogen removals, introducing EMMC-biobarrel technology to ATU design can be a
104
proper approach to improve the nitrogenous pollutant reduction of the system. Besides,
involving EMMC-biobarrel to ATU design may lead to many other advantages. Firstly,
since the biomass concentration can be much higher than the conventional activated
sludge process, the reactor volume can be minimized, resulting in a capital cost saving for
the land and aeration tank manufacturing. Secondly, the sludge production rate in
EMMC-biobarrel process is very low due to the high concentration of biomass
maintaining in the system, the cost for sludge waste management, therefore, can be
mjnimized.
5.1.2 Design Criteria
NSF (National Sanitation Foundation) Standard 40 is a certification for individual
wastewater treatment with capacity up to 1,500 gallon (s,670L) per day and leads to
approvals as Class I and Class II plant. The limitation for Class I effiuent is listed in
Table 5.1.
Table 5.1 NSF Class I emuent performance Hmits
BOD&SS pH Color Odor Foam Noise
30mg/L 6.0-9.0 Units IS Units Non- None <6Odba@20
(monthly offensive feet
average) .
Source: NSF evaluation of JET Model, 1998
Currently, most of the aerobic treatment units are used for treating the effiuent from
the conventional septic tank. The influent characteristics for ATUs may vary from case to
case. Table 5.2 presents the data of typical septic tank effiuent characteristics.
lOS
Table 5.2 Tbe characteristics of typical effluent from septic tank BODs TSS TKN NH3-N TN
(mg/L) (mg/L) (mg/L) (mg/L) (mg/L)
Mean 200 130 36 23 36
Median 190 130 36 23 36
Maximum 360 230 44 35 44
Minimum 98 82 24 IS 24
StdDev. 52 32 4.1 2.1 4.1
Source: Health Department Report, 2005, WA
The design criteria for aerobic EMMC-biobarrel treatment unit will be based on the
NSF Standard 40 Class I limit. Additionally, nitrogenous pollutant reduction will also be
considered. The design criteria are listed in Table 5.3.
Table 5.3 Dcsign criteria for aerobic EMMC-biobarrel unit Parameters Tbe EMMC-biobarrel system
Packing design Double-layer
Packing ratio 13%
Operational temperature 25±3"C
Operational mode Continuous flow
HRT 12 hours
BODs loading 0.5 kglm'/day
TN loading O.lglm'/day
BODs removal efficiency >95%
NH3-N removal efficiency >95%
TN removal efficiency >40%
pH in the emuent 6-7 pH units
Air flow rate 1.15I.JL void volume/min
Aeration schedule Continuous aeration
106
It was found that the characteristics of septic tank emuent are similar to those of
synthetic wastewater used in this study. Therefore, the system performance in the lab-
scale experiment can be used for the design purpose.
Although the system is able to achieve good performance at HRT of 6-9 hours, the
HRT in the aerobic unit is designed as 12 hours. This is because that the aerobic
treatment unit is individually used treatment facility, the frequency of maintenance is
much lower than that in the actual wastewater treatment plant Therefore, applying longer
HRT is to ensure the system performance under less monitor and maintenance.
5.1.3 Economic evalnation for the aerobic EMMC-biobarrel units with capacities of 400 and 1,500 GD (gallons/day)
The needed capacity of aerobic treatment unit is estimated by the number of the
people in the house. It is assumed each person will use approximately 75-100 gallons
(284-378L) of water per day. According to the EPA decentralized technology fact sheet
(2000), the capacity of existing commercial ATUs ranges from 400-1,500 GD
(gallons/day) (1,512 -5,670Uday), which are suitable for families with different sizes.
In the economic analysis, the aerobic EMMC-biobarrel units with capacities of 400
and 1,500 gallons/day were evaluated in order to provide a cost range for the system
applications.
5.1.3.1 Evaluation of capital cost
a. Cost of Reactor
High density linear polyethylene is suggested as proper material for EMMC-biobarrel
reactor (Kongsil, 2006). The volume of the reactor depends on the hydraulic retention
107
time applied. Since the HRT of the aerobic treatment unit is set up as 12 hours, the
mjnjmum volume of the reactor for the units with capacities of 1,500 gallons/day and 400
gallons/day are 750 and 200 gallons, respectively. The information of the reactors which
are suitable for the two units is presented in the Table 5.4.
Table 5.4 Information ofEMMC-biobarrel reaetors 400-0DUnit
Reactor Volume (gallon) 300
Effective Volume (gallon) 200
Manufacturer Snyder Inc.
Price ( $/unit) 610
Source: Kongsil (2006) Master ThesIS. USAbluebook (2006-2007).
b. Cost of main instruments
1,500-0D Unit
900
750
Sandman Inc.
1,111
Two main instruments involved in the aerobic unit process are the feeding pump and
air blower. The required capacities of the instruments can be determined based on the
design criteria and the reactor diameters.
T bl 5.5W ti f nired instrum ts" a e orma ono re en Feeding Pump Air Blower
400-0DUnit ADS Model EF04W2 Air blower (Rietschle
O.4HP Thomas Model HB-229)
Price: $256.2 0.67HP
Price: $650
1,500-0D Unit ADS Model EF04W2 Air blower (Rietschle
O.4HP Thomas Model HB-329)
Price: $256.2 1.14HP
Price: $620
*: Information source: USAbluebook 2006-2007.
108
c. Cost of carrier making
Materials Cost:
Carrier material cost analysis for a 5L EMMC-biobarrel reactor was conducted in
Chapter 4 (Fig. 4.26). For a 5L double-layer reactor with a packing ratio of 13%, the
materials cost for carrier making is estimated as $2.28 (plastic cage is not included). The
materials cost for carrier making is linear to the effective reactor volume. Therefore, for a
unit with effective volume of750 gallons (2,835 L), the scale up factor is 2,835/5=567.
Similarly, for the unit with effective volume of200 gallons (756 L), the scale up factor is
756/5=151.2. The cost for plastic cage, which serves for the carrier supporter, is
estimated as $125 and $35 for the big and small units, respectively.
The material cost for carrier making is snmmarized in Table 5.6.
Table 5 6 Materials cost evalnatlon . 400GDUnit 1,500 GD Unit
Effective Volume (gallon) 200 750
Cost for Chemicals and 345 1,293
Biobarrel ($)
Cost for Plastic Cage ($) 35 125
Subtotal ($) 580 2,168
Labor Cost:
Kongsil (2006) reported that the labor time for carrier making for a reactor with
effective volume of 740 gallons and packing ratio of 12.5% was estimated as 224 hours.
Assume the carrier making labor hour is linear to the volume which the carriers occupied
109
and labor cost is $151hr. The carrier making labor cost for the two units can be evaluated
as presented in Table 5.7.
Table 5.7 Labor cost for carrier Labor Hour (hr) Labor Cost ($)
Unit with 400 gallons/day 63 945
Unit with 1,500 gallons/day 236 3,540
It is found that the labor cost for carrier making is noticeably high. This is because
currently, the EMMC-biobarrel producing scale is relatively small due to the limitation of
time and equipment capability. The labor cost is expected to be reduced if the production
can be scaled up.
Co Other construction costs
Besides the costs for carrier making and reactor, other costs for necessary instrument
and site preparation are estimated as follows.
Table 5.8 Other costs Estimation Pipe System!fank Fitting $350 '"
Other Necessary Instruments"'''' $950"'''''''
Site PreparationlExcavation 15% of the total cost for EMMC-biobarrel tank
*: Data IS from Kongsil (2006) Master ThesIs . • "': Other necessary instruments include air distributor, flow meter, timer, alarm, etc . • "'''': Data is from Kongsil (2006) Master Thesis.
The total capital costs for these two units are summarized in Table 5.9. As shown,
the total capital costs for 400 and 1,500 GD units are estimated as $4,671 and $ 10,191,
respectively. These costs are less than or comparable with other commercial aerobic
treatment unit products which also involve the nitrogen reducing technologies which are
110
listed in Table 2.5, suggesting that it is economically feasible to apply aerobic EMMC-
biobarrel unit in the onsite wastewater treatment. Moreover, the capital cost for the unit
can be reduced by 1) reducing the labor cost for carrier making by increasing the
production scale and 2) optimizing the equipments selection such as pump and blower,
Le., employing the most economically equipments combination in the system
configuration. In other words, for the commercialization of aerobic EMMC-biobarrel unit,
more effort needs to be made to optimize the cost, which makes it more cost-competitive.
T bl 5 9 T tal ital tsanal is a e • 0 eap! cos JYSI 400GDUnit 1,500 GD Unit
EMMC-biobarrel Reactor $610 $1,111
Tank Carrier Making $1525 $ 5,708
Plastic Cage $35 $125
Subtotal $2,170 $6,944
Main Instruments Feeding Pump $256 $256
Air Blower $620 $650
Subtotal $876 $906
Other Costs Instruments $950 $950
Pipe System $350 $350
Site Preparation! $326 $ 1,041
Excavation
Subtotal $1,626 $2,341
Total $4,671 $10,191
111
5.1.3.2 Evaluation of annual O&M cost
Annual O&M costs can mainly be grouped into electricity cost and regular maintenance
cost
a. Electricity cost
Electricity consumption cost can be estimated based on the required machines
electrical power and operation condition. According to Table 5.5, the total power of the
main instruments for the two units are (0.4+ 1.14) = 1.54 lIP (1.15KW) and
(0.4+0.67)= 1.07 lIP (0.80 KW). Kongsil (2006) reported that the charge rate of
electricity consumption is estimated as $0. 19281KWh. The annual electricity costs
therefore can be calculated as:
400-GD Unit: 0.8KW*24h1day*365daylyear*$0.1928IKWh=$1.351
1500-GD Unit: 1.15k:w*24h1dav*365daylyear*$0.1928IKWh=$1.942.
b. Regular maintenance
It was reported that poor maintenance was concluded as the main cause for the
failure of the ATUs and it bas been suggested that proper maintenance for the life of the
ATU system is required to ensure the high quality emuent (Sexstone, et aI., 2000).
Assume the labor hour for the inspection and maintenance of these two units are same.
The regular inspection and maintenance will be conducted twice a year and labor time is
estimated as 5 hours for each time. Therefore, the labor cost for annual maintenance can
be calculated as: 5 hours*$ 151h"'2=$ I 50.
The total annual O&M cost, therefore are estimated as $1,942+$150=$2,092 for the
1500-GD unit and $1,351+$150=$1,501 for the 400-GD unit. Similar to the situations of
112
the commercial processes which involve the nitrogen reduction technology, the electricity
consumption of the aerobic EMMC-biobarrel system is relatively high. This problem is
expected to be solved by optimizing the aeration schedule, i.e. applying intermittent
aeration.
5.2 Land Limitedl Small Scale AppUcations
5.2.1 Technical potential
Being a compact biological system, EMMC-biobarrel process is ideal for land
limited or small scale application. Compared to the conventional activated sludge process
(ASP), EMMC-biobarrel possesses the capability of maintaining high solid retention time,
higher organic loading rate and higher COD removal efficiency while it is operated with
a low hydraulic retention time. Moreover, the capability ofEMMC-biobarrel process for
simultaneous carbon and nitrogen removal makes it an attractive alternative to meet the
increasingly strict nutrient release limitation.
5.2.2 Design criteria
As discussed in Chapter 4, the design and operational criteria ofEMMC-biobarrel
depend on the characteristics of the influent Table 5.10 gives the design and operation
criteria for the EMMC-biobarrel process for land limitedlsmall scale application which
are based on the results of Experiment 8, i.e., double-layer system achievements at HRT
of 6h with continuous aeration.
113
Table 5.10 Design criteria of the EMMC-biobarrel process for simultaneous removal of carbon and nitro2en in a single reactor Parameters The EMMC-biobarrel system
Packing design Double-layer
Packing retio 13%
Operational temperature 25±3"C
Opemtional mode Continuous flow
HRT 6 hours
BODs loading 0.80 kgfm'/day
TN loading O.l6gfm' /day
SCOD removal efficiency >95%
NH3-N removal efficiency >95%
TN removal efficiency 40%
pH in the effiuent 6-7 pH units
Aemtion schedule Continuousaemtion
5.2.3 Economic analysis for the EMMC-biobarrel process with 0.1 MGD capacity
5.2.3.1. Evaluation of Capital Cost
In geneml, the capital cost involves two main parts, land cost and construction cost.
Since the land cost is greatly different, depending on the nation and local situation and
the land requirement is quite small for the EMMC-biobarrel system, the land cost is not
included in the evaluation.
a. Reactor cost
The minimum required volume of reactor depends on the hydmulic retention time
(HRT). Based on the information of capacity (O.IMGD) and HRT (6h), the minimum
required volume can be calculated as:
114
100,000gallon _ 25000 allons (24h/6h) ,g
Assume safety factor for the volume estimation as 1.2, the total volume of the tank:
should be 25,000*1.2=30,000 gallons
The effective volume information for the aeration tank: of the EMMC-biobarrel
process is suggested as following:
Table 5 11 The volume information for 0 1 MGD- EMMC-biobarrel aeration tank . • Reactor diameter 21 ft (6.40 m)
Liquid height 10ft (3.05 m)
Total tank: volume 30,000 gallon
EMMC-biobarrel reactor liquid volume 25,000 gallon
The cost of a glass-fused-to-steel tank: with volume of76,000 gallons is suggested as
$125,000 by M&M Tanks Inc. (KongsiI, 2006). Assuming the price is linear to the
volume, the cost of a 30,000-gallon tank: made from same material is estimated as
$50,000.
b. Cost of main instruments
The information of the main instruments, i.e., air blower and feeding pump is listed
in Table 5.12.
Table 5.12 Information of reQuired Instruments '" Feeding pump (ABS Model EF05W2) Air blower (Rietschle Thomas Model HB-829)
Price: $405.7 Price: $2,238.8
Flow rate: 72 gpm @ head 20ft Max. air flow rate: 385 SCFM
Power: 0.5 HP Max. pressure: 160 IWG
Power: I 1.6 HP
*: Information source: USAbluebook 2006-2007.
115
According to Kongsil (2006), these instruments are estimated to be replaced every
five years of operational period. Therefore, the instruments replacement cost is estimated
as: $405.7+$2238.8=$2,644.5.
c. Carrier cost
Material Cost:
Carrier material cost analysis for a 5L EMMC-biobarrel reactor was conducted in
Chapter 4 (Fig. 4.26). For a 25,000 galIon (94,500L) unit, the scale up factor is
94,500/5= 18,900
As a result, the total carrier cost for the aerobic EMMC-biobarrel unit with packing
ratio of 13% is estimated as $2.28*18,900=$43,092.
Similar to the estimation for plastic cage supporter in the aerobic EMMC-biobarrel
treatment units, the cages cost can be calculated based on surface area of the cages. The
material cost is estimated as $2,000.
Labor Cost:
As discussed previously, the labor cost for carrier making needs to be adjusted when
the production is scaIing up. According to Kongsil's study (2006) , the labor cost for
carrier making for 73,500-gallon reactor with packing ratio of 12.5% is estimated as
$65,077. Therefore, the labor cost for the 25,000-gallon reactor with packing ratio of
13% can be estimated as ($65,077)*(25,000173,500)*(13/12.5) = $23,020.
116
d. Pipe system and other necessary equipments
The cost information for the pipe system and other necessary equipments is presented
in Table 5.13.
TableS. 13 S f i ti th 0 1 MGD EMMC bi b I ummary 0 capital costs or e • - 0 arre, process '" Item Material Cost Labor Cost Total Cost
EMMC- Carrier $43,092 $23,020 $66,112
biobarrel Reactor $50,000 $50,000
Tank Plastic cage $2000 $600 $3600
Subtotal $119,712
Air Air distributor $1,500 $525 $2,025
Providing Air blower $2,239 $600 $2,839
Unit Air flow meter $800 $800
Std. Media filter $250 $250
Subtotal $5,914
Influent Feeding pump $406 $406
Feeding Feeding flow rate $150 $150 $300
Unit control unit
Piping system and $200 $1,050 $1,250
tank fitting
Subtotal $1,956
Site $11971**
Preparation
Total $139,553
*: Labor cost IS estimated based on Kongsil's (2006) study. **: Cost for site preparation is assumed as 10% ofEMMC-biobarrel tank cost
117
5.2.3.2 Annual O&M cost
a. Electricity cost
Electricity consumption cost can be estimated based on the required machine
electrical power and operation condition. According to Table 5.12, the total power of
feeding pump and air blower is (0.5+11.6) =12.1 lIP (9.03KW) According to Kongsil
(2006), the charge rate of electricity consumption is estimated as $0.19281KWh. The
annual electricity cost can be calculated as:
9.03KW*24h!day*365day/year*$0.1928IKWh=$15,251.
b. Regular maintenance cost
According to Zhang (1995), EMMC process requires less operation and maintenance.
Normally, 7 times a week, 2 hours per time, 48 week per year. The safety factor of2 is
considered. Therefore, the labor cost for regular maintenance cost is estimated as:
2*7*48*2*15=$20,160.
The total annual O&M cost, therefore, is estimated as $15,251+$20,160=$35,441.
5.2.3.3 Calculadon ofNPW (Net Present Worth)
The life-span for of the treatment system is assumed as 15 years (Yang et al., 1997)
and the annual interest rate is assumed as 5.75% (Kongsil, 2006). The information for
calculating the NPW is summarized in the following table.
Table 5.14 Cost informadon for tbe 0.1 MGD EMMC-biobarrel proeess Capital Cost $139,553
Annual O&M Cost $35,441
Machines Replacement Cost
Annual interest rate
Life-span
$2,645
5.75%
15 years
118
Based on the above information, along with the assumption of carrier life of 15
years (Yang, et.al., 1997), the NPW (Net Present Worth) and AW (Annual Worth) can be
estimated as presented in the following Table 5.15.
1 Calis Ii th 0 1 MGD EMMC bi b I TableS. 5 ost an ~YSI or e • - o arre I process Cost of Annual Cost for
End of Year Cost of Capital O&M ReDlacement Cash Row 0 $139,553 -$139,553 1 $35,411 -$35,411 2 35411 -$35,411 3 35411 -$35,411 4 35411 -$35,411 5 35411 $2,645 -$38056 6 35411 -$35,411 7 35411 -$35411 8 35411 -$35,411 9 35411 -$35,411
10 35411 $2,645 -$38,056 11 35411 -$35,411 12 35411 -$35,411 13 35411 -$35,411 14 35411 -$35 411 15 35411 -$35,411
NPW= -$492,674 AW= -$49,902
For the design capacity of 0.1 MOD system and life span of 15 years, the NPW of
the EMMC-biobarrel process is approximately -$492,674 and the A W is -$49,902. The
cost of treating 1,000 gallons of wastewater per day is $492,6741[15*365*102]=$0.90.
5.2.3.4 Sensitivity Analysis
In the economic analysis of most engineering projects, sensitivity analysis is
required for the decision process (Sullivan, et al., 2003). In general, sensitivity analysis
determines how sensitive the situation is to the several factors of concern.
119
In the economic analysis for the O.lMGD EMMC-biobarrel wastewater treatment
process, the value ofNPW (or A W) can be affected by several factors. Among them, the
annual interest rate and electricity charge rate are two factors which may vary in the
actual applications. Therefore, the sensitivity analysis of the A W to these two factors was
conducted.
Sensitivity to Interest Rate
Figure 5.1 demonstrates the sensitivity graph of the A W to interest rate. It is found that
with the decrease of the interest rate, the annual cost for the process is reduced. Therefore,
if the lower interest rate is applied, the EMMC-biobarrel treatment plant will become
more cost-effectivf;l.
Interest Rate
-$30.000 ,--~-~~--~--~-_~-~_-~ o.po 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.0 11.0 12.0
o % % % % % % % % % ~ ~ ~
-$40.000
.. ... , . ---. ..... -------.-
I ·$50,000
-$60,000
Figure 5.1 Sensitivity to the Interest rate
Sensitivity to Electricity Charge Rate
Aerobic biological treatment process has large energy requirement Therefore, the
cost for the electricity can affect the economic result significantly. In U.S., the electricity
120
charge rate varies from state to state, ranging from $0.06-$0.38 per KWh. The sensitivity
graph of AW (annual worth) to the electricity charge rate is shown in Figure 5.2.
Apparently, the lower electricity charge rate leads to a lower annual cost. If the electricity
charge rate decreases from $0. I 928IKWh to $0.11KWh, the cost for the process can be
reduced about $5,000 per year.
,$40,000
Ii' i -$50,000 i(
-$60,000
-$70,000
0.05 0.1 0.15 02 025
Bectrlclty Charge _ ($/KWh)
Figure 5.2 Sensitivity to the electricity charge rate
5.3 Combined with MBR
0.3 0.35 0.4
MBR is a new interest in domestic wastewater treatment since it presents a means of
intensively biologically treatment for high COD or BOD wastewaters. However, like
other membrane processes, MBR is constrained by the tendency to membrane fouling,
which is the general term given to those phenomena responsible for increasing membrane
hydraulic resistance. In commercial MBR application, a number of options have been
developed for the fouling remediation including backwashing and/or chemical cleaning.
121
All these add to the operating costs from the chemical consumption and downtime
(Gander, et aI., 2000).
An effective approach to reduce membrane fouling is maintaining turbulent
conditions, that is, controlling the MLSS (mixed liquor suspended solid) concentration in
the reactor. Attach growth technology was employed to maintain the biomass
concentration and reduce the turbulence in the membrane reactor (Yamagiwa, 1995).
Although it was proved partially effective in reducing membrane fouling, the frequent
cleaning was still required in the early stages of treatment. In addition, the
microorganisms attached to the carrier tended to be re-suspended in the tank
mechanically at the end of treatment which again resulted in fouling.
Introducing EMMC-biobarrel technology to MBR design may be a proper solution to
membrane fouling. Theoretically, since the biomass accumulates inside the carriers and
hardly to be washed out, the biomass concentration in the reactor can be as high as over
10g/L (Su, 1999) while turbulence can be very low. In this study, it was found that for
double-layer EMMC-biobarrel process, the average concentration of SS, which
occasionally escape from the entrapment, was less than 15mg/L after 45 days of
operation. Therefore, it is expected that the membrane fouling can be dramatically
reduced without affecting the performance of the MBR Also, the co-existing aerobic and
anaerobic conditions in the systems may enhance the total nitrogen removal. On the other
hand, combined with membrane will definitely reduce the suspended solid concentration
in the effiuent from EMMC-biobarrel process and improve the reliability of this process.
In summary, the combination ofEMMC and MBR may successfully overcome the
disadvantages of both technologies. The suggested integration ofEMMC-biobarrel and
122
MBR processes is presented in Fig.5.3. However, this combination so far is just in
conceptual stage, more effort need to be made in practical aspects such as system design
and integration, performance evaluation and economic analysis.
Influent
EMMC-biobanel carrier
~
~:2jr"""7~~1---- Membranemodule
/-1---+---8-Suction pump
Aerator
Figure 5.3 Suggested EMMC-biobarrel and MBR integration
123
Chapter 6. Conclnsions and Recommendations
6.1 Conclusions
EMMC-biobarrel processes with single- and double- layer configurations were
investigated for simultaneously carbon and nitrogen removal from synthetic domestic
wastewater. Compared to intermittent aeration of Ih onl2h off, continuous aeration was
proved to be more suitable for the systems for achieving complete nitrification and
improved denitrification. At COD loading rate ofO.75kg/m3/day and NH3-N loading rate
ofO.I6kg/m3/day, more than 96% ofSCOD 1NH3-N removal and about 40% ofSTIN
removal were obtained from all systems. Long SRTs of about 200 days were achieved by
the single-layer system with packing ratio of 20% and double-layer system with packing
ratio of 13% due to the effective entrapment of biomass in the systems.
Compared to single-layer system, better developed oxygen transfer was observed
in double-layer system due to the lower packing ratio applied in the system. Besides, the
double-layer system demonstrated the potential in tolerating shock load. The cost analysis
showed that in the achievement of comparable performance, the capital cost for double
layer system (13%) is lower than that for single-layer system (20%). Therefore, it is more
economically and technically sounds to adopt double-layer configuration for the EMMC
biobarrel process design.
EMMC-biobarrel process is strongly recommended for land limited/small scale and
on-site wastewater treatment due to its small space requirement, high performance and
simple operation and maintenance. Economic evaluation showed the process is cost-
124
effective compared to the existing treatment facilities. Therefore, the EMMC-biobarrel
process is a promising technology for the wastewater treatment
6.2 Recommendations
I) The system's performance especially total nitrogen removal efficiency can be
highly affected by the influent CODIN ratio which can be varied from case to case
in the real wastewater treatment In this study, only synthetic wastewater with
CODIN ratios of 5 and 8 were investigated. Therefore, it is suggested to evaluate
the system's performance for treating synthetic wastewater influent with various
CODIN ratios in order to provide more reference for the actual application design.
2) According to the previous study (Cao, 1998), intermittent aeration is considered
as an effective approach to enhance the total nitrogen removal from the
wastewater. Although in this study the continuous aeration schedule was
concluded to be more suitable for carbon and nitrogen removal than the
intermittent aeration schedule of I h air on/2h air off, the optimal aeration
schedule still can be intermittent aeration with higher aeration/non-aeration ratio.
Thus, various intermittent aeration schedule and HRTs need to be investigated in
order to optimize the operational conditions.
3) The double layer configuration is proved to be more technically and economically
sound than the single layer one. In the future, further study concerning the mass
125
transfer in the double-layer system and modeling work are required in order to
optimize the system configuration (numbers of the layer).
4) Investigation of the integrated MBR-EMMC-biobarrel system is strongly
recommended since it may be a "break-through" for solving the membrane
fouling problem.
126
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