b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 2 1e2 7 2 8

Avai lab le a t www.sc iencedi rec t .com

ht tp : / /www.e lsev ier . com/ loca te /b iombioe

Start up study of UASB reactor treating press mud forbiohydrogen production

B. Radjaram a,*, R. Saravanane b,1

aDepartment of Civil Engineering, Pondicherry Engineering College, Puducherry 605014, IndiabEnvironmental Engineering Laboratory, Department of Civil Engineering, Pondicherry Engineering College, Puducherry 605014, India

a r t i c l e i n f o

Article history:

Received 14 January 2010

Received in revised form

25 February 2011

Accepted 4 March 2011

Available online 11 April 2011

Keywords:

Press mud

UASB

Biohydrogen

COD

Volatile solids

* Corresponding author. Tel.: þ91 413 264300E-mail addresses: radjaram@rediffmail.co

1 Tel.: þ91 413 2655281x210, þ91 93451 5600961-9534/$ e see front matter ª 2011 Elsevdoi:10.1016/j.biombioe.2011.03.016

a b s t r a c t

Anaerobic digestion of press mud mixed with water for biohydrogen production was

performed in continuous fed UASB bioreactor for 120 days. Experiment was conducted by

maintaining constant HRT of 30 h and the volume of biohydrogen evolved daily was

monitored. Various parameters like COD, VFA, Alkalinity, EC, Volatile solids, pH with

respect to biohydrogen production were monitored at regular interval of time. SBPR was

10.98 ml g�1 COD reduced d�1 and 12.77 ml g�1 VS reduced d�1 on peak yield of bio-

hydrogen. COD reduction was above 70 � 7%. Maximum gas yield was on the 78th day to

2240 ml d�1. The aim of the experiment is to study the startup process of UASB reactor for

biohydrogen production by anaerobic fermentation of press mud. The inoculum for the

process is cow dung and water digested in anaerobic condition for 30 days with municipal

sewage sludge. The study explores the viability of biohydrogen production from press mud

which is a renewable form of energy to supplement the global energy crisis.

ª 2011 Elsevier Ltd. All rights reserved.

1. Introduction Biotechnology of hydrogen production has provoked a broad

The rising concern about depleting oil reserves, harmful

effects of green house gas emissions and the necessity to

reduce emissions from power plants and vehicles are some of

the key factors that increase the urgency for development of

alternative energy options. Energy security is a major chal-

lenge, which needs imaginative and innovative solutions.

Fossil fuels are the major global energy resource but they

cause environmental problems during combustion. Hydrogen

is a promising energy alternative because it is clean, renew-

able and has a high energy yield of 122 kJ g�1. This yield is 2.75-

fold greater than that from hydrocarbon fuels. At present,

hydrogen is produced mainly from fossil fuels, biomass and

water using chemical or biological processes. Hydrogen can be

used for power generation and transportation at near zero

pollution.

7, þ91 9443748471 (mobilm (B. Radjaram), saravan37 (mobile); fax: þ91 413ier Ltd. All rights reserved

attention around the world as an environmental friendly

process [1e4]. Hydrogen production by microorganisms is

dividedinto twomainmodes:productionbyalgaeorphototropic

bacteria and production by anaerobic fermentation bacteria.

Currently, more research focuses on the use of algae and

phototropic bacteria [5e10]. However, the efficiency of hydrogen

production by phototropic microorganism is low and it cannot

be continuously operated in the absence of light. In contrast,

anaerobic hydrogen fermenting bacteria can produce hydrogen

continuously without the need for photo energy [11,12].

Biological hydrogen production processes have the advan-

tages of being less energy consuming. Fermentative bio-

hydrogenproduction gives highhydrogenproduction rates and

is capable of converting organic wastes into more precious

energy resources [4]. In all the studies concerning biohydrogen

production, a continuous stirred tank reactor (CSTR) is used for

e); fax: þ91 413 2643008.anae@gmail.com (R. Saravanane).2655101..

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 2 1e2 7 2 82722

continuous generation of hydrogen from organic wastes [4].

Because of its intrinsic structure, the CSTR is incapable to

maintain high levels of fermentative biomass for hydrogen

production, and its specifichydrogen-producing rate is scarcely

kept high [13]. To overcome this problem, an upflow anaerobic

reactor, with a similar structure to the upflow anaerobic sludge

blanket (UASB) reactor, was tested in this study.

An upflow anaerobic sludge blanket (UASB) process is

a widely applied anaerobic treatment system with high

treatment efficiency and a short hydraulic retention time

(HRT). Recently, UASB hydrogen production systems have

been used in granulation enrichment and granule micro-

structure [14,15]. However, the performance of hydrogen-

producing UASB systems has not been discussed in detail. A

systematic investigation of reactor characteristics, such as

operation stability, HRT dependence, sludge granulation and

sludge discharge is still lacking. Therefore the aim of this work

was to investigate the feasibility of biohydrogen production

from press mud using up flow anaerobic sludge blanket

bioreactor and to study the startup process of UASB reactor

using press mud for biohydrogen production.

During the acidogenesis of organic wastes, hydrogen,

carbon dioxide, volatile fatty acids (VFA), and sometimes

alcohols, are simultaneously produced [16]. The feasibility of

applying acidogenesis of organic wastes to produce hydrogen

has been widely confirmed at various laboratories [4,13,17].

Compared with photosynthetic bacteria, fermentative

bacteria produce hydrogen with a lower cost because they do

not need light provision and have simple requirements for

microbial growth [4]. Another attraction of anaerobic hyd-

rogen bioproduction is that highly concentrated organic

wastewater and biomass, such as municipal solid wastes,

sewage sludge, can be used as raw material, which can solve

pollution as well as generate hydrogen [4].

Although some studies have been conducted on mixed

cultures of anaerobic bacteria [11,18e25], the optimal condition

for hydrogen production has not been fully understood. The

accumulation of intermediate products in systems can inhibit

fermentation. In practical operation, high hydrogen yields are

associated with a mixture of acetate and butyrate as fermen-

tation products. However, little information is available for

anaerobic hydrogen production at pilot scale with mixed

microbial cultures, althoughpilot-scalestudy iscritical to testify

theproductivity before anewbiotechnology isput into full scale

operation, and using mixed microbial cultures is a more cost-

effective and promising approach to achieve hydrogen bio-

production in large scale. In addition, as a byproduct through

fermentation pathways, hydrogen production is affected by

fermentation end-products, including, acetic acid, propionic

acid, butyric acid, and lactic acid. But there is very limited

information of the correlation between fermentation pathways

and hydrogen production ability.

Ren [11] had confirmed that the acclimatized anaerobic

activated sludge had a high hydrogen producing ability (as high

as 10.4 m3 H2 m�3 reactor d�1) in a continuous reactor with an

available volume of 9.6 L. It has been found that a high cell

density (higher than 5 g L�1) in bioreactor is required to keep

high hydrogen yield, since low cell intensity cannot efficiently

convert organic substrates to hydrogen, especially at short

hydraulic retention time (HRT< 4h). Several studieshave found

that great amount of VFA and CO2 produced from highly

concentrated influent inhibited metabolic activities of anaer-

obicbacteria [12,26e28]. Thehydrogenproduction rate obtained

in molasses (29) HBR system was 5.57 m3 H2 m�3 reactor d�1

and yield was 26.13 mol kg�1 COD removed with OLR of

35e55 kg COD m�3. Ueno et al. [18] investigated the hydrogen

production rate by anaerobic micro flora in chemostat culture.

In light of the above developments, this work used sewage

sludge as the seed sludge source for hydrogen production in

a UASB system. Sucrose is readily found in this industrial

waste and was therefore used as the carbonaceous substrate

for hydrogen fermentation. The substrate has 3% sugar which

is an excellent natural nutrient for microorganism.

2. Materials & methods

2.1. Bioreactor system

A 20 L UASB biohydrogen-producing reactor was used in this

study. The plexi glass made lab scale UASB reactor has

a column of internal diameter 10 cm, height 190 cm (H/D > 10)

with a gas liquid separator at the top having internal diameter

of 20 cm and height 20 cm, having an effluent port at 15 cm.

HRT is based on the volume of the fluid between feed and

effluent port which is 20 L. Seven sampling ports were evenly

fixed over the entire height of the column. Total biomass level

in the reactorwaskept at around1/3rd theheight of the column

i.e. about 70 cm. The reactor was operated in continuous flow

mode. The temperature is kept in ambient condition. The

influent pH was kept in the range of 5.5e6 by addition of 0.1 N

HCL or NaOH. The influent flow rate is controlled by a peri-

staltic pump to maintain constant HRT of 30 h.

2.2. Seed microorganism

Sewage sludge contains a variety of microflora favoring bio-

hydrogenproduction in suspendedgrowth systems [30,31] and

might be a good source for cultivating granular sludge for

hydrogen production. The seed sludge was collected from

a municipal waste water treatment plant maintained by Pub-

lic Works Department, Govt. of Pondicherry. It was sieved

through a wire mesh of diameter 0.5 mm to remove the solid

materials that may block the flow in the pump. Cow dung was

mixedwithwater in the ratio 1:2 and digested under anaerobic

condition for 30 days by adjusting pH in the range of 5e6, in

batchmodewith the addition of nutrients. Later this cowdung

seed was filtered in wire mesh (0.5 mm) to remove the fibrous

materials. This cow dung filtrate and sewage was mixed (4:1)

heated at 70 �C for 1 h to inhibit the methanogens and fed into

the reactor. The characteristics of seed sludge viz. total solids

(TS), total dissolved solids (TDS), total suspended solids (TSS),

total volatile solids (TVS), total volatile dissolved solids (TVDS),

total volatile suspended solids (TVSS) etc. are given in Table 1.

2.3. Feed substrate

So far, majority of research work has been directed at

expensive pure substrates to a much lesser quantity of solid

waste [32]. In most studies on microbial production of

Table 2 e Biohydrogen production from various solid andliquid wastes.

Solid substrate Liquid Feed

MSW & slaughter house waste Waste Water

Food waste & sewage sludge Glucose

Sucrose pulped sugar beet &

water extract of sugar beet

Synthesis Gas

Wheat Powder Solution

Milled Paper Waste Starch Feedstock

Beer Lees Waste Beer Brewery Wastewater

Food Waste Cheese Processing Wastewater

Wheat Straw Waste Palm Oil Mill Effluent

Wheat Feed Olive Mill Waste

Sweet Sorgam Chemical Wastewater

Rice Slurry Molasses

Sewage Sludge e

Cassava Starch e

Cow Dung Compost e

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 2 1e2 7 2 8 2723

hydrogen, glucose or other pure chemicals were used as

a substrate [4]. Anaerobic digestion of organic waste produces

various volatile fatty acids (VFA), H2, CO2 and other interme-

diates [33]. The reactions involved in hydrogen production are

rapid and making them useful for treating large quantities of

organic wastes. Continuous production of hydrogen was also

tried at short HRT to prevent the growth of hydrogen

consumers [34]. However, there have been no studies on

continuous hydrogen production at enough HRT from organic

solid wastes except a few based on solid and liquid wastes

listed in Table 2. In this study, press mud, an organic solid

waste of sugar industry is used as substrate for the first time to

evaluate the feasibility of biohydrogen production.

Press mud, a semisolid residue from sugar industry, is

a byproduct obtained from cane juice before crystallizing

sugar. It is the filtered cake from the vacuum filter unit, where

the muddy juice is filtered and accumulated press mud is

continuously scraped and collected. It is disposed to farms for

feeding as manure without processing, as it is enriched

manure for agricultural land. About 4% of the sugar cane

crushed is converted to press mud. In India about 4.2 million

tonnes of pressmud is available from sugar industry annually.

It is acidic, fibrous, stingy, mild corrosive and a biodegradable

organic waste. Bacterial fermentation requires substrates

such as glucose and/or sucrose to obtain energy for growth

and maintenance, and produces several intermediate by-

products such as organic acids, alcohols and hydrogen during

the metabolic pathways. Press mud has 3% sugar in it. The

characteristics of press mud were given in Table 3.

2.4. Operation

The experimentwas conducted to investigate the biohydrogen

production by mixing press mud with water, in a lab scale

continuous flow UASB bioreactor at constant HRT of 30 h over

a period of 120 days to study the startup process (Fig. 1). Peri-

staltic pump (Ravel RH P 100 L) with tube ID ø 12mmwas used

for this process. The pressmudbeing a fibrousmaterial cannot

be pumped at low flow rate, as it blocks the silicon tube of the

pump. Hence it was decided to soak the press mud in water in

the ratio 1:7.5 (4 kg of press mud with 30 L water) for 1 h, filter

through wire mesh of 0.5 mm diameter pores to remove the

fibrous materials and feed the reactor with this filtrate liquid

having particulatemixture of solids less than 0.5mmonly. The

feed characteristics were given in Table 1. However during

startup period, for 10 days, the feed concentration was more

dilute (1: 10) soas toallowtheseed toacclimatizewith the fresh

substrate. The filtrate was fed into the feed tank fitted with

a mechanical stirrer, which stirs the feed for 3 min at regular

time interval of 20 min (operated by an electronic timer) to

prevent the settlement of solid particles in the tank.

Table 1 e Characteristic of seed and feed.

Substrate pH TS TDS TSS TVS

Seed 6.76 10.9 2.05 8.85 6.8

Feed 6.46 7.7 2.25 5.45 4.65

All units are in g L�1 except pH.

2.5. Analytical methods

Temperature, pH and biohydrogen produced were measured

daily with thermometer, pH probe and wet gas meter, while

the gas composition was analyzed using gas chromatograph

(Nucon GC). The Total Solids, volatile solids (VS), chemical

oxygen demand (COD), VFA, alkalinity, Electrical Conductivity

(EC) etc. were estimated once in a week by standard experi-

mental methods [35].

3. Results and discussion

3.1. Start up of UASB reactor

It has been found that a great amount of intermediate acidic

products were produced by anaerobic microorganism, which

could cause pH decline in fermentation systems treating feed

substrate. Therefore, aciduric fermentative bacterial comm-

unities, which can tolerate acidic products and low pH,

needed to be cultured in order to keep good hydrogen

production under high organic loading rate [36,37]. In order to

develop aciduric fermentative bacterial communities, the

reactor pH needed to be maintained at about 5.5 by adjusting

the pH of feedstock within the range of 5e6. Normally,

acidophilic fermentative bacterial communities were well

developed after culturing for 40 days. During the startup

period, the reactor system was fed continuously with diluted

substrate at strength of approximately 10 000 mg COD L�1 to

reach an OLR of 8000 to 16 000 kg m�3 d�1 with an HRT of 30 h

during the study period of 120 days. The pH in the reactor

decreased from 6.5 to 5.5 during the startup period, due to the

production of VFA, while biogas production, hydrogen yield

TVDS TVSS Total COD Alkalinity VFA

1 5.8 10.40 19.03 1.82

1 3.65 12.48 12.68 1.50

0

20

40

60

80

100

0250500750

1000125015001750200022502500

1 10 19 28 37 46 55 64 73 82 91 100 109 118

H2,

%

Bio

H2

prod

uced

, ml d

-1

Expt Days

Biohydrogen

H2 %

Fig. 2 e Trend of biohydrogen production and %H2 during

experimental period.

Table 3 e Characteristics of press mud.

Parametersa Press mud

pH 4.5e5

COD (%) 117.6

C/N ratio 24.04

Total solids (%) 29

Moisture content (%) 71

Total volatile solids (%) 84

Organic carbon (%) 48.80

Nitrogen (%) 2.05

Phosphorous (%) 0.65

Potassium (%) 0.28

Sodium (%) 0.18

Calcium (%) 2.7

Sulphate (%) 1.07

Sugar (%) 3

Wax (%) 1

a Average values.

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 2 1e2 7 2 82724

and COD removal efficiency gradually increased with time.

While the biohydrogen production started on the 29th day,

there was an unsteady yield for 76 days. After 76 days both

biogas yield and COD removal efficiency stabilized in the

reactor system, reaching at approximately 1600 ml d�1 and

70%, respectively. These results revealed that anaerobic acti-

vated sludge in this reactor had possessed a good acid-toler-

ance and stable hydrogen production ability, which indicated

a good acclimatization.

3.2. Continuous biohydrogen production

The reactor medium was tested once in a week from the

fourth week until steady state was established. In this study,

the steady state was referred to as a relatively stable hydrogen

Reactor column

0·1 m

Feed tank 200 L

Stirrer

MTimer

P

Drain

Gas liquid separator

Sampling ports

Effluent port

Gas meter

Peristaltic pump

1· 9 m

Fig. 1 e Schematic arrangement of biohydrogen production

system.

yield of reactor with a variation of �10%, during which the

COD and VS reduction, H2%, EC, alkalinity and VFA were

evaluated. The biohydrogen yield was nil in the initial stage

for 29 days, production started on 28th day later it was in the

range of 100e200 ml d�1 till 40th day. The gas production was

between 200 and 500 ml d�1 during 40e60 days. It was around

700e800 ml d�1 till 70th day. After 70 days the gas yield rose

above 1000 ml d�1 and was maximum on the 78th day to

2240 ml d�1. After 80 days the production stabilized between

1600 and 1900 ml d�1 with a fluctuation of �10% (Fig. 2). This

indicates that it requires more than 75 days of startup period

for acclimatization, since the feed contains particulate solids

suspended in liquid medium.

Biohydrogen yield of 890 ml kg�1 press mud added was

achieved in this process at a constant HRT of 30 h. Similar

studies on wheat feed [38] fermentation gave 56 L kg�1 feed at

HRT of 15 h and sweet sorgam [39] fermentation gave

10.41 L kg�1 feed. The hydrogen evolution rate of Rhodobacter

sphaeroides RV was only 1.4e1.6 L L�1 reactor d�1 [6] and

1.3 ml ml�1 porous glass media h�1 [40], and it can be

continuously operated only in the presence of light. Sewage

sludge digestion produced biohydrogen of 3.75 ml min�1 [41].

The H2% also increased from 10 to 59% from the initial gas

generation to the stable range. H2% was between 52 and 59%

during steady state condition (Fig. 2). Hydrogen being

a byproduct of fermentation process the formation of VFA has

direct effect on hydrogen production.

3.3. Effect of COD and volatile solid reduction onbiohydrogen yield

Hydrogen production from anaerobic fermentation process of

organic waste was dependent on COD removal. COD removal

0

20

40

60

80

100

02468

10121416

1 23 30 37 44 51 58 65 72 79 86 93 100 107 114 121

% C

OD

Red

ucti

on

CO

D L

oadi

ng r

ate,

g L

-1d-1

Expt days

COD loading rate% COD Reduction

Fig. 3 e COD loading rate and % COD reduction in UASB

reactor.

0

5

10

15

20

25

30

35

1 23 30 37 44 51 58 65 72 79 86 93 100 107 114 121

SBP

R, m

l g-1

d-1

Expt days

COD reduced

VS reduced

Fig. 4 e Specific Biohydrogen Production Rate for COD and

Volatile solids reduced with lapse of time.

5

6

7

0

5000

10000

15000

20000

25000

1 23 30 37 44 51 58 65 72 79 86 93 100 107 114 121

pH

VFA

, m

g L

-1

Expt days

VFA EffluentPH FeedPH Effluent

Fig. 6 e Effect of pH and VFA production.

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 2 1e2 7 2 8 2725

fluctuated in the initial startup stage and later stabilized after

80 days of operation. COD reduction was between 51 and 78%

during the entire period of study. COD reduction between 60

and 77% gave consistent gas yield (Fig. 3). This high COD

reduction is possible due to the large column height (H/D> 10)

which provides long mixing path way during substrate flow

from inlet to outlet. Also the biomass level up to one third the

height of the column was able to hold the biohydrogen

producing bacteria in the system. Thismakes the cell to digest

the substrate and release the biohydrogen from the reaction

process to the maximum possible quantity. SBPR was

10.98 ml g�1 COD reduced d�1 for maximum biohydrogen

yield. COD reductionwas above 70� 7%. During consistent gas

yield SBPR ranged between 7 and 11 ml g�1 COD reduced d�1.

Because of its intrinsic structure, especially the installation of

a gase solidseliquid separator [42], this upflow reactor

retained a high level of biomass of 16 g VS L�1 which is far

higher than the average biomass concentrations in CSTR.

Anaerobic fermentation of food waste in leaching bed

reactor gave biohydrogen yield of 21.2e41.5 ml g�1 COD at an

HRT of 25 h [43]. Biohydrogen yield was 26.13 mol kg�1 COD

reduced in molasses fermentation [29] and 1.8e2.3 mM g�1

COD fed in cheese processing waste water [44].

Biohydrogen yield gradually increased after 75 days and

was consistent around 1600 � 150 ml d�1, with SBPR of

12.77 ml g�1 VS d�1 reduced on peak yield. Though the SPBR

was 32.81 ml g�1 VS reduced d�1 the maximum during the

study, it was not constant. SPBR between 10 and 14 ml g�1

VS reduced d�1 gave consistent biohydrogen yield (Fig. 4). The

volatile solid concentration of feed increased in the initial

stage due to slowhydrolysis in the feed tank. After 30 days, the

feed hydrolyzed, particles break up is fine there by steady VS

concentration occurred. The system was able to take up

0102030405060708090

02468

10121416

1 23 30 37 44 51 58 65 72 79 86 93 100 107 114 121

% V

S R

educ

ed

VS

load

ing

rate

, g

L-1

d-1

Expt days

VS loading rate% VS Reduced

Fig. 5 e Volatile solid loading rate and reduction trend

along the experimental period.

increased volatile solid loading rate which shows the adapt-

ability of reactor to increased loadingwithout any reduction in

efficiency (Fig. 5). Co-digestion of municipal solid waste and

slaughter house waste gave an H2 yield of 52.5e71.3 ml g�1 VS

reduced [45]. Maximum specific hydrogen production rate,

9.33 L H2 g�1 VSS d�1, observed in rice winery waste [46]. There

is very limited information of the correlation between ferm-

entation pathways and hydrogen production ability. Ren [11]

had confirmed that the acclimatized anaerobic activated slu-

dge had a high hydrogen producing ability (as high as

10.4 m3 H2 m�3 reactor d�1) in a continuous reactor with an

available volume of 9.6 L.

3.4. VFA variations during biohydrogen production

Anaerobic fermentation is always accompanied by VFA

production. The VFA concentration distribution has been used

as an indicator for monitoring hydrogen production. The

amount of hydrogen produced from glucose is affected by

fermentation pathways and liquid endproducts [28,25]. As the

reactor has an H/D> 19, 1.9 timesmore than the normal UASB

reactor, the biomass concentration level increased from the

initial level of 15 cme120 cm. The dead cells which are light in

weight will tend to float and reach the top of reactor. It is

found that the sedimentation zone was very thick; the bed

zone has a thorough mixing of incoming fresh particles and

microorganisms existing in the reactor. The blanket zone is

having light weight particles floating in suspended state.

Above this is a layer of fluid through which the gas bubbles

released by digestion passes and get collected in the gas liquid

separator.

The VFA concentration in the effluent was high in the

startup stage and reduced gradually showing good indication

of acid to hydrogen conversion after 30 days. Later it started

increasing after 40 days from startup till 60th days. This is due

0

200

400

600

800

1000

0

5000

10000

15000

20000

25000

30000

1 23 30 37 44 51 58 65 72 79 86 93 100107 114121

EC

, mA

Alk

alin

ity,

mg

L-1

Expt Days

Alkalinity outletElectrical Conductivity

Fig. 7 e Variations in alkalinity and EC.

Table 4 e Test parameters during consistency period of biohydrogen yield.

No Exptdays

pHfeed

COD loadingrate, g L�1 d�1

% CODreduction

VFA effluentg L�1

ALK effluentg L�1

BioH2 producedml d�1

SBPR ml g�1

COD reduced d�1SBPR ml g�1

VS reduced d�1

1 79 5.3 15.18 78 13.5 19.03 1310 6.90 10.99

2 86 5.15 17.056 63 12.9 22.20 1900 10.98 12.77

3 103 5.48 17.79 70 13.8 19.03 1760 9.99 12.36

4 107 5.5 17.72 77 13.5 12.68 1770 8.87 14

5 115 5.63 17.7 74 14.4 19.03 1570 7.24 9.44

6 121 5.36 17.55 73 19.5 22.20 1680 8.00 14.09

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 2 1e2 7 2 82726

to the accumulation of the sludge in the reactor. The sludge

was removed at the rate of 2 L at port 4 daily. This reduces VFA

accumulation in the range below 15000 mg L�1. Later this was

repeated twice in a week to maintain the VFA level which is

the main route for bio hydrogen production (Fig. 5). Before the

yield increased above 1000 ml d�1, a separation of biomass

layer in the reactor occurred at 30 cm from the inlet port. The

biomass level was separated by 15 cm gap of liquid. This

separation occurred frequently once in every 3 days showing

the excellent anaerobic reaction. The separated layer lasted

for 4e12 h when the particles settle down there by releasing

the gas from the packed biomass. Sporadically discharging

sludge is a feasible means of dealing with sludge production

from a biological system. To evaluate the performance of

a UASB reactor, it is important to know whether the reactor is

operated at its maximum sludge holdup. Instead, the reactor

could be operated under conditions where the effluent settles

able solids concentration is minimized by periodically dis-

charging excess sludge before the maximum sludge holdup is

attained [47].

The UASB system is evaluated only based on sludge hold

up. A longer HRT reveals more carbohydrates are converted

into hydrogen. Ueno et al. [18] investigated the hydrogen

production rate by anaerobicmicro flora in chemostat culture.

Their results showed themaximumhydrogen production rate

was 198 mmol L�1 d�1 (4.44 m3 m�3 reactor d�1) and

a maximum hydrogen yield of 14 mmol g�1 carbohydrate

removed (0.63 m3 kg�1 LVSS d�1).

3.5. Variations in pH, alkalinity and EC

The pH of the reactor reduced below 5 during the startup

period due to excess volatile fatty acid production, a route of

biohydrogen generation. During the entire process the pHwas

maintained at 5e6. Though the influent pHwas kept around 5,

02468

101214

COD reduced VS reduced press mud added

SBP

R, m

l g-1

d-1

Parameter

SBPR

Fig. 8 e Comparison of SBPR for COD, VS reduced and press

mud added.

the effluent pH tends to rise to 6 during startup. At pH of 5.5

maximum biohydrogen was produced and if pH reached

above 6 the biohydrogen yield decreased (Fig. 6).

The Electrical Conductivity (EC) was high in the beginning

and reduced gradually to around 150 mA. This is due to

reduction in the alkalinity in the reactor. There is a decrease in

the VFA in the startup stage without biohydrogen generation

which is the stabilization of the system with substrate

feeding, when the alkalinity decreases gradually. Later the

VFA get converted to biohydrogen, a product of anaerobic

fermentation and stable during consistent biohydrogen yield.

An increase in the organic loading rate increases alkalinity.

The alkalinity was steady during startup period and declined

during consistent bio hydrogen yield due to formation of VFA

by fermentation process (Fig. 7).

It has been found that a high cell density (higher than5 g L�1

total solids) in bioreactor is required to keep high hydrogen

yield, since lowcell intensity cannot efficiently convert organic

substrates to hydrogen. Test parameters during consistency

period of biohydrogen yield are given in Table 4

4. Conclusions

From the experiment conducted for 120 days the following

observations were made.

1. SBPR was 10.98 ml g�1 COD reduced d�1 for maximum

biohydrogen yield. COD reduction was above 70 � 7%.

During consistent gas yield SBPR ranged between 7 and

11 ml g�1 COD reduced d�1

2. SBPR of 12.77 ml g�1 VS reduced d�1 on peak yield. SPBR

between 10 and 14 ml g�1 VS reduced d�1 gave consistent

biohydrogen yield.

3. The gas yield wasmaximum on the 78th day to 2240ml d�1.

After 80 days the production stabilized between 1600 and

1900ml d�1 with a fluctuation of�10%. This indicates that it

requires more than 75 days of startup period for acclima-

tization, since the feed contains particulate solids sus-

pended in liquid medium.

4. H2% was between 52 and 59% during steady state condition

5. Biohydrogen yield of about 890ml kg�1 pressmudaddedd�1

was obtained by this process (Fig. 8).

Hence, because of its higher hydrogen productivity of the

biomass concentration of biomass, the upflow reactor poss-

essed much higher volumetric hydrogen production rates.

Considering the above results and its stable operation for 17

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 2 1e2 7 2 8 2727

weeks, it might be concluded that this UASB reactor is a more

promising bio-system for hydrogen production from biode-

gradable organic solid waste medium viz. press mud.

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