performances of mesophilic anaerobic digestion systems treating poultry mortalities

This article was downloaded by: [Colorado College]On: 25 November 2014, At: 16:11Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number:1072954 Registered office: Mortimer House, 37-41 Mortimer Street,London W1T 3JH, UK

Journal of EnvironmentalScience and Health,Part B: Pesticides, FoodContaminants, andAgricultural WastesPublication details, including instructionsfor authors and subscription information:http://www.tandfonline.com/loi/lesb20

Performances ofmesophilic anaerobicdigestion systems treatingpoultry mortalitiesTen‐Hong Chen a & Jia‐Chern Wang a

a Department of Agricultural MachineryEngineering , National Chung‐HsingUniversity , Taichung, 40227, Taiwan,Republic of ChinaPublished online: 21 Nov 2008.

To cite this article: Ten‐Hong Chen & Jia‐Chern Wang (1998) Performancesof mesophilic anaerobic digestion systems treating poultry mortalities,Journal of Environmental Science and Health, Part B: Pesticides, FoodContaminants, and Agricultural Wastes, 33:4, 487-510

To link to this article: http://dx.doi.org/10.1080/03601239809373158

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy ofall the information (the “Content”) contained in the publicationson our platform. However, Taylor & Francis, our agents, and ourlicensors make no representations or warranties whatsoever as

http://www.tandfonline.com/loi/lesb20

http://dx.doi.org/10.1080/03601239809373158

to the accuracy, completeness, or suitability for any purpose ofthe Content. Any opinions and views expressed in this publicationare the opinions and views of the authors, and are not the viewsof or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verifiedwith primary sources of information. Taylor and Francis shall not beliable for any losses, actions, claims, proceedings, demands, costs,expenses, damages, and other liabilities whatsoever or howsoevercaused arising directly or indirectly in connection with, in relation toor arising out of the use of the Content.

This article may be used for research, teaching, and private studypurposes. Any substantial or systematic reproduction, redistribution,reselling, loan, sub-licensing, systematic supply, or distribution inany form to anyone is expressly forbidden. Terms & Conditions ofaccess and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

http://www.tandfonline.com/page/terms-and-conditions

http://www.tandfonline.com/page/terms-and-conditions

J. ENVIRON. SCI. HEALTH, B33(4), 487-510 (1998)

PERFORMANCES OF MESOPHILIC ANAEROBIC DIGESTION

SYSTEMS TREATING POULTRY MORTALITIES

Key Words: Poultry mortalities, anaerobic digestion, leachbed, upflowanaerobic sludge blanket, leachate recirculation

Ten-Hong Chen and Jia-Chern Wang

Department of Agricultural Machinery Engineering,National Chung-Hsing University,

Taichung, Taiwan 40227Republic of China

ABSTRACT

A closed-loop anaerobic digestion system consisting of a leachbed (LB) and an

upflow anaerobic sludge blanket (UASB) was tested as an alternative for the

disposal of poultry mortalities. This paper compares the performances of three LB-

UASB treatment systems with different initial moisture contents in the LBs. Each

LB was loaded with one chicken and 5, 10 or 18 liters of water. The LBs initially

carried out the hydrolysis/acidification phase while the UASBs the methanogenesis

phase. Due to repeated inoculation by the UASBs, the LBs with 10 and 18 liters of

water started producing methane on day 5, while the one with 5 liters of water on

day 19. However, methane production rates were low before day 40 for the LB

with 10 liters of water and day 60 for the other LBs. Methane production gradually

487

Copyright © 1998 by Marcel Dekker, Inc. www.dekker.com

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

488 CHEN AND WANG

improved as the LBs continued to receive ungranulated sludge from the UASBs.

The LBs eventually became balanced methane reactors. Continued balanced

fermentation in the LBs resulted in leachates with very low substrate concentrations

that could no longer support high-rate methanogenesis in the UASBs.

Consequently, methane production rates from the UASBs decreased quickly while

that from the LBs reached peak levels. Cumulative methane production from each

LB eventually exceeded that from its connecting UASB. After 118 days of

digestion, 414, 437 and 470 liters of methane were produced from the three

systems, respectively. Cumulative methane production from the LBs with 5 and 18

liters of water accounted for 63% of the total methane produced from their

respective systems. The LB with 10 liters of water produced 75% of the total

methane from that system. Methane yields ranged from 0.485 to 0.554 m3 (Kg TS)

1. About 86% of the initial dry weight was biodegraded. All three systems

performed very well with little operational problems. Overall, the system that

started with 10 liters of water in the LB performed the best. Strategy for enhancing

system performances and implementing farm applications are discussed.

INTRODUCTION

Chicken population in Taiwan was 101.8 million in 1995 (Taiwan Provincial

Government, 1996). At an average mortality rate of about 9.3%, about 8.6

million birds need to be disposed of annually. Being easily putrefiable, potential

of causing sanitary problems, spreading of diseases and, in the worst scenario,

smuggling of tainted meat into the market are of great concerns. To dispose of

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

MESOPHILIC ANAEROBIC DIGESTION SYSTEMS 489

mortalities properly is crucial to improving public health, sustaining animal

industry and protecting the environment.

In addition to the conventional disposal methods of burial, incineration and

rendering, aerobic composting is becoming popular in America (Donald and

Blake, 1992) and accepted by many states (Proctor, 1992). Chen and Shyu

(1998) proposed anaerobic digestion as yet another alternative for mortality

disposal. The advantage of anaerobic treatment is that it couples waste treatment

with methane production. Additionally, the process kills pathogens (Lee and

Shih, 1988; Shih, 1987; Turner et al., 1983). However, a thermophilic (55°C)

LB-UASB system treating poultry mortalities was severely inhibited due to high

concentrations of long-chained fatty acids (LCFA) arising from lipid hydrolysis

(Chen and Shyu, 1998). Furthermore, operation of the system was problematic

due to frequent feeding or recycling line breakage as a result of prolonged, almost

continuous recirculation. Methane production and conversion efficiency seemed

to improve with higher initial moisture content in the LB. Digestion at 35°C was

less inhibited, although there were still rooms for further improvements. The

objective of this study was to further examine the effects of initial moisture

contents in the LB and a smaller recycle ratio on performances of a mesophilic

LB-UASB system.

MATERIALS AND METHODS

Poultry Mortalities

Chickens were purchased from a local market when needed. The average live

weight of the chickens was 2192 grams. The chickens were slaughtered, their

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

490 CHEN AND WANG

blood drained and collected and their feathers plucked. Each dead bird,

simulating mortalities, was divided into four components for the experiments:

'carcasses, blood, viscera and feathers. ••'••

Experimental Set-up

The anaerobic digestion system used consisted of a leachbed (LB) and an

UASB reactor connected in a closed loop (Figure 1). Three systems were set up,

hereafter designated systems A, B and C. The reactors were made of Plexiglas.

Dimensions for the reactors are presented in Table 1. The reactors were

incubated in temperature-controlled chambers maintained at 35±1°C. Biogas

from each reactor was collected in a water displacement system, filled with

solution containing 25% NaCl and 0.5% citric acid.

Start-up

Chicken components, each in a No. 32 mesh nylon bag, were placed in the

LBs to start the experiment. One bird per LB. Five, ten and eighteen liters of

water were added to LB-A, LB-B and LB-C, respectively, to allow extra liquid

for recirculation. Each UASB was inoculated with about 50% (by volume) of

granular sludge obtained from I-Lan Brewery Plant (Taiwan Tobacco and Wine

Co.). The inoculum contained 40.47 grams of volatile suspended solids (VSS)

and had a specific methanogenic activity of 1.43 g COD (g VSS)'1 day1.

Operation

Liquid in both the LB and the UASB were recirculated by peristaltic pumps

six times daily at 30 minutes each. Liquid in the LB was recirculated by

pumping from the bottom and distributing over the chicken components from the

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


- Gas Sampling

35X

BiotasCollection

Feed Pump

Leachbed UASB

FIGURE 1

Schematics of experimental setup of an LB-UASB system.

top to promote leaching. Pumping recirculating liquid created an upflow velocity

of 0.7-0.9 m h"1 in the UASB. Leachate from the LB was fed to the UASB six

times per day. During feeding, appropriate volume of the leachate was pumped

to the UASB as influent while effluent from the UASB overflowed to the LB to

maintain constant liquid volumes in both reactors. Loading rates (LR) to the

UASB determined the volume of liquid to be transferred. The chemical oxygen

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

492 , CHEN AND WANG

TABLE 1

Reactors Dimensions and Some Operational Parameters

Reactor

DimensionDiameter(mm)Height(mm)Working volume

(dm3)

Recycle ratio

Liquid upflowvelocity(m h"1)

Svstem ALeachbed UASB

1950

5

NA

NA

960

3

1.4-304

0.7-0.9

Svstem BLeachbed UASB

2355

10

NA

NA

960

3

1.4-162

0.7-0.9

Svstem CLeachbed UASB

2360

18

NA

NA

960

3

1.4-132

0.7-0.9

demand (COD) of the leachate was monitored frequently and the data used for

calculating LRs to the UASB. The UASBs were started at an LR of 0.5 g COD

I"1 day"1 to avoid shock-loading the inoculum. The LR to the UASB was raised

in small steps (< 0.5 g COD I"1 week'1) if digestor performance remained

acceptable. Feeding of the UASB was discontinued when leachate concentration

became very low, but, the experiment continued until day 118.

Sampling and Analyses

Daily biogas production was determined from the volume of saline solution

displaced. Gas samples for composition analyses were taken through a septum

on top of the liquid displacement system (Figure 1). Gas composition was

analyzed with a thermal conductivity detector on a gas Chromatograph (GC,

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


Shimadzu GC-14A). A 3mm by 3m column packed with 60/80 mesh

Chromosorb 102 (Supelco Inc.) was used.

The initial dry weights of the chickens were determined. Additional chickens

were used to determine the COD of chicken components. Each of these chicken

was divided into five components: bones, meats, blood, viscera and feathers. The

components were freeze-dried and ground through a 0.5mm screen in a Cyclone

Sample Mill (UDY Corp.) before analyses. The COD analyses were performed

according to the Standard Methods (APHA, 1992).

Effluent from the LB and the UASB were sampled periodically for total solids

(TS), volatile solids (VS), pH, COD, volatile fatty acids (VFA) and long-chained

fatty acids (LCFA, Cg-C24) analyses. Liquid lost through sampling and

evaporation was replaced with tap water. The CODs of both filtered (through

Supoi*-450 filters, Gelman Sei.) and unfiltered samples were determined. The

difference between the filtered and the unfiltered CODs was taken to be the

sludge concentration. The TS and VS were analyzed according to the Standard

Methods. The pH was determined with a pH electrode. The VFA and LCFAs

were determined with a flame ionization detector on a GC (Hitachi 5000A). The

column and GC conditions for VFA analyses were as previously described (Chen

and Shyu, 1996). Samples for LCFA analyses were prepared in a two-hour one-

step extraction-transesterification procedure (Sukhija and Palmquist, 1988) and

frozen (-20°C) until analyzed. A 3mm by 2m column packed with 100/120

Chromosorb WAW, GP 10% SP-2330 was used for the LCFA analyses.

Nitrogen gas at a flow rate of 20 ml min"1 was the carrier gas. The injector,

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

494 CHEN AND WANG

column and detector temperatures were 220, 200 and 250°C, respectively.

Standards (Catalog nos. O 7756, 7506 and 7631) for the LCFAs analyses came

from Sigma (Sigma Chem. Co.). Individual LCFAs were calculated by

comparing peak areas of the samples to those of the standards.

On termination of the experiment, all nylon bags were retrieved from the

LBs, rinsed with water and dried to determine weight losses. The CODs of the

residual solids, the final fermentation liquid including the rinsate were also

determined for mass balancing purposes.

RESULTS

The average dry weight of the chickens was 853 grams. Addition of 5, 10

and 18 liters of water resulted in initial TS contents of 13.3%, 7.5% and 4.4%

for LB-A, LB-B and LB-C, respectively. The dry weight compositions of the

meat, bones, feathers, viscera and collected blood were 50.7, 29.1, 11, 8.3 and

0.9%, respectively. On a COD basis, meats, bones, feathers, viscera and blood

constituted 57.3, 23, 9.7, 9.3 and 0.6%, respectively, of a chicken.

Leachbed Performance

The mortalities started solubilizing quickly and produced a concentrated

leachate. A layer of oil appeared on the surface of the fermentation liquid on day

4, an indication that adipose tissues were being released from decomposing

chicken components. The leachate contained LCFAs, suggesting lipids hydrolysis

since lipids are hydrolyzed to LCFAs and glycerol (Hanaki et al., 1981).

However, the LCFA concentrations were low, at less than 1.4 g COD equivalent

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


per liter. Leachate CODs reached the maximum levels within 5 days after start-

up (Figure 2). With 5, 10 and 18 liters of water added, leachate COD

concentrations reached 44, 20 and 18 g I"1, respectively. Volatile fatty acids

(mostly acetate) contributed up to 70% of the CODs. The pH levels were

between 6-6.5. There was no CH4 in the biogas. Apparently, the fermentation

was unbalanced and the LBs were carrying out hydrolysis/acidification phase up

to this point.

The LB-B and the LB-C started producing methane on day 5, while methane

appeared in the biogas from LB-A on the 19th day. Thereafter, methane contents

of the biogas increased gradually. Concurrently, leachate CODs and VFAs were

decreasing while pH was increasing. Methane contents of the biogas levelled off

at about 80%, indicating that the LBs had matured as balanced methane reactors.

It took LB-B about 50 days to reach this level, while LB-A and LB-C took about

65 days. Methane production rates reached the maximum levels on days 70, 50

and 75 for LB-A, LB-B and LB-C, respectively, and remained at those levels

until day 87 (Figure 3). During these periods, LB-A was producing an average

of 6 1 CH4 day"1, while LB-B and LB-C were averaging 5 and 7.9 1 CH4 day"1,

respectively. Leachate COD concentrations from LB-B dropped below 400 mg

I"1 after day 57 (Figure 2). The LB-A and the LB-C reached the same stage on

days 68 and 80, respectively. Methane production rate from LB-B dropped below

2 1 day"1 when the operation was terminated on day 118.

On termination of the experiment, floating oil in LB-C disappeared almost

completely, while LB-B and LB-C still contained a thin layer of oil and fats. The

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

496 CHEN AND WANG

oOo

ou -

40 -

3 0 -

20-

10-

0 -

A A A Í - A ALB-ALB-B

- • • • LB-C

20 40 60Time, day

80 100 120

FIGURE 2

Leachate characteristics (COD, TVA and pH) and %CH4 in biogas from the LBs.

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


500

CH4 production rate

Cum. sludge

20 40 60 80

Time, day

FIGURE 3

100 120

Methane production rate and sludge accumulation in the LBs.

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

498 CHEN AND WANG

blood and viscera components disappeared completely. An average of 86.3% of

the carcasses was degraded. The remains were mostly bones. The feathers lost

77.3% weight. Overall, 14.1 % of the mortalities remained to be treated. Of the

remaining solids, 84.6% was bones and 15.4% feathers. Table 2 shows COD

distribution for the experiment. The many samples, residual solids, final

fermentation liquid and methane production accounted for 3.9%, 11.7%, 0.6%

and 83.7%, respectively of the total COD.

UASB Performance

Figures 4, 5 and 6 show the operating conditions and performances of UASB-

A, UASB-B and UASB-C, respectively. For the first 25 days, all UASBs

maintained nearly 100% COD reduction efficiencies even though influent CODs

were high and the LRs were increasing. Methane production rates continued to

follow the LRs closely, indicating stable methanogenesis and that methanogenesis

was not rate-limiting. As influent concentrations were decreasing due to efficient

COD reduction in the LBs, increasingly higher feeding rates were used to achieve

increasingly higher LRs. Consequently, the hydraulic retention times (HRT) were

becoming increasingly shorter. Prior to day 40, UASB-C had the shortest HRTs,

followed by UASB-B, then UASB-A. The LRs reached a maximum of about 4

g I'1 day"1 and could not be increased any further without lowering the HRT to

below 0.25 days after influent COD concentrations had dropped below 400 mg

I'1. A minimum HRT of 0.25 days was maintained to prevent excessive washout

from the UASBs. The LRs and methane production rates started to decrease due

to further decreases in influent concentrations. Feeding of UASB-B was

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


TABLE 2

COD Distribution during the Experiment

System

ALeachbed (w/ 5 1 H2O)UASBLB-UASB

BLeachbed (w/ 10 1 H2O)UASBLB-UASB

Leachbed (w/ 18 1 H2O)UASBLB-UASB

Average LB-UASB

as % of total

Chen and Shyu (1998)Leachbed (w/ 3 1 H2O)UASBLB-UASB

Sampling

83.92.2

86.1

43.81.3

45.1

43.21.9

45.1

58.8

3.9

11613.5

129.5

COD distribution, eram

CH4 prod.

750432

1182

929.3318.7

1248

854.6496.4

1351

1260.3

83.7

117369.1486.1

CODFinal residual

Liquid

6.2-0.41

5.8

11.3-1.5'9.8

13.8-0.3'13.5

9.7

0.6

103.54.7

108.2

Solids

1870

187

196.90

196.9

145.30

145.3

176.4

11.7

———

Total

1461

1499.8

1554.9

1505.2

100

'Calculated as (final COD concentration - initial COD concentration) x (liquidvolume). The final COD concentration was lower than the initial CODconcentration.

discontinued on day 65 while feeding of UASB-A and UASB-C stopped on days

75 and 84, respectively. At these times, the COD concentrations in the UASBs

were below 200 mg I'1. Throughout the experiment, the CODs of UASB-B were

generally lower than those of UASB-A and UASB-C. The LCFA (mostly

myristate) and VF A concentrations never exceeded 450 and 1400 mg COD

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

500 CHEN AND WANG

X

100

8.5

8 -

7.5-

o>ooo

ooo

3 -

2 -

1-

20 40 60Time, day

80 100

-o

oo

ou

100

-80

-60

-40

-20

co t¡¡

o3

•o<DCCDOO

120

FIGURE 4

Operating conditions (HRT and LR) and reactor performance for UASB-A.

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


>•v

HI,

X

4 0 -

30 -

2 0 -

10 -

0 -

11

\ I ' ̂\

20 40 60Time, day

80 100

4.5 >-4 S

ooo

-2 S

-1

- 6 0

- 4 0

- 2 0

ctüo

n

3

œirDco

120

FIGURE 5

Operating conditions (HRT and LR) and reactor performance for UASB-B.*

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

502 CHEN AND WANG

X

32-r30-

2 0 -

1 0 -

0 -

ñ J/ i

^ — •

. ^ ~

/

Ai

- 6

- 5

- 4

- 3

- 2

-1

- 0

100

40 60Time, day

80 100

a-ooo

cH5

120

FIGURE 6

Operating conditions (HRT and LR) and reactor performance for UASB-C.

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


equivalent per liter, respectively. The pH profiles of all UASBs were similar.

After dropping slightly to around 7.2, the pH rised gradually and levelled off at

above 7.5. Upon termination, UASB-A, UASB-B and UASB-C contained 73.5,

65.5 and 48.4 grams of VSS, respectively.

LB-UASB System Performance

The LB-UASB system initially behaved like a two-phase system with the LB

serving as the hydrolysis/acidification phase and the UASB the methanogenesis

phase. There was a lag of 45 days for system B and 60 days for systems A and

C before accelerated methanogenesis started in the LBs (Figure 7). As the LBs

progressed to become matured methane reactors, increasingly more substrate was

bioconverted into methane in the LBs before reaching the UASBs. Cumulative

methane production from each LB eventually exceeded that from its connecting

UASB. The cross-over points occurred on days 86, 64 and 84 for systems A, B

and C, respectively. After 118 days of fermentation, system A produced a total

of 414 liters of methane while system B produced 437 liters and system C

produced 470 liters. About 63% of the total methane from each system came

from the LB for systems A and C, while cumulative methane production from

LB-B accounted for 74.5% of the total from system B. Methane yields ranged

from 0.485 to 0.551 m3 (kg TS)"1, about two to three times that reported

previously (Chen and Shyu, 1998). Additionally, there was little operational

problems, such as foaming and feeding or recycling line breakage due to

prolonged recirculation. Shorter recycling time proved desirable.

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

504 CHEN AND WANG

400

cg

•oO

o

|

300 -

200-

Oa>

I 100 -

0400

300 -

200-

-£ 100 -

0400

o 300 -

200 -

o

3

u

System A

LBUASB

System B

System C

'

20 40 60Time, day

80 100 120

FIGURE 7

Cumulative methane production from the LB and UASB of each system.

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


DISCUSSION

The UASBs performed very well. They were able to generate methane

efficiently over the full range of LRs applied, keeping VFAs and LCFAs at low

levels throughout the experiment. The LBs produced at least 63 % of the methane

from each system, making significant contribution to the overall stabilization of

the mortalities. Together, the performances of the present LB-UASB systems

represent a significant improvement from that reported previously (Chen and

Shyu, 1998).

The LBs in this study started producing methane earlier than the 27 days

reported previously for a similar system but with 3 liters of water in the LB and

25% (v/v) inoculum in the UASB (Chen and Shyu, 1998). One could probably

attribute the faster start of methanogenesis to more granular sludge in the UASB

as it is well accepted that a large inoculum can reduce the duration of lag phase

in batch digestion. However, it must be pointed out that very little of the

granules overflowed to the LB. Thus, the granular sludge in the UASB

contributed, at best, indirectly to methanogenesis in the LB. Perhaps more

importantly, a higher inoculation rate and a more favorable LB environment

resulting from higher moisture contents effected the faster start of

methanogenesis; Since the LBs were batch-loaded with mortalities without

inoculum, bacteria needed for methanogenesis had to come primarily from

connecting UASBs during feeding operations. Less concentrated leachate from

an LB with a higher moisture content allowed higher flow rates through its

connecting UASB while maintaining the same LR. The resultant larger effluent

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

506 CHEN AND WANG

volume from the UASB carried more un-granulated methanogens to the LB to

effect a higher inoculation rate. Furthermore, an LB with a less concentrated

fermentation liquid was less inhibitory, hence more conducive to methanogenesis.

These explanations would also support the observation that the LBs with 10 and

18 liters of water started producing methane much earlier than the LB with 5

liters of water, although all three UASBs contained the same amount of inoculum.

Although the LBs started producing methane earlier than reported previously,

methane production rates were low until each LB had received about 100 g of

sludge from their respective UASB (Figure 3). The LB-B reached this level the

fastest, at around day 40, followed by LB-A and LB-C, at around day 60.

Possibly, had the LBs been inoculated with that amount of sludge from the start,

the lag periods could be much shorter. However, since large amount of inoculum

may not always be available in a real farm application, producing biomass in situ

as was the.case in this study may be a necessity. In addition to being the initial

methanogenic phase of the system, the UASBs were, in effect, vessels for

continuous biomass production for the LBs.

The time it took to transfer enough sludge to each LB depended on the sludge

concentration of effluent from respective UASB and volume of liquid transferred.

Both gas production rates and biomass growth rate of an UASB affected the

sludge concentration of its effluent while its HRT determined the volume of liquid

transferred; Biogas production and upflowing liquid during feeding and recycling

operations expanded its sludge bed, moving finer particles toward bed surfaces.

Gas bubbles erupting at bed surfaces suspended these particles, causing some of

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


which to be carried over to its connecting LB during feeding operations. Sludge

concentration of effluent from UASB-B peaked on day 42 at 22 g COD 1' (Figure

8), about twice that from UASB-A. Since gas production rates were similar for

all UASBs before day 45, the higher sludge concentrations of effluent from

UASB-B most likely reflected its higher growth rate under shorter HRTs (Figures

4 and 5). On the other hand, UASB-C had the lowest growth rate before day 50,

probably because its HRTs were too short for efficient biomass growth. Thus,

considering the inverse relationship between HRTs and leachate concentrations,

the initial moisture content of an LB may provide a tool for controlling growth

rate in the UASB and inoculation rate to the LB.

Although the UASBs in this study performed very well, yet their potentials

as high-rate digestors and as vessels for continuous inoculum production for the

LBs had not been fully exploited. The UASBs became idle once their connecting

LBs started accelerated methanogenesis, causing leachate concentrations to drop.

The operation can be made more efficient by scheduling several LBs in sequence

to maintain peak LRs to the UASB; Initially, the UASB and an LB would be

operated as described in this study. As methane production from the UASB

becomes marginal when leachate COD concentration from the LB becomes low,

the UASB would be disconnected and used to start up a second LB with next

batch of mortalities. Meanwhile, the off-line LB would continue independently

as a balanced methane reactor. The UASB moves on to a third LB when the

second LB becomes a balanced reactor and leachate from it can no longer support

high-rate methanogenesis in the UASB, and so on. A cycle is complete when the

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

508 CHEN AND WANG

QOUTO

CO

ocoOIDTO

_24co3

¿z -

20-18-

16-

14-

12-

10-

8-

6 -

4 -

2 -

0 -

JA ti

: •*:

IIÜ i

Vi Í

—•' —UASB-AUASB-BUASB-C

20 40 60Time, day

80 100

FIGURE 8

Sludge concentrations of effluents from the UASBs.

first LB stops active methane production. The LBs then operating and the UASB

constitute the system. The residual solid materials from the completed LB should

be removed and disposed of through other methods (such as incineration, burial,

etc.) while the liquid used to start up the next batch of mortalities. As for the

oils and fats, due to their slower stabilization, they can be skimmed off and

digested in a separate sludge digestor. The process then repeats itself. Reusing

the liquid not only reduces the volume of water used and wastewater needing

post-treatment, but should also facilitate a quick start-up since the liquid contains

un-granulated methanogens and associated enzymes.

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14


With the above-mentioned operational scheme in mind, the objective in

operating an LB-UASB system is to achieve high-rate methanogenesis in the LB

in the shortest possible time while sustaining performances of the UASB. Net

increases in VSS in the UASBs at the end of the experiment indicate that

excessive wash-out did not occur and the performances of the UASBs should be

sustainable. By the above criteria, system B performed the best by being the first

one to achieve the operational goal of the LB-UASB system, followed by systems

A and C.

CONCLUSIONS

The results from the present study represent a significant improvement from

that reported previously. After 118 days of anaerobic digestion in the LB-UASB

system, about 86% of the poultry mortalities was biodegraded. Methane

accounted for 83.7% of the total COD. The LBs made significant contribution

to the overall stabilization of the mortalities, accounting for at least 63% of the

bioconversion in each system. The UASBs performed very well. In addition to

being the initial methanogenic phase of the systems, the UASBs served as a vessel

for continuous inoculum production for the LBs. Ungranulated sludge from the

UASBs was crucial to the start-up and maturation of the LBs. Moisture content

in the LBs played an important role in the development of the LBs. The system

with 7.5% TS in the LB performed the best. The capacity of the system can be

further expanded by scheduling several LBs in sequence for one UASB to fully

exploit the UASB's potential as a high-rate digestor.

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

510 CHEN AND WANG

ACKNOWLEDGMENTS

Funding for this project was provided by the National Science Council of the

Republic of China through Grant No. NSCSó^H-B-OOS^S.

REFERENCES

American Public Health Association, "Standard Methods for the Examination ofWater and Wastewater" 18th Edn. APHA, American Water Works Associationand Water Environment Federation, Washington, D. C. (1992).

Chen, T.H. and Shyu, W.H., Biomass and Bioenergy. 11(5), 431-440 (1996).

Chen, T.H. and Shyu, W.H., Bioresource Technol. 63(1), 37-48 (1998).

Donald, J.O. and Blake, J.P., Proceedings National Poultry Waste ManagementSymposium. Oct. 6-8, Birmingham, AL, pp56-63, (1992).

Hanaki, K., Matsuo, T. and Nagase, M., Biotechnol. Bioeng. 23, 1591-1610(1981).

Lee, M.R. and Shih, J.C.H., Appl. Environ. Microbiol. 54, 2335-2341 (1988).

Proctor, G., Proceedings National Poultry Waste Management Symposium. Oct.6-8, Birmingham, AL, pp44-46, (1992).

Shih, J.C.H., Poultry Sci. 66, 946-950 (1987).

Sukhija, P.S. and Palmquist, D.L., J. Agric. Food Chem. 36(6), 1202-1206(1988).

Taiwan Provincial Government, "Agriculture Yearbook", Department ofAgriculture and Forestry, Taichung, Taiwan (1996).

Turner, J., Stafford, D.A., Hughes, D.E. and Clarkson, J., Agric. Wastes. 6,1-11 (1983).

Received: February 13, 1998

Dow

nloa

ded

by [

Col

orad

o C

olle

ge]

at 1

6:11

25

Nov

embe

r 20

14

performances of mesophilic anaerobic digestion systems treating poultry mortalities

Documents