effect of initial cod concentration, nutrient addition, temperature and microbial acclimation on...

Bioresource Technology 93 (2004) 109–117

Effect of initial COD concentration, nutrient addition,temperature and microbial acclimation on anaerobic treatability

of broiler and cattle manure

Gamze G€ung€or-Demirci, G€oksel N. Demirer *

Department of Environmental Engineering, Middle East Technical University, Inonu Bulvarı, 6531, Ankara, Turkey

Received 7 April 2003; received in revised form 28 October 2003; accepted 30 October 2003

Abstract

In this study, anaerobic treatability and biogas generation potential of broiler and cattle manure were investigated. For this

purpose, seven sets of anaerobic batch reactor experiments were performed using broiler and cattle manure and their mixtures in five

different ratios (100% broiler; 75% broiler, 25% cattle; 50% broiler, 50% cattle; 25% broiler, 75% cattle; 100% cattle). These manure

mixtures had two different initial chemical oxygen demand (COD) (12,000 and 53,500 mg/l) concentrations. The effects of initial

COD concentration, nutrient and trace metal supplementation, microbial acclimation and digestion temperature were investigated.

Results revealed that the efficiency of total COD removal was 32.0–43.3% and 37.9–50% for initial COD concentrations of 12,000

and 53,500 mg/l, respectively. The biogas yields observed for initial COD concentrations of 12,000 and 53,500 mg/l were 180–270

and 223–368 ml gas/g COD added, respectively. A decrease in biogas yield was observed as the fraction of broiler manure increased

in mixture of broiler and cattle manure at initial COD values of 53,500 mg/l.

� 2003 Elsevier Ltd. All rights reserved.

Keywords: Anaerobic; Broiler; Cattle; Poultry; Manure; Codigestion

1. Introduction

The production of farm animals in large scale units

has considerably increased in the world. It is this in-

crease that makes farm animal manure a major envi-

ronmental problem for both developed and developing

countries. In Turkey, the production of cattle and

poultry manure was approximately 20 million tons drymatter in year 2000 (SIS, 2002). The huge amount of

waste produced in a concentrated area, requires urgent

treatment and disposal solutions because ammonia and

greenhouse gases, CH4 and CO2, emitted from the waste

storage units may cause air pollution problems while

improper application of nitrogen and phosphorus to

land in animal manure can result in eutrophication of

*Corresponding author. Present address: Department of Biological

Systems Engineering, Washington State University, L.J. Smith Hall,

P.O. Box 646120, Pullman, WA 99164-6120, USA. Tel.: +1-509-335-

16-36; fax: +1-509-335-27-22.

E-mail address: [email protected] (G.N. Demirer).

0960-8524/$ - see front matter � 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/j.biortech.2003.10.019

surface water resources and pollution of soil and

groundwater. Until now, many options have been pro-

posed for the utilization, treatment and disposal of

animal manure. Land application (Sommer and

Hutchings, 2001; Araji et al., 2001), field treatment

(Martinez and Hao, 1996), pond systems (Wang et al.,

1996), composting (Imbeah, 1998; Guerra-Rodriguez

et al., 2001; Tiquia and Tam, 2002), ground injection(Morken and Sakshaug, 1998), constructed wetlands

(Knight et al., 2000; Clarke and Baldwin, 2002), reverse

osmosis (Th€orneby et al., 1999) and anaerobic treat-

ment are the examples of these alternatives. Anaerobic

digestion is a relatively efficient conversion process for

poultry litter producing a collectable biogas mixture

with an average methane content of 60%. The methane

produced by this process can be used as a fuel forboilers, as a replacement for natural gas or fuel oil and

can also be fired in engine-generators to produce elec-

tricity for on-farm use or sale to electricity companies.

The residual sludge is stable and can be used as a soil

fertilizer. For larger operations the gases would need to

be scrubbed to remove impurities but may then be

mail to: [email protected]

110 G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117

compressed and sold commercially to fuel companies

(Kelleher et al., 2002). Increasing cost of landfilling and

the energy tax on fossil fuels encourage the exploitation

of renewable energy sources, thus making anaerobic

digestion a highly competitive alternative for the treat-

ment of animal manure (Salminen and Rintala, 2002a).

However, it has to be kept in mind that anaerobic

digestion has to be followed by a polishing treatmentstep (aerobic or chemical) for discharge into a receiving

environment.

Although anaerobic treatment is an established and

proven technology for the treatment of animal manure

and has been widely studied by many researchers

(Huang and Shih, 1981; Mackie and Bryant, 1995;

Magbauna et al., 2001), very little broiler manure is

treated anaerobically. In Turkey, the number of broilersis equal to 75% of total poultry (SIS, 2002). Anaerobic

digestion and biogas production are especially suitable

for broiler breeding farms because large amount of

waste is produced due to the use of litter material and

these farms use too much energy for heating purposes.

Therefore, anaerobic digestion can be a valuable alter-

native for broiler manure treatment.

In many cases, poultry and cattle are produced on thesame farm. Codigesting these wastes in centralized

anaerobic digestion plants may be a good solution for

such situations (Tafdrup, 1994; Dagnall, 1995; Mæng

et al., 1999; Weiland, 2000). Previous studies have fo-

cused on digestion of broiler and cattle manure sepa-

rately. However, codigestion of these two materials has

not been fully investigated.

In this study, cattle and broiler manure and theirmixtures in different ratios (100% broiler; 75% broiler

and 25% cattle; 50% broiler and 50% cattle; 25% broiler

and 75% cattle; and 100% cattle manure) were anaero-

bically digested in batch reactors and the optimum

conditions for anaerobic treatment of these wastes were

investigated by varying several parameters, namely ini-

tial chemical oxygen demand (COD) and TS concen-

trations, digestion temperature and acclimation of thecultures used. The batch reactor type was chosen be-

cause in agricultural societies, complex process configur-

ations result in technical and operational problems.

Table 1

Characterization of cattle and broiler manure used in experiments

Parameter Broiler manure

TS, % 73.6± 0.1

VS, % of TS 87.7± 0.1

Total COD, mg/g dry matter 1244

Soluble CODa, % of total COD 10±0.6

TKN, mg N/g dry matter 12.4± 0.4

NH3-N, mg N/g dry matter 8.85± 0.35

TP, mg P/g dry matter 16.9± 1.6

aAnalyzed for three different samples having 5000, 10,000 and 20,000 mg

2. Methods

2.1. Waste characteristics

Cattle manure was obtained from a small farm,

having 25 dairy cattle. Broiler manure was taken from a

commercial poultry farm housing about 20,000 broilers.

Both wastes were characterized and kept refrigerated at4 �C until used. Their compositions are summarized in

Table 1.

2.2. Basal medium

Basal medium (BM) containing all the necessary

micro- and macro-nutrients for an optimum anaerobic

microbial growth was used in the experiments. The

composition of BM used in all experiments is as follows

(concentrations of the constituents are given in paren-

theses as mg/l): NH4Cl (1200), MgSO4 Æ 7H2O (400),

KCl (400), Na2S Æ 9H2O (300), CaCl2 Æ 2H2O (50),

(NH4)2-HPO4 (80), FeCl2 Æ 4H2O (40), CoCl2 Æ 6H2O(10), KI (10), MnCl2 Æ 4H2O (0.5), CuCl2 Æ 2H2O (0.5),

ZnCl2 (0.5), AlCl3 Æ 6H2O (0.5), NaMoO4 Æ 2H2O (0.5),

H3BO3 (0.5), NiCl2 Æ 6H2O (0.5), NaWO4 Æ 2H2O (0.5),

Cysteine (10), NaHCO3 (6000) (Demirer et al., 2000).

2.3. Analytical methods

COD concentrations were measured with a Hach

spectrophotometer (model: P/N 45600-02) and vials for

COD range of 0–1500 mg/l. Soluble COD was deter-

mined by filtering sample through 0.45 lm filter paper.

COD of the supernatant was measured by using Hachspectrophotometer. All other analyses were performed

according to standard methods (APHA, 1997).

pH measurements were performed with a pH meter

(Model 2906, Jenway Ltd., UK) and a pH probe

(G-05992-55, Cole Parmer Instrument Co., USA). Sus-

pended solids and volatile suspended solids were mea-

sured as described in Standard Methods 2540 D, E.

Total phosphorus and Total Kjeldahl nitrogen concen-trations were also determined by Standard Methods

4500-P-E and 4500-Norg, respectively (APHA, 1997).

Cattle manure

16.9± 0.1

83.2± 0.3

1237.5

10± 0.3

4.5 ± 0.2

2.35± 0.05

3.4 ± 0.5

/l of total COD.

G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117 111

Gas production in batch reactors was determined by

a water displacement device. The content of CH4 in

biogas was determined as follows. A known volume of

the headspace gas (V1) produced in a serum bottle used

in biochemical methane production (BMP) experiments

was syringed out and injected into another serum bottle

which contained 20 g/l KOH solution. This serum bottle

was shaken manually for 3–4 min so that all the CO2

and H2S were absorbed in the concentrated KOH

solution. The volume of the remaining gas (V2), whichwas 99.9% CH4, in the serum bottle was determined by

means of a syringe. The ratio of V2=V1 provided the

content of CH4 in the headspace gas (Erg€uder et al.,

2000). The analyses for characterization of the manure

and methane content determination of the biogas were

performed in duplicates and the calculated mean andstandard deviation values were reported in Tables 1

and 3.

2.4. Experimental set-up and procedures

In order to determine the anaerobic biodegradabilityand biogas production of cattle and broiler manure,

BMP experiments (Owen et al., 1979) were performed.

Experiments were conducted in 250 ml batch reactors

with 100 ml effective volume. Duplicates of five mixtures

of broiler and cattle manure, containing 100% broiler

(100B:0C); 75% broiler and 25% cattle (75B:25C); 50%

broiler and 50% cattle (50B:50C); 25% broiler and 75%

cattle (25B:75C); and 100% cattle manure (0B:100C)were prepared. Control reactors both with and without

basal medium were also run in all experiments to

determine the background gas production. Mixed

anaerobic cultures obtained from anaerobic sludge

digesters of the Ankara wastewater treatment plant were

used as seed.

After seeding, adding basal medium, where necessary,

and wastes, the reactors were flushed with CH4 gas for 4min to maintain anaerobic conditions and then sealed

with natural rubber stoppers and plastic screw-caps.

They were incubated in a temperature controlled room

at 35± 2 �C and gas production in each reactor was

Table 2

Details of BMP sets

Set no. Average COD

concentration,

mg/l

Average TS

concentration, %

Temperature, �C

Set 1 12,000 1 35

Set 2 12,000 1 35

Set 3 53,500 4.3 35

Set 4 53,500 4.3 35

Set 5 12,000 1 Ambient temperature

Set 6 12,000 1 35

Set 7 12,000 1 Ambient temperature

measured daily with the water displacement device.

After gas measurement the reactors were shaken once a

day manually.

The experiments in this study were divided into two

phases. During the first phase of BMP experiments, four

sets of reactors were operated and the effect of various

ratios of cattle and broiler manure and various COD

and TS concentrations on anaerobic treatability andmethane production was evaluated. In addition, in order

to observe the effect of nutrient supplementation on the

anaerobic digestion and codigestion of cattle and broiler

manure, these experiments were conducted both in the

presence and absence of BM. Two different initial COD

concentrations, 12,000 and 53,500 mg/l, with five dif-

ferent waste compositions were examined in the BMP

experiments.In the second phase, three sets of reactors were

operated. One was set up under ambient temperature to

observe the effect of temperature on unacclimated mixed

culture. Another was to investigate the effects of accli-

mation on the anaerobic digestion and codigestion of

cattle and broiler manure at 35 �C. The last set was

conducted to reveal the effect of the temperature

(ambient temperature versus 35 �C) on the batchanaerobic digestion with acclimated culture. The cul-

tures which were used in Sets 3 and 4 to treat five dif-

ferent mixtures of manure at 53,500 mg/l initial COD

concentration were taken at the end of experimental

period (91 days) and used as acclimated cultures in Sets

6 and 7. The cultures taken from one manure mixture

with a certain ratio in Sets 3 and 4 were used for the

treatment of manure mixture with the same ratio in Sets6 and 7. To determine the background biogas produc-

tion of the acclimated culture, control reactors were run

for each ratio of manure mixtures. Therefore, totally 95

batch reactors in seven BMP sets were established and

monitored during the study. The details of these seven

BMP sets are given in Table 2. Methane content of

biogas was measured three times for Sets 1, 2, 3 and 4

and two times for other sets as duplicates during theexperimental periods. The averages of these measure-

ments are shown in Table 3.

Culture type Nutrient addition Days operated

Unacclimated No 43

Unacclimated Yes 43

Unacclimated No 91

Unacclimated Yes 91

Unacclimated Yes 27

Acclimated Yes 31

Acclimated Yes 31

Table 3

Biogas yield and average methane content in the reactors

Set no. 100B:0C 75B:25C 50B:50C 25B:75C 0B:100C

Biogas yield at the end of experimental period, ml gas/g COD added

Set 1 255.4 230.4 269.8 231 242.2

Set 2 199.2 191.8 209.1 183.6 180.3

Set 3 223.4 283.7 314.8 330.2 359

Set 4 236.6 231.4 269.9 324.1 368.5

Set 5 181.7 173 136.9 107.5 101.5

Set 6 211.2 226.4 178.1 242.8 249.9

Set 7 61.7 75 151.8 87.8 94.9

Average methane content, %

Set 1 67± 6 65± 4 57± 5 64± 4 64± 3

Set 2 67± 6 68± 6 72± 5 69± 5 70± 4

Set 3 67± 3 59± 4 54± 4 53± 3 49± 5

Set 4 73± 3 66± 5 66± 4 61± 3 53± 5

Set 5 59± 5 60± 5 63± 6 62± 5 64± 6

Set 6 65± 5 62± 6 65± 4 60± 6 62± 5

Set 7 50± 5 55± 6 53± 4 54± 5 55± 4

(a)

0

100

200

300

400

Control100B:0C75B:25C50B:50C25B:75C0B:100C

(b)

Time, days0 10 20 30 40 50

Cum

ulat

ive

gas

prod

uctio

n, m

l

0

100

200

300

400

Fig. 1. BMP experiment results of Set 1 (a) (COD¼ 12,000 mg/l, no

BM, 35 �C, unacclimated culture), and Set 2 (b) (COD¼ 12,000 mg/l,

with BM, 35 �C, unacclimated culture).


3. Results and discussion

3.1. Sets 1 and 2––anaerobic digestion and codigestion at

12,000 mg/l initial COD concentration with and without

nutrient addition

In these sets of BMP experiments, the daily gas pro-

duction in each batch anaerobic reactor having 12,000mg/l COD and 1% TS concentrations and different cattle

and broiler manure compositions was monitored for

43 days. In order to compare the supplementation of

nutrient and trace metals on gas production, one of

these sets (Set 2) of reactors received BM. The initial

biomass concentration (as volatile suspended solids

(VSS)) in each reactor was 4410 mg/l. Thus, the initial

COD to biomass ratio obtained in the reactors was 2.7mg COD/mg VSS. Average gas production observed in

each reactor is presented in Fig. 1. These results reflected

the minimum treatment efficiency and biogas produc-

tion that could be obtained for the anaerobic cultures

used since microorganisms were not previously accli-

mated to cattle and broiler manure and the reactors

were not mixed.

In these sets, gas production was observed at highrates, about 19 ml/day for Sets 1 and 13 ml/day for Set 2

in the first 10–17 days, and at lower rates, about 3.5 ml/

day for Sets 1 and 3 ml/day in Set 2, in the remaining 26–

33 days. High initial gas production rates in first 10–17

days period was the result of consumption of easily

degradable COD. After this period of time, the amount

of easily degradable COD in the reactors decreased, and

as a consequence of this depletion, the gas productionrate was lower. At the beginning of the experiment,

soluble COD was used by microorganisms. Meanwhile,

the particulate matter was partially hydrolyzed by

acidogenic bacteria. Therefore, even though all substrate

in the reactors was not consumed completely during

the course of the experiment, the gas production rate

decreased since hydrolysis is a slow process. In the

hydrolysis phase, complex particulate compounds are

converted into soluble substrates. For many substrates,

especially for solids, hydrolysis often is the slowest and

the rate limiting step in anaerobic biodegradation pro-

cess (Schieder et al., 2000; Palmowski and M€uller, 2000).


When Fig. 1(a) and (b) were compared, a decrease in

biogas production was seen in Fig. 1(b). This indicated

that nutrients present in the manure were sufficient for

anaerobic microbial growth if sufficient amount of water

was present to dissolve them. Therefore, addition of

extra nutrient is not necessary at low COD and TS

concentrations.

The biogas yields as ml biogas/g COD added andaverage methane content of biogas in Sets 1 and 2 are

given in Table 3. The theoretical methane production

values were calculated by using the stoichiometric ap-

proach (Speece, 1996) and found as 474 ml/g of COD

consumed. This value was compared with the experi-

mental values and total COD reduction in the reac-

tors was calculated. Methane production and calculated

total COD reduction values for both Sets 1 and 2 aregiven in Table 4.

In Table 4, reduction in total COD was observed

between 37.4% and 43.3% in Set 1 and between 32% and

38.1% in Set 2. However, as indicated in Table 1, only

10% of total COD is soluble and readily available for

microorganisms. This means that soluble COD was re-

moved and the remaining approximately 30% reduction

in Set 1 and approximately 25% reduction in Set 2 wasfrom particulate COD. This indicated that hydrolysis of

particulate materials is an important mechanism in the

anaerobic treatment of manure.

3.2. Sets 3 and 4––anaerobic digestion and codigestion at

53,500 mg/l initial COD concentration with and without

nutrient addition

In these sets of BMP experiments, the daily gas pro-duction in each batch anaerobic reactor having 53,500

mg/l COD and 4.3% TS concentrations and different

cattle and broiler manure compositions was monitored

Table 4

Methane production and reduction in total COD in the reactors

Set no. 100B:0C 75B:25C 5

Methane production, ml

Set 1 205.3 181.7 1

Set 2 160.1 156.5 1

Set 3 800.9 895.6 9

Set 4 924.2 817.1 9

Set 5 128.6 124.6 1

Set 6 164.8 168.5 1

Set 7 37 49.5

Reduction in total COD, %

Set 1 43.3 38.3

Set 2 33.8 33

Set 3 37.9 42.4

Set 4 43.7 38.7

Set 5 27.1 26.3

Set 6 34.8 35.5

Set 7 7.8 10.4

for 91 days. In order to observe the effect of nutrient and

trace metal supplementation on gas production, one of

these sets (Set 4) received BM. The biomass concentra-

tion (as VSS) in each reactor was 1200 mg/l. Thus, the

initial COD to biomass ratio obtained in the reactors

was 44.6 mg COD/mg VSS. The purpose of selecting

such a high value was to observe the performance of the

anaerobic cultures for biodegrading cattle and broilermanure under elevated condition. Average gas produc-

tions monitored in each reactor are presented in Fig. 2.

The experimental results indicated that total gas

production decreased as the fraction of broiler manure

in the waste mixtures increased in both Sets 3 and 4. Gas

production rates were quite high (about 50 ml/day) at

the beginning of the experimental period especially in

reactors having a high ratio of cattle manure. In thesesets, this period is longer than Sets 1 and 2. This was

probably due to the high COD concentrations of the

reactors, which means more available substrate for

microorganisms. After this period of time, the amount

of easily degradable COD in the reactors decreased and

as a consequence of this depletion, the gas production

also decreased.

The biogas yields as ml biogas/g COD added andaverage methane content of biogas in Sets 3 and 4 are

given in Table 3. The theoretical methane production

was 2113.2 ml for these sets. This value was compared

with the experimental values and in this way, total COD

reduction in the reactors was calculated. Methane pro-

duction and calculated total COD reduction values for

both Sets 3 and 4 are given in Table 4. As in the case of

Sets 1 and 2, particulate COD removal was observed inthese two sets since only 10% of total COD is in soluble

form. Table 4 also shows that nutrient and trace metal

supplementation to the reactors caused an increase in

the total methane production except 75B:25C reactor.

0B:50C 25B:75C 0B:100C

84.6 177 186

80.6 152 151.5

09.5 936.2 941.2

52.9 1057.8 1044.9

03.5 80 78

38.9 174.8 185.9

96.5 56.9 62.6

38.9 37.4 39.2

38.1 32 32

43 44.3 44.5

45.1 50 49.4

21.8 16.9 16.5

29.3 36.9 39.2

20.3 12 13.2

(a)

0

500

1000

1500

2000

2500

(b)

Time, days0 20 40 60 80 100

Cum

ulat

ive

gas

prod

uctio

n, m

l

0

500

1000

1500

2000

2500 control100B:0C75B:25C50B:50C25B:75C0B:100C

Fig. 2. BMP experiment results of Set 3 (a) (COD¼ 53,500 mg/l, no

BM, 35 �C, unacclimated culture), and Set 4 (b) (COD¼ 53,500 mg/l,

with BM, 35 �C, unacclimated culture).

Time, days0 5 10 15 20 25 30

Cum

ulat

ive

gas

prod

uctio

n, m

l

0

50

100

150

200

250

control100B:0C75B:25C50B:50C25B:75C0B:100C

Fig. 3. BMP experiment results of Set 5 (COD¼ 12,000 mg/l, with

BM, ambient temperature, unacclimated culture).


This shows the positive effect of nutrient supplementa-

tion on digestion and codigestion of cattle and broiler

manure at 53,500 mg/l initial COD concentration.

3.3. Set 5––effect of temperature on anaerobic digestion

and codigestion with unacclimated culture

In Set 5, the influence of temperature on methaneproduction from broiler and cattle manure was investi-

gated at ambient temperature to investigate the feasi-

bility of anaerobic digestion under low temperature

conditions. Mixed anaerobic cultures, which were not

previously acclimated to the wastes were used as inocula.

The initial COD concentration was 12,000 mg/l in the

reactors. The initial biomass concentration (as VSS) in

each reactor was 5420 mg/l. Thus, the initial COD tobiomass ratio obtained in the reactors was 2.2 mg COD/

Table 5

Net biogas and methane productions at the end of 27 days for Sets 2 and 5

Reactor Net gas production in Set 2 (ml) CH4 production in Set 2

100B:0C 218 146.1

75B:25C 209.2 142.2

50B:50C 217.3 156.4

25B:75C 180.3 124.4

0B:100C 167.1 117

mg VSS. Average gas productions observed in each

reactor are presented in Fig. 3.

In this set acclimation period of the microorganisms

or the lag period before a significant gas production was

observed was 3–5 days. The acclimation period wasshort as the mixed anaerobic cultures were stored earlier

and used to the laboratory temperature which was 23.5

�C during the experimental period. After Day 3, biogas

production increased and progressed at an almost con-

stant rate.

The biogas yields and average methane content of

biogas in this set are presented in Table 3. Methane

production and calculated total COD reduction valuesfor Set 5 are given in Table 4. Since all the conditions

were similar and only the temperatures were different,

Sets 2 and 5 are compared in terms of biogas and

methane production in Table 5. When the net total gas

productions of Sets 2 and 5 at the end of 27 days were

considered, a noticeable decrease in the amount of

biogas was seen in Set 5 for reactors 50B:50C, 25B:75C

and 100B:0C. Net biogas production in the reactors100B:0C and 75B:25C were same in the Set 2. On the

other hand, methane production values were lower in

Set 5 than Set 2 in all reactors. This decreased efficiency

is the result of sensitivity of anaerobic systems to low

temperatures. When compared to aerobic systems,

anaerobic systems are considerably more sensitive to

temperature decreases. Methanogens are more sensitive

than acidogens in the anaerobic consortium and an

(ml) Net gas production in Set 5 (ml) CH4 production in Set 5 (ml)

218 128.6

207.6 124.6

164.3 103.5

129 80

121.8 78


unbalanced metabolism can occur at lower temperatures

when the acidogens produce volatile acids faster than

the methanogens convert them to methane (Speece,

1996).

As reported by Hobson (1991), it is the rate rather

than extent of the reactions that is affected by temper-

ature, and a lower digester temperature can be com-

pensated for by a longer retention time. However, sincelonger retention times mean greater reactor volumes,

ambient temperature operations may not be feasible for

some climates.

3.4. Set 6––effect of acclimation on anaerobic digestion

and codigestion

In Set 6, the effect of acclimation on anaerobic

digestion and codigestion of cattle and broiler manure

was investigated. The gas production of the reactors in

Set 6 was monitored daily for 31 day period. The results

of these measurements are given in Fig. 4(a). Like Set 5,initial COD concentration was 12,000 mg/l. In this set,

the biogas production trends of the reactors were quite

similar to Set 2 (Fig. 1(b) versus Fig. 4(a)). Rate of

biogas production was high in the first 15–20 days and

slowed down in the remaining 11–16 days. The biogas

yields and average methane content of biogas in this set

(a)

0

50

100

150

200

250

300

350

(b)

Time, days0 5 10 15 20 25 30 35

Cum

ulat

ive

gas

prod

uctio

n, m

l

0

50

100

150

200

250

300

350100B:0C100B:0C control75B:25C75B:25C control50B:50C50B:50C control25B:75C25B:75C control0B:100C0B:100C control

Fig. 4. BMP experiment results of Set 6 (a) (COD¼ 12,000 mg/l, with

BM, 35 �C, acclimated culture), and Set 7 (b) (COD¼ 12,000 mg/l,

with BM, ambient temperature, acclimated culture).

were given in Table 3. Methane production and calcu-

lated total COD reduction values for Set 6 are presented

in Table 4.

As all the conditions were similar except the culture

type, Sets 2 and 6 are compared in terms of biogas and

methane production in Table 6. When the net total gas

productions of Sets 2 and 6 at the end of 31 days were

taken into consideration, an increase in the amount ofbiogas and methane was seen in acclimated set (Set 6),

except reactor 50B:50C. Therefore, based on the results

of this set of experiment, preacclimation is strongly

recommended in order to increase the efficiency of

digestion process.

3.5. Set 7––effect of temperature on anaerobic digestion

and codigestion with acclimated culture

In Set 7, the effect of temperature (ambient versus 35

�C) on anaerobic digestion and codigestion of cattle and

broiler manure was investigated. The only difference of

this set from Set 5 is the use of microbial culture pre-viously acclimated to the waste at 35 �C. The gas pro-

duction of the reactors was monitored daily for a 31-day

period and the results are given in Fig. 4(b). The average

laboratory temperature during the experimental period

was 23 �C.During the first 10 days of this set of experiment,

biogas production rate was extremely low. However, the

rate of methanogenesis increased during the remaining21 days, indicating the acclimation of methanogenic

microbial population to the low incubation tempera-

tures. Methane production and calculated total COD

reduction values for Set 7 are given in Table 4.

Like the previous two sets, in Set 7, since all the

conditions were the same except for temperature with

Set 6 and culture type with Set 5, net total gas and

methane productions for Sets 7, 6 and 5 at the end of 27days were presented in Table 7. When total gas and

methane productions of Set 7 were compared to Set 6

(35 �C, acclimated), a noticeable decrease in both values

was noticed. This is because of the sensitivity of an-

aerobic systems to low temperatures. On the other hand,

when the net gas production values of this set were

compared with the Set 5 (ambient temperature, unac-

climated), it was seen that a lower amount of gas wasproduced in Set 7 although the culture was previously

acclimated to the wastes. Moreover, acclimation period

in this set was longer than the Set 5 (Figs. 3 and 4(b)).

The reason for such a case is the adaptation of accli-

mated culture, which was incubated at 35 �C before, to

the lower temperature. On the other hand the mixed

culture used in Set 5 was stored at laboratory tempera-

ture and it was already adapted to this temperature. Theresults of this set of experiments indicated that the


manure at ambient temperature is not as efficient as at

Table 6

Net biogas and methane productions at the end of 31 days for Sets 2 and 6

Reactor Net gas production in Set 2 (ml) CH4 production in Set 2 (ml) Net gas production in Set 6 (ml) CH4 production in Set 6 (ml)

100B:0C 225.1 150.8 253.5 164.8

75B:25C 215 146.2 271.7 168.5

50B:50C 226.9 163.4 213.7 138.9

25B:75C 192 132.5 291.3 174.8

0B:100C 180.9 126.6 299.9 185.9

Table 7

Net total gas and methane productions at the end of 27 days for Sets 7, 6 and 5

Reactor Net gas production

in Set 7 (ml)

CH4 production in

Set 7 (ml)

Net gas production

in Set 6 (ml)

CH4 production in

Set 6 (ml)

Net gas production

in Set 5 (ml)

CH4 production in

Set 5 (ml)

100B:0C 59.4 29.7 245.8 159.8 218 128.6

75B:25C 72.6 39.9 261.7 162.2 207.6 124.6

50B:50C 152.7 80.9 201.9 131.2 164.3 103.5

25B:75C 83.5 45.1 272.7 163.6 129 80

0B:100C 91.8 50.5 281.4 174.5 121.8 78


35 �C even with the use of culture previously acclimated

to the wastes and is not suggested since it requires very

long retention times.

4. Conclusions

This study indicated that at low COD (12,000 mg/l)

and TS (1%) concentrations, total COD removal and thebiogas yield for anaerobic digestion of broiler and cattle

manure and their mixtures in different ratios was 32.0–

43.3% and 180–270 ml gas/g COD added, respectively.

By taking into account that only 10% of total COD was

soluble, remarkable decrease in particulate COD was

observed. Nutrient supplementation did not increase the

digestion performance. This showed that nutrients

present in the manure are enough for anaerobic micro-bial growth if sufficient amount of water is present to

dissolve them. Therefore, at low COD and TS concen-

trations, addition of extra nutrient is not recommended.

Batch anaerobic digestion and codigestion of cattle

and broiler manure was possible at higher COD (53,500

mg/l) and TS (4.3%) concentrations with total COD

removal efficiency and biogas yield of 37.9–50% and

223–368 ml gas/g COD added, respectively. Cattlemanure led to better performance than broiler manure

in terms of methane production and COD reduction.

Performances of codigestion reactors decreased as the

fraction of broiler manure increased. Ammonia pro-

duced in protein degradation may cause problems in

anaerobic digestion as unionized ammonia inhibits

anaerobic microorganisms, particularly methanogens

(Angelidaki and Ahring, 1993). The higher nitrogencontent of poultry wastes as compared to manures from

other farm animals (Bujoczek et al., 2000) make them

difficult substrate for anaerobic digestion (Salminen and

Rintala, 2002a,b). Therefore, the performance decrease

observed as the fraction of broiler manure increased at

high COD values (Fig. 2) may be due to the ammonia

inhibition which needs to be further investigated. At

ambient temperature, efficiency of anaerobic digestion

decreased as a result of sensitivity of anaerobic systems

to low temperatures.

Preacclimation is strongly recommended in order toincrease the efficiency of the digestion process. The


manure at ambient temperature was not as efficient as at

35 �C even with the use of culture previously acclimated

to the wastes and is not suggested since it requires very

long retention times.

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effect of initial cod concentration, nutrient addition, temperature and microbial acclimation on...

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