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

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1 Bioresource Technology 93 (24) 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 23; received in revised form 28 October 23; accepted 3 October 23 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 (1% broiler; 75% broiler, 25% cattle; 5% broiler, 5% cattle; 25% broiler, 75% cattle; 1% cattle). These manure mixtures had two different initial chemical oxygen demand (COD) (12, and 53,5 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 % and % for initial COD concentrations of 12, and 53,5 mg/l, respectively. The biogas yields observed for initial COD concentrations of 12, and 53,5 mg/l were and 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 53,5 mg/l. Ó 23 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 increase that makes farm animal manure a major environmental problem for both developed and developing countries. In Turkey, the production of cattle and poultry manure was approximately 2 million tons dry matter in year 2 (SIS, 22). The huge amount of waste produced in a concentrated area, requires urgent treatment and disposal solutions because ammonia and greenhouse gases, CH 4 and CO 2, 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 64612, Pullman, WA , USA. Tel.: ; fax: address: demirer@wsu.edu (G.N. Demirer). surface water resources and pollution of soil and groundwater. Until now, many options have been proposed for the utilization, treatment and disposal of animal manure. Land application (Sommer and Hutchings, 21; Araji et al., 21), field treatment (Martinez and Hao, 1996), pond systems (Wang et al., 1996), composting (Imbeah, 1998; Guerra-Rodriguez et al., 21; Tiquia and Tam, 22), ground injection (Morken and Sakshaug, 1998), constructed wetlands (Knight et al., 2; Clarke and Baldwin, 22), reverse osmosis (Th orneby et al., 1999) and anaerobic treatment 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 6%. The methane produced by this process can be used as a fuel for boilers, as a replacement for natural gas or fuel oil and can also be fired in engine-generators to produce electricity 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 /$ - see front matter Ó 23 Elsevier Ltd. All rights reserved. doi:1.116/j.biortech

2 11 G. G ung or-demirci, G.N. Demirer / Bioresource Technology 93 (24) compressed and sold commercially to fuel companies (Kelleher et al., 22). 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 treatment of animal manure (Salminen and Rintala, 22a). However, it has to be kept in mind that anaerobic digestion has to be followed by a polishing treatment step (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., 21), very little broiler manure is treated anaerobically. In Turkey, the number of broilers is equal to 75% of total poultry (SIS, 22). 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 alternative for broiler manure treatment. In many cases, poultry and cattle are produced on the same 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, 2). Previous studies have focused on digestion of broiler and cattle manure separately. However, codigestion of these two materials has not been fully investigated. In this study, cattle and broiler manure and their mixtures in different ratios (1% broiler; 75% broiler and 25% cattle; 5% broiler and 5% cattle; 25% broiler and 75% cattle; and 1% cattle manure) were anaerobically digested in batch reactors and the optimum conditions for anaerobic treatment of these wastes were investigated by varying several parameters, namely initial chemical oxygen demand (COD) and TS concentrations, digestion temperature and acclimation of the cultures used. The batch reactor type was chosen because in agricultural societies, complex process configurations result in technical and operational problems. 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 2, broilers. Both wastes were characterized and kept refrigerated at 4 C until used. Their compositions are summarized in Table 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 parentheses as mg/l): NH 4 Cl (12), MgSO 4 Æ 7H 2 O (4), KCl (4), Na 2 S Æ 9H 2 O (3), CaCl 2 Æ 2H 2 O (5), (NH 4 ) 2 -HPO 4 (8), FeCl 2 Æ 4H 2 O (4), CoCl 2 Æ 6H 2 O (1), KI (1), MnCl 2 Æ 4H 2 O (.5), CuCl 2 Æ 2H 2 O (.5), ZnCl 2 (.5), AlCl 3 Æ 6H 2 O (.5), NaMoO 4 Æ 2H 2 O (.5), H 3 BO 3 (.5), NiCl 2 Æ 6H 2 O (.5), NaWO 4 Æ 2H 2 O (.5), Cysteine (1), NaHCO 3 (6) (Demirer et al., 2) Analytical methods COD concentrations were measured with a Hach spectrophotometer (model: P/N 456-2) and vials for COD range of 15 mg/l. Soluble COD was determined by filtering sample through.45 lm filter paper. COD of the supernatant was measured by using Hach spectrophotometer. All other analyses were performed according to standard methods (APHA, 1997). ph measurements were performed with a ph meter (Model 296, Jenway Ltd., UK) and a ph probe (G , Cole Parmer Instrument Co., USA). Suspended solids and volatile suspended solids were measured as described in Standard Methods 254 D, E. Total phosphorus and Total Kjeldahl nitrogen concentrations were also determined by Standard Methods 45-P-E and 45-Norg, respectively (APHA, 1997). Table 1 Characterization of cattle and broiler manure used in experiments Parameter Broiler manure Cattle manure TS, % 73.6 ± ±.1 VS, % of TS 87.7 ± ±.3 Total COD, mg/g dry matter Soluble COD a, % of total COD 1 ±.6 1 ±.3 TKN, mg N/g dry matter 12.4 ± ±.2 NH 3 -N, mg N/g dry matter 8.85 ± ±.5 TP, mg P/g dry matter 16.9 ± ±.5 a Analyzed for three different samples having 5, 1, and 2, mg/l of total COD.

3 G. G ung or-demirci, G.N. Demirer / Bioresource Technology 93 (24) Gas production in batch reactors was determined by a water displacement device. The content of CH 4 in biogas was determined as follows. A known volume of the headspace gas (V 1 ) produced in a serum bottle used in biochemical methane production (BMP) experiments was syringed out and injected into another serum bottle which contained 2 g/l KOH solution. This serum bottle was shaken manually for 3 4 min so that all the CO 2 and H 2 S were absorbed in the concentrated KOH solution. The volume of the remaining gas (V 2 ), which was 99.9% CH 4, in the serum bottle was determined by means of a syringe. The ratio of V 2 =V 1 provided the content of CH 4 in the headspace gas (Erg uder et al., 2). The analyses for characterization of the manure and methane content determination of the biogas were performed in duplicates and the calculated mean and standard deviation values were reported in Tables 1 and Experimental set-up and procedures In order to determine the anaerobic biodegradability and biogas production of cattle and broiler manure, BMP experiments (Owen et al., 1979) were performed. Experiments were conducted in 25 ml batch reactors with 1 ml effective volume. Duplicates of five mixtures of broiler and cattle manure, containing 1% broiler (1B:C); 75% broiler and 25% cattle (75B:25C); 5% broiler and 5% cattle (5B:5C); 25% broiler and 75% cattle (25B:75C); and 1% cattle manure (B:1C) 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 CH 4 gas for 4 min 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 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 and methane 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, and 53,5 mg/l, with five different 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 acclimation 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 batch anaerobic digestion with acclimated culture. The cultures which were used in Sets 3 and 4 to treat five different mixtures of manure at 53,5 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 Sets 6 and 7. To determine the background biogas production 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 the experimental periods. The averages of these measurements are shown in Table 3. Table 2 Details of BMP sets Set no. Average COD concentration, mg/l Average TS concentration, % Temperature, C Culture type Nutrient addition Days operated Set 1 12, 1 35 Unacclimated No 43 Set 2 12, 1 35 Unacclimated Yes 43 Set 3 53, Unacclimated No 91 Set 4 53, Unacclimated Yes 91 Set 5 12, 1 Ambient temperature Unacclimated Yes 27 Set 6 12, 1 35 Acclimated Yes 31 Set 7 12, 1 Ambient temperature Acclimated Yes 31

4 112 G. G ung or-demirci, G.N. Demirer / Bioresource Technology 93 (24) Table 3 Biogas yield and average methane content in the reactors Set no. 1B:C 75B:25C 5B:5C 25B:75C B:1C Biogas yield at the end of experimental period, ml gas/g COD added Set Set Set Set Set Set Set 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 7±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 6±5 63±6 62±5 64±6 Set 6 65±5 62±6 65±4 6±6 62±5 Set 7 5±5 55±6 53±4 54±5 55±4 3. Results and discussion 3.1. Sets 1 and 2 anaerobic digestion and codigestion at 12, mg/l initial COD concentration with and without nutrient addition In these sets of BMP experiments, the daily gas production in each batch anaerobic reactor having 12, mg/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 441 mg/l. Thus, the initial COD to biomass ratio obtained in the reactors was 2.7 mg COD/mg VSS. Average gas production observed in each reactor is presented in Fig. 1. These results reflected the minimum treatment efficiency and biogas production that could be obtained for the anaerobic cultures used since microorganisms were not previously acclimated to cattle and broiler manure and the reactors were not mixed. In these sets, gas production was observed at high rates, about 19 ml/day for Sets 1 and 13 ml/day for Set 2 in the first 1 17 days, and at lower rates, about 3.5 ml/ day for Sets 1 and 3 ml/day in Set 2, in the remaining days. High initial gas production rates in first 1 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 production rate 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 Cumulative gas production, ml (a) (b) Time, days Control 1B:C 75B:25C 5B:5C 25B:75C B:1C Fig. 1. BMP experiment results of Set 1 (a) (COD ¼ 12, mg/l, no BM, 35 C, unacclimated culture), and Set 2 (b) (COD ¼ 12, mg/l, with BM, 35 C, unacclimated culture). 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 process (Schieder et al., 2; Palmowski and M uller, 2).

5 G. G ung or-demirci, G.N. Demirer / Bioresource Technology 93 (24) 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 and average 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 approach (Speece, 1996) and found as 474 ml/g of COD consumed. This value was compared with the experimental values and total COD reduction in the reactors was calculated. Methane production and calculated total COD reduction values for both Sets 1 and 2 are given 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 1% of total COD is soluble and readily available for microorganisms. This means that soluble COD was removed and the remaining approximately 3% reduction in Set 1 and approximately 25% reduction in Set 2 was from particulate COD. This indicated that hydrolysis of particulate materials is an important mechanism in the anaerobic treatment of manure Sets 3 and 4 anaerobic digestion and codigestion at 53,5 mg/l initial COD concentration with and without nutrient addition In these sets of BMP experiments, the daily gas production in each batch anaerobic reactor having 53,5 mg/l COD and 4.3% TS concentrations and different cattle and broiler manure compositions was monitored 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 concentration (as VSS) in each reactor was 12 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 broiler manure under elevated condition. Average gas productions 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 5 ml/day) at the beginning of the experimental period especially in reactors having a high ratio of cattle manure. In these sets, 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 and average methane content of biogas in Sets 3 and 4 are given in Table 3. The theoretical methane production was 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 production 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 in these two sets since only 1% 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. Table 4 Methane production and reduction in total COD in the reactors Set no. 1B:C 75B:25C 5B:5C 25B:75C B:1C Methane production, ml Set Set Set Set Set Set Set Reduction in total COD, % Set Set Set Set Set Set Set

6 114 G. G ung or-demirci, G.N. Demirer / Bioresource Technology 93 (24) Cumulative gas production, ml (a) 25 control (b) 1B:C 2 75B:25C 5B:5C 25B:75C 15 B:1C Time, days Fig. 2. BMP experiment results of Set 3 (a) (COD ¼ 53,5 mg/l, no BM, 35 C, unacclimated culture), and Set 4 (b) (COD ¼ 53,5 mg/l, with BM, 35 C, unacclimated culture). This shows the positive effect of nutrient supplementation on digestion and codigestion of cattle and broiler manure at 53,5 mg/l initial COD concentration Set 5 effect of temperature on anaerobic digestion and codigestion with unacclimated culture In Set 5, the influence of temperature on methane production from broiler and cattle manure was investigated at ambient temperature to investigate the feasibility 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, mg/l in the reactors. The initial biomass concentration (as VSS) in each reactor was 542 mg/l. Thus, the initial COD to biomass ratio obtained in the reactors was 2.2 mg COD/ Cumulative gas production, ml control 1B:C 75B:25C 5B:5C 25B:75C B:1C Time, days Fig. 3. BMP experiment results of Set 5 (COD ¼ 12, mg/l, with BM, ambient temperature, unacclimated culture). 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 was short 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 constant 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 values for 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 5B:5C, 25B:75C and 1B:C. Net biogas production in the reactors 1B:C 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 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) CH 4 production in Set 2 (ml) Net gas production in Set 5 (ml) CH 4 production in Set 5 (ml) 1B:C B:25C B:5C B:75C B:1C

7 G. G ung or-demirci, G.N. Demirer / Bioresource Technology 93 (24) 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 temperature, and a lower digester temperature can be compensated for by a longer retention time. However, since longer retention times mean greater reactor volumes, ambient temperature operations may not be feasible for some climates 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, 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 2 days and slowed down in the remaining days. The biogas yields and average methane content of biogas in this set Cumulative gas production, ml (a) 1B:C 1B:C control 75B:25C 75B:25C control 5B:5C 5B:5C control 25B:75C 25B:75C control B:1C B:1C control (b) Time, days Fig. 4. BMP experiment results of Set 6 (a) (COD ¼ 12, mg/l, with BM, 35 C, acclimated culture), and Set 7 (b) (COD ¼ 12, mg/l, with BM, ambient temperature, acclimated culture). were given in Table 3. Methane production and calculated 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 of biogas and methane was seen in acclimated set (Set 6), except reactor 5B:5C. Therefore, based on the results of this set of experiment, preacclimation is strongly recommended in order to increase the efficiency of digestion process 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 previously acclimated to the waste at 35 C. The gas production 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 1 days of this set of experiment, biogas production rate was extremely low. However, the rate of methanogenesis increased during the remaining 21 days, indicating the acclimation of methanogenic microbial population to the low incubation temperatures. 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 27 days 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 anaerobic 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, unacclimated), it was seen that a lower amount of gas was produced 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 acclimated 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 temperature and it was already adapted to this temperature. The results of this set of experiments indicated that the anaerobic digestion and codigestion of cattle and broiler manure at ambient temperature is not as efficient as at

8 116 G. G ung or-demirci, G.N. Demirer / Bioresource Technology 93 (24) 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) CH 4 production in Set 2 (ml) Net gas production in Set 6 (ml) CH 4 production in Set 6 (ml) 1B:C B:25C B:5C B:75C B:1C 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) CH 4 production in Set 7 (ml) Net gas production in Set 6 (ml) CH 4 production in Set 6 (ml) Net gas production in Set 5 (ml) 1B:C B:25C B:5C B:75C B:1C CH 4 production in Set 5 (ml) 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, mg/l) and TS (1%) concentrations, total COD removal and the biogas yield for anaerobic digestion of broiler and cattle manure and their mixtures in different ratios was % and ml gas/g COD added, respectively. By taking into account that only 1% 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 microbial growth if sufficient amount of water is present to dissolve them. Therefore, at low COD and TS concentrations, addition of extra nutrient is not recommended. Batch anaerobic digestion and codigestion of cattle and broiler manure was possible at higher COD (53,5 mg/l) and TS (4.3%) concentrations with total COD removal efficiency and biogas yield of % and ml gas/g COD added, respectively. Cattle manure 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 produced in protein degradation may cause problems in anaerobic digestion as unionized ammonia inhibits anaerobic microorganisms, particularly methanogens (Angelidaki and Ahring, 1993). The higher nitrogen content of poultry wastes as compared to manures from other farm animals (Bujoczek et al., 2) make them difficult substrate for anaerobic digestion (Salminen and Rintala, 22a,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 to increase the efficiency of the digestion process. The anaerobic digestion and codigestion of cattle and broiler 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. References Angelidaki, I., Ahring, B.K., Thermophilic anaerobic digestion of livestock waste: effect of ammonia. Appl. Microbiol. Biotechnol. 38, APHA, Standard Methods for the Examination of Water and Wastewater. 19th ed., Washington, DC. Araji, A.A., Abdo, Z.O., Joyce, P., 21. Efficient use of animal manure on cropland economic analysis. Bioresour. Technol. 79, Bujoczek, G., Oleszkiewicz, J., Sparling, R., Cenkowski, S., 2. High solid anaerobic digestion of chicken manure. J. Agric. Eng. Res. 76, Clarke, E., Baldwin, A.H., 22. Responses of wetland plants to ammonia and water level. Ecol. Eng. 18, Dagnall, S., UK strategy for centralized anaerobic digestion. Bioresour. Technol. 52, Demirer, G.N., Duran, M., Erg uder, T.H., G uven, E., Ugurlu, O., Tezel, U., 2. Anaerobic treatability and biogas production potential studies of different agro-industrial wastewaters in Turkey. Biodegradation 11, Erg uder, T.H., G uven, E., Demirer, G.N., 2. Anaerobic treatment of olive mill waste in batch reactors. Process Biochem. 36,

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