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Effect of initial COD concentration, nutrient addition, temperature and microbial acclimation on anaerobic treatability of broiler and cattle manure
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 €r-Demirci, Go €ksel N. Demirer Gamze G€ ungo
*
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. Ó 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 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 20 million tons dry matter 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.: +1-509-33516-36; fax: +1-509-335-27-22. E-mail address: [email protected] (G.N. Demirer).
0960-8524/$ - see front matter Ó 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 proposed 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 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 60%. 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
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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 treatment 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 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., 2001), very little broiler manure is treated anaerobically. In Turkey, the number of broilers is 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 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, 2000). 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 (100% broiler; 75% broiler and 25% cattle; 50% broiler and 50% cattle; 25% broiler and 75% cattle; and 100% 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 20,000 broilers. Both wastes were characterized and kept refrigerated at 4 °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 parentheses as mg/l): NH4 Cl (1200), MgSO4 Æ 7H2 O (400), KCl (400), Na2 S Æ 9H2 O (300), CaCl2 Æ 2H2 O (50), (NH4 )2 -HPO4 (80), FeCl2 Æ 4H2 O (40), CoCl2 Æ 6H2 O (10), KI (10), MnCl2 Æ 4H2 O (0.5), CuCl2 Æ 2H2 O (0.5), ZnCl2 (0.5), AlCl3 Æ 6H2 O (0.5), NaMoO4 Æ 2H2 O (0.5), H3 BO3 (0.5), NiCl2 Æ 6H2 O (0.5), NaWO4 Æ 2H2 O (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 determined by filtering sample through 0.45 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 2906, Jenway Ltd., UK) and a pH probe (G-05992-55, Cole Parmer Instrument Co., USA). Suspended solids and volatile suspended solids were measured as described in Standard Methods 2540 D, E. Total phosphorus and Total Kjeldahl nitrogen concentrations were also determined by Standard Methods 4500-P-E and 4500-Norg, respectively (APHA, 1997).
Table 1 Characterization of cattle and broiler manure used in experiments Parameter
Broiler manure
Cattle manure
TS, % VS, % of TS Total COD, mg/g dry matter Soluble CODa , % of total COD TKN, mg N/g dry matter NH3 -N, mg N/g dry matter TP, mg P/g dry matter
73.6 ± 0.1 87.7 ± 0.1 1244 10 ± 0.6 12.4 ± 0.4 8.85 ± 0.35 16.9 ± 1.6
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
a
Analyzed for three different samples having 5000, 10,000 and 20,000 mg/l of total COD.
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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 H2 S were absorbed in the concentrated KOH solution. The volume of the remaining gas (V2 ), which was 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 and standard deviation values were reported in Tables 1 and 3. 2.4. 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 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 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
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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, 12,000 and 53,500 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 53,500 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 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 Set Set Set Set Set Set
12,000 12,000 53,500 53,500 12,000 12,000 12,000
1 1 4.3 4.3 1 1 1
35 35 35 35 Ambient temperature 35 Ambient temperature
Unacclimated Unacclimated Unacclimated Unacclimated Unacclimated Acclimated Acclimated
No Yes No Yes Yes Yes Yes
43 43 91 91 27 31 31
1 2 3 4 5 6 7
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Table 3 Biogas yield and average methane content in the reactors Set no.
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 Set 2 199.2 191.8 Set 3 223.4 283.7 Set 4 236.6 231.4 Set 5 181.7 173 Set 6 211.2 226.4 Set 7 61.7 75
100B:0C
75B:25C
269.8 209.1 314.8 269.9 136.9 178.1 151.8
231 183.6 330.2 324.1 107.5 242.8 87.8
242.2 180.3 359 368.5 101.5 249.9 94.9
Average methane content, % Set 1 67 ± 6 Set 2 67 ± 6 Set 3 67 ± 3 Set 4 73 ± 3 Set 5 59 ± 5 Set 6 65 ± 5 Set 7 50 ± 5
57 ± 5 72 ± 5 54 ± 4 66 ± 4 63 ± 6 65 ± 4 53 ± 4
64 ± 4 69 ± 5 53 ± 3 61 ± 3 62 ± 5 60 ± 6 54 ± 5
64 ± 3 70 ± 4 49 ± 5 53 ± 5 64 ± 6 62 ± 5 55 ± 4
65 ± 4 68 ± 6 59 ± 4 66 ± 5 60 ± 5 62 ± 6 55 ± 6
3. Results and discussion
400
(a)
3.1. Sets 1 and 2––anaerobic digestion and codigestion at 12,000 mg/l initial COD concentration with and without nutrient addition
Control 100B:0C 75B:25C 50B:50C 25B:75C 0B:100C
200 Cumulative gas production, ml
In these sets of BMP experiments, the daily gas production in each batch anaerobic reactor having 12,000 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 4410 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 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 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
300
100
0 400
(b)
300
200
100
0 0
10
20
30
40
50
Time, days
Fig. 1. BMP experiment results of Set 1 (a) (COD ¼ 12,000 mg/l, no BM, 35 °C, unacclimated culture), and Set 2 (b) (COD ¼ 12,000 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., 2000; Palmowski and M€ uller, 2000).
G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117
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 10% of total COD is soluble and readily available for microorganisms. This means that soluble COD was removed and the remaining approximately 30% 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. 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 production 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
113
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 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 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 50 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 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 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 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.
Table 4 Methane production and reduction in total COD in the reactors Set no.
100B:0C
75B:25C
50B:50C
25B:75C
0B:100C
Methane production, ml Set 1 205.3 Set 2 160.1 Set 3 800.9 Set 4 924.2 Set 5 128.6 Set 6 164.8 Set 7 37
181.7 156.5 895.6 817.1 124.6 168.5 49.5
184.6 180.6 909.5 952.9 103.5 138.9 96.5
177 152 936.2 1057.8 80 174.8 56.9
186 151.5 941.2 1044.9 78 185.9 62.6
Reduction in total COD, % Set 1 43.3 Set 2 33.8 Set 3 37.9 Set 4 43.7 Set 5 27.1 Set 6 34.8 Set 7 7.8
38.3 33 42.4 38.7 26.3 35.5 10.4
38.9 38.1 43 45.1 21.8 29.3 20.3
37.4 32 44.3 50 16.9 36.9 12
39.2 32 44.5 49.4 16.5 39.2 13.2
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250 Cumulative gas production, ml
(a) 2000
Cumulative gas production, ml
1500
1000
500
0 2500
1500
50
5
10
15 20 Time, days
25
30
Fig. 3. BMP experiment results of Set 5 (COD ¼ 12,000 mg/l, with BM, ambient temperature, unacclimated culture).
500 0 20
100
0
1000
0
150
0
(b) control 100B:0C 75B:25C 50B:50C 25B:75C 0B:100C
2000
control 100B:0C 75B:25C 50B:50C 25B:75C 0B:100C
200
40
60
80
100
Time, days
Fig. 2. BMP experiment results of Set 3 (a) (COD ¼ 53,500 mg/l, no BM, 35 °C, unacclimated culture), and Set 4 (b) (COD ¼ 53,500 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 53,500 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 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 12,000 mg/l in the reactors. The initial biomass concentration (as VSS) in each reactor was 5420 mg/l. Thus, the initial COD to biomass ratio obtained in the reactors was 2.2 mg COD/
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 50B:50C, 25B:75C and 100B:0C. Net biogas production in the reactors 100B: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
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 (ml)
Net gas production in Set 5 (ml)
CH4 production in Set 5 (ml)
100B:0C 75B:25C 50B:50C 25B:75C 0B:100C
218 209.2 217.3 180.3 167.1
146.1 142.2 156.4 124.4 117
218 207.6 164.3 129 121.8
128.6 124.6 103.5 80 78
G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117
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. 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 350
(a)
300 250
Cumulative gas production, ml
200 150 100 50 0 350
100B:0C 100B:0C control 75B:25C 75B:25C control 50B:50C 50B:50C control 25B:75C 25B:75C control 0B:100C 0B:100C control
300 250 200 150 100
(b)
50 0 0
5
10
15
20
25
30
35
Time, days
Fig. 4. BMP experiment results of Set 6 (a) (COD ¼ 12,000 mg/l, with BM, 35 °C, acclimated culture), and Set 7 (b) (COD ¼ 12,000 mg/l, with BM, ambient temperature, acclimated culture).
115
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 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 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 10 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
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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 75B:25C 50B:50C 25B:75C 0B:100C
225.1 215 226.9 192 180.9
150.8 146.2 163.4 132.5 126.6
253.5 271.7 213.7 291.3 299.9
164.8 168.5 138.9 174.8 185.9
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 75B:25C 50B:50C 25B:75C 0B:100C
59.4 72.6 152.7 83.5 91.8
29.7 39.9 80.9 45.1 50.5
245.8 261.7 201.9 272.7 281.4
159.8 162.2 131.2 163.6 174.5
218 207.6 164.3 129 121.8
128.6 124.6 103.5 80 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 the biogas 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 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 (53,500 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. 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., 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 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., 1993. Thermophilic anaerobic digestion of livestock waste: effect of ammonia. Appl. Microbiol. Biotechnol. 38, 560–564. APHA, 1997. Standard Methods for the Examination of Water and Wastewater. 19th ed., Washington, DC. Araji, A.A., Abdo, Z.O., Joyce, P., 2001. Efficient use of animal manure on cropland–economic analysis. Bioresour. Technol. 79, 179–191. Bujoczek, G., Oleszkiewicz, J., Sparling, R., Cenkowski, S., 2000. High solid anaerobic digestion of chicken manure. J. Agric. Eng. Res. 76, 51–60. Clarke, E., Baldwin, A.H., 2002. Responses of wetland plants to ammonia and water level. Ecol. Eng. 18, 257–264. Dagnall, S., 1995. UK strategy for centralized anaerobic digestion. Bioresour. Technol. 52, 275–280. € Demirer, G.N., Duran, M., Erg€ uder, T.H., G€ uven, E., Ugurlu, O., Tezel, U., 2000. Anaerobic treatability and biogas production potential studies of different agro-industrial wastewaters in Turkey. Biodegradation 11, 401–405. Erg€ uder, T.H., G€ uven, E., Demirer, G.N., 2000. Anaerobic treatment of olive mill waste in batch reactors. Process Biochem. 36, 243–248.
G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117 Guerra-Rodriguez, E., Diaz-Ravina, M., Vazquez, M., 2001. Cocomposting of chestnut burr and leaf litter with solid poultry manure. Bioresour. Technol. 78, 107–109. Hobson, P.N., 1991. The treatment of agricultural wastes. In: Wheatley, A. (Ed.), Anaerobic Digestion: A Waste Treatment Technology. Elsevier Applied Science, London, pp. 93–138. Huang, J.J.H., Shih, J.C.H., 1981. The potential of biological methane generation from chicken manure. Biotechnol. Bioeng. 23, 2307– 2314. Imbeah, M., 1998. Composting piggery waste: a review. Bioresour. Technol. 63, 197–203. Kelleher, B.P., Leahy, J.J., Henihan, A.M., O’Dwyer, T.F., Sutton, D., Leahy, M.J., 2002. Advances in poultry litter disposal technology––a review. Bioresour. Technol. 83, 27–36. Knight, R.L., Payne Jr., V.W.E., Borer, R.E., Clarke Jr., R.A., Pries, J.H., 2000. Constructed wetlands for livestock wastewater management. Ecol. Eng. 15, 41–55. Mackie, R.I., Bryant, M.P., 1995. Anaerobic digestion of cattle waste at mesophilic and thermophilic temperatures. Appl. Microbiol. Biotechnol. 43 (2), 346–350. Magbauna Jr., B.S., Adams, T.T., Johnston, P., 2001. Anaerobic codigestion of hog and poultry waste. Bioresour. Technol. 76, 165–168. Martinez, J., Hao, X., 1996. A field treatment plant for pig slurry. Water Sci. Technol. 34 (11), 87–92. Mæng, H., Lund, H., Hvelplund, F., 1999. Biogas plants in Denmark: technological and economic developments. Appl. Energy 64 (1–4), 195–206. Morken, J., Sakshaug, S., 1998. Direct ground injection of livestock waste slurry to avoid ammonia emission. Nutr. Cycl. Agroecosyst. 51, 59–63. Owen, W.F., Stuckey, D.C., Healey, J.B., Young, L.Y., McCarty, P.L., 1979. Bioassay for monitoring biochemical methane potential and anaerobic toxicity. Water Res. 13, 485–492.
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Palmowski, L.M., M€ uller, J.A., 2000. Influence of the size reduction of organic waste on their anaerobic digestion. Water Sci. Technol. 41 (3), 155–162. Salminen, E., Rintala, J., 2002a. Anaerobic digestion of organic solid poultry slaughterhouse waste––a review. Bioresour. Technol. 83, 13–26. Salminen, E.A., Rintala, J.A., 2002b. Semi-continuous anaerobic digestion of solid poultry slaughterhouse waste: effect of hydraulic retention time and loading. Water Res. 36, 3175–3182. Schieder, D., Schieder, R., Bischof, F., 2000. Thermal hydrolysis (TDH) as a pretreatment method for the digestion of organic waste. Water Sci. Technol. 41 (3), 181–187. Sommer, S.G., Hutchings, N.J., 2001. Ammonia emission from field applied manure and its reduction. Eur. J. Agronomy 15, 1– 15. Speece, R.E., 1996. Anaerobic Biotechnology for Industrial Wastewaters. Archae Press, USA. State Institute of Statistics (SIS), 2002. Statistical Yearbook of Turkey, 2001. Prime Ministry of Republic of Turkey, Ankara. Tafdrup, S., 1994. Centralized biogas plants combine agricultural and environmental and environmental benefits with energy production. Water Sci. Technol. 30 (12), 133–141. Th€ orneby, L., Persson, K., Tr€agardh, G., 1999. Treatment of liquid effluents from dairy cattle and pigs using reverse osmosis. J. Agricult. Eng. Res. 73 (2), 159–170. Tiquia, S.M., Tam, N.F.Y., 2002. Characterization and composting of poultry litter in forced-aeration piles. Process Biochem. 37, 869– 880. Wang, B., Dong, W., Zhang, J., Cao, X., 1996. Experimental study of high rate pond system treating piggery wastewater. Water Sci. Technol. 34 (11), 125–132. Weiland, P., 2000. Anaerobic waste digestion in Germany––Status and recent developments. Biodegradation 11, 415–421.
Effect of initial COD concentration, nutrient addition, temperature and microbial acclimation on anaerobic treatability of broiler and cattle manure €r-Demirci, Go €ksel N. Demirer Gamze G€ ungo
*
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. Ó 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 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 20 million tons dry matter 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.: +1-509-33516-36; fax: +1-509-335-27-22. E-mail address: [email protected] (G.N. Demirer).
0960-8524/$ - see front matter Ó 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 proposed 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 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 60%. 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
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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 treatment 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 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., 2001), very little broiler manure is treated anaerobically. In Turkey, the number of broilers is 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 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, 2000). 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 (100% broiler; 75% broiler and 25% cattle; 50% broiler and 50% cattle; 25% broiler and 75% cattle; and 100% 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 20,000 broilers. Both wastes were characterized and kept refrigerated at 4 °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 parentheses as mg/l): NH4 Cl (1200), MgSO4 Æ 7H2 O (400), KCl (400), Na2 S Æ 9H2 O (300), CaCl2 Æ 2H2 O (50), (NH4 )2 -HPO4 (80), FeCl2 Æ 4H2 O (40), CoCl2 Æ 6H2 O (10), KI (10), MnCl2 Æ 4H2 O (0.5), CuCl2 Æ 2H2 O (0.5), ZnCl2 (0.5), AlCl3 Æ 6H2 O (0.5), NaMoO4 Æ 2H2 O (0.5), H3 BO3 (0.5), NiCl2 Æ 6H2 O (0.5), NaWO4 Æ 2H2 O (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 determined by filtering sample through 0.45 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 2906, Jenway Ltd., UK) and a pH probe (G-05992-55, Cole Parmer Instrument Co., USA). Suspended solids and volatile suspended solids were measured as described in Standard Methods 2540 D, E. Total phosphorus and Total Kjeldahl nitrogen concentrations were also determined by Standard Methods 4500-P-E and 4500-Norg, respectively (APHA, 1997).
Table 1 Characterization of cattle and broiler manure used in experiments Parameter
Broiler manure
Cattle manure
TS, % VS, % of TS Total COD, mg/g dry matter Soluble CODa , % of total COD TKN, mg N/g dry matter NH3 -N, mg N/g dry matter TP, mg P/g dry matter
73.6 ± 0.1 87.7 ± 0.1 1244 10 ± 0.6 12.4 ± 0.4 8.85 ± 0.35 16.9 ± 1.6
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
a
Analyzed for three different samples having 5000, 10,000 and 20,000 mg/l of total COD.
G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117
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 H2 S were absorbed in the concentrated KOH solution. The volume of the remaining gas (V2 ), which was 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 and standard deviation values were reported in Tables 1 and 3. 2.4. 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 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 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
111
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, 12,000 and 53,500 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 53,500 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 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 Set Set Set Set Set Set
12,000 12,000 53,500 53,500 12,000 12,000 12,000
1 1 4.3 4.3 1 1 1
35 35 35 35 Ambient temperature 35 Ambient temperature
Unacclimated Unacclimated Unacclimated Unacclimated Unacclimated Acclimated Acclimated
No Yes No Yes Yes Yes Yes
43 43 91 91 27 31 31
1 2 3 4 5 6 7
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Table 3 Biogas yield and average methane content in the reactors Set no.
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 Set 2 199.2 191.8 Set 3 223.4 283.7 Set 4 236.6 231.4 Set 5 181.7 173 Set 6 211.2 226.4 Set 7 61.7 75
100B:0C
75B:25C
269.8 209.1 314.8 269.9 136.9 178.1 151.8
231 183.6 330.2 324.1 107.5 242.8 87.8
242.2 180.3 359 368.5 101.5 249.9 94.9
Average methane content, % Set 1 67 ± 6 Set 2 67 ± 6 Set 3 67 ± 3 Set 4 73 ± 3 Set 5 59 ± 5 Set 6 65 ± 5 Set 7 50 ± 5
57 ± 5 72 ± 5 54 ± 4 66 ± 4 63 ± 6 65 ± 4 53 ± 4
64 ± 4 69 ± 5 53 ± 3 61 ± 3 62 ± 5 60 ± 6 54 ± 5
64 ± 3 70 ± 4 49 ± 5 53 ± 5 64 ± 6 62 ± 5 55 ± 4
65 ± 4 68 ± 6 59 ± 4 66 ± 5 60 ± 5 62 ± 6 55 ± 6
3. Results and discussion
400
(a)
3.1. Sets 1 and 2––anaerobic digestion and codigestion at 12,000 mg/l initial COD concentration with and without nutrient addition
Control 100B:0C 75B:25C 50B:50C 25B:75C 0B:100C
200 Cumulative gas production, ml
In these sets of BMP experiments, the daily gas production in each batch anaerobic reactor having 12,000 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 4410 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 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 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
300
100
0 400
(b)
300
200
100
0 0
10
20
30
40
50
Time, days
Fig. 1. BMP experiment results of Set 1 (a) (COD ¼ 12,000 mg/l, no BM, 35 °C, unacclimated culture), and Set 2 (b) (COD ¼ 12,000 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., 2000; Palmowski and M€ uller, 2000).
G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117
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 10% of total COD is soluble and readily available for microorganisms. This means that soluble COD was removed and the remaining approximately 30% 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. 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 production 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
113
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 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 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 50 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 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 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 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.
Table 4 Methane production and reduction in total COD in the reactors Set no.
100B:0C
75B:25C
50B:50C
25B:75C
0B:100C
Methane production, ml Set 1 205.3 Set 2 160.1 Set 3 800.9 Set 4 924.2 Set 5 128.6 Set 6 164.8 Set 7 37
181.7 156.5 895.6 817.1 124.6 168.5 49.5
184.6 180.6 909.5 952.9 103.5 138.9 96.5
177 152 936.2 1057.8 80 174.8 56.9
186 151.5 941.2 1044.9 78 185.9 62.6
Reduction in total COD, % Set 1 43.3 Set 2 33.8 Set 3 37.9 Set 4 43.7 Set 5 27.1 Set 6 34.8 Set 7 7.8
38.3 33 42.4 38.7 26.3 35.5 10.4
38.9 38.1 43 45.1 21.8 29.3 20.3
37.4 32 44.3 50 16.9 36.9 12
39.2 32 44.5 49.4 16.5 39.2 13.2
114
G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117 2500
250 Cumulative gas production, ml
(a) 2000
Cumulative gas production, ml
1500
1000
500
0 2500
1500
50
5
10
15 20 Time, days
25
30
Fig. 3. BMP experiment results of Set 5 (COD ¼ 12,000 mg/l, with BM, ambient temperature, unacclimated culture).
500 0 20
100
0
1000
0
150
0
(b) control 100B:0C 75B:25C 50B:50C 25B:75C 0B:100C
2000
control 100B:0C 75B:25C 50B:50C 25B:75C 0B:100C
200
40
60
80
100
Time, days
Fig. 2. BMP experiment results of Set 3 (a) (COD ¼ 53,500 mg/l, no BM, 35 °C, unacclimated culture), and Set 4 (b) (COD ¼ 53,500 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 53,500 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 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 12,000 mg/l in the reactors. The initial biomass concentration (as VSS) in each reactor was 5420 mg/l. Thus, the initial COD to biomass ratio obtained in the reactors was 2.2 mg COD/
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 50B:50C, 25B:75C and 100B:0C. Net biogas production in the reactors 100B: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
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 (ml)
Net gas production in Set 5 (ml)
CH4 production in Set 5 (ml)
100B:0C 75B:25C 50B:50C 25B:75C 0B:100C
218 209.2 217.3 180.3 167.1
146.1 142.2 156.4 124.4 117
218 207.6 164.3 129 121.8
128.6 124.6 103.5 80 78
G. G€ung€or-Demirci, G.N. Demirer / Bioresource Technology 93 (2004) 109–117
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. 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 350
(a)
300 250
Cumulative gas production, ml
200 150 100 50 0 350
100B:0C 100B:0C control 75B:25C 75B:25C control 50B:50C 50B:50C control 25B:75C 25B:75C control 0B:100C 0B:100C control
300 250 200 150 100
(b)
50 0 0
5
10
15
20
25
30
35
Time, days
Fig. 4. BMP experiment results of Set 6 (a) (COD ¼ 12,000 mg/l, with BM, 35 °C, acclimated culture), and Set 7 (b) (COD ¼ 12,000 mg/l, with BM, ambient temperature, acclimated culture).
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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 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 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 10 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
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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 75B:25C 50B:50C 25B:75C 0B:100C
225.1 215 226.9 192 180.9
150.8 146.2 163.4 132.5 126.6
253.5 271.7 213.7 291.3 299.9
164.8 168.5 138.9 174.8 185.9
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 75B:25C 50B:50C 25B:75C 0B:100C
59.4 72.6 152.7 83.5 91.8
29.7 39.9 80.9 45.1 50.5
245.8 261.7 201.9 272.7 281.4
159.8 162.2 131.2 163.6 174.5
218 207.6 164.3 129 121.8
128.6 124.6 103.5 80 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 the biogas 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 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 (53,500 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. 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., 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 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.
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