Anaerobic slurry co-digestion of poultry manure and straw: effect of organic loading and temperature
- Azadeh Babaee1,
- Jalal Shayegan1Email author and
- Anis Roshani2
https://doi.org/10.1186/2052-336X-11-15
© Babaee et al.; licensee BioMed Central Ltd. 2013
Received: 7 May 2013
Accepted: 29 May 2013
Published: 3 July 2013
Abstract
In order to obtain basic design criteria for anaerobic digestion of a mixture of poultry manure and wheat straw, the effects of different temperatures and organic loading rates on the biogas yield and methane contents were evaluated. Since poultry manure is a poor substrate, in term of the availability of the nutrients, external supplementation of carbon has to be regularly performed, in order to achieve a stable and efficient process. The complete-mix, pilot-scale digester with working volume of 70 L was used. The digestion operated at 25°C, 30°C and 35°C with organic loading rates of 1.0, 2.0, 2.5, 3.0, 3.5 and 4.0 kg Volatile solid/m3d and a HRT of 15 days. At a temperature of 35°C, the methane yield was increased by 43% compared to 25°C. Anaerobic co-digestion appeared feasible with a loading rate of 3.0 kg VS/m3d at 35°C. At this state, the specific methane yield was calculated about 0.12 m3/kg VS with a methane content of 53–70.2% in the biogas. The volatile solid (VS) removal was 72%. As a result of volatile fatty acid accumulation and decrease in pH, when the loading rate was less than 1 or greater than 4 kg VS/m3d, the process was inhibited or overloaded, respectively. Both the lower and higher loading rates resulted in a decline in the methane yield.
Keywords
Introduction
In the past few decades, the large amounts of animal manure and slurries have been produced by the animal breeding sector as well as the wet organic waste streams represent a constant pollution risk with a potential negative impact on the environmental, if not managed optimally. When untreated or poorly managed, animal manure becomes a major source of air and water pollution. Nutrient leaching, mainly nitrogen, phosphorus and ammonia evaporation and pathogen contamination are some of the major threats [1]. The animal production sector is responsible for 18% of the overall greenhouse gas emissions, measured in CO2 equivalent and for 37% of the anthropogenic methane, which has 23 times the global warming potential of CO2 [2]. Annually, approximately 400 million tons of wastes have been produced by Iran livestock industry (cattle and poultry) and agriculture sector. It means that it really needs an integrated waste management.
Anaerobic co-digestion of organic matters results in waste stabilization as well as in biogas production. This gas usually contains more than 50% methane, and therefore it can be used as bio-fuel in power generation systems to produce heat and energy [3]. Wastes have been effectively used as biogas materials by various studies [4]. The other Benefits of the anaerobic digestion of animal manure are pathogen reduction through sanitation, improved fertilization efficiency, less nuisance from odors and flies and etc. [5]. Anaerobic digestion reduces the majority of pathogenic agents, if can be carried out under mesophilic or thermophilic conditions [6].
The anaerobic digestion of organic material is a complex process, involving a number of different degradation steps. The microorganisms that participate in the process may be specific for each degradation step and thus could have different environmental requirements such as temperature, pH, moisture, carbon source, nitrogen and C/N ratio. Many researchers have reported significant effects of temperature on the microbial community, process kinetics and stability and methane yield. Lower temperatures during the process are known to decrease microbial growth, substrate utilization rates, and biogas production. Moreover, lower temperatures may also result in an exhaustion of cell energy, a leakage of intracellular substances or complete lysis. In contrast, high temperatures lower biogas yield due to the production of volatile gases such as ammonia which suppresses methanogenic activities [7].
Animal waste often has very high total ammonia nitrogen concentrations due to presence of ammonia as well as protein and urea [8]. Nitrogen is an essential nutrient for anaerobic organisms [9], consequently, the inhibitory effects of ammonia, as far as is known, influence mainly the phase of methanogenesis in anaerobic reactors [10], released from decomposition of organic ammonia. It has been suggested that poultry manure is best treated with other wastes because of its high nitrogen content [11]. Crop residues represent another fraction of agricultural waste. Substantial quantities of unused stalks, straws and bark are produced from a variety of crops, which could be used for energy generation, but they are poor substrate in term of nitrogen and phosphate. Therefore, co-digestion of animal manure and crop residues can supply a proper C/N ratio for microorganisms. This ratio is the balance of food that a microbe requires in order to grow. The optimal C/N ratio is 20–30 and excess N can lead to ammonia inhibition of digestion [12]. The unbalanced nutrients are regarded as an important factor limiting anaerobic digestion of organic wastes. For the improvement of nutrition and C/N ratios, co-digestion of organic mixtures is employed.
In spite of high production of poultry manure, anaerobic digestion of this kind of organic waste has not been studied as much as cow and swine manure. Cow manure is a cellulose-rich component that high amount of cellulose and hemi- cellulose cause suitable C/N ratio and therefore it can be digested easily in anaerobic conditions. It is also a good fertilizer as it will not burn the plants. Inversely, poultry manure is an ammonia-rich component which cannot be used as a fertilizer because it will burn the plants as a result of high ammonia content. In order to obtain suitable C/N ratio, co-digestion of poultry manure has been done with hog manure, swine manure, fruit and vegetable wastes [13]. Co-digestion can utilize the nutrients and bacterial diversities in various wastes to optimize the digestion process. Co-digestion of poultry manure with wheat straw that has been done in this study may be considered as a new issue and the objective of the study is finding the optimum temperature and loading rate in a pilot-scale reactor that will be discussed fully below.
Material and methods
Waste characteristics
Characteristics of the feed solids as sampled
Parameters | Poultry manure | Straw |
---|---|---|
Ammonia nitrogen (w/w %) | 5.65 | 0.61 |
Total Nitrogen (w/w %) | 5.67 | 0.63 |
COD (w/w %) | 35.88 | 51.88 |
C/N ratio | 6.35 | 84.22 |
pH | 7.3 | ----- |
Experimental set-up
A cylindrical CSTR reactor with a working volume of 60 L (total digester volume 70 L) was operated at a 15d HRT for all runs. The reactor was fitted with a top plate, which supported the mixer, mixer motor and gas sampler. Sampling valves were located at positions corresponding to the top, middle and bottom layer of digester contents. The reactor had one outlet at the bottom for effluent removal. The contents of the reactor were mixed as controlled by a timer, which was activated for 30 min every hour. It was operated at 35°C and then was obtained at 30°C and 25°C.
Reactor operation
First, 40 L of anaerobic sludge from a dairy factory and 20 L water were transferred to the reactor. Daily feeding was commenced approximately 24 days after start-up. Raw waste characteristics over the study period are given in Table 1. The digestion operated at 25°C, 30°C and 35°C with organic loading rates of 1.0, 2.0, 2.5, 3.0, 3.5 and 4.0 kg VS/m3d. For preventing accumulation, because of daily feeding, 4 liters of content was removed every day. It was calculated according to HRT of 15 days. It is worth mentioning that gradual hydrolysis of cellulose caused the high amount of COD accumulation.
Analytical methods
The produced biogas was measured daily by water displacement method and its composition was measured by gas chromatograph. Total solids (TS), volatile solids (VS), pH and alkalinity were determined according to the APHA Standard Methods [14]. Total nitrogen (TN) was estimated by the Kjeldahl method [14].
Result
Effect of temperatures and feed loads on the methane yield
Methane yield of different loads and temperatures.
Effect of temperatures and feed loads on biogas composition
Variation of methane production in different loads and temperatures.
Effect of temperatures and feed loads on COD accumulation
Variation of COD in different loads and temperatures.
Effect of temperatures and feed loads on pH
The variation of pH at 35°C.
Discussion
Effect of temperatures and feed loads on the methane yield
Average characteristics of mixture of poultry manure and straw and the effluents
Parameter (in mg/ except pH & C/N) | Operating temperation (c) | |||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
35 | 30 | 24 | ||||||||||||||||
2 | 3 | 4 | 2 | 3 | 4 | 2 | 3 | 4 | ||||||||||
OLR (kgVs/m 2d) | Inf | Eff | Inf | Eff | Inf | Eff | Inf | Eff | Inf | Eff | Inf | Eff | Inf | Eff | Inf | Eff | Inf | Eff |
COD | 1185 | 1710 | 1783 | 3200 | 2360 | 4900 | 1185 | 1780 | 1783 | 3140 | 2360 | 5000 | 1185 | 2110 | 1783 | 3300 | 2360 | 5100 |
TS | 2275 | 1153 | 3408 | 1482 | 4550 | 2616 | 2275 | 1100 | 3408 | 2010 | 4550 | 2010 | 2275 | 2000 | 3408 | 2700 | 4550 | 4020 |
VS | 2000 | 750 | 300 | 840 | 4000 | 2290 | 2000 | 863 | 3000 | 900 | 4000 | 2400 | 2000 | 1048 | 3000 | 1170 | 4000 | 2440 |
Total nitrogen | NDa | 256 | ND | 240 | ND | 261 | ND | 192 | ND | 180 | ND | 235 | ND | 160 | ND | 68 | ND | 105 |
pH | ND | 7.5 | ND | 7.8 | ND | 7.5 | ND | 7.8 | ND | 7.8 | ND | 7.8 | ND | 7.0 | ND | 6.8 | ND | 6.7 |
Alkalinity | ND | 2100 | ND | 2980 | ND | 3000 | ND | 2200 | ND | 2100 | ND | 3200 | ND | 3800 | ND | 4000 | ND | 4000 |
C/N | 23.09 | 23.7 | 23.4 |
Effect of temperatures and feed loads on biogas composition
Decreases in the methane content indicated hydraulic and organic overload and insufficient buffering capacity in the digester that they led to a reduction in the methanogenic activity. Chae et al. [17] reported that the biogas composition differed according to digestion temperature. Methane contents in the biogas were 65.3%, 64.0% and 62.0% at 35°C, 30°C and 25°C, respectively.
Effect of temperatures and feed loads on COD accumulation
Decrease in the temperature had a negative effect on the metabolic rate of the microorganisms. For this reason, at 25°C COD increased sharply. Once 5100 mg/L, was reached, methane production decreased by 40% and VS removal dropped to 39%. In fact, the effect of temperature on organic removal rate did not seem to be uniform over the whole temperature spectrum. Chae et al. [17] reported that the digestion yield at a temperature of 25°C showed 82.6% of that at 35°C. These results were in agreement with previous results that showed an improvement in the biogas yields with increasing temperatures [18].
Effect of temperatures and feed loads on pH
The pH stabilized between 6.8±0.1 and 7.8±0.1 in all runs. Both total and free ammonia concentration varied a bit between stages. A wide range of inhibiting ammonia concentrations has been reported in the papers the amount of ammonia in the digester may also affect the production of hydrogen and removal of volatile solids. Total biogas production was unaffected by small increases in ammonia nitrogen while higher increases reduced the biogas production by 50% of the original rate. In the fluidized-bed anaerobic digester, the methane formation decreased at ammonium concentrations of greater than 6000 mg NH4–N/L. It was reported that methanogenic activity is decreased by 10% at ammonium concentrations of 1670–3720 mg NH4–N/L, while by 50% at 4090–5550 mg NH4–N/L, and completely zero at 5880–6000 mg NH4–N/L [19].
The free NH3±N concentrations calculated in this study were far below those reported as inhibitory because of a) dilution of digester content with water and b) adjustment of feed C/N ratio. It should also be noted that both methanogenic and acidogenic microorganisms have their optimal pH. There is a considerable potential of biogas production from anaerobic digestion of poultry manure that offers several environmental, agricultural and socio-economic benefits throughout biogas production as a clean and renewable fuel. The process worked well with a loading of 3.0 kgVS/m3d VS removal amounted 72%. The temperature had an influence on the ultimate methane yield, as well as the methane contents. The highest temperature caused the most methane yield (0.12 m3/kg VS); however, the yield did not linearly increase with increasing temperature. More amount of methane yield may be achieved by extension of the hydraulic residence time because of the high levels of TS in waste.
Conclusion
The study clearly indicates that anaerobic digestion is one of the most effective biological processes to treat a wide variety of solid organic waste products. The prime advantages of this technology include (i) organic wastes with a low nutrient content can be degraded by co-digesting with different substrates in the anaerobic bioreactors, and (ii) the process simultaneously leads to low cost production of biogas, which could be vital for meeting future energy-needs. However, different factors such as substrate and co-substrate composition and quality, environmental factors (temperature, pH, organic loading rate), and microbial dynamics contribute to the efficiency of the anaerobic digestion process, and must be optimized to achieve maximum benefit from this technology in terms of both energy production and organic waste management. This technology has tremendous application in the future for sustainability of both environment and agriculture, with the production of energy as an extra benefit.
Declarations
Acknowledgment
The authors would like to thank the Department of Chemical Engineering, Sharif University of Technology, for their providing help in the labs.
Authors’ Affiliations
References
- Oleskowicz-Popiel P, Seadi TA, Holm-Nielsen JB: The future of anaerobic digestion and biogas utilization. Bioresour Technol 2009, 100: 5478–5484. 10.1016/j.biortech.2008.12.046View ArticleGoogle Scholar
- Steinfeld H, Gerber P, Wasenaar T, Castel V, Rosales M, de Haan C: Livestock’s long shadow. Food and Agriculture Organization (FAO) of United Nations: Environmental issues and Options; 2006.Google Scholar
- Ojolo SJ, Oke SA, Animasahun K, Adesuyi BK: Utilization of poultry, cow and kitchen wastes for biogas production: comparative analyses. Iranian Journal of Environmental Health Science Engineering 2007,4(Suppl 4):223–228.Google Scholar
- Ojolo SJ, Bamgboye AI, Ogunsina BS, Oke SA: Analytical approach for predicting biogas generation in a municipal solid waste anaerobic digester. Iranian Journal of Environmental Health Science Engineering 2008,5(Suppl 3):179–186.Google Scholar
- Sommer SG, Moller HB, Petersen SO: Reduction in methane and nitrous oxide emission from animal slurry trough anaerobic digestion. In Proceedings of the Third International Symposium. Maastricht, Netherlands: Millpress Science Publisher; 2002:475–480.Google Scholar
- Takdastan A, Movahedian H, Jafarzadeh N, Bina B: The Efficiency of Anaerobic Digesters on Microbial Quality of Sludge in Isfahan and Shahinshahr Waterwaste Treatment Plant. Iranian Journal of Environmental Health Science Engineering 2005,2(Suppl 1):56–59.Google Scholar
- Khalid A, Arshad M, Anjum M, Mahmood T, Dawson L: The anaerobic digestion of solid organic waste. Waste Manag 2011, 31: 1737–1744. 10.1016/j.wasman.2011.03.021View ArticleGoogle Scholar
- Zeeman G, Wiegant WM, Koster-Treffers ME, Lettinga G: The influence of the total ammonia concentration on the thermophilicdigestion of cow manure. Agricultural Wastes 1985, 14: 19–35. 10.1016/S0141-4607(85)80014-7View ArticleGoogle Scholar
- Strik DPBTB, Domnanovich AM, Holubar PA: A pH-based control of ammonia in biogas during anaerobic digestion of artificial pig manure and maize silage. Process Biochem 2006, 41: 1235–1238. 10.1016/j.procbio.2005.12.008View ArticleGoogle Scholar
- Calli B, Mertoglu B, Inanc B, Yenigun O: Effects of high free ammonia concentrations on the performances of anaerobic bioreactors. Process Biochem 2005, 40: 1285–1292. 10.1016/j.procbio.2004.05.008View ArticleGoogle Scholar
- Callaghan FJ, Wase DA, Thayanithy K, Forster CF: Continuous Co-digestion of cattle slurry with fruit and vegetable wastes and chicken manure. Journal of Biomass & Bioenergy 2002, 27: 71–77.View ArticleGoogle Scholar
- Molnar L, Bartha I: High solids anaerobic fermentation for biogas and compost production. Biomass 1998, 16: 173–182.View ArticleGoogle Scholar
- Johnston PH, Adams TT, Magbanua J: Anaerobic co-digestion of hog and poultry waste. Bioresour Technol 2001, 76: 165–168. 10.1016/S0960-8524(00)00087-0View ArticleGoogle Scholar
- APHA: Standard methods for the examination of water and wastewater. 20th edition. Washington, DC: American Public Health Assoc; 1998.Google Scholar
- Alvarez R, Liden G: Semi-continuous co-digestion of solid slaughterhouse waste, manure, fruit and vegetable wastes. Renew Energy 2008, 33: 726–734. 10.1016/j.renene.2007.05.001View ArticleGoogle Scholar
- Salminen EA, Rintala J: Semi-continuous anaerobic digestion of solid poultry slaughterhouse waste: Effect of hydraulic retention time and loading. Water Res 2002, 36: 3175–3182. 10.1016/S0043-1354(02)00010-6View ArticleGoogle Scholar
- Chae KJ, Jang A, Kim IS, Yim SK: The effect of digestion temperature and temperature shock on the biogas yields from the mesophilic anaerobic digestion of swine manure. Bioresour Technol 2008, 99: 1–6. 10.1016/j.biortech.2006.11.063View ArticleGoogle Scholar
- Masse DI, Masse L: The effect of temperature on slaughterhouse wastewater treatment in anaerobic sequencing batch reactors. Bioresour Technol 2001, 76: 91–98. 10.1016/S0960-8524(00)00105-XView ArticleGoogle Scholar
- Sawayama S, Tada C, Tsukahara K, Yagishita T: Effect of ammonium addition on methanogenic community in a fluidized bed anaerobic digestion. Journal of Bioscience Bioenergy 2004, 97: 65–70.Google Scholar
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