A. Mirzaee; M. Soleymani; H. Bahrami; M. Norouzi Masir
Abstract
Introduction: Almost 18 percent of emitted greenhouse gasses in Iran come from livestock industries, especially from manure decomposition. With the anaerobic digestion of animal wastes, in addition to eliminating its disadvantages, biogas as a clean and renewable energy carrier is produced. In addition, ...
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Introduction: Almost 18 percent of emitted greenhouse gasses in Iran come from livestock industries, especially from manure decomposition. With the anaerobic digestion of animal wastes, in addition to eliminating its disadvantages, biogas as a clean and renewable energy carrier is produced. In addition, the resulting sludge is a more healthy and nutritious fertilizer for use in agriculture. One of the challenges of the bio-gas industry is to increase gas production efficiency. Various approaches are proposed to enhance manure digestion efficiency and increase biogas production, which can be mentioned below: Changing operating parameters such as temperature, hydraulic retention time (HRT), and particle size of the substrate; adding some effective additives; returning the resulting sludge into the digestion process and using bio-filters. Therefore in this study, in order to increase biogas production from poultry manure, two methods (co-digestion with rumen contents, and chicken intestine and its contents, and returning the slurry into the reactor) were tested. The alkaline composition of chicken manure and its high content of ammonia makes it difficult to digest alone, and co-digestion with high-carbon organic matter improves its digestibility.Materials and Methods: Polyethylene bottles were used as batch reactor units. In order to the possibility of gas exit, as well as taking samples of the digester, two valves were placed on the bottle cap. All digesters were placed in a hot water bath and a 700 watts electric heater and a thermostat were used respectively to supply heat and to keep the temperature constant. A U-shaped tube, connected to the reactor output pipe was used to measure the amount of produced gas. The volume of water removed from the tube was an indicator of produced gas. The experiment was carried out in two stages. In the first stage 21 reactors were used according to the design of the experiment which was a completely randomized design with 7 treatments (adding rumen fluid in three levels (10, 20, and 30 percent of chicken manure (weight basis), respectively), adding chicken intestines and its content in three levels (10, 20, and 30 percent of chicken manure (weight basis), respectively), and control treatment), and three replicates of each treatment. During the whole experiment period, the pH and temperature were kept constant, respectively between 7.2-8.2 and 40-35 °C (mesophilic range). In the second stage of the experiment, after all the treatments reached the end of their hydraulic retention time, the resulting sludge was filtered and the liquid part was returned to the cycle. Three treatments were also provided here (supplying 50% of the water required by sludge liquid, supplying 100% of the water required by sludge liquid, and control treatment (no liquefied sludge).Results and Discussion: Based on the results, although the type of organic supplementation had a significant effect on the amount of biogas production, the quantity of them had not. Treatments of chicken manure + 20%, 30%, and 10% of chicken intestines resulted in the highest amount of biogas production, respectively. But these three treatments were not significantly different. Also, the co-digestion of chicken manure with chicken intestines was more effective than the co-digestion of chicken manure with rumen fluid. The return of sludge, resulted from anaerobic digestion of chicken manure, again into the cycle, in addition to enhancing the amount of produced gas, can reduce the waiting time to start gas production by at least six days (in the treatment of providing 100% of required water from returned sludge). This can lead to continuous gas production and availability of sufficient gas in commercial gas-producing units. The effect of treatments on the time of reaching the cumulative gas production index to 100 mm was significant (α= 5%) and treatment of S100 reduced this duration by approximately 17 days (65%) and S50, for approximately 16 days (74%). Conclusion: According to the results of this study, co-digestion of chicken manure with cow rumen fluid did not have a significant effect on the increase of biogas production, but co-digestion of chicken manure with chicken intestine and its contents (at least by 20% of chicken manure (weight basis)) can have a significant effect on the increase in the production of biogas and can increase the amount of gas at least twice. The highest amount of gas volume was about 305 Ml.gr-1 VSadded and came from the treatment of co-digestion of chicken manure with 20% (weight base) chicken intestine and its contents. The return of the resulting sludge of anaerobic digestion of chicken manure, back into the cycle, in addition to increasing the amount of gas, can minimize the time it takes to start to produce gas and help to produce gas continuously. Moreover, the water used for digestion will also be significantly reduced (at least 50%).
