keywords: Biogas, blends, gas analyses, optimization, retention time
The potentials of optimizing biogas production using cow dung, pig dung and poultry droppings with sugar cane bagasse and water melon peel were studied. Proximate analyses as well as total solids, volatile solids, carbon content, and nitrogen content were determined on the wastes while microbial level, pH and temperature were determined on the slurry. The wastes were subjected to anaerobic digestion for 40 days at mesophilic temperature range of 20.5 to 48.5oC. Relative humidity, ambient temperature, pH, slurry temperature, and volume of gas were monitored and recorded on daily basis. The composition of gas generated from the mixture was 58.1-64.8% CH4, 31.0-37.7% CO2, and 0.8-1.4% H2S and 1.2-1.6% CO. The physico-chemical analysis of the feedstock in the digester revealed an initial pH of 5.43 which later went to 8.40 and later dropped to 5.25. Cumulative biogas yield of the blend with sugar cane bagasse, water melon peel and poultry droppings was higher than those of the blend with pig dung, sugar cane bagasse and water melon peel as well as the one with cow dung, sugar cane bagasse and water melon peel. However, the blending of bagasse and water melon peel with cow dung did not improve or optimize the biogas yield; instead, a steady state was established. This may be due to mutual inhibitions. Onset of gas flammability was observed on the 4th day for poultry droppings and its blends while for cow dung, pig dung and their blends it was observed on the 5th day. From the gas production analysis, the total volume of biogas was maximum in digester IV (138.2L) compared to digester II (16.6L), III (33.7L) and digester I (110.8L).
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