There is urgent need for proper waste management and development of alternate energy using wastes in developing countries. Optimal digestion mixture of substrates ensures that waste products of animals, industries etc. are optimized. This study was designed to determine the optimal mixing ratio of cow dung and poultry droppings in biogas production under tropical condition. The mixing ratio used were 100:0, 75:25, 50:50, 25:75 and 0:100 for cow dung (CD) and poultry droppings (PYD), respectively. The fermentation was carried out in five 30 L digesters locally fabricated. The biogas yields obtained in the work for the cow dung and poultry dropping mixture were in the order of 25% CD + 75% PYD > 100% CD + 00% PYD > 50% CD + 50% PYD > 00% CD + 100% PYD > 75% CD + 25% PYD. The kinetics of anaerobic digestion process of the various digestion mixtures was successfully evaluated with modified first order model equation; the result shows that poultry dropping (alone) has the highest short term biodegradability index of 2.4 while the 50% CD+50% PYD digester has the highest removal rate of the biodegradable fractions (k) of -0.199 among all the substrates. Thus, optimum mixing ratio for cow dung and poultry dropping suggested by the study is 25% CD + 75% PYD mixing ratio which gave 16.35 L/total mass of slurry (TMS) within the period under study.
Key words: Waste management, energy, cow dung, poultry droppings, biogas.
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