Abstract
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.
Highlights
In any livestock production system, animal droppings constitute an unavoidable by-product
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 has the highest short term biodegradability index of 2.4 while the 50% cow dung (CD)+50% poultry droppings (PYD) digester has the highest removal rate of the biodegradable fractions (k) of -0.199 among all the substrates
The maximum biogas production potential for the cow dung and poultry dropping mixture is in the order of 25% CD + 75% PYD > 100% CD + 00% PYD > 50% CD + 50% PYD > 00% CD + 100% PYD > 75% CD + 25% PYD
Summary
In any livestock production system, animal droppings constitute an unavoidable by-product. Biogas technology in which biogas is derived through anaerobic digestion of biomass, such as agricultural wastes, municipal and industrial waste (water) is one of such appropriate technology which could be adopted to ease environmental problems and enhance energy production. The benefit of co-digestion of substrates usually outweighs that of single digestion because of synergistic effects (Braun and Wellinger, 2002) It is necessary in the face of energy challenges facing developing countries, and mismanagement of cow and poultry wastes in the study area (which has constituted environmental nuisances) to determine the optimum mixing ratio of these major animal wastes produced in the region under tropical conditions for biogas production
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