EVALUATION OF BIOGAS YIELD FROM AVOCADO (Persea americana M.) PEEL WASTE CO-DIGESTED WITH GOAT MANURE

Biogas is a well-established fuel that can replace firewood and electricity as an energy source for cooking, lighting, heating and for other purposes in developing countries. Moreover, biogas is a clean, environmental friendly and renewable form of energy generated when micro-organisms degrade organic materials in the absence of oxygen. The aim of this study was to evaluate biogas production potential of avocado fruit peel wastes and goat manure in combination or separately under anaerobic condition. The experiment was carried out by completely randomized design using batch mode operated digesters under mesophilic (38oC) condition in the microbiology laboratory of Haramaya University in five proportions to have five treatments of substrate. That means the treatments were arranged randomly in the laboratory and done in three replications of five treatments. The digesters were filled with fresh avocado peel (AP) and goat manure (GM) in single or mixing at different proportions as follows; T1 (100% AP), T2 (70%AP+30% GM), T3 (50% AP +50% GM), T4 (30% AP+70% GM) and T5 (100% GM). In all treatments, Physico-chemical characters of substrate such as pH, Total solid (TS), Volatile Solid (VS) and organic carbon were measured before and after anaerobic digestion whereas Carbon to Nitrogen ratio was measured before anaerobic digestion. Before AD initial pH values of samples were adjusted within 6.8-7.2. Daily biogas yield was measured for about 30 days starting from the next day of inoculation using water displacement method. The experimental result showed that all measured pH, TS, VS, organic carbon and Carbon to Nitrogen ratios were significantly varied. The cumulative biogas yield measured from T1, T2, T3, T4 and T5 were 428.03 ml, 701.51 ml, 613.15 ml, 506.82 ml and 398.63 ml respectively. Evaluation of cumulative biogas production showed that substrate in a mix ratio of 70% AP + 30% GM produced the highest cumulative biogas yield (701.51 mL) as compared to the solo and mix ratio of other substrate. Therefore, this mix ratio of the two substrates suggesting an optimal mix ratio to produce the highest biogas yield. In general the experimental results showed that the increment in biogas yield, reduction in Volatile solids ,Total solids sand organic carbon can be significantly improved when avocado peel and goat manure are co-digested in 70% AP+30% GM mix ratio.