BIOGAS PRODUCTION FROM Guizotia scabra SUB-SPECIES scabra LEAVES CO-DIGESTED WITH COW DUNG

Alternative energy sources have recently become more and more attractive due to the increasing demand for energy, global warming, depletion of fossil fuels and high prices of petroleum-based fuels. One of the alternative sources of energy is Biogas. In this study, Guizotia scabra sub-species scabra was evaluated for its potential of biogas production codigested with Cow dung (CD ) in five mix ratios under mesophilic condition (38ºC) using batch digester in Botany laboratory of Haramaya University. In all treatments, total solids (TS), volatile solid (VS), organic carbon, and pH were measured before and after digestion. while, Organic carbon to Nitrogen ratio was measured before anaerobic digestion, and found in the range of optimal nutrient requirement for anaerobic microorganisms. The daily biogas production was subsequently measured by water displacement method for 30 days. All measured physico-chemical parameters of each substrate significantly varied between before and after anaerobic digestion (AD). Gas production was noticed in all of the substrate variation from the first day of digestion experiment and became almost zero at the 30th day in all substrates. The highest total biogas yield was obtained from 75% GS + 25%CD mix ratio (1168ml) while the lowest yield was obtained from CD alone (744ml). Assessment of cumulative biogas production revealed that substrate in a mix ratio of 75% GS and 25% CD (1168ml) showed the highest production, suggesting this mix ratio of the two substrates is an optimal mix to yield maximum amount of biogas. In general, results show that the increment of biogas yield, and VS and TS reduction can be significantly enhanced when GS and CD are co-digested. However, in order to get more biogas production from the substrate mixes with maximum biogas production (75% GS+25%CD) factors affecting the production such as temperature and pH should be evaluated at certain time intervals during anaerobic digestion (AD).