THE IMPACT OF TEMPERATURE PRETREATMENT ON BIOGAS YIELD FROM SAWDUST, CO-DIGESTED WITH COW DUNG

Abstract

Renewable resources play a significant role in reducing carbon dioxide emissions around the world, and with this in mind, biomass and waste is a candidate to be one of the most widely utilized renewable energy resources. Therefore, this research was conducted to investigate the production of biogas from saw dust, cow dung in solo or mix through anaerobic digestion with five treatment ratios, under mesophilic condition (38ºC) using batch digesters at Haramaya University for 30 days. Sawdust and cow dung were pretreated for three hours at 60, 80, and 100ºC. In all treatments, physico-chemical parameters such as total solid, volatile solid, organic carbon, nitrogen, and pH values were measured before and after anaerobic digestion. The initial pH value was observed for all the digesters with different temperatures pre-treatment. The results indicated that highest pH value (7.4±30.14) was observed in 100ºC pre-treatment with 100% SD (sawdust), whereas the lowest pH value (6.70±0.12) was observed in 100% CD (Cow dung) with 60ºC temperature pre-treatment. Comparison of pH values and after anaerobic digestion showed that pH values were significantly increased after anaerobic digestion for all treatments. Similarly, the total solids and volatile solids of the substrates were analyzed for all treatments before and after AD. The minimum %TS (90.00±1.28) was measured from the digester with 100% CD within 60ºC pre-treatment. Whereas the maximum %TS (94.00±1.00) was measured at 100% SD with 100ºC pre-treatment before AD. After anaerobic digestion in all treatments, the percentage of total solid contents was decreased. The highest % of organic carbon (37.14±1.19) was recorded from 100ºC temperature pre-treatment with a mixed ratio of 70% SD + 30 % CD. Whereas, the lowest carbon content (22.20±80) was observed in the 60ºC temperature pre-treatment within 100% CD. Among, the temperature pre-treatment 100ºC pre-treatment showed the highest concentration of nitrogen in 100% CD. Moreover, C/N ratios were analyzed and the results revealed that the highest C/N ratio was observed in 100ºC pre-treatment within 100% sawdust. The different temperature pre-treatment, 100ºC temperature pre-treatment with a mix ratio of 70% SD+30% CD showed the highest production of biogas in all treatments. However, the least biogas production was noticed with 60ºC temperature pre-treatment in the solo substrate (Sawdust and Cow dung). Overall, the results of this study indicate that the increase in biogas yield and reduction in volatile solids and total solids can be significantly enhanced when saw dust is co-digested with cow manure in a 70%:30% mix ratio with 100ºC temperature pre-treatment. Since this experiment was carried out on the co- digestion of sawdust and cow manure, further similar studies should be recommended on co-digestion of sawdust with other substrates