PRODUCTION OF BIOGAS FROM THE MIXTURE OF SAWDUST AND COW DUNG UNDER ANAEROBIC CONDITION

Abstract

Biogas is eco-friendly alternative renewable energy source produced through anaerobic digestion of organic compounds. In this study, biogas production was evaluated from sawdust (SD)and cow dung (CD) co-digestion in five mix ratios under mesophilic conditions (35ºC) using batch digesters in the micro biology Laboratory of Haramaya University to evaluate biogas production potential of sawdust through anaerobic digestion alone or in combination with cow dung .In 100%SD , 100% CD, 50% SDand 50% CD, 70%SD and 30%CD, and 30%SDand 70%CD treatments, total solids%, volatile solids%, organic carbon%, moisture content% and pH were measured before and after digestion while carbon to nitrogen ratio was measured before anaerobic digestion only. The daily biogas production was measured by water displacement method. All measured physicochemical parameters of each substrate showed significant variations. The maximum (82.02±0.24) and minimum (79.76±2.98), MC% before AD were measured in 50% SD and 50% CD) and 70%SD and 30%CD respectively.While after AD the maximum (88.9±1.59) MC% was measured in 100%CD and the minimum (83.87±1.38) MC% was measured in 100%SD. Likewise, the maximum (50.39±1.05) and minimum (46.01±0.52) C% before AD were measured in 50% SD, and 50% CD and 100%SD respectively. After AD degradation in organic carbon was highest (25.36 C%) for 70%SD and 30%CD. Generally %C after AD totaly reduced before AD. The maximum (7.51±0.37) and minimum (6.76±0.16) pH before AD were measured in 100%CD and 50%SD and 50%CD respectively. After anaerobic digestion, TS% and VS% of T1,T2,T3,T4,and T5treatments were significantly lower (32.21, 30.11, 28.36,25.8, 28.33 and 69.73, 67.1, 62.12, 42.24 and 68.29) than those of the treatments before AD. In this experiment, the carbon to nitrogen ratio of treatments T1, T2, T3, T4 and T5 before AD were24.60:1 , 31.05:1, 28.96:1 , 28.72:1 and 31.61:1 respectively. Biogas production was detected in both substrate and substrate mix ratios from the second day of digestion and declined to zero in about 31 days of incubation. The maximum (512.25ml) cumulative biogas was measured in 70%SD and 30%CD while the minimum (287.75 ml) was measured in100% CM. Assessment of cumulative biogas production revealed that the substrate mix ratio of 70% SD and 30% CD were superior (512.25ml) than others. Over all, 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 sawdust was co-digested with cow manure in 70%SD and 30% CD mix ratio.