Abstract:
Biogas is eco-friendly alternative renewable energy source produced through anaerobic digestion of organic compounds. In this study, biogas production was evaluated from Prosopis juliflora leaves(PJ) and cow manure (CM) co-digestion in five mix ratios under mesophilic conditions (38ºC) using batch digesters in the Botany Laboratory of Haramaya University to evaluate biogas production potential of Prosopis juliflora leaves through anaerobic digestion alone or in combination with cow manure. In 100%PJ, 100% CM, 75%PJ and 25% CM, 50%PJ and 50%CM, and 25%PJ and 75%CM 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 physico-chemical parameters of each substrate showed significant variations.The maximum (81. 6±0.8) and minimum (78.6±0.3), MC% before AD was measured in 50% PJ and 50% CM) and 100% CM respectively.While after AD the maximum (91.1±0.55) MC% was measured in 75%PJ and 25%CM and the minimum (82.2±0.8) MC% was measured in 25% PJ and 75% CM. Likewise, the maximum (44.5±0.42) and minimum (34±0.3) C% before AD was measured in100% PJ, and 100% CM respectively. After AD degradation of organic carbon was highest (19.2 C%) for 75%PJ and 25%CM. The maximum (7.2±0.01) and minimum (6.05±0.01) pH before AD was measured in 100% CM and 100% PJ respectively. After anaerobic digestion, TS% and VS% of all treatments were significantly lower (66.6, 50.9, 64.2, 64.8 and 55.3 and 2.5, 1.2, 34.4, 1.26 and 2) 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 were 23.9±00, 22.6±01, 22.7±0.3, 23.75±0.2 and 22.46±00 respectively. Biogas production was detected in both substrate and substrate mix ratios from the second day of digestion and declined to zero in about 28 days of incubation. The maximum (506 ml) cumulative biogas was measured in 25%CM and 75%PJ while the minimum (272 ml) was measured in100% CM. Assessment of cumulative biogas production revealed that the substrate mix ratio of 75% Prosopis juliflora and 25% cow manure was superior to others (506 ml). 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 Prosopis juliflora is co-digested with cow manure in 75%:25% mix ratio.