EFFECT OF INOCULUM TO SUBSTRATE RATIO ON BIOGAS PRODUCTION FROM DIGESTED GOAT PAUNCH MANURE

In this study goat paunch manure (GPM) was anaerobically digested under mesophilic condition to determine its biogas potential. Inoculum to substrate (I/S) ratios of 1.45, 2.2 and 4.3 were digested in biodigesters labeled R15, R10 and R5 respectively to determine the effect of substrate concentration on biogas production rates and accumulation. Biogas production accumulation was simulated using first order exponential rise and modified Gompertz equations. Results showed that I/S ratio had no significant effect on biogas production rate. Biogas production rate increased to the peak in the order of R10 (0.08856 Nm3kg-1VSd-1), R5 (0.07653 Nm3kg-1VSd-1) and R15 (0.05824 Nm3kg-1VSd-1) on 10th, 9th and 2nd day and decreased to zero on 30th, 29th and 30th day of the digestion period, respectively. Biogas production accumulation increased from 0.44273 to 1.00783 Nm3kg-1VS with I/S ratio increase. Coefficient of determination (R2) of the first order exponential rise regression ranged from 0.9602 to 0.9895, while R2 for modified Gompertz ranged from 0.9983 to 0.9992 showing better simulation of biogas production accumulation.