EFFECT OF INOCULUM TO SUBSTRATE RATIO ON BIOGAS PRODUCTION FROM SHEEP PAUNCH MANURE DIGESTED IN BATCH BIODIGESTERS

Abstract

In this study sheep paunch manure (SPM) was anaerobically digested under mesophilic condition to
determine its biogas potential. Three inoculums to substrate (I/S) ratios 1.3, 1.9 and 3.8 were digested in
biodigesters labeled R1, R2 and R3 respectively to determine the effect of substrate concentration on
biogas yield. Results showed that I/S ratio had significant effect on biogas production rate and
accumulation. Biogas production rate increased to their peak in the order of R3 (0.30526 Nm³/kgVSd),
R2 (0.15308 Nm³/kgVSd) and R1 (0.11009 Nm³/kgVSd) on day 5 and decreased to zero on day 27, 29
and 31 of the digestion period respectively. Biogas production accumulation increased from 0.57195 to
1.46784 Nm³/kgVS as I/S ratio increased from 1.3 to 3.8. Linear and exponential regression equations
were used to simulate biogas production rate while biogas production accumulation was simulated using
first order kinetic and modified Gompertz equations. Coefficient of determination (R²) of linear
regression equation of biogas production rate ranged from 0.707 to 0.797 while exponential regression
equation had R2 values that ranged from 0.7718 to 0.9929 showing better simulation. R² of first order
kinetic equation ranged from 0.9769 to 0.9827 while R² for modified Gompertz ranged from 0.9965 to
0.999. Thus modified Gompertz equation showed better simulation of biogas production accumulation.