Comparison of process stability in methane generation from palm oil mill effluent using dairy manure as inoculum

•This study investigated methane production from dairy manure as inoculum.•Addition of dairy manure improved both the start-up time and rate of biogas production.•Biogas production was achieved at ambient temperature.

The potential of methane production in a continuously stirred tank reactor (CSTR) was investigated using dairy manure as inoculum at pH 6.8 and 37 °C temperature in this study. Two identical anaerobic bioreactors namely CSTR1 and CSTR2 filled with palm oil mill effluent (POME) as a carbon source were used. CSTR1 was not added with the inoculum, while CSTR2 was added with dairy manure as inoculum. Both the reactors were allowed to run for 5 days (d) in batch condition at hydraulic retention time (HRT) 10 d. The CSTR2produced 0.85 L/d gas yield and 59% methane content compared to 0.39 L/d gas yield and 20% produced in CSTR1, respectively. A better chemical oxygen demand (COD) reduction percentage of 48% was found in CSTR2 compared to CSTR1 with 33%. The investigation showed that dairy manure as inoculum has a marked influence on the start-up period and the biogas production rate.