In this study, pilot-scale experiments were performed on the anaerobic digestion (AD) in a semicontinuous process using a continuously stirred tank reactor to determine the effects of organic loading rate (OLR), temperature, and mixing levels on biogas production yield. Fresh cow manure was considered the input feedstock of this study due to its high production volume. Response surface methodology (RSM) was employed to design and analyze experiments to optimize OLR, temperature, and mixing intensity in biogas production. The central composite design was applied as a RSM optimization tool. Four cubic mathematical models were derived to predict the responses. The optimization study was carried out to identify the highest yields achievable when temperature and mixing factors are minimized. Temperature and OLR have been found to have a greater influence on biogas production compared to mixing intensity. The AD process is significantly influenced by temperature. Variations in temperature, specifically near 40 and 55°C, lead to an increase in the rate of biogas production. Therefore, the best temperatures for biogas production rate are near 40 and 55°C. The results of the performed optimizations suggest to adopt OLR values range of 1.6–2.5 kgVSCow manure=m3 ⋅ day, and 2.5–3.4 kgVSCow manure=m3 ⋅ day in the case of temperature ranges 20–40°C and 40–55°C, respectively.
