Optimization of Process Condition for Methane Yield from Co-digestion of Both Thermochemically Treated Pig Manure and Napier Grass using Response Surface Methodology
Abstract
Pretreating pig manure (PM) and Pak Chong 1 Napier grass (NG) before co-digestion is essential for enhancing methane production. This study aims to optimize methane output under various experimental conditions using a semi-continuous laboratory-scale reactor and Response Surface Methodology. Different PM/NG ratios (1:2 to 2:1), organic loading rates (OLR) between 0.41 and 1.22 g VS/L, and dilution volumes (750 to 950 mL) were investigated, with cumulative methane production (CMP) as the primary response variable. The Box-Behnken design was employed, and data were analyzed using a quadratic model and analysis of variance to assess the significance of factors and their interactions. Over a 60-day period, the optimal parameters identified were a PM/NG ratio of 1.08, an OLR of 1.04 g VS/L, and a dilution volume of 903.54 mL, leading to a predicted CMP of 22,112 mL. The analysis indicated significant linear effects of OLR and dilution on methane production, along with notable interactions between the PM/NG ratio and OLR. The model's accuracy (R2 = 97.85%) showed a strong correlation with experimental data, achieving an actual CMP of 23,537 mL. This study applies OLR in batch tests to optimize biogas production, emphasizing its role in enhancing efficiency and stability for large-scale CSTRs.