Assessing the Environmental and Economic Viability of Biogas Production from Co-Anaerobic Digestion of Sawdust and Cow Dung Using Thermochemical Pretreatment in Nigeria

Abstract

This study investigated the co-anaerobic digestion of cow dung and sawdust with thermochemical pretreatment to enhance biogas yield and energy recovery. Sawdust was pretreated with sodium hydroxide and thermally conditioned before co-digestion with cow dung at 50:50 and 75:25 ratios. Results showed that pretreatment accelerated gas onset by 3–4 days and increased cumulative biogas yield, with the 75:25 mixture producing 48.25 L compared to 34.5 L in untreated samples. Methane fractions of 58–61% yielded calorific values of ~21 MJ/m3, aligning with reported ranges in Nigerian studies. Energy balance analysis revealed that while pretreatment improved methane recovery, its net benefit depended on substrate ratio: the 75:25 mixture achieved a superior net energy balance (1.015 MJ treated vs. 0.75 MJ untreated), whereas the 50:50 mixture showed reduced efficiency due to heating input. Microbial analysis confirmed high heterotrophic bacterial activity in the digestate, suggesting potential as a soil fertility enhancer. Economically, biogas offers a viable alternative to LPG, with biodigester installation costs offset by a two-year payback period and additional benefits from digestate utilization. The findings contribute valuable insights toward the optimization of co-digestion systems for renewable energy production and environmental sustainability in Nigeria’s waste-to-energy value chain.