Simulation-Based Assessment of Pretreatment-Assisted Anaerobic Co-Digestion Strategies for Cattle Manure and Wheat Straw in Small-Scale Biogas Systems

Small-scale biogas systems in developing regions are predominantly mono-digestion systems utilizing livestock manure as the primary feedstock. However, crop residues such as wheat straw offer significant potential for improving feedstock diversity and biogas production when applied in anaerobic co-digestion systems. Due to the recalcitrant nature of lignocellulosic biomass, pretreatment is required to enhance substrate degradability and methane production. In this study, the performance of integrated pretreatment and anaerobic co-digestion of cattle manure and wheat straw was evaluated using the modified ADM1_R3 model. Simulations were conducted under varying feedstock mixing ratios (0 to 100%wt wheat straw), pretreatment intensities (carbohydrate degradability levels of 50%, 67%, and 75%), organic loading rates (1 to 4 kgVSm−3day−1), and digester volumes (2, 4, and 6 m3). The results showed that increasing the wheat straw fractions improved biogas production, although with a slight reduction in methane. Pretreatment further enhanced overall process performance, with biogas production enhancement of between 40% and 56% across the different mixing ratios and degradability increase from 50 to 75%, while higher loading rates combined with higher pretreatment intensities increased the risk of process instability. The findings demonstrate the feasibility of this innovative approach of flexible small-scale co-digestion systems supported by appropriate pretreatment strategies. This study advances the application of anaerobic digestion modelling to small-scale biogas systems by providing an integrated framework for evaluating the effects of operational and design parameters on technical performance.