Analytical And Dynamic Simulation Modelling Of Household Biogas Digester For Domestic Energy Production From Organic Wastes

Household biogas digesters offer a practical renewable energy pathway for rural communities in developing countries, yet their design and performance evaluation are still largely guided by empirical rules of thumb rather than integrated predictive models. This study developed and validated a hybrid analytical and dynamic simulation model for evaluating the performance of a small-scale household biogas digester operating under mesophilic conditions. A steady-state analytical model, based on mass balance and stoichiometric principles, was developed from a baseline case synthesized from secondary data extracted from peer-reviewed literature. A complementary dynamic simulation model, incorporating first-order substrate degradation kinetics and an Arrhenius-type temperature correction, was implemented in MATLAB/Simulink to capture the transient behaviour of the anaerobic digestion process. The model tracked substrate degradation, biogas and methane generation, and energy output over a 38–40-day digestion cycle. Simulation results showed a peak biogas production rate of 1.04 m³/day at day 19, a cumulative biogas yield of approximately 30 m³, a peak methane production rate of 0.62 m³/day, and a peak energy output of 12.8 MJ/day. Comparison between the analytical and simulation outputs showed close agreement, with percentage differences below 5% across all evaluated parameters. Sensitivity analysis showed that operating temperature, hydraulic retention time, and volatile solids content significantly influenced digester performance, with 35°C, a 40-day retention time, and higher volatile solids concentrations producing the greatest biogas yields. Validation against independently published experimental data confirmed that the model reproduces the temperature-dependent trend of anaerobic digestion with good accuracy. Based on the findings of this study, it is recommended that household biogas digesters should preferably operate under mesophilic temperature conditions between 25°C and 35°C to enhance microbial activity and maximize biogas production.