A comparative experimental and kinetic modeling study of methane production from human feces: insights into methane production dynamics and engineering considerations

Introduction Human feces (HF) is an abundant and untapped bioresource that holds significant promise for decentralized anaerobic digestion-based energy recovery. However, the heterogeneity of its composition makes the predictability of methane yield highly challenging, thereby limiting reactor design, startup behavior, and process optimization. Methods In the present study, a biomethane potential assay was performed for 31 days using a mixed community-derived HF substrate at 35 °C ± 2 °C, and the experimental results were coupled with kinetic modeling to analyze methane production dynamics. Six kinetic models, including Modified Gompertz, First-order, Logistic, Richards, Cone, and Transfer Function models, were evaluated using nonlinear least squares regression. Results The cumulative methane yield reached 247.48 ± 5.83 NmL CH 4 g −1 VS, with approximately 90% of the total methane production occurring within 15 days, indicating relatively rapid methane production under the conditions of the present batch assay. Among the evaluated models, the Richards model provided the best fit to the experimental data (R 2 = 0.9973), followed by the Logistic and Modified Gompertz models. In contrast, the First-order model showed comparatively poorer performance for the present dataset, consistent with the limitations of its simple exponential formulation in representing a distinct lag phase preceding methane production. Discussion From a bioprocess engineering perspective, these findings suggest that kinetic model selection can substantially influence the characterization of methane production dynamics and estimation of key kinetic parameters relevant to anaerobic digestion performance. The comparative modeling approach developed in this study can contribute to providing a practical basis for evaluating kinetic models applied to heterogeneous substrates such as human feces and may support future reactor design, process optimization, and operational studies following validation under a wider range of feedstocks and operating conditions.