Physicochemical characterization and kinetic study of anaerobic digestion of cattle dung in a semi-batch reactor

• COD removal efficiency of 75.1% was achieved in anaerobic digestion of fresh cattle dung, abattoir wastewater inoculated with rumen content • Process kinetics follows mainly a first-order rate model with a rate constant of 0.0526 day -1 , followed by a Monod model at 0.1107 day -1 substrate utilization constant • A cumulative 0.0265 m 3 of biogas was generated and spent digestate contains rich mineral elements This study investigated the process kinetics of the anaerobic digestion of different wastes under mesophilic conditions. A slurry of cattle dung was anaerobically digested in fabricated 25-litre reactors for 24 days. The biogas volume, physicochemical, and microbial properties of the digesting slurry were determined every three days using standard procedures. Kinetic models based on the first-order, Monod, and Grau second-order expressions were employed to estimate the performance of the process. After the experiment, a cumulative 0.0265 m³ of biogas was produced, and significant variations in the physicochemical and microbial properties of the digestate were observed. The process kinetics of the digestion followed a first-order reaction with a rate constant of 0.0526 day -1 and 75.1% COD removal efficiency. For the Monod model, the maximum rate of substrate utilization and saturation constant was found to be 0.1107 day -1 and 1,326.34 mg/l respectively. Based on analytical parameter, this anaerobic digestion process followed both first-order kinetic and Monod models only, which shows that for maximum biogas production from animal waste, inoculation would be required.