Synergistic effect and kinetic evaluation of swine manure and waste kitchen oil co-digestion

While different biomass sources were commonly used in biogas systems, the synergistic effect was controversial, and the variety of models and criteria made it difficult to determine a best-fit equation. In this study, the evaluation of synergistic benefits and kinetic parameters was performed in a batch study fed by swine manure (SM) and waste kitchen oil (WKO) with four treatments (M4 (4 g-VSSM/L), M4F1, M4F2, and F2 (2 g-VSWKO/L)) and the control. The addition of WKO significantly increased the biogas yield (up to 1527±131 mL/g-VS), compared to 827 ± 109 mL/g-VS of SM mono-digestion, due to the higher biogas potential of WKO than that of SM. However, the co-digestion performance index (CPI) and linear relationship indicated no synergistic benefit. The kinetic analysis showed that the oily material had a longer lag phase (up to 0.65 d) compared to SM, indicating the necessity of combining the two substrates for system optimization. Four kinetic models exhibited high accuracy, and the Cone equation showed a better result on the longer lag-phase treatment. The high correlations between the AIC and BIC (R2=1), or MAPE and RMSE (R2=0.997), demonstrated the consistency between those parameters. The study revealed the consistency of CPI and linear regression to determine synergistic benefits, and kinetic parameters to evaluate the simulated models in AD systems.