Kinetic modeling and synergistic effects of anaerobic co-digestion of bovine ruminal waste and brewery spent grain

Given the global perspective inherent to increasing global industrialization, waste generation has caused a significant environmental impact. In this scenario, the use of industrial waste has driven research for the production of biogas, corroborating with the expectations of renewable energy production globally. Thus, the objective of this study was to evaluate the influence of different inoculum to substrate ratios (ISR) on methane yield, as well as the synergistic effects of adding brewery spent grain (BSG) in anaerobic co-digestion with bovine ruminal waste (BRW). Biochemical methane potential (BMP) assay was conducted to evaluate the effect on methane yield of different ISR (4, 2, and 1) at five different mixing ratios based on volatile solids (VS) between BRW:BSG (0:100, 25:75, 50:50, 75:25, and 100:0). In addition, the theoretical BMP of mono-digestion and the biodegradability of the substrates were also estimated. Five kinetic models were evaluated and compared for mono- and co-digestion (AcoD). The increase in methane yield was directly proportional to the increase in the proportion of ISR and BSG in the mixture. No substantial synergistic or antagonistic effects were observed for the AcoD of the substrates. However, the optimal mixture of 25% BRW with 75% BSG (%VS) was obtained by the desirability test for ISR 3.25, with a methane yield of 249.87 NmLCH4 gVS−1. The Cone model best fitted the experimental data regarding the statistical parameters for all conditions studied. Therefore, the tecno-economic assessment reveals the great potential of the AcoD of BRW with BSG in the generation of sustainable energy. •Brewery spent grain mono-digestion yielded the highest methane yield.•The brewery spent grain in the co-digestion improved the methane yields.•A higher inoculum to substrate ratio induced higher methane yield.•No substantial synergistic or antagonistic effects were observed for co-digestion.•Five kinetic models were compared and the Cone model best fitted the observed data.