Fusion of Vermicompost and Sewage Sludge as Dark Fermentative Biocatalyst for Biohydrogen Production: A Kinetic Study

Abstract

The present study explores the synergy between vermicompost and the anaerobic sewage sludge as inoculum for biohydrogen production using food waste as a substrate. Experiments were designed and performed in two phases of operation. In the first phase, the vermicompost (VC) was used as inoculum and food waste as substrate at three different organic loading rates of 10 gVS/L (VC1), 20 gVS/L (VC2), and 30 gVS/L (VC3). In the second phase of operation, the inoculums were combined with a proportion of 50% (VC+AS). The study showed an effective biohydrogen production of 20 gVS/L when the mixing ratio of vermicompost and anaerobic sludge was 50:50. The results inferred that effective synergy was observed between the combined consortia of the inoculum, which induces a more effective metabolic pathway for enhanced hydrogen production. H2 production was 33 mL/gVS (VC1), 48 mL/gVS (VC2), 35 mL/gVS (VC3), 46 mL/gVS (AS), and 50 mL/gVS (VC+AS). Heat pretreatment (100–120 °C) of the inoculum suppresses the methane-producing microorganisms and increases the hydrogen-producing microbes. In addition to hydrogen production, different metabolites are formed in the liquid phase, such as acetic acid, butyric acid, and propionic acid of 2.957 g/L, 4.286 g/L, and 2.123 g/L, respectively, with an energy content of 257 J/day with VC+AS. In addition, a kinetic model was studied for the cumulative hydrogen production curves using the modified Gompertz model, and the fit infers that the experimental data fitted well, with high coefficients of determination for VC+AS (R2 (G) > 0.99).