Kinetic investigations into the effect of inoculum to substrate ratio on batch anaerobic digestion of simulated food waste

Gandhi, B.P. and Otite, S.V. and Fofie, E.A. and Lag-Brotons, A.J. and Ezemonye, L.I. and Semple, K.T. and Martin, A.D. (2022) Kinetic investigations into the effect of inoculum to substrate ratio on batch anaerobic digestion of simulated food waste. Renewable Energy, 195. pp. 311-321. ISSN 0960-1481

Abstract

This anaerobic digestion (AD) study investigated the effect of inoculum to substrate ratio (ISR 4.00 to 0.25) on viability of methanogenesis using simulated food waste as substrate. Given the complexity of the AD process, this study considered the interdependency of AD parameters and their effect on biogas production, as the digestion progressed. Maximum methane production was between ISR 2.00 (139 ± 10 ml CH 4/g VS added) and 1.00 (152 ± 12 ml CH 4/g VS added); further decreases in ISR were found to result in system acidification. Under acidogenic conditions (ISR≤0.5) pH and the volatile fatty acid (VFA) profile were found to be strongly dependent on the ISR. In contrast to ISR 0.25, ISR 0.50 showed reverse beta oxidation, which resulted in increased concentrations of medium chain VFAs over the digestion period. Maximum total VFA (TVFA) concentrations that the system could survive with reversible acidification (ISR 1.00) was found to be 17.52 ± 0.02 g/l, whereas the maximum TVFA production was found to be 29.25 ± 0.73 g/l for ISR 0.50. Uniquely, this study also reports up to 55% anaerobic degradation of lignin in acidified reactors with ISR 0.25, which based on existing literature, points towards the involvement of specific bacterial strains.