Effect of inoculum/substrate ratio on dark fermentation for biohydrogen production from organic fraction of municipal solid waste

Hydrogen (H2) is meeting with increasing interest as possible alternative to fossil fuels for energy production. It can be produced both thermochemically and biologically from a number of organic substrates. H2 is usually employed in fuel cells, a technology aimed at producing electricity, characterized by low environmental impact and high efficiency. Similarly, dark fermentation (DF) of organic waste is gaining popularity because of its environmental compatibility and relatively high efficiency in the production of biogas (a mixture of CH4, CO2 and H2 in variable proportions). In this perspective, the organic fraction of Municipal Solid Waste (OFMSW) is an interesting substrate for biohydrogen (BioH2) production because of its large supply and its chemical composition able to sustain a vigorous growth of H2 producing microorganisms. In this work, the effect of inoculum to substrate ratio (ISR) (0.01, 0.07 and 0.14, dry weight basis) on mesophilic DF of OFMSW for BioH2 production was evaluated. Primary sewage sludge heated at 95 °C for 30 min was used as inoculum. Both the liquid and the gas phase produced during the DF were analysed, together with the microbial biomass growth, the amount of reducing sugars, the pH, and the biogas volume and composition. Our results show the possibility of using OFMSW as substrate in mesophilic DF process for BioH2 production. In particular, the best performance in terms of BioH2 production was obtained with ISR of 0.07.