Dark fermentative biohydrogen production from organic waste and application of by-products in a biorefinery concept
Low biohydrogen (H2) yields and limited use of process by-products from dark fermentation (DF) of waste biomass is limiting its scaled-up application. This study aims to investigate the effects of culture pH, substrate concentration, pre-treatment of substrate and inoculum adaptation on H2 yields during the DF of three organic wastes biomass (i.e. food waste, rice straw and olive mill wastewater). The results showed that the biodegradability of the substrates is important for the selection and application of optimal operational parameters aimed at enhancing H2 production.
Moreover, long-term operational feasibility and stability of dark fermentative H2 production was demonstrated using food waste and cheese whey in two semi-continuous thermophilic DF reactors. The effect of Organic Loading Rates (OLRs), Hydraulic Retention Times (HRTs) and co-substrates (buffalo manure) addition, as a source of alkalinity, on culture pH and H2 production stability was discussed. The results showed that combination of OLR, HRT and co-substrate addition could play a vital role in the culture pH and stability of H2 production.
The by-products of DF process were utilized for H2 production via photo fermentation (PF), while the waste stream generated from coupling of DF and PF processes was converted to methane in anaerobic digestion. The three-step conversion of food waste in a biorefinery concept increased the total energy yields. Moreover, PF also showed a good potential for concomitant production of H2 and polyhydroxybutyrate (biopolymer). Likewise, dry fermentation of waste biomass could be promising for the production of bioenergy and biochemicals (organic acids and alcohols) in a biorefinery concept.