Energy recovery from domestic food wastes via microbiological processes

In the present study the exploitation of typical household food wastes (HFW) was studied via their bioconversion to energy carriers i.e. the biofuels bio-ethanol, bio-hydrogen and methane. HFW was produced at municipality level and were heat dried and milled upon collection. Drying and milling were applied in order to prevent the biodegradation of the waste and to ensure its stable and unchanging composition during its storage. Two different approaches were tested using either a two-stage process or a two-stage configuration. In the first case dried HFW (DHFW) was initially subjected to extraction using warm water resulting to a liquid fraction (extract) and a solid residue. The rich in sugars extract was forwarded for ethanol production via mono-cultures and co-cultures of different yeast strains and also for hydrogen production via mixed acidogenic consortia. The remaining solid fraction produced from the extraction process was used as substrate for methane production via anaerobic digestion (AD). During the second approach the DHFW was directly used as substrate for the production of ethanol and hydrogen via simultaneous saccharification and fermentation and the effluents in both cases were subsequently subjected to AD, aiming to extra energy recovery via methane. Energy inputs and outputs were estimated based on the operational conditions of the reactors for each different scenario and the final energy balances were assessed. The results of the study indicated that the exploitation of the HFW is quite appealing leading to promising energy recovery in all cases.