PRODUCTION OF BIOHYDROGEN AND VOLATILE FATTY ACIDS FROM DEPHENOLIZED OLIVE MILL WASTEWATERS IN A SEQUENTIAL TWO-STEP ANAEROBIC PROCESS Extended abstract

A large variety of agro-wastes are actually investigated for their reliability as renewable sources: the possibility to employ some organic residues for the production of biomolecules, biofuels and biomaterials has fostered the born of the concept of second generation biorefineries, which differ from the first generation processes, since non dedicated crops are used as the feedstock. To this aim, Olive Mill Wastewaters (OMWs) are the most investigated wastes, due to their high organic content and to a high concentration of polyphenols, compounds that are natural antioxidant. If on the one hand OMWs are recalcitrant to biodegradation and their environmental impact can represent a serious issue, on the other hand these wastes show a biochemically interesting composition, rich of sugars, lipids, alcohols and organic acids. Recent studies have demonstrated that a lot of processes can be applied to OMWs, which can be exploited for the recovery of polyphenols, production of biofuels or chemicals such as Volatile Fatty Acids (VFAs). The latter can be used as precursors for biopolymers intracellular accumulation (i.e. polyhydroxyalkanoates, PHAs) by mixed microbial consortia (Beccari et al., 2009). In this respect, a continuous Packed Bed Biofilm Reactor (PBBR) performing OMW organic matter bioconversion into VFAs was developed (Bertin et al., 2010); moreover, a preliminary recovery of polyphenolic fraction of OMWs before their feeding to acidogenic digestion was also assessed (Scoma et al., 2011). In this way, a multi-target biorefinery scheme aimed at extensively valorizing OMWs has been designed: its backbone is represented by a two-step process dedicated to the recovery of polyphenols (by a fully eco-compatible procedure) and the anaerobic acidogenic digestion of the dephenolized effluent (OMWdeph). Recent studies have shown the feasibility of an interesting production of biohydrogen together with accumulation of VFAs, obtained by changing the Hydraulic Retention Time (HRT) on the developed acidogenic process fed with a dephenolized OMW (Scoma et al., 2013).