ENERGY RECOVERY FROM SINGLE AND DOUBLE STAGE ANAEROBIC DIGESTION OF FOOD WASTE: COMPARISON AND PERSPECTIVES

The performances of a single- and a double-stage AD process aimed at recovering CH4 and H2 + CH4, respectively, from food waste were compared in order to assess the benefits associated with the two-phases approach in terms of overall energy recovery. The results obtained suggest that a double-stage process where the first reactor is properly operated in order to make possible net H2 production, may ensure a 20% higher overall energy recovery, as a result, mainly, of a higher production of methane, as well as of the associated hydrogen production. The highest CH4 production observed for the two-stage process, despite the H2 recovered being a substrate for methanogenesis, was due to improved hydrolysis and fermentation of FW which allowed for a flow to be fed to the methanogenic reactor characterized by a suitable VFAs concentration.