Short and medium chain organic acids production from hydrolyzed food waste: technical–economic evaluation and insight into the product’s quality

Food waste (FW) was subjected to thermal-alkaline hydrolysis before to be used as source for organic acids (OAs) production under different temperatures and hydraulic regime in long-term acidification process. Mesophilic environment led to the highest acidification yield (0.87 g CODOAs/g VS) with chain-elongation process to caproic acid production (>9.0 g CODcap/L) occurring at lower HRT (2 days). The product's quality, in terms of OAs production and composition, was evaluated through a multivariate approach, which indicated that the mesophilic condition was also appropriate to steadily maintain the requested product's features. The specific gas production (SGP) from the solid-rich acidified residue was 0.47 Nm3/kg VS and, in a full-scale scenario of 150,000 kg FW/d, it can be potentially converted into 24.9 MWh/d as electrical energy. Also, according to the acidification performances, an overall OAs production of 7.2 ton/y has been estimated, generating a yearly economic outcome higher than 4,800,000 €.