Lactic acid fermentation of food waste in a semicontinuous SBR system: influence of the influent composition and hydraulic retention time.

Abstract Fermentation processes has been shown to be a good approach for food waste (FW) management. Among the commodities that can be bioproduced from using FW as organic substrate and exploiting its biodegradability, there is lactic acid (LA). LA has gained the interest of research because of its role in the production of polylactic acid plastics. In this study, the influence of the HRT (2-5 days) used during the fermentation of the liquid fraction (∼ 12 - 13 g COD/L) of FW on LA yield and concentration was investigated. Moreover, the changes of the chemical composition (in terms of carbohydrates and organic metabolites concentration) of the influent occurring in the feeding tank were monitored and its influence on the downstream fermentation process were examined. High instability characterized the reactor run with the optimal production yield obtained on day 129 at an HRT 2 d with 0.81 g COD/g COD. This study shows the importance of the fluctuating composition of FW, a very heterogeneous and biological active substrate, for the LA fermentation process. The non-steady state fermentation process was directly impacted by the instable influent and shows that a good FW storage strategy has to be planned to achieve high and constant LA production.