Improving the non-sterile food waste bioconversion to hydrogen by microwave pretreatment and bioaugmentation with Clostridium butyricum.

This work targeted the energy recovery from food waste (FW), aiming at the implementation of a potentially participative process of FW conditioning before the non-sterile biological conversion to hydrogen (H2). Food waste conversion was initially performed under sterile conditions, achieving a maximum H2 productivity of 249.5 ± 24.6 mL H2 (L h)-1 and a total H2 production to 4.1 ± 0.2 L L-1. The non-sterile operation was implemented as a way of process simplification, but the total H2 production decreased by 59% due to the FW native microorganisms. To counteract this effect, FW was submitted to acid, microwave (MW), and combined acid and MW pretreatment. The application of 4 min MW, 550 W, efficiently controlled the FW microbial counts. The Clostridium butyricum bioaugmented conversion of MW-pretreated FW accelerated the H2 production to 406.2 ± 8.1 mL (L h)-1 and peaked the total H2 production and conversion yield to 4.6 ± 0.5 L L-1 and 234.6 ± 55.6 mL (g sugar)-1, respectively. These results exceeded in 63, 12 and 4%, respectively, the H2 productivity, total production and sugar conversion yield obtained under sterile conditions, and are encouraging for the future implementation of increasingly responsible waste valorisation practices.