Addition of air-nanobubble water to mitigate the inhibition of high salinity on co-production of hydrogen and methane from two-stage anaerobic digestion of food waste

Most previous studies have focused on the effects of salt on anaerobic digestion (AD) for hydrogen or methane production. However, the effects of salt on two-stage AD and the related approaches to mitigate the adverse effects of high salinity on hydrogen and/or methane production were seldom addressed. In this study, addition of Air-nanobubble water (Air-NBW) was adopted to mitigate the inhibition of high salinity on co-production of hydrogen and methane from two-stage AD of food waste (FW). In the Air-NBW added reactors with 0–30 g NaCl/L, hydrogen yield was increased by 21–65% with the subsequent methane yield elevated by 14–43% when compared to the corresponding deionized water (DW) group. This study for the first time confirmed that when two-stage AD of FW was exposed to the same salinity level, addition of Air-NBW could enhance enzymatic activities at the individual stage. Results of electron transport system (ETS) activity further demonstrate that addition of Air-NBW may promote the electron transfer associated with the synthesis of hydrogen and methane. Therefore, an efficient approach for hydrogen and methane recovery from the two-stage AD of FW under high salinity was proposed through improving microbial electron transfer and corresponding enzymatic activities at each stage via Air-NBW addition.