Salinity impact on the metabolic and taxonomic profiles of acid and alkali treated inoculum for hydrogen production from food waste

This study evaluated the combined impact of salinity (2.5, 13, and 19.3 g NaCl/L) and inoculum pretreatment (acid/alkali) on the genomic and metabolic profiles of mesophilic fermentative bacteria for hydrogen (H2) production from food waste. Experimental results revealed that acid-treated inoculum showed the highest H2 yield (201.12 ± 13.84 mL H2/g of volatile solids added) under medium salinity levels compared to other experimental conditions. A 7–56% increase in H2 yield was observed for pretreated inoculum than untreated inoculum. Genomic analysis and metabolic pattern revealed that the H2 production was mainly through Clostridial-type fermentation under medium to high salinity levels, whereas Enterococcus-type fermentation under low salinity levels. Further, the genomic analysis uncovered that phyla Firmicutes (69.71–96.81%) and genus Clostridium sensu stricto 1 (33.28–94.04%) dominated during the exponential gas production phase. Overall, this study showed the significance of inoculum pretreatment for the bioconversion of food waste at different salinity levels.