Ferric oxide/date seed activated carbon nanocomposites mediated dark fermentation of date fruit wastes for enriched biohydrogen production

Abstract Biohydrogen production from biomass waste, not only addresses the energy demand in a renewable manner but also resolves the safe disposal issues associated with these biowastes. Also, scalable and low-cost techniques to enhance biohydrogen production have gained more attraction and are highly explored. In this research work, date-palm fruit wastes have been studied for their biohydrogen production potential using Enterobacter aerogenes by dark fermentation. Hydrogen yield and productivity were improved through the addition of iron oxide nanoparticles (Fe3O4 NPs) and its date seed activated carbon nanocomposites (Fe3O4/DSAC) to the fermentation media. Studies on discrete inclusions of these NPs showed that the appropriate dosage of NPs promoted, while higher dosages repressed the hydrogen production performance. Optimal dosage and fermentation time was observed as 150 mg/L and 24 h for both the additives. Fe3O4/DSAC nanocomposites showed better hydrogen production enhancement than Fe3O4 NPs. Maximum hydrogen yield of 238.7 mL/g was obtained for the 150 mg/L nanocomposites, which was 65.7% higher than that of the standalone Fe3O4 NPs and three folds higher than the yield of the control run without any NPs inclusion (78.4 mL/g). Metabolites analysis showed that the hydrogen evolution followed the ethanol-acetate pathway. Formation levels of longer chain propionate and butyrate co-metabolites were significantly low in the presence of Fe3O4/DSAC than Fe3O4. The carbon support in the nanocomposites acted as an adsorbent-buffer, which favored the medium pH in-addition to the stimulatory effects of Fe3O4 NPs. Cell growth and specific hydrogenase activity analysis were also performed to supplement the hydrogen production results. Gompertz and modified Logistic kinetic models were employed for kinetic modeling of experimental hydrogen production values. The Fe3O4/DSAC nanocomposites exhibited significant application potential for the production of biohydrogen from date fruit wastes.