Synergistic interaction of tween 20 and magnesium@ functionalized graphene oxide nano-composite for dual productivity of biohydrogen and biochar from onion peel waste

Abstract

This study aimed at developing a novel nano-composite enhancing fermentation/pyrolysis strategy for dual productivity of biohydrogen and biochar from onion peel waste (OPW). Biohydrogen productivity was maximized by adding tween 20 (T20) and magnesium@ functionalized graphene oxide (Mg@FGO) onto the fermentation of OPW. Three semi-continuous stirred tank reactors (CSTR1, CSTR2 and CSTR3) were respectively supplemented with OPW (control), OPW + T20, and OPW + T20+Mg@FGO and operated at constant retention time of 4.0 d. The hydrogen production rate (HPR) of 343.2 ± 36.2 mL/L/d and hydrogen yield (HY) of 30.30 ± 4.6 mL/g CODadded was obtained by CSTR2 which were greater than those achieved in the control (CSTR1) by 2-folds. Further improvement of H2 productivity >200% was achieved in CSTR3 supplemented with T20+Mg@FGO compared with CSTR1. The addition of T20+Mg@FGO in CSTR3 enhanced acetate fermentation pathway, the enzymatic activities and the biodegradation of phenolic compounds. Moreover, microbial diversity analysis of CSTR3 showed the dominance of the H2-producing bacteria related to Firmicutes, Planctomycetes, and Proteobacteria. Further, digestates collected from the CSTR3 were pyrolyzed at temperature of 550 °C, delivering biochar having multiple surface functional groups. Results confirm that adding T20+Mg@FGO onto the fermentation of OPW followed by digestate pyrolysis could be a sustainable strategy for fulfilling the renewable energy requirements.