Enhancement of biohydrogen production from sustainable orange peel wastes usingEnterobacterspecies isolated from domestic wastewater

Abstract

Five facultative anaerobic bacterial isolates were recovered from domestic wastewater. These isolates were identified based on the 16S rRNA as Enterobacter aerogenes (one isolate), Enterobacter cloacae (two isolates), and Cronobacter sakazakii (three isolates). These isolates were examined for their potential to evolve hydrogen on a glucose medium. The most potent hydrogen-producing isolates, E aerogenes (KY549389) and E cloacae (KY524293), were examined for their capacity to generate hydrogen, acetone, butanol, and ethanol using orange peel (OP) hydrolysate. OP powder was pretreated with n-hexane to remove the toxicity of d-limonene. Different concentrations (4%, 6%, and 8% w/v) of limonene-free OP were subjected to the boiling water (temperature of 100°C) or acid (HCl) treatments. The maximum fermentative H2 production of 1700 and 1620 mL/L was obtained from 6% OP hydrolysate extracted with boiling water using facultative anaerobic E aerogenes (KY549389) and E cloacae (KY524293), respectively. Hydrogen production efficiency was 0.99 and 1.19 mol H2/mol glucose for E aerogenes and E cloacae, respectively. The total fermentative acetone, butanol, and ethanol (ABE) generated by E aerogenes and E cloacae were 0.78 and 0.38 g/L including acetone (0.05 and 0.04 g/L), butanol (0.011 and 0.013 g/L), and ethanol (0.71 and 0.32 g/L), respectively. The maximum ABE productivity was 0.01 and 0.005 g/L/h generated at 60 g/L OP hydrolysate by E aerogenes and E cloacae, respectively. These strains were positive for nitrogen fixation (nitrogenase) capability estimated by the acetylene reduction assay. Application of OP hydrolysate without the addition of any nutritional components or reducing agent is considered an eco-friendly, economical, and commercial substrate for desired biofuel production.