Effect of graphene oxide and biochar as redox mediators addition on photo-fermentation biohydrogen production

The addition of graphene oxide promotes electron transfer between microorganisms in a photo-fermentative biohydrogen production system, while biochar improves the efficiency of hydrogen production by buffering the pH. In order to improve the efficiency of biohydrogen production, the effects of two redox mediators (ROMs), biochar and graphene oxide, at different concentrations on photo-fermentation biohydrogen production were studied. The results showed that the addition of graphene oxide and biochar decreased the redox potential (ORP) of the system. The lowest ORP was -286 mV (graphene oxide) and -290 mV (biochar), which represent that the reducing power of fermentation broth increased. When the addition of graphene oxide was 150 mg/L, the cumulative biohydrogen production reached the maximum of 404 mL, which was 46.3% higher than that of the control group without graphene oxide; When biochar was added at 1 g/L, the cumulative biohydrogen production reached the maximum of 383 mL, which was 45.9% higher than that of the control group. At the same time, the cumulative biohydrogen production was fitted by Gompertz equation, indicating that the kinetic parameters were very suitable to describe the effect of the addition of graphene oxide and biochar on the biohydrogen production from corn stalks by photo-fermentation.