Evaluation of biohydrogen yield potential and electron balance in the photo-fermentation process with different initial pH from starch agricultural leftover

•Photo-fermentation bio-H2 production from starch agricultural waste was analyzed.•Higher initial pH led to more substrates electrons were diverted to cell growth.•The optimal initial pH was 7 for HAU-M1 to produce H2 from starch food waste.•37.65% substrates electrons were diverted towards hydrogen at pH 7. Starch agricultural leftover is a potential substrate for photosynthetic bacteria to produce hydrogen. In this work, the effect of initial pH on photo-fermentation biohydrogen production process and electron balance were investigated. The modified Gompertz model was adopted, and hydrogen yield, sugar consumption and metabolite evolution were monitored with initial pH varying from 5 to 9. Results showed that hydrogen was produced mainly through acetic acid and butyric acid metabolism pathways when starch taken as carbon source. It was found that the maximum hydrogen yield (642 ± 22 mL) and highest hydrogen production rate (77.78 mL/(L·h)) were obtained at initial pH of 7. 37.65% substrates electrons diverted towards hydrogen. Lower hydrogen yield, hydrogen production rate and lower electrons diversion were obtained at other initial pH levels. Also, the lag phase time was 0.04 h when pH was 7, which was significantly lower than other levels.