Enhancement of hydrogen production during waste activated sludge anaerobic fermentation by carbohydrate substrate addition and pH control

► The combined influences of carbohydrate/protein (CH/Pr) ratio and pH on hydrogen production have not been documented. ► The optimal pH changed with the CH/Pr ratio during sludge fermentation for hydrogen production. ► The maximal hydrogen production was achieved at CH/Pr of 5.0 and pH 8. ► Two-step pH control strategy further improved hydrogen production by 17.6% compared with that at CH/Pr 5.0 and pH 8.