Simultaneous hydrogen and ethanol production from sweet potato via dark fermentation

The externally seeding strategy could enhance the hydrogen production from sweet potato with peak cumulative H2 production potential (HP) of 120 mmol H2/L-reactor using sewage sludge. However, the cow dung seed showed more ethanol production than hydrogen with peak concentration of 12,146 mg COD/L. Increasing the sweet potato concentration could enhance the HPR and HP values. Maximum HY of 1.24 mol H2/mol hexose was obtained at a substrate concentration of 150 g/L with an initial cultivation pH of 6.7 and particle diameter <1.19 mm using sewage sludge. The HPRmax, HY and HP values were affected slightly by the variations in sweet potato particle size. The peak total energy production yield of 1625 J/g sweet potato was obtained with sweet potato concentration of 150 g/L at pH 8.5 using sewage sludge.