Butanol and hydrogen gas are main products in butanol production by solventogenic Clostridia. Effects of pH and ferrous iron on hydrogen and butanol production by Clostridium beijerinckii IB4 were investigated in this work. With the increasing of the pH value, the hydrogen yields increased during acidogenic phase and decreased during solventogenic phase. Compared with the process without pH control, butanol and hydrogen increased by 15.43% and 11.77%, respectively, when pH was controlled at 5.2. Under the control of pH at 5.2 and supplementation of 250 mg/L of FeSO4 center dot 7H(2)O, the maximum hydrogen quantity of 8.24 L/L was obtained, and hydrogen productivity achieved 187 mL/L/h with yield of 145 mL/g glucose, which increased by 65%, 46% and 37%, respectively. However, butanol yield was reduced slightly by 4.8%. The reducing power was enhanced in solventogenic phase with supplementation of 250 mg/L FeSO4 center dot 7H(2)O, and the energy content of fuel produced in this process also remained stable. These results indicated that hydrogen production was enhanced by pH control and ferrous iron regulation, and butanol production performance was also maintained, which was favorable for coproduction of butanol and hydrogen in ABE fermentation. (C) 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.