Sequential System for Hydrogen and Methane Production from Sucrose Wastewater: Effects of Substrate Concentration and Addition of FE2+ Ions

A two-stage system is used for hydrogen (H2) and methane (CH4) production from sucrose wastewater. The H2- producing reactor is operated at pH, temperature (T) and hydraulic retention time (HRT) of 5.5, 35 ◦C, 24 h, respectively. While, operating conditions of 7–8 pH, 35 ◦C T and 144 h HRT are used to conduct the CH4 production stage. The effects of two different parameters as sucrose concentration (5, 10 and 20 g/L) and addition of ferrous ions (60 and 120 mg/L) are investigated. Both H2 and CH4 productions are increased at high sucrose concentrations. However, the optimum H2 and CH4 yields of 163.2 mL-H2/g-sucrose and 211.8 mL-CH4/g-TVS are obtained at 5 g-sucrose/L. At 5 g-sucrose/L, addition of Fe2+ increases the H2 yield to 192.5 and 176.2 mLH2/g-sucrose corresponding to 60 and 120 mg-Fe2+/L, respectively. Higher removal efficiencies and total energy recovery are measured using the two-stage system than the single-stage reactor.