Simultaneous coproduction of hydrogen and methane from sugary wastewater by an “ACSTRH–UASBMet” system

•A two-phase “ACSTRH–UASBMet” system was established in this study.•The optimum HRT of acidogenic and methanogenic reactor was determined.•Total energy recovery and conversion rate of substrate were calculated.•Sugary wastewater was promising for hydrogen and methane coproduction.

A two-phase “ACSTRH–UASBMet” system has been investigated at the stepwise decreased HRT for the simultaneous production of hydrogen and methane in this study. Hydrogen could be continuously produced from the two-phase hydrogen fermentation of sugary wastewater in ACSTR and effluents from hydrogen fermentation were converted into methane in UASB reactor. At optimum conditions (HRTH: 5 h, HRTMet: 15 h), the highest hydrogen production rate of 5.69 (±0.06) mmol L−1 h−1 was obtained from sugary wastewater and methane was continuously produced from effluents of hydrogen fermentation with a production rate of 3.74 (±0.13) mmol L−1 h−1. The total bioenergy recovery by coproduction of hydrogen and methane from sugary wastewater reached 19.37 W and a total of 92.41% of substrate was converted to the biogas (hydrogen and methane) with two-phase anaerobic fermentation.