Potential use and the energy conversion efficiency analysis of fermentation effluents from photo and dark fermentative bio-hydrogen production

- Photo- and dark-fermentation bio-hydrogen production processes were conducted.
- The fermentation effluent was adopted for bio-methane production.
- Energy conversion efficiencies of different fermentation procedures were calculated.
- Cogeneration of bio-hydrogen and bio-methane increases energy conversion efficiency.

Effluent of bio-hydrogen production system also can be adopted to produce methane for further fermentation, cogeneration of hydrogen and methane will significantly improve the energy conversion efficiency. Platanus Orientalis leaves were taken as the raw material for photo- and dark-fermentation bio-hydrogen production. The resulting concentrations of acetic, butyric, and propionic acids and ethanol in the photo- and dark-fermentation effluents were 2966 mg/L and 624 mg/L, 422 mg/L and 1624 mg/L, 1365 mg/L and 558 mg/L, and 866 mg/L and 1352 mg/L, respectively. Subsequently, we calculated the energy conversion efficiency according to the organic contents of the effluents and their energy output when used as raw material for methane production. The overall energy conversion efficiencies increased by 15.17% and 22.28%, respectively, when using the effluents of photo and dark fermentation. This two-step bio-hydrogen and methane production system can significantly improve the energy conversion efficiency of anaerobic biological treatment plants.