4. Conclusions
With molasses as substrate, the effect of HRT on biohydrogen production and operational stability of ethanol-type fermen- tation was studied in CSTR system. At HRT of 5 h, the highest HPR 12.27 mmol L1 h1 was obtained from ethanol-type fer- mentation in the pH range of 4.3e4.4. During the whole operation process, ethanol, butyrate and acetate were the predominant metabolites. A total COD concentration of ethanol and acetate accounted for above 73.3%of total soluble microbial products. The dual recovery of hydrogen and etha- nol from ethanol-type fermentation was promising to improve energy production rate and economic profit. The fermentative hydrogen system operated at HRT ¼ 5 h exhibi- ted the best energy production rate of 15.50 kJ L1 h1.