Simultaneous biohydrogen and bioethanol production from anaerobic fermentation with immobilized sludge

The effects of organic loading rates (OLRs) on fermentative productions of hydrogen and ethanol were investigated in a continuous stirred tank reactor (CSTR) with attached sludge using molasses as substrate. The CSTR reactor with attached sludge was operated under different OLRs, ranging from 8 to 24 kg/m(3)·d. The H(2) and ethanol production rate essentially increased with increasing OLR. The highest H(2) production rate (10.74 mmol/h·L) and ethanol production rate (11.72 mmol/h·L) were obtained both operating at OLR = 24 kg/m(3)·d. Linear regression results show that ethanol production rate (y) and H(2) production rate (x) were proportionately correlated and can be expressed as y = 1.5365x - 5.054 (r(2) = 0.9751). The best energy generation rate was 19.08 kJ/h·L, which occurred at OLR = 24 kg/m(3)·d. In addition, the hydrogen yield was affected by the presence of ethanol and acetic acid in the liquid phase, and the maximum hydrogen production rate occurred while the ratio of ethanol to acetic acid was close to 1.