Biological fermentative hydrogen and ethanol production using continuous stirred tank reactor

Hydrogen and ethanol are promising biofuels and have great potential to become alternatives to fossil fuels. The influence of organic loading rates (OLRs) on the production of fermentative hydrogen and ethanol were investigated in a continuous stirred tank reactor (CSTR) from fermentation using molasses as substrate. Four OLRs were examined, ranging from 8 to 32 kg/m3·d. The H2 and ethanol production rate in CSTR initially increased with increasing OLR (from 8 to 24 kg/m3 d). The highest H2 production rate (12.4 mmol/h l) and ethanol production rate (20.27 mmol/h l) were obtained in CSTR both operated at OLR = 24 kg/m3 d. However, the H2 and ethanol production rate tended to decrease with an increase of OLR to 32 kg/m3 d. The liquid fermentation products were dominated by ethanol, accounting for 31–59% of total soluble metabolities. Linear regression results show that ethanol production rate (y) and H2 production rate (x) were proportionately correlated which can be expressed as y = 0.5431x + 1.6816 (r2 = 0.7617). The total energy conversion rate based on the heat values of H2 and ethanol was calculated to assess the overall efficiency of energy conversion rate. The best energy conversion rate was 31.23 kJ/h l, occurred at OLR = 24 kg/m3 d.