Effect of Fe2+Fe2+ concentration on fermentative hydrogen production by mixed cultures

The effect of the Fe2+Fe2+ concentrations ranging from 0 to 1500 mg/L on the fermentative hydrogen production from glucose was investigated in batch tests by mixed cultures at 35 °C and initial pH 7.0. The experimental results showed that in certain concentration range, Fe2+Fe2+ was able to enhance the hydrogen production rate, the cumulative hydrogen quantity, and the hydrogen yield by the mixed cultures. The maximum cumulative hydrogen quantity of 302.3 mL and the maximum hydrogen yield of 311.2 mL/g glucose were obtained at the Fe2+Fe2+ concentration of 300 and 350 mg/L, respectively. The major soluble metabolites produced by the mixed cultures were ethanol, acetic acid, and butyric acid, with little or no propionic acid. The glucose degradation efficiency had the trend to decrease with increasing Fe2+Fe2+ concentrations from 0 to 1500 mg/L, but when the Fe2+Fe2+ concentrations were lower than 350 mg/L, the glucose degradation efficiency was between 96.25 and 98.78%, which is relatively high and kept unchanged with increasing Fe2+Fe2+ concentrations. In certain concentration range, Fe2+Fe2+ was able to enhance the biomass production yield. When the Fe2+Fe2+ concentrations were between 100 and 750 mg/L, there was a high biomass production yield plateau ranging from 259.2 to 334.2 mg/g glucose. The final pH value had the trend to decrease with increasing Fe2+Fe2+ concentrations from 0 to 1000 mg/L, and the lowest final pH value was about 4.3 at the Fe2+Fe2+ concentration of 1000 mg/L.