Sustainable bioenergy production from tofu-processing wastewater by anaerobic hydrogen fermentation for onsite energy recovery

The conversion efficiency of tofu-processing wastewater (TPW) into hydrogen and ethanol for energy source in a tofu-making factory was evaluated by testing various sludge types, initial cultivation pH values, temperatures and substrate concentrations. Experimental results indicated that a peak H2 production yield (HY) of 107.5 mL-H2/g COD and ethanol concentration of 2181 mg-COD/L were at 35 °C, TPW concentration 20 g-COD/L and pH 5.5–6.0 in batch tests. Peak H2 production rate of 1.73 L H2/L-d was obtained at HRT 8 h in a CSTR. Main soluble metabolic products were acetate and butyrate during TPW fermentation. The peak total energy (H2 and ethanol) production efficiency of 485 J/g COD (160 J/g COD from H2 and 325 J/g COD from ethanol) and rate of 43.3 kJ/L-d (19.6 kJ/L-d from H2 and 23.7 kJ/L-d from ethanol) were obtained at HRT 12 and 8 h, respectively. This could support up to 3.5% of the annual energy consumption in a tofu-making factory and also reduce the carbon dioxide emission up to 6.65 ton CO2 equivalents/y.