Single and combined effect of various pretreatment methods for biohydrogen production from food waste

Four individual pretreatment methods: ultrasonication, heat, acid, and base and three combined pretreatment methods comprising ultrasonication with heat (UH), ultrasonication with acid (UA), and ultrasonication with base (UB) were applied on the food waste. The effect of the seven pretreatment methods on food waste solubilization was first evaluated, and then batch experiments were conducted for biohydrogen production without using extra seed. UB pretreatment achieved the highest increase in soluble chemical oxygen demand (SCOD) and soluble protein of 33% and 40%, respectively. The highest increase in soluble carbohydrate of 31% was observed for UA pretreatment. Among the four individual pretreatment methods, ultrasonic pretreatment produced the highest hydrogen yield (as mL hydrogen per g initial volatile solid) of 97 mL/g VSinitial, while the lowest hydrogen yield of 46 mL/g VSinitial was observed for base pretreatment. In case of combined pretreatment methods, UA pretreatment had a positive effect on hydrogen production reflected by the highest hydrogen yield of 118 mL/g VSinitial. While UH and UB pretreatments had a negative impact on hydrogen yield reducing it from 97 mL/g VSinitial for ultrasonic only to 78 mL/g VSinitial for UH pretreatment and to 67 mL/g VSinitial for UB pretreatment. A hydrogen yield of 42 mL/g VSinitial was observed for the untreated food waste. UA had the highest final volatile fatty acids (VFAs) concentrations of 16,900 mg COD/L as well as highest acetate to butyrate (HAc/HBu) molar ratio of 1.87, while base pretreatment had the lowest final VFAs of 9700 mg COD/L and the lowest HAc/HBu ratio of 0.61.