Effect of surfactant assisted ultrasonic pretreatment on production of volatile fatty acids from mixed food waste

•Surfactant assisted UP reduced 27.5% of energy demand compared to UP alone.•Among four surfactants, Triton X100 led to the highest COD solubilization of 45.5%.•Surfactant assisted UP increased the VFAs’ yield by 1.1 to 1.9 times higher than those of controls.•The carbon conversion efficiency of food waste was enhanced by 83% due to pretreatment.•Acetic and propionic acid were the dominant VFAs.