Improving production of volatile fatty acids from food waste fermentation by hydrothermal pretreatment

•Hydrothermal pretreatment was applied to enhance VFAs production from food waste.•Food waste fermentation was inhibited at high hydrothermal temperature.•160 °C was found to be the optimal hydrothermal temperature for VFAs production.•High VFAs recovery was achieved by a liquid–liquid extraction method.

Food waste (FW) was pretreated by a hydrothermal method and then fermented for volatile fatty acid (VFAs) production. The soluble substance in FW increased after hydrothermal pretreatment (⩽200 °C). Higher hydrothermal temperature would lead to mineralization of the organic compounds. The optimal temperature for organic dissolution was 180 °C, at which FW dissolved 42.5% more soluble chemical oxygen demand than the control. VFA production from pretreated FW fermentation was significantly enhanced compared with the control. The optimal hydrothermal temperature was 160 °C with a VFA yield of 0.908 g/g VSremoval. Butyrate and acetate were the prevalent VFAs followed by propionate and valerate. FW fermentation was inhibited after 200 °C pretreatment. The VFAs were extracted from the fermentation broth by liquid–liquid extraction. The VFA recovery was 50–70%. Thus, 0.294–0.411 g VFAs could be obtained per gram of hydrothermally pretreated FW (in dry weight) by this method.