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.