Effects of ultrasonic and thermo-chemical pre-treatments on methane production from fat, oil and grease (FOG) and synthetic kitchen waste (KW) in anaerobic co-digestion

► Ultrasonic pre-treatment cannot effectively enhance biogas production. ► Ultrasonic pre-treatment introduced inhibitory effects on FOG co-digestion. ► Thermo-chemical pre-treatment enhanced biogas production from co-digestions. ► Non-linear regressions can accurately simulate and support discussion. ► COD solubilization (SCOD/COD%) can effectively reflect pre-treatment performance.