The effects of ultrasonic and thermo-chemical pre-treatments on the methane production potential of anaerobic co-digestion with synthetic kitchen waste (KW) or fat, oil and grease (FOG) were investigated. Non-linear regressions were fitted to accurately assess and compare the methane production from co-digestion under the various pre-treatment conditions and to achieve representative simulations and predictions. Ultrasonic pre-treatment was not found to improve methane production effectively from either FOG co-digestion or KW co-digestions. Thermo-chemical pre-treatment could increase methane production yields from both FOG and KW co-digestions. COD solubilization was found to effectively represent the effects of pre-treatment. A comprehensive evaluation indicated that the thermo-chemical pre-treatments of pH = 10, 55 degrees C and pH = 8, 55 degrees C provided the best conditions to increase methane production from FOG and KW co-digestions, respectively. The most effective enhancement of biogas production (288 +/- 0.85 mL CH4/g TVS) was achieved from thermo-chemically pre-treated FOG co-digestion, which was 9.9 +/- 1.5% higher than FOG co-digestion without thermo-chemical pre-treatment. (C) 2012 Elsevier Ltd. All rights reserved.