The effect of thermal pretreatment (55-160 degrees C) on the degradation characteristics of kitchen waste during anaerobic fermentation at medium temperature was investigated. The breakdown of both organics and inorganics and the enhancement of biogas production in batch tests caused by thermal pretreatment during subsequent anaerobic fermentation were examined. Considering the effect of the acidification products and ammonia nitrogen in the acidification phase on subsequent biogas production, the influencing factors and related characteristics of various fermentation types were investigated. The results indicate that thermal pretreatment cannot only promote the anaerobic degradability of KW and the biogas production from MW but can also reduce the retention time necessary for anaerobic acidification by five days. At 50-70 degrees C and 140-160 degrees C, the biogas production and organic removal rates of the subsequent anaerobic digestion process decreased slightly, whereas at 90 and 120 degrees C, superior results were achieved during digestion. (c) 2014 Elsevier Ltd. All rights reserved.