The anaerobic biodegradability of a Mix Of Municipal primary sludge (PS), thickened waste activated sludge (TWAS) and fat, oil, and grease (FOG) was assessed using semi-continuous feed, laboratory-scale anaerobic digesters operated at mesophilic (35 IQ and thermophilic (52 IQ temperature. Addition of a large FOG fraction (48% of the total VS load) to a PS + TWAS mix, resulted in 2.95 times larger methane yield, 152 vs, 449 mL methane @ STP/g VS added at 35 degrees C and 2.6 times larger methane yield, 197 vs. 512 mt. methane @ STP/g VS added at 52 degrees C. The high FOG organic load fraction was not inhibitory to the process. The results of this study demonstrate the benefit Of Sludge and FOG codigestion. (C) 2009 Elsevier Ltd. All rights reserved.