The following reagents, all in AR grade, were used for the experiments: anhydrous methanol (Apex Co. Ltd, >99.8%) for the esterification reaction, sulfuric acid (Labsystem, 98% purity) as catalyst. The mixing scum (fats, oil and grease, FOG) was collected from in-ground grease trap tanks that are installed between wastewater effluent points and the sewer system. Major source of wastewater entering grease traps came from commercial restaurants that are located in the PTT gas service station and retail business, a rest area of Thailand’s First Stage Expressway System (PTT Park, inbound and out- bound route of Bang Na-Bangkok Port Expressway). Before using the trap grease for biodiesel production, it was filtered with the muslin and then air-dried to get rid of water.