Effective Coagulation Technology for Treatment of Grease Filter Washwater

The treatment of grease filter washwater by chemical coagulation and sedimentation using different dosages of aluminum sulfate was investigated. Pollutant removal efficiency was measured in terms of total solids, pH and optical density. The process was found to be effective at the room temperature and the filter washwater pH (9.5). The optimum aluminum sulfate dosage was 2 g/L. The treatment reduced the total solids of the wastewater by 89.6%, and produced a supernatant with a pH of 4.15 and an optical density of 0.194 nm. A fully automated prototype was then constructed for the treatment of grease filter washwater. Three distinct layers were formed in the system (fat, liquid and sludge) and each was removed separately. The system successfully recovered over 80% recyclable water with a quality comparable to that of tap water. The combined mixture of sludge and fat (20%) contained high levels of heavy metals and was not suitable for bioconversion into value added product. However, dewatering the sludge using vacuum filtration reduced its volume to 0.8% of the original volume of washwater. As a result, about 99.2% of the washwater (treated water) is recycled in the washing operation.