Abstract
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.
Highlights
Wastewaters from food processing plants, restaurants and hospitals contain a wide variety of chemical, biological and physical constituents such as fat, meat, bone scraps, animal or fish entrails and excreta, blood and dairy wastes, pulp and peels of vegetable origin and detergents from washing [1]
Their compositions and contamination loads will vary greatly from one operation to another [2], they share several characteristics: (a) high strength compared to domestic wastewaters, (b) high concentrations of fats, oils and greases (FOG), soaps and waxes, (c) high biodegradability, (d) sufficient amount of nutrients such as nitrogen and phosphorous which are required for biological processes, (e) high concentrations of proteinaceous materials which deaminate to form large concentrations of ammonia in wastewater and (f) high concentrations of heavy metals, synthetic non-biodegradable organics, phthalates, pesticides (Dieldrin, Lindane, etc.), toluene, benzene, PAHs, acids, dioxins, furans, halogen compounds and pathogenic materials all of which are objectionable features of these wastes [1]
The total solids of the treated water was substantially lower than the washwater
Summary
Wastewaters from food processing plants, restaurants and hospitals contain a wide variety of chemical, biological and physical constituents such as fat, meat, bone scraps, animal or fish entrails and excreta, blood and dairy wastes, pulp and peels of vegetable origin and detergents from washing [1]. High concentrations of biodegradable materials in untreated food processing wastewaters will: (a) increase nutrient levels, which over-stimulate the growth of algae and other aquatic plants (blooms), (b) deplete dissolved oxygen as a result of decaying organic wastes, (c) increase sedimentation and chemical toxicity and (d) render water unfit for domestic, recreational and industrial use [2, 3, 4, 5, 6]. An example of these wastewaters is grease filter washwater. The washwater, which contains cleaning solution and grease particles, is fairly high in heavy metal content and pH and cannot be discharged directly to sewers or on land
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