Properties Influencing Fat, Oil, and Grease Deposit Formation

Abstract

Fat, oil, and grease (FOG) deposits are the reported cause of 50 to 75% of sanitary sewer overflows in the United States, resulting in 1.8 3 10 6 m 3 (500 mil. gal) of raw wastewater released into the environment annually. The objective of this research was to characterize the chemical and physical properties of FOG deposits. Twenty-three cities from around the United States contributed FOG samples for the study. The FOG deposits showed a wide range in yield strength (4 to 34 kPa), porosity (10 to 24%), and moisture content (10 to 60%), suggesting uncontrolled formation processes. A majority of these deposits display hard, sandstonelike texture, with distinct layering effects, suggesting a discontinuous formation process. The results found that 84% of FOG deposits contained high concentrations of saturated fatty acids and calcium, suggesting preferential accumulation. Water Environ. Res., 80, 2241Res., 80, (2008.

Efficient Fractionation and Analysis of Fatty Acids and their Salts in Fat, Oil and Grease (FOG) Deposits

“…These high levels of saturated fatty acids in FOG deposits indicate that selective deposition of both saturated acid salts and saturated fatty acids occurred during deposition of FOG deposits since typical cooking oils and animal fats contain significantly lower levels of saturated fatty acids. Palmitic acid is the predominant saturated fatty acid in both cooking oils and animal fats 10 . However, it can be seen that the concentrations of palmitic acid and its salts were 4-5 times higher than concentrations of stearic acid and its salts in these FOG deposits.…”

“…We postulate that after FOG growth has been initiated by the selective preferential precipitation of stearic acid salts, continued deposition will be less selective and other available varieties of fatty acid salts and fatty acids can precipitate on these seed crystals based on their relative availabilities. Interestingly, it has been demonstrated that oleic acid, the major unsaturated fatty acid in both cooking oils and animal fats 10 , undergoes biologically induced cleavage/reduction in estuary sediments to form palmitic acid and stearic acid that are in equilibrium with each other 12 . If these phenomena occur in sewer systems, the stearic acid undergoing equilibration could be captured by available calcium ions to provide an additional source for preferential calcium stearate precipitation.…”

Problems, Control, and Treatment of Fat, Oil, and Grease (FOG): A Review

“…Sodium oleate decreases the interfacial tension between the frying oil and the thin layer of water on the surface of the fried food, causing migration of the polar lipids from the frying oil to the fried food. Moreover, sodium soaps stimulate the foaming of frying oil and thus accelerate its oxidation 24 . The oxidation reaction, which is promoted by heat, light, and heavy metals, is a radical chain reaction that occurs rapidly under the frying conditions.…”

“…However, based on the evaluations of vitrified clay pipes VCP , which are used in some countries such as Malaysia, it was found that FOG deposition is not due primarily to the presence of calcium, but can be related to other minerals such as sodium and potassium. Moreover, the presence of high amounts of calcium and sodium in FOG deposits indicates that the deposit not only consist of FOG but also of metallic soaps formed during the hydrolysis reaction 5,23,24 . The aforementioned studies focused on the effect of calcium CaCO 3 on the formation of FOG deposits in sewer pipelines.…”

Impact of water source management practices in residential areas on sewer networks – a review

“…FOGs in sewer systems mostly originate from kitchens (food production) and showers (the use of soap) (Keener et al 2008). FOGs are very slowly digested and degraded by microorganisms (Cammarota & Freire 2006;Wakelin & Forster 1997).…”