Evidence for Fat, Oil, and Grease (FOG) Deposit Formation Mechanisms in Sewer Lines

Abstract

The presence of hardened and insoluble fats, oil, and grease (FOG) deposits in sewer lines is a major cause of line blockages leading to sanitary sewer overflows (SSOs). Despite the central role that FOG deposits play in SSOs, little is known about the mechanisms of FOG deposit formation in sanitary sewers. In this study, FOG deposits were formed under laboratory conditions from the reaction between free fatty acids and calcium chloride. The calcium and fatty acid profile analysis showed that the laboratory-produced FOG deposit displayed similar characteristics to FOG deposits collected from sanitary sewer lines. Results of FTIR analysis showed that the FOG deposits are metallic salts of fatty acid as revealed by comparisons with FOG deposits collected from sewer lines and pure calcium soaps. Based on the data, we propose that the formation of FOG deposits occurs from the aggregation of excess calcium compressing the double layer of free fatty acid micelles and a saponification reaction between aggregated calcium and free fatty acids.

Impacts and managerial implications for sewer systems due to recent changes to inputs in domestic wastewater – A review

“…Keener et al (2008) observed layering effects in larger FOG-deposits where sediment and other debris were found interspersed between the hardened soap layers and also reported that mineral deposits could be mistakenly identified as FOG. As long retention times has been reported for the necessary chemical reactions to occur and the actual deposits to form (He et al, 2011) the formation of FOG deposits will most likely occur in sewers with low flow velocities (Water Research Center, 2009). Dirksen et al (2013b) analysed plastic sewers (235 mm in diameter) with respect to sagging serving mainly residential areas in Amsterdam, Netherlands.…”

“…As in particular, palmitic acid has been shown to be involved in the formation mechanisms of FOG-deposits in sewers (He et al, 2011;Williams et al, 2012), Iasmin et al (2014) recommended selective removal of this oil in pre-treatment processes prior to any discharge of FOG-rich wastewater to sewers. Collection of FOG in jars distributed to individual households has been evaluated in field studies in Europe.…”

“…However, recent research has indicated a more complex chain of events is required for the actual formation to occur. Studies carried out in the U.S have indicated that FOGdeposits essentially are composed of metallic soaps due to a saponification process involving calcium and free fatty acids (He et al, 2011;Keener et al, 2008). The most recent studies have largely supported these observations although they have also found greater diversification in compositional structure among FOGdeposits (He et al, 2013;Iasmin et al, 2014;Williams et al, 2012).…”

Modifying the ADM1 Model to Predict the Operation of an Anaerobic Digester Co-digesting Municipal Sludge with Bakery Waste

“…Lipids degrade to long chain fatty acids by bacterial activities, and high concentrations of long chain fatty acids are inhibitory to anaerobic microorganisms (Tritt 1992). Lipid-rich material like food wastes from restaurants is not appropriate for municipal digesters since it can readily accumulate inside the digester walls, forming hardened deposit material and reducing the digester volume capacity (He et al 2011). BW, on the other hand, are not sufficiently lipid -or proteins-rich to cause this problem.…”

Recovery strategies of inhibition for mesophilic anaerobic sludge treating the de-oiled grease trap waste

“…Landfill of this waste is no longer permitted in many jurisdictions (Razaviarani et al, 2013). The direct drainage into the collection system is also illegal in most municipalities, because it can accumulate on pipe walls, and potentially form hardened deposits through a chemical reaction or a physical aggregation process (He et al, 2011). It was responsible for up to 47% of the reported blockages and 50e75% of sanitary sewer overflows as it tends to solidify, reduce conveyance capacity, and eventually block flow (Wang et al, 2013;Iasmin et al, 2014).…”