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ARS Home » Southeast Area » Raleigh, North Carolina » Market Quality and Handling Research » Research » Publications at this Location » Publication #294021

Title: Factors That Influence Properties of FOG Deposits and Their Formation in Sewer Collection Systems.

item LASMIN, MAHBUBA - North Carolina State University
item Dean, Lisa
item LAPPI, SIMON - North Carolina State University
item DUCOSTE, JOEL - North Carolina State University

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2013
Publication Date: 11/21/2013
Citation: Lasmin, M., Dean, L.L., Lappi, S.E., Ducoste, J.J. 2013. Factors That Influence Properties of FOG Deposits and Their Formation in Sewer Collection Systems.. Water Research. 49: 92-102.

Interpretive Summary: Blockages in sanitary sewers are often the result of fats and oils from food passing into the systems from food service establishments such as restaurants. These blockages cause environmental and public safety problems when they cause the sanitary sewers to overflow. How these blockages form is important information needed to prevent their production. Laboratory studies have found them to be the result of food fats forming soaps with calcium present in sewer lines. The most important factors in their formation was found to be the temperature and acidity of the water in the sewers and the calcium present to form the blocking material and how easily the calcium goes into solution so that it can combine with the food fats present to form the soap like compounds.

Technical Abstract: Understanding the formation of Fat, Oil, and Grease (FOG) deposits in sewer systems is critical to the sustainability of sewer collection systems since they have been implicated in causing sewerage blockages, which eventually lead to sanitary sewer overflows (SSOs). Recently, FOG deposits in sewer systems were found to have strong similarities with calcium-based fatty acid salts as a result of the chemical reaction called saponification. The objective of this study was to quantify the factors that may affect the formation of FOG deposits and their chemical and rheological properties. These factors included the types of fats used in Food Service Establishments (FSE’s), environmental conditions (i.e. pH and temperature), and the source of calcium in sewer systems. The results of this study showed that rheological properties of calcium-based fatty acid salts depend upon the solubility of the calcium source, which is related to pH and temperature of the system. The fatty acid profiles of the calcium-based fatty acid salts produced under alkali driven hydrolysis were identical to the profile of the fat source and did not match the profile of field FOG deposits, which displayed a high fraction of palmitic, a long chain saturated fatty acid. It is hypothesized that selective microbial metabolism of fats and/or biologically induced hydrogenation may contribute to the FOG deposit makeup in sewer systems. Therefore, selective removal of palmitic in pretreatment processes may be necessary prior to the discharge of FSE wastes into the sewer collection system.