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ARS Home » Southeast Area » Raleigh, North Carolina » Market Quality and Handling Research » Research » Publications at this Location » Publication #297212
Title: Understanding the Spatial Formation and Accumulation of Fats, Oils & Grease Deposits in the Sewer Collection System

Author
item DOMINIC, CHRISTOPHER - North Carolina State University
item SZAKASITS, M - North Carolina State University
item Dean, Lisa
item DUCOSTE, J - North Carolina State University

Submitted to: Water Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2013
Publication Date: 10/15/2013
Citation: Dominic, C.C., Szakasits, M.E., Dean, L.L., Ducoste, J.J. 2013. Understanding the Spatial Formation and Accumulation of Fats, Oils & Grease Deposits in the Sewer Collection System. Water Science and Technology. 68.8:1830-1836.

Interpretive Summary: When deposits of food grease build up in wastewater systems, the sanitary sewers overflow. All areas of the sewer lines are not the same due to changes that have to be made to accommodate the placement of the lines and natural changes that occur due to tree growth and street settling with time. This study examined the differences in the materials that form the deposits due to the differences in the makeup of the sewer lines. Since the acidity of the material discharged also changes, different levels of acidity were tested as well. It was found that unsaturated fatty acids common to liquid oils are less likely than saturated fatty acid found in solid fats to become incorporated into the sewer blockages.

Technical Abstract: Sanitary sewer overflows are caused by the accumulation of insoluble calcium salts of fatty acids, which are formed by the reaction between fats, oils and grease (FOG) and calcium found in wastewaters. Different sewer structural configurations (i.e., manholes, pipes, wet wells), which vary spatially, along with other obstructions (roots intrusion) and pipe deformations (pipe sags), may influence the detrimental buildup of FOG deposits. The purpose of this study was to quantify the spatial variation in FOG deposit formation and accumulation in a pilot-scale sewer collection system. The pilot system contained straight pipes, manholes, roots intrusion, and a pipe sag. Calcium and oil were injected into the system and operated at alkaline (pH = 10) and neutral (pH = 7) pH conditions. Results showed that solid accumulations were slightly higher at neutral pH. Fourier Transform Infrared (FTIR) analysis on the solids samples confirmed that the solids were indeed calcium-based fatty acid salts. However, the fatty acid profiles of the solids deviated from the profile found from FOG deposits in sewer systems, which were primarily saturated fatty acids. These results confirm the work done previously by researchers and suggest an alternative fate of unsaturated fatty acids that does not lead to their incorporation in FOG deposits in full-scale sewer systems.