ARS | Publication request: Evidence for fat, oil and grease (FOG) deposit formation mechanisms in sewer lines

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 8, 2011
Publication Date: May 14, 2011
Citation: He, X., Iasmin, M., Dean, L.L., Lappi, S., Ducoste, J.J., De Los Reyes, F.L. 2011. Evidence for fat, oil and grease (FOG) deposit formation mechanisms in sewer lines. Journal of Environmental Science and Technology. 1545(10):4385-4391.

Interpretive Summary: Sanitary sewer lines are subject to overflows causing pollution and conditions of health hazards due to blockages. These blockages are often due to food greases and fats being disposed of into drains at food service establishments and apartment complexes. This work used model systems to try to reproduce these conditions in the laboratory by combining free fatty acids and calcium chloride. The basis for this idea is that free fatty acids are compounds produced by the breakdown of food fats and soap products. When these compounds combine with calcium that can be present in concrete sewer lines, insoluble products will form that can enlarge and then cause blockages in the lines and subsequently backups and overflows of sewage. By comparison of material removed from actual blockages to those created in the laboratory, it was proven that this was the actually how the blockages were being formed.

Technical 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.