Factors Affecting the Formation of Fats, Oils, and Grease Deposits in Sewer Systems and Fate of FOG Deposit Forming Precursors in Sewer Systems (original) (raw)

This Final Report combines the reports for the two WRRI projects, as they are related, and being conducted by the same research team (PIs, grad student and undergraduate assistants). The objective of the first project was to quantify the effects of kitchen wastewater characteristics on fat, oil, and grease (FOG) deposit formation mechanism and rate. The objective of the second project was to test the hypothesis that FOG formation in sewers is caused via a saponificationlike reaction involving major chemical precursors: free fatty acids, a metal cation, and surfactant. Thus, the overall goal of the combined projects was to determine the mechanism(s) of FOG deposit formation in sewer lines, and to elucidate the role of various factors in the deposit phenomenon, with the end-goal of understanding how to control sewer line blockages due to FOG formation. The projects used a variety of techniques and methods to achieve these goals. Initial experiments were aimed at exploring the interplay of various hypothesized factors, such as oil type, calcium, potassium, and attachment surface (e.g., concrete coupons), and were conducted in batch tests using a jar apparatus. In parallel, a pipe loop system simulating a sewer line was constructed. These experiments were designed to induce the formation of FOG deposits in lab-scale. After many attempts, FOG deposits were formed in a batch system using grease interceptor (GI) effluent from a restaurant. To our knowledge, this is the first time that FOG deposits have been formed under lab conditions. FTIR analysis showed that the FOG deposits were 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 proposed 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.