Understanding the FOG deposit adhesion mechanism on different sewer line surfaces

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UNC-WRRI;494;WRRI Project ; 20-05-W

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The adhesion of fat, oil, and grease (FOG) deposits in sewer pipes causes 25% of the Sanitary Sewer Overflow (SSOs) in the USA. Additionally, the sewer collection system in the U.S is old and requires replacement or renovation. One potential solution to the FOG deposit accumulation challenges in the collection systems is to design new sustainable sewer line construction materials that reduces the adhesion of these deposits on sewer pipe walls. Previous research has only reported the FOG deposit formation mechanism and the factors affecting those formations. Yet, no research has been performed to understand the FOG deposits adhesion mechanism. This study provides an improved understanding of the FOG deposit adhesion mechanism inside sewer lines by testing various materials, i.e., concrete, PVC, granite, limestone, and porous ceramic materials for a 30-day FOG deposit adhesion test. The test materials were prepared by varying a number of surface properties such as surface roughness, porosity, pH, and surface chemical composition. After analyzing the FOG deposit adhesion test results on various test materials, research results revealed that only the sewer line materials containing calcium as a strong electropositive Lewis acid bonding sites resulted in the FOG deposit adhesion on their surface. In addition, samples having high surface roughness, pH, and porosity also resulted in higher FOG deposit accumulation on their surfaces. The FTIR analyses of FOG deposits formed on different sewer line materials showed that a high fraction of saponified calcium soaps were formed on concrete samples. Moreover, the percent soap content of the FOG adhered on concrete samples exhibit a spatial variation with the layer adjacent to the concrete surface had a higher percentage saponification (82%) compared to the layer adjacent to the wastewater interface (38%). The result of this study encourages municipalities to avoid the use of sewer system cleaning process that damages the surface of sewer lines and introduces additional surface roughness. Also, a regular cleaning of sewer lines is encouraged to avoid the FOG build-up by rinsing the weakly adhered FOG deposits.



FOG ; SSOs ; Surface Roughness ; Collection System ; Fly Ash