title: Mechanisms of fat, oil and grease (FOG) deposit formation in sewer lines.
abstract: FOG deposits in sewer systems have recently been shown to be metallic salts of fatty acids. However, the fate and transport of FOG deposit reactant constituents and the complex interactions during the FOG deposit formation process are still largely unknown. In this study, batch tests were performed to elucidate the mechanisms of FOG deposit formation that lead to sanitary sewer overflows (SSOs). We report the first formation of FOG deposits on a concrete surface under laboratory conditions that mimic the formation of deposits in sewer systems. Results showed that calcium, the dominant metal in FOG deposits, can be released from concrete surfaces under low pH conditions and contribute to the formation process. Small amounts of additional oil to grease interceptor effluent substantially facilitated the air/water or pipe surface/water interfacial reaction between free fatty acids and calcium to produce surface FOG deposits. Tests of different fatty acids revealed that more viscous FOG deposit solids were formed on concrete surfaces, and concrete corrosion was accelerated, in the presence of unsaturated FFAs versus saturated FFAs. Based on all the data, a comprehensive model was proposed for the mechanisms of FOG deposit formation in sewer systems.
authors.affiliation: Department of Civil, Construction and Environmental Engineering, North Carolina State University, Raleigh, NC 27695, USA.
authors.forename: Xia
authors.initials: X
authors.lastname: He
authors.forename: Francis L
authors.initials: FL
authors.lastname: de los Reyes
authors.forename: Michael L
authors.initials: ML
authors.lastname: Leming
authors.forename: Lisa O
authors.initials: LO
authors.lastname: Dean
authors.forename: Simon E
authors.initials: SE
authors.lastname: Lappi
authors.forename: Joel J
authors.initials: JJ
authors.lastname: Ducoste
mesh_terms: D002118:Calcium / Q000032:analysis; D005223:Fats / Q000032:analysis*; D005227:Fatty Acids / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D009821:Oils / Q000032:analysis*; D012722:Sewage / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors
chemical_list: D005223:Fats; D005227:Fatty Acids; D009821:Oils; D012722:Sewage; D002118:Calcium
keywords: Calcium; FOG deposit formation; Fat, Oil and Grease (FOG) deposits; Free fatty acids (FFAs); Sanitary sewer overflows (SSOs); Sewer lines