Biodegradation of wastewater components causing O&G deposits formation in sewers

The aim of the research was to compare the degree of biodegradation of oil contaminants present in municipal wastewater in dependence of the type of pollutants. Occurrence of oil contamination, free fatty acids (FFA) (as a result slow chemical hydrolysis of oil), and metallic soaps (as a saponification process with FFA) in wastewater may cause deposits on the walls of pipes and infrastructure. In this study, sodium acetate (CH₃OONa), sodium salts of fatty acids: sodium oleate (C₁₈H₃₃OONa), sodium stearate (C₁₈H₃₅OONa), and oily wastewater were used as exemplary substrates. Sodium acetate as a single substrate and oily wastewater were similarly biodegradable: 92.6%–95.9% (the chemical oxygen demand (COD) reduction) and 91.2%–96% (COD reduction), respectively. Lower efficiency at the beginning of the process was observed for sodium oleate and sodium stearate as single substrates: 88.1%–97.2% and 86.3%–96.1% of COD reduction, respectively. In the case of wastewater, COD removal was obtained at a similar level: 91.2%, 91.2%–89.6%, but four main fatty acids (palmitic (C₁₆H₃₁OOH), oleic (C₁₈H₃₃OOH), linoleic (C₁₈H₃₁OOH), and stearic acid (C₁₈H₃₅OOH)) were removed at various efficiencies, depending on the acid type (the length of the carbon chain and number of double bonds).