Comprehensive investigation of soybean oil-derived LCFAs on anaerobic digestion of organic waste: inhibitory effect and transformation

Abstract In China, as a popular cooking oil, a huge amount of waste soybean oil is discharged through household wastewater or food debris. In widely used anaerobic process, a mixture of long chain fatty acids (LCFAs) is readily generated from waste soybean oil, and could exert adverse impacts on anaerobic digestion. In this study, soybean oil-derived mixed LCFAs were used as targeted compounds, a series of experiments were conducted to investigate their inhibitory effects and transformation in anaerobic co-digestion with other organics. The soybean oil-derived mixed LCFAs showed strong inhibitory effects on anaerobic digestion of model organic waste with an IC50 value of 675 mg/L, and no obvious synergistic effects were observed. Furthermore, it was found that the mixed LCFAs exerted differentiated effects on different consortia, where the acidogenesis was enhanced by surfactant effects and aceticlastic methanogenesis were more seriously inhibited. The LCFAs profile indicated that linoleic acid was quickly degraded to oleic acid and palmitic acid, and accumulated at a high level until most of acetate and butyrate was degraded. In addition, the results of increased extracellular polymeric substances (EPS) content and unchanged cell viability suggested that the inhibitory effects of mixed LCFAs were recoverable, physical hindering effects other than bactericidal effects. These findings could provide additional information for anaerobic digestion of lipid rich organic waste.