Inhibitory effects of long chain fatty acids on anaerobic sludge treatment: biomass adaptation and microbial community assessment

Long chain fatty acids (LCFA) are known for introducing inhibitory effects on anaerobic sludge treating lipid-rich wastewater. In this study, batch experiments were conducted using three different types of sludge samples. Two sludge samples acclimated to lipids, and one non-acclimated sludge sample. The degradation of LCFA in the sludge samples was evaluated by dosing different concentration of selected LCFAs, i.e., oleic acid and palmitic acid, at a concentration range from 50 to 600 mg COD/L. The cumulative methane production as well as the LCFA concentration measured as fat, oil, and grease (FOG) were determined. The sludge samples were pre-incubated under unfed conditions to remove remaining biodegradable substrates. The batch tests were carried out with both pre-incubated and raw inoculum sludge. Oleic acid was better degraded than palmitic acid in all the evaluated sludge samples. Methane production, in terms of conversion extent, was higher with oleic acid compared to palmitic acid. The lipids-acclimated sludge samples showed better LCFA degrading performance than the non-acclimated sludge samples. At LCFA concentrations exceeding 400 mg/L, oleic and palmitic acid degradation was inhibited. The inhibitory effects seemed to affect the LCFA degradation to intermediate products. However, the subsequent methane production was not inhibited by the presence of high concentrations of LCFAs. The LCFA-acclimated sludge samples performed better in terms of LCFA degradation. Based on our present results, the implementation of sludge adaptation strategies is recommended to enhance the performance of anaerobic wastewater treatment systems treating lipid-rich wastewater. Microbial community analysis showed high abundance of the families Petrotogaceae, Kosmotogaceae, Synergistaceae and Psuedomonaceae.