Biological oxidation of choline-based ionic liquids in sequencing batch reactors: Biological oxidation of choline-based ionic liquids

BACKGROUND: Ionic liquids (ILs) are salts consisting of an organic cation and an organic or inorganic anion that are potential use for organic synthesis, biomass conversion, gas absorption, polymerization, metal extraction and lubrication. We examined the biodegradability of choline chloride (CholineCl), choline acetate (CholineAc) and choline bis(trifluoromethylsulfonyl)imide (CholineNTf₂) in a sequencing batch reactor (SBR) to assess the influence of the IL anion. RESULTS: Following acclimation, activated sludge exhibited good activity, and high COD (80–90%) and TOC removal (75–85%) with initial concentrations of CholineCl and CholineAc over the range 0.25–15 mmol L–¹. However, increased concentrations of CholineNTf₂ in the reactor feed had an inhibitory effect on the sludge. An analysis of the reaction effluent revealed the presence of the main intermediates of choline degradation: ethanol, and methyl‐, dimethyl‐ and trimethylamine. The initial and final microbial communities of the sludge were characterized by pyrosequencing analysis, and the latter was found to consist mainly of Alfa‐, Beta‐ and Gamma‐proteobacteria. CONCLUSION: Choline‐based ionic liquids can be efficiently removed in SBRs. Complete choline degradation (0.25–15 mmol L–1) was accomplished at a variable depletion rate depending on the particular IL anion (chloride, acetate or NTf₂). © 2019 Society of Chemical Industry