Ionic Liquids: Bacterial Degradation in Wastewater Treatment Plants

Abstract

Ionic liquids (ILs) are probably the kind of chemical compounds that have been most intensively investigated in the past 10 years. The potential applications of ILs cover practically all disciplines of chemistry, having received particular attention in separation processes, catalysis, electrochemistry, nanotechnology, and material science. This increasing use promotes the synthesis and application of the new IL compounds at larger scales. As a consequence, a parallel effort has been made by the scientific community to evaluate the potential environmental hazards of ILs. With equal focus, several researches have also made relevant progress in the development of effective treatments to recover or remove ILs from wastewaters and soils. Certainly, the current state of art in the field of ILs results from the cooperative and multidisciplinary work of experts from different scientific fields. In this work, the toxicity and biodegradability of ILs have been revised from the point of view of environmental engineers, centering the analysis on the expected need of managing ILs in a wastewater treatment plant (WWTP). For this purpose, the available standard tests and other methods to evaluate the toxicity of potential xenobiotic compounds are summarized. An overview of the reported toxicities of ILs toward different assays is presented, with particular emphasis in the available guidelines for designing ILs with low toxicity. The standardized tests for determining the biodegradability of xenobiotics are also collected and described. Lastly, the biodegradation behavior of ILs have been summarized, as evidenced in the bibliography, depending on their structural features and the biological systems used in the bioassays. Preliminary analysis, focused on relevant aspects on the toxicity and biodegradability of ILs, was performed in our laboratory using activated sludge. The main aim is to provide useful guidelines for the future development of biological processes for treating wastewater contaminated with ILs in a WWTP.

Assessment the ecotoxicity and inhibition of imidazolium ionic liquids by respiration inhibition assays

“…However, the potential application of such processes to a given effluent must consider some critical issues, as ecotoxicity and biodegradability. Preliminary results have revealed that there is insufficient evidence to confirm the degradation of imidazolium, thiazolium and pyridium ILs, whereas those derived from aliphatic amines and organic acids could be considered as potentially biodegradable (Peric et al, 2013;Neumann et al, 2014;Jordan and Gathergood, 2015;Diaz et al, 2016). In addition, the IL structure plays a key role on the inhibitory effect over the activated sludge performance.…”

A perspective on task-specific ionic liquids for the separation of rare earth elements

“…IL process design rarely deals with waste streams containing dissolved [NTf 2 ] − in water, 17 which can cause ecotoxicological issues due to the low biodegradability of the anion. 18,19 To help avoid this loss, the ILs can be made more hydrophobic by using cations with long alkyl chains. 20 Besides acting as diluents in extractions, ILs can also contribute to separation processes through solvent interactions 21 and ion-exchange mechanisms, 22,23 which allows for tuning the properties of specic extractants.…”

“…IL process design rarely deals with waste streams containing dissolved [NTf 2 ] − in water, 17 which can cause ecotoxicological issues due to the low biodegradability of the anion. 18,19 To help avoid this loss, the ILs can be made more hydrophobic by using cations with long alkyl chains. 20…”

Ion chromatography for monitoring [NTf2]− anion contaminants in pure and saline water

“…Ionic liquid toxicity is related to lipid membrane accumulation, 20 chemical structure, 21 and hydrophobicity, 22 all of which are linked to the solubility of ionic liquids in water. 23 Combined with the extremely low biodegradability of [NTf 2 ] À containing ionic liquids, 24,25 discharge of saturated wastewater into the environment could cause an ecotoxicological disaster. Ionic liquids have been compared to polychlorinated biphenyls (PCBs), 26 a persistent organic pollutant (POP), because of their similar physical and chemical properties.…”

“…29 Bacterial degradation of [NTf 2 ] À IL wastewater is difficult because of the low biodegradability of the anion. 24 Tertiary treatment options are required to remove [NTf 2 ] À from wastewater; however, to date there is very little research in this area. Biodegradation of ionic liquids can be improved by incorporating functional groups.…”