The influence of ionic liquids on activated sewage sludge communities has been systematically investigated. Ionic liquids substituted with short alkyl chains and polar anions showed a low inhibitory potential, but this was greater for highly hydrophobic ionic cations and anions. Even so, the results suggest that ionic liquids are unlikely to reduce the performance of domestic wastewater treatment plants.
For the past decade, ionic liquids (ILs) have attracted great interest in academia and industry. So far, several ionic liquids have been used in technological processes, from small-scale to industrial applications, which makes it increasingly likely that they will be released into the environment.
Researchers have been actively studying the environmental and toxicological behaviour of ionic liquids, but their influence on the activated sludge communities of wastewater treatment plants (WWTPs) has yet to be investigated.
This Polish–German study aims to fill this knowledge gap, by systematically investigating the influence of ionic liquids on activated sewage sludge communities.
The researchers tested the inhibition of activated sludge respiration (according to OECD guideline 209) using a selection of 19 different compounds, covering the chemical space of ionic liquids as comprehensively as possible.
In addition, to elicit the differences in sensitivities or tolerances towards ionic liquids, activated sludge was investigated from different domestic and industrial sources.
Generally speaking, the structure activity relationships of ionic liquid toxicity towards activated sludge are in good agreement with those found for other organisms and test systems.
The inhibitory potential of tested ionic liquids substituted with short alkyl chains (≤4) and polar anions was low. On the other hand, the toxic effects of highly hydrophobic ionic cations and anions were greater, although the concentrations causing 50% inhibition of oxygen uptake (IC50) were low, at <50 μM (<10 mg/l).
The researchers were able to demonstrate that the EC50 values from Vibrio fischeri can be used for a reliable assessment of the sludge inhibition potential of tested ionic liquids.
All the results are discussed in the context of their consequences for biodegradation processes, and the performance of wastewater treatment plants.
