Emerging contaminants in wastewater: A critical review on occurrence, existing legislations, risk assessment, and sustainable treatment alternatives

Abstract Emerging contaminants (ECs) have been a threat to the aqueous environment because of their persistent nature and ability to adversely affect the living organisms exposed to them for a prolonged duration. An increase in detection of varying ranges of ECs in different aqueous bodies has catalyzed research on their toxic effects and removal. However, a compilation of proper legislations in terms of permissible limits of the ECs in water and understanding the capability of the different treatment technologies in bringing down their concentration to non-toxic levels is an area that needs significant attention. In this context, this review provides a comprehensive assessment of occurrence, ecotoxicological effects, and treatment methods of ECs. Statutory guidelines of different environmental organizations have been compared with the calculated drinking water equivalent limit of the ECs. Furthermore, a comprehensive risk assessment analysis of the EC has been performed, and it was found that caffeine, bisphenol-A, diazinon, and malathion had high risk quotients. The performance of the different treatment technologies was assessed based on their ability to bring down the concentration of the ECs below the established statutory guidelines. Unlike most conventional treatment methods, many advanced hybrid treatment methods could reduce the concentration of the ECs below the guideline value. Technologies involving membrane bioreactor combined with reverse osmosis, ozonation, and membrane distillation proved to be very effective with more than 90% removal. The sustainability aspects of different treatment methods have also been covered in this review to help researchers identify suitable treatment methods for removing ECs.