The application of non-oxidizing biocides to prevent biofouling in reverse osmosis polyamide membrane systems: a review Luiz H. Da-Silva-Correa , Hayley Smith , Matthew C. Thibodeau, Bethany Welsh and Heather L. Buckley * Department of Civil Engineering, Centre for Advanced Materials and Related Technologies (CAMTEC) and Institute for Integrated Energy System (IESVic), University of Victoria, Victoria, BC, Canada, V8P 5C2 *Corresponding author. E-mail: hbuckley@uvic.ca LHD-S, 0000-0003-3525-1929; HS, 0000-0001-6385-8037; BW, 0000-0001-9916-8396; HLB, 0000-0001-7147-0980 ABSTRACT Biofouling of polyamide membranes is one of the main barriers faced by reverse osmosis (RO) technologies to supply fresh water. Currently, biofouling is addressed by feed water pretreatment using chlorine, followed by membrane cleaning. Chlorine damages polyamide mem- branes and also generates harmful disinfection byproducts. Thus, safer strategies are needed to prevent biofouling in polyamide membrane systems. This review investigates the applicability of the following non-oxidizing biocides in preventing and controlling biofouling in RO systems, including their antimicrobial efficiency, hazard levels, membrane compatibility, and applicability to drinking water treatment: (1) 2,2-dibromo-3-nitrilopropionamide (DBNPA); (2) 2-methyl-4-isothiazolin-3-one (MIT); (3) sodium bisulfite (SBS), (4) phenoxyethanol (PE), (5) sodium benzoate (SB). According to this review, MIT and DBNPA present most of the features attributed to an ideal anti-biofouling chemical but also are the most hazardous biocides. Due to safety and efficacy, none of the five chemicals were determined to be the final solution to address membrane biofouling. However, alternative RO biocide research is in early development and requires further investigation via bio- fouling prevention studies. Therefore, future research efforts on the investigation of economic, eco-friendly, and safe antifouling agents to prevent and treat biofouling in RO systems are paramount to promote sustainable water supply in water-stressed countries. Key words: biocides, biofouling prevention, efficacy, polyamide membranes, reverse osmosis, safety, water treatment HIGHLIGHTS • An evaluation framework for anti-biofouling safety and efficacy is developed. • DBNPA is a proficient model of biofouling prevention efficacy. • MIT is a good model for antimicrobial efficacy, although not for safety. • SBS is a reference for a membrane-compatible antimicrobial. • PE and SB are good models for safety in biofouling prevention studies. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). © 2022 The Authors AQUA — Water Infrastructure, Ecosystems and Society Vol 00 No 0, 1 doi: 10.2166/aqua.2022.118 corrected Proof Downloaded from http://iwaponline.com/aqua/article-pdf/doi/10.2166/aqua.2022.118/1001431/jws2022118.pdf by guest on 10 February 2022