Microbial Community Dynamics in Full-Scale Water Reuse Reverse Osmosis System Revealed by Longitudinal Monitoring Using Membrane Fouling Simulators

Membrane fouling, especially biofouling, hinders the efficiency of reverse osmosis (RO) membranes in water reuse, leading to higher energy consumption and operating costs. Understanding biofilm microbial community composition and dynamics is critical to developing biofouling mitigation strategies, but the need to sacrifice membrane modules has restricted the progress and scale-up of such research. In this study, membrane fouling simulators (MFSs) were adopted as an innovative, nondisruptive technique for temporal sampling and monitoring of RO biofilms, providing a reliable proxy for the dominant taxa that colonize full-scale RO membranes. Microbial communities in the MFSs gradually stabilized, becoming highly similar across sampling points between 6 months and 1 year of operation and matching samples from full-scale modules operated over the 1-year period. Three dominant taxa were identified: Mycobacterium (biofilm-forming, disinfection-resistant bacteria), Rickettsiales AB1 (parasitic bacteria), and Nitrosomonas (ammonia oxidizers), whose abundances correlated with water quality parameters, including temperature, ammonia nitrogen, and total chlorine. Co-occurrence network analysis of the MFS biofilm microbiome revealed two apparent microbial clusters: one centered around Mycobacterium and other taxa associated with extracellular polymeric substance (EPS) production and a second cluster composed of parasitic and ammonia-oxidizing bacteria that formed a separate ecological niche with weak connections to the EPS-producing group. These results highlight how MFSs can provide informative and frequent insight into RO biofilm structure and dynamics that, if further correlated with full-scale studies, may eliminate the need to sacrifice full-scale membrane elements.