How did chlorine-resistant bacteria (CRB) grow on reverse osmosis membranes and cause fouling?

Understanding the adhesion, growth, and biofilm development of chlorine-resistant bacteria (CRB) on reverse osmosis (RO) membranes is important for elucidating the microscopic mechanisms of biofouling. This study employed a typical CRB strain to systematically investigate its growth and fouling behavior on RO membranes. Temporal variations in CRB distribution and morphology, together with quantitative permeate flux decline, were analyzed to establish direct links between microstructural evolution and fouling performance deterioration. Three distinct developmental stages were demonstrated: (I) an initial aggregation stage (0-6 h), wherein CRB cell density increased slightly yet fouling layer resistance (R_f) rose substantially due to aggregate formation; (II) a cell proliferation stage (6-24 h), characterized by concurrent increases in cell density and R_f as CRB rapidly expanded and occupied the membrane surface; and (III) a matrix compaction stage (24-48 h), during which intensive EPS secretion filled intercellular voids, densified the biofilm matrix, and drove a further increase in R_f. This study elucidates the temporal shifts in fouling mechanisms, from aggregate-dominated resistance, to cell proliferation-driven surface coverage, and finally to EPS-induced matrix compaction, thereby providing mechanistic insight into the microprocesses governing CRB fouling on RO membrane.