• • After 3.5 years, RO membrane fouling exhibited pronounced spatial heterogeneity: inlet (RO1) developed dense bio-inorganic composite fouling with CaSO4 crystals and rod-shaped microbial aggregates (5–10 μm), while outlet (RO2) shifted to inorganic scaling with reduced microbial abundance (Proteobacteria from 77.11% to 64.79%). This necessitates distinct cleaning strategies for different membrane segments.
• • Microbial community at RO1 was dominated by Proteobacteria (77.11%), particularly Alphaproteobacteria (71.49%) and Xanthobacteraceae (35.29%), which secrete EPS to form biofilms, exacerbating fouling. Targeted pretreatment using non-chlorine oxidants (e.g., peracetic acid) can inhibit these biofilm formers.
• • At RO2, higher salinity drove a shift toward halotolerant taxa: Microbacteriaceae increased to 23.73% and Actinobacteriota to 24.76%, with EPS secretion elevated by 42% as an adaptive response. This indicates that salt-tolerant biofouling requires different control measures, such as optimizing antiscalant dosing.
• • RO system inlet pressure fluctuated seasonally by 15%–22% (summer vs. winter), correlating with water viscosity changes. This operational variability must be factored into membrane cleaning schedules and energy consumption forecasts to maintain system efficiency.