Linking Two-Year Seasonal Variability in Karun River Water Quality to the Operational Performance and Fouling Behavior of a Full-Scale Reverse Osmosis System

Abstract

The quality of feed water has a major influence on the operation stability and fouling properties of reverse osmosis processes; however, the impact of long-term surface water composition fluctuations under real conditions is still underexplored. The current investigation addressed the effect of two years of seasonal surface water characteristics on membrane operation and fouling potential. For a period of 24 months, raw water samples were collected on a monthly basis, and physicochemical parameters (total dissolved solids (TDS), electrical conductivity, turbidity, pH, alkalinity, hardness, major ions, silica, silt density index (SDI)) were calculated in terms of seasonal averages. Simultaneously, RO operational performance was evaluated in terms of membrane pressure difference, normalized permeate flow, specific energy consumption, and salt rejection. Water quality showed clear seasonal variation, with highest concentrations of TDS, hardness, calcium, chloride, sulfate, turbidity, and SDI in second year summer. SDI increased from 3.30 in the first-year winter to 6.05 in the second-year summer, indicating much more fouling potential. Consequently, the pressure difference in the membranes increased to about 180% of its original value, while permeate flow decreased to about 66% at the same time. The findings from correlation analysis show that SDI, TDS, hardness, calcium and sulfate are the most significantly correlated variables with the deterioration of RO performance. The results indicate the direct impact of seasonal variations in the source water quality on the degree of membrane fouling and hydraulic performance deterioration. Therefore, it is essential to continuously monitor the feed water and develop flexible management approaches accordingly, thus ensuring the stable performance and sustainability of RO systems.