Analysis of tubular NF plants in Scotland indicates that summer temperatures and redox-sensitive elements are correlated with membrane biofouling and shortened useful life

We investigate the effects of seasonal variations in water composition and temperature on the performance of two full-scale drinking water treatment plants in Scotland, equipped with tubular cellulose acetate nanofiltration membranes. Multiple environmental and water quality parameters, recorded over a 4.5-year period, were correlated against membrane permeance, cleaning frequency, and useful life. Membrane autopsies enabled the characterization of the foulant composition. Temporal variations in temperature at plant X led to significant biofouling (manifested by permeance losses of 30-50%, and bacteria detected on the membrane surface) during the summer months, when water temperatures exceeded 20 °C and microbiological activity was highest. Plant Y, in contrast, displayed smaller seasonal variations and was operationally stable without significant fouling. A pronounced increase in manganese and iron (up to 200 and 600 μg/L, respectively) in the lake water at plant X in summer was accompanied by elevated content (∼60 mg/m 2) of those metals on the membrane surface, which was consistent with lake thermal stratification and metal input from the sediment into the water column. Our work shows that membrane plants in regions supplied by standing surface water bodies, such as plant X, are more vulnerable to biofouling, especially during warmer months.