Effects of Alkaline Cleaning Agents on the Filtration Performance and Aging of Polyvinylidene Fluoride Membranes.

Polyvinylidene fluoride (PVDF) membranes are used in ultrafiltration systems for car wash water reuse, where frequent alkaline cleaning is required to maintain operational flux rates. Although NaOH-induced degradation of virgin PVDF membranes has been reported, its relevance under real industrial conditions remains poorly understood. This study investigates the long-term exposure of tubular PVDF membranes to alkaline car wash detergents and evaluates how the resulting structural changes influence permeate quality. During several months of pilot-scale operation with synthetic car wash wastewater and daily alkaline cleaning (pH > 11.5), permeate fluxes remained stable at 50-70 LMH despite pronounced membrane aging. Structural analyses revealed enlarged pore size, increased water permeability and reduced dextran retention, while FTIR confirmed dehydrofluorination of the polymer matrix. Despite the extensive degradation of the membrane skin layer, permeate turbidity, dissolved organic carbon, and surfactant concentrations remained stable throughout the operation. This stability was attributed to the persistent fouling layer, which acted as an effective secondary separation barrier and compensated for the loss of intrinsic membrane selectivity. These findings demonstrate that substantial PVDF degradation does not necessarily compromise permeate quality in car wash ultrafiltration systems, highlighting the dominant role of fouling-controlled separation under long-term alkaline cleaning regimes.