Integrated Ozonation–Adsorption Pretreatment and Polyvinylidene Fluoride/Tungsten Based Polyoxometalate Photocatalytic Membrane for Produced Water Treatment

Abstract

The growing expansion of industrial operations, particularly within the oil and gas sector, has led to a substantial increase in produced water generation, an effluent rich in recalcitrant organic and inorganic contaminants. Conventional membrane based separations remain limited by low permeability and severe fouling, necessitating the development of more robust and multifunctional treatment systems. In this study, a durable photocatalytic hybrid membrane composed of polyvinylidene fluoride integrated with tungsten based polyoxometalate was fabricated via phase inversion. The incorporation of 2 wt% tungsten based polyoxometalate notably enhanced both permeability and contaminant rejection through improved interfacial compatibility and photocatalytic activity. Controlled ultraviolet irradiation for five minutes further optimized surface hydrophilicity and pore structure, achieving an outstanding water flux of 158.83 L/(m² h), while excessive exposure induced pore densification and reduced flux. A synergistic adsorption–ozonation pretreatment for three hours was integrated prior to photofiltration, resulting in 89% chemical oxygen demand removal and 85% ammonia nitrogen removal, effectively minimizing fouling and enhancing overall system stability. Under optimized conditions the membrane exhibited a steady permeate flux of 145 L/(m² h) over 600 minutes and achieved removal efficiencies of 99.0% chemical oxygen demand, 99.5% ammonia nitrogen, 20.5% total dissolved solids, and 6.87% phenol. These results demonstrate the combined effects of tungsten based polyoxometalate incorporation and pretreatment integration in improving both separation performance and operational durability. This work provides a scalable and sustainable strategy toward next-generation hybrid photocatalytic membranes for advanced produced water purification.