Integrated pretreatment–membrane systems for water and wastewater treatment: A critical review on fouling control and combined process efficiency

Abstract

Membrane technologies such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are widely used for water and wastewater treatment due to their high separation efficiency of pollutants. However, membrane fouling remains the inherent challenge, leading to reduced flux, higher energy demand, and frequent chemical cleaning. Pretreatment plays an important role in controlling fouling, improving membrane lifespan, and maintaining stable operation. This review presents a comprehensive overview of state-of-the-art pretreatment approaches, ranging from conventional methods such as coagulation–flocculation, sedimentation, and adsorption to advanced processes like electrocoagulation, oxidation, biological pretreatment, and others. Particular emphasis is given on how different pretreatment methods target specific foulants, such as suspended solids, organic and inorganic matter, colloids, and biofilm-forming microorganisms, and reduce the type of pollutants. The effectiveness of each strategy in combination with the membrane filtration process is critically discussed in enhancing pollutant removal, reducing fouling propensity, and improving overall sustainability of the system. Further, the review discusses a rationale behind choosing a pretreatment process based on types of water, environmental sustainability, cost-effectiveness, and other factors. It concludes with the future research directions aimed at developing energy-efficient, cost-effective, and environmentally sustainable pretreatment technologies for the membrane filtration process.