A comprehensive review of RO membrane fouling: Mechanisms, categories, cleaning methods and pretreatment technologies

As the global water crisis intensifies, reverse osmosis (RO) membranes play a pivotal role in desalination and industrial water treatment. However, membrane fouling significantly hampers their effectiveness, reducing water quality and production rates while increasing operational costs and maintenance demands. This review addresses the critical gaps in understanding the mechanisms of fouling, categorizing it into four distinct types: inorganic scaling, organic fouling, biofouling, and colloidal fouling, each presenting unique challenges to membrane performance. We delve into both external and internal fouling mechanisms, highlighting how contaminants obstruct membranes through different pathways. Additionally, we provide an in-depth evaluation of existing cleaning methodologies, distinguishing between conventional methods and emerging non-conventional techniques such as osmotic backwashing and ultrasonic cleaning. While physical cleaning methods effectively address reversible fouling, chemical treatments remain essential for irreversible fouling, despite their potential risks to membrane integrity. Furthermore, we explore innovative pretreatment technologies that show promise in mitigating fouling and extending membrane lifespan. By synthesizing current knowledge and pinpointing specific areas for future research—particularly in emerging technologies—this review aims to enhance the operational efficiency of RO membranes and contribute to sustainable solutions for the escalating global water crisis.