Harnessing natural antifouling agents for enhancing water and wastewater treatment membranes

Over the past few decades, water treatment membranes have undergone significant advancements, which is evidenced by significantly improved water flux and pollutants’ separation efficiency. Notwithstanding, membrane fouling caused by organic, inorganic, and biological fouling remains a persistent challenge, leading to reduced permeate flux (or increasing transmembrane pressure), compromised membrane quality, and increased energy consumption. To address these matters, chemically synthesized antifouling agents have been incorporated into membrane materials; however, their adverse effects have often restricted their use and even banned. As an alternative, natural antifoulants that are less costly, non-toxic, and eco-friendly can be integrated on the membrane surface or into the matrices in direct form or modified. These natural antifoulants encompass polysaccharides, amino acids, peptides, enzymes, polyphenols, flavonoids, esters, organic and fatty acids, and polyalkenes derived from plants, herbs, seaweeds, microorganisms, and other sources. Numerous studies have highlighted the efficacy of natural antifouling agents in ameliorating fouling by endowing membranes with quorum quenching, hydrophilic, and biocidal effects, thus enhancing the efficiency and lifespan of membrane filtration systems. On top of that, natural polymer antifoulants and hydrogels such as cellulose, chitosan, starch, chitin, pectin, alginate, and lignin-based materials offer multiple benefits, including non-toxicity, biocompatibility, robustness, and hydrophilicity. With those in mind, this review aims to provide comprehensive insights into i) controlling membrane fouling, ii) the efficacy of existing natural antifoulants in membrane-based water treatment, iii) eco-friendly obtaining extraction methods using microwave, ultrasound, supercritical fluid, and deep eutectic solvents, and iv) exploring potential untapped natural antifouling agents (e.g., usnic acid, cardenolides, sanguinarine, chelerythrine, thymol, and carvacrol). We believe this review will be the conspicuous touchstone towards membrane fabrication utilizing nature-based species, promoting cost-effective, environmentally friendly, and advanced performance, and offering a critical perspective for future research.