Recent advances in coagulants in wastewater treatment

The discharge of industrial wastewater has become a critical environmental concern, necessitating the development of efficient and sustainable treatment solutions. Coagulation-flocculation (CF) is widely employed in wastewater treatment due to its effectiveness, cost-efficiency, and scalability. Herein, recent advances in coagulants and flocculants are reviewed, focusing on their mechanisms, classifications, and applications in removing contaminants such as dyes, pharmaceuticals, and heavy metals. While traditional aluminium- and iron-based coagulants are widely used, they present environmental and health concerns due to sludge generation and potential metal contamination. Consequently, research has shifted toward organic, hybrid, and natural coagulants derived from biopolymers, plant extracts, and other sustainable materials, offering improved performance and reduced environmental impact. Hybrid technologies combining CF with membrane filtration, photocatalysis, and adsorption enhance contaminant removal and improve process efficiency. While laboratory studies have demonstrated the potential of alternative coagulants and hybrid techniques, challenges remain in scaling them up for industrial applications. Challenges include the instability of plant extracts, batch-to-batch variability, lack of standardized quality control, and regulatory barriers to developing new coagulants. This review highlights recent advances in alternative coagulation–flocculation materials and computational modelling approaches, including dissipative particle dynamics, density functional theory, and molecular dynamics, to provide molecular-level insights into coagulation mechanisms. Future perspectives with a focus on optimising process parameters, minimising chemical usage, and leveraging artificial intelligence for real-time monitoring and process automation to improve wastewater treatment efficiency and sustainability were some suggested areas requiring attention to improve the CF process.