Application of Plant-Based Coagulants and Their Mechanisms in Water Treatment: A Review

This review describes the mechanisms of natural coagulants. It provides a good understanding of the two key processes of coagulation-flocculation: adsorption and charge neutralization, as well as adsorption and bridging. Various factors have influence the coagulation/flocculation process, including the effect of pH, coagulant dosage, coagulant type, temperature, initial turbidity, coagulation speed, flocculation speed, coagulation and flocculation time, settling time, colloidal particles, zeta potential, the effects of humic acids, and extraction density are explained. The bio-coagulants derived from plants are outlined. The impact of organic coagulants on water quality, focusing on their effects on the physicochemical parameters of water, heavy metals removal, and bacteriological water quality, is examined. The methods of extraction and purification of plant-based coagulants, highlighting techniques such as solvent extraction and ultrasonic extraction, are discussed. It also examines the parameters that influence these processes. The methods and principles of purification of coagulating agents, including dialysis, freeze-drying, ion exchange, electrophoresis, filtration, and centrifugation, are listed. Finally, it evaluates the sustainability of natural coagulants, focusing on the environmental, technical, and economic aspects of their use. At the end of this review, the readers should have a comprehensive understanding of the mechanisms, selection, extraction, purification, and sustainability of plant-based natural coagulants in water treatment.