Natural Coagulants as Sustainable Alternatives for Wastewater Treatment: A Review

Wastewater from agricultural, industrial, and pharmaceutical activities contains diverse contaminants requiring efficient remediation. Conventional coagulation is hindered by toxic sludge production and severe pH shifts. While natural coagulants are sustainable alternatives, the existing literature lacks a framework that bridges molecular mechanisms and industrial scaling. This review systematically synthesizes research from 1995 to 2026 across plant, animal, and microorganism matrices. Unlike previous reviews, this work uniquely links deep mechanistic analysis to techno-economic scalability and circular-economy integration. Quantitative synthesis demonstrates that animal and plant matrices achieve peak turbidity and suspended solids removals of 80–99.8%, while modified tannins and mucilages achieve up to 100% decolorization. Concurrently, microbial strains remove 64% to 93% of Chemical Oxygen Demand. Beyond bench-scale efficiencies, we evaluate a wide range of operating conditions (pH 2.58–9.1; dosages 2 mg/L to 5 g/L). Critical technological bottlenecks are explicitly addressed, detailing how to resolve the organic carbon paradox—where residual dissolved carbon risks microbial regrowth—through advanced spray-drying and hybrid dosing designs. Ultimately, this review delivers a data-driven framework to support the standardization and large-scale deployment of sustainable natural coagulation technologies globally.