Addressing water scarcity: Cationic polyelectrolytes in water treatment and purification

Synthetic cationic polyelectrolytes (CPEs) serve as coagulation and flocculation agents in wastewater treatment due to a synergy of inherent electrostatic interactions and hydrophilic properties. In wastewater treatment, CPEs act as coagulation and flocculation agents to aggregate impurities and enable water purification. New health and environmental-related regulations provide motivation for government agencies and industrial companies to reuse wastewater. Chemical structure, molecular weight, charge density and functionality of CPEs provide tailorability for specific purification needs. Cationic polyacrylamides, ammonium-based polymers, poly(allyldimethyl-ammonium chloride) and epichlorohydrin/dimethylamine-based polymers are the most common CPEs used as coagulation and flocculation agents because they are economical and water soluble with tunable charge densities at high molecular weights. Free radical polymerization, step-growth polymerization and post-polymerization modification methods afford each polymer system. This review highlights recent advancements in synthetic methods to yield CPEs, structure-property relationships as related to flocculation efficiency and a summary of their toxicity and environmental impact.