Conventional Treatment and PFAS Removal
Coagulation and flocculation—the addition of coagulants like aluminum sulfate or ferric chloride to aggregate suspended particles—is the first step in most conventional water treatment plants. For many contaminants, enhanced coagulation provides effective removal. For PFAS, conventional coagulation and flocculation is essentially ineffective, a fundamental limitation that drives the need for advanced treatment.
Why PFAS Resist Coagulation
Coagulation removes contaminants by charge neutralization and particle aggregation. PFAS are dissolved organic compounds—not particulate matter—and their anionic charge under drinking water pH conditions actually stabilizes them in solution rather than promoting aggregation. Studies consistently show <10% PFAS removal in conventional coagulation-flocculation-sedimentation treatment trains, with short-chain PFAS showing even less removal than long-chain compounds.
Jar Test Results and Full-Scale Confirmation
Extensive jar testing with various coagulants at different doses confirms that no coagulant type—alum, ferric sulfate, polyaluminum chloride, or enhanced coagulation with high coagulant doses—achieves meaningful PFAS removal from surface water sources. This finding has been confirmed in full-scale treatment plants where extensive conventional treatment delivers PFAS to distribution systems at concentrations matching source water.
Implications for Treatment Plant Design
The ineffectiveness of conventional coagulation for PFAS means that treatment plants relying solely on coagulation-filtration-disinfection provide essentially no PFAS protection regardless of how well they are operated. Supplemental treatment—GAC contactors, ion exchange, or membrane systems—must be added specifically for PFAS removal, representing significant capital investment beyond conventional treatment infrastructure.