Activated carbon–polymer composites for water treatment: A critical review

Powdered activated carbon (PAC) removes pollutants from water efficiently, but its fine particles are difficult to separate and reuse. A retained polymer shapes PAC into separable beads, films or flakes, or functionalizes granular activated carbon (GAC), but it dilutes the carbon and slows uptake. In some systems, the polymer also adds binding sites for specific contaminants. Such targeted binding is especially relevant for per- and polyfluoroalkyl substances (PFAS) and perchlorate, now among the most demanding drinking-water targets. Here we review activated carbon (AC) composites in which the polymer remains non-carbonized, covering fabrication, adsorption, continuous-flow performance, regeneration and life cycle assessment. Of 1596 Scopus and Web of Science records, 482 studies met the selection criteria; chitosan and alginate dominate, and only 12 involve polyolefins or other waste plastics. Although few studies test the composite against its parent AC, the controlled comparisons that exist reveal a consistent pattern: the composite adsorbed less unless the polymer carried binding groups matched to the target. Cationic coatings met this test, extending fixed-bed perchlorate service from 950 to 3250 bed volumes. Otherwise, the polymer impaired performance: a stabilizing polymer lowered PFAS distribution coefficients 1.3–3.5-fold, and alginate entrapment slowed benzene equilibration from about 1 h to 250 h. Dry BET surface area is a poor guide to performance in water: composites that lost 52–72% of their dry BET area still removed their target contaminants. Continuous-flow evidence is thin: only six column studies allow the contact time to be calculated, and no pressure-drop data were found. Five laboratory-scale life cycle assessments report 2.11–5.82 kg CO₂-eq per kilogram of composite, with pyrolysis the largest share, but none is treatment-based. Retained polymers therefore justify their cost when they add a contaminant-specific function, as cationic coatings do for PFAS and perchlorate; for recovery alone, the benefit has yet to be measured. We propose a minimum reporting set built on matched phase controls, hydrated-state kinetics, flow tests and treatment-based life cycle assessment.