High-efficiency removal of perfluorooctanoic acid from water by covalently bound hybrid coagulants (CBHyC) bearing a hydrophobic quaternary ammonium group

• Low-concentration PFOA was removed by a novel coagulant with an efficiency >99%.
• The coagulant is covalently bound hybrid with a hydrophobic quaternary ammonium.
• The coagulant has large size and high zeta potential than conventional coagulants.
• Counter-ion attraction and hydrophobic interaction result in efficient coagulation.

Perfluorooctanoic acid (PFOA) is one of global persistent organic pollutants (POPs). The currently available PFOA removal techniques are of high cost and only limited to bench scale. In the present work, a novel covalently bound hybrid coagulant (CBHyC) bearing a hydrophobic quaternary ammonium group was prepared and characterized. Its excellent PFOA removal performance was demonstrated. Compared with the conventional coagulants, it is a thicker, larger and more irregular aggregate with much higher zeta potential. CBHyCs with different Si/Al molar ratio (0.15, 0.3 and 0.6) and basicity (B) values (1.0, 2.0 and 2.5) were tested for the PFOA removal from a water solution containing 100 μg/L PFOA. The results indicate that CBHyCs can remove 99.6% PFOA and its Si/Al molar ratio and B value can affect its PFOA removal performance. The CBHyC with Si/Al = 0.3 and B = 2 showed the best PFOA removal performance and highly tolerance to pH of the PFOA solution. A PFOA removal mechanism including counter-ion attraction from quaternary ammonium groups, hydrophobic interaction between PFOA and the long chain alkyls of CBHyCs and hydrolytic polymerization on aluminum species was proposed. In all, CBHyCs is a very promising coagulant for the removal of PFOA in the drinking water and wastewater treatments.