Impact of Treatment Processes on the Removal of Perfluoroalkyl Acids from the Drinking Water Production Chain

Abstract

The behavior of polyfluoralkyl acids (PFAAs) from intake (raw source water) to finished drinking water was assessed by taking samples from influent and effluent of the several treatment steps used in a drinking water production chain. These consisted of intake, coagulation, rapid sand filtration, dune passage, aeration, rapid sand filtration, ozonation, pellet softening, granular activated carbon (GAC) filtration, slow sand filtration, and finished drinking water. In the intake water taken from the Lek canal (a tributary of the river Rhine), the most abundant PFAA were PFBA (perfluorobutanoic acid), PFBS (perfluorobutane sulfonate), PFOS (perfluorooctane sulfonate), and PFOA (perfluorooctanoic acid). During treatment, longer chain PFAA such as PFNA (perfluorononanoic acid) and PFOS were readily removed by the GAC treatment step and their GAC effluent concentrations were reduced to levels below the limits of quantitation (LOQ) (0.23 and 0.24 ng/L for PFOS and PFNA, respectively). However, more hydrophilic shorter chain PFAA (especially PFBA and PFBS) were not removed by GAC and their concentrations remained constant through treatment. A decreasing removal capacity of the GAC was observed with increasing carbon loading and with decreasing carbon chain length of the PFAAs. This study shows that none of the treatment steps, including softening processes, are effective for PFAA removal, except for GAC filtration. GAC can effectively remove certain PFAA from the drinking water cycle.The enrichment of branched PFOS and PFOA isomers relative to non branched isomers during GAC filtration was observed during treatment. The finished water contained 26 and 19 ng/L of PFBA and PFBS. Other PFAAs were present in concentrations below 4.2 ng/L The concentrations of PFAA observed in finished waters are no reason for concern for human health as margins to existing guidelines are sufficiently large.