Evaluation of the efficiency of selected wastewater treatment processes in removing selected perfluoroalkyl substances (PFASs)
By M.G. Kibambe, M.N.B. Momba, A.P. Daso, M.A.A. Coetzee
J Environ. Man.
January 7, 2020
In this study, the efficiencies of selected wastewater treatment plants (WWTPs) to remove selected perfluoroalkyl substances (PFASs) during wastewater treatment processes were evaluated. For this purpose, influent samples from Daspoort, Zeekoegat and Phola WWTPs, were initially screened for the presence of sixteen different PFASs of which only seven were detected. These include: perfluorobutanoic acid (PFBA), perfluoro-n-pentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), perfluorohexane sulfonate (L-PFHxS), and perfluorooctane sulfonate (L-PFOS).
To determine the concentrations of these PFASs, wastewater samples were subjected to solid-phase extraction followed by liquid chromatography-tandem mass spectrometry. The results showed that L-PFOS was the dominant compound with the highest concentration of 508 ± 258 ng/L at Daspoort WWTP. Overall, the three WWTPs could not achieve the complete influent-to-effluent removal of the PFASs and the best removals were observed at Zeekoegat WWTP.
The removal efficiency of the different unit processes varied from one plant to another and also from each type of PFASs. At Daspoort, the removal efficiency of the primary settling tanks was poor and the highest removal reached 39% for PFHxA. The activated sludge (AS) of this WWTP achieved the highest removal of 84% for the L-PFOS. At Zeekoegat, the AS achieved the highest removal of 94% for the L-PFOS. The anaerobic pond at Phola achieved a higher removal of 80% for the L-PFOS. However, no removal was observed downstream of the biological filter for the same compound. Poor removal efficiency was reported downstream of the wetland at Phola except for the PFOA (16%).