Parameters affecting the formation of perfluoroalkyl acids during wastewater treatment

• Largest PFAA dataset in liquid and solid samples from 5 wastewater treatment types.
• PFAAs generated from precursors breaking down during wastewater treatment.
• Temperature, HRT, and sludge digestion influenced the formation of PFAAs.
• Median log Kd were PFOS (3.73), PFDA (3.68), PFNA (3.25), PFOA (2.49), and PFHxA (1.93).
• Mass balance showed low PFAAs removal by sorption and high PFAAs loading in effluents.

This study examined the fate and behaviour of perfluoroalkyl acids (PFAAs) in liquid and solid samples from five different wastewater treatment types: facultative and aerated lagoons, chemically assisted primary treatment, secondary aerobic biological treatment, and advanced biological nutrient removal treatment. To the best of our knowledge, this is the largest data set from a single study available in the literature to date for PFAAs monitoring study in wastewater treatment. Perfluorooctanoic acid (PFOA) was the predominant PFAA in wastewater with levels from 2.2 to 150 ng/L (influent) and 1.9 to 140 ng/L (effluent). Perfluorooctanesulfonic acid (PFOS) was the predominant compound in primary sludge, waste biological sludge, and treated biosolids with concentrations from 6.4 to 2900 ng/g dry weight (dw), 9.7 to 8200 ng/g dw, and 2.1 to 17,000 ng/g dw, respectively. PFAAs were formed during wastewater treatment and it was dependant on both process temperature and treatment type; with higher rates of formation in biological wastewater treatment plants (WWTPs) operating at longer hydraulic retention times and higher temperatures. PFAA removal by sorption was influenced by different sorption tendencies; median log values of the solid–liquid distribution coefficient estimated from wastewater biological sludge and final effluent were: PFOS (3.73) > PFDA (3.68) > PFNA (3.25) > PFOA (2.49) > PFHxA (1.93). Mass balances confirmed the formation of PFAAs, low PFAA removal by sorption, and high PFAA levels in effluents.

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