Wastewater reuse using soil aquifer treatment (SAT) is a rational and realistic solution in countries and regions with limited freshwater resources. The behaviour and removal of perfluoroalkyl carboxylic acids (PFCAs) under long hydraulic retention times (HRTs) in SAT may warrant further investigation. In this study, actual treated effluent from a wastewater treatment plant (WWTP) was continuously treated using a pilot-scale SAT reactor with a designed HRT of 30 days, located in the WWTP; PFCA removal characteristics were investigated based on a 14-month monitoring period. Continuous SAT reactor operations were accomplished for 30 months under the designed HRT (28 days, as calculated by a tracer test); stable treatments were achieved during the period, represented by dissolved organic matter removal from 3.94 mgC/L to 0.701 mgC/L. Removal of PFCAs by SAT under an HRT of 28 days was found to be difficult, as indicated by perfluorooctanoic acid level from 18.4 to 19.0 ng/L. In addition, PFCA concentrations may be increased after SAT, probably due to the influences of PFCA precursors; this is indicated by the increase in perfluorononanoic acid from 11.6 to 14.1 ng/L. Based on the guideline values, further removal of PFCAs in SAT-treated effluent may be required.

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