Fate of Endocrine-Disrupting and Pharmaceutically Active Substances in Sand Columns Fed with Secondary Effluent

AbstractSorption and biotransformation of six endocrine disrupting compounds (EDCs) [estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethynylestradiol (EE2), 4-tert-octylphenol (4-t-OP), and bisphenol A (BPA)] and two pharmaceutically active compounds (PhACs) [ibuprofen (IBU) and naproxen (NAP)] were studied in microcosms and columns under conditions that simulate the percolation of effluent through sandy soil on reclaimed land in Singapore. Sorption isotherms followed a linear model, except for IBU and BPA, for which a Freundlich model was used, and for NAP, which sorbed too little to be measurable. Degradation experiment results showed that aerobic conditions were more favorable for the degradation of EDCs than anaerobic or anoxic conditions. E3 and 4-t-OP were totally removed within 40 days, whereas EE2, BPA, IBU, and NAP were persistent. However, under anaerobic conditions, E1 was formed from E2 and vice versa, reaching steady-state conditions after approximately 15 days. To simulate the groundwater (GW) recharge condition, eight laboratory-scale soil aquifer treatment (SAT)–saturated sand columns (each with a length of 1.0 m) were operated in series. Secondary effluent (SE) and ultrafiltered effluent augmented with the target compounds was applied to two identical sets of eight columns, respectively. With secondary effluent and ultrafiltered SE as the feed, the target compounds were completely removed after 8 m of infiltration, with the exception of NAP, which persisted at 1 μg/L in the effluent of recharged columns after an operating time of 3 pore volumes (PV). The higher removal rate in SE recharged columns is attributed to the higher nutrient content, microbial populations, and a longer period of acclimatization. Small-scale batch studies showed that E2, EE2, IBU, and NAP removal was primarily a result of biological transformation that was faster under aerobic than anaerobic conditions.