Assessment of the pharmaceutical active compounds removal in wastewater treatment systems at enantiomeric level. Ibuprofen and naproxen

The enantioselective degradation of ibuprofen and naproxen enantiomers was evaluated in five different wastewater treatment systems, including three constructed wetlands (vertical- and horizontal-flow configurations), a sand filter and an activated sludge wastewater treatment plant. In addition, injection experiments were carried out with racemic ibuprofen at microcosm- and pilot-scale constructed wetlands. Ibuprofen and naproxen have an asymmetric carbon atom and, consequently, two enantiomeric forms (i.e. S and R). The enantiomeric fraction (EF = S/(S + R)) in the raw sewage and effluents of various wastewater treatments were found to be compound-dependent (i.e. ibuprofen: EF influent = 0.73–0.90, EF effluent = 0.60–0.76; naproxen: EF influent = 0.88–0.90, EF effluent = 0.71–0.86). Of the two chiral pharmaceuticals, naproxen was the only one whose effluent EF correlated with its removal efficiency ( p < 0.05). The lack of correlation found for ibuprofen was attributable to the fact that its enantioselective degradation kinetics were different under prevailing aerobic and anaerobic conditions. Injection experiments of ibuprofen in constructed wetlands at microcosm and pilot-scale followed similar trends. Hence, under prevailing aerobic conditions, S-ibuprofen degraded faster than R-ibuprofen, whereas under prevailing anaerobic conditions, the degradation was not enantioselective. In summary, the naproxen EF measurements in wastewater effluents show that naproxen is a suitable alternative for evaluating the removal efficiency of treatment systems because its enantioselective degradation is similar under prevailing aerobic and anaerobic conditions.