Coupling of nanofiltration and UV, UV/TiO₂ and UV/H₂O₂ processes for the removal of anti-cancer drugs from real secondary wastewater effluent

The detection of anti-cancer drugs in surface waters at ng/L indicates that most wastewater treatment processes currently applied are not effective enough to remove these resilient compounds from wastewater. Therefore alternative treatment processes should be tested to avoid discharges in the environment of drugs that have been linked to genotoxic effects. The innovative contribution of this study stands in coupling nanofiltration with advanced oxidation processes to treat real secondary wastewater effluents spiked with 4 widely consumed anti-cancer drugs. Direct photolysis was found to be extremely effective to degrade etoposide and paclitaxel from the secondary effluent as well as from the highly concentrated retentate produced by nanofiltration. The two drugs were not detected after 10 min of exposure that corresponds to higher than 98% removals given the method detection limits by direct injection. This is equivalent to pseudo-first order degradation rate constants higher than 0.46 min^-1, which, to the best of the author's knowledge, has not yet been reported for paclitaxel in the literature. However, none of the tested oxidation processes (UV, UV/TiO₂ and UV/H₂O₂) using the reactor setup, exposure times and concentrations of TiO₂ and H₂O₂ tested, were able to degrade cyclophosphamide or ifosfamide effectively. Compared to literature data, this is probably related to the low amount of photons received by the treated media. Finally important aggregation of catalyst particles was observed in secondary effluent, and photocatalysis had no advantage compared to the other two processes tested.