Treatment of nanofiltration or reverse osmosis concentrates by UV/H2O2 indirect photolysis for the removal of anti-cancer drugs from real secondary wastewater effluents

Anti-cancer drugs have been detected in the aquatic environment due to their poor elimination in current wastewater treatment plants. These drugs pose a potential risk to aquatic organisms and humans once they have entered the water cycle. This work studies the UV/H2O2 treatment of nanofiltration (NF) and reverse osmosis (RO) retentates of secondary wastewater effluent (WWeff) for the removal of anti-cancer drugs and toxicity. This treatment was compared to the direct treatment of WWeff by UV photolysis and by UV/H2O2 treatment. The filtration of 5 selected anti-cancer drugs by a RO-SE membrane showed high rejections (>88%) for all drugs, while the NF-DL membrane provided poor rejections (<45% for most drugs). Therefore, only the RO retentate treatment by UV/H2O2 (RO-UV/H2O2) was tested. The degradation efficiency of the drugs by UV, UV/H2O2, and RO-UV/H2O2 was compared using a pseudo-first order degradation rate constant. Degradation rates of all drugs significantly increased with the addition of H2O2 due to HO. radicals generation. The rates for RO-UV/H2O2 were lower than direct WWeff treatment by UV/H2O2 due to an increased concentration of organic matter and ions in the retentate stream which inhibited the drug degradation. Acute toxicity on V. fischeri was assessed for the feed and all treated effluent streams. The feed showed no toxicity because the concentration of drugs was too small. The stream treated by direct UV photolysis showed no increase in toxicity. Conversely, the effluent streams treated by UV/H2O2 showed higher toxicity which was attributed to the formation of toxic by-products that were different than the UV by-products. Finally, a comparison of operating costs for four different treatments (UV, UV/H2O2, NF-UV/H2O2, and RO-UV/H2O2) was done through a basic economic analysis. The UV/H2O2 treatment showed the lowest operating costs. The RO-UV/H2O2 showed comparable costs due to the reduction in volume that needs to be treated by UV/H2O2.