Estimation of kinetic parameters and UV doses necessary to remove twenty-three pharmaceuticals from pre-treated urban wastewater by UV/H2O2

Abstract

In this work, the effectiveness of UV and UV/H2O2 to degrade twenty-three pharmaceutical compounds present in microfiltered secondary effluent of an urban wastewater treatment plant was investigated. Apparent kinetic constant and UV doses required for effective removal of the studied compounds were calculated using a custom-made photochemical reactor with a capacity of 25 Liters and an irradiance of 15.47 Wm−2. An optimal H2O2 dosage of 20 mg L−1 was determined. Antiinflammatory compounds, such as metamizole, diclofenac and ketoprofen, were mostly removed by photolysis. Caffeine and its metabolite paraxanthine were the compounds which displayed most resistance to oxidization by hydroxyl radicals generated in this process. The apparent kinetic constants and UV doses necessary to remove each pharmaceutical from the treated wastewater were calculated. Ciprofloxacin, diclofenac, ketoprofen and metamizole were degraded with UV doses lower than 100 mJ cm−2. However, UV doses of 2369 and 4318 mJ cm−2 were necessary to reduce caffeine and its metabolite paraxanthine to one tenth of their initial values. The mineralization of organic carbon and absorbance at 254 nm of the recycled water were also monitored. Though no change in dissolved organic carbon concentration was observed after UV/H2O2 treatment, UV absorbance at 254 nm decreased by 43%.