Impact of ions co-occurring in water on antibiotics degradation by UV-based advanced oxidation process

The pollution of natural water sources with antibiotics is an emerging environmental concern. This study evaluated the degradation efficiency of nine antibiotics in a mixed solution under different UV-based advanced oxidation processes. In the UV-only treatment, ciprofloxacin, cefalexin, and ceftiofur were fully degraded within 5 min, meropenem within 10 min, and penicillin G, roxithromycin, oxytetracycline, doxycycline, and sulfamethazine within 30 min. The effects of inorganic ions and organic matter were investigated due to their significant influence on the degradation performance of antibiotics. Chloride ion, sulfate ion, and humic acid negatively affected degradation, reducing mean degradation efficiency over a period of 15 min to 60-80 %, 57-97 %, and 74-79 %, respectively. In contrast, nitrate, phosphate, and bicarbonate enhanced degradation, with mean degradation efficiency exceeding 95 %. To further enhance the degradation efficiency, UV-based oxidants (persulfate, peroxide, and chlorine) were applied, achieving 95-100 % degradation within 15 min, except for roxithromycin, which required a longer incubation period for complete degradation. A bioluminescence assay showed relatively low acute toxicity of the antibiotics before and after treatments, with a maximum of 4.1 rTU observed during the UV/chlorine process in the presence of co-occurring ions. Notably, this is the first study to report on antibiotic degradation under realistic concentrations of antibiotics and co-occurring ions, demonstrating that the UV/chlorine process offers the most effective performance for antibiotic degradation.