Enoxacin degradation by photo-Fenton process combined with a biological treatment: optimization and improvement of by-products biodegradability

This study evaluates the effectiveness of coupling a photo-Fenton process with a biological treatment on the mineralization of enoxacin, an antibacterial agent belonging to the fluoroquinolones group. The influence of some operating parameters, such as UV light intensity, hydrogen peroxide and Fe(II) concentrations, on 50mgL(-1) enoxacin degradation and by-products mineralization was evaluated. The biodegradability of the target molecule was also investigated, reporting a BOD5 on COD ratio of 0.95 after 60min of irradiation at 15mmolL(-1) of H2O2, 0.5mmolL(-1) of Fe(II) and 30Wm(-2) of UV A light intensity. The monitoring of the advanced oxidation state (AOS) of the irradiated solution during the treatment displayed a maximal oxidation state of 0.25 for 90min of photo-degradation. A comparison between the photo-Fenton process and other oxidative processes [UV alone, UV/H2O2, H2O2, H2O2/Fe(II)] was carried out showing a marked improvement in enoxacin mineralization while combining UV A light with the Fenton reagent (41% of TOC decay improvement compared to the Fenton process). Finally, activated sludge culture for non-treated and pre-treated enoxacin at optimal conditions was conducted during 10days. The obtained TOC results reported a mineralization improvement with a maximal mineralization yield of 43% for the biodegradation of irradiated samples. The relevance of coupling the photo-Fenton process with a biological process for the enoxacin treatment was therefore proven.