Abstract
Degradation of norfloxacin (NOR) was studied using a combination of microwave and UV irradiation methods (MW/UV process). Remarkable synergistic effect was found between MW and UV light. The removal rate with the MW/UV process was much faster than that with UV light irradiation only. Degradation of NOR followed second-order kinetics and ~72% of NOR could be removed in the first 5 min of MW/UV reaction. Influence of inorganic ions (cations (K+, Mg2+, Ca2+, Cu2+) and anions (Cl−, SO42−, NO3−, CO32−)), humic acid (HA) and surfactants (cation, anion, and non-ionic) on the degradation of NOR by the MW/UV process was investigated. Among the ions, Cu2+ and NO3− ions inhibited the degradation of NOR. The presence of HA and surfactants in water showed a slight inhibition on the NOR removal. Furthermore, the NOR degradation in the MW/UV process was primarily caused by the ·OH-photosensitization steps. Seven intermediates formed by the oxidation of NOR were identified and three reaction pathways were proposed. Removals of NOR in tap water (TW), synthetic wastewater (WW), river water (RW), and seawater (SW) were also studied, which demonstrated that the MW/UV process was an effective oxidation technology for degrading fluoroquinolone antibiotics in different water matrices.
Highlights
Antibiotics have received increasing concern as emerging pollutants in recent years for their ubiquitous occurrence and ecological risks [1,2]
Continuous release of FQs into the aquatic environment might trigger the development of antibiotic resistant bacteria and genes [11,12,13,14,15], which would be even bigger threats to human health and ecosystem safety
Most FQs cannot be effectively removed by microbial processes in conventional wastewater treatment plants, due to the stability and poor biodegradability of the quinolone ring [16,17]
Summary
Antibiotics have received increasing concern as emerging pollutants in recent years for their ubiquitous occurrence and ecological risks [1,2]. Fluoroquinolones (FQs) are some of the most widely used broad-spectrum antibiotics for curing bacterial infections in humans, livestock and aquaculture [3,4]. Fluoroquinolones, especially norfloxacin (NOR), have been detected at relatively high levels in various water matrices such as wastewater effluents [5,6,7], surface water [8,9] and even drinking water [10]. Continuous release of FQs into the aquatic environment might trigger the development of antibiotic resistant bacteria and genes [11,12,13,14,15], which would be even bigger threats to human health and ecosystem safety. Most FQs cannot be effectively removed by microbial processes in conventional wastewater treatment plants, due to the stability and poor biodegradability of the quinolone ring [16,17]. It is of utmost importance to seek highly efficient technologies to remove
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