Efficiency And Mechanism Of Typical Antibiotics Degradation In Aquaculture Water By Combined UV/Chlorine Process

The aquaculture sector has grown quickly in recent decades as living standards have improved and demand for aquatic goods has increased,with China being the world’s largest producer of aquaculture products.Antibiotics are extensively employed in aquaculture,however because they are not properly absorbed and metabolized by organisms with a stable structure,a substantial amount of antibiotics are expelled and accumulate in the water column.Antibiotics are difficult to remove from traditional wastewater treatment procedures.Antibiotics in the water column not only influence aquatic creatures’ immunity,but they may also infiltrate the food chain,posing a hazard to food safety and human health.Antibiotic residues have become a major issue in China’s aquaculture business.Advanced Oxidation Processes（AOPs）are an emerging water treatment technology,which is a process of oxidative decomposition and mineralisation of hard-to-degrade pollutants in water by generating strong oxidative radicals（such as hydroxyl radicals,sulphate radicals and chlorine radicals）.It has the advantages of high reaction efficiency and high mineralisation rate.In this study,the antibiotics（ciprofloxacin and chloramphenicol）,which are frequently detected in the aquaculture water environment,were selected as the target,and the degradation characteristics and mechanism of the two antibiotics were investigated using a new UV/chlorine advanced oxidation process to investigate the feasibility of applying the UV/chlorine advanced oxidation process to degrade the antibiotics in aquaculture water.Compared with chlorination and UV irradiation alone,the UV/chlorine process was more effective in the removal of ciprofloxacin,with a removal rate of 99.31%.When the oxidant concentration was increased from 0.07 mM to 0.42 mM,the degradation rate of ciprofloxacin increased from 0.078 min^-1 to 0.106 min^-1.Neutral conditions were more favourable to the degradation and removal of ciprofloxacin.The coexistence of nitrate ions,natural organic matter and bovine serum protein in the water column inhibited the degradation of ciprofloxacin to different degrees.The degradation rate of chloramphenicol was 1.9 and 6.4 times higher than that of chlorination alone and UV alone,respectively.The degradation rate of chloramphenicol decreased continuously by increasing the p H of the reaction solution,and the degradation of chloramphenicol was fastest under acidic conditions and slowest under alkaline conditions.The rate of degradation of chloramphenicol in water increased with increasing oxidant concentration because the increased oxidant increased the quantum yield of reactive chlorine and the content of reactive radicals,which accelerated the oxidative degradation of chloramphenicol.The presence of bromine ions significantly promotes the degradation of chloramphenicol in water,while the presence of chloride ions inhibits the degradation of chloramphenicol.Coexisting ammonia nitrogen in water competes for reactive radicals in water,thus inhibiting the reaction of chloramphenicol with free radicals and reducing the reaction rate of chloramphenicol.The higher the concentration of natural organic matter,the more pronounced the inhibition of the degradation of chloramphenicol in water.Bovine serum protein competes with chloramphenicol for other reactive radicals such as ·OH,inhibiting the degradation and removal of chloramphenicol,and the rate of chloramphenicol degradation decreases with increasing concentrations of bovine serum protein.In this paper,the degradation products of ciprofloxacin and chloramphenicol in the UV/chlorine system were analysed by liquid chromatography mass spectrometry（LCMS）to provide insight into and suggest the degradation pathways of the two antibiotics.Toxicity analysis of the oxidation products was carried out using Chlorella vulgaris toxicology experiments and ECOSAR software,and experimental studies on the oxidative degradation of the antibiotics in real water were carried out.In conclusion,the UV/chlorine advanced oxidation process has potential for the degradation of antibiotics in aquaculture water.