Studies On Photochemical Degradation Of Typical Antibiotics

The occurrences of antibiotics in aquatic environments have attracted much concern from the public. Occurrences of the antibiotics cumulated in the environment and human body could threaten the function of the ecosystem directly and enhance the resistance of body bacteria to drugs, consequently jeopardizing human health.Oxytetracycline(OTC) and Sulfamethoxazole(SMZ), the most widely used antibiotics, have been chosen as the studying samples. Effects of main factors on photochemical degradation, the kinetics and reaction pathways of the processes were investigated respectively. It is the purpose of this research to better understand their environmental photochemical behavior so as to make use of the degradation technologies in the engineering. This paper is consisted of three parts described below.First part:The High Performance Liquid Chromatography (HPLC) method was adopted for determination of OTC and SMZ, and a set of detection methods was established on the basis of the reference literatures. To compare OTC and SMZ removal efficiency, their solutions were irradiated in two different light sources:high pressure mercury lamp and spherical xenon lamp. The effects of solution pH, DOM, NO3 on their photo-degradation were investigated by a set of experiments, and removal efficiency of TOC was also measured. The result shows that with the same initial concentration of 50mg/L and the same reaction time of 60min, the removal efficiency of OTC and SMZ reached 73.2% and 27.2% irradiated in UV, and 97.9% and 36.4% irradiated in day light respectively. This result indicates that OTC is more stable in photo-reaction and is degraded more difficultly than SMZ, which has been validated by the experimental data of only 17% reduction TOC of OTC solution comparison with 51.1% reduction TOC of SMZ. Their photolysis was enhanced with increasing pH value. The presence of low concentration of DOM seems to promote photolysis of OTC while high concentration retardate photolytic degradation. But the effect of DOM on SMZ photolysis was opposite to OTC. With the increase of NO3-, the photolysis rates of both OTC and SMZ increases.Second part:The photo-catalytic degradation of OTC in aqueous suspensions of TiO2 was studied. Effects of initial concentration of OTC, different irradiated levels, TiO2 dosage, solution pH, DOM and NO3- on the rates of degradation were investigated. The results show that the removal of OTC by photo-catalytic is effective and the rate of photo-degradation in aqueous solution follows first-order kinetics. The photo-degradation rate constant ranges from 0.0619 to 0.0130 min-1 corresponding to OTC concentration from 30 to 90 mg-L-1. Increasing TiO2 dosage leads to the photo-degradation rate constant increasing initially, followed by decreasing. Reduction of the rate constant has been observed when pH increasing. Its photo-degradation rate can be also affected by DOM and NO3- in aqueous solution. Comparing the reductions of TOC from two systems of UV and UV/T1O2, UV/TiO2 shows safer and more effective. By HPLC and FTIR, the degradation pathway of OTC in the process was proposed to arise from the cleavage and its substitution.Third part:Titanium dioxide sol was synthesized by sol-gel method with adulteration of HIO3 and Fe(NO3)3·9H2O in order so as to improve visible light catalytic activity. These nano-titania co-doped samples were characterized by XRD, TG-DTG and UV-Vis. Under 673K calcination temperature, the diameter of particles of iron and iodine co-doped titania powder obtained is 11.28nm, its absorption edge has a red shift from the UV-Vis spectra, and the absorption intensities are increased in the 400-600nm range. Photo-degradation experiments with Fe/I-TiO2 synthesized under different calcination temperature and mass percentage of Fe3+ were carried out. The best degradation for 50mg-L-1 OTC was observed in Fe-TiO2 with 673K calcination temperature and 0.05% co-doped Fe.