| In recent years, antibiotics have been widely used as drugs against infectious diseases. Intake by human or animal, only a few antibiotics occur metabolism, most of them was discharged into the municipal sewage system through the excretion of urine and feces. However, the traditional technologies of the sewage treatment plants often can not effectively remove these pollutants, the drugs or their metabolites ultimately into water environment, causing a series of environmental problems to human health, such as the wide spread of drug-resistant bacteria. It has become a hot research topic to develop new technology to remove antibiotics in water efficiently. At present, there is no research report about its degradation of antibiotic cefoperazone (CFPZ), which is one of the highest use rate of cephalosporin antibiotics. Therefore, the electro-Fenton (EF) and its enhanced processes were used to degrade CFPZ in the water using activated carbon fiber (ACF) cathode. Firstly, the effects of the electrode surface properties and gases atmosphere on the EF mechanisms were investigated. Then feasibility of EF process for complete degradation (partially mineralized) of CFPZ were examined, the biodegradabilty change and the intermediates were detected, then the possible degradation pathway was proposed. Secondly, the photoelectro-Fenton (PEF) process was used to mineralize CFPZ. Finally, the boron-doped diamond anode (BDD) strengthened PEF process was applied to achieve complete mineralization of CFPZ. The main results are as follows:(1) The EF mechanism:the influence of the ACF surface propertie and the gases atmosphere:The surface area of ACF cathode might affect the production of H2O2, the conversion of Fe2+/Fe3+ and the generation of ·OH in EF process. The electrogenerated H2O2 concentrations were measured in EF process using five kinds of ACF (ACF-1000, ACF-1300, ACF-1500, ACF-1600 and ACF-1800). The results showed that the higher the specific surface area of the ACF electrode, the more the production of H2O2. Each ACF with different specific surface areas all could electroreduce Fe3+ and maintain a high Fe2+ concentration in EF system, which was necessary for the continuously produced ·OH from Fenton reation. Gases atmosphere also might affect the generation of H2O2 and ·OH by influencing DO content in the EF system, the H2O2 and ·OH concentration were generated following the sequence of O2> Non-aeration> Air> N2. Under every gas atmosphere, the ACF cathode could reduce Fe3+ to Fe2+ efficiently.(2) Complete degradation and partial mineralization of CFPZ by EF process for improvement of biodegradability:Comparative degradation and menerlization of CFPZ in EF processes using ACF-1000 and ACF-1600 cathtodes was studied. Each degradation process followed the pseudo first order reaction kinetics, the degradation rate constants of EF using ACF-1000 ACF cathode and EF using ACF-1600 ACF cathode were 6.37× 1O-2 min-1 and 5.49×10-2 min-1, and TOC removal were 37.7% and 38.4%, respectively. The optimal conditions for degrating CFPZ in EF process using ACF-1600 ACF cathode were identified, i.e. I= 0.36 A, pH= 3.00,1.00 mM Fe2+ and 100 mL min-1 O2. Under this optimum condition,38.4% TOC was removed after 360 min EF electrolysis when a 500 mL 200 mg-L"1 CFPZ solution was treated. The BOD5/COD value increased from the initial CFPZ 0 to 0.19 after 360 min EF electrolysis, showing the biodegradability was improved significantly. When continuing the EF process to 480,600 and 720 min, the BOD5/COD value increased to 0.21,0.29 and 0.33, indicating that the solution was biodegradable, and could be futher treated by low-cost biochemical methods. Six aromatic intermediates of CFPZ were detected by the UPLC-QTOF-MS/MS system, while five carboxylic acids were analysed by Exclusion Chromatography, as well as NO3-, NH4+ ions were detected by IC method. On this basis, the possible degradation pathway of CFPZ in EF process was proposed.(3) Efficient mineralization of CFPZ by PEF treatment:64.8% TOC was removed after 360 min PEF electrolysis when a 125 mL 200 mg-L"1 CFPZ solution was treated under the optimum conditions, i.e. I= 0.36 A, pH= 3.00,1.00 mM Fe2+ and 100 mL min-1 O2, which was much higher than the TOC removal rates of AO-UVA (13.9%), AO-H2O2-UVA (28.8%), and EF (40.9%) processes. Comparative CFPZ degradation kinetics by AO-UVA, AO-H2O2-UVA, EF and PEF was inestivated, the CFPZ degradation in all these processes followed the pseudo first order reaction kinetics, the rate constants were 2.62×10-2 min-1,6.14×10-2 min-1,6.14 ×10-2 min-1 and 9.51×10=2 min-1, respectively. The effect of four kinds UV conditions (UVA, UVB, UVC and MWUV) on CFPZ mineralization was also studied, and after 360 min PEF treatment TOC removal were 64.8,64.0,70.0 and 72.5%, respectively.(4) Complete mineralization of CFPZ by BDD-PEF process:125 mL 200 mg-L-1 CFPZ could be completely degraded only within 20 min, and 91.5% TOC was removed after 360 min BDD-PEF electrolysis under the optimal conditions:I= 0.36 A, pH= 3.00,1.00 mM Fe2+ and 100 mL min-1 O2) indicating that BDD-PEF can quickly remove CFPZ, and achieve the completely mineralization of CFPZ. Five carboxylic acids formed in BDD-AO, BDD-EF and BDD-PEF processes, as well as 9.50 mg L-1 11.60 mg L- and 16.30 mg L-1 NH4+-N production in BDD-AO, BDD-EF and BDD-PEF processes, respectively. |
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