Study On The Removal Efficiency And Mechanism Of Trace Contaminants In Water By Potassium Ferrate Combined Process

Trace organic pollutants（Tr OCs）are widely present in human production and life,and have gradually become a hot issue for research by scholars around the world because of their many types,wide distribution,low concentrations,and difficulty in degradation,which are potential threats to the ecological environment and human health.In this study,the degradation pattern,oxidation mechanism,reaction pathway and toxicity of the typical endocrine disruptor bisphenol A（BPA）as the target pollutant were studied and evaluated in the UV/Potassium ferrate（UV/Fe（VI））process;in addition,the degradation patterns,oxidation mechanisms,degradation pathways and toxicity of typical drugs such as sulfamethoxazole（SMX）and diclofenac sodium（DCFs）were investigated in the ozone/potassium ferrate（O₃/Fe（VI））process,using them as target pollutants.The degradation of the target pollutants by different oxidation systems was investigated,and the results showed that UV/Fe（VI）process exhibited good degradation efficiency for the pollutants.The UV/Fe（VI）process in the p H 6 resulted in a degradation rate of 1.59×10^-6 M^-1min^-1 for BPA,with a removal rate of 91.46%.The effects of different influencing factors（such as temperature,p H and water conditions）on the degradation of target pollutants by UV/Fe（VI）and O₃/Fe（VI）processes were investigated.The results showed that the increase of temperature accelerated the removal rate of pollutants.And the reaction rate of BPA degradation by UV/Fe（VI）increased from 4.75×10^-7 M^-1 min^-1 to 8.78×10^-6 M^-1 min^-1 with the increase of p H.The quenching of free radicals and the inhibition of reactive oxide species showed that the dominant oxidants in the UV/Fe（VI）oxidation process were Fe（V）,Fe（IV）,O₂^·-and^·OH,etc.Combined with the analysis of the active sites of BPA,it was speculated that the demethylation,hydroxylation and ring opening reactions of BPA were the main degradation pathways in the UV/Fe（VI）system.The toxicity of the BPA and its intermediates was evaluated using ECOSAR software.The results showed that as the reactions proceeded,BPA and its intermediates were further converted to less toxic species for aquatic organisms,thus reducing the ecotoxicity of the reaction solutions.The O₃/Fe（VI）process was shown to exhibit good degradation efficiency for trace organic pollutants by comparing different oxidation systems.The removal rates of SMX and DCFs reached 73.4%and 77.8%,respectively,within 30 s.The removal rates of the target pollutants increased both with increasing oxidant concentration and decreasing pollutant concentration.The effects of different influencing factors（such as oxidant dosing,p H and water conditions）on the degradation of target pollutants by the O₃/Fe（VI）process were investigated.The results showed that the increase of p H was not favorable for the oxidative degradation of SMX and DCFs in the O₃/Fe（VI）system.In addition,the O₃/Fe（VI）process was also effective for the removal of pollutants from natural waters.The main reactive oxidants in the oxidation of SMX and DCFs by O₃/Fe（VI）were O₃,Fe（VI）,^·OH and Fe（V）/Fe（IV）,etc.In the O₃/Fe（VI）system,the reaction pathways of SMX mainly include self-coupling,hydroxylation,oxidation,methylation,S–N bond and C–S bond cleavage.Hydroxylation,condensation,decarboxylation,oxidation and C–N cleavage were the main degradation pathways of DCFs.The results of toxicity assessment showed that SMX and DCFs and their intermediates were further transformed into less toxic species for aquatic organisms,thus reducing the ecotoxicity of the reaction solutions.