Mechanism Of PPCPs Removal By Oxidation Of FeⅥ And Prediction Model Of Removal Rate

In recent years,the oxidation process of ferrate（FeⅥ）has been shown to be effective for the treatment of a variety of refractory organics,and FeⅥ removes pharmaceuticals and personal care products（PPCPs）from water mainly through oxidation,complexation,and adsorption/flocculation,but these mechanisms of action are not yet understood.It is important to reveal the mechanism of action of the process,identify the degradation intermediates and assess their toxicity,and elucidate the degradation pathways of pollutants to optimize the regulation of the FeⅥ process.In this thesis,the mechanism of action,intermediates and degradation pathways of the FeⅥ process in the removal of tetracyclines（TCs）were investigated using a combination of experimental and theoretical calculations,and quantitative structure activity relationship（QSAR）models for removal based on quantum chemical parameters was developed to provide a theoretical basis for predicting the removal rate and explaining the degradation mechanism of FeⅥ process from a microscopic perspective.The main research contents and results are as follows:（1）Based on experimental studies and theoretical calculations,the removal mechanism of TCs by FeⅥ was investigated.The experimental results showed that Fe³⁺generated by FeⅥ through autolytic-reduction would complex with TCs and contribute about 79%of the TCs removal,followed by oxidation（about 11%contribution）and adsorption/flocculation（about 10%contribution）.Thermodynamic and kinetic calculations showed that the complexation reaction between TCs and Fe³⁺occurred more readily than the oxidation reaction between FeⅥ and hydroxyl radicals（HO·）,indicating that the complexation reaction dominated the removal of TCs rather than the oxidation reaction between FeⅥ and HO·.（2）Identification of intermediates and degradation pathways were studied.In the process of FeⅥ oxidation,21,16,19 and 20 intermediates were identified from oxytetracycline（OTC）,tetracycline（TET）,doxycycline（DOX）and chlortetracycline（CTC）systems,respectively.The analysis revealed that hydroxylation,ring opening,carbon-carbon double bond reduction,rearrangement,and demethylation,deamidation,dehydration,deolation,decarbonylation,deacetylation,and deamination were the main pathways of TCs degradation and intermediates generation.The results of product toxicity prediction by applying ECOSAR software showed that 20 intermediates with electrophilic groups,carbamate groups and unsaturated bonds had higher toxicity than their parent TCs,and the reduction of intermediates with electrophilic groups,carbamate groups and unsaturated bonds should be controlled.（3）Study on prediction model of removal rate of PPCPs degraded by FeⅥ.A prediction model for the removal rate of FeⅥ process was constructed based on quantum chemical descriptors using multiple linear regression method,and the model was evaluated in terms of model fit,stability and application domain characterization.The results showed that the established model can be used to predict the removal rate of PPCPs in the FeⅥ process.Combining the physical significance of the variables in the model,the removal mechanism of PPCPs in the FeⅥ process was discussed from the microstructural perspective of the paper,and it was found that the removal rate of PPCPs in the FeⅥ process was correlated with the possibility of attack by nucleophilic reagents,bond order and the ability to form hydrogen bonds.