The Mediation In Of Fe(?)/Fe(?) Cyle In Fenton Stystems And Their Diethyltoluamide Degradation Performance

Pharmaceuticals and personal care products?PPCPs?were widely used in everyday life and most of them were accumulated in water environment in the form of parent drug or metabolite.PPCPs long-term exposure to low doses will severely affect the ecosystem and cause health hazards due to their low degradation rate and the high detection rate.As a kind of representative PPCPs,DEET?N,N-diethyl-m-toluamide?was widely used.To further augment the DEET wastewater treatment,the Fenton process was applied to treat the detoxmin?DEET?wastewater,and the optimal condition for the degradation of DEET was identified via response surface methodology,and also elucidated the intermediate or transformed products in order to propose a reaction pathway.Then,the reaction rate of Fe???reduction to Fe???was much slower,which caused the Fe???accumulation and high H₂O₂dosage,and as a result led to a reactivity decline and produced a large amount of iron precipitation in the Fenton reactions.Tacking into address these limitations,this paper also studied the effects of DEET degradation efficiency in the protocatechuic acid?PCA?promoted Fenton system.Finally,the possible reaction mechanism,the principal reactive species and the secondary pollution of PCA were discussed.The details of main research contents are as follows:The Fenton process was applied to treat the detoxmin?DEET?wastewater.The optimal condition for the degradation of DEET was identified via response surface methodology.A central composite design with quadratic model was used to evaluate the effects and interactions of these parameters,and the influential factors were the H₂O₂ dosage,Fe???concentration,initial p H and reaction time.The optical conditions are determined as follows:the initial p H=3.0,Fe???concentration is 0.25mmol/L,and H₂O₂ dosage is 1.0 mmol/L,the confirmatory experiment result is91.45%,which basically complies with the predicted value?92.31%?of fitted quadratic regression model.The five intermediates of DEET degradation by Fenton method were identified by GC-MS analysis,and the possible degradation pathway of DEET was inferred.In order to further improve iron circulation rate to reduce Fe???to Fe???at the Fenton system,complexing agent protocatechuic acid?PCA?was added into the Fenton system for the degradation efficiency of DEET improvement.Research had identified that greatly enhanced the degradation efficiency of DEET was achieved after the added PCA at the Fenton system.the optimal reaction conditions were found to be[DEET]₀=200?mol/L,H₂O₂=1.0 mmol/L,H₂O₂/Fe???=20:1,PCA/Fe???=1:1,p H=3.0,under which DEET was rapidly degraded 80%within 20 mins.In acidic conditions?p H=3.0?,we examined the chelating capacity of PCA with iron ion,which could form complexes with Fe???to prevent the iron precipitation.DEET degradation rate was dramatically enhanced because the PCA could act as a complexing agent or as a reducing agent,which had a rapid reduction Fe???to effectively promote Fe???/Fe???cycle.The utilization ratio of H₂O₂ determined by different like-Fenton systems confirmed the utilization ratio of H₂O₂ was improved in the Fenton system with PCA.We used the free radical scavengers of Tert-Butanol and p-benzoquinone to identify the mian oxidant effects was hydroxyl radicals?·OH?in the PCA-Fe???/H₂O₂ system.We employed total organic carbon to identify PCA itself could be mineralized in the PCA-Fe???/H₂O₂system under p H 3.0,which also became an environmentally friendly complexing agent.