Performance And Mechanism Of The Removal Of Contaminants Of Emerging Concern By Coupling Electrode With Persulfate

Contaminants of emerging concern?CECs?are usually produced and discharged because of human production or personal life,so they are widely present in natural environment now.Though CEC concentrations are of low level in natural environment,their structures are stable with strong bio-accumulation,and can persist in aqueous environment.Traditional water treatment processes cannot easily remove CECs,which significantly threatens safety of aqueous environment and body health.Therefore,to develop a simple,green,and efficient technology to remove CECs is rather important.Coupling electrode with persulfate?PS?can efficiently generate sulfate radical(SO₄^·-),hydroxyl radical?HO^·?,singlet oxygen?¹O₂?,and nonradical activated PS,making the technology promising in the field of drinking water,wastewater,and landfill leachate.There are many kinds of electrodes that can activate PS,but the mechanisms of removing CECs by coupling electrode with PS are still not clear.Performance and mechanisms of removing CECs by Fe anode/PS,graphite felt?GF?anode/PS,GF cathode/PS,boron-doped diamond?BDD?anode/PS,and BDD anode/sulfate systems are systematically investigated in this study.Activation of PS in Fe anode/PS system depends on the Fe²⁺released from Fe anode under the effect of electric field.Performance of removing CECs by Fe anode/PS system was better than that by Fe²⁺/PS system,because Fe²⁺is released constantly according to Faraday's law.Based on the results of radical quenching experiment and electron paramagnetic resonance?EPR?spectra,it was confirmed that degradation of oxcarbazepine?OXC?in Fe anode/PS system was attributed to the generation of SO₄^·-and HO^·.Degradation efficiency of OXC in Fe anode/PS system increased with the increase of PS dosage,and increased with the decrease of solution pH.The presence of NOM inhibited the degradation of OXC.Furthermore,a kinetic model was established to predict the degradation of OXC in Fe anode/PS system,and the model was verified under the condition of different current density and PS dosage.Reactions including electron transfer and hydroxyl substitution occurred during the degradation of OXC in Fe anode/PS.In GF anode/PS system,PS anions moved to and interacted with GF anode,which then were activated to SO₄^·-,HO^·and ¹O₂ under the effect of electric field.On the other hand,activation of PS in GF cathode/PS system mainly depended on the electron transfer on the cathode.Specifically,dissolved oxygen captured electrons to become superoxide radicals(O₂^·-),which can efficiently activate PS to SO₄^·-and HO^·because of its reducing ability.The results of radical quenching experiment and EPR spectra confirmed the presence of aforementioned reactive species.The degradation products of atrazine?ATZ?in GF anode/PS and GF cathode/PS systems are similar,and all products showed lower acute toxicity and chronic toxicity than ATZ.The recyclibity of GF electrodes is good.BDD anode/PS system showed good performance to degrade bisphenol A?BPA?in perchlorate,sulfate,and chloride electrolytes:In perchlorate electrolyte,the contribution to BPA degradation followed SO₄^·-,HO^·,and electrolysis.In sulfate electrolyte,the contribution to BPA degradation followed SO₄^·-,electrolysis,and HO^·.In chloride electrolyte,the contribution to BPA degradation followed reactive chlorine species,electrolysis,SO₄^·-,and HO^·.Moreover,in perchlorate electrolyte,hydroxyl substitution,aggregation,electron transfer reactions occurred during the degradation of BPA.Apart from these reactions,chloride substitutions also occurred in chloride electrolyte because of the participation of reactive chlorine species.Degradation of BPA in BDD anode/PS system performed well in effulent of wastewater treatment plant and landfill leachate.Direct oxidation on BDD anode in phosphate,perchlorate,nitrate,sulfate,and chloride electrolyte were also investigated,and all showed good performance on degradation of CECs.Generation of PS was detected in sulfate electrolyte,and yield rate of PS showed positive correlation with the degradation of CECs.The degradation efficiency of CECs increased with the increase of current density,and increased with the decrease of co-existence of NOM.In the aforementioned systems,the addition or generation of PS both enhanced the degradation of CECs in1 electrochemical oxidation processes.Therefore,the technology of coupling electrodes with PS has a promising future in practical applications.