Removal Of Refractory Organic Pollutants In Water By Electrochemical Activation Of Perisulfate With ACF Cathode

In recent years,with the development of industry and the improved standard of living,more and more refractory organic pollutants are frequently detected in water bodies.These refractory organic pollutants are difficulty to remove by traditional water treatment methods,and they can harm human health through bioaccumulation.Electrochemical activated persulfate?PS,including peroxymonosulfate?PMS?and peroxodisulfate?PDS??can produce strong oxidizing hydroxyl radicals?^·OH?and sulfate radicals(SO₄^·-)which can removal organic pollutants efficiently.However,this technology still has several disadvantages including low reaction rate,high energy consumption with unclear mechanism,which limit its application.To overcome these drawbacks mentioned above,this study adopted activated carbon fiber?ACF?as cathode,which has strong adsorption capability,to activate persulfate to remove the organic contaminants in water.Compared to metal cathode,ACF as cathode could increase solid-liquid surface mass transport,leading to a higher utilization efficiency of oxidizing agents and decreasing the overall energy consumption of the system.Meanwhile,aiming at the problem of ACF losing its adsorption capability after long-term service,saturated ACF was used as the cathode in the E-PS system.E-PS regeneration process could regenerate ACF in situ while mineralized the desorbed contaminants,providing new ways of activated carbon regeneration,decreasing the cost of ACF in the water treatment process.Firstly,this paper investigated the effect of single operating factor and water backgrounds on pollutants removal in E-ACF-PS system.Compared the reaction rate and energy cost of the system under different oxidizing conditions.Then,radical scavenger experiment was conducted to determine the kinds of reactive species and the pathway of reactive species generation,estimate the percentage of contribution of related reactions.Analyzed the pathway of pollutant through intermediates detected experiments.Investigated the reusability of ACF and study the protection mechanism of ACF in the system.In addition,evaluated the applicability of the E-ACF-PS system by the experiments of multiple organic decomposition,effect of actual water matrixes,and toxicity study of intermediates.Finally,the regeneration efficiency and mannerization efficiency of saturated ACF at cathode was explored,thus provide new ways of ACF reusing.The major contents and conclusions are listed below:?1?The removal efficiency of carbamazepine(CBZ,0.042 mmol L^-1)could reach96.36%as current density at 286 A m^-2 and PMS concentration at 50 mmol L^-1,which was much higher than electrochemical activated persulfate system with titanium coated platinum as cathode.Compared with E-ACF-PDS system,E-ACF-PMS has higher CBZ mannerization efficiency,and the energy consumption is only one third of that of E-ACF-PDS system.Single factor experiments showed that increasing oxidizing agent dosage,current density and pH could improve the CBZ removal efficiency significantly.The presence of Cl^-could enhance the removal of CBZ while the presence of PO₄^3-?HCO₃^-and NOMs inhibit it.?2?Free radical scavenger experiments indicate that the kinds of reactive species and their generation mechanism are different in E-ACF-PS system with different oxidizing agents.In E-ACF-PDS process,the reactive species are SO₄^·-and^·OH,which are generated by activated PDS at cathode.On the other hand,the reactive species in E-ACF-PMS system are SO₄^·-,^·OH,and singlet oxygen?¹O₂?,which could generate by activated PMS at both cathode and anode.Different from the way of generation of ¹O₂in other PMS activation systems,the generation of ¹O₂ in this process was mainly due to the reaction between PMS and^·OH at cathode.Moreover,the results of estimation of related reactions contribution shows that reactive species oxidation in E-ACF-PS played a major role in the removal of CBZ.Among those,in E-ACF-PMS process,^·OH is the main reactive species,and its steady-state concentration and contribution are 4.22×10^-12M and 45.92%,respectively.In E-ACF-PDS system,SO₄^·-is the main reactive species,its steady-state concentration and contribution are 5.84×10^-12 M and 36.63%,respectively.Finally,the intermediate analysis experiment shows that the difference of degradation pathway of intermediates of E-ACF-PMS and E-ACF-PDS systems are caused by ¹O₂ oxidation.?3?ACF multi-reuse experiments indicate that E-ACF-PS process could removal CBZ effectively after ACF recycles 50 times.Comparing SEM images,pore distribution and surface functional variations of ACF samples before and after long time service with or without current,it was found that the drawback of ACF being oxidized and lost reactivity by PS could overcome by electric field supplied.As spectated,the electric field can donate electrons in E-ACF-PS process,thus converting ACF from initiator to catalyst.Moreover,compared with E-ACF-PDS,E-ACF-PMS process has advantage of ACF reusability.?4?Application potential experiment showed that E-ACF-PS could remove multiple refractory organic pollutants?sulfamethoxazole,tetracycline,diclofenac,and phenol?effectively.Moreover,E-ACF-PS system could achieve the removal of CBZ and the recycle of ACF in surface water and tap water.Algae growth experiments illustrated that mild toxicity intermediates generated in E-ACF-PS process which inhibited the growth of algae.Compared with E-ACF-PDS,E-ACF-PMS is more promising in terms of applicability.?5?As far as the issue of ACF losing adsorption capability in long term service,the regeneration efficiency of ACF was evaluated?phenol saturated ACF as cathode?.The results showed that E-PS system could effectively desorb and mineralized phenol,thus overcoming the issue of secondary pollution which caused by the regeneration effluent in traditional electrochemical regeneration.Compared with PMS,PDS as oxidizing agent could greatly save the cost of regeneration.Moreover,adding PDS in twice can increase the utilization efficiency of oxidizing agents,thus increasing the mineralization efficiency of desorbed contaminants and regeneration efficiency of ACF.Under optimal condition(current density of 1A,100 mmol L^-1 PDS added twice,regeneration time of6h),the regeneration efficiency of ACF in E-PDS was 66%,while maintaining the TOC level in the regeneration solution only one fourth of that in traditional electrochemical regeneration.?6?The estimation of the contribution of related reactions demonstrated that with the decreasing of the PDS concentration,anode oxidation became the main process of phenol degradation.Therefore,phenol was preferably oxidized to intermediate?such as benzoquinone,hydroquinone,and catechol,etc.?instead of mineralized to CO₂ and H₂O,which could re-adsorb onto ACF.Besides,the free radicals produced in the system could continuously oxidize ACF,and cause the decrease of ACF adsorption capacity.Thus,it is hard to improve the regeneration efficiency of ACF in E-PDS regeneration process.However,the regeneration efficiency of ACF could still reach above 40%after3 times adsorption-regeneration.In conclusion,E-PDS regeneration methods could be proposed as a promising activated carbon regeneration technology in industry application.