In Situ Regeneration Of Saturated Activated Carbon Fiber By Electro-cathode Activated Oxone Process:Regeneration Efficiency And Mechanism Study

Phenol-containing wastewater is often produced in many industries such as the coal chemical industry,metallurgy,medicine,pesticide,plastic manufacturing,etc.If improperly disposed of and discharged into environmental water bodies,it will cause great harm to the water environment and water ecology and cause the potential threat of carcinogenicity,teratogenicity,and mutation to the human body due to the enrichment of the food chain.In fact,the effective disposal and safe reuse of phenol-containing wastewater have always been a hot issue in the field of water treatment.At present,the more mature treatment process for phenol-containing wastewater is usually activated carbon adsorption.After the process runs for a while,the activated carbon will gradually reach adsorption saturation and needs to be regenerated to restore its adsorption activity.It should be pointed out that the adsorption process essentially only concentrates phenolic organics from the liquid-phase wastewater onto the solid-phase activated carbon without degrading the pollutants.Therefore,the degradation of contaminants is reflected in the later stage of the regeneration process.Traditional thermal regeneration is a relatively common regeneration technology used in industry.However,this method uses mostly non-clean energy,which requires a lot of energy,and causes a large weight loss of activated carbon,and the effect of multiple cycles of regeneration is poor.In the context of China’s proposal of carbon peaking and carbon neutrality,the synergistic effect of reducing pollution and controlling carbon emissions in the water treatment process is significant,and thermal regeneration is obviously not the optimal choice.Electrochemical advanced oxidation regeneration uses relatively clean energy（electric energy）,and strong oxidizing active species can be generated during the regeneration process.It can not only regenerate activated carbon with low energy consumption,but also effectively mineralize the pollutants on the activated carbon,which is a promising clean regeneration technology.In this study,the common phenol in industrial production was used as a model pollutant.The electrochemical cathode/oxone（EC/Oxone）in-situ regeneration process was proposed to perform in-situ regeneration phenol-saturated activated carbon fiber（ACF）.The traditional electrochemical（EC/Pt）,Oxone,EC/Oxone,and electrochemical cathode/peroxysulfate（EC/PDS）regeneration processes for the regeneration efficiency of phenol-saturated ACF and the degradation efficiency of pollutants in the regeneration solution were systematically investigated.And combined with the energy consumption calculation,the pollutant degradation and carbon emission reduction effects of EC/Oxone regeneration process are evaluated.In addition,the optimal condition of EC/Oxone process was determined by the investigation of current density,regeneration time,oxidant concentration,dosing method,and other influencing factors.The mechanism of ACF regeneration by EC/Oxone process was clarified by identifying reactive oxygen species,estimating the contribution rate of related reactions,evaluating the oxidation and protection of ACF,exploring the migration and transformation of total organic carbon（TOC）and byproducts in the regeneration solution and ACF,and evaluating the multiple adsorption-regeneration cycles.The main contents and relevant conclusions of this paper are as follows:（1）ACF has a strong adsorption performance for phenol and can quickly remove it from water.The adsorption kinetics is more in line with the pseudo-second-order kinetic model.And the adsorption isotherm is more consistent with the Langmuir adsorption model,indicating that the adsorption process is multi-molecular layer heterogeneous adsorption.The maximum adsorption capacity of ACF for phenol was 282.48 mg g^-1,which is much higher than that of the traditional granular and powdered activated carbon materials.（2）Compared with EC/Pt,Oxone,and EC/PDS regeneration processes,EC/Oxone process can not only effectively restore the adsorption capacity of ACF in-situ,but also simultaneously degrade and mineralize the pollutants in the regeneration solution.Additionally,the energy consumption of the EC/Oxone process is only about 1/10 of that of the traditional electrochemical regeneration,indicating that the EC/Oxone process is a new type of green and low-carbon regeneration technology.（3）In the EC/Oxone regeneration process,there are three reactive oxygen species,including hydroxyl radical（^·OH）,sulfate radical(SO₄^·-),and singlet oxygen（¹O₂）.The proportions of^·OH,SO₄^·-,and ¹O₂ in phenol degradation are 52.04%,20.37%and10.05%,respectively.EC/Oxone regeneration process is dominated by^·OH,and a variety of reactive oxygen species synergistically and efficiently degrade pollutants desorbed from ACF.（4）Oxone oxidation will destroy the physical structure and chemical properties of ACF,while the cathode electric field can protect ACF from oxidative damage so that ACF can be better protected in EC/Oxone regeneration process.However,ACF can not recover all the original adsorption capacity because of the re-adsorption of some byproducts produced in the regeneration process.（5）When the current density is 57.14 m A cm^-2,the regeneration time is 6 h,the oxidant concentration is 75 m M,and the oxidant dosing method is batch dosing,the EC/Oxone regeneration process can reach the maximum regeneration efficiency of82.53%.（6）After 10 regeneration cycles,EC/Oxone process can still maintain a regeneration efficiency of about 60%,indicating that the process has stable and continuous regeneration performance.In conclusion,this paper proposed an EC/Oxone in-situ regeneration process,which is dominated by^·OH,and multiple reactive oxygen species synergistically degrade the desorbed pollutants from ACF.The mechanism of EC/Oxone process for in-situ regeneration of phenol-saturated ACF and simultaneous mineralization of pollutants were studied.The effects of different operating conditions on the regeneration efficiency of the process were investigated.And the stability and sustainability of the process were verified by energy consumption calculation and multiple adsorption-regeneration cycle experiments.This research has made a beneficial exploration on developing new regeneration technology in the field of water treatment under the background of carbon peaking and carbon neutral.The results of this paper can provide new ideas for the development of green frontier regeneration technology for pollution reduction and carbon control,which has good theoretical value and strong application prospects.