Release Performance Of Persulfate Sustained-release Material And Its Application In Degradation Of Phenanthrene In Groundwater

Polycyclic aromatic hydrocarbons（PAHs）are a class of"three consistent"organic pollutants that are widely concerned in soil and groundwater environments.In situ chemical oxidation（ISCO）is a commonly used remediation technology for groundwater organic pollution.The continuous release of chemical oxidizing agents during the in situ remediation process is the key to the long-term effect of this technology.The combination of in-situ chemical oxidation and slow-release technology can prolong the life of chemical oxidants,effectively enhance the oxidation efficiency at a unit dose,and reduce the cost waste and secondary pollution of excessive use of oxidants.In this Thesis,a sodium persulfate-paraffin wax（PW）sustained-release material（PS@PW）was prepared for the commonly used persulfate（PS）advanced oxidant.The release performance of PS@PW under static and dynamic conditions was evaluated,its degradation effect on phenanthrene was explored,and its application feasibility in long-term remediation of organically polluted sites was analyzed.The main conclusions are as follows:（1）PS@PW materials with different ratios and diameters were prepared by the melting and solidification method.The results of static release experiments show that the mass ratio of PS to PW has a great influence on the PS release of the material.When the proportion of PS is too small（PS:PW≤1:1）,the release effect is poor;when PS:PW≥1:1,the sustained release effect is generally better.When the mass ratio is the same,the larger the diameter of PS@PW,the longer the release time of PS,but the maximum release ratio of PS decreases.PS@PW material with PS:PW=2:1,h=70mm,D=22mm,the longest release time is 36d,and the PS release rate is 92%.（2）The Bhasker and Rigter-Peppas models were used to fit the PS release process from PS@PW.Combined with SEM characterization,it was determined that the release mechanism of PS in PS@PW is divided into two stages:the first stage is the PS dissolution stage on the surface of PS@PW,the mass transfer resistance is small and the release speed is fast;the second stage is the PS release stage within PS@PW,including PS dissolution and its concentration gradient diffusion in the material pores,the mass transfer resistance increases and the release speed becomes slower.（3）The experimental results of the dynamic release column show that PS@PW can continuously and stably release PS under dynamic conditions,and the PS concentration in the effluent has a long stable period.The matrix boundary diffusion model was used to determine the PS release diffusion coefficient of PS@PW.The PS@PW diffusion coefficient of PS@PW at PS:PW=2:1,h=70mm,and D=22mm was0.028cm2/d.On this basis,it is predicted that the service life of PS@PW with h=5000mm and D≥80mm is more than 280d.（4）In the degradation experiment,the removal rate of Fe²⁺activated PS@PW for low concentration phenanthrene（0.25、0.5、1mg/L）after 2h reaction was all bigger than 90%,and common anions（Cl^-,HCO₃^-）had certain removal rate of phenanthrene.In the third cycle,PS@PW reacted with phenanthrene for 2h and the removal rate was80%.The PS@PW prepared in this thesis can release PS for a long time and continuously degrade phenanthrene in groundwater.The above research conclusions can provide a scientific basis for PS@PW as a long-term oxidant for groundwater remediation of organically polluted sites.The Thesis has 45 pictures,19 tables,and 87 references...