Removal Of Triclosan From Soil By Activated Persulfate

Triclosan(TCS),as a personal care product,is a new broad-spectrum antibacterial agent,and is widely used in soap and toothpaste.During its production,transport and use processes,TCS could possiblely enter into environment.Owning to its low biodegradability,long half-life of 20-58 days,bioaccumulation and mobility,TCS can affect the soil nitrogen cycle as well as the structure and function of soil microbial communities.Therefore,it is of great theoretical importance to remove TCS in soil and study the underlying degradation mechanism.Activated persulfate oxidation processes are promising in-situ chemical oxidation technologies(ISCO)widely used for soil and water remediation due to its low cost,high efficiency,easy-to-operate and environmental friendly natures.However,up to now,previous studies focus on the degradation of TCS by R-AOPs in aquatic medias.It is still largely unkown how SR-AOPs degrade TCS in soil,especially the impact of different catalytic methods.Therefore,in present study,degradation of TCS in soil using Fe2+-activated persulfate and heat-activated persulfate and the degradation mechanisms and degradation products of two methods are emphatically compared.The main research results are as follows:1.Removing TCS from soil using Fe2+-activated persulfateFe2+-activated persulfate was used to degrade TCS in soil,and the effect of PS/Fe2+concentration,pH,anion and chelating agents on the degradation was studied.The results showed that after 240 minutes at 23OC,the degradation efficiency of contaminated soil with 50 mg·kg-1 TCS was 70%(9.4 mM PS and 9.4 mM Fe2+).Increasing PS/Fe2+ concentrations can enhance the degradation efficiency and acidic conditions are favorable for TCS degradation while the degradation was negligible at pH 6.5.The presence of low concentration of Cl-promotes the oxidation process whereas relatively high concentration of Cl-could slow down the process.The presence of HCO3-inhibited the removal of TCS.Moreover,the results of adding chelating agents(such as oxalic acid,citric acid and ethylenediaminetetraacetic acid(EDTA))on the degradation showed that citric acid and EDTA may enhance the degradation of TCS.On the contrary,oxalic acid reduced the degradation of TCS.The quenching studies using ethanol and tert-butanol revealed that SO4·-played the major role duing the TCS degradation.2.Removing TCS from soil using thermally activated persulfateThe degradation of TCS by thermally activated persulfate was studied and the effects of PS concentration,pH,temperature and natural organic matter on the degradation were taken into account.Researches showed that after 360 minutes at 50℃,the degradation efficiency of soil contaminated with 50 mg·kg-1 TCS reached 69%(9.4 mM PS).Increasing temperature and PS concentration could enhance the degradation of TCS.In contrast,the degradation rate decreased with increased pH levels.Adding natural organic substances(such as humic acid(HA))inhibited TCS degradation.Furthermore,the quenching studies using ethanol and tert-butanol as the quchening agents under different pH levels revealed that,SO4·-played a major role in acidic and neutral conditions and HO-was the primary radical in alkaline conditions.3.TCS degradation products and the degradation pathwaysThe intermediates of TCS under different oxidation methods were extracted and concentrated by solid phase extraction.A liquid chromatography-triple quadrupole mass spectrometry(LC-MS/MS)was used to analyse the intermediates.Ultimately,seven intermediates were identified and base on this,two degradation pathways were thus proposed.In the first pathway,cyclization,happened between-OH and-Cl groups under tSO4·-attack,which resulted in the removal of HCI and generation of product 2,8-DCDD.In the second pathway,phenolic hydroxylation happened.The formed TCS cations through electron transfer converted to hydroxylated TCS after combining with H2O.Afterwards,the hydroxylated TCS was oxidized to quinoid-type internediates by SO4·-.