| Polybrominated diphenyl ethers are typical pollutants in soil around electric waste(e-waste)recycling sites(EWRSs),which have attracted widespread attentionsdue toits potential harmful andbiotoxicity.To degrade BDE209,some reductive chemicals such as zero-valent iron have been introduced.BDE209 removal by reductive reactions often followed a stepwise debromination manner.Additionally,the low brominated intermediates are more difficult to be further reduced,which often results in incomplete debrominationthe.For this defect,this paper focuson the degradation of BDE209 by using advanced oxidation process,andexporing the performance and machenism of BDE209 in the different persulfate activation systems.The main research results of this paper were as follows:(1)In the ferrous activated persulfate system,a lower pH would result in a greater increase in the BDE209 removal efficiency,and the maximum removal efficiency was obtained at pH=3.0.The effects of sodium persulfate(PS)dosage and molar ratio of Fe2+/PS were also determined,and 0.2 mol L"1 and 0.5/1 were the best conditions,where the removal of BDE209 in soil could reach to about 53%after 6 h.Additionally,hydroxylamine(HA)was firstly introduced to a PS/Fe2+system,and resulted in a large enhancement of BDE209 removal efficiency.Compared to the controls,the degradation rate increased by 13%with the ratio of HA/Fe2+ 4/1,which might be because HA accelerated the transformation from Fe3+to Fe2+.Sodium gluconate(Glu)as an eco-chelate,has been introduced into a traditional iron activated sodium persulfate(PS)system(Fe:2+/PS).The results indicated that the PS/CA/Fe2+ oxidation could be an effective method for BDE209 removal,the removal of BDE209 can be up to 71.8%at pH=3.0.The degradation of BDE209 in the PS/CA/Fe2+ systemfollowed the pseudo-first order reaction kinetics.The rate constants(ki)of BDE209 removal indicated a quadratic curve relationship with initial persulfate concentrations:(kI=-0.019×[PS]02+0.031×[PS]0+0.007,R2=0.933.(2)In the heat activated persulfate system,higher temperature was beneficial to the removal of BDE209.The highest removal of BDE209 occurred at pH 5,about 53.8%of BDE209 was removed.Furthermore,the rate constants(ki)indicated quadraticcurve relationship with initial persulfate concentrations(kI=-0.293 ×[PS]02+0.267×[PS]0+0.046,R2=0.917,[PS]0=0.05-0.5 M)and a good linear relationship with initial BDE209 contents(kI=-0.004×[BDE209]0+0.312,R2=0.994).(3)The removal of BDE209 by using base activated persulfate was inefficient,eventhough as the high level of oxidants,only 30.3%of BDE209 was removed after 360 min reaction;To further enhance the BDE209 removal,base activated persulfate coupled with other activation methods(heat,ultrasolic and Fe2+-gluconate)was introduced.The results indicated that as the Fe2+-gluconate and persulfate ratio of 0.1/1,the destruction of BDE209 can up to 51.5%.In the base+ultrasonic activated persulfate system,theultrasound could hardly activate persulfate into free radicals,but can improve the BDE209 removal efficiency by promoting the BDE209 molecules desorpt from the soil and organic matters.In addition,ultrasound could facilitate the transfer of PS solution and free radicals into the macrophores and destruct the BDE209 that absorbed in the hard-to-reach locations,leading to more BDE209 molecules being oxidized;Compared with the sole base activated persulfate system,the degradation of BDE209 was increased by 11.7%.(4)The BDE209 degradation pathway under different activated persulfate systems are similar,followed by debromination reaction,free radicals succesively attacked the low brominated diphenyl ether,then mineralization into CO2,H2O,short chain carboxylic acid and other small molecules. |
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