The Degradation Of Iodinated Pollutants In Water By Ferrous/Persulfate Advanced Oxidation Technology

As a new kind of halogenated disinfection by-products,iodinated disinfection by-products?I-DBPs?have received more and more attention because of their strong cytotoxicity and genetic toxicity,and they are difficult to remove by conventional treatment.Iodoform?CHI₃?is one of typical refractory I-DBPS,while iodinated X-ray contrast media?ICM?is one of the most important iodine source of I-DBPS,and the advanced treatment of these pollutants became imperative.In this paper,iodoform and two representative ICMs such as iopamidol?IPM?and diatrizoate?DTZ?were treated by Fe???/PS advanced oxidation technology.The effects of PS concentration,molar ratio Fe???/PS,initial pH and temperature on degradation and deiodinate were investigated.Free radical inhibition experiments,electron paramagnetic resonance?EPR?,and free radical tracer experiments were used to investigate the free radicals in the reaction system.The possible products and paths of two kinds of ICMs were analyzed by DFT?density functional theory?quantum chemistry calculation.The conclusions were as follows:?1?Fe???/PS advanced oxidation is an efficient treatment for degradation and deiodination of CHI₃,and the removal rate is up to 83%when PS concentration is 15?M at normal temperature.Increasing PS dosage could improving CHI₃ removal rate and deiodination.1:5 is verified to be the optimum Fe???/PS mole ratio,and both of excessive and derisory Fe???are not good for CHI₃ degradation and deiodination at a certain PS dosage.Reducing initial p H?pH 3¹1?can promote CHI₃degradation and deiodination.In the range of 25⁴5?,higher temperature could enhance degradation ability and deiodination ability.In the free radical inhibition experiments,the contribution of SO₄^-·to CHI₃degradationisconfirmedbecausetheinhibitoryeffectof methanol?MeOH?is better than that of tert butyl alcohol?TBA?.Through the tracing on SO₄^-·and OH·by atrazine and nitrobenzene,it was found that the SO₄^-·was increased with the increase of PS concentration,but OH·did not change significantly,which means the increase of SO₄^-·leads to the enhancement of iodoform degradation rate and iodine removal ability.Under the condition of mole ratio Fe???/PS 1:5,the SO₄^-·and OH·content in the reaction system were the largest,which were more than in higher or lower ratio,producing the optimal CHI₃ degradation and deiodination.Increasing pH could reduce SO₄^-·but increase OH·,reducing the oxidation capacity of the system,which is bad for CHI₃removal.The increase of temperature was beneficial to the generation of SO₄^-·,but there was no obvious impact on OH·.And more SO₄^-·were generated at high temperature,enhancing degradation and deiodination ability.It is found all of the iodine removed are transformed into IO₃^-after the detection of iodine in the process.?2?Fe???/PS advanced oxidation is an efficient treatment for degradation and deiodination of IPM,and the maximum removal rate can be 61%at normal temperature.Increasing of PS concentration within1mM can enhance the degradation and deiodiation of IPM,while excessive PS won't.In a certain PS concentration,excessive Fe???and inadequate Fe???are both not good for degradation and deiodinate of IPM.The lower pH?pH 3¹1?of the solution is,the more effective degradation and deiodiate of IPM are obtained.Increasing temperature in the range of 25⁴5?is beneficial to the degradation and deiodiate of IPM.Considering comprehensively,the optimum conditions are verified to be PS 1mM,mole ratio Fe???/PS 1:10,pH 3 and 25?.The suppression test and EPR spectra showed that the combined effects of SO₄^-·and OH·contributed to degrade IPM,but OH·played a dominant role.Through DFT quantum chemical calculations,the possible reactions are hydroxylation,deiodination,deacetylation,and amine oxidation.The degradation of IPM by Fe???/PS advanced oxidation system is accompanied by iodine removal,and all of the iodine removed are transformed into IO₃^-.?3?Fe???/PS advanced oxidation is effective to degradate DTZ,and the maximum removal rate can be 69%at normal temperature.Increase of PS concentration within 10mM can promote the degradation of DTZ,while excessive PS won't enhance the degradation ability and deiodiation capacity.When PS concentration is constant,excessive Fe???and low Fe???are both not conducive to degradation and deiodinate of DTZ.Reducing initial pH?pH 3¹1?can promote DTZ degradation and deiodination.The increase of temperature in the range of 25⁴0?is beneficial to the degradation and deiodiate of DTZ.And Considering a variety of factors and costs,the optimum conditions are verified to be PS10mM,mole ratio Fe???/PS 1:10,p H 3 and 25?.The suppression test and EPR spectra showed that the combined effects of SO₄^-·and OH·contributed to degrade DTZ,but OH·played a dominant role.Through DFT quantum chemical calculations,the possible reactions are hydroxylation,deiodination,hydroxyl group oxidation,cleavage of amine moiety,decarboxylation,deacetylation,carboxylic acid group and iodine substitution.And DTZ-TP630-TP628-TP602 is seen as the main reaction pathway for the oxidation of DTZ by OH·after the compare of the energy barrier.The degradation of DTZ by Fe???/PS advanced oxidation system is accompanied by iodine removal,and all of the iodine removed are transformed into IO₃^-.