Study On Adsorption Removal Of Toxic Intermediates Produced In Electro-oxidation By Carbonaceous Materials

Advanced oxidation process(AOPs)can produce strong oxidizing species,which can effectively degrade refractory organic pollutants.However,the operation cost is higher than other technologies.Incomplete oxidation of organic pollutants leads to highly toxic organic intermediates.In this paper,AOPs and adsorption processes were combined to study the removal of these highly toxic intermediates and the reduction of their toxicity and removal.The toxic intermediates produced during electrochemical oxidation of azo dye Acid Orange ? were employed for the combined process.Acid Orange ? was firstly subjected to electrochemical oxidation.It was found that that the content of cyclic intermediate products was highest at 1 h of electro-oxidation treatment.The solution treated by 1 h of electro-oxidation was treated by activated carbon fiber(ACF)adsorption.Effect of solution pH,adsorption temperature and coexisting ions were investigated.It was found that the removal efficiency of cyclic intermediate decreased with an increase of solution pH.Most of the uptake of cyclic intermediates occurred in the initial stage.Pseudo-second-order kinetic model well described the adsorption process,indicating that the chemical adsorption was the control step of the adsorption process.The uptake of cyclic intermediates decreased with increasing reaction temperature,indicating an exothermic and spontaneous adsorption process in nature.FTIR analysis confirmed the uptake of these cyclic intermediates on the ACF.Toxicity test using vibrio fisher showed that the adsorption process could effectively reduce the toxicity theoxidation-treated solution.As one of the highly toxic intermediates generated during electrochemical oxidation,1,4-benzoquinone was adsorbed by corn straw biochar prepared in laboratory.It was found that the biochar prepared under 600 ? of pyrolytic temperature outperformed those biochars pyrolyzed under other tempeartures.Further,the biochar pyrolyzed under 600 ? was used for the column adsorption test.The breakthrough curves became flat at alkaline pH conditions,lower intial concentration,lower flow rate and higher bed depth.These conditions were advantageous for the removal of 1,4-benzoquinone.Presence of CaCl2 was not favroable for the adsorptive removal of 1,4-benzoquinone.The adsorption processes were simulated,and the results showed that Thomas,Clark and BDST model could fit the experimental data better,indicating that the uptake of 1,4-benzoquinone molecules on the biochar surface occurred via monomolecular layer and polymolecular layer adsorption,mass transfer resistance increased gradually during the whole adsorption process.Moreover,the simulated results by BDST model indicated that the adsorption capacity increased gradually with decreased adsorption rate.In the column adsorption processes,the desorption process was found to finish within 60 min when 0.1 mol/L NaOH solution was used to elute the used biochar.The adsorption capacity of the used biochar can be recovered by about 40%.