| The industrial wastewater of printing and dyeing is pollution source of refractory organic compounds all over the world.It is featured by complicated organic matter composition,high density,poor biodegradability and toxicity.These effluents cause serious pollution to environment.The environmental pollution in China which is a large country having textile dyeing and printing industry,has become more and more serious too since increase of dye wastewater discharge after the reform and opening up.Therefore,we choose a new method called glow discharge plasma(GDEP)system to degrade simulated dye wastewater(the typical basic dye Basic Violet 16)and obtain a desired treated result in this work.The main results are as follows:We investigated four influence factors such as degradation time,conductivity,voltage and initial concentration of dye on degradation by desired experiments and got optimum reaction conditions in degradation:the decolorization rate of 200 mL,20 mg/L of basic violet 16 can reach 97.5%in 20 minutes by GDEP degradation at 600 V and the dye faded almost.With the increase of voltage in the GDEP system,the concentration of the active particles like OH·and H2O2 increased leading to promote the degradation effect.Considering the bearing capacity of the electrode,we choose 600 V as working voltage at last.When the initial dye concentration is increased,the decolorization rate is reduced at the same degradation time,and the entire degradation process follows first-order kinetic characteristics.Increasing the conductivity(i.e.increasing concentration of supporting electrolyte)can make the decolorization rate of Basic Violet 16 reach 95%within 10 minutes,and the complete fading time is 10 minutes earlier.The optimum reaction conditions are:working voltage is 600 V;initial dye concentration<1 00 mg/L;supporting electrolyte concentration is 2 g/L.In order to reduce energy consumption,the degradation effect of Fenton reagent in the GDEP system was studied further:it was found that the threshold voltage VD of the non-Fenton system glow discharge was 450 V,while it reduced to 375 V in the Fenton system,and the glow of plasma was brighter and stronger than before.Under the same conditions,the decolorization rate of Fenton system reached 99.4%at 60 min with degrading 100 mg/L of basic violet 16 simulated dye solutions,while the non-Fenton system was only 61.18%.In the Fenton system,H2O2 was not detected while the OH concentration is much higher than that of the non-Fenton system due to H2O2 was consumed largely by Fe2+and OH·was generated then.At the same time,the floccules of Fe(OH)3 and Fe(OH)n produced in the Fenton system play a promoted role for degradation by bonding the anionic recognition sites of the dye molecules,adsorption and co-precipitation.The Fenton system reduces energy consumption to a certain extent and provides a better solution for applications.Promoting effect of O2 during degradation was studied in this experiment:the emission spectrum and salicylic acid capture method were used for qualitative and semiquantitative analysis of OH produced in the GDEP degradation system while the potassium permanganate titration method was used to measure the H2O2 concentration during the degradation.The results show that the decolorization of Basic Violet 16 was accelerated after passing through O2 gas.The OH concentration is very little difference in the system adding O2 or not while H2O2 increased with O2.H2O2 promotes the degradation effect to a certain extent by synergy with UV and O3 which were produced by GDEP.It's worth noting that OH of the system would be consumed by adding excess H2O2(>10 mmol/L)and then the reaction progress was inhibit on the contrary.Cl·promotes the system degradation effect:it was found that the using KC1 as supporting electrolyte also promoted the degradation in GDEP system at same voltage,the decolorization rate of Basic Violet 1 6 can reach 96.19%at 10 min.In comparison,the decolorization rate is only 34.93%with Na2SO4 as supporting electrolyte with same concentration.The effect of Na+,K+and SO42-were excluded for they are all stable ions.It is deduced that this promotion is caused by free chlorine or chlorine-containing radicals comes from GDEP system.However,the presence of free chlorine was not detected in the GDEP degradation system at working voltage of 600 V by the DPD detection method and thereby the influence of free chlorine was excluded.But the degradation reaction was significantly suppressed after adding Na2S2O3 as scavenger for chlorine free radical.It is deduced that the addition of KCl generates Cl·and ClO·in the GDEP system,and ClO·can degradate the intermediate product phenol and Cl·can directly react with NH4+to produce NO3-and NO2-and thus promote the overall degradation.Reasonable degradation mechanism and reaction pathway were studied in this paper.We investigated the intermediate products by using CFA,IC,LC/MS,and GC/MS.According to intermediate products and the time that they appeared,some important intermediates in the pathway were analyzed as follows:basic Violet 16 was first degraded into indole structures and N,N-diethyl-4-methylaniline by OH attack,and then both of them were converted to phenol.Through chemical reactions such as hydroxylation and ring opening,four organic small molecular acids including succinic acid,lactic acid,formic acid and acetic acid come from further degradation of phenol.At the same time,the pH value of the system decreased firstly and then increased,and the electrical conductivity increased all the time.It is consistent with the result that the content of small molecule acids and ionizable substances all increased in the possible pathway.Most of the amino group falling off from the compounds exists in the form of NH4+,and part of them eventually changed to NO3-,NO2-and N2 by attack of Cl and ClO·.The TOC removal rate of basic violet 16 can reach 59.16%at 180 min,and these part organic compounds were finally mineralized into CO2 and H2O.The free radicals like OH and ClO· played key roles in the entire degradation process. |
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