Pathways And Application Of Oxidative Degradation Of Typical Organic Pollutants

Based on the processes of organic pollutants degradation, it is composed ofoxidation reactions. Oxidation technology can be used in treatment of persistent andtoxic organic pollutants in quite short period with minimized secondly pollution, whichmakes it a focus in recent environmental researches. Because the targeted pollutants canbe destroyed completely, advanced oxidation processes are also namely as destructivetechnology, which have found more and more wide applications currently.Experimental researches in this study can be described as three stages:â‘ powerfulEC-MS technology was used to look into the details in the complete organic pollutantsoxidative degradation and the photocatalytic degradation processes;â‘¡the effectivenessof oxidation processes was confirmed by applying Fenton’s reaction and iron-carbonelectrolysis technology in landfill leachate treatment;â‘¢mechanisms of environmentaloxidation processes were reviewed and probed into based on previous water-solubledyes oxidative degradation data.In part I experiments, the results are as follows:There are two series of experiments, namely oxidative degradation of two typicalantibiotics based on EC-MS technology, and ultraviolet degradation of chlortetracyclineand products identification with organic mass spectrometer.Taking advantage of EC-MS technology, oxidative degradation tendencies ofchlortetracycline in three pH conditions, namely pH=3.0,6.8and10.0were compared,and possible derivative products of chlortetracycline in natural environment wereidentified. Oxidative degradation products of chlortetracycline with the electric potentialrising from0to+2500mV were identified with organic mass spectrometer in threedifferent pH conditions. More than10product positive ion peaks are of interest, some ofwhich have got their possible molecular formulas. In pH=3.0system，when the voltagein EC reached1120mV, CTC showed the tendency of degradation; in pH=6.8system,when the voltage in EC reached1264mV, CTC showed the tendency of degradation; inpH=10.0system, when the voltage in EC reached1510mV, CTC showed the tendencyof degradation. In pH=3.0system，when the voltage in EC reached1822mV, hydroxylradicals were generated; in pH=6.8system，when the voltage in EC reached1948mV,hydroxyl radicals were generated; in pH=10.0system，when the voltage in EC reached2020mV, hydroxyl radicals were generated. As for the production of product m/z=495, the highest ion intensity of this ion in pH=3.0was1.4×10⁶; in pH=6.8system, it was6.0×10⁵and in pH=10.0system, it was10.0×10⁵. It was believed as an evident thatelectrical chemistry oxidative degradation of CTC was initiated by the attacking fromhydroxyl radicals.In UV degradation experiments, middle-pressure immersion UV lamp （TQ150,150W） was used as the core of the UV reactor, provided with quartz burner and quartzcooling water jacket. The reaction system was composed of methanol and pure water, assolvent, and ammonium acetate as buffer agent, chlortetracycline as the UV degradationtarget. In addition to the investigation on the UV degradation processes of CTC in3different pH conditions, effects of zero-valent iron, zinc oxide, titanium dioxide andFe（II） were studied. Based on the result, it was found in acidic system, CTC is moststable under UV radiation, while in alkaline condition, CTC is most active to degrade.Zero valent iron can promote the UV degradation of CTC in pH=3.0system, and thepositive ion peak m/z=534of the complex of iron ion with CTC was identified. It wasbelieved that in acid system, zero valent iron was transferred into Fe（II） and Fe（III） ions,which would contribute as the catalytic agents in UV-Fenton’s system. The othernecessary part of Fenton’s reaction is hydroperoxide, which was produced by UVirradiation in the system. Although methanol was reported as a kind of free radicalquenching agent, but UV radiation-induced hydroperoxide generation is so rapid thatthe Fenton’s reaction can take place. In neutral system （pH=6.8）, zero valent iron canhardly be transferred into Fe（II） or Fe（III） ions into the solution and there was noevidence that zero valent iron itself can not promote the UV degradation of CTC. Inaddition, there was no positive ion peak m/z=534of the complex of iron ion with CTCidentified.In pH=3.0system, introduction of0.1mmol/L Fe（II） can promote the UVdegradation of CTC obviously, and also the positive ion peak m/z=534of the complexof iron ion with CTC identified. Zinc oxide exerted different effects in different systemsin UV degradation of CTC. In pH=3.0system, rapid chemical reaction took placebetween zinc oxide and CTC. In pH=10.0and pH=6.8systems, zinc oxide can promoteUV degradation of CTC obviously. Several positive ion peaks of the products wereidentified, including two kinds of complex of CTC with zinc ions.For application of Fenton’s process in landfill leachate treatment, when pH=3andFe²⁺/H₂O₂molar concentration ratio was1:30, COD remoal of landfill leachate was inthe range of40%⁵0%and UV254removal was in the range of30⁴0%. For application of iron-carbon electrolysis process in landfill leachate treatment,effect of flow-in iron-carbon column is better than mixed immersion of iron scraps andcarbon grapes for the remoal of COD and turbudity. In the experiment conditions,COD removal of landfill leachate was60%and turbudity remoal was as high as94%with flow-in iron-carbon column even in weakly acidic condition.Experiment results listed in part III experiment was carried out previously andextracted from published thesises of the candidate herself, based on which, the pathwayand mechanisms were reconsidered to provide reliable basis for effective oxidationtechnology development suitable for organic pollutants treatment.In conclusion, in this study, real landfill leachate of high-concentration organicpollutants, simplified water-soluble dyes water solutions and chlortetracyclinemethanol-water solution were selected as the research systems, Fenton’s oxidationprocess, iron-carbon internal electrolysis method, UV-Fenton process, EC-MStechnology and UV reactor coupled with organic mass spectrometer were used foroxidative degradation research. The research covered the preliminary determination oftreatment efficiency to the reckoning on reaction steps, to the identification of productsand intermediate products in the oxidative degradation processes by the powerful MStechnology. Wishing it can make contribution to new flexible technologies developmentfor the treatment of distributed waste water.