| The traditional biological treatment has some limitations because of natural gas purification plant overhaul wastewater contains the characteristics of large quantity fluctuations and has uneasy degradation substance of methyl diethanolamine (MDEA),In this paper,taking the overhaul wastewater as research object,based on the theory of sulfate radical in the advanced oxidation techno logy, the effects of MDEA degradation was studied under the different activate methods of persulfate,the main factors for the production of sulfate radical were pointed out,the mechanism of MDEA oxidized by sulfate radical was analyzed, meanwhile, Coupling the three-dimensional electrode with the activated persulfate technology,the conditions,effects and mechanism of reaction were explored; the effects of C1 ,CO32-,HCO3 on sulfate radical oxidated MDEA were studied. The main conclusions were as follows:In the study of heat-activated persulfate, The COD removal rate of overhaul wastewater was positively correlated with the activate temperature and concentration of sodium persulfate, negatively correlated with initial pH.The COD removal rate reached 40% when the activate temperature in 80℃,Sodium persulfate concentration of 4000mg/L,the initial pH=3.Thermodynamic analysis showed that the reaction process is endothermic reaction, raising temperature was conducive to the degradation of MDEA, the apparent activation energy was 29.5KJ/mol.The information of infrared spectrum showed that main process of MDEA degradation by heat-activated Na2S2Os was bond broken of C-N to produce alcohol or nitro compounds, and then it was degraded by oxidation.GC-MS analysis verified that the main degradation products were acid substances, such as malonic acid. According to the dynamic model of heat-activated/Ps system, the content of sulfate radical was 3.306×10-5mol/L.In the study of Fe0-activated persulfate,the COD removal rate of overhaul wastewater were positively correlated with the dosage of Fe0, negatively correlated with initial pH. The COD removal rate of overhaul wastewater reached 30% when Sodium persulfate concentration of 4000mg/L,ZVI dosage at 1500mg/L,the initial pH=3.Through the detection of concentration change of Fe2+,Fe3+,S2O82- in the reaction system, that the main activation substance in the Fe0-activated persulfate system is Fe2+, rapid release and accumulation of Fe2+ will compete sulfate radicals, resulting in a low removal rate.According to XRD analysis on the surface of Fe0 after reaction, the main substance on the oxidated Fe0 surface was Fe2O3, which can verify the rapid transformation from Fe2+to Fe3+, caused less effectively utilization of Fe2+, therefore, it is an effective means to improve Fe0-activated efficiency by reducing the particle size.Coupling the three-dimensional electrode with the activated persulfate technology,the research shows that when Sodium persulfate concentration of 200mg/L,the initial pH=7,Voltage of 50V, reaction time 2h,TOC and COD removal rate reach 60.33% and 60.33% respectively,The addition of probe compounds showed that Na2S2O8 not only worked as an electrolyte in the reaction, but also produced the oxidizing substance of SO4-·. The removal efficiency of combined process was 10% higher than that of three-dimensional electrode, and also increased 20% as compared with single activated persulfate system. Timely adding Na2S2Os can make the COD removal rate increased 18%.The effect of inorganic anions on the degradation of sulfate radical was studied,The existence of Cl-,CO32-,HCO3- exhibited inhibitory effect on degradation of MDEA,The concentration of Cl-has inhibitory effect on the degradation of MDEA, The concentration of CO32- and HCO3- was positively correlated with inhibition of MDEA degradation. Cl- would react with sulfate radical to generate Cl- and Cl2-, so that the concentration of S2O82- and Cl-was changed in the system.In the reaction system with the existence of CO32-, the master inhibiting anion would vary with the concentration of CO32-,Response surface analysis showed that the three anions exist in the system at the same time,the significantly inhibitory effect on sulfate radical was presented as following:Cl-> CO32->HCO3-. |
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