Study On Treatment Of Refractory Organic Compounds In Water By Advanced Persulfate Oxidation Technology

In recent decades,with industry and agriculture development in our country,the environmental problems have become increasingly serious,especially the water pollution problem,some recalcitrant and toxic organic pollutantsare are discharged into water,arousing people's attention increasingly.Compared with the traditional water pollution treatment technology,which requires harsh reaction conditions(temperature and pH),high energy consumption,high maintenance cost and other disadvantages,the advantages of advanced persulfate oxidation technology are more obvious.Under light,heat and other conditions,persulfate can generate sulfate radical(SO4-·).SO4-·has a higher redox potential(2.5-3.1V)compared with OH·(1.9-2.7 V),and SO4-· is more stable.In addition,persulfate has good water solubility,high stability at room temperature,low price and mild reaction product.In this research,activated persulfate advanced oxidation technology system was set up and the efficiency and mechnism of different activation systems were investigated.The main conclusions are as follows:(1)Comparing the degradation of MB and MO at different temperature and initial concentration of persulfate.According to the results,under the conditions of 8 mmol · L-1 Na2S2O8 and 70? the removal efficience of methylene blue reached 99%after 20 min,the removal efficience of methylene orange reached 97%after 30 min in a thermal-Na2S2O8 system.While in the UV-Na2S2O8 system,methylene blue removal efficiency was 99%within 90min and methylene orange removal efficiency was 95%within 120 min under the conditions of 8 mmol·L-1 Na2S2O8.In the Fe2+-Na2S2O8 system,methylene blue removal efficiency was 98%within 20 min under the conditions of 1.2 mmol·L-1 Na2S2O8 and 0.2 mmol·L-1Fe2+;the removal efficience of methylene blue reached 99%within 30 min under the conditions of 1.0 mmol·L-1 Na2S2O8 and 0.2 mmol·L-1Fe+2.Comparing mineralization effects of the three systems on two substrates within 180 min,it was showed that:thermal-Na2S2O8 system was best and UV-Na2S2O8 system was better than Fe2+-Na2S2O8 system.The degradation efficiency of MB was higher than that of MO in three activation systems.(2)Results showed that the presence of HCO3-,NO3-and C1-inhibited the degradation of MB and MO.According to the inhibitory effect by HCO3-,it was showed that:Fe2+-Na2S2O8 system was most obvious and UV-Na2S2O8 system was better than thermal-Na2S2O8 system.According to the inhibitory effect by NO3-,it was showed that:Fe2+-Na2S2O8 system was most obvious and thermal-Na2S2O8 system was better than UV-Na2S2O8 system.Comparing with the inhibitory effect by C1-,it was showed that:Fe2+-Na2S2O8 system was most obvious and UV-Na2S2O8 system was slightly better than thermal-Na2S2O8 system.(3)Comparing MB,MO degradation in the presence of different radical trapping agents(MA,TBA),it could be known that both SO4-·and OH · play important roles in the degradation process of MB,MO in three kinds of system,SO4-·play a major role in the degradation process of MB,MO in thermal-Na2S2O8 system,both SO4-· and · OH play a major roles in the degradation process of MB,MO in UV-Na2S2O8 system,· OH play a major roles in the degradation process of MB,MO in Fe2+-Na2S2O8 system.The result of LC-MS indicated that the process of MB degradation is the open-chain of C-N bond and S-Cl bond firstly,and then Thiazine ring open-loop,small molecules of organic matter are formed and eventually mineralized into CO2 and H2O.The process of MO degradation is the chromophore-N=N-bond breaks firstly,and then MO is further degraded to phenols and other small molecular organics,and finally mineralized into CO2 and H2O.