| Brominated flame retardants(BFR)are widely used in the production process of electronic equipment,plastics and textiles due to their good heat resistance,oxidation resistance and flame retardancy.In the process of use,BFR will inevitably enter into ponds,lakes,rivers and other water bodies,causing pollution to the water environment.Tetrabromobisphenol s(TBBPS),as one of BFR,has carcinogenic effect,hepatotoxicity and endocrine system damage.Therefore,it is particularly important to select appropriate and effective methods to treat TBBPS in water and reduce its harm to the ecological environment and human body.Dielectric barrier discharge(DBD)is widely used in plasma water treatment because of its large discharge area,uniform and stable effect.However,how to produce more active substances and how to use them effectively has always been the research focus in the field of plasma water treatment.It is found that the active substances generated by bubbling can diffuse into the water phase through free diffusion,which can effectively increase the gas-liquid mass transfer interface and promote the absorption and utilization of active substances.Another way to improve the efficiency of gas-liquid mass transfer is to increase the specific surface area between gas and liquid.Using liquid film reactor can not only enhance the absorption of active substances,but also enhance the removal of organic pollutants.In order to improve the removal efficiency of organic pollutants in wastewater treatment,a bubble-film hybrid discharge plasma reactor was developed.The existence of liquid film can strengthen the formation and mass transfer process of active substances.On the one hand,the liquid film causes streamer discharge and surface dielectric barrier discharge to be ignited simultaneously,which reduces the initial voltage,increases the discharge intensity and improves the production efficiency of active substances.On the other hand,the liquid film expands the plasma water interface and improves the utilization efficiency of active substances by means of enhanced mass transfer process.It is found that liquid film exists and the effect is the best when the water and gas flow rate is 140 mL/min and 1.8 L/min,respectively.The removal experiments of TBBPS show that the plasma reactor can remove organic pollutants quickly and effectively.When the initial concentration of TBBPS was 50 mg /L and the treatment capacity was 100 m L,the removal rate could reach 100 %when the discharge voltage was 12.8 kV and the water gas flow rate was 160 mL/min and 2.0 L/min,respectively.At the same time,compared with the case without liquid film,the maximum yield of active substance can be increased by more than 80 % and the mass transfer efficiency can be increased by more than 20 % in the presence of liquid film.The above results show that the bubble-film multi-stage discharge enhanced process is of great significance for the removal of organic pollutants in wastewater treatment.Through the analysis of the intermediate process of TBBPS degradation by bubble-film hybrid discharge plasma,it can be found that with the continuous generation of TBBPS intermediate products and the generation of nitric acid,the p H of the solution decreases and the conductivity increases.At the same time,it was found that TBBPS gradually decomposed into small molecules with the extension of treatment time,which led to the decrease of TOC and biological toxicity during the degradation process.In addition,the reaction mechanism and degradation path of TBBPS treated by bubble-film hybrid dielectric barrier discharge system were discussed by LC-MS analysis. |
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