Removal Of Typical Refractory Organic Pollutants From Waters By Plasma Technology

In recent years,with the rapid development of industrialization and urbanization in the world,textile printing and dyeing wastewater,pesticide wastewater,petrochemical wastewater,pharmaceutical wastewater and other organic wastewater in a large number of production enterprises,organic wastewater contain a large number of refractory organic pollutants（ROPs）.Refractory organic wastewater has complex components（such as organic dyes,organic cyanide,heterocyclic compounds,polycyclic aromatic hydrocarbons,etc.）,and has the characteristics of high toxicity,high concentration and poor biochemical performance.Therefore,the removal of ROPs in water is an important problem to be solved urgently.However,existing water treatment processes are difficult to effectively remove ROPs,and plasma technology has significant advantages and potential in treating these refractory organic compounds compared with other technologies.In this paper,plasma technology was used to study the treatment of simulated aqueous solution containing benzene ring refractory organic pollutants（such as methyl orange）and chain refractory organic pollutants（such as perfluorbutane sulfonic acid）,optimize the process conditions and explore the removal mechanism,so as to achieve effective removal of ROPs.The main results were detailed as below.Stainless steel needle as high voltage discharge electrode,porous stainless steel plate as the ground electrode,excitation plasma device corona discharge,the water containing benzene organic pollutants methyl orange（MO）and chain organic pollutants perfluorbutane sulfonic acid（PFBS）plasma treatment,respectively.The effects of voltage,discharge time,discharge spacing,and needle number on ROPs removal were investigated by single factor experiment.The results showed that the removal rates of MO and PFBS reached 96.7%and 48.3%,respectively,when the voltage was 25 k V,the discharge spacing was 27 mm,the number of needles was 7,and the discharge time was 60 min.In order to reduce energy consumption,increase the effective area of plasma and further improve the removal effect of ROPs,a new reactor was designed for plasma experiment.Plasma directly bombards water surface and reacts with refractory organic pollutant molecules at gas-liquid interface.The reaction efficiency was improved,and the optimal operation conditions of the reactor were optimized by response surface methodology:discharge voltage was 20 k V,discharge spacing was 20mm,and discharge needle number was 5.Under the same energy consumption condition,the degradation rate increased from 40.5%to 95.1%after running for 60 min.In order to further enhance the oxidation effect,two catalytic ions were added to explore the synergistic effect with the plasma,and the reaction conditions were optimized to improve the degradation effect.Compared with the single plasma,the degradation efficiency and energy yield of MO in the mixed plasma/PS/Fe²⁺system were significantly improved after 60 min running,and the degradation rate increased from 95.1%to 99.2%It provides theoretical support for the engineering application of plasma technology.In order to investigate the application effect and removal mechanism of ROPs-contaminated water by plasma technology,the degradation products of perfluorooctanoic acid（PFOA）in water treated by plasma technology were analyzed by HIGH performance liquid chromatography tandem mass spectrometry（HPLC-MS）.The wavelengths and peaks of the representative functional groups of MO containing benzene ring were analyzed by UV-VIS spectrophotometry,and the degradation path and mechanism of MO containing benzene ring were explored from the aspect of molecular structure.Through qualitative identification and quantitative analysis of the by-products in the plasma process,the results show that ROPs can be gradually degraded by direct oxidation in the plasma process.The results show that plasma technology is an effective method to remove ROPs,and the catalytic ion is beneficial to the removal of ROPs.It provides theoretical basis and technical support for the effective control and treatment of ROPs pollution and the application of plasma technology in the field of organic wastewater treatment.