The Study On The Treatment Of Nitrobenzene Wastewater By Electrolytic Method

Nitrobenzene is a kind of organic pollutants from various fields of industries. Because it is difficult to be biodegraded and has carcinogenicity, teratogenicity, reproductive toxicity and large amount of annual emissions all over the world, China and many other countries have listed it as environmental pollutants of priority control. Electrolysis as a technology to treat water is environmental friendly, and it is characterized as strong capacity of treating pollutants, easy control over the operating conditions, small size of equipment and no secondary pollution, it is thus attracting more and more attentions in recent years. The past researches mainly focused on the efficiency of treating organic wasted water with electrolysis, while the researches on the specific mechanism in the process of electrochemistry are far from adequacy.With the carbon rod as a battery electrode, the present research adopted four factors—the initial concentration of nitrobenzene, voltage, electrolyte (Na₂SO₄) concentration, and electrolysis time, and determined four levels for each factor to design orthogonal experiment, mainly intending to study the influence degree and mechanisms of each factor upon the nitrobenzene removal rate in the process of treating wastewater simulated from nitrobenzene through electrolytic method. The results reveal that the factors influencing nitrobenzene removal rate are listed in the following orders according to their importance in the process: voltage, electrolysis time, the initial concentration of nitrobenzene and electrolyte (Na₂SO₄) concentration. The best electrolysis conditions are as follows: the concentration of nitrobenzene was 0.1 ml·L^-1, the concentration of Na₂SO₄ was 10g·L^-1, electrolysis voltage was 15V, and electrolysis time was 120min. The present research points out that it will consume much energy to transform nitrobenzene into inorganic substance by electrolytic method, so it is economically reasonable to transform pollutants into substances easy to be biodegraded.The emphasis of the present research is analysis of possible intermediates in the course of nitrobenzene electrolysis and description of its degradation process. Based on the previous researches, the present research combines advanced high performance liquid chromatograph with specific experimental phenomena, and finds that if wastewater simulated from nitrobenzene is treated with carbon battery electrode in a low voltage, substances such as Aniline, p-Nitrophenol, Hydroquinone, p-Kun, maleic acid, adipic acid, etc. will be produced in the process. In particular, the present research detects that the yellow substance produced in nitrobenzene electrolysis is p-Kun. After a comprehensive and systematic summary upon the previous researches about mechanisms of treating wasted water simulated from phenol, aniline, p-Nitrophenol and nitrobenzene, the present research proposes some generality lying in the degraded mechanisms of treating aromatic compounds, and points out that p-Kun is the final intermediates for the substances with benzene ring before they open their rings. Judged from the found and speculated intermediates produced from nitrobenzene electrolysis, the direct and indirect anodic oxidation plays an important role in the degradation of nitrobenzene, and even in complete mineralization. Meanwhile, cathode has reduction of nitrobenzene into some types of anilines substances easier to be degraded. So anode and cathode together contribute to degradation of nitrobenzene. Finally, the present research describes the main reactions occurring on anode and cathode in the process of electrolysis.