Treatment Of Toxic Substances In Bleaching Effluent With Electrochemical Oxidation Process

The cost of conventional water treatment technologies is high and the degradation efficiency is poor since the organic compounds of paper-making bleaching effluent have a series of characteristics,such as the rich kinds,high toxicity and hard degradability. In this paper,firstly the target contaminant (TCP) is processed and then the bleaching effluent is treated with Ti/RuO2-IrO2 coated electrodes which have the higher oxygen evolution potential,chemical stability, corrosion resistance and catalytic activity by the electrochemical oxidation method. Experiments show that this method is an effective way to degrade the toxic substances in bleaching effluent. The main contents and results are as follows:1) The study presents the degradation of 2,4,6-trichlorophenol (TCP) with electrochemical oxidation process to investigate the effect of different process parameters on its degradation efficiency and to study the degradation mechanism and degradation laws. Results show that the degradation efficiency of TCP is related to the external potential,the amount of electrolyte,the initial PH and concentration of solution and the electrolysis time. Under the conditions of external potential 7V,pH=3,Na2SO410g/L,the degradation efficiency of TCP whose initial concentration is 0.025g/L reaches over 99% by using Ti/IrO2-RuO2 coated electrodes after 150min. It shows that TCP is degraded by the combined action of OH and the anode surface’s directed oxidation under the acidic condition; while under the acidic condition the main action is oxidation of the OH. Under the optimum experimental conditions,the degradation pathway of TCP is that Cl- is separated from benzene under the attack of OH to form dichloro hydroquinone, dichloro benzoquinone, dichloro catechol, then the unsaturated carboxylic acid containing chlorine is generated by open-loop or TCP is directly took off a chlorine ions by electrochemical reaction to generate benzenediol, p-benzoquinone, then the unsaturated carboxylic acid containing chlorine is formed by open-loop. Degradation of TCP conforms the laws of first order kinetics in the reaction system.2) The study presents the degradation of toxic substances in bleaching effluent with electrochemical oxidation method to investigate the degradation efficiencies of the single stage (Do, Eop) and the mixing stage (volume ratio of Do:Eop is 1:1) and to analyze the changes of each stage bleaching effluent’s toxicity, AOX, compositions of pollutants before and after degradation.The results show that waste water of Do stage is the most toxic and the type and content of pollutants are the most abundant,because the toxicity is mainly provided by chlorinated phenols, chlorobenzene and aromatic compounds; Waste water of Eop stage is smaller toxic and the main pollutants are aliphatic compounds and fewer chloride; Toxicity and the amount of pollutants’content of the mixing stage’s (Do+Eop) waste water is in between Do and Eop stage. After electrochemical degradation,under the conditions of the applied voltage 7V,the initial conductivity 12.35us/cm,the processing time 240min,the Do,Eop and mixing stage (Do+Eop) waste water’s CODCr removal rates respectively are 57.7%,37.5%,43.5% and color removal rates respectively are 90.2%,82.3%, 83.1%; Toxicity level of waste water of Do and mixing stage (Do+Eop) are dropped from medium toxicity to low toxicity and the removal rates of AOX respectively are 66.29%,70.24%,while waste water of Eop stage is non-toxic and the removal efficiency of AOX is 100%. Treated waste water of Do stage can’t be detected chlorinated phenols and chlorobenzene and the content of aromatic compounds are reduced, while the content of aliphatic hydrocarbon compounds are increased; The type and content of aliphatic compounds of the treated waste water of Eop stage are substantially reduced,and chlorinated organic compounds and aromatic compounds are also reduced; The type and content of organic compounds of the treated waste water of mixing stage (Do+Eop) are in between Do and Eop stage separated degradation.3) The CODcr,color,toxicity of waste water of each stage can be singly reduced by electrochemical oxidation process,but the plates are easily passivated and it wastes more energy. While the electrochemistry-ultrasound combined process and electrochemistry-aerobic combined process can improve the plates’ efficiency and reduce costs. The electrochemical oxidation technologies are partly improved by the electrochemistry-ultrasound combined process to greatly improve the degradation efficiency of each stage’s waste water and the toxicity level of the treated waste water is reduced to non-toxic, which shows that ultrasonic waves have the enhanced effects on the degradation of waste water with electrochemical process. The degradation efficiency of aromatic compounds, aliphatic compounds of waste water of each stage with electrochemistry-aerobic combined process is better than the electrochemistry-ultrasound combined process,but the degradation efficiency of chloride is weaker than the electrochemistry-ultrasound combined process,which shows that the aerobic method in the electrochemistry-aerobic combined process has limitations to remove the organic compounds and removal efficiency of toxic substances is poor,but the degradation of organic compounds with electrochemistry-ultrasound combined process is nonselective.