| Organic nitrate industry played an important role in economic development of China. But the wastewater from process of nitrification is characterized by containing so many by-products, high toxicity and low biodegradability. Therefore, it can not be easily degraded by microorganism unless adding effective pretreatment process. Oxidation and reduction of chemical agents is a common pretreatment process, the technology of ZVI+Fenton+coagulation has preferably result in nitrification wastewater pretreatment, it has been widely used in projects. Nevertheless, this technology has limited effect on biodegradability increasing and toxicity reducing, for another, solid waste from the process pertains to risk solid waste and has high treatment cost. Above all, it is dangerous to the environment.So far, electrochemical process in dealing with refractory organics has gained fair development. The process of electro-reduction and electro-oxidation can increase the biodegradability of refractory organics. As a kind of green technology, it is characterized by no chemical agents dosing and no secondary pollution generating. This article attempts to adopt electro-reduction-oxidation as pretreatment process of nitrification wastewater, investigate the effects of o-nitrotoluene (ONT) transformation and removal on wastewater toxicity reduction in this system. Also above the application in actual nitrification wastewater. Aiming at the need, two kinds of electro reactors are designed, they realize the intergration of electro-reduction-oxidation by complete mixing flow and continuous flow style.In the study of o-nitrotoluene and nitrification wastewater degradation by electro-reduction-oxidation, some conclusions have been reached:1. Electro-reduction reinforces the following oxidation in o-nitrotoluene degradation, occurs in SUVA、CODcr and toxicity removal. The reduction of ONT on cathode in line with the first order kinetics equation, and controlled by diffusion rate. The main intermediate products of reduction procedure are nitrosotoluene o-toluidine, azotoluene and oxidation azotoluene. The final product is o-toluidine, by conversion percent of 95.7%. Orthogonal tests show that the main influence factors of o-nitrotoluene reduction and o-toluidine conversion are current density, initial concentration and initial pH.2. O-toluidine, the main product of o-nitritoluene reduction, can be well degraded in electro-oxidation process, by removal rate of 85% and mineralization rate of 48.5%. Main influence factors of o-toluidine removal rate and mineralization rate are current density and initial concentration. Anode material, supporting electrolyte and hydroxyl radicals masking agent also have effect on o-toluidine oxidation. The main intermediate products of oxidation procedure are o-methyl benzoquinone, o-nitrotoluene and azotoluene, they are further oxidized to little molecular acid and finally mineralized. The toxicity of the solution rises since generation of o-methyl benzoquinone, then declines with degradation of it.3. In order to verify the application feasibility of electro-reduction-oxidation process, treatment efficiency on the actual nitrification is investigated. By the contrast of continuous flow reactor and continuous stirred tank reactor, the latter has a more narrow electrode spacing, lager electrode area contacting to the wastewater. Therefore, the continuous flow reactor has better performance by reducing the retention time of 30%. The process has SUVA removal rate of 57.8% and CODcr removal rate of 28.5%. Current density and retention time are the main controls parameters. Considering treatment efficiency and economical efficiency, current density of 20mA · cm-2 and reduction、oxidation retention time of 120min are optimum conditions. Electro-reduction-oxidation can remarkably improve the B/C of the wastewater, by 0.115 rising to 0.435. It can also reduce the toxicity of the wastewater, by TU reduction rate of 85.4%. |
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