| With the development of agriculture and industries, discharged nitrogen cause worse environmental problem. Biological denitrification is one of importance removal nitrogen technologis. The high effective denitrification technology is concerned in environmental fields because of conventional biotreatment lower efficiency. Recently, it is reported that radox mediators like quinones compound can accelerate transmission of electronic between electron donor and electron acceptor and the reduction rate of pollution can be enhanced by quinones, which include azo dye, PCBs, nitroaromatic and so on. But it has little research in the accelerating denitrification by redox mediators. Therefore, this paper is carried out to study the catalytic mechanism and effect of five redox mediators during the denitrification process.In this study, five redox mediators with similar chemical structure(AQS, a-AQS, AQDS,1,5-AQDS and 2,7-AQDS) were seclected to explore the characteristic of accelerating Paracoccus versutus sp.GW1 denitrification process and The quinone respiration characteristic of Paracoccus versutus sp. GW1 was studied. The experiment results suggested that quinone can be utilized by Paracoccus versutus sp. GW1 as electron acceptors in the respiratory chain and reduced hydroquinone; Optimum conditions of redox mediators accelerating Paracoccus versutus sp. GW1 denitrification process were temperature 35℃, pH (7.0) and C/N ratio 6 respectively. The nitrate tolerated concentration was 1000mg/L; Batch experiments were carried out to determine the catalyst effect on the denitrification at temperature 35℃. The five redox mediators could enhance the removal nitrate efficiency and the denitrification efficiency, which were enhanced 1.14-1.63 fold and 1.12-2.02 fold respectively; The accelerating order was AQDS> 1,5-AQDS>2,7-AQDS> AQS>a-AQS. The stabilized ORP values with redox mediator were lower around 50-92 mV than the control; The pH change with redox mediator during the removal nitrate processes was similar to the conventional removal nitrate process; Redox mediators had the best accelerating effect and a linear correlation was found for the denitrification rate K and the redox mediators concentration C in the range of 0～0.32 mmol/L.At the same time, the biocatalysis mechanism of the redox mediators was also studied from two aspects of electrochemistry (cyclic voltammetry), biochemistry (electron transport inhibitors). The conclusions are listed as followed:First, redox mediators could offset or reduce the inhibitory effect of electron transport chain inhibitors and redox mediators accelerating of denitrification is closely to electron transport. Second, the redox mediators can promote the generation and accumulation of nitrite, and the accelerating site of redox mediators located between N ADH and NaR in the electron transports process. In addition, the electrochemical characteristics of redox mediators in the cyclic voltammograms indicated that redox potential (Eo1) of redox mediators are similar to the Eo’of NAD(P)H reductase to CoQ, and were between -270mv and -70mv. Redox mediators may play a transmission role of electron in electron transport chain from NAD(P)H reductase to CoQ. At last, the redox mediators change of ORP decreased quickly and the stable potential is lower than the control. It is propitious to eliminate nitrate.This experiment put forword a great improvement of the redox mediator’s application in water treatment. Redox mediator provides an effective way to solve the problem that denitrification rate is low. The result for the practical application of redox mediators has laid a theoretical and technical basis. |
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