Redox activity and accelerating capacity of model redox mediators during biodenitrification

Abstract

The aim of this study was to analyse different model redox mediatiors: anthraquinone-2,7-disulphonate (2,7-AQDS), anthraquinone-1-sulphonate (α-AQS), anthraquinone-2-sulphonate (AQS) and anthraquinone-2,6-disulphonate (AQDS), with regard to the structureactivity relationship indicated by their cyclic voltammograms, their chemical structure, their oxidationreduction potential and their capacity to accelerate the denitrification reaction during denitrification. Compared to the control, the nitrate removal after 21 h of denitrification was enhanced by a factor of 1.94, 1.56, 1.56 and 1.3 by 2,7- AQDS, AQDS, AQS and α-AQS, respectively. The ranking of the mediators based on their reduction potential (EAp) was 2,7-AQDS > AQDS ≥ AQS > α-AQS. EAp was positively correlated with accelerating the denitrification in experiments using 0.024 mmol.L-1 redox mediator, 360 mg L-1 NO3--N and 5.0 g L-1 of dry cell weight. Practical computational approaches (the frontier orbital theory and the atoms-in-molecules theory) and inductive and resonance effects were also used to explain and assess how the molecular structure and stability of the redox mediators affect the accelerating capacity during denitrification.