Redox activity and accelerating capacity of model redox mediators during biodenitrification

The aim of this study was to analyse different model redox mediatiors: anthraquinone-2,7-disulphonate (2,7-AQDS), anthraquinone-1-sulphonate (alpha-AQS), anthraquinone-2-sulphonate (AQS) and anthraquinone-2,6-disulphonate (AQDS), with regard to the structure-activity relationship indicated by their cyclic voltammograms, their chemical structure, their oxidation-reduction 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 alpha-AQS, respectively. The ranking of the mediators based on their reduction potential (E-P(A)) was 2,7-AQDS > AQDS AQS > alpha-AQS. E-P(A) was positively correlated with accelerating the denitrification in experiments using 0.024 mmol center dot 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.