Effects of different quinoid redox mediators on the simultaneous removal of p-cresol and sulphide in a denitrifying process.

The catalytic effects of different quinoid redox mediators (RM) on the simultaneous removal of sulphide and p-cresol in a denitrifying process were evaluated in batch studies. 2-Hydroxy-1,4-naphthoquinone (LAW) and anthraquinone-2,6-disulphonate (AQDS) did not significantly affect the sulphide oxidation rate, which, in contrast, was increased 14% in the presence of 1,2-naphthoquinone-4-sulphonate (NQS). The input of NQS on the oxidation of sulphide was also favourably reflected in a 13% higher sulphate production. All RM promoted a higher (up to 34% compared to the control lacking RM) degree of mineralization of p-cresol. LAW also supported a 47% higher denitrifying yield (Y(N2)), compared to the control lacking quinones. Nevertheless, AQDS and NQS decreased the Y(N2) by 12-13%. Our results suggest that a proper scrutiny should be conducted before deciding the sort of quinone to be applied in denitrifying processes. The heterogeneous effects observed also advise to consider both the respiratory rates and the yields as important parameters for deciphering the impact of RM on denitrifying processes.