Simultaneous nitrification and p-cresol oxidation in a nitrifying sequencing batch reactor

The tolerance, kinetic behavior and oxidizing ability of a nitrifying sludge exposed to different initial concentrations of p-cresol (25–150 mg/l) were evaluated in a sequencing batch reactor (SBR) fed with 200 mg NH4+-N/l d. The nitrifying SBR operated up to 300 mg/l d of p-cresol, achieving simultaneously the complete ammonium oxidation to nitrate and the total consumption of p-cresol and its transitory intermediates from the culture. p-Cresol induced a significant decrease in the values for specific rates of ammonium consumption, showing that the ammonium oxidation pathway was mainly inhibited. After 7 months of operation in SBR, the specific rates of NH4+-N oxidation, NO3−-N formation, and total organic carbon consumption were 0.6 g NH4+-N/g microbial protein-N h, 0.3 g NO3−-N/g microbial protein-N h, and 0.24 g total organic carbon/g microbial protein h, respectively. The microbial growth rate was always low (maximum value of 12.2±0.4 mg protein-N/l d) and settleability of the sludge was good with sludge volume index values lower than 21 ml/g. The oxidation of p-cresol and its intermediates was carried out faster throughout the cycles and nitrification inhibition decreased with the number of cycles.