A nitrifying continuous stirred tank reactor was used as multipurpose bioreactor and it was operated for 325 days at 220 mg NH(4)(+)-N/L d, 89 mg p-cresol-C /L d and 36-76 mg S(2-)/L d. The bioreactor was fed in sequential way, firstly with ammonium, achieving a consumption efficiency of 89%, with a nitrate yield of 0.99. Afterward, p-cresol was fed, achieving ammonium and p-cresol consumption efficiencies of 95% and 100%, respectively. The nitrate yield was higher and no aromatic intermediaries from p-cresol were detected. Finally sulfide was fed and the consumption efficiencies for all substrates were of 100%, being nitrate, HCO(3)(-) and sulfate the end products. The kinetic results showed that biological sulfide consumption was 13-fold faster than the chemical oxidation. This is the first time that a nitrifying reactor can be used for multiple purposes and also for the simultaneous removal of ammonium, sulfide and p-cresol in one step. (C) 2010 Elsevier Ltd. All rights reserved.