Complete and simultaneous removal of ammonium and m-cresol in a nitrifying sequencing batch reactor

Abstract

The kinetic behavior, oxidizing ability and tolerance to m-cresol of a nitrifying sludge exposed to different initial concentrations of m-cresol (0-150mgCL(-1)) were evaluated in a sequencing batch reactor fed with 50mg NH4 (+)-NL(-1) and operated during 4months. Complete removal of ammonium and m-cresol was achieved independently of the initial concentration of aromatic compound in all the assays. Up to 25mgm-cresol-CL(-1) (C/N ratio of 0.5), the nitrifying yield (Y-NO3 (-)) was 0.86±0.05, indicating that the nitrate was the main product of the process; no biomass growth was detected. From 50 to 150mgm-cresol-C L(-1) (1.0≤C/N≤3.0), simultaneous microbial growth and partial ammonium-to-nitrate conversion were obtained, reaching a maximum microbial total protein concentration of 0.763gL(-1) (247% of its initial value) and the lowest Y-NO3 (-) 0.53±0.01 at 150mgm-cresol-CL(-1). m-Cresol induced a significant decrease in the values of both specific rates of ammonium and nitrite oxidation, being the ammonium oxidation pathway the mainly inhibited. The nitrifying sludge was able to completely oxidize up to 150mgm-cresol-CL(-1) by SBR cycle, reaching a maximum specific removal rate of 6.45gm-cresol g(-1) microbial protein-Nh(-1). The number of SBR cycles allowed a metabolic adaptation of the nitrifying consortium since nitrification inhibition decreased and faster oxidation of m-cresol took place throughout the cycles.