Removal of nitrogen and organic matter in a radial-flow aerobic-anoxic immobilized biomass reactor used in the posttreatment of anaerobically treated effluent

This work reports on the removal of organic matter and nitrogen in a radial-flow aerobic-anoxic immobilized biomass (RAIB) reactor fed with domestic sewage pretreated in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor. Polyurethane foam was used as support material for biomass attachment in both reactors. In batch experiments, a first-order kinetic model with residual concentration represented the organic matter removal rate, whereas nitrogen conversion followed a pseudo-first-order reaction in series model, with kinetic constants k1 (ammonium to nitrite) and k2 (nitrite to nitrate) of 0.25 and 6.62 h(-1), respectively. The RAIB reactor was operated in continuous-flow mode and changes in the airflow rate and hydraulic retention time were found to interfere in the apparent kinetic constants to the nitritation (k1) and nitratation (k2). Nitrification and denitrification were achieved in the partially aerated RAIB reactor operating with hydraulic retention times of 3.3 h and 2.7 h in the aerobic and anoxic zones, respectively. Ethanol was added in the anoxic zone of the reactor to promote denitrification. The effluent flow of the RAIB reactor presented a COD of 52 mg l(-1), and concentrations of 2 mg N - NH4(+)1(-1), 1.24 mg N - N02(-)1(-1) and 3.46 mg N - N03(-)1(-1).