Upgrading wastewater treatment plants by the use of biofilm carriers, oxygen addition and pre-treatment in the sewer network

In upgrading of treatment plants for enhanced nitrification there are three strategies (1) the existing process may be optimised with respect to the biological activity, (2) the biological activity may be increased by changing to a process with a higher capacity, and (3) a combination of 1 and 2. The potential of the first strategy in a KMT moving bed biofilm process (the kaldnes process) is presented in this paper. The nitrification capacity was enhanced by using pure oxygen resulting in an increased oxygen concentration, and the specific biomass activity was increased by removing organic matter and sulphide in the sewer network by addition of nitrate to the wastewater. The results show that the nitrification capacity may be increased by 30-40% by pre-treatment of wastewater in the sewer network and increased by 40-50% by using an increased oxygen concentration in the first step of the nitrification reactor. Oxygen concentrations below 12 mg O2/l and/or the amount of biomass were found to be the limiting factors at ammonium concentrations above 5-7 mg NH4-N/l.