Model-based evaluation of two BNR processes - UCT and A(2)N

The activity of denitrifying P-accumulating bacteria (DPB) has been verifie d to exist in most WWTPs with biological nutrient removal (BNR). The modifi ed UCT process has a high content of DPB. A new BNR process with a two-slud ge system named A(2)N was especially developed to exploit denitrifying deph osphatation. With the identical inflow and effluent standards, an existing full-scale UCT-type WWTP and a designed A2N process were evaluated by simul ation. The used model is based on the Delft metabolical model for bio-P rem oval and ASM2d model for COD and N removal. Both processes accommodate deni trifying dephosphatation, but the A(2)N process has a more stable performan ce in N removal. Although excess sludge is increased by 6%, the A(2)N proce ss leads to savings of 35, 85 and 30% in aeration energy, mixed liquor inte rnal recirculation and land occupation respectively, as compared to the UCT process. Low temperature has a negative effect on growth of poly-P bacteri a, which becomes to especially appear in the A2N process. (C) 2001 Elsevier Science Ltd. All rights reserved