PHOSPHORUS AND NITROGEN REMOVAL WITH MINIMAL COD REQUIREMENT BY INTEGRATION OF DENITRIFYING DEPHOSPHATATION AND NITRIFICATION IN A 2-SLUDGESYSTEM

Denitrifying dephosphatation enables the removal of phosphorus and nit rogen with minimal use of GOD, minimal oxygen consumption and minimal surplus sludge production. Moreover it would make aeration only necess ary For nitrification. Therefore we have studied an anaerobic-anoxic ( A(2)) sequencing batch reactor (SBR) coupled to a nitrification SBR. D enitrifying phosphorus removing bacteria (DPB) and nitrifiers were com pletely separated in two sludges in these two SBRs. The nitrified supe rnatant was recirculated from the nitrification SBR to the A(2) SBR wh ere nitrate was utilized by DPB as an electron acceptor for phosphorus removal. The technical feasibility for simultaneous phosphorus and ni trogen removal in the proposed two-sludge system was evaluated. The be nefits of two-sludge systems over single-sludge systems were also disc ussed. It could be concluded that the separation of the nitrification step leads to an optimal process design for the application of denitri fying dephosphatation. The two-sludge system showed stable phosphorus and nitrogen removal, and enabled the removal of 15 mg-P/l and 105 mg N/l at the expense of only 400 mg-COD/l acetic acid. Stoichiometric ca lculations showed that, in the two-sludge system the required COD can be up to 50% less than for conventional aerobic phosphorus and nitroge n removal systems. Moreover oxygen requirements and sludge production can be decreased in significant amounts of about 30 and 50%, respectiv ely. Copyright (C) 1996 Elsevier Science Ltd