Controlled biomass removal - The key parameter to achieve enhanced biological phosphorus removal in biofilm systems

In contrast to enhanced biological phosphorus removal (EBPR) in activated s ludge systems mass transfer processes have a major influence on overall pho sphorus removal in biofilm reactors. Based on results from a laboratory sca le sequencing batch biofilm reactor (SBBR) and from a mathematical model th e influence of the following processes on EBPR in biofilms was evaluated: ( 1) mass transfer limitation for oxygen (2) mass transfer limitation for org anic substrate, (3) lack of controlled removal of biomass from the system. It was shown that mass transfer of soluble components (oxygen and organic s ubstrate) had only a minor effect on overall phosphorus removal. Soluble co mponents fully penetrate the biofilm at certain times during the SBBR cycle as a consequence of SBBR operation with large concentration variations ove r the cycle time. The limiting processes for EBPR is the efficient removal of phosphorus rich biomass from the reactor. Biomass at the base of the bio film that is not removed during backwashing will release accumulated phosph orus due to lysis or endogenous respiration and will not contribute to net phosphorus removal. For efficient operation of EBPR in biofilm systems regu lar and intensive backwashing resulting in thin biofilms is suggested. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.