The significance of zonation in a denitrifying, phosphorus removing biofilm

A biofilm for simultaneous removal of N and P was developed using a continu ous lab-scale setup alternating between anaerobic and anoxic conditions. BI OSTYR was used as carrier material. Result, showed an exponential increase in initial anaerobic P-release rate for the first month and subsequently a constant rate. The theory of 1/2 and 0 order of reaction in the bulk watts depending on penetration depth into the film was verified for anaerobic P-r elease using batch tests. Stoichiometric coefficients were for anaerobic P- release to COD-uptake 0.25 g P/g COD and for anoxic P-uptake to nitrate rem oval 0.06 mol P/mol e(-). Both values are low compared to the literature fo r enriched denitrifying cultures which is taken as an indication of the pre sence of competing bacteria with the capacity of storing GOD. Since the val ues did not change during the build up period it appears that the competing bacteria survive well with the continuous alternating mode of operation. ( C) 1999 Elsevier Science Ltd. All rights Reserved.