The significance of zonation in a denitrifying, phosphorus removing biofilm

A biofilm for simultaneous removal of N and P was developed using a continuous lab-scale setup alternating between anaerobic and anoxic conditions. BIOSTYR was used as carrier material. Results showed an exponential increase in initial anaerobic P-release rate for the first month and subsequently a constant rate. The theory of and 0 order of reaction in the bulk water depending on penetration depth into the film was verified for anaerobic P-release 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 removal 0.06 mol P/mol e−. Both values are low compared to the literature for enriched denitrifying cultures which is taken as an indication of the presence of competing bacteria with the capacity of storing COD. Since the values did not change during the build up period it appears that the competing bacteria survive well with the continuous alternating mode of operation.