Effect of Denitrification on the pH in Biofilms

The experiments in this study have confirmed that the pH inside a denitrifying biofilm may be considerably higher than the pH in the bulk liquid. This has been verified by simultaneous measurements of the pH at the rear of the biofilm and in the bulk liquid. The experiments were performed in a laboratory fixed film unit (rotating drum biofilm reactor). A mathematical model is developed to describe the pH-profile in the denitrifying biofilm. The predictions made by the model were verified experimentally. The diffusion coefficients of nitrate, carbon dioxide and bicarbonate were determined to be about 50% of the corresponding values in pure water. The kinetic experiments performed as part of the verification studies result in kinetic parameter values in agreement with previous findings. The pH increase is favoured by for example a low alkalinity and a deep active biofilm.