pH-decrease in nitrifying biofilms

Nitrification is an acidity producing process. It has been shown theoretically that the diffusional resistance to the transport in the biofilm of the inorganic carbon species as affected by the acidity production in a nitrifying biofilm gives rise to a decreased pH in the interior of the biofilm. These theoretical results have been verified on biofilms developed on the surfaces of a rotating drum under well controlled laboratory conditions.

The results show clearly the drop in pH as predicted by theory. The phenomenon can give rise to unexpected effects on the performance of nitrifying biofilms, when most of the bacteria work under a much lower pH than the pH measured in the bulk water.