Substrate consumption by an activated sludge with changing bacterial size and form

A theoretical analysis of substrate consumption by bacterial cell populations with different size and form was performed. The following processes were considered: the substrate transport from solution into the bacterial cell, the substrate fermentative transformations in the cell, and cell adaptation to environmental conditions. It was shown that at low substrate concentration, the cylindrical form of bacteria grows much faster then the spherical form. This relationship serves to explain the bulking process of an activated sludge caused by an overgrowth of filaments.