The role of diffusion in the activated sludge process

Abstract

Diffusional resistance can theoretically restrict the availability of nutrients inside activated sludge flocs. This resistance is not likely to have a significant impact on substrate removal rates since substrate removal rates are relatively slow. Kinetic models can therefore predict organic substrate removal with reasonable accuracy while neglecting diffusional resistance. However, the substrate concentration profile generated by diffusional resistance can inhibit the growth of certain bacterial species. In order to determine the competition between bacteria inside the floe or growth of a specific organism, such as the study of bulking or nitrification in activated sludge, diffusional limitations must be considered.