Diffusion in Aerobic Granular Sludge

Abstract

A large part of the wastewater produced worldwide is discharged without any treatment. This has several negative consequences, including the spread of diseases and contamination of the environment. One method to treat wastewater is called aerobic granular sludge (AGS), an advanced, compact technology that uses granules. Granules are spherical aggregates of microorganisms and biopolymers. Different microorganisms break down different pollutants within the granules. The microorganisms rely on the mass transfer of pollutants into the granule. This occurs through diffusion, a passive mode of transport that is driven by a concentration difference. Diffusion is an essential aspect of AGS as well as other biofilm processes. Most previous research has shown that diffusion in granules and biofilms is a complex process. The diffusion behaviour varies between biofilms, within the biofilm, and between different molecules. At the same time, granule and biofilm models use a simple approach to describe diffusion. These models often use a single diffusion coefficient for the entire granule or biofilm. It is unclear how valid these simplifications are and how much they influence the accuracy of the model outcomes. In this dissertation, we studied different aspects of diffusion in granules to verify and extend previous research on the complexity of diffusion. The resulting information was then used to evaluate the impact on granule models.