Heterogeneous Diffusion in Aerobic Granular Sludge
- van den Berg, Lenno
- Kirkland, Catherine M. [ Montana State University: Civil Engineering ] [ Center for Biofilm Engineering ]
- Seymour, Joseph D. [ Montana State University: Chemical & Biological Engineering ] [ Center for Biofilm Engineering ]
- Codd, Sarah L. [ Montana State University: Mechanical & Industrial Engineering ] [ Center for Biofilm Engineering ]
- van Loosdrecht, Mark C. M.
- de Kreuk, Merle K.
Aerobic granular sludge (AGS) technology allows simultaneous nitrogen, phosphorus, and carbon removal in compact wastewater treatment processes. To operate, design, and model AGS reactors, it is essential to properly understand the diffusive transport within the granules. In this study, diffusive mass transfer within fullâ€scale and labâ€scale AGS was characterized with nuclear magnetic resonance (NMR) methods. Selfâ€diffusion coefficients of water inside the granules were determined with pulsedâ€field gradient NMR, while the granule structure was visualized with NMR imaging. A reactionâ€diffusion granuleâ€scale model was set up to evaluate the impact of heterogeneous diffusion on granule performance. The selfâ€diffusion coefficient of water in AGS was ∼70% of the selfâ€diffusion coefficient of free water. There was no significant difference between selfâ€diffusion in AGS from fullâ€scale treatment plants and from labâ€scale reactors. The results of the model showed that diffusional heterogeneity did not lead to a major change of flux into the granule (<1%). This study shows that differences between granular sludges and heterogeneity within granules have little impact on the kinetic properties of AGS. Thus, a relatively simple approach is sufficient to describe mass transport by diffusion into the granules.