A mathematical model with adequate complexity integrating hydraulics, biofilm and microbial conversion processes is successfully developed for a continuously moving bed biofilter performing tertiary nitrification. The model was calibrated and validated using data from Nether Stowey pilot plant in UK. For the model, the mixing is approximated using tanks-in-series approach, the biofilm is described using a one-dimensional multi-species model, and the microbial processes are described by ASM1. A scenario analysis with the model revealed that the temperature has a significant impact on the ammonium removal efficiency, doubling nitrification capacity every 5 degrees C increase. However, at temperatures higher than 20 degrees C, the biofilm thickness starts to decrease due to increased decay rate. The influent nitrogen load was also found to be influential on the filter performance, while the hydraulic loading had relatively negligible impact. Overall, the calibrated model can now reliably be used for design and process optimization purposes.
- moving bed sand filter
- tertiary treatment