Residence Time Distribution and the Investigation of Bed Movement in a Continuously Operated Upflow Filter (COUF) for Tertiary Wastewater Treatment

This paper describes an investigation to define the liquid phase flow regime in a continuously operated upflow filter (COUF) together with an assessment of the relative motion of the solid (filter media) phase. The importance of such measurements in the development of a model for these systems, including aerated biological filtration versions is discussed. Initial work was carried out on a model-scale demonstrator unit using Rhodamine WT fluorescent dye tracing for liquid phase studies. Initial outputs show that the liquid phase residence time distribution (RTD) is well approximated by a plug flow assumption. The pattern in which individual particles of the bed move during the operation of the COUF was also investigated on the demonstrator using colored beads as a tracer. The gross movement of the bed and the internal mixing regime described can be regarded as analogous to RTD. Techniques were developed whereby bed movement in the cleaning process could be measured and assessed over time, leading to the generation of 3D bed movement visualisation plots. This work could potentially lead to developments of technologies that could better clean the media and lead to a more even bed movement allowing the filter to operate more efficiently.