Nitrifying Continuous Upflow Filters: Understanding Large Scale Plant from Laboratory and Pilot Scale Experiments

Continuous up-flow filters (CoUFs) are principally designed to be used in tertiary wastewater treatment for the removal of particulate solids, prior to final effluent discharge. However, good designs are adaptable and with the addition of aeration this type of plant can also act as effective nitrifying filters (ACoUFS). Given the difficulties of evaluating operational plant in situ, relatively few studies have been made at full scale. Instead, in order to understand and improve the performance of such plant, laboratory and pilot scale studies are more usually undertaken though there is always an element of uncertainty in how such results will transfer to full-scale operation. Here, based on a series of previous studies, a logical route from small scale laboratory work, via pilot plant studies to operation at full scale is presented. The process starts with a laboratory scale screen involving critical selection of media, followed by the evaluation of the media for both bulk hydrodynamic properties, principally pressure drop, and then for biofilm support and basic nitrifying capability. This is then extended at pilot scale into the macroscopic behaviour of the moving bed, hydrodynamic studies and to the nitrification itself. The transfer of the results to full scale plant is then discussed.