The locally resolved filtration process for removal of phosphorus and micropollutants with GAC

Flocculation filtration in deep bed is one of the techniques to achieve advanced phosphorus removal. In addition to particle retention and phosphorus removal, granular activated carbon may serve as a filtration medium but also as an adsorption bed for micropollutants. The aim of the study was to investigate the simultaneous elimination of total phosphorus (TP) and selected micropollutants. In the first part of the study the target phosphorus threshold of 0.2 mg/L TP in the filtrate was achieved in a dual-bed media filter with anthracite and sand up to filter velocities of 16 m/h. By using a detailed sampling protocol and headloss curves, the influence of different operation modes on retention could be identified. Afterwards, the filter media were replaced by three types of GAC. In all filter beds substantial differences were found in the mode and efficiency of particle retention. This led to different filter run times, which is one of the main parameters for efficient and economical filter operation. Specific curves were generated for the different bed materials showing the dependency of filter run time on the specific load of suspended solids. Elimination of micropollutants in a GAC 4 x 8 mesh filter bed was low due to coarse grains and low empty bed contact time (EBCT). The application of GAC 8 x 14 mesh filter bed resulted in high elimination of most micropollutants. These results can be applied when choosing filter bed material. This may involve a compromise between filter run time and adsorption of micropollutants.