Hydraulic of activated carbon filters washing in water treatment plants

During backwashing high-speed gravity filters with water, the filter medium expands and the water level above the filter rises, so that the impurities that have accumulated on it during the filtration process, and which are lighter than the material of the medium, are taken to the sewer through the overflow. The size of the expansion depends on the speed of the water flow through the filter medium during washing, as well as on the viscosity of the water, which changes depending on its temperature. For filter mediums such as quartz sand or a combination of sand and other materials (anthracite, tuff, zeolites, etc.), there are various methods in the literature for determining water flow rates during washing the layer of the applied medium, which enable its expansion sufficient to remove impurities. However, for adsorptive materials such as granulated activated carbon, which has recently been increasingly used as final filtration in the purification of drinking water, there are still no formulas that could reliably give valid results for calculating the washing rates of such filters. In the paper, the author presents his own attempt to solve this problem, relying first of all on practical experience gained by monitoring the 36-years operation of PPV "Makiš" in Belgrade, as well as on experimental curves of renowned world manufacturers of activated carbons.