Gravity filters, used to treat drinking water, are commonly built within large tanks filled with different layers of granular media. Water containing impurities is usually fed in at the top of the filter and allowed to percolate down through the filter media. The graphic to the right shows flow streamlines entering a gravity filter where four different layers of filter media are in use. In this simulation, each granular layer was assigned different porous media properties. The primary objective of the analysis was to improve the distribution of flow through the filter media.
Once in use, a cleaning method known as backwashing is commonly used to clean gravity filters. In backwash mode, flows within the filter are reversed. This fluidises the media bed and releases captured impurities into the backwash flow. The backwash flow is then treated as an effluent.
Blue Hill Hydraulics uses numerical methods to simulate the performance of gravity filters and to evaluate the effectiveness of backwashing schemes. The results of these studies have been used to improve the lifespan and function of many gravity filters.