Course: BFM 203 Water Treatment and Control

Lecture

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Slow Sand Filtration

In a slow sand filtration system, water is drawn down through the sand by gravity, similar to gravity filtration. Particles are removed by straining, adsorption, and biological action. The filtering rate ranges from 0.015 to 0.15 gmp/sq. ft. The majority of particulate removal takes place in the top seven inches of sand; physical removal is required when clogging occurs. This sytem requires only a minimal operation and maintenance budget; however,the system is not widely used due to the large physical area required for the system and the need to manually backwash filters. Following is a diagram of a slow sand filter.