Lets Take A Closer Look At Sand Filters

A typical sand filter system consists of two or three chambers or basins. The first is the sedimentation chamber, which removes floatables and heavy sediments. The second is the filtration chamber, which removes additional pollutants by filtering the runoff through a sand bed. The third is the discharge chamber. The treated filtrate normally is then discharged through an underdrain system either to a storm drainage system or directly to surface waters. Sand filters are able to achieve high removal efficiencies for sediment, biochemical oxygen demand (BOD), and fecal coliform bacteria. Total metal removal, however, is moderate, and nutrient removal is often low. Figure 5 illustrates one type of configuration. Typically, sand filters begin to experience clogging problems within 3 to 5 years. Accumulated trash, paper, debris should be removed every six months or as needed. Corrective maintenance of the filtration chamber includes removal and replacement of the top layers of sand and gravel as they become clogged. Table 1 provides some typical removal efficiencies for specific pollutants.

Grated Cover Solid Cover

Grated Cover Solid Cover

Grite (Fabric Wrapped Over Entire Grate Opening)

Figure 5. Example of a sand filter configuration. Table 1. Typical removal efficiencies.

Grite (Fabric Wrapped Over Entire Grate Opening)

Figure 5. Example of a sand filter configuration. Table 1. Typical removal efficiencies.

Pollutant

Percent Removal

Pollutant

Percent Removal

Fecal coliform

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