Filtration Through a Granular Bed:

tion is a process in which water is passed through a bed in order for particles and certain microorganisms to be retained within the bed. This can occur by several methods, the main one being to prevent the passage of particles that are larger than the space that separates the bed grains.

Slow filters are the oldest, and its name is due to the speed with which the water passes through the filter. Because of this, its area is considerably larger than that of other filters. This filter retains most of the particles in the first layer of the bed.

Rapid single bed filters are formed only by sand and stands out as having a higher speed of the water compared with the slow filters, so its area is considerably less to treat the same amount of water. Additionally, this type of filter is not only efficient in the most superficial layer, but also retains particles and microorganisms throughout the entire bed, hence its depth is greater than that of a slow filter.

 Rapid mixed bed filters stand out for having a bed of anthracite accompanying the sand bed. Anthracite is a type of coal similar in size to sand. Compared with sand bed filters, mixed bed filters allow longer filtering runs.

The flow of clarified water through the filter medium can be both ascending or descending, depending on the characteristics of each project.  This causes the filter to clog every certain number of hours, which requires the installation of a filter media washing system that reverses the direction of flow.

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