The Basics of Multi-Media Filters

The Basics of Multi-Media Filters

WaterProfessionals

ÂŽ

www.WaterProfessionals.com

Multi-Media Filter Operation A properly operated and well-maintained multi-media filter will remove dirt, rust, silt and other particles down to 10-25 microns. When coagulants are added upstream of the filter, multi-media filters can also remove suspended particles smaller than 10 microns.

A multi-media filter usually consists of 3 layers of media containing anthracite coal, sand, and garnet.

It also has a supporting layer of (non-filtering) gravel at its bottom. The lighter and larger anthracite coal sits on the top of the filter, with the sand in the middle and the heavier, denser garnet layer at the bottom.

This type of filter arrangement removes the largest-sized dirt particles at the topmost part of the media, while retaining the smaller particles deeper and deeper within the filter. Thus, the entire media bed acts as a 3-stage filter that allows more efficient particle removal, as well as much longer run-times in between backwashes.

Industrial Multimedia Filter Diagram

Page 1 of 2

Š 2015 WaterProfessionalsŽ

1-800-999-4195

The Basics of Multi-Media Filters

WaterProfessionals

®

www.WaterProfessionals.com

Service Flow A multi-media filter’s ideal service flow will depend largely on the filter’s size. The size of the multimedia filter used should be carefully selected based on water usage and desired flow rates. Flow rates that are too low for a filter will result in a loss of water pressure, while flow rates that are too high can dislodge previously trapped particles.

Care and Maintenance Once the filtration medium fills with turbidity, the multi-media filter must be backwashed to clean the bed. During backwash, the flow of water through the filter is reversed, so as to loosen the filter media and remove the solids trapped within the filter bed. After a thorough backwash, the filter bed is left to settle and to re-stratify; then a final rinse is performed to remove any remaining loose dirt.

The multi-media filter is then ready to be placed back into service.

Over time, the jagged edges of the filtration media used in a multi-media filter can become rounded or dull, resulting in reduced effectiveness. A highly trained service technician will be able to tell you if it is time to replace your filtration media, as well as perform routine maintenance to ensure maximum performance.

When is a Multi-Media Filter Recommended?

Suspended solids contain minute particles such as clay, grit, silt, algae, organic matter, and other microorganisms. A multi-media filter is typically used to help reduce the “turbidity”, or level of suspended solids present in feedwater.

Multi-media filters are required when water has a high turbidity level, or Silt Density Index (SDI).

Filtering water with high levels of turbidity is necessary to prevent downstream filters from prematurely fouling. Feedwater with a high level of suspended solids can lead to high-pressure drops, which in turn reduces the effectiveness of downstream filtration equipment, such as ion exchange resin beds and reverse osmosis membranes.

Page 2 of 2

© 2015 WaterProfessionals®

1-800-999-4195