Modifying a backwash trough to reduce media loss

Since the 1960s, many rapid sand filters have been modified to become high-rate filters, and dual media have replaced sand. A common problem caused by this change is excessive loss of anthracite coal medium (5-10 percent annually) under regular filter-washing practices. This happens because the spac...

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Bibliographic Details
Published in:Journal - American Water Works Association 1997-12, Vol.89 (12), p.47-59
Main Authors: Kawamura, Susumu, Najm, Issam N., Gramith, Karl
Format: Article
Language:English
Subjects:
Aluminum
Applied sciences
Backwash
Baffles
Carbon
Drinking water
Drinking water and swimming-pool water. Desalination
Exact sciences and technology
Filter Media
Flow distribution
Flow velocity
Granular Activated Carbon
Particulate matter
Pilot projects
Pollution
Polyethylene
Production capacity
Storage tanks
Subdrains
Tap water
Washing
Water filtration
Water purification
Water temperature
Water treatment and pollution
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Summary:Since the 1960s, many rapid sand filters have been modified to become high-rate filters, and dual media have replaced sand. A common problem caused by this change is excessive loss of anthracite coal medium (5-10 percent annually) under regular filter-washing practices. This happens because the space between the top of the filter bed and the top of the wash troughs is insufficient for the lightweight coal grains, even though it was adequate for the rapid sand filter beds. Also, rather tight spacing of wash troughs for old filter designs aggravates the loss of coal grains. The authors evaluate the loss of granular actived carbon (GAC) after existing rapid sand beds are converted to GAC beds without raising the concrete wash troughs. Results of the pilot study indicate that a simple baffle configuration can reduce media loss by as much as 70 percent.
ISSN:0003-150X
1551-8833
DOI:10.1002/j.1551-8833.1997.tb08339.x