The City of Thief River Falls, Minnesota was in need of a water treatment plant upgrade including replacement of the underdrain, media and troughs in four existing gravity filters. The plant was originally built in 1954, with a refurbishment of filters and controls in 1980. The plant had been well maintained, but the equipment had reached end of life. The project provided an opportunity for The City to upgrade its system with the latest technology, including stainless steel underdrains and simultaneous air and water backwash.
Tonka Water proposed the BLEU™ underdrain paired with the Simul-Wash™ backwash system, which allowed for all filter components to be supplied by one manufacturer. Tonka Water was selected to supply this equipment for the gravity filter upgrade.
The City treats a river water source using lime softening followed by media filtration. The water flows through solids contact clarifiers, then into media filters to capture any unsettled solids. The filter is bedded with dual media, directly retained by the BLEU™ underdrain system. During backwash, water flows back through the underdrain laterals while air is applied simultaneously through separate slotted pipes between them. Adding air between the laterals ensures that the media is uniformly cleansed, eliminating dead zones. The Simul-Wash™ backwash troughs prevent media loss while sustaining a simultaneous air and water backwash. Only one trough is required per twelve foot wide filter due to its unique design.
No dead zones
Uniform flow distribution
Integrates well for retrofits and new construction
Resistant to pressure surges
Ease of installation
Optimized for air and water backwash