The City of LaSalle, Illinois, has worked with Tonka Water, a Kurita brand, since their filters were installed in 1992. After nearly 30 years of service, the city was assessing how to ensure a similar duration of additional life. In lieu of a full replacement, they decided to refurbish the existing filter equipment.
The city’s water treatment plant had two Tonka Water horizontal pressure filters for iron and manganese removal, which were designed to treat up to 1,115 gallons per minute (gpm) of water from the city’s wells. The filters included Kurita’s Simul-Wash, which uses air and water simultaneously during backwash. With these types of filters, most customers can expect a life cycle of 30 years, although longer is possible depending on operating conditions and attention to maintenance.
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| Each 10-foot diameter by 38-foot-long horizontal pressure filter has three cells in the “end-piped” configuration to minimize necessary building space. |
Though the filter media was replaced once in 2008 as part of a plant upgrade project, the city was noticing shorter filter runs requiring more frequent backwashing to maintain treatment quality. This is not unusual. Media changes over time, affecting the filter bed properties that impact run length and other performance characteristics. A typical media life is 15 years. The LaSalle filter would need new media, but at the time, replacing the media alone would fall short of the city’s longevity goals. With the equipment approaching 30 years of life, a more substantial refurbishment was justified to mitigate age-related concerns around filter components and appurtenances. Otherwise, the other option would be a full replacement.
The city’s filters were well maintained, making refurbishment a viable option for the desired additional equipment life. This resulted in considerable savings in capital cost while streamlining project timeline and sitework as compared to a full replacement of equipment.
Knowing these updates needed to occur, the city budgeted for a major refurbishment and Kurita helped them assess the best path forward. Kurita provided a complete filter refurbishment package to replace critical components, including Simul-Wash backwash troughs, while advising on operational adjustments to allow continued treatment during construction.
Simul-Wash is proven to provide the b
est media cleaning and can save approximately 50% of backwash water when compared to conventional methods of similar duration. The backwash system provides optimal cleaning of media filters while minimizing water waste.
With the goal of achieving an additional 30 years of service, the city decided to replace all of the filter internals, including media, gravel, underdrains, air scour grids, and backwash troughs. The existing manways were also replaced with larger 24-inch diameter dome-style manways with hinges to better accommodate the work and allow easier future access. The empty vessels were sandblasted and painted to ensure steel integrity during the additional years of service.
The existing stainless steel Simul-Wash troughs would have likely endured, but replacing the troughs allowed for unobstructed contractor work inside the filter cells and provided peace of mind. Once completed, new troughs were installed into each filter cell using Kurita’s bolt-together Simul-Wash trough, which was designed for field retrofits of existing pressure filters. The trough components individually fit through standard manways sizes and are manually assembled within the filter using conventional attachment hardware.
In all, Tonka Water’s filter refurbishment scope included:
- Underdrain system: PVC construction header-lateral piping, encased in concrete with gravel-retaining nozzles (replaced existing steel plate underdrain)
- Filter media: dual media of GreensandPlus™ and anthracite, including graded support gravels (replaced similar media in kind)
- Air scour grids: PVC construction header-lateral system (replaced existing similar system)
- Simul-Wash backwash troughs: bolt-together design for in-vessel assembly
- Access manways: 24” diameter domed and hinged manways (replaced existing 14” x 18” elliptical for greater access)
- Valves: butterfly type with electric actuators (replaced existing filter function valves)
Because the city had two filters, they were able to isolate one during construction while the other remained in service. This allowed for continuous treatment to prevent disruption to the city’s water supply. Kurita advised the city on alternative operating conditions for a single filter, including proper flow rates and chemical feed doses, to ensure the finished water continued to meet acceptable drinking water standards during construction.
The results of the Kurita filter refurbishment were immediate, including longer filter runs and less frequent backwashes. The greater value is in the security and assurance of a system that will continue to meet the city’s goals well into the future. With continued diligence for routine maintenance and the support of Tonka Water, a Kurita brand, the city can expect upwards of 30 years of additional life from their system.