CASE STUDY:
Why, Arizona
Electromedia® Removes Arsenic from 150ppb to Below 3ppb
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Primary filtration reduces second stage demand.

Background

Arizona State Highways 85 and 86 meet in Pima County in southwestern Arizona. The intersection used to form a “Y” and gave birth to a town name. The unusual name comes from a state law that at the time required town names have three letters, so “Y” became Why. What’s not so unusual is that the town of Why, like many Arizona communities, has high levels of arsenic in their well water that requires treatment.

During winter, the town’s population grows with the arrival of snowbirds attracted to the areas’ natural desert setting and average temperature of 70 degrees. Why Utility Company has three water wells to supply the Town’s 100 service connections and regular population of approximately 400, along with its seasonal visitors. All three wells have arsenic levels that exceed the allowable limit set by the Environmental Protection Agency (EPA) of arsenic of 10 parts per billion. Only one well is currently available with raw water arsenic at 150 ppb.

The Challenge

The main challenge was getting the town's arsenic levels which were in excess of 150 ppb down below the Maximum Contaminant Level of 10 ppb as determined by the EPA and to also satisfy the requirements the Arizona Department of Environmental Quality.

Filtronics pilot tested the well water at Why Utility Company with a combined flow from two wells. The result of the testing indicated the need for two stage filtration. The primary stage was coagulation and filtration with Filtronics Electromedia® filter. The arsenic in the treated water from the primary stage was reduced to 11 to 18 ppb. The second stage filter was an adsorptive unit that dropped the arsenic to less than 3 ppb.

Design and construction of the full scale facility followed pilot testing. Funding for the project came from Pima County and USDA Rural Development funds. Ultimately, Tres Rios Consulting of Tempe, Arizona was responsible for the final design and start up phases of the project. The facility has been producing clean, potable water with arsenic levels well below the maximum contaminant level (MCL) of 10 ppb since the summer of 2008.

Water is pumped from the wells through the Electromedia® filter in the coagulation and filtration process. The stream is split, still under pressure, with partial flow to two adsorptive filters and into two on-site ground storage tanks. These two tanks supply backwash water to the filter for its four minute cycle. Water is boosted by two other pumps in a duty-stand-by arrangement to the distribution system, eventually reaching their hill top storage tanks.

The Surprise Solution                                                                              

A surprise came in the results for the full scale system. With some adjustments to the treatment chemistry, the Electromedia® filter in the primary treatment stage consistently reduces the arsenic from 151 ppb to less than 3 ppb, lessening the demand on the second stage.

The full scale adsorptive filters now take a sidestream of about 30% of the flow, instead of the planned 100%. The absorptives ensure that water in the town of Why is in compliance with the Arizona Department of Environmental Quality and US EPA limits. The lower than expected usage and lower levels of arsenic to the absorptive filters will extend the life of the adsorptive media by a factor of more than three. Overall operating costs have been significantly reduced by the performance of the primary filter. Due to the effectiveness of the primary stage, it is considered likely that upon further testing, the secondary stage of filtration will be unnecessary, which will reduce chemical and operating costs even further.

Conclusion

Vern Denning, Why Utility Co., Inc.’s Vice President says “The plant is functioning automatically and taking arsenic from 150 ppb to 1 or 2 ppb. The system is great and Why is very pleased with it.”

The answer to the Town of Why’s arsenic treatment problem was brought forward by the collaborative effort of the town staff, their consulting engineer, installation contractor, and equipment suppliers.