Sustainable Water System for Arsenic Treatment

Michael R. Boyd

A sustainable business is an enterprise that has no negative impact on the global or local environment, community, society or economy. The business must incorporate the three basic principles of sustainability in its business decisions: money, people and the environment.

Sahuarita Water Co. LLC (SWC) is a sustainable business, ensuring that its system operations fully address all current and potential environmental concerns while maintaining a profit and a positive balance sheet. SWC is located approximately 20 miles south of Tucson, Ariz. The water company is a privately owned water utility covering a 4.7-sq-mile area and providing water to more than 12,000 residents living in more than 4,700 homes. It also supplies water to three campuses of the Sahuarita Unified School District and several commercial properties.

Sustainable Growth

In 2008, Layne Christensen was brought in to drill, case and develop a new production well with all the associated pumping equipment. Along with the new well, SWC had two existing wells, both over the maximum contaminant level of 10 ppb of arsenic. The decision was made to centrally treat these wells to minimize capital and operating costs, maintain the visual aesthetics of the town and minimize commercial traffic coming and going to these plants.

SWC looked at both coagulation filtration and adsorption for the application. With only nine full-time employees and a system that needed to be operational within the year, the decision was made to go with adsorption to reduce required maintenance and the cost of hauling sludge. Two adsorption media were tested side‐by‐side, one of which was Layne Christensen's LayneRT, a hybrid iron‐based adsorption resin.

At the completion of the pilot study, the LayneRT produced 23,000 bed volumes (BVs) before breaking through to 10 ppb of arsenic. Aside from LayneRT outperforming the other system by more than 50% in capacity of arsenic removed per bed volume, other factors weighed into the decision made by SWC. As a resin-based media, it produces no fines, does not require backwashing and produces no onsite waste: all factors that reduce operator maintenance and required training.

“The ease of operation of a LayneRT adsorption system as a simple filter, as opposed to the complex backwashing needs of [the other] system matched the minimum staff impact philosophy [SWC] had adopted for the arsenic treatment system,” said SWC President Mark Seamans.

Proactive Measures

To be a sustainable business, the first items that needed to be considered in the evaluation process were the capital and operational costs of the system and the potential liability down the line in regard to arsenic-laden wastes. SWC decided to be proactive and selected a technology that minimized the liability associated with arsenic-laden wastes. Using a regenerable resin, the waste is generated off site by Layne Christensen and disposed of in a hazardous landfill even though the waste currently passes all the state and federal requirements for disposal at a standard landfill.

Not only does this approach reduce the operational cost of the system while eliminating the potential legal battle should the regulations change, but it also incorporates an honest concern for the well‐being of the environment and the future of the people in the community. Layne Water Technologies guaranteed 59,715 BVs through the lead vessels after the system was scaled up, and those vessels were taken offline for regeneration at the beginning of August.

When the vessels were taken offline at 8 ppb of effluent arsenic, they had treated 66,082 BVs. Because SWC is locked into a regeneration rate that includes loading, unloading, regeneration and transportation, the extra BVs achieved are extra money in its pocket. The regeneration takes place at the new 60,000-sq‐ft Layne Water Technologies NSF‐certified regeneration facility in Phoenix.

Maintaining a water system with sustainability in mind is a difficult task when treating for any constituent. In SWC’s case, the constituent was arsenic and the technology selected was LayneRT based on money, potential liability, a secured quality of life for the people in the community and a general concern for the environment. This is why SWC is a sustainable company striving to meet the triple bottom line.

Michael R. Boyd is a technical sales engineer at Layne Water Technologies. Boyd can be reached at [email protected] or 602.345.8600.