Sandia and Kirtland Air Force Base test existing and new arsenic removal technologies at existing well

By 2006, according to a recently finalized EPA regulation, US drinking water shall contain less than 10 parts per billion of arsenic, a naturally occurring element that is thought to cause cancer when ingested at higher concentrations over long periods of time.

Arsenic levels in water from thousands of municipal groundwater supplies in the US, particularly in the western US, exceed the new limit by tens of ppb. (The current limit is 50 ppb.)

Communities are looking for treatment technologies that might reduce the cost of complying with the new regulation.

This summer Sandia and Kirtland Air Force Base are operating one of a growing number of arsenic-removal test facilities in the country.

The results of field tests conducted here should have national implications. Data from the tests will be shared widely to help communities and other water suppliers in their search for cost-effective arsenic-treatment technologies.

At a KAFB well station just inside the base’s Truman Gate, Sandia has designed and Kirtland has installed a filtration unit that allows the team to test a variety of existing and emerging technologies for extracting arsenic from drinking water, including several approaches recently developed at Sandia.

The well supplies some one million gallons per day, which is about one-fourth of the base’s average daily water needs. The arsenic content of Well 15 averages about 15 ppb.

"This is going to be an issue for us, so we thought it would be good to help Sandia with its field tests so they can have a look at the data from a real well," says Pat Montano, KAFB Water Quality Program Manager.

The field tests began May 24. Portions of Well 15 water are being flowed periodically through columns of activated alumina, a commercially available sorbent the EPA has designated as one of the Best Available Technologies for removing arsenic from drinking water down to the sub 10 ppb range.

Sandia project leader Nadim Khandaker (6118) says it will take several weeks to determine how thoroughly the activated alumina strips arsenic from the water and how long before the alumina granules are too saturated to filter out arsenic below the 10 ppb limit.

Then, with the activated alumina performance data as a baseline, the team will begin putting other treatment technologies to the test.

Among the Sandia-developed approaches to be tested are Specific Anion Nanoengineered Sorbents (SANS) — a family of proprietary formulations of mixed metal oxides that remove arsenic from water by trapping it permanently within the SANS’ chemical structures. SANS developers include Dave Teter, Pat Brady, Jim Krumhansl (all 6118), and Nadim (Lab News, March 9, 2001).

In small-scale laboratory batch and column tests with water containing 300 ppb arsenic, the SANS material outperformed activated alumina by about a factor of ten.

"We need to try SANS at a real well with real arsenic concentrations using real valves, pumps, etc.," says Nadim.

Well 15 water will be flowed through columns of granular SANS to verify whether the materials’ performance scales up to real-world situations.

Two other sorbents developed by Bob Moore (6849) also will be tested — a stabilized metal hyroxide and a doped activated carbon, both of which trap arsenic on their surfaces.

Following the sorbent trials the team will test an improved approach to coagulation/microfiltration, a common method of removing arsenic from drinking water. (Essentially, coagulant materials dissolved in the water bond with arsenic, then clump together into larger particles that are filtered out.)

A SANS-like nanoengineered enhancing agent developed at Sandia will be added to conventional coagulants. In previous laboratory tests, small amounts of these SANS enhancers significantly improved the effectiveness of standard ferric chloride coagulants.

The approach could reduce the cost of arsenic removal, says Nadim.

Other Sandia approaches to be tested include nanoengineered calcium oxide and magnesium oxide enhancers that could reduce the cost of lime-softening water treatment approaches.

The plumbing equipment used for the field tests incorporates a modular design so many different technologies and approaches can be tested, says Nadim. The equipment will remain at the well station following this summer’s test series for possible tests of future technologies.

The SANS and other Labs-developed treatment technologies have never been field tested before, says Nadim, so it’s too early to predict the possible outcomes.

"Our small-scale experimentation and models tell us the SANS will significantly outperform other approaches, but any engineer knows to wait for the data," he says. "The field tests will tell us how long a column of these is going to last in real water."

The data also will provide scientifically objective information about the performance of the Sandia technologies relative to commercial systems and might also help the team design future water-treatment systems, he says.

The field tests should have national and international implications, depending on how well the Sandia approaches perform, says Henry Westrich, Manager of Geochemistry Dept. 6118.

"This technology has the potential for dramatic reductions in water-treatment costs, especially for rural and small water utilities in the US and the world," he says.

Other project team members include Capt. Mike Dunlop and Mark Dalzell (both KAFB); Prof. Bruce Thompson and Greg Gartland (both University of New Mexico); Howard Anderson (6118), and Paul Baca (6245).

The field tests are funded through the Laboratory Directed Research and Development program and sponsored by Sandia’s Water Initiative, which supports the development of technologies that make water supplies safe, secure, and sustainable.