Next-Generation Arsenic Removal

A novel process gives spent adsorptive media — and utilities' budgets — new life.

The U.S. Environmental Protection Agency feels your pain.

That's what the EPA seems to be saying through its Arsenic Removal Technology Demonstration Program. Initiated in 2002 — the same year federal limits were dropped from 50 micrograms per liter (μg/L) to 10 μg/L — the program seeks out and verifies low-cost solutions for utility

The latest breakthrough shows tremendous promise: The first (and only) full-scale deployment is saving the participating utility $20,000 to $30,000 per year. The savings are gained by backwashing and regenerating, rather than repurchasing, iron-based adsorptive media — a major development considering many utilities' tight budgets and the rising cost of replacement media.

The EPA partnered with Battelle, an applied science and technology development company, to demonstrate the ability of a caustic solution (sodium hydroxide) to strip the arsenic from spent media in a lab setting. In 2009 the project went full-scale at Twentynine Palms Water District in California, where it has since been adopted as regular operating procedure, post-EPA demonstration program, and continues to thrive.

Startup requirements for media regeneration are relatively modest — chemicals, feed pumps, and tanks — but there are certain mitigating factors, discussed below, that should be evaluated before adopting the process. The right candidates, however, could be on the cusp of significant savings.

The Arsenic Problem … And Solution
Arsenic is an odorless and tasteless semi-metal that is naturally present in aquifers throughout the country, and thus also shows up in well water. At concentrations above the EPA's maximum contaminant level (MCL) of 10 μg/L, arsenic can cause skin damage, circulatory problems, and an increased risk of cancer. It is a common issue for many small communities — and an expensive one.

"A lot of people are out of compliance because they just can't afford the cost of arsenic treatment," said Ray Kolisz, operations manager for Twentynine Palms, who often travels to waterquality conferences to speak on adsorptive media regeneration. For traditional treatment, the biggest expense is purchasing new media. According to EPA research engineer Tom Sorg, 80 percent of utilities that treat arsenic do so with adsorptive media, and 80 percent of the operating cost is for media replacement. Sorg, who was responsible for taking regeneration from the lab to Twentynine Palms, also noted that ironbased media, particularly Bayoxide® E33, is the industry standard for arsenic removal. Other types of adsorptive media include activated alumina (AA) and titanium- and zirconium-based media, but full-scale regeneration, at this stage, is exclusive to iron-based media.

The typical process consists of media inside the pressure vessel(s), where the arsenic adsorbs onto the media. As it starts to lose its adsorption capability, the media is replaced with new, virgin media.

The cost savings came through as expected, but the performance of the regenerated media was eye-opening.

The new process features upflow regeneration utilizing 4 percent caustic solution (pH of 13) to strip the arsenic off the media. A second step, neutralization, injects 93 percent sulfuric acid into the flow stream to lower the pH of the treated water. The resulting hazardous-waste effluent must be handled appropriately, whether sent into the public sewer system (if available), treated on-site, and/or hauled offsite. Equipment requirements for Twentynine Palms were two HDPE tanks (3,200 gal) to collect wastewater, a tank (1,000 gal) and pump for the caustic solution, an acid-dosing pump, and a pH meter.

Twentynine Palms also underwent minor pipe modifications to the existing treatment system, including plumbing for upflow and downflow application of the reagent, before regeneration could begin.

Details here

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