Arsenic New Mexico Seminar Showcases Several Innovative Treatment Methodologies—A Review
By Tom Carmody and Richard S. Dennis
Summary: Arsenic in drinking water—and what levels should be deemed acceptable—has been a hot-button issue for some time. Last October, a meeting in New Mexico was organized to help bring water treatment industry leaders together to identify where problems lie and what solutions may exist for various communities.
Arsenic, an environmental hot topic, is a naturally occurring heavy metal released into water supplies from erosion of rocks and soil. Long-term exposure to arsenic has proven to result in serious health effects such as cancer, cardiovascular disease, diabetes and reproductive problems. There are two different forms of Arsenic—arsenite or arsenic III [As (III)], and arsenate or arsenic V [As (V)]. Arsenic V is the most common form and easier to remove from drinking water. As III, which is generally soluble, is more difficult to remove and more hazardous to human health. High concentrations of arsenic are found mostly at the foothills of mountain ranges in the United States. Western states and parts of the Midwest and New England show higher arsenic levels well above the newly approved U.S. Environmental Protection Agency (USEPA) standard of 10 parts per billion (ppb).
Although these areas have the highest concentrations of arsenic overall, communities throughout the country have high levels of arsenic in their drinking water. Roughly 13 million Americans obtain their drinking water from public water systems that exceed the new maximum contaminant level (MCL) of 10 ppb and must comply with the regulation by January 2006.
With that date looming closer, identifying cost-effective and commercially proven methods for arsenic removal treatment technologies becomes increasingly important. To provide such a forum, Severn Trent Services, of Fort Washington, Pa., and Black & Veatch, of Kansas City, Missouri, co-hosted a conference last fall to discuss arsenic removal solutions in New Mexico. Topics for discussion included arsenic chemistry, arsenic removal treatment options, pilot testing and full-scale design and installation. Co-sponsors included the city of Rio Rancho, N.M., and the University of New Mexico. As the first in a series of planned arsenic discussions the one-day, free conference was held Oct. 24 in Albuquerque.
Dr. Bruce Thomson, of the University of New Mexico’s Department of Civil Engineering, presented a summary of arsenic chemistry relevant to environmental issues and water and wastewater treatment. Highlights of his discussion include arsenic in the natural environment, solution chemistry, oxidation-reduction, adsorption reactions, analytical considerations and health effects of arsenic. Supported by documentation from the U.S. Geological Society (USGS) and his own research, Dr. Thomson emphasized that New Mexico has a higher incidence for arsenic levels in drinking water when compared to the nation as a whole. In fact, about 20 percent of communities in New Mexico with affected wells have an arsenic concentration of 10 ppb, while nationally less than 10 percent of communities reach that level.
Supplementing an in-depth technical presentation on the solution chemistry of arsenic, Dr. Thomson was quick to distinguish a few important points about arsenic. The element has two oxidation states, As (III) and As (V), that can each contain notable characteristics. As (III) is non-ionic at a neutral pH, has a high solubility and is more toxic to many organisms. As (V) is ionic at a neutral pH, less soluble and has strong adsorption potential. When analyzing the element, there’s no accepted method of preserving the oxidation state. Nonetheless, various arsenic analytical methods currently exist, including hydride generation, spectroscopic and electrochemical. Dr. Thomson detailed hydride generation and two sub-categories of the spectroscopic analytical method. A comparison of the advantages and disadvantages for each method presented is listed in Table 1.
A complete water quality analysis of source water is necessary since all water qualities vary, even in similar regions. And certain water quality conditions can affect different removal technologies’ effectiveness. It’s important to determine basic values such as pH, total dissolved solids (TDS), hardness, alkalinity, arsenic and sulfate (SO4) levels. An extended analysis of metals, total suspended solids (TSS), total organic carbon (TOC), fluoride (F), selenium oxide (SiO2) and As (III) is also recommended. Thus, a comprehensive water analysis is instrumental in determining the best treatment selection, often eliminating the need for a site-specific pilot study. Simply, water analysis is key to treatment economics.
Arsenic treatment options
Jonathan Clement, drinking water research director at Black & Veatch, presented an overview of adsorption and physical removal treatment technologies, noting points to consider in their selection process and optimization. Options for physical removal via membranes were presented—microfiltration, nanofiltration, and ultrafiltration or reverse osmosis (RO). Adsorbents including granulated ferric hydroxide or oxide media, activated alumina, ion exchange, granular activated carbon (GAC), ferrichite and ferric-laden zeolite were included in the discussion. As Clement noted, granulated ferric hydroxide or fixed-bed adsorbers are the most common treatment approach because of their simplicity, long media life, and easy and economical operation.
The view from Rio Rancho
To help New Mexico utilities gain a local perspective on arsenic removal, Larry Webb, utilities director for the City of Rio Rancho, N.M., presented results of a pilot program recently completed at the city’s municipal water system facility. Rio Rancho’s arsenic problems first began when 13 wells within the district, which lies north of Albuquerque, were found to contain arsenic levels exceeding the 10 ppb MCL. These wells ranged in arsenic concentrations from 11-49 ppb with accompanying flow rates of 550-2,800 gallons per minute (gpm), totaling 23.7 million gallons a day (mgd). The city didn’t plan to install a centralized treatment system, and began examining a technology that could be installed at the wellhead. Ideally, its arsenic treatment program would be a simple system that generated minimal waste, wasted minimal water and relied on a proven technology.
During an inorganic contaminant workshop held February 2000 in Albuquerque, John Simms of Severn Trent Water (STW) presented a paper highlighting the results from the its SORBä 33 arsenic removal process using a granular ferric oxide media undertaken at STW locations. The city of Rio Rancho now had a new technology to examine for its water treatment system, leading CH2MHill to perform an engineering study to evaluate the operating and capital cost impact of undertaking the SORB 33 process. CH2MHill also evaluated other criteria including waste generated, water lost and complexity of the process.
With a clear direction established, iron adsorption was determined to be the lowest capital cost by far, and a viable present value-cost option. The SORB 33 process was simple and proven. The city of Rio Rancho would need to prove that the SORB 33 process was suitable to treat its complex New Mexico water. Together with Severn Trent Services, Rio Rancho initiated the first pilot program for arsenic removal in New Mexico and the first U.S pilot for the SORB 33 process. The pilot was constructed and operated at Rio Rancho’s most difficult well containing arsenic levels of 49 ppb, pH 8.9 and vanadium 78 ppb. Vanadium is an interferant to arsenic removal.
Rio Rancho pilot results prove the SORB 33 process removes arsenic levels well below 10 ppb from high As and pH waters. With an empty bed contact time (EBCT) of three minutes, arsenic breakthrough occurred at approximately 40,000 bed volumes. After exhaustion, the media can be sent to a non-hazardous landfill for disposal, meeting the toxic characteristics leaching procedure (TCLP) test. All combined, the overall process economics are better then predicted in the preliminary report. During this year, the first full-scale removal system is expected to be installed and will run for one full year before additional systems are considered. From 2004-2006, Rio Rancho plans to phase in the additional 12 systems requiring arsenic removal treatment, enabling the city to meet USEPA compliance by 2006.
Meanwhile, Webb vehemently urged his peers to execute arsenic treatment technologies well ahead of the time “bulge” that can be expected in 2006, especially since a complete evaluation of the technology can take up to two years. The manufacturer knows the timeline in an arsenic removal project can include pre-qualification (three to six months), technology selection (three to six months), pilot validation (up to 12 months), full scale system procurement (four to six months), first system installation (three to 12 months), and procurement and installation of remaining systems (six to nine months). Webb also urged participants to focus development efforts around adsorption technology.
Operational systems’ size
Greg Gilles, vice president of AdEdge Technologies Inc., presented detailed material for small system compliance in New Mexico. AdEdge currently has a partnership with High River Environmental Technologies to focus on providing arsenic treatment solutions to local small systems. With pilot studies already under way, Gilles noted most systems with arsenic above 10 ppb in New Mexico are small systems and, since few small system treatment options are cost effective and simple, adsorption offers the lowest cost treatment alternative. Small systems tend to be the most economically sensitive to treatment cost and have little previous treatment experience.
Gilles noted the granular ferric oxide media has a high arsenic capacity similar to amorphous iron hydroxide, with extremely robust mechanical properties while the media is dry, easy to handle, stable in shipment, and produced from a reliable source.
Public water systems preparing for the January 2006 compliance date must identify cost-effective and commercially proven methods for arsenic removal treatment technologies. This process should begin with a basic understanding of arsenic chemistry, complete water quality analysis, and possible pilot or laboratory demo work of available treatment options. Undertaking these basic steps will assist a public water system in setting a schedule for compliance that includes minimizing the risk and monetary investment needed for a full-scale arsenic removal treatment system.
About the authors
Tom Carmody, program manager of the arsenic treatment program at Severn Trent Services, of Fort Washington, Pa., has over 20 years of experience in water, wastewater, technology development and business management. Carmody is a chemical engineer with an undergraduate degree from Cornell University. Severn Trent and Black & Veatch plan to co-host their next seminar in Phoenix, tentatively scheduled for late March. For future conference information, contact Severn Trent at email@example.com
Richard S. Dennis is separation product manager at Severn Trent Services. Dennis has been in the water treatment industry for 29 years. He has a bachelor’s degree in chemical engineering from Lehigh University. He can be reached at (813) 886-9331, (813) 886-0651 (fax) or email: firstname.lastname@example.org