Taos, a town in northern New Mexico with 8,000 residents, was awarded an arsenic removal treatment system as part of the U.S. EPA’s Arsenic Removal Demonstration Program in January 2005. Nationwide, about five percent of municipalities will have to treat drinking water to meet the new EPA standard of 10 parts per billion (ppb) in drinking water. In New Mexico, that number is closer to 20 percent. One of the most common rocks containing arsenic in the state is pyrite or "fool's gold." Silica-rich volcanic rocks and some sandstones and mudstones commonly found in the state also contain high amounts of arsenic.
SORB 33®
The SORB 33® arsenic removal system was selected for use at the Taos facility over two other competing technologies. In February 2006, a SORB 33® APU (arsenic package unit)‑450 was installed at Taos’ Well # 8 building to treat 450 gallons per minute (gpm), all of the well pump’s capacity.
The SORB 33 APU is designed for arsenic removal at the wellhead of small water systems. The APU products are standard package units, engineered to remove arsenic contamination to less than 10 ppb across a complete range of drinking water systems up to 450 gpm. Mirroring the larger SORB 33 systems, the APU operates under the same principal of pumping source water through a vessel or series of vessels containing the new pelletized Bayoxide® E33P granular ferric oxide media. As the contaminated water passes through the media, arsenic is adsorbed and removed to the required level until the media reaches its capacity. The spent media, which meets toxicity characteristic leaching procedure requirements, is then removed and disposed as non-hazardous waste. The SORB 33 APU system design and operation does not require the cleaning, regeneration or other complex process steps required by competitive technologies.
Special Design Details
At the Taos facility, the 21’L x 7’W x 9’H skid-mounted SORB 33 APU unit consists of three 5¼‑Ø FRP adsorbers and 195 ft³ of Bayoxide® E33P iron oxide media, which was installed in four parts through the wall behind the system. The well water has a slightly elevated arsenic level of 14 ppb and is low in TDS, but it has a very high pH of 9.5. The system was designed with a pH reduction pretreatment process to lower the water’s alkalinity and improve the Bayoxide® E33P media arsenic adsorption performance. Fifteen ppb of carbon dioxide gas is injected into the water downstream to lower the water’s pH to 7.4, an optimum level that allows maximum adsorption without the need for pH readjustment. The gas is diffused into the water using a porous membrane housed in side-stream piping that feeds well water to the adsorbers. Complete gas dissolution occurs within 10 feet of piping.
Carbon dioxide liquid is supplied in 480 lb. glass dewars delivered weekly to the well house, and the SORB 33 system has an emergency backup unit including two 50 lb. high pressure CO2 cylinders. The dewars and cylinders are stored in a separate, ventilated room.
Results:
The system’s results have been impressive. Arsenic levels have been reduced to less than 0.4 ppb at current bed volumes of 8,000 BVs. Arsenic levels did not reach 10 ppb until 111,000 BVs, representing a media life of approximately 26 months.
The SORB 33 system and Bayoxide® E33 media also have been successfully tested at EPA Arsenic Removal Demonstration Programs in Arizona, Michigan, Maryland and New Hampshire.
For more information, email info@severntrentservices.com