Arsenic Removal Technology Installed Despite Limited Time and Space
In 2001 Aqua Pennsylvania, Inc., one of the country’s largest investor-owned water utilities, began development on the Meyers Tract well system, a new water treatment facility in Collegeville, Pa. Testing on the source wells revealed elevated arsenic (As) levels, measuring approximately 12 µg/L in one well, and about 15 µg in the second well. Although these levels did not exceed the 2001 arsenic maximum contaminant level (MCL) of 50 µg/L, Aqua Pennsylvania knew the U.S. Environmental Protection Agency (EPA) would be lowering the MCL for arsenic in drinking water to 10 µg/L in January 2006 and that some type of treatment would be needed if this supply was to remain available to the public.
Finding the best treatment technology to address the problem was just one of the challenges facing the company. Aqua Pennsylvania also needed to find equipment that would fit into its existing facility and that could be manufactured, delivered and installed in time for the heavy demand of the summer months.
Zoning restrictions did not allow for expansion of the footprint of the well water treatment facility, so a system had to be found that would operate within the existing building. The available space in the building was about 20 feet long by 12 feet wide by nine-and-a-half feet high, and access to the equipment had to be available within this footprint.
Because Aqua Pennsylvania did not have a discharge permit for the suburban Philadelphia site or access to sewers for any innocuous water, the As removal process could not generate a significant amount of wastewater.
The company initiated a program piloting different types of As removal processes. Most of the arsenic removal systems being considered would have required up to double the available space for chemical feed storage and wastewater tanks. The system chosen was Severn Trent Services’ SORB 33™ As Removal System, which fit neatly into the existing space.
At the heart of the SORB 33 system design is the Bayoxide® E33 iron-based adsorption media developed by LANXESS (formerly Bayer AG) in cooperation with Severn Trent. The media has a high capacity for arsenic and, unlike other iron-based adsorptive media, is delivered in a dry crystalline form. The granular ferric oxide Bayoxide E33 product is robust, easy-to-handle and has NSF Standard 61 approval.
During system operation, water from the source well is pumped through a fixed bed pressure vessel, or series of vessels, containing the Bayoxide E33 media. As the water passes through the fixed bed of media, the arsenic is removed to less than 10 µg until the media reaches its capacity. The spent media – which passes the Toxicity Characteristic Leachate Procedure (TCLP) test categorizing it as non-hazardous – is then removed and disposed of as non-hazardous waste. Unlike several other As removal technologies, there is no complex on-site regeneration or flocculation, making the SORB 33 process simple and reliable while minimizing labor and operator skill requirements. The media’s high capacity for arsenic enables long operating cycles of six to 24 months between media change-out, thus minimizing operational and maintenance requirements.
The skid-mounted SORB 33 system is 164 inches long by about 77 inches wide and 114 inches high. Because of its standard packaged design, the system was fabricated and shipped to the Meyers Tract site less than two months after the order was placed. The system was shipped as a unit, partially disassembled, brought in through a six-feet-wide by seven-feet-high double door, and reassembled inside the building. Other work included partial interior modifications of the building and relocating chemical feed and other equipment while keeping the station in service, with only minor shut downs for tie-in to the new equipment. A hatchway also was installed in the building roof to facilitate gravity media fill into the adsorber vessels directly from large sacks.
The construction, delivery and installation took three months – approximately one to two months less than would typically be expected for such a project. The station was placed into service in July 2004. Since the beginning of its operation, the system has produced water with an arsenic level of less than 2.0 µg, which is the laboratory detection limit for As. The only maintenance required, as expected, has been the occasional “backwash” or “fluffing” of the beds every few months. It’s anticipated that the media will require replacement in approximately two years.
The SORB 33 system allowed Aqua Pennsylvania to rapidly install a system to meet the summer loading needs of the area while meeting municipal zoning restrictions. And while reducing As levels to below the new MCL of 10 µg was the primary goal of installing the system, SORB 33 has far exceeded expectations by helping reduce As levels to below the level of laboratory detection.
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