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/L in the second well.
Although these levels did not exceed the 2001 As maximum contaminant level (MCL) of 50 µg/L, Aqua Pennsylvania knew the U.S. Environmental Protection Agency (EPA) would be lowering the MCL for As in drinking water to 10 µg/L in January 2006. Accordingly, some type of treatment would be needed if this water supply were 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. Equipment 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 selected that would not only remove arsenic effectively below the MCL, but would also operate within the existing building,” said Joseph Ritter, manager, Treatment/QC, with Aqua Pennsylvania. “The available space in the building was about 20 ft long by 12 ft wide by 91/2 ft high, and access to the equipment had to be available within this footprint.”
Initiating new programs
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.
With this in mind, the company initiated a program piloting different types of As removal processes, from natural zeolite to ferric chloride dosing combined with green sand filtration. Aqua Pennsylvania contracted with CET Engineering Services to find a commercially available technology that could meet these criteria.
Most of the As 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 system design is the Bayoxide E33 iron-based adsorption media developed by LANXESS, formerly Bayer AG, in cooperation with Severn Trent specifically for the removal of As from drinking water.
“The media has a high capacity for arsenic and, unlike other iron-based adsorptive media, is delivered in a dry crystalline form,” said Rich Dennis, separation products manager for Severn Trent Services. “The granular ferric oxide Bayoxide E33 product is robust, easy-to-handle and has NSF 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 As is removed to less than 10 µg/L until the media reaches its capacity. The spent media—which passes the Toxicity Characteristic Leachate Procedure test categorizing it as non-hazardous—is then removed and disposed of as non-hazardous waste. The cost of disposal is less than 1% of the overall operating cost.
“Unlike several other arsenic removal technologies, there is no complex onsite regeneration or flocculation, making the SORB 33 process simple and reliable while minimizing labor and operator skill requirements,” said Dennis. “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.”
Providing quality water
The Meyers Tract source wells have a combined capacity of more than 350 gallons per minute (gpm), though only one well is currently permitted for operation—its capacity is 185 gpm. The second well is in reserve for when the needs of the growing local population exceed the safe capacity of the current system. The SORB 33 system installed in the Collegeville facility is designed to handle a 300-gpm flow rate. This design bypasses approximately 30% of the water from both wells, blending the treated and untreated waters to produce a final effluent of less than 5 µg/L As.
With initial design criteria geared toward producing water with less than 5 µg/L, the system would provide the best quality water for consumers while assuring full compliance with all state and federal regulations.
The skid-mounted SORB 33 system is 164 in. long by about 77 in. wide and 114 in. 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. Neither the assembled SORB system nor any of the competitive systems considered during the pilot testing and evaluation stage would fit through the Meyers Tract facility’s entryway. As a result, the system was shipped as a unit, partially disassembled, brought in through a 6-ft-wide by 7-ft-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.
“Of the chemical feed equipment, the phosphate corrosion inhibitor feed was of particular concern,” Ritter said. “It had to be installed into the plant effluent line to prevent any phosphate-treated water from coming in contact with the media, which can reduce the effectiveness of the arsenic removal and shorten the expected life of the media. 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 system was completed and commissioned in May 2004.
The station was inspected by the Pennsylvania Department of Environmental Protection, an operating permit issued and the system 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/L, which is the laboratory detection limit for arsenic,” Ritter said. “The only maintenance required, as expected, has been the occasional ‘backwash’ or ‘fluffing’ of the beds every few months based on pressure differential. It’s anticipated that the media will be replaced at the end of its useful life—about 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 maintaining good relations with neighbors.
According to Ritter, “while reducing arsenic levels to half the new MCL of 10 µg/L was the primary goal, the SORB 33 has far exceeded our expectations by helping reduce arsenic levels to below the level of laboratory detection.”
