Hilltown Township, Pa., lies in the western corner of historic Bucks County. Located about 35 miles north of Philadelphia, the Township is home to the rolling farmland and 200-year-old farmhouses.
According to the Hilltown Water and Sewer Authority, the township is also home to naturally occurring arsenic in its groundwater. When measured in early 2003, arsenic levels in surrounding groundwater measured between 15 and 20 parts per billion (ppb). When the United States Environmental Protection Agency (EPA) reduced the federal arsenic standard to a maximum contamination level of 10 ppb in drinking water beginning January 2006, the authority had to act.
Testing the Waters
“We volunteered for the Environmental Technology Verification Program and tested an iron-based adsorption treatment technology from ADI International,” said Butch Erwin, operations manager, Hilltown Water and Sewer Authority. “The pilot test provided valuable information for our future system requirements, which included not only the reduction of arsenic levels, but of manganese and iron levels, too.”
The feed water for the verification test was drawn from an on-site chlorine detention tank containing groundwater that had been disinfected with sodium hypochlorite. The feed water—with an average total arsenic concentration of 21 ppb and a pH of 7.6—was treated with sulfuric acid to lower the pH to 6.4 prior to treatment. When operated under the manufacturer’s specified conditions for the site and at the design flow rate of 1.7 gallons per minute (gpm), the ADI system reduced the total arsenic concentration from an average of 21 ppb in the feed water to an average of 7 ppb in the treated water.
Although the arsenic removal system was judged to be effective, iron and manganese levels remained high. While the levels were not health risks, they did lead to customer complaints of discolored water and mineral deposits in bathtubs, showers, sinks and toilets.
The Best Solution
According to Erwin, the need to add sulfuric acid to the water was another reason to look for an alternative arsenic treatment technology. “Adding sulfuric acid to the treatment unit represented not only an additional step, but an additional expense as well. And from a safety standpoint, we’d prefer not to have to keep undiluted sulfuric acid on site.”
Nevertheless, Erwin and his colleagues were convinced of the efficacy of iron-based media, so they investigated similar technologies. The SORB 33 arsenic removal system utilizing Bayoxide E33 media from Severn Trent Services had been selected for use at several other EPA demonstration sites, so Erwin decided to find out more about the technology. When he learned that Severn Trent also was introducing the Omni-SORB iron and manganese pre-treatment system, he considered the possibility that the combined technologies might provide the ideal solution for Hilltown Township’s water filtration needs.
The SORB adsorption process and technology is designed to economically remove arsenic contamination below 4 ppb across a range of water treatment applications. Bayoxide E33 is a dry/robust, ferric oxide media designed with a high capacity for arsenic. Adsorption is a simple and reliable continuous process for arsenic removal. The pump-and-treat process does not require any complex on-site regeneration or flocculation, minimizing labor and operator skill requirements.
The life of adsorptive media, including iron oxide based ones, is dependent on site-specific raw water quality conditions. Bayoxide E33 media will not remove cations and anions other than arsenic. These ions generally compete for the same adsorption sites as arsenic; hence, the resulting effect is to reduce the media’s capacity to adsorb arsenic.
The new Omni-SORB granular filter media was specifically designed to provide removal of iron and manganese compounds from water and wastewater supplies. Unlike other iron and manganese removal media, Omni-SORB is not a processed mineral. It is an engineered product using refined manganese that has high catalytic activity for oxidation and adsorption of these metals. These catalytic properties allow the media to be efficiently used without the addition of potassium permanganate, a strong oxidant required for iron and manganese removal with greensand and other media.
The Township installed a 300 gpm SORB 33 system in February 2006. The system incorporated a three-stage adsorber vessel treatment technology in which the Omni-SORB pre-treatment system removes the iron and manganese prior to water entering an adsorber containing the Bayoxide E33 media for arsenic removal.
The system is automated with a touch screen operator interface; however, the Township chose to switch the backwashing function to a manual operation. The Township operated the system at 260-265 gpm, bypassing 70 gpm, which is combined with the treated water at the end of the process. The remainder of the water is treated by two arsenic vessels and one iron/manganese vessel.
“The Omni-SORB system gave us the opportunity to address the needs for iron, manganese and arsenic reduction at the same time,” Erwin said. “And the equipment has a very small footprint, so we achieved cost savings in using a smaller building to house the equipment.”
Since installation, the system has made “a huge difference,” according to Erwin. Arsenic levels have been reduced to 4 ppb. Manganese levels are now less than half of what they were (.015 ppm), and iron levels are “virtually zero,” he said. “We’ve pretty much eliminated iron as a problem.”
Also, with the previous arsenic removal system, flushing the network required two full weeks twice a year. Today, despite the fact the Township’s distribution system has expanded by about 25%, the flushing time has been cut by two to three days.
“We’ve been very happy with the SORB 33 and Omni-SORB systems,” Erwin said. “In fact, we’re designing the systems into another well that has been closed for the past year because of high arsenic levels. We’re sold on these technologies.”
Nadia Abbott is the marketing manager for Severn Trent Services. She can be reached at 215-997-3733 or by email at email@example.com.