Mar 22, 2007

Arsenic Treatment Proves Effective

In the summer of 2006, Isolux Technologies was selected to implement an arsenic, iron and manganese treatment solution for a residential development located in the rural outskirts of Boise, Idaho.
Following the construction and sale of the first several large-scale residential homes on the tract, occupancy was halted by the Idaho Department of Public Health following an analytical evaluation of the drinking water quality. It was identified that the groundwater supply contained several contaminants significantly exceeding drinking water standards.
In particular, arsenic was detected at 690 parts per billion (ppb), iron at 2.4 parts per million (ppm) and manganese at 314 ppb.
With help from the Idaho Department of Public Health and with local support from Water Treatment Technologies, Isolux designed and fabricated a 20 gal per minute (gpm) redundant arsenic treatment unit equipped with pretreatment for the removal of iron and manganese. The design incorporated the patented arsenic adsorbent cartridges that allow a small system footprint and ease of exhausted media replacement. The system was installed and made operational in October 2006.

Treatment design

Given the exceptionally poor water quality associated with the site, treatment for the removal of multiple contaminants was required. Having treated both iron and manganese and arsenic, Isolux concluded that the oxidation-precipitation-filtration technique for iron and manganese removal, followed by arsenic adsorption, represents the most effective solution for trouble-free long-term operation.
The iron and manganese pretreatment system includes an oxidation step utilizing chlorine addition. Due to the residential application of the treatment system, liquid chemical addition with a metering pump was not utilized. Liquid chlorine is a hazardous material and a leak in a residential setting can be serious. Therefore, a dissolving feed chlorine-based solid oxidant, certified to NSF Standard 61, was used.
Following oxidation, the source water is filtered through two 13 x 54 in. fiberglass vessels containing oxidizing manganese oxide-based media. The two vessels operate in parallel, treating a designed flow capacity of 20 gpm. From the iron and manganese filtration vessel, the water passes through a particulate filter prior to entering the arsenic treatment system.
The arsenic treatment system configuration designated for the Idaho project included two vertical vessels, each containing four 42 x 5 in. arsenic treatment cartridges. The cartridges are packed with zirconium-based adsorbent media. The media react both physically and chemically to effect rapid adsorption of the arsenic, typically requiring no pretreatment and absolutely no backwash. Due to the elevated concentration of arsenic at the Idaho site, the two vessels are plumbed in a lead/lag configuration to provide redundant, precautionary treatment.
The treated product water flows to a 300 gal storage tank prior to supplying the distribution system. On an automated, prescribed frequency, the storage tank supplies backwash water through a booster pump to the iron and manganese filtration system at nearly 20 gpm. The backwash of the iron and manganese system is necessary to remove particulate iron oxide and manganese oxide build up from the surface of the media, ensuring effective long-term operation.

Results

The system was placed in operation and monitored routinely by Water Treatment Technologies to determine the effectiveness of treatment. The Isolux system was capable of removing the elevated levels of arsenic to non-detectable levels (<1.5 ppb), effectively removing arsenic to well below the drinking water standard of 10 ppb.
Additionally, the iron and manganese levels were reduced to within the range of the drinking water standards.
As a result of the Isolux treatment system effectiveness, identical systems were installed in the constructed residential homes, and the Idaho Department of Public Health has granted occupancy permits for each dwelling.

About the author

Jim Knoll is the business manager for Isolux Technologies. He can be reached at 908/797-7480 or by e-mail at [email protected].

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