The Stonington pond has a high organic amber color and contains TOC levels of approximately 12 to 17 mg/L.Click here to enlarge image"Deer Isle is a poorly fractured granite island, which means that water does not naturally pool to form wells," said Roger Stone, Superintendent of the Stonington Water Company. "What limited water resources we have cannot adequately provide the potable water the town needs. This impacts not only Stonington residents, but the island's economy as well. We simply needed to expand our water resources."
Upon consulting Maine's government officials, Stonington was awarded a community development block grant. Subsequently, the Stonington Water Company embarked on a project to treat the town's pond water and well water.
Reclaiming the pond would not be a simple matter. The surface water, which has a high organic amber color, contains TOC levels of approximately 12 to 17 mg/L, low turbidity and low alkalinity. Stonington evaluated conventional water treatment methods using iron or aluminum. However, town officials did not want to deal with chemical sludge handling and disposal because of the water treatment facility's remote location. This limited treatment alternatives.
After evaluating several alternatives, the Stonington Water Company selected Ionics to purify the pond water and supplement the town's existing water supply. Headquartered in Watertown, MA, Ionics is a worldwide provider of water and wastewater treatment solutions.
The water supply agreement covered design, engineering, manufacturing, installation, start-up, commissioning and operating of the water treatment plant. Construction of the plant began in May 2001 and it went online in early August.
Ionics custom-designed a dual water treatment solution which combined three treatment technologies: ozonation, ultrafiltration (UF) and nanofiltration (NF).
For color removal, the system employs ozone micro-flocculation followed by UF membrane filtration. By adding ozone to the high TOC water source, organic material and biological contaminants are significantly reduced. The ozone addition forms very small bubbles that microflocculate the organic matter, so that it can then be filtered through the UF membrane.
To achieve the drinking water standard of 15 CoPt units, the plant uses a loose NF membrane after UF membrane filtration. This allowed for total color reduction of the feedwater from approximately 600 color units to essentially zero, without the creation of a chemical sludge that would need to be disposed.
"By using ozone, UF and NF, the desired level of water quality is achieved without the production of waste sludge materials associated with other water treatment technologies," Stone said. "Due to Stonington's remote location, sludge removal would have been extremely difficult."
Similarly, Ionics was able to alleviate Stonington's water well woes.
"Stonington has drilled about five miles of wells that average 345 feet in depth. However, the lack of fractures in the granite has left the Stonington Water Company with only one good and seven mediocre wells. Ionics assessed the situation and installed a water filtration solution that filtered the well water as well as the pond water," Stone said.
To insulate the entire system against the harsh northeastern winters, the system is housed in a brick building that was built in 1910 a building which also houses a World War II diesel surplus engine restored as an emergency pump.
"We are extremely pleased with the results," Stone said. "Ionics' combined technologies have allowed Stonington to meet the water demand for the 2001 tourist season. The treated pond water is clean and the wells are pumping an ample supply of water for residents and businesses." WW/
