Trio of treatment technologies for island
The century-old remote fishing community of Stonington is one of two towns on Deer Isle, Maine on the US' eastern seaboard. As if painted by Claude Monet, Stonington is a portrait of rural living. It hugs a cove that is lined with majestic spruce trees, pink granite ledges and moored fishing boats. Its vistas of open fields, serene woods and sparkling water lure visitors from around the country, making Stonington a tourist's delight. Each year thousands of summer vacationers journey to this secluded hamlet to enjoy the island's old world Victorian charm and modest way of life.Although Stonington's remote location and picturesque waterscapes make it a haven for tourists, artists and the like, those very attractions have threatened the drinking water supply, and, subsequently, the island's economy. During the peak tourist months and at the height of lobster season, Stonington's drinking water supply becomes severely depleted and the Stonington Water Company often mandates a water restriction to help alleviate the shortage. The town's water wells have a low yield, and its indigenous pond is badly discoloured.
Upon consulting Maine's government officials, Stonington was awarded a community development block grant. Subsequently, it embarked on a project to treat Stonington's pond and well water.
Reclaiming the pond would not be a simple matter. The surface water, which has a high organic amber colour, contains TOC levels of approximately 12 to 17 mg/L, low turbidity and low alkalinity.
Stonington evaluated conventional water treatment methods, which depend on chemical coagulation using a metal coagulant, such as iron or aluminium. However, Stonington did not want to deal with chemical sludge handling and disposal, because of the water treatment facility's remote location. This severely limited treatment alternatives for this surface water supply.
After evaluating several water treatment solution providers, the Stonington Water Company selected Ionics to purify the pond water and supplement the town's existing water supply. The water supply agreement covered design, engineering, manufacturing, installation, start-up, commissioning and operating of the water treatment plant in Stonington, Maine. In May 2001, construction of the plant began and, by early August, the plant went online, producing fresh drinking water for residents and tourists alike.
Ionics custom-designed a dual water treatment solution which combined three advanced treatment technologies: ozonation, ultrafiltration (UF) and nanofiltration (NF).
For colour removal, the Ionics 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.
No sludge residue
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 colour reduction of the feedwater from approximately 600 colour 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,' says Stone. 'Due to Stonington's remote location, sludge removal would have been extremely difficult.'
Similarly, Ionics was able to alleviate Stonington's water well woes.
Stone continues, '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.'
To insulate the entire system against the harsh northeastern winters, the Ionics 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,' says Roger Stone. '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.'