Trio of treatment technologies for island

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.’