Water reuse

Man-made or constructed wetlands can be used to treat non-traditional water sources that could then be used in power plants.

Clemson University researchers have shown that man-made or constructed wetlands can be used to treat non-traditional water sources, which could then be used in power plants.

Four kinds of non-traditional water sources were treated during the researchers’ tests: ash basin water, simulated cooling water, flue gas desulphurisation water and produced water, or water that is extracted from the ground along with oil and natural gas.

All of the water sources contained contaminants such as salts, heavy metals and hydrocarbons. In addition, all were capable of causing bio-fouling or corrosion because of their pH, ionic strength or nutrient content.

Recognising the differences in each water source, unique wetland treatment systems were designed and constructed for each type of water.

The artificial wetlands were created in large (70 to 250-gallon) vats containing vegetation that would be found in natural wetlands, such as California bulrush and narrow-leaf cattail. Each type of water was gravity fed through its own series of vats, residing for about 24 hours in each.

Before and after treatment, researchers measured pH, temperature, dissolved oxygen, hardness, alkalinity and conductivity, along with the levels of contaminants.

Test results showed that constructed wetland treatment systems could remediate all four non-traditional water sources for reuse or discharge.

Since constructed wetland treatment systems cost 10–50 per cent less than conventional treatment systems, they could provide an economical alternative to conventional water-treatment approaches, which are comparatively costly and are often unable to achieve new, rigorous water-quality standards.

The pilot-scale test was supported by the US Department of Energy (DOE) Office of Fossil Energy.

Flue gas desulphurisation water was treated in a constructed wetlands system consisting of five ‘reactors’ planted with vegetation found in natural wetlands. The water treated was received from an operating coal-fired power plant in the south-eastern US