Ozone has been used to disinfect drinking water for more than a century. Of the 450 large-scale water and wastewater treatment plants that use the gas, virtually all—more than 96%—are drinkingwater operations.

But ozone can be used for more than purification. "Many communities are turning to ozone for taste and odor control," says Jeff Neeman, assistant director of water treatment technology for Black& Veatch's global water business.

Ozone is also used to oxidize inorganic compounds such as iron and manganese, as well as microconstituents like endocrine-disrupting chemicals (EDCs), pharmaceuticals, and personal careproducts (PPCPs).

Although the long-term treatment benefits are clear, high capital-investment costs have prevented the process from being more widely embraced by water and wastewater treatment managers.

Ozone must be created on-site by a special generator that passes dry, clean air through a high-voltage electric discharge. The result is an ozone concentration of about 1% or 10,000 mg/L.

At the same time, though, operating and maintenance costs for an ozonation system are lower than those of other treatment methods.

Ed Malter, superintendent of sanitary services for the city of Springfield, Mo., says that ozone peroxide is 2 to 3 cents/million gallons versus 15 to 20 cents/million gallons using UV peroxide.