Although it's been used in water treatment for more than a century, ozone is becoming an increasingly attractive option for drinking water systems nationwide. Currently it is used in nearly 450 large-scale treatment plants in the United States.
That translates to more than 1 million gallons/day, according to Jeff Neeman, assistant director of water treatment technology for Black & Veatch's global water business. Of those plants, less than 5% are wastewater treatment facilities. Yet he does recognize the potential market for ozone in the treatment of wastewater.
Ozonation provides more than just disinfection. "Many communities are turning to ozone for taste and odor control," Neeman says. It is also used for the oxidation of inorganic compounds like iron and manganese and microconstituents like endocrine-disrupting chemicals (EDCs) and pharmaceuticals and personal care products (PPCPs), the removal of which is growing in importance to protect public health. Ozone's counterparts are less effective against those compounds, removing little to none of them. UV is only useful in EDC/PPCP removal when energy and dosage levels are substantially increase.
As health research uncovers more chlorine-resistant pathogens, the strength of a treatment method like ozonation may be preferred. Additionally, the most recent study on ozone, completed by the AWWA Research Foundation, reveals that its effectiveness in compound removal from drinking water could be recognized after only two minutes of contact time, which is much more rapid than the speeds for chlorine, chlorine dioxide and UV/hydrogen peroxide.
Despite its benefits, ozonation remains a costly option. Although the long-term benefits are clear, there are higher capital expenses. Major costs include the construction necessary to make ozone processing possible and in the generation itself, which requires high amounts of electric charge to generate it from air, according to Ed Malter, superintendent of sanitary services for the city of Springfield, Mo. However, the operating and maintenance fees are lower than that of other treatment methods (2 to 3 cents/million gallons with ozone peroxide versus 15 to 20 cents/million gallons using UV peroxide).
Treatment methods for both drinking water and wastewater do not necessarily need to exist in competition with one another but can instead complement each other depending on the need and type of water.
Ozone is instrumental in both drinking and wastewater because of its numerous abilities beyond basic disinfection, such as improved filter performance and the disinfection of Giardia and other viruses. The strength and affordability of UV is also applicable to both kinds of water, ideal for removal of Cryptosporidium in freshwater and offering benefits to wastewater disinfection. Although the benefits of ozone are evident, it does produce bromates, a less-than-desirable byproduct that requires pH suppression, ammonia addition, or other reduction methods.
All of this makes it evident that there is no clear-cut winner in water management but rather a preferred processing based on the type of need.