Organic chemicals are responsible for off tastes and odors in drinking water. Algae and bacteria release such chemicals into the water (following an algae bloom). Geosmin, responsible for “earthy” odors, and 2-methylisoborneol (MIB), responsible for “musty” odors, are two examples of compounds that cause T&O. In addition to aesthetic impacts, certain types of blue-green algae produce toxic compounds (“algal toxins”), which can have both acute and chronic impacts on animals and humans. Microcystin is perhaps the best-know algal toxin, as it is regulated in several states/provinces and by the World Health Organization.
Due to their small molecular weight and limited ability to adsorb to carbon, these compounds are difficult to remove. Traditionally, water plants use powdered activated carbon, granular activated carbon, ozone, or potassium permanganate to remove the compounds responsible for taste and odor.
UV technologies are currently experiencing rapid growth in municipal drinking water disinfection applications. For many utilities UV is the best option to comply with the enhanced disinfection requirements or provide a secondary barrier to chlorine-resistant pathogens. This is primarily based on UV's ability to inactivate many microorganisms, especially Cryptosporidium, without forming harmful disinfection byproducts. In addition, there is a growing awareness of UV-based advanced oxidation processes for treating micropollutants in water. Many studies have recently identified UV-oxidation (UV in combination with hydrogen peroxide) as an efficient means to treat T&O-causing compounds in drinking water.
The following article describes the nature of the T&O problem, describes traditional solutions, and details the use of UV-oxidation for the simultaneous treatment of T&O/algal toxins and disinfection. Finally, the installation of UV-oxidation at Cornwall, Ontario, Canada is described.