Chlorine dioxide-- a powerful, highly selective oxidant-- is an important tool for meeting drinking water quality goals while maintaining compliance with tightening regulatory restrictions on treatment by-product levels.
Chlorine dioxide has been used to treat public drinking water supplies in the United States for more than fifty years as a complement, and more often in recent years, as an alternative to chlorine. Chlorine dioxide is used to achieve a variety of water treatment objectives, from the inactivation of pathogenic waterborne organisms (disinfection) to the improvement of the water quality through destruction of contaminants (oxidation).
Chlorine dioxide is an extremely effective disinfectant, which rapidly inactivates bacteria, viruses and protozoa, including Giardia; it is even effective, to some extent, against the highly resistant encysted parasite Cryptosporidium.
Chlorine dioxide is effective over a wide pH range. It has been proven especially useful for taste, odor, and algae control and to oxidize iron and manganese. It destroys phenols without producing chlorophenols. It destroys sulfides and cyanides. Pre-oxidation with chlorine dioxide improves coagulation and often extends filter runs. Treatment of filter backwash water extends filter runs and enhances “ripening” of filter media.
High-purity chlorine dioxide does not produce chlorinated by-products (THM, HAA) associated with chlorination, nor does it oxidize bromide ion to bromate ion, unless photolyzed. Chlorine dioxide has two principle by-products: chlorite ion (ClO2-), chlorate ion (ClO3-).
Chlorine dioxide may be deployed synergistically, with other treatment processes, including: ozone, UV, chlorine and monochloramines, as part of a multiple-barrier approach to water treatment.
Chlorine dioxide use for the treatment of municipal wastewater at centralized plants has been investigated, but has not generally been practiced because it has been considered prohibitively expensive compared to treatment of community wastewater with chlorine gas. Exceptions have included tertiary treatment of wastewater intended for reuse (e.g., irrigation), mostly in arid areas with scarce water resources.
Chlorine dioxide has been evaluated for the treatment of combined sewer overflow (CSO), the occasional mixing and overflow of storm sewer and sanitary sewer flows that occurs during severe weather, mostly in older cities where storm and sanitary sewers are connected.
Pilot-scale studies supported by USEPA have shown chlorine dioxide produced by the CDG Gas:Solid process to be superior in effectiveness and similar in cost to chlorination/dechlorination.
Before handling any chemical, persons are advised to acquire training in the handling and use of such materials, and to become fully familiar with applicable Material Safety Data Sheets and operating manuals.
In the United States, the use of chlorine dioxide is for many purposes regulated by agencies of the Federal Government, especially: EPA, FDA, OSHA. The transportation of chemicals is regulated by DOT. State and local regulatory agencies may also have jurisdiction. Before chlorine dioxide is used for any purpose, the user should become fully informed about any and all applicable governmental rules, regulations and codes.