Water sanitation district installs a mixed-oxidant generator and eliminates potential hazards of using chlorine gas disinfection

In mid-January 2000, the North Table Mountain Water Sanitation District, located approximately 30 miles northwest of Denver, CO, completed the installation of a new disinfection system that eliminates the potential hazards associated with chlorine gas. The new system is an onsite mixed-oxidant generator that does not use or produce any hazardous materials. In addition to improving safety conditions for the water plant employees and the neighboring community, the system also has reduced disinfection by-products, chlorine taste in the water, use of lime for pH adjustment, and the total amount of chlorine necessary for disinfection.

North Table Mountain Water Sanitation District is a surface water treatment plant that currently treats about 5 million gallons per day (gpd) of water during peak season and uses approximately 75 pounds per day of chlorine. The new system generator, manufactured by Albuquerque, NM-based MIOX Corporation, called the MIOX-503, utilizes three electrolytic cells, each with a capacity of 50 pounds per day of chlorine, for a total capacity of 150 pounds per day. The excess capacity allows for room for growth of the community and redundancy should one of the cells need to be taken offline.

Safety concerns were the primary reason for upgrading to onsite generation
According to District Engineer and Manager Rick Jeschke, the "Safety concerns were the primary reason for upgrading to onsite generation. New residential neighborhoods are being developed close to the water plant, and the poisonous chlorine gas previously used for water disinfection posed a significant liability issue for the plant."

In addition, North Table Mountain had to comply with U.S. Environmental Protection Agency (EPA) regulations for completion of a Risk Management Plan (RMP) associated with use of chlorine gas. This plan includes an offsite consequence analysis, a five-year accident history, a prevention program, and an emergency response plan, with compliance audits every three years. With the upgrade to mixed-oxidant generation, no RMP is necessary, since the only materials used in generation of the mixed oxidants are salt, water and electricity.

Noticeable improvements occur after one week of new system operation
Within one week after start-up of the new system, North Table Mountain observed some favorable changes in their treatment processes. The level of chlorine residual, which prevents re-infection in the distribution system, has stabilized. The plant has seen an overall reduction of 33% in the amount of disinfectant used, which correlates to the mixed-oxidant disinfectant solution being approximately 1.4 times stronger than chlorine gas. They have also observed a 50% decrease in use of lime, which is used for pH adjustment. Jeschke says that he "can no longer smell a chlorine odor at the water treatment plant or in the sink's tap water at the office located nearby."

Six months later, TTHMs and HAAs decrease by 44%
In July of 2000, the plant completed their first disinfection by-product (DBP) testing after conversion to the new disinfection system. The conversion to mixed-oxidant disinfection from chlorine gas resulted in a 44% decrease in the formation of both Total Trihalomethanes (TTHMs) and Halo Acetic Acids (HAAs). With the combination of their MIOX generator and conversion to a new flocculation system, North Table Mountain is well under even the Stage II limits of the Disinfectants and Disinfection By-Products Rule, which states a limit of 40 µg/L for TTHMs and 20 µg/L for HAAs. Current DBP levels at the site are only 23 µg/L for TTHMs and only 16 µg/L for HAAs.

North Table Mountain is pleased with the operation of the MIOX unit to date. According to Jeschke, "We're really happy with the unit. We got it started and it just goes on its own. It doesn't require much attention." North Table Mountain showcased their plant during the American Water Works Association (AWWA) Exposition, an international water conference being held in Denver, Colorado, in June of 2000, with multiple tours out to the site.

For more information, contact MIOX Corporation at 5500 Midway Park Place NE, Albuquerque, NM 87109; Phone 505-343-0090; Fax: 505-343-0093; E-mail: info@miox.com.

Information provided by MIOX Corporation