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Final Decision to Certify Hazardous Waste Environmental Technology


TriOx Ozone Treatment for Cooling Tower Water

The following is excerpted from:

Published Weekly by the Office of Administrative Law
Register 94, No. 40-Z
October 7, 1994
pp 1596-1598

The California Environmental Protection Agency, Department of Toxic Substances Control (Department) has made a final decision to certify the following company's hazardous waste environmental technology listed below:

6918 Sierra Court
Dublin, CA 94568

TriOx Ozone Treatment
for Cooling Tower Water

Chapter 412, Statutes of 1993, Section 25200.1.5., Health and Safety Code, enacted by Assembly Bill 2060 (Weggeland) and effective January 1, 1994 authorizes the Department to certify the performance of hazardous waste environmental technologies.

DTSC's notice to certify was published in the California Regulatory Notice Register Volume 94, No. 40-Z. The DTSC's final certification shall be effective from October 7, 1994 to October 7, 1997.

Additional information supporting DTSC's final certification decisions is available from:

California Environmental Protection Agency
Department of Toxic Substances Control
Office of Pollution Prevention and Technology Development
P.O. Box 806
301 Capitol Mall, 1st Floor
Sacramento, California 95812-0806
(916) 322-3670

A description of the technology to be certified, the final certification statement and the certification limitations for the technology follows:

TriOx Ozone Treatment
for Cooling Tower Water

Technology Description

Management of water from cooling towers generally includes control of biological fouling, microbially induced corrosion, and pathogenic bacteria. Traditional industry practices for control of biological growth in cooling towers include the addition of chemical biocides. Chemicals used for this purpose include compounds such as glutaraldehyde, tributyltin oxide, quaternary ammonium salts, or other organic or inorganic compounds. The California Department of Pesticide Regulation regulates the use of biocides in cooling towers. Publicy Owned Treatment Works (POTWs) regulate discharge of blowdown from cooling towers. POTWs have increasingly restricted discharge of contaminants in blowdown water to their sewer systems.

TriOx, of Dublin California, manufactures an ozone treatment system which replaces chemical biocides with a computer controlled continuous ozonation system for control of biological growth in cooling towers. TriOx leases the system to users. The lease includes continuous computer monitoring, control of key operational parameters, and unit maintenance. In a typical system, water from the cooling tower is piped to the TriOx unit. Ozone is dissolved into the water using a patented static mixer. The system may also include an integrated reverse osmosis system, if necessary, for control of minerals in the water. This system produces very low mineral content ozonated water which is returned to the cooling tower, and high mineral content reject water which is discharged to the sewer. When operated in this manner, the unit can substantially reduce the volume of blowdown water, replacing it with a smaller volume of higher total dissolved solids (TDS) effluent.

Certification Statement

The TriOx cooling tower water treatment system is hereby certified by the Department of Toxic Substances Control (Department) as a Pollution Prevention Technology. The system has been shown to provide an effective alternative to the use of chemical biocides in cooling tower water when operated, monitored, and maintained in accordance with TriOx's standards and specifications. TriOx has patents covering their ozone generating cells, their static mixers which minimize ozone off-gassing, and their ozone and mineral removal system for control of contaminants in captured and recirculating water. The use of ozone minimizes the production, transport, handling, and management of toxic biocides. This decreases hazardous waste generation from residual biocides and potential risks from spills, leaks, discharges, or other releases of these chemicals. Ozone as a biocide is not intended to replace anti-scaling or corrosion control measures. Where it has been determined that such measures are appropriate, the TriOx ozone system may be used in conjunction with their reverse osmosis system and/or other ozone-compatible anti-scaling or corrosion control methods.

The TriOx system is capable of maintaining a residual concentration of 0.02 to 0.04 ppm of dissolved ozone in cooling tower water. Ozone concentrations are continually monitored using an oxidation-reduction potential probe which is correlated with the ozone residual. The system has been shown to be capable of maintaining less than 100 colony forming units per mL of free-floating bacteria in the cooling tower water, compared with in excess of one million colony forming units per mL in untreated systems. The ozonation has also been shown to be capable of maintaining the system free from visible slime on surfaces contacted by the ozonated water.

Certification Limitations/Disclaimer

This Certification is specific to the pollution prevention aspects of the technology. The Certification does not constitute an authorization for use in a particular application. The U.S. Environmental Protection Agency, the California Department of Pesticide Regulation, and other appropriate federal, state, and local agencies should be contacted for information on regulatory requirements related to the use of biocides in cooling towers.

The Department makes no express or implied warranties as to the performance of TriOx products or equipment. Nor does the Department warrant that the TriOx products are free from any defects in workmanship or material caused by negligence, misuse, accident, or other causes. The Department has not conducted independent testing to confirm the information submitted by TriOx, published in the literature, or gathered from other sources.

The Department does believe, however, that the manufacturer's product or equipment can achieve the performance levels set out in this Certification when used in accordance with the manufacturer's specifications. Said belief is based on a review of data submitted by TriOx and information gathered from independent sources.

This Certification is issued as part of the pilot project for the California Environmental Technology Certification Program, which has been established under the authority of the Health and Safety Code, Division 20, Section 25200.1.5. The pilot project purpose is to delineate the practical aspects of the program that will be adopted in regulations which are under development. Consequently, this Certification may be subject to additional conditions which will be required in these regulations, including, but not limited to, the duration of the Certification, continuing monitoring and oversight requirements, and Certification amendment procedures, including decertification.

By accepting this Certification, the manufacturer assumes, for the duration of this Certification, responsibility for maintaining the quality of the manufactured equipment and materials and service at a level equal or better than was provided to obtain this Certification and agrees to be subject to quality monitoring by the Department as required by the law under which this Certification is granted.

Certification Basis

This Certification is based on information and data provided by TriOx, published literature information, and discussions with ozone system users, POTWs, and others with expertise in cooling towers and ozone.

TriOx provided information on their system and literature and data demonstrating the performance of ozonation systems for cooling towers. During a visit to TriOx's headquarters in Dublin, California, TriOx showed Department staff the system components and the computer system used to monitor the units. The effectiveness of an ozonation system is highly dependent on the specific conditions under which it operates. As part of their lease, TriOx determines the appropriate system configuration and maintains the system quality. The computer monitoring and control is an integral part of the process quality control.

Representatives of four TriOx customers were interviewed by telephone. One customer uses two systems for cooling towers. The use of ozone eliminated their need for on-site storage of chlorine as a biocide (their alternative to ozone). This eliminates the corresponding costs for a permit to store chlorine. Another company also uses two TriOx systems for cooling towers. This company determined that they had a small reduction in blowdown, they lessened the hazard rating of their scale and corrosion control chemicals, and they eliminated the need to use acid for pH control. A third customer has used a TriOx system for over three years. They determined that the system reduced their water usage by 30,000 gallons per day. With less blowdown, they now add an ozone-compatible corrosion control chemical to prevent corrosion. The final user contacted has used a TriOx system for over four years. They indicated that the system has reduced their blowdown, and saves them approximately $2,000 per month compared with chemical treatment. All customers were very satisfied with the systems. In addition, two of the users operate TriOx systems for uses not covered by the Certification.

Representatives of eight POTW's were interviewed by telephone regarding their requirements for discharge of blowdown water from cooling towers. All the POTWS's regulate discharges of heavy metals and, in some cases, of TDS. The ozonation system does not use heavy metals. A reverse osmosis system will increase the concentration of TDS in water discharged to the sewer, while substantially decreasing its volume.

Several published studies were reviewed which demonstrate that ozone is an effective biocide in cooling towers. Additional information on ozone and cooling towers was obtained during telephone interviews with nine experts in these fields.

Ozone is generated at the point of use. In the event of a power loss or other system upset the ozone generator will automatically cease operation. This eliminates the possibility of spills or large releases. Chemical biocides used in other systems must be prepared, transported, stored, and handled, with the resultant possibility of spills or other releases. Ozone in cooling towers does not pose a significant threat to the public due to the short half-life of any ozone stripped from the system.

The low residual concentration on ozone in the cooling water minimizes the possibility that ozone offgas could reach the Occupational Safety And Health 8-hour standard of 0.1 ppm.

System Specifications

The TriOx cooling water ozonation system includes an ozone generator, an ozone contactor or a reverse osmosis mineral removal unit (if needed), a programmable computer interface connected by modem to computers at the TriOx headquarters, and detectors for monitoring oxidation/reduction potential, conductivity, and other parameters. All components are contained in a locked cabinet or otherwise inaccessible to unauthorized access. The system is leased to customers, and is under the continuous computer monitoring and control of TriOx. TriOx provides operational control modifications and maintenance, as needed. TriOx monitors, controls, and maintains the quality of the system and its performance.

Regulatory Considerations

Ozone generators used in pesticidal applications are regulated by the U.S. Environmental Protection Agency (US EPA) as devices, rather than as chemicals. The California Department of Pesticide Regulation should be contacted for information on the regulatory status of ozone generators in specific applications.

The Uniform Fire Code, Article 90, provides a conditional exemption for small ozone generators.

Local POTWs may regulate the blowdown and other aqueous discharges from cooling towers to sewer systems. Local/Regional Air Quality Management Districts and Air Pollution Control Districts may regulate vapors, gases, and drift emitted from cooling towers.

For more information, contact us at:

Department of Toxic Substances Control
Office of Pollution Prevention and Technology Development
P.O. Box 806
Sacramento, California 95812-0806
Phone: (916) 322-3670
Fax: (916) 327-4494
e-mail: techdev@dtsc.ca.gov

File last updated: October 31, 1996

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