Page 7: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Trichloroethylene
6.0 Treatment Technology
Municipal water filtration plants that rely on conventional water treatment techniques (coagulation, sedimentation, precipitative softening, filtration and chlorination) have been found to be ineffective in reducing concentrations of TCE in drinking water (Robeck & Love, 1983). Two common water treatment technologies that, when combined, are effective in removing TCE are air stripping and activated carbon.
Air stripping has been found to be effective in removing VOCs such as TCE from groundwater. Air stripping is effective in stripping large quantities of TCE from water, but at low rates of removal (Russell et al., 1992).
Adsorption onto activated carbon is widely used to remove synthetic organic compounds such as TCE from drinking water, if the activated carbon filter bed is deep enough (Russell et al., 1992).
Combining air stripping and activated carbon into a two-step treatment train has been shown to improve TCE removal. In a municipal-scale treatment plant combining these processes, air stripping is used in the first step for bulk removal of the majority of the TCE from the water, and activated carbon is used in the second step to remove most residual TCE from the water. TCE levels below 1 µg/L can be achieved in municipal drinking water supplies using these methods (U.S. EPA, 1985b).
Generally, it is not recommended that drinking water treatment devices be used to provide additional treatment to municipally treated water. In cases where individual households obtain drinking water from private wells or the drinking water is contaminated by low concentrations of TCE, private residential water treatment devices may be an option for removing TCE from drinking water.
A number of residential treatment devices from various manufacturers are available that are affordable and can remove TCE from drinking water to make it compliant with the applicable guidelines or regulations. Filtration systems may be installed at the faucet (point of use) or where water enters the home (point of entry). Point-of-entry systems are preferred for VOCs such as TCE because they provide treated water for bathing and laundry as well as for cooking and drinking. Certified point-of-use treatment devices are currently available for the reduction of VOCs, including TCE. Although certified point-of-entry treatment devices cannot be purchased off the shelf, systems can be designed and constructed with certified materials. Periodic laboratory testing should be conducted on both the water entering a treatment device and the water it produces to verify that the treatment device is effective.
Health Canada does not recommend specific brands of drinking water treatment devices, but it strongly recommends that consumers look for a mark or label indicating that the device has been certified by an accredited certification body as meeting the appropriate NSF International (NSF)/American National Standards Institute (ANSI) standards. These standards have been designed to safeguard drinking water by helping to ensure the material safety and performance of products that come into contact with drinking water. Certification organizations provide assurance that a product or service conforms to applicable standards. In Canada, the following organizations have been accredited by the Standards Council of Canada (www.scc.ca) to certify drinking water devices and materials as meeting NSF/ANSI standards:
- Canadian Standards Association International (www.csa-international.org);
- NSF International (www.nsf.org);
- Water Quality Association (www.wqa.org);
- Underwriters Laboratories Inc. (www.ul.com);
- Quality Auditing Institute (www.qai.org); and
- International Association of Plumbing and Mechanical Officials (www.iapmo.org).
Treatment devices to remove TCE from untreated water (such as from a private well) should be certified for the removal of either TCE or VOCs. In the case of TCE, these treatment devices are certified to reduce TCE levels from an average influent (challenge) concentration of 0.3 mg/L to a maximum finished effluent concentration of 0.005 mg/L or less (NSF International, 2005). Treatment devices that are certified to remove TCE or VOCs incorporate some type of adsorption technology, usually activated carbon, or utilize reverse osmosis, usually in combination with one or more adsorption-type filters.
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