For decades, municipalities have utilized chlorine as a primary disinfectant for surface water sources, to inactive microbial pathogen such as Giardia. While the benefits of chlorination are well documented, a side effect of chlorination is that residual chlorine can react with naturally occurring organics in water to form disinfection byproducts (DBPs) such as total trihalomethanes (THMs) or five haloacetic acids (HAA5s). These byproducts may lead to increased health risks if present at high enough levels. To address the issue of DBP formation, in late 2005 the EPA finalized the Stage 2 DBP rule to protect public health by limiting exposure to these disinfectant byproducts.
The Stage 2 DBP rule builds upon earlier regulations, by requiring municipal water systems to meet maximum contaminant levels (80 ppb for THM, 60 ppb for HAA5) as an average at each compliance monitoring location (instead of as a system-wide average as in previous rules). The rule applies to approximately 75,000 municipal water systems; a small subset of these will be required to make treatment changes to comply with the rule.
One treatment change which can be employed by municipalities to reduce DBPs in drinking water is to employ granular activated carbon (GAC). GAC can be utilized to remove organic precursurs of DBPs, or adsorb the DBPs themselves. For surface water treatment (precursor or DBP removal), coal-based carbons have been the traditional product choice, however, Siemens recently introduced a new, proprietary product as a cost effective alternative to coal-based carbons. The AquaCarb® CX Series carbons have the high microporous structure of coconut shell-based carbon combined with the faster kinetics of bituminous coal-based carbons and exhibit a higher adsorption capacity than coal-based carbon for surface water treatment, with greater throughput before carbon breakthrough. The result is a lower lifecycle cost for the customer, and a lower cost for complying with DBP regulations and managing taste and odor issues. The product can be considered as a performance alternative to coal-based activated carbon for surface water treatment, where taste and odor removal, disinfection byproduct (DBP) or DBP precursor removal, or bulk organic and total organic carbon (TOC) removal are required.
For more information about disinfection by-products removal, contact the Information Desk, Monday through Friday, 8 a.m. to 5 p.m, Eastern Standard Time: 1.866.926.8420 or 1.724.772.1402 or email@example.com
Treating Water With Chlorine Dioxide Reduces THMs, Improves Taste for Arkansas Water Treatment Plant
The 1.8 MGD Greenwood Water Treatment Plant was built in 1964 and upgraded in 1992. The facility provides drinking water to a population of more than 7,000 and, like many small towns, Greenwood has faced major decisions about how to remain in compliance with the Safe Drinking Water Act. Because its water supply is provided by a very shallow lake (less than 10-feet deep), sourcewater quality can vary widely. “We often get a lot of organics, and this had brought about high trihalomethanes (THMs) in our finished water when we prechlorinated,” says Greenwood Water Superintendent, Mack Cochran. THMs were running more than 115 mg/l and as high as 175 mg/l.
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Southeastern Municipality Uses Chlorine Dioxide to Control THMs in Drinking Water
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Use of Chlorine Dioxide Improves Taste and Odor and Controls THMs