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.