By Rick Andrew
Many residential water treatment products incorporate activated carbon. From granular activated carbon (GAC) inline filters to carbon block filters to pre- and post-filters on RO systems, activated carbon plays a very important role. In some cases, it is the primary water treatment medium. In others, it serves a secondary function of improving taste or odor of the treated water. Activated carbon is used in products certified under all of the NSF/ANSI Drinking Water Treatment Unit (DWTU) Standards. Activated carbon itself may be certified as a DWTU Component under Standard 42.
Activated carbon is also widely used in municipal water treatment, both as powdered activated carbon (PAC) and GAC. For this end use, it may also be certified under NSF/ANSI Standard 61. In fact, some carbon products are certified both to Standard 42 and Standard 61.
Because of its wide application in water treatment and its use in products covered by many different standards, certification of activated carbon is deserving of special attention. There are questions regarding which standard to certify carbon to and impacts of carbon on DWTU end products being certified. Some of these issues deal with the properties and technical specifications of activated carbon—pore structure, activation processes, washing procedures and so forth. There is the question, “How does activated carbon work?”
In order to help manufacturers, carbon suppliers and others understand the technical issues of carbon and the issues with certification of carbon and products containing carbon, NSF and PACS, Inc. teamed up for a first-ever activated carbon course at NSF International on May 3 and 4.
Sponsorship of a training course dedicated to activated carbon
The course was sponsored by a joint effort of NSF’s Center for Public Health Education (CPHE) and PACS, Inc. NSF’s Center for Public Health Education was founded in 1999 to offer public, on-site and web-based training on a wide range of public health and environmental subjects, including food safety, water quality, NSF product standards, worker health and safety and management systems.
PACS, Inc. is in its third decade of providing technical services. PACS specializes in activated carbon adsorption and other sorbents, working primarily with scientists and engineers to perform laboratory testing, on-site environmental evaluations for industrial hygiene, asbestos and mold, consulting services, as well as training courses and focused conferences.
By teaming up, CPHE and PACS were able to bring world-class knowledge of carbon and certification of carbon together in one course.
A two-day course provides intensive training
The course was conducted over two days. The instructor for Day One was Dr. Henry Nowicki of PACS, Inc. Topics of Day One focused on the technical aspects of activated carbon. Discussions included the importance of source materials, and why source material selection must be based on the application. For example, activated carbon from a coconut shell source has very different adsorptive properties than activated carbon from a wood source because the source materials are very different in terms of their physical structure. (See Nowicki’s article Selecting the Best Activated Carbon for the Process Application, in the May 2005 issue of WC&P).
The physical structure of coconut shells leads to activated carbon that has some very high energy pores, necessary for effective reduction of trace concentrations of organic contaminants from water. Other materials with different physical structures will not produce activated carbons that have these high-energy pores. They may have large overall adsorptive capacities, but they will not have the high energy pore structure required to adsorb organic contaminants at trace concentrations from water.
Day One also covered some of the technical specifications of activated carbon, and what these specifications mean. Iodine number, molasses number and other specifications can be confusing in terms of how the specification relates to the performance of an activated carbon for various applications.
Additionally, Dr. Nowicki discussed some aspects of treatment system design, monitoring, and engineering, as well as software packages that can help manufacturers as they work to design new activated carbon treatment systems and improve current ones.
Day Two covered different ground, as I instructed the group on certification issues of activated carbon and products containing activated carbon. The test methods for certifying carbon to Standard 61, Section 7 were covered. Under Section 7, GAC and PAC have slightly different conditioning and exposure protocols because they are treated differently when used by municipal water treatment plants. GAC is wetted and backwashed prior to exposure, whereas PAC is not. Also, GAC has different exposure sequence than PAC.
Standard 61 also involves a process called “normalization”. This is a mathematical procedure to adjust the results obtained under the exposure conditions used in the testing laboratory to reflect the usage levels of the product in a real world application. See Table 1 for a comparative analysis of Standard 61, Section 7 treatment of GAC and PAC in terms of conditioning, exposure, analysis and normalization.
The material safety evaluation of activated carbon under Standard 42 was the next topic on Day Two. Standard 42 does not distinguish between GAC and PAC and has a completely different exposure protocol than does Standard 61. The exposure involves water with a different chemical makeup than in Standard 61 and it is performed with less wetting and conditioning than the GAC procedures in Standard 61. Also, the exposure is performed in a housing under 50-psig inlet pressure. Finally, there is no normalization under Standard 42, because the exposure already reflects real-world use applications.
The contaminant reduction test procedures for DWTUs are an important consideration with respect to activated carbon, especially those for reduction of organic contaminants. The efficiency of activated carbon in reducing trace concentrations of organic contaminants in water is strongly negatively impacted by the presence of total organic carbon in the water. Total organic carbon is present in many water supplies utilizing a surface water source, because it is derived from decaying vegetation and other organic materials in surface water. In order to help ensure that activated carbon DWTUs will work well when used on this type of water supply, the Standard 53 requires that the test water for testing reduction of organic contaminants must contain total organic carbon.
A uniquely focused course that will be offered again
Feedback from course participants has been very positive. The course is unique, in that it blends the expertise of two organizations to provide both product technical education as well as very useful information regarding certification over a two-day, intensive format. And it addresses activated carbon, a medium that is used across many different products and applications. As a result of this positive feedback, CPHE plans to offer this course in the future. The specific content will be adjusted slightly to address new information, possible changes to the Standards and participant feedback. These changes will take an already excellent course opportunity to a new level of value.
About the author
Rick Andrew has been with NSF International for over six years, working with certification of residential drinking water products. He has been the Technical Manager of the Drinking Water Treatment Units Program for over three years. His previous experience was in the area of analytical and environmental chemistry consulting. Andrew has a bachelor’s degree in chemistry and an MBA from the University of Michigan. He can be reached at 1-800-NSF-MARK or email: [email protected]