Volume 45 Number 3
Material Extraction Testing of Activated Carbon: A Tale of Two Standards
One of the driving philosophies of all water product-related ANSI/NSF standards is the only way to ensure compliance is testing. These standards contain various requirements for many different types of products and, in almost all cases, conformance with a given requirement is established through testing according to a specific protocol.
The central issue of all these standards is safe water. Consumers and regulators in the United States demand high quality water with strict limits on residual contaminant levels. And, in keeping with the philosophy of testing to verify conformance, the standards have test protocols to verify water products don’t contribute unacceptable levels of contaminants to the water that’s in contact with them.
Activated carbon is no exception. There are material safety requirements for activated carbon used for drinking water purposes. Conformance with these requirements is verified through material extraction testing. There are actually two different standards with distinctly different requirements and material extraction test protocols—ANSI/NSF Standard 42 and ANSI/NSF Standard 61. This article examines why there are two standards, in which circumstances each standard applies, and what work is being done to try to harmonize the requirements of these standards.
This prompted the Joint Committee on DWTUs to develop a material extraction testing protocol with minimal conditioning prior to exposure to the test water. Standard 42 requires carbon be exposed to water under 50 pounds per square inch (psi) pressure. To comply with this requirement, the test is conducted with carbon packed in a housing. The protocol specifies the carbon be flushed according to the manufacturer’s instructions, and then exposed to the test water for 24 hours. This water is saved. The carbon is then flushed again according to the manufacturer’s instructions, and exposed to the test water for another 24 hours. This water is also saved. The carbon is then flushed one final time according to the manufacturer’s instructions, and exposed to the test water for a final 24 hours. This water is saved, and composited with the two samples of water saved from the first two exposures. The final composite sample is the exposure sample that’s analyzed for residual contaminants.
Activated carbon, typically in granular or powdered (GAC or PAC) form, may be utilized in municipal water treatment applications. In comparison to POU/POE applications, very large volumes of carbon are commonly used in adsorption “beds” to capture contaminants during the water treatment process. This intended end-use involves constant flow with no stagnation.
Standard 61, Section 7 also outlines the general requirements for the evaluation of media including manufacturer use instructions, specifics for sample preparation, sample conditioning, and testing of products such as PAC and GAC. Before PAC or GAC media may be analyzed, the GAC sample must be wetted or completely immersed in tap water prior to conditioning for 16 hours +/-1 hour. PAC isn’t wetted unless specified in accordance with the manufacturer’s instructions. After the sample has been properly wetted, GAC undergoes a conditioning or backwashing phase for 30 minutes +/- 2 minutes, or in accordance with manufacturer instructions. PAC isn’t backwashed because of the small particle size.
Next, the media sample is exposed to the reagent water required to generate water samples that will be analyzed. The vessel is covered and placed on a magnetic stirrer for 60 minutes +/-5 minutes. Immediately following the exposure period, the liquid portion is filtered to separate the water and media for analysis.
The analytical testing for PAC or GAC involves analysis for formulation and process dependent analytes and at least the minimum analytes specified in table 7.1 of ANSI/NSF Standard 61-2002. Currently, the minimum list of analytes includes antimony, arsenic, barium, beryllium, cadmium, chromium, copper, lead, mercury, selenium, and thallium as well as GC/MS (base neutral acid scans) and radionuclides. After the data are generated, it’s normalized based on the testing situation and evaluated for compliance against the single product allowable concentration (SPAC) noted in Annex A of ANSI/NSF Standard 61.
To simplify the situation for suppliers and purchasers of media, the Joint Committees on DWTUs and Drinking Water Additives have created a cooperative task group. This group is investigating the concept of harmonizing the materials’ requirements for media between the standards. They must first conduct testing to determine comparability of test results on the same media under both standards. Once that work is done, the group will proceed toward developing a harmonized protocol that will have as minimal an impact on currently conforming carbons and other media as possible, while meeting the goals of ensuring safe water for all usage patterns of related products.
Dual certification of carbon
About the authors