Multi-Contaminant Removal With Granular Activated Carbon (GAC) In Drinking Water Filtration

For years, the U.S. EPA has recognized granular activated carbon (GAC) as a best available technology for a wide range of organic contaminants.  GAC is proven to be a highly effective solution for removing multiple contaminants from drinking water, including total organic carbon (TOC), disinfection byproducts (DBPs), per- and polyfluoroalkyl substances (PFAS), 1,2,3-tricholoropropane (1,2,3-TCP), taste and odor (T&O), volatile organic compounds (VOCs), and algal toxins.

Historical Use Of GAC

Initially used to tackle taste and odor, GAC filtration has been a part of drinking water treatment since the 1930s in the United States. With the passage of the Safe Drinking Water Act (SDWA) 50 years ago, GAC treatment has evolved to encompass additional target contaminants such as VOCs, TOC, DBPs, and more. Today, GAC filters are the treatment of choice for difficult new challenges like PFAS.

Why is GAC filtration the treatment of choice for such a vast variety of contaminants?

Simply put, unlike other treatment technologies, GAC media is not manufactured to target one specific contaminant. Instead, GAC media removes organic contaminants in the water stream, regardless of type, through the process of adsorption. Adsorption is governed by the kinetics of diffusion and is powered by electrostatic forces, called Van der Waals forces, which cause the organic contaminant to stick to the surface of the GAC media, thereby removing it from the water stream. Diffusion is governed by both media properties and contaminant properties and describes the time required for the contaminant in the water to be adsorbed onto the media. Several organic contaminants share similar diffusion characteristics, thereby making it possible to remove multiple contaminants simultaneously in one GAC filter, provided there is enough contact time and media capacity. For whole house residential carbon filters, sizing to allow sufficient contact time is important, as is renewing the media before it is exhausted. A filter will remove chlorine for years after it loses its ability to remove VOCs or PFAS.

Using GAC For Multiple Contaminants

For residential city water treatment, either for the whole house or for drinking water only, carbon filtration is the unchallenged first choice. Sometimes other media may be added, like ion exchange resin added to some carbon block filters to add lead removal properties to the filter, or KDA, added to increase the longevity of the carbon, but in all cases carbon itself is the workhorse ingredient.