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Posted on: July 19, 2018

Granular Activated Carbon Explained and Latest Sweeney Results

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How Does CFPUA Use Granular Activated Carbon to Treat Water?

As an advanced water treatment plant, CFPUA’s Sweeney Plant pulls water from the Cape Fear River and utilizes a range of different treatment technologies including ozone, ultraviolet purification, and chlorine disinfection to turn it into drinking water. Processes such as these ensure levels of contaminants, both man-made and naturally occurring, are reduced or eliminated before the water is distributed to homes and businesses throughout New Hanover County.

While each treatment technology is different, granular activated carbon is a technology that can be used in several different processes. One such process is called biofiltration—in which carbon stays in place for long periods of time and acts as a substrate for the growth of naturally occurring microbes. These microbes help remove organic compounds that may lead to the formation of disinfection byproducts in the distribution system.

Granular activated carbon is used in this process because it is effective in encouraging the growth of microbes and because it can also absorb contaminants at the same time, producing secondary benefits for the process. Biofiltration occurs towards the end of the treatment process after the water has been treated with ozone, settling has taken place, and a secondary ozonation step has been completed. CFPUA has been using biofiltration with granular activated carbon for over 20 years.

Due to the discovery of GenX and other per-fluorinated compounds in our source water, CFPUA is considering the addition of another treatment process based on granular activated carbon. In this process, the carbon would be changed frequently, rather than left to grow microbes, so it can absorb per-fluorinated compounds. This process would occur near the end of the treatment process, after filtration and before the water is treated with ultraviolet light. As the carbon media fill with compounds, CFPUA staff will remove the media and send it for regeneration, where the compounds are treated with extremely high temperatures that incinerate the per-fluorinated compounds.

CFPUA is currently in the process of negotiating a design contract for the potential upgrade. Staff intends to bring a recommended contract to the Board in September 2018.


Most Recent Results for GenX Sampling at the Sweeney Water Treatment Plant

CFPUA has received GenX results for June 27, 2018, for the finished water at Sweeney Water Treatment Plant. Levels of the compound continue to be below the North Carolina Department of Health and Human Services health goal of 140 parts per trillion.

Most recent test results for per-fluorinated compounds.


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