Xylem solution removes PFAS compounds from water utility’s supply well

After a drinking water well in Maine became contaminated with two perfluoroalkyl substances (PFAS), the local water utility acted quickly to understand treatment options. The utility worked with our internal experts to pilot several carbons leading to the selection of the most cost-effective solution. The solution from Evoqua, now a Xylem company, uses granular activated carbon from coconut shells, which gives the utility up to 160% longer bed life than coal-based alternatives and 40% lower life cycle costs.

Water is the lifeblood of community and industry in the picturesque seacoast towns of Kennebunk, Kennebunkport and Wells, Maine, where tourism, farming, and commercial fishing drive the local economy.

When a well supplying drinking water to the community was found to be contaminated with PFAS, the local water utility acted quickly to address it. The Kennebunk, Kennebunkport & Wells Water District (KKWWD) needed a solution to remove the two types of PFAS found: perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).

PFAS have extreme chemical stability, are resistant to degradation, and bio-accumulate in the blood and certain organs of the body.

While the full health impact of PFAS is still being determined, lab studies have linked PFAS to liver injury as well as adverse effects on growth, development, and reproduction.

Finding the source of the PFAS contamination

In the KKWWD supply well, the combined level of the two contaminants, at 50 parts per trillion (ppt), was within the combined Health Advisory Limit of 70 ppt as recommended by the U.S. Environmental Protection Agency at that time. KKWWD decided to proactively shut down the affected well as a precautionary measure and evaluate the best course of action.

First, KKWWD needed to solve a mystery: where did the contaminants come from? PFAS compounds are typically associated with industrial activity and the use of fire retardants at military installations. Neither of these applications were an exact match for this community. Investigation ultimately pieced together a chain of cause and effect: agricultural runoff from a local farm that had applied soil enhancers made with biosolids from a municipal wastewater plant, combined with fly ash that came from a local paper mill (since closed).

Treatment technologies for PFAS removal

Xylem has worked with many municipalities like KKWWD as a leading provider of PFAS treatment technologies, including granular activated carbon (GAC) and single-pass ion exchange resin, available in permanent or emergency mobile assets.

With years of experience in PFAS removal and a technology-agnostic approach to filtration solutions, the team of experts was well-suited to identify and provide the most cost-effective solution for the project.

KKWWD expressed a preference for GAC, based on experience and familiarity with the technology. The team examined water quality data and advised the utility on a pilot test of several types of carbon, including the competitor’s, to determine which would perform best for their local water chemistry.

Testing of multiple types of GAC systems turned up an effective, efficient solution. It uses Evoqua’s HP^® 1220SYS high-pressure liquid-phase adsorption system containing AquaCarb^® 1230CX enhanced coconut-based carbon.

As water passes through the system, the granular activated carbon adsorbs the PFAS contaminants. In a lead-lag system, two or more adsorption vessels are used in a series. When the carbon bed reaches exhaustion, the carbon adsorption system is serviced by a third party based on the utility’s disposal preference.

Test results for the well in Maine showed that the solution using coconut-based carbon, compared to other tested carbons, would provide significantly longer full-scale run time before requiring service.

200 million gallons of treated water

The system has been operating successfully since it was placed into service, producing more than 200 million gallons of treated water. KKWWD fully expects to meet their goal of 250 million gallons of water per year from these filters and is moving ahead with a permanent structure to house the system.

“Our goal is to continuously produce drinking water with non-detect levels,” says Norm Labbe, KKWWD Superintendent. “With Evoqua’s lead-lag system, we should have no problem.”

In addition, KKWWD met another important goal: removing PFAS without impacting their water rate plan. KKWWD was able to implement a solution that added minimally to capital costs. The overall impact to ratepayers will be about $0.03 - $0.04/day, and customers won’t see the increase for several years. Labbe says, “It’s still cheaper than buying water from an outside water utility and it keeps us independent.”

Note: non-detectable levels may vary with method of analysis and application.