An airport located in the Northeastern United States uses de-icing fluid in the winter to assist in cold weather operations. The used fluid is pumped and transported to two storage lagoons on the edge of the airport property, and is then metered into a sewer line that discharges to the local municipal sewage treatment plant. The lagoon water contains a variety of PFAS compounds, including PFBS, PFDA, PFDoA, PFHpA, PFHxA, PFHxS, PFNA, PFOA and PFOS. With increased focus on PFAS leaving the airports in the state, the stakeholders in the area have pushed for limited PFAS leaving storage lagoons. The water also contains elevated levels of propylene glycol from the de-icing fluid and elevated levels of suspended solids and iron, making it a chemically and physically complex water matrix for PFAS treatment. The propylene glycol is highly biodegradable, resulting in elevated levels of BOD, TOC and COD.
This particular airport has had recent AFFF releases, as well as failed groundwater remediation treatment plants, so extra attention was placed on this system to make sure it achieved the desired results.
The customer saw this project coming but was delayed longer than anticipated before issuing the purchase order. This delay resulted in a rapid response situation to get treatment up and running before the lagoons reached capacity. ECT2 received the purchase order with one of the lagoons at its maximum capacity, leaving the airport with limited storage space remaining. The system needed to be deployed quickly, with full confidence it would meet the treatment objectives, and stay within the project budget. The project objective was to discharge water with a PFAS concentration of PFOS and PFOA at less than 70 ppt.
Additionally, the lagoon water had unknown organics and PFAS concentration. The only water samples tested came from the summer, so the results were not typical of the winter environment. The water flowed into the lagoons in batches; each storm brought a different level of water as well as a different volume of deicing fluid, depending on how many flights were scheduled, and how long it had been since the last storm came through. This variability provided complications for the design team regarding incoming analytical results.
ECT2 quickly deployed a pilot skid to get ahead of the full treatment plant and generate learnings to prevent any unforeseen PFAS breakthrough. The selection of the filter media resulted in minimal competition between the high concentration of glycol/fatty acids and PFAS. After an initial equilibration period, the majority of the glycols and fatty acids passed through the system with little to no change in PFAS adsorption.
The 20 GPM capable treatment plant was installed in a single 40’ shipping container which allowed for easy deployment to the site and rapid “plug and play” on-site readiness. The PFAS removal system includes a proprietary pretreatment filtration step to remove suspended solids, iron and other fouling agents and specialized ion exchange resins for PFAS removal. The system also includes the ability to simulate future treatment conditions and allows operators to predict when PFAS breakthrough may occur.
As anticipated, the most significant challenge to date has been managing the iron fouling and bio-growth that occurs on the pretreatment media and resin. This has been successfully managed using a combination of oxidizing and non-oxidizing biocides. Laboratory R&D was conducted during the early stages of the project to find an effective biocide that would not interfere with PFAS removal, and could be easily degraded/removed before discharging the treated water.
Water from each of the two lagoons is pumped to a frac tank, then pumped through the treatment plant to a storage tank and then sampled prior to discharge. The flow through the system averages 12-15 GPM. No resin or pretreatment media changeouts were required for the initial season of treatment. The project objective was to discharge water with a PFAS concentration below 70 ppt. The treatment plant met all project objectives, with treated water PFAS concentrations consistently less than non-detect for the approximately 440,000 gallons of lagoon water treated to date.