An airport located in the United States uses de-icing fluid in the winter to assist in cold weather operations. The used fluid is pumped and transported to storage lagoons and is then metered into a sewer line that discharges to the local municipal sewage treatment plant. The lagoon water may contain a variety of PFAS compounds as well as 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.
As a proactive measure to remove PFAS from wastewater discharge, a rapid response was requested to get treatment up and running before the lagoons reached capacity. 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 10 ppt.
Additionally, the lagoon water had unknown organics and unknown PFAS concentration. The stormwater flowed into the lagoons in batches; each weather event brought a different level of water as well as a different volume of deicing fluid. 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 any PFAS which may be present. After an initial equilibration period, the majority of the glycols and fatty acids passed through the system without expected 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 organic dispersant. Laboratory R&D was conducted during the early stages of the project to find an effective organic dispersant that would not interfere with PFAS removal, and could be easily degraded/removed before discharging the treated water.
Water from each lagoon is pumped to a frac tank, and 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 10 ppt. The treatment plant met all project objectives, with treated water PFAS concentrations consistently less than non-detect for the approximately 1.2 million gallons of lagoon water treated to date.