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Tacoma reports promising PFAS pilot at Central Treatment Plant; city says scaling and cost questions remain
Summary
City of Tacoma Environmental Services told its Infrastructure Planning and Sustainability Committee that a 2024 pilot using foam fractionation plus hydrothermal alkaline treatment removed long-chain PFAS and achieved more than 99% degradation under ideal conditions, but staff said the work remains at pilot scale and noted power, chemical-use and flow constraints for full-scale deployment.
Tacoma’s Infrastructure Planning and Sustainability Committee heard a briefing Feb. 11 from Tiffany Ryan, assistant division manager in the city’s Environmental Services science and engineering division, on a PFAS (per- and polyfluoroalkyl substances) pilot test and related regulatory requirements.
Ryan told the committee the city’s laboratory — accredited for EPA methods for both PFAS and 6PPQ and equipped in 2023 with an LC-triple-quad instrument — has analyzed biosolids (TAGRO) since 2019 and performs tens of thousands of analyses annually with a 16-person staff. "We're currently the only lab in Washington state to be accredited by EPA analytical methods for both PFAS and 6PPQ," she said.
Why it matters: PFAS are persistent, manufactured chemicals linked in studies to cancer and other health risks. Ryan said treatment plants collect PFAS from upstream discharges (households and industry) and that recent regulatory drivers are increasing testing and scrutiny. She cited a new NPDES permit for the Central Treatment Plant that requires quarterly PFAS testing at the plant endpoint and a state law (referred to in the briefing as Senate Bill 5033) that, according to Ryan, requires sampling for PFAS in biosolids beginning in January 2027; she said Ecology is expected to deliver additional biosolids analysis and recommendations by 2029.
Pilot and results: The 2024 pilot at the Central Treatment Plant combined foam fractionation (to concentrate PFAS from an effluent stream) with a hydrothermal alkaline treatment (HALT) to destroy PFAS. Ryan said the foam fractionation step removed long-chain compounds such as PFOS and PFOA and that, under the best-performing operating conditions tested, HALT "achieved greater than 99% total PFAS degradation." She added that in tested runs, individual regulated PFAS were reduced to non-detect values.
Limits and trade-offs: Ryan cautioned that the pilot ran at about 5 gallons per minute, and she said scaling to treatment-plant throughput would require handling flows “well over” 150 gallons per minute; that larger-scale operation would drive much higher power and chemical use; and that the team observed clogging issues in the pilot that were not seen in bench tests. She called source-reduction and industrial pretreatment measures the most effective near-term approaches to reducing PFAS entering the system and said the technology may be more immediately practical when deployed at industrial dischargers rather than at full plant scale.
Partnerships, funding and next steps: The pilot was carried out in partnership with the University of Washington Tacoma, ECT2 and Aquaga (vendor spellings in the briefing varied). Ryan said the project was primarily funded by outside agencies, that the final pilot report is expected later this year, and that Environmental Services plans outreach to industrial partners and regional PFAS working groups. On costs, Ryan said she did not have a top-line figure available at the briefing but offered to follow up with the committee.
Committee questions and follow-up: Members pressed on detection limits (parts-per-billion and parts-per-trillion scales), the difference between wastewater and drinking-water testing, the lab’s ability to concentrate samples to meet low detection thresholds, and whether Tacoma Public Utilities (TPU) is conducting separate drinking-water testing. Ryan said drinking-water analysis is performed separately, that labs can use concentration techniques to reach lower limits of detection, and that more pilots and data will be needed to assess feasibility and cost of plant-scale implementation. The committee asked that Environmental Services share the full pilot report and any cost information when available.
The meeting packet and follow-up materials: Chair Walker said committee members had been emailed follow-up documents (a green-resilience funding letter and a technical advisory letter on Tacoma Dome access improvements) and that those documents would be posted to Legistar.
The committee moved to adjourn at the end of the meeting.
Sources: Committee briefing and Q&A with Tiffany Ryan to the Infrastructure Planning and Sustainability Committee, Feb. 11, 2026.
