St. Cloud PFAS Pilot Begins Phase 3 Sludge Testing

A mobile treatment system being tested at St. Cloud’s Nutrient, Energy, and Water Recovery Facility has moved into the next stage of a pilot examining whether PFAS and other organic waste can be destroyed instead of transferred into another waste stream.

374Water reported July 28, 2026, that its mobile AirSCWO system completed Phase 2 testing of Class A biosolids and began Phase 3 testing of untreated pre-anaerobic-digestion sludge. The company says field work is expected to continue through mid-September.

What the St. Cloud pilot is testing

The project is being conducted under a $600,000 Waste Destruction Services contract with the City of St. Cloud. Barr Engineering and 374Water are involved in the work, which is also part of a Minnesota-funded demonstration project evaluating supercritical water oxidation.

In plain terms, supercritical water oxidation uses very high heat and pressure to test whether difficult organic materials, including PFAS, can be broken down. That is different from simply moving chemicals from wastewater into biosolids, spent granular activated carbon, treated water or another residual that still requires management.

Phase 2 focused on Class A biosolids produced through a low-temperature thermal hydrolysis process supplied by Lystek International. Sampling has been completed, but the performance data remain under analysis. Phase 3 is examining untreated sludge before it enters the facility’s anaerobic-digestion process.

374Water has cited solids and PFAS-reduction results from earlier campaigns in Orlando. Those figures are not results from the St. Cloud Phase 3 test, and the current project has not yet established a final PFAS-performance result for the local facility.

Why the project matters beyond one facility

St. Cloud’s wastewater recovery facility serves the city and six surrounding communities and handles roughly 10 million gallons of wastewater per day, according to the city’s 2024 biosolids report. That makes the site a municipal-scale setting for testing how a treatment process might work.

The Minnesota project is designed to examine more than PFAS destruction. Its evaluation includes energy use and possible recovery, treated-water quality, residual solids, nutrient recovery, operating requirements and the feasibility of future reuse.

City materials describe PFAS monitoring and the pilot as a preventive, research-oriented effort. They also caution that full-scale implementation remains a long way off. The mobile unit is a test installation, not an approved permanent replacement for the city’s existing biosolids-management system.

What happens next

The key information still to come is the analyzed performance data from the testing, followed by formal project reporting and any future review by the city and state. Those steps will help determine whether the process can meet technical and operational requirements without creating unacceptable energy, water, solids or maintenance burdens.

For St. Cloud residents, the immediate change is the shift in the material being tested—not a change to wastewater service or a final decision on future treatment. Any permanent adoption would require additional technical findings, cost analysis and public or governmental review.

Sources

• 374Water Phase 2 and Phase 3 update, July 28, 2026
• Minnesota LCCMR approved work plan
• City of St. Cloud Biosolids Management Program Annual Report 2024
• KNSI St. Cloud PFAS pilot report