Demonstration of Smoldering Combustion (STAR) Treatment of PFAS‐impacted Soils and Other Wastes
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Geosyntec subsidiary Savron was contracted by the U.S. Department of Defense (DoD) Strategic Environmental Research and Development Program (SERDP) to demonstrate the application of STAR smoldering-based technology to treat per- and polyfluoroalkyl substances (PFAS), a family of thousands of emerging contaminants, in soils or investigative derived wastes (IDW).

PFAS often contaminates soil or granular activated carbon (GAC) spent from treating water (surface, ground, or waste).

Geosyntec Scope of Services

Savron conducted two sets of laboratory column experiments, the first of which explored smoldering of sand mixed with GAC to determine the operating temperature of the self-sustaining process where no energy input is needed after ignition. The second set explored the extent to which PFAS (including individual compounds such as PFOA, PFOS, PFHxS, PFBS, PFNA, and PFHpA) sorbed to a surrogate soil or GAC was eliminated by smoldering.

STAR was found to be a self-sustaining reaction when GAC was mixed with soil over a wide range of GAC concentrations and injected air flow values. Also, a GAC:sand ratio of 40g per kg of soil consistently achieved temperatures greater than 1000oC, which is required to decompose PFAS. Smoldering treatment eliminated all PFAS from the contaminated surrogate and soil containing contaminated GAC. About 30% of the fluorine on the PFAS was captured as hydrogen fluoride indicating complete destruction of PFAS. The remaining fluorine released in the emissions was associated with volatile organofluorine compounds that are absorbed well by GAC and can be subsequently treated.

Notable Accomplishments

Additional work was recommended to further improve the mass balance of the PFAS destruction, as well as address impacts of heterogeneity on the smoldering process. Savron's work thus far indicates that STAR can be a far more economical and environmentally friendly alternative to digging up contaminated soils, or containerizing IDW,  and disposing of them in hazardous waste landfills or by conventional incineration.

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Project Summary

  • Location: U.S.A.
  • Client: Strategic Environmental Research and Development Program
  • Project Practice Areas: Contaminated Sites
  • Type of Facility: Laboratory
  • Services Provided: Laboratory column testing
  • Type of Work: Column testing
  • Governing Regulation: Federal and state