The objective of this project is to demonstrate the commercial viability of ex situ smoldering (STARx) for treatment of soils impacted by per- and polyfluoroalkyl substances (PFAS). PFAS destruction typically requires significant energy due to the inherent stability of the substances, which can prove troublesome for locations with limited power infrastructure. Furthermore, mobilization or construction of large installations in remote locations to treat impacted soils is not always economically feasible, thereby limiting options to off-site disposal and import of clean backfill. This project addresses both of these challenges with the STARxpress system: a mobile, rapidly-deployable, and energy-efficient plant leveraging STARx to treat PFAS-impacted soils. 

Smoldering is a self-sustaining, flameless form of combustion that can achieve PFAS destruction temperatures with the use of low concentrations of a supplementary fuel (e.g., spent granular activated carbon [GAC]). Treatment is initiated at the base of the soil pile, with the smoldering front propagating upwards in a thin reaction zone. The STARxpress system includes two treatment units, each with a 35 m³ batch treatment capacity, and containerized ancillary equipment and plant controls. The STARxpress system is designed for simple and rapid mobilization to a site, requiring minimal ground preparation and limited on-site setup. Removal of PFAS and fluorinated breakdown products in emissions can be achieved via vapor-phase GAC prior to release through a stack. When spent, this GAC can be recycled for use as supplementary fuel in subsequent treatment batches. A complete cycle, including loading and unloading, is anticipated to take between 4-7 days depending on soil characteristics. Once the treated soil has undergone confirmatory sampling, it can be reused as fill on-site. Along with treatment and sampling activities during the demonstration period, a small-scale field study of treated soil revegetation will be performed. 

The STARx technology is energy-efficient, as the combustion front continues in the absence of external energy input following a brief, one-time, local ignition event, provided a sufficient quantity of injection air continues to be supplied. Common construction equipment, such as a skid steer and backhoe, can be used to mix and load the soil into the treatment units. Previous work has demonstrated successful treatment of PFAS-impacted soils to near or below detection limits through smoldering, with less than 1% of the initial PFAS mass found in the emissions. (Anticipated Project Completion - 2024)