What is In Pile Thermal Desorption (IPTD®)?

If you are not familiar with thermal treatment, then In Pile Thermal Desorption (IPTD^®) is something you have probably never heard of before. You may be wondering, what is it? How does it work? Can it be applied to my site?

In this blog post, I will provide a concise introduction to IPTD, how it works, and what sites and contaminants are good candidates for this thermal technology.

What is IPTD?

IPTD is the application of TerraTherm’s patented thermal conductive heating (TCH) technology in a specially engineered pile-type structure, rather than in situ. With IPTD, the soil is first excavated and placed into the pile structure for consolidation and water infiltration management. TCH wells are then installed in the pile structure either vertically, as would typically be done in situ, or horizontally, depending on the design and size of the pile.

The electric heater elements installed in the TCH wells heat the soil via thermal conduction to remove the contaminants via volatilization and mineralization from the soil. Vapor extraction wells are placed in the pile to remove the vapors produced during treatment, including steam and volatilized contaminants.  These vapors are sent to a treatment system to meet vapor and liquid (condensed steam) emission standards prior to discharge. 

How does IPTD work?

With IPTD, the pile structure is isolated and protected from the elements, either with insulated concrete sides and a cover, or a temperature-rated high-density polyethylene cover and insulation. This protection allows the soil to be heated and dried efficiently to reach the temperatures required for remediation of recalcitrant contaminants, such as PFAS, PCBs, dioxins, pesticides, and PAHs (200 to 350°C, depending on the contaminant mix). As heating progresses, steam is generated from any pore water existing in the soil until the soil is dry and the contaminants present in the soil eventually volatilize and/or breakdown. The generated steam and contaminant vapors are extracted from the pile via screened vapor extraction wells and processed through a temporary treatment system specifically designed and constructed for the project.

What sites are good candidates for IPTD?

IPTD is best suited for treatment of higher concentration contaminants that are difficult to treat by other means and for which disposal costs are high. It is also commonly applied to sites where the soil to be treated is spread over a large, shallow area, as applying TCH in situ in such a scenario would be cost-prohibitive. In these cases, treatment becomes much more economical when the soils are excavated and transferred into a more consolidated pile structure for treatment, thus requiring less thermal wellfield infrastructure and energy.

Due to the protection from water infiltration that the IPTD technology provides, TCH heating can be used to heat the soil above 100°C once all the existing pore water is boiled off, and ultimately reach temperatures as high as 350-500°C. This allows for targeting of the high boiling point contaminants that cannot always be treated with other thermal technologies or applications.

Although IPTD can be used to target VOCs (e.g., BTEX, CVOCs, etc.), it is typically used for treatment of high boiling point recalcitrant SVOCs such as PFAS, PCBs, dioxins, pesticides, and PAHs.

IPTD Case Study

The herbicide Agent Orange is a defoliant chemical used during the Vietnam War.  Nearly five decades after the war, soil at the Da Nang airport remained heavily contaminated by residues of the herbicide, including dioxins.  The U.S. Agency for International Development (USAID) funded and implemented a large-scale remediation project in partnership with the Vietnam Ministry of National Defense.

TerraTherm’s role included design, construction, operation, and decommissioning of the IPTD treatment system and treatment of the contaminated soil and sediments in two sequential phases. Following successful completion of both phases, more than 120,000 cubic yards of soil and sediment were treated.  Contaminant concentrations were reduced from a range of 2,461 to an average of 0.199 ppt.  Extracted vapors and liquids were effectively captured and treated and all stringent human health and environmental discharge, worker, and resident standards were met. Read more about the dioxin treatment at Da Nang Airport project.

If you’re considering IPTD technology for an upcoming project, or simply want to learn more, contact our team of thermal remediation experts today.