In-Pile thermal desorption for treatment of Dioxin-Contaminated soil in Japan


A demonstration of thermal treatment of dioxin-contaminated soil was completed in Japan, under the sponsorship of the Japan Ministry of the Environment. TerraTherm’s proprietary In-Pile Thermal Desorption process was demonstrated to successfully treat the soil to the required standard of 1,000 picograms of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) toxic equivalents (TEQ) per gram (i.e., pg-TEQ/g), over a 28 day operation period, where the soil was heated to a minimum temperature of 325oC and exposed to vacuum extraction. Offgases were treated using thermal oxidation and activated carbon adsorption, meeting the Japanese air emission standards. A detailed environmental impact assessment was completed, with favorable outcome for the thermal process.

Dioxins are extremely toxic and recalcitrant compounds known to accumulate in soil and sediment and bioaccumulate in the food chain. These contaminants are important in most industrialized countries, including Japan (EMAI 2007, MOE 2008). Laboratory and field data from US projects have indicated that heating soil to 325oC with a residence time of several days is sufficient for thorough dioxin destruction and removal (Baker and LaChance 2003). Dioxins are hydrophobic and adsorbed strongly to soils and sediments. Therefore, many sites contaminated with dioxins have relatively shallow impacts (less than 1 m deep). For such sites, the geometry does not favor In Situ Thermal Desorption (ISTD), due to the large surface area and heat losses. Instead, placement and treatment of the contaminated material in piles, also known as In-Pile Thermal Desorption (IPTD), can lead to favorable geometries and offers options to insulate the treatment cell. A successful demonstration of IPTD was completed by Baker et al. (2002). In addition, a large field-scale treatment of a wood-treating site where large amounts of dioxins had been released was completed successfully using ISTD (Yargeau and Bierschenk 2007). The treated soil was demonstrated to meet the California standards for residential soils (1 ìg/kg 2,3,7,8-TCDD TEQ = 1,000 pg-TEQ/g). This paper presents a demonstration of IPTD conducted on dioxin-contaminated soil in Japan (Baker et al. 2009).

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