Theme: 02. Assessing Remediation Effectiveness

Topic Area: 02b. Remedy Implementation: Assessing Performance and Costs

Formatted Title:

Use of In-Place, Steam Regenerable Activated Carbon in the Treatment of Chlorinated Volatile Organic Compounds at ISTR Sites

Background/Objectives:

In situ thermal remediation (ISTR) is a well-established technology for removal of chlorinated volatile organic compounds (CVOCs) from contaminated soils. For sites with low to moderate amounts of contamination (as measured by total contaminant mass) it is customary to treat the resulting vapor stream with granular activated cabon (VGAC). This VGAC has a fixed capacity, beyond which it will no longer absorb containments. This approach also requires periodic change out of the VGAC, which is a labor-intensive process and generates a waste stream. The ability to regenerate the carbon “in place” with low pressure steam allows for a more streamlined operation and less carbon that needs to be subsequently disposed or regenerated offsite, thereby decreasing costs and improving sustainability.

Approach/Activities:

At a recent high-mass CVOC site, a containerized steam regenerable VGAC system was deployed. The system consisted of two carbon beds in parallel, with the capability to fully regenerate each bed in place. The regeneration process consisted of applying steam to desorb the contaminants, condensing and subsequently collecting the condensed non-aqueous phase product (NAPL) that was produced. Once steaming was complete, the bed was dried, then cooled, so that it could be subsequently put back into service. The performance of the system will be compared to that of a non-regenerable system. Overall, carbon consumption, destruction removal efficiency (DRE) and energy usage to create the steam used in the regeneration process will be reviewed. The merits and drawback of this regenerable system will be discussed.

Results/Lessons Learned:

The system operated over a period of 215 days. After some initial tuning of the system, the regenerable carbon vessels removed 14,680 lbs of containment over the course of treatment, with a DRE in excess of 95% for the majority operations, and an average DRE of 93.8%. Each regenerable vessel contained 3,000 lbs of carbon (VGAC) and could absorb approximately 400 lbs of Trichloroethylene (TCE), the primary site contaminant, prior to regeneration. During peak loading, when TCE concentrations and mass loading rates in excess of 3,500,000 mg/m³, and 41 lbs/hr, respectively, were observed. Based on this, each vessel was regenerated once per day, resulting in a total of two regeneration cycles per day during peak operation. Despite the high loading rates, the system performed admirably. Further, the addition of polishing carbon after the regenerable system increased the overall DRE to 97%, however the majority of the mass (>99%) was removed by the regenerable unit, resulting in a net savings of over 100,000 pounds of VGAC. Based on these results, it is concluded that the ability to regenerate the carbon in place adds significant value for chlorinated sites with moderate to high contamination mass.

Samuel Nienstedt

Affiliation

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(Group 1, Poster Board #46) Use of In-Place, Steam Regenerable Activated Carbon in the Treatment of Chlorinated Volatile Organic Compounds at ISTR Sites