Thermal Desorption/Gas Phase Chemical Reduction at the New Bedford Harbor Superfund Site, New Bedford, Massachusetts

Site Name:

New Bedford Harbor Superfund Site

Location:

New Bedford, Massachusetts

Period of
Operation:

November 1996

Cleanup
Type:

Field demonstration

Vendor:

Beth K├╝mmling
ELI Eco Logic International, Inc.
143 Dennis Street
Rockwood, Ontario N0B 2K0
Canada
Telephone: (519) 856-9591 (ext. 203)
Fax: (519) 856-9235
E-mail: kummlib@eco-logic-intl.com

Technology:
Thermal Desorption/Gas Phase Chemical Reduction (GPCR)
- Pilot-scale test of Eco Logic's GPCR process - thermal desorption followed by gas phase chemical reduction
- Three main components - a thermal reduction mill (TRM), a GPCR reactor, and a gas scrubbing and compression system
- TRM - operated with indirect heat, using a molten tin bath (heated by propane) to transfer heat to the sediments; volatilized organic compounds and steam were removed from the TRM using hydrogen sweep gas which was vented to the GPCR reactor
- GPCR reactor - operated in a hydrogen atmosphere at a minimum temperature of 900 C. As the gas passed through the reactor (typical residence time of 4 to 10 seconds), the organics were reduced to methane and hydrochloric acid, which were sent to the gas scrubber
- Gas scrubbing and compression system - two-stage caustic scrubbing system; scrubbed gas compressed and stored before being burned in the Excess Gas Burner prior to release to the atmosphere
- Pilot testing included acclimation runs to provide preliminary data for optimizing process conditions and performance verification runs to evaluate the process

Cleanup Authority:
CERCLA
- ROD signed April 1990

EPA RPM:
James M. Brown
U.S. EPA Region 1 (MC HBO)
1 Congress Street, Suite 1100
Boston, MA 02114-2023
Telephone: (617) 918-1308
E-mail: brown.jim@epa.gov

Contaminants:
PCBs
- Maximum concentrations in sediments of more than 200,000 mg/kg

Waste Source:
Discharge of polychlorinated biphenyl (PCB)-contaminated wastewater from electronics manufacturing

Type/Quantity of Media Treated:
Sediment
- Fine sandy silt with some clay-sized particles present; some small shell fragments present
- Moisture content - 50% by weight

Purpose/Significance of Application:
Demonstration of thermal desorption/gas phase chemical reduction to treat PCB-contaminated sediments

Regulatory Requirements/Cleanup Goals:
Target goals for demonstration were 50 mg/kg for PCBs and the Toxicity Characteristic Leaching Procedure (TCLP) criteria for metals

Results:
- TRM reduced PCB concentrations to 28 to 77 mg/kg in treated sediment, with an average of 52 mg/kg; the PCB desorption efficiency ranged from 98.36 to 99.52%, with an average of 99.06%; total dioxin and furan concentrations were reduced by an average of 93%
- GPCR reactor achieved a PCB destruction efficiency ranging from 99.99972% to 100%; the average destruction efficiency for total dioxins and furans was 99.9923 and 99.99959, respectively
- TCLP metals concentrations in the treated sediment were below the regulatory criteria

Cost Factors:
- Projected full-scale costs for thermal desorption/gas phase chemical reduction of sediments were $11,114,000, including $5,865,000 in capital costs and $5,249,000 in O&M costs.
- Projected full-scale costs were based on treating 18,000 tons of sediment, for a unit cost of $617 per ton

Description:
The New Bedford Harbor Superfund Site is located along the northwestern shore of Buzzards Bay in New Bedford Massachusetts, approximately 55 miles south of Boston. From the 1940s to 1978, PCB-contaminated wastewater from electronics manufacturing operations was discharged onto the shoreline and into the harbor. Site investigations determined that sediments were contaminated with PCBs and heavy metals. The site was listed on the National Priorities List in September 1983. The ROD for a five acre area known as the "Hot Spot area" included dredging of PCB-contaminated sediments followed by incineration. However, due to opposition to incineration, EPA postponed the incineration component of the Hot Spot remedy to explore alternative treatment technologies. EPA evaluated four technologies as possible alternatives to incineration - solvent extraction/dechlorination, vitrification, thermal desorption/gas phase chemical reduction, and solidification/stabilization. This report covers the pilot-scale test of a thermal desorption/gas phase chemical reduction process.

The pilot test was performed using Eco Logic's GPCR process, which consisted of a TRM, a GPCR reactor, and a gas scrubbing and compression system. During the pilot test, the concentration of PCBs in the treated sediment from the TRM ranged from 28 to 77 mg/kg, with an average of 52 mg/kg. The TRM PCB desorption efficiency ranged from 98.36 to 99.52%, with an average of 99.06%, and the total dioxin and furan concentrations were reduced by an average of 93%. The PCB concentrations in treated sediment were higher than Eco Logic expected, and may be attributed to the treated sediment accumulating in the auger. The GPCR reactor achieved a destruction efficiency ranging from 99.99972% to 100% for PCBs and an average destruction efficiency for total dioxins and furans of 99.9923 and 99.99959, respectively. TCLP metals concentrations in the treated sediment were below the regulatory criteria. The pilot-scale TRM unit did not allow for the collection of isokinetic (flow representative) gas samples. The vendor concluded that the results of the pilot study can be used for a summary assessment of performance, but that additional data would be needed to draw definitive conclusions regarding dioxin and furan production and the concentrations of contaminants downstream of the TRM.