Combining Low-Energy Electrical Resistance Heating with Biotic and Abiotic Reactions for Treatment of Chlorinated Solvent DNAPL Source Areas
ER-200719
Objective
Three relatively mature technologies—enhanced in situ bioremediation (ISB), in situ iron-based reduction using zero-valent iron (ZVI), and thermal treatment using electrical resistance heating (ERH)—have been demonstrated independently for treating residual DNAPL source zones. Despite the numerous benefits of in situ technologies, associated remedial time frames are relatively long due to limitations in mass transfer of contaminants from the residual to the dissolved phase, where contaminants are available for destruction. While thermal treatment through ERH rapidly removes large quantities of residual mass from subsurface environments, high capitol and maintenance costs and the requirement for vapor control and secondary waste treatment make this technology infeasible at many sites. The objective of this project is to demonstrate the benefits of combining low-energy ERH with either ISB or iron-based reduction using injectable ZVI, including the extent to which contaminant degradation is enhanced during heating compared to ambient temperatures, the relative contribution of biotic and abiotic contaminant degradation mechanisms at different temperatures, and the cost-benefit of applying low-energy heating with in situ treatments.
Technology Description
This demonstration combines the three technologies described below.
Low-Energy Electrical Resistance Heating - Historically, ERH has been used to treat soil and groundwater aggressively in contaminant source areas by increasing subsurface temperatures to the boiling point of water. At this temperature, steam is created in situ and contaminants are directly volatilized. The steam acts as a carrier gas to strip volatiles from the subsurface and route them to the surface under vacuum for treatment. The low-energy ERH approach is based on raising subsurface temperatures to approximately 30 to 60° C to enhance the rate of biotic and abiotic contaminant dechlorination. This less aggressive approach will use electrodes installed on a wider spacing using boring, pile-driving, or direct-push technology and will eliminate vapor and steam recovery and treatment. As a result, the total cost of ERH can be reduced by 50 to 75%.
In Situ Bioremediation - ISB for chlorinated ethenes has been investigated, demonstrated, and deployed at numerous sites. Biostimulation techniques use injection of amendments as electron donors to grow indigenous bacteria capable of dechlorinating chloroethenes. In cases where complete dechlorination to nonhazardous end products cannot be obtained by indigenous bacteria, bioaugmentation has been applied to inoculate the subsurface with bacteria that are capable of complete dechlorination. Effective distribution of bacteria is a key consideration.
Iron-Based Contaminant Dechlorination - ZVI is chemically reactive with many contaminants. Injectable ZVI can directly provide a reactive particle for in situ contaminant dechlorination. Recently, use of polymers and emulsified solutions of micron-size iron have been demonstrated for distributing reactive iron in the subsurface. Iron-catalyzed dechlorination by the typical elimination reaction is potentially advantageous compared to biotic dechlorination because hazardous byproducts are not produced. Similar reactions also can be induced by sediment-associated iron that is reduced chemically or biologically.
Benefits
This combined technology approach is expected to provide more rapid source area cleanup than the in situ technologies alone but without the high cost of conventional ERH associated with boiling the entire water column and extracting and treating contaminants at the surface. Collectively, this demonstration will provide key performance metrics that can be used to evaluate the potential for application of combined thermal and in situ treatments for chlorinated solvent-contaminated sites. (Anticipated Project Completion - 2011)
Points of Contact
Document Types
- Fact Sheet - Brief project summary with links to related documents and points of contact.
- Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
- Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
- Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
- Guidance - Instructional information on technical topics such as protocols and user’s guides.
- Workshop Report - Summary of workshop discussion and findings.
- Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
- Model/Software - Computer programs and applications available for download.
- Database - Digitally organized collection of data available to search and access.