Reductive dechlorination is a natural biological process in which specialized microorganisms remove chlorine atoms from chlorinated solvents under anaerobic conditions, ultimately converting many contaminants into harmless end products.
The Importance of Reductive Dechlorination
Reductive dechlorination is one of the primary biological processes used to remediate chlorinated solvent contamination during in situ bioremediation. It is commonly associated with contaminants such as tetrachloroethylene (PCE), trichloroethylene (TCE), dichloroethylene (DCE), vinyl chloride, and other chlorinated compounds found at industrial facilities, manufacturing sites, dry cleaners, and similar locations.
Unlike some remediation methods that transfer contaminants from one place to another, reductive dechlorination biologically transforms contaminants into progressively less harmful compounds. When the proper microorganisms, groundwater chemistry, and site conditions are present, the process can continue until the contaminants are converted to harmless ethene.
Successful reductive dechlorination depends on much more than selecting the right remediation products. Site geology, groundwater flow, amendment distribution, and the biological conditions within the treatment zone all influence how effectively the process will occur.
How Reductive Dechlorination Works
Reductive dechlorination occurs under anaerobic conditions where oxygen has been depleted. Specialized microorganisms use chlorinated compounds during their natural biological processes, removing chlorine atoms one step at a time while replacing them with hydrogen. As each chlorine atom is removed, the contaminant becomes less chlorinated until complete degradation can occur.
To support this process, microorganisms require food. Electron donors provide that food, allowing microbial populations to grow and remain active. As microorganisms consume the electron donor, they create and maintain the reducing conditions needed for continued biological activity.
Some contaminated sites naturally contain the microorganisms needed for complete reductive dechlorination, while others do not. In these situations, bioaugmentation cultures containing specialized microorganisms may be introduced to enhance treatment. Regardless of the products selected, successful remediation depends on creating favorable biological conditions throughout the treatment zone so microorganisms have access to both the contaminants and the food needed to sustain treatment.
Because every site is different, environmental professionals evaluate groundwater chemistry, oxidation-reduction potential (ORP), dissolved oxygen, pH, contaminant concentrations, groundwater flow, and soil characteristics before selecting a remediation strategy. These site-specific conditions determine how quickly reductive dechlorination can occur and which treatment approach is most appropriate.
How Reductive Dechlorination Is Used
Reductive dechlorination is widely used during in situ remediation of groundwater contaminated with chlorinated solvents. It is particularly effective where anaerobic biological treatment is the preferred remediation strategy and where contaminants remain dissolved within groundwater or are slowly released from source areas.
The process is frequently enhanced through the addition of electron donors that provide long-term food for microorganisms. At sites where naturally occurring microbial populations are insufficient to complete contaminant degradation, bioaugmentation may also be incorporated into the treatment program.
Environmental professionals commonly monitor groundwater chemistry, contaminant concentrations, dissolved oxygen, and ORP throughout the remediation process to confirm that the biological conditions necessary for reductive dechlorination are developing and being maintained.
RNAS Technical Insight
One of the most common misconceptions is that reductive dechlorination begins simply by injecting an electron donor. In reality, successful treatment depends on creating the right biological environment throughout the contaminated area. If amendments are not properly distributed, microorganisms may never reach portions of the contaminant plume, even though groundwater chemistry appears favorable in monitoring wells.
At RNAS, product selection is only part of the solution. Understanding site conditions, selecting the appropriate electron donor, establishing anaerobic conditions when necessary, and achieving good amendment distribution are all essential to long-term remediation success.
Related RNAS Products
- Newman Zone OS is designed to rapidly remove dissolved oxygen and help establish the anaerobic conditions required for enhanced biological treatment.
- Newman Zone 55 and Newman Zone HRO provide long-term food for microorganisms after anaerobic conditions have been established.
- Newman Zone QR75 and Newman Zone QR90 provide soluble electron donors for applications where more rapid biological stimulation is desired.
- SDC-9 bioaugmentation culture may be used when specialized microorganisms are needed to support complete degradation of chlorinated solvents.
- Neutral Zone helps maintain favorable pH conditions that support long-term microbial activity during biological remediation..
« Back to Glossary Index