The Increasing Importance of Abiotic Degradation of Chlorinated Solvents

By: Will Harms, Bioremediation Services Practitioner and Laurel Seus, Remediation Microbiologist

Abiotic mechanisms responsible for natural and enhanced detoxification of chlorinated compounds like tetrachloroethene (PCE, tetrachloroethylene) and trichloroethene (TCE, trichloroethylene) are increasingly recognized for their credible role in holistic in-situ remediation of chlorinated solvents. The reason? The means to understand and measure abiotic degradation of chlorinateds is finally emerging – making way for more effective and less expensive treatment options.

The Department of Defense (DoD) has two dedicated environmental research programs, the Strategic Environmental Research and Development Program (SERDP), and the Environmental Security Technology Certification Program (ESTCP). Among all things remediation, SERDP/ESTCP is keenly focused on abiotic natural attenuation (ANA) and on iron-based in-situ chemical reduction (ISCR) techniques. Together, these abiotic treatment research initiatives focus on:

• practical metrics of performance,
• enhancing utility of solvent-reactive biogenic iron minerals,
• factors that control abiotic degradation rates, and
• use of dissolved iron additives (Fe(II), Fe²⁺).

SERDP/ESTCP’s investment in researching abiotic mechanisms of chlorinated detoxification not only benefits the DoD but extend to private site owners and the entire remediation industry. These learnings are made readily available to the public and SERDP/ESTCP research reports are respected by regulatory agencies.

For example, take the recent work of Sherer et al., 2019¹ entitled Biologically Mediated Abiotic Degradation (BMAD) of Chlorinated Ethenes: A New Conceptual Framework found conditions that favor active precipitation of metastable reactive mineral intermediates (RMIs) onto surfaces of aquifer materials that lead to effective detoxification of chlorinated compounds in groundwater include relatively high dissolved iron concentrations and relatively high groundwater flow rates.

This means that adding dissolved iron to in-situ treatment zones may be a more effective and less expensive option than emplacement of broadly accepted metallic iron products like zero valent iron (ZVI). At EHS Support, the concept to adding dissolved iron (Fe²⁺) (like ferrous gluconate) instead of particulate iron products like ZVI is not new. In fact, we are close to implementing an in-situ source remedy at one of our client trichloroethylene TCE sites that will use soluble ferrous gluconate along with emulsified biostimulants to gain maximum TCE detoxification through in-situ chemical reduction-enhanced anaerobic bioremediation.

If you would like to discuss biologically mediated abiotic degradation in more detail, EHS Support’s team of subject matter experts are here to help:

Will Harms, Bioremediation Services Practitioner

Laurel Seus, Remediation Microbiologist

John Bartos, Senior Remediation Hydrogeological Engineer

Richard Landis, Senior Engineer

Source:

¹Michelle Scherer, Drew Latta, Anke Neumann, David Cwiertny, and Rula Deeb. 2019. Biologically Mediated Abiotic Degradation (BMAD) of Chlorinated Ethenes: A New Conceptual Framework. SERDP Final Report ER-2532. Feb 12, 2019.