In-Situ Chemical Reduction (ISCR)
Chemical Reduction refers to an abiotic process that typically occurs under extremely electronegative conditions with similar results as anaerobic enhanced bioremediation. ISCR is effective on chlorinated ethenes, metals, explosives, and a variety of other compounds. Common reductants include zero valent iron (ZVI), nano-ZVI, metal sulfides, polysulfides, and other compounds.
Chemical reductants may be injected into the subsurface (ISCR) or blended into the soil matrix. Advantages over enhanced bioremediation includes speed of reaction and greater likelihood of success due to the lack of reliance on microbial processes alone. Chemical reduction is typically slower than chemical oxidation where molecular bonds are broken versus substitution of electrons on the carbon chain (i.e. hydrogen ions for chlorine ions). ISCR treatments may be performed by direct plume area injection or more commonly by creating a liquid or solid phase PRB along the down-gradient plume extent.
An example of chemical reduction using ZVI in the treatment of tetrachloroethene is depicted in the generalized reaction below. In this reaction, the oxidation of the ZVI results in the release of H+ ions that are substituted for chlorine ions in the carbon structure.
