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In situ Treatment Technologies
Published in Rong Yue, Fundamentals of Environmental Site Assessment and Remediation, 2018
In situ chemical reduction (ISCR) uses a reductant, or a material that can generate reductant, to detoxify the contaminants via chemical reduction in the subsurface. The specific detoxification process varies for different groups of contaminants. For organic contaminants, ISCR transforms them to potentially less toxic or nontoxic compounds. For inorganic contaminants such as metals, ISCR reduces their oxidation status and therefore immobilizes them by adsorption or precipitation, as in the case of hexavalent chromium (Cr[VI]). The commonly used ISCR reagents include zero-valent iron (ZVI), ferrous iron, sodium dithionite, calcium polysulfide, and hydrogen with a catalyst, as discussed in the following subsections.
Remedial Actions
Published in Benjamin Alter, Environmental Consulting Fundamentals, 2019
In situ chemical reduction (ISCR) remediates contamination in the subsurface by creating reducing conditions that are designed to remove halogens and other negatively charged ions from the molecular structure of a contaminant. In ISCR, the contaminant “accepts” electrons provided by a reducing agent, thereby transforming the contaminant into a harmless or less harmful molecule.
In situ electrochemical manipulation of oxidation-reduction potential in saturated subsurface matrices
Published in Journal of Environmental Science and Health, Part A, 2018
Paul H. Fallgren, John J. Eisenbeis, Song Jin
In situ chemical reduction (ISCR) remedial technologies are currently widely recognized as options to treat contaminated groundwater systems (i.e., if the pollutant is resistant to oxidation and/or can be readily reduced). ISCR technologies may include engineered strong reductants such as zero-valent iron (ZVI or Fe0) often used in permeable reactive barriers and moderately strong reductants such as sodium dithionite or calcium polysulfide.[6,22] Dolfing et al.[22] described that the most important features of ISCR technologies are their propensity to produce H2 and low redox potential. ISCR technologies perform best in environments with low redox potential (near the corresponding dominant redox couple standard reduction potential), and often the presence of the ISCR chemical itself may lower redox potential. One ISCR method is in situ redox manipulation (ISRM) that utilizes a soluble chemical reductant (i.e., sodium dithionite) to reduce any Fe3+-bearing minerals/solids to Fe2+-bearing minerals/solids, which decreases redox potential.[24,25] Current ISRM methods are promising and may be easily applied due to the primary reductant being water-soluble; however, as with other ISCR technologies, the effectiveness is limited by the properties of the in situ matrix, where low permeability may prevent practical distribution of the chemical reductants.