In situ chemical reduction (ISCR) refers to the chemical reduction of contaminants at lower oxidation reduction potential (and dissolved oxygen (conditions, typically using zero valent iron (ZVI).
In most cases, chemical reduction through ZVI is applied to chlorinated solvent sites. Chemical reduction can also be used in conjunction with in situ chemical oxidation (ISCO) applications, where the generated superoxide radicals are utilized in the ISCO process to address contaminants like chlorinated ethanes and methanes.
For metals contamination, calcium polysulfide is often applied to reduce contaminants, like hexavalent chromium, by reducing ORP with anerobic bio substrates.
When using ZVI to reduce chlorinated solvents, hydrolysis and the beta elimination pathway are the primary chemical reactions. There is, however, a small percentage of the reaction that will also follow the dechlorination pathway for degradation to ethene.
ISCR is primarily used for source reduction, DNAPL zones being the exception (unless emulsified zero valent iron [eZVI] is used). It can also be utilized in reactive treatment zones in the plume. It is generally applied in fine grained soils where liquids cannot be effectively distributed. It is often combined with bio substates and bioaugmentation for a more aggressive abiotic/biotic treatment that minimizes production of daughter products.
In transmissive zones, ZVI is can be applied in the colloidal size range, but otherwise it’s applied in the micro-scale range into finer grained formations or bedrock.
ISCR is an excellent choice when a more aggressive and persistent approach is required to meet contaminant destruction goals, and bioremediation and ISCO aren’t up to the task.
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