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In Situ Chemical Reduction (ISCR)

At a Glance

Regenesis_Icon_Mechanisms Regenesis_Icon_Trackable-Contaminents Regenesis_Icon_Concentration

Mechanism:

Treatable Contaminants:‚‚

Concentrations:

Biogeochemical Reduction

Combines biological and chemical reduction to treat contaminants

Chlorinated Ethanes, Chlorinated Ethenes, Haloalkanes, Pesticides, Herbicides, Energetics, Hexavalent Chromium

  Treats high to low concentrations

Regenesis_Icon_Time

Regenesis_Icon_Conditions Regenesis_Icon_Applied-Frec

Time:

Conditions:

Applications Frequency:

Rapid treatment time

(weeks to months)

Works in saturated and unsaturated zones

Single application effectiveness

(Usually applied with an electron donor like 3-D Microemulsion)

About In Situ Chemical Reduction (ISCR)

ZVI products, such as MicroZVI and CRS, are used in soil and groundwater remediation as an in situ chemical reduction (ISCR) reagents. Chemical reduction is the process of adding or donating electrons to contaminants (while chemical oxidation is the process of removing or accepting electrons from contaminants). The ZVI acts as a reducing agent to provide electrons directly to the contaminant for degradation or to support processes that require electrons to degrade contaminants.

Abiotic Degradation

Zero-valent iron can provide an abiotic degradation pathway involving the direct reaction of ZVI with groundwater contaminants. The abiotic, “beta-elimination pathway” for chlorinated ethenes is shown in the bottom of Figure 1. The abiotic pathway involves short-lived dichloroacetylene and chloroacetylene intermediates, bypasses the formation cDCE and VC, and ultimately results in ethene and ethane.

Figure 1

Figure 1: ISCR or beta-elimination (double-line arrows). Beta-elimination avoids the formation of cDCE and VC.

Biological Degradation

Biological degradation involves the destruction of contaminants by anaerobic bacteria that are supported by the molecular hydrogen that is produced by the fermentation of organic hydrogen donors or by the reaction of ZVI with water. The biological degradation pathway for perchloroethene (PCE) and trichloroethene (TCE) is provided in Figure 2. This pathway, called reductive dechlorination (or hydrogenolysis), involves the sequential replacement of a chlorine atom with a hydrogen atom and is always accompanied by the formation cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). Many common anaerobic bacteria can transform PCE to TCE and then to cDCE, but only Dehalococcoides ethenogenes (DHC) can transform cDCE and VC to ethene.

Figure 2

Figure 2: Reductive dechlorination sequentially replaces chlorine atoms with hydrogen atoms. The intermediates cDCE and VC are more toxic than parent compounds PCE and TCE.

 

Supplementing dechlorinating bacteria with zero-valent iron and organic hydrogen donors can enable more rapid and complete biodegradation. Zero-valent iron quickly deoxygenates groundwater and provides an electrochemically reducing environment that is highly fertile for the microbes involved in anaerobic bioremediation. In many situations this favorable environment can be sustained for several years.

ISCR-Enhanced Bioremediation

ISCR-enhanced bioremediation is a term describing the remediation approach that combines zero-valent iron (ZVI), an organic hydrogen donor, and contaminant-degrading microbes (native or bioaugmented) in order to degrade contaminants in soil and groundwater. This approach is most commonly used for chlorinated contaminants, e.g. chlorinated ethenes. ISCR-enhanced bioremediation is particularly effective because it stimulates anaerobic biological degradation by rapidly creating a reducing environment favorable to reductive dichlorination. Furthermore, ISCR-enhanced bioremediation may limit the formation of undesirable daughter products such as cDCE and VC by degrading parent compounds via direct chemical reduction.

ISCR-enhanced bioremediation can be used to treat contaminants such as chlorinated solvents, haloalkanes, and chlorinated pesticides. Contaminants that are resistant to abiotic degradation (e.g. 1,2-dichloroethane or dichloromethane) and compounds that can inhibit bioremediation (e.g. 1,1,1-trichloroethane or chloroform) may be effectively treated by ISCR-enhanced bioremediation. ISCR-enhanced bioremediation can be used for source zones, plumes, and barrier applications.

Typical Soil and Groundwater Remediation Application Methods:

Application/Injection:

  • Permanent injection wells
  • Direct-push injection points

ISCR Agents such as MicroZVI and CRS, are diluted with water on-site and easily applied into the subsurface using low pressure injections.

Learn More:

FAQs about In Situ Chemical Reduction (ISCR)

In Situ Chemical Reduction (ISCR) is remediation process that combines both biological processes and metallic particle driven abiotic pathways to chemically reduce chlorinated contaminants into harmless end products. Chemical reduction is the process of adding or donating electrons to contaminants. The ZVI acts as a reducing agent to provide electrons directly to the contaminant for degradation or to support processes that require electrons to degrade contaminants.

In Situ Chemical Reduction (ISCR) has a rapid treatment time of weeks to months with typically a single application.

In Situ Chemical Reduction is an effective solution for your contamination problem if you require a reducing agent to provide electrons directly to the contaminant for degradation or to support processes that require electrons to degrade contaminants.