Chemical remediation is a method of soil and groundwater remediation by using various chemical reagents. It is considered the most effective technique for dealing with different contaminants. At Hanis Consulting, we use diverse techniques, such as In-situ Chemical Oxidation (ISCO) and In-situ Chemical Reduction (ISCR).
In-situ Chemical Oxidation treats different kinds of organic contaminants such as fuels and solvents. By injecting chemical oxidants into contaminated areas, the ISCO technique results in complete contamination removal in-situ (on-site), causing minimal disturbance for existing residents. It has wide application because of its unobtrusiveness and cost-effectiveness.
In-situ Chemical Reduction involves adding a reducing agent to a contaminated area. It changes the toxicity of highly toxic contaminants, for example, hexavalent chromium, reducing it to non-toxic trivalent chromium. ISCR achieves successful results with a single application, which is why it is considered one of the most time-effective remediation techniques.
Chemical remediation is an in-situ chemical process used to remove hazardous chemicals from the environment. It uses various methods depending on the application, but most involve oxidation or reduction reactions with inorganic or organic compounds. Chemical Oxidation is an in situ remediation technology that can be applied to groundwater, soils, and many different contaminants. It is a chemical technology where strong oxidants are injected or mechanically mixed into the treatment zone to promote destructive abiotic degradation reactions. Strong oxidants include ozone, hydrogen peroxide, persulfate, permanganate, among others. The primary purpose of chemical oxidation is to degrade organic pollutants. Hydroxyl radicals are typically formed during the process. The hydroxyl radical can effectively degrade most organics by attacking them at their weakest carbon-carbon bond. Peroxide is applied more sparingly in some cases due to its instability. Chemical oxidation is especially effective for removing chlorinated solvents, which are notoriously difficult to remove from groundwater.
Chemical Reduction is an in situ chemical treatment where electron donors are injected into the subsurface or mechanically mixed into the treatment zone, promoting reactions that generate strong reducing conditions that convert contaminants into more benign species. This technology is also referred to as Reductive Dechlorination. It can be used to treat a broad range of compounds, including chlorinated aliphatic hydrocarbons (carcinogenic and non-carcinogenic) chlorinated ethanes and ethylene, and aromatic compounds such as the solvents DCE and TCE. The required electron donors can include naturally occurring organic materials such as humic substances or feldspar minerals, or synthetic substances such as ethanol. The reduced product is often a carbon dioxide or simple inorganic salt depending on the specific contaminant. Chlorinated aliphatic hydrocarbons are resistant to biological degradation at low concentrations, so this process has been used to degrade highly impacted sites with these contaminants.
Chemical reduction operates similarly where nitrate (NO3-) and sulfate (SO4-) ions convert contaminants into less mobile and more degradable forms. Thus, the contaminants are no longer present in their original form but have been transformed into a new chemical that may be more available to naturally occurring bacteria. The contaminants may also be attached to mobile ions such as sodium and calcium through ion exchange reactions, which can reduce groundwater concentrations of the contaminant. In addition, reduction followed by aerobic bioremediation or phytoremediation has been shown to achieve more significant contaminant mass removal than either process alone.
Chemical Reduction is an isolated component of a more robust approach known as Bioreduction-Augmented Chemical Oxidation (BACO). This technology utilizes microbial action and chemicals to speed up hazardous material degradation rates. BACO is usually implemented after first using chemical oxidation treatment to deplete the oxygen content of the treatment zone, which inhibits bioreduction. This technology is an established treatment option for refractory chlorinated ethenes and has also been applied to trichloroethylene (TCE).
Chemical Reduction is part of a larger approach known as Soil Washing. This process typically involves removing soil or sediment that contains hazardous compounds through elutriation, centrifugation, filtration, or flocculation. These techniques are used to remove chemicals from water-soluble forms to physically isolate them for storage or disposal and to separate residual soil particles from contaminated groundwater that may be present in nearby wells. The contaminants can then be removed from the isolated solids by several methods. Chemical Reduction is one of these methods that can degrade the contaminants into less harmful or mobile chemical species.
The chemical reduction has also been used at contaminated sites where it was necessary to mitigate soil contamination without disrupting buildings, roads, utilities, etc. This technology has been disclosed as an excellent option for isolated subsurface areas with relatively high contaminant levels because it does not require excavation.
