Using Peroxides for Remediation
When accidents happen, remediation of sites containing potentially toxic materials often has to take place quickly and efficiently, and a robust remediation plan can make this happen. In contamination cases where it is not possible or cost effective to remove affected soil, in-situ chemical oxidation (ISCO) methods can be very effective in quickly neutralizing these materials, rather than removing the contaminants. The ISCO process involves the injection of a liquid or gas into the soil, resulting in oxidation and the direct destruction of contaminants. ISCO can also contribute to the indirect reduction of contaminants in the soil by raising the level of dissolved oxygen in the groundwater, which in turn enhances biodegradation.
One of the most widely used ISCO agents is hydrogen peroxide, an inexpensive and widely available remediation agent that provides chemical oxidation of soil and groundwater contaminants, leaving no harmful by-products. This paper describes peroxide products and their effects on contaminants, the situations where peroxides can be efficiently used for site remediation, and factors to keep in mind when selecting a peroxide product vendor as part of your remediation strategy.
What are Peroxides?
A peroxide is a compound that contains an oxygen-oxygen single bond or a peroxide anion. The simplest and most stable of the peroxides is hydrogen peroxide, or H2O22; a readily available oxidizer that is used for a variety of industrial processes. Hydrogen peroxide in its pure form is colorless and odorless, but is generally supplied in diluted form for safety purposes. Household grades are 3-6%, but industrial grades are available as high as 70%. Because of the unstable nature of the oxygen-oxygen bond, hydrogen peroxide is only found naturally in small amounts, and is primarily synthesized for industrial use by the anthraquinone process, although “greener” manufacturing processes are being explored., When used as a remediation agent, hydrogen peroxide naturally decomposes into oxygen and water, raising the oxygen levels in the soil. The elevated oxygen encourages aerobic bacteria to become active and consume organic contaminants, breaking them down into less harmful compounds.
Catalyzed hydrogen peroxides (CHP) are a combination of hydrogen peroxide and a catalyst, generally ferrous iron, which work together to generate hydroxyl free radicals, which are among the strongest oxidants that can be used in water. These free radicals then actively oxidize organic compounds into stable inorganic compounds, including carbon dioxide, oxygen, and salts. The chemical reactions that take place with CHP can be complex, but they are extremely effective at neutralizing organic compounds. While the reactions of CHPs have been understood since the 19th century, they were only put into practice for remediation purposes beginning in the 1980s. As regulations for clean water have increased, the use of peroxides for remediation projects has become more widespread.
How are Peroxides Deployed for Site Remediation?
At a remediation site, peroxides are introduced into the soil through infiltration galleries or injection wells, with depths depending on the depth of contamination. Injection wells are also used to monitor the concentration of contaminants and track the performance of the remediation process.
When hydrogen peroxide is used without a catalyst, it is generally delivered into injection wells or monitoring wells via a gravity feed at regular time intervals. In CHP applications, an injection unit is often used to deliver the catalyzed peroxide under pressure as a continuous feed to the injection points in the plume. In this case, the mixture is injected to the deepest contaminated layer first, working upward. In some cases, acids are used to adjust the pH of the soil to improve the performance of the peroxide. In this case, the acid is added to the soil first, and stainless steel injectors must be used.
Peroxides or other ISCO processes are often deployed in conjunction with other remediation methods, depending on the specific details of the contaminated site. For example, soil excavation, air sparging, or dual-phase extraction may be used to remediate the immediate source of the contaminant (such as the area directly around a leaking underground storage tank), while the peroxides are used to remediate the plume in the area outside of the immediate source. Also, non-homogeneous geological formations may also lead to the use to multiple remediation methods to most effectively neutralize and/or remove contaminants.
It is critical to assess the scope of the contamination at the site to determine the optimal array of injection wells, the required depths for injection, and the concentration of peroxide to be used in order to maximize the effectiveness of the operation. These approaches can then be verified through benchtop testing, pilot wells, and continual monitoring during the remediation operation.
Why Choose Peroxides?
Peroxides can be used to effectively neutralize organic compounds such as chlorinated solvents or gasoline products. For example, CHP is effective in neutralizing many contaminants, including:
- Chlorinated aliphatic compounds (chloroethenes, chloroethanes, chloromethanes)
- Chlorinated aromatic compounds (Chlorophenols, polychlorinated biphenyls/dioxins/furans)
- Hydrocarbon compounds (benzene, toluene, ethylbenzene, xylene (BTEX), methyl tert-butyl ether (MTBE), polycyclic aromatic hydrocarbons)
The oxidation process can also reduce the toxicity of other compounds. The use of hydrogen peroxide as a remediation treatment can quickly reduce the concentration of contaminants, which is critical when these contaminants could affect deeper layers of soil or groundwater.10
Benefits of Peroxides over Other Remediation Methods
Peroxides are an attractive remediation agent for many reasons.
- Cost and Availability - Hydrogen peroxide is inexpensive and readily available, as it is used for a wide variety of industrial applications outside of remediation.
- Reliable Chemistry - The oxidation process is very well understood and predictable, and can be applied to many different soil and groundwater contaminants.
- Rapid Treatment – A site can be remediated in a relatively short timeframe depending on the scope of contamination and complexity of the geology, with timeframes ranging in days or weeks, not months or years.
- In-situ Treatment – Treatment in place minimizes overall structural disturbance of the ground layers and prevents potential movement of contaminants.
- No By-Products – The oxidation process results in carbon dioxide, oxygen, and water, not other by-products that require removal. Any hydrogen peroxide that is not consumed by the oxidation process naturally breaks down to oxygen and water.
- Part of Remediation Strategy – Peroxides can be combined effectively with other remediation methods where required.
Concerns about Use of Peroxides
As with all remediation products, a comprehensive decontamination strategy must be designed to ensure that peroxides are deployed in a safe manner. Depending on the situation, the pH level of the soil may need to be carefully controlled. Also, processes must be in place to control in-situ heat and gas production as the oxidation process proceeds. A significant amount of heat can be created by the oxidation process, particularly when using CHPs and significant iron, manganese, or other contaminants are present.
The efficiency of the oxidizing process can be affected by the permeability of the soil, changes in the soil structure, and highly alkaline soil, so a full site study must be performed prior to selecting a remediation method and designing a comprehensive remediation strategy. Bench testing, pilot wells, and continual monitoring can ensure that the remediation operations live up to their design.
Choosing a Peroxides Vendor
Like many remediation products, peroxides have specific handling and storage requirements[SBK1] , and it’s important to select a vendor that understands these requirements.
Because peroxides are an oxidizer, they release both oxygen and heat when they decompose. Solutions with a lower percentage of hydrogen peroxide can readily absorb the heat and oxygen, but this is more difficult for higher concentrations. Therefore, proper transport and storage methods are critical. Peroxide containers must be stored on poly skids, and must have proper ventilation to prevent spontaneous combustion. Because hydrogen peroxide has a short shelf life, it must be used fairly quickly after delivery to ensure efficacy.
It is also helpful to select a vendor that can provide peroxides in the volume that you need, whether it’s 1 gallon or a full tanker truck. Remediation sites aren’t always easily accessible, so a vendor should not only be able to give you the peroxide product you need, but also deliver it properly and safely to where you need it. Look for vendors with experience delivering remediation products directly to contaminated sites.
Peroxides may be subject to local handling regulations, so work with a vendor that is familiar with the regulations in the remediation area. The Department of Transportation (DOT) considers hydrogen peroxide concentrations above 20% an oxidizer, so containers must be properly marked, documented, and transported according to DoT regulations. Also, peroxides can be used as a precursor for drug manufacture or explosives development. Choose a vendor that understands the requirements of both the Drug Enforcement Agency (DEA) and the Department of Homeland Security (DHS) for proper storage of these products.
 H. Riedl and G. Pfleiderer, U.S. Patent 2,158,525 (2 October 1936 in USA, and 10 October 1935 in Germany) to I. G. Farbenindustrie, Germany
 Munter, Rein (2001). "Advanced Oxidation Processes–Current Status and Prospects.". Proceedings of the Estonian Academy of Sciences. Chemistry. 50 (2): 59–80. http://www.kirj.ee/public/va_ke/k50-2-1.pdf
 https://clu-in.org/download/contaminantfocus/pcb/ISCO-600R06072.pdf, p.3
 https://navfac.navy.mil/content/dam/navfac/Specialty%20Centers/Engineering%20and%20Expeditionary%20Warfare%20Center/Environmental/Restoration/er_pdfs/i/ navfac-ev-fs-isco-20110914.pdf