Ex-Situ Chemical Oxidation
Ex-situ chemical oxidation involves mixing an oxidizing compound with contaminated groundwater in a vessel. The oxidizing compound can be a solution (e.g., sodium hypochlorite in water) or a gas (e.g., ozone). The oxidizing agents most commonly used for the chemical treatment of organic contaminants are ozone, hydrogen peroxide, hypochlorites, chlorine, and chlorine dioxide. The treatment chemicals typically mineralize most organic compounds to carbon dioxide, water, and salts. The main advantage of ex-situ chemical oxidation as opposed to in-situ chemical oxidation is that it allows sufficient time for oxidation to occur in a controlled environment.
Limitations and Concerns
Incomplete oxidation or formation of intermediate contaminants may occur depending upon the contaminants and oxidizing agents used.
The process is not cost-effective for high contaminant concentrations because of the large amounts of oxidizing agent required.
When chlorine is used for oxidation, undesirable substitution products such as chloromethanes can form.
Chemicals other than contaminants may consume oxidizing agents, increasing treatment cost and creating the potential for forming undesirable byproducts.
This technology can be used to treat halogenated and nonhalogenated volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs). It has been experimented with polychlorinated biphenyls (PCBs) and ordnance compounds.
Technology Development Status
This is a commercially available technology.
Other Resources and Demonstrations
See Neil Jaques, ÒAn Innovative Approach to Remediation,Ó Estates Review, April/May 2006, pp. 116-117,
Abstract: For the past 10 months, free-phase oil and trichloroethene contamination at a 3-ha former ceramics and spark plug factory site on St. Peter's Road in Rugby (UK) has been addressed with a combination of in situ and ex situ remediation techniques. Supplementing an in-situ multi-phase extraction system with ex situ chemical oxidation has rarely been attempted in the UK. In May 2005, with 80% of the site covered by buildings, the site contractor had to decide how to implement a quick, cost-effective, and environmentally sustainable remediation strategy while the factory continued to operate. Following the site investigation, the first step was to install a 70-well, in-situ, multi-phase vacuum extraction system at the southern section of the site to initiate mass recovery. Subsequently, about 1,000 m3 of contaminated soil were excavated, moved to the southern part of the site, and treated using ex-situ chemical oxidation. Bench-scale tests performed with a series of oxidants on site soil samples identified potassium permanganate as the most successful oxidant. In full-scale treatment, the potassium permanganate was aggressively mixed into the soil using a Morowetz soil windrow turner, a machine traditionally used for green waste composting.