Solar detoxification uses the ultraviolet energy in sunlight to destroy contaminants. The contaminated medium is mixed with a catalyst (e.g., titanium dioxide) and fed into an illuminated reactor. Ultraviolet light activates the catalyst, forming reactive chemicals known as “radicals.” These are oxidizing agents. When they come into contact with contaminants, they break them down into non-toxic byproducts such as carbon dioxide and water.
For contaminated soil, vacuum extraction is used to remove contaminants from soils. After the contaminants are condensed, they are fed into the reactor. For contaminated groundwater, the groundwater passes over the catalyst. An advantage of this system over conventional treatment processes, such as those using granular activated carbon or air stripping, is that it destroys the toxic compounds.
Limitations and Concerns
The process can only be used effectively during the daytime with normal sunlight intensity. Weather changes affect destruction rates.
Large spaces are required for the reactor. The larger the reactor, the more efficient the process.
Biological fouling or physical fouling from suspended solids or precipitated iron limit photochemical reactions and reduce effectiveness.
Destruction should be monitored.
Technology Development Status
The technology has been field tested.
Other Resources and Demonstrations
See the descriptions of Vapor-Phase Thermal Oxidation, Catalytic Destruction, and UV Oxidation and Ultra-Violet Treatment.
See http://unesdoc.unesco.org/images/0012/001287/128772e.pdf for a description of the first known treatment of contaminated groundwater by solar detoxification (i.e., photocatalysis). It was demonstrated at Lawrence Livermore National Laboratory (LLNL) in Livermore, California. The field experiment used available trough technology and demonstrated the technical feasibility of this application. The system consisted of two solar troughs, each approximately 100 feet long, and it treated trichloroethylene-contaminated water. The process yielded water that met drinking-water standards. Another demonstration was located at Tyndall Air Force Base in Florida. Groundwater there was contaminated by benzene, toluene, ethyl benzene, and xylene (BTEX).