In this process, vacuum extraction is used to remove contaminants from soils. After condensation, contaminants are mixed with a semiconductor catalyst such (e.g., titanium dioxide), and fed through a reactor which is illuminated by sunlight. Ultraviolet light activates the catalyst, which results in the formation of reactive chemicals known as 'radicals'. These radicals are powerful oxidizers that break down the contaminants into non-toxic by-products such as carbon dioxide and water.
A big advantage of solar detoxification over conventional treatment processes such as those using granular activated carbon or air stripping is that it completely destroys the toxic compounds in the water instead of simply removing or displacing them. The solar process also has no atmospheric emissions.
The target contaminant group for solar detoxification is VOCs, SVOCs, solvents, pesticides, and dyes. The process may also remove some heavy metals from water.
Factors that may limit the applicability and effectiveness of solar detoxification include:
- It can only be effectively used during the daytime with normal intensity of sunlight.
- Biological fouling or physical fouling with suspended solids or precipitated irons would limit its effectiveness.
DOE has demonstrated the use of solar energy to remediate contaminated soil at pilot scale. The process has been successfully tested, decontaminating ground water at a former naval air facility. A 4-month field test was conducted on the grounds of Lawrence Livermore National Laboratory (LLNL). The ground water contamination there dates back to World War II, when the facility was a naval air base. Trichloroethylene (TCE) and other volatile organic compounds that were used to clean engine parts now contaminate the ground water. The field test was a huge success, proving the detoxification process works. The process brought the contaminants to levels well below the 5 parts per billion (ppb) EPA standard.