Aeration

Description

Aeration is a well-developed technology in the cleanup and wastewater treatment industries. It is a process that promotes volatilization and biological degradation by bringing contaminated media into contact with the air. Aeration technologies include activated sludge, rotating biological contacters, trickling filters, air stripping, air sparging and bioventing (these latter three technologies are described separately). In air strippers, for example, water is allowed to cascade through a series of slats or baffles in a tower, while the air rises in a countercurrent flow. Other methods include blowing air through jets into the water in a tank and the use of mechanical aeration devices that propel water droplets through the air. Many other configurations are possible, including baffled tanks through which the water is forced to flow. Aeration has also been used to remove radon gas from drinking water. In this system, an air blower forces air into several treatment tanks. The radon is then stripped from the water and vented outside the treatment area. Overall radon removal efficiency ranged from 90 percent to 99.6 percent.

Limitations and Concerns

When the contaminated water is high in volatile organic compounds (VOCs), contaminants removed through aeration — that is, off-gases — must still be treated. When spray irrigation is selected as the aeration technology, off-gas treatment is not feasible. There is a major concern that this treatment merely transfers contaminants from the water to the air. Consequently, it’s important to evaluate risks related to increases in contaminant loading of air and to monitor air quality continuously. If aeration is used to diffuse radon gas, an off-gas treatment system may be required.

Aeration promotes biodegradation only in systems where the oxygen-rich air has time to nourish bacteria. Consequently, open systems, such as air stripping, do not take advantage of this attribute.

Oxygen is not the only food source for bacteria that reduce VOCs, and it is used relatively quickly. The extent and rate of biodegradation also depend on the contaminant, contaminant concentration, and geochemical factors.

As in other biodegradation technologies, byproducts and rates of degradation must be carefully monitored.

This technology does not reduce radio-toxicity. Residuals may require further treatment and/or disposal.

Applicability

The target contaminant groups for aeration are semi-volatile organic compounds (SVOCs), pesticides and fuels. VOCs can be stripped followed by off-gas treatments. Radon may also be treated with aeration.

Technology Development Status

The technology is commercial.

Web Links

http://www.frtr.gov/matrix2/section4/4_37.html

Other Resources and Demonstrations

See description of Air Stripping, Air Sparging and Bioventing.

See http://www.epa.gov/superfund/resources/radiation/pdf/techguide.pdf for a description of aeration used to remove radon from water.