Environmental Enlightenment #124

By Ami Adini -
Reissued January 20, 2015

This is a SHORT, LIGHT and SIMPLE newsletter. Its purpose is to rekindle in the initiated terminology they have once learned, and enlighten the uninitiated on terms they may have heard but never knew the meaning of.

Air Stripping

Air stripping is a process where volatile organic compounds (VOCs) transfer from water to air by bubbling a stream of air through the water. The volatile compounds vaporize into the bubbles.   bubbles2

Volatilization into the bubbles operates on the same principle that vaporizes water into air. The greater the surface of the water exposed to air, the greater the rate of evaporation in total mass per time. Introducing air bubbles to the water increases the surface area of the contaminated water exposed to air many-fold.

In the case of contaminated groundwater, the stripping takes place inside the aquifer. Aquifer is a word coined from Latin aqua (water) and ferre (to bear). An aquifer is a formation of earth materials (rock, sand, clay, silt, and gravel) that bears water. The water resides in and moves through the pores. The aquifer part of the formation is also called the ”saturated zone,” because the pores are saturated (completely filled) with water.

Stripping is a process that transfers contaminants from one medium to another. In the case of air stripping as it applies to cleanup of groundwater, the air moves through the water as bubbles and strips the contaminants. The contaminants enter the air bubbles and get carried upward, collected and transferred to an aboveground unit for separation or destruction.

Air stripping is used to separate VOCs from water. Some compounds that have been successfully separated from water using air stripping include gasoline, benzene, toluene, ethylbenzene, xylenes, chloroethane, TCE, DCE, and PCE.

To understand how air stripping works, click on Henry’s Law for a brief illustration. Henry’s Law measures the extent to which a chemical will separate from water and enter into the air. It establishes characteristic numbers (constants) for substances. The higher the constant, the more likely is for the respective substance to separate from water. Air stripping is effective only for substances having Henry’s Law constants greater than 0.01. Here are some comparative values:

carbon monoxide
oxygen
carbon dioxide
tetrachloroethene (PCE)
trichloroethene (TCE)
hydrogen sulfide
benzene
methyl tert-butyl ether (MTBE)
0.001
0.001
0.034
0.06
0.10
0.10
0.18
1.70
    naphthalene
PCBs
hydrogen chloride
ammonia
methanol
ethanol
hydrogen peroxide
2.1
3.0
20
61
220
220
71000

R. Sander: Henry’s law constants ( http://www.mpch-mainz.mpg.de/~sander/res/henry.html)

For example, the table shows that MTBE will strip nearly 10 times faster than benzene and 17 times faster than TCE.

You can find past issues of our  "Environmental Enlightenment" at amiadini.com Wealth of information about environmental site assessments in the real estate transactions and issues concerning assessment and cleanup of contamination in the subsurface soil and groundwater.

Call me if you have any questions. There are no obligations.

Ami Adini
Ami Adini & Associates, Inc.
Environmental Consultants
Underground Storage Tank Experts
818-824-8102; 818-824-8112 fax
mail@amiadini.com
www.amiadini.com

Ami Adini is a mechanical engineer, California Registered Environmental Assessor, Level II (Exp.), and president of AMI ADINI & ASSOCIATES, INC. (AA&A), an environmental consulting firm specializing in all phases of environmental site assessments and rehabilitation of contaminated sites. AA&A specializes in practical solutions to environmental concerns using the highest standards of ethics and integrity while providing its clients with maximum return on their investments.