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5.20 CHAPTER FIVE

FIGURE 5.10 Some common shapes of plastic packing. (Source: U.S. Environmental Protection Agency.)

Exhaust Emission Considerations. The emission of contaminated exhaust air from
packed column air stripping systems creates potential air quality problems. The transfer
of VOCs from water to air might be a concern depending on site or local regulations, type
of VOC, proximity to human habitation, exposure of treatment plant workers, local air
quality, local meteorological conditions, daily quantity of water to be processed, and the
contamination level. Also, sulfur compounds in the raw water can result in odor problems
in the vicinity of a packed column.
The emission rate must be evaluated in the context of applicable air quality regula-
tions and other site-specific factors. Air emission regulations are expressed in terms of
permissible emission rates (lb/day or lb/h) or projected ground level concentrations
(mg/m3). If the treatment plant's emission rate is unacceptable, the column or plant pro-
cess may be changed to bring the installation into compliance. Treatment options cur-
rently available to remove organics from off-gas include
• Packed column design modification
• Thermal incineration of the gas
• Catalytic incineration of the gas
• Ozone destruction
• Vapor-phase carbon adsorption
The least costly method of achieving compliance with air regulations is usually to mod-
ify the packed column design to dilute the emissions. Possible modifications include in-
creasing the tower height, airflow rate, and exhaust gas velocity. If these steps are insuf-
ficient to achieve compliance, a vapor-phase treatment component may be required.
Thermal incineration of packed column off-gas has the disadvantage of high energy
requirements. Catalytic incineration has lower temperature requirements but is currently