Environmental Engineering Reference
In-Depth Information
Contaminated water
Gas permeable membrane
Treate d
groundwater
Extracted VOC (e.g., 1,4-dioxane)
FIGURE 7.2 Overview of pervaporation process. [After Pintauro, P.N. and Jian, K., 1995, United States
Patent 5,387,378: Integral asymmetric l uoropolymer pervaporation membranes and method of making the
same. Assignee: Tulane University, New Orleans. http://www.patentstorm.us/patents/5387378-description.
html (accessed October 12, 2007).]
Much higher 1,4-dioxane l ux rates, on the order of 30-100 g/(m 2 h) and efi ciencies, with sepa-
ration factors two to three orders of magnitude higher, were achieved by using blended membranes
composed of chitosan and nylon 66 (Smitha et al., 2006). Proportions of these two components were
varied, and their tensile, mechanical, thermal, and molecular characteristics were evaluated with a
variety of 1,4-dioxane feed mixtures. Because this testing was performed at percent-level concen-
trations and the pervaporation method is generally used for separation of liquids in industrial manu-
facturing scenarios, it is not clear whether these materials would be effective at the part per billion
concentration levels and gallons per minute l ow rates typically being evaluated in groundwater
remediation programs.
7.1.4 S UMMARY
Some level of 1,4-dioxane removal from conventional ex situ air-stripping systems is achievable
under ideal circumstances, but in most cases, it is unlikely that this technology will achieve the
removal levels required. The ART In-Well technology—which maximizes air stripping—along
with several other physical, chemical, and biological processes has been shown to reduce 1,4-
dioxane levels from high concentrations, but the exact mechanism for the removal is not known.
Pervaporation has been demonstrated to be capable of separating 1,4-dioxane from water at high
percent levels at rates that may be applicable in some ex situ situations. It is not clear how effective
these latter two technologies would be at the lower concentration levels typically found at most
1,4-dioxane-contaminated sites.
7. 2 S O R P T I O N
The “sorption” process refers to a combination of chemical adsorption and physical absorption of a
contaminant to a “sorptive” medium. Some materials, like engineered resins, are specii cally used
for one process or the other (i.e., they are either “absorptive” or “adsorptive”), whereas other materi-
als, such as clays and activated carbons, can be used for both processes. Different chemicals often
have an afi nity for one process over another. Many types of sorptive media are used to remove
contaminants from groundwater, most commonly in tandem with a “pump-and-treat” system,
although some technologies can be applied in situ . For the typical ex situ system, the sorptive
 
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