Stripping Volatile Organic Compounds and
Petroleum Hydrocarbons From
Water by Tray Aeration
DAVID F. LABRANCHE AND M. ROBIN COLLINS
taminants that have a wide range of physical and
INTRODUCTION
thermodynamic properties.
Contaminated groundwater is perhaps the
most ubiquitous target of hazardous waste
Remediation options
remediation efforts in the United States. Volatile
Currently, the most promising and preferred
organic chemicals (VOCs) and petroleum prod-
method for fully remediating VOCs and petro-
ucts have been consistently identified as the most
leum hydrocarbons from groundwater is bio-
common groundwater contaminants, particularly
remediation (Rose 1994). Bioremediation schemes,
at Department of Defense sites. As of September
however, operate most efficiently when the con-
1991, the Department of Defense (DOD) had iden-
centration in the water of the most common VOCs
tified 17,660 sites with potential hazardous waste
and petroleum hydrocarbons (the biological sub-
contamination of soil or groundwater (Rose 1994).
strate) is relatively dilute. The common VOC and
Of these, the DOD estimates that 7,313 sites will
petroleum contaminants are only slightly to mod-
require remediation. According to a 1992 General
erately biodegradable, having optimal BOD5/
Accounting Office (GAO), the federal government
COD ratios <0.40 (U.S. EPA 1985). High concen-
trations (≤1/3rd of solubility values) of VOCs in
faces nearly 0 billion in cleanup costs for DOD
and Department of Energy (DOE) sites before the
water are easily reduced by many methods. The
end of the decade. Effective and efficient treat-
cost-effective method chosen most often is to
ment methods are needed to meet this cleanup
pump the VOC contaminated groundwater to the
challenge (U.S. GAO 1992).
surface then transfer the contaminants to a solid
Because of the highly mechanized nature of
phase adsorber by air stripping. Recent research
DOD operations, VOCs and a wide variety of
indicates that high concentrations of petroleum
petroleum fuels are used and stored in large quan-
hydrocarbons in groundwater can also be effec-
tities at nearly every installation. The most preva-
tively reduced by pumping followed by above-
lent VOC groundwater contaminants at DOD sites
ground treatments such as solid-phase adsorp-
are chlorinated solvents (Rose 1994), which are
tion (Borden and Kao 1992). The dominant
generally denser than water and only slightly
hydrocarbons that make up gasoline, i.e., ben-
soluble. The most prevalent petroleum contami-
zene, toluene, ethylbenzene and the xylenes
nants at DOD sites are gasoline (including avia-
(BTEX), are aromatics, which are highly volatile
and amenable to air stripping due to their high
tion fuel) and diesel fuel, both of which are lighter
Henry's law constants (API 1983). However, the
than water and insoluble (U.S. EPA 1990). Experi-
dominant hydrocarbons found in diesel fuel are
ence at numerous groundwater remediation sites
paraffins (API 1976). These hydrocarbons are
has shown that despite the density differences
much less volatile than BTEX, having large mol-
between VOCs and petroleum hydrocarbons, they
ecules with molecular weights ranging from 142.3
are frequently found mixed in the aquifer due to
(decane) to 394.8 (octacosane). Long-chain hydro-
sorption to soils and water table fluctuations.
carbons (paraffins and larger) are nearly insoluble
Treatment processes employed to remediate the
in water and typically exist in both a soluble and
groundwater must be capable of handling con-
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