Groundwater treatment process

A continuous process for the extraction of halogenated hydrocarbons from a dilute, halogenated hydrocarbon-containing aqueous fluid, in high efficiency, while dramatically reducing the stripping medium requirement for the extraction and without substantially increasing the amount of halogenated hydrocarbons discharged to the atmosphere.

BACKGROUND 
This invention relates to a novel process for removing halogenated 
hydrocarbons from dilute, halogenated hydrocarbon-containing aqueous 
fluids. More particularly, this invention relates to a novel process for 
removing trace amounts of halogenated hydrocarbons, such as 
1,2-dichloroethane, 1,1-dichloroethane, 1,1,2,2-perchloroethylene, 
1,1,2-trichloroethane, ethylene dibromide, methylene bromide and the like 
from contaminated ground water. 
Methods for the removal of trace hydrocarbons from aqueous and vapor 
streams are extensive and vary widely. For example, U.S. Pat. No. 
4,495,056 teaches steam stripping, carbon adsorption, biological 
treatment, and activated sludge treatment to purify water. Beall, U.S. 
Pat. No. 4,517,094, teaches adsorption of organic contaminants on two 
media: (1) organoclay and (2) granulated carbon. Von Klock et al., U.S. 
Pat. No. 5,106,507, utilize a stripping gas and a bed of activated carbon 
to remove hydrocarbon contaminants. Miller, U.S. Pat. No. 4,892,664, 
provides a method for decontaminating water which is contaminated by small 
concentrations of dissolved volatile organic compounds, the method 
comprising introducing the contaminated water into an air stripping column 
wherein the contaminants are stripped with air, pretreating the organic 
compounds-carrying air in a preheater, and passing the heated air through 
a catalytic stage that oxidized the organic compounds. U.S. Pat. No. 
4,544,488 discloses the use of an induced draft air stripper and carbon 
adsorption bed to remove volatile organic chemical from water. 
Carberry, U.S. Pat. No. 4,846,934 and U.S. Pat. No. 4,966,654 discloses a 
system for removing hydrocarbon contaminants from groundwater and 
moisture-laden soil. The system of Carberry comprises a steam stripping 
tower which is operated at subatmospheric pressure, a series of condensers 
and separators, and finally a carbon adsorber to remove any remaining 
uncondensed hydrocarbon contaminants. 
Robbins, U.S. Pat. No. 4,236,973, utilizes a vapor such as air or steam to 
strip organic contaminants having a boiling point in excess of 200.degree. 
C. from pH adjusted water. Once stripped, the stripping vapor and organic 
contaminants can be passed into a scrubber wherein the vapor and 
contaminants are contacted with a stream of caustic or other material 
which preferentially absorbs the contaminants from the vapor. 
Robbins, U.S. Pat. No. 4,783,242, describes a distillation system for 
removing vaporizable components from an aqueous medium comprising: a 
distillation column using steam to vaporize the vaporizable components, a 
condenser means to condense at least a portion of the vapor from the 
distillation column, a separator means to separate vapor from a 
recirculated fluid in the separator means, and a thermal compressor means 
to remove vapors from the separator means and inject motive steam into the 
column. According to Robbins, the vaporizable components include 
trichloroethane, propylene chlorohydrin, bromine, methylene chloride, 
benzene, toluene, and mixtures thereof. 
McGill, U.S. Pat. No. 3,898,058, provides a process for removal of 
hydrocarbons by the application of a vacuum to a contacting vessel in 
which a contaminated water stream is caused to flow across packing 
material or trays for efficient gas removal. The removed hydrocarbon 
materials are then compressed, condensed and further separated to remove 
gaseous and/or liquid hydrocarbons from the system. 
While the foregoing provide a multitude of methods for removal of 
contaminants from groundwater, there continues to be a need for efficient, 
yet cost effective means for reducing groundwater contaminants while at 
the same time reducing the amount of contaminants discharged to the 
atmosphere. 
SUMMARY OF THE INVENTION 
This invention provides, inter alia, a process for the extraction of 
halogenated hydrocarbons from a dilute, halogenated hydrocarbon-containing 
aqueous fluid, in high efficiency, while dramatically reducing the 
stripping medium requirement for the extraction and without substantially 
increasing the amount of halogenated hydrocarbons discharged to the 
atmosphere. Remarkably, the purposes of this invention are accomplished 
without the need for a carbon adsorption system to remove trace 
halogenated organics from the stripping medium used to extract the 
halogenated hydrocarbons from the aqueous fluid. Thus, the purchase and/or 
regeneration of a carbon adsorption bed, or alternate means of adsorption, 
is avoided. 
Accordingly, in one embodiment, this invention provides a process for 
substantially reducing the amount of halogenated hydrocarbons in a dilute, 
halogenated hydrocarbon-containing aqueous fluid. The process comprises: 
(a) introducing dilute, halogenated hydrocarbon-containing aqueous fluid 
into an upper portion of an upright enclosed chamber; (b) introducing a 
stripping medium into a lower portion of the chamber whereby the stripping 
medium intimately contacts the dilute, halogenated hydrocarbon-containing 
aqueous fluid in a countercurrent manner; (c) removing halogenated 
hydrocarbon-depleted aqueous fluid from the lower portion of the chamber; 
(d) removing halogenated hydrocarbon rich vapor stream from the upper 
portion of the chamber; (e) condensing at least a portion of the 
halogenated hydrocarbon rich vapor stream thereby forming a halogenated 
hydrocarbon rich liquid; and (f) contacting a non-condensed portion of the 
halogenated hydrocarbon rich vapor stream with an absorbing fluid whereby 
the amount of halogenated hydrocarbons in the contacted non-condensed 
portion is reduced by at least about 85 wt. % based on the initial weight 
of halogenated hydrocarbons in the non-condensed portion. 
Not only does this invention provide a facile economic means for removal of 
hydrocarbons from dilute aqueous streams using a stripping medium, it also 
provides a means for removal of about 85 to about 99 wt. % or more of the 
hydrocarbons which may be present in the stripping medium prior to 
discharge of stripping medium to the atmosphere. Accordingly, the process 
of this invention may be used to reduce the level of hydrocarbons in 
groundwater without substantially increasing the amount of hydrocarbons 
discharged to the atmosphere.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a preferred embodiment, the process of this invention features an energy 
efficient continuous process for substantially reducing the amount of 
halogenated hydrocarbons in a dilute, halogenated hydrocarbon-containing 
aqueous fluid. The process comprises: (a) continuously introducing dilute, 
halogenated hydrocarbon-containing aqueous fluid into an upper portion of 
an upright, elongated, enclosed chamber containing contact packing 
material; (b) continuously introducing steam into a lower portion of the 
enclosed chamber below the contact packing whereby the steam contacts the 
dilute, halogenated hydrocarbon-containing aqueous fluid in a 
countercurrent manner within the enclosed chamber; (c) continuously 
removing halogenated hydrocarbon-depleted aqueous fluid from the lower 
portion of the enclosed chamber; (d) continuously removing a vapor stream 
containing halogenated hydrocarbon and steam from the upper portion of the 
enclosed chamber; (e) continuously condensing at least a portion of the 
halogenated hydrocarbon and steam in the vapor stream from the upper 
portion of the enclosed chamber thereby forming a halogenated 
hydrocarbon-rich liquid form; and (f) continuously contacting a 
non-condensed portion of the vapor stream from the upper portion of the 
enclosed chamber with an absorbing fluid whereby the amount of halogenated 
hydrocarbon in the vapor stream is substantially reduced. 
Accordingly, this invention utilizes conventional apparatus connected by 
conventional piping and conduits. However, the invention provides a novel 
combination of conventional apparatus which is utilized in a unique 
process to obtain unexpected results. 
For the purposes of this invention, the terms "dilute, halogenated 
hydrocarbon-containing aqueous fluid" and/or "contaminated ground water" 
define aqueous mediums containing an amount of halogenated hydrocarbon 
compound(s) within the range of from about 0.1 ppm to saturation at about 
9000 ppm or more. "Halogenated hydrocarbon-depleted aqueous fluid" as used 
herein means aqueous fluid in which the organic contaminants have been 
substantially reduced. 
In many areas of the United States, ground water may be contaminated by 
trace amounts of organic compounds. While this invention may be applicable 
to the removal of any organic contaminants from groundwater, it is 
particularly useful in removing halogenated hydrocarbons such as 
1,2-dichloroethane, 1,1-dichloroethane, 1,1,2,2-dichloroethylene, 
1,2-dichlorothylene, carbon tetrachloride, perchlorethylene, 
trichlorothylene, 1-1-dichloroethane, 1,1,2-trichloroethane, chloroform, 
1-chloro-2-bromopropane, 1,4-dichlorobutane, 1,2,3,4-tetrachlorobutane, 
1,1,1,2,2,2-hexachloroethane, 1,1,1,2-tetrachloroethane, 
1,1,2,2-tetrachloroethylene, hexachlorobutadiene, pentachlorobutadiene, 
tetrachlorobenzene, pentachlorobenzene, hexachlorobenzene, methylene 
bromide, ethylene dibromide, and the like. The amount of halogenated 
organic compounds in the ground water can vary widely with proximity to 
the originating source. Generally, the groundwater will contain less than 
1 wt. % organic contaminants and usually less than 9,000 ppm organic 
contaminants. 
Initially, halogenated hydrocarbon-containing aqueous fluid is desirably 
treated to remove any entrained solids and/or oily residue which may be 
present in the aqueous stream. Then the solids free dilute, halogenated 
hydrocarbon-containing aqueous fluid is introduced into the upper portion 
of an upright enclosed chamber. 
The enclosed chamber may be an empty vessel, however, it is highly 
preferred that the vessel contain packing material or distributor trays 
for providing intimate contact between the contaminated groundwater and 
the stripping medium. For purposes of this invention, the enclosed chamber 
containing packing material and/or distributor trays will be referred to 
hereinafter as a "stripping column". When packing material is used, it is 
highly desirable that the packing material be inert to halogenated 
hydrocarbons and stripping medium with which it comes in contact. Suitable 
packing material may consist of beads, saddles, pellets, rods, and the 
like which are formed from plastics, ceramic, metals, clays, silicas, or 
other inert materials, with ceramic saddles being particularly preferred. 
The stripping column desirably contains internal fluid distribution 
conduits located above and below the packed section. The stripping column 
may also contain a demister for reducing the carryover of entrained fluid 
out of the stripping column in the gas or vapor stream. The design of such 
a stripping column for contact between a stripping medium and the aqueous 
fluid is well within the skill of those in the art. Thus, any suitable 
upright stripping column may be used provided there is sufficient contact 
between the aqueous fluid and stripping medium to remove more than about 
85 weight percent of halogenated hydrocarbons from the aqueous fluid. 
In order to reduce the amount of halogenated hydrocarbons in the aqueous 
fluid, a stripping medium is introduced into the lower portion of the 
stripping column so that the stripping medium contacts the aqueous fluid 
in a countercurrent manner. Suitable stripping media include air, steam, 
carbon dioxide, argon, nitrogen, helium, and the like. It is particularly 
preferred to use steam when the contaminants are halogenated hydrocarbons 
since steam can be condensed thereby limiting the potential for 
atmospheric pollution. 
Once contacted, a halogenated hydrocarbon-rich vapor stream is removed from 
the upper portion of the stripping column and a halogenated 
hydrocarbon-depleted aqueous fluid is removed from the lower portion of 
the stripping column. It is preferred that the halogenated 
hydrocarbon-depleted fluid contain less than about 10 ppm of halogenated 
hydrocarbons, more preferably less than about 1 ppm halogenated 
hydrocarbons, and most preferably from about 0.01 to about 0.2 ppm 
halogenated hydrocarbons or lower, depending on the volume of the 
halogenated hydrocarbon-depleted fluid removed from the lower portion of 
the stripping column. 
The halogenated hydrocarbon rich vapor stream exiting the upper portion of 
the stripping column is then fed to a condenser whereby at least a portion 
of the halogenated hydrocarbon rich vapor stream is condensed thereby 
forming an aqueous phase, an organic phase, and a non-condensed portion. 
The aqueous phase may still contain a low level of halogenated hydrocarbon 
due to the solubility of halogenated hydrocarbons in water. Hence, this 
aqueous phase is typically recycled to the stripping column for further 
removal of contaminants. The organic phase will contain a substantial 
amount of halogenated hydrocarbons which are removed from the dilute, 
halogenated hydrocarbon-containing aqueous fluid. This organic stream may 
be collected and sold, burned, or otherwise disposed of. 
The non-condensed portion of the halogenated hydrocarbon-rich vapor stream 
is then fed to a second enclosed chamber whereby it is contacted with an 
absorbing fluid in a countercurrent manner thereby removing halogenated 
hydrocarbons from the non-condensed portion. Thus, the discharge to the 
atmosphere from the second enclosed chamber is essentially free of 
halogenated hydrocarbons. By the term "essentially free" is meant that 
more than about 85 wt. %; more preferably, more than about 95 wt. %; and 
most preferably, more than about 99 wt. % of the halogenated hydrocarbons 
initially present in the non-condensed portion are removed by the absorber 
fluid. Accordingly, there is little need to utilize subsequent adsorption 
means such as carbon adsorption or activated clays for removal of 
halogenated hydrocarbons which may be present in the non-condensed 
portion. In a particularly preferred embodiment, the absorber fluid is 
collected from the bottom portion of the second enclosed chamber and fed 
to the stripping column for removal of halogenated hydrocarbons from the 
absorber fluid. 
The absorber fluid is typically an aqueous fluid which may contain a low 
level of halogenated hydrocarbons. By "low level" is meant less than about 
100 ppm, most preferably about 50 ppm or less halogenated hydrocarbons. 
When the absorber fluid is pure water, e.g. water containing undetectable 
limits of halogenated hydrocarbons, the discharge of halogenated 
hydrocarbons to the atmosphere from the second enclosed chamber may be 
essentially zero, i.e. the level of halogenated hydrocarbons remaining in 
the non-condensed portion exiting the upper portion of the second enclosed 
chamber is undetectable by conventional means such as gas chromatographic 
analysis, infrared spectroscopy, nuclear magnetic resonance and the like. 
In yet another embodiment, the vents from storage tanks containing 
halogenated hydrocarbons, or dilute, halogenated hydrocarbon-containing 
aqueous fluids, may also be fed to the second enclosed chamber before 
discharge of the tank vents to the atmosphere. Such storage tank vents may 
contain halogenated hydrocarbon vapors depending on the concentration of 
halogenated hydrocarbons in the stored fluids, their vapor pressure, and 
the temperature of the storage tanks. In some cases, such as when the 
storage tanks are located at a distance from the second chamber, a third 
chamber may be used in series or parallel with the second chamber for 
absorbing hydrocarbons from the tanks' vent stream. 
In a particularly preferred embodiment, the stripping column for contact of 
the stripping medium and dilute, halogenated hydrocarbon-containing 
aqueous fluid is operated under subatmospheric pressure. Preferably the 
pressure of the stripping column is in the range of from about 1 mm Hg to 
about 600 mm Hg, and most preferably, from about 20 mm Hg to about 200 mm 
Hg. The optimum reduced pressure within the stripping column is that 
pressure which is sufficient to effectively strip a major portion of the 
halogenated hydrocarbons from the aqueous fluid at the desired 
temperature. In general, a reduced pressure of about 40 mm Hg to about 160 
mm Hg and more often from about 60 mm Hg to about 120 mm Hg gives good 
results. 
The halogenated hydrocarbon-containing aqueous fluid fed to the stripping 
column is typically operated at ambient temperature. In general, the 
temperature of the halogenated hydrocarbon-containing aqueous fluid 
obtained from containment wells is in the range of 0.degree. to 40.degree. 
C. It is highly preferred that the absorber fluid used in the second 
enclosed chamber be as cool as practical. Typically the operating 
temperature of the second enclosed chamber ranges from about 20.degree. to 
about 30.degree. C. for groundwater absorber fluids. 
The present invention stripping column, which is operated under 
subatmospheric conditions, can be constructed of any material which can 
withstand the subatmospheric conditions without collapsing and which is 
not adversely affected by contact with halogenated compounds, organic or 
inorganic. Such materials as metals or metal alloys (e.g. titanium, 
tantalum, carbon steel, and nickel alloys), carbon steel lined with acid 
brick, rubber, thermoplastic and the like are suitable. Especially useful 
materials of construction are carbon steel or reinforced plastics such as 
fiberglass reinforced plastics (e.g., fiberglass reinforced polyester) and 
carbon fiber reinforced plastics (e.g., graphite fiber reinforced 
polyester). These materials should be rated to withstand full service 
vacuum at temperatures up to 120.degree. C. for short periods of time. 
However, in normal operations, operating temperatures will typically be 
about 30.degree. C. or lower with an operating pressure near 40 mm Hg. In 
the most preferred embodiment, carbon steel is the material of choice for 
subatmospheric pressure operation. 
DETAILED DESCRIPTION OF THE DRAWINGS 
Having described the process of the invention, reference is now made to 
FIG. 1. Dilute, halogenated hydrocarbon-containing aqueous fluid 2 is fed 
to the upper portion of stripping column 10 which preferably contains 
contact packing. Stripping medium 6 is fed to the lower portion of 
stripping column 10 whereby it contacts aqueous fluid 2 in a 
counter-current manner in the contact packing. It is particularly 
desirable to feed aqueous fluid 2 into the stripping column at a point 
above the contact packing, and to feed the stripping medium 6 into the 
stripping column at a point below the contact packing. 
Halogenated hydrocarbon-depleted aqueous fluid 8 is removed from the bottom 
portion of stripping column 10 whereby it may be disposed of as a 
non-hazardous stream. In the preferred embodiment, aqueous fluid 8 is at a 
temperature which avoids thermal pollution, e.g. in the range 20.degree. 
C. to 50.degree. C. Halogenated hydrocarbon rich vapor 16 is removed from 
the top portion of stripping column 10 by vacuum forming device 26 (which 
device may be a vacuum pump, direct contact condenser and vacuum pump, or 
steam jet ejector) which provides a subatmospheric pressure in stripping 
column 10. The discharge stream 28 from vacuum forming device 26 is fed to 
condenser 30 which cools the halogenated hydrocarbon rich vapor stream 
sufficiently to allow formation of cooled stream 32 containing an aqueous 
phase, an organic phase, and a non-condensed portion. The coolant for 
condenser 30 may be selected from a wide range of materials which can 
provide sufficient cooling of discharge stream 28 so that a condensed 
portion of stream 28 is formed. Such fluids may include stream 24, 
described below, which is the discharge liquid stream from absorbing 
column 36. 
Cooled stream 32 is fed to phase separator 12 wherein halogenated 
hydrocarbon organic stream 14 is separated from aqueous stream 4 
containing a minor amount of halogenated hydrocarbons and a 
non-condensable vapor stream 18 containing a minor amount of halogenated 
hydrocarbons and stripping medium. By "minor amount" is meant less than 
about 40 wt. % of the total weight of the vapor and liquid stream 32. 
Non-condensable vapor stream 18 is then fed to the bottom portion of second 
enclosed chamber 36 wherein it is contacted in a countercurrent manner 
with absorber fluid 22 which may be pure water or an aqueous source having 
a low level of halogenated hydrocarbon contaminants such as halogenated 
hydrocarbon-depleted stream 8 which is fed to the upper portion of second 
enclosed chamber 36. In a preferred embodiment, various storage tank vent 
streams 20 containing halogenated hydrocarbon vapors may also be fed to 
the lower portion of second enclosed chamber 36 for removal of trace 
amounts of halogenated hydrocarbons. Stream 34 exiting the top portion of 
second enclosed chamber 36 is essentially free of halogenated hydrocarbons 
and may be safely vented to the atmosphere. Liquid stream 24 exiting the 
bottom portion of second enclosed chamber 36 contains halogenated 
hydrocarbons and therefore it is preferably treated for removal of 
halogenated hydrocarbons by recycle to stripping column 10. Since liquid 
stream 24 is typically cooler than stream 28 exiting vacuum forming device 
26, it may be practical to utilize stream 24 to condense at least a 
portion of the halogenated hydrocarbon rich vapor stream 28 in condenser 
30. 
In order to further illustrate the invention, the following example is 
given. This example should not be construed as limiting the invention in 
any way. 
EXAMPLE 
Contaminated groundwater (170 liters per minute at 4.degree.-32.degree. C. 
and containing 1000 ppm of halogenated hydrocarbons principally 
1,2-ethylene dichloride) is fed into the upper portion of stripping column 
10 containing contact packing. Steam (45 to 365 kilograms per hour) is fed 
into the lower portion of stripping column 10 below the contact packing. 
Stream 8 exiting the bottom of stripping column 10 contains 0.05 ppm 
halogenated hydrocarbons at a flow rate of 360 liters per minute. Exiting 
the top of stripping column 10 is a halogenated hydrocarbon rich vapor 
stream 16 containing 12 kilograms of halogenated hydrocarbons and 48 
kilograms of steam which is fed to vacuum pump 26 and partial condenser 
30. Cooled stream 32 exiting partial condenser 30 contains 3.4 liters per 
minute mixed aqueous phase and organic phase, and 1.13 cubic meters per 
minute non-condensable phase which are then fed to phase separator 12 
wherein 3.37 liters per minute organic phase containing 98 wt % 
halogenated organics is removed. The aqueous stream 4 (0.4 liters per 
minute containing 9000 ppm halogenated organics is recycled to stripping 
column 10. Non-condensable stream 18 containing 1360 grams per hour of air 
and 454 grams per hour of halogenated hydrocarbons is fed to second 
enclosed chamber 36 wherein it is contacted with 189 liters per minute of 
water containing 50 ppm of halogenated hydrocarbons. Also entering the 
bottom of the second enclosed chamber 36 is 250 grams per hour of 
halogenated hydrocarbons and 4.5 kilograms per hour of air from various 
storage tank vent streams. Exiting the bottom of second enclosed chamber 
36 is liquid stream 24 (189 liters per minute) containing 112.5 ppm 
halogenated hydrocarbons. Exiting the top of second enclosed chamber 36 is 
vapor stream 34 containing about 5 grams per hour of halogenated 
hydrocarbons. If pure water is used as the absorber fluid 22, vapor stream 
34 exiting the top of scrubbing column 36 contains no detectible amount of 
halogenated hydrocarbons. The stripping column 10 is operated at about 
30.degree. C. and 31 mm Hg, and the second enclosed chamber 36 is operated 
at about 21.degree. to 24.degree. C. and 760 mm Hg. 
The process is very energy efficient in light of the fact that the amount 
of steam required to operate the process at subatmospheric pressure is 
much less than that which would be required to operate the same process at 
atmospheric pressure because of the reduced equilibrium temperature of the 
dilute, halogenated hydrocarbon-containing fluid at the reduced pressure. 
Accordingly, the present process and apparatus provides a means of 
conserving energy when recovering halogenated hydrocarbon from dilute, 
halogenated hydrocarbon-containing aqueous fluids. 
Variations of the invention are within the spirit and scope of the appended 
claims.