United States
Environmental Protection
Agency
Office of
Research and Development
Cincinnati, OH 45268
EPA/540/R-95/511a
August 1995
SEPA
Abstract
The U.S. Environmental Protection Agency (EPA) has
focused on policy, technical, and informational issues
related to exploring and applying new technologies to
Superfund site remediation. One EPA initiative to
accelerate the development, demonstration, and use of
innovative technologies for site remediation is the
Superfund Innovative Technology Evaluation (SITE)
Program.
EPA SITE technology capsules summarize the latest
information available on selected innovative treatment
and site remediation technologies. The capsules assist
EPA remedial project managers, EPA on-scene
coordinators, contractors, and other remedial managers
in the evaluation of site-specific chemical and physical
characteristics to determine a technology's applicability
for site remediation.
This capsule contains information on the cross-flow
pervaporation technology developed by ZENON
Environmental, Inc. (ZENON). The technology is designed
to remove volatile organic compounds (VOC) from
aqueous media. In early 1995, a full-scale ZENON system
was evaluated at a former disposal area on Naval Air
Station North Isjand (NASNI) in Coronado, California.
Groundwater at the site is contaminated with
trichloroethene (TCE) and other organic compounds.
Results of the demonstration are summarized in the
Performance Data section of this capsule. Results from
a 1993 pilot-scale SITE demonstration of the technology
in Burlington, Ontario, Canada, are also summarized in
the Performance Data section.
Introduction
The ZENON pervaporation technology is a membrane-
based process that removes VOCs from aqueous
matrices. The ZENON cross-flow pervaporation
technology uses an organophilic membrane made of
nonporous silicone rubber, which is permeable to organic
compounds but highly resistant to degradation. The
composition of the membrane causes organics in solution
to adsorb to it; the organics then diffuse through the
membrane by a vacuum and condense into a highly
concentrated liquid called permeate. The permeate
separates into aqueous and organic phases. The organic
phase can either be disposed of or sent off site for further
processing to recover the organics. The aqueous phase
is sent back to the pervaporation unit for retreatment.
The ZENON technology effectively removes organic
contamination from groundwater and other aqueous
waste streams. The technology is not practical for
reducing VOC concentrations to most regulatory limits,
notably drinking water standards. It is best suited for
reducing high concentrations of VOCs to levels that can
be reduced further and more economically by
conventional treatment technologies, such as carbon
/TV
u£& Printed on Recycled Paper
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
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adsorption. According to the developer, once the ZENON
technology is installed and equilibrated, it requires
minimal support from on-site personnel.
The full-scale SITE demonstration of the ZENON
technology took place at a former disposal area referred
to as Site 9, on NASNI in Coronado, California. The
demonstration was performed as a cooperative effort by
EPA, the U.S. Navy, ZENON, and Canadian
environmental agencies. Site 9 groundwater is
contaminated with VOCs, primarily TCE. The purpose
of the demonstration was to (1 ) evaluate the technology's
removal efficiency for TCE concentrations in groundwater,
and (2) determine if TCE concentrations could be reduced
to the federal maximum contaminant level (MCL) for TCE
of 5 micrograms per liter
The demonstration results showed that the ZENON
system removed TCE from groundwater by an average
of 97.3 percent. Sixteen of 18 comparisons of treated
water samples to untreated samples showed average
TCE removal efficiencies of 99.3 percent. However, the
average TCE concentration in the treated water was
approximately 1 ,380 jug/L, which did not meet the federal
MCL.
The ZENON cross-flow pervaporation technology was
also evaluated based on the nine criteria used for decision
making in the Superfund feasibility study (FS) process.
Table 1 presents the results of the evaluation.
Technology Description
The ZENON pervaporation technology involves modules
containing dense polymeric membranes. Each
membrane consists of a nonporous organophilic polymer,
similar to silicone rubber, formed into capillary fibers
measuring less than 1 millimeter in diameter. Silicone
rubber exhibits high selectivity toward organic compounds
and is highly resistant to degradation. The capillary fibers
are aligned in parallel on a plane and spaced slightly
apart. This arrangement of capillary fibers forms one
membrane layer.
Separate membrane layers are aligned in series, as
shown in Figure 1 , with the interior of the capillary fibers
exposed to a vacuum (about 1 pound per square inch
absolute). The number of membranes used in a particular
system depends on expected flow rates, contaminant
concentrations in the untreated water, and target
concentrations for contaminants in the treated water.
Process temperatures may be elevated to improve
treatment; however, temperatures are kept at or below
165°F (75 °C).
The organophilic composition of the membrane causes
organics to adsorb into the capillary fibers. The organics
migrate to the interior of the capillary fibers and are then
extracted from the membrane by the vacuum.
Figure 2 displays a schematic diagram of the ZENON
cross-flow pervaporation system in a typical field
application. Contaminated water is pumped from an
equalization tank through a 200-micron prefilter to remove
debris and silt particles, and then into a heat exchanger
that raises the water temperature to about 165 °F (75 °C).
The heated contaminated water then flows into the
pervaporation module. Organics and small amounts of
water are extracted from the contaminated water, and
treated water exits the pervaporation module and is
discharged from the system.
The extracted organics and small amount of water is
called permeate. As the permeate exits the membranes,
it is drawn into a condenser by the vacuum, where the
organics and any water vapor are condensed. Because
emissions are vented from the system downstream of
the condenser, organics are kept in solution, thus
minimizing air releases.
The condensed permeate contains highly concentrated
organic compounds and has a significantly reduced
volume compared to the untreated water. Because of
this high concentration, the liquid permeate generally
separates into aqueous and organic phases, rendering
the organic fraction potentially recoverable. The organic
phase permeate is pumped from the condenser to
storage, while aqueous phase permeate can either be
returned to the pervaporation module for further treatment
or removed for disposal.
Technology Applicability
The ZENON cross-flow pervaporation technology
removes VOCs from aqueous matrices, such as
groundwater, wastewaters, and leachate. The technology
can treat a variety of concentrations; however, it is best
suited for reducing high concentrations of VOCs to levels
that can be reduced further and more economically by
conventional treatment technologies, such as carbon
adsorption. The technology can also remove a number
of semivolatile organic compounds (SVOC) and
petroleum hydrocarbons. Both the pilot-scale and
full-scale demonstrations have evaluated the ZENON
technology's treatment of contaminated groundwater.
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Table 1: Evaluation Criteria for the ZENON Technology
CRITERION
1 Overall Protection of
Human Health and the
Environment
ZENON TECHNOLOGY PERFORMANCE
Provides short- and long-term protection by reducing
contaminants in water. Can be part of a pump-and-treat system
to prevent further groundwater contamination and off-site
migration. Worker protection is required when handling
concentrated permeate.
2 Compliance with Federal ARARs
3 Long-Term Effectiveness
and Performance
Requires compliance with National Pollutant Discharge
Elimination System (NPDES) and Safe Drinking Water Act
(SDWA) limitations for discharge. Storage of concentrated
permeate requires compliance with Resource Conservation and
Recovery Act (RCRA) hazardous waste storage requirements.
Emission controls are needed to ensure compliance with air
quality standards.
Effectively removes groundwater contaminants. Involves
disposal of some residuals (wastewater and permeate).
4 Reduction of Toxicity,
Mobility, or Volume
Through Treatment
5 Short-Term Effectiveness
Reduces the toxicity of groundwater by the removal of
contaminants.
Contaminants are removed upon completion of treatment.
Presents potential short-term risks to workers from moving and
handling of concentrated permeate.
6 Implementability
Easy to implement and transport. Requires minimal site
preparation and utilities, and minimal operational support.
7 Cost
ZENON estimates treatment costs from $2.00 to $4.00 per 1000
gallons of contaminated water.
8 Community Acceptance
The small risk to the community and permanent removal of
contaminants make public acceptance of this technology likely.
9 State Acceptance
If remediation is conducted as part of RCRA corrective actions,
state regulatory agencies may require permits.
Notes:
a Applicable or relevant and appropriate requirements
b Actual cost of a remediation technology is highly specific and dependent on the original and target cleanup levels,
contaminant concentrations, groundwater characteristics, and volume of water.
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—VOCs —
To Condenser
Figure 1: ZENON Cross-Flow Pervaporation Module
A full-scale ZENON pervaporation system is easily
transportable and can fit in a small semi-trailer. It is a
stand-alone technology but can be used in series with
other conventional technologies such as soil washing,
carbon adsorption, or flocculation with solids removal.
Contaminated aqueous media can be pumped directly
to the pervaporation module; however, it is recommended
that water be equalized in a bulk tank before entering the
system. Depending on local pretreatment standards,
treated water exiting the ZENON system may be
discharged to a publicly owned treatment works (POTW).
To comply with NPDES or SDWA limitations, further
treatment with a separate technology is usually required.
Pervaporation provides an alternative approach to treating
organic-contaminated water at sites where conventional
air stripping or carbon adsorption are currently used.
Unlike air stripping, pervaporation releases low amounts
of VOCs to the outside air. Also, the pervaporation
membranes do not require replacement and disposal,
unlike activated carbon. Because contaminants pass
through the membrane, it can be used for an extensive
period of time (years) before degradation requires
replacement.
Technology Limitations
As noted previously, the prefilter prevents solids from
reaching the pervaporation module and inhibiting the
movement of organics through the membrane. Solids
can clog the prefilter, requiring it to be cleaned frequently.
Influent with a high alkalinity or high amounts of calcium
or iron can cause scaling of the system. In these cases,
anti-scalents can be added to the untreated water as a
preventive measure.
The ZENON technology does not remove inorganic
contamination and can only remove a limited number of
SVOCs and petroleum hydrocarbons. Dissolved heavy
metals in groundwater have not adversely affected the
treatment ability of the technology.
VOCs with water solubilities of less than 2 percent are
generally suited for removal by pervaporation. Highly
soluble organics, such as alcohols, are not effectively
removed by a single-stage pervaporation process. Also,
low-boiling VOCs, such as vinyl chloride, tend to remain
in the vapor phase after moving through the condenser.
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Contaminated
Water ~
-CH>
Carbon Filter
o->
Carbon Filter
"Tank Air Vent
D Carbon Filter
Egualization
Tank
PERVAPORATION MODULE
Prefilter
Heat
Exchanger
Feed Pump
Treated ^
Water Carbon Filters
Permeate
To
Discharge L
Vacuum Pump and
K-Q-
Water and
Organics For Recycle,
Disposal, or
Further Treatment
Figure 2: ZENON Cross-Flow Pervaporation System
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For elevated concentrations of most low-boiling VOCs, a
carbon filter placed on the vacuum vent ensures that
contaminants are not released to the outside air.
The system has proven effective in reducing VOC
concentrations in groundwater to near MCLs. However,
lowering concentrations to below MCLs may require
multiple passes through the pervaporation module, which
can prove impractical when compared to other
technologies, such as carbon adsorption. Water
containing high concentrations of contaminants, including
light nonaqueous phase liquids (LNAPL) and dense
nonaqueous phase liquids (DNAPL), also require multiple
passes through the module. To decrease the number of
passes, LNAPLs and DNAPLs should be removed from
water before it enters the system.
Water quality standards normally will riot allow water
exiting the ZENON system to be discharged directly into
surface water bodies. Depending on local standards,
treated water may be acceptable for discharge to a local
POTW. During the demonstration at NASNI, treated water
required additional treatment through a series of two 1,000-
pound carbon filters for polishing. VOC concentrations
were then monitored with an on-site gas chromatograph
(GC), and the water was discharged to the sanitary sewer.
The ZENON system tested at NASNI could achieve a
maximum flow rate of 11 gallons per minute (gpm), which
is the largest capacity of the technology to date. Sites
requiring treatment at higher flow rates will require multiple
systems or additional pervaporation modules.
Process Residuals
The ZENON system generates two waste streams:
treated water and concentrated permeate. As noted
above, treated water may require further treatment to
meet local or site-specific discharge requirements.
Permeate usually separates into an organic and an
aqueous phase. The organic phase permeate is pumped
from the condenser to storage, while aqueous phase
permeate can either be returned to the pervaporation
module for further treatment or removed for disposal.
During the NASNI demonstration, the system treated
about 65,000 gallons of contaminated groundwater
producing about four 55-gallon drums of permeate. The
aqueous permeate was pumped from the drums through
the 1,000-pound carbon filters and discharged to the
sanitary sewer. The organic permeate was transferred
to one 55-gallon drum which was sent to a treatment
facility for incineration.
Depending on the application and local regulations,
personal protective equipment, along with field laboratory
waste, may require disposal at a licensed disposal facility.
Site Requirements
Because a full-scale ZENON cross-flow pervaporation
system is shipped to sites in a semi-trailer, access roads
at treatment sites are necessary. The ZENON system is
mounted in a steel enclosure measuring about 12 by
7 by 7 feet. The enclosure is slightly elevated from the
ground, allowing it to be moved with a large forklift or a
small crane. The enclosure must be placed on a hard
surface, preferably an asphalt or concrete pad, although
packed soil will support it.
The ZENON system requires utility hook-ups for electricity
and water. A full-scale ZENON system capable of
11 gpm requires 460-volt, 3-phase, 15-ampere service.
During shakedown, clean water is necessary to verify
that all components are operating correctly before
contaminated water enters the system. Clean water is
also needed for decontaminating process equipment and
for health and safety. Permeate must be stored in drums
or bulk tanks, which under RCRA regulations, requires
secondary containment and possibly permits. A
receptacle for treated water, such as bulk tanks or sewer
lines, is also necessary. A small office trailer and a
telephone are recommended for moderate- to long-term
operations.
Performance Data
The ZENON cross-flow pervaporation technology has
been demonstrated under the SITE Program at the pilot-
scale and full-scale levels. The objectives of both
demonstrations were to determine the technology's ability
to remove VOCs from contaminated groundwater and to
determine the percent removal for each contaminant of
concern. Results for each demonstration are summarized
in the following sections.
Pilot-Scale Demonstration
The pilot-scale demonstration of the ZENON technology
was performed in October 1993, at a small site just south
of Burlington, Ontario, containing groundwater
contaminated with petroleum hydrocarbons. Benzene,
ethylbenzene, toluene, and total xylenes (BTEX) were
the critical contaminants. Demonstration objectives were
achieved by collecting untreated and treated water eight
times over an 8-hour period, while the system operated
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at a flow rate of 0.2 gpm. The system was equipped with
a small carbon filter to minimize releases of VOCs from
the vacuum vent of the system to the surrounding air. A
photoionization detector was used to monitor the air
released from the vacuum vent.
Analytical results indicated that BTEX concentrations
were significantly reduced in treated groundwater
samples compared to untreated samples (see Table 2).
Removal efficiencies averaged 98 percent. No VOC
releases from the vacuum vent after carbon filtration were
detected during the pilot-scale demonstration.
Full-Scale Demonstration
The full-scale demonstration of the ZENON technology
was performed during February 1995, at a former waste
disposal area at NASNI, referred to as Site 9. Site 9 was
used for over 40 years as a disposal area for a wide range
of wastes; however, organics are the primary groundwater
contaminants. TCE was selected as the contaminant of
concern for the demonstration because of its
identification, through groundwater sampling, as the
primary contaminant at Site 9, at varying concentrations
among monitoring wells.
During the initial stages of the demonstration,
groundwater was pumped from a series of existing
monitoring wells at the site to two 21,000-gallon steel
bulk tanks for equalization. Rust particles from the interior
of the tanks caused the prefilter to easily clog, requiring
frequent cleanings. The particles also caused fouling
and scaling problems with the pervaporation module,
reducing its treatment efficiency. Eventually, groundwater
was pumped directly from the monitoring wells to the
system; however, because of high calcium bicarbonate
concentrations in the groundwater, scaling of the
pervaporation module continued. After attempts with a
variety of chemicals, ZENON settled with an anti-scalent
similar to zinc phosphate, which proved fairly effective.
TCE influent concentrations were varied by altering the
flow rates into the system from the selected wells.
Demonstration objectives were achieved by collecting
samples of untreated and treated groundwater over five
8-hour sampling runs; air samples were collected directly
from the vacuum vent of the system before and after a
carbon filter. Flow rates of the system ranged from 2 to
11 gpm; influent TCE concentrations ranged from 33 to
240 milligrams per liter (mg/L). After the third run,
sampling was delayed to allow cleaning of the
pervaporation module. Sampling ended after 4 hours
into the fifth run because of a corroded stainless steel
tube on the pervaporation module.
Table 3 presents analytical results for groundwater.
Removal efficiencies for TCE averaged about
97.3 percent. The highest levels of contaminant removal
were achieved when the system operated at a flow rate
of about 5.5 gpm with an influent concentration of about
230 mg/L of TCE. Removal efficiencies were lowest when
the system operated at about 2 gpm with an influent
concentration of about 40 mg/L of TCE. Although the
system significantly reduced TCE concentrations in the
groundwater to an average of 1.37 mg/L (1,370 (JQ/L),
the federal MCL of 5 /L/g/L was not achieved.
VOC releases from the vacuum vent of the system ranged
from 2,500 milligrams per cubic meter (mg/m3) to 21,000
mg/m3. The data indicate that VOC releases from the
vent increased with higher VOC influent concentrations;
varying flow rates appeared to have little affect on air
releases. Analytical results for air released from the
vacuum vent of the system are shown in Table 4. Samples
were also taken from the vent after air was allowed to
pass through a 55-gallon carbon filter. Analytical results
indicate that the carbon was 99.9 percent effective in
removing the VOCs.
Technology Status
The SITE demonstration at NASNI represents the first
full-scale use of the ZENON cross-flow pervaporation
technology. As noted, the full-scale system is portable
and requires minimal site preparation. Multiple
pervaporation modules can be added to the system to
accommodate a variety of sites. The technology is best
suited for reducing high concentrations of VOCs to levels
that can be reduced further and more economically by
conventional treatment technologies. The technology
provides an alternative approach to treating
organic-contaminated water at sites where conventional
treatment technologies are used, such as air stripping or
carbon adsorption.
Disclaimer
The data presented in this technology capsule have
passed internal laboratory quality assurance checks but
have not been reviewed by EPA Risk Reduction
Engineering Laboratory Quality Assurance personnel.
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Table 2: BTEX Concentrations in water
Sample
Number Untreated
Concentration
(pg/L)
1 700
1D 720
2 340
3 360
4 360
5 700
6 370
7 370
8 650
Average 509
Benzene
Treated
Concentration
(M9fl-)
11
6
11
11
7
9
8
10
8
9
Percent
Removal
98%
99%
97%
g"?o/
98%
99%
98%
97%
99%
98%
Untreated
Concentration
(M9/L)
150
150
110
110
110
130
120
130
120
113
Ethylbenzene
Treated
Concentration
(M9/L)
2
1
3
2
2
2
2
2
2
2
Percent
Removal
99%
99%
97%
98%
98%
99%
98%
99%
98%
98%
Untreated
Concentration
(M9/L)
490
500
260
280
27Q
450
290
290
400
358
Toluene
Treated
Concentration
(M9/L)
6
4
7
6
4
5
5
6
5
5
Percent
Removal
99%
99%
97%
98%
99%
99%
98%
98%
99%
98%
Untreated
Concentration
(H9/L)
820
840
570
630
650
800
670
700
700
709
Total Xylenes
Treated
Concentration
(pg/L)
13
8
14
12
9
11
11
12
11
11
Percent
Removal
98%
99%
98%
98%
99%
99%
98%
98%
98%
98%
Note:
D Duplicate sample
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Table 3: TCE Concentrations in water
4 verage
Total Average Percent Removal
Untreated Concentration
(mg/L)
40
43
33
42
40
41
44
48
48
42
33
35
38
37
36
220
220
240
240
230
130
120
125
Treated Concentration
(mg/L)
0.17
1.0
3.8
11
3.9
ND"
0.09
0.16
0.19
0.11
0.32
0.27
0.22
0.24
0.26
0.45
0.40
0.51
0.46
0.46
2.7
2.7
2.7
Percent Removal
99.5%
97.7%
88.5%
733%
89.9%
>993%
993%
99.7%
99.6%
99.8%
99.0%
992%
99.4%
99.4%
993%
993%
993%
993%
993%
993%
973%
973%
97.9%
97.3%
Notes:
a A sampling run is defined as one 8-hour period at a given flow rate.
b Not detected.
c Sampling run was abbreviated due to system failure.
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Table 4: TCE Concentrations in Air
Average
Groundwater TCE Untreated Treated
Run Concentration Flow Rate Grab Concentration Concentration *> Percent
Number (mg/L) (gpm) Number (mg/m>) (mg/m>) Removal
1a 40 2.10-2.15 1 6,100 0.02
2 5,500 0.05
2 42 5.16-5.21 1 3,700 0.02
2 2,500 ND<=
3 36 1 7,300 ND
2 7,200 ND
4 230 546 1 18,000 0.17
2 20,000 0.01
5d 125 11.18-11.23 1 21,000 0.71
Average 95 10,100 0.11
99.9%
99.9%
99.9%
>99.9%
>99.9%
>99.9%
99.9%
99.9%
99.9%
99.9%
Notes:
a A sampling run is defined as one 8-hour period for a given flow rate.
b Concentration after vented air passed through a carbon filter.
c Not detected
d Sampling run was abbreviated due to system failure.
Sources of Further Information
Ron Turner
EPA Project Manager
U.S. EPA National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7775 FAX: (513) 569-7620
Philip Canning
Manager, Process Engineering
ZENON Environmental, Inc.
845 Harrington Court
Burlington, Ontario, Canada L7N 3P3
(905) 639-6320 FAX: (905) 639-1812
10
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Environmental Protection Agency
National Risk Management
Research Laboratory (G-72)
Cincinnati, OH 45268
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