United States
Environmental Protection
Agency
EPA/540/MR-95/511
June 1995

SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
Zenon Cross-Flow Pervaporation Technology
ZENON Environmental, Inc.
Technology Description: Pervaporation is a process that employs
a membrane to remove volatile organic compounds (VOC) from
aqueous matrices. Figure 1 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 pref ilter 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 a
pervaporation module containing dense polymeric membranes.
The membrane material is a nonporous organophilic polymer,
such as silicone rubber, formed into capillary fibers measuring less
than 1 mm in diameter. Silicone rubber is highly permeable to
organic compounds and resistant to degradation. The capillary
fibers are aligned parallel on a plane and spaced slightly apart. This
arrangement of capillary fibers forms one membrane layer.
Separate membrane layers are aligned in series, with the interior
of the capillary fibers exposed to a vacuum (about 1 lb/in2, 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.
The organophilic composition of the membrane causes organics to
adsorb to the membrane (capillary fibers). The organics migrate to
the interior of the capillary fibers and are then extracted from the
membrane by the vacuum. This organic migration into the fibers
creates a concentration gradient that tends to facilitate transport.
Contaminated water passing through the pervaporation module is
depleted of organics and exits the ZENON system for reuse or
discharge.
Organic vapor and small amounts of water extracted from the
contaminated water through the membranes 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 permeate condenser, organics are kept in
solution, thus minimizing air releases.
The liquid 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 containment vessel to storage
while aqueous phase permeate can either be returned to the
pervaporation module forfurthertreatment or removed for disposal.
Waste Applicability: Cross-flow pervaporation can be applied to
aqueous matrices contaminated with liquids containing VOCs
such as solvents, degreasers, and gasoline. 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
Carbon Filter	Carbon Filter
PERVAPORATION MODULE
Figure 1. Zenon Cross-Flow Pervaporation System

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negligible amounts of VOCs to the outside air. Unlike activated
carbon, the treatment medium does not require replacement and
disposal. Periodic cleaning of the membranes is necessary to
enhance treatment.
A full-scale ZENON pervaporation system can be easily transported
and requires only an electrical source. For large applications, a
pervaporation unit containing multiple modules can be used.
Considerations When Using Pervaporation: As noted, the prefilter
prevents solids from reaching the pervaporation module and
inhibiting the movement of organics through the membrane. Water
containing high concentrations of solids can clog the prefilter,
requiring it to be cleaned frequently.
VOCs with water solubilities of less than 20,000 parts per million
(ppm) are generally suited for removal by pervaporation. Highly
soluble organics, such as alcohols, are not effectively removed by
a single-stage pervaporation process. Low-boiling volatile
compounds, such as vinyl chloride, tend to remain in the vapor
phase after moving through the condenser. For conditions involving
elevated concentrations of low-boiling VOCs, a carbon filter placed
on the vacuum vent ensures that contaminants are not released to
the outside air. 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.
Technology Demonstration: In 1991, under EPA's Emerging
Technology Program, bench-scale testing of the ZENON
pervaporation process was performed in Burlington, ON. In late
1993, under EPA's SITE Program, a pilot-scale pervaporation unit
was successfully evaluated at a hydrocarbon-contaminated
groundwater site just south of Burlington.
In February 1995, a full-scale ZENON pervaporation system was
evaluated during a SITE demonstration at a former waste disposal
area at Naval Air Station North Island in San Diego, CA. Groundwater
in the area contains elevated concentrations of trichloroethylene
(TCE), as well as other contaminants. The demonstration was
conducted as a cooperative effort among EPA, ZENON, the Naval
Environmental Leadership Program, Environment Canada, and
the Ontario Ministry of Environment and Energy.
The focus of the demonstration was to determine the system's
effectiveness in removing TCE from contaminated groundwater.
The removal of other VOCs, semivolatile organic compounds, and
total recoverable petroleum hydrocarbons was also monitored. To
determine the removal efficiency of the pervaporation system,
EPA collected samples of untreated groundwater, treated
groundwater, and vapor emissions over 8-hr sampling runs. The
system was operated at influent flow rates ranging from 2 to 11
gallons per minute (gpm) with TCE concentrations up to 250 ppm.
A portable gas chromatograph (GC) unit was used to provide field
data and identify the pervaporation system's optimal operating
conditions. The GC unit was also used to ensure that treated
groundwater to be discharged to the sanitary sewer was within
assigned contaminant limits.
Preliminary demonstration results, based on field GC data, indicate
that the ZENON pervaporation system was about 98% efficient in
removing TCE from groundwater. The system achieved this removal
efficiency with TCE influent concentrations up to 250 ppm at a flow
rate of 10 gpm or less. T reatment efficiency of the system remained
fairly consistent throughout the demonstratiorifhowever, at a flow
rate near 2 gpm, the treatment efficiency decreased during the 8-
hr sampling run due to mineral scaling problems.
Detailed information on the technology's capabilities and the
results of the ZENON SITE demonstration will be discussed in the
forthcoming SITE Technology Capsule and the Innovative
Technology Evaluation Report.
For Further Information:
EPA Project Manager:
Ron Turner
U.S. EPA Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7775 FAX: (513) 569-7787
Technology Developer:
Philip Canning
Manager, Process Engineering
Zenon Environmental, Inc.
845 Harrington Court
Burlington, ON, Canada L7N 3P3
(905) 639-6320 FAX: (905) 639-1812
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
EPA/540/MR-95/511

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