vvEPA
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 11b/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 for further treatment 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
'—D-*
- Tank Air Vent
iCarbon Filter
Contaminated
Water
j
-»
Eq
jaliza
Tank
Polymeric
Prefilter Membranes
I Moat \
Pv^tnnor A,
u n^rT , ll I
> M U >W '
Feed Pump J ^'^ Tp
tion / T
"wate? Carbon Filters ^
i—9 — n-a-Q»To
1 Discharge
•^ — > — Condenser l_
V» Vacuum Pump and
Outlet to Vent
Carbon Water
and Organics For Recycle,
> • Disposal, or
Further Treatment
f Permeate
PERVAPORATION MODULE
Figure 1. Zenon Cross-Flow Pervaporation System
Printed on Recycled Paper
-------
United States
Environmental Protection
Agency
EPA/540/MR-95/511
June 1995
oEPA
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 11b/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 for further treatment 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
O-*
For Recycle,
Disposal, or
Further Treatment
Equalization
Tank
Permeate
PERVAPORATION MODULE
Figure 1. Zenon Cross-Flow Pervaporation System
Printed on Recycled Paper
------- |