United States Office of

Environmental Protection Research and Development

Agency CIncinnati, OH 45268

EPN/540/R-95/511 a

August 1995

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 Island (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 membranebased 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

@ Printed on Recycled Paper
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 @g/L).

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 1,38Opg/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 o

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 oC).

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 ZENON TECHNOLOGY PERFORMANCE

1 Overall Protection of

Human Health and the

Environment

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’ 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.

3 Long-Term Effectiveness Effectively removes groundwater contaminants. Involves

and Performance disposal of some residuals (wastewater and permeate).

4 Reduction of Toxicity,

Mobility, or Volume

Through Treatment

5 Short-Term Effectiveness

6 Implementability

7 Cost b

8 Community Acceptance

9 State Acceptance

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

handling of concentrated permeate.

Easy to implement and transport. Requires minimal

preparation and utilities, and minimal operational support.

and

site

ZENON estimates treatment costs from $2.00 to $4.00 per 1000

gallons of contaminated water.

The small risk to the community and permanent removal of

contaminants make public acceptance of this technology likely.

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.

3
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.

lnfluent 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.

4
5
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 not 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 ,OOOpound 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 pilotscale 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
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 ug/L),

the federal MCL of 5 pg/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.

7

Table 3: TCE Concentrations in water

Run Number Flow Rate

(gallons per minute)

Grab Number Untreated Concentration

(mg/L)

Treated Concentration

(mg/L)

Percent Removal

V 2.10-2.15 1 40 0.17 99.5%

2 43 1.0 97.7%

3 33 3.8 88.5%

4 42 11 73.8%

Average 40 3.9 89.9%

2 5.16 - 5.21 1 4 1 NDb >99.9%

2 44 0.09 99.8%

3 48 0.16 99.7%

4 48 0.19 99.6%

A verage 42 0.11 99.8%

3 9 1 . . - 33 0.32 99.0%

2 . 35 0.27 992%

3 38 0.22 99.4%

4 37 0.24 99.4%

A verage 36 0.26 99.3%

4 5.46 1 220 0.45 99.8%

2 220 0.40 99.8%

3 240 0.51

4 240 0.46 99.8%

A verage 230 0.46 99.8%

5

c 11.18-11.23 1 130 2.7 97.9%

2 120 2.7 978%

A verage 125 2.7 97.9%

Total Average Percent Removal 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.
Table 4: TCE Concentrations in Air

Run

Number

Average

Groundwater TCE

Concentration

(mg/L)

Flow Rate

(gpm)

la 40 2.10 - 2.15 1

2

2 42 5.16 - 5.21 1

2

Grab

Number

Untreated

Concentration

(mg/mz)

Treated

Concentration

tmg/mz)

6,100 0.02

5,500 0.05

3,700 0.02

2,500

3 36 1 7,300 ND

2 7,200 ND

Percent

Removal

99.9%

99.9%

99.9%

>99.9%

>99.9%

>99.3%

4 230 546 1 18,000 0.17 99.9%

2 20,000 0.01 99.9%

54 125 11.18 -11.23 1. 21,000 0.71 99.9%

Average 95 10,100 0.11 99.9%

Notes: a A sampling run is defined as one a-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-l 812

10
United States

Environmental Protection Agency

National Risk Management

Research Laboratory (G-72)

Cincinnati, OH 45268

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