r/EPA
United States
Environmental Protection
Agency
Storm Water Technology Fact Sheet
Sorbent Materials in Storm Water Applications
DESCRIPTION
Sorbent materials (which include absorbents and
adsorbents) have specific physical and/or chemical
properties that allow them to attract specific types of
liquids and/or gases. Absorbents and adsorbents
function in different ways. In general, absorbent
materials attract compounds into their pore spaces;
adsorbents attract materials to their surfaces but do
not allow them to penetrate into their pore spaces
(U.S. EPA, accessed 2000). The American Society of
Testing and Materials (ASTM) has defined absorption
by absorbent materials as "a process where the
material taken is distributed throughout the body of the
absorbing material." Adsorption is "a process where
the material taken is distributed over the surface of the
adsorbing material." Both processes can essentially
"capture" sorbed materials, concentrating them or
removing them from solution. Thus, either process
allows captured materials to be more easily removed
from a media.
Recent research has shown that sorbent materials can
be used in storm water applications to remove oil and
grease (O&G). High concentrations of O&G can
cause toxicity in receiving waters, and most discharge
regulations require that there be no discharge of oily
wastes that produce a sheen on the surface of the
receiving water.
Sources of oil and grease in storm water include O&G
sorbed to trash and other debris; O&G sorbed to
particulates; emulsified oils (small drops of oil
suspended in storm water); free floating oil; and
suspended oil (CDS Technologies, 2000, literature
provided by manufacturer). Research shows that
between 83 and 98 percent of total hydrocarbons in
storm water runoff are associated with paniculate
matter, and evidence suggests that a significant portion
of these particles are settleable solids, such as
sediments (Hoffman, et. al, 1982). Therefore, storm
water Best Management Practices (BMPs) designed to
remove sediments may also remove some oil and
grease associated with the sediments.
Typically, only free-floating oil concentrations are
measured and reported in storm water studies (CDS
Technologies, Inc., 2000). Concentrations of free
floating oil and grease typically range between 10-35
mg/L for urban storm water runoff (U. S. EPA, 1999a),
although concentrations can vary widely and are
dependent on catchment characteristics (Hoffman, et
al., 1982; and Stenstrom, etal., 1984).
Because the specific gravity of free floating O&G is
lower than that of O&G sorbed to sediments, it can be
difficult to remove through traditional gravity separation
BMPs. Storm water BMPs such as oil/water
separators are designed to reduce influent flow rates,
which enhances gravity separation of oil and water
over the length of the unit. The use of coalescing plates
may further enhance oil/water separation. However,
these systems must retain relatively large volumes of
storm water in order to function effectively, and
therefore they may not be practical where space is
limited. Therefore, many BMPs are designed
specifically to remove these hydrocarbons through
higher-rate physical interactions.
One method for removing free floating oils and grease
from storm water is through the use of sorbent
materials. Sorbent materials have traditionally been
used to clean up spills, such as for soaking up fuel
spilled on a roadway. More recently, however,
sorbent materials have been incorporated into storm
water BMPs to improve water quality from storm
water runoff. Sorbent materials are currently being
utilized within BMPs placed in storm water catch
basins, sumps, or other parts of a storm sewer system
to capture hydrocarbons and other toxic chemicals and
prevent them from being carried through the storm
water system.
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APPLICABILITY
Sorbent materials are usually used in areas where
storm water runoffis likely to have a high amount of oil
and grease. Because much of the oil and grease in
urban storm water originates from motor vehicles,
through engine drippings, exhaust, and maintenance
activities, most storm water BMPs using sorbent
materials are placed near roadways, parking areas, and
service stations (Hoffman, etal., 1982; and Stenstrom,
etal., 1984).
Sorbent materials are diverse, allowing them to be
utilized in several different types of BMP applications,
including new and retrofit applications. While many
vendors market sorbent materials, relatively few
sorbent manufacturers have developed and marketed
materials to remove oil and grease from storm water.
This Fact Sheet discusses only those sorbents currently
used in storm water BMPs.
ADVANTAGES AND DISADVANTAGES
Listed below are some of the advantages and
disadvantages of using sorbent materials to remove oil
and grease in storm water BMPs.
Advantages
Sorbent materials can be applied to a variety
of storm water applications. There are
numerous types of natural and manufactured
sorbents and a wide range of BMPs that use
them, including catch basin and curb inlet
inserts, skimmers, and filters. These BMPs
can be applied at almost any point in a storm
system, and can be retrofitted into an existing
system or installed into a new system.
• Many units are easily installed because they do
not require specialized equipment. For
example, the OARS® Passive Skimmer is hung
on hooks from a manhole cover;
DrainGuard™ products are suspended from a
geotextile fabric that can be stretched
underneath a grate over a catch basin or a curb
inlet.
Storm water BMPs using sorbent materials are
relatively easy to operate and maintain. Many
sorbent materials change colors when they
need to be replaced; others use pop-up
indicators that extrude through the grate when
capacity is reached.
These BMPs are passive structures with no
moving parts, and thus they are not susceptible
to mechanical failure or breakdown.
Most synthetic sorbents retain their shape and
will not break down under field conditions.
Some sorbents are enclosed in polypropylene
encasements to prevent damage from
ultraviolet exposure. Others, such as the
DrainGuard™ catch basin and curb opening
systems, are held within a polypropylene
"sock" that is supported by a rigid frame which
ensures that the insert maintains its shape as
storm water flows through it.
These sorbents are designed to retain sorbed
contaminants and minimize the potential for
leaching. Most sorbents discussed in this Fact
Sheet meet RCRA requirements prohibiting the
release of sorbed liquids, making them
acceptable at RCRA Subtitle D landfills.
Disadvantages
Sorbent materials require frequent inspection
to ensure that the sorbent material is not fully
used or "spent". Each type of sorbent material
has a maximum sorbent capacity based on its
chemical composition and volume. When this
capacity is reached, the sorbent will no longer
capture oil and grease and must be replaced.
Sorbent material can capture only the free oil
and grease present in the water column. It
cannot capture emulsified oils.
A California Department of Transportation
(CalTrans) study involving drain inlet inserts
with sorbent materials found that units clogged
frequently, causing flow bypass and ponding
(Othmer, et. al., 2001). Large litter and
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debris, such as leaves, clogged the inserts,
decreasing the system's hydraulics and
reducing sorting capability.
Mostlocal jurisdictions require proper disposal
of used sorbent, either through landfilling or
incineration. Proper handling and disposal of
used sorbent material is discussed in more
detail in the Operation and Maintenance
section of this Fact Sheet.
MEDIA CHARACTERISTICS
Sorbents can be divided into three basic categories:
natural organic, natural inorganic, and synthetic. Table
1 describes the three materials and their sorbent
capacities. This Fact Sheet focuses on synthetic
sorbents; however, many BMPs can be fitted with
natural organic or inorganic sorbents to help absorb oil
and grease.
PERFORMANCE
Fact Sheet on Hydrodynamic Separators, EPA 832-F-
99-017). The researchers floated sorbents on the
surface of an unmodified CDS unit, introducing free oil
at an approximate rate of 25 mg/L. This concentration
is within the range of 10 to 35 mg/L which has been
reported as the average storm water oil and grease
concentration in urban runoff (U. S. EPA 1999a). The
researchers measured concentrations of oil and grease
in the effluent to determine removal efficiencies.
Removal efficiencies for the different sorbents ranged
from 41 to 87 percent at a flow rate of 8 L/s (125
gpm). All but one of the tested sorbents removed at
least 77 percent of the oil and grease. The removal
rates appeared to depend on the flow rate of the
influent. OARS® sorbent material was tested at three
flow rates, ranging from 5 to 12 L/s (75 to 190 gpm).
This flow rate is within a range of 30 to 75 percent of
the design flow of the CDS device used in the
experiments. Analysis of the removal rates from these
experiments showed that, in general, the lower the flow
rate, the higher the removal rate. Table 2 summarizes
the results.
Stenstrom and Lau (1998) tested five different
sorbents, includingRubberizer® and OARS® media, in
a Continuous Deflection Separation (CDS) device for
their ability to remove free oil and grease. A CDS
device is an on-line hydrodynamic separator (see EPA
TABLE 1 MEDIA CHARACTERISTICS
The Rubberizer® and OARS® sorbents showed similar
levels of performance in these tests. Both were denser
than the influent, causing them to float just below the
circulation pattern that allowed them to achieve high
removal efficiencies for surface oil and some emulsified
Type of Media1
Description
Sorbent Capacity
1. Organic
2. Inorganic
3. Synthetic
3a. Rubberizer®
3b. OARS® Smart
Sponge
Leaf compost, peat moss, straw, hay, sawdust, ground
corncobs, feathers, and other readily available carbon-based
products.
Clay, perlite, vermiculite, glass wool, sand or volcanic ash.
Man-made materials similarto plastics, such as polyurethane,
polyethylene, and nylon fibers.
Non-toxic, non-hazardous polymers
Combination of petroleum derived co-polymers
3c. Imbiber Beads™ Solid, spherical plastic particles
3 to 15 times their
weight in oil
4 to 20 times their
weight in oil
Up 70 times their
weight in oil
1 Ib material adsorbs
1.9 to 2.5 L (0.5 to 0.67
gal) of oil
2-14.5 times its
weight in oil
Each bead absorbs up
to 27 times its own vol.
1 For more detailed information visit http://www.epa.qov/oilspill/sorbents.htm
Source: EPA, 2000; Abtech Industries, 2000; Haz-Mat Response Technologies, 2000; and IMTECH, 2000.
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TABLE 2 OIL & GREASE REMOVAL IN
A CDS UNIT USING SORBENT MEDIA
Sorbent
Type
Nanofiber
OARS®
OARS®
OARS®
Rubberizer®
Sponge Rok
Xsorb
No Sorbent
Flow
(GPM)
125
75
125
190
125
125
125
125
Percent Removal of 25
mg/L Oil and Grease
87
94
86
82
86
41
79
77
Source: Stenstrom and Lau, 1998.
oils.
The researchers also measured oil and grease effluent
concentrations 30 minutes after oil and grease pumping
was stopped to determine whether oils leached out of
the sorbents. Effluent oil and grease concentrations
were generally less than 1 mg/L for all trials, indicating
that most sorbents retained oil and grease. The only
sorbent with a residual oil and grease concentration
greater than 1.0 mg/L was Rubberizer®, which had a
1.96 mg/L oil and grease concentration in the effluent
30 minutes after oil and grease pumping had been
stopped. The researchers speculate that this increased
leaching rate may be the result of Rubberizer's® high Q
value, which is a measure of the ratio of the oil and
grease absorbed per mass of sorbent (Stenstrom and
Lau, 1998).
Few other studies have directly tested the oil sorption
efficiencies of sorbent materials, but several studies do
compare the efficiencies of different BMPs that use oil
sorbent materials. While these studies do not provide
specific comparisons of sorbent materials because of
the confounding effects of the types of BMPs utilized,
they do illustrate the effectiveness of different BMPs
that use sorbent materials in storm water applications.
The Rouge River National Wet Weather
Demonstration Project monitored four on-line media
filter devices (Hydrocartridge®, alternately using
Rubberizer® and Woolzorb® media; StreamGuard™,
using Rubberizer® media; Gullywasher™, using
cellulose media; and the grate inlet skimmer box, which
also used cellulose media) for a 19 month period at
two gas station sites in southeast Michigan. The study
found that all four units removed some debris,
sediment, and oil; however, the Hydrocartridge®
retained almost twice the amount of oil as the next most
effective device (Alsaigh, et. al., 1999, see Table 3).
The authors concluded that the Hydrocartridge® and
the StreamGuard™ devices absorbed more oils and
grease than the skimmer box and the Gullywasher™,
and pose two potential explanations for the observed
differences:
• The Hydrocartridge® and StreamGuard™ may
have been better able to retain water, thereby
slowing the flow and allowing the media to
absorb oil; or
The absorbents used by the Hydrocartridge®
and the StreamGuard™ were more effective at
removing oils than the cellulose media used by
the skimmer box and the Gullywasher™ .
The authors did not directly test these possibilities, and
therefore they make no conclusions as to which of them
caused the Hydrocartridge® and the StreamGuard™
devices to absorb more oils and grease than the
skimmer box and the Gullywasher™ (Alsaigh, et. al.,
1999).
TABLE 3 OIL ABSORPTION
EFFICIENCIES OF FOUR STORM
WATER BMPS UTILIZING SORBENT
MATERIALS
Device
Average Oil
Captured/Gallon
Filtered ((mg/kg)/1,000
gal)
Hydrocartridge®
StreamGuard™
Gullywasher™
Grate Inlet Skimmer Box
9,700
5,000
2,100
700
Source: Alsaigh, et. al., 1999.
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The results allow some comparison between
Rubberizer®, a synthetic polymer, and Woolzorb®, a
natural wool fiber product. Both of these sorbent
materials were used in the Hydrocartridge® BMP over
the course of this project - Rubberizer® during six
observation periods and Woolzorb® during two
observation periods. The efficiency of Rubberizer®
media ranged from a low of 200 mg/kg of oil captured
per 1,000 gallons of storm water filtered to a high of
46,700 mg/kg of oil captured per 1,000 gallons of
storm water filtered. The efficiency range of the
Woolzorb® media overlaps that of the Rubberizer®
media. The Woolzorb® media absorbed 11,500
mg/kg oil per 1,000 gallons of storm water filtered
during the first observation period, and 2,600 mg/kg oil
per 1,000 gallons of storm water filtered during the
second period observed (Alsaigh, et. al., 1999).
The California Department of Transportation
conducted a comprehensive study to evaluate two
drain inlet inserts for their suitability for retrofitting into
existing highway infrastructure. As part of this study,
CalTrans estimated the pollutant removal efficiencies of
three Fossil Filter™ units containing Fossil Rock, an
amorphous alumina silicate, and three DrainGuard™
units containing Rubberizer® media, installed at sites in
District 7 (Los Angeles County) maintenance stations
(Othmer Jr. et. al., 2001). These maintenance stations
were ideal for testing the units' hydrocarbon removal
capabilities because they are used for vehicle storage,
fueling, and/or maintenance operations. One Fossil
Filter™ and one StreamGuard™ unit were installed at
each site to allow within-site comparisons. The units
were monitored from September 1999 through May
2000, with routine maintenance conducted according
to the manufacturer's recommended schedule to
reduce the likelihood of clogging. When it became
apparent that the systems clogged at a much higher
than expected rate, maintenance schedules were
increased. However, even the increased maintenance
schedules did not prevent clogging during storms and
resulting system bypass.
The authors concluded that both units reduced
hydrocarbons in storm water, but that site-specific
conditions, such as flow rates, dictated the
effectiveness of the unit. The mass balances were
calculated, then converted to percent removal values to
determine hydrocarbon removal efficiencies. The
authors noted that removal efficiencies may be low
because bypass occurred frequently for both types of
units. In addition, they note that the Fossil Filter™ unit
often became clogged, further reducing removal
efficiency. Hydrocarbon removal ranged from 5 to 7
percent for the Fossil Filter™ and from 2 to 31 percent
for the StreamGuard™. StreamGuard™ achieved
higher hydrocarbon removal efficiency at two of three
sites studied. The authors also emphasize that the
units' intensive maintenance requirements are a factor
to be considered when determining which BMP is
appropriate for a specific application.
OPERATION AND MAINTENANCE
The basic operations and maintenance (O&M)
requirements for sorbent materials include periodic
checks to ensure that they have not reached their
sorbing capacity or become clogged. The frequency of
visits and cleaning of sediment and debris from BMPs
using sorbent materials depends on the type of BMP
and the area in which it is located. In general, all
BMPs using oil sorbent materials should be inspected
at least monthly. If the material is placed in an area
where it is susceptible to a high oil loading rate, the
BMP should be inspected and serviced more
frequently. BMPS should be checked immediately in
the event of an oil spill.
Inspections depend on the individual unit and vary from
monthly to quarterly. For example, the Ultra-Urban™
Filter should be serviced quarterly to remove
accumulated sediment and debris and to check the
sorbent. The manufacturer recommends that OARS®
Passive Skimmer systems be inspected at least once a
month to check the position of the skimmer and ensure
that it remains on top of the water for maximum oil
removal efficiency. The unit should be changed when
the sorbent material has turned from its original light
color to a dark color, indicating that it has reached its
maximum oil sorbing capacity. This changeout
schedule depends on the specific application. AbTech
estimates that a skimmer installed in an oil/water
separator lasts between two weeks and three months,
while a skimmer installed in a hydrodynamic separator
will last two months to one year. Changeout involves
removing the skimmer and replacing it with a new unit.
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Foss Environmental recommends monthly inspections
of its StreamGuard™ catch basin insert until the
operator becomes familiar with how often the system
needs to be cleaned of grit and sediment. The filter
pack should be visually inspected and sediment
removed, if necessary. To maximize removal
efficiency, the catch basin insert system should be
emptied and cleaned when it has accumulated 30 cm
(12 inches) of sediment.
Disposal/Recycling
A sorbent must be replaced once it is spent or has
reached its maximum sorting capacity. Most of the
sorbents discussed in this Fact Sheet can be removed
and replaced easily by the user once they are spent.
Depending on the type of sorbent, there are four
different options for disposal: recycle, waste-to-energy
(WTE), cement kilns and landfills.
Recycling offers an alternative to disposing of used oil
sorbent materials. For example, CRT Recycling
Service, Inc., recycles many types of used sorbent
using a patent pending technology that effectively
removes contaminants from both inorganic absorbent
materials, such as clay and diatomaceous earth, and
most synthetic absorbent materials, such as mats, pads,
socks, and rolls. These absorbent materials can be
reused after processing, with little change in their
overall appearance or absorptive capacity. CRI has
had success recycling both generic and proprietary
sorbents.
WTE facilities utilize spent products to produce
electricity as an alternative energy source. Cement
kilns also utilize used products as an alternative fuel to
produce Portland cement. The last option for disposal
is landfilling the material. Most of the spent media has
passed the EPA Toxicity Characteristic Leachate
Procedures and the Paint Filter Test, qualifying it for
acceptance at RCRA Subtitle D Landfills (i.e., most
municipal landfills).
COSTS
AbTech Industries markets several storm water BMPs
that use the OARS® Smart Sponge technology,
including the OARS® Passive Skimmer, the OARS®
Ultra-Urban™ Filter curb opening insert, and the
OARS® Ultra-Urban™ Filter catch basin insert.
Skimmer prices range from $18-$72, and skimmers
are usually replaced when their sorbent capacity has
been reached. AbTech's curb opening inserts cost
$250, while catch basin inserts cost between $400 and
$600. These units are used until their sorbent capacity
is reached, and then the entire unit is replaced. Under
normal operating conditions, the entire recyclable filter
units should be replaced at least every three years.
Foss Environmental StreamGuard™ catch basin inserts
(using the sorbent filter pack consisting of Rubberizer®
media) sell for $93 each, with multiple packs available
at a reduced cost. These inserts can be installed by
the user, minimizing installation costs.
Imbiber Beads® Absorbent Pillows, which can be used
in several different types of storm water BMPs, are
sold in 18-pillow packs for approximately $275.
REFERENCES
Other Related Fact Sheets
Catch Basin Cleaning
EPA832-F-99-011
September 1999
Handling and Disposal of Residuals
EPA832-F-99-015
September 1999
Hydrodynamic Separators
EPA 832-F-99-017
September 1999
Water Quality Inlets
EPA 832-F-99-029
September 1999
Other EPA Fact Sheets can be found at the following
web address:
http://www.epa.gov/owm/mtb/mtbfact.htm
1. AbTech Industries, 2000. Literature provided
by manufacturer.
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2.
9.
10.
11.
Alsaigh, R, J. Boerma, A. Ploof, and L.
Regenmorter, 1999. Rouge River National
Wet Weather Demonstration Project,
Nonpoint Work Plan No. URBSW5, Task
No. 3, Evaluation of On-Line Media Filters in
the Rouge River Watershed.
American Society of Testing and Materials,
1993. Standard Methods of Testing
Sorbent Performance of Absorbents. F
716-82 (Reapproved 1993).
American Society of Testing and Materials,
1996. Standard Guide for Containment by
Emergency Response Personnel of
Hazardous Materials Spills. F 1127-88
(Reapproved 1996).
American Society of Testing and Materials,
1999. Standard Test Method for Sorbent
Performance of Adsorbents. F 726-99
(Reapproved 1993).
Caltrans-C SUS-UCD Stormwater Unit (study
conducted by California DOT), August 2000.
Brian Currier, Caltrans-CSUS-UCD
Storm water Unit, personal communication with
Parsons, Inc.
12.
CDS Technology, Inc., 2000.
provided by manufacturer.
Literature
CRI Recycling Service Inc., 2000. Literature
provided by manufacturer.
CRI Recycling Service Inc., 2000. John
Summerfield, CRI Recycling Service, Inc.,
personal communication with Parsons, Inc.
Haz-Mat Response Technologies, Inc., 2000.
Literature provided by manufacturer.
Haz-Mat Response Technologies, Inc., 2000.
Shirley Washum, Haz-Mat Response
Technologies, Inc., personal communication
with Parsons Engineering Science, Inc.
13.
14.
15.
16.
17.
18.
19.
20.
Hoffman, E.J., J. Latimer, G. Mills, and J.
Quinn, 1982. "Petroleum Hydrocarbons in
Urban Runoff from a Commerical Land Use
Area." Journal of the Water Pollution
Control Federation 54, No. 11, pp. 1517-
1525.
IMTECH 2000.
manufacturer.
Literature provided by
Katers, J.F., and J. Summerfield, 2000. "Oil
Recovery from Absorbent Materials."
Othmer Jr., E.F, G. Friedman, J.S. Borroum,
and B.K. Currier, 2001. "Performance
Evaluation of Structural BMPs: Drain Inlet
Inserts (Fossil Filter™ and StreamGuard™)
and Oil Water Separator." Submitted to
American Society of Civil Engineers annual
conference.
Stenstrom, M.K., G. Silverman, and T.
Bursztynsky, 1984. "Oil and Grease in Urban
Stormwaters." Journal of Environmental
Engineering 110, No. 1, pp. 58-72.
Stenstrom, M. K. and Sim-Lin Lau, 1998.
Oil and Grease Removal by Floating
Sorbent in a CDS Device. Los Angeles.
Prepared for CDS Technologies.
Stenstrom, M.K., 2001. M.K. Stenstrom,
personal communication with Parsons, Inc.
U.S. EPA, 1999a. "Evaluating Simple, Cost
Effective Solutions for Reducing Storm Water
and Urban Runoff Pollution: Santa Monica Bay
Restoration Project." Coastlines,
January/February 1999. Internet site at
http://epa.gov/owow/estuaries/
coastlines/janfeb99/center/insert.html,
accessed August 2000.
U.S. EPA, 1999b. Sorbents. Internet site at
http://epa.gov/oilspill/sorbents.htm. accessed
July 2000.
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ADDITIONAL INFORMATION
AbTech Industries
Robert Liguori
41 10 N. Scottsdale Road, Suite 235
Scottsdale, AZ 85251
CDS Technologies, Inc.
Robert Howard
16360 South Monterey Road, Suite 250
Morgan Hill, CA 95037
CRI Recycling Service
John Summerfield
101 Hagen Drive
Woodville, WI 54028
Foss Environmental
Bill Pola
P.O. Box 80327
Seattle, WA 98 108
Haz-Mat Response Technologies, Inc.
Shirley Washum
4626 Santa Fe Street
San Diego, CA 92 109
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for use by the U. S . Environmental Protection Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
1200 Pennsylvania Avenue, NW
Mail Code 4204M
Washington, D.C. 20460
Office of Water
EPA 832-F-02-020
September 2002
2002
THE YEAR OF
QJ5AN WATER
IMTB
Excellence in compliance through optimal technical^ sotuttons
MUNICIPAL TECHNOLOGY BRANCH
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