United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-115 Oct. 1981
Project Summary
Inorganic Contaminant
Removal from Drinking
Water by Reverse Osmosis
Martin R. Huxstep
The removal of inorganic contami-
nants from drinking water was studied
using two reverse osmosis (RO) treat-
ment systems. A high pressure (400
psi) and low pressure system (200
psi). each having a rated capacity of
1.82 L/sec (28.9 gpm) of product
water, were used to evaluate their
capability for removing various inor-
ganic contaminants.' A groundwater
was spiked with varying concentra-
tions of fluoride, nitrate, arsenic III,
and arsenic V, and runs of 2 to 5 days
ware conducted to determine rejec-
tions. Removal data were also col-
lected on the natural constituents in
the feed water of total dissolved
solids, hardness, calcium, magnesium,
chloride, sodium, and sulfate.
. For all contaminants and natural
constituents measured, the high pres-
sure system operated at 265 to 359
psig more effectively removed the
inorganic contaminants than did the
low pressure system operated at 163
to 187 psig. High pressure system
removals ranged from 80 to 99 per-
. cent; low pressure, from 10 to 85
percent. Percent removals varied with
the ion measured, but the order, from
best to worst, was about the same for
each system. The order for the high
pressure system was: (1) arsenic V, (2)
fluoride, (3) nitrate, and (4) arsenic III.
For the low pressure system: (1) arsenic
V, (2) fluoride, (3) arsenic III, and (4)
nitrate. Percent removal was also
independent of the initial concentra-
tion.
This Project Summary was devel-
oped by EPA's Municipal Environmen-
tal Retearch Laboratory. Cincinnati,
OH. to announce key findings of the
research project that is fully docu-
mented in 'a separate report of the
same title (see Project Report ordering
information at back).
Introduction
RO has been used successfully for
desalting sea waterand brackish waters
for many years. Compared with other
drinking water treatment methods, its
relatively high cost has limited its
application in this field. Technological
advances, however, have generated
considerable interest for use on drinking
waters with high total dissolved solids
and on those having specific contami-
nants that cannot be easily removed by
other methods.
One major advantage of RO is its
effectiveness to remove almost all
inorganic substances. Information is
generally available on the rejection
capabilities for the common natural
. constituents in drinking water, such as
sodium, chloride, or sulfate, but lacking
on the rejection of specific contaminants
such as arsenic and selenium.
This study was undertaken to develop
. data on removing the inorganic con-
taminants included in EPA National
Interim Primary Drinking Water Regula-
tions by RO. Tests were conducted
using two parallel pilot plant RO sys-
tems: (1) a low pressure (200 psi)
system housing low rejection mem-
-------
branes and (2) a high pressure (400 psi)
system with high rejection membranes.
Test runs lasting from 1 to 5 days were
carried out by spiking a natural ground-
water with known concentrations of
contaminants and measuring their
removal by each RO system. Removal
data were also obtained on some of the
natural constituents in the feed water
such as total dissolved solids, calcium,
magnesium, chloride, sodium, and
sulfate. The results of the first series of
tests for the removal of fluoride, nitrate,
arsenic III, and arsenic V are reported in
this first progress report.
Results
Because of several problems, unre-
lated to the RO systems, the two systems
were operated under three slightly
different sets of operating conditions
(pressure). The test data on the natural
substances suggest, however, that
these changes did not significantly
influence the performance of the sys-
tems for removing the spiked contami-
nants.
As was anticipated, the test data
show a very significant difference in the
capabilities between the two RO sys-
tems for removing all spiked and natural
constituents monitored. The low pres-
sure system, which requires about one-
half the energy used by the high pressure
system, achieved rejections of about 50
percent or less than that achieved by the
high pressure system. Data also show
that rejection of the contaminants on a
percent basis was independent of the
feed concentration and the order of
effectiveness for removing spiked and
natural constituents was nearly the
same for each system (Table 1).
Conclusions
The investigation clearly indicated
that the high pressure system was
Table 1.
Percentage Removal of Natural and Spiked Constituents Monitored
Reverse Osmosis Systems, % Removal
Constituents
High Pressure
Low Pressure
Natural
Sulfate
Magnesium
Calcium
Total Hardness
Radium-226
Total Dissolved Solids
Chloride
Sodium
>99
96-98
96-98
97-98
97
93-96
87-95
88-93
82-84
63-67
64-67
64-66
62
45-52
42-45
36-44
Spiked
Arsenic V
Fluoride
Nitrate
Arsenic III
91 -98
90-93
76-80
63 - 70
77-81
56-62
6-24
12-35
significantly more effective for removing
all substances measured. The low pres-
sure system achieved a very wide range
of removals and was very ineffective for
removing nitrate and arsenic III.
Because of its low rejection charac-
teristics, the low pressure system is
ofily effective on source water having
contaminant concentrations slightly
above the maximum contaminant levels
(MCL). The high pressure system, al-
though it requires about twice the
energy, is much more effective, and
blending of feed and product waters
could be accomplished to affect the
difference in energy costs.
The full report was submitted in ful-
fillment of Cooperative Agreement No.
RC-805207 by Charlotte Harbor Water
Association, Inc., under the sponsorship
of the U.S. Environmental Protection
Agency.
Martin R. Huxstepis with the Charlotte Harbor Water Association, Inc., Harbour
Heights, FL 33950.
Thomas J. Sorg is the EPA Project Officer (see below).
The complete report, entitled "Inorganic Contaminant Removal from Drinking
Water by Reverse Osmosis," (Order No. PB 81-224 420; Cost: $8.00, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA2216t
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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