United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-88/057 Jan. 1989
c/EPA Project Summary
Manganese Dioxide Coated
Filters for Removing
Radium from Drinking Water
Marc Y. Menetrez, David G. Anderson, and Edward P. Stahel
Research was performed using
manganese dioxide (MnO2) to
demonstrate that above pH 3 cations
are adsorbed from solution in the
order of their affinity, and that the
interaction is characterized by the pH
dependence of the metal. The
relationship of the zero point charge
of pH and the solution ionic strength
effects on interfacial surface poten-
tial and adsorption have been
addressed. Characteristics of MnC>2
behavior, structure, and stability
found in research investigation were
reviewed.
Most of this study was on the use
of Mn<>2 coated filters for the
removal of radium. A few comparison
tests on radium removal with ion
exchange were also made.
Specifically, these tests have shown
that acrylic fiber filters coated with
Mn(>2 will remove radium from water.
For a high hardness water with pH =
7.4, total radium removal was 14,200
pCi/g MnO2 before the MCL of 5 pCi/L
was exceeded; and for a low
hardness water with pH = 4.5, total
radium removal was 5,000 pCi/g MnO2
before the MCL of 5 pCi/L was
exceeded. Hardness passed through
the MnO2 filters with little change;
therefore, radium was highly
preferred over hardness.
A step-by-step process for the
preparation of acrylic fiber filters
coated with MnO? is included in the
full report.
Tri/s Project Summary was devel-
oped by EPA's Risk Reduction
Engineering Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
As of August 1, 1982, a total of 39
public water systems, or 1.9% of the
systems tested in North Carolina, were
found to be in violation of the 5 pCi/L
combined radium limit. When a water
system is found to have levels of
combined radium activity that exceed the
standard, the system owner is
responsible for correcting the problem. If
utilizing another water source is not
realistic, then effective treatment to
remove excess radium would be re-
quired. Ion exchange, lime-soda soft-
ening, and reverse osmosis have been
demonstrated to be effective techniques
for radium removal.
Adsorption onto MnC>2 coated filters is
a treatment alternative that has been
tested sparingly but never used to
remove radium from drinking water.
Extensive testing of MnOa filters in the
laboratory, in the pilot plant, and in full-
scale application is the focus of this
report. The use of Mn02 coated filters
has been examined for metal removal
and more extensively for radium removal
in conjunction with efficiency, cost, safe
use of application, and usefulness
compared with other forms of treatment.
Flowthrough MnO2 Filter
Preparation System
A system to produce MnOa filters with
a heavy MnC>2 loading was designed,
constructed, and operated successfully.
The flowthrough filter preparation system
is described in detail in the full report.
The system has been successfully used
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to generate MnOg fiber in both a
prewoven filter element form as well as a
loose-staple form. The acrylic-based
MnOa fiber in both forms exceeded the
previous limit of 10% to 13% MnC>2 (by
weight). Loadings of 20% to 25% MnO2
(by weight) were consistently produced
with the flowthrough filter preparation
system. A filter element 10 in. (25.4 cm)
long weighing an average of 250 g with
an average loading of 22.5% would
consist of 56.25 g MnOa and 193.75 g
acrylic-base fiber. The flowthrough filter
preparation system was also used in
washing the prepared fiber before
packaging. Preparing Mn02 fiber with the
system took less than 1 day/batch to
produce the filters. The cost of chemical
was less than $2/10-in. filter element,
or less than $8/kg of prepared fiber.
The examination of the prepared
MnC-2 filter elements revealed that when
the Mn02 filter is installed and rinsed
(with 3 to 5 filter volumes), no organic,
soluble manganese, insoluble MnC>2, or
fiber is released to the effluent stream.
This indicates that MnC>2 fiber can be
used to treat drinking water without
contributing unwanted contaminants. The
State of North Carolina, Department of
Human Resources, Solid and Hazardous
Waste Branch, examined the MnC>2 fiber
for leaching under landfill conditions. The
results of the (EPA) toxicity test revealed
no leaching of any form of manganese or
other inorganics at pH 5 conditions. This
should allow the disposal of the MnC>2
filters in landfills in North Carolina,
pending approval for radium.
Radium Analysis
A modified process for analyzing
radium in water was devised and
structured, and the results compared
with EPA through a quarterly sample
analysis and report program. The
analysis procedure followed is described
in Appendix B of the full report.
Results
Bleed Stream Testing
The bleed stream testing of the MnC>2
filter in the Highland Park water system
and the Gateway Mobile Home Park
water system revealed that radium was
removed and that hardness was passed
through the filter relatively unchanged.
The bleed stream results for the
Highland Park water system (Table 1)
show that total radium removal in excess
of 86% can be expected for a treated
volume of at least 22,653 L at a flowrate
of 11.36 L/m per 25.4-cm filter element.
At this level of radium removal, the
influent concentration of 36.4 pCi/L total
radium is reduced to a maximum effluent
concentration of 5 pCi/L total radium, the
U.S. EPA Regulation. The single, 25.4-
cm filter element consisting of
approximately 250 g of MnOg fiber
removed 0.801 [iCi total radium before
decreasing to an efficiency of less than
86%. At an Mn02-to-fiber loading of
22.5% (56.25 g of MnO2), the total
radium-to-MnOa ratio of 14,200 pCi/g
MnC-2 was demonstrated prior to
reaching the 5 pCi/L limit. The halfway
point to breakthrough (or the point at
which 50% efficiency was reached)
occurred after approximately 57,000 L of
water was treated, and the total
breakthrough of radium occurred after
approximately 160,000 L of water was
treated.
Bench-top testing of a sample frc
the Highland Park water system w
performed. The 202.5-L sample w
pumped through 15 g of MnC-2 fib
containing approximately 3.35 g of MnC
at a rate of 0.75 L/min. The resu
indicated that the influent concentrati
of 36.4 pCi/L was reduced to zero in t
effluent. A total of 7,370 pCi of to
radium was removed, or 2,180 pCi
total radium per gram of Mn02. Tl
removal efficiency never changed frc
100%, therefore, no conclusions can I
made regarding total uptake of radiui
However, a considerable volume of wal
was treated while maintaining to!
removal.
The bleed stream results for tl
Gateway Mobile Home Park wat
system (Table 2) show that total radit
removal in excess of 66% can I
expected for a treated volume of at \e<
28,000 L at a flowrate of 11.4 Urn p
25.4-cm filter element. At this level
radium removal, the influent conce
tration of 13.2 pCi/L total radium
reduced to a maximum effluent conce
tration of 5 pCi/L total radium, the U.
EPA Regulation. The single, 25.4-c
filter element consisting of approximate
250 g of MnC>2 fiber removed 0.222 n
total radium before decreasing to <
efficiency of less than 66%. At a MnO
to-fiber loading of 22.5% (56.25 g
Mn02), the total radium-to-Mn02 ral
of 5,000 pCi/g MnC-2 was demonstrat<
prior to reaching the 5 pCi/L limit. Tl
halfway point to breakthrough (or 50
efficiency) occurred after approximate
42,000 L of water was treated, and tl
total breakthrough of radium occum
after approximately 85,000 L of wat
was treated.
Table 1.
Highland Park Field Study; Bleed Stream Field Test - Total Radium Removal Efficiency and Uptake*
Effluent Radium (pCi/L) Total Flowf (ft3) Removal Efficiency Total Uptake (nd) Uptake (nCilg MnO2)
2.4
5.5
14.5
17
22
27.5
30
31.5
32.5
34.5
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
0.934
0.849
0.602
0.533
0.396
0.245
0.176
0.135
0.107
0.052
481.39
918.89
1,228.96
1,503.63
1,707.52
7,833.53
1,924.14
1,993.52
2,048.73
2,075.64
8.56
16.34
21.85
26.73
30.36
32.60
34.21
35.44
36.42
36.90
" For 25.4-cm long filter element, influent total radium concentration = 36.4 pCi/L, pH = 7.4, and total hardness
= 227 mgIL as CaCO3.
t Multiply by 28.32 to convert ft3 to liters.
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Table 2. Gateway Field Study; Total Radium Removal Efficiency and Uptake'
Effluent Radium (pCi/L) Total Flowf (ft3) Removal Efficiency Total Ra Uptake (nCi) Uptake (nCi/g MnO2)
2.0
4.5
7.0
9.0
12.5
13.2
500
1,000
1,500
2,000
2,500
3,000
0.848
0.659
0.470
0.318
0.053
0.000
158.58
281.75
369.54
429.00
438.91
438.91
2.82
5.01
6.57
7.63
7.80
7.80
* For 25.4-cm long filter element, influent total radium concentration = 13.2 pd/L, pH
= 23 mgIL as CaCOy.
t Multiply by 28.32 to convert ft3 to liters.
4.5, and total hardness
In-LJne Testing
In-line field testing utilized three
standard water filtration housings. Each
housing held twenty-one 25.4-cm filter
elements. The three stainless steel
housings were situated in series to
extend filter life. The in-line field test
results for the Highland Park water
system indicated that the removal
efficiency of total radium was less than
that exhibited with the bleed stream field
test. The point halfway to breakthrough
of total radium was reached almost
immediately for the three-filter housing
system containing three canisters of
twenty-one 25.4-cm MnC>2 fiber
elements. This rapid decrease in filter
efficiency was also recorded for the three
filter housing systems containing one
20-iim, one 5-iim, and one MnOa filter
element housing. The decreased
capacity of the MnC>2 filters was believed
to be caused by a high suspended solids
loading on the filters. Large amounts of
clay and silt were found coating the filter
elements.
This fouling of the MnC-2 sites greatly
decreased the ability of the filter to
adsorb radium. Even after passing
through a 20-iim and a 5-|im pleated
paper filter element, significant amounts
of fine suspended material were found
building on the Mn02 filter element. The
reduced capacity of the in-line field test
apparatus is believed to be caused by an
improperly drilled and cased well. This
problem was not encountered with the
bleed stream testing and only became
apparent when treating the entire well
flow of 125 Urn and 75,700 L/day.
Conclusions
The successful removal of radium with
MnC>2 coated filters appears conditional
to the lack of fouling agents in the
influent stream. Coating of the MnC>2
sites greatly reduces the interfacial
ittracting forces. Maximum adsorption
efficiency is expected when only the
target ion in solution is present. The
bleed stream tests resulted in greater
amounts of radium loading for the
Highland Park water system and lower
radium loading for the Gateway water
system. This is believed to be caused by
the different levels of pH of these two
ground water sources. The pH 7.4 of the
Highland Park water system allowed for a
higher degree of adsorption than did the
pH 4.5 of the Gateway water system.
In-lab, bench-top investigation on
the removal of dissolved metals has
indicated that radium ions as well as
interfering ions in solution are adsorbed
by MnOg. The results of metal removal
with MnC-2 fiber showed that low
concentrations of cadmium, calcium,
cobalt, cesium, iron, and manganese can
also be removed from solution by
adsorption onto Mn02 fiber.
The ion exchange comparison column
bleed stream results were inconclusive in
that they lacked actual breakthrough
information. A column of MnOa fiber
152.4-cm length and 5.08-cm diam-
eter treated approximately 76,000 L of
influent water containing 13.2 pCi/L total
radium without any variation from an
effluent level of 0 pCi/L total radium. A
column of ion exchange resin 60.96-cm
length and 5.08-cm diameter treated
76,000 L of water containing 13.2 pCi/L
total radium, without any significant
variation from 0 pCi/L total radium in the
effluent. At this point the ion exchange
column was regenerated with a 0.85
molar calcium chloride solution because
the resin was mistakenly expected to be
spent. An additional 78,000 L of water
was treated with this column. Again, no
variation from zero total radium dis-
charge was observed. No conclusions
could therefore be made regarding
column life, efficiency, or comparisons of
hydrogen ion exchange to calcium ion
exchange.
The MnO2 fiber can be used for
treatment of drinking water for the
removal of radium. Tests also showed
that MnC-2 adsorbs other metals,
specifically cadmium, calcium, cesium,
cobalt, iron, and manganese. The bleed
stream tests showed that radium was
highly preferred over calcium and
magnesium. A treatment application for
radium involving an inability to regen-
erate resin because of the disposal of
regenerant brine or backwash could
eliminate the use of ion exchange resin.
In these circumstances, MnC>2 coated
filters could possibly be used for
treatment and the filter disposed of in a
sanitary landfill (pending approval by
state authorities).
The full report was submitted in partial
fulfillment of Cooperative Agreement
CR-811119-01 by North Carolina State
University under the sponsorship of the
U.S. Environmental Protection Agency.
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Edward P. Stahel, Marc Y. Menetrez, and David G. Anderson are with the North
Carolina State University, Raleigh.NC 27695-7905.
Richard P. Lauch is the EPA Project Officer (see below).
The complete report, entitled "Manganese Dioxide Coated Filters for Removing
Radium from Drinking Water," (Order No. PB 89-110 1261 AS; Cost:
$19.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
••:•;; V '-, EPA (.
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Official Business
Penalty for Private Use $300
EPA/600/S2-88/057
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60604
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