Page 1 of 1
Nicholas MELAS -
FW: Disinfection of drinking water
From:
?
"solzman" <solzman@sbeglobal.net>
To:?
<melasn@ipcb.state.il.us>
Date:?
6/17/2008 4:54 PM
Subject:
FW: Disinfection of drinking water
RECEIVED
CLERK'S OFFICE
JUN
1
7
2008
STATE OF ILLINOIS
Pollution Control
gna•d
Dear Mr. Melas:
It was a great pleasure to meet you yesterday and a privilege to share some of my views with you regarding a
cleaner Chicago River. I attach
the first research report on the novel zerovalent iron approach. I hope you find it
interesting. I like it, not only for its virus-eliminating features, but for its low cost and low-energy requirements.
I look forward to future conversation around this idea. If you have additional questions regarding this approach
please call on me.
Again my thanks for your work for Illinois waterways and for the future of Chicago.
Very Cordially,
David M. Solzman, Ph.D
file://C: \Documents and Settings\MelasN\Local Settings \ Temp \GW)00001.HTM
?
6/18/2008
Environ. Sci. Technol
2005,
39,
9263-9269
Removal and Inactivation of
Waterborne Viruses Using
Zerovalent Iron
YOUWEN YOU," IIE HAN,t
PEI C. CHIU,
t
AND YAN
Department of Plant and Soil Sciences and Department of
Civil and Environmental Engineering, University of Delaware,
Newark, Delaware 19716
A
daunting challenge facing the water industry and
regulators is how to simultaneously control microbial
pathogens, residual disinfectant, and disinfection byproducts
in drinking water, and to do
so
at an acceptable cost. Of
the different pathogens, viruses are especially problematic
due to their small size, high mobility, and resistance to
chlorination and filtration. In the past decade, zerovalent
iron has been used to treat a wide variety of organic and
inorganic contaminants from groundwater. However, iron
has not been tested against biological agents. This study
examined the effectiveness of commercial zerovalent iron to
remove two viruses, OX174 and MS-2, from water.
Removal of these viruses by iron granules in batch reactors
was first-order, and the rate was likely controlled by
external mass transfer. Most of the viruses removed from
solution were either inactivated or irreversibly adsorbed
to iron. In a flow-through column containing zerovalent iron
(with 20 min of iron contact time), the removal efficiency
for both viruses was 4-log in an initial pulse test, and over
5-log in the second pulse test after passage of 320 pore
volumes of artificial groundwater. We assume that the
improved efficiency was due to continuous formation of
new iron (oxyhydrIoxides which served as virus adsorption
sites. To our knowledge, this is the first demonstration
of biological agent removal from water by zerovalent iron.
Results of this study suggest zerovalent iron may be
potentially useful for disinfecting drinking water and
wastewater, thereby reducing our dependence on chlorine
and reducing the formation of disinfection byproducts.
Introduction
Microbial pathogens in drinking water present a serious threat
to public health. Sources of microbial contamination include
leaking septic tanks and sewer lines, landfills, land disposal
of biosolids, wastewater discharge and reuse, and runoff and
infiltration from animal waste-amended fields
(1, 2).
The
EPA Science Advisory Board (3) cited drinking water con-
tamination as one of the highest remaining environmental
risks and microbial contamination as the greatest challenge
in health risk management for drinking water suppliers. The
Surface Water Treatment Rule (SWIT) and Interim Enhanced
Correspondingauthor phone: 302-831-6962:fax: 302-831-0605;
e-mail: yjin@udel.edu.
Department of Plant and Soil Sciences.
l
Department of Civil
and Environmental Engineering.
*Currently a research associate at the School of Veterinary
Medicine, University of Pennsylvania, Kennett Square,
PA.
swrR
were established to regulate microbial contaminants
in drinking water systems using surface water or groundwater
under direct influence of surface water. The 1986 and 1996
Safe Drinking Water Act (SDWA) Amendments required EPA
to establish national primary drinking water regulations
requiring disinfection to control microbial contaminants for
all public water systems, including systems supplied by
groundwater sources (4). More recently, the EPA promulgated
Long Term 1 Enhanced SWIM and proposed Long Term 2
Enhanced SWTR to specify treatment requirements for
reducing microbial pathogens in drinking water (5, 6).
Despite continued efforts to regulate water quality and
improve treatment practices, microbial pathogens continue
to threaten drinking water safety. Epidemiological studies
(7-9) have found a link between gastrointestinal diseases
and tap water, even when water quality guidelines were met.
The occurrence of illnesses was found to correspond to short-
term turbidity breakthrough from individual filters in the
water treatment plant (10). In addition, data collected by the
Centers for Disease Control and Prevention (CDC) and EPA
(4) indicate that almost as many waterborne disease out-
breaks were reported between 1971 and 1996 for systems
with disinfection that was inadequate or interrupted (134
outbreaks) as for systems without disinfection (163 outbreaks)
during the same period.
Viruses have been shown to be responsible for ap-
proximately 80% of disease outbreaks for which infectious
agents were identifiable (II). A recent study by Abbaszadegan
et al.
(12)
on the occurrence of pathogens in groundwater
analyzed samples collected from 448 sites in 35 states in the
United States for various indicators of fecal contamination,
including total coliform,
E. coli,
somatic and male-specific
coliphages, and human viruses. It was found that 31.5% of
the samples were positive for one or multiple pathogenic
viruses using polymerase chain reaction (PCR), and human
viruses were detected by cell culture in 4.8% of all the samples.
Although viruses are not the only pathogens found in water
supplies, they are far smaller (-0.01-0.1 pm) than bacteria
and protozoan cysts and thus are removed to a lesser extent
by filtration. As a result, viruses can travel much longer
distances in the subsurface
(13,14),
and treatment processes
such as filtration are generally less effective in removing
viruses (15). In addition, chlorination, which is the dominant
disinfection method used in the United States, has been
shown to be less effective against viruses and protozoa than
bacteria
(16, 17).
For the past decade, zerovalent iron has been used in
subsurface permeable reactive barriers (PRBs) for ground-
water remediation
(18, 19).
While initially proposed to treat
chlorinated solvents in contaminated aquifers, zerovalent
iron has since been shown to be effective in removing a broad
range of organic and inorganic pollutants, including heavy
metals, Freons, radionuclides, pesticides, and nutrients (20).
Zerovalent iron can remove contaminants from water
through one of two processes: reduction or adsorption. For
contaminants such as chlorinated solvents, the treatment
involves primarily reduction (21), whereas for phosphate and
arsenic, the main removal mechanism appears to be ad-
sorption to iron oxides and hydroxides, which are formed
during iron corrosion in water
(22, 23).
Iron corrosion initially
forms amorphous iron hydroxides,
which
then transform
into
more stable oxides and oxyhydroxides such as magnetite,
goethite, and lepidocrocite, depending on the solution
composition and redox conditions
(24-26).
A number of studies have shown that iron oxides can
remove and inactivate viruses in water
(11,27-29).
Although
10.1091/es050829j CCC: $30.25?
C 2005 American Chemical Society
VOL. 39, NO. 23, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY •
9283
Published on Web 11/02/2005
the mechanism for the removal and inactivation is not fully
understood, the process has been suggested to involve
adsorption of virus particles to iron (oxyhydr)oxides through
electrostatic attraction
(11,30).
This is followed by inactivation
of adsorbed viruses due to the strong attachment force, which
causes the viruses to disintegrate or become noninfective
(11, 27).
These studies suggest an intriguing possibility that
zerovalent iron may continuously remove and inactivate
viruses in water through corrosion and formation of (oxy-
hydr)oxides at the iron surface. Although zerovalent iron has
been tested against a large number of organic and inorganic
contaminants, it has never been shown to remove biological
agents from water. This study was prompted to assess the
effectiveness of zerovalent iron to remove and inactivate
waterborne viruses and evaluate its potential for water and
wastewater treatment applications.
Materials and Methods
Virus Selection and Assay. Two bacteriophages, MS-2 and
OX174, were selected as model viruses for this study because
they have been used as surrogates for human enteric viruses
in previous studies due to their structural resemblance to
many human enteric viruses and their ease of use
(31, 32).
MS-2 is an icosahedral single-stranded RNA phage with a
diameter of 26.0-26.6 nm (33) and an isoelectric point (pHiep)
of 3.9 (34). MS-2 was obtained from the American Type
Culture Collection (ATCC 15597B1) and grown on bacterial
lawns of
E. coil
(ATCC 15597). OX174 is a spherical single-
stranded DNA phage with a diameter of 23 nm and a pHiep
of 6.6 (35). It was grown on an
E. colt
host (ATCC 13706).
Concentrations of infective #X174 and MS-2 particles were
determined by the plaque-forming unit assay using the agar
overlay method (36). Briefly, I mL of host culture and 1 mL
of diluted virus sample were added to a trypticase soy agar
(TSA) tube, and the mixture was poured onto a TSA plate.
The plates were solidified for 15 min and placed in a 37 °C
incubator for 5 and 12 h for 0)(174 and MS-2, respectively.
Viable virus concentration was determined by counting the
plaques in the host lawn and reported as plaque-forming
units per milliliter (pfu/ mL). Only dilutions that resulted in
10-300 plaques per plate were accepted for quantification
(i.e., the limit of quantification was set to be 10 pfu/plate for
this study). All virus assays were performed in duplicate.
Iron and Sand. The zerovalent iron used for this study
was commercial iron particles (ETI8/50) obtained from
Peerless Metal Powders & Abrasive (Detroit, MI). The iron
was used as received without pretreatment. The specific
surface area of the Peerless iron was 1.67 m
2/
8, as measured
by the Brunauer -Emmett-Teller (BET) adsorption method
with nitrogen. This value is within the range reported by
other authors for Peerless iron [e.g., 1.50 m2/ g by Alowitz
and Scherer (37) and 2.53 m2/ g by Su and Puls (22)]. In
addition to zerovalent iron, the Peerless iron also contained
magnetite, maghemite, and graphite, as determined by X-ray
powder diffraction with Cu Ka radiation using a Philips/
Norelco diffractometer. Accusand (Unimin, Le Sueur, MN)
with the following particle size distribution was used for the
column experiment: 9% of 0.1-0.25 mm, 69.8% of 0.25-0.5
mm, and 21.2% of 0.5-LO mm. The properties of Accusand
have been well-characterized in a laboratory study (38). It
consisted essentially of quartz with trace levels of organic
matter and metal oxide coating. The sand was treated to
remove metal ions and oxides using a citrate buffer solution
containing 44.1 g/L of sodium citrate (Na 2C31-1307
.
2H20) and
10.5 g/L of citric acid, following a procedure modified from
Mehra and Jackson (39). The detailed treatment procedure
is given in Chu et al. (27). After the treatment, the iron content
decreased from 32.5 mg iron/kg sand to below the detection
limit (0.02 mg iron/kg sand), as determined by extraction
with 0.05 M sodium dithionite (Na
2S2O4)
and 0.4 M sodium
WNW 5•1•4••
FIGURE 1. Schematic d agrem of column experiment setup.
citrate and quantification using inductively coupled plasma
(ICP).
Artificial Groundwater. An artificial groundwater (AGW)
was used as the background solution; it contained 0.075 mM
of CaCl2, 0.082 mM of MgC12
, 0.051 mM of KCI, and 1.5 mM
of NaHCO3
(ionic strength 2 mM). After autoclaving and
vacuum degassing, the pH of the AGW was adjusted to 7.5
using 0.1 M NaOH or HCI prior to use.
Batch Experiments. Both batch and column experiments
were conducted in a large refrigerator at 5 ± 1 °C to avoid
inactivation of the viruses due to high temperature. Batch
experiments were conducted to study the kinetics of virus
removal by Peerless iron particles. Stock solutions of 0X174
and MS-2 were diluted in AGW to the desired titer (-105
pfu /mL). Experiments were performed using 250-mL amber
borosilicate bottles prepared in duplicate. Following addition
of 1.0 g of iron particles, the bottles were filled completely
(free of headspace) with virus solution and sealed im-
mediately with an open-hole screw cap and a Teflon-lined
silicone septum (10/90 mil, Ailtech, Deerfield, IL). Care was
taken to prevent trapping of air bubbles during filling and
capping of the bottles as viruses can be inactivated at the
air-water interface
(40, 41).
The sealed bottles were shaken
end-over-end at 20 rpm in a refrigerator. At different elapsed
times, 1.0 mL of virus-free AGW was injected into the bottle
through a fully inserted 5.5-in. stainless steel side port needle
(Popper & Sons, New York), and simultaneously a 1-mL
sample was displaced through an inserted 2-in. stainless steel
side port needle (Alltech). The different needle lengths were
used to ensure spatial separation of injection and sampling
points to prevent sample dilution. Side port needles were
used to minimize damage to septa and avoid introduction
of air. The 1-mL sample was analyzed immediately for viable
virus concentration by the plaque assay.
To determine whether virus removal was due to reversible
adsorption to iron or irreversible adsorption and inactivation,
solution was discarded after the last sample was taken and
250 mL of 3% beef extract solution (BEX, pH 9.5) was added
to the bottle to extract viruses from iron particles. BEX is a
high-ionic strength enzyme digest of beef protein and has
been shown to effectively detach viruses adsorbed to various
surfaces (42). The bottle was then shaken at 5 °C for 30 min
and concentrations of viable viruses in BEX were measured.
Controls (without iron) were set up in an identical fashion
to assess any background adsorption and/or inactivation of
the viruses during the experiment.
Column Experiments. Column experiments were con-
ducted to evaluate the effectiveness of iron to remove viruses
from water under continuous, saturated flow conditions and
over an extended operation time. The experiment was
performed using a setup (Figure 1) similar to that in our
previous studies
(43,44).
Two identical glass chromatography
9264 • ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 23, 2005
= 0.9689
y • -0.013x - 0.0202
• 0.9259
k1' • 0.013/m1n • 0.78/6
20
?
40
?
60?
80
?
100?
120
?
140
Time (min)
columns of 3.8-cm i.d. and 10-cm length were used. The
control column was wet-packed with oxide-removed sand
by pouring sand into an AGW-filled column at 1-cm
increments while stirring with a glass rod to remove any
attached air bubbles (43). The iron column was packed in a
similar manner with 3 cm of oxide-removed sand followed
by 7 cm of 1:1 (v/v) mix of oxide-removed sand and Peerless
iron particles. The iron mass in the packed iron column was
approximately 150 g.
Each column was flushed with 10 pore volumes (10 PVs)
of autoclaved and degassed AGW at a flow rate of 0.5 mL/
min. The flow rate was then increased to 1 mL/ min and
flushing was continued for another hour to establish a steady-
state flow condition prior to virus introduction. This gives a
residence time of 41 min in the sand column and 58 min in
the iron column. Given the iron content of 35 vol %, the
effective contact time with iron In the iron column was
20 min.
For each pulse test, a solution containing –105
pfu/mL
each of OX174 and MS-2 and 50 ppm of bromide was
introduced into both columns at approximately 1 mL/ min
for 5 PVs using a peristaltic pump. Effluent samples from
both columns were collected in 6-mL tubes at 5-min intervals
(i.e., 5 mL of sample/tube) using a fraction collector. After
the 5-PV slug input, the influent was switched back to the
virus-free background solution (sterilized, degassed, and pH-
adjusted AGW), and effluent samples were collected for
another 5 PVs. Pumping of the background solution was
continued at –1 mL/ min for 10 days (>320 PVs) before the
second pulse test was conducted. The effluent concentrations
of the viruses and bromide were determined by the plaque
assay and ion chromatography (Doinex, Sunnyvale, CA),
respectively.
Results and Discussion
Batch Experiments. Figure 2 shows the removal of MS-2
and OX174 from the solution in batch reactors containing 1.0
g of iron particles. The aqueous concentrations of viable MS-2
and 0174 decreased continuously over 2 h, and the removal
appeared to follow first-order kinetics. In contrast, in the
absence of iron, no removal of either virus was observed at
5 °C during the same time period (data not shown). This
indicates that both viruses were removed from solution by
iron particles. Result of the BEX recovery test shows that
only 0.13% of the MS-2 and 0.16% of the 0174 adsorbed
were viable and could be recovered from the iron particles.
Therefore, most of the viruses removed from solution were
either irreversibly adsorbed or rendered noninfective. Using
eq 1, the first-order rate constants for MS-2 and 49X174
removal at pH 7.5 were estimated to be 0.0231 ± 0.0038 and
0.0130 ± 0.0020 min-', respectively.
In [virus] = In [virus], –
ki t
(1)
In eq 1, [virus] is the infective virus concentration in solution
at time t, [virus]. is the initial virus concentration measured
before iron addition, and k
t
is the apparent first-order virus
removal rate constant.
Because removal of virus from water by iron particles in
a batch reactor involves multiple steps, the observed first-
order rate constants may reflect the rate of any one of these
processes or their combination: mass transfer of virus from
bulk solution to the exterior surface of an iron particle,
diffusion of virus in pores within an iron particle, and
adsorption of virus to a surface site. Although kinetic data
for the intraparticle diffusion and adsorption of viruses are
not available, it is possible to estimate the external mass
transfer rate constant (kw, s- using the procedure described
by Arnold et al. (45). km r is the product of mass transfer
coefficient (k
1
, m/s) and the ratio of particle geometric surface
0
y•-0.0231x - 0.2101
-1
r-
5
Time (min)
FIGURE 2. Pseudo-first-order removal of the bacteriophages MS-2
and 0174 in AGW in batch reactors containing 1.0 g of Peerless
iron granules. Initial virus concentrations xl 10
5
pfu/mL Shaking
speed = 20 rpm.
area to solution volume
(a, m-').
If external mass transfer is
slow relative to the other processes, the overall rate constant
(k,) would be comparable to kur. Conversely, if another
process is rate-limiting, kw would be significantly larger than
k1.
The mass transfer between bulk solution and suspended
particles in a mixed batch system is controlled largely by the
velocity of the particles relative to the fluid; that is, the
particles' terminal velocity (46). Using the semi-theoretical
eq 2
(46, 47)
for mass transfer to spherical particles moving
at their terminal velocity with a Reynolds number greater
than 1, the minimum mass transfer rate coefficient
(14)
can
be calculated, as shown below.
Sh (7ctdp/
Dw)
= 2 + 0.6 (Re)°
5 (Sc)° 33 =
2 + 0.6 (d
p u/v)" (v/D„,,)033
(2)
In eq 2, Sh, Re, and Sc are dimensionless Sherwood number,
Reynolds number, and Schmidt number, respectively,
kr,
is
the minimum (uncorrected) mass transfer coefficient (m/s),
dp
is iron particle diameter (-5 x 10-
4
m), D,., is the diffusion
coefficient of the viruses in water (m2/s),
u is the terminal
velocity of the iron particles (m/s), and
v
is the kinematic
viscosity of water at room temperature (1.02E-6 m
2/ s). Using
a corrected Stokes' Law (48), the terminal velocity of iron
particles
(u)
was calculated to be 0.18 m/ s, with a corre-
sponding Re of 87. The
a.,
values of the two viruses
are
expected to be similar because of their similar sizes. Using
an assumed diameter of 23 nm for both viruses and either
the Stokes–Einstein equation
(49)
or an empirical equation
proposed by Wilke and Chang (50),
a,
was calculated to be
60?
80?
100?
120
140
VOL. 39, NO. 23. 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY •
9265
PV
FIGURE 3. Breakthrough curves of bromide tracer from columns
packed with
oxide-removed sand only and oxide-removed sand
plus iron granules.
2.0 x 10-" m2/s.
The Sherwood and Schmidt numbers based
on this Dm are 5.4 x 10-4 and 206, respectively.
K
can then
be calculated to be 7.8 x 10-6 m/s using eq 2. Harriou
(96)
suggested that, in a mildly stirred batch system without an
impeller, the actual mass transfer coefficient (k
L)
is likely to
be 1.2 to 1.5 times
kt.
Because 1.5 was used as a correction
factor in an earlier study to estimate kr and a good agreement
with experimental data was observed (45), we used 1.5 to
obtain an estimated Ict of 1.2 x 10-5 m/s. Finally, based on
the iron mass (1.0 g) and liquid volume (250 mL) used, an
assumed spherical particle geometry, and an estimated
nominal density of 6500 kg/ m3
for the iron, we calculated
the geometric surface area-to-solution volume ratio (a) to
be 7.4 m-l
. Therefore, the external mass transfer rate constant
km, = kra = 8.7 x lr s- 1 , or 0.0052 min I.
This calculated
kmT
value is a factor of 2 -4 lower than the
apparent removal rate constants for MS-2 and #X174 (Figure
2). Since
lc,
must be smaller than or equal to kw, this
underestimation is most likely due to the assumptions and
uncertainties involved in our calculations, especially those
related to the estimation of diffusivity D v, (since viruses are
much larger and more massive than dissolved molecules)
and surface area concentration
a
(which was probably
underestimated since the iron particles were not spherical).
Nonetheless, the estimated kar argues that external mass
transfer was probably the rate-limiting process that controlled
the overall rate of virus removal from solution in our batch
reactors.
Column Experiments. The bromide breakthrough curves
from the sand column and the iron column are shown in
Figure 3. The two breakthrough curves essentially overlap,
indicating that the water flow conditions in both columns
are very similar. These curves are well-described by the
equilibrium convection—dispersion equation (51), indicating
that there was no physical nonequilibrium in either column.
Using the bromide breakthrough data, we calculated the pore
volumes of the sand and iron columns to be 41 and 58 mL,
respectively.
The breakthrough curves of MS-2 and 0X174 from the
sand column and the iron column are shown in Figure 4.
Although MS-2 was retained slightly in the sand column, as
indicated by the greater tailing than the bromide tracer
breakthrough curves, complete breakthrough of MS-2 was
observed in both pulse tests, with 108% and 94% recovery,
respectively. #Xl 74 was retained more significantly than MS-
2, with approximately half of the input viral particles retained
in the sand column (49% and 42% recovery from the two
pulse tests, respectively). Similar retention of 03(174 by the
same type of sand has been found to be reversible, and
adsorbed 0X174 could be recovered completely when eluted
with beef extract solution (43). While the mechanism for the
more pronounced retention of 0X174 by clean sand is unclear,
it may be related to the higher pHleaof 0X174 (6.6) than MS-2
(3.9). The higher pH
im
, probably resulted in a lower net
negative charge of 0)(174 than MS-2 in AGW (pH 7.5) and
thus a weaker electrostatic repulsion between *XI 74 and
sand particles, which could be overcome more easily by the
van der Waals attraction. Although MS-2 and 0X174 behaved
differently in terms of their retention in the sand column,
the overall removal of both phages by clean sand was limited.
In sharp contrast, the breakthrough concentration of MS-2
from the iron column in the first pulse test, conducted shortly
after packing, was only about 0.01% of the influent concen-
tration, barely above the limit of quantification (10 pfu/plate)
for the plaque assay. The breakthrough concentration of MS-2
in the second pulse test conducted 10 days later was even
lower, with all data points more than 10 times below the
limit of quantification. These breakthrough concentrations
correspond to 4-log (i.e., 99.99%) removal of MS-2 by Peerless
iron in the first pulse test and more than 5-log (>99.999%)
removal in the second test after 320 PVs of AGW had passed
the iron column. The breakthrough curves of #X174 tell
essentially the same story: Removal of 0X174 by iron in the
first pulse test was approximately 4-log and increased to over
5-log in the second pulse test after passage of 320 PVs of
AGW. If we assume first-order kinetics (eq 1) for virus removal
in the iron column, a 4-log removal would correspond to a
rate constant of 0.3 min-
1 in the (7-cm) section of the column
that contained 50% Peerless iron.
The virus removal in the iron column most likely occurred
via interactions with the iron oxides, such as magnetite and
maghemite, present in the iron. Adsorption and inactivation
of viruses by iron oxides, as well as other metal oxides, have
been widely reported. Murray and Laband
(52)
found that
poliovirus was adsorbed to aluminum and iron oxides. Both
magnetite and hematite have been shown to adsorb a variety
of viruses
(28, 53, 59).
In field and laboratory experiments,
Ryan et al.
(11)
observed inactivation of the viruses MS-2
and PRD1 on the surface of iron oxide-coated quartz sand.
In our previous study using oxide-removed sand and Ottawa
sand containing metal oxides (identified as primarily
goethite), we found significant differences in the transport
and survival of MS-2 and 0)(174 (27). In a recent study using
goethite-coated sand, we further showed that 90% of MS-2
and 95% of 0X174 were removed (55) and the removal was
due mainly to inactivation rather than reversible adsorption
(27, 55).
The additional 1- to 2-log removal in the second
pulse test was most likely due to formation of new iron oxides
(i.e., new adsorption sites) resulting from corrosion of
zerovalent iron during the 10-day period. Although removal
via filtration could not be completely excluded, it was
probably negligible since the iron column had a higher
porosity than the sand column, where virus removal was
minimal, and no pressure buildup or flow rate reduction
was observed over this period.
To our knowledge, this is the first demonstration of
biological agent removal from water by zerovalent iron. The
batch experiments show that removal of two bacteriophages
by commercial iron was rapid, with rates approaching the
limit of external mass transfer. The removal appeared to be
largely due to irreversible adsorption or inactivation of the
viruses. The column study illustrates that in a flow-through
system, over 5-log removal of both viruses could be achieved
within an effective contact time with iron of 20
min.
Furthermore, the column data suggest that, as water flowed
through the iron column, new iron (oxyhydr)oxides were
formed continuously to serve as new adsorption sites, and
9266 • ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 23. 2005
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Sand Column, t
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8 10 12
PV
FIGURE
4. Breakthrough curves of MS-2 and
(X-174
from sand and iron columns in two pulse tests conducted shortly after packing
It = Oland after passage of over 320 PVs of AGW It= 10 d). The limit of quantification corresponds to 10 pfu/plate of undiluted sample.
Note that when a sample produced zero plaque, a calculated virus concentration corresponding to 1 pfu/plate was assigned for plotting
purposes. These data points should he regarded as upper limits of the actual virus concentrations in the samples.
the capacity of iron to remove waterborne viruses could be
sustained or even improved.
Potential Applications.
These findings may have impor-
tant implications for the treatment of water and wastewater.
The greatest challenge facing the water industry and regula-
tory agencies today is, arguably, how to simultaneously
control microbial pathogens, disinfection byproducts (DBPs),
and residual disinfectant in drinking water—and to do so at
an acceptable cost. Chlorine is by far the most common
disinfectant in the United States to control microbial
pathogens, used by approximately 80% of large water
treatment facilities (serving over 10
000
people) and almost
all of the smaller water systems (56). While largely effective
to remove bacteria, chlorine was found to be less effective
against viruses and protozoa
(16, 17).
Disinfection with
chlorine also has many serious drawbacks, including forma-
tion of toxic DBPs, such as trihalomethanes and haloacetic
acids, through reaction of chlorine with humic materials. In
addition, accidental and deliberate release of chlorine gas
can have catastrophic consequences, and is listed by the
Homeland Security Council as one of the National Planning
Scenarios (57). Moreover, some chlorine-manufacturing
facilities still use mercury cell electrolysis, a process that can
release large quantities of mercury. Therefore, it is desirable
to minimize chlorine use and storage in water and wastewater
treatment facilities and elsewhere. For these reasons, alter-
native disinfection technologies, such as UV and membrane
filtration, have received considerable attention in recent
years.
Zerovalent iron may help to disinfect water and waste-
water and therefore reduce or eliminate chlorine use. For
example, iron may be incorporated into a sand filter that
precedes coagulation. Such an iron filtration system can pre-
disinfect source water and may replace pre-chlorination,
VOL. 39, NO. 23, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY • 9267
which is practiced by many water treatment facilities. The
corrosion products formed, namely ferrous and ferric ions,
are common coagulants and can improve the efficiency of
coagulation. Pretreatment of source water with zerovalent
iron may enable water treatment plants to meet the
disinfection goal by using lower chlorine dosage or replacing
chlorine with another disinfectant such as chloramines,
especially when viruses are the target agents that determine
the disinfection requirement. For drinking water systems
using membrane processes, zerovalent iron can help to
ensure adequate removal of viruses, which are more difficult
to filter out than other pathogens.
In addition to virus removal, a significant advantage of
zerovalent iron is co-removal of natural organic matter, the
precursor of DBPs. It has been shown that natural organic
matter such as humic acid adsorbs to iron oxides (58, 59).
As source water flows through a medium containing zero-
valent iron, iron oxides would be formed constantly through
iron corrosion and humic acid would be removed from water
continuously. Through removal of viruses and humic ma-
terials, iron may provide an economical option to simulta-
neously reduce risks associated with viral pathogens, dis-
infectants, and DBPs.
For wastewater treatment, zerovalent iron may also help
to remove microbial agents in treated effluent and reduce
chlorine use. These features, along with the ability of iron to
effectively dechlorinate wastewater
(60)
and remove phos-
phate (61), strongly suggest the potential utility of zerovalent
iron for pathogen, chlorine, and nutrient control in waste-
water management.
While we believe this discovery represents an innovative
and potentially cost-effective approach to disinfect water,
much research is needed to understand the capacity and
limitations of zerovalent iron and to develop this process
further for large-scale applications. Among the important
issues are long-term performance of zerovalent iron, its
effectiveness to remove human viruses and other microor-
ganisms such as bacteria and protozoa, and the impact of
water chemistry (e.g., dissolved oxygen, pH, and buffering
capacity) and constituents (humic and fulvic acids, and
dissolved and suspended solids) on the functioning of iron.
In addition, the exact mechanisms involved in adsorption
and inactivation of viruses by zerovalent iron need to be
better understood in order to ensure the robustness of the
process and the safety of iron-disinfected water.
Acknowledgments
This study was supported in part by the United State
Department of Agriculture (USDA) under research grant
USDA-NRI 2001-01235. Partial support from the Delaware
Water Resources Center through its graduate fellowship
program is also acknowledged. We thank Liping Zhang for
her assistance with the batch experiments and Peerless Metal
Powders and Abrasive for providing the iron granules for
this study.
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