Bacterial adhesion to metal oxide-coated surfaces in the presence of silicic acid.

Abstract

This study investigated the effect of silicic acid to the adhesion of Bacillus subtilis to metal oxide-coated surfaces. The first sets of column experiments were conducted under various concentrations of silicic acid. The second and third experiments were performed under various concentrations of sulfate and nitrate to compare the results from silicic acid. Bacterial breakthrough curves were obtained by monitoring effluent, and mass recoveries were quantified from these curves. The results show that, at silicic acid concentrations between 0 and 0.2 mM, bacteria were negatively charged, while the charges of metal oxides were changed from positive to negative. Bacterial adhesion to metal oxide-coated surfaces decreased sharply with increasing silicic acid concentration (bacterial mass recovery increased from 11.5 to 82.2%), as a result of the hindrance effect of silicic acid adsorbed onto metal oxide-coated surfaces. Between 0.2 and 10 mM, both bacteria and metal oxides were negatively charged. Bacterial adhesion remained constant (mass recovery were 80.5 to 82.2%), despite the increasing silicic acid concentration, possibly as a result of the hindrance effect of polymerized silicic acid. That is, the bacterial approach to the metal oxide-coated surfaces could be disturbed through steric hindrance of polymerized silicic acid, which compensates the potential enhancement effect from the electrical double layer compression. The results also illustrate that the effect of silicic acid on bacterial adhesion was greater than those of sulfate and nitrate. This study demonstrates that silicic acid can play a significant role in bacterial interaction with metal oxide-coated surfaces.

Full text

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Bacterial Adhesion to Metal Oxide-Coated
Surfaces in the Presence of Silicic Acid
Seong-Jik Park, Song-Bae Kim*
ABSTRACT:
adhesion of Bacillus subtilis to metal oxide-coated surfaces. The first sets
of column experiments were conducted under various concentrations of
silicic acid. The second and third experiments were performed under
various concentrations of sulfate and nitrate to compare the results from
silicic acid. Bacterial breakthrough curves were obtained by monitoring
effluent, and mass recoveries were quantified from these curves. The
results show that, at silicic acid concentrations between 0 and 0.2 mM,
bacteria were negatively charged, while the charges of metal oxides were
changed from positive to negative. Bacterial adhesion to metal oxide-
coated surfaces decreased sharply with increasing silicic acid concentra-
tion (bacterial mass recovery increased from 11.5 to 82.2%), as a result of
the hindrance effect of silicic acid adsorbed onto metal oxide-coated
surfaces. Between 0.2 and 10 mM, both bacteria and metal oxides were
negatively charged. Bacterial adhesion remained constant (mass recovery
were 80.5 to 82.2%), despite the increasing silicic acid concentration,
possibly as a result of the hindrance effect of polymerized silicic acid. That
is, the bacterial approach to the metal oxide-coated surfaces could be
disturbed through steric hindrance of polymerized silicic acid, which
compensates the potential enhancement effect from the electrical double
layer compression. The results also illustrate that the effect of silicic acid
on bacterial adhesion was greater than those of sulfate and nitrate. This
study demonstrates that silicic acid can play a significant role in bacterial
interaction with metal oxide-coated surfaces. Water Environ. Res., 83, 470
(2011).
This study investigated the effect of silicic acid to the
KEYWORDS:
surfaces, Bacillus subtilis.
Bacterial adhesion, silicic acid, metal oxide-coated
doi:10.2175/106143010X12851009156204
Introduction
Bacterial adhesion to metal oxide-coated surfaces is of
considerable interest, with respect to bacterial transport in aquifers
and their removal in water filtration systems. In geochemically
heterogeneous aquifers, the negatively charged bacteria can attach
favorably to the positively charged metal oxide surfaces (Dong et
al., 2002; Hall et al., 2005; Kim, Park, Lee, and Kim, 2008;
Silliman et al., 2001). The surface-modified granular media with
metal oxides can enhance bacterial removal in water filtration
systems (Kim, Park, Lee, Choi, and Kim, 2008; Lukasik et al.,
1999; Truesdail et al., 1998). Bacterial attachment to granular
porous media can be influenced by the properties of porous media
(i.e., grain size and surface charge), characteristics of bacteria
(i.e., cell size, shape, surface charge, and hydrophobicity), and
solution chemistry (i.e., pH, ionic strength, and solution
composition) (Ams et al., 2004; Fontes et al., 1991; Gannon et
al., 1991; Jiang et al., 2007; Lee et al., 2008; Park and Kim, 2009;
Park et al., 2009).
Oxyanions, such as phosphate, carbonate, sulfate, and nitrate are
widely present in aquatic environments (Appelo and Postma, 1994;
Sposito, 1989). Some oxyanions can be adsorbed on the metal
(aluminum, iron, and manganese) oxides via surface complexation
(Goh etal.,2008;Hiemstra etal.,2004;KatsoyannisandZouboulis,
2002). Oxyanions present in the aqueous phase can affect the
interactions of biocolloids (bacteria and viruses) with metal oxides.
Researchers have investigated the influence of oxyanions on the
adsorption of biocolloids to metal oxides (Foppen et al., 2008; Park
et al., 2009; Ryan et al., 1999; You et al., 2003; Zhuang and Jin,
2003).These studies examined thehindrance effect of phosphate on
the attachment of bacteriophage PRD1 to iron-oxide-coated sand
(Ryan et al., 1999); the adverse effect of phosphate and carbonate
on viral attachment to aluminum-oxide-coated sand (Zhuang and
Jin, 2003); the influence of sulfate, phosphate, and nitrate on the
sorption of bacteriophage MS2 to layered double hydroxides (You
et al., 2003); the effect of phosphate on the adhesion of Escherichia
coli to goethite (Foppen et al., 2008); and the hindrance and
enhancement effects of phosphate on bacterial attachment to iron
oxide depending on the phosphate concentration (Park et al., 2009).
Silicon (Si) is the main element in the Earth’s crust. It is released
into aquatic environments during weathering of silicon-containing
minerals andpresent at concentrations varyingfrom 5 to75 mg/L in
natural water (Iler, 1979). In most natural solutions, dissolved
silicon exists as H4SiO4(monosilicic acid or monosilicate), which
is the dominant monomeric silicon species (Dove and Rimstidt,
1994). At pH 9 and above, negatively charged monomeric silicic
acids, such as H3SiO42and H2SiO422, were formed, as a result of
the deprotonation of H4SiO4. At high silicon concentrations,
H4SiO4condenses to form polymerized species, such as dimeric,
trimeric, tetrameric, or oligomeric silicic acid (Alverez and Sparks,
1985, Applin, 1987; Iler, 1979). The equilibria of H4SiO4 in
aqueous phase are as follows (Hiemstra et al., 2007):
H4SiO4<H3SiO4{zHzlog K~{9:82
ð1Þ
H4SiO4<H2SiO42{z2Hzlog K~{23:27
ð2Þ
2H4SiO4<Si2O2OH
ðÞ5
{zHzzH2O log K~{8:50
ð3Þ
The presence of silicic acid in the aqueous phase can influence
interactions of contaminants with metal oxides. Several research-
Environmental Biocolloid Engineering Laboratory, Department of Rural
Systems Engineering, Seoul National University, Seoul, Korea.
*Kwanak-ro 599, Kwanak-gu, Department of Rural Systems Engineering,
Seoul National University, Seoul 151-921, Korea; e-mail: songbkim@snu.
ac.kr.
470Water Environment Research, Volume 83, Number 5

Page 2

ers have investigated the influence of silicic acid on arsenic
removal by iron and aluminum oxides, showing that silicic acid
significantly reduced arsenic removal by competing for surface
sites and lowering the surface charge of adsorbents (Hsu et al.,
2008; Luxton et al., 2006, 2008; Meng et al., 2000; Roberts et al.,
2004; Swedlund and Webster, 1999; Youngran et al., 2007).
Others also demonstrated that selenite removal using iron-coated
granular activated carbons was affected by silicic acid (Zhang et
al., 2008). Silicic acid may play an important role in bacterial
adhesion to metal-oxide-coated surfaces. To our knowledge,
however, no experimental studies have been performed on this
subject.
Therefore, bacterial adhesion to metal-oxide-coated surfaces
was investigated in the presence of silicic acid. The first sets of
column experiments were conducted with Bacillus subtilis under
various concentrations of silicic acid. The second and third
experiments also were performed under various concentrations of
sulfate and nitrate to compare the results from silicic acid.
Bacterial breakthrough curves were obtained by monitoring
effluent, and mass recoveries were quantified from these curves.
Materials and Methods
Bacteria and Culture Preparation.
obtained from the Korea Culture Center for Microorganisms
(Seoul, Korea) was used in the experiment. All glassware and
materials used in this study were sterilized by autoclaving at
121uC and 17.6 psi for 20 minutes to prevent any interference by
other microorganisms. Initially, the freeze-dried bacteria were
revived in 250-mL Erlenmeyer flasks containing 100 mL of LB
medium (10 g tryptone, 5 g yeast extract, 5 g sodium chloride
[NaCl] in 1 L of deionized water at pH 7.0) over a period of
84 hours at 30uC. Approximately 1 mL of culture then was
transferred to a volume of 500 mL LB broth, and the bacteria were
incubated over a period of 84 hours at 30uC. The suspension was
centrifuged at 4uC and 10 000 rpm for 15 minutes. The
supernatant was removed and replaced with deionized water to
prevent bacterial growth. Diluted bacteria were centrifuged again
under the same conditions, washed three times with deionized
water, and resuspended in solution to an optical density of 0.5 at
600 nm (OD600).
The bacterial cell size was determined by taking cell images
with transmission electron microscopy (JEM 1010, Jeol, Japan).
The images were imported into an image-processing program
(Image-Pro Plus, Media Cybernetics Inc., Bethesda, Maryland)
and analyzed. The cell length and width of B. subtilis were 1.67 6
0.31 mm and 0.77 6 0.07 mm, respectively, which is equivalent to
a diameter of 1.18 6 0.10 mm. The net surface electrostatic
characteristics of cells were analyzed with an electrophoretic
light-scattering spectrophotometer (ELS-8000, Otsuka Electron-
ics, Japan). Electrophoretic mobility was determined for the
bacterial surface (pH 5 6.8, temperature 5 25uC, and ionic
strength < 0 mM) and converted to zeta potentials using the
Smoluchowski equation (231.9 6 3.2 mV). The hydrophobicity
of bacteria was determined by the microbial adhesion to
hydrocarbons (MATH) with n-hexadecane (Merck, Darmstadt,
Germany) as the assay hydrocarbon (Rosenberg et al., 1980). The
hydrophobicity of B. subtilis was determined to be 3.4 6 1.3
(hydrophilic).
Porous Media.
Quartz sand (Jumunjin Silica, Gangneung,
Korea) was used to prepare the metal-oxide-coated sand.
B. subtilis ATCC 6633
Mechanical sieving was conducted with US Standard Sieves
(Dong Ah Testing Machine Co., Seoul, Korea) Nos. 35 and 10.
Sand fractions with a grain size of 0.5 to 2.0 mm and a mean
diameter of 1.0 mm were used in the experiments. Before use,
sand was washed twice using deionized water to remove
impurities on the surface, and wet sand was autoclaved at
121uC and 17.6 psi for 20 minutes, cooled to room temperature
(approximately 20 to 25uC), and oven-dried at 105uC for 1 to
2 days. For preparation of the metal-oxide-coated sand,
AlCl3N6H2O (2.2g) and FeCl3N6H2O (2.75g) were dissolved in
deionized water (100 mL), and the solution pH was adjusted with
6 N sodium hydroxide (NaOH). The quartz sand (200 g) was
added to the AlCl3N6H2O and FeCl3N6H2O solution and then
mixed in a rotary evaporator (90uC, 80 rpm, for 20 minutes) to
remove water in the suspension by heating (Hahnvapor, Hahnshin
Scientific Co., Buchon, Korea). The coated sand was dried at
150uC for 6 hours, washed with deionized water, and then dried
again at the same conditions. Field emission scanning electron
microscope (FESEM) analysis with energy dispersive X-ray
spectrometer (EDS) analysis was performed using a scanning
electron microscope (Supra 55VP; Carl Zeiss, Oberkochen,
Germany) to examine the presence of aluminum and iron on the
coated sand. The FESEM image and EDS pattern of the coated
sand are shown in Figure 1. In addition, SEM image and the EDS
pattern of quartz sand were provided elsewhere (Kim, Park, Lee,
Choi, and Kim, 2008).
Figure 1—Metal-oxide-coated sand: (a) FESEM (bar =
1 m mm), and (b) pattern of EDS.
Park and Kim
May 2011 471

Page 3

Column Experiments.
were conducted using a Plexiglas column (inner diameter 5
2.5 cm, height 5 10 cm) packed with metal-oxide-coated sands
(mass of medium 5 78.0 6 0.8 g). A column was packed for each
experiment by the tap-fill method to attain a bulk density of 1.589
6 0.017 g cm23and a porosity of 0.401 6 0.007. The first set of
column experiments (1a to 5b) was performed under various
concentrations of silicic acid (0 to 10 mM). The pH of silicic acid
solution was in the range 6.38 to 11.36. Silicic acid solution was
prepared from sodium-based chemicals, including Na2SiO3N9H2O
(sodium metasilicate nonahydrate). The column was connected to
a high-pressure liquid chromatography pump (Series II, Scientific
Systems, Inc., State College, Pennsylvania) operating at a rate of
0.35 mL/min. Before bacterial injection, the packed column was
flushed upward with 15 pore volumes of silicic acid solution to
achieve a steady-state flow condition. The bacteria (0.5 OD600)
were introduced downward into the column for 60 minutes with
silicic acid solution. After completing bacterial injection, the same
solution was introduced again to the column. Effluent samples
were collected using an auto collector (Retriever 500, Teledyne,
Lincoln, Nebraska) at regular intervals. Effluents were analyzed
for bacterial concentration. Bacterial concentration was deter-
mined by measuring the optical density of the effluent using a
UV-visible spectrophotometer (Helios, Thermo, Cambridge,
United Kingdom) at 600 nm (OD600). The pH and electrical
conductivity of solutions were measured with a pH probe
(9107BN, Orion, Beverly, Massachusetts) and an electrical
conductivity probe (815PDL, Istek, Seoul, Korea), respectively.
To compare the results from the first experiments, the second (6a
to 9b) and third (10a to 12b) experiments were performed under
various concentrations (0.1 to 10 mM) of sulfate and nitrate
solutions. The solutions also were prepared from sodium-based
chemicals, including sodium sulfate (Na2SO4) and sodium nitrate
(NaNO3). The pH values of the sulfate and nitrate solutions were
5.58 to 5.86 and 6.20 to 6.34, respectively. The bacterial mass
recoveries (Mr) in the effluent were quantified by the following
equation:
0
B
Three sets of column experiments
Mr~
R?
C0t0
0
Cdt
B
@
1
C
C
A|100 (%)
ð4Þ
Where
C 5 bacterial concentration at the effluent (mg/L),
C05 initial concentration of bacteria (mg/L), and
t05 duration of bacteria injection (injection time) (minutes).
The effective ionic strength (Ie) of the solution was calculated
from the stoichiometric ionic strength (I) using the following
expression (Langmuir, 1997):
I~1
2
X
(cimiz2
i)
ð5Þ
Where
ci5 activity coefficient of ion i,
mi5 concentration of ion i (mM), and
zi5 charge of ion i.
The activity coefficient of ion i is calculated by the Debye-
Hu ¨ckel equation, as follows (Langmuir, 1997):
logci~{Az2
i
ffiffi
I
p
p
1zBai
ffiffi
I
ð6Þ
Where
ai5 ion size parameter.
At 25uC, A and B, temperature-dependent parameters, corre-
spond to 0.5092 and 0.3293, respectively. The experimental
conditions and bacterial mass recoveries are summarized in
Table 1. All of the experiments were performed in duplicate.
Calculation of DLVO Interaction.
Verwey-Overbeek (DLVO) theory is used to calculate interaction
energies between bacteria and collector surfaces. The total
interaction energy in the DLVO theory can be calculated from
the sum of the London van der Waals attraction and electrostatic
double-layer repulsion (Redman et al., 2004; Truesdail et al.,
1998). Sphere-plate geometry was assumed when the interaction
energies between the bacteria and media surfaces were calculated.
The repulsive electrostatic double-layer interaction energy (wEDL)
was calculated using the following expression (Hogg et al., 1966):
?
?
Where
The Derjaguin-Landan-
wEDL~pe0erap 2QpQcln1zexp {kd
ð
ð
Þ
Þ
1{exp {kd
??
z Q2
pzQ2
c
?
ln 1{exp {2kd
½ðÞ?g
ð7Þ
e05 dielectric permittivity in a vacuum (F/m),
er5 relative dielectric permittivity of water (2),
ap5 bacterial radius (m),
d 5 separation distance between the bacterium and the
collector surface (m),
k 5 inverse Debye length (1/m), and
Qpand Qc5 surface potentials of the bacterial cell and collector
(mV).
The retarded van der Waals attractive interaction energy
(wVDW) was determined by the following expression (Gregory,
1981; Redman et al., 2004):
wVDW~{Aap
6d
1z14d
l
??{1
ð8Þ
Where
A 5 Hamaker constant of the interacting media (bacteria-water-
collector surface), and
l 5 characteristic wavelength of the dielectric (assumed to be
100 nm).
The value of 6.5 3 10221J was used for the Hamaker constant.
Results and Discussion
Bacterial Breakthrough Curves and Mass Recoveries.
bacterial breakthrough curves (BTCs) obtained from the column
experiments with metal-oxide-coated sand under various concen-
trations of silicic acid are presented in Figure 2a. The BTCs had
well-defined single peaks and can be divided into three groups,
depending on the relative peak concentrations. The first group
(experiments 1a and 1b) had relative peak concentrations ranging
from 0.124 to 0.127. This group had an influent silicic acid
concentration of 0.0 mM, with mass recoveries ranging from 11.3
The
Park and Kim
472 Water Environment Research, Volume 83, Number 5

Page 4

to 11.7%. The second group (experiments 2a and 2b) had peak
concentrations of 0.543 to 0.544. This group had a silicic acid
concentration of 0.1 mM, with mass recoveries of 55.8 to 62.7%.
The third group (experiments 3a to 5b) had peak concentrations of
0.667 to 0.746. This group had silicic acid concentrations from 0.2
to 10 mM, with mass recoveries ranging from 79.3 to 83.4%
(Table 1).
The bacterial BTCs from the column experiments under various
concentrations of sulfate and nitrate are shown in Figures 2b and
2c, respectively. The BTCs also had well-defined single peaks.
Depending on the relative peak concentrations, the BTCs in
sulfate can be divided into two groups. The first group
(experiments 6a to 8b) had relative peak concentrations ranging
from 0.224 to 0.249. This group had influent sulfate concentra-
tions from 0.1 to 1.0 mM, with mass recoveries ranging from 22.2
to 25.2%. The second group (experiments 9a and 9b) had peak
concentrations of 0.341 to 0.351. This group had a sulfate
concentration of 10 mM, with mass recoveries of 34.9 to 35.5%.
In addition, the BTCs in nitrate (experiments 10a to 12b) had
relative peak concentrations from 0.087 to 0.115, with mass
recoveries of 9.0 to 11.1% (Table 1).
Effect of Silicic acid on Bacterial Adhesion.
silicic acid on bacterial adhesion to metal-oxide-coated surfaces
can be observed by plotting bacterial mass recovery as a function
of silicic acid concentration (Figure 3). The plot can be divided
into two phases. In the first phase, where the silicic acid
concentrations were between 0 and 0.2 mM, the mass recovery
increased sharply with increasing silicic acid concentration. In the
second phase, where the silicic acid concentrations were between
0.2 and 10 mM, however, the mass recoveries remained constant
with increasing silicic acid concentration.
The effect of
The phenomenon observed in the first phase can be attributed to
the hindrance effect of silicic acid on bacterial adhesion to the
metal-oxide-coated surfaces. It is known that silicic acid adsorbs
to metal oxide surfaces via inner-sphere complexes (Doelsch et
al., 2001; Hansen et al., 1994; Vempati et al., 1990). According to
Houston et al. (2008), who have applied nuclear magnetic
resonance techniques to silicon adsorption experiments, silicon
adsorbed strongly to aluminum oxides, forming aluminosilicate
via inner-sphere complexes. Other studies (Doelsch et al., 2003;
Luxton et al., 2006; Wonisch et al., 2008) also have demonstrated
that H4SiO4had a high affinity for iron (hydr)oxide surfaces,
forming inner-sphere complexes through the ligand-exchange
mechanism with surface hydroxyl groups. In our experiments,
silicic acid introduced to the coated sand column before and with
bacterial injection could occupy the surface sites available for
bacterial adhesion. In addition, silicic acid adsorbed to the
surfaces could induce the positively charged surface sites to
become less positive and even negative. Note that the zeta
potentials of metal oxides decreased from 21.9 to 223.8 mV with
increasing silicic acid concentrations from 0 to 0.2 mM
(Figure 4). Therefore, the electrostatic interaction between
negatively charged bacteria and silicic acid-adsorbed surfaces
could become less attractive and even repulsive, causing a
decrease in bacterial adhesion.
In the second phase, both bacteria and metal oxides were
negatively charged (Figure 4). According to the DLVO theory, the
increase in the ionic concentration of the carrying solution leads to
a decrease in the thickness of the electrical double layers and in
the average distance between surfaces carrying like-charges,
resulting in the reduction of electrostatic repulsion between
bacteria and surfaces and the promotion of bacterial adhesion. In
Table 1—Column experimental conditions and results for bacteria under various concentrations of silicic acid,
sulfate, and nitrate.
ExperimentSolution
Concentration
(mM)pH
Electrical Conductivity
(m mS/cm)
Ionic strength
(mM)
Mass recovery
(%)
1a
1b
2a
2b
3a
3b
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
9a
9b
10a
10b
11a
11b
12a
12b
Deionized water
Deionized water
Na2SiO3
Na2SiO3
Na2SiO3
Na2SiO3
Na2SiO3
Na2SiO3
Na2SiO3
Na2SiO3
Na2SO4
Na2SO4
Na2SO4
Na2SO4
Na2SO4
Na2SO4
Na2SO4
Na2SO4
NaNO3
NaNO3
NaNO3
NaNO3
NaNO3
NaNO3
0
0
0.1
0.1
0.2
0.2
1
1
10
10
0.1
0.1
0.2
0.2
1
1
10
10
0.1
0.1
1
1
10
10
6.38
6.38
7.15
7.15
9.72
9.72
10.51
10.44
11.36
11.36
5.76
5.76
5.65
5.65
5.58
5.58
5.86
5.86
6.20
6.20
6.34
6.34
6.29
6.29
5.0
4.8
22.5
22.5
42.5
42.5
280.4
292.7
3240.0
3220.0
33.4
32.2
60.0
60.0
279.0
279.0
2300.0
2300.0
22.0
21.9
129.1
129.1
1143.0
1143.0
0.0
0.0
0.3
0.3
0.6
0.6
2.5
2.5
18.9
18.9
0.3
0.3
0.6
0.6
2.5
2.5
18.8
18.8
0.1
0.1
1.0
1.0
9.0
9.0
11.3
11.7
55.8
62.7
80.9
83.4
79.9
81.0
79.3
82.1
22.2
23.7
24.1
25.2
22.9
24.4
34.9
35.5
11.0
11.1
10.1
10.7
9.0
11.0
Park and Kim
May 2011473

Page 5

the second phase, however, the bacterial adhesion remained
constant, despite the increasing silicic acid concentration, which
was not consistent with the DLVO theory. As shown in Figure 5,
the interaction energy barrier between the bacteria and the
negatively charged metal oxide surface became lower with the
increasing silicic acid concentration, from 0.2 to 10 mM.
However, the calculated interaction energies were not consistent
with our result, showing that bacterial attachment was not
enhanced at high silicic acid concentrations (.1 mM). This
phenomenon can be ascribed to the hindrance effect of
polymerized silicic acid to bacterial adhesion. The polymerization
of H4SiO4has been reported by several researchers (Alverez and
Sparks, 1985; Applin, 1987; Bo ¨schel et al., 2003), who have
shown that silicic acid underwent polymerization at relatively low
concentrations (.1.1 mM). The size of polymerized silicic acid
ranged from 1.8 to 2.5 nm (Dietzel and Usdowski, 1995; Doelsch
et al., 2003; Iler, 1979) and up to radii of 75 to 85 nm (Bo ¨schel et
al., 2003). In our experiments, the polymerized silicic acid can
hinder the approach of bacteria to the attractive energy located a
few nanometers away from the metal-oxide-coated surfaces,
compensating for the potential enhancement effect from the
electrical double-layer compression. That is, bacterial adhesion
could not be enhanced, despite the increasing ionic strength, as a
result of the steric hindrance of polymerized silicic acid.
Comparison with Effects of Sulfate and Nitrate.
of silicic acid on bacterial adhesion to metal-oxide-coated surfaces
The effect
Figure 2—Breakthrough curves of Bacillus subtilis
obtained from column experiments in metal-oxide-
coated sand under various concentrations of (a) silicic
acid (1a and 1b = 0 mM, 2a and 2b = 0.1 mM, 3a and 3b =
0.2 mM, 4a and 4b = 1 mM, and 5a and 5b = 10 mM); (b)
sulfate (6a and 6b = 0.1 mM, 7a and 7b = 0.2 mM, 8a and
8b = 1 mM, and 9a and 9b = 10 mM); and (c) nitrate (10a
and 10b = 0.1 mM, 11a and 11b = 1 mM, and 12a and 12b
= 10 mM).
Figure 3—Bacterial mass recoveries in metal-oxide-
coated sand under various concentrations of silicic
acid, sulfate, and nitrate.
Figure 4—Zeta potentials of bacteria and metal oxides
under various concentrations of (a) silicic acid, (b)
sulfate, and (c) nitrate.
Park and Kim
474 Water Environment Research, Volume 83, Number 5