Int. J. Environ. Sci. Tech., 8 (2), 237-244, Spring 2011
ISSN: 1735-1472
© IRSEN, CEERS, IAU
A. Tirgar et al.
Removal of airborne hexavalent chromium using alginate as a
biosorbent
1
1
A. Tirgar; 2*F. Golbabaei; 3J. Hamedi; 4K. Nourijelyani
Department of Social Medicine, School of Medicine, Babol University of Medical Sciences, Babol, Iran
2
Department of Occupational Health, School of Public Health and Institute of Public Health Research, Tehran
University of Medical Sciences, Tehran, Iran
3
Microbial Biotechnology Laboratory, School of Biology, College of Science, University of Tehran, Tehran, Iran
4
Department of Epidemiology and Biostatistics, School of Public Health and Institute of Public Health Research,
Tehran University of Medical Sciences, Tehran, Iran
Received 5 July 2010;
revised 25 December 2010;
accepted 6 January 2011;
available online 1 March 2011
ABSTRACT: Airborne hexavalent chromium has been classified as a human respiratory carcinogen and long term
exposure has been known to cause ulceration and perforation of the nasal septum, bronchitis, asthma, and liver and
kidney damage. Chromium electroplating plants are the major sources of atmospheric chromium and packed-bed
scrubbers are the common control devices used to reduce emission of chromic acid mist from electroplating bathes.
The feasibility of a new method to remove this pollutant using alginate beads as a biomass derivative was investigated
by one factor at a time approach and Taguchi experimental design. Polluted air with different chromium mist
concentrations (10-5000 µg/m3) was contacted to alginate beads (3.3-20 g/L), floating in distilled water with adjusted
pH (3-7), using an impinger at different temperatures (20 and 35oC), and various velocities (1.2 and 2.4 m/s).
Although there were no statistical significant differences between factor levels, the higher ions removal efficiencies
were achieved at lower levels of air velocities, pollution concentrations, higher levels of pHs, temperatures, and
sorbent concentrations.
Keywords: Alginat; Biosorbent; Chromium mist; Control; Electroplating; Novel system
INTRODUCTION
Hexavalent chromium, Cr (VI), has been classified
as a human respiratory carcinogen and allergen
(Ashley et al., 2003; Guertin et al., 2005; Hara et al.
2010; Nickens et al., 2010). Long term exposure to
airborne Cr (VI) has been known to cause ulceration
and perforation of the nasal septum, bronchitis,
asthma, and liver and kidney damages in exposed
workers (Kumar et al., 2005; Costa and klein, 2006).
Cr (VI) emission is associated with a number of
industrial sources including metal plating, tanning,
chr omat e ore processi ng and spray painting
operation; combustion sources such as automobiles
and incinerators (Ashley et al., 2003; Park et al., 2004;
Babel and Opiso, 2007; Pandey et al., 2010). Thus,
controlling of chromium emission is an important issue
*Corresponding Author Email: gol128@sphtums.com
Tel.: +9821 6646 5404; Fax: +9821 6646 2267
in both industrial hygiene and environmental
protection (Nwachukwu et al., 2010).
Chromium electroplating plants are the major
sources of atmospheric chromium (Kuo and Wang,
2002; OSHA 2006; Tirgar et al., 2007), and Packed-Bed
Scrubbers (PBS) are the common controlling devices
used to reduce emission of chromic acid mist from
electroplating bathes. Such industries should spend
considerable money for scrubber wastewater treatment.
Treatment of industrial effluents having less than about
0.1 g/L of dissolved metal ions by conventional
processes presents several disadvantage, such as high
operational cost, low efficiency, and generation of solid
waste-often toxic, that may require safety disposal
protocols or even further treatment (Ibanez and Umetsu,
2002; Aliabadi et al., 2006; Abdel-Ghani and Elchaghaby,
2007; Goyal et al., 2008; Nameni et al., 2008).
A. Tirgar et al.
The capacity of biological entities to uptake heavy
metal ions from dilute aqueous solutions is well
documented and it can be considered as an alternative
to be used under conditions where conventional
processes lost competitiveness (Park and Park, 2006;
Rafati et al., 2010; Sethuraman and Balasubramanian,
2010; Vinodhini and Das, 2010). The biological treatment
could be an alternative method to clean-up industrial
wastewaters containing heavy metals. However, these
processes are very sensitive to the characteristics of
the effluent, as temperature, pH and chemical
composition.
The use of dead biomass and biomass derivatives
(biosorbent materials) for removal of heavy metals from
aqueous solutions has been widely studied in recent
years. These systems are less expensive than the
traditional physicochemical processes. They do not
need nutrients and are resistant to the physicalchemical properties of heavy metal solutions (Araujo
and Teixeira, 1997).
Alginate, an exopolymer extracted mainly from
brown seaweeds, has been used for a long time in
several industrial applications. Among recent
application, alginate has been used as a cell
immobilization material and as a biosorbent material
for removal of divalent heavy metals, such as Cu2+,
Co2+, UO2+ and Zn2+ from aqueous solutions. Alginate
showed good metal sorption efficiency (Araujo and
Teixeira, 1997; Veglio et al., 2002).
There are few reports about airborne heavy metal
removal using a biomass derivative. Thus, in this
project, alginate beads efficiency (as a biosorbent) for
airborne Cr(VI) removal was studied in Public Health
School and Public Health Research Institute , Tehran
University of Medical Sciences, Iran (2006-7). The aim
of this work was to investigate the feasibility of
developing a method to remove airborne Cr (VI) mist.
MATERIALS AND METHODS
Airborne Cr (VI) generation
The predominant constituent in chromiumelectroplating bath is CrO3, although these might be
amount of additives (usually 1 % H2SO4) used in shop
(Kuo and Wang, 1999). Thus, an electroplating bath
was prepared as the source of Cr (VI) mist emission in
pilot scale (Fig. 1). Detail of this system which equipped
with a special sampling chamber and had a homogenous
airborne Cr (VI) atmosphere, has been reported in our
previous paper (Tirgar et al., 2006a).
Chemicals
Sodium alginate [Sigma-Aldrich Co.] was used. All
the other chemicals were analytical grade and
purchased from Merck Co.
Beads preparation
Calcium alginate beads were prepared by dropping
a 3 % (w/v) sodium alginate aqueous solution to a
I
H
B
C
G
A
D
F
E
A: Rectifier, B: Cathode, C: Anode, D: Electroplating bath, E: Anti acid pump, F and G: Valves,
H: Plexiglas case (sampling chamber) I: Hood
Fig. 1 : Set up of the mist generation system and sampling chamber
238
Int. J. Environ. Sci. Tech.,
8 (2),et237-244,
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A. Tirgar
al.
stirred 2 % (w/v) CaCl2 solution. Beads were stirred in
CaCl2 solution on the orbital shaker at 250 rpm for 24
hours. Then, they were washed three times with distilled
water and kept in a 2 % CaCl 2 solution at 4 ºC.
Immediately before use, the calcium alginate beads were
washed again three times with distilled water and the
excess water was absorbed on paper filter (Araujo and
Teixeira, 1997; Göksungur, et al., 2003).
filter cassette (part B) containing a 5.0 µm pore size
polyvinyl chloride (PVC) membrane filter (MSA,
Pittsburgh, USA). C) a personal sampling pump
(Model 224-PCXR3; SKC, Blandford Forum, UK)
calibrated for air flow rate of 1 or 2.0 ± 0.1 L/min.
Sampling train without biosorbent
Sampling train without biosorbent (Water train)
was completely the same as biosorbent train except
Midget Impinger contained 15 mL only water with
adjusted similar pH. Sampling duration for all samples
were the same, i.e. 60 min.
The difference between chromium concentration
in biosorbent train and water train was considered as
alginate -bounded chromium. The percent of adsorbed
chromium ions was evaluated as [(CW-CB)/CW] ×100.
CW and CB are the concentration of the metal ions in
the water and biosorbent solution (mg/L) after
sampling, respectively.
Bead characterization
The mean diameter of beads was determined in 10
groups of 50 alginate beads using a micrometer
(2.87±0.06 mm). The mean weight of the beads was
determined using 10 samples of 20 beads (14.81±0.71
mg). The solid content of the alginate beads were
weighted before and after drying [7.04±0.32 % (w/w)].
The biosorbent was dried in an oven at 60 ºC over night
(for 24 h).
Metal binding capacity
In order to find out optimum removal condition and
Cr (VI) binding capacity, two sampling trains were used
simultaneously (Fig. 2).
Optimization of biosorption conditions by one factor
at a time approach
Effect of pH on the biosorption rate was
investigated in the pH range 3.0-7.0. The pH was
adjusted with 0.1 M HNO3 or NaOH at the beginning
of the experiments. The effect of pollutant
concentration was studied at three different levels
(low, medium, and high) between 10-5000 µg/m3. Also
th e effect of biosor bent concentr at ion was
determined at three different levels (3.3, 10, and 20
mg/mL).
Sampling train with biosorbent
Sampling train with biosorbent (Biosorbent train)
consisted of the following compartments: A) a special
and standard air sampler named Midget Impinger (SKC,
Blandford Forum, UK) containing alginate beads and
15 mL water with adjusted pH in thermostatically
controlled water bath (Fig. 2). B) a 37-mm polystyrene
Homogenous atmosphere
B
C
A
B
A: Air sampler
B: Polystyrene cassette
C: Personal sampling Pump
C
Biosorbent
train
A
Fig. 2: Set up of the sampling trains
239
Water
train
Removal of airborne hexavalent chromium
A. Tirgar et al.
optimization. The results presented below represent
the mean values of at least three replications.
Optimization of biosorption conditions by Taguchi
method
To study the effects of important parameters on
airborne Cr (VI) removal, five factors and two levels for
each factor were studied by L16 (25) Taguchi orthogonal
array (Table 1) (Roy, 2001). The analyses of data were
done by Qualitek-4 statistical software.
Secondary optimization
Table 2 shows the descriptive data and the ANOVA
test results for 64(16 runs with 4 replications) collected
samples under the Taguchi experimental design. As
indicated, there is no significant difference between
the two levels of the main factors on Cr (VI) removal
under the optimized levels (P>0.05), also, there were
no significant interactions between factors.
Analytical method
The metal content in all experiments were measured
using a Shimadzu AA 680 non-flame atomic absorption
spectrometer. The instrument response was periodically
checked with known standards. A calibration curve
obtained with a correlation coefficient was 0.98 or
greater. The samples were read three times and the mean
value, as well as the relative standard deviation was
computed. The samples were diluted as required to
remain with in the calibration linear range. The 357.7 nm
wavelength was used for chromium ions studied
(Cornelis, 1994).
Effect of pH
According to Park et al., 2006. Cr (VI) can be removed
from the aqueous solution by nonliving biomass
through two mechanisms. In mechanism I (direct
reduction), Cr (VI) is directly reduced to Cr (III) in the
aqueous phase by contact with electron-donor groups
of the biomass. However, reduction could occur only
under strongly acidic conditions (pH<2.5). Mechanism
II (indirect reduction) consist of three steps: 1. The
binding of anionic Cr (VI) ion species to positively
charged groups present on the biomass surface; 2.
The reduction of Cr (VI) to Cr (III) by adjacent electrondonor groups; 3. The release of the Cr (III) ions into
the aqueous phase due to electronic repulsion between
the positively charged groups and Cr (III) ions or Crbinding. If there is a small number of an electron-donor
group in the biomass or protons in the aqueous phase,
the chromium bound on the biomass can remain in
hexavalent state. Therefore, a portion of mechanisms I
RESULTS AND DISCUSSION
Primary optimization
Screening test results on pH, pollutant and sorbent
concentrations using one factor at a time experimental
design was presented in Fig. 3. The plots show the
highest Cr (VI) removal obtained at pH 5, low pollution
and medium sorbent concentrations. Other conditions
including pH 6, medium pollutant and high sorbent
concentration in the second preference of removal
efficiency is considered to be used for secondary
Run
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Table 1: Removal percent of Cr(VI) by calcium alginate at different runs according L16 orthogonal array
Air Velocity (m/s)
Alginate (g/L)
pH
Temperature (°C)
Cr6+ (µg/m3)
Cr 6+ removal (%)
1.12
10
5
20
<50
36.90
1.12
10
5
35
50.500
32.35
1.12
10
6
20
50.500
41.67
1.12
10
6
35
<50
39.94
1.12
20
5
20
50.500
39.64
1.12
20
5
35
<50
35.92
1.12
20
6
20
<50
50.35
1.12
20
6
35
50.500
44.71
2.24
10
5
20
50.500
42.57
2.24
10
5
35
<50
44.00
2.24
10
6
20
<50
34.00
2.24
10
6
35
50.500
54.09
2.24
20
5
20
<50
30.74
2.24
20
5
35
50.500
36.63
2.24
20
6
20
50.500
34.60
2.24
20
6
35
<50
29.66
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8 (2),et237-244,
Spring 2011
A. Tirgar
al.
is in the ionic form CrOH2+ (and a trace amount of
Cr(OH)45+ ) (Araujo and Teixeira, 1997).
Pandy et al. (2003) reported, adsorptions of
chromium by the calcium alginate beads suggest that
the functional group present in calcium alginate are
the carboxyl groups of gulucronate and mannurate
residues (Pandey et al., 2003). When the pH is higher
than 3-4, the carboxyl groups are deportonated and
40
10
10
0
0
3
6
5
4
removal (%)
20
7
pH
30
20
+6
+6
20
40
30
Cr
removal (%)
30
Cr
Cr +6
removal (%)
and II is dependent on the biosorption system, such
as solution pH, temperature, biomass and Cr (VI)
concentrations (Park et al., 2006).
According to the speciation diagram of Cr (III)
complexes in aqueous solutions, from Leyva-Ramos et
al. (1995), at pH 2 the molar percentage of Cr3+ is 98 %
of the total amount of chromium in solution , while at
pH 4 this value decreases to about 40 % and almost 60 %
Low
0
High
Medium
10
Low
Medium
High
Sorbent concentration
Pollution concentration
Fig. 3 Screening test results as a function of pH, pollution, and sorbent concentrations at 20oC and air velocity of 2.24 m/s
6+
Cr removal (%)
pH value
Sorbent con.
Temprature
Pollution con.
Air velocity
50
35
1
2
1
2
1
2
1
2
1
2
Factor levels
Fig. 4: Effect of air velocity, solution pH, sorbent concentration, pollution concentration, and temperature levels on Cr (VI)
removal by alginate beads
Table 2: Descriptive data for 64 samples collected under Taguchi experimental design and its statistical test result
Factor
pH
Temperature
Sorbent concentration
Pollution concentration
Air velocity
Levels
Cr (V I) rem oval (% )
SD
P-Value
1
2
1
2
1
2
1
2
1
2
38.43
39.29
37.31
40.41
36.97
40.75
40.32
37.41
39.44
38.28
6.20
7.89
6.86
6.96
4.51
8.51
6.93
6.93
5.79
8.17
0.83
241
0.46
0.36
0.49
0.78
A. Tirgar et al.
left with negative charge. Therefore, at pHs above 3-4,
the negatively charged carboxylate group may attract
the positively charged chromium ions consequently
binding and removing the Cr (VI) ions from solution.
At pHs lower than 3-4, the carboxyl groups become
porotonated and no longer attract the positively
charged chrome ions (Gardea-Torresdey et al., 1996).
Araujo and Teixiera studied the effect of pH on
metal adsorption at 2-4 and reported that there was a
higher trivalent chromium adsorbed at pH 4 (Araujo
and Teixeira, 1997).
Gardea-Torresdey et al. (2002) reported the same
result. They showed that the unmodified alfalfa biomass
(this biomaterial binds predominantly through carboxyl
ligands) and carboxyl ion exchange resin (WTO1S)
displayed similar pH dependent trends and the optimal
binding pH for these biosorbents was between 5 and 6
(Gardea-Torresdey et al., 2002) (Fig . 4).
of Cr (III) on calcium alginate beads (Araujo and Teixeira,
1997), while our results and the results reported by
Kacar et al. (2002) indicated that adsorption of Cr(VI)
ions on calcium alginate beads was not significantly
dependent on temperature at range 15-35 ºC (Kacer et
al., 2002). In nature, biosorption is largely physicochemical and an energy-independent mechanism,
therefore, it is less likely affected by temperature.
Effect of air pollution concentration
Airborne Cr (VI) with different concentrations (<50
and 50-500 µg/m3) were treated to evaluate the influence
of pollution concentration on sorption behavior of
alginate beads.
As depicted in Fig. 4, although an increase in Cr (VI)
concentration had no drastic effect on removal
efficiency (40.32±6.93 vs. 37.41±6.93), higher adsorption
yields were observed at lower concentration of metal
ions. Similar trend has been reported by other
researchers (Chand et al., 1994; Kacer et al., 2002;
Ahalya et al., 2005; Tirgar et al., 2006b ).
Effect of sorbent concentration
As Table 2 and Fig. 4 show, increasing alginate
concentration between 3.3 to 20 mg/mL enhanced Cr (VI)
removal, however, there is no significant difference
between the chromium removal in concentrations 10
and 20 mg/mL (P>0.05). Chand et al. reported that, higher
sorbent concentration gave the greater Cr (VI) removal
percent. However, up to a certain level and beyond
that, more or less constant removal was observed
(Chand et al., 1994).
Results in general, have revealed that the Cr (VI)
removal from air is not strongly affected by the sorbent
concentration at the range of 10 and 20 mg/mL.
Effect of air velocity
In order to investigate the effect of contact time and
agitation rate on Cr (VI) removal, polluted air samples
were passed through the sorbent medium with different
air velocity. Fig. 4 and Table 2 show that Cr (VI) uptake
decrease with the increase in air velocity, however,
there is no statistical significant difference between Cr
(VI) uptake at 1.12 and 2.24 m/s (P>0.05). Consequently,
it can be concluded that, however agitation facilitates
a proper contact between the metal ions in solution
and biomass binding sites and thereby it promotes
effective transfer of sorbate ions to the sorbent sites
(Ahalya et al., 2005), higher air velocity leads to
reduction of contact time (passing faster through
sorbent medium) and less adsorption.
Effect of temperature
The temperature of the adsorption medium could be
important for energy demands mechanisms in metal
biosorption. Energy-independent mechanisms are less
likely to be affected by temperature since the processes
responsible for biosorption are largely physicochemical in nature (Kacer et al., 2002).
As it shown in Table 2 and Fig. 4, maximum binding
capacity values were mostly at 35 ºC but the ANOVA
test result shows no statistical significant difference
between the two levels (40.41±6.96 vs. 37.31± 6.86)
(P>0.05). Thus, the biosorption of Cr (VI) by alginate
appeared to be temperature independent in the range
of 20 to 35 ºC.
Araujo and Teixeira reported that the higher
temperature (in the range of 10 to 27) favors the sorption
CONCLUSION
It can be concluded that, biosorption is an efficient
process for the removal of Cr (VI) mist in a wide range
of pollution concentration. Obviously, higher removal
efficiency could be obtainable, using suitable alginate
producer biomass or alginate derivatives.
Based on our experiments, the optimum condition
with maximum yield for removal of Cr (VI) by alginate
beads are as follows:
Lower levels of air velocity, and pollution
concentration,
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8 (2),
237-244, Spring 2011
Tirgar
et al.
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Higher levels of pH sorbent concentration and
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Also, it was shown that proposed airborne Cr (VI)
removal system can work in broad range of working
conditions that makes it more feasible at industrial scale.
ACKNOWLEDGEMENTS
Special thanks to School of Public Health and Public
Health Research Institute, Tehran University of Medical
Sciences for providing funding to this research (Grant
Number 2655). Likewise, to Mrs. P. Jamee for her
valuable assistance in samples analyses.
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AUTHOR (S) BIOSKETCHES
Tirgar, A., MSPH., Ph.D., Assistant professor, Department of Social Medicine, School of Medicine, Babol University of Medical Sciences,
Babol, Iran. Email: a_tirgar@yahoo.com
Golbabaei, F., MSPH., Ph.D., Professor, Department of Occupational Health, School of Public Health, Tehran University of Medical
Sciences, Tehran, Iran. Email: fgolbabaei@sina.tums.ac.ir
Hamedi, J., Ph.D., Assistant professor, Microbial Biotechnology Laboratory, School of Biology, College of Science, University of
Tehran, Tehran, Iran. Email: jhamedi@khayam.ut.ac.ir
Nourijelyani, K., MSPH., Ph.D., Associate professor, Department of Epidemiology and Biostatistics, School of Public Health, Tehran
University of Medical Sciences, Tehran, Iran. Email: nouri4@yahoo.com
How to cite this article: (Harvard style)
Tirgar, A.; Golbabaei, F.; Hamedi, J.; Nourjelyani, K., (2011). Removal of airborne hexavalent chromium using alginate as a biosorbent.
Int. J. Environ. Sci. Tech., 8 (2), 237-244
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