Effect of pH on Biosorption of Basic Dye Malachite Green
bt Algae
Kawin Pansamrit and Suneerat Ruangsomboon *
1
Program in Fisheries Science, Division of Animal Production Technology and Fisheries,
Faculty of Agricultural Technology, King Mongkut’s Institute of Technology
Ladkrabang, Bangkok, Thailand
Abstract
The optimal pH for malachite green (basic dye OT 70701 A) removal from solution by 13 genus
of algae (Acanthophora sp., Gracilaria sp., Solieria sp., Padina sp., Turbinaria sp., Dictyota sp.,
Sargassum sp., Caulerpa lentillifera, Caulerpa sertularioides., Cladophora sp., Ulva rigida, Ulva
intestinalis, Chaetomorpha sp., Spirulina platensis and Phormidium angustissimum) was studied.
Dried algal cells were added in malachite green solution with initial concentration of 5 mg/L at
initial pH 2, 3, 4, 5, 6, 7 and 8 and shaking for 3 h. The optimum pH for malachite green sorption
by Solieria sp. was 5, S. platensis., U. intestinalis and U. rigida was 7 and other genus of algae
was 6. Padina sp. showed significantly higher biosorption ability, 4.28±0.03 mg/g dry wt., than
other algae (p<0.05). Our data indicated that these algae showed high malachite green removal
ability at between pH 5-7.
Keywords: algae, basic dye, biosorption, malachite green, optimal pH
1. Introduction
Treatment of dye eluents presents several problems mainly due to the toxicity and recalcitrance of
dyestufs. Discharge of dye eluents into the natural streams may be toxic to the aquatic lives [1].
Color affects the nature of water and inhibits the sunlight penetration into the stream and reduces
photosynthetic activity. Some of the dyes are carcinogenic and mutagenic of aquatic ecosystems
[2]. Malachite green, basic (cationic) dye, has been extensively used all over the world as a
fungicide and ectoparasiticide in aquaculture and very dangerous and has highly cytotoxic
property against mammalian cells [3]. The use of biomaterials as sorbents for the treatment of
wastewaters will provide as a potential alternate to the conventional treatment and inexpensive
ways of removing dyes from large volumes of eluents [1]. Algae are photosynthetic organisms
distributed in nearly all parts of the world and in all kinds of habitats [4]. Thus, algae are
ubiquitous naturally and serve as one of the biomaterials with high capacity for removing dye
from contaminated waters. Marungrueng and Pavasant reported that many functional groups (such
as carboxyl, carbonyl, hydroxyl, phosphoryl and amide) making up the algae cell wall played the
important roles in dye removal [5].
Several factors play important roles in dye bioremediation. Among these factors, pH, dye
concentrations, and amount of biomass of biomaterials are quite important [6]. It’ s has been
Corresponding author. Tel-Fax: 66(2)-3298517
E-mail: krsuneer@kmitl.ac.th
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reported that pH not only affects the dye biosorption capacity but also the solubility of dyes [7]
and surface binding-sites of cell wall of algae contains several charged group [8]. Therefore pH is
an important factor in dye removal.
The aim of the present study was to evaluate the effect of pH on malachite green removal
from aqueous solution by algae and to evaluate the ability and potential use of algae to remove
malachite green.
2. Materials and Methods
2.1 Macroalgae and Microalgae (cyanobacteria)
Marine macroalgae were collected from natural and aquatic farm. Caulerpa lentillifera, Caulerpa
sertularioides and Acanthophora sp. were collected from Banjong Farm, Chachoengsao province
on May. Cladophora sp., Chaetomorpha sp., Ulva rigida and Ulva intestinalis were collected from
Trat coastal aquaculture station, Trat province on May. Sargassum sp., Dictyota sp. and
Turbinaria sp. were collected from Chonburi province on March. Padina sp. were collected from
Trat province. Gracilaria sp. and Solieria sp. were collected from Samutsakron province on April.
The algae were washed with water to remove the surface-adhered particles and dried with sun
light then powdered to study the malachite green removal ability.
Cyanobacteria (Spirulina platensis and Phormidium angustissimum) were obtained from
the King Mongkut’s Institute of Technology Ladkrabang, Faculty of Agricultural Technology,
Program in Fisheries Science, Division of Animal Production Technology and Fisheries (KMITL,
Bangkok, Thailand). S. platensis was cultured in Zarrouk’s medium and P. angustissimum was
cultured in BG-11 medium under continuous illumination of 30 µmol photons/m2/s at 28±2ºC. The
cyanobacterial cells at 2 weeks period of culture (late exponential phase) were harvested by
filtration and dried at 60 ºC. and powdered before studying the malachite green removal ability.
2.2 Basic dye removal ability
To study the basic dye removal ability (qeq): 0.01 g (dry weight) of algal cells was added in 10 mL
solution of malachite green at concentrations of 5 mg/L at pH 2, 3, 4, 5, 6, 7 and 8 in a 125-mL
Erlenmeyer flask. The flasks were shaken at 120 rpm on a shaker at 25 °C for 180 min. Then algal
cells were separated by filtration. Malachite green remained in solution was analyzed. The values
of qeq were calculated using the mass balance equation: qeq = V(Ci-Ceq)/M where Ci is the initial
dye concentration (mg/L), Ceq is the final concentration of dye solution (mg/L), V is the volume of
solution (mL), and M is algal dry weight (g).
2.3 Basic dye and Statistical analysis
Basic dye (malachite green) concentration was analyzed by a spectrophotometer (Becthai,
Thailand) at wavelength 618 nm. All experiments were conducted in three replicates. Significant
differences were determined using analysis of variance (ANOVA) with 95% confidence
(probability limit of p<0.05).
3. Results and Discussion
Malachite green removal ability of algae with various pH of solution was shown in Table 1 and
Figure 1. The optimum pH for malachite green removal by Solieria sp. was 5, S. platensis, U.
intestinalis and U. rigida was 7 and other genus of algae was 6. At their optimum pH, Padina sp.
showed significantly higher removal ability, 4.28±0.03 mg/g dry wt., than other algae (p<0.05).
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Solieria sp. (0.50±0.03 mg/g dry wt.) and Chaetomorpha sp. (0.61±0.02 mg/g dry wt.) showed
significantly lower dye removal ability than other algae (p<0.05).
This study indicates that the aqueous solution pH exerts profound influence on the
sorptive uptake of dyes presumably due to its impact on both the surface binding-sites of cell wall
of algae which contains different functional groups such as carboxyl, hydroxyl, sulphate and other
charged group and the ionization or aggregation process of the dye molecules [8]. This can be
explained on the basis of zero point charge for algal biomass that the isoelectric point would be pH
3.0 [1, 4].
Table 1. Basic dye removal ability ( mg/g dry wt.) of algae with various pH (initial dye
concentration of 5 mg/l)
pH
Algae
2
3
4
5
6
7
8
Red algae
Acanthophora sp.
0.47±0.01cA
0.82±0.02cB 1.32±0.02eC
1.74±0.01cD 2.29±0.03eF
2.10±0.01cE
2.08±0.02cE
Gracilaria sp.
1.45±0.02fA
1.67±0.02eB 2.69±0.06hC
2.71±0.01jC
3.32±0.01fD
3.25±0.01gD
Solieria sp.
Brown algae
0.22±0.03bA
0.32±0.05aB 0.39±0.01aBC 0.50±0.03abD 0.49±0.02aD 0.47±0.01aCD 0.45±0.01aCD
Padina sp.
2.15±0.03iA
2.30±0.04fgB 2.60±0.02hC
2.65±0.01iC
4.28±0.03kF
3.43±0.02fghD 3.57±0.02hiE
Turbinaria sp.
2.43±0.05jA
2.77±0.04hB 3.01±0.02iC
3.10±0.02lC
4.05±0.03jE
3.41±0.02fgD 3.49±0.02hiD
iA
3.48±0.02ghiE 3.48±0.01hE
1.35±0.06eA
1.51±0.09dB 2.90±0.02iC
2.91±0.02kC 4.10±0.02jE
3.60±0.01iD
3.63±0.01iD
Caulerpa sertularioides
1.68±0.04hA
1.78±0.07eA 2.54±0.03hB
2.57±0.01hB 3.17±0.03gD 2.68±0.01eC
2.76±0.02fC
Caulerpa lentillifera
0.43±0.03cA
0.92±0.01cB 2.14±0.02fC
2.13±0.01gC 2.32±0.02eE
2.23±0.00cD
2.18±0.03cdCD
Cladophora sp.
1.54±0.02gA
2.35±0.02gB 2.66±0.05hC
2.71±0.01jC
3.58±0.00hiD 3.53±0.05hiD
3.90±0.04iE
0.72±0.02bC
0.71±0.01bC
0.82±0.01bC
0.75±0.03bC
0.33±0.02aB 0.54±0.02bC
0.54±0.02bC 0.61±0.02abD 0.52±0.01aC
0.54±0.02aC
0.56±0.01dA
0.83±0.04cA 1.40±0.16eB
1.48±0.01eB
2.41±0.16eD
0.41±0.05cA
0.90±0.02cB 1.07±0.03dC
1.39±0.03dD 2.55±0.04fF
0.34±0.02
0.47±0.01
0.47±0.01
aC
3.81±0.01
hiF
Sargassum sp.
Green algae
abC
3.07±0.03
lD
2.11±0.01
aB
2.35±0.01
gC
Dictyota sp.
aA
2.22±0.01
fB
3.75±0.04hE
Ulva rigida
0.1±0.02
Ulva intestinalis
0.16±0.04abA
0.51±0.06bA 0.73±0.02cB
0.75±0.02cB
Chaetomorpha sp.
Cyanobacteria
0.10±0.01aA
Spirulina platensis
Phormidium angustissimum
0.72±0.07
bcD
0.78±0.01cE
2.00±0.14dC 2.44±0.10dD
2.21±0.01cE
2.23±0.02dE
The same small letter in each row mean absence of statistical differences (p>0.05)
The same capital letter in each column mean absence of statistical differences (p>0.05)
At a higher pH above this zero point charge, the surface of biomass gets negatively
charged, which enhances the positively charged of dye cations through electrostatic force of
attraction and at lower pH, the surface charge may get positively charged (i.e. protonation of the
cell wall), thus making (H+) ions compete effectively with dye cations toward actives sorption
sites causing a decrease in the amount of adsorbed dye [1, 4, 8]. Many studies have been done on
effect of initial pH solution on the color removal effciency of malachite green solution by green
algae. Cosmarium sp. Malachite green removed ability was analyzed over a pH range from 2.0 to
11.0. It shown that an increase in pH from 4.0 to 6.0 leads to a threefold increase in decolorization
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134
rate, which is reached the maximum value of 92.4% at the pH of 9.0 and the color removal
effciency from 26.3% to 68.4% for an increase in pH from 3.0 to 4.0 [4].
i
h
g
h
g
g
f
de
d
d
bc
a
c
e
ab
Figure 1. Basic dye removal ability (qeq, mg/g dry wt.) of algae with optimal pH (initial dye
concentration of 5 mg/l). The same small letter mean absence of statistical differences (p>0.05)
The influence of initial dye solution pH of malachite green removal by a fresh water
algae Pithophora sp. at different solution pH ranging from 2 to 7 at initial malachite green
concentration 50 mg/L was studied. It was shown that maximum of 64.4 mg/g of dye was
adsorbed at a pH of 6 [1]. The optimum initial pH for malachite green removal by brown algae
Turbinaria conoides biomass at initial dye concentration 100 mg/L was found to be 8.0 and
showed maximum adsorption capacity 66.6 mg/g [9].
The effect of pH on removal of basic dye, methylene blue using green alga Enteromorpha
spp. was investigated for values between 2 and 10. The sorption capacity was minimum at pH 2
(40.21 mg/g) and increased up to pH 6, then remained nearly constant (70.35 mg/g) over the initial
pH ranges of 6–10 [10]. The percentage sorption of methylene blue by giant duckweed Spirodela
polyrrhiza at initial pH between 2-11 was reported. S. polyrrhiza showed minimum sorption at the
initial pH 2, and the percentage sorption of methylene blue was not significantly altered (p>0.05)
when the initial pH was increased from 3 to 11. S. polyrrhiza showed maximum adsorption
capacity between 126.58-129.87 mg/g [11].
4. Conclusions
The optimal pH for malachite green ( basic dye OT 70701 A) removal by Soliera sp. was 5,
Spirulina platensis, Ulva intestinalis and Ulva. rigida was 7 and Acanthophora sp., Gracilaria sp.,
Padina sp., Turbinaria sp., Dictyota sp., Sargassum sp., Caulerpa lentilifera, Caulerpa
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sertularioides, Cladophora sp., Chaetomorpha sp. and Phormidium angustissimum was 6. Padina
sp. showed the highest malachite green removal ability.
5. Acknowledgements
This study was grants by the National Research Council of Thailand.
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