Application of guar gum for the removal of dissolved lead from wastewater

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Industrial Crops & Products
journal homepage: www.elsevier.com/locate/indcrop
Research Paper
Application of guar gum for the removal of dissolved lead from wastewater
Sumona Mukherjeea,⁎
, Soumyadeep Mukhopadhyayb
, Muhammad Zakwan Bin Zafric
,
Xinmin Zhana
, Mohd Ali Hashimc
, Bhaskar Sen Guptad
a
Department of Civil Engineering, School of Engineering and Informatics, National University of Ireland, Galway, Ireland
b
Scientific Event Ltd, 31, Cannon Street, Seton Park, Winchburgh, Broxburn, EH52 6WN, Scotland, UK
c
Department of Chemical Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia
d
Water Academy, School of Energy, Geoscience, Infrastructure and Society, Heriot-Watt University, Edinburgh Campus, Scotland, EH14 4AS, UK
A R T I C L E I N F O
Keywords:
Heavy metal
Lead
Biopolymer
Guar gum
Zeta potential
Coagulation/flocculation
A B S T R A C T
Lead (Pb) is a toxic heavy metal with highly recalcitrant property. It easily accumulates in the food chain by
interacting with calcium and iron components of the biomolecules of living organisms. The aim of the study was
to develop an efficient method to treat heavy metal containing turbid wastewater without the introduction of
any secondary source of pollutants. Guar gum, a long chain polysaccharide was used to remove Pb2+
from turbid
wastewater containing kaolinite. Guar gum is extracted from the seed of leguminous shrub Cyamopsis tetra-
gonoloba commonly known as guaran. Potassium alum, a commonly used inorganic coagulant was also studied
in order to compare its Pb2+
removal efficiency with the biopolymer. It was observed that guar gum could
achieve 83% removal, at an initial Pb concentration of 15 mg L−1
. Optimization study using response surface
methodology was used to determine the optimal process parameters. FTIR and zeta potential measurement of
guar gum-Pb2+
aggregates were used to determine the removal mechanism. FTIR absorption peaks at
3618.79 cm−1
in the flocs indicate hydrogen bonding between Pb2+
and guar gum. Compact and well-formed
flocs by guar gum are indicated by the SEM micrographs. In addition to the formation of compact sludge, guar
gum is nontoxic and biodegradable and hence highly recommended for treatment of metal containing waste-
water. The requirement of ultra-low amount of biopolymer in the range of 1.25 mg L−1
to treat the relatively
high volume of water provides an additional financial advantage.
1. Introduction
Lead is a post-transition metal with high toxicity, affecting the
central nervous system, liver, kidney and basic cellular processes and
brain function in human beings (Fu and Wang, 2011). Elemental lead
has been used for thousands of years by human beings. Pb found its way
into the atmosphere and the aquatic systems through combustion of
fossil fuels, smelting of sulphide ore and through into acid mine drai-
nage (Gupta et al., 2001). The use of lead in manufacturing processes is
being phased out from the beginning of the 20th century; however, lead
acid battery industry remains one of the largest users of lead in its end
product. The survey of some storage battery factories showed that the
pH of the wastewater ranged between 1.6–2.9 and that the soluble lead
in the wastewater was in the range of 5–15 mg/L (Bahadir et al., 2007).
The recycling of lead acid batteries also generates large quantities of
heavy metal containing wastewater. Lead is highly reactive and easily
finds its way into the living systems by interacting with calcium, iron,
and zinc (Goyer, 1997). Therefore, removal of Pb from wastewater is
essential.
Removal of heavy metals from wastewaters can be achieved by
various chemical, biological and physicochemical processes (Fu and
Wang, 2011; Fu et al., 2012; Tang et al., 2014; Wan Ngah and Hanafiah,
2008). ‘Coagulation and flocculation’ is one such physicochemical
process that has been used in the treatment of different types of was-
tewaters since it is highly efficient and a cost effective process for re-
moval of fine particulate matters and other pollutants (Bartby, 1981;
Lee et al., 2012). Common chemical coagulants such as inorganic salts
of iron and aluminium tend to produce high sludge volume and residual
metal ions in the treated water resulting in secondary pollution, in-
creasing handling and disposal costs (Bartby, 1981; Lee et al., 2014). In
recent years, biopolymers such as chitosan, tannin, gums and cellulose
have been studied for the removal of contaminants from wastewater
(Beltrán Heredia and Sánchez Martín, 2009; Das et al., 2012; Freitas
et al., 2015; Mishra and Bajpai, 2005; Mukherjee et al., 2014; Renault
et al., 2009). Biopolymers tend to produce compact flocs and do not
cause any secondary pollution in the treated water. Also, they are
http://dx.doi.org/10.1016/j.indcrop.2017.10.022
Received 30 March 2017; Received in revised form 9 October 2017; Accepted 10 October 2017
⁎
Corresponding author.
E-mail addresses: sumona.mukherjee@nuigalway.ie, sumona_m@ymail.com (S. Mukherjee).
Industrial Crops & Products 111 (2018) 261–269
Available online 06 November 2017
0926-6690/ © 2017 Elsevier B.V. All rights reserved.
T

inexpensive and easily available (Bartby, 1981; Mukherjee et al., 2014;
Oladoja, 2015).
Guar Gum is a biopolymer extracted from the seed of leguminous
shrub Cyamopsis tetragonoloba, commonly known as guaran. The plant
is widely grown in the Indian subcontinent, USA, Australia, and Africa.
It can grow well in sandy soil with little rain and lots of sunshine. It is
an annual plant and is tremendously draught resistant (Altrafine Gums,
2014). The guar plant grows to a height of 0.609 m–2.74 m and re-
sembles soybean plant in appearance. The plant’s flower buds start out
white and change to a light pink as the flower opens. The flowers turn
deep purple and are followed by fleshy seed pods which ripen and
harvested in summer. The seed pods grow in bunches giving guar the
common name cluster-bean and each pod can have up to 5–6 round
seeds. The biopolymer is extracted from the seeds (Mudgil et al., 2014)
and is a polysaccharide composed of mannose backbone and galactose
side branch on every alternate mannose units (Altrafine Gums, 2014).
Recent studies have shown that it can be applied for the treatment of
drinking water, industrial effluent and removal of persistent organic
pollutants (Kee et al., 2015; Mukherjee et al., 2013; Sen Gupta and Ako,
2005). The objective of this work was to evaluate the feasibility of using
guar gum to remove Pb2+
from wastewater for the very first time. The
efficiency of guar gum in the removal of Pb2+
has been compared to a
conventional inorganic coagulant potassium alum and attempt has been
made to understand the mechanism of Pb2+
removal through FTIR and
zeta potential studies.
2. Material and methods
2.1. Simulated wastewater and chemicals
Synthetic wastewater was prepared by combining lead nitrate (Pb
(NO3)2) solution and kaolinite suspension. 250 mg L−1
stock solution of
Pb (NO3)2 was prepared. The wastewater was prepared by mixing 0.1 g
kaolinite into 1 L distilled water and was allowed to stand for 30 min.
Fig. 1. (A) Chemical structure of guar gum showing the position of
Galactose (G) and Mannose (M) in the guar gum polymer chain (Ding
et al., 2008); Fig. 2.1. (B) Guar gum seed and powder.
Table 1
Experimental design summary.
Variables Actual values for the coded values
-α −1 0 +1 +α
Dose of flocculants, mgL-1 (A) 0.41 0.75 1.25 1.75 2.09
pH (B) 2.32 3 4 5 5.68
Initial Pb concentration, mgL−1
, (C) 1.59 5 10 15 18.41
Table 2
Actual design of the experiment.
Run Dose (mgL−1
) pH Initial Concentration of Pb (mgL−1
)
1 1.25 4 18.4
2 0.41 4 10
3 0.75 3 15
4 1.25 4 10
5 1.75 5 15
6 0.75 5 5
7 1.25 4 10
8 1.75 3 15
9 0.75 3 5
10 2.1 4 10
11 1.25 5.6 10
12 1.25 2.3 10
13 1.25 4 10
14 1.25 4 1.6
15 1.25 4 10
16 1.25 4 10
17 1.75 3 5
18 0.75 5 15
19 1.75 5 5
20 1.25 4 10
S. Mukherjee et al. Industrial Crops & Products 111 (2018) 261–269
262

The supernatant liquid with resulting turbidity of 64 FAU was decanted
and used for the experiments. For each experiment 250 mL of the
wastewater was used. The pH of the suspension was adjusted prior to
the addition of Pb (NO3)2.
Guar gum is obtained by grinding the endosperm of the guar beans.
Food grade Guar gum 3500/200 was purchased from F Gutkind
Co & Ltd. Fig. 1 shows the chemical structure of guar gum. A solution of
1000 mg L−1
concentration was obtained by dissolving 0.1 g of guar
gum in 100 mL distilled water. To avoid any growth of moulds new
guar gum solution were prepared every twelve hours. Potassium Alum
(aluminium potassium sulphate dodecahydrate; KAl(SO4)2) was added
directly to the water sample.
2.2. Analytical methods
The simulated wastewater was analysed for different physico-
chemical parameters such as turbidity, pH, heavy metal concentration
and zeta potential. The HACH DR/890 portable spectrophotometer was
used to measure the turbidity. The Pb2+
concentration in the samples
was analysed using ICP-OES (Perkin-Elmer Optima 7000DV) and
Perkin-Elmer multi-metal standard solution. The zeta potential of the
water samples was analysed by the Zetasizer Nano ZS. The pH was
measured using Metler Toledo Delta 320 pH meter. The FTIR of the
flocs was measured in Bruker Vertex (United States) 70/70 V spectro-
photometer and the SEM micrographs were obtained using the ZEISS
Auriga Scanning electron microscope operating with SE2 detector.
Fig. 2. Variation of Pb removal by guar gum at different pH values and guar gum dose at fixed initial Pb concentration. The Box-whisker plot represents maximum score, 75th percentile
(Upper Quartile), Median, 25th percentile (Upper Quartile) and Minimum Score.
263

2.3. Flocculation and removal of heavy metals
Clarification of the wastewater was performed using a jar test ap-
paratus (Phipps and Bird 7790-402 Jar Tester). Guar gum and po-
tassium alum dose was fixed through jar test studies. Treatment of the
wastewater was done in 500 mL glass beakers at different dosages of the
biopolymer and potassium alum and the supernatant solution was
analysed for Pb removal. The pH of the wastewater in each beaker was
first adjusted by 0.1N H2SO4/NaOH. After obtaining the desired pH
levels, the Pb solution was added, thus constituting the wastewater.
After addition of the Pb2+
the solution was mixed thoroughly for two
minutes prior to the addition of the coagulant. The coagulant was dosed
to the homogenised solution and the mixing processes were initiated in
two stages. The first flash mixing at 250 rpm for 5 min followed by slow
mixing at 60 rpm for 15 min. After 15 min of mixing, the flocs were
allowed to settle for 30 min and samples were collected for analysis. To
prevent Pb from precipitating, the samples were preserved by the ad-
dition of 1% HNO3 v/v acid.
2.4. Experimental design and data analysis
The design of experiment, mathematical modelling and optimiza-
tion were done by response surface methodology using Design Expert 7
software (Hamid et al., 2016; Subramonian et al., 2015). The central
composite model was used for optimization of the chief operating
parameters. Three important parameters viz., dose of guar gum
Fig. 3. Response surface plot of Pb removal due to addition of Guar
gum: Effect of Dose (pH = 4.0).
Fig. 4. Response surface plot of Pb removal due to addition of Guar
gum: Effect of pH.
Table 3
Optimum conditions and their desirability.
Flocculant Dose pH Pb Conc Optimization Validation
Pb Removal Desairability Pb Removal % Error
Guar gum 0.88 3 15 56.97 0.67 59 3.56%
264

(flocculant), pH of the wastewater and initial heavy metal concentra-
tion were optimised. Their central values were 1.25 mg L−1
, 4 and
10 mg L−1
, respectively (Table 1). The low, middle and high levels of
each variable are designated as −α, 0 and +α, respectively. The range
of the variables was fixed based on preliminary experiments.
The interaction among operating parameters and response was as-
certained by graphically analysing the data by ANOVA. A second order
polynomial equation was applied to explain the behaviour of the vari-
ables and the response (Eq. (1)):
∑ ∑ ∑ ∑= + + +
= = ⊇ =
y β β x β x β x x0
i 1
k
i i
i 1
k
ii i
2
i j
k
i 1
k
ij i j
(1)
where, y = predicted response, β0 = offset term, βi = linear effect,
βii = squared effect, βij = interaction effect. The detailed experimental
design, as generated by the software, is shown in Table 2.
3. Results and discussion
3.1. Performance of guar gum and potassium alum for the removal of lead
Preliminary studies were conducted in order to determine the per-
formance of potassium alum and guar gum for removal of Pb2+
from
wastewater. It was found that potassium alum was not as effective as
guar gum in the removal of Pb2+
. The percent removal was found to be
only 29% from an initial Pb concentration of 15 mg L−1
at pH 5 and a
potassium alum dose of 0.1 g L−1
. However, the turbidity removal by
potassium alum is high (54%). As observed by Omar and Al-Itawi
(2007), Pb2+
has an affinity for kaolinite and has been used as an ad-
sorbent for the removal of Pb2+
from wastewater (Jiang et al., 2010;
Salem and Akbari Sene, 2011). In our case, the removal of Pb2+
through attachment with suspended kaolinite particles was prohibited
by the presence of positively charged Al3+
ions, the hydrolysed product
of potassium alum. This is because Al3+
and the Pb2+
are both posi-
tively charged causing repulsion between the two species and a com-
petition for the active sites on kaolinite particles.
The Box-Whisker plot (Fig. 2) of guar gum’s performance at dif-
ferent pH and dose shows that both pH of wastewater and dose of
flocculent influences the removal of Pb2+
. At pH 5 and flocculent dose
of 1.25 mg L−1
the highest Pb2+
removal of 85% is achieved. It was
also observed that higher removal is obtained with higher initial Pb2+
concentration, indicating the potential of guar gum to remove Pb2+
from highly concentrated wastewaters. The flocculation of the sus-
pended particles in the wastewater by guar gum is achieved through
polymer bridging as shown by the zeta potential values of the solutions
after guar gum addition (Mishra and Bajpai, 2005). The zeta potential
at pH 3 is lowest at −4.9 mV, which is an increase from −34.9 mV of
the original wastewater. Also, the Pb2+
removal is decreased at higher
guar gum dose as repulsion between the polymer chain occurs at higher
polymer concentration preventing the flocculation of the particles.
3.2. Optimization of guar gum performance
The response surface methodology for optimising different oper-
ating parameters for percent Pb removal was used to generate the fol-
lowing reduced second order polynomial equation:
=− + × + × + × +
× × − × × −
× −
Pb Removal 193.29 96.32 Dose 73.84 pH 5.17 Pb Conc
1.72 Dose Pb Conc 1.07 pH Pb Conc 48.06
Dose 5.87 pH
- 0.08 Pb Conc
2 2
2
To determine the significance of this model, ANOVA was applied
which evaluates the variations in different groups of data and adjudge if
their mean values are equal (Bezerra et al., 2008). Fisher’s F-test value
of 156.06 with a very low probability of (P model > F = 0.0001)
(Table 1A) indicates the model is significant (Liu et al., 2004). In the
graph of the predicted values versus actual data show that the 45° line
should uniformly divide the data points (Fig. 1A).
The accuracy of prediction of a response model can also be de-
termined by the predicted R2
. In case of the removal of Pb2+
, the
predicted R2
value is 0.96, which is in reasonable agreement with the
adjusted R2
value of 0.98. Also, the signal to noise ratio of 41.46 is
indicative of adequate precision (Aghamohammadi et al., 2007; Mason
et al., 2003).
Fig. 5. SEM micrographs of guar gum flocs: (A) surface morphology
(8000X) (B) cross-section of flocs (16,000X).
265

3.2.1. Effect of dose
The Fig. 3 shows the response surface plot for Pb2+
removal with
respect to variation of dose. It can be seen that with the gradual in-
crease in guar gum dose from 0.75 mg L−1
, the removal of Pb2+
in-
creases and is maximum at 1.25 mg L−1
. About 83% Pb2+
removal is
achieved at a dose of 1.25 mg L−1
and an initial Pb2+
concentration of
15 mg L−1
of Pb2+
. Further increase in dose results in decrease of Pb2+
removal as flocculation of the suspended particles is inhibited. This is
due to the increased repulsive energy between the polymer chains at
higher dose, which causes the resuspension of the suspended particles
(Abdel-Shafy and Abo-El-Wafa, 1987; Mukherjee et al., 2014). This
observation also supports the fact that Pb2+
removal is achieved by the
combined effect of hydrogen bonding of Pb2+
with the biopolymer and
also its adsorption on the surface of the kaolinite particles in the was-
tewater.
3.2.2. Effect of pH
pH has a significant impact on the removal of Pb2+
. At pH 3 the
removal of Pb2+
is low and gradually increases at higher pH (Fig. 4). At
pH 6, Pb precipitates; in order to ascertain the efficiency of guar gum in
the removal of Pb2+
ions all experiments were carried out below pH 5.
At pH 3, Pb2+
removal is lowest in spite of the fact that the zeta po-
tential is − 4.92 mV (an increase from − 34.9 mV of the wastewater).
A near neutral zeta potential is indicative of better flocculation poten-
tial. However, in this case at low pH and high H+
ion concentration
results in a competition between Pb2+
ions and H+
for the active sites
on guar gum. As the H+ ions are smaller in size they are preferred over
the heavier Pb2+
. Under such condition, the major removal is obtained
by the adsorption of Pb2+
ions onto the suspended kaolinite particles of
the wastewater. However, at higher pH, the H+
ion concentration de-
creases and more active sites of the guar gum long chain are available
for binding with Pb2+
ions.
Fig. 6. FTIR spectra of (A) Kaolinite, (B) Guar gum powder, (C) flocs
obtained by Guar gum and (D) flocs obtained by Potassium Alum.
266

3.2.3. Process optimization and model validation
Optimization of Pb2+
removal was carried out by a multiple re-
sponse function known as desirability function. The target is to opti-
mize different combinations of process parameters for optimum Pb2+
removal. In order to achieve maximum desiaribility Pb2+
removal by
guar gum, the pH and initial Pb2+
concentration was kept within the
range and guar gum dose was kept at minimum keeping in mind en-
vironmental sustainability and econimic constraints. The optimal points
of the factors was astertained by additional experiments at the derived
optimal conditions. Table 3 shows the optimal conditions and their
desirability. It can be said that the model obtained was an adequate
prediction of Pb2+
removal with a relatively small error of 3.56%
(Table 3).
3.3. Physiochemical characteristics of the flocs
Fig. 5 shows the surface morphology of the flocs. The cross-section
of the flocs reveals the neatly arranged layers of sediments, indicating
the compact nature of the flocs.
Fig. 6 shows the FTIR spectra of guar gum powder and the dried
flocs produced by guar gum and potassium alum. The FTIR study was
done to ascertain Pb2+
removal mechanism. The guar gum powder has
a peak at 3423.9 cm−1
and 1223.5 cm−1
indicating OeH and CeO
stretch respectively indicating the presence of aliphatic alcohol groups.
In the guar gum flocs, the broad peaks of the alcohol groups in guar
gum powder are replaced by OeH free stretch at 3685.7 cm−1
and
OeH hydrogen bonded stretch at 3618.8 cm−1
. This shows that He
bonding between Pb2+
and guar gum was an important factor in its
removal. It is worth noting that peaks at 3649 cm−1
and 3619 cm−1
in
potassium alum flocs indicate the Al–-OeH stretch marking the pre-
sence of kaolinite in the floc sample. The peaks as shown in the flocs is
also indicative of kaolinite present in the water samples, which was
settled during the flocculation process. The peaks at a lower wavelength
of 700–686 cm−1
indicate the presence of Si-O (quartz) bonds. The
peaks at υ of 470 cm−1
to 452 cm−1
indicate the presence of Si-O-Si
bending from the kaolinite in both floc samples obtained from po-
tassium alum and guar gum.
4. Conclusion
This study shows the application of guar gum, a biodegradable
polysaccharide for the removal of Pb2+
from turbid wastewater con-
taining kaolinite. About 83% Pb2+
removal was achieved at a floccu-
lent dose of 1.25 mg L−1
and pH 5. The inorganic coagulant potassium
alum could remove only 29% Pb2+
. The inter-ionic repulsion between
Al3+
ions and Pb2+
ions is suggested as the main impediment towards
the removal of Pb2+
. The optimization study indicated the impact of
important design parameters such as dose and pH on the removal of
Pb2+
. A high R2
value (0.99) for the regression model equation, in-
dicates adequate agreement between the experimental data and the
model. FTIR absorption spectra indicate physiochemical interaction
between guar gum and Pb2+
resulting in the capture of Pb2+
and its
subsequent removal. The SEM micrographs indicate the production of
compact flocs. Guar gum is a biodegradable nontoxic polysaccharide,
widely available and inexpensive (Seeli and Prabaharan, 2016), and is
highly recommended for wastewater treatment where the introduction
of secondary pollutants during treatments is an increasing concern
(Chen, 2004; Fu and Wang, 2011; Garcia-Segura et al., 2017). In this
study, guar gum has proved to be effective for the removal of Pb2+
from
the wastewater. Further studies need to be done to ascertain its efficacy
in multi-metal systems and its interaction with other pollutants.
Acknowledgements
The authors acknowledge the funding provided by the Irish
Research Council Postdoctoral fellowship (No: GOIPD/2016/188) and
National University of Ireland, Galway and the University of Malaya.
Appendix A
See Table A1.
See Fig. A1.
Table A1
Statistical models obtained from the ANOVA for turbidity removal.
Source Sum of
Squares
df Mean
Square
F Value p-value
Prob > F
Model 7271.03 8 908.88 156.06 < 0.0001 significant
A-Dose 147.63 1 147.64 25.35 0.0004
B-pH 3595.84 1 3595.85 617.42 < 0.0001
C-Pbconc 751.51 1 751.52 129.04 < 0.0001
AC 148.64 1 148.64 25.52 0.0004
BC 227.17 1 227.17 39.01 < 0.0001
A2
2080.11 1 2080.11 357.16 < 0.0001
B2
496.46 1 496.46 85.24 < 0.0001
C2
55.88 1 55.88 9.59 0.0102
Residual 64.06 11 5.82
Lack of Fit 48.12 6 8.02 2.52 0.1651 not significant
Pure Error 15.94 5 3.19
Cor Total 7335.09 19
Std. Dev. 2.41 R-Squared 0.9913
Mean 62.63 Adj R-Squared 0.9849
C.V.% 3.85 Pred R-Squared 0.9601
Press 292.80 Adeq Precision 41.456
267

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