water
Article
Adsorption of Patent Blue V from Textile Industry
Wastewater Using Sterculia alata Fruit Shell Biochar:
Evaluation of Efficiency and Mechanisms
Balendu Shekher Giri
1,2,
* , Mandavi Goswami
1
, Prabhat Kumar
1
, Rahul Yadav
1
,
Neha Sharma
3
, Ravi Kumar Sonwani
1
, Sudeep Yadav
4
, Rajendra Prasad Singh
5
,
Eldon R. Rene
6
, Preeti Chaturvedi
2
and Ram Sharan Singh
1,
*
1
Department of Chemical Engineering and Technology, Indian Institute of Technology (BHU), Varanasi,
Uttar Pradesh 221005, India; mandavigs@gmail.com (M.G.); prabhat.kumar.che15@itbhu.ac.in (P.K.);
rahul.yadav.che15@itbhu.ac.in (R.Y.); raviks.rs.che16@itbhu.ac.in (R.K.S.)
2
Aquatic Toxicology Laboratory, Environmental Toxicology Group, Council of Scientific and Industrial
Research-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhawan, 31, M.G. Marg, Lucknow,
Uttar Pradesh 226001, India; preetichaturvedi@iitr.res.in
3
Amity Institute of Microbial Technology, Amity University, Noida, Uttar Pradesh 201313, India;
nehabiochemistry@gmail.com
4
Department of Chemical Engineering, Bundelkhand Institute of Engineering & Technology (BIET), Jhansi,
Uttar Pradesh 284128, India; sudeep2406@gmail.com
5
Department of Municipal Engineering, Southeast University, Nanjing 210096, China; rajupsc@hotmail.com
6
Department of Water Supply, Sanitation and Environmental Engineering, IHE Delft Institute for Water
Education, P.O. Box 3015, 2601DA Delft, The Netherlands; e.raj@un-ihe.org
* Correspondence: balendushekher23@gmail.com (B.S.G.); rssingh.che@itbhu.ac.in (R.S.S.)
Received: 8 April 2020; Accepted: 8 July 2020; Published: 16 July 2020
Abstract:
Biochar prepared from Sterculia alata fruit shell showed a better performance for dye
removal than the biomass from Sterculia alata fruit shell. The important process parameters—namely
the pH, the amount of biochar, the initial dye concentration and the contact time—were optimized in
order to maximize dye removal using biochar of Sterculia alata fruit shell as the bio-sorbent. The results
from this study showed that the maximum adsorption of dye on the biochar was obtained at a
biochar dosage of 40 g/L, at a contact time of 5 h, and an initial dye concentration of 500 mg/L (pH 2.0;
temperature 30
±
5
◦
C). The increase in the rate adsorption with temperature and the scanning
electron microscopic (SEM) images indicated the possibility of multilayer type adsorption which was
confirmed by better fit of the Freundlich adsorption isotherm with the experimental data as compared
to the Langmuir isotherm. The values n and R
2
in the Freundlich isotherm were found to be 4.55 and
0.97, respectively. The maximum adsorption capacity was found to be 11.36 mg/g. The value of n > 1
indicated physical nature of the adsorption process. The first and second order kinetics were tested,
and it was observed that the adsorption process followed the first-order kinetics (R
2
= 0.911).
Keywords: Patent Blue V; Langmuir isotherm; Freundlich isotherm; SEM; removal efficiency
1. Introduction
Water pollution due to toxic industrial effluent which contains various pollutants, such as
dye, acids, etc., have become a global environmental problem. Dyes or dye components are major
pollutants in the effluent from industries such as textiles, pulp and paper, leather, etc. [
1
,
2
]. Due to
various applications, the production of pigments and dyestuffs is increasing continually and annually
~700,000 tonnes of pigments and dyes are produced in the world, wherein India’s contribution is
Water 2020, 12, 2017; doi:10.3390/w12072017 www.mdpi.com/journal/water
Water 2020, 12, 2017 2 of 16
~80,000 tonnes [
3
–
5
]. The dyes exhibit poor biodegradability and, therefore, cause long-term ecological
damage. The presence of dye in the water bodies and soil pose various problems including toxicity
of water bodies and soil, change in the quality of water, toxicity to the microorganisms/biocatalysts
present in the water, percolation of dyes in the underground water through soil, entry in the food chain
which result in various health effects on human beings and animals [
6
,
7
]. Dye is present at various
concentrations in several wastewater streams and it can also cause toxic effects on aquatic organisms,
microbes and prevent seed germination [8].
Different techniques such as biological treatment, ozone treatment, adsorption, and chemical
oxidation have been tested by the researchers to remove dyes from wastewater. Among all these
suggested technologies, adsorption is most promising and considered to be a convenient technique for
removal of dyes because of its low cost, easy operation and high removal capacity [
9
,
10
]. Nano materials,
as adsorbents, also provide various advantages such as high surface area, porous structure and thermal
stability [
11
,
12
]. However, the production cost of the nano-based materials is still high; hence, it prohibits
its application for commercial purposes. Activated carbon is another commonly reported adsorbent
for dye removal because it has excellent adsorption capacity [
8
,
13
,
14
]. Nowadays, the application of
biochar for wastewater treatment is being explored by different researchers [
2
]. The major advantage of
biochar is its low cost of production, because it is generally produced using agro waste and it provides
relatively good adsorption capacity [
15
], durability, and it may be regenerated and used multiple
times [
16
,
17
]. Biochar is usually produced using pyrolysis of the biomass. The process parameters
during pyrolysis affect the physicochemical characteristics of the biochar [
8
,
16
]. Chemical modification
of biochar using acids, bases or polymers may result in better adsorption efficiency because of increased
surface area, modified chemical functionality and presence of high-affinity adsorption sites [
16
]. From a
kinetic modeling perspective, adsorption isotherms [
18
,
19
] are used to describe the mechanism of
adsorption on the surface of adsorbent, and these isotherms provide values of kinetic parameters
that can be used to design full scale adsorption towers. Adsorption kinetics provides information
about the rate at which the pollutant is adsorbed [
15
]. Generally, first-order, second-order reversible or
irreversible and pseudo-first, pseudo-second order models are applied to the experimental data [16].
In this study, biochar prepared using Sterculia alata fruit shell, an agro waste, was used to remove
Patent Blue V dye from wastewater. This dye is mainly present in the effluent of the carpet and
textile industry of Varanasi and Bhadohi, Uttar Pradesh, India. This is the first report that shows
the application of Sterculia alata fruit shell for preparing biochar, and its ability for dye removal
was explored.
2. Materials and Methods
2.1. Materials (Adsorbate and Adsorbent)
Sterculia alata fruit shells were used as the raw material for the production of biochar. It was
collected from the trees located in Indian Institute of Technology (BHU) campus, Varanasi, India.
The Patent Blue V dye used in this study was purchased from a local chemical supplier. The wavelength
(630 nm) corresponding to the maximum absorption was determined using scanning mode of an
UV-Visible Spectrophotometer (Elico, Hyderabad, India). The dye stock solution of the required
concentration was prepared by dissolving a known amount of dye in distilled water.
2.2. Preparation of Biochar
In the first step, the biomass was ground to increase the surface area and then pyrolyzed at
500
◦
C by increasing the temperature at the rate of 10
◦
C min
−1
to convert into biochar [
20
]. Nitrogen
was purged in a Pyrolyzer for 60 min at the rate of 100 cm
3
min
−1
to maintain the inert atmosphere.
The biochar obtained after pyrolysis was washed with distilled water and thereafter dried at 110
◦
C and
finally impregnated with NaOH to improve its adsorption capacity [
21
]. The NaOH activation method
was used to improve the sorption properties of the tested biochar. Thermally treated biochar (3 g)
Water 2020, 12, 2017 3 of 16
was mixed with 40 mL of 4 M NaOH and incubated at room temperature for 2 h, under intermittent
shaking (15 min interval) conditions. After NaOH impregnation, the excess solution was discarded
with vacuum filtering and the chemically treated solid was dried overnight in an oven at 105
◦
C.
The dried sample was heated in a quartz-tube furnace to 800
◦
C, at a heating rate of 3
◦
C min
−1
under
inert atmospheric conditions (N
2
flow = 2 L min
−1
) for 2 h. After activation, the samples were taken out
from the heating element and cooled down to ambient temperature under nitrogen flow. The activated
samples were washed using 2 L of deionized (DI) water followed by 0.1 M HCl solution (200 mL) and
washed again with DI water until the pH of filtrates was ~7.0. The washed activated carbon samples
were dried in an oven at 105
◦
C and stored in a desiccator for further analysis. Each activated sample
was denoted as “N-treatment temperature AC” (e.g., N-300AC for activated carbon from N-300).
2.3. Characterization of Biochar and Sterculia alata Biomass
The biochar produced from Sterculia alata biomass was characterized in order to evaluate its
physico-chemical properties. Scanning electron microscopy (SEM) analysis was performed using a
JEOL JSM-6400 Scanning Microscope (JEOL, Tokyo, Japan) with low vacuum of 30 Pa, voltage 20 kV
and 10–12 mm working distance from the detector. The results were used to compare the changes in
the structural and surface characteristics of the biochar samples before and after treatment of Patent
Blue dye V. The effect of adsorption on the porosity was clearly visible from the SEM results shown
in Figure 1a,b. Dispersive X-ray Spectroscopy (EDX) with SEM analysis provides rapid qualitative
or semi-quantitative analysis of the biochar’s elemental composition [
7
,
22
,
23
]. Elemental analysis on
the biochar surface was also conducted at different time intervals, simultaneously with the SEM-EDX
(Oxford Instruments Link ISIS, and Oxfordshire, UK) and the results are given in Table 1.
Water 2018, 10, x FOR PEER REVIEW 4 of 16
(a)
(b)
Figure 1. SEM morphology of Sterculia alata fruit shell biochar for the adsorption of Patent Blue V dye;
(a) before adsorption; (b) after adsorption.
2.4. Batch Adsorption Tests
Batch adsorption tests were conducted in Erlenmeyer flasks (V = 250 mL) and the potential of
biochar to remove Patent Blue V dye was ascertained. The flasks contained different initial
concentrations of the dye solution (in 100 mL) and known amount of biochar was added according
to the desired adsorbent dose. The batch studies were carried out at different temperatures (30 °C, 35
°C and 53 °C), pH (2.0, 4.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0 and 12.0), concentrations of dye in the wastewater
(0, 10, 20, 50, 100, 500 mg/L) and adsorbent dose in order to evaluate the optimum process parameters.
The final concentration of dye solutions was measured using an UV-visible spectrophotometer at 630
nm, at a fixed contact time. The dye removal (R) was calculated using Equation (1).
R = (C0 − Ct) × 100/C0 (1)
Where, C
0 = initial concentration (mg/L) and Ct = dye concentration at time, t (mg/L).
The percentage adsorption of PB (V) dye and equilibrium adsorption capacity, q
e (mg/g), was
calculated using Equations (2) and (3):
Adsorption
(
%
)
=
(
−
)
× 100
(2)
=
(
−
)
×
(3)
Where C
0 and Ce are the initial and equilibrium concentrations of PB (V) (mg/L), respectively, V is the
volume of the dye solution (L), and W is the weight of biochar (g).
2.5. Adsorption Isotherm Models
The Freundlich [24] and Langmuir [7,23] type adsorption models were used to fit the
experimental data. The model equations are shown in Equations (4) and (5).
Freundlich Isotherm: log q = log K
F + 1/n × log Ceq (4)
Langmuir isotherm: 1/q = 1/q
0
+ 1/(K
L
− q) × 1/C
eq
(5)
Where q = amount of dye adsorbed (mg of dye per g of adsorbent); KF = parameter related to the
adsorption; n = measure of sorption intensity (value of n [1, 10]); K
L = Langmuir constant; q0 =
maximum value of sorption capacity; C
eq = Equilibrium dye concentration (mg/L).
The Langmuir isotherm explains a monolayer adsorption of molecules over a surface having a
finite number of adsorption sites of same energy, which are fully available for interaction. The
Freundlich isotherm explains about a multilayer adsorption with interaction between the adsorbed
Figure 1.
SEM morphology of Sterculia alata fruit shell biochar for the adsorption of Patent Blue V dye;
(a) before adsorption; (b) after adsorption.
Table 1. Elemental composition by EDX analysis of biochar and biomass samples.
Elements
Biochar Biomass
Weight % Atomic % Weight % Atomic %
C 72.4 78.7 52.7 61.5
N 6.38 5.95 0 0
O 16.7 13.6 41.6 36.5
P 0.52 0.22 0 0
K 2.76 0.92 5.71 2.05
Mg 0.60 0.32 0 0
Ca 0.68 0.22 0 0
Water 2020, 12, 2017 4 of 16
Fourier Transform Infrared (FTIR) analysis of the biochar samples was conducted before and after
adsorption of Patent Blue V dye and the results is shown in Table 2. Before FTIR analysis, the biochar
samples were well-ground and mixed with KBr solution to 0.1% (wt. basis) and then pressed into
pellets to obtain the FTIR spectra. The spectra of these biochar samples were measured using a Bruker
Vector 202 FTIR spectrometer (OPUS 2.0 software, Berlin, Germany).
2.4. Batch Adsorption Tests
Batch adsorption tests were conducted in Erlenmeyer flasks (V = 250 mL) and the potential
of biochar to remove Patent Blue V dye was ascertained. The flasks contained different initial
concentrations of the dye solution (in 100 mL) and known amount of biochar was added according to
the desired adsorbent dose. The batch studies were carried out at different temperatures (30
◦
C, 35
◦
C
and 53
◦
C), pH (2.0, 4.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0 and 12.0), concentrations of dye in the wastewater
(0, 10, 20, 50, 100, 500 mg/L) and adsorbent dose in order to evaluate the optimum process parameters.
The final concentration of dye solutions was measured using an UV-visible spectrophotometer at
630 nm, at a fixed contact time. The dye removal (R) was calculated using Equation (1).
R = (C
0
− C
t
) × 100/C
0
(1)
where, C
0
= initial concentration (mg/L) and C
t
= dye concentration at time, t (mg/L).
The percentage adsorption of PB (V) dye and equilibrium adsorption capacity, q
e
(mg/g),
was calculated using Equations (2) and (3):
Adsorption
(
%
)
=
(
Co − Ce
)
Co
× 100 (2)
q
e
=
(
Co − Ce
)
W
× V (3)
where C
0
and C
e
are the initial and equilibrium concentrations of PB (V) (mg/L), respectively, V is the
volume of the dye solution (L), and W is the weight of biochar (g).
2.5. Adsorption Isotherm Models
The Freundlich [
24
] and Langmuir [
7
,
23
] type adsorption models were used to fit the experimental
data. The model equations are shown in Equations (4) and (5).
Freundlich Isotherm: log q = log K
F
+ 1/n × log C
eq
(4)
Langmuir isotherm: 1/q = 1/q
0
+ 1/(K
L
− q) × 1/C
eq
(5)
where q = amount of dye adsorbed (mg of dye per g of adsorbent); K
F
= parameter related to the
adsorption; n = measure of sorption intensity (value of n [1, 10]); K
L
= Langmuir constant; q
0
= maximum
value of sorption capacity; C
eq
= Equilibrium dye concentration (mg/L).
The Langmuir isotherm explains a monolayer adsorption of molecules over a surface having a finite
number of adsorption sites of same energy, which are fully available for interaction. The Freundlich
isotherm explains about a multilayer adsorption with interaction between the adsorbed molecules
over heterogeneous surfaces, assuming that adsorbent surface sites have different binding energies.
Water 2020, 12, 2017 5 of 16
Table 2. FTIR analysis of biochar and biomass of Sterculia alata fruit shell, before and after the adsorption experiments
Biochar before Adsorption Biomass before Adsorption Biochar after Adsorption Biomass after Adsorption
Wavelength (cm
−1
)
Bond Type
Wavelength (cm
−1
)
Bond Type
Wavelength (cm
−1
)
Bond Type
Wavelength (cm
−1
)
Bond Type
3594.4 O-H (free) 3349.1 Weak N-H (2
◦
amine) 3218.7 O-H (H bonded) 3649.2 O-H (free)
3219.8 O-H (bonded) 2900.6 CH
3
, CH
2
& CH, O-H (very broad) 2930.2 CH
3
, CH
2
, CH ( 2 or 3 bands) 3299.8 O-H (bending)
2699.3 C-H (aldehydes C-H) 2153.7 Si-H silane,-M=C=O, N=C=S 1971.9 C=C (asymmetric stretch) 3045.2 =C-H & =CH
2
2258.6 C≡N (sharp) 1728.6 C=O (saturated aldehyde) 1728.3 C=O (saturated aldehydes) 2938.2 CH
3
, CH
2
, CH
1538.6 NH
2
scissoring 1440.3 CH
2
-CH
3
(bending) (1
◦
amine) 1651.3 C=O (amide) 2346.4 Si-H silane, P-H
1435.8 -CH
2
bending 1019.6 P-H bending P-OR esters, Si-OR 1425.5 -CH
2
bending 1565.4 NH
2
scissoring
876.7 =C-H & = CH
2
889.3 S-OR esters 1043.1 C-O-H bending 1421.1 -CH
2
bending, C-O-H
722.7 C-H bending & ring 714.5 S-OR esters 689.2 C-O, C-N 1195.0 C-N, C-O, C=S,
567.8 C-H deformation 514.3 S-S (disulfide) 1049.3 P-H bending, S=O
847.3
C-H bending & puckering
