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Desalination and Water Treatment
www.deswater.com
doi: 10.5004/dwt.2019.24304
168 (2019) 252–260
November
Lead(II) biosorption from aqueous solutions by Trichoderma fungus:
equilibrium and thermodynamic study
Amin Allah Zareia,b, Edris Bazrafshana,b,*, Mohsen Navarib,c
aDepartment of Environmental Health Engineering, School of Health, Torbat Heydariyeh University of Medical Sciences,
Torbat Heydariyeh, Iran, emails: ed_bazrafshan@yahoo.com (E. Bazrafshan), aminallahzarei@gmail.com (A.A. Zarei)
bHealth Sciences Research Center, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran
cDepartment of Laboratory Sciences, School of Paramedical Sciences, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran
Received 22 April 2018; Accepted 17 April 2019
abstract
Lead is one of the trace metal ions and environmental pollutants that can be hazardous to humans
and other organisms. The present study was conducted to evaluate the efficiency of Trichoderma
fungus in biosorption of lead ions (Pb2+) from aqueous solutions. Hence, the optimal conditions for
fungal growth were determined to investigate the effects of critical parameters affecting biosorp-
tion process, including pH, mixing rate, contact time, temperature and initial lead concentration.
The findings of the experiments showed that the Trichoderma fungus could grow well within 24 h at
pH and temperature equal to 5°C and 25°C, respectively. The highest growth rate in these conditions
was 0.51 g/100 mL of broth medium. Maximum biosorption rate of Pb2+ (98.8%) occurred at pH = 6
and initial concentration of 25 mg/L Pb2+. It was also found that mixing rate could have a positive
effect on increasing the removal of Pb2+ by Trichoderma fungus. Evaluation of biosorption system
behavior based on biosorption models determined that Langmuir model is the most appropriate
one to explain the biosorption behavior. Under these conditions, the maximum biosorption capacity
was obtained equal 25.05 mg Pb2+/g, which is very close to the value predicted by Langmuir model.
Keywords: Biosorption; Lead; Trichoderma fungus; Isotherm
1. Introduction
Pollutants are considered among the most damaging
factors to ecosystems. Trace metals, among these, are of
great importance because of their physiological effects on
living organisms, being non-biodegradable toxic in small
quantities, and their affinity to accumulate in the tissues,
among others [1,2]. These metals are found naturally in
the environment at different amounts; however, there are
various other emission sources of these metals. Nowadays,
human activities such as production of large amounts of
sewage and solid wastes in urban, industrial and agricul-
tural areas, widespread use of fossil fuels and extensive use
of trace metals in industrial processes have led to increased
concentrations of these metals in the environment. As a
result, contamination of water supplies with trace metals
due to the discharge of urban and industrial sewage, runoff
and improper management of solid wastes have led to the
penetration of these metals into living organisms, including
humans as final consumers [3–5].
Arsenic, lead, copper, cadmium, mercury, chromium,
copper, silver, zinc and nickel are the most common trace
metals found in wastewater [6]. Among these, in terms of
emission rate, lead is the most extensive toxic heavy metal
in the environment [7]. The widespread use of lead in gas-
oline, its use in the production of chemical fertilizers and
production of large amounts of wastewater containing lead
in industries such as printing, painting, batteries, glass, etc.
have caused inevitable pollution arising from it in water
resources and industrial wastewaters [8]. The presence of
253A.A. Zarei et al. / Desalination and Water Treatment 168 (2019) 252–260
lead in the body can cause kidney and liver dysfunction,
damage to the reproductive system, anemia, reduced intel-
lectual quality (IQ), and many other metabolic complications.
Hence, it is necessary to find effective ways to reduce and
remove it from aqueous solutions [9]. In this regard, there
are many methods, such as chemical precipitation [10], coag-
ulation [10], ion exchange [11], membrane technology [12]
and adsorption by various adsorbents (low-cost adsorbents
and natural biomass) for removal of heavy metals from water
and wastewater [13,14]. Each of these methods has its own
advantages and disadvantages. Chemical pre-concentration
and oxidation–reduction reactions have low efficiency at low
concentrations of heavy metals, and generate high and per-
sistent deposits. Ion exchange, membrane technology and
adsorption on activated carbon are, on the other hand, expen-
sive methods. Thus, recent investigations have led research-
ers to design and develop biosorption techniques aiming to
obtain high-efficiency and low-cost approaches [15,16].
Biosorption is the ability of biomass to collect metal
ions from wastewaters through indirect metabolic activities
or physicochemical adsorption methods. Some important
advantages of biosorption compared with other methods
are cost-effectiveness, high efficiency, minimum biochemical
deposits and the possibility of recycling the metal ions.
Algae, molds, yeasts, bacteria and fungi are among these
biosorbents [17,18]. The mechanism of metal ions bio-
sorption by biosorbents is a complex process. Biosorbents
structure, chemical properties of metal ion solution and
environmental conditions affect the efficiency of biosorption
mechanism. Metal biosorption by living cells is achieved in
two stages. In the first phase, the metal ions are absorbed by
the interaction between the metal ions and functional groups
on the surface of cell walls. This step can be done quickly
and independently through one of the bonding mechanisms,
including coordination, complexation, ion exchange and
physical biosorption. In the second phase, by means of active
bio sorption mechanisms, the metal ions penetrate into the
cell membrane and enter into the cell. Thus, the first phase
of the biosorption is passive and rapid, but the second phase
is active and gradual [19,20].
Before crossing the cell membrane and penetrating into
the cytoplasm, all metal ions pass through the cell wall. The
cell wall contains a variety of polysaccharides and proteins.
Therefore, the cell wall is composed of many sites which
are capable to bond with metal ions. Because of the differ-
ences in the composition of the cell walls in living organ-
isms, the type and level of metal ions that form the bonds
are different [21,22]. Fungi are classified as a large group
of eukaryotic organisms that are heterotrophs and need
to breakdown organic compounds to get their energy and
carbon for growth and proliferation. Among the various
species of fungi, Trichoderma species are beneficial fungi that
are found nearly in all soils [23]. These fungi are the most
common species in cultivation, and are employed in agri-
cultural sciences for biological control of soil pathogens as
well [24]. Application of Trichoderma species in wastewater
treatment have been reported by researchers. For example,
treatment of tannery effluent [25], textile effluent [26] and
wastewater containing pharmaceutically active compounds
[27] have been studied by some researchers. Nevertheless,
the performances of these fungi in biosorption of lead
ions under critical operating variables such as pH, contact
time, lead concentration and temperature have rarely been
reported. Hence, this study was performed to investigate
the bio sorption of lead ions (Pb2+) from aqueous solutions by
Trichoderma fungus.
2. Materials and methods
2.1. Preparation of metal solution
All chemicals in this study were obtained from Merck
(Germany). To prepare the stock solution of Pb2+ ion
(1,000 mg/L), 1.6 g of Pb(NO3)2 was dissolved in 1,000 mL
volumetric flask with double-distilled water. All the other metal
ion concentrations were obtained by diluting this solution
in double distilled water using volumetric flasks. Lactic acid
and potassium hydroxide (3%) were used to adjust the pH
of the samples.
2.2. Preparation of Trichoderma fungus
A Trichoderma fungus sample was obtained from Iranian
Research Organization for Science and Technology (IROST)
and was cultured in Mycology Laboratory of Medical School
at Zahedan University of Medical Sciences, Iran. The sam-
ple was aseptically cultured in sterile petri dishes containing
PDA (Potato Dextrose Agar, composition, autoclave-steril-
ized at 110°C for 10 min) and was incubated at 24°C for three
to 4 d to form visible colonies on agar [28].
250 mL flasks containing 100 mL of broth medium (con-
taining 250 g/L potato extract, 20 g/L dextrose and 0.25 g/L
tetracycline antibiotic, autoclave-sterilized at 110°C for 10 min)
were used to assess the influence of study parameters on the
biosorption process. To achieve this, Trichoderma fungus sin-
gle colonies on agar medium were picked to inoculate the
sterilized media aseptically and the flasks were placed in
the incubator shaker to permit fungus in broth medium to
grow enough prior to contact with metal ions. At this stage,
the parameters affecting growth, including pH, temperature,
incubation time and mixing rate were examined to achieve
optimal growth of the fungus (optimum biosorbent dosage).
It must be noted that fungal growth was determined grav-
imetrically after drying in an oven at 80°C for 8 h, cooling
it to room temperature in a desiccator and weighing [29].
All experiments were repeated three times and the calcu-
lated mean values were reported as the result.
2.3. Measurement of Pb2+ ions concentration and
dependent variables
After determining the optimal conditions of growth, cer-
tain concentrations of Pb2+ ions were added aseptically to
fungus cultured in broth medium grown to optimum bio-
sorbent dosage. After setting variables according to the
purpose of each phase, the flasks were placed back into the
incubator shaker. In this study, in order to achieve optimal
biosorption conditions, the effects of most important param-
eters that would have an impact on the process, including
solution pH, initial concentration of Pb2+ ions, mixing rate,
contact time and temperature were studied (Table 1). After
the elapse of retention time, the biosorption rate of Pb2+
ions was measured by analyzing the supernatant by flame
A.A. Zarei et al. / Desalination and Water Treatment 168 (2019) 252–260254
atomic adsorption spectroscopy (FAAS) using a Shimadzu
AA-6650 machine (Japan). The readings of remaining Pb+2
ions in the samples by FAAS were repeated three times.
The obtained results were converted to concentration using
the calibration curve and linear equation. Biosorption capac-
ity of biosorbent and Pb2+ ion removal efficiency and were
calculated according to the following equations:
q
CC V
M
e
e
=
−×
()
()
0
(1)
Removal efficiency
ECC
C
t
()
()
=−×
0
0
100 (2)
In Eq. (1) qe is weight of metal ion biosorbed per gram of
biomass (mg/g); C0 and Ce are the initial and equilibrium liq-
uid phase concentration of Pb2+ (mg/L), respectively; V is the
volume of the solution (L); and M is the weight of biosorbent
(g). In Eq. (2) E is the percentage of Pb2+ ion removal by the
fungal biomass; C0 and Ct represent the initial and final (after
biosorption) lead concentrations (mg/L), respectively [30–32].
At the end of the experiments, the weight of biosorbent
was calculated based on the weight of the water-free fungus
as follows: the contents of each flask were centrifuged and
the pellet was placed inside a glass desiccator at 105°C for
48 h, and then the weight was measured.
2.4. Biosorption process modeling
In the biosorption process in a solid–liquid system, the
components of the solution will accumulate and concentrate
on the solid surface, and this process will continue until
equilibrium is reached. Two parameters including qe (the
equilibrium biosorption capacity) and Ce (the final equilib-
rium concentration of adsorbate after the equilibrium) are
used to describe such equilibrium. Biosorption isotherm
refers to the relationship between changes in the amounts of
adsorbate and concentration of adsorbent remaining in the
solution at a constant temperature and can describe the reac-
tion mechanisms between adsorbate and adsorbent. A plot
of Ce/qe, that is, biosorption isotherms have various forms for
different systems and thus are described using different mod-
els. In this study, biosorption system behavior was evaluated
based on Langmuir, Freundlich, Dubinin–Radushkevich
(DRK) and Temkin isotherm models. Linear equations for
each of these models are shown below [33,34]. In Langmuir
model (Eq. (3)), qe (mg/g) is the amount of Pb2+ ions bio-
sorbed per specific amount of biosorbent, Ce is equilibrium
concentration of the Pb2+ ions in solution (mg/L), KL (L/mg) is
Langmuir constant, and qm (mg/g) is the maximum amount
of Pb2+ required to form a monolayer.
11
11
qq qK C
em mL e
()
=+ (3)
The Freundlich model (Eq. (4)) is an empirical relation
between qe and Ce. It is obtained by assuming a heteroge-
neous surface with non-uniform distribution of the biosorp-
tion sites on the biosorbent surface, and can be expressed by
the following equation:
lo
glog logqK
n
C
eF e
=+
1 (4)
where KF and 1/n are the Freundlich constants related to
biosorption capacity and biosorption intensity, respectively.
The Freundlich constants can be obtained by drawing the
logqe vs. logCe based on experimental data.
In Temkin model (Eq. (5)), the surface absorption the-
ory was corrected considering possible reactions between
adsorbent–adsorbent and adsorbent–adsorbate.
qBKBC
eTe
=+
ln ln
(5)
where KT and B are Temkin constants, and B is related to the
heat of biosorption.
The empirical equation of Dubinin–Radushkevich model
(Eq. (6)) has been widely used to describe the adsorption
of gases and vapors on microporous solids, and can be
written as:
lo
gln qq
em
=−
βε2 (6)
where β (mol2/kJ2) is a constant connected with the mean free
energy of biosorption per mole of the adsorbate, qm (mg/g)
is the theoretical saturation capacity, and ε is the Polanyi
potential.
3. Results and discussion
3.1. Optimization of biosorbent growth
Living and growing fungi cells are recruited as biosor-
bent; the quantities of biosorbent and available active sites
on its surface are effective on the biosorption efficiency of
metal ions. In other words, an improvement in the biosor-
bent quantity would increase the amount of available active
sites and functional groups suitable for complex formation
and metal ion extraction, leading to an enhancement of metal
ion removal efficiency. Hence, as the first goal, determination
of optimal conditions for growth of fungi cells, were stud-
ied. In this regard, effects of various parameters on fungal
growth were evaluated (Figs. 1a–d). As is clear from Fig. 1,
the maximum fungal growth rate for each parameter was as
follows: pH = 5, contact time of 24 h, a temperature of 298 K
and mixing rate of 250 rpm. When these optimum conditions
were combined, a mean of 5.1 g of biomass per 1 L of broth
Table 1
Range of experimental parameters
Parameter Ranges
pH 2–8
Mixing rate (rpm) 150–350
Lead concentration (mg/L) 25–200
Temperature (°C) 20–35
Contact time (min) 30–270
255A.A. Zarei et al. / Desalination and Water Treatment 168 (2019) 252–260
medium (5.1 g/L) was gained, which was considered as the
optimum biosorbent dosage in the following steps of the
study.
3.2. Effect of solution pH on removal of Pb2+ by Trichoderma
fungus
The solution pH is one of the most important parame-
ters affecting the biosorption of metal ions by biosorbents.
It can cause substantial changes in the efficiency of biosorp-
tion processes through acting on the cell wall of biosorbents
and the chemistry of metal ions [35–37]. To investigate the
effect of solution pH on the biosorption in the studied sys-
tem, seven 250 mL flasks suitable for growth of the cultured
Trichoderma fungus were selected and adjusted to the pH
values of 2–8. The solution containing Pb2+ ions was added
to the mentioned samples to achieve final concentration of
50 mg Pb2+/L, and the samples were placed in the incubator
shaker for 24 h.
Fig. 2 shows the effect of initial pH of solution on
the removal of Pb2+ ions and the biosorption capacity of
biosorbents. As it turns out, the highest rate of lead removal
by biosorbents (82.4%) was obtained at pH equal 6, which
was selected as the optimum pH. Similar to current results,
in a study performed by Say et al. [38] on biosorption of
metal ions using the filamentous fungus Phanerochaete chrysos-
porium, the highest removal rate was observed at pH = 6.
Less biosorption was found at pH lower than 6, so that the
lowest removal level (35.6%) was seen at pH = 2. This obser-
vation could be due to protonation of functional groups on the
surface of fungi at acidic pH values. Hence, the total charge
of the fungal surface would be positive in such conditions
and repulsive forces between the fungal positive surface
and metal ion positive charge could inhibit the ion biosorp-
tion on the surface of fungi. On the other hand, in acidic
pH values, the protons in the environment could compete
with metal ions in being absorbed on the surface of biosorbents,
causing decreased biosorption. With increasing pH values, the
total charge of the cell wall and the fungal surface would
increasingly become more negative and anionic active sites
will be created on its surface. This would lead to an increase
in their ability to form complexes with lead(II) ions and thus
(a) (b)
(c) (d)
Fig. 1. Effect of various parameters on growth of Trichoderma fungus, (a) time, (b) pH, (c) mixing rate, and (d) temperature
A.A. Zarei et al. / Desalination and Water Treatment 168 (2019) 252–260256
higher removal efficiency will be achieved. The observed
reduction in the biosorption process at pH values >6 can be
attributed to the formation of hydroxide deposits or mixed
hydroxide complexes that impede the metal ions biosorp-
tion on the adsorbent. Similar findings were reported by
other researchers [14,16,39]. Similar findings were reported
by Al-Homaidan et al. [40] for bio sorption of cadmium by
Spirulina platensis dry biomass (which maximum biosorp-
tion efficiency equal 78% was observed at pH 7–8). Also,
the results of this study in agreement with the findings of
Kariuki et al. [41] on biosorption of lead using rogers mush-
room biomass ‘Lepiota hystrix’, which found optimum pH
of 4.5–6.0 for maximum lead biosorption from aqueous
solutions.
3.3. Effect of mixing rate on Pb2+ ion biosorption by
Trichoderma fungus
The appropriate and adequate contact of pollutant and
adsorbent surface through suitable mixing in liquid medium
can lead to accelerated biosorption of pollutants, improving
the biosorption process, and reducing the equilibrium time.
The present study examined the effect of mixing rate on Pb2+
ion biosorption at the mixing rate of 150–350 rpm with the
concentration of 50 mg/L Pb2+ ion and at pH of 6 during a
period of 90 min. As shown in Fig. 3, lead removal efficiency
was improved from 83.6% to 92.8% by increasing the mixing
rate from 150 to 250 rpm, and then it was nearly constant
or reduced slightly at increased mixing rates. These findings
can be interpreted as a result of breaking the bonds between
metal ions and biosorbent surface at high mixing rates, or be
due to occupation of the active sites on the adsorbent. These
results agree with findings from the study of Foroutan et al.
[42] regarding the lead biosorption from aqueous solution
using shrimp peel. The results of their study showed that by
increasing the mixing rate up to 200 rpm, the lead biosorp-
tion efficiency increased by 94.3% [42].
3.4. Effect of contact time on Pb2+ ion biosorption by
Trichoderma fungus
Another parameter affecting the efficiency of metal ions
biosorption on biosorbents is contact time, which determines
the kinetics and time tested [43]. The effects of contact
time on the Pb2+ ions biosorption was analyzed in a range
of 30–240 min of contact time, concentration of 50 mg/L
Pb2+ ions, pH = 6, mixing rate of 250 rpm and temperature
of 25°C. Fig. 4 shows the effect of contact time on the bio-
sorption efficiency of Pb2+ ions and absorptive capacity.
According to Fig. 4, it is clear that both biosorption efficiency
and biosorption capacity of adsorbent at the beginning of
the experiment are rising with steep slope in a manner that
within an interval of 30–120 min of contact time, biosorp-
tion efficiency and capacity rose from 71.6% and 7.02 mg/g
to 96.8% and 9.49 mg/g, respectively. After 120 min, both
factors remain almost constant. Concordantly, Abdel-Aty
et al. [44] observed the highest amount of lead adsorbed by
Anabaena sphaerica fungus after 120 min of testing. The high
rate of Pb2+ ions biosorption at the beginning of the process
can be attributed to the abundance of available active sites
on the biosorbents and high concentration of metal ions.
Biosorption efficiency is reduced over time with the occu-
pation of the active sites by metal ions and a reduction in
the concentration of ions. Thus, the contact time of 120 min
in this study could be regarded as the equilibrium point of
35.6
82.4
6.65
8.94
6
7
8
9
10
30
40
50
60
70
80
90
123456789
qe, mg/g
Removal Efficiency, %
Initial pH
Removal efficiency
Biosorption capacity
Fig. 2. Effect of initial pH on Pb2+ ions biosorption by Trichoderma
fungus (at 25°C, mixing rate = 150 rpm, biosorbent dosage
= 5.1 g/L, initial Pb2+ concentration = 50 mg/L, contact time =
90 min).
83.60
92.80
8.20
9.10
8.0
8.5
9.0
9.5
10.0
80
82
84
86
88
90
92
94
125150 175200 225250 275300 325350 375
qe, mg/g
Removal Efficiency, %
Mixing rate, rpm
Removal efficiency
Biosorption capacity
Fig. 3. Effect of mixing rate on Pb2+ ion biosorption by Trichoderma
fungus (at 25°C, pH = 6, contact time = 90 min, biosorbent
dosage = 5.1 g/L, initial Pb2+ concentration = 50 mg/L).
71.60
96.80
7.02
9.49
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
70
75
80
85
90
95
100
0306090120 150180 210240
qe, mg/g
Removal Efficiency, %
Contact time, min
Removal efficiency
Biosorption capacity
Fig. 4. Effect of contact time on Pb2+ ions biosorption by
Trichoderma fungus (at 25°C, pH = 6, mixing rate = 250 rpm, initial
Pb2+ concentration = 50 mg/L).
257A.A. Zarei et al. / Desalination and Water Treatment 168 (2019) 252–260
biosorption process, which could be considered as an opti-
mum contact time for the rest of experiments.
3.5. Effect of initial Pb2+ ions concentration and temperature on its
biosorption by Trichoderma fungus
Initial concentration of pollutants and temperature are
always regarded as important parameters on biosorption
process efficiency. Temperature can affect chemical reaction
rate, and initial concentration of pollutant is the driving
force in the mass transfer rate of adsorbate to the biosorbent
surface. Fig. 5 indicates the effect of initial Pb2+ ions concen-
tration on biosorption efficiency at different temperatures.
As shown in Fig. 5 and similar to the results reported by
Abdel-Aty et al. [44], the most biosorption efficiency at all
temperatures was achieved at lower Pb2+ concentrations and,
biosorption process efficiency was decreased by increasing
the concentration of the Pb2+ ions. For example, at tempera-
ture 20°C, maximum removal efficiency equal 95.6% has
been found at lower concentration of Pb2+ solution (25 mg/L)
and a minimum removal efficiency of Pb2+ ions (equal 58.4%)
has been obtained at initial concentration of 200 mg/L by
Trichoderma fungus. Although, the biosorption process effi-
ciency was decreased by rising concentrations of Pb2+ ions,
biosorption capacity of biosorbent had an upward trend
(Fig. 6). As shown in Fig. 6, the Pb2+ ions biosorption capacity
of the Trichoderma fungus increased from 4.69 to 22.92 mg/g
(at 20°C) as the initial Pb2+ concentration was varied from
25 to 200 mg/L. Similar trends were observed for other stud-
ied temperatures.
The increase of biosorption capacity of biosorbent with
an increase in Pb2+ ions concentration is probably due to
higher interaction between metal ions and the biosorbent.
Similar findings were reported by Rathinam et al. [45] for
cadmium biosorption by seaweed, and by Das and Guha [46]
for chromium removal by biomass of Termitomyces clypeatus.
Analyzing the efficiency of temperature on the biosorp-
tion process indicates that removal efficiency was increased
with increasing temperature from 20°C to 25°C. Probably
due to increased diffusion coefficient of lead ions, their
affinity was enhanced for complex formation and adhe-
sion to the fungal surface. Thus, in the present study, the
highest biosorption rate (98.8%) of Pb2+ ions occurred at
25°C and the concentration of 25 mg/L Pb2+, and the low-
est rate (58.45%) took place at 20°C and the concentration
of 200 mg/L. Extraction efficiency is reduced at lower tem-
peratures due to reduced mass transfer rate and diffusion
coefficient. The removal efficiency was again declined
slightly over 25°C. This could be due to high temperatures
unsuitable for growing fungi and variations in the superfi-
cial active sites [16,31–33]. Findings of Al-Homaidan et al.
[40] on biosorption of cadmium by Spirulina platensis dry
biomass showed that maximum biosorption efficiency equal
87% was achieved at 26°C, which is in agreement with the
results of this study.
3.6. Biosorption isotherms and kinetics
We further decided to study biosorption isotherms in
our system, since the related findings could be helpful in
understanding the mechanisms of the biosorption and pol-
lutant affinity to adsorbent. In this regard, after plotting
each of the biosorption models and determining their cor-
relation coefficient, it can be observed which one of bio-
sorption curves fits with empirical data of the biosorption
process, indicating the type of equation governing process.
Furthermore, biosorption intensity and adsorbent capac-
ity to absorb pollutants can be measured according to the
isotherm constants [16].
In the present study, Langmuir, Freundlich, Temkin
and DRK biosorption isotherms were examined and the
respective graphs were drawn on the basis of experimen-
tal data. Figs. 7a–d display the linear models of the studied
isotherms and Table 2 presents the correlation coefficients
and the aforementioned isotherm constants. Given the cor-
relation coefficients for different biosorption models at the
temperatures of 20°C–35°C, it can be concluded that the
biosorption of Pb2+ ions by Trichoderma fungus is most con-
sistent, in decreasing order, with Langmuir, DRK, Temkin
and Freundlich models. Based on the experimental findings,
the maximum biosorption capacities of the adsorbent were
observed at 20°C, 25°C, 30°C and 35°C, respectively equal
58.45
98.8
55
60
65
70
75
80
85
90
95
100
20 40 60 80 100120 140160 18
02
00
Removal Efficiency, %
Initial concentration of Pb
2+
, mg/L
20 °C
25 °C
30 °C
35 °C
Fig. 5. Effect of initial concentration of Pb2+ ions on biosorption
by Trichoderma fungus at different temperature (pH = 6, mixing
rate = 250 rpm, contact time = 120 min).
4.84
9.66
17.80
24.47 24.88
0
5
10
15
20
25
30
020406080100 120140 160180 20
0220
qe(mg/g)
Initial concentration of Pb
2+
, mg/L
Fig. 6. Effect of initial concentration of Pb2+ ions on biosorption
capacity by Trichoderma fungus at 25°C (pH = 6, mixing
rate = 250 rpm, contact time = 120 min).
A.A. Zarei et al. / Desalination and Water Treatment 168 (2019) 252–260258
to 22.92, 24.88, 25.06 and 24.29 mg/g, which are very close
to those obtained by Langmuir model. This is confirmed
by comparing the empirical findings with the constants of
Langmuir mode. Thus, it is concluded that the biosorption
process on all active sites was based on an identical mecha-
nism and biosorption occurs as a monolayer. Sari and Tuzen
[47] and Morosanu et al. [48] have reported similar results.
Findings of Morosanu et al. [48] have been shown that the
calculated sorption capacities were in good agreement with
the uptake capacity of Langmuir model. In addition, find-
ings of Morosanu et al. [48] on biosorption of cadmium by
Spirulina platensis dry biomass showed that Langmuir model
to be in better correlation with experimental data (R2 = 0.92).
Furthermore, the results of Kariuki et al. [41] on biosorption
of lead using rogers mushroom biomass ‘Lepiota hystrix’ con-
firmed the suitability of Langmuir isotherm model.
Two kinetics models, namely pseudo-first-order and
pseudo-second-order were used in this study to investi-
gate the biosorption of Pb2+ ions on Trichoderma fungus
(Table 3). Where qt (mg/g) and qe (mg/g) are the biosorption
capacities of Pb2+ ions at time t (min) and equilibrium, respec-
tively. k1 (min–1) and k2 (g/mg min), are the rate constants of
the pseudo-first-order and pseudo-second-order models,
respectively. As it can be seen from Figs. 8, 9 and Table 3,
the data well fitted with the second-order kinetics model
(R2 > 0.99). On the other hand, the pseudo-second- order
models can well describe the experimental data, indicat-
ing that the biosorption process was controlled by chemi-
cal interaction. Based on the findings of Kariuki et al. [41]
on biosorption of lead using roger’s mushroom biomass
(a) (b)
(c) (d)
Fig. 7. Isotherms for biosorption of Pb2+ ions on Trichoderma fungus. (a) Langmuir isotherm, (b) Freundlich isotherm, (c) Temkin
isotherm, and (d) DRK isotherm.
Table 2
Isotherm parameters for biosorption of Pb2+ ions on Trichoderma
fungus at different temperatures
Temperature, KConstantIsotherm
model 308303298293
0.27440.31380.86060.2442bLangmuir
isotherm 24.1526.6623.823.25qm
0.99600.95810.99360.9696R2
6.066.918.605.92Kf
Freundlich
isotherm 2.892.993.463.16n
0.93410.90780.92560.8918R2
0.23130.22800.25830.2567BTemkin
isotherm 0.00330.00790.000470.0056Kt
0.99580.98750.97380.9587R2
0.0000750.000640.000060.0003βDRK
isotherm 3.103.173.163.04qm
0.98680.97760.97760.9808R2
259A.A. Zarei et al. / Desalination and Water Treatment 168 (2019) 252–260
‘Lepiota hystrix’, the biosorption process follows second-
order kinetics.
4. Conclusion
Being able to grow in most settings, Trichoderma fungus
is one of the fungi used to remove pollutants from the envi-
ronment. Studying the effects of variables related to the
biosorption process determined that the maximum biosorp-
tion rate of lead ions (98.8%) occurs after 120 min of testing
at pH equal 6 and the temperature of 25°C, which is close to
the ambient temperature. Moreover, the removal efficiency
was enhanced by increasing the mixing rate and was reduced
by raising the concentration of Pb2+ ions. The biosorption
system behavior was evaluated, and the suitability of the
Langmuir model for the analysis of the biosorption process
was demonstrated. Collectively, these results showed that
Trichoderma fungus as a biosorbent has high biosorption
capacity for the removal of Pb2+ ions from aqueous solutions.
Acknowledgment
The authors would like to thank Health Research Deputy
of Torbat Heydariyeh University of Medical Sciences for
financial support in carrying out this research (Project
No: A-101350-1).
Symbols
B — Temkin constant
C0 — Initial concentration in aqueous phase
Ce — Equilibrium concentration in aqueous phase
E — Removal efficiency
k — Rate constant
KF — Freundlich constant
KL — Langmuir constant
KT — Temkin constant
M — Mass of biosorbents
n — Freundlich constant
qe — Adsorption capacity at equilibrium
qm — Maximum adsorption capacity
qt — Adsorption capacity at time t
T — Temperature
V — Volume of the solution
β — Dubinin–Radushkevich constant
ε — Polanyi potential
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