Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal web link: http://www.jett.dormaj.com  
https://doi.org/10.47277/JETT/9(1)138  
Adsorption of High Chromium Concentrations  
from Industrial Wastewater Using Different  
Agricultural Residuals  
El-Baz A. A., Hendy I., Dohdoh A. M., Srour M. I. *  
Environmental Engineering Department, Faculty of Engineering, Zagazig University, Zagazig, Sharkia 44519, Egypt  
Received: 23/08/2020  
Accepted: 25/09/2020  
Published: 20/03/2021  
Abstract  
Hexavalent chromium Cr (VI) is a toxic material used in many industries such as tanneries and electroplating industries. Most of the  
previous researches studied the removal of chromium at lower concentrations up to 600 mg/L but did not tackle the behavior at higher  
concentrations, which resemble the real concentration of studied tanneries effluents. The present research is a comparative study of  
different agricultural low cost adsorbents in the removal of high Chromium concentration from industrial wastewater up to 1000 mg/L,  
compared to a commercial activated carbon. The tested adsorbents are (Banana Waste (BW), Sawdust (SD), Phragmites Australis (PA),  
Sugarcane Bagasse (SCB), Pea pod peels (PPP) and Rice straw (RS)). The materials were chemically pretreated with acid-alkali except  
BW was treated with acid only, to improve adsorbent metal binding capacity. Batch experiments were conducted to study the effect of  
pH, adsorbent dosage, contact time, initial Chromium concentration and temperature on the removal efficiency of Chromium from  
wastewater. The experiments were conducted in two sets, one for lower concentration (25-50-100-200-400) mg/L and the other for  
higher concentration (600-800-1000) to simulate the concentration of Chromium in tannery industry effluents. At 1000 mg/L initial  
concentration, BW achieved the optimum removal efficiency of 73.28% at pH = 3, adsorbent dosage = 25 g/L and contact time of 3  
o
hours with the adsorption capacity was 39 mg/g. For SD at pH=2, 3 hours contact time, 10 g/L dosage, and 30 C the removal ratio was  
6
4.83% and the adsorption capacity was 86.30 mg/g. The equilibrium data for various agricultural adsorbents was being tested with  
various adsorption isotherm models such as Langmuir, Freundlich and Tempkin. At low concentrations, AC, BW, PA and SCB follows  
Freundlich isotherm model while SD follows Langmuir isotherm model. At higher concentrations, BW, SD, PA follows Langmuir  
isotherm while SCB follows Tempkin isotherm model. To evaluate the mechanism of Cr adsorption on different adsorbents, Pseudo-  
first-order and Pseudo-second-order equations were used. The adsorption process follows Pseudo-second-order for all adsorbents, which  
confirms the chemisorption of Cr (VI) on different adsorbents.  
Keywords: Chromium; adsorption; low cost adsorbents; Industrial wastewater; isotherms; kinetics; high concentrations  
1
(
VI) on ecosystem and public health (4). According to WHO,  
1
Introduction  
the maximum allowable limits for chromium in wastewater is  
1
A wide range of toxic inorganic and organic chemicals are  
.0 mg/L while in drinking water is 0.05 mg/L (5).  
The process of tanning using chromium compounds is one  
discharged into the environment as industrial wastes, causing  
critical pollution problems (1). Water pollution caused by toxic  
heavy metal ions has become a serious environmental problem.  
A serious health hazard results from dissolved heavy metals  
escaping into the environment, which accumulate throughout  
the food chain in living tissues, multiplying their effects (2).  
Chromium is an important heavy metal that is released into  
natural water from various sources, including electronics,  
electroplating, metallurgical, and leather tanning industries (3)  
4). It is found in nature in two different forms as trivalent  
chromium (Cr (III)) and hexavalent chromium (Cr (VI)) (5) (6)  
7) (8). Chromium (III) is relatively insoluble and useful  
micronutrient for human, plants, and animals metabolism  
whereas chromium (VI) is primary contaminant and more  
toxic, carcinogenic and mutagenic to living organisms than  
other heavy metals (9) (7). In addition, it also has an effect on  
human skin, liver, kidney, and respiratory organs (10).  
Therefore, it is necessary to eliminate Cr (VI) from the  
environment, in order to prevent the deleterious impact of Cr  
of the most common methods of processing the hides. Around  
0-70 % of chromium reacts with the hides in this process. In  
6
other words, about 30-40% of the chromium remains in the  
solid and liquid. Hence, the wastewater of tanning process is an  
important source of chromium pollution. In addition, it is  
desirable to recover chromium from the wastewater (11) (12).  
A number of methods are available for the removal of heavy  
metals from aqueous solution. These methods include chemical  
precipitation, ion exchange, membrane separation process,  
electrocoagulation and adsorption (2)(13)(7). Although the  
chemical precipitation has traditionally been the most used  
method (14), it suffers from many draw backs like incomplete  
removal, requirement of sizable quantities of treatment  
chemicals and production of large amount of toxic sludge. A  
variety of other treatment technologies were considered and  
evaluated. Techniques such as the exchange of ions and the  
adsorption using products from naturally occurring materials  
(
(
Corresponding author: Environmental Engineering Department, Faculty of Engineering, Zagazig University, Zagazig, Sharkia 44519,  
Egypt, Tel./Fax: +0020552304987; Email: mohamedsrour20102005@gmail.com.  
122  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
such as activated carbon have been considered as better  
alternatives. The exorbitant cost involved with ion exchange  
makes it prohibitive for wide application (15). Among all these  
methods, adsorption is the most popular since it is a very simple  
technique due to its convenience, ease of operation, and  
versatility (16) (9). This process can minimize or eliminate  
various types of pollutants and has therefore a wide range of  
applications in wastewater treatment (13).  
The most common used adsorbents are nanomaterials and  
activated carbon as they have large surface area, adsorption  
capacity and microporous structure but their cost are high (9).  
Therefore, it is necessary to look for a cheaper and easily  
available alternate. Consequently, a large number of available  
low-cost adsorbents including agro-based material are used to  
remove Chromium from polluted wastewater. The most  
popular adsorbents prepared from agricultural wastes are  
Banana Waste (BW), Sawdust (SD), Sugarcane Bagasse  
of (2-7), biochar dosages (0.5 – 5 g/L), initial Cr (VI)  
concentrations (20-200 g/L) and contact time till 300 min at  
o
30 C. (20) used the modification of PPP with NaOH and HCl  
to increase the adsorptive characteristics of PPP. Many  
methods for modification of Rice Straw were done to increase  
its adsorption of heavy metals. First of all is the biochar  
o
production at different temperatures of 300, 500 and 700 C as  
investigated by (3). (33) modified RS with acid treatment using  
nitric acid and CaO and alkali treatment using NaOH and urea.  
Modification with NaOH only is used by (34). (35) modified  
the rice husk with tartaric acid while (36) used KOH for the  
production of rice straw carbon (RSC) and rice straw activated  
carbon (RSAC). Activated Carbon (AC) is considered the best  
adsorbent for heavy metal because of the large internal surface  
area, pours availability and high microporous(37). AC is  
preferred for its very high surface areas, porous sorbent ,  
functional groups, high capacity, high rate of adsorption, great  
capacity to adsorb a wide range of pollutants, fast kinetics and  
a high quality treated effluent (38). On the other hand, the main  
disadvantages of AC are its very expensive cost, requires  
complexing agents to improve its removal performance and its  
performance is dependent on the type of carbon (39) (40). Most  
of the previous studies gave great attention to low concentration  
(
SCB), Phragmites Australis (PA), Pea Pod Peels (PPP) and  
Rice straw (RS). Many researchers seek the optimum operating  
parameters for each of these adsorbents including pH,  
adsorbent dosage, initial concentration and contact time as well  
as preparation methods. (17) used 0.1 N NaOH and 0.5 N  
NaOH as a chemical preparation for Banana Waste (BW) to  
increase its adsorption capacity. Although the pH is an  
important parameter; its effect and optimum value is a  
controversial topic, (18) reported that optimum removal  
achieved at pH of 1, while (19) and (20) found that optimum  
pH was at pH 3. On the other hand; (21) concluded that the  
optimum pH was 7. Different adsorbent dosage ranges were  
used to find the effect of dosage on Cr (VI) removal. The  
optimum dosage was 0.4, 4 and 20 gm/L according to (18), (19)  
and (20). The initial concentration was studied also in a range  
of 1 to 70 mg/L by (18), (21) and (20) while (19) studied the  
effect of initial concentration at 100 to 600 mg/L. The contact  
time also was studied from 10 minutes to 270 minutes. Finally,  
-
1
for heavy metals( 5 – 400 mgL ) and studied the effect of low  
cost adsorbents in the removal of such metals but they didn’t  
study the effect of these materials on high concentration.  
Therefore, the main objective of this study is to investigate the  
effect of these materials on the removal of Chromium from low  
and high concentration industrial wastewater up to 1000 mg/L.  
2
Material and Methods  
2
.1 Adsorbents Preparation and Treatment  
In the current study, the effectiveness of six low cost  
adsorbent materials in the removal of Chromium from tannery  
industrial wastewater compared to the efficiency of charcoal  
Activated Carbon (AC) was investigated. The materials are  
BW, SD, SCB, PA, PPP and RS. The utilized materials are  
solid waste that will increase environmental pollution problems  
if not properly disposed of. BW, PPP and SCB are collected  
from fruit sellers and farmhouse while SD is collected from  
wood workshops; RS from fields and finally PA are collected  
from El-Agoa canal in Zagazig city, located at the Nile Delta  
zone of Egypt. Each utilized material was treated as followed:  
the effect of temperature was studied in a range from 10 to  
o
7
0 C.  
Different studies were applied on Sawdust for the  
adsorption of Cr (VI) at a pH range of 1 to 11 and using  
different dosages from 4 to 24 gm/L, the examined initial  
concentration ranged from 5 to 500 mg/L and contact time from  
1
0 up to 1100 minutes. The optimum removal efficiency was at  
lower pH according to (S. Gupta & Babu, 2009, (22). (10) and  
9) Whereas (23) found that the optimum removal at pH value  
(
(
1) it was dried at sunlight for a week and then washed many  
of 6 after 1 hour contact time, using 1g/L dosage and 20 mg/L  
initial concentration. Many researches used raw Sugarcane  
bagasse (SCB) and modified Sugarcane bagasse for the  
adsorption of chromium from polluted water. Washed SCB  
with distilled water is examined at pH range from 1 to 7 for  
different time intervals at low chromium concentrations  
ranging from 5 to 120 mg/L (24) (25) (26) (27) (28) (2).  
Modifications on SCB was done through carbonization under  
times with distilled water to get rid of any dusts, impurities and  
inorganic materials. (2) Oven dried at 90°C for three days (5 h  
daily). (3) The material was then grinded and sieved through  
100 and 200 mesh (Standard Sieves Dual Manufacturing Co.,  
USA) for uniform size distribution. (4) The powder was then  
washed several times with distilled water to get rid of lighter  
materials and other impurities. (5) The adsorbents were then  
used in one of three ways. First, used directly. Second, dipped  
in 0.1 N NaOH for 9 hours and washed with distilled water to  
remove the lignin and then dried again then rinsed separately  
with double-distilled water two times and dipped into 0.1 N  
HCl for 9 hours again to remove traces of alkalinity (16).  
Third, dipped in HCL only for 9 hours. Finally, the treated  
adsorbents were thoroughly washed with double-distilled  
water, then dried in a desiccator and stored there.  
2 2 4  
N flow (29) or through chemical modification using H SO to  
increase its surface area and the degree of micro porosity(30).  
Phragmites Australis is used as a new low cost adsorbent for  
the removal of COD, BOD,TSS and TDS as it is available  
around drains and also causes environmental problems (31).  
Phragmites Australis is also used in constructed wetlands to  
remove Chromium, Boron, Nitrogen and Phosphorous from  
tannery industrial wastewater because of its ability to adapt to  
climatic conditions. The optimum removal efficiency for Cr  
was 48% at HRT = 3 days when the initial concentration was  
2.2 Preparation of Chromium Solution  
All the chemicals used are of analytical grade (AR). A  
0
.23 mg/L(32). Biochar was produced using pyrolysis process  
stock solution of 1000 mg/L of Cr (VI) is prepared by  
dissolving 2.8287 g of 99.9% potassium dichromate (K Cr  
in the presence of nitrogen gas on Green Pea Pod Peels (GPPP)  
to be used in Cr (IV) removal under different conditions(4). (4)  
studied the potential of using biochar from GPPP in a pH rang  
2
2 7  
O )  
in 1000 ml of distilled water. This solution is diluted as required  
to obtain standard solutions containing 25-50-100-200-400-  
123  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
6
00 and 800 mg /L of Cr (VI). pH adjustment is done using 0.5  
where, Q  
m
and b are Langmuir constants related to the sorption  
N HCl and 0.5 N NaOH solutions.  
capacity (the amount of adsorbate required to form a single  
monolayer on unit mass of adsorbent (mg/g)), and sorption  
energy which quantitatively reflects the affinity between the  
2
.3 Adsorption Kinetics  
In the adsorption process, it is important to study the  
e
adsorbent and adsorbate (L/mg) , respectively. C is the  
equilibrium concentration in (mg/L) , and q is the amount of  
adsorbate adsorbed per unit weight of adsorbent (mg/g) at  
equilibrium (21). The plot of C versus C /q gives a linear form  
if the adsorption equilibrium obeys Langmuir equation. An  
extended analysis of the Langmuir equation can be made based  
kinetics of the adsorption to understand and predict how time  
affects mobility and retention of heavy metals. In order to  
define the adsorption kinetics of heavy metal ions, the kinetic  
parameters for the adsorption process were studied at different  
time intervals(6). The Pseudo–first-order and Pseudo–second-  
order equations are the most popular models used to describe  
the kinetics of Chromium adsorption. The general expression  
for Pseudo–first-order equation model is:  
e
e
e
e
on a dimensionless equilibrium parameter, R  
the separation factor,  
L
, also known as  
1
RL  
=
(6)  
dqt  
1 + b Cꢃ  
=
k(q − q )  
(1)  
e
t
dꢀ  
If the value of R  
adsorption, while if R  
adsorption, and if R = 1, this represents the linear adsorption,  
while the adsorption operation is irreversible if R = 0.  
L
obtained between 0 and 1, it is a favorable  
where q  
e
and q  
t
(mg/g) are the adsorption capacities at  
L
> 1, this denotes an unfavorable  
equilibrium and at any time t and k is the Pseudo–first-order  
rate constant (hr ). By applying the boundary conditions after  
integration of both sides from t = 0 to t = t and q = 0 to q =q ,  
t t t  
the linear form of the equation becomes:  
L
-1  
L
2.4.2 Freundlich Isotherm Model  
The Freundlich model supposes that the adsorption of metal  
푘
ions takes place on a non-ideal heterogeneous surface by  
multilayer adsorption. For adsorption from solution, the  
Freundlich isotherm is expressed in the linear form as:  
log(푞 − 푞 ) = 푙표푔푞 −  
ꢁ
(2)  
푒
푡
푒
2
.303  
The values of q  
are calculated from the slope and intercept of the plots of log  
- q ) versus t (18). The Pseudo–second-order chemisorption  
e
and k at different initial concentrations  
logqe = log K + n logC  
e
(7)  
F
F
(
q
e
t
kinetic rate equation is also expressed as:  
(mg1–1/n L1/n g−1) is the Freundlich constant, which  
f
where, K  
indicates the relative adsorption capacity of the adsorbent; the  
larger its value, the higher the capacity. and n is the adsorption  
dqt  
ꢂ
t
F
=
k (q − q )  
(3)  
ꢂ
e
dꢀ  
intensity or the heterogeneity of the sorbent; the more  
heterogeneous the surface, the larger its value. and is also  
known as Freundlich coefficient(6). If the value of n is unity,  
then the partition is independent of their concentration between  
the two phases. The value of n below unit therefore indicates  
normal adsorption, while the value of n above one indicates co-  
operative adsorption(21).  
where q  
e
and q  
t
(mg/g) are the adsorption capacities at  
2
equilibrium and at any time t and k is the Pseudo–second-order  
rate constant (g/mg/hr). By applying the boundary conditions  
after integration of both sides from t = 0 to t = t and q  
, the integrated form of the equation becomes:  
t
= 0 to q  
t
=q  
t
ꢀ
1
1
2
.4.2 Tempkin Isotherm Model  
=
+
ꢂ
e
ꢀ
(4)  
qt k q  
qe  
The Tempkin isotherm explained the nature of  
ꢂ
adsorption heterogeneous system. The Tempkin isotherm  
assumes that the adsorption heat linearly decreases with  
increasing adsorption capacity(9). The linear form of Tempkin  
equation is given by:  
The rate constant k  
adsorption capacity q are calculated from the slope and  
intercept of the linear plot of t (time) Vs t/q (19).  
2
(g/mg/hr)and equilibrium  
e
t
2
.4 Adsorption Isotherm Models  
In order to understand the distribution of the metal ions in  
qe = B ln AT + B ln Ce  
(8)  
T
T
the liquid and solid phases at equilibrium at a certain  
temperature, there is a need to fit the different isotherm models  
with the experimental data (23). The most applied isotherm  
models are; Langmuir, Freundlich and Tempkin models.  
where, B = (RT)/b , T is the absolute temperature in K and R  
T
T
o
is the universal gas constant (8.314 J/mol. K). The constant b  
is related to the heat of adsorption (J/mol), A is the equilibrium  
T
T
binding constant (L/g) corresponding to the maximum binding  
energy. Most of the previous studies are limited to the removal  
of low initial Cr concentrations (5 – 600 mg/L). The main  
objective of the present study is to examine the adsorption  
capacity of different low cost agricultural waste materials at  
high Cr concentrations (600-1000 mg/L). The above review  
illustrated that there are many different methods for absorbent  
preparation. Moreover, extensive studies concerning the  
operating parameters are recommended. In the present study  
the optimum operating parameters (including pH, adsorbent  
dosage, initial concentration and contact time as well as  
preparation methods) for the six different adsorbents (BW, SD,  
SCB, PA, PPP and RS) will be assessed. Activated Carbon will  
be examined as standard and reference adsorbent.  
2
.4.1 Langmuir Isotherm Model  
Langmuir equation is based on the assumptions that  
maximum adsorption occurs on a saturated mono-layer of  
adsorbate molecules on the adsorbent surface that the energy of  
adsorption is constant and that there is no transmigration of  
adsorbate in the plane of the surface(18). The linearized form  
is:  
Ce  
1
1
+ Ce  
=
(5)  
qe b Qm Qm  
124  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
2
.5 Batch Experiments  
3
Results and Discussion  
Using observations of the sorption studies to optimize the  
The batch experiments were conducted in 50 ml conical  
flasks. The amount of adsorbent was added in 20 ml of aqueous  
Cr (VI) solutions, and then mixed in water bath mechanical  
pH, adsorbent dosage, initial chromium concentration, contact  
time, and temperature have been plotted to determine the  
feasibility of sorption system along with its mechanisms  
through kinetics. The results of batch studies were compared  
for different adsorbents used in the study. The effect of  
treatment method for materials also have been studied.  
o
shaker at 30 C. The treated solution is finally filtered before  
analysis. The main investigated parameters are in Table (1).  
The high concentration range was studied in a range of 600  
to 1000 mg/L based on the characterization of real samples  
from El-Robiekey factories for tanning in Badr city-Egypt and  
Quesna tanneries in Quesna city-Egypt, which ranged from 560  
3.1 Effect of Adsorbent Preparation Methods and Treatment  
to 970 mg/L  
.
Figure (1) shows the effect of preparation methods on the  
sorption efficiency. The experiments were performed at pH 3,  
0 mg/L initial concentration, 1hr contact time, 5 g/L adsorbent  
2
.6 Instruments  
All measurements were conducted according to standard  
5
O
dosage and 30 C. The results indicated that the chemical  
treatment of the adsorbent using NaOH followed by HCl  
achieved higher removal efficiency. BW was the only  
adsorbent that shows higher efficiency when treated with HCL  
only.  
methods. The concentration of Chromium ions in the influent  
as well as the effluent was measured using Atomic Absorption  
Spectrophotometer (ThermoFisher–iCE 3000 series) model  
with air –acetylene gas and wave length of 357.9 nm in the  
faculty of Agriculture central laboratory- Zagazig University,  
Egypt.  
Table 1: Various parameters considered during batch experimental study.  
Initial Cr (VI)  
concentration  
Adsorbent  
dosage (g/L)  
Contact  
time (hr)  
o
Parameter  
pH  
Temperature ( C)  
(
mg/L)  
Initial Cr (VI)  
concentration  
2
5-400  
5
1
1
3
3
30  
30  
30  
30  
Adsorbent dosage  
Contact time  
pH  
50  
2-20  
50  
5
5
1-5  
1
3
50  
1-6  
Initial Cr (VI)  
concentration  
6
00-1000  
optimum  
optimum  
optimum  
optimum  
optimum  
optimum  
30  
Temperature  
1000  
30-70  
3
.2 Effect of pH on Cr adsorption  
The pH of a solution is regarded as a significant parameter  
BW SD SCB PA  
PPP RS  
in the adsorption of Cr ions. The effect of pH on the efficiency  
of the different adsorbents compared to the activated carbon  
were investigated at the following conditions initial  
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
o
concentration = 50 mg/L, dosage = 5 g/L, 30 C and contact time  
1
hr. The results revealed that Cr ions adsorption by the  
materials were highly pH-dependent as shown in Figure (2).  
Each material has its own behavior at different pH values, most  
of the examined material show high removal at low pH 2 to 3.  
BW as well as AC achieved its optimum efficiency at pH 3. It  
was evident that the most prevalent form of Cr (VI) in aqueous  
-
solution  
was  
), dichromate (Cr  
dominant form of Cr (VI) at initial pH of 2 is acid chromate  
acid  
chromate  
(HCrO  
4
),  
chromate  
-2  
-2  
7
O ) and other oxyanions of Cr. The  
(
CrO  
4
2
without NaOH & HCl  
HCl only  
-1 -1  
4 4  
HCrO ). Increase in pH facilitates the conversion of HCrO  
-2 -2  
to other forms, CrO  
(
Figure 1: Effect of adsorbent preparation methods  
4
2 7  
and Cr O . At lower pH, the adsorbent  
has a positive charge because of protonation, and dichromate ion  
exists as anion and the electrostatic forces developed between  
125  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
them, resulting in a high adsorption at lower pH. The removal  
efficiency of Cr (VI) reduced significantly at higher pH due to  
reach an equilibrium when put in contact with the different  
adsorbents. Fig. (4) Shows the percentage removal of Cr for  
different value of contact time ranging from 1 to 5 hours at pH  
3, Cr initial concentration = 50 mg/L, adsorbent dosage of 5 g/L  
-
-2  
the competition between OH and chromate ions (CrO  
4
), where  
the former being the dominant species reach the adsorbent  
surface more quickly than chromium species (18)(41)(42). It is  
well-known fact that the surface adsorbs anions favorably in low  
o
and 30 C temperature. Fig. (4) Indicated that increasing the  
contact time from 1 to 3 hours, increased the percentage  
removal, because of the large number of active sites available  
for adsorption and high rate of adsorption at first. After that, the  
percentage removal of Cr reaches slowly to higher values or  
remains constant as the active sites is about to be saturated.  
Hence, the equilibrium time obtained is 3 hours for the Cr  
adsorption on all adsorbents except for PPP and RS as they  
gave unsatisfying results so they we refused in further  
experiments for higher concentrations. These results agree with  
the trends of (31), (45), (46) and (47) . The optimum Chromium  
removal percentage obtained at 3 hours equilibrium time was  
for BW with 80.91% at pH = 3 and 10 g/L dosage followed by  
73.79% for SD at the same conditions.  
+
pH range due the presence of H ions, whereas the surface is  
active for the adsorption of cations at higher pH values due to  
-
the accumulation of (OH ) ions (16). The highest value obtained  
was 82.83 % for sawdust at pH=2. Similar observations for best  
removal efficiency were reported by (19) at pH= 3, (9) at pH =  
2
and (7) at pH = 3.  
3
.3 Effect of Adsorbent Dosage on Cr Adsorption  
As shown in Figure (3-a), the percentage chromium removal  
is directly proportional to adsorbent dose. The effect of  
adsorbent dosage was studied at pH=3, contact time = 1 hr, initial  
o
chromium concentration of 50 mg/L and at 30 C. Using 5 g/L  
of BW is sufficient to adsorb about 80% Cr (VI) having 50 mg/L  
initial concentration within 1.0 h. On further increasing, the  
adsorbent dose to 20 g/L the removal efficiency was observed to  
be almost constant. This may be due to some of the adsorption  
sites remaining unsaturated during the adsorption process. The  
increase in the adsorbent dosage provides more exchangeable  
sites or surface area of the adsorbent. Interference among  
binding sites owing to increased adsorbent dosage cannot be  
ruled out as this will result in low specific uptake (31).  
AC  
PA  
BW  
SD  
RS  
SCB  
PPP  
100  
80  
60  
40  
20  
0
AC  
BW  
SD  
SCB  
PA  
PPP  
RS  
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
5
10  
15  
20  
25  
Adsorbent Dosage (g/L)  
Figure 3-a: Effect of adsorbent dosage on Cr adsorption efficiency  
AC  
PA  
BW  
SD  
RS  
SCB  
PPP  
25  
0
1
2
3
4
5
6
7
20  
15  
10  
5
0
pH  
Figure 2: Effect of pH on Cr adsorption efficiency  
Similarly, 20 g/L adsorbent dose of sawdust adsorbs more  
than 60% at pH 3.0; Phragmites Australis adsorbs more than  
5% at pH 3.0. Matching trends were also reported by (6), (43)  
4
and (2) (44) (26). The increase in Cr (VI) removal with increase  
in adsorbents amount is due to the increase in surface area and  
adsorption sites available for adsorption. In contrast, the  
amount adsorbed for unit mass of adsorbents decreases as the  
dose of adsorbent increases (Fig. 3-b). At low adsorbent dose,  
all active adsorbent sites are completely exposed and occupied  
by the Cr (VI), which is excessive, saturating the surface and  
0
5
10  
15  
20  
25  
Adsorbent Dosage (g/L)  
e
Figure 3-b: Effect of adsorbent dosage on adsorption Capacity (q )  
3
.5 Effect of initial concentration on Cr adsorption  
Cr (VI) adsorption is greatly affected by the initial  
concentration of Cr (VI) in aqueous solutions. In the present  
study, the adsorption experiments were performed to study the  
effect of initial Cr (VI) concentration at the following conditions:  
e
yielding the higher q , while the decrease in unit adsorption  
with increased adsorbent dose is mainly due to the unsaturation  
of adsorption sites during the adsorption phase. The maximum  
adsorption capacity was 17.6 mg/g achieved by using BW  
compared to 21 mg/g for AC at 2 g/L dosage. Similar trend was  
reported by (4), (6) and (45).  
o
dosage amount 5 g/L, pH=3, contact time =1hr and at 30 C. Fig.  
(
5-a) shows the effect of initial concentration at low values ranged  
from 25 to 400 mg/L. The results show that with increase in Cr  
VI) concentration from 25 to 400 mg/L, the percentage removal  
decreases and adsorption capacity increases.  
(
3
.4 Effect of Contact Time on Cr Adsorption  
The effect of contact time on Cr adsorption on the different  
materials is important to define the time required for Cr (VI) to  
126  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
at 800 mg/L and finally reached 73.3% at 1000 mg/L using 25  
g/L dosage. The decrease in removal efficiency by increasing  
the initial concentration was due to the occupation of the active  
sites of adsorbent at higher concentrations.  
AC  
PA  
BW  
PPP  
SD  
RS  
SCB  
1
00  
8
6
4
2
0
0
0
0
0
AC  
PA  
BW  
PPP  
SD  
RS  
SCB  
5
4
3
2
1
0
0
0
0
0
0
0
1
2
3
4
5
6
CONTACT TIME (HRS)  
Figure 4: Effect of contact time on Cr adsorption efficiency  
0
100  
200  
300  
400  
500  
The decrease in percentage removal can be illustrated by  
the fact that all the adsorbents had a fixed number of active  
sites, which would have become saturated above a certain  
concentration. The increase in adsorption capacity with  
increase in Cr (VI) concentration as shown in Fig. (5-b) may be  
due to the higher adsorption rate and utilization of all active  
sites available for the adsorption at higher concentration.  
Banana waste achieved the optimum removal efficiency of  
about 84% at Chromium initial concentration of 25 mg/L  
followed by sawdust with removal efficiency of about 76%  
then by Phragmites Australis and sugarcane bagasse with  
removal efficiency of 48%. These results match the trend of (6),  
Cr(VI) Initial Concentration (mg/L)  
Figure 5-b: Effect of Cr initial concentration on adsorption Capacity  
These results agree with (19) results on Grafted Banana  
Peels(GBP) which study the Cr (VI) for concentration from 100  
to 600 mg/L. However, the adsorption capacity increased by  
increasing the initial concentration and decreasing the dosage  
because at higher concentrations the rate of adsorption  
increased and increasing the dosage from 10 gm/L to 20 gm/L  
reduces the capacity from about 70 to 40 mg/g. As the dosage  
decreased, it absorbs most of the Cr (VI) found but increasing  
the amount of adsorbents about some level can leads to  
overlapping of adsorbent particles, which make it unsaturated.  
The optimum removal efficiency at initial concentration of 600  
mg/L was 77.8% for (BW) at pH=3, 25 gm/L dosage. The  
adsorption capacity of 86.3 mg/g for SD using 10 gm/l dosage  
at 1000 mg/L Cr concentration is the maximum value found  
followed by 74.78 mg/g for BW of 10 gm/L dosage at 1000  
mg/L concentration. The maximum adsorption capacity  
reported by (6) at 400 mg/L initial Cr (VI) concentration was  
(
2), (34), (4), (48) and (45). At the highest concentration of 200  
mg/L, BW registered the optimum removal efficiency of  
0.2%.  
6
AC  
PA  
BW  
PPP  
SD  
RS  
SCB  
1
00  
8
6
4
2
0
0
0
0
0
4
1.45 mg/g. The high adsorption capacity for BW and SD at  
higher concentration is due to the active functional groups on  
their surface and high fixed carbon content. Carboxylic (–  
-1  
COOH) at about (3400-3650) cm , carbonyl at about (1670-  
-1  
780) cm and hydroxyl (–OH) groups at about (1429-1639)  
-1  
1
cm are the most common found groups on agricultural waste  
surface which are responsible for binding Cr(VI) from aqueous  
solution as shown in Fig. (7) and (8) for BW and SD from  
literature respectively (13). BW contains about 65 % of fixed  
carbon which enhance its Cr(VI) adsorption capacity(49).  
Scanning electron microscopy (SEM) is also a measure for  
surface morphology of an adsorbent which can be an indication  
for the surface area and pores size of it. The surface of  
adsorbent before adsorption showed irregular heterogeneous  
structure which became flattened after adsorption as a result of  
metal ion adsorption. Fig (9) and (10) shows the SEM for BW  
and raw sawdust (R-SD) and modified sawdust (MSD) from  
literature.  
0
100  
200  
300  
400  
500  
CR(VI) INITIAL CONCENTRATION (MG/L)  
Figure 5-a: Effect of Cr initial concentration on adsorption efficiency  
3
.6 Effect of high initial concentration on Cr adsorption  
The four absorbents achieved higher removal efficiency at  
00 mg/L initial concentration (Banana waste (BW), Sawdust  
4
(
SD), Phragmites Australis (PA) and sugarcane bagasse (SCB))  
will be investigated at higher concentration of 600,800 and  
000 mg/L. Figures (6-a), (6-b), (6-c) and (6-d) show the  
1
removal efficiencies of the examined adsorbent at high  
concentrations and their capacities in mg/g. The adsorbents  
were examined at different three dosages (10-20-25) gm/L. The  
optimum pH for BW was 3, while it was 2 for the rest and the  
contact time was 3 hours for all experiments. Fig. (6-a) shows  
the performance of BW at high concentrations, the dosages  
changed from 10 to 20 and then 25 gm/L. The optimum  
removal at 600 mg/L was 77.8% which was decreased to 75.2%  
3
.7 Effect of Temperature on Cr Adsorption  
The effect of temperature on Chromium adsorption was  
tested on the four adsorbent achieved high efficiency. The pH,  
dosage and contact time for BW, SD, SCB and PA were 3,2,2,2  
and 25,10,10,10 gm/l and 3,5,5,3 hours respectively. The initial  
concentration was maintained constant at 1000 ppm. As shown  
in Fig. (7), it is observed that the percentage removal of  
127  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
Chromium increases by increasing the temperature from 30 to  
o
%R at 10 gm/l  
R at 25 gm/l  
qe at 20 gm/l  
%R at 20 gm/l  
qe at 10 gm/l  
qe at 25 gm/l  
7
0 C for all materials. This increase is due to the increase of the  
rate of adsorption at higher temperature which indicates that the  
adsorption process is endothermic(50). The optimum removal  
%
o
was for sawdust at 70 C by 82% followed 80.7% for banana  
o
waste at 60 C. Similar results were reported by (20), (6) and  
4
3
2
1
0
0
0
0
0
40  
30  
20  
10  
0
(
27).  
%
%
R at 10 gm/l  
R at 25 gm/l  
%R at 20 gm/l  
qe at 10 gm/l  
qe at 25gm/l  
qe at 20 gm/l  
6
00  
800  
1000  
80  
60  
40  
20  
0
80  
60  
40  
20  
0
Initial Concentration (mg/L)  
Figure 6-d: Performance of SCB at high Cr concentrations  
600  
800  
1000  
Initial Concentration (mg/L)  
Figure 6-a: performance of BW at high Cr concentrations  
%
R at 10 gm/l  
R at 25 gm/l  
qe at 20 gm/l  
%R at 20 gm/l  
qe at 10 gm/l  
qe at 25 gm/l  
%
1
5
0
00  
0
5
0
0
6
00  
800  
1000  
Initial Concentration (mg/L)  
Figure 6-b: Performance of SD at high Cr concentrations  
%
R at 10 gm/l  
R at 25 gm/l  
qe at 20 gm/l  
%R at 20 gm/l  
qe at 10 gm/l  
qe at 25 gm/l  
%
6
5
4
3
2
1
0
0
0
0
0
0
0
60  
50  
40  
30  
20  
10  
0
Figure 7: FTIR spectrum of banana peel dust [before and after Cr(VI)  
adsorption] (18)  
3
.8 Adsorption Kinetics  
In order to understand the kinetic behavior of the  
adsorption process for Cr (VI) removal using the four tested  
materials at high concentration (BW, SD, PA and SCB)  
compared with that of AC, the Pseudo-first- order and Pseudo-  
second- order models are considered to fit the kinetic  
experimental data. The different parameters of the two models  
are calculated and tabulated in Table (2).  
6
00  
800  
1000  
Initial Concentration (mg/L)  
Figure 6-c: Performance of PA at high Cr concentrations  
128  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
Figure 9: SEM for banana peel (a-before adsorption and b-after  
adsorption) (18)  
3
.8.2 Pseudo-second-order Kinetic Model  
The kinetic experimental data are also fitted with the  
Pseudo-second- order kinetic model. The second order kinetic  
parameters, K and q are calculated for different adsorbents  
using the slope and intercept of the graph of the linear form  
between t/q versus time as shown in Fig. (9). The obtained  
2
e
values of K and q and (R ) for Cr (VI) adsorption using  
different adsorbents are given in Table (2). The predicted  
equilibrium adsorption capacities are close to that obtained  
2
from the experimental data. The value of K are found to be less  
2
e
Figure 8: FTIR spectrum of sawdust [before and after Cr(VI)  
adsorption] (22)  
t
2
3
.8.1 Pseudo-first-order Kinetic Model  
The applicability of the Pseudo-first- order kinetic model  
to the experimental data are tested by plotting the linear form  
e t  
as a graph of log (q -q ) versus time Fig (8). The estimated  
values of the Pseudo-first- order kinetic parameters, K and q  
than 1 which suggests the higher rate of adsorption at initial  
stage and further decrease with the lapse of time. High values  
e
2
along with the regression coefficient (R ) are in Table (2). The  
2
of R (0.9977, 0.9986, 0.9924, 0.9837 and 0.9352) obtained for  
2
values of (R ) are estimated as 0.9712, 0.9975, 0.7865, 0.9911  
the removal of Cr (VI) using AC, BW, SD, PA and SCB  
respectively, show the agreement between the experimental  
data and the second order kinetic model.  
and 0.6318 for the removal of Cr (VI) using AC, BW, SD, PA  
and SCB respectively. These values indicate the non-agreement  
of the Pseudo-first- order kinetic model to the experimental  
data. The experimental value of the adsorption capacities at  
equilibrium are 9.05, 9.02, 8.41, 5.04 and 6.52 mg/g  
respectively. The predicted values of adsorption capacities  
using the Pseudo-first- order kinetic model are 8.26, 0.51, 6.76,  
The predicted values of adsorption capacities using the  
Pseudo-second- order kinetic model are 8.47, 8.79, 10.05, 5.21  
and 7.97 mg/g respectively, which matches the experimental  
values of adsorption capacities for the mentioned adsorbents.  
This confirms the applicability of the Pseudo-second- order  
kinetic model to fit the experimental data and confirms the  
chemisorption of Cr (VI) on the adsorbents during the  
adsorption process. In chemisorption (chemical adsorption),  
the Chromium sticks to the adsorbent surface by forming a  
chemical bond (usually covalent) and tend to find sites that  
maximize their coordination number with the surface (44).  
These results agree with most of the previous studies on  
adsorbents like, (6), (20), (18), (19), (31), (9) and (22).  
2
.24 and 3.83 mg/g respectively. This disagreement between  
the experimental and predicted adsorption capacities confirms  
that the Pseudo-first-order kinetic model cannot explain the  
behavior of Cr (VI) adsorption on the different types of used  
adsorbents.  
129  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
Figure 10: SEM images of (a) R-SD at 1000 magnification, (b) R-SD at 5000 magnification (c) MSD at 1000 magnification, and (d) MSD at 5000  
magnification (9)  
BW  
SD  
SCB  
PA  
3.9 Adsorption Isotherm Study  
An adsorption isotherm is characterized by certain  
8
8
7
7
6
6
5
5
5
0
5
0
5
0
5
0
constants that express the surface properties and the affinity of  
the adsorbent towards Cr (VI) adsorption (51). The equilibrium  
data for the adsorption of Cr (VI) using these adsorbents fits  
into various isotherm models which results in a suitable model  
that can be used for the design of an adsorption process. The  
most used isotherm models in adsorption process are  
Langmuir, Freundlich and Tempkin isotherm models.  
Therefore, in the present work, Langmuir, Freundlich and  
Tempkin isotherm models for different adsorbents are  
considered and are discussed in the following sections. The  
various isotherm parameters are estimated and tabulated in  
Table (3), (4) and (5) respectively.  
2
5
35  
45  
55  
65  
75  
TEMPERATURE OC  
Figure 7: Effect of temperature on Cr adsorption efficiency  
Table 2: the kinetic constants for Cr removal using different adsorbents  
Equation  
Material  
Parameter  
Activated Carbon (AC)  
Banana waste (BW)  
Sawdust (SD)  
Phragmites Australis (PA)  
Sugarcane Bagasse (SCB)  
Pseudo-first-order  
Pseudo-second-order  
Qe (exp.)  
mg/g)  
(
-
1
R2  
R2  
K (hr )  
2.76  
q
e
(cal.) (mg/g)  
K
1.24  
6.12  
0.104  
0.435  
0.091  
2
(g/mg .hr)  
e
q (cal.) (mg/g)  
0.9712  
0.9975  
0.7866  
0.9911  
0.6318  
8.26  
0.51  
6.76  
2.24  
3.83  
0.9977  
0.9987  
0.9924  
0.9837  
0.9352  
8.473  
8.798  
10.05  
5.21  
9.05  
9.02  
8.41  
5.04  
6.52  
0.481  
0.787  
0.404  
0.405  
7.972  
130  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
AC  
BW  
SD  
PA  
2
SCB  
AC  
BW  
SD  
PA  
SCB  
1
y = -0.1757x + 0.3508  
y = -0.1759x + 0.5829  
R² = 0.6318  
R² = 0.9911  
0
0
1
3
4
5
6
-
-
-
-
-
-
1
2
3
4
5
6
y = -0.3421x + 0.8299  
R² = 0.7865  
y = -0.2087x - 0.2948  
R² = 0.9975  
y = -1.2018x + 0.9169  
R² = 0.9712  
Time (hrs)  
Figure 8: Pseudo-first-order model for different adsorbents  
AC  
BW  
SD  
PA  
SCB  
AC  
BW  
SD  
PA  
SCB  
1.2  
1.0  
0.8  
0.6  
0.4  
0.2  
0.0  
y = 0.1919x + 0.0846  
R² = 0.9837  
y = 0.1254x + 0.1714  
R² = 0.9352  
y = 0.0995x + 0.0949  
R² = 0.9924  
y = 0.118x - 0.0112  
R² = 0.9977  
y = 0.1138x - 0.0021  
R² = 0.9987  
0
1
2
3
4
5
6
Time (hrs)  
Figure 9: Pseudo-second-order model for different adsorbents  
3
.9.1 Langmuir Isotherm  
The isotherm data has been linearized using the Langmuir  
equation and is plotted between C versus C /q which is shown  
concentration may be due to the higher adsorption rate and the  
utilization of all the active sites available for the adsorption at  
higher concentration. The Langmuir constant, b, which denotes  
adsorption energy, is found to be 0.0424, 0.0301, 0.0327,  
0.0076 and 0.0102 L/mg at low concentrations for AC, BW,  
SD, PA and SCB respectively. Langmuir constant b for low  
concentration was found 0.0016, 0.0122, 0.0415 and 0.0015 for  
the last four materials respectively. The value of coefficient of  
e
e
e
in Fig. (10)(a),(b) for low concentrations (25-50-100-200) and  
for high concentrations (400-600-800-1000) respectively. The  
Langmuir parameters Q  
adsorbents and are given in Table (3). The Langmuir constant  
, which is a measure of the monolayer adsorption capacity  
of the adsorbents, is obtained as 26.20, 31.51, 13.02, 19.72 and  
3.49 mg/g for AC, BW, SD, PA and SCB respectively in the  
m L  
, b and R are estimated for different  
Q
m
2
correlation (R = 0.986, 0.8614, 0.9531, 0.7611 and 0.7747)  
1
obtained for AC, BW, SD, PA and SCB at low concentrations  
do not support the monolayer adsorption of Cr (VI) onto the  
different adsorbents except for sawdust which was 0.9531. On  
equilibrium pH value of 3 for all adsorbents at low  
concentrations. At the optimum conditions for the best four  
materials at high concentration, the increase in Cr (VI) initial  
concentration to (400-600-800-1000) mg/L increases the  
2
the other hand, it is found that the value of R is very close to  
unit at higher concentrations for BW,SD and SCB which  
confirms the monolayer adsorption of Cr(VI) at these  
adsorbents.  
m
monolayer adsorption capacity Q to 105.84, 29.86, 19.30 and  
3.83 mg/g for AC, BW, SD, PA and SCB respectively. The  
increase in adsorption capacity with an increase in the Cr (VI)  
7
131  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
(
a)  
AC  
BW  
SD  
PA  
SCB  
AC  
BW  
SD  
PA  
SCB  
20  
15  
10  
5
0
y = 0.0742x + 7.2822  
R² = 0.7747  
y = 0.0507x + 6.6878  
R² = 0.7611  
y = 0.0768x + 2.3519  
y = 0.0382x + 0.8997  
R² = 0.986  
R² = 0.9531  
y = 0.0317x + 1.0553  
R² = 0.8614  
0
20  
40  
60  
80  
100  
120  
140  
160  
180  
Ce  
(
b)  
BW  
SD  
PA  
SCB  
BW  
SD  
PA  
SCB  
40  
35  
30  
25  
20  
15  
10  
5
0
y = 0.0518x + 1.2501  
R² = 1  
y = 0.0335x + 2.7499  
R² = 1  
y = 0.0135x + 9.0842  
R² = 0.9493  
y = 0.0094x + 5.7476  
R² = 0.9998  
1
00  
200  
300  
400  
500  
600  
700  
800  
Ce  
Figure 10: Langmuir isotherm (a) at low conc., (b) at high conc  
The dimensionless parameter, R  
adsorption favorability is found to be in a range of 0.1 to 0.62  
0 < R < 1) which confirms the favorable adsorption process  
for Cr (VI) removal using different adsorbents. Though the R  
value obtained is very high for some adsorbents, in order to find  
out if a better fit is possible with other isotherms, the results are  
analyzed with other two isotherms available in the literature.  
L
, which is a measure of  
are 0.49, 0.54, 0.34, 0.63 and 0.52 for AC, BW, SD, PA and  
SCB at low concentrations respectively and 0.73, 0.15, 0.05  
and 0.60 for the last four adsorbents at high concentrations  
(
L
2
F
respectively. The obtained values of n are less than 1 for both  
low and high concentrations which supports the chemisorption  
phenomena during Cr (VI) adsorption on all adsorbents at  
different conditions (52). It is found that the coefficient of  
correlation obtained from the Freundlich isotherm model for  
adsorbents ranges from 0.9405 to 0.9988, which is higher than  
that for Langmuir isotherm model as given in Table (4). These  
results support the possibility of heterogeneous adsorption on  
multi-layers. The obtained result indicates that the equilibrium  
data is fitted well with the Freundlich isotherm model at low  
concentrations for all adsorbents except for SD. Similar  
observations were recorded by (21) when they study the  
adsorption of Cr (VI) on Banana Trunk Fibers (BTF) and  
reinforced Chitosan Bio composite (CTB).  
3
.9.2 Freundlich Isotherm  
The Freundlich constants, K  
f
(mg/g) and n are obtained by  
versus log C as shown in Fig.  
11) (a), (b) for low concentrations (25-50-100-200) mg/L and  
for high concentrations (400-600-800-1000) mg/L  
respectively. The values of K are 1.46, 1.38, 1.34, 0.70 and  
.78 for AC, BW, SD, PA and SCB at low concentrations  
respectively and 0.77, 2.72, 3.12 and 0.88 for the last four  
adsorbents at high concentrations respectively. The values of n  
plotting the graph between log q  
e
e
(
f
0
f
132  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
Table 3: Langmuir parameters for Cr removal using different adsorbents  
Langmuir Constants for low concentrations  
o
At 303 K  
R
L
R2  
Maximum monolayer  
Langmuir  
constant L/mg (b)  
qe (exp.)  
mg/g  
Adsorbent  
favorable if  
< R < 1  
Best error  
distribution  
coverage mg/g (Q  
m
)
0
L
Activated carbon (AC)  
26.20  
0.0424  
0.26  
0.986  
21.46  
Banana waste (BW)  
Sawdust (SD)  
31.51  
13.02  
0.0301  
0.0327  
0.33  
0.31  
0.8614  
0.9531  
24.38  
11.13  
Phragmites Australis  
1
9.72  
0.0076  
0.0102  
0.62  
0.56  
0.7611  
0.7747  
11.07  
8.88  
(PA)  
Sugarcane bagasse (SCB)  
13.49  
o
At 303 K  
Langmuir Constants for high concentrations  
R
L
R2  
Maximum monolayer  
Langmuir  
constant L/mg (b)  
Adsorbent  
favorable if  
< R < 1  
Best error  
distribution  
qe (exp.)  
coverage mg/g (Q  
m
)
0
L
Banana waste (BW)  
Sawdust (SD)  
105.84  
29.86  
0.0016  
0.0122  
0.43  
0.1  
0.9998  
1
39.02  
26.58  
Phragmites Australis  
1
9.30  
0.0415  
0.0015  
0.03  
0.48  
1
18.59  
37.34  
(PA)  
Sugarcane bagasse (SCB)  
73.83  
0.9493  
Table 4: Freundlich parameters for Chromium using different adsorbents  
Freundlich Constants for low concentrations  
At 303 oK  
Adsorbent  
Relative adsorption capacity of  
adsorbent related to the bonding  
energy (KF)  
Heterogeneity factor representing the  
deviation from linearity of adsorption  
(nF)  
R2  
Best error  
distribution  
Activated carbon  
Banana waste  
Sawdust  
1.46  
1.38  
1.34  
0.70  
0.78  
0.49  
0.54  
0.34  
0.63  
0.52  
0.9905  
0.9755  
0.9405  
0.9693  
0.9200  
Phragmites Australis  
Sugarcane bagasse  
At 303 oK  
Freundlich Constants for high concentrations  
Relative adsorption capacity of  
adsorbent related to the bonding  
energy (KF)  
Heterogeneity factor representing the  
deviation from linearity of adsorption  
(nF)  
R2  
Best error  
distribution  
Adsorbent  
Banana waste  
0.77  
2.72  
3.12  
0.88  
0.73  
0.15  
0.05  
0.60  
0.9988  
0.9891  
0.9950  
0.9642  
Sawdust  
Phragmites Australis  
Sugarcane bagasse  
133  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
(
a)  
AC  
BW  
SD  
PA  
SCB  
AC  
BW  
SD  
PA  
SCB  
1.6  
1.4  
1.2  
1.0  
0.8  
0.6  
0.4  
0.2  
0.0  
y = 0.4905x + 0.3798  
R² = 0.9905  
y = 0.3354x + 0.2936  
R² = 0.9405  
y = 0.5434x + 0.32  
R² = 0.9755  
y = 0.5192x - 0.2427  
R² = 0.92  
y = 0.6303x - 0.3603  
R² = 0.9693  
0
.5  
0.7  
0.9  
1.1  
1.3  
1.5  
1.7  
1.9  
2.1  
2.3  
log Ce  
(
b)  
BW  
SD  
PA  
SCB  
BW  
SD  
PA  
SCB  
1.7  
1.6  
1.6  
1.5  
1.5  
1.4  
1.4  
1.3  
1.3  
1.2  
y = 0.6008x - 0.1284  
R² = 0.9642  
y = 0.7292x - 0.2652  
R² = 0.9988  
y = 0.1501x + 1.0018  
R² = 0.9891  
y = 0.0471x + 1.1374  
R² = 0.995  
2
.1  
2.2  
2.3  
2.4  
2.5  
2.6  
2.7  
2.8  
2.9  
log Ce  
Figure 11: Freundlich isotherm (a) low conc., (b) high conc  
3
.9.3 Tempkin Isotherm  
e
A plot of q versus ln C at a constant temperature shown  
in Fig (12) (a), (b) is used to calculate the Tempkin isotherm  
constants, A and b which are tabulated in Table (5) for low  
ranges from 0.8442 to 0.9982, which is lower than Langmuir  
and Freundlich for all adsorbents except for SCB at higher  
concentrations which was 0.9747 more than the R calculated  
e
2
T
T
for the other two isotherm models. The summary of the  
2
and high concentrations respectively. Tempkin isotherm model  
takes the adsorbent adsorbate interactions in consideration(53).  
The constant A  
calculated values of regression coefficient (R ) and isotherms  
parameters for the adsorption of Cr (VI) on AC, BW, SD, PA  
and SCB at both low and high concentrations are tabulated in  
Table (6). From Table (6), it is clear that AC, BW, PA and SCB  
follow the multi-layer adsorption theory of Freundlich isotherm  
T
obtained from Tempkin isotherm model are  
.51, 0.40, 0.65, 0.11 and 0.14 L/g for AC, BW, SD, PA and  
0
SCB at low concentrations respectively and 0.018, 1.69, 0.005  
and 0.012 L/g for the last four materials at high concentrations  
2
that gave the highest R at low concentrations. While SD at low  
respectively. The constant b  
T
obtained for Tempkin isotherm  
concentration besides BW,SD and PA at high concentrations  
follow the monolayer adsorption of Langmuir isotherm that  
gave a R value near or equal to the unit. Finally SCB at higher  
model are 478.69, 409.69, 1116.56, 722.30 and 1002.22 for  
AC, BW, SD, PA and SCB at low concentrations respectively  
and 121.79, 664.25, 120.80 and 140.03 for the last four  
materials at high concentrations respectively. The obtained  
2
concentration is the only adsorbent which fits to Tempkin  
2
isotherm with R value of 0.9747.  
2
coefficient of determination (R ) for Tempkin isotherm model  
134  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
Table 5: Tempkin parameters for Cr removal using different adsorbents  
Tempkin Constants for low concentrations  
(A ) (L/g) (b (B = RT/b  
o
At 303 K  
2
Adsorbent  
T
T
)
T
T
)
R best error distribution  
Activated carbon  
Banana waste  
Sawdust  
0.51  
0.40  
0.65  
0.11  
0.14  
478.69  
409.69  
1116.56  
722.30  
1002.22  
5.26  
6.15  
2.26  
3.49  
2.51  
0.9799  
0.8933  
0.8858  
0.8762  
0.8442  
Phragmites Australis  
Sugarcane bagasse  
o
At 303 K  
Tempkin Constants for high concentrations  
2
Adsorbent  
(A ) (L/g) (b (B = RT/b  
T
T
)
T
T
)
R best error distribution  
Banana waste  
Sawdust  
Phragmites Australis  
Sugarcane bagasse  
0.018  
1.69  
0.005  
0.012  
121.79  
664.25  
120.80  
140.03  
20.67  
3.79  
20.84  
17.98  
0.9982  
0.9920  
0.9994  
0.9747  
(
a)  
AC  
BW  
SD  
PA  
SCB  
AC  
BW  
SD  
PA  
SCB  
30  
25  
20  
15  
10  
5
0
y = 6.1459x - 5.5942  
R² = 0.8933  
y = 5.26x - 3.5197  
R² = 0.9799  
y = 3.486x - 7.6203  
R² = 0.8762  
y = 2.2551x - 0.9883  
R² = 0.8858  
y = 2.5124x - 4.8914  
R² = 0.8442  
1
.0  
1.5  
2.0  
2.5  
3.0  
3.5  
4.0  
SD  
4.5  
5.0  
5.5  
ln Ce  
(
b)  
BW  
SD  
PA  
SCB  
BW  
PA  
SCB  
4
4
3
3
2
2
1
5
0
5
0
5
0
5
y = 17.982x - 80.025  
R² = 0.9747  
y = 20.674x - 82.725  
R² = 0.9982  
y = 3.7906x + 1.9878  
R² = 0.992  
y = 20.844x - 109.2  
R² = 0.9994  
4
.8  
5.0  
5.2  
5.4  
5.6  
5.8  
6.0  
6.2  
6.4  
6.6  
6.8  
ln Ce  
Figure 12: Tempkin isotherm (a) at low conc., (b) at high conc  
135  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
Table 6: Summary of isotherms constants for different adsorbents at low and high concentrations.  
o
At 303 K  
Langmuir Constants  
Freundlich Constants  
Tempkin Constants  
Adsorbent  
Q
m
b
R
L
R2  
K
F
n
F
R2  
A
T
b
T
B
T
R2  
Activated  
carbon  
2
6.20  
0.0424  
0.0301  
0.0327  
0.0076  
0.0102  
0.26  
0.33  
0.31  
0.62  
0.56  
0.986  
0.8614  
0.9531  
0.7611  
0.7747  
1.46  
1.38  
1.34  
0.70  
0.78  
0.49  
0.54  
0.34  
0.63  
0.52  
0.9905  
0.9755  
0.9405  
0.9693  
0.9200  
0.51  
0.40  
0.65  
0.11  
0.14  
478.69  
409.69  
1116.56  
722.30  
1002.22  
5.26  
6.15  
2.26  
3.49  
2.51  
0.9799  
0.8933  
0.8858  
0.8762  
0.8442  
Banana waste  
Sawdust  
31.51  
13.02  
Phragmites  
Australis  
1
1
9.72  
3.49  
Sugarcane  
bagasse  
o
At 303 K  
Langmuir Constants  
Freundlich Constants  
Tempkin Constants  
Adsorbent  
Banana waste  
Sawdust  
Q
m
b
R
L
R2  
K
F
n
F
R2  
A
T
b
T
B
T
R2  
105.84  
29.86  
0.0016  
0.0122  
0.0415  
0.0015  
0.43  
0.1  
0.9998  
0.77  
2.72  
3.12  
0.88  
0.73  
0.15  
0.05  
0.60  
0.9988  
0.9891  
0.9950  
0.9642  
0.018  
1.69  
121.79  
664.25  
120.80  
140.03  
20.67  
3.79  
0.9982  
0.9920  
0.9994  
0.9747  
1
Phragmites  
Australis  
1
7
9.30  
3.83  
0.03  
0.48  
1
0.005  
0.012  
20.84  
17.98  
Sugarcane  
bagasse  
0.9493  
4
Conclusions  
Ethical issue  
Authors are aware of, and comply with, best practice in  
publication ethics specifically with regard to authorship  
(avoidance of guest authorship), dual submission, manipulation  
of figures, competing interests and compliance with policies on  
research ethics. Authors adhere to publication requirements  
that submitted work is original and has not been published  
elsewhere in any language.  
The study reveals that BW and SD are the best adsorbents  
for the removal of Cr (VI) from industrial wastewater for both  
low and high concentrations. At higher concentration of 1000  
mg/L, (BW) gives the best removal efficiency of about 73%  
using 25 gm/L dosage, pH= 3 and 3 hours contact time. The  
maximum adsorption capacity of 86 mg/g at 1000 mg/L was  
obtained for (SD) at its optimum conditions. Preparation and  
treatment method has a vital effect on the adsorption  
characteristics for each adsorbent. BW treated with HCl only  
shows the best results while other adsorbents give highest  
removal efficiencies when treated with acid-alkali treatment.  
The Chromium adsorption capacity of all the investigated  
materials is highly dependent on pH and achieves high  
efficiency at low pH 2-3. The Chromium adsorption capacity  
is highly dependent on dosage, initial concentration, contact  
time and temperature. In the present study, all adsorbents  
follow Pseudo-second-order kinetic model with high regression  
coefficient. The equilibrium isotherm data for AC, BW, PA and  
SCB at low concentrations were best fitted to Freundlich  
isotherm while SD at low concentrations and BW, SD and PA  
at higher concentrations were following Langmuir isotherm.  
SCB at high concentrations is the only adsorbent fitted to  
Tempkin isotherm.  
Competing interests  
The authors declare that there is no conflict of interest that  
would prejudice the impartiality of this scientific work.  
Authors’ contribution  
All authors of this study have a complete contribution for  
data collection, data analyses and manuscript writing.  
References  
1
2
.
.
.
Meroufel B, Zenasni MA, George B. Valorisation and modification of  
saharan clay for removal of Cu(II), Ni(II), Co(II) and Cd(II) from  
aqueous solutions. Polish J Environ Stud. 2020;29(2):1287–92.  
Kamal El Dean AM, Hashem EY, Ahmed MM, Mohamed MA,  
Hussain SM. Removal of chromium(VI) from wastewater using citric  
acid modified sugarcane bagasse. Eur Chem Bull. 2019;8(5):141–9.  
Zhou J, Chen H, Thring RW, Arocena JM. Chemical Pretreatment of  
Rice Straw Biochar: Effect on Biochar Properties and Hexavalent  
3
136  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
Chromium Adsorption. Int J Environ Res [Internet]. 2019;13(1):91–  
24. Gupta VK, Mohan D, Sharma S, Park KUKT. Removal of chromium (  
VI ) from electroplating industry wastewater using bagasse fly ash —  
a sugar industry waste material. 1999;  
25. SINGH SK. REMOVAL OF HEXAVALENT CHROMIUM Cr (VI)  
BY USING SUGARCANE BAGASSE AS AN LOW COST  
ADSORBENT. Indian J Sci Res. 2017;13(1):73–6.  
26. Kumari P. Application of Sugarcane Bagasse for the Removal of  
Chromium ( Vi ) and Zinc ( Ii ) From Aqueous Solution. Int Res J Eng  
Technol. 2017;04:1670–3.  
27. Sivakumar D, Shankar D, Mahalakshmi R, Deepalakshmi K. Kinetic  
Model Studies on Removal of Hexavalent Chromium-Sugarcane  
Bagasse Powder. Int Res J Multidiscip Sci Technol. 2017;2(5):37–43.  
28. Bashir S, Hussain Q, Akmal M, Riaz M, Hu H, Ijaz SS, et al. Sugarcane  
bagasse-derived biochar reduces the cadmium and chromium  
bioavailability to mash bean and enhances the microbial activity in  
contaminated soil. J Soils Sediments. 2018;18(3):874–86.  
1
05. Available from: https://doi.org/10.1007/s41742-018-0156-1  
4
5
6
7
.
.
.
.
Shakya A. Green Pea Pod Biochar as a Low-Cost Adsorbent: An  
Alternative Approach for the Removal of Cr (VI) from Aqueous  
Solution. Int J Pure Appl Biosci. 2018;6(4):375–86.  
Gunatilake SK. Removal of Cr ( III ) Ions from Wastewater using  
Sawdust and Rice Husk Biochar Pyrolyzed at Low Temperature.  
2
017;(May).  
Gupta S, Babu B V. Removal of toxic metal Cr(VI) from aqueous  
solutions using sawdust as adsorbent: Equilibrium, kinetics and  
regeneration studies. Chem Eng J. 2009;150(2–3):352–65.  
Ullah R, Ahmad W, Ahmad I, Khan M, Iqbal Khattak M, Hussain F.  
Adsorption and recovery of hexavalent chromium from tannery  
wastewater over magnetic max phase composite. Sep Sci Technol  
[Internet].  
2020;00(00):1–14.  
Available  
from:  
https://doi.org/10.1080/01496395.2020.1717531  
8
9
.
.
Ihsanullah, Abbas A, Al-Amer AM, Laoui T, Al-Marri MJ, Nasser MS,  
et al. Heavy metal removal from aqueous solution by advanced carbon  
nanotubes: Critical review of adsorption applications. Sep Purif  
Technol. 2016;157:141–61.  
Chakraborty R, Verma R, Asthana A, Vidya SS, Singh AK. Adsorption  
of hazardous chromium (VI) ions from aqueous solutions using  
modified sawdust: kinetics, isotherm and thermodynamic modelling.  
Int J Environ Anal Chem [Internet]. 2019;00(00):1–18. Available from:  
https://doi.org/10.1080/03067319.2019.1673743  
29. Karri RR, Sahu JN, Meikap BC. Improving efficacy of Cr (VI)  
adsorption process on sustainable adsorbent derived from waste  
biomass (sugarcane bagasse) with help of ant colony optimization. Ind  
Crops Prod [Internet]. 2020;143(June 2019):111927. Available from:  
https://doi.org/10.1016/j.indcrop.2019.111927  
30. Bahadur KD, Paramatma M. Adsorptive removal of Cr( VI ) from  
aqueous solution by sugarcane biomass. Res  
J Chem Sci.  
2014;4(5):32–40.  
31. Shahawy A El. RSC Advances dissolved solids by environmentally  
friendly and economical dried Phragmites australis †. 2018;40511–28.  
32. García-Valero A, Martínez-Martínez S, Faz Á, Terrero MA, Muñoz  
MÁ, Gómez-López MD, et al. Treatment of wastewater from the  
tannery industry in a constructed wetland planted with phragmites  
australis. Agronomy. 2020;10(2):1–15.  
1
1
0. Suseno Ahmad, Wijaya K, Trisunayati.W S. Ournal of. Asian J Chem.  
016;28(2):347–50.  
1. Minas F, Chandravanshi BS, Leta S. Chemical precipitation method for  
chromium removal and its recovery from tannery wastewater in  
Ethiopia. Chem Int. 2017;3(May):291–305.  
2
1
2. Bedemo A, Chandravanshi BS, Zewge F. Removal of trivalent  
chromium from aqueous solution using aluminum oxide hydroxide.  
Springerplus. 2016;5(1).  
3. Pathak PD, Mandavgane SA, Kulkarni BD. Fruit peel waste as a novel  
low-cost bio adsorbent. Rev Chem Eng. 2015;31(4):361–81.  
4. Yogeshwaran V, Priya AK. Removal of Hexavalent Chromium (Cr6 )  
Using Different Natural Adsorbents – A Review. Ssrn. 2017;8(6):6–  
33. Mousa WM, Soliman SI, Shier HA. Removal of some Heavy Metals  
from Aqueous Solution Using Rice Straw. 2013;9(3):1696–701.  
34. Brahmaiah T, Spurthi L, Chandrika K, Ramanaiah S, Prasad KSS.  
KINETICS OF HEAVY METAL ( Cr & Ni ) REMOVAL FROM THE  
WASTEWATER BY USEING LOW COST ADSORBENT.  
2015;4(11):1600–10.  
1
1
35. Hegazi HA. Removal of heavy metals from wastewater using  
agricultural and industrial wastes as adsorbents. HBRC J [Internet].  
1
1.  
1
1
5. Devi B, Jahagirdar A, Ahmed M. Adsorption of Chromium on  
Activated Carbon Prepared from Coconut Shell. Adsorption [Internet].  
2013;9(3):276–82.  
http://dx.doi.org/10.1016/j.hbrcj.2013.08.004  
Available  
from:  
2
012;2(5):364–70.  
Available  
from:  
36. Elmolla ES, Hamdy W, Kassem A, Abdel Hady A. Comparison of  
different rice straw based adsorbents for chromium removal from  
aqueous solutions. Desalin Water Treat. 2016;57(15):6991–9.  
37. Ioannidou O, Zabaniotou A. Agricultural residues as precursors for  
activated carbon production-A review. Renew Sustain Energy Rev.  
2007;11(9):1966–2005.  
http://www.academia.edu/download/30843873/BJ25364370.pdf  
6. Sharma PK, Ayub S, Tripathi CN. Isotherms describing physical  
adsorption of Cr(VI) from aqueous solution using various agricultural  
wastes as adsorbents. Cogent Eng [Internet]. 2016;3(1). Available  
from: http://dx.doi.org/10.1080/23311916.2016.1186857  
1
1
7. Prastuti OP, Septiani EL, Kurniati Y, Widiyastuti, Setyawan H. Banana  
peel activated carbon in removal of dyes and metals ion in textile  
industrial waste. Mater Sci Forum. 2019;966 MSF:204–9.  
8. Mondal NK, Samanta A, Chakraborty S, Shaikh WA. Enhanced  
chromium(VI) removal using banana peel dust: isotherms, kinetics and  
thermodynamics study. Sustain Water Resour Manag. 2018;4(3):489–  
38. Valentín-Reyes J, García-Reyes RB, García-González A, Soto-  
Regalado E, Cerino-Córdova F. Adsorption mechanisms of hexavalent  
chromium from aqueous solutions on modified activated carbons. J  
Environ Manage. 2019 Apr 15;236:815–22.  
39. Giraldo-Gutiérrez L, Moreno-Piraján JC. Pb(II) and Cr(VI) adsorption  
from aqueous solution on activated carbons obtained from sugar cane  
husk and sawdust. J Anal Appl Pyrolysis. 2008;81(2):278–84.  
40. Mohan D, Pittman CU. Activated carbons and low cost adsorbents for  
remediation of tri- and hexavalent chromium from water. J Hazard  
Mater. 2006;137(2):762–811.  
41. Kumar A, Jena HM. Adsorption of Cr(VI) from aqueous phase by high  
surface area activated carbon prepared by chemical activation with  
ZnCl2. Process Saf Environ Prot [Internet]. 2017;109(Vi):63–71.  
Available from: http://dx.doi.org/10.1016/j.psep.2017.03.032  
42. AL-Othman ZA, Ali R, Naushad M. Hexavalent chromium removal  
from aqueous medium by activated carbon prepared from peanut shell:  
Adsorption kinetics, equilibrium and thermodynamic studies. Chem  
9
7.  
1
2
2
9. Ali A, Saeed K, Mabood F. Removal of chromium (VI) from aqueous  
medium using chemically modified banana peels as efficient low-cost  
adsorbent. Alexandria Eng J [Internet]. 2016;55(3):2933–42. Available  
from: http://dx.doi.org/10.1016/j.aej.2016.05.011  
0. Sharma PK, Ayub S, Tripathi CN. Isotherms describing physical  
adsorption of Cr(VI) from aqueous solution using various agricultural  
wastes as adsorbents. Cogent Eng [Internet]. 2016;3(1):1–20.  
Available from: http://dx.doi.org/10.1080/23311916.2016.1186857  
1. Rahim M, Mas Haris MRH. Chromium (VI) removal from neutral  
aqueous media using banana trunk fibers (BTF)-reinforced chitosan-  
based film, in comparison with BTF, chitosan, chitin and activated  
carbon. SN Appl Sci [Internet]. 2019;1(10):1–11. Available from:  
https://doi.org/10.1007/s42452-019-1206-9  
Eng  
J
[Internet].  
2012;184:238–47.  
Available  
from:  
http://dx.doi.org/10.1016/j.cej.2012.01.048  
43. Brahmaiah T, Spurthi L, Chandrika K, Ramanaiah S, Sai Prasad KS.  
Kinetics of heavy metal (Cr & Ni) removal from the wastewater by  
using low cost adsorbent. Prasad al World J Pharm Pharm Sci.  
2015;4(11):1600–10.  
44. Bernard E, Jimoh A, Odigure JO. Heavy Metals Removal from  
Industrial Wastewater by Activated Carbon Prepared from Coconut  
Shell. 2013;3(8):3–9.  
2
2
2. Ng ZG, Lim JW, Isa MH, Pasupuleti VR, Yunus NM, Lee KC.  
Adsorptive removal of hexavalent chromium using sawdust:  
Enhancement of biosorption and bioreduction. Sep Sci Technol  
[Internet].  
2017;52(10):1707–16.  
Available  
from:  
https://doi.org/10.1080/01496395.2017.1296868  
3. Gunatilake SK. Removal of Cr ( III ) Ions from Wastewater using  
Sawdust and Rice Husk Biochar Pyrolyzed at Low Temperature. Int J  
Innov Educ Res. 2016;4(4):44–54.  
45. Nigam M, Rajoriya S, Rani Singh S, Kumar P. Adsorption of Cr (VI)  
ion from tannery wastewater on tea waste: Kinetics, equilibrium and  
137  
Journal of Environmental Treatment Techniques  
2021, Volume 9, Issue 1, Pages: 122-138  
thermodynamics studies.  
019;7(3):103188.  
https://doi.org/10.1016/j.jece.2019.103188  
J
Environ Chem Eng [Internet].  
50. Tang C, Zhang R, Wen S, Li K, Zheng X, Zhu M. Adsorption of  
Hexavalent Chromium from Aqueous Solution on Raw and Modified  
Activated Carbon. Water Environ Res. 2009;81(7):728–34.  
2
Available from:  
4
6. Abdel OE, Reiad NA, Elshafei MM. A study of the removal  
characteristics of heavy metals from wastewater by low-cost  
adsorbents. J Adv Res [Internet]. 2011;2(4):297–303. Available from:  
http://dx.doi.org/10.1016/j.jare.2011.01.008  
51. Maheshwari U, Gupta S. Removal of Cr(VI) from wastewater using  
activated neem bark in a fixed-bed column: interference of other ions  
and kinetic modelling studies. Desalin Water Treat [Internet].  
2016;57(18):8514–25.  
Available  
from:  
4
4
4
7. Migahed F, Abdelrazak A, Fawzy G. Batch and continuous removal of  
heavy metals from industrial effluents using microbial consortia. Int J  
Environ Sci Technol. 2017;14(6):1169–80.  
8. Amin MT, Alazba AA, Shafiq M. Adsorptive Removal of Reactive  
Black 5 from Wastewater Using Bentonite Clay: Isotherms, Kinetics  
and Thermodynamics. 2015;15302–18.  
http://dx.doi.org/10.1080/19443994.2015.1030709  
52. Maheshwari U, Gupta S. Removal of Cr(VI) from wastewater using  
activated neem bark in a fixed-bed column: interference of other ions  
and kinetic modelling studies. Desalin Water Treat. 2016;57(18):8514–  
25.  
53. Foo KY, Hameed BH. Insights into the modeling of adsorption  
isotherm systems. Chem Eng J. 2010;156(1):2–10.  
9. Ingole RS, Lataye DH, Dhorabe PT. Adsorption of phenol onto Banana  
Peels Activated Carbon. KSCE J Civ Eng. 2017;21(1):100–10.  
138