This document summarizes a study on optimizing the adsorption of methylene blue dye onto sugarcane bagasse using a two-level factorial design. The researchers investigated the effects of contact time, initial dye concentration, shaking rate, and adsorbent dosage on the adsorption capacity of sugarcane bagasse. Their results showed the optimal conditions were 58 minutes contact time, 150 mg/L initial dye concentration, 250 rpm shaking rate, and 0.1 g adsorbent dosage. Under these conditions, the theoretical maximum adsorption capacity closely matched the experimental value. Statistical analysis confirmed the significance of these factors and optimal conditions in maximizing dye removal by sugarcane bagasse.

1. International Conference on Chemistry and Environmental Science Research 2014 (ICCESR 2014)
Optimization Study On Adsorption of Methylene Blue on
Sugarcane Bagasse using Two Level Full Factorial Design
Wong Shi Ting1
, Nik Ahmad Nizam Nik Malek1
*, Auni Afiqah Kamaru1
, Mahmud A. S.
Khalifa1
and Nor Suriani Sani2
1
Faculty of Biosciences and Medical Engineering, Universiti Teknologi Malaysia, 81310 UTM, Johor
2
Nanotechnology Research Alliance, Universiti Teknologi Malaysia, 81310 UTM, Skudai, Johor
*niknizam@fbb.utm.my
ABSTRACT
The adsorption study of methylene blue (MB) by sugarcane bagasse was performed based on
statistical approach using two-level factorial design. The effect of several factors affecting the
adsorption capacity of sugarcane bagasse namely contact time (15 – 60 min), shaking rate (50 –
250 rpm), initial MB concentration (50 – 150 mg/L) and adsorbent dosage (0.1 – 0.5 g) were
studied. The optimum adsorption capacity of MB on sugarcane bagasse was found at 58 min
contact time, 150 mg/L of MB with shaking rate of 250 rpm and adsorbent dosage of 0.1 g.
Theoretical adsorption at equilibrium, qe, (24.52 mg/g) at this condition matched closely with the
experimental value (22.25 mg/g).
Keywords: Sugarcane bagasse, Methylene blue, Adsorption, Two-level factorial design
Introduction
In Malaysia, 22 % of industrial wastewater was discharged by textile industries [1]. Dyes
that contains in industrial wastewater must be treated before being discharged to the environment
due to it adverse effects to human as it can cause skin irritation, toxic, allergic, mutagenic and
carcinogenic [2]. Currently, the removal and recovery of dyes is by the adsorption method since
it is cheaper, efficient and ease in operation [3]. Sugarcane bagasse, one of adsorbent that has
been proven having high adsorption capacity for various dyes such as basic blue 69 and basic red
22 [4-5]. Sugarcane bagasse is cheaper compared to other solid support like cellulose pulp,
chitosan and synthetic polymers [6]. In this study, the sugarcane bagasse, the low cost

2. International Conference on Chemistry and Environmental Science Research 2014 (ICCESR 2014)
agricultural waste biomass adsorbent has been used to remove dye from water. The effect of
adsorbent dosage, initial methylene blue concentration, shaking rate and contact time on the
removal of methylene blue dye from aqueous solution have been investigated using 2-level
factorial design. Factorial design is a tool that can be used to design experiments. An experiment
using factorial design allows examining simultaneous effects of multiple independent variables
and their degree of interaction [7-8]. In one-factor-at-a-time (OFAT), each experiments run
consider only one factor, numerous run are required to get adequate information about the set of
conditions contributing to the problem. The advantage of factorial designs over OFAT is they are
more efficient and they allow interaction among studied factors to be detected.
Materials and Methods
Sugarcane bagasse (SB) has been collected from juice shop in Johor Bahru, Malaysia.
Sugarcane waste was firstly placed below sunlight. The pith fragments and fiber were crashed to
tiny parts and dried at 90 °C in an oven for 24 hours. Sugarcane bagasse (SB) was changed to
fine particles by crushing them using a stainless steel blender. The SB fragments were washed
with distilled water under constant stirring at 60-70 °C to remove the remaining sugars, filtered
by single filtration and washed again with ethanol 95%, and dried at 90 °C. Lastly, the sample
was washed again with the hexane-ethanol (1:1) with a soxhlet apparatus for 4 hours to eliminate
lignin extracted and extractives from blending process. It was dried at 90 °C in an oven and
stored at room temperature.
A two level (24
) full factorial experimental design was employed with four main factors,
namely; contact time (A), initial methylene blue concentration (B), shaking rate (C) and
adsorbent dosage (D). The investigated factor levels and range are given in Table 1. The
experimental design and statistical significance of investigated factors and their combinations
were carried out using Design Expert 6.0.4 software. A multiple regression analysis was
conducted based on the first-order response function as given in Equation 1.
𝑌 = 𝛽0 + 𝛽𝑖 𝑋𝑖 + 𝛽𝑖 𝑋𝑖 𝑋𝑗 + 𝜀 (1)

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where β0, βi, βij are regression coefficients for the intercept, linear and interactions among
factors, respectively, y, is the response vector for qe and R, whereas Xi and Xj are the
independent factors in coded units, and ε is the error term. The fitness of regression model was
evaluated by calculating the coefficient of determination (R2
) [9].
Table 1: Experimental range and levels of independent variables for adsorption of methylene
blue by sugarcane bagasse
Variable Symbol Unit Low level (-1) High level (+1)
Contact time A min 15 60
Initial MB concentration B mg/L 50 150
Shaking rate C rpm 50 250
Adsorbent dosage D g 0.1 0.5
The residual methylene blue concentration was measured by collecting the supernatant
and was analyzed using VIS spectrophotometer (VIS NANOCOLOR macherey-nagel, German)
at wavelength of 661 nm. The methylene blue concentration was calculated from a calibration
curve of absorbance versus dye concentration. Then, the adsorption amount at equilibrium, qe
(mg/g), was calculated by Equation 2
𝑞 𝑒
=
( 𝐶𝑖
− 𝐶 𝑒 ) 𝑉
𝑊
[2]
where qe is the amount of methylene blue adsorption at equilibrium (mg/g), Ci and Ce (mg/L) are
the methylene blue concentration at initial and equilibrium, respectively, V (L) is the volume of
the solution, and w (g) is the weight of SB used.
Results and Discussion
Regression Analysis
Based on 2-level factorial design, interactions of variables, on adsorption capacity of
sugarcane bagasse are summarized in the regression equation, Eq (3):

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Adsorption at equilibrium, qe (mg/g) =
11.53 + 0.19A + 3.94B + 0.29C -6.36D + 0.13AB -
0.20AD + 0.12BC - 1.42 BD - 0.24 CD - 0.14 ABD
(3)
The factor with positive values for their coefficients can improve the respective response vector
for an increase in the level of those factors, whereas negative value of the coefficients suggests
their inverse relationship with the response vectors [9].
ANOVA Study
Interpretation of result was analyzed using the analysis of variance (ANOVA) as
appropriate to the experimental design used. This method was used for comparison of the
significance factors among the four variables influencing the adsorption capacity of SB.
Screening design (24
) was used to detect the factors or independent variables that had higher
impact on the response variable adsorption at equilibrium (qe). The results are tabulated in Table
2.
Table 2: Analysis of variance (ANOVA) for selected factorial model influenced the adsorption
of methylene blue on the sugarcane bagasse
Source Sum of Square DF Mean Square F Value a
Prob > F
Model 2795.43 10 279.54 3748.61 < 0.0001
A 1.80 1 1.80 24.10 < 0.0001
B 744.25 1 744.25 9980.23 < 0.0001
C 4.14 1 4.14 55.56 < 0.0001
D 1941.53 1 1941.53 26035.47 < 0.0001
AB 0.82 1 0.82 11.02 0.0019
AD 1.87 1 1.87 25.10 < 0.0001
BC 0.69 1 0.69 9.24 0.0041
BD 96.49 1 96.49 1293.86 < 0.0001
CD 2.87 1 2.87 38.53 < 0.0001
ABD 0.97 1 0.97 12.98 0.0008
Curvature 45.60 1 45.60 611.45 < 0.0001
R-Squared 0.9989 Pred-R-Squard 0.9981

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Adj R-Squard 0.9986 Adeq Precision 170.861
The “Pred R-Squared” of 0.9981 is in reasonable agreement with the “Adj R-
Squared” of 0.9986.
Values of “Prob > F” less than 0.05 indicate model terms are significant.
The probability value (p-value) for each term and interaction is listed in Table 2. A p-
value that less than 0.05 defines the factors is significant. The model is significant with a
probability of less than 0.0001. This means that the regression model which has been generated
to describe the correlation of adsorption at equilibrium (qe) with the analyzed factors was
accurate. Regression coefficient, R2
value of 0.9989, indicated model adequacy and shows that
the model is workable and can be accepted. Sum of squares (Table 2) of each factor quantifies its
importance in the process and as the value of the sum of squares increases, the significance of the
corresponding factor in the undergoing process also increases [10]. F values of 4 factors were as
follows: Fcontact time (A) = 24.10, Finitial concentration of methylene blue (B) = 9980.23, Fshaking rate (C) = 55.56,
Fadsorbent dosage (D) = 26035.47. The result of F-test meant that the 4 factors were all significant in
influencing the adsorption capacity of SB. Value of ―prob > F‖ less than 0.0500 indicates model
term was significant. The ―Curvature F-value‖ of 611.45 implies there is significant curvature
(as measured by the differences between the average of the center points and the average of the
factorial points) in the design space. In addition, the ―Pre R-Squares‖ of 0.9981 is in reasonable
agreement with the ―Adj R-Squared‖ of 0.9986.
Normal Probability Plot of Residuals
Figure 1: Normal probability plots of residuals for adsorption of MB by SB

6. International Conference on Chemistry and Environmental Science Research 2014 (ICCESR 2014)
The normality of the data can be determined by plotting a normal probability plot of the
residuals. If the data points on the lot fall fairly close to the straight line, then the data are
normally distributed. The normal probability plot of the residuals for adsorption of methylene
blue on sugarcane bagasse is shown in Figure 1. It can be seen from this figure that the data
points are fairly close to the straight line and it indicates that the experiments are normally
distributed population [10].
In this case, the optimal condition for the adsorption capacity of sugarcane bagasse that
was determined as A, B, C, D, AB, AD, BC, BD, CD, ABD are significant model term where
contact time (A) was 58 min, initial [MB] (B) was 150 mg/L, shaking rate (C) was at 250 rpm
with 0.1 g of adsorbent dosage (D) which can be referred in Figure 2.
Figure 2: Factors that significantly influenced the adsorption capacity of sugarcane bagasse toward methylene blue
analyzed using 2-Level-Factorial Design
The optimum and significant factor of initial [MB] in this adsorption study was 150.00
mg/L which indicated that higher [MB] is needed to achieve the highest adsorption capacity. The
initial dye concentration is a driving force that can overcome mass transfer resistance which
exists between the dye molecules in aqueous solution and adsorbent particles. Thus, the number
of dye molecules that compete to adsorb on the adsorbent increases at higher initial dye
concentration thus leading to higher adsorption capacity [11]. Nasuha et al. (2010) reported that
the adsorption capacity of adsorbent was proportional to the initial concentration of MB. They

7. International Conference on Chemistry and Environmental Science Research 2014 (ICCESR 2014)
found that there was a significant increment in the adsorption capacity of tea waste from 18.6 to
134 mg/g when the concentration of MB dye was increased from 50 to 500 mg/L [12].
Therefore, it can be concluded that the initial dye concentration was the most significant factor
for adsorption capacity [9].
In this study, the optimum contact time and adsorbent dosage for achieving the highest
adsorption capacity were 58 minutes and 0.1 g, respectively. The interaction between the effect
of time and the weight of adsorbent on the percentage removal of MB reveals that time have the
direct effect on the adsorption process. As more time of operation means more contact times are
needed for transferring mass from solid to liquid phase until equilibrium is reached [13].
Equilibrium time is an important parameter for economical wastewater treatment. As the contact
time increases, the rate of adsorption decreases depending on the chemical characteristics on the
surface [14]. According to Uddin et al. (2009) the percentage removal of MB increased with the
increase in adsorbent dosage, but the adsorption density (qe) of MB decreased with the increment
in adsorbent dosage [15].
The optimum shaking rate during the screening factors for adsorption capacity of
sugarcane bagasse was at 250 rpm. The influence of increasing the shaking rate is to decrease the
liquid film or boundary layer surrounding the adsorbent particles [16]. The higher shaking rate
lead to the higher contact between the adsorbent and the dyes thus increase in adsorption
capacity of the adsorbents.
Conclusion
According to the analysis, the optimum process conditions for the MB removal by
sugarcane bagasse include contact time 58 min, initial methylene blue concentration of 150
mg/L, shaking rate at 250 rpm and adsorbent dosage of 0.1 g (Figure 1). Theoretical adsorption
at equilibrium, qe (24.52 mg/g) at this condition matches very well with the experimental value
(22.25 mg/g). The experimental value is 91% of the predicted value. Sugarcane bagasse has
been proven to be an effective low-cost adsorbent for the removal of MB via adsorption from
aqueous solution.

8. International Conference on Chemistry and Environmental Science Research 2014 (ICCESR 2014)
Acknowledgement
Author would like to acknowledge Universiti Teknologi Malaysia (UTM) and Ministry of
Education Malaysia for financial support under Research University Grant Tier 1 (Vot No:
08H01) and Faculty of Biosciences and Medical Engineering, UTM.
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