Dye colour is highly visible even in a

Dye is a
substance that is used for
imparting colour to alter the existing colour shade to a substrate. Dye becomes
an incredible material as it has an ionising yet an aromatic organic compound that possesses an affinity towards the material
being applied (Zhong et al., 2010). Unlike paint, they do not build on upon
the material surface but being absorbed into the pores of the material because dye molecule has a smaller size than the pores of the material. It is chemically bonded to the
surface and become a part of the material.

 

However, the extensive usage of dyes in
industries produced a large amount of
wastewater with intense colour and the colour is highly visible even in a small
quantity. The growth of industries also increases
the discharge of residual colour metal in water as they need a substantial
amount of water in their manufacturing process. Besides, the high demand for
textile products and also increased the usage of synthetic dyes both have
contributed to the severe water pollution. There is also no official document
that states the limiting amount of colour that can be discharged in the
effluents (Zhong et al., 2010). This is why the unlimited amount of dyes
are released into the water are still
continuing until today.

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              Cationic dyes, also known as
basic dyes are a class of synthetic dyes.
This coloured compound is called basic dyes because it contains a positive electrical charge which is attracted to the
negative charge on fibre molecule to form a salt. Basic dyes are effective
colouring agent and it can be applied to many textiles including wool, silk and
cotton. Methylene blue (MB) is one type of cationic dyes which is blue in
colour. It is popularly used as a colourant
in food, paper and also dying cotton and wools. Unfortunately, when MB is disposed in water without treatment, it could
contribute to major water pollution and aquatic organisms will die. MB dyes are
considered toxic and have carcinogenic properties. Therefore, the removal of
this dyes from wastewater is vital to protect the environment as well as the
well-being (Gottipati
& Mishra, 2010).

 

Recently, many
conventional methods that have been used to remove dyes from the water involves
high cost, difficult to apply, and produce chemical sludge (Bhatnagar
& Minocha, 2006). These physical, biological and chemical
methods were investigated to clear up the colour of wastewater but have been relatively ineffective.  Biological methods
take a long time to degrade the dyes while chemical method can cause
pollution to the water being treated (Shendkar et al., 2013). A more effective and cheaper ways are strictly needed to treat wastewater that
used only small amounts of chemical and energy.

 

Adsorption is a well-known technique that
has been observed to be a better technique because of the simplicity and
flexibility, easy to operate and most importantly does not form dangerous substances (Khan et al., 2005). The most popular adsorbent used is
adsorbent but it is an expensive process. This
cause number of research work have been studied to find efficient and
low-cost adsorbent to remove Methylene blue dyes from wastewater (Ehrampoosh,
2011).

 

Biomass refers to none – fossilised and biodegradable organic materials originates
from a plant, animal and microorganisms.
The use of biomass as an adsorbent can reduce the emission of carbon dioxide as
well as the greenhouse effect (Umoren et al., 2013). In this study, the fruit shell of Cassia fistula is studied as an
adsorbent to evaluate the efficiency of this plant for the removal of Methylene
blue dyes in aqueous solution. In the previous
study, the ash of Cassia fistula seed
has been used to adsorb Congo red dye from aqueous solution (Amuda et al., 2014). The results concluded that it has a
considerable potential as an adsorbent in the future.

Dyes are basically an organic compound
that can bind themselves to surface in order to provide a bright and long-lasting colour. The discharge of dyes into
the water streams causes many diseases to human and an environment where the growth of bacteria is blocked and can cause
harm to aquatic life (Rahman et al., 2012). Most of them are complex molecules and
resistance to many things such as the action of detergent (Amrhar et al., 2015).

      
Several conventional methods that are already existed for the treatment
of coloured wastewater including chemical, biological and physical method has
been proved to be limited in small and medium scaled industries. Dyes are
difficult to biodegrade even after extensive treatment, so the colour might
still present in the water. They were less efficient, difficult to apply,
expensive process, produce sludge and also use electricity. Thus, adsorption
process is done to remove Methylene blue dyes by using adsorbent obtained from the fruit shell of Cassia Fistula.     

 

The aim of this research is to investigate the
potentiality of Cassia fistula’s
fruit shell as an adsorbent for removing Methylene blue dyes from aqueous
solution. Specific objectives include:

a)     
To
produce adsorbent from Cassia fistula’s fruit
shell.

b)     
To
study the effect of different parameters including adsorbent dosage, pH, MB
concentration, temperature and contact time.

c)     
To
characterise the adsorption of dyes using
moisture content, ash content, bulk density, SEM, FTIR, and pHpzc studies.

d)    
To
determine the adsorption isotherm of MB over the adsorbent produced.

 

This study can contribute
to a clean environment as it helps to
reduce water pollution. The degradation of the environment has become a serious
problem for the existence and survival of human beings as well all life on
Earth. Water pollution due to dyeing industry is one of the heavily polluting
industries because a large quantity of
effluent is being discharged into the
water.

This research can contribute to the alternatives of treating the
wastewater. The adsorbent used in this study is a low-cost adsorbent and this natural adsorbent will not cause any
harm to our Earth. The widespread of uses of adsorbent as a method for water
treatment is strongly recommended due to the higher efficiency, low cost and flexible technique. This research also
can be used in the present industry to
adsorb dye released by the factory before
further treatment.

This study focus on the use of biomass
from the fruit shell of Cassia fistula. The
adsorbent produced were then tested on the adsorption
of Methylene blue dye. The colour reduction of the dye at different initial
concentration of MB, adsorbent dosage, temperature, initial pH and contact time
is observed in this study.

Dyes
are a coloured compound and are being
applied to numerous substrates for example to textiles, paper and also foods (Dash, 2010).
Dyes contain chromophores to give rise to colour and the other group, auxochromes such as carboxylic acid to enable
the bonding to fibre and modify the colour. Dyes can be produced from both
natural and synthetic sources. Natural dyes are organic compounds mainly
derived from natural sources without any chemical process. A great source of
this dyes is from plants, animals,
insects, and minerals. Due to increase in population and industrial activities,
natural dyes do not meet the global demands and their application has been limited mainly in the food industry (Dawood & Sen, 2014).
Table 2.1 above shows the most common
natural dyes used in textile industries.

 

Synthetic
dyes have become popular due to its long-lasting colour, variety choices of colour
and would not lose their pigmentation as easily as natural dyes. These are the
reasons why synthetic dyes have evolved
into a multi-billion dollar industry. Synthetic dyes made up from chemical
compounds that may contain elements such as mercury, chromium, lead, benzene
and toluene. (Maria et al., 2013).
Being exposed to these elements can be very dangerous to human body and
environment because it has high toxicity.

Mainly,
dyes are classified based on the usage in textile industry such as anionic,
cationic and non-ionic dyes (Pathania et al.,
2017).
Cationic dyes are also called as basic dyes because it has positive ions in the
molecular structure of chromophores. This class of synthetic dyes are water
soluble and form a

coloured
cationic salt which then reacts with the
anionic structure on the substrate surface (Filipi & Milichovský, 2014).
There are applied to substrate with anionic character to produce bright shades with high tinctorial values.

Methylene
Blue (MB) also known as methylthioninium chloride is heterocyclic aromatic
compounds with a molecular formula of (C16H18N3CSI.H2O).
It appeared as a solid, dark green powder at room temperature and produces a
blue solution when dissolved in water. The chemical structure of MB is shown in Figure 2.1.

Methylene blue is one of the cationic dyes which is used in textile industry
for example dyeing of cotton and wools. MB is widely used in human
and medicine for therapeutic and diagnostic procedures including as a stain in
bacteriology and also antiseptic and disinfectant (Prasad & Santhi, 2012).
In medicine, Methylene blue was the first synthetic drug to be created
originally used as a malaria treatment (Koch, 2013).MB
also commonly used by a biologist as a
dye to assist in the identification of bacteria
and widely used as a

bacterial
infection preventive. Although MB is not strongly hazardous, it can cause
harmful side effects to human and aquatic animals (Umoren et al., 2013).The
common side effects include vomiting, high blood pressure and also allergic
reactions (Pathania et al., 2017).

Water
pollution is a worldwide problem
particularly in a textile industry where large quantities of dyes are discharged to the
wastewater from dyeing process. As textile industries have been the largest consumer of dyes, the demand for
dye in the world will continue to rise in the incoming years because of
increase in human population. The
effluent of dyestuff from textile industry was declared as one of the major
source of water pollution within the global when considering of both volume and
composition of dyes (Dasuqkhi et al.,
2013).
The stability and fastness of dyes attract
the producers of dyes and they are consequently producing dyestuff which is more difficult to degrade after being used.

 

The
released of dyes into the wastewater cause
severe detrimental effects on a human
being and aquatic life. For a human being,
these intermediates can damage the vital organs such as heart, brain, kidney
and central nervous system. They also can interfere
the transmission of sunlight for the photosynthetic activity of aquatic
organisms (Maryam, 2013).
Most of the dyes

are
considered toxic and have carcinogen properties which make the water inhibitor to aquatic life. As dyes are designed
to resist breakdown with time, it cannot be easily removed by conventional
treatment due to their complex structure and synthetic origins (Ehrampoosh, 2011).
Therefore, it is urged for the researcher
to find out the way to removes such toxic dyes from the wastewater.

Theoretically,
there is a great number of separation processes tailored to remove dyes such as
a conventional method. Conventional
method consists of a combination of the physical, chemical and biological process. Some
of the disadvantages of this treatment are the constant high electrical energy
requirement, high cost for supervision, maintain and also construction. There
is also some issues of ecological disposal of the sludge waste (De Filippis et
al., 2013).
Table 2.2 shows some advantages and disadvantages of conventional treatment for
wastewater.

 

Biological methods are applied in industrial effluents so that microorganisms such as
bacteria, yeast, algae and fungi able to build up and degrade different
pollution. However, their application is restricted because of technical
constraint. It also requires a large area and has
less flexibility in operation (Sharma, 2014).
Despite many organic molecules are degraded, other molecules are recalcitrant due to their complicated chemical
structure

Coagulation
is one example of a chemical method which
is an expensive
method and creates a disposal problem although the dyes are removed.
There is also the possibility that a secondary pollution problem will arise because of excessive chemical used (Tripathi & Ranjan, 2015).
Recently, other techniques known as
advanced oxidation technique has been
applied successfully to degrade pollution but they are very costly and consume
high chemical reagents (Lopez-Nuñez et
al., 2014).

Physical
methods such as membrane-filtration are
the prime method used in drinking water and wastewater treatment (Kharub, 2012).
Generally, the dye molecule will clog the membrane and limits the separation
process afterwards. It also has a limited
lifetime before membrane fouling happened. Adsorption by adsorbent has been a
popular method to treat wastewater but its widespread use is restricted due to
high cost. Therefore, adsorption by using low-cost
adsorbent become great alternatives to
the adsorbent. It is a popular separation
process and an effective approach for water treatment due to its low initial
cost, flexible, simple design, ease of operation and does not result in

the
formation of harmful substances (De Filippis et
al., 2013).

 

The adsorbent is the material upon
whose surface the adsorption takes place. Adsorption is the accumulation of
particles (adsorbate) at the surface of a solid or liquid (adsorbent). The
basic principle for adsorption is the mass transfer of a molecule from a liquid
into the solid surface. The adsorbent is
manufactured in such a way as to produce porous particles to attract and holds
organic molecules. This process occurs because:

                               
i.           
The contaminant has low
solubility in the liquid or gas

                             
ii.           
The contaminant has
greater affinity for the adsorbent than for the liquid

                           
iii.           
The combination of two

 Major types of adsorbents used are activated
alumina, silica gel, activated carbon,
molecular sieved and organic polymers (Christmann, 2011).
Most adsorbents such as adsorbent are
manufactured but a few such as zeolites occur
naturally. Each adsorbent has its own
characteristics such as porosity, pore structure and the nature of its
adsorbing surfaces (Bash, 2015).
Adsorbent is
amazingly useful in many applications and industries including drying, humidity
control and remediation task. They are applied in industry for semiconductors,
pharmaceuticals, food processing, packaging, energy production, pollution
control and waste management. In food processing, for example, the adsorbent is
used to make food and other product last longer in a damp environment.

In
recent times, several approaches for the growth of economic and potent adsorbent have been studied including low-cost adsorbent obtained from biomass for
removal of dyes. Some of the adsorbents have been efficiently used

 

(Radenovi et al,
2011). The bonds that form between solute molecules and specific
surface chemical groups have all the properties of true chemical bonds and are
characterized by relatively large heats of adsorption

 

The
effects of four adsorption variables which are initial concentration of MB,
adsorbent dosage, temperature, initial pH, and contact time are investigated in
this study.

The
distribution of dye molecule between the liquid phase and the adsorbent is a
measure of the position of equilibrium in the adsorption process and can be
expressed by one series of isotherm models. The adsorption isotherm models are utilised to describe the interaction behaviour
among adsorbate and adsorbent (García et al.,
2014). In this study,
Langmuir and Freundlich isotherm models were used to describe the adsorption
equilibrium data from the adsorption of methylene blue.

The
Langmuir isotherm describes that the adsorption of MB onto the surface of
adsorbent requires three assumptions (Pathania et al., 2017):

·        
The surface of the
adsorbent is in contact with a solution containing an adsorbate which is
strongly attracted to the surface.

·        
The surface has a
specific number of sites where the solute molecules can be adsorbed

·        
The adsorption involves
the attachment of only one layer of molecule to the surface

The
Langmuir adsorption isotherm has been successfully applied to many pollutant
adsorption processes (Chairgulprasert et
al., 2013)
Langmuir model is described by the following Equation (3):

 =

 +

. Ce                              (Equation 1)

where
KL (L/mg) is Langmuir constant
and qmax (mg/g) is the maximum adsorption capacity.

The
Freundlich isotherm model describes that the adsorption of solutes from a
liquid to a solid surface (Hashem & El-Khiraigy, 2013).
The Freundlich model can be represented by Equation (4):

In
qe = In KF +

 In
Ce                                              (Equation 2)

where
Ce (mg/L) is the equilibrium concentration of dye in solution, qe (mg/g) is the amount of dyes adsorbed at equilibrium. KF and 1/n
are Freundlich constant where n indicates the degree of to which an adsorption
process is favourable and KF (mg/g)(L/mg)1/n is the
adsorption capacity of the adsorbent.