Removal of basic dye from synthetic wastewater using sugarcane bagasse modified with propionic acid

 

Sandra Sajen¹, Jephin Varughese Jose¹, Sandeep Bukke¹, Chaithanya Sudha M²*, Saladi S.V. Subbarao³, V.R. Mandla⁴

¹Post Graduate Student, School of Civil and Chemical Engineering, VIT University, Vellore

⁴Assistant Professor, School of Civil and Chemical Engineering, VIT University, Vellore

³Associate Professor, School of Civil and Chemical Engineering, VIT University, Vellore

⁴Professor, School of Civil and Chemical Engineering, VIT University, Vellore

 

ABSTRACT:

AIM: The aim of the present study was to prepare natural adsorbent from sugar cane bagasse modified with propionic acid for the removal of basic dye ‘Methylene Blue’ from synthetic wastewater. OBJECTIVE:  Adsorption experiments were performed to determine the optimum conditions of time, adsorbent dosage, adsorbent size, agitation speed, dye concentration and pH.  MATERIAL AND METHODS: The sugarcane bagasse was procured and washed thoroughly with water. The bagasse was dried in sun for two days (Nevine 2008). It was then oven dried for 24 hours at 120 °C temperature (Hajira et al. 2012). The bagasse was crushed in the mixer until it turned fine powder and sieved to the sizes of 0.6, 0.3 and 0.15 mm. The efficiency of adsorption was influenced by various factors such as contact time, adsorbent dosage, size of the adsorbent, concentration of dye, pH and rpm. Each factor was optimized experimentally. BACKGROUND:  The release of coloured waste water in to the natural streams such as rivers causes severe problems in the aquatic environment. The presence of dyes will absorb and reflect the sunlight entering the water thus hindering the process of photosynthesis in plants. This will reduce the water quality in natural streams and it also affects the human health. The dyes can also cause allergic diseases, skin irritations, cancer and mutations. RESULTS:  The results indicated that the adsorbent showed good sorption potential and maximum dye removal was observed at pH 7.Within 8 minutes of operation about 81.5% of the dye was removed from the solution. The sorption curve was well fitted to the Langmuir model. The adsorption capacity of dye at optimum conditions was found to be 60 mg/L. Langmuir adsorption isotherms have been analysed and it gives high correlation factor (R² > 0.98). Kinetic study shows that the adsorption process follows pseudo second order reaction with good correlation factor (R² > 0.99).

 

 

1. INTRODUCTION:

Dyes are materials which are utilized in industries such as tannery, paper, plastic, printers, colour photography and textiles to colour their items and it is also used as additives in petroleum products. There are about ten thousand dyes are commercially available and over seven hundred thousand tonnes of dye stuffs are produced every year around the world (Bharathi and Ramesh 2013). It is assessed that about 2% of the dye stuffs produced are released in to the effluents annually. This will produce large amount of coloured waste water.

 

The release of coloured waste water in to the natural streams such as rivers causes severe problems in the aquatic environment. The presence of dyes will absorb and reflect the sunlight entering the water thus hindering the process of photosynthesis in plants. This will reduce the water quality in natural streams and it also affects the human health. The dyes can also cause allergic diseases, skin irritations, cancer and mutations.

 

Conventional biological water treatment methods are not effective in treating waste water containing dyes due to its low biodegradability. Commonly it is treated with physical and chemical methods (Garg et al. 2003). These treatment methods are efficient in removing the dyes but they are costly and have functioning problems (Kapdan et al. 2000). The adsorption process is usually used in industries to remove a dye which involves adsorption of molecules on to several adsorbents (Porter et al. 1999). Mostly activated carbon is used as the adsorbent. The main drawbacks of using activated carbon are the high cost involved in the production and regeneration of the adsorbent.

 

The search for the low cost adsorbent to work as an alternative to the activated carbon leads to the use of natural adsorbents. The benefits of using natural adsorbents are low cost, easily available, good adsorption capacity and it does not cause any harmful effect to the environment. In this study the natural adsorbent prepared from sugarcane bagasse was used to remove methylene blue dye from aqueous solution. Sugarcane bagasse is a fibrous material which remains after the removal of juice from sugarcane (Hajira et al. 2012). Methylene Blue is a basic dye with molecular formula C₁₆H₁₈N₃SCl and it is used in various industries and medical fields.    

 

2. MATERIALS:

2.1 Preparation of the adsorbent:

The sugarcane bagasse was procured and washed thoroughly with water. The bagasse was dried in sun for two days (Nevine 2008). It was then oven dried for 24 hours at 120 °C temperature (Hajira et al. 2012). The bagasse was crushed in the mixer until it turned fine powder and sieved to the sizes of 0.6, 0.3 and 0.15 mm.

 

2.2 Activation of the bagasse:

The bagasse was mixed thoroughly with Propionic acid and kept in the oven for drying at a temperature of 60˚C for a period of 48 hours (Abdel El-Aziz et al. 2012). The dried sugar cane bagasse was activated and stored in a glass container and denoted as Bagasse Modified with Propionic Acid (BMPA). It was stored in a dark place and used freshly for the adsorption studies. The dye was prepared for different concentration of 3, 15, 21, and 30 mg/L.  For the initial analysis, the rounds per minute (rpm) value was set at 250 as followed by Dereje et al. 2014.

 

3. METHODOLOGY:

The efficiency of adsorption was influenced by various factors such as contact time, adsorbent dosage, size of the adsorbent, concentration of dye, pH and rpm. Each factor was optimized experimentally.

 

3.1 Effect of contact time:

The efficiency of the adsorbent can be explained on the basis of the rate of intake of dye by the adsorbent (Abdel El-Aziz et al. 2012). To study the variation of percentage removal of dye with contact time, the solutions were tested at different time intervals. Solutions were drawn at 2, 4, 8, 10, 15, 30, 60, 120, 240 minutes and it is tested with UV Spectrophotometer.

 

3.2 Effect of adsorbent dosage:

To study the effect of adsorption on dosage of the sugarcane bagasse, adsorbent dosages were varied for the dye concentrations under consideration. It was tested for 0.1, 0.2, 0.6 and 1 g.

 

3.3 Effect of adsorbent size:

Adsorption is a surface phenomenon. Therefore it is necessary to analyze the effect of adsorbent size on the dye removal efficiency. The sizes of adsorbent used were 0.6, 0.3 and 0.15 mm. The adsorbent sieved into different sizes was added to the dye solutions and variation in dye removal efficiency was observed.

 

3.4 Effect of rpm:

The speed at which the agitation is carried out will affect the external boundary film of the adsorbent and the distribution of the dye in water. The variation was studied by changing the speed of rotation of adsorbent- adsorbate solutions while keeping other parameters constant. The RPM was varied between 50, 100, 200 and 250 (Dereje et al. 2014).

 

3.5 Effect of pH:

The degree of ionization and the surface charge of the adsorbent will depend upon the pH value of the solution. Therefore it is necessary to optimize the pH to attain maximum efficiency. The pH was varied by adding 0.1 N Hydrochloric Acid (HCl) and 0.1 N of sodium hydroxide (NaOH). The test was conducted for a pH of 2, 4, 7 and 9 (Abdel El-Aziz et al. 2012).

 

3.6 Effect of dye concentration:

All the other parameters were kept constant and the dye concentration was varied between 3, 15, 21, 30, 45, 60 mg and the effect was studied (Abdel El-Aziz et al. 2012).

 

3.7 Kinetic and Equilibrium Study:

Kinetic study was conducted to found the type of order (pseudo-first order or pseudo-second order) followed by the adsorption process. Equilibrium studies were also done to analyse the type of isotherm followed by adsorption.

 

3.8 FTIR, SEM and XRD Analysis:

Instrumental analysis by Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and X-Ray diffraction (XRD) analysis were further included to study the adsorption phenomenon by sugarcane bagasse in detail. The changes in the surface and internal structure of the sugarcane bagasse were studied.

 

4. Results and Discussion:

Sugarcane bagasse was dried and powdered and later activated with propionic acid. It was used to study the effectiveness of sugarcane bagasse in adsorbing methylene blue dye from the water. The study was conducted at different conditions and the effect of each parameter on the adsorption phenomenon was studied in detail.

 

4.1 Effect of contact time:

The adsorption rate was maximum at the initial stages of contact time (0-10 minutes) (Fig.1). This may be due to the rapid diffusion and adsorption of the basic dye on the macrospores surface of the treated bagasse (Abdel El-Aziz et al. 2012). After a period of 10 minutes the uptake decreased and then almost remained a constant.

 

Fig 1. Effect of contact time

 

The sudden decrease can be reasoned as it is due to the completion of monolayer adsorption. When adsorption is complete, further removal dye takes place due to the transportation of dye from the exterior to the interior surface sites of the bagasse (Nevine 2008). The plotted graph patterns ware almost similar for the different dye concentrations considered. Since the dye intake increased to a maximum value in the initial 8 minutes, the contact time was optimized to 8 minutes.

 

4.2 Effect of adsorbent dosage:

The initial adsorption increased with the increase in the amount of adsorbent added. This is due to the higher available number of adsorption sites available on BMPA, similar observations were made by Abdel El-Aziz et al. (2012). The adsorbent dose for which maximum removal efficiency obtained was 0.6 g after which the adsorption rate varied less (Fig. 2). This indicates that the behavior of the treated bagasse surface is active towards adsorption of the basic dye (Abdel El-Aziz et al. 2012).

 

Fig. 2. Effect of adsorbent dosage

 

4.3 Effect of adsorbent size:

The percentage of removal efficiency of dye increased with the decrease in the size of BMPA. This is because as the size of the bagasse decreases, surface area is increasing providing larger sites for the dye adsorption. It is important to study the influence of the size of adsorbent so as to achieve optimum utilization of the adsorbent (Abdel El-Aziz et al. 2012). Here 0.15 mm size was optimized for the further tests (Fig. 3).

 

Fig 3. Effect of adsorbent size

 

4.4 Effect of rpm:

The effect of mechanical agitation was observed and it was seen that as the rpm increased the percentage of dye removal rate also increased. This is because the mixing will affect the external boundary of the adsorbents making it react more with the dye. From the Fig.4 it can be seen that the adsorption was maximum at 250 rpm value.

 

Fig 4. Effect of RPM

 

4.5 Effect of pH:

From Figure 5 that the pH increased till 4 the adsorption rate also increased. Further increase in pH showed slight change in the percentage removal of dye. Therefore it can be concluded that the increase in pH does not affect the removal rate much of the basic dye (Abdel El-Aziz et al. 2012).

 

Fig 5. Effect of pH

 

4.6 Effect of initial dye concentration:

As the initial dye concentration increased, adsorption capacity also increased. The graph obtained was almost linear (Fig. 6) with R² value almost equal to 1.  This point out that the low cost BMPA can be used for treating waste water polluted with high concentrations of basic dye.

 

Fig 6. Effect of Initial Dye Concentration

 

The optimized parameters obtained from the experiments are shown in Table 1. The optimum contact time for the efficient removal of dye was found to be 8 minutes after which it remained a constant. The efficient size of the adsorbent was 0.15 mm and the adsorbent dosage was found out to be 0.6 g. the pH was optimized to 7. And the mechanical agitation was kept at 250 rpm and the optimum dye concentration was found to be 60 mg/L.

 

Table 1 Optimum Conditions

1.	Contact time	8 minutes
2.	Adsorbent dosage	0.6 g
3.	Adsorbent size	0.15 mm
4.	Mechanical agitation	250 rpm
5.	pH	7
6.	Initial dye concentration	60 mg/L

 

4.7 Equilibrium Study:

The surface characteristics and adsorption mechanisms of the adsorbent is best explained by the equilibrium isotherms. The most accepted isotherms are the Langmuir and Freundlich system. The adsorption for Methylene blue was best explained by Langmuir isotherm with a high correlation factor     R² > 0.98.

 

Fig 7. Equilibrium Study

 

According to the assumptions of the Langmuir isotherm theory, adsorption happens at specific homogenous sites of the adsorbent. After a dye molecule gets adsorbed at a particular site, no further adsorption is possible within that site as the saturation level has been reached i.e., monolayer adsorption. Also no interactions take place between the adsorbate particles on adjacent sites. The Langmuir isotherm is given by the Eq.1

 

q_e = Q_m K_a C_e/ (1+K_a C_e)                                              (1)

 

where q_e (mg/g) is the amount of dye adsorbed at equilibrium and is found out by Eq.2,

 

q_e= (initial concentration (mg/L) - final concentration (mg/L)) x Volume (L )/ adsorbent dosage(g)              (2)

 

C_e (mg/L) is equilibrium concentration and Q_m and K_a are constants which can be obtained from the slope and intercept from the graph of the linear plot C_e/q_e versus C_e.

 

4.8 Kinetic Study:

To investigate the adsorption process more, pseudo-first order and pseudo-second order reactions were used. It was found out that the adsorption followed pseudo-second order best. K₂ is the rate of constant of pseudo -second order equation (mg g^-1 min^-1). The pseudo- second order rate is given by Eq 3.

 

t/q_t = 1/h + t/q_e                                                             (3)

where q_e and q_t are the amount of dyes adsorbed in mg/g at equilibrium in time t with R² > 0.99

 

Fig 8. Kinetic Study

 

The correlation factors indicated strong relationship between the parameters under study indicates that it follows pseudo-second order kinetics. The nature of the graph indicates that chemisorption is taking place. Similar results were obtained by Nevine (2008).

 

5. Instrumental analysis for adsorption:

The chemical structure for the sugarcane bagasse before treating with propionic acid, after treatment with the propionic acid and after adsorption was studied in detail using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and X-Ray diffraction (XRD) . SEM and XRD were used to determine the morphological and structural information.

 

5.1 Fourier Transform Infrared (FTIR) spectroscopy:

Sucrose is found in almost all plants, but it occurs at concentrations high enough for economic recovery only in sugarcane. It is a disaccharide or a double sugar composed of one molecule of glucose linked with fructose.

 

9(a)

 

9 (b)

 

9 (c)

Fig 9. (a) FTIR graph for Raw Sugarcane bagasse,

(b) FTIR graph  for Raw Bagasse modified with Propionic acid

(c) FTIR for sugarcane bagasse after adsorption of methylene blue dye

The peaks in the Fig.9a show the presence of the aldehyde and ketone groups in the bands 1710 cm^-1 - 1665 cm^-1. Also the C-H bending and presence of methyl group can also be observed. The C-O stretch also indicates the presence of the alcohol group in the sucrose. Figure 9b confirms the presence of propionic acid on the sugarcane. This can be identified from C=O bond formation seen at the peak of 1699.29 cm^-1. Broad O-H stretch can also be identified from the graph at 2500 cm^-1 - 3500cm^-1 band range. From Fig.9c it can be verified that the sugarcane adsorbed the Methylene blue dye. This can be verified from the C-H methylene bending and N-H bend in 1650-1580 cm^-1 band range and C-Cl bond stretch in 850-550 cm^-1 band range as seen in the figure 9

 

5.2 Scanning Electron Microscopy (SEM):

In order to obtain information on surface morphologies, SEM analysis was carried out. The results were as seen below. Magnification was done in a range of 717 X to 2000 X. From the EDX analysis that is shown in Fig.10 (b) it can be seen that the presence of carbon and oxygen is prominent in the raw sugarcane bagasse.

 

Fig. 10 (a). SEM image for raw sugarcane bagasse,               (b). SEM-EDX for raw sugarcane bagasse

 

Figure 11(a) shows the SEM image for the sugarcane bagasse treated with propionic acid. It was done for a magnification of 2000 X. It can be observed that the surface was subjected to modification when treated with the acid. This can be easily identified from the pores developed on the surface. From the Figure10 (b) and 11(b) it was seen that the carbon weight% increased from 53.46 to 57.27 and the oxygen showing the addition of propionic acid.

 

Fig. 11(a). SEM image for BMPA,                                                      Fig 13(b).  SEM-EDX  for BMPA

 

Fig. 12 (a). SEM image for sugarcane bagasse after adsorption of methylene blue dye,

(b). SEM-EDX for Sugarcane bagasse after Adsorption of Methylene blue dye

 

SEM analysis for sugarcane bagasse after adsorption of methylene blue was done at a magnification of 2000 X as seen in Fig.12 (a). The presence of Cl, S, N, C  in Fig.12(b) conforms the adsorption of methylene blue dye by the sugarcane bagasse.

 

5.3 X-Ray diffraction (XRD) analysis:

The XRD graphs for the sugarcane bagasse at the three stages are as given below. All the three graphs were similar in shape. Presence of the sharp peaks at 15 and 22 in Figure 13(a), 13(b) and 13(c) indicates the evidence of treatment on fibers of the sugarcane bagasse. The increase in the inter planar distance in relation with the bagasse fibers are indicated by the position of the peaks (Pereira et al. 2011). This is due to the changes that the surface undergoes when it is treated with propionic acid and the adsorption of dye by the sugarcane bagasse.

 

          

13 (a)                                                                                                                  13(b)

 

13(c)

Fig13 (a). XRD graph for raw sugarcane bagasse, (b). XRD graph for BMPA, (c) XRD graph for sugarcane bagasse after adsorption of methylene blue dye

 

6. CONCLUSION:

The study on BMPA showed that it is an effective adsorbent and it can be used for the removal of methylene blue dye from water. The effective contact time was found to be 8 minutes after which it was saturated. The optimum adsorbent dosage was found to be 0.6 g and adsorbent size was 0.15 mm. The efficient pH value was found to be 7 and agitation value was 250 rpm. The adsorption mechanism showed that it followed Langmuir isotherm and the kinetic study indicated that it followed the pseudo-second order reaction. It can therefore be concluded that the BMPA can be used as an eco-friendly and economical adsorbent and can replace the more expensive adsorbents like the activated carbon for removal of dyes from water.

 

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