International Research Journal of Environment Sciences________________________________ ISSN 2319–1414Vol. 3(6), 48-55, June (2014) Int. Res. J. Environment Sci. International Science Congress Association 48 Removal of Phenol from Wastewater Using Chemically Treated Coconut Stalk: (CocosnuciferaGirish C.R.and Swaroop M. ShajahanDepartment of Chemical Engineering, MIT, Manipal University, Manipal – 576104, INDIA Available online at: www.isca.in, www.isca.me Received 15th May 2014, revised 8th June 2014, accepted 18th June 2014 AbstractIn the present work, the potential of coconut stalk, an agricultural material reused as adsorbent for the phenol removal from wastewater was investigated. The influence of different experimental parameters on the adsorption was investigated. The experimental data were analysed by the various isotherm models. The data were found to follow Freundlich model showing that the process was physical adsorption. The kinetic data were tested by different kinetic equations. The kinetic data obeyed pseudo-first-order kinetic equation. The adsorption capacity of the adsorbent was found to be 38.24 mg/g. Keywords: Coconut stalk, phenol, kinetic, equilibrium, adsorption capacity. IntroductionPhenol and its derivative compounds are one of the organic pollutants that are toxic to human beings and to the environment and are designated as priority pollutants. The wastewater released from different industries like petroleum refineries, petrochemical, textile, leather, coal conversion, wood preserving industry, phenolic resin, paint manufacturing, ferrous industry, rubber and pulp and paper industries contains an array of pollutants. Phenol is considered to be one of the key pollutants found in these wastewaters, since it is having wide variety of commercial applications. The phenol will have harmful effect on both human beings and environment in various ways. The European Union laid a ceiling concentration of maximum 0.5 g/l of total phenol in drinking water. A number of treatment methods like biodegradation, biosorption, membrane separation, pervaporation, extraction, distillation and adsorption using activated carbons prepared had been reviewed by Girish and Murty to remove phenolic compounds. Activated carbon is used for the phenol removal from wastewater by adsorption. But the drawback with the activated adsorbent is costly and it has to be produced from starting material which is expensive. This has urged a flourishing research interest for the activated carbon production from various agricultural by-products for wastewater treatment. Girish and Murty reviewed the various agricultural by-products utilized for activated carbon production. These by products were found to be cheap, renewable, easily available and effective alternative materials for the adsorption process. A number of raw materials have been used as adsorbents for the phenol removal from wastewater. These include rubber seed coat, tamarindusindica10, beet pulp11, coir pith12, rice husk ash13 and jute fibre14. The present work explores the suitability of coconut stalk based chemically treated carbon for the phenol removal from aqueous solutions. The investigation of effect of variables like pH, dosage and temperature on adsorption was studied. To verify the various adsorption isotherm, kinetic models for the process and the adsorption capacity. Material and Methods Adsorbent preparation: Coconut leaves stalk (Cocosnucifera) were collected from South Travancore region. The material was initially cleaned to remove all the dirt matter and dried at 50C for 24 hours. It was grinded and sieved to fine size particles. The proximate analysis of the raw carbon sample was carried out. The adsorbent was prepared by treating the raw carbon with different chemicals like 2M sulphuric acid, 2M phosphoric acid and 2M hydrochloric acid. Initially the powder was mixed with the various chemicals overnight and was dried in an oven at 80C for 5 hours15. Then excess water was added to remove excess of chemical and washing is carried out till a clear solution was obtained and pH was stabilised. The removal capacity of phenol, particle size and surface area for all the chemically treated carbons was studied. Then depending on the initial experimental results, adsorbent treated with HCl was considered for further experiments. Characterization of adsorbent: The moisture content was found by heating the carbon sample in an oven heated at 110C for 60 minutes. The left carbon residue was heated in a muffle furnace at 750C for about 8 h and at 900C for 10 minutes to estimate the ash content and volatile matter respectively. The adsorbent particle size was evaluated by Particle size analyser (CILAS 1064, France). The determination of surface area and pore volume were found using BET apparatus (Smart Instruments, Mumbai). The functional groups of carbon surface were estimated by Fourier transform infrared (FTIR) spectroscopy instrument (Shimadzu, Japan). International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(6), 48-55, June (2014) Int. Res. J. Environment Sci. International Science Congress Association 49 Adsorbate: The analytical grade Phenol was obtained from Merck India Ltd. The stock solution prepared by dissolving the calculated quantity of phenol in distilled water. The solutions of required initial concentration 25 to 150 mg/L were prepared by diluting from the original stock solution. Hydrochloric acid, Sulphuric acid and Orthophosphoric acid purchased from SD Fine Chemicals, India, AR grade were used for the chemical treatment of carbon. Adsorption Experiments: The variation of experimental conditions like pH, adsorbent dose, contact time and temperature on the adsorption were studied for the phenol removal from aqueous solution. The solution pH was varied from 2 to 12 by the addition of either 0.1 M NaOH or 0.1 M HCl to the solution and the carbon dosage varied from 0.25 to 4.5 gfor the initial experiments. After optimizing the above parameters, the isotherm and dynamic studies were performed. The equilibrium experiments were conducted in 250 mL conical flasks containing 200mL of different concentrations (25, 50, 75, 100, 125 and 150mg/L) of phenol under the optimum conditions. The flasks were agitated in a thermo shaker at 130rpm speed and 298 K for 6 h till equilibrium was established. After the equilibrium time, the phenol concentration were analysed using double beam U-V spectrophotometer (UV-1700, Shimadzu, Japan) by measuring the absorbance at a wavelength of 270 nm. All the experiments were conducted in duplicates. The phenol adsorbed per gram of carbon () was determined using the expression: qe=  \n (1) where  is the equilibrium adsorption capacity (mg/g), is the volume of phenol solution (L), is the phenol initial concentration (mg/L), \r is the phenol equilibrium concentration (mg/L), and (g) is the mass of the carbon powder taken. The percentage removal of the phenol is given by %Removal =   (2) The dynamic studies performed were similar to those of equilibrium experiments except that the samples were collected regularly and the phenol concentration was estimated. The adsorption capacity at time t, q, is given by:  \n (3) Results and Discussion Characterisation of the adsorbent: The proximate analysis of the raw carbon obtained showed volatile matter, moisture content, ash and fixed carbon content to be 37%, 5.1%, 7.2% and 50.7% respectively. The particle size, surface area and removal capacity of various chemically treated carbons are examined and shown in table 1. From the obtained results, the carbon treated with was taken for further studies. The FTIR spectra of adsorbent treated with HCl before and after phenol adsorption are shown in figure 1. From the spectra it was shown that the peak at 3394 cm 1 is because of O-H stretching in phenol, the peak at 2854 cm 1 is assigned to O-H of carboxylic group, the peak at 1266 cm 1 indicates the C-O bond of carboxylic acid, the band at 879 cm 1 is because of C-H bond of aromatic group. The band at 1627 cm 1 is because of C=C aromatic ring stretching [16, sub 10] and the band at 1033 cm 1is because of stretching vibration of C-O of carboxyl group16. From the figure it was observed that the peaks of C-O bond of carboxylic acid and C=C aromatic changed from 1266 cm 1 and 1627 cm 1 to 1218 cm 1 and 1589 cm-1 respectively. Table-1 The table showing the various properties of chemically treated carbons Carbons (treated with chemicals) Untreated H 3 PO 4 H 2 SO 4 HCl Specific surface area m/g 109.62 215.43 185.20 348.13 Pore volume, /g 0.1086 0.2211 0.1856 0.2717 Particle size, µm 30.55 16.95 13.25 11.09 % Phenol removal 70.26 82.3 86.8 92.4 Influence of pH: The pHalters the ionization of the phenol molecule17. Phenol is having a low dissociation tendency with pKa value of 9.8. When pH of the solution is more than pKa, then phenol dissociates into phenolate ions and there is repulsion forces between phenolate ions and negatively charged carbon surface. This will lead to decrease in adsorption. At pH of the solution less than the pKa value, unionized phenol gets attracted to the positively charged carbon surface and thus the adsorption increases. As can be seed from the figure 2, the decrease in removal upto pH 7 was gradual, thereafter it decreases abruptly. Therefore the optimum value of pH was found to be 7.5. The same nature of results were observed in work18. Effect of adsorbent dosage: The influence of carbon dose on phenol removal was investigated by conducting the experiments at adsorbent dosages of 0.25 to 4.5 g. Figure 3 show the influence of carbon dosage on the phenol removal. It was found that the phenol removal increased by increasing adsorbent dosage. After the equilibrium, it was found that53.9 to 90.4% removal was obtained for carbon dosage of 0.25 to 1.5 g/l respectively. It was found that the phenol removal increased due to the enhancement of the sorption surface and increase in the number of adsorption sites19. It was found that the optimum carbon dosage was 1.5 g/l respectively. Similar results were obtained in work20. International Research Journal of Environment Vol. 3(6), 48-55, June (2014) International Science Congress Association The FTI Environment Sciences_______________ _________________________ International Science Congress Association Figure-1 The FTI R of coconut stalk before and after adsorption Figure-2 Plot of pH v/s % removal of phenol _________________________ ______ ISSN 2319–1414 Int. Res. J. Environment Sci. 50 International Research Journal of Environment Vol. 3(6), 48-55, June (2014) International Science Congress Association Figure-3 Plot of adsorbent dosage v/s percent removal of phenol Figure-4 Plot of temperature v/s % removal of phenol The effect of temperature: The influence of temperature on the phenol removal at various concentrations, onto adsorbent treated with HCl were investigated and shown in experiments were conducted at different temperatures of 298,308, 318 and 3 28 K. It is observed from the the % removal of phenol decreased by increasing temperature from 298 to 328K. This may be because of decreased active sites on the surface showing that adsorption between phenol and HCl treated carbon follows an exothermic process. Further experiments were carried out at 298 K. Isotherm Studies: The experimental data was investigated with the various isotherm models. The Langmuir isotherm proposed for adsorption on the surface having a fixed number of unifo rm sites in a single layer. The model explains adsorption occurring uniformly on the adsorbent and distribution of energy takes place uniformly on the surface. Environment Sciences_______________ _________________________ International Science Congress Association Plot of adsorbent dosage v/s percent removal of phenol Plot of temperature v/s % removal of phenol The influence of temperature on the phenol removal at various concentrations, onto adsorbent treated with HCl were investigated and shown in figure 4. The experiments were conducted at different temperatures of 28 K. It is observed from the figure 4, that the % removal of phenol decreased by increasing temperature from 298 to 328K. This may be because of decreased active sites on the surface showing that adsorption between phenol and exothermic process. Further The experimental data was investigated with Langmuir isotherm 21is proposed for adsorption on the surface having a fixed number of rm sites in a single layer. The model explains adsorption occurring uniformly on the adsorbent and distribution of energy The Langmuir isotherm is given by:  =   Where Ce is the adsorbate concentration at equilibrium, qe is the adsorption capacity at equilibrium, Q constants.The values of  and are calculated from the plot of \r versus \r (Figure 5). The experimental data were proposed to Langmuir isotherm and the isotherm constants with the regression coefficient values are represented in The important parameter of the Langmuir model is the dimensionless constant called the separation factor, R by: =  ! where b is the Langmuir constantand the values of R type of isotherm22 . The adsorption is irreversible for R favourable for 0 R 1, linear for R �1.The values of R were varying from 0.170039 to 0.551419906 which shows favourable adsorption. The Freundlich isotherm explains that adsorption occurs on heterogeneous surfaces and interaction occurs between adsorbate molecules. It also explains that the energy of adsorpt ion decreases exponentially with the adsorption process23. The Freundlich equation is given by logq = log K+ log Ce where q is amount adsorbed at equilibrium (mg /g), C adsorbate equilibrium concentration (mg/ L), K constant (mg/ g)(L/mg)1/n and 1/n is dimensionless constant. The linear plot of ln against ln  of and . The determined values of K coefficient for Freundlich model are represented in Figure - Linearized form of Langmuir isotherm _________________________ ______ ISSN 2319–1414 Int. Res. J. Environment Sci. 51 The Langmuir isotherm is given by: (4) concentration at equilibrium, qe is the adsorption capacity at equilibrium, Q and b are isotherm are calculated from the plot of The experimental data were proposed to Langmuir isotherm and the isotherm constants with the regression coefficient values are represented in table 2. The important parameter of the Langmuir model is the dimensionless constant called the separation factor, R , given (5) where b is the Langmuir constantand the values of R L shows the . The adsorption is irreversible for R = 0, 1, linear for R = 1 and unfavourable for were varying from 0.170039 to 0.551419906 which shows favourable adsorption. The Freundlich isotherm explains that adsorption occurs on heterogeneous surfaces and interaction occurs between adsorbate molecules. It also explains that the energy of ion decreases exponentially with the adsorption The Freundlich equation is given by (6) adsorbed at equilibrium (mg /g), C e is equilibrium concentration (mg/ L), K is the isotherm and 1/n is dimensionless constant.  (Figure 6) gives the values The determined values of K , n and the regression coefficient for Freundlich model are represented in table 2. - 5 Linearized form of Langmuir isotherm International Research Journal of Environment Vol. 3(6), 48-55, June (2014) International Science Congress Association Figure-6 The linear plot of Freundlich isotherm The Temkin isotherm24 was investigated to study the energy distribution pattern in the adsorbent layers and also the interactions between adsorbate. The Temkin isotherm is given by lnq = B ln A + B lnC where A and B are isotherm constants. The linear plot of Temkin isotherm plot is shown in f ig corresponding isotherm parameters are given in table 2, it shows that the experimental data follows Freundlichisotherm model with R = 0.99881than the Langmuir isotherm with R = 0.97132 and Temkin isotherm with R 0.93544. It also suggests that adsorption occurs on heterogeneous sites in multilayers on the adsorbent with random distribution of energy level. The values of different isotherm The various isotherm constants for adsorption Langmuir isotherm   (mg/g)  (L/mg) 2 (mg/g)/ (l/mg) 38.24 0.03254 0.97132 The monolayer adsorption Adsorbent rubber seed coat tamarindusindica beet pulp coir pith rice husk ash jute fibre coconut stalk Environment Sciences_______________ _________________________ International Science Congress Association The linear plot of Freundlich isotherm was investigated to study the energy pattern in the adsorbent layers and also the (7) The linear plot of ig ure 7 and the corresponding isotherm parameters are given in table 2. From it shows that the experimental data follows = 0.99881than the Langmuir = 0.97132 and Temkin isotherm with R = also suggests that adsorption occurs on heterogeneous sites in multilayers on the adsorbent with random distribution of energy level. The values of different isotherm constants are shown in t able 2. Thecomparison of different adsorbents and coconut stalk adsorbent with their capacities are represented in table 3. From t able 3, it can be concluded that coconut stalk material is an effective adsorbent for removing phenol from wastewater. Figure - Linearized plot of Temkin isotherm Kinetics of the adsorption: The dynamic studies have been conducted to explain the adsorption mechanism. From the different kinetic models, it was concluded that the adsorption depends on the chemical nature of material, experimental conditions and the mas s transfer process. Therefore, the various kinetic models were tested to explain the adsorption mechanism process and the rate- determining step. Table-2 The various isotherm constants for adsorption Freundlich isotherm Temkin isotherm $ % (mg/g)/ (l/mg) (1/n)n R B 1.3499 1.20231 0.9981 0.6705 Table-3 The monolayer adsorption capacity of various adsorbents m (mg/g) 56 80 89.5 48.31 14.382 181 38.24 _________________________ ______ ISSN 2319–1414 Int. Res. J. Environment Sci. 52 able 2. Thecomparison of different adsorbent with their capacities are able 3, it can be concluded that coconut stalk material is an effective adsorbent for removing - 7 Linearized plot of Temkin isotherm The dynamic studies have been conducted to explain the adsorption mechanism. From the different kinetic models, it was concluded that the adsorption depends on the chemical nature of material, experimental s transfer process. Therefore, the various kinetic models were tested to explain the adsorption mechanism determining step. Temkin isotherm & (L/mg) 5.12807 0.93544 Reference 9 10 11 12 13 14 Present work International Research Journal of Environment Vol. 3(6), 48-55, June (2014) International Science Congress Association The Lagergrenpseudo-first- order kinetic model log (q-q) = log q – ()*+,-, t where qt is the adsorption capacity at any time (mg/g) and k the rate constant,(min 1) for the pseudo-first - rate constantkad and adsorption capacity qe were obtained from the linear plots of log (qe- qt) versus t (as shown in values ofad and the regression coefficient are represented in table 4. It was observed that the regression coefficient values for the pseudo-first- order kinetic model were high. It was also found that th e theoretical values agreed closely with the experimental values supporting the pseudo - model which shows reversible physical adsorption nature of result was reported by works26, 27. Figure-8 The plot showing the pseudo-first- order kinetic model Figure-9 The plot showing pseudo-second- order model The pseudo-second- order kinetic model is given by Ho ./0 = + t Environment Sciences_______________ _________________________ International Science Congress Association order kinetic model 25 is given by (8) qt is the adsorption capacity at any time (mg/g) and k ad is - order model. The adsorption capacity qe were obtained from qt) versus t (as shown in figure 8) The and the regression coefficient are represented in coefficient values for order kinetic model were high. It was also e theoretical values agreed closely with the - first-order kinetic model which shows reversible physical adsorption 25. Similar order kinetic model order model order kinetic model is given by Ho 28 (9) where h is the adsorption rate (mg/g.min) and k is the rate constant for the pseudo-second- order model (g/ mg. min). The values of q and k are obtained from the linear plot of t /q versus t, shown in figure 9. The experimental and theoretical values, along with regression coefficients are represented in table 4. It can be obse rved from Table 4, that for the adsorbent, the R values were relatively low and the experimental and theoretical values of adsorption capacity deviated to a large extent. Thus showing a poor fit of experimental result to the second order model. The diff usion mechanism can be understood by investigating the Weber and Morris model29= k t1/2 + C where, C is the boundary layer thickness and intraparticle diffusion rate constant. The values of C and k obtained from the slope and intercept of the plot of which is shown in figure 10. The values of diffusion constant k are shown in plot passes through the origin, then intr be the rate determining step. From the the intraparticle diffusion is not the Figure- 10 The linear plot of intraparticle diffusion model ConclusionIn the current study, showed that chemically treated adsorbent produced from coconut stalk was an phenol removal from aqueous solution. The characterisation of the adsorbent carried out signifies the efficacy of the adsorbent. It was investigat ed that the removal capacity was found to vary with adsorbent dosage, initial concentration, pH and temperature. The equilibrium data followed the Freundlich isotherm and the kinetic data obeyed pseudo The plots for intra particle diffus ion model do not pass through the origin, signifying that more than one step affects the adsorption. The equilibrium adsorption capacity was 38.24 mg/g. _________________________ ______ ISSN 2319–1414 Int. Res. J. Environment Sci. 53 where h is the adsorption rate (mg/g.min) and k is the rate order model (g/ mg. min). The and k are obtained from the linear plot of t /q t 9. The experimental and theoretical q values, along with regression coefficients are represented in rved from Table 4, that for the adsorbent, values were relatively low and the experimental and theoretical values of adsorption capacity deviated to a large extent. Thus showing a poor fit of experimental result to the usion mechanism can be understood by investigating the (10) is the boundary layer thickness and p is the intraparticle diffusion rate constant. The values of C and k p are obtained from the slope and intercept of the plot of versust1/2 10. The values of intra particle are shown in table 5. If the qt versus t1/2 passes through the origin, then intr aparticle diffusion will From the figure. 10, it signifies that rate determining step. 10 The linear plot of intraparticle diffusion model study, showed that chemically treated adsorbent produced from coconut stalk was an prospective adsorbent for phenol removal from aqueous solution. The characterisation of the adsorbent carried out signifies the efficacy of the adsorbent. ed that the removal capacity was found to vary with adsorbent dosage, initial concentration, pH and temperature. The equilibrium data followed the Freundlich isotherm and the kinetic data obeyed pseudo -first-order model. ion model do not pass through the origin, signifying that more than one step affects the adsorption. The equilibrium adsorption capacity was 38.24 International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(6), 48-55, June (2014) Int. Res. J. Environment Sci. International Science Congress Association 54 Table-4 The constants of pseudo-first-order and pseudo-second-order kinetic models Pseudo first order kinetic Pseudo second order kinetic conc, mg/L Qe,exp,(mg/g) * 10 - (min-1) Qe,cal (mg/g) Qe,cal (mg/g) * 10 - 4 (g/mg.min) h (mg/g.min) 25 3.08 7.254 2.9475 0.96376 3.953 7.7055 0.03046 0.9806 50 6.1066 6.932 5.7806 0.96862 7.9365 9.108 0.05737 0.97778 75 9.08 6.8399 8.6678 0.97303 11.9517 5.74 0.0821 0.97724 100 12.053 6.72 11.593 0.97927 16.12 4.002 0.1040 0.97562 125 14.946 6.632 14.459 0.98094 20.24 3.04 0.1246 0.97398 150 17.852 6.471 17.374 0.98259 24.48 2.38 0.14267 0.96964 Table-5 The values of constants of intraparticle diffusion model Intraparticle diffusion Conc Ki c R 2 25 0.15719 0.11232 0.94101 50 0.31359 0.09475 0.95553 100 0.46889 0.01276 0.96678 150 0.66741 -0.5847 0.97126 200 0.82909 -0.5736 0.98238 250 0.92884 -0.2171 0.97531 References 1.Banat, F. 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