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Reduction of COD and color of dyeing effluent from a cotton textile mill by adsorption onto bamboo-based activated carbon
Journal of Hazardous Materials 172 (2009) 1538–1543
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Reduction of COD and color of dyeing effluent from a cotton textile mill by adsorption onto bamboo-based activated carbon A.A. Ahmad, B.H. Hameed ∗ School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia
a r t i c l e
i n f o
Article history: Received 21 March 2009 Received in revised form 6 August 2009 Accepted 6 August 2009 Available online 13 August 2009 Keywords: Bamboo waste Activated carbon Textile effluent Adsorption Isotherms
a b s t r a c t In this work, activated carbon was prepared from bamboo waste by chemical activation method using phosphoric acid as activating agent. The activated carbon was evaluated for chemical oxygen demand (COD) and color reduction of a real textile mill effluent. A maximum reduction in color and COD of 91.84% and 75.21%, respectively was achieved. As a result, the standard B discharge limit of color and COD under the Malaysian Environmental Quality act 1974 was met. The Freundlich isotherm model was found best to describe the obtained equilibrium adsorption data at 30 ◦ C. The Brunauer–Emmett–Teller (BET) surface area, total pore volume and the average pore diameter were 988.23 m2 /g, 0.69 cm3 /g and 2.82 nm, respectively. Various functional groups on the prepared bamboo activated carbon (BAC) were determined from the FTIR results. © 2009 Elsevier B.V. All rights reserved.
1. Introduction In Malaysia as well as in all Asian countries, textile industry is very flourishing with the attendant large volumes of highly contaminated effluent wastewater containing: detergents, oils, suspended and dissolved solids, toxic, biodegradable and non-biodegradable matters, dyes and alkaline substances [1,2] that poses serious environmental problems because of their color and high organic matter (COD) [3,4]. Considering a typical cotton textile mill in Penang, Malaysia, the main textile processes start from fiber production in the case of synthetic fiber, followed by spinning to convert the fiber to yarn. Yarn is then strengthened with sizing chemicals like starch, polyvinyl alcohol and wax so that it can withstand vigorous movements when weaved into fabric in high speed weaving looms. The fabric weaved must then be pretreated before dying, printing and finishing. Various chemicals are used in the pretreatment. Fabrics are de-sized with either enzyme or oxidative chemicals and scoured using sodium hydroxide and detergents. Bleaching is normally done using hydrogen peroxide to remove the natural color of the fiber and to make the fabric white. Fabric is then mercerized using highly concentrated sodium hydroxide for stabilization. During dyeing and printing operations, many types of dyes are used e.g., disperse, reactive, vat, etc. in the presence of dyeing auxiliaries and chemicals [5].
∗ Corresponding author. Tel.: +60 45996422; fax: +60 45941013. E-mail address: [email protected] (B.H. Hameed). 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.08.025
Consequently, the amount of wastewater generated from all these processes is very high and highly contaminated [6]. The current wastewater treatment scheme at the study site consists of screening, pre-neutralization, anaerobic lagoon, post-neutralization, activated sludge process and sedimentation. However, this existing wastewater treatment scheme is inadequate (Table 1) to produce treated wastewater that meets the local discharge limits, especially in terms of COD and color [5]. Biological treatment process is generally efficient in biological oxygen demand (BOD), reduction and screening also addresses the suspended solids removal to a reasonable extent, but the dissolved non-biodegradable complex organic dyes is a main challenge to the existing treatment units [7]. Conventionally, adsorption processes using activated carbons are widely used to remove color and heavy metal pollutants from wastewaters. However, commercially available activated carbon is becoming too expensive. In the last few years, special emphasis has been placed on the preparation of activated carbons from several agricultural by-products due to the growing interest in low-cost activated carbons from renewable sources, especially for application in wastewater treatment. Researchers have studied the production of activated carbon from sugar beet bagasse [8], apricot shell [9], sunflower seed hull [10], coconut shells [11], rubber seed coat [12], oil palm fiber [13], rattan [14], date stones [15], plum kernels [16] and palm empty fruit bunch [17]. Bamboo is a grass, the most diverse group of plants in the grass family. It is an enduring, versatile, highly renewable material and abundant natural resource in Malaysia because it takes only few months to grow to maturity. It has been traditionally used to con-
A.A. Ahmad, B.H. Hameed / Journal of Hazardous Materials 172 (2009) 1538–1543
struct various living facilities and tools [18]. Bamboo has been used for furniture and construction it is longer than other hardwoods, strong, tough and low-cost material. Conversion of bamboo to a value-added product such as activated carbon will help to solve part of the problem of wastewater treatment in Malaysia [19]. The advantage of using agricultural by-products as raw materials for manufacturing activated carbon is that these raw materials are abundant, renewable and potentially less expensive [20]. Activated carbons are produced by physical or/and chemical activation methods. Physical activation involves two stages, carbonization and subsequent partial gasification with steam, carbon dioxide or air, usually at high temperature (800–1000 ◦ C), while chemical activation requires only one stage and at lower temperature (450–700 ◦ C) in comparison to physical activation. Therefore, it can improve the pore development in the carbon structure, leading to high adsorption capacity, reduced reaction time and higher product yield [21]. The chemical activation of lignocellulosic materials with phosphoric acid has been extensively investigated from the development of porosity [22–25] and mechanism of degradation from the precursor point of view [26,27]. The purpose of this work was to prepare activated carbon from bamboo waste (BAC) by chemical activation method using phosphoric acid and to find out the possibility of using this adsorbent for the color and COD reduction in real dyeing wastewater from a cotton textile mill operating in Penang State, Malaysia. 2. Materials and methods 2.1. Sampling Textile wastewater (TWW) samples at the factory’s discharge point after the activated sludge treatment unit were collected from a cotton textile mill in Penang, Malaysia. The main products of this industry is white, dyed and printed 100% cotton and polyester/cotton blended woven fabric with a production rate of about 10 million yards a month. The main processes are pretreatment, dyeing, printing and finishing. The plant produces about 250 m3 /h of water with main pollutants as given in Table 1 [28]. The samples were stored at ≤5 ◦ C to avoid any change in its physico-chemical characteristics before use. Table 1 shows the basic quality parameters of the wastewater samples i.e. BOD, COD, color, pH, temperature, suspended solids, turbidity, conductivity, oil and grease, which were analyzed in our laboratory according to the methods prescribed in APHA [29]. Table 1 shows the original effluent has a color and COD of 450–650 Pt/Co and 200–260 mg/L, respectively. 2.2. Preparation and characterization of activated carbon Raw material (bamboo waste) was collected from a local furniture shop, Penang State, Malaysia. It was washed with hot
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distilled water to remove dust-like impurities, dried at 105 ◦ C, ground and sieved (200–300 m) to discrete sizes. Chemical activation method using phosphoric acid (purity 85% Merck, Germany) was used to activate the raw material. In a typical batch production, 40 g of raw material was impregnated by certain amount of 40 wt% concentrated phosphoric acid with occasional stirring. The amount of phosphoric acid solution used was adjusted to give a certain impregnation ratio. Subsequently, the impregnated samples were air dried under sunlight for 3 days. Activation of the phosphoric acid impregnated precursor was carried out at temperature of 500 ◦ C for 2 h under purified nitrogen (99.995%) flow (150 cm3 /g) at a heating rate of 10 ◦ C/min in a horizontal tubular furnace. After activation, the sample was cooled to room temperature with the same heating rate and washed sequentially several times with hot distilled water (70 ◦ C) until the pH of the washing solution reached 6–7. Finally the sample was dried in an oven at 110 ◦ C for 24 h and then stored in plastic containers. The activated carbon yield was calculated based on Eq. (1). Yield (%) =
wc × 100 wo
(1)
where wc is the dry weight of final activated carbon and wo is the dry weight of precursor. Textural characterization of the BAC was carried out by N2 adsorption at 77K using ASAP 2020 Micromeritics instrument by Brunauer–Emmett–Teller (BET) method, using the software of Micromeritics. The Brunauer–Emmett–Teller (BET), Langmuir surface area, total pore volume for pores, and average pore diameter were thus determined. Surface morphology and the presence of porosity of the activated carbon prepared in this work were studied using scanning electron microscopy (SEM) analysis (Model Leo Supra 50VP Field Emission, UK). In addition, the surface functional groups of the prepared activated carbon were detected by Fourier transform infrared (FTIR) spectroscope (FTIR-2000, Perkin-Elmer). The spectra were recorded from 4000 to 400 cm−1 . 2.3. Batch mode treatment of wastewater samples All the experiments were carried out at temperature 30 ◦ C in batch mode. The experiments were run in different flasks of 250 mL capacity using an average shaker’s speed of 120 rpm. The influence of various operating parameters was studied by varying one parameter and keeping the others constant. The desired pH was maintained using dilute NaOH (0.1N)/HCl (0.1N) solutions. The initial COD and color index were 251.65 mg/L and 486.87 Pt/Co, respectively. To determine the contribution of the adsorbent dose to color and COD reduction, 100 mL of sample was treated with different doses of adsorbent ranging between 0.10 and 1.0 g, the other conditions includes treatment time of 24 h, pH of 3 and initial
Table 1 Physico-chemical analysis of textile wastewater (final effluent-after biological treatment). Parameters pH Temperature BOD COD Color Turbidity (Nephalometer turbidity unit) Conductivity Suspended solid Oil and grease
Unit
Value
Standard Ba
– C mg/L mg/L Pt/Co NTU mS/cm mg/L mg/L
7–8 27–30 <50 200–260 450–650 11.44 2.25 <50 3–5
5.5–9.0 – 50 100 – – – – –
◦
a Environmental Quality (Sewage and Industrial Effluents) Regulations, 1979, under the Laws of Malaysia-Malaysia Environmental Quality Act 1974 [28]. Standard B refers to discharges outside catchment area.
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3. Results and discussion 3.1. BET, SEM and FTIR of the activated carbon
Fig. 1. SEM image of bamboo-based activated carbon (magnification = 500×).
color and COD of the sample were 486.87 Pt/Co and 251.65 mg/L, respectively. The pH studies were performed with constant initial concentration, adsorbent dose (0.30 g) and contact time 28 h but with varying pH from 2 to 12 using dilute NaOH or HCl solutions for the adjustment. Effect of contact time of the adsorbent with wastewater samples was investigated by agitating 100 mL sample, pH 3, constant initial concentrations and adding 0.30 g adsorbent for different time periods varying between 1 and 28 h. At elapse of each set contact time, thus the treated wastewater sample was filtered through 0.45 m filter papers before analyses. The samples were analyzed using a DR2800 spectrophotometer (CECIL 1000 series, Cambridge, UK) at wavelengths of 620 and 455 nm for COD and color, respectively. The amount of adsorption at equilibrium, qe , was calculated from Eq. (2): qe =
(Co − Ce )V m
(2)
where Co and Ce are the liquid-phase concentrations of adsorbate at initial and at equilibrium, respectively. V (mL) is the volume of the solution and m (g) is the mass of dry adsorbent used. The reduction percentage at time t can be calculated as follows: %=
Co − Ct × 100 Co
(3)
The BET surface area, Langmuir surface area, total pore volume and average pore diameter of the prepared activated carbon were 988.23 m2 /g, 1561.164 m2 /g 0.696 cm3 /g and 2.82 nm, respectively. The maximum value of activated carbon yield was found to be 30.213%. Besides, the average pore diameter of the activated carbon was found to be 2.82 nm, indicating that the activated carbon prepared was in the mesopores region according to the International Union of Pure and Applied Chemistry (IUPAC), pores are classified as micropores (<2 nm diameter), mesopores (2–50 nm diameter) and macropores (>50 nm diameter) [30]. The phosphoric acid incorporated into the interior of the precursor particle restricted the formation of tar as well as other liquids such as acetic acid and methanol and inhibited the particle shrinkage or volume contraction during heat treatment. On one hand, the restricted shrinkage and limited volatile release might facilitate the conservation of porous structures present in the precursor. On the other hand, after washing the final product, the extraction of deeply penetrated acid led to the creation of tremendous porosity. This also resulted in high yield for the adsorbent than did the thermal activation process [26]. However, the carbons with an enhanced mesoporosity can be obtained from phosphoric acidpromoted activated carbon by subsequent activation [31]. Fig. 1 shows the SEM image of the derived activated carbon. Many large pores in a honeycomb shape were clearly found on the surface of the activated carbon. The well-developed pores had led to the large surface area and porous structure of the activated carbon. Fig. 2, the FTIR spectrum obtained for the prepared activated carbon displayed the following bands; 3736 and 3617 cm−1 was attributed to (O–H) vibrations in hydroxyl groups. The location of hydrogen-bonded OH groups, usually in the range of 3200–3750 cm−1 for alcohols and phenols, involved in hydrogen bonding may be due to adsorbed water [32]; 2373 cm−1 denotes C O stretching from ketones, aldehydes or carboxylic groups, while 1538 cm−1 is C C stretching vibration of the aromatic rings. The relatively intense band at 1052 cm−1 can be assigned to alcohol groups (R–OH) [33] whilst the band at 674 cm−1 is C–O–H twist broad. The FTIR spectra obtained was in agreement with the results reported in the studies carried out on activated carbons prepared from rice straws [34] and cherry stones [35]. The main surface functional groups present on the phosphoric acid impregnated BAC are presumed to be phenols, carboxylic acids (or carboxylic anhydrides
Fig. 2. FTIR spectra of BAC.
A.A. Ahmad, B.H. Hameed / Journal of Hazardous Materials 172 (2009) 1538–1543
Fig. 3. Effect of adsorbent dosage on the adsorption of color and COD onto BAC (temperature: 30 ◦ C, initial color concentration: 486.87 Pt/Co, initial COD concentration: 251.65 mg/L, pH 3, V = 100 mL).
if they are close together) and carbonyl groups (either isolated or arranged in quinone-like fashion), all of which are typical acidic functional groups [26]. These acidic surface functional groups are favourable for removal of color and COD [26]. 3.2. Effect of activated carbon dose Fig. 3 gives the variation of percentage reduction for the color and COD removal versus BAC dose. The color and COD removal increased with increase in the quantity of BAC up to 0.30 g, thereafter, any increase did not exert any significant increase in the removal of either COD or color. The maximum percentage of color and COD removed form the textile wastewater are noted as 89.139% and 72.116%, respectively by using 0.30 g. A similar observation was previously reported for the treatment of pulp and paper mill wastewaters with poly aluminium chloride and bagasse fly ash [36]. 3.3. Effect of solution pH The effect of solution pH was studied on color and COD reduction by BAC at temperature of 30 ◦ C, dosage of 0.30 g, 120 rpm shaker’s speed and initial COD and color concentrations of 251.65 mg/L and 486.87 Pt/Co, respectively. The solution pH was varied between 2 and 12. The result of this effect is as shown in Fig. 4. The maximum color and COD reduction obtained at pH 2–4. The reason for better adsorption capacity observed at lower pH levels might be attributed to the presence of larger number of H+ ions. This in turn, neutralized the negatively charged adsorbent surface. A lower
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Fig. 5. Effect of treatment time on the adsorption of color and COD on BAC (temperature = 30 ◦ C, initial color concentration: 486.87 Pt/Co, initial COD concentration: 251.65 mg/L, pH 3, m = 0.30 g/100 mL solution).
adsorption values at higher pH may be due to the abundance of OH− ions and because of ionic repulsion between the negatively charged active sites of the adsorbent. Similar results were reported for the treatment of pulp and paper mill wastewaters with poly aluminium chloride and bagasse fly ash [36]. 3.4. Effect of contact time on COD and color Fig. 5 shows the effect of contact time on percentage of reduction of color and COD. It is found that the rate of removal was rapid during the initial 1–8 h and thereafter, no significant change in the rate of removal was observed. Possibly, at the beginning, the solute molecules were adsorbed by the exterior surface of adsorbent particles, so the adsorption rate was fast. When the adsorption of the exterior surface reached saturation, the molecules will need to diffuse through the pores of the adsorbent into the interior surface of the particle. This phenomenon takes relatively long contact time. Fig. 5 indicates the formation of monolayer coverage at the outer interface of the adsorbents at the early stage. The curved portion shows the influence of monolayer adsorption and surface mass transfer, whereas the linear part at the later period of contact shows the effect of intra-particle diffusion. Color and COD reduction obtained at optimum conditions (pH 3, m = 0.30 g/100 mL and time 10 h, initial color concentration: 486.87 Pt/Co and initial COD concentration: 251.65 mg/L) were 91.84% and 75.21%, respectively. Table 2 lists the comparison of the maximum percentage of color and COD removed by various adsorbents. The activated carbon prepared in this work showed relatively large percentage of color and COD removed, as compared to some previous works reported in the literature. 3.5. Adsorption isotherms 3.5.1. Langmuir isotherm The Langmuir isotherm [42] which has been successfully applied to many other real adsorption processes was used to explain the adsorption of color and COD onto BAC. The data obtained from the adsorption experiment conducted during the present investigation was fitted using different adsorbent doses into the isotherm equation. The linear form of Langmuir isotherm equation is given as: Ce 1 1 = Ce + qe qm KL qm
Fig. 4. Effect of solution pH on the adsorption of color and COD onto BAC (temperature: 30 ◦ C, initial color concentration: 486.87 Pt/Co, initial COD concentration: 251.65 mg/L, m = 0.30 g/100 mL solution).
(4)
where Ce is the equilibrium concentration of the adsorbate, qe is the amount of adsorbate adsorbed per unit mass of adsorbent,
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Table 2 Comparison of the maximum percentage of color and COD removal by various adsorbents. Adsorbent types
Type of wastewater
COD removal (%)
Color removal %
Ref.
Bamboo-based activated carbon (BAC) Bagasse fly ash (BFA) Coconut shell carbon (ATSAC) Coconut fibers carbon (ATFAC) Rice husk carbon (ATRHC) Mixed adsorbent carbon (MAC) Carbon developed from fertilizer waste Pecan shell-based carbon dioxide-activated carbon (PSC) Powdered activated carbon (PAC)
Textile wastewater Pulp and paper wastewaters Industrial (mixed) Industrial (mixed) Industrial (mixed) Domestic Industrial Municipal wastewater Textile wastewater
75 50 46–71 50–74 45–73 96 >50 >70 78
91 55 – – – – – – 86
This work [36] [37] [37] [37] [38] [39] [40] [41]
qm and KL are Langmuir constants related to adsorption capacity and rate of adsorption, respectively. The saturation monolayer can be represented by plotting of Ce /qe versus Ce in a linear graphical relation indicating the applicability of the model for different adsorbent doses (figure not shown). The maximum adsorption capacities for color and COD were 29.154, 24.396 mg/L, respectively with R2 greater than 0.97. 3.5.2. Freundlich isotherm The Freundlich isotherm [43] is commonly used for a heterogeneous surface energy system. The well-known logarithmic form of Freundlich isotherm is given by the following equation: log qe = log KF +
1 log Ce n
(5)
where Ce is the equilibrium concentration of the adsorbate, qe is the amount of adsorbate adsorbed per unit mass of adsorbent, KF and n are Freundlich constants with n giving an indication of how favorable is the adsorption process and KF is the adsorption capacity of the adsorbent. The Freundlich isotherm has been illustrated to be a special case of heterogeneous surface energies but it can be easily extended to this case. The slope of 1/n ranging between 0 and 1 is a measure of adsorption intensity or surface heterogeneity, where the surface becomes more heterogeneous as its value gets closer to zero [44]. A value for 1/n below one indicates a normal Langmuir isotherm while 1/n above one is indicative of cooperative adsorption [45]. The plot of log qe versus log Ce (figure not shown) gave a straight line with slope of 1/n; whereas KF was calculated from the intercept value. The values of 1/n for color and COD were 0.342, 0.322 and the values of KF were 0.464, 0.191, respectively with R2 greater than 0.99. 3.5.3. Temkin isotherm The data were also fitted to Temkin and Pyzhev [46] isotherm. The heat of adsorption of all the molecules in the layer would decrease linearly with coverage due to adsorbate/adsorbate interactions [47]. The Temkin isotherm has been used in the form as follows: qe =
RT ln(KT Ce ) b
(6)
Eq. (6) can be linearized as: qe = B ln KT + B ln Ce
(7)
where RT/b = B. b and KT are constants. KT is the equilibrium binding constant corresponding to the maximum binding energy and constant B is related to the heat of adsorption. A plot of qe versus ln Ce (figure not shown) enables the determination of the isotherm constants KT and B. The values of constant B for color and COD were 80.47, 67.155 and the values of KT were 376.01, 224.84, respectively with R2 greater than 0.95. The three isotherms models have been tested and the equilibrium data fits well to all adsorption isotherms. The Freundlich model was found to be the best fit with R2 which were higher than
0.99 at the range of adsorbent doses considered. Conformation of the experimental data with the Freundlich isotherm equation indicated the heterogeneous nature of bamboo-based activated carbon surface. 4. Conclusions The present investigation revealed that bamboo is a promising precursor to be used in the preparation of activated carbon for the reduction of color and COD from cotton textile wastewater. It was converted by chemical activation into effective adsorbent with relatively large BET surface area and was found to be mesoporous. The equilibrium data fitted to Langmuir, Freundlich and Temkin isotherms. However, the equilibrium data were best described by Freundlich isotherm model. Under conditions pH 3, m = 0.30 g/100 mL solution and time = 10 h, color and COD reduction were found to be 91.84% and 75.21%, respectively. As a result, the standard B discharge limit of color and COD under the Malaysian Environmental Quality were met. The surface area of the bamboo-based activated carbon derived in this work was considered relatively high besides being mesopores. Acknowledgements The authors acknowledge the research grant provided by Universiti Sains Malaysia under the RU Grant Scheme (RU Grant No. 814005) that resulted in this article. References [1] A. Pela, E. Tokat, Color removal from cotton textile industry wastewater in an activated sludge system with various additives, Water Res. 36 (2002) 2920–2925. [2] B.Y. Gao, Y. Wang, Q.Y. Yue, J.C. Wei, Q. Li, Color removal from simulated dye water and actual textile wastewater using a composite coagulant prepared by polyferric chloride and polydimethyldiallylammonium chloride, Sep. Purif. Technol. 54 (2007) 157–163. [3] G. Chen, L. Lei, X. Hu, P.L. Yue, Kinetic study into the wet air oxidation of printing and dyeing wastewater, Sep. Purif. Technol. 31 (2003) 71–76. [4] D. Georgiou, J. Hatiras, A. Aivasidis, Microbial immobilization in a two stage fixed-bed reactor pilot plant for on-site anaerobic decolorization of textile wastewater, Enzyme Microb. Technol. 37 (2005) 597–605. [5] J.P.A. Dhas, Removal of colour and COD from textile wastewater using limestone and activated carbon, M.Sc. Thesis, University of Science Malaysia, Malaysia, 2006. [6] S.H. Lin, M.L. Chen, Treatment of textile wastewater by chemical methods for reuse, Water Res. 31 (4) (1997) 868–876. [7] P. Kumar, B. Prasad, I.M. Mishra, S. Chand, Decolorization COD reduction of dyeing wastewater from a cotton textile mill using thermolysis and coagulation, J. Hazard. Mater. 153 (2008) 635–645. [8] Y. Onal, C. Akmil-Bas, C. Sarıcı-Ozdemir, S. Erdogan, Textural development of sugar beet bagasse activated with ZnCl2 , J. Hazard. Mater. 142 (2007) 138–143. [9] B. Karagozoglu, M. Tasdemir, E. Demirbas, M. Kobya, The adsorption of basic dye (Astrazon Blue FGRL) from aqueous solutions onto sepiolite, fly ash and apricot shell activated carbon: kinetic and equilibrium studies, J. Hazard. Mater. 147 (2007) 297–306. [10] N. Thinakaran, P. Baskaralingam, M. Pulikesi, P. Panneerselvam, S. Sivanesan, Removal of Acid Violet 17 from aqueous solutions by adsorption onto activated carbon prepared from sunflower seed hull, J. Hazard. Mater. 151 (2008) 316–322.
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Reduction of COD and color of dyeing effluent from a cotton textile mill by adsorption onto bamboo-based activated carbon A.A. Ahmad, B.H. Hameed ∗ School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia
a r t i c l e
i n f o
Article history: Received 21 March 2009 Received in revised form 6 August 2009 Accepted 6 August 2009 Available online 13 August 2009 Keywords: Bamboo waste Activated carbon Textile effluent Adsorption Isotherms
a b s t r a c t In this work, activated carbon was prepared from bamboo waste by chemical activation method using phosphoric acid as activating agent. The activated carbon was evaluated for chemical oxygen demand (COD) and color reduction of a real textile mill effluent. A maximum reduction in color and COD of 91.84% and 75.21%, respectively was achieved. As a result, the standard B discharge limit of color and COD under the Malaysian Environmental Quality act 1974 was met. The Freundlich isotherm model was found best to describe the obtained equilibrium adsorption data at 30 ◦ C. The Brunauer–Emmett–Teller (BET) surface area, total pore volume and the average pore diameter were 988.23 m2 /g, 0.69 cm3 /g and 2.82 nm, respectively. Various functional groups on the prepared bamboo activated carbon (BAC) were determined from the FTIR results. © 2009 Elsevier B.V. All rights reserved.
1. Introduction In Malaysia as well as in all Asian countries, textile industry is very flourishing with the attendant large volumes of highly contaminated effluent wastewater containing: detergents, oils, suspended and dissolved solids, toxic, biodegradable and non-biodegradable matters, dyes and alkaline substances [1,2] that poses serious environmental problems because of their color and high organic matter (COD) [3,4]. Considering a typical cotton textile mill in Penang, Malaysia, the main textile processes start from fiber production in the case of synthetic fiber, followed by spinning to convert the fiber to yarn. Yarn is then strengthened with sizing chemicals like starch, polyvinyl alcohol and wax so that it can withstand vigorous movements when weaved into fabric in high speed weaving looms. The fabric weaved must then be pretreated before dying, printing and finishing. Various chemicals are used in the pretreatment. Fabrics are de-sized with either enzyme or oxidative chemicals and scoured using sodium hydroxide and detergents. Bleaching is normally done using hydrogen peroxide to remove the natural color of the fiber and to make the fabric white. Fabric is then mercerized using highly concentrated sodium hydroxide for stabilization. During dyeing and printing operations, many types of dyes are used e.g., disperse, reactive, vat, etc. in the presence of dyeing auxiliaries and chemicals [5].
∗ Corresponding author. Tel.: +60 45996422; fax: +60 45941013. E-mail address: [email protected] (B.H. Hameed). 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.08.025
Consequently, the amount of wastewater generated from all these processes is very high and highly contaminated [6]. The current wastewater treatment scheme at the study site consists of screening, pre-neutralization, anaerobic lagoon, post-neutralization, activated sludge process and sedimentation. However, this existing wastewater treatment scheme is inadequate (Table 1) to produce treated wastewater that meets the local discharge limits, especially in terms of COD and color [5]. Biological treatment process is generally efficient in biological oxygen demand (BOD), reduction and screening also addresses the suspended solids removal to a reasonable extent, but the dissolved non-biodegradable complex organic dyes is a main challenge to the existing treatment units [7]. Conventionally, adsorption processes using activated carbons are widely used to remove color and heavy metal pollutants from wastewaters. However, commercially available activated carbon is becoming too expensive. In the last few years, special emphasis has been placed on the preparation of activated carbons from several agricultural by-products due to the growing interest in low-cost activated carbons from renewable sources, especially for application in wastewater treatment. Researchers have studied the production of activated carbon from sugar beet bagasse [8], apricot shell [9], sunflower seed hull [10], coconut shells [11], rubber seed coat [12], oil palm fiber [13], rattan [14], date stones [15], plum kernels [16] and palm empty fruit bunch [17]. Bamboo is a grass, the most diverse group of plants in the grass family. It is an enduring, versatile, highly renewable material and abundant natural resource in Malaysia because it takes only few months to grow to maturity. It has been traditionally used to con-
A.A. Ahmad, B.H. Hameed / Journal of Hazardous Materials 172 (2009) 1538–1543
struct various living facilities and tools [18]. Bamboo has been used for furniture and construction it is longer than other hardwoods, strong, tough and low-cost material. Conversion of bamboo to a value-added product such as activated carbon will help to solve part of the problem of wastewater treatment in Malaysia [19]. The advantage of using agricultural by-products as raw materials for manufacturing activated carbon is that these raw materials are abundant, renewable and potentially less expensive [20]. Activated carbons are produced by physical or/and chemical activation methods. Physical activation involves two stages, carbonization and subsequent partial gasification with steam, carbon dioxide or air, usually at high temperature (800–1000 ◦ C), while chemical activation requires only one stage and at lower temperature (450–700 ◦ C) in comparison to physical activation. Therefore, it can improve the pore development in the carbon structure, leading to high adsorption capacity, reduced reaction time and higher product yield [21]. The chemical activation of lignocellulosic materials with phosphoric acid has been extensively investigated from the development of porosity [22–25] and mechanism of degradation from the precursor point of view [26,27]. The purpose of this work was to prepare activated carbon from bamboo waste (BAC) by chemical activation method using phosphoric acid and to find out the possibility of using this adsorbent for the color and COD reduction in real dyeing wastewater from a cotton textile mill operating in Penang State, Malaysia. 2. Materials and methods 2.1. Sampling Textile wastewater (TWW) samples at the factory’s discharge point after the activated sludge treatment unit were collected from a cotton textile mill in Penang, Malaysia. The main products of this industry is white, dyed and printed 100% cotton and polyester/cotton blended woven fabric with a production rate of about 10 million yards a month. The main processes are pretreatment, dyeing, printing and finishing. The plant produces about 250 m3 /h of water with main pollutants as given in Table 1 [28]. The samples were stored at ≤5 ◦ C to avoid any change in its physico-chemical characteristics before use. Table 1 shows the basic quality parameters of the wastewater samples i.e. BOD, COD, color, pH, temperature, suspended solids, turbidity, conductivity, oil and grease, which were analyzed in our laboratory according to the methods prescribed in APHA [29]. Table 1 shows the original effluent has a color and COD of 450–650 Pt/Co and 200–260 mg/L, respectively. 2.2. Preparation and characterization of activated carbon Raw material (bamboo waste) was collected from a local furniture shop, Penang State, Malaysia. It was washed with hot
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distilled water to remove dust-like impurities, dried at 105 ◦ C, ground and sieved (200–300 m) to discrete sizes. Chemical activation method using phosphoric acid (purity 85% Merck, Germany) was used to activate the raw material. In a typical batch production, 40 g of raw material was impregnated by certain amount of 40 wt% concentrated phosphoric acid with occasional stirring. The amount of phosphoric acid solution used was adjusted to give a certain impregnation ratio. Subsequently, the impregnated samples were air dried under sunlight for 3 days. Activation of the phosphoric acid impregnated precursor was carried out at temperature of 500 ◦ C for 2 h under purified nitrogen (99.995%) flow (150 cm3 /g) at a heating rate of 10 ◦ C/min in a horizontal tubular furnace. After activation, the sample was cooled to room temperature with the same heating rate and washed sequentially several times with hot distilled water (70 ◦ C) until the pH of the washing solution reached 6–7. Finally the sample was dried in an oven at 110 ◦ C for 24 h and then stored in plastic containers. The activated carbon yield was calculated based on Eq. (1). Yield (%) =
wc × 100 wo
(1)
where wc is the dry weight of final activated carbon and wo is the dry weight of precursor. Textural characterization of the BAC was carried out by N2 adsorption at 77K using ASAP 2020 Micromeritics instrument by Brunauer–Emmett–Teller (BET) method, using the software of Micromeritics. The Brunauer–Emmett–Teller (BET), Langmuir surface area, total pore volume for pores, and average pore diameter were thus determined. Surface morphology and the presence of porosity of the activated carbon prepared in this work were studied using scanning electron microscopy (SEM) analysis (Model Leo Supra 50VP Field Emission, UK). In addition, the surface functional groups of the prepared activated carbon were detected by Fourier transform infrared (FTIR) spectroscope (FTIR-2000, Perkin-Elmer). The spectra were recorded from 4000 to 400 cm−1 . 2.3. Batch mode treatment of wastewater samples All the experiments were carried out at temperature 30 ◦ C in batch mode. The experiments were run in different flasks of 250 mL capacity using an average shaker’s speed of 120 rpm. The influence of various operating parameters was studied by varying one parameter and keeping the others constant. The desired pH was maintained using dilute NaOH (0.1N)/HCl (0.1N) solutions. The initial COD and color index were 251.65 mg/L and 486.87 Pt/Co, respectively. To determine the contribution of the adsorbent dose to color and COD reduction, 100 mL of sample was treated with different doses of adsorbent ranging between 0.10 and 1.0 g, the other conditions includes treatment time of 24 h, pH of 3 and initial
Table 1 Physico-chemical analysis of textile wastewater (final effluent-after biological treatment). Parameters pH Temperature BOD COD Color Turbidity (Nephalometer turbidity unit) Conductivity Suspended solid Oil and grease
Unit
Value
Standard Ba
– C mg/L mg/L Pt/Co NTU mS/cm mg/L mg/L
7–8 27–30 <50 200–260 450–650 11.44 2.25 <50 3–5
5.5–9.0 – 50 100 – – – – –
◦
a Environmental Quality (Sewage and Industrial Effluents) Regulations, 1979, under the Laws of Malaysia-Malaysia Environmental Quality Act 1974 [28]. Standard B refers to discharges outside catchment area.
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3. Results and discussion 3.1. BET, SEM and FTIR of the activated carbon
Fig. 1. SEM image of bamboo-based activated carbon (magnification = 500×).
color and COD of the sample were 486.87 Pt/Co and 251.65 mg/L, respectively. The pH studies were performed with constant initial concentration, adsorbent dose (0.30 g) and contact time 28 h but with varying pH from 2 to 12 using dilute NaOH or HCl solutions for the adjustment. Effect of contact time of the adsorbent with wastewater samples was investigated by agitating 100 mL sample, pH 3, constant initial concentrations and adding 0.30 g adsorbent for different time periods varying between 1 and 28 h. At elapse of each set contact time, thus the treated wastewater sample was filtered through 0.45 m filter papers before analyses. The samples were analyzed using a DR2800 spectrophotometer (CECIL 1000 series, Cambridge, UK) at wavelengths of 620 and 455 nm for COD and color, respectively. The amount of adsorption at equilibrium, qe , was calculated from Eq. (2): qe =
(Co − Ce )V m
(2)
where Co and Ce are the liquid-phase concentrations of adsorbate at initial and at equilibrium, respectively. V (mL) is the volume of the solution and m (g) is the mass of dry adsorbent used. The reduction percentage at time t can be calculated as follows: %=
Co − Ct × 100 Co
(3)
The BET surface area, Langmuir surface area, total pore volume and average pore diameter of the prepared activated carbon were 988.23 m2 /g, 1561.164 m2 /g 0.696 cm3 /g and 2.82 nm, respectively. The maximum value of activated carbon yield was found to be 30.213%. Besides, the average pore diameter of the activated carbon was found to be 2.82 nm, indicating that the activated carbon prepared was in the mesopores region according to the International Union of Pure and Applied Chemistry (IUPAC), pores are classified as micropores (<2 nm diameter), mesopores (2–50 nm diameter) and macropores (>50 nm diameter) [30]. The phosphoric acid incorporated into the interior of the precursor particle restricted the formation of tar as well as other liquids such as acetic acid and methanol and inhibited the particle shrinkage or volume contraction during heat treatment. On one hand, the restricted shrinkage and limited volatile release might facilitate the conservation of porous structures present in the precursor. On the other hand, after washing the final product, the extraction of deeply penetrated acid led to the creation of tremendous porosity. This also resulted in high yield for the adsorbent than did the thermal activation process [26]. However, the carbons with an enhanced mesoporosity can be obtained from phosphoric acidpromoted activated carbon by subsequent activation [31]. Fig. 1 shows the SEM image of the derived activated carbon. Many large pores in a honeycomb shape were clearly found on the surface of the activated carbon. The well-developed pores had led to the large surface area and porous structure of the activated carbon. Fig. 2, the FTIR spectrum obtained for the prepared activated carbon displayed the following bands; 3736 and 3617 cm−1 was attributed to (O–H) vibrations in hydroxyl groups. The location of hydrogen-bonded OH groups, usually in the range of 3200–3750 cm−1 for alcohols and phenols, involved in hydrogen bonding may be due to adsorbed water [32]; 2373 cm−1 denotes C O stretching from ketones, aldehydes or carboxylic groups, while 1538 cm−1 is C C stretching vibration of the aromatic rings. The relatively intense band at 1052 cm−1 can be assigned to alcohol groups (R–OH) [33] whilst the band at 674 cm−1 is C–O–H twist broad. The FTIR spectra obtained was in agreement with the results reported in the studies carried out on activated carbons prepared from rice straws [34] and cherry stones [35]. The main surface functional groups present on the phosphoric acid impregnated BAC are presumed to be phenols, carboxylic acids (or carboxylic anhydrides
Fig. 2. FTIR spectra of BAC.
A.A. Ahmad, B.H. Hameed / Journal of Hazardous Materials 172 (2009) 1538–1543
Fig. 3. Effect of adsorbent dosage on the adsorption of color and COD onto BAC (temperature: 30 ◦ C, initial color concentration: 486.87 Pt/Co, initial COD concentration: 251.65 mg/L, pH 3, V = 100 mL).
if they are close together) and carbonyl groups (either isolated or arranged in quinone-like fashion), all of which are typical acidic functional groups [26]. These acidic surface functional groups are favourable for removal of color and COD [26]. 3.2. Effect of activated carbon dose Fig. 3 gives the variation of percentage reduction for the color and COD removal versus BAC dose. The color and COD removal increased with increase in the quantity of BAC up to 0.30 g, thereafter, any increase did not exert any significant increase in the removal of either COD or color. The maximum percentage of color and COD removed form the textile wastewater are noted as 89.139% and 72.116%, respectively by using 0.30 g. A similar observation was previously reported for the treatment of pulp and paper mill wastewaters with poly aluminium chloride and bagasse fly ash [36]. 3.3. Effect of solution pH The effect of solution pH was studied on color and COD reduction by BAC at temperature of 30 ◦ C, dosage of 0.30 g, 120 rpm shaker’s speed and initial COD and color concentrations of 251.65 mg/L and 486.87 Pt/Co, respectively. The solution pH was varied between 2 and 12. The result of this effect is as shown in Fig. 4. The maximum color and COD reduction obtained at pH 2–4. The reason for better adsorption capacity observed at lower pH levels might be attributed to the presence of larger number of H+ ions. This in turn, neutralized the negatively charged adsorbent surface. A lower
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Fig. 5. Effect of treatment time on the adsorption of color and COD on BAC (temperature = 30 ◦ C, initial color concentration: 486.87 Pt/Co, initial COD concentration: 251.65 mg/L, pH 3, m = 0.30 g/100 mL solution).
adsorption values at higher pH may be due to the abundance of OH− ions and because of ionic repulsion between the negatively charged active sites of the adsorbent. Similar results were reported for the treatment of pulp and paper mill wastewaters with poly aluminium chloride and bagasse fly ash [36]. 3.4. Effect of contact time on COD and color Fig. 5 shows the effect of contact time on percentage of reduction of color and COD. It is found that the rate of removal was rapid during the initial 1–8 h and thereafter, no significant change in the rate of removal was observed. Possibly, at the beginning, the solute molecules were adsorbed by the exterior surface of adsorbent particles, so the adsorption rate was fast. When the adsorption of the exterior surface reached saturation, the molecules will need to diffuse through the pores of the adsorbent into the interior surface of the particle. This phenomenon takes relatively long contact time. Fig. 5 indicates the formation of monolayer coverage at the outer interface of the adsorbents at the early stage. The curved portion shows the influence of monolayer adsorption and surface mass transfer, whereas the linear part at the later period of contact shows the effect of intra-particle diffusion. Color and COD reduction obtained at optimum conditions (pH 3, m = 0.30 g/100 mL and time 10 h, initial color concentration: 486.87 Pt/Co and initial COD concentration: 251.65 mg/L) were 91.84% and 75.21%, respectively. Table 2 lists the comparison of the maximum percentage of color and COD removed by various adsorbents. The activated carbon prepared in this work showed relatively large percentage of color and COD removed, as compared to some previous works reported in the literature. 3.5. Adsorption isotherms 3.5.1. Langmuir isotherm The Langmuir isotherm [42] which has been successfully applied to many other real adsorption processes was used to explain the adsorption of color and COD onto BAC. The data obtained from the adsorption experiment conducted during the present investigation was fitted using different adsorbent doses into the isotherm equation. The linear form of Langmuir isotherm equation is given as: Ce 1 1 = Ce + qe qm KL qm
Fig. 4. Effect of solution pH on the adsorption of color and COD onto BAC (temperature: 30 ◦ C, initial color concentration: 486.87 Pt/Co, initial COD concentration: 251.65 mg/L, m = 0.30 g/100 mL solution).
(4)
where Ce is the equilibrium concentration of the adsorbate, qe is the amount of adsorbate adsorbed per unit mass of adsorbent,
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Table 2 Comparison of the maximum percentage of color and COD removal by various adsorbents. Adsorbent types
Type of wastewater
COD removal (%)
Color removal %
Ref.
Bamboo-based activated carbon (BAC) Bagasse fly ash (BFA) Coconut shell carbon (ATSAC) Coconut fibers carbon (ATFAC) Rice husk carbon (ATRHC) Mixed adsorbent carbon (MAC) Carbon developed from fertilizer waste Pecan shell-based carbon dioxide-activated carbon (PSC) Powdered activated carbon (PAC)
Textile wastewater Pulp and paper wastewaters Industrial (mixed) Industrial (mixed) Industrial (mixed) Domestic Industrial Municipal wastewater Textile wastewater
75 50 46–71 50–74 45–73 96 >50 >70 78
91 55 – – – – – – 86
This work [36] [37] [37] [37] [38] [39] [40] [41]
qm and KL are Langmuir constants related to adsorption capacity and rate of adsorption, respectively. The saturation monolayer can be represented by plotting of Ce /qe versus Ce in a linear graphical relation indicating the applicability of the model for different adsorbent doses (figure not shown). The maximum adsorption capacities for color and COD were 29.154, 24.396 mg/L, respectively with R2 greater than 0.97. 3.5.2. Freundlich isotherm The Freundlich isotherm [43] is commonly used for a heterogeneous surface energy system. The well-known logarithmic form of Freundlich isotherm is given by the following equation: log qe = log KF +
1 log Ce n
(5)
where Ce is the equilibrium concentration of the adsorbate, qe is the amount of adsorbate adsorbed per unit mass of adsorbent, KF and n are Freundlich constants with n giving an indication of how favorable is the adsorption process and KF is the adsorption capacity of the adsorbent. The Freundlich isotherm has been illustrated to be a special case of heterogeneous surface energies but it can be easily extended to this case. The slope of 1/n ranging between 0 and 1 is a measure of adsorption intensity or surface heterogeneity, where the surface becomes more heterogeneous as its value gets closer to zero [44]. A value for 1/n below one indicates a normal Langmuir isotherm while 1/n above one is indicative of cooperative adsorption [45]. The plot of log qe versus log Ce (figure not shown) gave a straight line with slope of 1/n; whereas KF was calculated from the intercept value. The values of 1/n for color and COD were 0.342, 0.322 and the values of KF were 0.464, 0.191, respectively with R2 greater than 0.99. 3.5.3. Temkin isotherm The data were also fitted to Temkin and Pyzhev [46] isotherm. The heat of adsorption of all the molecules in the layer would decrease linearly with coverage due to adsorbate/adsorbate interactions [47]. The Temkin isotherm has been used in the form as follows: qe =
RT ln(KT Ce ) b
(6)
Eq. (6) can be linearized as: qe = B ln KT + B ln Ce
(7)
where RT/b = B. b and KT are constants. KT is the equilibrium binding constant corresponding to the maximum binding energy and constant B is related to the heat of adsorption. A plot of qe versus ln Ce (figure not shown) enables the determination of the isotherm constants KT and B. The values of constant B for color and COD were 80.47, 67.155 and the values of KT were 376.01, 224.84, respectively with R2 greater than 0.95. The three isotherms models have been tested and the equilibrium data fits well to all adsorption isotherms. The Freundlich model was found to be the best fit with R2 which were higher than
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