2158
© IWA Publishing 2013 Water Science & Technology
|
68.10
|
2013
Adsorption of chloro-anilines from solution by modified peanut husk in fixed-bed column Shenglong Zhang, Randi Zhang, Wei Xiao and Runping Han
ABSTRACT Natural peanut husk (NPH) modified with hexadecyl trimethyl ammonium bromide (CTAB) was used as adsorbent to remove 2,5-dimethoxy-4-chloroaniline (DMCH) from solution in a fixed-bed column. Fourier transform infrared spectroscopy analysis and X-ray fluorescence of NPH and modified peanut husk (MPH) showed that CTAB had been introduced onto the surface of NPH. The effects of flow rate and bed depth on breakthrough curves were studied. The Thomas model and the Yan model were selected to fit the column adsorption data and the results showed that the Yan model was better at
Shenglong Zhang Randi Zhang Wei Xiao Runping Han (corresponding author) School of Chemistry and Molecular Engineering, Zhengzhou University, 100 Kexue Road, Zhengzhou, 450001, China E-mail: [email protected]
predicting the breakthrough curves. The adsorption quantity was up to 6.46 mg/g according to the Yan model. The bed depth service time model was used to calculate the critical bed depth from experimental data and it was directly related to flow rate. As a low-cost adsorbent, MPH is promising for the removal of DMCH from solution. Key words
| 2,5-dimethoxy-4-chloroaniline, breakthrough curves, column adsorption, modified peanut husk
INTRODUCTION Aromatic amines are frequently used by the chemical industry, for example, as the raw material in the manufacture of dyes, rubbers, pesticides, and herbicides, and in pharmaceutical preparation, etc. These compounds have significant harmful effects for public health and environmental quality, and aniline-containing wastewater has produced a series of serious environmental problems due to its high toxicity and accumulation in the environment (Gu et al. ). Among the different processes often adopted for elimination of refractory pollutants, adsorption seems to be a good choice in terms of cost and operation for the removal of aniline and its derivatives (Crini ; Gu et al. ). Adsorption on commercial activated carbon may be an effective process for removal of refractory pollutants from wastewater, but it is too expensive and the regeneration of spent activated carbon is relatively difficult with loss of mass (Aksu ; Gupta & Suhas ). Thus attention has been focused on the development of low-cost adsorbents for the application of wastewater treatment. As an alternative to activated carbon, agricultural residues or by-products from renewable sources are less expensive and have been widely used in the past two decades for removing aromatic pollutants from effluents. Several reviews have doi: 10.2166/wst.2013.464
been published (Aksu ; Gupta & Suhas ; Bhatnagar & Sillanpaa ). Peanut husk is one of the potential adsorbent materials. It has been selected for removal of cationic pollutants, such as dyes and heavy metals (Johnson et al. ; Song et al. ). However, for anionic pollutants, its adsorption ability is smaller. In order to improve the stability and also to enhance the adsorption capacity, the modification of agricultural by-products using various methods proves to be extremely useful. Surfactant has been used to modify coir pith (Namasivayam & Sureshkumar ), barley straw (Oei et al. ; Ibrahim et al. a, b), and wheat straw (Su et al. ) for the removal of anionic and polar pollutants. However, few investigations have been reported using peanut husk modified by surfactants for adsorption of aniline and its derivatives. In this research, the surface of natural peanut husk (NPH) was modified using a cationic surfactant, hexadecyl trimethyl ammonium bromide (CTAB), in order to increase adsorption capacity towards polar pollutants from solution. 2,5-Dimethoxy-4-chloroaniline (DMCA; see Appendix, available online at http://www.iwaponline.com/wst/068/464. pdf), available in refined chemical processes (as intermediate
2159
S. Zhang et al.
|
Adsorption of chloro-anilines by modified peanut husk
of dyes and pharmaceuticals), can be released to wastewater during the preparation process. It was selected as the target pollutant as it is very difficult to biodegrade (chloroaromatic rings is more refractory) in wastewater treatment. The experiment was performed in fixed-bed column mode. The Thomas model and Yan model were selected to fit experimental data in order to determine the better model to predict the experimental data while the bed depth service time (BDST) model was used to calculate the critical bed depth.
MATERIALS AND METHODS Preparation of modified peanut husk Original peanut husk was collected from its natural habitat in farmland, in Luoyang City, China. It was extensively washed with tap water to remove soil and dust, then washed with distilled water, and next dried in an oven at 80 C. Dry peanut husk was crushed into powder and sieved through 20–40 mesh and renamed NPH. NPH was placed in a desiccator for use. Five grams of NPH and 250 mL solution (1% CTAB) were added to one 500-mL conical flask. Then, the mixtures were shaken by an orbital shaker with 100 rpm at room temperature (293 K) for 24 h. The modified peanut husk (MPH) was separated from the mixtures and washed with distilled water several times to remove superficially retained CTAB. Finally, MPH was dried at 333 K overnight and stored in an airtight glass bottle. W
Characterization of NPH and MPH by X-ray fluorescence and Fourier transform infrared spectroscopy (FTIR) Inorganic elemental compositions were obtained by an Xray fluorescence spectrometer (Philips PW 2404 X-ray fluorescence, The Netherlands). FTIR of NPH and MPH was determined to analyse the functional groups on the surface of adsorbents. Two milligrams of NPH or MPH were mixed with 100 mg of spectroscopy grade KBr powder, dried at irradiation by FTIR lamp, and the mixtures were pressed into small tablets. FTIR spectra were recorded using a PE-1710 FTIR (USA) instrument in the range of 4,000–400 cm–1 with a resolution of 4 cm–1. DMCA solution The DMCA used in this work was purchased from Luoyang Chemical Corporation, China. The working solutions of
Water Science & Technology
|
68.10
|
2013
DMCA (40 mg/L) were prepared in distilled water. The pH solution was near 8.0 and was not adjusted during the experiment. Adsorption performance in fixed-bed column mode Continuous adsorption processes in fixed-bed column were performed in a glass column (1 cm inner diameter and 25 cm height), and packed with a fixed mass of MPH. Three different bed depths (3.5, 5.2, and 8.5 cm, corresponding to 0.5, 0.75, and 1.3 g MPH, respectively) were investigated at a constant flow rate of 4.5 mL/min. A constant bed depth of 5.2 cm was examined at variable flow rates (1.7, 4.5, and 7.2 mL/min). DMCA solution was pumped at selected flow rates by a peristaltic pump (in down flow mode) and the effluent was collected at appropriate intervals. DMCA concentration was measured according to adsorption law by the absorbance changes at wavelength of maximum absorbance (230 nm) (Shimadzu Brand UV3000).
RESULTS AND DISCUSSION Composition of inorganic elements and FTIR of NPH and MPH Similar to vegetable biomass, peanut husk is composed of cellulose, hemi-cellulose, and lignin, etc. There are some inorganic elements confirmed by the X-ray fluorescence analysis, such as Si, Ca, K, Fe, Mg and Al. The contents of the main elements (as oxides) for NPH were SiO2 19.5%, CaO 45.8%, K2O 2.63%, MgO 5.48%, Fe2O3 4.37%, and Al2O3 6.64%, respectively. For MPH, it was Br 8.99%, SiO2 15.9%, CaO 36.9%, K2O 5.77%, MgO 1.90%, Fe2O3 5.37%, and Al2O3 2.4%. The element Br for MPH was detected, and some elements were eluted. The result implied that CTAB had been introduced onto the surface of NPH. FTIR spectroscopy was done for preliminary quantitative analysis of major functional groups present in adsorbents. Figure 1 shows the FTIR spectrum of NPH and MPH. It was difficult to confirm each peak appearing in Figure 1 as the composition and structure of NPH is complex. Discrete analysis of FTIR was performed in a previous study (Song et al. ). The IR spectra of NPH are mainly composed of vibration of OH (3,418 cm1), CH3 (2,926, 1,373 cm1), C5 5O (1,739 cm1), aromatic 1 ring (1,510 cm ) and CO (1,423 cm1 from carboxyl group, 1,054 cm1), which were from carbohydrates,
2160
Figure 1
S. Zhang et al.
|
|
Adsorption of chloro-anilines by modified peanut husk
Water Science & Technology
|
68.10
|
2013
FTIR spectrum of NPH (top) and MPH (bottom).
lignin, and cellulose that existed in NPH. For MPH, the absorption intensity of CH3 (2,924, 1,375 cm1) increased while the shoulder peak of CH2 (2,854 cm1) was resolved. This was due to the increase in the aliphatic carbon content (from CTAB) in MPH. These results also showed that CTAB had been inserted into the surface of NPH. However, location of the main peaks from MPH only shifted slightly and this showed that the main structure and composition of NPH remained intact after CTAB modification.
The effect of different bed depth on breakthrough curves In batch mode (data not shown), there is little change with regard to the adsorption quantity of DMCA on MPH at pH 6–12. The solution pH of DMCA was 8.5 and it was not adjusted. The adsorption quantity only slightly decreased with the increase of concentration of the sodium chloride (co-existing in solution). At an initial concentration of 100 mg/L and dose of adsorbent 1 g/L
2161
S. Zhang et al.
|
Adsorption of chloro-anilines by modified peanut husk
(contact time 100 min to adsorption equilibrium), values of adsorption quantities were 3 and 15 mg/g for NPH and MPH, respectively, and this showed that adsorption capacity was markedly improved after CTAB modification. The advantages of the column adsorption process can offer easier continuous operation and scale-up. The effects of bed height and flow rate on DMCA adsorption were studied in a fixed-bed column. The breakthrough curves in terms of Ct/C0 versus time t at different conditions can be obtained from column experiments. The breakthrough curves at different bed depths are shown in Figure 2. It was observed that the breakthrough curves became steeper as the bed height decreases. This showed that an increase in bed depth favored removal of DMCA due to a higher surface area; in other words, higher number of active sites at higher bed depth. Thus efficiency of adsorption mainly depended upon the amount of adsorbent available. The breakthrough time and exhaustion time increased with an increase in bed height since more time was required to exhaust more adsorbent. However, the slope of the breakthrough curve decreased as the bed height increased. This was due to an increase in axial dispersion of DMCA over the column with an increase in column height. This increase resulted in an increased volume of pollutant solution treated with a higher percentage of DMCA removal (Aksu & Gonen ). The effect of flow rate on breakthrough curves The breakthrough curves at various flow rates are also shown in Figure 2. It can be seen that the breakthrough curves become steeper as the flow rate increases while the
Water Science & Technology
|
68.10
|
2013
time to reach saturation increased at lower flow rates. Hence, lower flow rates were desirable for effective removal of DMCA in column mode. For NPH, the breakthrough curve is very steep and the breakthrough time was shorter (data not shown). Thus it can be concluded that the adsorption capacity of peanut husk was markedly increased after CTAB modification. This result was consistent with batch adsorption. The reason was due to adsorption of cationic surfactants onto the adsorbent surface. The non-polar portion (alkyl) of CTAB may interact with the solid surface through hydrophobic bonding and the polar (positively charged) head group directed towards the bulk of the solution, so the surface is potentially positive (Namasivayam & Sureshkumar ). In solution, some groups in NPH, such as lignin and cellulose, lose hydrogen ions and form a potential negative surface. Thus another possible action between NPH and CTAB is the electrostatic attraction of surfactant cations on the NPH surface which offers a negative charge (Namasivayam & Sureshkumar ). Therefore, there may be Van der Waals force, hydrogen bonds and hydrophobic attraction between CTAB on the surface of NPH and DMCA according to the structures of DMCA and CTAB. Modeling of column study results Modeling of data available from column studies facilitate scale-up potential. To describe the column breakthrough curves obtained at different bed heights and flow rates, the Thomas model and Yan model were adopted. The BDST model was selected to obtain the critical bed depth. Thomas model and Yan model Thomas model (Aksu & Gonen ): Ct 1 ¼ C0 1 þ expðkTh q0 x=v kTh C0 tÞ
(1)
Yan model (Yan et al. ): Ct 1 ¼1 C0 1 þ ðvt=bÞa
(2)
From the value of b, the value of q0 can be estimated using the following equation (Yan et al. ): Figure 2
|
Breakthrough curves and predicted curves at different bed depths (Z) and flow rate (v) (C0 ¼ 40 mg/L).
q0 ¼
bC0 x
(3)
2162
S. Zhang et al.
|
Adsorption of chloro-anilines by modified peanut husk
Water Science & Technology
where kTh is the Thomas rate constant (mL/(min·mg)); q0 is the equilibrium DMCA uptake per g of the adsorbent (mg/g); x is amount of adsorbent in the column (g); v is the flow rate of the solution passing through the column (mL/min). The value of Ct/C0 is the ratio of effluent and influent DMCA concentrations. The value of t is flow time (min). a and b (mL) are parameters of the Yan model. Data obtained from column experiments were used to fit the Thomas model and Yan model. The parameters and values of R 2 (coefficient of determination) and sum of squared errors (SS) according to nonlinear regressive analysis are listed in Table 1, respectively. From Table 1, the values of kTh became bigger with the flow rate increasing. With the bed depth increasing, the values of kTh became smaller while the value of q0 increased. The Yan model can minimize the error that results from use of the Thomas model, especially with lower and higher breakthrough curve times. The trend of values of q0 and b was similar to values of q0 from the Thomas model with the change in experimental conditions. Adsorption quantity (q0) obtained from the Yan model was from 3.33 to 6.46 mg/g. Compared to values of q0 at the same conditions listed in Table 1, the value of q0 from the Yan model was smaller than that from the Thomas model, respectively. It was also found that the value of R 2 from the Yan model was larger while the value of SS was smaller at the same experimental condition. Furthermore, at all conditions, the predicted breakthrough curves from the Yan model showed better agreement with the experimental
Table 1
|
|
68.10
|
2013
curves (shown in Figure 2). Thus it was concluded that the Yan model was better to predict breakthrough curves than the Thomas model. Several researchers have studied metal and dye removal by adsorption in column mode and similar results were obtained (Yan et al. ; Wu et al. ; Song et al. ). The bed depth/service time analysis (BDST) model The BDST model is based on physically measuring the capacity of the bed at different breakthrough values. The BDST model works well and provides useful modeling equations for the changes of system parameters (Goel et al. ). A modified form of the equation that expresses the service time at breakthrough, t, as a fixed function of operation parameters is the BDST model: t¼
N0 1 C0 ln 1 Z Ka C0 C0 F Ct
(4)
where F is influent linear velocity (cm min1); N0 is adsorption capacity (mg/L); Ka is rate constant in BDST model (L/(mg·min)); and Z is bed depth of column (cm). The service time at breakthrough point, tb, was chosen as that when the effluent DMCA concentration attained 5% of the influent concentration and was plotted against bed height. At a given linear flow rate (5.73 cm/min), the curve tb vs Z was found to be linear (figure not shown): tb ¼ 1.053Z 1.706, suggesting that the BDST model applied to this system was valid (with R² ¼ 0.946). The
Parameters of Thomas model and Yan model C0 (mg/L)
v (mL/min)
Z (cm)
q0 (mg/g)
R2
kTh (mL/min mg)
SS
Thomas model 40
4.5
3.5
4.38 ± 0.06
2.90 ± 0.40
0.896
0.00818
40
4.5
5.2
4.74 ± 0.05
2.60 ± 0.33
0.914
0.00823
40
4.5
8.6
7.32 ± 0.03
1.97 ± 0.13
0.876
0.0124
40
1.7
5.2
4.13 ± 0.03
1.54 ± 0.13
0.966
0.00444
40
7.2
5.2
3.73 ± 0.08
5.15 ± 0.53
0.951
0.00395
Yan model
Note: SS ¼
P
2
40
4.5
3.5
1.44 ± 0.06
56.0 ± 1.8
4.08 ± 0.14
0.985
0.00114
40
4.5
5.2
1.63 ± 0.08
80.5 ± 2.6
4.24 ± 0.09
0.982
0.00172
40
4.5
8.6
1.46 ± 0.07
210.0 ± 6.5
6.46 ± 0.20
0.981
0.00184
40
1.7
5.2
2.28 ± 0.09
73.0 ± 1.4
3.84 ± 0.07
0.991
0.00114
40
7.2
5.2
1.83 ± 0.05
63.2 ± 1.1
3.33 ± 0.06
0.994
0.00041
ðq qc Þ =ðn 2Þ, q and qc are the experimental value and calculated value according to the model, respectively.
2163
S. Zhang et al.
|
Adsorption of chloro-anilines by modified peanut husk
Water Science & Technology
slope of the BDST straight line and its intercept allowed values of N0 237.4 mg/L and Ka 0.0431 L/mg min to be obtained. The critical bed depth (Z0) was also determined in this work; it corresponds to the bed depth required for preventing the outlet DMCA concentration from being over 5% of the influent concentration at time t ¼ 0; this theoretical depth of MPH was then obtained by taking Cb¼ 0.05 C0 and by substituting t ¼ 0 in Equation (4). F C0 ln 1 Z0 ¼ Ka N0 Cb
(5)
Usually, values of N0 and Ka changed slightly with different flow rates; the critical bed depth Z0 can be calculated and was 0.63, 1.65, 2.67 cm at flow rates of 1.7, 4.2, and 7.2 mL/ min, respectively. This result implied that Z0 is directly related to flow rate. This meant that DMCA adsorption onto MPH ought to be efficient only if bed heights Z were over Z0.
CONCLUSION Analysis of NPH and MPH by FTIR and X-ray fluorescence implied that there was CTAB on the surface of MPH. Higher bed depth and lower flow rate were advantageous for DMCA adsorption. Column experimental data can be better fitted by the Yan model while values of critical bed depth were calculated by BDST. MPH as a low-cost adsorbent is available to remove DMCA from solution.
ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (J1210060).
REFERENCES Aksu, Z. Application of biosorption for the removal of organic pollutants: a review. Process Biochem. 40 (3–4), 997–1026.
|
68.10
|
2013
Aksu, Z. & Gonen, F. Biosorption of phenol by immobilized activated sludge in a continuous packed bed: prediction of breakthrough curves. Process Biochem. 39 (5), 599–613. Bhatnagar, A. & Sillanpaa, M. Utilization of agro-industrial and municipal waste materials as potential adsorbents for water treatment - a review. Chem. Eng. J. 157 (2–3), 277–296. Crini, G. Non-conventional low-cost adsorbents for dye removal: a review. Bioresour. Technol. 97 (9), 1061–1085. Goel, J., Kadirvelu, K., Rajagopal, C. & Garg, V. K. Removal of lead(II) by adsorption using treated granular activated carbon: batch and column studies. J. Hazard. Mater. 125 (1– 3), 211–220. Gu, X. H., Zhou, J. T., Zhang, A. L., Wang, P., Xiao, M. & Liu, G. F. Feasibility study of the treatment of aniline hypersaline wastewater with a combined adsorption/bioregeneration system. Desalination 227 (1–3), 139–149. Gupta, V. K. & Suhas Application of low-cost adsorbents for dye removal: a review. J. Environ. Manage. 90 (8), 2313–2342. Ibrahim, S., Fatimah, I., Ang, H. M. & Wang, S. B. a Adsorption of anionic dyes in aqueous solution using chemically modified barley straw. Water Sci. Technol. 62 (5), 1177–1182. Ibrahim, S., Wang, S. B. & Ang, H. M. b Removal of emulsified oil from oily wastewater using agricultural waste barley straw. Biochem. Eng. J. 49 (1), 78–83. Johnson, P. D., Watson, M. A., Brown, J. & Jefcoat, I. A. Peanut hull pellets as a single use sorbent for the capture of Cu(II) from wastewater. Waste Manage. 22 (5), 471–480. Namasivayam, C. & Sureshkumar, M. V. Anionic dye adsorption characteristics of surfactant modified coir pith, a waste lignocellulosic polymer. J. Appl. Polym. Sci. 100 (2), 1538–1546. Oei, B. C., Ibrahim, S., Wan, S. B. & Ang, H. M. Surfactant modified barley straw for removal of acid and reactive dyes from aqueous solution. Bioresour. Technol. 100 (18), 4292–4295. Song, J. Y., Zou, W. H., Bian, Y. Y., Su, F. Y. & Han, R. P. Adsorption characteristics of methylene blue by peanut husk in batch and column mode. Desalination 265 (1–3), 119–125. Su, Y. Y., Zha, B. L., Xiao, W. & Han, R. P. Adsorption behavior of light green anionic dye using cationic surfactant modified wheat straw in batch and column mode. Environ. Sci. Pollut. Res. 20 (8), 5558–5568. Wu, X. L., Wang, Y., Liu, J. L., Ma, J. Y. & Han, R. P. Study of Malachite Green adsorption onto natural zeolite in fixed-bed column. Desalin. Water Treat. 20 (1–3), 228–233. Yan, G., Viraraghavan, T. & Chen, M. A new model for heavy metal removal in a biosorption column. Adsorpt. Sci. Technol. 19 (1), 25–43.
First received 21 May 2013; accepted in revised form 8 July 2013. Available online 24 October 2013
Copyright of Water Science & Technology is the property of IWA Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
© IWA Publishing 2013 Water Science & Technology
|
68.10
|
2013
Adsorption of chloro-anilines from solution by modified peanut husk in fixed-bed column Shenglong Zhang, Randi Zhang, Wei Xiao and Runping Han
ABSTRACT Natural peanut husk (NPH) modified with hexadecyl trimethyl ammonium bromide (CTAB) was used as adsorbent to remove 2,5-dimethoxy-4-chloroaniline (DMCH) from solution in a fixed-bed column. Fourier transform infrared spectroscopy analysis and X-ray fluorescence of NPH and modified peanut husk (MPH) showed that CTAB had been introduced onto the surface of NPH. The effects of flow rate and bed depth on breakthrough curves were studied. The Thomas model and the Yan model were selected to fit the column adsorption data and the results showed that the Yan model was better at
Shenglong Zhang Randi Zhang Wei Xiao Runping Han (corresponding author) School of Chemistry and Molecular Engineering, Zhengzhou University, 100 Kexue Road, Zhengzhou, 450001, China E-mail: [email protected]
predicting the breakthrough curves. The adsorption quantity was up to 6.46 mg/g according to the Yan model. The bed depth service time model was used to calculate the critical bed depth from experimental data and it was directly related to flow rate. As a low-cost adsorbent, MPH is promising for the removal of DMCH from solution. Key words
| 2,5-dimethoxy-4-chloroaniline, breakthrough curves, column adsorption, modified peanut husk
INTRODUCTION Aromatic amines are frequently used by the chemical industry, for example, as the raw material in the manufacture of dyes, rubbers, pesticides, and herbicides, and in pharmaceutical preparation, etc. These compounds have significant harmful effects for public health and environmental quality, and aniline-containing wastewater has produced a series of serious environmental problems due to its high toxicity and accumulation in the environment (Gu et al. ). Among the different processes often adopted for elimination of refractory pollutants, adsorption seems to be a good choice in terms of cost and operation for the removal of aniline and its derivatives (Crini ; Gu et al. ). Adsorption on commercial activated carbon may be an effective process for removal of refractory pollutants from wastewater, but it is too expensive and the regeneration of spent activated carbon is relatively difficult with loss of mass (Aksu ; Gupta & Suhas ). Thus attention has been focused on the development of low-cost adsorbents for the application of wastewater treatment. As an alternative to activated carbon, agricultural residues or by-products from renewable sources are less expensive and have been widely used in the past two decades for removing aromatic pollutants from effluents. Several reviews have doi: 10.2166/wst.2013.464
been published (Aksu ; Gupta & Suhas ; Bhatnagar & Sillanpaa ). Peanut husk is one of the potential adsorbent materials. It has been selected for removal of cationic pollutants, such as dyes and heavy metals (Johnson et al. ; Song et al. ). However, for anionic pollutants, its adsorption ability is smaller. In order to improve the stability and also to enhance the adsorption capacity, the modification of agricultural by-products using various methods proves to be extremely useful. Surfactant has been used to modify coir pith (Namasivayam & Sureshkumar ), barley straw (Oei et al. ; Ibrahim et al. a, b), and wheat straw (Su et al. ) for the removal of anionic and polar pollutants. However, few investigations have been reported using peanut husk modified by surfactants for adsorption of aniline and its derivatives. In this research, the surface of natural peanut husk (NPH) was modified using a cationic surfactant, hexadecyl trimethyl ammonium bromide (CTAB), in order to increase adsorption capacity towards polar pollutants from solution. 2,5-Dimethoxy-4-chloroaniline (DMCA; see Appendix, available online at http://www.iwaponline.com/wst/068/464. pdf), available in refined chemical processes (as intermediate
2159
S. Zhang et al.
|
Adsorption of chloro-anilines by modified peanut husk
of dyes and pharmaceuticals), can be released to wastewater during the preparation process. It was selected as the target pollutant as it is very difficult to biodegrade (chloroaromatic rings is more refractory) in wastewater treatment. The experiment was performed in fixed-bed column mode. The Thomas model and Yan model were selected to fit experimental data in order to determine the better model to predict the experimental data while the bed depth service time (BDST) model was used to calculate the critical bed depth.
MATERIALS AND METHODS Preparation of modified peanut husk Original peanut husk was collected from its natural habitat in farmland, in Luoyang City, China. It was extensively washed with tap water to remove soil and dust, then washed with distilled water, and next dried in an oven at 80 C. Dry peanut husk was crushed into powder and sieved through 20–40 mesh and renamed NPH. NPH was placed in a desiccator for use. Five grams of NPH and 250 mL solution (1% CTAB) were added to one 500-mL conical flask. Then, the mixtures were shaken by an orbital shaker with 100 rpm at room temperature (293 K) for 24 h. The modified peanut husk (MPH) was separated from the mixtures and washed with distilled water several times to remove superficially retained CTAB. Finally, MPH was dried at 333 K overnight and stored in an airtight glass bottle. W
Characterization of NPH and MPH by X-ray fluorescence and Fourier transform infrared spectroscopy (FTIR) Inorganic elemental compositions were obtained by an Xray fluorescence spectrometer (Philips PW 2404 X-ray fluorescence, The Netherlands). FTIR of NPH and MPH was determined to analyse the functional groups on the surface of adsorbents. Two milligrams of NPH or MPH were mixed with 100 mg of spectroscopy grade KBr powder, dried at irradiation by FTIR lamp, and the mixtures were pressed into small tablets. FTIR spectra were recorded using a PE-1710 FTIR (USA) instrument in the range of 4,000–400 cm–1 with a resolution of 4 cm–1. DMCA solution The DMCA used in this work was purchased from Luoyang Chemical Corporation, China. The working solutions of
Water Science & Technology
|
68.10
|
2013
DMCA (40 mg/L) were prepared in distilled water. The pH solution was near 8.0 and was not adjusted during the experiment. Adsorption performance in fixed-bed column mode Continuous adsorption processes in fixed-bed column were performed in a glass column (1 cm inner diameter and 25 cm height), and packed with a fixed mass of MPH. Three different bed depths (3.5, 5.2, and 8.5 cm, corresponding to 0.5, 0.75, and 1.3 g MPH, respectively) were investigated at a constant flow rate of 4.5 mL/min. A constant bed depth of 5.2 cm was examined at variable flow rates (1.7, 4.5, and 7.2 mL/min). DMCA solution was pumped at selected flow rates by a peristaltic pump (in down flow mode) and the effluent was collected at appropriate intervals. DMCA concentration was measured according to adsorption law by the absorbance changes at wavelength of maximum absorbance (230 nm) (Shimadzu Brand UV3000).
RESULTS AND DISCUSSION Composition of inorganic elements and FTIR of NPH and MPH Similar to vegetable biomass, peanut husk is composed of cellulose, hemi-cellulose, and lignin, etc. There are some inorganic elements confirmed by the X-ray fluorescence analysis, such as Si, Ca, K, Fe, Mg and Al. The contents of the main elements (as oxides) for NPH were SiO2 19.5%, CaO 45.8%, K2O 2.63%, MgO 5.48%, Fe2O3 4.37%, and Al2O3 6.64%, respectively. For MPH, it was Br 8.99%, SiO2 15.9%, CaO 36.9%, K2O 5.77%, MgO 1.90%, Fe2O3 5.37%, and Al2O3 2.4%. The element Br for MPH was detected, and some elements were eluted. The result implied that CTAB had been introduced onto the surface of NPH. FTIR spectroscopy was done for preliminary quantitative analysis of major functional groups present in adsorbents. Figure 1 shows the FTIR spectrum of NPH and MPH. It was difficult to confirm each peak appearing in Figure 1 as the composition and structure of NPH is complex. Discrete analysis of FTIR was performed in a previous study (Song et al. ). The IR spectra of NPH are mainly composed of vibration of OH (3,418 cm1), CH3 (2,926, 1,373 cm1), C5 5O (1,739 cm1), aromatic 1 ring (1,510 cm ) and CO (1,423 cm1 from carboxyl group, 1,054 cm1), which were from carbohydrates,
2160
Figure 1
S. Zhang et al.
|
|
Adsorption of chloro-anilines by modified peanut husk
Water Science & Technology
|
68.10
|
2013
FTIR spectrum of NPH (top) and MPH (bottom).
lignin, and cellulose that existed in NPH. For MPH, the absorption intensity of CH3 (2,924, 1,375 cm1) increased while the shoulder peak of CH2 (2,854 cm1) was resolved. This was due to the increase in the aliphatic carbon content (from CTAB) in MPH. These results also showed that CTAB had been inserted into the surface of NPH. However, location of the main peaks from MPH only shifted slightly and this showed that the main structure and composition of NPH remained intact after CTAB modification.
The effect of different bed depth on breakthrough curves In batch mode (data not shown), there is little change with regard to the adsorption quantity of DMCA on MPH at pH 6–12. The solution pH of DMCA was 8.5 and it was not adjusted. The adsorption quantity only slightly decreased with the increase of concentration of the sodium chloride (co-existing in solution). At an initial concentration of 100 mg/L and dose of adsorbent 1 g/L
2161
S. Zhang et al.
|
Adsorption of chloro-anilines by modified peanut husk
(contact time 100 min to adsorption equilibrium), values of adsorption quantities were 3 and 15 mg/g for NPH and MPH, respectively, and this showed that adsorption capacity was markedly improved after CTAB modification. The advantages of the column adsorption process can offer easier continuous operation and scale-up. The effects of bed height and flow rate on DMCA adsorption were studied in a fixed-bed column. The breakthrough curves in terms of Ct/C0 versus time t at different conditions can be obtained from column experiments. The breakthrough curves at different bed depths are shown in Figure 2. It was observed that the breakthrough curves became steeper as the bed height decreases. This showed that an increase in bed depth favored removal of DMCA due to a higher surface area; in other words, higher number of active sites at higher bed depth. Thus efficiency of adsorption mainly depended upon the amount of adsorbent available. The breakthrough time and exhaustion time increased with an increase in bed height since more time was required to exhaust more adsorbent. However, the slope of the breakthrough curve decreased as the bed height increased. This was due to an increase in axial dispersion of DMCA over the column with an increase in column height. This increase resulted in an increased volume of pollutant solution treated with a higher percentage of DMCA removal (Aksu & Gonen ). The effect of flow rate on breakthrough curves The breakthrough curves at various flow rates are also shown in Figure 2. It can be seen that the breakthrough curves become steeper as the flow rate increases while the
Water Science & Technology
|
68.10
|
2013
time to reach saturation increased at lower flow rates. Hence, lower flow rates were desirable for effective removal of DMCA in column mode. For NPH, the breakthrough curve is very steep and the breakthrough time was shorter (data not shown). Thus it can be concluded that the adsorption capacity of peanut husk was markedly increased after CTAB modification. This result was consistent with batch adsorption. The reason was due to adsorption of cationic surfactants onto the adsorbent surface. The non-polar portion (alkyl) of CTAB may interact with the solid surface through hydrophobic bonding and the polar (positively charged) head group directed towards the bulk of the solution, so the surface is potentially positive (Namasivayam & Sureshkumar ). In solution, some groups in NPH, such as lignin and cellulose, lose hydrogen ions and form a potential negative surface. Thus another possible action between NPH and CTAB is the electrostatic attraction of surfactant cations on the NPH surface which offers a negative charge (Namasivayam & Sureshkumar ). Therefore, there may be Van der Waals force, hydrogen bonds and hydrophobic attraction between CTAB on the surface of NPH and DMCA according to the structures of DMCA and CTAB. Modeling of column study results Modeling of data available from column studies facilitate scale-up potential. To describe the column breakthrough curves obtained at different bed heights and flow rates, the Thomas model and Yan model were adopted. The BDST model was selected to obtain the critical bed depth. Thomas model and Yan model Thomas model (Aksu & Gonen ): Ct 1 ¼ C0 1 þ expðkTh q0 x=v kTh C0 tÞ
(1)
Yan model (Yan et al. ): Ct 1 ¼1 C0 1 þ ðvt=bÞa
(2)
From the value of b, the value of q0 can be estimated using the following equation (Yan et al. ): Figure 2
|
Breakthrough curves and predicted curves at different bed depths (Z) and flow rate (v) (C0 ¼ 40 mg/L).
q0 ¼
bC0 x
(3)
2162
S. Zhang et al.
|
Adsorption of chloro-anilines by modified peanut husk
Water Science & Technology
where kTh is the Thomas rate constant (mL/(min·mg)); q0 is the equilibrium DMCA uptake per g of the adsorbent (mg/g); x is amount of adsorbent in the column (g); v is the flow rate of the solution passing through the column (mL/min). The value of Ct/C0 is the ratio of effluent and influent DMCA concentrations. The value of t is flow time (min). a and b (mL) are parameters of the Yan model. Data obtained from column experiments were used to fit the Thomas model and Yan model. The parameters and values of R 2 (coefficient of determination) and sum of squared errors (SS) according to nonlinear regressive analysis are listed in Table 1, respectively. From Table 1, the values of kTh became bigger with the flow rate increasing. With the bed depth increasing, the values of kTh became smaller while the value of q0 increased. The Yan model can minimize the error that results from use of the Thomas model, especially with lower and higher breakthrough curve times. The trend of values of q0 and b was similar to values of q0 from the Thomas model with the change in experimental conditions. Adsorption quantity (q0) obtained from the Yan model was from 3.33 to 6.46 mg/g. Compared to values of q0 at the same conditions listed in Table 1, the value of q0 from the Yan model was smaller than that from the Thomas model, respectively. It was also found that the value of R 2 from the Yan model was larger while the value of SS was smaller at the same experimental condition. Furthermore, at all conditions, the predicted breakthrough curves from the Yan model showed better agreement with the experimental
Table 1
|
|
68.10
|
2013
curves (shown in Figure 2). Thus it was concluded that the Yan model was better to predict breakthrough curves than the Thomas model. Several researchers have studied metal and dye removal by adsorption in column mode and similar results were obtained (Yan et al. ; Wu et al. ; Song et al. ). The bed depth/service time analysis (BDST) model The BDST model is based on physically measuring the capacity of the bed at different breakthrough values. The BDST model works well and provides useful modeling equations for the changes of system parameters (Goel et al. ). A modified form of the equation that expresses the service time at breakthrough, t, as a fixed function of operation parameters is the BDST model: t¼
N0 1 C0 ln 1 Z Ka C0 C0 F Ct
(4)
where F is influent linear velocity (cm min1); N0 is adsorption capacity (mg/L); Ka is rate constant in BDST model (L/(mg·min)); and Z is bed depth of column (cm). The service time at breakthrough point, tb, was chosen as that when the effluent DMCA concentration attained 5% of the influent concentration and was plotted against bed height. At a given linear flow rate (5.73 cm/min), the curve tb vs Z was found to be linear (figure not shown): tb ¼ 1.053Z 1.706, suggesting that the BDST model applied to this system was valid (with R² ¼ 0.946). The
Parameters of Thomas model and Yan model C0 (mg/L)
v (mL/min)
Z (cm)
q0 (mg/g)
R2
kTh (mL/min mg)
SS
Thomas model 40
4.5
3.5
4.38 ± 0.06
2.90 ± 0.40
0.896
0.00818
40
4.5
5.2
4.74 ± 0.05
2.60 ± 0.33
0.914
0.00823
40
4.5
8.6
7.32 ± 0.03
1.97 ± 0.13
0.876
0.0124
40
1.7
5.2
4.13 ± 0.03
1.54 ± 0.13
0.966
0.00444
40
7.2
5.2
3.73 ± 0.08
5.15 ± 0.53
0.951
0.00395
Yan model
Note: SS ¼
P
2
40
4.5
3.5
1.44 ± 0.06
56.0 ± 1.8
4.08 ± 0.14
0.985
0.00114
40
4.5
5.2
1.63 ± 0.08
80.5 ± 2.6
4.24 ± 0.09
0.982
0.00172
40
4.5
8.6
1.46 ± 0.07
210.0 ± 6.5
6.46 ± 0.20
0.981
0.00184
40
1.7
5.2
2.28 ± 0.09
73.0 ± 1.4
3.84 ± 0.07
0.991
0.00114
40
7.2
5.2
1.83 ± 0.05
63.2 ± 1.1
3.33 ± 0.06
0.994
0.00041
ðq qc Þ =ðn 2Þ, q and qc are the experimental value and calculated value according to the model, respectively.
2163
S. Zhang et al.
|
Adsorption of chloro-anilines by modified peanut husk
Water Science & Technology
slope of the BDST straight line and its intercept allowed values of N0 237.4 mg/L and Ka 0.0431 L/mg min to be obtained. The critical bed depth (Z0) was also determined in this work; it corresponds to the bed depth required for preventing the outlet DMCA concentration from being over 5% of the influent concentration at time t ¼ 0; this theoretical depth of MPH was then obtained by taking Cb¼ 0.05 C0 and by substituting t ¼ 0 in Equation (4). F C0 ln 1 Z0 ¼ Ka N0 Cb
(5)
Usually, values of N0 and Ka changed slightly with different flow rates; the critical bed depth Z0 can be calculated and was 0.63, 1.65, 2.67 cm at flow rates of 1.7, 4.2, and 7.2 mL/ min, respectively. This result implied that Z0 is directly related to flow rate. This meant that DMCA adsorption onto MPH ought to be efficient only if bed heights Z were over Z0.
CONCLUSION Analysis of NPH and MPH by FTIR and X-ray fluorescence implied that there was CTAB on the surface of MPH. Higher bed depth and lower flow rate were advantageous for DMCA adsorption. Column experimental data can be better fitted by the Yan model while values of critical bed depth were calculated by BDST. MPH as a low-cost adsorbent is available to remove DMCA from solution.
ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (J1210060).
REFERENCES Aksu, Z. Application of biosorption for the removal of organic pollutants: a review. Process Biochem. 40 (3–4), 997–1026.
|
68.10
|
2013
Aksu, Z. & Gonen, F. Biosorption of phenol by immobilized activated sludge in a continuous packed bed: prediction of breakthrough curves. Process Biochem. 39 (5), 599–613. Bhatnagar, A. & Sillanpaa, M. Utilization of agro-industrial and municipal waste materials as potential adsorbents for water treatment - a review. Chem. Eng. J. 157 (2–3), 277–296. Crini, G. Non-conventional low-cost adsorbents for dye removal: a review. Bioresour. Technol. 97 (9), 1061–1085. Goel, J., Kadirvelu, K., Rajagopal, C. & Garg, V. K. Removal of lead(II) by adsorption using treated granular activated carbon: batch and column studies. J. Hazard. Mater. 125 (1– 3), 211–220. Gu, X. H., Zhou, J. T., Zhang, A. L., Wang, P., Xiao, M. & Liu, G. F. Feasibility study of the treatment of aniline hypersaline wastewater with a combined adsorption/bioregeneration system. Desalination 227 (1–3), 139–149. Gupta, V. K. & Suhas Application of low-cost adsorbents for dye removal: a review. J. Environ. Manage. 90 (8), 2313–2342. Ibrahim, S., Fatimah, I., Ang, H. M. & Wang, S. B. a Adsorption of anionic dyes in aqueous solution using chemically modified barley straw. Water Sci. Technol. 62 (5), 1177–1182. Ibrahim, S., Wang, S. B. & Ang, H. M. b Removal of emulsified oil from oily wastewater using agricultural waste barley straw. Biochem. Eng. J. 49 (1), 78–83. Johnson, P. D., Watson, M. A., Brown, J. & Jefcoat, I. A. Peanut hull pellets as a single use sorbent for the capture of Cu(II) from wastewater. Waste Manage. 22 (5), 471–480. Namasivayam, C. & Sureshkumar, M. V. Anionic dye adsorption characteristics of surfactant modified coir pith, a waste lignocellulosic polymer. J. Appl. Polym. Sci. 100 (2), 1538–1546. Oei, B. C., Ibrahim, S., Wan, S. B. & Ang, H. M. Surfactant modified barley straw for removal of acid and reactive dyes from aqueous solution. Bioresour. Technol. 100 (18), 4292–4295. Song, J. Y., Zou, W. H., Bian, Y. Y., Su, F. Y. & Han, R. P. Adsorption characteristics of methylene blue by peanut husk in batch and column mode. Desalination 265 (1–3), 119–125. Su, Y. Y., Zha, B. L., Xiao, W. & Han, R. P. Adsorption behavior of light green anionic dye using cationic surfactant modified wheat straw in batch and column mode. Environ. Sci. Pollut. Res. 20 (8), 5558–5568. Wu, X. L., Wang, Y., Liu, J. L., Ma, J. Y. & Han, R. P. Study of Malachite Green adsorption onto natural zeolite in fixed-bed column. Desalin. Water Treat. 20 (1–3), 228–233. Yan, G., Viraraghavan, T. & Chen, M. A new model for heavy metal removal in a biosorption column. Adsorpt. Sci. Technol. 19 (1), 25–43.
First received 21 May 2013; accepted in revised form 8 July 2013. Available online 24 October 2013
Copyright of Water Science & Technology is the property of IWA Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
