- Email: [email protected]
Preparation and characterization of titania nanoparticle produced from Ti-flocculated sludge with paper mill wastewater
Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Preparation and characterization of titania nanoparticle produced from Ti-flocculated sludge with paper mill wastewater Suk-Hyun Na a, Ho Kyong Shon b, Jong Beom Kim a,c, Hee Ju Park c, Jong-Ho Kim a,c,* a
School of Applied Chemical Engineering & The Institute for Catalysis Research, Chonnam National University, Gwangju 500-757, Republic of Korea Faculty of Engineering and Information Technology, University of Technology, Sydney (UTS), P.O. Box 123, Broadway, NSW 2007, Australia c Photo & Environmental Technology Co., LTD., Gwangju 500-460, Republic of Korea b
A R T I C L E I N F O
Article history: Received 17 June 2010 Accepted 18 August 2010 Available online 2 March 2011 Keywords: Paper mill wastewater Flocculation Sludge Titania Titanium tetrachloride Recycling
A B S T R A C T
Sludge disposal after flocculation with paper mill wastewater is one of the most costly and environmentally problematic challenges. In this study, an effective sludge recycling process was proposed using Ti-salt coagulant instead of the currently used Fe-salt. Paper mill wastewater flocculation using TiCl4 and FeCl3 coagulants was investigated for organic removal and precipitation efficiency. A large amount of titania nanoparticle was produced after incineration of sludge of Ti-salt flocculation in paper mill wastewater. The titania nanoparticle was characterized in terms of physical and chemical properties. Results showed that the removal efficiency of organic matter at the optimum concentrations of Ti- and Fe-salt was 69% and 65%, respectively. The removal of turbidity was 99%. Titania recovered from 600 8C incineration of the settled sludge consisted of the anatase titania structure. The titania from printing paper mill wastewater showed irregularly aggregated structures with round shape of dimension of 10–15 nm as a primary crystal growth. Various dopant materials were found to be carbon (4.3%), magnesium (0.9%), aluminium (1.9%), silicon (1.7%), sulphur (0.7%) and calcium (3.8%). 60% of acetaldehyde concentration under UV irradiation was removed with the titania nanoparticles produced from the printing paper mill wastewater. ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction The pulp and paper industry is one of the largest industries to produce a large amount of wastewater (240–300 m3/ton of product) in the world [1,2]. The wastewater from wood pulping and paper production consists of a considerable amount of pollutants such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), toxicity and color. These high concentrations of pollutants also generate a serious environmental impact when discharging to the river system, e.g., slime growth, thermal impacts, scum formation, color problems, and aesthetic defects [3]. As such, it is essential to select an appropriate treatment method in removing high concentrated multi-component pollutants, which complies with increasing stringent regulations. Paper and pulp wastewater can be treated by physicochemical (flocculation, flotation, adsorption, oxidation, membrane technology), electrical (electrocoagulation, electrochemical) and biologi-
* Corresponding author at: Chonnam National University, Gwangju 500-757, Republic of Korea. Tel.: +82 62 530 1888; fax: +82 62 530 1889. E-mail address: [email protected] (J.-H. Kim).
cal (aerobic, anaerobic) processes [2–10]. Pokhrel and Viraraghavan [2] reported that combinations of anaerobic and aerobic biological treatment processes are efficient in the removal of soluble biodegradable organic pollutants. However, lignocellulosic materials present in paper mill wastewater cannot be removed by biological processes. Color can be eliminated by fungal treatment, flocculation, chemical oxidation, and ozonation and chlorinated phenolic compounds and adsorable organic halides can be reduced by adsorption, ozonation and membrane filtration techniques. Among the various treatment methods, flocculation has been recognized as one of the most effective processes due to high colloidal suspended solids and different characteristics of the paper and pulp wastewater [11,12]. Flocculation of paper mill wastewater mainly uses inorganic salt, e.g., aluminium sulphate, iron salts, and polyaluminium chloride, while the use of synthetic polymers like hexamethylene epichlorohydrin polycondensate, polyethyleneimine, polyacrylamide, natural polymers like chitosan has also been investigated by many research workers [5,13]. Stephenson and Duff [14] observed that the removal of total carbon, color and turbidity was 88%, 90% and 98%, respectively, using ferric chloride, ferrous sulphate, aluminium chloride and aluminium sulphate. However, the main drawback of flocculation is to produce a large amount of
1226-086X/$ – see front matter ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2011.02.022
S.-H. Na et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
278
settled floc (sludge) after treatment. Thus, an additional process for sludge disposal is mostly required, which is landfill, ocean dumping, fertilizer, etc. Sludge disposal is one of the most costly and environmentally problematic challenges in treating paper mill wastewater. An effective sludge recycling process after flocculation has been developed by our group [15,16]. We investigated the possibility of sludge recovery using a Ti-salt coagulant. Sludge produced after Tisalt flocculation of wastewater was incinerated to produce a valuable nanoparticle, namely titanium dioxide (titania). An amount as high as 40 mg-titania/L wastewater of titania nanoparticle was produced from wastewater sludge generated by the Tisalt flocculation [15]. To date, the Ti-salt flocculation has been applied to drinking water [17], seawater [18], biologically treated sewage effluent [19] and dye wastewater [20]. However, none of previous studies have used the Ti-salt coagulant to treat a pulp and paper mill wastewater. The objectives of this study were (i) to compare the efficiency of paper mill wastewater flocculation using FeCl3 and TiCl4 as coagulants in terms of COD removal, pH variation and the precipitation efficiency, (ii) to produce titania nanoparticle from the incineration of the Ti-flocculated sludge and (iii) to characterize titania in terms of X-ray diffraction (XRD), scanning election microscopy/energy dispersive X-ray (SEM/EDX), transmission electron microscopy (TEM), and photodecomposition of acetaldehyde.
settled sludge in mL occupied by 1 g of dry sludge solids after 30 min of settling in a 1 L graduated cylinder. The following equation [1] shows the computation of the SVI (mL/g): SVI ¼
settled sludge volume in mL=L after 30 min 1000 mixed liquor suspended solids in mg=L
(1)
2.3. Titania characteristics After incineration treatment of the collected sludge produced from the paper mill wastewaters, a white powder was produced. Here, the powder was characterized in terms of high resolution XRD (D/MaxUltima, Rigaku, Japan), SEM/EDX (S4700, HITACHI, Japan) and HR-TEM (Tecnai F20, Philips, Holland). Adsorption and photocatalytic oxidation of acetaldehyde over UVA-illuminated TiO2 produced from the paper mill wastewaters were studied using a cuboid stainless (Top-face glass) airtight reactor with a total volume of 2 L. The reactor was equipped with two 10 W, 352 nm UVA lamps (Sankyo Denki, F10T8BL, Japan) and had three rubber openings; the first was used for the injection of acetaldehyde, the second connected to an air pump to ensure mixing of air inside the reactor and the third as sampling aperture connected to a gas chromatograph GC/HID (M600D, YoungLin, Korea) with Supel-Q PLOT capillary column (30 m 0.52 mm) for measuring acetaldehyde concentration variations. 3. Results and discussion
2. Experimental
3.1. Flocculation performance with TiCl4 and FeCl3 coagulants
2.1. Paper mill wastewater Two paper mill wastewaters were withdrawn from a printing paper mill wastewater treatment plant in Jellanamdo and a newspaper printing paper mill wastewater treatment plant in Chungcheongdo, South Korea. Table 1 shows the water characteristics of the two paper mill wastewaters used in this study. For an accurate experiment, the initial values of the pHs of two paper mill wastewater were neutralized to pH 7 with NaOH and H2SO4. The water quality was measured using standard methods for the examination of water [21]. 2.2. Flocculation with FeCl3 and TiCl4 coagulants Two coagulants (FeCl3 and TiCl4) were used in the flocculation experiments with two paper mill wastewater sources. The FeCl3 coagulant was used to compare the flocculation performance with TiCl4. The paper mill wastewater with two coagulants was stirred rapidly for 1 min at 100 rpm, followed by 20 min of slow mixing at 30 rpm, and 30 min of settling. Different concentrations of FeCl3 and TiCl4 coagulants were added to identify a corresponding optimum dosage. COD and turbidity were measured using standard methods [21] and the pH was recorded using a pH meter (Thermo Orion, USA). The decantability test to investigate the settling velocity of the settled floc after different flocculations was measured in terms of sludge volume index (SVI) using 1 L Imhoff cones by a volumetric method [22]. The SVI is the volume of
Table 1 Water characteristics of paper mill wastewaters used. Item
Printing paper wastewater
Newspaper wastewater
pH CODCr (mg/L) SS (mg/L) Turbidity (NTU)
6.91 1604 2040 800
7.98 2016 4530 1550
3.1.1. COD removal and pH variation The jar-test was performed with two paper mill wastewaters. Fig. 1 shows the pH variation and the COD removal after flocculation of paper mill wastewaters by using TiCl4 and FeCl3. As the concentration of coagulants increased, the pH decreased. In the case of the printing paper mill wastewater, when pH reached between 3 and 4, the high removal of COD was found, suggesting that the point zero of zeta potential with the Ti-salt flocculation is around pH 3.5. The initial COD concentration of the printing and newspaper mill wastewaters was 1604 and 2016 mg/L, respectively. With the printing paper mill wastewater, the optimum concentrations of Ti- and Fe-salt were found to be 7.19 Ti-mg/L and 11.73 Fe-mg/L, respectively. The removal efficiency at the optimum concentrations of Ti- and Fe-salt was 69% and 65%, respectively. On the other hand, the removal efficiency of COD with Ti- and Fe-salt coagulants in the newspaper mill wastewater was lower than that of the printing paper mill wastewater. This is probably due to the initial pH effect. Higher initial pH in wastewater seems to be required with high concentration of a coagulant to achieve a point zero of zeta potential. Although turbidity removal was not shown, the removal of turbidity was 99% at the initial turbidity of 800 and 1550 NTU for both coagulants. As such, the use of TiCl4 is feasible and has more advantages because the benefits generated from titania production by the incineration of sludge will make it better than FeCl3 that produces sludge which needs to be disposed of. 3.1.2. Decantability test The settability test of the settled floc after Ti- and Fe-salt flocculation was investigated in terms of SVI measurement. Fig. 2 presents the SVI values obtained at the respective optimum dosages of Ti- and Fe-salt flocculation. It should be noted that a range of 50–150 mL/g SVI value represents a stabilized sludge index [22]. The SVI value after Ti-salt flocculation was 150 mL/g, whereas that after Fe-salt flocculation was 380 mL/g. This suggests
[()TD$FIG]
S.-H. Na et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
279
Fig. 1. COD removal and pH variation of paper mill wastewater flocculation (A: printing paper mill and B: newspaper mill wastewater) by using FeCl3 and TiCl4.
that the Ti-salt sludge indicates more stabilized sludge compared to the Fe-salt sludge. Shon et al. [15] found that the size of Ti-salt floc sludge is bigger than that of Fe- and Al-salt floc. 3.2. Characteristics of titania 3.2.1. XRD pattern Sludge generated from the Ti-salt flocculation of two paper mill wastewaters was incinerated at 600 8C. Shon et al. [15] reported that this temperature could be considered as the most effective in terms of energy saving and photocatalytic activity of the generated titania. Fig. 3 shows XRD pattern to identify the structure of the powder produced from incineration of the Ti-salt settled floc. XRD results showed that the anatase structure was predominant in both titania. According to the intensity of the XRD patterns, titania produced from printing paper mill wastewater showed higher crystallization than that produced from newspaper paper mill wastewater. Due to the impurities of wastewater quality, both [()TD$FIG]
powders produced an unidentified structures at u = 298. In this study, the titania produced from the printing paper mill wastewater indicated better structure of titania. Thus, the remaining titania characteristics are mainly carried out with the titania produced from the printing paper mill wastewater. 3.2.2. Visual observation The SEM image of titania is shown in Fig. 4. Commercially available P-25 titania showed regular round shaped nanoparticles of 25 nm in size (data not shown). However, the titania produced from Ti-salt flocculated sludge with printing paper mill wastewater showed irregularly aggregated structures with round shape. Table 2 shows the EDX results of the titania generated from printing paper mill wastewater. The titania consisted of 31% of titanium and 56% of oxygen together with carbon, calcium, aluminium and silicon. Shon et al. [15] found carbon and phosphorus dopants in titania produced from synthetic wastewater which represented biologically treated sewage effluent. However, the titania produced from the printing paper mill wastewater included various dopant materials such as carbon (4.3%), magnesium (0.9%), aluminium (1.9%), silicon (1.7%), sulphur (0.7%) and calcium (3.8%). This is probably due to differences in
[()TD$FIG]
Fig. 2. SVI obtained at the optimum dosages of Ti- and Fe-salt flocculation.
Fig. 3. XRD pattern of powder produced from incineration of the Ti-salt settled floc at 600 8C with the paper and newsprint mill wastewaters.
[()TD$FIG]
[()TD$FIG]
S.-H. Na et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
280
Fig. 4. SEM image of titania produced from printing paper mill wastewater. Table 2 Atomic percentage of titania produced from printing paper mill wastewater. Atom
Atomic percentage (%)
Atom
Atomic percentage (%)
C O Mg Al
4.27 55.87 0.87 1.85
Si S Ca Ti
1.73 0.73 3.79 30.90
chemical compositions between synthetic wastewater and printing paper mill wastewater from which both catalysts were generated. TEM photographs of the titania showed round shape with estimated dimension of 10–15 nm as a primary crystal growth (Fig. 5). The round shape of the titania nanoparticle was not uniform, had several structural defects and were interconnected at certain sites. 3.2.3. Photocatalytic activity The photocatalytic oxidation of acetaldehyde with the titania produced from the printing paper mill wastewater using Ti-salt coagulant was compared with that with the titania prepared from the newspaper mill wastewater (Fig. 6). The acetaldehyde
[()TD$FIG]
Fig. 5. High-resolution transmission electron microscope image of titania produced from the printing paper mill wastewater.
Fig. 6. Photodecomposition of acetaldehyde by titania under UV irradiation (amount of TiO2 = 0.5 g; initial concentration of acetaldehyde = 2000 ppmv; UV irradiation = UV black light three 10 W lamps).
concentration decrease was measured by using a GC. The difference from initial concentration was calculated in terms of adsorption and photo-oxidation percentage. Acetaldehyde was adsorbed onto titania surface in dark conditions for 60 min (lamp off). The removal after 60 min adsorption was negligible and the concentration (around 1900 ppmv) was slightly lower than the initial concentration (2000 ppmv) for both titania. When UV lamps were on, 60% of acetaldehyde concentration was removed with the titania nanoparticle produced from the printing paper mill wastewater, while the photo-oxidation of the titania produced from the newspaper mill wastewater was marginal. This suggests that the titania from the printing mill wastewater has the high potential use for decomposing volatile organic contaminants. 4. Conclusions Flocculation using TiCl4 and FeCl3 with printing paper mill and newspaper mill wastewaters was performed and two coagulants used were compared for COD removal and settling ability of the settled floc. The settled floc after Ti-salt flocculation was incinerated to produce titania nanoparticle. The titania produced from different paper mill wastewater sources was characterized in terms of XRD, SEM/EDX, TEM and the photodecomposition of acetaldehyde under UV-irradiation. According to the results obtained the following conclusions can be drawn: The removal efficiency of COD at the optimum concentrations of Ti- and Fe-salt was 69% and 65%, respectively. The removal of turbidity was 99% at the initial turbidity of 800 and 1550 NTU for both coagulants. The SVI value after Ti-salt flocculation was 150 mL/g, whereas that after Fe-salt flocculation was 380 mL/g. The anatase titania structure was predominant after incineration of both sludge from printing and newspaper wastewater. The titania from printing paper mill wastewater consisted of irregularly aggregated structures with round shape of dimension of 10–15 nm as a primary crystal growth, including various dopant materials such as carbon (4.3%), magnesium (0.9%), aluminium (1.9%), silicon (1.7%), sulphur (0.7%) and calcium (3.8%). The removal of acetaldehyde after 60 min adsorption was negligible. However, when UV lamps were on, 60% of acetaldehyde concentration was removed with the titania nanoparticles produced from the printing paper mill wastewater, while the photo-oxidation of the titania produced from the newspaper mill wastewater was marginal.
S.-H. Na et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
Acknowledgements This work was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (20090094057) and the Center for Photonic Materials and Devices at Chonnam National University. This study was partially supported by CRC-CARE. This subject is supported by Korea Ministry of Environment as ‘‘Converging technology project’’. References [1] S. Lacorte, A. Latorre, D. Barcelo, A. Rigo, A. Malmqvist, T. Welander, Trends Anal. Chem. 22 (2003) 725. [2] D. Pokhrel, T. Viraraghavan, Sci. Total Environ. 333 (2004) 37. [3] S.S. Wong, T.T. Teng, A.L. Ahmad, A. Zuhairi, G. Najafpour, J. Hazard. Mater. B135 (2006) 378. [4] E. Chamarro, A. Marco, S. Esplugas, Water Res. 35 (2001) 1047. [5] V.C. Srivastava, I.D. Mall, I.M. Mishra, Physichem. Eng. Aspects 260 (2005) 17. [6] Y. Zhang, C. Ma, F. Ye, Y. Kong, H. Li, Desalination 236 (2009) 349. [7] T. Leiviska¨, H. Nurmesniemi, R. Po¨ykio¨, J. Ra¨mo¨, T. Kuokkanen, J. Pellinen, Water Res. 42 (2008) 3952. [8] H. Ma, B. Wang, Y. Wang, J. Hazard. Mater. 145 (2007) 417.
281
[9] T. Leiviska¨, J. Ra¨mo¨, H. Nurmesniemi, R. Po¨ykio¨, T. Kuokkane, Water Res. 43 (2009) 3199. [10] G. Thompson, J. Swain, M. Kay, C.F. Forster, Bioresour. Technol. 77 (2001) 275. [11] A.C. Rodriques, M. Boroski, N.S. Shimada, J.C. Garcia, J. Nzaki, N. Hioka, J. Photochem. Photobiol. A: Chem. 194 (2008) 1. [12] H. Katja, S. Mika, J. Research, Chem. Environ. 11 (2007) 96. [13] H. Ganjidoust, K. Tatsumi, T. Yamagishi, R.N. Gholian, Water Sci. Technol. 35 (1997) 291. [14] R.J. Stephenson, S.J.B. Duff, Water Res. 30 (1996) 781. [15] H.K. Shon, S. Vigneswaran, I.S. Kim, J. Cho, G.J. Kim, J.B. Kim, J.-H Kim, Environ. Sci. Technol. 41 (2007) 1372. [16] S.H. Na, H.K. Shon, J.B. Kim, H.J. Park, D.L. Cho, I.E. Saliby, J.H. Kim, J. Korean Ind. Eng. Chem. 16 (2010) 96. [17] B.C. Lee, S. Kim, H.K. Shon, S. Vigneswaran, S.D. Kim, J. Cho, I.S. Kim, K.H. Choi, J.B. Kim, H.J. Park, J.-H. Kim, J. Nanopart. Res. 11 (2009) 2087. [18] Y. Okour, I.E. Saliby, H.K. Shon, S. Vigneswaran, J.-H. Kim, J. Cho, I.S. Kim, Desalination 249 (2009) 53. [19] Y. Okour, H.K. Shon, I. El Saliby, R. Naidu, J.B. Kim, J.H. Kim, Bioresour. Technol. 101 (2009) 1453. [20] J.B. Kim, H.J. Park, H.K. Shon, D.L. Cho, G.J. Kim, S.W. Choi, J.H. Kim, J. Nanosci. Nanotechnol. 10 (2010) 3260. [21] APHA, Standard Methods for the Examination of Water and Wastewater, 20th ed., Am. Publ. Hlth. Assoc., Washington, DC, 1998. [22] L.S. Clescen, A.E. Greenberg, Standard Methods for the Examination of Water and Wastewater, 19th ed., Eaton AD, APHA, Report No. 331, Washington APM, Washington, DC, 1995.
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Preparation and characterization of titania nanoparticle produced from Ti-flocculated sludge with paper mill wastewater Suk-Hyun Na a, Ho Kyong Shon b, Jong Beom Kim a,c, Hee Ju Park c, Jong-Ho Kim a,c,* a
School of Applied Chemical Engineering & The Institute for Catalysis Research, Chonnam National University, Gwangju 500-757, Republic of Korea Faculty of Engineering and Information Technology, University of Technology, Sydney (UTS), P.O. Box 123, Broadway, NSW 2007, Australia c Photo & Environmental Technology Co., LTD., Gwangju 500-460, Republic of Korea b
A R T I C L E I N F O
Article history: Received 17 June 2010 Accepted 18 August 2010 Available online 2 March 2011 Keywords: Paper mill wastewater Flocculation Sludge Titania Titanium tetrachloride Recycling
A B S T R A C T
Sludge disposal after flocculation with paper mill wastewater is one of the most costly and environmentally problematic challenges. In this study, an effective sludge recycling process was proposed using Ti-salt coagulant instead of the currently used Fe-salt. Paper mill wastewater flocculation using TiCl4 and FeCl3 coagulants was investigated for organic removal and precipitation efficiency. A large amount of titania nanoparticle was produced after incineration of sludge of Ti-salt flocculation in paper mill wastewater. The titania nanoparticle was characterized in terms of physical and chemical properties. Results showed that the removal efficiency of organic matter at the optimum concentrations of Ti- and Fe-salt was 69% and 65%, respectively. The removal of turbidity was 99%. Titania recovered from 600 8C incineration of the settled sludge consisted of the anatase titania structure. The titania from printing paper mill wastewater showed irregularly aggregated structures with round shape of dimension of 10–15 nm as a primary crystal growth. Various dopant materials were found to be carbon (4.3%), magnesium (0.9%), aluminium (1.9%), silicon (1.7%), sulphur (0.7%) and calcium (3.8%). 60% of acetaldehyde concentration under UV irradiation was removed with the titania nanoparticles produced from the printing paper mill wastewater. ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction The pulp and paper industry is one of the largest industries to produce a large amount of wastewater (240–300 m3/ton of product) in the world [1,2]. The wastewater from wood pulping and paper production consists of a considerable amount of pollutants such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), toxicity and color. These high concentrations of pollutants also generate a serious environmental impact when discharging to the river system, e.g., slime growth, thermal impacts, scum formation, color problems, and aesthetic defects [3]. As such, it is essential to select an appropriate treatment method in removing high concentrated multi-component pollutants, which complies with increasing stringent regulations. Paper and pulp wastewater can be treated by physicochemical (flocculation, flotation, adsorption, oxidation, membrane technology), electrical (electrocoagulation, electrochemical) and biologi-
* Corresponding author at: Chonnam National University, Gwangju 500-757, Republic of Korea. Tel.: +82 62 530 1888; fax: +82 62 530 1889. E-mail address: [email protected] (J.-H. Kim).
cal (aerobic, anaerobic) processes [2–10]. Pokhrel and Viraraghavan [2] reported that combinations of anaerobic and aerobic biological treatment processes are efficient in the removal of soluble biodegradable organic pollutants. However, lignocellulosic materials present in paper mill wastewater cannot be removed by biological processes. Color can be eliminated by fungal treatment, flocculation, chemical oxidation, and ozonation and chlorinated phenolic compounds and adsorable organic halides can be reduced by adsorption, ozonation and membrane filtration techniques. Among the various treatment methods, flocculation has been recognized as one of the most effective processes due to high colloidal suspended solids and different characteristics of the paper and pulp wastewater [11,12]. Flocculation of paper mill wastewater mainly uses inorganic salt, e.g., aluminium sulphate, iron salts, and polyaluminium chloride, while the use of synthetic polymers like hexamethylene epichlorohydrin polycondensate, polyethyleneimine, polyacrylamide, natural polymers like chitosan has also been investigated by many research workers [5,13]. Stephenson and Duff [14] observed that the removal of total carbon, color and turbidity was 88%, 90% and 98%, respectively, using ferric chloride, ferrous sulphate, aluminium chloride and aluminium sulphate. However, the main drawback of flocculation is to produce a large amount of
1226-086X/$ – see front matter ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2011.02.022
S.-H. Na et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
278
settled floc (sludge) after treatment. Thus, an additional process for sludge disposal is mostly required, which is landfill, ocean dumping, fertilizer, etc. Sludge disposal is one of the most costly and environmentally problematic challenges in treating paper mill wastewater. An effective sludge recycling process after flocculation has been developed by our group [15,16]. We investigated the possibility of sludge recovery using a Ti-salt coagulant. Sludge produced after Tisalt flocculation of wastewater was incinerated to produce a valuable nanoparticle, namely titanium dioxide (titania). An amount as high as 40 mg-titania/L wastewater of titania nanoparticle was produced from wastewater sludge generated by the Tisalt flocculation [15]. To date, the Ti-salt flocculation has been applied to drinking water [17], seawater [18], biologically treated sewage effluent [19] and dye wastewater [20]. However, none of previous studies have used the Ti-salt coagulant to treat a pulp and paper mill wastewater. The objectives of this study were (i) to compare the efficiency of paper mill wastewater flocculation using FeCl3 and TiCl4 as coagulants in terms of COD removal, pH variation and the precipitation efficiency, (ii) to produce titania nanoparticle from the incineration of the Ti-flocculated sludge and (iii) to characterize titania in terms of X-ray diffraction (XRD), scanning election microscopy/energy dispersive X-ray (SEM/EDX), transmission electron microscopy (TEM), and photodecomposition of acetaldehyde.
settled sludge in mL occupied by 1 g of dry sludge solids after 30 min of settling in a 1 L graduated cylinder. The following equation [1] shows the computation of the SVI (mL/g): SVI ¼
settled sludge volume in mL=L after 30 min 1000 mixed liquor suspended solids in mg=L
(1)
2.3. Titania characteristics After incineration treatment of the collected sludge produced from the paper mill wastewaters, a white powder was produced. Here, the powder was characterized in terms of high resolution XRD (D/MaxUltima, Rigaku, Japan), SEM/EDX (S4700, HITACHI, Japan) and HR-TEM (Tecnai F20, Philips, Holland). Adsorption and photocatalytic oxidation of acetaldehyde over UVA-illuminated TiO2 produced from the paper mill wastewaters were studied using a cuboid stainless (Top-face glass) airtight reactor with a total volume of 2 L. The reactor was equipped with two 10 W, 352 nm UVA lamps (Sankyo Denki, F10T8BL, Japan) and had three rubber openings; the first was used for the injection of acetaldehyde, the second connected to an air pump to ensure mixing of air inside the reactor and the third as sampling aperture connected to a gas chromatograph GC/HID (M600D, YoungLin, Korea) with Supel-Q PLOT capillary column (30 m 0.52 mm) for measuring acetaldehyde concentration variations. 3. Results and discussion
2. Experimental
3.1. Flocculation performance with TiCl4 and FeCl3 coagulants
2.1. Paper mill wastewater Two paper mill wastewaters were withdrawn from a printing paper mill wastewater treatment plant in Jellanamdo and a newspaper printing paper mill wastewater treatment plant in Chungcheongdo, South Korea. Table 1 shows the water characteristics of the two paper mill wastewaters used in this study. For an accurate experiment, the initial values of the pHs of two paper mill wastewater were neutralized to pH 7 with NaOH and H2SO4. The water quality was measured using standard methods for the examination of water [21]. 2.2. Flocculation with FeCl3 and TiCl4 coagulants Two coagulants (FeCl3 and TiCl4) were used in the flocculation experiments with two paper mill wastewater sources. The FeCl3 coagulant was used to compare the flocculation performance with TiCl4. The paper mill wastewater with two coagulants was stirred rapidly for 1 min at 100 rpm, followed by 20 min of slow mixing at 30 rpm, and 30 min of settling. Different concentrations of FeCl3 and TiCl4 coagulants were added to identify a corresponding optimum dosage. COD and turbidity were measured using standard methods [21] and the pH was recorded using a pH meter (Thermo Orion, USA). The decantability test to investigate the settling velocity of the settled floc after different flocculations was measured in terms of sludge volume index (SVI) using 1 L Imhoff cones by a volumetric method [22]. The SVI is the volume of
Table 1 Water characteristics of paper mill wastewaters used. Item
Printing paper wastewater
Newspaper wastewater
pH CODCr (mg/L) SS (mg/L) Turbidity (NTU)
6.91 1604 2040 800
7.98 2016 4530 1550
3.1.1. COD removal and pH variation The jar-test was performed with two paper mill wastewaters. Fig. 1 shows the pH variation and the COD removal after flocculation of paper mill wastewaters by using TiCl4 and FeCl3. As the concentration of coagulants increased, the pH decreased. In the case of the printing paper mill wastewater, when pH reached between 3 and 4, the high removal of COD was found, suggesting that the point zero of zeta potential with the Ti-salt flocculation is around pH 3.5. The initial COD concentration of the printing and newspaper mill wastewaters was 1604 and 2016 mg/L, respectively. With the printing paper mill wastewater, the optimum concentrations of Ti- and Fe-salt were found to be 7.19 Ti-mg/L and 11.73 Fe-mg/L, respectively. The removal efficiency at the optimum concentrations of Ti- and Fe-salt was 69% and 65%, respectively. On the other hand, the removal efficiency of COD with Ti- and Fe-salt coagulants in the newspaper mill wastewater was lower than that of the printing paper mill wastewater. This is probably due to the initial pH effect. Higher initial pH in wastewater seems to be required with high concentration of a coagulant to achieve a point zero of zeta potential. Although turbidity removal was not shown, the removal of turbidity was 99% at the initial turbidity of 800 and 1550 NTU for both coagulants. As such, the use of TiCl4 is feasible and has more advantages because the benefits generated from titania production by the incineration of sludge will make it better than FeCl3 that produces sludge which needs to be disposed of. 3.1.2. Decantability test The settability test of the settled floc after Ti- and Fe-salt flocculation was investigated in terms of SVI measurement. Fig. 2 presents the SVI values obtained at the respective optimum dosages of Ti- and Fe-salt flocculation. It should be noted that a range of 50–150 mL/g SVI value represents a stabilized sludge index [22]. The SVI value after Ti-salt flocculation was 150 mL/g, whereas that after Fe-salt flocculation was 380 mL/g. This suggests
[()TD$FIG]
S.-H. Na et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
279
Fig. 1. COD removal and pH variation of paper mill wastewater flocculation (A: printing paper mill and B: newspaper mill wastewater) by using FeCl3 and TiCl4.
that the Ti-salt sludge indicates more stabilized sludge compared to the Fe-salt sludge. Shon et al. [15] found that the size of Ti-salt floc sludge is bigger than that of Fe- and Al-salt floc. 3.2. Characteristics of titania 3.2.1. XRD pattern Sludge generated from the Ti-salt flocculation of two paper mill wastewaters was incinerated at 600 8C. Shon et al. [15] reported that this temperature could be considered as the most effective in terms of energy saving and photocatalytic activity of the generated titania. Fig. 3 shows XRD pattern to identify the structure of the powder produced from incineration of the Ti-salt settled floc. XRD results showed that the anatase structure was predominant in both titania. According to the intensity of the XRD patterns, titania produced from printing paper mill wastewater showed higher crystallization than that produced from newspaper paper mill wastewater. Due to the impurities of wastewater quality, both [()TD$FIG]
powders produced an unidentified structures at u = 298. In this study, the titania produced from the printing paper mill wastewater indicated better structure of titania. Thus, the remaining titania characteristics are mainly carried out with the titania produced from the printing paper mill wastewater. 3.2.2. Visual observation The SEM image of titania is shown in Fig. 4. Commercially available P-25 titania showed regular round shaped nanoparticles of 25 nm in size (data not shown). However, the titania produced from Ti-salt flocculated sludge with printing paper mill wastewater showed irregularly aggregated structures with round shape. Table 2 shows the EDX results of the titania generated from printing paper mill wastewater. The titania consisted of 31% of titanium and 56% of oxygen together with carbon, calcium, aluminium and silicon. Shon et al. [15] found carbon and phosphorus dopants in titania produced from synthetic wastewater which represented biologically treated sewage effluent. However, the titania produced from the printing paper mill wastewater included various dopant materials such as carbon (4.3%), magnesium (0.9%), aluminium (1.9%), silicon (1.7%), sulphur (0.7%) and calcium (3.8%). This is probably due to differences in
[()TD$FIG]
Fig. 2. SVI obtained at the optimum dosages of Ti- and Fe-salt flocculation.
Fig. 3. XRD pattern of powder produced from incineration of the Ti-salt settled floc at 600 8C with the paper and newsprint mill wastewaters.
[()TD$FIG]
[()TD$FIG]
S.-H. Na et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
280
Fig. 4. SEM image of titania produced from printing paper mill wastewater. Table 2 Atomic percentage of titania produced from printing paper mill wastewater. Atom
Atomic percentage (%)
Atom
Atomic percentage (%)
C O Mg Al
4.27 55.87 0.87 1.85
Si S Ca Ti
1.73 0.73 3.79 30.90
chemical compositions between synthetic wastewater and printing paper mill wastewater from which both catalysts were generated. TEM photographs of the titania showed round shape with estimated dimension of 10–15 nm as a primary crystal growth (Fig. 5). The round shape of the titania nanoparticle was not uniform, had several structural defects and were interconnected at certain sites. 3.2.3. Photocatalytic activity The photocatalytic oxidation of acetaldehyde with the titania produced from the printing paper mill wastewater using Ti-salt coagulant was compared with that with the titania prepared from the newspaper mill wastewater (Fig. 6). The acetaldehyde
[()TD$FIG]
Fig. 5. High-resolution transmission electron microscope image of titania produced from the printing paper mill wastewater.
Fig. 6. Photodecomposition of acetaldehyde by titania under UV irradiation (amount of TiO2 = 0.5 g; initial concentration of acetaldehyde = 2000 ppmv; UV irradiation = UV black light three 10 W lamps).
concentration decrease was measured by using a GC. The difference from initial concentration was calculated in terms of adsorption and photo-oxidation percentage. Acetaldehyde was adsorbed onto titania surface in dark conditions for 60 min (lamp off). The removal after 60 min adsorption was negligible and the concentration (around 1900 ppmv) was slightly lower than the initial concentration (2000 ppmv) for both titania. When UV lamps were on, 60% of acetaldehyde concentration was removed with the titania nanoparticle produced from the printing paper mill wastewater, while the photo-oxidation of the titania produced from the newspaper mill wastewater was marginal. This suggests that the titania from the printing mill wastewater has the high potential use for decomposing volatile organic contaminants. 4. Conclusions Flocculation using TiCl4 and FeCl3 with printing paper mill and newspaper mill wastewaters was performed and two coagulants used were compared for COD removal and settling ability of the settled floc. The settled floc after Ti-salt flocculation was incinerated to produce titania nanoparticle. The titania produced from different paper mill wastewater sources was characterized in terms of XRD, SEM/EDX, TEM and the photodecomposition of acetaldehyde under UV-irradiation. According to the results obtained the following conclusions can be drawn: The removal efficiency of COD at the optimum concentrations of Ti- and Fe-salt was 69% and 65%, respectively. The removal of turbidity was 99% at the initial turbidity of 800 and 1550 NTU for both coagulants. The SVI value after Ti-salt flocculation was 150 mL/g, whereas that after Fe-salt flocculation was 380 mL/g. The anatase titania structure was predominant after incineration of both sludge from printing and newspaper wastewater. The titania from printing paper mill wastewater consisted of irregularly aggregated structures with round shape of dimension of 10–15 nm as a primary crystal growth, including various dopant materials such as carbon (4.3%), magnesium (0.9%), aluminium (1.9%), silicon (1.7%), sulphur (0.7%) and calcium (3.8%). The removal of acetaldehyde after 60 min adsorption was negligible. However, when UV lamps were on, 60% of acetaldehyde concentration was removed with the titania nanoparticles produced from the printing paper mill wastewater, while the photo-oxidation of the titania produced from the newspaper mill wastewater was marginal.
S.-H. Na et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 277–281
Acknowledgements This work was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (20090094057) and the Center for Photonic Materials and Devices at Chonnam National University. This study was partially supported by CRC-CARE. This subject is supported by Korea Ministry of Environment as ‘‘Converging technology project’’. References [1] S. Lacorte, A. Latorre, D. Barcelo, A. Rigo, A. Malmqvist, T. Welander, Trends Anal. Chem. 22 (2003) 725. [2] D. Pokhrel, T. Viraraghavan, Sci. Total Environ. 333 (2004) 37. [3] S.S. Wong, T.T. Teng, A.L. Ahmad, A. Zuhairi, G. Najafpour, J. Hazard. Mater. B135 (2006) 378. [4] E. Chamarro, A. Marco, S. Esplugas, Water Res. 35 (2001) 1047. [5] V.C. Srivastava, I.D. Mall, I.M. Mishra, Physichem. Eng. Aspects 260 (2005) 17. [6] Y. Zhang, C. Ma, F. Ye, Y. Kong, H. Li, Desalination 236 (2009) 349. [7] T. Leiviska¨, H. Nurmesniemi, R. Po¨ykio¨, J. Ra¨mo¨, T. Kuokkanen, J. Pellinen, Water Res. 42 (2008) 3952. [8] H. Ma, B. Wang, Y. Wang, J. Hazard. Mater. 145 (2007) 417.
281
[9] T. Leiviska¨, J. Ra¨mo¨, H. Nurmesniemi, R. Po¨ykio¨, T. Kuokkane, Water Res. 43 (2009) 3199. [10] G. Thompson, J. Swain, M. Kay, C.F. Forster, Bioresour. Technol. 77 (2001) 275. [11] A.C. Rodriques, M. Boroski, N.S. Shimada, J.C. Garcia, J. Nzaki, N. Hioka, J. Photochem. Photobiol. A: Chem. 194 (2008) 1. [12] H. Katja, S. Mika, J. Research, Chem. Environ. 11 (2007) 96. [13] H. Ganjidoust, K. Tatsumi, T. Yamagishi, R.N. Gholian, Water Sci. Technol. 35 (1997) 291. [14] R.J. Stephenson, S.J.B. Duff, Water Res. 30 (1996) 781. [15] H.K. Shon, S. Vigneswaran, I.S. Kim, J. Cho, G.J. Kim, J.B. Kim, J.-H Kim, Environ. Sci. Technol. 41 (2007) 1372. [16] S.H. Na, H.K. Shon, J.B. Kim, H.J. Park, D.L. Cho, I.E. Saliby, J.H. Kim, J. Korean Ind. Eng. Chem. 16 (2010) 96. [17] B.C. Lee, S. Kim, H.K. Shon, S. Vigneswaran, S.D. Kim, J. Cho, I.S. Kim, K.H. Choi, J.B. Kim, H.J. Park, J.-H. Kim, J. Nanopart. Res. 11 (2009) 2087. [18] Y. Okour, I.E. Saliby, H.K. Shon, S. Vigneswaran, J.-H. Kim, J. Cho, I.S. Kim, Desalination 249 (2009) 53. [19] Y. Okour, H.K. Shon, I. El Saliby, R. Naidu, J.B. Kim, J.H. Kim, Bioresour. Technol. 101 (2009) 1453. [20] J.B. Kim, H.J. Park, H.K. Shon, D.L. Cho, G.J. Kim, S.W. Choi, J.H. Kim, J. Nanosci. Nanotechnol. 10 (2010) 3260. [21] APHA, Standard Methods for the Examination of Water and Wastewater, 20th ed., Am. Publ. Hlth. Assoc., Washington, DC, 1998. [22] L.S. Clescen, A.E. Greenberg, Standard Methods for the Examination of Water and Wastewater, 19th ed., Eaton AD, APHA, Report No. 331, Washington APM, Washington, DC, 1995.