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Characteristics of phenol degradation by immobilized activated sludge
Journal of Industrial and Engineering Chemistry 15 (2009) 323–327
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Characteristics of phenol degradation by immobilized activated sludge Sook-Young Lee a, Young-Nam Chun b, Sun-Il Kim c,* a
Research Center for Proteineous Materials, Chosun University, Gwangju 501-759, Republic of Korea BK21 Team for Hydrogen Production, Department of Environmental Engineering, Chosun University, Gwangju 501-759, Republic of Korea c Department of Chemical and Biochemical Engineering, Chosun University, Gwangju 501-759, Republic of Korea b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 19 May 2008 Accepted 18 November 2008
The effects of various factors involved in phenol degradation through an immobilized activated sludge with a photo-crosslinked resin were investigated. The immobilized activated sludge showed a higher relative activity of phenol degradation across a broader range of pH than free activated sludge. A higher rate of phenol degradation was observed when the bead size was smaller. The phenol degradation in the free activated sludge was inhibited at the 3000 mg/L of phenol, while that in the immobilized activated sludge was maintained at the same concentration for 28 h without any inhibition. The degradation rates of phenol were not directly proportional to the increasing amount of immobilized bead dosage, but the phenol degradation was completed in a shorter time than that for the free activated sludge. For the repeated reaction of immobilized activated sludge, the relative activity is increased up to eight times after seven repeated initial cycles. Continued treatment of immobilized activated sludge showed more than 95% of phenol removal efficiency under a loading rate of 5.59 kg-phenol/(m3 d), which is twice as large as the loading rate for the free activated sludge. ß 2009 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Keywords: Phenol Immobilized activated sludge Wastewater Loading rate
1. Introduction The immobilized microbe system is utilized in various wastewater treatment processes [1–5]. Advantages of this system over the activated sludge process include the sustenance of microbes in a high concentration and the reduced bulking effect [6–9]. In addition, the adversary effect from hazardous material is minimal, and the microbes can be selected to suit the wastewater characteristics, while it is also possible to separate and recycle the immobilized microbes after wastewater treatment [10]. For immobilizing microbes, both the natural and synthetic polymers are used as materials, but synthetic polymers such as polyvinylalcohol, polyacrylamide, and photo-crosslinked resin are used for their high gel strength required for wastewater treatment application [11–13]. Phenol wastewater is discharged from the processes of coal tar distillation, production of polymer resin, oil purification, medical supply manufacturing, and coke in steel mills [14,15]. The water supply system with phenol inflow forms chlorophenol during the chlorine disinfection process, which induces foul odor and emesis. Since phenol wastewater in high concentration requires more stable and efficient treatment method because of high biochemical
* Corresponding author. E-mail address: [email protected] (S.-I. Kim).
resistance, studies have been actively conducted on the fluidized bed biofilm and phenol-decomposing microbe [16–21]. However, phenol degradation by immobilized microbe has not been thoroughly studied. Therefore, this study attempted to efficiently treat the phenol wastewater by immobilizing the activated sludge capable of degrading phenol on the photo-crosslinked resin. Effects of pH and concentration of phenol wastewater, size of immobilized beads on the phenol degradation capability was evaluated. In addition, we explored the possibility of continued use and preservation of the immobilized activated sludge.
2. Experimental Aerobic activated sludge, a complex consortium of microorganisms mainly containing bacteria [22] obtained from wastewater treatment plant in a steel mill was used in this study. The harvested cells were accommodated with synthetic phenol wastewater for 30 days, and it was used as the immobilized activated sludge. The composition of synthetic phenol wastewater is shown in Table 1 [23]. For batch experiment, a reaction tank of 500 mL capacity was used, and 1 L reaction tank is made of acrylic for the continued treatment. The immobilized activated sludge and the non-immobilized activated sludge (free activated sludge) were placed into each reaction tank with synthetic wastewater, and
1226-086X/$ – see front matter ß 2009 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry. doi:10.1016/j.jiec.2008.11.007
S.-Y. Lee et al. / Journal of Industrial and Engineering Chemistry 15 (2009) 323–327
324
Table 1 Composition of synthetic phenol wastewater.
3. Results and discussion
Components
Concentration (mg/L)
3.1. Effect of pH on the degradation of phenol
NH4Cl KH2PO4 NaHCO3 MgSO47H2O CaCl22H2O FeCl36H2O Phenol
102.0 24.0 50.0 7.0 1.4 0.1 300–1000
aerated from bottom at a flow rate of 1000 mL/min. Concentration of the reaction tank with free activated sludge was set to 3000 mg/ L (MLSS), and the corresponding concentration of immobilized activated sludge was introduced to the other reaction tank. For the reactors, temperature was maintained at 25 8C, and pH was controlled at 7.0 0.5 by adding 0.5 M of NaHCO3. Photo-crosslinked resin (ENTG-3800: Kansai Paint Co.) from polyethylene and polypropylene was used as the immobilizing material. The forming agent was Na-alginate, and polymerizer was 2-hydroxy isobutyl phenol. Fig. 1 shows the bead preparation step for immobilized activated sludge. The concentrated activated sludge was suspended into distilled water, and mixed with ENTG-3800, Na-alginate, and 2-hydroxy isobutyl phenol. This mixture was injected to 0.2 M CaCl2 solution using a syringe. The solution was irradiated under UV (Toshiba Chemical Lamp FL 20BL: wave length range 300– 400 nm) for 3 min, and 3 mm sized bead was prepared. This immobilized activated sludge was accommodated with synthetic wastewater for 10 days. A concentration analysis on phenol was conducted through absorbance test with 4-aminoantipyrine, and pH was measured with a pH meter (Conning, 440, USA).
Immobilized microbes can have a broader pH range to decompose phenol than the non-immobilized microbes. The optimal pH condition was evaluated for the degradation of phenol by immobilized activated sludge, and the degradation activity of immobilized activated sludge was compared with that of the free activated sludge. Experimental results are shown in Fig. 2, and relative activity is the ratio of degradation rate at each pH to the one at pH 7 for phenol degradation. That is: Relative activityð%Þ ¼
degradation rate at each pH 100 degradation rate at pH 7
where the degradation rate is amount of decomposed phenol per volume and hour, and the unit is mg-phenol/(h V). Optimal pH for the immobilized and the free activated sludge was at the same pH 7. However, the relative activity of free activated sludge was 8% at pH 3, and 57% at pH 10. For the immobilized activated sludge, the relative activity was 33% at pH 3, and 72% at pH 10. The higher relative activity in immobilized activated sludge is attributed to the longer activated range from immobilized activated sludge. Difference in optimal pH condition and active range is due to the electrostatic property of immobilizing material [24]. 3.2. Effect of immobilized bead size on the degradation of phenol The degradation rate of phenol was evaluated on the basis of the bead size of immobilized activated sludge. The average diameter of bead is manufactured to be 1.0, 2.5, and 5.0 mm, and the tested phenol concentrations were 350, 700, 1400, and 2800 mg/L.
Fig. 1. Procedure for the immobilization of activated sludge with a photo-crosslinked resin.
S.-Y. Lee et al. / Journal of Industrial and Engineering Chemistry 15 (2009) 323–327
325
Fig. 2. Effect of pH on the phenol degradation by free and immobilized activated sludge (phenol concentration, 700 mg/L; initial pH, 3; temperature, 25 8C).
Experimental results are given in Fig. 3. The smaller the bead size at each phenol concentration, the faster degradation was progressed. At 2800 mg/L of phenol concentration, the phenol degradation time was 25, 35, 48 for 1.0, 2.5, 5.0 mm of bead size, respectively. The shorter the degradation time, the smaller bead size in immobilized activated sludge is expected from the facilitated oxygen diffusion into the media [25]. In this study, preparation of immobilized beads smaller than 2.5 mm was practically difficult, so immobilized bead with the average diameter of 2.5 mm was utilized for further experiments. 3.3. Effect of phenol concentration Phenol degradation rates of immobilized and free activated sludge were tested at synthetic wastewater concentrations of 500, 1000, 2000, and 3000 mg/L. 150 mL of immobilized activated sludge (apparent volume) was entered into 400 mL of synthetic wastewater, and aerated from the bottom of the reaction tank. 2850 mg/L of free activated sludge (the same amount of immobilized activated sludge) was entered into the reaction tank. Experimental results are presented in Fig. 4. Free activated sludge can decompose phenol in 2000 mg/L or less for 20 h or less. For 3000 mg/L, it can degrade phenol to 1000 mg/L after 30 h. On the other hand, the immobilized activated sludge can decompose phenol in 2000 mg/L or less for 24 h. For 3000 mg/L, it decomposes most phenol after 28 h. In less than 2000 mg/L of phenol concentration, the free activated sludge is superior to the
Fig. 4. Effect of phenol concentration on the phenol degradation.
immobilized activated sludge in phenol degradation. However, in a phenol concentration greater than 3000 mg/L, that trend was found to be reversed. This is attributed to the fact that the free activated sludge has a lower resistance in oxygen diffusion than the immobilized activated sludge at less than 2000 mg/L of phenol concentration, which is a suitable range for phenol degradation. However, at a phenol concentration greater than 3000 mg/L, the high concentration of phenol has an adversary effect on the degradation. The higher degradation rate in immobilized activated sludge owes it to the dilution of phenol while penetrating polymer gel without direct contact with the activated sludge [26]. 3.4. Effect of immobilized bead dosage on the degradation of phenol Fig. 5 shows the effect of bead volume on the phenol degradation with the immobilized activated sludge. When 25, 50, 100, and 200 mL (apparent volume) of the immobilized bead was entered into synthetic wastewater with 700 mg/L of phenol concentration, the decomposition time was 48, 24, 12, and 8 h, respectively. The phenol degradation rate (mg-phenol/(mLbead h)) was 0.58 when 25–100 mL of immobilized bead was dosed, but it was 0.44 for 200 mL of immobilized bead. The decomposition rate was not proportional to the dosage, but the decomposition time was shortened by the larger amount of microbes in the immobilized beads. 3.5. Degradation activity of phenol caused by the repeated reaction of immobilized activated sludge
Fig. 3. Effect of bead sizes on the phenol degradation.
The relative activity of repeated reaction of the immobilized activated sludge is shown in Fig. 6. For 400 mL of synthetic wastewater with 500 mg/L of phenol concentration, 150 mL of
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S.-Y. Lee et al. / Journal of Industrial and Engineering Chemistry 15 (2009) 323–327 Table 2 Removal efficiency of phenol under various preservation conditions. Period (days)
Removal efficiency of phenol (%) Anaerobic condition
20 40 80
Fig. 5. Effect of bead volume on the phenol degradation of the immobilized activated sludge.
immobilized activated sludge was introduced for reaction. When phenol was completely decomposed, the wastewater was replaced with new one, and this was regarded as one cycle. The degradation rate per unit time at the 1st cycle was considered as 100% for relative activity. After the 2nd cycle, the relative activity was calculated from the ratio between the following cycle and the 1st one. The degradation rate at the 1st cycle was 10.40 mg/(L h). The degradation rate of the immobilized activated sludge increased as it was repeated. At 7th cycle, it was 83.30 mg/(L h), which is 8 times larger than the 1st. This may be attributed to the fact that microbes are propagated not only inside the immobilizing biofilm but also into the surface of the biofilm during repeated usage [25].
Aerobic condition
Distilled water
Wastewater
Distilled water
Wastewater
88.80 86.60 51.80
88.80 86.70 48.10
88.80 86.60 70.40
88.80 86.70 86.30
in the synthetic wastewater or distilled water, 700 mg/L of phenol was almost all decomposed in 24 h. Since 86.60% of degradation capability was achieved even after 40 days of preservation, we found that the phenol degradation activity can be maintained at least for 40 days without substrate in distilled water. However, after 80 days of preservation, the phenol degradation activity was maintained only for synthetic wastewater with aerobic conditions. In the other conditions, only 51.80–70.40% of the phenol degradation activity remained. Therefore, to preserve the immobilized activated sludge for 80 days or longer, it should be stored in the solution with phenolic substance in aerobic condition. 3.7. Continued degradation of phenol by immobilized activated sludge The continued degradation behavior of phenol was tested using immobilized activated sludge and free activated sludge, and the results are shown in Fig. 7.
3.6. Preservation of immobilized activated sludge Table 2 presents the degradation capability of the immobilized activated sludge after a long preservation period. 150 mL of immobilized activated sludge was entered into 400 mL of synthetic wastewater with 700 mg/L of phenol concentration for complete degradation. Then, it was placed to 400 mL of distilled water without phenolic substance and new wastewater for 20, 40, and 80 days at room temperature in aerobic and anaerobic conditions. After the corresponding storage time is passed, the phenol degradation capability of the immobilized activated sludge is evaluated for 400 mL of synthetic wastewater with 700 mg/L of phenol. After 20 days of immobilized activated sludge preservation
Fig. 6. Relative activity of repeated reaction of the immobilized activated sludge.
Fig. 7. Loading rates and effluent concentrations during continuous reaction.
S.-Y. Lee et al. / Journal of Industrial and Engineering Chemistry 15 (2009) 323–327
For the continued degradation experiment, the phenol load was started from 0.93 kg-phenol/(m3 d), and was gradually increased. For immobilized activated sludge, more than 95% of removal efficiency was achieved even when the load was increased to 3.92 kg-phenol/(m3 d) for 30 days of experiment. After 45 days, the increment of phenol load to 9.93 kg-phenol/(m3 d) decreased the removal efficiency to 88.5%. The removal efficiency was stabilized to 95% by reducing the phenol load to 5.59 kg-phenol/(m3 d) after 50 days. The initial test condition for continued decomposition with free activated sludge was the same as the one with the immobilized activated sludge. Under 1.86 kg-phenol/(m3 d) of phenol load, more than 99% of removal efficiency was achieved. At 30 days, the increment of phenol load to 5.59 kg-phenol/(m3 d) reduced the efficiency to 82.5%, and it was stabilized at 92.5% by lowering the phenol load to 2.79 kg-phenol/(m3 d). For the continued treatment of phenol, the immobilized activated sludge achieved more than 95% of removal efficiency under 5.59 kg-phenol/(m3 d) of phenol load, which is twice the load with the free activated sludge. 4. Conclusions We evaluated the influential factors of the activated sludge capable of phenol decomposition immobilized on photo-crosslinked resin. The immobilized activated sludge showed a broader range of pH and higher relative activity than the free activated sludge. The smaller the diameter of the immobilized bead, the shorter the phenol degradation time. Under a high concentration of phenol, the immobilized activated sludge had a greater degradation rate than the free activated sludge. Although the phenol degradation rate is not directly proportional to the dosage, the bigger the dosage of immobilized bead, the greater the phenol degradation. For the repeated reaction of immobilized activated sludge, the relative activity is increased up to 8 times of the initial value after 7 repeated cycles. After the 20 days preservation of immobilized activated sludge in synthetic wastewater and distilled water under aerobic or anaerobic condition, 700 mg/L of phenol was almost decomposed after 24 h. For 40 days of preservation under distilled water, 86.6% or more of phenol was decomposed. In addition, the
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immobilized activated sludge can be preserved for 80 days if it is stored in synthetic wastewater under an aerobic condition. Continued treatment of immobilized activated sludge showed more than 95% of phenol removal efficiency under 5.59 kg-phenol/ (m3 d) of loading rate, which is twice as large as the loading rate with free activated sludge. Acknowledgement This study was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (NO. R01-2006-000-10355-0). References [1] S.M. Ratusznei, J.A.D. Rodrigues, E.F.M. Camargo, M. Zaiat, W. Borzani, Bioresour. Technol. 75 (2000) 127. [2] G. Gonza´lez, G. Herrera, M.T. Garcı´a, M. Pen˜a, Bioresour. Technol. 80 (2001) 137. [3] K.C. Chen, C.Y. Chen, J.W. Peng, J.Y. Houng, Water Res. 36 (2002) 230. [4] H.R. Kariminiaae, K. Kanda, F. Kato, J. Biosci. Bioeng. 95 (2003) 128. [5] W.C. Kuo, T.Y. Shu, J. Hazard. Mater. 113 (2004) 147. [6] M. Petruccioli, J. Duarte, F. Federici, J. Biosci. Bioeng. 90 (2000) 381. [7] P. Chudoba, R. Pujol, H. Emori, J.C. Bourdelot, J.M. Rovel, Prog. Biotech. 11 (1996) 710. [8] B.Y. Chen, S.Y. Chen, J.S. Chang, Process Biochem. 40 (2005) 3434. [9] W.K. Lee, J. Chung, W. Bae, S.J. Park, Y. Kim, Y.W. Lee, D.W. Park, J. Ind. Eng. Chem. 10 (2004) 959. [10] G. Akay, E. Erhan, B. Keskinler, O.F. Algur, J. Membr. Sci. 206 (2002) 61. [11] I.S. Chang, C.I. Kim, B.U. Nam, Process Biochem. 40 (2005) 3050. [12] J.M. Oh, D.H. Lee, Y.S. Song, S.G. Lee, S.W. Kim, J. Ind. Eng. Chem. 13 (2007) 429. [13] D.H. Lee, C.H. Park, J.M. Yeo, S.W. Kim, J. Ind. Eng. Chem. 12 (2006) 777. [14] S. Cao, G. Chen, X. Hu, P.L. Yue, Catal. Today 88 (2003) 37. [15] H. Jiang, Y. Fang, Y. Fu, Q.X. Guo, J. Hazard. Mater. 101 (2003) 179. [16] S.L. Pai, Y.L. Hsu, N.M. Chong, C.S. Sheu, C.H. Chen, Bioresour. Technol. 51 (1995) 37. [17] E. Horozova, N. Dimcheva, Z. Jordanova, Stud. Surf. Sci. Catal. 110 (1997) 1239. [18] A.P. Terzyk, J. Colloid Interface Sci. 268 (2003) 301. [19] B. Tryba, T. Tsumura, M. Janus, A.W. Morawski, M. Inagaki, Appl. Catal. B: Environ. 50 (2004) 177. [20] H.H. Chou, J.S. Huang, Chemosphere 59 (2005) 107. [21] S.S. Hong, C.S. Ju, C.G. Lim, B.H. Ahn, K.T. Lim, G.D. Lee, J. Ind. Eng. Chem. 7 (2001) 99. [22] M. Mathew, T. Stephenson, Environ. Technol. 92 (1997) 883. [23] T. Yamagishi, J. Leite, S. Ueda, F. Yamaguchi, Y. Suwa, Water Res. 35 (2001) 3089. [24] J. Grzechulska, A.W. Morawski, Appl. Catal. B: Environ. 46 (2003) 415. [25] A. Viggiani, G. Olivieri, L. Siani, A. Di Donato, A. Marzocchella, P. Salatino, P. Barbieri, E. Galli, J. Biotechnol. 123 (2006) 464. [26] G.M. Zhou, H.H.P. Fang, Water Sci. Technol. 36 (1997) 135.
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Characteristics of phenol degradation by immobilized activated sludge Sook-Young Lee a, Young-Nam Chun b, Sun-Il Kim c,* a
Research Center for Proteineous Materials, Chosun University, Gwangju 501-759, Republic of Korea BK21 Team for Hydrogen Production, Department of Environmental Engineering, Chosun University, Gwangju 501-759, Republic of Korea c Department of Chemical and Biochemical Engineering, Chosun University, Gwangju 501-759, Republic of Korea b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 19 May 2008 Accepted 18 November 2008
The effects of various factors involved in phenol degradation through an immobilized activated sludge with a photo-crosslinked resin were investigated. The immobilized activated sludge showed a higher relative activity of phenol degradation across a broader range of pH than free activated sludge. A higher rate of phenol degradation was observed when the bead size was smaller. The phenol degradation in the free activated sludge was inhibited at the 3000 mg/L of phenol, while that in the immobilized activated sludge was maintained at the same concentration for 28 h without any inhibition. The degradation rates of phenol were not directly proportional to the increasing amount of immobilized bead dosage, but the phenol degradation was completed in a shorter time than that for the free activated sludge. For the repeated reaction of immobilized activated sludge, the relative activity is increased up to eight times after seven repeated initial cycles. Continued treatment of immobilized activated sludge showed more than 95% of phenol removal efficiency under a loading rate of 5.59 kg-phenol/(m3 d), which is twice as large as the loading rate for the free activated sludge. ß 2009 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Keywords: Phenol Immobilized activated sludge Wastewater Loading rate
1. Introduction The immobilized microbe system is utilized in various wastewater treatment processes [1–5]. Advantages of this system over the activated sludge process include the sustenance of microbes in a high concentration and the reduced bulking effect [6–9]. In addition, the adversary effect from hazardous material is minimal, and the microbes can be selected to suit the wastewater characteristics, while it is also possible to separate and recycle the immobilized microbes after wastewater treatment [10]. For immobilizing microbes, both the natural and synthetic polymers are used as materials, but synthetic polymers such as polyvinylalcohol, polyacrylamide, and photo-crosslinked resin are used for their high gel strength required for wastewater treatment application [11–13]. Phenol wastewater is discharged from the processes of coal tar distillation, production of polymer resin, oil purification, medical supply manufacturing, and coke in steel mills [14,15]. The water supply system with phenol inflow forms chlorophenol during the chlorine disinfection process, which induces foul odor and emesis. Since phenol wastewater in high concentration requires more stable and efficient treatment method because of high biochemical
* Corresponding author. E-mail address: [email protected] (S.-I. Kim).
resistance, studies have been actively conducted on the fluidized bed biofilm and phenol-decomposing microbe [16–21]. However, phenol degradation by immobilized microbe has not been thoroughly studied. Therefore, this study attempted to efficiently treat the phenol wastewater by immobilizing the activated sludge capable of degrading phenol on the photo-crosslinked resin. Effects of pH and concentration of phenol wastewater, size of immobilized beads on the phenol degradation capability was evaluated. In addition, we explored the possibility of continued use and preservation of the immobilized activated sludge.
2. Experimental Aerobic activated sludge, a complex consortium of microorganisms mainly containing bacteria [22] obtained from wastewater treatment plant in a steel mill was used in this study. The harvested cells were accommodated with synthetic phenol wastewater for 30 days, and it was used as the immobilized activated sludge. The composition of synthetic phenol wastewater is shown in Table 1 [23]. For batch experiment, a reaction tank of 500 mL capacity was used, and 1 L reaction tank is made of acrylic for the continued treatment. The immobilized activated sludge and the non-immobilized activated sludge (free activated sludge) were placed into each reaction tank with synthetic wastewater, and
1226-086X/$ – see front matter ß 2009 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry. doi:10.1016/j.jiec.2008.11.007
S.-Y. Lee et al. / Journal of Industrial and Engineering Chemistry 15 (2009) 323–327
324
Table 1 Composition of synthetic phenol wastewater.
3. Results and discussion
Components
Concentration (mg/L)
3.1. Effect of pH on the degradation of phenol
NH4Cl KH2PO4 NaHCO3 MgSO47H2O CaCl22H2O FeCl36H2O Phenol
102.0 24.0 50.0 7.0 1.4 0.1 300–1000
aerated from bottom at a flow rate of 1000 mL/min. Concentration of the reaction tank with free activated sludge was set to 3000 mg/ L (MLSS), and the corresponding concentration of immobilized activated sludge was introduced to the other reaction tank. For the reactors, temperature was maintained at 25 8C, and pH was controlled at 7.0 0.5 by adding 0.5 M of NaHCO3. Photo-crosslinked resin (ENTG-3800: Kansai Paint Co.) from polyethylene and polypropylene was used as the immobilizing material. The forming agent was Na-alginate, and polymerizer was 2-hydroxy isobutyl phenol. Fig. 1 shows the bead preparation step for immobilized activated sludge. The concentrated activated sludge was suspended into distilled water, and mixed with ENTG-3800, Na-alginate, and 2-hydroxy isobutyl phenol. This mixture was injected to 0.2 M CaCl2 solution using a syringe. The solution was irradiated under UV (Toshiba Chemical Lamp FL 20BL: wave length range 300– 400 nm) for 3 min, and 3 mm sized bead was prepared. This immobilized activated sludge was accommodated with synthetic wastewater for 10 days. A concentration analysis on phenol was conducted through absorbance test with 4-aminoantipyrine, and pH was measured with a pH meter (Conning, 440, USA).
Immobilized microbes can have a broader pH range to decompose phenol than the non-immobilized microbes. The optimal pH condition was evaluated for the degradation of phenol by immobilized activated sludge, and the degradation activity of immobilized activated sludge was compared with that of the free activated sludge. Experimental results are shown in Fig. 2, and relative activity is the ratio of degradation rate at each pH to the one at pH 7 for phenol degradation. That is: Relative activityð%Þ ¼
degradation rate at each pH 100 degradation rate at pH 7
where the degradation rate is amount of decomposed phenol per volume and hour, and the unit is mg-phenol/(h V). Optimal pH for the immobilized and the free activated sludge was at the same pH 7. However, the relative activity of free activated sludge was 8% at pH 3, and 57% at pH 10. For the immobilized activated sludge, the relative activity was 33% at pH 3, and 72% at pH 10. The higher relative activity in immobilized activated sludge is attributed to the longer activated range from immobilized activated sludge. Difference in optimal pH condition and active range is due to the electrostatic property of immobilizing material [24]. 3.2. Effect of immobilized bead size on the degradation of phenol The degradation rate of phenol was evaluated on the basis of the bead size of immobilized activated sludge. The average diameter of bead is manufactured to be 1.0, 2.5, and 5.0 mm, and the tested phenol concentrations were 350, 700, 1400, and 2800 mg/L.
Fig. 1. Procedure for the immobilization of activated sludge with a photo-crosslinked resin.
S.-Y. Lee et al. / Journal of Industrial and Engineering Chemistry 15 (2009) 323–327
325
Fig. 2. Effect of pH on the phenol degradation by free and immobilized activated sludge (phenol concentration, 700 mg/L; initial pH, 3; temperature, 25 8C).
Experimental results are given in Fig. 3. The smaller the bead size at each phenol concentration, the faster degradation was progressed. At 2800 mg/L of phenol concentration, the phenol degradation time was 25, 35, 48 for 1.0, 2.5, 5.0 mm of bead size, respectively. The shorter the degradation time, the smaller bead size in immobilized activated sludge is expected from the facilitated oxygen diffusion into the media [25]. In this study, preparation of immobilized beads smaller than 2.5 mm was practically difficult, so immobilized bead with the average diameter of 2.5 mm was utilized for further experiments. 3.3. Effect of phenol concentration Phenol degradation rates of immobilized and free activated sludge were tested at synthetic wastewater concentrations of 500, 1000, 2000, and 3000 mg/L. 150 mL of immobilized activated sludge (apparent volume) was entered into 400 mL of synthetic wastewater, and aerated from the bottom of the reaction tank. 2850 mg/L of free activated sludge (the same amount of immobilized activated sludge) was entered into the reaction tank. Experimental results are presented in Fig. 4. Free activated sludge can decompose phenol in 2000 mg/L or less for 20 h or less. For 3000 mg/L, it can degrade phenol to 1000 mg/L after 30 h. On the other hand, the immobilized activated sludge can decompose phenol in 2000 mg/L or less for 24 h. For 3000 mg/L, it decomposes most phenol after 28 h. In less than 2000 mg/L of phenol concentration, the free activated sludge is superior to the
Fig. 4. Effect of phenol concentration on the phenol degradation.
immobilized activated sludge in phenol degradation. However, in a phenol concentration greater than 3000 mg/L, that trend was found to be reversed. This is attributed to the fact that the free activated sludge has a lower resistance in oxygen diffusion than the immobilized activated sludge at less than 2000 mg/L of phenol concentration, which is a suitable range for phenol degradation. However, at a phenol concentration greater than 3000 mg/L, the high concentration of phenol has an adversary effect on the degradation. The higher degradation rate in immobilized activated sludge owes it to the dilution of phenol while penetrating polymer gel without direct contact with the activated sludge [26]. 3.4. Effect of immobilized bead dosage on the degradation of phenol Fig. 5 shows the effect of bead volume on the phenol degradation with the immobilized activated sludge. When 25, 50, 100, and 200 mL (apparent volume) of the immobilized bead was entered into synthetic wastewater with 700 mg/L of phenol concentration, the decomposition time was 48, 24, 12, and 8 h, respectively. The phenol degradation rate (mg-phenol/(mLbead h)) was 0.58 when 25–100 mL of immobilized bead was dosed, but it was 0.44 for 200 mL of immobilized bead. The decomposition rate was not proportional to the dosage, but the decomposition time was shortened by the larger amount of microbes in the immobilized beads. 3.5. Degradation activity of phenol caused by the repeated reaction of immobilized activated sludge
Fig. 3. Effect of bead sizes on the phenol degradation.
The relative activity of repeated reaction of the immobilized activated sludge is shown in Fig. 6. For 400 mL of synthetic wastewater with 500 mg/L of phenol concentration, 150 mL of
326
S.-Y. Lee et al. / Journal of Industrial and Engineering Chemistry 15 (2009) 323–327 Table 2 Removal efficiency of phenol under various preservation conditions. Period (days)
Removal efficiency of phenol (%) Anaerobic condition
20 40 80
Fig. 5. Effect of bead volume on the phenol degradation of the immobilized activated sludge.
immobilized activated sludge was introduced for reaction. When phenol was completely decomposed, the wastewater was replaced with new one, and this was regarded as one cycle. The degradation rate per unit time at the 1st cycle was considered as 100% for relative activity. After the 2nd cycle, the relative activity was calculated from the ratio between the following cycle and the 1st one. The degradation rate at the 1st cycle was 10.40 mg/(L h). The degradation rate of the immobilized activated sludge increased as it was repeated. At 7th cycle, it was 83.30 mg/(L h), which is 8 times larger than the 1st. This may be attributed to the fact that microbes are propagated not only inside the immobilizing biofilm but also into the surface of the biofilm during repeated usage [25].
Aerobic condition
Distilled water
Wastewater
Distilled water
Wastewater
88.80 86.60 51.80
88.80 86.70 48.10
88.80 86.60 70.40
88.80 86.70 86.30
in the synthetic wastewater or distilled water, 700 mg/L of phenol was almost all decomposed in 24 h. Since 86.60% of degradation capability was achieved even after 40 days of preservation, we found that the phenol degradation activity can be maintained at least for 40 days without substrate in distilled water. However, after 80 days of preservation, the phenol degradation activity was maintained only for synthetic wastewater with aerobic conditions. In the other conditions, only 51.80–70.40% of the phenol degradation activity remained. Therefore, to preserve the immobilized activated sludge for 80 days or longer, it should be stored in the solution with phenolic substance in aerobic condition. 3.7. Continued degradation of phenol by immobilized activated sludge The continued degradation behavior of phenol was tested using immobilized activated sludge and free activated sludge, and the results are shown in Fig. 7.
3.6. Preservation of immobilized activated sludge Table 2 presents the degradation capability of the immobilized activated sludge after a long preservation period. 150 mL of immobilized activated sludge was entered into 400 mL of synthetic wastewater with 700 mg/L of phenol concentration for complete degradation. Then, it was placed to 400 mL of distilled water without phenolic substance and new wastewater for 20, 40, and 80 days at room temperature in aerobic and anaerobic conditions. After the corresponding storage time is passed, the phenol degradation capability of the immobilized activated sludge is evaluated for 400 mL of synthetic wastewater with 700 mg/L of phenol. After 20 days of immobilized activated sludge preservation
Fig. 6. Relative activity of repeated reaction of the immobilized activated sludge.
Fig. 7. Loading rates and effluent concentrations during continuous reaction.
S.-Y. Lee et al. / Journal of Industrial and Engineering Chemistry 15 (2009) 323–327
For the continued degradation experiment, the phenol load was started from 0.93 kg-phenol/(m3 d), and was gradually increased. For immobilized activated sludge, more than 95% of removal efficiency was achieved even when the load was increased to 3.92 kg-phenol/(m3 d) for 30 days of experiment. After 45 days, the increment of phenol load to 9.93 kg-phenol/(m3 d) decreased the removal efficiency to 88.5%. The removal efficiency was stabilized to 95% by reducing the phenol load to 5.59 kg-phenol/(m3 d) after 50 days. The initial test condition for continued decomposition with free activated sludge was the same as the one with the immobilized activated sludge. Under 1.86 kg-phenol/(m3 d) of phenol load, more than 99% of removal efficiency was achieved. At 30 days, the increment of phenol load to 5.59 kg-phenol/(m3 d) reduced the efficiency to 82.5%, and it was stabilized at 92.5% by lowering the phenol load to 2.79 kg-phenol/(m3 d). For the continued treatment of phenol, the immobilized activated sludge achieved more than 95% of removal efficiency under 5.59 kg-phenol/(m3 d) of phenol load, which is twice the load with the free activated sludge. 4. Conclusions We evaluated the influential factors of the activated sludge capable of phenol decomposition immobilized on photo-crosslinked resin. The immobilized activated sludge showed a broader range of pH and higher relative activity than the free activated sludge. The smaller the diameter of the immobilized bead, the shorter the phenol degradation time. Under a high concentration of phenol, the immobilized activated sludge had a greater degradation rate than the free activated sludge. Although the phenol degradation rate is not directly proportional to the dosage, the bigger the dosage of immobilized bead, the greater the phenol degradation. For the repeated reaction of immobilized activated sludge, the relative activity is increased up to 8 times of the initial value after 7 repeated cycles. After the 20 days preservation of immobilized activated sludge in synthetic wastewater and distilled water under aerobic or anaerobic condition, 700 mg/L of phenol was almost decomposed after 24 h. For 40 days of preservation under distilled water, 86.6% or more of phenol was decomposed. In addition, the
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immobilized activated sludge can be preserved for 80 days if it is stored in synthetic wastewater under an aerobic condition. Continued treatment of immobilized activated sludge showed more than 95% of phenol removal efficiency under 5.59 kg-phenol/ (m3 d) of loading rate, which is twice as large as the loading rate with free activated sludge. Acknowledgement This study was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (NO. R01-2006-000-10355-0). References [1] S.M. Ratusznei, J.A.D. Rodrigues, E.F.M. Camargo, M. Zaiat, W. Borzani, Bioresour. Technol. 75 (2000) 127. [2] G. Gonza´lez, G. Herrera, M.T. Garcı´a, M. Pen˜a, Bioresour. Technol. 80 (2001) 137. [3] K.C. Chen, C.Y. Chen, J.W. Peng, J.Y. Houng, Water Res. 36 (2002) 230. [4] H.R. Kariminiaae, K. Kanda, F. Kato, J. Biosci. Bioeng. 95 (2003) 128. [5] W.C. Kuo, T.Y. Shu, J. Hazard. Mater. 113 (2004) 147. [6] M. Petruccioli, J. Duarte, F. Federici, J. Biosci. Bioeng. 90 (2000) 381. [7] P. Chudoba, R. Pujol, H. Emori, J.C. Bourdelot, J.M. Rovel, Prog. Biotech. 11 (1996) 710. [8] B.Y. Chen, S.Y. Chen, J.S. Chang, Process Biochem. 40 (2005) 3434. [9] W.K. Lee, J. Chung, W. Bae, S.J. Park, Y. Kim, Y.W. Lee, D.W. Park, J. Ind. Eng. Chem. 10 (2004) 959. [10] G. Akay, E. Erhan, B. Keskinler, O.F. Algur, J. Membr. Sci. 206 (2002) 61. [11] I.S. Chang, C.I. Kim, B.U. Nam, Process Biochem. 40 (2005) 3050. [12] J.M. Oh, D.H. Lee, Y.S. Song, S.G. Lee, S.W. Kim, J. Ind. Eng. Chem. 13 (2007) 429. [13] D.H. Lee, C.H. Park, J.M. Yeo, S.W. Kim, J. Ind. Eng. Chem. 12 (2006) 777. [14] S. Cao, G. Chen, X. Hu, P.L. Yue, Catal. Today 88 (2003) 37. [15] H. Jiang, Y. Fang, Y. Fu, Q.X. Guo, J. Hazard. Mater. 101 (2003) 179. [16] S.L. Pai, Y.L. Hsu, N.M. Chong, C.S. Sheu, C.H. Chen, Bioresour. Technol. 51 (1995) 37. [17] E. Horozova, N. Dimcheva, Z. Jordanova, Stud. Surf. Sci. Catal. 110 (1997) 1239. [18] A.P. Terzyk, J. Colloid Interface Sci. 268 (2003) 301. [19] B. Tryba, T. Tsumura, M. Janus, A.W. Morawski, M. Inagaki, Appl. Catal. B: Environ. 50 (2004) 177. [20] H.H. Chou, J.S. Huang, Chemosphere 59 (2005) 107. [21] S.S. Hong, C.S. Ju, C.G. Lim, B.H. Ahn, K.T. Lim, G.D. Lee, J. Ind. Eng. Chem. 7 (2001) 99. [22] M. Mathew, T. Stephenson, Environ. Technol. 92 (1997) 883. [23] T. Yamagishi, J. Leite, S. Ueda, F. Yamaguchi, Y. Suwa, Water Res. 35 (2001) 3089. [24] J. Grzechulska, A.W. Morawski, Appl. Catal. B: Environ. 46 (2003) 415. [25] A. Viggiani, G. Olivieri, L. Siani, A. Di Donato, A. Marzocchella, P. Salatino, P. Barbieri, E. Galli, J. Biotechnol. 123 (2006) 464. [26] G.M. Zhou, H.H.P. Fang, Water Sci. Technol. 36 (1997) 135.