Article pubs.acs.org/IECR
Fabricating a Flocculant with Controllable Cationic Microblock Structure: Characterization and Sludge Conditioning Behavior Evaluation Wei Chen,†,‡ Huaili Zheng,*,†,‡ Qingqing Guan,†,§ Houkai Teng,∥ Chuanliang Zhao,† and Chun Zhao†
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†
Key Laboratory of the Three Gorges Reservoir Region’s Eco-Environment, State Ministry of Education, Chongqing University, Chongqing 400045, China ‡ National Centre for International Research of Low-Carbon and Green Buildings, Chongqing University, Chongqing 400045, China § School of Environmental Engineering, Nanjing Institute of Technology, Nanjing 211167, China ∥ National Research Center of Industrial Water Treatment Engineering and Technology, Tianjin Chemical Research and Design Institute, Tianjin 300131, China S Supporting Information *
ABSTRACT: A new flocculant with cationic microblock structure was prepared by using template polymerization. Acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DAC) were used as monomers, and sodium polyacrylate was used as the template. The reactivity ratio, 1 H NMR, 13C NMR, and thermogravimetric analysis were employed to characterize the structural properties of products. Results show that, with the addition of the template, the reactivity ratio of DAC increased, whereas that of AM decreased. Evident microblock structure was synthesized in copolymers when the molar ratio of template to DAC was 1.0. Activated sludge dewatering experiment results reveal that the cationic microblocky flocculant exhibited superior dewatering efficiency, and a low moisture content of 71% and a specific resistance of 1.99 × 1012 m·kg−1 were acquired at pH 7.0 and a 40 mg L−1 dosage. The enhanced charge neutralization and bridging effect of the cationic microblocky flocculant contributed to the formation of floc with a large size and compact structure.
1. INTRODUCTION
which can reduce the sludge moisture content and diminish cake compressibility.8,9 Acrylamide (AM) and cationic monomers were polymerized via solution polymerization, disperse polymerization, and inverse emulsion polymerization to produce CPAM.10−13 However, a deficiency in the aforementioned polymerization methods exists: The cationic units are distributed randomly in the CPAM molecular chain. The cationic units located on the loops and tails of the chain are simply wasted, as shown in Figure 1a. Thus, insufficient cationic charges are present at the adsorption sites to neutralize counterions. By contrast, if the cationic units exhibit a blocky distribution, as shown in Figure 1b, then the adsorption sites between copolymer and negatively charged particle segments would be strong and the cationic charges would be more efficiently utilized, leading to a more acceptable flocculation performance. Thus, adjusting the sequence structure of the cationic units and forming a cationic
The increasing worldwide establishment and operation of sewage treatment plants have facilitated a better aquatic environment and have resulted in an important shift in waste streams from liquid phase to semisolid phase.1 Large amounts of waste-activated sludge, which represent 1% or 2% of treated wastewater but contain from 50% to 80% of the pollution, have to be disposed of because the activated sludge process is the most important treatment technology for an extensive range of wastewaters.2,3 Notably, sludge with >97% water content is highly compressible but difficult to dewater mainly because small negatively charged particles are distributed evenly in the form of a stable colloidal suspension.2,4 Chemical conditioning prior to mechanical dewatering is generally required to destabilize the particulate system and reduce the sludge volume.5−7 Sludge conditioning, along with polyelectrolyte dosing, is a colloidal process of flocculation. In recent years, cationic polyacrylamide (CPAM) has been among the most commonly used polyelectrolytes for sludge conditioning because of its low impact on the environment and its abilitly to neutralize the surface charge of solid particles and bridge particles through its long polymer chain to form larger flocs, © 2016 American Chemical Society
Received: Revised: Accepted: Published: 2892
November 6, 2015 February 9, 2016 February 22, 2016 February 22, 2016 DOI: 10.1021/acs.iecr.5b04207 Ind. Eng. Chem. Res. 2016, 55, 2892−2902
Article
Industrial & Engineering Chemistry Research
2. MATERIALS AND METHODS 2.1. Materials. AM, DAC, and template sodium polyacrylate (NaPAA) used in this experiment were of technical grade, whereas the remaining reagents were of analytical grade. The monomer AM was purchased from Chongqing Lanjie Tap Water Company (Chongqing, China). DAC was obtained from Guangchuangjing Company (Shanghai, China). NaPAA was a gift from Shandong Xintai Water Treatment (Zaozhuang, China), the molecular weight of which is 3000. Photoinitiator 2,2′-azobis (2-methylpropionamide) dihydrochloride (V-50) was purchased from Ruihong Biological Technology (Shanghai, China). All aqueous and standard solutions used in the experiment were prepared with deionized water. 2.2. Synthesis of Copolymers. The template polymerization technique was used to synthesize the copolymers. The reaction was initiated by ultraviolet (UV) irradiation.8,18 Figure S1 in the Supporting Information illustrates the overview of template polymerization and the scheme of the reaction route for the preparation of copolymers. Predetermined amounts of monomers (AM, 126.61 mmol; DAC, 42.21 mmol) and urea (0.80 mmol) were added to a quartz reaction vessel, and NaPAA was added according to the molar ratio of template NaPAA to cationic monomer DAC (T/D) of 0.0, 0.5, 1.0, and 1.5. Deionized water was then poured into the reaction vessel to reach a monomer mass ratio of 30%. Then, the pH of the reaction solution was adjusted to 4.5 by 0.5 M HCl and NaOH. Prior to the addition of the photoinitiator, the aqueous solution was completely deoxygenated by bubbling with nitrogen gas for 30 min. The reaction vessel was exposed to radiation from a 500 W high-pressure mercury lamp.8,19 After 60 min of radiation, 2 h of aging at room temperature was conducted to increase the polymerization degree. The copolymer was dissolved in water, and the pH was adjusted to TPAD-0.5 > TPAD1.0. A lower sediment height indicates a lower sludge volume. Thus, the small sludge volume of TPAD-1.0 indicates that the flocs formed by cationic microblocky flocculants possess a compact and dense structure. In addition to floc density, the floc diameter of conditioned sludge of the four flocculants was also investigated. Figure 9 illustrates the floc size distribution of the conditioned sludge of the four flocculants at the end of the flocculation process. The results show that the diameter of TPAD-1.0 is the largest and that of TPAD-0.0 is the smallest. As a result, the combined effect of the compact structure and large size of floc formed by TPAD-1.0 effectively enhanced settleability. Other than settleability and size distribution, the morphology of sludge flocs conditioned by the four flocculants was captured by a camera, and the results are illustrated in Figure 10. The morphology of sludge flocs conditioned by TPAD-1.0 in a beaker presented a beehive-shaped model that is large and densely granulated and with many large voids that were distributed on the floc surface. The sludge aggregates were tightly linked together and closely overlapped. By contrast, the morphology of sludge flocs conditioned by TPAD-0.0 uniformly filled the beaker and presented a fine sand shape, which was loose and small and with a loosely reticular structure. The density, diameter, and morphology of sludge flocs are a combined effect of charge neutrality, bridging effect, and patch mechanism.17 The ζ-potential of the four flocculants shown in Figure 5c revealed that the main mechanism of TPAD-1.0 in the flocculation process is charge neutralization. The flocculants with blocky distributed cationic groups presented a stronger adsorption/charge neutralization capacity, whereas the floccu-
Figure 7. Effect of pH on (a) FCMC, (b) SRF, and (c) ζ-potential of conditioned sludge.
of conditioned sludge were analyzed in terms of settling rate, size distribution, and morphology. Settleability of sludge flocs is closely related to floc density and size.40 Settleability has been used as a viable index to 2899
DOI: 10.1021/acs.iecr.5b04207 Ind. Eng. Chem. Res. 2016, 55, 2892−2902
Article
Industrial & Engineering Chemistry Research
Figure 9. Sludge floc size distribution for (a) TPAD-0.0, (b) TPAD-0.5, (c) TPAD-1.0, and (d) TPAD-1.5.
ization test results of reactivity ratio, 1H NMR, 13C NMR, and TGA showed that a copolymer with microblock structure was successfully synthesized. When T/D is 1.0, evident block structures were observed in the copolymer chain. The activated sludge dewatering experiment result demonstrated that the cationic microblocky flocculants effectively improved the dewatering behavior. High intrinsic viscosity of flocculants and pH 3−8 are the optimal conditions for sludge dewatering. When all cationic units exhibited a blocky distribution, a lower moisture content of 71% and a specific resistance of 1.99 × 1012 m kg−1 were acquired at the dosage of 40 mg L−1 in the sludge dewatering process. In addition, sludge floc formed by cationic microblocky flocculant presented a higher settling rate, larger size, and denser floc structure, which can be attributed to the enhanced charge neutralization ability and absorption and bridging effect of the cationic microblock structure in the flocculant polymer chain.
lants with randomly distributed cationic units did not. Therefore, more particles were tightly absorbed on the polymer chain, and a larger and denser structure of flocs was formed by the cationic microblocky flocculant. In addition to the charge neutralization mechanism, the bridging effect also played an important role in floc growth. The repulsion between charged segments induced chain expansion and embedding into the sludge solution because of the number of cationic microblock segments distributed along the polymer chain.42 The elongated linear molecular chains induced a significant bridging effect. Therefore, the number of particles adsorbed by the cationic microblock structure was more than the number adsorbed by the random cationic segments. As a result, a large and compact aggregation was formed with the enhanced charge neutralization ability and bridging effect of the cationic microblocky flocculant.
4. CONCLUSION In this study, high dewatering efficiency flocculants with a cationic microblock structure were synthesized by a UVinitiated template polymerization technique. The character2900
DOI: 10.1021/acs.iecr.5b04207 Ind. Eng. Chem. Res. 2016, 55, 2892−2902
Article
Industrial & Engineering Chemistry Research
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.5b04207. Scheme of template polymerization, reaction route for the preparation of copolymer, and the calculation process of Kelen−Tüdös methods in reactivity ratio measurement (PDF)
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REFERENCES
(1) Brown, R. K.; Harnisch, F.; Dockhorn, T.; Schröder, U. Examining sludge production in bioelectrochemical systems treating domestic wastewater. Bioresour. Technol. 2015, 198, 913. (2) Lin, Q.; Peng, H.; Zhong, S.; Xiang, J. Synthesis, characterization, and secondary sludge dewatering performance of a novel combined silicon-aluminum-iron-starch flocculant. J. Hazard. Mater. 2015, 285, 199. (3) Shi, Y.; Yang, J.; Yu, W.; Zhang, S.; Liang, S.; Song, J.; Xu, Q.; Ye, N.; He, S.; Yang, C.; Hu, J. Synergetic conditioning of sewage sludge via Fe2+/persulfate and skeleton builder: Effect on sludge characteristics and dewaterability. Chem. Eng. J. 2015, 270, 572. (4) He, D.-Q.; Wang, L.-F.; Jiang, H.; Yu, H.-Q. A Fenton-like process for the enhanced activated sludge dewatering. Chem. Eng. J. 2015, 272, 128. (5) Wolski, P.; Zawieja, I. Hybrid conditioning before anaerobic digestion for the improvement of sewage sludge dewatering. Desalin. Water Treat. 2014, 52, 3725. (6) Chen, Z.; Zhang, W.; Wang, D.; Ma, T.; Bai, R. Enhancement of activated sludge dewatering performance by combined composite enzymatic lysis and chemical re-flocculation with inorganic coagulants: Kinetics of enzymatic reaction and re-flocculation morphology. Water Res. 2015, 83, 367. (7) Wang, L.-F.; He, D.-Q.; Tong, Z.-H.; Li, W.-W.; Yu, H.-Q. Characterization of dewatering process of activated sludge assisted by cationic surfactants. Biochem. Eng. J. 2014, 91, 174. (8) Zheng, H. L.; Sun, Y. J.; Zhu, C. J.; Guo, J. S.; Zhao, C.; Liao, Y.; Guan, Q. Q. UV-initiated polymerization of hydrophobically associating cationic flocculants: Synthesis, characterization, and dewatering properties. Chem. Eng. J. 2013, 234, 318. (9) Zheng, H.; Liao, Y.; Zheng, M.; Zhu, C.; Ji, F.; Ma, J.; Fan, W. Photoinitiated Polymerization of Cationic Acrylamide in Aqueous Solution: Synthesis, Characterization, and Sludge Dewatering Performance. Sci. World J. 2014, 2014, 1. (10) Bi, K.; Zhang, Y. Kinetic study of the polymerization of dimethyldiallylammonium chloride and acrylamide. J. Appl. Polym. Sci. 2012, 125, 1636. (11) Abdollahi, M.; Alamdari, P.; Koolivand, H.; Ziaee, F. A comprehensive study on the kinetics of aqueous free-radical homoand copolymerization of acrylamide and diallyldimethylammonium chloride by online 1H NMR spectroscopy. J. Polym. Res. 2013, 20, 1. (12) Ondaral, S.; Usta, M.; Gumusderelioglu, M.; Arsu, N.; Balta, D. K. The synthesis of water soluble cationic microgels by dispersion polymerization: Their performance in kaolin deposition onto fiber. J. Appl. Polym. Sci. 2009, 116, 1157. (13) Shang, H.; Zheng, Y.; Liu, J. Synthesis in inverse emulsion and decolorization properties of hydrophobically modified cationic polyelectrolyte. J. Appl. Polym. Sci. 2011, 119, 1602. (14) Połowiński, S. Template polymerisation and co-polymerisation. Prog. Polym. Sci. 2002, 27, 537. (15) Zhang, Y.; Wu, F.; Li, M.; Wang, E. The influence of polyallylammonium chloride template on the structure of AM/AA copolymers. Acta. Polym. Sin. 2005, 874. (16) Abdel-Aziz, H. M.; Hanafi, H. A.; Abozahra, S. F.; Siyam, T. Preparation of Poly(acrylamide-maleic Acid) Resin by Template Polymerization and Its Use for Adsorption of Co(II) and Ni(II). Int. J. Polym. Mater. 2010, 60, 89. (17) Zheng, H.; Sun, Y.; Guo, J.; Li, F.; Fan, W.; Liao, Y.; Guan, Q. Characterization and Evaluation of Dewatering Properties of PADB, a
Figure 10. Morphology and photomicrographs of sludge flocs for (a) TPAD-0.0, (b) TPAD-0.5, (c) TPAD-1.0, and (d) TPAD-1.5.
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VSS/TSS = Proportion of microorganism in the activated sludge FCMC = Filter cake moisture content SRF = Specific resistance to filtration rAM = Reactivity ratio of AM monomer in AM and DAC monomer pair rDAC = Reactivity ratio of DAC monomer in AM and DAC monomer pair
AUTHOR INFORMATION
Corresponding Author
*Tel.: +86 23 65120827. Fax: +86 23 65120827. E-mail: zhl@ cqu.edu.cn. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (Projects 21177164 and 21477010) and Graduate Student Research Innovation Project in Chongqing (CYB14045).
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ABBREVIATIONS AM = Acrylamide DAC = Acryloyloxyethyltrimethylammonium chloride NaPAA = Sodium polyacrylate 1 H NMR = Proton nuclear magnetic resonance 13 C NMR = Carbon nuclear magnetic resonance spectroscopy TGA = Thermogravimetric analysis CPAM = Cationic polyacrylamide UV = Ultraviolet T/D or T:D = Molar ratio of template NaPAA to cationic monomer DAC TPAD = Template polymer P(AM-DAC) 2901
DOI: 10.1021/acs.iecr.5b04207 Ind. Eng. Chem. Res. 2016, 55, 2892−2902
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Industrial & Engineering Chemistry Research Highly Efficient Cationic Flocculant. Ind. Eng. Chem. Res. 2014, 53, 2572. (18) Zhu, J.; Zheng, H.; Jiang, Z.; Zhang, Z.; Liu, L.; Sun, Y.; Tshukudu, T. Synthesis and characterization of a dewatering reagent: cationic polyacrylamide (P(AM-DMC-DAC)) for activated sludge dewatering treatment. Desalin. Water Treat. 2013, 51, 2791. (19) Liao, Y.; Zheng, H.; Qian, L.; Sun, Y.; Dai, L.; Xue, W. UVInitiated Polymerization of Hydrophobically Associating Cationic Polyacrylamide Modified by a Surface-Active Monomer: A Comparative Study of Synthesis, Characterization, and Sludge Dewatering Performance. Ind. Eng. Chem. Res. 2014, 53, 11193. (20) Kennedy, J. P.; Kelen, T.; Tüdös, F. Analysis of the linear methods for determining copolymerization reactivity ratios. II. A critical reexamination of cationic monomer reactivity ratios. J. Polym. Sci., Polym. Chem. Ed. 1975, 13, 2277. (21) Bera, P.; Saha, S. K. Water-soluble copolymers of acrylamide with diacetone-acrylamide and N-t-butylacrylamide on aqueous montmorillonite surface: synthesis and characterisation. Eur. Polym. J. 2000, 36, 411. (22) Duan, W.; Deng, Q.; Li, S.; Ma, Z. Preparation of Polyacrylamide with High Relative Molecular Mass and High Cationic Degree Through Inverse Emulsion Polymerization. Petrochem. Technol. (Beijing, China) 2011, 40, 968. (23) Liu, J. T. Determination on cationic degree of cationic polyacrylamide by infrared analysis. China Pulp Pap. Ind. 2013, 34, 42. (24) Shang, H.; Liu, J.; Zheng, Y.; Wang, L. Synthesis, Characterization, and Flocculation Properties of Poly(acrylamide-methacryloxyethyltrimethyl Ammonium Chloride-Methacryloxypropyltrimethoxy Silane). J. Appl. Polym. Sci. 2009, 111, 1594. (25) Gorin, K. V.; Sergeeva, Y. E.; Butylin, V. V.; Komova, A. V.; Pojidaev, V. M.; Badranova, G. U.; Shapovalova, A. A.; Konova, I. A.; Gotovtsev, P. M. Methods coagulation/flocculation and flocculation with ballast agent for effective harvesting of microalgae. Bioresour. Technol. 2015, 193, 178. (26) Wang, J. P.; Yuan, S. J.; Wang, Y.; Yu, H. Q. Synthesis, characterization and application of a novel starch-based flocculant with high flocculation and dewatering properties. Water Res. 2013, 47, 2643. (27) Qi, Y.; Thapa, K. B.; Hoadley, A. F. A. Application of filtration aids for improving sludge dewatering properties − A review. Chem. Eng. J. 2011, 171, 373. (28) Hill, A.; Candau, F.; Selb, J. Properties of hydrophobically associating polyacrylamides: influence of the method of synthesis. Macromolecules 1993, 26, 4521. (29) Volpert, E.; Selb, J.; Candau, F. Influence of the Hydrophobe Structure on Composition, Microstructure, and Rheology in Associating Polyacrylamides Prepared by Micellar Copolymerization. Macromolecules 1996, 29, 1452. (30) Yang, Z. L.; Gao, B. Y.; Li, C. X.; Yue, Q. Y.; Liu, B. Synthesis and characterization of hydrophobically associating cationic polyacrylamide. Chem. Eng. J. 2010, 161, 27. (31) Chai, W.; Zhang, Y.; Hou, Y. Well-defined cationic polyacrylamides with dot-charges: synthesis via an aqueous living RAFT polymerization, characterization, and intrinsic viscosity. Polym. Chem. 2013, 4, 1006. (32) Higashihara, T.; Takahashi, A.; Tajima, S.; Jin, S.; Rho, Y.; Ree, M.; Ueda, M. Synthesis of block copolymers consisting of poly(3hexylthiophene) and polystyrene segments through ionic interaction and their self-assembly behavior. Polym. J. 2010, 42, 43. (33) Abdollahi, Z.; Frounchi, M.; Dadbin, S. Synthesis, characterization and comparison of PAM, cationic PDMC and P(AM-co-DMC) based on solution polymerization. J. Ind. Eng. Chem. 2011, 17, 580. (34) Samanta, H. S.; Ray, S. K. Synthesis, characterization, swelling and drug release behavior of semi-interpenetrating network hydrogels of sodium alginate and polyacrylamide. Carbohydr. Polym. 2014, 99, 666. (35) Lafuma, F.; Durand, G. 13C NMR spectroscopy of cationic copolymers of acrylamide. Polym. Bull. 1989, 21, 315.
(36) Brar, A. S.; Mukherjee, M.; Chatterjee, S. K. Compositional sequence determination of acrylamide/alkyl acrylate copolymers by NMR spectroscopy. Polym. J. 1998, 30, 664. (37) Vu, C.; Cabestany, J. Characterization of cationic water-soluble polyacrylamides. J. Appl. Polym. Sci. 1991, 42, 2857. (38) Wang, L.; Li, G.; Zhang, Y.; Xiao, H. Synthesis and evaluation of P(AM-b-DADMAC) as fixative for dissolved and colloidal substances. J. Appl. Polym. Sci. 2013, 130, 4040. (39) Meraz, K. A. S.; Vargas, S. M. P.; Maldonado, J. T. L.; Bravo, J. M. C.; Guzman, M. T. O.; Maldonado, E. A. L. Eco-friendly innovation for nejayote coagulation−flocculation process using chitosan: Evaluation through zeta potential measurements. Chem. Eng. J. 2016, 284, 536. (40) Niu, M.; Zhang, W.; Wang, D.; Chen, Y.; Chen, R. Correlation of physicochemical properties and sludge dewaterability under chemical conditioning using inorganic coagulants. Bioresour. Technol. 2013, 144, 337. (41) Citeau, M.; Larue, O.; Vorobiev, E. Influence of salt, pH and polyelectrolyte on the pressure electro-dewatering of sewage sludge. Water Res. 2011, 45, 2167. (42) Guan, Q.; Zheng, H.; Zhai, J.; Zhao, C.; Zheng, X.; Tang, X. M.; Chen, W.; Sun, Y. Effect of Template on Structure and Properties of Cationic Polyacrylamide: Characterization and Mechanism. Ind. Eng. Chem. Res. 2014, 53, 5624. (43) Chen, W.; Zheng, H.; Teng, H.; Wang, Y.; Zhang, Y.; Zhao, C.; Liao, Y. Enhanced Coagulation-Flocculation Performance of IronBased Coagulants: Effects of PO43- and SiO32- Modifiers. PLoS One 2015, 10, e0137116. (44) Huang, X.; Gao, B.; Rong, H.; Yue, Q.; Zhang, Y.; Teng, P. Effect of using polydimethyldiallylammonium chloride as coagulation aid on polytitanium salt coagulation performance, floc properties and sludge reuse. Sep. Purif. Technol. 2015, 143, 64. (45) Lu, L.; Pan, Z.; Hao, N.; Peng, W. A novel acrylamide-free flocculant and its application for sludge dewatering. Water Res. 2014, 57, 304. (46) Chen, Y.; Chen, Y.-S.; Gu, G. Influence of pretreating activated sludge with acid and surfactant prior to conventional conditioning on filtration dewatering. Chem. Eng. J. 2004, 99, 137.
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DOI: 10.1021/acs.iecr.5b04207 Ind. Eng. Chem. Res. 2016, 55, 2892−2902
