hydroxide (alkalizing agent) in combination with iron(II) sulfate (mineral coagulant) was studied as influenced by the nature and concentration of an organic ...
Russian Journal of Applied Chemistry, Vol. 76, No. 12, 2003, pp. 1951!1954. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 12, 2003, pp. 2000!2003. Original Russian Text Copyright + 2003 by Kurenkov, Gogolashvili, Molgacheva, Gaisina.
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ENVIRONMENTAL PROBLEMS ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ OF CHEMISTRY AND TECHNOLOGY
Cationic Polymers as Organic Coagulants in Water Treatment at Heat and Electric Power Plants V. F. Kurenkov, E. L. Gogolashvili, I. V. Molgacheva, and A. I. Gaisina Kazan State Technological University, Kazan, Tatarstan, Russia Tatarenergo Joint-Stock Company, Kazan, Tatarstan, Russia Energoprogress Engineering Center, Kazan, Tatarstan, Russia Received June 2, 2003
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Abstract The efficiency of water treatment with organic coagulants (cationic polymers) and calcium hydroxide (alkalizing agent) in combination with iron(II) sulfate (mineral coagulant) was studied as influenced by the nature and concentration of an organic coagulant and concentration of a mineral coagulant.
Coagulation treatment of natural water to remove coarse and colloidal admixtures is an important stage of water pretreatment at heat and electric power plants (HEPPs). Pretreatment is usually performed with various salts of Al(III), Fe(II), and Fe(III) (mineral coagulants); for simultaneous water softening, this process is often combined with liming [Ca(OH)2 is added to the treated water]. To intensify the treatment after liming and coagulation, natural water was treated with Praestol highmolecular-weight polyacrylamide flocculants [1]. The use of flocculants at the water-treatment installation the Kazan HEPP-2 improved the quality of water passed through ion-exchanging filters in further stages of water treatment and was economically efficient. In the recent decades, organic polymeric coagulants have found increasing application; these water-soluble cationic polymers are mainly used for treatment of wastewater and more complete dehydration of precipitates. Positively charged macromolecules of organic coagulants interact with negatively charged pollutant particles in water, causing their destabilization and rapid flocculation to form coarser aggregates. Mineral coagulants are less expensive, but organic coagulants provide more efficient removal of colloidal and dispersed particles. It should be noted that, in the absence of mineral coagulants, the salt content in purified water would be lower, which, in turn, should decrease the load on the ion-exchange filters and the mineralization of wastewater. Moreover, the concen-
trations of organic coagulants required for water treatment are significantly smaller than those of mineral compounds; they can be used in a wide pH range and do not affect the acidity of the medium. Organic coagulants for water treatment are widely used in the Republic of South Africa [2]. The longtime use of organic coagulants (Zetafloc LP526 polyamines) significantly improved the quality of drinking water and decreased its cost. Its has been found [2] that the best results are obtained in a narrow concentration range of organic coagulants, whereas the overcharge of a mineral coagulant does not affect the quality of purified water. Good results have been obtained with Kemazur 4535 organic coagulant in the stage of water pretreatment at a water-desalinating electrodialysis installation of a cement plant in Tunisia [3]. The water fed into this installation was characterized by wide fluctuations of the content of colloidal and dispersed particles, and the optimal charge of the organic coagulant and flocculant substantially improved the quality of desalinated water and prolonged the service life of the filters. It should be noted that the organic coagulants are most widely used in North America, in contrast to Europe, where various inorganic coagulants are preferred [4]. Previously [5], we studied the water treatment with organic coagulants formed by degradation of highmolecular-weight cationic Praestols [copolymer of
1070-4272/03/7612-1951 $25.00 C 2003 MAIK
[Nauka/Interperiodica]
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Fig. 1. Turbidity t vs. the sedimentation time t of natural water in the presence of various coagulants. Concentrations: Ca(OH)2 3.0 mg-equiv l!1, FeSO4 10 mg l!1, and organic coagulant 1 mg l!1. Coagulants: (1) Ca(OH)2 + FeSO4, (2) 1 + FL 15, (3) 1 + FL 28 P3, and (4) 1 + FL 45C.
acrylamide (AA) with N-acrylamidopropyl-N, N, Ntrimethylammonium chloride (APTMAC)]. The resulting low-molecular-weight cationic Praestols improve the efficiency of water treatment, but comparison of their effect with that of water-soluble polymers of other classes, e.g., poly-2-hydroxypropylenedimethylammonium chlorides and polydiallyldimethylammonium chloride, is advisable. In this study, we analyzed the performance of poly2-hydroxypropylenedimethylammonium chlorides and polydiallyldimethylammonium chloride (organic coagulants) used in combination with calcium hydroxide in the presence and absence of iron(II) sulfate (mineral coagulant). EXPERIMENTAL In the tests, we used cationic poly-2-hydroxypropylenedimethylammonium chlorides FL 15 (MD = 7 0 104) and FL 28 P3 (MD = 4 0 105) and polydiallyldimethylammonium chloride FL 45C [MD = (133) 0 10 5] purchased from SNF FLOERGER company (France):
gg ; = 99 =;=;
CH3 Ä[ÄN+ÄCH3ÄCHÄCH2Ä]nÄ Cl! CH3
OH
( F L 15; F L 28 P3 ) CH2
Ä[ÄCH2ÄCH CHÄ]nÄ
CH2 CH2 N+ Cl! H3C CH3 ( F L 45C )
Iron(II) sulfate FeSO4 . 7H2O [technical-grade green vitriol, GOST (State Standard) 6981375] and a saturated solution of construction lime Ca(OH)2 (GOST 9179377) were used as coagulants. The initial and purified water was analyzed using chemically pure and analytically pure grade reagents; all solutions were prepared in distilled water. The experiments were performed using river water samples taken at the water scoop of the Kazan HEPP-2 (total hardness 3.8 mg-equiv l!1, alkalinity 2.4 mg-equiv l!1, permanganate oxidizability (PO) 11.0 317.3 mg O l!1, and total content of iron 1593240 mg l!1). The coagulation tests were carried out by the standard procedure [6] and by sedimentation analysis, using an LAM-1 laboratory turbidity analyzer [7]. The optimal charges of Ca(OH)2 and FeSO4 solutions were calculated in conformity with regulations [6]. The tests were performed as follows. First, natural water samples (150 cm3) were placed in cylinders with ground-glass stoppers, and then the reagents were added in the following order: Ca(OH)2 solution, mineral coagulant, and, finally, organic coagulant. All the reagents were added successively at 1-min intervals. Then the mixture was agitated by carefully mixed turning-over the cylinder five times (to preserve the sludge structure), poured into a cylindrical optical cell, and the variation of the optical density of the resulting suspension with time was recorded. The measurements were carried out in the same cylinder at a depth of 90 mm from the surface (l 670 nm, l 35.2 mm). First, we analyzed the effect of organic coagulants on the sedimentation of the disperse phase in natural water after its treatment with calcium hydroxide and mineral coagulant. Figure 1 shows how the water turbidity varies in the absence (curve 1) and in the presence of various organic coagulants (curves 23 4). The tests were carried out at constant concentrations of Ca(OH)2, FeSO4, and polymers. As seen, the turbidity of water considerably decreases upon addition of organic coagulants owing to intensive sedimentation of the dispersed particles. Comparison of the data of Fig. 1 at t = const shows that the effect on the suspension clarification increases in the order FL 15 < FL 28 P3 < FL 45C (passing from curve 2 to curve 4, Fig. 1). A chemical analysis of the initial and purified water showed that organic polymers do not affect the pH and hardness of water being treated, and only PO values and iron content decrease. Therefore, we evaluated the effect of organic coagulants on the removal of iron compounds and natural organic compounds from natural water. The total content of organic compounds and iron in water was determined from the PO
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values (mg O l!1) and by photometry, respectively. The analyses of the initial and clarified water were performed using the known procedures [8]. The effect of the concentration of the organic coagulants on the PO values and content of iron in water is illustrated in Tables 1 and 2, respectively. As seen from these data, the efficiency of water treatment increases with increasing concentration of the organic coagulant. It should be noted that the content of organic and iron compounds decreases even with small additions of organic coagulants. We also compared the results of water treatment upon substitution of the mineral compound with organic coagulant at optimal and decreased concentrations of iron(II) sulfate. The optimal charge of iron(II) sulfate of 40 mg l!1 was determined by analysis of the initial water and confirmed by special coagulation tests. The results obtained are listed in Table 3. It can be seen that lowering the charge of iron(II) sulfate from 40 to 10 mg l!1 leads to a decrease in the efficiency of water treatment, i.e., the content of residual iron in the treated water grows. Upon substitution of the mineral coagulant with FL 54C, the efficiency of water treatment improves, this organic coagulant provides more complete removal of organic compounds and iron from water as compared with the effect of the mineral coagulant at its optimal charge of 40 mg l!1. Figure 2 shows the effect of FL 45C organic flocculant on PO (curve 1) and content of iron compounds (curve 2). These parameters of the water treatment efficiency upon addition of the optimal charge (40 mg l!1) of the mineral coagulant are 58 and 69% of the initial values, respectively. As seen from Fig. 2, addition of even insignificant amounts of organic coagulant provides better purification of water as compared with the mineral coagulant. Our experimental data show that the mineral coagulant FeSO4 can be replaced with with an organic coagulant in pretreatment of water at heat and electric power plants. In this case, use of water-soluble cationic polymers FL 15, FL 28 P3, and FL 45C not only provides more complete removal of impurities but also decreases the salt content in the wastewater. For example, at FeSO4 concentration of 40 350 mg l!1, the content of sulfate ions in water increases by 53 20 g m!3. Moreover, we should remember that, in the flood period, the coagulant is usually taken in a double amount, which increases the pollution of water with sulfate ions. In the subsequent stages of water pretreatment, the ion-exchange filters sorb the sulfate anions, but in the course of filter regeneration they RUSSIAN JOURNAL OF APPLIED CHEMISTRY
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Table 1. Oxidizability PO of the clarified water as influenced by the concentration of organic coagulants, coc (FeSO4 10 mg l!1, PO of initial water 8.48 mg O l!1)
ÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ ³ PO (% of the initial value) Polymer ³ at indicated coc, mg l!1 brand ÃÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄ ³ 0 ³ 0.1 ³ 1.0 ³ 5.0 ³ 10.0 ÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄ FL 15 ³ 81 ³ 81 ³ 65 ³ 62 ³ 53 FL 28 P3 ³ 81 ³ 52 ³ 50 ³ 47 ³ 41 FL 45C ³ 81 ³ 61 ³ 61 ³ 36 ³ 41 ÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄ
Table 2. Content of iron in the clarified water as influenced by the concentration of organic coagulants coc (FeSO4 10 mg l!1, total content of iron compounds in initial water 198 mg l!1)
ÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ ³ Iron concentration (% of the initial value) Polymer ³ at indicated coc, mg l!1 brand ÃÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄ ³ 0 ³ 0.1 ³ 1.0 ³ 5.0 ³ 10.0 ÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄ FL 15 ³ 78 ³ 55 ³ 55 ³ 44 ³ 53 FL 28 P3 ³ 78 ³ 64 ³ 56 ³ 35 ³ 27 FL 45C ³ 78 ³ 66 ³ 52 ³ 34 ³ 42 ÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄ
Table 3. Efficiency of water treatment with mineral (FeSO4) and organic (FL 45C) coagulants (initial water: PO 14.8 mg O l!1 and iron content 204 mg l!1)
ÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Purified water Charge, mg l!1 ³ ÄÄÄÄÄÂÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄ FeSO4 ³FL 45C³PO, % of the initial³Fetot, % of the initial ÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 40 ³ ³ 58 ³ 69 10 ³ ³ 52 ³ 99 ³ 5 ³ 32 ³ 27 ÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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pass into wastewater. Thus, use of organic coagulants significantly decreases the salt content in wastewater and improves the environmental situation at wastewater discharge sites.
Fig. 2. Quality parameters of clarified water, A: (1) permanganate oxidizability and (2) total iron content, vs. the concentration of FL 45C organic coagulant, coc. Ca(OH)2 content 3.0 mg-equiv l!1. No. 12
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CONCLUSIONS (1) Poly-2-hydroxypropylenedimethylammonium chlorides FL 15 and FL 28 P3 and polydiallyldimethylammonium chloride FL 45C can be used as effective organic coagulants in the stage of water pretreatment at heat and electric power plants. (2) The turbidity of water and the content of organic impurities and iron compounds in water decrease upon its treatment with organic coagulants in combination with calcium hydroxide both with and without iron(II) sulfate mineral coagulant. REFERENCES 1. Kurenkov, V.F., Gogolashvili, E.L., Saifutdinov, R.R., et al., Zh. Prikl. Khim., 2001, vol. 74, no. 9, pp. 1551 1554. 2. Nozaic, D.J., Freese, S.D., and Thompson, P., Water
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Sci. Technol. Water Supply, 2001, vol. 1, pp. 43 50. 3. Bouguecha, S. and Dhahbi, M., Desalination, 2002, vol. 151, pp. 75 86. 4. Shelley, S.A., Chem. Eng. (USA), 1997, vol. 104(6), pp. 63 64, 66. 5. Kurenkov, V.F., Gogolashvili, E.L., Molgacheva, I.V., et al., Zh. Prikl. Khim., 2003, vol. 76, no. 5, pp. 800 803. 6. Rukovodyashchie ukazaniya po izvestkovaniyu vody na elektrostantsiyakh (Master Guideline on Liming of Water at Heat and Electric Power Plants), Moscow: STsNTI, 1973. 7. Kurenkov, V.F., Gogolashvili, E.L., and Isakov, A.A., in Struktura i dinamika molekulyarnykh sistem: Sbornik statey (Structure and Dynamics of Molecular Systems: Collection of Papers), Ioshkar-Ola: 2001, issue 8, part 2, pp. 116 120. 8. Unifitsirovannye metody analiza vod (Standard Methods of Water Analysis), Lur’e, Yu.Yu., Ed., Moscow: Khimiya, 1973.
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