Thematic Division: Chemical Technology.
Subdivision: High-Molecular Compound
_____________________________________________________________________________
Review
Registration Code of Publication: po36
Received December, 15. 2002
APPLICATION OF POLYACRYLAMIDE FLOCCULANTS FOR WATER TREATMENT
© Valery F. Kurenkov,1*+ Hans-Georg Hartan,2 and Fedor I. Lobanov3
1
Institute of Polymers. Kazan State Technological University. K. Marx St., 68. Kazan 420015. Russia. E-mail: kuren@cnit.ksu.ras.ru
2
Stockhausen GmbH and Co. KG. Bäkerpfad 25. D-47705 Krefeld. Germany. Fax: +49 (2151) 381595
3
Open Companies “Stockhausen Eurasia. Technics and an Environment”.1-st Road travel, 1. Moscow 113545. Russia.
E-mail: lobanov–stockhausen–etu@genetika.ru
____________________________________________
*Leader of the thematic course; +Corresponding author
Keywords: water treatment, flocculants, coagulants, polyacrylamide, polymers of acrylamide, water-soluble copolymers, polyelectrolyts.
Abstract
General patterns of water treatment with the use of polyacrylamide and its anionic and cationic derivatives have been considered in the absence
and presence of mineral coagulants. The influence of such characteristics as concentration, molecular weight, nature, chemical composition and
conformation of flocculant macromolecules, concentration and nature of the coagulant, the way and time of flocculant and coagulant dosage, as well as
the quality of the original water and conditions of water preparation on water treatment efficiency have been shown.
Contents
Introduction
1. Treatment of natural water with coagulants and flocculants.
2. Decoloration of natural water with coagulants and flocculants.
3. Treatment of waste waters with coagulants and flocculants.
Conclusions
References
Introduction
Treatment of natural water and sewage is closely linked to preservation of the environment and is thus an actual present day
problem. During the last decades there have been noticed substantial increase of the content of heavy metals, mineral oil, poorly-oxidable
organic compounds, synthetic surfactants, pesticides and other pollutants from insufficiently treated effluents of industrial and municipal
enterprises in open water reservoirs. In spite of the great number of elaborations reported in literature [1-4], the problem of natural
water and sewage treatment has not yet been solved. Hence, the technology of water treatment needs further perfection which mainly
includes the ways of intensive use of reagents, in particular flocculants. For these purposes water-soluble high-molecular compounds
among which the most widespread and universal are polyacrylamide flocculants are used [5-10]. As a result of their application the
efficiency of removal of heavy metals is increased by 95%, compounds of phosphorus – by more than 90%, suspensions - by more than
80%, organic substances - by more than 75% [7]. Besides, flocculation water treatment is characterized by low capital and operational
expenses as compared to the other methods of water treatment[1]. A number of monographs [2-4,6,9] and reviews [10-14] are devoted to
the problems of flocculation model and real disperse systems using polyacrylamide flocculants. In view of this information and taking
into account the most significant latest data, the present review considers the basic patterns of treating natural waters and sewage with
polyacrylamide (PАА) and its anionic and cationic derivatives in the presence and absence of mineral coagulants, as well as the most
efficient ways of intensive water treatment.
Results and Discussion
1. Treatment of Natural Water with Coagulants and Flocculants.
Natural water is a complex colloid system containing organic and inorganic substances as well as thin-dispersed components.
Besides, the quality of natural water can vary seasonally and depending on their chemical and dispersed composition. Therefore the
industrial tests should take into account the quality of original water and specific characteristics of waterworks stations. The influence
of these factors on water treatment is reported in literature [1,3,4,15] and the role of coagulants is reviewed in monographs [16,4],
that is why these questions were not considered in detail in the present review. One of the primary tasks of water treatment
technology is the choice of optimal reagents for each water source, conditions of their application and necessary doses. In order to
remove suspension and colloid-dispersed substances from natural water our waterworks stations until recently have basically used
aluminum sulfate (АS) as a coagulant, and flocculant - PAA. With the development of new reagents there appeared the need for
estimating their efficiency as compared to АS and PАА, and tests have been carried out on water treatment efficiency in different
cities and regions of Russia. Separate data on treatment of open reservoir water with the use of coagulants and flocculants have been
reported in the works published in recent years [17-19].
Valery F. Kurenkov - professor (Ph.D. in chemistry) at Plastic Technology department, Kazan State
Technological University. Defended the theses: 1969 – Ph.D. level (Kazan Chemical Engineering Institute),
1982 - for Doctor's degree (Institute for the Chemistry of High-Molecular Compounds, Kiev) on specialization
"Chemistry of High-Molecular Compounds"; professor (1984). Membership: a member of Doctorate and Expert
Councils at KGTU. Honoured titles: Soros Professor (1994), Honored Scientist of Tatarstan Republic (2002).
Published more than 500 works in Russian and foreign journals, author of 2 monographies, 4 textbooks and 30
reviews.
Scope of scientific interests: chemistry and physical chemistry of high-molecular compounds; kinetics and
mechanism for polymerization of ionogenic monomers; synthesis, chemical conversion and application of watersoluble polymers.
© Химия и компьютерное моделирование. Бутлеровские сообщения. 2002. Vol.3. № 11. ______ Ул. К. Маркса, 68. 420015 Казань. Татарстан. Россия. _____
31
Review ______________________________________________________________________ V.F. Kurenkov, H.-G. Hartan, and F.I. Lobanov
The technology of the river Don water treatment
used at waterworks stations (Novocherkassk)is based on
the application of binary reagents - high-molecular
flocculant Fennopol A-321 with coagulants - aluminum
hydroxochloride (AHOC) and АS [20]. The influence of
coagulants on turbidity of the treated water at the stage of
sedimentation is shown in fig. 1. As it is seen, in a wide
range of concentration AHOC provides more complete
purification of water and its optimal dose is less than that of
АS. Additives of Fennopol (a doze 0.15-0.2 mg·1−1)
efficiently treated water at temperature 20o С and reduced
the coagulant dose down to 2-4 mg·1−1. Aeration of water
Fig. 1. Dependence of water turbidity N (mg·1−1) on time t (min) with application of
at the stage of its mixture with reagents accelerated the
aluminum hudroxochloride (1,2,3) and aluminum sulfate (1’, 2’, 3’).
desorbing process of carbonic acid formed owing to the
Doses (in recalculation on Al2O3) of coagulant Cc (mg·1−1): 5 (1,1’); 15 (2,2’); 30 (3,3’).
hydrolysis of coagulant, and increased the completeness of
hydrolysis. Removal of carbonic gas from the sphere of reaction of hydrolysis facilitated the formation of dense flacks, their fast
sedimentation and clarification of water.
Comparison of action of АS (К1) and AHOC (K2) in the absence and presence of PАА on the river Volga water treatment at
waterworks КUP "Water canal" (Kazan) is given in work [21]. Results of the tests which have been carried out during the summer
period of 1999, are shown in table 1.
The table data demonstrate the improvement of normative parameters of
Table 1. Influence of aluminum sulfate (К1) and aluminum
the treated water on replacing АS with HOCA. Additional introduction of PAA
hudroxochloride (K2) in a combination with PАА on quality of
after coagulants did not prove to be efficient, since the original water in July,
the cleared water in various days of tests [CAI = 4 mg·1−1 CP=0.15
1999 was not characterized as substantially polluted.
mg·1−1]. Flocculant entered after coagulant in 2 min.
At Rublev waterworks of "Mosvodokanal" (a moskvoretskij source) there
−1
Color index,
Turbidity,
Concentration, mg·1
have
been
tested a pilot plant of "Dеgremon"Co for water treatment using binary
−1
deg
mg·1
Al
Fe
Mn
reagents - coagulants АS and aluminum оxichloride (AОC) with anionic
Initial water
flocculants ASP 25 [a copolymer acrylamide (АА) with sodium acrylate (Na62
2.5
0
0.9
0.16
АA) with the content of ionogenic units α = 5 mol%] [18]. The tests were carried
•
(3.8)
(0)
(0.8)
(0.14)
(46)
out in 1997-1998 during all seasonal changes of quality of original water. АS
SanPiN regulations
appeared to be more efficient with warm original water, and within winter period
20
1.5
0.5
0.3
0.2
AOC turned out to be more efficient. The use of coagulants and flocculant
Purified water
Coagulant К2
effectively reduced the basic characteristics of impurity of water after
20
0.3
0.2
0.2
0.06
sedimentation: turbidity - by 80-85%, color index - by 50-60%, permanganate
(20)
(0.5)
(0.1)
(0.18)
(--)
oxidizability - by 40-50%, iron content - by 90%, ammonium - up to 0.1 mg·1−1
15
0.1
0.1
0.15
0.08
and the content of phytoplankton - by 97-98% (even with rough flowering water).
(23)
(0.4)
(0.1)
(0.22)
(0.05)
The influence of an interval between the moment of introduction of АS
17
0.2
0.2
0.2
0.07
and anionic flocculant Маgnafloc LT27 on water treatment is considered in work
20
0.3
0.2
0.2
0.05
Coagulant К1
[22]. With the small dose of flocculant (0.02 mg·1−1) and the dose of coagulant 5
22
0.9
0.2
--mg·1−1 the time interval of 30-120 sec between the dosage of the reagents did not
(18)
(0.2)
(0.1)
(0.15)
(0.05)
influence the color index of water, and with a greater dose of flocculant (0.30
21
0.7
0.4
--mg·1−1) and the same coagulant dose, with the increase of time interval between
(20)
(0.2)
(0.2)
(0.3)
(0.04)
dosages of reagents the color index of water was reduced. The increase of the
21
1.1
0.3
--interval up to the moment of input of flocculant facilitated more complete
21
0.8
0.1
--sorption of humic substances by the particles of aluminum hydroxide and the
22
0.7
0.2
--subsequent sorption of flocculant (see table 2).
20
0.7
0.2
0.25
0.04
*In brackets the data for joint application
Now in Perm the Joint-Stock Company "Moscow- Stokhauzen-Perm", using
coagulants with PАА are resulted.
the German technology, launches the production of highly efficient flocculants,
Praestols, which have high molecular weight (М), 100% content of the basic substance, and produces a wide spectrum of marks of nonionic,
anionic and cationic polymers adapted to various kinds of suspensions and the processes of their separation. We shall consider the results of
application of Praestols in the absence and in combination with coagulants for decolouration and treatment of natural water.
On the basis of model researches on kaolin suspension [23,24] the comparison of quality of natural water treated with various
flocculants in combination with АS has been carried out [25]. The flocculants used were ammoniac PАА commercially produced by J.M.
Sverdlov plant (Dzerzhinsk), nonionic Praestol 2500 (PАА), anionic Praestols 2515 TR, 2530 TR and 2540 TR (copolymers АА with
Na-АA) commercially produced by Joint-Stock Company "Moscow-Stokhauzen-Perm". Characteristics of flocculants are given in table 3.
Samples of hydrolyzed PАА (HPАА) - B (D), Е and hydrolyzed Praestol (I) were obtained in working conditions on the plant for
dissolution of polymer by alkaline hydrolysis of samples B, A and G respectively. Alkaline hydrolysis was used for partial replacement
of AA groups of PAA with Na-AA groups and was carried out under the conditions established on the basis of previous
Feodor I. Lobanov - professor, (Ph.D. in Chemistry), director of the firm "Stokhauzen Eurasia. Engineering and
Environment". Defended the theses: 1968 - for Ph.D. Level (M.V. Lomonosov Moscow State University), 1983 - for
Doctor's degree (State Research Institute for Rare-Metal Industry), professor (1984).
Scope of scientific interests: use of water-soluble polymers for purifying natural and waste water, environmental
protection.
32 _________________
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© Chemistry and Computational Simulations. Butlerov Communications. 2002. Vol.3. No.11. 31.
APPLICATION OF POLYACRYLAMIDE FLOCCULANTS FOR WATER TREATMENT
Table 2. The effect of intervals between the moments of introduction
of aluminum sulfate and Magnafloc LT27 on quality of water
treatment (coagulant dose - 5.0 mg·1−1, temperature of water 40o C).
Dose of
flocculant,
mg·1−1
0
0.02
0.02
0.02
0.30
0.30
0.30
Time
interval, s
0
30
60
120
30
60
120
Treated water
Color index,
Turbidity,
deg
mg·1−1
23.5
1.3
18.0
0.4
18.0
0.4
18.0
0.4
21.0
0.4
20.0
0.4
19.0
0.4
___________________________________________ 31-40
Table 3. Characteristics of flocculants.
Sample
Flocculant
[ η ],
cm3·g–1
Мη·10–6
А
B
C
D
Е
G
H
I
J
K
PАА
PАА
HPАА
HPАА
HPАА
Praestol 2500
Praestol 2515 TR
Praestol 2515 TR
Praestol 2530 TR
Praestol 2540 TR
900
580
580
580
900
1550
1500
1500
1800
1600
4.2
2.3
1.3
1.2
2.2
8.7
4.4
4.0
4.6
4.4
Content of indicated units in
copolymer, mol.%
acrylamide
Sodium acrylate
100
0
100
0
89
11
82
18
82
18
97
3
89
11
83
17
80
20
72
28
researches [26-28]. Fig. 2 shows the influence of concentration of flocculants (Cp) on flocculation effect (D), which was calculated by the
formula [29]
D = (no - n) / n,
where no and n - accordingly optical density of water (it is determined
by the turbidimetric procedure) in the absence and presence of the flocculant (and coagulant).
The experiments with a sample of natural water
(turbidity 4.2 mg·1−1, color index 48.5 deg, alkalinity
1.5 mg·1−1) at concentration of coagulant Сc=6×10-3%
have shown the increase of D with the growth of
concentration for all flocculants. This is the result of
growing concentration of macromolecular bridges
formed at adsorption of macromolecules on the surface
of dispersed phase particles which led to the formation
of large units from the particles of the dispersed phase
and macromolecules and reduced the stability of the
system. Comparison of the data in fig. 2 at Сp=сonst,
shows the increase of values D at transition from
homopolymers to copolymers (curves 1,2 and 1’,2’). At
the identical chemical composition of macromolecules
(see table 3) samples Praestol (curves 2,2’) are
characterized by greater volumes of D as compared to
PАА and HPАА (curves 1,1’) owing to greater values
Fig. 2. Dependence of flocculation effect D on concentration of commercial joint venture polymers (%).
of M for Praestol (see table 3). It is known [30], that
1 - PАА (sample А), 1’ - HPАА (sample E), 2 - Praestol (sample G), 2’ - Praestol (sample I).
with the increase of M the root-mean-square sizes of
macromolecular balls in the solution (r2)1/2 increase. This facilitates the coverage of the greater number of dispersed phase particles with
polymeric bridges, increases the sizes of flocks and finally the flocculation effect. From fig. 2 also follows, that compliance to norm D =
0.7 (determined at n = 0.021 and λ = 540 nanometers or at n = 0.172 and λ = 364 nanometers, corresponding turbidity of purified water)
is reached at smaller values of Cp for Praestol as compared to PАА and HPАА [with identical chemical composition of samples (see
table 3)]. The values of D have also been noted to increase with the growth of Сc (at Cp= const).
On samples of anionic Praestol with close values of M (see table 3) it is shown, that the dependence D = f (α), where α - the
content of groups Na-AA, is extreme (fig. 3а). This is the consequence of similar dependence of ηsp/Cp=f(α) (at Сp=сonst) (fig. 3б). The
changes of ηsp/Cp=f(α) are cymbate to [η] and hence (r2)1/2 value changes, which follows from Flory equation [31]
[η] =Ф (r2)3/2/М.
As it is seen from fig. 3a, the maximal values of D correspond to values α=15-20 mol%. Apparently, thus the optimal proportion
between the charge density and flexibility of macromolecules which provides the greatest value (r2)1/2 is realized. This facilitates the
coverage with polymeric bridges of the greater number of dispersed phase particles, the increase of D and flock sizes. The data of fig. 3a
also allow to note, that with the increase of Cp the character of dependence D=f (α) becomes more obvious (transition from curve 1 to
curve 3) owing to the increase in concentration of polymeric bridges between particles of dispersed phase.
On the basis of laboratory researches on model kaolin suspension [32] the experimental-industrial tests of binary reagents – PAA
(sample B), HPAA (sample C and D) and anionic Praestol 2515 (sample G) in combination with AS on the river Volga water treatment
at waterworks KUP “Water canal” (Kazan) in autumn-winter of 1998 [27,28] have been carried out. According to the data given in table
4, application of Praestol 2515 during the autumn period (temperature of water 13o С, color index 50-52 deg, turbidity 4.2-5.1 mg·1–1,
total alkalinity 1.84-2.00 mg-equiv·1–1) provided water treatment meeting the required norms [33].
Hans-Georg Hartan (Ph.D. in natural sciences (1976)) - president of firm "Stokhausen GmH and Co. KG" (1996 till now), chairman of the Board of Directors of Russian-German firm "Moscow-Stokhausen-Perm" (1996 - till now).
Author of 7 patents, 4 reviews and some publications.
Scope of scientific interests: synthesis, properties and application of water-soluble polymers for intensifying
technological processes and purifying potable and waste water.
© Химия и компьютерное моделирование. Бутлеровские сообщения. 2002. Т.3. №11.
________________
E-mail: info@kstu.ru
________________ 33
Review ______________________________________________________________________ V.F. Kurenkov, H.-G. Hartan, and F.I. Lobanov
а
D 1,1
3
0,9
2
0,7
1
0,5
0
20
40
Fig. 3. Dependence of flocculation effect D (а) and ηsp/Cp (см3·г−1) (b) on the content of Na-AA α links (mol. %)
in macromolecules of Praestol at various concentrations of Cp.Сc= 6×10–3 %; Cp ×105 (%): 1 - 12, 2 - 20, 3 - 32, b - 200.
Table 4. The effect of PAA (sample B), HPAA (sample C and D) and Praestol 2515 (sample G)
in combination with aluminum sulfate on the quality of treated water.
Date
Flocculant
01.10
02.10
03.10
04.10
02.12
21.12
28.12
03.12
20.12
21.12
27.12
22.12
23.12
25.12
Praestol (G)
---//-----//-----//--PАА ( B)
---//-----//--HPАА ( D )
---//--HPАА ( C )
---//--Praestol (G)
---//-----//---
Сc,
mg·1–1
13
13
17
17
35
34
35
35
34
34
35
34
34
34
Сp ,
mg·1–1
0.014
0.012
0.014
0.014
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.014
0.019
0.022
Turbidity, mg·1–1
Before treatment
After treatment
4.4
0.7
4.9
0.9
5.1
0.8
4.2
1.0
2.1
1.7
2.2
1.2
1.9
1.2
3.5
0.8
2.2
1.4
2.2
1.2
2.2
1.0
2.2
1.2
2.8
1.4
2.0
0.7
Al, mg·1–1
After treatment
0.3
0.2
0.3
0.2
0.8
0.8
0.4
0.5
0.5
0.4
0.4
0.5
0.5
0.4
During the winter period (temperature of water 0.2о С, color index 52-53 deg, turbidity 2.0-3.5 mg·1–1, total alkalinity 1.99-2.10
mg-equiv·1–1) PАА did not provide the required quality of water treatment (table 4), and after application of HPАА and Praestol 2515
larger and well settling flakes were formed, which improved the filtering process, turbidity of waters was reduced and the content of
aluminum, as well as other parameters of treated water also met the requirements. It was accomplished using 7-13 times smaller doses of
high-molecular Praestol 2515 as compared to HPАА (see table 4).
Comparison of quality of the river Volga water treatment with nonionic Praestol 2500 (Pr) and its partially hydrolized derivative
(HPr) was carried out at "Kazanorgsintez" JSC waterworks during the summer period of 2000 [34]. The technological circuit of water
treatment consisted of two lines with identical structure of treatment works (the chamber of flakes-formation, horizontal sediment bowls
and quartz filters) with productivity 1700 m3·h–1. On one line Pr was fed, and on the other - HPr and from each line the basic parameters
of treated water were taken. The data are given in table 5.
Table 5. The effect of flocculants Praestol (Pr) and hydrolyzed Praestol (HPr)
(the content of Na-AA 19 mol. %) in combination with aluminum sulfate on
the quality of treated water.
Apparently, water treatment with application of Рr and HPr
provides the quality of potable water that meets the requirements of
specifications [33]. Other parameters of treated water also correspond
Сc,
Сp ,
Treated water
to the norms. Thus qualitative water treatment was provided with
–1
–1
–1
Data
mg·1
Turbidity, mg·1
AI (III), mg·1
small doses of Praestol 2500. The table data confirm, that at
Pr
HPr
Pr
HPr
replacement of Рr with HPr turbidity of water was reduced by 18%,
1.06
13
0.015
1.10
0.97
0.33
0.28
and the content of Al+3 - by 26%. Thus, the improvement of water
2.06
13
0.017
1.16
1.09
0.32
0.27
3.06
14
0.013
1.12
1.02
0.30
0.24
treatment quality and reduction of operational costs have been
5.06
13
0.010
1.34
1.26
0.38
0.29
accomplished.
10.06
16
0.017
1.16
1.15
0.24
0.17
Application of AS for water treatment at many waterworks
11.06
14
0.013
1.20
1.11
0.19
0.16
has revealed a number of shortcomings, such as low efficiency at low
12.06
16
0.016
1.01
0.90
0.21
0.15
13.06
16
0.013
1.31
0.61
0.18
0.16
temperature of water, the use of great dosages of the reagent and the
risk of exceeding the maximal concentration limits on aluminum and iron content in potable water [4]. Therefore it is worth while
searching new effective reagents for water treatment. As colloid impurities in natural waters and sewage, as well as the particles of the
majority of suspensions are charged negatively, for their removal the application of cationic flocculants is indispensable.
Flocculation properties of anionic (А) and cationic flocculants (К) are investigated at water treatment (with concentration of
dispersed phase 2.7%), selected from sediment tanks of waterworks [35]. Flocculant A is copolymer of АА with Na-АA, and flocculant
K – copolymer of АА with dimethylaminoethylmetacrylate hydrochloride (DMAEM HC). As a quantitative characteristic of flocculation
effect the following parameter was used
D = (V – V0) / V0,
where V and V0 – are accordingly the sedimentation rates of the dispersed phase in water (defined at sedimentation in
cylinders) in the presence and absence of the flocculant.
There has been established the increase of D values with the concentration growth of flocculants A and K (Cp). At close
agreement of values of M and the content of ionogenic groups in macromolecules, the value D increased with the replacement of
flocculant K with A. This is the consequence of more efficient adsorption of negatively charged macromolecules of flocculant A on
34 _________________
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© Chemistry and Computational Simulations. Butlerov Communications. 2002. Vol.3. No.11. 31.
___________________________________________ 31-40
dispersed phase particles as compared to positively charged macromolecules of flocculant K. The concentration growth of the dispersed
phase in water (Сd) decreased the value D owing to the reduction of the ratio Cp/Cd at Сp=const. At addition into water of surface-active
substance (ОP-10) the values D increase more essentially for flocculant K, than for flocculant A. In this case molecules ОP-10, adsorbed
on dispersed particles, facilitate the local adsorption of flocculant K macromolecules. For flocculant A there has been noted the reduction
(in presence of ОP-10) of the root-mean-square sizes of macromolecular balls in the solution (r2)1/2, which resulted in the reduction of D.
At waterworks station (Kemerovo) the reasons for the increase of the content of residual aluminum in potable water were
analyzed, and to diminish this parameter reagent AS was replaced with aluminum hydrosulphate (АHS), and the reagent ammoniac PАА
was replaced with low-molecular cationic flocculant VPC-402 (polydimethyldiallylammonium chloride), commercially produced at
"Kaustik", Sterlitamak [36]. Experiments were carried out on the pilot plant of the firm Preussag Noell at temperature of water 20o С.
Two filter-cycles have been analysed using the same doses of reagents at waterworks stations. Fig. 4 shows the dependence of water
turbidity and concentration of residual aluminum in filtered water CAL on filter-cycles operation time for the river Tom' water treatment
with the use of АHS (2 mg·1–1 Al2O3) with VPC-402 (0.2 mg·1–1), and AS with PАА in the same doses.
APPLICATION OF POLYACRYLAMIDE FLOCCULANTS FOR WATER TREATMENT
Fig. 4. Dependence of turbidity of water N (mg·1−1) (1-3) and concentration of residual aluminum in filtered water CAI (mg·1−1) (4)
on time t (h) for filter-cicles of the river Tom' water treatment on pilot plant of the firm Preussag Noell.
a - for aluminum hudrosulfate (2 mg·1−1 Al2O3) and VPC-402 (0.2 mg·1−1);
b - for aluminum sulfate (2 mg·1−1 Al2O3) and PАА (0.2 mg·1−1). Water: 1 - original, 2 - clarified, 3 - filtered.
The turbidity of water leaving sedimentation tank did not differ from the original one, and after filters was still as high as 2
mg·1−1, which proves the work of the plant to be inefficient. Better work of sedimentation tank was ensured with the application of AHS
and VPC-402 and the quality of filtered water met the requirements of specifications on turbidity. The content of the residual aluminum
did not exceed 0.1 mg·1−1 whereas on using AS with ammoniac PАА it was 0.2 mg·1−1.
In work [37] there have been presented the results of the river Don water treatment at waterworks station (Rostov-on-Don)
with the use of cationic flocculant VPC-402, which has been applied as the only reagent since March, 1994. On introducing the
flocculant into the chambers of flake formation water clarification in sedimentation tanks was weak, and turbidity of the treated
water substantially exceeded the norms for potable water quality. Therefore the flocculant was fed into the soaking lines of pumps
at the intermediate pump station located 3 km away from the sewage disposal plant. Thus interaction of flocculant with colloidal
pollutants in water started in pipes and increased the turbidity of cleanable water as compared to the river water, that facilitated
the further efficient water clarification in sedimentation tanks. In table 6 there are given the results of water clarification with
coagulant (1993) and flocculant (1995), and in table 7 the parameters of quality of water treatment are presented.
Table 6. The effect of flocculant VPC-402 and aluminum sulfate on the quality of water
treatment at waterworks station (Rostov-on-Dоn).
Average
per year
1993
1995
Doses of reagents , mg·1−1
Turbidity, mg·1−1
VPC-402
aluminum sulfate
Origin
In mixture
After sedimentation tank
--0.23
19.9
---
12.5
13.3
12.2
7.7
5.3
3.7
Treated
1.1
0.96
According to the data of tables 6 and 7, flocculant VPC-402, as compared to coagulant AS, provided deeper and steadier year
round effect of water clarification in sedimentation tanks and filters. Addition of flocculant VPC-402 into water without diluting it has
allowed to simplify and reduce the price of the design of the reagent facilities as well as their operation. According to table 7, the
replacement of coagulant АS with flocculant VPC-402 has lowered the content of residual aluminum in treated water, and the other
parameters of treated water changed equally. In comparison with AS at the use of flocculant VPC-402, the required effect of water
treatment was provided with an order less dozes of reactants.
Tests of cationic flocculant VPC-402 at water works (Novosibirsk), carried out in autumn during the high water, showed the efficiency of the
reagent with low temperature water [38].
Influence of flocculants - anionic Magnafloc LT27 and cationic Magnifloc LT 573C in combination with coagulant АS on color
index and turbidity of the river Dnepr water treatment at Dneprovskoj waterworks (Kiev) is considered in work [22]. Experiments are
carried out using the technique of tentative contact coagulation-flocculation [39]. At dose AS 5 mg·1−1 the greater extent of clarification
and decoloration of water was provided with only small doses (0.01-0.05 mg·1−1) of Magnafloc LT27, and the excess of these doses
increased the coloration of the treated water (see table 8). Magnifloc LT 573C in small doses increased the coloration of water and only
in greater doses - 0.5-1.25 mg·1−1 (the dose of coagulant 2.5-5.0 mg·1−1) reduced turbidity and coloration of the treated water (see table
9). Preliminary ozonization and chlorination of water did not increase the treatment efficiency.
Work [40] contains data on the efficiency of open reservoir water treatment and drinking water production with the use of AS
and a number of flocculants – cationic Praestols 611and 650 (copolymers of АА with N-acrylamidopropile-N,N,N-trimethylammonium
chloride), anionic Praestols 2530 and 2540, PАА produced in Leninsk-Kuznetsk, nonionic PAА of joint-stock company "Bеraton"
(Berezniki), nonionic PАА N-600 produced at S.M. Kirov factory (Perm) and composite coagulant-flocculant CF-91 produced at KPP
(Volzhskij). The most significant reduction of the content of residual aluminum and fitoplanctone in water, as well as the increase of
sedimentation rate is noted with the use of Praestol 650 during spring and summer periods and Praestol 2515 in winter conditions
© Химия и компьютерное моделирование. Бутлеровские сообщения. 2002. Т.3. №11.
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Review ______________________________________________________________________ V.F. Kurenkov, H.-G. Hartan, and F.I. Lobanov
(optimal doses of flocculants made up 0.05-0.2 mg·dm-3). The results of tests with the use of binary reagents - AS and AОC with Praestol
650 and PАА N-600 for water treatment at waterworks (Ekaterinburg) are shown in table 7.
Treatment of water with Praestol 650 in comparison with PАА N-600 has allowed to lower the flocculant consumption 2.5-3
times and to produce the treated water which quality corresponds to normative parameters. The combination at water treatment of
Praestol 650 with AS or AОC has provided better water clarification, reducing CPC, oxidability, the content of iron, guminic and fulvic
acids. The content of residual aluminum is reduced to the minimal limit of detection in water, the dose of coagulant is reduced by 1015%, and productivity of waterworks is increased owing to the higher degree of water treatment.
Table 7. The effect of flocculant VPC-402 and aluminum sulfate on quality
of water treatment at waterworks (Rostov-on-Dоn).
Parameters
Color index, deg
РН
Solid residual, mg·1−1
Hardness, mg-equiv·1–1
Alcalinity, mg-equiv·1–1
Chlorides, mg·1−1
Sulfates, mg·1−1
Аmmonia, mg·1−1
Nitrites, mg·1−1
Nitrates, mg·1−1
Iron, mg·1−1
Aluminum, mg·1−1
Zinc, mg·1−1
Copper, mg·1−1
Manganese, mg·1−1
Oil products, mg·1−1
Average annual data
1993 year (aluminum sulfate)
1995 year ( VPC-402)
Water
Water
River Don
Treated
River Don
Treated
17
7
18
8
8.2
7.8
8.1
7.8
928
924
781
780
7.75
7.75
6.57
6.57
3.6
3.4
3.4
3.3
154
156
115
117
280
278
230
229
0.37
0.13
0.43
0.15
0.058
0.003
0.057
0.005
3.88
3.03
3.59
2.75
0.40
0.17
0.58
0.23
0.07
0.18
0.07
0.08
0.012
0.009
0.009
0.001
0.021
0.016
0.020
0.016
0.054
0.028
0.110
0.084
0.15
0.05
0.10
0.05
In work [41] it is pointed out that among several dozens of the investigated coagulants and flocculants the most efficient for
water treatment are medium- and high-based aluminum polychlorides which were applied with cationic Praestol 611 ВС and 650 ВС.
Table 9. The effect of flocculant Маgnifloc LT573С
and aluminum sulfate on quality of water treatment at 4o С.
Table 8. The effect of flocculant Маgnafloc LT27
and aluminum sulfate on quality of water treatment at 30o С.
Doses of reagents, mg·1−1
Al2(SO4)3
Magnafloc LT 27
0
0
0.02
0
0.02
0.01
0.02
0.02
0.02
0.05
0.02
0.07
0.02
0.10
0.02
0.30
Treated water
Color index, deg
Turbidity, mg·1−1
23.0
0.5
21.0
0.5
18.0
0.3
18.0
0
18.0
0
21.0
0
21.0
0
22.0
0
Doses of reagents, mg·1−1
Al2(SO4)3
Magnifloc LT573
0
0
0.02
0
0.02
0.015
0.02
0.025
0.02
0.050
0.02
0.150
0.02
0.250
0.02
0.500
Treated water
Color index, deg
Turbidity, mg·1−1
23.0
4.0
18.0
0.4
15.0
0.4
15.0
0.4
15.0
0.4
15.0
0.4
15.0
0.4
14.5
0.4
Table 10. The effect of aluminum sulfate (К1) and aluminum oxocloride (К2) with Praestol 650 (F1)
and PАА H-600 (F2) on decrease of parameters of water treatment (in %).
Parameters
Color index
Turbidity
Oxidizability
Iron (common)
CPC
Humic acids
Fulvic acids
К2 + F1
84.3
72.1
69.7
86.2
51.2
57.6
50.8
Two-level treatment
К 2 + F2
К 1 + F1
76.3
82.4
65.5
69.5
61.3
64.4
79.4
84.5
35.1
48.2
41.4
53.5
45.3
48.2
К 1 + F2
70.0
64.5
62.2
80.3
40.1
44.7
43.0
К 2 + F1
80.5
78.0
73.0
83.2
58.9
56.3
54.4
Contact coagulation
К2
К 1 + F1
72.4
79.5
74.0
60.4
62.0
69.9
78.0
77.9
45.2
48.6
44.3
55.1
47.0
42.8
К1
70.0
55.4
55.9
75.4
39.8
43.8
39.6
At the stage of preliminary water treatment at the thermal power station the efficiency of the use of anionic and cationic Praestols
together with iron sulfate and alkalizing agent calcium hydroxide [42,43] has been proved. Reagent processing was carried out on one
party of river water from the work cycle of the Kazan thermoelectric power station - 2 (general hardness 4.1 mg-equiv·1–1, alkalinity 2.85
mg-equiv·1–1, рН 8.34, content of SiO2 6.05 mg·1–1). The flocculation effect was estimated with the formula:
D = (V – V0) / V0,
where V and V0 – are the rates of the 50% water turbidity change in the absence and presence of Praestol.
The efficiency of iron recovery was evaluated from the following equation:
DFe = (CFe0 - CFe ) / CFe0,
where CFe and CFe0 – are, respectively, the content of iron in water after coagulation in the presence and absence of
Praestol as compared to the original water (%).
The recovery of organic compounds was evaluated by the following parameter:
Dor = (Cox0 - Cox) / Cox0,
where Cox and Cox0 – are the permanganate oxidizability of water in the presence and absence of Praestol as compared
to the original water.
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___________________________________________ 31-40
At constant concentration of alkalizing agent and coagulant the values of D, DFe, Dor and ηsp/Cp (at Cp=const) dramatically
change with the content of ionogenic fragments (α) for anionic Praestols (maximal value at α=11 mol%) and cationic ones (maximal
value at α=20 mol%) which is due to the change of size of flocculant macromolecular balls in the solution (r2)1/2. In work [43] the
analysis of polydispersity of system by a technique [44] is carried out, and it is shown that the least degree of polydispersity of particles
of the dispersed phase in water is observed in the system containing anionic Praestol with α =11 mol% and cationic Praestol with α =20
mol%, the same systems are characterized by big sizes of particles. These facts explain the reasons for high rates of sedimentation of
particles of dispersed phase in water in the presence of anionic and cationic Praestol of the specified structure. It has also been shown that
anionic Praestols provide the greater flocculation effect as compared to cationic Praestols. Thus, cationic Praestols remove iron and
organic substances from water, which probably happens due to the formation of intramolecular complexes [45] between positively
charged macromolecules of flocculant and negatively charged macromolecules of guminic and fulvic acids and their complexes with
iron, contained in water after its alkalizing up to рН 11. In the presence of cationic Praestol with α =20 mol% the high degree of water
treatment still remains after the reduction of its concentration down to 0.4 mg·1−1 and concentration of coagulant - to 15 mg·1−1.
APPLICATION OF POLYACRYLAMIDE FLOCCULANTS FOR WATER TREATMENT
2. Decolouration of natural water with coagulants and flocculants.
An important and insufficiently investigated problem of water treatment is decolouration of water. For the successful solution of
this problem there is needed a thorough study of the nature of water coloration taking into account the influence of antropogenic
admixtures in each definite water source and different factors contributing to intensification of water decolouration. In central Russia
decolouration of natural water is not a significant problem, but it is important for surface water treatment in Sibiria, the Far East and the
Extreme North of Russia with color index up to 200-300 deg and turbidity not exceeding 25 mg·1−1. Such waters are not easy to treat up
to normative parameters. Out of two major representatives humus substances - guminic and fulvous acids - the most soluble are fulvic
acids. They are characterized by a high degree of oxidability and substantially smaller M of compounds and their associates [46]. Due to
high solubility fulvous acids make up the basic part of the dissolved organic substances in surface waters [47].
The color index of natural water is effected by different factors and consequently for each source of water supply application of
various methods of water decolouration is used. Among various methods of natural water decolouration (reagents, electrо- and
electrochemical coagulation, membrane filtering, flotation, treatment with macroporous ionits, ozonization and sorption, treatment in
bioreactors, complex use of oxidizers together with UV-radiation) the most widely spread is flocculation with the use of PАА, coagulant
AS, chlorine and, if necessary, alkalizing. Qualitative water treatment up to normative parameters can not be attained flocculants. At
chlorination of water enriched with organic substances, a significant amount of chloroform and other chlororganic compounds are
formed. Besides, the influence of oxidizers (chlorine and ozone) on compounds of humus substances in complexes with ions of heavy
metals results in full allocation of toxic substances from nontoxic complexes [48]. The stability of the dispersed systems containing
guminic and fulvous acids in low-molecular electrolyts complicates the flakes formation and increases the content residual aluminum in
potable water. The increase of the coagulant dose for destabilization of the dispersed system results in quality deterioration of the treated
water due to the content of ions of aluminum. Besides the interaction of the products of hydrolysis of AS with fulvous acids stimulates
the formation of soluble and hardly removable complexes [49].
On the basis of literary data analysis it has been revealed, that one of the efficient coagulants for decolouration of water is
AHOC. With the purpose of an intensification of operation of waterworks stations and improvement of potable water quality in work
[50] it is offered to carry out decolouration of natural water (chromaticity 98 hailstones, turbidity 0.9-1.2 mg·1−1, alkalinity 0.98 mgeqiv·1−1) with binary reagents - SA and AHOC with PАА. Using I.V. Tyurin method [51], it was found that water under investigation
contained only fulvous acids. It was shown that without preliminary chlorination the decrease of chromaticity begins at the use of AHOC
and AS in doses 6 and 12 mg·1−1 accordingly (dose of PАА 0.5 mg·1−1), and at doses of 17 and 20 mg·1−1 accordingly, and constant
dose of flocculant water treatment reaches normative parameters. Sharp decrease of chromaticity with doses 12-16 mg·1−1 is accountable
for the reduction of the degree of functional group dissociation of fulvous acids and increase of content of hydrocomplexes is due to
lowering рН of water to 6.5 (see fig. 5).
Fig. 4 . The effect of coagulant CС (mg·1−1) dose on color
index C (deg) of the river Vakh treated water.
1 - aluminum hidroxocloride; 2 - aluminum sulfate. Cp= 0.5 mg·1−1.
Fig. 5. The effect of coagulant CС (mg·1−1) dose on рН
of treated water without preliminary chlorination.
1 - aluminum hidroxocloride, 2 - aluminum sulfate Cp = 0.5 mg·1−1.
The efficiency of coagulant treatment of preliminary chlorinated and non-chlorinated water is practically identical, though
preliminary chlorination with doses from 4 to 9 mg·1−1 allows to reduce the color index by 15-20 deg., which does not serve for
coagulant economy, but additionally pollutes water with chlorine-organic compounds and results in overexpenditure of chlorine. At does
of coagulants higher than 20 mg·1−1 the efficiency of chlorination was not observed. With application of AS, sharp decrease of рН (fig.
5) was observed and alkalizing was required.
In a wide interval of concentrations of AHOC (5-35 mg·1−1) the residual aluminum in treated water was not found (see table 11),
and at concentration of AS 15 mg·1−1 the content of residual aluminum did not exceed the normative parameter. It was noted that AHOC
insignificantly reduces рН of both original water (fig. 5) and chlorinated water. Thus, in optimal region of рН for identical extraction
fulvic acids it is required less AHOC, than AS.
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Review ______________________________________________________________________ V.F. Kurenkov, H.-G. Hartan, and F.I. Lobanov
Table 11. The effect of aluminum sulfate and aluminum hydroxochloride in combination with PАА on quality of treated water.
Parameter
Dose AI203, mg·1−1
Dose PАА, mg·1−1
Color index, deg
Concentration of suspended
substances, mg·1−1
РН
Aluminum, mg·1−1
Coagulants
Original
water
98
1.3
5
0.5
115
0
Aluminum hydroxocloride
15
25
35
0.5
0.5
0.5
20
11
12
0
0
0
45
0.5
12
0
5
0.5
104
0
15
0.5
25
0
7.28
--
7.3
0.5
7.24
0
6.80
2.15
7.15
2.1
6.75
0.45
7.10
0
7.05
0
Aluminum sulfate
25
35
0.5
0.5
18
15
0
0
5.2
2.25
4.62
4.48
45
0.5
25
0
4.5
6.22
The results of the laboratory researches are in good agreement with industrial tests on decolouration of the river Vakh high-color waters
(color index - 154 deg, turbidity - 10.4 mg·1−1, alkalinity 0.2 mg-equv·1−1) [50]. In fig. 6 the change of chromaticity of the river Vakh water is
shown at the use of binary reagents - AS and AHOC with PАА. As is seen from fig. 6, AHOC reduces the color index better than AS. At dose of
AHOC 10 mg·1−1 color index is reduced by 10 deg., and in the case of AS the efficient decrease of chromaticity does not occur even at the doze
20 mg·1−1.
For decolouration of water there can be used anionic and cationic Praestols in combination with AS. For the efficient use of
Praestols the data are required on interrelation of flocculation properties with characteristics of polymers, the latter are covered in
literature quite insufficiently. Therefore in works [52,53] influence of molecular characteristics of flocculants and technical factors of
decolouration of water solutions with humus substances (with color index 226 deg by bichromate-Co scale) were studied under the
combined action of binary reagents – anionic and cationic Praestols with AS. The effect of water decolouration (E) was estimated with
the formula:
E = (n0 - n) / n,
where n0 and n – accordingly, optical density of water ( determined by photocalorimetric method)
in the absence and presence of coagulant and flocculant.
The increase of E values is noted at the change from simultaneous reagent dosage to the consecutive dosage of reagents and at change,
as well as at the change of the input order from “flocculant + coagulant” to “coagulant + flocculant”. The latter is the evidence of discrepancy
and irreversibility of processes of adsorption of macromolecules on particles of humus substances. The introduction of cationic flocculant [53]
followed by coagulant facilitated the formation of complex bridges of type coagulant - humus substances - flocculant, the latter fragment of
which was formed by intramolecular complexes [45] due to interaction of free (not combined with coagulant) carboxylic and hydroxyl groups of
guminic acids with amino-groups of cationic flocculant. With the growth of concentration and M at anionic Praestol [52] and cationic Praestol
[53] values E grow owing to the increase in concentration of polymeric bridges and increase of (r2)1/2 of macromolecules of flocculant which
facilitated the coverage by polymeric bridges of a great number of molecules of humus substances, enlarged the sizes of floculs and accelerated
their sedimentation. There were registered greater values E at cationic Praestol as compared to anionic Praestol, despite the big values of M at
anionic Praestol [52]. This is the consequence of more efficient binding of guminic acids with cationic Praestol in intramolecular complexes [45].
There has been revealed the extreme character of change of E and ηsp/Cp (Cp=const) depending on the content of ionic units α in the
macromolecules of anionic (maximal at α=20 mol%) and cationic Praestols (maximal at α=27 mol%), as well as the extreme character of change
of value E depending on рН of the media ( maximal at рН 7). These results are caused by dependence of decolouration and viscosity on values
(r2)1/2 for macromolecules of flocculants in the solution. The revealed regularities of water decolouration on the model solutions of humus
substances under the action of AS in combination with anionic and cationic Praestols, undoubtedly, should be modeled in real dispersed systems.
3. Treatment of waste water with coagulants and flocculants.
The process of waste water treatment and dehydration of deposits is substantially influenced by the nature and concentration of
pollutants, technical parameters of flocculation as well as by the molecular characteristics of organic flocculants [3,4,19,54]. However,
the flocculation properties of polyacrylamide flocculants used for waste water treatment are investigated insufficiently.
In work [55] clarification of sewage of textile manufacture (the average size of dispersed phase particles is 6·10–5 m) with anionic
(А) and cationic flocculants (К) is considered. Copolymer АА with Na-АA, and copolymer АА with DMAEMA HC were used
respectively as flocculants A and K. There has been noted the increase of flocculation effect with the growth of MM at flocculant A as
the result of greater (r2)1/2, which improves the ability of macromolecules to bind a greater number of dispersed phase particles by
polymer bridges. In the wide area of the content of ionogenic groups in macromolecule α for flocculant A (α=7-30 mol%) the
flocculation effect is maximal and does not depend on α. As against flocculant A, the application flocculant K has appeared to be
inexpedient for treating sewage of textile manufacture.
The efficiency of application of anionic and cationic flocculants in combination with AS for the treatment of rinsing water,
polluted with polymeric fillers, is estimated in work [56]. The most qualitative water treatment was provided by anionic flocculant Flotin
(mixture of PАА with polyacrylic acid) in combination with AS, but the use of cationic flocculant Timacsol-P (polymer of
dimethylsulfate DMAEMA) did not allow to destabilize the pollutants in water. However, sedimentation of the weighed substances in
contact clarifying tanks at rinsing water treatment has revealed a significant advantage of cationic flocculants as compared to sulphatic
PPA and Flotin [57]. The effect of rinsing water treatment with Timacsol-P without coagulant is higher, than that of Flotin with AS
(smaller content weighed substances and ions of aluminum is observed). As is seen from table 12, the use of anionic flocculant without
coagulant does not give appreciable effect on rinsing water treatment.
Table 12. The efect of flocculants Timacsol-P, Flotin and PАА on the quality of treated water after 120 min of upholding.
Flocculants
PAA
Flotin
Timacsol-P
Dose, mg·1−1
PAA
Al2(SO4)3
2–3
30 - 60
3–4
--4–5
---
Parameters of water quality
РН
Al3+, mg·1−1
Weighed substances, mg·1−1
6 – 10
4.0-4.6
2.6 - 7.1
26 – 42
6.2-7.0
2.1 - 5.2
2–4
6.5-7.3
0.8 - 1.2
Feoverall, mg·1−1
0.20 - 0.28
0.18 - 0.29
0.20 - 0.23
The maximal clarification of water is marked on using Тimacsol-P and at common use of PАА and AS. In this case the optimal
dose of PАА makes up 2-3 mg·1−1, when applied with AS (doses 30-60 mg·1−1), and the optimal dose of Timacsol-P makes up 4-5
mg·1−1 (with concentration in rinsing waters of weighed substances 42-172 mg·1−1, content of iron 0.65 mg·1−1, ions of aluminum 12
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mg·1−1). All the parameters [except for Al3+ (0.8-7.1 mg·1−1)] of water treated with PАА together with coagulant, and Тimacsol-P meet
the requirements of specifications.
Work [58] discusses the ways of optimization of sewage treatment used at dye shops of wall-paper factories for disposal of
water-soluble dyes, casein glue, kaolin and latex using flocculants and coagulants. Optimal hydrodynamic conditions of flocculation are
determined: time of stirring in sedimentation tank is 10 mines with the gradient of stirring speed 15-20 min–1 which reduces the duration
of upholding the sewage from 16-18 to 2-3 hours. Industrial tests on sewage treatment with application of nonionic PАА with low M,
nonionic PАА N-150, as well as anionic flocculant A-930 with high M, were carried out. The best flocculation activity of anionic
flocculant, as compared to other polymers, has been proved, the former demonstrating substantial reduction of the color index of water
and changing the structure of sewage. Introduction of flocculant A-930 increased the efficiency of detention of weighed substances at
centryfugation from 55-63 to 90-95%, with humidity of dehydrated deposit making up 75-78%. It has been noted that for the increase of
efficiency of the process of waste water clarification it is necessary to maintain the рН of treated water within the limits of 7.5–8.0.
Treatment of manufacturing water of tannic operations in tanning industry with application of flocculant Fennopol A-321
(copolymer АА with Na-AK, α = 6 mol%) and calcinated soda allowed to intensify the process of separation of chrome hydroxide
suspension [59]. Introduction of flocculant and warming the mixture up to 80o С reduced the time of sedimentation 4 times, reducing the
volume of the formed deposit 2-2.5 times which resulted in as low concentration of trivalent chrome content as 10 mg·1−1.
The technology of treatment of oil-containing sewage, described in work [60], provides for application of both flocculant
Fennopol A-321 and AS. The discharge of solutions of reagents was made before sedimentation tanks into the pipeline of waste water (at
the distance of 0.5 km from distribution chamber) with the time of stay of reagents 5-6 mines (1 variant) and directly into the distribution
chamber with the time of stay of reagents 0.6 min (2 variant). Doses of flocculant 0.3 mg·1−1 and coagulant 2.5-9 mg·1−1 provided the
60% removal of mineral oil (1 variant) and 42% (2 variant), decrease of CPC by 80% (1 variant) and by 30% (2 variant), and without
reagent treatment the efficiency of mineral oil removal in sedimentation tanks made up 25%, and CPC-30%. At the 1-st variant of the
reagents discharge the productivity of sedimentation tanks grew by 25% as compared to the design data. Thus, longer contact of reagents
with oil-containing sewage at intensive stirring intensifies the process of flocculation, and the use of optimal construction designs of
amalgamators and flake formation chambers increased the efficiency of removal of pollutants 1.5-3 times and reduced the reagents
expenditure.
The effect of lime and cationic flocculants (VPC-402, produced by "Kaustik" (Sterlitamak) and К 100, К 131, КNF, F 100, F
200, produced by scientific research institutes Chimpolymer (Volzhsk), on deposit dehydration in sewage disposal plants of waterworks
stations (Charkov) is considered in work [61]. Researches were carried out with crude deposit from initial sedimentation tanks, using the
mixture of deposits from initial sedimentation tanks and excessive active silt, condensed active silt, fermented mixture of crude deposit
and excessive active silt, aerobic-stabilized active silt. Doses of flocculants were 0.05-1%, and coagulant 0.75-1% from weight of dry
substance depending on the kind of deposit. The rate of deposit dehydration was defined on Bjuchner funnel. Processing of deposits with
coagulant together with flocculants caused neutralization of the surface charge and consolidation of deposit particles, which resulted in
sharp decrease of their specific resistance to filtration and intensification of the filtration process. So, with small doses of flocculant (0.10.2%) the filtration rate grew 3-5 times for the crude deposit, 4 times - for fermented mixtures and 2.5 times - for active silt as compared
to non-reagent filtering, and 1.5 times for all deposits as compared to processing with just flocculants. The addition of flocculants
together with coagulant changed the structure of deposits and reduced the content of binded water. Thus use of coagulant allowed to
reduce considerably the dose of flocculant.
Anionic Praestol 2540 (dose 6 mg·1−1) in combination with AS (dose 60 mg·1−1) [62] increased the rate of sedimentation of
particles at the flotation products treatment 1.5 times as compared to experiments without coagulant. Similar results were obtained at the
use of the mixture of anionic Praestol 2540 and cationic flocculant VPC-402 with the ratio 3:1. Additives of Praestol without coagulant
facilitated the increase of sedimentation rate of particles 1.3-1.6 times and the decrease of concentration of the hard phase in the treated
layer by 20-40% as compared to ammoniac PАА and polyethylenoxide. However, in another work [63] the strong antagonistic effect of
action of the mixture of anionic and cationic flocculants was fixed, which, in the authors’ opinion, is caused by selective interactions
between oppositely charged macromolecules.
APPLICATION OF POLYACRYLAMIDE FLOCCULANTS FOR WATER TREATMENT
Conclusions
On the basis of experimentally defined regularities it is necessary to note, that polyacrylamide flocculants in absence and in
combination with mineral coagulants can be successfully used for treating both natural water and sewage, disposing them from weighed
and colloid-dispersed substances. Optimization of the process of water treatment can not be organized to a precise algorithm: a great
number of factors have to be taken into account. The efficiency of water treatment is influenced with characteristics of flocculant (nature,
a chemical composition, molecular weight, conformation of macromolecules and concentration of flocculants) and coagulant (nature and
concentration), technology factors (the way and the moment of flocculant and coagulant dosage, efficiency of stirring, duration of
mixture, etc.), as well as the quality of the original water (chemical and dispersed composition, рН value and temperature). Undoubtedly,
knowing all these factors, it is possible to intensify clearing and decolouration of natural water and sewage, as well as to carry out the
process of controlled water treatment with the aim of obtaining treated water meeting the requirements of quality specifications for
potable water and the requirements of consumers.
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