RU2218310C1 - Method of purification of low-cloudy color waters - Google Patents

Abstract

FIELD: economic-drinking water supply; purification and sanitation of the surface water sources. SUBSTANCE: invention relates to the methods of water purification and sanitation in the surface water sources by treatment with a aluminum- bearing coagulant and the subsequent water clarification by filtration and may be used predominantly in the field of economic - drinking water supply, in particular at purification and sanitation of the low- cloudy color waters. The invention provides, that at two-stage treatment of the low-cloudy color water with a aluminum- bearing coagulant and introduction at the first stage of a deficient dose of aluminum sulfate with subsequent clarification of the water by filtration, at the second stage the water is added with aluminum oxychloride at the ratio 1 : (4-5) by Al₂O₃ in respect to the amount before injected aluminum sulfate, and the total amount of injected aluminum-bearing coagulants is determined from a relationship:

where D_c is the total amount of a coagulant, mg/l; Col is the color of the clarified water, degrees. EFFECT: invention providing high degree water purification allows to reduce consumption of the coagulant at simultaneous increase of duration of the filtration cycle. 2 tbl

Description

 The invention relates to methods for purifying water from surface water sources and can be used mainly in the field of domestic and drinking water supply, in particular when treating low-turbid colored waters.

 Known and widely used is a method of purification of low-turbid colored water, including its one-stage treatment with an aluminum-containing coagulant (which is used as aluminum sulfate or aluminum oxychloride) and subsequent clarification of water by filtration [1].

 This method in most cases allows you to get water of the required quality by color, however, it is associated with a significant consumption of coagulant and causes a relatively short filter cycle due to the deterioration of the degree of water purification by such indicators as the content of residual aluminum and oxidizability.

 The closest technical solution to the claimed one is a method for purification of low turbid colored water, including its two-stage treatment with aluminum sulfate, followed by filtration [2].

 This method compared with the above is more effective, because it allows you to slightly increase the duration of the filter cycle while reducing the consumption of coagulant.

 At the same time, from modern positions, which are based, on the one hand, increased requirements for the quality of purification of low-turbid colored waters by such indicators as residual aluminum content and oxidizability, and on the other, requirements to reduce the cost of treatment. This, in turn, requires a reduction in the consumption of reagents used, and this method cannot be considered as sufficiently effective.

 The aim of the invention is the development of such a method of purification of low-turbid colored water, in which, along with a high degree of purification (corresponding to modern requirements), coagulant savings would be achieved while increasing the duration of the filter cycle.

где D_к - суммарное количество коагулянта, мг/л; Ц - цветность очищаемой воды, град.The goal is achieved according to the invention by the fact that in a two-stage treatment of low-colored colored water with an aluminum-containing coagulant with the introduction of a deficient dose of aluminum sulfate in the first stage and subsequent clarification of the water by filtration in the second stage, aluminum oxychloride is added in an amount of 1: (4-5) by Al ₂ About ₃ in relation to the amount of previously introduced aluminum sulfate, and the total amount of introduced aluminum-containing coagulants is determined from the ratio

where D _to - the total amount of coagulant, mg / l; C - the color of the purified water, deg.

 Example 1

Three water samples are prepared with a turbidity of 3.5-5.0 mg / l and a color of 36, 62 and 115 degrees, respectively. Each of the water samples is purified by coagulation and filtration. Moreover, in all series of experiments, an aluminum-containing coagulant is used, and filtering is carried out on a column loaded with granite chips with d _equiv = 1.05 mm and a layer height of 1.6 m. The filtration speed is kept constant and equal to 7.5 m / h.

Water samples with different colors, depending on the series of experiments, are treated with a coagulant as follows:
1 series: aluminum sulfate is introduced into water once;
2 series: aluminum sulfate is introduced into water in two stages with a time gap between stages of 60 s;
3 series: aluminum sulfate is introduced into the water in the first stage, and aluminum oxychloride in the second stage, providing a time gap between the stages of 60 s.

 The experiments conducted are aimed at determining the minimum dose of coagulant, which would ensure a decrease in the color of the treated water to a value not exceeding 10 degrees, i.e. to determine the relationship between the dose of coagulant necessary to obtain the required degree of purification and the color of the purified water.

 The results of the experiments are given in table. 1.

 As can be seen from the data obtained, a two-stage introduction of aluminum-containing coagulant into water is more preferable, since it allows reducing the dose of coagulant necessary to obtain the required degree of purification of colored water.

 Moreover, the use of aluminum oxychloride in the second stage of coagulation instead of aluminum sulfate provides the opportunity to reduce the total consumption of coagulant by almost 20%.

 At the same time, from the data presented in the table, it follows that there is a fairly clear correlation between the color of the treated water (in a wide range from 36 to 115 degrees) and the required minimum total dose of coagulant administered in two stages (aluminum sulfate is introduced in the first stage, in the second aluminum oxychloride), providing a decrease in the color of the treated water to a value of ≤10 degrees (the value of the pan-European standard).

где D_к - суммарная доза алюминийсодержащего коагулянта, мг/л; Ц - цветность очищаемой воды, град.This dependence can be represented by the ratio

where D _to - the total dose of aluminum-containing coagulant, mg / l; C - the color of the purified water, deg.

 Example 2

 Water with a turbidity of 3.7 mg / l and a color of 62 degrees. purified by coagulation, carried out in two stages, the first of which is introduced into the water of aluminum sulfate, and the second - aluminum oxychloride, after which it is filtered.

 In this case, the parameters of the filter load in the column and the accepted filtering speeds are similar to those shown in example 1.

а отношение между количеством коагулянтов (по Al₂O₃), вводимых на первой и второй стадиях, изменяли от 6:1 до 3:1.Several series of experiments are carried out in which the total dose of aluminum-containing coagulant was 9 mg / L in Al ₂ O ₃ , i.e. was selected from the relation

and the ratio between the number of coagulants (for Al ₂ O ₃ ) introduced in the first and second stages was changed from 6: 1 to 3: 1.

 The following filtrate quality indicators were used as criteria for cleaning efficiency: color no more than 10 degrees, oxidizability no more than 5 mg / l, residual aluminum content no more than 0.5 mg / l, and also filter cycle duration not less than 12 hours.

 The results of the experiments are given in table. 2.

 As can be seen from the table. 2 data, the specified criteria for cleaning efficiency corresponds to the ratio between the amounts of coagulant introduced in the first and second stages, as (4-5): 1.

 With these ratios in water, after the coagulant is introduced, at the first stage, a large number of small flakes of aluminum hydroxide are formed, which, thanks to the developed interface, sorb organic compounds that color the water well.

 However, when the ratio is greater than 5: 1, the duration of the filter cycle is reduced, because in water, in addition to small flakes, a certain amount of medium-sized flakes is also formed, which ultimately leads to a reduction in the duration of the filter cycle due to premature siltation of the load.

 On the contrary, when the ratio is less than 4: 1, the duration of the filter cycle is reduced due to a decrease in the degree of sorption of organic substances by flakes during coagulation.

 Thus, the advantage of the claimed method over the known ones is its high efficiency, due to the saving of the coagulant and the increase in the duration of the filter cycle while achieving the quality of purification of low-turbid colored water that meets modern requirements.

Sources of information
1. Kastalsky A.A., Mints D.M. Water preparation for drinking and domestic water supply. - M.: Stroyizdat, 1962, p. 54-60.

 2. Babenkov E.D. Water purification by coagulants. - M .: Nauka, 1977, p. 270 and 271 (prototype).

Claims (1)

The method of purification of low-turbid colored water, including its two-stage treatment with an aluminum-containing coagulant with the introduction of a deficient dose of aluminum sulfate in the first stage of purification and subsequent clarification of the water by filtration, characterized in that in the second stage aluminum oxychloride is added in the amount of 1: (4-5) by Al ₂ About ₃ in relation to the amount of previously introduced aluminum sulfate, the total amount of introduced aluminum-containing coagulant is determined from the ratio:

where D _to - the total amount of coagulant Al ₂ About ₃ , mg / l; C is the color of the source water, deg.

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