RU2186033C1 - Method of improvement of drinking water quality by freezing and thawing - Google Patents

Abstract

FIELD: technology of water treatment. SUBSTANCE: invention relates to methods of treatment and desalting water. Method of improvement of drinking water quality by freezing and thawing involves water freezing in a vessel exhibiting ratio of height to transverse section linear size = ≥ 2. Ice is melted in the same vessel at temperature below 30 C and the upper purified layer of liquid by volume ≤ 75% of the total volume of frozen water is poured off (siphoned off). In the process of thawing a vessel is immovable in vertical state and purified water pouring out is carried out in 24 h after thawing termination, not later. A single use of a method ensures to decrease the total salt content in water by 20-65%. After repetition of method with respect to the purified water the total content of salts can be decreased to the desired value. Invention can be used for treatment of drinking water, industrial flows, desalting saline and subsaline waters in homes and industry. EFFECT: improved method of improvement of water quality. 2 dwg

Description

 The invention relates to a technology for purification and desalination of water and can be used for purification of drinking water, industrial effluents, desalination of saline and brackish water in the home and industry.

 Freezing can be carried out in cone-shaped vessels, expanding upward, or in an oblique bulb that rotates around its axis. To obtain the phase of the concentrate and desalted liquid, the zone melting method is also used [Stadnik AS, Dedkov Yu.M. Freezing as a method of concentration of impurities in water / Chemistry and technology of water. 1981. T. 3. 3. S. 227-233]. The author of the work [Puchko V.I. A new way of desalination by freezing / Hydrotechnics and land reclamation. 1949. 3. P.46-55] recommends freezing ice piles, during subsequent melting of which receive desalinated water. Physico-chemical processes that occur during such desalination are described in [Mitin M.F. Desalination of water by natural freezing / Hydrotechnics and land reclamation. 1963. 2. S.20-27].

In the application [Method for producing melt water and a generator of melt water. Application 97100446/13 Russia. IPC ⁶ C 02 F 1/22 / Kuznetsov E.S., Soloviev E.F. Claim 01/14/97, publ. November 10, 1998, Bull. 31] proposes a combined method, characterized in that the process of freezing water and thawing ice is carried out partially and alternately in two containers. The method is complicated in hardware and technological content.

 A simpler combined method, the closest we offer in this application, is proposed in the patent [Method for improving the quality of drinking water by freezing / Pat. 2077160. Sosnovsky A.V., Ivlev S.A., Samoilov B. C., German V.V. Application 94011389/26. Claim 04/01/94, publ. 04/10/97 g]. This patent describes a method for improving the quality of drinking water by freezing, which consists in freezing, crushing and melting ice, characterized in that ice is frozen up to 70-90% of the water volume, ice melting is carried out by thermal insulation of its side and lower surfaces to form 30 -55% of the volume of ice melt runoff with its subsequent removal. The remaining pure ice is melted completely and 15-60% of the pure water of its originally taken volume for desalination is obtained.

The disadvantages of the method:
1. It is necessary to control the degree of freezing, which is difficult under natural conditions (when air temperature and wind speed change).

 2. It is necessary to crush ice.

 3. It is necessary to control the degree of melting of ice in the conditions of its thermal insulation.

 4. Relatively low yield (15-60%) of pure water.

 We propose a free from these drawbacks, an extremely simple way to improve water quality. The method is based on the fact that when melting salt ice, the brine is first thawed, which flows to the bottom of the vessel. Partially thawed ice floats on the surface of salt water and melts, giving layers of ever cleaner water. Thus, a salt concentration gradient arises along the height of the melt water column, which remains in a motionless vessel for a sufficiently long time. To obtain pure water, the upper layer of the liquid column is siphoned, and the lower, concentrated and containing suspended and colloids suspended in the bottom remains in the vessel. This part of the liquid is drained into the drain. The nature of the distribution of salts along the height of the liquid column is practically independent of the freezing regime and the thawing temperature. Only the degree of desalination of the purified fraction of water depends on the thawing temperature. The freezing mode and the position of the vessel do not affect the final result, therefore, freezing can be carried out uncontrollably.

Defrosting can be carried out at any temperature up to 30 ^o C, which will affect the duration of the process and the degree of water purification (with decreasing temperature of the defrosting, the degree of purification increases). At a thawing temperature above 30 ^o With the cleaning effect becomes insignificant, since thermal diffusion erodes the border of saline and clean water.

In order to form a layer of purified water during thawing, the height of the liquid column must be sufficient. According to our data, the separation into layers of purified and salt water will be distinct when using a vessel in which the ratio of the height of the liquid column to its diameter (linear cross-sectional size) ≥2. After ice thawing, the concentration gradient of salts along the height of the liquid column in a fixed vessel remains at room temperature for about a week, although diffusion gradually averages the concentration over the entire volume. Therefore, the discharge of clean water should be done no later than one day after thawing, it is better - no later than 1 hour. With a decrease in the storage temperature of the thawed liquid, this time can be increased. For example, at 10 ^o With the interval between thawing and discharge can reach 5 days, and at 7 ^o With 14 days.

To illustrate the foregoing, we present the data of experiments obtained by freezing and thawing tap water using standard plastic bottles with a capacity of 1.5 liters as vessels. The volume of filled water in one bottle was 1.4 liters. As a measure of integral salt content, the specific electrical conductivity of water was used. A common measure of the total content of salts and water-insoluble impurities is the dry residue, so we conducted experiments to establish a correlation between the dry residue and the electrical conductivity of water. For the studied tap water, this correlation is expressed by the equation
C _co = 1.06 • H,
where C _co - solids content, mg / l,
N - electrical conductivity, μS / cm,
1.06 is the coefficient of transition from electrical conductivity to the solids content.

 The established correlation allows us to conclude that the electrical conductivity is the parameter that sufficiently accurately characterizes the total salt content of the studied water.

Figure 1 presents the curves of changes in the electrical conductivity of water after freezing at -20 ^o C and thawing at 8 ^o C (curve 1) and 22 ^o C (curve 2). It can be seen from this drawing that in the lower layer, which is 400 cm ³ in volume by volume ^of water, the salt concentration gradually increases as it approaches the bottom of the vessel, and in the upper layer with a volume of 1000 cm ³ it remains constant. To obtain pure water, the siphon tube is immersed to the boundary separating the upper clean layer of water, and it is siphoned (Fig. 2). Pure water can also be drained by piercing a hole in the side wall of the plastic bottle at the level of the layer of contaminated and clean water (FIG. 2). The contaminated water remaining in the vessel is poured into the drain. From one bottle with a capacity of 1.5 liters with a fill of 1.4 liters of source water, 1 liter of pure water is obtained (the yield of pure water is 71.5%). When thus treated with tap water with an initial electrical conductivity of 202 μS / cm, 1 liter of pure water with an electrical conductivity of 160 μS / cm was obtained (thawing at 22 ^° C for 1 day) and in another experiment, 1 liter of water with an electrical conductivity of 90 μS / cm ( thawing at 8 ^o C for 14 days). Therefore, in the first embodiment, the degree of desalination was 20.8%, and in the second embodiment, 65.5%. Repeating the method with respect to purified water reduces the total salt content to any desired value.

 The proposed method allows you to clean the water also from colloids and suspensions. After thawing the ice, we always found a water-insoluble precipitate at the bottom of the vessel, although the initial water seemed completely transparent and the control filtration did not reveal a suspension.

 We conducted the experiments several times with changing freezing conditions in a wide range, while the distribution of the concentration of salts in the column of thawed liquid was always clearly reproduced.

The proposed method is technically simple and can easily be implemented both in industry and in everyday life. Its implementation in everyday life does not require any costs: plastic bottles are now available, and clean water can be drained not by a siphon tube, but by piercing a hole on the side of the interface between clean and contaminated water (Fig. 2). In order to establish this level, before the start of the experiment, 400 cm ^{3 of} water is poured into the bottle and a mark is made on the wall of the vessel, which coincides with the liquid level. Then add another 1000 cm ^{3 of} water and then carry out the process according to the described procedure.

 In areas with a continental climate, freeze in the winter using natural cold, in other situations, freezing is carried out using refrigeration machines.

Claims (1)

A method of improving the quality of drinking water by freezing and thawing, characterized in that the source water is frozen in a vessel with a height to linear cross-sectional dimension of ≥2, ice is melted in the same vessel at a temperature of up to 30 ^o C and the upper purified liquid layer with a volume of ≤75 % of the total volume of frozen water is drained (siphon), while thawing is carried out so that the vessel is stationary in an upright position, and the purified water is drained no later than one day after the end of thawing.

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