RU2234464C1 - Method for purifying of sewage water from suspended substances - Google Patents

Abstract

FIELD: methods for purifying of natural and sewage water from solid and liquid dispersed substances with the use of reactants.

SUBSTANCE: method involves introducing coagulant; mixing and separating sediment by settling; using as coagulant mixture of aluminum sulfate (alumina) and aluminum hydroxychloride used in the ratio of (0.3-0.7):(0.7-0.3) on conversion to aluminum; introducing coagulant in an amount of from 0.05 to 0.5 mg of Al per 1 dm³ for purifying of river water and in an amount of from 5.0 to 20 mg of Al per 1 dm³ for purifying of weakly contaminated industrial sewage water depending on initial cloudiness of water under treatment process. Method may be used for purifying of municipal and industrial sewage water of chemical enterprises engaged in production and processing of polymers, in particular, of rubbers and production of rubber-based articles. Method allows aluminum consumption to be reduced by at least 2 times depending on composition and extent of cloudiness of water under treatment process.

EFFECT: increased efficiency and reduced consumption of aluminum.

3 cl, 2 tbl, 2 ex

Description

The invention relates to the purification of natural and wastewater from solid and liquid dispersed substances, in particular to the development of a method for treating household and drinking water, as well as slightly contaminated wastewater from industrial sites of chemical plants, where the main production is associated with the production and processing of polymers, mainly rubbers and rubber products based on them.

A known method of treating wastewater containing a solid or liquid dispersed phase, which boils down to adding aluminum sulfate (alumina) to the treated water (A.K. Zapolsky, A.A. Baran. Coagulants and flocculants in water treatment processes. Leningrad, “Chemistry” ”, 1987, p. 42 -47). The disadvantage of this method is the relatively small content of the water-soluble part (aluminum sulfate, about 65%); therefore, when using this coagulant, it is necessary to continuously remove sludge (about 35%) from the preparation zone of the reagents.

A known method of treating wastewater containing a solid or liquid dispersed phase, which boils down to the addition of aluminum hydroxychloride (GOHA) to the treated water (RF patent No. 2083495). The main disadvantage of this method is the high cost of aluminum hydroxychloride (GOA), in addition, due to the narrow pH range at which it works effectively, its use is difficult.

The aim of the invention is to develop a cost-effective method of purifying waters containing a solid or liquid dispersed phase by using the optimal ratio of coagulants (aluminum hydroxychloride (GOXA) and alumina), which in the proposed ratio give a significantly greater cleaning effect than when using each component individually. Since the cost of coagulants depends on the proportion of aluminum content in it, then when calculating the optimal ratio of coagulants, conversion to aluminum was used, i.e. by the proportion of aluminum in the substance or mixture.

The selected ratio of the mixture of GOHA and aluminum sulfate is explained by the different pH values of the water being purified, the cost of purification, as well as the different resistance of the dispersed substances to the action of coagulants.

As an example (1), we consider the process of preparing household water. Coagulation is carried out by three different coagulants: aluminum sulfate (alumina), aluminum hydroxychloride (GOHA), and the proposed coagulant, consisting of a mixture of aluminum hydroxychloride (GOHA) and alumina in a weight ratio in terms of aluminum (1: 1), then SK. To illustrate the effect of coagulants, the river water was artificially clouded with a kaolin suspension to a turbidity value of 10 mg / dm ³ , which approximately corresponds to the turbidity of river water during heavy rains and spring floods.

Example 1

In 15 vessels with a capacity of 1.5 dm ³ pour 1 liter of river water, which has the following quality indicators:

pH 6.8; turbidity - 10.0 mg / DM ³ .

In the first five vessels with stirring we add a coagulant - alumina in doses, in terms of Al, from 0.05 mg to 2.0 per 1 dm ^{3 of} purified water. In the second series of vessels we add the GOHA coagulant in the same doses - 0.05 to 2.0 mg per 1 dm ^{3 of} purified water in terms of Al. In the third series (the next 5 vessels), a mixed coagulant (SC) is added in the same calculated doses. After the coagulation process and 1.5 hours of settling, the purified water is analyzed according to GOST 2874-82.

The main indicator of the effectiveness of a reagent in the process of coagulation is the turbidity, mg / DM ³ . Since coagulants selected in accordance with analogues and the proposed mixed one (SC) contain Al, the presence of which is normalized by SanPiN for drinking water (not more than 0.5 mg / dm ³ ), it is also one of the main criteria the effectiveness of coagulants.

The results of the experiments of example 1 are shown in table 1.

As can be seen from the table, in order to achieve the required turbidity (not more than 1.5 mg / dm ³ ), the required proportion of SC coagulant (a mixture of alumina and GOA) is halved and amounts to 0.05 mg Al per 1 dm ³ compared with alumina (1 , 0 mg Al per 1 dm ³ ) and GOA (1.0 mg Al per 1 dm ³ ), when used separately. The residual aluminum content in this case does not exceed the required norm for household drinking water. The use of the proposed mixture as a coagulant in an amount of more than 0.5 mg per 1 dm ³ in terms of Al is unacceptable due to the occurrence of the stabilization phenomenon caused by an overdose of coagulant.

Example 2

This example substantiates the use of the proposed method for the purification of slightly contaminated chemical stocks by using the optimal ratio of coagulants of alumina and aluminum hydroxychloride (GOHA). The purified water (lightly contaminated chemical drains and surface runoff from the territory of industrial sites of chemical plants) has an initial turbidity value of 25 mg / dm ³ .

In three rows, in each of which 10 cylinders with a capacity of 1.5 dm ³ , pour 1.0 dm of technical water. An alumina solution is added to the first row of cylinders in amounts from 0.5 to 80 mg (in terms of Al) per 1 dm ^{3 of} purified water. In the second and third rows, respectively, a solution of GOX and a mixed coagulant is added. After the coagulation process, the test water is subjected to analyzes, the results of which are presented in table 2.

As can be seen from table 2, the required turbidity (not higher than 6.0 mg / dm ³ ) when using SC is achieved at a dose of 20 mg (Al) per 1 dm ^{3 of} purified water, whereas with separately applied alumina and GOA, the required result was not achieved even at 80.0 mg / dm ³ in terms of aluminum, i.e. the cleaning effect at a dose of 20.0 mg / dm ³ in terms of Al is: 55.2% (alumina), 58.0% (GOHA) and 81.2% - mixed coagulant (SC). A further increase in the dose of mixed coagulant does not make sense for two reasons: firstly, the process of stabilization of the system begins, and secondly, it contradicts the task of saving aluminum.

From the above examples it follows that the use of the proposed method for purification of household drinking water and slightly contaminated chemical waste water gives significant aluminum savings of 2 or more times depending on the composition and degree of turbidity of the treated water.

Claims (3)

1. A method of treating wastewater from suspended solids, including introducing a coagulant, mixing and separating the precipitate formed by sludge, characterized in that, in order to reduce the cost of the process and increase the degree of purification, a mixture of aluminum sulfate (alumina) and aluminum hydroxychloride is used as a coagulant ( GOXA), taken in the mass ratio (0.3-0.7) :( 0.7-0.3) in terms of aluminum. 2. The method according to claim 1, characterized in that the coagulant is administered in an amount of 0.05-0.5 mg Al per 1 DM ³ when treating river water, depending on its initial turbidity. 3. The method according to claim 1, characterized in that the coagulant is administered in an amount of 5.0-20 mg Al per 1 dm ³ when treating slightly contaminated industrial effluents, depending on its initial turbidity.