RU2469957C2 - Method of purifying wastewater from car wash - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: two-stage flotation is performed. First initial stage of pressure flotation, during which water is dissolved in purified water, is combined with filtration stage until small bubbles of air start releasing. The following second stage of flotation is carried out with switching off installation and to the moment until small air bubbles start to release. Foam layer, formed on filter surface is removed from installation. Invention ensures simplification of purification process and reduction of installation volume, increase of method efficiency in particular acceleration of purification and increase of ecological safety of purification process.

EFFECT: purified water satisfies imposed on it hygienic requirements of Sanitary rules and requirements.

Description

The invention relates to methods for wastewater treatment and can be used in the treatment of both industrial and domestic wastewater, in particular wastewater from washing cars.

A known method of wastewater treatment by flotation by saturating the wastewater with air or any gas that dissolves in water under pressure (Gvozdev V.D., Ksenofontov B.S. Treatment of industrial wastewater and disposal of sludge. - M .: Chemistry, 1988. p. .98-102).

When pressure is released from wastewater, air dissolved in it or some other gas in the form of bubbles is released. At the same time, finely dispersed hydrophobic substances adhere to the bubbles and, in the form of particle-bubble complexes, float, forming a foam layer that contains pollution particles. The foam layer by gravity or using a special device is periodically or continuously removed into the sludge collector. The purified liquid is discharged from the zone below the formation of particle-bubble flotation complexes. Using this known method allows to achieve a cleaning effect in the range of 70-80%.

A significant disadvantage of the known method is the low floating rate of particle-bubble photocomplexes due to the small size of the bubbles. The low floating rate of these flotation complexes leads to the fact that some of them follow the flow of discharged purified liquid, which leads to a sharp decrease in the cleaning efficiency.

Another method of wastewater treatment by flotation is known, including wastewater treatment by flotation, carried out by aeration of wastewater with air bubbles and other gases and further separation of the resulting particle-bubble flotation complexes from water (Ksenofontov B.S. Wastewater treatment: flotation and thickening of sediments. - M .: Chemistry, 1992, p. 45-46).

In the aforementioned known method, the dispersion of air and other gases in water occurs mechanically, for example, by ejecting air due to the movement of a fluid flow at a speed of about 8, 12 m / s or when it is suctioned in a reduced pressure zone when the fluid flow is rotated using a mixer (impeller). The gas (air) bubbles formed behind the ends of the rotating blades of the mixer come into contact with the particles of contamination, which in most cases leads to the appearance of particle-bubble flotation complexes. The size of the resulting bubbles is more than 0.01 mm When air or other gases are dispersed using a stirrer, intense coalescence of bubbles occurs, which leads to a significant change in their size, and in the zone of rotation of the bourgeoisie the size of the bubbles is of the order of 0.01-0.5 mm or more, and in the upper zone, where separation occurs flotation complexes from water and their transition into a foam layer, the size of the bubbles reaches 1.0-10.0 mm or more. At the same time, water purified from particles of impurities is discharged from the floating particle-bubble floatation zone. As a result, the diverted water stream captures part of the particle-bubble flotation complexes, as well as individual particles and bubbles that are not loaded with pollution particles, which leads to a decrease in the efficiency of wastewater treatment in this way. The cleaning effect does not exceed 70-85%.

A method of wastewater treatment is known from RU 94016575, 04.20.1996, including flotation treatment of wastewater by aeration of wastewater with air bubbles and other gases and further separation of the particle-bubble flotation complexes from water. Moreover, in the zone of separation of the flotation complexes from water, lattices with a variable size of the holes are installed, with holes with a minimum size in the range of 0.01-0.5 mm located at the bottom, and holes with a maximum size in the range of 1.0-10.0 mm at the top , and the direction of movement of the purified water is perpendicular to the plane of the lattice.

Thus, the principles of wastewater treatment have long been known (sedimentation, flotation, electrocoagulation, mechanical filtration, sorption, etc.). Their combination is also widely used in production. However, all known schemes (methods) of water purification are based on their uninterrupted operation for a long time, i.e. without stopping the equipment. In reverse water treatment systems for car washes, the opposite is true.

Installations stop and turn on several times per hour; this happens automatically when filling the tank with purified water, from where the devices for supplying water to the sink are fed. Therefore, it is not necessary to talk about the equilibrium operating mode of the installation.

The technical task of the claimed invention is to simplify the process of water treatment, accelerate it and increase the environmental safety of the water treatment process.

The stated technical problem is achieved by a method of wastewater treatment from car washing, including flotation in two stages, while the first initial stage of pressure flotation, in which the air is dissolved in the purified water, is combined with the filtration stage on the filter until small air bubbles are released, released during the passage of the initial layer of filters, and the subsequent second stage of flotation is carried out when the unit is turned off and the resulting foam layer on the surface of the filter is removed from ki.

The claimed method of wastewater treatment is based on the use of a quasi-equilibrium wastewater treatment process, which is called "for the good." It is proposed to use two processes (pressure flotation and mechanical filtration) together, i.e. combine them. When pressure flotation is used in traditional purification schemes, at its initial stage, air dissolves in water, then the water is throttled and discharged into the volume where small air bubbles are released in the water and then it is necessary to allow the water to settle so that the air can reach the surface of the water, entraining contamination in the form of foam.

The following is a detailed description of the claimed as an invention method of wastewater treatment from washing cars and storm drains.

So, in the inventive method, it is proposed to use its initial stage in pressure flotation, namely, the process of dissolving air in water and immediately after that, without waiting for the release of small air bubbles, to direct water to the filtration. Filtration is carried out, for example, on fine loose material, in particular on river or quartz sand. When passing through the initial layer of the filter, the water pressure drops, and tiny air bubbles begin to stand out from it, which will be located in the filter volume. These air bubbles cannot float, because held on top by a layer of filter load. As the volume of water passing through the filter increases, more and more air bubble nuclei form in the sand layer. All this allows to increase the contact time of air bubbles with water, and therefore, to better saturate it with atmospheric oxygen while reducing the volume of the flotation chamber and reducing the pressure of the water-air mixture during pressure flotation by almost two times, from 3.0-3.5 atm to 1 atm. The part of the air (insoluble) that does not dissolve in water (excess) is pressed against the filter surface by the dynamic pressure of water, forming a layer of small air bubbles, i.e. a layer of foam on the surface of the filter. A layer of foam prevents the penetration of petroleum products, insoluble fats, fine suspension, etc. in the sand filter layer (subject to certain concentrations of these substances in water), coalescence (coalescence, coalescence) and accumulation of contaminants on the surface of the foam occur. With this method of wastewater treatment, the second stage of flotation does not occur during the operation of the installation, but when it is turned off. The dynamic pressure of the water is removed, and air bubbles rise to the surface of the water, entraining pollution. Used, in particular, the sand filter does not work so much in volume as in the filtration surface. When air bubbles rise from the surface of the filter, its partial regeneration occurs, including due to the restoration of the shape of the bubbles when the pressure inside the unit is removed. Air bubbles in the filter volume cannot independently rise to the surface of the water. In an idle installation, they continue to give air oxygen to the water through diffusion. The regeneration of the filter load is carried out by the traditional method, namely, by backwashing, in which air bubbles are also removed from the filter volume.

Specifically, the method for wastewater treatment from car washes in general is carried out in a treatment plant as follows.

In operating mode, the jet pump takes water from the pit and delivers it to the flotator. The process pump is fed from the flotator with water. The pump pressurizes the nozzle in front of the jet pump, where air dissolves in water. From the flotator, water flows by gravity into the filter of mechanical cleaning, and then into the tank of clean water.

Upon reaching the maximum level of purified water in the tank, a float switch disables the intake of water from the pit, and the unit is put into standby mode. In this case, the foam formed during flotation is removed from the installation. When purified water is consumed, the level in the clean water tank decreases, and at some point the float switch switches on the unit. At the outlet of the installation, water passes through a fine cartridge if necessary. The filter is flushed by a submersible pump after the unit is manually switched from the “work” mode to the “flush” mode.

Claimed as an invention, a method of wastewater treatment from car washes allows:

- better saturate the water with atmospheric oxygen and reduce the content of BOD and COD (biological and chemical oxygen scavengers) in the water at a lower working pressure of the water-air mixture, including at the time of an idle installation;

- significantly reduce the installation volume;

- increase the time interval of the filter between washing cycles due to partial regeneration of the filter surface at the time of stopping the installation.

The water purified by the claimed method meets the requirements for SNiP and SamPiN.

Claims (1)

A method of treating wastewater from a car wash, including flotation in two stages, the first initial stage of pressure flotation, which is the dissolution of air in the treated water, is combined with the filtration stage on the filter until small air bubbles are released during the passage of the initial layer filters, and the subsequent second stage of flotation is carried out when the installation is turned off and the resulting foam layer on the surface of the filter is removed from the installation.