RU2530041C1 - Method of purifying industrial waste water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes homogenising waste water, correcting pH to a value not lower than 10.5, mixing with aluminium sulphate solution and a flocculant solution with concentration of 0.1-0.2 wt %. The method includes pressure floatation by feeding into the waste water 40-60 m³/h of a purified recycled effluent at pressure of 0.11-0.25 MPa while simultaneously feeding compressed air and removing floatation sludge. Before feeding into the waste water, the purified recycled effluent is treated with an ultrasonic field with frequency of 25-35 kHz. Correction of pH is carried out by adding to the waste water a suspension of slaked lime or sodium hydroxide or sodium carbonate solution. Flocculant consumption is equal to 30-40 mg/l. The flocculant used is high-molecular weight cationic flocculants. Ultrasonic field treatment is carried out using a water-gas ejector with a jet-edge generator while feeding compressed air into the ejector at a pressure of 0.25-0.45 MPa.

EFFECT: simple purification process, reducing time for purification from ions of nonferrous and heavy metals, suspended substances, oils and fats to 16-20 min while maintaining given purification efficiency.

6 cl, 1 tbl, 5 ex

Description

The invention relates to the field of purification of industrial wastewater by flotation and can be used in the purification of industrial wastewater from metallurgical, food, pharmaceutical, leather, textile, paint and varnish industries containing non-ferrous and heavy metal ions, a large amount of suspended solids, oils and fats.

A known method of flotation wastewater treatment, including introducing into the wastewater a suspension of flocculant - activated sludge, aluminum sulfate and an aqueous solution of carbon dioxide with a pH of 2-11, subsequent saturation of the wastewater with air dissolved under a pressure of 0.5 MPa and separation into a treated effluent and removed the foam layer is slime (SU 1835802, C02F 1/24, publ. 06/19/1995).

However, the known method is not suitable for wastewater treatment, which contain compounds of non-ferrous and heavy metals, for example, chromium (III) compounds, as well as coarse and finely divided suspended solids and fats.

The closest in technical essence and the achieved technical result is a method for wastewater treatment of leather production containing chromium (III) compounds. The purification method is designed to handle effluent discharges from which chromium-containing effluents have already been isolated, and includes two-stage averaging of wastewater with filtration to remove coarse impurities, mixing wastewater with a concentration of finely dispersed impurities 3500-3600 mg / l with aluminum sulfate solution in an amount of 12-20 mg / l with a correction of the pH of the mixture to 6.4-7.5 by the introduction of sulfuric acid and milk of lime (suspension of slaked lime in lime water). The resulting mixture of wastewater, finely dispersed impurities and aluminum sulfate is fed to a pressure flotator, where the mixture is saturated with air supplied under a pressure of 0.35-0.50 MPa. The resulting precipitate containing mechanical impurities is removed, and the treated effluents are returned to the mixer reactor, where the effluent is mixed with aluminum sulfate. The return of effluents is necessary to maintain the required concentration of fine impurities in the reactor in the range of 3500-3600 mg / l, which is a characteristic feature of the known method.

The installation for carrying out the known method includes a drive connected to the mains, averager of the first stage, a grating filter, a drive-averaging device of the second stage, a mesh filter, a mixing reactor with aluminum sulfate, a flotator with a device for saturating wastewater with air, a collecting tank for treated wastewater, a sewage return pipe to mixing reactor (RU 2145575, C02F 1/52, publ. 02.20.2000.).

The disadvantage of this method is the inefficiency of its use in the treatment of effluents containing compounds of chromium (III) and other metals, as well as a sufficiently large cleaning time and the difficulty of ensuring the required process parameters, in particular, the difficulty of monitoring and maintaining the concentration of fine impurities in the range of 3500-3600 mg / l in the effluent returned to the mixing reactor.

The objective and technical result of the invention is to simplify the cleaning process, reduce the cleaning time, expand the technological capabilities of the method by ensuring the purification of all wastewater, including effluents containing trivalent chromium ions and other metals.

The technical result is achieved by the fact that the method of treating industrial wastewater includes averaging wastewater, mixing them with aluminum sulfate solution and adjusting the pH, pressure flotation during saturation of the wastewater with air and removing sludge, while adjusting the pH by averaging before mixing with aluminum sulfate solution to a value of at least 10.5, before pressure flotation, a freshly prepared aqueous solution of flocculant with a concentration of 0.1-0.2 wt.% is added to the mixture, and the saturation of wastewater with air during flotation is ut forced feeding in their working volume of purified Photo pressure 0,11-0,25 MPa after processing a ultrasonic field with a frequency of 25-35 kHz while supplying compressed air to it.

The technical result is also achieved in that the pH correction is carried out by adding a substance selected from the group to the wastewater: slaked lime slurry, sodium hydroxide solution, sodium carbonate solution; flocculant consumption is 30-40 mg / l; as a flocculant, high molecular weight cationic flocculants are used based on a substance selected from the group: polyacrylamide, a copolymer of acrylamide with dimethylaminoethyl methacrylate, methyl sulfate and benzenesulfonate salts of dimethylaminoethyl methacrylate, polyethyleneimine; ultrasonic field treatment of the treated return flow using a water-gas ejector with a gas-jet ultrasound generator when compressed air is supplied to the ejector under a pressure of 0.25-0.45 MPa, and the treated purified return flow when feeding it into the waste water volume is 40- 60 m ³ / h.

The invention can be illustrated by examples of a method for treating wastewater after metalworking and wastewater from a leather industry using a unit containing known elements: a coarse impurity purification device connected by pipelines, an averager, a pressure flotator, and a wastewater saturation device with air — a gas-water ejector with a gas-jet ultrasound generator, collection tank for treated effluents, flocculant input device, scraper device and sludge collector, recirculator insulating the pump valves.

The method using the installation containing these elements is as follows.

After standard mechanical filtration for cleaning of coarse impurities on gratings and / or grids, the runoff, which can contain up to 100 mg / l of chromium (III) ions and other metals, up to 1500 mg / l of fat and up to 10 000 mg / l of suspended solids particle sizes less than 2 mm, served in the averager - a sufficient capacity tank, where the stock is averaged with constant stirring. When averaging to correct the pH to a value of at least 10.5, slurry of lime with a concentration of 4.0-4.5 wt.% And a solution of aluminum sulfate with a concentration of 8-12 wt.% Are added to the stock. The consumption of aluminum sulfate in this case is 20-30 mg / l.

A similar result can be achieved by using a mixture of a solution of aluminum sulfate and solutions of sodium hydroxide or carbonate. This treatment coagulates trivalent chromium and other metals in the form of water-insoluble hydroxides. Then, the stock is fed with a conventional feed pump to the pressure line of the flotator. Before the mixture enters the flotator, a flocculant solution in a concentration of 0.1-0.2 wt.% At a flow rate of 30-40 mg / l is added to it using a standard input device. The specified device may consist of dosing pumps of type ND 2.5 E, supplying the flocculant solution to the pressure line of the flotator through a pressure compensator. As the flocculant, known high molecular weight cationic flocculants are used based on a substance selected from the group: polyacrylamide, a copolymer of acrylamide with dimethylaminoethyl methacrylate, methyl sulfate and benzenesulfonate salts of dimethylaminoethyl methacrylate (poly-N, N, N, N-methylmethylmethylmethylmethylmethylmethylmethylmethylmethylmethylmethylmethylmethylmethyl methyl N-methacryloyloxyethyltrimethylammonium benzenesulfonate, etc.) polyethyleneimine. For the implementation of the method, the most effective are ZETAG and SUPERFLOC grades based on polyacrylamide in the form of polyelectrolytes with an active substance content of at least 50%.

Wastewater is fed through the pressure line to the flotator, where it is saturated with air. The saturation of wastewater in the flotator is carried out by forced supply into their volume of a part of the purified reverse flow at a pressure of 0.11-0.25 MPa after it is treated with an ultrasonic field with a frequency of 25-35 kHz with simultaneous supply of compressed air into it. The optimal flow rate of the treated purified runoff, returned in the form of a two-phase air-water mixture to the bottom of the flotator, depends on the volume of the flotator and is 40-60 m ³ / h.

The thickened fleet sludge is removed from the upper part of the flotator, then it is degassed and transported to the mechanical dewatering section, and the purified stock from the lower part of the external camera of the flotator is fed to the collection tank.

Part of the purified runoff (recycled water) from the collection tank or from the flotator after removal of the flotation sludge through the valve is forcibly supplied under pressure of 0.25-0.45 MPa with a pump through the line to the ultrasonic field processing device, which is made in the form of a known water-gas ejector equipped with gas-jet ultrasound generator (for example, gas-dynamic ultrasonic water-gas ejector (GUVD) manufactured by Energomashavtomatika LLC - http://npoema.ru/prod/17).

A stream of purified reverse flow flows from the ejector nozzle into the working chamber, creates a vacuum in it and enters the nozzle equipped with a diffuser. At the same time, compressed air at a pressure of 0.25-0.45 MPa is supplied (injected) into the working chamber of the ejector through the nozzles of a gas-jet ultrasound generator, which leads to the formation of an ultrasonic field with a frequency of 25-35 kHz in the working chamber. In this case, the specific power of the ultrasonic field can reach more than 100 W / cm ² and the pressure in the zone of the ejector diffuser is 0.11-0.25 MPa. The application of an ultrasonic field ensures the formation of a two-phase air-water mixture in the diffuser zone with air bubbles with sizes of 15-25 microns.

The obtained two-phase air-water mixture passing through the ejector is forcedly under pressure of 0.11-0.25 MPa and enters the lower part of the flotator (flow rate 40-60 m ³ / h), where it is mixed with the effluent from the mixing reactor to form flakes sediment, which after surfacing is removed from the flotator. The duration of pressure flotation is 16-20 minutes. The purified stock is pumped to the intermediate settling zone, and then sent to biological treatment.

The parameters of the proposed method and the efficiency of wastewater treatment by examples in comparison with the method of the prototype are presented in the table.

In examples 1 and 4, the wastewater treated after metal working, containing, mg / l:

ions of chromium (III), copper and aluminum - up to 100,

industrial oils - up to 1500,

suspended solids with particle sizes less than 2 mm (mechanical suspensions, aluminum powder) - up to 10,000.

In examples 2, 3, 5, the wastewater of leather industry containing, mg / l, is subjected to purification:

chromium (III) ions - up to 100,

fats - up to 1500,

suspended solids with particle sizes less than 2 mm - up to 10,000.

The above examples do not limit the possibility of implementing this method within the claimed limits for wastewater treatment of any other production from non-ferrous and heavy metals, suspended solids and fats.

As a result of the implementation of the method according to the invention, the time for purification of industrial wastewater from non-ferrous and heavy metals, suspended solids, oils and fats is reduced to 16-20 minutes, providing a given efficiency of the cleaning processes. The implementation of the method is simplified because it does not require constant monitoring of the composition of the circulating wastewater, which can significantly simplify the cleaning process and use a simple device diagram for its implementation.

Table Method Parameters Parameter value by examples Prototype method one 2 3 four 5 pH of wastewater after averaging 10.5 10.7 10.9 10.6 10.8 less than 10 PH correction agent Sodium hydroxide solution Slaked lime slurry Sodium Carbonate Solution Slaked lime slurry Sodium Carbonate Solution Sulfuric acid and milk of lime The substance is the active base of the flocculant Polyethyleneimine Polyacrylamide GARDEN* DMAEM methyl sulfate salt ** Benzene sulfonate salt DMAEM *** - The concentration of flocculant,% 0.10 0.15 0.20 0.14 0.16 - Flocculant consumption, mg / l thirty 35 40 32 38 - The frequency of the ultrasonic field, kHz 25 thirty 35 27 33 - Pressure when applying compressed air to the ejector, MPa 0.25 0.35 0.45 0.30 0.40 - The flow rate of the treated purified return flow supplied to wastewater, m ³ / h 40 fifty 60 45 55 - Pressure when supplied to the wastewater treated treated return flow, MPa 0.11 0.18 0.25 0.15 0.20 0.35-0.50 **** Duration of flotation, min twenty eighteen 16 17 19 thirty The cleaning efficiency,%, from:

- ions of Cr ³⁺ , Cu ²⁺ , Al ³⁺ 98.7 99.1 98.9 98.7 98.9 - - suspended solids with particle sizes less than 2 mm 98.9 99,2 99.0 99.0 98.9 98.7-99.0 - oils and fats 99.0 99.3 99,2 99.1 99,2 98.7-99.0 Note: * - copolymer of acrylamide with dimethylaminoethyl methacrylate ** - methyl sulfate salt of dimethylaminoethyl methacrylate (poly-N, N, N, N-methacryloyloxyethyltrimethylammonium methyl sulfate) *** - benzenesulfonate salt of dimethylaminoethyl methacrylate (poly-N, N, N, N-methacryloyloxyethyltrimethylammonium benzenesulfonate) **** - saturation pressure of the mixture of wastewater and aluminum sulfate with air

Claims (6)

1. A method of treating industrial wastewater, including averaging wastewater, mixing them with aluminum sulphate solution and adjusting the pH, pressure flotation when the wastewater is saturated with air and removing sludge, characterized in that the pH is adjusted by averaging before mixing with aluminum sulphate to values of at least 10.5, before pressure flotation, a freshly prepared aqueous solution of flocculant with a concentration of 0.1-0.2 wt.% is added to the mixture, and the wastewater is saturated with air during flotation by forced supply in their volume under pressure 0,11-0,25 MPa purified circulating flow after processing a ultrasonic field with a frequency of 25-35 kHz while supplying compressed air to it. 2. The method according to claim 1, characterized in that the pH correction is carried out by adding to the waste water a substance selected from the group: slaked lime slurry, sodium hydroxide solution, sodium carbonate solution. 3. The method according to claim 1, characterized in that the flow rate of the flocculant is 30-40 mg / L. 4. The method according to claim 1, characterized in that high molecular weight cationic flocculants are used as a flocculant based on a substance selected from the group: polyacrylamide, a copolymer of acrylamide with dimethylaminoethyl methacrylate, methyl sulfate and benzenesulfonate salts of dimethylaminoethyl methacrylate, polyethyleneimine. 5. The method according to claim 1, characterized in that the treatment of the purified return flow by an ultrasonic field is carried out using a water-gas ejector with a gas-jet ultrasound generator when compressed air is supplied to the ejector under a pressure of 0.25-0.45 MPa. 6. The method according to claim 1, characterized in that the flow rate of the treated purified return flow when it is supplied to the waste water volume is 40-60 m ³ / h.