RU2749711C1 - Method for purification of industrial waste water. - Google Patents

Abstract

FIELD: water purification.SUBSTANCE: invention relates to the purification of natural and waste water and can be used in the purification and disposal of industrial waste water from the pool of preliminary soaking of wood. Wastewater treatment includes the stages of filtering the effluent to remove particles with a fraction of more than 3 mm, feeding it to the inlet pumping pool for equalizing the effluent and then feeding it through a pump to a flotation unit, including a tubular flocculator, to which a coagulant and a flocculant are added in the form of solutions. The flocculant is a copolymer of acrylamide and sodium acrylate at a dosage of 1-5 g/l, and the coagulant is aluminum sulfate Al2(SO4)3at a dosage of 400-500 ml/l or titanium coagulant TU 262212-001-45527070-2006 at a dosage of 500- 600 ml/l. At the stage of adding the coagulant the water is made alkaline. From the tubular flocculator, the effluent enters the tank of the flotation unit, where the effluent is treated with microbubble aeration to form a layer of flotation foam on the surface of the effluent, consisting of solid particles and gas bubbles. The foam is removed by a separator integrated into the flotation unit and transferred to a foam hopper, from where it is pumped by an eccentric screw pump to dewater the sludge using a screw press. Water is passed through a plate separator with inclined plates, where light sediment formations are retained, rising up and forming a layer of flotation foam on the surface of the water, which is sent to a screw press to remove excess moisture and drain the sediment. Heavy sediment formations descend to the bottom of the tank into the storage hopper, and the purified water after the separator is directed upward through the channel to the outlet collector.EFFECT: provides full utilization of the resulting precipitation, due to this, a waste-free production for the treatment of wastewater from small woodworking enterprises is created, there is a decrease in capital, operating and energy costs.1 cl, 1 dwg, 4 tbl

Description

The invention relates to the field of physical and chemical treatment of natural and waste waters and can be used in the purification and disposal of industrial waste water from the pool of preliminary soaking of raw materials (wood). Industrial waste water is generated as a result of the processing of wood in a cooking tank (basin), which is part of a production line for the production of plywood. Before peeling, tree trunks are soaked in water at a temperature of 40-45 ° C. The raw material moves through the pool using a chain conveyor. In order to give the wood the properties necessary for further processing (softening), to increase the water temperature and intensify the softening process, the wood is treated with steam. The pool has a concrete body and a composite shelter. As a result of wood processing, water pollution is formed. The proposed method makes it possible to maximally purify industrial wastewater from pollution with the possibility of both reuse of treated water and their safe release into natural water bodies.

The following technical solutions are known from the prior art.

There is a known method of wastewater treatment (RF patent No. 2156749, published 09/27/2000), including filtration, flotation with a sorbent and settling, while a vegetable sorbent is introduced as a sorbent as a sorbent into the drain that has passed the grate and grease trap, the mixture is subjected to pneumatic flotation or electroflotation, filtered through a sorption charge and sent to an homogenizer and then to a multi-stage biological treatment unit by communities of attached and free-floating microorganisms; the resulting sediments, isolated at all stages of water purification, flotation concentrate, regeneration water, used filtration load are sent to the sediment utilization unit, where, after anaerobic-aerobic treatment, thickening, and the processed solid component is sent for further use, for example, in agriculture.

The disadvantages of this method are: the use of sorbents and the complexity and multistage nature of the cleaning process, which requires the involvement of laborious manual labor, taking into account the small volume of production - this affects the stability of the treatment plant, the cleaning scheme involves processes and devices that require highly qualified service personnel.

Also known is a method of wastewater treatment (RF patent No. 2214972, published on October 27, 2003), which consists in the fact that a coagulant with a flocculant and an activating additive are introduced into the water to be purified at a mass ratio of the activating additive to the coagulant with a flocculant equal to 0-500 wt.h ., additionally treated water is treated with elastic vibrations with an intensity that ensures the implementation of cavitation in water with a level of cavitation noise in the frequency range of 500-500000 Hz not less than 50 dB throughout the reactor volume and acoustic macro- and microflows at a rate of not less than 1% of the vibrational velocity a surface that transmits elastic vibrations in a liquid, while the purified water is treated by all of the above methods simultaneously in a combined mode and the resulting solid-phase suspensions are separated.

The disadvantage of this method is that devices for its implementation require special equipment, while it is energy-consuming, long-lasting, applicable for waters with an average degree of pollution (for oil up to 200 mg / l) and is not effective enough.

The closest analogue of the patented method is a wastewater treatment method (RF patent No. 110368, published on November 20, 2011), which includes stages at which a coagulant is dosed into a static mixer, intensive mixing in a turbulent mode and complete dispersion of the coagulant in water. Then the flocculant solution is supplied and the process of agglomeration of colloidal aluminum into large floccules takes place in the flotation device, and mixing with saturated water. Further, when entering the vacuum zone, there was an intense release of air in the form of tiny bubbles, which, moving up to the surface of the liquid, carried away the pollution. All selected contaminants were collected on the surface in the form of flotation sludge with a spiral collector and discharged into a sludge collection tank. The purified water was discharged from the middle part along the height of the skimmer into the purified water tank.

The disadvantage of such an installation is the high energy consumption of the process of preparing a finely dispersed water-air mixture, due to the need to maintain a high pressure in the saturator and a low value of gas filling of the resulting water-air mixture (the value of the gas filling coefficient ϕ = 0.01-0.05).

The technical problem solved by the proposed method is to increase the degree of wastewater treatment coming from the raw material preparation pool, while simplifying the design and reducing the cost of electricity and reagents.

The task is solved by the optimal arrangement of the stages of water purification and the maximum processing of the resulting sludge.

The technical result consists in the complete utilization of the resulting precipitation, due to this, a waste-free production for the purification of wastewater from small woodworking enterprises is created, there is a decrease in capital, operating and energy costs.

The claimed technical result is achieved through the implementation of the wastewater treatment method, which includes stages in which the wastewater is filtered, removing particles with a fraction of more than 3 mm, is fed into the inlet pumping pool, where the wastewater flow is equalized and then, by means of a pump, is fed into the flotation unit, including a tubular flotation device , to which a coagulant and a flocculant are added in the form of solutions, from the tubular flocculator, the effluent enters the tank of the flotation unit, where the effluent is treated with microbubble aeration to form a layer of flotation foam on the surface of the effluent, consisting of solid particles and gas bubbles, which is removed by a scraper integrated into the flotation unit. installation, and transferred to a funnel for foam, from where the foam is pumped by an eccentric screw pump for dewatering sludge using a screw press, passing water through a plate separator with inclined plates, where light sediment formations are retained, rising up and forming a layer of the fleet foam on the surface of the water, which is sent to the screw press to remove excess moisture and drain the sludge, heavy sludge formations sink down to the bottom of the tank into the storage hopper, and the purified water after the separator is directed upward through the channel to the outlet collector.

In a particular case of implementing the method, a polyacrylamide polymer is used as a flocculant, which is a copolymer of acrylamide and sodium acrylate at a dosage of 1-5 g / l.

In a particular case of implementing the method, aluminum sulfate Al ₂ (SO ₄ ) _{3 is} used as a coagulant at a dosage of 400-500 ml / l, or titanium coagulant at a dosage of 500-600 ml / l.

In the particular case of the method, the water at the stage of adding the coagulant is made alkaline with Ca (OH) ₂ lime, CaO or Na ₂ CO ₃ soda at a dosage of 250-350 mg / l.

The non-clogging tilting plate separator increases the usable separation area, which allows high hydraulic loads in a small footprint. The inclined plates hold the thin layers of sediment until they become thick and compact, and finally detach from the plate surface and quickly slide up or down along the plate surface. Separation of light and heavy components of the sludge and additional treatment of flotation foam containing light components of the sludge can improve the quality of water purification and make it suitable for release, mixing them with water entering biological treatment at existing WWTP, or for releasing water into a water body (for example , into the river), or for a closed cycle of work with the return of water to the soaking basin.

Next, the solution is explained with reference to figure 1, which shows the following.

FIG. 1 - technological scheme of wastewater treatment.

The circulation system without cleaning has no practical application due to the accumulation of the concentration of toxic and pollutants. Based on these analyzes, the wastewater from the raw material soaking pool is a colloidal solution containing a large amount of organic matter in dissolved and undissolved form. Based on this, the most effective method (up to 80% of the effect) of any purification unit for a given class of solutions is the use of a reagent system with the development of an exposure mode for a coagulant, flocculant and related substances. Coagulation in this case is the main reagent method. Physical methods of purification (flotation, filtration, settling, aeration, various mechanical methods, so-called rotary screens, filter press, etc.) mainly determine the removal of undissolved substances. An exception is processing on membranes (nanofiltration), but for the purposes of this work, this method is not considered due to the economic unreasonableness of its application (the cost of cleaning and replacing membrane modules is excessively high).

Waste from the pool with wood 1 flows by gravity into the receiving tank 2, made of concrete, from where it is pumped into the supply tank 3 of the pre-treatment unit for mechanical cleaning from coarse dirt.

Precleaner 4, such as the Huber RoDisk, removes dirt particles up to 3 mm in size and includes a rotary sieve and a combined grit trap.

Taking into account the uneven nature of the flow, a pumping basin (reservoir 5) is used to accumulate waste water and stabilize the composition of the flow.

The filtered wastewater is directed to the inlet pumping pool 5 (made of concrete). In the pumping basin, the effluent flow is leveled.

From the pool, the effluent is fed to the flotation unit 6, where physical and chemical treatment takes place. A HUBER complex flotation unit was used to complete the project. The flotation is preceded by a chemical stage, in which a coagulant is added to the treated water. The reagent powder is dissolved in tap water and dosed into the process. Reagent preparation unit 6.1 is equipped with a stirrer and dispenser. As a coagulant, aluminum sulfate Al ₂ (SO ₄ ) _{3 is used} , which forms a poorly soluble aluminum hydroxide, which violates the stability of the components of the system of oppositely charged colloidal particles and the sorption of contaminants on the surface of the resulting coagulant flakes. The solubility of Al (OH) ₃ decreases with increasing temperature and is minimal at pH 5.5-7.5. Coagulation of the initial waste water was carried out at various doses (100, 200, 300, 350, 400, 500, 600, 700 mg / l), covering the range of the assumed optimal dose of 100-700 ml / l (Table 1).

In the course of experimental laboratory studies, trial coagulation of the effluent with alkalinization with soda was carried out (Table 2), while it was found that the best formation and settling of sludge flakes occurs when the dose ratio of the alkalizing reagent and coagulant is 250-300 mg / l to 400-500 mg / l respectively. With a dosage of soda less than 250 mg / l and a coagulant less than 400 mg / l, no flakes are observed, or the flakes are very small and settle poorly, with a dosage of 350 mg / l of soda and a coagulant of more than 500 mg / l, the flakes are very large, but the process is poorly formed deposition.

Also, a titanium coagulator TU 2163-001-87707082-2012, which is a powder material and is a composition consisting of titanium dioxide, aluminum trichloride hexahydrate, aluminum chloride hydroxide, aluminum hydroxide, can be used as a coagulant. The coagulant powder is mixed with water in the desired ratio by weight (Table 1). Stir until smooth. Mixing time before use should be at least 20 minutes.

Trial coagulation was carried out at doses of 100, 200, 300, 400, 500, 600 mg / l. at t _water = 25 ° С.

In samples 1 and 2 (see Table 4) cotton is finely dispersed, evenly distributed in volume, no sedimentation was observed, in sample 3 flakes are formed immediately, cotton is well-formed, large, dense, sedimentation of the bulk occurs in 20 minutes. After 20 minutes of settling, a precipitate of 1.5 cm was formed. In sample 4, flakes are formed immediately, cotton is well-formed, large, dense, precipitation occurs intensively in 15 minutes. After 20 minutes of settling, a precipitate of 3.5 cm was formed, after an hour it was compacted to 3 cm. In sample 5, 6, flakes are formed immediately, cotton is well-formed, large, dense, precipitation occurs intensively in 10 minutes. After 20 minutes of settling, a precipitate of 4.5 cm was formed, after an hour it was compacted to 3 cm.

Conclusion: Based on the data in Table 4, the optimal dose of titanium coagulant is 500-600 mg / l.

During the operation of the chemical stage, the flocculant from the solution preparation unit 6.2 is dosed in the form of a solution into a tubular flocculator as part of the flotation unit. As a flocculant, a polyacrylamide polymer is used, which is a copolymer of acrylamide and sodium acrylate at a dosage of 1-5 g / l. When introduced into waste water, the specified reagent during flotation forms clots on the surface, which insignificantly affect the overall cleaning effect, while the collection of foam is simplified.

From the tubular flocculator, the effluent goes directly to pressure flotation. In a skimmer, gas bubbles attach to the surface of the solid particles. Due to their float ability, light bubble and particulate formations float to the surface. The mixed flow is directed upward into the tank 9 of the skimmer, where it is evenly distributed over its entire width. Laminar conditions provide optimal conditions for the separation of the phases of the solution. The flakes, consisting of solid particles and gas, rise to the surface of the water, where they form a layer of foam (flotation foam), which is scraped off into a funnel 8 for flotation foam, where it is further dehydrated. And the purified water enters the outlet collection 7.

The scraper is made in the form of a plate separator, which makes it possible to additionally drain the foam. Flotation foam is pumped by an eccentric screw pump for sludge dewatering using a screw press 8.2. The non-clogging plate separator increases the usable separation area, which allows high hydraulic loads in a small footprint. While the water is directed downward through the holes between the inclined plates, the floating flakes travel a short distance and attach to the bottom surface of the top plate, and heavy particles descend a short distance to the top surface of the bottom plate. The plate holds the thin layers until they become thick and compact, and finally detach from the plate surface and quickly slide up or down along the plate surface. The separated light formations slide up and rise to the surface of the water, where they form a layer of flotation foam. Heavy sludge deposits slide and sink down to the bottom of the tank into the sludge hopper, from where they are removed by an eccentric screw pump or discharged by gravity using a pneumatic gate. The flotation foam dewatering unit is also supplied with flocculant from the unit for its preparation 8.1. The addition of a reagent stabilizes the foam and makes it easier to collect.

The purified water, after it has passed down into the plate separator, rises up again through the channel to the outlet collector 7. The water level in the tank and the depth of immersion of the scraper are adjusted by changing the position of the overflow - the submerged partition. Up to 30% of the discharged water is reused for pressurized water treatment. The multistage centrifugal pump generates a pressure of about 6 bar. The compressor supplies compressed air (> 12%) to the pump rotor, which creates small bubbles with a large surface to quickly saturate the water. The process of water saturation with air is completed in the pressure supply pipeline. Saturated water enters through the outlet valve, where microbubbles with a diameter of 20 to 40 microns are formed when the saturated water pressure suddenly drops. In the supply line, the microbubbles are thoroughly mixed with the incoming effluent so that all the particles come into intimate contact with a suitable number of microbubbles. Pressure flotation with reagent treatment is a highly efficient method of purification of a solution obtained as a result of thermal soaking of wood.

The flotation foam obtained as a result of flotation is sent to a screw press to remove excess moisture and dry it to a sediment with a moisture content of 75-78%.

Treated wastewater flows by gravity into the sewage pumping station (SPS). From the sewage pumping station, the treated wastewater is sent to the circulating water supply circuit for reuse, or to the sewerage network to lower the water level in the pool.

Treatment facilities are necessary to purify water to levels that allow them to be discharged by mixing them with water supplied to biological treatment at the existing WWTP, or to discharge water into a water body (Bolshaya Izhorka river), or to provide for a closed cycle of work with the return of water to the soaking basin ...

The proposed wastewater treatment scheme provides for 3 operating modes:

A. Closed cycle of work with the return of water to the pool;

B. A cycle of work with a partial return of purified water to the pool, the surplus is discharged into the sewer;

B. Mode of technological cleaning of the BZS (complete discharge of all waters from the pool for bottom cleaning).

Claims (2)

1. A method of wastewater treatment, including the stages at which the wastewater is filtered, removing particles with a fraction of more than 3 mm, is fed to the inlet pumping pool, where the wastewater flow is equalized and then, by means of a pump, is fed into the flotation unit, including a tubular flocculator, to which coagulant is added and a flocculant in the form of solutions, while the flocculant is a copolymer of acrylamide and sodium acrylate at a dosage of 1-5 g / l, and a coagulant is aluminum sulfate Al ₂ (SO ₄ ) ₃ at a dosage of 400-500 ml / l or titanium coagulant TU 262212 -001-45527070-2006 at a dosage of 500-600 ml / l, while the water is alkalized at the stage of adding the coagulant, then from the tubular flocculator, the effluent enters the tank of the flotation unit, where the effluent is treated with microbubble aeration to form a layer of flotation foam on the surface of the effluent, consisting of from solid particles and gas bubbles, which is removed by a separator integrated into the flotation unit and transferred to a foam funnel, from where the foam is pumped by an eccentric screw pump for sludge dewatering using a screw press, passing water through a plate separator with inclined plates, where light sediment formations are retained, rising up and forming a layer of flotation foam on the water surface, which is sent to a screw press to remove excess moisture and drainage sediment, heavy sediment formations fall down to the bottom of the tank into the storage hopper, and the purified water after the separator is directed upward through the channel to the outlet collector. 2. A method of wastewater treatment according to claim 1, characterized in that the water at the stage of adding the coagulant is made alkaline with Ca (OH) ₂ , CaO or soda Na ₂ CO ₃ at a dosage of 250-350 mg / l.

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