FI95234B - Method and apparatus for purifying aqueous solutions or the like - Google Patents

Abstract

The objet of the invention is a method and device for purifying aqueous solutions or the like, where the component to be removed, for example in a dissolved or solid state, is converted to the solid phase, the said method including the addition of coagulating and flocculating agents; the separation of larger solid particles from the suspension thus obtained by settling; and the removal of the remaining components from the suspension by electroflotation. The invention is intented especially for purifying water and technical solutions of different types of dissolved and solid substances. In the method, electroflotation is used to remove the remaining components by saturating the suspension with the gas released in the electrolysis in connection with turbulence and by removing the foam in laminar conditions. In the electroflotation device (10) the chamber (30) consists of a gas saturation chamber (12) in which is mounted an electrode unit (13) for saturating the suspension with the gas released in the electrolysis, and of a flotation compartment (15), in which is mounted an electrode unit (18) for foaming.

Description

95234

METHOD AND APPARATUS FOR CLEANING AQUEOUS SOLUTIONS OR THE LIKE

RELEASE FOR THE RELEASE OF THE RELEASE AGAINST VAT

The invention relates to a method and apparatus for purifying aqueous solutions or the like, in which the component to be removed, which may be in dissolved or solid form, is transferred to a solid phase, comprising adding coagulants and flocculants, separating larger solids by clarification and removing remaining components by electrical flotation. through. The invention relates in particular to the purification of water and technical solutions from various types of dissolved and solid substances.

Known methods of water purification include purification processes with coagulants and flocculants, in which the reagents are introduced into the liquid to be purified in solution, as disclosed in Finnish patent application 890493. Finnish patent 77 008 discloses a process

A common disadvantage of the above processes is the low efficiency of the devices that separate the formed flocs from the liquid stream, the large losses of liquids during the removal of coagulant that has risen to the surface or settled, which usually requires additional measures to remove excess water, and the need to collect precipitate from several points. from the surface. Furthermore, considering that the consumption of the coagulant is 20-200 g per cubic meter of liquid to be purified, it is quite clear that the slowness of the separation process and the high loss of anode metal lead to uncompetitiveness with a required cleaning capacity of more than 10 m3 / h.

U.S. Patent 4,156,648 discloses an apparatus for utilizing the above methods. The publication describes a process diagram and an apparatus for purifying water from contaminants using centrifugal force to separate solid parts of the sludge, coagulation and flocculation to settle large flocs and sludges in a thin-layer settling tank. The slurry solution from the settling tank is saturated in a pressurized state with a gas which, in another normal pressure state, is allowed to discharge from the slurry solution as a foam. Providing a pressure chamber of -10 is cumbersome and expensive.

U.S. Patent 3,816,274 discloses a method for separating fat from a waste solution emulsion. The separation is performed in two successive spaces separated by a partition. In the first state, the solution is made to pass past the anodes so that the pH of the solution rapidly drops by several units, whereby the fat emulsion decomposes. In the second space, the fat is allowed to separate without being promoted by gas or the like. German Offenlegungsschrift DE 25 00 455 discloses the treatment of waste water by electrofoaming in one space 20. German application DE 29 44 283 discloses an electroflotation method for treating wastewater in two successive spaces separated by a partition. The first mode is the electrode unit. The foam formed in the second state • · --25 is allowed to rise freely to the surface of the water.

A disadvantage of the above-mentioned known methods is that in the second stage, i.e. the foam or fat separation stage, no attempt has been made to prevent the mixing of the foam / degreased water and the foam / fat-containing water, due to the difference in density between the foam-containing water and the pure water. The purified heavier water also flows backwards along the bottom of the flotation space, while lifting lighter, more foamy water towards the top of the space and further clean water: .35 per outlet. Clean water is thus recirculated to strain the cleaning process and 3 95234 of untreated water flows towards the clean water outlet.

German application DE 40 24 424 further discloses an electroflotation method in which the water to be purified is first passed through an electrode unit, after which the water is allowed to flow freely through the flotation unit to separate the foam from the water. The rise of the foam is not facilitated by electrolytic gas or other gas formation.

It is an object and object of the present invention to provide a new method and apparatus for eliminating the above-mentioned deficiencies in the prior art purification processes, streamlining the process and increasing the efficiency of sludge separation.

The features of the invention are as set out in claims 1 and 4.

In the process according to the invention, the removal of the components remaining in the slurry solution by electric flotation is carried out by impregnating the slurry solution with electrolytic gas in connection with turbulence and removing the foam under laminar conditions. In addition, a preferred embodiment of the invention is characterized in that a precipitant which is a water-soluble substance or a fine sorbent or a combination thereof is added to the aqueous solution.

Suitable soluble precipitants are saline solutions, e.g. iron oxide sulphates, which together with the component to be removed form water-insoluble components. A suitable sorbent is also, for example, activated carbon.

The electric flotation device according to the invention has a chamber formed by a gas impregnation chamber in which an electrode unit is mounted for impregnating the slurry solution with the gas released in the electrolysis, and a flotation space. fitted with an electrode unit for flotation.

4,95234

The invention provides a method and apparatus which can be used for the treatment of waste water from food, chemical, varnish and paint production plants or for the treatment of technical solutions in mountain chemical and metallurgical plants, which contain small amounts of useful, recoverable components and e.g. Heavy metal salts.

The invention will now be described by way of example with reference to the accompanying drawings, in which

Figure 1 shows a cleaning method 10 according to the invention in block diagram form;

Figure 2 shows diagrammatically the cleaning process of Figure 1 and the cleaning device according to the invention.

Fig. 3 shows the electric flotation device according to Fig. 2 in a cross-sectional view along the line A-A and yl-15 seen from the left.

Figure 1 shows a cleaning method according to the invention in block diagram form. The process for purifying water and technical solutions from different types of dissolved and solid components is carried out as follows: a salt solution acting as a precipitant is added to the stream of water or technical solution, which together with the component to be removed forms insoluble components which settle as a precipitate. In place of or in combination with the precipitant solution, a finely dispersed sorbent can be added to the mixture, which sorbs the ion of the compound or useful component to be separated from the aqueous solution. The resulting slurry solution is treated with a coagulant and a flocculant. The solid sludges are removed by precipitation and clarification, and the finely dispersed solid phase is removed by electrofoaming, i.e. electroplating.

According to the invention, the electric flotation process is performed in two steps, which are combined in the same device. Ensim-. In this step, the slurry solution is impregnated with bubbles of electrolytic gases which are separated due to the high density of the electrolysis current, substantially more than 20 mA / cm 2, in the turbulence process of the slurry solution to be purified. In the second step, the foam is separated in the flotation chamber of the chamber with a minimal laminar flow of liquid and an electrolysis current density of substantially less than 20 mA / cm 2.

Figure 2 is a schematic diagram of the structure of a cleaning device according to the invention with which the process shown in Figure 1 is carried out. The purification equipment used in the purification process consists mainly of reagent dosing units 1, 2 and 3, mixer 4, clarifier 5, tank spaces 6 and 7, clarifier and precipitator 9, electric flotation device 10, defoamer 22 and foam separator.

A filling pocket 11, a gas impregnation space 12 and a flotation space 15 are built into the chamber 30 of the electric frothing device 10. The gas impregnation space 12 is separated from the flotation or flotation space 15 by a partition 16. A flue solution damper 17 is mounted in the flotation space 15. The lower part of the purified liquid discharge device 21 is separated from the lower part of the flotation space 15 by a partition 20. A vertically displaceable shutter flap 24 at the top of the discharge device 21 adjusts the height of the liquid relative to the direction of liquid flow to the bottom of the electric flotation device 10.

The supply of current to the electrode units 13 and 18 is effected 30 via direct current conductors connected to the rails 14 and 19. The current from the DC source is e.g. pulsed, as a result of which the polarization of the current can be reversed. The aim is to prevent the electrodes from passivating too quickly and to achieve a smooth, efficient gas evolution. The material of the plate electrodes is, for example, stainless steel 6 95234, which is in principle almost insoluble. Electrodes made of other corrosion-resistant materials, such as platinum, acid-resistant steel or platinum-titanium, can also be used.

The purification of aqueous or technical solutions is carried out as follows: wastewater is fed to mixer 4, simultaneously to clarifier 5 and tanks 6 and 7 from reagent dosing units 1, 2 and 3 alternately 10 finely dispersed sorbent and / or saline, and / or precipitating coagulant and flocculant. The resulting slurry solution is mixed in the mixer 4 with compressed air, which is led along the supply line 8 through a perforated hose attached to the bottom of the mixer 4.

The pretreated slurry solution is fed to a precipitator 9, where solid parts of the slurry and large flocs are separated from it, which are removed in stages through the bottom of the precipitator 9. If necessary, additional coagulant and flocculant can be fed to the precipitator 9 from the dosing units 2 and 3.

From the precipitator 9, the slurry solution, from which the largest particles have already been separated, is fed with the removable, dissolved and / or finely dispersed ingredients into the receiving pocket 11 of the chamber 30 of the electric flotation device 10. From there the slurry solution is completely immersed in the liquid. The electrodes 13 of the gas saturator 12 undergo the first stage of the process, i.e. the intensive release of gas, whereby the gas bubbles rising above the electrode unit 13 cause strong vortices in the solution. An adjustable partition 16 separating the gas saturator 12 and the flotation space 15, substantially 1/3 -5/6 parts, partially closes the foam outlet from the gas saturator 12. In the space 12, turbulence is enhanced when the outlet channel is partially or completely closed. 35 with inclined, adjustable partition 16.

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The sludge solution saturated with bubbles of the electrolysis gases is led to the flotation space 15 of the electric flotation device 10. The so-called the base mass rises to the surface of the liquid after the treatment of the slurry solution in the gas impregnator 12 and the solid particles remaining in the slurry solution 5 are transferred to the foam due to the gas bubbles formed in the electrode unit 18 of the frothing space 15. The flow of the slurry solution in the flotation space 15 is laminar and the densities of the electrolysis current are lower than in the gas impregnator 12. The laminarity of the flow of the slurry solution 10 is secured by damping grilles 17 mounted above the electrode unit 18.

In the flotation space 15, the foam accumulated on the surface of the liquid is removed from the process by a foam vacuum remover 22 which periodically removes the low-water upper layer of the foam 15 upstream and downstream. The periodicity of defoaming is controlled by the operating frequency of the defoamer 22. The solid component is separated from the foam by means of a vacuum with a foam separator 23. The water purified from the solids from the flotation space as described above is completely discharged 20 through the slots of the electrode unit 18 in the liquid and the discharge device 21. The discharge device 21 is provided with a sludge stream separator 20, which prevents solids from entering the clean liquid stream leaving the electric flotation device 10. In the electric foaming device 10 .. 25, the height of the surface level of the slurry solution is adjusted by the shutter flap 24.

Fig. 3 shows the electric flotation device 10 according to Fig. 2 in a cross-sectional view along the line A-A seen from above. The slurry solution from the settling granule, from which the largest particles are separated, is fed with the components to be removed into the receiving pocket li of the electric flotation device 10. From there, the slurry solution passes from the gaps between the plates of the electrode unit to the gas saturator 12. In the gas saturator 12, the gas bubbles released from the electrode unit cause strong vortices in the solution. By partially closing the outlet channel with the inclined partition 16, turbulence is enhanced. The sludge solution saturated with bubbles of electro- * 95234 δ lysis gases is led to the flotation space 15. The so-called sludge solution. the base mass rises to the surface of the liquid after treatment of the slurry solution in the gas saturator 12 and the solid particles remaining in the slurry solution are transferred to the foam due to the gas bubbles formed in the electrode unit of the flotation space 15. The flow of the slurry solution is laminar and the densities of the electrolysis current are lower than in the gas impregnator 12. The laminarity of the flow of the slurry solution is ensured by damping grilles 17 mounted 10 above the electrode unit. The purified water is removed through the slots of the electrode unit and the discharge device 21. The discharge device 21 is provided with a sludge flow separator which prevents solids from entering the clean liquid stream leaving the electric flotation device 10.

In space 10, the surface level of the slurry solution is adjusted by a shutter top 24.

According to a preferred application example, the purification method and apparatus according to the invention are used for the purification of wastewater from the meat processing industry. The effluent of the plant 20 is fed to the plant effluent 4, which contains, for example, 750 mg / l of sludge, 44 mg / l of total phosphorus and has a biological oxygen demand (BOD) of 1000 mg 02 / l. The dosing unit 1 is fed with a solution of iron oxide sulphate in an amount of 120 g / m 3 based on the salt, which acts as a phosphorus precipitant. Dosing unit 2 is fed with a coagulant solution of aluminum sulphate in an amount of 30 g / m 3 and dosing unit 3 is fed with a solution of flocculant, polyacrylamide, in an amount of 4 g / m 3.

After mixing, the slurry solution formed in the mixer 4 is fed to a precipitator 9, where the solid slurry settles to the bottom and is removed. From the precipitator 9, the slurry solution with its removable components is directed to an electric flotation device 10, where the slurry solution is impregnated with bubbles of electrolytic gases in the impregnation chamber 12 with an electrolytic current density of 40 mA / cma. A portion of the solid phase rises immediately to the surface of the slurry solution after exiting the gas impregnator 12 9 95234.

The slurry solution is further directed to the flotation chamber 15, where the final treatment of the wastewater takes place by electrolysis at a current density of 10 mA / cm 2. The purified water is removed from the device 5 via a discharge device 21. The dirt accumulates in the foam in the flotation space and, if necessary, is removed by a defoamer 22. The foam yield does not exceed 8.0% and its solid phase content is 2.2%. The following specific values have been found for purified water: 10 - precipitated substances 44 - 60 mg / l - total phosphorus content 1.1 - 2.1 mg / l - BOD 350 - 390 mg / l

The purification rate, calculated on the basis of sludge, is 93% and on the basis of phosphorus 96%.

According to another preferred embodiment, the treatment method and apparatus according to the invention are used for the treatment of oily wastewater. The oily feed water containing 360 mg of oil / l is fed to a mixer 4, which is also sequentially fed with 20 g / m3 of comminuted activated carbon, 50 g / m 3 of aluminum sulphate coagulant and 2 g / m 3 of polyacrylamide flocculant. After mixing, the slurry solution is fed to an electric flotation device 10, where gas impregnation is carried out at a density of the electrolysis current 25 of 40 mA / cm 2 and flotation at a density of the electrolysis current of 8 mA / cm 2. After the process, the oil content of the purified water does not exceed 1.0 mg / l. I foam. ·. the yield is 0.7 to 1.2%.

According to a third preferred embodiment, the purification method and apparatus according to the invention are used for the purification of wastewater from a tannery from chromium and other contaminants. The tannery effluents contain 480 mg / l of sludge 95234 10, 230 mg / l of sulphides, 160 mg / l of total chromium, and a COD of 1280 mg 02 / l. The wastewater is fed to a mixer 4, to which 280 g / m3 of iron monoxide sulphate is metered in to precipitate sulphides and regenerate chromium ions. Aluminum sulphate coagulant and polyacrylamide flocculant are also fed to this in amounts of 100 g / m 3 and 4 g / m 3, respectively. The slurry solution prepared in this way is fed to the precipitation tank 9, and after the precipitation tank 9, the slurry solution is directed to an electric flotation device.

10 The solid phase of the slurry solution is separated at an electrolysis current density of 30 mA / cm2 in a gas saturator 12 and 8 mA / cm2 in flotation mode 15. Purified water contains precipitates 35 mg / l, sulphides less than 2.0 mg / l, total chromium less than 0.1 mg / l, COD = 240 mg / l.

According to a fourth preferred embodiment, the purification method and apparatus according to the invention are used for the removal of heavy metal ions from wastewater from a refinery and / or a chemical plant. According to the analysis, the starting solution contains 0.7 mg / l of silver, 4.8 mg / l of lead and 20 mg / l of copper 21. Sodium sulphide in an amount of 35 g / m3 is used as precipitant. The finely dispersed precipitate of heavy metal sulphide settled in the sludge tank is flocculated with polyacrylamide at a concentration of 1.0 g / m3. The removal of the solid phase from the slurry solution is carried out at a density of 20 mA / cm2 of the electrolysis current of the gas saturator 12 and at a current density of 5 mA / cm2 in the flotation space. Silver and lead ions are practically absent from the purified technical solution and the concentration of copper ions does not exceed 0.1 mg / l. The foam yield was 0.05%. 1 e

It will be apparent to those skilled in the art that various embodiments of the invention may vary within the scope of the claims set forth below.

Claims (7)

A method for purifying aqueous solutions or the like, wherein the component to be removed is transferred to a solid phase, the method comprising: 5. adding a precipitant, coagulants and / or flocculants; - separating the larger solid particles from the slurry solution thus obtained by clarification, and - removing the remaining components from the slurry solution by electric flotation, characterized in that the remaining components are removed in the following two separate successive steps: (12) in the turbulent process with gas bubbles produced by electrolysis, the electric current density in the electrolysis being more than 20 mA / cm 2, and (b) in an electric flotation step in which a slurry solution passed from the gas impregnation chamber (12) to the flotation chamber (16) the components remaining by electric flotation and in which the flow is kept laminar by means of a low electrolysis current and slurry flow dampers (17) on top of the electrodes (18) before it is passed to the electrode to the unloading device (21) located below. Method according to Claim 1, characterized in that in the electric flotation, the electrodes of the electrode units (13, 18) are attached to rails (14, 19) to which a reversible polarizing pulse current is applied from the power supply to prevent passivation of the electrodes. Process according to Claim 1, characterized in that the precipitating agent is a water-soluble substance or a fine sorbent or a combination thereof. 12 95234 Apparatus for carrying out the method according to claims 1, 2 or 3, wherein the apparatus comprises means (1, 2, 3, 4) for adding pretreatment agents, a clarification basin (5, 9) or the like and an electric flotation device (10), 5 characterized in that the electrical flotation device ( 10) comprises - a gas impregnation chamber (12) fitted with an electrode unit (13) for impregnating the slurry solution with the gas released in the electrolysis, 10. a flotation chamber (15) fitted with an electrode unit (18) and a multi-cell structure slurry flow damper (17) mounted on the electrode unit; - a partition wall (16) mounted between the gas impregnation chamber (12) and the flotation space (15), and a discharge device (21) located below the 15th electrode unit (18). Device according to Claim 4, characterized in that the electrodes of the electrode units (13, 18) are arranged on rails (14, 19) to which a reversible polarizing current of polarization can be applied from the power supply to prevent passivation of the electrodes. Device according to Claim 4 or 5, characterized in that the electrode units (13, 18) are made of a substantially insoluble material 25, such as stainless steel or the like. Device according to Claim 4, 5 or 6, characterized in that the partition wall (16) is adjustable. 13 9E234