JPH047078A - Apparatus and method for flotation separation of suspended matter - Google Patents

Abstract

PURPOSE:To enhance the separation efficiency of suspended matter by providing an air dissolving part dissolving air in a suspension by bringing the suspension into contact with compressed air through a diaphragm impervious to a liquid but pervious to air. CONSTITUTION:The diaphragm 11 used in a membrane type gas-liquid contact module being an air dissolving apparatus has a property not transmitting a liquid in a liquid phase but transmitting air under a use condition. The diaphragm 11 is a non-homogenous or composite membrane consisting of a porous support layer and a dense layer substantially having no pores or an open cell porous membrane or hollow yarn like membrane with oxygen transmission speed of 1X10<-7> cm<3>/cm<2>, sec, cmHg or more, air bubble generating pressure of 0.5kgf/cm<2>G or more and oxygen transmission speed of 1X1<-6> cm<3>/cm<2>, sec, cmHg or more. Further, the air to be dissolved in a suspension is compressed to 0.3-30kgf/cm<2>G or the suspension is pressurized to 0.5-10kgf/cm<2>G. By this method, the separation efficiency of suspended matter is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improved method for separating suspended solids, particularly to a flotation separation method, and particularly to a pressure separation method.

The invention also relates to a pressurized flotation device for suspended solids.

The present invention is applicable to treatment of oil-containing wastewater from petroleum refining, automobiles, machining, etc., treatment of wastewater containing carbon particles, treatment of wastewater from paper factories, separation of SS in water, concentration of sludge, and separation of bacterial cells in culture tanks. It can be applied to mineral flotation, separation and concentration of suspended solids dispersed in other liquids.

[Prior Art] The flotation separation method is a gravity separation method used when the density of the suspended IA substance is lower than that of the liquid that is the dispersion medium. It is applied by creating air bubbles in the material that adhere to the suspended matter and reduce its apparent density. In particular, when the density difference between the suspended solids and the liquid is very small, the sedimentation rate becomes very small, making it difficult to apply the coagulation-sedimentation method, and this method is effective for such objects. Furthermore, even if the suspended matter has a lower specific gravity than water, which is a dispersion medium, such as oil,
The method of attaching air bubbles is effective in improving the separation rate. Since the float that floats up at this time contains air, it has a lower liquid content than the sediment that has settled and separated. Taking advantage of this feature, it is also used to thicken sludge in wastewater treatment chambers.

In order to generate microscopic bubbles in a liquid (unless otherwise specified, the discussion will be based on typical liquids such as water or water/8 liquids. These are sometimes referred to as aqueous media), gas ( A widely used method is to pressurize air, which is a typical gas (unless you refuse to bring it in), dissolve it in water, and then release it to atmospheric pressure, which is called the pressurized flotation method. When air is dissolved in water under pressure and then released to atmospheric pressure, extremely fine bubbles are generated, but these bubbles tend to occur at discontinuous interfaces between liquids and solids, and discontinuous interfaces between liquids. It has a nature. The pressure levitation method utilizes this principle.

As shown in Figure 1, the pressurized flotation separator for wastewater treatment by boat consists of a raw water pressurizing pump 2, a compressor 6, an air dissolution tank 3, a pressure reducing valve 4, an excess air discharge valve 5, and a flotation separator. It consists of a tank 7, to which various instruments and piping are attached. Raw water containing suspended solids is pressurized by a pressure pump 2 and enters an air dissolution tank 3. In the air dissolution tank 3,
Air pressurized by a separate compressor 6 is introduced as bubbles from the bottom of the tank, and a part of the air is dissolved into the suspension under pressure. It is expelled inside.

The air-dissolved suspension is reduced in pressure to around normal pressure by a pressure reducing valve 4 and is led to a flotation tank 7. Suspended substances float to the surface in the tank 7 and are separated. At this time, in order to prevent the flocs coagulated in front of the pressure reducing valve from being destroyed when passing through, raw water or a part of it or other fresh water 8. An improved method has also been proposed in which a required amount of sulfuric acid is dissolved under pressure, mixed with the raw water 1 which has been agglomerated and coagulated in the mixing section 9, and then sent to the flotation tank 7. This method has the advantage that the clarity of the treated water is considerably improved, especially for wastewater that requires a coagulation operation.

However, in the above device, air must be blown into the liquid using a compressor, or the air dissolution efficiency is poor, and a large amount of air must be blown in order to achieve a certain air solubility. There is an inconvenience.

[Problem to be solved by the invention]

The present invention has excellent air dissolution efficiency during suspension;
High separation efficiency and compact design
An object of the present invention is to provide a pressurized flotation separation device and a separation method for f5 substances.

[Means for Solving the Problems] The present invention provides a diaphragm that does not permeate liquid but allows gas to pass through, in an apparatus that dissolves gas in a suspension and floats and separates the suspended matter with bubbles. A suspended solid flotation separation device and a liquid, characterized by having a gas dissolving unit as a component, which dissolves a gas in a suspension by bringing the suspension into contact with an added gas through a Gas is dissolved in the suspension under pressure through a diaphragm that does not permeate but gas permeates, and then the pressure is brought to normal pressure. This invention relates to a patented flotation separation method that is characterized by a high pressure. Further, the present invention provides that the diaphragm of the gas dissolving part is a heterogeneous membrane or a composite membrane consisting of a porous support layer and a dense layer having substantially no pores, or that the diaphragm of the gas dissolving part is a
X I O-7crE /c director, seccmHg or more, or bubble generation pressure 0.5 kgf / cnl
G or more, and oxygen permeation rate I x 10-6cr
The present invention relates to the above-mentioned device characterized in that it is a continuous porous membrane having an A/cisec, cmHg or more, or a hollow fiber shape. Furthermore, the present invention provides that the gas dissolved in the suspension is 0.
The above method is characterized in that the suspension is pressurized at 3 to 30 kgf/cfflG, or the suspension is pressurized at 0.5 to 10 kgf/crlrG.

FIG. 3 shows the configuration of an apparatus for using the present invention in Examples;
Explaining along FIGS. 4 and 5, in FIG. 3, a suspension liquid (hereinafter referred to as raw water) 1 is pressurized by a pressure pump 2, and guided to a membrane module 10, which is a gas dissolving section.
Air is dissolved while flowing in contact with the diaphragm (11 in FIG. 5) inside the module, and is discharged from the module, the pressure is reduced by the pressure reducing valve 4 provided as required, and the air is sent to the flotation separation tank 7. On the other hand, air pressurized by a compressor 6 is injected into the opposite side of the diaphragm of the membrane module.

The air side of the membrane module is equipped with a gas outlet (fifth
15) in the figure and a gas exhaust valve 5 are provided to exhaust part of the air introduced into the module.

In the example shown in FIG. 4, instead of raw water, other additional water is pressurized by the pressure pump 2 and introduced into the membrane module 10, and after dissolving air, it is mixed with the raw water in the mixing section 9. , and sent to the flotation separation tank 7. In this case as well, as in the case of FIG. 3, it is also possible to provide a pressure reducing valve 4 and an air vent valve 5 for reducing the pressure of the air-dissolved water to normal pressure, if necessary.

Hereinafter, the constituent elements of the present invention will be explained in detail. Diaphragm (
(Hereinafter, also simply referred to as a membrane), under the conditions of use, liquid does not pass through the membrane while it remains in the liquid phase, but gas passes through it. Furthermore, in a system where pressurized gas and liquid come into contact with each other through a membrane, the gas is substantially prevented from becoming bubbles and being diffused into the liquid. That is, in the present invention, the dominant mechanism is that the gas supplied to one side of the membrane permeates the membrane under pressure and dissolves in the liquid without forming bubbles, and the generated bubbles come into contact with the liquid. The mechanism of dissolution due to this is not dominant.

Membranes with these characteristics include gas separation membranes, pervaporation membranes,
It can be selected from diaphragms called gas-liquid contact membranes, precision filtration membranes, ultrafiltration membranes, reverse osmosis membranes, and the like. First, a preferred membrane for the present invention is a heterogeneous membrane or composite membrane (hereinafter simply referred to as a heterogeneous membrane or composite membrane) consisting of a porous layer and a non-porous layer. The structure of a heterogeneous membrane or composite membrane consists of a non-porous layer that blocks liquid permeation, and a porous layer that maintains the strength of the membrane and does not cause gas permeation resistance.
This is a preferable structure in order to achieve a high gas permeation rate while maintaining the necessary pressure resistance. In use, it is preferred that the side in contact with the liquid be a non-porous layer. The heterogeneous membrane or composite membrane that can be used in the present invention has an oxygen permeation rate, which is a representative gas permeation rate, of I x 10-7cra/crM,
It is preferable that it is sec, cmHg or more. If the oxygen permeation rate is less than this value, the gas permeation rate into the liquid will be low, resulting in disadvantages such as requiring a large membrane area, high gas force and liquid pressure. The oxygen permeation rate is measured according to ASTM D 1434.

When such a non-porous homogeneous membrane, heterogeneous membrane or composite membrane is used as a diaphragm, even if the gas pressure is increased, the gas will not become diffused and the gas will dissolve in the liquid on the membrane surface. However, in cases where the difference between gas pressure and liquid pressure is too large, resulting in significant supersaturation on the liquid side, or when insufficient flow rate or insufficient stirring on the liquid side causes gas to exceed membrane permeation rate or dissolution rate in liquid, etc. may cause bubbles to form on the liquid side surface of the membrane.

However, even in this case, the amount of bubbles generated is significantly smaller than in so-called aeration. In the present invention, if the amount of bubbles generated is 1/2 o or less of the treated water V (volume during use), it is considered that the bubbles are not caused by aeration, and such cases are also included in the present invention.

Non-porous homogeneous membranes such as silicone rubber can also be used in the present invention. Although non-porous membranes generally have drawbacks such as lower oxygen permeation rate and lower pressure resistance than heterogeneous membranes and composite membranes, they are still preferable membranes in terms of providing aeration.

Another type of membrane that is more preferred in the present invention has a bubble generation pressure of 0.5 kgf/cufG or more in the liquid used, and an oxygen permeation rate of I x 10-''cnl/
cfflsec, continuous porous membrane with ci+Hg or more (
(hereinafter simply referred to as a porous membrane). The present invention does not care whether the porous membrane has an asymmetric structure or whether it is a target membrane. In the present invention, the oxygen permeation rate needs to be one order of magnitude higher in the case of a porous membrane than in the case of a heterogeneous membrane or a composite membrane. If the oxygen permeation rate is less than this value, the rate of air dissolution into water will be low and a large membrane area will be required.

When a porous membrane is used as a diaphragm, when the pressure on the gas side is higher than the pressure on the liquid side and the pressure difference exceeds a certain value, the gas pushed out from the pores overcomes the surface tension of the liquid.
Bubbles form on the surface of the membrane on the liquid side, creating an aeration state. The minimum pressure difference between the gas side and the liquid side that results in a diffused state is called the bubble generation pressure. The bubble generation pressure is determined by the pore diameter, the surface energy of the membrane material, and the surface tension of the liquid. Bubble generation pressure 1. Normally, liquid is measured at atmospheric pressure, so it is expressed as gas gauge pressure. The porous membrane used in the present invention has a bubble generation pressure of 0.5 kgf in the liquid used.
/cYiYG or higher, and in the present invention, it is desirable to operate under conditions in which bubbles do not occur, that is, in a pressure range that does not cause an aeration state. Even if the pressure difference between the gas and liquid is less than the bubble generation pressure, a small amount of bubbles may be generated for the same reason as in the case of a heterogeneous membrane or a composite membrane, but this is allowed in the present invention.

If the liquid is an aqueous medium: Is it necessary for the membrane to be hydrophobic so that water cannot pass through the membrane through the pores and the pores cannot be blocked by water? If the hydrophobicity is strong, the bubble generation pressure will be low, and the conditions of use will be limited. Furthermore, membranes with a large average pore diameter or membranes with a wide pore size distribution are also undesirable because they result in low bubble generation pressure.

In the present invention, although some bubble generation is allowed, the dissolution mechanism is basically based on the dissolution mechanism on the membrane surface rather than gas dissolution due to aeration. Therefore, the entire amount of gas introduced into the gas-liquid contact module can be dissolved, making it possible to reduce the compressor capacity (and omit the exhaust valve for excess gas. However, if the gas is a mixed gas such as air, ,and,
Particularly when a heterogeneous membrane, a composite membrane, or a non-porous homogeneous membrane with gas selectivity is used as a diaphragm, components with poor membrane permeability, such as nitrogen, or components with low solubility in liquids, such as argon, may be used. Low concentration components may be concentrated in the gas phase near the diaphragm, reducing gas dissolution efficiency.

In order to avoid such problems, it is also possible to provide a gas discharge valve in the gas-liquid contact module to discharge the concentrated gas. Even in this case, the amount of discharged air may be about 1/20 to 1/2 of the amount of supplied air, and the loss of pressurized air is significantly smaller than in the case of conventional air pressurized dissolution tanks.

The pressure of the gas supplied to the membrane module is 0.3 to 30k.
gf/c! llG is preferred, 1 to 10 kgf/
cIaG is more preferred. Higher pressures allow for savings in membrane area and additional liquid volume, but increase the cost of electricity for gas compression. In particular, in the case of a method in which gas is dissolved in additional liquid and then mixed with spring water, the gas pressure is 3 to 10 kg.
It is preferable to set f/cfflG high and dissolve at a high concentration because the amount of additional liquid can be saved and the capacity of the flotation tank can be reduced. The gas can be compressed using a compressor, but it can also be used directly from another source of compressed gas.

The pressure of the liquid introduced into the membrane module is 0.5-10k.
gf/c++lG, 1-5kgf/c+fl
G is preferred.

The liquid pressure mentioned here refers to the module inlet pressure. The higher the pressure, the higher the saturation point of gas dissolution, making it possible to melt at a higher concentration.Especially in the case of a method in which air is dissolved in additional water and mixed with raw water, the amount of additional water must be reduced. is possible and preferable, but if it is too high, the operating power cost of the pressurizing pump increases. The pressure loss of the module under operating conditions is 0.5 kgf/c+flG
If this is the case, there is no need to provide a pressure reducing valve, but if the liquid pressure is greater than the pressure loss of the module, a pressure reducing valve is provided between the module and the flotation tank.

In the present invention, unlike in the case of a gas melting tank, there is virtually no restriction on the pressure difference between the gas and the liquid, and the gas pressure and the liquid pressure can be independently set to preferred values. That is, not only does the liquid and gas need not be at the same pressure, but also an operating condition in which the pressure on the liquid side is higher than the pressure on the gas side is also possible. The maximum allowable pressure difference between gas and liquid varies depending on the type of diaphragm used.

If the diaphragm is a heterogeneous or composite membrane, the permissible pressure difference is limited only by the pressure resistance of the diaphragm.

On the other hand, when using a porous membrane, under conditions where the gas side pressure is higher, the pressure needs to be below the bubble generation pressure to prevent aeration, and under conditions where the liquid side pressure is higher, the pressure must be lower than the bubble generation pressure. , it is necessary that the pressure difference be below that which does not cause liquid to penetrate into the pores.

In the present invention, the contact time for dissolving gas can be reduced to about a few tenths of a second to more than ten seconds, which is less than 1/10 of that of conventional gas dissolving tanks, so the device for dissolving gas is significantly smaller. Moreover, since the pressure difference between the gas and the liquid is absorbed by the diaphragm, there is no need for a pressure-resistant container.

Any shape of the diaphragm can be adopted, such as a flat membrane or a tubular 1 hollow fiber, but a hollow fiber is preferred because it provides a large surface area. However, when raw water is introduced into a gas-liquid contact module, flat membranes or tubular membranes are preferred to prevent clogging. The module can take any conventional shape suitable for membrane geometry. When the diaphragm is a hollow fiber or a tubular membrane, it may be of an external perfusion type in which the raw water flows in contact with the outside of the hollow fiber, or an internal perfusion type in which the raw water flows in contact with the inside. Further, when the membrane is a flat membrane, a spiral type is preferable. FIG. 5 shows the shape of an internal perfusion type gas-liquid contact module using hollow fiber membranes 11, which is used in an embodiment of the present invention. That is, raw water or fresh water is introduced into the module from the overnight body inlet 14, flows in contact with the inside of the hollow fibers 11, and then
The liquid is discharged through the liquid discharge port 15. On the other hand, compressed gas is introduced from the gas inlet 16 into the space between the outside of the hollow fiber 11 and the housing 12, passes through the hollow fiber membrane, and is dissolved in the liquid.

In addition, some of the gas is removed from the air vent 1 provided as necessary.
It is discharged from 7. In use, it is also possible to install a plurality of modules in parallel or in series.

The liquid used as a dispersion medium for raw water treated in the present invention is not particularly limited, and can be generally applied, such as water, saline, aqueous solution, acid, alkali, petroleum, and organic liquid, among others:
Of particular importance are water, saline solutions, and aqueous solutions. In the method of dissolving a gas in a liquid and then mixing it with the stock solution, there are no particular restrictions on the additional liquid, and a portion of the stock solution or a portion of the stock solution from which suspended substances have been removed may be used as a separate flow. , the dispersion medium after flotation separation may be recovered and used, or a liquid other than these may be used.

It is also possible to add a flocculant to the raw water if the suspended matter is poorly flocculated. In addition, in order to prevent the bubbles generated from the liquid containing dissolved gas from coalescing into large bubbles before the flotation tank and causing excessive agitation, a gas-liquid separation tank is installed before the flotation tank. It is also possible to provide one. Note that any shape can be used for the flotation separation tank and the mixing section.

However, there are no particular restrictions on the f5 material, and it can be applied to objects to which normal flotation separation can be applied. Examples include solids such as SS components used in wastewater treatment, liquids such as oil and paint components dispersed in aqueous media, microorganisms, algae, and food residues.

The gas used in the present invention is not particularly limited, and for example, air, oxygen, nitrogen, inert gas, carbon dioxide gas, etc. can be used, and among these, air is particularly important.

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

Example 1 Poly(4-methylpentene-
1), spinning temperature 290″C, trough l-300
Melt spinning is carried out at a temperature of 21°C, and the obtained hollow fiber intermediate is
Heat treatment at 0°C1 stretching ratio (DR) 1.1, treatment time 5 seconds, temperature 25°C, cold stretching at DR=1.2, temperature 150
°C, hot stretching at DR=1.4, and temperature 180″C,
By heat fixing with DR=0.9, the outer diameter is 485μ
A hollow fiber membrane with an inner diameter of 380 μm was obtained. When this membrane was observed with a scanning electron microscope, many pores with a diameter of 0.1 μm were observed on the inner surface of the hollow fiber membrane, but almost none were observed on the outer surface. Furthermore, although a 70% ethanol aqueous solution was injected into the inside of this membrane at 0.5 kgf/cfflG, no liquid permeation was observed. From this, it can be seen that this membrane is a heterogeneous membrane that does not have pores connecting both the inner and outer surfaces. The gas permeation rate of this membrane is the oxygen permeation rate of 6.51 x 10-6 crl/cd, se
ccmHg, nitrogen permeation rate 1.58 x 10-6ci
/C11T, sec.

cm Hg, and the oxygen/nitrogen separation factor was 4.12.

Using this membrane, a module with a diameter of 20 cm, a hollow fiber length of 1.0 m, and a hollow fiber inner surface area of 25 rr'r as shown in FIG. was created. The valve 5 connected to the air vent 17 of the module was closed and no air was discharged.

Factory wastewater containing fine activated carbon powder with a suspended solids amount (SS) of 335 ■/l was processed at a flow rate of 3.0 rT? /hr was introduced into the module. When the module outlet pressure was adjusted to 1.7 kgf/c+flG using the pressure control valve 4, the module population pressure was 2.3 kgf/cfflG.
Met. Meanwhile, 3.0 kg of air is pumped into the compressor.
f,/CTII G was pressurized and introduced into the gas inlet of the module.

The wastewater from the pressure reducing valve was led to a rectangular box-shaped flotation tank with a scraper and a tank capacity of 18 mm and a flotation area of 13 mm, where it was separated into treated water and sludge. The residence time in the flotation tank was approximately 12 minutes. SS of treated water at this time is 87■/
n, and 248 ■/p of SS were removed.

Comparative Example 1 The same suspension as in Example 1 was introduced into a sedimentation tank instead of the pressure flotation separator, and the SS of the treated water was 105 ■/! Met.

Example 2 The same apparatus as in Example 1 was prepared except that the pressure regulating valve 4 was not provided, and a treatment experiment was conducted using this apparatus. Using the same suspension as in Example 1 as raw water, the water pressure was 0.56 kg.
When introduced into the module at f/c4G, the flow rate is 3.0rf
/hr. On the other hand, the air pressure is 0.5 kgf/cm
Introduce the gas into the module's gas inlet with G, and 21 /win
Excess air was evacuated.

The wastewater from the pressure reducing valve was led to a rectangular box-shaped flotation separation tank with a scraper and a tank capacity of 18 volumes and a flotation area of 13%, where it was separated into treated water and sludge. The residence time in the flotation tank was approximately 12 minutes. 33 of the treated water at this time is 99 [I
Ig/I! , and 236 ■/i SS were removed.

Example 3 A hollow fiber membrane was produced in the same manner as in Example 1, except that the heat treatment was performed at a fixed length and the heat treatment time was 1 minute. The obtained hollow fiber had an outer diameter of 510 μm and an inner diameter of 400 μm.
When this film was observed with a scanning electron microscope, it was found that
Many pores with a diameter of 0.1 μm were observed on both the inner and outer surfaces of the hollow fiber membrane.

In addition, the inside of this membrane; this 70% ethanol aqueous solution was
When pressure was applied at 5kgf/c+flG, the membrane area was 1
Transmitted at a rate of 136 cnt/min per rri. From this, it can be seen that this membrane is a porous membrane having pores connecting both the inner and outer surfaces. The gas permeation rate of this membrane is 8.64 x 10-'cut
/cffl, seccmHg, nitrogen permeation rate 9.23
X L O-'ci/all, seccmHg, and the oxygen/nitrogen separation coefficient was 0.935.

Using this membrane, a module having the same shape as in Example 1 was assembled, and the device shown in FIG. 3 was manufactured. Using this device, the treatment was carried out under the same conditions as in Example 1 except that the air pressure was 2.0 kgf/crAG, and the SS of the obtained treated water was 80 mg/f and 255 mg/jl.
! SS has been removed.

Example 4 A hollow fiber membrane manufactured by the same method as in Example 1 had an outer diameter of 263 μm and an inner diameter of 210 μm, and no etal permeation was observed, an oxygen permeation rate of 1, and an OI x 10.
-5 crl/ctA, sec, cmHg, nitrogen permeation rate 2, 62 X 10-6 cn! /c++t, sec
, cmHg, and the oxygen/nitrogen separation factor was 3.85. This membrane was made into a material with a diameter of 10 cm as shown in FIG.
A water purification device having the configuration shown in No. 4 was fabricated by assembling the module into a module with a hollow fiber length of 0.5 m and a membrane area of 13 mm. However, the valve 5 connected to the excess air outlet 17 was closed.

Well water was introduced into the module at a flow rate of 0.5 rn'/hr, and the module outlet pressure was adjusted to 4.0 kg using pressure control valve 4.
When adjusted to be f/cnG, the module inlet pressure was 4.5 kgf/cfflG. on the other hand,
Air is compressed to 4.5 kgf/cT
IiG was pressurized and introduced into the gas inlet of the module.

The air-dissolved water exiting the pressure control valve 4 is mixed with factory wastewater containing fine activated carbon powder, which is introduced at a flow rate of 3.0 m/hr, in the mixing section 9, and is floated in the same manner as that used in Example 1. When the water was led to a separation tank and separated into treated water and sludge,
SS of treated water is 85mg, #, and S of 250■/l
S was removed.

Example 5 Using the same membrane and module as in Example 3, an apparatus having the configuration shown in FIG. 4 was manufactured. When the treatment was carried out using this apparatus under the same conditions as in Example 4, the SS of the treated water was 91.
■/! Therefore, 244/1 SS were removed.

〔effect〕

The present invention has many advantages over conventional suspended solids flotation separation devices using gas dissolution tanks. First, it can reduce operating power costs. This is because there is less loss of pressurized gas and the pressure of the liquid can be lowered. Second, it is possible to omit the gas dissolution tank, which is a pressure-resistant container, the pressure reducing valve, and the exhaust valve for excess gas. Thirdly, compared to a gas dissolution tank, a gas-liquid contact module has a volume that is 1/10 to 1/1/1 that of a gas dissolution tank.
100, it is very compact. Fourthly, even in the method of directly dissolving gas in raw water, a pressure reducing valve can be omitted, so there is little decrease in separation efficiency. Fifth, in the method of dissolving the gas in the additional liquid and then mixing it with the stock liquid, it is possible to dissolve the gas at a high concentration, so the amount of additional liquid is small and the capacity of the separation tank is also small. It's over.

[Brief explanation of drawings]

Figures 1 and 2 are conceptual diagrams showing the configuration of a pressurized flotation separation device for wastewater treatment by boat fishing, and Figures 3 and 4 show the configuration of the flotation separation device of the present invention. It is a conceptual diagram. Moreover, FIG. 5 is a partial vertical cross-sectional front view of a membrane module used in an embodiment of the present invention. The symbols in each l refer to the following. 1... Suspension liquid, 2... Pressure pump, 3... Air dissolution tank, 4... Pressure reducing valve, 5... Gas discharge valve, 6
...Compressor 7...Flotation separation tank, 8.
... Fresh water, 9... Mixing section, 10... Membrane module,
11...Hollow fiber membrane, 12...Housing, 13...
- Resin sealing part, 14...Liquid inlet, 15...Liquid outlet, 16...Gas inlet, 17...Gas outlet. Figure 1 Figure 2 Agent Katsutoshi Takahashi Figure 5 Procedure amendment (voluntary) June 8, 1990

Claims (1)

[Claims] 1. In an apparatus that dissolves gas in a suspension and then floats the suspended substance with bubbles to separate it, the suspended substance is suspended through a diaphragm that does not permeate liquid but permeates gas. 1. An apparatus for flotation and separation of suspended solids, characterized by having as a component a gas dissolving section that dissolves gas in a suspension by bringing a liquid into contact with a pressurized gas. 2. The device according to claim 1, wherein the diaphragm of the gas dissolving part is a heterogeneous membrane or a composite membrane comprising a porous support layer and a dense layer having substantially no pores. 3. The diaphragm in the gas dissolving part has an oxygen permeation rate of 1 x 10^-^
3. The device according to claim 2, wherein the pressure is 7 cm^3/cm^2, sec, cmHg or more. 4. The diaphragm of the gas dissolving part has a bubble generation pressure of 0.5 kgf.
/cm^2G or more, and the oxygen permeation rate is 1×10
2. The device according to claim 1, wherein the device is a continuous porous membrane having a pressure of ^-^6cm^3/cm^2, sec, cmHg or more. 5. The device according to claim 1, 2, 3 or 4, wherein the diaphragm of the gas dissolving part is hollow fiber shaped. 6. A method for flotation separation of suspended solids, which comprises dissolving gas in a suspension under pressure through a diaphragm through which liquids and gases can pass, and then bringing the pressure to normal pressure. 7. Gas is dissolved in a suspension under pressure through a diaphragm that does not allow liquid to pass through but allows gas to pass through, and then a suspension in which no gas is dissolved is mixed therein, and then the pressure is brought to normal pressure. A flotation separation method for suspended solids. 8. Gas dissolved in the suspension is 0.3 to 30 kgf/c
8. The method according to claim 6, wherein the pressure is applied at m^2G. 9. The method according to claim 6 or 7, wherein the suspension is pressurized at 0.5 to 10 kgf/cm^2G.