WO2009087921A1

WO2009087921A1 - Method for treating oil-containing waste water and apparatus for treating oil-containing waste water

Info

Publication number: WO2009087921A1
Application number: PCT/JP2008/073688
Authority: WO
Inventors: Takashi Yamada; Hideyuki Nakashima
Original assignee: Asahi Organic Chemicals Industry Co., Ltd.
Priority date: 2008-01-11
Filing date: 2008-12-26
Publication date: 2009-07-16
Also published as: TW200934734A; JP2009165915A; CN101910068A; KR20100108367A

Abstract

Disclosed is a method for treating an oil-containing waste water which can reduce the necessary amount of a flocculant used as compared with the conventional treatment using floatation separation. Also disclosed is an apparatus for treating an oil-containing waste water. A suspension material, which can capture or adsorb an oil contained in an oil-containing waste water, is added to the oil-containing waste water. Alternatively, a suspension material, which has captured or adsorbed an oil contained in an object oil-containing waste water previously mixed with the suspension material, is removed from the waste water by a floatation separation process. Thereafter, a flocculant is allowed to act on the waste water to remove the oil contained in the waste water.

Description

Method and apparatus for treating oil-containing wastewater

The present invention relates to a method and apparatus for treating wastewater containing oil generated in various industries such as cleaning, cleaning, steel, machining, food processing, and the like, and more specifically, removing oil in wastewater. The present invention relates to a method for treating oil-containing wastewater and a treatment apparatus therefor.

Conventionally, oil-containing wastewater treatment methods include a specific gravity separation method that removes oil using the specific gravity difference between the oil and water in the wastewater, or by supplying air bubbles to the wastewater and attaching bubbles to the oil in the wastewater. A floating separation method was used which was removed by concentrating to the surface.

As for the specific gravity separation method, for example, an oil-containing wastewater treatment apparatus that divides by a partition plate and uses an oil-water separation tank having a communication hole in the lower part of the partition wall to float and remove the oil component on the upper surface of the water surface. Proposed. 7 and 8, an oil-containing wastewater treatment apparatus using a conventional specific gravity separation method is communicated with a hollow box-shaped oil-water separation tank 101 and one end of the oil-water separation tank 101, that is, an upstream end. And the discharge pipe 103 communicated with the other end of the oil / water separation tank 101, that is, the downstream end, and the introduction pipe 102 is communicated with a manhole or the like provided in the middle of the side groove of the road. In the process of introducing waste water containing oil into the oil / water separation tank 101 through the introduction pipe 102 and flowing down the oil / water separation tank 101 from upstream to downstream, The oil component is separated and only water is discharged from the discharge pipe 103 to the sewer. The oil / water separation tank 101 of the processing apparatus includes a rectangular tubular precast concrete block (hereinafter referred to as a PC block) 104, 104... And a plurality of

partition plates

105, 106 that are in contact with the end face of the PC block 104. , 106... And

end plates

107 and 108 for closing both ends of the oil / water separation tank 101, and the PC block 104 and the

partition plates

105, 106, 106. By closing the end faces of the

PC blocks

104a and 104g with the

end plates

107 and 108, the inside is formed into a hollow box shape partitioned by a partition wall.

With the configuration described above, when waste water containing oil flows into the oil / water separation tank 101 through the introduction pipe 102, the mud, dust and other foreign matters contained in the waste water are precipitated, and the foreign matters are separated from the partition plate 105. The waste water containing oil does not flow down to the downstream side, and flows downstream through the communication hole 109, and because of the difference in specific gravity between the oil and water, the oil with light specific gravity rises upward and has a high specific gravity. The water sinks downward, and most of the oil is blocked by the partition plate 106 and accumulates on the upstream side of the partition plate 106, and the wastewater flows down through the communication hole 110 formed in the lower part of the partition wall, and passes through the discharge pipe 103. By repeating the process released to the outside, water and oil can be separated from the oil-containing wastewater. (See Patent Document 1).

However, in the processing apparatus using the specific gravity separation method described above, in order to separate the water and oil in the oil-containing wastewater, the residence time in the oil / water separation tank 101 is lengthened to promote the difference in specific gravity between water and oil. For this purpose, there is a problem that the processing apparatus must be enlarged. There is also a problem that separation is insufficient in a short time.

As an example of the flotation separation method, a flotation separation method represented by a pressure flotation separation method comprising a flotation separation tank, a pressure pump, and a treatment liquid circulation system for pressure-dissolving air in the treatment liquid and its There is a treatment equipment for oil-containing wastewater by the equipment. In FIG. 9, the oil-water separator using the conventional pressurized flotation separation method includes a nozzle 201 in which a treatment tank 209 supplies a liquid to be treated mixed with air, and a large bubble removal unit 202 that removes insoluble air. A large bubble discharge pipe 203 for flowing a branch flow of the liquid to be treated, which is provided on the upper side in the vicinity of the outlet of the large bubble removing unit 202 and mixed with air, and

liquid level detectors

204 and 205 are provided to separate the water to be treated. Separating section 206, floating oil receiver 207, and shielding plate 208 that separates separating section 206 and floating oil receiver 207. The processing tank 209 is connected to the lower part of the processing tank 209. The circulation pipe 210 and the discharge pipe 212 to which the discharge control valve 211 branched in the middle of the circulation pipe 210 is connected, and the liquid supply pipe 214 to be processed to which the liquid control valve 213 for controlling the liquid supply amount is connected. When, An air introduction pipe 216 to the air flow control valve 215 is connected for controlling the flow rate of air, a pump 217, a processor of oil-containing waste water and pressurized feed pipe 218 is closed to connect.

With the configuration described above, the gas-liquid mixed fluid of the liquid to be processed and air pressurized to 0.3 to 0.8 MPa by the pump 217 is introduced into the treatment tank 209 through the nozzle 201. The oil bubbles contained in the liquid to be treated are connected to each other, and the oil component is floated and concentrated on the upper part of the treatment tank 209. Water and oil could be separated from each other. (See Patent Document 2).

Further, as shown in FIG. 10, in the conventional method for treating oil-containing wastewater, a suspended substance (hereinafter referred to as SS) or oil that has been agglomerated in the flotation separation process after acting a flocculant on the wastewater. In some cases, oil was removed from the wastewater.

JP 2004-321916 A JP 2003-154205 A

However, in the processing apparatus using the pressure levitation separation method described above, there is a problem that as the oil content in the wastewater becomes smaller, it becomes difficult to adhere to fine bubbles and it becomes difficult to float and concentrate on the upper part of the processing apparatus. Even if the oil content in the wastewater is small, it is thought that if the oil content is increased using a flocculant, it will be easier to adhere to fine bubbles, but as in the conventional method for treating oil-containing wastewater, When the flocculant is allowed to act on the wastewater, the SS and oil components that have been agglomerated in the flotation separation step are floated and separated, and the oil content is removed from the wastewater. However, since the flocculant acts, there is a problem that a large amount of the flocculant must be used until the desired oil removal performance is obtained.

The present invention has been made in view of the problems of the prior art as described above, and the treatment of oil-containing wastewater that has made it possible to reduce the amount of coagulant used compared to the conventional treatment using flotation separation. It is an object to provide a method and a processing apparatus.

The configuration of the oil-containing wastewater treatment method and treatment apparatus in the present invention for solving the above problems will be described with reference to FIG. 1. The first aspect of the present invention is to treat the wastewater containing oil in the wastewater. A step of removing the oil from the wastewater by adding the suspended material and then removing the suspended material from the wastewater; or, in the method of treating wastewater containing oil, the wastewater is suspended beforehand. The method includes the step of removing the oil from the wastewater by removing the suspended solid from the wastewater, and includes the following configuration as a preferred embodiment.

The suspended substance is a substance having a hydrophobic interaction with the oil in the wastewater.

The median diameter of the particles in the suspended substance is larger than 5 μm and has a particle size distribution smaller than 2 mm.

The wastewater treatment method includes a pretreatment step, a flotation separation step, a flocculant addition step, and a biological treatment step, and after removing oil in the wastewater by a suspended substance in the flotation separation step, To make the flocculant act on the treated water obtained in the floating separation process.

The flotation separation process is any one of pressurized flotation separation, normal pressure flotation separation, and foam separation.

A separation tank in the levitation separation step for at least one of the fine bubbles generated by using the means for shearing the bubbles generated by the means for generating only the bubbles and the fine bubbles generated from the means for shearing the bubbles themselves Supply into the oil-containing wastewater inside and separate with foam.

The second aspect of the present invention generates only bubbles provided in a separation tank of an oil separation wastewater treatment device including at least a pretreatment device, a flotation separation device, a flocculant addition device, and a biological treatment device. A device for shearing the bubbles and / or generating fine bubbles is disposed above the device to be generated, and includes the following configuration as a preferred embodiment.

The device that generates only the bubbles is a diffuser plate, and the device that shears the bubbles and / or generates fine bubbles is a self-contained fine bubble generator.

Since the method and apparatus for treating oil-containing wastewater according to the present invention have the above-described configuration, the following excellent effects can be obtained.
(1) Since the oil contained in the wastewater can be efficiently removed, the oil concentration in the treated water can be reduced to about ¼ compared to the case where the flocculant is previously applied to perform the floating separation step.
(2) Since the oil content contained in the wastewater can be efficiently removed, the amount of the flocculant used can be reduced to about 1/3 compared to the case where the flocculant is preliminarily acted on and the floating separation step is performed.
(3) Since the amount of air supplied into the foam separation tank can be increased and the bubble diameter can be made fine, and a large amount of fine bubbles can be generated in the foam separation tank, it is possible to efficiently produce oil-containing wastewater. Oil can be removed.
(4) The treatment facility can be set compactly, operation management is easy, and a certain treated water quality can be obtained.

It is a processing flow of the oil content wastewater which this invention intends. It is the cross-sectional schematic diagram which showed an example of the floating separation apparatus used for the foam separation process in this invention. It is the graph which showed transition of the particle size distribution in the oil concentration of the to-be-processed water for every processing time in Example 1 of this invention. It is the graph which showed transition of the particle size distribution in SS of to-be-processed water for every processing time in Example 1 of the present invention. It is the graph which showed transition of the oil content density | concentration of the to-be-processed water for every process time in Example 1 and Comparative Example 1 of this invention. It is the graph which showed transition of SS for to-be-processed water for every processing time in Example 1 and comparative example 1 of the present invention. It is a top view which shows the outline | summary of the example of a processing apparatus of the oil containing wastewater using the conventional specific gravity separation method. FIG. 8 is a cross-sectional view taken along the line AA in FIG. It is a cross-sectional schematic diagram which shows the outline | summary of the example of a processing apparatus of the oil-containing wastewater using the conventional pressurization flotation separation method. It is a processing flow of the oil containing wastewater which the prior art intends.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Separation tank 2 Inlet 3 Foam separation water outlet 4 Outlet 5 Shield plate 6 Self-contained fine bubble generator 7 Air diffuser plate 8 Intake port 9 Intake port 10 Blower 11 Bubble 12 Fine bubble 13 Foam

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 6, but it goes without saying that the present invention is not limited to the embodiments. FIG. 1 is a treatment flow of oil-containing wastewater intended by the present invention. FIG. 2 is a schematic cross-sectional view of an example of a flotation separation apparatus used for foam separation processing in the present invention. FIG. 3 is a graph showing the transition of the particle size distribution in the oil concentration of the water to be treated for each treatment time in Example 1 of the present invention. FIG. 4 is a graph showing the transition of the particle size distribution in the SS of the water to be treated for each treatment time in Example 1 of the present invention. FIG. 5 is a graph showing changes in the oil concentration of the water to be treated for each treatment time in Example 1 and Comparative Example 1 of the present invention. FIG. 6 is a graph showing the transition of SS of the water to be treated for each treatment time in Example 1 and Comparative Example 1 of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 6. In the method for treating oil-containing wastewater according to the present invention, the waste water contains a suspended substance capable of trapping or adsorbing the oil in the waste water or the treated water in which the suspended substance is mixed in advance. After the suspended substance that has been captured or adsorbed is removed in the floating separation step, the flocculant is allowed to act to remove the oil content of the wastewater.

When the flocculant is allowed to act at the beginning of the treatment process as in the conventional method for treating oil-containing wastewater, the flocculant is consumed even for SS and oil that can be floated and separated without acting the flocculant. The amount of agent added increases. In the present invention, it is possible to efficiently remove the oil even if the amount of the flocculant is suppressed by adding the flocculant after removing these SS and oil in advance by the floating separation step.

In the present invention, suspended substances are present in a series of treatment steps of the treatment method and treatment apparatus for oil-containing wastewater. This is necessary to capture or adsorb oil in the wastewater to the suspended matter before the flotation separation step. In addition, the capture or adsorption of the oil may be an effect due to the shape of the suspended substance, but is preferably an effect due to the material.

The suspended substance used in the treatment method and treatment apparatus for oil-containing wastewater preferably has a median particle diameter of more than 5 μm and less than 2 mm. The smaller the median diameter of the particles in the suspended substance, the larger the surface area of the particles. Therefore, the contact efficiency with the oil in the wastewater is improved, and the oil is easily captured or adsorbed. However, as a result of intensive studies by the present inventors, the median diameter of particles that can be floated and concentrated in the floating separation step is larger than 5 μm. Conversely, if the median diameter of the particles in the suspended substance becomes too large, it will be difficult to float in the floating separation step, and the surface area of the particles will be small. For this reason, in order to prevent the phenomenon that contact efficiency with the oil component in wastewater falls and it becomes difficult to capture or adsorb the oil component, it is preferably smaller than 2 mm. Furthermore, it is a premise that the suspended substance in the present invention is removed from the treated water in the treatment process, but if it remains in the treated water, it may be measured as a suspended substance in the water quality analysis. is there. Suspended substances in water quality analysis are premised on removing large suspended substances with a sieve having a pore diameter of 2 mm in advance for measurement, so even if suspended substances of 2 mm or more are mixed, there is a possibility that they will not be reflected in water quality analysis. . Accordingly, if the median diameter of the suspended substance particles is smaller than 2 mm, it can be accurately determined whether or not it remains in the water to be treated, so that the validity of the technology can be accurately determined.

The median diameter is a particle diameter corresponding to a cumulative 50% in the particle diameter distribution. In general biological treatment, the median diameter of oil particles is preferably 1 to 100 μm, but the smaller the median diameter in this range, the better.

The flocculant in the present invention is an inorganic flocculant such as sulfate band, polyaluminum chloride, ferric sulfate, ferric chloride, and a polymer flocculant such as polyacrylamide, dimethylaminoethyl acrylate, or chitosan.

In addition, as the flocculant, an inorganic flocculant or a polymer flocculant may be used alone, but it is preferable that the flocculant is agglomerated with an inorganic flocculant in advance, and then the polymer flocculant is added for aggregation. It is preferable to coagulate with an inorganic coagulant and then use a polymer coagulant together to increase the coagulation floc and strengthen the coagulation floc and facilitate solid-liquid separation.

In the present invention, the flotation separation step used in the treatment method and treatment apparatus for oil-containing wastewater may be any of pressure flotation separation, normal pressure flotation separation, and foam separation, but is preferably foam separation. Pressure flotation separation and atmospheric pressure flotation separation require the power of a scraper or the like to scrape the floss that has floated, but usually the wastewater contains detergents, proteins, or other surface-active substances. In addition, the foam separation is preferable because the floss floated by foaming the water to be treated is spontaneously discharged out of the system as the foam separation water, and no separate power is required.

In the present invention, the air supplied to the foam separation tank is preferably fine bubbles. If the air volume is the same, the finer the bubble diameter, the larger the number of bubbles, and the easier it is to diffuse and disperse in the foam separation tank. This is preferable because the amount of oil in the wastewater can be efficiently separated and discharged.

In the present invention, the fine bubble is generated by generating a bubble by a device that generates only the bubble and then shearing the bubble by a device that shears the bubble and / or generated from the device itself that shears the bubble. It is preferable to do. This is because a device that generates only bubbles is provided below the device that generates fine bubbles, and the bubbles generated from the device that generates only bubbles rise to the position of the device that generates the fine bubbles and are fine with respect to the bubbles. A water flow containing fine bubbles is generated by a device that generates a water flow containing bubbles, and the bubbles are sheared and supplied by the water flow containing the fine bubbles, thereby increasing the amount of air supplied into the foam separation tank and the bubbles. It is preferable because the diameter can be reduced and a large amount of fine bubbles can be generated in the foam separation tank.

In the present invention, the device that generates only bubbles is preferably a diffuser plate. This is preferable because it has a simpler structure and is easier to handle than other bubble generating devices.

The apparatus used for the foam separation process of the present invention will be described with reference to FIG. The separation tank 1 has two parts: a part that preferentially covers the amount of air for generating fine bubbles to be supplied into the apparatus, and a part that preferentially refines the bubbles. The apparatus used for the foam separation process includes an inlet 2 through which the water to be treated flows into the side surface of the separation tank 1, an outlet 3 through which the foam separation water is discharged at the top of the separation tank 1, and a treated water at the bottom of the separation tank 1. An outflow port 4 through which the treated water flows out is provided. The separation tank 1 is provided with three stages of shade-shaped shielding plates 5 having an inclined part that penetrates the center and decreases in diameter toward the upper part from the middle part to the upper part in the tank. Further, a self-contained fine bubble generating device 6 is provided at a position slightly below the intermediate portion in the separation tank 1, and diffuses at a position below the self-contained fine bubble generating apparatus 6 and not reaching the bottom of the separation tank 1. A plate 7 is provided. The self-contained microbubble generator 6 communicates with an intake port 8 that communicates with external air, and the diffuser plate 7 communicates with an intake port 9 that communicates with a blower 10.

Next, the operation of the embodiment of the present invention will be described. After adding suspended substances that can capture or adsorb oil in wastewater to oil-containing wastewater that has undergone a pretreatment process such as a screen or a sand settling tank, suspended substances that have captured or adsorbed oil in the wastewater are floated and separated By removing, oil is removed from the wastewater. If suspended substances are mixed in the oil-containing wastewater in advance, there is no need to add new suspended substances, and the suspended substances that are trapped or adsorbed by the oil in the wastewater are removed as they are in the floating separation process. Thus, oil is removed from the waste water. The inorganic water and / or polymer flocculant is added to the water to be treated after the flotation separation process to remove the SS and oil from the water to be treated by coagulation and precipitation, and the supernatant water is transferred to the post-treatment process. .

In addition, the suspended substance in the embodiment of the present invention is a substance having affinity for oil in any shape or material, and a substance capable of capturing or adsorbing oil in wastewater. Any substance having a hydrophobic interaction with oil may be used, and a fibrous substance is particularly preferable. Pile yarns used for cleaning mops and the like are preferred. Examples of the material include cotton, polyamide, polyester, rayon, acrylic, and vinylon. Among polyamides, nylon is particularly preferable. The shape of the yarn may be either a span type or a filament type. The strength of the yarn is not particularly limited. The suspended substance is preferably in the form of a porous material such as a sponge or a mesh.

In addition, it is preferable that the amount of the suspended substance added to the waste water is added so that the concentration of the suspended substance is 700 mg / L or more and 10,000 mg / L or less. If the oil-containing wastewater does not contain sufficient suspended substances, it is necessary to add a suspended substance that can capture or adsorb the oil in the wastewater until the above concentration is satisfied. In addition, if the concentration of the suspended substance is too high, the suspended substance removed in the treatment process increases and the amount of waste increases, so the concentration of the suspended substance is preferably 10,000 mg / L or less.

Next, in the present invention, an oil content removal test was performed using the above-described embodiment. The measurement method of the test is shown below.
(1) Measurement of particle size distribution The particle size distribution is measured using a combination of a He-Ne laser and a W lamp as the light source, and a laser diffraction / scattering particle size distribution measuring apparatus LA-500 (manufactured by Horiba) based on the Mie scattering theory. It was performed using.
(2) Measurement of Oil Concentration The oil concentration was measured using an oil concentration meter OCMA-305 (Horiba Seisakusho) based on the non-dispersive infrared absorption method based on extraction of H-997 solvent (Horiba Seisakusho). .
(3) Measurement of SS The measurement of SS was performed using a glass fiber filter paper (GF / B manufactured by Whatman) by a method based on JISK010214.

In the present invention, the oil removal test of the oil-containing wastewater is tested for each of Example 1 and Comparative Example 1, and the factory wastewater from the cleaning industry is used as the oil-containing wastewater, and the foam separation device, the coagulation tank, and the coagulation sedimentation tank are installed in the processing equipment. Used, the oil content concentration and SS of the treated water after foam separation treatment time and coagulation sedimentation were measured. The particle size distribution was measured in the water to be treated for each foam separation treatment time. In addition, the factory wastewater from the cleaning industry used for the test contained suspended substances that can capture or adsorb oil in the wastewater, so it is necessary to separately add suspended substances that can capture or adsorb oil in the wastewater. There wasn't. The suspended substance contained in the oil-containing waste water used in Example 1 and Comparative Example 1 is a pile thread made of nylon or cotton used for a cleaning mop, and the concentration of the suspended substance is 2630-3650 mg / L. It was. The test results are shown in FIGS.

[Example 1]
As an oil removal test for oil-containing wastewater, a coagulant was allowed to act on the water to be treated obtained in the flotation separation process by foam separation to obtain treated water after coagulation precipitation.

[Comparative Example 1]
As an oil removal test for oil-containing wastewater, after allowing a flocculant to act, treated water was obtained through a flotation separation process by foam separation.

(Oil content removal test conditions for oil-containing wastewater)
・ Processing time for foam separation: 60 (minutes)
・ Coagulant used: Sulfuric acid band (Kurosaki Chemical Co., Ltd.)
Anionic polymer flocculant A-120 (manufactured by Ebara Engineering Service)
-Addition amount of sulfuric acid band: 400 (mg / L) with respect to the amount of wastewater containing oil
-Addition amount of polymer flocculant: 0.8 (% by weight) with respect to the amount of wastewater containing oil
・ Sulfate band aggregation condition: 150 (rpm) 2 minutes → 40 (rpm) 2 minutes ・ Polymer flocculant aggregation condition: after sulfate band aggregation condition, 150 (rpm) 2 minutes ・ Precipitation time after aggregation: 5 (minutes)
-Effective capacity of foam separator: 4 (L)

FIG. 3 is a graph showing the oil concentration for each particle size by measuring the particle size distribution of the water to be treated for each foam separation treatment time, integrating the oil concentration with the frequency of each particle size in each treated water. . The median diameter in the oil-containing wastewater at the start of the test was 27 μm, and the oil concentration at the particle diameter was 282 mg / L. By performing foam separation for 60 minutes, the median diameter was 5 μm, and the oil concentration at the particle diameter was It became 48 mg / L, and the median diameter and the oil concentration at the particle diameter decreased with each treatment time. Further, the median diameter in the oil concentration was less likely to decrease when the treatment time exceeded 10 minutes, and the median diameter did not decrease from 5 μm even after 40 minutes.

FIG. 4 is a graph showing the SS for each particle diameter by measuring the particle size distribution of the water to be treated for each foam separation treatment time, integrating SS with the frequency of each particle diameter in each water to be treated. The median diameter in the oil-containing wastewater at the start of the test was 27 μm, and the SS in the particle diameter was 213 mg / L. By performing foam separation for 60 minutes, the median diameter was 5 μm, and the SS in the particle diameter was 48 mg / L. L, and the median diameter and SS at the particle diameter decreased at each treatment time. Further, the median diameter in SS showed a small decreasing tendency when the treatment time exceeded 10 minutes, and the median diameter did not decrease from 5 μm even after 40 minutes or longer.

FIG. 5 is a graph showing changes in the oil concentration for each processing step of Example 1 and Comparative Example 1. In Example 1, the oil concentration decreased from 3440 mg / L to 885 mg / L by performing the foam separation treatment for 20 minutes, but the oil concentration decreased only slightly to 630 mg / L even when the treatment was further performed up to 60 minutes. There wasn't. However, when the flocculant was allowed to act thereafter, the oil concentration was reduced to 97 mg / L, indicating excellent oil removal performance. On the other hand, in Comparative Example 1, the oil concentration was slightly decreased from 2820 mg / L to 2470 mg / L by the action of a flocculant, but then the foam concentration was 2470 mg by performing foam separation treatment for 20 minutes. / L to 420 mg / L. However, even when the treatment was further continued for 60 minutes, the oil concentration was reduced only to 410 mg / L. Therefore, it can be seen that Example 1 has about four times as much oil removal performance as Comparative Example 1.

FIG. 6 is a graph showing the transition of SS for each processing step of Example 1 and Comparative Example 1. In Example 1, although the SS was reduced from 2630 mg / L to 937 mg / L by performing the foam separation treatment for 20 minutes, the SS was not significantly reduced to 637 mg / L even when the treatment was further performed for 60 minutes. It was. However, SS was reduced to 277 mg / L by applying a flocculant thereafter, and excellent SS removal performance was exhibited. On the other hand, in Comparative Example 1, the SS increased from 3650 mg / L to 10600 mg / L by the action of the flocculant. This is because the SS is enlarged due to the action of the flocculant, and many flocs are mixed in the SS measurement. Then, SS was reduced from 10600 mg / L to 570 mg / L by performing the foam separation treatment for 20 minutes. However, even when the treatment was further continued for 60 minutes, the SS decreased only to 470 mg / L. Therefore, it was confirmed that Example 1 had about twice the SS removal performance as compared with Comparative Example 1.

From the above, in this embodiment, the suspended matter capable of capturing or adsorbing oil in the wastewater is added, or the oil in the wastewater is captured or adsorbed with respect to the water to be treated in which suspended substances are mixed in advance. After removing suspended solids in the flotation separation step, if the step of removing the oil content of the wastewater by using a flocculant is used, the oil removal performance is about 4 times that of the conventional treatment method, and the SS removal performance. Can be improved about twice. Furthermore, by performing a flotation separation process before the flocculant acts on the oil-containing wastewater, it is possible to prevent polluted substances and suspended substances that can be sufficiently separated by flotation without aggregating with the flocculant, and oil adhering to the suspended substances. Therefore, the amount of the flocculant used can be reduced to about 1/3 as compared with the conventional flotation separation process.

Claims

A method for treating wastewater containing oil, comprising the steps of removing the oil from the wastewater by adding a suspended material to the wastewater and then removing the suspended material from the wastewater. Treatment method of contained wastewater.
In a method for treating wastewater containing oil, the wastewater contains a suspended substance in advance, and has a step of removing the suspended matter from the wastewater to remove the oil from the wastewater. Wastewater treatment method.
The method for treating oil-containing wastewater according to claim 1 or 2, wherein the suspended substance is a substance having a hydrophobic interaction with the oil in the wastewater.
The method for treating oil-containing wastewater according to any one of claims 1 to 3, wherein the median diameter of the particles in the suspended substance is larger than 5 µm and has a particle size distribution smaller than 2 mm.
The wastewater treatment method includes a pretreatment step, a flotation separation step, a flocculant addition step, and a biological treatment step, and after the oil in the wastewater is removed by a suspended substance in the flotation separation step, the flotation step The method for treating oil-containing wastewater according to claim 1, wherein a flocculant is allowed to act on the treated water obtained in the separation step.
The method for treating oil-containing wastewater according to claim 5, wherein the flotation separation step is one of pressurized flotation separation, normal pressure flotation separation, and foam separation.
A separation tank in the levitation separation step for at least one of the fine bubbles generated by using the means for shearing the bubbles generated by the means for generating only the bubbles and the fine bubbles generated from the means for shearing the bubbles themselves The method for treating oil-containing wastewater according to claim 6, wherein the oil-containing wastewater is supplied into the oil-containing wastewater to separate the foam.
In an oil-containing wastewater treatment device including at least a pretreatment device, a flotation separation device, a flocculant addition device, and a biological treatment device, above the device that generates only bubbles provided in the separation tank of the flotation separation device, An apparatus for shearing air bubbles and / or generating fine air bubbles is provided.
9. The apparatus for treating oil-containing wastewater according to claim 8, wherein the device that generates only bubbles is a diffuser plate, and the device that shears the bubbles and / or generates fine bubbles is a self-contained fine bubble generator.