JPH0780443A - Treatment of oil-containing waste water - Google Patents

Abstract

PURPOSE:To remove an oil component simply, inexpensively and efficiently by a method wherein oil-containing waste water and a silica flocculation liq. are mixed to form a precipitate which is, in turn, grown into a floc state and air bubbles are bonded to flocs to float the flocs under normal pressure to perform solid-liquid separation. CONSTITUTION:At the time of treatment, at first, the oil-containing waste water in a drain pit 1 is sent to a precipitate growing tank 6 by a pump 2 through an inflow pipe 201 equipped with a flowmeter 202 while the silica flocculation liq. in a tank 4 is sent to a mixing part 3 through an inflow pipe 201 by a pump 5. Next, the resulting mixture is introduced into the precipitate growing tank 6 equipped with a stirrer 7 and a precipitate is formed to be grown into flocs. If necessary, the mixture is introduced into a precipitate gathering tank 8 equipped with a stirrer 9 to grow flocs. Continuously, a precipitate growing soln. is introduced into a floating separation tank 10 equipped with a hollow fiber device 11 and fine air bubbles are bonded to flocs to float the flocs under normal pressure to perform solid-liquid separation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating oil-containing wastewater, and more specifically, an oil for adsorbing and aggregating the oil contained in the wastewater using a silica-based coagulating liquid and floating the oil at atmospheric pressure to remove the oil. The present invention relates to a method for treating contained wastewater.

[0002]

BACKGROUND OF THE INVENTION Conventionally, a pressurized flotation treatment method has been generally used as a means for removing oil contained in waste water. In this conventional method, while adjusting the pH of waste water containing oil, an Al-based or Fe-based coagulating liquid is added and mixed, and then the precipitation generation time is maintained to form a precipitate (floc). Next, a polymer flocculant is added to maintain the time required for increasing the size of flocs. Then, slow agitation is carried out to complete agglomeration, and this is introduced into a flotation separation tank and subjected to pressure flotation treatment in the flotation separation tank for solid-liquid separation into flocs and water.

In such a pressure flotation treatment, air is mixed under pressure with pressure water using the liquid in the flotation tank as a driving force to dissolve the air, and the air is jetted into the flotation tank to reduce the pressure. Generates fine bubbles and raises the flocs,
Since flocs and water are separated, a pressure pump and pipes are needed to use the liquid in the flotation tank as a driving force, and a pressure tank for dissolving air in water under pressure is required. It becomes necessary and there is a problem that equipment cost and electric power cost rise. Further, there is a problem that the treatment process is complicated and diversified.

Therefore, as a means for solving such a drawback, atmospheric pressure levitation treatment using an Al-based or Fe-based flocculating liquid has been proposed. That is, as an example of the conventionally known atmospheric pressure flotation treatment, in the flotation tank, a hollow fiber having fine pores on the surface is arranged, and air is fed into the hollow fiber to directly blow fine bubbles into water. A method is known in which a precipitate is fed, the precipitate is floated under normal pressure, and solid-liquid separation is performed.

According to this method, it is possible to eliminate the need for a pressurizing pump, piping or the like or a pressurizing tank in the pressurization floating process, and it is possible to reduce the equipment cost and the electric power cost. However, Al-based and F used in conventional atmospheric levitation treatment
The e-based coagulating liquid adsorbs oil, oil emulsion, etc.,
Since the function of agglomerating is extremely weak, when actually used, a large amount of Al-based or Fe-based aggregating liquid is used to form a large amount of aluminum hydroxide or iron hydroxide precipitates (addition of alkali), Oil is physically trapped in these precipitates, and a polymer flocculant is further administered to increase the floc shape.

Therefore, a large amount of sludge is generated due to the coagulant that has been administered, and there is a problem that the treatment cost must be borne. Further, some of the Al ions and Fe ions and some of the polymer coagulant remain in the water, and there is concern about the effect on the environment.

As a result of actually using an Al-based or Fe-based flocculating liquid during the atmospheric pressure floating treatment, it was found that the oil removal efficiency was extremely low.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to reduce the equipment cost and the electric power cost by a simple treatment process and compact equipment, and without generating a large amount of sludge. An object of the present invention is to provide a method for treating oil-containing wastewater that is environmentally friendly and has a high oil removal efficiency.

[0009]

The inventor of the present invention has come to the present invention as a result of extensive studies to solve the above problems.

That is, in the method for treating oil-containing wastewater according to the present invention, wastewater containing oil is introduced into the mixing section, and the composite crystalline mineral / amorphous mineral of silica is dissolved in the mixing section with a reducing acid or a neutral acid. The silica-based flocculent solution obtained in this way is mixed and stirred, and then the mixture is introduced into a precipitation growth tank to form a precipitate in the precipitation growth tank to grow into a floc, and if necessary, the floc is enlarged, and then the precipitation is increased. The growth liquid is guided to the flotation separation tank, and in the flotation separation tank, fine bubbles are directly discharged from the lower portion of the flotation separation tank to attach the bubbles to the flocs to float the flocs under normal pressure for solid-liquid separation. To do.

In a preferred embodiment of the present invention, at least one hollow fiber device having hollow fibers having fine pores on its surface is installed in the floating separation tank, and air is fed into the hollow fibers. Sending fine bubbles directly into the water through the holes,
It is to float flocs under normal pressure and separate them into solid and liquid.

The present invention will be described in detail below.

The silica-based aggregation liquid used in the present invention is obtained by dissolving the silica-based aggregation liquid raw material in a reducing acid or a neutral acid, preferably dilute sulfuric acid. Alternatively, the precipitate may be filtered after dissolution. When dilute sulfuric acid is used, the precipitate is mainly composed of CaSO ₄ .2H ₂ O.

As the silica-based flocculant raw material, silica composite crystalline minerals / amorphous minerals such as natural cristobalite,
While minerals of SiO ₂ containing 15 to 95 wt%, such as blast furnace slag is used, preferably 15 to SiO ₂
It is a blast furnace slag containing 50% by weight.

The silica-based coagulating liquid raw material is used by pulverizing or pulverizing a silica composite crystalline mineral / amorphous mineral, and optionally oxidizing a sulfur content or blending activated carbon, and after pulverizing or pulverizing The particle size is preferably 5 mm or less, 4 mm
The following is more preferable, and in order to further increase the dissolution rate in dilute sulfuric acid, fine powder of 150 mesh or less is preferable.

Next, an example of the method for treating oil-containing wastewater according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a flow chart showing an example of a method for treating oil-containing wastewater according to the present invention.

In FIG. 1, 1 is a drainage pit for storing oil-containing drainage, and 2 is a drainage pump. Reference numeral 3 is a mixing section for mixing the waste water and the silica-based coagulating liquid, for example, a static mixer or a high speed stirrer (150 rpm to 250 rp).
m) is used.

Reference numeral 4 denotes a silica-based coagulation liquid tank for storing a silica-based coagulation liquid obtained by dissolving the silica-based coagulation liquid raw material with dilute sulfuric acid, and 5 denotes a silica-based coagulation liquid pump. To add the silica-based coagulating liquid, it is preferable to add it to the inflow pipe 201 in front of the mixing section 3, but it is also possible to add it directly to the mixing section 3.

Reference numeral 6 is a precipitation growth tank for forming flocs to grow a precipitate, 7 is a stirrer, 8 is a precipitation collecting tank for enlarging the flocs as necessary, 9 is a stirrer, and 10 is a floater. A separation tank, 11 is a hollow fiber device provided in the floating separation tank. 12 is an air supply means, 1
3 is a treated water discharge line, and 14 is a sludge discharge line.

In order to treat the oil-containing wastewater using each of the above equipment, first, the oil-containing wastewater stored in the drainage pit 1 is quantitatively transferred to the precipitation growth tank 6 using the drainage pump 2 through the inflow pipe 201. send. Flow meter 20 for quantitative liquid transfer
2 may be monitored and manually adjusted, but it is also preferable to automatically adjust by opening and closing a control valve (not shown) that works in conjunction with the flow meter 202.

On the other hand, an appropriate amount of the silica-based coagulation liquid is injected from the silica-based coagulation liquid tank 4 into the inflow pipe 201 by using the silica-based coagulation liquid pump 5 according to the flow rate of waste water and the oil content. After the silica-based coagulating liquid is injected into the inflow pipe 201, the mixing unit 3
Mixed in. The mixing section 3 may be a simple pipe, but it is also preferable to use a static mixer.
Alternatively, a high-speed stirring tank may be installed to replace it. In the following description, the case where a static mixer is used will be mainly described.

If the static mixer 3 is used, the wastewater and the silica-based coagulating liquid can be immediately and efficiently mixed, and especially when a small amount of the silica-based coagulating liquid is added to a large amount of the wastewater, the static mixer 3 is used. Is preferably used. That is, when a small amount of silica-based coagulation liquid is added to a large amount of wastewater, OH ^- and metal ions in the wastewater react with the monomer silica in the coagulation liquid, and due to pH fluctuations, sufficient diffusion occurs. This is because gelation of silica may proceed while the oil content in the waste water is not adsorbed by the monomer silica, and the oil content removal effect may not be sufficiently achieved. Therefore, it is not necessary to use the special static mixer 3 when there is no such an adverse effect.

Next, the mixed solution is rapidly stirred by the stirrer 7 in the precipitation growth tank 6. The rotation speed of the stirrer is preferably 100 to 200 rpm. The residence time in the precipitation growth tank 6 is preferably in the range of 30 to 150 seconds. Precipitation is sufficiently generated in the precipitation growth tank 6 by continuing stirring.

If a larger floc is required,
Alternatively, the oil concentration in the waste water may be high, or flocs may be difficult to be formed depending on the pH value of the precipitation growth solution. In that case, therefore, the precipitation collecting tank 8 is preferably provided. The settling tank 8 is slowly stirred by the stirrer 9, so that the flocs can be increased in size. The rotation speed of the stirrer is preferably 30 to 80 rpm. The residence time in the precipitation growth tank 6 is preferably in the range of 30 to 150 seconds.

Next, the particles are introduced into the flotation / separation tank 10 for levitating the aggregates under normal pressure. As the hollow fiber device 11 provided in the floating separation tank 10, for example, the hollow fiber device 11 having the configuration shown in FIG. 2 is used.

That is, in FIG. 2, reference numeral 110 denotes an air introducing pipe, and one end of a hollow fiber 111 having a plurality of through holes is fixed to the air introducing pipe 110 so as to allow air to pass therethrough. It is fixed in a spiral shape around the air introduction pipe 110 with one end as a base point through a partition member 112.
The partition member 112 is radially formed around the air introducing pipe 110, and by providing a fixing groove for fixing the hollow fiber 111 to the partition member 112, one hollow fiber 111 is attached to the air introducing pipe 110. You can wind it regularly when you wind it around. It is also preferable to fix the hollow fiber 111 in the fixing groove by a method such as welding after it is wound.

Reference numeral 113 is a cylindrical body having openings at both ends, and is fixed to the partition member 112 at both ends. The cylindrical body 113 is made of transparent resin in this embodiment, but is not particularly limited. Reference numeral 114 is a support member provided on the outer periphery of the air introduction pipe 110, and also has a function of fixing the partition member 112.

In this way, the one-stage module 115 which is an element for constructing the hollow fiber device 11 is formed. A plurality of such module stages can be connected to form a hollow fiber module (for example, 20 stages as one module). Therefore, when the required supply amount of air is small, the number of stages may be reduced, and when the required supply amount is large, the number of stages may be increased.

The method for forming the hollow fiber device 11 is not limited to the above-described embodiment, and for example, a plurality of stages of modules may be integrally formed without forming each stage.

The hollow fiber device 11 having the above structure is arranged in the floating separation tank 10 with the Y direction facing the liquid surface. Therefore, when air is sent to the hollow fiber device 11, fine bubbles are released from the Y direction.

In the present invention, it is preferable that the hollow fiber device is provided with a draft for causing water circulation in the tank below the separation tank. Further, a large number of hollow fiber devices 11 can be provided to send fine air to the entire surface of the flotation / separation tank 10.
The arrangement and the number can be changed appropriately.

When air is fed from the air supply means 12, for example, a compressor to the hollow fiber device 11, fine air bubbles are generated in the flotation / separation tank 10, and the air bubbles adhere to the flocs to increase the buoyancy and float.

Since some of the flocs settle in the flotation / separation tank 10 and do not come into contact with air bubbles, it is also preferable to provide a means in the flotation / separation tank 10 for floating the sedimented flocs.

In the present invention, the compressed air is supplied from the compressor used as the air supply means 12, but when fine air bubbles are generated in the floating separation tank 10, they are not in a pressurized state due to pressure loss. Atmospheric levitation,
Further, since it is not configured to discharge the pressurized water into the flotation separation tank 10 by using the treated water as driving water, it is distinguished from the pressurized flotation described later.

The floated flocs become sludge, which is discharged by a sludge scraper (not shown) and discharged to the outside of the system through a sludge discharge line 14. The treated water is discharged from the middle part of the floating separation tank 10 through a treated water discharge line 13.

When the treated water is used as intermediate water,
Sterilization by ultraviolet sterilization, bactericide administration, ozone sterilization, etc. is preferred. It is also preferable to adjust the pH of the treated water.

[0038]

EXAMPLES The present invention will now be described in more detail based on the examples of the present invention, but the present invention is not limited to the examples.

Example 1 (Production of Silica-based Aggregate) Blast furnace slag (Ca basicity 1.
15, powder particle size 150 mesh or less) 42.5 g 1N
It was dissolved with 1 liter of (1 normal) dilute sulfuric acid to prepare a silica-based aggregating solution (SiO ₂ concentration of about 12000 ppm). The required amount was created in this way.

(Explanation of Apparatus Used) Using the apparatus shown in FIG. 1, oil-containing kitchen wastewater treatment was performed.

The amount of waste water was set as shown in Table 1. Mixing part 3
A static mixer was used. Further, the silica-based coagulating liquid pump 5 has 0.5 to 5.0 m per 1 liter of waste water.
The one having the ability to supply 1 was used.

The effective volume of the precipitation growth tank 6 is 35 liters, the precipitation collecting tank is 100 liters, the agitator 7 has a rotation speed of 150 to 250 rpm, and the agitator 9 has a rotation speed of 60 to 80 rpm. Using.

The floating separation tank had an effective capacity of 500 liters, and one hollow fiber device of 90φ × 20 stages per module was used.

(Example of treatment) Wastewater having the properties shown in Table 1 was treated, and the n-hexane extract substance (oil content) was measured based on JIS K 0102.

The processing results are as shown in Table 1.

Comparative Example 1 For comparison, the PAC aggregating liquid (polyaluminum chloride) was added in an amount shown in Table 1 in place of the silica-based aggregating liquid while adjusting the pH with a NaOH solution. Further, 5 ppm of a polymer flocculant was used. The treating apparatus was the same as that in Example 1, but necessary pH adjusting apparatus and the like were added.

The processing results are as shown in Table 1.

[0048]

[Table 1] As is clear from Table 1, according to the processing method of the present invention,
It can be seen that the oil is effectively treated.

Embodiment 2 Processing No. 1 of Embodiment 1 In 1-1, the same experiment was conducted by replacing the oil-containing kitchen drainage with the cutting oil-containing drainage containing the oil and the surfactant. The addition amount of the silica-based aggregation liquid was 20 ml / liter. The analysis is based on COD (chemical oxygen consumption) and N-hexane according to JIS K 01.
02. The results are shown in Table 2.

[0050]

[Table 2] Example 3 Process No. of Example 1 In 1-1, the same experiment was conducted by replacing the oil-containing kitchen drainage with the machining oil-containing drainage containing the oil and the surfactant. The addition amount of the silica-based aggregation liquid was 10 ml / liter. The analysis items were the same as in Example 2. The results are shown in Table 3.

[0051]

[Table 3] Example 4 Process No. of Example 1 In 1-1, the same experiment was performed by replacing the oil-containing kitchen wastewater with the heavy oil-containing wastewater containing the oil and the surfactant. The composition of the wastewater was as follows.

Seawater 1 liter Heavy oil 50 ml Surfactant 10 g / liter The addition amount of the silica-based coagulating liquid was 20 ml / liter.

As a result of the treatment, the N-hexane content was 20 ppm.

Embodiment 5 Processing No. 1 of Embodiment 1 In 1-1, the same experiment was conducted by replacing the oil-containing kitchen wastewater with the heavy oil emulsion. The properties of the wastewater were as follows.

Fresh water 1 liter Heavy oil emulsion 50 ml / liter The addition amount of the silica-based coagulating liquid was 5 ml / liter.

As a result of the treatment, N-hexane content was 18 ppm.

[0057]

As is apparent from the above description, according to the present invention, it is possible to reduce the facility cost and the power cost, generate a large amount of sludge, be environmentally friendly, and further reduce the oil content. It is possible to provide a method for treating oil-containing wastewater with high removal efficiency of oil.

The effective removal of oil according to the present invention is considered to be firstly due to the influence of the monomer-silica contained in the silica-based coagulating liquid. That is, the monomer / silica has a function of adsorbing and aggregating oil. This function is not found in Al-based, Fe-based, and polymer-based coagulants. These are the characteristics of the monomer / silica, that is, during the process of polymerization of the monomer / silica and gelation, micelles are rapidly formed with the oil in water, etc., and an interaction with inorganic ions occurs. Join together,
By accelerating the gelation reaction of silica.

Secondly, by combining the silica-based flocculating liquid having such an excellent flocculating function with the atmospheric pressure floating treatment, in particular, with the hollow fiber device, an unprecedented high-performance oil removal process can be realized. . That is, even if the conventional Al-based or Fe-based coagulant was combined with the atmospheric pressure floating treatment, the high-performance oil removal process was never realized.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of an oil-containing wastewater treatment method according to the present invention.

FIG. 2 is a perspective view of an essential part showing an example of a hollow fiber floating separation device.

[Explanation of symbols]

 1: Drainage pit 2: Drainage pump 3: Mixing part 4: Silica-based flocculating liquid tank 5: Silica-based flocculating liquid pump 6: Sedimentation growth tank 7: Stirrer 8: Sedimentation collecting tank 9: Stirrer 10: Floating separation tank 11 : Hollow fiber device 12: Air supply means 13: Treated water discharge line 14: Sludge discharge line

[Procedure amendment]

[Submission date] December 1, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

On the other hand, an appropriate amount of silica-based coagulation liquid is injected from the silica-based coagulation liquid tank 4 into the inflow pipe 201 by using the silica-based coagulation liquid pump 5 according to the flow rate of waste water and the oil content. After the silica-based coagulating liquid is injected into the inflow pipe 201, the mixing unit 3
Mixed in. The mixing section 3 may be a simple pipe, but a static mixer can also be used.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

If the static mixer is used, the wastewater and the silica-based coagulating liquid can be immediately and efficiently mixed, and it is particularly preferable when a small amount of the silica-based coagulating liquid is added to a large amount of the wastewater. That is, when a small amount of silica-based aggregation liquid is added to a large amount of wastewater, OH ⁻ or metal ions in the wastewater react with the monomer silica in the aggregation liquid,
This is because, due to the change in pH, gelation of silica may progress while the oil content in the wastewater is not sufficiently aggregated or adsorbed by the monomer silica, and the oil content removal effect may not be sufficiently achieved. Therefore, it is not necessary to use a special static mixer when there is no such a problem. Further, in the present invention, when a simple pipe is used in the mixing section 3 without using a static mixer, the silica-based aggregation liquid can be directly added to the aggregation growth tank 6. Therefore, in this case, the coagulation and growth tank 6 also functions as the mixing section 3. Further, when a static mixer is used for the mixing section 3, the coagulation and growth tank 6 may or may not be omitted.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

Next, when the precipitation-growing tank 6 is provided, it is rapidly stirred by the stirrer 7 in the precipitation-growing tank 6. The rotation speed of the stirrer is preferably 100 to 200 rpm. The residence time in the precipitation growth tank 6 is preferably in the range of 30 to 150 seconds. Precipitation is sufficiently generated in the precipitation growth tank 6 by continuing stirring.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction content]

The floating separation tank had an effective capacity of 500 liters, and three hollow fiber devices each having 90φ × 10 stages were used.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0048

[Correction method] Change

[Correction content]

[0048]

[Table 1] As is clear from Table 1, according to the processing method of the present invention,
It can be seen that the oil is effectively treated.

Claims (2)

[Claims] 1. A waste water containing oil is introduced into a mixing section, and a silica-based coagulating liquid obtained by dissolving a silica complex crystal mineral / amorphous mineral with a reducing acid or a neutral acid is mixed and stirred in the mixing section. Then, the mixture is introduced into a precipitation growth tank, and a precipitate is formed in the precipitation growth tank to grow into flocs, and if necessary, the flocs are enlarged, and then the precipitation growth solution is introduced into a flotation separation tank, and the flotation separation tank is introduced. 2. A method for treating oil-containing wastewater, characterized in that the fine bubbles are directly discharged from the lower part of the flotation / separation tank to adhere the bubbles to the flocs to float the flocs under normal pressure for solid-liquid separation. 2. At least one hollow fiber device containing a hollow fiber having fine pores on its surface is arranged in the flotation tank, and air is fed into the hollow fiber to directly generate fine bubbles from the fine pores in water. 2. The method for treating oil-containing wastewater according to claim 1, wherein the flocs are levitated under normal pressure and solid-liquid separated.