JPS5834191B2 - emulsion - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for treating emulsified oil-containing wastewater.

In recent years, wastewater discharged from various factories has polluted rivers and other areas, causing so-called pollution problems.

Among such wastewater, large amounts of oil-containing wastewater are generated in machinery factories such as metal processing factories, and in order to discharge it outside the factory, consideration must be given to avoid causing environmental pollution, and there are legal restrictions. Emission standards have been established and regulations have come into effect.

In such oil-containing wastewater, oil may be isolated on the surface as floating oil, but in many cases oil is dispersed in the wastewater in the form of an emulsion with or without floating oil.

Floating oil can be easily collected and removed by installing a partition wall against the flow of wastewater to stop the flow near the surface.
What is dispersed in wastewater in the form of an emulsion is
Since the amount of wastewater is large and the emulsion is not easily destroyed, it is difficult to remove it, and this wastewater causes pollution as contaminated water.

Conventionally, as a method of treating such emulsion-like oil-containing wastewater to separate water and oil, emulsion breaking with acid is carried out to float and separate some of the oil, and the remaining oil is then treated with general wastewater treatment, for example by adding a flocculant. The so-called flocculation-sedimentation method involves slow stirring, or the addition of a large amount of flocculant (for example,
A method is known in which oil is floated and separated using a flotation method.

However, in the former method, acid is added, which consumes the acid and requires countermeasures against corrosion caused by the acid, and in addition, it is necessary to neutralize it again, which is expensive.The latter method requires the addition of a large amount of flocculant. However, it has the disadvantage that the sludge volume is 30%, which places a large burden on sludge treatment.

In addition, oil-containing wastewater discharged from metal processing factories has a complex composition and is in the form of an emulsion containing unidentified surfactants or surfactants due to their origins, so it is impossible to completely break the emulsion. It has been industrially difficult to sufficiently remove oil using conventional coagulation-sedimentation methods and flotation methods.

An object of the present invention is to provide a method for treating emulsified oil-containing wastewater using a pressure flotation method that separates oil and dischargeable water without adding a special acid to break the emulsion. To provide a method for treating emulsion-like oil-containing wastewater that separates oil and dischargeable water, which requires only a small amount of addition, and to industrially process large amounts of emulsion-like oil-containing wastewater discharged from machine factories, etc. by the pressure flotation method. The objective is to provide a method for treating wastewater by separating oil and water, and preventing pollution.

The above purpose is to convert emulsion-like oil-containing wastewater to pH 9 to 12.
After adjusting with calcium hydroxide, a mixture of sulfuric acid clay and ferric sulfate is added as a flocculant, stirred under pressure while blowing air, and released to normal pressure to float and separate the oil. This can be achieved by

The present inventor completed the present invention as a result of studying various methods for treating and cleaning emulsion-like oil-containing wastewater.

The present inventor has discovered that sulfate bread earth, polyaluminum chloride, sodium aluminate, ferrous sulfate, and sulfuric acid are added when river water, well water, etc. are treated to remove organic matter and used as drinking water or industrial water. A flocculant such as ferric iron, ferrous chloride, or Kotsubarasu chloride is added to emulsion-like oil-containing wastewater to form flocs, and the oil dispersed in emulsion is floated and separated by blowing air under pressure. When we tried adjusting the pH to various pH values to see if the oil could be removed, we found that when calcium hydroxide was used as the adjusting agent and a mixture of sulfuric acid and ferric sulfate was used as the flocculant, the oil could not be flocculated and separated. They discovered that this can be carried out satisfactorily and completed the present invention.

The method of the present invention will be explained in detail below.

In the method of the present invention, the emulsion-like oil-containing wastewater to be treated is, for example, oil discharged from a machine factory dispersed in water in the form of an emulsion.According to experiments, the amount of n-hexane extracted substances is Preferably, the amount is in the range of 20 to 500 mg/x and the pH is in the range of 7 to 9.

Moreover, the oil contained may be mineral oil, animal or vegetable fat or oil.

For example, in the case of a metal processing factory, these oils include raw material anti-stick oil, cutting oil, etc.

Further, although the oil is in an emulsion state due to a surfactant, the method of the present invention can be applied even if the surfactant is an ionic surfactant or a nonionic surfactant.

It is particularly effective when applied to anionic surfactants and nonionic surfactants.

In addition, the wastewater generated when oil used in casting or heat treatment of steel is washed off with water or hot water often becomes an emulsion due to the effects of the heat treatment mentioned above, and an unidentified surfactant is generated. However, the method of the present invention can be effectively used in such cases as well.

Furthermore, the method of the present invention can be widely used to treat emulsion-like oil-containing wastewater generated not only in metal processing factories but also in petroleum product manufacturing factories, steel factories, food factories, and the like.

The method of the present invention is effective for washing off the cleaning solution in the degreasing process of a factory, for example, after immersing metal products in a cleaning solution containing about 1500 mg/l of surfactant. This includes the waste water generated when washing the liquid that comes on the skin with water or hot water.

Further, when the above-mentioned washing liquid becomes saturated with oil and becomes unusable and is to be discarded, it is preferable to apply the method of the present invention after diluting it to the above-mentioned amount of n-hexane extract.

The method of the present invention is to adjust the pH of emulsion-like oil-containing wastewater before such treatment, and the pH adjustment value is 9 to 1.
2, more preferably 9.5 to 11, and calcium hydroxide is used as the adjusting agent for this adjustment.

When the pH adjustment value is less than 9, oil is not removed sufficiently.

The use of calcium hydroxide as a pH adjusting agent is based on the discovery that oil cannot be sufficiently floated and separated when other adjusting agents such as caustic soda are used.

The method for adding calcium hydroxide may be slaked lime or quicklime, and it is sufficient that calcium hydroxide or Ca ions and OH ions are present by adding it to water.

Among these, it is preferable to pour out lime milk (concentration 5 to 20%) from a tank where it is stirred, because the input amount can be adjusted and it can be uniformly added to the wastewater to be treated.

Next, the flocculant added in the present invention is a mixture of bread earth sulfate and ferric sulfate, such as M, I, C, and S.

(Mizusawa Chemical Industry Co., Ltd. product).

This is because when other flocculants are used, oil cannot be floated and separated sufficiently.

Further, the amount of the flocculant to be added is preferably about 115 to 10 times the weight of the n-hexane extracted substance, and more preferably 1
/2 to 5 times the weight.

Although it may be added in the form of a powder, it is more convenient to dissolve it in water because it is easier to control the amount added, and the dispersion after addition is faster and more uniform.

As described above, in the method of the present invention, pH adjustment and flocculant addition are performed, and the order of these is that after pH adjustment, flocculant addition is performed.

Next, in the method of the present invention, the emulsion-like oil-containing wastewater whose pH has been adjusted as described above and a flocculant added thereto is stirred under pressure while blowing air, or the flocculant is added to the emulsion-like oil-containing wastewater whose pH has been adjusted. Stirring is carried out under pressure while blowing air at the same time.

The method and degree of pressurization is 1 to 10'Ig/cI by pumping or blowing compressed air. LG preferably 2~5kg/cr? The LG is pressurized, and the amount of air blown is preferably 0.5 to 2 times the volume (normal pressure) of the wastewater to be treated, and stirring is preferably performed at high speed with a stirrer.

The method of the present invention described above is preferably carried out continuously when a large amount of emulsified oil-containing wastewater is to be treated, but it can also be carried out batchwise.

According to the method of the present invention as described above, when emulsion-like oil-containing wastewater is adjusted to pH 9 to 12 with calcium hydroxide and a flocculant is added, flocs are generated, and oil is contained or adsorbed in the flocs.

When the wastewater in such a state is stirred under pressure while blowing air, air is dissolved into the flocs, and when the flocs are released to normal pressure, the flocs float due to air bubbles.

In addition to the above, if an anionic polymer flocculant, such as acrylamide-sodium acrylate copolymer, is added as a flocculation aid after the flocs are generated, the flocs will become larger, promoting flotation, and floating objects. It is desirable to use a coagulation aid because the volume of the coagulation agent can be reduced to about 3% of the total volume.

The wastewater after oil is floated and separated from the emulsion-like oil-containing wastewater by the above-described method of the present invention can be further completely removed by removing traces of suspended matter in the wastewater using a sand filter, for example. The wastewater can also be treated and made into a wastewater that can be discharged.

According to the method of the present invention, unlike conventional methods, acid is not used, so there is no need to consume acid, there is no need to prevent corrosion of equipment due to acid, and only a small amount of flocculant can be added.
The emulsion-like oil-containing wastewater is treated sufficiently, i.e., the residual oil content (as n-hexane extracted material) is extremely small.
For example, oil can be removed to a level of 2 mg/g of wastewater or less.

In addition, oil can be sufficiently removed from emulsion-like oil-containing wastewater through a series of processes such as adjusting the pH, adjusting the amount of flocculant added, adding a flocculating aid, and floating the oil under pressure.
Suitable for continuous treatment of large amounts of wastewater.

Conventionally, in order to remove floating solids and organic matter in river water by flocculation by settling and removing the suspended solids and organic matter in the water, the pH adjustment value was adjusted to 7.
Whereas the flocculant was added as a value of 5 to 8, in the present invention, the adjusted value is 9 to 1, especially in emulsion-like oil-containing wastewater.
The above effect was obtained by using calcium hydroxide as the adjusting agent and using a mixture of ferric sulfate and ferric sulfate as the flocculant.

This effect was achieved because in the pressurized flotation method of the present invention, compressed air is blown into the air, so the carbon dioxide contained in the air lowers the pH and reacts with calcium hydroxide, a pH adjuster, to form minute carbon dioxide. It is thought that this is because calcium is produced and, in combination with the action of the specific flocculant, promotes flocculation of the emulsion-like oil.

Examples will be described below. Example 1 After degreasing a machined metal product such as cutting or welding by immersing it in a water tank containing a 1500 mg/It surfactant aqueous solution, the surfactant aqueous solution attached to the metal product was removed in another water tank. The oil-containing wastewater washed with water and hot water was used as the wastewater to be treated.

The floating oil in the oil-containing wastewater is first removed by an oil fence, and the emulsion-like oil-containing wastewater obtained there (n-
Hexane extract substance 300-400mg/11pH8-9
) was added with 10% milk of lime to a pH adjustment tank while stirring to adjust the pH to 10 to 10.5, and then transferred to a high-pressure stirring tank (multistage centrifugal pump), where flocculants M, I, and C were added.

S, (Mizusawa Chemical Industry ■Product, aluminum sulfate, ferric sulfate mixture A12031o, 5%, F20338%) 3
Add 60mg/l of wastewater, 4-5kg/cI? In L,
After stirring at high speed with a multi-stage centrifugal pump while sucking 11 parts of air under normal pressure per 11 parts of waste water, float while adding flocculation aid Sanpo IJ-305 (product of Sankyo Kasei Kogyo Co., Ltd., acrylamide and sodium acrylate copolymer) 8 mg/l of waste water. The treated waste liquid was transferred to the tank.

In the flotation tank, the scum in which the flocs floated occupied about 3% of the volume, and the treated waste liquid from which the scum was removed was further rapidly passed through a sand filter to remove suspended solids.

The wastewater thus obtained had an oil content (as n-hexane extracted material) of 1.6 mg/l of wastewater and a pH of 7±1.

This is the wastewater standard (n-hexane extracted substance 5mg/Amg
/pH 5.8 to 8.6).

Example 2 Emulsion-like oil-containing wastewater similar to Example 1 (however, n-hexane extracted substance 200 to 300 mg/1 as oil content)
3. pI (s ~9) was adjusted to pH 11 with 10% milk of lime.
, 5 to 12, flocculant M, 1. C, 8゜350mg/
Add 1 liter of waste water and add 8 mg/flocculation aid Sunpoly-305.
The waste water was treated in the same manner as in Example 1 except for the waste water.

The wastewater thus obtained had an oil content (as n-hexane extracted material) of 1.0 mg/l or less and a pH of 7±1.

Comparative Example 1 Emulsion-like oil-containing wastewater similar to Example 1 (however, n-hexane extracted substance 300 to 400 mg/1 as oil content)
pH 7-8) was adjusted to pH 8.5-9 with caustic soda,
The same procedure as in Example 1 was carried out except that 1000 mg of polyaluminum chloride/l of waste water was added as a flocculant, and 8 mg/l of waste water was added as a flocculating aid Sanpo IJ-305.

The wastewater thus obtained had an oil content (10 mg/1 lpHV±1 as n-hexane extracted material).

Comparative Example 2 The same procedure as in Example 1 was carried out except that the 10% milk of lime in Example 1 was changed to a 10% caustic soda aqueous solution.

The wastewater obtained through this treatment has an oil content of 20 mg/7 and a pH of 8±.
It was 1.

Comparative Example 3 In Comparative Example 5 (described later), 10% milk of lime had a pH of 8.5.
The procedure was the same as in Example 2 except that the values were changed to 9 to 9.

The wastewater obtained by this treatment has an oil content of 8 ml1/A'1 pH6
,5±1.

Comparative Example 4 The same procedure as in Example 1 was carried out except that the condensing agent was changed to crystalline ferrous sulfate.

The wastewater obtained by this treatment has an oil content of 10/13. pH7±
It was 1.

Comparative Example 5 Emulsion-like oil-containing wastewater similar to Example 1 (however, the oil content was 20 to 30 m9/13.p of n-hexane extracted material).
H7-8) was adjusted to pH 9.5-10 using 10% lime milk, and the flocculant polyaluminum chloride (analytical value AA20310
．． 3%) 110 μ/l of waste water was added, and flocculation aid Sanpo I was added.
J-305 to 3111I! / Example 1 except that 1 waste water was added.
I did the same thing.

The wastewater thus obtained had an oil content (as n-hexane extracted material) of 2.7 to 2.9 μ/l or less and a pH of 7±1.

Claims (1)

[Claims] 1 After adjusting the emulsion-like oil-containing wastewater to pH 9 to 12 with calcium hydroxide, a mixture of pancreatic sulfate and ferric sulfate is added as a flocculant, stirred under pressure while blowing air, and released to normal pressure. A method for treating emulsion-like oil-containing wastewater, which comprises separating the oil by flotation.