JPH0796284A - Treatment of oil-containing waste water - Google Patents

Abstract

PURPOSE:To efficiently obtain treated water reduced in the concn. of oil by using a reduced addition amt. of a flocculant at the time of the treatment of oil-containing waste water. CONSTITUTION:An oil adsorbent composed of an oil-swellable powdery org. polymer is added to raw water to adsorb the oil in the raw water and this raw water is introduced into a rapid stirring tank 1. A flocculant is added to the raw water in the rapid stirring tank under rapid stirring to flocculate the oil in the raw water to further adsorb the oil. A polymeric flocculant is added to the raw water introduced into a slow stirring tank 2 to form flocs under slow speed stirring. The flocculated soln. is introduced into a pressure floating tank 3 to be subjected to pressure floating separation. The floated scum is treated in a sludge tank 6 and a part of separated water is returned to a pressure water making device 5 while the remainder thereof is discharged as treated water.

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 in which a flocculant is added to the oil-containing wastewater to perform coagulation treatment.

[0002]

2. Description of the Related Art When a liquid fuel such as heavy oil or Orimuljeon (emulsion containing about 70% of orinocotal) is used in a thermal power plant or the like, oil-containing wastewater containing these liquid fuels is discharged. Conventionally, as a method for treating such oil-containing wastewater, polyaluminum chloride (PA
C), an inorganic flocculant such as vanadium sulfate and iron salt is added to perform flocculation treatment, and flocs are separated by sedimentation separation or pressure floating separation.

However, such a conventional processing method has the following problems. 1) In any of the above methods, it is necessary to add a large amount of inorganic coagulant in order to remove the liberated oil. 2) In the method of performing sedimentation separation after aggregation, a thin oil film is formed on the surface layer of the water surface, so that the oil film contaminates the sand layer of the filter in the subsequent step, and the concentration of n-hexane extract in the treated water becomes high. 3) In the method of pressure-floating separation after aggregation, the mixing ratio of pressurized water (pressurized water / (raw wastewater + pressurized water)) is usually 20 to 50%.
However, the levitation tank becomes large, and the amount of treated water returned is large.

On the other hand, in order to remove the oil component floating on the water surface, an oil adsorbent composed of a powdered organic polymer is sprayed to adsorb the oil component. Such an oil adsorbent is used. However, it is difficult to separate the oil from the emulsion in which the oil is finely dispersed.

By the way, in Japanese Patent Publication No. 56-51035, a step of adding an inorganic coagulant to raw wastewater in the presence of an anionic surfactant to form flocs at pH 4.0 to 5.7, followed by addition of oil carbon. And a step of treating with an organic polymer coagulant at a wastewater pH of 5.8 to 8.5, and then a step of separating and removing aggregated pollutants and oil carbon from the wastewater. Have been described.

The above-mentioned method is a method of adsorbing oily oil and BOD and COD in the state of emulsion to oil carbon, but oil carbon has a small adsorption capacity and is excellent in removing a small amount of oily matter and BOD and COD. However, it is not suitable for processing large amounts of oil. For this reason, in the above method, most of the oil content needs to be removed by the coagulant, so that it is necessary to add a large amount of the inorganic coagulant.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to treat oil-containing wastewater by which treated water having a low oil concentration can be efficiently obtained with a small amount of a flocculant. Is to propose.

[0008]

Means for Solving the Problems The present invention is a method for adding a flocculant to oil-containing wastewater to perform coagulation treatment, wherein an oil adsorbent comprising an oil-swelling powdery organic polymer is added to the oil-containing wastewater. Most of all, it is a method for treating oil-containing wastewater, which comprises adding an aggregating agent to perform an aggregating treatment.

The wastewater to be treated by the treatment method of the present invention is an oil component such as a hydrocarbon-based mineral oil or petrochemical, such as kerosene, light oil, gasoline, spindle oil, orimulsion, heavy oil A, heavy oil B, Wastewater containing mineral oils such as C heavy oil, aromatic hydrocarbons, straight chain hydrocarbons, halogenated hydrocarbons and other oils, and may contain surfactants and other organic substances. . The shape of the oil component existing in the wastewater is not limited and may be any of solid, liquid and emulsion forms.

The oil adsorbent used in the treatment method of the present invention is an adsorbent composed of an oil-swelling powdery organic polymer, and examples thereof include polystyrene polybutadiene block copolymers, polystyrene polyisoprene block copolymers, polynorbornenes and the like. An oil swelling oil adsorbent composed of a rubber-like organic polymer such as a mixture of Moreover, a commercially available product can be used, for example, Long Clean S-100 (trademark, manufactured by Kurita Water Industries Ltd.). These oil adsorbents preferably have a particle size of 0.001 to 1 mm and a bulk specific gravity of 0.2 to 0.35.

The polystyrene polybutadiene block copolymer used as an oil adsorbent is a block copolymer composed of polystyrene blocks and polybutadiene blocks. As a specific example thereof, polystyrene blocks and polybutadiene blocks are arranged alternately. In addition to the prepared block copolymer, a branched or radial block copolymer can be used.

The ratio of the polystyrene block to the polybutadiene block is preferably such that the polystyrene block is smaller in weight ratio, and the polystyrene block is 20 to 50.
It is desirable that the amount is less than 35% by weight, preferably 35 to 45% by weight, and the polybutadiene block is more than 50% by weight and 80% by weight or less, preferably 55 to 65% by weight. This block copolymer has a molecular weight of 100,000-40
50,000, preferably 150,000 to 300,000
0 is desirable.

The polystyrene polyisoprene block copolymer used as an oil adsorbent is a block copolymer composed of a polystyrene block and a polyisoprene block, and specific examples thereof include a polystyrene block and a polyisoprene block. In addition to the block copolymer in which the groups are alternately arranged, a branched or radial block copolymer can be used. The polystyrene block and polyisoprene block ratios and molecular weights are preferably the same as those of the polystyrene polybutadiene block copolymer.

The polynorbornene used as an oil adsorbent is a polymer containing norbornene as a structural unit, and specific examples thereof include bicyclo [2.2.
1] A ring-opening polymer or a ring-opening copolymer of heptene-2 or a derivative thereof. As a derivative, a hydrogen atom of bicyclo [2.2.1] heptene-2 is substituted with an alkyl group such as methyl or ethyl, an alkoxy group such as methoxy or ethoxy, a carboxylic acid ester group, a cyan group, a vinyl group, or a halogen. Some of them are listed. Two or more substituents may be substituted, or two or more types may be substituted. The polynorbornene has a molecular weight of 300,000 to 4,000,000, preferably 2,000,000 to 3,000,000.

Such oil adsorbents include orimulsion,
Since it has excellent adsorbability for oil components such as A heavy oil, C heavy oil, etc., it can be suitably used for treating wastewater containing these oil components. The amount of the oil adsorbent added is 5 to 20% by weight, preferably 5 to 10% by weight, based on the oil content in the water to be treated.

In the present invention, the oil adsorbent as described above is added to the oil-containing wastewater, and the aggregating agent is added to perform the aggregating treatment. The order of adding the oil adsorbent and the coagulant is not particularly limited, but it is preferable to add the oil adsorbent before aggregation starts. In this case, it is generally desirable to add the oil adsorbent first, but if there is a time difference between the addition of the flocculant and the start of flocculation, such as when flocculation starts after pH adjustment after coagulant addition, flocculation It is also possible to add the oil adsorbent after adding the agent and before starting the aggregation.

As the coagulant, polyaluminum chloride,
Inorganic flocculants such as vanadium sulfate, ferric chloride, ferrous sulfate and ferric sulfate can be used. The amount of inorganic flocculant added is 400
~ 1200 mg / l, preferably 600-900 mg / l
It is desirable to set it as l. With such an inorganic flocculant, or alternatively, poly (meth) acrylamide, a hydrolyzate thereof, poly (meth) acrylic acid, a nonionic property such as (meth) acrylamide and an alkylamino (meth) acrylamide copolymer, Anionic, cationic or amphoteric organic polymeric flocculants can also be used. The amount of the organic polymer coagulant added is 2 to 20 mg / l, preferably 4 to 8 mg / l.

A preferred coagulation treatment method is to add an oil adsorbent to oil-containing wastewater and stir and mix, then add an inorganic coagulant to adjust pH and cause rapid agitation to cause coagulation. Flock is grown by adding and stirring slowly. At this time, the addition of the oil adsorbent adsorbs most of the oil components floating on the surface of the wastewater and the oil components in the form of emulsion. The oil adsorbent that has adsorbed the oil content and the remaining oil content are combined by agglomeration, so that the oil content is further adsorbed. Then, due to the growth of flocs, agglomerates are further bound and the remaining oil and suspension are also integrated to form huge flocs.

When the oil content is removed only by the coagulation treatment, a large amount of coagulant is required because flocs are formed so as to enclose the oil content. However, in the present invention, the oil adsorbent that adsorbs the oil content is aggregated. Therefore, the amount of the coagulant used is reduced. Further, even if the oil is adsorbed only by the oil adsorbent, the oil adsorbed in the emulsion cannot be completely adsorbed. As it proceeds, the separation of the oily substance in the emulsion becomes easy.

After the flocs are formed as described above, the flocs are separated by solid-liquid separation. As the solid-liquid separation method, any method such as sedimentation separation, pressure floating separation, and filtration can be adopted, but since the oil content is floatable, an oil adsorbent with a low specific gravity is used and a coagulant is added. It is preferable to reduce the amount for the pressure floating separation, and particularly preferable is a combination of the pressure floating separation and filtration.

[0021]

Embodiments of the present invention will now be described with reference to the drawings.
FIG. 1 is a flow sheet showing a method for treating oil-containing wastewater according to an embodiment. In the figure, 1 is a rapid stirring tank, 2 is a slow stirring tank, 3 is a pressure flotation tank, 4 is a water storage tank, 5 is a pressurized water production apparatus, 6 is a sludge tank, and 7 is a filter.

In the treatment method shown in FIG. 1, first, the oil adsorbent 12 having a small bulk specific gravity is added to the raw water 11 and stirred and mixed in the line to adsorb the oil component, and the mixed water is introduced into the rapid stirring tank 1. In the rapid stirring tank 1, the inorganic coagulant 13 and, if necessary, the pH adjuster 14 are added and rapidly stirred to perform coagulation, and oil is further adsorbed on the oil adsorbent. Since the oil adsorbent that has adsorbed the oil floats on the liquid surface, the flocculating liquid 15 containing the floating oil adsorbent is overflowed and introduced into the slow stirring tank 2.

In the slow stirring tank 2, the organic polymer coagulant 16
And, if necessary, a pH adjuster 17 is added and gently stirred to grow flocs. At this time, the oil adsorbent, residual oil and other suspended particles are entrapped in the flocs,
Huge flocs are formed. Since the flocs generated here float, the flocculating liquid 18 containing the floating flocs 18
Is mixed with the pressurized water 19 produced by the pressurized water producing apparatus 5 and sent to the pressurized flotation tank 3. The pressurized water is produced by sending air to the pressurized water producing device 5 by the compressor 8 and dissolving it under pressure.

Since the pressurized water is decompressed in the pressurized levitation tank 3, the dissolved air becomes fine bubbles, which adhere to the flocs and float up to form scum. Since the floc floatability is good, the mixing ratio of the pressurized water may be smaller than that in the case where no oil adsorbent is used.
Even in the case of 0%, the oil adsorbent and the flocs can be almost completely floated. Therefore, the capacity of the pressure floating tank 3 can be reduced.

The scum generated in the pressure flotation tank 3 is a clearance 2.
After scraping at 0 and storing as sludge 21 in the sludge tank 6, a process such as dehydration is performed. The separated liquid 22 of the pressurized flotation tank 3 is introduced into the water storage tank 4, and a part of it is supplied to the pressurized water production device 5 as raw water 23 for producing pressurized water. The remainder is filtered by a filter 7 filled with a filter material such as sand and discharged as treated water 24. When the separated liquid 22 has little turbidity, the filtration operation can be omitted.

In the above treatment method, the aggregation is carried out while the oil adsorbent is adsorbed on the oil adsorbent, so that the aggregation effect is improved and the addition amount can be reduced. Further, since the oil content is removed by oil adsorption and aggregation, the removal rate is high even when the amount of the flocculant used is small. Further, since the mixing ratio of the pressurized water can be reduced, the pressurized flotation tank can be downsized and the amount of returned water can be reduced.

Example 1 Floor washing wastewater of a thermal power plant containing orimulsion as an oil component was treated by the treatment method of FIG. The processing conditions and results are shown in Table 1.

Comparative Example 1 The same wastewater as in Example 1 was treated by the treatment method of FIG. 1 except that no oil adsorbent was used. The processing conditions and results are shown in Table 1.

Comparative Example 2 The same wastewater as in Example 1 was treated by the coagulating sedimentation treatment method without using an oil adsorbent. Table 1 shows the processing conditions and results.
Shown in.

Comparative Example 3 An oil adsorbent was added to the same waste water as in Example 1, and pressure separation was carried out. The processing conditions and results are shown in Table 1.

[0031]

[Table 1] (Footnote of Table 1) * 1 Long Clean S-100, manufactured by Kurita Water Industries Ltd.,
Trademark * 2 8% liquid vanadium sulfate (containing 8% by weight of Al ₂ O ₃ )
Addition amount * 3 Organic polymer * 4 Oil film formed on the surface of the processing tank

From the results of Table 1, the treatment method of Example 1 is
Compared with the conventional flocculation pressure flotation treatment that does not use an oil adsorbent (Comparative Example 1), the amount of inorganic flocculant added can be reduced and the treatment can be performed by reducing the mixing ratio of pressurized water, and the oil removal rate can also be increased. You can see that it is expensive. Further, the treatment method of Example 1 can reduce the addition amount of the inorganic coagulant as compared with the conventional coagulation-sedimentation treatment (Comparative Examples 1 and 2) that does not use an oil adsorbent,
Moreover, it can be seen that the oil removal rate is also high. Further, the treatment method of Example 1 has a higher oil removal rate than the method of Comparative Example 3, and the suspended particles also flocculate and float, whereby clear water can be obtained. However, as shown in Comparative Example 3, it is understood that the floating oil can be adsorbed and removed only by adding the oil adsorbent, but the emulsion oil cannot be adsorbed and treated, so that the oil removal rate is low.

[0033]

EFFECTS OF THE INVENTION According to the present invention, an oil adsorbent comprising an oil-swelling powdery organic polymer is added to oil-containing wastewater, and an aggregating agent is added for aggregating treatment.
Treated water having a low oil content can be efficiently obtained with a small amount of the flocculant added.

[Brief description of drawings]

FIG. 1 is a flow sheet showing a method for treating oil-containing wastewater according to an embodiment.

[Explanation of symbols]

 1 Rapid stirring tank 2 Slow stirring tank 3 Pressurized flotation tank 4 Water storage tank 5 Pressurized water production equipment 6 Sludge tank 7 Filter 8 Compressor

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[Procedure amendment]

[Submission date] October 8, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (1)

[Claims] 1. A method of performing coagulation treatment by adding a coagulant to oil-containing wastewater, wherein an oil adsorbent composed of an oil-swelling powdery organic polymer is added to the oil-containing wastewater to form a coagulant. A method for treating oil-containing wastewater, which comprises adding and performing coagulation treatment.