Method and device for recovering oil from oil-containing waste liquid

Abstract

This method for recovering oil from an oil-containing waste liquid includes an extraction step for extracting an oil-containing waste liquid using a solvent to transfer oil in the oil-containing waste liquid to the solvent, a separation step for separating the solvent containing the extracted oil and the waste liquid, and an oil recovery step for separating and recovering the oil from the separated solvent containing the oil, the method for recovering oil being characterized in that the solvent is n-hexane, the oil concentration in the oil-containing waste liquid supplied to the extraction step is 1,000-5,000 mg / L, the volume ratio (solvent / waste liquid ratio) of the solvent to the oil-containing waste liquid is 0.01-0.05, and the oil concentration in the solvent containing the oil separated in the separation step is 4 mass% or greater. Provided is a method for recovering oil from an oil-containing waste liquid, the method making it possible to efficiently separate and recover oil from the oil-containing waste liquid through a solvent extraction method.

Description

Method and device for recovering oil from oil-containing waste liquid

[0001] The present invention relates to a method and apparatus for recovering oil from oil-containing waste liquid, and more particularly to a method and apparatus for recovering oil from oil-containing waste liquid using solvent extraction.

[0002] Water treatment for separating and recovering oil from oil-containing wastewater typically involves separation using a separation weir (oil trap) that utilizes the fact that oil floats on water, or flotation treatment using micro-air or micro-air and chemicals (see, for example, Patent Document 1). Furthermore, a method is also conceivable in which the oil is distributed to the solvent side by solvent extraction using a solvent and a mixer settler, and then the solvent is volatilized to recover the oil.

[0003] The oil separated in this way has a high energy content and is highly useful. Furthermore, using the separated and recovered oil as an energy source also leads to waste reduction, so waste-to-energy recovery, including waste-to-energy power generation using oil, is expected to become increasingly important in the future in order to create a recycling-oriented society.

[0004] Japanese Patent Application Laid-Open No. 2021-171748

[0005] Among conventional oil-water separation technologies, in the flotation process, the separated components are contaminated with components other than oil, i.e., non-oil SS components contained in the wastewater, components derived from chemicals, and water. Therefore, to separate only the oil and use it for fuel, a process of removing these contaminants through refining using centrifugation or other methods is required. In the separation and recovery of oil by solvent extraction, the solvent used for extraction is nonpolar, so impurities such as hydrophilic substances such as ions are not captured, making it a suitable method for using the recovered oil. However, there are few examples of solvent extraction being applied to wastewater treatment, and currently there is no knowledge regarding the treatment conditions required for application.

[0006] An object of the present invention is to provide a method and apparatus for recovering oil from oil-containing waste liquid, which can efficiently separate and recover oil from oil-containing waste liquid by solvent extraction.

[0007] As a result of extensive research aimed at solving the above problems, the inventors have found that by controlling the oil concentration of the oil-containing waste liquid to be subjected to solvent extraction and the volume ratio of the solvent used for extraction to the oil-containing waste liquid to appropriate values, it is possible to efficiently separate and recover oil from the oil-containing waste liquid by solvent extraction.

[0008] [1] A method for recovering oil from an oil-containing waste liquid, comprising: an extraction step of extracting an oil-containing waste liquid with a solvent to transfer the oil in the oil-containing waste liquid to the solvent; a separation step of separating the extracted oil-containing solvent from the waste liquid; and an oil recovery step of separating and recovering the oil from the separated oil-containing solvent, wherein the solvent is n-hexane, the oil concentration in the oil-containing waste liquid supplied to the extraction step is 1000 to 5000 mg / L, the volume ratio of the solvent to the oil-containing waste liquid (solvent / waste liquid ratio) is 0.01 to 0.05, and the oil concentration in the oil-containing solvent separated in the separation step is 4 mass% or more.

[0009] [2] In the oil recovery step, the oil is separated from the oil-containing solvent by heated distillation to recover the solvent, and the recovered solvent is reused in the extraction step. [1] A method for recovering oil from an oil-containing waste liquid.

[0010] [3] In the separation by heated distillation, the heat of the separated solvent or oil is used to heat the solvent containing the oil using a heat exchanger or a heat pump. [2] The method for recovering oil from an oil-containing waste liquid.

[0011] [4] The method for recovering oil from an oil-containing waste liquid according to any one of [1] to [3], further comprising a concentration step of concentrating the oil-containing waste liquid or a dilution step of diluting the oil-containing waste liquid prior to the extraction step.

[0012] [5] The method for recovering oil from an oil-containing waste liquid according to any one of [1] to [4], wherein the oil-containing waste liquid is any one of waste liquids from a manufacturing plant for parts such as automobiles containing mineral oil, aqueous cutting waste liquid, waste liquids from paper or paper pulp factories containing turpentine oil, waste liquids from oil refineries containing animal and vegetable oils, food and beverage factories, or waste liquids from food and beverage industry businesses.

[0013] [6] An apparatus for recovering oil from an oil-containing waste liquid, comprising: an extraction means for extracting an oil-containing waste liquid with a solvent to transfer oil in the oil-containing waste liquid to the solvent; a separation means for separating the extracted oil-containing solvent from the waste liquid; and an oil recovery means for separating and recovering the oil from the separated oil-containing solvent, wherein the solvent is n-hexane, the oil concentration in the oil-containing waste liquid supplied to the extraction means is 1000 to 5000 mg / L, the volume ratio of the solvent to the oil-containing waste liquid (solvent / waste liquid ratio) is 0.01 to 0.05, and the oil concentration in the oil-containing solvent separated by the separation means is 4 mass% or more.

[0014] [7] The oil recovery means is a means for separating the oil from the solvent containing the oil by heated distillation, and has a liquid supply means for supplying the solvent from which the oil has been separated by the oil recovery means to the extraction means. The oil recovery device from oil-containing waste liquid described in [6].

[0015] [8] The oil recovery device from the oil-containing waste liquid described in [7], which has a heat exchanger or heat pump for heating the solvent containing the oil using the heat of the solvent or the oil separated by the heated distillation.

[0016] [9] The oil recovery device from oil-containing waste liquid according to any one of [6] to [8], further comprising a concentrating means for concentrating the oil-containing waste liquid or a diluting means for diluting the oil-containing waste liquid, in a stage preceding the extraction means.

[0017]

[10] The oil-containing waste liquid is any one of waste liquids from automobile or other parts manufacturing factories containing mineral oil, aqueous cutting waste liquid, waste liquids from paper or paper pulp factories containing turpentine oil, waste liquids from oil refineries containing animal and vegetable oils, food and beverage factories, or waste liquids from food and beverage industry businesses [6] to [9]. The oil recovery device from oil-containing waste liquid.

[0018] According to the present invention, oil can be efficiently separated and recovered from oil-containing wastewater by solvent extraction. According to the present invention, the oil content in oil-containing wastewater, which inhibits wastewater treatment, can be significantly reduced, and high-purity oil can be recovered and effectively reused as an energy source in various fields. Furthermore, according to the present invention, the amount of waste generated, such as sludge containing a large amount of oil, which has previously been discarded as waste, can be significantly reduced. Therefore, the industrial utility value of the present invention is extremely great.

[0019] FIG. 1 is a flow diagram showing a method and apparatus for recovering oil from oil-containing waste liquid according to an embodiment of the present invention.

[0020] Before describing the embodiments of the method and apparatus for recovering oil from oil-containing waste liquid according to the present invention, the mechanism of solvent extraction according to the present invention will be described.

[0021] Oil-containing wastewater typically contains enough oil to supply more energy than is required for the heated distillation process to separate the oil from the oil-containing solvent after solvent extraction. However, in a system where n-hexane is used as an extraction solvent to extract oil from the oil-containing wastewater, the n-hexane used in the extraction is evaporated to separate and recover the residual oil, the evaporated n-hexane is naturally cooled (air-cooled), recovered, and used repeatedly for extraction, and the recovered oil is used as fuel (energy source), the energy required to evaporate the n-hexane is thought to account for the majority of the energy consumed (however, energy consumption other than solvent evaporation includes pump power for continuous processing and solvent loss).

[0022] Therefore, from the perspective of energy balance, the following equation must be true: Energy consumed (amount of heat required to heat n-hexane containing oil up to its boiling point and then evaporate all of the n-hexane) < Energy gained (amount of heat obtained by burning the recovered oil).

[0023] Based on the basic calorific value information for n-hexane and oil shown in Table 1 below, if the consumed energy is assumed to be electricity (efficiency 100%) and the acquired energy is also assumed to be electricity (efficiency for generating electricity from oil is approximately 25%), the oil concentration in the n-hexane containing the extracted oil must be 4% by mass or more, as shown in Table 2 below.

[0024]

[0025]

[0026] On the other hand, if a large amount of oil or other components dissolves in the solvent during solvent extraction, the specific gravity and viscosity of the resulting mixture of solvent and oil will increase, which will result in the mixture being more susceptible to the incorporation of solids and water, making it difficult to extract and separate pure oil from the oil-containing wastewater. For these reasons, limiting the range of the extracted oil concentration in the solvent from which the oil was extracted is effective in efficiently extracting the oil from the oil-containing wastewater into the solvent.

[0027] As described above, by pretreating the oil-containing wastewater to be extracted by concentration or dilution or other methods as necessary to set the oil concentration within a predetermined range, limiting the amount of solvent used, and further setting the oil concentration in the solvent containing the extracted oil to a predetermined value or higher, the separation of the solvent and water is improved and the loss of solvent to the water can be kept below a certain amount. Furthermore, the appropriate size of the oil extraction equipment can be determined for the amount of extracted oil, allowing for efficient extraction of the oil into the solvent.

[0028] Based on this mechanism, efficient solvent extraction can be achieved by controlling the oil concentration of the oil-containing waste liquid to be extracted and the volume ratio of the solvent to the oil-containing waste liquid at this oil concentration (hereinafter sometimes simply referred to as the "solvent / waste liquid ratio") within a predetermined range, and by controlling the oil concentration in the solvent containing the extracted oil to a predetermined value or higher. Furthermore, the separated and recovered oil can be efficiently and effectively utilized as an energy source.

[0029] In the present invention, the oil concentration in the oil-containing waste liquid to be subjected to solvent extraction is 1000 to 5000 mg / L. If the oil concentration of the oil-containing waste liquid is less than 1000 mg / L, there will be insufficient recovered oil as an energy source for the thermal distillation of the solvent (n-hexane) after extraction. On the other hand, if the oil concentration exceeds 5000 mg / L, as described above, the specific gravity and viscosity of the mixture of the oil and the solvent from which the oil was extracted will increase, making it impossible to recover high-purity oil. Furthermore, separation of the oil after extraction will become difficult, and solvent loss will also increase. From these perspectives, the oil concentration in the oil-containing waste liquid to be subjected to solvent extraction is preferably 1000 to 3000 mg / L, more preferably 1200 to 2500 mg / L.

[0030] In the present invention, the solvent (n-hexane) and oil-containing waste liquid are subjected to solvent extraction so that the solvent / waste liquid ratio is 0.01 to 0.05. If the solvent / waste liquid ratio is less than 0.01, the amount of solvent used in the extraction is too small, preventing efficient oil extraction and resulting in residual oil in the oil-containing waste liquid. On the other hand, if the solvent / waste liquid ratio exceeds 0.05, the amount of solvent used in the extraction is too large, which is uneconomical. Furthermore, the oil concentration in the n-hexane is low, which is undesirable from the perspective of increasing the size of the extraction equipment. From these perspectives, the solvent / waste liquid ratio is preferably 0.02 to 0.04, and more preferably 0.025 to 0.03.

[0031] In the present invention, the oil concentration of the solvent after oil extraction from the oil-containing waste liquid is set to 4% by mass or more. Therefore, when extraction is performed using n-hexane according to the present invention, the oil concentration of the n-hexane after extraction is set to 4% by mass or more, preferably 4 to 12% by mass, and more preferably 4 to 7% by mass, from the viewpoints of oil separation efficiency and thermal energy efficiency in solvent regeneration.

[0032] An embodiment of a method and apparatus for recovering oil from an oil-containing waste liquid according to the present invention, which is carried out by controlling the oil concentration of the oil-containing waste liquid and the solvent / waste liquid ratio, will be described below with reference to Fig. 1. However, the present invention is not limited to the following and can be practiced with various modifications within the scope of the present invention.

[0033] FIG. 1 is a flow diagram showing a method and apparatus for recovering oil from oil-containing waste liquid according to an embodiment of the present invention.

[0034] The oil-containing waste liquid to be treated in the present invention is a water-based waste liquid with a water content of 85% by mass or more, such as a thick oil-containing waste liquid generated from petroleum processes, steel rolling processes, papermaking or paper pulp manufacturing, metal cutting processes, food manufacturing, leather manufacturing, kitchens, sewage, etc. Specific examples include aqueous cutting waste liquid, turpentine oil-containing wastewater discharged from papermaking or pulp factories, and food wastewater, but are not limited to these. The oil in the oil-containing waste liquid may be either mineral oil or animal or vegetable oil.

[0035] The oil concentration of these oil-containing waste liquids is usually about 0.05 to 1% by mass (500 to 10,000 mg / L). Therefore, if the oil concentration of the oil-containing waste liquid to be treated in the present invention is outside the range of 1,000 to 5,000 mg / L, a concentration step for concentrating the oil-containing waste liquid or a dilution step for diluting the oil-containing waste liquid is provided before the extraction step.

[0036] More specifically, examples of oil-containing waste liquid include waste liquid from automobile and other parts manufacturing factories containing mineral oil, waste liquid from paper and pulp factories containing turpentine oil, and waste liquid from oil refineries, food and beverage factories, or food and beverage industries containing animal and vegetable oils. The oil-containing waste liquid may also be waste liquid containing organic matter extracted into a non-polar solvent.

[0037] In Fig. 1, oil-containing wastewater is introduced into a membrane separation device 2 via a pipe 1 and concentrated to the aforementioned oil concentration by membrane separation. A portion of the permeate that has passed through the membrane is returned to the membrane separation device 2 via a pipe 4A. The remainder of the permeate is sent to a wastewater treatment facility (not shown) via a pipe 4B and treated.

[0038] The concentrated water from the membrane separation device 2 and the extraction solvent are supplied to a mixing section 6a of an extraction device 6 via a pipe 5 and a pipe 7, respectively, at the solvent / waste liquid ratio mentioned above.

[0039] The concentrated water and extraction solvent supplied to the mixing section 6a are mixed in the mixing section 6a, and the oil in the concentrated water is incorporated into the solvent. In other words, the oil in the concentrated water dissolves in the extraction solvent. The solvent with dissolved oil and the concentrated water (residual liquid) from which the oil has been extracted are naturally separated (gravity separation) in the separation section 6b, and the solvent with dissolved oil is supplied to the cold heat source flow path of the heat exchanger 9 via pipe 8. This solvent with dissolved oil exchanges heat with solvent vapor flowing through the cooled fluid flow path, is heated, and is introduced into the distillation column 11 via pipe 10. In the distillation column 11, the solvent (n-hexane) with a lower boiling point than the oil flows to the top of the column, and the oil with a higher boiling point flows to the bottom of the column. The solvent vapor is supplied from the distillation column 11 to the cooled fluid flow path of the heat exchanger 9 via pipe 12, where it is cooled by heat exchange with the extractor effluent (low-temperature liquid) flowing through the cold heat source flow path, becoming a liquid solvent. This liquid solvent is sent to the mixing section 6a of the extractor 6 via a pipe 7 and is reused as the extraction solvent. Note that the solvent lost due to migration into the treated water (described later) or evaporation from the extractor is replaced by a new solvent supplied from outside the system.

[0040] The separated oil is extracted from the bottom of the distillation column 11 via a pipe 14. This oil is used as a liquid fuel or a combustion improver for power generation and various other purposes. If necessary, the recovered oil may be subjected to further treatment.

[0041] A residual liquid from which the oil has been extracted is taken out from the separation section 6b of the extractor 6 via a pipe 20. This residual liquid is sent to a membrane separator 21 such as a reverse osmosis membrane separator, and the solvent component (residual solvent) in the residual liquid is concentrated by membrane separation.

[0042] The permeated water that has permeated the membrane 21a of the membrane separation device 21 is taken out as treated water via a pipe 22. The concentrated water from the membrane separation device 21 is discharged via a pipe 23 and sent to a waste liquid treatment step (not shown) for concentration treatment, wastewater treatment, or the like.

[0043] In the above embodiment, the oil-containing waste liquid is subjected to membrane separation treatment in the membrane separation device 2 to increase the oil concentration, but oil that can be easily separated from water can be separated using an oil-water separator that uses specific gravity differences or micro-air, and then the liquid can be sent to the extraction device 6 immediately or after undergoing separation treatment such as membrane separation treatment as necessary.

[0044] The extractor 6 may be either a continuous type or a batch type. Continuous liquid-liquid extraction apparatuses used on an industrial scale include mixer-settler types, spray towers, countercurrent contact towers, and perforated plate towers (perforated plate towers). The extractor may be any of these or other types.

[0045] In the present invention, n-hexane (boiling point 67°C) is used as the extraction solvent, which has a boiling point lower than that of the oil to be separated (approximately 250 to 600°C). Therefore, even when separating oil from a solvent containing oil by extraction through heated distillation, it is more energy efficient than directly distilling the oil-containing waste liquid.

[0046] In Figure 1, the solvent is regenerated by separating the oil from the oil-containing solvent by heated distillation. For solvent regeneration, heated distillation, which utilizes the boiling point difference between the oil and the solvent, is suitable. Both batch and continuous distillation can be used for heated distillation, and methods such as flash distillation, plate columns, and packed columns can be used. In addition to heated distillation, vacuum distillation can also be used to separate the oil from the oil-containing solvent.

[0047] As described above, in the present invention, the oil concentration in the oil-containing waste liquid to be subjected to extraction is 1000 to 5000 mg / L. Therefore, if the oil concentration of the oil-containing waste liquid is lower than the above range, the oil-containing waste liquid is concentrated by gravity separation, pressure flotation, a membrane separator, or other concentration means prior to extraction treatment. On the other hand, if the oil concentration in the oil-containing waste liquid to be subjected to extraction is higher than the above range, the oil-containing waste liquid is diluted using a dilution mixing tank or the like to dilute the oil-containing waste liquid with industrial water, tap water, wastewater from a system separate from the target oil-containing wastewater, drain water, or the like.

[0048] In order to promote the separation of oil from the oil-containing waste liquid, a salt such as sodium chloride, an alkali, or an acid may be added to the oil-containing waste liquid prior to the extraction treatment. For example, in the case of sodium chloride, the oil separation efficiency can be increased by adding about 0.1 to 30% by mass of sodium chloride to an oil-containing waste liquid containing about 0.05 to 1% by mass of oil, or by lowering the pH to about 2.

[0049] As described above, the oil concentration of the solvent after oil extraction from the oil-containing waste liquid is set to 4% by mass or more. Therefore, when extraction is performed using n-hexane according to the present invention, the oil concentration of the n-hexane after extraction should be 4% by mass or more, preferably 4 to 12% by mass, and more preferably 4 to 7% by mass, thereby improving the oil separation efficiency and the thermal energy efficiency in solvent regeneration.

[0050] In Fig. 1, the membrane separation device 21 separates the remaining substances in the waste liquid (residual liquid) after oil separation using a membrane separation process such as a reverse osmosis membrane, but an adsorption process such as activated carbon may be used to separate the solvent component in the waste liquid (residual liquid) after oil separation. The remaining solvent may also be decomposed by adding an oxidizing agent or by biological treatment.

[0051] The effects of the present invention will be demonstrated below by way of experimental examples instead of working examples.

[0052] Experimental Example 1: Assuming the wastewater from the washing of dairy products as an oil-containing wastewater, a simulated oil-containing wastewater was prepared by diluting milk (milk fat 3.5% by mass, non-fat milk solids 8.4% by mass, water 88.1% by mass) with pure water, and an oil extraction experiment using n-hexane was conducted. Milk, pure water, and n-hexane were placed in a 2000 mL capped flask and shaken horizontally at 180 rpm for 30 minutes to perform the extraction procedure. The mixture was then placed in a separatory funnel and allowed to stand for 30 minutes to separate the n-hexane and aqueous phases. The transparent portion of the n-hexane phase was collected, and the n-hexane was evaporated in a thermostatic bath at 80°C. The weight of the remaining residue was measured. Note that in some cases, the n-hexane phase was almost an emulsion with no transparent portion (poor separation). In such cases, the transparent portion was collected by centrifugation (3000 rpm, 10 minutes). The results are shown in Table 3.

[0053] The maximum extraction concentration in Table 3 is the concentration assuming that all of the oil (milk fat) in the sample (milk diluted with pure water) is extracted into the n-hexane used for extraction, and the extraction rate is a value with this concentration as the denominator and the actual extraction concentration as the numerator.

[0054] The criteria for judging separability are as follows: <Separability> ○: Good separability △: Separable ×: Not separable

[0055]

[0056] Table 3 reveals the following: The smaller the solvent / waste liquid ratio and the greater the oil concentration in the sample, the worse the separability tends to be. When the solvent / waste liquid ratio is 0.01, separation becomes impossible when the oil concentration in the sample exceeds 5000 mg / L, reaching 8750 mg / L. On the other hand, when the solvent / waste liquid ratio is high, the oil concentration in n-hexane (extraction concentration) does not reach the 4 mass% concentration required by the aforementioned energy balance, but this can be met by reducing the solvent / waste liquid ratio. In other words, it can be seen that there are appropriate oil concentrations in the oil-containing waste liquid, solvent / waste liquid ratios, and extraction concentrations when solvent-extracting oil from oil-containing waste liquid using n-hexane.

[0057] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-197548, filed on November 21, 2023, and is incorporated by reference in its entirety.

[0058] 2, 21 Membrane separation device 6 Extraction device 11 Distillation column

Claims

1. A method for recovering oil from oil-containing waste liquid, comprising: an extraction step of extracting oil-containing waste liquid with a solvent to transfer oil in the oil-containing waste liquid to the solvent; a separation step of separating the extracted oil-containing solvent from the waste liquid; and an oil recovery step of separating and recovering the oil from the separated oil-containing solvent, wherein the solvent is n-hexane; the oil concentration in the oil-containing waste liquid supplied to the extraction step is 1000 to 5000 mg / L; the volume ratio of the solvent to the oil-containing waste liquid (solvent / waste liquid ratio) is 0.01 to 0.05; and the oil concentration in the oil-containing solvent separated in the separation step is 4 mass% or more.

2. A method for recovering oil from an oil-containing waste liquid as described in claim 1, wherein in the oil recovery process, the oil is separated from the solvent containing the oil by heated distillation to recover the solvent, and the recovered solvent is reused in the extraction process.

3. A method for recovering oil from oil-containing waste liquid as described in claim 2, wherein the heat of the separated solvent or oil is utilized to heat the oil-containing solvent using a heat exchanger or heat pump during separation by heated distillation.

4. A method for recovering oil from an oil-containing waste liquid as described in claim 1 or 2, further comprising a concentrating step of concentrating the oil-containing waste liquid or a diluting step of diluting the oil-containing waste liquid prior to the extraction step.

5. A method for recovering oil from oil-containing waste liquid as described in claim 1 or 2, wherein the oil-containing waste liquid is any one of waste liquids from a manufacturing plant for automobile parts or the like containing mineral oil, aqueous cutting waste liquid, waste liquids from a paper or pulp and paper factory containing turpentine oil, waste liquids from an oil refinery containing animal and vegetable oils, a food and beverage factory, or waste liquids from the food and beverage industry.

6. An apparatus for recovering oil from oil-containing waste liquid, comprising: an extraction means for extracting oil-containing waste liquid with a solvent to transfer oil in the oil-containing waste liquid to the solvent; a separation means for separating the extracted oil-containing solvent from the waste liquid; and an oil recovery means for separating and recovering oil from the separated oil-containing solvent, wherein the solvent is n-hexane; the oil concentration in the oil-containing waste liquid supplied to the extraction means is 1000 to 5000 mg / L; the volume ratio of the solvent to the oil-containing waste liquid (solvent / waste liquid ratio) is 0.01 to 0.05; and the oil concentration in the oil-containing solvent separated by the separation means is 4 mass% or more.

7. The oil recovery means is a means for separating the oil from the solvent containing the oil by heated distillation, and the oil recovery device from oil-containing waste liquid described in claim 6 has a liquid supply means for supplying the solvent from which the oil has been separated by the oil recovery means to the extraction means.

8. An apparatus for recovering oil from oil-containing waste liquid as described in claim 7, comprising a heat exchanger or heat pump for heating the oil-containing solvent using the heat contained in the solvent or oil separated by the heated distillation.

9. An apparatus for recovering oil from an oil-containing waste liquid as described in claim 6 or 7, further comprising a concentrating means for concentrating the oil-containing waste liquid or a diluting means for diluting the oil-containing waste liquid, located upstream of the extraction means.

10. An oil recovery device from oil-containing waste liquid as described in claim 6 or 7, wherein the oil-containing waste liquid is any one of waste liquids from automobile or other parts manufacturing factories containing mineral oils, aqueous cutting waste liquids, waste liquids from paper or pulp and paper factories containing turpentine oils, and waste liquids from oil refineries, food and beverage factories, or food and beverage industry businesses containing animal and vegetable oils.

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