JPH08267095A - Biological treatment of oil-containing waste water - Google Patents

Abstract

PURPOSE: To prevent the deposition of oil on the surface of a separation membrane at the time of biologically treating an oil-contg. waste water by treating the waste water added with a saponin-contg. agent in a biological treating tank and then separating solid from liq. in a membrane separator. CONSTITUTION: A membrane separator 3 is set in an aeration tank 2 for aerating the waste water from a food factory added with a saponin-contg. agent to biologically treat the waste water, and the treated water separated therein from solid is sent to a treated water tank 4. Since a negative pressure is exerted on the inside of an ultrafilter membrane into which plural sets of two membranes are incorporated in the separator 3, the treated water is sucked from the outside. Meanwhile, an aerator 5 is arranged below the separator 3 to remove the deposit on the membrane surface by aeration. By this method, the oil in the waste water is easily digested and decomposed by the emulsifying action of saponin, hence the membrane permeating flux is not decreased due to the deposition of oil on the membrane surface, and solid and liq. stably separated in the membrane separator 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a membrane permeation flow when oil (normal hexane extract) adheres to the membrane surface when activated sludge and the like produced as a result of biological treatment of waste water are subjected to solid-liquid separation by a membrane separator. The present invention relates to an improved biological treatment method for oil-containing wastewater that prevents a decrease in flux, and particularly to an optimal biological treatment method for treating wastewater containing oil at a high concentration, such as in kitchen wastewater and food processing plants. Further, the present invention relates to a biological treatment method suitable for treating wastewater containing a high concentration of salt.

[0002]

2. Description of the Related Art Recently, activated sludge treatment (a type of biological treatment)
Membrane separation technology is drawing attention as a solid-liquid separation technology that replaces the subsequent precipitation separation, and research and practical applications are being promoted in the fields of human waste treatment and water supply. This is membrane separation (membrane treatment)
In the case of, because there is no obstacle for solid-liquid separation due to bulking or sludge floating, the installation area is small, and the treated water of stable water quality can be obtained. This is also due to the fact that the film is being improved and mass production effects are beginning to occur.

As described above, the membrane separation method has an extremely excellent advantage as a solid-liquid separation technique in wastewater treatment. However, when a large amount of oil is contained in the wastewater, oil adheres to the membrane surface. There is a problem that the membrane permeation flux (flux) is significantly lowered, and finally the treatment becomes impossible.

However, this has not been given much importance in the past. It is said that the emission standard of the normal hexane extract (oil content) in the human waste treatment plant and the sewage treatment plant is 30 ppm or less (the upper standard is provided), while the oil component is hardly treated by the biological treatment. Therefore, in the previous stage, it is removed by pressure floating, grease trap, centrifugal separation, etc. to reduce the concentration, and the conventional membrane separation device is intended to treat the wastewater thus low oil differentiated. Therefore, if wastewater containing oil with high concentration (sometimes several hundred ppm) such as kitchen wastewater and food processing plant is biologically processed and directly applied to the membrane separation device, it will be clogged immediately and become unprocessable. It will be.

Therefore, when the wastewater containing a high concentration of oil is subjected to biological treatment and then membrane separation is to be performed, it is necessary to reduce the oil content in the wastewater in advance. The degree is 30 ppm or less in view of the above wastewater standards, but it is necessary to be 5 to 10 ppm or less for stable treatment over a long period of time. That is, even if the dissolved oxygen in the wastewater is sufficient,
The oil covers the microorganisms and inhibits the intake of oxygen, resulting in a lack of oxygen and a decrease in activity. This phenomenon is seen at around 10 ppm. At around 20 ppm, this effect becomes noticeable. Currently, most of the oil is removed by pressure levitation. In the case of small-scale drainage, grease trap is also used, but in the case of pressure floating treatment, there is an advantage that SS can be removed at the same time.

[0006]

However, this pressurized flotation treatment requires a large amount of coagulant, requires power costs, and the aerated air emits a foul odor, and the separated oil content is decomposed. It is extremely problematic that it gives off a bad odor and takes time to process it.

Furthermore, the biggest difficulty in floating under pressure is the oil content (SS
Well) cannot be removed sufficiently. Conventionally, aeration has been performed for a long time or a large amount of coagulant has been added to reduce the amount as much as possible, but it is extremely difficult to set 10ppm or even 30ppm or less. Therefore, if oil adheres to the surface of the film, it is extremely difficult to remove it, and the processing capacity is extremely reduced. The only method for removing the oil adhering to the membrane is to pull the membrane above the water surface for cleaning or replace the membrane itself.

Further, in the case of the grease trap, if the accumulated oil is not always removed, it will flow out, and the bad odor of the removed oil or the removed oil will cause the operator physical and physical pain. In addition, in the case of centrifugal separation, there are problems that it is costly and labor-intensive, and that the offensive odor of the removed oil deteriorates the environment. Furthermore, a technique has also been proposed in which an alkali is added to the waste water to remove the oil content adhering to the membrane surface (Japanese Patent Laid-Open No. Sho 5)
No. 8-183981) cannot be used for biological treatment because the change in pH threatens the survival of microorganisms.

[0009]

In view of the above circumstances, the present inventor has completed the method of the present invention as a result of diligent research, and is characterized in that wastewater containing oil is biologically treated. In such a case, the wastewater to which the saponin-containing agent has been added is treated in the biological treatment tank, and then solid-liquid separated by the membrane separator.

Here, the term "drainage" refers to all the water to be treated including domestic wastewater, industrial wastewater, etc., but mainly the wastewater containing a large amount of oil. For example, it is wastewater from the food service industry and food processing factories, and miscellaneous wastewater from households also contains a large amount of oil. Except for human waste water (sewage sludge), it also contains a lot of oil. The oil component means a normal hexane extract (norhex component). It is said that the water quality standard for treated water of Norheki component is several to several tens of ppm, but 600 to 700 ppm in wastewater from food processing factories and food service industries.
May also be included.

Next, the biological treatment method of waste water is a treatment method of decomposing and removing organic matter contained in the waste water by the action of microorganisms, and is a method widely used for treating a large amount of waste water. Depending on the treatment method, there are an activated sludge method, a contact aeration method, a high-speed oxidation method and the like, but in any case, it is necessary to finally solid-liquid separate sludge from clean treated water.

A membrane separation method uses a membrane for this solid-liquid separation. The membrane processing equipment includes flat type, tubular type,
There are various types such as hollow fiber type and spiral type, and depending on the type of membrane, the reverse osmosis membrane (RO membrane),
Various materials such as ultrafiltration membranes (UF membranes) and microfiltration membranes (MF membranes) are used. Currently, ultrafiltration membranes are commonly used in wastewater treatment because of their relatively low permeation pressure compared to other membranes, the ability to withstand high solids loadings, and the wide selection of molecular weight fractions. In addition, the ultrafiltration membrane ensures removal of SS, E. coli, viruses and high molecular weight organic substances.

The membrane separation device introduces wastewater that has been aerated in the aeration tank or the contact aeration tank. Depending on the shape of the membrane separation device, it may be stored inside the aeration tank or the contact aeration tank before use. It may be done (inferred rare film method). In these cases, the settling tank is unnecessary. Further, it has an effect of removing oil adhering to the surface of the film by aeration. Alternatively, the membrane separation device may be housed in a settling tank, and aeration may be performed intermittently. Intermittent aeration has the advantages that anaerobic and aerobic conditions alternate and denitrification is performed, and the deposits on the film are not solid and dense, and removal by aeration can be performed easily. In this way, the membrane separation device may be installed as it is by using the conventional biological treatment device, but when a new biological treatment device is installed, the settling tank is not required, so the installation area is significantly increased. Can be reduced.

Next, the saponin-containing agent is charged upstream from the aeration tank during the wastewater treatment process. What is saponin?
A type of glycoside contained in plants, which is a generic name for producing colloidal aqueous solutions that are remarkably bubbly like soap, and is found in many plants. The type of saponin used in the present invention is not limited, but from the viewpoint of cost and stable supply, it is preferable that the content of the saponin in the plant is large and the plant is present in a large amount and can be stably obtained. From this perspective,
The saponins obtained from quillaja saponins, yucca, rafts, soybeans, sugar beets and the like are preferable. Of these, quillaja saponin extracted from a soap tree (scientific name: Quilaia saponaria Mol. Rosaceae) native to Chile, Bolivia, Peru, etc. in South America is particularly preferable. This is a triterpene type glycoside represented by the chemical formula 2 in which quillaic acid having the structure of the chemical formula 1 is used as an aglycone (a non-carbohydrate part of the glycoside). This is because there are few saponins, and an extract with a relatively high saponin content can be obtained.

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As the saponin-containing agent, an extract (including a solvent) extracted from a plant may be used as it is, or a purified product itself may be used. The extraction method may be an ordinary method and can be performed with a lower alcohol such as ethanol. Furthermore, a refined product or an extract may be used in the form of powder, granules, or tablets. The extract extracted from the plant contains a large amount of sugars and proteins, but depending on the type of membrane, these may act undesirably.
In such a case, the purified product may be used alone, or the purified product may be added to the extract for use.

By the way, the present inventor has found that saponin is effective in the biological treatment process of sewage. This is because saponin is a glycoside, it serves as a nutrient for microorganisms and has a high oxygen content. It is speculated that the efficiency of treatment is improved as a result of the fact that, as a result, they help the reproduction of microorganisms. Further, in the present invention, it is considered that the emulsifying and degrading action of the oil component plays an important role. That is, when a saponin-containing agent is added to wastewater containing a high concentration of oil, it is emulsified by its emulsifying action and microorganisms are easily digested and decomposed, and most of it is finally converted into sludge. In addition, the remaining oil is also emulsified, so that it rarely adheres to the surface of the film.

This emulsifying action can be achieved with synthetic detergents and other synthetic surfactants, but it cannot be used for wastewater treatment because it greatly inhibits the activity of microorganisms. In contrast, saponins are safe, natural surfactants that humans can ingest. Further, salts such as salt firmly adhere to the surface of the ultrafiltration membrane to inhibit solid-liquid separation, but the saponin-containing agent is recognized to effectively prevent the adhesion of salts.

The amount of the saponin-containing agent added varies depending on the concentration of the oil component in the wastewater, but is usually 0.01 to 1.0 ppm, particularly 0.12 to 0.4 ppm (content 4% liquid) in terms of the purified product in the wastewater. Is about 3 to 10 ppm). In the case of the liquid saponin-containing agent, it is advisable to add it by a method such as constantly dropping with a metering pump. In the case of solid formulations such as tablets and granules,
It is advisable to add appropriate amounts at appropriate intervals. The saponin-containing agent is added to the aeration tank or the adjustment tank upstream of the aeration tank.

The treated water obtained by the method of the present invention is
It may be discharged as it is, or may be subjected to a tertiary treatment and discharged. In some cases, this treated water can be used as tap water. In particular, kitchen wastewater from the food service industry can be reused as toilet flushing water and wash water, and toilet drainage and kitchen drainage from service areas on expressways can be treated.
It is most suitable for circulatory use as flushing water or flush water for toilets. Moreover, since saponin passes through the low molecular weight organic ultrafiltration membrane, regenerated water or circulating water contains a saponin component, which causes nitrogen compounds such as urea to adhere to the toilet bowl and cause coloration or give off a bad odor. There is also an effect to prevent.

[0020]

【Example】

(Embodiment 1) Next, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 shows an experimental apparatus used in the method of the present invention, in which food factory wastewater (water intake from a conditioning tank) stored in a raw water tank 1 is intermittently and quantitatively sent to an aeration tank 2, where aeration is performed for biological treatment. . A membrane separation device 3 is housed inside the aeration tank 2, and the treated water that has undergone solid-liquid separation here is sent to a treated water tank 4. In the actual device, the aeration tank 2
Try to pull the sludge out of it. This membrane separation device 3 is
Since two ultrafiltration membranes are assembled as a set and a negative pressure is applied to the inside of the two membranes, the treated water is sucked from the outside and collected and treated. It is configured to be sent to the water tank 4. In addition, the film used 10 sheets of 0.4 m ² . Further, since the aeration device 5 is arranged below the membrane separation device 3, the deposits on the surface of the membrane are removed by this aeration.

When this raw water (BOD: about 1,200 ppm, normal hexane extract: about 120 ppm) was treated with the above experimental apparatus at a rate of 600 liters / day, the treated water contained almost no normal hexane extract. (BOD is less than 10ppm). However, after 7 days, the membrane surface was covered with oil, and the permeation flux of the membrane was extremely reduced, so that the treatment became impossible. Therefore, when the adhered oil was removed with a brush, the membrane permeation flux was recovered, but after several days, the treatment became impossible again, so the experiment was stopped.

Under the same conditions as above, the raw water was treated by adding 10 ppm of 4% Kiraya Sapponni as a saponin-containing agent, and the membrane permeation flux was hardly reduced even after one month, and the treatment was performed well. It was

Since the treated water contains few BOD and COD components and no Escherichia coli, it can be sufficiently used as a tap water. Therefore, it is possible to sufficiently withstand the circulation use of toilet drainage in the service area.

[0024] These results were obtained because the oil component was emulsified by the saponin-containing agent and was easily decomposed by bacteria, and the bacteria were activated to efficiently decompose the emulsified oil component. It is thought that it was caused by being absorbed or adsorbed by sludge.

(Embodiment 2) FIG. 2 is a system diagram of wastewater treatment in a service area in which the method of the present invention is carried out.
The wastewater from the kitchen 6 merges with the wastewater from the public toilet 8 through the grease trap 7 (optional), and is sent to the septic tank 9. The drainage is passed through the screen 10 and the adjusting tank 11 and the aeration tank 1
2 is subjected to biological treatment and is subjected to solid-liquid separation in the membrane separation device 13. Treated water (medium water) is circulated and used as flush water for flush toilets and flush water. Part of the water in the aeration tank 12 is discharged, and the concentrated sludge is extracted. In this case, the saponin-containing agent digests and decomposes oil in kitchen wastewater and toilet wastewater, and the remaining oil is emulsified and dispersed, so that it does not adhere to the surface of the membrane and hinder solid-liquid separation. Enables stable processing over time. Further, salt in the waste water is also prevented from solidifying and adhering to the membrane surface. In addition, the saponin component remains in the treated water, and this prevents nitrogen compounds such as urea from adhering to the surface of the toilet bowl, so that coloring and offensive odor can be prevented.

[0026]

As described above in detail, according to the method of the present invention, when the wastewater containing oil is biologically treated, the wastewater containing the saponin-containing agent is treated in the biological treatment tank and then solidified by the membrane separation device. Liquid separation. Therefore, the following effects are produced. Since the oil content in the waste water is in a form that is easily digested and decomposed by microorganisms due to the emulsifying action of saponin, etc., the reduction of the membrane permeation flux due to the oil content in the waste water adhering to the surface of the membrane is prevented. Therefore, solid-liquid separation of the wastewater containing oil, which has been impossible or difficult to put into practical use in the past, can be stably performed in the membrane separation device. The membrane separation method is an ideal alternative to the solid-liquid separation in the settling tank, which has been the most problematic in the biological treatment process of wastewater because of the reduction of the installation area and the improvement of the separation performance. The treatment of the oil content, which is the only drawback, by the method of the present invention, will occupy a solid position in the wastewater treatment field. Moreover, by adding a saponin-containing agent, DO (dissolved oxygen)
As a result, the purification efficiency is improved and the biological treatment itself is efficiently performed, providing the ultimate wastewater treatment method. The treated water obtained by the method of the present invention can also be used as tap water. As a result, it can be reused as toilet water,
It will be possible to significantly reduce water charges.

[Brief description of drawings]

FIG. 1 is a schematic view of an experimental apparatus used in the method of the present invention.

FIG. 2 is a wastewater treatment system diagram in a service area where the method of the present invention is implemented.

[Explanation of symbols]

 1 Raw water tank 2 Aeration tank 3 Membrane separation device 4 Treated water tank 5 Aeration device 6 Kitchen 7 Grestrap 8 Public toilet 9 Separation tank 10 Screen 11 Adjustment tank 12 Aeration tank 13 Membrane separation device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C02F 3/12 ZAB C02F 3/12 ZABS

Claims (5)

[Claims] 1. When biologically treating wastewater containing oil, the wastewater with a saponin-containing agent added is treated in a biological treatment tank and then subjected to solid-liquid separation in a membrane separation device. Biological treatment method. 2. The biological treatment method for oil-containing wastewater according to claim 1, wherein the membrane separation device is installed in an aeration tank or a subsequent treatment tank. 3. The biological treatment method for oil-containing wastewater according to claim 2, wherein aeration is carried out from below the membrane separation device to remove oil adhering to the membrane surface. 4. The method for biological treatment of oil-containing wastewater according to claim 3, wherein intermittent aeration is performed. 5. A water treatment system in which a saponin-containing agent is added to toilet drainage or kitchen drainage for biological treatment, and then treated water subjected to solid-liquid separation by a membrane separator is circulated and used as toilet flush water or wash water. Item 2. A biological treatment method for oil-containing wastewater according to item 1.