JPH10272486A - Blological treatment of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the abnormal generation of Arcella to which the clogging of meshes of a membrane is attributed and to secure water treatment stabilized for a long period of time by introducing waste water into a vessel incorporating a submerged membrane device to keep MLSS in the vessel high, and also performing intermittent aeration from below the submerged membrane device. SOLUTION: Waste water of high MLSS adjusted by using active sludge in a terminal treatment plant is accumulated in a raw water tank 1 and is intermittently and quantitatively sent to an aeration tank 2, where it is aerated to be subjected to biological treatment. Furthermore, a saponin containing agent is fed to the aeration tank 2 or to upstream thereof. In the aeration tank 2, a membrane separator 3 into which plural sets of ultrafiltration membranes are incorporated in a set of 2 is housed, and treated water which has been subjected to solid-liquid separation there is sent to a treated water tank 4. Since when the saponin containing agent is added, oxygen dissolving efficiency is improved to provide a superaerated state, an aeration device 5 arranged under the membrane separator 3 is operated under intermittent aeration to decrease Arcella and also remove material stuck on the membrane surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for solid-liquid separation of activated sludge resulting from biological treatment of wastewater using a submerged membrane device. The present invention relates to an improved method for treating wastewater biologically, which prevents the flux from being reduced.

[0002]

2. Description of the Related Art Recently, activated sludge treatment (a kind of biological treatment)
Membrane separation technology has attracted attention as a solid-liquid separation technology that can replace sedimentation separation, and research and commercialization in the fields of human waste treatment and sewerage have been advanced. This is membrane separation (membrane treatment)
In the case of (1), there is no obstacle to solid-liquid separation due to bulking or sludge floating, and the installation area is small, and the treated water of stable water quality is obtained. In addition, the improvement of the film has been progressed, and the effect of mass production has been produced. Above all, the submerged membrane device, in which the membrane separation unit is installed inside the aeration layer or the precipitation layer, has the advantage that the water flow of aeration and agitation always cleans the membrane surface, eliminating the need for a special cleaning device. There is.

[0003] As described above, the membrane separation method has an extremely excellent advantage as a solid-liquid separation technique in wastewater treatment.
However, in particular, in the case of a submerged membrane apparatus, the higher the MLSS of the liquid to be treated, the more stable the liquid to be treated, so that the liquid to be treated is not sufficiently stirred and the supply of oxygen varies. MLSS
Is about 3,000 to 9,000 ppm in the ordinary activated sludge method, but is as high as 10,000 to 20,000 ppm in the submerged membrane apparatus. This is to prevent over-aeration due to aeration for cleaning the membrane surface, resulting in an increase in nitrifying bacteria and easy clogging. In addition, at present, a sufficient membrane permeation flux (flux) cannot be obtained, and there is also a problem with the service life.

Further, if the normal hexane extract (oil) is contained in the waste water, the oil adheres to the membrane,
It has been clarified in experiments by the present inventor that processing is impossible in a short period of time. Usually, if the normal hexane extract is contained at 5 to 10 ppm, at most 20 ppm, the treatment becomes difficult.

[0005]

Therefore, the present inventor has proposed:
As a result of intensive studies to address these problems, as a result of adding a saponin-containing agent to wastewater to be treated, good results were obtained, especially in the latter (clogging by oil). However, in spite of this, the film was clogged in a relatively short period of time, and it was difficult to continue the treatment. Therefore, the present inventor further continued the research, and found that the addition of the saponin-containing agent improved the oxygen dissolving efficiency, resulting in overaeration, resulting in an abnormally large amount of round small Alkera, a kind of nitrifying bacteria. It was found that this caused clogging of the membrane.

[0006]

In view of the above situation, the present inventor has completed the method of the present invention as a result of diligent research, and is characterized by the fact that wastewater is treated biologically. , The wastewater to which the saponin-containing agent has been added is led into a tank incorporating a submerged membrane device, and the MLS in the tank is introduced.
It keeps S high (1.5-25,000 ppm) and controls the supply of oxygen by intermittent aeration from below the submerged membrane device, and controls the occurrence of abnormal Alkera that causes membrane clogging. is there.

[0007] Here, the wastewater refers to all the water to be treated including domestic wastewater, industrial wastewater, etc., regardless of the presence or absence of oil.
Next, the biological treatment method of wastewater is a treatment method of decomposing and removing organic substances contained in wastewater by the action of microorganisms, and is a method widely used for treating a large amount of wastewater. Depending on the treatment method, there are an activated sludge method, a contact aeration method, a high-speed oxidation method, and the like. In any case, it is necessary to finally separate solid and liquid sludge from clean treated water. What uses a membrane for this solid-liquid separation is a membrane separation method. In the present invention, an underwater membrane system using an ultrafiltration membrane is used.

Next, the saponin-containing agent is charged upstream of the aeration tank during the wastewater treatment process. What is saponin?
A type of glycoside contained in plants, which is a collective term for producing a colloid aqueous solution that is extremely millet like soap, and is found in many plants. In the present invention, the type of saponin used is not limited. However, from the viewpoint of cost and stable supply, it is preferable that the saponin has a large content in the plant and that the plant exists in a large amount and can be obtained stably. From this perspective,
Saponin obtained from Kiraya saponin, yucca, squid raft, soybean, sugar beet, and the like are preferable. Among them, particularly preferred is Kirayasaponin extracted from a soap tree (scientific name: Quilaia saponaria Mol. Rosaceae) native to Chilly, Bolivia, Peru and the like in South America. This is a triterpene-based glycoside that uses quilayanic acid as an aglycone (the non-saccharide portion of the glycoside), and is one of the few saponins whose structure and analytical techniques have been elucidated, and has a relatively high saponin-containing concentration. This is because an extract is obtained.

As the saponin-containing agent, an extract (including a solvent) extracted from a plant may be used as it is, or may be a purified product itself. The extraction may be carried out by a conventional method, for example, by extraction with a lower alcohol such as ethanol. Furthermore, those obtained by processing purified products or extracts into powder, granules, or tablets are also used. Note that the extract extracted from the plant contains a large amount of saccharides and proteins, but these may act unfavorably depending on the type of membrane.
In such a case, it is preferable to use only the purified product or to add the purified product to the extract.

By the way, the present inventor has found that saponin is effective in the biological treatment process of sewage, but this is because saponin is a nutrient for microorganisms because it is a glycoside and has a high oxygen content. It is presumed that, together with helping the propagation of microorganisms, treatment efficiency is improved. Further, in the present invention, it is considered that the emulsifying and decomposing action of the oil 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 becomes a form in which microorganisms are easily digested and decomposed, and finally, most of them are converted into sludge. Further, since the remaining oil is also emulsified, it is less likely to adhere to the surface of the film. Furthermore, the viscosity of the high MLSS wastewater itself is reduced, and the membrane is well washed with bubbles.

Although this emulsifying action is possible with a synthetic detergent or other synthetic surfactant, it cannot be used for wastewater treatment because it greatly inhibits the activity of microorganisms. Saponins, on the other hand, are safe natural surfactants that can be consumed by humans. Further, salts such as salt are firmly adhered to the surface of the ultrafiltration membrane to inhibit solid-liquid separation, and the saponin-containing agent has an effect of effectively preventing such salt adhesion.

The amount of the saponin-containing agent to be added is 0.01 to 1.0 ppm, particularly 0.12 to 0.4 ppm in terms of purified product relative to the wastewater.
(3 to 10 ppm as a 4% liquid). For the addition of a liquid saponin-containing agent, a method such as constant dropping with a metering pump may be employed. In the case of solid preparations such as tablets and granules, an appropriate amount may be added at appropriate intervals. The location where the saponin-containing agent is added is, for example, an aeration tank or an adjustment tank upstream thereof. Even if the concentration of the normal hexane extract becomes as high as about 200 ppm by adding the saponin-containing agent, the treatment can be performed without any problem. Furthermore, if the wastewater to which the oil is added is continuously treated for a long time (several tens of days), the oil-decomposing bacteria are acclimated, and even if the normal hexane extract of 500 ppm or more is present in the wastewater, it can be treated without clogging. became.

On the other hand, when a saponin-containing agent is added, the oxygen dissolving efficiency is improved, resulting in an over-aerated state. Therefore, intermittent aeration is performed to stop the aeration at appropriate intervals. When the aeration is stopped, the ORP decreases and the Alkera decreases. Fifteen
If the aeration is stopped for more than a minute, Alkera will decrease, but if it is stopped for a long time, it will hinder the cleaning of the membrane surface,
The suspension is performed for 10 to 30 minutes, more preferably around 15 minutes. However, if the aeration is stopped for about 20 to 30 minutes and aeration is performed for 40 to 20 minutes, the drainage system becomes anaerobic and denitrification is promoted.

[0014] 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 then discharged. In some cases, this treated water can be used as a middle water supply. In particular, kitchen wastewater from the food service industry is reused as flush water or flush water for toilets, and toilet wastewater and kitchen wastewater from service areas on expressways are treated,
It is most suitable for circulating use as toilet flush water or flush water. Moreover, since saponin passes through the ultrafiltration membrane because of low-molecular-weight organic substances, regenerated water and circulating water contain saponin components, which cause nitrogen compounds such as urea to adhere to the toilet bowl and cause coloration and foul odor. Also has the effect of preventing.

[0015]

【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 high MLSS wastewater adjusted to 20,000 ppm in MLSS was prepared in an aeration tank 2 using activated sludge from a terminal treatment plant in Osaka Prefecture stored in a raw water tank 1. It is sent and aerated here for biological treatment. Inside the aeration tank 2, a membrane separation device 3 is housed, and the treated water subjected to solid-liquid separation here is sent to a treated water tank 4. In an actual apparatus, sludge is drawn from the aeration tank 2. This membrane separation device 3
Because two sets of ultrafiltration membranes are incorporated in a set and negative pressure is applied inside the two membranes,
The treated water is sucked from the outside, collected, and sent to the treated water tank 4. The film is 0.4m
² of those were used 10 sheets. Since the aeration device 5 is disposed below the membrane separation device 3, the deposits on the surface of the membrane are removed by this aeration.

The drainage contains about 200 ppm of a salad oil manufactured by Company N and 4% of Kiraya Saponi as a saponin-containing agent.
The content is 10 ppm. The aeration is 45
Intermittent aeration was performed for 15 minutes. When this wastewater was treated at a rate of 600 liters / day by the above-mentioned experimental apparatus, the membrane permeation flux hardly decreased even after one month, and the treatment was performed well. In this treated water, BOD
Since it has few COD components and no Escherichia coli, it can be sufficiently used as a middle water supply. Therefore,
It can fully withstand the circulating use of toilet drainage in service areas. The result of this is that
It is presumed that the oil was emulsified by the saponin-containing agent and was easily decomposed by bacteria, and that the bacteria were activated and the emulsified oil was efficiently decomposed and adsorbed on sludge. still,
In the case of the comparative experiment in which the saponin-containing agent was not added, the surface of the membrane was covered with oil in about 2 days, and the treatment became impossible.

(Example 2) After the above experiment was continued for 60 days, wastewater with a normal hexane extract having a concentration of 500 ppm was treated, and similarly good treatment was performed.

[0018]

As described above in detail, according to the method of the present invention, in the case where the waste water is subjected to solid-liquid separation by a submerged membrane separation device, the waste water containing the saponin-containing agent is added to the tank in which the submerged membrane device is incorporated. , The MLSS in the tank is kept high, and intermittent aeration is performed from below the submerged membrane device to control the generation of nitrifying bacteria which causes clogging of the membrane. Therefore,
The following effects are obtained. The addition of the saponin-containing agent improves the agitation of the wastewater, and activates the microorganisms to perform favorable biological treatment such as removal of BOD. The intermittent aeration suppresses the mass generation of nitrifying bacteria such as Alquera, which is a major cause of clogging, and ensures long-term stable water treatment. In particular, even if a large amount of oil is contained in the wastewater, it will be in a form that is easily digested and decomposed by microorganisms due to the emulsifying action of saponin and the like. A reduction in flux is prevented. Therefore, solid-liquid separation of wastewater containing oil, which has been impossible or difficult in the past, can be stably performed by the membrane separation device.

[Brief description of the drawings]

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

[Explanation of symbols]

 Reference Signs List 1 Raw water tank 2 Aeration tank 3 Membrane separation device 4 Treatment water tank 5 Aeration device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 65/08 B01D 65/08 C02F 1/44 C02F 1/44 K 11/14 11/14 D

Claims (3)

[Claims] When wastewater is subjected to solid-liquid separation by a submerged membrane separation device, the wastewater to which a saponin-containing agent has been added is guided into a tank incorporating the submerged membrane device, and the MLSS in the tank is provided.
A biological treatment method for wastewater, characterized in that the wastewater is kept high while intermittently aerating from below the submerged membrane device to control the generation of nitrifying bacteria that cause clogging of the membrane. 2. The biological treatment method for wastewater according to claim 1, wherein the submerged membrane separation device is installed in an aeration tank or a subsequent treatment tank. 3. The method according to claim 1, wherein the intermittent aeration has an aeration stop time of at least 15 minutes.