JP3284903B2 - Biological treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological treatment method, and more particularly to a biological treatment method for efficiently separating biological sludge by a filter immersed in a biological reaction tank.

[0002]

2. Description of the Related Art In a biological treatment apparatus such as an activated sludge for decomposing organic substances in water by a biological reaction, a sedimentation separation means such as a sedimentation basin is generally used for solid-liquid separation of the biological sludge. However, the conventional biological treatment apparatus provided with a sedimentation pond at the latter stage of the biological reaction tank has the following problems.

[0003] In the sedimentation treatment for sedimentation and separation of sludge due to a difference in specific gravity, there is a limit to the sludge separation performance, and the quality of treated water deteriorates when the inflow load changes or when bulking occurs.

[0004] For this reason, when a high quality of treated water is required, equipment such as a rapid filter and a strainer is required downstream of the sedimentation basin. An operation to return the biological sludge separated in the final sedimentation tank to the biological reaction tank is also required. Even if the sludge return operation or the sludge concentration control is performed, troubles such as scum generation or sludge floating in the final sedimentation basin occur, and the water quality often deteriorates. Since the sedimentation basin requires a large installation space,
Industrially disadvantageous.

[0005] On the other hand, instead of sedimentation and separation, biological sludge may be separated by ultrafiltration membrane or microfiltration membrane. According to this membrane separation treatment, high-quality treated water from which SS is highly removed can be obtained without requiring a large space such as a sedimentation pond.

[0006] However, in the membrane separation treatment using an ultrafiltration membrane or a microfiltration membrane, the operating energy is large, and a substance blocked by the membrane (this membrane contaminant is mainly composed of a high-molecular-weight microbial metabolite or the like). ) Contaminates the membrane, and the filtration performance is reduced due to blockage of the membrane pores. Therefore, there is a disadvantage that periodic chemical cleaning is essential.

In order to solve such a problem in the membrane separation treatment, a filter provided with a filter cloth is immersed in a biological reaction tank, and filtered water having passed through the filter cloth of the filter is taken out as treated water. It has been considered that biological sludge is separated into solid and liquid.

FIG. 5 is a cross-sectional view showing such a biological reaction tank (a swirling flow type deep tank aeration tank) for supplying oxygen necessary for a biological reaction to one side of the biological reaction tank 1. Diffuser 2
Is provided, and the filter body 3 is provided on the other side.

The filter 3 is composed of a flat filter unit 3A provided with a filter cloth such as a non-woven fabric, which is vertically stacked. The water is extracted from a treated water discharge collecting pipe 4 provided so as to communicate with the filtration side of the cloth, and stored in a treated water discharge trough 6 via a siphon pipe 5. 7 is a partition wall.

[0010] In the biological reaction tank 1, the updraft is generated on one side of the tank provided with the diffuser 2 by the air diffused from the diffuser 2, and the downward flow is generated on the other side provided with the filter 3. Is generated, a gentle circulation flow (swirl flow) of the liquid in the tank is formed (arrow F). By this circulating flow, a uniform cross flow is given to the surface of the filter cloth of the filter body 3, and the filtration proceeds.

In practice, the filtration by the filter 3 is carried out with a layer of adhering activated sludge particles formed on the surface of the filter cloth of the filter 3 as the filtration proceeds (dynamic filtration layer; hereinafter, simply referred to as “filtration layer”). It may be called.) That is, although the filter cloth of the filter body 3 substantially allows the activated sludge particles to pass through, under the condition where the driving pressure of the filtration is small, an adhering layer of the activated sludge particles is formed on the surface of the filter cloth. The adhering layer makes it possible to prevent the activated sludge particles from passing therethrough.

The air diffuser 2 is provided on the side opposite to the side on which the filter 3 is provided, and is not provided below the filter 3. Since air bubbles generated by the air diffusion are mostly separated in the upward flow portion, the filter body 3 does not directly come into contact with the air bubbles diffused by the air diffusion tube 2. Therefore, the filter layer formed on the filter cloth surface of the filter body 3 during the biological treatment and the filtration treatment does not peel off due to bubbles. Thereby, the filtration process is performed stably, and the quality of the treated water is also stable. If the air diffuser 2 is provided below the filter 3, the formation of the filtration layer of the filter 3 becomes unstable due to the air bubbles generated by the air diffusion of the air diffuser 2, and the quality of treated water is undesirably reduced.

In the biological reaction tank 1, the water level of the treated water discharge trough 6 is set lower than the water level of the biological reaction tank 1, and the filtration is advanced by using the head difference ΔH as a driving force.

As a simple operation, the siphon breaker 8 is opened, and the siphon pipe 5 is opened.
There is a method of backflowing the filtered water held in the rising section 5A. In addition, a separate backwash pump is provided, and siphon pipe 5
There is also a method of forcing the backwash water to flow backward.

In resuming the treatment water after the backwash, the siphon breaker 8 is closed, the vacuum valve 9 is opened, and the siphon tube 5 is evacuated to fill the siphon tube 5 with water. As described above, the filtration by the head difference ΔH is restarted.

[0016]

However, even when such a filter body made of a filter cloth is immersed in a biological reaction tank, there is a problem that the filtration speed is reduced when filtration is continued for a long period of time. The cause of this decrease in filtration rate is
It is to consolidate the filtration layer formed on the surface of the filter cloth.

As described above, by performing the backwashing of the filter,
Although the filtration rate can be recovered by removing the filtration layer, in the case of a large-scale filtration unit, it is difficult to perform uniform backwashing, and uneven backwashing occurs due to non-uniformity of backwashing. For this reason, there was a problem that the filtration rate could not be sufficiently recovered even if back washing was performed.

The present invention solves the above-mentioned conventional problems, and effectively prevents compaction of the filter layer of a filter body immersed and arranged in a biological reaction tank and thereby prevents a reduction in filtration speed, thereby achieving stable and efficient filtration. It is an object of the present invention to provide a biological treatment method that allows continuous filtration.

[0019]

According to the present invention, there is provided a biological treatment method comprising: a biological reaction tank; and an air diffusion tube provided at one side of the biological reaction tank for supplying oxygen required for the biological reaction. ,
A biological reaction comprising: a filter provided on the other side in the biological reaction tank; and a ventilation pipe provided below the filter in the biological reaction tank for supplying a gas for washing the filter. An apparatus, wherein the filter cloth constituting the filter body allows activated sludge particles to pass therethrough, but the filter cloth is formed on the surface of the filter cloth to form an adhering layer of activated sludge particles. In a biological treatment method of supplying raw water and taking out filtered water of the filter as treated water, the filter body is intermittently stopped by taking out treated water from the filter and supplying gas from the vent pipe. Characterized in that the attached layer on the surface of the substrate is peeled off.

In the present invention, gas is intermittently supplied from a vent pipe provided below the filter, and the filter is exposed to a gas-liquid mixed flow sweep to effectively reduce the density of the filter layer. It can be peeled off. For this reason, a decrease in the filtration speed due to the consolidation of the filtration layer is prevented.

If the filtration is continued during the separation of the filtration layer by the gas supply from the ventilation pipe, the filtering action by the filter body cannot be obtained, the sludge-containing biological treated water flows out, and the turbidity of the treated water decreases. Getting worse. For this reason, in the present invention, during the removal operation of the filtration layer, filtration is not performed, and
Of the treated water is stopped.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are sectional views showing an example of a biological treatment apparatus suitable for carrying out the biological treatment method of the present invention.
In FIG. 2, members having the same functions as those shown in FIG. 5 are denoted by the same reference numerals.

The biological treatment apparatus shown in FIG. 1 is different from the conventional apparatus shown in FIG. 5 only in that a ventilation pipe 10 is provided below the filter 3, and the other parts have the same configuration.

In this embodiment, oxygen necessary for a biological reaction is supplied from an aeration tube 2 provided at an intermediate depth in a biological reaction tank 1, and a filter 10 for washing a filter 3 is supplied from an aeration tube 10. Supply gas.

Since the air diffuser 10 is provided at an intermediate depth of the biological reaction tank 1, air can be sufficiently diffused by a general medium-pressure blower. Since it is provided at the bottom of the biological reaction tank 1 of the tank aeration tank, it is necessary to supply gas using a high-pressure blower having a discharge pressure larger than the water depth pressure.

In the present embodiment, at the time of biological reaction treatment, raw water is supplied to the biological reaction tank 1 and oxygen-containing gas such as air is diffused from the air diffuser 2 to perform biological treatment, and the biological treatment liquid is filtered. Filter through body 3 and as described above, head difference ΔH
The filtered water is taken out to the treated water discharge trough 6 as treated water by the filtration driving force of

In washing the filter body 3, the supply of raw water is stopped, the siphon breaker 8 is opened, and the liquid in the rising section SA of the siphon tube 5 is first made to flow backward as described above. The body 3 is backwashed. Thereafter, by aeration through the ventilation pipe 10, the filter layer on the surface of the filter cloth of the filter body 3 is washed and removed by the sweeping of the gas-liquid mixed flow. In this washing, the filter layer is in a state where it is easily peeled off by backwashing. Therefore, the filter layer can be efficiently peeled off by a gas-liquid mixed flow by aeration from the ventilation pipe 10.

During this time, since the water level in the biological reaction tank 1 and the water level in the siphon tube 5 are the same, no filtration is performed.

After washing such a filter, the aeration from the ventilation pipe 10 is stopped, the vacuum valve 9 is opened and the vacuum is evacuated to fill the inside of the siphon pipe 5, and the filtration is resumed. Restart the supply of raw water for biological treatment.

In the apparatus shown in FIG. 2, the treated water discharge collecting pipe 4 of the filter 3 is directly connected to the treated water discharge trough 6, and the treated water discharge trough 6 is provided with a water stop valve 6A. 1 is different from the apparatus shown in FIG.

In this apparatus, similarly to the apparatus shown in FIG.
The biological treatment liquid is filtered based on the head difference ΔH between the water level of the treated water discharge trough 6 and the water level of the biological reaction tank 1.

When the filter 3 is washed, the water stop valve 6A of the trough 6 is closed so that the water level of the trough 6 and the water level of the biological reaction tank 1 are at the same position, and the filtration is stopped. Then, as in the case of FIG. 1, aeration is performed through the ventilation pipe 10 to wash and remove the filter layer attached to the filter cloth of the filter body 3.

After the washing, the water stop valve 6A is opened, a head difference ΔH is provided between the water level of the biological reaction tank 1 and the water level of the trough 6, and the filtration of the biological treatment liquid is resumed.

In the present invention, it is preferable to carry out the separation and washing of the filtration layer of the filtration body before the filtration layer is compacted, and it depends on the sludge properties and the sludge concentration in the biological reaction tank. Specifically, it is preferable to perform the cleaning periodically once every 1 to 24 hours.

The peeling cleaning time and the amount of ventilation for peeling and cleaning may be any conditions under which the filtration layer of the filter can be peeled off, and the peeling and cleaning time is usually about 1 to 60 minutes. The amount of ventilation is preferably about 0.1 to ² m ³ / m ² · Hr per 1 m ² of surface area of the filter 3.

In general, air is used as a gas for washing the filter.

In the present invention, at the time of this stripping cleaning,
The filtration, that is, the removal of the treated water is stopped. This filtration stop time may be matched with the peeling and washing time, but after peeling and washing, it takes several minutes to form a filtration layer on the filter cloth surface of the filter body. May be made slightly longer, and after about 1 to 5 minutes have passed after the completion of the peeling and washing, the flow of water and the filtration may be restarted.

At the time of this stripping cleaning, the air from the air diffuser may be continued. However, since the gas-liquid mixed flow (ascending flow) by the gas supply from the vent pipe smoothly sweeps the surface of the filter body. For this reason, it is preferable to prevent the downward flow due to the air diffusion by the air diffuser from being generated in the filter body installation part. It is preferable to stop qi. However, in this case, it is necessary to use an oxygen-containing gas such as air as a cleaning gas from the ventilation pipe.

The apparatus shown in FIGS. 1 and 2 is an example of an apparatus suitable for carrying out the present invention, and the present invention is not limited to the illustrated embodiment.

For example, FIGS. 1 and 2 show a deep-water aeration tank as a biological reaction tank. However, the biological reaction tank used in the present invention is not limited to a deep-water aeration tank at all. good. The partition wall in the biological reaction tank is not necessarily required, and may be omitted. However, as shown in the figure, providing a partition wall in the center of the biological reaction tank is preferable because a circulating flow can be generated stably. . Further, such a biological reaction tank may be an aeration tank of an activated sludge treatment device that decomposes organic substances, or may be a nitrification tank that removes nitrogen. When performing denitrification, a partition wall is provided in the tank, for example, a denitrification section is provided on the upstream side, and a nitrification section is provided on the downstream side, and a return pipe is provided from the nitrification section to the denitrification section. It can also be provided to take out treated water.

In the present invention, a non-woven fabric or a woven fabric is used as the filter cloth of the filter. As the woven cloth, a woven cloth whose surface is raised is preferable. Since the surface of the nonwoven fabric is substantially flat, a bridge is easily formed on the surface, and the sludge particles can be efficiently captured.

If the thickness of the filter cloth is excessively large, sludge may accumulate in the filter cloth and cause clogging. Conversely, if the thickness of the filter cloth is too small, the strength is reduced and the filter cloth is easily broken. Therefore, the thickness of the filter cloth is preferably about 0.1 to 1 mm.

The filter cloth used in the present invention is one through which sludge particles can pass. Specifically, the filter cloth has a separation particle size (size of sludge particles to be separated) of 10 μm or more, particularly 30 to 1000.
Those having pores of μm are preferred.

The material of the fibers constituting the filter cloth is not particularly limited, and metal fibers such as copper and polymer fibers such as polyester and polypropylene can be used.

[0046]

The present invention will be described more specifically with reference to the following examples.

Example 1 A biological treatment of synthetic sewage containing a fish meat extract as a main component was carried out using the experimental apparatus shown in FIG.

In FIG. 3, 21 is a raw water tank, 22 is a biological reaction tank, 23 is a filter, 24 is a vent pipe, 25 is a diffuser pipe,
26 is a partition wall, 27 is a sedimentation tank, P ₁ and P ₂ are pumps, B
Is a blower, and V ₁ and V ₂ are valves. Reference numerals 31 to 35 denote pipes.

[0049] Synthesis sewage raw water tank 21 flows from line 31 with a pump P ₁ in the bioreactor 22. The inside of the biological reaction tank 22 is diffused by the blower B from the diffuser tube 25. The biological treatment water is filtered by the filter 23 and extracted from the pipe 32. Overflow water of the bioreactor 22 is withdrawn from the pipe 33, is solid-liquid separated in the precipitation tank 27, the separated sludge comprises a pump P ₂ pipe 3
The liquid is returned to the biological reaction tank 22 from 4 and the separated liquid is discharged from 35. The solid-liquid separation means is provided to keep the water level of the biological reaction tank constant.

In this experimental apparatus, synthetic sewage was introduced B
It was introduced into the biological reaction tank 22 so that the OD amount was 300 mg / L. The MLSS of the biological reaction tank 22 is about 4000 mg.
/ L, BOD-SS load is 0.15kg / kg
・ It was a day.

The effective area of the filter body 23 provided in the biological reaction tank 22 is 0.4 m ³ , and the filter cloth is a polyester nonwoven fabric made by Unitika (product number 20157 WTD, weight per unit area: 15).
g / m ² , separated particle size 100 μm, thickness 0.11 mm). The filtered water (treated water) of the filter 23 was taken out with a head difference of 6 cm as a driving pressure.

For 7 days from the start of water passage, the treatment was continued without performing the washing operation of the filter. As a result, the filtration speed gradually decreased from the initial 0.7 m / day to 0.2 m / day.

Then, the water supply was stopped for 24 hours and the ventilation pipe 2
After performing aeration at 4 to 4.4 m ³ / Hr to peel off and wash the filtration layer of the filter 23, the aeration of the ventilation pipe 24 was stopped and water flow was resumed. 7m /
Recovered until the day. Thereafter, once a day, the water flow was stopped for one hour, and the filter layer of the filter body 23 was peeled off and cleaned by aeration from the ventilation pipe 24 (that is, water flow was performed for 23 hours, and cleaning was performed for one hour). The filtration speed of 0.7 m / day could be maintained stably.

When the filter layer of the filter 23 was peeled off and washed, the air diffusion from the air diffuser 25 was also stopped.

The time-dependent change in the filtration rate in this experiment is as shown in FIG. 4, and it was confirmed that a high filtration rate could be stably maintained by intermittently peeling and washing the filter layer of the filter. .

During the experimental period, synthetic sewage water quality BOD:
The quality of the treated water is BOD: 5 mg for 300 mg / L
/ L was almost constant, and the quality of the treated water did not decrease by peeling and washing the filter layer of the filter body 23.

[0057]

As described in detail above, according to the biological treatment method of the present invention, when the biological treatment and the filtration are performed in the biological reaction tank in which the filter is immersed in the tank, the filter adheres to the filter. By effectively peeling and removing the filtration layer, it is possible to prevent a decrease in filtration speed due to consolidation of the filtration layer,
A stable and effective biological treatment can be continued for a long time.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a biological treatment apparatus suitable for carrying out the present invention.

FIG. 2 is a sectional view showing another embodiment of the biological treatment apparatus suitable for carrying out the present invention.

FIG. 3 is a system diagram showing an experimental apparatus used in Example 1.

FIG. 4 is a graph showing a change over time in a filtration rate in Example 1.

FIG. 5 is a sectional view showing a conventional example.

[Description of Signs] 1 Biological reaction tank 2 Aeration tube 3A Filtration unit 3 Filter body 4 Treated water discharge collecting pipe 5 Siphon pipe 6 Treated water discharge trough 7 Partition wall 8 Siphon breaker 10 Vent pipe 21 Raw water tank 22 Biological reaction tank 23 Filtration Body 24 Ventilation pipe 25 Diffusion pipe 27 Sedimentation tank

──────────────────────────────────────────────────続 き Continued on the front page (73) Patent holder 000001063 Kurita Water Industries Ltd. 3- 4-7 Nishishinjuku, Shinjuku-ku, Tokyo (73) Patent holder 000006655 Nippon Steel Corporation 2 Otemachi, Chiyoda-ku, Tokyo 2 6-3-3 (72) Inventor Hitoshi Daido 2-2-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside the Sewerage Bureau, Tokyo (72) Inventor Noriyuki Tajima 2-1-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Tokyo Sewer Within the Bureau (72) Inventor Tetsuo Hasegawa 5200 Sankajiri, Kumagaya City, Saitama Prefecture Inside Hitachi Metals Co., Ltd. Kurita Kogyo Co., Ltd. (72) Kunihiro Iwasaki 3-4-7 Nishi Shinjuku 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo In-house (72) Inventor Naoya Takahashi 20-1 Shintomi, Futtsu-shi, Chiba In-house Nippon Steel Corporation (72) Inventor Mitsuo Kondo 2-6-1 Otemachi, Chiyoda-ku, Tokyo Nippon Steel Corporation (56) References "Johkasou Kenkyu Vol.8 No.1 1996", Japan Environmental Improvement Education Center, published March 27, p27-3 (58) Fields surveyed (Int. Cl. ⁷ , DB name) C02F 3/12 B01D 29/62 B01D 65/02 520 B01D 69/14 C02F 1/44

Claims (2)

(57) [Claims] 1. A biological reaction tank, an air diffusion tube installed on one side of the biological reaction tank for supplying oxygen necessary for biological reaction, and installed on another side of the biological reaction tank A bioreactor comprising: a filtered body that has been removed; and a ventilation pipe provided below the filter body in the biological reaction tank and for supplying a gas for cleaning the filter body. The filter cloth, which allows the activated sludge particles to pass through, supplies raw water to a biological reaction apparatus that performs filtration by forming a deposit layer of activated sludge particles on the surface of the filter cloth,
In the biological treatment method for removing filtered water from the filter as treated water, intermittently stopping the removal of treated water from the filter and supplying gas from the ventilation pipe to deposits on the surface of the filter. A biological treatment method characterized in that a layer is peeled off. 2. An intermittent process for removing treated water from said filter.
Stop feeding and supply gas from the vent pipe
When peeling off the deposit layer on the surface of the filter, the air
2. The method according to claim 1, wherein air diffusion from the pipe is stopped.
Object processing method.