JP2000342911A - Dynamic filter body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic filter body capable of keeping a filter flux stable for a long time by effectively washing even the interior of the filter body to prevent the accumulation of turbidity in the filter body. SOLUTION: A dynamic filter body 3 has a support, the filter cloth provided along the outer surface of the support and having a mesh size permitting suspended particles to substantially pass and a flow channel 5 of filtered water transmitted through the filter cloth and collects suspended particles by the dynamic filter layer formed on the surface of the filter cloth. An air supply means a is provided to the flow channel 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dynamic filter for filtering water containing suspended particles such as activated sludge.
In particular, the present invention relates to a dynamic filter which is immersed in a biological reaction tank and is suitable as a filter for activated sludge filtration for efficiently separating activated sludge and obtaining biologically treated water.

[0002]

2. Description of the Related Art As means for solid-liquid separation of activated sludge when sewage such as sewage and industrial wastewater is treated by activated sludge, the present applicant has previously immersed a filter provided with a filter cloth in a biological reaction tank. Various patent applications have been filed for an activated sludge filtration device that separates activated sludge by solid-liquid separation by extracting filtered water that has passed through the filter cloth of the filtration body as treated water, and a filtration body used for the same. JP-A-10-192880, JP-A-11-19677 and the like).

[0003] Filtration by this filter is actually carried out by a layer of adhering activated sludge particles formed on the surface of the filter cloth of the filter as the filtration proceeds (dynamic filtration layer; hereinafter simply referred to as "filtration layer"). There is.)
That is, the filter cloth of the filter is substantially 2 m thick made of a nonwoven fabric of metal or polymer fiber that allows activated sludge particles to pass through.
m, but under the condition that the driving pressure for filtration is small, an adhering layer of activated sludge particles is formed on the surface of the filter cloth, and the adhering layer can prevent the passage of the activated sludge particles. Become like

FIG. 3 is a cross-sectional view showing the basic structure of the above-mentioned conventional activated sludge filtration apparatus. A diffuser pipe 2 for supplying oxygen required for a biological reaction to one side of a biological reaction tank 1 is shown. Is provided on the other side, and the filter body 3 is provided.
A ventilation pipe 4 is provided below the bottom.

[0005] The filter body 3 are those comprising a filter cloth such as a nonwoven fabric, permeate water valve V ₁ that has passed through the filter cloth
And discharged out of the system as treated water. Reference numeral 6 denotes a partition wall for rectifying the liquid flow in the tank by aeration (this partition wall is not essential,
You don't have to. ). 7 is a backwash water tank, at the time of backwashing operates the pump P, backwash water is fed to the filter body 3 with the valve V _2. B is a blower, by a valve V ₃ or V ₄ is opened, air is supplied to the sparger 2 or vent pipe 4. Reference numeral 8 denotes a raw water introduction pipe.

[0006] Usually, a filter 3 is provided in the biological reaction tank 1.
Are arranged in parallel to form a filtration unit,
The filtered water outlet pipes of the filter body 3 are connected to each other by a header pipe.

In this activated sludge filtration device, oxygen necessary for a biological reaction is supplied from the air diffuser 2, and a gas for washing the filter 3 is supplied from the ventilation tube 4.

[0008] In the biological reaction tank 1, the updraft occurs on one side of the tank provided with the diffuser 2 due to the air diffused from the diffuser 2, and the downflow flows on the other side provided with the filter 3. That happens,
A gentle circulation flow (swirl flow) of the liquid in the tank is formed. 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.

The diffuser tube 2 is provided on the side opposite to the side where the filter body 3 is provided, and is not provided below the filter body 3. Since the filter body 3 is separated, the filter body 3 does not directly come into contact with air bubbles generated by the air diffuser 2. Therefore, the filtration layer formed on the surface of the filter cloth 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 stabilized.

In this activated sludge filtration apparatus, the water level at the open end of the filtered water discharge pipe 5 is set lower than the water level of the biological reaction tank 1, and the filtration proceeds with this water level difference (head difference) ΔH as a driving force. .

In this activated sludge filtration device, if the filtration is continued for a long time, the filtration speed decreases due to the compaction of the filtration layer formed on the surface of the filter cloth of the filter body 3.

Accordingly, in order to prevent the filtration layer from being compacted, the flow of water is stopped and the filter 3 is subjected to gas-liquid mixing by intermittently aerating from a ventilation pipe 4 provided below the filter 3. Exposed to the flow sweep (hereinafter referred to as “primary air cleaning”
It may be called. ). Thereby, the filtration layer which is being consolidated can be effectively peeled and removed, and a decrease in filtration speed due to the consolidation of the filtration layer can be prevented. Further, during or after the aeration, the backwashing water in the backwash water tank 7 (usually, treated water is used) is backflowed into the filter body 3 to perform backwashing.

If the filtration is continued during the separation of the filtration layer due to the aeration from the ventilation pipe 4, the filtering action by the filter body 3 cannot be obtained, and the sludge mixture in the biological reaction tank 1 flows out, and the filtered water Turbidity worsens. Therefore, the removal of the filtered water is stopped during the operation of separating the filtration layer.

Therefore, in the biological reaction tank 1, the operation is performed such that the filtration step and the air washing and backwashing steps are alternately and repeatedly performed according to a time chart. Once every 24 hours
It is performed for about 60 minutes. In addition, since the filtered water obtained immediately after the restart of the filtration after the air washing and backwashing steps is often turbid, the initial filtered water is returned to the biological reaction tank 1 until clear filtered water is obtained. In some cases.

[0015]

In such a dynamic filtration, in order to maintain a stable filtration flux and the quality of the filtered water, the filtration flux is appropriately set, and a filtration layer formed on the outer surface of the nonwoven fabric is formed. As described above, it is necessary to prevent the filtration layer from being densified by periodically exfoliating it by aeration from below the filter.

However, unlike the membrane filtration, the dynamic filtration uses a filter cloth such as a nonwoven cloth having openings through which suspended particles can pass substantially. Therefore, fine turbidity cannot be completely prevented. During or immediately after aeration from below the filter, the turbid matter flows into the filter. Most of the turbidity that has flowed into the filter body flows out of the system together with the filtered water, but a part of the turbid matter accumulates in the lower part of the filter body, and the secondary side of the nonwoven fabric (the back side, ie, inside the filter body). To form a cake layer.
In the case of the backwashing by injecting the backwash water into the filter body, these cannot be effectively discharged out of the filter body, which causes a long-term decrease in filtration flux and an increase in filtrate turbidity. Becomes

The present invention solves the above-mentioned conventional problems and effectively maintains the filtration flux for a long period of time by effectively cleaning the inside of the filtration body and preventing the accumulation of turbidity in the filtration body. It is an object of the present invention to provide a dynamic filter capable of performing the following.

[0018]

A dynamic filter according to the present invention comprises a support, a filter cloth provided along the outer surface of the support and having openings for substantially passing suspended particles, A dynamic filter for forming suspended particles by forming a dynamic filtration layer on a surface layer of the filter cloth, comprising: supplying a gas to the flow path. An air supply means is provided.

In the dynamic filter of the present invention, the gas is blown into the flow passage of the filtered water by the air supply means (hereinafter, this operation is referred to as "secondary air cleaning"), so that it adheres to the flow passage. The accumulated turbid matter is separated and broken to form a fine suspension, which can be easily discharged out of the filter. Therefore, a decrease in the filtration flux and a decrease in the quality of the filtered water due to accumulation of turbid matter in the filter body are prevented.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a dynamic filter according to the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing an embodiment of a dynamic filter of the present invention. FIG. 1 (a) is a partially cutaway front view,
(B) is a schematic cross-sectional view along the line BB in (a).

The filter 31 has a non-woven fabric 34 as a filter cloth attached to both sides of a support 32 via a net spacer (net-like body) 33, and is fixed by a mounting frame 35. The support 32 is formed of a frame-shaped member whose portion facing the nonwoven fabric 34 is a hollow portion 32B.
Nonwoven fabric 3 via net spacer 33 so as to close 2B
4 is attached and fixed by an attachment frame 35. Further, two pipes 36 communicating from the upper end face side of the support 32 to the hollow portion 32B of the support 32 are provided.
There are two pipes 37 communicating from the end face side of the bottom to the cavity 32B of the support 32.

The support 32 is not particularly limited as long as it supports a nonwoven fabric and has sufficient rigidity to withstand the water pressure when immersed and placed in a water tank, and is not particularly limited. A plate or frame made of a metal, synthetic resin such as polyvinyl chloride, ABS resin, polyester, or ceramics such as aluminum oxide is preferable.

The non-woven fabric 34 is made of a polymer such as polyester or polypropylene, or a metal material such as copper or stainless steel, and has a mesh size of 30 μm or more, preferably 30 to 1000 μm, and a thickness of 30 to 1000 μm. Is 2mm
Hereinafter, those having a thickness of 0.1 to 1 mm are particularly preferable in order to prevent clogging of the nonwoven fabric and perform stable filtration.

The net spacer 33 may have a mesh size of 5 mm or less, preferably 0.4 to 1.7 mm, and various types can be used.

By lining the nonwoven fabric 34 with such a fine net spacer 33, the nonwoven fabric 34
The filtration flux on the surface is made uniform, the dynamic filtration layer is evenly formed on the surface of the nonwoven fabric 34, and clear filtered water can be stably obtained.

It is preferable that the net spacer 33 and the non-woven fabric 34 are joined and integrated. Thus, by integrating the net spacer 33 and the non-woven fabric 34, the strength of the non-woven fabric 34 is increased, and Accumulation of turbidity between them can be prevented. It is desirable to join the entire nonwoven fabric 34 and the spacer 33 from the viewpoints of filtration performance and strength, but it is also possible to join the nonwoven fabric 34 and the spacer 33 only partially such as in a lattice shape or at the end. In this case, examples of the joining method include an adhesive, heat, pressure, and a mechanical method. Examples of the adhesive include polyamide and polyester. There is also a method of combining a plurality of joining methods, for example, a method of bonding a nonwoven fabric and a spacer with an adhesive and joining the rollers by applying pressure while applying heat (for example, 100 to 200 ° C.).

When the hollow body 32B is provided in the support 32, as in the case of the filter 31 shown in FIG. 1, if the support is large, the flatness of the nonwoven fabric 34 may not be maintained only by the wire mesh spacer 33. is there. In this case, a wire mesh spacer having a wide mesh width and rigidity is further provided under the net spacer 33, and the nonwoven fabric 34 and the net spacer 33 are provided.
Is preferably supported. Further, the nonwoven fabric 34 and the net spacer 33 may be supported using a support or a support rod which does not impair the filtration or the filtered water flow path.

In the present embodiment, the filtered water that has passed through the nonwoven fabric 34 is taken out through the cavity 32 B of the support 32 and the pipe 37.

At this time, since the nonwoven fabric 34 used for the filter 31 has a larger opening than the activated sludge particles, a small amount of turbid or activated sludge particles are mixed into the filtered water as described above. These turbid and activated sludge particles tend to settle down. Therefore, it is preferable that the filtered water is taken out from a pipe 37 provided at a lower part of the filter 31 in order to prevent the same from being deposited in the filter 31 and to be discharged together with the filtered water.

In the filter 31 of this embodiment, as described below,
A pipe for backwashing and a pipe for secondary-side air cleaning are connected to the pipe 37 for removing filtered water.

A plurality of such filter bodies 31 can be connected in series and used as a filtration unit.

Hereinafter, an example of a procedure for cleaning a filter according to the present invention will be described with reference to FIG. 2, which is a cross-sectional view showing an embodiment of an activated sludge filter using such a filter. In FIG. 2, members having the same functions as those shown in FIG. 3 are denoted by the same reference numerals.

In the filter body 3 shown in FIG. 2, the pipe 36 in FIG. 1 is used as the air release pipe 10, and the pipe 37 in FIG. a secondary air cleaning pipe 9 having a side air cleaning valve V _5, is obtained by connecting a vacuum pipe 11 having a vacuum valve V ₆ and the vacuum pump VP, other activated sludge filtration apparatus shown in FIG. 2 The configuration is the same as that of the activated sludge filtration device shown in FIG.
Also, a filtration unit is formed by connecting a plurality of filtration bodies 3 in series,
The piping of each filter is assembled in a header tube (not shown).

Conventionally, as described above, the operation of the apparatus comprises a filtration step and a primary air cleaning and backwashing step in which the cake layer formed on the outer surface of the non-woven fabric is aerated from the lower part of the filter body by the following procedures. Was repeated periodically (1 to 8 times / day).

The aeration air valve V ₃ is closed, the cleaning air valve V ₄ is opened and aeration is performed from the lower part of the filter 3 through the ventilation pipe 4, and the cake layer formed on the outer surface of the nonwoven fabric of the filter 3 is peeled off. Thereafter, by closing the valves V ₄ and terminates the primary air wash. The amount of aeration at this time is 10 m ³ / hr / m ² or more per horizontal sectional area of the filtration unit, and the aeration time is 2 to 3
More than one minute, usually several minutes to 30 minutes is required. Also,
Left open aeration air valve V ₃ may be carried out this primary air washing but, valve V ₃ from the viewpoint of energy saving
Is preferably closed. Incidentally, in this primary air cleaning filtration water valve V ₁ is closed, to stop the filtration.

During or after the above steps, the backwash valve V ₂ is opened, and the washing water is injected into the filtered water discharge pipe 5 from the backwash water tank 7 by the pump P (or may flow naturally).
The turbidity and air deposited in the pipe 5 are pushed out. This amount of backwash water needs to be about 0.1 m / sec or more as the flow velocity in the pipe.

The valve V ₂ for backwashing is closed, the valve V ₃ for aerated air is opened to make a normal aerated state, and after a swirling flow is formed in the tank, the valve V ₁ for filtered water is opened to perform a filtration step. To resume.

If the primary air cleaning and backwashing step and the filtration step are repeatedly performed for a long time, as described above, SS accumulates in the lower part of the filter body 3 (secondary side), A cake layer is formed on the spacer portion, and a reduction in filtration flux and an increase in turbidity of filtration water occur. In the dynamic filter of the present invention, in order to prevent this, air is blown into the filter 3 from the lower part of the filter 3 to accumulate SS in the lower part of the filter.
And the cake layer formed on the surface of the net spacer is peeled off. Then, secondary side air cleaning is performed to discharge the finely divided or peeled SS out of the system as filtered water or the like.

This secondary side air cleaning step includes the following [1]-
This is performed according to the procedure of [3].

[0041] [1] or during the filtration step in the primary air wash, open the secondary air cleaning valve V _5, the filter body 3
Aeration inside. At this time, most of the exhaled air does not pass through the non-woven fabric of the filter 3 and is discharged out of the system through the air release pipe 10 above the filter 3. At this time, the amount of air is 20 m ³ / hr per horizontal sectional area of the hollow portion of the filter 3.
/ M ² or more, especially 100 m ³ / hr / m ² or more. Note that this secondary air cleaning if during the filtration process, filtration water valve V ₁ was a closed.

[0042] [2] secondary air cleaning after completion, in order to the secondary-side air cleaning valve V ₅ are closed, and discharging the air filtered water discharge pipe 5 to restore the filtered water siphon, reverse open the washing water valve V _2, or water injection from backwash tank 7 by a pump P, or opened vacuum valve V _6, it absorbs water in the vacuum pump VP and the like. These operations may be performed continuously and in combination.

[3] When the siphon of the filtered water discharge pipe 5 recovers, the flow returns to the filtration step. Since SS inside the filter is discharged into the initial filtered water, the SS is discharged outside the system or returned to the biological reaction tank 2 until it becomes clear.

After performing the secondary side air cleaning,
By introducing the washing water into the filter from one of the upper and lower pipes of the filter and discharging it from the other pipe, the turbid matter can be more effectively removed.

The frequency of the secondary air cleaning may be performed during or immediately after the primary air cleaning, but may be performed once every several days to several months. It is set appropriately according to the operating conditions. The secondary side air cleaning time varies depending on the frequency and the amount of air, but a few minutes to 30 minutes is sufficient.

The dynamic filter shown in FIG. 1 and the activated sludge filter shown in FIG. 2 are examples of the dynamic filter of the present invention and an example of its application. It is not limited to the illustrated one.

The dynamic filter of the present invention is not limited to an aeration tank for activated sludge treatment, a filtration water tank disposed downstream of the aeration tank, a nitrification tank for nitrification denitrification treatment, and a filtration water tank subsequent to various biological treatments. It can be effectively applied as a filter for filtering various types of water containing suspended particles.

[0048]

The present invention will be described more specifically with reference to comparative examples and examples.

Comparative Example 1 A swirling flow of a nitrification tank of a treatment apparatus in which a synthetic sewage obtained by diluting a stock solution prepared with nutrients such as tuna extract, glucose fructose syrup, and phosphorus with city water is subjected to circulating nitrification denitrification In the section, the filter shown in FIG. 1 having the following specifications was installed, and dynamic filtration was performed.

In this treatment apparatus, the total capacity of the denitrification tank (anoxic tank) and the nitrification tank is about 2.4 m ³ , the overall residence time (HRT) is 10 to 13 hr, and the total BOD tank load is 0. The operation of the nitrification tank MLSS is performed under the conditions of 4 to 0.5 kg / m ³ / day and 5500 to 6500 mg / L.

[Specification of Filtration Body] Size: 500 × 500 × 15 mm Effective filtration area: about 0.38 m ² / sheet Non-woven fabric: Polyester non-woven fabric (25 g / basis weight)
m ² ) with a net spacer (20 mesh) bonded and integrated The filtration operation is to repeat the primary side air cleaning and backwashing step and the filtration step by the above-mentioned procedures, and the primary side air cleaning is The operation is performed once every three hours for four minutes, and the air volume at this time is 20 to 40 m ³ per horizontal cross-sectional area of the filtration unit.
/ Hr / m ² . During the primary air cleaning, backwashing was performed for 1 minute at a flow rate of 0.3 m / sec in the tube.

Under these operating conditions, the filtration flux was about 2.5 m
/ Day, but as shown in FIG.
In about a week, the filtration flux decreased. Further, before and after the reduction of the filtration flux, a phenomenon that the turbidity of the filtered water suddenly increased was also observed as shown in FIG. When the filter was taken out and checked, there was almost no cake layer on the surface of the nonwoven fabric, there was accumulation of SS in the lower part of the hollow portion of the filter, and the cake layer was thin on the secondary side of the net spacer and was formed almost all over. . The decrease in filtration flux is presumed to be due to the SS inside the filter body and the cake layer on the secondary side, and the sudden deterioration of the turbidity of the filtered water was due to the SS accumulated in the lower part being sucked into the filtered water for some reason. Estimated.

Example 1 As a countermeasure for Comparative Example 1, in Comparative Example 1, secondary-side air cleaning was performed at the time point A in FIG. 4 according to the above-described procedures [1] to [3]. At this time, the amount of air was set to about 100 m ³ / hr / m ² per horizontal sectional area of the hollow portion of the filter for 5 minutes, and then SS generated by peeling or the like was discharged out of the system as filtered water. The filtration flux was restored by this operation.

Next, at the time point B in FIG.
Similarly, secondary side air cleaning was performed at ³ / hr / m ² ,
In several days, the filtration flux decreased, and the condition of the filter was the same as in Comparative Example 1.

From the above, in order to obtain a stable filtration flux, it is judged that the air amount of the secondary side air washing is slightly insufficient at about 20 m ³ / hr / m ² , and about 100 m ³ / hr / m ² . The operation was performed in the same manner as in Comparative Example 1 except that the secondary-side air cleaning for 5 minutes was performed once every seven days. As shown in FIG. 4, the filtration flux was stable, and Also, the turbidity of the filtered water was well maintained.

[0056]

As described in detail above, according to the dynamic filter of the present invention, the inside of the filter can be effectively cleaned to prevent accumulation of turbidity in the filter, and as a result, filtration can be performed. By maintaining the flux stably, high-quality treated water can be stably obtained over a long period of time.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of a dynamic filter of the present invention, wherein FIG. 1 (a) is a partially cutaway front view, and FIG. 1 (b) is a cross-sectional view taken along line BB in FIG. 1 (a). It is.

FIG. 2 is a cross-sectional view showing an embodiment of an activated sludge filtration device to which the dynamic filter of the present invention is applied.

FIG. 3 is a sectional view showing a conventional activated sludge filtration device.

FIG. 4 is a graph showing the change over time of the filtration flux in Comparative Example 1 and Example 1.

FIG. 5 is a graph showing the change over time in the turbidity of filtered water in Comparative Example 1 and Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Biological reaction tank 2 Aerator tube 3 Filter body 4 Vent pipe 5 Filtration water discharge pipe 6 Partition wall 7 Backwash water tank 9 Secondary side air washing pipe 10 Air escape pipe 11 Vacuum pipe 31 Filter body 32 Support body 33 Net spacer 34 Non-woven fabric 35 mounting frame

Continuation of the front page (71) Applicant 000006655 Nippon Steel Corporation 2-6-3 Otemachi, Chiyoda-ku, Tokyo (71) Applicant 000005083 Hitachi Metals, Ltd. 1-2-1 Shibaura, Minato-ku, Tokyo ( 72) Inventor Hitoshi Daido 2-8-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside the Tokyo Metropolitan Sewerage Bureau (72) Inventor Eiji Aso 2-2-1-1, Nishishinjuku, Shinjuku-ku Tokyo, Tokyo Inside the Tokyo Metropolitan Sewerage Bureau (72) Inventor Kazuo Suzuki 3-4-7 Nishi Shinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Co., Ltd. (72) Inventor Shigeki Sawada 3-4-2-7 Nishi-Shinjuku, Shinjuku-ku Tokyo 2-6-3 Otemachi, Chiyoda-ku, Tokyo In-house Nippon Steel Corporation (72) Inventor Naoya Takahashi 20-1 Shintomi, Futtsu-shi, Chiba In-house Nippon Steel Corporation (72) Inventor Kazunari Ochiai Saitama 5200 Sankajiri, Kumagaya-shi, Japan Hitachi Metals, Ltd. (72) Inventor Mutsuro Nagai 52 Migajiri, Kumagaya-shi, Saitama 00 address F-term in Hitachi Metals, Ltd. (reference) 4D028 BC03 BC05 BC17 BD17

Claims (1)

[Claims] 1. A support, a filter cloth provided along an outer surface of the support and having openings for substantially passing suspended particles, and a flow passage of filtered water passing through the filter cloth. A dynamic filter body for forming suspended particles by forming a dynamic filtration layer on a surface layer of the filter cloth, wherein a gas supply means for supplying gas to the flow passage is provided. Filter body.