JP2000279984A - Biological treatment equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biological treatment equipment capable of sufficiently preventing clogging of a membrane. SOLUTION: This equipment is provided with: a water treatment tank 3 into which water to be treated 2 is allowed to flow; an immersion membrane 4 immersed in the water to be treated 2 in the tank 3; suspended solid matter 8 allowed to exist in the wastewater to be treated 2 in the tank 3; an air diffuser for fluidizing the suspended solid matter 8 in the water to be treated 2 in the tank 3; biological sludge for subjecting the water to be treated 2 to biological treatment; a sludge withdrawal means for withdrawing the sludge 9 and the suspended solid matter 8 in the sludge 9 from the tank 3; a suspended solid matter separation vessel 12 for separating the sludge 9 and the suspended solid matter 8, both of which are withdrawn by the sludge withdrawal means, from each other; and a return means for returning the separated solid matter 8 in the vessel 12 to the tank 3; wherein since the sludge 9 is accumulated in the tank 3 by the membrane separation and the suspended solid matter 8 is liable to be incorporated into the sludge 9, the sludge 9 and the suspended solid matter 8 in the tank 3 are withdrawn from the tank 3 by the sludge withdrawal means and the suspended solid matter 8 is separated from the sludge 9 in the suspended solid matter separation vessel 12 and the separated solid matter 8 is returned to the water treatment tank 3 by the return means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological treatment apparatus for separating a wastewater containing organic substances such as sewage and industrial wastewater by membrane while immersing the wastewater in biological treatment. The present invention relates to a biological treatment apparatus that can also wash an immersion film with suspended solids.

[0002]

2. Description of the Related Art A biological treatment apparatus for subjecting organic wastewater, such as sewage or industrial wastewater, to biological separation with biological sludge and separating the organic wastewater with a submerged membrane is known. As an example of such a biological treatment apparatus, one disclosed in Japanese Patent Application Laid-Open No. 7-328624 is known. This device immerses and arranges a hollow fiber membrane in the water to be treated in a treatment tank, and separates the water to be treated with the hollow fiber membrane. Further, a microorganism-immobilized carrier, fine activated carbon, and the like are added to the water to be treated. Then, the microorganism-immobilized carrier and the fine activated carbon are fluidized by aeration to prevent the hollow fiber membrane from being clogged.

[0003]

However, in the biological treatment apparatus described in the above-mentioned conventional publication, the hollow fiber membrane is closed in a relatively short period of time, and the membrane separation cannot be continued for a long time. There was a case.

[0004] In view of the above circumstances, an object of the present invention is to provide a biological treatment apparatus capable of sufficiently preventing membrane blockage.

[0005]

Means for Solving the Problems The present inventors have studied the above problems, and as a result, during the membrane separation, carriers and the like may be taken into excess sludge at the bottom of the treated water tank. It has been found that the amount of the carrier fluidized in the water to be treated decreases, and the hollow fiber membrane is clogged in a relatively short period of time because the cleaning effect of the hollow fiber membrane gradually decreases. Thus, the present inventors have conducted intensive studies and as a result, by separating the excess sludge and the carrier taken into the sludge and returning the carrier to the treatment water tank, it is possible to sufficiently prevent the reduction of the membrane washing effect. Was found.

Here, in order to prevent the deterioration of the cleaning effect of the membrane, it is conceivable to discharge suspended solids taken into excess sludge while replenishing new suspended solids, but this significantly increases running costs. That would be.

Therefore, the invention according to claim 1 exists in a treatment water tank into which water to be treated flows, an immersion film immersed and disposed in the treatment water in the treatment water tank, and an immersion film in the treatment water in the treatment water tank. In a biological treatment apparatus including a suspended solid, an aerator for fluidizing the suspended solid in the water to be treated, and a biological sludge for biologically treating the water to be treated, the suspended solid taken in from the treated water tank into excess sludge and excess sludge. Sludge withdrawing means for extracting the sludge, floating solid separation tank for separating excess sludge and suspended solids withdrawn by the sludge withdrawing means, and return means for returning the suspended solids of the suspended solid separation tank to the treatment water tank. I do.

According to the present invention, the suspended solids are fluidized in the water to be treated in the treated water tank by the air diffuser, and the water to be treated is separated by the immersion membrane while being biologically treated by the biological sludge. When the membrane separation is continued, excess sludge gradually accumulates in the treatment water tank, and a part of the suspended solids may be taken into the excess sludge. For this reason, the amount of fluidized floating solids decreases, and the cleaning effect on the immersion film may decrease. Therefore, the excess sludge in the treated water tank and the suspended solids taken therein are withdrawn by the sludge extracting means and sent to the suspended solid separation tank, where the excess sludge and the suspended solids are separated. The separated suspended solids are returned to the treated water tank by the return means. Therefore, even if the amount of suspended solids fluidized in the water to be treated in the treated water tank decreases, the amount of suspended solids fluidized in the treated water can be made substantially constant, and the cleaning effect on the immersion film can be substantially reduced. It can be kept constant.

In the invention according to claim 2, the floating solids separation tank is provided with dilution water for separating excess sludge and floating solids, and the concentration of the excess sludge in the dilution water is set to 0.7% by weight or less. Preferably it is possible. In this case, the floating speed of the suspended solids is improved as compared with the case where the concentration of the excess sludge exceeds 0.7% by weight, and the suspended solids tend to be easily separated from the excess sludge.

[0010] In the invention according to claim 3, it is preferable that wastewater containing organic matter is used as the diluting water, and the diluting water flows into the treated water tank as the water to be treated. in this case,
Organic matter-containing wastewater is effectively used as dilution water.

Further, the invention according to claim 4 exists in the treatment water tank into which the treatment water flows, the immersion film immersed in the treatment water in the treatment water tank, and the treatment water in the treatment water tank. In a biological treatment apparatus including a floating solid, an aerator for fluidizing the floating solid in the water to be treated, and a biological sludge for biologically treating the water to be treated, withdrawing excess sludge and floating solids in the excess sludge from the treatment water tank. Sludge withdrawal means, floating solids separation tank for separating excess sludge and suspended solids withdrawn by sludge withdrawal means, collection tank for collecting suspended solids separated in suspended solids separation tank, and treatment of suspended solids in the collection tank And returning means for returning to the water tank.

According to the present invention, the suspended solids are fluidized in the water to be treated in the treated water tank by the air diffuser, and the water to be treated is separated by the immersion membrane while being biologically treated by the biological sludge. When the membrane separation is continued, excess sludge gradually accumulates in the treatment water tank, and a part of the suspended solids may be taken into the excess sludge. For this reason, the amount of fluidized floating solids decreases, and the cleaning effect on the immersion film may decrease. Therefore, the excess sludge in the treated water tank and the suspended solids therein are withdrawn from the treated water tank by the sludge extracting means and sent into the suspended solids separation tank to separate the excess sludge from the suspended solids. The separated suspended solids are collected in a collection tank. Then, the suspended solids are returned to the treated water tank by the return means according to the membrane pressure difference of the immersion membrane or periodically. Therefore, it is possible to adjust the amount of the suspended solids fluidized in the water to be treated in accordance with the differential pressure of the immersion film or the like, and it is possible to prevent a reduction in the cleaning effect on the immersion film.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the biological treatment apparatus of the present invention will be described. In all the drawings, the same or equivalent components are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a schematic view showing an embodiment of the biological treatment apparatus of the present invention. As shown in FIG. 1, the biological treatment device 30 receives the water 2 to be treated through the treated water inflow line L1, the inflow pump 1 installed in the treated water inflow line L1, and the treated water inflow line L1. And a treated water tank 3. Therefore, the treated water 2 is accommodated in the treated water tank 3, and biological sludge for biologically treating the organic matter in the treated water 2 is charged into the treated water 2. In the treatment water tank 3, a plurality of flat membrane elements 4 as immersion membranes are arranged in parallel at appropriate intervals. The membrane element 4 is not particularly limited as long as it separates the water to be treated 2 into treated water and solids. Examples thereof include a reverse osmosis membrane, a nanomembrane, an ultrafiltration or microfiltration membrane, and a hollow fiber membrane. Used.

A water collecting pipe is connected to each of the membrane elements 4, and the water collecting pipe is connected to one discharge line L2. A suction pump 5 is attached to the discharge line L2. Further, the biological treatment device 30 includes an air diffuser 31. The air diffuser 31 performs air scrubbing of the membrane element 4 and forms a circulating flow of the water 2 to be treated in the treatment water tank 3. The air diffuser 31 includes, for example, an air diffuser 7 disposed below the membrane element 4 to generate bubbles 6 and a blower 19 connected to the air diffuser 7 via a line L6.

A suspended solid 8 is introduced into the water 2 to be treated. As the suspended solid 8, a substance which is easily fluidized in the water to be treated 2 and has a specific gravity smaller than 1 is used. This is because the floating solids 8 are floated and separated in the floating solid separation tank 12 described later. The particle size of the suspended solid 8 is not particularly limited as long as it does not cause blockage between the adjacent membrane elements 4, but is preferably about 1 to 3 mm from the viewpoint of recovery and prevention of outflow. The shape of the floating solid 8 may be, for example, a bead, a grain, a column, or a hollow, but is preferably a bead from the viewpoint of reducing damage to the film surface. As a material of the floating solid 8, for example, a plastic such as polypropylene or polyethylene is used. The amount of the suspended solids 8 added to the treated water tank 3 is, for example, about 3 to 10% by volume.

The biological treatment apparatus 30 includes a sludge withdrawal line L3 connected to the treatment water tank 3 for removing excess sludge in the treatment water tank 3, a sludge withdrawal pump 10 installed on the sludge withdrawal line L3, And a level controller (LS) 11 for adjusting the water level of the wastewater. The sludge withdrawal pump 10 allows excess sludge to be withdrawn from the treated water tank 3 through the sludge withdrawal line L3. Excess sludge is extracted so as to maintain the concentration of excess sludge in the water 2 to be treated in the treatment water tank 3 at a constant value (for example, 1.5 to 2% by weight). In addition, the sludge extraction line L3 and the sludge extraction pump 10 constitute sludge extraction means.

The sludge withdrawal line L3 is connected to a floating solid separation tank 12 for separating excess sludge 9 and floating solids 8 therein. The inside of the floating solid separation tank 12 contains dilution water 1
3, the dilution water 13 dilutes the excess sludge 9 and separates the excess sludge 9 from the suspended solids 8. Dilution water 1
As 3, industrial water or the like may be used, but it is preferable to use raw water (organic matter-containing wastewater) such as sewage or industrial wastewater. To this end, a raw water supply line L4 for flowing raw water as dilution water 13 is connected to the suspended solid separation tank 12, and a raw water pump 14 is installed in the raw water supply line L4.

A mixing vessel 15 connected to the raw water supply line L4 and the sludge extraction line L3 is fixed in the suspended solid separation tank 12. As the mixing container 15, it is preferable to use one having an opening at the top. The use of such a container 15 is for surely preventing the suspended solids 8 from being discharged while being taken in the excess sludge 9. In addition, the upper portion 12a of the floating solid separation tank 12 preferably has a cone shape from the viewpoint of densely separating the separated floating solids 8 at the upper portion.

Further, the bottom 12b of the floating solid separation tank 12
Is connected to a surplus sludge discharge line L5 for extracting surplus sludge 9, and a discharge valve 16 is installed in the surplus sludge discharge line L5. The bottom 12 of the floating solid separation tank 12
The shape of b is preferably cone-shaped from the point that the excess sludge 9 is concentrated at the lower part.

The above-mentioned treated water inflow line L1 is connected to a suspended solid separation tank 12, and the suspended solids 8 separated in the suspended solid separation tank 12 by the inflow pump 1 are returned to the treated water tank 3 to be diluted with dilution water. 13 flows into the treated water tank 3 as the water to be treated 2. In addition, the to-be-processed water inflow line L1
And the inflow pump 1 constitute a means for returning the suspended solids 8.

Next, the operation of the biological treatment apparatus 30 having the above-described configuration will be described.

First, the inflow pump 1 is operated, and the water to be treated 2 flows into the treated water tank 3 through the treated water inflow line L1. On the other hand, the blower 19 is operated, air is supplied to the line L6, and bubbles 6 are generated from the air diffuser 7. As a result, a circulating flow in the tank is formed in the water to be treated 2 in the treated water tank 3, and the floating solids 8 are fluidized accordingly. The suspended solids 8 are washed by rubbing the membrane surface while passing between the membrane elements 4 to prevent blockage of the membrane surface. At this time, the water to be treated 2 is biologically treated with biological sludge. On the other hand, the suction pump 5 is operated, and the water
Is subjected to membrane separation, and the treated water by the membrane separation is separated into membrane elements 4
From the treated water tank 3 through a water collecting pipe and a discharge line L2. At this time, since the liquid level in the treated water tank 3 is lowered by the suction of the treated water 2, the treated water 2 is stored in the treated water tank 3 based on the liquid level measured by the level controller 11 so as to keep the liquid level constant. Supplied to

When the water 2 to be treated in the treated water tank 3 is subjected to membrane separation by the membrane element 4 while being biologically treated by the biological sludge, surplus sludge gradually accumulates in the treated water tank 3, and a part of the suspended solids 8 becomes surplus. May be taken into sludge. For this reason, the amount of the floating solids 8 to be fluidized may decrease, and in this case, the cleaning effect on the membrane surface of the membrane element 4 decreases.

Then, the sludge withdrawing pump 10 is operated, and the excess sludge and the suspended solids 8 taken into the excess sludge are adjusted so that the concentration of the excess sludge in the treatment water tank 3 becomes constant (for example, 1.5 to 2% by weight). It is withdrawn from the treated water tank 3 through the sludge withdrawal line L3 and supplied into the mixing container 15 of the suspended solids separation tank 12. At this time, in the floating solid separation tank 12, the excess sludge 9 is opened by opening the extraction valve 16 so that the concentration of the excess sludge 9 in the dilution water 13 becomes a certain concentration (preferably 0.7% by weight) or less. It is extracted through the sludge discharge line L5. The extraction valve 16 is opened in conjunction with the sludge extraction pump 10. At this time, raw water is supplied from the raw water supply line L4 into the mixing vessel 15 so as to replenish the dilution water 13 discharged from the floating solid separation tank 12.

When the excess sludge 9 and the floating solids 8 taken in the sludge 9 are supplied into the floating solid separation tank 12, the excess sludge 9 and the floating solids 8 are separated, and the separated floating solids 8 float. To the top of the floating solids separation tank 12. The dense floating solids 8 are returned to the treated water tank 3 through the treated water inflow line L1 together with the dilution water 13. Therefore, even if the amount of floating solids 8 fluidized in the water 2 to be treated in the treated water tank 3 is reduced by the incorporation of the suspended solids 8 into the excess sludge 9, the floating solids fluidized in the water 2 to be treated are reduced. 8 can be kept almost constant, and the membrane surface cleaning effect on the membrane element 4 can be kept almost constant. Therefore, blockage of the membrane is sufficiently prevented, and the membrane separation process can be continued for a long time.

Next, a second embodiment of the biological treatment apparatus of the present invention will be described.

FIG. 2 is a schematic view showing a second embodiment of the biological treatment apparatus of the present invention. As shown in FIG. 2, the biological treatment device 40 of the second embodiment differs from the biological treatment device of the first embodiment in the following points.

That is, the sludge extraction line L 3 is connected to the raw water supply line L 4, and the treated water inflow line L 1 is connected to the lower portion 12 b of the suspended solid separation tank 12. here,
The to-be-processed water inflow line L1 has an uppermost portion 12a in the floating solids separation tank 12 in order to maintain the liquid level in the floating solids separation tank 12.
It is almost equal to the liquid level inside. Furthermore, a recovery tank 18 for recovering the floating solids 8 in the floating solids separation tank 12 is connected to the floating solids separation tank 12 via a recovery line L8. A return line L7 for returning the suspended solids 8 to the treated water tank 3 is connected to the recovery tank 18, and a return pump 20 is installed on the return line L7.

Therefore, the excess sludge 9 in the treated water tank 3 and the suspended solids 8 taken in the sludge are converted into the sludge withdrawal line L
The raw water is sent to the raw water supply line L4 through 3 and is introduced into the mixing vessel 15 in the floating solid separation tank 12 while being diluted by the raw water in the raw water supply line L4. Then, the suspended solids 8 are separated from the excess sludge 9 and float. The suspended solids 8 that have floated are sent to the collection tank 18 through the collection line L8. The suspended solids 8 collected in the collection tank 18 are returned to the treated water tank 3 through the return line L7 when the membrane differential pressure of the membrane element 4 becomes equal to or higher than a certain value or periodically. Therefore, it is possible to adjust the amount of the floating solids 8 fluidized in the water 2 to be treated, and it is possible to prevent a reduction in the membrane surface cleaning effect on the membrane element 4. Therefore, the membrane separation process can be continued for a long time.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the raw water is used as the diluting water 13 and the diluting water 13 is used as the water to be treated 2. However, the raw water may be used as the water 2 to be treated.

Reference Example 1 As a suspended solid, specific gravity 0.8
5. By taking as an example the case of using a bead-shaped floating solid made of polypropylene having an average particle diameter of 3 mm, it was examined whether or not the floating solid was separated by diluting excess sludge. This suspended solid was added in an amount of 3% based on the capacity of the treatment water tank. Then, the synthetic sewage sludge obtained in the treated water tank was diluted with tap water to produce respective mixed solutions having a sludge concentration of 0.1 to 2.0% by weight, and the speed at which the suspended solids floated was measured. The result is shown in FIG. In addition, the floating speed was measured as follows. That is, one floating solid (bead) is grasped with scissors and brought to the bottom of a 3 l beaker (height: 20 cm), and the time of floating from the point at which the floating solid is released to a height of 20 cm is measured with a stopwatch. From that time, the floating speed of the suspended solid at that sludge concentration was measured.

As shown in FIG. 3, when the content is less than 1.3% by weight, the suspended solid does not float and accumulates in the sludge, but as the sludge concentration decreases, the floating speed gradually increases, and the suspended solid separates from the sludge. It turned out to be easier. In particular, it was found that when the sludge concentration was 0.7% by weight or less, the suspended solids were easily separated from the sludge.

[0034]

As described above, according to the biological treatment apparatus of the present invention, even when the suspended solids are taken into the excess sludge in the treated water tank, the amount of the suspended solids fluidized in the treated water is reduced. Is prevented. For this reason, a decrease in the cleaning effect on the immersion film is prevented, and the membrane separation process can be continued for a long time.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of the biological treatment device of the present invention.

FIG. 2 is a schematic view showing another embodiment of the biological treatment device of the present invention.

FIG. 3 is a graph showing the relationship between the floating speed of suspended solids and sludge concentration in Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inflow pump (return means), 2 ... Water to be treated, 3 ... Treatment tank, 4 ... Membrane element (immersion membrane), 7 ... Aeration tube (Aerator), 8 ... Floating solid, 9 ... Excess sludge, 10 ... Sludge extraction pump (sludge extraction means), 12 ... Floating solid separation tank,
13: dilution water, L6: line (aerator), 18: recovery tank, 19: blower (aerator), 20: return pump (return means), 30: biological treatment device, 31: air diffuser, L1
... inflow line for treated water (return means), L3 ... sludge extraction line (sludge extraction means), L7 ... return line (return means).

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Claims (4)

[Claims] A treatment tank into which the treatment water flows, an immersion film immersed in the treatment water in the treatment tank, and a suspended solid present in the treatment water in the treatment water tank. An aeration device for fluidizing the suspended solids in the water to be treated, and a biological sludge for biologically treating the water to be treated, wherein the biological sludge is taken into the excess sludge and the excess sludge from the treated water tank. Sludge withdrawing means for withdrawing the suspended solids, a floating solids separation tank for separating the excess sludge and the floating solids withdrawn by the sludge withdrawing means, and the treatment of the floating solids separated by the floating solids separation tank. A biological treatment apparatus, comprising: a return unit that returns the water to a water tank. 2. The floating solids separation tank is provided with dilution water for separating the excess sludge and the floating solids, and the concentration of the excess sludge in the dilution water can be 0.7% by weight or less. The biological treatment apparatus according to claim 1, wherein the biological treatment apparatus is provided. 3. The biological treatment apparatus according to claim 2, wherein an organic matter-containing wastewater is used as the dilution water, and the dilution water flows into the treatment water tank as the water to be treated. 4. A treated water tank into which the treated water flows, an immersion film immersed and disposed in the treated water in the treated water tank, and a floating solid present in the treated water in the treated water tank. In a biological treatment apparatus comprising: an aerator for fluidizing the suspended solids in the water to be treated; and biological sludge for biologically treating the water to be treated, the biological fluid is taken into the excess sludge and the excess sludge from the treated water tank. Sludge withdrawing means for withdrawing the suspended solids, a floating solid separation tank for separating the excess sludge and the floating solids withdrawn by the sludge withdrawing means, and collecting the floating solids separated in the floating solid separation tank. A biological treatment apparatus comprising: a recovery tank; and a return unit that returns the suspended solids in the recovery tank to the treated water tank.