JPH0244880Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention relates to the structure of a wastewater treatment device that utilizes aerobic microorganisms such as activated sludge.

(Prior technology) Conventional wastewater treatment using activated sludge and other aerobic microorganisms includes the activated sludge method, sprinkled bed method, rotating disk method, and contact oxidation method, all of which use organic matter in wastewater as a nutrient source. This method removes organic matter by breeding aerobic microorganisms, but it cannot be said that sufficient treatment has been achieved unless the water from which organic matter has been removed is completely separated from the grown microorganisms.

The usual separation method is sedimentation separation using the coagulation-sedimentation properties of aerobic microorganisms, and the water is separated into supernatant water and sludge. In order to maintain a constant microbial concentration in the aeration tank, most of the settled sludge is returned to the aeration tank, the surplus is disposed of in an appropriate manner, and the supernatant water is used as treated water or can be further filtered. It is released into the river.

However, in these methods, the coagulation and sedimentation separation properties of aerobic microorganisms greatly affect the water quality of the treated water, so management is focused on these factors, and in order to satisfy this, the amount of aeration, sludge concentration, type of microorganisms, etc. The scope of application is carefully selected, and it is difficult to manage in terms of industrial operation.
Moreover, it has drawbacks such as difficulty in achieving stable and high-level processing.

In order to overcome these drawbacks, methods have been proposed in which water and sludge are separated by filtration instead of by sedimentation. In this method, a bed filled with a layer of material with relatively small particle size is installed at the bottom of the aeration tank, a water collection section is installed at the bottom of this bed, and the wastewater continuously supplied to the aeration tank is passed through an aeration pipe installed in the tank. The organic matter in the wastewater is adsorbed and decomposed by the aeration of air bubbles ejected from the sludge and the action of aerobic microorganisms in the activated sludge. The treated water is filtered through the bed, separated from sludge, collected in a water collection area, and discharged outside the tank. The water discharged outside the tank is sent to the upper part of the treated water storage tank by a riser pipe and is stored there, but treated water exceeding a certain amount is discharged from an overflow pipe at the upper part of the storage tank. As time passes, a dense layer of sludge forms on the upper surface of the floor, and microorganisms proliferate inside the floor, gradually eliminating voids and making it extremely difficult for treated water to pass through. In that case, stop the supply of raw water to the aeration tank and transfer of treated water to the storage tank, and use a pump to squirt water for backwashing from the treated water storage tank from the water collection section to the upper part of the floor. The sludge adhering to the surface is removed, the sludge in the bed is pushed out, the voids are restored, and the same wastewater treatment as above is repeated.

In wastewater treatment work using the above method,
A detailed investigation into the phenomenon of obstruction to the passage of treated water through the bed as the treatment time progressed revealed the following. In other words, the aeration pipe that releases air bubbles during drainage in the aeration tank is installed near the floor surface, so the water near the floor surface contains the released fine air bubbles. The air bubbles that are sucked into the floor gather together to form an air layer and become trapped in the floor, which obstructs the passage of water and is one of the reasons why it is eventually impossible for treated water to flow out. Become. The formation of this air layer within the bed is so remarkable that the pressure inside the bed becomes lower than the pressure outside (aeration zone side) with the upper surface of the bed as a boundary. This inevitably occurs when the inflow water becomes larger than the outflow water due to increase in volume, and the water level in the aeration tank becomes higher than the water level in the treated water storage tank. This phenomenon is further accelerated by the formation of an air layer within the bed, making it difficult to continue water treatment.

Furthermore, in the above-mentioned filtration system, the water collected in the water collection section provided at the bottom of the floor is led out and sent to the treated water storage tank, but the piping for this delivery keeps the liquid level in the aeration tank constant. Because it is necessary to maintain the water above that level, it is raised to that height and connected to the treated water storage tank.
There is no problem as long as there is no air tank on the floor, but once an air layer forms in the floor, the air passes through the water collection section, combines with water, and is pushed out into the treated water supply pipe to the treated water storage tank. It was found that the rising part of this feed pipe constitutes an air lift, which reduces the pressure in the bed and further increases the suction of air bubbles.

(Purpose of the present invention) The present invention aims to eliminate the drawbacks of the above-mentioned apparatus for separating sludge by a filtration method using activated sludge, and to provide a wastewater treatment apparatus which is further simplified in structure. This is the purpose.

(Description of the Drawings) FIG. 1 is a schematic longitudinal sectional front view of an example of the device of the present invention.

In the figure, 1 is an aeration tank and 2 is a floor, which is formed by filling the bottom of the aeration tank 1 with relatively small-grained materials such as silica stone, silica sand, and anthracite in a layered manner to a desired height. be done. 3 is the water collection part,
It is installed at the bottom of floor 2. For example, the structure is one in which many pipes with many pores are arranged radially from the opening position of the central drainage pipe.
Alternatively, a flat round or rectangular chamber with a large number of pores bored in its upper surface and, if necessary, on its side surfaces, is used. Reference numeral 4 denotes an aeration pipe, which is positioned slightly above the upper surface of the floor 2, and its structure may be similar to the above-mentioned water collection section 3, for example, and air bubbles are uniformly bubbled into the aeration tank 1. It may have any structure. 5 is a blower that sends air to the aeration pipe 4; 6 is a pipe that introduces raw water; and 7 is a conduit that delivers the treated water collected in the water collection section 3 to the treated water storage tank 8.
The connecting portion in is the lower part of the storage tank 8. That is, the connecting portion may be opened at the bottom of the storage tank 8 as shown in the figure, or may be opened at a lower part of the side wall of the storage tank 8 near the bottom. Further, in the illustrated embodiment, the storage tank 8 shares a part of the side wall with a part of the side wall of the aeration tank 1, but the storage tank 8 may be made independent. Even in that case, the conduit 7 should be made as short as possible.
It is best to place them close together. 9 is a treated water overflow pipe provided relatively above the treated water storage tank 8; 10 is a pump for backwashing; 11 is a liquid level in the aeration tank 1; and 12 is a liquid level in the treated water storage tank 8.

To operate this device, the pipe 6 must be connected to the aeration tank 1.
A constant amount of raw water is continuously supplied to the tank, and at the same time, air is bubbled out from the air diffuser pipe 4. Activated sludge is kept in the aeration tank 1, and organic matter in the raw water is adsorbed and decomposed by the action of aerobic microorganisms in this activated sludge, and the treated water is passed through the bed 2 and separated from the sludge. , the separated treated water passes through the water collection section 3 and continues along the conduit 7 as shown by arrow A.
The water flowing in the direction of the treated water is sent to the treated water storage tank 8, and the water that exceeds the overflow pipe 9 is discharged, and this water is either discharged as is or is passed through the filter again and then discharged. .

When water flows from the water collection section 3 to the storage tank 8, the conduit 7
The pump 10 provided in the tank 8 is not operated, and the treated water is fed to the storage tank 8 only by water pressure. Therefore, for a while after the start of rotation, the liquid levels 11 and 12 are at the same level.

As time passes further, a sludge layer is gradually formed on the surface of the bed 2, resulting in excessive resistance to water and reducing the excess amount, causing the liquid level 11 in the aeration tank 1 to rise.
A pressure difference occurs across the surface layer of the floor, causing air bubbles to be sucked into the floor, creating an air layer. When this happens, the backwashing pump 10 is activated and the storage tank 8
Flow the treated water in the pipe 7 in the direction of arrow B,
The treated water is spouted from the pores provided in the water collection part 3,
Removes sludge adhering to the surface layer of floor 2,
Exclude excessive resistance on floor 2. When the excessive resistance approaches zero, the operation of the pump 10 is stopped. pump 1
0 stops operating, the water flows again in the direction of arrow A in the conduit 7, and the wastewater treatment is restarted.
The above operations are repeated.

As the pump 10 for backwashing, in order to avoid the height of the route of the conduit 7, it is preferable to use, for example, a centrifugal pump (particularly a centrifugal line pump) with a suction pipe and a discharge pipe coaxial, and a pump with a low head and high volume is suitable. There is. By using such a high-capacity pump, the sludge layer on the floor surface can be destroyed and removed by backwashing with a small amount of water in an extremely short period of time.

The backwash water used for each backwash uses a part of the treated water stored in the treated water storage tank 8, and the amount used per time is determined by a level switch etc. installed in the treated water storage tank 8. controlled. The amount of water used for one backwashing may be small, usually about 1/2 to 1/3 of the floor volume.

The time to start backwashing by starting the backwashing pump 10 is from the time when the liquid level 11 in the aeration tank 1 begins to rise above the liquid level 12 in the treated water storage tank 8, and when the liquid level 11 and the liquid level 12 are It is preferable that the difference is in the range of up to 30 cm, preferably up to 10 cm, more preferably up to 3 cm. The smaller this liquid level difference is, the easier it is to remove excess resistance within the bed. In terms of time, it is best to repeat the cycle of treating raw water for 30 to 90 minutes and then backwashing. The time for this cycle is determined in advance depending on the supply amount of treated water, water quality, etc., and can be automated using a timer or the like.

Although the installation of a valve in the conduit 7 is not shown, the use of the valve is not required during normal operation. However, a valve is required when stopping operation for equipment repair, etc., so it is recommended to provide one, although it is not particularly shown.

(Effects of the invention) The present invention has the structure described above and has the following effects.

(b) Since the device of the present invention separates water and sludge by overpassing, instead of using the conventional method of separating water and sludge by sedimentation, there is no need to worry about the flocculation and sedimentation of sludge, and it is important for management purposes. Constraints are reduced.

(b) Even if a filtration method is used to separate water and sludge, the device of the present invention does not have a rising part to serve as a conduit for sending wastewater from the aeration tank to the treated water storage tank, so it may be caused by the phenomenon of air lift. There are no problems.

(c) The pipe for discharging treated water from the aeration tank and the pipe for sending backwash water to the floor are shared by the same pipe, and there is no need for a switching valve to switch between discharging treated water and supplying backwash water. It is not only cheaper, but also easier to manage.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional front view of an example of the device of the present invention. In the figure, 1 is the aeration tank, 2 is the floor, 3 is the water collection part, 4 is the aeration pipe, 7 is the conduit connecting the aeration tank and the treated water storage tank,
8 is a treated water storage tank, and 10 is a pump.

Claims (1)

[Scope of utility model registration request] Consisting of an aeration tank 1 and a treated water storage tank 8, the aeration tank 1
A filter bed 2 is formed at the bottom of the filter bed 2, an aeration pipe 4 is provided near the surface of the filter bed 2, a water collection section 3 is provided at the bottom of the filter bed 2, and the water collection section 3 and the bottom of the treated water storage tank 8 are connected. are connected by a conduit 7 having a pump 10 in the middle, and this pump 10 is arranged so as to send the water in the treated water storage tank 8 to the water collection part 3 when the pump 10 is in operation, and when the pump 10 is not in operation, the aeration is carried out. A wastewater treatment device using activated sludge in which water in a water collection section 3 flows into a treated water storage tank 8 through a conduit 7 due to water pressure in a tank 1.