TW202132227A - Aeration tank, sewage treatment apparatus, and sewage treatment method - Google Patents

Abstract

This aeration tank includes: a tank body; a carrier which is provided inside the tank body and holds nitrifying bacteria and denitrifying bacteria therein; a cylindrical member which is spaced apart from the inner wall of the tank body and has an open end in the vertical direction; and a first air diffusing device provided immediately below the cylindrical member. An aerobic region having an upward flow and an anaerobic region having a downward flow are formed in the tank body, and the carrier circulates in a manner of alternately passing through the aerobic region and the anaerobic region. In a plan view, the outer edge of the first air diffusing device may be located on the inside of the inner edge of the cylindrical member.

Description

Aeration tank, sewage treatment device and sewage treatment method

One embodiment of the present invention relates to an aeration tank, a sewage treatment device, and a sewage treatment method.

In the past, as a sewage treatment device used for the purification treatment of excrement, household drainage, etc., a sewage treatment device equipped with an "aeration tank using a mobile carrier" has been known. This type of aeration tank allows a porous carrier with aerobic bacteria and anaerobic bacteria attached to flow in the tank body to simultaneously remove organic components and nitrogen components in sewage. In addition, since the carrier flows in the tank body, it has the following characteristics: high-efficiency contact of sewage, microorganisms and oxygen, and high sewage treatment capacity can be realized.

As a sewage treatment device equipped with an "aeration tank using a mobile carrier", the sewage treatment device described in Patent Document 1 is already known. In this sewage treatment device, the ammonia nitrogen or organic nitrogen in the sewage is contacted with nitrifying bacteria in the outer layer of the porous carrier located in an aerobic environment to convert into nitrate nitrogen or nitrite nitrogen . Next, contact the nitrate nitrogen or nitrite nitrogen in the inner layer of the porous carrier in an anaerobic environment with denitrification bacteria (bacteria that have the effect of converting nitrogen compounds into molecular nitrogen) , To convert to nitrogen. In short, according to the technique described in Patent Document 1, since organic components are removed in the outer layer of the porous carrier and nitrogen components are removed in the inner layer of the porous carrier, very small sewage treatment can be realized. Device.

『Patent Literature』 "Patent Document 1": Japanese Patent Publication No. H8-71579

As described in Patent Document 1, when nitrogen is removed from the inner layer of the porous carrier, the anaerobic area (the area where the nitrogen is removed) of the porous carrier decreases successively, and the denitrification function is reduced. problem. Therefore, in the sewage treatment device described in Patent Document 1, by using a cylindrical or angular column with a length of 300 mm or more and 600 mm or less, and the diameter of the cross section or the diagonal length of 30 mm or more and 50 mm or less The shape of the carrier is used as a porous carrier to expand the anaerobic area in order to solve the problem. However, with the use of a porous carrier with a large size, since the total area of the aerobic region (a region where organic components are removed) is relatively reduced, there is room for improvement from the viewpoint of processing efficiency.

One of the problems of one embodiment of the present invention is to suppress the decrease of the denitrification function in sewage treatment using a flowing carrier.

The aeration tank in an embodiment of the present invention includes: a tank body, a carrier provided inside the tank body and maintaining the nitrifying bacteria and denitrification bacteria inside, separated by a distance from the inner wall of the tank body A cylindrical member provided with an open end in the vertical direction, and a first diffuser provided directly below the cylindrical member.

In a top view, the outer edge of the first diffuser may also be located inside the inner edge of the cylindrical member.

The aeration tank may further include a second aeration device provided at a distance from the cylindrical member. At this time, the aforementioned cylindrical member may be located on a straight line connecting the pair of second diffuser devices.

In one embodiment of the present invention, the aeration tank is located inside the tank body and has: an aerobic area with upward flow and an anaerobic area with downward flow, while maintaining nitrifying bacteria and denitrifying bacteria in The internal carrier interacts and circulates through the aforementioned aerobic zone and the aforementioned anaerobic zone.

The aerobic region may be formed inside a cylindrical member having an open end in the vertical direction, and the anaerobic region may be formed around the cylindrical member. In addition, the amount of dissolved oxygen in the anaerobic region may be 1/10 or less of the amount of dissolved oxygen in the aerobic region.

The sewage treatment device in an embodiment of the present invention is provided with the aeration tank and a sedimentation tank provided downstream of the aeration tank.

The aeration tank and the precipitation tank can also be communicated through a carrier screen arranged on the inner wall of the tank body.

An air diffuser can also be provided inside the aforementioned sedimentation tank.

The sewage treatment device may further include a sludge return device that returns the sludge of the aeration tank and the sedimentation tank to the upstream side.

In one embodiment of the present invention, the sewage treatment method is to form an aerobic area with upward flow and an anaerobic area with downward flow inside the tank body, so that nitrifying bacteria and denitrifying bacteria are maintained in The internal carrier circulates through the aforementioned aerobic zone and the aforementioned anaerobic zone alternately.

The aerobic area may be formed by dispersing air from below in a cylindrical member having an open end in the vertical direction.

It is also possible to form the aerobic area inside the cylindrical member and form the anaerobic area around the cylindrical member by selectively dispersing air inside the cylindrical member.

The following describes the implementation of the present invention with reference to the drawings and the like. However, the present invention can be implemented in various forms within the scope not departing from its gist, and is not limited by the description of the description of the implementation forms exemplified below. The drawings are to make the description clearer. Compared with the actual state, the drawings show schematic representations of the width, thickness, shape, etc. of each part, but it is an example after all and does not limit the interpreter of the present invention. In this specification and the drawings, components that have the same functions as those described in relation to the existing drawings are sometimes labeled with the same symbols, and repeated descriptions are omitted.

[Structure of sewage treatment system]

FIG. 1 is a diagram showing the structure of a sewage treatment system 10 according to an embodiment of the present invention. As shown in Figure 1, the sewage treatment system 10 of this embodiment includes an adjustment tank 11, a carrier flow aeration tank 12, a sedimentation tank 13, a sludge return device 14, a sludge concentration storage tank 15, a disinfection tank 16 and a discharge Slot 17. However, the example shown in FIG. 1 is only an example, and the sewage treatment system 10 of this embodiment is not limited to this example.

The adjustment tank 11 is a treatment tank that uniformizes fluctuations in water quality by temporarily storing and mixing raw water. In addition, the adjustment tank 11 also plays a role in making the flow rate of the sewage supplied to the downstream side carrier flow aeration tank 12 constant.

The carrier flow aeration tank 12 is a treatment tank for removing organic matter and nitrogen in sewage. The removal of organic matter (oxidative decomposition) can be carried out by the action of aerobic bacteria in an aerobic environment. With the action of aerobic bacteria, organic matter can be decomposed into water and carbon dioxide. The oxygen required for oxidative decomposition can be supplied using a diffuser or the like. Nitrogen removal (denitrogenation) can be carried out by the action of anaerobic bacteria in an anaerobic environment. Specifically, first, ammonia nitrogen or organic nitrogen can be converted into nitrate nitrogen or nitrite nitrogen by nitrifying bacteria. Afterwards, nitrate nitrogen or nitrite nitrogen can be reduced to nitrogen by denitrifying bacteria. The detailed functions of the carrier flow aeration tank 12 of this embodiment will be described in detail later.

The sedimentation tank 13 is a treatment tank that mixes the sludge discharged from the carrier flow aeration tank 12 and the treated water to stand still, and uses the density difference between the sludge and the treated water to settle and separate the sludge.

The sludge return device 14 is a device for returning the sludge separated in the sedimentation tank 13 to the adjustment tank 11 on the upstream side. The sludge return device 14 is constituted by, for example, an air lift pump and a return pipe. The sludge return device 14 has a function of automatically measuring sludge. With this function, the sludge return device 14 has a function of adjusting the amount of sludge sent back to the adjustment tank 11 and the like so that the amount of sludge in the carrier flow aeration tank 12 becomes a set value. In addition, the sludge return device 14 of this embodiment can return sludge from both the sedimentation tank 13 and the carrier flow aeration tank 12. In addition, the sludge returning device 14 can not only return the conveyed sludge to the adjustment tank 11 but also return it to the carrier flow aeration tank 12.

The sludge thickening storage tank 15 is a processing tank with "the function of thickening the sludge conveyed from the carrier flow aeration tank 12 and the sedimentation tank 13 by the sludge return device 14" and the "function of storing the concentrated sludge". In this embodiment, the sludge concentration is increased by the precipitation concentration method in which the supernatant liquid (supernatant liquid) is extracted after the sludge is settled. In this embodiment, the sludge conveyed from the carrier flow aeration tank 12 or the sedimentation tank 13 is temporarily stored in the sludge concentration storage tank 15 and then returned to the adjustment tank 11 or the carrier flow aeration tank 12.

The disinfection tank 16 is a treatment tank that has the function of bringing the treated water discharged from the sedimentation tank 13 into contact with the medicament to perform disinfection (sterilization) to make it hygienic and safe water.

The drainage tank 17 is a tank for storing the treated water disinfected by the disinfection tank 16. The treated water stored in the drainage tank 17 is discharged to the sewer or the like.

Next, the sewage treatment device 100 constituted by the carrier flow aeration tank 12, the sedimentation tank 13, and the sludge return device 14 in the sewage treatment system 10 of the present embodiment will be described in detail.

[Structure of sewage treatment plant]

FIG. 2 is a diagram showing the structure of a sewage treatment device 100 according to an embodiment of the present invention. In this embodiment, although an example in which the carrier flow aeration tank 12 and the precipitation tank 13 are integrated is disclosed, they can also be constructed in the form of separate treatment tanks.

The tank body 110 is a component of the outer frame of the carrier flow aeration tank 12 and the precipitation tank 13. The trough body 110 can be made of plastic, steel, steel, concrete, etc., but it is not limited to those materials. In this embodiment, a partition 112 is provided inside the tank body 110. That is, the tank main body 110 is divided into a first treatment tank (carrier flow aeration tank 12) and a second treatment tank (precipitation tank 13) by the partition 112. In addition, in this specification, the "tank body" in the carrier flow aeration tank 12 includes the tank body 110 and the partition 112 that surround the area functioning as the carrier flow aeration tank 12. The groove body 110 and the partition 112 may be an integrally formed object, or may be separate entities. In addition, although an example of dividing the tank body 110 into two processing tanks by the partition 112 is disclosed here, it may also be divided into three or more processing tanks.

In this embodiment, a carrier screen 114 is provided on the partition 112 provided on the inner side of the tank body 110. In short, the carrier flow aeration tank 12 and the precipitation tank 13 communicate with each other through the carrier screen 114. In this embodiment, the carrier screen 114 is disposed at the opening 112 a of the partition 112. Specifically, the carrier screen 114 is arranged at the open end on the upstream side of the opening 112a, that is, the open end on the side of the carrier flow aeration tank 12 (the open end on the side opposite to the side of the sedimentation tank 13).

The carrier screen 114 is a member in which a plate-shaped member is provided with a plurality of through holes of a specified size. The carrier screen 114 plays a role of preventing the carrier 150 from flowing out of the carrier flow aeration tank 12 to the sedimentation tank 13 while passing the sludge water from the carrier flow aeration tank 12 to the sedimentation tank 13. As the carrier screen 114, for example, a mesh member, a punching plate (a member made of metal, resin, etc., which has been punched by punching), etc. can be used.

A raw water inflow pipe 116, a raw water metering tank 117, and a raw water supply pipe 118 are provided on the upstream side of the tank body 110. The raw water measuring tank 117 has a function of measuring the sewage (raw water) discharged from the upstream device (the adjustment tank 11 in this embodiment) through the raw water inflow pipe 116. In this embodiment, by using the raw water metering tank 117, an appropriate amount of sewage can be supplied to the carrier flow aeration tank 12 through the raw water supply pipe 118.

Inside the tank body 110, a cylindrical member 120 is provided at a distance from the inner wall (and the partition 112) of the tank body 110. The cylindrical member 120 is a tubular member having an open end in the up-down direction, and is made of a plastic material or the like. As shown in FIG. 2, the cylindrical member 120 is configured to be submerged in sewage 160 during operation. In addition, the outer shape of the cylindrical member 120 is not limited to a cylindrical shape, and may be a polygonal shape such as a prismatic shape. In addition, the length of the cylindrical member 120 should be 300 mm or more and 3000 mm or less (500 mm or more and 2000 mm or less is preferable), and the diameter of the cross section or the diagonal length should be 30 mm or more and 250 mm or less (Preferably 50 mm or more and 200 mm or less).

In addition, a first aeration device 130 and a second aeration device 135a to 135c are provided inside the tank main body 110. The first diffuser 130 and the second diffuser 135a to 135c are connected to the air supply pipe 137 connected to a blower (not shown).

The first diffuser 130 is a device that generates bubbles, and is installed directly below the cylindrical member 120. In this embodiment, the bubbles generated by the first diffuser 130 pass through the inside of the cylindrical member 120 while rising toward the sewage surface 160a. In order to achieve such a structure, the diameter or width of the first diffuser 130 becomes smaller than the diameter or width of the cylindrical member 120. In other words, in a top view, the outer edge of the first diffuser 130 is located inside the inner edge (the contour of the inner wall) of the cylindrical member 120. However, it is not limited to this example, and the diameter or width of the first diffuser 130 may be equal to the diameter or width of the cylindrical member 120.

The second aeration devices 135a to 135c are also devices that generate bubbles. In this embodiment, the second aeration devices 135a and 135b are installed in the carrier flow aeration tank 12. The second aeration device 135c is installed in the sedimentation tank 13. In this embodiment, the second aeration device 135a is provided near the inner wall of the tank body 110, and the second aeration device 135b is provided near the partition 112. In short, the second air diffusers 135a and 135b are provided at a distance from the cylindrical member 120.

The second aeration device 135c is arranged close to the partition 112 in the interior of the sedimentation tank 13. In the case of such an arrangement, the upward flow generated by the bubbles generated from the second diffuser 135c will form a vortex near the back surface of the carrier screen 114 (the surface on the side of the sedimentation tank 13). In addition, the upward flow generated by the air bubbles generates a water flow on the carrier screen 114 from the sedimentation tank 13 to the carrier flow aeration tank 12. Therefore, according to this embodiment, the carrier 150 attached close to the surface of the carrier screen 114 (the surface on the carrier flow aeration tank 12 side) can be pushed back to the carrier flow aeration tank 12 side. The second diffuser 135c may be intermittent or continuous diffuser.

The sludge return device 14 includes air lift pumps 142 a and 142 b, a sludge return pipe 144, a sludge measuring tank 145, and a sludge supply pipe 146. The air lift pump 142 a is arranged inside the carrier flow aeration tank 12 and plays a role of sucking up the sludge accumulated on the bottom of the carrier flow aeration tank 12. In the same way, the air lift pump 142b is arranged inside the sedimentation tank 13 and plays a role of sucking up the sludge accumulated on the bottom of the sedimentation tank 13.

As described above, in this embodiment, the carrier 150 attached to the carrier screen 114 is detached from the carrier screen 114 by the action of the second diffuser 135c provided in the sedimentation tank 13. At this time, the biofilm (activated sludge) detached from the surface of the carrier 150 settles on the bottom of the carrier flow aeration tank 12. In short, in the vicinity of the partition 112, the sludge detached from the carrier 150 is easy to accumulate. Therefore, the air lift pump 142 a provided in the carrier flow aeration tank 12 is arranged in the vicinity of the partition 112.

The sludge returning device 14 has the function of returning the sucked sludge to the adjustment tank 11 or the carrier flow aeration tank 12. The sludge returning device 14 of this embodiment discloses an example of returning the sucked sludge to the upstream side of the carrier flow aeration tank 12. The sludge sucked by the air lift pumps 142 a and 142 b is supplied to the sludge measuring tank 145 through the sludge return pipe 144. The sludge measuring tank 145 has a function of measuring the sludge sucked up from the downstream equipment (in this embodiment, the carrier flow aeration tank 12 and the sedimentation tank 13). In this embodiment, by using the sludge metering tank 145, an appropriate amount of sludge is sent back to the carrier flow aeration tank 12 through the sludge supply pipe 146, and the amount of sludge inside the carrier flow aeration tank 12 is adjusted. It becomes the set value. In addition, although the drawing is omitted, the sludge return pipe 144 is connected to the sludge measuring tank 145 via the sludge thickening storage tank 15 shown in FIG. 1. In other words, in this embodiment, the sludge transported by the air lift pumps 142a and 142b is temporarily stored in the sludge thickening storage tank 15, and then an appropriate amount of sludge is returned to the adjustment tank 11 or Carrier flow aeration tank 12. However, it is not limited to this example, the sludge return device 14 may also directly return the sludge to the adjustment tank 11 or the carrier flow aeration tank 12 without passing through the sludge concentration storage tank 15.

In the tank body 110 with the above structure, the carrier 150 that maintains nitrifying bacteria and denitrifying bacteria in the interior is set to be 20% or more and 35% or less (with 25% or more) relative to the volume of the carrier flow aeration tank 12 And 30% or less is preferred) filling rate (volume occupancy rate) to fill. In addition, experimentally, it is known that if the filling rate is less than 20%, the denitrification function will decrease, and if the filling rate exceeds 35%, the fluidity of the carrier will deteriorate.

Considering the fluidity in the tank, the carrier 150 preferably has a specific gravity of approximately 1. In addition, the carrier 150 has an external dimension of 10 mm or more and 300 mm or less (preferably 10 mm or more and 30 mm or less), and the cross-section diameter or diagonal length is 10 mm or more and 50 mm or less (10 mm or more) And 30 mm or less is preferred) cylindrical, cylindrical or angular columnar porous carrier. If the external dimensions and the diameter of the cross-section or the length of the diagonal exceed these numerical ranges, the fluidity will deteriorate and it is not good. And, on the contrary, if the external dimensions and the cross-sectional diameter or the diagonal length are lower than these numerical ranges, the anaerobic area inside the carrier 150 described later will be reduced, so the denitrification capacity will be poor. . In addition, if a cylindrical carrier with three equal sides is used as the carrier 150, since sewage will travel at an equal speed from all surfaces, it is advantageous in the management of sewage treatment.

As the material of the carrier 150, for example, urethane resin or polyethylene resin can be used. In particular, it is desirable for the carrier 150 to have abrasion resistance. In the case of using a urethane resin, it is preferable to use an ether-based open-cell polyurethane. In this embodiment, a prismatic urethane porous carrier is used.

However, the size and material of the carrier 150 are not limited to the above examples as long as the nitrifying bacteria are maintained in the outer layer of the carrier 150 and the denitrifying bacteria are maintained in the inner layer. According to the findings of the present inventors, a free sample thickness of 30 mm and a wind speed of 2 m/sec are used for air filtration resistance P of 10 mmH ₂ O or more and 100 mmH ₂ O or less made of polyethylene or polyurethane The carrier 150 is preferably a material cut from a plate-shaped member made of an acid ester.

[Structure of sewage treatment method]

The operation (that is, the sewage treatment method) of the sewage treatment device 100 having the above structure will be described.

As shown in FIG. 2, sewage 160 supplied from the raw water supply pipe 118 is accumulated inside the carrier flow aeration tank 12 and the sedimentation tank 13. In the case of this embodiment, since the carrier flow aeration tank 12 and the sedimentation tank 13 are connected through the carrier screen 114, the height of the sewage surface 160a of the carrier flow aeration tank 12 and the sedimentation tank 13 is the same.

In the carrier flow aeration tank 12, a plurality of carriers 150 are dispersed in the sewage 160. When the sewage treatment device 100 is in operation, these multiple carriers 150 flow through the air bubbles generated from the first diffuser 130 and the second diffuser 135a and 135b in the carrier flow aeration tank 12 flow.

At this time, directly above the first diffuser 130 and the second diffuser 135a and 135b, an upward flow is generated due to the rising air bubbles. Therefore, the sewage 160 pushed up to the sewage surface 160a while waiting for the upward flow will descend toward the bottom of the tank body 110 in the area where the first diffuser 130 and the second diffuser 135a and 135b are not present. In short, a downward flow is generated between the first diffuser 130 and the second diffuser 135a and between the first diffuser 130 and the second diffuser 135b. Therefore, in the carrier flow aeration tank 12, a backflow of sewage 160 as shown by an arrow in FIG. 2 is generated, and by this backflow, a plurality of carriers 150 flow (circulate) in the tank.

Here, the area directly above the first diffuser 130 and the second diffuser 135a to 135c is referred to as "aeration area". In this embodiment, the area directly above the first diffuser 130 is referred to as the first diffuser area 162, and the area directly above the second diffuser 135a to 135c is referred to as the second diffuser area. 162a～162c.

In the first aeration area 162, the first aeration device 130 is used to send in a sufficient amount of air for the activity of aerobic bacteria. Since the first aeration region 162 is a region formed by ejecting a large amount of oxygen with high dissolution efficiency, the amount of dissolved oxygen is very high compared to other regions. In particular, inside the cylindrical member 120, since a large number of bubbles are supplied in a narrow space, the oxygen concentration becomes extremely high. Therefore, the area inside the cylindrical member 120 is maintained in an aerobic environment. In this embodiment, the area located in an aerobic environment like the area inside the cylindrical member 120 is referred to as an "aerobic area".

In addition, although the second aeration regions 162a and 162b of the present embodiment are diffused, they are not regions with a high dissolved oxygen content like the first aeration region 162. The second aeration devices 135a and 135b are, after all, aeration devices for the circulation of sewage, and only need to generate bubbles to the extent that an upflow is generated. Therefore, the second aeration device 135a and 135b may have a smaller amount of air supply than the first aeration device 130.

In addition, the area between the first aeration area 162 and the second aeration area 162a and the area between the first aeration area 162 and the second aeration area 162b is referred to as a "non-aeration area." The non-aeration area 164 is an area in which the amount of dissolved oxygen is less than the area inside the cylindrical member 120, and is maintained in an anaerobic environment. In the present embodiment, the area located in an anaerobic environment like the area around the cylindrical member 120 is referred to as an "anaerobic area". In addition, in this embodiment, it is important to maintain the non-aeration area 164 in an anaerobic environment. For example, it is desirable that the non-aeration area 164 has a dissolved oxygen content of 1/3 or less (1/5 or less is better, and 1/10 or less is better) compared to the first aeration area 162. For example, the dissolved oxygen amount of the first aeration area 162 is preferably 0.8 mg/L or more, and the dissolved oxygen amount of the non-aeration area 164 is preferably 0.3 mg/L or less.

As described above, in the present embodiment, by selectively dispersing the air inside the cylindrical member 120 (that is, dispersing the air inside the cylindrical member 120, and not dispersing the air around the cylindrical member 120). Air), in the carrier flow aeration tank 12, an aerobic area with upward flow (specifically, the first diffusion area 162 inside the cylindrical member 120) and an anaerobic area with downward flow ( Specifically, it is the non-aspiration area 164). In addition, as shown by the arrow in FIG. 2, the plurality of carriers 150 circulate so as to rise in the aerobic area and decrease in the anaerobic area. That is, the carrier 150 of this embodiment circulates through the aerobic area and the anaerobic area alternately.

When the carrier 150 is located in the aerobic region, the oxidative decomposition of organic matter (carbide) caused by aerobic bacteria actively proceeds in the outer layer portion of the carrier 150 (the portion close to the outer surface of the carrier 150). That is, in the case of the carrier flow aeration tank 12 of this embodiment, organic matter is efficiently decomposed inside the cylindrical member 120 where the aerobic region is formed. Therefore, inside the cylindrical member 120, the biochemical oxygen demand (BOD) in the sewage 160 decreases.

If the BOD in the sewage 160 decreases, the outer layer of the carrier 150 will become ammonia instead of organic matter and be oxidized. Specifically, on the inner side of the cylindrical member 120, nitrification of ammonia nitrogen or organic nitrogen by nitrifying bacteria, which are aerobic bacteria, is performed on the outer layer of the carrier 150. Through this nitrification, ammonia nitrogen or organic nitrogen is converted into nitrate nitrogen or nitrite nitrogen. The nitrate nitrogen or nitrite nitrogen converted in the outer layer of the carrier 150 continues to advance to the inner layer of the carrier 150.

Since the inner layer of the carrier 150 is not sufficiently supplied with oxygen, it becomes an oxygen-deficient area, that is, an anaerobic area. In the anaerobic region formed in the inner layer of the carrier 150, denitrification bacteria are mainly operating to reduce nitrate nitrogen or nitrite nitrogen into nitrogen (denitrification). The converted nitrogen is discharged into the atmosphere through the sewage 160.

Through the above process, inside the carrier 150, nitrification caused by nitrifying bacteria is performed in the outer layer, and denitrification caused by denitrifying bacteria is performed in the inner layer. In this way, the oxidative removal of organic matter and the removal of nitrogen can be simultaneously realized in the carrier flow aeration tank 12 of this embodiment.

Here, the reason for allowing the carrier 150 to alternately pass through the aerobic area and the anaerobic area in the sewage treatment device 100 of the present embodiment will be explained.

As described above, in the interior of the carrier 150, nitrification by nitrifying bacteria is performed in the outer layer, and denitrification by denitrifying bacteria is performed in the inner layer. However, as described in the aforementioned Patent Document 1, if the aeration treatment is continuously performed, there is a problem that the nitrogen removal rate gradually decreases. In Patent Document 1, the following method is adopted: assuming that the decrease in nitrogen removal rate is caused by the decrease of the anaerobic area inside the carrier, the size of the carrier is increased to relatively expand the anaerobic area inside the carrier. In contrast, in the carrier flow aeration tank 12 of this embodiment, different from the method described in Patent Document 1, the following method is adopted: the denitrification is activated by deliberately applying pressure to the denitrification bacteria inside the carrier Bacteria to maintain denitrification.

The inventors of the present invention believe that the aforementioned decrease in the nitrogen removal rate is due to the denitrification bacteria becoming accustomed to the state of lack of oxygen. Denitrification bacteria will actively reduce nitrate nitrogen (denitrification) in order to obtain the oxygen required for the decomposition of organic matter or ammonia at the start of the operation. However, it is conceivable that if denitrification bacteria are used to an environment where nitrate nitrogen is often supplied, they will lose their motivation to acquire oxygen and become low in activity. In short, the inventors of the present invention believe that active nitrification by nitrifying bacteria in the outer layer of the carrier 150 may be a cause of low activity of denitrifying bacteria.

Therefore, the inventors decided to intermittently suppress the progress of nitrification in the outer layer of the carrier 150 and make a state where nitrate nitrogen or the like is not supplied to the inner layer of the carrier 150 to deliberately exert pressure on the denitrification bacteria. That is, the inventors of the present invention believe that by placing the denitrifying bacteria in an intermittently lacking oxygen state, the denitrifying bacteria can maintain a state of actively demanding oxygen (in short, an activated state).

As described above, the carrier flow aeration tank 12 of this embodiment has the following structure: By placing the carrier 150 in an anaerobic environment (anaerobic area) for a certain period of time instead of constantly placing the carrier 150 in aerobic environment In a sexual environment (aerobic zone), the operation of the denitrification bacteria in the inner layer of the carrier 150 is activated. That is, the sewage treatment device 100 including the carrier flow aeration tank 12 of this embodiment can maintain the state that the carrier 150 alternately passes through the aerobic area and the anaerobic area, so that the The activity of denitrification bacteria is maintained, and the chronological decrease of denitrification is inhibited.

[Specific structure of carrier flow aeration tank]

3 and 4 are diagrams showing the specific structure of a sewage treatment device 100 according to an embodiment of the present invention. More specifically, (A) of FIG. 3 is a plan view of the sewage treatment device 100. Fig. 3(B) is a side view of the sewage treatment device 100. FIG. 4 is a cross-sectional view of the inside of the carrier flow aeration tank 12 in the sewage treatment device 100 viewed along the longitudinal direction of the tank body 110. In addition, the symbols used in FIG. 3(A), FIG. 3(B), and FIG. 4 refer to the same members as the symbols used in FIG. 1 and FIG. 2.

In the example shown in Fig. 3(A) and Fig. 3(B), two cylindrical members, namely, cylindrical members 120a and 120b, are arranged inside the tank body 110. The first diffuser 130a is arranged below the cylindrical member 120a, and the first diffuser 130b is arranged below the cylindrical member 120b. However, the number of cylindrical members 120 is not limited to this example. One cylindrical member 120 may be arranged inside the carrier flow aeration tank 12, or more than three cylindrical members 120 may be arranged.

In addition, three air lift pumps 142a to 142c are arranged inside the tank body 110. Among the three air lift pumps 142 a to 142 c, the air lift pumps 142 a and 142 c are arranged inside the carrier flow aeration tank 12, and the air lift pump 142 b is arranged inside the sedimentation tank 13.

In addition, second aeration devices 135a to 135c are arranged inside the tank body 110. The second aeration devices 135 a and 135 b are both arranged in the vicinity of the tank body 110 or the partition 112 in the interior of the carrier flow aeration tank 12. In addition, the aforementioned cylindrical members 120a and 120b (and the first diffuser 130a and 130b) are arranged on a straight line connecting the pair of second diffuser 135a and 135b. The second aeration device 135c is arranged in the vicinity of the partition 112 in the interior of the sedimentation tank 13. As described above, the upward flow formed by the second aeration device 135c also plays a role of detaching the carrier 150 attached to the surface of the carrier screen 114 (the surface on the side of the carrier flow aeration tank 12) from the carrier screen 114.

As shown in Fig. 3(B) and Fig. 4, the upper part of the carrier screen 114 is located above the sewage surface 160a of the sewage 160. In the present embodiment, the carrier 150 is pushed back into the carrier flow aeration tank 12 by the water flow when the sewage surface 160a pushed upward due to the upward flow of the second diffuser 135c returns to the bottom. side. Therefore, the upper part of the carrier screen 114 is located above the sewage surface 160a, so that the water flow can directly act on the carrier screen 114, which has the effect of making the carrier 150 easily separated from the carrier screen 114. However, it is not limited to this example, and the carrier screen 114 can also be completely submerged in the sewage 160.

And, in the example shown in Fig. 3(A), Fig. 3(B) and Fig. 4, the aforementioned cylindrical members 120a and 120b, the first diffuser 130a and 130b, and the second diffuser 135a to 135c The air lift pumps 142a to 142c are arranged on the same straight line, and the carrier screen 114 is also arranged on the same straight line.

In the sewage treatment device 100 having the above structure, the inner sides of both the cylindrical members 120a and 120b function as an aerobic area, and the surrounding area functions as an anaerobic area. Therefore, the activity of the denitrifying bacteria existing in the carrier 150 can be efficiently enhanced in the inside of the carrier flow aeration tank 12. That is, it is possible to suppress the reduction of the denitrification function in the sewage treatment using the carrier flow, and it is possible to improve the treatment efficiency of the sewage treatment device 100.

(Modification 1)

In this embodiment, although the second aeration devices 135a and 135b are provided inside the carrier flow aeration tank 12 to return the sewage 160, the embodiment is not limited to this structure. For example, since a large amount of air is sent into the cylindrical member 120, a strong upward flow is generated, and negative pressure is generated around the opening end of the lower side of the cylindrical member 120. In short, the circumference of the cylindrical member 120 (between the cylindrical member 120 and the inner wall of the tank body 110, or between the cylindrical member 120 and the partition 112) naturally forms a return flow as shown by the arrow in FIG. 2 (Reflow from the upper end to the lower end of the cylindrical member 120).

Therefore, even if the second aeration devices 135a and 135b are omitted from the carrier flow aeration tank 12 in the structure shown in FIG. 2, the carrier 150 can be circulated through the aerobic area and the anaerobic area alternately.

(Modification 2)

In this embodiment, although an example in which the tank body 110 is divided into the carrier flow aeration tank 12 and the precipitation tank 13 by the partition 112 is described, the embodiment is not limited to this structure. For example, when the scale of the sewage treatment device 100 is small (that is, when the tank body 110 is small), the tank body 110 can also be divided into the carrier flow aeration tank 12 and the tank body 110 using the carrier screen 114 Sedimentation tank 13. In this case, since the sedimentation tank 13 is provided with the second aeration device 135c, a water flow is formed from the sedimentation tank 13 to the carrier flow aeration tank 12, and the clogging of the carrier screen 114 can be prevented. By providing the second air diffuser 135c close to the carrier screen 114, the clogging of the carrier screen 114 can be further prevented with high efficiency.

The embodiments of the present invention and its modifications can be implemented in appropriate combinations as long as they do not contradict each other. Based on the aeration tank, sewage treatment device, and sewage treatment method of the above-mentioned implementation type, a person with ordinary knowledge in the technical field to which the present invention pertains adds, deletes, or changes the design of appropriate constituent elements, or performs procedures Additions, omissions, or changes in conditions are also included in the scope of the present invention as long as they have the gist of the present invention.

Moreover, even if it is other effects that are different from the effects brought about by the above-mentioned implementation modes, those that are clear from the description in this specification, or those who have general knowledge in the technical field of the present invention Those who are easy to predict among them should be understood as those facilitated by the present invention.

10: Sewage treatment system 11: adjustment slot 12: Carrier flow aeration tank 13: sedimentation tank 14: Sludge return device 15: Sludge thickening storage tank 16: Disinfection tank 17: Drainage trough 100: Sewage treatment plant 110: Slot body 112: divider 112a: opening 114: Carrier Screen 116: Raw water inflow pipe 117: Raw water metering tank 118: Raw water supply pipe 120: Cylindrical parts 120a, 120b: cylindrical parts 130, 130a, 130b: the first diffuser 135a～135c: The second diffuser 137: Air Pipe 142a～142c: Air lift pump 144: Sludge return pipe 145: Sludge metering tank 146: Sludge supply pipe 150: carrier 160: sewage 160a: sewage surface 162: First Dispersion Area 162a～162c: The second diffuse area 164: Non-dispersion area

<Figure 1> is a diagram showing the structure of a sewage treatment system of one embodiment of the present invention. <Figure 2> is a diagram showing the structure of a sewage treatment device of one embodiment of the present invention. <Figure 3> is a diagram showing the specific structure of a sewage treatment device of an embodiment of the present invention. <Figure 4> is a diagram showing the specific structure of a sewage treatment device of one embodiment of the present invention.

12: Carrier flow aeration tank

13: sedimentation tank

14: Sludge return device

100: Sewage treatment plant

110: Slot body

112: divider

112a: opening

114: Carrier Screen

116: Raw water inflow pipe

117: Raw water metering tank

118: Raw water supply pipe

120: Cylindrical parts

130: The first diffuser

135a~135c: The second diffuser

137: Air Pipe

142a, 142b: Air lift pump

144: Sludge return pipe

145: Sludge metering tank

146: Sludge supply pipe

150: carrier

160: sewage

160a: sewage surface

162: First Dispersion Area

162a~162c: The second diffuser area

164: Non-dispersion area

Claims (13)

An aeration tank, comprising: a tank body, a carrier that is arranged inside the tank body and maintains nitrifying bacteria and denitrification bacteria inside, and is arranged at a distance from the inner wall of the tank body and has an open end in the up and down direction A cylindrical member, and a first diffuser provided directly below the cylindrical member. The aeration tank according to claim 1, wherein in a plan view, the outer edge of the first diffuser is located inside the inner edge of the cylindrical member. The aeration tank according to claim 1, which further includes a second aeration device provided at a distance from the aforementioned cylindrical member. An aeration tank, which has an aerobic area with an upward flow and an anaerobic area with a downward flow in the tank body. At the same time, a carrier that maintains nitrifying bacteria and denitrifying bacteria in the interior is alternately passed through the aerobic area. The sexual zone and the aforementioned anaerobic zone circulate in a way. The aeration tank according to claim 4, wherein the aerobic region is formed inside a cylindrical member having an open end in the vertical direction, and the anaerobic region is formed around the cylindrical member. The aeration tank according to claim 4 or 5, wherein the amount of dissolved oxygen in the anaerobic zone is less than 1/3 of the amount of dissolved oxygen in the aerobic zone. A sewage treatment device comprising: the aeration tank according to any one of claims 1 to 5, and a sedimentation tank provided downstream of the aeration tank. The sewage treatment device according to claim 7, wherein the aeration tank and the precipitation tank are connected through a carrier screen provided on the inner wall of the tank body. The sewage treatment device according to claim 7, which is provided with an air diffuser inside the aforementioned sedimentation tank. The sewage treatment device according to claim 7, which further includes a sludge return device that returns the sludge of the aeration tank and the sedimentation tank to the upstream side. A sewage treatment method, which forms an aerobic area with an upward flow and an anaerobic area with a downward flow in the tank body, so that the carrier that maintains the nitrifying bacteria and the denitrifying bacteria in the interior can alternately pass through the aerobic area The sexual zone and the aforementioned anaerobic zone circulate in a way. The sewage treatment method according to claim 11, wherein the aerobic area is formed by dispersing air from below inside a cylindrical member having an open end in the vertical direction. The sewage treatment method according to claim 12, wherein the aerobic area is formed in the cylindrical member by selectively dissipating air inside the cylindrical member, and the aerobic area is formed around the cylindrical member. Anaerobic area.

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