JP7488387B2 - Wastewater Treatment System - Google Patents

Description

The present invention relates to a wastewater treatment system.

In wastewater treatment, in addition to removing organic matter (oxidation) using the activated sludge method, nitrogen-containing compounds such as ammonia nitrogen (hereafter referred to as nitrogen components) are also removed. Nitrogen components in wastewater can be removed, for example, by nitrification (oxidation to nitrate nitrogen) using nitrifying bacteria in an aerobic environment, and then denitrification (reduction to nitrogen gas) using denitrifying bacteria in an anaerobic environment.

Patent Document 1 describes a biological nitrogen removal device (wastewater treatment system). This biological nitrogen removal device is equipped with a denitrification treatment tank into which the influent (wastewater) to be treated flows, a nitrification treatment tank into which the water to be treated flows after passing through the denitrification treatment tank, a final settling tank in which activated sludge is separated by settling from the water to be treated that has been aerated and discharged as treated water, and an aeration device (bubble generator) that sends air to the nitrification treatment tank.

Patent Document 2 describes a wastewater treatment method in which atmospheric oxygen is introduced into the wastewater through an oxygen-permeable membrane by natural aeration without power. In this wastewater treatment method, a biofilm that grows on the membrane surface oxidizes ammonia nitrogen in the wastewater to generate nitrate nitrogen, and the nitrate nitrogen is then diffused away from the biofilm into the wastewater in an anaerobic environment, where it is denitrified.

Patent Document 3 describes a combined treatment septic tank (wastewater treatment system). This combined treatment septic tank is equipped with a cylindrical body made of an oxygen-permeable membrane installed in place of an anaerobic filter bed tank (denitrification tank) and a contact aeration tank (nitrification tank), and a biological treatment tank. The cylindrical body is immersed in the biological treatment tank. A double membrane structure of a biofilm of aerobic microorganisms and a biofilm of anaerobic microorganisms is formed on the outer periphery of the cylindrical body. In this combined treatment septic tank, a biological treatment process in which organic matter is decomposed by aerobic microorganisms and anaerobic microorganisms, and a ventilation process in which air is blown into the cylindrical body are carried out.

Japanese Patent Application Laid-Open No. 11-244894 JP 2003-211185 A JP 2016-43281 A

In the wastewater treatment system described in Patent Document 1, if nitrogen components are to be sufficiently nitrified, the capacity of the nitrification treatment tank must be increased. In addition, if the capacity of the nitrification treatment tank cannot be increased, the nitrogen components of the treated water cannot be sufficiently reduced. As described in Patent Documents 2 and 3, if oxygen is supplied to wastewater in an anaerobic environment through an oxygen-permeable membrane, it is possible to reduce energy consumption (hereinafter simply referred to as energy saving) and to achieve compactness by omitting or making the nitrification tank smaller. However, due to problems such as measures to prevent damage such as breakage of the oxygen-permeable membrane and insufficient oxygen supply due to excessive growth of biofilms, forced aeration is required in reality, and sufficient energy saving is not achieved, so there is room for improvement.

The present invention was made in consideration of this situation, and its purpose is to provide an energy-saving wastewater treatment system.

The characteristic configuration of the wastewater treatment system of the present invention for achieving the above-mentioned object is that it comprises a treatment tank for storing water to be treated, the treatment tank having an anaerobic treatment section which performs anaerobic treatment of the water to be treated, and an aerobic treatment section which is connected to the anaerobic treatment section downstream of the anaerobic treatment section and performs aerobic treatment of the water to be treated, the aerobic treatment section having a bubble generating section which generates bubbles, the anaerobic treatment section having an oxygen permeation section including an oxygen permeable membrane which allows oxygen to pass through, the water depth of the oxygen permeation section being less than 0.5 m, and all of the oxygen permeation section being immersed in a water depth which is less than 50 percent of the maximum water depth of the water to be treated in the aerobic treatment section.

In this wastewater treatment system, a biological denitrification reaction is carried out. According to the above configuration, the aerobic treatment section performs aerobic treatment on the water to be treated. In the aerobic treatment section, aerobic treatment is performed by using oxygen in the treatment water and nitrifying bacteria to promote oxidation (so-called nitrification, hereinafter simply referred to as "nitrification") of nitrogen-containing compounds (hereinafter referred to as "nitrogen components") such as ammonia nitrogen in the treatment water. As a result, the nitrogen components in the treatment water are converted to nitrate nitrogen. According to the above configuration, the area near the top of the bubble generating section in the treatment tank becomes an aerobic area with a high dissolved oxygen concentration because oxygen is supplied from the bubbles generated in the bubble generating section. The aerobic treatment section is an aerobic area in the treatment tank by oxygen supplied from the bubbles generated in the bubble generating section.

According to the above configuration, the anaerobic treatment unit performs anaerobic treatment on the water to be treated. In the anaerobic treatment unit, in an anaerobic environment, the denitrifying bacteria in the treatment water and the organic matter that serves as nutrients for the denitrifying bacteria reduce nitrate nitrogen to produce nitrogen (so-called denitrification, hereafter referred to simply as "denitrification"). Through this nitrification and denitrification, the treated water is purified by decomposing and removing nitrogen-containing compounds.

According to the above configuration, a biofilm containing mainly nitrifying bacteria that nitrifies the nitrogen components in the treatment water with oxygen supplied from the oxygen permeable membrane is formed on the surface of the oxygen permeable membrane, and the nitrogen components are nitrified. In other words, according to the above configuration, nitrification can be performed both in the aerobic region formed by the bubble generating unit and in the biofilm formed on the surface of the oxygen permeable membrane. Note that the oxygen supplied from the oxygen permeable membrane is consumed completely within the biofilm, so the anaerobic environment of the external (outside) region of the biofilm is maintained.

According to the above configuration, the oxygen permeable section is immersed in a shallow water area less than 50% of the maximum water depth of the water to be treated, so even if water penetrates into the membrane due to damage to the oxygen permeable membrane, the water can be removed by blowing low-pressure air. Therefore, the air pressure blown (supplied) to the oxygen permeable section can be low, realizing energy savings in the oxygen permeable section. In addition, because the air blown can be low-pressure, a simple blower can be used, reducing the cost of the system. For example, instead of using a blower that can blow air at high pressure but is expensive to install, a low-cost fan can be used as the blower.

Also, the bubble generating unit is usually immersed in deep water (for example, at least 50 percent deeper than the maximum water depth of the treatment tank), and so air needs to be supplied at a pressure proportional to the water pressure at that water depth. However, with the above configuration, nitrification also progresses with the oxygen supplied from the oxygen permeation unit. This makes it possible to reduce the amount of oxygen (air) that needs to be supplied from the bubble generating unit. This makes it possible to reduce the overall energy required to supply oxygen for nitrification in the treatment tank.

In addition, with the above-mentioned configuration, the oxygen permeable section is immersed in a shallow water area, making it easy to access from above the water surface and easy to maintain. In other words, external stimuli such as vibrations can be easily applied from above the water surface, making it extremely easy to remove biofilms that have grown too much on the oxygen permeable membrane. As a result, it is possible to avoid a decrease in the efficiency of nitrification in the oxygen permeable section.

A further characteristic feature of the wastewater treatment system according to the present invention is that the oxygen permeation section has a permeation unit including a plurality of cylindrical sections in which the oxygen permeable membrane is formed in a cylindrical shape, and the permeation unit is immersed along the water surface of the water to be treated.

According to the above configuration, the cylindrical portion is an oxygen-permeable membrane formed in a cylindrical shape, and air can flow through the inside. The permeation unit is formed by bundling a plurality of cylindrical portions. The cylindrical portion is arranged horizontally along the horizontal plane (water surface) as a permeation unit. By arranging the cylindrical portion horizontally, the area of the oxygen-permeable membrane can be increased without increasing the installation depth (depth of water to which the oxygen-permeable membrane is immersed). Therefore, even when considering the intrusion of water into the membrane due to damage to the oxygen-permeable membrane, a low pressure of air is sufficient to supply to the oxygen-permeable membrane, and energy saving can be achieved in the oxygen-permeable portion, and the area of the oxygen-permeable membrane can be increased to improve the nitrification efficiency on the oxygen-permeable membrane (in the biofilm). In addition, since the cylindrical portion is arranged horizontally, it is easy to access from above the water surface, and maintenance is improved. This makes it extremely easy to remove the biofilm formed on the oxygen-permeable membrane when the biofilm grows too large.

A further characteristic feature of the wastewater treatment system according to the present invention is that the anaerobic treatment section and the aerobic treatment section are partitioned and arranged in the same treatment tank.

According to the above configuration, the treatment tank is divided into an anaerobic treatment section and an aerobic treatment section. For example, the treatment tank can be divided into an upstream region and a downstream region by a partition wall, with the upstream region being the anaerobic treatment section and the downstream region being the aerobic treatment section, or the treatment tank can be divided into upper and lower regions in the vertical direction (up and down direction) by a partition wall, with one region (e.g. the upper region) being the anaerobic treatment section and the other region (e.g. the lower region) being the aerobic treatment section. In particular, when the treatment tank is divided into upper and lower regions in the vertical direction, the oxygen permeation section and the bubble generation section can be arranged so as to overlap when viewed in the vertical direction, making it possible to make the treatment tank more compact.

A further characteristic feature of the wastewater treatment system according to the present invention is that the treatment tank has a first tank and a second tank arranged downstream of the first tank, the oxygen permeation section is immersed in the first tank, and the bubble generation section is immersed in the second tank.

According to the above configuration, the first tank in which the oxygen permeable portion is immersed is an anaerobic treatment portion, and not only does denitrification proceed in the outer region of the biofilm, but nitrification also proceeds in the inner region of the biofilm. The second tank is an aerobic treatment portion, and nitrification takes place. In this way, when the treatment tank has a first tank and a second tank, the treatment efficiency of each tank is improved by making the first tank an anaerobic treatment portion and the second tank an aerobic treatment portion. Even when the first tank is an anaerobic treatment portion, the oxygen supplied from the oxygen permeable membrane of the oxygen permeable portion is consumed in the biofilm formed on the oxygen permeable membrane, so that the first tank as a whole is maintained in an anaerobic environment. Therefore, denitrification in the first tank is not inhibited.

Another characteristic feature of the wastewater treatment system of the present invention is that the water depth of the anaerobic treatment section is 0.5 m or less.

According to the above configuration, since the water depth of the first tank is kept to a shallow depth of 0.5 m or less, an extremely low pressure is sufficient for the air supplied to the oxygen permeable section. This allows energy savings to be achieved. In addition, since the oxygen permeable membrane is immersed in a particularly shallow depth of 0.5 m or less, it is easy to access from above the water surface and is highly maintainable. In addition, external stimuli such as vibrations can be applied very easily from above the water surface. As a result, if a biofilm formed on the oxygen permeable membrane grows too much, it can be very easily removed.

FIG. 2 is a schematic side view of the treatment tank according to the first embodiment. FIG. 2 is a schematic diagram of a top view of a treatment tank according to the first embodiment. FIG. 1 is an explanatory diagram of a wastewater treatment system and a treatment train. FIG. 2 is an explanatory diagram of a cross-sectional structure of a transmission unit. FIG. 2 is an explanatory diagram of a cross-sectional structure of a permeation unit on which a biofilm is formed. FIG. 2 is an explanatory diagram of the cross-sectional structure of an oxygen-permeable membrane and a biofilm. FIG. 11 is a schematic diagram of a treatment tank according to a second embodiment. FIG. 13 is a schematic diagram of an arrangement of transmission units according to another embodiment. FIG. 11 is a schematic diagram of a treatment tank according to another embodiment.

The following describes a wastewater treatment system according to an embodiment of the present invention, based on the drawings.

[First embodiment] [Explanation of overall configuration]
1 and 2 show a schematic configuration of a wastewater treatment system 100 that purifies wastewater (water to be treated) flowing in. The wastewater treatment system 100 is installed in a sewage treatment plant or the like. The wastewater treatment system 100 includes a treatment tank R that stores wastewater continuously flowing in from upstream, an oxygen permeation section 3 that supplies oxygen to the wastewater stored in the treatment tank R through an oxygen permeable membrane 30, and a bubble generation section 6 that generates bubbles B (see FIG. 1) to supply oxygen to the wastewater stored in the treatment tank R. The treatment tank R has an anaerobic tank 1 (an example of a first tank, an example of an anaerobic treatment section) and an aerobic tank 2 (an example of a second tank, an example of an aerobic treatment section) downstream of the anaerobic tank 1. The oxygen permeation section 3 is immersed in the wastewater stored in the anaerobic tank 1. The bubble generation section 6 is immersed in the wastewater stored in the aerobic tank 2.

In this embodiment, the wastewater flowing into the treatment tank R contains at least nitrogen-containing compounds such as ammonia nitrogen (hereinafter referred to as "nitrogen components") and organic matter. In the treatment tank R, nitrification (an example of aerobic treatment) in which nitrogen components are oxidized to nitrite nitrogen and nitrate nitrogen, and denitrification (an example of anaerobic treatment) in which nitrite nitrogen and nitrate nitrogen are reduced to nitrogen, are carried out. Hereinafter, nitrite nitrogen and nitrate nitrogen will be collectively referred to simply as "nitrate nitrogen."

As shown in FIG. 3, the wastewater treatment system 100 of this embodiment includes a primary sedimentation tank 91 upstream of the treatment tank R and a final sedimentation tank 99 downstream of the treatment tank R. The wastewater treatment system 100 may have multiple treatment series N1, N2, N3, etc., each having a primary sedimentation tank 91, a treatment tank R, and a final sedimentation tank 99. In this embodiment, the treatment series N1, N2, and N3 are all equivalent. Below, the treatment series N1 will be described, but the same applies to the treatment series N2 and N3. In this embodiment, the concept of wastewater stored in the treatment tank R includes the concept of a so-called mixed liquid in which suspended solids (SS) including nitrifying bacteria and denitrifying bacteria as activated sludge are present in a suspended state.

[Explanation of each part]
The primary sedimentation tank 91 is a tank for settling and removing a portion of the sludge contained in the wastewater that flows in. Wastewater containing nitrogen components and organic matter that was not removed in the primary sedimentation tank 91 flows into the treatment tank R (anaerobic tank 1).

As shown in Figures 1 and 2, the treatment tank R has one anaerobic tank 1 and one aerobic tank 2 connected in series downstream of the anaerobic tank 1. Wastewater that flows into the anaerobic tank 1 is retained in the anaerobic tank 1 for a predetermined time before flowing into the aerobic tank 2. Wastewater that flows into the aerobic tank 2 is retained in the aerobic tank 2 for a predetermined time before flowing out. In the aerobic tank 2, nitrification mainly proceeds. In the anaerobic tank 1, denitrification mainly proceeds, and nitrification also proceeds. A portion of the wastewater that flows out from the aerobic tank 2 is pumped by a pump (not shown) or the like through the return flow path 9 and returned (supplied) to the anaerobic tank 1 (see Figure 3). Hereinafter, the treated water returned to the anaerobic tank 1 through the return flow path 9 is referred to as the nitrification liquid.

The anaerobic tank 1 is a tank in which wastewater is maintained in an anaerobic environment (an environment with little dissolved oxygen). In the anaerobic tank 1, denitrification is mainly carried out, and nitrification is also carried out. As shown in FIG. 1, an oxygen permeable section 3 having an oxygen permeable membrane 30 is immersed in the anaerobic tank 1.

In the anaerobic tank 1, oxygen is supplied to the wastewater through the oxygen permeable membrane 30, and nitrification proceeds near the surface of the oxygen permeable membrane 30. The area of the anaerobic tank 1 other than the area near the surface of the oxygen permeable membrane 30 is maintained in an anaerobic environment, and denitrification proceeds due to denitrifying bacteria. Details of nitrification in the oxygen permeable section 3 and the oxygen permeable membrane 30 will be described later together with details of the oxygen permeable section 3.

The anaerobic tank 1 is a tank that is shallower than the aerobic tank 2, for example, with a maximum water depth (the distance in the vertical direction V from the water surface to the deepest bottom surface of the tank, hereinafter referred to as water depth d1) of about 0.3 m to 5 m. The water depth d1 of the anaerobic tank 1 is set to less than 50% of the water depth d2, which is the maximum water depth of the aerobic tank 2 described below. In this embodiment, the water depth d1 of the anaerobic tank 1 is 0.5 m.

The aerobic tank 2 is a tank in which the wastewater is kept in an aerobic environment (an environment rich in dissolved oxygen). As shown in FIG. 1, the bubble generating unit 6 is immersed in the aerobic tank 2. In the aerobic tank 2, air is supplied (aeration) by bubbling from the bubble generating unit 6, and oxygen is supplied to the wastewater by dissolving oxygen from the bubbles B (so-called aeration). This maintains the aerobic environment in the aerobic tank 2. In the aerobic tank 2, nitrification using the oxygen supplied by the bubble generating unit 6 progresses. The aerobic tank 2 is a tank deeper than the anaerobic tank 1, for example, with a maximum water depth of about 3 m to 10 m. In this embodiment, the maximum water depth d2 of the aerobic tank 2 (treatment tank R) is 5 m. Details of the bubble generating unit 6 will be described later. A part of the wastewater discharged from the aerobic tank 2 to the final settling tank 99, or a part of the wastewater aerobically treated in the aerobic tank 2 is returned to the anaerobic tank 1 as a nitrification liquid (see FIG. 3).

The final settling tank 99 is a settling tank that receives wastewater discharged from the aerobic tank 2 (treatment tank R) and allows activated sludge and other substances in the wastewater to settle. In this embodiment, the sludge that settles in the final settling tank 99 is returned to the anaerobic tank 1 via the return flow path 9 (see Figure 3).

The air bubble generating unit 6 is an aeration device that supplies supplied air by bubbling it into the wastewater of the aerobic tank 2. The air bubble generating unit 6 is fixed to the bottom of the aerobic tank 2, which is, for example, 5 m deep. The air bubble generating unit 6 has an air diffuser tube (not shown) with multiple holes as an air diffusion mechanism for blowing out the supplied air. The air bubble generating unit 6 supplies air at a predetermined blowing pressure from a blower 76, such as a fan or blower, via an air blower tube 76a.

In this embodiment, the bubble generating unit 6 is immersed in water at a depth of 5 m. Therefore, in order to supply sufficient air (oxygen) against the water pressure and to promote sufficient nitrification in the aerobic tank 2, air with a static pressure of, for example, 60 kPa is supplied from the blower 76. In this case, a blower is used as the blower 76.

The oxygen permeation section 3 is a device that supplies oxygen contained in the supplied air to the wastewater through the oxygen permeation membrane 30. The oxygen permeation section 3 is immersed in the anaerobic tank 1. The oxygen permeation section 3 has a permeation unit 33 having the oxygen permeation membrane 30, and a pair of manifolds 35 that are distribution channels that supply and discharge air to the permeation unit 33. In this embodiment, the permeation unit 33 and the pair of manifolds 35 are entirely immersed in the anaerobic tank 1.

As shown in FIG. 4, the permeation unit 33 has a base material 32 and a cylindrical portion 31 in which the oxygen permeable membrane 30 is formed in a hollow fiber shape (long, thin cylinder shape). The permeation unit 33 is configured by bundling multiple cylindrical portions 31 on the surface of the base material 32, forming a linear rod-shaped unit as shown in FIG. 1 and FIG. 2. One end of each cylindrical portion 31 is connected to the supply air manifold 35, and the other end is connected to the exhaust air manifold 35.

As shown in Figures 1 and 2, the oxygen permeable section 3 receives air at a predetermined pressure from a blower 73, such as a fan or blower, through a blower pipe 73a connected to the manifold 35 on the intake side, and supplies the oxygen contained in the supplied air to the wastewater through the oxygen permeable membrane 30. The manifold 35 on the exhaust side is open to the outside through the exhaust pipe 73b, and the air that has passed through the tubular section 31 is released to the outside.

The oxygen-permeable membrane 30 formed as the tubular portion 31 is a membrane material having oxygen permeability, which allows oxygen ( _O2 ) contained in the air (gas G in FIG. 6) flowing through the inside of the tubular portion 31 to pass through and supply the oxygen to the wastewater outside the tube, as shown in FIG. 5 .

As shown in Figures 5 and 6, a biofilm L is formed on the membrane surface of the oxygen-permeable membrane 30. As shown in Figure 6, the biofilm L in this embodiment includes a first biofilm La that grows adjacent to the membrane surface (outer surface) of the oxygen-permeable membrane 30 and mainly contains nitrifying bacteria, and a second biofilm Lb that grows on the outer surface side of the biofilm L and mainly contains denitrifying bacteria.

In the first biofilm La, nitrifying bacteria oxidize (nitrify) nitrogen components (e.g., _NH4 ⁺ ) in the wastewater using oxygen ( _O2 ) supplied from the oxygen-permeable membrane 30 to generate nitrate nitrogen ( _NOx- ⁾ . In the first biofilm La, the oxygen supplied from the oxygen-permeable membrane 30 is completely consumed. In the anaerobic tank 1, the first biofilm La nitrifies some of the nitrogen components in the wastewater.

In this embodiment, as described above, nitrification can be performed in the aerobic tank 2 and the first biofilm La in the anaerobic tank 1, so the aerobic tank 2 can be made more compact than when nitrification is performed only in the aerobic tank 2. This allows the treatment tank R and the entire wastewater treatment system 100 to be made more compact.

In the second biofilm Lb and in the area outside the second biofilm Lb (in the wastewater other than the oxygen permeation section 3 of the anaerobic tank 1 and the biofilm L), denitrifying bacteria use organic matter (BOD) in the wastewater as a nutrient source to reduce (denitrify) nitrate nitrogen (NO _x ^- ) and release nitrogen (N ₂ ). The nitrate nitrogen denitrified in the anaerobic tank 1 is both that produced by the first biofilm La and that contained in the nitrified liquid returned from the aerobic tank 2 to the anaerobic tank 1. In the anaerobic tank 1, for example, 70% of the total nitrogen components that flow into the anaerobic tank 1 (treatment tank R) are reduced to nitrogen (denitrified). The nitrate nitrogen that was not denitrified in the anaerobic tank 1 flows out of the treatment tank R via the aerobic tank 2.

If the biofilm L grows excessively (if the membrane becomes too thick), the supply of nitrate nitrogen to the inside of the membrane (the area where oxygen can be supplied from the oxygen permeable membrane 30) may be hindered, and nitrification may not proceed efficiently. For this reason, the oxygen permeation section 3 and the anaerobic tank 1 may be provided with a mechanism (not shown, hereinafter referred to as a "shedding mechanism") for causing the excessively grown biofilm L to fall off from the oxygen permeable membrane 30. Examples of the shedding mechanism include a mechanism for generating a water current near the permeation unit 33 or shaking the permeation unit 33.

In this embodiment, the water depth d1 of the anaerobic tank 1 is 0.5 m, and the oxygen permeable section 3 is merely immersed in a water depth of less than 0.5 m. In this embodiment, the water depth d3 (see FIG. 1) from the water surface to the bottom end of the cylindrical section 31 is 0.3 m. Therefore, the static pressure of the air required to supply air to the cylindrical section 31 is at most less than 10 kPa, even when considering the intrusion of water into the oxygen permeable membrane 30 due to damage to the membrane. Therefore, it is sufficient to use a fan as the blower 76. This reduces the power required for supplying air. In addition, the system cost can be reduced by using an inexpensive blower 76 (e.g., a fan).

The permeation unit 33 is immersed (placed) in the wastewater from the anaerobic tank 1 with the tubular portion 31 facing sideways along the water surface (horizontal surface). This makes it possible to avoid increasing the installation depth (depth of water immersion) of the tubular portion 31 when increasing the area of the oxygen permeable membrane 30. This means that even if the area of the oxygen permeable membrane 30 is increased, there is no need to increase the static pressure of the air required to supply air to the tubular portion 31, which saves energy.

The permeation unit 33 is merely immersed in a shallow position of about water depth d3 with the cylindrical part 31 facing sideways along the water surface (horizontal surface). Therefore, even if a falling-off mechanism that directly shakes the permeation unit 33 is provided in the permeation unit 33, it is not necessarily required to place the falling-off mechanism inside the anaerobic tank 1 (in the wastewater). For example, it is sufficient to place the main body of the falling-off mechanism outside the anaerobic tank 1 (above the water surface, outside the wastewater) and connect only a part of the connecting mechanism for shaking to the permeation unit 33 through the wastewater. In addition, in the case of a falling-off mechanism that indirectly shakes the permeation unit 33 by a water flow or the like, the entire mechanism can be placed outside the anaerobic tank 1. By placing the falling-off mechanism outside the anaerobic tank 1, it is preferable because it improves maintainability.

Second Embodiment
In the first embodiment, as shown in Figures 1 and 2, the treatment tank R has an anaerobic tank 1 and an aerobic tank 2 downstream of the anaerobic tank 1. In the present embodiment, instead, as shown in Figure 7, the treatment tank R is a single tank partitioned (upper and lower) in the vertical direction V by a partition wall D, but the other configurations are similar.

The treatment tank R is at least partially partitioned in the vertical direction V by a partition D, and is partitioned into a first area 1A on the water surface side (another example of an anaerobic treatment unit) and a second area 2A on the bottom side (another example of an aerobic treatment unit). The maximum water depth d4 from the water surface to the partition D is set to about 0.3 m to 5 m, similar to the water depth d1 of the anaerobic tank 1 in the first embodiment. In this embodiment, the water depth d4 is 0.5 m. The maximum water depth from the water surface to the partition D is the distance from the water surface to the top surface of the partition D at the deepest position. The water depth d4 should be set to less than 50% of the water depth d2, which is the maximum water depth of the treatment tank R, similar to the water depth d1.

The second area 2A corresponds to the aerobic tank 2 of the first embodiment, and is an area that is maintained in a primarily aerobic environment. The bubble generating unit 6 is immersed in the second area 2A, as in the aerobic tank 2 of the first embodiment. The second area 2A is supplied with oxygen by the bubble generating unit 6, and is maintained in a primarily aerobic environment, where nitrification by nitrifying bacteria progresses.

In this embodiment, it is preferable to immerse the air bubble generating unit 6 at a water depth of 50% or more of the maximum water depth d2 of the treatment tank R. As a result, the oxygen contained in the air bubbles B supplied from the air bubble generating unit 6 is consumed mainly by nitrification before it reaches the water surface of the treatment tank R. Therefore, the area with a shallow water depth of less than 50% of the maximum water depth d2 in the treatment tank R, particularly the first area 1A, is kept anaerobic.

The first area 1A corresponds to the anaerobic tank 1 of the first embodiment, and is an area maintained in an anaerobic environment as described above. The first area 1A is immersed in the oxygen permeable section 3, similar to the anaerobic tank 1 of the first embodiment. In the first area 1A, denitrification proceeds in the second biofilm Lb in the first area 1A and in the area outside the second biofilm Lb, and nitrification proceeds in the first biofilm La in the second area 2A and the first area 1A.

In this embodiment, the oxygen permeable section 3, the partition wall D, and the bubble generating section 6 are arranged in this order from the water surface toward the bottom of the treatment tank R, and the oxygen permeable section 3, the partition wall D, and the bubble generating section 6 are arranged so as to overlap in the vertical direction V. This inhibits the supply of bubbles B rising from the bubble generating section 6 to the vicinity of the oxygen permeable section 3. In other words, the first region 1A is a region in which the supply of bubbles B from the bubble generating section 6 is inhibited by the partition wall D.

The treatment tank R is agitated by the upward flow of bubbles B generated by the bubble generating unit 6. This agitation causes the wastewater newly flowing in from the initial settling tank 91, the wastewater from the first area 1A, and the wastewater from the second area 2A to circulate between the first area 1A and the second area 2A. This circulation causes the nitrate nitrogen nitrified in the second area 2A to be supplied to the first area 1A and denitrified. Note that the oxygen dissolved in the wastewater in the second area 2A is consumed by nitrification, so the wastewater flowing from the second area 2A to the first area 1A is anaerobic. The bubble generating unit 6 may be provided with an agitator (not shown) to promote the circulation of the wastewater.

In this embodiment, a partition wall D is arranged to cover the underside of the oxygen permeable section 3 with respect to the flow of bubbles B rising from the bubble generating section 6 so that the bubbles B rising from the bubble generating section 6 do not come into contact with the cylindrical section 31 of the oxygen permeable section 3. This prevents the bubbles B rising from the bubble generating section 6 from coming into contact with the cylindrical section 31, causing the biofilm L on the membrane surface of the oxygen permeable membrane 30 to detach, thereby preventing the inhibition of nitrification in the first biofilm La of the biofilm L. This allows the efficiency of nitrification in the first region 1A to be maintained high.

In this way, an energy-efficient and compact wastewater treatment system can be provided.

[Another embodiment]
(1) In the above embodiment, the permeation unit 33 is immersed in the wastewater with the tubular portion 31 oriented horizontally along the water surface (horizontal plane). However, the orientation of the tubular portion 31 is not limited to horizontal. As shown in Fig. 8, the tubular portion 31 may be immersed in the wastewater with the tubular portion 31 oriented vertically along the vertical direction V. Fig. 8 illustrates the case where the tubular portion 31 immersed in the anaerobic tank 1 is immersed vertically, but the same applies to the case where the tubular portion 31 is immersed in the first region 1A.

(2) In the above first embodiment, the treatment tank R has one anaerobic tank 1 and one aerobic tank 2 connected in series downstream of the anaerobic tank 1. However, the anaerobic tank 1 may be a plurality of tanks. For example, as shown in FIG. 9, the anaerobic tank 1 may be composed of three tanks, for example, tanks 11, 12, and 13, and these tanks 11, 12, and 13 may be connected in series in this order from the upstream. In this case, it is preferable to arrange the tanks 11, 12, and 13 so that they overlap in the vertical direction V, because this allows the anaerobic tank 1 to be formed compactly. The water depth of the anaerobic tank 1 (tanks 11, 12, and 13) is shallower than that of the aerobic tank 2. Therefore, instead of constructing one deep tank, for example, the tanks 11, 12, and 13 can be arranged so as to be stacked in the vertical direction V. This allows the anaerobic tank 1 to be made compact.

(3) In the above embodiment, the oxygen permeable section 3 is immersed in the anaerobic tank 1, and the permeation unit 33 and manifold 35 are entirely immersed in the anaerobic tank 1. However, the oxygen permeable section 3 is not limited to being entirely immersed in the anaerobic tank 1. For example, at least a pair of manifolds 35 and the air inlets and outlets of each tubular section 31 of the permeation unit 33 connected thereto may be disposed above the water surface. This is preferable because it makes it difficult for water to enter the interior of the tubular section 31 even if the oxygen permeable membrane 30 of the tubular section 31 is torn (broken).

(4) In the above first embodiment, the oxygen permeation section 3 is immersed in the wastewater stored in the anaerobic tank 1, but this is not limited to the above. The oxygen permeation section 3 may be immersed in the wastewater from the anaerobic tank 1 to the aerobic tank 2.

The configurations disclosed in the above embodiment (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, so long as no contradiction arises. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these embodiments. They can be modified as appropriate within the scope of the purpose of the present invention.

The present invention can be applied to wastewater treatment systems installed in sewage treatment plants and the like. It can also be applied not only to sewage treatment plants, but also to industrial wastewater treatment, etc.

1: Anaerobic tank (first tank, anaerobic treatment section)
1A: First area (anaerobic treatment section)
2: Aerobic tank (second tank, aerobic treatment section)
2A: Second area (aerobic treatment section)
3: Oxygen permeation section 6: Air bubble generation section 30: Oxygen permeation membrane 31: Cylindrical section 33: Permeation unit 73: Blower 76: Blower 100: Wastewater treatment system B: Air bubbles L: Biofilm R: Treatment tank V: Vertical direction

Claims (5)

A treatment tank for storing the water to be treated is provided.
The treatment tank comprises:
an anaerobic treatment unit that performs anaerobic treatment on the water to be treated;
an aerobic treatment unit connected to the anaerobic treatment unit downstream of the anaerobic treatment unit and performing aerobic treatment on the water to be treated;
The aerobic treatment unit has an air bubble generating unit that generates air bubbles,
The anaerobic treatment unit has an oxygen permeation unit including an oxygen permeable membrane that allows oxygen to permeate,
The water depth of the oxygen permeable section is less than 0.5 m,
A wastewater treatment system, wherein all of the oxygen permeation sections are immersed at a water depth that is less than 50 percent of the maximum water depth of the water to be treated in the aerobic treatment section. The oxygen permeation section has a permeation unit including a plurality of cylindrical sections in which the oxygen permeation membrane is formed in a cylindrical shape,
2. The wastewater treatment system according to claim 1, wherein the permeation unit is immersed along the surface of the water to be treated. The wastewater treatment system according to claim 1 or 2, wherein the anaerobic treatment section and the aerobic treatment section are partitioned and arranged in the same treatment tank. The treatment tank includes a first tank and a second tank disposed downstream of the first tank,
The oxygen permeable portion is immersed in the first tank,
The wastewater treatment system according to claim 1 , wherein the air bubble generating unit is immersed in the second tank. The wastewater treatment system according to any one of claims 1 to 4, wherein the water depth of the anaerobic treatment section is 0.5 m or less.

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