JP7577576B2 - Sedimentation tank, oxygen permeable membrane unit, and method for operating the sedimentation tank - Google Patents

Description

The present invention relates to a sedimentation tank, an oxygen permeable membrane unit, and a method for operating the sedimentation tank.

Conventionally, there is known a settling tank that treats turbid water (water to be treated) that contains pollutants (see, for example, Patent Documents 1 and 2). In this settling tank, the pollutants contained in the turbid water are allowed to settle by their own weight and accumulate.

The settling tank described in Patent Document 1 is equipped with multiple underwater membranes stretched against the water flow, and as the turbid water passes between these membrane sheets, the flow is rectified and pollutants are allowed to settle.

The settling tank described in Patent Document 2 is equipped with multiple inclined plates inside the settling tank, and flat membranes in a mesh-like shape for filtering turbid water are fixed to the openings of the inclined plates. The permeated water that has permeated the flat membranes passes through the internal space of the inclined plates and is discharged to the outside, while the pollutants settle, and the pollutants that do not settle adhere to the surface of the flat membranes. The pollutants that have adhered to the flat membranes are peeled off and removed by air.

JP 2014-151297 A Japanese Patent Application Publication No. 7-275610

When the sedimentation tank described in Patent Document 1 is applied to a primary sedimentation tank installed upstream of a biological treatment tank in a sewage treatment plant, the pollutants are simply removed by settling in the primary sedimentation tank, which places a heavy burden on the biological treatment tank. Furthermore, even if the sedimentation tank described in Patent Document 2 is applied to a primary sedimentation tank, the air can only peel off and remove the pollutants attached to the flat membrane, and does not go so far as to create an aerobic environment.

Therefore, there is a demand for a sedimentation tank, an oxygen permeable membrane unit, and an operating method for the sedimentation tank that can reduce the load on the biological treatment tank.

A characteristic configuration of the sedimentation tank according to the present invention is a sedimentation tank installed upstream of a biological treatment tank for biologically treating water to be treated, the sedimentation tank having an inlet into which the water to be treated flows and an outlet through which the water to be treated flows into the biological treatment tank, and comprising: a sedimentation tank for settling pollutants contained in the water to be treated; a collector disposed inside the sedimentation tank for scraping up and accumulating the pollutants; and an oxygen-permeable membrane unit disposed inside the sedimentation tank at least on the outlet side and including an oxygen-permeable membrane that allows oxygen to pass through, the oxygen-permeable membrane unit being inclined so as to be closer to the outlet than to the inlet as it moves in the settling direction of the pollutants, and the oxygen-permeable membrane unit performs biological treatment on the water to be treated by dropping the pollutants and supplying an oxygen-containing gas from the inside of the oxygen-permeable membrane.

When the water to be treated has a high concentration of substances to be treated, such as nitrogen-containing compounds and organic matter, flowing through it, such as in a settling tank installed upstream of a biological treatment tank that biologically treats the water to be treated, it was thought that supplying an oxygen-containing gas would not increase the dissolved oxygen concentration, making biological treatment meaningless. However, the inventors have arrived at this invention based on their new knowledge that biological treatment can be performed in a settling tank.

In the oxygen-permeable membrane unit of this configuration, oxygen supplied from the inside of the oxygen-permeable membrane permeates the oxygen-permeable membrane, and a biological film of nitrifying bacteria and the like that nitrifies the nitrogen components in the water being treated is formed on the surface of the oxygen-permeable membrane, and the nitrogen components are nitrified to produce nitrate nitrogen. This nitrate nitrogen is reduced by the denitrifying bacteria in the water being treated and the organic matter that serves as nutrition for the denitrifying bacteria to produce nitrogen gas. In this way, in the oxygen-permeable membrane unit, the nitrogen-containing compounds in the water being treated are decomposed and removed through nitrification and denitrification, and the water is purified.

In other words, in this configuration, the oxygen-containing gas is not blown into the water to be treated, but is supplied to the inside of the oxygen-permeable membrane, so that even if the water to be treated has a high concentration of the target substance such as nitrogen-containing compounds, as in the case of a settling tank installed upstream of the biological treatment tank, there is no need to blow a large amount of oxygen-containing gas into the water to be treated, and biological treatment can be performed efficiently. In addition, since this oxygen-permeable membrane unit is installed at least on the outlet side inside the settling tank, it is possible to reduce the concentration of the target substance in the water to be treated that flows out to the biological treatment tank, thereby reducing the load on the biological treatment tank and reducing the amount of energy consumed. Furthermore, since biological treatment is performed without blowing a large amount of oxygen-containing gas into the water to be treated, there is no risk of sludge that has settled to the bottom of the settling tank being stirred up in the water.
In addition, if the oxygen-permeable membrane unit is tilted so that it is closer to the outlet than to the inlet as the pollutants settle, the pollutants that collide with the oxygen-permeable membrane unit can be allowed to fall smoothly. Moreover, tilting the oxygen-permeable membrane unit makes it easier for floating pollutants in the water to be treated to be captured by the oxygen-permeable membranes, allowing biological treatment to proceed efficiently.

Another characteristic feature is that the oxygen-permeable membrane unit includes an oxygen supplier through which the oxygen-containing gas flows, and the oxygen-permeable membrane is formed as a flat membrane disposed on the outer surface of the oxygen supplier.

By using a flat oxygen-permeable membrane as in this configuration, biological treatment can be performed using the oxygen-permeable membrane to purify the water being treated, and floating pollutants that do not settle and flow downstream are caused to collide with the oxygen-permeable membrane and settle, increasing the amount of settled sludge in the settling tank, which can be used for methane fermentation treatment, etc., to increase the amount of biogas. Furthermore, by placing a flat oxygen-permeable membrane on the outer surface of a highly durable oxygen supplier, durability can also be increased.

Another characteristic feature is that the oxygen permeable membrane is disposed on both the front and back outer surfaces of the oxygen supplier .

Another characteristic feature is that the inclination angle of the oxygen-permeable membrane unit is greater than 0 degrees and equal to or less than 60 degrees.

Another characteristic feature is that the oxygen-permeable membrane unit is arranged in an upper region that is in the opposite direction to the settling direction of the contaminants from the scraper when viewed from the side.

As in this configuration, by utilizing the upper area that is located in the opposite direction to the settling direction of the polluted material from the collector, it is possible to place an oxygen-permeable membrane unit without improving the settling tank.

Another characteristic feature is that the settling tank is provided with a pair of troughs on at least both side walls on the outlet side, through which the water to be treated flows, and the oxygen-permeable membrane unit is disposed across the flow path between the pair of troughs.

As in this configuration, by arranging an oxygen-permeable membrane unit across the flow path between a pair of troughs, the oxygen-permeable membrane unit straightens the water being treated, allowing the separation of pollutants and biological treatment to proceed smoothly. As a result, it is possible to prevent problems such as turbulence occurring in the water being treated in the settling tank, causing pollutants to overflow.

Another characteristic feature is that the settling tank is provided with an outlet through which the pollutants collected and accumulated by the collector are discharged into a methane fermentation tank.

By discharging pollutants into a methane fermentation tank as in this configuration, the increased amount of settled sludge can be used for methane fermentation processing.

The characteristic configuration of the oxygen-permeable membrane unit of the present invention is that it is an oxygen-permeable membrane unit that is immersed at least in the downstream side of a sedimentation basin installed upstream of a biological treatment tank that biologically treats the water to be treated, and is equipped with an oxygen supplier that circulates oxygen-containing gas inside, and a flat-membrane-shaped oxygen-permeable membrane that is arranged on the outer surface of the oxygen supplier and allows oxygen to permeate, and is inclined so that the closer to the outlet of the sedimentation basin than the inlet of the water to be treated as the direction of settling of the pollutants in the water to be treated progresses, and the pollutants are allowed to fall while the oxygen-containing gas is supplied to the inside of the oxygen-permeable membrane, thereby performing biological treatment on the water to be treated.

The oxygen-permeable membrane unit of this configuration does not blow oxygen-containing gas into the water to be treated, but supplies oxygen-containing gas to the inside of the oxygen-permeable membrane, so that even if the water to be treated has a high concentration of the target substances such as nitrogen-containing compounds, as in a settling tank installed upstream of the biological treatment tank, there is no need to blow a large amount of oxygen-containing gas into the water to be treated, and biological treatment can be performed efficiently. In addition, this oxygen-permeable membrane unit is installed inside the settling tank at least on the outlet side, and floating pollutants contained in the water to be treated can be efficiently removed by colliding with them and settling them before being discharged into the biological treatment tank. The oxygen-permeable membrane unit of this configuration makes it possible to lower the concentration of the target substances in the water to be treated that flows out to the biological treatment tank, thereby reducing the load on the biological treatment tank.

The feature of any of the above-mentioned operating methods for the sedimentation tank is that the water to be treated is circulated from the inlet to the outlet, the collector is operated to collect and accumulate the settled pollutants, and the oxygen-containing gas is supplied from the inside of the oxygen-permeable membrane to perform biological treatment on the water to be treated.

As described above, this method makes it possible to lower the concentration of the target substance in the water being treated that is discharged into the biological treatment tank, thereby reducing the load on the biological treatment tank. In addition, by collecting and accumulating pollutants, the amount of sludge that can be used as the raw material for methane fermentation can be secured.

FIG. 2 is an explanatory diagram of a treatment series in a wastewater treatment system. FIG. 2 is a schematic side view of a primary sedimentation tank. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 2 is a schematic perspective view of an oxygen-permeable membrane unit. FIG. 5 is a schematic perspective view showing details of the oxygen-permeable membrane unit shown in FIG. 4. FIG. 11 is a schematic perspective view of an oxygen-permeable membrane unit according to a modified example. FIG. 2 is an enlarged cross-sectional view of an oxygen permeable membrane and a biofilm.

Below, an embodiment of a settling tank, an oxygen permeable membrane unit, and an operating method for a settling tank according to the present invention will be described with reference to the drawings. In this embodiment, the settling tank will be described as a primary settling tank X that constitutes part of a wastewater treatment system 100. However, the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the gist of the present invention.

[Overall structure]
1 shows a schematic configuration of a wastewater treatment system 100 that purifies inflowing wastewater (an example of water to be treated). The wastewater treatment system 100 is installed in a sewage treatment plant or the like. The wastewater treatment system 100 includes a biological treatment tank R that biologically treats wastewater that continuously flows in from upstream. The biological treatment tank R includes an anaerobic treatment device 1 and an aerobic treatment device 2 downstream of the anaerobic treatment device 1.

In this embodiment, the wastewater flowing into the biological treatment tank R contains at least nitrogen-containing compounds such as ammonia nitrogen (hereinafter referred to as "nitrogen components") and organic matter. In the biological treatment tank R, nitrification (aerobic treatment) is carried out to oxidize nitrogen components to nitrite nitrogen and nitrate nitrogen, and denitrification (anaerobic treatment) is carried out to reduce nitrite nitrogen and nitrate nitrogen to nitrogen gas. Hereinafter, nitrite nitrogen and nitrate nitrogen will be collectively referred to simply as "nitrate nitrogen."

The wastewater treatment system 100 of this embodiment includes a primary sedimentation tank X (an example of a sedimentation tank) upstream of the biological treatment tank R, and a final sedimentation tank 99 downstream of the biological treatment tank R. The wastewater treatment system 100 may have multiple treatment series N1, N2, N3, etc., each having a primary sedimentation tank X, a biological treatment tank R, and a final sedimentation tank 99. These treatment series N1, N2, N3 are all equivalent. Below, the treatment series N1 will be described, but the same applies to the treatment series N2 and N3. Note that the concept of wastewater stored in the biological treatment tank R in this embodiment 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 X is a tank for settling and removing some of the soil, impurities, and sludge contained in the wastewater that flows in. Wastewater containing nitrogen components and organic matter that was not removed in the primary sedimentation tank X flows into the biological treatment tank R (anaerobic treatment device 1). Details of the primary sedimentation tank X will be described later.

The biological treatment tank R has at least one anaerobic treatment device 1 and at least one aerobic treatment device 2 connected in series downstream of the anaerobic treatment device 1. Wastewater that flows into the anaerobic treatment device 1 is retained in the anaerobic treatment device 1 for a predetermined time and then flows into the aerobic treatment device 2. Wastewater that flows into the aerobic treatment device 2 is retained in the aerobic treatment device 2 for a predetermined time and then flows out. In the aerobic treatment device 2, nitrification mainly proceeds. In the anaerobic treatment device 1, denitrification mainly proceeds, and nitrification also proceeds at the same time. A portion of the wastewater that flows out from the aerobic treatment device 2 is pumped via a return flow path 9 by a pump (not shown) or the like and returned (supplied) to the anaerobic treatment device 1. Hereinafter, the treated water returned to the anaerobic treatment device 1 via the return flow path 9 is referred to as nitrification liquid.

The biological treatment tank R is not limited to the above configuration, and may be configured to have an anaerobic treatment tank, an anoxic treatment tank, and an aerobic treatment tank in which a portion of the wastewater flowing out from the aerobic tank is returned to the anoxic tank to perform anaerobic-anoxic-aerobic denitrification, or may be configured to have an anaerobic treatment tank, a first anoxic tank, a first aerobic tank, a second anoxic tank, a second aerobic tank, ... an Nth anoxic tank, and an Nth aerobic tank in which an anaerobic-anoxic-aerobic process is performed using a step-inflow type multistage nitrification denitrification process, or may be configured to have a first anoxic tank, a first aerobic tank, a second anoxic tank, a second aerobic tank, ... an Nth anoxic tank, and an Nth aerobic tank in which a step-inflow type multistage nitrification denitrification process is performed, or may be configured as a single biological reaction tank in which the upstream side is an anaerobic and anoxic region and the downstream side is an aerobic region within one tank, rather than providing separate anaerobic and aerobic tanks. In any configuration, denitrification proceeds in the anaerobic treatment tank or anoxic tank.

The anaerobic treatment device 1 is a tank in which wastewater is maintained in an anaerobic environment (an environment with little dissolved oxygen). In the anaerobic treatment device 1, denitrification is mainly performed, but nitrification also occurs. In the anaerobic treatment device 1, oxygen is supplied to the wastewater through an oxygen-permeable membrane (not shown), and nitrification proceeds near the surface of the oxygen-permeable membrane. The areas of the anaerobic treatment device 1 other than the area near the surface of the oxygen-permeable membrane are maintained in an anaerobic environment, and denitrification proceeds by denitrifying bacteria.

The aerobic treatment device 2 is a tank in which wastewater is maintained in an aerobic environment (an environment rich in dissolved oxygen). An air bubble generating section (not shown) is immersed in the aerobic treatment device 2. In the aerobic treatment device 2, air is supplied (aeration) by bubbling from the air bubble generating section, and oxygen is supplied to the wastewater by dissolving oxygen from the air bubbles (so-called aeration). This maintains an aerobic environment in the aerobic treatment device 2. In the aerobic treatment device 2, nitrification and decomposition of organic matter progress using the oxygen supplied by the air bubble generating section. A portion of the wastewater discharged from the aerobic treatment device 2 to the final settling tank 99, i.e., a portion of the wastewater aerobically treated in the aerobic treatment device 2, is returned to the anaerobic treatment device 1 as nitrification liquid.

The final settling tank 99 is a tank that receives wastewater discharged from the aerobic treatment device 2 and allows the 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 treatment device 1 via the return flow path 9.

[Primary sedimentation tank]
2 and 3, the primary settling tank X has an inlet 51 through which wastewater flows in and an outlet 52 through which the wastewater flows out to a biological treatment tank R (anaerobic treatment device 1), and is equipped with a settling tank 5 in which soil, impurities, and sludge (an example of pollutant) contained in the wastewater are allowed to settle. Inside the settling tank 5 in this embodiment, a collector 4 that collects and accumulates sludge, and a plurality of oxygen-permeable membrane units 3 including oxygen-permeable membranes 30 that allow oxygen to pass through are arranged.

The settling tank 5 is a rectangular parallelepiped tank, and a discharge pit 53 is formed at the bottom on the upstream side, sloping like a mortar, for discharging sludge accumulated by the collector 4. The discharge pit 53 is provided with a discharge port 53a for discharging sludge using the power of a pump (not shown). The settling tank 5 is provided with a pair of troughs 54 for overflowing wastewater on at least both side walls on the outlet 52 side (upper downstream side). The troughs 54 are arranged over an area of about one-third of the settling tank 5 on the outlet 52 side (upper upstream side) of the settling tank 5. The wastewater from which the sludge has settled and been removed overflows the troughs 54 and flows out from the outlet 52.

The scraper 4 is equipped with a pair of chains 41 arranged on both sides of the settling tank 5, and a plurality of sprockets 42 (four in FIG. 2) that rotate and support each of the chains 41. A long, thin, plate-shaped scraper (not shown) that scrapes up sediments such as sludge is provided across the pair of chains 41, and both ends of the scraper are fixed to the pair of chains 41. By rotating the sprockets 42 with the power of a motor or the like, the chain 41 to which the scraper is attached rotates, and the scraper scrapes up the settled sediments and accumulates them in the discharge pit 53. The discharge outlet 53a discharges the sediments such as sludge scraped and accumulated by the scraper 4 into a methane fermentation tank (not shown). The sediments such as sludge are then used as raw materials for methane fermentation treatment in the methane fermentation tank. This sludge and other sediments may be discharged into a methane fermentation tank (not shown) without any special treatment, or may be subjected to solid-liquid separation treatment using known concentration or dehydration processes before being discharged into a methane fermentation tank (not shown).

The scrapers fixed to the chains 41 of the collector 4 are arranged over almost the entire bottom of the settling tank 5 in a side view, and are arranged over less than half of the area of the settling tank 5 at the upper part on the outlet 52 side of the settling tank 5. As a result, at least the upper downstream area of the interior of the settling tank 5 is an empty space where the collector 4 is not present. In other words, this empty space is an upper area that is in the opposite direction to the settling direction of sludge and other pollutants from the collector 4 in a side view.

The oxygen-permeable membrane units 3 are provided at least on the outlet 52 side inside the settling tank 5. These oxygen-permeable membrane units 3 are arranged in an empty space where the collector 4 is not present. These oxygen-permeable membrane units 3 may be upright along the direction of gravity, but are preferably inclined. In this case, the inclination angle is configured to be greater than 0 degrees and equal to or less than 60 degrees so that the more the oxygen-permeable membrane units 3 move in the settling direction (downward) of the contaminants such as sludge, the closer they are to the outlet 52 than the inlet 51. If the inclination angle of the oxygen-permeable membrane units 3 exceeds 60 degrees, contaminants will accumulate on the upper surface of the oxygen-permeable membrane 30 located above the oxygen-permeable membrane units 3, which is not preferable.

The oxygen-permeable membrane unit 3 is disposed across the flow path between the pair of troughs 54 (overall so as to block the flow path), and is disposed across approximately one-third of the area of the settling tank 5 on the outlet 52 side (upper downstream side) of the settling tank 5. The multiple oxygen-permeable membrane units 3 are disposed at a predetermined interval so as to overlap in a plan view. Note that "disposing the oxygen-permeable membrane unit 3 across the flow path between the pair of troughs 54" means that the oxygen-permeable membrane unit 3 has a width of 90% or more of the flow path between the pair of troughs 54.

In this way, by utilizing the empty space in the opposite direction to the settling direction of the pollutants from the scraper 4, it is possible to place the oxygen-permeable membrane unit 3 without improving the primary settling tank X (by utilizing the existing primary settling tank X). Also, by placing the oxygen-permeable membrane unit 3 across the flow path between a pair of troughs 54, the oxygen-permeable membrane unit 3 straightens the wastewater, allowing separation of pollutants and biological treatment to proceed smoothly. As a result, it is possible to prevent inconveniences such as turbulence occurring in the treated water in the settling tank 5 and pollutants overflowing.

As in this embodiment, by tilting the oxygen permeable membrane unit 3 so that it is closer to the outlet 52 than the inlet 51 in the direction of sedimentation of the pollutants, the pollutants that collide with the oxygen permeable membrane unit 3 can be smoothly dropped. In addition, by tilting the oxygen permeable membrane unit 3, floating pollutants contained in the wastewater are more likely to be captured by the oxygen permeable membrane 30, allowing biological treatment to proceed efficiently. Moreover, since the multiple oxygen permeable membrane units 3 are arranged at a predetermined interval so that they overlap in a plan view, the floating pollutants are effectively captured by the oxygen permeable membrane 30, and the wastewater from which the floating pollutants have been removed is guided toward the trough 54.

Air (an example of an oxygen-containing gas) is supplied to this oxygen-permeable membrane unit 3 from a blower 31b composed of a fan, blower, or the like at a low blowing pressure of 20 kPa or less. The settling tank 5 is provided with a supply pipe 31 that supplies air to the oxygen-permeable membrane unit 3 via the blower 31b, and a discharge pipe 32 that discharges the gas with a reduced oxygen concentration contained in the air from the oxygen-permeable membrane unit 3 to the outside (atmosphere). The air supplied from the supply pipe 31 is stored in a junction pipe 31a and is supplied to the oxygen-permeable membrane unit 3 via a plurality of distribution pipes 31c that branch from the junction pipe 31a to each oxygen-permeable membrane unit 3. The gas discharged from each oxygen-permeable membrane unit 3 is discharged from a plurality of distribution pipes 32b via the junction pipe 32a.

The oxygen-permeable membrane unit 3 performs biological treatment of wastewater by supplying air from the inside of the oxygen-permeable membrane 30. As shown in Figs. 4 and 5, the oxygen-permeable membrane unit 3 has a support 35 (an example of an oxygen supplier) that allows air to flow inside, and a pair of oxygen-permeable membranes 30 that are arranged to surround the support 35 and are formed in the shape of flat membranes that allow oxygen to pass through. A plurality of oxygen-permeable membrane units 3 are suspended from a plurality of support columns 36 fixed to a frame body 37 to form a module. These multiple oxygen-permeable membrane units 3 are arranged at a predetermined interval with each inclined by a spacer 38. As another example, as shown in Fig. 6, the oxygen-permeable membrane unit 3 has a housing 33 (an example of an oxygen supplier) that allows air to flow inside, and a pair of oxygen-permeable membranes 30 that are arranged (fixed) on a pair of side surfaces (outer surfaces) of the housing 33 and are formed in the shape of flat membranes that allow oxygen to pass through, and a plurality of oxygen-permeable membrane units 3 are integrated by a connecting plate 34 to form a module.

The support 35 shown in Figs. 4 and 5 has a plurality of gas flow paths Af along the direction of gravity inside, and is made of resin, nonwoven fabric, or the like having a large number of fine holes (not shown) on the entire pair of sides to which the pair of oxygen permeable membranes 30 are in close contact. In addition, the pair of oxygen permeable membranes 30 are formed with a sealing portion 30a fixed by welding or the like at the periphery so as to form an upper space 35a that distributes air evenly to each gas flow path Af when the support 35 is housed inside. The housing 33 shown in Fig. 6 is made of a metal material or a resin material having a meandering gas flow path Af inside by being partitioned by a plurality of partition plates 33a arranged in the vertical direction. In addition, a large number of fine holes (not shown) are formed on the entire pair of sides to which the oxygen permeable membranes 30 are fixed, and air is evenly released from these fine holes toward the oxygen permeable membrane 30.

The oxygen permeable membrane 30 is composed of a flat membrane material with oxygen permeability that allows oxygen contained in the air flowing inside the housing 33 to pass through and supply it to the wastewater outside the oxygen permeable membrane 30. This flat membrane material includes a microporous sheet formed of a resin or the like that allows oxygen to pass through from the inside and prevents wastewater from passing through from the outside to the inside, and a biofilm layer that retains microorganisms is formed on the outside of this microporous sheet by wastewater treatment. In this embodiment, the flat membrane surface of the oxygen permeable membrane 30 provided on the support 35 or housing 33 is provided at an angle to the flow direction of the wastewater in the settling tank 5.

In this way, by using the flat-membrane oxygen-permeable membrane 30, floating pollutants that do not settle but flow downstream can be collided with the oxygen-permeable membrane 30 and allowed to settle, and the oxygen-permeable membrane 30 can be used for biological treatment to purify the wastewater. Furthermore, by fixing the flat-membrane oxygen-permeable membrane 30 to the housing 33, durability can also be increased.

The oxygen permeable membrane unit 3 is entirely immersed in wastewater so that oxygen contained in the supplied air is supplied to the wastewater through the oxygen permeable membranes 30. Therefore, in order to prevent the wastewater from backflowing when the oxygen permeable membrane 30 is damaged, the multiple distribution pipes 31c for supplying air to the multiple oxygen permeable membranes 30 are provided with stop valves Va that allow air to flow and block the flow of fluid due to the intrusion of wastewater. Similarly, the multiple distribution pipes 32b for discharging air from the multiple oxygen permeable membranes 30 are provided with stop valves Vb that allow air to flow and block the flow of fluid due to the intrusion of wastewater. In other words, each of the multiple distribution pipes 31c, 32b is provided with stop valves Va, Vb that allow air to flow from the supply pipe 31 to the oxygen permeable membrane unit 3 and gas to flow from the oxygen permeable membrane unit 3 to the discharge pipe 32 and block the intrusion of wastewater from the oxygen permeable membrane unit 3 to the supply pipe 31 and the discharge pipe 32.

The water stop valve Va provided in the distribution pipe 31c that communicates with the supply pipe 31 is composed of a known check valve or the like that opens when it receives air back pressure and closes when it receives drainage fluid pressure in the opposite direction to the air flow direction. The water stop valve Vb provided in the distribution pipe 32b that communicates with the discharge pipe 32 is composed of a known air vent valve or the like that opens when the water level drops and closes when the water level rises due to a float rising.

As shown in FIG. 7, a biofilm L is formed on the membrane surface of the oxygen-permeable membrane 30. In this embodiment, the biofilm L 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, the nitrifying bacteria oxidize (nitrify) the nitrogen components (e.g., _NH4 ⁺ ) in the wastewater using oxygen 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. Note that in the anaerobic treatment device 1, the first biofilm La nitrifies some of the nitrogen components in the wastewater.

In the second biofilm Lb and in the area outside the second biofilm Lb (in the wastewater other than the oxygen-permeable membrane unit 3 and the biofilm L), denitrifying bacteria use the organic matter (BOD) in the wastewater as a nutrient source to reduce (denitrify) nitrate nitrogen (NO _x ^- ) and release nitrogen (N ₂ ) gas. Note that in order to clean the biofilm L attached to the oxygen-permeable membrane 30, a separate cleaning mechanism may be provided that uses bubble injection, mechanical vibration, ultrasonic shaking, or the like.

In this way, oxygen supplied from the inside of the oxygen-permeable membrane 30 permeates the oxygen-permeable membrane 30, and a biofilm L of nitrifying bacteria and the like that nitrifies the nitrogen components of the wastewater is formed on the surface of the oxygen-permeable membrane 30, and the nitrogen components are nitrified to produce nitrate nitrogen. This nitrate nitrogen is reduced by the denitrifying bacteria in the wastewater and the organic matter that serves as nutrition for the denitrifying bacteria to produce nitrogen gas. This nitrification and denitrification decomposes and removes the nitrogen-containing compounds in the wastewater, purifying it.

In this embodiment, air is not blown into the wastewater, but is supplied to the inside of the oxygen permeable membrane 30. Therefore, even if the wastewater has a high concentration of the target substances to be treated, such as nitrogen-containing compounds, as in the primary sedimentation tank X installed upstream of the biological treatment tank R, there is no need to blow a large amount of air into the wastewater, and biological treatment can be performed efficiently. By efficiently performing biological treatment, the amount of primary sedimentation sludge increases, and by using it for methane fermentation treatment, etc., it is expected that the amount of biogas will increase. In addition, since the oxygen permeable membrane unit 3 is installed at least on the outlet 52 side inside the sedimentation tank 5, floating pollutants contained in the wastewater can be efficiently removed by colliding with them and settling them before being discharged into the biological treatment tank R. As a result, it is possible to reduce the concentration of the target substances to be treated in the wastewater discharged into the biological treatment tank R, and the load on the biological treatment tank R and the amount of energy consumed can be reduced. Furthermore, since biological treatment is performed without blowing a large amount of oxygen-containing gas into the wastewater, there is no risk of sludge and the like that has settled to the bottom of the sedimentation tank 5 being stirred up in the water.

[Operation method of primary sedimentation tank]
As shown in FIG. 2, the operating method of the primary sedimentation tank X described above includes a circulation procedure for circulating wastewater from the inlet 51 to the outlet 52 of the sedimentation tank 5, a collection procedure for collecting and collecting pollutants such as settled sludge by operating the collector 4, and a treatment procedure for performing biological treatment on the wastewater by supplying air from the inside of the oxygen-permeable membrane 30.

In the flow procedure, wastewater is circulated from the inlet 51 to the outlet 52, so that clumps of pollutants settle by their own weight, and floating pollutants that collide with the flat oxygen-permeable membrane 30 settle. In the accumulation procedure, the settled pollutants are collected in the discharge pit 53 and discharged from the outlet 53a, thereby removing the pollutants from the wastewater. In the treatment procedure, oxygen supplied from the inside of the oxygen-permeable membrane 30 permeates the oxygen-permeable membrane 30, and nitrification (aerobic treatment) is performed, in which the nitrogen components contained in the wastewater are oxidized to nitrite nitrogen and nitrate nitrogen, and denitrification (anaerobic treatment) is performed, in which the nitrite nitrogen and nitrate nitrogen are reduced to nitrogen gas. As a result, it is possible to reduce the concentration of the target substance in the wastewater discharged to the biological treatment tank R.

[Other embodiments]
(1) The multiple oxygen permeable membrane units 3 may be arranged along the direction of gravity without being inclined, or may be inclined so that they are farther from the outlet 52 than the inlet 51 as they move in the direction of the settlement of the pollutants.
(2) Since the sludge that settles in the final sedimentation tank 99 is returned to the anaerobic treatment device 1 via the return flow path 9, an oxygen permeable membrane unit 3 may be provided at least on the outlet side inside the final sedimentation tank 99 (an example of a sedimentation tank).
(3) The oxygen-permeable membrane unit 3 may be provided with a portion of the oxygen-permeable membrane unit 3 including the distribution pipes 31c and 32b disposed above the water surface, thereby eliminating the need for the water stop valves Va and Vb. In this case, the upper end of the oxygen-permeable membrane 30 shown in FIG. 4 may be open.

6 has a meandering gas flow path Af formed therein by the partition plate 33a, but a plurality of parallel linear gas flow paths communicating with distribution pipes 31c, 32b branching from junction pipes 31a, 32a respectively merging with the supply pipe 31 and the exhaust pipe 32 may be formed therein. In this case, the junction pipe 31a merging with the supply pipe 31 is provided above the oxygen-permeable membrane unit 3, and the junction pipe 32a merging with the exhaust pipe 32 is provided below the oxygen-permeable membrane unit 3.
(5) In the above-described embodiment, a module is formed by connecting multiple oxygen-permeable membrane units 3 with support columns 36 or connecting plates 34, but a single oxygen-permeable membrane unit 3 may be used, or multiple oxygen-permeable membrane units 3 may be installed individually without being connected.
(6) In the above-described embodiment, a plurality of oxygen-permeable membrane units 3 may be provided in the vertical and horizontal directions. In this case, the plurality of oxygen-permeable membrane units 3 may be aligned vertically and horizontally, or may be arranged in a staggered manner.

(7) The collector 4 may be provided only at the bottom of the settling tank 5 , and a plurality of oxygen-permeable membrane units 3 may be disposed in the empty space formed in the upper region of the settling tank 5 .
(8) The oxygen-permeable membrane unit 3 may be disposed so as not to block the flow path between the pair of troughs 54 , but may be disposed, for example, with a width that is half the width of the flow path between the pair of troughs 54 .

The present invention can be used in a sedimentation tank installed upstream of a biological treatment tank, an oxygen-permeable membrane unit installed in the sedimentation tank, and a method for operating the sedimentation tank.

3: Oxygen permeable membrane unit 4: Collector 5: Settling tank 30: Oxygen permeable membrane 33: Housing (oxygen supplier)
35: Support (oxygen donor)
51: inlet 52: outlet 54: trough R: biological treatment tank X: primary sedimentation tank (sedimentation tank)

Claims (9)

A sedimentation tank installed upstream of a biological treatment tank that biologically treats the water to be treated,
A sedimentation tank having an inlet through which the water to be treated flows and an outlet through which the water to be treated flows into the biological treatment tank, and for settling contaminants contained in the water to be treated;
A scraper disposed inside the settling tank for scraping and accumulating the polluted matter;
an oxygen-permeable membrane unit provided inside the settling tank at least on the outlet side, the oxygen-permeable membrane unit including an oxygen-permeable membrane;
The oxygen permeable membrane unit is inclined so as to be closer to the outlet than to the inlet in a settling direction of the contaminants,
The oxygen-permeable membrane unit is a sedimentation basin that performs biological treatment on the water to be treated by allowing the pollutants to fall and supplying an oxygen-containing gas from the inside of the oxygen-permeable membrane. The oxygen-permeable membrane unit includes an oxygen supplier that allows the oxygen-containing gas to flow therethrough,
2. The settling basin according to claim 1, wherein the oxygen permeable membrane is formed as a flat membrane disposed on the outer surface of the oxygen supplier. 3. The settling tank according to claim 2, wherein the oxygen permeable membrane is disposed on both the front and back outer surfaces of the oxygen supplier . 4. The settling basin according to claim 1, wherein the inclination angle of the oxygen-permeable membrane unit is greater than 0 degrees and is not greater than 60 degrees . 5. The settling basin according to claim 1, wherein the oxygen-permeable membrane unit is disposed in an upper region that is opposite to the settling direction of the polluted matter relative to the collector when viewed from the side. The settling tank is provided with a pair of troughs on at least both side walls of the outlet side through which the water to be treated overflows,
The settling basin according to claim 1 , wherein the oxygen-permeable membrane unit is disposed across the flow path between the pair of troughs. The settling tank according to any one of claims 1 to 6 , wherein the settling tank is provided with a discharge outlet for discharging the pollutants collected and accumulated by the collector into a methane fermentation tank. An oxygen-permeable membrane unit that is immersed at least downstream of a sedimentation tank installed upstream of a biological treatment tank that biologically treats water to be treated,
The oxygen supplying device includes an oxygen-containing gas flowing through the oxygen supplying device, and a flat oxygen-permeable membrane that is disposed on an outer surface of the oxygen supplying device and allows oxygen to pass therethrough.
The inclination is such that the more the contaminants in the water to be treated settle, the closer the outlet of the settling tank is to the inlet of the water to be treated,
The oxygen-permeable membrane unit performs biological treatment on the water to be treated by allowing the pollutants to fall and supplying the oxygen-containing gas to the inside of the oxygen-permeable membrane. A method for operating a sedimentation tank according to any one of claims 1 to 7 , comprising:
The water to be treated is caused to flow from the inlet to the outlet,
By operating the scraper, the settled pollutants are scraped and accumulated,
A method for operating a sedimentation basin in which the oxygen-containing gas is supplied from the inside of the oxygen-permeable membrane to perform biological treatment on the water to be treated.

Images