JP2004209452A - Biological treatment tank and biological treatment method for wastewater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological treatment tank for wastewater which requires no supply of motive power than necessary from outside for prevention of carrier settling and aeration, forms a circulation flow in the treatment tank, prevents clogging by smoothly separating carriers and a screen, and enables a sufficient carrier return, and a biological treatment method. <P>SOLUTION: A carrier separation screen 7 is installed on the outflow side of the biological treatment tank for the wastewater, containing the carriers, on which microorganisms have been immobilized, in suspension. Circulation ducts 17, 17a for the carrier return are installed along both the bottom sides of the treatment tanks 1a-1c from the bottom of a duct wall surface 4f disposed on the front side of the screen 7 and having a partition plate 19 and movable partition members 20, 20a. A suction flow of water to be treated, flowing in from ejector pipes 8, 8a installed on the inflow wall surface 2, forms an ejector type mixing region of the water to be treated and the return flow of the carriers. As a result, the carriers can be separated by a downflow on the front side of the screen 7 to prevent the clogging, and carrier stagnation in the circulation ducts 17, 17a can be prevented. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a biological treatment tank for wastewater that biologically performs sewage treatment using a microorganism-immobilized carrier, and a biological treatment method for wastewater using the treatment tank.
[0002]
[Prior art]
As one of new biological treatment methods for wastewater, a microorganism-fixing method for fixing microorganisms on a carrier and removing eutrophic components such as nitrogen and phosphorus has been developed. In this method, as shown in FIG. 12 as an example, generally, a pellet-shaped carrier A is charged into a treatment tank 21 filled with water to be treated such as wastewater, and microorganisms for treating wastewater are fixed to the carrier A. The microorganisms in the treatment tank 21 are maintained at a high concentration (for example, see Patent Document 1).
[0003]
In the processing tank 21 shown in FIG. 12, an aeration device 22 communicating with an air supply source is provided at the bottom, and a carrier separation device having an inclined screen 23 is provided inside the processing tank 21. In order to effectively suppress clogging, a moving wall device 27 in which an endless belt 26 is wound around pulleys 25 and 25a connected to a drive shaft of a motor 24 substantially in parallel with the screen 23 is provided. Is provided.
[0004]
When the water to be treated is stirred by the air finely diffused from the aeration device 22, oxygen is supplied to the microorganisms fixed to the carrier, and the water to be treated and the carrier A flow in a mixed state. The nitrogen in the water to be treated is biologically treated, and the water to be treated descends between the screen 23 and the facing surface 26A of the belt 26 over the upper end of the moving wall device 27, and passes through the screen. , From the outlet 28. In this process, due to the orbital movement of the belt 26 of the moving wall device 27, the flow velocity of the parallel flow of the water to be treated given to the screen 23 increases, and the cleaning effect of the screen 23 is enhanced.
[0005]
In another example, as shown in FIG. 13, a baffle plate 32 having upper and lower openings is disposed, and a sewage treatment system in which a propeller-type agitator 34 supported by a column 33 is provided at a lower opening. A tank 31 is disclosed (for example, see Patent Document 2). In the sewage treatment tank 31, by operating the propeller type stirrer 34, the circulation of the water to be treated flowing from the inflow port 35 vertically above and below the baffle plate 32 for each section divided by the baffle plate 32. Since the flow is formed, the carrier A is dispersed throughout the processing tank 31 without being biased toward the outlet 36. In addition, by operating the blower 37 and diffusing air from the aeration device 38, a swirling flow is generated in each section divided by the baffle plate 32, and the sufficiently biologically treated water is screened. Flows out of the outlet 36 provided with a.
[0006]
Further, as an apparatus for separating the carrier adhered to the screen, an apparatus for removing the carrier by a suction power of a submerged stirring aeration apparatus and a shearing force caused by a downward flow over the entire screen induced by a circulation pump has been developed (for example, Non-Patent Document 3).
[0007]
[Patent Document 1]
JP-A-2002-86177 ([0006] to [0026])
[Patent Document 2]
JP-A-7-136679 ([0005] to [0015])
[Non-Patent Document 3]
Proceedings of the 36th Sewerage Research Conference (1999), 577-P. 579
[0008]
[Problems to be solved by the invention]
However, in the sewage treatment tank 21 disclosed in Japanese Patent Application Laid-Open No. 2002-86177, the sewage treatment tank 21 faces the front side of the screen 23 in order to further apply a forced flow to the downward flow of the water to be treated and enhance the cleaning effect of the screen 23. A moving wall device 27 driven by a motor is provided. On the other hand, in Japanese Unexamined Patent Publication No. Hei 7-136679, a baffle plate 32 is provided in a sewage treatment tank 31 to form a circulating flow of water to be treated. In order to prevent the uneven distribution of A, a propeller type stirrer 34 is provided at the lower opening of the baffle plate 32. For this reason, in any case, it requires extra power more than the power required for stirring and aeration to supply oxygen to microorganisms fixed to the carrier to prevent sedimentation of the carrier, and to prevent screen clogging, Equipment costs, such as initial costs increasing by installing the above-mentioned devices in order to improve the return and dispersion of the carrier to the processing tank, and running costs increasing by operating and managing them. And there is a problem in terms of energy consumption. Further, even when using an underwater aeration device for carrier separation, stirring power by a circulation pump is required in addition to the power required for aeration.
[0009]
In addition, when a power failure occurs, it takes several seconds to several tens of seconds before the emergency power supply starts, and during this time, when there is no flow of the water to be removed from the screen to remove the carrier, any of the above cases The screen may be instantaneously clogged and the wastewater and the carrier may overflow from the treatment tank.
[0010]
Therefore, an object of the present invention is to form a circulating flow in a treatment tank and smoothly separate a carrier and a screen without requiring power supply other than prevention of carrier sedimentation and aeration from the outside, and clogging of the screen. It is an object of the present invention to provide a biological treatment tank and a biological treatment method for wastewater in which no carrier is generated and the carrier is returned well.
[0011]
[Means for Solving the Problems]
In order to solve the above problem, the present invention employs the following configuration.
[0012]
That is, a screen for separating the carrier installed on the outflow side of the water to be treated in the wastewater treatment tank containing the microorganism-fixed carrier in a floating state, a duct wall facing the front side of the screen, and a lower end of the duct wall And a circulation duct formed by a return duct wall surface of the carrier from the side to the inflow side along the bottom of the treatment tank, and the wastewater treatment biological treatment tank, which flows into the inflow side of the treatment tank. Means for converting potential energy based on the water level difference with the upstream side to kinetic energy so as to form a suction flow of the water to be treated was provided to constitute a biological treatment tank for wastewater.
[0013]
The biological treatment tanks are usually arranged in series, and water to be treated such as sewage is biologically treated. Since the water level in the treatment tank on the upstream side is higher, for example, as shown in FIG. There is a water level difference Δh between the treatment tanks. Due to the water level difference Δh, the water to be treated in the adjacent upstream biological treatment tank 1a flows from the lower opening 3 provided in the inflow side wall surface 2 of the biological treatment tank 1. At this time, the potential energy of the upstream processing tank 1a is converted into kinetic energy when passing through the lower opening 3, and the momentum of the water to be treated forms a suction flow that draws in the surrounding fluid in the processing tank 1. You.
[0014]
As described above, when attention is paid to the biological treatment tank 1, the suction flow of the inflowing water to be treated is generated upward in the flow path formed by the inflow side wall surface 2 and the partition plate T on the inflow side thereof. An ejector type mixing zone M is formed on the inflow side. The water to be treated is mixed with the carrier A while being stirred by the underwater stirrer 6 in the reaction zone 5 formed by the outer wall surfaces 4a, 4b, and 4c of the circulation duct 4, and biologically treated. On the front side, a downward flow of the water to be treated mixed with the carrier A is formed. By this downward flow, the clogging can be prevented by removing the carrier A from the screen 7 without supplying external energy such as electric power, and the biologically treated water passes through the screen 7 and flows downstream. Out of the treatment tank 1b, and a part of the water to be treated becomes the return flow of the circulation duct 4 so that the carrier A can flow to the inflow side of the treatment tank 1. In this way, the water to be treated and the returned carrier A are mixed in the ejector-type mixing area M formed on the inflow side, and a circulating flow is formed in the treatment tank.
[0015]
The water level difference Δh is determined by the cross-sectional area of the lower opening 3, that is, the area of the ejector section and the processing flow rate of the water to be processed, and is determined so that a suction flow required for forming a circulating flow in the processing tank is generated. The cross-sectional area of the ejector unit is designed in accordance with the processing flow rate. Further, the water to be treated can be introduced laterally from the upstream treatment tank to generate a suction flow.
[0016]
Then, the return flow including the carrier A flowing to the upstream side of the processing tank 1 in the circulation duct 4 is subjected to the action of the suction flow on the inflow side, that is, the ejected type mixing area formed by the ejector effect. The water is mixed with water and sent to the reaction zone 5. Due to the mixing effect of the water to be treated and the carrier A in the ejector type mixing zone M, the biological treatment of the water to be treated in the reaction zone 5 is effectively performed. It is.
[0017]
Here, when examining the fluidity of the return flow returning the carrier in the circulation duct, the momentum conservation equation in the ejector-type mixing zone is:
ρ (W₁V₁ ²+ W₂V₂ ²) + (W₁+ W₂) (P−Δp) = ρW₃V₃ ²+ W₃p ---- (1)
And the pressure loss Δp of the return flow including the carrier in the circulation duct is
Δp = λL [(W₀+ W₄) / (2W₀W₄)] × ρV₄/ 2-------------(-)
Becomes
Where W₀: Screen width W₁~ W₄: Channel height (m) V at each position shown in FIG.₁~ V₄: Flow velocity at each position (m / s) λ: Pressure loss coefficient
L: Length of circulation duct at bottom of treatment tank (m) ρ: Density (1000 kg / m)³)
Δh: water level difference between treatment tanks.
When equation (1) and equation (2) are made simultaneous,
Δp = λL [(W₀+ W₄) / (2W₀W₄)] × ρV₄/ 2 = ρ [W₁W₂/ W₃ ²] (V₁ ²-V₂)²  −−−−−−−−−−−−−−−−−−−− (3)
Flow velocity V of the incoming treated water₁Is the flow rate Q of the water to be treated₀And the area of the lower opening 3, that is, the area of the ejector, the equation (3) is₂Is a quadratic equation for
V₂= [Α ± (α × β)^0.5] × V₁/ (Α-β)---------------------(-)
Becomes
Where α = W₁W₂/ W₃, β = λL [(W₀+ W₄) / (4W₀W₄ ³)] × W₂ ²It is.
[0018]
For example, the flow rate Q of the water to be treated₀= 1260m³/ H, W₀= 4 (m), W₁= 0.088 (m), W₂= 0.2 (m), W₄= 0.2 (m), L = 5 (m), Δh = 50 (mm), and the pressure loss coefficient λ is estimated to be λ = 0.2 in consideration of the fact that the viscosity increases due to the inclusion of the carrier. And equation (4), the return flow velocity V₂Is found and this V₂From equation (3), the pressure loss Δp in the circulation duct at the bottom of the processing tank is obtained from equation (3), and the flow velocity V of the return flow in the circulation duct 4 is calculated using equation (2).₄Is found. This flow velocity V₄Is calculated, the flow rate Q of the return flow including the carrier A₄= V₄× W₄× W₀× 3600 = 817m³/ H. Now, assuming that the charging rate of the carrier A into the treatment tank (the ratio to the amount of water in the tank) is 10%, the ratio R of the carrier contained in the return flow in the circulation duct is roughly as follows:
R = (1260 + 817) × 0.1 / 817 ≒ 0.25
Becomes That is, the content of the carrier A in the return stream is about 25%, good fluidity is maintained, and a circulating flow is smoothly formed in the treatment tank.
[0019]
A plurality of wastewater biological treatment tanks containing a carrier in which microorganisms are immobilized in a floating state are connected in series via a partition wall provided with a passage portion for the water to be treated, and the carrier is provided on the outflow side of the lowest biological treatment tank. A screen for separation, a duct wall facing the front side of the screen, and a bottom end of the processing tank from a lower end side of the duct wall, and penetrates the partition wall to reach an inflow side of the most upstream biological treatment tank. A biological treatment tank for drainage comprising a circulation duct formed by a return duct wall surface of a carrier, and an upstream side for forming a suction flow of inflowing water to be treated on an inflow side of the treatment tank. A means for converting potential energy based on the difference in water level to kinetic energy can be provided to constitute a biological treatment tank for wastewater.
[0020]
In such an apparatus configuration, at the inflow side of the most upstream processing tank, the water level difference Δh required to generate a suction flow by means of converting potential energy into kinetic energy is determined by the most upstream processing tank and the most upstream processing tank. Since it is only necessary to secure the difference between the upstream processing tank and the upstream processing tank, the difference in water level of the entire processing tank can be suppressed. Also, the screen may be provided only in the most downstream processing tank, and the ejector mixing area may be provided only on the inflow side of the most upstream processing tank. Is simple and economical. Further, the carrier A is returned from the lowermost processing tank 1h to the uppermost processing tank 1f by the circulation duct, so that uneven distribution of the carrier in the downstream processing tank is prevented.
[0021]
The means for converting the potential energy into kinetic energy is an ejector pipe provided at a lower portion of the inflow side wall surface of the treatment tank. The water to be treated flowing from the upstream side and the circulation duct are sucked by the effect of the ejector pipe. It is desirable to form an ejector-type mixing zone for mixing the return flow of the carrier from the substrate.
[0022]
According to this configuration, the flow rate of the water to be treated flowing out of the inflow pipe into the treatment tank becomes larger than when the inflow port is provided on the inflow side wall surface across the width of the treatment tank. And the carrier returned from the most downstream processing tank via the circulation duct are more effectively mixed.
[0023]
A circulation duct may be formed by connecting a duct wall facing the screen front side and a duct wall on the inflow side by a connecting pipe.
[0024]
In this case, since the cross section of the connecting pipe has an axially symmetrical shape, the duct height can be increased, so that the risk of blockage of the duct by contaminants is further reduced. Further, as a connecting pipe for forming a circulation duct from the bottom of the processing tank, an existing commercially available pipe material can be used, which is economical.
[0025]
It is desirable to incorporate an aeration device in an ejector-type mixing area formed on the inflow side of the processing tank.
[0026]
With this configuration, the air supplied to the ejector-type mixing area by the aeration device exerts an air lift effect in addition to the original aeration effect. Therefore, even when the required water level difference Δh cannot be secured, The suction force necessary to generate the flow can be supplemented.
[0027]
A duct wall facing the front side of the screen branches to both sides of the bottom of the processing tank, and a flow path extends from a lower end of the branched duct wall to an inflow side along the bottom on both sides of the processing tank. A circulation duct for returning the carrier is formed such that each flow path extends upward along the inflow side wall surface, and the ejector pipes are respectively provided inside the circulation duct extending upward to perform biological treatment of wastewater. A tank can also be configured.
[0028]
In the wastewater biological treatment tank, both bottom portions are generally formed in a slope shape that is inclined downward from the side surface to the bottom surface along the longitudinal direction in order to prevent accumulation of carriers. As described above, by providing a flow path in the longitudinal direction from the outflow side to the inflow side at the bottoms on both sides of the processing tank, the space at the bottoms on both sides of the processing tank formed in a slope can be effectively used. can do. Thereby, the circulation duct does not need to be provided in the processing tank, and the reaction zone for biological treatment is substantially widened, so that the volume in the processing tank can be more effectively used.
[0029]
It is desirable that the ejector tube has a flow rate adjusting means.
[0030]
The flow velocity in the circulation duct for returning the carrier is 30 mm / s or less from the viewpoint of preventing pressure loss in the duct, and 10 cm / s or more from the viewpoint of preventing the carrier from sinking and staying in the duct. Because of the necessity, the speed is usually as low as 10 to 30 cm / s, and there is a risk that the inside of the circulation duct may be blocked by foreign substances such as fibers in the drainage or a membrane secreted by microorganisms. When one of the ejector tubes is closed by the flow rate adjusting means, the flow of the closed circulation duct also stops, so that the water level difference (Δh) on the inflow side of the processing tank increases. Due to the increase in the water level difference (Δh), the amount of water to be treated flowing out of the other ejector pipe increases, and the flow velocity in the circulation duct also increases. Removal is possible.
[0031]
An internal space formed on the screen side of the duct wall facing the front side of the screen is divided by a partition plate, and the lower ends thereof are respectively connected to flow paths reaching the inflow side along the bottoms on both sides of the processing tank. Preferably, the circulation duct is formed, and a movable partition member for preventing the carrier from flowing from the processing tank is provided at an upper portion of the duct wall corresponding to each of the divided internal spaces.
[0032]
If the flow rate of the wastewater is considerably lower than the designed flow rate of the wastewater treatment tank, the flow velocity of the return flow in each circulation duct is small, and there is a risk that the carrier may settle at the bottom of the circulation duct and stay there. For this reason, if the movable part partition member is attached to the duct wall surface to prevent the carrier from flowing into one of the internal spaces divided by the partition plate, the suction flow by the ejector tube is continued. Into the circulation duct extending from the lower end side of the internal space, treated water containing no carrier that has passed through the screen of the other divided internal space flows in, and sedimentation and accumulation of the carrier in the circulation duct can be prevented. .
[0033]
The circulation duct may be provided with a pipe for supplying the water to be treated in the upstream water tank into which the treated water and / or the carrier is not charged.
[0034]
With this configuration, since the upstream water tank has a higher water level, the water to be treated is introduced into the circulation duct without the need for a pump, and the sedimentation or stagnation of the carrier at the bottom of the duct can be prevented. In this case, it is effective to supply a part of the treatment water from the treatment tank to the circulation duct in order to prevent the sludge in the water to be treated introduced into the circulation duct from being accumulated for a long time. The upstream-side water tank includes both a drainage storage tank into which the carrier is not charged and the treatment tank into which the carrier is charged.
[0035]
It is desirable to provide an air vent pipe along the bottom of the processing tank so that one end communicates with the circulation duct and the other end projects from the water surface in the processing tank.
[0036]
In this case, since the generation of air traps in the circulation duct can be prevented, the return flow smoothly flows, and the return of the carrier is not hindered.
[0037]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the attached FIGS.
[0038]
FIGS. 2A and 2B show the first embodiment, in which a biological treatment tank 1c is a connected biological treatment tank in which a plurality of biological treatment tanks are arranged in series, and is located at an intermediate position. It is a biological treatment tank. On the outflow side of the biological treatment tank 1c, a screen 7 for separating the carrier extends over the entire width of the treatment tank 1c and its height is higher than the level H of the water to be treated such as sewage in the treatment tank 1c. It is installed to become. A plurality of ejector tubes 8 are provided in the width direction below the inflow side wall surface 2 of the treatment tank 1c so that water to be treated flows from the adjacent upstream biological treatment tank 1d and flows upward, for example. ing. On the front side of the screen 7, a required interval S₁A duct wall 4a extending downward from the upper portion and extending over the entire width of the processing tank 1c is provided to face the same. Similarly, a required distance S from the ejector pipe 8 is also provided on the inflow side of the processing tank 1c.₂Thus, a duct wall surface 4b extending upward from the lower portion on the inflow side and extending over the entire width of the processing tank 1d is provided.
[0039]
As shown in FIG. 2 (b), there is a water level difference Δh between the processing tank 1c and the processing tank 1d on the upstream side thereof. Since it is determined from the area, that is, the sum of the cross-sectional areas of the ejector pipes 8, the flow rate of the water to be treated is adjusted so that the suction flow of the water to be treated causes a required water level difference to generate a circulating flow in the treatment tank 1c. Thus, the area of the ejector unit is designed.
[0040]
Each of the duct wall surfaces 4a and 4b is provided so that its height is lower than the water level H of the processing tank 1c, and is connected at its lower part by a connecting pipe 9 as shown in FIG. 2 (c). Thus, a circulation duct 4 in which the inflow side and the outflow side communicate with each other is formed. As in the case of the inflow side wall surface 2, a plurality of openings 3b are provided in the width direction below the outflow side wall surface 10 of the processing tank 1c, and each of the openings 3b is adjacent to the downstream processing side. An ejector tube 8a similar to the ejector tube 8 protruding toward the tank 1e is provided, and this ejector tube 8a is an ejector tube on the inflow side of the processing tank 1e on the downstream side. Further, the bottom of the processing tank 1c is formed so as to incline upward from the center to the both sides, as shown in the bottom shape of the duct wall 4a shown in FIG. Have been.
[0041]
Pellets such as PEG (polyethylene glycol) in which microorganisms such as nitric acid bacteria are immobilized in a reaction zone 5 formed by the duct wall surfaces 4a and 4b, the side walls 11 and 11a of the processing tank 1c, and the outer surface of the connecting pipe 9. Of the carrier A is stirred by the underwater stirrer 6 provided on the side wall 11 of the processing tank 1c to prevent sedimentation, and is aerated so that the carrier A is mixed in a suspended state in the water to be treated.
[0042]
The first embodiment of the present invention is configured as described above, and its function will be described below.
[0043]
As shown in FIG. 2, there is a water level difference Δh between the biological treatment tank 1c and the biological treatment tank 1d on the upstream side, and the water level difference Δh causes the inflow side wall surface of the biological treatment tank 1d. The to-be-processed water flows in from the processing tank 1d on the upstream side by the ejector pipe 8 provided in 2. At that time, as described above, the potential energy of the upstream processing tank 1a is converted into kinetic energy when passing through the ejector pipe 8, and the momentum of the water to be treated draws in the surrounding fluid in the processing tank 1. A suction flow occurs.
[0044]
The circulation flow is formed between the inflow side and the outflow side of the processing tank 1c by the action of the suction flow, that is, the ejector effect, and the carrier A is transferred to the screen 7 by the downward flow generated on the front side of the screen 7. Adhesion is prevented, and even if a power failure occurs, clogging of the screen 7 does not occur. Then, in the ejector mixing area M, the carrier A returned to the inflow side through the circulation duct 4 and the water to be treated are mixed, and this mixed fluid is supplied to the reaction area 5 and Of the carrier can be made uniform, and the biological treatment of the water to be treated can be effectively performed.
[0045]
FIGS. 3A and 3B show a second embodiment, in which three drainage biological treatment tanks 1f, 1g, and 1h are provided with a partition wall provided with a passage portion of the untreated water. A screen 7 for carrier separation is installed only on the outflow side of the most downstream biological treatment tank 1h, and only the lower part of the inflow side wall surface 2 of the most upstream biological treatment tank 1f is treated. A plurality of ejector tubes 8 are provided in the width direction of the tank 1f. A required interval S is provided on the front side of the screen 7.₁A duct wall 4d extending downward from the upper portion and extending over the entire width of the processing tank 1h is provided to face the same. Similarly, on the inflow side of the processing tank 1f, a required distance S from the ejector pipe 8 is also provided.₂A duct wall surface 4e extending upward from the lower portion on the inflow side and extending over the entire width of the processing tank 1d is provided.
[0046]
Each of the duct wall surfaces 4d and 4e is provided so that its height is lower than the water level H of the processing tanks 1f and 1h, and is connected at its lower part by a connecting pipe 9a penetrating the partition walls 12 and 12a. Thus, a circulation duct 4 in which the inflow side and the outflow side communicate with each other is formed. Then, on the inflow side, the treated water that has flowed in and the carrier A that has returned in the circulation duct 4 are mixed by the suction flow from the ejector tube 8 by the ejector tube 8 and the duct wall surface 4e. An ejector type mixing area M is formed.
[0047]
In such an apparatus configuration, on the inflow side of the most upstream processing tank 1f, the water level difference Δh required to generate the suction flow is equal to the upstream processing tank 1j adjacent to the most upstream processing tank 1f. Therefore, the total water level difference can be suppressed low between the processing tanks 1f to 1h. The screen 7 may be provided only in the most downstream processing tank 1h, and the ejector mixing area M may be formed only on the inflow side of the most upstream processing tank 1f. The device configuration when connected is simple and economical.
[0048]
As shown in FIG. 4, if the aeration device 13 is provided below the ejector type mixing area M, that is, below the ejector pipe 8, it is difficult to secure a required water level difference Δh due to the air lift effect. In this case, the suction force to the inflow side of the water to be treated can be supplemented.
[0049]
FIG. 5 shows a third embodiment, in which three biological treatment tanks 1a, 1b, and 1c respectively provide passage ports 14 and 14a of the water to be treated, similarly to the biological treatment tank shown in FIG. In this case, the duct wall 4f extending downward facing the front side of the screen 7 provided in the most downstream processing tank 1c is connected to the processing tank 1c through the provided partition walls 12 and 12a. The duct wall surfaces 4g and 4h are formed to be branched to both sides of the bottom. From the front ends of the branched duct walls 4g, 4h, they are formed by duct walls 4j, 4k provided inclining along the bottoms on both sides of the processing tank 1c and the inner walls at both bottoms of the processing tanks 1a-1c. Duct walls 4m and 4n are provided so that the flow path reaches the inflow side and further extends upward along the inflow side wall surface 2 and the side wall surfaces 11b and 11c, respectively, of the processing tank 1a. A circulation duct 4 for returning the carrier is formed by a flow path formed by the wall surfaces 4f, 4j, 4m and 4g, 4k, 4n. The ejector tubes 8, 8 are inserted into the portions extending above the circulation ducts 4, 4 on both sides, respectively. In the middle of the circulation duct 4 along the bottoms on both sides of the processing tank 1b, there are provided air vent pipes 15 each having one end communicating with the circulation duct 4 and the other end projecting from the water surface in the processing tank. .
[0050]
Usually, on both sides of the bottom of the wastewater biological treatment tank, a slope inclined from the side surface to the bottom surface is formed along the longitudinal direction in order to prevent accumulation of carriers. As described above, if the duct wall surfaces 4j and 4k having a slope shape are provided along the longitudinal direction on both sides of the bottom of each of the processing tanks 1a to 1c, the duct wall surfaces 4j and 4k have a function of preventing the accumulation of carriers. The space at both bottoms of each of the processing tanks 1a to 1c can be effectively used, and the circulation duct does not need to be passed through each processing tank. Thereby, the reaction zone for biological treatment with the water to be treated by the carrier can be made larger, and the volume in the treatment tank can be used more effectively.
[0051]
In addition, since the return flow of the carrier passes through the circulation duct 4 and is exhausted out of the processing tank from the air vent pipe 15, a large amount of fine air bubbles do not stay in the processing tanks 1a to 1c, and the occurrence of air pockets is prevented. As a result, the return flow smoothly flows, and the return of the carrier is not hindered. Furthermore, since the ejector pipe 8 is provided inside the portion extending above the circulation duct 4 on the inflow side, mixing of the carrier returned in the circulation duct 4 and the water to be treated flowing out of the ejector pipe 8 is effective. Is done. As shown in FIG. 4, an aerator may be provided below the inflow side of the processing tank 1a, and uniform mixing of the carrier returned to the processing tank 1a is promoted by the air lift effect.
[0052]
FIG. 6 shows a fourth embodiment, in which the biological treatment tanks 1a, 1a, and 2b are arranged from the lower end of a duct wall surface 4f having side plates on both sides, facing the front side of a screen 7 provided in the most downstream biological treatment tank 1c. One ends of connecting pipes 9b and 9c provided along both sides of the bottom are connected to duct wall surfaces 4g and 4h branched on both sides of the bottoms of 1b and 1c, respectively. Circulation ducts 17 and 17a are formed connected to the mixing pipes 16 and 16a extending upward along 2, respectively. Flow control means, ie, valves 18 and 18a, are provided on the inlet sides of the mixing tubes 16, 16a, ie, the ejector tubes 8, 8a provided inside the upwardly extending circulation duct. As the valves 18 and 18a, a gate valve, a butterfly valve, an eccentric cast valve, or the like can be used. Further, as shown in FIG. 4, an aeration device can be provided on the inflow side of the processing tank 1a, and the same effect as in FIG. 5 can be obtained. Further, as shown in FIG. 5, an air vent pipe having one end communicating with the connecting pipes 9b and 9c and the other end projecting from the water surface in the processing tank is provided in the middle of the connecting pipes 9b and 9c. You can also.
[0053]
Thus, by providing the valves 18 and 18a on the entrance sides of the ejector tubes 8 and 8a, for example, the valve 18 is fully closed, and the flow from the ejector tube 8 into the biological treatment tank 1a and the circulation duct 17 Is stopped, the difference in water level at the inflow side wall surface 2 increases fourfold. Thereby, the flow velocity from the ejector pipe 8a with the valve 18a opened to the inside of the processing tank 1a increases, and the flow velocity in the circulation duct 17a also increases due to the suction flow by the ejector effect. It is possible to remove foreign substances such as fibers adhering to the membrane and films secreted by microorganisms. By the same operation, the inner surface of the circulation duct 17 can be cleaned.
[0054]
As described above, a plurality of circulation ducts can be provided, as described above, in addition to a total of two along the bottom sides of the processing tanks 1a to 1c, and a plurality of ejector tubes can be provided. Generally, when n sets of circulation ducts and ejector pipes are provided, when one ejector pipe is closed by the valve operation, the water level difference at the inflow side wall surface 2 becomes [n / (n-1)].²Becomes With the increase in the water level difference, the flow velocity from the open ejector pipe into the treatment tank increases, so that the flow velocity in the circulation duct increases, and the effect of cleaning the inner surface of the duct increases.
[0055]
Here, the relationship between the treatment flow rate, that is, the flow rate of the water to be treated into the treatment tank 1a, the difference in water level on the inflow side, and the flow velocity in the circulation ducts 17 and 17a is quantitatively considered as follows. FIG. 7 shows a processing flow rate of 1110 m³/ H in the biological treatment tank (see FIG. 6), the inner diameter of each of the ejector tubes 8 and 8a is 320 mm, and the inner diameter of each of the circulation ducts 17 and 17a is 750 mm. 9 shows the results of an experiment on the relationship with the flow velocity.
[0056]
In the two-lung operation in which the valves 18 and 18a are fully opened, when the water level difference is 300 mm, the flow velocity in the circulation ducts 17 and 17a is about 31 cm / s. At this time, the ratio of the inflow flow rate to the circulation flow rate is approximately 0.8. Here, when one-lung operation in which one valve, for example, the valve 18 is closed, is performed, the water level difference increases to 1200 mm, and accordingly, the flow velocity in the circulation duct is temporarily increased to about 51 cm / s. be able to. In this state, the ratio of the inflow flow rate to the circulation flow rate is reduced to about 0.65, so that the performance of removing the carrier adhering to the surface of the screen 7 is reduced, and the screen 7 starts to close. However, by operating the valve 18, the total closing time of the ejector tube 8 is shortened, and by repeating the short-time full closing operation, the flow rate of about 51 cm / s is obtained while the closing of the screen 7 does not progress. This makes it possible to remove the foreign matter and the film attached to the inner wall surface of the circulation duct. In some biological treatment tanks, a water level difference of 1200 mm cannot be secured. In such a case, by performing a valve operation such as the above-described short-time full closing operation and a partial closing operation therebetween, the average flow velocity per unit time in the circulation duct is increased to clean the inner wall of the circulation duct. In addition, it is possible to remove foreign substances and films attached to the inner surface of the circulation duct wall.
[0057]
FIG. 8 shows a fifth embodiment, in which the internal space on the screen 7 side of the duct wall 4f having side plates on both sides facing the front side of the screen 7 is divided by a partition plate 19, The duct walls 4g, 4h branched from the lower end to both sides of the bottom of the treatment tank 1c are connected to connecting pipes 9b, 9c provided along both sides of the bottom of the biological treatment tanks 1a, 1b, 1c. Movable partition members 20 and 20a are provided for preventing the carrier from flowing from the processing tank 1c into each of the divided internal spaces. The movable partition members 20 and 20a are formed such that when mounted on the duct wall surface 4f, the upper ends thereof are higher than the water surface to be treated. Other than these, it has the same configuration as the drainage biological treatment tank shown in FIG. 6. As described above, the inner diameters of the ejector pipes 8 and 8a are each 320 mm, and the inner diameters of the circulation ducts 17 and 17a are each 750 mm. In addition, similarly to the case of the wastewater biological treatment tank in FIG. 6, an aeration device can be provided on the inflow side of the treatment tank 1a, and the above-described effects can be obtained.
[0058]
A method for preventing the sedimentation and stagnation of the carrier in the circulation ducts 17 and 17a using the movable partition members 20 and 20a will be described below based on experimental results. The inflow rate of the water to be treated is 1110m³/ H, in a biological treatment tank designed to have a flow rate of 300 m / h, for example.³/ H, the flow velocity in the circulation ducts 17 and 17a reaches only about 8 cm / s, and at such a flow velocity of the return flow, the carrier may settle and stay in the circulation ducts 17 and 17a. Is big. In order to avoid this settling and stagnation, one movable partition member, for example, the movable partition member 20 is fitted into the duct wall surface 4f. Since the upper end of the fitted movable partition member 20 is higher than the surface of the water to be treated, the carrier does not flow into the internal space into which the movable partition member 20 is fitted, and therefore does not flow into the circulation duct 17. .
[0059]
The valves 18 and 18a are fully opened, and the water to be treated flows into the treatment tank 1a from the ejector pipe 8 to generate the suction flow by the ejector effect as described above. The treated water that has passed through the screen 7 from the internal space into which the 20a has not been fitted passes through the screen 7 in the reverse direction and flows into the circulation duct 17 as shown in FIG. By continuing this state, the inside of the circulation duct 17 can be replaced with treated water containing no carrier. After completion of the replacement, when the valve 18 is fully closed and the one-lung operation is performed in which the inflow of the water to be treated from the ejector tube 8 is stopped, the flow rate of the return flow is about 14 cm / s in the other circulation duct 17a. And the sedimentation / retention of the carrier can be prevented. FIG. 10 shows a normal processing state in which the movable partition member 20 is not fitted. From each internal space divided by the partition member, the water to be treated passes through the screen 7 and the carrier A is After passing through the circulation ducts 17 and 17a, they are returned from the mixing pipes 16 and 16a into the processing tank by a suction flow. FIG. 9 shows that the treated water that has passed through the screen 7 is re-permeated in the opposite direction by inserting the movable partition member 20, and the carrier A returned through the circulation duct 17 is replaced with the treated water. FIG. Similarly, by inserting the movable partition member 20a into the duct wall surface 4f, the circulation duct 17a is replaced with treated water, and the flow velocity of the return flow of the other circulation duct 17 is reduced to about 14 cm / s described above. It is possible to perform one-lung operation in which the carrier is raised to prevent sedimentation / retention of the carrier.
[0060]
FIG. 11 shows a sixth embodiment. As shown in FIG. 9, instead of the treated water containing no carrier having passed through the screen 7 permeating the screen 7 in the opposite direction and flowing into the circulation duct, as shown in FIG. Further, a state is shown in which water to be treated is allowed to permeate the screen 7 in the reverse direction from the upstream water tank by the supply pipe 21 and is guided into the circulation duct 17. Since the upstream water tank has a higher water level, the water to be treated can be easily supplied without the need for a pump. In this case, in order to prevent the sludge contained in the water to be treated from accumulating in the circulation duct 17, a part of the treatment water transmitted through the screen 7 may be returned from the supply pipe 21 a to the circulation duct 17. desirable. The supply pipes 21 and 21a can be similarly installed on the circulation duct 17a.
[0061]
【The invention's effect】
As described above, according to the present invention, water flows into the inflow side of the wastewater treatment tank for performing wastewater treatment using the carrier on which microorganisms are immobilized, due to the difference in water level of the water to be treated with the upstream wastewater treatment tank. A suction flow that draws in the fluid around the water to be treated is generated, an ejector-type mixing area is formed on the inflow side of the treatment tank, and a circulating flow is formed in the treatment tank. Even without supplying energy, it is possible to prevent the carrier from adhering to the carrier separation screen, and to avoid clogging of the screen even when a power failure occurs. In addition, since no external energy is used for forming the circulation flow, the apparatus configuration can be simplified, and it is economical.
[0062]
Further, by the action of the suction flow, that is, the ejector effect, the carrier and the water to be treated are returned to the inflow side without settling or staying in the circulation duct, and the mixed water is mixed in the treatment tank. The carrier is supplied to the reaction zone, and the distribution of the carrier in the treatment tank can be made uniform, so that the biological treatment is effectively performed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a suction flow of wastewater in a biological treatment tank according to an embodiment of the present invention.
FIG. 2A is a plan view of the biological treatment tank according to the first embodiment.
(B) A longitudinal side view of the biological treatment tank of (a).
(C) A perspective view showing a main part of the biological treatment tank of (a).
FIG. 3A is a plan view of a wastewater biological treatment tank according to a second embodiment.
(B) A longitudinal side view of the biological treatment tank of (a).
FIG. 4 is a longitudinal sectional side view showing a main part on the inflow side of the biological treatment tank for wastewater shown in FIG. 3;
FIG. 5 is a perspective view of a biological treatment tank for wastewater according to a third embodiment.
FIG. 6 is a perspective view of a biological treatment tank for drainage with a part of the fourth embodiment cut out.
FIG. 7 is an explanatory diagram showing a relationship between an inflow flow rate, a water level difference, and a flow velocity in a circulation duct in the wastewater biological treatment tank in FIG. 6;
FIG. 8 is a perspective view of a biological treatment tank for drainage with a part of the fifth embodiment cut out.
FIG. 9 is an explanatory diagram showing the flow of the carrier and the water to be treated during the normal operation of the wastewater biological treatment tank in FIG. 7;
FIG. 10 is an explanatory view showing a state in which the movable partition member of the biological treatment tank for drainage of FIG. 7 is fitted to prevent the inflow of carriers.
FIG. 11 is a perspective view of a biological treatment tank for drainage in which a part of the sixth embodiment is cut away.
FIG. 12 is a cross-sectional view of a conventional biological treatment tank for wastewater.
FIG. 13 is a cross-sectional view of another prior art wastewater biological treatment tank.
[Explanation of symbols]
1, 1a to 1h: biological treatment tank 2, 2a: inflow side wall 3: lower opening
4: Circulation duct 4a to 4n: Duct wall surface 5: Reaction zone
6: Underwater stirrer 7: Screen 8, 8a: Ejector tube
9, 9a, 9b, 9c: connecting pipe 10: outflow side wall surface
11, 11a to 11c: side wall 12, 12a: partition 13: aeration device
14, 14a: passage opening 15: air vent tube 16, 16a: mixing tube
17, 17a: Circulation duct 18, 18a, 18b: Valve 19: Partition plate
20, 20a: movable partition member 21, 21a: supply pipe
A: Carrier H: Water level M: Ejector mixing area
S₁, S₂: Interval T: Partition plate

Claims (13)

A screen for separating the carrier installed on the outflow side of the water to be treated in the wastewater treatment tank containing the microorganism-fixed carrier in a floating state, a duct wall facing the front side of the screen, and a lower end of the duct wall And a circulation duct formed by a return duct wall surface of the carrier reaching the inflow side along the bottom of the processing tank, wherein the biological treatment tank for drainage is provided. A biological treatment tank for wastewater, comprising means for converting potential energy based on a water level difference with an upstream side into kinetic energy so as to form a suction flow of water. A plurality of wastewater biological treatment tanks containing a carrier in which microorganisms are fixed in a suspended state are connected in series via a partition wall provided with a passage section for the water to be treated, and the carrier separation tank is installed at the outflow side of the lowest biological treatment tank. Screen, a duct wall facing the front side of the screen, and a carrier extending from the lower end of the duct wall along the bottom of the processing tank, penetrating the partition and reaching the inflow side of the most upstream biological treatment tank. A wastewater treatment tank provided with a circulation duct formed by a return duct wall surface and an upstream side so as to form a suction flow of water to be treated flowing into an inflow side of the treatment tank. A biological treatment tank for wastewater, comprising means for converting potential energy based on a water level difference into kinetic energy. The means for converting the potential energy into kinetic energy is an ejector pipe provided at a lower portion of the inflow side wall surface of the treatment tank. The water to be treated flowing from the upstream side and the circulation duct are sucked by the effect of the ejector pipe. The wastewater biological treatment tank according to claim 1 or 2, wherein an ejector-type mixing zone for mixing the return flow of the carrier from the wastewater is formed. 4. The biological treatment of wastewater according to claim 1, wherein a circulation duct is formed by connecting a duct wall facing the screen front side and an inflow side duct wall with a connecting pipe. Tank. The wastewater biological treatment tank according to any one of claims 1 to 4, wherein an aeration device is incorporated in an ejector-type mixing area formed on an inflow side of the treatment tank. A duct wall facing the front side of the screen branches to both sides of the bottom of the processing tank, and a flow path extends from a lower end of the branched duct wall to an inflow side along the bottoms on both sides of the processing tank. Is formed to extend upward along the inflow side wall surface, and a circulation duct for returning the carrier is formed, and the ejector tubes are provided inside the circulation duct extending upward. The wastewater biological treatment tank according to claim 3. The wastewater biological treatment tank according to claim 6, wherein the ejector pipe includes a flow rate adjusting unit. An internal space formed on the screen side of the duct wall facing the front side of the screen is divided by a partition plate, and the lower ends thereof are respectively connected to flow paths reaching the inflow side along the bottoms on both sides of the processing tank. Wherein the circulation duct is formed, and a movable partition member for preventing inflow of the carrier from the processing tank is provided at an upper portion of the duct wall, corresponding to each of the divided internal spaces. The wastewater biological treatment tank according to claim 6 or 7. The drainage system according to any one of claims 1 to 8, wherein the circulation duct is provided with a pipe for supplying treated water and / or water to be treated in an upstream water tank into which a carrier is not charged. Biological treatment tank. 10. A circulation duct along the bottom of the processing tank, wherein an air vent pipe is provided such that one end communicates with the circulation duct and the other end projects from the water surface in the processing tank. A biological treatment tank for wastewater according to any of the above. A wastewater biological treatment method for biologically treating wastewater using a carrier on which microorganisms are fixed, wherein a circulation duct for returning the carrier separated by a screen provided on the outflow side of the water to be treated to the inflow side In the drainage biological treatment tank provided with, a suction flow of the water to be treated is generated on the inflow side, and a circulating flow is formed between the inflow side and the outflow side of the treatment tank by an ejector effect due to the suction flow. A biological treatment method for wastewater, wherein the carrier is prevented from adhering to the screen, and the carrier is returned to an inflow side through a circulation duct and mixed with water to be treated. The wastewater biological treatment method according to claim 11, wherein the suction flow is generated using the wastewater biological treatment tank according to any one of claims 1 to 10. 13. The biological treatment method for wastewater according to claim 11, wherein the suction flow is formed by a difference in water level of the water to be treated between the wastewater biological treatment tanks.

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