Fluidized-bed-type biological treatment device and method for operating same

Abstract

Provided are a fluidized-bed-type biological treatment device and a method for operating the same, said fluidized-bed-type biological treatment device including: a tank body 2 storing a flowable carrier C; a screen 7 provided in the tank body 2 and separating the carrier to guide treated water to a discharge port; a partition plate 8 partitioning the inside of the tank body 2 into a rectification region, where the screen 7 is disposed, and a reaction region, where biological treatment is performed; an air diffusion member 9 for causing air bubbles to flow along a surface of the screen 7 on the rectification region side; and an opening 11 provided in an upper part of the partition plate 8 for allowing the carrier to pass from the rectification region to the reaction region.

Description

Fluidized bed biological treatment device and its operating method

[0001] The present invention relates to a fluidized-bed biological treatment device for treating wastewater, and more particularly to a fluidized-bed biological treatment device having a tank body provided with a screen for separating the carriers from the treated water. The present invention also relates to a method for operating the fluidized-bed biological treatment device.

[0002] Fluidized-bed biological treatment systems using carriers with high concentrations of microorganisms attached thereto are known for the purpose of increasing the load on biological treatment systems for wastewater and improving water quality. It is also known that screens are used as a means for solid-liquid separation of the carriers (Patent Documents 1 and 2).

[0003] Patent Document 2 describes a method of cleaning a screen by tilting the screen so that it faces the treated water outlet of the tank body and diffusing air from below the screen using an air diffuser. Also, Figure 3 of Patent Document 2 describes a method of cleaning a screen by providing a partition plate parallel to the screen. By providing the partition plate in this manner, air bubbles from the air diffuser flow along the screen, improving the cleaning effect of the screen.

[0004] Japanese Patent Application Laid-Open No. 7-47390 Japanese Patent Application Laid-Open No. 2020-138185

[0005] In the case of a fluidized bed biological treatment device in which a partition plate is provided opposite a screen, as in Patent Document 2, if the device is operated at a high agitation speed to sufficiently diffuse the carriers within the tank in order to increase the treatment capacity of the device, the flow velocity and flow rate within the tank will increase, and the bubbles diffused from the aeration means will be swept away by the swirling flow, resulting in insufficient cleaning of the screen.

[0006] An object of one aspect of the present invention is to provide a fluidized bed biological treatment device and an operating method thereof in which the screen is cleaned with air bubbles from an aeration means, so that the screen can be cleaned sufficiently.

[0007] A fluidized bed biological treatment device according to one embodiment of the present invention comprises a tank body containing fluid carriers, a screen provided within the tank body for separating the carriers and directing treated water to an outlet, a partition plate for dividing the interior of the tank body into a rectifying region in which the screen is disposed and a reaction region in which biological treatment is carried out, an aeration member for causing air bubbles to flow along the surface of the screen facing the rectifying region, and an opening provided at the top of the partition plate for transporting carriers from the rectifying region to the reaction region.

[0008] In one aspect of the present invention, the screen is arranged facing the side wall surface of the tank body, the space between the screen and the side wall surface of the tank body forms a filtered water chamber, and the side wall surface of the tank body is provided with the outlet for filtered water overflow facing the filtered water chamber.

[0009] In one aspect of the present invention, the partition plate extends vertically along the screen, the lower end of the partition plate is located lower than the lower end of the screen, and the upper end of the partition plate is located higher than the water level in the reaction region and the water level in the straightening region within the tank body.

[0010] In one aspect of the present invention, the partition plate has a main plate facing the screen, the opening is provided in the upper part of the main plate, and the air diffusion member is arranged between the main plate and a downward extension surface of the front surface of the screen.

[0011] In one aspect of the present invention, the air diffusion member is disposed closer to the downward extension surface than the midpoint between the main plate and the downward extension surface.

[0012] In one aspect of the present invention, the opening is provided with an opening / closing member.

[0013] The method for operating a fluidized bed biological treatment device of the present invention is a method for operating such a fluidized bed biological treatment device of the present invention, and comprises a steady cleaning step in which a steady amount of air is diffused from the aeration element, and a strong cleaning step in which the amount of air diffused from the aeration element is greater than that in the steady cleaning step.

[0014] In one embodiment of the operating method of the present invention, the opening is closed in the steady cleaning step, and the opening is opened in the strong cleaning step, and the carrier is returned from the flow straightening region through the opening to the reaction region.

[0015] According to one embodiment of the fluidized bed biological treatment device and its operating method of the present invention, the diffusion of bubbles into the tank body is prevented, the screen is efficiently cleaned, and clogging of the screen by the carriers or biofilms attached to the carriers is suppressed, thereby enabling stable biological treatment.

[0016] In one aspect of the present invention, the partition plate has a main plate facing the screen, the opening is provided in the upper part of the main plate, and the air diffuser is disposed between the main plate and the downward extension of the front surface of the screen. This reduces the horizontal cross-sectional area of ​​the flow straightening region and enhances the cleaning effect of the screen by the diffused air bubbles. In addition, carriers that have entered the flow straightening region are more likely to gather in the opening and be transported to the reaction region.

[0017] In one aspect of the present invention, an opening / closing member is provided at the opening in the upper part of the partition plate. In this aspect, when the water level in the reaction region or the rectification region changes due to operating conditions, the opening can be opened / closed or the opening degree can be adjusted appropriately depending on the situation.

[0018] In one embodiment of the present invention, a fluidized-bed biological treatment device is operated by performing steady-state cleaning with a predetermined aeration rate during biological treatment of wastewater, followed by strong cleaning in which a greater aeration rate than that used during steady-state cleaning is temporarily sprayed. During the strong cleaning, the carriers are promoted to move from the rectification region to the reaction region through the openings in the upper part of the partition plate.

[0019] In one embodiment of the method of the present invention, the biological treatment is anaerobic biological treatment, and aeration is carried out so that the sum of the dissolved oxygen (DO) weight of the influent raw water and the weight of dissolved oxygen on the water surface or due to aeration does not exceed 10% of the total weight obtained by adding the weight of oxygen from the components to be treated contained in the influent raw water. This allows the DO contained in the water transferred from the rectification region to the reaction region to be quickly consumed, even when aeration is carried out with an oxygen-containing gas, thereby maintaining the anaerobic state of the reaction region.

[0020] It is a longitudinal cross-sectional view of a fluidized bed biological treatment device according to an embodiment. It is a longitudinal cross-sectional view taken along the line II-II in Fig. 1. It is a horizontal cross-sectional view taken along the line III-III in Fig. 1. It is an enlarged view of a part of Fig. 1.

[0021] Hereinafter, a fluidized bed biological treatment device and an operating method thereof according to an embodiment will be described with reference to FIGS.

[0022] This fluidized bed biological treatment device 1 includes a tank body 2, a drive shaft 3 disposed at the axial center of the tank body 2, and a rotor (agitating blade) 4 fixed to the drive shaft 3. In this embodiment, a bearing (not shown) is provided on the bottom surface of the tank body 2, and the lower end of the drive shaft 3 is supported by this bearing, but the drive shaft 3 may also be suspended from above. The drive shaft 3 is driven to rotate by a drive unit M.

[0023] In this embodiment, the tank body 2 is a rectangular tank having a square horizontal cross section as shown in FIG. 3, but the tank body 2 may have other shapes such as a cylindrical tank.

[0024] An inlet 5 for raw water (water to be treated) is provided at the top of one wall surface 2a of the tank body 2, and an outlet (overflow port) 10 for treated water is provided at the top of the other wall surface 2b on the opposite side. The inlet 5 is located higher than the outlet 10. Note that a raw water inlet pipe may be provided instead of the inlet 5. In this embodiment, the fluidized bed biological treatment device 1 is an anaerobic biological treatment tank, and the top surface of the tank body 2 is closed by a top plate (not shown).

[0025] A screen 7 extending in the vertical direction is provided so as to face the other wall surface 2b. In this embodiment, since the other wall surface 2b is flat, the screen 7 is also flat. The screen 7 is preferably made of a bar screen, mesh, wedge wire, punched metal, or the like.

[0026] The gap between both sides of the flat screen 7 extending in the vertical direction and the wall surface 2b is closed by a side plate 7a (Fig. 3), and the gap between the bottom edge of the screen 7 and the wall surface 2b is closed by a bottom plate 7b (Fig. 1).

[0027] The upper end of the screen 7 extends above the lower edge of the outlet 10, preferably to the upper edge of the outlet 10 or above.

[0028] The area between the screen 7 and the wall surface 2b of the tank body 2 is a filtered water chamber 6 surrounded by the screen 7, side plate 7a, and bottom plate 7b. The outlet 10 is disposed so as to face the inside of the filtered water chamber 6. WL1 indicates the water level at the lower edge of the outlet 10.

[0029] In this embodiment, the screen 7 extends in a substantially vertical direction, but is not limited to this. For example, the screen 7 may extend in a diagonal direction so that the screen approaches the wall surface 2b at the bottom, so that the distance between the screen 7 and the wall surface 2b of the tank body 2 is shorter at the bottom than at the top. In this case, the lower end 7e of the screen 7 may contact the wall surface 2b. When the lower end of the screen 7 is disposed so as to contact the wall surface 2b of the tank body 2, the bottom plate 7b can be omitted.

[0030] Partition plates 8 are provided extending in the vertical direction so as to surround the screen 7. The upper ends of the partition plates 8 extend above the upper end of the screen 7. The inner region of the partition plates 8 (the region closer to the screen 7 than the partition plates 8) is the flow straightening region D, and the outer region of the partition plates 8 (the region closer to the rotor 4) is the reaction region R.

[0031] The partition plate 8 has a U-shaped horizontal cross section and includes a main plate 8a facing the screen 7 and a pair of side plates 8b (FIG. 3) that close the gap between both sides of the main plate 8 and the wall surface 2b.

[0032] The main plate 8a and the side plate 8b of the partition plate 8 preferably extend at an angle of within ±10°, particularly within ±5°, from the vertical direction, and more preferably extend in a direction substantially vertical.

[0033] The horizontal width of the main plate 8 a is slightly larger than the horizontal width of the screen 7 .

[0034] The lower end of the partition plate 8 is located below the lower end of the screen 7 and above the bottom surface 2f of the tank body 2. An opening D' is formed between the lower end 8e of the partition plate 8 and the wall surface 2b, and water containing the carrier C can flow from the reaction region R to the rectification region D through this opening D'.

[0035] An air diffusing member 9 such as an air diffuser pipe is provided to cause air bubbles to flow along the surface of the screen 7 facing the main plate 8a (hereinafter sometimes referred to as the front surface of the screen). The air diffuser pipe preferably extends in a direction parallel to the width direction of the screen 7 and has a length equal to or shorter than the width of the screen 7.

[0036] In this embodiment, as shown in Figure 4, the air diffusing member 9 is disposed above the lower end 8e of the partition plate 8 and below the lower end 7e of the screen 7. The air diffusing member 9 is preferably disposed closer to the downward extension surface F of the front surface of the screen 7 than the midpoint between the downward extension surface F and the main plate 8a. This allows the air bubbles diffused from the air diffusing member 9 to rise along the front surface of the screen 7, and deposits on the front surface of the screen 7 are efficiently peeled off and removed. Note that, when the screen 7 is disposed in an oblique direction rather than a vertical direction as described above, it is preferable to dispose the air diffusing member 9 as close to the wall surface 2b of the tank body 2 as possible.

[0037] An opening 11 is provided at the top of the main plate 8a for transferring water and carriers from the rectification area D to the reaction area R when the water level in the rectification area D inside the partition plate 8 is higher than the lower end of the opening 11.

[0038] The width of the opening 11 is preferably 50% or more of the width of the screen 7. The width of the opening 11 is also preferably 150 cm or less. This allows the carriers remaining near the water surface in the flow straightening region D to be efficiently returned to the reaction region R through the opening 11.

[0039] The lower edge of the opening 11 is located lower than the lower end of the inlet 5. The difference in height between the lower edge of the opening 11 and the lower end of the inlet 5 is preferably 40 cm or less, and particularly 10 to 30 cm. The upper edge of the opening 11 is located higher than the lower end of the inlet 5. The difference in height between the upper edge of the opening 11 and the lower end of the inlet 5 is preferably 40 cm or less, and particularly 10 to 30 cm. The vertical width of the opening 11 is preferably about 20 to 60 cm.

[0040] This allows the carriers to be efficiently transported from the flow rectifying region D to the reaction region R. In particular, the air lift effect of the air diffused from the air diffuser 9 may cause the water level in the flow rectifying region D to rise above the water level in the reaction region R, but even in such a case, the carriers can be efficiently transported from the flow rectifying region D to the reaction region R.

[0041] 1, the water level in the reaction region R and the water level in the rectifying region D are depicted as being at the same height, but as mentioned above, the water level in the reaction region R and the water level in the rectifying region D can change depending on the operating conditions. For example, when the raw water flow rate is high, the water level in the reaction region R rises, and when the air diffusion rate of the air diffusion member 9 is high, the water level in the rectifying region D rises. In addition, the water level in the rectifying region D also fluctuates depending on the water level in the reaction tank (not shown) provided downstream of the fluidized bed biological treatment device 1.

[0042] Although not shown, an opening / closing member may be provided at the opening 11. The opening / closing member is preferably one that can adjust the opening degree of the opening 11, and for example, one that is made up of a plate that can move up and down along the opening 11, a guide rail that guides the up and down movement of the plate, and a stopper that stops the plate at a desired height, etc., is used, but is not limited to this.

[0043] The rotor 4 is disposed near the center in the vertical direction of the drive shaft 3. The height H of the upper edge of the rotor 4 (height from the bottom surface 2f of the tank body 2; the same applies below) ２ is the water depth H of the tank body 2 １ The vertical width H of the rotor 4 is preferably 20 to 80%, more preferably 50 to 70%. ３ is the water depth H of the tank body 2 １ The height H of the lower edge of the rotor 4 is preferably 5 to 60%, more preferably 10 to 40%. ４ is the tank water depth H １A range of 20 to 80%, particularly 20 to 70%, and especially 30 to 50% is preferred.

[0044] In this embodiment, the rotor 4 is provided in only one stage in the vertical direction, but it may be provided in two or more stages. When the rotors are provided in two or more stages, the height of the upper edge of the rotor of the uppermost stage is set to the above-mentioned H ３ +H ４ The height of the lower edge of the lowest rotor is in the range of H ４ The total width of each rotor is within the range of H ３ It is preferable that the range is:

[0045] The vessel body 2 is filled with a carrier C. The carrier may be made of any material, but a granular gel of a polymer crosslinked body that is resistant to wear is preferred.

[0046] Examples of resin materials for the gel carrier include polyolefin, PVA, PEG, (poly)acrylamide, N-substituted acrylamide, (poly / meth)acrylic acid or alkali metal salts thereof, alginic acid, polyalkylene oxide, dimethylaminoethyl (meth)acrylate (DAM), diacetone alcohol (DAA), polyalkylene oxide, etc. More specific examples include sodium polyacrylate, copolymers of sodium acrylate and acrylamide, copolymers of sodium acrylate and sodium acrylamido 2-methylpropanesulfonate, terpolymers of sodium acrylate, acrylamide, and sodium acrylamido 2-methylpropanesulfonate, and homopolymers or copolymers of tertiary salts or quaternary ammonium salts of dimethylaminoethyl (meth)acrylate with acrylamide, etc.

[0047] The average particle size of the carrier C is preferably 1 to 10 mm, and particularly preferably 3 to 5 mm. If it is smaller than this, it may be difficult to separate the carrier C from the water, and if it is larger, it may hinder flow. It is desirable for the carrier C to settle when stirring is stopped, and the true specific gravity is 1.0 to 1.3 g / cm. ３ It is desirable that the density is 1.1 to 1.2 g / cm ３ It is desirable that:

[0048] The amount of carrier packed is preferably an amount such that the bulk volume of the carrier is 5 to 50% of the volume of the reaction region R below the water level WL1. If the amount of carrier is less than this, the treatment efficiency may be reduced, and if it is more than 50%, the stirring power may become excessive.

[0049] In the fluidized bed biological treatment device 1 configured as described above, raw water (organic matter-containing wastewater) is supplied into the tank body 2 through the raw water inlet 5 while the rotor 4 is rotated by the drive device M, and biological treatment is carried out. In this embodiment, the organic matter in the raw water is anaerobic biologically treated by microorganisms carried on the carriers C. In this embodiment, the aeration member 9 is disposed within the flow straightening area D surrounded by the partition plate 8, so that the air bubbles diffused from the aeration member 9 rise along the screen 7 without being affected by the swirling flow caused by the rotor 4.

[0050] The rotation speed of the drive shaft 3 of the rotor 4 is preferably adjusted so that the G value is 100 to 200, and is preferably set to approximately 5 to 20 rpm.

[0051] A portion of the water being stirred in the reaction region R in the tank body 2 flows around the underside of the partition plate 8 and enters the space (flow straightening region D) between the partition plate 8 and the screen 7. The filtered water then passes through the screen 7 and flows into the filtrate chamber 6, overflowing from the outlet 10 and being taken out as treated water.

[0052] Since deposits adhere to the front surface of the screen 7, air is diffused from the air diffusing member 9, and the air bubbles are caused to rise along the front surface of the screen 7, thereby removing the deposits from the front surface of the screen 7. Note that hereinafter, this operation may be referred to as cleaning the screen 7.

[0053] In this embodiment, the flow straightening area D is surrounded by the partition plate 8, which prevents the diffusion of bubbles into the reaction area R in the tank body 2, thereby efficiently cleaning the screen 7 and suppressing clogging of the screen 7 by the carrier C, biofilm, etc.

[0054] Methods for cleaning the screen 7 include steady cleaning, in which a predetermined flow rate of gas is continuously sprayed from the aeration member 9 to continuously clean the surface of the screen 7 while the fluidized bed biological treatment device 1 is in operation, and strong cleaning, which is performed when blockage of the screen 7 is suspected, when accumulated deposits need to be removed, or when carriers have accumulated between the screen 7 and the partition plate 8.

[0055] In steady-state cleaning, it is preferable to constantly spray a predetermined flow rate of gas from the aeration member 9 while the fluidized-bed biological treatment device 1 is in operation, but spraying may be stopped intermittently.

[0056] During strong cleaning, the amount of aeration is temporarily increased to at least twice that during steady cleaning, preferably about 3 to 5 times, and the duration is preferably from several seconds to several tens of seconds (e.g., 5 to 70 seconds). During this strong cleaning, the amount of air bubbles in the water increases on the front side of the screen 7, reducing the fluid density of the liquid-gas mixture. This increases the flow rate of filtered water passing through the screen 7, due to the same principle as an air lift pump. Therefore, during strong cleaning, it is preferable to open the openings 11 and transfer the water in the flow straightening region D inside the partition plate 8 to the reaction region R through the openings 11, preventing the flow rate of filtered water from becoming excessive.

[0057] The gas diffused from the diffusing member 9 is preferably a gas with a low oxygen content in order to maintain the anaerobic conditions within the tank body 2, but there is no problem in using an oxygen-containing gas such as air. When using an oxygen-containing gas, it is desirable to operate the reactor so that the sum of the dissolved oxygen weight in the influent raw water and the dissolved oxygen weight on the water surface or due to the diffused gas does not exceed 10% of the total weight, including the oxygen weight of the components to be treated contained in the influent raw water. Under these conditions, even when an oxygen-containing gas is diffused, the DO (dissolved oxygen) contained in the water transferred from the rectifying region D to the reaction region R is quickly consumed by the microorganisms in the reaction region R, thereby maintaining the anaerobic conditions of the reaction region R.

[0058] It is also desirable to add excess organic substances such as methanol and IPA (isopropanol), which are consumed by the microorganisms in the tank body 2 during respiration, in addition to the amount according to the treatment load.

[0059] Tank volume load: 0.3 kgN / m ３ / d or more, for example, 0.3 to 10 kgN / m ３ If the load is equal to or greater than a predetermined value, even if a small amount of oxygen gas is mixed into the reaction region R, DO is immediately consumed by the microorganisms in the reaction region R, and anaerobic conditions can be maintained. On the other hand, if the load is too high, the amount of suspended sludge increases too much in addition to the sludge adhering to the carrier, increasing the risk of clogging the screen 7 with sludge.

[0060] According to the fluidized bed biological treatment device 1 and its operating method of this embodiment described above, the diffusion of bubbles from the rectification area D to the reaction area R within the tank body 2 is prevented, the screen 7 is efficiently cleaned, and clogging of the screen 7 by the carrier C or biofilms attached to the carrier is suppressed, thereby enabling stable biological treatment.

[0061] The above-described embodiment is an example of the present invention, and the present invention may be embodied in other forms.

[0062] For example, in the above embodiment, the outlet 10, the screen 7 and the partition plate 8 are arranged near the center of the width of the side wall surface 2b of the tank body 2, but they may also be arranged at the corners of the tank body 2.

[0063] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-183370, filed on October 25, 2023, and is incorporated by reference in its entirety.

[0064] DESCRIPTION OF SYMBOLS 1 Fluidized bed biological treatment device 2 Tank body 3 Drive shaft 4 Rotor 5 Inlet 6 Filtrate chamber 7 Screen 8 Partition plate 8a Main plate 9 Aeration member 10 Outlet (overflow port) 11 Opening

Claims

1. A fluidized bed biological treatment device comprising: a tank body containing fluid carriers; a screen provided within the tank body for separating the carriers and directing treated water to an outlet; a partition plate which divides the inside of the tank body into a straightening area in which the screen is located and a reaction area in which biological treatment is carried out; an aeration member for causing air bubbles to flow along the surface of the screen facing the straightening area; and an opening provided in the upper part of the partition plate for transporting the carriers from the straightening area to the reaction area.

2. A fluidized bed biological treatment device as claimed in claim 1, wherein the screen is provided facing the side wall surface of the tank body, the space between the screen and the side wall surface of the tank body forms a filtrate water chamber, and the side wall surface of the tank body is provided with the outlet for filtrate water overflow facing the filtrate water chamber.

3. A fluidized bed biological treatment apparatus as claimed in claim 2, wherein the partition plate extends vertically along the screen, the lower end of the partition plate is located lower than the lower end of the screen, and the upper end of the partition plate is located higher than the water level in the reaction area and the water level in the straightening area within the tank body.

4. A fluidized bed biological treatment device according to claim 3, wherein the partition plate has a main plate facing the screen, the opening is provided in the upper part of the main plate, and the aeration member is disposed between the main plate and a downward extension surface of the front surface of the screen.

5. A fluidized bed biological treatment device according to claim 4, wherein said air diffusing member is disposed on the downward extension surface side of the midpoint between said main plate and said downward extension surface.

6. The fluidized bed biological treatment device according to claim 1, wherein an opening and closing member is provided at said opening.

7. A method for operating a fluidized bed biological treatment device for treating raw water with the fluidized bed biological treatment device according to any one of claims 1 to 6, comprising: a steady cleaning process in which aeration is performed from the aeration member at a steady volume of air; and a strong cleaning process in which the volume of air diffused from the aeration member is made greater than that in the steady cleaning process.

8. The fluidized bed biological treatment device is the fluidized bed biological treatment device of claim 6, and a method for operating a fluidized bed biological treatment device as claimed in claim 7, wherein the opening is closed in the steady cleaning step, and the opening is opened in the strong cleaning step, and the carrier is returned from the flow straightening area through the opening to the reaction area.

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