JP4274975B2 - Cleaning method for carrier separation screen, cleaning device therefor, and sewage treatment device - Google Patents

Description

  The present invention relates to a method for cleaning a screen for separating a carrier on which microorganisms for biological treatment are immobilized, biological cleaning apparatus, a cleaning apparatus thereof, and the cleaning apparatus. The present invention relates to a sewage treatment apparatus.

  The reaction vessel has a carrier on which microorganisms for biological treatment are immobilized, and after biological treatment by introducing organic wastewater into the reaction vessel, the biologically treated wastewater is treated in the reaction vessel. A method of separating the microbial immobilization carrier (hereinafter, also simply referred to as a carrier) with a grid-like screen has been performed.

  If the separation of the carrier in the screen is continued for a certain time or longer, the screen will eventually become clogged with substances adhering to the screen, and thereby the flow of treated water discharged from the reaction tank through the screen. Since the sewage and the carrier may flow out of places other than the screen, it is necessary to clean the screen by an appropriate means.

  As a method of cleaning the screen, a diffuser tube is horizontally installed on the upstream side (anti-transmission side) of the screen so as to be close to the lower part of the screen, and holes having a diameter of about 10 mm are opened in the diffuser tube at intervals of about several tens of mm. As a result, the buoyancy of the bubbles released from the air diffuser creates an ascending water flow in the vicinity of the screen, and the shear force of the water flow and the fibers in the sludge in which the gas-liquid interface of the bubbles is directly attached to the surface of the screen A screen that separates the carrier by utilizing the fact that the fibrous substance or carrier is accompanied by the flow of the gas-liquid interface by contacting the fibrous substance or carrier, and the fibrous substance or carrier is peeled off from the screen. A cleaning method is adopted. (For example, refer to Patent Document 1).

  That is, Patent Document 1 is provided with a biological reaction tank, a carrier for supporting nitrifying bacteria, and an aeration device for supplying oxygen to the nitrifying bacteria of the carrier. A nitrification tank unit having an outlet of the liquid to be treated for preventing the outflow of water and a water channel connected thereto, and one or a plurality of the nitrification tank units are arranged in the biological reaction tank, and are generated by the air diffuser. A sewage nitrification apparatus is described in which a liquid to be treated in a biological reaction tank is circulated and circulated in a nitrification tank unit to effect nitrification by an air lift effect.

In addition, it is thought that the force which peels off the fibrous substance, support | carrier, etc. which adhered to the screen from a screen is larger than the shearing force by an ascending water flow, and the force by which a bubble touches a screen directly.
Japanese Patent Publication No. 5-46279

  However, simply by installing an air diffuser tube on the upstream side (anti-permeation side) of the screen so as to be close to the lower part of the screen, a large amount of bubbles ride on the rising water flow from the upstream side toward the transmission side. Most of the path through which the air bubbles passing through the screen and released from the air diffuser rise to the surface of the water is downstream of the screen.

  Therefore, the effect of peeling off the substance adhering to the upstream side of the screen is small. Therefore, in order to improve the effect of peeling off substances such as fibrous substances and carriers adhering to the screen surface by bubbles, as many bubbles as possible are generated from the air diffuser. However, in order to generate a large amount of bubbles, the power of the diffuser tube becomes excessive, the running cost of the facility becomes so large that it cannot be ignored, and it cannot be realized as a realistic facility.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to efficiently wash the carrier separation screen, the washing apparatus, and the sewage treatment apparatus having the washing apparatus. Is to provide.

  The inventor of the present invention has a small effect of cleaning the screen by the bubbles in the prior art because the bubbles released from the air diffuser are small (because the buoyancy is small), and the small bubbles are easily influenced by the water flow passing through the screen. In order to achieve the above object, the present inventor conducted an analysis as described below, because it was thought that the main cause was movement along with the water flow.

As shown in FIG. 1, when the screen 1 is arranged in the vertical direction, the water flow uniformly flows in the vertical direction with respect to the screen 1, and the bubbles 2 are spherical. Note that the actual shape of the bubbles is so various that it cannot be specified by a known shape expression. The equation of motion of the bubble 2 in the horizontal direction is expressed by the following equation 1, and the equation of motion of the bubble 2 in the vertical direction is expressed by the following equation 2.
dU / dt = − ((3C _D ρ _l ) / 16Dρ _g ) | U | U Equation 1
dV / dt = ((ρ _l −ρ _g ) / ρ _g ) g − ((3C _D ρ _l ) / 16Dρ _g ) | V | V Equation 2
Where U is the horizontal flow velocity, V is the vertical flow velocity, D is the bubble diameter, C _D is the fluid resistance coefficient, ρ _l is the fluid density, ρ _g is the bubble density, g is the acceleration of gravity, t is time.

In FIG. 1, it seems that it is preferable that the vertical flow velocity V, which is a flow along the surface of the screen 1, is large in order to increase the peeling force of the substance attached to the screen due to bubbles. That is, in order for the horizontal flow velocity U to remain unchanged in the initial state and the vertical flow velocity V to accelerate and increase, the smaller the fluid resistance coefficient C _D than the equations 1 and 2, It turns out to be advantageous.

The resistance coefficient of the sphere in the flow has been found experimentally and is shown in FIG. The dotted line in FIG. 2 shows Stokes' law of resistance. As shown in FIG. 2, the resistance coefficient has a correlation with the Reynolds number. When the relationship between the Reynolds number _Re and the flow velocity is shown for each movement in the horizontal direction (x) and the vertical direction (y), It is expressed as equation (3).

R _e x = ρ _l UD / μ, R _e y = ρ _l VD / μ (3)
Note that μ is the viscosity coefficient of the fluid.

  From FIG. 2, it can be seen that the Reynolds number may be increased to reduce the resistance coefficient, and the bubble diameter D may be increased to increase the Reynolds number from Equation (3).

  Based on the above analysis results, the present inventor has found that it is preferable to increase the bubble diameter in order to efficiently wash the carrier separation screen due to the peeling effect by bubbles.

  That is, the carrier separation screen cleaning method of the present invention is arranged by disposing an air diffuser at the lower part of the screen on the upstream side of the screen, and peeling off the substance adhering to the screen by the large diameter bubbles released from the air diffuser. The material attached to the screen can be removed efficiently.

  In addition, the carrier separation screen cleaning device of the present invention can efficiently remove substances adhering to the screen by disposing an air diffuser that discharges large-diameter bubbles at the lower portion of the screen on the upstream side of the screen. .

The present invention has the following effects.
(1) According to the first aspect of the present invention, large径気bubbles can strip the substance adhering to the screen while rising vertically along the screen surface efficiently.
(2) According to the invention described in claim 2 , a cleaning device suitable for carrying out the invention described in claim 1 can be provided.
(3) According to the invention described in claim 3 , it is possible to provide a sewage treatment apparatus that does not cause the carrier to flow out.

  That is, the method for cleaning a carrier separation screen according to the present invention introduces organic sewage into a sewage treatment apparatus having a carrier on which microorganisms for biologically treating organic sewage are immobilized. After biologically treating the sewage, the carrier on which the microorganisms are immobilized is separated by a screen, and the screen for separating the carrier is washed in the method for treating sewage in which the biologically treated water is permeated downstream through the screen. The method is characterized in that an air diffuser is disposed at the lower part of the screen upstream of the screen, and the substance adhering to the screen is peeled off by the large diameter bubbles discharged from the air diffuser.

  Further, the carrier separation screen cleaning device of the present invention has a carrier on which microorganisms for biologically treating organic wastewater are immobilized, and after biologically treating organic wastewater with the microorganisms, An apparatus for cleaning a screen for separating a carrier in a sewage treatment apparatus that separates a carrier on which microorganisms are immobilized with a screen and allows biologically treated water to pass through the screen to the downstream side. It is characterized by disposing a diffuser that discharges large-diameter bubbles at the bottom of the screen.

  Since the screen used in the cleaning method and the cleaning apparatus of the present invention need only have a structure that does not allow the carrier to permeate, it is not limited to the lattice-shaped screen, and punching metal, wedge wires, and the like can be used as the screen.

Regarding the present invention having such characteristics, the following numerical analysis and sewage treatment experiment were conducted as the best mode for carrying out the invention, and will be described in order.
(1) Numerical analysis The inventor obtained the flow of water and the locus of bubbles by numerical analysis using a calculation model of a sewage treatment apparatus as shown in FIG. In FIG. 3, 3 and 4 are the inflow part (shaded part) of to-be-processed water, 5 is a stirrer, 6 is the suction part of a stirrer, 7 is the discharge part of a stirrer, 8 is a screen surface, 9, 10, 11 Is the outflow part (shaded part) of treated water. Using the numerical analysis model as described above, further numerical analysis was performed under the following preconditions.

Aeration amount = 2.4 Nm ³ / min
Screen area = 24.3m ²
Passing water volume = 1108m ³ / hr
Passing flux = 0.0123m / sec
(A) Analysis results in the case of small-diameter bubbles FIG. 4 shows the locus of bubbles on the screen surface when bubbles with a diameter of 15 mm are discharged so as to be close to the lower screen portion on the upstream side of the lattice-like screen.

  As shown in FIG. 4, after the bubbles released from the position near the screen lower part on the upstream side of the screen rise slightly along the lower part of the screen, the bubbles are influenced by the water flow discharged from the stirrer 6. , Reaches the downstream side, and rises along the downstream screen surface.

  It can be seen that the reverse flow generated at the upper part of the screen appears and rises again on the upstream side of the screen.

As is clear from comparison with FIG. 5 to be described later, it can be seen that a small diameter bubble having a diameter of about 15 mm has a small screen cleaning area.
(B) Analysis results in the case of large-sized bubbles FIG. 5 shows the locus of bubbles on the screen surface when bubbles having a diameter of 100 mm are released so as to be close to the lower screen portion on the upstream side of the lattice-shaped screen.

  As shown in FIG. 5, the bubbles released all at once from a position near the screen lower part on the upstream side of the screen rise about 1/3 to 1/2 in the height direction along the screen surface, and then the agitator 6 Under the influence of the water flow discharged from, it passes through the screen and reaches the downstream side, and rises along the downstream screen surface.

  Then, it can be seen that a large amount of bubbles rise along the screen as shown in the upstream side of the screen again due to the backflow generated at the upper part of the screen.

  As apparent from the comparison with FIG. 4, the upward movement of buoyancy is increased by using large-sized bubbles, and the effect of peeling off substances such as fibrous substances and carriers attached to the screen by the large-sized bubbles. It can be expected to improve.

  In this numerical analysis, the flow velocity of the jet flow by the stirrer was as high as 1 m / sec. Therefore, even in the case of this large-diameter bubble, it was seen that it passed through the screen and reached the downstream side. If not, most of the large-sized bubbles released from the position close to the lower screen portion on the upstream side of the screen are expected to rise along the screen surface on the upstream side.

In an actual machine, a stirrer is not necessarily provided, and stirring by a diffuser system may be used.
(2) An example of a sewage treatment experiment using an actual machine simulation device Based on the above numerical analysis results, an actual sewage treatment device simulating an actual sewage treatment device with a scale of 1/8 was used. For example, light-weight small substances such as cylinders, pellets, etc. with biological treatment microorganisms attached with resins such as polyethylene, polypropylene, urethane, beads, which are solidified biological treatment microorganisms with plastics such as polyethylene glycol, Experiments on the treatment of sewage containing substances such as pellets and other lightweight small substances) were conducted. The experimental apparatus is shown in FIG. The nature of the sewage used in the experiment is as described below.

SS = 100mg / liter
COD = 80mg / liter
BOD = 160mg / liter
In FIG. 6, 12 is a carrier return pipe, 13 is a sewage suction nozzle, 14 is an ejector, 15 is a grid-like screen, and 16 is an air diffuser. Each section from the first section 17 through the second section 18 to the third section 19 is partitioned by substantially rectangular partition walls 20, 21, 22. In FIG. 6, the partition walls 20, 21, and 22 are partially broken to make the device easy to see. As a matter of course, the discharge-side partition wall 23 in which the screen 15 is disposed through the partition walls 20, 21, and 22. The side surface leading to is sealed with a side wall.

  Sewage discharged from a pump (not shown) on the right side of the partition wall 20 is sucked by a small-diameter nozzle 13, and the sewage and the carrier returned by the carrier return pipe 12 are sucked by an ejector 14 having an enlarged diameter portion. Then, it is discharged from the discharge port 24, reaches the third section 19 through the openings 25 and 26 provided at the lower portions of the partition walls 21 and 22, and is formed on the surface of the screen 15 by the bubbles released from the diffuser 16. The adhered substance is peeled off, and the biologically treated water is discharged through the screen 15.

Next, the experimental results when small diameter bubbles or large diameter bubbles are discharged from the air diffuser using such an experimental apparatus will be described.
(A) When using a diffuser tube that discharges small-diameter bubbles In the experimental apparatus as shown in FIG. Used and screen washing experiments were performed.

That is, the sewage having the above properties was passed for 2 hours at a passing water amount of 15.6 m ³ / hr, and the minimum aeration amount when the screen 15 was blocked by the substance was investigated.

As a result, in order to prevent the screen 15 from being blocked, an aeration amount of at least 20 NL / min was required.
(B) When an air diffuser that discharges large-diameter bubbles is used In the experimental apparatus as shown in FIG. 6, as the air diffuser 16, a diffuser of an air diffuser having a diffuser hole with a diameter of 13 mm provided in a tube with a diameter of 100 mm is used. A suction port of a diffuser as shown in FIG. 7 (13 mm in diameter, see number 27 in FIG. 7) was connected to the pores, and a screen cleaning experiment was conducted.

That is, the sewage having the above characteristics was passed for 2 hours at a passing water amount of 15.6 m ³ / hr, and the minimum aeration amount when the screen 15 was blocked with the substance was investigated.

  As a result, in order to prevent the screen 15 from being blocked, an aeration amount of 5 NL / min was sufficient.

In the air diffuser shown in FIG. 7, the screen is not clogged even with an aeration rate of 5 NL / min, and the air diffuser shown in FIG. 7 has an aeration amount that is 1/4 that of an air diffuser tube having a large number of 10 mm diameter holes. It is possible to achieve the same cleaning effect.
(3) Air diffuser capable of discharging large diameter bubbles FIG. 7A is a plan view of an air diffuser capable of discharging large diameter bubbles, and FIG. 7B is a side sectional view thereof. It is.

  In FIG. 7, 27 is an air suction port, 28 is a lower cylinder part, and the lower cylinder part 28 enters the upper cylinder part 29. The upper cylinder part 29 is sealed with an umbrella part 30. The top part of the lower cylinder part 28 is shielded by a shielding material 31 that can be raised and lowered. A plurality of air discharge ports 32 are provided at the lower outer periphery of the upper cylindrical portion 29.

  Next, the cleaning operation of the screen by the air diffuser of FIG. 7 will be described.

  The air sucked from the air suction port 27 rises inside the lower cylindrical portion 28 and reaches the shielding material 31. Among the bubbles that have reached the shielding material 31, those that have overcome the water pressure in the chamber 33 above the shielding material 31 push the shielding material 31 and enter the chamber 33.

  In this way, the bubbles that have entered the chamber 33 one after another push down the water surface in the chamber 33 to form an air pocket. Eventually, the air reservoir has a triangular air outlet 32 (in this embodiment, a total of ten air outlets are formed, but the number of air outlets and the size of the air outlets are the sewage to be actually treated. The air in the air pool is discharged as bubbles of a certain size from the air discharge port 32.

  The bubbles released from the air discharge port 32 are accumulated at the lower part of the flange portion 34 constituting the umbrella portion 30, and the bubbles are combined into a large diameter bubble. The large-sized bubbles thus formed are discharged from the outer end portion of the flange portion 34 and rise in the water.

  As the air in the air reservoir is released from the air discharge port 32, the water level of the air reservoir rises again, and the upper chamber 33 is filled with water.

  Of the bubbles sucked from the air suction port 27 as described above, the one that overcomes the water pressure of the chamber 33 above the shielding material 31 pushes the shielding material 31 and enters the chamber 33 to form an air pocket. . Eventually, when the air reservoir reaches the triangular air discharge port 32, it is discharged from the air discharge port 32 as bubbles of a certain size, and these bubbles are released at the lower part of the flange portion 34 constituting the umbrella portion 30. Combined to form large-diameter bubbles and rise in water.

The operation as described above is repeatedly performed in the air diffuser of FIG. 7, and the screen 15 is effectively cleaned with the large-diameter bubbles.
(4) Numerical analysis of screen cleaning effect due to difference in bubble size In the case of using the calculation model as shown in FIG. 3, in order to exclude the influence of the jet discharged from the stirrer, suction by the stirrer With no discharge, numerical analysis was performed under the following preconditions.

Aeration amount = 2.4 Nm ³ / min
Screen area = 24.3m ²
Passing water volume = 1108m ³ / hr
Passing flux = 0.0123m / sec
FIG. 8A shows a bubble locus when the bubble diameter is 15 mm, and FIG. 8B shows a bubble locus when the bubble diameter is 100 mm.

As is apparent from a comparison between FIG. 8A and FIG. 8B, as shown in FIG. 8B, the amount of bubbles rising along the front surface of the screen is increased by setting the bubble diameter to 100 mm. It can be seen that the cleaning area due to bubbles increases.
(5) Numerical analysis of bubble diameter suitable for screen cleaning When a calculation model as shown in FIG. 3 is used, there is no suction and discharge by the stirrer in order to exclude the influence of the jet discharged from the stirrer. In the state, when the following preconditions were adopted and the flow rate of treated water was changed, a numerical analysis of the bubble diameter suitable for screen cleaning was performed.

Aeration amount = 2.4 Nm ³ / min
Screen area = 24.3m ²
Passing water amount = 111 to 1108 m ³ / hr
Passing flux = 0.00123 to 0.0123 m / sec
When the passing water amount is 222 m ³ / hr, the bubble locus when the bubble diameter is 500 mm is shown in FIG. 9A, and the bubble locus when the bubble diameter is 600 mm is shown in FIG. 9B.

  As is clear from the comparison between FIG. 9A and FIG. 9B, in FIG. 9A (when the bubble diameter is 500 mm), all the bubbles are raised on the front of the screen, which is very efficient. It can be seen that the screen can be cleaned.

  On the other hand, in FIG. 9B (when the bubble diameter is 600 mm), since some of the bubbles are directed toward the back side of the screen in the intermediate portion in the height direction of the screen, FIG. It is considered that the cleaning effect due to the bubbles is slightly lower than that in the case of 500 mm), and the maximum bubble diameter with this passing water amount is 500 mm.

  In addition, since the buoyancy is larger when the bubble diameter is 600 mm, the straightness is expected to improve more than 500 mm, but the reason why some of the bubbles of 600 mm go to the back side of the screen is that the aeration is constant in this numerical analysis Therefore, if the bubble diameter is increased, the discharge frequency of bubbles is lowered, and the upward flow formed on the front surface of the screen may be slightly weakened.

  Then, when the bubble diameter is gradually reduced, the minimum bubble diameter when all bubbles rise on the front of the screen is obtained in the same manner, the maximum diameter is represented by the symbol “○”, and the minimum diameter is represented by the symbol “●”. This is shown in FIG.

  FIG. 10 shows the relationship between the screen passing flux thus obtained and the maximum bubble diameter and the minimum bubble diameter.

  As apparent from FIG. 10, it is understood that the screen can be cleaned under the widest range of operating conditions by setting the bubble diameter to 200 to 250 mm.

  In FIG. 10, when the diameter is smaller than the minimum bubble diameter, the buoyancy is also reduced due to the small bubbles. Therefore, the small bubbles are easily influenced by the water flow passing through the screen and move to the back side of the screen together with the water flow. Therefore, the amount of bubbles rising on the front surface of the screen decreases as the bubble diameter decreases.

  The sewage treatment apparatus having the carrier separation screen cleaning apparatus of the present invention may be an aerobic biological treatment apparatus or an anaerobic biological treatment apparatus (such as a denitrification treatment apparatus), and causes the carrier to flow into the biological treatment tank. I just need it. However, in the case of an anaerobic biological treatment apparatus, it is necessary to make it a condition that does not inhibit anaerobic in the tank by screen cleaning with air. Further, the air diffuser is not limited to the one shown in FIG. 7, and any diffuser may be used as long as it has a structure capable of discharging large diameter bubbles.

It is a figure which shows simply the motion direction of the bubble with respect to a screen. It is a figure which shows the relationship between the Reynolds number and the resistance coefficient of a sphere. It is a figure which shows the calculation model for a numerical analysis. It is a figure which shows the locus | trajectory of the bubble on the screen surface in case the diameter of a bubble is 15 mm by numerical analysis. It is a figure which shows the locus | trajectory of the bubble on the screen surface in case the diameter of a bubble is 100 mm by numerical analysis. It is a partially broken perspective view of the experimental apparatus used for the sewage treatment experiment. Fig.7 (a) is a top view of the diffuser which can discharge | release a large diameter bubble, FIG.7 (b) is the sectional side view. FIG. 8A is a diagram showing the locus of bubbles on the screen surface when there is a bubble diameter of 15 mm by numerical analysis (no suction and discharge by a stirrer), and FIG. 8B is a bubble by numerical analysis. It is a figure which shows the locus | trajectory of the bubble on the screen surface in case the diameter of 100 mm is (it is neither suction nor discharge by a stirrer). FIG. 9A is a diagram showing the locus of bubbles on the screen surface when there is a bubble diameter of 500 mm by numerical analysis (no suction and discharge by a stirrer), and FIG. 9B is a bubble by numerical analysis. It is a figure which shows the locus | trajectory of the bubble on the screen surface in case the diameter of this is 600 mm (there is no suction and discharge by a stirrer). It is a figure which shows the relationship between a screen passage flux and the largest bubble diameter and the minimum bubble diameter which can wash | clean a screen effectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screen 2 Bubble 3 Inflow part of to-be-processed water 4 Inflow part of to-be-processed water 5 Stirrer 6 Suction part of agitator 7 Discharge part of agitator 8 Screen surface 9 Discharge part of treated water 10 Discharge part of treated water 11 Treatment Water discharge section 12 Carrier return pipe 13 Sewage suction nozzle 14 Ejector 15 Screen 16 Air diffuser 17 First section 18 Second section 19 Third section 20 Partition wall 21 Partition wall 22 Partition wall 23 Partition wall 24 Discharge port 25 Opening 26 Opening portion 27 Air suction port 28 Lower cylinder portion 29 Upper cylinder portion 30 Cover portion 31 Shielding material 32 Air discharge port 33 Chamber 34 Flange portion

Claims (3)

Organic sewage is introduced into a sewage treatment apparatus having a carrier on which microorganisms for biologically treating organic sewage are immobilized, and the organic sewage is biologically treated with the microorganisms, and then the microorganisms are screened. Is a method of washing a screen for separating a carrier in a method of treating sewage in which biologically treated water is allowed to permeate downstream through the screen, and is disposed at a lower portion of the screen on the upstream side of the screen. In the cleaning method of the carrier separation screen, in which a diffuser is disposed and the substance attached to the screen is peeled off by the large-diameter bubbles released from the diffuser , the large-diameter bubble has a lower side having an air suction port at the bottom. The cylinder part is inserted into the upper cylinder part, the upper cylinder part is sealed with a lid part, the top part of the lower cylinder part is shielded with a vertically movable shielding material, and a plurality of air discharge ports are provided at the lower outer periphery of the upper cylinder part. That air diffusion using a device, carrier separation screen cleaning method characterized in that it is obtained by the air is released from the air discharge port. Having a carrier on which microorganisms for biologically treating organic wastewater are immobilized, biologically treating organic wastewater with the above microorganisms, and then separating the carrier on which the microorganisms are immobilized with a screen. An apparatus for cleaning a screen for separating a carrier in a sewage treatment apparatus that allows treated water to pass through the screen to the downstream side, and discharges large diameter bubbles to the lower part of the screen on the upstream side of the screen In the apparatus for cleaning a carrier separation screen, the air diffuser has a lower cylinder part having an air suction port in the lower part entered into the upper cylinder part, and the upper cylinder part is sealed with a lid part. An apparatus for cleaning a carrier separation screen, characterized in that a top portion is shielded by a vertically movable shielding material, and a plurality of air discharge ports are provided at an outer peripheral lower portion of an upper cylindrical portion . An apparatus for treating sewage comprising the apparatus for cleaning a carrier separation screen according to claim 2 .

Images