JP2020022957A - Water treatment method and water treatment apparatus - Google Patents

Abstract

To provide a water treatment method capable of efficiently maintaining concentration of a treatment object substance remaining in a tank in a high state after inflow of waste water and discharge of treatment water.SOLUTION: The water treatment method of this embodiment is a water treatment method which includes an operation cycle step of repeating: an inflow/discharge step of discharging biological treatment water in a reaction tank 10 from a discharge port 28 while flowing waste water into the reaction tank 10 from an inflow port 26; a biological treatment step of biological treatment of the waste water in the reaction tank 10 with a biological sludge; and a sedimentation step of sedimentation of the biological sludge in the reaction tank 10. The discharge port 28 is provided at a water level in the reaction tank 10, the inflow port 26 is provided at a position lower than an interface position of a biological sludge layer formed at a bottom of the reaction tank 10 in the sedimentation step, and the waste water is supplied to the biological sludge layer in a horizontal direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technology of a water treatment method and a water treatment device.

  BACKGROUND ART Conventionally, an activated sludge method utilizing an aggregate of microorganisms (aerobic biological sludge) called floc has been used for biological wastewater treatment. However, in the activated sludge method, when the floc (aerobic biological sludge) is separated from the treated water in the sedimentation basin, the surface area of the sedimentation basin must be very large because the sedimentation speed of the floc is slow. In addition, the processing speed of the activated sludge method depends on the sludge concentration in the biological treatment tank, and the processing speed can be increased by increasing the sludge concentration. However, solid-liquid separation failure such as bulking occurs. May not be able to maintain the processing.

  On the other hand, in the anaerobic biological treatment, it is general to utilize an aggregate of microorganisms called granules, which are densely aggregated and granular. Granules have a very high sedimentation velocity and microorganisms are densely gathered, so that the sludge concentration in the biological treatment tank can be increased, and high-speed treatment of wastewater can be realized. However, the anaerobic biological treatment has problems such as the limited number of wastewater to be treated and the necessity of maintaining the treated water temperature at 30 to 35 ° C., as compared with the aerobic treatment (activated sludge method, etc.). In some cases. In addition, the anaerobic biological treatment alone has poor water quality, and when discharged into a river or the like, it may be necessary to separately perform an aerobic treatment such as an activated sludge method.

  In recent years, it has been clarified that the use of a semi-batch treatment device that intermittently flows wastewater into a reaction tank can form not only anaerobic biological sludge but also aerobic biological sludge and highly sedimentable granulated biological sludge. (For example, see Patent Documents 1 to 4). The granulated biological sludge has, for example, an average particle size of 0.2 mm or more and a sedimentation speed of 5 m / h or more. In the semi-batch type biological treatment, one reaction tank has four functions such as (1) inflow of wastewater, (2) biological treatment of a substance to be treated, (3) sedimentation of biological sludge, and (4) discharge of treated water. Generally, the steps are repeated.

  Patent Document 5 discloses a semi-batch type organism that repeatedly performs three steps of (1) inflow of wastewater and discharge of treated water, (2) biological treatment of a substance to be treated, and (3) sedimentation of biological sludge. A processing method is disclosed. As a result, biological sludge having a high sedimentation property such as granulated biological sludge can be obtained.

WO 2004/024638 JP 2008-212878 A Japanese Patent No. 4975541 Japanese Patent No. 4804888 JP-A-2006-77931

  By the way, in the semi-batch type biological treatment, a concentration gradient of a substance to be treated (for example, an organic substance) to be biologically treated in the tank is formed, specifically, in a satiety state (the concentration of the substance to be treated in the tank is high). It is considered that the formation of a cycle of a state of aging and a state of starvation (a state in which the concentration of the substance to be treated in the tank is low) is an important factor in obtaining highly sedimentable biological sludge. However, in semi-batch type biological treatment that discharges treated water along with inflow of wastewater, wastewater containing the substance to be treated that flows into the tank is discharged out of the tank together with the treated water without making sufficient contact with biological sludge. May be done. Therefore, it is difficult to increase the concentration of the substance to be treated remaining in the tank after the inflow of wastewater / after the discharge of treated water. As a result, it may be difficult to form highly sedimentable biological sludge.

  In addition, in a semi-batch type biological treatment that discharges treated water together with inflow of wastewater, a system in which the inflow of wastewater into the reactor is installed at the bottom of the reactor and the wastewater is supplied in an upward flow Then, not only is the installation of the distributor expensive, but when the distributor is installed, there is a concern that the biological sludge may be blocked at the inlet and a short-circuit flow may occur, so that periodic maintenance is required.

  Therefore, an object of the present invention is to provide a water treatment method and a water treatment apparatus capable of efficiently setting the concentration of a substance to be treated remaining in a tank after inflow of wastewater / discharge of treated water. It is in.

  The present invention is a water treatment method for biologically treating wastewater using a reaction tank containing biological sludge in a tank provided with an inlet and an outlet, wherein the water is introduced into the reaction tank from the inlet. An inflow / discharge step of discharging biological treatment water in the reaction tank from the discharge port while inflowing wastewater; a biological treatment step of biologically treating the wastewater in the reaction tank with biological sludge; A settling step of settling the biological sludge, wherein the discharge port is disposed at a water level in the reaction vessel, and the inflow port is configured to set at least a part of the drainage in the settling step In the water treatment method, the biological sludge layer formed at the bottom of the reaction tank is supplied horizontally.

  Further, in the water treatment method, it is preferable that the inflow port is disposed at a position lower than an interface position of the biological sludge layer formed at the bottom of the reaction tank in the settling step.

  In the water treatment method, it is preferable that a pipe extending in a vertical direction is connected to the inflow port, and the drainage be supplied to the inflow port by gravity from the pipe.

  Further, in the water treatment method, the inside of the reaction tank is partitioned by a partition into a first chamber into which the wastewater is introduced and a second chamber for performing the operation cycle step, and the discharge port is the second chamber. Provided on the chamber side, and arranged at a water level in the second chamber, the inflow port is provided on the partition wall such that the first chamber and the second chamber communicate with each other, and in the settling step, It is preferable that the wastewater is disposed at a position lower than the interface of the biological sludge layer formed at the bottom of the second chamber, and the wastewater is supplied horizontally into the biological sludge layer formed at the bottom of the second chamber.

  In the water treatment method, it is preferable that the reaction tank is a square water tank, and the inflow port and the discharge port are provided on the same surface of the square water tank.

In the water treatment method, the flow velocity v (cm / sec) of the drainage water at the inlet and the horizontal distance N (m) from the inlet to the side surface of the reaction tank facing the inlet are: It is preferable to satisfy the following expression.
20 ≦ v / N ^1/2 ≦ 80

  Further, the present invention further comprises a reaction tank for containing biological sludge in a tank provided with an inlet and an outlet, and while the wastewater flows into the reaction tank from the inlet, the reaction from the outlet is performed. An inflow / discharge step of discharging biologically treated water in a tank, a biological treatment step of biologically treating the wastewater in the reaction tank with biological sludge, and a sedimentation step of settling the biological sludge in the reaction tank. A water treatment device that performs a repetitive operation cycle step, wherein the outlet is installed at a water level in the reaction tank, and the inflow port is configured to set at least a part of the drainage to the bottom of the reaction tank in the settling step. This is a water treatment device for supplying horizontally into the formed biological sludge layer.

  In the water treatment apparatus, it is preferable that the inflow port is installed at a position lower than an interface position of a biological sludge layer formed at the bottom of the reaction tank in the settling step.

  In the water treatment apparatus, it is preferable that a pipe that extends in a vertical direction is provided, the pipe be connected to the inflow port, and the supply of the wastewater to the inflow port be performed by gravity from the pipe.

  Further, in the water treatment apparatus, the reaction tank includes a partition that partitions the inside of the tank into a first chamber into which the wastewater is introduced and a second chamber in which the operation cycle process is performed. The first chamber is provided on the side of the second chamber, and is arranged at a water level in the second chamber, and the inflow port is provided on the partition wall such that the first chamber and the second chamber communicate with each other. In the sedimentation step, it is preferably disposed at a position lower than the interface position of the biological sludge layer formed at the bottom of the second chamber, and the drainage water is preferably supplied horizontally to the biological sludge layer formed at the bottom of the second chamber. .

  Further, in the water treatment apparatus, it is preferable that the reaction tank is a rectangular water tank, and the inflow port and the discharge port are provided on the same surface of the square water tank.

In the water treatment apparatus, the flow rate v (cm / sec) of the drainage water at the inlet and the horizontal distance N (m) from the inlet to the side surface of the reaction tank facing the inlet are: It is preferable to satisfy the following expression.
20 ≦ v / N ^1/2 ≦ 80

  According to the present invention, it is possible to provide a water treatment method and a water treatment apparatus capable of efficiently increasing the concentration of a substance to be treated remaining in a tank after inflow of wastewater / discharge of treated water. It becomes possible.

(A) is a schematic sectional view showing an example of a water treatment device according to the present embodiment, and (B) is a schematic top view showing an example of the water treatment device according to the present embodiment. It is a schematic cross section which shows an example of the state of the water treatment apparatus at the time of a biological treatment process. It is a schematic cross section which shows an example of the state of the water treatment apparatus at the time of a sedimentation process. It is a schematic cross section which shows an example of the state of the water treatment apparatus at the time of an inflow / discharge process. It is a schematic top view which shows an example of the square-shaped reaction tank employ | adopted in a large-scale processing plant. It is a schematic top view which shows another example of the square-shaped reaction tank employ | adopted in a large-scale processing plant. (A) is a schematic cross-sectional view showing another example of a square-shaped reaction tank used in a large-scale processing plant, and (B) is a square-shaped reaction tank used in a large-scale processing plant. It is a schematic top view which shows another example of. (A) is a schematic cross-sectional view showing another example of the water treatment apparatus of the present embodiment, and (B) is a schematic top view showing another example of the water treatment apparatus of the present embodiment. (A) is a schematic cross-sectional view showing another example of the water treatment apparatus of the present embodiment, and (B) is a schematic top view showing another example of the water treatment apparatus of the present embodiment. (A) is a sectional view showing another example of the water treatment apparatus of the present embodiment, and (B) is a schematic top view showing another example of the water treatment apparatus of the present embodiment. (A) is a schematic cross-sectional view showing another example of the water treatment apparatus of the present embodiment, and (B) is a schematic top view showing another example of the water treatment apparatus of the present embodiment. (A) is a schematic cross-sectional view showing another example of the water treatment apparatus of the present embodiment, and (B) is a schematic top view showing another example of the water treatment apparatus of the present embodiment. It is a figure which shows the result of the bromine ion residual rate with respect to the flow velocity of the inflow port in Examples 2 and 3. It is a figure which shows transition of SVI5 and SVI30 which are the sedimentation index of the sludge in a reaction tank. It is an input sludge and a sludge observation photograph 50 days after startup.

  An embodiment of the present invention will be described below. The present embodiment is an example for implementing the present invention, and the present invention is not limited to the present embodiment.

  FIG. 1A is a schematic cross-sectional view illustrating an example of a water treatment apparatus according to the present embodiment, and FIG. 1B is a schematic top view illustrating an example of the water treatment apparatus according to the present embodiment. As shown in FIG. 1A, a water treatment apparatus 1 includes a reaction tank 10, a raw water introduction apparatus including a raw water introduction pipe 12, a raw water pump 14, and an electromagnetic valve 16, and a diffuser including a blower 18 and an air diffusion pipe 20. An apparatus, a treated water collecting channel 22 and a control device 24 are provided. In FIG. 1B, the air diffuser including the blower 18 and the air diffuser 20 and the control device 24 are omitted.

  The reaction tank 10 according to the present embodiment includes an inlet 26 through which wastewater flows into the tank. In the reaction tank 10 shown in FIG. 1, a plurality of inlets 26 are provided on one side surface of the reaction tank 10. The inflow port 26 is disposed at a position lower than the interface position of the biological sludge layer formed on the bottom of the reaction tank 10 in the sedimentation step described below, and is opened in the horizontal direction. From the biological sludge layer. Here, the horizontal direction defined in the present specification includes a substantially horizontal direction. The substantially horizontal direction includes a direction having an inclination angle of 10 ° or less with respect to a horizontal direction (usually, a direction parallel to a direction in which the flat surface of the bottom of the reaction tank extends).

  Although the number of the inlets 26 is not particularly limited, it is preferable that the number of the inlets be plural in order to enhance the diffusibility of drainage. In the case where a plurality of inlets 26 are installed, it is preferable to arrange them at intervals of, for example, 0.5 m to 5 m from the viewpoint of improving the diffusibility of drainage. If the inlet 26 is opened so as to supply the wastewater into the biological sludge layer in the horizontal direction, the inlet 26 is located at a position higher than the interface position of the biological sludge layer formed on the bottom of the reaction tank 10 in the settling process. You may.

  Further, the reaction tank 10 of the present embodiment includes an outlet 28 for discharging treated water biologically treated in the reaction tank 10. In the reaction tank 10 shown in FIG. 1, an outlet 28 is provided on a side opposite to one side of the reaction tank 10 in which the inlet 26 is provided. The outlet 28 is arranged at the level of the water surface of the reaction vessel 10 (substantially, the lower end of the outlet 28 is located at the level of the water level of the reaction vessel 10). In the present embodiment, as described later, since the treated water is discharged together with the inflow of the wastewater, the water level of the reaction tank 10 does not substantially fluctuate.

  The raw water introduction pipe 12 constituting the raw water introduction device is connected to the inlet 26 from outside the reaction tank 10. The raw water introduction pipe 12 is provided with a raw water pump 14 and an electromagnetic valve 16 that constitute a raw water introduction device. The raw water pump 14 and the electromagnetic valve 16 are electrically connected to the control device 24. The raw water introduction device is not limited to the above device configuration as long as it has a function of supplying drainage to the inflow port 26 provided in the reaction tank 10.

  The treated water collecting channel 22 shown in FIG. 1 is installed outside the reaction tank 10 and communicates with the inside of the reaction tank 10 through a discharge port 28 provided in the reaction tank 10.

  The blower 18 constituting the air diffuser is connected to the air diffuser 20, and aeration gas such as oxygen and air is sent to the air diffuser 20 by the blower 18, and the aeration gas is supplied into the reaction tank 10 by the air diffuser 20. Is done. Thereby, the water in the reaction tank 10 flows and is stirred. Although not described in the drawings, for example, a stirring device in which the stirring blades rotate with the rotation of the motor may be installed in the reaction tank 10 to stir the water in the reaction tank 10. The water treatment apparatus 1 shown in FIG. 1 is intended for biological treatment under aerobic conditions, but is also applicable to biological treatment under anaerobic conditions. When processing is performed under anaerobic conditions, a stirring device may be installed without installing a diffuser.

  The control device 24 includes, for example, a microcomputer configured with a CPU that calculates a program, a ROM and a RAM that stores the program and the calculation result, and an electronic circuit, and has a function of controlling the operation of the air diffuser and the raw water introduction device. It has.

  Hereinafter, an example of the operation of the water treatment apparatus 1 of the present embodiment will be described.

  The electromagnetic valve 16 is opened by the control device 24, and the raw water pump 14 is operated, so that the wastewater passes through the raw water introduction pipe 12 and flows into the reaction tank 10 from the inlet 26. It is desirable that biological sludge be charged in the reaction tank 10 in advance.

  FIG. 2 is a schematic cross-sectional view illustrating an example of a state of the water treatment device during the biological treatment step. When the water level of the waste water in the reaction tank 10 reaches a predetermined water level, the control device 24 closes the electromagnetic valve 16, stops the operation of the raw water pump 14, and starts the blower 18. Thereby, as shown in FIG. 2, the aeration gas is supplied from the diffuser 20 into the reaction tank 10, and the wastewater and the biological sludge in the reaction tank 10 are stirred. Then, the wastewater in the reaction tank 10 is biologically treated with biological sludge (biological treatment step), and the substances to be treated (eg, organic substances) in the wastewater are decomposed.

  FIG. 3 is a schematic cross-sectional view illustrating an example of a state of the water treatment device during the settling process. After performing the biological treatment step for a predetermined time, the operation of the blower 18 is stopped by the control device 24, and the stirring and aeration of the wastewater in the reaction tank 10 are stopped. Thereby, as shown in FIG. 3, the settling of the biological sludge is performed (settling step), and the biological sludge layer 30 is formed on the bottom of the reaction tank 10.

  FIG. 4 is a schematic cross-sectional view showing an example of the state of the water treatment device during the inflow / outflow process. After the settling process is performed for a predetermined time and the biological sludge layer 30 is formed on the bottom of the reaction tank 10, the raw water pump 14 is operated by the control device 24, the electromagnetic valve 16 is opened, and the wastewater is drained. The raw water is supplied to the inlet 26 from the raw water introduction pipe 12. Thereby, as shown in FIG. 4, the wastewater is supplied from the inlet 26 to the biological sludge layer 30 in the horizontal direction, and the biologically treated water that has been biologically treated in the reaction tank 10 is discharged from the outlet 28. The water is discharged to the catchment channel 22 (inflow / discharge process). The treated water is discharged from the treated water collecting channel 22 to the outside of the water treatment apparatus 1. Then, after performing the inflow / outflow process for a predetermined time, the process returns to the biological treatment process described above. That is, an operation cycle in which the inflow / discharge process, the biological treatment process, and the sedimentation process are repeated is performed.

  Here, it is thought that the extracellular matrix (EPS) produced by bacteria affects the formation of highly sedimentable biological sludge (eg, granulated biological sludge) in the above operation cycle. In order to form EPS, it is important to form a concentration gradient of the substance to be treated that is biologically treated in the reaction tank 10. For example, when biologically treating organic matter in wastewater, it is important to form a concentration gradient of organic matter, and when biologically treating a nitrogen-containing substance such as ammonia nitrogen or nitrate nitrogen, a nitrogen-containing substance is required. It is important to form a concentration gradient. The concentration gradient of the substance to be treated increases the concentration of the substance to be treated in the reaction tank 10 in the inflow / emission step (saturated state), and causes the substance to be treated in the reaction tank 10 to be consumed in the biological treatment step. Is formed by lowering the concentration of the substance to be treated in the reaction tank 10 (starved state). Then, as in the present embodiment, in the inflow / discharge process, by allowing the wastewater to flow horizontally into the biological sludge layer 30 from the inflow port 26, it is possible to ensure a sufficient path for the wastewater to contact the biological sludge. As a result, the substance to be treated in the wastewater is likely to remain in the tank. Thereby, in the inflow / discharge process, the concentration of the substance to be treated remaining in the reaction tank 10 can be efficiently increased, and the concentration gradient of the substance to be treated in the reaction tank 10 can be increased. . As a result, it becomes possible to form biological sludge having high sedimentation, and it is possible to improve the biological treatment speed. When the wastewater is supplied into the biological sludge layer 30 in an upward flow (that is, wastewater is supplied vertically into the biological sludge layer 30), the thickness of the biological sludge layer 30 formed in the reaction tank 10 is increased. If the water is not thick to some extent, it is not possible to secure a sufficient path for the wastewater to come into contact with the biological sludge, and it is difficult to efficiently increase the concentration of the substance to be treated remaining in the reaction tank 10. However, in the case of the horizontal inflow of the present embodiment, even when the biological sludge layer 30 formed in the reaction tank 10 is thin, compared with the case of the upward flow described above, the wastewater is drained. Since a sufficient path for contacting with the target is ensured, the concentration of the substance to be treated remaining in the reaction tank 10 can be increased. Moreover, according to the water treatment apparatus 1 of the present embodiment, unlike a conventional water treatment apparatus, it is not necessary to install a distributor for inflow of wastewater, so that an increase in facility costs and operation management costs is suppressed. You. In particular, it is considered that by applying the water treatment apparatus 1 of the present embodiment as a water treatment apparatus for a large-scale treatment facility, facility costs and operation management costs can be effectively reduced.

  The highly sedimentable biological sludge formed by the water treatment apparatus 1 of the present embodiment may be used for its own biological treatment, or may be taken out of the reaction tank 10 and supplied to another biological treatment tank. The other biological treatment tank may be a semi-batch type as in the present embodiment, or a continuous type in which biological treatment is performed while continuously introducing wastewater. Thereby, for example, the biological treatment speed in another biological treatment tank can be improved. Further, the biological treatment water obtained by the water treatment apparatus 1 of the present embodiment may be supplied to another biological treatment tank (continuous or semi-batch type). Thereby, for example, it is possible to improve the quality of the biological treatment water.

  The operating conditions and modified examples of the water treatment apparatus of the present embodiment will be described below.

  The wastewater applied to the water treatment apparatus 1 of the present embodiment is, for example, a biodegradable substance such as food processing factory wastewater, chemical factory wastewater, semiconductor factory wastewater, machine factory wastewater, sewage, human waste, or river water. Wastewater containing the target substance). The substance having biodegradability is, for example, an organic substance, a nitrogen-containing substance such as ammoniacal nitrogen, nitrate nitrogen, or the like. For example, when biologically treating wastewater containing organic matter, the organic matter in the wastewater is decomposed into carbon dioxide by contact with biological sludge (microorganisms). In addition, for example, when biologically treating wastewater containing a nitrogen-containing substance, the nitrogen-containing substance in the wastewater is decomposed into nitrogen gas by contact with biological sludge (microorganisms).

  If the wastewater applied to the water treatment apparatus 1 according to the present embodiment contains a large amount of fats and oils, the biological treatment may be adversely affected. It is preferable to remove oils and fats to about 150 mg / L or less, for example, by an existing method such as coagulation pressure flotation and adsorption.

  The BOD concentration in the wastewater applied to the water treatment device 1 of the present embodiment is not particularly limited. In general, the BOD concentration in wastewater in which it is difficult to form highly sedimentable biological sludge is in the range of 50 to 200 mg / L, but according to the water treatment apparatus 1 according to the present embodiment, Even in the range of the BOD concentration, it is possible to form a biological sludge having high sedimentation. In addition, in the water treatment apparatus 1 according to the present embodiment, for example, it is possible to form a biological sludge having a sedimentation index of SVI30 of 50 mL / g or less and SVI5 of 70 mL / g or less.

  In the inflow / outflow process, increasing the concentration of the substance to be treated in the reaction tank 10 (to increase the substance to be treated in the reaction tank 10 at the time of starting the biological treatment step) is effective for forming granules. The residual ratio of the substance to be treated in the reaction tank 10 in the discharge step is preferably 50% or more, more preferably 70% or more. Here, the residual ratio of the substance to be treated in the reaction tank 10 indicates the ratio of the concentration of the substance to be treated in the tank after the inflow / outflow process to the concentration of the substance to be treated in the wastewater.

  The installation position of the inlet 26 is not particularly limited as long as it is lower than the interface position of the biological sludge layer 30 formed on the bottom of the reaction tank 10 in the settling step. Assuming that the effective water depth is designed to be 2 m to 8 m, and the interface height of the biological sludge layer 30 is operated at 10% to 50% of the height of the reaction tank 10, the inflow port 26 is connected to the reaction tank 10. It is preferably installed at a height within 4 m from the bottom, more preferably at a height within 2 m, even more preferably at a height within 1 m.

  The inflow rate of the drainage water is preferably, for example, in a range of 10% or more and 100% or less. The inflow rate of the wastewater is a ratio of the inflow amount of the wastewater in one operation cycle to the effective volume in the reaction tank 10. Here, in order to increase the concentration of the substance to be treated remaining in the reaction tank 10, it is better to set the inflow rate of the wastewater as high as possible. On the other hand, the higher the inflow rate of the wastewater, the more the wastewater is discharged. There is a concern that treated water will deteriorate due to short-circuits in the water. Therefore, in view of these, it is more preferable that the inflow rate of the wastewater be in the range of 20% or more and 80% or less. However, as long as a treatment device such as an activated sludge tank is installed at the subsequent stage of the reaction tank 10 and the quality of the final treated water after the latter treatment device is not deteriorated, the inflow rate of the wastewater is not particularly limited, and for example, exceeds 100%. It is also possible to use When the inflow rate of the wastewater exceeds 100%, it is preferable to set the upper limit of the inflow rate of the wastewater to 200% or less in order to suppress a decrease in the number of operation cycles.

  The inflow / discharge process time is determined, for example, according to the inflow rate of the wastewater and the flow rate of the wastewater to the reaction tank 10. By the way, when the water area load of the reaction tank 10 which is a value obtained by dividing the flow rate of the wastewater to the reaction tank 10 by the horizontal sectional area of the reaction tank 10 is set high, the light sludge fraction in the sludge is selectively removed from the system. It is possible to discharge and leave a highly sedimentable sludge fraction in the tank, which promotes the formation of highly sedimentable biological sludge.However, during the start-up period when the sedimentation of sludge is not high, There is a concern that sludge in the tank may flow out and the biological treatment function may deteriorate. On the other hand, when the water area load of the reaction tank 10 is set low, the selection effect of the sludge decreases, and when the inflow rate of the wastewater is increased, the inflow / discharge process time becomes long, and the formation of sludge with high sedimentability There is a concern that this will be difficult. In view of the above circumstances, the water area load on the reaction tank 10 is preferably 0.5 m / h or more and 20 m / h or less, and more preferably 1 m / h or more and 10 m / h or less. If the water area load of the reaction tank 10 can be set high with the improvement of the sedimentation property of the biological sludge in the tank, the water area of the reaction tank 10 can be set according to the sedimentation property of the biological sludge. It is also possible to increase the load and shorten the inflow / drainage process time according to the water area load and the inflow rate of wastewater.

  The sludge concentration in the reaction tank 10 in the biological treatment step is preferably, for example, in the range of 1,500 to 30,000 mg / L from the viewpoint of maintaining the soundness of the sludge (sedimentation, activity, etc.). Further, the sludge load is preferably in the range of 0.05 to 0.60 kg-BOD / kg-MLSS / day from the viewpoint of maintaining the soundness of the sludge, and 0.1 to 0.5 kg-BOD / day. More preferably, it is in the range of kg-MLSS / day. The biological treatment process time is set, for example, so that the sludge load is in the above range. When the sludge load is higher than the above range or when the sludge concentration is higher than the above range, it is desirable to pull out the biological sludge from the inside of the reaction tank 10.

  The pH in the reaction tank 10 is desirably set in a range suitable for general microorganisms, for example, preferably 6 to 9, and more preferably 6.5 to 7.5. When the pH value is out of the above range, it is preferable to add an acid or an alkali to adjust the pH so as to be in the above range. The dissolved oxygen (DO) in the reaction tank 10 is desirably 0.5 mg / L or more, particularly preferably 1 mg / L or more under aerobic conditions.

  The time of the sedimentation step is not particularly limited as long as it is a time from the end of the biological treatment step to the formation of the biological sludge layer 30 on the bottom of the reaction tank 10. It is preferable that the time is such that the height of the sludge interface becomes 10% to 50% of the height of the reaction tank 10.

  The shape of the reaction tank 10 is not limited to a square shape as shown in FIG. 1, but may be, for example, a cylindrical shape. The rectangular reactor 10 is employed in a large-scale treatment plant such as a sewage treatment plant. Hereinafter, an example of a square reaction tank used in a large-scale treatment plant will be described.

  FIG. 5 is a schematic top view showing an example of a rectangular reaction tank used in a large-scale treatment plant. The rectangular reaction vessel 10 shown in FIG. 5 is a rectangular reaction vessel having a pair of opposed long side walls (10a, 10b) and a pair of opposed short side walls (10c, 10d) in a horizontal sectional view. It is. A plurality of inlets 26 are provided on one long side wall 10 a of the reaction tank 10, and an outlet 28 is provided on the other long side wall 10 b of the reaction tank 10. Further, a treated water collecting channel 22 is provided outside the other long side wall 10 b, and the treated water collecting channel 22 communicates with the inside of the reaction tank 10 via a discharge port 28. Although not shown in the drawings, the outlet 28 is disposed at the water level in the reaction tank 10, and the inlet 26 is lower than the interface position of the biological sludge layer formed at the bottom of the reaction tank 10 in the settling process. Is located in the position. Then, the wastewater is supplied from the inlet 26 into the biological sludge layer in the horizontal direction.

  In the case of the reaction tank 10 employed in a large-scale treatment plant, the ratio of the horizontal sectional area of the reaction tank 10 to the effective water depth of the reaction tank 10 tends to increase. As a square-shaped reaction tank employed in a large-scale treatment plant, for example, [(long side wall length + short side wall length) / effective water depth] is preferably 1 m / m or more, More preferably, it is 1.8 m / m 2 or more. However, in the conventional water treatment apparatus in which the wastewater flows into the reaction tank 10 in an upward flow by the distributor, [(length of the long side wall + length of the short side wall) / effective water depth] is 1 m / m or more. The use of a reaction tank may significantly increase facility costs and operation management costs in terms of drainage diffusivity and distributor maintenance. On the other hand, if the water treatment apparatus of the present embodiment employs a reaction tank in which [(long side wall length + short side wall length) / effective water depth] is 1 m / m or more, no distributor is required. Therefore, the increase in facility costs and operation management costs can be suppressed as compared with the above-described conventional water treatment apparatus. Therefore, the water treatment device of the present embodiment is particularly suitable as a water treatment device for a large-scale treatment facility.

  It is preferable that the inlet 26 and the outlet 28 are installed at the inlet 26 on one long side wall 10a and the outlet 28 at the other long side wall 10b. When the inlet 26 is installed on one short side wall 10c and the outlet 28 is installed on the other short side wall 10d, compared with the case where the inlet 26 and the outlet 28 are installed on the long side walls (10a, 10b). Since the horizontal distance from the inlet 26 to the outlet 28 increases, the contact efficiency between the wastewater and the biological sludge layer decreases, and the concentration of the target substance remaining in the reaction tank 10 may decrease. .

  The horizontal distance from the inlet 26 to the outlet 28 is, for example, preferably within 10 m, more preferably within 6 m, from the viewpoint of suppressing a decrease in the concentration of the substance to be treated remaining in the reaction tank 10. When the horizontal distance from the inlet 26 to the outlet 28 exceeds 10 m, it is difficult to efficiently contact the wastewater with the biological sludge layer, and the concentration of the substance to be treated remaining in the reaction tank 10 is reduced. There are cases.

  FIG. 6 is a schematic top view showing another example of a square-shaped reaction tank employed in a large-scale treatment plant. The reaction tank 10 shown in FIG. 6 has a first inlet 26a provided on one side surface of the reaction tank 10, and a second inlet 26b provided between the first inlet 26a and the outlet 28. . Each of the inlets (26a, 26b) is disposed at a position lower than the interface position of the biological sludge layer formed on the bottom of the reaction tank 10 in the settling step.

  FIG. 7A is a schematic cross-sectional view showing another example of a square-shaped reaction tank employed in a large-scale processing plant, and FIG. FIG. 4 is a schematic top view showing another example of the reaction tank having the shape of a circle. The reaction tank 10 shown in FIG. 7 includes the first inlet 26a and the second inlet 26b described above. In the reaction tank 10, a first treated water collecting passage 22a and a second treated water collecting passage 22b are provided. The first treated water collecting channel 22a is installed inside a side surface opposite to the one side surface of the reaction tank 10 provided with the first inlet 26a, and the second treated water collecting passage 22b is connected to the first treated water collecting channel. It is provided between 22a and the 1st inflow port 26a. The treated water in the reaction tank 10 shown in FIG. 7 flows over the side walls of the first treated water collecting passage 22a and the second treated water collecting passage 22b, and the first treated water collecting passage 22a and the second treated water collecting passage 22b. And flows out of the reaction tank 10. That is, the first treated water collecting passage 22a and the second treated water collecting passage 22b shown in FIG. 7 function as the outlet 28 described above.

  When the horizontal distance between the inflow port provided on one side of the reaction tank and the discharge port provided on the side opposite to the one side is long, the reaction tank 10 shown in FIGS. As described above, it is preferable to provide one or more inlets and outlets between the inlet provided on one side of the reaction tank and the outlet provided on the side opposite to the one side. As a result, the contact efficiency between the wastewater and the biological sludge layer increases, and the concentration of the target substance remaining in the reaction tank tends to increase.

  FIG. 10A is a cross-sectional view illustrating another example of the water treatment apparatus of the present embodiment, and FIG. 10B is a schematic top view illustrating another example of the water treatment apparatus of the present embodiment. . In FIGS. 10A and 10B, the air diffuser including the blower 18 and the air diffuser 20 and the control device 24 are omitted. In FIG. 10, a raw water introduction pipe 12 is introduced into a central portion of the reaction tank 10, and is branched into a plurality of drainage inlets (26 a, 26 b) in the reaction tank 10. The treated water collecting channels (22a, 22b) are installed on two opposite sides of the reaction tank 10. The outlets of the drainage inlets (26a, 26b) are installed toward the respective treated water collecting channels (22a, 22b). In order to increase the residual ratio of the substance to be treated during the inflow / outflow process, it is preferable that the flow velocity at the inflow port calculated from the distance between the inflow port and the side face of the reaction tank is not less than a certain value. On the other hand, when the distance from the inlet to the side of the reaction tank facing the tank is long and it is difficult to keep the flow velocity high, by employing this embodiment, the distance from the inlet to the outlet is reduced, Even when the flow velocity at the inflow port is low, it is possible to increase the residual ratio of the substance to be treated during the inflow / outflow process.

  FIG. 8A is a schematic cross-sectional view illustrating another example of the water treatment apparatus of the present embodiment, and FIG. 8B is a schematic top view illustrating another example of the water treatment apparatus of the present embodiment. is there. In FIG. 8B, the air diffuser including the blower 18 and the air diffuser 20 and the control device 24 are omitted. In the water treatment apparatus 2 shown in FIG. 8, the same components as those of the water treatment apparatus 1 shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The water treatment apparatus 2 illustrated in FIG. 8 includes a distribution path 13 and a raw water pipe 15. The raw water introduction pipe 12 is connected to an upper end of a raw water pipe 15 via a distribution path 13. The raw water pipe 15 is a pipe extending in the vertical direction, and its upper end is located above the water level in the reaction tank 10, and its lower end is connected to the inlet 26. In the present specification, the pipe extending in the vertical direction includes a pipe extending in the substantially vertical direction. The substantially vertical direction includes a direction having an inclination angle of 30 ° or less with respect to the vertical direction. In addition, the raw water pipe 15 may be provided outside the reaction tank 10.

  In the inflow / discharge process of the water treatment apparatus 2 shown in FIG. 8, the electromagnetic valve 16 is opened by the control device 24, and the wastewater is supplied from the raw water introduction pipe 12 to the raw water pipe 15 via the distribution path 13. Then, the wastewater flows down in the raw water pipe 15 by gravity and is supplied in a horizontal direction from the inlet 26 into the biological sludge layer formed in the reaction tank 10. In addition, when the wastewater flows into the reaction tank 10, the biologically treated water in the reaction tank 10 is discharged from the outlet 28 to the treated water collecting channel 22. As described above, in the water treatment apparatus 2 shown in FIG. 8, the drainage can be caused to flow into the reaction tank 10 by gravity without using a pump, so that it is possible to reduce the cost of operation. For example, it is suitable for a sewage treatment plant having a large amount of treated water.

  FIG. 9A is a schematic cross-sectional view illustrating another example of the water treatment apparatus of the present embodiment, and FIG. 9B is a schematic top view illustrating another example of the water treatment apparatus of the present embodiment. is there. In FIG. 9B, the air diffuser including the blower 18 and the air diffuser 20 and the control device 24 are omitted. In the water treatment apparatus 3 shown in FIG. 9, the same components as those of the water treatment apparatus 1 shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The water treatment apparatus 3 shown in FIG. 9 has a distribution path 13 and a partition wall 17. The partition wall 17 is provided upright in the reaction tank 10 to partition the inside of the reaction tank 10 into a first chamber 10f and a second chamber 10g. An opening communicating the first chamber 10f and the second chamber 10g is provided below the partition 17, and the opening serves as the inflow port 26 described above. The discharge port 28 is provided on the side surface on the second chamber 10g side, and communicates with the treated water collecting channel 22 provided outside the second chamber 10g.

  In the reaction tank 10 shown in FIG. 9, the first chamber 10f partitioned by the partition 17 is a room for receiving drainage, and the second chamber 10g partitioned by the partition 17 is used for the above-mentioned operation cycle (inflow / outflow process, biological This is the room where the processing step and the settling step are performed.

  In the inflow / discharge process of the water treatment apparatus 3 shown in FIG. 9, the electromagnetic valve 16 is opened by the control device 24, and the wastewater is supplied from the raw water introduction pipe 12 to the first chamber 10 f via the distribution path 13. Then, the wastewater passes through the first chamber 10f and is supplied in a horizontal direction from the inlet 26 into the biological sludge layer formed on the bottom of the second chamber 10g. In addition, when the wastewater flows into the second chamber 10g, the biologically treated water in the second chamber 10g is discharged from the outlet 28 to the treated water collecting channel 22. After the inflow / outflow process, a biological treatment process and a sedimentation process are performed in the second chamber 10g.

  The shape of the opening (inflow port 26) provided in the partition wall 17 is not particularly limited, and may be a rectangular shape, a circle or an ellipse, or the like. In addition, at least one opening (inflow port 26) may be formed in the partition 17.

  The position of the partition wall 17 is not particularly limited. However, the position of the first chamber 10f in the vertical sectional view of the reaction tank 10 is such that the wastewater can be efficiently brought into contact with the biological sludge layer in the second chamber 10g. It is preferable that the partition wall 17 is provided so that the width ratio is 1/2 or less with respect to the width of the second chamber 10g, and it is more preferable that the partition wall 17 is provided so that the width ratio becomes 1/5 or less.

  FIG. 11A is a schematic cross-sectional view illustrating another example of the water treatment apparatus of the present embodiment, and FIG. 11B is a schematic top view illustrating another example of the water treatment apparatus of the present embodiment. is there. In FIG. 11B, the air diffuser including the blower 18 and the air diffuser 20 and the control device 24 are omitted. In the water treatment apparatus 4 shown in FIG. 11, the same components as those of the water treatment apparatus 1 shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The reaction tank 10 shown in FIG. 11 is a rectangular reaction tank having a pair of opposed walls (10a, 10b) and a pair of opposed walls (10c, 10d) in a horizontal sectional view. A plurality of inlets 26 are provided on one long side wall 10a of the reaction tank 10 and an outlet 28 is also provided. The discharge port 28 is arranged at a water level in the reaction tank 10, and the inflow port 26 is arranged at a position lower than the interface position of the biological sludge layer formed at the bottom of the reaction tank 10 in the settling process. Then, the waste water is supplied from the inlet 26 into the biological sludge tank in the horizontal direction. When the inflow port 26 and the discharge port 28 are installed on the same wall surface, the wastewater is ejected from the inflow port 26 into the sediment with a flow velocity of a certain level or more, and the wastewater reaches the wall surface opposite to the inflow port. In addition, since it does not rise as it is toward the outlet as an ascending flow, it is possible to prevent a short path of the substance to be treated.

  FIG. 12A is a schematic cross-sectional view illustrating another example of the water treatment apparatus of the present embodiment, and FIG. 12B is a schematic top view illustrating another example of the water treatment apparatus of the present embodiment. is there. In FIG. 12B, the air diffuser including the blower 18 and the air diffuser 20 and the control device 24 are omitted. In the water treatment apparatus 5 shown in FIG. 12, the same components as those of the water treatment apparatus 1 shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The water treatment apparatus 5 shown in FIG. 12 includes a distribution path 13 and a raw water pipe 15. The raw water introduction pipe 12 is connected to an upper end of a raw water pipe 15 via a distribution path 13. The raw water pipe 15 is a pipe extending in the vertical direction, and its upper end is located above the water level in the reaction tank 10, and its lower end is connected to the inlet 26. In the present specification, the pipe extending in the vertical direction includes a pipe extending in the substantially vertical direction. The substantially vertical direction includes a direction having an inclination angle of 30 ° or less with respect to the vertical direction. In addition, the raw water pipe 15 may be provided outside the reaction tank 10. Also in the water treatment device 5, similarly to the above-mentioned water treatment device 4, the inlet 26 and the outlet 28 are installed on the same wall surface.

  Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples.

(Example 1)
The following test was performed using the reaction tank shown in FIG. As the reaction tank, a reaction tank having a length of 146 mm (L), a width of 208 mm (W), a height of 300 mm (effective water depth of 200 mm (H)) and an effective volume of 6.1 L was used. A partition was installed at a position 25 mm away from one side of the reaction tank, and an inlet (opening) was provided at the lower end of the partition. The outlet was provided on the side opposite to one side of the reaction tank. The position of the outlet was set at the water level in the reaction tank.

  A sodium bromide solution (40 mgBr / L) was used as wastewater used for the test. Drainage and activated sludge were charged into the second chamber of the reaction tank and aerated and stirred for a predetermined time (biological treatment step). After the biological treatment step, the reaction tank was allowed to stand for a predetermined time (settling step). After the settling process, wastewater is supplied to the first chamber, and the biologically treated water in the second chamber is discharged from the discharge port while the wastewater is supplied horizontally from the inflow port into the biological sludge layer in the second chamber (inflow). / Discharge process). The flow rate of the wastewater was 0.6 m / h as a water area load, and the inflow / drainage process time was 32 minutes (the wastewater inflow amount was 150% of the effective volume of the water tank).

The bromine ion concentration in the reaction vessel after the inflow / outflow step was measured, and the residual bromine ion rate in the reaction vessel at the end of the inflow / outflow step was evaluated by the following equation. Table 1 shows the results. Since bromine ions are substances that are not easily affected by adsorption to biological sludge or biological reactions, if the residual rate of bromine ions in the reaction tank shows a high value, the concentration of the target substance remaining in the reaction tank Is also high.
Bromine ion remaining rate = (bromine ion concentration in reaction tank / hydrogen ion concentration in wastewater) × 100

(Comparative Example 1)
The same reaction tank as in Example 1 was used except that a current plate was installed in the second chamber of the reaction tank. The current plate is a rectangular plate of 250 cm ² (120 mm × 208 mm), and a plurality of holes having a diameter of 4 mm are formed in the entire plate. The rectifying plate was horizontally installed at a position 6 mm above the bottom of the second chamber (a position higher than the inlet of the partition). That is, the wastewater (sodium bromide solution) flows into the lower part of the current plate in the second chamber from the inflow port, and is then supplied upward from the holes in the current plate. Furthermore, since the biological sludge layer formed by the sedimentation step is formed on the current plate, the wastewater is supplied from the holes into the biological sludge layer in an upward flow.

  Similarly, in Comparative Example 1, the bromine ion concentration in the reaction tank after the inflow / discharge step was measured, and the residual ratio of bromine ions in the reaction tank at the end of the inflow / discharge step was evaluated. Table 1 shows the results.

  In Comparative Example 1, the residual ratio of bromine ions was 70%, whereas in Example 1, the residual ratio of bromine ions was improved to 82%. As described above, the embodiment in which the wastewater was supplied from the inlet into the biological treatment tank on the bottom of the reaction tank in the horizontal direction was compared with the comparative example in which the wastewater was supplied in the biological treatment tank in the upward flow, and Thus, it can be said that the concentration of the substance to be treated remaining in the reaction tank can be efficiently increased to the same level or more.

(Examples 2 and 3)
The following test was performed using the reaction tank shown in FIG. As the reaction tank, a reaction tank having a length of 438 mm (L), a width of 125 mm (W), a height of 750 mm (effective water depth of 600 mm) and an effective volume of 33 L was used. An inlet was provided at the bottom of the side surface of the reaction tank (a surface of 125 × 750). However, in Example 2, the outlet was provided on the side opposite to the side on which the inflow port was installed, and in Example 3, the outlet was provided on the same side as the side on which the inflow was installed. The positions of the outlets of Examples 2 and 3 were set at the water level in the reaction tank.

  Sodium bromide solution (40 mgBr / L) was used as waste water used for the test. Drainage water and activated sludge were charged into the reaction tank and aerated and stirred for a predetermined time (biological treatment step). After the biological treatment step, the reaction tank was allowed to stand for a predetermined time (settling step). After the sedimentation step, wastewater was supplied through the drainage inlet so as to hit the settled sludge in the horizontal direction, and the biologically treated water in the reaction tank was discharged from the discharge port (inflow / drainage step). At that time, the flow rate of the wastewater at the inlet was changed and supplied within the range of the conditions shown in Table 2. The supply amount was 100% of the effective volume of the reaction tank. N in the table is a horizontal distance N (m) from the inlet to the side surface of the reaction tank facing the inlet.

  The bromine ion concentration in the reaction tank after the inflow / outflow step was measured, and the bromine ion remaining rate in the reaction tank at the end of the inflow / outflow step was evaluated by the above equation. The result is shown in FIG.

FIG. 13 is a diagram showing the results of the bromine ion residual ratio with respect to the flow rate at the inlet in Examples 2 and 3. As shown in FIG. 13, the residual ratio of bromine ions was 50% or more under any of the conditions. Among the implemented conditions, the highest residual rate was obtained under the condition of a flow velocity of 37.8 cm / sec at the inlet. From the above, when the flow velocity v at the inlet is in the range of [N ^1/2 × 20] ≦ v ≦ [N ^1/2 × 80], the residual ratio of the target substance in the wastewater in the inflow / outflow process is 50%. It was confirmed that this was the case. In addition, a comparison was made between the inlet and outlet on the same side and the opposite side of the reaction tank side, and the condition where both were installed on the same side resulted in a higher residual ratio of bromine ions. It was confirmed that the discharge port was preferably installed on the same side.

(Example 4)
Next, a test was performed using the reaction tank shown in FIG. As the reaction tank, a reaction tank having a length of 3 m, a width of 1 m, an effective water depth of 5 m, and an effective volume of 15 m ³ was used. An inlet was installed at the lower part of the side of the reaction tank, and an outlet was installed on the same side as the side where the inlet was installed. The outlet was located at the surface of the water in the reactor. The test method was the same as that in Example 3 except that the flow velocity conditions at the inlet were as shown in Table 3.

  The results of the bromine ion residual ratio were 91% under the condition 7, 76% under the condition 8, and 86% under the condition 9, all of which were 70% or more.

(Example 5)
The following granule formation test was performed using the reaction tank shown in FIG. As the reaction tank, a reaction tank having a length of 220 mm (L), a width of 125 mm (W), a height of 400 mm (effective water depth of 300 mm) and an effective volume of 33 L was used. An inlet was provided at the bottom of the side surface of the reaction tank (125 × 220 surface). An outlet was provided on the side opposite to the side where the inlet was installed. The position of the outlet was set at the water level in the reaction tank. N in this reactor was 0.22 m.

The operation process was an operation in which the inflow / discharge process, the aeration process, and the sedimentation process were repeated. Activated sludge from a sewage treatment plant was introduced into the reaction tank as initial sludge, and the change in the properties of the sludge in the reaction tank was investigated. Simulated sewage containing bonito extract and peptone as main components was used as influent water, and the BOD was 100 mg / L. In the inflow / outflow process, the simulated sewage was introduced from an inlet provided on the side of the reaction tank so as to come into contact with the sludge, and the flow rate at the inlet was set to a range of 11-28 cm / sec (v / N ^1/2 of v / N ^1/2 ). The value ranges from 23.5 to 60). The inflow amount of the wastewater in one inflow / outflow process was set to 100% of the effective volume of the reaction tank.

FIG. 14 shows the transition of SVI5 and SVI30 which are the sedimentation index of the sludge in the reaction tank. In addition, SVI5 is a sedimentation index of biological sludge, and is determined as follows. First, 1 L of sludge is put into a 1 L measuring cylinder, and after stirring, the sludge interface is measured when the sludge is allowed to stand for 5 minutes or 30 minutes. Then, the volume ratio (%) of the sludge in the measuring cylinder is calculated. Next, the MLSS (mg / L) of the sludge is measured. These are applied to the following equation to calculate SVI5 or SVI30. The smaller the value of SVI5 or SVI30, the higher the sedimentation property of the sludge.
SVI (mL / g) = Volume ratio occupied by sludge × 10,000 / MLSS

  As shown in FIG. 14, no change was observed in SVI during the first 15 days of the startup, and both SVI5 and SVI30 changed at 300-350 mL / g. Thereafter, a sharp decrease in SVI was confirmed, and formation of sludge having a good sedimentation property of 20 mL / g in both SVI5 and SVI30 was confirmed 35 days after startup.

  FIG. 15 shows the input sludge and a sludge observation photograph 50 days after startup. Each bar indicates 500 μm. As shown in FIG. 15, the input sludge was composed of dispersed sludge, whereas the sludge after 50 days was composed of good granular sludge of about 200 to 300 μm.

  1-5 water treatment device, 10 reaction tank, 10a, 10b long side wall, 10c, 10d short side wall, 10f first room, 10g second room, 12 raw water introduction pipe, 13 distribution channel, 14 raw water pump, 15 raw water Piping, 16 solenoid valve, 17 partition, 18 blower, 20 diffuser pipe, 22 treated water catchment channel, 24 controller, 26 inlet, 28 outlet, 30 biological sludge layer.

Claims (12)

In a tank provided with an inlet and an outlet, using a reaction tank containing biological sludge, a water treatment method for biologically treating wastewater,
An inflow / discharge step of discharging biological treatment water in the reaction tank from the discharge port while flowing the wastewater into the reaction tank from the inflow port; and biologically treating the wastewater in the reaction tank with biological sludge. A biological treatment step, and a settling step of settling the biological sludge in the reaction tank, comprising an operation cycle step to repeat,
The outlet is disposed at a water level in the reaction vessel,
The water treatment method, wherein the inflow port supplies at least a part of the wastewater in a horizontal direction into a biological sludge layer formed at the bottom of the reaction tank in the settling step.   The water treatment method according to claim 1, wherein the inflow port is disposed at a position lower than an interface position of a biological sludge layer formed at the bottom of the reaction tank in the settling step. A vertically extending pipe is connected to the inflow port,
The water treatment method according to claim 1, wherein the supply of the wastewater to the inflow port is performed by gravity from the pipe. The reaction tank is partitioned by a partition into a first chamber into which the wastewater is introduced and a second chamber for performing the operation cycle step,
The outlet is provided on the second chamber side, and is disposed at a water level in the second chamber,
The inflow port is provided in the partition wall such that the first chamber and the second chamber communicate with each other, and is located at a position lower than an interface position of a biological sludge layer formed at the bottom of the second chamber in the settling step. 3. The water treatment method according to claim 1, wherein the wastewater is supplied in a horizontal direction into a biological sludge layer formed at a bottom of the second chamber. 4.   The water treatment according to any one of claims 1 to 3, wherein the reaction tank is a square water tank, and the inflow port and the discharge port are provided on the same surface of the square water tank. Method. The flow velocity v (cm / sec) of the drainage water at the inlet and a horizontal distance N (m) from the inlet to the side surface of the reaction tank facing the inlet satisfy the following expression. The water treatment method according to claim 1.
20 ≦ v / N ^1/2 ≦ 80 In a tank provided with an inlet and an outlet, a reaction tank containing biological sludge is provided,
An inflow / discharge step of discharging biological treatment water in the reaction tank from the discharge port while flowing wastewater into the reaction tank from the inflow port; and biologically treating the wastewater in the reaction tank with biological sludge. A biological treatment step, a sedimentation step of sedimentation of the biological sludge in the reaction tank, a water treatment apparatus performing an operation cycle step to repeat,
The outlet is installed at a water level in the reaction vessel,
The water treatment apparatus, wherein the inflow port supplies at least a part of the wastewater in a horizontal direction into a biological sludge layer formed in a bottom portion of the reaction tank in the settling step.   The water treatment apparatus according to claim 7, wherein the inflow port is provided at a position lower than an interface position of the biological sludge layer formed at the bottom of the reaction tank in the settling step. With vertically extending piping,
9. The water treatment apparatus according to claim 7, wherein the pipe is connected to the inlet, and the drainage is supplied to the inlet by gravity from the pipe. 10. The reaction tank includes a partition for partitioning the inside of the tank into a first chamber into which the wastewater is introduced and a second chamber for performing the operation cycle process.
The outlet is provided on the second chamber side, and is disposed at a water level in the second chamber,
The inflow port is provided in the partition wall such that the first chamber and the second chamber communicate with each other, and is located at a position lower than an interface position of a biological sludge layer formed at the bottom of the second chamber in the settling step. 9. The water treatment apparatus according to claim 7, wherein the wastewater is supplied horizontally to a biological sludge layer formed at the bottom of the second chamber. 9.   The water treatment according to any one of claims 7 to 9, wherein the reaction tank is a square water tank, and the inflow port and the discharge port are provided on the same surface of the square water tank. apparatus. The flow velocity v (cm / sec) of the drainage at the inlet and the horizontal distance N (m) from the inlet to the side surface of the reaction tank facing the inlet satisfy the following expression. The water treatment device according to any one of claims 7 to 11.
20 ≦ v / N ^1/2 ≦ 80