Water treatment method and water treatment device

Abstract

Provided are a water treatment method and a water treatment device that make it possible to improve a granule existence ratio in a continuous biological treatment tank in the water treatment device configured to charge granule sludge formed in a semi-batch type reaction tank into the continuous biological treatment tank and treat the granule sludge by membrane separation. The water treatment method includes: a continuous biological treatment step for biologically treating water to be treated, with biological sludge, while causing the water to be treated to continuously flow into a continuous biological treatment tank (14) and stirring the water to be treated by a stirring device (26); a membrane separation step for separating biologically treated water obtained in the continuous biological treatment step and the biological sludge by a filtration membrane; and a sludge supply step for supplying granule sludge formed in a semi-batch type biological treatment tank (12) to the continuous biological treatment tank (14). The peripheral speed of stirring by the stirring device (26) in the continuous biological treatment step is 120 cm / sec or less.

Description

Water treatment method and water treatment apparatus

[0001] The present invention relates to a water treatment method and a water treatment apparatus.

[0002] While the activated sludge method, which consists of a reaction tank containing biological sludge for wastewater treatment and a sedimentation tank for solid-liquid separation of treated water and biological sludge, is the mainstream method for biological treatment of wastewater, the quality of treated water due to solid-liquid separation depends on the settling performance of the sludge, and the quality of treated water may deteriorate depending on the properties of the sludge.

[0003] In such biological treatments, a wastewater treatment system is known in which granular sludge formed in a semi-batch reactor is introduced into a continuous biological treatment tank and treated by membrane bioreactor (MBR) (see, for example, Patent Document 1). In the wastewater treatment system of Patent Document 1, the granular treated water generated in the semi-batch reactor may be supplied to the continuous biological treatment tank or discharged outside the system.

[0004] It is known that granule formation is promoted by repeatedly alternating between satiety and starvation. Systems have been proposed that create these conditions within a granule formation tank to induce granule formation, and then feed the formed granules into mainstream activated sludge treatment or MBR. For example, as described in Patent Document 2, a method is known in which the granule formation tank is operated under semi-batch conditions, where there are sufficient organic matter immediately after the inflow of raw water under satiety conditions, and near the end of the reaction time, the treatment is complete and there is almost no dissolved organic matter under starvation conditions to promote granule formation.

[0005] Furthermore, there are methods such as installing a granule-forming tank in the mainstream and intermittently adding methanol to the granule-forming tank, as described in Patent Document 3 for nitrogen treatment, to create temporal fluctuations in organic matter concentration within the granule-forming tank, or setting the granule-forming tank and the denitrification tank installed behind it to be under saturation conditions and the denitrification tank under starvation conditions.

[0006] However, in the wastewater treatment devices described in Patent Documents 1-3, the granules may shrink within the wastewater treatment device, and the granule abundance in the continuous biological treatment tank may not increase.

[0007] On the other hand, in biological treatment of wastewater using filtration membranes, the membrane cost accounts for a high proportion of the total equipment cost. Therefore, increasing the flux of the filtration membrane (the amount of filtration per day relative to the filtration membrane area (unit: m / day)) is very effective in reducing equipment costs. However, increasing the flux of the filtration membrane can lead to problems such as the pores of the filtration membrane becoming clogged with biological sludge, which increases the differential pressure of the membrane and makes stable operation difficult.

[0008] Patent Document 1 discloses a method for increasing the flux of a filtration membrane, which involves using granular sludge with a particle size of 100 μm or more and setting the proportion of granular sludge in the reaction tank to 10% or more. In addition to increasing the flux, an advantage of increasing the proportion of granular sludge in the reaction tank is that the oxygen transfer rate is improved by reducing the sludge viscosity, which in turn makes it possible to reduce the power of the aeration blower. A system is shown in which granular sludge is formed in a semi-batch biological treatment tank and supplied to a continuous biological treatment tank where a membrane separation activated sludge reaction is performed, as a method for increasing the proportion of granular sludge in the reaction tank. In this method, it is important to stably supply granular sludge from the semi-batch biological treatment tank to the continuous biological treatment tank, but the detailed method for doing so is not disclosed in Patent Document 1. Furthermore, in this system, if there are large fluctuations in the inflow load to the system, granular formation in the semi-batch biological treatment tank may become unstable, making it difficult to stably supply granular sludge to the continuous biological treatment tank.

[0009] Japanese Patent Publication No. 2018-030085, Japanese Patent Publication No. 5963668, Japanese Patent Publication No. 5355314

[0010] The object of the present invention is to provide a water treatment method and a water treatment apparatus that improve the granule content in a continuous biological treatment tank in which granule sludge formed in a semi-batch reaction tank is introduced and treated by membrane separation.

[0011] Another object of the present invention is to provide a water treatment method and a water treatment apparatus that enable stable granule formation, granule supply, and stable treatment even when there are fluctuations in the inflow load, in a water treatment where granule sludge formed in a semi-batch biological treatment tank is supplied to a continuous biological treatment tank and treated by membrane separation.

[0012] The present invention relates to a water treatment method comprising: a continuous biological treatment step in which water to be treated is continuously fed into a continuous biological treatment tank and treated with biological sludge while being stirred by an agitator; a membrane separation step in which the biologically treated water obtained in the continuous biological treatment step and the biological sludge are separated by a filtration membrane; and a sludge supply step in which granular sludge formed in a semi-batch biological treatment tank is supplied to the continuous biological treatment tank, wherein the peripheral speed of stirring by the agitator in the continuous biological treatment step is 120 cm / sec or less.

[0013] In the water treatment method described above, it is preferable that the granular sludge has an average particle size of 200 μm or more, and that the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

[0014] In the water treatment method described above, it is preferable to include a circulation step in which sludge is circulated from the sludge outlet to the sludge inlet of the continuous biological treatment tank using an air-lift pump as the circulation pump.

[0015] In the water treatment method described above, the amount of membrane cleaning air per unit volume of the continuous biological reaction tank is 6.4 m³. ３ / h / m ３ The following is preferable.

[0016] The present invention relates to a water treatment apparatus comprising: a continuous biological treatment means for continuously flowing treated water into a continuous biological treatment tank and biologically treating the treated water with biological sludge while stirring with a stirring device; a membrane separation means for separating the biologically treated water obtained by the continuous biological treatment means and the biological sludge with a filtration membrane; and a sludge supply means for supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the peripheral speed of the stirring by the stirring device in the continuous biological treatment means is 120 cm / sec or less.

[0017] In the water treatment apparatus, it is preferable that the granular sludge has an average particle size of 200 μm or more, and the granular sludge is supplied to the continuous biological treatment tank so that the abundance ratio of the granules is 10% or more with respect to the amount of sludge in the continuous biological treatment tank.

[0018] In the water treatment apparatus, it is preferable to provide circulation means for circulating sludge from the sludge outlet of the continuous biological treatment tank to the sludge inlet using an air lift pump as a circulation pump.

[0019] In the water treatment apparatus, the amount of membrane cleaning air per tank volume of the continuous biological reaction tank is preferably 6.4 m ３ / h / m ３ or less.

[0020] The present invention includes a continuous biological treatment process for continuously flowing treated water into a continuous biological treatment tank and biologically treating the treated water with biological sludge, a membrane separation process for separating the biologically treated water obtained by the continuous biological treatment process and the biological sludge with a filtration membrane, and a sludge supply process for supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the ratio of the BOD sludge load of the continuous biological treatment tank to the semi-batch biological treatment tank is 10 to 30%.

[0021] In the water treatment method, it is preferable to supply the granular sludge to the continuous biological treatment tank so that the abundance ratio of the granules is 10% or more with respect to the amount of sludge in the continuous biological treatment tank. <000009​In the water treatment method, it is preferable to change the inflow ratio of the water to be treated from the continuous biological treatment tank to the semi-batch biological treatment tank from 30% or less to 70% or more.

[0023] The present invention includes a continuous biological treatment means for continuously flowing water to be treated into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge, a membrane separation means for separating the biologically treated water obtained by the continuous biological treatment means and the biological sludge by a filtration membrane, and a sludge supply means for supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank. The ratio of the BOD sludge load of the continuous biological treatment tank to the semi-batch biological treatment tank is 10 to 30%. It is a water treatment device.

[0024] In the water treatment device, it is preferable to supply the granular sludge to the continuous biological treatment tank so that the abundance rate of the granules is 10% or more with respect to the amount of sludge in the continuous biological treatment tank.

[0025] In the water treatment device, it is preferable to change the inflow ratio of the water to be treated from the continuous biological treatment tank to the semi-batch biological treatment tank from 30% or less to 70% or more.

[0026] The present invention includes a continuous biological treatment step of continuously flowing water to be treated containing a BOD (Biochemical Oxygen Demand) component into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation step of separating the biologically treated water obtained in the continuous biological treatment step and the biological sludge by a filtration membrane; an inflow step of flowing at least a part of the water to be treated into a semi-batch biological treatment tank; an aeration step of treating the water to be treated by aeration; a sedimentation step of sedimenting sludge by sedimentation; and a sludge supply step of sequentially repeating a discharge step of discharging treated water containing the formed granular sludge and supplying it to the continuous biological treatment tank. It is a water treatment method in which the amount of BOD per day flowing into the semi-batch biological treatment tank is adjusted to be substantially constant.

[0027] In the water treatment method described above, it is preferable to adjust the amount of BOD per day flowing into the semi-batch biological treatment tank by adjusting at least one of the time of the inflow process and the time of the aeration process in the semi-batch biological treatment tank.

[0028] In the water treatment method described above, it is preferable to adjust the amount of BOD per day flowing into the semi-batch biological treatment tank by adjusting the amount of water to be treated flowing into the semi-batch biological treatment tank in the inflow process.

[0029] In the aforementioned water treatment method, it is preferable to monitor the water quality in the semi-batch biological treatment tank during the aeration process and adjust the amount of load flowing into the semi-batch biological treatment tank based on the fluctuations in water quality.

[0030] The present invention is a water treatment apparatus comprising: a continuous biological treatment means for continuously flowing water to be treated containing BOD components into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation means for separating the biologically treated water obtained from the continuous biological treatment means from the biological sludge using a filtration membrane; and a sludge supply means for sequentially repeating an inflow step of flowing at least a portion of the water to be treated into a semi-batch biological treatment tank, an aeration step of treating the water to be treated by aeration, a sedimentation step of settling the sludge by sedimentation, and a discharge step of discharging treated water containing the formed granular sludge and supplying it to the continuous biological treatment tank, wherein the amount of BOD flowing into the semi-batch biological treatment tank per day is adjusted to be substantially constant.

[0031] In the water treatment apparatus described above, the semi-batch biological treatment tank is further provided with time adjustment means for adjusting the time of each process, and it is preferable that the daily amount of BOD flowing into the semi-batch biological treatment tank is adjusted by adjusting at least one of the time of the inflow process and the time of the aeration process in the semi-batch biological treatment tank.

[0032] The water treatment apparatus further comprises a flow rate adjustment means for adjusting the flow rate of the water to be treated that flows into the semi-batch biological treatment tank, and it is preferable that the daily BOD amount flowing into the semi-batch biological treatment tank is adjusted by adjusting the amount of water to be treated that flows into the semi-batch biological treatment tank in the inflow process.

[0033] Preferably, the water treatment apparatus further includes monitoring means for monitoring the water quality in the semi-batch biological treatment tank during the aeration process, and adjusts the amount of load flowing into the semi-batch biological treatment tank based on the fluctuations in water quality.

[0034] The present invention provides a water treatment method and a water treatment apparatus that improve the granule content in a continuous biological treatment tank in which granule sludge formed in a semi-batch reaction tank is introduced and treated by membrane separation.

[0035] Furthermore, the present invention provides a water treatment method and water treatment apparatus that enable stable granule formation, granule supply, and stable treatment even when there are fluctuations in the inflow load, in a water treatment where granule sludge formed in a semi-batch biological treatment tank is supplied to a continuous biological treatment tank and treated by membrane separation.

[0036] This is a schematic diagram showing an example of a water treatment apparatus according to an embodiment of the present invention. This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. This is a schematic diagram showing an example of a semi-batch biological treatment ((1) inflow / discharge process, (2) biological treatment process, (3) sedimentation process, (4) sludge supply process) in the water treatment apparatus 5 according to an embodiment of the present invention. This is a diagram showing an example of the outline of the water quality profile inside the tank of the semi-batch biological treatment tank in the water treatment apparatus 5 according to an embodiment of the present invention. This is a graph showing the average particle size (μm) of granule sludge in the reaction tank against the number of days (days) of treatment in Example 1. This is a graph showing the average particle size (μm) of granule sludge in the reaction tank and the granule abundance (%) against the number of days (days) of treatment in Example 2. This is a graph showing the average particle size (μm) of granule sludge in the reaction tank and the abundance (%) of each particle size (μm) of granules in the reaction tank against the treatment time (h) in Example 3, where Figure 8(a) shows that the membrane washing air amount per tank volume is 6.4 m ３ / h / m ３ In this case, Figure 8(b) shows that the membrane cleaning air volume per tank volume is 24.6 m³. ３ / h / m ３ The results for this case are shown.

[0037] Embodiments of the present invention will be described below. This embodiment is just one example of how the present invention can be implemented, and the present invention is not limited to this embodiment.

[0038] <First Embodiment> Figure 1 shows a schematic of an example of a water treatment apparatus according to an embodiment of the present invention, and its configuration will be described.

[0039] The water treatment apparatus 1 comprises a semi-batch biological treatment tank 12 and a continuous biological treatment tank 14. The water treatment apparatus 1 may also include a treated water tank 10 for storing the water to be treated.

[0040] In this specification, "continuous" refers to a method as opposed to the batch method, and is distinguished from the semi-batch method, which repeatedly performs the inflow of water to be treated, biological treatment, sludge settling, and discharge of treated water in a single reaction tank. Furthermore, in this embodiment, the continuous method is not limited to a method in which water to be treated is continuously supplied to the reaction tank and operated, but may also refer to a method in which water to be treated is supplied to the reaction tank by a pump that utilizes a principle such as reciprocating motion, such as a diaphragm pump, or a simulated continuous water flow method in which a water tank to be treated is installed upstream of the reaction tank, and the operation and stopping of the pump are controlled according to the water level in the water tank to be treated (the pump is operated when the water level is high, and the pump is stopped when the water level is low) to supply water to the reaction tank.

[0041] In the water treatment apparatus 1, the treated water outlet of the treated water tank 10 and the treated water inlet of the continuous biological treatment tank 14 are connected by a treated water inflow line 30 via a pump 18 and a valve 24. A submersible membrane module 28 is installed inside the continuous biological treatment tank 14, and a biological treated water discharge line 38 is connected to the biological treated water outlet of the submersible membrane module 28 via a pump 42. A treated water inflow line 32, branched from the treated water inflow line 30, is connected to the treated water inlet of the semi-batch biological treatment tank 12 via a valve 22. The sludge outlet of the semi-batch biological treatment tank 12 and the sludge inlet of the continuous biological treatment tank 14 are connected by a biological sludge supply line 34. A treated water discharge line 40 is connected to the treated water outlet of the semi-batch biological treatment tank 12. The sludge outlet of the continuous biological treatment tank 14 and the sludge inlet of the continuous biological treatment tank 14 are connected by a circulation line 36 via a circulation pump 20. The continuous biological treatment tank 14 is equipped with a stirring device 26 for stirring the liquid inside the tank. The stirring device 26 is structured such that, for example, a shaft attached to a motor rotates when driven by a drive device such as a motor, and stirring blades attached to the tip of the shaft rotate along with the rotation of the shaft. However, the stirring device is not limited to the above configuration. In addition, the continuous biological treatment tank 14 may be divided into a tank in which the stirring device is installed and a tank in which the immersion type membrane module 28 is installed. In that case, sludge may be circulated from the sludge outlet of the tank in which the immersion type membrane module 28 is installed to the sludge inlet of the tank in which the immersion type membrane module 28 is installed, or sludge may be circulated from the sludge outlet of the tank in which the immersion type membrane module 28 is installed to the sludge inlet of the tank in which the stirring device is installed.

[0042] In the semi-batch biological treatment tank 12, granular sludge is formed by repeating four processes: (1) inflow / discharge process, (2) biological treatment process, (3) sedimentation process, and (4) sludge supply process. The semi-batch biological treatment tank 12 may be equipped with an agitator, air pump, aeration device, etc. The aeration device is connected to the air pump, and gas such as air supplied from the air pump is supplied into the semi-batch biological treatment tank 12 through the aeration device. The agitator, for example, is structured such that a shaft attached to a motor rotates when driven by a drive device such as a motor, and agitator blades attached to the end of the shaft rotate along with the rotation of the shaft. However, the agitator is not limited to the above configuration.

[0043] The water treatment device 1 may have a control device 16 that controls the amount of water to be treated supplied to the semi-batch biological treatment tank 12 and the continuous biological treatment tank 14, the amount of sludge (circulated sludge) supplied from the sludge outlet to the sludge inlet of the continuous biological treatment tank 14 (circulation amount), and the stirring rotation speed of the stirring device 26. The control device 16 is connected to the pump 18, circulation pump 20, valve 22, valve 24, stirring device 26, etc., so as to be able to communicate by wired or wireless electrical connection.

[0044] An example of the operation of the water treatment method and water treatment apparatus 1 according to this embodiment will be described.

[0045] The water to be treated is stored in the water treatment tank 10 shown in Figure 1. Examples of water to be treated include wastewater from food processing plants, chemical plants, semiconductor plants, machinery plants, sewage, human waste, and river water. The water to be treated may also contain biodegradable organic matter. If the water to be treated contains organic matter that is difficult to decompose by biodegradation, it is desirable to remove it beforehand by performing physicochemical treatment such as flotation separation, coagulation and pressurized flotation, or adsorption.

[0046] First, with valve 24 open, pump 18 is operated, and the water to be treated in the water tank 10 flows continuously into the continuous biological treatment tank 14 through the water inflow line 30. In the continuous biological treatment tank 14, for example, under aerobic conditions, biological treatment of the water to be treated is carried out using biological sludge while being stirred by the agitator 26 (continuous biological treatment process). As will be described later, granular sludge generated in the semi-batch biological treatment tank 12 is supplied to the continuous biological treatment tank 14, and biological treatment of the water to be treated is carried out using biological sludge containing this granular sludge.

[0047] Furthermore, when the pump 42 is activated, the suction pressure (negative pressure) from the pump 42 is applied to the immersed membrane module 28 through the biological treated water discharge line 38, and the biological treated water and biological sludge treated in the continuous biological treatment tank 14 are separated by the filtration membrane of the immersed membrane module 28 (membrane separation step). The filtered water (biologically treated water from which biological sludge has been removed) that has passed through the filtration membrane of the immersed membrane module 28 is then discharged through the biological treated water discharge line 38.

[0048] The circulation pump 20 may be operated so that sludge is circulated from the sludge outlet to the sludge inlet of the continuous biological treatment tank 14 through the circulation line 36 (circulation process).

[0049] When operating the semi-batch biological treatment tank 12, the valve 22 is open and the pump 18 is operated, and the water to be treated in the water tank 10 flows into the semi-batch biological treatment tank 12 through the water to be treated inflow line 30 and the water to be treated inflow line 32. The treated water in the semi-batch biological treatment tank 12 is discharged from the treated water discharge line 40 ((1) Inflow / Discharge Process).

[0050] The water to be treated is allowed to flow into the semi-batch biological treatment tank 12 until a predetermined amount is reached, the pump 18 is stopped, and the valve 22 is closed. Next, for example, an air pump is activated to supply air or other gas into the semi-batch biological treatment tank 12 from the aeration device, and a stirring device is activated to stir the water to be treated in the semi-batch biological treatment tank 12, thereby performing biological treatment of the water to be treated ((2) Biological Treatment Process).

[0051] After the biological treatment process of the water to be treated is carried out for a predetermined time, the air pump and agitator are stopped, and the biological treatment process is completed. After the biological treatment is completed, the granulated biological sludge in the semi-batch biological treatment tank 12 is allowed to settle for a predetermined time, and solid-liquid separation is performed in the semi-batch biological treatment tank 12, separating the granulated sludge from the treated water ((3) Settlement process).

[0052] The granular sludge formed in the semi-batch biological treatment tank 12 is supplied to the continuous biological treatment tank 14 through the biological sludge supply line 34 ((4) Sludge supply process). The supply of granular sludge from the semi-batch biological treatment tank 12 may be carried out in (3) Settlement process, in (2) Biological treatment process, or in the discharge process of (1) Inflow / Discharge process.

[0053] The treated water discharged from the treated water discharge line 40 may be supplied to at least one of the continuous biological treatment tank 14, the water to be treated tank 10, and the treated water tank for storing the treated water, or it may be discharged outside the system.

[0054] In this way, by repeating steps (1) to (4) above in the semi-batch biological treatment tank 12, the biological sludge in the semi-batch biological treatment tank 12 is granulated, and granular sludge is formed.

[0055] The process in the semi-batch biological treatment tank 12 basically consists of four steps that are repeated: (1) inflow / discharge, (2) biological treatment, (3) sedimentation, and (4) sludge supply. However, a waiting step may be added between (1) inflow / discharge and (2) biological treatment, or (4) sludge supply may be omitted as needed. In addition, in (1) inflow / discharge, inflow and discharge may be performed simultaneously, or the inflow may be performed after the discharge.

[0056] In the water treatment apparatus according to this embodiment, the continuous biological treatment tank 14, the agitator 26, etc., function as a continuous biological treatment means that continuously flows the water to be treated into the continuous biological treatment tank and agitates it with the agitator while biologically treating the water with biological sludge. The immersed membrane module 28, the pump 42, etc., function as a membrane separation means that separates the biologically treated water and biological sludge obtained from the continuous biological treatment means using a filtration membrane. The semi-batch biological treatment tank 12, the biological sludge supply line 34, etc., function as a sludge supply means that supplies granular sludge formed in the semi-batch biological treatment tank 12 to the continuous biological treatment tank 14. The circulation pump 20, the circulation line 36, etc., function as a circulation means that circulates sludge from the sludge outlet to the sludge inlet of the continuous biological treatment tank 14.

[0057] In the water treatment method and water treatment apparatus 1 according to this embodiment, the peripheral speed of stirring by the stirring device 26 in the continuous biological treatment tank 14 in the continuous biological treatment process is set to 120 cm / sec or less. The inventors have found that by setting the peripheral speed of stirring by the stirring device 26 in the continuous biological treatment process to 120 cm / sec or less, the granule presence rate in the continuous biological treatment tank 14 is improved. As the granule presence rate in the continuous biological treatment tank 14 increases and the properties of the sludge (e.g., sludge viscosity) improve, it is possible to reduce the aeration air volume when cleaning the membrane of the immersion type membrane module 28 by aeration in the continuous biological treatment tank 14. Furthermore, in a water treatment system in which granular sludge formed in a semi-batch reaction tank is introduced into a continuous biological treatment tank and treated by membrane separation, the granule content in the continuous biological treatment tank 14 is improved by operating the stirring speed of the agitator 26 in the continuous biological treatment tank 14 within an appropriate range, the amount of membrane cleaning gas used when cleaning the membrane of the immersion type membrane module 28 by aeration in the continuous biological treatment tank 14, and by using an airlift pump as a circulation pump in the circulation process to return the sludge.

[0058] In the continuous biological treatment process, the peripheral speed of stirring by the stirring device 26 in the continuous biological treatment tank 14 should be 120 cm / sec or less, but it is preferable to set it in the range of 120 cm / sec to 262 cm / sec. If the peripheral speed of stirring in the continuous biological treatment tank 14 is less than 120 cm / sec, the granules in the continuous biological treatment tank 14 will accumulate at the bottom, and if it exceeds 262 cm / sec, the particle size of the granules may decrease.

[0059] The granular sludge formed in the semi-batch biological treatment tank 12 is sludge that has undergone self-granulation, and is, for example, biological sludge with an average particle size of 200 μm or more.

[0060] Whether or not granular sludge has formed can be determined by measuring the particle size distribution of the sludge in the semi-batch biological treatment tank 12, and when the average particle size reaches 200 μm or more, it can be determined that granular sludge has formed. Alternatively, the SVI value can be measured periodically by a sedimentation test of the sludge in the semi-batch biological treatment tank 12, and when the SVI5 value calculated from the volume ratio after 5 minutes of sedimentation falls below a predetermined value (for example, 100 mL / g or less), it can be determined that granular sludge has formed (note that the lower the SVI value and the larger the average particle size, the better the granular sludge can be judged to be).

[0061] In the water treatment method and water treatment apparatus 1 according to this embodiment, it is preferable to supply granule sludge having an average particle size of 200 μm or more, generated in the semi-batch biological treatment tank 12, to the continuous biological treatment tank 14 such that the granule presence rate is 10% or more relative to the amount of sludge in the continuous biological treatment tank 14, and more preferably 20% or more. If the granule presence rate is less than 10% relative to the amount of sludge in the continuous biological treatment tank 14, the effect of adding the granules may not be obtained.

[0062] In the circulation process of circulating granular sludge from the sludge outlet to the sludge inlet of the continuous biological treatment tank 14, it is preferable to use an air-lift pump as the circulation pump, which sends a gas such as air into the lift pipe and pumps up the liquid by the force of the gas. By using an air-lift pump as the circulation pump in the circulation process, the granular sludge occupancy rate in the continuous biological treatment tank 14 is improved.

[0063] In the continuous biological treatment tank 14, the membrane of the immersed membrane module 28 may be cleaned by aeration. In the cleaning of the membrane of the immersed membrane module 28 by aeration, the amount of cleaning air volume per tank volume is, for example, 6.4 m ３ / h / m ３ or less, and may be, for example, 3.2 m ３ / h / m ３ or more and 6.4 m ３ / h / m ３ or less. When the amount of cleaning air volume per tank volume exceeds 6.4 m ３ / h / m ３ , the particle size of the granular sludge may become smaller. When it is less than 3.2 m ３ / h / m ３ , the cleaning of the membrane may be insufficient.

[0064] In the water treatment method and the water treatment apparatus 1 according to the present embodiment, the control device 16 controls the operation of the pump 18 that supplies the treated water to the semi-batch biological treatment tank 12 and the continuous biological treatment tank 14, the operation of the circulation pump 20 that circulates the sludge from the sludge outlet to the sludge inlet of the continuous biological treatment tank 14, the opening and closing of the valve 22 that adjusts the inflow rate of the treated water into the semi-batch biological treatment tank 12, the opening and closing of the valve 24 that adjusts the inflow rate of the treated water into the continuous biological treatment tank 14, etc., to automatically control the supply amount of the treated water to the semi-batch biological treatment tank 12 and the continuous biological treatment tank 14, the supply amount (circulation amount) of the sludge (circulating sludge) from the sludge outlet to the sludge inlet of the continuous biological treatment tank 14, etc.

[0065] Furthermore, the control device 16 may adjust the stirring rotation speed of the stirring device 26 to automatically control the peripheral speed of stirring in the continuous biological treatment tank 14. The control device 16 may also automatically adjust the stirring rotation speed of the stirring device 26 based on the viscosity and concentration of the sludge in the continuous biological treatment tank 14 so that the peripheral speed of stirring by the stirring device 26 in the continuous biological treatment tank 14 is 120 cm / sec or less.

[0066] The following describes the various components of the water treatment device 1.

[0067] The immersion membrane module 28 consists of at least one module, for example, a filtration membrane housed in a sealable container. The filtration membrane installed in the immersion membrane module 28 can be any known filtration membrane, such as an ultrafiltration membrane or a microfiltration membrane. The shape of the filtration membrane is not particularly limited and can be any of the following: a hollow fiber membrane, a tubular membrane, a flat membrane, or a spiral membrane. Any water flow method, such as an internal pressure type or an external pressure type, can be applied to the immersion membrane module 28.

[0068] Examples of filtration membrane materials include organic membranes such as chlorinated polyethylene (CPE), polyvinyl chloride (PVC), polyethersulfone (PES), and cellulose acetate (CA), as well as inorganic membranes made of ceramic. The pore size of the filtration membrane can be, for example, in the range of 0.01 to 0.4 μm.

[0069] In the water treatment method and water treatment apparatus 1 according to this embodiment, the flux of the filtration membrane is affected by the type and properties of the water to be treated, the properties of the sludge, the area and material of the filtration membrane, etc., but even if it is set to, for example, 1.1 m / day or more, or even 1.3 m / day or more, the increase in the suction pressure of the filtration membrane is suppressed, and stable operation is possible.

[0070] The membrane separation means for separating the biologically treated water and biological sludge in the continuous biological treatment tank 14 by a filtration membrane is not limited to an immersed membrane module 28, but may also be an external membrane module. Specifically, a membrane module may be installed outside the continuous biological treatment tank 14, and the biologically treated water and biological sludge in the continuous biological treatment tank 14 may be supplied to the external membrane module via piping or the like for membrane filtration treatment.

[0071] The continuous biological treatment tank 14 may be a biological treatment system using a standard activated sludge method for treating organic matter, or a nutrient removal system such as A2O (Anaerobic-Anoxic-Oxic Process) or AO (Anaerobic-Oxic Process) (a system that includes an anaerobic treatment tank or an anaerobic treatment tank), or a biological treatment system such as the oxidation ditch method or the step-inflow multi-stage activated sludge method. It may also be a device that performs biological treatment in the presence of a carrier such as polyurethane, plastic, or resin.

[0072] Furthermore, as described above, by supplying granular sludge with an average particle size of 200 μm or more, generated in the semi-batch biological treatment tank 12, to the continuous biological treatment tank 14 in such a way that the granule presence ratio is 10% or more relative to the amount of sludge in the continuous biological treatment tank 14, it is possible to create an aerobic state outside the granules and an anaerobic state inside the granules. As a result, the denitrification reaction occurs even when dissolved oxygen is present in the bulk water (aerobic state), so it is not always necessary to install an anaerobic tank in a nutrient removal system.

[0073] The continuous biological treatment tank 14 should be operated, for example, when the sludge concentration in the tank is in the range of 2,000 to 20,000 mg / L. In addition, in order to maintain the integrity of the biological sludge (settling properties, activity, etc.), the sludge load should be in the range of 0.05 to 0.6 kg BOD / MLSS / day, and preferably in the range of 0.1 to 0.5 kg BOD / MLSS / day.

[0074] The proportion of granular sludge in the continuous biological treatment tank 14 is determined by a laser diffraction particle size analyzer or the like. If the proportion of granular sludge does not reach 10%, it is desirable to supply biological sludge containing granular sludge with an average particle size of 200 μm or more from the semi-batch biological treatment tank 12 to the continuous biological treatment tank 14 again at a predetermined time and flow rate. This operation may be performed by an operator, or the proportion of granular sludge may be adjusted using a control device that can appropriately control the supply amount of granular sludge while measuring the particle size distribution of the sludge in the continuous biological treatment tank 14 with a laser diffraction particle size analyzer or the like. This control device may be the same as the control device 16 described above, or a different device may be used.

[0075] The MLSS concentration in the semi-batch biological treatment tank 12 should be operated in the range of, for example, 2000 to 20000 mg / L. Furthermore, in order to maintain the integrity of the biological sludge (settling properties, activity, etc.), it is preferable to maintain an appropriate sludge load. For example, granular sludge should be withdrawn from the tank so that it is maintained in the range of 0.05 to 0.60 kg BOD / MLSS / day, preferably 0.1 to 0.5 kg BOD / MLSS / day.

[0076] In the formation of granular sludge in the semi-batch biological treatment tank 12, it is sufficient to appropriately control the settling time and the inflow rate of water to be treated per batch. The settling time, during which stirring (including stirring by aeration) is stopped and the sludge is allowed to settle, is calculated from the distance from the water surface to the target sludge interface position and the sludge settling velocity. For example, it should be set between 4 minutes / m and 15 minutes / m, and preferably between 5 minutes / m and 10 minutes / m.

[0077] The inflow rate of treated water into the semi-batch biological treatment tank 12 (the ratio of treated water flowing in to the effective volume during the reaction) can be, for example, in the range of 20% to 120%, and preferably in the range of 40% to 120%. It is believed that sludge granulation progresses as the sludge repeatedly experiences states of very high organic matter concentration (immediately after the inflow process, saturated state) and very low organic matter concentration (towards the end of the biological treatment process, starved state). Therefore, from the viewpoint of forming granular sludge, it is desirable to have as high an inflow rate of treated water as possible. On the other hand, the higher the inflow rate of treated water, the larger the capacity of the pump 18 becomes, and the higher the cost. For this reason, in terms of granular sludge formation and cost reduction, an inflow rate of treated water in the range of 40% to 120% is preferred.

[0078] The pH in the semi-batch biological treatment tank 12 should be adjusted to a range suitable for general biological treatment, for example, 6 to 9, and preferably to a range of 6.5 to 7.5. If the pH value falls outside this range, it is preferable to adjust the pH using an acid or alkali. When adjusting the pH in the semi-batch biological treatment tank 12, it is preferable to perform the pH adjustment while the tank is being stirred rather than when it is not being stirred, as this allows for appropriate measurement of the pH value.

[0079] The dissolved oxygen (DO) in the semi-batch biological treatment tank 12 should be, for example, 0.5 mg / L or more, which is suitable for general biological treatment, and preferably 1 mg / L or more.

[0080] The control device 16 can be a programmable logic controller (PLC) or a personal computer (PC). The control device 16 is composed of a microcomputer and electronic circuits, for example, which consist of calculation means such as a CPU for calculating programs, and storage means such as ROM and RAM for storing programs and calculation results, and has the above-mentioned functions.

[0081] <Second Embodiment> Figure 2 shows a schematic of an example of a water treatment apparatus according to an embodiment of the present invention, and its configuration will be described.

[0082] The water treatment device 3 comprises a semi-batch biological treatment tank 102 and a continuous biological treatment tank 104. The continuous biological treatment tank 104 may be divided into an upstream reaction tank 104a and a downstream membrane separation tank 104b, which are connected at the upper or lower part of the tank. A sedimentation tank 100 may be provided upstream of the water treatment device 3. The water treatment device 3 may also include a treated water tank for storing the treated water from the sedimentation tank 100.

[0083] A treated water inlet line 114 is connected to the treated water inlet of the sedimentation tank 100. The treated water outlet of the sedimentation tank 100 and the treated water inlet of the reaction tank 104a of the continuous biological treatment tank 104 in the water treatment device 3 are connected by a treated water inlet line 120. At least one immersed membrane module 118 is installed in the membrane separation tank 104b of the continuous biological treatment tank 104, and a biological treated water discharge line 128 is connected to the biological treated water outlet of the immersed membrane module 118. A treated water inlet line 122, branched from the treated water inlet line 120, is connected to the treated water inlet of the semi-batch biological treatment tank 102. The sludge outlet of the semi-batch biological treatment tank 102 and the sludge inlet of the reaction tank 104a of the continuous biological treatment tank 104 are connected by a biological sludge supply line 124. The treated water outlet of the semi-batch biological treatment tank 102 and the treated water inlet of the reaction tank 104a of the continuous biological treatment tank 104 are connected by a treated water line 130. The sludge outlet of the membrane separation tank 104b of the continuous biological treatment tank 104 and the sludge inlet of the reaction tank 104a are connected by a circulation line 126. The reaction tank 104a of the continuous biological treatment tank 104 is equipped with an agitator 116 for agitating the liquid inside the continuous biological treatment tank 104. The agitator 116 is structured such that, for example, a shaft attached to a motor rotates when driven by a drive device such as a motor, and agitator blades attached to the tip of the shaft rotate along with the rotation of the shaft. However, the agitator is not limited to the above configuration.

[0084] The water treatment device 3 may also include a recovery device 106 for recovering granules from the sludge generated in the continuous biological treatment tank 104. The sludge outlet of the membrane separation tank 104b and the sludge inlet of the recovery device 106 are connected by a sludge line 132, and the recovered sludge outlet of the recovery device 106 and the recovered sludge inlet of the membrane separation tank 104b are connected by a recovered sludge line 134. An excess sludge discharge line 136 is connected to the excess sludge outlet of the recovery device 106. A liquid cyclone or the like can be used as the recovery device.

[0085] In the semi-batch biological treatment tank 102, granular sludge is formed by repeating four processes: (1) inflow / discharge process, (2) biological treatment process, (3) sedimentation process, and (4) sludge supply process. The semi-batch biological treatment tank 102 may be equipped with an agitator, an air pump, an aeration device 112, etc. The aeration device 112 is connected to the air pump, for example, and gas such as air supplied from the air pump is supplied into the semi-batch biological treatment tank 102 through the aeration device 112. The agitator is structured such that, for example, a shaft attached to a motor rotates when driven by a drive device such as a motor, and agitator blades attached to the end of the shaft rotate along with the rotation of the shaft. However, the agitator is not limited to the above configuration.

[0086] The water treatment device 3 may have a control device that controls the amount of water to be treated supplied to the semi-batch biological treatment tank 102 and the continuous biological treatment tank 104, the amount of sludge (circulating sludge) supplied from the membrane separation tank 104b to the reaction tank 104a, and the stirring speed of the stirring device 116. The control device is connected to pumps, valves, etc. that adjust the amount of water to be treated supplied to the semi-batch biological treatment tank 102 and the continuous biological treatment tank 104, pumps, valves, etc. that adjust the amount of sludge (circulating sludge) supplied from the membrane separation tank 104b to the reaction tank 104a, and the stirring device 116, etc., so as to be able to communicate by wired or wireless electrical connection.

[0087] An example of the operation of the water treatment method and water treatment apparatus 3 according to this embodiment will be described.

[0088] The water to be treated is sent to the sedimentation tank 100 as needed through the water to be treated inflow line 114, where sedimentation treatment is performed (sedimentation treatment process). The water to be treated after sedimentation treatment in the sedimentation tank 100 is continuously flowed into the continuous biological treatment tank 104 through the water to be treated inflow line 120.

[0089] Examples of water to be treated include wastewater from food processing plants, chemical plants, semiconductor plants, machinery factories, sewage, human waste, and river water. Furthermore, the water to be treated may contain organic matter that is difficult to decompose biologically. If the water to be treated contains organic matter that is difficult to decompose biologically, it is desirable to remove it beforehand by physicochemical treatment such as flotation separation, coagulation and pressurized flotation, or adsorption.

[0090] In the reaction tank 104a of the continuous biological treatment tank 104, for example, under anaerobic conditions, the water to be treated is biologically treated with biological sludge while being stirred by the agitator 116 (continuous biological treatment process). As will be described later, the granular sludge produced in the semi-batch biological treatment tank 102 is supplied to the continuous biological treatment tank 104, and the water to be treated is biologically treated using the biological sludge containing this granular sludge.

[0091] Furthermore, in the membrane separation tank 104b, which is in communication with the reaction tank 104a, suction pressure (negative pressure) from a pump installed in the biological treated water discharge line 128 is applied to the immersed membrane module 118 through the biological treated water discharge line 128, and the filtration membrane of the immersed membrane module 118 separates the biological treated water and biological sludge treated in the continuous biological treatment tank 104 (membrane separation step). The filtered water (biologically treated water from which the biological sludge has been removed) that has passed through the filtration membrane of the immersed membrane module 118 is then discharged through the biological treated water discharge line 128.

[0092] For example, sludge may be circulated from the membrane separation tank 104b to the reaction tank 104a through the circulation line 126 by a circulation pump or the like (circulation process).

[0093] The sludge generated in the continuous biological treatment tank 104 is sent to the recovery device 106 through the sludge line 132, where the granules present in the sludge may be recovered (recovery step). The recovered granular sludge is returned to the continuous biological treatment tank 104 through the recovered sludge line 134. The sludge from which the granules have been removed is discharged through the excess sludge discharge line 136.

[0094] When operating the semi-batch biological treatment tank 102, the water to be treated flows into the semi-batch biological treatment tank 102 through the water to be treated inlet line 120 and the water to be treated inlet line 122. The treated water in the semi-batch biological treatment tank 102 is discharged from the treated water line 130 ((1) Inlet / Discharge Process).

[0095] The water to be treated is introduced into the semi-batch biological treatment tank 102 until a predetermined amount is reached. For example, an air pump is activated to supply air or other gas into the semi-batch biological treatment tank 102 from the aeration device 112, and a stirring device is activated to stir the water to be treated in the semi-batch biological treatment tank 102, thereby performing biological treatment of the water to be treated ((2) Biological Treatment Process).

[0096] After the biological treatment process of the water to be treated is carried out for a predetermined time, the air pump and agitator are stopped, and the biological treatment process is completed. After the biological treatment is completed, the granulated biological sludge in the semi-batch biological treatment tank 102 is allowed to settle for a predetermined time, and solid-liquid separation is performed in the semi-batch biological treatment tank 102, separating the granulated sludge from the treated water ((3) Settlement process).

[0097] The granular sludge formed in the semi-batch biological treatment tank 102 is supplied to the continuous biological treatment tank 104 through the biological sludge supply line 124 ((4) Sludge supply process). The supply of granular sludge from the semi-batch biological treatment tank 102 may be carried out in (3) Settlement process, in (2) Biological treatment process, or in the discharge process of (1) Inflow / Discharge process.

[0098] The treated water discharged from the treated water line 130 is supplied to the reaction tank 104a of the continuous biological treatment tank 104. Some or all of the treated water discharged from the treated water line 130 may be released outside the system.

[0099] In this way, by repeating steps (1) to (4) above in the semi-batch biological treatment tank 102, the biological sludge in the semi-batch biological treatment tank 102 is granulated, and granular sludge is formed.

[0100] The process in the semi-batch biological treatment tank 102 basically consists of four steps that are repeated: (1) inflow / discharge, (2) biological treatment, (3) sedimentation, and (4) sludge supply. However, a waiting step may be added between (1) inflow / discharge and (2) biological treatment, or (4) sludge supply may be omitted as needed. In addition, in (1) inflow / discharge, inflow and discharge may be performed simultaneously, or the inflow may be performed after the discharge.

[0101] In the water treatment apparatus according to this embodiment, the continuous biological treatment tank 104, the agitator 116, etc., function as a continuous biological treatment means that continuously flows the water to be treated into the continuous biological treatment tank and biologically treats the water with biological sludge. The immersed membrane module 118, etc., function as a membrane separation means that separates the biologically treated water and biological sludge obtained from the continuous biological treatment means by a filtration membrane. The semi-batch biological treatment tank 102, the biological sludge supply line 124, etc., function as a sludge supply means that supplies granular sludge formed in the semi-batch biological treatment tank 102 to the continuous biological treatment tank 104. The circulation line 126, etc., function as a circulation means that circulates sludge from the membrane separation tank 104b of the continuous biological treatment tank 104 to the reaction tank 104a.

[0102] In the water treatment method and water treatment apparatus 3 according to this embodiment, the ratio of the BOD sludge load in the continuous biological treatment tank 104 to the semi-batch biological treatment tank 102 is set to 10-30%. The inventors have found that by setting the ratio of the BOD sludge load in the continuous biological treatment tank 104 to the semi-batch biological treatment tank 102 to 10-30%, the granule presence rate in the continuous biological treatment tank 104 is improved. By keeping the sludge load in the continuous biological treatment tank 104 per day low, at 10-30% of that of the semi-batch biological treatment tank 102, it is possible to maintain a high granule content in the continuous biological treatment tank 104. Furthermore, by keeping the granule presence rate above a predetermined value, it is possible to keep the viscosity of the sludge low, and this effect increases the oxygen transport efficiency and reduces the amount of aeration in the continuous biological treatment tank 104. Furthermore, by incorporating granules into the continuous biological treatment tank 104, it is expected that effects such as an improvement in critical flux (flux at which the membrane differential pressure rises sharply) and an increase in membrane separation flux can be expected. In addition, this treatment method utilizes granules and is a membrane separation activated sludge method that can suppress greenhouse gas emissions.

[0103] The ratio of the BOD sludge load in the continuous biological treatment tank 104 to the semi-batch biological treatment tank 102 should be 10 to 30%, preferably 30% or less, and more preferably 10 to 20%. If the ratio of the BOD sludge load in the continuous biological treatment tank 104 to the semi-batch biological treatment tank 102 is less than 10%, it can cause self-decomposition of sludge or membrane separation problems due to increased sludge concentration, and if it exceeds 30%, the granule presence may decrease. The ratio of the BOD sludge load in the continuous biological treatment tank 104 to the semi-batch biological treatment tank 102 can be adjusted according to the sludge concentration in the semi-batch biological treatment tank 102 and the continuous biological treatment tank 104.

[0104] The BOD sludge load in the semi-batch biological treatment tank 102 should be, for example, 0.15 to 0.3 kg BOD / kg MLSS / day, and preferably 0.20 to 0.25 kg BOD / kg MLSS / day. If the BOD sludge load in the semi-batch biological treatment tank 102 is less than 0.15 BOD / kg MLSS / day or more than 0.3 kg BOD / kg MLSS / day, granule formation may become difficult.

[0105] The BOD sludge load in the continuous biological treatment tank 104 should be, for example, 0.015 to 0.1 kg BOD / kg MLSS / day, and preferably 0.015 to 0.06 kg BOD / kg MLSS / day. If the BOD sludge load in the continuous biological treatment tank 104 is less than 0.015 BOD / kg MLSS / day or more than 0.1 kg BOD / kg MLSS / day, the sludge properties may deteriorate, making membrane separation difficult.

[0106] In the water treatment method and water treatment apparatus 3 according to this embodiment, it is preferable to supply the granular sludge generated in the semi-batch biological treatment tank 102 to the continuous biological treatment tank 104 such that the granule content is 10% or more relative to the amount of sludge in the continuous biological treatment tank 104. By having a granule content of 10% or more relative to the amount of sludge in the continuous biological treatment tank 104, the viscosity of the sludge decreases, the oxygen dissolution efficiency increases, and the critical flux increases, enabling stable membrane separation.

[0107] In the water treatment method and water treatment apparatus 3 according to this embodiment, it is preferable to vary the ratio of water to be treated flowing from the continuous biological treatment tank 104 to the semi-batch biological treatment tank 102 to 30% or less per predetermined time from 70% or more. This creates load fluctuations within the continuous biological treatment tank 104, further improving the granule presence rate.

[0108] By changing the distribution ratio of treated water to the mainstream, including the continuous biological treatment tank 104, and the semi-batch biological treatment tank 102 that forms granules, load fluctuations are induced in the mainstream continuous biological treatment tank 104. This creates load fluctuations (formation of periods of satiety and starvation) not only in the semi-batch biological treatment tank 102, which is operating in a semi-batch manner, but also in the continuous biological treatment tank 104, thereby promoting granule formation. By keeping the sludge load in the semi-batch biological treatment tank 102 high and the sludge load in the continuous biological treatment tank 104 low, periods of satiety and starvation are created in the semi-batch biological treatment tank 102 and the continuous biological treatment tank 104, further granule formation can be promoted.

[0109] The granular sludge formed in the semi-batch biological treatment tank 102 is sludge that has undergone self-granulation, and is, for example, biological sludge with an average particle size of 200 μm or more.

[0110] Whether or not granular sludge has formed can be determined by measuring the particle size distribution of the sludge in the semi-batch biological treatment tank 102, and when the average particle size reaches 200 μm or more, it can be determined that granular sludge has formed. Alternatively, the SVI value can be measured periodically by a sedimentation test of the sludge in the semi-batch biological treatment tank 102, and when the SVI5 value calculated from the volume ratio after 5 minutes of sedimentation falls below a predetermined value (for example, 100 mL / g or less), it can be determined that granular sludge has formed (note that the lower the SVI value and the larger the average particle size, the better the granular sludge can be judged to be).

[0111] In the continuous biological treatment tank 104, the membrane of the immersion-type membrane module 118 may be cleaned by aeration. In cleaning the membrane of the immersion-type membrane module 118 by aeration, the amount of membrane cleaning gas per unit tank volume is, for example, 6.4 m³. ３ / h / m ３ Below, 3.2m ３ / h / m ３ Preferably 5.4 m ３ / h / m ３ Below, 3.5m ３ / h / m ３ The above is recommended. The membrane cleaning gas volume per tank volume is 6.4 m³.３ / h / m ３ If it exceeds 3.2 m, the particle size of the granule sludge may decrease. ３ / h / m ３ If the value is less than this, the membrane may not be cleaned properly.

[0112] In the water treatment method and water treatment apparatus 3 according to this embodiment, the control device may automatically control the amount of water to be treated supplied to the semi-batch biological treatment tank 102 and the continuous biological treatment tank 104, as well as the amount of sludge (circulated sludge) supplied from the membrane separator tank 104b to the reaction tank 104a, by controlling the operation of the pumps that supply water to be treated to the semi-batch biological treatment tank 102 and the continuous biological treatment tank 104, the operation of the circulation pump that circulates sludge from the membrane separator tank 104b of the continuous biological treatment tank 104 to the reaction tank 104a, the opening and closing of valves that adjust the amount of water to be treated flowing into the semi-batch biological treatment tank 102, and the opening and closing of valves that adjust the amount of water to be treated flowing into the continuous biological treatment tank 104. The control device may also automatically control the ratio of the inflow of water to be treated from the semi-batch biological treatment tank 102 to the continuous biological treatment tank 104.

[0113] Furthermore, the control device may adjust the stirring rotation speed of the stirring device 116 to automatically control the peripheral speed of stirring in the continuous biological treatment tank 104. The control device may also automatically adjust the stirring rotation speed of the stirring device 116 based on the viscosity and concentration of the sludge in the continuous biological treatment tank 104, so that the peripheral speed of stirring by the stirring device 116 in the continuous biological treatment tank 104 is, for example, 120 cm / sec or less.

[0114] The following describes the various components of the water treatment device 3.

[0115] The immersion membrane module 118 is composed of, for example, at least one module housing a filtration membrane. Examples of known filtration membranes installed in the immersion membrane module 118 include ultrafiltration membranes and microfiltration membranes. The shape of the filtration membrane is not particularly limited and examples include hollow fiber membranes, tubular membranes, flat membranes, and spiral membranes. Any water flow method, such as internal pressure type or external pressure type, can be applied to the immersion membrane module 118.

[0116] Examples of materials for the filtration membrane include organic membranes such as polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyethersulfone (PES), and cellulose acetate (CA), as well as inorganic membranes made of ceramic. The molecular weight cutoff of the filtration membrane is, for example, in the range of 5,000 to 360,000, with a preferred range of 10,000 to 360,000. The pore size of the filtration membrane is, for example, in the range of 0.01 to 0.1 μm, with a preferred range of 0.01 to 0.03 μm.

[0117] In the water treatment method and water treatment apparatus 3 according to this embodiment, the flux of the filtration membrane is affected by the type and properties of the water to be treated, the properties of the sludge, the area and material of the filtration membrane, etc., but even if it is set to, for example, 0.5 m / day or more, or even 1.0 m / day or more, the increase in the suction pressure of the filtration membrane is suppressed, and stable operation is possible.

[0118] The membrane separation means for separating the biologically treated water and biological sludge in the continuous biological treatment tank 104 by a filtration membrane is not limited to an immersed membrane module 118, but may also be an external membrane module. Specifically, a membrane module may be installed outside the continuous biological treatment tank 104, and the biologically treated water and biological sludge in the continuous biological treatment tank 104 may be supplied to the external membrane module via piping or the like for membrane filtration treatment.

[0119] The continuous biological treatment tank 104 may be a biological treatment system using a standard activated sludge method for treating organic matter, or a nutrient removal system such as A2O (Anaerobic-Anoxic-Oxic Process) or AO (Anaerobic-Oxic Process) (a system that includes an oxygen-free treatment tank or an anaerobic treatment tank), or a biological treatment system such as the oxidation ditch method or the step-inflow multi-stage activated sludge method. It may also be a device that performs biological treatment in the presence of a carrier such as polyurethane, plastic, or resin.

[0120] Furthermore, as described above, by supplying granular sludge having an average particle size of, for example, 200 μm or more, generated in the semi-batch biological treatment tank 102, to the continuous biological treatment tank 104 such that the granule presence ratio is, for example, 10% or more of the sludge volume in the continuous biological treatment tank 104, it is possible to create an aerobic state outside the granules and an anaerobic state inside the granules. As a result, denitrification reactions occur even when dissolved oxygen is present in the bulk water (aerobic state), so it is not always necessary to install an anaerobic tank in a nutrient removal system.

[0121] The continuous biological treatment tank 104 should be operated, for example, when the sludge concentration inside the tank is in the range of 2,000 to 20,000 mg / L.

[0122] The proportion of granular sludge in the continuous biological treatment tank 104 is determined by a laser diffraction particle size analyzer or the like. If the proportion of granular sludge does not reach 10%, it is desirable to supply biological sludge containing granular sludge with an average particle size of 200 μm or more from the semi-batch biological treatment tank 102 to the continuous biological treatment tank 104 again at a predetermined time and flow rate. This operation may be performed by an operator, or the proportion of granular sludge may be adjusted using a control device that can appropriately control the supply amount of granular sludge while measuring the particle size distribution of the sludge in the continuous biological treatment tank 104 with a laser diffraction particle size analyzer or the like. This control device may be the same as the one described above, or a different device may be used.

[0123] The MLSS concentration in the semi-batch biological treatment tank 102 should be operated within a range of, for example, 2000 to 20000 mg / L.

[0124] In the formation of granular sludge in the semi-batch biological treatment tank 102, it is sufficient to appropriately control the settling time and the inflow rate of water to be treated per batch. The settling time, during which stirring (including stirring by aeration) is stopped and the sludge is allowed to settle, is calculated from the distance from the water surface to the target sludge interface position and the sludge settling velocity. For example, it should be set between 4 minutes / m and 25 minutes / m, and preferably between 5 minutes / m and 20 minutes / m.

[0125] The inflow rate of treated water into the semi-batch biological treatment tank 102 (the ratio of treated water flowing in to the effective volume during the reaction) can be, for example, in the range of 20% to 120%, and preferably in the range of 40% to 120%. It is believed that sludge granulation progresses as the sludge repeatedly experiences states of very high organic matter concentration (immediately after the inflow process, saturated state) and very low organic matter concentration (towards the end of the biological treatment process, starved state). Therefore, from the viewpoint of forming granular sludge, it is desirable to have as high an inflow rate of treated water as possible. On the other hand, the higher the inflow rate of treated water, the larger the pump capacity becomes, and the higher the cost. For this reason, in terms of granular sludge formation and cost reduction, an inflow rate of treated water in the range of 40% to 120% is preferred.

[0126] The pH in the semi-batch biological treatment tank 102 should be adjusted to a range suitable for general biological treatment, for example, 6 to 9, and preferably to a range of 6.5 to 7.5. If the pH value falls outside this range, it is preferable to adjust the pH using an acid or alkali. When adjusting the pH in the semi-batch biological treatment tank 102, it is preferable to perform the pH adjustment while the tank is being stirred rather than when it is not being stirred, as this allows for appropriate measurement of the pH value.

[0127] The dissolved oxygen (DO) in the semi-batch biological treatment tank 102 should be, for example, 0.5 mg / L or more, which is suitable for general biological treatment, and preferably 1 mg / L or more.

[0128] The recovery device 106 can be any device capable of recovering granular sludge from the continuous biological treatment tank 104, and there are no particular restrictions. For example, a liquid cyclone type device can be used as the recovery device 106.

[0129] The control device can be a programmable logic controller (PLC) or a personal computer (PC). The control device consists of a microcomputer and electronic circuits, for example, which include calculation means such as a CPU for calculating programs, and storage means such as ROM and RAM for storing programs and calculation results, and has the above-mentioned functions.

[0130] <Third Embodiment> Figure 3 shows an overview of an example of a water treatment apparatus according to an embodiment of the present invention, and its configuration will be described.

[0131] The water treatment device 5 comprises a semi-batch biological treatment tank 50 and a continuous biological treatment tank 52. The water treatment device 5 may also include a tank for storing the water to be treated.

[0132] In the water treatment system 5, a treated water inlet line 70 is connected to the treated water inlet of the continuous biological treatment tank 52. An immersed membrane module 68 is installed inside the continuous biological treatment tank 52, and a biological treated water discharge line 76 is connected to the biological treated water outlet of the immersed membrane module 68 via a biological treated water pump 62. A treated water inlet line 72, branched from the treated water inlet line 70, is connected to the treated water inlet of the semi-batch biological treatment tank 50 via a treated water pump 58. The treated water outlet of the semi-batch biological treatment tank 50 and the treated water inlet of the continuous biological treatment tank 52 are connected by a treated water / sludge supply line 74 via a treated water pump 60. A water quality measuring device 56 is installed in the semi-batch biological treatment tank 50 as a monitoring means for monitoring the water quality inside the tank during the aeration process in the semi-batch biological treatment tank 50.

[0133] The continuous biological treatment tank 52 may be equipped with a blower 78 and aeration devices 80 and 82. The aeration device 80 is installed on the bottom surface of the continuous biological treatment tank 52, and the aeration device 82 is installed on the bottom surface below the immersion type membrane module 68 in the continuous biological treatment tank 52. The aeration devices 80 and 82 are each connected to the blower 78, and gas such as air supplied from the blower 78 is supplied into the continuous biological treatment tank 52 through the aeration devices 80. The continuous biological treatment tank 52 may also be equipped with a stirring device for stirring the liquid inside the tank. The stirring device has a structure in which, for example, a shaft attached to a motor rotates when driven by a drive device such as a motor, and stirring blades attached to the end of the shaft rotate along with the rotation of the shaft. However, the stirring device is not limited to the above configuration.

[0134] In the semi-batch biological treatment tank 50, granular sludge is formed by repeating four processes: (1) inflow process, (2) aeration process, (3) sedimentation process, and (4) discharge process. The semi-batch biological treatment tank 50 may be equipped with an agitator, a blower 64, an aeration device 66, etc. The aeration device 66 is connected to the blower 64, and gas such as air supplied from the blower 64 is supplied into the semi-batch biological treatment tank 50 through the aeration device 66. The agitator has a structure in which, for example, a shaft attached to a motor rotates when driven by a drive device such as a motor, and agitator blades attached to the end of the shaft rotate along with the rotation of the shaft. However, the agitator is not limited to the above configuration.

[0135] The water treatment device 5 may have a control device 54 as a control means for controlling the amount of water to be treated supplied to the semi-batch biological treatment tank 50 and the continuous biological treatment tank 52, the amount of treated water (including granular sludge) supplied from the semi-batch biological treatment tank 50 to the continuous biological treatment tank 52, and the amount of aeration in the semi-batch biological treatment tank 50. The control device 54 is connected to the water quality measuring device 56, the water to be treated pump 58, the treated water pump 60, the blower 64, etc., so as to be able to communicate by wired or wireless electrical connection.

[0136] An example of the operation of the water treatment method and water treatment apparatus 5 according to this embodiment will be described.

[0137] The water to be treated, which contains BOD (biochemical oxygen demand) components, is continuously flowed into the continuous biological treatment tank 52 through the water to be treated inflow line 30.

[0138] Examples of water to be treated include wastewater from food processing plants, chemical plants, semiconductor plants, machinery factories, sewage, human waste, and river water. Furthermore, the water to be treated may contain biodegradable organic matter. If the water to be treated contains organic matter that is difficult to decompose, it is desirable to remove it beforehand by physicochemical treatment such as flotation separation, coagulation and pressurized flotation, or adsorption.

[0139] In the continuous biological treatment tank 52, for example, a blower 78 is operated, and gas such as air is supplied into the continuous biological treatment tank 52 from the aeration device 80 to aerate it, and under aerobic conditions, the biological treatment of the water to be treated with biological sludge is carried out, for example, while stirring with an agitator (continuous biological treatment process). Alternatively, gas such as air may be supplied from the aeration device 82 to the immersed membrane module 68 to perform membrane surface cleaning aeration. As will be described later, granular sludge generated in the semi-batch biological treatment tank 50 is supplied to the continuous biological treatment tank 52, and the biological treatment of the water to be treated is carried out using the biological sludge containing this granular sludge.

[0140] Furthermore, the biological treatment water pump 62 is activated, and the suction pressure (negative pressure) from the biological treatment water pump 62 is applied to the immersed membrane module 68 through the biological treatment water discharge line 76. The filtration membrane of the immersed membrane module 68 separates the biological treatment water and biological sludge treated in the continuous biological treatment tank 52 (membrane separation process). The filtered water (biological treatment water from which biological sludge has been removed) that has passed through the filtration membrane of the immersed membrane module 68 is then discharged through the biological treatment water discharge line 76.

[0141] Figure 4 shows an example of the operation of a semi-batch biological treatment system, i.e., a semi-batch biological treatment tank 50. As shown in Figure 4(1), when the semi-batch biological treatment tank 50 is operated, the treated water pump 58 is operated, and the treated water flows into the semi-batch biological treatment tank 50 through the treated water inflow line 70 and the treated water inflow line 72 ((1) Inflow process). While the treated water pump 58 is operating, the flow rate of the treated water flowing into the continuous biological treatment tank 52 decreases.

[0142] The water to be treated flows into the semi-batch biological treatment tank 50 until a predetermined amount is reached, and as shown in Figure 4(2), the water to be treated pump 58 is stopped. Next, for example, the blower 64 is activated, and gas such as air is supplied into the semi-batch biological treatment tank 50 from the aeration device 66 to aerate the water. At the same time, for example, the stirring device is activated, and the water to be treated in the semi-batch biological treatment tank 50 is stirred, thereby performing biological treatment of the water to be treated ((2) Aeration step).

[0143] As shown in Figure 4(3), after the aeration process of the water to be treated is carried out for a predetermined time, the blower 64 and the stirring device are stopped, and the aeration process is completed. After the aeration is completed, the granulated biological sludge in the semi-batch biological treatment tank 50 is allowed to settle for a predetermined time, and solid-liquid separation is performed in the semi-batch biological treatment tank 50, separating the granulated sludge from the treated water ((3) Settlement process).

[0144] As shown in Figure 4(4), the treated water in the semi-batch biological treatment tank 50 is supplied to the continuous biological treatment tank 52 through the treated water / sludge supply line 74 by operating the treated water pump 60 ((4) discharge process). The supply of granular sludge from the semi-batch biological treatment tank 50 to the continuous biological treatment tank 52 may be carried out in (3) sedimentation process or in (2) aeration process.

[0145] In this way, by repeating steps (1) to (4) above in the semi-batch biological treatment tank 50, the biological sludge in the semi-batch biological treatment tank 50 is granulated, and granular sludge is formed.

[0146] The process in the semi-batch biological treatment tank 50 basically consists of four steps that are repeated: (1) inflow step, (2) aeration step, (3) sedimentation step, and (4) discharge step. However, if necessary, inflow and discharge may be performed simultaneously in step (1).

[0147] In the semi-batch biological treatment tank 50, the treated water / sludge supply line 74 may be installed near the water surface, and the treated water may be supplied to the continuous biological treatment tank 52 in a push-out flow manner in accordance with the operation of the treated water pump 58. In this way, the (1) inflow process and the (4) discharge process can be carried out simultaneously in the semi-batch biological treatment tank 50.

[0148] The treated water discharged from the semi-batch biological treatment tank 50 may be entirely supplied to the continuous biological treatment tank 52, or a portion of the treated water may be mixed with the biologically treated water discharged from the immersed membrane module 68 of the continuous biological treatment tank 52 before discharge. This makes it possible to reduce the amount of water separated by membrane in the continuous biological treatment tank 52, thereby reducing the risk of membrane clogging, or enabling operation with a higher flux.

[0149] In the water treatment apparatus 5 according to this embodiment, a continuous biological treatment tank 52 and the like continuously flows the water to be treated into the continuous biological treatment tank and functions as a continuous biological treatment means for biologically treating the water to be treated with biological sludge. An immersed membrane module 68, a biologically treated water pump 62, and the like function as a membrane separation means for separating the biologically treated water and biological sludge obtained from the continuous biological treatment means using a filtration membrane. A semi-batch biological treatment tank 50, a treated water / sludge supply line 74, and the like function as a sludge supply means for supplying granular sludge formed in the semi-batch biological treatment tank 50 to the continuous biological treatment tank 52.

[0150] In the water treatment method and water treatment apparatus 5 according to this embodiment, the amount of BOD flowing into the semi-batch biological treatment tank 50 of the water to be treated is predicted, and the amount of BOD flowing into the semi-batch biological treatment tank 50 per day is adjusted to be substantially constant. As a result, the granular sludge formed in the semi-batch biological treatment tank 50 is supplied to the continuous biological treatment tank 52, enabling stable granule formation, granule supply, and stable treatment even if there are fluctuations in the inflow load. Even when the fluctuations in the inflow load are large (for example, when the ratio of the maximum load per hour to the average load per day is 1.25 or more), by keeping the BOD load fluctuations to the semi-batch biological treatment tank 50 as constant as possible, stable granule formation and granule supply are achieved, and the stability of the entire system treatment can be achieved by treating the load that is not allowed to flow into the semi-batch biological treatment tank 50 in the continuous biological treatment tank 52.

[0151] Based on the predicted daily inflow BOD of the water to be treated, at least one of the inflow process time and the aeration process time in the semi-batch biological treatment tank 50 may be adjusted, or the inflow rate of the water to be treated in the inflow process in the semi-batch biological treatment tank 50 may be adjusted. For example, the daily BOD flowing into the semi-batch biological treatment tank 50 can be adjusted by adjusting at least one of the following: the operating time of the water to be treated pump 58 that supplies the water to be treated to the semi-batch biological treatment tank 50 (i.e., the inflow process time of the water to be treated), the flow rate of the water to be treated pump 58 that supplies the water to be treated to the semi-batch biological treatment tank 50 (i.e., the inflow rate of the water to be treated in the inflow process), or the operating time of the blower 64 (i.e., the aeration process time). The control device 54, the treated water pump 58, the blower 64, etc. function as time adjustment means to adjust the time of each process in the semi-batch biological treatment tank, and the control device 54, the treated water pump 58, etc. function as flow rate adjustment means to adjust the flow rate of the treated water flowing into the semi-batch biological treatment tank 50.

[0152] The time of the water to be treated inflow process, or the flow rate of the water to be treated pump 58, may be adjusted by either one or both. (1) In the inflow process, the water to be treated is supplied to the semi-batch biological treatment tank 50 using the water to be treated pump 58, and the amount of BOD per day flowing into the semi-batch biological treatment tank 50 can be adjusted by the flow rate of the water to be treated pump 58. Alternatively, an electric valve or electric gate can be installed in the water to be treated inflow line 72, and the amount of BOD per day flowing into the semi-batch biological treatment tank 50 can be adjusted by opening and closing the electric valve or electric gate. In this case, the electric valve or electric gate functions as a flow rate adjustment means for adjusting the flow rate of the water to be treated flowing into the semi-batch biological treatment tank 50.

[0153] The amount of BOD flowing into the semi-batch biological treatment tank 50 (BOD load) is determined and predicted, for example, based on the treatment status due to aeration within the semi-batch biological treatment tank 50. If a large amount of treatment is predicted in the semi-batch biological treatment tank 50, the BOD load is adjusted. The BOD load is basically determined by the length of time required for the aeration process, but for example, a basic aeration time per predetermined period (e.g., one day) is set, and the BOD load is determined by comparing that time with the actual aeration process time. BOD load adjustment is performed by lengthening the aeration process, shortening the inflow process, or reducing the flow rate of the treated water pump 58. The water quality in the semi-batch biological treatment tank 50 during the aeration process may be monitored, and the amount of load flowing into the semi-batch biological treatment tank 50 may be adjusted based on the fluctuations in water quality. The treatment status of pollutants by aeration in the semi-batch biological treatment tank 50 can be monitored by directly measuring the water quality of the treated water, such as BOD and ammonia nitrogen components, using a water quality measuring device 56. However, it can also be predicted using alternative water quality parameters, such as pH and conductivity.

[0154] Adjusting the daily BOD amount flowing into the semi-batch biological treatment tank 50 is preferably done by adjusting at least one of the inflow process time and the aeration process time in the semi-batch biological treatment tank, as this allows for easy adjustment of the BOD load. For granule formation, it is preferable to maintain a constant or higher inflow amount of treated water in each inflow process, so it is more preferable to adjust using only the aeration process. Furthermore, as a means of adjusting the BOD amount, it is preferable to adjust the flow rate of the treated water pump in the semi-batch biological treatment tank.

[0155] By repeatedly performing the four processes described above—(1) inflow process, (2) aeration process, (3) sedimentation process, and (4) discharge process—the BOD load is predicted, and if the BOD load rises above a predetermined value, for example, the BOD inflow into the semi-batch biological treatment tank 50 is adjusted to remain as constant as possible so as not to increase. This enables a stable supply of granules from the semi-batch biological treatment tank 50 to the continuous biological treatment tank 52, and consequently, enables the maintenance of stable treatment performance.

[0156] In the water treatment method and water treatment apparatus 5 according to this embodiment, the amount of BOD flowing into the semi-batch biological treatment tank 50 per day is adjusted to be substantially constant. Here, "substantially constant" means that the daily fluctuation range of the amount of BOD supplied to the semi-batch biological treatment tank 50 is, for example, 20% or less.

[0157] The amount of treated water supplied from the semi-batch biological treatment tank 50 to the continuous biological treatment tank 52 may be adjusted by adjusting the flow rate and operating time of the treated water pump 60.

[0158] The granular sludge formed in the semi-batch biological treatment tank 50 is sludge that has undergone self-granulation, and is biological sludge with an average particle size of, for example, 200 μm or more. The average particle size of the granular sludge is preferably in the range of 200 μm to 3000 μm, and more preferably in the range of 300 μm to 500 μm. If the average particle size of the granular sludge is less than 200 μm, the membrane filtration performance in the continuous biological treatment tank 52 may decrease, and if it exceeds 3000 μm, the stirring performance in the continuous biological treatment tank 52 or the semi-batch biological treatment tank 50 may decrease.

[0159] Whether or not granular sludge has formed can be determined by measuring the particle size distribution of the sludge in the semi-batch biological treatment tank 50, and when the average particle size reaches, for example, 200 μm or more, it can be determined that granular sludge has formed. Alternatively, the SVI value can be measured periodically by a sedimentation test of the sludge in the semi-batch biological treatment tank 50, and when the SVI5 value calculated from the volume ratio after 5 minutes of sedimentation falls below a predetermined value (for example, 100 mL / g or less), it can be determined that granular sludge has formed (note that the lower the SVI value and the larger the average particle size, the better the granular sludge can be judged to be).

[0160] In the water treatment method and water treatment apparatus 5 according to this embodiment, it is preferable to supply granular sludge having an average particle size of 200 μm or more, generated in the semi-batch biological treatment tank 50, to the continuous biological treatment tank 52 such that the granule presence rate relative to the amount of sludge in the continuous biological treatment tank 52 is, for example, 10% or more, preferably 20% or more, and more preferably 50% or more. If the granule presence rate relative to the amount of sludge in the continuous biological treatment tank 52 is less than 10%, the membrane filtration performance in the continuous biological treatment tank 52 may decrease.

[0161] The following describes the various components of the water treatment device 5.

[0162] The water quality measuring device 56 is not particularly limited as long as it is capable of measuring the water quality in the semi-batch biological treatment tank 50. Examples of water quality measuring devices 56 include BOD measuring devices, COD (Chemical Oxygen Demand) measuring devices, ammonia nitrogen concentration measuring devices, pH measuring devices, and conductivity measuring devices. Of these, pH measuring devices are preferred in terms of maintainability and operating costs.

[0163] Figure 5 shows an example of the overview of the water quality profile inside the semi-batch biological treatment tank 50. During the aeration process in the semi-batch biological treatment tank 50, the substances to be treated gradually decompose. After a predetermined time, the concentration of biodegradable substances to be treated becomes almost constant. By understanding the time it takes for this concentration to become almost constant (the treatment time of the substances to be treated), it is possible to predict the amount of BOD load on the semi-batch biological treatment tank 50 in that cycle. In order to predict the amount of BOD load, the relationship between the amount of BOD load and the treatment time of the substances to be treated should be understood in advance, and a decision can be made based on this. The relationship between the amount of BOD load and the treatment time of the substances to be treated may also be affected by the water temperature, so it is preferable to understand the relationship between the amount of BOD load and the treatment time of the substances to be treated according to the water temperature in advance and adjust according to the water temperature conditions. In order to accurately understand the amount of BOD load on the semi-batch biological treatment tank 50 in the cycle, it is preferable to keep the sludge concentration inside the semi-batch biological treatment tank 50 as constant as possible. In order to maintain the sludge concentration in the semi-batch biological treatment tank 50 as constant as possible, it is preferable to pre-determine the amount of sludge discharged in order to maintain the sludge concentration as constant as possible in relation to a predetermined BOD load. The amount of sludge discharged may be adjusted based on the daily sludge concentration measurement results in the semi-batch biological treatment tank 50. Alternatively, a sensor capable of determining the sludge concentration may be installed in the semi-batch biological treatment tank 50, and the amount of sludge discharged may be automatically adjusted to adjust the sludge concentration based on the values ​​of the sensor. The sensor for determining the sludge concentration is not particularly limited, but for example, transmitted light type or scattered light type sensors can be used.

[0164] The immersion membrane module 68 consists of at least one module, for example, a filtration membrane housed in a sealable container. The filtration membrane installed in the immersion membrane module 68 can be any known filtration membrane, such as an ultrafiltration membrane or a microfiltration membrane. The shape of the filtration membrane is not particularly limited and can be any of the following: a hollow fiber membrane, a tubular membrane, a flat membrane, or a spiral membrane. Any water flow method, such as an internal pressure type or an external pressure type, can be applied to the immersion membrane module 68.

[0165] Examples of materials for the filtration membrane include organic membranes such as polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyethersulfone (PES), and cellulose acetate (CA), as well as inorganic membranes made of ceramic. The molecular weight cutoff of the filtration membrane is, for example, in the range of 5,000 to 360,000, with a preferred range of 10,000 to 360,000. The pore size of the filtration membrane is, for example, in the range of 0.01 to 0.1 μm, with a preferred range of 0.01 to 0.03 μm.

[0166] In the water treatment method and water treatment apparatus 5 according to this embodiment, the flux of the filtration membrane is affected by the type and properties of the water to be treated, the properties of the sludge, the area and material of the filtration membrane, etc., but even if it is set to, for example, 0.6 m / day or more, or even 1.0 m / day or more, the increase in the suction pressure of the filtration membrane is suppressed, and stable operation is possible.

[0167] The membrane separation means for separating the biologically treated water and biological sludge in the continuous biological treatment tank 52 using a filtration membrane is not limited to an immersed membrane module 68, but may also be an external membrane module. Specifically, a membrane module may be installed outside the continuous biological treatment tank 52, and the biologically treated water and biological sludge in the continuous biological treatment tank 52 may be supplied to the external membrane module via piping or the like for membrane filtration treatment.

[0168] The continuous biological treatment tank 52 may be a biological treatment system using a standard activated sludge method for treating organic matter, or a nutrient removal system such as A2O (Anaerobic-Anoxic-Oxic Process) or AO (Anaerobic-Oxic Process) (a system that includes an oxygen-free treatment tank or an anaerobic treatment tank), or a biological treatment system such as the oxidation ditch method or the step-inflow multi-stage activated sludge method. It may also be a device that performs biological treatment in the presence of a carrier such as polyurethane, plastic, or resin.

[0169] Furthermore, as described above, by supplying granular sludge with an average particle size of, for example, 200 μm or more, generated in the semi-batch biological treatment tank 50 to the continuous biological treatment tank 52 in such a way that the granule content is, for example, 10% or more of the total sludge volume in the continuous biological treatment tank 52, it becomes possible to create an aerobic state outside the granules and an anaerobic state inside the granules. As a result, denitrification reactions occur even when dissolved oxygen is present in the bulk water (aerobic state), so it is not always necessary to install an anaerobic tank in a nutrient removal system.

[0170] The continuous biological treatment tank 52 should be operated, for example, when the sludge concentration in the tank is in the range of 2,000 to 20,000 mg / L. In addition, in order to maintain the integrity of the biological sludge (settling properties, activity, etc.), the sludge load should be in the range of 0.05 to 0.6 kg BOD / MLSS / day, and preferably in the range of 0.1 to 0.5 kg BOD / MLSS / day.

[0171] The proportion of granular sludge in the continuous biological treatment tank 52 is determined by a laser diffraction particle size analyzer or the like. If the proportion of granular sludge does not reach, for example, 10%, it is desirable to supply biological sludge containing, for example, granular sludge with an average particle size of 200 μm or more from the semi-batch biological treatment tank 50 to the continuous biological treatment tank 52 again for a predetermined time and flow rate. This operation may be performed by an operator, or the proportion of granular sludge may be adjusted using a control device that can appropriately control the supply amount of granular sludge while measuring the particle size distribution of the sludge in the continuous biological treatment tank 52 with a laser diffraction particle size analyzer or the like. This control device may be the same device as the control device 54 described above, or a different device may be used.

[0172] The MLSS concentration in the semi-batch biological treatment tank 50 should be operated in the range of, for example, 2000 to 20000 mg / L. Furthermore, in order to maintain the integrity of the biological sludge (settling properties, activity, etc.), it is preferable to maintain an appropriate sludge load. For example, granular sludge should be withdrawn from the tank so that it is maintained in the range of 0.05 to 0.60 kg BOD / MLSS / day, preferably 0.1 to 0.5 kg BOD / MLSS / day.

[0173] In the formation of granular sludge in the semi-batch biological treatment tank 50, the sedimentation time and the inflow rate of water to be treated per batch should be appropriately controlled. The sedimentation time, during which stirring (including stirring by aeration) is stopped and the sludge is allowed to settle, is calculated from the distance from the water surface to the target sludge interface position and the sludge settling velocity. For example, it should be set between 4 minutes / m and 15 minutes / m, and preferably between 5 minutes / m and 10 minutes / m.

[0174] The inflow rate of treated water into the semi-batch biological treatment tank 50 (the ratio of treated water flowing in to the effective volume during the reaction) can be, for example, in the range of 20% to 120%, and preferably in the range of 40% to 120%. It is believed that sludge granulation progresses as the sludge repeatedly experiences states of very high organic matter concentration (immediately after the inflow process, saturated state) and very low organic matter concentration (towards the end of the aeration process, starved state). Therefore, from the viewpoint of forming granular sludge, it is desirable to have as high an inflow rate of treated water as possible. On the other hand, the higher the inflow rate of treated water, the larger the capacity of the treated water pump 58 becomes, and the higher the cost. For this reason, in terms of granular sludge formation and cost reduction, an inflow rate of treated water in the range of 40% to 120% is preferred.

[0175] The dissolved oxygen (DO) in the semi-batch biological treatment tank 50 should be, for example, 0.5 mg / L or more, which is suitable for general biological treatment, and preferably 1 mg / L or more.

[0176] The control device 54 can be a programmable logic controller (PLC) or a personal computer (PC). The control device 54 is composed of a microcomputer and electronic circuits, for example, which consist of calculation means such as a CPU for calculating programs, and storage means such as ROM and RAM for storing programs and calculation results, and has the above-mentioned functions.

[0177] This specification includes the following embodiments: [1] A water treatment method comprising: a continuous biological treatment step of continuously flowing water to be treated into a continuous biological treatment tank and biologically treating the water with biological sludge while stirring with an agitator; a membrane separation step of separating the biologically treated water obtained in the continuous biological treatment step from the biological sludge using a filtration membrane; and a sludge supply step of supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the peripheral speed of stirring by the agitator in the continuous biological treatment step is 120 cm / sec or less.

[0178] [2] A water treatment method according to [1], wherein the granular sludge has an average particle size of 200 μm or more, and the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

[0179] A water treatment method according to [3], [1], or [2], comprising a circulation step of circulating sludge from the sludge outlet to the sludge inlet of the continuous biological treatment tank using an airlift pump as a circulation pump.

[0180] A water treatment method according to any one of [4] [1] to [3], wherein the amount of membrane washing air per unit volume of the continuous biological reaction tank is 6.4 m ３ / h / m ３ The following water treatment method is used.

[0181] [5] A water treatment apparatus comprising: a continuous biological treatment means for continuously feeding water to be treated into a continuous biological treatment tank and agitating the water with a biological sludge while agitating the water with a biological sludge; a membrane separation means for separating the biologically treated water obtained from the continuous biological treatment means from the biological sludge using a filtration membrane; and a sludge supply means for supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the peripheral speed of agitation by the agitator in the continuous biological treatment means is 120 cm / sec or less.

[0182] A water treatment apparatus according to [6] and [5], wherein the granular sludge has an average particle size of 200 μm or more, and the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

[0183] A water treatment apparatus according to [7], [5], or [6], comprising a circulation means for circulating sludge from the sludge outlet to the sludge inlet of the continuous biological treatment tank using an airlift pump as a circulation pump.

[0184] A water treatment apparatus according to any one of [8], [5] to [7], wherein the amount of membrane washing air per unit volume of the continuous biological reaction tank is 6.4 m３ / h / m ３ The following is a water treatment device.

[0185] [9] A water treatment method comprising: a continuous biological treatment step of continuously flowing water to be treated into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation step of separating the biologically treated water obtained in the continuous biological treatment step and the biological sludge using a filtration membrane; and a sludge supply step of supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the ratio of the BOD sludge load of the continuous biological treatment tank to the semi-batch biological treatment tank is 10 to 30%.

[0186] A water treatment method according to

[10] and [9], characterized in that the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

[0187] A water treatment method according to

[11] , [9], or

[10] , characterized in that the ratio of the water to be treated flowing into the semi-batch biological treatment tank to the continuous biological treatment tank is changed from 30% or less to 70% or more.

[0188]

[12] A water treatment apparatus comprising: a continuous biological treatment means for continuously flowing water to be treated into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation means for separating the biologically treated water obtained from the continuous biological treatment means and the biological sludge using a filtration membrane; and a sludge supply means for supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the ratio of the BOD sludge load of the continuous biological treatment tank to the semi-batch biological treatment tank is 10 to 30%.

[0189] A water treatment apparatus according to

[13] and

[12] , characterized in that the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

[0190] A water treatment apparatus according to

[14] ,

[12] , or

[13] , characterized in that the ratio of the water to be treated flowing from the continuous biological treatment tank to the semi-batch biological treatment tank is changed from 30% or less to 70% or more.

[0191]

[15] A water treatment method comprising: a continuous biological treatment step of continuously flowing water to be treated containing BOD components into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation step of separating the biologically treated water obtained in the continuous biological treatment step from the biological sludge using a filtration membrane; and a sludge supply step of sequentially repeating an inflow step of flowing at least a portion of the water to be treated into a semi-batch biological treatment tank, an aeration step of treating the water to be treated by aeration, a settling step of settling the sludge by sedimentation, and a discharge step of discharging treated water containing the formed granular sludge and supplying it to the continuous biological treatment tank, wherein the amount of BOD flowing into the semi-batch biological treatment tank per day is adjusted to be substantially constant.

[0192] A water treatment method according to

[16] and

[15] , wherein the daily amount of BOD flowing into the semi-batch biological treatment tank is adjusted by adjusting at least one of the time of the inflow process and the time of the aeration process in the semi-batch biological treatment tank.

[0193] A water treatment method according to

[17] ,

[15] , or

[16] , wherein the daily amount of BOD flowing into the semi-batch biological treatment tank is adjusted by adjusting the amount of water to be treated in the inflow step in the semi-batch biological treatment tank.

[0194] A water treatment method according to any one of

[18] ,

[15] to

[17] , wherein the water quality in the tank during the aeration process in the semi-batch biological treatment tank is monitored, and the amount of load flowing into the semi-batch biological treatment tank is adjusted based on the fluctuations in the water quality.

[0195]

[19] A water treatment apparatus comprising: a continuous biological treatment means for continuously flowing water to be treated containing BOD components into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation means for separating the biologically treated water obtained from the continuous biological treatment means and the biological sludge with a filtration membrane; and a sludge supply means for sequentially repeating an inflow step of flowing at least a portion of the water to be treated into a semi-batch biological treatment tank, an aeration step of treating the water to be treated by aeration, a sedimentation step of settling the sludge by sedimentation, and a discharge step of discharging treated water containing the formed granular sludge and supplying it to the continuous biological treatment tank, wherein the amount of BOD flowing into the semi-batch biological treatment tank per day is adjusted to be substantially constant.

[0196] A water treatment apparatus according to

[20] and

[19] , further comprising a time adjustment means for adjusting the time of each process in the semi-batch biological treatment tank, wherein the daily amount of BOD flowing into the semi-batch biological treatment tank is adjusted by adjusting at least one of the time of the inflow process and the time of the aeration process in the semi-batch biological treatment tank.

[0197] A water treatment apparatus according to

[21] ,

[19] , or

[20] , further comprising a flow rate adjustment means for adjusting the flow rate of the water to be treated flowing into the semi-batch biological treatment tank, wherein the daily BOD amount flowing into the semi-batch biological treatment tank is adjusted by adjusting the amount of water to be treated flowing into the inflow step in the semi-batch biological treatment tank.

[0198] A water treatment apparatus according to any one of

[22] ,

[19] to

[21] , further comprising monitoring means for monitoring the water quality in the tank during the aeration process in the semi-batch biological treatment tank, and characterized in that the amount of load flowing into the semi-batch biological treatment tank is adjusted based on the fluctuations in water quality.

[0199] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0200] <Example 1> In the water treatment apparatus shown in Figure 1, granular sludge was added to a 5 L reaction tank, and a test was conducted in which a stirring device was installed and the peripheral speed was varied. The peripheral speed conditions were 260 cm / sec, 120 cm / sec, and 94 cm / sec.

[0201] The granule abundance, average particle size, and sludge abundance of each particle size were measured using a particle size distribution analyzer (Malvern Master Kaiser 3000).

[0202] Figure 6 shows the average particle size (μm) of granular sludge in the reaction tank as a result of the number of days (days) elapsed during the treatment process in Example 1.

[0203] As a result, differences in average particle size were observed depending on the peripheral speed. When the peripheral speed was 260 cm / sec, the average particle size decreased from 300 μm to 200 μm after one day from the start of the test, and further decreased to 150 μm after four days. On the other hand, when the peripheral speed was 120 cm / sec and 94 cm / sec, the average particle size hardly decreased after four days of testing. In other words, it was found that by operating the stirring device at a peripheral speed of 120 cm / sec or less, it is possible to maintain a high proportion of granular sludge in the reaction tank.

[0204] <Example 2> In the water treatment apparatus shown in Figure 1, the abundance and average particle size of granules in the membrane separation tank were set to 7m ３ An experiment was conducted using the reaction vessel, varying the peripheral speed of the stirring device. A flat membrane was used as the membrane. The aeration airflow rate for membrane washing per unit of tank volume was 6.4 m³. ３ / h / m ３ The peripheral speed of the agitator was set to 353 cm / sec during period (1) and 118 cm / sec during period (2) in Figure 7. The amount of granular sludge added was kept constant at 0.2 kg / day during periods (1) and (2). The sludge concentration in the membrane separator was also set to 8000 mg / L.

[0205] Figure 7 shows the average particle size (μm) and granule content (%) of the granule sludge in the reaction tank as a result of the number of days (days) elapsed during the treatment process in Example 2.

[0206] During period (1), the granule content was less than 10%, resulting in a low granule content. However, during period (2), by setting the peripheral speed of the stirrer to 118 cm / sec, the granule content became 10% or more, and the average particle size also became 100 μm or more.

[0207] <Example 3> In the water treatment apparatus shown in Figure 1, the granule abundance in the membrane separation tank and the amount of membrane washing air per unit tank volume were determined as follows: sludge concentration of 8000 mg / L and volumetric load of 0.5 kg / m³. ３ The test was conducted under the condition that the peripheral speed of the stirring device was 120 cm / sec or less per day. The amount of membrane washing air per unit volume was 24.6 m³ when using a 12 L reaction vessel. ３ / h / m ３ Under these conditions, when using a 23L reaction vessel, the result is 6.4m ３ / h / m ３ Each vehicle was operated for 100 hours under these conditions.

[0208] Figure 8 shows the average particle size (μm) of granule sludge in the reaction tank and the percentage of each particle size (μm) of granules in Example 3 as a function of the elapsed processing time (h). Figure 8(a) shows that the membrane washing air volume per tank volume was 6.4 m³. ３ / h / m ３ In this case, Figure 8(b) shows that the membrane cleaning air volume per tank volume is 24.6 m³. ３ / h / m ３ The results for this case are shown.

[0209] The amount of membrane cleaning air per unit tank volume is 6.4 m³. ３ / h / m ３ When operated in this configuration, no significant change in the prevalence of each particle size was observed, and the average particle size also decreased by about 7%. On the other hand, when the membrane cleaning air volume per tank volume was 24.6 m³ ３ / h / m ３ In this case, the prevalence of smaller particle sizes increased, and the average particle size also decreased by 37%.

[0210] Thus, it was found that by setting the peripheral speed of stirring by the agitator in the continuous biological treatment process to 120 cm / sec or less, the granule content in the continuous biological treatment tank is improved in a water treatment system in which granule sludge formed in a semi-batch reaction tank is introduced into a continuous biological treatment tank and treated by membrane separation.

[0211] <Example 4> Using the water treatment apparatus shown in Figure 2, experiments were conducted by varying the ratio of BOD sludge load from the continuous biological treatment tank to the semi-batch biological treatment tank.

[0212] It was found that by setting the ratio of BOD sludge load in the continuous biological treatment tank to the ratio of BOD sludge load in the semi-batch biological treatment tank to 10-30%, the granule content in the continuous biological treatment tank is improved in a water treatment system in which granule sludge formed in the semi-batch reaction tank is introduced into the continuous biological treatment tank and treated by membrane separation.

[0213] 1, 3, 5 Water treatment equipment, 10 Water to be treated, 12 Semi-batch biological treatment tank, 14 Continuous biological treatment tank, 16 Control device, 18, 42 Pumps, 20 Circulation pumps, 22, 24 Valves, 26 Agitator, 28 Immersion membrane module, 30, 32 Water to be treated inflow line, 34 Biological sludge supply line, 36 Circulation line, 38 Biologically treated water discharge line, 40 Treated water discharge line, 50 Semi-batch biological treatment tank, 52 Continuous biological treatment tank, 54 Control device, 56 Water quality measuring device, 58 Water to be treated pump, 60 Treated water pump, 62 Biologically treated water pump, 64, 78 Blower, 66, 80, 82 Aeration device, 68 Immersion membrane module, 70, 72 Water to be treated inflow line, 74 Treated water / sludge supply line, 76 Biologically treated water discharge line, 100 102 Sedimentation tank, 104 Semi-batch biological treatment tank, 104a Continuous biological treatment tank, 104b Reaction tank, 106 Recovery device, 112 Aeration device, 114, 120, 122 Treatment water inflow line, 116 Agitator, 118 Submersible membrane module, 124 Biological sludge supply line, 126 Circulation line, 128 Biologically treated water discharge line, 130 Treated water line, 132 Sludge line, 134 Sludge recovery line, 136 Excess sludge discharge line.

Claims

1. A water treatment method comprising: a continuous biological treatment step in which water to be treated is continuously fed into a continuous biological treatment tank and biologically treated with biological sludge while being stirred by an agitator; a membrane separation step in which the biologically treated water obtained in the continuous biological treatment step and the biological sludge are separated by a filtration membrane; and a sludge supply step in which granular sludge formed in a semi-batch biological treatment tank is supplied to the continuous biological treatment tank, wherein the peripheral speed of stirring by the agitator in the continuous biological treatment step is 120 cm / sec or less.

2. A water treatment method according to claim 1, characterized in that the granular sludge has an average particle size of 200 μm or more, and the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

3. A water treatment method according to claim 1 or 2, characterized in that it includes a circulation step of circulating sludge from the sludge outlet to the sludge inlet of the continuous biological treatment tank using an airlift pump as a circulation pump.

4. A water treatment method according to any one of claims 1 to 3, wherein the amount of membrane washing air per unit volume of the continuous biological reaction tank is 6.4 m³. ３ / h / m ３ A water treatment method characterized by the following:

5. A water treatment apparatus comprising: a continuous biological treatment means for continuously feeding water to be treated into a continuous biological treatment tank and biologically treating the water with biological sludge while stirring it with an agitator; a membrane separation means for separating the biologically treated water obtained from the continuous biological treatment means and the biological sludge using a filtration membrane; and a sludge supply means for supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the peripheral speed of stirring by the agitator in the continuous biological treatment means is 120 cm / sec or less.

6. A water treatment apparatus according to claim 5, characterized in that the granular sludge has an average particle size of 200 μm or more, and the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

7. A water treatment apparatus according to claim 5 or 6, characterized in that it comprises a circulation means for circulating sludge from the sludge outlet to the sludge inlet of the continuous biological treatment tank using an airlift pump as a circulation pump.

8. A water treatment apparatus according to any one of claims 5 to 7, wherein the amount of membrane washing air per unit volume of the continuous biological reaction tank is 6.4 m³. ３ / h / m ３ A water treatment apparatus characterized by the following:

9. A water treatment method comprising: a continuous biological treatment step of continuously flowing water to be treated into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation step of separating the biologically treated water obtained in the continuous biological treatment step from the biological sludge using a filtration membrane; and a sludge supply step of supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the ratio of the BOD sludge load of the continuous biological treatment tank to the semi-batch biological treatment tank is 10 to 30%.

10. A water treatment method according to claim 9, characterized in that the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

11. A water treatment method according to claim 9 or 10, characterized in that the ratio of the flow of water to be treated from 30% or less to 70% or more to the flow of water to be treated from the flow of water to the semi-batch biological treatment tank to the flow of water to be treated from 30% or less to 70% or more.

12. A water treatment apparatus comprising: a continuous biological treatment means for continuously flowing water to be treated into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation means for separating the biologically treated water obtained from the continuous biological treatment means and the biological sludge using a filtration membrane; and a sludge supply means for supplying granular sludge formed in a semi-batch biological treatment tank to the continuous biological treatment tank, wherein the ratio of the BOD sludge load of the continuous biological treatment tank to the semi-batch biological treatment tank is 10 to 30%.

13. A water treatment apparatus according to claim 12, characterized in that the granular sludge is supplied to the continuous biological treatment tank such that the proportion of granules relative to the amount of sludge in the continuous biological treatment tank is 10% or more.

14. A water treatment apparatus according to claim 12 or 13, characterized in that the ratio of the flow of water to be treated from 30% or less to 70% or more to the flow of water to be treated from the continuous biological treatment tank to the semi-batch biological treatment tank.

15. A water treatment method comprising: a continuous biological treatment step of continuously flowing water to be treated containing BOD components into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation step of separating the biologically treated water obtained in the continuous biological treatment step from the biological sludge using a filtration membrane; and a sludge supply step of sequentially repeating an inflow step of flowing at least a portion of the water to be treated into a semi-batch biological treatment tank, an aeration step of treating the water to be treated by aeration, a settling step of settling the sludge by sedimentation, and a discharge step of discharging treated water containing the formed granular sludge and supplying it to the continuous biological treatment tank, wherein the amount of BOD flowing into the semi-batch biological treatment tank per day is adjusted to be substantially constant.

16. A water treatment method according to claim 15, characterized in that the daily amount of BOD flowing into the semi-batch biological treatment tank is adjusted by adjusting at least one of the time of the inflow process and the time of the aeration process in the semi-batch biological treatment tank.

17. A water treatment method according to claim 15 or 16, characterized in that the daily amount of BOD flowing into the semi-batch biological treatment tank is adjusted by adjusting the amount of water to be treated in the inflow step in the semi-batch biological treatment tank.

18. A water treatment method according to any one of claims 15 to 17, characterized in that the water quality in the tank during the aeration process in the semi-batch biological treatment tank is monitored, and the amount of load flowing into the semi-batch biological treatment tank is adjusted based on the fluctuations in the water quality.

19. A water treatment apparatus comprising: a continuous biological treatment means for continuously flowing water to be treated containing BOD components into a continuous biological treatment tank and biologically treating the water to be treated with biological sludge; a membrane separation means for separating the biologically treated water obtained from the continuous biological treatment means and the biological sludge using a filtration membrane; and a sludge supply means for sequentially repeating an inflow step of flowing at least a portion of the water to be treated into a semi-batch biological treatment tank, an aeration step of treating the water to be treated by aeration, a sedimentation step of settling the sludge by sedimentation, and a discharge step of discharging treated water containing the formed granular sludge and supplying it to the continuous biological treatment tank, wherein the amount of BOD flowing into the semi-batch biological treatment tank per day is adjusted to be substantially constant.

20. A water treatment apparatus according to claim 19, further comprising a time adjustment means for adjusting the time of each process in the semi-batch biological treatment tank, wherein the daily amount of BOD flowing into the semi-batch biological treatment tank is adjusted by adjusting at least one of the time of the inflow process and the time of the aeration process in the semi-batch biological treatment tank.

21. A water treatment apparatus according to claim 19 or 20, further comprising flow rate adjustment means for adjusting the flow rate of the water to be treated flowing into the semi-batch biological treatment tank, wherein the adjustment of the daily BOD amount flowing into the semi-batch biological treatment tank is performed by adjusting the amount of water to be treated flowing into the inflow step in the semi-batch biological treatment tank.

22. A water treatment apparatus according to any one of claims 19 to 21, further comprising monitoring means for monitoring the water quality in the tank during the aeration process in the semi-batch biological treatment tank, and characterized in that the amount of load flowing into the semi-batch biological treatment tank is adjusted based on the fluctuations in the water quality.

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