Wastewater treatment system and wastewater treatment method

Abstract

To provide a wastewater treatment system that has a low running cost and is applicable to all types of biological treatment methods.SOLUTION: A wastewater treatment system comprises: a solid-liquid separation unit 10 having a plurality of solid-liquid separators 11A-11C arranged in parallel, and flow regulators 12A-12C which are respectively arranged in the upper stage of the solid-liquid separators 11A-11C and are capable of regulating the amount of organic wastewater distributed to the solid-liquid separators 11A-11C; and a biological treatment apparatus 20 which is arranged in the lower stage of the solid-liquid separation unit 10 and biologically treats the organic wastewater by microorganisms. The plurality of solid-liquid separators 11A-11C include a first solid-liquid separator 11A with a screen having relatively coarse openings, and second solid-liquid separators 11B, 11C with screens having relatively fine openings.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a system and method for treating organic wastewater by biological treatment. [Background technology]

[0002] In the treatment of organic wastewater such as sewage, biological treatment methods have traditionally been used to remove nitrogen, phosphorus, and other contaminants using the action of microorganisms. Such biological treatment methods require the removal of solids, such as garbage and screen residue, from the wastewater to a certain extent before the microbial treatment. Therefore, wastewater treatment systems that use biological treatment methods typically include a solid-liquid separation means for separating solids from the wastewater, located upstream of the reaction tank where the microbial treatment is performed.

[0003] For example, the wastewater treatment system disclosed in Patent Document 1, which applies a nitrification-denitrification method to remove nitrogen, includes a denitrification tank, which is a reaction tank, and multiple primary sedimentation tanks arranged in parallel above the nitrification tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-38389 Summary of the Invention [Problem to be solved by the invention]

[0005] The removal rate of nitrogen, phosphorus, and other substances using biological treatment is greatly affected by the ratio of the BOD concentration (biochemical oxygen demand) of the organic wastewater flowing into the reaction tank to the nitrogen concentration or phosphorus concentration (BOD / N ratio or BOD / P ratio); for example, to efficiently remove nitrogen, it is said that the BOD / N ratio must be at least 3. Therefore, in wastewater treatment systems that use biological treatment, it is necessary to control the BOD / N ratio or BOD / P ratio of the wastewater flowing into the reaction tank to an appropriate value.

[0006] In the case of a wastewater treatment system such as that disclosed in Patent Document 1, when the BOD / N ratio of the wastewater flowing into the reaction tank is not an appropriate value, measures have been taken to increase or decrease the amount of organic matter flowing into the reaction tank by supplying a hydrogen donor (e.g., methanol) to the reaction tank or by bypassing the primary settling tank and flowing the organic wastewater directly into the reaction tank.

[0007] However, supplying a hydrogen donor to the reactor tank increases the running costs, and bypassing the primary sedimentation tank may damage the membrane separation device in the membrane bioreactor activated sludge process, which uses a membrane separation device instead of a final sedimentation tank.

[0008] The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a wastewater treatment system which has low running costs and is applicable regardless of the type of biological treatment method. [Means for solving the problem]

[0009] To achieve the above-mentioned object, the wastewater treatment system according to the present invention includes a solid-liquid separation unit having a plurality of solid-liquid separation devices arranged in parallel and flow rate adjusting devices arranged above each of the solid-liquid separation devices and capable of adjusting the amount of organic wastewater flowing through the solid-liquid separation devices; a biological treatment device arranged below the solid-liquid separation units and performing biological treatment on the organic wastewater using microorganisms; a water quality sensor that detects an index value related to the water quality of the organic wastewater biologically treated in the biological treatment device; and a control device that controls the flow rate adjusting device based on the water quality and adjusts the distribution of the organic wastewater circulated to the plurality of solid-liquid separation devices. The plurality of solid-liquid separation devices include: specified a first solid-liquid separator provided with a mesh screen; From the screen of the first solid-liquid separator and a second solid-liquid separator provided with a fine-mesh screen. The index value is at least one of a nitrogen concentration and a phosphorus concentration, and the control device increases the amount of organic wastewater circulated to the first solid-liquid separation device when the index value exceeds a predetermined upper limit value, and increases the amount of organic wastewater circulated to the second solid-liquid separation device when the index value falls below a predetermined lower limit value. It is characterized by the following.

[0010] In the wastewater treatment system described above, the organic wastewater that passes through the first solid-liquid separator equipped with a relatively coarse-mesh screen contains more organic matter than the organic wastewater that passes through the second solid-liquid separator equipped with a relatively fine-mesh screen. Therefore, by adjusting the distribution of the organic wastewater flowing through the multiple solid-liquid separators included in the solid-liquid separation unit using a flow control device, it is possible to adjust the amount of organic matter flowing into the biological treatment device. For example, if it is necessary to increase the amount of organic matter flowing into the biological treatment device, the amount of organic wastewater flowing through the first solid-liquid separator can be increased. Conversely, if it is necessary to decrease the amount of organic matter flowing into the biological treatment device, the amount of organic wastewater flowing through the second solid-liquid separator can be increased.

[0011] Furthermore, with the above configuration, the amount of organic matter flowing into the biological treatment device can be adjusted simply by adjusting the distribution of organic wastewater flowing through the solid-liquid separation device, thereby keeping running costs low. Furthermore, with the above configuration, when a membrane bioreactor is applied to a wastewater treatment system, solids above a certain size can be removed in the solid-liquid separation device, and there is no risk of damaging the membrane separation device, so the membrane bioreactor can be applied without any problems.

[0012] As mentioned above, if the amount of organic matter flowing into the biological treatment device is inappropriate, the quality of the treated organic wastewater (hereinafter sometimes referred to as treated water) may deteriorate. With the above configuration, the index value related to the water quality of the treated water can be monitored, and the amount of organic matter flowing into the biological treatment device can be increased or decreased depending on the deterioration of the water quality, thereby making it possible to improve the water quality.

[0013] In wastewater treatment systems designed to remove nitrogen and phosphorus, if the amount of organic matter flowing into the biological treatment device is insufficient relative to the load of nitrogen and phosphorus, the removal rate of nitrogen and phosphorus by biological treatment decreases, resulting in increased nitrogen and phosphorus concentrations in the treated water. In other words, whether the amount of organic matter flowing into the biological treatment device is insufficient can be determined based on the nitrogen and phosphorus concentrations of the treated water. High nitrogen and phosphorus concentrations in the treated water indicate an insufficient amount of organic matter flowing into the biological treatment device. Therefore, with the above-described configuration, control can be performed to increase the amount of organic matter flowing into the biological treatment device when the nitrogen and phosphorus concentrations of the treated water detected by the water quality sensor exceed a preset upper limit. This increases the removal rate of nitrogen and phosphorus by biological treatment, thereby enabling the nitrogen and phosphorus concentrations of the treated water to be reduced to or below their upper limits.

[0014] In wastewater treatment systems designed to remove nitrogen and phosphorus, increasing the amount of organic matter flowing into the biological treatment device increases the rate of nitrogen and phosphorus removal by the biological treatment, lowering the nitrogen and phosphorus concentrations in the treated water. However, excessive organic matter flowing into the biological treatment device also increases the BOD load in the biological treatment, necessitating the injection of large amounts of air to oxidize and decompose the excess BOD, increasing running costs. Therefore, with the above configuration, control can be performed to reduce the amount of organic matter flowing into the biological treatment device when the nitrogen and phosphorus concentrations in the treated water detected by the water quality sensor fall below a preset lower limit, thereby preventing excessive organic matter flowing into the biological treatment device.

[0015] In the wastewater treatment system according to the present invention, the solid-liquid separator is preferably a rotary filter type solid-liquid separator.

[0016] The rotary filter type solid-liquid separation device is smaller than a conventional settling tank, yet can treat the same or even larger amounts of water. Therefore, the above configuration makes it possible to save the space required to install the wastewater treatment system.

[0017] In the wastewater treatment system according to the present invention, it is preferable that the flow rate adjusting device is a movable weir.

[0018] According to the above configuration, the amount of organic wastewater flowing through the solid-liquid separator can be freely adjusted by the movable weir.

[0019] In order to achieve the above object, the wastewater treatment method according to the present invention comprises: specified a first solid-liquid separator provided with a mesh screen; From the screen of the first solid-liquid separator a solid-liquid separation step in which organic wastewater is circulated through a plurality of solid-liquid separation devices arranged in parallel, including a second solid-liquid separation device provided with a fine-mesh screen; and a biological treatment step in which the organic wastewater that has passed through the plurality of solid-liquid separation devices is circulated through a biological treatment device. a detection step of detecting an index value related to the water quality of the organic wastewater biologically treated in the biological treatment device; before record water and a distribution adjusting step of adjusting the distribution of the organic wastewater circulated to the plurality of solid-liquid separation devices based on the quality of the organic wastewater. The index value is at least one of a nitrogen concentration and a phosphorus concentration, and in the distribution adjustment step, when the index value exceeds a predetermined upper limit value, the amount of organic wastewater circulated to the first solid-liquid separation device is increased, and when the index value falls below a predetermined lower limit value, the amount of organic wastewater circulated to the second solid-liquid separation device is increased. It is characterized by:

[0020] In the solid-liquid separation process, the organic wastewater that passes through the first solid-liquid separator equipped with a relatively coarse-mesh screen contains more organic matter than the organic wastewater that passes through the second solid-liquid separator equipped with a relatively fine-mesh screen. Therefore, with the above configuration, the amount of organic matter flowing into the biological treatment device can be adjusted by adjusting the distribution of organic wastewater flowing through the multiple solid-liquid separators included in the solid-liquid separation unit. Furthermore, with the above configuration, the amount of organic matter flowing into the biological treatment device can be adjusted simply by adjusting the distribution of organic wastewater flowing through the solid-liquid separators, thereby reducing running costs. Furthermore, with the above configuration, when a membrane bioreactor is used in a wastewater treatment system that performs a wastewater treatment method, solids above a certain size can be removed in the solid-liquid separator, eliminating the risk of damage to the membrane separator, allowing the membrane bioreactor to be used without any problems. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a block diagram showing a schematic configuration of a wastewater treatment system according to the present invention. [Figure 2] FIG. 1 is a diagram showing a specific configuration of a solid-liquid separator and a biological treatment device in a wastewater treatment system. [Figure 3] FIG. 1 is a diagram illustrating adjustment of the amount of organic matter flowing into a biological treatment device based on the nitrogen concentration of the treated water. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of a wastewater treatment system and a wastewater treatment method using the same according to the present invention will be described, taking as an example a wastewater treatment system that applies a nitrification-denitrification method for the purpose of removing nitrogen contained in organic wastewater such as sewage. However, the wastewater treatment system according to the present invention is not limited to the nitrification-denitrification method, and can be applied to any biological treatment method that biologically treats organic wastewater.

[0023] <Configuration of wastewater treatment system> 1, the wastewater treatment system includes a solid-liquid separation unit 10 for separating solids such as garbage and screen residue from organic wastewater that has passed through a settling basin (not shown), a biological treatment device 20 for biologically treating the organic wastewater from which the solids have been separated by the solid-liquid separation unit 10, a water quality sensor 30 for detecting an index value related to the water quality of the organic wastewater that has been biologically treated by the biological treatment device 20, and a control device 40 for controlling the solid-liquid separation unit 10 based on the detection results of the water quality sensor 30. In the following description, the organic wastewater that flows to the solid-liquid separation unit 10 may be referred to as water to be treated W1, the organic wastewater from which the solids have been separated by the solid-liquid separation unit 10 may be referred to as separated water W2, and the organic wastewater that has been biologically treated by the biological treatment device 20 may be referred to as treated water W3.

[0024] [Solid-liquid separation unit] The solid-liquid separation unit 10 includes a plurality of solid-liquid separators 11A to 11C arranged in parallel, in this embodiment, first to third solid-liquid separators 11A to 11C. Each of the solid-liquid separators 11A to 11C is provided with a screen having an opening of 0.1 to 2.0 mm. Of these, the screen provided in the first solid-liquid separator 11A is specified The screens provided in the second and third solid-liquid separators 11B and 11C have a mesh size of, for example, 0.7 mm. twist The mesh size is small, for example, 0.3 mm. Note that the above mesh size is an example, and the screens that can be used in the wastewater treatment system of the present invention are not limited to this.

[0025] For example, as shown in Fig. 2, in this embodiment, the first to third solid-liquid separators 11A to 11C are rotary filter type separators. For convenience, Fig. 2 shows only the first solid-liquid separator 11A, but the second and third solid-liquid separators 11B and 11C have the same structure as the first solid-liquid separator 11A except for the screen openings, and therefore their description will be omitted. Furthermore, the solid-liquid separator 11A shown in Fig. 2 is an example of a rotary filter type separator, and other rotary filter types may also be used.

[0026] The first solid-liquid separation device 11A has a filter unit 111 in which panel filters serving as screens are connected in an endless band shape, and multiple rotors 112 for moving each panel filter of the filter unit 111. The filter unit 111 is arranged at an angle across the flow path of the water to be treated W1 that flows into the first solid-liquid separation device 11A. Rotation of the rotor 112 moves the panel filter from below to above on the primary side into which the water to be treated W1 flows, thereby capturing solids by the panel filter and separating them from the water to be treated W1. Solids adhering to the panel filter of the filter unit 111 are removed by a scraper 113 that scrapes off the solids from the front side of the panel filter and a spray 114 that sprays cleaning water from the back side of the panel filter to remove the solids. Meanwhile, the separated water W2 that has passed through the filter unit 111 flows out of the first solid-liquid separation device 11A, merges with the separated water W2 from the second and third solid-liquid separation devices 11B and 11C, and is circulated to the biological treatment device 20.

[0027] The panel filter, ie, the screen of the filter unit 111 is replaceable, and a screen with an appropriate mesh size can be used depending on the properties of the water to be treated W1 or the target removal rate.

[0028] The solid-liquid separation unit 10 further includes movable weirs 12A-12C as flow rate control devices, respectively arranged above the solid-liquid separators 11A-11C. The movable weirs 12A-12C have openable and closable gates and drive mechanisms for opening and closing the gates, and may be known lift weirs or undulating weirs. The amount of water W1 to be treated flowing through each of the solid-liquid separators 11A-11C can be adjusted by controlling the opening and closing of the gates of the movable weirs 12A-12C.

[0029] [Biological treatment equipment] For example, as shown in FIG. 2, the biological treatment device 20 is a circulating nitrification / denitrification type membrane separation activated sludge treatment device having an anoxic tank 21 and an aerobic tank 22 provided with a separation membrane 23. In the aerobic tank 22, ammonia nitrogen in the separated water W2 that flows into the biological treatment device 20 is nitrified by nitrifying bacteria and converted into nitrate nitrogen. This nitrate nitrogen is circulated to the anoxic tank 21 as an activated sludge mixed liquid. In the anoxic tank 21, the nitrate nitrogen is denitrified by denitrifying bacteria and converted into nitrogen gas, which is discharged into the atmosphere. In the separation membrane 23, the activated sludge mixed liquid with a reduced nitrogen concentration is membrane filtered. In this way, treated water W3 with a reduced nitrogen concentration is discharged from the biological treatment device 20. The discharged treated water W3 is reused or discharged into a river or the like.

[0030] [Water quality sensor] The water quality sensor 30 detects at least the nitrogen concentration as an index value related to the water quality of the treated water W3 discharged from the biological treatment device 20. The water quality sensor 30 transmits the detected nitrogen concentration to the control device 40 as a signal.

[0031] [Control device] Based on the signal received from the water quality sensor 30, the control device 40 generates a signal for controlling the opening and closing operation of the gates of the movable weirs 12A to 12C, and transmits the signal to the drive mechanisms of the movable weirs 12A to 12C.

[0032] <First embodiment of wastewater treatment method> The wastewater treatment method according to the present invention includes a solid-liquid separation step, a biological treatment step, and a distribution adjustment step.

[0033] The solid-liquid separation step is a step in which the water to be treated W1 that has passed through the grit basin is passed through first to third solid-liquid separators 11A to 11C to separate solids such as garbage and screen residue from the water to be treated W1.

[0034] The biological treatment step is a step in which the separated water W2 that has passed through the first to third solid-liquid separators 11A to 11C is passed through a biological treatment device 20, and nitrogen is removed from the separated water W2 by biological treatment.

[0035] The distribution adjustment process is a process in which the control device 40 adjusts the distribution of the treated water W1 circulating through the first to third solid-liquid separation devices 11A to 11C based on the water quality of the treated water W3 that has been biologically treated in the biological treatment device 20.

[0036] The nitrogen removal rate by the biological treatment device 20 varies depending on the properties of the separated water W2 flowing into the biological treatment device 20, particularly the BOD / N ratio. Therefore, if the BOD / N ratio of the separated water W2 is unstable, the nitrogen concentration of the treated water W3 discharged from the biological treatment device 20 will also be unstable. The treated water W3 discharged from the biological treatment device 20 usually has an allowable limit for the nitrogen concentration determined depending on the purpose of reuse or the discharge destination. Therefore, it is necessary to adjust the BOD / N ratio of the separated water W2 flowing into the biological treatment device 20 so that the nitrogen concentration of the treated water W3 does not exceed the allowable limit.

[0037] Therefore, in the distribution adjustment process, the control device 40 compares the nitrogen concentration of the treated water W3 detected by the water quality sensor 30 with an upper limit value set lower than the allowable limit value at predetermined time intervals, as shown in Fig. 3. When the nitrogen concentration of the treated water W3 exceeds the upper limit value (t1), the control device 40 controls the opening and closing of the gates of the movable weirs 12A-12C to adjust the distribution of the treated water W1 circulating through the first to third solid-liquid separation devices 11A-11C so as to increase the amount of the treated water W1 distributed to the first solid-liquid separation device 11A. In other words, the control device 40 increases the amount of water to be treated W1 circulating through the first solid-liquid separation device 11A by a predetermined amount, and reduces the total amount of water to be treated W1 circulating through the second and third solid-liquid separation devices 11B and 11C by that amount.

[0038] When the amount of water W1 to be treated flowing through the first solid-liquid separator 11A, which has a lower solid removal rate than the second and third solid-liquid separators 11B and 11C, increases, the amount of organic matter derived from solids increases in the overall separated water W2 sent to the biological treatment device 20 through the first to third solid-liquid separators 11A to 11C, resulting in an increase in the BOD / N ratio. As a result, the nitrogen removal rate by biological treatment increases, and the nitrogen concentration of the treated water W3 discharged from the biological treatment device 20 eventually begins to decrease. The control device 40 controls the amount of water W1 to be treated flowing through the first solid-liquid separator 11A to increase until the nitrogen concentration of the treated water W3 falls below the upper limit. This prevents the discharge of treated water W3 with a nitrogen concentration exceeding the allowable limit.

[0039] On the other hand, if the amount of organic matter flowing into the biological treatment device 20 increases, more air must be blown into the aerobic tank 22 to compensate for the oxygen consumed in the biological reaction, which increases running costs. Therefore, in the distribution adjustment process, the control device 40 compares the nitrogen concentration of the treated water W3 detected by the water quality sensor 30 with a lower limit value set lower than the upper limit value at predetermined time intervals. Then, when the nitrogen concentration of the treated water W3 falls below the lower limit value (t2), the control device 40 controls the opening and closing of the gates of the movable weirs 12A-12C to adjust the distribution of the treated water W1 circulating through the first to third solid-liquid separation devices 11A-11C so as to increase the amount of the treated water W1 distributed to the second and third solid-liquid separation devices 11B and 11C. In other words, the control device 40 increases the total amount of the water to be treated W1 circulating through the second and third solid-liquid separation devices 11B and 11C by a predetermined amount, and reduces the amount of the water to be treated W1 circulating through the first solid-liquid separation device 11A by the same amount.

[0040] When the amount of water W1 being treated increases through the second and third solid-liquid separators 11B and 11C, which have a higher solid removal rate than the first solid-liquid separator 11A, the amount of organic matter derived from solids in the separated water W2 passing through the first to third solid-liquid separators 11A to 11C and sent to the biological treatment device 20 decreases, resulting in a decrease in the BOD / N ratio. As a result, the nitrogen removal rate through biological treatment decreases, and the nitrogen concentration of the treated water W3 discharged from the biological treatment device 20 eventually begins to increase. The control device 40 controls the amount of water W1 being treated being treated through the second and third solid-liquid separators 11B and 11C until the nitrogen concentration of the treated water W3 reaches or exceeds a lower limit. This prevents excessive organic matter from entering the biological treatment device, reducing running costs.

[0041] Furthermore, the nitrogen concentration of the treated water W3 may continue to rise as the amount of organic matter flowing into the biological treatment device 20 decreases even after it reaches or exceeds the lower limit value, but when the nitrogen concentration exceeds the upper limit value, control is again performed to increase the amount of organic matter flowing into the biological treatment device 20, as described above.

[0042] <Other embodiments> (1) In the wastewater treatment system of the above-described embodiment, one solid-liquid separator (first solid-liquid separator 11A) having a relatively coarse mesh screen is provided, while two solid-liquid separators (second and third solid-liquid separators 11B and 11C) having relatively coarse mesh screens are provided. However, the number of solid-liquid separators is not limited to this, and there may be one or more solid-liquid separators having relatively coarse mesh screens and one or more solid-liquid separators having relatively coarse mesh screens. When multiple solid-liquid separators having relatively coarse mesh screens and one or more solid-liquid separators having relatively fine mesh screens are provided, the amount of organic matter flowing into the biological treatment device can be more precisely adjusted.

[0043] (2) In the wastewater treatment system of the above-described embodiment, two types of screens with different mesh sizes are used. However, the types of screens are not limited to this, and three or more types of screens with different mesh sizes, for example, screens with mesh sizes of 0.3 mm, 0.5 mm, and 0.7 mm, may be used. When three or more types of screens with different mesh sizes are used, the amount of organic matter flowing into the biological treatment device can be more precisely adjusted.

[0044] (3) In the rotary filter-type solid-liquid separators 11A-11C described above, as the rotation speed of the rotor 112 increases and the rotation speed of the endless filter unit 111 increases, the amount of solids trapped by the panel filter and removed by the scraper 113 or spray 114 per unit time increases. That is, in the rotary filter-type solid-liquid separators 11A-11C described above, the organic matter removal rate can be adjusted by adjusting the rotation speed of the rotor 112. In the wastewater treatment system and wastewater treatment method of the above-described embodiment, the amount of organic matter flowing into the biological treatment device is adjusted by adjusting the distribution of organic wastewater circulating through the multiple solid-liquid separators 11A-11C. However, the present invention is not limited to this. The rotation speed of the rotor 112 may be adjusted in addition to the distribution of organic wastewater. In this case, the amount of organic matter flowing into the biological treatment device 20 can be more precisely adjusted. Furthermore, depending on the structure of a rotary filter type solid-liquid separator, the treatment capacity (i.e., the flow rate of treated water flowing through the solid-liquid separator per unit time) may increase or decrease depending on the rotation speed of the rotor. In a wastewater treatment system employing such solid-liquid separators, the distribution of the water to be treated flowing through each solid-liquid separator can be adjusted by controlling the rotation speed of the rotor instead of or in addition to controlling a flow rate adjusting device such as a movable weir.

[0045] (4) In the wastewater treatment system of the above-described embodiment, a rotary filter type solid-liquid separator is used. However, the type of solid-liquid separator is not limited to this, and any separator that separates solids using a screen, such as a drum screen type or a bar screen type, may be used.

[0046] (5) In the wastewater treatment system of the above-described embodiment, a movable weir is used as the flow rate control device. However, the type of flow rate control device is not limited to this and may be, for example, a valve, a pump, or a combination thereof.

[0047] (6) In the above-described embodiment, a biological treatment device is used that is intended to remove nitrogen. However, the type of biological treatment device is not limited to this, and it may be intended to remove phosphorus, or both nitrogen and phosphorus. In this case, the control device adjusts the distribution of organic wastewater circulating through the solid-liquid separation device when either or both of the nitrogen concentration and phosphorus concentration detected by the water quality sensor exceed a limit value.

[0048] (7) When the organic wastewater flowing into a wastewater treatment plant temporarily increases due to heavy rainfall during rainy weather, conventional wastewater treatment systems take measures such as bypassing the organic wastewater that exceeds the processing capacity of the solid-liquid separation device to a biological treatment device or discharging it directly into a river, etc. However, when bypassing to the biological treatment device, there is a risk of causing damage when a membrane separation activated sludge treatment device is adopted, and when discharging directly into a river or the like, there is a problem that the water quality of the discharge destination deteriorates. On the other hand, in the wastewater treatment system according to the present invention, the solid-liquid separation device provided with a relatively coarse screen can achieve a high treatment water volume because the removal rate of solids is low. Therefore, as an emergency operation during water increase, the amount of organic wastewater flowing through the solid-liquid separation device may be increased. Thereby, it is possible to avoid or reduce the risk of damage to the membrane separation activated sludge treatment device or the deterioration of the water quality of the discharge destination, because it is possible to prevent or at least reduce the generation of organic wastewater that bypasses the biological treatment device without being subjected to solid-liquid separation treatment or is directly discharged into a river or the like.

Explanation of Signs

[0049] 10: Solid-liquid separation unit 11A: First solid-liquid separation device 11B: Second solid-liquid separation device 11C: Third solid-liquid separation device 12A: Movable weir 12B: Movable weir 12C: Movable weir 20: Biological treatment device 21: Anaerobic tank 22: Aerobic tank 23: Separation membrane 30: Water quality sensor 40: Control device 111: Filter unit 112: Rotor 113: Scraper 0>114: Spray W1: Treated water [[ID=​​

Claims

1. a solid-liquid separation unit including a plurality of solid-liquid separation devices arranged in parallel and flow rate adjusting devices arranged in the upper stages of the solid-liquid separation devices, respectively, capable of adjusting the amount of organic wastewater flowing through the solid-liquid separation devices; a biological treatment device that is disposed in a lower stage of the solid-liquid separation unit and that biologically treats organic wastewater using microorganisms; a water quality sensor for detecting an index value relating to the water quality of the organic wastewater biologically treated in the biological treatment device; a control device that controls the flow rate adjusting device based on the water quality and adjusts the distribution of the organic wastewater that is circulated to the plurality of solid-liquid separation devices, the plurality of solid-liquid separation devices include a first solid-liquid separation device provided with a screen having a predetermined mesh size, and a second solid-liquid separation device provided with a screen having a finer mesh size than the screen of the first solid-liquid separation device, the index value is at least one of a nitrogen concentration and a phosphorus concentration, The control device When the index value exceeds a predetermined upper limit value, the amount of organic wastewater circulated through the first solid-liquid separation device is increased; a wastewater treatment system that increases the amount of organic wastewater that is circulated to the second solid-liquid separation device when the index value falls below a predetermined lower limit.

2. The wastewater treatment system according to claim 1 , wherein the solid-liquid separator is a rotary filter type solid-liquid separator.

3. The wastewater treatment system according to claim 1 or 2, wherein the flow rate adjusting device is a movable weir.

4. A solid-liquid separation process in which organic wastewater is circulated through a plurality of solid-liquid separation devices arranged in parallel, the solid-liquid separation devices including a first solid-liquid separation device provided with a screen having a predetermined mesh size and a second solid-liquid separation device provided with a screen having a finer mesh size than the screen of the first solid-liquid separation device; a biological treatment step in which the organic wastewater that has passed through the plurality of solid-liquid separation devices is circulated through a biological treatment device; a detection step of detecting an index value related to the water quality of the organic wastewater biologically treated in the biological treatment device; and a distribution adjusting step of adjusting the distribution of the organic wastewater circulated to the plurality of solid-liquid separation devices based on the water quality, the index value is at least one of a nitrogen concentration and a phosphorus concentration, In the distribution adjusting step, When the index value exceeds a predetermined upper limit value, the amount of organic wastewater circulated through the first solid-liquid separation device is increased; the amount of organic wastewater flowing through the second solid-liquid separation device is increased when the index value falls below a predetermined lower limit.

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