Water treatment facility and water treatment method

Abstract

To provide a water treatment facility with a biofilm which can make water to be treated at a certain flow rate without requiring aeration, stirring, or the like to treat the water to be treated.SOLUTION: A water treatment facility 100 includes: a supply channel 10 for supplying water to be treated; and a biological treatment tank 30 to which the water to be treated is supplied from the supply channel 10. The biological treatment tank 30 includes: a plurality of biofilm treatment units 40 which treat the water to be treated; and partitions 31 which form a plurality of compartments 32 in the biological treatment tank 30. The biofilm treatment units 40 are disposed in the compartments 32. The adjacent compartments 32 are in communication with each other via communication parts 31a, 31b formed in the partitions 31. The partitions 31 form a meandering flow channel of the water to be treated continuous from an upstream compartment 32U to a downstream compartment 32L in the biological treatment tank 30.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a water treatment facility and a water treatment method. [Background technology]

[0002] There is provided a water treatment facility for treating water to be treated using a biofilm and suspended microorganisms in activated sludge. In the water treatment facility, a biofilm treatment unit, which is configured to attach a biofilm and supply oxygen to the biofilm, is immersed in the water to be treated in a treatment tank, and at the same time, the suspended microorganisms contained in the activated sludge in the treatment tank are used to treat the water to be treated.

[0003] The treatment of the wastewater proceeds specifically through nitrification and denitrification reactions. Nitrification is a reaction in which ammonia nitrogen is converted to nitrite and nitrate nitrogen by the action of aerobic nitrite and nitrite bacteria. Denitrification is a reaction in which soluble nitrate nitrogen is reduced to nitrogen gas by the action of anaerobic denitrifying bacteria.

[0004] In conventional activated sludge treatment, water treatment facilities generally require separate treatment tanks for both nitrification and denitrification reactions. However, in treatment using biofilms, both reactions take place in the biofilm, making it possible to treat the water to be treated in the same treatment tank.

[0005] The water treatment facility described in Patent Document 1 is configured to treat the water to be treated by immersing a plurality of biofilm treatment units in the water to be treated in a treatment tank. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-33681 A Summary of the Invention [Problem to be solved by the invention]

[0007] In order to improve the treatment efficiency of the water to be treated by the biofilm, it is important to improve the contact efficiency between the water to be treated and the biofilm in which the above-mentioned two reactions proceed. In order to improve the contact efficiency, it is effective to stir the water to be treated to induce a constant flow rate in the water to be treated around the biofilm. However, in the water treatment equipment described in Patent Document 1, the flow rate of the water to be treated flowing from the inlet 2a to the outlet 2b in the tank is low, and the flow rate is not constant in the tank, so the contact efficiency is poor.

[0008] In order to induce a constant flow rate in the water being treated inside the biofilm unit, it is necessary to agitate the water by aeration through air supply, or to mechanically agitate the water to increase the flow rate, etc. In such cases, the initial cost and running cost of the equipment for aeration or agitation are required.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a water treatment facility that uses a biofilm and can treat the water to be treated by inducing a constant flow rate in the water to be treated without the need for aeration or stirring. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the water treatment equipment according to the first invention comprises a biological treatment tank and a supply passage for supplying the water to be treated to the biological treatment tank, the biological treatment tank having a plurality of biofilm treatment units for treating the water to be treated, an activated sludge having the water to be treated and sludge, and partitions forming a plurality of compartments in the biological treatment tank, the biofilm treatment units are arranged in the compartments, adjacent compartments are connected to each other via communication parts formed in the partitions, and a serpentine activated sludge flow path is formed in the biological treatment tank that continues from the upstream compartment through the communication parts to the downstream compartment.

[0011] According to this, the water treatment facility has a meandering flow path formed in a biological treatment tank that connects each compartment, and a biofilm treatment unit is placed in each compartment. The water to be treated in the activated sludge flows from the upstream compartment to the downstream compartment along the meandering flow path and is biologically treated continuously in the biofilm treatment units. During this process, the activated sludge is agitated, and a constant flow rate suitable for treatment is induced in the activated sludge.

[0012] The water treatment equipment according to the second invention comprises a solid-liquid separation section which separates activated sludge from biological treatment water treated in a biological treatment tank, and a return device which returns the activated sludge at least on the downstream side of the serpentine flow path of the biological treatment tank to a section located at least on the upstream side of the serpentine flow path of the biological treatment tank.

[0013] According to this, the water treatment facility separates activated sludge from the biological treatment water by settling in the solid-liquid separation section, and can return activated sludge on the downstream side of the biological treatment tank to the biological treatment tank.

[0014] The supply passage of the water treatment facility according to the third aspect of the present invention is branched to supply the water to be treated to each compartment.

[0015] According to this, in the water treatment facility, organic matter required for the treatment of the water to be treated is stably supplied to each compartment, and therefore the treatment in the biological treatment tank is promoted.

[0016] The return device for a water treatment facility according to the fourth invention returns the activated sludge separated by the solid-liquid separation section to a section located at least upstream of the serpentine flow path of the biological treatment tank.

[0017] According to this, the return device returns and circulates the activated sludge separated by the solid-liquid separation unit to the upstream side of the biological treatment tank, so that the water to be treated in the activated sludge can be treated in a superimposed manner in the biological treatment tank. Therefore, the water treatment facility can promote the treatment of the water to be treated in the biological treatment tank.

[0018] The water treatment facility according to the fifth invention is provided with an auxiliary treatment tank which is connected to the downstream side of the serpentine flow path and the upstream side of the solid-liquid separation section, and which serves to auxiliary treat the biologically treated water which has been treated in the biological treatment tank, and the auxiliary treatment tank has an aeration device which diffuses air into the activated sludge.

[0019] According to this, the auxiliary treatment tank can supplement the treatment of the water to be treated that is contained in the biological treatment water and that has been insufficiently treated in the biological treatment tank due to load fluctuations or the like.

[0020] The auxiliary treatment tank of the water treatment facility according to the sixth invention has a suction device which sucks activated sludge in the most downstream compartment and sends it to the auxiliary treatment tank.

[0021] According to this, the flow rate of the activated sludge in the meandering passage of the biological treatment tank temporarily increases, which further increases the contact efficiency between the water to be treated and the biofilm. In addition, the activated sludge with an increased flow rate stirs up the suspended microorganisms that had settled at the bottom of the meandering passage, which is expected to have the effect of increasing the contact efficiency between the water to be treated and the suspended microorganisms.

[0022] The return device of the water treatment equipment according to the seventh invention returns the activated sludge separated by the solid-liquid separation section and / or the activated sludge in the auxiliary treatment tank to a section located at least upstream of the serpentine flow path of the biological treatment tank.

[0023] According to this, the return device returns the activated sludge separated by the solid-liquid separation unit and / or the activated sludge in the auxiliary treatment tank to the biological treatment tank, so that the water to be treated in the activated sludge can be treated in the biological treatment tank and the auxiliary treatment tank in a superimposed manner. Also, the activated sludge concentration required in the auxiliary nitrification tank can be maintained. Therefore, the water treatment facility can promote the treatment of the water to be treated in the biological treatment tank.

[0024] The biological treatment tank of the water treatment facility according to the eighth invention has at least one compartment in which no biofilm treatment unit is placed, upstream of the compartment in which the biofilm treatment unit is placed.

[0025] According to this, in at least one compartment of the biological treatment tank, the flow rate of the activated sludge can be increased by reducing the cross-sectional area of ​​the flow path of the compartment without being restricted by the size of the biofilm treatment unit, and the accumulation of activated sludge on the bottom of the compartment can be suppressed. The water to be treated is supplied to the downstream compartment while being kept in a state where it is thoroughly mixed with the suspended microorganisms, and is treated in the biofilm treatment unit. Therefore, the water treatment facility can promote the treatment of the water to be treated in the biological treatment tank.

[0026] The supply passage of the water treatment facility according to the ninth aspect of the present invention supplies the water to be treated to a section in which no biofilm treatment unit is disposed.

[0027] According to this, the activated sludge is supplied to a section where a biofilm treatment unit is not installed, and then the flow rate is increased within the section. This promotes mixing of the water to be treated with the suspended microorganisms. The water to be treated, with its mixing with the suspended microorganisms promoted, is then supplied to the downstream section and treated in the biofilm treatment unit. Therefore, the water treatment facility can promote the treatment of the water to be treated in the biological treatment tank.

[0028] The return device of the water treatment equipment according to the 10th invention has a control unit that controls the amount of returned activated sludge (hereinafter referred to as returned sludge), and the control unit controls the amount of returned sludge so that the linear velocity of the activated sludge flowing through the serpentine flow path becomes a predetermined value.

[0029] According to this, the control unit maintains the linear velocity of the activated sludge in the biological treatment tank at a constant value. Therefore, the water treatment facility can promote treatment in the biological treatment tank by maintaining the linear velocity of the activated sludge at a linear velocity suitable for treatment.

[0030] The control unit of the water treatment facility according to the eleventh aspect of the present invention has a control unit that controls the amount of returned sludge, and the control unit varies the amount of returned sludge.

[0031] According to this, the control unit intentionally varies the flow rate of the activated sludge in the biological treatment tank within a predetermined range. This flow rate variation causes the hollow fiber membrane to oscillate, preventing adhesion of the biofilms to each other and improving the contact efficiency between the water to be treated and the biofilms. At the same time, the amount of returned sludge is controlled to the minimum necessary, thereby achieving energy-saving operation.

[0032] The return device of the water treatment equipment according to the 12th invention has a control unit that controls the amount of returned sludge, and the control unit controls the amount of returned sludge in accordance with the water quality of the activated sludge flowing through the serpentine flow path.

[0033] According to this, the control unit controls the amount of returned sludge depending on the water quality of the water flowing through the meandering flow path. Therefore, the water treatment facility can maintain a constant water quality in the biological treatment tank. At the same time, energy-saving operation is achieved by controlling the amount of returned activated sludge to the minimum necessary.

[0034] The control unit of the water treatment facility according to the thirteenth aspect of the present invention controls the amount of returned sludge depending on the nitrate nitrogen concentration of the activated sludge flowing through the serpentine flow path.

[0035] According to this, the control unit increases the amount of return sludge to the biological treatment tank when the nitrate nitrogen concentration in the auxiliary treatment tank becomes high. Therefore, the water treatment facility can promote treatment in the biological treatment tank and the auxiliary treatment tank. At the same time, energy-saving operation is performed by controlling the amount of return sludge to the minimum necessary.

[0036] The solid-liquid separation section of the water treatment facility according to the fourteenth invention is a settling tank.

[0037] According to this, the solid-liquid separation section can separate the activated sludge from the treated water into solid and liquid by settling the activated sludge in the settling tank.

[0038] The solid-liquid separation section of the water treatment facility according to the fifteenth aspect of the present invention comprises a solid-liquid separation tank and a membrane separation unit provided in the solid-liquid separation tank.

[0039] According to this, the solid-liquid separation section can separate the activated sludge from the treated water by separating the activated sludge using the membrane separation unit in the solid-liquid separation tank.

[0040] The water treatment equipment according to the 16th invention comprises a biological treatment tank and a supply passage for supplying the water to be treated to the biological treatment tank. The biological treatment tank has a plurality of biofilm treatment units which treat the water to be treated, and partitions which form a plurality of compartments within the biological treatment tank. The biofilm treatment units are arranged within the compartments, and adjacent compartments are connected via communication parts formed in the partitions. A serpentine flow path for the water to be treated is formed within the biological treatment tank, continuing from the upstream compartment through the communication parts to the downstream compartment.

[0041] According to this, the water treatment facility has a serpentine flow path formed in a biological treatment tank that connects each compartment, and a biofilm treatment unit is disposed in each compartment. The water to be treated flows from the upstream compartment to the downstream compartment along the serpentine flow path and is continuously biologically treated in the biofilm treatment units. During this process, the water to be treated is stirred, and a constant flow rate suitable for treatment is induced in the water to be treated. In addition, the water to be treated with the induced flow rate stirs up the biofilm that has settled to the bottom of the serpentine flow path, thereby preventing blockage of the serpentine flow path due to accumulation of biofilm.

[0042] The water treatment equipment of the 17th invention is the water treatment equipment of the 16th invention, which is provided with a return device that returns biological treatment water from a section located at least downstream of the serpentine flow path of the biological treatment tank to a section located at least upstream of the serpentine flow path of the biological treatment tank.

[0043] According to this, the return device returns and circulates the water to be treated downstream of the biological treatment tank to the upstream side of the biological treatment tank, so that the water to be treated in the activated sludge can be treated in the biological treatment tank in a superimposed manner. Therefore, the water treatment facility can promote the treatment of the water to be treated in the biological treatment tank.

[0044] The water treatment method according to the 18th invention comprises: This water treatment method includes a supply process for supplying the water to be treated into a biological treatment tank which treats the water to be treated, and a biological treatment process for treating the water to be treated supplied by the supply process with a plurality of biofilm treatment units provided in the biological treatment tank. In the treatment process, the water to be treated supplied into the biological treatment tank in the supply process flows through a serpentine flow path formed in the biological treatment tank which is continuous from the upstream side to the downstream side, and is treated by biofilms attached to the biofilm treatment units arranged on the serpentine flow path and by suspended microorganisms in the biological treatment tank.

[0045] According to this system, the water to be treated is biologically treated continuously in the biofilm treatment unit while flowing through a meandering flow path that connects each compartment formed in the biological treatment tank. During this process, the activated sludge containing the water to be treated is stirred, and a constant flow rate suitable for treatment is induced in the activated sludge. Effect of the Invention

[0046] According to the present invention, the water treatment facility has a serpentine flow path formed in a biological treatment tank that connects each compartment, and a biofilm treatment unit is disposed in each compartment. The water to be treated flows from the upstream compartment to the downstream compartment along the serpentine flow path and is biologically treated continuously in the biofilm treatment units. During this process, the activated sludge containing the water to be treated is agitated by being bent in the serpentine flow path, and a constant flow velocity suitable for treatment is induced in the activated sludge. [Brief description of the drawings]

[0047] [Figure 1] 1 is a schematic diagram of a water treatment facility including a water treatment apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of a biofilm treatment unit and a partially enlarged cross-sectional view of the unit. [Diagram 3] FIG. 2 is a vertical cross-sectional view of a biological treatment tank. [Figure 4] FIG. 4 is a cross-sectional view of a biological treatment tank according to a second embodiment of the present invention. [Diagram 5] FIG. 11 is a schematic diagram of a water treatment facility including a water treatment apparatus according to a third embodiment of the present invention. [Figure 6]FIG. 11 is a schematic diagram of a water treatment facility including a water treatment apparatus according to a fourth embodiment of the present invention. [Figure 7] 13 is a schematic diagram of a water treatment facility including a water treatment apparatus according to a modified example of the embodiment. FIG. [Figure 8] FIG. 11 is a vertical cross-sectional view of a biological treatment tank according to a fifth embodiment of the present invention. [Figure 9] FIG. 13 is a schematic diagram of a water treatment facility including a water treatment apparatus according to a sixth embodiment of the present invention. [Figure 10] 13 is a schematic diagram of a water treatment facility including a water treatment apparatus according to a modified example of the embodiment. FIG. [Figure 11] 4 is a flowchart showing a calculation process in a control unit. [Figure 12] 13 is a flowchart showing a calculation process in a control unit according to a seventh embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] First embodiment Hereinafter, a water treatment facility 100 according to a first embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference characters and description thereof will not be repeated.

[0049] First, a water treatment facility 1 including a water treatment equipment 100 according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of a water treatment facility 1 including a water treatment equipment 100 according to a first embodiment of the present invention.

[0050] [Water treatment facilities] As shown in FIG. 1, the water treatment facility 1 includes a primary sedimentation tank 6, a water treatment device 100, and a disinfection tank .

[0051] The primary sedimentation tank 6 receives raw water, settles sludge, and discharges untreated water.

[0052] The water treatment facility 100 includes a supply line 10, a treatment tank 20, a final settling tank 60 (an embodiment of a settling tank that is an example of a solid-liquid separation section), and a return device 70.

[0053] The supply line 10 supplies the supernatant water with a low sludge content in the primary sedimentation tank 6 (hereinafter referred to as the water to be treated) to the treatment tank 20. The supply line 10 branches midway through the supply, and supplies the water to be treated to the treatment tank 20 in a branched manner.

[0054] The treatment tank 20 includes a biological treatment tank 30 and an auxiliary nitrification tank 50 (an example of an auxiliary treatment tank). The biological treatment tank 30 includes a plurality of biofilm treatment units 40 and a partition wall 31.

[0055] The biofilm treatment unit 40, which will be described in detail later, biologically treats the water to be treated using a biofilm 46, with nitrification and denitrification reactions proceeding in parallel. In this embodiment, the biofilm treatment unit 40 is configured as a membrane aerated biofilm reactor (MABR). MABR is a biological water treatment method that has attracted attention in recent years due to its advantages in terms of reducing environmental impact.

[0056] The partitions 31 are disposed in the biological treatment tank 30 to form a plurality of compartments 32 in the biological treatment tank 30. A biofilm treatment unit 40 is disposed in each of the formed compartments 32. The partitions 31, which will be described in detail later, form a serpentine flow path in the biological treatment tank 30 that continues from the upstream compartment 32U to the downstream compartment 32L.

[0057] The auxiliary nitrification tank 50 is connected to the downstream side of the serpentine flow path and upstream side of the final sedimentation tank 60. The auxiliary nitrification tank 50 supplements the treatment of the water to be treated (hereinafter referred to as the biologically treated water) that has been treated in the biological treatment tank 30. In other words, the auxiliary nitrification tank 50 supplements the treatment of the water to be treated that is contained in the biologically treated water and is not sufficiently treated in the biological treatment tank 30 due to load fluctuations or the like.

[0058] Specifically, the auxiliary nitrification tank 50 compensates for any insufficient nitrification reaction in the biological treatment tank 30. Any insufficient denitrification reaction is compensated for by the final settling tank 60 and return device 70, which will be described later.

[0059] The auxiliary nitrification tank 50 has an aeration device 51. The aeration device 51 diffuses air into the biologically treated water that has been treated in the biological treatment tank 30. By diffusing air by the aeration device 51, the microorganisms in the activated sludge contained in the biologically treated water become aerobic, and the nitrification reaction of the water to be treated proceeds.

[0060] The final settling tank 60 is supplied with the biologically treated water that has been treated in the auxiliary nitrification tank 50 and settles the sludge. That is, the final settling tank 60 is supplied with the biologically treated water and separates the sludge from the biologically treated water and the supernatant water from which the sludge has been removed (hereinafter referred to as treated water), that is, performs solid-liquid separation. The suspended microorganisms in the sludge enter an anaerobic state and proceed with the denitrification reaction in the water to be treated.

[0061] The disinfection tank 7 is supplied with treated water from the final sedimentation tank 60. The disinfection tank 7 performs disinfection and sterilization treatment to ensure the safety of the treated water before it is discharged. When the TN value (total nitrogen: the total amount of nitrogen compounds contained in the treated water) of the treated water supplied falls below a predetermined value, the treated water is discharged into a river or the like.

[0062] The return device 70 returns the sludge that has settled in the final settling tank 60 to the treatment tank 20 as returned sludge in order to maintain the activated sludge concentration required in the auxiliary nitrification tank 50. The return device 70 also returns the water to be treated that contains nitrite and nitrate nitrogen in the final settling tank 60 to the treatment tank 20 as returned nitrification liquid together with the returned sludge in order to make up for the insufficient treatment of the denitrification reaction in the treatment tank 20 and the final settling tank 60 described above. The returned nitrification liquid undergoes a denitrification reaction in the treatment tank 20 in a superimposed manner.

[0063] Specifically, the return device 70 has a first return pump 71, a control unit 72, a first return line 73, and a first flow meter 74. The first return pump 71 returns the returned sludge to the treatment tank 20 through the first return line 73. The control unit 72 controls the flow rate of the first return pump 71 to control the return amounts of the returned sludge and the returned nitrification liquid.

[0064] With the above configuration, the water treatment facility 1 treats the water to be treated, which is supplied from the primary sedimentation tank 6 via the supply line 10, in the water treatment equipment 100. The water treatment facility 1 also returns the returned sludge and the returned nitrified liquid to the treatment tank 20 by the return device 70 of the water treatment facility 100. The treated water that has completed the treatment is discharged into a river or the like via the disinfection tank 7.

[0065] In the following explanation, in each of the treatment tanks 20, 30, 50 and the section 32 formed in the biological treatment tank 30, the side closer to the primary sedimentation tank 6 in the water treatment facility 1 will be referred to as the "upstream side," and the side closer to the final sedimentation tank 60 will be referred to as the "downstream side."

[0066] [Biofilm treatment unit] Next, the biofilm treatment unit 40 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram of the biofilm treatment unit 40 and a partially enlarged cross-sectional view of the same unit. The biofilm treatment unit 40 includes a plurality of hollow fiber membranes 45, a biofilm 46, blowers 41, 41d, air supply passages 42, 42d, an air supply side housing 43, an exhaust side housing 47, an exhaust passage 48, and a membrane air diffuser 49.

[0067] A plurality of hollow fiber membranes 45 are arranged in parallel so as to extend in the longitudinal direction of the treatment unit. The hollow fiber membranes 45 have gas permeability, and can selectively allow oxygen in the air supplied into the hollow fiber membranes 45 to pass from the inner surface 45a side to the outer surface 45b side (broken line arrow 8 in FIG. 2). The hollow fiber membranes 45 are mainly composed of a porous membrane, but may be a composite membrane of a porous membrane and a porous membrane. A biological membrane 46 is formed on the outer surface 45b of the hollow fiber membranes 45.

[0068] The biofilm 46 is derived from microorganisms, and as shown in the partially enlarged cross-sectional view of Fig. 2, is formed on the outer surface 45b of the hollow fiber membrane 45. Since oxygen is supplied from the inner surface 45a side of the hollow fiber membrane 45 toward the biofilm 46 on the outer surface 45b, the biofilm 46 has an oxygen concentration gradient in the thickness direction of the biofilm 46.

[0069] As a result, the biofilm 46 becomes in an aerobic state with a higher oxygen concentration toward the inner periphery side 46a (the hollow fiber membrane 45 side), and the nitrification reaction proceeds. On the other hand, the biofilm 46 becomes in an anaerobic state with a lower oxygen concentration toward the outer periphery side 46b, and the denitrification reaction proceeds in parallel. In order to promote the denitrification reaction on the outer periphery side 46b, it is necessary to supply an appropriate amount of organic matter as a carbon source for the denitrifying bacteria. For this reason, it is necessary to maintain the concentration of the water to be treated and the activated sludge in the biological treatment tank 30 at optimal concentrations.

[0070] The blower 41 supplies air to the air supply side housing 43 through the air supply passage 42 in order to supply oxygen to the biofilm 46. The blower 41d supplies air to the membrane air diffuser 49 through the air supply passage 42d. The membrane air diffuser 49 cleans the biofilm 46.

[0071] One end face of the hollow fiber membrane 45 is fixed to the air intake side housing 43 via a potting material (adhesive). Air supplied from the blower 41 through the air intake path 42 into the air intake side housing 43 flows into the hollow fiber membrane 45 from one end face of the hollow fiber membrane 45, and is supplied from inside the hollow fiber membrane 45 to the biofilm 46.

[0072] The other end face of the hollow fiber membrane 45 is fixed via a potting material to the exhaust side housing 47. After the air is supplied from one end face of the hollow fiber membrane 45, the remaining air that has not been supplied from inside the hollow fiber membrane 45 to the biofilm 46 is exhausted from the other end face of the hollow fiber membrane 45 to the exhaust side housing 47.

[0073] The exhaust path 48 connects the exhaust side housing 47 to the outside of the equipment, thereby discharging the air (off-gas) exhausted into the exhaust side housing 47 to the outside of the equipment.

[0074] With the above configuration, the biofilm treatment unit 40 advances a nitrification reaction of the water to be treated on the inner circumferential side 46a of the biofilm 46, and a denitrification reaction of the water to be treated on the outer circumferential side 46b. In order to promote these reactions, it is important to agitate the water to be treated and increase the contact efficiency between the water to be treated and the biofilm 46.

[0075] [Biological treatment tank] Next, the configuration of the biological treatment tank 30 will be described with reference to Fig. 3. Fig. 3 is a vertical cross-sectional view of the biological treatment tank 30.

[0076] 3, the biological treatment tank 30 has a plurality of biofilm treatment units 40 and a plurality of partition walls 31. Each partition wall 31 has a communication part 31a or a communication part 31b. The biological treatment tank 30 also has a bottom wall 30a and an outer peripheral wall 30b.

[0077] 3, in this embodiment, the partition wall 31 is disposed in a direction perpendicular to the direction from the upstream side to the downstream side in the biological treatment tank 30. As a result, the compartments 32 are formed by being surrounded by the bottom wall 30a, the outer peripheral wall 30b and the partition wall 31 of the biological treatment tank 30, and are arranged side by side in the direction from the upstream side to the downstream side in the biological treatment tank 30.

[0078] The communicating portion 31a of the partition wall 31 is provided at the lower end of the partition wall 31, and the communicating portion 31b is provided at the upper end of the partition wall 31. The communicating portions 31a, 31b are alternately arranged from the upstream partition wall 31 toward the downstream partition wall 31. As a result, each compartment 32 communicates with the adjacent compartment 32 along the bottom and top of each compartment 32 alternately. Therefore, a serpentine flow path is formed in the biological treatment tank 30, which meanders vertically from the upstream compartment 32U to the downstream compartment 32L.

[0079] That is, the serpentine flow path has alternate downward flow paths 5 in which the activated sludge flows downward and upward flow paths 4 in which the activated sludge flows upward. A biofilm treatment unit 40 is disposed in each compartment 32.

[0080] As a result, the activated sludge flows from the upstream section 32U to the downstream section 32L along the serpentine flow path and is biologically treated continuously in the biofilm treatment unit 40. During this process, the activated sludge is agitated by being bent in the serpentine flow path, and a constant flow rate suitable for treatment is induced in the activated sludge.

[0081] 3, the supply path 10 is branched, and outlets 10a at the lower ends of the branched supply paths 10 are disposed on the upstream side of the respective compartments 32. The water to be treated is then supplied to the upstream side of each compartment 32. That is, the water to be treated is supplied to a plurality of locations within the serpentine flow path.

[0082] As a result, the water treatment facility 100 can reduce the concentration gradient of ammonia nitrogen contained in the water to be treated in the biological treatment tank 30, for example, compared to a case where the water to be treated is supplied to one location on the upstream side in the biological treatment tank 30. In other words, when the water to be treated is supplied to one location on the upstream side, the concentration of ammonia nitrogen in the water to be treated is high on the upstream side and low on the downstream side, increasing the difference in the concentration of ammonia nitrogen in the water to be treated between the upstream side and the downstream side. In contrast, by branching the water to be treated and supplying it, the difference in the concentration of ammonia nitrogen in the water to be treated between the upstream side and the downstream side is reduced.

[0083] As described above, in order to promote the denitrification reaction, it is necessary to appropriately supply organic matter as a carbon source for the denitrifying bacteria. Therefore, in the water treatment facility 100, the concentration gradient of the water to be treated in the biological treatment tank 30 is reduced, and the organic matter necessary for the denitrification reaction is stably supplied to each compartment 32, so that the denitrification reaction in the biological treatment tank 30 can be promoted.

[0084] Second embodiment Next, a biological treatment tank 130 according to a second embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view of the biological treatment tank 130 according to the second embodiment of the present invention, seen from above. The biological treatment tank 130 is a modified example of the biological treatment tank 30 described above. The biological treatment tank 130 also has a plurality of biofilm treatment units 40, a plurality of partition walls 131, a bottom wall 130a, and an outer peripheral wall 130b. The partition wall 131 has communication parts 131a, 131b.

[0085] 4, the partition wall 131 is disposed in a direction perpendicular to the direction from the upstream side to the downstream side in the biological treatment tank 130. That is, similar to the biological treatment tank 30, the compartment 132 is formed by being surrounded by the bottom wall 130a, the outer peripheral wall 130b and the partition wall 131 of the biological treatment tank 130, and is arranged side by side in the direction from the upstream side to the downstream side in the biological treatment tank 130.

[0086] In the following description, the horizontal rightward direction when looking at the downstream section 132L from the upstream section 132U will be simply referred to as the "right" direction, and the horizontal leftward direction will be simply referred to as the "left" direction.

[0087] The communicating portion 131a of the partition wall 131 is provided at the right end of the partition wall 131, and the communicating portion 131b is provided at the left end of the partition wall 131. The communicating portions 131a, 131b are alternately arranged from the upstream partition wall 131 toward the downstream partition wall 131. As a result, each compartment 132 communicates with the adjacent compartment 132 along the right end and left end of each compartment 132 alternately. Therefore, a serpentine flow path is formed in the biological treatment tank 130, serpentinely flowing in the left-right direction from the upstream compartment 132U to the downstream compartment 132L.

[0088] That is, the serpentine flow path alternates between rightward flow paths 105 in which activated sludge flows to the right and leftward flow paths 104 in which activated sludge flows to the left. A biofilm treatment unit 40 is disposed in each compartment.

[0089] As a result, similarly to the biological treatment tank 30 of the first embodiment, the water to be treated in the activated sludge flows along the serpentine flow path from the upstream section 132U to the downstream section 132L and is biologically treated continuously in the biofilm treatment unit 40. During this process, the activated sludge is agitated by being bent in the serpentine flow path, and a constant flow rate suitable for treatment is induced in the activated sludge.

[0090] 4, the supply path 110 is branched, and outlets 110a of the branched supply path 110 are disposed on the upstream side of each of the sections 132. The water to be treated is supplied to the upstream side of each of the sections 132. That is, the water to be treated is supplied to a plurality of locations in the serpentine flow path.

[0091] As a result, similarly to the biological treatment tank 30, the concentration gradient of ammonia nitrogen in the water to be treated in the biological treatment tank 130 is suppressed, and therefore the denitrification reaction is promoted.

[0092] Of course, by arranging the partition walls in a form other than that of this embodiment, it is possible to form a meandering flow path other than that shown in this embodiment.

[0093] Third embodiment Next, a water treatment system 200 according to a third embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 is a schematic diagram of a water treatment facility 2 including a water treatment system 200 according to the third embodiment of the present invention.

[0094] 5, the auxiliary nitrification tank 50 in the water treatment facility 200 further includes an air lift device 52 (an example of a suction device) and a separation wall 53. The air lift device 52 has an aeration device that diffuses air into the activated sludge in the section 54 before auxiliary treatment from the bottom of the auxiliary nitrification tank 50 in a section 54 in the auxiliary nitrification tank 50 separated by the separation wall 53. The air diffusion generates an upward flow in the activated sludge, and the amount of activated sludge supplied to the auxiliary nitrification tank 50 temporarily increases.

[0095] As a result, a suction pressure is generated from the downstream section 32L of the biological treatment tank 30 toward the auxiliary nitrification tank 50, and therefore, in the water treatment equipment 200, the flow rate of the activated sludge in the serpentine flow path of the biological treatment tank 30 temporarily increases. In addition, the oxygen content (DO value) in the treated water increases as aeration is performed by the air lift device 52. Therefore, the water treatment equipment 200 can promote the nitrification reaction of the water to be treated in the auxiliary nitrification tank 50.

[0096] Fourth embodiment Next, a water treatment system 300 according to a fourth embodiment of the present invention will be described with reference to Fig. 6. Fig. 6 is a schematic diagram of a water treatment facility 3 including a water treatment system 300 according to the fourth embodiment of the present invention.

[0097] 6, the water treatment facility 300 has a return device 370. The return device 370 returns and circulates a mixture of the water to be treated containing nitrate nitrogen and suspended microorganisms in the auxiliary nitrification tank 50 as a circulating nitrification liquid to at least the section 32U located upstream of the serpentine flow path of the biological treatment tank 30.

[0098] Specifically, the return device 370 further includes a second return pump 76, a second return line 77, and a second flow meter 78. The second return pump 76 circulates the nitrification liquid in the auxiliary nitrification tank 50 by returning it to the treatment tank 20 through the second return line 77. The control unit 72 controls the flow rate of the second return pump 76 to control the return amount of the circulating nitrification liquid.

[0099] As a result, the return device 370 returns the circulating nitrification liquid from the auxiliary nitrification tank 50 to the upstream side of the treatment tank 20, and the denitrification reaction of the circulating nitrification liquid proceeds in a superimposed manner in the treatment tank 20. Therefore, the water treatment facility 300 can make up for the insufficient treatment of the denitrification reaction in the treatment tank 20.

[0100] As shown in Fig. 7, the return device 370d of the water treatment equipment 300d may be configured so as not to include the auxiliary nitrification tank 50 shown in Fig. 6. Fig. 7 is a schematic diagram of a water treatment facility 3d including a water treatment equipment 300d according to a modified example of the present embodiment.

[0101] As shown in Figure 7, the return device 370d of the water treatment equipment 300d circulates the circulating nitrification liquid from section 32L located at least on the downstream side of the serpentine flow path in the biological treatment tank 30 to section 32L located at least on the upstream side of the serpentine flow path in the biological treatment tank 30.

[0102] Specifically, the return device 370d has a second return pump 76, a second return path 77d, and a second flow meter 78. The second return pump 76 circulates the circulating nitrification liquid in the biological treatment tank 30 by returning it from the most downstream section 32L of the biological treatment tank 30 to the upstream side of the treatment tank 320 through the second return path 77d. The control unit 72 controls the flow rate of the second return pump 76 to control the return amount of the circulating nitrification liquid.

[0103] In this modification, the return device 370d also returns the circulating nitrified liquid in the biological treatment tank 30 to the upstream side of the treatment tank 320, and the denitrification reaction of the circulating nitrified liquid proceeds in a superimposed manner in the treatment tank 320. Therefore, the water treatment equipment 300d can make up for the shortage of the denitrification reaction in the treatment tank 320. In addition, the circulating nitrified liquid, whose flow rate is induced by flowing through the serpentine flow path, stirs up the biofilm that has settled at the bottom of the serpentine flow path, and the water treatment equipment 300d can prevent the blockage of the serpentine flow path due to the accumulation of the biofilm.

[0104] Fifth embodiment Next, a biological treatment tank 430 according to a fifth embodiment of the present invention will be described with reference to Fig. 8. Fig. 8 is a vertical cross-sectional view of the biological treatment tank 430 according to the fifth embodiment of the present invention.

[0105] 8, the biological treatment tank 430 has at least one compartment 432N in which a biofilm treatment unit 40 is not arranged, upstream of the compartment 432E in which the biofilm treatment unit 40 is arranged. Specifically, in this embodiment, the biofilm treatment unit 40 is arranged only in the compartment 432 having the upward flow path 4, and is not arranged in the compartment 432 having the downward flow path 5 upstream of the compartment 432. Of course, in another embodiment, the biofilm treatment unit 40 may be configured to be arranged in the compartment 432 having the downward flow path 5.

[0106] 8, the flow path cross-sectional area of ​​the section 432N in which the biofilm treatment unit 40 is not arranged is smaller than the flow path cross-sectional area of ​​the section 432E in which the biofilm treatment unit 40 is arranged. Since the biofilm treatment unit 40 is not arranged in the section 432N in the biological treatment tank 430, the flow path cross-sectional area of ​​the section 432N can be reduced without being restricted by the size of the biofilm treatment unit 40.

[0107] The biological treatment tank 430 can increase the flow rate of the activated sludge in the section 432N by reducing the cross-sectional area of ​​the flow path of the section 432N. Suspended microorganisms that are not sufficiently mixed with the water to be treated tend to accumulate at the bottom of the section 432. However, the biological treatment tank 430 can suppress the accumulation of suspended microorganisms by increasing the flow rate of the activated sludge in the section 432N and stirring the suspended microorganisms. Then, the water to be treated is supplied to the section 432E downstream of the section 432N in a state in which the accumulation of suspended microorganisms is suppressed, so that the concentration gradient of the activated sludge in the section 432E becomes small, and the contact efficiency between the water to be treated and the suspended microorganisms in the section 432E is increased. Therefore, the biological treatment tank 430 can promote the treatment of the water to be treated.

[0108] Furthermore, the outlet 410a at the lower end of the supply passage 410 is disposed upstream of a section 432N in which no biofilm treatment unit 40 is disposed. Thus, the water to be treated is supplied to the upstream side of the section 432N.

[0109] The water to be treated is mixed with suspended microorganisms after being supplied to the upstream side of the section 432N, and the flow rate is increased due to the small cross-sectional area of ​​the flow path of the section 432N. As a result, the mixing of the water to be treated with suspended microorganisms is promoted in the section 432N before the water reaches the communication part (431a) that communicates from the section 432N to the section 432E. Then, the water to be treated is supplied to the downstream section 432E in a state in which the mixing with suspended microorganisms is promoted, so that the concentration gradient of the water to be treated and the suspended microorganisms in the section 432E becomes small, organic matter necessary for the denitrification reaction is stably supplied to the biofilm treatment unit 40, and the contact efficiency between the water to be treated and the suspended microorganisms is also increased. Therefore, the biological treatment tank 430 can promote the treatment of the water to be treated.

[0110] Sixth embodiment Next, a water treatment system 900 according to a sixth embodiment of the present invention will be described with reference to Fig. 9. Fig. 9 is a schematic diagram of a water treatment facility 9 including a water treatment system 900 according to the sixth embodiment of the present invention.

[0111] In the above-described embodiments, the water treatment plants 100, 200, and 300 have a final settling tank 60 (an example of a settling tank) as an embodiment of the solid-liquid separation section. As shown in Fig. 9, the water treatment plant 900 has a solid-liquid separation device 960 as another embodiment of the solid-liquid separation section. The solid-liquid separation device 960 specifically has a solid-liquid separation tank 61, a membrane separation unit 62 provided in the solid-liquid separation tank 61, and a treated water supply channel 63.

[0112] In this embodiment, the membrane separation unit 62 is configured as an MBR (Membrane BioReactor: membrane separation activated sludge method). The MBR is an activated sludge method that performs solid-liquid separation by membrane filtration, and is capable of performing advanced solid-liquid separation while being a compact and energy-saving system. The solid-liquid separation tank 61 is supplied with biologically treated water that has been treated in the treatment tank 20. The membrane separation unit 62 is provided in the solid-liquid separation tank 61, and separates sludge and treated water from the supplied biologically treated water. The treated water supply channel 63 supplies the separated treated water to the disinfection tank 7.

[0113] As in the first embodiment, the return device 70 returns the sludge separated in the solid-liquid separation device 960 as returned sludge to the treatment tank 20 in order to maintain the activated sludge concentration required in the auxiliary nitrification tank 50. Moreover, in order to make up for the insufficient treatment of the denitrification reaction in the treatment tank 20 described above, the return device 70 returns the water to be treated containing nitrite and nitrate nitrogen in the solid-liquid separation device 960 as returned nitrification liquid together with the returned sludge to the treatment tank 20. The returned nitrification liquid undergoes a denitrification reaction in the treatment tank 20 in a superimposed manner.

[0114] As a result, the biologically treated water treated in the treatment tank 20 is subjected to high-level solid-liquid separation by the solid-liquid separator 960, and the treated water is sent to the disinfection tank 7, while the returned sludge and returned nitrification liquid are returned to the treatment tank 20. Therefore, the water treatment facility 900 can promote the treatment of the water to be treated.

[0115] As shown in Fig. 10, water treatment equipment 900d may be configured so that the membrane separation unit 62 in Fig. 9 is provided in an auxiliary nitrification tank 950. Fig. 10 is a schematic diagram of a water treatment facility 9d including water treatment equipment 900d according to a modified example of the present embodiment. In this case, the water treatment facility 900d has a return device 970. As in the fourth embodiment, the return device 970 returns and circulates the circulating nitrification liquid, which is a mixture of the water to be treated containing nitrate nitrogen and suspended microorganisms in the auxiliary nitrification tank 950, to at least the section 32U located upstream of the serpentine flow path of the biological treatment tank 30.

[0116] In this modification, the water treatment equipment 900d also returns the circulating nitrification liquid in the auxiliary nitrification tank 950 to the upstream side of the treatment tank 920, and causes the denitrification reaction of the circulating nitrification liquid to proceed in a superimposed manner in the treatment tank 920. Therefore, the water treatment equipment 900d can make up for the shortage of the denitrification reaction in the treatment tank 920.

[0117] [Calculation processing in the control unit] Next, the calculation process in the control unit 72 will be described with reference to Fig. 1, Fig. 6 and Fig. 11. Fig. 11 is a flowchart showing the calculation process in the control unit 72.

[0118] 1, the return device 70 of the water treatment facility 100 has a first return pump 71 and a control unit 72. The control unit 72 controls the flow rate of the first return pump 71 to control the amount of returned sludge and returned nitrified liquid (hereinafter simply referred to as "returned sludge amount") to the biological treatment tank 30. The return device 70 also has a first flow meter 74 that measures the amount of returned sludge. The first flow meter 74 is disposed midway through a first return line 73 that connects the first return pump 71 to a return destination of the sludge and nitrified liquid. The control unit 72 can accurately predict the linear velocity of the treated water mixed with the treated water, returned sludge, and returned circulating liquid in the biological treatment tank 30 (hereinafter simply referred to as the "linear velocity of activated sludge") from the supply amount of treated water from the supply line 10, the amount of returned sludge obtained through the first flow meter 74, and the flow path cross-sectional area of ​​the serpentine flow path.

[0119] The control unit 72 controls the amount of returned sludge so that the linear velocity of the activated sludge in the biological treatment tank 30 falls within a predetermined range.

[0120] As shown in Figure 11, in step S11, the control unit 72 predicts the linear velocity of activated sludge in the biological treatment tank 30 from the supply amount of water to be treated from the supply line 10, the amount of returned sludge obtained through the first flow meter 74, and the flow path cross-sectional area of ​​the serpentine flow path.

[0121] If the linear velocity of the water to be treated is outside the predetermined range (NO in step S12) and exceeds the upper limit of the predetermined range (YES in step S14), the control unit 72 reduces the flow rate of the first return pump 71 below the specified flow rate (step S15) to reduce the amount of returned sludge. After that, the control unit 72 acquires the linear velocity of the activated sludge again (step S11) and repeats the same cycle until the linear velocity of the activated sludge falls within the predetermined range.

[0122] If the linear velocity of the activated sludge is outside the predetermined range (NO in step S12) and is less than the lower limit of the predetermined range (NO in step S14 and YES in step S16), the control unit 72 increases the flow rate of the first return pump 71 above the specified flow rate (step S17) to increase the amount of returned sludge. Thereafter, the linear velocity of the activated sludge is acquired again (step S11), and the same cycle is repeated until the linear velocity of the activated sludge falls within the predetermined range.

[0123] If the obtained linear velocity of the activated sludge is within a predetermined range (YES in step S12), the control unit 72 maintains the flow rate of the first return pump 71 at a specified flow rate (step S13), and the process ends (END).

[0124] This allows the control unit 72 to maintain a constant linear velocity of the activated sludge flowing through the serpentine flow path in the biological treatment tank 30. Therefore, the water treatment facility 100 can promote nitrification and denitrification reactions in the biological treatment tank 30 by maintaining the linear velocity of the activated sludge at a linear velocity suitable for treatment.

[0125] The linear velocity of the activated sludge is preferably 5 to 50 cm / min. When the linear velocity of the activated sludge is in this range, the water to be treated can be appropriately stirred around the biofilm 46, thereby optimizing the treatment efficiency of the water to be treated.

[0126] In the biofilm treatment unit 40, adjacent biofilms 46 may adhere to each other, decreasing the contact efficiency between the water to be treated and the biofilms 46. In response to this, the control unit 72 may be configured to intentionally vary the amount of sludge returned to the biological treatment tank 30 within a predetermined range.

[0127] As a result, the control unit 72 varies the flow rate of the activated sludge in the biological treatment tank 30 within a predetermined range. When the flow rate of the activated sludge varies, the hollow fiber membrane 45 is oscillated, and the attached biofilm 46 is separated. Therefore, the water treatment facility 100 can improve the contact efficiency between the water to be treated and the biofilm 46. In addition, the water treatment facility 100 can be operated in an energy-saving manner by controlling the amount of returned sludge to the minimum necessary.

[0128] 6, the return device 370 of the water treatment facility 300 has a second flowmeter 78. The second flowmeter 78 is disposed in the middle of a second return line 77 connecting the second return pump 76 and the return destination of the circulating nitrification liquid. When it is difficult to control the linear velocity of the activated sludge in the biological treatment tank 30 within a predetermined range using only the first return pump 71 shown in this embodiment (when it is difficult to further increase the pump flow rate of the first return pump 71 in step S17 of FIG. 11), the water treatment facility 300 may be configured such that the control unit 72 further controls the second return pump 76 using the flow rate of the circulating nitrification liquid acquired through the second flowmeter 78.

[0129] 11, the control unit 72 predicts the linear velocity of the activated sludge in the biological treatment tank 30 using the flow rate of the circulating nitrification liquid obtained through the second flow meter 78 in addition to the supply amount of water to be treated from the supply path 10, the return sludge amount obtained through the first flow meter 74, and the flow path cross-sectional area of ​​the serpentine flow path. Then, in step S17, when it is necessary to increase the pump flow rate, the control unit 72 controls the second return pump 76 in addition to the first return pump 71 as a control target.

[0130] As a result, even if it is difficult to control the linear velocity of the activated sludge in the biological treatment tank 30 to be within a predetermined range using only the first return pump 71, the control unit 72 can control the linear velocity of the activated sludge to be within a predetermined range by controlling the second return pump 76 as well. Therefore, the water treatment facility 300 can promote nitrification and denitrification reactions in the biological treatment tank 30 by maintaining the linear velocity of the activated sludge at a linear velocity suitable for treatment.

[0131] Seventh embodiment Next, the calculation process in the control unit 72 according to the seventh embodiment of the present invention will be described with reference to Fig. 1, Fig. 6 and Fig. 12. Fig. 12 is a flowchart showing the calculation process in the control unit 72 according to the seventh embodiment of the present invention. As shown in Fig. 1, the return device 70 has a nitrate nitrogen concentration meter 75. The nitrate nitrogen concentration meter 75 is disposed in the most downstream section in the treatment tank 20 as shown in Fig. 1.

[0132] In order to promote the denitrification reaction in the biological treatment tank 30, it is effective to return the returned nitrification liquid and the circulating nitrification liquid to the upstream section 32U of the biological treatment tank 30, which is in an anoxic state, to increase the contact efficiency between the water to be treated and the biofilm and suspended microorganisms, and to treat the returned nitrification liquid and the circulating nitrification liquid in a superimposed manner. For this reason, in this embodiment, the control unit 72 controls so as to increase the amount of returned sludge, returned nitrification liquid, and circulating nitrification liquid returned from the final settling tank 60 to the biological treatment tank 30 when the nitrate nitrogen concentration in the most downstream section of the treatment tank 20 reaches or exceeds a predetermined value.

[0133] As shown in FIG. 12, in step S21, the control unit 72 acquires the nitrate nitrogen concentration in the most downstream section of the treatment tank 20 through the nitrate nitrogen concentration meter 75.

[0134] If the acquired nitrate nitrogen concentration is equal to or higher than the predetermined value (YES in step S22), the control unit 72 increases the flow rate of the first return pump 71 above the specified flow rate (step S23) to increase the amount of returned activated sludge and circulating nitrification liquid. After that, the control unit 72 checks the nitrate nitrogen concentration in the biological treatment tank 30 again (step S21), and repeats the same cycle until the nitrate nitrogen concentration becomes less than the predetermined value.

[0135] If the acquired nitrate nitrogen concentration is less than the predetermined value (NO in step S22), the control unit 72 maintains the flow rate of the first return pump 71 at a specified flow rate (step S24), and the process ends (END).

[0136] As a result, when the nitrate nitrogen concentration in the most downstream section of the treatment tank 20 reaches or exceeds a predetermined value, the control unit 72 increases the amount of returned sludge and circulating nitrifying liquid returned to the upstream section 32U of the biological treatment tank 30. Therefore, the water treatment equipment 100 can increase the contact efficiency between the water to be treated and suspended microorganisms in the biological treatment tank 30, and promote the denitrification reaction in the biological treatment tank 30 by treating the returned circulating liquid and the circulating nitrifying liquid in a superimposed manner. In addition, the water treatment equipment 100 can operate in an energy-saving manner by controlling the amount of returned sludge to the minimum necessary.

[0137] To repeat, as shown in Fig. 6, the water treatment facility 300 has a second return pump 76. When it is difficult to control the nitrate nitrogen concentration to be less than a predetermined value using only the first return pump 71 shown in this embodiment (when it is difficult to further increase the pump flow rate of the first return pump 71 above the specified flow rate in step S23 of Fig. 12), the water treatment facility 300 may be configured such that the control unit 72 further controls the second return pump 76.

[0138] That is, when it is necessary to increase the pump flow rate in step S23 of FIG. 12, the control unit 72 controls the second return pump 76 as well as the first return pump 71 as a control target.

[0139] As a result, even if it is difficult to control the first return pump 71 alone to return a predetermined amount of returned nitrifying liquid to the biological treatment tank 30 when the nitrate nitrogen concentration in the treatment tank 20 becomes equal to or higher than a predetermined value, the control unit 72 can control the second return pump 76 to be included in the control targets and control the circulating nitrifying liquid in the auxiliary nitrifying tank 50 to be returned to the biological treatment tank 30. Therefore, the water treatment facility 300 can promote the denitrification reaction in the biological treatment tank 30 by treating the returned nitrifying liquid and the circulating nitrifying liquid in a superimposed manner.

[0140] Furthermore, the calculation processing of the control unit 72 according to the first embodiment of the present invention and the calculation processing of the control unit 72 according to the sixth embodiment described above may be configured so that both calculation processings are performed in parallel or in series.

[0141] [Water treatment method] Next, a water treatment method according to an embodiment of the present invention will be described with reference to Figure 3 again. The water treatment method includes a supplying step and a biological treatment step.

[0142] In the supply process, the water to be treated is supplied to the biological treatment tank 30, which treats the water to be treated. In the biological treatment process, the water to be treated supplied in the supply process is treated in a plurality of biofilm treatment units 40 contained in the biological treatment tank 30. In the treatment process, the water to be treated supplied into the biological treatment tank 30 in the supply process flows through a serpentine flow path formed so as to be continuous from the upstream side to the downstream side within the biological treatment tank 30, and is treated in the biofilm treatment units 40 arranged on the serpentine flow path.

[0143] As a result, the water to be treated is biologically treated continuously in the biofilm treatment unit 40 while flowing through a meandering flow path that connects each of the compartments 32 formed in the biological treatment tank 30. During this process, the water to be treated is agitated, and a constant flow rate suitable for treatment is induced in the water to be treated.

[0144] The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to the above embodiments, and can be implemented in various forms without departing from the spirit of the present invention. The drawings are mainly schematic illustrations of each component for ease of understanding, and the thickness, length, number, spacing, etc. of each component shown in the drawings are different from the actual ones due to the convenience of drawing. In addition, the material, shape, dimensions, etc. of each component shown in the above embodiments are merely examples and are not particularly limited, and various modifications are possible within a range that does not substantially deviate from the configuration of the present invention. [Explanation of symbols]

[0145] 1. Water treatment facilities 6 Primary Sedimentation Tank 7 Disinfection tank 10 Supply route 20 Treatment tank 30 Biological treatment tank 31 Bulkhead 31a,31b Communication part 32 plots 40 Biofilm Treatment Unit 45 Hollow fiber membrane 46 Biofilm 50 Auxiliary nitrification tank (auxiliary treatment tank) 51 Air diffuser 52 Air lift device (suction device) 60 Final sedimentation tank (sedimentation tank) 70 Return device 71 First return pump 72 Control section 73 1st Return Route 74 1st flow meter 75 Nitrate Nitrogen Concentration Meter 76 Second return pump 77 2nd Return Route 78 2nd flow meter 100 Water treatment facilities

Claims

1. A biological treatment tank; A supply line for supplying the water to be treated to the biological treatment tank; Equipped with The biological treatment tank is A plurality of biofilm treatment units for treating the water to be treated; Activated sludge containing water to be treated and suspended microorganisms; Partition walls that form multiple compartments in the biological treatment tank; having The biofilm treatment unit is disposed within the compartment, Adjacent compartments communicate with each other via communication portions formed in the partition walls, A water treatment facility comprising: a biological treatment tank having a meandering flow path for activated sludge formed therein, the meandering flow path continuing from an upstream compartment through a communication part to a downstream compartment.

2. a solid-liquid separation section that separates activated sludge from the biologically treated water that has been treated in the biological treatment tank; a return device that returns activated sludge at least on the downstream side of the meandering flow path of the biological treatment tank to a section located at least on the upstream side of the meandering flow path of the biological treatment tank; The water treatment facility according to claim 1 , comprising:

3. 3. The water treatment facility according to claim 1, wherein the supply passage is branched to supply the water to be treated to each compartment.

4. 3. The water treatment facility according to claim 2, wherein the return device returns the activated sludge separated by the solid-liquid separation section.

5. an auxiliary treatment tank that is connected to the downstream side of the meandering flow path and the upstream side of the solid-liquid separation section and that auxiliary treats the biological treatment water treated in the biological treatment tank; 3. The water treatment facility according to claim 2, wherein the auxiliary treatment tank has an aeration device for diffusing air into the activated sludge.

6. 6. The water treatment facility according to claim 5, wherein the auxiliary treatment tank has a suction device for suctioning activated sludge in the most downstream compartment and sending it to the auxiliary treatment tank.

7. The water treatment facility according to claim 5, characterized in that the return device returns the activated sludge separated by the solid-liquid separation section and / or the activated sludge in the auxiliary treatment tank to a section located at least upstream of the serpentine flow path of the biological treatment tank.

8. 3. The water treatment facility according to claim 1, wherein the biological treatment tank has at least one compartment in which a biofilm treatment unit is not disposed, upstream of the compartment in which the biofilm treatment unit is disposed.

9. The water treatment facility according to claim 8 , wherein the supply passage supplies the water to be treated to a section in which no biofilm treatment unit is disposed.

10. The return device has a control unit for controlling the amount of activated sludge returned, 8. The water treatment facility according to claim 2, wherein the control unit controls the amount of activated sludge returned so that the linear velocity of the activated sludge flowing through the serpentine flow path becomes a predetermined value.

11. The returning device has a control unit for controlling the amount of returned activated sludge, 8. The water treatment facility according to claim 2, wherein the control unit varies an amount of the returned activated sludge.

12. The returning device has a control unit for controlling the amount of returned activated sludge, 8. The water treatment facility according to claim 2, wherein the control unit controls the amount of activated sludge returned in accordance with the water quality of the activated sludge flowing through the meandering flow path.

13. The water treatment facility according to claim 12, wherein the water quality of the activated sludge is a nitrate nitrogen concentration of the activated sludge.

14. The water treatment facility according to claim 2 , wherein the solid-liquid separation section is a settling tank.

15. 3. The water treatment facility according to claim 2, wherein the solid-liquid separation section comprises a solid-liquid separation tank and a membrane separation unit provided in the solid-liquid separation tank.

16. A biological treatment tank; A supply line for supplying the water to be treated to the biological treatment tank; Equipped with The biological treatment tank is A plurality of biofilm treatment units for treating the water to be treated; Partition walls that form multiple compartments in the biological treatment tank; having The biofilm treatment unit is disposed within the compartment, Adjacent compartments communicate with each other via communication portions formed in the partition walls, A water treatment facility, comprising: a biological treatment tank having a meandering flow path for water to be treated, the flow path continuing from an upstream compartment through a communication part to a downstream compartment.

17. The water treatment facility according to claim 16, further comprising a return device that returns biologically treated water from a section located at least downstream of the serpentine flow path of the biological treatment tank to a section located at least upstream of the serpentine flow path of the biological treatment tank.

18. A supply step of supplying the water to be treated to a biological treatment tank that treats the water to be treated; a biological treatment process in which the water to be treated supplied by the supply process is treated by a plurality of biofilm treatment units provided in a biological treatment tank; A water treatment method comprising: The treated water supplied to the biological treatment tank in the supply process is A water treatment method characterized in that in a treatment process, water flows through a continuous serpentine flow path formed in a biological treatment tank from the upstream side to the downstream side, and is treated in a biofilm treatment unit arranged on the serpentine flow path.

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