Raw water treatment method and raw water treatment device

Abstract

A raw water treatment method having a step for treating raw water using a raw water treatment device (1) provided with a biological treatment tank (10) and a membrane separation activated sludge treatment unit (12), and an inflow step for bypass-flowing a part of the raw water into an activated sludge treatment tank (32) without passing through the biological treatment tank (10), a membrane separation activated sludge treatment unit (12) for treating first treated water, which has been biologically treated in a biological treatment tank (10) that accommodates a carrier (36) that holds aerobic microorganisms, is provided with an activated sludge treatment tank (32) that accommodates activated sludge and into which first treated water having been biologically treated in the biological treatment tank (10) flows, and a membrane separation device (34) that separates the first treated water from the activated sludge treatment tank (32). The membrane separation device (34) performs membrane treatment on the second treated water subjected to biological treatment in the activated sludge treatment tank (32), and in the inflow step, the inflow amount of the raw water in the bypass inflow is controlled on the basis of the nitrogen concentration and the phosphorus concentration in the third treated water treated by the membrane separation device (34).

Description

Technical Field

[0001] The invention relates to a raw water treatment method and a raw water treatment device. Background Art

[0002] As a technology for treating organic wastewater, there is known a technology that combines biological treatment using carriers (hereinafter, sometimes referred to as carrier method) with membrane separation activated sludge treatment (hereinafter, sometimes referred to as MBR treatment). This technology can have the following two advantages: high-speed treatment based on the carrier method can be performed, and clarified treated water based on the MBR treatment can be obtained.

[0003] For example, Patent Document 1 discloses a technique for treating organic wastewater by connecting two or more biological treatment tanks in series. However, when reducing the amount of sludge generated in the subsequent biological treatment tank, the nitrogen component contained in the sludge is dissolved into the treated water, and the nitrogen component not used in the bacterial synthesis remains. Therefore, when treating wastewater containing a large amount of nitrogen, there is a problem of exceeding the nitrogen drainage standard. In such a case, a method of reducing the nitrogen component by performing denitrification treatment by separately setting an anaerobic tank is proposed, but more space is required, and the treatment system becomes more complicated. In addition, as with nitrogen, phosphorus that is worried about remaining in the treated water cannot be reduced.

[0004] In addition, for example, Patent Documents 2 and 3 disclose a technology of bypassing a portion of the organic drainage and supplying it to the MBR treatment tank of the subsequent stage by bypassing the biological treatment tank of the previous stage. In Patent Documents 2 and 3, there is a process of measuring the drainage load of the biological treatment tank of the previous stage and automatically controlling the bypass volume, but in such a method, it is impossible to track the deterioration of the treated water caused by changes in the reaction field such as sludge properties, and it may be impossible to suppress the dissolution of nitrogen and phosphorus. In addition, since the removal target substances of the organic drainage are measured online, the stability of the measurement is generally reduced when there are many solid components in the organic drainage, and the accuracy cannot be fully obtained, and it is sometimes difficult to properly control the operation. Moreover, as in Patent Document 4, when the drainage with a relatively high concentration is used as the measurement object, there is a situation where the maintenance and management of the sensor and the structure take time, and the burden of the operation and management operation becomes large.

[0005] Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 4892917 Patent Document 2: Japanese Patent No. 5575316 Patent Document 3: Japanese Patent No. 5922406 Patent Document 4: Japanese Patent Application Publication No. 2021-159845 Summary of the invention Technical problem to be solved by the invention An object of the present invention is to suppress the outflow of nitrogen and phosphorus into treated water in raw water treatment combining biological treatment using carriers and membrane separation activated sludge treatment.

[0006] Technical solutions to solve problems The raw water treatment method of the present invention comprises the following steps: a raw water treatment step, in which raw water is treated using a raw water treatment device, the raw water treatment device comprising a biological treatment tank and a membrane separation activated sludge treatment unit, the biological treatment tank accommodates a carrier holding aerobic microorganisms, the membrane separation activated sludge treatment unit comprises an activated sludge treatment tank and a membrane separation device, the activated sludge treatment tank is supplied with first treated water that has been biologically treated in the biological treatment tank and accommodates activated sludge, the membrane separation device performs membrane treatment on second treated water that has been biologically treated in the activated sludge treatment tank; and an inflow step, in which a part of the raw water bypasses and flows into the activated sludge treatment tank without passing through the biological treatment tank, in which the inflow amount of the raw water that bypasses and flows in is controlled based on the nitrogen concentration and phosphorus concentration in the third treated water that has been treated by the membrane separation device.

[0007] In addition, in the raw water treatment method, preferably, there is a nitrogen source and phosphorus source adding process for adding a nitrogen source and / or a phosphorus source to the biological treatment tank, and in the adding process, the addition amount of the nitrogen source and / or the phosphorus source is controlled based on the inflow amount of the raw water flowing into the bypass.

[0008] In addition, the raw water treatment method preferably includes an inorganic coagulant adding step, in which an inorganic coagulant is added to the activated sludge treatment tank when the phosphorus concentration in the third treated water treated by the membrane separation device is greater than a given value.

[0009] In addition, the present invention provides a raw water treatment device for treating raw water, the raw water treatment device comprising: a biological treatment tank that accommodates a carrier carrying aerobic microorganisms; a membrane separation activated sludge treatment unit, which has an activated sludge treatment tank and a membrane separation device, the activated sludge treatment tank is for a first treated water that has been biologically treated in the biological treatment tank to flow into, and accommodates activated sludge, and the membrane separation device performs membrane treatment on a second treated water that has been biologically treated in the activated sludge treatment tank; a bypass line that allows a portion of the raw water to bypass and flow into the activated sludge treatment tank without passing through the biological treatment tank; and a control unit that controls the inflow of the raw water flowing in the bypass line based on the nitrogen concentration and phosphorus concentration in the third treated water treated by the membrane separation device.

[0010] In addition, in the raw water treatment device, preferably, there is a nitrogen source and / or phosphorus source adding unit for adding a nitrogen source and / or a phosphorus source to the biological treatment tank, and the nitrogen source and / or phosphorus source adding unit controls the addition amount of the nitrogen source and / or the phosphorus source based on the inflow amount of the raw water flowing in the bypass pipeline.

[0011] In addition, in the raw water treatment device, it is preferred that there is an inorganic coagulant adding unit for adding an inorganic coagulant to the activated sludge treatment tank, and when the phosphorus concentration in the third treated water after treatment by the membrane separation device is above a given value, the inorganic coagulant adding unit adds the inorganic coagulant to the activated sludge treatment tank.

[0012] Effects of the Invention According to the present invention, in the raw water treatment combining biological treatment using carriers and membrane separation activated sludge treatment, outflow of nitrogen and phosphorus into treated water can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram showing an example of the structure of the raw water treatment device according to the present embodiment.

[0014] Figure 2 It is a graph showing daily changes in the raw water bypass ratio to the activated sludge treatment tank and the soluble BOD sludge load relative to the raw water flow rate in the example.

[0015] Figure 3 This is a graph showing daily changes in the total nitrogen concentration (TN concentration) and the phosphate phosphorus concentration (PO4-P concentration) of the treated water treated by the membrane separation device of the example.

[0016] Figure 4 It is a graph showing the relationship between the soluble BOD sludge load of the activated sludge treatment tank in the comparative example, reference example 1 and reference example 2 and the TN concentration of the treated water.

[0017] Figure 5 It is a graph showing the relationship between the soluble BOD sludge load of the activated sludge treatment tank and the PO4-P concentration of the treated water in the comparative example, reference example 1 and reference example 2. DETAILED DESCRIPTION

[0018] Hereinafter, an embodiment of the present invention will be described. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

[0019] Figure 1 It is a schematic diagram showing an example of the structure of the raw water treatment device according to the present embodiment. Figure 1The raw water treatment device 1 shown includes a biological treatment tank 10, a membrane separation activated sludge treatment unit 12, a control device 14, pumps (16a, 16b, 16c), a nitrogen concentration detector 18, a phosphorus concentration detector 20, an inflow line (22a, 22b), a bypass line 24, a treated water discharge line 26, a sludge discharge line 28, and a flow control valve (30a, 30b). The membrane separation activated sludge treatment unit 12 includes an activated sludge treatment tank 32 and a membrane separation device 34. The membrane separation device 34 may be, for example, a separation membrane module including a separation membrane. Figure 1 In the raw water treatment device 1 , the membrane separation device 34 is provided in the activated sludge treatment tank 32 .

[0020] The inflow line 22a is connected to the biological treatment tank 10. In addition, a pump 16a and a flow control valve 30a are provided in the inflow line 22a. One end of the inflow line 22b is connected to the biological treatment tank 10, and the other end of the inflow line 22b is connected to the activated sludge treatment tank 32. One end of the bypass line 24 is connected to the inflow line 22a, and the other end of the bypass line 24 is connected to the inflow line 22b. In addition, a flow control valve 30b is provided in the bypass line 24. The treated water discharge line 26 is connected to the treated water outlet of the membrane separation device 34. In addition, a pump 16b, a nitrogen concentration detector 18, and a phosphorus concentration detector 20 are provided in the treated water discharge line 26. The sludge discharge line 28 is connected to the activated sludge treatment tank 32. In addition, a pump 16c is provided in the sludge discharge line 28. The control device 14 and the flow rate regulating valves ( 30 a , 30 b ), and the control device 14 and the nitrogen concentration detector 18 and the phosphorus concentration detector 20 are electrically connected, for example.

[0021] The biological treatment tank 10 is filled with a carrier 36 that holds aerobic microorganisms. The aerobic microorganisms held by the carrier 36 are microorganisms that can decompose organic matter in the raw water flowing into the biological treatment tank 10 under aerobic conditions. Activated sludge is contained in the activated sludge treatment tank 32. Activated sludge is sludge containing microorganisms that can decompose organic matter in the treated water and raw water flowing into the activated sludge treatment tank 32 under aerobic conditions.

[0022] An aerator 38 is provided at the bottom of the biological treatment tank 10 and the activated sludge treatment tank 32. The aerator 38 is connected to a blower 40, for example, and air supplied from the blower 40 is supplied from the aerator 38 into the biological treatment tank 10 and the activated sludge treatment tank 32.

[0023] The nitrogen concentration detector 18 may be any device capable of detecting the nitrogen concentration in the treated water, and examples thereof include a total nitrogen concentration meter (TN meter), an ammonia concentration meter, etc. The phosphorus concentration detector 20 may be any device capable of detecting the phosphorus concentration in the treated water, and examples thereof include a total phosphorus concentration meter (TP meter), a phosphoric acid concentration meter, etc.

[0024] The control device 14 is composed of, for example, a microcomputer and an electronic circuit composed of a CPU that calculates a program, a ROM and a RAM that store the program and the calculation results, and reads out a given program stored in the ROM and executes the program to control the operation of the raw water treatment device 1. For example, the control device 14 controls the opening and closing degrees of the flow control valves 30a and 30b based on the nitrogen concentration and phosphorus concentration in the treated water, thereby controlling the inflow amount of raw water flowing in the bypass line 24. In addition, the control device 14 may be configured to control the operation of the pump 16 and the blower 40, for example.

[0025] In order to grasp the inflow amount of raw water flowing in the bypass line 24, flow rate measuring devices may be installed in the inflow line 22a and the bypass line 24. In order to check the quality of treated water, a total organic carbon meter (TOC meter) may be installed in the treated water discharge line 26.

[0026] Next, an example of the operation of the raw water treatment device 1 according to the present embodiment will be described.

[0027] The control device 14 operates the pump 16a and opens the flow control valve 30a to a given opening, thereby supplying raw water from the inflow line 22a to the biological treatment tank 10. At this time, the control device 14 may open the flow control valve 30b to a given opening, thereby allowing a portion of the raw water passing through the inflow line 22a to bypass the bypass line 24 and flow into the activated sludge treatment tank 32.

[0028] The control device 14 operates the blower 40 to supply air from the aeration device 38 into the biological treatment tank 10. Then, in the biological treatment tank 10, organic matter in the raw water is biologically treated under aerobic conditions by the microorganisms held by the carriers 36. The treated water (first treated water) treated in the biological treatment tank 10 flows into the activated sludge treatment tank 32 through the inflow line 22b.

[0029] In addition, the control device 14 operates the blower 40 to supply air from the aeration device 38 to the activated sludge treatment tank 32. Then, in the activated sludge treatment tank 32, the first treated water flowing in from the inflow line 22b and the organic matter in the raw water flowing in from the bypass line 24 are biologically treated by activated sludge under aerobic conditions. In addition, the control device 14 operates the pump 16b to pass the treated water (second treated water) biologically treated in the activated sludge treatment tank 32 into the membrane separation device 34, remove the sludge in the second treated water, and discharge the treated water (third treated water: filtered water from which the sludge is removed) that has passed through the separation membrane of the membrane separation device 34 to the outside of the system from the treated water discharge line 26. In addition, the control device 14 operates the pump 16c to discharge the sludge accumulated in the activated sludge treatment tank 32 from the sludge discharge line 28 to the outside of the system.

[0030] Next, an example of flow rate control of raw water flowing into the activated sludge treatment tank 32 by bypass will be described. First, the nitrogen concentration and phosphorus concentration in the third treated water detected by the nitrogen concentration detector 18 and the phosphorus concentration detector 20 are input to the control device 14. Then, when at least one of the input nitrogen concentration and phosphorus concentration is equal to or greater than a predetermined given value (the given value may be determined for each of the nitrogen concentration and the phosphorus concentration, or may be shared), the control device 14 controls the opening of the flow control valves 30a and 30b so that the inflow of raw water flowing in the bypass line 24 is increased. For example, when raw water does not flow into the bypass line 24, the opening of the flow control valves 30a and 30b is controlled so that a given inflow of raw water flows into the bypass line 24. Alternatively, for example, when raw water flows into the bypass line 24, the opening of the flow control valves 30a and 30b is controlled so that an inflow of raw water increased to a given ratio relative to the inflow of raw water at that time flows into the bypass line 24. When the nitrogen concentration and phosphorus concentration in the treated water detected by the nitrogen concentration detector 18 and the phosphorus concentration detector 20 are lower than a predetermined given value as a result of continuing the operation in which the inflow of raw water flowing through the bypass line 24 is increased, the control device 14 preferably controls the opening of the flow control valves 30a and 30b to reduce the inflow of raw water flowing through the bypass line 24. For example, the opening of the flow control valves 30a and 30b is controlled to stop the inflow of raw water into the bypass line 24. In addition, for example, the opening of the flow control valves 30a and 30b is controlled so that raw water whose inflow is reduced to a given ratio relative to the current inflow of raw water flowing through the bypass line 24 flows through the bypass line 24. In order to perform stable treatment, the predetermined given value is preferably set to a range of 0.6 to 1 times the treatment target value. In addition, in order to stabilize the treatment in the biological treatment reactor, the upper limit of the inflow of raw water flowing through the bypass line 24 is preferably set to 90% of the raw water flow rate.

[0031] Generally, the treatment progresses faster in the activated sludge treatment tank 32 at the subsequent stage than in the biological treatment tank 10 at the previous stage, and therefore, the BOD volume load of the activated sludge treatment tank 32 at the subsequent stage has to be low load. In such a case, nitrogen and phosphorus are sometimes eluted from the activated sludge and other bacterial bodies, or nitrogen and phosphorus that are not used for bacterial body synthesis sometimes remain, which deteriorates the water quality of the treated water. However, in the present embodiment, as described above, the inflow of raw water that bypasses and flows into the activated sludge treatment tank 32 is controlled based on the nitrogen concentration and phosphorus concentration of the treated water, so that the BOD volume load of the activated sludge treatment tank 32 can be suppressed from becoming low load. As a result, it is possible to suppress the excessive dissolution of nitrogen and phosphorus from the bacterial bodies of the activated sludge in the activated sludge treatment tank 32, and suppress the outflow of nitrogen and phosphorus into the treated water.

[0032] Hereinafter, each structure, treatment conditions, etc. of the raw water treatment device 1 of this embodiment will be described in detail.

[0033] The raw water to be treated is, for example, organic wastewater discharged from chemical plants including sewage treatment plants and food plants, semiconductor plants / liquid crystal plants, pulp plants, and other fields, and any water can be treated by biological treatment.

[0034] From the viewpoint of further suppressing the outflow of nitrogen and phosphorus into the treated water, the BOD volume load of each of the biological treatment tank 10 and the activated sludge treatment tank 32 is preferably 0.5 kgBOD / (m 3 ·d) or more, more preferably 1.0 kgBOD / (m 3 ·d) or more, more preferably 1.5 kgBOD / (m 3 Considering the residual organic matter in the treated water and the outflow of nitrogen and phosphorus, the upper limit of the BOD volume load is preferably 6 kgBOD / (m 3 d) or below.

[0035] From the viewpoint of further suppressing the outflow of nitrogen and phosphorus into the treated water, the BOD sludge load of the activated sludge treatment tank 32 is preferably in the range of, for example, 0.005 to 0.15 kgBOD / (kgMLSS·d).

[0036] The sludge retention time (SRT) of the activated sludge treatment tank 32 also depends on the volume load, and is preferably in the range of 5 to 50 days, and more preferably in the range of 20 to 40 days. If the SRT becomes longer, autoxidation of microorganisms in the sludge occurs, and high molecular substances such as those that do not pass through the separation membrane accumulate in the activated sludge treatment tank 32, which may cause clogging of the membrane. In addition, if the SRT is short, the sludge becomes dispersed, which may cause clogging of the separation membrane.

[0037] The pH of the water in the biological treatment tank 10 and the activated sludge treatment tank 32 is not particularly limited as long as it is within a range suitable for general biological treatment, and is preferably within a range of 6 to 9, and more preferably within a range of 6.5 to 7.5. The pH of the water in the biological treatment tank 10 and the activated sludge treatment tank 32 is adjusted by adding a pH adjuster to each tank. Examples of the pH adjuster include acidic agents such as hydrochloric acid, alkaline agents such as sodium hydroxide, and the like.

[0038] The dissolved oxygen (DO) of the water in the biological treatment tank 10 and the activated sludge treatment tank 32 is not particularly limited as long as it is an oxygen amount required for general biological treatment, but is preferably 0.5 mg / L or more, and more preferably 1 mg / L or more, for example.

[0039] The water temperature of the biological treatment tank 10 and the activated sludge treatment tank 32 is not particularly limited as long as it is within a range suitable for general biological treatment, and is preferably within a range of 15°C to 35°C, and more preferably within a range of 20°C to 30°C.

[0040] It is preferred to add a nitrogen source and / or a phosphorus source as a nutrient to the biological treatment tank 10. When adding a nitrogen source and a phosphorus source to the biological treatment tank 10, it is preferred to control the amount of the nitrogen source and / or the phosphorus source added based on the inflow of raw water flowing through the bypass line 24. The following is an example of a control method. A nitrogen source supply line provided with a first pump and a phosphorus source supply line provided with a second pump are provided in the biological treatment tank 10. In addition, an inflow meter for detecting the inflow of raw water per unit time is provided in the bypass line 24. Then, the inflow per unit time detected by the inflow meter is input to the control device 14. When the inflow is below a given value, the control device 14 operates the first pump and the second pump to supply the nitrogen source from the nitrogen source supply line to the biological treatment tank 10, and to supply the phosphorus source from the phosphorus source supply line to the biological treatment tank 10. Then, when the inflow exceeds a given value, the control device 14 stops the operation of the first pump and the second pump, and stops the supply of the nitrogen source and the phosphorus source. In addition, for example, the control device 14 substitutes the inflow per unit time detected by the inflow meter into a map (or a formula, a table, etc.) that predefines the inflow per unit time and the addition amount of the nitrogen source and the addition amount of the phosphorus source, and a map (or a formula, a table, etc.) that predefines the inflow per unit time and the addition amount of the phosphorus source, to obtain the addition amount of the nitrogen source and the phosphorus source, and controls the output of the first pump and the second pump to supply the obtained addition amount of the nitrogen source and the phosphorus source. In addition, the above-mentioned map stipulates the following relationship: if the inflow increases, the addition amount of the nitrogen source and the phosphorus source decreases, and if the inflow decreases, the addition amount of the nitrogen source and the phosphorus source increases.

[0041] The nitrogen source is not particularly limited, but examples thereof include ammonium chloride, ammonium sulfate, diammonium hydrogen phosphate, urea, etc. The phosphorus source is not particularly limited, and examples thereof include phosphoric acid, sodium phosphate, potassium phosphate, etc. In addition to the nitrogen source and the phosphorus source, inorganic salts such as iron, manganese, and calcium may be supplied to the biological treatment tank 10 as a nutrient. In addition, it is preferred that no nitrogen source and phosphorus source are added to the activated sludge treatment tank 32.

[0042] The carrier 36 in the biological treatment tank 10 can be a known carrier, for example, a plastic carrier, a sponge carrier, a gel carrier, etc. Among them, from the viewpoint of cost and durability, a sponge carrier is preferred, for example, a sponge carrier made of polyurethane is preferred. The carrier 36 is not limited to a flowing type flowing in the biological treatment tank 10, and can also be a fixed type in which a filler tube filled with the carrier 36 is arranged in the biological treatment tank 10. The shape of the carrier 36 is not particularly limited, and tetrahedral shapes such as cubes, granular shapes, spherical shapes, granular shapes, cylindrical shapes, fibrous shapes, membrane shapes, etc. can be cited. The amount of carrier 36 added to the biological treatment tank 10 is preferably in the range of 10% to 70% relative to the tank volume, for example. In addition, the carrier 36 can also be added to the activated sludge treatment tank 32.

[0043] The membrane separation device 34 of this embodiment is exemplified as an immersed type membrane separation device 34 installed in the activated sludge treatment tank 32, but it is not limited thereto, and may be an external tank type membrane separation device 34 installed outside the activated sludge treatment tank 32. Among them, from the viewpoint of the installation area of ​​the device and the operating power, the immersed type membrane separation device 34 is preferably used.

[0044] Examples of the shape of the separation membrane provided in the membrane separation device 34 include a flat membrane type, a hollow fiber type, a tubular type, a spiral type, and the like. Examples of the material of the impregnated membrane include organic membranes such as polyethylene (PE), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polyether sulfone (PES), and cellulose acetate (CA), and inorganic membranes made of ceramics. The pore size of the separation membrane is preferably 1.0 μ m or less, preferably with a pore diameter of 0.1 μ The separation membrane is preferably operated at a permeation flow rate of about 0.1 to 0.8 m / day, and more preferably operated at a permeation flow rate of 0.2 to 0.6 m / day.

[0045] When the phosphorus concentration in the treated water after being treated by the membrane separation device 34 is above a predetermined given value, it is preferred to add an inorganic coagulant to the activated sludge treatment tank 32. For example, an inorganic coagulant supply line provided with a pump is provided in the activated sludge treatment tank 32. Then, when the phosphorus concentration input from the phosphorus concentration detector 20 is above a predetermined given value, the control device 14 operates the pump to supply the inorganic coagulant from the inorganic coagulant supply line to the activated sludge treatment tank 32. By such an operation, the phosphorus concentration in the treated water can be rapidly reduced. As the inorganic coagulant, it can be a conventionally known inorganic coagulant, for example, polyaluminum chloride (PAC), ferric chloride, etc. It is preferred that the amount of the inorganic coagulant added is set to be above the theoretically required amount. In the case of PAC (assuming Al2O3 = 10.5wt%), the theoretical requirement is 15.7mg / L relative to a phosphorus concentration of 1mg / L; in the case of ferric chloride (assuming FeCl3 = 38wt%), the theoretical requirement is 13.8mg / L relative to a phosphorus concentration of 1mg / L.

[0046] Example Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0047] <Example> use Figure 1 The raw water treatment device shown in the figure implements a continuous water flow test of simulated wastewater (raw water). However, the control device is not used, and the opening and closing control of the flow control valve and the operation control of the pump are manually performed. In addition, before implementing the continuous water flow test, an acclimation process is set up. Specifically, only raw water is introduced into the biological treatment tank, and while confirming the BOD concentration of the treated water, the BOD volume load is increased, and at the same time, the microorganisms are fully attached to the carrier. The biological treatment tank after the acclimation process is combined with the membrane separation activated sludge treatment unit, and the continuous water flow test is started. In addition, activated sludge acclimated with the raw water is put into the activated sludge treatment tank.

[0048] <Conditions for continuous water flow test> Volume of biological treatment tank: 12L Biological treatment tank carrier: hydrophobic polyurethane sponge carrier The carrier filling rate of the biological treatment tank is 20% based on the bulk volume. Separation membrane of membrane separation device: PVDF hollow fiber membrane Filtration Flux of membrane separation device: 0.4m / d ※ Filtration Flux refers to the amount of water treated per unit membrane area of ​​the separation membrane and is calculated as follows: Filtration Flux = Raw water flow rate ÷ Membrane area of ​​separation membrane Volume of activated sludge treatment tank: 24L Sludge concentration in activated sludge treatment tank (MLSS): 8000mg / L Sludge extraction from the activated sludge treatment tank: Sludge was extracted once a day so that the MLSS became 8000 mg / L.

[0049] Representative values ​​of raw water BOD concentration: 500, 1000, 1500 mg / L (Comparative Example, Reference Example 1 and Reference Example 2 described below: 1000 mg / L) Matrix in raw water: sucrose, sodium acetate, propionic acid, 2-propanol Nitrogen and phosphorus in raw water: Adjust with ammonium chloride and phosphoric acid to make BOD:N:P=100:5:1 Other required trace elements: add trace element solution to the raw water Raw water SS: None Raw water flow: 54L / d (bypassing the activated sludge treatment tank as appropriate) Total BOD volume load: 1.5kgBOD / (m 3 d) ※Total BOD volume load is calculated as follows: Total BOD volume load = Raw water BOD concentration × Inflow volume ÷ Total tank volume of biological treatment tank and activated sludge treatment tank In addition, during all the experimental periods, the soluble BOD removal rate of the biological treatment tank was 95% or more, and the ammonia nitrogen concentration and phosphate phosphorus concentration were also able to be removed by 95% or more. The soluble BOD removal rate of the biological treatment tank was calculated as follows.

[0050] Soluble BOD removal rate in biological treatment tank = (raw water BOD concentration - dissolved BOD concentration in biological treatment tank) ÷ raw water BOD concentration In addition, since there is no SS in the raw water, the raw water BOD = dissolved BOD. The dissolved BOD concentration in the biological treatment tank is 0.45 μ m BOD concentration after filtering and removing suspended components.

[0051] Each item shown in Examples (and Comparative Examples and Reference Examples described later) was calculated as follows.

[0052] (1) Soluble BOD sludge load in activated sludge treatment tank = ((Soluble BOD concentration in biological treatment tank × raw water flow rate to biological treatment tank) + (Bypass inflow of raw water to activated sludge treatment tank × Soluble BOD concentration of raw water)) ÷ (Sludge concentration in tank × tank volume) In addition, since there is no SS in the raw water, the raw water BOD = soluble BOD.

[0053] (2) Sludge retention time in activated sludge treatment tank = (sludge concentration in tank × tank volume) ÷ (extracted sludge concentration × extracted water volume) (3) BOD sludge conversion rate = sludge volume produced in activated sludge treatment tank ÷ total BOD removal (4) Amount of sludge generated in the activated sludge treatment tank = ((sludge concentration in the activated sludge treatment tank after a given period of time - initial sludge concentration in the activated sludge treatment tank) × tank volume of the activated sludge treatment tank) + (extracted sludge concentration × amount of water extracted) (5) Total BOD removal = (raw water BOD concentration - BOD concentration of membrane separation water in the activated sludge treatment tank) × raw water flow rate (6) The suction pressure is a value measured by a pressure gauge (GC67, manufactured by Nagano Keiki Co., Ltd.) installed in the treated water discharge line. The suction pressure is recorded and expressed as the average daily increase in suction pressure over a given period.

[0054] Figure 2 The raw water bypass ratio to the activated sludge treatment tank and the daily changes in the soluble BOD sludge load relative to the raw water flow rate in the example are shown. Figure 3 The daily changes of the total nitrogen concentration (TN concentration) and the phosphate phosphorus concentration (PO4-P concentration) of the treated water after treatment by the membrane separation device of the embodiment are shown. In the embodiment, the water flow test was conducted during the first 5 days without bypassing the raw water into the activated sludge treatment tank. Then, after confirming the increase in the nitrogen concentration and phosphorus concentration in the treated water after treatment by the membrane separation device, the raw water was bypassed and flowed into the activated sludge treatment tank. In addition, from the start of water flow to the 18th day, the raw water BOD concentration was set to 1000 mg / L, and from the 19th to the 25th day, the raw water BOD concentration was set to 1500 mg / L, and then the raw water BOD concentration was set to 500 mg / L for operation. The target values ​​in this experiment were set to TN concentration: 10 mg / L or less, and PO4-P: 2 mg / L or less.

[0055] like Figure 3As shown in the figure, during the period when the raw water was not bypassed to flow into the activated sludge treatment tank, the TN concentration and PO4-P concentration of the treated water (hereinafter referred to as treated water) treated by the membrane separation device increased and exceeded the target value. Since the TN concentration and PO4-P concentration of the treated water exceeded the target value, the raw water bypass rate to the activated sludge treatment tank was set to 28% to 39% during the period from the 7th day to the 11th day, so that the raw water bypass flowed into the activated sludge treatment tank, and as a result, the TN concentration and PO4-P concentration of the treated water were able to reach the target value. In addition, the soluble BOD sludge load of the activated sludge treatment tank varied from 0.08 to 0.1 kgBOD / (kgMLSS·d). During the period from the 14th day to the 18th day, the raw water bypass rate to the activated sludge treatment tank was reduced to 17% to 22% for operation. As a result, although the TN concentration and PO4-P concentration of the treated water increased, they were still able to maintain the target value. During this period, the soluble BOD sludge load of the activated sludge treatment tank varied from 0.05 to 0.06 kgBOD / (kgMLSS·d). According to the above results, by controlling the inflow of raw water bypassing the activated sludge treatment tank based on the TN concentration and PO4-P concentration of the treated water, the outflow of nitrogen and phosphorus into the treated water can be suppressed, and the operation management can be performed to obtain good treated water quality. In addition, by increasing the raw water bypass ratio, better treated water quality can be obtained.

[0056] After the 19th day, the operation was performed with the raw water BOD concentration fluctuating. However, even if the raw water concentration fluctuated, the outflow of nitrogen and phosphorus into the treated water was suppressed by controlling the raw water inflow into the activated sludge treatment tank according to the TN concentration and PO4-P concentration of the treated water (i.e., the raw water bypass ratio to the activated sludge treatment tank), and the operation management was able to obtain good treated water quality. In addition, the soluble BOD sludge load of the activated sludge treatment tank during the experiment ranged from 0.03 to 0.11 kgBOD / (kgMLSS·d).

[0057] <Comparative Example and Reference Example 1 and Reference Example 2> In the comparative example, the test was conducted in the same manner as in the example except that the raw water was not bypassed to flow into the activated sludge treatment tank. In addition, in reference examples 1 and 2, although the raw water was bypassed to flow into the activated sludge treatment tank, the raw water bypass ratio was not controlled according to the TN concentration and PO4-P concentration of the treated water, but the raw water bypass ratio was simply increased. In addition, the test was conducted in the same manner as in the example. In reference examples 1 and 2, except for the different sludge retention time in the activated sludge treatment tank, the other conditions were the same. Regarding the sludge retention time in the activated sludge treatment tank, reference example 1 was set to 30 days, and reference example 2 was set to 40 days.

[0058] Figure 4The relationship between the soluble BOD sludge load in the activated sludge treatment tank and the TN concentration of the treated water in the comparative example, reference example 1, and reference example 2 is shown. Figure 5 The relationship between the soluble BOD sludge load of the activated sludge treatment tank and the PO4-P concentration of the treated water in the comparative example, reference example 1 and reference example 2 is shown. In the comparative example, the soluble BOD sludge load of the activated sludge treatment tank is less than 0.02 kgBOD / (kgMLSS·d), the TN concentration of the treated water is above 20 mg / L, and the PO4-P concentration is above 4 mg / L. In the comparative example, since the raw water is not bypassed into the activated sludge treatment tank, the soluble BOD sludge load becomes low as described above, and the disintegration of the sludge in the activated sludge treatment tank proceeds, so it is considered that nitrogen and phosphorus are dissolved into the treated water. In reference examples 1 and 2, by increasing the raw water bypass ratio and increasing the soluble BOD sludge load of the activated sludge treatment tank, the TN concentration and PO4-P concentration of the treated water can meet the target values. On the other hand, the soluble BOD sludge load required to set the TN concentration and PO4-P concentration to the target value is 0.1 kgBOD / (kgMLSS·d) or more in Reference Example 1, and 0.05 kgBOD / (kgMLSS·d) or more in Reference Example 2. Therefore, in order to manage using the soluble BOD sludge load, it is necessary to grasp the numerical range for obtaining the target water quality in advance or during actual operation. However, since it is believed that this range varies depending on the operating state, it is assumed that it is difficult to manage using the soluble BOD sludge load during actual operation.

[0059] Table 1 shows the average daily increase in suction pressure of the separation membrane during operation of the examples, comparative examples, reference examples 1 and 2, the sludge retention time in the activated sludge treatment tank, and the BOD sludge conversion rate.

[0060] [Table 1] The comparative example in which the raw water is not bypassed into the activated sludge treatment tank has a lower BOD sludge conversion rate than the embodiment in which the raw water is bypassed. This is because, by not implementing the bypass of the raw water, the organic matter load of the activated sludge treatment tank becomes lower, and the disintegration of the sludge proceeds. As a result, the sludge retention time of the comparative example becomes longer, and substances such as biopolymers that promote membrane clogging accumulate, so the average daily increase in suction pressure becomes larger. On the other hand, in the embodiment in which the raw water is bypassed, no significant increase in suction pressure is found. However, it is generally believed that due to predation and self-digestion between organisms, the volume reduction is promoted by increasing the sludge retention time, so it is believed that the optimal sludge retention time also needs to be considered. According to the above results, by bypassing the raw water into the activated sludge treatment tank, it is possible to suppress the dissolution of nitrogen and phosphorus into the treated water and the increase in the suction pressure of the separation membrane and operate. In addition, instead of grasping the soluble BOD sludge load that can maintain the target water quality, the inflow of raw water into the activated sludge treatment tank is adjusted based on the nitrogen and phosphorus concentrations of the treated water. This can suppress the elution of nitrogen and phosphorus into the treated water even when there is a change in the raw water, and can operate while maintaining good treated water quality.

[0061] Description of symbols 1: Raw water treatment device 10: Biological treatment tank 12: Membrane separation activated sludge treatment unit 14: Control device 16a~16c: Pump 18: Nitrogen concentration detector 20: Phosphorus concentration detector 22a, 22b: Inflow pipeline 24: Bypass line 26: Treated water discharge pipeline 28: Sludge discharge pipeline 30a, 30b: Flow control valve 32: Activated sludge treatment tank 34: Membrane separation device 36: Carrier 38: Aeration device 40: Blower.

Claims

1. A method for treating raw water, characterized in that: It has the following processes: A raw water treatment step, treating raw water using a raw water treatment device, the raw water treatment device comprising a biological treatment tank and a membrane separation activated sludge treatment unit, the biological treatment tank containing a carrier holding aerobic microorganisms, the membrane separation activated sludge treatment unit comprising an activated sludge treatment tank and a membrane separation device, the activated sludge treatment tank being fed with first treated water that has been biologically treated in the biological treatment tank and containing activated sludge, and the membrane separation device performing membrane treatment on second treated water that has been biologically treated in the activated sludge treatment tank; as well as In the inflow step, a part of the raw water is bypassed and flows into the activated sludge treatment tank without passing through the biological treatment tank, In the inflow step, the inflow amount of the raw water in the bypass inflow is controlled based on the nitrogen concentration and the phosphorus concentration in the third treated water treated by the membrane separation device.

2. The method for treating raw water according to claim 1, characterized in that: The raw water treatment method comprises a nitrogen source and phosphorus source adding step, in which a nitrogen source and / or a phosphorus source is added to the biological treatment tank. In the adding step, the amount of the nitrogen source and / or the phosphorus source added is controlled based on the amount of the raw water flowing in through the bypass.

3. The method for treating raw water according to claim 1 or 2, characterized in that: The raw water treatment method includes an inorganic coagulant adding step of adding an inorganic coagulant to the activated sludge treatment tank when the phosphorus concentration in the third treated water treated by the membrane separation device is equal to or higher than a given value.

4. A raw water treatment device for treating raw water, characterized in that: The raw water treatment device comprises: A biological treatment tank that accommodates a carrier carrying aerobic microorganisms; A membrane separation activated sludge treatment unit, comprising an activated sludge treatment tank, the activated sludge treatment tank being used to flow into the first treated water that has been biologically treated in the biological treatment tank and accommodating the activated sludge, and the membrane separation device performing membrane treatment on the second treated water that has been biologically treated in the activated sludge treatment tank; a bypass line for bypassing a portion of the raw water and flowing into the activated sludge treatment tank without passing through the biological treatment tank; as well as A control unit controls an inflow rate of the raw water flowing through the bypass line based on a nitrogen concentration and a phosphorus concentration in the third treated water treated by the membrane separation device.

5. The raw water treatment device according to claim 4, characterized in that: The raw water treatment device comprises a nitrogen source and phosphorus source adding unit, which adds a nitrogen source and / or a phosphorus source to the biological treatment tank. The nitrogen source and phosphorus source adding unit controls the addition amount of the nitrogen source and / or the phosphorus source based on the inflow amount of the raw water flowing in the bypass line.

6. The raw water treatment device according to claim 4 or 5, characterized in that: The raw water treatment device includes an inorganic coagulant adding unit for adding an inorganic coagulant to the activated sludge treatment tank. The inorganic coagulant adding unit adds the inorganic coagulant to the activated sludge treatment tank when the phosphorus concentration in the third treated water treated by the membrane separation device is equal to or higher than a given value.

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