Water treatment method and water treatment device

Abstract

The purpose of this invention is to provide a water treatment method that suppresses the outflow of nitrogen, such as ammonia nitrogen, into the treated water during multi-stage biological treatment of water containing organic matter by using two or more reaction tanks filled with carriers arranged in series. The water treatment method of the present invention includes the following steps: a biological treatment step in which two or more reaction tanks filled with carriers containing microorganisms are connected in series to biologically treat water containing organic matter under aerobic conditions; and an inflow step in which a portion of the water containing organic matter is diverted from the preceding reaction tank to the subsequent reaction tank, wherein the amount of the diverted water containing organic matter is controlled so that the BOD volumetric loading of each reaction tank is 0.5 kg / (m³). 3.d) and above.

Description

Technical Field

[0001] This invention relates to a water treatment method and a water treatment apparatus. Prior Technology

[0002] In recent years, the use of fluidized bed biological treatment methods has been adopted not only in small and medium-sized wastewater treatment equipment such as septic tanks and food factories, and overseas wastewater treatment plants, but also in large-scale wastewater treatment equipment in semiconductor factories. Compared with the conventional suspended activated sludge process, the fluidized bed biological treatment method can handle high loads, thus simplifying the reaction tank. It also eliminates the need to consider sludge settling properties during treatment, and is easier to operate and manage than conventional methods.

[0003] In particular, the multi-stage treatment method, which uses two or more reaction tanks filled with carriers in series to biologically treat water containing organic matter, allows the BOD volumetric load of the first reaction tank to operate at a high load. Organic matter is roughly removed in the first reaction tank, and fine removal is carried out in the reaction tanks after the second stage, thus effectively treating organic matter from raw water.

[0004] For example, Patent Document 1 proposes a technique for controlling the SS load of the reaction tanks after the second stage in a multi-stage treatment method for biological treatment of water containing organic matter by arranging two or more reaction tanks filled with carriers in series, thereby suppressing the amount of sludge production to a lower level (Patent Document 1).

[0005] For example, Patent Document 2 proposes a method for controlling the amount of nitrogen source injected to maintain the ammonia concentration in biologically treated water below a predetermined value. [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent No. 5895663 [Patent Document 2] Japanese Patent Application Publication No. 9-1172 Summary of the Invention

[0007] [The problem the invention aims to solve]

[0008] However, as in Patent Document 1, when the amount of sludge produced in the reaction tanks after the second stage is reduced, the volumetric load of the BOD from the raw water needs to be reduced to a lower load in the later stages. As a result, there will be nitrogen sources dissolved from the bacteria or nitrogen sources not used in the synthesis of the bacteria, which will cause the nitrogen concentration of the treated water to deteriorate.

[0009] Therefore, the object of the present invention is to provide a water treatment method and water treatment apparatus for suppressing the outflow of nitrogen such as ammonia into the treated water in a multi-stage treatment process in which "two or more reaction tanks filled with carriers are arranged in series for biological treatment of water containing organic matter". [Methods for solving problems]

[0010] The water treatment method of the present invention is characterized by comprising the following steps: a biological treatment step, wherein two or more reaction tanks filled with carriers containing microorganisms are connected in series to biologically treat water containing organic matter under aerobic conditions; and an inflow step, wherein a portion of the water containing organic matter is diverted to a subsequent reaction tank instead of passing through the preceding reaction tank; in the inflow step, the amount of the water containing organic matter diverted is controlled so that the BOD volumetric load of each reaction tank is 0.5 kg / (m³·d) or more.

[0011] Furthermore, in this water treatment method, during the inflow step, it is preferable to detect the nitrogen concentration in the reaction tank or the nitrogen concentration of the treated water discharged from the reaction tank, and based on the detection result of the nitrogen concentration, control the amount of water containing organic matter that flows in separately.

[0012] Furthermore, the water treatment method further includes an addition step of adding a nitrogen source to the reaction tank. In this addition step, it is preferable to detect the nitrogen concentration in the reaction tank or the nitrogen concentration in the treated water discharged from the reaction tank, and control the amount of nitrogen source added to the reaction tank based on the detection result of the nitrogen concentration.

[0013] Furthermore, in this water treatment method, the BOD load of the carrier in each of the reaction tanks is preferably 1.7 kg / (m³-carrier·d) or higher.

[0014] Furthermore, the water treatment apparatus of the present invention preferably includes: a reaction tank group, comprising two or more reaction tanks filled with carriers containing microorganisms arranged in series to perform biological treatment on water containing organic matter under aerobic conditions; a diversion pipeline to divert a portion of the water containing organic matter from the upstream reaction tank to the downstream reaction tank; and a control unit to control the amount of the water containing organic matter diverted into the downstream reaction tank so that the BOD volumetric load of each reaction tank is 0.5 kg / (m³·d) or more.

[0015] Furthermore, the water treatment apparatus preferably includes a detector for detecting the nitrogen concentration in the reaction tank or the nitrogen concentration in the treated water discharged from the reaction tank.

[0016] Furthermore, in this water treatment device, the control unit preferably controls the amount of water containing organic matter that flows into the device based on the detection result of the nitrogen concentration detected by the detector.

[0017] Furthermore, the water treatment apparatus preferably includes a nitrogen source addition device for adding nitrogen to the reaction tank; the control unit controls the amount of nitrogen source added to the reaction tank based on the detection result of the nitrogen concentration detected by the detector.

[0018] Furthermore, in this water treatment device, the BOD load of the carrier in each of the reaction tanks is preferably 1.7 kg / (m³-carrier·d) or higher. [Invention Effects]

[0019] Through this invention, in a multi-stage treatment process where two or more carrier-filled reaction tanks are connected in series to biologically treat water containing organic matter, the outflow of nitrogen such as ammonia nitrogen into the treated water can be suppressed. Simple Explanation of the Diagram

[0020] Figure 1 is a schematic diagram showing an example of the configuration of a water treatment device according to this embodiment. Figure 2 is a schematic diagram showing another example of the configuration of a water treatment device according to this embodiment. Figure 3 is a schematic diagram showing an example of a reaction tank group with three reaction tanks. Figure 4 shows the changes in BOD volumetric load of the third reaction tank and the concentration of ammonia nitrogen in the treated water discharged from the third reaction tank. Figure 5 shows the relationship between the BOD volumetric load of the third reaction tank and the ammonia nitrogen concentration in the treated water discharged from the third reaction tank. Implementation

[0021] The following describes an embodiment of the present invention. This embodiment is one example of implementing the present invention, and the present invention is not limited to this embodiment.

[0022] Figure 1 is a schematic diagram showing an example of the configuration of a water treatment apparatus according to this embodiment. The water treatment apparatus 1 shown in Figure 1 includes a group of reaction tanks including a first reaction tank 10 and a second reaction tank 12, a treatment water tank 14, a control device 22, a pump 24, a detector 26, inflow pipelines 16a and 16b, a branch pipeline 18, and a treatment water pipeline 20.

[0023] An inflow pipeline 16a is connected to the inlet of the first reaction tank 10. One end of the inflow pipeline 16b is connected to the outlet of the first reaction tank 10, and the other end of the inflow pipeline 16b is connected to the inlet of the second reaction tank 12. One end of the treated water pipeline 20 is connected to the outlet of the second reaction tank 12, and the other end of the treated water pipeline 20 is connected to the inlet of the treated water tank 14. One end of the branch pipeline 18 is connected to the inflow pipeline 16a, and the other end of the branch pipeline 18 is connected to the inflow pipeline 16b. A pump 24 is installed on the branch pipeline 18. The control device 22 is electrically connected to the pump 24 and the detector 26, for example.

[0024] The reaction tank group is configured such that the first reaction tank 10 is the front section, the second reaction tank 12 is the rear section, and the first reaction tank 10 and the second reaction tank 12 are connected in series. Alternatively, the reaction tank group can be configured such that two or more reaction tanks are connected in series.

[0025] The first reaction tank 10 and the second reaction tank 12 are filled with carriers 28 containing microorganisms. The carriers 28 are not particularly limited, and for example, plastic carriers, sponge carriers, gel carriers, etc. can be cited.

[0026] An aeration device 30 is provided at the bottom of the first reaction tank 10 and the second reaction tank 12. The aeration device 30 is connected to a blower (not shown), and air supplied from the blower is supplied from the aeration device 30 to the first reaction tank 10 and the second reaction tank 12.

[0027] Screens 32 are installed near the outlets of the first reaction tank 10 and the second reaction tank 12. By installing screens 32, the carrier 28 is prevented from being discharged from the outlets of each reaction tank.

[0028] A detector 26 is installed in the treatment tank 14. The detector 26 is a device for detecting the nitrogen concentration in the treated water. The detector 26 can be used for both online and offline measurements. The nitrogen concentration detected by the detector 26 can be at least one of the following: total nitrogen (TN), ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen. The ammonia nitrogen concentration detected can be based on feedback from experimental measurements, such as absorption spectroscopy or ion chromatography, but real-time online measurements using ion electrode methods or potentiometric methods are preferred. For the detection of nitrate nitrogen and nitrite nitrogen, since the organic load range is within the range where nitrification is unlikely, a TN meter or ammonia meter is more ideal.

[0029] The control device 22 is, for example, a microcomputer and circuitry consisting of a CPU for processing programs, ROM and RAM for storing programs and processing results. It controls the operation of the water treatment device 1 by reading and executing predetermined programs stored in ROM, etc. Specifically, the control device 22 adjusts the output of the pump 24 to control the flow rate of water containing organic matter flowing in the branch line 18. Furthermore, the control device 22 can, for example, control the output of the pump 24 based on the nitrogen concentration detected by the detector 26, thereby controlling the flow rate of water containing organic matter flowing in the branch line 18.

[0030] Next, the operation of the water treatment device 1 according to this embodiment will be explained.

[0031] Water containing organic matter is supplied to the first reaction tank 10 via inlet pipe 16a. At this time, pump 24 is activated via control device 22, supplying a portion of the organic-containing water flowing through inlet pipe 16a to the second reaction tank 12 via diversion pipe 18 (inlet step). In the second reaction tank 12, treated water discharged from the first reaction tank 10 is also supplied via inlet pipe 16b. Then, air is supplied to the first reaction tank 10 and the second reaction tank 12 from aeration device 30. Under aerobic conditions, the organic matter in the water containing organic matter in the first reaction tank 10 and the second reaction tank 12 is biologically treated by microorganisms attached to carrier 28 (biological treatment step). The treated water in the first reaction tank 10 is supplied to the second reaction tank 12 via inlet pipe 16b, and the treated water in the second reaction tank 12 is supplied to the treated water tank 14 via treated water pipe 20.

[0032] During the inflow step, control device 22 adjusts the output of pump 24 to control the flow rate of organic-containing water flowing in the branch line 18, so that the BOD volumetric load of each of the first reaction tank 10 and the second reaction tank 12 is 0.5 kg / (m³·d) or higher. The BOD volumetric load of the reaction tank is the amount of BOD flowing into the tank per day (BOD concentration × flow rate of water into the reaction tank), relative to the tank volume, and is calculated using the following formula: BOD volumetric loading of the reaction tank = BOD concentration × inflow rate / reaction tank volume Here, the inflow volume of the first reaction tank 10 is the organic water flowing into the first reaction tank 10 from the inflow pipe 16a, and the inflow volume of the second reaction tank 12 is the sum of the organic water flowing into the second reaction tank 12 from the diversion pipe 18 and the treated water flowing into the second reaction tank 12 from the first reaction tank 10.

[0033] The control device 22 stores the above formula, and after the operator inputs the BOD volumetric load of each reaction tank (set to 0.5 kg / (m³·d) or higher), the water containing organic matter, the BOD concentration in each reaction tank, and the tank volume, the inflow rate of each reaction tank is calculated from the above formula. Furthermore, in cases where the BOD concentration of the water containing organic matter flowing in the inflow pipe 16a varies, it is preferable, for example, to install a detector (TOC meter, etc.) for detecting the TOC concentration of the water containing organic matter in the inflow pipes 16a and 16b, and to deduce the BOD concentration from the detected TOC concentration. Specifically, a graph (or formula and table, etc.) showing the relationship between the BOD concentration and TOC concentration of the water containing organic matter is prepared in advance through experiments, and these are stored in the control device 22. Then, the control device 22 substitutes the TOC concentration detected by the detector installed on the inflow line 16a into a graph (or formula and table, etc.) showing the relationship between the BOD concentration and TOC concentration of water containing organic matter to calculate the BOD concentration, and regards it as the BOD concentration in the first reaction tank 10 of the above formula. Similarly, the TOC concentration detected by the detector installed on the inflow line 16b is substituted into the graph (or formula and table, etc.) to calculate the BOD concentration, and regards it as the BOD concentration in the second reaction tank 12 of the above formula.

[0034] Control device 22 adjusts the output of pump 24 to control the flow rate of water containing organic matter flowing in the branch line 18, so that the flow rate of water into each reaction tank is equal to or greater than the calculated flow rate into each reaction tank. Through such control, the water treatment device 1 of this embodiment operates such that the BOD volumetric load of each of the first reaction tank 10 and the second reaction tank 12 is 0.5 kg / (m³·d) or greater.

[0035] In general, in multi-stage treatment systems with two or more reactors connected in series, the later stages require lower BOD volumetric loads. This results in residual nitrogen sources dissolved from the bacteria or nitrogen sources not used for bacterial synthesis, leading to a deterioration in the nitrogen concentration of the treated water flowing into the treatment tank 14. However, in this embodiment, by diverting a portion of the water containing organic matter into the later reactors instead of the earlier ones, the amount of this diverted water is controlled to maintain a BOD volumetric load of 0.5 kg / (m³·d) or higher in each reactor. This suppresses excessive nitrogen dissolution from the bacteria and prevents nitrogen from flowing out (leaking) into the treated water discharged from the reactor group.

[0036] The BOD volumetric loading rate of each reactor in the reactor group should be above 0.5 kg / (m³·d). However, from the perspective of further suppressing nitrogen outflow into the treated water discharged from the reactor group, it is preferable to be above 1.5 kg / (m³·d), and more preferably above 2.5 kg / (m³·d). Considering the residual organic matter and nitrogen outflow in the treated water, the upper limit of the BOD volumetric loading rate of each reactor in the reactor group is preferably below 6 kg / (m³·d).

[0037] Furthermore, from the viewpoint of "more stably suppressing nitrogen leaching into the treated water discharged from the reaction tank group," the control device 22 preferably controls the flow rate of organic-containing water flowing in the branch line 18 based on the nitrogen concentration in the treated water detected by the detector 26. However, the flow rate of organic-containing water flowing in the branch line 18 is controlled in a manner that prevents the BOD volumetric load of each reaction tank from falling below 0.5 kg / (m³·d). For example, the control device 22 stores a critical value for nitrogen concentration and, when the nitrogen concentration in the treated water detected by the detector 26 exceeds the critical value, performs a predetermined amount of control by increasing the flow rate of organic-containing water flowing in the branch line 18. For example, the control device 22 can also store a graph (or formula and table, etc.) showing the specified nitrogen concentration and the amount of water containing organic matter flowing in the branch line 18, and substitute the nitrogen concentration in the treated water detected by the detector 26 into the graph to calculate the amount of water containing organic matter flowing in the branch line 18, so as to control the amount of water containing organic matter flowing in the branch line 18.

[0038] Detector 26 can also be installed in the reaction tank. In this case, control device 22 adjusts the flow rate of water containing organic matter flowing in the branch line 18 based on the nitrogen concentration detected by detector 26 in the reaction tank. When detector 26 is installed in the reaction tank, it can be installed in at least one of the multiple reaction tanks constituting the reaction tank group, but it is preferable to install it in at least the last reaction tank, and more preferably in each reaction tank.

[0039] Figure 2 is a schematic diagram showing another example of the configuration of a water treatment apparatus according to this embodiment. In the water treatment apparatus 2 of Figure 2, components identical to those in the water treatment apparatus 1 of Figure 1 are labeled with the same symbols and their descriptions are omitted. The water treatment apparatus 2 of Figure 2 includes an addition device for adding nitrogen sources to the first reaction tank 10 and the second reaction tank 12. The addition device shown in Figure 2 includes a nitrogen source addition pipe 34 and an addition pump 36 installed on the nitrogen source addition pipe 34. The addition pump 36 and the control device 22 are electrically connected, for example.

[0040] In the water treatment device 2 shown in Figure 2, the control device 22 activates the addition pump 36, which adds nitrogen source stored in the storage tank (not shown) to each reaction tank through the nitrogen source addition pipe 34. This allows the nitrogen necessary for biological treatment under aerobic conditions to be supplied to the wastewater containing organic matter. Therefore, even when the amount of nitrogen required for aerobic treatment is insufficient in the wastewater containing organic matter, treated water with a low organic matter concentration can still be stably obtained.

[0041] However, from the viewpoint of more stably suppressing nitrogen leaching into the treated water discharged from the reaction tank group, the control device 22 is preferably based on the nitrogen concentration in the treated water detected by the detector 26 to control the amount of nitrogen source supplied to each reaction tank. For example, the control device 22 stores a critical value for nitrogen concentration, and when the nitrogen concentration in the treated water detected by the detector 26 exceeds the critical value, it controls the output of the dosing pump 36 to suppress the amount of nitrogen source supplied to each reaction tank. Alternatively, the control device 22 may also store a graph (or formula and table, etc.) of a specified nitrogen concentration and the amount of nitrogen source to be added, and substitute the nitrogen concentration in the treated water detected by the detector 26 into the graph to calculate the amount of nitrogen source to be added, thereby controlling the amount of nitrogen source supplied to each reaction tank.

[0042] When detector 26 is installed in the reaction tank, control device 22 controls the amount of nitrogen source supplied to the reaction tank based on the nitrogen concentration detected by detector 26 in the reaction tank. When detector 26 is installed in the reaction tank, it can be installed in at least one of the plurality of reaction tanks constituting the reaction tank group, but it is preferred to install it in at least the last reaction tank, and more preferably in each reaction tank.

[0043] The nitrogen source is not particularly limited; for example, ammonium chloride, ammonium sulfate, diammonium hydrogen phosphate, and urea can be used. Additionally, waste ammonium sulfate generated in the factory can also be utilized.

[0044] When supplying nitrogen to the reaction tanks, the nitrogen source can be supplied to at least one of the multiple reaction tanks constituting the reaction tank group, but it is preferable to supply the nitrogen source to all the reaction tanks constituting the reaction tank group. This allows for the stable production of treated water with low organic matter concentrations. Furthermore, since the amount of nitrogen source added to each reaction tank is controlled based on the nitrogen concentration detected by detector 26, nitrogen leakage into the treated water is prevented.

[0045] When the BOD concentration of the organic-containing water flowing into pipeline 16a fluctuates, it is preferable to install a detector (such as a TOC meter) for detecting the TOC concentration of the organic-containing water in pipeline 16a, and to calculate the BOD concentration from the detected TOC concentration. Similarly, when the nitrogen concentration of the organic-containing water fluctuates, it is preferable to install a detector (such as a TN meter or ammonia meter) in pipeline 16a to detect the nitrogen concentration. In aerobic treatment, the necessary ratio of nitrogen concentration to BOD concentration in the organic-containing water varies depending on the substrate, but a ratio of 100:3 to 5 is commonly used as a baseline. By measuring the BOD and nitrogen concentrations of the organic-containing water, the amount of nitrogen that is insufficient relative to the baseline nitrogen concentration can be calculated, and an initial value for the addition amount can be set. Then, the addition amount can be controlled based on the nitrogen concentration in the reaction tank. Furthermore, for more complex control situations, artificial intelligence or machine learning can be combined.

[0046] Figure 3 is a schematic diagram showing an example of a reaction tank group with three reaction tanks. In the reaction tank group shown in Figure 3, components identical to those shown in Figures 1 and 2 are labeled with the same symbols, and their descriptions are omitted. The reaction tank group shown in Figure 3 is configured by sequentially connecting the first reaction tank 10, the second reaction tank 12, and the third reaction tank 15 in series. An inflow pipe 16a is connected to the inlet of the first reaction tank 10. One end of the inflow pipe 16b is connected to the outlet of the first reaction tank 10, and the other end of the inflow pipe 16b is connected to the inlet of the second reaction tank 12. One end of the inflow pipe 16c is connected to the outlet of the second reaction tank 12, and the other end of the inflow pipe 16c is connected to the inlet of the third reaction tank 15. A treated water pipe 20 is connected to the outlet of the third reaction tank 15. One end of the branch line 18a is connected to the inflow line 16a, and the other end of the branch line 18a is connected to the inflow line 16b. Also, one end of the branch line 18b is connected to the branch line 18a, and the other end of the branch line 18b is connected to the inflow line 16c.

[0047] A pump 24 and valve 40a are installed on the branch line 18a, and a valve 40b is installed on the branch line 18b. When the reaction tank group shown in FIG3 is applied to the water treatment device of this embodiment, for example, the pump 24 and valves 40a and 40b can be electrically connected to the aforementioned control device 22 (not shown), and the operation, stop, and output of the pump 24 can be controlled through the control device 22, as well as the opening and closing degree of valves 40a and 40b. Furthermore, a detector 26 and a treatment tank 14 can also be appropriately installed as needed.

[0048] When water containing organic matter flows into each reaction tank, the control device 22 adjusts the opening and closing degree of valves 40a and 40b to ensure that the BOD volumetric load of each of the first reaction tank 10, the second reaction tank 12, and the third reaction tank 15 is 0.5 kg / (m³·d) or higher, and adjusts the output of pump 24 accordingly to control the flow rate of water containing organic matter flowing through the branch lines 18a and 18b. Furthermore, the control device 22 can control the flow rate of water containing organic matter flowing through the branch lines 18a and 18b based on the nitrogen concentration in the reaction tank or the nitrogen concentration in the treated water detected by detector 26. Also, if the aforementioned nitrogen source addition device is provided, the amount of nitrogen source added from the addition device to each reaction tank can be controlled based on the nitrogen concentration in the reaction tank or the nitrogen concentration in the treated water detected by detector 26. Details regarding the control of the flow rate of water containing organic matter and the control of the amount of nitrogen source added are as described above and are therefore omitted here.

[0049] From the perspective of microbial cultivation, the pH value of each reaction tank in the reaction tank group is preferably adjusted to a slightly acidic to slightly alkaline state, and even more preferably to a pH range of 6 to 8.

[0050] The dissolved oxygen concentration in each reaction tank constituting the reaction tank group is preferably above 0.5 mg / L, and more preferably above 1 mg / L.

[0051] From the perspective of improving water quality, pressurized flotation devices or sedimentation tanks can be installed after the reaction tank group, or a treatment device using membrane separation of activated sludge can be installed. Furthermore, a clarification membrane or RO membrane can be installed as a water recovery device in the downstream section.

[0052] Carrier 28 can be exemplified by plastic carriers, sponge carriers, gel carriers, etc., and among these, sponge carriers are preferred from the point of view of cost and durability.

[0053] From the perspective of improving the processing speed of biological treatment, the number of units (pores) of carrier 28 is preferably 30 or more per 25mm, more preferably 30 or more per 25mm and less than 100 per 25mm, even more preferably 40 or more per 25mm and less than 100 per 25mm, and most preferably 46 or more per 25mm and less than 100 per 25mm.

[0054] The number of units in carrier 28 is obtained based on JISK65400-1 (Appendix 1). Specifically, (1) a test piece (carrier) with a thickness of 10 mm and a width and length of 100 mm or more is collected; (2) a test device is prepared, which is a magnifying glass with a magnification of 5 times or more. The magnifying glass can move left and right and is equipped with a memory that can measure the moving distance; (3) the test piece is placed on the platform of the test device, and the number of units within 10 mm on the straight line is calculated while the magnifying glass is moved (the measurement positions are 3); (4) the number of units N is calculated by N=n×2.5 (N is the number of units (units / 25 mm), n is the number of units within 10 mm), and the average value of the 3 positions is simplified to an integer number according to JISZ8401.

[0055] From the perspective of improving the processing speed of biological treatment, the surface area of ​​the carrier 28 is preferably 3000 m² / m³ or more, more preferably 3500 m² / m³ or more, even more preferably 4000 m² / m³ or more, and most preferably 4500 m² / m³ or more. The upper limit of the surface area of ​​the carrier 28 can be determined by considering the number of units and the size of the carrier, and there is no particular limitation.

[0056] From the perspective of improving the treatment speed of biological treatment, the bio-attached amount of carrier 28 is preferably 500 mg / L or more, and even more preferably 1000 mg / L or more. The more bio-attached amount of carrier 28, the better, and there is no specific upper limit, such as 5000 mg / L.

[0057] The shape of the carrier 28 is not particularly limited, and can be cubic, granular, spherical, flat, cylindrical, fibrous, or thin film.

[0058] The size of the carrier 28 is not particularly limited; it can be appropriately set according to the size of the reaction vessel and the shape of the carrier. For example, if it is cubic, the length of one side is preferably in the range of 3 to 20 mm; if it is spherical, the diameter is preferably in the range of about 0.5 to 20 mm. The size of the carrier 28 can be measured using calipers or a microscope.

[0059] In order to create a flow state inside the reaction vessel, the specific gravity of the carrier 28 is at least greater than 1.0, preferably 1.1 or more in terms of true specific gravity, and preferably 1.01 or more in terms of apparent specific gravity.

[0060] The amount of carrier 28 added to the reaction tank is preferably in the range of 10-70% of the volume of the reaction tank. If the amount of carrier 28 added is less than 10% of the volume of the reaction tank, the reaction rate may be reduced. If it exceeds 70%, the carrier 28 may not flow easily, and under long-term operation, blockage caused by sludge may cause short-circuiting of the raw water, resulting in deterioration of the treated water quality.

[0061] Furthermore, in each reaction tank, from the viewpoint of suppressing nitrogen outflow into the treated water, the optimal BOD load per carrier is 1.7 kg / (m³-carrier·d) or higher.

[0062] The water containing organic substances to be treated, for example, is organic wastewater discharged in sewage treatment, food factories, chemical factories, semiconductor factories, liquid crystal factories, pulp factories and other fields, as long as biological treatment is applicable. Also, it is effective for wastewater that can be biologically treated but has a slow treatment speed and requires a large treatment device. For example, it is also effective for treatments such as tetramethylammonium hydroxide (TMAH) treatment, dioxane treatment, and oil treatment used in liquid crystal factories. In particular, in the case of aerobic treatment of low-molecular-weight organic substances such as alcohols and organic acids, since the amount of sludge generated is small, the amount of nitrogen required during treatment for organic substances is small, and nitrogen is likely to remain, it is particularly effective. Also, in the case where the wastewater contains a high concentration of BOD and the limit of the nitrogen concentration in the treated water is strict, this method is particularly effective. For example, it is preferably when the BOD concentration is 300 mg / L or more. [Examples]

[0063] Hereinafter, examples and comparative examples are given to explain the present invention in more detail, but the present invention is not limited to the following examples.

[0064] Using the wastewater from a semiconductor factory, a continuous water flow test was carried out on the water treatment device with a three-stage series reaction tank group shown in Figure 3.

[0065] <Test conditions> Volume of reaction tank: 72 L × 3 tanks Carrier: Sponge carrier made of hydrophobic polyurethane Carrier filling rate: Filling 30% of the total volume Representative value of wastewater BOD concentration: 1950 mg / L

[0066] Ammonium chloride and diammonium hydrogen phosphate were added to the wastewater in such a way that BOD:N:P = 100:3:0.6. Also, for other necessary trace elements, a trace element solution was used and added to the wastewater in the same way as nitrogen and phosphorus.

[0067] <Volume of wastewater> Comparative example: Reaction tank 10 is 190 L / d, shunt pipeline 18a is 162 L / d, shunt pipeline 18b is 8 L / d Example: Reaction tank 10 is 190 L / d, shunt pipeline 18a is 162 L / d, shunt pipeline 18b is 52 L / d

[0068] <BOD volume load> Representative values ​​for total BOD volumetric loading (from drainage): 3.25 kg / (m³·d) for the comparative example and 3.64 kg / (m³·d) for the exemplary example. Representative values ​​for the BOD volumetric load (from drainage) of reaction tank 10: 5.15 kg / (m³·d) for both the comparative and exemplary cases. Representative values ​​for the BOD volumetric load (from drainage) of reaction tank 12: 4.39 kg / (m³·d) for both the comparative and exemplary cases. BOD volumetric load of reaction tank 15 (from drainage): Refer to Table 1 below.

[0069] Furthermore, throughout the entire experimental period, the dissolved BOD removal rate in the first reaction tank 10 and the second reaction tank 12 was above 98%, and the ammonia nitrogen concentration in the treated water discharged from the first reaction tank 10 and the second reaction tank 12 was less than 1 mg / L. Also, nitrate nitrogen and nitrite nitrogen were not detected in any of the treated water samples, and no nitrification reaction was observed.

[0070] The comparative example test was conducted by increasing the BOD volumetric load to meet the conditions of the comparative example while confirming the BOD concentration of the treated water, followed by approximately three weeks of water flow to allow sufficient microorganisms to attach to the carrier. During the comparative example test, the drainage flow rate was changed as described above, and the implementation example was then initiated.

[0071] Table 1 and Figure 4 show the changes in BOD volumetric load of the third reaction tank 15 and the ammonia nitrogen concentration in the treated water discharged from the third reaction tank 15.

[0072] [Table 1] Comparative example Example After a number of days (days) 1 2 3 4 8 12 twenty two Treatment water NH4-N concentration (mg / L) 11 twenty four 6.9 0.3 1.3 1.0 1.1 BOD volumetric load of the third stage reactor (kg / m³·d) 0.22 0.08 0.5 1.2 1.1 1.4 1.0

[0073] As shown in Table 1 and Figure 4, the BOD volumetric load also changes due to the variation in the concentration of BOD in the wastewater and the variation in the amount of water flowing into the third reaction tank 15.

[0074] On days 1 and 2 (comparative examples), the volume of drainage flowing through the diversion pipeline was relatively small, so that the BOD volumetric loading of the third reaction tank 15 was approximately 0.2 kg / (m³·d). The dissolved BOD concentration of the treated water in the first and second reaction tanks 10 and 12 was 30-38 mg / L, while that in the third reaction tank 15 was 8-10 mg / L. Thus, although organic matter was treated in the third reaction tank 15, the ammonia nitrogen concentration in the treated water remained above 10 mg / L. Furthermore, the BOD loading per carrier at this time was approximately 0.7 kg / (m³-carrier·d).

[0075] On the other hand, starting from day 3 (Example), the flow rate of drainage water flowing in the branch line was increased, thereby increasing the BOD volumetric loading. On day 3, with a BOD volumetric loading of 0.5 kg / (m³·d), the organic matter concentration was the same as in the comparative example, but the ammonia nitrogen concentration of the treated water was 6.9 mg / L, lower than in the comparative example. At this time, the BOD loading per carrier was approximately 1.7 kg / (m³·d). From day 4 onwards, water was flowed with a BOD volumetric loading in the range of 1.0 to 1.4 kg / (m³·d), resulting in a treated water with a dissolved BOD concentration of 10 to 15 mg / L and an ammonia nitrogen concentration of approximately 1 mg / L. At this time, the BOD loading per carrier was approximately 3.3 to 4.7 kg / (m³·d). Thus, by setting the BOD volumetric load of each reaction tank to 0.5 kg / (m³·d) or higher, the leakage of ammonia nitrogen can be suppressed.

[0076] Figure 5 shows the relationship between the BOD volumetric load of the third reaction tank 15 and the ammonia nitrogen concentration of the treated water discharged from the third reaction tank 15. As shown in Figure 5, since the BOD volumetric load is related to the ammonia nitrogen concentration of the treated water, it can be used as the discharge reference value for the target nitrogen concentration to control the amount of water flowing in the diversion pipeline.

[0077] 1,2: Water treatment equipment 10: First Reaction Tank 12: Second Reaction Tank 14: Water Treatment Tank 15: Third Reaction Tank 16a, 16b, 16c: Inflow pipelines 18, 18a, 18b: Diversion lines 20: Water pipeline treatment 22: Control device 24: Pump 26: Detector 28: Carrier 30: Aeration device 32: Screen 34: Nitrogen source addition piping 36: Add a pump 40a, 40b: Valves

Claims

1. A water treatment method comprising the following steps: a biological treatment step, wherein two or more reaction tanks filled with carriers containing microorganisms are connected in series to biologically treat water containing organic matter under aerobic conditions; and an inflow step, wherein a portion of the water containing organic matter is diverted to a subsequent reaction tank instead of passing through the preceding reaction tank; in the inflow step, the volume of the diverted water containing organic matter is controlled such that the BOD volumetric loading of each reaction tank is 0.5 kg / (m³·d) or higher.

2. The water treatment method as described in claim 1, wherein, In this inflow step, the nitrogen concentration in the reaction tank or the nitrogen concentration of the treated water discharged from the reaction tank is detected, and the amount of organic water flowing into the diverted water is controlled based on the detection result of the nitrogen concentration.

3. The water treatment method as described in claim 1 or 2 further includes the following steps: an addition step, in which a nitrogen source is added to the reaction tank; in the addition step, the nitrogen concentration in the reaction tank or the nitrogen concentration in the treated water discharged from the reaction tank is detected, and the amount of nitrogen source added to the reaction tank is controlled based on the detection result of the nitrogen concentration.

4. The water treatment method as described in claim 1 or 2, wherein, The BOD load of the carrier in each of the reaction tanks is 1.7 kg / (m³ - carrier·d) or higher.

5. A water treatment apparatus, comprising: a reaction tank group, wherein two or more reaction tanks filled with a carrier containing microorganisms are connected in series to perform biological treatment on water containing organic matter under aerobic conditions; a diversion pipeline, wherein a portion of the water containing organic matter is diverted to a subsequent reaction tank instead of passing through the preceding reaction tank; and a control unit, which controls the amount of the diverted water containing organic matter to ensure that the BOD volumetric load of each reaction tank is 0.5 kg / (m³·d) or more.

6. The water treatment apparatus as claimed in claim 5 further includes: a detector for detecting the nitrogen concentration in the reaction tank or the nitrogen concentration in the treated water discharged from the reaction tank.

7. The water treatment apparatus as described in claim 6, wherein, The control unit controls the amount of organic-containing water flowing into the diverted stream based on the nitrogen concentration detected by the detector.

8. The water treatment apparatus as described in claim 6 or 7 further comprises: an adding device for adding a nitrogen source to the reaction tank; and a control unit for controlling the amount of nitrogen source added to the reaction tank based on a detection result of a nitrogen concentration detected by the detector.

9. The water treatment apparatus as described in any one of claims 5 to 7, wherein, The BOD load of the carrier in each of the reaction tanks is 1.7 kg / (m³ - carrier·d) or higher.

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