Method for treating organic wastewater and apparatus for treating organic wastewater

Abstract

To provide a method for treating organic wastewater and an apparatus for treating organic wastewater capable of performing stable solid-liquid separation with a membrane while maintaining high treatment efficiency in a treatment in which membrane separation is performed at a latter stage of biological treatment of organic wastewater.SOLUTION: There is provided a method of treating organic wastewater by biological treatment of organic wastewater under aerobic conditions using a reaction tank 12 equipped with carriers 44 and by membrane separation of SS components in the biologically treated water, in which a BOD:nitrogen weight ratio of the organic wastewater flowing into the reaction tank 12 is less than 100:3, a dissolved nitrogen concentration in the reaction tank 12 is maintained at 5 mg / L or less, a nitrogen source is added to the reaction tank 12 to maintain a BOD:nitrogen ratio of 1 to 3 in the organic wastewater so as to perform biological treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating organic wastewater and an apparatus for treating organic wastewater. [Background technology]

[0002] The biological treatment using activated sludge is generally used to treat organic wastewater, but the BOD volume load is 0.5 to 1.0 kg / m 3 / day, so a large site area is required. On the other hand, biological treatment methods using carriers have a BOD volumetric load of 1.5 kg / m 3 It is possible to achieve a high load of more than 1000 kJ / day, and the site area can be reduced.

[0003] As shown in Patent Document 1, membrane separation has been proposed as a solid-liquid separation method for treated water from a fluidized-bed biological treatment process using a carrier. While good treated water can be obtained by performing solid-liquid separation of sludge using a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane), in high-load treatment where the BOD volume load is set high, the sludge tends to adhere to the membrane, posing a problem for stable operation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-208560 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a method for treating organic wastewater, which is capable of performing stable solid-liquid separation using a membrane while maintaining high treatment efficiency, in a process in which membrane separation is performed in a subsequent stage of biological treatment of organic wastewater, and an apparatus for treating organic wastewater. [Means for solving the problem]

[0006] The present invention relates to a method for treating organic wastewater, which comprises biologically treating organic wastewater under aerobic conditions in a reaction tank equipped with a carrier and separating SS components in the biologically treated water using a membrane, wherein the BOD:nitrogen weight ratio of the organic wastewater flowing into the reaction tank is less than 100:3, and the soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less; Maintaining a soluble phosphorus concentration in the reaction tank of 0.1 mg / L or more; The method for treating organic wastewater further comprises adding a nitrogen source to the reaction tank so that the weight ratio of BOD:nitrogen in the organic wastewater becomes 100:1-3, and then carrying out the biological treatment.

[0008] In the method for treating organic wastewater, the reaction tank is composed of two or more reaction tanks connected in series, and in at least one of the two or more reaction tanks connected in series, the BOD:nitrogen weight ratio of the organic wastewater flowing into the reaction tank is less than 100:3, and the soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less; Maintaining a soluble phosphorus concentration in the reaction tank of 0.1 mg / L or more; It is also preferable to carry out the biological treatment by adding a nitrogen source to the reaction tank so that the weight ratio of BOD:nitrogen in the organic wastewater becomes 100:1-3.

[0009] In the method for treating organic wastewater, the reaction tank is a fluidized bed reaction tank, and the BOD volume load of the reaction tank is 1.5 kg / m 3 / day or more is preferable.

[0010] The present invention relates to an organic wastewater treatment device that biologically treats organic wastewater under aerobic conditions in a reaction tank equipped with a carrier and separates SS components in the biologically treated water using a membrane, wherein the BOD:nitrogen weight ratio of the organic wastewater flowing into the reaction tank is less than 100:3, and the soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less; Maintaining a soluble phosphorus concentration in the reaction tank of 0.1 mg / L or more; The biological treatment is carried out by adding a nitrogen source to the reaction tank so that the weight ratio of BOD:nitrogen in the organic wastewater becomes 100:1-3.

[0012] In the organic wastewater treatment device, the reaction tank is composed of two or more reaction tanks in series, and in at least one of the two or more reaction tanks in series, the BOD:nitrogen weight ratio of the organic wastewater flowing into the reaction tank is less than 100:3, and the soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less; Maintaining a soluble phosphorus concentration in the reaction tank of 0.1 mg / L or more; It is also preferable to carry out the biological treatment by adding a nitrogen source to the reaction tank so that the weight ratio of BOD:nitrogen in the organic wastewater becomes 100:1-3.

[0013] In the organic wastewater treatment device, the reaction tank is a fluidized bed reaction tank, and the BOD volume load of the reaction tank is 1.5 kg / m 3 / day or more is preferable. [Effects of the Invention]

[0014] The present invention provides a method for treating organic wastewater and an apparatus for treating organic wastewater, which are capable of performing stable solid-liquid separation using a membrane while maintaining high treatment efficiency in a process in which membrane separation is performed in a subsequent stage of biological treatment of organic wastewater. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing an example of the configuration of a treatment device for organic wastewater according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing another example of the configuration of the organic wastewater treatment device according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0017] An example of an organic wastewater treatment apparatus according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0018] The organic wastewater treatment device 1 shown in Figure 1 biologically treats organic wastewater under aerobic conditions in a reaction tank 12 equipped with a carrier 44, and separates the SS components in the biologically treated water using a membrane. The treatment device 1 includes, for example, a reaction tank 12 equipped with a carrier 44 for biologically treating the organic wastewater under aerobic conditions, a membrane separation device 48 for membrane separation of the SS components in the biologically treated water obtained by the biological treatment, a detector 20 as a soluble nitrogen concentration detection means for detecting the soluble nitrogen concentration in the reaction tank 12, a nitrogen source addition means for adding a nitrogen source to the reaction tank 12, and a control device 16 as a control means for controlling the addition of the nitrogen source to the reaction tank 12 so that the BOD:nitrogen weight ratio of the organic wastewater flowing into the reaction tank 12 is less than 100:3, the soluble nitrogen concentration in the reaction tank 12 is maintained at 5 mg / L or less, and the BOD:nitrogen weight ratio of the organic wastewater is 100:1 to 100:3. The treatment device 1 may include a phosphorus source adding means for adding a phosphorus source to the reaction tank 12 .

[0019] The treatment device 1 may include a raw water tank 10 for storing organic wastewater, which is raw water, a biological treatment water tank 14 for storing biologically treated water, a nitrogen source tank 26 for storing a nitrogen source, and a phosphorus source tank 32 for storing a phosphorus source. The treatment device 1 may include a detector 21 as a soluble phosphorus concentration detection means for detecting the soluble phosphorus concentration in the reaction tank 12. The treatment device 1 may also include a BOD measurement means for measuring the BOD of the organic wastewater flowing into the reaction tank 12.

[0020] In the treatment apparatus 1 shown in Figure 1, one end of an inlet line 22 is connected to the raw water outlet of the raw water tank 10, and the other end of the inlet line 22 is connected to the inlet of the reaction tank 12. A raw water pump 18 is installed in the inlet line 22. One end of a nitrogen source addition line 28 is connected to the inlet line 22 downstream of the raw water pump 18, and the other end of the nitrogen source addition line 28 is connected to the nitrogen source tank 26. One end of a phosphorus source addition line 34 is connected to the inlet line 22 downstream of the raw water pump 18, and the other end of the phosphorus source addition line 34 is connected to the phosphorus source tank 32. A nitrogen source addition pump 30 is installed in the nitrogen source addition line 28, and a phosphorus source addition pump 36 is installed in the phosphorus source addition line 34. One end of a biological treatment water line 24 is connected to the outlet of the reaction tank 12, and the other end of the biological treatment water line 24 is connected to the inlet of the biological treatment water tank 14. One end of a biologically treated water line 50 is connected to the outlet of the biological treatment tank 14, and the other end of the biologically treated water line 50 is connected to the inlet of the membrane separation device 48. One end of a treated water line 52 is connected to the outlet of the membrane separation device 48. The nitrogen source tank 26, the nitrogen source addition line 28, the nitrogen source addition pump 30, etc. function as nitrogen source addition means for adding a nitrogen source to the reaction tank 12, and the phosphorus source tank 32, the phosphorus source addition line 34, the phosphorus source addition pump 36, etc. function as phosphorus source addition means for adding a phosphorus source to the reaction tank 12.

[0021] The control device 16 is connected to the raw water pump 18, the nitrogen source addition pump 30, the phosphorus source addition pump 36, the detector 20, and the detector 21 by wired or wireless electrical connections, etc.

[0022] The reaction vessel 12 is filled with carriers 44 that hold microorganisms. The carriers 44 are not particularly limited, but examples thereof include plastic carriers, sponge-like carriers, and gel-like carriers.

[0023] An aeration device 46 is installed at the bottom of the reaction tank 12 as an oxygen-containing gas supply means for supplying an oxygen-containing gas such as air. The aeration device 46 is connected to, for example, a blower (not shown), and the oxygen-containing gas such as air supplied from the blower is supplied from the aeration device 46 into the reaction tank 12.

[0024] The reaction tank 12 is equipped with a detector 20 for detecting the soluble nitrogen concentration in the reaction tank 12 and a detector 21 for detecting the soluble phosphorus concentration in the reaction tank 12. The detectors 20 and 21 may be installed in the biological treatment tank 14 or the biological treatment water line 24. The soluble nitrogen concentration and soluble phosphorus concentration of the biological treatment water detected by the detectors 20 and 21 in the biological treatment tank 14 or the biological treatment water line 24 may be used as the soluble nitrogen concentration and soluble phosphorus concentration in the reaction tank 12. The soluble nitrogen includes, for example, nitrogen derived from the nitrogen source supplied from the nitrogen source addition means, and ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, etc. that were originally contained in the organic wastewater. The soluble phosphorus includes, for example, phosphorus derived from the phosphorus source supplied from the phosphorus source addition means, and phosphorus compounds that were originally contained in the organic wastewater.

[0025] The control device 16 is composed of, for example, a microcomputer and electronic circuits, which are composed of a CPU that executes programs and ROM and RAM that store programs and calculation results. The control device 16 reads and executes a predetermined program stored in the ROM or the like, and controls the operation of the treatment device 1. The control device 16 has a function of controlling the addition of a nitrogen source to the reaction tank 12 so that the BOD:nitrogen weight ratio of the organic wastewater flowing into the reaction tank 12 is less than 100:3, the soluble nitrogen concentration in the reaction tank 12 is maintained at 5 mg / L or less, and the BOD:nitrogen weight ratio of the organic wastewater is 100:1 to 3. The control device 16 controls, for example, the operation and stop of the raw water pump 18. The control device 16 also controls, for example, the operation and stop of the nitrogen source addition pump 30 and the opening and closing of a valve provided in the nitrogen source addition line 28, based on the BOD in the organic wastewater and the soluble nitrogen concentration detected by the detector 20. Furthermore, the control device 16 controls the operation and stopping of the phosphorus source addition pump 36 and the opening and closing of the valve provided in the phosphorus source addition line 34, for example, based on the soluble phosphorus concentration detected by the detector 21, etc.

[0026] The organic wastewater treatment method and the operation of the treatment device 1 according to this embodiment will be described.

[0027] The organic wastewater to be treated in the treatment device 1, that is, the organic wastewater to be introduced into the raw water tank 10, is wastewater containing organic matter.

[0028] When the raw water pump 18 is operated by the control device 16, organic wastewater in the raw water tank 10 is supplied to the reaction tank 12 through the inlet line 22. Then, an oxygen-containing gas such as air is supplied to the reaction tank 12 from the aeration device 46, and under aerobic conditions, the organic matter in the organic wastewater in the reaction tank 12 is biologically treated by microorganisms attached to the carriers 44 (biological treatment process). The biologically treated water treated in the reaction tank 12 is supplied to the biological treatment tank 14 through the biologically treated water line 24. The biologically treated water stored in the biological treatment tank 14 is supplied to the membrane separation device 48 through the biologically treated water line 50, where the SS components and the like are separated by membrane separation (membrane separation process). The treated water that has undergone membrane separation is discharged through the treated water line 52.

[0029] As a result of extensive research, the present inventors have found that in a process of performing membrane separation in the latter stage of biological treatment of organic wastewater, by performing biological treatment while maintaining a BOD:nitrogen weight ratio of the organic wastewater flowing into reaction tank 12 of less than 100:3, maintaining the soluble nitrogen concentration in reaction tank 12 in a nitrogen-depleted state of 5 mg / L or less, and adding a nitrogen source to reaction tank 12 so that the BOD:nitrogen weight ratio of the organic wastewater is 100:1 to 3, stable membrane solid-liquid separation can be performed in membrane separation device 48, which separates SS components in the biologically treated water, while maintaining high treatment efficiency. This makes it possible to improve the filtration performance of solid-liquid separation using a membrane in the latter stage of biological treatment of organic wastewater. In this specification, a BOD:nitrogen weight ratio of organic wastewater of less than 100:3 means that the nitrogen is less than 3 parts by weight per 100 parts by weight of BOD in the organic wastewater, and a BOD:nitrogen weight ratio of organic wastewater of 100:1-3 means that the nitrogen is 1-3 parts by weight per 100 parts by weight of BOD in the organic wastewater.

[0030] An example of controlling the soluble nitrogen concentration will be described below.

[0031] In the treatment device 1, the nitrogen source addition pump 30 is operated by the control device 16 to introduce the nitrogen source into the reaction tank 12. At this time, the control device 16 calculates the supply amount of the nitrogen source from a predetermined weight ratio in which the BOD:nitrogen weight ratio of the organic wastewater is less than 100:3, and controls the nitrogen source addition pump 30 so that the calculated supply amount of nitrogen source is supplied into the reaction tank 12. The BOD of the organic wastewater may be measured as needed by installing a BOD measuring device in the raw water tank 10 or the inlet line 22 as a BOD measuring means. The BOD of the organic wastewater may be measured, for example, according to the method specified in JIS K0102. Because measuring the BOD using this method can take time, the BOD may be measured in advance before operating the treatment device 1. Alternatively, for example, a TOC measuring device may be installed in the raw water tank 10 or the inlet line 22 as a BOD measuring means to detect the TOC of the organic wastewater and estimate the BOD from the detected TOC. Because TOC can be measured quickly, the BOD of the organic wastewater can be determined at any time while the treatment device 1 is operating by estimating the BOD from the TOC. The measured BOD is stored in the control device 16 for calculating the amount of nitrogen source to be supplied. The amount of nitrogen in the organic wastewater may also be measured as needed. The measured amount of nitrogen is stored in the control device 16 for calculating the amount of nitrogen source to be supplied.

[0032] Then, the control device 16 controls the nitrogen source addition pump 30 so as to maintain the above-calculated supply amount of the nitrogen source, for example, if the soluble nitrogen concentration detected by the detector 20 is 5 mg / L or less and the weight ratio of BOD:nitrogen in the organic wastewater is in the range of 100:1 to 3. Furthermore, if the soluble nitrogen concentration detected by the detector 20 exceeds 5 mg / L, the control device 16 limits the output of the nitrogen source addition pump 30 to reduce the supply amount of the nitrogen source.

[0033] The soluble phosphorus concentration in the reaction tank 12 is preferably maintained at 0.1 mg / L or higher, more preferably in the range of 0.5 to 1.0 mg / L, with residual phosphorus. When the phosphorus concentration in the reaction tank 12 is low and the soluble phosphorus concentration detected by the detector 21 is less than 0.1 mg / L, the control device 16 may operate the phosphorus source addition pump 36 to introduce a phosphorus source into the reaction tank 12. Even when the phosphorus concentration in the organic wastewater is high and the soluble phosphorus concentration detected by the detector 21 exceeds 0.1 mg / L, the phosphorus source addition pump 36 may be operated to introduce a phosphorus source into the reaction tank 12. However, taking into consideration discharge standards and the like, the upper limit of the soluble phosphorus concentration in the reaction tank 12 is preferably maintained at 8 mg / L or lower, more preferably at 4 mg / L or lower.

[0034] The soluble nitrogen concentration and soluble phosphorus concentration in the reaction tank 12 are preferably detected by online analysis using a detector, but if a detector is not installed, manual analysis by an operator may also be performed.

[0035] Alternatively, for example, a detector 20 may be installed in the raw water tank 10, and the soluble nitrogen concentration in the reaction tank 12 may be estimated from the soluble nitrogen concentration in the organic wastewater. In this case, for example, a map (or a formula, a table, etc.) showing the correlation between the soluble nitrogen concentration in the organic wastewater and the soluble nitrogen concentration in the reaction tank 12 may be created in advance through experiments or the like, and stored in the control device 16. The control device 16 then estimates the soluble nitrogen concentration in the reaction tank 12 by applying the sum of the soluble nitrogen concentration in the organic wastewater detected by the detector 20 and the soluble nitrogen concentration calculated from the supply amount of the nitrogen source set so that the BOD:nitrogen weight ratio of the organic wastewater is in the range of 100:1 to 3 to the map or the like. If the estimated soluble nitrogen concentration in the reaction tank 12 exceeds 5 mg / L and the BOD:nitrogen weight ratio of the organic wastewater is higher than 100:3, the control device 16 limits the output of the nitrogen source addition pump 30 to reduce the supply amount of the nitrogen source.

[0036] Alternatively, for example, a detector 21 may be installed in the raw water tank 10, and the soluble phosphorus concentration in the reaction tank 12 may be estimated from the soluble phosphorus concentration in the organic wastewater. In this case, for example, a map (or a formula, a table, etc.) showing the correlation between the soluble phosphorus concentration in the organic wastewater and the soluble phosphorus concentration in the reaction tank 12 may be created in advance through experiments or the like, and stored in the control device 16. The control device 16 then applies the soluble phosphorus concentration in the organic wastewater detected by the detector 21 to the map or the like to estimate the soluble phosphorus concentration in the reaction tank 12. If the estimated soluble phosphorus concentration in the reaction tank 12 is less than 0.1 mg / L, the control device 16 may operate the phosphorus source addition pump 36 to introduce a phosphorus source into the reaction tank 12.

[0037] FIG. 2 is a schematic diagram showing another example of the configuration of an organic wastewater treatment device according to this embodiment. In the treatment device 2 of FIG. 2, components similar to those of the treatment device 1 of FIG. 1 are designated by the same reference numerals, and their description will be omitted. The treatment device 2 of FIG. 2 includes a reaction tank group having a first reaction tank 12a and a second reaction tank 12b as reaction tanks. The reaction tank group is configured such that the first reaction tank 12a is in the upstream stage and the second reaction tank 12b is in the downstream stage, with the first reaction tank 12a and the second reaction tank 12b arranged in series. Note that the reaction tank group may also be configured such that the reaction tanks are arranged in three or more stages in series.

[0038] In the treatment apparatus 2 shown in FIG. 2, one end of an inlet line 22a is connected to the raw water outlet of the raw water tank 10, and the other end of the inlet line 22a is connected to the inlet of the first reaction tank 12a. A raw water pump 18 is installed in the inlet line 22a. One end of a nitrogen source addition line 28a is connected to the inlet line 22a downstream of the raw water pump 18, and the other end of the nitrogen source addition line 28a is connected to the nitrogen source tank 26a. One end of a phosphorus source addition line 34a is connected to the inlet line 22a downstream of the raw water pump 18, and the other end of the phosphorus source addition line 34a is connected to the phosphorus source tank 32a. A nitrogen source addition pump 30a is installed in the nitrogen source addition line 28a, and a phosphorus source addition pump 36a is installed in the phosphorus source addition line 34a. One end of an inlet line 22b is connected to the outlet of the first reaction tank 12a, and the other end of the inlet line 22b is connected to the inlet of the second reaction tank 12b. One end of a nitrogen source addition line 28b is connected to the inlet line 22b, and the other end of the nitrogen source addition line 28b is connected to the nitrogen source tank 26b. One end of a phosphorus source addition line 34b is connected to the inlet line 22b, and the other end of the phosphorus source addition line 34b is connected to the phosphorus source tank 32b. A nitrogen source addition pump 30b is installed in the nitrogen source addition line 28b, and a phosphorus source addition pump 36b is installed in the phosphorus source addition line 34b. One end of a biologically treated water line 24 is connected to the outlet of the second reaction tank 12b, and the other end of the biologically treated water line 24 is connected to the inlet of the biological treatment tank 14. One end of a biologically treated water line 50 is connected to the outlet of the biological treatment tank 14, and the other end of the biologically treated water line 50 is connected to the inlet of the membrane separation device 48. One end of a treated water line 52 is connected to the outlet of the membrane separation device 48. The nitrogen source tank 26a, the nitrogen source addition line 28a, the nitrogen source addition pump 30a, etc. function as a nitrogen source addition means for adding a nitrogen source to the first reaction tank 12a, and the nitrogen source tank 26b, the nitrogen source addition line 28b, the nitrogen source addition pump 30b, etc. function as a nitrogen source addition means for adding a nitrogen source to the second reaction tank 12b.The phosphorus source tank 32a, the phosphorus source addition line 34a, the phosphorus source addition pump 36a, etc. function as phosphorus source adding means for adding a phosphorus source to the first reaction tank 12a, and the phosphorus source tank 32b, the phosphorus source addition line 34b, the phosphorus source addition pump 36b, etc. function as phosphorus source adding means for adding a phosphorus source to the second reaction tank 12b.

[0039] The control device 16 is connected to the raw water pump 18, the nitrogen source addition pumps 30a and 30b, the phosphorus source addition pumps 36a and 36b, the detectors 20a and 20b, and the detectors 21a and 21b by wired or wireless electrical connections.

[0040] The first reaction tank 12a and the second reaction tank 12b are each filled with carriers 44 that hold microorganisms.

[0041] Aeration devices 46a, 46b are installed at the bottom of the first reaction tank 12a and the second reaction tank 12b, respectively, as oxygen-containing gas supply means for supplying an oxygen-containing gas such as air. A blower (not shown) is connected to each of the aeration devices 46a, 46b, and the oxygen-containing gas such as air supplied from the blower is supplied from the aeration devices 46a, 46b to the inside of the first reaction tank 12a and the second reaction tank 12b, respectively.

[0042] The first reaction tank 12a is equipped with a detector 20a for detecting the soluble nitrogen concentration in the first reaction tank 12a and a detector 21a for detecting the soluble phosphorus concentration in the first reaction tank 12a. The second reaction tank 12b is equipped with a detector 20b for detecting the soluble nitrogen concentration in the second reaction tank 12b and a detector 21b for detecting the soluble phosphorus concentration in the second reaction tank 12b. The detectors 20a and 21a in the first reaction tank 12a may be installed upstream of the connection point of the nitrogen source addition line 28b and the phosphorus source addition line 34b in the inlet line 22b. The soluble nitrogen concentration and soluble phosphorus concentration of the biological treatment water detected by the detectors 20a and 21a in the inlet line 22b may be used as the soluble nitrogen concentration and soluble phosphorus concentration in the first reaction tank 12a. The detectors 20b and 21b in the second reaction tank 12b may be installed in the biological treatment water tank 14 or the biological treatment water line 24. The soluble nitrogen concentration and soluble phosphorus concentration of the biological treatment water detected by detector 20b and detector 21b in the biological treatment water tank 14 or the biological treatment water line 24 may be used as the soluble nitrogen concentration and soluble phosphorus concentration in the second reaction tank 12b.

[0043] The control device 16 controls, for example, the operation and stop of the raw water pump 18. Furthermore, the control device 16 controls, for example, the operation and stop of the nitrogen source addition pumps 30a, 30b and the opening and closing of the valves provided in the nitrogen source addition lines 28a, 28b based on the BOD in the organic wastewater and the soluble nitrogen concentration detected by the detectors 20a, 20b. Furthermore, the control device 16 controls, for example, the operation and stop of the phosphorus source addition pumps 36a, 36b and the opening and closing of the valves provided in the phosphorus source addition lines 34a, 34b based on the soluble phosphorus concentration detected by the detectors 21a, 21b.

[0044] Next, the operation of the processing device 2 shown in FIG. 2 will be described.

[0045] When the raw water pump 18 is operated by the control device 16, organic wastewater in the raw water tank 10 is supplied to the first reaction tank 12a through the inlet line 22a. Then, an oxygen-containing gas such as air is supplied to the first reaction tank 12a from the aeration device 46a, and under aerobic conditions, the organic matter in the organic wastewater is biologically treated by microorganisms attached to the carriers 44 in the first reaction tank 12a (first biological treatment step). The first biologically treated water treated in the first reaction tank 12a is supplied to the second reaction tank 12b through the inlet line 22b. Then, an oxygen-containing gas such as air is supplied to the second reaction tank 12b from the aeration device 46b, and under aerobic conditions, the organic matter in the first biologically treated water is biologically treated by microorganisms attached to the carriers 44 in the second reaction tank 12b (second biological treatment step). The biologically treated water treated in the second reaction tank 12b is supplied to the biological treatment tank 14 through the biologically treated water line 24. The biologically treated water stored in the biological treatment tank 14 is supplied to the membrane separation device 48 through a biologically treated water line 50, where SS components and the like are separated by membrane (membrane separation process). The treated water that has undergone membrane separation is discharged through a treated water line.

[0046] Here, when the reactors are configured with two or more stages, biological treatment can be performed by adding a nitrogen source to at least one of the reactors so that the BOD:nitrogen weight ratio of the organic wastewater flowing into the reactor is less than 100:3, the soluble nitrogen concentration in the reactor is maintained at 5 mg / L or less, and the BOD:nitrogen weight ratio of the organic wastewater is 100:1 to 3. This allows stable membrane solid-liquid separation in a membrane separation device that separates SS components in the biologically treated water while maintaining high treatment efficiency. Note that when the reactors are configured with two or more stages, it is preferable to perform biological treatment by adding a nitrogen source to the first reactor so that the BOD:nitrogen weight ratio of the organic wastewater flowing into the first reactor is less than 100:3, the soluble nitrogen concentration in the first reactor is maintained at 5 mg / L or less, and the BOD:nitrogen weight ratio of the organic wastewater is 100:1 to 3. In this case, most of the organic matter is removed in the first-stage reaction tank, and less organic matter needs to be removed in the second-stage reaction tank. Therefore, even without controlling the second and subsequent reaction tanks to maintain the soluble nitrogen concentration at 5 mg / L or less and the BOD:nitrogen weight ratio of the organic wastewater at 100:1-3, stable membrane solid-liquid separation can be performed in the membrane separation device that separates the SS components in the biologically treated water while maintaining high treatment efficiency throughout the system.

[0047] The operating conditions of the treatment apparatus of this embodiment will be described below.

[0048] From the viewpoint of growing microorganisms, the pH in the reaction tank 12 is preferably adjusted to, for example, a weak acidity to a weak alkalinity, and more preferably adjusted to a pH range of 6 to 8. An acid or alkali may be used as the pH adjuster.

[0049] The dissolved oxygen concentration in the reaction tank 12 is, for example, preferably 0.5 mg / L or more, and more preferably 1 mg / L or more. There is no particular upper limit to the dissolved oxygen concentration in the reaction tank 12, but it is, for example, 5.0 mg / L or less.

[0050] The reaction tank 12 may be either a fixed bed type in which the carrier does not flow, or a fluidized bed type in which the carrier flows. A fluidized bed type reaction tank is preferred because it has advantages such as being less likely to cause short-passing of raw water, being easy to maintain, and having low installation costs.

[0051] The BOD volume load of the reactor 12 (or the BOD volume load of all reactors in the case of a group of reactors) is 1.5 kg / m 3 / day or more is preferable, 2.0 kg / m 3 The upper limit of the BOD volume load of the reaction tank 12 is not particularly limited, but is, for example, 8.0 kg / m 3 / day or less.

[0052] The nitrogen source is not particularly limited as long as it is a nitrogen compound, and examples thereof include ammonium chloride, ammonium sulfate, diammonium hydrogen phosphate, urea, etc. Excess waste ammonium sulfate generated in factories can also be used.

[0053] The phosphorus source is not particularly limited as long as it is phosphoric acid or a phosphorus compound, and examples thereof include dipotassium phosphate, disodium phosphate, monopotassium phosphate, monosodium phosphate, and ammonium phosphate.

[0054] Nutrients and trace elements other than nitrogen and phosphorus sources may be added to the organic wastewater, such as calcium, magnesium, iron, copper, zinc, and manganese.

[0055] Examples of the carrier 44 include a plastic carrier, a sponge-like carrier, and a gel-like carrier, among which a sponge-like carrier is preferred in terms of cost and durability.

[0056] In order to improve the processing speed of biological treatment, the number of cells (number of pores) of the carrier 44 is preferably 30 cells / 25 mm or more, more preferably 30 cells / 25 mm or more and 100 cells / 25 mm or less, even more preferably 40 cells / 25 mm or more and 100 cells / 25 mm or less, and particularly preferably 46 cells / 25 mm or more and 100 cells / 25 mm or less. The number of cells of the carrier is determined, for example, based on JIS K 65400-1 (Annex 1).

[0057] The surface area of the carrier 44 is preferably 3000 m2 in order to improve the processing speed of the biological treatment. 2 / m 3 More preferably, 3500m 2 / m 3 More preferably, 4000m 2 / m 3 More preferably, 4500m 2 / m 3 The upper limit of the surface area of the carrier can be determined in consideration of the number of cells, the size of the carrier, etc., and is not particularly limited.

[0058] In order to improve the processing speed of biological treatment, the amount of attached organisms on the carrier 44 is preferably 500 mg / L or more, and more preferably 1000 mg / L or more. The larger the amount of attached organisms on the carrier, the better, and there is no particular upper limit, but the upper limit is, for example, 5000 mg / L.

[0059] The shape of the carrier 44 is not particularly limited, and examples thereof include quadrangular shapes such as cubes, granular shapes, spherical shapes, pellet shapes, cylindrical shapes, fibrous shapes, and film shapes.

[0060] The size of the carrier 44 is not particularly limited and may be set appropriately depending on the size of the reaction vessel 12, the shape of the carrier, etc. For example, if the carrier is cubic, the length of one side is preferably in the range of 3 to 20 mm, and if the carrier is spherical, the diameter is preferably in the range of about 0.5 to 20 mm. The size of the carrier 44 can be measured using a vernier caliper, a microscope, etc.

[0061] In order to form a fluidized state inside the reaction vessel 12, the specific gravity of the carrier 44 is, for example, at least greater than 1.0, and preferably a true specific gravity of 1.1 or greater, or an apparent specific gravity of 1.01 or greater.

[0062] The amount of carrier 44 introduced into reaction tank 12 is preferably in the range of 10 to 70% of the volume of reaction tank 12. If the amount of carrier 44 introduced is less than 10% of the volume of reaction tank 12, the reaction rate may be slow, and if it exceeds 70%, the carrier 44 becomes difficult to flow, and during long-term operation, raw water may short-pass due to clogging by sludge, etc., resulting in a deterioration in the quality of biologically treated water.

[0063] The membrane used in the membrane separation device 48 is, for example, an organic membrane, and is not particularly limited as long as it is capable of filtering out SS components (suspended solids) and the like in the biological treatment water, but examples include an ultrafiltration membrane (UF membrane), a microfiltration membrane (MF membrane), etc. The nominal pore size of the ultrafiltration membrane is 0.01 μm or more and less than 0.1 μm, and the pore size of the microfiltration membrane is 0.1 μm or more and 0.3 μm or less.

[0064] Examples of the organic membrane material include polyethersulfone (PES), polysulfone (PS), cellulose acetate (CA), polyethylene (PE), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polycarbonate (PC).

[0065] The membrane separation device 48 is, for example, a modular membrane filtration device, and is a pressurized membrane filtration device having a filtration membrane sealed in a cylindrical container (casing) such as a cylindrical one. Examples of the filtration membrane include a tubular membrane and a hollow fiber membrane. The liquid passing method for the filtration membrane may be either an internal pressure type or an external pressure type. A submerged flat membrane may be used as the membrane separation device 48.

[0066] In order to maintain the SS concentration in the membrane separation device 48 low and set the filtration rate high, it is preferable that the sludge separated into solid and liquid by the membrane in the membrane separation device 48 not be allowed to flow into the reaction tank 12 equipped with the carrier 44. [Example]

[0067] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0068] [Test conditions] Reaction tank volume: 2L Carrier: Hydrophobic polyurethane sponge carrier (cell count: 46 / 25 mm, shape: cubic) Carrier filling rate: 20% filling by volume Retention time in reactor: 6 hours BOD volume load of reactor: approx. 3.2 kg / m 3 / day Water temperature in the reactor: about 20°C, Dissolved oxygen concentration (DO) in the reactor: 2 mg / L or more pH in the reactor: 6.5 to 8.0 Organic wastewater: wastewater containing isopropyl alcohol (BOD approx. 800 mg / L (BOD / TOC = 2.7), N 2 mg / L or less, P 0.1 mg / L or less)

[0069] The biologically treated water from the fluidized-bed biological treatment was suction filtered using an ultrafiltration membrane (UF membrane) (external pressure type, hollow fiber membrane, material: PVDF) at a flux of 3.0 m / day, and the transmembrane pressure difference during this process was evaluated.

[0070] <Comparative Example 1> Ammonium chloride as a nitrogen source and phosphoric acid as a phosphorus source were added to the raw organic wastewater, and the BOD:N:P ratio was set to 100:6.6:1.1 before being fed into the reactor. The soluble nitrogen concentration of the biologically treated water was 19 mg / L, meaning that nitrogen remained, and the soluble phosphorus concentration was 4.4 mg / L, meaning that phosphorus remained. The transmembrane pressure of the UF membrane was 36 kPa, and the BOD removal rate was 2.8 kg / m. 3 It was / day.

[0071] <Comparative Example 2> The amounts of ammonium chloride and phosphoric acid added were reduced from the operating conditions of Comparative Example 1, and the BOD:N:P ratio was adjusted to 100:4.7:0.5 before being inflowed into the reactor. The soluble nitrogen concentration of the biologically treated water was 13 mg / L, indicating a nitrogen residual state, and the soluble phosphorus concentration was 0.06 mg / L, indicating a phosphorus depletion state. The transmembrane pressure of the UF membrane was 33 kPa, and the BOD removal rate was 2.9 kg / m 3 / day, which was equivalent to that of Comparative Example 1.

[0072] Example 1 The amounts of ammonium chloride and phosphoric acid added were reduced from the operating conditions of Comparative Example 1, and the BOD:N:P ratio was adjusted to 100:2.8:0.9 before being inflowed into the reactor. The soluble nitrogen concentration of the biologically treated water was 1.1 mg / L (ammoniacal nitrogen concentration 0.3 mg / L), indicating a nitrogen-depleted state, and the soluble phosphorus concentration was 2.8 mg / L, indicating a phosphorus-remaining state. The transmembrane pressure of the UF membrane was significantly reduced to 12 kPa. The BOD removal rate was 2.7 kg / m 3 / day, maintaining a high removal rate.

[0073] <Example 2> The amounts of ammonium chloride and phosphoric acid added were reduced from the operating conditions of Comparative Example 1, and the BOD:N:P ratio was adjusted to 100:1.9:0.9 before being inflowed into the reactor. The soluble nitrogen concentration of the biologically treated water was 1.0 mg / L (ammoniacal nitrogen concentration 0.2 mg / L), indicating a nitrogen-depleted state, and the soluble phosphorus concentration was 3.6 mg / L, indicating a phosphorus-remaining state. The transmembrane pressure of the UF membrane was significantly reduced to 14 kPa. The BOD removal rate was 2.4 kg / m 3 / day, maintaining a high removal rate.

[0074] Example 3 The amounts of ammonium chloride and phosphoric acid added were reduced from the operating conditions of Comparative Example 1, and the BOD:N:P ratio was adjusted to 100:1.0:0.8 before being inflowed into the reaction tank. The soluble nitrogen concentration of the biologically treated water was 2.6 mg / L (ammoniacal nitrogen concentration 0.4 mg / L), indicating a nitrogen-depleted state, and the soluble phosphorus concentration was 5.3 mg / L, indicating a phosphorus-remaining state. The transmembrane pressure of the UF membrane was significantly reduced to 11 kPa. The BOD removal rate was 2.1 kg / m 3 / day, maintaining a high removal rate.

[0075] <Comparative Example 3> The amounts of ammonium chloride and phosphoric acid added were reduced from the operating conditions of Comparative Example 1, and the BOD:N:P ratio was adjusted to 100:0.2:0.8 before being inflowed into the reactor. The soluble nitrogen concentration of the biologically treated water was 1.6 mg / L, indicating a nitrogen-depleted state, and the soluble phosphorus concentration was 6.5 mg / L, indicating a phosphorus-remaining state. Although the transmembrane pressure of the UF membrane was low at 9 kPa, the BOD removal rate was 1.3 kg / m 3 / day, showing a significant decrease in removal rate.

[0076] From the above results, it was found that stable membrane treatment can be carried out while maintaining high treatment efficiency by maintaining the soluble nitrogen concentration in the reaction tank at a nitrogen-depleted state of 5 mg / L or less, adding a nitrogen source so that the BOD:nitrogen weight ratio of the organic wastewater is 100:1-3, and maintaining the soluble phosphorus concentration in the reaction tank in a phosphorus-retaining state. The transmembrane pressure difference of the UF membrane in the downstream of biological treatment can be kept at 20 kPa or less, and the BOD removal rate can be increased to 2 kg / m. 3 / day or more.

[0077] As described above, the method of the present invention enabled stable solid-liquid separation using a membrane while maintaining high treatment efficiency in a treatment in which membrane separation is carried out in the subsequent stage of biological treatment of organic wastewater. [Explanation of symbols]

[0078] 1, 2 treatment device, 10 raw water tank, 12 reaction tank, 12a first reaction tank, 12b second reaction tank, 14 biological treatment tank, 16 control device, 18 raw water pump, 20, 20a, 20b, 21, 21a, 21b detector, 22, 22a, 22b inlet line, 24, 50 biological treatment water line, 26, 26a, 26b nitrogen source tank, 28, 28a, 28b nitrogen source addition line, 30, 30a, 30b nitrogen source addition pump, 32, 32a, 32b phosphorus source tank, 34, 34a, 34b phosphorus source addition line, 36, 36a, 36b phosphorus source addition pump, 44 carrier, 46, 46a, 46b aeration device, 48 membrane separation device, 52 treated water line.

Claims

1. A method for treating organic wastewater, comprising biologically treating organic wastewater under aerobic conditions in a reaction tank equipped with a carrier, and separating SS components in the biologically treated water using a membrane, a nitrogen source is added to the reaction tank so that the weight ratio of BOD:nitrogen of the organic wastewater flowing into the reaction tank is less than 100:3, the soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less, the soluble phosphorus concentration in the reaction tank is maintained at 0.1 mg / L or more, and the weight ratio of BOD:nitrogen of the organic wastewater is 100:1 to 3, and the biological treatment is carried out.

2. The method for treating organic wastewater according to claim 1, The reaction tank is composed of two or more reaction tanks arranged in series, and in at least one of the two or more reaction tanks in series, a BOD:nitrogen weight ratio of the organic wastewater flowing into the reaction tank is less than 100:3, a soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less, a soluble phosphorus concentration in the reaction tank is maintained at 0.1 mg / L or more, and a nitrogen source is added to the reaction tank so that the BOD:nitrogen weight ratio of the organic wastewater is 100:1 to 3.

3. The method for treating organic wastewater according to claim 1 or 2, The reactor is a fluidized bed reactor, and the BOD volume load of the reactor is 1.5 kg / m ３ / day or more.

4. An organic wastewater treatment device that biologically treats organic wastewater under aerobic conditions in a reaction tank equipped with a carrier and separates SS components in the biologically treated water using a membrane, a nitrogen source is added to the reaction tank so that the weight ratio of BOD:nitrogen of the organic wastewater flowing into the reaction tank is less than 100:3, the soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less, the soluble phosphorus concentration in the reaction tank is maintained at 0.1 mg / L or more, and the weight ratio of BOD:nitrogen of the organic wastewater is 100:1 to 3,

5. The organic wastewater treatment device according to claim 4, The reaction tank is composed of two or more reaction tanks in series, and in at least one of the two or more reaction tanks in series, a nitrogen source is added to the reaction tank so that the weight ratio of BOD:nitrogen of the organic wastewater flowing into the reaction tank is less than 100:3, the soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less, the soluble phosphorus concentration in the reaction tank is maintained at 0.1 mg / L or more, and the weight ratio of BOD:nitrogen of the organic wastewater is 100:1 to 3, and the biological treatment is carried out.

6. The organic wastewater treatment device according to claim 4 or 5, The reactor is a fluidized bed reactor, and the BOD volume load of the reactor is 1.5 kg / m ３ / day or more.

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