Method for acclimatizing activated sludge, method for treating organic wastewater, and organic wastewater treatment device

Abstract

To provide an acclimation method for activated sludge, a method for treating organic wastewater, and an apparatus for treating organic wastewater that enables stable, efficient, and energy-saving biological treatment of organic wastewater.SOLUTION: A method for acclimating activated sludge includes introduction of organic wastewater containing organic nitrogen into a treatment tank containing activated sludge, and addition of ammonia-form nitrogen to the organic wastewater in the treatment tank so that the weight ratio of BOD-to-ammonia nitrogen ratio of the organic wastewater in the treatment tank becomes 100:5.0 to 20.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Since the 1950s, when Japan's period of rapid economic growth began, four major pollution-related diseases (Minamata disease, Niigata Minamata disease, Itai-itai disease, and Yokkaichi asthma) have emerged, bringing environmental problems to light affecting water quality, soil, and air. In response to these issues, various pollution bills were enacted at the Pollution Diet in the 1970s, and Japan's environmental problems have seen some improvement. However, the problem of eutrophication in enclosed waters (inland bays, lakes, and inland seas) remains, and water quality standards have been strengthened to reduce the amount of nitrogen, phosphorus, and organic matter flowing into these waters. Furthermore, technological advances in industries such as machinery manufacturing and surface treatment have led to the discharge of organic wastewater containing various types of pollutants, creating a demand for efficient and reliable treatment technologies.

[0003] For example, Japanese Patent Laid-Open Publication No. 2022-42385 (Patent Document 1) describes a method for maintaining nitrogen and phosphorus concentrations in a reaction tank with the aim of preventing a significant decrease in the BOD removal rate in organic wastewater and suppressing the amount of excess sludge generated by biological treatment. Specifically, Patent Document 1 describes a method for treating organic wastewater in which organic wastewater is biologically treated under aerobic conditions in a reaction tank equipped with a carrier, in which a nitrogen source is added to the organic wastewater flowing into the reaction tank and the soluble phosphorus concentration in the reaction tank is maintained at 0.1 mg / L or higher to perform biological treatment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-42385 Summary of the Invention [Problem to be solved by the invention]

[0005] As described in Patent Document 1, it has been known for some time that a phosphorus source or a nitrogen source is supplementarily added to organic wastewater in order to promote the growth of microorganisms and the decomposition of organic matter in the reaction tank. However, adding too much nitrogen source to organic wastewater is undesirable because it leads to an increase in the amount of excess sludge generated, and therefore Patent Document 1 proposes controlling the soluble nitrogen concentration and soluble phosphorus concentration in the reaction tank so that the soluble nitrogen concentration in the reaction tank is maintained at 5 mg / L or less and the soluble phosphorus concentration is maintained at 0.1 mg / L or more.

[0006] However, organic wastewater generally has a wide variety of properties, with some having high and some having low soluble nitrogen concentrations. Furthermore, organic wastewater may contain organic matter, such as heavy metals that inhibit living organisms and sparingly soluble organic nitrogen. Therefore, depending on the properties of the organic wastewater flowing into the reaction tank, the biological treatment may not proceed efficiently even with the method described in Patent Document 1, and further investigation is needed.

[0007] Other methods for removing nitrogen from organic wastewater include the activated sludge method described in Patent Document 1, as well as physicochemical treatment methods such as an ion exchange resin method, a filtration method using a reverse osmosis membrane, an ammonia stripping method, an electrolytic denitrification method, an electrodialysis method, and an evaporation method. However, these methods have problems such as increased running costs due to energy consumption and the generation of by-products.

[0008] In view of the above problems, the present invention provides a method for acclimating activated sludge, a method for treating organic wastewater, and an apparatus for treating organic wastewater, which are capable of stably, efficiently, and energy-savingly biologically treating organic wastewater. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems and have found that it is effective to add ammonia nitrogen to organic wastewater to keep the weight ratio of BOD to ammonia nitrogen in the organic nitrogen within a predetermined range during a predetermined period, particularly during the acclimation of activated sludge, and then perform steady-state operation after acclimating the activated sludge.

[0010] Based on the above findings, in one aspect, the present invention provides a method for acclimating activated sludge, comprising the steps of introducing organic wastewater containing organic nitrogen into a treatment tank containing activated sludge, and adding ammonia nitrogen so that the weight ratio of BOD:ammonia nitrogen in the organic wastewater in the treatment tank becomes 100:5.0 to 20, thereby acclimating the activated sludge.

[0011] In one embodiment of the activated sludge acclimation method according to the present invention, phosphate phosphorus is further added so that the weight ratio of BOD:phosphate phosphorus in the organic wastewater in the treatment tank becomes 100:0.3 to 2.0.

[0012] In another embodiment of the activated sludge acclimation method according to the present invention, organic wastewater containing 80% by weight or more of organic nitrogen among the forms of nitrogen contained in the organic wastewater is introduced into a treatment tank.

[0013] In another aspect, the present invention provides a method for treating organic wastewater, comprising: an acclimation step of introducing organic wastewater containing organic nitrogen into a treatment tank containing activated sludge, and adding ammonia nitrogen to acclimate the activated sludge so that the weight ratio of BOD:ammonia nitrogen in the organic wastewater in the treatment tank becomes 100:5.0 to 20; and a biological treatment step of stopping the addition of ammonia nitrogen after the acclimation step, introducing the organic wastewater into the treatment tank, and biologically treating the organic wastewater in the presence of activated sludge under aerobic conditions.

[0014] In one embodiment, the method for treating organic wastewater according to the present invention further comprises an alkaline coagulation and precipitation treatment step in which the organic wastewater is coagulated under alkaline conditions using an iron reagent, and heavy metals are removed as unwanted substances and subjected to solid-liquid separation, before the organic wastewater is introduced into the biological treatment step.

[0015] In another embodiment of the organic wastewater treatment method according to the present invention, the acclimation step and biological treatment step include a denitrification step in which organic wastewater is denitrified to obtain a denitrified liquor, a nitrification step in which the denitrified liquor is nitrified to obtain a nitrified liquor, and a circulation step in which the nitrified liquor is circulated to the denitrification step, and the acclimation step includes adding ammonia nitrogen to the organic wastewater in the denitrification step and acclimating activated sludge in the denitrification step. By adding ammonia nitrogen to the denitrification tank, ammonia nitrogen flows into the nitrification tank under aerobic conditions, and the activated sludge in both the denitrification tank and the nitrification tank can be acclimated.

[0016] In yet another aspect, the present invention provides a denitrification tank for denitrifying organic wastewater containing organic nitrogen to obtain a denitrified liquid; a nitrification tank for nitrifying a denitrified liquid to obtain a nitrified liquid; a circulation line for circulating the nitrified liquid to the denitrification tank; ammonia nitrogen adding means for adding ammonia nitrogen so that the weight ratio of BOD to ammonia nitrogen of the organic wastewater in the denitrification tank becomes 100:5.0 to 20; and control means for controlling the operation of the ammonia nitrogen adding means so that ammonia nitrogen is added to the denitrification tank during acclimation treatment of the activated sludge contained in the denitrification tank. The present invention is a treatment device for organic wastewater, comprising: [Effects of the Invention]

[0017] According to the present invention, there are provided a method for acclimating activated sludge, a method for treating organic wastewater, and an apparatus for treating organic wastewater, which are capable of biologically treating organic wastewater stably, efficiently, and in an energy-saving manner. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a flow chart showing an example of a method for acclimating activated sludge according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing an example of an organic wastewater treatment device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Embodiments of the present invention will be described below with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. Note that the embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of component parts to those described below.

[0020] (organic wastewater) The organic wastewater usable in the embodiments of the present invention is not particularly limited, and various types of wastewater requiring biological treatment can be used. For example, organic wastewater generated in various industrial wastewater treatment processes, sewage treatment processes, and human waste treatment processes, as well as organic wastewater generated in various factories such as soft drink manufacturing plants, food processing plants, food manufacturing plants, fertilizer manufacturing plants, machinery factories, automobile factories, slaughterhouses, meat processing facilities, and meat processing plants, can be suitably used. In addition, raw sewage, raw human waste, and dehydrated separated liquid after dehydration of wastewater sludge can also be used as organic wastewater in the present embodiment. The nitrogen in these organic wastewaters is primarily in the form of organic nitrogen. Organic wastewater may also contain heavy metals and sparingly soluble organic matter with molecular weights of several hundred or more.

[0021] In particular, in this embodiment, among the nitrogen forms contained in organic wastewater, biological treatment can be carried out stably, efficiently, and in an energy-saving manner not only for organic wastewater with a low organic nitrogen concentration, but also for organic wastewater containing 80% by weight or more, in one embodiment 90% by weight or more, and in another embodiment 95% by weight or more of organic nitrogen. Specifically, although not limited to the following, stable biological treatment is possible even for organic wastewater containing a high concentration of organic nitrogen, such as an organic nitrogen concentration of 5 to 100 mg / L or 100 to 200 mg / L.

[0022] The nitrogen content in organic wastewater is typically 80 to 99.8 wt% of total nitrogen as organic nitrogen, 0.2 to 20 wt% as inorganic nitrogen, and 0 to 3 wt% as ammonia nitrogen. In one embodiment, the nitrogen content in the organic wastewater is 98.5 wt% as organic nitrogen, 1.5 wt% as inorganic nitrogen, and ammonia nitrogen at or below the lower limit of quantification (less than 0.1 mg / L), and the organic wastewater contains nitrogen in the form of almost entirely organic nitrogen. The inventors have confirmed through their studies that even with such organic wastewater, biological treatment can be carried out stably, efficiently, and with energy savings.

[0023] Organic wastewater may contain components other than organic nitrogen, such as heavy metals and metal smut that inhibit living organisms, as well as grease, machine oil, etc. The components other than organic nitrogen vary depending on the properties of the organic wastewater to be treated, but include, for example, metallic substances such as copper (Cu), nickel (Ni), cadmium (Cd), zinc (Zn), cobalt (Co), chromium (Cr), and lead (Pb), as well as free oil and solid grease. These can be measured as the inorganic nitrogen concentration contained in the organic wastewater. The components other than organic nitrogen contained in organic wastewater may typically be 20% by weight or less, 10% by weight or less in one embodiment, and 5% by weight or less in another embodiment.

[0024] The Fenton treatment, a physicochemical treatment, was investigated for such organic wastewater with high organic nitrogen concentrations, but its effectiveness was limited. Furthermore, when evaporation treatment was performed after removing heavy metals from the organic wastewater, the resulting treated water contained little residual organic matter and nitrogen, and was well treated, but various problems arose, such as the formation of scale in the concentrator, increased running costs, and a limited amount of water that could be treated.

[0025] On the other hand, one of the features of this embodiment is that biological treatment is performed on organic wastewater containing organic nitrogen, which allows for energy-saving treatment of organic wastewater with less by-products produced compared to physicochemical treatment.

[0026] (Activated sludge acclimation method) The method for acclimating activated sludge according to an embodiment of the present invention includes an acclimation step of introducing organic wastewater containing organic nitrogen into a treatment tank containing activated sludge, and adding ammonia nitrogen so that the weight ratio of BOD:ammonia nitrogen in the organic wastewater in the treatment tank becomes 100:5.0 to 20, thereby acclimating the activated sludge.

[0027] FIG. 1 shows an example of a treatment flow for the acclimation step. Note that FIG. 1 is merely an example, and the steps may be omitted or the order of steps may be changed depending on the treatment situation. In this acclimation step, in step S1, for example, organic wastewater is introduced into treatment tanks, such as a denitrification tank and a nitrification tank, containing activated sludge, to initiate acclimation of the activated sludge in the denitrification tank and the nitrification tank. Conditions for acclimating the activated sludge include, for example, a BOD-SS load in the nitrification tank of 0.1 to 1.9 kg / (kg·d), more preferably 0.1 to 1.2 kg / (kg·d), and even more preferably 0.1 to 0.8 kg / (kg·d). Aeration is performed as necessary to maintain the dissolved oxygen concentration in the nitrification tank at 2.0 to 8.0 mg / L, more preferably 5.0 to 8.0 mg / L. The pH in the nitrification tank is adjusted to 6.0 to 8.0, more preferably 7.5 to 8.0. In the nitrification tank, the nitrification reaction progresses even during the acclimation of the activated sludge, causing the pH to decrease, so it is preferable to maintain the alkalinity at 100 to 400 mg / L using a chemical such as sodium bicarbonate.

[0028] In step S2, the supply of chemicals to the treatment tank containing activated sludge begins. Chemicals that can be added include ammonia nitrogen and a biological activator to enhance the biological activity of the activated sludge. For example, if the weight ratio of BOD:ammonia nitrogen in the organic wastewater in the denitrification tank and nitrification tank is less than 100:5.0, the acclimation of the activated sludge may not proceed smoothly, and the acclimation process may take a long time. Even if the weight ratio of BOD:ammonia nitrogen exceeds 100:20, there is no significant adverse effect on the treatment of organic nitrogen and organic matter, but the pH will drop significantly due to the nitrification reaction, making it difficult to control. Therefore, it is preferable to adjust the addition of ammonia nitrogen taking into account the acclimation status of the activated sludge.

[0029] In this embodiment, the weight ratio of BOD:ammonia nitrogen is more preferably 100:5.0 to 20, even more preferably 100:10 to 20, and even more preferably 100:15 to 20. By adjusting the weight ratio of BOD:ammonia nitrogen in the organic wastewater to fall within the above range, the acclimation step can be completed quickly, and the inside of the treatment tank can be made suitable for treating the organic wastewater to be treated.

[0030] Examples of ammonia nitrogen that can be added to the treatment tank include ammonium chloride, ammonium sulfate, urea, etc. For example, by properly preparing the ammonia nitrogen to be 0.004 to 0.01% by weight and adding it in the form of a solution, mixing can be accelerated and biological treatment can proceed more stably.

[0031] It is preferable to further add phosphate phosphorus as a bioactivator to be added to the treatment tank. By supplying phosphate phosphorus to the organic wastewater in the treatment tank, the activity of the activated sludge in the treatment tank can be increased, and the acclimation process can be completed more quickly. The phosphate phosphorus is preferably supplied so that the weight ratio of BOD:phosphate phosphorus of the organic wastewater in the treatment tank becomes 100:0.3 to 2.0, and more preferably 100:1.0 to 2.0. As the phosphate phosphorus, for example, potassium dihydrogen phosphate, potassium phosphate, ammonium phosphate, etc. are suitably used.

[0032] Adding trace metal elements to the treatment tank as a chemical is preferable because it replenishes the trace metal elements necessary for biological treatment using microorganisms. In particular, when alkaline coagulation and precipitation treatment is performed as a pretreatment before biological treatment of organic wastewater, the trace metal elements necessary for microorganisms may be removed during the alkaline coagulation and precipitation treatment. In such cases, if the organic wastewater lacks trace metal elements, which are a factor in the composition of bacterial cells, various effects may be felt on aerobic microorganisms and bacterial cells that decompose organic nitrogen, as well as on nitrifying bacteria and nitrite-oxidizing bacteria involved in nitrification reactions.

[0033] Examples of trace metal elements to be added include magnesium (Mg), iron (Fe), molybdenum (Mo), cobalt (Co), calcium (Ca), zinc (Zn), manganese (Mn), copper (Cu), etc. The concentrations of these elements introduced are preferably always introduced at a weight ratio relative to the BOD in the organic wastewater of BOD:iron:magnesium:molybdenum:calcium=100:0.3-1.0:0.3-1.0:0.01-0.03:1.0-4.0, and more preferably at a ratio of BOD:iron:magnesium:molybdenum:calcium=100:0.6-1.0:0.6-1.0:0.02-0.03:2.0-4.0.

[0034] Trace metal elements are preferably introduced into the treatment tank at concentrations that do not exceed the threshold concentration of activated sludge. When cobalt is introduced as an added trace metal element, the concentration introduced is preferably 0.5 mg / L or less, which does not exceed the threshold concentration of activated sludge, more preferably 0.1 to 0.4 mg / L or less, and even more preferably 0.02 to 0.10 mg / L. The concentration introduced of nickel is preferably 0.5 mg / L or less, which does not exceed the threshold concentration of activated sludge, more preferably 0.01 to 0.4 mg / L or less, and even more preferably 0.02 to 0.04 mg / L. The concentration introduced of zinc is preferably 1.0 mg / L or less, which does not exceed the threshold concentration of activated sludge, more preferably 0.2 to 0.9 mg / L, and even more preferably 0.2 to 0.4 mg / L. Typically, but not limited to, the ratio of BOD:iron:magnesium:calcium:zinc:cobalt:manganese:copper:molybdenum:nickel is 100:0.6:0.6:4.0:0.04:0.02:0.11:0.02:0.02:0.01. Trace metal elements can be introduced into the treatment tank by preparing a solution containing the specified metals. Note that these trace metal elements may actually inhibit microorganisms if their concentration exceeds 1.0 mg / L.

[0035] The pH in the treatment tank during the acclimation step is preferably 7.0 to 8.0, and more preferably strictly maintained at 7.5 to 8.0. The water temperature is preferably 20°C or higher, and more preferably maintained at 20°C to 30°C.

[0036] In step S3, it is determined whether or not the acclimation of the activated sludge in the treatment tank is complete. The completion of the acclimation of the activated sludge can be determined by the removal rate of organic nitrogen derived from the organic wastewater. Specifically, it can be determined that the acclimation is complete when the removal rate of organic nitrogen is 80% or more. The completion of the acclimation can also be determined by the removal rate of BOD. Specifically, it can be determined that the acclimation is complete when the removal rate of BOD derived from the organic wastewater is 85% or more. If the acclimation is not complete, the process returns to step S2. If the acclimation is complete, the process proceeds to step S4, where the supply of ammonia nitrogen is stopped. Then, steady-state operation is started in step S5.

[0037] According to the activated sludge acclimation method of the present invention, in the activated sludge acclimation step, ammonia nitrogen is added to the organic wastewater in the treatment tank so that the BOD:ammonia nitrogen weight ratio is 100:5.0-20. After the activated sludge is acclimated, the addition of ammonia nitrogen is stopped and steady-state operation is carried out. By acclimating the activated sludge sufficiently in advance in the activated sludge acclimation step, the addition of ammonia nitrogen becomes unnecessary during steady-state operation. This reduces the amount of chemical solution used compared to conventional methods such as those described in Patent Document 1, which monitors the soluble nitrogen concentration and constantly controls it to below a predetermined value, enabling more efficient biological treatment.

[0038] As a result of the biological treatment by adding ammonia nitrogen in the acclimation step, aerobic microorganisms and bacterial cells that decompose persistent organic nitrogen are produced in the treatment tank. These microorganisms decompose the organic nitrogen, and ammonia nitrogen is generated as a result of the decomposition. As a result, biological treatment is carried out according to the type of persistent organic nitrogen, and sufficient ammonia nitrogen suitable for steady operation is produced. Therefore, according to the organic wastewater treatment method of the embodiment of the present invention, artificial addition of ammonia nitrogen is not necessary during steady operation.

[0039] Compared to organic wastewater with a low organic nitrogen concentration, organic wastewater with a high organic nitrogen concentration contains sufficient nitrogen sources as nutrients necessary for biological treatment, and it has generally been thought that adding a nitrogen source is unnecessary. However, it has been found that when persistent organic nitrogen is included, the nutrients necessary for biological treatment may be insufficient, resulting in poor treatment. In particular, organic wastewater with an organic nitrogen content of 80% by weight or more requires a long time for activated sludge to acclimate, and sufficient treatment performance may not be achieved even during steady-state operation.

[0040] According to the activated sludge acclimation method of the present invention, by further adding ammonia nitrogen as a nitrogen source other than the nitrogen contained in the organic wastewater, preferably to organic wastewater containing 80% by weight or more of organic nitrogen, the acclimation of the activated sludge in the treatment tank is more reliable, and biological treatment can be applied to organic wastewater containing persistent organic nitrogen, metal elements, etc. By reliably acclimating the activated sludge in the acclimation step, control of the addition of ammonia nitrogen during steady-state operation is no longer necessary, and treatment efficiency can be improved.

[0041] (Organic wastewater treatment equipment) An example of an organic wastewater treatment device according to an embodiment of the present invention is shown in Figure 2. The treatment device according to the embodiment of the present invention can include a biological treatment unit 10 that biologically treats organic wastewater containing organic nitrogen, and a pretreatment unit 20 that performs pretreatment on the organic wastewater.

[0042] The biological treatment unit 10 includes a denitrification tank 11 that denitrifies organic wastewater to obtain a denitrified liquid, a nitrification tank 12 that nitrifies the denitrified liquid to obtain a nitrified liquid, a circulation line 14 that circulates the nitrified liquid to the denitrification tank 11, ammonia nitrogen addition means 15 that adds ammonia nitrogen so that the weight ratio of BOD:ammonia nitrogen in the organic wastewater in the denitrification tank 11 becomes 100:5.0 to 20, and control means 18 that controls the operation of the ammonia nitrogen addition means 15 so that ammonia nitrogen is added to the denitrification tank during acclimation of the activated sludge contained in the denitrification tank.

[0043] The pretreatment unit 20 comprises an alkaline coagulation tank 21 in which organic wastewater is subjected to coagulation treatment under alkaline conditions using an iron reagent, a solid-liquid separation tank 22 in which the treated water that has been subjected to alkaline coagulation treatment is subjected to solid-liquid separation and heavy metals are separated as unwanted substances, an iron reagent adding means 23 that adds the iron reagent to the alkaline coagulation tank 21, and a pH adjuster adding means 24 and a coagulant adding means 25 that can add a pH adjuster to the alkaline coagulation tank 21.

[0044] In the alkaline coagulation tank 21, the organic wastewater is preferably subjected to alkaline coagulation and precipitation treatment to remove inhibitors of biological treatment. These inhibitors include heavy metals (Cu, Ni, Cd, Zn, Co, Cr, and Pb) exceeding the threshold concentration in activated sludge, as well as poorly soluble organic matter such as free oil and solid fats and oils. The alkaline coagulation tank 21 is connected to an iron reagent addition means 23 and a pH adjuster addition means 24. The iron reagent added by the iron reagent addition means 23 may be any iron reagent containing ferric ions, such as polyferric sulfate, copper chloride, and ferric chloride. The iron reagent is preferably introduced into the alkaline coagulation tank 21 at a weight ratio relative to the BOD in the organic wastewater of 100:1.0-10, preferably 100:1.0-7.0, and more preferably 100:5.0.

[0045] The type of pH adjuster is not particularly limited, but examples thereof include aqueous sodium hydroxide solution, sulfuric acid, hydrochloric acid, and nitric acid. The coagulation pH is preferably adjusted to 8.5 or higher, at which point heavy metals are insolubilized in the treatment tank, more preferably 9.0 or higher, and even more preferably 10.0. The water temperature is set to 20°C or higher, and more preferably 25°C to 30°C.

[0046] The solid-liquid separation tank 22 is a device for separating the alkaline coagulation-treated water that has been subjected to alkaline coagulation treatment in the alkaline coagulation tank 21 into solid and liquid. Various solid-liquid separation devices can be used as the solid-liquid separation tank 22, such as a membrane filtration device, a centrifugal separator, or a settling tank. A coagulant or coagulation aid such as an inorganic coagulant or a polymer coagulant, more typically a polymer coagulant, is supplied into the solid-liquid separation tank 22 via coagulant addition means 25.

[0047] The denitrification tank 11 is an apparatus that receives the alkaline coagulation-sedimentation-treated water that has been solid-liquid separated in the solid-liquid separation tank 22, and reduces the nitrification-treated water, which has been oxidized to nitrate nitrogen in the organic wastewater through a denitrification reaction by facultative anaerobic bacteria, to nitrogen gas under anaerobic conditions. A circulation line 14 is connected to the denitrification tank 11 for circulating the digested water produced in the nitrification tanks 12 and 13. The pH of the alkaline coagulation-sedimentation-treated water flowing into the denitrification tank 11 is preferably maintained at 7.0 to 8.0, at which the denitrification reaction proceeds stably.

[0048] In the denitrification process, when 1 mg of nitrate nitrogen is denitrified, hydroxide ions equivalent to 2.86 mg of sodium hydroxide are generated. Supplying the hydrogen ions generated in the nitrification process to the denitrification tank 11 by circulating the nitrification-treated water is expected to have the effect of reducing the amount of neutralizing agent used, but it is preferable to further install neutralization means 17 that adds a neutralizing agent to the denitrification tank 11 as a neutralizing agent facility, as this will further stabilize the pH in the denitrification tank 11. There are no particular restrictions on the neutralizing agent, but the alkali used is an aqueous sodium hydroxide solution, and the acids used are sulfuric acid, hydrochloric acid, and nitric acid.

[0049] The water temperature in the denitrification tank 11 is preferably 20°C or higher, at which point the denitrification reaction proceeds easily, and more preferably kept at 25°C to 30°C. The BOD source required for the denitrification reaction can be the BOD contained in the organic wastewater. If this is not available, it is preferable to add methanol from the outside as an electron donor.

[0050] As described above, when the organic wastewater contains a sufficient amount of nitrogen (organic nitrogen) as a nutrient necessary for biological treatment relative to its BOD, the introduction of a nitrogen source is generally deemed unnecessary. However, if the organic nitrogen is persistent, the nutrients necessary for biological treatment will be insufficient, resulting in poor treatment. Therefore, to promote the emergence and generation of aerobic microorganisms that contribute to the oxidative decomposition of persistent organic nitrogen, another form of nitrogen (ammonia nitrogen) contained in the organic wastewater is introduced into the denitrification tank 11 only during activated sludge acclimation so that the weight ratio of BOD:ammonia nitrogen is 100:7.0-20, more preferably 100:10-20, and even more preferably 100:15-20. This enables stable, efficient, and energy-saving biological treatment of organic wastewater.

[0051] The amount of phosphate phosphorus introduced into the denitrification tank 11 is preferably at a weight ratio of 100:0.3 or greater relative to the BOD content of the organic wastewater, with a BOD:phosphate phosphorus ratio of 100:0.3 or greater being more preferred, and a ratio of 100:0.3 to 2.0 being even more preferred, with a ratio of 100:1.0 to 2.0 being even more preferred. Furthermore, organic wastewater, particularly wastewater discharged from machinery manufacturers and surface treatment companies, contains heavy metals and organic matter that inhibit bioremediation. To accommodate a wide range of such wastewater, alkaline coagulation treatment using an iron reagent can be performed as a pretreatment step before biological treatment to remove the phosphate phosphorus from the organic wastewater. This can lead to a shortage of ammonia nitrogen and phosphate phosphorus, which function as nutrients for biological treatment in the denitrification tank 11.

[0052] According to this embodiment, the ammonia nitrogen adding means 15 and the bioactivator adding means 16 are connected to the denitrification tank 11, and the ammonia nitrogen and phosphate phosphorus are added to the denitrification tank 11 or to the piping or storage tank (not shown) upstream of the denitrification tank 11, thereby enabling smooth sludge acclimation under anaerobic and aerobic conditions. Furthermore, since the alkaline coagulation treatment also removes trace metals necessary for heterotrophic bacteria, such as denitrifying bacteria, and autotrophic bacteria, such as nitrifying bacteria and nitrite-oxidizing bacteria, which are involved in the denitrification reaction, it is desirable to add the trace metal elements to the denitrification tank 11. This ensures acclimation of the activated sludge in the denitrification tank 11, and allows for more appropriate treatment in the downstream nitrification tanks 12 and 13.

[0053] Nitrification tanks 12 and 13 are devices that acclimate activated sludge using ammonia nitrogen introduced from denitrification tank 11 and then use the activated sludge to aerobically oxidize and decompose organic nitrogen and organic matter. Nitrification tanks 12 and 13 may each be a single tank, but to further promote sludge acclimation and oxidative decomposition of organic matter and organic nitrogen, it is preferable to have two or more tanks as shown in Figure 2. The pH of nitrification tanks 12 and 13 is preferably maintained at 7.0 to 8.0, and more preferably at 7.5 to 8.0, which facilitates the nitrification reaction.

[0054] The amount of alkali required to neutralize the hydrogen ions generated during nitrification treatment is 5.71 mg of sodium hydroxide per 1 mg of ammonia nitrogen. The alkaline agent used to neutralize the hydrogen ions in nitrification tanks 12 and 13 is preferably sodium hydroxide or sodium carbonate or sodium bicarbonate, which are carbon sources necessary for the nitrification reaction. The alkalinity in nitrification tanks 12 and 13 is preferably 100 mg / L or higher, and more preferably 200 mg / L or higher, but from the perspective of preventing scale buildup, the upper limit of alkalinity is preferably 500 mg / L or lower.

[0055] The water temperature is preferably 20°C or higher, at which point the nitrification reaction proceeds easily, and more preferably kept between 25°C and 30°C. The dissolved oxygen concentration (DO) in the nitrification tanks 12 and 13 is preferably 4 mg / L or higher, at which point the oxidative decomposition reaction of organic nitrogen and the nitrification reaction proceed easily, and it is more preferable to maintain it at 6 mg / L or higher. The treated water that has passed through the nitrification and denitrification process is then subjected to solid-liquid separation. There are no particular restrictions on the solid-liquid separation, and examples include MBR and natural sedimentation in a settling tank.

[0056] The control means 18 is mainly connected to the ammonia nitrogen adding means 15, the biological activator adding means 16, and the neutralization means 17, and controls the operation or stop of the ammonia nitrogen adding means 15, the biological activator adding means 16, and the neutralization means 17. The control means 18 is connected to a measuring device (not shown) that measures the properties of the treated organic wastewater provided in the organic wastewater treatment device shown in Figure 2, and may control the supply flow rate of each chemical solution by the ammonia nitrogen adding means 15, the biological activator adding means 16, and the neutralization means 17 based on the measurement results of the organic wastewater output from the measuring device. The control means 18 is composed of a mechanical valve such as a solenoid valve, and selectively opens the valve only during the acclimation process of the activated sludge in the denitrification tank 11, allowing ammonia nitrogen to be supplied to the denitrification tank 11.

[0057] (Method for treating organic wastewater) A method for treating organic wastewater according to an embodiment of the present invention can be carried out, for example, using an organic wastewater treatment apparatus shown in Fig. 2. That is, the method for treating organic wastewater according to the embodiment of the present invention comprises an acclimation step in which organic wastewater containing organic nitrogen is introduced into a treatment tank containing activated sludge, and ammonia nitrogen is added to acclimate the activated sludge so that the weight ratio of BOD:ammonia nitrogen in the organic wastewater in the treatment tank becomes 100:5.0 to 20, and a biological treatment step in which the addition of ammonia nitrogen is stopped after the acclimation step, the organic wastewater is introduced into the treatment tank, and the organic wastewater is biologically treated in the presence of activated sludge under aerobic conditions.

[0058] In one embodiment, the pretreatment unit 20 preferably includes an alkaline coagulation and precipitation treatment step in which the organic wastewater is coagulated under alkaline conditions using an iron reagent before being introduced into the biological treatment step, and heavy metals are separated into solid and liquid components as unwanted substances.

[0059] In another embodiment, the biological treatment unit 10 includes a denitrification step in which organic wastewater is denitrified in a denitrification tank 11 to obtain a denitrified liquid, a nitrification step in which the denitrified liquid is nitrified in nitrification tanks 12 and 13 to obtain a nitrified liquid, and a circulation step in which the nitrified liquid is circulated to the denitrification step via a circulation line 14, and it is preferable that the acclimation step add ammonia nitrogen to the organic wastewater in the denitrification step and acclimate the activated sludge in the denitrification step.

[0060] According to the organic wastewater treatment device and treatment method of the embodiment of the present invention, by providing an acclimation step in which activated sludge is acclimated by adding ammonia nitrogen so that the weight ratio of BOD to ammonia nitrogen in the organic wastewater in the treatment tank becomes 100:5.0 to 20, the acclimation of activated sludge is ensured, and stable biological treatment can be performed even for organic wastewater containing persistent organic nitrogen. As a result, stable, efficient, and energy-saving biological treatment of organic wastewater is possible. [Example]

[0061] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0062] Organic wastewater containing heavy metals and organic nitrogen was subjected to alkaline coagulation treatment, and the treated water (hereinafter referred to as biological treatment raw water) was used to conduct a batch-type standard activated sludge treatment test.The nitrogen content of this biological treatment raw water was 98.5% organic nitrogen, 1.5% inorganic nitrogen, and no ammonia nitrogen was detected, with organic nitrogen accounting for most of the nitrogen.The test conditions are shown below.

[0063] Example 1 In Example 1, for each biological treatment raw water shown in Table 1, 93.6 mg / L of ammonia nitrogen and 4.7 mg / L of phosphate phosphorus were added in the activated sludge acclimation process so that the BOD:N:P ratio was 100:20:1.0.

[0064] Example 2 In Example 2, 20.2 mg / L of ammonia nitrogen and 4.0 mg / L of phosphate phosphorus were added to each of the biological treatment raw waters shown in Table 1 in the activated sludge acclimation step so that the BOD:N:P ratio was 100:5.0:1.0. In Example 2, trace metal elements were also added so that the BOD:iron:magnesium:calcium:zinc:cobalt:manganese:copper:molybdenum:nickel ratio was 100:0.6:0.6:4.0:0.04:0.02:0.11:0.02:0.02:0.01.

[0065] (Comparative Example) In the comparative example, for each biological treatment raw water shown in Table 1, 4.0 mg / L of phosphate phosphorus was added in the activated sludge acclimation process so that the BOD:P ratio was 100:1.0, and acclimation was performed without adding ammonia nitrogen.

[0066] (adaptation condition) Reaction volume (L): 2-3L MLSS in reaction volume (mg / L): 1,300-2,500 mg / L Reaction time (h): 6~24h ·BOD-SS load [kg / (kg d)]: 0.21~0.77 ·BOD-Volume load [kg / (m 3 ·d)]:0.42~1.62 ·Water temperature (℃): Approx. 20.1~23.4℃

[0067] (Evaluation method) The raw water and treated water were filtered using glass fiber filters with a particle retention capacity of 1 μm, and then subjected to water quality analysis. MnThe analytical method for organic nitrogen was to measure oxygen consumption using potassium permanganate. The BOD was measured using the diaphragm electrode method. NOx-N and ammonia nitrogen were measured using an automatic chemical analyzer (BLTEC total nitrogen / total phosphorus automatic analyzer). For organic nitrogen, the value obtained by subtracting the ammonia nitrogen value from the Kjeldahl method value was used.

[0068] <Measurement results> (Comparative Example) When the BOD-SS load was 0.33 [kg / (kg·d)], the organic nitrogen in the biologically treated water was 47.6 mg / L, and only a small amount of organic nitrogen was oxidized and decomposed by biological treatment (removal rate: 8.1%). If the organic nitrogen is not oxidized and decomposed, the nitrogen removal effect of the biological nitrification denitrification method cannot be obtained, and therefore the removal of nitrogen that causes eutrophication cannot be expected. In addition, the COD of the biologically treated water at this time was Mn The residual amount was 172 mg / L and the BOD was 209 mg / L, and the organic matter removal by biological treatment was slight (COD Mn Removal rate: 29.2%, BOD removal rate: 47.1%).

[0069] Example 1 At a BOD-SS load of 0.23 [kg / (kg·d)], the organic nitrogen in the biologically treated water was reduced to 9.0 mg / L (removal rate: 82.7%), a 74.6 pt improvement in removal rate compared to the comparative example. However, the decomposition rate of organic nitrogen at this time was 1.8 mg-Org-N / L / h, and the NOx-N generated by the nitrification reaction was 6.4 mg / L, which was small compared to Example 2 described below. This is presumably because the alkaline coagulation treatment before biological treatment removed organic matter that inhibits living organisms, and also removed trace metals necessary for autotrophic bacteria such as nitrifying bacteria and nitrite-oxidizing bacteria. In addition, as organic nitrogen was removed, BOD and COD Mn The BOD of the biologically treated water was 10.4 mg / L, and the COD Mn The organic matter was treated well (BOD removal rate: 97.9%, COD Mn Removal rate: 83.4%).

[0070] Example 2 At a BOD-SS load of 0.77 kg / (kg·d), the organic nitrogen in the biologically treated water was reduced to 9.2 mg / L, confirming organic nitrogen removal even at loads higher than those of the Comparative Example and Example 1. The organic nitrogen decomposition rate was high at 6.2 mg-Org-N / L / h, approximately 3.4 times that of Example 1. Furthermore, at a BOD-SS load of 0.21 kg / (kg·d), the NOx-N in the biologically treated water was 16.2 mg / L, approximately 2.5 times higher than that of Example 1. This is presumably due to the activation of nitrifying bacteria and nitrite-oxidizing bacteria involved in the nitrification reaction by introducing trace metal elements below the threshold concentration of activated sludge after alkaline coagulation treatment.

[0071] From the above, it was shown that various organic wastewaters can be treated by the treatment flow according to Examples 1 and 2 of the present invention. In Example 2, the BOD of the biologically treated water was 13.1 mg / L and the COD Mn The BOD removal rate was 96.8%, and the COD was 33.1 mg / L and 6.9 mg / L, respectively, confirming that the treatment of organic nitrogen and organic matter was also good. Mn Removal rate: 85.6%, organic nitrogen removal rate: 85.0%).

[0072] [Table 1] [Explanation of symbols]

[0073] 10...Biological treatment section 11...Denitrification tank 12, 13...Nitrification tank 14...Circulation line 15...Means for adding ammonia nitrogen 16...Means for adding bioactive agent 17...Neutralization means 18...Control means 20...Pre-processing section 21...Alkaline coagulation tank 22…Solid-liquid separation tank 23...Iron reagent addition means 24...Means for adding pH adjuster 25...Flocculant addition means

Claims

1. A method for acclimatizing activated sludge, comprising the steps of introducing organic wastewater containing organic nitrogen into a treatment tank containing activated sludge, and adding ammonia nitrogen so that the weight ratio of BOD:ammonia nitrogen in the organic wastewater in the treatment tank becomes 100:5.0 to 20, thereby acclimatizing the activated sludge.

2. 2. The method for acclimating activated sludge according to claim 1, further comprising adding phosphate phosphorus so that the weight ratio of BOD:phosphate phosphorus of the organic wastewater in the treatment tank becomes 100:0.3 to 2.

0.

3. 3. The method for acclimating activated sludge according to claim 1, wherein the organic wastewater contains 80% by weight or more of organic nitrogen among the forms of nitrogen contained in the organic wastewater and is introduced into the treatment tank.

4. an acclimation step of introducing organic wastewater containing organic nitrogen into a treatment tank containing activated sludge, and adding ammonia nitrogen to the organic wastewater in the treatment tank so that the weight ratio of BOD:ammonia nitrogen in the organic wastewater in the treatment tank becomes 100:5.0 to 20, thereby acclimating the activated sludge; a biological treatment step in which the addition of the ammonium nitrogen is stopped after the acclimation step, the organic wastewater is introduced into the treatment tank, and the organic wastewater is biologically treated under aerobic conditions in the presence of the activated sludge; A method for treating organic wastewater, comprising:

5. 5. The method for treating organic wastewater according to claim 4, further comprising an alkaline coagulation and sedimentation treatment step in which, before the organic wastewater is introduced into the biological treatment step, the organic wastewater is subjected to coagulation treatment under alkaline conditions using an iron reagent, thereby separating heavy metals into undesired substances through solid-liquid separation.

6. The acclimation step and the biological treatment step a denitrification step of denitrifying the organic wastewater to obtain a denitrified liquid; a nitrification step of nitrifying the denitrified liquid to obtain a nitrified liquid; a circulation step of circulating the nitrification liquid to the denitrification step; Including, 6. The method for treating organic wastewater according to claim 4, wherein the acclimation step comprises adding the ammonium nitrogen to the organic wastewater in the denitrification step, and acclimating the activated sludge in the denitrification step.

7. a denitrification tank for denitrifying organic wastewater containing organic nitrogen to obtain denitrified liquid; a nitrification tank for nitrifying the denitrified liquid to obtain a nitrified liquid; a circulation line for circulating the nitrification liquid to the denitrification tank; ammonia nitrogen adding means for adding ammonia nitrogen to the organic wastewater in the denitrification tank so that the weight ratio of BOD:ammonia nitrogen becomes 100:5.0 to 20; a control means for controlling the operation of the ammonia nitrogen adding means so that the ammonia nitrogen is added to the denitrification tank during acclimation treatment of the activated sludge contained in the denitrification tank; An organic wastewater treatment device comprising:

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