BIOLOGICAL NITRIFICATION METHOD AND BIOLOGICAL NITRIFICATION SYSTEM

Abstract

To provide a biological nitrification method and a biological nitrification system capable of treating treated water containing high concentrations of ammonia nitrogen at a high nitrification rate, and downsizing a treatment system with high safety and cost effective.SOLUTION: When making treated water pass through a nitrification tank 5 loaded with a plurality of bio-retainers 6 having an average density of 1.0 to 1.4 g / cm3, the linear velocity ratio (LVair / LVwaterconduction) between the linear velocity of treated water LVwaterconduction [m / h] and the linear velocity of air in the stored water in the nitrification tank 5 LVair [m / h] is 5.0 or less, and the biological nitrification method is characterized in that a filling ratio calculated by the following equation (1) is 25 vol.% or more. Filling rate (volume%)=((total volume of the plurality of bio-retainers 6) / (sum of the total volume of the plurality of bio-retainers 6 and the volume of stored water in the nitrification tank 5))×100 ... Formula (1).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a bionitrification method and a bionitrification system. [Background technology]

[0002] A biological nitrification reaction is known in which ammoniacal nitrogen in water to be treated is converted to nitric acid by microorganisms. Ammoniacal nitrogen may be contained in, for example, groundwater, well water, lake water, river water, industrial wastewater, etc. A common biological nitrification method for treating water containing a low concentration of ammoniacal nitrogen is the fixed-bed push flow method, in which the water to be treated is passed as a push flow through a fixed bed formed by packing a filter medium to which microorganisms such as nitrifying bacteria are attached (for example, Patent Document 1, Non-Patent Documents 1 and 2).

[0003] For example, in a fixed-bed push flow type biological nitrification system 100A shown in Fig. 5, water to be treated containing ammonia nitrogen is stored in a nitrification tank 105A from a supply pipe 104A. A filter layer 106A filled with a filter medium such as stone, ceramics, synthetic resin, etc. is formed in the nitrification tank 105A. When the water to be treated is passed through the filter layer 106A, the ammonia nitrogen is converted to nitrate nitrogen by microorganisms such as nitrifying bacteria attached to the surface of the filter medium, and the water is treated.

[0004] In the fixed-bed push flow type biological nitrification system 100A, the water to be treated is passed through the filter layer 106A so as to have a push flow. That is, the water to be treated is passed through the filter layer 106A so that there is no mixing or diffusion in the flow direction in the nitrification tank 105A, and the velocity in the direction perpendicular to the flow direction is uniform. After that, the treated water after biological nitrification flows out from the outlet pipe 110A. According to the fixed bed plug flow system, the nitrification reaction of the water to be treated containing a low concentration of ammonia nitrogen can be carried out uniformly.

[0005] On the other hand, as a biological nitrification method for water to be treated that contains a high concentration of ammonia nitrogen, there is a fluidized bed mixed flow method in which carriers holding microorganisms are circulated in a nitrification tank while the water to be treated is passed through the carriers (e.g., Patent Documents 2 and 3). For example, in a fluidized bed mixed flow type biological nitrification system 100B shown in Fig. 6, water to be treated is supplied to nitrification tank 105B while air is supplied to the stored water in nitrification tank 105B from aeration unit 107. When the water to be treated flows into nitrification tank 105B, it is instantly mixed with the stored water, making the concentration of the entire stored water uniform. In the fluidized bed mixed flow method, the organism holder 106B carrying nitrifying bacteria and the like is fluidized in the stored water in the nitrification tank 105B. When the organism holder 106B comes into contact with the water to be treated, ammonia nitrogen is converted to nitrate nitrogen and treated. The fluidized bed mixed flow system can treat water containing a high concentration of ammonia nitrogen. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-288417 A [Patent Document 2] JP 2017-202473 A [Patent Document 3] JP 2011-212670 A [Non-patent literature]

[0007] [Non-Patent Document 1] Groundwater purification using iron bacteria, Kobelco Pantech Technical Report, Vol. 45 No. 2, p. 16-24 (2002) [Non-Patent Document 2] Case studies of coagulation, sedimentation / flotation separation, and granular layer filtration for users, 5.3 Ultra-high-speed, chemical-free biological treatment equipment using groundwater as raw water Japan Liquid Clarification Technology Association, p.64-67(2019) Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the general fixed bed, push flow type treatment methods such as those described in Patent Document 1 and Non-Patent Documents 1 and 2, the nitrification rate per nitrification tank is 0.1 kgN / m 3 In addition, when the wastewater containing a high concentration of ammonia nitrogen is treated using the fixed bed plug flow method, the treatment system becomes large.

[0009] In the method of Patent Document 2, the bulk volume of the nitrifying bacteria-supporting carrier relative to the effective water volume is small (30% by volume in Example 1, which is equivalent to 20% by volume when converted into a packing ratio in the present invention described below). However, according to the inventor's investigation, if the volume ratio is higher than this, there is a problem that the fluidity of the nitrifying bacteria-supporting carrier decreases, resulting in dead space and short-circuiting. This may make it impossible to perform the nitrification reaction uniformly in the water to be treated. Furthermore, since the nitrification rate depends on the volume ratio of the nitrifying bacteria-supporting carrier in the nitrification tank, the method of Patent Document 2 does not allow the volume ratio of the nitrifying bacteria-supporting carrier to be increased any further, and therefore it is not possible to further improve the nitrification rate. In addition, in the method of Patent Document 2, the nitrification rate per nitrification tank is low, and in order to treat water containing a high concentration of ammoniacal nitrogen, it becomes necessary to further increase the number of nitrification tanks, which results in a problem of an increase in the size of the treatment system.

[0010] In Patent Document 3, the O2 concentration of the high-concentration oxygen gas supplied to the gas phase of the nitrification tank is set to 80-90%, and nitrification treatment is performed under high-load conditions. However, supplying high-concentration oxygen gas with an O2 concentration of 80-90% to the gas phase of the nitrification tank is disadvantageous in terms of cost and has safety issues.

[0011] The present invention provides a biological nitrification method and a biological nitrification system that can treat water containing a high concentration of ammoniacal nitrogen at a high nitrification rate, enable the treatment system to be miniaturized, and is highly safe and advantageous in terms of cost. [Means for solving the problem]

[0012] As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by maintaining (i) the average density of the bioretainers, (ii) a specific packing rate of the bioretainers, and (iii) the ratio of the linear air supply velocity to the linear water flow velocity of the water to be treated within a specific range. The inventors have found that a high nitrification rate can be achieved by carrying out the nitrification reaction under these specific conditions, and have completed the present invention.

[0013] The present invention has the following aspects. [1] A biological nitrification method for treating ammonia nitrogen in water to be treated; 3 When the water to be treated is passed through a nitrification tank loaded with a plurality of biological retainers, the linear velocity of the water to be treated is LV 通水 [m / h] and the linear velocity LV of the air in the water stored in the nitrification tank 空気 [m / h] and linear velocity ratio (LV 空気 / LV 通水 ) is 5.0 or less, and the filling rate calculated by the following formula (1) is 25 volume % or more. Filling rate (volume %) = ((total volume of multiple biological retainers) / (sum of total volume of multiple biological retainers and volume of stored water in the nitrification tank)) × 100 Formula (1) [2] The biological nitrification method according to [1], wherein the biological support has a porous carrier and nitrifying bacteria supported on the carrier. [3] Furthermore, the linear velocity LV 空気 The biological nitrification method of [1] or [2], in which the flow rate is 30 m / h or less. [4] When the iron content of the treated water is more than 0.5 mg / L, the linear velocity ratio (LV 空気 / LV 通水 ) is 0.20 to 5.0. [5] Average density is 1.0-1.4g / cm 3a water supply pipe for supplying water to the nitrification tank; a water flow rate adjusting means provided in the water supply pipe for adjusting the flow rate of the water to be treated supplied to the nitrification tank; an aeration device for supplying air to the water stored in the nitrification tank; and a control device electrically connected to at least the water flow rate adjusting means and the aeration device; 通水 [m / h] and the linear velocity LV of the air in the water stored in the nitrification tank 空気 [m / h] and linear velocity ratio (LV 空気 / LV 通水 ) is 5.0 or less, and a filling rate calculated by the following formula (1) is 25 volume % or more. Filling rate (volume %) = ((total volume of multiple biological retainers) / (sum of total volume of multiple biological retainers and volume of stored water in the nitrification tank)) × 100 Formula (1) [6] The biological nitrification system according to [5], wherein the biological retainer has a porous carrier and nitrifying bacteria retained on the carrier. [7] The control unit controls the linear velocity LV 空気 A biological nitrification system as described in [5] or [6], with a flow rate of 30 m / h or less. [8] When the iron content of the water to be treated is more than 0.5 mg / L, the control unit 空気 / LV 通水 ) is 0.20 to 5.0. Effect of the Invention

[0014] According to the present invention, there is provided a biological nitrification method and a biological nitrification system which can treat water containing a high concentration of ammoniacal nitrogen at a high nitrification rate, enable the treatment system to be miniaturized, and are highly safe and advantageous in terms of cost. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic configuration diagram showing an example of a biological nitrification system according to an embodiment. [Diagram 2]FIG. 2 is a schematic diagram for explaining a method for measuring the average density of a plurality of organism retainers. [Diagram 3] FIG. 2 is a schematic diagram for explaining a method for measuring the average density of a plurality of organism retainers. [Figure 4] FIG. 2 is a schematic configuration diagram showing another example of a biological nitrification system according to an embodiment. [Diagram 5] FIG. 1 is a schematic diagram showing an example of a conventional biological nitrification system. [Figure 6] FIG. 1 is a schematic diagram showing an example of a conventional biological nitrification system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] As used herein, the following terms have the following meanings: "Ammoniacal nitrogen" refers to nitrogen contained in water as ammonium salts. It is also called ammoniacal nitrogen. The symbol "~" indicating a range of numerical values ​​means that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0017] <Water to be treated> In one embodiment, the water to be treated is not particularly limited as long as it contains at least ammonia nitrogen. For example, groundwater, well water, lake water, river water, industrial water, sewage, wastewater, etc. can be mentioned. However, the water to be treated is not limited to these examples.

[0018] In addition to ammonia nitrogen, the water to be treated may further contain anions such as bicarbonate ions, nitrate ions, sulfate ions, and chloride ions, cations such as iron ions, manganese ions, calcium ions, and magnesium ions, organic matter, bacteria, etc. However, the components of the water to be treated are not limited to these. The main components of the organic matter in the water to be treated include humic acid, fulvic acid, etc. However, the water to be treated may contain organic matter other than these exemplified components.

[0019] The content of ammoniacal nitrogen in the water to be treated is not particularly limited, but is, for example, within the range of 0.1 to 15 mg / L. When the content of ammoniacal nitrogen is 0.5 mg / L or more, preferably 1 mg / L or more, the merit of applying a biological nitrification method and a nitrification system that can realize a high nitrification rate is further increased. When a high concentration of ammoniacal nitrogen is contained (for example, when the content of ammoniacal nitrogen is 15 to 50 mg / L), it is preferable to use multiple nitrification tanks. The iron content of the water to be treated is not particularly limited, but is, for example, in the range of 0 to 20 mg / L. According to the biological nitrification method and nitrification system of one embodiment, a high nitrification rate can be achieved even when the water to be treated contains iron.

[0020] <Bionitrification System> FIG. 1 is a schematic configuration diagram showing an example of a biological nitrification system according to an embodiment. The biological nitrification system 1A comprises: a lifting pump 3 for pumping up well water (an example of water to be treated) from a well 2; a treated water supply pipe 4A having a first end connected to the lifting pump 3 and a second end connected to the bottom of the nitrification tank 5; a water flow rate adjustment means (not shown) provided midway through the treated water supply pipe 4A for adjusting the flow rate of the treated water supplied to the nitrification tank 5; an aeration section 7, an air supply pipe 8 and a blower 9 of an aeration device that diffuses air within the nitrification tank 5; a control device (not shown) electrically connected to the water flow rate adjustment means and the aeration device; and a treated water outflow pipe 10A connected to a wall surface near the top of the nitrification tank 5.

[0021] The water to be treated supply pipe 4A supplies well water from the well 2 as the water to be treated into the nitrification tank 5. A water flow rate measuring means (not shown) for measuring the amount of water to be treated supplied to the nitrification tank 5 and a water flow rate adjusting means are provided midway through the water to be treated supply pipe 4A. An example of the water flow rate adjusting means is a flow rate adjusting valve. Examples of the water flow rate measuring means include a rotameter and an electromagnetic flowmeter. The untreated water supply pipe 4A may be provided with a water quality meter for measuring the iron content and ammoniacal nitrogen content of the untreated water to be supplied to the nitrification tank 5.

[0022] The nitrification tank 5 is for treating ammonia nitrogen in the water to be treated by biological nitrification reaction using the organism retainers 6. The nitrification tank 5 is loaded with a plurality of organism retainers 6. In the nitrification tank 5, a plurality of organism retainers 6 are loaded to form an organism retainer region 11. In the organism retainer region 11, each organism retainer 6 is loaded so as to be able to swing when the water to be treated is passed through it. In the nitrification tank 5, the water to be treated is brought into contact with each of the biological holders 6 in the biological holder area 11, and ammonia nitrogen in the water to be treated is oxidized to produce treated water. The linear velocity of the water to be treated passing through the biological holder 6 is LV 通水 [m / h].

[0023] The bioretainer region 11 may be formed by covering the bottom of the nitrification tank 5 with a plurality of bioretainers 6 and stacking the plurality of bioretainers 6 in multiple stages in the height direction of the nitrification tank 5.

[0024] The volume of the nitrification tank 5 is not particularly limited. For example, it may be 0.1 to 100 m 3 The material of the nitrification tank 5 is not particularly limited. Examples include acrylic resin, fiber-reinforced resin, etc. From the viewpoint of facilitating observation of the organism holder 6 in the nitrification tank 5, a transparent material is preferable, and acrylic resin is more preferable.

[0025] The organism retainer 6 is a carrier that retains nitrifying bacteria. That is, the organism retainer 6 has a carrier and nitrifying bacteria retained on the carrier. The shape of the carrier is not particularly limited, and examples thereof include a cube, a rectangular parallelepiped, a sphere, a cone, a polygonal pyramid, a cylinder, and a filament. However, in consideration of the ease of shaking during water flow and the ease of loading into the nitrification tank 5, a rectangular parallelepiped, a cube, and a sphere are preferred. Furthermore, the shapes of the carriers in the multiple organism holders 6 do not all need to be the same, and they may be different shapes. From the viewpoint of making it easier to maintain the oscillating state and to make it easier to carry out the nitrification reaction uniformly, it is preferable that the carriers have the same shape, but this is not necessarily limited to this.

[0026] As the carrier, a porous carrier is preferable because it can support nitrifying bacteria on the surface and inside of the carrier, i.e., it can support a large number of nitrifying bacteria and further improve the nitrification rate. When the carrier is porous, the nitrifying bacteria may be supported inside the carrier. The pore size of the porous carrier is preferably about 0.01 to 3 mm, more preferably about 0.05 to 1 mm, and even more preferably about 0.1 to 0.5 mm.

[0027] In particular, sponge carriers are preferred because they can maintain the support of nitrifying bacteria well and minimize damage to pumps and piping. Examples of materials for the sponge carrier include polyvinyl alcohol, polyethylene glycol, and polyurethane.

[0028] The apparent surface area of ​​the sponge carrier is 300 m 2 / m 3 More than 600m is preferable. 2 / m 3 When the apparent surface area of ​​the sponge carrier is equal to or greater than the lower limit, the surface area is sufficiently large, and the contact efficiency with the water to be treated is increased. In addition, the sponge carrier is more likely to retain nitrifying bacteria, and the oxygen supply efficiency is also increased, resulting in a higher nitrification rate.

[0029] The nitrifying bacteria include known nitrifying bacteria used in biological nitrification of ammonia nitrogen. Nitrosomonas is a representative nitrifying bacteria, which is autotrophic and basically uses carbon dioxide as the only carbon source. It does not require an organic substrate and can grow in the presence of ammonia, but its growth rate is extremely slow. Therefore, in order to increase the nitrification rate, it is necessary to carry out an operation to hold a large amount of nitrifying bacteria in the nitrification tank. Therefore, it is preferable to hold the nitrifying bacteria on a carrier rather than as suspended cells. An example of a method for supporting nitrifying bacteria on a carrier is to introduce the carrier into a nitrification tank of an existing water treatment system and grow the nitrifying bacteria on the surface of the carrier.

[0030] The average density of the bioretainer 6 is 1.0 to 1.4 g / cm 3 and 1.05 to 1.30 g / cm 3 is preferably 1.10 to 1.20 g / cm 3 Here, the average density of the organism support 6 is the average density when each organism support 6 supports nitrifying bacteria in a wet state. The wet state will be described later. If the average density of the organism retainers 6 is equal to or greater than the lower limit of the aforementioned range, the organism retainers 6 will sink into the stored water in the nitrification tank 5. Therefore, the water to be treated will come into uniform contact with the entirety of the multiple organism retainers 6, and the nitrification reaction will tend to occur uniformly in the nitrification tank 5. If the average density of the organism retainer 6 is equal to or less than the upper limit of the range, the organism retainer 6 is easily oscillated. Therefore, the organism retainer 6 can be kept oscillating even without aeration by an aeration device when water is passed through. As a result, the energy consumption of the aeration device can be reduced, providing further advantages in terms of cost. Therefore, if the average density of the organism retainers 6 is within the above range, the organism retainers 6 can oscillate in the stored water when the water to be treated passes through them, so that impurities (such as SS) in the water to be treated are less likely to adhere to the organism retainers 6. As a result, the organism retainers can be easily oscillated when water passes through them, improving the contact efficiency between the water to be treated and each organism retainer, and improving the nitrification rate. This is also advantageous in terms of cost.

[0031] The average density of the bioretainer can be calculated as follows. First, the mass m [g] of a plurality of bioretainers is measured. For example, as shown in Fig. 2, a container 20 with a known volume is placed on a mass meter 30, and the bioretainers 6 are removed from the nitrification tank and loaded into the container 20 so that the bulk volume is constant. To keep the bulk volume constant, a reference line L is drawn on the side of the container 20 with a known volume, and the bioretainers 6 are loaded into the container 20 so that the reference line L coincides with the top surface of the uppermost bioretainer 6.

[0032] When the biological holder is removed from the nitrification tank, the retained water adhering to the carrier drips off the biological holder. The mass of this dripping retained water is not included in the mass m [g] of the multiple biological holders. In this embodiment, a bulk volume of 500 cm is removed from the nitrification tank. 3 The bioretainer is defined as being in a "wet state" when water droplets stop dripping for 5 seconds or more. Such a bioretainer in a wet state is loaded into the container 20. The process of removing the bioretainers from the nitrification tank and loading them into container 20 is then repeated, and the mass of the multiple bioretainers when their total bulk volume reaches a predetermined value is recorded as the mass m [g] of the multiple bioretainers.

[0033] Next, the volume V [cm 3 3, water is poured from a separately prepared beaker 40 into a container 20 loaded with wet organism retainers 6 until a predetermined bulk volume is reached, i.e., up to the reference line L, and the spaces between the organism retainers 6 are filled with water. At this time, the amount of water poured from the beaker 40 into the container 20 is measured, and the difference between the predetermined bulk volume and the amount of water poured from the beaker 40 is taken as the volume V [cm of the multiple organism retainers. 3 ]. Finally, the mass m [g] of the multiple bioretainers is expressed as the volume V [cm 3 ] to obtain the average density of the bioretainer 6 m / V [g / cm 3 ].

[0034] The average volume of one bioretainer is 0.03 to 5.00 cm, taking into consideration the shaking caused by water flow. 3 is preferable, and 0.06 to 1.00 cm 3 More preferably, 0.10 to 0.30 cm 3 It is considered that it is more preferable. If the volume of one bioretainer is equal to or greater than the lower limit of the above range, the bioretainer is less likely to flow in the nitrification tank, and the nitrification rate is likely to be improved. If the volume of one bioretainer is equal to or less than the upper limit of the above range, the LV 空気 It is considered that the biological support is easily shaken even if the size is relatively small. Here, the average volume of one biological retainer is the total volume of a plurality of biological retainers in the nitrification tank divided by the number of biological retainers in the nitrification tank. Furthermore, in a plurality of bioretainers, the volumes of each bioretainer do not all need to be the same, and may be different from one another.

[0035] The bioretainer can be prepared, for example, as follows. The carrier is cultured by passing water through the nitrification tank of an existing biological nitrification system. For example, the density of a new porous carrier is 1g / cm because it contains air inside. 3 It is often less than this value. When the carrier is cultured in a nitrification tank, air gradually escapes from the carrier and nitrifying bacteria adhere to the carrier. The density of the carrier in a wet state containing nitrifying bacteria and water is 1.0 to 1.4 g / cm. 3 The culture is continued in water until the bacteria reach the range of 0.1% to 1.0%, to prepare a bioretainer.

[0036] In the biological nitrification system 1A shown in Fig. 1, the air diffuser is configured to include an air diffuser section 7 located near the bottom of the nitrification tank 5, an air supply pipe 8 that supplies air to the air diffuser section 7, a blower 9 provided at one end of the air supply pipe 8, and an air supply amount adjustment means (not shown) provided midway along the air supply pipe 8 between the air diffuser section 7 and the blower 9. In principle, the air diffuser is intended to aerate and remove solid matter adhering to the surface of the organism retainer 6. However, the aerated air at this time can also serve as an oxygen source for the nitrifying bacteria in the organism retainer 6.

[0037] Examples of the aeration unit 7 include an aeration tube with an aeration hole (not shown), an aeration ball, a diffuser, etc. The aeration device removes solid matter adhering to the surface of the organism holder 6 by air bubbles supplied from the aeration unit 7 into the nitrification tank 5. The linear velocity of the air supplied to the stored water in the nitrification tank 5 is LV 空気 [m / h].

[0038] The air supply amount adjusting means may be, for example, a gate valve, a butterfly valve, or the like. However, in the biological nitrification system according to one embodiment, when the iron content of the water to be treated is 0.5 mg / L or less, an aeration device is not necessary, and the aeration unit 7, air supply pipe 8, blower 9, etc. can be omitted.

[0039] The treated water outlet pipe 10A is for taking out the treated water from the nitrification tank 5. An outflow volume measuring means (not shown) for measuring the volume of treated water flowing out from the nitrification tank 5 and an outflow volume adjusting means (not shown) for adjusting the flow rate of treated water flowing through the treated water outflow pipe 10A are provided midway along the treated water outflow pipe 10A. Examples of the outflow amount measuring means include a rotameter, an electromagnetic flowmeter, and the like. An example of the outflow rate adjusting means is a flow rate adjusting valve.

[0040] The control device includes an interface unit (not shown), a storage unit (not shown), a processing unit (not shown), a determination unit (not shown), a control unit (not shown), and the like. The interface unit electrically connects the control unit with the water flow measurement means, the water flow adjustment means, the water quality meter, the outflow measurement means, the outflow adjustment means, the blower and the air adjustment means of the air diffuser.

[0041] The memory section stores the linear velocity ratio (LV 空気 / LV 通水 ) and the operating conditions of the biological nitrification system 1A for calculating the filling rate calculated by the following formula (1). Filling rate (volume %)=((total volume of the plurality of biological retainers 6) / (sum of the total volume of the plurality of biological retainers 6 and the volume of the stored water in the nitrification tank 5))×100 Formula (1)

[0042] The operating conditions stored in the memory unit include, for example, the projected area of ​​the nitrification tank 5, the average density of the biological holder 6 (1.0 to 1.4 g / cm 3 (values ​​within the range of 100%), the total mass and number of the organism holders 6 loaded in the nitrification tank 5, the supply amount of water to be treated, the outflow amount of treated water, and the amount of air supplied to the air diffuser.

[0043] In the biological nitrification system 1A, the "total volume of the plurality of biological supports 6" in formula (1) is the sum of the volumes of all the biological supports 6 that make up the biological support region 11. This "total volume of the biological supports" can be calculated, for example, by dividing the total mass of all the biological supports 6 placed in the nitrification tank 5 by the average density of the biological supports.

[0044] In the biological nitrification system 1A, the "volume of stored water in the nitrification tank 5" in formula (1) is the total volume of the water to be treated and the treated water present in the nitrification tank 5. This "volume of stored water in the nitrification tank 5" can be calculated, for example, from the integrated value of the supply amount of the water to be treated measured by the water flow rate measuring means and the integrated value of the outflow amount of the treated water measured by the outflow rate measuring means.

[0045] The processing unit can perform the following operation 1. Calculation 1: The total volume of the plurality of organism holders 6 and the volume of the stored water in the nitrification tank 5 are calculated, and then the packing rate of the organism holders 6 is calculated from the above formula (1).

[0046] The processing unit can also perform the following operation 2. Calculation 2: LV from the flow rate value of the water flow rate adjustment means and the projected area of ​​the nitrification tank 5 通水 Calculate LV from the supply value of the air amount adjusting means and the projected area of ​​the nitrification tank 5. 空気 Calculate the linear velocity ratio (LV 空気 / LV 通水 ) is calculated.

[0047] The judgment unit judges whether the filling rate of the organism holder 6 calculated by the processing unit is 25 volume % or more; 空気 / LV 通水 ) is 5.0 or less; and whether the iron content of the treated water measured by a water quality meter is 1.0 mg / L or more.

[0048] The control unit controls the biological nitrification system 1A based on the judgment result in the judgment unit, the operating conditions of the biological nitrification system 1A stored in the memory unit, etc. In particular, the control unit controls the filling rate of the organism holder 6 to 25 volume % or more and the linear velocity ratio (LV 空気 / LV 通水 ) is controlled to be 5.0 or less. For example, if the judgment unit determines that the filling rate of the biological retainer 6 is less than 25 volume %, the control unit can control the water flow rate adjustment means to reduce the supply of treated water and reduce the volume of stored water in the nitrification tank 5; or control the outflow rate adjustment means to increase the outflow rate of treated water and reduce the volume of stored water in the nitrification tank 5.

[0049] On the other hand, the linear velocity ratio (LV 空気 / LV 通水 ) is determined to be greater than 5.0, the control unit reduces the amount of air supplied by the air diffusion unit 7 to 空気 By controlling the air volume adjustment means to lower the LV [m3 / h], or by increasing the supply of water to be treated, 通水 By controlling the water flow rate adjustment means to increase the LV 通水 The outflow rate adjusting means can be controlled to increase the flow rate [m / h]. In addition, if the iron content of the treated water is judged to be more than 0.5 mg / L in the judgment section, LV 空気 / LV 通水 The control unit controls the air amount adjusting means to adjust the amount of air supplied by the aeration unit 7 so that LV is 0.20 to 5.0; and adjusts the flow rates of the water flow rate adjusting means and the outflow rate adjusting means. 通水 You can adjust the following.

[0050] The processing unit, the determination unit and the control unit may be realized by dedicated hardware, or may be composed of a memory and a central processing unit (CPU), and the functions of the processing unit, the determination unit and the control unit may be realized by loading into the memory and executing a program for realizing the functions of the processing unit, the determination unit and the control unit. The control device may be connected with an input device, a display device, etc. as peripheral devices. Examples of the input device include input devices such as a display touch panel, a switch panel, and a keyboard. Examples of the display device include display devices such as a liquid crystal display device and a CRT.

[0051] <Biological nitrification method> An example of a nitrification method using the biological nitrification system 1A will be described below. First, a plurality of organism retainers 6 cultured in a nitrification tank of an existing biological nitrification system are loaded into the nitrification tank 5 of the biological nitrification system 1A. At this time, it is advisable to leave a space between the organism retainers 6 for rocking so that the organism retainers 6 can rock when water is passed through them.

[0052] Next, the water pump 3 provided at one end of the water supply pipe 4A is driven to supply the water to be treated containing ammonia nitrogen from the well 2 through the water supply pipe 4A to the nitrification tank 5, where it is stored in the nitrification tank 5. As water is stored in the nitrification tank 5 at this time, the spaces between the biological holders 6 in the biological holder region 11 are filled with water. As the water storage continues, the biological holder 6 at the top of the biological holder region 11 becomes immersed in the stored water.

[0053] (Biological nitrification reaction) When the water to be treated is passed through the biological retainer region 11 in the nitrification tank 5, the water to be treated comes into contact with the biological retainers 6. Then, ammoniacal nitrogen in the water to be treated is oxidized to nitrate nitrogen by the nitrifying bacteria in the biological retainer 6. In this manner, the water to be treated containing ammoniacal nitrogen is treated in the nitrification tank 5 to produce treated water. At this time, in the biological nitrification system 1A, the water to be treated is passed through the multiple biological retainers 6 in the biological retainer region 11 as an upward flow.

[0054] When water is stored in the nitrification tank 5, the filling rate calculated by the following formula (1) is set to 25% by volume or more. Filling rate (volume %)=((total volume of the plurality of biological retainers 6) / (sum of the total volume of the plurality of biological retainers 6 and the volume of the stored water in the nitrification tank 5))×100 Formula (1)

[0055] In this embodiment, the packing rate calculated by formula (1) is set to 25% by volume or more, so that the nitrification rate is sufficiently high. In terms of increasing the nitrification rate, the packing rate calculated by formula (1) is preferably set to 32% by volume or more, more preferably set to 42% by volume or more, and even more preferably set to 45% by volume or more. The upper limit of the filling rate calculated by the above formula (1) is 100% by volume, but in terms of agitating the biological retainer 6 when water is passed through it, it is preferable to set it to 65% by volume or less, more preferably 60% by volume or less, and even more preferably 55% by volume or less.

[0056] (Filling rate control) When the determination section of the control device determines that the filling rate of the organism retainer 6 is less than 25% by volume, the control section can control the water flow rate adjustment means to reduce the supply of water to be treated and reduce the volume of the stored water in the nitrification tank 5; or control the outflow rate adjustment means to increase the outflow rate of treated water and reduce the volume of the stored water in the nitrification tank 5. In addition to reducing the volume of the stored water, the organism retainer 6 may be replenished in the nitrification tank 5 manually by an operator or automatically by the control device.

[0057] (Linear velocity ratio control) In this embodiment, the linear velocity ratio (LV 空気 / LV 通水 ) is set to 5.0 or less. With this configuration, the biological holder can be kept in a state of oscillation for a long time when water is passed through it, the nitrification reaction can be carried out uniformly, and the water to be treated containing a high concentration of ammonia nitrogen can be treated at a high nitrification rate. In addition, since there is no need to supply air more than necessary, it is advantageous in terms of cost and safety. Therefore, the linear velocity ratio (LV 空気 / LV 通水 ) is preferably set to a value of 0.1 to 4.0, and more preferably set to a value of 0.5 to 1.0.

[0058] The control device judges the linear velocity ratio (LV 空気 / LV 通水) is determined to be greater than 5.0, the control unit reduces the amount of air supplied by the air diffusion unit 7 to 空気 By controlling the air volume adjustment means to lower the LV [m3 / h], or by increasing the supply of water to be treated, 通水 By controlling the water flow rate adjustment means to increase the LV 通水 The outflow rate adjusting means can be controlled to increase the flow rate [m / h].

[0059] L.V. 通水 The LV is not particularly limited, but is preferably in the range of 5 to 40 m / h, more preferably 8 to 30 m / h, and even more preferably 10 to 15 m / h. 通水 If is equal to or greater than the lower limit of the range, the organism holder 6 is likely to swing. 通水 When the ratio is equal to or less than the upper limit of the above range, the nitrification reaction efficiency is easily maintained, and the nitrification rate is easily improved.

[0060] (LV 空気 Control of The amount of air diffused from the air diffuser 7 of the air diffuser can be adjusted to any amount by an air amount adjusting means (not shown). 空気 The LV is preferably 50 m / h or less, and more preferably 30 m / h or less. When the iron content of the water to be treated is 0.5 mg / L or less, the LV 空気 It is preferable that the flow rate is 0 m / h, i.e., no air is supplied.

[0061] In the biological nitrification system according to one embodiment, when the amount of components that can adhere to the surface of the biological retainer 6 is small, for example when the iron content of the water to be treated is 0.5 mg / L or less, aeration by an aeration device is not necessary. This is because the biological retainer 6 oscillates when water is passed through it, so that solid matter is less likely to adhere to the surface of the biological retainer 6. Omission of aeration provides a further advantage in terms of cost. On the other hand, when the iron content of the water to be treated is, for example, more than 0.5 mg / L, particularly 1.0 mg / L or more, there is a possibility that a large amount of solid matter such as iron hydroxide produced during the nitrification reaction will adhere to the surface of the biological retainer. 空気 / LV 通水 It is preferable to adjust the amount of air supplied from the aeration unit 7 into the nitrification tank 5 by driving the aeration device so that the ratio of the aeration rate to the total aeration rate is 0.20 to 5.0. This is because solid matter adhering to the surface of the organism retainer 6 can be removed by aeration, thereby increasing the nitrification rate. Other than that, LV 空気 / LV 通水 LV from the flow rate of the water flow rate adjustment means and the outflow rate adjustment means so that 通水 may be adjusted.

[0062] <Mechanism of action> In the bionitrification method according to one embodiment described above using one example, (i) the average density of the bioretainer, (ii) the specific packing rate of the bioretainer, and (iii) the linear velocity ratio (LV 空気 / LV 通水 ) satisfy the above-mentioned three conditions. Therefore, the biological retainer can oscillate in the nitrification tank when water is passed through, and solid matter is less likely to adhere to the surface of the biological retainer. In addition, the nitrification reaction can be carried out uniformly. As a result, the reaction efficiency of the nitrification reaction by the biological retainer is improved. In addition, because the biological retainer can oscillate, the water to be treated comes into efficient contact with the entire biological retainer when passing through it. As a result, even if the filling rate of the biological retainer is set to 25% by volume or more, it is possible to prevent the occurrence of short-circuiting flow and the occurrence of dead spaces that do not come into contact with the biological retainer 6, and the nitrification rate is improved, thereby achieving an excellent nitrification rate.

[0063] According to this embodiment, since an excellent nitrification rate can be achieved, there is less need to increase the number of nitrification tanks, and the nitrification tanks themselves can be made smaller. In addition, since air is supplied to the nitrification tank instead of high-concentration oxygen gas, the safety is high. In addition, the linear velocity ratio (LV 空気 / LV 通水Since the amount of air supply is controlled so that the airflow is within a specified range, the energy consumption of the air diffuser is reduced, which is also advantageous in terms of cost. Therefore, according to one embodiment of the biological nitrification method, the treatment water containing a high concentration of ammoniacal nitrogen can be treated at a high nitrification rate, the treatment system can be made compact, it is highly safe, and it is also advantageous in terms of cost.

[0064] For example, in a fluidized bed mixed flow type nitrification method as described in Patent Document 2, when the packing rate becomes 25 volume % or more, dead space and short circuit flow occur due to poor fluidity of the carrier, so there is a limit to how quickly the nitrification rate can be increased. In contrast, in this embodiment, the organism retainer oscillates when water is passed through, and the water to be treated comes into contact with the organism retainers efficiently overall. Therefore, even if the predetermined filling rate is set to 25% by volume or more, it is possible to prevent the occurrence of short-circuiting flow and the occurrence of dead spaces where the water does not come into contact with the organism retainers, and as a result, the nitrification rate can be increased.

[0065] In this embodiment, the biological retainer can be swung in the water stored in the nitrification tank. Therefore, when the iron content of the water to be treated is 0.5 mg / L or less, the solid matter attached to the surface of the biological retainer can be sufficiently removed without aeration by an aeration device, and the efficiency of the nitrification reaction can be maintained high to achieve a high nitrification rate. In this case, the energy consumption of the aeration device can be further reduced, resulting in a significant cost effect. On the other hand, as shown in the examples described later, even when the iron content of the water to be treated exceeds 0.5 mg / L, ammoniacal nitrogen can be treated at a high nitrification rate.

[0066] Furthermore, since the biological nitrification system 1A described above has the configuration described above, the biological nitrification method according to the embodiment described above can be carried out by using the biological nitrification system 1A, and the above-mentioned mechanism of action can be exerted.

[0067] <Other embodiment examples> Although one embodiment has been described above by showing one embodiment, the present invention is not limited to the embodiment disclosed in this specification, and can be appropriately modified and implemented without departing from the gist of the invention. The embodiment disclosed in this specification can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention.

[0068] For example, biological nitrification system 1B shown in Fig. 4 differs from biological nitrification system 1A in that a treated water supply pipe 4B is connected to a wall surface near the top of nitrification tank 5, and a treated water outlet pipe 10B is connected to the bottom of nitrification tank 5. In this biological nitrification system 1B, when the treated water is passed through the biological holder 6, the treated water flows downward from the upper side to the lower side of the biological holder region 11. Even when the water to be treated flows downward as in the biological nitrification system 1B, the same effects as in the biological nitrification system 1A can be obtained, and a high nitrification rate can be realized.

[0069] In addition, the number of nitrification tanks is not limited to one, and may be multiple. For example, when the ammonia nitrogen content of the water to be treated is 2 mg / L or less, the number of nitrification tanks may be one, but when the ammonia nitrogen content of the water to be treated is 2 to 6 mg / L, the number of nitrification tanks may be increased to multiple, or the number of nitrification tanks equipped with an aeration device to promote the nitrification reaction may be one. For example, the number of nitrification tanks equipped with an aeration device may be increased by one every time the ammonia nitrogen content increases by about 6 mg / L. The aeration device is not limited to the type shown in the figure, and various types of aeration devices can be used. In addition, a DO meter that measures the dissolved oxygen concentration (DO) of the water stored in the nitrification tank 5 may be used.

[0070] Although not shown in the figures, a pre-treatment device that performs pre-treatment on the water to be treated that is supplied to the nitrification tank 5 and a post-treatment device that performs post-treatment on the treated water flowing out from the nitrification tank 5 may be used below. The pre-treatment device and the post-treatment device may be installed as appropriate depending on the water quality of the water to be treated and the water quality of the treated water. Examples of the pretreatment device include a raw water storage tank, a dissolved oxygen supplying device, a sand filter tower, etc. In order to increase the efficiency of the biological nitrification reaction, it is also preferable to install a separate dissolved oxygen supplying device. The dissolved oxygen supplying device is an aeration device for supplying dissolved oxygen, and is different from the aeration device in the above-mentioned embodiment. When there are multiple biological nitrification tanks in the raw water storage tank or between the raw water storage tank and the biological nitrification tank, it is better to install this aeration device between each biological nitrification tank so as not to directly affect the shaking state of the biological retainer in the biological nitrification tank. Examples of downstream treatment devices include an ion exchange treatment tank, a flocculant addition device, an oxidant addition device, a sand filtration tower, a membrane filtration device, a disinfectant addition device, and the like. The use of the final treated water after the second stage treatment is not particularly limited, and examples thereof include, but are not limited to, use as domestic water, drinking water, etc. EXAMPLES

[0071] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[0072] <Preparation of treated water> Ammonium chloride and iron sulfate heptahydrate were added to the collected groundwater to prepare the following treated water (1) to (4). The groundwater temperature at the time of collection was 17±1°C, the alkalinity was 85 mg / L, and the pH was 7.6±0.2. Treated water (1): Simulated groundwater with an ammonia nitrogen concentration of 2.5 mg / L and an iron ion concentration of 0.0 mg / L. Treated water (2): Simulated groundwater with an ammonia nitrogen concentration of 2.5 mg / L and an iron ion concentration of 0.5 mg / L. Treated water (3): Simulated groundwater with an ammonia nitrogen concentration of 2.5 mg / L and an iron ion concentration of 1.0 mg / L. Treated water (4): Simulated groundwater with an ammonia nitrogen concentration of 2.5 mg / L and an iron ion concentration of 3.0 mg / L.

[0073] <Test system construction> (biological support) A polyurethane sponge carrier with a 5 mm square cube (Technoform Japan Co., Ltd., "Waterflex AQ-15") was prepared as the sponge carrier. The density of the sponge carrier before water culture was 0.044 g / cm 3 These sponge carriers were cultured in the nitrification tank of an existing biological nitrification system, and about 11 kg (about 13,000 pieces) of biological retainers were prepared. After the culture, the biological retainers were scooped out of the nitrification tank and held on the water surface. When water droplets stopped dripping for more than 5 seconds, the biological retainers were judged to be in a wet state, and were then loaded into a 10 L graduated container. When the bioretainer was finished loading into the 10 L graduated vessel, the mass m of the bioretainer was 5776 g. After that, water was poured from a separately prepared beaker into the graduated container in which the bioretainers were loaded to fill the spaces between the bioretainers with water, and when the water level reached the 10 L mark, the water pouring was stopped. The amount of water poured from the separately prepared beaker at this time was 4767 cm 3 Therefore, the volume of the bioretainer, V, was set to 10,000 cm 3 (10L)-4767cm 3 =5233cm 3 It was decided. Therefore, the average density of the bioretainer is 5776g / 5233cm 3 ≒1.1g / cm 3 It was calculated that:

[0074] (nitrification tank) Two cylindrical transparent acrylic tanks were connected in series. Each tank had a diameter of 150 cm, a height of 750 cm, and an effective water volume of 13.5 L. An aeration ball was installed at the bottom of each tank. The first and second tanks were each loaded with approximately 6 kg of biological retainers and used as tanks for nitrification reactions. In addition, the raw water storage tank and treated water at the outlet of the first tank were aerated using a dissolved oxygen supply device until the dissolved oxygen concentration was fully saturated before being passed through the tank.

[0075] (Biological nitrification system) A biological nitrification system similar to biological nitrification system 1A shown in Figure 1 was prepared, except for the number of nitrification tanks. As mentioned above, the raw water storage tank and treated water from the outlet of the first tank were aerated using a dissolved oxygen supply device until the dissolved oxygen concentration was fully saturated, and then the water was passed through the system. With all of the biological retainers in the nitrification tank immersed in the stored water, air was continuously supplied from the air diffuser at the bottom of the tank, and the LV 空気 The LV was gradually increased from 0m / h, 10m / h, 30m / h, and 60m / h, and the rocking state of the loaded biological support weighing about 11 kg was visually confirmed. 空気 At 30 m / h, about half of the bioretainers started to flow, but the rest of the bioretainers were able to maintain the oscillating state. 空気 When the flow rate was 60 m / h, almost all of the bioretainers were flowing. On the other hand, while measuring the ammonia nitrogen concentration of the treated water after the nitrification reaction, the amount of water passing through was gradually increased, and the LV was set so that the ammonia concentration of the treated water in the second tank could be maintained at 0.1 mg / L or less. 通水 The maximum value of [m3 / h] was obtained. As a result, in the case of the biological nitrification system of this example, the maximum value was 17.8 m3 / h.

[0076] <Measurement method> (LV 空気 ) Air supply volume [m 3 / h] is the projected area of ​​the tank [m 2 Divide by LV 空気 [m / h] was calculated.

[0077] (LV 被処理水 ) Supply volume of treated water [m 3 / h] is the projected area of ​​the tank [m 2 Divide by LV 被処理水 [m / h] was calculated.

[0078] <Examples 1 to 6 and Comparative Examples 1 to 7> The water to be treated (1) was passed through the biological retainer in the nitrification tank under the conditions shown in Table 1. LV 空気 In each example where the flow rate was 0 m / h, no air was supplied, and in the other examples, air was continuously supplied from an air diffuser. LV after starting water flow 通水 As the concentration of ammonia in the treated water increased gradually, the biological nitrification reaction could not keep up, and ammonia nitrogen concentrations of 0.1 mg / L or more were detected in the treated water. 3 On the other hand, the LV that can maintain the ammonia nitrogen concentration in the treated water at 0.1 mg / L or less was 通水 The maximum water flow rate M [m 3 / d] and the nitrification rate v [kgN / m 3 / d] was calculated. The results are shown in Table 1.

[0079] Nitrification rate v[kgN / m 3 / d] was calculated as follows: Nitrification rate v[kgN / m 3 / d] = (ammonia nitrogen concentration in the treated water [kg / m 3 ]-Ammonia nitrogen concentration in treated water [kg / m 3 ])×LV 通水 The maximum water flow rate M [m 3 / d]÷Tank volume [m 3 ]

[0080] The nitrification rate was then evaluated according to the following criteria, and the results are shown in Table 1. ◎: Nitrification rate is 0.44kgN / m 3 / d or more. 〇: Nitrification rate is 0.25kgN / m 3 / d over 0.44kgN / m 3 / d or less. △: Nitrification rate is 0.22kgN / m 3 / d over 0.25kgN / m 3 / d or less. ×: Nitrification rate is 0.22kgN / m 3 / d or less.

[0081] <Example 7> A biological nitrification reaction was carried out in the same manner as in Example 6, except that a biological nitrification system similar to the biological nitrification system 1B shown in Figure 4 was prepared, that is, that the water to be treated was passed through the multiple biological retainers 6 in the biological retainer region 11 as a downward flow. As in Example 1, the nitrification rate v [kgN / m 3 The results are shown in Table 1.

[0082] [Table 1]

[0083] As shown in Table 1, the average density of the bioretainer, the packing ratio of the bioretainer and the linear velocity ratio (LV 空気 / LV 通水 ) satisfies the specified reaction conditions, excellent nitrification rate can be achieved. Furthermore, as shown in the results of Examples 6 and 7 in Table 1, excellent nitrification rates were achieved in both the upward and downward water flow directions.

[0084] Regarding the oscillating state in each example, in Comparative Examples 1 to 5, all of the biological retainers flowed and could not maintain the oscillating state. In contrast, in Examples 1 to 7, the biological retainers were able to maintain the oscillating state. In Comparative Example 6, although the oscillating state of the biological retainers was maintained, it is believed that the nitrification rate decreased due to the low packing rate. In Comparative Example 7, manganese sand (average density 2.0 g / cm3) was used as a filter medium in the biological nitrification tank. 3 ) was filled to 50% by volume and water was passed through. As a result, the average density of the bioretainers was high, making them difficult to shake. In addition, dead spaces and short-circuiting were likely to occur, and solid matter was likely to adhere to the surface of the bioretainers, causing blockages, which reduced the contact efficiency between the water to be treated and each bioretainer. Another reason for the lower nitrification rate compared to the other examples is thought to be that the bioretaining capacity of the manganese sand was lower than that of the bioretainers in the examples.

[0085] <Examples 8 to 13> In Examples 8 to 13, reaction conditions were examined when the water to be treated contained iron. Specifically, the nitrification rate v [kgN / m 3 / d] was calculated and evaluated.

[0086] [Table 2]

[0087] As shown in Tables 1 and 2, air was not supplied from the air diffuser, and the LV 通水 In Example 8, the LV 通水 It was possible to achieve an excellent nitrification rate similar to that of Example 3, in which the flow rate was 12.5 m / h. From this result, it was considered that even when the iron content was 0.5 mg / L, aeration by an aeration device was not necessary and the energy consumption of the aeration device could be reduced. On the other hand, when the iron content was more than 0.5 mg / L (for example, 1.0 mg / L), the nitrification rate decreased by about 50% as shown in the results of Example 9 in which aeration was not performed.

[0088] As shown in the results of Examples 10 to 13, when the iron content exceeds 0.5 mg / L, air is supplied by an air diffuser and the linear velocity ratio (LV 空気 / LV 通水 By keeping the linear velocity ratio (LV) below 5.0, a good nitrification rate was achieved. 空気 / LV 通水 It was believed that by setting the ratio of iron to iron in the range of 0.20 to 5.0, an excellent nitrification rate could be achieved even with an increased iron content.

[0089] As shown in the results of Examples 11 and 13, the linear velocity ratio (LV 空気 / LV 通水 When the iron content was set to 1.0 mg / L or 3.0 mg / L, an extremely good nitrification rate was achieved when the iron content was set to 0.7. [Explanation of symbols]

[0090] 1. Biological nitrification system 2. Well 3. Water Pump 4. Treated water supply pipe 5 Nitrification tank 6 Biological support 7. Aeration section (aeration device) 8 Air supply pipe (air diffuser) 9 Blower (air diffuser) 10 Treated water outflow pipe

Claims

1. A biological nitrification method for treating ammonia nitrogen in water to be treated, comprising the steps of: Average density is 1.0 to 1.4 g / cm ３ When the water to be treated is passed through a nitrification tank loaded with a plurality of biological retainers in an upward or downward direction, The linear velocity LV of the water to be treated 通水 [m / h] and the linear velocity LV of the air in the water stored in the nitrification tank 空気 [m / h] and linear velocity ratio (LV 空気 / LV 通水 ) is 5.0 or less, and the packing rate of the organism holder calculated by the following formula (1) is 32 volume % or more. Filling rate (volume %)=((total volume of multiple biological retainers) / (sum of total volume of multiple biological retainers and volume of stored water in the nitrification tank))×100 (Equation 1)

2. A biological nitrification method for treating ammonia nitrogen in water to be treated, comprising: The iron content of the treated water is more than 0.5 mg / L, When the water to be treated is passed through a nitrification tank loaded with a plurality of biological retainers having an average density of 1.0 to 1.4 g / cm 3 in an upward or downward direction, A biological nitrification method characterized in that the linear velocity ratio (LV air / LV water flow) of the linear velocity of the water to be treated, LV water flow [m / h], and the linear velocity of the air in the stored water in the nitrification tank, LV air [m / h], is 0.20 to 5.0, and the filling rate of the organism holder, calculated by the following formula (1), is 25 volume % or more. Filling rate (volume %)=((total volume of multiple biological retainers) / (sum of total volume of multiple biological retainers and volume of stored water in the nitrification tank))×100 (Equation 1)

3. 3. The biological nitrification method according to claim 1, wherein the biological support comprises a porous carrier and nitrifying bacteria supported on the carrier.

4. Furthermore, the linear velocity LV 空気 The biological nitrification method according to any one of claims 1 to 3, wherein the flow rate is 30 m / h or less.

5. A biological nitrification method described in any one of claims 1 to 4, wherein the treated water is groundwater, well water, lake water or river water, and for obtaining domestic water or drinking water from the treated water.

6. Average density is 1.0 to 1.4 g / cm ３ a nitrification tank loaded with a plurality of bioretainers each of which is a water supply pipe for supplying the water to be treated to the nitrification tank in an upward or downward flow; a water flow rate adjusting means provided in the water supply pipe for adjusting the flow rate of the water to be treated supplied to the nitrification tank; an aeration device for supplying air to the water stored in the nitrification tank; A control device electrically connected to at least the water flow rate adjusting means and the air diffuser; Equipped with The control device includes: The linear velocity LV of the water to be treated 通水 [m / h] and the linear velocity LV of the air in the water stored in the nitrification tank 空気 [m / h] and linear velocity ratio (LV 空気 / LV 通水 ) is 5.0 or less, and the filling rate of the organism holder, calculated by the following formula (1), is 32 volume % or more. Filling rate (volume %)=((total volume of multiple biological retainers) / (sum of total volume of multiple biological retainers and volume of stored water in the nitrification tank))×100 (Equation 1)

7. A nitrification tank loaded with a plurality of biological retainers having an average density of 1.0 to 1.4 g / cm 3 ; a water supply pipe for supplying the water to be treated to the nitrification tank in an upward or downward flow; a water flow rate adjusting means provided in the water supply pipe for adjusting the flow rate of the water to be treated supplied to the nitrification tank; an aeration device for supplying air to the water stored in the nitrification tank; A control device electrically connected to at least the water flow rate adjusting means and the air diffuser; Equipped with The control device includes: When the iron content of the water to be treated exceeds 0.5 mg / L, the linear velocity ratio (LV air / LV water flow) between the linear velocity LV water flow [m / h] of the water to be treated when passing through and the linear velocity LV air [m / h] of the air in the stored water in the nitrification tank is set to 0.20 to 5.0, and the biological nitrification system has a control unit that sets the filling rate of the biological holder to 25 volume % or more, as calculated by the following formula (1). Filling rate (volume %)=((total volume of multiple biological retainers) / (sum of total volume of multiple biological retainers and volume of stored water in the nitrification tank))×100 (Equation 1)

8. 8. The biological nitrification system according to claim 6 or 7, wherein the biological support has a porous carrier and nitrifying bacteria supported on the carrier.

9. The control unit determines the linear velocity LV 空気 The biological nitrification system according to any one of claims 6 to 8, wherein the flow rate is 30 m / h or less.

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