JP2024057217A - Rocking biological nitrification method and rocking biological nitrification device - Google Patents

Abstract

[Problem] The object of the present invention is to provide an oscillating biological nitrification method and an oscillating biological nitrification device that can treat water containing a high concentration of ammonia nitrogen at a high nitrification rate and also allows the treatment device to be made compact. [Solution] The following requirements 1 to 4 are satisfied. Requirement 1: The three-dimensional size of one organism holder 6 exceeds 5 mm in the maximum length direction and fits into a sphere with a diameter of 20 mm. Requirement 2: The ratio of the cross-sectional area S of the outlet of the water to be treated supply pipe 4 to the bottom area S of the nitrification tank 5 is 0.01 to 0.5. Requirement 3: The linear velocity ratio of the linear velocity LV water flow [m/h] of the water to be treated to the linear velocity LV gas [m/h] of the gas in the nitrification tank 5 is 0.3 to 6.0. Requirement 4: The filling rate calculated by the following formula (1) is 75% or more. Filling rate (%) = (bulk volume of multiple biological retainers) / (available water volume in nitrification tank) x 100 ... formula (1) [Selected figure] Figure 1

Description

The present invention relates to an agitated biological nitrification method and an agitated biological nitrification device.

A biological nitrification reaction is known in which ammonia nitrogen in water to be treated is converted to nitrate nitrogen by microorganisms. Ammonia nitrogen may be contained in, for example, groundwater, well water, lake water, river water, and industrial wastewater.
As a method for biological nitrification of water containing a high concentration of ammonia nitrogen, there is a fluidized bed mixed flow method in which the water to be treated is passed through a nitrification tank while circulating carriers holding microorganisms (for example, Patent Document 1).

According to the fluidized bed mixed flow type biological nitrification device shown in Figure 1 of Patent Document 1, the water to be treated can be supplied to the nitrification tank from the water to be treated supply pipe while air is supplied from the aeration unit to the stored water in the nitrification tank. When the water to be treated flows into the nitrification tank, it is instantly mixed with the stored water. As a result, the concentration of the entire stored water becomes uniform.

In the fluidized bed mixed flow method, a biological retainer carrying nitrifying bacteria and the like is fluidized in the water stored in the nitrification tank. When the biological retainer comes into contact with the water to be treated, ammonia nitrogen is converted to nitrate nitrogen and treated. The treated water flows out of the tank through the treated water outflow pipe. The fluidized bed mixed flow method can treat water to be treated that contains a high concentration of ammonia nitrogen.

JP 2017-202473 A

However, in the method of Patent Document 1, the bulk volume of the nitrifying bacteria-supporting carrier relative to the effective water volume is small. In Example 1 of Patent Document 1, the bulk volume is 30%.
However, according to the study by the inventors, if the bulk volume is increased beyond this value, the fluidity of the nitrifying bacteria-supporting carrier decreases, which causes problems such as dead space and short-circuiting. The occurrence of dead space and short-circuiting can cause unreacted ammonia nitrogen to be mixed into the treated water. As a result, there is a risk that the nitrification reaction cannot be performed uniformly in the treated water.

The nitrification rate depends on the volume ratio of the nitrifying bacteria-supporting carrier in the nitrification tank. In the method of Patent Document 1, the volume ratio of the nitrifying bacteria-supporting carrier cannot be increased any further, and therefore the nitrification rate cannot be further improved.
In addition, in the method of Patent Document 1, the nitrification rate per nitrification tank is low. In order to treat water containing a high concentration of ammonia nitrogen, it is necessary to further increase the number of nitrification tanks, which causes a problem of an increase in the size of the treatment device.

The object of the present invention is to provide an oscillating biological nitrification method and an oscillating biological nitrification device that can treat water containing a high concentration of ammonia nitrogen at a high nitrification rate and that also allows for the miniaturization of the treatment device.

As a result of intensive research, the inventors of the present invention have come up with the idea of setting (i) the size of the organism _holder , (ii) the _ratio of the cross-sectional area S of the outlet of the supply pipe for the water to be treated to the bottom area S of the _{nitrification} tank (S _outlet /S _{nitrification tank)} , (iii) the linear velocity ratio (LV gas/LV _water ) between the linear velocity LV _water flow [m/h] of the water to be treated and the linear velocity LV _gas [m/h] of the gas in the stored water in the nitrification tank, and (iv) the packing rate of the organism holder within a predetermined range. It has been found that when the nitrification reaction is carried out under these specific conditions, the water to be treated can be uniformly dispersed, thereby realizing a high nitrification rate, and the present invention has been completed.

The present invention has the following aspects.
[1] A rocking biological nitrification method for treating ammonia nitrogen in water to be treated, which satisfies the following requirements 1, 2, 3, and 4 when the water to be treated is passed through a plurality of biological retainers loaded in a nitrification tank.
Requirement 1: The three-dimensional size of one of the bioretainers exceeds 5 mm in the maximum length direction and fits into a sphere having a diameter of 20 mm.
Requirement 2: The ratio S _outlet /S _{nitrification tank of} the cross-sectional area S of the outlet of the supply pipe of the water to be treated into the nitrification tank to the bottom area S of _{the nitrification tank} is 0.01 to 0.5.
Requirement 3: The linear velocity ratio (LV _gas /LV water flow) between the linear velocity LV _{water flow} [m/h] of the water to be treated and the linear velocity LV _gas [m/h] of the gas in the stored _water in the nitrification tank is 0.3 to 6.0.
Requirement 4: The filling rate calculated by the following formula (1) is 75% or more.
Filling rate (%) = (bulk volume of multiple biological retainers) / (available water volume in nitrification tank) × 100 ... formula (1)
[2] The rocking type biological nitrification method according to [1], wherein the biological support has a porous carrier and nitrifying bacteria supported on the carrier.
[3] The rocking type biological nitrification method according to [1] or [2], wherein the water to be treated is passed through as an upward flow.
[4] A oscillating biological nitrification apparatus comprising: a nitrification tank loaded with a plurality of biological retainers; a treated water supply pipe for supplying treated water into the nitrification tank; a water flow rate adjustment means for adjusting the flow rate of the treated water supplied into the nitrification tank; a gas supply device for supplying gas to the stored water in the nitrification tank; and a control device electrically connected to at least the water flow rate adjustment means and the gas supply device; the control device performs control that satisfies the following requirements 3 and 4; and satisfies the following requirements 1 and 2.
Requirement 1: The three-dimensional size of one of the bioretainers exceeds 5 mm in the maximum length direction and fits into a sphere having a diameter of 20 mm.
Requirement 2: The ratio S _outlet /S _{nitrification tank of} the cross-sectional area S of the outlet of the water to be treated supply pipe to the bottom area S of the _{nitrification} tank is 0.01 to 0.5.
Requirement 3: The linear velocity ratio (LV _gas /LV water flow) between the linear velocity LV _{water flow} [m/h] of the water to be treated and the linear velocity LV _gas [m/h] of the gas in the stored _water in the nitrification tank is 0.3 to 6.0.
Requirement 4: The filling rate calculated by the following formula (1) is 75% or more.
Filling rate (%) = (bulk volume of multiple biological retainers) / (available water volume in nitrification tank) × 100 ... formula (1)
[5] The oscillating biological nitrification apparatus described in [4], _wherein the cross-sectional area S of the outlet of the treated water _supply pipe is the same as or larger than the cross-sectional area S of the treated water supply _pipe .
[6] The rocking type biological nitrification apparatus according to [4] or [5], wherein a plurality of the discharge outlets are arranged in the nitrification tank.

The present invention provides an oscillating biological nitrification method and an oscillating biological nitrification device that can treat water containing a high concentration of ammonia nitrogen at a high nitrification rate and also allows for the miniaturization of the treatment device.

FIG. 1 is a schematic diagram showing an example of an oscillation-type biological nitrification apparatus according to an embodiment. FIG. 2 is a schematic diagram for explaining a method for measuring the average density of a plurality of organism retainers. FIG. 2 is a schematic diagram for explaining a method for measuring the average density of a plurality of organism retainers. 4 is a schematic diagram showing an example of a discharge port of a water-to-be-treated supply pipe. FIG. 4 is a schematic diagram showing an example of a discharge port of a water-to-be-treated supply pipe. FIG. 4 is a schematic diagram showing an example of a discharge port of a water-to-be-treated supply pipe. FIG. FIG. 2 is a schematic diagram showing an example of a rocking type biological nitrification device used in the examples.

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

<Water to be treated>
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, and wastewater can be mentioned. However, the water to be treated is not limited to these examples.

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.

The content of ammoniacal nitrogen in the treated water 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 advantage of applying the rocking type biological nitrification method and rocking type biological nitrification device 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 more than 15 mg/L and is 50 mg/L or less), 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 an embodiment of the rocking type biological nitrification method and rocking type biological nitrification device, a high nitrification rate can be achieved even when the water to be treated contains iron.

Below, several embodiments of the present invention will be described with reference to the drawings as appropriate. The dimensional ratios in the drawings are for the convenience of explanation and may differ from the actual ones. In addition, in the drawings, the same components are indicated by the same reference numerals, and descriptions of overlapping components may be omitted.

<Swing-type biological nitrification device>
The oscillating biological nitrification apparatus 1 shown in Figure 1 comprises: a lifting pump (not shown) for pumping up raw water (an example of water to be treated); a treated water supply pipe 4 having a first end connected to the lifting pump and a second end opening in the nitrification tank 5; a water flow rate adjustment means (not shown) provided midway through the treated water supply pipe 4 for adjusting the flow rate of the water to be treated supplied near the bottom of the nitrification tank 5; a plurality of biological retainers 6 loaded in the nitrification tank 5; an aeration device (not shown) for supplying gas to the stored water in the nitrification tank; a control device (not shown) electrically connected to the water flow rate adjustment means and the aeration device; a screen 8 located near the liquid level in the nitrification tank 5; and a treated water outflow pipe 7 connected to the screen 8.

The water to be treated supply pipe 4 supplies raw water, such as well water, 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 in the water to be treated supply pipe 4.
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 4 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 .
A dissolved oxygen supplying means such as an aeration tank may be provided in the water to be treated supply pipe 4. The dissolved oxygen supplying means is for supplying dissolved oxygen to the water to be treated.

The second end of the treated water supply pipe 4 is an outlet 4a that opens in the nitrification tank 5. In the oscillating biological nitrification device 1, the pipe diameter of the treated water supply pipe 4 gradually increases as it approaches the second end. The expanded pipe diameter near the outlet 4a is maintained at a constant size. The larger the pipe diameter of the treated water supply pipe 4, the easier it is to uniformly disperse the treated water in the nitrification tank 5. Also, the larger the pipe diameter of the outlet 4a, the easier it is to uniformly disperse the treated water in the nitrification tank 5.

The ratio S _outlet /S _{nitrification tank} of the cross-sectional area S _outlet of the water supply pipe 4 to the bottom area S of _{the nitrification tank} is 0.01 to 0.5 (requirement 2). The ratio S _outlet /S _{nitrification tank} is preferably 0.3 or less, more preferably 0.2 or less. If the ratio S _outlet /S _{nitrification tank} is equal to or less than the upper limit of the numerical range, the organism holder 6 is unlikely to flow back into the water supply pipe 4. In addition, air bubbles are likely to move from the water supply pipe 4 to the nitrification tank 5 during aeration. The bottom area S _{nitrification tank} is the horizontal cross-sectional area of the nitrification tank near the outlet.
The cross-sectional shape of the untreated water supply pipe 4 is not particularly limited. For example, it may be substantially circular, elliptical, or rectangular. From the viewpoint of availability, it is preferable that the cross section is substantially circular.

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 biological retainers 6 are loaded to form a biological retainer region 11. In the biological retainer region 11, each biological retainer 6 is loaded so as to oscillate when the water to be treated is passed through it. The linear velocity of the water to be treated passed through the biological retainer 6 in the nitrification tank 5 is the LV _{water pass} [m/h].

The LV _{water flow rate} [m/h] can be calculated by dividing the water flow rate [ ^m3 /h] by the cross-sectional area S [ ^m2 ] of the nitrification tank 5. The cross-sectional area S is the average value of the horizontal cross-sectional areas at each vertical position from the bottom of the nitrification tank 5 (or the upper surfaces of support plates such as perforated blocks, strainers, screens, and grids that support the carriers at the bottom) to the water level at which water overflows when the water is flowing.

The nitrification tank 5 oxidizes the ammonia nitrogen in the water to be treated to produce treated water by contacting each of the biological retainers 6 in the biological retainer region 11 with the water. The biological retainer region 11 may be formed by covering the bottom of the nitrification tank 5 with multiple biological retainers 6 and stacking multiple biological retainers 6 in multiple stages in the height direction of the nitrification tank 5.

The size of the nitrification tank 5 can be designed depending on the amount of water to be treated. Therefore, the volume of the nitrification tank 5 is not particularly limited. For example, the volume of the nitrification tank 5 can be within the range of 0.1 to ¹⁰⁰ m3. In addition, the shape of the nitrification tank 5 is not particularly limited, but the nitrification tank 5 relates to a gas-liquid-solid three-phase flow reaction tank. Therefore, a shape that has as few obstacles as possible that hinder the flow of the gas-liquid-solid three phases is preferable, and a shape with few projections and recesses is particularly preferable. For example, a cylindrical shape or a square shape can be mentioned. From the viewpoint of workability, a nitrification tank having a square cross section is preferable.

The material of the nitrification tank 5 is not particularly limited. Among various materials, materials with excellent pressure resistance are preferable. Examples include concrete, iron alloys, acrylic resin, and fiber-reinforced resin. In terms of ease of processing the nitrification tank 5, a panel tank (FRP tank) is preferable.

The organism retainer 6 is a carrier that retains nitrifying bacteria. The three-dimensional size of one organism retainer 6 is such that the maximum length exceeds 5 mm and the organism retainer 6 can fit into a sphere having a diameter of 20 mm (requirement 1).
The organism holder 6 has a carrier and nitrifying bacteria held on the carrier. The shape of the carrier is not particularly limited as long as requirement 1 is satisfied. Examples of the shape of the carrier 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 of loading into the nitrification tank 5, a rectangular parallelepiped, a cube, and a sphere are preferred.

In multiple organism holders 6, the shapes of the carriers 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.

The carrier is preferably a porous carrier, since more nitrifying bacteria can be supported by supporting the nitrifying bacteria on the surface and inside of the carrier, and the nitrification rate can be further improved. 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.

In particular, a sponge carrier is preferred because it can maintain the support of nitrifying bacteria well and minimize damage to pumps and piping. The porosity of the sponge carrier is preferably about 85 to 99%, and more preferably about 90 to 97%.
Examples of materials for the sponge carrier include polyvinyl alcohol, polyethylene glycol, and polyurethane.
The true density of the sponge carrier is preferably 0.90 to 1.50 g/cm ³ , more preferably 1.00 to 1.40 g/cm ³ , and even more preferably 1.00 to 1.20 g/cm ³ .

The apparent surface area of the sponge carrier is preferably 300 ^m2 / ^m3 or more, more preferably 600 ^m2 / ^m3 or more. When the apparent surface area of the sponge carrier is equal to or more than the lower limit, the surface area is sufficiently large, and the contact efficiency with the water to be treated is high. In addition, it is easy to retain nitrifying bacteria, the oxygen supply efficiency is also high, and the nitrification rate is further increased.

The nitrifying bacteria include known nitrifying bacteria used in biological nitrification of ammonia nitrogen. For example, nitrifying bacteria such as Nitrosomonas are autotrophic, and basically use carbon dioxide as the only carbon source. They do not require an organic substrate and can grow in the presence of ammonia nitrogen, but their growth rate is extremely low. In order to increase the nitrification rate, an operation is required 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 bodies.
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 device and grow the nitrifying bacteria on the surface of the carrier.

The average density of the organism retainer 6 is preferably 1.00 to 2.00 g/ ^cm3 , more preferably 1.05 to 1.40 g/ ^cm3 , and even more preferably 1.10 to 1.20 g/ ^cm3 . Here, the average density of the organism retainer 6 is the average density in a wet state in which each organism retainer 6 retains nitrifying bacteria. 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 range, the organism retainers 6 are likely to settle in the stored water in the nitrification tank 5, and therefore the oscillating state can be maintained. Therefore, the organism retainers 6 do not flow excessively. As a result, the water to be treated moves toward the outlet and gradually comes into contact with a number of organism retainers 6, and the nitrification reaction is likely to proceed. If the average density of the organism retainers 6 is equal to or less than the upper limit of the range, the organism retainers 6 are likely to oscillate.
Therefore, if the average density of the organism retainers 6 is within the above range, the organism retainers 6 are easily swung in the stored water by the flow of the water to be treated. Therefore, impurities (such as SS) in the water to be treated are less likely to adhere to the organism retainers 6. As a result, the contact efficiency between the water to be treated and each organism retainer is improved, and the nitrification rate is increased.

The average density of the bioretainer can be calculated as follows.
First, the mass m [g] of the plurality of organism supports 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 organism supports 6 are removed from the nitrification tank and loaded into the container 20 so that the bulk volume is constant. To make the bulk volume constant, for example, a reference line L is drawn on the side of the container 20 with a known volume, and the plurality of organism supports 6 can be loaded into the container 20 so that the reference line L coincides with the top surface of the uppermost organism support 6.

When the organism holder is removed from the nitrification tank, the retained water adhering to the carrier drips off the organism holder. The mass of the dripped retained water is not included in the mass m [g] of the multiple organism holders. In this embodiment, an organism holder with a bulk volume of about ⁵⁰⁰ cm3 is scooped out of the nitrification tank and held on the water surface. The time when water droplets stop dripping for 5 seconds or more is defined as the "wet state" of the organism holder. The organism holder in such a wet state is loaded into the container 20.
Thereafter, the operation of removing the biological retainers from the nitrification tank and loading them into container 20 is repeated, and the mass when the total bulk volume of the multiple biological retainers reaches a predetermined value is recorded as the mass m [g] of the multiple biological retainers.

Next, the volume V [ ^cm3 ] of the multiple organism supports is measured. As shown in Fig. 3, water is poured from a separately prepared beaker 40 into a container 20 loaded with wet organism supports 6 until a predetermined bulk volume is reached, i.e., up to the reference line L, filling the spaces between the organism supports 6 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 [ ^cm3 ] of the multiple organism supports.
Finally, the mass m [g] of the plurality of biosupports is divided by the volume V [cm ³ ] of the biosupports to obtain the average density m/V [g/cm ³ ] of the biosupports 6 .

Taking into consideration the oscillation during water flow, the average volume of one organism retainer is preferably 0.03 to 5.00 ^cm3 , more preferably 0.06 to 1.00 ^cm3 , and even more preferably 0.10 to 0.30 ^cm3 . When the volume of one organism retainer is equal to or greater than the lower limit of the above range, solid-liquid separation of the organism retainer using a screen 8 or the like becomes easy. When the volume of one organism retainer is equal to or less than the upper limit of the above range, the organism retainer is likely to oscillate even with a relatively small LV _gas .
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.

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 device. For example, the density of a new porous carrier is often less than 1 g/ ^cm3 because it contains air inside.
When the carrier is cultured in a nitrification tank, air gradually escapes from the carrier and the nitrifying bacteria adhere to the carrier. The carrier is cultured in a water flow until the density of the carrier containing the nitrifying bacteria and water in a wet state is within the range of 1.0 to 1.4 g/ ^cm3 , for example, to form a biological retainer.

1 again, treated water outlet pipe 7 is for taking out treated water from nitrification tank 5. Treated water outlet pipe 7 is connected to screen 8. Treated water is once collected on screen 8 and then flows out of nitrification tank 5 through treated water outlet pipe 7.
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 7 are provided midway through the treated water outflow pipe 7.
Examples of the outflow measuring means include a rotameter and an electromagnetic flowmeter.
An example of the outflow rate adjusting means is a flow rate adjusting valve.

The air diffuser is an example of a gas supplying device. The linear velocity of the gas supplied to the stored water in the nitrification tank 5 is LV _gas [m/h].
The aeration device may be configured to include an aeration section located near the bottom of the nitrification tank 5; a gas supply pipe for supplying gas to the aeration section; a blower provided at one end of the gas supply pipe; and a gas supply amount adjustment means (not shown) provided midway along the gas supply pipe between the aeration section and the blower.

In principle, the aeration device is used to aerate and remove solid matter adhering to the surface of the biological retainer 6. With the aeration device, the air bubbles supplied into the nitrification tank can remove solid matter adhering to the surface of the biological retainer 6.

The gas supplied by the air diffuser is not particularly limited as long as it can agitate the organism holder 6, but a safe gas that does not inhibit the nitrification reaction and does not cause explosions or corrosion is preferable.
The gas may be, for example, air or an inert gas such as argon or nitrogen.

In the rocking type biological nitrification apparatus 1, the opening surface of the gas supply pipe is the aeration section, but in other examples the aeration section may be, for example, an aeration tube, an aeration ball, or a diffuser with a diffusion hole formed therein.
The gas supply amount adjusting means may be, for example, a gate valve, a butterfly valve, or control of blower frequency by an inverter.

The control device includes an interface unit (not shown), a memory 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 to the water flow measurement means, the water flow adjustment means, the water quality meter, the outflow measurement means, the outflow adjustment means, the blower of the air diffuser, and the gas supply adjustment means.

The memory unit stores the linear velocity ratio (LV _gas /LV _{water flow} ) and the operating conditions of the oscillating type biological nitrification device 1 for calculating the filling rate calculated by the following formula (1), etc.
Filling rate (%)=(bulk volume of multiple organism holders 6/available water volume in nitrification tank 5)×100 Equation (1)

LV _gas [m/h] is the linear velocity of gas in the water stored in the nitrification tank. LV _gas [m/h] is calculated by the following formula (2).
LV _gas [m/h]=amount of gas supplied by aeration device [m ³ /h]/cross-sectional area of nitrification tank S [m ² ] Equation (2)

The LV _{water flow rate} [m/h] is the linear velocity of the water being treated as it flows through the multiple organism retainers. The LV _{water flow rate} is calculated by the following formula (3).
LV _{water flow rate} = water flow rate [m ³ /h] / cross-sectional area of nitrification tank S [m ² ] Equation (3)

Examples of operating conditions stored in the memory unit include the cross-sectional area S of the outlet 4a of the treated water supply pipe 4 ( _outlet) , the bottom area S of the nitrification tank 5 _{(nitrification tank)} , the sum of the volumes of the multiple biological holders 6, the effective water volume in the nitrification tank 5, the cross-sectional area S of the nitrification tank 5, the bulk volume, total mass, and number of the biological holders 6 loaded in the nitrification tank 5, the average density of the biological holders 6, the amount of water to be treated supplied, the amount of treated water flowing out, and the amount of gas supplied into the nitrification tank 5.

In the oscillating biological nitrification device 1, the "bulk volume of the multiple biological retainers 6" in formula (1) is the sum of the volumes of all the biological retainers 6 that make up the biological retainer region 11. In other words, the "bulk volume of the multiple biological retainers" is the volume that the assembly of the biological retainers in a stationary state occupies within the space of the effective water volume when multiple biological retainer carriers are placed in the nitrification tank.

The "bulk volume of the bioretainer" can be calculated by multiplying the height from the bottom of the bioretainer carrier (or the top surface of a support plate such as a perforated block, strainer, screen, or grid that supports the carrier at the bottom, if such a support plate is present) to the top surface of the bioretainer carrier when all of the bioretainers 6 placed in the nitrification tank, which is uniform in height, are left to stand, by the cross-sectional area S of the container.

In the rocking type biological nitrification apparatus 1, the "effective water volume in the nitrification tank 5" in formula (1) is the total volume of the water to be treated and the organism retention carrier present in the nitrification tank 5. This "effective water volume in the nitrification tank 5" is the empty volume up to the overflow water level of the nitrification tank 5. It can be calculated by multiplying the distance (effective water level hT) from the bottom of the nitrification tank 5 (if there are support plates such as perforated blocks, strainers, screens, grids, etc. that support the carriers at the bottom, the top surfaces of these support _plates ) to the water level that overflows when water is passed through by the cross-sectional area S of the nitrification tank 5.

The processing unit can perform the following operation 1.
Calculation 1: S _outlet /S _{nitrification tank is} calculated from the ratio of the cross-sectional area S of the outlet of the treated water supply pipe _to the bottom area S of the nitrification tank.

The processing unit can perform the following operation 2.
Calculation 2: The bulk volumes of the multiple organism holders 6 and the available water volume in the nitrification tank 5 are calculated, and then the packing rate of the organism holders 6 is calculated from the above formula (1).

The processing unit can perform the following operation 3.
Calculation 3: The LV _{water flow rate} is calculated from the flow rate value of the water flow rate adjustment means and the cross-sectional area S of the nitrification tank 5, and the LV _gas is calculated from the supply value of the gas supply rate adjustment means and the cross-sectional area S of the nitrification tank 5, and the linear velocity ratio (LV _gas /LV _{water flow rate} ) is calculated.

The determination unit may determine, for example, at least one of the following items:
- Whether the linear velocity ratio (LV _gas /LV _water ) is within the range of 0.3 to 6.0 (requirement 3).
Whether or not the filling rate of the organism holder 6 calculated in the processing section is 75% or more (requirement 4).
- Whether the iron content of the treated water measured with a water quality meter is 0.5 mg/L or more.

The control unit controls the oscillating biological nitrification device 1 based on the judgment result in the judgment unit, the operating conditions of the oscillating biological nitrification device 1 stored in the memory unit, etc. In particular, the control unit executes control to satisfy requirements 3 and 4.

When the determining unit determines that the linear velocity ratio (LV _gas /LV _{water flow} ) is less than 0.3, the control unit can carry out the following control.
- Controlling the gas supply amount adjustment means so as to increase the amount of gas supplied by the aeration section and increase the LV _gas [m/h].
Controlling the water flow rate adjustment means to reduce the supply rate of water to be treated and lower the LV _{water flow rate} [m/h].
- Controlling the outflow rate adjustment means to reduce the outflow rate of treated water and lower the LV _{water flow} rate [m/h].

When the determining unit determines that the linear velocity ratio (LV _gas /LV _{water flow} ) is greater than 6.0, the control unit can carry out the following control.
Controlling the gas supply amount adjustment means to reduce the amount of gas supplied by the aeration section and lower the LV _gas [m/h].
- Controlling the water flow rate adjustment means so as to increase the supply rate of water to be treated and increase the LV _{water flow rate} [m/h].
- Controlling the outflow rate adjustment means to increase the outflow rate of treated water and increase the LV _{water flow} rate [m3/h].

For example, when the determining section determines that the filling rate of the organism holder 6 is less than 75%, the control section can carry out the following control.
Controlling the water flow rate adjusting means so as to reduce the amount of water to be treated and thereby reduce the volume of water stored in the nitrification tank 5.
- Controlling the outflow rate adjustment means so as to increase the outflow rate of treated water and reduce the volume of stored water in the nitrification tank 5.

In addition, when the judgment section judges that the iron content of the water to be treated is 0.5 mg/L or more, the control section may carry out the following control.
Controlling the gas supply amount adjusting means so as to adjust the amount of gas supplied by the aeration section.
-Adjusting the flow rate of the water flow rate adjusting means and the outflow rate adjusting means to adjust the LV _{water flow rate} .

The processing unit, the determination unit, and the control unit may be realized by dedicated hardware. The processing unit, the determination unit, and the control unit may also be configured by a memory and a central processing unit (CPU). In the case of a CPU, the functions of the processing unit, the determination unit, and the control unit may be realized by loading a program for realizing the functions of the processing unit, the determination unit, and the control unit into memory and executing the program.

The control device may be connected to peripheral devices such as an input device and a display device. Examples of the input device include a display touch panel, a switch panel, a keyboard, and the like. Examples of the display device include a liquid crystal display device, a CRT, and the like.

<Swing-type biological nitrification method>
An example of a nitrification method using the rocking type biological nitrification device 1 will now be described.
First, a plurality of organism holders 6 cultured in a nitrification tank of an existing biological nitrification apparatus are loaded into the nitrification tank 5 of the rocking type biological nitrification apparatus 1 .
The three-dimensional size of each organism retainer 6 exceeds 5 mm in the maximum length direction and fits into a sphere with a diameter of 20 mm (requirement 1). Therefore, each organism retainer 6 rocks when the water to be treated is passed through it. When the organism retainers 6 are loaded, it is advisable to leave a space between the organism retainers 6 for rocking so that the organism retainers 6 can rock when the water is passed through them.

Next, the water to be treated that contains ammonia nitrogen is supplied to the nitrification tank 5 through the water to be treated supply pipe 4 and stored in the nitrification tank 5. At this time, as water is stored in the nitrification tank 5, the water also fills the spaces between the biological holders 6 in the biological holder region 11. If water continues to be stored thereafter, the biological holder 6 at the top of the biological holder region 11 becomes immersed in the stored water.

When water is stored in the nitrification tank 5, the filling rate calculated by the following formula (1) is set to 75% or more.
Filling rate (%)=(bulk volume of multiple organism holders 6)/(available water volume in nitrification tank 5)×100 Formula (1)

(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 retainer 6. Ammoniacal nitrogen in the water to be treated is then oxidized to nitrate nitrogen by the nitrifying bacteria in the biological retainer 6. In this way, the water to be treated containing ammoniacal nitrogen is treated in the nitrification tank 5 to produce treated water.

The apparent volume of the sponge carrier expands by aeration with gas while water is passing through it, and the expansion rate at this time is preferably within the range of 2 to 25%. The expansion rate is calculated by the following formula (4).
Expansion rate (%)=(volume [m ³ ] occupied by the plurality of organism holders 6 in the nitrification tank 5 when water is flowing−bulk volume [m ³ ] of the plurality of organism holders 6 when left stationary)/(available water volume [m ³ ] in the nitrification tank 5)×100 (Equation (4))

(S _outlet /S _{nitrification tank} : requirement 2)
In this embodiment, when the water to be treated is passed through, the ratio of S _outlet /S _{nitrification tank} is set within the range of 0.01 to 0.5.
The ratio of S _outlet /S _{nitrification tank} is preferably 0.02 or more, more preferably 0.05 or more. By setting the ratio of S _outlet /S _{nitrification tank} to 0.01 or more, the water to be treated is uniformly dispersed in the nitrification tank 5, thereby realizing a high nitrification rate.
The ratio of S _outlet /S _{nitrification tank} is preferably 0.3 or less, more preferably 0.2 or less. By setting the ratio of S _outlet /S _{nitrification tank} to 0.5 or less, the organism retention carrier 6 is less likely to flow back into the treated water supply pipe 4. In addition, since air bubbles can easily move from the treated water supply pipe 4 into the nitrification tank 5 during aeration, a high nitrification rate can be achieved.

(LV _gas /LV _{water flow} : requirement 3)
In this embodiment, when the water to be treated is passed through, the linear velocity ratio (LV _gas /LV _{water passing} ) is set to 0.3 to 6.0. The linear velocity ratio (LV _gas /LV _{water passing} ) is preferably 0.5 to 6.0, and more preferably 2.0 to 4.0.
If the linear velocity ratio (LV _gas /LV _{water flow} ) is within the above-mentioned numerical range, the nitrification rate can be increased while preventing solids such as iron from adhering to the surface of the organism holder 6. In particular, if the iron content of the water to be treated is more than 1.0 mg/L, there is a possibility that a large amount of solids such as iron hydroxide produced during the nitrification reaction will adhere to the surface of the organism holder. In this case, it may be particularly beneficial to set the linear velocity ratio (LV _gas /LV _{water flow} ) to 0.3 or more.

The LV _{water flow} can be adjusted, for example, by adjusting the flow rate of the water flow rate adjusting means and the outflow rate adjusting means.
The LV _{water flow rate} is not particularly limited, but is preferably within the range of 5 to 40 m/h, more preferably 8 to 30 m/h, and even more preferably 10 to 25 m/h. If _{the LV water flow rate} is equal to or higher than the lower limit of the range, the organism holder 6 is likely to oscillate. If the LV _{water flow rate} is equal to or lower than the upper limit of the range, the nitrification reaction efficiency is likely to be maintained, and the nitrification rate is likely to be further improved.

The LV _gas can be adjusted, for example, by the gas supply amount of the air diffuser. The amount of gas diffused from the air diffuser of the air diffuser can be adjusted to an arbitrary amount by the gas supply amount adjusting means.
The LV _gas is not particularly limited, but in terms of agitating the biological holder 6 and reducing the electrical energy required for gas supply, the LV _gas is preferably in the range of 3 to 100 m/h, more preferably in the range of 20 to 60 m/h.

(Filling rate: requirement 4)
In this embodiment, the filling rate calculated by formula (1) is set to 75% or more when the water to be treated is passed through the treatment tank. Therefore, the nitrification rate is sufficiently high. In terms of increasing the nitrification rate, the filling rate calculated by formula (1) is preferably set to 75% or more, more preferably set to 80% or more, and even more preferably set to 85% or more.
The upper limit of the filling rate calculated by the above formula (1) is 100%, but in terms of agitating the biological holder 6 when water is passed through it, it is preferable to set it to 100% or less, more preferably 98% or less, and even more preferably 95% or less.

(Upward flow)
In the rocking type biological nitrification apparatus 1, the water to be treated is passed as an upward flow through the multiple biological retainers 6 in the biological retainer region 11. By passing the water to be treated as an upward flow as in this embodiment, a state in which the biological retainers are easily rocked even during aeration can be achieved.

<Mechanism of action>
In the rocking biological nitrification method according to the embodiment described above using an example, (i) the size of the biological holder, (ii) the area ratio (S _outlet /S _{nitrification tank} ), (iii) the linear velocity ratio (LV _gas /LV _{water flow} ), and (iv) the filling rate of the biological holder satisfy predetermined conditions. Therefore, the following advantages can be provided. Therefore, the water to be treated containing a high concentration of ammonia nitrogen can be treated at a high nitrification rate, and the treatment device can be made compact.

- Because the biological retainer can oscillate in the nitrification tank when water is passed through it, solid matter is less likely to adhere to the surface of the biological retainer, improving the efficiency of the nitrification reaction by the biological retainer.
- _The cross-sectional area S of the outlet of the treated water supply pipe is not excessively large. Therefore, the gas for rocking the organism retainer can be sufficiently supplied into the tank while preventing the organism retainer from flowing back into the outlet of the treated water supply pipe, thereby achieving a high nitrification rate. As a result, the treated water containing a high concentration of ammonia nitrogen can also be treated. In addition, the treatment device can be made smaller.
Since the organism retainer can oscillate, the water to be treated comes into contact with the entire organism retainer efficiently when the water passes through it. As a result, even if the filling rate of the organism retainer is set to 75% or more, it is possible to prevent the occurrence of short-circuiting and the occurrence of dead spaces that do not come into contact with the organism retainer 6. This improves the nitrification rate and realizes an excellent nitrification rate.
According to the present embodiment, an excellent nitrification rate can be achieved. Therefore, there is less need to increase the number of nitrification tanks. In addition, the nitrification tanks themselves can be made smaller.

For example, in a fluidized bed mixed flow type nitrification method as described in Patent Document 1, when the packing rate reaches 75% or more, dead spaces and short-circuiting 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 biological retainer oscillates when water is passed through, so the treated water comes into contact with the multiple biological retainers efficiently overall. Therefore, even with a predetermined filling rate of 75% 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 biological retainers, and as a result, the nitrification rate can be increased. The biological nitrification reaction in this embodiment can also be said to be a oscillating bed push-out flow method.

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 1.0 mg/L or less, the solid matter attached to the surface of the biological retainer can be sufficiently removed even if the LV _gas is relatively low, so that the efficiency of the nitrification reaction can be maintained high. As a result, a high nitrification rate can be achieved. In this case, the energy consumption due to aeration can be reduced.
On the other hand, as shown in the examples described later, even when the iron content of the water to be treated exceeds 1.0 mg/L, ammoniacal nitrogen can be treated at a high nitrification rate.

Furthermore, since the oscillating biological nitrification device 1 described above has the configuration described above, the oscillating biological nitrification method according to the above-mentioned embodiment can be implemented by using the oscillating biological nitrification device 1, and the above-mentioned mechanism of action can be exerted.
For example, when using an oscillating biological nitrification apparatus equipped with one nitrification tank such as the oscillating biological nitrification apparatus 1, even if the residence time of the treated water is set to 30 min or less, it is possible to reduce the ammoniacal nitrogen of the treated water containing a high concentration of ammoniacal nitrogen of 5 mg/L or more to approximately less than 0.1 mg/L. Therefore, when treating the treated water containing a high concentration of ammoniacal nitrogen of 1 mg/L or more, for example, the present invention can be particularly suitably applied to the application of making the treated water potable.

<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 present 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.
Some examples of modified examples are shown below, but the embodiment is not limited to these modified examples.

For example, in the rocking biological nitrification device 1 shown in Fig. 1, the cross-sectional area S of the discharge port of the treated water supply pipe 4 is larger than that _{of the supply pipe} , but in other examples, _{the cross} -sectional area S of the discharge port of the treated water supply pipe may be the same as that of _{the treated water supply pipe} . Some examples are shown in Figs. 4, 5, and 6.
_The cross-sectional area S of the outlet 11a of the water to be treated supply pipe 11 shown in Fig. 4 is the same as the cross-sectional area S of the water to be treated _supply pipe 11. Like the outlet 11a, the outlet at the second end of the water to be treated supply pipe may be the open end of the water to be treated supply pipe.
5 is larger than the cross-sectional area S of the outlet 12a of the water to be treated supply pipe 12. Like the _outlet 12a, the shape of the outlet at the second end of the water to be treated supply pipe may be _cylindrical .
6 has _a cross-sectional area S of the outlet 13a of the water to be treated supply pipe 13, which is larger than the cross-sectional area S of the water to be treated _supply pipe 13. Like the outlet 13a, the shape of the outlet at the second end of the water to be treated supply pipe may be a horn shape whose lower end is the widest.

In the rocking type biological nitrification apparatus 1 shown in Fig. 1, only one discharge port of the treated water supply pipe 4 is disposed in the nitrification tank 5, but in other examples, multiple discharge ports may be disposed in the nitrification tank. For example, the second end of the treated water supply pipe 4 may be branched into multiple outlets. In this case, the opening surface of each of the branched ends may be disposed in the nitrification tank 5.
When a plurality of outlets are disposed in the nitrification tank, the water to be treated can be more uniformly dispersed. In this case, it is preferable that the ratio of the cross-sectional area S of at least one of the plurality _{of outlets} to the bottom area S of the _{nitrification tank} is 0.01 or more, and it is more preferable that the ratio of S _outlet /S _{nitrification tank} for all of the plurality of outlets is 0.01 or more.

In the rocking biological nitrification apparatus 1 shown in FIG. 1, the water to be treated is passed through the multiple biological retainers 6 in the biological retainer region 11 as an upward flow, but in other examples, the water to be treated may be passed through the biological retainers 6 as a downward flow from the top to the bottom of the biological retainer region 11.
The same effect can be obtained even when the water to be treated is passed through the system in a downward flow, so that a high nitrification rate can be achieved.

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. However, 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. Furthermore, 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.
A dissolved oxygen (DO) meter for measuring the dissolved oxygen concentration in the water stored in the nitrification tank 5 may be used.

A pre-treatment device that performs pre-treatment on the water to be treated that is supplied to the nitrification tank 5, or a post-treatment device that performs post-treatment on the treated water that flows out from the nitrification tank 5 may be used. 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, etc.

Examples of upstream treatment devices include a raw water storage tank, a dissolved oxygen supply device, and a sand filter tower. To increase the efficiency of the biological nitrification reaction, it is also preferable to install a separate dissolved oxygen supply device. The dissolved oxygen supply device is an aeration device for supplying dissolved oxygen, and is different from the aeration device mentioned in the above embodiment. If 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 rocking 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, and a disinfectant addition device.
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 and drinking water.

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

<Preparation of treated water>
Raw water quality: Iron sulfate heptahydrate was added to the collected groundwater to prepare simulated groundwater with an iron ion concentration of 0.3 to 3.0 mg/L. Ammonium chloride was further added to the collected groundwater to adjust the ammoniacal nitrogen concentration. 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.

<Construction of test equipment>
A test apparatus 50 shown in Fig. 7 was constructed. The test apparatus 50 has a nitrification tank 5, a water-to-be-treated supply pipe 14, a screen 8, and a treated water outflow pipe 7. The discharge port 14a of the water-to-be-treated supply pipe 14 opens downward in the nitrification tank 5. The diameter of the discharge port 14a is the same as the diameter of the water-to-be-treated supply pipe 14.

(Biological Support)
As the sponge carrier, a 5 mm square cubic polyurethane sponge carrier ("Waterflex AQ-15" manufactured by Technoform Japan Co., Ltd.) was prepared. The density of the sponge carrier before the water-passing culture was 0.044 g/cm ^3. These sponge carriers were subjected to water-passing culture in the nitrification tank of an existing biological nitrification device, and about 10 kg (about 6,500 pieces) of biological holders were prepared. After the water-passing culture, the biological holders were scooped out of the nitrification tank and held on the water surface. When the water droplets stopped dripping for 5 seconds or more, the biological holders were judged to be in a wet state, and were loaded into a 10 L graduated container.

When the loading of the bioretainers into the 10 L graduated container was completed, the mass m of the bioretainers was 5785 g. Thereafter, water was poured from a separately prepared beaker into the graduated container in which the bioretainers had been 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 ⁴⁷⁷⁰ cm3. The volume V of the bioretainers was set to 10000 ^cm3 (10 L) - 4770 ^cm3 = 5230 ^cm3 .
Therefore, the average density of the organism retainer was calculated to be 5785 g/5230 cm ³ ≈ 1.1 g/cm ^3. A number of organism retainers were placed in the water tank so that the bulk volume was within the range of 60 to 95%.

(Nitrification tank)
A transparent acrylic tank with a rectangular cross section was used. The top of the tank was open to the atmosphere. The front width of the tank was 500 mm, the side depth was 150 mm, and the height was 2300 mm. The effective water volume of the tank was 150 L. When passing water, the water to be treated was supplied from the bottom of the tank, and an outlet was installed at the top of the tank, so that the water to be treated would flow upward when passing water.

The supply rate of the water to be treated was 12.5 L/min (LV _{water flow} : 10 [m3/h]). A hole was drilled at a height of 800 mm in the water tank, and the water supply pipe was extended so as to run along the side of the tank in a vertical downward direction at 90 degrees. The length of the water supply pipe to be treated was 500 mm, and the inner diameter of the pipe varied depending on the location in the pipeline, but was within the range of 30 to 134 mm.
The outlet of the raw water supply pipe was installed at a height of 300 mm from the bottom of the tank. An aeration pipe was also installed at the bottom of the tank so that gas was supplied uniformly into the tank. The gas supply rate was 3.8 to 75.0 L/min (LV _gas : 3 to 240 m/h).
In the examples, air (atmospheric air) that had not been subjected to any particular pretreatment was used as the gas.

(Swing-type biological nitrification device)
The amount of ammonium chloride added to the water to be treated was gradually increased while measuring the ammonia nitrogen concentration of the treated water after the nitrification reaction. The ammonia nitrogen concentration of the treated water was measured when the ammonia nitrogen concentration of the treated water reached 0.1 mg/L. In this way, the maximum nitrification rate at which the ammonia nitrogen concentration value of the treated water could be maintained at 0.1 mg/L or less was determined. The nitrification rate was calculated as follows.

<Measurement method>
(Nitrification rate)
When the amount of ammonium chloride added to the raw water was gradually increased after the start of water flow, the biological nitrification reaction could not keep up, and the ammoniacal nitrogen concentration in the treated water exceeded 0.1 mg/L. The nitrification rate [kgN/ ^m3 /d] per nitrification tank at that time was calculated as follows:
Nitrification rate [kgN/m ³ /d]=(ammonia nitrogen concentration in water to be treated [kg/m ³ ]−ammonia nitrogen concentration in treated water [kg/m ³ ])×water flow rate [m ³ /d]÷water tank volume [m ³ ]

The evaluation criteria for nitrification rate are as follows:
⊚: The nitrification rate is 0.8 kgN/m ³ /d or more.
◯: The nitrification rate is more than 0.5 kgN/m ³ /d and less than 0.8 kgN/m ³ /d.
Δ: The nitrification rate is more than 0.22 kgN/m ³ /d and 0.5 kgN/m ³ /d or less.
×: The nitrification rate is 0.22 kgN/m ³ /d or less.

(S _outlet /S _{nitrification tank} )
The ratio of S _outlet /S _{nitrification tank} was calculated by dividing the cross-sectional area [m ² ] of the treated water supply pipe by the bottom area [m ² ] of the tank.

(Filling rate)
The packing ratio was calculated from the above formula (1).

(LV _gas )
The LV _gas [m/h] was calculated from the above formula (2).

(LV _{water flow} )
The LV _{water flow rate} [m/h] was calculated from the above formula (3).

<Examples 1 to 6>
The water to be treated was passed through the biological retainer in the nitrification tank under the conditions shown in Table 1. In each example, the diameter of the water to be treated supply pipe 14 was changed to change the cross-sectional area S of the _outlet 14a, and the S _outlet /S _{nitrification tank} was changed. The results are shown in Table 1.

From the results shown in Table 1, it was found that the nitrification rate tends to increase by increasing the area ratio S _outlet /S _{nitrification tank} to 0.01 or more. However, when the S _outlet /S _{nitrification tank} is larger than 0.05, although the nitrification rate itself is high, the improvement effect is difficult to obtain.

<Examples 7 to 11>
The water to be treated was passed through the biological retainer in the nitrification tank after changing the conditions shown in Table 2. The results are shown in Table 2. Table 2 also shows the results of Example 4 for reference.

From the results shown in Table 2, it was found that a higher nitrification rate than that of the conventional technology can be obtained by adjusting the linear velocity ratio (LV _gas /LV _{water flow} ) within the range of 0.3 to 6.0. As shown in Table 5, the conventional nitrification rate is about 0.2 kgN/m ³ /d.

<Examples 12 to 15>
The water to be treated was passed through the biological retainer in the nitrification tank after changing the conditions shown in Table 3. The results are shown in Table 3. Table 3 also shows the results of Example 4 for reference.

From the results shown in Table 3, it was found that by appropriately adjusting the linear velocity ratio (LV _gas /LV _{water flow} ), a high nitrification rate could be obtained even when the iron concentration was high (Examples 13 to 15).

<Examples 16 to 18>
After changing the conditions shown in Table 4, the water to be treated was passed through the biological retainer in the nitrification tank. The results are shown in Table 4. Table 4 also shows the results of Example 4 for reference.

The results shown in Table 4 show that the higher the loading rate of the bioretainer, the higher the nitrification rate tends to be. This is thought to be because it can support a large number of nitrifying bacteria.

<Comparative Examples 1 and 2>
After changing the conditions to those shown in Table 5, the water to be treated was passed through the biological retainer in the nitrification tank.

From the results of the above-mentioned examples and comparative examples, it was found that the nitrification rate can be improved by setting (i) the size of the biological holder, (ii) the ratio S _outlet /S _{nitrification tank} , (iii) the linear velocity ratio (LV _gas /LV _{water flow} ), and (iv) the filling rate of the biological holder within a predetermined range. It was confirmed that the nitrification rate decreased when the filling rate of the biological holder was less than 75% (Comparative Example 2) or when the linear velocity ratio (LV _gas /LV _{water flow} ) was 0 (Comparative Example 1).
Therefore, the water to be treated containing a high concentration of ammonia nitrogen can be treated at a high nitrification rate. Since there is little need to install two or more nitrification tanks, the treatment device can be made smaller.

According to one aspect of the present invention, there is provided an oscillating biological nitrification method and an oscillating biological nitrification device that can treat water containing a high concentration of ammonia nitrogen at a high nitrification rate and also allows for a compact treatment device.

Reference Signs List 1 Swing-type biological nitrification device 4 Treated water supply pipe 5 Nitrification tank 6 Biological holder 7 Treated water outflow pipe

Claims (6)

A shaking biological nitrification method for treating ammonia nitrogen in treated water,
A rocking biological nitrification method, which satisfies the following requirements 1, 2, 3 and 4 when the water to be treated is passed through a plurality of biological retainers loaded in a nitrification tank.
Requirement 1: The three-dimensional size of one of the bioretainers exceeds 5 mm in the maximum length direction and fits into a sphere having a diameter of 20 mm.
Requirement 2: The ratio S _outlet /S _{nitrification tank of} the cross-sectional area S of the outlet of the supply pipe of the water to be treated into the nitrification tank to the bottom area S of _{the nitrification tank} is 0.01 to 0.5.
Requirement 3: The linear velocity ratio (LV _gas /LV water flow) between the linear velocity LV _{water flow} [m/h] of the water to be treated and the linear velocity LV _gas [m/h] of the gas in the stored _water in the nitrification tank is 0.3 to 6.0.
Requirement 4: The filling rate calculated by the following formula (1) is 75% or more.
Filling rate (%) = (bulk volume of multiple biological retainers) / (available water volume in nitrification tank) × 100 ... formula (1) The shaking biological nitrification method according to claim 1, wherein the biological support has a porous carrier and nitrifying bacteria supported on the carrier. The shaking biological nitrification method according to claim 1 or 2, in which the water to be treated is passed through as an upward flow. a nitrification tank loaded with a plurality of biological retainers;
a water-to-be-treated supply pipe for supplying water to be treated into the nitrification tank;
a water flow rate adjusting means for adjusting the flow rate of the water to be treated supplied to the nitrification tank;
a gas supplying device that supplies gas to the stored water in the nitrification tank;
a control device electrically connected to at least the water flow rate adjusting means and the gas supply device;
Equipped with
The control device executes control that satisfies the following requirements 3 and 4,
A rocking biological nitrification device that satisfies the following requirements 1 and 2.
Requirement 1: The three-dimensional size of one of the bioretainers exceeds 5 mm in the maximum length direction and fits into a sphere having a diameter of 20 mm.
Requirement 2: The ratio S _outlet /S _{nitrification tank of} the cross-sectional area S of the outlet of the water to be treated supply pipe to the bottom area S of the _{nitrification} tank is 0.01 to 0.5.
Requirement 3: The linear velocity ratio (LV _gas /LV water flow) between the linear velocity LV _{water flow} [m/h] of the water to be treated and the linear velocity LV _gas [m/h] of the gas in the stored _water in the nitrification tank is 0.3 to 6.0.
Requirement 4: The filling rate calculated by the following formula (1) is 75% or more.
Filling rate (%) = (bulk volume of multiple biological retainers) / (available water volume in nitrification tank) × 100 ... formula (1) The oscillating biological nitrification apparatus of claim 4, _wherein the cross-sectional area S of the outlet of the treated water _supply pipe is the same as or larger than the cross-sectional area S of the treated water supply _pipe . The oscillating biological nitrification device according to claim 4 or 5, wherein a plurality of the discharge ports are disposed within the nitrification tank.

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