JP2022153861A - Biological nitrification method and biological nitrification system - Google Patents

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

The present invention relates to a bio-nitrification method and a bio-nitrification system.

A biological nitrification reaction is known in which ammoniacal nitrogen in water to be treated is converted to nitric acid by microorganisms. Ammonia nitrogen may be contained in, for example, groundwater, well water, lake water, river water, industrial wastewater, and the like.
As a general biological nitrification method for water to be treated containing low-concentration ammonia nitrogen, the water to be treated is forced through a fixed bed formed by filling a filter medium to which microbes such as nitrifying bacteria are adhered. There is a bed extrusion flow system (for example, Patent Document 1, Non-Patent Documents 1 and 2).

For example, in the fixed-bed push-flow biological nitrification system 100A shown in FIG. 5, water to be treated containing ammoniacal nitrogen is stored in the nitrification tank 105A from the supply pipe 104A. In the nitrification tank 105A, a filter layer 106A filled with filter media such as stones, ceramics, synthetic resins, etc. is formed. When the water to be treated is passed through the filter layer 106A, ammonia nitrogen is converted to nitrate nitrogen by microorganisms such as nitrifying bacteria adhering to the surface of the filter medium.

In the biological nitrification system 100A of the fixed bed extrusion flow type, the water to be treated is passed through the filter layer 106A so as to form an extrusion 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 the biological nitrification treatment flows out from the outflow pipe 110A.
According to the fixed-bed extrusion flow system, the nitrification reaction of the water to be treated containing low-concentration ammoniacal nitrogen can be carried out uniformly.

On the other hand, as a method for biological nitrification of water to be treated containing a high concentration of ammonia nitrogen, there is a fluidized bed mixed flow method in which the water to be treated is passed while circulating and flowing carriers holding microorganisms in a nitrification tank (for example, , Patent Documents 2 and 3).
For example, in the fluidized bed mixed flow type biological nitrification system 100B shown in FIG. 6, the water to be treated is supplied to the nitrification tank 105B while air is supplied from the air diffuser 107 to the water stored in the nitrification tank 105B. When the water to be treated flows into the nitrification tank 105B, it is instantly mixed with the stored water, and the concentration of the entire stored water becomes uniform.
In the fluidized bed mixed flow system, the biological support 106B carrying nitrifying bacteria etc. is fluidized in the retained water in the nitrification tank 105B. When the biological support 106B and the water to be treated come into contact with each other, ammonia nitrogen is converted to nitrate nitrogen and treated.
According to the fluidized bed mixed flow system, water to be treated containing a high concentration of ammoniacal nitrogen can be treated.

JP 2005-288417 A JP 2017-202473 A Japanese Unexamined Patent Application Publication No. 2011-212670

Groundwater Purification Treatment Using Iron Bacteria, Shinko Pantech Technical Report, Vol. 45 No. 2, p. 16-24 (2002) Collection of flocculation/sedimentation/flotation separation/granular layer filtration case studies for users, 5.3 Ultra-high-speed chemical-free biological treatment equipment using groundwater as raw water, Japan Liquid Clarification Technology Industry Association, p. 64-67 (2019)

However, in general fixed-bed extrusion flow processes such as the methods of Patent Document 1 and Non-Patent Documents 1 and 2, the nitrification rate per nitrification tank is as low as about 0.1 kgN/m ³ /d. In addition, when the water to be treated containing a high concentration of ammoniacal nitrogen is applied to the treatment of the fixed bed extrusion flow system, there is also the problem that the treatment system becomes large-sized.

In the method of Patent Document 2, the bulk volume of the nitrifying bacteria-supporting carrier is small relative to the amount of effective water (30% by volume in Example 1, which is 20% by volume when converted to the filling rate in the present invention described later. ). However, according to the studies of the present inventors, if the volume ratio is higher than this, the fluidity of the nitrifying bacteria-carrying carrier is lowered, resulting in the problem of dead space and short-circuit flow. As a result, there is a possibility that the nitrification reaction cannot be uniformly performed on the water to be treated.
In addition, 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 cannot further increase the volume ratio of the nitrifying bacteria-supporting carrier, and further improvement of the nitrification rate is desired. can't
In addition, in the method of Patent Document 2, the nitrification rate per one nitrification tank is low, and in order to treat the water to be treated containing a high concentration of ammoniacal nitrogen, it becomes necessary to further increase the number of nitrification tanks. Another problem is that the system becomes large.

In Patent Document 3, the concentration of O ₂ in the high-concentration oxygen gas supplied to the gas phase of the nitrification tank is 80-90%, and the nitrification process is performed under high load conditions. However, supplying high-concentration oxygen gas with an O ₂ concentration of 80 to 90% to the gas phase portion of the nitrification tank is disadvantageous in terms of cost and poses a problem in terms of safety.

INDUSTRIAL APPLICABILITY The present invention is capable of treating water to be treated containing a high concentration of ammoniacal nitrogen at a high rate of nitrification, enabling downsizing of the treatment system, high safety, and a biological nitrification system that is advantageous in terms of cost. I will provide a.

As a result of extensive studies, the present inventors found that (i) the average density of the biological support, (ii) the specific filling rate of the biological support, and (iii) the air supply linear velocity with respect to the water flow linear velocity of the water to be treated The inventors have found that the above problem can be solved by maintaining the ratio of , within a predetermined range. The present 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.

The present invention has the following aspects.
[ ¹ ] A biological nitrification method for treating ammonia nitrogen in water to be treated; When _{passing water} : _Linear velocity ratio (LV _air /LV _{water flow} ) is 5.0 or less, and the filling rate calculated by the following formula (1) is 25% by volume or more.
Filling rate (% by volume)=((total volume of a plurality of biological supports)/(total volume of a plurality of biological supports and the volume of water stored in the nitrification tank))×100 Equation (1 )
[2] The biological nitrification method according to [1], wherein the biological support comprises a porous carrier and nitrifying bacteria retained on the carrier.
[3] The biological nitrification method of [1] or [2], wherein the linear velocity LV _air is 30 m/h or less.
[4] When the iron content of the water to be treated is more than 0.5 mg/L, the linear velocity ratio (LV _air /LV _{water flow} ) is set to 0.20 to 5.0, [1] to The biological nitrification method according to any one of [3].
[5] a nitrification tank loaded with a plurality of biological supports having an average density of 1.0 to 1.4 g/cm ³ ; a water supply pipe to supply water to be treated to the nitrification tank; a water flow adjusting means provided in a treated water supply pipe for adjusting the flow rate of the water to be treated supplied to the nitrification tank; an air diffuser for supplying air to the water stored in the nitrification tank; a control device electrically connected to the _water volume adjusting means and the air diffuser; The linear velocity ratio (LV _air / LV _{water flow} ) to the linear velocity LV _air [m / h] of the air in the stored water is set to 5.0 or less, and the filling rate calculated by the following formula (1) A bio-nitrification system having a control unit of 25% by volume or more.
Filling rate (% by volume)=((total volume of a plurality of biological supports)/(total volume of a plurality of biological supports and the volume of water stored in the nitrification tank))×100 Equation (1 )
[6] The biological nitrification system of [5], wherein the biological support comprises a porous carrier and nitrifying bacteria retained on the carrier.
[7] The biological nitrification system of [5] or [6], wherein the control unit sets the linear velocity LV _air to 30 m/h or less.
[8] The control unit sets the linear velocity ratio (LV _air /LV _{water flow} ) to 0.20 to 5.0 when the iron content of the water to be treated exceeds 0.5 mg/L. , the biological nitrification system according to any one of [5] to [7].

EFFECTS OF THE INVENTION According to the present invention, water to be treated containing a high concentration of ammoniacal nitrogen can be treated at a high nitrification rate, the treatment system can be downsized, and the biological nitrification method and the biological nitrification method are highly safe and advantageous in terms of cost. A nitrification system is provided.

1 is a schematic configuration diagram showing an example of a biological nitrification system according to one embodiment; FIG. FIG. 4 is a schematic diagram for explaining a method for measuring the average density of a plurality of biological supports; FIG. 4 is a schematic diagram for explaining a method for measuring the average density of a plurality of biological supports; FIG. 2 is a schematic configuration diagram showing another example of the biological nitrification system according to one embodiment; 1 is a schematic configuration diagram showing an example of a conventional biological nitrification system; FIG. 1 is a schematic configuration diagram showing an example of a conventional biological nitrification system; FIG.

The following terms used herein have the following meanings.
"Ammoniacal nitrogen" refers to nitrogen contained in water as an ammonium salt. It is also called ammonia nitrogen.
"-" indicating a numerical range means that the numerical values before and after it are included as lower and upper limits.

<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. Examples include ground water, well water, lake water, river water, factory water, sewage, and waste water. However, the water to be treated is not limited to these examples.

In addition to ammonia nitrogen, the water to be treated contains 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. It may contain more. However, the components of the water to be treated are not limited to these.
Main components of organic matter in the water to be treated include humic acid and fulvic acid. However, the water to be treated may contain organic matter other than these exemplified components.

The content of ammonia 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 advantage of applying a biological nitrification method and a nitrification system capable of realizing a high nitrification rate is further increased. In the case of containing a higher concentration of ammonium nitrogen (for example, when the content of ammonium nitrogen is 15 to 50 mg/L), it is preferable to use a multistage nitrification tank.
The iron content of the water to be treated is not particularly limited, but is, for example, within the range of 0 to 20 mg/L. According to the biological nitrification method and nitrification system according to one embodiment, a high nitrification rate can be achieved even when the water to be treated contains iron.

<Biological nitrification system>
FIG. 1 is a schematic configuration diagram showing an example of a biological nitrification system according to one embodiment.
The biological nitrification system 1A includes a pump 3 for pumping well water (an example of water to be treated) from a well 2; a first end connected to the pump 3; water flow rate adjusting means (not shown) provided in the middle of the water supply pipe 4A to adjust the flow rate of the water to be treated supplied to the nitrification tank 5; nitrification an air diffuser 7, an air supply pipe 8 and a blower 9 of an air diffuser for diffusing air in the tank 5; a control device (not shown) electrically connected to the water flow adjusting means and the air diffuser; a treated water outlet pipe 10A connected to the wall surface near the top of the nitrification tank 5;

The to-be-treated water supply pipe 4A supplies the well water of the well 2 into the nitrification tank 5 as the to-be-treated water. In the middle of the water-to-be-treated supply pipe 4A, a water-flow measuring means (not shown) for measuring the amount of the water to be treated supplied into the nitrification tank 5; and a water-flow adjusting means are provided.
For example, a flow control valve can be used as the water flow control means.
Examples of water flow measuring means include a rotameter, an electromagnetic flowmeter, and the like.
The to-be-treated water supply pipe 4A may be provided with a water quality meter for measuring the iron content and ammonia nitrogen of the to-be-treated water supplied to the nitrification tank 5 .

The nitrification tank 5 is for treating ammonia nitrogen in the water to be treated by a biological nitrification reaction using the biological support 6 . A plurality of biological supports 6 are loaded in the nitrification tank 5 .
In the nitrification tank 5, a biosupport region 11 is formed by loading a plurality of biosupports 6 therein. In the biological support area 11, each biological support 6 is loaded so as to be swingable when water to be treated flows.
The nitrification tank 5 brings the water to be treated into contact with each biological support 6 in the biological support region 11 to oxidize the ammonia nitrogen in the water to be treated water. The linear velocity of the water to be treated flowing through the biological support 6 is LV _{water flow} [m/h].

The biological support area 11 may be formed by covering the bottom of the nitrification tank 5 with a plurality of biological supports 6 and stacking the plurality of biological supports 6 in the height direction of the nitrification tank 5 in multiple stages. good.

The volume of the nitrification tank 5 is not particularly limited. For example, it can be in the range of 0.1 to 100 m ³ . Also, the material of the nitrification tank 5 is not particularly limited. For example, acrylic resins, fiber-reinforced resins, and the like can be used. A transparent material is preferable, and an acrylic resin is more preferable in terms of easy observation of the biological support 6 in the nitrification tank 5 .

The biological support 6 is a carrier holding nitrifying bacteria. That is, the biological support 6 has a carrier and nitrifying bacteria held by the carrier. The shape of the carrier is not particularly limited, but examples thereof include cubes, rectangular parallelepipeds, spheres, cones, polygonal pyramids, cylinders, filaments and the like. However, a rectangular parallelepiped, a cube, or a sphere is preferable in consideration of the ease of loading into the nitrification tank 5 and the ability to oscillate when water is passed through.
Further, in a plurality of biological support bodies 6, the shape of each carrier does not have to be the same as each other, and may be different from each other. Although each carrier preferably has the same shape from the viewpoint of easy maintenance of the rocking state and easy uniform nitrification reaction, it is not necessarily limited to this.

As the carrier, a porous carrier is preferable because it can carry nitrifying bacteria on the surface and inside of the carrier, that is, it can carry a large amount of nitrifying bacteria, further improving the rate of nitrification. When the carrier is porous, nitrifying bacteria may be carried 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, even more preferably about 0.1 to 0.5 mm.

In particular, a sponge carrier is preferable because it can maintain good support of nitrifying bacteria and minimize damage to pumps and pipes.
Materials for the sponge carrier include polyvinyl alcohol, polyethylene glycol, polyurethane and the like.

The apparent surface area of the sponge carrier is preferably 300 m ² /m ³ or more, more preferably 600 m ² /m ³ or more. When the apparent surface area of the sponge carrier is at least the above lower limit, the surface area is sufficiently large, and the contact efficiency with the water to be treated increases. In addition, the nitrifying bacteria are easily retained, the oxygen supply efficiency is increased, and the nitrification rate is further increased.

Examples of nitrifying bacteria include known nitrifying bacteria used for biological nitrification of ammoniacal nitrogen. Nitrosomonas typified by nitrifying bacteria are autotrophic, basically using carbon dioxide gas as the sole carbon source, and can grow in the presence of ammonia without requiring an organic substrate, but their growth rate is extremely low. Therefore, in order to increase the nitrification rate, it is necessary to maintain a large amount of nitrifying bacteria in the nitrification tank. Therefore, it is preferable to retain the nitrifying bacteria in a state of being carried on a carrier instead of floating cells.
As a method for supporting nitrifying bacteria on a carrier, for example, there is a method in which the carrier is put into a nitrification tank of an existing water treatment system and the nitrifying bacteria grow on the surface of the carrier.

The average density of the biological support 6 is 1.0-1.4 g/cm ³ , preferably 1.05-1.30 g/cm ³ , more preferably 1.10-1.20 g/cm ³ . Here, the average density of the biological support 6 is the average density in a wet state in which each biological support 6 retains nitrifying bacteria. Wet conditions will be discussed later.
If the average density of the biological support 6 is equal to or higher than the lower limit of the above range, the biological support 6 settles in the water retained in the nitrification tank 5 . Therefore, the water to be treated uniformly comes into contact with the whole of the plurality of biological supports 6 , and the nitrification reaction tends to occur uniformly within the nitrification tank 5 .
If the average density of the biological support 6 is equal to or less than the upper limit of the above range, the biological support 6 is easily rocked. Therefore, the rocking state of the organism retainer 6 can be maintained without aeration by an air diffuser when water is passed. As a result, the energy consumption of the air diffuser can be reduced, which can provide further cost advantages.
Therefore, if the average density of the organism support 6 is within the above range, the organism support 6 will be able to oscillate in the pooled water when the water to be treated flows. It becomes difficult to adhere to the holder 6 . As a result, the biological support is easily rocked when water is passed through, so that the contact efficiency between the water to be treated and each biological support is improved, and the nitrification rate is improved. Moreover, it is advantageous in terms of cost.

The average density of the biological support can be calculated as follows.
First, the mass m [g] of a plurality of biological supports is measured. For example, as shown in FIG. 2, with a container 20 having a known volume placed on a mass meter 30, the biological support 6 is taken out from the nitrification tank and loaded into the container 20 so that the bulk volume is constant. do. Here, in order to keep the bulk volume constant, a reference line L is drawn on the side surface of the container 20 whose volume is known, and the organism holding body 6 is placed so that the reference line L and the upper surface of the organism retainer 6 on the uppermost stage are aligned. A body 6 is loaded into a container 20 .

When the biological support is taken out from the nitrification tank, the retained water adhering to the carrier drips from the biological support. The mass of this dripped stored water shall not be included in the mass m [g] of the plurality of biological supports. In the present embodiment, a biological support having a bulk volume of about 500 cm ³ is scooped out from the nitrification tank and held on the water surface, and the "wet state" of the biological support is defined as the time when water droplets stop dripping for 5 seconds or more. . The container 20 is loaded with such a wet biological support.
After that, the operation of taking out the biological supports from the nitrification tank and loading them into the container 20 is repeated, and the mass of the plurality of biological supports when the total bulk volume of the plurality of biological supports reaches a predetermined value is the mass of the plurality of biological supports m[ g].

Subsequently, the volume V [cm ³ ] of a plurality of biological supports is measured. As shown in FIG. 3, water is poured from a separately prepared beaker 40 into a container 20 loaded with a wet biological support 6 until it reaches a predetermined bulk volume, that is, up to a reference line L, and the biological support 6 is Fill the space between them 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 defined as the volume V [cm ³ ] of the plurality of biological supports.
Finally, the mass m [g] of the plurality of biological supports is divided by the volume V [cm ³ ] of the biological support to obtain the average density m/V [g/cm ³ ] of the biological support 6 .

The average volume of one biological support is preferably 0.03 to 5.00 cm ³ , more preferably 0.06 to 1.00 cm ³ , and more preferably 0.10 to 0 0.30 cm ³ is considered more preferred. If the volume of one biological support is equal to or higher than the lower limit of the above range, it is considered that the biological support is less likely to flow in the nitrification tank, and the nitrification rate tends to increase. If the volume for one organism support is equal to or less than the upper limit of the above range, it is considered that the organism support will easily swing even if the LV _air is relatively small.
Here, the average volume for one biological support is a value obtained by dividing the total volume of a plurality of biological supports in the nitrification tank by the number of biological supports in the nitrification tank.
Moreover, in a plurality of biological supports, the volumes of the individual biological supports do not all need to be the same, and may differ from each other.

A biological support can be prepared, for example, as follows.
The carrier is passed through and cultured using a nitrification tank of an existing biological nitrification system. For example, a new porous carrier often has a density of less than 1 g/cm ³ because it contains air inside.
As the carrier is cultured in water in the nitrification tank, air is gradually released from the carrier, and the nitrifying bacteria adhere to the carrier. Then, water-flow culture is performed until the density in a wet state containing nitrifying bacteria and water reaches a range of 1.0 to 1.4 g/cm ³ to obtain a biological support.

The air diffuser in the biological nitrification system 1A shown in FIG. It comprises a blower 9 provided at one end; The air diffuser is, in principle, for aerating and removing the solid matter adhering to the surface of the biological support 6 . However, the air aerated at this time can also serve as an oxygen source for the nitrifying bacteria in the biological support 6 .

Examples of the air diffuser 7 include an air diffuser having air diffusion holes (not shown), an air diffuser bulb, and a diffuser. The air diffuser removes solid matter adhering to the surface of the biological support 6 by air bubbles supplied from the air diffuser 7 into the nitrification tank 5 . The linear velocity of the air supplied to the water stored in the nitrification tank 5 is LV _air [m/h].

Examples of the air supply amount adjusting means include a gate valve and a butterfly valve.
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, the air diffuser is unnecessary, and the air diffuser 7, the air supply pipe 8 and the blower 9 etc. can be omitted.

The treated water outflow pipe 10A is for taking out the treated water from the nitrification tank 5. As shown in FIG.
In the middle of the treated water outflow pipe 10A, an outflow measuring means (not shown) for measuring the amount of treated water flowing out from the nitrification tank 5; Means (not shown) are provided.
Examples of outflow measuring means include a rotameter, an electromagnetic flowmeter, and the like.
For example, a flow control valve can be used as the outflow control means.

The control device includes an interface section (not shown), a storage section (not shown), a processing section (not shown), a determination section (not shown), a control section (not shown), and the like.
The interface section electrically connects the flow rate measuring means, the flow rate adjusting means, the water quality meter, the outflow rate measuring means, the outflow rate adjusting means, the blower of the air diffuser, the air rate adjusting means, and the control section. It is.

The storage unit stores the operating conditions and the like of the biological nitrification system 1A for calculating the linear velocity ratio (LV _air /LV _{water flow} ) and the filling rate calculated by the following formula (1).
Filling rate (% by volume)=((total volume of a plurality of biological supports 6)/(sum of total volume of a plurality of biological supports 6 and volume of water stored in the nitrification tank 5))×100 formula (1)

The operating conditions stored in the storage unit include, for example, the projected area of the nitrification tank 5, the average density of the biological support 6 (a value within the range of 1.0 to 1.4 g/cm ³ ), and the inside of the nitrification tank 5. The total mass and number of the biological support bodies 6 loaded in the chamber, the supply amount of the water to be treated, the outflow amount of the treated water, the air supply amount in the air diffuser, and the like can be mentioned.

In the biological nitrification system 1A, the “total volume of the plurality of biological supports 6” in the formula (1) is the sum of the volumes of all the biological supports 6 forming the biological support region 11. This "total volume of biological support" can be calculated, for example, by dividing the total mass of all biological supports 6 put into the nitrification tank 5 by the average density of the biological supports.

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

The processing unit can perform operation 1 below.
Calculation 1: Calculate the total volume of the plurality of biosupports 6 and the volume of the water retained in the nitrification tank 5, and then calculate the filling rate of the biosupports 6 from the above equation (1).

The processing unit can also perform operation 2 below.
Calculation 2: LV _{water flow} is calculated from the flow rate value of the water flow rate adjusting means and the projected area of the nitrification tank 5, and LV _air is calculated from the supply value of the air flow rate adjusting means and the projected area of the nitrification tank 5, and the linear velocity Calculate the ratio (LV _air /LV _{water flow} ).

The determination unit determines whether the filling rate of the biological support 6 calculated by the processing unit is 25% by volume or more; the linear velocity ratio (LV _air /LV _{water flow} ) is 5.0 or less and whether or not the iron content of the water to be treated measured by a water quality meter is 1.0 mg/L or more.

The control unit controls the biological nitrification system 1A based on the determination result of the determination unit, the operating conditions of the biological nitrification system 1A stored in the storage unit, and the like. In particular, the control unit controls the filling rate of the biological support 6 to 25% by volume or more and the linear velocity ratio (LV _air /LV _{water flow} ) to 5.0 or less.
For example, when the determination unit determines that the filling rate of the biological support 6 is less than 25% by volume, the control unit reduces the supply amount of the water to be treated so as to reduce the volume of the water stored in the nitrification tank 5. It is possible to control the water flow adjusting means; or to control the outflow adjusting means so as to increase the outflow of the treated water and reduce the volume of the water retained in the nitrification tank 5 .

On the other hand, when the determination unit determines that the linear velocity ratio (LV _air /LV _{water flow} ) is greater than 5.0, the control unit reduces the amount of air supplied by the air diffuser 7 to LV _air [m/h ] or control the air amount adjustment means to lower; or control the water flow rate adjustment means to increase the LV _water flow rate [m / h] by increasing the supply rate of the water to be treated; outflow of treated water It is possible to control the outflow amount adjustment means so as to increase the amount and increase the LV _{water flow} [m/h].
In addition, when the determination unit determines that the iron content of the water to be treated is greater than 0.5 mg / L, the control unit so that the LV _air / LV _{water flow} is 0.20 to 5.0 controls the air amount adjusting means so as to _adjust the amount of air supplied by the air diffuser 7; can.

The processing unit, determination unit, and control unit may be implemented by dedicated hardware, and are configured by a memory and a central processing unit (CPU) to implement the functions of the processing unit, determination unit, and control unit. The function may be implemented by loading a program for the function into a memory and executing the program.
An input device, a display device, and the like may be connected to the control device as peripheral devices. Examples of input devices include input devices such as display touch panels, switch panels, and keyboards. Examples of the display device include a liquid crystal display device and a display device such as a CRT.

<Biological nitrification method>
An example of a nitrification method using the biological nitrification system 1A will be described below.
First, a plurality of biological support bodies 6 that have been passed through and 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 preferable to leave a space for rocking between the living body holders 6 so that the living body holders 6 can swing when the water flows.

Next, the water pump 3 provided at one end of the water supply pipe 4A to be treated is driven to supply the water to be treated containing ammonia nitrogen from the well 2 to the nitrification tank 5 through the water supply pipe 4A to be treated. and stored in the nitrification tank 5. At this time, when the nitrification tank 5 is filled with water, the spaces between the biological support bodies 6 in the biological support area 11 are also filled with water. If water storage is continued thereafter, the uppermost biological support 6 in the biological support area 11 is immersed in the stored water.

(Biological nitrification reaction)
When the water to be treated in the nitrification tank 5 is passed through the biological support area 11 , the water to be treated comes into contact with the biological support 6 . Then, the ammonia nitrogen in the water to be treated is oxidized by the nitrifying bacteria in the biological support 6 to become nitrate nitrogen. In this manner, the water to be treated containing ammoniacal nitrogen is treated in the nitrification tank 5 to obtain treated water. At this time, in the biological nitrification system 1A, the water to be treated is passed through the plurality of biological support bodies 6 in the biological support area 11 as an upward flow.

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 (% by volume)=((total volume of a plurality of biological supports 6)/(sum of total volume of a plurality of biological supports 6 and volume of water stored in the nitrification tank 5))×100 formula (1)

In this embodiment, since the filling rate calculated by the formula (1) is set to 25% by volume or more, the nitrification rate is sufficiently high. In order to increase the nitrification rate, the filling rate calculated by the above formula (1) is preferably 32% by volume or more, more preferably 42% by volume or more, and even more preferably 45% by volume or more. .
Although the upper limit of the filling rate calculated by the formula (1) is 100% by volume, it is preferably 65% by volume or less in terms of rocking the biological support 6 when water is passed, and 60% by volume. % or less, more preferably 55 volume % or less.

(Control of filling rate)
When the determination unit of the control device determines that the filling rate of the biological support 6 is less than 25% by volume, the control unit reduces the supply amount of the water to be treated to decrease the volume of the stored water in the nitrification tank 5. or control the outflow adjusting means to increase the outflow of treated water and reduce the volume of water stored in the nitrification tank 5 . In addition to reducing the volume of the retained water, the biological support 6 may be replenished into the nitrification tank 5 manually by an operator or automatically by a control device.

(Control of linear velocity ratio)
In this embodiment, the linear velocity ratio (LV _air /LV _{water flow} ) is set to 5.0 or less. According to such a configuration, it is possible to maintain the vibrating state of the biological support for a long time when the water is passed through, and the nitrification reaction can be uniformly performed, and the water to be treated containing a high concentration of ammoniacal nitrogen can be treated at a high nitrification rate. become. Moreover, since it is not necessary to supply air more than necessary, it is advantageous in terms of cost and safety is enhanced. Therefore, the linear velocity ratio (LV _air /LV _{water flow} ) is preferably 0.1 to 4.0, more preferably 0.5 to 1.0.

When the determination unit of the control device determines that the linear velocity ratio (LV _air /LV _{water flow} ) is greater than 5.0, the control unit reduces the amount of air supplied by the air diffusion unit 7 to increase the LV _air [ m/h] to be low; or control the water flow rate adjusting means to increase the LV _water flow rate [m/h] by increasing the supply rate of the water to be treated; It is possible to control the outflow amount adjustment means so as to increase the outflow amount of water and increase the LV _{water flow} [m/h].

Although the LV _{water flow} is not particularly limited, it 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. When the LV _water flow is equal to or higher than the lower limit of the range, the organism support 6 tends to swing. When the LV _water flow is equal to or less than the upper limit of the above range, the nitrification reaction efficiency can be easily maintained, and the nitrification rate can be further improved.

(LV _air control)
The amount of air diffused from the diffuser section 7 of the air diffuser can be adjusted to an arbitrary amount by an air amount adjusting means (not shown). For example, the LV _air is preferably 50 m/h or less, more preferably 30 m/h or less, in terms of rocking the organism support 6 . When the iron content of the water to be treated is 0.5 mg/L or less, it is preferable to set the LV _air to 0 m/h, that is, not to supply air, from the viewpoint of reducing energy consumption.

In the biological nitrification system according to one embodiment, when the amount of components that can adhere to the surface of the biological support 6 is small, such as when the iron content of the water to be treated is 0.5 mg/L or less, scattering Aeration with an air device is not required. This is because the organism retainer 6 oscillates when water is passed through, so solids are less likely to adhere to the surface of the organism retainer 6 . Eliminating aeration provides additional cost advantages.
On the other hand, for example, when the iron content of the water to be treated exceeds 0.5 mg/L, particularly when it is 1.0 mg/L or more, solids such as iron hydroxide generated during the nitrification reaction are biologically retained. Large amounts may adhere to the surface of the body. Therefore, it is preferable to adjust the amount of air supplied from the air diffuser 7 into the nitrification tank 5 by driving the air diffuser so that the LV _air /LV _{water flow} ratio is 0.20 to 5.0. This is because the solid matter adhering to the surface of the biological support 6 can be aerated and removed, and the nitrification rate can be increased.
Alternatively, the LV _{water flow rate may be adjusted from each flow rate of the water} flow rate adjusting means and the outflow rate adjusting means so that the LV _air /LV _water flow rate is 0.20 to 5.0.

<Mechanism of action>
In the biological nitrification method according to one embodiment described using the above example, (i) the average density of the biological support, (ii) the specific filling rate of the biological support, and (iii) the linear velocity ratio (LV _air / LV _{water flow} ) satisfies a predetermined condition. Therefore, the biological support can be oscillated in the nitrification tank when water is passed through, and solid matter is less likely to adhere to the surface of the biological support. In addition, the nitrification reaction can be carried out uniformly. As a result, the reaction efficiency of the nitrification reaction by the biological support is improved.
In addition, since the biological support is rockable, the water to be treated efficiently comes into contact with the entire biological support when the water is passed. As a result, it is possible to prevent the occurrence of short-circuit currents and the occurrence of dead spaces not in contact with the biological support 6, even though the filling rate of the biological support is 25% by volume or more. can be realized.

According to this embodiment, an excellent nitrification rate can be achieved, so the need to increase the number of nitrification tanks is reduced, and the size of the nitrification tank itself can be reduced. Moreover, since air is supplied into the nitrification tank instead of the high-concentration oxygen gas, safety is high. In addition, since the air supply amount is suppressed so that the linear velocity ratio (LV _air /LV _{water flow} ) is within a predetermined range, the energy consumption of the air diffuser is reduced, which is advantageous in terms of cost.
Therefore, according to the biological nitrification method according to one embodiment, the water to be treated containing a high concentration of ammoniacal nitrogen can be treated at a high nitrification rate, the treatment system can be downsized, the safety is high, and the cost is high. But it is advantageous.

For example, in a nitrification method using a fluidized bed mixed flow method as disclosed in Patent Document 2, when the filling rate is 25% by volume or more, dead space and short-circuit flow occur due to poor fluidity of the carrier. There is a limit.
On the other hand, in the present embodiment, the organism-supporting bodies oscillate when water is passed through, and the water to be treated efficiently contacts the plurality of organism-supporting bodies as a whole. Therefore, it is possible to prevent the generation of short-circuit current and the generation of dead space that does not come into contact with the biological support even when the predetermined filling rate is 25% by volume or more, and as a result, the nitrification rate can be increased.

In this embodiment, the biological support is oscillatable 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 adhering to the surface of the biological support can be sufficiently removed without aeration using an air diffuser, and the nitrification reaction efficiency is improved. can be maintained high to achieve a high nitrification rate. In this case, the energy consumption of the air diffuser can be further reduced, resulting in a significant cost effect.
On the other hand, as shown in Examples below, ammonia nitrogen can be treated at a high nitrification rate even when the iron content of the water to be treated exceeds 0.5 mg/L.

Further, since the biological nitrification system 1A described above has the above-described configuration, the biological nitrification method according to the above-described embodiment can be implemented by using the biological nitrification system 1A, and the above-described mechanism of action can be exhibited.

<Other embodiment examples>
Although one embodiment has been shown and described above, the present invention is not limited to the embodiment disclosed in this specification, and can be implemented with appropriate modifications within the scope of the invention. The embodiments disclosed herein can be embodied in various other forms, and various omissions, substitutions, and modifications are possible without departing from the scope of the invention.

For example, the biological nitrification system 1B shown in FIG. It differs from the nitrification system 1A. In the biological nitrification system 1B, when the water to be treated is passed through the biological support body 6, the water to be treated flows downward from the upper side to the lower side of the biological support area 11 as a downward flow.
Even when the water to be treated flows downward as in the biological nitrification system 1B, the same effect as in the biological nitrification system 1A can be obtained, and a high nitrification rate can be achieved.

In addition, the number of nitrification tanks is not limited to one, and may be plural. For example, if the ammoniacal nitrogen content of the water to be treated is 2 mg/L or less, the number of nitrification tanks may be one. The number of nitrification tanks may be increased to a plurality, or the number of nitrification tanks provided with an air diffuser to promote the nitrification reaction may be one. For example, each time the content of ammonia nitrogen increases by about 6 mg/L, the number of nitrification tanks provided with a diffuser may be increased by one.
The air diffuser is also not limited to the illustrated form, and various forms of air diffuser can be employed. Alternatively, a DO meter for measuring the dissolved oxygen concentration (DO) of the water stored in the nitrification tank 5 may be used.

Hereinafter, although illustration is omitted, a pre-treatment device for pre-treatment of the water to be treated supplied to the nitrification tank 5 or a post-treatment device for post-treatment of the treated water flowing out from the nitrification tank 5 may be used. The pre-treatment device and the post-treatment device can be appropriately installed according to the quality of the water to be treated, the quality of the treated water, and the like.
Examples of the pretreatment device include a raw water storage tank, a dissolved oxygen supply device, a sand filter tower, and the like. In order 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 in the above-described embodiments. 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, the It should be placed between the tanks.
Examples of the post-treatment device include an ion exchange treatment tank, a coagulant addition device, an oxidant addition device, a sand filtration tower, a membrane filtration device, a sterilant addition device, and the like.
The use of the final treated water after post-treatment is not particularly limited. Examples include, but are not limited to, domestic water, drinking water, and the like.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to the following descriptions.

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

<Construction of test system>
(biological support)
As a 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 water culture was 0.044 g/cm ³ . These sponge carriers were passed through and cultured in a nitrification tank of an existing biological nitrification system to prepare approximately 11 kg (approximately 13,000 pieces) of biological supports. After water culture, the biological support was scooped out from the nitrification tank and held on the water surface. When water droplets stopped dripping for 5 seconds or more, the biological support was judged to be in a wet state, and the liquid was placed in a 10 L graduated container. loaded.
When the biological support was completely loaded into the 10 L graduated vessel, the mass m of the biological support was 5776 g.
After that, water was poured from a separately prepared beaker into the graduated container charged with the biological support to fill the space between the biological supports, and when the water surface reached the 10 L scale, the water supply was stopped. At this time, since the amount of water poured from a separately prepared beaker was 4767 cm ³ , the volume V of the biological support was set to 10000 cm ³ (10 L)−4767 cm ³ =5233 cm ³ .
Therefore, the average density of the biological support was calculated as 5776 g/5233 cm ³ ≈1.1 g/cm ³ .

(Nitrification tank)
Two cylindrical transparent acrylic water tanks were connected in series. Each water tank has a diameter φ of 150 cm, a height of 750 cm, and an effective water volume of 13.5 L. A diffuser ball was provided at the bottom of each water tank. Each of the first and second tanks was filled with about 6 kg of biological support, and was used as a tank for nitrification reaction. The raw water storage tank and the treated water at the outlet of the first tank were aerated by a dissolved oxygen supply device until the dissolved oxygen concentration was sufficiently saturated, and then passed through.

(Biological nitrification system)
As a biological nitrification system, the same system as the biological nitrification system 1A shown in FIG. 1 was prepared except that the number of nitrification tanks was different. As described above, the raw water storage tank and the treated water from the outlet of the first tank were aerated by the dissolved oxygen supply device until the dissolved oxygen concentration was sufficiently saturated, and then passed through.
With all of the biological supports in the nitrification tank immersed in the stored water, air was continuously supplied from the diffuser bulb at the bottom of the tank, and the LV _air was changed to 0 m/h, 10 m/h, 30 m/h, and 60 m/h. h, and the rocking state of the loaded biological support of about 11 kg was visually confirmed. As a result, when the LV _air was 30 m/h, approximately half of the biological support began to flow, but the rest of the biological support was able to maintain a rocking state. When the LV _air was 60 m/h, almost all biosupports flowed.
On the other hand, while measuring the ammonia nitrogen concentration of the treated water after the nitrification reaction, the amount of water passing is gradually increased, and the LV _{water passing} so that the ammonia concentration value of the treated water in the second tank can be maintained at 0.1 mg / L or less. The maximum value of [m/h] was obtained. As a result, in the case of the biological nitrification system of this example, the maximum value was 17.8 m/h.

<Measurement method>
(LV _air )
LV _air [m/h] was calculated by dividing the air supply amount [m ³ /h] by the projected area of the water tank [m ² ].

(LV _{treated water} )
LV _{treated water} [m/h] was calculated by dividing the supply amount of treated water [m ³ /h] by the projected area [m ² ] of the water tank.

<Examples 1 to 6, Comparative Examples 1 to 7>
Under the conditions shown in Table 1, the water to be treated (1) was passed through the biological support in the nitrification tank. In each case where the LV _air was set to 0 m/h, no air was supplied, and in the other examples, air was continuously supplied from diffuser balloons.
When the LV _{water supply} was gradually increased after the start of water supply, the biological nitrification reaction could not catch up, and an ammonia nitrogen concentration of 0.1 mg/L or more was detected in the treated water. Each ammonia nitrogen concentration [kg/m ³ ] in the water to be treated and the treated water at that time was measured. On the other hand, the water flow rate M [m ³ /d] at the maximum value of LV _{water flow} that can maintain the ammonia nitrogen concentration in the treated water at 0.1 mg / L or less was obtained, and the nitrification rate v [kgN / m ³ /d] was calculated. Table 1 shows the results.

The nitrification rate v [kgN/m ³ /d] was calculated as follows.
Nitrification rate v [kgN/m ³ /d] = (Ammonia nitrogen concentration in treated water [kg/m ³ ]−Ammonia nitrogen concentration in treated water [kg/m ³ ]) × At maximum value of LV _{water flow} Water flow rate M [m ³ /d] ÷ water tank volume [m ³ ]

Then, the nitrification rate was evaluated according to the following criteria. Table 1 shows the results.
A: The nitrification rate is over 0.44 kgN/m ³ /d.
Good: The nitrification rate is more than 0.25 kgN/m ³ /d and 0.44 kgN/m ³ /d or less.
Δ: The nitrification rate is more than 0.22 kgN/m ³ /d and 0.25 kgN/m ³ /d or less.
x: The nitrification rate is 0.22 kgN/m ³ /d or less.

<Example 7>
As the biological nitrification system, the same system as the biological nitrification system 1B shown in FIG. A biological nitrification reaction was carried out in the same manner as in Example 6, except for the above. The nitrification rate v [kgN/m ³ /d] was calculated and evaluated in the same manner as in Example 1. Table 1 shows the results.

As shown in Table 1, when three of the average density of the biological support, the filling rate of the biological support, and the linear velocity ratio (LV _air /LV _{water flow} ) satisfy predetermined reaction conditions, a superior nitrification rate can be achieved. rice field.
Moreover, as shown in the results of Examples 6 and 7 in Table 1, excellent nitrification rates were achieved in both upward and downward water flow directions.

Regarding the rocking state of each example, in Comparative Examples 1 to 5, all of the biological supports flowed and the rocking state could not be maintained. On the other hand, in Examples 1 to 7, the rocking state of the biological support could be maintained. In Comparative Example 6, although the vibrating state of the biological support was maintained, the nitrification rate decreased due to the low filling rate. In Comparative Example 7, the biological nitrification tank was filled with 50% by volume of manganese sand (average density: 2.0 g/cm ³ ) as a filter medium, and water was passed through the tank. As a result, since the average density of the biological support was high, it was difficult to rock it. In addition, a dead space and a short-circuit flow are likely to occur, and clogging is likely to occur due to adhesion of solids to the surface of the biological support, resulting in poor contact efficiency between the water to be treated and each biological support. In addition, the fact that manganese sand has a lower ability to retain organisms than the organism retainers of Examples is also considered to be one of the reasons why the nitrification rate is lower than that of other Examples.

<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 obtained in the same manner as in <Examples 1 to 6 and Comparative Examples 1 to 7> except that the treatment conditions were changed as shown in Table 2 below. was calculated and evaluated.

As shown in Tables 1 and 2, in Example 8 in which the LV _water flow rate was 12.5 m/h without supplying air from the air diffuser ball, the LV water flow rate was the same as in Example 3 in which the LV _water flow rate was 12.5 m/h. A moderately good nitrification rate could be realized. From this result, even if the iron content is 0.5 mg/L, it was considered that the aeration by the air diffuser was not necessary and the energy consumption of the air diffuser 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 without aeration.

As shown in the results of Examples 10 to 13, when the iron content is more than 0.5 mg / L, air is supplied by an air diffuser, and the linear velocity ratio (LV _air / LV _{water flow} ) is A good nitrification rate could be achieved by maintaining it at 5.0 or less. Thus, it was thought that by setting the linear velocity ratio (LV _air /LV _{water flow} ) to 0.20 to 5.0, an excellent nitrification rate could be achieved even if the iron content increased.

As shown in the results of Examples 11 and 13, when the linear velocity ratio (LV _air /LV _{water flow} ) is 0.7, even if the iron content is 1.0 mg/L, it is 3.0 mg/L. However, a very good nitrification rate could be achieved.

1 biological nitrification system 2 well 3 pump 4 water supply pipe to be treated 5 nitrification tank 6 biological support 7 air diffuser (air diffuser)
8 Air supply pipe (air diffuser)
9 blower (air diffuser)
10 Treated water outflow pipe

Claims (8)

A biological nitrification method for treating ammoniacal nitrogen in water to be treated,
When the water to be treated is passed through a nitrification tank loaded with a plurality of biological supports having an average density of 1.0 to 1.4 g/cm ³ ,
The linear velocity ratio (LV _air /LV _{water flow} ) between the linear velocity LV _{water flow} [m/h] of the water to be treated and the linear velocity LV _air [m/h] of the air in the stored water in the nitrification tank is set to 5 0.0 or less, and the filling rate calculated by the following formula (1) is 25% by volume or more.
Filling rate (% by volume)=((total volume of a plurality of biological supports)/(total volume of a plurality of biological supports and the volume of water stored in the nitrification tank))×100 Equation (1 ) 2. The biological nitrification method according to claim 1, wherein said biological support comprises a porous carrier and nitrifying bacteria held on said carrier. Furthermore, the biological nitrification method according to claim 1 or 2, wherein the linear velocity LV _air is 30 m/h or less. Any one of claims 1 to 3, wherein when the iron content of the water to be treated exceeds 0.5 mg/L, the linear velocity ratio (LV _air /LV _{water flow} ) is 0.20 to 5.0. or the biological nitrification method according to item 1. a nitrification tank loaded with a plurality of biological supports having an average density of 1.0 to 1.4 g/cm ³ ;
a to-be-treated water supply pipe for supplying to-be-treated water to the nitrification tank;
a water flow rate adjusting means provided in the to-be-treated water supply pipe for adjusting the flow rate of the to-be-treated water supplied to the nitrification tank;
an air diffuser that supplies air to the water stored in the nitrification tank;
a control device electrically connected to at least the water flow adjusting means and the air diffuser;
with
The control device is
The linear velocity ratio between the linear velocity LV _{water flow} [m/h] when the water to be treated flows and the linear velocity LV _air [m/h] _of the air in the water stored in the nitrification tank (LV _air /LV flow _Water ) is 5.0 or less, and the biological nitrification system has a control unit that sets the filling rate calculated by the following formula (1) to 25% by volume or more.
Filling rate (% by volume)=((total volume of a plurality of biological supports)/(total volume of a plurality of biological supports and the volume of water stored in the nitrification tank))×100 Equation (1 ) 6. The biological nitrification system according to claim 5, wherein said biological support comprises a porous carrier and nitrifying bacteria held on said carrier. The biological nitrification system according to claim 5 or 6, wherein said control unit sets said linear velocity LV _air to 30 m/h or less. The control unit sets the linear velocity ratio (LV _air /LV _{water flow} ) to 0.20 to 5.0 when the iron content of the water to be treated is more than 0.5 mg/L. The biological nitrification system according to any one of 5 to 7.

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