JP7479998B2 - Biological Nitrification Equipment - Google Patents

Description

The present invention relates to a biological nitrification device.

Groundwater may contain ammonia nitrogen. Ammonia nitrogen in drinking water is generated in the early stages of decay and decomposition of organic matter, and has been treated as a pollution indicator. However, it was deleted from the Ministerial Ordinance on Water Quality Standards (Ministry of Health and Welfare Ordinance No. 56 of 1978) and does not fall under the 51 current drinking water quality standards (Ministry of Health, Labour and Welfare Ordinance on Water Quality Standards (Ministry of Health, Labour and Welfare Ordinance No. 101 of 2003, revised in 2014)).
Chlorine disinfection is essential when groundwater is used for drinking. When groundwater contains ammonia nitrogen, not only does it consume 8 to 10 times as much chlorine as the ammonia nitrogen, but it is also difficult to control the chlorine concentration, so it is common to remove ammonia nitrogen in a process prior to chlorine disinfection.
The breakpoint method is a common method for removing ammonia nitrogen, which involves adding 8 to 10 times the amount of chlorine relative to the concentration of ammonia nitrogen, and removing the ammonia nitrogen as nitrogen gas by the reaction of ammonia with chlorine. However, this method has the disadvantage of requiring a large amount of chlorine, which increases the cost of treatment. In addition, groundwater with a high concentration of ammonia nitrogen contains a high concentration of natural organic matter such as humic substances, so there is a high risk of the concentration of disinfection by-products such as trihalomethanes being increased by the reaction of these natural organic matter with chlorine.
In addition, the physicochemical method of treating ammonia nitrogen is the removal method using ion exchange resins. The least expensive method is biological nitrification (not a method of removing ammonia nitrogen, but a reaction that converts ammonia nitrogen into nitrate nitrogen through a biological oxidation reaction) or nitrification denitrification.

The occurrence of biological nitrification (i.e. bionitrification) in the field of drinking water treatment has been known since the days of slow sand filtration. Slow sand filtration is a method of filtration using silica sand as a filter medium, with a slow downward flow filtration rate of 4 to 5 m/day. It was invented in the UK in 1829 and has since spread throughout Europe and the rest of the world.
The Keage Water Purification Plant in Kyoto City, where the first modern water supply facility was introduced in Japan, adopted a British-style slow sand filtration system. This slow sand filtration system was a simple and highly efficient filtration system that used microorganisms and algae that lived on the surface of the filter media to attach suspended matter and microorganisms, including pathogens, in the raw water and filter them. Furthermore, when ammonia was present in the raw water, nitrifying bacteria grew, and in addition to the filtration action, biological nitrification reactions also occurred at the same time, which had the advantage of producing more stable purified water. However, when ammonia nitrogen was present at a high concentration of 2 mg/L, it consumed about 8 mg/L of dissolved oxygen (DO), consuming the entire amount of dissolved oxygen in the raw water, causing the treated water to become anaerobic and putrefy, resulting in unsanitary purified water. In the postwar advanced society where pollution was occurring, the slow sand filtration system was replaced by the American-style rapid sand filtration system when the ammonia nitrogen in rivers exceeded 2 mg/L.

However, if a means for supplying oxygen and a means for retaining nitrifying bacteria are provided, biological nitrification can be carried out inexpensively, and therefore various biological nitrification apparatuses have been devised and put to practical use.
Patent Document 1 describes a biological nitrification apparatus in which the filter medium is granular zeolite and the oxygen supply means is an aeration means at the top of the filter layer.
Non-Patent Document 1 describes a biological nitrification apparatus in which the filter media is anthracite and silica sand, and the oxygen supply means is an aeration means in the raw water storage tank.
Non-Patent Document 2 describes a biological nitrification apparatus in which the filter media is anthracite and silica sand, and the oxygen supply means is a gas-liquid contact tank with a gas-liquid ejector above the filter layer.
In Non-Patent Document 3, the filter medium is a spherical fiber filter medium having a diameter of 5 to 7 mm, and a filler-type aeration device is provided in the raw water storage tank as an oxygen supply means.
In Non-Patent Document 4, the filter medium is a special sintered porous filter medium, and a filler-type aeration device is provided in the raw water storage tank as an oxygen supply means.
The biological nitrification devices described in Patent Document 1 and Non-Patent Documents 1 to 3 are downflow filtration devices, while the biological nitrification device described in Non-Patent Document 4 is an upflow filtration device.
In the above-mentioned known examples, when a new device is installed, active inoculation with nitrifying bacteria or addition of filter media with nitrifying bacteria attached thereto is not carried out, and instead, during a trial run, the nitrifying bacteria present suspended in the raw water and air are left to attach and grow on the surface of the filter media, and it takes approximately one month before biological nitrification treatment is possible.

In this situation, the applicant for this patent has applied for and obtained a patent for an invention relating to a device that promotes biological nitrification by immersing a biological contact carrier, which has multiple string-like fibers that are likely to support nitrifying bacteria fixed to its structure, in an aquarium and aerating the aquarium (Patent Document 2).

The inventors have also invented a water treatment method for extracting nitrifying bacteria-supported carriers from a nitrification tank while sufficiently suppressing a decrease in nitrification efficiency, in which water to be treated containing ammonia nitrogen is treated in a first nitrification tank 10 filled with nitrifying bacteria-supported carriers 200 in a state in which the carriers can be extracted, to produce first treated water, and the first treated water is treated in a second nitrification tank 20 filled with nitrifying bacteria-supported carriers 200 to produce second treated water, the ammonia concentration or ammonia nitrogen concentration of the second treated water is measured, and when the nitrifying bacteria-supported carriers 200 are extracted from the first nitrification tank 10, when the ammonia concentration or ammonia nitrogen concentration has remained below a predetermined threshold for a predetermined period of time or longer, 50% or less by volume of the nitrifying bacteria-supported carriers 200 filled in the first nitrification tank 10 are extracted from the first nitrification tank 10, and the first nitrification tank is replenished with carriers not carrying nitrifying bacteria (Patent Document 3). In this method, the nitrifying bacteria carrier 200 is extracted from the first nitrification tank 10 by introducing compressed air through an air supply pipe 62 into the lift pipe 61 of the air lift pump 60, and discharging the treated water in the first nitrification tank 10 out of the system through the water discharge pipe 63 of the lift pipe 61 based on the difference between the water density in the first nitrification tank 10 and the water density in the lift pipe 61. The nitrifying bacteria carrier 200 is discharged in the form of a slurry, accompanied by the water flow.

The water treatment system 1 (FIG. 1) described in Patent Document 3 is a three-phase gas-liquid-solid fluidized tank, and therefore requires a solid-liquid separator 12 for separating the solid, i.e., the nitrifying bacteria-supported carrier 200. In order to separate the nitrifying bacteria-supported carrier 200, which is a cubic sponge carrier with a size of 3 to 5 mm square, a stainless steel wedge wire screen 300 as shown in FIG. 2 is suitable. The wedge wire screen 300 is a screen that is characterized by being less likely to clog, being strong, and having high precision, and is formed by welding wedge wires 301, which are wires with an inverted triangular cross section, arranged at equal intervals on a support rod 302 and forming slits. The inverted triangular shape of the wedge wire 301 makes it difficult for solids to clog the screen when the solids pass through, and the slits are wide at the end, so that the screen is less likely to clog with solids, and even if the screen does clog, the backwash effect is high, and the screen is easy to maintain. Stainless steel is the standard material for the wedge wire screen 300, as it has excellent strength and durability and can reduce running costs.
Generally, tanks used in water treatment plants are made of reinforced concrete (RC) because of their large treatment capacity. In the case of small-scale water treatment plants with small treatment capacity, tanks made of steel plates are sometimes used.
When attaching a wedge wire screen as shown in FIG. 2 to a water tank made of reinforced concrete or steel plate, it is often attached in a way that partitions the outlet of the treated water as shown by the dashed diagonal line (solid-liquid separator 12) in FIG. 1. Since the solids to be separated are cubic in shape with sides of 3 to 5 mm, it is preferable to form a sliding groove-like gap in the wall surface in order to seal between the wall surface of the water tank and the wedge wire screen 300. To insert the wedge wire screen into the sliding groove-like gap, it is preferable to process the wedge wire screen 303a (303b) with support members by welding frame-like support members 305a (305b) to the four sides of the wedge wire screen main body 304a (304b) (FIG. 3). However, as the screen area increases, the load also increases, so attention must be paid to the grooves that form the sliding groove-like gap and the mounting strength. Water tanks used in conventional water treatment plants are made of reinforced concrete or steel plate, and have the advantage that sufficient strength can be given by anchor bolts or welding.

JP 2013-059705 A Patent No. 6414394 JP 2017-202473 A

Kobelco Pantech Technical Report, Kobelco Pantech Co., Ltd., 2002, Vol. 45, No. 2, pp. 16-24 "Ultra-high-speed chemical-free biological treatment equipment using groundwater as raw water", Case studies of coagulation, sedimentation, flotation separation and granular layer filtration for users, Japan Liquid Clarification Technology Industry Association, 2001, pp. 64-67 Shozo Kuroki, Shigeru Sugisawa; Environmental Technology, 2001, Vol. 30, No. 12, pp. 18-22 Groundwater ammonia reduction system, Tohkemy Co., Ltd. [Retrieved August 7, 2020], Internet URL https://www.tohkemy.co.jp/products/actysomonasu/

In a water treatment device for making groundwater containing ammonia nitrogen potable, each tank in the water treatment plant up to the receiving tank under the Water Supply Act (Act No. 177 of 1957) is required to conform to the receiving tank, and it is essential that the tank can be inspected from all six sides. For this reason, the bottom of a reinforced concrete underground tank cannot be inspected, and it is required to use a land-based tank. Currently, the most commonly used receiving tank is a panel tank made of FRP or stainless steel. These FRP panel tanks and stainless steel tanks are usually prefabricated, and the use of reinforcing materials such as supports is minimized as much as possible, and pressure resistance and water resistance are ensured only by the unit-shaped panel. For this reason, as shown in FIG. 4, the panel member has an uneven structure as shown in FIG. 4, and is shaped to disperse the water pressure of the stored water. In addition, the manhole has a small unit-shaped panel structure with a diameter of 600 mm as specified by law. In addition, since the installation of pipes to the water tank is basically premised on connecting the water supply and drainage pipes, the flat area for the pipe installation is narrow and only a maximum of about 200 mm of pipes can be installed. Furthermore, the flat area for installing the pipes is restricted to a specific part of the unit panel.
The structure in which the pipes are passed horizontally through the pipe mounting seats of the panel tank, the ends are connected to TS flanges, and the circular screen is bolted, posed the problem that it was not possible to give the biological contact carrier the function of solid-liquid separation. If pipe mounting seats were to be provided on the four flat parts of one surface of the tank, the mounting piping would become complicated.
For these reasons, in biological nitrification apparatus using panel tanks, there is a restriction on increasing the screen area of the wedge wire screen, making it difficult to increase the amount of water passing through.

The objective of the present invention is to provide a biological nitrification device using a panel tank that has an improved water flow rate through the solid-liquid separation device.

[1] A groundwater biological nitrification device using a panel tank,
A biological nitrification tank is provided using the panel tank as a tank body,
The biological nitrification tank is a circulating flow tank that biologically treats the water to be treated using a nitrifying bacteria-supporting carrier,
The biological nitrification tank has an outlet for discharging treated water obtained by biologically treating the water to be treated outside the tank,
A cylindrical wedge wire screen is connected to the outlet.
Biological nitrification device.
[2] The biological nitrification apparatus according to [1], wherein the cylindrical wedge wire screen is detachably connected to the outflow portion.
[3] The panel water tank has an upper manhole,
The biological nitrification apparatus according to [1] or [2], wherein the cylindrical wedge wire screen is arranged below the upper manhole.
[4] The biological nitrification apparatus according to any one of [1] to [3], wherein the cylindrical wedge wire screen is arranged in the ascending flow section or the descending flow section of the circulating flow of the water to be treated in the biological nitrification tank.
[5] The biological nitrification apparatus according to any one of [1] to [4], wherein the cylindrical wedge wire screen has a holding portion and a guide portion.
[6] The biological nitrification device according to any one of [1] to [5], wherein the nitrifying bacteria-supporting carrier is a square sponge-like carrier having a side length of 3 to 10 mm and carrying nitrifying bacteria.
[7] The biological nitrification apparatus according to any one of [1] to [6], wherein the bulk volume of the nitrifying bacteria-supporting carrier is less than 60% by volume of the effective volume of the biological nitrification tank.
[8] The outflow section includes a pipe seat mounting portion provided on a side wall of the panel tank, an internal discharge pipe rising from the pipe seat mounting portion toward an upper portion in the biological nitrification tank, and an external discharge pipe rising from the pipe seat mounting portion toward an upper portion outside the biological nitrification tank,
The wedge wire screen is attached to the end of the internal exhaust pipe opposite to the pipe seat attachment portion,
The bottom of the internal exhaust pipe and the bottom of the external exhaust pipe are connected via or through the pipe seat attachment portion, and the internal exhaust pipe and the external exhaust pipe form a U-shaped pipe.
The biological nitrification device according to any one of [1] to [7].

The present invention provides a biological nitrification device using a panel tank, which has an improved water flow rate through the solid-liquid separation device.

FIG. 1 is a schematic diagram showing an example of the water treatment system disclosed in Patent Document 3. As shown in FIG. FIG. 2 is a photograph showing an example of a wedge wire screen. 3A and 3B are schematic diagrams showing examples of a wedge wire screen with support members: (A) a wedge wire screen with square support members, and (B) a wedge wire screen with round support members. 4A and 4B are schematic diagrams showing an example of a panel member of a panel aquarium, in which (A) is a front view and (B) is a side view. FIG. 5 is a schematic diagram showing an example of a biological nitrification apparatus of the present invention. FIG. 6 is a schematic diagram showing the solid-liquid separator, the internal discharge pipe, and the pipe seat mounting portion in the biological nitrification apparatus of the present invention. FIG. 7 is a schematic diagram showing the configuration of a wedge wire screen in the biological nitrification apparatus of the present invention. 8A and 8B are photographs showing the wedge wire screen in the biological nitrification apparatus of the present invention. (A) is a photograph of the wedge wire screen viewed diagonally upward from inside the biological nitrification tank, and (B) is a photograph of the wedge wire screen viewed from a manhole in the biological nitrification tank.

In the present invention, the numerical range expressed using "to" includes both end numerical values.
In the present invention, “A or B” means either A or B.
In the present invention, the volume of a gas is the volume at 0° C. and 101.325 kPa.
In the present invention, the "panel water tank" refers to a water tank formed by joining a plurality of polygonal panels (such as thin plate panels) liquid-tightly.
In the present invention, "ammonia nitrogen" refers to nitrogen that exists in water in the form of ammonia (molecules) and nitrogen that exists in the form of ammonium ions.
In the present invention, "nitrate nitrogen" means nitrogen that exists in water in the form of nitrate ions.
In the present invention, "nitrite nitrogen" means nitrogen present in the form of nitrite ions.
In the present invention, the term "carrier" refers to a base material for supporting microorganisms. In particular, a carrier supporting nitrifying bacteria used in biological nitrification treatment is referred to as a "nitrifying bacteria-supporting carrier".

<Biological nitrification device>
Hereinafter, an embodiment of the biological nitrification apparatus of the present invention will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited to the embodiment described below, and various modifications are possible without departing from the gist of the present invention.
In addition, in each drawing used in the following description, characteristic parts may be enlarged for convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may differ from the actual ones. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples.

FIG. 5 is a schematic diagram showing an example of a biological nitrification apparatus having two biological nitrification tanks connected in series.
The biological nitrification apparatus 402 comprises a pre-aeration tank 410 which aerates the water to be treated supplied from a raw water tank (not shown) through a water to be treated supply flow path 500 to produce pre-aeration treated water, a first biological nitrification tank 420 which treats the pre-aeration treated water transferred from the pre-aeration tank 410 through a pre-aeration treated water transfer flow path 501 to produce first treated water, a second biological nitrification tank 430 which treats the first treated water transferred from the first biological nitrification tank 420 through the first treated water transfer flow path 502 to produce second treated water, a transfer pump 461 provided midway through the water to be treated supply flow path 500, a water flow measuring device 462 provided midway through the water to be treated supply flow path 500 to measure the amount of water to be treated supplied to the pre-aeration tank 410, and a control device (not shown) electrically connected to the blower and air volume adjustment means of the aeration apparatus described later, the transfer pump 461, and the water flow measuring device 462.
The pre-aeration tank 410 may be omitted and the raw water to be treated may be directly introduced into the first biological nitrification tank 420 .

(Water to be treated)
The water to be treated is groundwater containing ammonia nitrogen.

(Pre-aeration tank)
The pre-aeration tank 410 comprises a tank body 411 which is a panel water tank, and an aeration device 413 inserted into the bottom of the tank body 411 .
The tank body 411, which is a panel tank, preferably has an upper manhole.

The flow rate of the water to be treated flowing into the pre-aeration tank 410 is controlled by a transfer pump 461 and a water flow measuring device 40 provided in the middle of the water to be treated supply flow path 500 connected to the pre-aeration tank 410. That is, in the biological nitrification apparatus 402, the transfer pump 461, the water flow measuring device 40, and a control device (not shown) electrically connected thereto constitute a control mechanism that controls the retention time of the water to be treated in the pre-aeration tank 410.
The water flow measurement device 40 may be, for example, a rotameter or an electromagnetic flow meter.
In the biological nitrification apparatus 402, the retention time of the water to be treated is controlled by the control mechanism.

The aeration device 413 includes an aeration section 414 located at the bottom of the tank body 411 , an air supply section 415 that supplies air to the aeration section 414 , and an air amount adjusting means 417 provided midway along the air supply section 415 .
The air diffusion section 414 may be, for example, an air diffusion pipe or an air diffusion cylinder having air diffusion holes (not shown).
The air amount adjusting means 417 may be, for example, a gate valve or a butterfly valve.
The aeration amount in the pre-aeration tank 410 is not particularly limited.

(First biological nitrification tank)
The first biological nitrification tank 420 is a so-called fluidized bed type biological nitrification tank, which includes a tank body 421 which is a panel tank, a solid-liquid separation device 422 for separating the nitrifying bacteria-supporting carrier 600 and the first treated water, an internal discharge pipe 428 having one end connected to the solid-liquid separation device 422, a pipe seat mounting portion 429 to which the other end of the internal discharge pipe 428 is connected, and an aeration device 423 inserted into the bottom of the tank body 421.
The tank body 421, which is a panel tank, preferably has an upper manhole.

The aeration device 423 comprises an aeration section 424 located at the bottom of the tank body 421, an air supply section 425 that supplies air to the aeration section 424, a blower 426 provided midway through the air supply section 425, and an air volume adjustment means 427 provided midway through the air supply section 425 between the aeration section 424 and the blower 426.
The air diffusion section 424 may be, for example, an air diffusion pipe or an air diffusion cylinder having air diffusion holes (not shown).
The air amount adjusting means 427 may be, for example, a gate valve or a butterfly valve.
The amount of aeration in the first biological nitrification tank 420 is not particularly limited.

The internal discharge pipe 428 extends from a pipe seat mounting portion 429 into the water to be treated in the first biological nitrification tank 420, and a solid-liquid separator 422 is attached to the end opposite the pipe seat mounting portion 429 (Figure 6).
It is preferable that the internal discharge pipe rises from the pipe seat mounting portion 429 into the water to be treated in the first biological nitrification tank 420 .

(Second biological nitrification tank)
The second biological nitrification tank 430 is a so-called fluidized bed type biological nitrification tank, which includes a tank body 431 which is a panel tank, a solid-liquid separation device 432 for separating the nitrifying bacteria-supporting carrier 700 and the second treated water, an internal discharge pipe 438 having one end connected to the solid-liquid separation device 432, a pipe seat mounting portion 439 to which the other end of the internal discharge pipe 438 is connected, an external discharge pipe 503 having one end connected to the pipe seat mounting portion 439, and an aeration device 433 inserted into the bottom of the tank body 431.
The tank body 431, which is a panel tank, preferably has an upper manhole.

The aeration device 433 comprises an aeration section 434 located at the bottom of the tank body 431, an air supply section 35 that supplies air to the aeration section 434, a blower 436 provided midway through the air supply section 35, and an air volume adjustment means 437 provided midway through the air supply section 35 between the aeration section 434 and the blower 436.
The air diffusion section 434 may be, for example, an air diffusion tube or an air diffusion cylinder having air diffusion holes (not shown).
The air amount adjusting means 437 may be, for example, a gate valve or a butterfly valve.
The amount of aeration in the second biological nitrification tank 430 is not particularly limited.

The internal discharge pipe 438 extends from the pipe seat mounting portion 429 into the water to be treated in the second biological nitrification tank 430, and a solid-liquid separator 432 is attached to the end opposite the pipe seat mounting portion 439 (Figure 6).
It is preferable that the bottom of the internal exhaust pipe 438 and the bottom of the external exhaust pipe 503 are connected via or through a pipe seat attachment portion, and that the internal exhaust pipe 438 and the external exhaust pipe 503 form a U-shaped pipe.

(Control device)
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 blower and air volume adjustment means of the aeration device, the transfer pump 461, the water flow rate measuring device 462, etc. to the control unit.

The memory unit stores the operating conditions of the biological nitrification device 402 and the like.
The processing unit performs calculations such as calculating the residence time of the water to be treated in the pre-aeration tank 410 from the amount of water to be treated measured by the water flow rate measuring device 462 .
The determination section performs a determination as to whether or not the residence time of the water to be treated in the pre-aeration tank 410 calculated by the processing section is within a range that is set in advance and stored in the memory section.
The control unit controls the biological nitrification device 402 based on the determination result in the determination unit, the operating conditions of the biological nitrification device 402 stored in the memory unit, etc. For example, the control unit controls the transfer pump 461 based on the amount of water to be treated that is set in advance and stored in the memory unit, and controls the blower 416 (426) and air amount adjustment means 417 (427) of the aeration device 413 (423) based on the amount of air that is set in advance and stored in the memory unit.

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

(Nitrifying bacteria support carrier)
The nitrifying bacteria-supported carrier 600 and the nitrifying bacteria-supported carrier 700 in the biological nitrification device 402 are carriers in which nitrifying bacteria are supported on the surface of the carrier. When the carrier is porous, the nitrifying bacteria may be supported inside (in the pores) of the carrier.

The shape of the carrier is not particularly limited, but is at least one selected from the group consisting of a rectangular parallelepiped (including a cube), a sphere, a cylinder, and a filament. Two or more shapes may be used in combination as the carrier. If the shape of the carrier is a rectangular parallelepiped or a cylinder, the corners may be chipped or rounded. If the shape of the carrier is a sphere, it does not have to be a perfect sphere. The shape of the carrier is preferably a square shape, that is, an approximately rectangular parallelepiped. Here, an approximately rectangular parallelepiped is not limited to a hexahedron with all faces being rectangular (including a square), but is basically a hexahedron composed of six faces, and may have chipped corners or rounded corners. When the shape of the carrier is square, the length of one side is not particularly limited, but is preferably 3 to 10 mm, more preferably 3 to 7 mm, and even more preferably 3 to 5 mm. If the length of one side of the square carrier is 3 to 10 mm, the surface area per mass of the carrier can be increased, and the amount of nitrifying bacteria carried can be increased, thereby further improving the nitrification performance.

The carrier is preferably porous because nitrifying bacteria can be supported on the surface and inside of the carrier. With a porous carrier, nitrifying bacteria can be supported not only on the surface but also inside of the carrier, so that a larger number of nitrifying bacteria can be supported, and nitrification performance is further improved.
In addition, as the porous carrier, a sponge-like carrier is more preferable because it can maintain the support of nitrifying bacteria well and minimize damage to the pump and piping. Here, "sponge" means a porous soft material with countless fine holes inside.
The material of the sponge-like carrier is not particularly limited, but is at least one selected from the group consisting of polyvinyl alcohol, polystyrene rubber, and polyurethane, and polyurethane is preferred because of its good durability. Two or more types of materials for the sponge-like carrier may be used in combination.

The bulk volume of the nitrifying bacteria-supporting carriers 600 in the first biological nitrification tank 420 is preferably less than 60% by volume of the effective volume of the first biological nitrification tank 420 .
The bulk volume of the nitrifying bacteria-supporting carriers 700 in the second biological nitrification tank 430 is preferably less than 60 volume % of the effective volume of the second biological nitrification tank 430 .
It is preferable that the sum of the bulk volume of the nitrifying bacteria-supporting carrier 600 in the first biological nitrification tank 420 and the bulk volume of the nitrifying bacteria-supporting carrier 700 in the second biological nitrification tank 430 is less than 60 volume % of the sum of the effective volume of the first biological nitrification tank 420 and the effective volume of the second biological nitrification tank 430.
When the bulk volume of the nitrifying bacteria-supported carrier 600 in the first biological nitrification tank 420 and the bulk volume of the nitrifying bacteria-supported carrier 700 in the second biological nitrification tank 430 are less than 60 volume % of the effective volume of each of the first biological nitrification tank 420 and the second biological nitrification tank 430, the nitrifying bacteria-supported carrier 600 and the nitrifying bacteria-supported carrier 700 can easily flow within each tank, and the oxygen necessary for the growth of nitrifying bacteria can be sufficiently supplied to the nitrifying bacteria, making it easy to improve nitrification performance.

The nitrifying bacteria include known nitrifying bacteria used in biological nitrification of ammonia nitrogen. Nitrifying bacteria is a general term for ammonia oxidizing bacteria (nitrite producing bacteria) such as Nitrosomonas bacteria, Nitrosococcus bacteria, and Nitrosospira bacteria, and nitrite oxidizing bacteria (nitrate producing bacteria) such as Nitrobacter bacteria and Nitrospira bacteria. Nitrifying bacteria are facultative aerobic chemoautotrophs, and use ammonia nitrogen and carbonic acid as substrates. Nitrifying bacteria can grow using carbonic acid as the only carbon source, but their growth rate is extremely low. Therefore, in order to maintain a high biological nitrification reaction, an operation is required to hold a large amount of nitrifying bacteria in the tank. Therefore, it is preferable to hold the nitrifying bacteria in a state supported on a carrier rather than as suspended cells.
An example of a method for supporting nitrifying bacteria on a carrier is to place the carrier in a nitrification tank of an existing water treatment system and allow the nitrifying bacteria to grow on the surface of the carrier.

(Solid-liquid separation device)
The solid-liquid separator 422 (432) in the biological nitrification system 402 is a cylindrical wedge wire screen (FIG. 7).
The cylindrical wedge wire screen 422 is preferably detachably connected to an outlet port for discharging treated water from the biological nitrification tank outside the tank.
7, the wedge wire screen 422 has a wedge wire screen body 422a in which the wedge wires are arranged horizontally and the support rods are arranged vertically. The slits formed by the wedge wires are aligned horizontally.
The screen surface area of a cylindrical wedge wire screen is, for example, 250 mm in diameter and 400 mm in length, which is approximately 300,000 ^mm2 , which is an overwhelmingly larger screen area than the approximately 50,000 ^mm2 screen surface area of a flat wedge wire screen attached to a conventional panel member.
The biological nitrification tank, which is a panel tank, preferably has an upper manhole, and the cylindrical wedge wire screen is preferably disposed below the upper manhole.
The wedge wire screen preferably has a guide portion 422b and a support portion 422c in addition to a wedge wire screen body 422a (FIG. 7).
The guide portion 422b makes it easier to attach and detach the wedge wire screen to and from the internal discharge pipe 428.
The holding portion 422c makes it easier to maintain the wedge wire screen from the upper manhole of the panel tank.
Figure 8 shows photographs of the wedge wire screen in use. Photograph A shows the wedge wire screen viewed diagonally upward from inside the biological nitrification tank, and photograph B shows the wedge wire screen viewed from a manhole inside the biological nitrification tank.
This has the advantage that the screen area can be set arbitrarily by arbitrarily setting the outer diameter and length of the cylindrical wedge wire screen.
By using a cylindrical screen structure, the area required for separation can be made sufficiently large, allowing the solid-liquid separation device to be set up in one location and for the part located in the manhole to be given a solid-liquid separation function with a removable structure.
Furthermore, by installing this cylindrical wedge wire screen in the ascending or descending portion of the circulating flow that constitutes the gas-liquid three-phase fluidized bed, it is possible to minimize the phenomenon in which the sponge-like carrier is pressed against the screen surface and causes blockage.
The discharge pipe connected to the cylindrical wedge wire screen has a U-shaped pipe structure with the external discharge pipe via the pipe seat mounting part of the panel tank. By maintaining the discharge pipe in a full pipe state, no buoyancy is generated in the discharge pipe inside the tank, and no upward stress is generated in the pipe seat mounting part.

Biological nitrification method
An example of a biological nitrification method using the biological nitrification device 402 will be described.

(Pre-aeration treatment)
By operating a transfer pump 461 provided midway along the treated water supply flow path 500, the treated water is supplied from a raw water storage tank (not shown) through the treated water supply flow path 500 to the pre-aeration tank 410, and the treated water is stored in the pre-aeration tank 410.
The water to be treated is groundwater containing ammonia nitrogen.

The supply of the treated water to the pre-aeration tank 410 continues while controlling the water volume using a control mechanism, i.e., a transfer pump 461 and a water flow measuring device 462 electrically connected to a control device (not shown), so that the residence time of the treated water in the pre-aeration tank 410 is a predetermined time.

While the water to be treated is being supplied to the pre-aeration tank 410, the aeration device 413 is driven to diffuse air from the aeration section 414 into the pre-aeration tank 410 at a preset air volume.
The amount of air diffused from the aeration section 414 of the aeration device 413 can be adjusted (controlled) to an arbitrary amount of air by the air amount adjusting means 417. The amount of air (aeration amount) is preferably adjusted (controlled) to be 20 ^m3 / ^m3 /h or more per tank.

(Biological nitrification treatment)
The water to be treated in the pre-aeration tank 410 is transferred to the first biological nitrification tank 420 through a pre-aeration treated water transfer flow path 501, and the pre-aeration treated water is stored in the first biological nitrification tank 420. Furthermore, the pre-aeration treated water in the first biological nitrification tank 420 is transferred to the second biological nitrification tank 430 through a first treated water transfer flow path 502, and the first treated water is stored in the second biological nitrification tank 430.

Nitrifying bacteria-supporting carrier 600 extracted from an existing biological nitrification apparatus is placed in biological nitrification tank 420 of biological nitrification apparatus 402, and nitrifying bacteria-supporting carrier 700 similarly extracted from an existing biological nitrification apparatus is placed in second biological nitrification tank 430.
The bulk volume of the nitrifying bacteria-supporting carriers 600 in the first biological nitrification tank 420 is preferably less than 60% by volume of the effective volume of the first biological nitrification tank 420, and more preferably 20 to 50% by volume.
The bulk volume of the nitrifying bacteria-supporting carriers 700 in the second biological nitrification tank 430 is preferably less than 60 volume % of the effective volume of the second biological nitrification tank 430 .
It is preferable that the sum of the bulk volume of the nitrifying bacteria-supporting carrier 600 in the first biological nitrification tank 420 and the bulk volume of the nitrifying bacteria-supporting carrier 700 in the second biological nitrification tank 430 is less than 60 volume % of the sum of the effective volume of the first biological nitrification tank 420 and the effective volume of the second biological nitrification tank 430.

The pre-aeration treated water discharged from the pre-aeration tank 410 is transferred through the pre-aeration treated water transfer flow path 501 to the first biological nitrification tank 420, while the aeration device 423 is driven to diffuse air from the aeration section 424 into the first biological nitrification tank 420 at a preset amount of air.
When air is diffused from the bottom of the first biological nitrification tank 420 , a swirling current consisting of an upward current and a downward current is generated in the first biological nitrification tank 420 , and the nitrifying bacteria-supporting carriers 600 flow freely in the first biological nitrification tank 420 .
The flow velocity of the upward flow in the swirling flow is not particularly limited, but is preferably 0.1 to 0.5 m/s.
The amount of air diffused from the aeration section 424 of the aeration device 423 can be adjusted (controlled) to any desired amount by the air amount adjusting means 427 .

The first treated water discharged from the first biological nitrification tank 420 through the solid-liquid separation device 422 is transferred to the second biological nitrification tank 430 through the first treated water transfer flow path 502, while the aeration device 433 is driven to diffuse a preset amount of air into the second biological nitrification tank 430 from the aeration section 434.
When air is diffused from the bottom of the second biological nitrification tank 430 , a swirling current consisting of an upward current and a downward current is generated in the second biological nitrification tank 430 , and the nitrifying bacteria-supporting carriers 600 flow freely in the second biological nitrification tank 430 .
The flow velocity of the upward flow in the swirling flow is not particularly limited, but is preferably 0.1 to 0.5 m/s.
The amount of air diffused from the aeration section 434 of the aeration device 433 can be adjusted (controlled) to an arbitrary amount by the air amount adjusting means 437 .

In the first biological nitrification tank 420, air containing oxygen is supplied from the aeration section 424 of the aeration device 423. When oxygen is supplied into the first biological nitrification tank 420, the ammonia nitrogen in the pre-aeration treatment water is oxidized to nitrate by the nitrifying bacteria in the nitrifying bacteria-supporting carrier 600 in the first biological nitrification tank 420. In this manner, the water to be treated containing ammonia nitrogen is treated in the biological nitrification tank 420 to produce the first treated water.
In the second biological nitrification tank 430, air containing oxygen is supplied from the aeration section 434 of the aeration device 433. When oxygen is supplied into the second biological nitrification tank 430, the ammonia nitrogen in the first treated water is oxidized to nitrate by the nitrifying bacteria in the nitrifying bacteria-supporting carrier 700 in the second biological nitrification tank 430. In this manner, the water to be treated containing ammonia nitrogen is treated in the second biological nitrification tank 430 to produce second treated water.
Ammonia nitrogen is biologically nitrified through a two-step reaction as shown in the following formula.
(1) _2NH3 + _3O2 → 2H ⁺ + _2NO2- ⁺ _2H2O
(2) _2NO2- ⁺ _O2 ^→ _2NO3-
Equation (1) is the reaction catalyzed by ammonia oxidizing bacteria, and equation (2) is the reaction catalyzed by nitrite oxidizing bacteria.
Equation (1) and equation (2) are combined to obtain equation (3).
(3) _2NH3 + _4O2 →2H ⁺ _2H2O ⁺ _2NO3-
That is, 2 moles of ammonia react with 4 moles of oxygen to produce 2 moles of nitrate ions.

The second treated water discharged from the second biological nitrification tank 430 through the solid-liquid separation device 432 is discharged outside the biological nitrification device 402 through the external discharge pipe 503.

[Action and Effect]
By adopting a cylindrical wedge wire screen as a solid-liquid separation device, the screen area can be made much larger than that of conventional flat wedge wire screens, making it possible to significantly increase the water flow rate.

The biological nitrification device of the present invention exhibits excellent nitrification performance and can increase the amount of water passing through the solid-liquid separation device, making it suitable for use in drinking water purification treatment facilities.

1...water treatment system, 10...first nitrification tank, 11...tank body, 12...solid-liquid separation device, 13...aeration device, 14...aeration section, 15...air supply pipe, 16...blower, 17...air amount adjustment means, 20...second nitrification tank, 21...tank body, 22...solid-liquid separation device, 23...aeration device, 24...aeration section, 25...air supply pipe, 26...blower, 27...air amount adjustment means, 30...ion exchange device, 40...water flow rate measuring device, 50...concentration measuring device, 60...air lift pump, 61...lift pipe, 62...air supply pipe, 63...water discharge pipe, Reference Signs List 100: Treated water supply flow path, 101: First treated water transfer flow path, 102: Second treated water transfer flow path, 103: Third treated water transfer flow path, 104: Bypass flow path, 200: Nitrifying bacteria support carrier, 300: Wedge wire screen, 301: Wedge wire, 302: Support rod, 303a, 303b: Wedge wire screen with support member, 304a, 304b: Wedge wire screen body, 305a, 305b: Support member, 306: Panel member, 307 ...flat portion, 308...uneven portion, 402...biological nitrification apparatus, 410...pre-aeration tank, 411...tank body, 413...aeration device, 414...aeration section, 415...air supply section, 416...blower, 417...air amount adjustment means, 420...first biological nitrification tank, 421...tank body, 422...solid-liquid separation device, 422a...wedge wire screen body, 422b...guide section, 422c...holding section, 423...aeration device, 424...aeration section, 425...air supply section, 426...blower, 427...air amount adjustment means, 428...internal exhaust Outlet pipe, 429...pipe seat mounting part, 430...second biological nitrification tank, 431...tank body, 432...solid-liquid separation device, 433...aeration device, 434...aeration section, 435...air supply section, 436...blower, 437...air amount adjustment means, 438...internal exhaust pipe, 439...pipe seat mounting part, 461...transfer pump, 462...water flow rate measuring device, 500...treated water supply flow path, 501...pre-aeration treated water transfer flow path, 502...first treated water transfer flow path, 503...external exhaust pipe, 600...nitrifying bacteria support carrier, 700...nitrifying bacteria support carrier

Claims (8)

A biological nitrification device for groundwater using a panel tank,
A biological nitrification tank is provided using the panel tank as a tank body,
The biological nitrification tank is a circulating flow tank that biologically treats the water to be treated using a nitrifying bacteria-supporting carrier,
The biological nitrification tank has an outlet for discharging treated water obtained by biologically treating the water to be treated outside the tank,
A cylindrical wedge wire screen is connected to the outlet.
Biological nitrification device. The biological nitrification apparatus of claim 1, wherein the cylindrical wedge wire screen is removably connected to the outlet. The panel tank has an upper manhole,
3. The biological nitrification apparatus of claim 1 or 2, wherein the cylindrical wedge wire screen is disposed below the upper manhole. The biological nitrification apparatus according to any one of claims 1 to 3, wherein the cylindrical wedge wire screen is disposed in the upward flow section or the downward flow section of the circulating flow of the water to be treated in the biological nitrification tank. The biological nitrification apparatus according to any one of claims 1 to 4, wherein the cylindrical wedge wire screen has a holding portion and a guide portion. The biological nitrification device according to any one of claims 1 to 5, wherein the nitrifying bacteria-supporting carrier is a square sponge-like carrier with a side length of 3 to 10 mm, on which nitrifying bacteria are supported. The biological nitrification apparatus according to any one of claims 1 to 6, wherein the bulk volume of the nitrifying bacteria-supporting carrier is less than 60% by volume of the effective volume of the biological nitrification tank. The outflow section includes a pipe seat mounting portion provided on a side wall of the panel tank, an internal discharge pipe rising from the pipe seat mounting portion toward an upper portion in the biological nitrification tank, and an external discharge pipe rising from the pipe seat mounting portion toward an upper portion outside the biological nitrification tank,
The wedge wire screen is attached to the end of the internal exhaust pipe opposite to the pipe seat attachment portion,
The bottom of the internal exhaust pipe and the bottom of the external exhaust pipe are connected via or through the pipe seat attachment portion, and the internal exhaust pipe and the external exhaust pipe form a U-shaped pipe.
The biological nitrification apparatus according to any one of claims 1 to 7.

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