JP2009247255A - Method for cleaning breeding water and apparatus for cleaning breeding water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cleaning breeding water, which does not utilize a biodegradable plastic and safely, stably and continuously removes nitrate nitrogen by a simple operation. <P>SOLUTION: The method for cleaning breeding water includes a deoxygenation process for reducing the amount of oxygen dissolved in a certain amount of water contained in breeding water W<SB>2</SB>collected from a breeding water tank T, a carbon dioxide dissolution process for dissolving carbon dioxide in breeding water W<SB>2</SB>, a nitrogen fixation process for passing the breeding water W<SB>2</SB>having passed through the deoxygenation process and the carbon dioxide dissolution process to a nitrogen fixation tank 3A composed of a filter medium assembly and packed with a microorganism carrier 32 and a breeding water supply process for supplying returning breeding water W<SB>3</SB>having passed through the nitrogen fixation process to the breeding water tank T. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and apparatus for removing nitrate nitrogen contained in breeding water in a breeding aquarium.

As a method of removing (denitrifying) nitrate nitrogen (nitrate ions) contained in the breeding water in the breeding tank, for example, a biodegradable plastic (carbon source) covered with a continuous porous material is introduced into the breeding water. A method of implanting and growing denitrifying bacteria, which are facultative anaerobic bacteria, on the surface of biodegradable plastics (see Patent Document 1) and a nitrification tank and a denitrification tank are provided in parallel in a circulation line for circulating breeding water , Using nitrifying bacteria (autotrophic bacteria) in the nitrification tank to reduce ammonia nitrogen and nitrite nitrogen to nitrate nitrogen (nitrification) and use denitrifying bacteria (heterotrophic bacteria) in the denitrification tank A method of reducing (denitrifying) nitrate nitrogen generated by nitrification to nitrogen is known (see Patent Document 2).
Japanese Patent Laid-Open No. 10-85782 JP 2000-126794 A

  In the breeding water purification method of Patent Document 1, since biodegradable plastic components decomposed by the action of microorganisms may diffuse into the breeding aquarium, heterotrophic bacteria other than denitrifying bacteria (for example, pathogenic bacteria) grow. There is a fear. Further, in the breeding water purification method of Patent Document 1, since it is difficult to control the amount of denitrification, it may take time until the nitric acid concentration in the breeding water tank is stabilized. In addition, due to unforeseen circumstances, ammonia, nitrous acid, and hydrogen sulfide may increase to such an extent that they cause harm to domestic animals.

  In the breeding water purification method of Patent Document 2, an anaerobic atmosphere that easily causes denitrification is created in the denitrification tank by intermittently passing the breeding water through the denitrification tank. If provided, the control becomes complicated and the amount of breeding water introduced into the denitrification tank may be limited.

  From this point of view, the present invention is a breeding water purification method and breeding water that does not use biodegradable plastics and can remove nitrate nitrogen stably and continuously with a simple operation with little danger. It is an object to provide a purification device.

  The breeding water purification method according to the present invention that solves such problems includes a deoxygenation process that reduces the amount of dissolved oxygen contained in breeding water obtained from a breeding aquarium, and a carbon dioxide dissolution process that dissolves carbon dioxide in the breeding water. And a nitrogen fixation process for passing the breeding water that has passed through the deoxygenation process and the carbon dioxide dissolution process to a nitrogen fixation tank filled with a microorganism carrier comprising an aggregate of filter media, and the breeding water that has undergone the nitrogen fixation process And a breeding water supply process for returning to the breeding aquarium.

  According to the breeding water purification method according to the present invention, breeding water having a low dissolved oxygen atmosphere containing carbon dioxide is supplied into the nitrogen fixing tank. Activity of some of the bacteria classified as facultative anaerobic bacteria used as a carbon source) becomes active, nitrate nitrogen is consumed for growth of nitrogen-fixing bacteria, and nitrate nitrogen is fixed as cells Therefore, it becomes possible to reduce the nitrate nitrogen concentration in the breeding water. Moreover, according to the present invention, breeding water in a low-dissolved oxygen atmosphere containing carbon dioxide is continuously supplied into the nitrogen fixing tank, so that nitrate nitrogen can be removed stably and continuously. This eliminates the need for a device for intermittent water flow.

  In addition, in the said deoxygenation process, the amount of dissolved oxygen contained in the said breeding water can also be reduced by supplying carbon dioxide more than the amount of saturated dissolved carbon dioxide to the breeding water acquired from the breeding water tank. If it does in this way, since a deoxygenation process and a carbon dioxide melt | dissolution process will be performed simultaneously, it becomes possible to reduce dissolved oxygen with the simplified apparatus.

  In the breeding water supply process, oxygen may be supplied to the breeding water that has undergone the nitrogen fixation process. If it does in this way, since the amount of dissolved oxygen in the breeding water returned to the breeding tank can be increased, it becomes possible to maintain the quality of the breeding water in the breeding tank in a good state. Oxygen may be supplied to the breeding water by supplying a mixed gas containing oxygen (for example, the atmosphere).

  Since nitrogen-fixing bacteria take nitrate nitrogen into the body and assimilate, most of the nitrate nitrogen removed from the breeding water in the breeding tank remains in the system in an assimilated state with nitrogen-fixing bacteria. Will do. Therefore, if the balance in the nitrogen fixing tank is lost due to some factor, the nitrogen compound assimilated to the nitrogen fixing bacteria is supplied again into the breeding tank, and the quality of the breeding water may be deteriorated. If such a problem is a concern, the nitrogen fixing tank may be backwashed, or the microbial carrier may be taken out of the nitrogen fixing tank and the nitrogen-fixing bacteria carried on the microbial carrier may be washed away. . In this way, nitrate nitrogen assimilated by the nitrogen-fixing bacteria is taken out of the system together with the nitrogen-fixing bacteria, so that it is possible to reduce the risk that ammonia and nitrite ions are regenerated.

  The breeding water purification apparatus according to the present invention that solves the above-described problems includes a circulation line for circulating the breeding water in the breeding aquarium, and a deoxygenation means for reducing the amount of dissolved oxygen contained in the breeding water obtained from the breeding tank. A breeding water purification apparatus comprising: a carbon dioxide dissolving means for dissolving carbon dioxide in the breeding water; and a nitrogen fixing tank formed by filling a microorganism carrier comprising an aggregate of filter media, wherein the deoxygenation means comprises: It is provided on the upstream side of the nitrogen fixing tank.

  According to the breeding water purification apparatus according to the present invention, breeding water having a low dissolved oxygen atmosphere is supplied into the nitrogen fixing tank, so that the activity and proliferation of the nitrogen fixing bacteria in the nitrogen fixing tank becomes active. That is, since nitrate nitrogen is assimilated to nitrogen-fixing bacteria, the nitrate nitrogen concentration in the breeding water can be reduced. Moreover, according to the present invention, breeding water in a low dissolved oxygen atmosphere is continuously supplied into the nitrogen fixing tank, so that nitrate nitrogen can be removed stably and continuously. A device for passing water is also unnecessary. In the present invention, if the microorganism carrier is sand and combined with a known backwash device, the washing operation can be performed automatically.

  According to the present invention, it is possible to remove nitrate nitrogen safely, stably and continuously with a simple operation without requiring a biodegradable plastic or an anaerobic tank and without going through a complicated process. Become.

  An example of the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings.

The breeding water purification apparatus A according to the present embodiment includes a circulation line 1 for circulating the breeding water W ₁ in the breeding aquarium T, water quality adjusting means 2, nitrogen fixing means 3 and oxygen supply means provided in the circulation line 1. 4 is provided.

The breeding tank T has nitrification means (circulation line B1, circulation pump B2, bottom filtration layer B3) for nitrification by nitrifying bacteria, and protein removal means (circulation line C1, circulation pump C2, protein for removing proteins). skimmer C3), breeding water W temperature adjusting means adjusting the temperature of ₁ (temperature sensor D1, thermo controller D2, heater D3, cooler D4) and the like are attached.

The circulation line 1 is a flow path (pipe) from the water intake 11 to the water outlet 12 provided in the breeding water tank T, and connects the water quality adjusting means 2, the nitrogen fixing means 3 and the oxygen supply means 4 in series. . The circulation line 1 is provided with a circulation pump 13 for circulating the breeding water W _{1 to} W ₅ and a valve 14 for adjusting the flow rate.

Water conditioning unit 2, there is provided on the upstream side of the nitrogen-fixing means 3, a function of reducing the amount of dissolved oxygen contained in the rearing water W ₂ obtained from the breeding aquarium T, carbon dioxide breeding water W ₂ And a function of dissolving the water (that is, a function of increasing the amount of dissolved carbon dioxide in the breeding water W ₂ ). That is, the water quality adjusting means 2 of this embodiment functions as a deoxygenating means for reducing the amount of dissolved oxygen contained in the breeding water W ₂ and also functions as a carbon dioxide dissolving means for dissolving carbon dioxide in the breeding water W _2. .

  Although there is no restriction | limiting in the structure of the water quality adjustment means 2, the thing of this embodiment is open | released from the open container 21 which the upper surface opened, the carbon dioxide gas cylinder (carbon dioxide supply source) 22 which supplies a carbon dioxide, and this carbon dioxide gas cylinder 22 And a pipe 23 leading to the container 21.

In the present embodiment, as the flow of breeding water W ₂ in an open container 21 is down, an inlet provided in an upper portion of the open container 21, is provided with the outlet at the bottom, breeding water W ₂ It is not intended to limit the direction of flow.

The nitrogen fixing means 3 is provided on the downstream side of the water quality adjusting means 2 and has a function of fixing nitrate nitrogen (nitrate ions) contained in the breeding water W ₃ that has passed through the water quality adjusting means 2. . The nitrogen fixing means 3 of this embodiment includes two nitrogen fixing tanks 3A and 3A provided in series. The nitrogen fixing tank 3 </ b> A includes a sealed container 31 and a microorganism carrier 32 filled in the sealed container 31.

Although not intended to limit the direction of the flow of the breeding water W ₃ in the sealed container 31, in the present embodiment, the upstream nitrogen fixing tank 3 </ b> A faces downward, and the downstream nitrogen fixing tank 3 </ b> A It is facing upward. That is, in the upstream nitrogen fixing tank 3A, an inlet is provided in the upper part of the sealed container 31 and an outlet is provided in the lower part. In the downstream nitrogen fixing tank 3A, an inlet is provided in the lower part of the sealed container 31. And an outlet at the top.

  The microbial carrier 32 is composed of an aggregate of filter media. There is no restriction on the material of the filter medium, and porous materials such as porous glass, porous ceramic, coral sand, natural resin or synthetic resin sponge, activated carbon, and nonporous materials such as natural rock and glass are used. be able to. Further, the size and shape of the filter medium are not limited, and for example, a filter medium shaped into a spherical shape, a polyhedral shape, a columnar shape, a cylindrical shape, a ring shape, a flat plate shape, a sand shape, a gravel shape, a gravel shape, or the like is used. However, it is desirable to use one having a particle size or thickness of 5 mm or less so that the inside thereof does not enter an anaerobic state (a state in which almost no dissolved oxygen or binding oxygen exists). This makes it possible to suppress the generation of ammonia, nitrite ions, hydrogen sulfide and the like that are highly toxic to aquatic organisms.

The oxygen supply means 4 is provided on the downstream side of the nitrogen fixing means 3 and has a function of dissolving oxygen in the breeding water W ₄ that has passed through the nitrogen fixing means 3 (that is, the amount of dissolved oxygen in the breeding water W ₄ The function to increase.

  The configuration of the oxygen supply means 4 is not limited, but in the present embodiment, the open containers 41 and 41 whose upper surfaces are open, the air blower (oxygen supply source) 42 for sending out the atmosphere, and the open containers 41 and 41 from the air blower 42 are provided. And pipes 43 and 43 extending to 41.

In addition, in this embodiment, although the inflow port is provided in the upper part of the open container 41 and the outflow port is provided in the lower part so that the flow of the breeding water W ₄ in the open container 41 may face downward, the breeding water W ₄ It is not intended to limit the direction of flow.

The air blower 42 supplies air to the open containers 41, 41 via the pipes 43, 43, but the air blower 42 also supplies air to the breeding water W ₁ in the breeding water tank T via the pipe 44. (Oxygen) is supplied.

Next, the breeding water purification method according to this embodiment will be described. The breeding water purification method according to the present embodiment includes a deoxygenation process, a carbon dioxide dissolution process, a nitrogen fixation process, and a breeding water supply process. Incidentally, breeding water _{W 1} in the breeding aquarium T shall dissolved oxygen is maintained about 7 mg / liter, pH is in the 8-8.5.

The deoxygenation process is a process of reducing the amount of dissolved oxygen contained in the breeding water W ₂ obtained from the breeding tank T. In the present embodiment, by utilizing the water conditioning unit 2 have been deoxygenated process, the breeding water W ₂ in an open container 21 by supplying the saturated dissolved amount of carbon dioxide or carbon dioxide, breeding water W ₂ The amount of dissolved oxygen contained in is reduced. Incidentally, as in the deoxygenation process of the present embodiment, the amount of dissolved oxygen in breeding water W ₃ flowing out (breeding water W ₃ that has passed through the deoxidation process) from the outlet of the open container 21, is about 3.0 mg / l The discharge amount of the carbon dioxide cylinder 22 is set. If the amount of dissolved oxygen in the breeding water W ₃ that has undergone the deoxygenation process is too small in the amount of saturated dissolved oxygen in the breeding water W ₂ before the deoxygenation process, a portion of the nitrogen fixing tank 3A may become anaerobic. (There is a possibility that obligate anaerobic bacteria may propagate), so it is desirable that the amount of dissolved oxygen in the breeding water W ₃ that has undergone the deoxygenation process be a predetermined value or more. This predetermined value varies depending on the type of filter medium, the degree of packing, the amount of water delivered, the water quality, etc., so the lower limit is determined while measuring the amount of nitrous acid generated, etc., but about 2.5 to 3 mg / liter preferable.

The carbon dioxide dissolution process is a process of dissolving carbon dioxide in the breeding water W ₂ obtained from the breeding tank T. That is, the carbon dioxide dissolution process is a process of increasing the amount of dissolved carbon dioxide in the breeding water W ₂ obtained from the breeding tank T. In the present embodiment, since carbon dioxide is supplied in the deoxygenation process, the carbon dioxide dissolution process is performed in parallel with the deoxygenation process. The pH of breeding water in which carbon dioxide is almost saturated is about 6.

The nitrogen fixation process is a process in which the breeding water W ₃ that has passed through the deoxygenation process and the carbon dioxide dissolution process is passed through the nitrogen fixation tank 3A. That is, the nitrogen fixing process is a process of supplying the breeding water W ₃ having a low dissolved oxygen atmosphere containing a large amount of carbon dioxide into the nitrogen fixing tank 3A. When the breeding water W ₃ is supplied into the nitrogen fixing tank 3A, the activity / proliferation of nitrogen fixing bacteria in the nitrogen fixing tank 3A (part of bacteria classified as facultative anaerobic bacteria using carbon dioxide as a carbon source) ( Anabolic nitric acid reduction) becomes active. That is, nitrate ions are consumed for the growth of nitrogen-fixing bacteria, and nitrate ions are fixed as cells, so that the nitrate ion concentration in the breeding water W ₃ decreases.

The breeding water supply process is a process in which the breeding water W ₄ that has undergone the nitrogen fixation process is returned to the breeding tank T. In this embodiment, after the atmosphere is supplied to the breeding water W ₄ that has undergone the nitrogen fixation process, It has returned to. In the present embodiment, the oxygen supply means 4 is used to supply the atmosphere, and the atmosphere is supplied from the air blower 42 to the breeding water W ₄ in the open container 41, so that the dissolved oxygen amount of the breeding water W ₄ is reduced. While increasing the amount, the amount of dissolved carbon dioxide is decreased. In this embodiment, the amount of the air blower 42 released so that the dissolved oxygen amount and pH of the breeding water W ₅ flowing out from the outlet of the downstream open container 41 are suitable for the aquatic organisms in the breeding water tank T. And the number of open containers 41 are set.

According to the breeding water purification apparatus A and the breeding water purification method according to the present embodiment described above, the breeding water W ₃ containing carbon dioxide and having a low dissolved oxygen atmosphere is continuously supplied into the nitrogen fixing tank 3A. Therefore, it is possible to remove nitrate nitrogen safely, stably and continuously, and an apparatus for intermittent water passing becomes unnecessary.

In addition, if the breeding water purification apparatus A is used in combination with nitrification means or protein removal means, the nitrate ion concentration of the breeding water W ₁ in the breeding tank T is 10 ppm even if the number of times of water change or water supply is reduced. It becomes possible to maintain to the extent.

  Moreover, according to the breeding water purification apparatus A according to the present embodiment, since the deoxygenation process and the carbon dioxide dissolution process are performed simultaneously, the amount of dissolved oxygen is reduced with a simplified apparatus. It becomes possible to increase the amount of dissolved carbon dioxide.

The nitrogen-fixing bacteria living in the nitrogen fixing tank 3A assimilate by taking nitrate ions into the body, so that most of the nitrate ions removed from the breeding water W ₃ are assimilated by the nitrogen-fixing bacteria. It will remain in the system. Therefore, the balance of nitrogen fixation tank 3A for some reason is lost, the nitrogen compounds have been assimilated to the nitrogen fixing bacteria is supplied again to the rearing water tank T, there is a possibility to deteriorate the quality of breeding water W _1. When such a problem is concerned, the nitrogen fixing tank 3A is regularly backwashed, or the microbial carrier 32 is taken out from the nitrogen fixing tank 3A, and the nitrogen-fixing bacteria carried on the microbial carrier 32 are used. It is recommended to wash out regularly. In this way, nitrate ions assimilated by the nitrogen-fixing bacteria are taken out of the system together with the nitrogen-fixing bacteria, so that it is possible to reduce the risk that ammonia and nitrite ions are regenerated.

Further, in this embodiment, since the increased amount of dissolved oxygen nitrogen fixation process breeding water W ₄ passed through, it is possible to maintain the quality of breeding water W ₁ in the breeding aquarium T in good condition .

  The total breeding water volume of the breeding tank T shown in FIG. 1 is 720 liters, the capacity of the nitrogen fixing tank 3A is 30 liters (total of 60 liters), the capacity of the open container 41 of the oxygen supply means 4 is 30 liters (total of 60 liters), Experiments were performed to confirm the effect of the breeding water purification method according to the present embodiment with 2.5 kg of living organisms (5 kg of 0.5 kg of red snapper). Table 1 shows experimental conditions and experimental results.

As shown in Table 1, the flow rate in the nitrogen fixing tank 3A and the oxygen supply means 4 is 2.0 liters / minute, and carbon dioxide is not supplied to the water quality adjusting means 2 for 60 days (1st to 60th day). When aquatic organisms were bred while continuing to be fed, the nitrate ion concentration, which was 9 ppm at the start of the bred, increased to 60 ppm. From 61st day, the flow rate in the nitrogen fixing tank 3A and the oxygen supply means 4 was 1.0 liter / min As a result, the nitrate ion concentration remained at a value around 60 ppm. On the 68th day, the flow rate in the nitrogen fixing tank 3A and the oxygen supply means 4 is lowered to 0.5 liter / min, and carbon dioxide is supplied to the water quality adjusting means 2 so as to be the breeding water purification method according to the present embodiment. When the breeding water W ₃ containing carbon dioxide and having a low dissolved oxygen atmosphere is supplied into the nitrogen fixing tank 3A, the dissolved oxygen concentration in the nitrogen fixing tank 3A becomes about 3 mg / liter immediately after the start of the supply of carbon dioxide, Thereafter, the nitrate ion concentration gradually decreased. Five days after the start of the supply of carbon dioxide (72nd day), the nitrate ion concentration stayed within a certain range of about 7-8 ppm, and was maintained for 30 days (73-102 days). . In addition, from the 68th day to the 102nd day, there was no difference in the amount of dissolved oxygen between the inlet and the outlet of the nitrogen fixing tank 3A, which was 2.5 to 3 mg / liter. The phenomenon described above is as follows: (1) The flow rate of the nitrogen fixing tank 3A and the oxygen supply means 4 is lowered to 1.0 liter / minute, so that it dissolves in a part of the filter medium filled in the sealed container 31 or a gap between the filter media. Oxygen drops, facultative anaerobic bacteria begin to propagate, (2) Carbon dioxide can be used as a carbon source among the bacteria classified as facultative anaerobic bacteria by supplying carbon dioxide in this state It can be explained that the bacteria propagated rapidly.

  After that, when the supply of carbon dioxide was stopped, nitrogen gas was supplied instead, and the dissolved oxygen concentration in the nitrogen fixing tank 3A was kept at 2.5 to 3 mg / liter, the nitrate ion concentration in the breeding water tank T Gradually began to increase, reaching 30 ppm on the 23rd day after switching to nitrogen gas, and 160 ppm on the next 24th day. This value almost coincides with the concentration expected from the breeding for 126 days without applying the present invention (estimated from the tendency for 60 days from the start of breeding). This phenomenon is due to the fact that (1) facultative anaerobic bacteria can no longer grow and nitrate ions are no longer immobilized due to the loss of carbon dioxide supply. It can be explained that it was killed from the shortage and decomposed.

In addition, you may change suitably the procedure of the above-mentioned breeding water purification method.
For example, in the above-described embodiment, the case where the deoxygenation process and the carbon dioxide dissolution process are performed in parallel (when the water quality adjusting means 2 serves as both the deoxygenation means and the carbon dioxide dissolution means) is exemplified. It may be done separately. That is, a deoxidizing unit for reducing the dissolved oxygen content in the rearing water W ₂ obtained from the breeding aquarium T, and carbon dioxide dissolving means for dissolving carbon dioxide in breeding water W ₂ may be provided separately. In this case, it is desirable that the carbon dioxide dissolving means is provided on the downstream side of the deoxygenating means, and the carbon dioxide dissolving process is performed after the deoxygenating process. In addition, when performing a deoxygenation process and a carbon dioxide dissolution process separately, you may perform a deoxygenation process using bubbling by an inert gas (for example, nitrogen gas) other than a carbon dioxide, or a vacuum deaeration apparatus. .

Moreover, you may change the structure of an above-described breeding water purification apparatus.
For example, in the above-described embodiment, an example in which two nitrogen fixing tanks 3A are provided is illustrated, but this is not intended to limit the number of nitrogen fixing tanks 3A. Although illustration is omitted, the nitrogen fixing tank 3A may be one, or may be three or more. In the above-described embodiment, the case where the plurality of nitrogen fixing tanks 3A are provided in series is illustrated, but may be provided in parallel.

  In the above-described embodiment, the oxygen supply unit 4 including two open containers 41 is illustrated, but the number of the open containers 41 is not limited. Although illustration is omitted, the number of open containers 41 may be one, or three or more. In the above-described embodiment, the case where the plurality of open containers 41 are provided in series is illustrated, but may be provided in parallel.

Further, when only aeration carried out in the breeding aquarium T can maintain a dissolved oxygen amount of breeding water W ₁ to an appropriate state may be omitted oxygen supply means 4.

It is a circulation filtration system diagram for demonstrating the structure of the breeding water purification apparatus which concerns on one Embodiment of this invention.

Explanation of symbols

1 Circulation line 2 Water quality adjustment means (deoxygenation means, carbon dioxide dissolution means)
3 nitrogen fixation means 3A nitrogen-fixing tank 4 oxygen supply means T breeding aquarium W ₁ to _W-5 breeding water

Claims (6)

A deoxygenation process that reduces the amount of dissolved oxygen contained in the breeding water obtained from the breeding tank;
Carbon dioxide dissolution process to dissolve carbon dioxide in breeding water,
A nitrogen fixation process of passing the breeding water that has passed through the deoxygenation process and the carbon dioxide dissolution process into a nitrogen fixation tank filled with a microorganism carrier comprising an aggregate of filter media;
A breeding water purification method comprising a breeding water supply process of returning breeding water that has undergone the nitrogen fixation process to the breeding tank.   In the deoxygenation process, the amount of dissolved oxygen contained in the breeding water is reduced by supplying carbon dioxide more than a saturated dissolved carbon dioxide amount to breeding water obtained from the breeding aquarium. The breeding water purification method as described.   3. The breeding water purification method according to claim 2, wherein in the breeding water supply process, oxygen is supplied to the breeding water that has undergone the nitrogen fixation process.   4. The breeding water purification method according to claim 3, further comprising a washing process of back washing the nitrogen fixing tank.   4. The breeding water purification method according to claim 3, further comprising a washing step of taking out the microorganism carrier from the nitrogen fixing tank and washing away the nitrogen-fixing bacteria carried on the microorganism carrier. A circulation line for circulating the breeding water in the breeding tank,
Deoxygenation means for reducing the amount of dissolved oxygen contained in the breeding water obtained from the breeding tank;
Carbon dioxide dissolving means for dissolving carbon dioxide in the breeding water;
A breeding water purification apparatus comprising: a nitrogen fixing tank formed by filling a microbial carrier composed of an aggregate of filter media,
A breeding water purification apparatus characterized in that the deoxygenation means is provided upstream of the nitrogen fixing tank.

Images