JP2006272307A - Method and system for purifying water of natural water area or water of water tank in which natural water is put using microbubbles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and small-sized purification apparatus for efficiently purifying the water of a polluted natural water area, the water of an aquatic animal living polluted water area or the water of a water tank in which natural water is put by a simple constitution, and a water tank for growing an aquatic animal capable of growing the aquatic animal over a long period of time without replacing water and requiring cleaning. <P>SOLUTION: Water is continuously taken in from the polluted natural water area to introduce the same into a microbubble contact treatment tank and, after microbubbles are brought into contact with the water taken in from the microbubble contact treatment tank to subject the same to biological aeration treatment, the treated water is continuously returned and circulated to the polluted natural water area through a filter bed. By bringing microbubbles into contact with microorganisms living in the polluted natural water area, the propagation speed of microorganisms is enhanced to activate the microorganisms to nitrify or nitrate ammoniacal nitrogen. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a purification method and a purification system for natural water areas using microbubbles.

Water is a basic solvent for dissolving a substance, and pure water represented by the chemical formula H ₂ O generally does not exist in nature. For example, seawater contains many salts, and a small amount of salts and organic matter are dissolved in land water.
Oxygen dissolved in water is called dissolved oxygen (DO) and is indispensable for maintaining the life of aquatic organisms. In nature, many chemical reactions occur in aqueous solutions, and the dissolved state of substances affects the reaction.
A microbubble is defined as a fine bubble having a size effect of 10 to several tens of micrometers (μm) when the bubble is generated. (Note that the microbubbles at the time of occurrence are then compressed and reduced in water). Like the air, the bubbles contain about 20% oxygen, about 80% nitrogen, and argon, carbon dioxide, etc. as trace components. These microbubbles have physical and chemical properties different from ordinary bubbles (macrobubbles).

[Characteristics of microbubbles]
Bubbles of gas (macro bubbles) generated in the water tank vessel rise rapidly due to the difference in specific gravity of air and water, and the diameter increases as the water pressure decreases in the upper layer and bursts on the surface of the water phase.
On the other hand, microbubbles generated under negative pressure in the apparatus stay in water for a relatively long time, and finally disappear in water. The characteristics of microbubbles as bubbles are reviewed from Stokes law, Laplace pressure, and Henry law.
Bubble rising speed is expressed by Stokes' equation (1)
^{V = (ρs-ρF) gD} 2 / 18μ formula (1)
It is represented by The bubble rising speed (V) is expressed by ρs (particle density), ρF (liquid density), g (gravity acceleration), D (particle diameter), and μ (viscosity coefficient of liquid). And very slow.
Bubbles are gas bodies existing in water and usually have a spherical gas-liquid interface. In microbubbles, the surface tension of water acts on the gas / liquid interface, and the pressure of the internal gas rises. The pressure difference ΔP between the outside and inside of the bubble is Laplace's formula (2)
ΔP = γ / R Formula (2)
Where γ is the surface tension of water and R is the size of the bubbles. The gas pressure inside the bubbles having a diameter of 1 μm is 3 to 4 atmospheres.
According to Henry's law, the solubility of a gas increases in proportion to the pressure, and DO is about 8 ppm at 1 atmosphere of atmospheric pressure (partial pressure of oxygen; 0.2 atmosphere) at room temperature. Microbubbles with a small diameter have a large specific surface area and a high oxygen dissolution rate, and the local concentration of oxygen is considered to increase in the vicinity. The microbubble surface is negatively charged (-35 mV with distilled water), and the zeta potential is strongly alkaline, -100 mV, and a pH of 3 or less shows a positive potential. Oxygen dissolved in water is oxidative, while negative charge is reductive, and the microbubble surface may have both oxidizing and reducing atmospheres.
The effects of these microbubbles must be distinguished between direct chemical reactions with fast reaction rates and large free energy changes, and biological reactions, which are relatively mild reactions.

  In the conventional purification system for contaminated natural water areas or aquarium water containing natural water due to macro bubbles, a long time and a large-scale device are required, which is expensive.

This invention solves the said subject, and is invention of the following structure.
(1) After continuously taking water from a contaminated natural water area and introducing it into a microbubble contact treatment tank, the microbubbles are brought into contact with the water taken in the treatment tank and subjected to biological aeration treatment, and then passed through a filtration layer. A method for purifying natural aquatic water using microbubbles or aquarium water containing natural water, wherein the water is continuously returned to and circulated to the natural water.
(2) The description of (1) above, wherein microbubbles are brought into contact with microorganisms inhabiting natural water areas to increase and activate the microorganism growth rate, thereby nitrifying or nitrating ammoniacal nitrogen Water purification method using natural microbubbles.
(3) After continuously taking water from contaminated natural waters inhabited by aquatic animals, introducing it into a microbubble contact treatment tank, and contacting microbubbles with the water taken in the treatment tank, and then subjecting the microorganism to aeration A method for nurturing aquatic animals using microbubbles, wherein the water is continuously returned to the natural water area through the filtration layer, or aquarium water containing natural water is circulated.
(4) By bringing microbubbles into contact with microorganisms inhabiting natural water areas or aquarium water containing natural water, microbial growth rate is increased and activated, and ammonia nitrogen is nitritized or nitrated. A method for nurturing aquatic animals using microbubbles as described in (3) above.
(5) Contaminating natural waters inhabited by aquatic animals or water taking means for continuously taking water from aquariums containing natural water, and microbubbles are brought into contact with the water taken out by the water taking means for microbial aeration treatment. Microbubble contact treatment tank, filtration device for filtering microbial aeration-treated water derived from the treatment tank, and purified water continuously returning and circulating purified water derived from the filtration device to the natural water A purification system for natural aquatic water using microbubbles or aquarium water containing natural water, characterized by comprising return means.
(6) In the microbubble contact treatment tank, the microbubbles are brought into contact with microorganisms living in the natural water area to increase and activate the microbial growth rate to nitrite or nitrate the ammoniacal nitrogen. A purification system of natural aquatic water or aquarium water containing natural water by microbubbles as described in (5) above.

According to the method of the present invention, it is possible to efficiently purify contaminated natural water areas, aquatic animal habitat contaminated water areas, or aquarium water containing natural water with a simple configuration.
Further, according to the system of the present invention, it is possible to efficiently purify contaminated natural water areas or aquatic animal habitat contaminated water areas with a simple and small device configuration.
If the invention system of the present application is applied to an aquatic animal breeding water tank, it is possible to grow an aquatic animal for a long time without replacing water and without cleaning.

Next, an embodiment of the present invention will be described.
First, the results of various experiments using microbubbles will be described.
[Microbubble experiment and measurement]
For microbubble treatment (hereinafter abbreviated as MB treatment), an M2 type bubble generator (trade name: swivel type microbubble generator that generates microbubbles with an average cell diameter of 10-20 microns manufactured by Nano Planet Research Laboratories) And 30 L, 20 L, or 5 L (liter) water tanks, and the air amount was 100 to 1000 mL / min, and was performed at room temperature (20 to 30 ° C.).
The sample was prepared by adding ammonium chloride, sodium nitrite, potassium nitrate, or a commercially available surfactant (SDS; sodium dodecyl sulfate, SDBS; sodium dodecylbenzenesulfonate) to the water of the pond, and no nutrient salts were added. . An experiment through normal microbubbles instead of microbubbles is defined as B treatment. As a control experiment, tap water was subjected to ion exchange, activated carbon filtration, and filter treatment.
Since this water does not contain salts or fungi, it is referred to as distilled water for convenience. Ammonia was measured by indophenol spectrophotometry, nitric acid and nitrous acid were measured by ion chromatography, and surfactant was quantified by toluene extraction-spectrophotometry using ethyl violet and TOC measurement.

[Nitrogen oxidation]
1. Oxidation-reduction method of nitrogen Oxidation is a reaction in which oxygen is added to nitrogen, and hydrogen reacts in reduction. At this time, oxygen is calculated as -2 and hydrogen is calculated as +1, and the oxidation number of the nitrogen atom is obtained.
As shown in FIG. 1, the oxidation number of nitrogen of the nitrogen molecule (N ₂ ) is set to 0, and ammonia (NH ₃ ) or ammonia ion (NH ₄ ⁺ ) having an oxidation number of −3 is obtained by the reduction reaction. On the other hand, the oxidation reaction results in nitrite having an oxidation number of +3 (HNO ₂ , nitrite ion; NO ₂ ⁻ ) and +5 nitric acid (HNO ₃ , nitrate ion; NO ₃ ⁻ ).
The potential of this oxidation-reduction reaction is expressed by the Nernst equation.
E = E0−0.0591 / nlog ([reduced form] / [oxidized form]) 25 ° C. Formula (3)
E is the potential of the system, E ₀ is a standard redox unit specific to the chemical species involved in the reaction, and n is the number of electrons involved in the reaction.
In the system, when an oxidant having a high potential is consumed due to an oxidation reaction, the potential decreases. Conversely, when a reducing agent is consumed in a reduction reaction, the potential increases. The oxidation-reduction potential is O ₂ / H ₂ O (1.23 V), nitrous acid / ammonia / (0.86 V), and nitric acid / nitrous acid (0.94 V), although it varies depending on the pH of the solution and the state of presence. In addition, the potential is related to the free energy of the reaction, and the reaction involving microorganisms is also a chemical reaction at the molecular level.

2. Inorganic nitrogen Nitrogen is an essential element for living organisms and is abundant in proteins that make up the human body. In nature, microorganisms fix nitrogen in the atmosphere and nitrogen is used by animals and plants through the food chain.
In the natural world, circulation of nitrogen molecule → “nitrogen fixation” → ammonia → “nitrification” → nitrite → “nitrification” → nitric acid → “denitrification” → nitrogen molecule is balanced. Most of the inorganic nitrogen (90% or more) generated by the decomposition of proteins and the like is ammonia, which is adsorbed by positively charged soil particles and used as plant fertilizer. Under aerobic conditions, ammonia is oxidized to nitrite and nitric acid by nitrifying bacteria.
Negatively charged nitrate ions elute from the soil and dissolve in water, and the presence of excess causes pollution of rivers, lakes and groundwater.
In modern times, ammonia is produced industrially from hydrogen and nitrogen by the Born Harbor method, but the use of excess chemical fertilizers causes environmental problems such as eutrophication.
Since nitric acid and nitrous acid cause methemoglobinosis, 10 mg / L for drinking water (groundwater environmental standards; 1999, ministerial ordinance on water quality standards based on the Water Supply Act; 2003). The wastewater standard (Water Pollution Control Law) of 100 mg / L is also established for the wastewater from the etc. as inorganic nitrogen.

3. Oxidation of nitrogen by microbubbles Ammonia and nitrous acid were added to distilled water, and a microbubble treatment was performed as a microbubble and control experiment, but there was no change after 90 hours (FIG. 2).
This result indicates that there is no chemical oxidation of inorganic nitrogen by microbubbles, or there is no detectable production of reduced nitrogen and no reduction of oxidized nitrogen.
On the other hand, the water in the pond contained 2-3 ppm nitric acid, 0.5 ppm nitrous acid, and a small amount of ammonia (in winter), and each salt of nitrogen was added to this water to use as sample water.
As shown in FIG. 3, when MB treatment was performed on pond water, ammonia decreased immediately after the treatment and disappeared after 20 hours. Nitrous acid decreased → increased → decreased → disappeared, and nitric acid became a constant value after increasing. Nitrifying bacteria, which are autotrophic bacteria, do not require organic substances as nutrients, but the oxidation rate of ammonia is slow, and a wastewater treatment plant can be aerated at a water temperature of 20-30 ° C. and pH = 6.8-8.5. Many. For pond water, the rate of ammonia reduction by B treatment was slower than MB treatment.
Nitrifying bacteria lose their activity due to the inhibition of the enzyme reaction by special chemical substances according to the bacterial species. This method can be used for indirect verification of the presence of bacteria. When allylthiourea was added to the pond water before MB treatment, the oxidation reaction of ammonia to nitrous acid was inhibited, and nitric acid was not produced. Nitrite produced by the action of ammonia oxidizing bacteria is oxidized into nitric acid by the nitrite oxidizing bacteria. This reaction is inhibited by chloric acid. When sodium chlorate is added, ammonia is oxidized to nitrous acid by ammonia oxidizing bacteria, so ammonia is initially reduced and nitrite is increased. However, because chloric acid inhibits the oxidation of nitrite to nitric acid by nitrite-oxidizing bacteria, oxidation stopped at the nitrite stage, and the nitrite concentration became constant.
These results suggest activation of the oxidation reaction of ammonia to nitric acid by microorganisms such as ammonia-oxidizing bacteria (nitrosomonas) and nitrite-oxidizing bacteria (nitrobactor) by microbubbles. It has the effect of increasing the rate of oxidation to nitric acid.

4). Denitrification and microbubbles Nitric acid and nitrous acid are removed from the system by denitrifying bacteria as nitrogen molecule or nitrogen oxide gas. This bacterium is a heterotrophic bacterium and requires energy such as methanol and sugar and carbon that forms the skeleton of the bacterium. It uses oxygen in an aerobic condition and uses nitric acid in an anaerobic atmosphere. Although potassium nitrate was added so that it might become 10 ppm and MB processing was performed about the water of the pond which added glucose, nitric acid was not decreased. Therefore, air-microbubbles are effective for an oxidation reaction using dissolved oxygen, but there are limits to application to an anaerobic atmosphere reduction reaction such as denitrification.

[Surfactant]
1. Surfactant properties When two different phases such as water and oil or water and air are in contact, the substance dissolved in either phase is adsorbed on the contact surface (interface) of the two phases and the area of the two-phase interface is minimized. Interfacial tension (also called surface tension when one of the phases is a gas) acts. This action of lowering the interfacial tension is referred to as surface activity, and a substance having a remarkable effect in a small amount is called a surfactant. For example, the reason why the aqueous solution of the detergent containing the surfactant is foamed is that the interfacial tension between air and water is lowered. Surfactants have two parts with different properties in the molecule. The portion that is not easily dissolved in water and easily adaptable to oil is called a lipophilic group, and is mainly composed of long-chain aliphatic hydrocarbons or aromatic hydrocarbons. On the other hand, the portion that binds to water is called a hydrophilic group and consists of a group that easily hydrates, such as carboxylic acid, sulfonic acid, and ammonium ion. When oil is added to water, it does not dissolve in each other, so it separates into two phases. When a surfactant is added thereto, the lipophilic group dissolves in the oil droplet, and the hydrophilic group covers the surface of the oil droplet. As a result, the oil droplet is dissolved (solubilized) or dispersed (emulsified) in water. If the hydrophilic group is ionic, the oil droplets are charged and become particles of the same charge, making it difficult to agglomerate. Surfactants such as soaps and detergents are widely used in daily life, and various types are synthesized and sold depending on the purpose of use.

2. Degradation mechanism The SDS used in the degradation test this time is dodecanol, which is a higher alcohol, and an ester of sulfuric acid as shown in formulas (4) and (5). It hydrolyzes relatively quickly under alkaline and acidic conditions. , Raw material alcohol and sulfuric acid.
C ₁₂ H ₂₅ OH + H ₂ SO ₄ ⇔ C ₁₂ H ₂₅ OSO ₈ H + H ₂ O
Formula (4)
C ₁₂ H ₂₅ OSO ₈ H + NaOH = C ₁₂ H ₂₅ OSO ₈ Na (solid, SDS) + H ₂ O
Formula (5)

Although not as noticeable as pond water, SDS added to distilled water has a decrease in concentration due to primary decomposition when MB treated, and is considered to be partially hydrolyzed chemically.
Primary decomposition C ₁₂ H ₂₅ OSO ₈ Na + H ₂ O → C ₁₂ H ₂₅ OH + NaHSO ₄
Formula (6)
Secondary decomposition C ₁₂ H ₂₅ OH + 18O ₂ → 12CO ₂ + 13H ₂ O
Formula (7)
However, SDBS having a sulfone group directly bonded to a benzene ring, which is often used in synthetic detergent for laundry, is stable and difficult to decompose by chemical methods. No degradation of SDBS by MB treatment in distilled water was observed.
The hydrophobic part of the surfactant is made of hydrocarbons and is easily broken down into microorganisms. Biodegradation refers to a phenomenon in which organic carbon compounds are decomposed into carbon dioxide and water when converted to cellular materials and used as an energy source by the action of microorganisms. This process is
1) Primary degradation: the minimum degradation required to change the properties of the substance,
2) Decomposition until the environment accepts: Decomposition action until it loses unfavorable environmental properties,
3) Final decomposition: carbon dioxide, water, decomposition action to make minerals such as hydrophilic part salts,
It is divided into.
The actual reaction in nature is complex, and the biodegradation of SDBS depends on the enzyme produced by the microorganism a. Alkyl chain scission and oxidation to carboxylic acid, b. Cleavage of the benzene ring, c. Elimination of the sulfone group, d. It consists of mineralization of reduced organic carbon compounds into water and carbon dioxide and incorporation into microorganisms, but details are unknown.
This time, regardless of the general biodegradation test method for detergents (JIS K3363, etc.), the pond water was treated with MB, and ethyl violet corresponding to methylene blue activity (corresponding to primary degradation that lost surface activity) was tested. Changes in the secondary decomposition (organic carbon mineralization) with time were examined by extraction with toluene as an ion-absorption spectrophotometry and by TOC measurement. FIG. 5 shows the change over time in the primary decomposition of SDS when the pond water is MB treated. The primary decomposition was completed after 18 hours in the pond water MB treatment, after 24 hours in the B treatment, and after 68 hours in the standing. The dissolved enzyme was saturated in both MB treatment and B treatment, and it changed under time when left standing, so that it was difficult to maintain the aerobic properties in the entire container.
FIG. 6 shows the measurement results of total organic carbon (TOC). The TOC originally contained in the pond water is 3.3 ppm, and distilled water is almost 0 ppm. Considering the TOC baseline of pond water, SDS is almost mineralized after 18 hours in the MB treatment, and part of the organic carbon component remains in the B treatment.
SDBS was subjected to primary treatment after about 50 hours by MB treatment. However, accurate measurement was not possible for TOC due to bubble formation.

Next, the purification system for natural water of the present invention will be described in detail with reference to several drawings.
Example 1:
FIG. 7 is an example in which the present invention is applied to aquarium water of aquatic animals (fish),
Water containing microbubbles is ejected from the microbubble generator 1 embedded in the organic polluted water (natural water taken from the pond) in the aquarium 2, and the microbubbles come into contact with the organic polluted water and dissolve in water. The amount of oxygen increases.
Then, as a result of the proliferation of microorganisms present in the water and consumption of organic pollutants, the contaminated water is purified.
Further, the water contacted with the microbubbles passes over the upper end of the partition wall 2 ′ (overflow) and enters the filtration device chamber 3, where solid matter such as dead microorganisms is captured and filtered by the filter medium 6, and the pipe line 5 and again introduced into the microbubble generator 1 via the pump 4 on the way.
As described above, the organic contaminated water is circulated in the purification system, and the purified water is always supplied as the aquatic animal 10 environmental water.

Example 2:
FIG. 8 is another example in which the present invention is applied to aquarium water of aquatic animals (fish).
Water containing microbubbles is ejected from the microbubble generator 1 embedded in the organic polluted water (natural water taken from the pond) in the aquarium 2, and the microbubbles come into contact with the organic polluted water and dissolve in water. The amount of oxygen increases.
Then, as a result of the proliferation of microorganisms present in the water and consumption of organic pollutants, the contaminated water is purified.
Further, the water contacted with the microbubbles is filtered by the embedded strainer 7, where solids such as microbial dead bodies are captured and filtered, and again via the pipe 5 and through the pump 4 on the way, the microbubbles are again collected. Introduced into the generator 1.
As described above, the organic contaminated water is circulated in the purification system, and the purified water is always supplied as the aquatic animal 10 environmental water.

Example 3:
FIG. 9 is another example in which the present invention is applied to aquarium water of aquatic animals (fish).
Water containing microbubbles is ejected from the microbubble generator 1 embedded in the organic polluted water (natural water taken from the pond) in the aquarium 2, and the microbubbles come into contact with the organic polluted water and dissolve in water. The amount of oxygen increases.
Then, as a result of the proliferation of microorganisms present in the water and consumption of organic pollutants, the contaminated water is purified.
Further, the water contacted with the microbubbles is filtered by the partition wall 8 made of the filter medium, where solid matter such as dead bodies of microorganisms are captured and filtered, and stored in the storage chamber, and then via the pipe line 5, It is again introduced into the microbubble generator 1 via the pump 4.
As described above, the organic contaminated water is circulated in the purification system, and the purified water is always supplied as the aquatic animal 10 environmental water.

Example 4:
FIG. 10 is another example in which the present invention is applied to aquarium water of aquatic animals (fish).
Purified water having an increased amount of dissolved oxygen in the water is supplied into the water tank 2.
Organic polluted water (natural water taken from the pond) is taken from the bottom of the aquarium 2 and introduced into the organic sewage treatment auxiliary device 9 via the pipeline 5.
The organic sewage treatment auxiliary device 9 is equipped with a microbubble generator 1 and a filter medium 6, in which water containing microbubbles is ejected, the microbubbles come into contact with the organic contaminated water, and the amount of dissolved oxygen in the water As a result of the increase in microorganisms and the consumption of organic pollutants, the contaminated water is purified.
Then, the water contacted with the microbubbles is filtered by the filter medium 6, where solids such as dead bodies of microorganisms are captured and filtered, and are led out to the water tank 2 through the pipe line 5.
As described above, the organic contaminated water is circulated in the purification system, and the purified water is always supplied as the aquatic animal 10 environmental water.

According to the above examples, ammonia nitrogen was drastically reduced, water quality was improved by nitrification, and long-term growth of seafood and aquatic organisms (including marine organisms) in natural water areas and aquariums became possible.
And the water tank was not soiled, no cleaning was required, and no water replacement was required.

Point pollution that can identify pollution sources such as wastewater associated with production activities at factories and offices, and nonpoint pollution that has a wide range of effects due to difficulty in identifying pollution sources such as fertilizers, pesticides, and household wastewater. There is a difference. Point contamination requires a relatively small amount of high-concentration wastewater to be treated.
On the other hand, Nonpoint contamination has a low concentration of pollutants but is wide-ranging. Therefore, it is necessary to treat a huge amount, and a purification cycle by natural organisms becomes important. This time, we deal with relatively low concentrations of chemical species as an application of microbubble technology. Although direct chemical effects on the reaction of microbubbles could not be detected, microbubbles are useful for biological reactions utilizing microorganisms. Microbubbles using natural air are thought to be useful for treatment reactions in an aerobic atmosphere in an open natural environment.

Explanatory drawing of the oxidation and reduction state of nitrogen. The graph which shows the change of various inorganic nitrogen by a microbubble process (20-23 degreeC). The graph which shows the change of various inorganic nitrogen by a macro bubble process (27-29 degreeC). The graph which shows the change of various inorganic nitrogen by a microbubble process (26-30 degreeC). The graph which shows the microbubble process effect with respect to SDS containing water. The graph which shows the micro bubble processing effect with respect to SDS containing water, and a macro bubble processing effect. Explanatory drawing of an example of the purification system of the aquatic organism water tank by a microbubble. Explanatory drawing of the other example of the purification system of the aquatic organism water tank by microbubble. Explanatory drawing of the other example of the purification system of the aquatic organism water tank by microbubble. Explanatory drawing of the other example of the purification system of the aquatic organism water tank by microbubble.

Explanation of symbols

1: microbubble generator, 2: water tank, 3: filtration device room,
4: Pump, 5: Pipe line, 6: Filter material,
7: Strainer, 8: Filter media partition wall,
9: Organic wastewater treatment auxiliary device, 10: Aquatic animal.

Claims (6)

Water is continuously taken from a contaminated natural water area and introduced into a microbubble contact treatment tank. After the microbubbles are brought into contact with the water taken in the treatment tank and subjected to biological aeration treatment, the natural water area is passed through the filtration layer. A method for purifying natural water using microbubbles, which is continuously returned to water and circulated. The microbubble according to claim 1, wherein the microbubble is brought into contact with a microorganism inhabiting a natural water area to increase and activate the microorganism growth rate to nitrite or nitrate the ammoniacal nitrogen. Natural water purification method. Water is continuously taken from contaminated natural waters inhabited by aquatic animals, introduced into a microbubble contact treatment tank, and microbubbles are brought into contact with the water taken in the treatment tank, followed by microbial aeration treatment, and then a filtration layer. A method for nurturing aquatic animals using microbubbles, wherein the water is continuously returned and circulated to the natural water. 4. The microbubble according to claim 3, wherein the microbubble is brought into contact with a microorganism inhabiting a natural water area to increase and activate the microorganism growth rate to nitrite or nitrate the ammoniacal nitrogen. How to cultivate aquatic animals. From water intake means for continuously taking water from contaminated natural waters inhabited by aquatic animals, a microbubble contact treatment tank for contacting microbubbles with the water taken out by the water intake means, and microbial aeration treatment, and from the treatment tank A micro apparatus comprising: a filtration device that filters the derived microorganism-aerated treated water; and purified water return means that continuously returns and circulates purified water derived from the filtration device to the natural water area water. Natural water purification system using bubbles. In the microbubble contact treatment tank, the microbubbles are brought into contact with microorganisms living in the natural water area to increase and activate the microorganism growth rate, thereby nitrifying or nitrating ammonia nitrogen. A natural water area water purification system using microbubbles according to claim 5.

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