JP2023111655A - Water treatment apparatus and water treatment method - Google Patents

Abstract

To provide a water treatment apparatus with low consumption of a denitrification carrier in a denitrification process and an improved denitrification rate per unit weight of the denitrification carrier.SOLUTION: A water treatment apparatus includes a water storage containing treated water, a denitrification tank containing a denitrification carrier loaded with denitrifying bacteria, and a microorganism reduction treatment part for reducing the number of aerobic heterotrophic bacteria in the treated water, the microorganism reduction treatment part being located in the middle of a transfer path of the treated water from the water storage to the denitrification tank.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a water treatment apparatus and a water treatment method using denitrifying bacteria.

From the standpoint of environmental protection, the standards for wastewater containing ammonium nitrogen generated from agriculture, fish farming, and the like are becoming stricter. In addition, it is not preferable from the viewpoint of eutrophication of rivers and the like to discharge wastewater containing ammonium nitrogen into rivers and seas.
In order to solve this problem, a nitrification reaction has been used in which ammonium nitrogen is oxidized into relatively less toxic nitrate nitrogen by the action of microorganisms. However, although nitrate nitrogen is less toxic than ammonia, it is undoubtedly harmful, and it is desirable to further reduce nitrate nitrogen to nitrogen.

From this point of view, in recent years, techniques have been developed for removing ammonium nitrogen from wastewater using a two-step reaction using microorganisms. That is, the method uses a nitrification reaction that converts ammonia into nitric acid and a denitrification reaction that decomposes nitric acid into nitrogen. If it is decomposed to nitrogen, it can be discharged into the air without imposing a burden on the environment.

Among the above reactions using microorganisms, in the reaction of converting ammonia into nitric acid in the first stage, bacteria that naturally settle in calcium-based substrates such as shells that are discarded as they are are often used. On the other hand, in the denitrification reaction in which nitric acid is converted to nitrogen in the second stage, denitrifying bacteria that live in a polymer such as cellulose are often used as a base material.

In Patent Document 1, cellulose or the like is used as a base material for the denitrification reaction. The principle is that "biodegradable polymers such as natural polymers and biodegradable synthetic resins serve as substrates or hydrogen donors for the growth and proliferation of dependent (organic) trophic bacteria, and the amount of dissolved oxygen in water is extremely low. In the presence of nitrogen oxides such as nitrite and nitrate, denitrifying bacteria, which are facultative anaerobic microorganisms that use oxygen in nitrogen oxides for respiration and reduce and remove nitrogen oxides, are highly biodegradable. It swarms on the molecule and implants.”

Patent Documents 2 and 3 disclose techniques in which biodegradable resins are exemplified as substrates that can be used in the denitrification reaction in addition to cellulose.

JP-A-10-85782 Japanese Unexamined Patent Application Publication No. 2014-24000 JP 2010-88307 A

However, in the techniques described in these patent documents, denitrification carriers such as cellulose and biodegradable resins are consumed as carbon sources by microorganisms during water treatment. requires replenishment of the denitrifying carrier to maintain the denitrifying carrier above the required amount. There is also room for improvement in that the denitrification rate per unit weight of the denitrification carrier is low due to the large consumption of the denitrification carrier.
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a water treatment apparatus that consumes less denitrifying carrier during denitrifying treatment and that has an improved denitrifying rate per unit weight of the denitrifying carrier.

As a result of extensive studies, the present inventors have found that the above problems can be solved by reducing the number of aerobic heterotrophic bacteria in the water to be treated prior to the denitrification reaction, and have completed the present invention. . That is, the present invention is as follows.

[1]
a water reservoir containing water to be treated;
a denitrifying tank containing a denitrifying carrier carrying denitrifying bacteria;
a microorganism reduction treatment unit that reduces the number of aerobic heterotrophic bacteria in the water to be treated;
A water treatment apparatus, wherein the microorganism reduction treatment unit is arranged in the middle of a transfer route of the water to be treated from the water reservoir to the denitrification tank.
[2]
The water treatment apparatus according to [1], wherein the microorganism reduction treatment unit is an ultraviolet irradiation unit that irradiates the water to be treated with ultraviolet rays.
[3]
The water treatment device according to [1] or [2], wherein the denitrification carrier contains a biodegradable resin.
[4]
The water treatment device according to [3], wherein the biodegradable resin is a biodegradable polyester having a structural unit derived from dicarboxylic acid.
[5]
The water treatment apparatus according to any one of [1] to [4], further comprising a nitrification tank containing a nitrification carrier carrying nitrifying bacteria.
[6]
The water treatment apparatus according to any one of [1] to [5], wherein the water to be treated is breeding water for aquatic organisms.
[7]
A microorganism reduction step for reducing the number of aerobic heterotrophic bacteria in the water to be treated;
A denitrification step in which the water to be treated that has undergone the microorganism reduction step is supplied to a denitrification tank containing a denitrification carrier carrying denitrifying bacteria, and denitrification is performed;
A water treatment method, comprising:

ADVANTAGE OF THE INVENTION According to this invention, the consumption of the denitrification carrier accompanying denitrification treatment is small, and the water treatment apparatus with which the denitrification rate per unit weight of the denitrification carrier was improved can be provided.
The objects and effects of the present invention are not limited to those specifically described above, but include those that will be apparent to those skilled in the art from the entire specification.

(a) and (b) are schematic diagrams each showing an example of a water treatment apparatus according to a first embodiment of the present invention. 1 is a schematic diagram of a breeding apparatus in Example 1. FIG.

The present invention will be described in detail below, but the description of the constituent elements described below is an example (representative example) of embodiments of the present invention, and the present invention is not limited to these contents, and the Various modifications can be made within the scope of the gist.

<1. Water treatment equipment>
A water treatment apparatus according to a first embodiment of the present invention includes a water reservoir in which water to be treated is stored,
A denitrifying tank containing a denitrifying carrier carrying denitrifying bacteria; and a microorganism reduction treatment section for reducing the number of aerobic heterotrophic bacteria in the water to be treated, wherein the microorganism reduction treatment section is provided with a It is arranged in the middle of the transfer route of the water to be treated leading to the denitrification tank.

The water treatment apparatus according to this embodiment is an apparatus for removing nitrogen from water containing inorganic nitrogen such as ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen. When the water to be treated contains ammonium nitrogen, the water treatment apparatus is provided with a nitrification tank described later, the ammonium nitrogen is converted to nitrite nitrogen and/or nitrate nitrogen, and this is treated in a denitrification tank. Remove nitrogen. Water to be treated containing inorganic nitrogen is not particularly limited, and may be, for example, water for breeding aquatic organisms. The breeding water may be fresh water or sea water. As for seawater, its salinity is not limited.

A preferred embodiment of an example of the water treatment apparatus according to this embodiment will be described below with reference to FIG. 1(a). FIG. 1(a) shows a circulation-type water treatment apparatus 10. FIG. Arrows in FIG. 1(a) indicate the direction of water transfer in the water treatment apparatus. In this circulation-type water treatment apparatus 10, the water to be treated in the water reservoir 11 is sequentially transferred to the microorganism reduction treatment unit 13 and the denitrification tank 14, and returned to the water reservoir 11 after being purified. In addition, the water treatment apparatus according to the present embodiment is not limited to a circulation system, and may be a free-flowing system.

(water reservoir)
The water reservoir 11 is not particularly limited as long as it can store the water to be treated, and examples thereof include a pond and a water tank. The size, shape, etc. of the water reservoir can also be appropriately selected according to the application.

(denitrification tank)
The denitrification tank 14 is a tank containing a denitrification carrier carrying denitrifying bacteria that convert nitrate nitrogen and nitrite nitrogen into nitrogen.

The denitrifying carrier is a base material that attaches denitrifying bacteria that convert nitrate nitrogen and nitrite nitrogen to nitrogen and supplies a carbon source necessary for denitrification. It is not necessary for all the denitrifying carriers to carry denitrifying bacteria, and it is sufficient that the denitrifying bacteria are carried to such an extent that nitrate nitrogen from the water to be treated can be sufficiently converted into nitrogen according to the application.
As the denitrifying carrier, a wide range of substrates on which denitrifying bacteria adhere and grow can be used, including substrates containing polymers such as cellulose and biodegradable resins. Among them, the denitrification carrier preferably contains a biodegradable resin (hereinafter, a denitrification carrier containing a biodegradable resin is sometimes referred to as a "biodegradable resin base material").

The biodegradable resin forming the biodegradable resin substrate is not particularly limited, and can be appropriately selected from known biodegradable resins and used. Known biodegradable resins generally include PLA (polylactic acid), PBS (polybutylene succinate), PCL (polycaprolactone), and PHB (polyhydroxybutyrate) resins.

Preferred biodegradable resins include biodegradable polyesters. Among biodegradable polyesters, biodegradable polyesters having dicarboxylic acid-derived structural units are preferred, and biodegradable polyesters having dicarboxylic acid-derived structural units and diol-derived structural units are more preferred.

Dicarboxylic acids include oxalic acid, malonic acid, succinic acid, adipic acid, glutaric acid, suberic acid, azelaic acid, sebacic acid, terephthalic acid, isophthalic acid, and phthalic acid. The biodegradable resin preferably has two or more structural units derived from dicarboxylic acid. When using a biodegradable resin having two or more types of dicarboxylic acid-derived structural units, the denitrification rate is faster than when using a biodegradable resin having one type of dicarboxylic acid-derived structural unit, and high denitrification performance. This is because there is a tendency to show

Among the above dicarboxylic acids, the biodegradable resin preferably has structural units derived from succinic acid, that is, PBS-based biodegradable resins having butylene succinate units as main repeating units are preferred. Specific examples of PBS-based biodegradable resins include polybutylene succinate, poly(butylene succinate/adipate) (PBSA), poly(butylene succinate/carbonate), poly(butylene adipate/terephthalate) (PBAT). ), poly(ethylene terephthalate/succinate) and the like are preferred examples. In particular, PBSA is preferable because it is highly biodegradable and because it can supply the carbon source necessary for denitrification in a sustained release manner. Furthermore, PBSA is more easily decomposed than other biodegradable resins, and is therefore preferable as a substrate or hydrogen donor for the growth and proliferation of denitrifying bacteria.

Resins such as polylactic acid and PHA may be mixed in the biodegradable resin base material. This is because a biodegradable resin base material can be used as a carbon source for a long period of time by mixing a biodegradable resin having a structural unit derived from a dicarboxylic acid and these resins having different biodegradability.
Moreover, the biodegradable resin base material may contain components other than the resin, such as calcium carbonate and calcium stearate. If the content of these components is 40% by mass or less relative to the biodegradable resin, the fine powder resulting from these components will fall off from the base material, increasing the surface area of the polymer and effectively performing denitrification. can be done.

The shape of the denitrification carrier is not particularly limited, and may be pellet-like, bulk-like (rectangular, spherical, three-dimensional network, etc.), flake-like, particulate, fibrous, or any other shape. Considering the ease of filling, it is preferably in the form of flakes, particles, fibers, or the like. In the case of particles, the short diameter and the long diameter are preferably 0.5 mm or more and 7 mm or less, respectively.

Further, when the denitrification carrier is a biodegradable resin base material, the biodegradable resin base material includes, for example, wires containing a thermoplastic resin that are bent and entangled and that the wires contact each other at a contact portion where the wires contact each other. It is possible to adopt a mode in which the three-dimensional net-like molded article is integrated by fusion bonding, and the wire rod contains a biodegradable resin. Such a three-dimensional network molded product can be obtained, for example, by the following method. That is, when a plurality of wires are extruded from a melted biodegradable resin (thermoplastic resin) such as PBSA through a die of an extruder, a bending force acts on the extruded wires to bend them into a loop shape. The looped wires are entwined and heat-sealed at the points where the wires come into contact with each other, so the wire is sandwiched between rolls and passed through a water bath to cool and solidify to a certain thickness. It is possible to obtain a three-dimensional network molded article in which the wires are randomly entangled.

The amount of denitrifying carrier placed in the denitrifying tank may be determined according to the denitrifying rate per 1 kg of denitrifying carrier and the amount of nitrogen discharged from aquatic organisms per day.

In this embodiment, the consumption of the denitrifying carrier accompanying the denitrifying treatment is suppressed as compared with the conventional technology, but the volume of the denitrifying carrier gradually decreases over the long term. For example, when the volume of the denitrifying carrier is approximately halved, the denitrifying performance can be maintained by replenishing the decreased volume.
When the denitrification carrier is fibrous, it loses its fibrous structure as the denitrification reaction progresses, and the denitrification carrier breaks into small pieces. In such a state, the denitrification performance can be maintained by replenishing with new fibers.

The denitrifying bacteria are not particularly limited, and can be appropriately selected from known bacteria having denitrifying ability, but heterotrophic bacteria such as facultative anaerobic heterotrophic bacteria are preferred.

The denitrifying carrier preferably further carries biodegradable resin-decomposing bacteria in addition to denitrifying bacteria. The biodegradable resin-degrading bacteria adhere to the biodegradable resin substrate and decompose the biodegradable resin. As a result, more carbon sources are supplied to the denitrifying bacteria than when the denitrifying carrier does not carry biodegradable resin-degrading bacteria, and the growth or activity of the denitrifying bacteria is promoted, resulting in denitrification speed and denitrification. This is because the amount can be improved. As the biodegradable resin-degrading bacteria, known bacteria capable of decomposing biodegradable resins can be appropriately used.

(Nitrification tank)
When the water treatment apparatus according to this embodiment is used for purifying water to be treated containing ammonia nitrogen, the water treatment apparatus preferably includes a nitrification tank 12 for converting ammonia into nitric acid. The nitrification tank 12 is preferably a tank containing a nitrification carrier in which nitrification bacteria that convert ammonia to nitric acid are supported. By converting ammonia into nitric acid, this nitric acid is reduced to nitrogen in the denitrification tank, so more nitrogen content can be removed from the water to be treated.

The nitrification carrier is not particularly limited, and includes, for example, base materials containing alkaline earth metals such as calcium, polyurethane sponges, and the like. Among these, base materials containing alkaline earth metals are preferred as nitrification carriers. In the nitrification tank, the pH of the water in the nitrification tank becomes low due to the nitric acid produced by the nitrifying bacteria. By using a base material containing an alkaline earth metal, the pH can be adjusted to promote the growth of the nitrifying bacteria. Because you can. Substrates containing alkaline earth metals include, for example, shells containing calcium, coral sand, and the like. Shells, coral sand, etc. may be placed in the purifying device as they are, may be placed after being roughly pulverized, or may be placed after being finely pulverized.

Nitrifying bacteria are not particularly limited, and can be appropriately selected and used from known bacteria having nitrifying ability.

FIG. 1(a) shows a mode in which the nitrification tank 12 and the denitrification tank 14 are arranged on one channel, but the nitrification tank and the denitrification tank are arranged on separate channels. may be In the embodiment in which the nitrification tank 12 and the denitrification tank 14 are arranged on one channel, the nitrification tank 12 is arranged in the middle of the transfer route of the water to be treated from the water reservoir 11 to the denitrification tank 14. is preferred.
In addition, although the nitrification tank 12 and the denitrification tank 14 are provided as separate tanks in FIG. 1(a), the nitrification tank and the denitrification tank may be the same tank. In this case, a nitrifying carrier carrying nitrifying bacteria and a denitrifying carrier carrying denitrifying bacteria are arranged in one tank, and the nitrifying carrier and the denitrifying carrier are separated by a fiber separator, filter paper, or the like. good too.

(Microorganism reduction processing unit)
The water treatment apparatus according to this embodiment has a microorganism reduction treatment unit 13 that reduces the number of aerobic heterotrophic bacteria in the water to be treated. The microorganism reduction treatment unit 13 is arranged in the middle of the transfer route of the water to be treated from the water reservoir 11 to the denitrification tank 14, and is a mechanism for supplying water containing few aerobic heterotrophic bacteria to the denitrification tank 14. be. By passing the water to be treated through the microorganism reduction treatment unit 13 before being supplied to the denitrification tank 14, the aerobic heterotrophic bacteria in the water to be treated are removed or inactivated, and the denitrifying bacteria are preferentially in the denitrification tank 14. denitrification support can be consumed as a carbon source. In addition, in the denitrification tank 14, it is possible to suppress inconveniences such as consumption of the denitrification carrier by aerobic heterotrophic bacteria other than the denitrifying bacteria and inhibition of the denitrification reaction. As a result, most of the denitrifying carrier is consumed by the denitrifying bacteria, so it is thought that the consumption of the denitrifying carrier is reduced and the denitrifying rate per unit weight of the denitrifying carrier is improved.

Here, in the present specification, an aerobic heterotrophic bacterium is a microorganism that grows and / or proliferates by consuming a carbon source, and acquires energy by using organic matter as an electron donor and oxygen as an electron acceptor. Microorganisms that Aerobic heterotrophic bacteria compete with denitrifying bacteria to oxidatively decompose the biodegradable resin, leading to inhibition of the denitrifying reaction and wasteful consumption of the biodegradable resin.
Further, reducing the number of aerobic heterotrophic bacteria in the water to be treated means that the number of aerobic heterotrophic bacteria in the water to be treated is more than before it is supplied to the microorganism reduction treatment part. means that it decreases over time.

The microorganism reduction treatment unit 13 is not particularly limited as long as the aerobic heterotrophic bacteria in the water to be treated can be removed or inactivated to suppress the number of aerobic heterotrophic bacteria entering the denitrification tank 14, and various aspects are possible. can be Specific microorganism reduction processing unit 13 includes a UV irradiation unit that irradiates the water to be treated with ultraviolet (UV) light; an ozone sterilization device that supplies gas containing ozone to the water to be treated; and a photocatalyst such as titanium oxide. reaction vessel; filtration bed for physically removing microorganisms; Of these, the microorganism reduction processing unit 13 is preferably a UV irradiation unit because it is low cost, has a high efficiency of inactivating microorganisms, and can even kill viruses.

UV-C (wavelength 100 to 280 nm), which is easily absorbed by the cell membranes and DNA of microorganisms, is suitable for the UV emitted by the UV irradiation unit. As the UV irradiation part, a low-pressure mercury UV lamp (such as a quartz discharge tube) that can irradiate UV with a wavelength of 254 nm, which is said to have particularly high sterilization power, is mainly used, but a longer-life LED lamp can also be used. good.

When a UV irradiation unit is used as the microorganism reduction processing unit 13, the amount of ultraviolet irradiation necessary for removing or inactivating aerobic heterotrophic bacteria depends on the type of aerobic heterotrophic bacteria in the water to be treated. It is preferably 1,000 to 100,000 μW·SEC/cm ² . Further, the ultraviolet irradiation intensity is a value obtained by dividing the above-mentioned ultraviolet irradiation amount by the hydraulic residence time of the sterilizer (the time for the water to be treated to pass through the UV irradiation space of the UV irradiation unit). For example, if the water to be treated has a hydraulic retention time of 1 second and an ultraviolet irradiation amount of 20,000 μW·SEC/cm ² is required, the ultraviolet irradiation intensity should be 20,000 μW/cm ² .

In FIG. 1(a), the microorganism reduction treatment unit 13 is arranged in the middle of the transfer route of the water to be treated from the nitrification tank 12 to the denitrification tank 14, but the microorganism reduction treatment unit 13 As long as the purpose of removing or inactivating the aerobic heterotrophic bacteria and suppressing the number of aerobic heterotrophic bacteria entering the denitrification tank can be achieved, the arrangement is not limited. That is, the microorganism reduction treatment unit 13 may be provided in the middle of the transfer route of the water to be treated from the water reservoir 11 to the denitrification tank 14 . Therefore, for example, as shown in FIG. The microorganism reduction treatment section 13 may be arranged in the middle of the transfer route of the water to be treated reaching the tank 12 (the arrow in FIG. 1(b) indicates the transfer direction of the water in the water treatment apparatus.) .

(Other configurations)
The water treatment apparatus according to this embodiment may have other configurations not shown in FIG. 1(a). Other mechanisms include transfer means, such as a pump and a siphon, for transferring the water to be treated so that it flows through the microorganism reduction treatment section and the denitrification tank in this order.
When the water treatment apparatus according to the present embodiment is applied to a circulation system breeding apparatus for aquatic organisms, other mechanisms include an air pump for increasing the oxygen concentration of the water returned to the breeding tank; An ultraviolet irradiator for killing bacteria, viruses, etc. in water; a heater and/or cooler for adjusting the temperature of the water to be treated; and the like.

<2. Water treatment method>
A second embodiment of the present invention includes a microorganism reduction step for reducing the number of aerobic heterotrophic bacteria in the water to be treated, and a denitrifying carrier carrying denitrifying bacteria in the water to be treated that has undergone the microorganism reduction step. and a denitrification step of supplying the water to a denitrification tank for denitrification. The water treatment method according to this embodiment can be carried out by using the water treatment apparatus according to the first embodiment.
The water treatment method according to the present embodiment may include a nitrification step in which water to be treated is supplied to a nitrification tank containing a nitrification carrier supporting nitrifying bacteria, and nitrification is performed. The step of performing the nitrification step is not particularly limited, but is preferably before the microorganism reduction step or between the microorganism reduction step and the denitrification step.

The water treatment apparatus according to the first embodiment of the present invention and the water treatment method according to the second embodiment of the present invention can be suitably used for purifying breeding water for aquatic organisms. Aquatic organisms to be bred may be organisms that live in water, and typical examples include freshwater fish such as salmon, trout, sweetfish, and char; crustaceans such as crabs and shrimp; By breeding aquatic organisms such as seafood while purifying breeding water according to the first and second embodiments of the present invention, daily growth rate (SGR) and feed efficiency (FE) can be improved.

As used herein, daily growth rate (SGR) is the extent of growth of an aquatic organism within a given breeding period and is calculated according to formula (I).
Daily growth rate (% body weight/day) =
(ln W ₁ −ln W ₂ )×100/rearing period (days) (I)
W ₁ : Weight of aquatic organism at the end of the breeding period W ₂ : Weight of the aquatic organism at the start of the breeding period

Further, as used herein, feed efficiency (FE) is the ratio of the weight gain of aquatic organisms to the amount of feed supplied during an arbitrary breeding period, and is calculated according to formula (II). A higher feed efficiency value means that the feed was efficiently consumed for the growth of aquatic organisms.
Feed efficiency (%) =
Body weight gain of aquatic organisms (g) / dry matter feeding amount or dry matter feeding amount (g) × 100 (II)

EXAMPLES The present invention will be described in more detail below with reference to examples, but it goes without saying that the scope of the present invention is not limited to the embodiments shown in the examples below.

<Example 1>
(Installation of rearing equipment)
A breeding apparatus 20 of closed circulation system shown in FIG. 2 was installed. In the breeding apparatus 20, the breeding water in the breeding tank 21 is passed through the circulation line to the filter tank 22, the nitrification tank 23, the UV irradiation unit 24, the denitrification tank 25, and the UV sterilizer 26 in sequence. It is cleaned and returned to the breeding tank 21 . Incidentally, when the breeding water was transferred to the denitrification tank 25, the breeding water was sprayed on the denitrification carrier in the denitrification tank by a shower and supplied to the denitrification tank.
Details of each part of the breeding apparatus 20 are as follows.

・Filtration tank 22
A water tank filled with glass wool was used as the filter tank 22 .

・ Breeding tank 21
A water tank with a capacity of 200 L was used as the breeding tank 21 .

・Nitrification tank 23
10 kg of sea urchin shells carrying nitrifying bacteria was used as a nitrification carrier. A nitrification tank 23 was prepared by filling this nitrification carrier into a water tank with a capacity of 200 L and acclimating sea urchin shells for two months using ammonia-containing rainbow trout breeding wastewater. Aerobic conditions were maintained in the nitrification tank 23 by performing ventilation at a rate of 250 mL/sec.

・Denitrification tank 25
A 300 g PBSA resin mat-like compact was used as a denitrification carrier. This denitrifying carrier was filled in a 20 L capacity water tank. The denitrification tank 25 is formed by carrying denitrification bacteria on the denitrification carrier by passing the water to be treated through this tank.

・UV irradiation unit 24 and UV sterilizer 26
As the UV irradiation unit 24 and the UV sterilization device 26, Iwaki Co., Ltd. UV sterilization lamp "Lacey UV sterilization lamp UVF-1000 type" (UV lamp: ozoneless quartz discharge tube (U-shaped tube), ultraviolet wavelength: 254 nm, ultraviolet irradiation intensity : 22,000 μW/cm ² ) was used.

(Raising rainbow trout)
Seventeen rainbow trout with an average body weight of 107.2 g were placed in the breeding tank 21 of the breeding apparatus 20 and kept at a water temperature of 14°C for 100 days. During this breeding period, the breeding water was circulated at a water flow rate of 8,640 L/day and passed through a water treatment device to purify the breeding water. During the breeding period, UV irradiation was constantly performed by the UV irradiation unit 24 and the UV sterilization device 26 . During the breeding period, the amount of feed per day (daily feeding rate) was 0.6 to 1.0% of the weight of the rainbow trout, and the total amount of feed during the breeding period was 2355 g.

<Comparative Example 1>
Rainbow trout were raised in a rearing apparatus in the same manner as in Example 1, except that the water treatment apparatus was not provided with a UV irradiation unit.

<Reference example 1>
Rainbow trout were raised in a rearing apparatus in the same manner as in Comparative Example 1, except that the denitrifying bacteria-carrying molded PBSA resin mat was not placed in the denitrifying tank.

<Evaluation of nitrate nitrogen and nitrite nitrogen>
In Example 1, Comparative Example 1, and Reference Example 1, the breeding water in the breeding tank was periodically sampled during the breeding period, and nitrate nitrogen and nitrite nitrogen in the breeding water were measured.
Specifically, in accordance with JIS K 0102 43.1.5, using Tosoh Corporation ion chromatography system "IC-2010" and Tosoh Corporation column "TSKgel SuperIC-Anion HS", ion chromatography method Nitrate nitrogen and nitrite nitrogen were measured by
Nitrite nitrogen was hardly detected throughout the breeding period. Table 1 shows the concentrations of nitrate nitrogen before and after the start of the test.

<Evaluation of biodegradable resin consumption and denitrification rate>
The biodegradable resin consumption and denitrification rate were determined according to the following formula. Table 1 shows the results.
(1) Nitrate nitrogen accumulation = (nitrate nitrogen concentration at the end of the breeding period - nitrate nitrogen concentration at the start of the breeding period) x total tank capacity (2) nitrate nitrogen treatment amount = nitrate nitrogen of Reference Example 1 Accumulation amount - Nitrate nitrogen accumulation amount in Example 1 or Comparative Example 1 (3) Consumption amount of biodegradable resin = Weight of biodegradable resin at the end of the breeding period - Biodegradable resin at the start of the breeding period Weight (4) 1 kg of biodegradable resin and denitrification rate per day = nitrate nitrogen treatment amount ÷ ((weight of biodegradable resin at start of breeding period + weight of biodegradable resin at end of breeding period) /2) ÷ test days

Here, the total tank capacity was 420 L (breeding tank capacity 200 L + nitrification tank capacity 200 L + denitrification tank capacity 20 L).
The weights of the biodegradable resin at the start and end of the breeding period are the weights of the denitrifying carrier at the start and end of the breeding period, respectively. The weight of the biodegradable resin at the end of the breeding period was measured after washing the denitrification carrier remaining at the end of the breeding period with tap water to remove the attached biofilm, etc., and drying at room temperature. .

<Evaluation of daily growth rate and feed efficiency of rainbow trout>
The weight of the rainbow trout was measured before and after the breeding period, and the daily growth rate (SGR) was calculated according to the above formula (I), and the feed efficiency (FE) was calculated according to the above formula (II). Table 1 shows the results.

A comparison between Example 1 and Reference Example 1 shows that in Example 1, nitrate nitrogen concentration was reduced due to denitrification, and the water quality after water treatment was suitable for rearing aquatic organisms. I understand that. Further, in Example 1, in which the UV irradiation unit is arranged in the middle of the breeding water transfer route from the breeding tank to the denitrification tank, the UV irradiation unit is arranged in the middle of the breeding water transfer route from the breeding tank to the denitrification tank. The consumption of the biodegradable resin due to denitrification was suppressed, and the denitrification rate per unit weight of the biodegradable resin was improved as compared with Comparative Example 1 in which the denitrification was not performed. Furthermore, in Example 1, since the amount of biodegradable resin consumed is small, it is possible to reduce the frequency with which the biodegradable resin needs to be replenished during water treatment, and work efficiency is high. This is because, in Example 1, before denitrification in the denitrification tank, the number of aerobic heterotrophic bacteria other than denitrifying bacteria in the breeding water was reduced by UV irradiation, and the number of aerobic heterotrophic bacteria other than denitrifying bacteria was reduced. It is believed that this is because the consumption of the biodegradable resin as a carbon source by bacteria could be suppressed.

Further, from Table 1, aquatic organisms are bred while purifying the breeding water using the water treatment apparatus of Example 1 in which the UV irradiation unit is arranged in the middle of the breeding water transfer route from the breeding tank to the denitrification tank. As a result, the daily growth rate and feed efficiency are improved as compared with the case of using the water treatment apparatus of Comparative Example 1 in which the UV irradiation unit is not arranged in the middle of the transfer route of the breeding water from the breeding tank to the denitrification tank. shown. This is due to factors other than the concentration of nitrate nitrogen, such as the fact that the microbial flora balance in each tank changed due to the installation of the UV irradiation unit in the middle of the transfer route of the breeding water from the breeding tank to the denitrification tank. guessed.

10 Water treatment device 11 Water reservoir 12 Nitrification tank 13 Microorganism reduction treatment unit 14 Denitrification tank 20 Breeding device 21 Breeding tank 22 Filtration tank 23 Nitrification tank 24 UV irradiation part 25 Denitrification tank 26 UV sterilizer

Claims (7)

a water reservoir containing water to be treated;
a denitrification tank containing a denitrification carrier carrying denitrifying bacteria;
a microorganism reduction treatment unit that reduces the number of aerobic heterotrophic bacteria in the water to be treated;
The water treatment apparatus, wherein the microorganism reduction treatment unit is arranged in the middle of the transfer route of the water to be treated from the water reservoir to the denitrification tank. 2. The water treatment apparatus according to claim 1, wherein the microorganism reduction treatment section is an ultraviolet irradiation section that applies ultraviolet rays to the water to be treated. The water treatment device according to claim 1 or 2, wherein the denitrification carrier contains a biodegradable resin. The water treatment device according to claim 3, wherein the biodegradable resin is a biodegradable polyester having structural units derived from dicarboxylic acid. The water treatment apparatus according to any one of claims 1 to 4, further comprising a nitrification tank containing a nitrification carrier carrying nitrifying bacteria. The water treatment apparatus according to any one of claims 1 to 5, wherein the water to be treated is breeding water for aquatic organisms. A microorganism reduction step for reducing the number of aerobic heterotrophic bacteria in the water to be treated;
A denitrification step in which the water to be treated that has undergone the microorganism reduction step is supplied to a denitrification tank containing a denitrification carrier carrying denitrifying bacteria for denitrification;
A water treatment method, comprising:

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