Electrolysis equipment for aquaculture, recirculating water treatment systems for aquaculture, and electrolysis methods for aquaculture.

Abstract

DEPCT69 The electrolysis subunit (13) is composed of at least one part of the electronic instrument. Electrolysis performs the electrolysis of the water used for cultivation in the area where the water for cultivation is stored. Retaining or flowing in that manner results in the formation of chloric acid compounds and the breakdown of ammonia. Ammonium ions in water for electrolysis subculture (13), including electrode subculture. (55) including the first electrode (55A) and the second electrode (55B) provided in the area and sub-area. Voltage Applications (51) are designed to apply voltage between electrodes. The voltage application subsection (51) switches between the first state of electrolytic operation. The sis in the area is performed by applying a voltage to the first electrode (55A) as the anode and the second electrode. The second electrode (55B) is the cathode and the second state of the application of voltage to the second electrode (55B). It is the anode and the first electrode (55A) is the cathode;

Description

Electrolysis device for aquatic organism cultivation, circulating water treatment system for aquatic organism cultivation, and electrolysis method for aquatic organism cultivation

[0001] The present disclosure relates to an electrolysis device for aquatic organism aquaculture, a circulating water treatment system for aquatic organism aquaculture, and an electrolysis method for aquatic organism aquaculture.

[0002] A closed-loop aquaculture system is known as an example of a system for cultivating aquatic organisms. In a closed-loop aquaculture system, leftover feed and excrement discharged by the organisms are decomposed and purified in a filtration tank, and the water is circulated. In typical closed-loop aquaculture systems, microorganisms are mainly used to decompose and purify nitrogen compounds in the breeding water. Patent Document 1 proposes this type of technology.

[0003] Patent No. 7345037

[0004] In the aquaculture management system disclosed in Patent Document 1, ammonia is generated in the aquarium due to the metabolic activity of aquatic organisms and the decomposition of organic matter such as leftover food, so the breeding water is circulated and passed through a filter tank for biological filtration, where the ammonia is decomposed and converted into less toxic nitrate. The filter tank contains nitrifying bacteria (microorganisms) that oxidize ammonia in oxygen-containing water and convert it into nitrite and then nitrate.

[0005] However, when a purification method using microorganisms, as in Patent Document 1, is adopted, there is a problem that the purification ability becomes dependent on the microorganisms. In response to this problem, the inventors of the present application envisioned a method for decomposing ammonia contained in salty breeding water, in which the salty breeding water is electrolyzed to produce sodium hypochlorite, and this sodium hypochlorite is then reacted with ammonia present in the breeding water to directly decompose it into nitrogen. This method allows ammonia to be decomposed with less reliance on microorganisms, and the generation of nitrite, nitrate, and the like can be reliably suppressed during the decomposition process.

[0006] However, this method has the problem that deposits caused by electrolysis tend to adhere to the surface of the electrodes during electrolysis. When deposits adhere to the surface of the electrodes in this way, the generation of sodium hypochlorite is suppressed and the rate of ammonia decomposition tends to decrease.

[0007] One of the objectives of the present disclosure is to provide a technology that can decompose ammonia in water using electrolysis when cultivating aquatic organisms, and that makes it easy to remove the deposits that form on the surface of the electrodes.

[0008] An electrolysis device for cultivating aquatic organisms, which is one aspect of the present disclosure, is an electrolysis device used in a circulating water treatment system that circulates and treats salty breeding water from a breeding tank, which is a tank for cultivating aquatic organisms, and that returns the treated breeding water to the breeding tank. The electrolysis device includes an electrolysis unit that, in an area where the breeding water is stored or flows, electrolyzes the breeding water to generate chlorate compounds, and reacts the generated chlorate compounds with ammonia or ammonium ions in the breeding water to decompose the ammonia or ammonium ions in the breeding water. The electrolysis unit includes an electrode unit having a first electrode and a second electrode disposed in the area, and a voltage application unit that applies a voltage between the first electrode and the second electrode. The voltage application unit is switchable between a first state in which the electrolysis is performed in the area by applying a voltage so that the first electrode is an anode and the second electrode is a cathode, and a second state in which a voltage is applied so that the second electrode is an anode and the first electrode is a cathode.

[0009] One circulating water treatment system for aquatic organism cultivation that is one aspect of the present disclosure is a circulating water treatment system for aquatic organism cultivation that is equipped with the above-mentioned electrolysis device for aquatic organism cultivation, and includes: a removal section that removes at least solids in a first area where the breeding water sent from the breeding tank is stored or flows; an electrolysis section that performs the electrolysis of the breeding water in a second area where the breeding water that has passed through the first area is stored or flows; and an activated carbon section that removes at least residual chlorine using activated carbon in a third area where the breeding water that has passed through the second area is stored or flows.

[0010] One aspect of the present disclosure is a circulating water treatment system for aquatic organism cultivation, which is a circulating water treatment system for aquatic organism cultivation equipped with the above-mentioned electrolysis device for aquatic organism cultivation, and comprises: an electrolysis tank configured to store or flow the breeding water; and a reaction tank configured to store or flow the breeding water discharged from the electrolysis tank, wherein the interior of the electrolysis tank is the area, and the electrolysis tank has a first guide path that does not guide water located below a first height within the electrolysis tank to the outside, but guides water located above the first height to the outside of the electrolysis tank, and the reaction tank has a second guide path that does not guide water located below a second height within the reaction tank to the outside of the reaction tank, but guides water located above the second height to the outside of the reaction tank.

[0011] An electrolysis method for cultivating aquatic organisms, one aspect of the present disclosure, is an electrolysis method used in a circulating water treatment system that circulates and treats breeding water from a breeding tank, which is a tank for cultivating aquatic organisms and contains salty breeding water, and returns the treated breeding water to the breeding tank. The method uses an electrolysis unit that includes an electrode unit having a first electrode and a second electrode, and a voltage application unit that applies a voltage between the first electrode and the second electrode, and with the first electrode and the second electrode arranged in a region where the breeding water is stored or flows, the voltage application unit applies a voltage between the electrodes to electrolyze the breeding water to generate a chlorite compound, and the generated chlorite compound is reacted with ammonia or ammonium ions in the breeding water to decompose the ammonia or ammonium ions in the breeding water. The voltage application unit switches between a first state in which the electrolysis is performed in the region by applying a voltage so that the first electrode is an anode and the second electrode is a cathode, and a second state in which a voltage is applied so that the second electrode is an anode and the first electrode is a cathode.

[0012] The technology disclosed herein can decompose ammonia or ammonium ions in water using electrolysis when cultivating aquatic organisms, and also makes it easy to remove deposits that form on the surface of the electrodes.

[0013] FIG. 1 is an explanatory diagram conceptually illustrating a circulating water treatment system of a first embodiment. FIG. 2 is a block diagram simply illustrating the electrical configuration of the circulating water treatment system of FIG. 1. FIG. 3 is an explanatory diagram simply illustrating the configuration of a removal unit, an electrolysis tank, etc. of the circulating water treatment system of FIG. 1. FIG. 4 is an explanatory diagram showing a more specific example of the configuration of FIG. 3. FIG. 5 is an explanatory diagram simply illustrating the configuration of an electrolysis tank, a reaction tank, etc. of the circulating water treatment system of FIG. 1. FIG. 6 is an explanatory diagram simply illustrating the configuration of the electrolysis tank of the circulating water treatment system of FIG. 1 viewed from a different direction than FIG. 5. FIG. 7 is an explanatory diagram showing specific examples of a residual chlorine removal tank, a standby tank, etc. of the circulating water treatment system of FIG. 1. FIG. 8 is an explanatory diagram simply illustrating the configuration of a removal unit, an electrolysis tank, etc. of a circulating water treatment system of a second embodiment. FIG. 9 is an explanatory diagram simply illustrating the configuration of an electrolysis tank, a reaction tank, etc. of a circulating water treatment system of a third embodiment. FIG. 10 is an explanatory diagram showing specific examples of the residual chlorine removal tank, the switching unit, the standby tank, etc. of the circulating water treatment system of the fourth embodiment.

[0014] Each of the following [1] to

[13] is an example of a characteristic technique included in this disclosure.

[0015] [1] An electrolysis device for use in a circulating water treatment system that is a tank for cultivating aquatic organisms and that treats breeding water containing salt from a breeding tank while circulating the breeding water and returns the treated breeding water to the breeding tank, the electrolysis device comprising: an electrolysis unit that, in an area where the breeding water is stored or flows, electrolyzes the breeding water to generate chlorate compounds, and reacts the generated chlorate compounds with ammonia or ammonium ions in the breeding water to decompose the ammonia or ammonium ions in the breeding water; the electrolysis unit has an electrode unit having a first electrode and a second electrode disposed in the area, and a voltage application unit that applies a voltage between the first electrode and the second electrode; and the voltage application unit switches between a first state in which the electrolysis is performed in the area by applying a voltage so that the first electrode is an anode and the second electrode is a cathode, and a second state in which a voltage is applied so that the second electrode is an anode and the first electrode is a cathode.

[0016] The electrolysis device described in [1] above electrolyzes salt-containing breeding water to produce a chlorate compound (e.g., sodium hypochlorite), which then reacts with ammonia or ammonium ions present in the breeding water to directly decompose it into nitrogen, reliably suppressing the generation of nitrite, nitric acid, and other compounds during the decomposition process. However, if this method is adopted without taking any measures, there is a concern that deposits will adhere to the electrode surfaces and hinder electrolysis. However, the electrolysis device described above can be switched between a first state in which electrolysis is performed by applying a voltage so that the first electrode is the anode and the second electrode is the cathode, and a second state in which a voltage is applied so that the second electrode is the anode and the first electrode is the cathode. Therefore, deposits that have adhered to the electrode surfaces due to continuous electrolysis can be easily detached from the electrodes by switching. Therefore, this electrolysis device easily removes deposits that have deposited on the electrode surfaces.

[0017] [2] The electrolysis device for cultivating aquatic organisms described in [1], wherein the electrode unit comprises an electrode holder that holds the first electrode and the second electrode, and the first electrode, the second electrode, and the electrode holder are integrally configured; the circulating water treatment system is provided with an electrolysis tank configured to store or flow the breeding water, the interior of the electrolysis tank is the region; and the integrally configured electrode unit is detachable from the electrolysis tank.

[0018] In the electrolysis device of [2] above, the electrode unit, which is an integral structure of the first electrode, the second electrode, and the electrode holder, is detachable from the electrolysis tank, making it easy to remove the electrode unit for cleaning. In particular, the promotion of precipitate removal by switching and the simplification of the work of attaching and detaching the electrode unit have a synergistic effect, making cleaning even easier.

[0019] [3] The electrolysis device for cultivating aquatic organisms according to [1] or [2], further comprising an electrolysis tank configured to store or allow the breeding water to flow, the interior of the electrolysis tank being the region, and further comprising a guide unit that guides and collects deposits that have sunk from the electrode units in the electrolysis tank toward a predetermined position in the electrolysis tank.

[0020] The electrolysis device of [3] above can automatically collect precipitates that have sunk from the electrode section toward a predetermined position using the induction section, so that not only can the precipitates be detached from the electrode section, but the detached precipitates can also be easily collected.

[0021] [4] An electrolysis device for cultivating aquatic organisms according to any one of [1] to [3], comprising an electrolysis tank configured to store or allow the breeding water to flow, the interior of the electrolysis tank being the region, and further comprising a discharge section having a tube for discharging precipitates that have sunk from the electrode section within the electrolysis tank, the discharge section taking in the precipitates into the tube at a position below the electrode section and discharging the precipitates from the electrolysis tank through the tube.

[0022] The electrolysis device of [4] above can take in and discharge the precipitate that has sunk from the electrode part into a tube at a position below the electrode part, thereby preventing the precipitate from dispersing during the discharge process and being easily carried to subsequent processes.

[0023] [5] An electrolysis device for cultivating aquatic organisms according to any one of [1] to [4], comprising an electrolysis tank configured to store or flow the breeding water, the interior of the electrolysis tank being the area, and the electrolysis tank having a guide path that does not guide water located below a predetermined height within the electrolysis tank to the outside of the electrolysis tank, but guides water located above the predetermined height to the outside of the electrolysis tank.

[0024] The electrolysis device of [5] above can guide the supernatant water located above a predetermined height to the outside, and can make it difficult for the precipitate that has sunk below the predetermined height to be guided outside the electrolysis tank.

[0025] [6] The electrolysis apparatus for cultivating aquatic organisms according to [5], wherein the predetermined height is above the lower end of the electrode unit.

[0026] In the electrolyzer of the above [6], the precipitate that separates from the electrode portion and sinks downward from the lower end is less likely to be guided to the outside of the electrolytic cell.

[0027] [7] An electrolysis device for cultivating aquatic organisms according to any one of [1] to [6], comprising an electrolysis tank configured to store or allow the breeding water to flow, the interior of the electrolysis tank being the region, the electrode unit being positioned on the surface side of the breeding water within the electrolysis tank, and further comprising a water flow generating unit that causes the breeding water introduced into the electrolysis tank from outside the electrolysis tank to flow upward from below the electrode unit within the electrolysis tank.

[0028] The electrolysis device of [7] above can generate a water flow in the electrolysis tank so that the water flows upward from the bottom of the electrode section, making it easier for new rearing water to be introduced to the electrode section, thereby further increasing the efficiency of electrolysis.

[0029] [8] The electrolysis device for cultivating aquatic organisms described in any one of [1] to [7], wherein the voltage application unit periodically switches between an operation of electrolyzing the rearing water by continuing the first state and an operation of electrolyzing the rearing water by continuing the second state.

[0030] The electrolysis device of [8] above can periodically remove deposits and periodically clean the electrodes.

[0031] [9] A circulating water treatment system for cultivating aquatic organisms, equipped with the electrolysis device for cultivating aquatic organisms described in any one of [1] to [8], comprising: a removal section that removes at least solids in a first area where the culture water sent from the culture tank is stored or flows; an electrolysis section that performs the electrolysis of the culture water in a second area where the culture water that has passed through the first area is stored or flows; and an activated carbon section that removes at least residual chlorine with activated carbon in a third area where the culture water that has passed through the second area is stored or flows.

[0032] The circulating water treatment system described in [9] above can remove solids contained in the breeding water in the first zone using a removal unit. Furthermore, in this circulating water treatment system, ammonia or ammonium ions can be decomposed in the second zone after the water has passed through the first zone using an electrolysis unit. The removal unit removes solids before electrolyzing the breeding water, reliably preventing solids from interfering with the electrolysis and facilitating successful electrolysis. Furthermore, in this circulating water treatment system, activated carbon can be used in the third zone where the breeding water that has passed through the second zone is stored or flows. Therefore, even if chlorate compounds not used in the decomposition of ammonia or ammonium ions are contained in the breeding water in the third zone, these chlorate compounds can be effectively removed by the activated carbon unit. Thus, the circulating water treatment system reliably reduces solids such as feces and leftover food in the breeding water after passing through the third zone, and reliably suppresses nitrogen compounds such as ammonia, ammonium ions, nitrite, and nitrate, providing significant advantages in terms of purifying and detoxifying the breeding water.

[0033]

[10] A circulating water treatment system for cultivating aquatic organisms equipped with the electrolysis device for cultivating aquatic organisms described in any one of [1] to [8], comprising: an electrolysis tank configured to store or flow the breeding water; and a reaction tank configured to store or flow the breeding water discharged from the electrolysis tank, wherein the interior of the electrolysis tank is the region, the electrolysis tank has a first guide path that does not guide water located below a first height in the electrolysis tank to the outside, and guides water located above the first height to the outside of the electrolysis tank, and the reaction tank has a second guide path that does not guide water located below a second height in the reaction tank to the outside of the reaction tank, and guides water located above the second height to the outside of the reaction tank.

[0034] In the circulating water treatment system of

[10] above, since the supernatant water located above the first height in the electrolysis tank can be guided to the outside of the electrolysis tank, even if a precipitate detaches from the electrodes and sinks, the precipitate is unlikely to be guided to the outside of the electrolysis tank. Even if some of the precipitate is discharged from the electrolysis tank and enters the reaction tank, the supernatant water located above the second height in the reaction tank can be guided to the outside of the reaction tank. Therefore, the precipitate that has entered the reaction tank is likely to settle in the reaction tank and is unlikely to be guided to the outside of the reaction tank.

[0035]

[11] An electrolysis method for aquatic organism cultivation used in a circulating water treatment system that treats salty breeding water while circulating it from a breeding tank that is a tank for cultivating aquatic organisms, and returns the treated breeding water to the breeding tank, comprising: an electrolysis unit including an electrode unit having a first electrode and a second electrode; and a voltage application unit that applies a voltage between the first electrode and the second electrode; the first electrode and the second electrode are disposed in a region where the breeding water is stored or flows; the voltage application unit applies a voltage between the electrodes to electrolyze the breeding water to generate a chlorite compound, and the generated chlorite compound is reacted with ammonia or ammonium ions in the breeding water to decompose the ammonia or ammonium ions in the breeding water; and the voltage application unit switches between a first state in which the electrolysis is performed in the region by applying a voltage so that the first electrode is an anode and the second electrode is a cathode, and a second state in which a voltage is applied so that the second electrode is an anode and the first electrode is a cathode.

[0036] The electrolysis method

[11] described above electrolyzes salty breeding water to produce a chlorate compound (e.g., sodium hypochlorite), which then reacts with ammonia or ammonium ions present in the breeding water to directly decompose into nitrogen, reliably suppressing the generation of nitrite, nitric acid, and other compounds during the decomposition process. However, when using this method, there is a concern that deposits will adhere to the electrode surfaces and hinder electrolysis unless special measures are taken. However, the electrolysis method described above can be switched between a first state in which electrolysis is performed by applying a voltage so that the first electrode is the anode and the second electrode is the cathode, and a second state in which a voltage is applied so that the second electrode is the anode and the first electrode is the cathode. Therefore, deposits that have adhered to the electrode surfaces due to continuous electrolysis can be easily removed by switching the state. Therefore, this electrolysis method makes it easy to remove deposits that have formed on the electrode surfaces.

[0037]

[12] The electrolysis method for cultivating aquatic organisms described in

[11] , which uses an electrolysis tank configured to store or flow the breeding water, arranges the electrode unit so that the interior of the electrolysis tank is the area, and performs the operation in the first state, the operation in the second state, and switching between the first state and the second state using the voltage application unit while continuously introducing the breeding water into the electrolysis tank and discharging the breeding water from the electrolysis tank and replacing the breeding water.

[0038] The electrolysis method of

[12] above allows the operation of the first state, the operation of the second state, and switching between the first state and the second state to be performed while continuously supplying and discharging rearing water to and from the electrolysis tank, thereby replacing the rearing water. This allows the electrodes to be purified while circulating the rearing water more efficiently.

[0039]

[13] The electrolysis method for cultivating aquatic organisms described in

[11] or

[12] , wherein the voltage application unit periodically switches between an operation of electrolyzing the rearing water by continuing the first state and an operation of electrolyzing the rearing water by continuing the second state.

[0040] The electrolysis method of

[13] above allows the deposits to be periodically removed, and the electrodes to be periodically cleaned.

[0041] First Embodiment 1. Overview of a Circulating Water Treatment System 1 Used for Cultivating Aquatic Organisms The circulating water treatment system 1 illustrated in Fig. 1 is a system used for cultivating aquatic organisms. The circulating water treatment system 1 is configured as a closed-circulation aquaculture system that treats the breeding water in a breeding tank 3 containing salt-containing breeding water outside the breeding tank 3 and then circulates the treated breeding water back to the breeding tank 3, thereby circulating water. When cultivating aquatic organisms in the breeding tank 3, the circulating water treatment system 1 operates to continuously raise the aquatic organisms in the breeding tank 3 and to decompose and purify residual food remaining in the breeding water during breeding in the breeding tank 3 and feces and urine discharged by the organisms during breeding in the breeding tank 3 in a process of circulating the water from the breeding tank 3 and returning it to the breeding tank 3.

[0042] As shown in Figure 1, the circulating water treatment system 1 mainly includes a breeding tank 3, a removal section 5, an electrolysis tank 11, a reaction tank 15, a filtration tank 17, an activated carbon tank 21, a standby tank (water quality adjustment tank) 25, and a treatment section 31. The circulating water treatment system 1 also includes a temperature controller 35, a filter 37, and the like. The electrical configuration of the circulating water treatment system 1 is, for example, as shown in Figure 2. Various types of aquatic organisms can be raised in the breeding tank 3, and suitable examples include fish, crustaceans, and shellfish, although other types (e.g., squid, octopus, etc.) may also be used.

[0043] 2. Configuration and Operation of Each Part (Breeding Tank) The breeding tank 3 shown in FIG. 1 is a tank for breeding and cultivating aquatic organisms. Salty breeding water, such as artificial seawater or natural seawater, is contained within the breeding tank 3, and aquatic organisms, such as fish and shellfish, are raised in this breeding water. The "salty breeding water" contained in the breeding tank 3 is preferably a liquid with an NaCl content of 0.5% by mass or more. In the example shown in FIG. 1 , multiple (e.g., four) breeding tanks 3 are provided, and the breeding water in these breeding tanks 3 is guided to a filter 37, filtered by the filter 37, and internally circulated so that it is distributed from the filter 37 to the multiple breeding tanks 3. The temperature of the breeding water in the breeding tanks 3 is adjusted to a desired set temperature by a temperature regulator 35. Although multiple breeding tanks 3 are used in the example shown in FIG. 1 , a single aquarium may be used.

[0044] (Removal Unit) The removal unit 5 shown in Fig. 1 functions to remove at least solid matter in a first region where the breeding water sent from the breeding tank 3 is stored or flows. The breeding water from the breeding tank 3 is guided to the removal unit 5 through a flow path 41. As shown in Fig. 3, the removal unit 5 includes an ozone generator 9, a foam separator 7, a storage tank 60, an inlet 62, an outlet 64, and a discharge unit 66. In Fig. 3 and other figures, the symbol W conceptually indicates a portion of the circulating breeding water.

[0045] The storage tank 60 is a tank that stores the rearing water introduced from an area upstream of the removal unit 5. In the example of Fig. 1, the area upstream of the removal unit 5 is an area inside the rearing tank 3. The rearing water may be caused to flow from the rearing tank 3 to the storage tank 60 by using a pump or by utilizing a difference in elevation.

[0046] The ozone generator 9 corresponds to an example of an ozone generating unit, and generates ozone, for example, by a known method, and supplies the generated ozone to the foam separator 7. The method for introducing ozone from the ozone generator 9 into the foam separator 7 is not particularly limited, and examples include a method in which ozone generated by the ozone generator 9 is supplied through an inlet for introducing air provided in the foam generating unit of a known foam separator. The foam separator 7 generates foam containing the ozone generated by the ozone generator 9, and operates to adsorb solids contained in the rearing water in a first region where the rearing water sent from the rearing tank 3 is stored or flows, into the foam. In the example of FIG. 3 , the first region is the interior region of the storage tank 60.

[0047] The inlet section 62 is a flow path that introduces the rearing water stored in the storage tank 60 into the foam separator 7. The outlet section 64 is a flow path that returns the rearing water that has passed through the foam separator 7 from the foam separator 7 to the storage tank 60. The discharge section 66 has a flow path that discharges the rearing water stored in the storage tank 60 to a region subsequent to the removal section 5. In the examples of Figures 1 and 3, the region subsequent to the removal section 5 is a region within the electrolysis tank 11.

[0048] In the removal section 5, solid matter such as feces and leftover feed, removed proteins from fish and shellfish metabolism, bacteria, viruses, parasites, etc. contained in the rearing water introduced into the foam separator 7 are removed from the rearing water by adhering them to fine bubbles generated within the foam separator 7. Moreover, the bubbles generated within the foam separator 7 contain ozone, and therefore have a high bactericidal effect, and this bactericidal effect also acts on the rearing water that passes through the foam separator 7 and returns to the outlet section 64. This operation reliably prevents contaminants from flowing into the electrolysis tank 11 in the subsequent process and reliably prevents the contaminants from interfering with the electrolysis in the electrolysis tank 11.

[0049] In the example of Figure 3, the flow path 41 is connected to the storage tank 60 near the bottom 60A, and the rearing water from the flow path 41 is supplied into the storage tank 60 from a position near the bottom end of the side of the storage tank 60. The inlet (the entrance for taking in rearing water) of the introduction unit 62 is located near the bottom 60A in the storage tank 60, making it easy to take in the rearing water immediately after it is introduced into the storage tank 60 from the flow path 41. Meanwhile, the rearing water that has passed through the foam separator 7 is discharged by the discharge unit 64 to a position closer to the discharge unit 66 than the flow path 41. The discharge outlet (the outlet for discharging rearing water) of the discharge unit 64 is located closer to the water surface W1 than the bottom 60A of the storage tank 60. The discharge unit 66 is configured as a flow path that flows the rearing water in the storage tank 60 toward the outside of the storage tank 60. The discharge unit 66 is configured not to guide water located below a predetermined first level in the storage tank 60 to the outside of the storage tank 60, but to guide water located above the first level to the outside of the storage tank 60. The first level is the height of the lower end of the boundary between the storage tank 60 and the inner wall surface of the flow path of the discharge unit 66, and when the water level of the breeding water in the storage tank 60 is higher than this first level, the water in the area higher than the first level is discharged from the discharge unit 66.

[0050] More specifically, the removal unit 5 shown in FIG. 3 can be configured as shown in FIG. 4 . In the specific example of FIG. 4 , a foam separator 7 is provided with a foam generation unit 8 and a foam separation tank 7A. Furthermore, an inlet (water intake) of an introduction unit 62 configured as a pipe is located near the bottom of the storage tank 60 and close to the flow path 45 in the storage tank 60, and a filter 61 is provided to cover this inlet. Of the rearing water stored in the storage tank 60, the rearing water that can pass through the filter 61 is introduced into the foam separator 7 from the introduction unit 62. The filter 61 is configured to block the passage of large particles and allow the passage of small particles, and is configured, for example, in a mesh shape. Although not shown in FIG. 4 , a pump may be provided to move the rearing water through the introduction unit 62 and into the foam separator 7.

[0051] In the configuration shown in Figure 4, the foam generator 8 injects ozone-containing gas generated by an ozone generator 9 into the breeding water flowing in from the inlet 62, causing bubbles of ozone-containing gas to be contained in the breeding water passing through the foam generator 8. The breeding water that has passed through the foam generator 8 flows into the foam separation tank 7A via the inlet 63, which is configured as a pipe, as breeding water containing ozone-containing bubbles. In the foam separation tank 7A, bubbles with attached solids are separated so that they collect near the water surface, and the collected bubbles are discharged to the outside of the foam separation tank 7A through the discharge path 65. Meanwhile, the breeding water at the bottom of the foam separation tank 7A is discharged near the water surface of the storage tank 60 via the outlet 64, which is configured as a pipe. The outlet (discharge port) of the outlet 64 is positioned so that a vortex is generated in a certain direction in the breeding water stored in the storage tank 60. The discharge section 66, which is configured as a discharge flow path, is arranged near the water surface of the storage tank 60, and the supernatant of the breeding water stored in the storage tank 60 is discharged from the discharge section 66.

[0052] (Electrolysis Tank) The electrolysis tank 11 shown in FIG. 5 is a tank for performing electrolysis and is a tank in which the rearing water that has passed through the removal unit 5 is stored or flows. The internal region of the electrolysis tank 11 is a region in which the rearing water that has passed through the first region (the region within the storage tank 60 in the example of FIG. 3 ) is stored or flows, and corresponds to an example of the second region. The electrolysis tank 11 is provided with an electrolysis unit 13. The electrolysis unit 13 electrolyzes the rearing water in the second region to generate a chlorate compound (e.g., sodium hypochlorite), and the generated chlorate compound reacts with ammonia or ammonium ions in the rearing water to decompose the ammonia or ammonium ions. Furthermore, since the chlorate compound is generated by the electrolysis unit 13 in the electrolysis tank 11, the rearing water can be sterilized, deodorized, and decolorized.

[0053] In the electrolysis tank 11, electrolysis is carried out as shown in the following formula (1): 2NaCl + 3H ２ O→NaClO+NaCl+2H ２ O+H ２ ↑・・・(1)

[0054] Then, the decomposition of ammonia or the decomposition of ammonium ions occurs through the chemical reactions shown in the following formulas (2) and (3): ３ + 3NaClO → N ２ ↑+3NaCl+3H ２ O...(2) 2NH ４ ＋ + 3NaClO → N ２ ↑+3H ２ O+3NaCl+2H ＋ ...(3)

[0055] 5, the internal region of the electrolytic cell 11 is the "region" where the electrode unit 55 is disposed and where electrolysis takes place. The electrolytic cell 11 is provided with an electrolysis unit 13. The electrolysis unit 13 has an electrode unit 55 having a first electrode 55A and a second electrode 55B disposed in the "region" (second region), and a voltage application unit 51 that applies a voltage between the first electrode 55A and the second electrode 55B.

[0056] The voltage application unit 51 includes a control device 52 and a drive circuit 53. The control device 52 is an information processing device having an information processing unit, a storage unit, a communication unit, etc., and is capable of performing various controls and various calculations. The drive circuit 53 is a circuit that applies a voltage between the first electrode 55A and the second electrode 55B in response to a command from the control device 52.

[0057] The electrode unit 55 includes an electrode holder 55C that holds a first electrode 55A and a second electrode 55B. The first electrode 55A, the second electrode 55B, and the electrode holder 55C are integrally configured. The integrally configured electrode unit 55 is detachably attached to the electrolytic cell 11. The configuration for detachably attaching the electrode unit 55 to the electrolytic cell 11 is not particularly limited. For example, the electrode holder 55C may be placed on a mounting base provided on the electrolytic cell 11 when the electrode unit 55 is attached, and the electrode holder 55C may be detached from the mounting base when the electrode unit 55 is removed. In the example shown in FIG. 5 , a plurality of first electrodes 55A and a plurality of second electrodes 55B are provided, and both the plurality of first electrodes 55A and the plurality of second electrodes 55B are formed into plate shapes using a metal material. In the electrode unit 55, the first electrodes 55A and the second electrodes 55B are alternately arranged at intervals. The plurality of first electrodes 55A are short-circuited to each other and are electrically connected to a first terminal of the drive circuit 53 via a conductive path 54A. The plurality of second electrodes 55B are short-circuited to each other and are electrically connected to a second terminal of the drive circuit 53 via a conductive path 54B. In the example of Fig. 5, the first electrodes 55A and the second electrodes 55B are alternately arranged at intervals.

[0058] The electrodes used in the electrolytic cell 11 are preferably made of a metal material that is resistant to corrosion by seawater and has a high efficiency in generating chloric acid compounds. For example, an electrode in which the surface of titanium is coated with a platinum-iridium alloy can be suitably used. Platinum has excellent conductivity and corrosion resistance, iridium has excellent durability and chemical stability, and the platinum-iridium alloy has a uniform and smooth surface. An electrode in which the surface of titanium is coated with a platinum-iridium alloy can be used as both an anode and a cathode. Note that the electrode example described here is merely an example. If the electrode reversal method described below is not used, an electrode in which titanium is coated with ruthenium or the like may be used as the anode, or other materials may be used.

[0059] A part or all of the electrode unit 55 is disposed on the water surface W2 side of the rearing water in the electrolysis tank 11, with the rearing water being interposed between the first electrode 55A and the second electrode 55B. Meanwhile, the electrolysis tank 11 is provided with a water flow generator 57, which generates a water flow from the lower side of the electrode unit 55 toward the upper side (electrode unit side).

[0060] The water current generating unit 57 is configured to cause rearing water introduced into the electrolytic cell 11 from outside the electrolytic cell 11 through the flow path 42 to flow upward from below the electrode unit 55 within the electrolytic cell 11. The flow path 42 is a flow path that allows rearing water discharged through the discharge unit 66 to flow into the electrolytic cell 11. The flow path 42 may be formed by the discharge unit 66 or may be formed as a flow path continuing to the discharge unit 66. The water current generating unit 57 has a first partition wall 57A. The first partition wall 57A is a wall that separates the electrolytic cell 11 into a predetermined upstream region and a predetermined downstream region. The downstream region is downstream of the first partition wall 57A and is the region where the electrode unit 55 is provided. The upstream region is upstream of the first partition wall 57A and upstream of the downstream region.

[0061] In the example shown in Fig. 5, the upstream region is the internal region of the first breeding water flow chamber 11A, which is defined by the first partition wall 57A and the outer peripheral wall and bottom wall 11Z of the electrolytic cell 11 upstream of the first partition wall 57A, and is the region into which the breeding water flows from the flow path 42. An opening is provided on the bottom wall side of the first breeding water flow chamber 11A to allow the breeding water in the first breeding water flow chamber 11A to move to the second breeding water flow chamber. In the example shown in Fig. 5, this opening is defined by the lower end of the first partition wall 57A and the outer peripheral wall and bottom wall 11Z of the electrolytic cell 11.

[0062] The downstream region is the internal region of the second rearing water flow chamber 11B, which is defined by the first partition wall 57A, the second partition wall 57B, and the portion of the outer wall and bottom wall 11Z of the electrolytic cell 11 between the first and second partition walls 57A and 57B. This region is where part or all of the electrode unit 55 is located. The height of the upper end of the second partition wall 57B in the second rearing water flow chamber 11B is lower than the height of the upper end of the outer wall of the electrolytic cell 11. If water enters the second rearing water flow chamber 11B beyond the upper end of the second partition wall 57B, the water will flow over the second partition wall 57B to the downstream side of the second rearing water flow chamber 11B. This configuration allows rearing water to be introduced into the second rearing water flow chamber 11B through the opening on the lower side and then discharged over the upper end of the second partition wall 57B. This generates a water flow that rises from below the electrode unit 55 toward the electrode unit 55.

[0063] 5, the second partition wall 57B is provided, but the second partition wall 57B does not have to be provided. In this case, the entire downstream side of the first partition wall 57A in the electrolytic cell 11 is the downstream region, and the first partition wall 57A and the portions of the outer peripheral wall and bottom wall 11Z of the electrolytic cell 11 downstream of the first partition wall 57A form the second breeding water flow chamber 11B.

[0064] As shown in Figure 6, the electrolytic cell 11 is provided with a guide section 58. The guide section 58 functions to guide and collect precipitates that have sunk from the electrode section 55 within the electrolytic cell 11 toward a predetermined position within the electrolytic cell 11. In the examples shown in Figures 5 and 6, the predetermined position is located above a portion of the bottom wall 11Z. In the examples shown in Figures 5 and 6, a third breeding water flow chamber 11C is formed downstream of the second breeding water flow chamber 11B by the second partition wall 57B, the outer wall of the electrolytic cell 11, and a portion of the bottom wall 11Z downstream of the second partition wall 57B, and the predetermined position is located above a portion of the bottom wall 11Z in the third breeding water flow chamber 11C. The guide section 58 includes an inclined section 58A having an inclined surface that is inclined vertically. The inclined surfaces of the inclined portions 58A and 58B constitute the inner wall surfaces of the third rearing water flow chamber 11C, and when a sinking object (e.g., precipitate) reaches the inclined surface of the inclined portion 58A within the third rearing water flow chamber 11C, the object is guided by the inclined surface as it sinks further, and is guided to the vicinity of the predetermined position on the bottom wall 11Z. The inclined surfaces of the inclined portions 58A and 58B guide the object sinking along these inclined surfaces in a predetermined first direction perpendicular to the up-down direction (specifically, toward the discharge portion 59 in the first direction).

[0065] As shown in Figures 5 and 6, the electrolytic cell 11 is provided with discharge units 59. In the example shown in Figure 5, discharge units 59 are provided in two locations. However, this is not limiting, and the number of discharge units 59 may be one or three or more. Discharge unit 59 has a tube 59A for discharging precipitate that has sunk from the electrode unit 55 in the electrolytic cell 11, and an opening / closing unit 59B for opening and closing this tube 59A. Discharge unit 59 functions to take the precipitate into tube 59A at a position below the electrode unit 55 and to discharge the precipitate from the electrolytic cell 11 through tube 59A.

[0066] In the examples shown in Figures 5 and 6, the opening / closing unit 59B is, for example, a valve that is manually operated to switch between a closed state and an open state of the tube 59A. The opening / closing unit 59B may also be a solenoid valve that can be controlled to open or close. In either case, when the opening / closing unit 59B is in the open state, the breeding water is discharged through the tube 59A from near the predetermined position in the electrolytic cell 11. If a precipitate settles near the predetermined position, the precipitate is discharged together with the breeding water through the tube 59A. In the examples shown in Figures 5 and 6, the tube 59A is a fixed tube permanently installed in the electrolytic cell 11, but it may also be a tube that can be attached and detached from the electrolytic cell 11. When the water is discharged from near the predetermined position through the tube, the water may be discharged by utilizing the water pressure within the electrolytic cell 11, or by suction or flow using a pump or the like.

[0067] As shown in Figures 5 and 6, the electrolytic cell 11 is provided with a first guide path 56. The first guide path 56 is an example of a guide path. The first guide path 56 functions as a flow path to guide water located above the first level to the outside of the electrolytic cell 11, while not guiding water located below the first level to the outside of the electrolytic cell 11. The first level is an example of a predetermined level. In the example of Figure 5, the water level W2 of the breeding water in the electrolytic cell 11 is higher than the lower end of the inner wall of the flow path at the entrance of the first guide path 56 (the boundary with the first guide path 56, which is the exit of the electrolytic cell 11). This allows water near the water level in the electrolytic cell 11 to exceed the bottom of the first guide path 56 and flow into the first guide path 56. In the example of Figure 5, the height of the lower end of the inner wall of the flow path at the entrance of the first guide path 56 is the first level (predetermined level), and this first level (predetermined level) is higher than the lower end of the electrode unit 55. The height of the lower end of the electrode unit 55 is the height of the lowest position among the plurality of first electrodes 55 A and the plurality of second electrodes 55 B. The first guide path 56 functions to flow the rearing water in the electrolysis tank 11 toward the reaction tank 15.

[0068] (Reaction Tank) The reaction tank 15 stores rearing water supplied from the electrolysis tank 11 through the flow path 43, ensuring time for the ammonia or ammonium ions contained in the stored rearing water to react with the chlorate compounds (e.g., sodium hypochlorite) produced in the electrolysis tank 11, thereby promoting their chemical reaction. The flow path 43 may be formed by the first guide path 56, or may be formed as a flow path continuing to the first guide path 56. If all of the ammonia or ammonium ions present in the rearing water in the electrolysis tank 11 do not completely react with the chlorate compounds and flow out of the electrolysis tank 11, and if the chlorate compounds produced in the electrolysis tank 11 do not completely react and flow out of the electrolysis tank 11, then either or both of the chemical reactions represented by the above formulas (2) and (3) occur in the reaction tank 15, resulting in the decomposition of the ammonia or ammonium ions.

[0069] As shown in FIG. 5 , a second guide path 72 is provided in the reaction tank 15. The second guide path 72 functions as a flow path to guide water located above the second level in the reaction tank 15, while not guiding water located below the second level out of the reaction tank 15. In the example of FIG. 5 , the water level W3 of the breeding water in the reaction tank 15 is located above the lower end of the inner wall of the flow path at the entrance of the second guide path 72 (the boundary with the second guide path 72, which is the exit of the reaction tank 15). This allows water near the water surface in the reaction tank 15 to exceed the bottom of the second guide path 72 and flow into the second guide path 72. In the example of FIG. 5 , the height of the lower end of the inner wall of the flow path at the entrance of the second guide path 72 is the second height. The second guide path 72 functions to direct the breeding water in the reaction tank 15 toward a downstream process in the reaction tank 15.

[0070] A filtration tank 17, which constitutes a detection region for detecting residual chlorine, is provided downstream of the reaction tank 15. The filtration tank 17 is configured to store rearing water supplied from the reaction tank 15 through a flow path 44 and direct the rearing water to a flow path 45. The flow path 44 is a flow path through which rearing water discharged through a second guide path 72 flows into the filtration tank 17. The flow path 44 may be formed by the second guide path 72 or may be configured as a flow path continuing to the second guide path 72. In the example of FIG. 1 , the flow path that directs rearing water from the reaction tank 15 to the activated carbon tank 21 is formed by the flow path 44, the filtration tank 17, and the flow path 45. However, other configurations (e.g., a configuration in which a pipe continues from the reaction tank 15 to the activated carbon tank 21 without providing the filtration tank 17) may be used as long as the rearing water flows from the reaction tank 15 to the activated carbon tank 21.

[0071] The first residual chlorine sensor 19 detects the concentration of residual chlorine in the rearing water after it passes through the electrolysis tank 11 and before it flows into the residual chlorine removal tank (specifically, the activated carbon tank 21). For example, it detects the concentration of residual chlorine in the rearing water in the region where the rearing water flows from the reaction tank 15 to the activated carbon tank 21. In the representative example shown in FIG. 1 , the first residual chlorine sensor 19 detects the residual chlorine in the rearing water in the filtration tank 17. In this specification, residual chlorine refers to the combined chlorine and free chlorine remaining in the rearing water. The total amount of chlorine, which is the sum of the amounts of combined chlorine and free chlorine contained in the rearing water, is the residual chlorine amount. By detecting the residual chlorine in the rearing water in the region between the reaction tank 15 and the activated carbon tank 21, the first residual chlorine sensor 19 can measure the amount of chlorine compounds remaining after the decomposition of ammonia or ammonium ions in the electrolysis tank 11 and the reaction tank 15.

[0072] (Residual Chlorine Removal Tank) In the example of FIG. 5 , an activated carbon tank 21 is provided as an example of a residual chlorine removal tank. The residual chlorine removal tank removes at least residual chlorine from the breeding water. The function of the residual chlorine removal tank is to remove residual chlorine from the breeding water by passing the breeding water through a residual chlorine removal unit. The activated carbon tank 21 illustrated in FIG. 5 is a tank that stores the breeding water that has passed through the reaction tank 15. Specifically, the activated carbon tank 21 is a tank located downstream of the detection area (in the example of FIG. 1 , the area within the filtration tank 17) where the first residual chlorine sensor 19 is located. The activated carbon tank 21 functions to remove chlorine acid compounds (e.g., sodium hypochlorite) generated in the electrolysis tank 11. The activated carbon tank 21 is provided with an activated carbon unit 23 equipped with activated carbon, which corresponds to an example of a residual chlorine removal unit. The activated carbon unit 23 removes at least residual chlorine and residual ozone from the breeding water in the activated carbon tank 21 using activated carbon. In the example of FIG. 1, the internal region of the activated carbon tank 21 corresponds to an example of the third region, which is a region where the rearing water that has passed through the second region is stored or flows.

[0073] In the activated carbon tank 21, for example, the reaction shown in the following formula (4) occurs, and excess chloric acid compounds that have not been used in the decomposition of ammonia or ammonium ions can be removed: HClO + C → CO + H ＋ +Cl － ...(4)

[0074] The activated carbon tank 21 illustrated in Fig. 5 can be configured, for example, as shown in Fig. 7. In the example of Fig. 7, the activated carbon tank 21 is configured as a flow path for the rearing water, and the internal space of the flow path is filled with activated carbon granules to form an activated carbon section 23. The activated carbon tank 21 is configured so that the rearing water flows through gaps within the activated carbon section 23 (specifically, the gaps in the internal space filled with activated carbon granules). As the rearing water flowing in through the inlet 21A of the activated carbon tank 21 passes through the gaps between the numerous granules in the activated carbon tank 21, residual chlorine and ozone contained in the rearing water are adsorbed by the activated carbon, and the rearing water discharged from the outlet 21B is rearing water from which some or all of the chlorine and ozone have been removed.

[0075] (Standby Tank) The breeding water introduced into the activated carbon tank 21 from the flow path 45 passes through the internal region of the activated carbon tank 21, is discharged into the flow path 46, and flows through the flow path 46 into the breeding tank 25. The standby tank 25 is a tank in which the breeding water that has passed through the activated carbon tank 21 is stored and whose quality is inspected before it is returned to the breeding tank 3. The internal region of the standby tank 25 corresponds to an example of the fourth region, and is a region in which the breeding water that has passed through the third region described above is stored or flows before it is returned to the breeding tank 3.

[0076] The second residual chlorine sensor 27 is a sensor that detects the concentration of residual chlorine contained in the breeding water in the fourth zone where the breeding water that has passed through the third zone is stored or flows before returning to the breeding tank 3. In the example of Fig. 1, the second residual chlorine sensor 27 detects the concentration of residual chlorine contained in the breeding water in the standby tank 25. When residual chlorine leaks out due to deterioration of the activated carbon provided in the activated carbon section 23, the second residual chlorine sensor 27 can more accurately detect fluctuations in the concentration of residual chlorine caused by such leakage.

[0077] The ammonium ion sensor 29 is a sensor that detects the concentration of ammonium ions contained in the breeding water in the fourth zone where the breeding water that has passed through the third zone described above is stored or flows before returning to the breeding tank 3. In the example of Figure 1, the sensor detects the concentration of ammonium ions contained in the breeding water in the standby tank 25. When ammonium ions do not completely react in the electrolysis tank 11 or the reaction tank 15 and remain, the ammonium ion sensor 29 can more accurately detect fluctuations in the concentration of these ammonium ions.

[0078] The pH sensor 28 is a sensor that measures the pH (hydrogen ion exponent) of the breeding water in the fourth region where the breeding water that has passed through the third region is stored or flows before returning to the breeding tank 3. In the example of Figure 1, the pH sensor 28 measures the pH of the breeding water in the standby tank 25 and provides the control device 52 with a value specifying the pH of the breeding water in the standby tank 25.

[0079] In the standby tank 25, an aeration device (not shown) performs aeration to remove CO2 from the breeding water. The breeding water in the standby tank 25 then flows into the breeding tank 3 through the flow path 47. The operation of flowing the breeding water from the standby tank 25 to the breeding tank 3 through the flow path 47 can be switched between a state in which the breeding water continuously flows from the standby tank 25 to the breeding tank 3, and a state in which the flow of the breeding water from the standby tank 25 to the breeding tank 3 is stopped or blocked.

[0080] 3. Control of the Circulating Water Treatment System 1 (Configuration for Control) In the circulating water treatment system 1, the breeding water in the breeding tank 3 is circulated through the removal unit 5, electrolysis tank 11, reaction tank 15, filtration tank 17, activated carbon tank 21, and standby tank 25 in this order. Pumps (not shown) for moving the breeding water are provided at multiple locations along the circulation path that circulates the breeding water from the breeding tank 3 and returns it to the breeding tank 3. The control device 52 shown in Figure 2 controls the activation and stopping of the pumps. Furthermore, the control device 52 controls the activation and stopping of the temperature regulator 35, the activation and stopping of the ozone generator 9, the activation and stopping of the foam separator 7, the activation and stopping of the electrolysis unit 13, the operation of the treatment unit 31, etc.

[0081] The control device 52 shown in FIG. 2 receives the detection values ​​of the first residual chlorine sensor 19, the second residual chlorine sensor 27, the pH sensor 28, and the ammonium ion sensor 29. The detection value input from the first residual chlorine sensor 19 indicates the concentration of residual chlorine contained in the breeding water in the aforementioned detection region (specifically, in the filtration tank 17). The detection value input from the second residual chlorine sensor 27 indicates the concentration of residual chlorine contained in the breeding water in the aforementioned fourth region (specifically, in the standby tank 25). The detection value input from the pH sensor 28 indicates the pH (hydrogen ion exponent) of the breeding water in the aforementioned fourth region (specifically, in the standby tank 25). The detection value input from the ammonium ion sensor 29 indicates the concentration of ammonium ions contained in the breeding water in the aforementioned fourth region (specifically, in the standby tank 25).

[0082] (Control of Electrolysis) The control device 52 corresponds to an example of a control unit and controls the electrolysis of the electrolysis unit 13. The control device 52 may control the electrolysis of the electrolysis unit 13 based on the measurement results of the ammonium ion sensor 29 and the first residual chlorine sensor 19, or may control the electrolysis of the electrolysis unit 13 based on the measurement results of the ammonium ion sensor 29, or may control the electrolysis of the electrolysis unit 13 based on the measurement results of the first residual chlorine sensor 19. When controlling the electrolysis of the electrolysis unit 13 based on the measurement results of the ammonium ion sensor 29, the control device 52 may, for example, feedback-control the current flowing between the first electrode 55A and the second electrode 55B so that the detection value of the ammonium ion sensor 29 is equal to or less than a predetermined value. When controlling the electrolysis of the electrolysis unit 13 based on the measurement results of the first residual chlorine sensor 19, the control device 52 may, for example, feedback-control the current flowing between the first electrode 55A and the second electrode 55B so that the detection value of the first residual chlorine sensor 19 is within a predetermined range.

[0083] The ammonia concentration and available chlorine concentration in the rearing water (e.g., seawater) used in this embodiment can be determined based on the discontinuous chlorination method. For example, in the first state, where the concentrations of ammonia and ammonium ions in the rearing water are equal to or greater than a certain concentration relative to the available residual chlorine concentration, the effective residual chlorine concentration increases as the amount of chlorate compound added increases. On the other hand, in the second state, where ammonia or ammonium ions are present but their concentrations are equal to or less than the certain concentration relative to the available residual chlorine concentration, the effective residual chlorine concentration decreases even when the chlorate compound is added because they are consumed in reactions with ammonia or ammonium ions. Furthermore, in the third state, where ammonia and ammonium ions are absent, the effective residual chlorine concentration increases as the amount of chlorate compound added increases. If the pH, salinity, and temperature of the rearing water are constant, the certain concentrations can be considered fixed values.

[0084] The control device 52 is configured to be able to detect the current flowing between the first electrode 55A and the second electrode 55B in the electrolysis unit 13, and continuously monitors the current flowing between the first electrode 55A and the second electrode 55B. The control device 52 can monitor the current flowing between the first electrode 55A and the second electrode 55B in various ways. For example, the control device 52 may detect the current using a current sensor and acquire the value detected by the current sensor, or may have other configurations. The control device 52 then controls the current flowing between the first electrode 55A and the second electrode 55B based on the detection value of either or both of the ammonium ion sensor 29 and the first residual chlorine sensor 19.

[0085] The control device 52 may perform first current control to control the current flowing between the first electrode 55A and the second electrode 55B based on the detection values ​​of both the ammonium ion sensor 29 and the first residual chlorine sensor 19. The larger the current flowing between the first electrode 55A and the second electrode 55B, the more electrolysis is promoted, and the greater the amount of chlorine acid compounds generated. Therefore, when performing the first current control, the control device 52 adjusts the current flowing between the first electrode 55A and the second electrode 55B so that the ammonium ion concentration value (detected value) detected by the ammonium ion sensor 29 is equal to or less than a first threshold value. The first threshold value may be 0 or a value slightly greater than 0. On the other hand, in the absence of ammonia and ammonium ions, the greater the current flowing between the first electrode 55A and the second electrode 55B, the higher the available chlorine concentration. Therefore, the control device 52 adjusts the current flowing between the first electrode 55A and the second electrode 55B so that the current range is such that the detection value of the ammonium ion sensor 29 is below the first threshold value and the value (detection value) of the residual chlorine amount detected by the first residual chlorine sensor 19 is below the second threshold value.

[0086] The control device 52 may perform second current control to control the current flowing between the first electrode 55A and the second electrode 55B based on the detection value of the ammonium ion sensor 29, without using the detection value of the first residual chlorine sensor 19. When performing the second current control, the control device 52 also adjusts the current flowing between the first electrode 55A and the second electrode 55B so that the value of the ammonium ion concentration detected by the ammonium ion sensor 29 (detection value) is equal to or less than the first threshold value. The first threshold value may be 0 or may be a value slightly greater than 0. When performing the second current control, the control device 52 repeats "current adjustment control in which the current flowing between the first electrode 55A and the second electrode 55B is controlled to a set current value, electrolysis is performed for a certain period of time, and then the value of the ammonium ion concentration detected by the ammonium ion sensor 29 (detection value) is confirmed." In this control, if the detection value of the ammonium ion sensor 29 exceeds the first threshold in the previous current adjustment control, the next current adjustment control is performed so that the next set current value is a current value that is increased by a predetermined percentage (e.g., 10%) from the set current value used in the previous current adjustment control. On the other hand, if the detection value of the ammonium ion sensor 29 in the previous current adjustment control is equal to or less than the first threshold, the next current adjustment control is performed so that the next set current value is the set current value used in the previous current adjustment control. In this manner, electrolysis can be performed while gradually increasing the current until the detection value of the ammonium ion sensor 29 becomes equal to or less than the first threshold. When the detection value of the ammonium ion sensor 29 becomes equal to or less than the first threshold, electrolysis can be performed while maintaining that current state.

[0087] The control device 52 may perform third current control to control the current flowing between the first electrode 55A and the second electrode 55B based on the detection value of the first residual chlorine sensor 19, without using the detection value of the ammonium ion sensor 29. When performing the third current control, the control device 52 repeats "current adjustment control to control the current flowing between the first electrode 55A and the second electrode 55B to a set current value, perform electrolysis for a certain period of time, and then check the value (detection value) of the amount of residual chlorine detected by the first residual chlorine sensor 19." In this control, when the set current value in the previous current adjustment control is increased by a predetermined percentage (for example, 10%) compared to the set current value in the current adjustment control before last, if the value (detected value) of the residual chlorine amount detected in the previous current adjustment control is smaller than the value (detected value) of the residual chlorine amount detected in the current adjustment control before last, it can be assumed that the above-mentioned second state is occurring, so in this case, in the next current adjustment control (current current adjustment control), the current adjustment control is performed so that the set current value is increased by a predetermined percentage (for example, 10%) from the set current value used in the previous current adjustment control.In other words, while the value of the detected residual chlorine amount is decreasing, the current adjustment control is performed each time so that the set current value is gradually increased. On the other hand, when control is performed to gradually increase the set current value in this manner, if the set current value in the previous current adjustment control is increased by a predetermined percentage (e.g., 10%) compared to the set current value in the current adjustment control before last, and the value (detected value) of the residual chlorine amount detected in the previous current adjustment control is greater than the value (detected value) of the residual chlorine amount detected in the current adjustment control before last, it can be assumed that the above-mentioned third state is occurring.In this case, in the next current adjustment control (current current adjustment control), current adjustment control is performed so that the set current value is a current value that is reduced by a predetermined percentage (e.g., 10%) from the set current value used in the previous current adjustment control.In addition, when the set current value in the previous current adjustment control is reduced by a predetermined percentage (for example, 10%) from the set current value in the current adjustment control before last, if the value of the residual chlorine amount (detected value) detected in the previous current adjustment control is smaller than the value of the residual chlorine amount (detected value) detected in the current adjustment control before last, current adjustment control is performed so that the set current value in the next current adjustment control (current current adjustment control) is a current value reduced by a predetermined percentage (for example, 10%) from the set current value used in the previous current adjustment control.On the other hand, if the value of the residual chlorine amount (detected value) detected in the previous current adjustment control is greater than the value of the residual chlorine amount (detected value) detected in the current adjustment control before last, current adjustment control is performed so that the set current value in the next current adjustment control (current current adjustment control) is a current value increased by a predetermined percentage (for example, 10%) from the set current value used in the previous current adjustment control.

[0088] (Control based on monitoring of residual chlorine) When a predetermined measurement result is obtained by the second residual chlorine sensor 27, the treatment unit 31 may operate to remove residual chlorine from the breeding water in the fourth area, or may operate to stop the breeding water in the fourth area from being returned to the breeding tank 3.

[0089] For example, the treatment unit 31 may supply a neutralizing agent to the breeding water before returning to the breeding tank 3 when the residual chlorine concentration (detection value) detected by the second residual chlorine sensor 27 exceeds a predetermined value. Suitable neutralizing agents include, for example, sodium thiosulfate, catechin, polyphenol, and cysteine. In the example of FIG. 7 , a neutralizing agent supplying device 31A that supplies a neutralizing agent to the breeding water in the fourth region is provided as at least a part of the treatment unit 31. Specifically, for example, the control device 52 and the neutralizing agent supplying device 31A function as the treatment unit 31 and the neutralizing agent supplying unit. When the residual chlorine concentration (detection value) detected by the second residual chlorine sensor 27 exceeds a predetermined value, the control device 52 may issue a neutralizing agent supplying command to the neutralizing agent supplying device 31A. In response to this neutralizing agent supplying command, the neutralizing agent supplying device may operate to supply a "neutralizing agent that neutralizes the residual chlorine" into the standby tank 25.

[0090] The treatment unit 31 may be configured to switch the flow path so that the rearing water flows from the standby tank 25 to another area instead of returning it to the breeding tank 3 when the detected residual chlorine concentration by the second residual chlorine sensor 27 exceeds a predetermined value. For example, a three-way valve (not shown) may be provided in the flow path 47, and the destination of the rearing water flowing through the flow path 47 may be switched between the breeding tank 3 and another area by the three-way valve. In this example, the control device 52 and the three-way valve may function as the treatment unit 31. Specifically, the control device 52 may control the three-way valve so that the destination of the rearing water is the breeding tank 3 when the detected residual chlorine concentration by the second residual chlorine sensor 27 is equal to or less than a predetermined value, and so that the destination of the rearing water is the other area when the detected residual chlorine concentration by the second residual chlorine sensor 27 exceeds the predetermined value.

[0091] Alternatively, when the detected value of the residual chlorine concentration detected by the second residual chlorine sensor 27 exceeds a predetermined value, the treatment unit 31 may block the flow path that flows the breeding water from the standby tank 25 to the breeding tank 3 to stop the return of the breeding water to the breeding tank 3, or may stop the circulation of the breeding water in the system 1 to stop the return of the breeding water to the breeding tank 3. For example, an on-off valve (not shown) may be provided in the flow path 47 so that when the on-off valve is open, the flow in the flow path 47 is permitted, and when the on-off valve is closed, the flow in the flow path 47 is closed. In this example, the control device 52 and the on-off valve can function as the treatment unit 31. Specifically, the control device 52 controls the on-off valve so that when the detected value of the residual chlorine concentration detected by the second residual chlorine sensor 27 is equal to or less than a predetermined value, the on-off valve is opened, and when the detected value of the residual chlorine concentration detected by the second residual chlorine sensor 27 exceeds the predetermined value, the on-off valve is closed. In this example, when the on-off valve is shut off, the pump that circulates the rearing water in the system may be stopped to prevent the standby tank 25 from overflowing, and a flow path may be provided so that the rearing water can escape from the standby tank 25 to another area when the water level in the standby tank 25 exceeds a certain level.

[0092] (Control Based on pH Monitoring) In this embodiment, an adjuster supplying device 32 is provided to supply a pH adjuster to the breeding water in the fourth region. In the example of Figure 7, the adjuster supplying device 32 is configured to supply a pH adjuster to the breeding water in the standby tank 25. The control device 52 instructs the adjuster supplying device 32 on the supply time and supply rate, and the adjuster supplying device 32 supplies the pH adjuster at the supply time and supply rate instructed by the control device 52.

[0093] The pH adjuster supplied from the adjuster supply device 32 can be, for example, any of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, and sodium bicarbonate. Sodium carbonate or sodium bicarbonate is more preferably used, and sodium carbonate is even more preferably used. When using sodium carbonate, sodium bicarbonate, calcium carbonate, or the like as the pH adjuster, it is advisable to use an aqueous solution containing any of them. Using sodium carbonate, which has a high pH, ​​has the advantage of being a strong alkali, making it easy to raise the pH of the breeding water and less likely to disrupt the ion balance. Sodium bicarbonate has the advantage of being less likely to disrupt the ion balance and capable of exerting a pH buffering function. Note that the pH of the pH adjuster is preferably 11.5 or less to prevent the pH adjustment effect from being inhibited by the precipitation of magnesium contained in seawater.

[0094] There are various methods of control by the control device 52, but for example, the control device 52 may perform on / off control so as to operate the adjuster supply device 32 to supply a pH adjuster having a pH greater than the first reference value at a predetermined supply rate when the pH of the rearing water detected by the pH sensor 28 falls below a first reference value, and to stop the supply of pH adjuster by the adjuster supply device 32 when the pH of the rearing water detected by the pH sensor 28 exceeds a second reference value while the adjuster supply device 32 is supplying the pH adjuster. Note that in the above example, the first reference value and the second reference value may be the same or different.

[0095] In order to reduce the consumption of the pH adjuster, a solid material of calcium carbonate (for example, pellets) may be provided in the fourth region (for example, the internal region of the flow paths 46, 47 or the standby tank 25).

[0096] In the above example, the timing of supplying the pH adjuster is controlled, but instead of this method, the pH adjuster may be continuously supplied at a constant supply rate.

[0097] 4. Electrode Cleaning As shown in FIG. 5 , in this embodiment, the control device 52 and the drive circuit 53 function as a voltage application unit 51. The voltage application unit 51 operates to switch between a first state in which a voltage is applied to the first electrode 55A as an anode and the second electrode 55B as a cathode to perform electrolysis within the "region" (specifically, within the electrolytic cell 11) and a second state in which a voltage is applied to the second electrode 55B as an anode and the first electrode 55A as a cathode. For example, the voltage application unit 51 periodically switches between an operation in which rearing water is electrolyzed by continuing the first state and an operation in which rearing water is electrolyzed by continuing the second state. When the switching is performed periodically, the switching cycle may be, for example, every several tens of minutes, every few hours, every other day, or any other cycle.

[0098] The timing at which the voltage application unit 51 switches between the first state and the second state is not limited to periodic timing, and may be timing when a predetermined condition is met. For example, the voltage application unit 51 may switch between the first state and the second state when a certain operating time of the circulating water treatment system 1 has elapsed since the previous switching, when a detected value by a sensor reaches a predetermined value, when a randomly determined timing is reached, or at other timings.

[0099] In this embodiment, the first state of operation is continuously performed in which the voltage application unit 51 continuously applies a voltage to make the first electrode 55A an anode and the second electrode 55B a cathode while "changing the breeding water" is performed so that the breeding water is continuously guided from the flow path 42 to the electrolysis cell 11 and discharged from the electrolysis cell 11 to the first guide path 56. If a switching condition is met during the first state of operation, the first state is switched to the second state while "changing the breeding water" is performed. After the switch, the second state of operation is continuously performed in which a voltage is continuously applied to make the second electrode 55B an anode and the first electrode 55A a cathode while "changing the breeding water". If a switching condition is met during the second state of operation, the second state is switched to the first state while "changing the breeding water". In this manner, the first state of operation and the second state of operation are alternately performed. It should be noted that while the operation in the first state or the operation in the second state is continuing, the operation may be continued without interruption, or the operation may be temporarily interrupted for some reason.

[0100] 5. Example of Effects In the above example, the circulating water treatment system 1 may correspond to an example of an electrolyzer, and the electrolysis unit 13 may correspond to an example of an electrolyzer. This electrolyzer or an electrolysis method using the electrolyzer electrolyzes salty breeding water to generate a chlorate compound (e.g., sodium hypochlorite), which then reacts with ammonia or ammonium ions present in the breeding water to directly decompose into nitrogen. This effectively suppresses the generation of nitrite, nitric acid, and other substances during the decomposition process. However, if this method is adopted without taking any measures, there is a concern that deposits will adhere to the electrode surfaces and inhibit electrolysis. However, the electrolyzer can be switched between a first state in which electrolysis is performed by applying a voltage so that the first electrode 55A serves as an anode and the second electrode 55B serves as a cathode, and a second state in which a voltage is applied so that the second electrode 55B serves as an anode and the first electrode 55A serves as a cathode. This allows deposits that have adhered to the electrode surfaces during continuous electrolysis to easily detach from the electrodes. Therefore, this electrolyzer can easily remove deposits that deposit on the surfaces of the electrodes.

[0101] Continuous electrolysis of salty aquarium water can result in the formation of magnesium-based deposits on the cathode, covering the electrode. When deposits cover the electrode, the amount of sodium hypochlorite generated gradually decreases or becomes unstable. To prevent this, applying physical force to the deposits on the electrode and periodically cleaning them can be considered. However, frequent mechanical cleaning can easily damage the electrode, shortening its lifespan and performance. Furthermore, cleaning by scraping the electrode surface or by using water pressure requires manual labor, making automation, labor-saving, and stable operation difficult. However, the electrolysis device described above can effectively suppress or eliminate this problem.

[0102] In the above electrolyzer, the electrode unit 55, which is an integral structure of the first electrode 55A, the second electrode 55B, and the electrode holder 55C, is detachable from the electrolytic cell 11, which facilitates the removal of the electrode unit 55 for cleaning. In particular, the promotion of the removal of deposits by switching and the facilitation of the attachment and detachment of the electrode unit 55 have a synergistic effect, making cleaning even easier.

[0103] The electrolysis device described above can automatically collect the precipitates that have sunk from the electrode part 55 toward a predetermined position using the induction part 58, and therefore can easily not only detach the precipitates from the electrode part 55 but also collect the detached precipitates.

[0104] The electrolysis device described above can take in and discharge the precipitate that has sunk from the electrode unit 55 into the pipe 59A of the discharge unit 59 at a position below the electrode unit 55, thereby preventing the precipitate from dispersing during the discharge process and becoming more likely to flow into subsequent processes.

[0105] The electrolyzer can guide supernatant water located above a predetermined height in the electrolytic cell 11 to the outside, and can make it difficult for precipitates that have sunk below the predetermined height to be guided outside the electrolytic cell 11. More specifically, because the predetermined height is above the lower end of the electrode unit 55, precipitates that detach from the electrode unit 55 and sink below the lower end are difficult to guide outside the electrolytic cell 11.

[0106] The electrolysis device described above can use the water flow generating unit 57 to generate a water flow within the electrolysis tank 11 that moves the water upward from below the electrode unit 55, making it easier for new rearing water to be introduced to the electrode unit 55 and further increasing the efficiency of electrolysis.

[0107] In the above electrolysis device, the operation of electrolyzing the rearing water by continuing the first state is periodically switched to the operation of electrolyzing the rearing water by continuing the second state, so that the precipitates can be periodically removed and the electrodes can be periodically cleaned.

[0108] The circulating water treatment system 1 can remove solids contained in the breeding water in the first zone using the removal unit 5. Furthermore, in the second zone after the breeding water passes through the first zone, the circulating water treatment system 1 can decompose ammonia or ammonium ions using the electrolysis unit 13. Since the breeding water is electrolyzed after the removal of solids using the removal unit 5, the solids are prevented from interfering with the electrolysis, facilitating successful electrolysis. Furthermore, the circulating water treatment system 1 can remove residual chlorine using the activated carbon unit 23 in the third zone where the breeding water that passed through the second zone is stored or flows. Therefore, even if chlorate compounds not used in the decomposition of ammonia or ammonium ions are contained in the breeding water in the third zone, these chlorate compounds can be effectively removed by the activated carbon unit. Thus, the circulating water treatment system 1 reliably reduces solids such as feces and leftover food in the breeding water after passing through the third zone, and reliably suppresses nitrogen compounds such as ammonia, nitrite, and nitrate, providing significant advantages in terms of purifying and detoxifying the breeding water.

[0109] In the circulating water treatment system 1, the supernatant water located above the first height in the electrolysis tank 11 can be guided to the outside of the electrolysis tank 11, so that even if a precipitate detaches from the electrodes and sinks, the precipitate is less likely to be guided to the outside of the electrolysis tank 11. Even if some of the precipitate is discharged from the electrolysis tank 11 and enters the reaction tank 15, the supernatant water located above the second height in the reaction tank 15 can be guided to the outside of the reaction tank 15, so that the precipitate that has entered the reaction tank 15 is more likely to settle in the reaction tank 15 and is less likely to be guided to the outside of the reaction tank 15.

[0110] In the electrolysis method using the circulating water treatment system 1 or the above-mentioned electrolysis device, the rearing water can be continuously introduced into the electrolysis tank 11 and discharged from the electrolysis tank 11, thereby replacing the rearing water, while operating in the first state, operating in the second state, and switching between the first state and the second state. This allows the rearing water to be circulated more efficiently while cleaning the electrodes.

[0111] Second Embodiment The following description relates to a second embodiment. The circulating water treatment system 1 and the aquaculture method using this system 1 according to the second embodiment differ from the first embodiment in that the removal unit 5 shown in Fig. 1 has a configuration as shown in Fig. 8 instead of the configuration as shown in Figs. 3 and 4 , but is the same as the first embodiment except for the configuration of the removal unit 5. Therefore, in the following description, for the configurations other than Fig. 3 , it is assumed that the configurations of Figs. 1, 2, 5, 6, and 7 are used, and the symbols, names, etc. attached to these figures will be used as appropriate.

[0112] In the example of Figure 8, the removal unit 5 is configured to introduce rearing water introduced from an upstream region of the removal unit 5 into a foam separator 7, and then pass the rearing water through the foam separator 7 to a downstream region different from the upstream region. The upstream region is a region within the breeding tank 3. The downstream region is a region within the electrolytic cell 11. In the removal unit 5, rearing water supplied from the upstream region of the removal unit 5 is introduced into the foam separator 7 through a flow path 41 (the flow path 41 corresponds to an example of an inlet path), and then passes through the foam separator 7 to be discharged to a "downstream region of the removal unit 5" (e.g., a region within the electrolytic cell 11) different from the source region (e.g., a region within the breeding tank 3) where the inlet of the flow path 41 (inlet path) is located. In the removal section 5, the entire amount of rearing water flowing in from the rearing tank 3 via the flow path 41 is sent into the foam separator 7, and there is no flow path from the rearing tank 3 to the electrolysis tank 11 without passing through the foam separator 7. Of the rearing water sent to the foam separator 7, all but the removed matter that is removed together with the bubbles in the foam separator 7 is sent from the foam separator 7 to the electrolysis tank 11 via the flow path 43. The operation of the foam separator 7 is the same as in the first embodiment, and in this example as well, ozone-containing bubbles are generated in the foam separator 7.

[0113] In this way, in the second embodiment of the circulating water treatment system 1, when solids are removed by the removal section 5, the rearing water introduced from the previous process area is introduced into the foam separator 7, and then passed through the foam separator 7 and discharged to a subsequent process area that is different from the previous process area.This allows the circulating rearing water to pass through the foam separator 7 more reliably, further enhancing the effectiveness of solid removal and the effects of sterilization and disinfection by ozone.

[0114] <Third Embodiment> The following description relates to the third embodiment. The circulating water treatment system 1 and the aquaculture method using this system 1 according to the third embodiment differ from the first embodiment in that the configuration shown in Figure 9 is used instead of the configuration shown in Figure 5. Specifically, the third embodiment is the same as the first embodiment except that inclined portions 58C, 58D, 58E, and 58F and discharge portions 110 and 112 are provided in addition to the configuration shown in Figure 5. Therefore, in the following description, for the configuration other than that shown in Figure 5, it is assumed that the configurations shown in Figures 1 to 4, 6, and 7 are used, and the symbols, names, etc. attached to these figures are used as appropriate.

[0115] As shown in FIG. 9 , the electrolytic cell 11 is provided with a discharge unit 110 in addition to the discharge unit 59. The discharge unit 110 includes a tube 110A for discharging precipitate that has sunk from the electrode unit 55 within the electrolytic cell 11, and an opening / closing unit 110B for opening and closing the tube 110A. The discharge unit 110 functions to take precipitate into the tube 110A below the electrode unit 55 and discharge the precipitate from the electrolytic cell 11 through the tube 110A. The opening / closing unit 110B is, for example, a valve that can be manually switched between a closed and open state for the tube 110A. The opening / closing unit 110B may also be a solenoid valve that can be controlled to open or close. In either case, when the opening / closing unit 110B is in the open state, the breeding water is discharged through the tube 110A from near a predetermined position within the electrolytic cell 11. If precipitate settles near the predetermined position, the breeding water is discharged through the tube 110A together with the breeding water.

[0116] In the example of FIG. 9 , in addition to inclined portions 58A and 58B, inclined portion 58C is provided. The inclined surface of inclined portion 58C is inclined with respect to the up-down direction, and inclined portion 58C guides an object sinking along the inclined surface of inclined portion 58C so as to move in the up-down direction and a second direction perpendicular to the first direction (specifically, so as to move in the second direction toward discharge portion 59). Furthermore, in the example of FIG. 9 , inclined portion 58D is provided. The inclined surface of inclined portion 58D is inclined with respect to the up-down direction, and inclined portion 58D guides an object sinking along inclined portion 58D so as to move in the second direction (specifically, so as to move in the second direction toward discharge portion 110).

[0117] In the example of FIG. 9 , the reaction tank 15 is also provided with a discharge unit 112. The discharge unit 112 includes a pipe 112A for discharging precipitates that have sunk within the reaction tank 15 and an opening / closing unit 112B for opening and closing the pipe 112A. The discharge unit 112 functions to take the sinking objects into the pipe 112A and discharge them through the pipe 112A. The opening / closing unit 112B is, for example, a valve that can be manually switched between a closed and open state for the pipe 112A. Note that the opening / closing unit 112B may also be a solenoid valve that can be controlled to open and close. In either case, when the opening / closing unit 112B is in the open state, the breeding water is discharged through the pipe 112A from near a predetermined position within the reaction tank 15. If an object settles near the predetermined position, the object is discharged together with the breeding water through the pipe 112A. The reaction tank 15 is also provided with inclined portions 58E and 58F. The inclined surfaces of the inclined portions 58E, 58F are inclined in the vertical direction, and each of the inclined portions 58E, 58F guides the object sinking along the inclined surface of each inclined portion so as to move in the second direction (specifically, so as to move in the second direction toward the discharge portion 112).

[0118] 9, the pipes 59A, 110A, and 112A are permanently installed fixed pipes, but they may be removable pipes. Furthermore, when discharging any of the pipes, the water may be discharged by utilizing the water pressure in the tank, or by suction or flow using a pump or the like.

[0119] <Fourth Embodiment> The following description relates to the fourth embodiment. The circulating water treatment system 1 and the aquaculture method using this system 1 according to the fourth embodiment differ from the first embodiment in that a configuration as shown in Figure 10 is used instead of the configuration as shown in Figure 7, and differs from the first embodiment in that, in addition to the configuration as shown in Figure 7, a switching unit 140 is provided midway through the flow path 46. Other configurations are the same as those of the first embodiment. Therefore, in the following description, the configurations other than the switching unit 140 are assumed to be the same as those of Figures 1 to 7, and the symbols, names, etc. assigned to these figures will be used as appropriate.

[0120] In the fourth embodiment of the circulating water treatment system 1, a switching valve 142 is provided in the switching unit 140, and the switching valve 142 can switch the path for flowing the rearing water discharged from the residual chlorine removal tank (e.g., the activated carbon tank 21) into the flow path 46 to either a flow path 143A that does not pass through the second removal unit 146, or a flow path 143B that passes through the second removal unit 146.

[0121] The second removal tank 144 is configured as a flow path for the breeding water, and the internal space of the flow path is filled with a component (e.g., calcium sulfite granules) that removes residual chlorine, thereby constituting the second removal unit 146. The second removal tank 144 is configured as a flow path with an inlet and an outlet, and in a typical example, the internal space is filled with calcium sulfite granules. When the selector valve 142 is set so that the destination of the outflow from the selector valve 142 is flow path 143B, the breeding water that passes through the selector valve 142 and flows into the inlet of the second removal tank 144 passes through gaps in the internal space of the second removal tank 144 (numerous gaps between calcium sulfite), and residual chlorine and residual ozone contained in the breeding water are removed by the calcium sulfite. The breeding water discharged from the outlet of the second removal tank 144 to the downstream flow path 46 is breeding water from which some or all of the chlorine and ozone have been removed.

[0122] In this configuration, when the residual chlorine concentration detected by the second residual chlorine sensor 27 is below a reference value, the control device 52 switches the switching valve 142 so that rearing water flows from the residual chlorine removal tank (e.g., activated carbon tank 21) to flow path 143A and does not flow to flow path 143B. On the other hand, when the residual chlorine concentration detected by the second residual chlorine sensor 27 exceeds the reference value, the control device 52 switches the switching valve 142 so that rearing water flows from the residual chlorine removal tank (e.g., activated carbon tank 21) to flow path 143B and does not flow to flow path 143A. In this way, when the residual chlorine concentration detected by the second residual chlorine sensor 27 becomes relatively high, the rearing water from the residual chlorine removal tank (e.g., activated carbon tank 21) can be switched to flow through the second removal unit 146, and residual chlorine can also be removed by the second removal unit 146. Note that the control method described here is merely an example, and the timing and duration of rearing water flow into the second removal tank 144 are not limited to the above example.

[0123] <Other Embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings. For example, any combination of features of the above-described or following embodiments is possible within a range that does not contradict. Furthermore, any feature of the above-described or following embodiments may be omitted unless explicitly stated as essential. Furthermore, the above-described embodiments may be modified as follows.

[0124] In the above-described embodiment, ozone is supplied as a gas to the foam separator 7, generating bubbles containing ozone, but the configuration may also be such that instead of ozone, another gas (e.g., air) is supplied, generating bubbles of the other gas.

[0125] In the above-described embodiment, the second region is the internal region of the electrolytic cell 11 configured as a cell having a portion for storing rearing water, but the electrolytic cell 11 may also be configured as a flow path without a portion for storing water, and this internal region may be the second region.

[0126] In the above-described embodiment, the reaction tank 15 is configured as a tank having a portion for storing rearing water, but it may also be configured as a flow path without a portion for storing rearing water.

[0127] In the above-described embodiment, the first residual chlorine sensor 19 is positioned to detect the concentration of residual chlorine in the rearing water in the filtration tank 17, but it may also be configured to detect the concentration of residual chlorine in the flow path from the reaction tank 15 to the activated carbon tank 21.

[0128] In the above-described embodiment, the internal region of the activated carbon tank 21 configured as a tank having a portion for storing rearing water is the third region, but the activated carbon tank 21 may also be configured as a flow path without a storage portion, and this internal region may be the third region.

[0129] In the above-described embodiment, the fourth region is the internal region of the waiting tank 25 configured as a tank having a portion for storing rearing water, but the waiting tank 25 may also be configured as a flow path without a portion for storing water, and this internal region may be the fourth region.

[0130] In the above-described embodiment, as shown in Figures 1 and 7, the residual chlorine removal tank is provided with an activated carbon tank 21 having an activated carbon section 23 filled with activated carbon granules. However, calcium sulfite granules may be used instead of activated carbon granules in the activated carbon section 23, and the residual chlorine removal tank may be filled with calcium sulfite granules. In this example, the residual chlorine removal tank may be configured as a flow path having an inlet and an outlet, and the internal space of the flow path may be filled with calcium sulfite granules. In this example, the rearing water flowing in through the inlet of the residual chlorine removal tank passes through the gaps in the internal space (the gaps between the calcium sulfite particles), whereby residual chlorine and ozone contained in the rearing water are removed by the calcium sulfite. The rearing water discharged from the outlet is rearing water from which some or all of the chlorine and ozone have been removed.

[0131] In the configuration of the fourth embodiment shown in FIG. 10 , the switching unit 140 is provided midway along the flow path 46. However, in any of the configurations of the first to third embodiments, the switching unit 140 may be provided midway along the flow path 47 in the configuration of FIG. 1 (for example, at the position of the two-dot chain line X in FIG. 1 ). In this case, by performing control similar to that of the fourth embodiment described above, the path for flowing the rearing water discharged from the standby tank 25 into the flow path 47 may be switched to either a flow path 143A that does not pass through the second removal unit 146, or a flow path 143B that does pass through the second removal unit 146, so that the rearing water that has passed through either the flow path 143A or the second removal unit 146 may be supplied to the breeding tank 3.

[0132] In any of the above-described embodiments, a biological tank may be provided in the region before the breeding water discharged from the breeding tank flows into the second region, in which ammonia or ammonium ions in the breeding water are reduced by organisms. In this case, for example, in the circulating water treatment system 1 ( FIG. 3 ) of the first embodiment, a biological tank may be provided between the storage tank 60 and the electrolysis tank 11, and the breeding water flowing out from the storage tank 60 may flow into the biological tank, and the breeding water flowing out from the biological tank may flow into the electrolysis tank 11. Alternatively, in the circulating water treatment system 1 ( FIG. 8 ) of the second embodiment, the breeding water flowing out from the foam separator 7 may flow into the biological tank, and the breeding water flowing out from the biological tank may flow into the electrolysis tank 11. In this example, the biological tank is preferably configured to receive the breeding water flowing out from the breeding tank 3 via a flow path or the like and to store the inflowing breeding water. On the other hand, the biological tank preferably contains, for example, nitrifying bacteria (microorganisms) that oxidize ammonia to nitrite and subsequently nitrate, as an example of the organisms. In such a configuration, ammonia or ammonium ions contained in the breeding water flowing into the biotask are reduced by the microorganisms, and the breeding water with reduced ammonia or ammonium ions flows from the biotask directly or via another region into the electrolysis tank 11. The order of the removal unit and the biotask may be such that the breeding water flows into the biotask via the removal unit, or the breeding water flows into the removal unit via the biotask. Alternatively, part or all of the biotask may double as the removal unit. In either case, it is sufficient that part or all of the breeding water flowing from the breeding tank 3 and into the electrolysis tank 11 flows into the electrolysis tank 11 via the biotask. In the above example, the biotask is configured to hold breeding water and microorganisms therein. However, instead of or in addition to this configuration, the ammonia or ammonium ions contained in the breeding water may be reduced by the action of other organisms. Furthermore, the number of biotasks is not limited to one, and multiple biotasks may be present. For example, instead of the above-mentioned "biotask for holding microorganisms," the biotask may be configured to raise vegetables or other plants as "organisms."In this case, the breeding water flowing in from the breeding tank 3 directly or via another area may be temporarily stored or flowed in the biotank, and the breeding water in the biotank may be continuously or intermittently supplied to the plants to grow them, thereby causing the plants to absorb the ammonia or ammonium ions in the breeding water and purify the water. This "circulating water treatment system using both a biotank and an electrolysis tank" can reduce ammonia or ammonium ions in the biotank before the electrolysis unit 11 decomposes the ammonia or ammonium ions. Therefore, compared to a configuration in which the reduction of ammonia or ammonium ions in the breeding water is performed solely by the electrolysis unit 11, the burden on the electrolysis unit 11 can be reduced, and the power consumption required for electrolysis can be easily reduced. On the other hand, because the reduction of ammonia or ammonium ions in the breeding water is not performed solely by the biotank, the ammonia or ammonium ions in the water can be more effectively decomposed in a manner that is less dependent on organisms. Furthermore, the above-mentioned circulating water treatment system produces a chloric acid compound (e.g., sodium hypochlorite) in the second region (the region within the electrolysis tank 11) into which the breeding water that has passed through the biological tank flows, so that not only can ammonia or ammonium ions be removed, but also bacteria or viruses can be sterilized or inactivated if they are contained in the breeding water that has passed through the biological tank.

[0133] It should be noted that the embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the embodiments disclosed herein, but is intended to include all modifications within the scope indicated by the claims or the scope equivalent to the claims.

[0134] 1: Circulating water treatment system 3: Breeding tank 5: Removal section 7: Foam separator 9: Ozone generator 11: Electrolysis tank 11A: First breeding water flow chamber 11B: Second breeding water flow chamber 11C: Third breeding water flow chamber 11Z: Bottom wall 13: Electrolysis section 15: Reaction tank 17: Filtration tank 19: First residual chlorine sensor 21: Activated carbon tank (residual chlorine removal tank) 23: Activated carbon section (residual chlorine removal section) 25: Standby tank 27: Second residual chlorine sensor 29: Ammonium ion sensor 31: Treatment section 35: Temperature controller 37: Filter 41, 42, 43, 44, 45, 46, 47: Flow path 51: Voltage application section 52: Control device 53: Drive circuit 54A : Conductive path 54B : Conductive path 55 : Electrode section 55A : First electrode 55B : Second electrode 55C : Electrode holding section 56 : First guide path 57 : Water flow generating section 57A : First partition wall 57B : Second partition wall 58 : Guide section 58A, 58B : Inclined section 59 : Discharge section 59A : Pipe 59B : Opening / closing section 60 : Storage tank 60A : Bottom 62 : Inlet section 64 : Outlet section 66 : Discharge section 72 : Second guide path W1 : Water surface W2 : Water surface W3 : Water surface

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