Sludge purification system and sludge purification method

Abstract

To provide a sludge purification system that can reduce the volume of sludge layers accumulated in rivers, lakes, etc., without the need for dredging, and that does not adversely affect the ecosystem as a result of sludge purification. [Solution] The sludge purification system 1 for purifying the sludge layer is equipped with an ultrasonic transmitter / receiver 120, a means for estimating the depth of the sludge layer, a nanobubble supply means 210, and a supply height adjustment means 220. Surface reflected waves from at least the surface of the sludge layer are observed by the ultrasonic transmitter / receiver, and the surface depth is estimated by the depth estimation means. The height (depth) at which the nanobubble-dissolved water is circulated by the supply means is adjusted by the supply height adjustment means to a depth that does not stir up the sludge layer, and the nanobubbles are supplied to the sludge layer by utilizing the sinking behavior of the nanobubbles in water. As a result, sludge can be purified without adversely affecting the ecosystem.

Description

Technical Field

[0001] The present invention relates to a sludge purification system and a sludge purification method for promoting the decomposition of organic substances contained in a sludge layer and purifying sludge by supplying nanobubbles into water to activate aerobic bacteria at the bottom of the water in rivers, lakes, artificial ponds, harbors, etc. where sludge has accumulated.

[0002] Conventionally, it has been generally understood that bubbles generated in water rise. However, in recent years, it has been reported that nanobubbles with a diameter of less than 1000 nanometers may show a behavior of not rising but moving downward in water (hereinafter, this behavior is simply referred to as sinking). For example, in 2024, at Kyushu Institute of Technology, the above-mentioned behavior of nanobubbles was confirmed by observation using a dark-field microscope.

[0003] Specifically, the present invention relates to a sludge purification system and the like that, even when the water containing nanobubbles (hereinafter referred to as nanobubble-dissolved water) is refluxed to the water area to be purified by observing and grasping the surface depth of the sludge layer and reaching the sludge layer by utilizing the above-mentioned behavior of nanobubbles, does not lift the sludge and cause adverse effects on the ecosystem. Furthermore, it relates to a sludge purification system and the like that enables the formulation of a purification plan suitable for the sludge distribution situation of each water area to be purified and the evaluation of the progress of purification.

Background Art

[0004] Sludge deposited in rivers, lakes, etc. has adverse effects such as bad odors, impacts on ship navigation, inhibition of the growth of aquatic organisms, generation and release of methane gas into the atmosphere, etc. Therefore, dredging work has been conventionally carried out according to the amount of sludge deposition. In dredging work, the sludge layer deposited on the bottom of the water is dug down and recovered by a crane, and the recovered sludge is transported to a water treatment facility. Then, in the water treatment facility, organic substances in the sludge are decomposed using sedimentation treatment, a centrifuge, etc. Furthermore, the silica sand separated by dehydration is transported from the water treatment facility to a landfill site.

[0005] Incidentally, the composition of sludge is said to be approximately 65% ​​by weight of water, 5% to 15% by weight of organic matter that causes adverse environmental impacts, and the remainder being silica sand. Dredging, which involves collecting the entire sludge to remove organic matter which is only a part of it, is inefficient. Moreover, since the sludge excavated by cranes can disperse into the water and potentially suffocate aquatic organisms, there is a need for a technology that can reduce the volume and purify the sludge by decomposing organic matter, as an alternative to physical removal such as dredging.

[0006] Patent Document 1 discloses a water treatment device technology that improves the seabed environment using a simpler method than dredging. According to the technology described in this document, bottom water is taken from the area to be purified, dissolved gases such as nitrogen and carbon dioxide are removed, oxygen is dissolved in it, and then it is returned to the seabed of the area to be purified. By slowly returning the treated water with dissolved oxygen from an inlet placed near the seabed, it is possible to improve the seabed environment without spreading accumulated pollutants or bottom water with low oxygen content.

[0007] However, the technology described in Patent Document 1 generates bubbles in water with a diameter of 1 μm to 2 mm, also known as microbubbles or millibubbles. Because bubbles of this size have poor dissolution efficiency, it was necessary to remove carbon dioxide and other gases beforehand using a degassing section. This degassing section requires a depressurization section at a height of 6 m or more relative to the water surface, which makes the entire water treatment system large and necessitates a large float with a deep draft. On the other hand, in rivers and lakes where sludge has accumulated, the water depth is often 3 m or less, and the technology described in this document is difficult to apply to rivers and lakes where dredging work is required, thus having the problem of lacking versatility.

[0008] Furthermore, since microbubbles are used in technologies to separate oil, microplastics, etc., from water due to their buoyancy, they have the property of floating to the water surface, albeit more slowly than millibubbles. Therefore, if the water inlet is located far enough away from the sludge layer, most microbubbles will simply float to the surface without reaching the sludge, and will not be able to sufficiently activate aerobic bacteria.

[0009] However, the technology described in Patent Document 1 does not measure the surface depth of the sludge layer, and its configuration does not allow for adjustment of the water inlet's position, making it difficult to position the water inlet at an appropriate depth. In addition, since the water depth of natural rivers and lakes fluctuates with the seasons, the distance between the water inlet and the sludge layer increases during seasons with high water volume, which reduces the effectiveness of sludge purification.

[0010] Patent Document 2 discloses a water quality improvement device that improves water quality by supplying bubble-mixed water to a sludge layer. According to the technology described in this document, an unmanned vessel is equipped with a floating body that functions as a means of supplying bubble-mixed water. This floating body has a water reservoir, and by storing water in the reservoir, the floating body is made to settle on the surface of the sludge layer and function as an anchor. Furthermore, the floating body is made to settle on the bottom and have its discharge port thrust into the sludge layer, and the bubble-mixed water is injected into the sludge layer.

[0011] The problem was that the injection of aerated water stirred up the sludge layer, mixing the water and sludge at the bottom, which increased the likelihood of aquatic life suffocating. Therefore, while it could be applied to artificial ponds, it was difficult to apply to natural rivers and lakes. Furthermore, injecting aerated water through a discharge port inserted into the sludge layer required a large pump with high pressure capacity, increasing both the overall size of the device and its power consumption. When these were mounted on an unmanned vessel, the continuous cruising time was shortened, resulting in poor purification efficiency.

[0012] Furthermore, the unmanned vessel, which is designed for autonomous navigation, is equipped with a bubble-mixed water generation device, and navigates to a designated area based on map information of the water area to be purified and GPS signals. When water quality improvement is carried out, that area is recorded as improved, and the vessel moves to the next area to be improved, thereby enabling autonomous improvement operation.

[0013] However, even in Patent Document 2, the sludge layer was not observed, and the water quality improvement was determined to have been carried out simply by the passage of a predetermined time. As a result, there was a problem in that the water quality could not be operated appropriately according to the distribution of sludge, as it was possible to move to the next area before the sludge had been sufficiently purified, or that the water quality improvement could be carried out in an area without sludge. Furthermore, since the thickness of the sludge before and after the water quality improvement was carried out was unknown, there was also a problem in that the effectiveness of the purification work could not be properly evaluated.

[0014] Furthermore, the applicant has disclosed in Patent Document 3 a technology for a sludge thickness measuring device capable of measuring the thickness of a sludge layer. According to this technology, it is possible to simultaneously observe the surface depth and bottom depth of the sludge layer with only one transmitter / receiver that emits ultrasonic waves of a single wavelength. Therefore, the applicant has diligently researched a technology that can efficiently purify a sludge layer without stirring the sludge and water at the bottom of the water, utilizing the technology described in Patent Document 3, and has completed the present invention. [Prior art documents] [Patent Documents]

[0015] Patent Document 1: Japanese Unexamined Patent Publication No. 2003-126884 Patent Document 2: Japanese Unexamined Patent Publication No. 2018-79449 Patent Document 3: Japanese Unexamined Patent Publication No. 2023-133749 [Overview of the project] [Problems that the invention aims to solve]

[0016] The problem that this invention aims to solve is to provide a sludge purification system and method that purifies sludge by facilitating the decomposition of organic matter in the sludge by aerobic bacteria, utilizing the behavior (phenomenon) of nanobubbles sinking toward the sludge layer, by installing a nanobubble dissolved water outlet at a depth that does not stir up the sludge layer based on the surface depth estimated by the transmission and reception of ultrasonic waves.

[0017] In the following explanations, the term "means" is used to describe the common technical ideas between the sludge purification system (an invention of a product) and the sludge purification method (an invention of a method), such as "depth estimation means" and "supply means." However, this is merely a definition of the term. Therefore, for the inventions of a product (inventions 1 through 7), "means" may be replaced with "device." For the supply height adjustment means, "means" may be replaced with "structure." [Means for solving the problem]

[0018] The first invention of the present invention is a sludge purification system for purifying a sludge layer accumulated on the bottom of a sea, comprising an ultrasonic transmitter / receiver, a means for creating sludge distribution information, a means for supplying nanobubbles, and a means for adjusting the supply height, wherein the transmitter / receiver is a single transmitter / receiver that transmits and receives ultrasonic waves at frequencies reflected from the surface and bottom surface of the sludge layer, the sludge distribution information creation means comprises a means for moving the transmitter / receiver, a means for identifying latitude and longitude, a processing means, and a storage means, the moving means moves at least the transmitter / receiver to observation points dispersed throughout the water area to be purified, and the latitude and longitude identification means acquires latitude and longitude information for each of the observation points. The processing means functions as a sludge layer depth estimation means and a drawing means, the depth estimation means estimates the surface depth of the sludge layer from the starting point of the gradually increasing surface reflected wave from the surface received by the transmitter / receiver, and estimates the bottom depth of the sludge layer from the starting point of the gradually increasing bottom reflected wave from the bottom surface received after the surface reflected wave has gradually decreased, the storage means associates the numerical information of the surface depth and bottom depth with the latitude and longitude information at all observation points to create and store sludge distribution information consisting of 3D point cloud data, and the drawing means associates the sludge distribution information read from the storage means with the latitude and longitude information in the map information of the water area to be purified, and draws the estimated shape of the sludge layer in the entire water area to be purified as 3D map information, thereby representing the range including observation points with a relatively large amount of sludge accumulation. The system visualizes the nanobubble supply points for selection, and the supply means comprises a water pumping means and a nanobubble generating means, and is installed in the water area to be purified at the supply points selected based on the three-dimensional map information. When the pumping means pumps up water from the water area to be purified and returns it as nanobubble-dissolved water, the generating means generates nanobubbles with a diameter of less than 1 μm from oxygen concentrated by an oxygen concentrator or generated from the atmosphere, and dissolves the nanobubbles in the pumped water. The supply height adjustment means adjusts the depth to which the nanobubble-dissolved water is returned by the pumping means to a depth that does not stir up the sludge layer, based on the surface depth at the supply point, thereby supplying the nanobubbles to the sludge layer by utilizing their sinking behavior in water.

[0019] The surface depth, which is the distance from the water surface to the surface of the sludge layer, is estimated using an ultrasonic transmitter / receiver and a means for estimating the depth of the sludge layer. The ultrasonic transmitter / receiver only needs to be able to transmit and receive frequencies that are reflected at least by the sludge surface. Selecting ultrasonic waves with a frequency of 25 kHz or less that are reflected by both the sludge surface and the bottom surface is preferable because it also allows for the estimation of the thickness of the sludge layer. The transmitter / receiver and depth estimation means are preferable when mounted on an unmanned observation vessel, as this allows for periodic autonomous observation of the surface depth.

[0020] The pumping means constituting the nanobubble supply means can be any well-known pump, and its form is not limited. The pump may be a submersible pump in which the main body is immersed in water, or it may be a pump in which only the intake and discharge ports are immersed in water without immersing the main body. The nanobubble generation means generates nanobubbles in the water pumped up from the water area to be purified by the pumping means. Therefore, nanobubble-dissolved water is returned to the water area to be purified from the discharge port of the pumping means. The nanobubble generation method can be any well-known ejector type, high-speed swirling liquid flow type, micropore type, etc., and is not limited.

[0021] The supply height adjustment means can adjust the depth to which the pumping means recirculates the nanobubble-dissolved water into the water area to be purified. The installation depth of the discharge port is set to a depth that does not stir up the sludge layer when the pumping means recirculates the nanobubble-dissolved water, based on a pre-estimated surface depth of the sludge layer. The ease with which the sludge layer is stirred up is not uniquely limited, as it depends not only on the water content and organic matter content of the sludge but also on the pumping capacity of the pumping means. For example, in the case of sludge with the average component ratio described above and a surface depth of approximately 3m, a position approximately 0.5m to 1.5m above the surface of the sludge layer is preferable.

[0022] The configuration of the supply height adjustment means is not limited. For example, an injection pipe extending from a submersible pump can be supported by a support wire stretched between a pair of support piles, and the installation depth of the discharge port at the tip of the injection pipe can be adjusted by changing the tension of the support wire. Alternatively, the installation depth of the discharge port of the submersible pump can be adjusted by a frame installed on a float or the like. This installation depth may remain constant throughout the year, or it may be readjusted according to the amount of fluctuation in the surface depth observed periodically. The adjustment of the installation depth may be done manually by an operator, or it may be automatically adjusted by an elevator or the like. Furthermore, if the supply means and the supply height adjustment means are mounted on a float or the like, and nanobubbles are released from a fixed point, it is preferable to secure power via a wired connection.

[0023] According to the first invention, for each water area to be purified such as rivers, lakes, etc., even if environmental conditions such as sludge deposition conditions, undulation conditions of the water bottom, water depth, etc. are different, nanobubbles can be supplied to the sludge layer so as to suit the unique environmental conditions of the water area to be purified. Since the nanobubbles are supplied to the sludge by utilizing the behavior (phenomenon) of the nanobubbles sinking in water, the nanobubbles spread in a cloud-like manner along the sludge surface, promoting the decomposition of organic substances by aerobic bacteria, and gradually separating water and silica sand from the sludge layer. As a result, it is easy to apply to rivers, lakes, etc. where dredging work is difficult, and it has an unprecedented advantageous effect of being able to provide a highly versatile sludge purification system.

[0024] According to the first invention, the transceiver transmits ultrasonic waves at a frequency capable of estimating the surface depth and the bottom depth of the sludge layer. And for each observation point, sludge distribution information based on three-dimensional point cloud data is created and stored in the storage means. According to this sludge distribution information, since the sludge thickness can be calculated from the difference between the surface depth and the bottom depth, not only the surface depth of the sludge but also the sludge thickness (deposition amount) can be grasped integrally. Regarding the observation date and time information, it may be based on the creation date and time of the sludge distribution information, or the date and time information may be acquired together with the latitude and longitude information from the latitude and longitude specifying means. The moving means may be an unmanned boat or a manned boat and is not limited. As long as the processing means acquires the observation data via the communication means, it does not have to be moved together with the transceiver.

[0025] The latitude and longitude specifying means is preferably a quasi-zenith satellite system such as Michibiki (registered trademark), but in an area where it cannot be used, any well-known GPS locator may be used. By grasping the sludge thickness and supplying nanobubbles centered on the point with a large deposition amount, the nanobubbles can be effectively used for purification. Also, by storing the sludge thickness, even if the surface depth fluctuates due to rising water or drought, the change over time of the sludge deposition amount can be grasped. Further, in order to easily and intuitively grasp the distribution of the sludge, a three-dimensional diagram is drawn based on the point cloud data in the three-dimensional coordinate system by drawing means such as well-known 3D CAD software.

[0026] Thus, when formulating a purification plan suitable for the specific sludge distribution situation for each water area to be purified, it is easy to consider the location for installing the nano-bubble supply means. Furthermore, since the amount of change in sludge thickness over time can be calculated through regular observation, local governments can easily grasp the progress of purification and accurately evaluate the purification plan, achieving an unprecedented advantageous effect.

[0027] Also, when the surface side of the sludge layer gradually starts to turn into sandy ground as the sludge layer is purified, the two-layer structure of the sludge layer and the bottom sandy ground layer changes to a three-layer structure of the surface silica sand layer, the sludge layer, and the bottom sandy ground layer. Then, the ultrasonic transmitter and receiver will observe the reflected waves sequentially reflected at the three interfaces of the surface silica sand layer, the surface of the sludge layer, and the bottom of the sludge layer. Therefore, it is possible to confirm that the purification of the sludge layer is in progress by observing the reflected wave from the surface silica sand layer.

[0028] Furthermore, according to the first invention, the estimated shape of the sludge layer across the entire water area to be purified is drawn as three-dimensional map information by the drawing means, and the range including the observation points with a relatively large deposition amount is visualized by highlighting it with hatching or the like. The nano-bubble supply point is selected based on the drawn three-dimensional map information. Therefore, the position where the supply means supplies nano-bubbles can be set as an appropriate position not only in terms of height (depth) but also in terms of location (latitude and longitude).

[0029] The second invention of the present invention is the sludge purification system of the first invention, characterized in that the supply height adjustment means restricts the depth for refluxing the nano-bubble dissolved water to a depth of 0.5 m or more from the water surface.

[0030] From the water surface to a depth of approximately 0.5m (hereinafter referred to as the surface layer), the water temperature is higher than at greater depths, resulting in greater water convection. Even if nanobubble-containing water is circulated in this surface layer, the sinking of the nanobubbles may be hindered. When purifying rivers or other bodies of water with current, the nanobubbles may be carried away to areas without sludge before reaching the sludge layer, meaning that some of the nanobubbles may not contribute to the purification of the sludge.

[0031] Therefore, according to the second invention, by limiting the adjustment range of the depth to which the nanobubble-dissolved water is circulated to depths deeper than the surface layer, the influence of convection in the surface layer is reduced. For example, it is sufficient to partially restrict the operating range of the elevator that serves as the height adjustment means. As a result, even in rivers and brackish lakes that are susceptible to the influence of water flow, it is easier to supply nanobubbles to the sludge layer accumulated at a predetermined location, resulting in a highly versatile effect.

[0032] The third invention of the present invention is a sludge purification system for purifying a sludge layer accumulated on the bottom of a sea, comprising an ultrasonic transmitter / receiver, a means for creating sludge distribution information, a means for supplying nanobubbles, and a means for adjusting the supply height, wherein the transmitter / receiver is a single transmitter / receiver that transmits and receives ultrasonic waves at frequencies reflected from the surface and bottom of the sludge layer, and the sludge distribution information creation means comprises a means for moving the transmitter / receiver, a means for identifying latitude and longitude, a processing means, and a storage means, wherein the moving means moves at least the transmitter / receiver to observation points dispersed throughout the water area to be purified, and the latitude and longitude The latitude identification means acquires latitude and longitude information for each observation point, the processing means functions as a means for estimating the depth of the sludge layer and a means for estimating the amount of sludge purification, the depth estimation means estimates the surface depth of the sludge layer from the starting point of the gradually increasing surface reflected wave from the surface received by the transmitter / receiver, and estimates the bottom depth of the sludge layer from the starting point of the gradually increasing bottom reflected wave from the bottom surface received after the surface reflected wave has gradually decreased, and the storage means associates the latitude and longitude information with the numerical information of the surface depth and bottom depth for all observation points from the 3D point cloud data. The system creates and stores sludge distribution information, and the supply means comprises a water pumping means and a nanobubble generating means, and is installed at a desired location in the water area to be purified based on the sludge distribution information, and when the pumping means pumps up water from the water area to be purified and returns it as nanobubble-dissolved water, the generating means generates nanobubbles with a diameter of less than 1 μm from oxygen concentrated by an oxygen concentrator or generated from the atmosphere, dissolves the nanobubbles in the pumped water, and the supply height adjustment means adjusts the depth at the location to which the nanobubble-dissolved water is returned by the pumping means. Based on the surface depth, the nanobubbles are supplied to the sludge layer by adjusting the depth to prevent stirring up the sludge layer, utilizing their sinking behavior in water; the depth estimation means repeatedly observes the bottom depth and surface depth of the sludge layer at each observation point during the nanobubble supply period; the sludge distribution information creation means creates and stores the sludge distribution information associated with the observation date and time information; and the purification amount estimation means performs a smoothing process on the 3D point cloud data of the sludge distribution information associated with the observation date and time information and observation points.The system is characterized by numerically correcting the estimated surface and bottom depths of the sludge layer at adjacent observation points so that they are smoothly continuous, creating a 3D map information showing the estimated shape of the sludge layer based on the corrected estimated values, identifying the amount of change in sludge thickness over time during the supply period from the difference in 3D map information for each observation date and time, and estimating at least the total weight or total volume of purified sludge in the entire water body targeted for purification.

[0033] According to the third invention, sludge distribution information is generated multiple times at each observation point with intervals in between, and the amount of change in sludge over time is determined from the difference in sludge thickness contained in the 3D point cloud data for each observation date and time. Furthermore, the total weight or total volume of purified sludge in the entire water area is estimated from the sum of the sludge reduction amounts at each observation point. Since the weight of sludge varies from water area to water area depending on the content of organic matter and silica sand, if a more accurate value is required, it is advisable to perform a component analysis of the collected sludge to determine its specific gravity.

[0034] Furthermore, the smoothing processing means removes data from specific observation points in the 3D point cloud data that have been found to be outliers when compared with observation data from adjacent observation points, and corrects the 3D point cloud data so that the undulations of the sludge layer connect smoothly with those of adjacent observation points. The smoothing processing is described in detail in Example 1 and Figure 7.

[0035] This allows us to show the weight and volume of sludge purification in a way that is easily comparable to dredging work, and provides suitable evidence for evaluating purification plans, not only for deciding whether to continue purification work, but also for local governments to formulate new or additional purification plans. This offers advantages not found in conventional technologies.

[0036] The fourth invention of the present invention is a sludge purification system for purifying a sludge layer accumulated on the bottom of a sea, comprising an ultrasonic transmitter / receiver, a means for creating sludge distribution information, a means for supplying nanobubbles, and a means for adjusting the supply height, wherein the transmitter / receiver is a single transmitter / receiver that transmits and receives ultrasonic waves at frequencies reflected from the surface and bottom of the sludge layer, the sludge distribution information creation means comprises a means for moving the transmitter / receiver, a means for identifying latitude and longitude, a processing means, and a storage means, wherein the moving means moves at least the transmitter / receiver to observation points dispersed throughout the water area to be purified, and the latitude and longitude identification means However, the latitude and longitude information for each observation point is acquired, and the processing means functions as a means for estimating the depth of the sludge layer and a means for confirming the state in which a surface silica sand layer separated from the sludge layer is stacked above the sludge layer, the depth estimation means estimates the surface depth of the sludge layer from the starting point of the gradual increase of the surface reflected wave from the surface received by the transmitter / receiver, and estimates the bottom depth of the sludge layer from the starting point of the gradual increase of the bottom reflected wave from the bottom surface received after the surface reflected wave has decreased, and the storage means stores the numerical information of the surface depth and the bottom depth for all observation points. The report associates the latitude and longitude information to create and store sludge distribution information consisting of 3D point cloud data, the supply means comprises a water pumping means and a nanobubble generating means, and is installed at a desired location in the water area to be purified based on the sludge distribution information, the pumping means pumps up water from the water area to be purified and returns it as nanobubble dissolved water, the generating means generates nanobubbles with a diameter of less than 1 μm from oxygen concentrated by an oxygen concentrator or generated from the atmosphere, dissolves the nanobubbles in the pumped water, and the supply height adjustment means adjusts the pumping means The depth at which the nanobubble-dissolved water is recirculated is adjusted to a depth that does not stir up the sludge layer, based on the surface depth at the location, so that the nanobubbles are supplied to the sludge layer by utilizing their sinking behavior in water, the depth estimation means further repeatedly observes the bottom depth and surface depth of the sludge layer at each observation point during the nanobubble supply period, the sludge distribution information creation means creates and stores the sludge distribution information associated with the observation date and time information, and the surface silica sand layer confirmation means uses the sludge distribution information to check the ultrasonic waveform of the previous observation date and time,By comparing the ultrasonic waveform of a later observation date with that of the earlier observation date, if a second phenomenon is confirmed in the ultrasonic waveform of the later observation date, where a third increasing point is observed after two increasing and decreasing points, within the depth range from the point of increasing surface reflection waves from the sludge layer to the point of decreasing surface reflection waves, then the depth at the first observed increasing point in the ultrasonic waveform of the later observation date is stored in the storage means as the surface depth of the surface silica sand layer, the depth at the second increasing point as the surface depth of the sludge layer, and the depth at the third increasing point as the bottom depth of the sludge layer. This allows for the confirmation of the presence or absence of the surface silica sand layer and the thickness of the layered surface silica sand layer based on the surface depths of the surface silica sand layer and the sludge layer.

[0037] According to the fourth invention, the surface silica sand layer confirmation means allows confirmation, based on the observed change in ultrasonic waveform, that a surface silica sand layer has appeared above the sludge layer due to the progress of sludge purification. When a surface silica sand layer is formed, the ultrasonic waveform, which previously showed two types of waves (surface reflected waves and bottom reflected waves), will now show three types of waves: a silica sand surface reflected wave from the surface silica sand layer, and surface and bottom reflected waves from the sludge layer (three points of gradual increase are confirmed). When this second phenomenon is observed, it can be said that a surface silica sand layer has appeared. The confirmation of the surface silica sand layer is described in detail in Example 1 and Figures 10 and 11. This makes it possible to more reliably grasp the progress of sludge purification.

[0038] The fifth invention of the present invention is a sludge purification system of the first to fourth inventions, wherein the moving means is a small unmanned vessel that automatically navigates along a route that follows a plurality of observation points whose latitudes and longitudes are set in advance, and the small unmanned vessel is equipped with at least the transmitter / receiver and the latitude / longitude identification means and is movable independently of the supply means, and the processing means also functions as an automatic navigation control means and a transmission control means for the transmitter / receiver, and the storage The means stores the latitude and longitude information of the observation points, and the route information, which includes a first navigation route and a second navigation route. The first navigation route is a route that sequentially follows a group of first observation points set at latitude and longitude locations dispersed throughout the entire area to be purified, and the second navigation route is a route that sequentially follows a group of second observation points set at latitude and longitude locations that complement adjacent first observation points. The automatic navigation control means first follows the first navigation route. The unmanned vessel is made to navigate automatically, and the transmission control means acquires the latitude and longitude information from the latitude and longitude identification means, and when the small unmanned vessel reaches each of the first observation points, the transmitter / receiver transmits the ultrasonic waves toward the sludge layer to observe the surface depth and bottom depth of the sludge layer, and when the observation along the first navigation path is completed, the automatic navigation control means further makes the small unmanned vessel navigate automatically to follow the second navigation path, and the transmission control The means is characterized by acquiring the latitude and longitude information from the latitude and longitude identification means, and when the small unmanned vessel reaches each of the second observation points, transmitting the ultrasonic waves from the transmitter / receiver toward the sludge layer to observe the surface depth and bottom depth of the sludge layer, and the sludge distribution information creation means creating the sludge distribution information by supplementing the 3D point cloud data observed along the first navigation path with the 3D point cloud data observed along the second navigation path.

[0039] According to the fifth invention, a small unmanned vessel that automatically navigates along a predetermined route is equipped with an ultrasonic transmitter / receiver and a means for determining latitude and longitude. A processing means that constitutes a means for creating sludge distribution information detects from the acquired latitude and longitude information that the small unmanned vessel has reached an observation point, and controls the transmitter / receiver to transmit and receive ultrasonic waves to observe the sludge and autonomously create sludge distribution information. Furthermore, after observations are completed along a first navigation route that follows a group of first observation points, the accuracy of the observation results can be improved by performing observations along a second navigation route that follows a group of second observation points located in positions that complement the first group of observation points.

[0040] This significantly reduces the workload for observers, even when regularly monitoring the distribution of the sludge layer, and provides an easy-to-operate sludge purification system. Furthermore, since the small unmanned vessel is separate and independent from the nanobubble supply system and is portable, a single small unmanned vessel can be used for observations in different water areas to be purified, and parts of the system can be shared.

[0041] The sixth invention of this invention is a sludge purification system according to the first to fourth inventions, characterized in that the nanobubble supply capacity per unit of the supply means is capable of dissolving 200 million or more nanobubbles per 1 mL of water, and the dissolved oxygen content can be increased by 1.5 mg / L or more compared to the raw water.

[0042] According to the sixth invention, the nanobubble supply capacity of a single supply means is 200 million or more per 1 mL (milliliter), and the dissolved oxygen content (DO value) can be increased by 1.5 mg / L or more compared to the raw water. A nanobubble supply capacity of 600 million or more per mL is more preferable. This makes it possible to supply nanobubble-dissolved water with a high DO value, thereby improving the purification efficiency of the sludge layer.

[0043] The seventh invention of the present invention is a sludge purification method for purifying a sludge layer accumulated on the bottom of a body of water by supplying nanobubbles to the water by sinking, comprising a sludge distribution information creation step, a supply point determination step, a supply depth adjustment step, and a nanobubble supply step, wherein in the sludge distribution information creation step, ultrasonic waves of a frequency reflected from the surface and bottom of the sludge layer are emitted and received at observation points dispersed throughout the water body to be purified, the surface depth and bottom depth of the sludge are estimated, the estimated surface depth and bottom depth are associated with the latitude and longitude information of each observation point and stored to create sludge distribution information consisting of 3D point cloud data, and in the supply point determination step, the created sludge distribution information is supplied to the water body to be purified The system is characterized by mapping the estimated shape of the sludge layer in the water area to be purified to the longitude and latitude information in the map information and rendering it as 3D map information, thereby visualizing the area including observation points with relatively large amounts of sludge accumulation for use in selecting nanobubble supply points, determining supply points for supplying nanobubble-dissolved water based on the 3D map information, adjusting the depth at which the nanobubble-dissolved water is recirculated in the supply depth adjustment step, with the nanobubble supply means installed at the supply point, to a depth that does not stir up the sludge layer based on the surface depth at the supply point, and supplying the nanobubble-dissolved water from the supply means towards the sludge layer by sinking during the supply step.

[0044] According to the seventh invention, similar to the first invention, by supplying nanobubble-dissolved water into the water without stirring up the sludge layer, it is possible to purify only the sludge layer without adversely affecting the ecosystem. Furthermore, a sludge purification plan can be developed to suit the different sludge layer accumulation conditions for each water body to be purified. Each step can be carried out using the means described in claim 1 and subsequent claims. [Effects of the Invention]

[0045] According to the first aspect of the present invention, it is possible to provide a sludge purification system that is easy to apply to rivers, lakes, and other bodies of water where dredging is difficult, thus offering a unique advantage over conventional systems. Furthermore, it is easy to consider the locations for installing nanobubble supply means when formulating a purification plan that is suitable for the specific sludge distribution conditions of each target water body. In addition, since the amount of change in sludge thickness over time can be calculated through periodic observation, it is possible for local governments to easily grasp the progress of purification and accurately evaluate the purification plan, thus offering a unique advantage over conventional systems. According to the second invention of this invention, even in rivers and brackish lakes that are susceptible to the effects of water flow, it is possible to target and supply nanobubbles to the sludge layer accumulated at a predetermined location, resulting in a highly versatile effect. According to the third invention of this invention, it is possible to show the weight and volume of sludge purification in a way that is easy to compare with dredging work, and in evaluating the purification plan, it is possible to provide evidence that is suitable not only for deciding whether or not to continue the purification work, but also for local governments to formulate new or additional purification plans, thus providing advantageous effects not found in conventional technology.

[0046] According to the fourth invention of this invention, it becomes possible to more reliably grasp the progress of sludge purification. According to the fifth invention of this invention, even when the distribution of the sludge layer is observed periodically, the work of observers can be significantly reduced, and an easy-to-operate sludge purification system can be provided. Furthermore, since the small unmanned vessel is separated and independent from the nanobubble supply means and is portable, even a single small unmanned vessel can perform observations in different water areas to be purified, and a part of the system can be shared. In addition, the accuracy of the observation results can be improved by performing observations along a second navigation route that follows a second group of observation points located in positions that complement the first group of observation points. According to the sixth invention of this invention, nanobubble-dissolved water with a high DO value can be supplied, thereby improving the purification efficiency of the sludge layer. According to the seventh invention of this invention, similar to the first invention, it is possible to purify only the sludge layer without adversely affecting the ecosystem. [Brief explanation of the drawing]

[0047] [Figure 1] Overall diagram of the sludge purification system (Example 1). [Figure 2] Diagram illustrating the configuration of the sludge purification system (Example 1). [Figure 3] Diagram of the sludge layer purification process (Example 1). [Figure 4] Detailed process diagram for observing the sludge layer (Example 1). [Figure 5] Diagram illustrating the setting of observation points and navigation routes (Example 1). [Figure 6] Diagram illustrating the observation of surface depth and bottom depth (Example 1). [Figure 7] Point cloud data constituting sludge distribution information (Example 1). [Figure 8] 3D map information created from sludge distribution information (Example 1). [Figure 9] Diagram illustrating the supply height adjustment mechanism (Example 1). [Figure 10] Diagram illustrating the sludge purification process (Example 1). [Figure 11] Diagram illustrating the changes in reflected waves associated with sludge purification (Example 1). [Figure 12] Results of the sludge layer purification test (Example 1). [Figure 13] A specific example of a sludge purification system when floats are installed (Example 2). [Modes for carrying out the invention]

[0048] The sludge purification system for cleaning the sludge layer is equipped with an ultrasonic transmitter / receiver, a means for estimating the depth of the sludge layer, a means for supplying nanobubbles, and a means for adjusting the supply height. Surface reflected waves from at least the surface of the sludge layer are observed by the ultrasonic transmitter / receiver, and the surface depth is estimated by the depth estimation means. The height (depth) at which the nanobubble-dissolved water is circulated by the supply means is adjusted by the supply height adjustment means to a depth that does not stir up the sludge layer. Since the nanobubbles are supplied to the sludge layer by sinking using the sinking behavior in water, the sludge is not stirred up, and the sludge layer can be purified without adverse effects on the ecosystem such as suffocation of aquatic organisms. [Examples]

[0049] In Example 1, a sludge purification system 1 that purifies the sludge layer by releasing nanobubbles with a higher oxygen concentration than air into water will be described with reference to Figures 1 to 12. Figure 1 shows an overall diagram of the sludge purification system, and Figure 2 shows a block diagram illustrating the configuration of the sludge purification system. Figure 3 shows a diagram of the sludge layer purification process, and Figure 4 shows a detailed process diagram related to the observation of the sludge layer.

[0050] Figure 5 shows an explanatory diagram regarding the setting of observation points and navigation routes, and Figure 6 shows an explanatory diagram regarding the observation of the surface depth and bottom depth of the sludge layer. Figure 7 shows a graph of the 3D point cloud data that constitutes the sludge distribution information. Figure 8 shows 3D map information created from the sludge distribution information. Figure 9 shows a specific example of a supply height adjustment means. Figure 10 shows an explanatory diagram of the sludge purification process, and Figure 11 shows an explanatory diagram of the change in reflected waves accompanying purification. Figure 12 shows the results of the sludge layer purification test.

[0051] The sludge purification system 1 is broadly composed of a sludge layer observation device 100 and a purification device 200 (see Figures 1 and 2). The observation device 100 is a small unmanned vessel 110 (see Figure 1(A)) used as a means of transport. The small unmanned vessel 110 is equipped with an ultrasonic transmitter / receiver 120, a latitude and longitude identification means 130, a processing means 140, a storage means 150, and a battery 160. Alternatively, the small unmanned vessel may be equipped with a communication means 170 to transmit observation data to an external device (such as a general-purpose computer).

[0052] First, let's describe the outline of the small unmanned vessel 110. The small unmanned vessel is equipped with a propulsion screw 111 at least at the rear end of the hull, and side floats 112 on the left and right sides of the hull, with the side floats and the hull connected by a shaft. The dimensions of the small unmanned vessel are approximately 140 cm in length, approximately 90 cm in width, and approximately 85 cm in height from the bottom of the hull to the top of the satellite receiving antenna 131 which constitutes the latitude and longitude determination means 130, and it weighs approximately 25 kg. Therefore, the hull is small and has a shallow draft, making it applicable to shallow artificial ponds and the like.

[0053] The transmitter / receiver 120 is mounted on the bottom of the hull of a small unmanned vessel. Specifically, it is the transmitter / receiver disclosed in Patent Document 3, and one transmitter / receiver can emit ultrasonic waves of one frequency to observe surface and bottom reflected waves of the sludge layer. The frequency of the ultrasonic waves is not limited as long as it can confirm the phenomenon that part of it is reflected at the surface of the sludge layer (the boundary between water and sludge) and part of it is reflected at the bottom of the sludge layer (the boundary between sludge and seabed silica sand). Ultrasonic waves with a frequency of 25 kHz or less are suitable because they can receive both reflected waves with high accuracy. The ultrasonic wave transmission method emits 20 pulse waves per second, and the reliability of the observation data is improved by acquiring the time-dependent change in the received intensity of the reflected waves.

[0054] The latitude and longitude determination means 130 is a well-known satellite receiving antenna 131, with a total of four antennas provided: one at the front and rear ends of the top surface of the fuselage, and one each on the top surface of the side floats. In Japan, the latitude and longitude determination means can acquire latitude, longitude, and date / time information of the observation point with high accuracy by communicating with the Quasi-Zenith Satellite System 1000, which consists of six or more artificial satellites (see Figure 1(B)). In areas where the Quasi-Zenith Satellite System is not available, the latitude and longitude information of the observation point can be acquired by communicating with a well-known GPS satellite system that uses four artificial satellites.

[0055] The processing means 140 and the storage means 150 are housed together with the battery 160 in the internal space of the hull of the small unmanned vessel 110 (see Figure 1(A)). The processing means 140 may be a well-known central processing unit (CPU) or PLC (programmable logic controller) of a general-purpose computer. The storage means 150 may be a well-known storage device such as an HDD, SSD, or USB memory. A communication means 170 for communication with an external device may be provided to allow the external device to acquire the observation data stored in the storage device. The communication means may be wireless communication or wired communication using a USB cable or the like.

[0056] The processing means 140 functions as an automatic navigation control means 141 for the small unmanned vessel, an ultrasonic transmission control means 142 for the transmitter / receiver, a sludge layer depth estimation means 143, and a sludge distribution information creation means 144 (see upper part of Figure 2). Here, it also functions as a drawing means 145 for drawing 3D map information from the sludge distribution information, and a purification amount estimation means 146 for estimating the amount of sludge purification. Note that each function of the processing means may be operated independently by the processing means 150 installed on the small unmanned vessel, or it may be operated in cooperation with a second processing means that constitutes an external device.

[0057] The automatic navigation control means 141 first reads navigation information 151 concerning the water area to be purified, which is pre-stored in the memory means 150. The navigation information includes observation point information 152 and route information 153 concerning the order in which to visit each observation point. The automatic navigation control means 141 drives and controls the propeller 111 (see Figure 1(A)) and automatically navigates the small unmanned vessel 110 from its current location toward the next observation point to be reached, based on the latitude and longitude information acquired by the latitude and longitude identification means 130.

[0058] When the transmission control means 142 confirms that the small unmanned vessel has reached the observation point based on the latitude and longitude information acquired by the latitude and longitude identification means 130, it transmits ultrasonic waves from the transmitter / receiver 120 and observes the reflected waves. The depth estimation means 143 estimates the surface depth and bottom depth of the sludge layer based on the observation data of these reflected waves. The detailed principle of depth estimation has already been disclosed in Patent Document 3, so in this embodiment it will be briefly described along with the explanation in Figure 6.

[0059] The sludge distribution information creation means 144 associates the detailed latitude and longitude information and date / time information obtained by the latitude and longitude identification means 130 with the estimated surface depth and bottom depth to create 3D point cloud data for that observation point. From the difference between the surface depth and bottom depth, which is information in the Z-axis direction (elevation direction) that constitutes this 3D point cloud data, the thickness of the sludge layer can be estimated regardless of seasonal variations in water depth. By repeating this at all observation points, sludge distribution information 154 showing the sludge deposition situation in the entire water area to be purified is created.

[0060] The created sludge distribution information 154 can be sequentially stored in the storage means 150 by associating it with at least the depth information 155 and the latitude / longitude information 156, but it is preferable to also associate and store the date and time information 157 of the observation time. In this case, when the sludge layer is observed again after a period of time has passed, the temporal changes of the sludge layer can be estimated from the difference value of the 3D point cloud data. For example, if the difference value between the surface depth and the bottom depth at the same observation point has decreased, it can be proven that the volume of the sludge layer is decreasing, i.e., that purification is progressing.

[0061] The purification amount estimation means 146 estimates the volume or weight of the purified sludge layer based on the temporal changes in the sludge layer throughout the entire water area to be purified. This purification amount information 158 may be stored in the storage means 150 as sludge distribution information, or in a second storage means that constitutes an external device. This makes it easier to evaluate not only local changes in the sludge layer, but also the specific extent to which sludge is purified and how much of the water and silica sand components are separated in the water area to be purified. In the case of volume estimation, the volume reduction of the sludge layer can be calculated and estimated using a 3D map information creation application that smooths well-known 3D point cloud data. In the case of weight estimation, it may be simply estimated from the average specific gravity of the sludge and the volume reduction, but since the composition of the sludge differs depending on the water area to be purified, a sample of the sludge may be collected and analyzed, and a detailed estimation may be made using the specific gravity according to the environmental conditions.

[0062] Now, the purification device 200 that constitutes the sludge purification system 1 will be explained with reference to Figure 1(C) and the lower part of Figure 2. The purification device 200 is equipped with a nanobubble supply means 210 and a supply height adjustment means 220. The supply means 210 consists of a pumping means 230, a nanobubble generation means 240, and a high-concentration oxygen supply means 250, and is equipped with an AC power supply 260 to operate them. The pumping means 230 can be a well-known submersible pump 231 and a supply pipe 232. The submersible pump 231 continuously sends raw water obtained from the water area to be purified to the generation means 240, the generation means 240 generates nanobubbles in the raw water to produce nanobubble-dissolved water, the nanobubble-dissolved water is pumped through the supply pipe 232 and the nanobubble-dissolved water is returned to the water area 300 to be purified from the outlet 233 of the supply pipe (see Figure 1(C)).

[0063] If the submersible pump 231 is to be installed in shallow water up to a depth of approximately 1 m, a pumping capacity of 80 L / min (liters / minute) is sufficient (see Figure 1(C)). If it is to be installed at a depth greater than 1 m, a submersible pump with a higher pumping capacity should be used. The submersible pump 231, which is immersed in water, is surrounded by a cage 235 with a filter 234 to prevent algae and other debris from clogging the intake. A float 236 is provided on the outer surface of the cage to reduce the weight of the submersible pump 231 on the support wire 221, which will be described later. The supply pipe 232 only needs to be long enough to supply the nanobubble-dissolved water generated in the water by the generating means 240 to the desired depth, and the material is not limited. For example, polyvinyl chloride pipes connected with fittings are preferable because they do not rust and are less prone to sagging. The diameter of the supply pipe is wider at the outlet 233 at the tip compared to the rest of the pipe, in order to slow down the discharge rate of the nanobubble-dissolved water.

[0064] The generating means 240 can be any well-known nanobubble generating device corresponding to the nanobubble generation method, and may be an ejector type, a micropore type, or any other. Here, an ejector nozzle 241 is provided. The supply performance of the nanobubble generating device should be such that, when using high-concentration oxygen, the DO value (dissolved oxygen amount) of the generated nanobubble dissolved water is improved by 1.5 mg / L (milligrams / liter) or more compared to the DO value of the raw water. As such an ejector type generating means, the nanobubble generating device disclosed in Japanese Patent Publication No. 7573921 is suitable.

[0065] As will be described in detail in the nanobubble generation test and sludge purification test described later, the ejector-type nanobubble generator disclosed in the aforementioned patent publication was able to improve the DO value of tap water from approximately 9.43 mg / L of raw water to approximately 15.0 mg / L. According to the information disclosed in Patent No. 7573921, it is said that the device has the supply capacity to dissolve nanobubbles smaller than 100 nm at a rate of approximately 200 million (bubbles / mL) per milliliter, and approximately 640 million nanobubbles / mL if the nanobubbles are smaller than 1000 nm. In addition, even with the well-known micropore type, the DO value improved from approximately 9.43 mg / L of raw water to approximately 11.3 mg / L, and in all cases, the effect of sludge purification was demonstrated.

[0066] The high-concentration oxygen supply means 250 consists of an air compressor 251, an oxygen concentrator 252, and a control panel 253 for these. For example, the well-known PSA method (pressure swing adsorption method) is acceptable. Briefly explaining the PSA method, the air compressor 251 takes in air, compresses it, and pumps it to the oxygen concentrator 252. Then, nitrogen is removed by a nitrogen adsorbent stored in the oxygen concentrator 252, and oxygen is concentrated. It is preferable to concentrate the oxygen to a high concentration of approximately 80% to 90% beforehand and then supply it to the generating means 240 through the gas supply pipe 254 (see Figure 1(C)) that constitutes the oxygen concentrator 252 to generate nanobubble dissolved water, as this easily enhances the activation effect of aerobic bacteria contained in the sludge layer. The AC power source can be commercial power or a generator, and is not limited. The installation depth of the submersible pump 231 is not limited, but if the installation depth is greater, it is advisable to select a submersible pump with high pumping capacity.

[0067] The supply height adjustment means (structure) 220 here consists of a support pile and a support wire (see Figure 1(C)). The support pile is installed on land so that the support wire is stretched directly above the nanobubble supply point, which is determined based on the sludge distribution information. The supply pipe described above is then suspended and fixed to the support wire. By adjusting the height at which the support wire is stretched by locking it to the support pile, the structure allows for adjustment of the height position of the supply pipe in conjunction with the support wire.

[0068] At this time, taking into consideration the length of the leading end 237 of the supply pipe, the observed surface depth of the sludge layer, and the height from the support wire 221 to the water surface, the height at which the support wire 221 is secured to the support pile 222 is raised or lowered, and the installation depth of the discharge port 233 of the supply pipe, which is immersed in water, is set to a depth at which the sludge layer will not be stirred up even when nanobubble-dissolved water is recirculated. The depth at which the sludge layer will not be stirred up is not uniquely limited, as it also depends on the pumping capacity of the submersible pump. Details will be described later with reference to Figure 9.

[0069] If the supply height is adjusted using the support wire 222, the relative distance between the sludge layer surface and the outlet 233 of the supply pipe remains unchanged even if the water level of the water body 300 to be purified fluctuates seasonally, eliminating the need for periodic height adjustment of the support wire. Furthermore, if the installation depth of the outlet 233 of the supply pipe is set so that it does not enter the surface layer of the water body to be purified, the influence of convection is reduced, making it less likely for the phenomenon of nanobubble sinking to be hindered. This point will also be discussed later with reference to Figure 9.

[0070] Here, the overall process of the sludge purification process will be briefly explained with reference to Figure 3, and the details of each process will be explained sequentially with reference to Figures 4 to 9. Figure 4 shows the detailed steps S100 to S180 included in S10. Figure 5 shows the process of setting the information necessary for the automatic navigation of the small unmanned vessel corresponding to S100 and S110. In Figures 5 and below, the planar shape of the water area 300 to be purified is shown as a roughly rectangular shape for ease of understanding, but it is of course not limited to this.

[0071] Figure 6 shows the process of estimating the surface depth and bottom depth of the sludge layer by transmitting and receiving ultrasonic waves from transmitters and receivers corresponding to S140 and S150. Figure 7 shows a specific example of sludge distribution information created based on the observed information. Figure 8 shows the process of determining the nanobubble supply point corresponding to S20. Figure 9 shows the process of adjusting the nanobubble supply depth corresponding to S30.

[0072] The sludge purification process includes, in order, a process for creating sludge distribution information (S10), a process for determining nanobubble supply points derived from the sludge distribution information (S20), a process for adjusting the nanobubble supply depth using a supply height adjustment means (S30), and a process for supplying nanobubbles to purify the sludge layer by installing the purification device in the target water area (S40). A purification amount estimation process (S50) for estimating the amount of sludge purification may be included as a process after S40.

[0073] In the process of creating sludge distribution information (S10), first, observation point information for transmitting and receiving ultrasound within the water area to be purified is set (S100). More specifically, a general-purpose computer or the like, separate from the observation device, is used to create map information of the water area to be purified, with latitude and longitude information associated with the actual water area to be purified 300 (see Figure 5(A)). The map information may be created from satellite images or from survey map information based on survey control points 301 (see the black square in Figure 5(A)), and the method of creation is not limited.

[0074] Next, multiple observation points 400 are set on the map information of the water area 300 to be purified (see black circles in Figure 5(B)). Here, assuming that sludge purification is carried out in Japan, the positive X-axis is set to east longitude and the positive Y-axis is set to north latitude on the diagram. Then, the setting of observation point information is completed by storing the information regarding the setting of observation points in the memory means of the observation device (S100). In the route information setting process (S110), the navigation route of the small unmanned vessel is set (see Figure 5(C)). Specifically, the order in which the observation points will be visited is created on a general-purpose computer.

[0075] Observations of the sludge layer may be made multiple times by changing the observation point and navigation route. If a series of observations is performed two or more times, more accurate sludge distribution information can be created (see Figures 5(C) and (D)). For example, in the first navigation route 410, a navigation route is set from the observation point 401 at the southwestern end of the water area to be purified to the observation point 402 at the northwestern end. In detail, the navigation route is set to proceed in the positive Y-axis direction (north direction) from the observation point 401 at the southwestern end. When the observation point 403 at the northern end on the same longitude is reached, the navigation route is set to proceed towards the adjacent observation point 404 in the positive X-axis direction (east direction) (Figure 5(C)).

[0076] Next, the navigation path is set to proceed in the negative Y-axis direction (south). When the southernmost observation point 405 is reached on the same longitude, the navigation path is set to proceed towards the adjacent third observation point 406 in the positive X-axis direction (east). This is repeated, setting the navigation path so that it meanders through each observation point and reaches the last observation point at the northeastern end. This completes the setting of the first navigation path. If the setting of only the first navigation path is to be completed, the path information setting process (S110) is completed here.

[0077] The second navigation route 420 is set up to complement the group of first observation points 400 that constitute the first navigation route by changing at least one of the observation points or the navigation route from the first navigation route (see Figure 5(D)). The group of second observation points 421 that constitute the second navigation route may be set up by changing only a part of the first observation points 400. The setting procedure is the same as for the first navigation route and will therefore be omitted. By conducting multiple observations with different observation points and navigation routes, it becomes possible to create 3D information that more closely approximates the sludge deposition situation in the area to be cleaned when smoothing the 3D point cloud data to create sludge distribution information (see the smoothed surface depth and bottom depth lines in Figure 7).

[0078] From S120 onward, a small unmanned vessel is transported to the area to be purified, and observations begin there. In S120, the latitude and longitude information and date / time information of the small unmanned vessel's position are continuously acquired by communication with the Quasi-Zenith Satellite System or GPS using a latitude and longitude identification means. In S130, the small unmanned vessel begins automatic navigation based on the observation point information and route information stored in the memory means in S100 and S110. In S140, when the latitude and longitude information acquired by the small unmanned vessel roughly matches the initial observation point, the transmitter / receiver emits and receives ultrasonic waves.

[0079] In S150, the surface depth and bottom depth of the sludge layer 510 are estimated. Here, the depth estimation will be briefly explained with reference to Figure 6, but for details, please refer to Patent Document 3 disclosed by the present applicant. Ultrasonic waves generated from the transmitter / receiver 120 located at the water surface 500 (see the downward arrow in Figure 6(A)) are partially reflected as surface reflected waves α at the sludge layer surface 511 (the interface between the water 501 and the sludge layer 510). Furthermore, a portion of the ultrasonic waves that penetrate the sludge layer (see the downward white arrow in Figure 6(A)) is reflected as bottom reflected waves β at the bottom surface 512 of the sludge layer (the interface between the sludge layer 510 and the sandy layer 520 below it).

[0080] The transmitter / receiver 120 estimates the surface depth Z1 from the water surface to the sludge layer surface from the timing when it begins to observe the surface reflected wave α after transmitting ultrasound (the starting point of the gradual increase in α in Figure 6(B)). Furthermore, when the phenomenon of the reflected wave intensity starting to increase again is observed after the surface reflected wave α has begun to attenuate, the bottom depth Z2 is estimated using the starting point when it begins to observe the bottom reflected wave β (the starting point of the gradual increase in β in the same figure). Note that when the intensity of the reflected wave increases at a depth of 1.0 m or less (see the dashed line in the same figure), it is excluded from the sludge depth estimation as it is assumed that the ultrasound was reflected by aquatic organisms or algae.

[0081] The sludge thickness t1 can be estimated from the difference in depth between Z1 and Z2. In S160, observation data is created by associating the estimated surface depth Z1 and bottom depth Z2 with latitude / longitude information and date / time information. This group of observation data constitutes 3D point cloud data as sludge distribution information. In S170, the observation data is stored in a memory device mounted on a small unmanned vessel. In S180, the small unmanned vessel moves to the next observation point. Steps S140 to S180 are repeated until the last observation point, creating 3D point cloud data (see Figure 7).

[0082] In step 20 (see Figure 3), the process of determining the nanobubble supply point, the point where the nanobubble-dissolved water described above is returned to the water area to be purified is determined based on the three-dimensional point cloud data (see Figure 7) that constitutes the sludge distribution information. Figure 7(A) shows a graph of the Z-axis direction (depth) fluctuating along the X-axis direction (longitude) at a specific latitude (Y-axis). Figure 7(B) shows a graph of the Z-axis information (depth) fluctuating along the Y-axis information (latitude) at a specific longitude (X-axis).

[0083] In each graph, the surface depth is shown as a line graph obtained by smoothing the point cloud data. For the bottom depth, the observation data before smoothing is shown as circles to make the benefits of smoothing easier to understand, and the bottom depth after smoothing is shown as a smoothed line graph. Here, smoothing refers to using the statistical characteristics of point cloud data from consecutive observation points to remove outlier observation data and correct the estimated surface depth and bottom depth to smoothly continuous values. Of course, the corrected depth estimate may differ from the depth estimate based on the gradual increase in the surface reflection wave α and bottom reflection wave β as described above.

[0084] Furthermore, by smoothing the depth in the X-axis direction and the depth in the Y-axis direction and combining them, it is possible to obtain an estimated shape of a smooth sludge layer throughout the entire water area to be purified. This makes it possible to accurately determine the depth at which nanobubble-dissolved water should be recirculated. For smoothing the point cloud data, well-known noise reduction methods such as statistical methods and moving least squares (MLS) can be used. Since the smoothing process is computationally intensive, the processing means of the observation device may function as a smoothing processing means (device) on its own, but it is preferable to have it function as a smoothing processing means (device) in cooperation with a second processing means, which is an external general-purpose computer.

[0085] Regarding bottom depth, the presence of solid components such as stones in the sludge layer makes it more susceptible to noise (outliers) compared to surface depth. Therefore, unsmoothed 3D point cloud data exhibits large numerical variance due to outliers (see the circles in Figure 7). On the other hand, the bottom depth after smoothing undergoes convergence of numerical variance, resulting in a relatively smooth bottom depth that can be corrected to provide more reliable sludge distribution information. The difference between the surface depth and bottom depth after this smoothing process is used to estimate the sludge thickness, and this is combined with latitude and longitude information to determine the appropriate nanobubble supply location.

[0086] At this time, by plotting 3D map information showing the sludge distribution information on the planar map information of the water area 300 to be purified, it becomes possible to spatially understand the amount of sludge accumulation (see Figure 8). For example, if locations with a large amount of sludge accumulation are indicated by hatching or coloring, it becomes easier to consider where to install the supply points. Here, to make it easier to understand, the hatching density is increased at locations with a large amount of sludge accumulation. From this 3D map information, support wires 221 are stretched to cross or traverse locations with a large amount of sludge accumulation. The plotting of the 3D map information should also be handled by an external device with high processing capacity (second processing means) rather than the processing means of the observation device.

[0087] Step 30, the supply height adjustment process, includes the installation of support piles 222, the tensioning of support wires 221, the suspension of supply pipes 232, and the adjustment of the tensioning height of the support wires (see Figure 9). First, a pair of support piles 222, 222 are driven into the ground on both banks of the water body 300 to be purified, flanking the nanobubble supply point (see Figure 9(A)). The support piles 222 may have a reference line for the burial depth and markings for height adjustment. Then, the support wires 221 are stretched horizontally across the pair of support piles.

[0088] Here, the tension height Z0 of the support wire 221, relative to the water surface 500, is adjusted based on the length L1 of the supply pipe hanging from the support wire and the surface depth Z1 of the sludge layer estimated in advance by the observation device. For example, if the hanging length L1 of the supply pipe is 4m and the surface depth Z1 is 3.5m, the tension height Z0 is adjusted so that it is approximately 1.0m to 2.0m above the water surface, such that the relative distance D1 between the discharge port at the tip of the supply pipe and the surface of the sludge layer is at least approximately 0.5m to 1.5m. These values ​​are just examples and are not limited to them.

[0089] Once the tensioning height of the support wire 221 is tentatively determined, the support wire is tensioned using the tensioner 223 located near the end of the support wire to minimize slack (see Figure 9(C)). Then, at least the supply pipe 232 is suspended and fixed to the tensioned support wire (see Figure 9(B)). The planar position from which the leading end 237 of the supply pipe is suspended is the position determined in step 20. If necessary, the locking device 224 attached to the support pile 222 may be temporarily loosened to fine-tune the height and horizontality of the support wire.

[0090] By adjusting the installation depth of the supply pipe in this way, it is possible to adjust it to a height where the sludge layer is not stirred up even by the release of nanobubble-dissolved water (see Figures 9(B) and 9(C)). The relative distance D1 is preferably within the range described above, but by selecting a submersible pump with low pumping capacity, the relative distance D1 from the surface of the sludge layer can be set to approximately 0.3m, which is less than approximately 0.5m.

[0091] Furthermore, the installation depth of the discharge outlet is preferably such that the relative distance D2 from the water surface is greater than 0.3m in winter and 0.5m in summer, so that the sinking supply of nanobubbles is not obstructed by convection in the surface layer of the water body to be purified. In the case of shallow artificial ponds, etc., with a surface depth of less than 1m, the installation depth of the discharge outlet may be in the surface layer.

[0092] Here, we will briefly explain the tensioner 223 and locking device 224 for the support wire (see Figure 9(C)). The tensioner is a tensioner for horizontal lifelines used in construction work, etc. The locking device 224 can be, for example, a joint fitting for single pipes. The joint fitting for single pipes consists of an eye bolt 226 for locking the hook 225 at the end of the support wire and a ring portion 227 that is inserted into and attached to the support pile 222. By tightening the eye bolt 226 from the side of the support pile, the ring portion 227 is fixed to the support pile, and the locked support wire is also fixed. By loosening the eye bolt 226 and sliding the ring portion 227 along the support pile 222, the support wire can be positioned at any desired height.

[0093] Here, the process of sludge purification using nanobubbles will be explained with reference to Figure 10. When nanobubble-containing water is recirculated to a height that does not stir up the sludge, the nanobubbles gradually sink toward the surface of the sludge layer 510. The nanobubbles, having slowly sunk to a depth adjacent to the sludge layer, diffuse widely along the surface in a cloud-like manner without stirring the sludge layer, and the water adjacent to the sludge layer is replaced by water 502 with a high dissolved oxygen content (DO value) (see Figure 10(A)). These nanobubbles remain adjacent to the sludge layer for a long period of time, inactivating anaerobic bacteria present on the surface of the sludge layer and activating aerobic bacteria to promote the decomposition of organic matter.

[0094] A secondary effect of this invention is that, as anaerobic bacteria are inactivated, the fermentation mode of organic matter in the sludge layer changes from anaerobic fermentation to aerobic fermentation. That is, the methane gas produced by anaerobic fermentation is replaced by the same mole amount of carbon dioxide produced by aerobic fermentation. Since the global warming coefficient (GWP) of methane gas is approximately 33 times that of carbon dioxide, this invention, which can suppress the generation of methane gas, is expected to contribute to mitigating global warming.

[0095] Furthermore, although the organic matter content of the sludge layer 510 is only about 5% to 15% by weight, as the decomposition of the sludge progresses, water components trapped in the sludge layer diffuse into the water area 300 to be purified, causing the sludge layer to decrease significantly in volume (see sludge thickness t1 and sludge thickness t2 after volume reduction in Figure 10(B)). As purification progresses further, the silica sand separated from the sludge becomes layered on top of the sludge layer (see sludge thickness t3 after volume reduction and surface silica sand layer thickness t4 in Figure 10(C)). When this surface silica sand layer 530 becomes clearly visible, changes begin to occur in the reflected ultrasonic waves. Therefore, by also using the treatment means as a surface silica sand layer confirmation means (device) and observing the changes in ultrasonic waves, the progress of sludge purification can be reliably evaluated and proven. Here again, the treatment means may function as a standalone unit mounted on the observation device, or it may be linked with external equipment.

[0096] Here, the ultrasonic waves observed on the surface silica sand layer 530 will be explained with reference to Figure 11. When the surface silica sand layer is stacked, the ultrasonic waves emitted from the ultrasonic transmitter / receiver 120 are partially reflected by the surface of the surface silica sand layer 530 and observed as a silica sand surface reflected wave P, while the remaining portion penetrates into the surface silica sand layer. The ultrasonic waves that penetrate into the surface silica sand layer are observed as a surface reflected wave α and a bottom reflected wave β, similar to the case when the sludge layer 510 is exposed (Figure 11(A)). Since these three types of reflected waves are observed with a time difference, even with a single transmitter / receiver emitting ultrasonic waves of a single frequency, it is possible to estimate the silica sand surface depth Z4 (newly observed), the surface depth Z3 of the sludge layer after volume reduction (change from Z1 to Z3), and the bottom depth Z2 of the sludge layer (unchanged).

[0097] Since the received ultrasonic wave intensity increases with each observation of the silica sand surface reflection wave P, surface reflection wave α, and bottom reflection wave β, depths Z4, Z3, and Z2 can be estimated from the time difference when the starting point of the gradual increase in the received wave intensity of each reflection wave is observed. The presence or absence of the silica sand surface reflection wave P can be determined by comparing the ultrasonic waveform at the previous observation date and time (for example, the start date of sludge purification) (Figure 6(B)) with the ultrasonic waveform at a second observation date and time after a predetermined period has elapsed (Figure 11(B)).

[0098] Specifically, in the range from the surface reflection wave α to the bottom reflection wave β observed at the previously observed time (range from Z1 to Z2), a second phenomenon is confirmed in which the ultrasonic waveform consists of three types of reflected waves, including three increasing points (Z4, Z3, Z2) and two decreasing points (the decreasing points of the silica sand surface reflection wave P and the surface reflection wave α). When this second phenomenon is observed, the purification of the sludge layer can be reliably confirmed. When the second phenomenon is observed, it is assumed that purification has progressed sufficiently at that location, and it is advisable to move the nanobubble supply point to a location with a different latitude and longitude within the target water area 300.

[0099] (Purification Test 1) Here, the results of the purification test 1 conducted in a lake in Aichi Prefecture, Japan, will be explained with reference to Figure 12. Figure 12(A) shows the change in ignition loss % over time at point A, where the amount of sludge accumulation was large, and at point B, located approximately 50 m away from point A. Figure 12(B) shows the change in surface depth over time at point B and its vicinity. Ignition loss % here refers to the estimated organic matter content from the mass % lost by combustion after burning the residue remaining after removing water from the sludge.

[0100] The test period was from March 28, 2025 to June 30, 2025, and the nanobubble supply period was 88 days, from April 4, 2025 to June 30, 2025. The change in ignition loss % over time was compared using sludge collected on May 19, 2025 and sludge collected on June 30, 2025. Therefore, data for the change in surface depth over time was also extracted from May 19, 2025 to June 30, 2025, to ensure the same period. With the cooperation of the lake administrator, a restricted area was established, an intrusion prevention fence was installed within the restricted area, and the purification device was installed inside the intrusion prevention fence. In addition, roofs and privacy walls were installed to protect against wind and rain, ensuring that the test was conducted in a completely confidential environment.

[0101] In this purification test 1, a well-known micropore type nanobubble generator was used. Furthermore, the ejector type nanobubble generator, described above as suitable as a generation method for the present invention, was confirmed to have higher purification capacity than the nanobubble generator used in purification test 1 in purification test 2, which will be described later. Therefore, a detailed description of the micropore type nanobubble generator's configuration is omitted due to its complexity.

[0102] At location A, near the nanobubble supply point, the ignition loss percentage decreased from 12% to 8.6%, confirming that the decomposition of organic matter in the sludge was progressing (see Figure 12(A)). Even at location B, approximately 50m away from location A, the ignition loss percentage decreased from 10.7% to 7.7%, confirming that the nanobubbles were spreading over a wide area and sludge purification was progressing. Furthermore, according to the graph of the change in surface depth over time (see Figure 12(B)), a reduction in sludge volume of approximately 10cm to 12cm was confirmed over approximately 40 days from May 19 to June 30 of the same year. Although not shown in the figure, a reduction in sludge volume of several centimeters was confirmed within a 100m x 100m area.

[0103] Due to the enormous amount of data, the diagram is omitted, but as a result of supplying nanobubbles over an 88-day period from April 4th to June 30th, a reduction in the volume of the sludge layer was confirmed to be approximately 30 cm over a wide area of ​​50 m x 50 m, and approximately 7.6 cm over a 100 m x 100 m area. Calculating the sludge volume reduction from the difference in 3D point cloud data yielded approximately 700 m 3 This was the case. When converting to weight, it is preferable to collect sludge and perform a component analysis. Assuming that the ignition loss is approximately 11% by weight, water is approximately 67% by weight, and silica sand is approximately 12% by weight, the weight of the sludge is approximately 1.24 tons per cubic meter, so the total weight of the purified sludge in purification test 1 is estimated to be approximately 870 tons.

[0104] (Purification Test 2) In purification test 2, a performance comparison test of nanobubble generators was conducted. Test apparatus 1 is a well-known micropore type nanobubble generator used in purification test 1. Test apparatus 2 is a nanobubble generator disclosed in Japanese Patent Publication No. 7573921, which uses an ejector nozzle equipped with a flow straightening means. The test location was a warehouse managed by the applicant. The test method involved setting up two test tanks made of transparent acrylic pipes with a diameter of 50 cm and a height of 120 cm, and pouring in sludge collected from the lake shown in purification test 1 to a thickness of approximately 50 cm.

[0105] Then, in one of the two test tanks, nanobubble-dissolved water generated by test device 1 was added to a depth of approximately 50 cm, and nanobubble-dissolved water generated by test device 2 was added to the other to a depth of approximately 50 cm. After that, a cover sheet was placed on the water surface to prevent the agitation of the sludge. No replacement, additional addition, or agitation of the sludge was performed. The test period was five days, from October 23 to October 28, 2025.

[0106] On October 23, the initial DO values ​​immediately after the generation of nanobubble-dissolved water were 9.43 mg / L for raw water (tap water), 11.3 mg / L for test device 1, and 15.0 mg / L for test device 2. Immediately after adding the nanobubble-dissolved water to the test tank on the same day, the DO values ​​decreased to 10.1 mg / L for test device 1 and to 12.8 mg / L for test device 2.

[0107] Three days later, on October 26th, the sludge layer in the test tank of test apparatus 1 had settled by approximately 0.5 cm, and the sludge layer in the test tank of test apparatus 2 had settled by approximately 2 cm. In both cases, the exposure of silica sand was visually confirmed, but the sludge purification was more pronounced in test apparatus 2. Also on October 26th, water samples were taken from two locations: a first position 10 cm below the water surface and a second position 5 cm above the sludge layer, and the DO values ​​were measured.

[0108] In the test tank of test apparatus 1, the DO value of the water taken at position 1 was 9.57 mg / L, and the DO value of the water taken at position 2 was 8.45 mg / L. On the other hand, in the test tank of test apparatus 2, the DO value of the water taken at position 1 was 11.72 mg / L, and the DO value of the water taken at position 2 was 8.59 mg / L. From these results, it appears that test apparatus 2 maintained a higher DO value at position 1, partly because the initial DO value was higher.

[0109] However, at the second location near the sludge, the DO value decreased significantly in all cases, suggesting that the dissolved oxygen level decreased due to the purification of the sludge. In particular, in the test tank of test apparatus 2, as mentioned above, the surface depth of the sludge layer had decreased by 2 cm, demonstrating that sludge can be purified without stirring or aerating the sludge layer by supplying nanobubble dissolved water with a high DO value.

[0110] Furthermore, on October 28th, five days after the start of the test, turbidity had occurred up to a height of approximately 10 cm from the sludge surface, suggesting that silica sand components and other substances trapped within the sludge were released as the sludge purification progressed. When the DO values ​​were tested, the DO value of the water taken at the first position in the test tank of test apparatus 1 was 9.12 mg / L, and the DO value of the water taken at the second position was 7.08 mg / L. On the other hand, in the test tank of test apparatus 2, the DO value of the water taken at the first position was 11.08 mg / L, and the DO value of the water taken at the second position was 6.75 mg / L.

[0111] The DO value test conducted on this day showed that although the DO value at the first position was lower for test device 1, the DO value at the second position was lower for test device 2. From these test results, it can be inferred that the nanobubble-dissolved water generated by test device 2 reacted more rapidly with the sludge, resulting in faster purification. The results of purification test 2 showed that test device 2 was superior as a nanobubble generator. Based on these results, it can be expected that applying test device 2 to purification test 1 will increase the amount of sludge purified. [Examples]

[0112] In Example 2, a specific example of a sludge purification system 2 suitable for large lakes and marshes will be described with reference to Figure 13. Each figure in Figure 13 shows the state in which the height position for circulating nanobubble-dissolved water has been adjusted to adapt to changes in water volume. The only differences from Example 1 are that the purification device 200 is installed on the float 600, the configuration of the supply height adjustment means 220, and the length of the supply pipe 232, so the rest will not be explained.

[0113] The supply height adjustment means 220 may be a lifting structure in which an operator manually raises and lowers the submersible pump, or it may be an automatically adjustable lifting device. Here, we will describe the case in which the submersible pump 231 itself is raised and lowered using the lifting device 610. The lifting device 610 consists of a main shaft 611 that extends in the vertical direction, a lifting section 612 that can move up and down along the main shaft, and a drive device 613 for the lifting section. For example, it may be a well-known underwater hydraulic cylinder or water pressure cylinder used in marine surveys, or a well-known ball screw mechanism if the drive section is not submerged in water.

[0114] Since the submersible pump body can be raised and lowered by the lifting device, even if the water volume fluctuates with the seasons and the surface depth from the water surface to the sludge surface changes (see Z5 and Z6 in Figure 13), the distance h between the nanobubble dissolved water outlet 233 and the sludge layer 510 surface can be kept constant or at a desired distance. The drive device 613 may be driven by manual operation by an operator, or it may be automatically controlled in cooperation with an observation device according to the amount of change in surface depth observed periodically.

[0115] This allows the nanobubble-dissolved water to be recirculated to a depth that is less affected by water volume fluctuations and does not stir up the sludge layer, even when the purification device 200 is installed on the float 600. The float 600 has the size and buoyancy to accommodate the purification device, and an anchor 601 extending from the float is installed on the seabed to prevent the nanobubble supply point from changing significantly. The supply pipe is shorter than that of Example 1 because it is an integrated structure with the ejector nozzle.

[0116] (others) In this embodiment, for the sake of ease of understanding, we have described an example of operation using one observation device and one purification device, but of course, multiple devices can be used in combination. When installing multiple purification devices, it is advisable to distribute them across the water area to be purified. In this case, it is possible to miniaturize each purification device, making it suitable for shallow artificial ponds and the like. In this embodiment as well, as a technical concept common to both the invention of a product and the invention of a method, the structure of the sludge purification system is described using the word "means," such as processing means, storage means, and pumping means. However, all of these may be replaced with words that indicate a physical object, such as "processing device," "memory device," and "pumping device." • Although the term "means" is used for each function of the processing means, such as "automatic navigation control means," it is also permissible to replace "means" with "device." Regarding the means for adjusting the supply height, the term "means" may be replaced with words that describe an object, such as "structure," "mechanism," or "device." The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The technical scope of the present invention is indicated by the claims, not limited to the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of Symbols]

[0117] 1,2...Sludge purification system, 1000...Quasi-zenith satellite system, 100... Observation equipment, 110...Small unmanned vessel (means of transport), 111...Propeller, 112...Side floats, 120...transmitter / receiver, 130...latitude and longitude determination means, 131...satellite receiving antenna, 140... Processing means, 141... Automatic navigation control means, 142... Transmission control means, 143...Means for estimating depth, 144...Means for creating sludge distribution information, 145... Drawing means, 146... Purification amount estimation means, 150...Memory devices, 151...Navigation information, 152...Observation point information, 153...Path information, 154...Sludge distribution information, 155...Depth information, 156... Latitude and longitude information, 157... Date and time information, 158... Purification amount information, 160...Battery, 170...Communication means, 200...Purification device, 210...Supply means, 220... Supply height adjustment means, 221... Support wire, 222... Support pile, 223...Tensioner, 224...Locking device, 225...Hook 226... Eyebolt, 227... Ring part, 230... Pumping means, 231... Submersible pump, 232... Supply pipe, 233... Discharge port, 234...filter, 235...cage body, 236...float body, 237...front part 240... Generating means, 241... Ejector nozzle, 250... means of supplying high-concentration oxygen, 251... air compressor, 252...Oxygen concentrator, 253...Control panel, 254...Gas supply pipe, 260...AC power supply, 300...Water area to be purified, 301...Survey control point, 400... Observation point, 410... First navigation route, 401... Observation point at the southwestern end, 402... Observation point at the northwestern end, 403...Northernmost observation point, 404...Second row observation point, 405... Observation point at the southern end, 406... Observation point in the third row, 420...Second navigation route, 421...Second observation point, 500...Water surface, 501...Water, 502...Water with high dissolved oxygen concentration 510...Sludge layer, 511...Surface of the sludge layer, 512...Bottom of the sludge layer, 520...Sandy layer, 530...Surface silica sand layer, α...surface reflected wave, β...bottom reflected wave, P...silica sand surface reflected wave, Z1, Z3...surface depth, Z2...bottom depth, Z4...silica sand surface depth, Z0...The tension height of the support wire relative to the water surface. t1...Sludge thickness, t2, t3...Sludge thickness after volume reduction, t4...Thickness of the surface silica sand layer. L1... Hanging length of the supply pipe, D1...Relative distance from the surface of the sludge layer, D2...Relative distance from the water surface. 600...Float, 601...Anchor 610... Lifting device, 611... Main shaft, 612... Lifting section, 613... Drive unit

Claims

1. A sludge purification system that cleanses the sludge layer accumulated at the bottom of the water, It includes an ultrasonic transmitter / receiver, a means for creating sludge distribution information, a means for supplying nanobubbles, and a means for adjusting the supply height. The aforementioned transmitter / receiver is a single transmitter / receiver that transmits and receives ultrasonic waves of a frequency reflected from the surface and bottom surface of the sludge layer. The sludge distribution information creation means comprises a means for moving the transmitter / receiver, a means for identifying latitude and longitude, a processing means, and a storage means. The aforementioned transport means moves at least the transmitter / receiver to observation points dispersed throughout the entire water body to be purified. The latitude and longitude identification means acquires latitude and longitude information for each observation point, The processing means functions as a means for estimating the depth of the sludge layer and a means for drawing it. The depth estimation means estimates the surface depth of the sludge layer from the starting point of the gradual increase of the surface reflected wave received by the transmitter / receiver from the surface, and estimates the bottom depth of the sludge layer from the starting point of the gradual increase of the bottom reflected wave received from the bottom surface after the surface reflected wave has decreased. The storage means associates the latitude and longitude information with the numerical information of the surface depth and the bottom depth at all observation points to create and store sludge distribution information consisting of three-dimensional point cloud data. The drawing means associates the sludge distribution information read from the storage means with the latitude and longitude information in the map information of the water area to be purified, and draws the estimated shape of the sludge layer in the entire water area to be purified as three-dimensional map information, thereby visualizing the area including observation points with relatively large amounts of sludge accumulation, for use in selecting nanobubble supply points. The supply means comprises a water pumping means and a nanobubble generating means, and is installed in the water area to be purified at the supply point selected based on the three-dimensional map information. When the aforementioned pumping means pumps up water from the water area to be purified and returns it as nanobubble dissolved water, The generating means generates nanobubbles with a diameter of less than 1 μm from oxygen concentrated by an oxygen concentrator or from the atmosphere, and dissolves the nanobubbles in the pumped water. The supply height adjustment means adjusts the depth to which the nanobubble dissolved water is recirculated by the pumping means to a depth that does not stir up the sludge layer, based on the surface depth at the supply point. The nanobubbles are supplied to the sludge layer by utilizing their sinking behavior in water. A sludge purification system characterized by the following features.

2. The supply height adjustment means restricts the depth to which the nanobubble-dissolved water is recirculated to a depth of 0.5 m or more below the water surface. The sludge purification system according to feature 1.

3. A sludge purification system that cleanses the sludge layer accumulated at the bottom of the water, It includes an ultrasonic transmitter / receiver, a means for creating sludge distribution information, a means for supplying nanobubbles, and a means for adjusting the supply height. The aforementioned transmitter / receiver is a single transmitter / receiver that transmits and receives ultrasonic waves of a frequency reflected from the surface and bottom surface of the sludge layer. The sludge distribution information creation means comprises a means for moving the transmitter / receiver, a means for identifying latitude and longitude, a processing means, and a storage means. The aforementioned transport means moves at least the transmitter / receiver to observation points dispersed throughout the entire water body to be purified. The latitude and longitude identification means acquires latitude and longitude information for each observation point, The processing means functions as a means for estimating the depth of the sludge layer and a means for estimating the amount of sludge to be purified. The depth estimation means estimates the surface depth of the sludge layer from the starting point of the gradual increase of the surface reflected wave received by the transmitter / receiver from the surface, and estimates the bottom depth of the sludge layer from the starting point of the gradual increase of the bottom reflected wave received from the bottom surface after the surface reflected wave has decreased. The storage means associates the latitude and longitude information with the numerical information of the surface depth and the bottom depth at all observation points to create and store sludge distribution information consisting of three-dimensional point cloud data. The supply means comprises a water pumping means and a nanobubble generating means, and is installed at a desired location in the water area to be purified based on the sludge distribution information. When the aforementioned pumping means pumps up water from the water area to be purified and returns it as nanobubble dissolved water, The generating means generates nanobubbles with a diameter of less than 1 μm from oxygen concentrated by an oxygen concentrator or from the atmosphere, and dissolves the nanobubbles in the pumped water. The supply height adjustment means adjusts the depth to which the nanobubble dissolved water is recirculated by the pumping means to a depth that does not stir up the sludge layer, based on the surface depth at the location. The nanobubbles are supplied to the sludge layer by utilizing their sinking behavior in water. The depth estimation means further causes the bottom depth and surface depth of the sludge layer to be repeatedly observed at each of the observation points during the nanobubble supply period. The sludge distribution information creation means creates and stores the sludge distribution information associated with the observation date and time information. The purification amount estimation means numerically corrects the three-dimensional point cloud data of the sludge distribution information associated with the observation date and time information and the observation point by smoothing the data so that the surface depth and bottom depth of the sludge layer at adjacent observation points become smoothly continuous estimated values. Based on the corrected estimated values, it creates three-dimensional map information showing the estimated shape of the sludge layer. From the difference in the three-dimensional map information for each observation date and time, it identifies the amount of change in sludge thickness over time during the supply period and estimates at least the total weight or total volume of sludge purified in the entire water area to be purified. A sludge purification system characterized by the following features.

4. A sludge purification system that cleanses the sludge layer accumulated at the bottom of the water, It includes an ultrasonic transmitter / receiver, a means for creating sludge distribution information, a means for supplying nanobubbles, and a means for adjusting the supply height. The aforementioned transmitter / receiver is a single transmitter / receiver that transmits and receives ultrasonic waves of a frequency reflected from the surface and bottom surface of the sludge layer. The sludge distribution information creation means comprises a means for moving the transmitter / receiver, a means for identifying latitude and longitude, a processing means, and a storage means. The aforementioned transport means moves at least the transmitter / receiver to observation points dispersed throughout the entire water body to be purified. The latitude and longitude identification means acquires latitude and longitude information for each observation point, The processing means functions as a means for estimating the depth of the sludge layer and as a means for confirming the state in which a surface silica sand layer separated from the sludge layer is stacked above the sludge layer. The depth estimation means estimates the surface depth of the sludge layer from the starting point of the gradual increase of the surface reflected wave received by the transmitter / receiver from the surface, and estimates the bottom depth of the sludge layer from the starting point of the gradual increase of the bottom reflected wave received from the bottom surface after the surface reflected wave has decreased. The storage means associates the latitude and longitude information with the numerical information of the surface depth and the bottom depth at all observation points to create and store sludge distribution information consisting of three-dimensional point cloud data. The supply means comprises a water pumping means and a nanobubble generating means, and is installed at a desired location in the water area to be purified based on the sludge distribution information. When the aforementioned pumping means pumps up water from the water area to be purified and returns it as nanobubble dissolved water, The generating means generates nanobubbles with a diameter of less than 1 μm from oxygen concentrated by an oxygen concentrator or from the atmosphere, and dissolves the nanobubbles in the pumped water. The supply height adjustment means adjusts the depth to which the nanobubble dissolved water is recirculated by the pumping means to a depth that does not stir up the sludge layer, based on the surface depth at the location. The nanobubbles are supplied to the sludge layer by utilizing their sinking behavior in water. The depth estimation means further causes the bottom depth and surface depth of the sludge layer to be repeatedly observed at each of the observation points during the nanobubble supply period. The sludge distribution information creation means creates and stores the sludge distribution information associated with the observation date and time information. The surface silica sand layer confirmation means compares the ultrasonic waveform from an earlier observation date and time with the ultrasonic waveform from a later observation date based on the sludge distribution information. In the depth range from the point of gradual increase of surface reflected waves from the sludge layer at the previously observed date and time, through the point of gradual decrease of the surface reflected waves, to the point of gradual increase of bottom reflected waves from the sludge layer, If, in the ultrasonic waveform observed at a later date and time, a second phenomenon is confirmed in which a third increasing point is observed after passing two increasing and decreasing points, the depth at the first observed increasing point in the ultrasonic waveform at the later date and time is stored in the storage means as the surface depth of the surface silica sand layer, the depth at the second increasing point as the surface depth of the sludge layer, and the depth at the third increasing point as the bottom depth of the sludge layer. From the surface depth of the surface silica sand layer and the surface depth of the sludge layer, it is possible to confirm the presence or absence of the surface silica sand layer and the thickness of the stacked surface silica sand layer. A sludge purification system characterized by the following features.

5. The aforementioned means of transportation is a small unmanned vessel that automatically navigates along a route that follows a set of observation points with predetermined latitudes and longitudes. The small unmanned vessel is equipped with at least the transmitter / receiver and the latitude / longitude identification means, and is movable independently of the supply means. The processing means also functions as an automatic navigation control means and a transmission control means for the transmitter / receiver. The aforementioned storage means stores the latitude and longitude information of the observation point, and the first navigation route and the second navigation route as route information. The first navigation route is defined as a route that sequentially follows a group of first observation points set at points of latitude and longitude dispersed throughout the entire area to be purified. The second navigation route is defined as a path that sequentially follows a group of second observation points set at latitudes and longitudes that complement adjacent first observation points. The automatic navigation control means first causes the small unmanned vessel to automatically navigate along a first navigation path, The transmission control means acquires the latitude and longitude information from the latitude and longitude identification means, and when the small unmanned vessel reaches each of the first observation points, it transmits the ultrasonic waves from the transmitter / receiver toward the sludge layer to observe the surface depth and bottom depth of the sludge layer. When observation along the first navigation path is completed, the automatic navigation control means further causes the small unmanned vessel to automatically navigate along the second navigation path. The transmission control means acquires the latitude and longitude information from the latitude and longitude identification means, and when the small unmanned vessel reaches each of the second observation points, it transmits the ultrasonic waves from the transmitter / receiver toward the sludge layer to observe the surface depth and bottom depth of the sludge layer. The sludge distribution information creation means creates the sludge distribution information by supplementing the three-dimensional point cloud data observed along the first navigation route with the three-dimensional point cloud data observed along the second navigation route. A sludge purification system according to any one of claims 1 to 4, characterized in that it is the same as described in any one of claims 1 to 4.

6. The nanobubble supply capacity per unit of the supply means is capable of dissolving 200 million or more nanobubbles per 1 mL of water, and is capable of increasing the dissolved oxygen content by 1.5 mg / L or more compared to the raw water. A sludge purification system according to any one of claims 1 to 4, characterized in that it is the same as described in any one of claims 1 to 4.

7. A method for purifying sludge by supplying nanobubbles to the water and purifying the sludge layer accumulated at the bottom of the water, This process includes a sludge distribution information creation process, a supply point determination process, a supply depth adjustment process, and a nanobubble supply process. In the process of creating the sludge distribution information, ultrasonic waves of a frequency reflected from the surface and bottom of the sludge layer are transmitted and received at observation points dispersed throughout the water area to be purified, the surface depth and bottom depth of the sludge are estimated, and the estimated surface depth and bottom depth are associated with the latitude and longitude information of each observation point and stored to create sludge distribution information consisting of three-dimensional point cloud data. In the supply point determination step, the created sludge distribution information is associated with the longitude and latitude information in the map information of the water area to be purified, and the estimated shape of the sludge layer in the water area to be purified is drawn as three-dimensional map information. This visualizes the area including observation points with relatively large amounts of sludge accumulation for use in selecting nanobubble supply points, and based on the three-dimensional map information, it is determined that these are supply points for supplying nanobubble-dissolved water. In the supply depth adjustment step, with the nanobubble supply means installed at the supply point, the depth at which the nanobubble-dissolved water is recirculated is adjusted to a depth that does not stir up the sludge layer, based on the surface depth at the supply point. In the supply process, nanobubble-dissolved water is supplied from the supply means toward the sludge layer by settling. A method for purifying sludge characterized by the following features.

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