JP2012082649A - Method and device to improve water quality of tidal river - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device to improve water quality of a tidal river capable of effectively purifying water in a predetermined setting range in the tidal river.SOLUTION: A range where river water is to be purified is set in a tidal river 1. Then, backwater means 13 and 14 are arranged at a most upstream side and a most downstream side in the setting range A respectively. After a water purification device 12 purifies the river water which is taken from the tidal river 1 through water intake means 11 arranged at an arbitrary position in the tidal river 1, the river water is returned to the tidal river through the backwater means 13 arranged at the most upstream side of the setting range A during time from high tide to low tide or through the backwater means 14 arranged at the most downstream side of the setting range A during time from low tide to high tide.

Description

  The present invention relates to a water quality improvement method and apparatus for tidal rivers.

  In the vicinity of the estuary of urban rivers, bad odors and water quality become cloudy due to the inflow of miscellaneous wastewater and sludge accumulated on the riverbed.

  As a water quality improvement system and method for such a river, it has water intake means for taking river water of a tidal river with tides and water return means for returning the taken river water to the tidal river. In the river water quality improvement system that improves the water quality of the tidal river, the water intake means takes water from the bottom layer where the dissolved oxygen concentration of the tidal river is low, and the return water means means the bottom layer of the water area downstream from the bottom layer. There is one that returns water to the part (see, for example, Patent Document 1).

  In relation to this, the heat of the taken river water is used for air conditioning (for example, refer to Patent Document 2), and a modified material with good water permeability is filled in a muddy / water quality improvement cylinder. In addition, there is a structure in which a muddy / water quality improvement cylinder filled with a reforming material is embedded in the bed of a tidal river (see, for example, Patent Document 3).

JP 2010-104968 A JP 2009-229034 A JP 2005-279324 A

  However, in any case, the tidal rivers are full of tides, so the purified return water and the reformed material supplied to the tidal rivers from the return water means will flow from the upstream from high tide to low tide. It flows downstream, and from low tide to high tide, it flows from downstream to upstream, and it is repeated twice a day, so it diffuses upstream and downstream, and the reforming effect at a specific location Cut in half.

  The present invention provides a water quality improvement method and apparatus for a tidal river that can efficiently purify a preset range set in the tidal river in view of the above-described problems of the prior art. It is an object.

According to the present invention, the above problem is solved as follows.
(1) In the water quality improvement method for a tidal river, a range to be purified is set in the tidal river, return water means are arranged on the most upstream side and the most downstream side of the setting range, After the river water of the tidal river taken from the water intake means placed anywhere in the river is purified by the water purification device, the return water means placed at the most upstream side of the setting range from high tide to low tide The water is returned to the tidal river more, and from low tide to high tide, it is returned to the tidal river from the water return means arranged at the most downstream side of the setting range.

  According to such a method, from high tide to low tide, the river water purified by the return means arranged at the most upstream side of the setting range is returned to the tidal river, and the purified river water is returned from the upstream side. River water flowing downstream can be spread over the set range. From low tide to high tide, the river water purified by the return water located at the most downstream side of the set range The purified river water can be put on the river water flow from the downstream side to the upstream side, and can be spread over the set range. Can be well purified.

(2) In the above item (1), the water intake means is disposed at an arbitrary location within the set range in the tidal river.

  According to such a method, the anoxic river water within the set range in the tidal river can be pumped up by the water means, purified, and returned from another location. It can be further promoted.

(3) In the above paragraph (1) or (2), the number of return water means is three or more, and one or more return water means are disposed between the upstream end and the downstream end of the set range. Regardless of the tides, river water that has always been purified is supplied to the return means in the middle.

  According to such a method, the purified water is constantly supplied from the return means in the middle, and the purified river water is converted from the upstream to the downstream from the high tide to the low tide. It is possible to carry the purified river water on the river water flow from the downstream side to the upstream side at low tide to high tide, and return it at the upstream end and downstream end of the set range. It is possible to cover a range that cannot be covered only with purified river water that circulates from the water means, so that the set range can be set longer. That is, it can be purified at once over a long range of tidal rivers.

(4) In the water quality improvement method for tidal rivers, a range to be purified is set in the tidal river, and aeration means are arranged on the most upstream side and the most downstream side of the setting range. At times, the tidal river is aerated from the aeration means arranged at the most upstream side of the setting range, and the tidal river is aerated from the aeration means arranged at the most downstream side of the setting range from low tide to high tide.

  According to such a method, during high tide and low tide, the river water is aerated by the aeration means arranged at the most upstream side of the setting range, and the air bubbles at that time and the river water purified by aeration are discharged from the upstream side. It is possible to spread the river water on the downstream side and reach the set range.At low tide to high tide, the river water is aerated by the aeration means arranged at the most downstream side of the set range. Air bubbles and river water purified by aeration can be put on the river water flow from the downstream side to the upstream side and spread over the set range. Can be well purified.

(5) In the water quality improvement device for the tidal river, the water intake means for taking the river water of the tidal river, the water purification device for purifying the river water taken by the water intake means, and the river water purified by the water quality purification device, A plurality of return water means capable of returning water to a plurality of tidal rivers spaced apart from each other and a switching means for switching between the return water means for supplying river water purified by the water purification device are provided.

With such a configuration, water return means are disposed at both ends of the upstream and downstream sides of the setting range to be purified in the tidal river, and water intake means is disposed at any location of the tidal river. After the river water of the tidal river taken from the water intake means is purified by the water purification device, it is returned to the tidal river from the return water means located upstream from the high tide to the low tide. From the time of high tide to the time of high tide, the set range can be efficiently purified continuously for 24 hours a day by returning water to the tidal river from the return water means arranged on the downstream side.
Switching of the return water means for supplying the purified river water can be easily performed by the switching means.

(6) In the above paragraph (5), the switching means is a return water means arranged upstream of the tidal river from high tide to low tide, and the tidal river from low tide to high tide. It is assumed that a control device is provided for controlling to supply purified river water to the return water means disposed on the downstream side.

  With such a configuration, the switching means is automatically switched in a timely manner based on the tides, so there is no need to rely on manual switching operations.

(7) In the above item (5) or (6), the water purification device is provided with means for injecting a water purification agent into the taken river water.

  With such a configuration, the anoxic river water in the tidal river can be quickly purified.

(8) In the water quality improvement device for a tidal river, an upstream aeration device for installation upstream of the tidal river, a downstream aeration device for installation downstream of the tidal river, and the upstream A switching device that selectively switches between the operation of the side aeration device and the operation of the downstream side aeration device is provided.

With such a configuration, an upstream aeration device is disposed at the upstream end of the setting range to be purified in the tidal river, and a downstream aeration device is also disposed at the downstream end. The upstream aeration device is activated during low tide, and the downstream aeration device is activated during low tide to high tide, so that the set range can be efficiently purified continuously for 24 hours a day. it can.
In addition, since the water quality improvement device can be configured with only two aeration devices and their operation switching device, the structure of the device can be simplified and the cost can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the water quality improvement method and apparatus of a tidal river which can purify the setting range preset to the tidal river efficiently can be provided.

It is a schematic diagram which shows 1st Embodiment of the water quality improvement apparatus of the tidal river of this invention, and the 1st implementation point of the water quality improvement method of the tidal river of this invention using the same. It is a schematic diagram which shows 2nd Embodiment of the water quality improvement apparatus of the tidal river of this invention, and the 2nd implementation point of the water quality improvement method of the tidal river of this invention using the same. It is a schematic diagram which shows 3rd Embodiment of the water quality improvement apparatus of the tidal river of this invention, and the 3rd implementation point of the water quality improvement method of the tidal river of this invention using the same. It is a schematic diagram which shows 4th Embodiment of the water quality improvement apparatus of the tidal river of this invention, and the 4th implementation point of the water quality improvement method of the tidal river of this invention using the same.

Next, a first embodiment of the tidal river water quality improvement apparatus of the present invention will be described with reference to FIG.
In FIG. 1, a sludge layer 3 is deposited on the river bed 2 of the tidal river 1, a seawater layer 4 flows into the upper layer from the downstream side, and fresh water flows down into the upper layer from the upstream side. The state in which the freshwater layer 5 is formed is schematically shown. Since seawater has a higher specific gravity than fresh water, the sea water layer 4 is located below the fresh water layer 5.

The left side in FIG. 1 is upstream of the tidal river 1, and the right side is downstream.
As the tides rise and fall, the boundary surface between the seawater layer 4 and the freshwater layer 5 rises at high tide and falls at low tide.
In addition, hydrogen sulfide and methane gas are generated between the sludge layer 3 and the seawater layer 4 and cause odor.

  As shown in FIG. 1, a tidal river water quality improvement apparatus 10 according to the present invention includes a water intake means 11 for taking river water from a tidal river 1 and a water quality purification apparatus 12 for purifying river water taken by the water intake means 11. And a plurality of (two in this example) return water means 13, 14 that can return the river water purified by the water quality purification device 12 to a plurality of locations in the tidal river 1 that are separated from each other, and the water quality purification device 12 And switching means 20 for switching between the return water means 13 and 14 for supplying purified river water.

  The water intake means 11 includes a flexible water intake hose 11a and a suction port 11b attached to the tip thereof. Each of the water return means 13, 14 includes a flexible water return hose 13a, 14a and a tip thereof. And the discharge ports 13b and 14b attached to the.

  The water purification device 12 is connected to the gas dissolving device 15 and the base end of the water intake hose 11a, and draws up river water from the suction port 11b and supplies the water to the gas dissolving device 15, and a compressor 17 that compresses air. And an oxygen generator 18 that separates the air compressed by the compressor 17 into oxygen and nitrogen, releases nitrogen into the atmosphere, and supplies oxygen or ozone as a water purification agent to the gas dissolving device 15; In the gas dissolving device 15, an outlet pipe 19 for taking out the purified river water obtained by dissolving the oxygen or ozone supplied from the oxygen generator 18 into the river water taken by the water intake means 11 to obtain high-concentration oxygen-dissolved water. I have.

A switching means 20 is connected to the outlet pipe 19.
The switching means 20 may be manually operated, but in this example, it is automatically controlled by the control device 22.
The control device 22 compares the tide table data stored in the memory (not shown) with the current time of the timer (not shown), and the current time is between high tide and low tide of the tide table data. In some cases, the return water means 13 disposed on the upstream side of the tidal river 1, and in the same way between low tide and high tide, the return water means 14 disposed on the downstream side of the tidal river 1. In addition, it is preferable to control to supply purified river water.
Tide table data can be obtained from receivers such as mobile phones and personal computers.

  Alternatively, as shown by a two-dot chain line in FIG. 1, a tide level sensor 21 provided at an appropriate position in the tidal river 1 is connected to the control device 22, and based on tide tidal data detected by the tide level sensor 21. From high tide to low tide, the return water means 13 is arranged upstream of the tidal river 1, and from low tide to high tide, the return water is arranged downstream of the tidal river 1. The means 14 may be controlled to supply purified river water.

  Any tide level sensor 21 can be used as long as it measures the water level of the tidal river 1 over time and can determine the time of high tide and low tide based on comparison with past measurement data. But you can.

  Next, a first implementation point of the water quality improvement method for a tidal river of the present invention that actually improves the water quality of the tidal river 1 using the water quality improvement device 10 for the tidal river will be described.

  First, the range (henceforth the setting range A) which is going to improve water quality among the tidal river 1 is set. The setting range A is preferably determined based on the capacity of the water purification device 12, the river width, the amount of water, the state of contamination, and the like, but is preferably about 500 meters, for example.

  Next, the upstream water return means 13 is immersed in the upstream end of the setting range A, and the downstream water return means 14 is immersed in the downstream end of the setting range A. At this time, it is preferable to immerse the outlets 13b and 14b of the water return means 13 and 14 so that they are located around the boundary between the sludge layer 3 and the seawater layer 4.

The water intake means 11 is preferably immersed in a suitable location on the downstream side within the set range A, but may be immersed in the tidal river 1 outside the set range A when there is no suitable place for soaking. .
Further, the water intake means 11 is preferably arranged so that the suction port 11b is located in the seawater layer 4 slightly above the sludge layer 3 so as to take in high-concentration salt water in the seawater layer 4. .

  In this state, when the gas dissolving device 15, the pumping pump 16, the compressor 17, and the oxygen generating device 18 are operated, river water is pumped from the seawater layer 4 from the suction port 11 b of the water intake means 11, and is supplied to the gas dissolving device 15. The air that is supplied and compressed by the compressor 17 is separated into oxygen and nitrogen in the oxygen generator 18, the nitrogen is discharged into the atmosphere, and the oxygen or ozone is compressed, and the gas dissolving device. 15 is supplied.

  In the gas dissolving device 15, the oxygen or ozone supplied from the oxygen generator 18 is dissolved in the river water taken by the water intake means 11, and the purified river water that has become high-concentration oxygen-dissolved water is discharged from the outlet pipe. 19 is discharged.

The purified river water discharged from the outlet pipe 19 reaches the switching means 20, where it is switched in the following manner and selectively supplied to the return water means 13,14.
That is, during the period from high tide to low tide, the purified river water flows from the outlet pipe 19 to the return water hose 13a side of the return water means 13 disposed on the upstream side, and is between the low tide and high tide. At this time, the purified river water is controlled by the control device 22 so as to flow out from the outlet pipe 19 to the return water hose 14a side of the return water means 14 arranged on the downstream side.

  As a result, from high tide to low tide, the purified river water is returned between the sludge layer 3 and the seawater layer 4 in the tidal river 1 from the discharge port 13b of the upstream return water means 13. Then, along with the flow of the tide at that time, it flows from the upstream side to the downstream side of the setting range A, and the poor oxygen salt water in the setting range A is replaced with high-concentration oxygen-dissolved water to purify the setting range A.

  In addition, during the period from low tide to high tide, water is returned between the sludge layer 3 and the seawater layer 4 in the tidal river 1 from the discharge port 14b of the return water means 14 on the downstream side. Along with this, the flow flows from the downstream side of the setting range A toward the upstream side, and the poor oxygen salt water in the setting range A is replaced with the high-concentration oxygen-dissolved water to purify the setting range A.

  In this way, the purified river water flows from the upstream side to the downstream side of the setting range A from high tide to low tide, and the purified river water flows from the setting range A to the low tide. By flowing from the downstream side toward the upstream side, the setting range A can be efficiently purified continuously for 24 hours a day.

  Next, with reference to FIG. 2, about 2nd Embodiment of the water quality improvement apparatus of the tidal river of this invention, and 2nd implementation point of the water quality improvement method of the tidal river of this invention using the same explain. Note that the same devices and members as those in FIG. 1 are given the same reference numerals and illustrated, and the description thereof is omitted because it is redundant.

  As shown in FIG. 2, the tidal river water quality improvement apparatus 10 of the second embodiment includes a return water means 13 for the upstream end of the setting range A and a return water means 14 for the downstream end. One or a plurality (in this example, one is shown for simplicity of explanation) of intermediate water return means 23 are provided.

  Like the other return water means 13, 14, the return water means 23 includes a flexible return water hose 23 a having a base end connected to the switching means 20, and a discharge port 23 b attached to the tip thereof. It has.

  In the second implementation point of the tidal river water quality improvement method of the present invention using the tidal river water quality improvement apparatus 10 of the second embodiment, the setting range A ′ is longer than the previous setting range A. , For example, 1000 meters, upstream return water means 13 is disposed at the upstream end of the set range A ′, and downstream return water means 14 is disposed at the downstream end, and the set range A ′. The return water means 23 for the intermediate part is disposed in any manner in the same manner as the other return water means 13, 14 at an arbitrary position in the inside, preferably the center of the set range A ′.

In this state, the water purification device 12 is operated in the same manner as in the first embodiment, and the switching means 20 is switched and controlled in the following manner.
That is, during the period from high tide to low tide, the purified river water is supplied from the outlet pipe 19 to the return water means 13 for the upstream end and the return water means 23 for the intermediate part. Supplies the purified river water from the outlet pipe 19 to the return water means 14 for the downstream end and the return water means 23 for the intermediate part.
Therefore, the purified water is always supplied to the intermediate return water means 23 regardless of the tides.

Then, during the period from high tide to low tide, the purified river water returned from the upstream end return water means 13 rides on the river water flow from the upstream side to the downstream side, and is set as shown in FIG. The purified river which purified the 1st section A1 from the upstream end of range A 'to the middle point P where the return water means 23 for the middle part was arranged, and was returned from the return water means 23 for the middle part The water rides on the flow of river water from the upstream side to the downstream side, and purifies the second section A2 from the intermediate point P to the downstream end of the set range A ′ shown in FIG.
Also, from low tide to high tide, the purified river water returned from the downstream end return water means 14 rides on the river water flow from the downstream side to the upstream side to purify the second section A2. The purified river water returned from the intermediate return water means 23 rides the river water flow from the downstream side to the upstream side to purify the first section A1.

  Therefore, by increasing the number of the return water means 23 for the intermediate part, it is not possible to cover only the purified river water circulating from the return water means 13 and 14 provided at the upstream end and the downstream end of the setting range A ′. The range can be covered, and thus the set range A ′ can be set longer. That is, it can be purified at once over a long range of tidal rivers.

FIG. 3 shows a third embodiment of a water quality improvement device for a tidal river of the present invention and a third implementation point of a water quality purification method for a tidal river of the present invention using the same.
In the first and second embodiments, the river water taken by the water intake means 11 is purified by aeration in the water quality purification device 12, and the water is selectively circulated by the return water means 13, 14, 23. However, in the third embodiment of the present invention shown in FIG. 3, a range to be purified is set in the tidal river 1, and the aeration apparatus is provided at the most upstream side and the most downstream side of the set range A. (Aeration means) 31 and 32 are arranged. From high tide to low tide, the tide river 1 is aerated by the aeration device 31 arranged on the most upstream side of the setting range A. From low tide to high tide The tidal river 1 is aerated by the aeration device 32 arranged on the most downstream side of the setting range A.

  The aeration device 31 for the upstream of the tidal river 1 and the aeration device 32 for the downstream of the tidal river 1 are respectively a receiver tank 33 and a compressor for supplying compressed air to the receiver tank 33. 34, a flexible hose 35 having a base end connected to the receiver tank 33, and a plurality of small holes 36 provided on the top surface or outer peripheral surface of the hose 35 and provided on the top surface or the outer peripheral surface. And a diffused gas 37 placed on the river bed 2.

  Although the diffused gas 37 is schematically shown in the illustrated example, a large number of branch pipes (not shown) are connected to both sides of a base pipe (not shown) connected to the hose 35, and the upper surface of the branch pipe is connected. A diffuser tube type in which a large number of small holes 36 are provided on the outer peripheral surface, a diffuser plate type in which a large number of small holes 36 are provided on the upper surface of the hollow plate-like body, or a portion in which a large number of small holes 36 are provided It is preferable to use one of a diffused sheet type formed by a flexible sheet or a combination thereof.

  The compressor 34 in the aeration apparatus 31 disposed on the upstream side of the tidal river 1 and the compressor 34 in the aeration apparatus 32 disposed on the downstream side are electrically connected to a switching device 38, and the switching device 38 The compressor 34 in the upstream aeration device 31 is operated from high tide to low tide, the compressor 34 in the downstream aeration device 32 is inoperative, and the upstream aeration device from low tide to high tide. The compressor 34 in 31 is inoperative, so that the compressor 34 in the downstream aeration device 32 is activated, either manually, or automatically controlled based on the tide table and the information of the tide level sensor 21 similar to the control device 22 described above. It is switched by.

  Therefore, according to the third embodiment, the tidal river 1 is aerated by the aeration device 31 arranged at the most upstream side of the setting range A from the high tide to the low tide. The river water purified by dissolving oxygen flows downstream, the setting range A of the tidal river 1 is purified, and the aeration apparatus disposed at the most downstream side of the setting range A from low tide to high tide. The tidal river 1 is aerated by 32, the bubbles at that time, and the river water purified by dissolving oxygen by aeration flow upstream, and the setting range A of the tidal river 1 is purified 24 times a day. The set range A can be efficiently purified over time.

FIG. 4 shows a fourth embodiment of a water quality improvement device for a tidal river of the present invention and a fourth implementation point of a water quality purification method for a tidal river of the present invention using the same.
In the fourth embodiment, the receiver tank 33 and the compressor 34 in the aeration apparatus 31 and the aeration apparatus 32 of the third embodiment are shared.
That is, a switching device 40 similar to the switching means 20 in the first embodiment is connected to the other end of the outlet pipe 39 whose one end is connected to the receiver tank 33 to which compressed air is supplied by one compressor 34. The switching device 40 selectively supplies the compressed air in the receiver tank 33 to the hose 35 in the upstream aeration device 31 and the hose 35 in the downstream aeration device 32.

  The switching device 40 is switched by a control device 41 similar to the control device 22 in the first embodiment, using the compressed air in the receiver tank 33 from the high tide to the low tide at the upstream aeration device 31. In addition, the compressed air in the receiver tank 33 is controlled so as to be supplied to the hose 35 in the downstream aeration apparatus 32 from the low tide to the high tide.

  Therefore, in the fourth embodiment, not only the same operations and effects as in the third embodiment can be achieved, but also the number of parts can be reduced and the structure can be simplified as compared with the third embodiment. Can be planned.

  In the third and fourth embodiments, one or a plurality of aeration devices are arranged between the upstream end and the downstream end of the setting range A, and the aeration device in the intermediate portion is always operated. By setting, a long setting range A can be set in the tidal river 1 as in the second embodiment, and the long range of the tidal river 1 can be purified at once.

The present invention is not limited to the above-described embodiments, and can be implemented in various modified forms without departing from the scope of the claims.
For example, the water purification device 12 can be one having a filtering means, one having a purification means by microorganisms, one injecting a chemical for purification, or a combination thereof.

  The control device 22 is incorporated in a main control device (not shown) of the entire device for controlling and monitoring the gas dissolving device 15, the pumping pump 16, the compressor 17, the oxygen generator 18 and the like in the water purification device 12. It is preferable to control and monitor the switching unit 20 together with the other devices described above by the control device so that if any abnormality occurs in each of those devices, it can be notified promptly.

DESCRIPTION OF SYMBOLS 1 Tidal river 2 River bed 3 Sludge layer 4 Seawater layer 5 Fresh water layer 10 Water quality improvement device 11 of tidal river Water intake means 11a Water intake hose 11b Inlet 12 Water quality purification device 13, 14 Water return means 13a, 14a Water return hose 13b, 14b Discharge port 15 Gas dissolving device 16 Pumping pump 17 Compressor 18 Oxygen generator 19 Outlet pipe 20 Switching means 21 Tide level sensor 22 Control device 23 Return water means 23a Return water hose 23b Discharge ports 31, 32 Aeration device (aeration means)
33 receiver tank 34 compressor 35 hose 36 small hole 37 diffused gas 38 switching device 39 outlet pipe 40 switching device 41 control device A, A ′ setting range A1 first section A2 second section P midpoint

Claims (8)

  Set the range to be purified in the tidal river, arrange return water means at the most upstream side and the most downstream side of the setting range, and from the water intake means arranged at any place of the tidal river After the river water of the tidal river taken is purified by a water purification device, it is returned to the tidal river from the water return means arranged at the most upstream side of the setting range from high tide to low tide, and from the low tide. A method for improving the water quality of a tidal river, characterized by returning water to the tidal river from the water return means arranged at the most downstream side of the set range at high tide.   The water quality improvement method for a tidal river according to claim 1, wherein the water intake means is disposed at an arbitrary location within a set range of the tidal river.   There are three or more return water means, and one or more return water means are arranged between the upstream end and the downstream end of the set range. 3. The method for improving the water quality of a tidal river according to claim 1 or 2, characterized in that the river water that is constantly purified is supplied.   Set the range to be purified in the tidal river, arrange aeration means on the most upstream side and the most downstream side of the set range, and place it on the most upstream side of the set range from high tide to low tide A method for improving the water quality of a tidal river, characterized in that the tidal river is aerated from the aeration means and the tidal river is aerated from the aeration means arranged at the most downstream side of the set range from low tide to high tide. Water intake means for taking water from the tidal river,
A water purification device for purifying river water taken by water intake means;
A plurality of return means capable of returning river water purified by the water purification device to a plurality of tidal rivers separated from each other;
A water quality improvement device for a tidal river, comprising switching means for switching a return water means for supplying river water purified by the water quality purification apparatus.   The switching means is a return water means to be placed upstream of the tidal river from high tide to low tide, and a return water to be placed downstream of the tidal river from low tide to high tide. 6. The water quality improvement device for a tidal river according to claim 5, wherein the means is provided with a control device for controlling to supply purified river water.   The water quality improvement device for a tidal river according to claim 5 or 6, wherein the water quality purification device includes means for injecting a water quality purification agent into the taken river water. An upstream aeration device for installation upstream of a tidal river;
A downstream aeration device for installation downstream of the tidal river;
A water quality improvement device for a tidal river, comprising a switching device that selectively switches between the operation of the upstream aeration device and the operation of the downstream aeration device.

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