JPH07290084A - Water quality improving device - Google Patents

Abstract

PURPOSE:To provide a water quality improving device capable of energy- savingly replenishing dissolved oxygen at the bottom of the waters as the source of the area of polluted water. CONSTITUTION:Plural hollow-fiber membranes 2a having a hollow part 2b and pierced with many gas-permeable holes to communicate the hollow part 2b with the outside are bundled to constitute a hollow-fiber bundle 2. The bundle 2 is held by a base material 3 having a passage communicated with the hollow part 2b, and a gas feed pipe 4 is connected to the base material 3. The water quality improving unit 1 consists of the hollow-fiber bundle 2, base material 3 and gas feed pipe 4, and a gas blowing device is connected to the gas feed pipe 4. The pressure in the hollow part 2b of the bundle 2 is maintained below the bubble point, and the oxygen-contg. gas is blown.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a reservoir for river water, landscape
The present invention relates to a water quality improving device installed in a water polluted water region such as a hydrophilic pond, a lake, a dam reservoir, a canal or a harbor, and particularly to a water quality improving device capable of eliminating DO deficiency in the bottom layer of the water polluted water region.

[0002]

[Prior Art] Reservoir for river water, scenic / hydrophilic pond, lake,
Although water pollution in dam reservoirs and water areas such as canals and harbors has been regarded as a problem in recent years, there are still few examples of water quality improvement. Currently, as practical or research and development water quality improvement technology, one that recycles sewage secondary treated water by filtration and ozone treatment and reuse as murmuring water, one that suppresses algae by installing a bubble tower in a dam reservoir, park Some are equipped with air diffusers at the bottom of the pond to diffuse air, and some are introduced into the gravel contact oxidation device to purify river water.

[0003]

Although the respective effects can be recognized in each of the above examples, there are the following problems. In other words, the water quality improvement technology that reuses the sewage secondary treated water is sufficient for maintaining a clear stream as murmuring water, but has the problem of high desalination quality. Moreover,
When the flow-down destination of the babbling water becomes a vast accumulated water area such as Shukei Pond, since the babbling water contains many nutrients that cause eutrophication, eutrophication of this water area is unavoidable, Due to lack of dissolved oxygen (DO) in the bottom layer, natural purification capacity is lost, which may lead to water pollution and generation of malodorous gas.

When a bubble tower is installed in a dam reservoir, due to rising bubbly flow and water temperature difference, it forms a downward flow from the middle layer to the surface layer, a downflow from the surface layer to the middle layer, and a gentle circulation flow, and the sunlight necessary for the propagation of algae spreads. Algae can be moved to the middle region where there is no water and their reproduction can be suppressed. However, the formation of this circulating flow is susceptible to inflow of rainwater, fluctuations in the amount of stored water used, fluctuations in water temperature distribution, etc., and its effect may be insufficient. Even if the bubble column shows sufficient function, the eutrophication state of the whole water area does not change, and especially in the bottom layer where dead bodies of organisms living in the whole water area are accumulated.
O deficiency becomes serious, and the water (water) pollution such as occurrence of blue tide phenomenon in fresh water due to seasonal water temperature distribution change cannot be prevented, in addition to deterioration of the purification function of nature (organism).

As a DO replenishing method for the bottom layer of a pond or the like, it is generally considered that air bubbles are released from a diffuser plate or the like, but the dissolution efficiency due to rising bubbles is low and most of the supplied air is atmospheric. There is a waste to release to, most DO
It is difficult to efficiently perform DO supply to the bottom layer, which requires In addition, a water treatment device such as a gravel contact oxidation device that has been partially put into practical use for purification of river water requires a treatment tank because the water to be treated stays (reacts) for several hours or more. It is often difficult to secure a vast installation space outside the water area for installation, and there is a problem that the installation and operation costs will also be high.

The present invention has been made in view of the above points, and it is possible to eliminate the DO deficiency in the bottom layer of a polluted water area and improve the water quality by recovering the natural purification ability of organisms living in the bottom layer with energy saving. The purpose is to provide a device.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a water quality improving element comprising a porous membrane having a hollow portion and a large number of gas permeation holes communicating the hollow portion with the outside, and the water quality improving element. While holding the improvement element, having a base material having a communication passage communicating with the hollow portion of the water quality improvement element, and an air supply pipe connected to this base material, a water quality improvement unit installed at the bottom of the water, and A water quality improving device, characterized in that it is connected to an air sending pipe, and an air sending device for sending an oxygen-containing gas whose pressure in the hollow part of the water quality improving element is equal to or lower than a bubble point, and a porous part having a hollow part. A porous body, a porous membrane provided on the inner surface or the outer surface of this porous body, and an air supply pipe connected to the hollow portion, a water quality improving unit arranged at the bottom of the water, and the air supply pipe. The pressure inside the hollow part of the porous body is connected to the bubble point. An air supply device for supplying an oxygen-containing gas to the bottom, and a water quality improving device characterized by comprising: a hollow part; and a large number of gas permeation holes communicating the hollow part with the outside. A plurality of water quality improving elements consisting of a porous body formed, and holding the water quality improving element at both ends thereof, a base material having a communication passage communicating with the hollow portion of the water quality improving element, and the plurality of water quality A joint material connecting the base materials of the improvement element, and an air supply pipe connected to the base material, a water quality improvement unit arranged at the bottom of the water, and connected to the air supply pipe, of the water quality improvement element An air supply device for supplying an oxygen-containing gas so that the pressure in the hollow portion becomes equal to or lower than the bubble point.

[0008]

According to the present invention, the oxygen-containing gas is supplied from the air supply device into the water quality improving unit. In this case, since the pressure in the water quality improving element of the water quality improving unit or the hollow portion inside the porous body is equal to or lower than the bubble point, dissolved oxygen is replenished from the water quality improving element or the porous body to the bottom of the water without bubbles. Therefore, oxygen in the oxygen-containing gas can be dissolved in the bottom of the water without waste.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment An embodiment of the present invention will be described below with reference to the drawings. 1 (a) (b) and FIG. 2 are views showing a first embodiment of a water quality improving device according to the present invention.

Of these, FIGS. 1 (a) and 1 (b) are views showing the structure of the water quality improving device, and FIG. 2 is a view showing a state in which a plurality of water quality improving units are arranged on the bottom surface in water.

As shown in FIGS. 1 (a) and 1 (b), a water quality improving unit 1 includes a hollow fiber bundle 2 as a water quality improving element composed of a floating porous membrane having a large number of gas permeation holes, and a hollow fiber bundle 2. A base material 3 for holding the hollow fiber bundle 2 and having a communication path (not shown) communicating with the hollow portion 2b of the hollow fiber bundle 2, and an air supply pipe 4 connected to the base material 3 and communicating with the hollow portion 2b of the hollow fiber bundle 2. Composed.

The hollow fiber bundle 2 has a plurality of hollow fiber membranes 2a having an outer diameter of about 0.3 to several mm and a gas permeation hole of about 0.1 μm, which is generally used in water treatment filtration. The hollow fiber membranes 2a are hollow portions 2b in the hollow portions 2a. In this embodiment, a material that floats in water due to buoyancy is selected as the hollow fiber membrane 2a. The floating upper end of the hollow fiber bundle 2 has a sealed terminal shape in FIG. 1B, but both ends of the hollow fiber bundle 2 are fixed to the base material 3, and the floating upper end of the hollow fiber bundle 2 is A general U-shaped one may be used. The air supply pipe 4 is provided with another water quality improvement unit 1 and a joint 5 for pipe connection with an air supply main pipe described later, but the joint 5 may be provided on the base material 3.

As shown in FIG. 2, an air supply device 9 for supplying an oxygen-containing gas, for example, air, is connected to the air supply pipe 4 via an air supply main pipe 7 described later. Air is fed so that the pressure in the hollow portion 2b in the hollow fiber membrane 2a becomes equal to or lower than the bubble point (1 to 2 × 10 ⁵ pa).

Further, in FIG. 2, for example, three water quality improvement units 1 shown in FIG. 1 are connected in series via a joint 5 of an air supply pipe 4, and a series of water quality improvement units 1 are connected, one end of which is maintained. Main air supply 7 through open / close valve 6 for
The sealing material 8 is attached to the other end of the joint 5 of the water quality improving unit 1 which is the farthest part from the air supply main pipe 7. In the air supply main 7, a required number of a series of water quality improvement units 1 are freely arranged on the bottom surface of the polluted water area. A sealing material 8 is also attached to the farthest part of the air supply main 7 from the air supply device 9. These series of water quality improvement units 1 are installed in the form of being installed on the bottom surface of the polluted water area. Since such a bottom surface is generally undulated, soft tubes are used as the air supply tube 4 and the air supply main tube 8 and the like, and the joint material 5 can be easily detached in consideration of maintenance. Stuff used. In addition, as described above, the hollow fiber bundle 2, the base material 3, and the air pipe 4
Constitutes a water quality improving unit 1, and a series of water quality improving units 1 and an air feeding device 9 connected to the water quality improving unit 1 via an air feeding main pipe 7 constitute a water quality improving device.

Next, the operation of this embodiment having such a configuration will be described. First, the oxygen-containing gas is supplied from the air supply device 9 to the main air supply pipe 7 so that the pressure in the hollow portion 2b of the hollow fiber bundle 2 becomes a required pressure below the bubble point. Compressed air is generally sufficient as the oxygen-containing gas, but when high-concentration oxygen or pure oxygen is used, the purpose of supplying oxygen at a lower pressure is achieved. Oxygen-containing gas is the main air supply pipe 7
Is supplied to the hollow fiber bundles 2 of each water quality improvement unit 1 from the hollow fiber bundles 2 through the gas permeation holes so that no bubbles are generated in the nearby water, that is, DO is replenished without bubbles.

When DO is supplied bubblelessly from the hollow fiber bundle 2 through the gas permeation holes in this way, the hollow fiber membrane 2a
Due to the gas-liquid contact between the internal gas and the external liquid that is performed through the multiple gas permeation holes, the oxygen in the fed oxygen-containing gas is dissolved in the water without difficulty. The DO replenishment rate by gas-liquid contact depends on the gas-liquid contact area, the saturated DO and the actual DO.
It increases in proportion to the difference between the above and the higher the oxygen concentration of the oxygen-containing gas and the higher the pressure of the oxygen-containing gas. 0.1 used as a hollow fiber bundle 2 for water treatment filtration
When the hollow fiber membrane 2a having gas permeation holes of about μm is used, the inside of the hollow portion 2b of the hollow fiber membrane 2a is 1 to 2 × 10 ⁵ Pa.
By setting the pressure lower than the bubble point pressure of
The lack of DO in water near the hollow fiber bundle 2 can be eliminated. Even when the inside of the hollow portion 2b is set to be equal to or lower than the bubble point pressure, the actual air supply pressure from the air supply device 9 is a pressure to which a water depth equivalent amount is added. Further, when the deterioration of the polluted water area is large, or when the density of the bottom surface of the water quality improvement unit 1 needs to be reduced and the DO supply by air is insufficient, high-concentration oxygen or pure oxygen may be used instead of air. .
The size of the gas permeation holes of the hollow fiber membrane 2a is preferably 0.45 μm or less in order to prevent invasion of water-borne bacteria into the hollow interior and to maintain the air supply pressure as high as possible, and the effective rate is gas-liquid. A larger size is desirable to increase the contact area.

During this time, the hollow fiber bundle 2 floats in the water by buoyancy and becomes a water grass-like form, which contributes to water purification,
Suitable breeding areas for small animals, fishes, etc. are formed, which brings about the effect of restoring the natural purification ability of polluted water areas. Further, by arranging the water quality improvement unit 1 in an appropriate distribution on the bottom surface of the polluted water area, the DO shortage of the bottom layer of the polluted water area where the natural purification function has been lost due to the DO shortage in the related art can be eliminated in energy saving. . A biologically active area in the bottom layer based on the water quality improvement unit 1 having a larger contact area is formed, and the natural purification function is sufficiently exerted.

As described above, according to this embodiment, since the upper end of the hollow fiber bundle 2 is not fixed and floats in a nearly vertical shape, the dissolution of DO and the diffusion in water are promoted, and the natural purification ability is improved. The vertical width of the bottom layer exerted can be expanded. In addition, the service life of natural sediments can be increased. Even if the natural sediment deposits and the surface area of the hollow fiber bundle 2 in the underwater portion decreases, the decrease in the surface area can be supplemented by increasing the pressure setting of the oxygen-containing gas. In addition, when the air feed pipe 4 and the air feed main pipe 7 of the individual water quality improvement units 1 or a series of water quality improvement units 1 are made to be soft pipes, when the amount of natural sediment deposited increases, a hook rod or the like may be used. The water quality improving unit 1 can be easily moved slightly upward, and the effect of the water quality improving device can be maintained for many years. Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. 3 and 4. As shown in FIG. 3, the water quality improvement unit 10 is constructed by planarly assembling a pair of base materials 12 and a pair of air supply pipes 13,
Both ends of the hollow fiber bundle 11 as the water quality improving element are fixed to the opposing base materials 12 and are assembled in a plane as a whole. Although the air supply pipe 13 is provided with the joint 14, the joint 14 may be provided on the base material 12.

The hollow fiber bundle 11 comprises a hollow fiber membrane 2a having a hollow portion 2b in which a large number of gas permeation holes are formed (FIG. 1).
(B)). Instead of the hollow fiber bundle 11, a tubular body or a woven hollow fiber may be used. FIG. 4 shows a partial configuration in which the woven hollow fiber 11a is used as a water quality improving element. Figure 3
The water quality improving unit 10 shown in FIG. 4 and the water quality improving unit 1 of the first embodiment are arranged on the bottom surface of the polluted water area to form a water quality improving device.

An air supply device 9 is connected to the joint 14 via the air supply main pipe 7 and the like, and the hollow part 2b is connected by the air supply device 9.
Air is delivered so that the internal pressure is below the bubble point.

Next, the operation of this embodiment having such a configuration will be described.

In FIG. 3, since the hollow fiber bundle 11 has a large surface area, the efficiency of DO replenishment and natural purification is high.
When a tubular body made of an organic material is used instead of the hollow fiber bundle 11, the surface area is smaller than that of the hollow fiber bundle 11, but the mechanical strength is increased and a stronger water quality improvement unit 10 can be configured.

In FIG. 4, a woven hollow fiber 11a is a hollow fiber membrane 2a (see FIG. 1 (b)) used for the hollow fiber bundle 11, which is woven to improve the supporting strength of the hollow fiber membrane 2a. Then, the water quality improvement unit 10 having a large surface area that can maximize the total surface area of the hollow fiber membrane 2a is configured.

The hollow fiber bundle 11 or the woven hollow fiber 11a in this embodiment is arranged in a plane near the bottom of the polluted water area. Therefore, it is suitable for natural purification near the bottom of the bottom layer. The bottom surface is where natural sediments are deposited, and since there is a lot of organic matter, when the DO shortage is resolved, the maximum natural purification capacity will be exhibited in the polluted water area.

As shown in FIG. 3 and FIG. 4, in this embodiment, the water quality improving unit 10 can be used in a state where it is lightly covered with natural sediment, so that the purpose can be achieved without damaging the landscape.

As the tubular body used in place of the hollow fiber bundle 11, not only an organic material but also an inorganic material such as ceramics or metal sintered can be used.
In this case, the mechanical strength of the water quality improvement unit 10 improves. Third Embodiment A third embodiment of the present invention will be described with reference to FIGS. 5A and 5B, the third embodiment is similar to FIG.
And any one of the water quality improvement units 10 shown in FIG.
0 is configured. That is, as shown in FIG. 5 (a), the integrated water quality improvement unit 20 is formed by combining the water quality improvement units 10 in a planar manner in multiple stages, and each water quality improvement unit 10 has a base material 12 and an air supply material. It is connected to either 13 or the joint 14. Also, FIG. 5 (b)
As shown in, the integrated water quality improvement unit 22 may be configured by vertically connecting a plurality of water quality improvement units 10. The connection form of the water quality improvement unit 10 is shown in FIG.
Not limited to the examples shown in (a) and (b), they may be connected in an inclined shape. These integrated type water quality improvement units 20 and 22 are
And, like the water quality improvement units 1 and 10 of the second embodiment, the water quality improvement device is arranged on the bottom surface 21.

Next, the operation of this embodiment having such a configuration will be described. Since the integrated water quality improvement units 20 and 22 of this embodiment reach a position higher than the bottom surface,
The natural purification ability is exerted over a wide range from the bottom to the top of the bottom layer, and the service life to natural sediments can be increased. In addition, the integrated type water quality improvement unit 2 of this embodiment
Since 0 and 22 are more rigidly configured, their original functions can be maintained for many years. Further, unless the polluted water area is a completely closed area, there is a water flow in the bottom layer of the water area, and the integrated water quality improvement units 20 and 22 project upward from the bottom surface. You can Therefore, the integrated type water quality improvement device 20, 2
It is also possible to contribute to the improvement of water quality in the downstream area from the installation location of No. 2. Therefore, when water quality improvement in a predetermined polluted water area is carried out, the water quality improvement device 20,
By arranging 22 and arranging the integrated type water quality improving devices 20 and 22 in the upstream region of a predetermined polluted place, the water quality can be improved more effectively. in this case,
A better design can be made according to the height position and strength of the polluted water flow and the situation of the inflow floating sediment. Fourth Embodiment A fourth embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 6A, the water quality improving unit 32 includes a flat plate-shaped porous body 30 having a hollow portion, an air supply pipe 31 connected to the hollow portion, and a gas provided on the inner surface of the porous body 30. And a porous membrane having permeation holes. The porous body 30 is made of an inorganic material such as ceramics or sintered metal, or an organic material such as rubber or plastics, and the porous membrane is made of the same or different material as the porous body 30 and has gas permeation holes. I have many. The inside of the porous membrane is
Although it is a hollow portion, the shape of the hollow portion does not matter as long as there is a gap in which the oxygen-containing gas can freely diffuse. The outer surface of the porous body 30 has a large number of pores larger than the gas permeation pores of the porous membrane. The size of the gas permeation holes of the porous membrane is the same as in the first embodiment described above. In addition, FIG.
As shown in (b), the water quality improvement unit 34 may be composed of a block-shaped porous body 33 such as a rock. Also,
An air supply device 9 (see FIG. 2) is connected to the air supply pipe 31,
The air supply device 9 supplies air so that the inside of the hollow portion has a pressure below the bubble point.

The water quality improvement units 32 and 34 according to the present embodiment can be manufactured in the shape of natural rocks, and even if they are arranged on the bottom surface of the polluted water area, there is no unnaturalness and there is a landscape advantage. The porous film may be provided on either the outer surface or the inner surface of the porous bodies 30, 33. Fifth Embodiment FIG. 7 (a) (b) and FIG. 8 show a fifth embodiment of the present invention.
This will be described with reference to (a) and (b). As shown in FIGS. 7A and 7B, the water quality improving unit 40 has a hollow soft porous membrane 41 as a water quality improving element having a large number of gas permeation holes.
And a base material 42 fixed to both ends of the porous film 41
And a sealing member 44 attached to the terminal base material 42 of the porous membrane 41 at the far end, and a joint material 43 for connecting the base materials 42 of the plurality of porous membranes 41 to each other. To be done. The gas permeation holes of the porous membrane 41 are similar to those of the first embodiment, and the porous membrane 41 is formed in a tubular body as shown in FIG. 7 (a).

Further, as shown in FIG. 7B, the hollow fiber bundle 4 is not limited to the tubular body, and the hollow fiber bundle 4 may be used as the water quality improving element. In this case, the base material 46 and the hollow fiber bundle 45 are
They are integrated by the fixing portion 47 of. As shown in FIG. 7B, when the water quality improving element is composed of the hollow fiber bundle 45 and has a floating property, a sinking material is used as the base material 46, the joint material 43, or the sealing material 44, and the water quality improving unit 40 is used. Make the whole submerged. As the joint material 43 and the sealing material 44, a general-purpose material called a joint can be usually used.

As shown in FIG. 8, the water quality improvement unit 40
Is freely arranged on the bottom surface of the polluted water area, and the terminal base materials 42 and 46 without the sealing material 44 are connected to the air supply main pipe 49 through the on-off valve 48 for maintenance. . The air supply main tube 49 is connected to an air supply device 9 (see FIG. 2) that supplies the oxygen-containing gas so that the inside of the hollow portion of the porous membrane or the hollow fiber bundle has a pressure below the bubble point.

According to this embodiment, the water quality improvement unit 40
Has a single elongated shape composed of the soft porous membrane 41 or the hollow fiber membrane 45, so that it can be freely arranged according to the undulations of the bottom surface of the polluted water area and the conditions of obstacles. Further, the length of the water quality improvement unit 40 can be adjusted according to the degree of water quality improvement, and the water quality improvement unit can be easily pulled up so that the rope can be strung during the pulling up maintenance. Sixth Embodiment A sixth embodiment of the present invention is provided in the water quality improvement unit 1, 10, 20, 22, 32, 34, 40 or the terminal portion of the air supply main 7, 49 in each of the above embodiments. Sealing material 8, 4
In place of 4, a capillary or a minute flow rate valve is attached, and the other parts are the same as those in the above-mentioned respective embodiments.

In this embodiment, the pressure of oxygen-containing gas is the same as that of the above-mentioned embodiments in that the water quality improving units 1, 10, 20,
The pressure below the bubble point is maintained in 22, 32, 34 and 40. Capillaries or minute flow valves attached instead of the sealing materials 8 and 44 discharge bubbles of oxygen-containing gas into water at a set minute flow rate while maintaining this pressure.

In the above-mentioned respective embodiments in which the sealing materials 8 and 44 are attached, the oxygen-containing gas supplied from the air supply mains 7 and 49 is the water quality improving unit 1, 10, 20, 22, 32, 3.
It dissolves in water without bubbles only from 4,40 gas permeation holes. By the way, since the dissolved amount of oxygen in the oxygen-containing gas is generally larger than the dissolved amount of other coexisting gases, the main air supply pipes 7, 49 or a series of water quality improvement units 1, 10, 20, When the air feeding distance of 22, 32, 34, 40 becomes long, the diffusion and replenishment of oxygen in the gas phase accompanied by the movement of the entire oxygen containing gas becomes insufficient, and the oxygen containing gas in the far portion away from the air feeding device becomes Oxygen concentration decreases,
The DO supply capacity may decrease. In such cases,
By attaching a capillary or a minute flow rate valve, the entire oxygen-containing gas can be sufficiently moved to a distant part of the air feeding distance, and the DO replenishing ability can be prevented from being lowered.
The mounting position of the capillary or the like is not limited to the farthest portion of the air supply distance, and may be provided in the middle of the air supply distance as necessary.

Although the consumption of the oxygen-containing gas slightly increases due to the bubbling of the oxygen-containing gas by the capillaries or the like, it can be made much smaller than that of the conventional diffuser plate.

[0035]

As described above, according to the present invention,
Since oxygen in the oxygen-containing gas can be dissolved without difficulty in the bottom of the underwater, which is the source of the polluted water area, the DO deficiency at the bottom can be eliminated in an energy-saving manner by the bubbleless water quality improvement device. Further, the water quality of the polluted water area is improved by the natural purification ability of the bottom-dwelling organisms based on this water quality improvement device. Further, since the water quality improvement device is installed at the bottom of the polluted water area, it does not require a new large installation space on land unlike a normal water treatment device.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a water quality improving device according to the present invention.

FIG. 2 is a plan configuration diagram of a first embodiment of a water quality improving device according to the present invention.

FIG. 3 is a configuration diagram showing a second embodiment of the water quality improving device according to the present invention.

FIG. 4 is a diagram showing a modification of the water quality improving device shown in FIG.

FIG. 5 is a conceptual diagram of an integrated water quality improving device showing a third embodiment of the water quality improving device according to the present invention.

FIG. 6 is a configuration diagram showing a fourth embodiment of the water quality improving device according to the present invention.

FIG. 7 is a configuration diagram showing a fifth embodiment of the water quality improving device according to the present invention.

FIG. 8 is a layout view of the water quality improvement device shown in FIG. 7.

[Explanation of symbols]

 1,10,32,34,40 Water quality improvement unit 2,11,45 Water quality improvement element 3,12,42,46 Base material 4,13,31 Air supply pipe 5,14 Joint 30,33 Porous body 41 Porous membrane

Claims (7)

[Claims] 1. A water quality improving element comprising a porous membrane having a hollow portion and having a large number of gas permeation holes communicating with the outside and the hollow portion, and holding the water quality improving element,
A base material having a communication passage communicating with the hollow portion of the water quality improving element, and an air supply pipe connected to this base material, a water quality improving unit installed at the bottom of the water, and connected to the air supply pipe, A water quality improving device, comprising: an air supply device that supplies an oxygen-containing gas so that the pressure inside the hollow portion of the water quality improving element becomes equal to or lower than the bubble point. 2. The water quality improving device according to claim 1, wherein the porous membrane is a floating hollow fiber membrane. 3. The water quality improving apparatus according to claim 1, wherein the base material and the air supply pipe are assembled in a planar manner, and the water quality improving element is laid between the base materials to assemble the water quality improving unit in a planar manner. 4. The water quality improving device according to claim 3, wherein the water quality improving element is arranged in a woven shape. 5. The water quality improving device according to claim 3, wherein the water quality improving units are provided in multiple stages. 6. A porous body having a hollow portion, a porous membrane provided on the inner surface or the outer surface of the porous body, and an air supply pipe connected to the hollow portion, and arranged at the bottom of the water. A water quality improving unit, and an air supply device that is connected to the air supply pipe and that supplies an oxygen-containing gas so that the pressure in the hollow portion of the porous body is equal to or lower than the bubble point. Improvement device. 7. A plurality of water quality improving elements comprising a porous body having a hollow portion and having a large number of gas permeation holes communicating the hollow portion and the outside, and the water quality improving element having both end portions. While holding with, a base material having a communication path communicating with the hollow portion of the water quality improving element, a joint material connecting the base materials of the plurality of water quality improving elements, and an air supply pipe connected to the base material. A water quality improving unit that is disposed at the bottom of the water, and an air feeding device that is connected to the air feeding pipe and that feeds the oxygen-containing gas so that the pressure inside the hollow portion of the water quality improving element is below the bubble point. A water quality improvement device characterized by being provided.