JP6112604B2 - Constructed wetland for water quality improvement - Google Patents

Description

  The present invention relates to an artificial wetland for improving water quality, and more particularly to an artificial wetland for improving water quality that utilizes the decomposition action of microorganisms on organic substances and nutrient salts.

  Although sewage treatment facilities including sewage systems are taking measures for pollution of business wastewater and domestic wastewater, municipalities with small populations still have low sewage treatment rates. For example, in Western countries, the use of constructed wetlands is advancing as a measure against small-scale pollution in rural areas where sewerage is difficult to spread. Artificial wetlands are those constructed artificially for the main purpose of wastewater treatment. In Japan, artificial wetlands are attracting attention as a method for treating sewage in rural areas where the population is declining.

  For example, Patent Document 1 discloses, as a subsidence type constructed wetland system, a first subsidence type vertical wetland, a second subsidence type vertical wetland, and a subsidence type horizontal wetland that are arranged so as to sequentially distribute sewage. What is provided is disclosed. Here, in the first and second vertical wetlands, a pumice layer having a fine particle size is arranged in the upper layer, a pumice layer having a coarse particle size is arranged in the lower layer, and the vertical peat is arranged vertically from the upper layer to the lower layer. A horizontal underdrain that is connected to the vertical underdrain is disposed at the bottom of the lower layer to perform oxidative sewage purification. In the horizontal wetland, a pumice layer with a coarse particle size is arranged at the entrance and exit in the horizontal direction where sewage flows, and a pumice layer with a fine particle size is arranged in the upper layer, and a volcanic ash-based corrosive soil layer is arranged in the lower layer It has a horizontal underdrain at the bottom, and performs reductive sewage purification.

JP 2008-68211 A

  In Japan, where the land is small and it is difficult to secure land, it is desirable to reduce the land area required for constructed wetlands.

The artificial wetland for improving water quality according to the present invention is an artificial wetland for improving water quality that utilizes the decomposition action of microorganisms on organic matter and nutrients, and a filter bed in which a biofilm or a plant rhizosphere microorganism group is formed, Stacked filter beds stacked vertically in a direction where water falls due to gravity, air communication pipes communicating with the atmosphere, and between the upper and lower filter beds adjacent to each other in the stacked filter beds A plurality of through holes provided on the bottom side of the upper filter bed along the vertical direction, and a plurality of through holes provided on the ceiling side of the lower filter bed along the vertical direction, The water from the upper filter bed can be dripped into the lower filter bed, and air is supplied to the upper filter bed and the lower filter bed connected to the air communication pipe. Function as an air supply layer, A filter bed between pipe conduit der Ru extending in the horizontal direction, are arranged on the bottom side of the lowermost filter bed in stacked filter bed section, the drainage pipe for draining water from the bottom of the lowermost filter bed When provided with a filter bed between conduit has a network structure having a mesh through holes, mesh is made of a resin pipe evenly distributed on the outer periphery, characterized in Rukoto.

  In the constructed wetland for improving water quality according to the present invention, the stacked filter bed portion preferably has two or more filter beds, and the thickness of the lower filter bed is preferably larger than the thickness of the upper filter bed. .

In artificial wetland for water quality improvement according to the present invention, filter media disposed in the filter bed, the particle size of the upper side of the filter medium is water receiving side is not coarse than the particle size of the filter medium of the lower stage is water discharge side It is preferable.

  In the artificial wetland for improving water quality according to the present invention, it is preferable to include a blower that sends air into the air communication pipe.

  The constructed wetland for improving water quality according to the present invention includes an air communication pipe communicating with the atmosphere, and at least two or more filter bed pipes are arranged, and the filter bed pipe arranged on the upper stage side is a lower stage. It is preferable that the amount of air supplied from the air communication pipe is larger than that between the filter bed pipes disposed on the side.

  The artificial wetland for improving water quality according to the present invention includes an air communication pipe communicating with the atmosphere, and at least two pipes between the filter beds are arranged, and the pipe between the filter beds arranged on the upper stage side is air communication. It is preferable that it is connected to a pipe and is not connected to an inter-filter bed pipe disposed on the lower side.

  With the above configuration, when constructing an artificial wetland by stacking multiple stages of filter beds in the vertical direction where water falls due to gravity, by placing an air supply layer between the filter beds to be stacked, it is due to microorganisms about organic matter and nutrient salts The decomposition action can be sufficiently performed. Thereby, the site area required for the constructed wetland can be reduced.

It is a figure which shows the structure of the artificial wetland for water quality improvement in embodiment which concerns on this invention. FIG. 2 is a detailed view of FIG. 1. It is a figure which shows two examples of the resin pipes which comprise the air supply layer used for the artificial wetland for water quality improvement in embodiment which concerns on this invention. It is a figure which compares the oxygen concentration of the artificial wetland for water quality improvement in embodiment which concerns on this invention with the artificial wetland of a prior art. In the artificial wetland for water quality improvement in embodiment which concerns on this invention, it is a schematic diagram which shows how to advance that water quality is improved. In the artificial wetland for water quality improvement in embodiment which concerns on this invention, it is a figure which shows the example in which a stacked filter bed part has an oxidizing region and a reducing region. In the artificial wetland for water quality improvement in embodiment which concerns on this invention, it is a figure which shows the example of the structure which changes gradually from oxidizing property to reducing property from the upper stage side of a stacked filter bed part to a lower stage.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. The dimensions, shapes, types of filter media, the number of stacked filter beds, and the like described below are examples for explanation, and can be appropriately changed according to the specifications of the constructed wetland.

  In the following, corresponding elements in all drawings are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a cross-sectional view showing the configuration of an artificial wetland 10 for improving water quality. The artificial wetland 10 for improving water quality is a sewage treatment facility that discharges as treated water with reduced BOD (Biochemical Oxygen Demand) by utilizing the decomposition action of microorganisms on organic substances and nutrients contained in supplied sewage. The BOD processed here includes organic BOD and nitrogenous BOD. Organic BOD may be referred to as carbonized BOD, and nitrogenous BOD may be referred to as N-BOD.

  Below, the artificial wetland 10 for water quality improvement is called the artificial wetland 10 unless otherwise indicated. Although it is not a component of the constructed wetland 10 in FIG. 1, the soil 2 of the facility where the constructed wetland 10 is laid, the reed 4 planted in the constructed wetland 10, the sewage 6 supplied to the constructed wetland 10, the constructed wetland The treated water 8 discharged from 10 is illustrated.

  The artificial wetland 10 is disposed inside the waterproof frame 12 for partitioning the soil 2 so that the sewage 6 and the water being treated do not flow out. The constructed wetland 10 includes a stacked filter bed portion 20 in which filter beds 22, 24, 26, and 28 in which biofilms or plant rhizosphere microorganisms are formed are stacked in four stages in the vertical direction in which water falls by gravity. Further, the stacked filter bed section 20 includes an inter-filter bed pipe line 40 having a function as an air supply layer provided between the filter beds 22, 24, 26, and 28. In the example of FIG. 1, an air supply line 42 between the filter bed 22 and the filter bed 24, an air supply line 44 between the filter bed 24 and the filter bed 26, and an air between the filter bed 26 and the filter bed 28. A supply line 46 is provided for each. Further, a drainage pipe 60 is provided on the bottom side of the lowermost filter bed 28 in the stacked filter bed 20 and drains water from the bottom of the lowermost filter bed 28. The air supply pipes 42, 44, 46 are connected to an air communication pipe 70 that communicates with the atmosphere. The drainage pipe 60 also has a function as an air supply pipe for supplying air to the lowermost filter bed 28.

  The biofilm is a film of microorganisms attached to gravel, sand, and soil disposed on the filter beds 22, 24, 26, and 28. For example, a slimy layer is attached to gravel and sand in a river flow, and this layer is a film made of organic matter and nutrients contained in water and microorganisms that eat them. This membrane is a biofilm. The plant rhizosphere microorganism group is a community of microorganisms in the soil that eats organic matter and nutrients around the root of the reed 4 in FIG.

  Microorganisms included in the biofilm or plant rhizosphere microorganism group include BOD oxidizing bacteria and nitrifying bacteria. BOD-oxidizing bacteria take saccharides and organic acids into the body, and oxidatively decompose most of them by enzymatic reaction within about 48 hours. In addition, starch, protein, and lipid are reduced in molecular weight by hydrolysis and then oxidatively decomposed by enzymatic reaction. In this case, it takes time to lower the molecular weight. Nitrifying bacteria oxidize ammonia nitrogen in water to nitrate nitrogen, and then take over the denitrification step by denitrifying bacteria in an oxygen-free environment, thereby decomposing ammonia into nitrogen gas. In this way, treated water with reduced BOD by decomposing organic matter and nutrients contained in sewage by utilizing BOD oxidizing bacteria, nitrifying bacteria, and denitrifying bacteria contained in biofilms and plant rhizosphere microorganisms And can.

  FIG. 2 is a detailed configuration diagram of the constructed wetland 10. In FIG. 2, the illustration of the soil 2, the reed 4, the sewage 6, and the treated water 8 discharged to the outside in FIG. 1 is omitted, and instead, the mid-treatment water 7 and the treated water 8 inside the artificial wetland 10 are used. Illustrated.

  The waterproof frame 12 is a rectangular parallelepiped box that forms the outer shape of the artificial wetland 10 and has an opening on the upper side. Each element constituting the constructed wetland 10 is accommodated in the waterproof frame 12. As the waterproof frame 12, it is possible to use a frame formed of concrete in a desired shape, coated with a waterproof resin on the inner wall, or pasted or laid with a waterproof resin sheet.

  The filter beds 22, 24, 26, and 28 stacked in four stages through the filter bed pipe line 40 are sewage treatment layers in which a filter medium capable of forming a biofilm or a plant rhizosphere microorganism group is laid. The direction from the upper side to the lower side of the sheet of FIG. 2 is the vertical direction in which water falls due to gravity.

  Along the vertical direction, the uppermost filter bed 22 uses gravel having a coarse particle size as a filter medium. Specifically, shale gravel 30 having a particle size of about 5 mm to about 10 mm is used. The filter bed 22 is uniformly arranged in both the thickness direction and the plane of the shale gravel 30. An example of the thickness of the filter bed 22 is about 50 mm to about 600 mm. For example, the thickness of the filter bed 22 can be about 350 mm.

  The second-stage filter bed 24 from the top has two layers in the thickness direction of the filter medium. On the lower layer side, gravel having a coarse particle size is used as in the filter medium of the first-stage filter bed 22 from the top. That is, shale gravel 30 having a particle size of about 5 mm to about 10 mm is used. On the upper layer side, gravel or sand having a finer particle size than the lower layer side is used. Specifically, shale gravel 32 having a particle size of about 1 mm to 5 mm is used. It is preferable to make the thickness of the gravel 32 thicker than the thickness of the gravel 30. For example, the thickness of the gravel 32 is preferably 3 times or more the thickness of the gravel 30. As an example, the total thickness of the filter bed 24 is about 350 mm, the thickness of the gravel 30 is about 50 mm, and the thickness of the gravel 32 is about 300 mm.

  The third-stage filter bed 26 from the top has three layers in the thickness direction of the filter medium. Gravel with a coarse particle diameter is used for the lowest layer side like the filter medium of the first-stage filter bed 22. That is, shale gravel 30 having a particle size of about 5 mm to about 10 mm is used. For the intermediate layer, gravel or sand having a finer particle size than the lower layer side is used. Specifically, shale gravel 32 having a particle size of about 1 mm to 5 mm is used. On the uppermost layer side, sand or soil having a finer particle size than the intermediate layer is used. Specifically, fine sand 34 having a particle size of less than about 1 mm is used. It is preferable to make the thickness of the gravel 32 thicker than the thickness of the gravel 30 and make the fine sand 34 thicker than the thickness of the gravel 32. For example, the thickness of the fine sand 34 may be three times or more the total thickness of the gravel 30 and the gravel 32.

  The lowermost filter bed 28 has a three-layer configuration in the thickness direction of the filter medium, as in the third filter bed 26 from the top. The lowermost filter bed 28 may be the same as the third-stage filter bed 26 from the top. However, in order to effectively perform a denitrification process by denitrifying bacteria as an anaerobic environment, the lowermost filter bed 28 is used. It is preferable to make the total filter bed thickness thicker than the total filter bed thickness of the third stage filter bed 26.

  In the stacked filter bed part 20, as the sewage flows from the upper stage toward the lower stage, the organic matter BOD is reduced by the activity of the BOD oxidizing bacteria. When organic matter BOD is reduced to some extent, nitrifying bacteria that decompose ammonia nitrogen into nitrate nitrogen by oxidation can also be activated. In view of this, it is preferable to provide an environment where oxygen supply is sufficient even on the lower side where the organic matter BOD is sufficiently reduced.

  The inter-filter bed pipe 40 is a pipe line provided between the upper filter bed and the lower filter bed adjacent to each other in the stacked filter bed, and at least water from the upper filter bed. Can be dropped onto the lower filter bed. In addition, in the inter-filter bed pipe 40, if the stacked filter beds 20 are left as they are, the entire filter bed becomes thick, oxygen in the filter bed is deficient, and the activities of BOD oxidizing bacteria and nitrifying bacteria become weak. Therefore, it has a function as an air supply layer in which oxygen is supplied in the middle. In FIG. 1 and FIG. 2, the stacked filter bed 20 is composed of four stages of filter beds 22, 24, 26, and 28, so that air supply lines 42, 44, and 46 are respectively provided between the filter beds adjacent in the vertical direction. Be placed.

  The air supply pipes 42, 44, 46 are constituted by a resin pipe 50 having a perforated structure on the outer periphery. The resin pipe 50 includes a pipe body 52 having a cylindrical or elliptical cross section, openings 54 and 56 at both ends, and opening holes provided on the outer periphery, and the bottom side of the upper filter bed along the vertical direction. And a plurality of through holes 59 provided on the ceiling side of the lower filter bed along the vertical direction. The through holes 58 and 59 are used to drop air into the pipe section of the pipe body 52 through the function of supplying air to the upper filter bed and the lower filter bed, and water 7 in the middle of processing from the upper filter bed. It has the function of supplying water to the lower filter bed. That is, the through holes 58 and 59 are air supply holes and water passage holes.

  The air supply pipes 42, 44, and 46 are pipes obtained by extending the resin pipe 50 in the horizontal direction. Extending in the horizontal direction without an inclination angle prevents the water dripping through the through hole 58 from becoming uneven along the extending direction of the pipeline, and the air supplied to the filter bed. This is because the amount is made uniform along the extending direction of the pipe.

  FIG. 3A shows a resin pipe 50 used for the air supply pipes 42, 44, 46. The resin pipe 50 is a plastic product obtained by molding a high-density polyethylene resin into a mesh shape, and the mesh opening ratio is about 7 to 15%. Since the mesh is evenly distributed on the outer periphery, the resin pipe 50 is used, and a plurality of the meshes are arranged side by side without any gaps on the filter bed corresponding to the lower stage, and the filter bed corresponding to the upper stage is arranged thereon. Thus, the stacked filter bed portion 20 with the inter-filter bed conduit 40 of FIGS. 1 and 2 can be formed.

  As the resin pipe 50, a culvert pipe NETRON (registered trademark) manufactured by Mitsui Chemicals, Inc. can be used. As another example, the resin pipe 51 shown in FIG. 3 (b) is a culvert pipe NEODRAIN (registered trademark) manufactured by Mitsui Chemicals, and is a corrugated perforated pipe line in which a thick part is provided in a spiral shape. is there. Since the thick portion is provided in a spiral shape, the rigidity as a pipe line is high.

  Returning again to FIG. 2, the air supply pipes 42, 44, and 46 are provided between the filter beds 22, 24, 26, and 28 constituting the stacked filter bed portion 20, respectively. , 24, 26, and 28 can be supplied with air from the inside of the stacked filter bed 20 in addition to supplying air from the atmosphere in contact with the uppermost surface layer of the stacked filter bed 20. For example, the first-stage filter bed 22 receives air supply from the atmosphere in contact with the surface layer and from both sides of the through hole 58 on the ceiling side of the air supply pipe line 42 in contact with the bottom layer. The second-stage filter bed 24 receives air supply from both sides of the through hole 59 at the bottom of the air supply conduit 42 in contact with the surface layer and the through hole 58 on the ceiling side of the air supply conduit 44 in contact with the bottom layer. Similarly, the third-stage filter bed 26 receives air supply from both sides of the through hole 59 at the bottom of the air supply conduit 44 in contact with the surface layer and the through hole 58 on the ceiling side of the air supply conduit 46 in contact with the bottom layer. . The fourth-stage filter bed 26, which is the lowermost stage, supplies air from both a through-hole 59 at the bottom of the air supply pipe 46 in contact with the surface layer and a through-hole 66 on the ceiling side of the drain pipe 60 described below. Receive.

  The drain pipe 60 is a drain for draining water from the bottom of the lowermost filter bed 28. The drain pipe 60 has a pipe main body 62 having a rectangular cross section, a drain port 64 that is an opening on one side of the pipe main body 62, and a plurality of through holes 66 provided in the ceiling. The opening on the other side of the conduit main body 62 is closed by the waterproof frame 12. The through hole 66 has a function of dropping the treated water 8 from the lowermost filter bed 28 to the pipe portion of the pipe body 62 and guiding the water to the drain port 64. Note that the air in the drainage pipe 60 passes through the through hole 66, and the bottom layer of the lowermost filter bed 28 comes into contact with the air in the drainage pipe 60. As described above, the drain pipe 60 has an air supply function with respect to the lowermost filter bed 28.

  The drain pipe 60 can be used by arranging a plurality of appropriate through holes 66 in the ceiling of the pipe main body 62 having a rectangular cross section and arranging it on the bottom of the waterproof frame 12. Instead of this, a support plate may be disposed along the inner peripheral wall of the bottom of the waterproof frame 12, and a snowboard plate having a plurality of through holes 66 may be placed on the support plate. In this case, the pipe body 62 is a combination of the support plate and the drainboard plate. The cross section of the drain pipe 60 may be other than a rectangular shape. For example, the resin pipes 50 and 51 described in FIGS. 3A and 3B may be used for the drainage pipe 60. In this case, for example, a plurality of resin pipes 50 and 51 are arranged in parallel at the bottom of the waterproof frame 12.

The air communication pipe 70 is a pipe arranged in the vertical direction in the artificial wetland 10. The air communication pipe 70 is disposed on the side of the openings 54 and 56 at both ends of the air supply pipes 42, 44 and 46, respectively. In the example of FIG. 2, the air supply pipes 42, 44, 46 are arranged along the left-right direction on the paper surface inside the waterproof frame body 12, so the air communication pipe 70 is on the waterproof frame body 12 on the paper surface. Are arranged at the left and right ends, respectively. Each air communication pipe 70 has a pipe body 72, an upper opening 74 in the vertical direction, and a lower opening 76. The upper opening 74 is open to the atmosphere. In FIG. 2, the opening 74 is completely open toward the sky, but an appropriate cover is provided on the opening 74 so that rain and surrounding earth and sand do not enter the air communication pipe 70. The cover is structured such that gas communicates but liquid and solid prevent inflow. Opening 7 6 on the lower side is connected to the open hole provided in the drain line 60.

  Further, the air communication pipe 70 is provided with a plurality of opening holes in the side wall at intervals along the vertical direction, and the opening holes 54 and the opening portions 54 at both ends of the air supply pipes 42, 44, 46 are provided. 56 is connected.

  That is, in the air communication pipe 70 disposed on the left side of the paper surface of FIG. 2, the opening hole provided in the side wall in the vertical direction is connected to the opening 54 at the left end of each of the air supply pipes 42, 44, 46. Similarly, in the air communication pipe 70 disposed on the right side of the paper surface of FIG. 2, an opening hole provided in the side wall in the vertical direction is connected to the opening 56 at the right end of each of the air supply pipes 42, 44, 46. .

  The fan 78 provided above the air communication pipe 70 is a blower that sends air into the air communication pipe 70. As a result, air can be fed into the air supply pipes 42, 44, 46 through the opening 74 on the upper side of the air communication pipe 70 and the openings 54 of the air supply pipes 42, 44, 46. . The fan 78 may be driven by a motor, or may be a windmill that rotates by receiving wind that is an atmospheric flow and thereby sends the wind to the air communication pipe 70.

  The effects of the above configuration will be further described with reference to FIGS. FIG. 4 is a diagram showing a result of comparison of the oxygen concentration in the filter bed between the above configuration and the conventional technology. In these figures, the vertical axis is the vertical position of one filter bed, and the upper side of the paper is the upper layer side of the filter bed, and the lower side of the paper is the lower layer side of the filter bed. The horizontal axis is the horizontal position in one filter bed. In these figures, the magnitude of the oxygen concentration in the filter bed is shown by the density of diagonal lines and vertical and horizontal lines. The greater the density of the diagonal and vertical and horizontal lines, the higher the oxygen concentration. That is, these figures are diagrams showing the distribution of the oxygen concentration in the cross-sectional view of one filter bed by the density of the oblique lines and vertical and horizontal lines.

  FIG. 4A shows the case of the filter beds 22, 24, and 26 described with reference to FIGS. The filter bed 22 is in contact with the atmosphere on the upper layer side, and is in contact with the air supply pipe line 42 on the lower layer side. The filter bed 24 is in contact with the air supply conduit 42 on the upper layer side and in contact with the air supply conduit 44 on the lower layer side. The filter bed 26 is in contact with the air supply conduit 44 on the upper layer side and in contact with the air supply conduit 46 on the lower layer side. As described above, the filter beds 22, 24, and 26 described with reference to FIGS. 1 and 2 are in contact with the air on both the upper layer side and the lower layer side, and are supplied with oxygen. Therefore, FIG. 4A shows that the oxygen concentration is maximized on the upper layer side and the lower layer side of the filter bed, and the oxygen concentration is minimized at an intermediate portion along the vertical direction of the filter bed.

  FIG. 4B shows the case of a conventional filter bed. For example, the filter bed of the underground flow constructed wetland described in the cited document 1 is in contact with the atmosphere on the upper layer side, but is in contact with a horizontal underdrain that drains. Therefore, although oxygen is supplied from the upper layer side, the lower layer side is hardly supplied with oxygen. In another conventional technique, there is an example in which treated water discharged from the lower layer side is directly immersed in soil in which artificial wetlands are embedded. In this case, oxygen is supplied from the upper layer side, but oxygen is not supplied from the lower layer side. Therefore, FIG. 4B shows that the oxygen concentration is maximized on the upper layer side of the filter bed and the oxygen concentration is minimized on the lower layer side of the filter bed.

  FIG. 5 is a conceptual diagram showing changes in BOD when a plurality of filter beds of artificial wetlands are arranged and sewage is sequentially treated. The horizontal axis is the number of stages of the filter bed, which corresponds to the distance that sewage flows through the filter bed. The inflow side is a place where sewage flows in, and a place where sewage flows into the uppermost layer of the first-stage filter bed. When the sewage finishes flowing in the first stage, it flows into the uppermost layer of the second stage filter bed. By repeating this, the outflow side is a place where treated water is discharged from the fourth stage filter bed. The vertical axis in the upper diagram is the amount of organic BOD, and the vertical axis in the lower diagram is the amount of N-BOD.

  When the sewage is supplied to the uppermost layer side of the filter bed, the sewage flows through the filter bed from the upper layer side to the lower layer side by gravity. If the filter bed depth, which is the distance in the vertical direction of the filter bed, is 65 cm, for example, there are differences depending on what kind of gravel, sand, soil, etc. the filter bed is composed of, and there are also differences depending on the temperature. To give an example, the sewage passes through the filter bed in about 5 minutes in summer, about 30 minutes in winter, and about 15 minutes in spring or autumn. During this passage, BOD of sewage adheres to the biofilm of the filter bed or the plant rhizosphere. Then, organic substances and nitrides are decomposed over time by the activities of BOD oxidizing bacteria and nitrifying bacteria. The time required for decomposition varies depending on the filter bed configuration, temperature, and the like, but is, for example, about 48 hours.

Therefore, if sewage is continuously supplied, the BOD contained in the sewage that has passed through the filter bed is reduced. In the schematic diagram of FIG. 4, each time the sewage passes through one filter bed, the amount of organic matter BOD is shown to be halved. If the initial organic matter BOD of the sewage flowing into the constructed wetland is 1000 (mg / 1000 cm ³ ), it will be 500 (mg / 1000 cm ³ ) after passing through the first stage filter bed, and after passing through the second stage filter bed. 250 (mg / 1000 cm ³ ), 125 (mg / 1000 cm ³ ) after passing through the third stage filter bed, and 62.5 (mg / 1000 cm ³ ) after passing through the fourth stage filter bed.

In general sewage sewage, the amount of N-BOD is smaller than the amount of organic BOD. In FIG. 5, the amount of organic BOD in the initial wastewater is shown as 1000 (mg / 1000 cm ³ ), and the amount of N-BOD is shown as 200 (mg / 1000 cm ³ ). Since nitrifying bacteria that process N-BOD are less active than oxidized BOD bacteria, if the amount of organic matter BOD is larger than the amount of N-BOD, most of the supplied oxygen is taken by oxidized BOD bacteria, and nitrified Does not turn to fungus. When the organic matter BOD is decomposed and reduced by oxidized BOD bacteria and reaches the same amount as N-BOD, N-BOD degradation by nitrifying bacteria and the like starts. In the example of FIG. 5, the amount of organic BOD is approximately the same as the amount of N-BOD in the third-stage filter bed, and the amount of N-BOD begins to decrease from this point.

  When the amount of organic matter BOD is several times the amount of N-BOD as in the model of FIG. 5, the amount of organic matter BOD is first reduced by the activity of oxidized BOD bacteria, and then the amount of organic matter BOD is reduced by the activity of nitrifying bacteria. -The amount of BOD begins to decrease. The decomposition of N-BOD is performed in an oxidation stage that requires oxygen and a subsequent reduction stage that does not require oxygen. Therefore, in order to reduce the amount of N-BOD smoothly, in the case of the model of FIG. 5, it is preferable that the filter bed has reducibility from the 4th stage.

  As described above with reference to FIGS. 1 and 2, even when the stacked filter bed 20 has a structure in which a plurality of filter beds are arranged in the vertical direction, a plurality of filter beds are arranged in a plane as in the prior art. The same applies to the structure to be arranged. In the prior art of Patent Document 1, two filter beds for purifying oxidative sewage are connected, and then a filter bed for purifying reductive sewage is disposed. Thus, in the prior art, the structure of the filter bed for purifying oxidative sewage that supplies oxygen and the structure of the filter bed for purifying oxygen-free reduced sewage are separated.

  In the structure of FIGS. 1 and 2, as described with reference to FIG. 4, the oxygen concentration is lowest in the middle portion of the filter bed. Therefore, by appropriately setting the filter bed thickness, which is the vertical dimension of the filter bed, it is possible to supply oxygen sufficiently in one filter bed to activate the activities of oxidized BOD bacteria and nitrifying bacteria. It is possible to create a region and a reducible region in which the activity of denitrifying bacteria can be made active in anoxic conditions. In particular, in order to make the activity of the denitrifying bacteria more active, it is better to widen the reducing region, so it is better to increase the filter bed thickness. As described in the model of FIG. 5, the activity of nitrifying bacteria begins, and the activity of denitrifying bacteria subsequently begins in the filter beds disposed downstream of the plurality of filter beds. Therefore, by reducing the thickness of the filter bed disposed on the upstream side among the plurality of filter beds and further increasing the thickness of the filter bed disposed on the downstream side, the activity of oxidized BOD bacteria, Both nitrifying bacteria and activities of denitrifying bacteria can be achieved. In the example of FIG. 1 and FIG. 2, the stacked filter bed 20 is preferably two or more filter beds, and the lower filter bed is preferably thicker than the upper filter bed.

  In one stacked filter bed 20, in order to make the oxidizing environment and the reducing environment more positively compatible, the supply of oxygen to the portion of the filter bed that is desired to be the reducing environment may be narrowed or cut off. In the example of the stacked filter bed 20 having the model characteristics of FIG. 5, the oxygen supply to the fourth-stage filter bed 28 may be restricted or cut off. For example, it is assumed that the opening 76 leading to the drainage pipe 60 is closed at the bottom of the air communication pipe 70 and the oxygen supply from the drainage pipe 60 to the fourth-stage filter bed 28 is shut off. Further, the resin pipe 50 disposed between the third-stage filter bed 26 and the fourth-stage filter bed 28 narrows or completely closes the opening 54 communicating with the air communication pipe 70 to a small opening area. To do.

  The model in FIG. 5 is an example of purification characteristics in the constructed wetland 10, and the sewage 6 supplied to the constructed wetland 10 has various organic BOD and N-BOD configurations. For example, there are cases where the sewage 6 is mostly organic BOD and contains little N-BOD, and conversely, there are cases where the sewage 6 has an overwhelmingly large N-BOD and a small amount of organic BOD. Therefore, it is preferable to design the arrangement of the oxidizing environment and the reducing environment of the stacked filter bed 20 according to the configuration of the organic BOD and N-BOD in the sewage 6. FIG. 6 and FIG. 7 are diagrams showing two examples of the constructed wetland 11 that performs layout design of an oxidizing environment and a reducing environment according to the characteristics of the sewage 6.

  FIG. 6 is a diagram showing an example of designing the stacked filter bed section 20 having N = n stages of filter beds so that several stages on the upper stage side are oxidizing regions and several stages on the lower stage side are reducing areas. It is. Here, the filter bed in the oxidizing region is representative, the filter bed 21 in the uppermost stage (N = 1), the filter bed 21 in the lower stage (N = 2), and the filter bed in the reducing region. The lowermost filter bed 21 (N = n) and the upper filter bed 21 (N = n−1) are shown. Here, the opening connecting part of the air communication pipe 71 and the drain pipe 60 is closed and closed. Further, a resin pipe 50 (N = n-2), a resin pipe 50 (N = n-1), a resin pipe 50 (N = n) t and an air communication pipe facing the filter bed 21 in the reducing region. The opening connecting portion 71 is also closed and closed.

  In this way, by switching the connection relationship between the resin pipe 50 and the drain pipe 60 and the air communication pipe 71 from the communication state to the closed state at a predetermined stage, the upper filter side of one stacked filter bed 20 The predetermined number of filter beds 21 can be used as the oxidizing region, and the lower filter bed 21 can be used as the reducing region.

  FIG. 7 is a diagram showing an example of a configuration in which the stacked filter bed 20 having N = n stages of filter beds gradually changes from oxidizing to reducing from the upper side to the lower side of the stacked filter bed 20. is there. Here, the opening area of the opening 80 at the portion where the air communication pipe 71 and the resin pipe 50 at each stage are connected is set to be smaller from the upper stage side to the lower stage side. Further, the opening area of the opening 82 where the drain pipe 60 and the air communication pipe 71 are connected is also set to be appropriately small. The opening 80 (N = n−1) and the opening 82 related to the lowermost filter bed (N = n) may be closed.

  In this way, by setting the opening area of the opening 80 where the resin pipe 50 and the air communication pipe 71 are connected to be smaller from the upper stage side toward the lower stage side, one stacked filter bed part 20 is formed. About the some filter bed 21 to comprise, it can be made to change gradually from a state with large oxidizability to a state with large reducibility from the upper stage side to the lower stage side.

  2 soil, 4 reeds, 6 sewage, 7 treated water, 8 treated water, 10,11 artificial wetland, 12 waterproof frame, 20 stacked filter beds, 21, 22, 24, 26, 28 filter beds, 30, 32 Gravel, 34 Fine sand, 40 Filter bed pipe, 42, 44, 46 Air supply pipe, 50, 51 Plastic pipe, 52 Pipe body, 54, 56, 74, 76, 80, 82 Opening, 55 , 77 Closed part, 58, 59, 66 Through hole, 60 Drain pipe, 62 Pipe body, 64 Drain port, 70, 71 Air communication pipe, 72 Pipe body, 78 Fan.

Claims (6)

An artificial wetland for improving water quality that utilizes the microbial decomposition of organic matter and nutrients,
A filter bed part in which a plurality of filter beds in which biofilms or plant rhizosphere microorganisms are formed are stacked in a vertical direction in which water falls by gravity; and
An air communication pipe communicating with the atmosphere;
In the stacked filter bed, a plurality of through holes provided between the upper filter bed and the lower filter bed adjacent to each other in the stack, provided on the bottom side of the upper filter bed along the vertical direction, A plurality of through holes provided on the ceiling side of the lower filter bed along the direction, and water from the upper filter bed can be dripped into the lower filter bed, and air connected to the communication pipe has a function as an air supply layer for supplying air to and the upper side of the filter bed and the lower side the filter bed, and between Ru conduit der extending horizontally filter bed pipes,
A drain line that is disposed on the bottom side of the bottom filter bed in the stacked filter bed and drains water from the bottom of the bottom filter bed;
Equipped with a,
The pipe between the filter beds is
Has a network structure having a mesh through holes, artificial wetland for water quality improvement network is characterized Rukoto consists of a resin pipe evenly distributed on the outer circumference. In the artificial wetland for water quality improvement according to claim 1 ,
The stacked filter bed has two or more filter beds,
An artificial wetland for improving water quality, wherein the lower filter bed is thicker than the upper filter bed. In the constructed wetland for water quality improvement according to claim 1 or 2 ,
The filter medium placed on the filter bed is
Artificial wetland for water quality improvement the particle size of the filter medium of the upper side is a water receiving side is characterized also crude Ikoto than the particle size of the filter medium of the lower stage is water discharge side. In the artificial wetland for water quality improvement of any one of Claim 1 to 3 ,
An artificial wetland for improving water quality, comprising a blower that feeds air into an air communication pipe. In the artificial wetland for water quality improvement of any one of Claim 1 to 4 ,
Filtration beds conduit is arranged at least two or more, the filter bed between pipe disposed on the upper side, the amount of air supplied from the air communication tube than the filter bed between conduit arranged in the lower side An artificial wetland for improving water quality, characterized by its abundance. In the artificial wetland for water quality improvement of any one of Claim 1 to 4 ,
Filtration beds conduit is arranged at least two or more, the filter bed between pipe disposed on the upper side is connected to the air communication pipe, it is not connected to the filter bed between conduit arranged in the lower side An artificial wetland for improving water quality.

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