JP2012183494A - Percolating water cleaning ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a percolating water cleaning ground which can be adopted without being limited by a groundwater level or the like, and can effectively purify nitrate nitrogen-contaminated water.SOLUTION: The percolating water cleaning ground 1 is configured by laminating up and down, an upper layer 2 composed by a first material that is sand or a material having the particle diameter finer than that of sand, and a lower layer 3 composed by a second material that is a material having the particle size rougher than that of the first material at the upper position from a groundwater level WL, wherein a cleaning part 4 in which a sustained release organic matter 5 is mixed with the first material is formed in the lower end of the upper layer 2.

Description

  The present invention relates to a seepage water purification ground.

In the ground containing high concentration of nitrogen due to excessive fertilization, etc., contaminated infiltrated water may permeate due to rainfall, which may contaminate groundwater.
As a method for preventing the diffusion of such pollutants, there is a case where a purification layer is formed in the ground by a biological denitrification method, and denitrification is performed before decontamination before the contaminated permeated water flows into the groundwater area.

In order to promote biological denitrification of nitrate nitrogen, supply of organic substances and formation of an anaerobic environment are effective.
For example, in Patent Document 1, in order to promote biological nitrogen of nitrate nitrogen, a layer with low water permeability (purification layer 103) in which a sustained-release organic substance 104 is mixed in unsaturated ground (natural ground 102). ) Is provided at a position higher than the groundwater level WL, thereby disclosing an osmotic water purification ground 101 for supplying organic matter, forming an anaerobic environment, and securing a residence time.

JP 2009-11947 A

  However, in the conventional seepage water purification ground 101, when the amount of seepage water temporarily increases, such as when there is a lot of rainfall, there is a risk that the water level will rise and surface drowning will occur. When the ground surface is a field or the like as in an agricultural area or the like, surface groundwater causes root rot, so it is desirable to form the purification layer 103 of the seepage water purification ground 101 at a relatively deep position. However, when the groundwater level WL is high, the depth necessary to prevent surface flooding may not be ensured.

  Therefore, this invention makes it a subject to propose the osmotic water purification ground which can be employ | adopted without being limited to a groundwater level etc. and was able to purify nitrate nitrogen pollution water effectively. .

  In order to solve the above problems, the present invention provides an upper layer composed of sand or a material having a particle diameter finer than that of sand, and a second material that is a material having a coarser particle diameter than the first material. Is a permeated water purification ground layered vertically above and below the groundwater level, and a lower part of the upper layer has a purification unit in which a sustained-release organic substance is mixed with the first material. It is characterized by being formed.

According to such a permeated water purification ground, a lower layer composed of a second material having a coarse particle size (for example, gravel) is provided below an upper layer made of the first material having a fine particle size (sand or a material finer than sand). As a result, a capillary barrier (a water-impervious layer formed by the difference in capillary force between the upper layer and the lower layer) is formed between the upper layer and the lower layer, and permeated water from the ground surface is prevented from penetrating the capillary barrier. The function enables the purification unit to retain water.
And in the purification | cleaning part with which sustained-release organic substance was mixed, since it becomes easy to form anaerobic environment with high saturation, biological denitrification is accelerated | stimulated. Therefore, the nitrate nitrogen contaminated water that has permeated from the surface side is purified in the purification section and discharged to the lower layer.

In addition, if the permeated water from the surface side exceeds the water retention capacity of the purification unit (upper layer), the capillary barrier breaks through and drains downward (lower layer), so the water level rises and the surface water is submerged. There is no fear.
In the present specification, “sand” has a particle size classified as sand by the soil classification.

  Moreover, if the water permeable sheet which prevents that said 1st material flows out into the said lower layer is interposed in the interface of the said upper layer and the said lower layer, the fall of the water retention capability of an upper layer can be prevented. . That is, when the first material flows out to the lower layer, the density of the upper layer is reduced, and the water retention capacity of the upper layer is reduced. Therefore, the water permeable sheet prevents the first material from flowing out, thereby preventing a decrease in water retention capacity.

  If the laminated structure composed of the upper layer and the lower layer is laminated in a plurality of stages, purification of nitrate-nitrogen-contaminated water is performed a plurality of times before reaching the groundwater, so that purification performance can be further improved. .

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to employ | adopt the osmotic water purification | cleaning ground which purifies nitrate nitrogen pollution water, without being limited to topographic shape.

It is sectional drawing which shows the outline | summary of the permeated water purification | cleaning ground which concerns on embodiment of this invention. It is sectional drawing which shows typically the water retention condition of the seepage water purification ground. (A) is sectional drawing which shows typically the test model of an Example, (b) is a graph which shows saturation distribution after the steady state in an Example. It is a graph which shows the relationship of time and the accumulated water amount, accumulated wastewater amount, water retention amount, sand layer void volume, and time in Examples. It is sectional drawing which shows the outline | summary of the conventional permeated water purification ground.

Hereinafter, preferred embodiments of the present invention will be described.
The permeated water purification ground 1 of the present embodiment purifies nitrate nitrogen eluted from a field or the like before reaching the ground water surface in an agricultural land or the like. As shown in FIG. In the inside, the upper layer 2 and the lower layer 3 are configured to be stacked vertically above and below the groundwater level WL.

The upper layer 2 is made of a first material which is a material classified as sand in the soil classification or a material having a particle diameter finer than that of sand. In this embodiment, excavated soil generated by excavating the natural ground G is used. The material constituting the first material is sand or so-called sandy soil mainly composed of sand. The first material is desirably a material having a water permeability greater than 1 × 10 ⁻⁴ cm / sec.
In addition, you may form the upper layer 2 with the sand etc. which were carried in.

At the lower end portion of the upper layer 2, a purification portion 4 in which a sustained-release organic material 5 is mixed with the first material is formed.
The purification | cleaning part 4 is formed so that the position where the water retention capability by the capillary force of the 1st material (upper layer 2) is high may be included. Although the layer thickness of the purification unit 4 is not limited, in this embodiment, as shown in FIG. 2, the purification unit 4 performs purification so as to have a layer thickness that can include a region where the saturation level is 80% or more. Part 4 is formed.

  In addition, the upper surface and the lower surface (the boundary surface between the upper layer 2 and the lower layer 3) of the purification unit 4 are formed flat (substantially horizontal) so that permeated water does not flow out along the purification unit 4.

  The lower layer 3 is composed of a second material that is a material having a coarser particle diameter than the first material. In this embodiment, crushed stone is employed as the second material, but the material constituting the second material is not limited as long as the material has a coarser particle diameter than the first material. For example, materials classified as gravel in the soil classification are desirable.

  In the present embodiment, the lower layer 3 is formed directly above the groundwater level WL so that the lower surface of the lower layer 3 is in contact with the groundwater surface. It may be separated upward from WL. Moreover, even if it is a case where 2nd material is arrange | positioned in the position lower than the groundwater level WL on construction, the position of the lower surface of the lower layer 3 is recognized as a groundwater surface (groundwater level WL).

  As shown in FIG. 1, a water permeable sheet 6 made of a nonwoven fabric or the like is interposed at the boundary surface between the upper layer 2 and the lower layer 3. In addition, the material which comprises the water-permeable sheet 6 is not limited to a nonwoven fabric, The material which can permeate | transmit a water | moisture content without allowing the 1st material which comprises the upper layer 2, and the sustained release organic substance 5 to pass through. What is necessary is just to select suitably from the inside and to employ | adopt.

  The permeated water purification ground 1 is formed by laminating the lower layer 3 and the upper layer 2 in this order after excavating the ground G. In the present embodiment, excavation of the ground G is performed up to the groundwater level WL, but the excavation range is not limited.

  The lower layer 3 is formed by spreading crushed stone or the like on the floored surface (the surface of the ground G). Although the thickness of the lower layer 3 is not limited, it is about 30 cm in this embodiment.

  When the lower layer 3 is spread and leveled, the upper surface of the lower layer 3 is covered with the water-permeable sheet 6.

Next, the mixed soil in which the excavated soil and the sustained-release organic material are mixed in advance is spread on the water-permeable sheet 6 to form the purification unit 4. Although the layer thickness of the purification | cleaning part 4 is not limited, In this embodiment, it shall be about 20 cm thick.
The mixing of the excavated earth and the sustained-release organic substance may be performed on the ground or on the upper layer 2.

  After the purification unit 4 is formed, the excavated earth and sand are backfilled to complete the upper layer 2.

According to the seepage water purification ground 1, as shown in FIG. 2, a lower layer 3 made of crushed stone (gravel) having a particle diameter larger than that of sand is provided under the upper layer 2 made of sand or the like. A capillary barrier is formed between the upper layer 2 and the lower layer 3. Therefore, by the permeation suppression function of the capillary barrier, the permeated water w1 from the ground surface is retained at the lower end portion of the upper layer 2, and the saturation s is increased.
Since the purification unit 4 is formed in a portion of the ground that is anaerobic and has a high degree of saturation s, biological denitrification is promoted, and the permeation water w1 is retained due to the permeation suppression function of the capillary barrier. Time can be secured. Therefore, the permeated water w1 containing the nitrogen compound eluted from the fertilizer and the like flows out to the lower layer 3 as the purified water w2 denitrified in the purification unit 4, so that the contaminated water is prevented from penetrating into the groundwater.

In addition, when the permeated water w1 from the surface side temporarily exceeds the water retention capacity of the upper layer 2 (purification unit 4) due to heavy rain or the like, the capillary barrier breaks through and is drained to the lower layer 3. There is no risk of surface flooding (dam up) due to rising water levels in the upper layer 2.
That is, according to the permeated water purification ground 1 of this embodiment, the biological denitrification promotion area | region with a low risk of surface drowning can be formed in unsaturated ground.

  Moreover, since there is no possibility that dam up will occur, the seepage water purification ground 1 can be formed even if the groundwater level WL is high.

  Moreover, since the water-permeable sheet 6 is interposed at the boundary surface between the upper layer 2 and the lower layer 3, the first material of the upper layer 2 is prevented from entering the gap of the lower layer 3. That is, it is possible to prevent the density of the upper layer from being lowered due to the first material flowing out to the lower layer, and thus to prevent the water retention capacity of the upper layer from being lowered. Moreover, clogging is unlikely to occur in the lower layer 3, and as a result, deterioration of the water permeability of the lower layer 3 is prevented.

  Since it can be constructed using locally generated soil, it can be formed easily and inexpensively.

  Since the upper surface and the lower surface of the purification unit 4 are flat, the permeated water does not diffuse along the surface of the purification unit 4. Therefore, the permeated water containing the pollutant flows into the lower layer 3 after being retained in the purification unit 4 and denitrified.

The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention.
For example, a permeated water purification ground including a plurality of purification sections 4, 4,... May be configured by laminating a plurality of layers of a laminated structure including the upper layer 2 and the lower layer 3 including the purification section 4. Thereby, denitrification of the permeated water w1 can be performed a plurality of times, and the purification performance is further improved.

Next, the Example which concerns on the water retention performance of the water-permeable purification ground 1 is shown.
In this example, the water retention performance of the upper layer was confirmed by an indoor test using the column 10.

In this test, as shown in FIG. 3A, water is poured from above into the column 10 in which the upper layer 20 and the lower layer 30 are laminated, and the amount of drainage from the drain port 11 formed on the lower surface of the column 10 is measured. did. Moreover, after completion | finish of a test (after water injection), the sample was left still overnight and the moisture content distribution of the upper layer 20 was measured.
The amount of water injected at one time was 300 mL for the first time and 200 mL for the second and subsequent times, and water was injected five times in total every 15 minutes.

The column 10 was a cylindrical PVC column having an inner diameter of 10.4 cm and a height of 25.0 cm.
The upper layer 20 employs sand as the first material and has a height of 15 cm. In addition, the lower layer 30 employs gravel as the second material and has a height of 5 cm. A nonwoven fabric was interposed as a water-permeable sheet at the interface between the upper layer 20 and the lower layer 30. A perforated plate 12 for preventing the second material from flowing out was disposed on the bottom surface of the column 10. Table 1 shows initial conditions of the samples (first material and second material) in the column 10.

  FIG. 4 shows the accumulated water amount, accumulated drainage amount, retained water amount (difference between accumulated water amount and accumulated drainage amount), and sand layer void volume in this test.

  As shown in FIG. 4, in the initial stage (stage where the number of water additions is small), there is a difference in the linearity between the cumulative water addition and the total wastewater discharge. Showed a similar shape, and the water retention amount was constant. That is, since the osmotic water that has been added is retained by the upper layer 20 by the water retention capacity, a difference occurs in the distribution of the amount of water added and the amount of drainage. On the other hand, when the amount of water retained in the upper layer 20 became a constant value, the distribution of the amount of water added and the amount of drainage became equivalent.

Moreover, the water distribution (saturation distribution after steady state) of the upper layer 20 after the end of the test is shown in FIG. FIG. 3B shows a moisture characteristic curve (VG drainage, VG feed water) of standard sand according to van Genuchten's equation as a comparative example of the measured value of the moisture distribution. As shown in FIG.3 (b), the moisture characteristic in the water-permeable purification | cleaning ground 1 in which the sand layer and the gravel layer were laminated | stacked became a curve with about 15% of low saturation from distribution of a water supply process.
Therefore, it is considered that the permeated water having a saturation degree of about 15% can be retained in the upper layer 20. In addition, it was demonstrated that permeated water exceeding the water retention capacity was drained.

DESCRIPTION OF SYMBOLS 1 Permeated water purification ground 2 Upper layer 3 Lower layer 4 Purification part 5 Sustained release organic substance 6 Water-permeable sheet G Jiyama

Claims (3)

An upper layer composed of sand or a first material that is finer particle size than sand;
A lower layer composed of a second material that is a material having a coarser particle diameter than the first material, and an infiltration water purification ground layered up and down above the groundwater level,
An osmotic water purification ground, wherein a purification part in which a sustained-release organic substance is mixed with the first material is formed at a lower end part of the upper layer.   The osmotic water purification ground according to claim 1, wherein a water-permeable sheet for preventing the first material from flowing into the lower layer is interposed at a boundary surface between the upper layer and the lower layer. .   The percolated water purification ground according to claim 1 or 2, wherein a laminated structure composed of the upper layer and the lower layer is laminated in a plurality of stages.

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