JP3735707B2 - Removal of nitrate nitrogen from soil seepage water - Google Patents

Removal of nitrate nitrogen from soil seepage water Download PDF

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JP3735707B2
JP3735707B2 JP2001353363A JP2001353363A JP3735707B2 JP 3735707 B2 JP3735707 B2 JP 3735707B2 JP 2001353363 A JP2001353363 A JP 2001353363A JP 2001353363 A JP2001353363 A JP 2001353363A JP 3735707 B2 JP3735707 B2 JP 3735707B2
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soil
layer
nitrate nitrogen
water
electron donor
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JP2003145185A (en
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琢也 川西
良茂 林
啓祐 花木
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Kanazawa University NUC
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Kanazawa University NUC
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【０００１】
【発明の属する技術分野】
本発明は、環境保全、水処理に係り、特に土壌浸透水からの硝酸態窒素の除去方法に関する。
【０００２】
【従来の技術】
近年、硝酸態窒素による地下水の汚染が世界各地で生じている。これは、農地（水田を除く）や排水の土壌浸透処理場など、硝酸態窒素が浸透する土壌において、その土壌が好気性に保たれることにより脱窒が生じないためである。
【０００３】
土壌浸透水から窒素を除去する方法としては、特開２０００−２９６３９４公報、および特開２０００−２８８５６３公報に記載された方法が知られている。いずれも、土壌中に不透水性の構造物を設置し、その内部に水がある程度溜まる形にすることによって、土壌内に嫌気性の部分を生じさせるものである。
【０００４】
また、土壌に有機物層を埋め込む、いわゆる多段土壌層法も開発されている（1993、T.Wakatsuki, H.Esumi, S.Omura, High performance and N&P removable on-site domestic waste water treatment system by multi-soil-layering method (In G.Ho and K.Mathew ed., Water Science and Technology, Volume 27, No.1, Appropriate Waste Management Technologies所収)、Pergamon Press, Oxford, pp 220(31-40)）。この方法は、ジュート袋などの有機物を多段状に入れておくもので、設置に手間がかかる。しかも、有機物が好気的に分解してロスが生じるおそれがあり、過度に嫌気性状態が続くのを防ぐために曝気が必要であるなどの問題点もある。
【０００５】
さらに、排水の土壌浸透水からの窒素除去では、特開平５−１０４０８５号公報に記載されているように植物による吸収を期するものが挙げられる。一般に植物の吸収による窒素除去は、脱窒よりも効率が悪いのみならず、冬季の吸収が期待できない。
【０００６】
その他、土壌浸透水からの窒素除去としては、湿地などに水を浸透させ、土壌と植物との作用で窒素を除去する方法が特開平９−４７７７９号公報に記載されている。この方法は、湿地、休耕田、あるいは水田など湛水状態での土壌を利用した技術であり、畑や土壌表層数十センチを好気性に保つ必要のある排水土壌浸透処理場には適用することができない。
【０００７】
【発明が解決しようとする課題】
本発明は、畑や土壌表層数十センチを好気性に保つ必要のある排水土壌浸透処理場に適用することができ、構造物を設けることなく、効率よく簡便に脱窒を行なうことが可能な、土壌浸透水からの硝酸態窒素の除去方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
上記課題を解決するために、本発明は、硝酸態窒素を含有する土壌浸透水から硝酸態窒素を除去する方法であって、土壌中の下層の上に、電子供与体が混入された電子供与体混入層を直接接して設ける工程と、前記電子供与体混入層の上のみに選択的に、低透水性土壌層を直接接して設ける工程と、前記電子供与体混入層に向けて、前記低透水性土壌層の深さ方向に前記土壌浸透水を通過させ、前記土壌浸透水への酸素の供給を抑制する工程と、前記酸素供給が抑制された土壌浸透水を、前記下層に向けて前記電子供与体層の深さ方向に通過させて前記電子供与体に接触させて脱窒を行なうことにより、前記硝酸態窒素の濃度を低減する工程と、前記硝酸態窒素が低減された前記土壌浸透水を、前記下層に浸透させる工程とを具備することを特徴とする方法を提供する。
【０００９】
本発明にかかる硝酸態窒素の除去方法は、従来の窒素除去方法とは異なり、土壌浸水量が大きいほど土壌含水率が高くなるという性質を利用し、特に構造物を設けずとも窒素除去効果を得ることを可能とした。
【００１０】
特に、土壌の物理性（透水性、保水性、および気体の拡散）を利用しているので、本発明の硝酸態窒素の除去方法においては、土壌に水が浸透している場での酸素供給を抑制して、脱窒による窒素除去を促進することが可能である。また、土壌に水が浸透しない場合には、土壌は好気性を回復し、土壌の嫌気化による害を防ぐことができる。
【００１１】
【発明の実施の形態】
以下、図面を参照して本発明を詳細に説明する。
【００１２】
図１に本発明にかかる硝酸態窒素の除去方法の一例の概念図を示す。図示するように、土壌１１中に低透水性の土壌層１２を設置し、この低透水性土壌層１２の下方には、脱窒のための電子供与体となる物質である硫黄などを混入した層１３が設けられる。硝酸態窒素を含有した水が低透水性土壌層１２に浸透すると、この低透水性土壌層１２での含水率が上昇して地表からの酸素供給が抑制される。酸素供給が抑制された硝酸態窒素含有水がさらに電子供与体混入層１３に浸透すると、ここでは無酸素条件が達せられて、脱窒菌の働きにより窒素が除去される。その結果、下層１４に浸透する水の硝酸態窒素濃度は、層１１を浸透する水のそれよりも低いものとなる。
【００１３】
低透水性土壌層１２は、例えば、地表から０〜２００ｃｍ程度の深さに、０．５〜５０ｃｍ程度の層厚で設けることができる。この場合の低透水性土壌層における水分飽和度を、図２のグラフに示す。低透水性土壌層１２における水分飽和度は、図２のグラフに示されるように０．９程度であり、その上下の層よりも低透水性であることがわかる。なお、低透水性土壌層１２における水分飽和度は、土壌に水が浸透している状態で、土壌の有効水分飽和度がほぼ１となることが好ましい。有効水分飽和度が低くなると、酸素供給を十分抑制することが困難となる。
【００１４】
こうした低透水性土壌層１２には、その飽和透水係数が浸透水量にほぼ等しいものを収容することが好ましい。飽和透水係数は、粘度質土壌に砂を混合するなどによって調整することができる。図３のグラフには、低透水性土壌における粘土質土壌の割合と飽和透水係数との関係を示す。例えば、粘土質土壌が含有されない場合には、飽和透水係数は１程度であり、粘土質土壌を１００％とすることによって、飽和透水係数は０．０１程度に減少する。こうした関係に基づいて、低透水性土壌を適切に調製することができる。なお、混合される粘土質土壌の径が１０ｍｍおよび５０ｍｍの場合でも、図３に示されるように飽和透水係数に大きな違いは生じない。
【００１５】
低透水性土壌層１２は、図４に示すように低透水性層２２とバッファ層２１との二つの層に分けることもできる。バッファ層２１には、低透水性層２２よりも一桁以上高い飽和透水係数を有する土壌を収容する。この方法により、低透水性層土壌の飽和透水係数よりも大きな浸透水量となった場合でも、溢流を生じずに、また土壌層１１下層が飽和になるのを避けることができる。なお、バッファ層２１の厚さは、低透水性層２２の厚さの３〜１０倍程度とすることが好ましい。
【００１６】
バッファ層２１の飽和透水係数が十分高い場合、具体的には、低透水性層２２の飽和透水係数よりも１０倍程度以上大きい場合には、低透水性土壌層の飽和透水係数に等しい浸透水量から、飽和透水係数の約ａ／ｂ倍までの浸透水量に対応することができる。ここで、ａはバッファ層厚さを表わし、ｂは低透水性土壌層厚さを表わす。
【００１７】
また、低透水性土壌層１２の下方に設けられる電子供与体混入層１３には、例えば、硫黄が電子供与体物質として含有される。この場合、中和のためにほぼ同重量の炭酸カルシウム等の中和剤を混入することが好ましい。硫黄の含有量は、収容される土壌全体に対して質量で５％程度とすることが好ましい。１０％程度となると、温暖化ガスである亜酸化窒素を発生する懸念がある。一方、投入量が少なくなると、耐用年数あるいは硫黄補給までの期間が短くなる。
【００１８】
硫黄および炭酸カルシウムに加えて、稲わら、おがくず、および生分解性プラスチック等を電子供与体物質として用いることもできる。
【００１９】
電子供与体混入層１３の厚さは、処理すべき浸透水量、浸透水中の硝酸態窒素濃度、および期待する耐用年数等に応じて適宜決定することができる。
【００２０】
なお、図示していないが、低透水性土壌層１２中に硫黄および炭酸カルシウムなどの電子供与体物質を混入してもよい。この場合には、土壌浸透水への酸素供給の抑制と土壌浸透水からの脱窒との両方を、単一の層で行なうことが可能となる。低透水性土壌層中に混入する場合においても、硫黄および炭酸カルシウム等の電子供与体物質の含有量は、前述と同様の理由から質量で０〜１０％程度とすることが好ましく、５％程度とすることがより好ましい。
【００２１】
次に、具体例を示して本発明をさらに詳細に説明する。
【００２２】
実験に用いる装置の構成を表わす概略図を、図５に示す。本発明の方法を行なうカラムＡ１においては、試料土壌層Ａ３（埼玉県農業試験場の圃場から採取）の下方に、低透水性土壌層Ａ４および電子供与体混入層Ａ５が順次設けられている。具体的には、層Ａ４には、飽和透水係数が１ｍｄ-1の土壌と０．０１ｍｄ-1の土壌とを混合して調製した飽和透水係数０．１ｍｄ-1の土壌を収容し、層Ａ５には、硫黄および炭酸カルシウムをそれぞれ質量で５％となるようにＡ３土壌に混合したものを収容した。層Ａ５の下方には前述と同様のＡ３土壌層を配置し、カラムの底部には礫層Ａ６を設けた。さらに、各土壌層にはＦＲＤ式土壌水分計Ａ７を設置した。
【００２３】
なお、図５中の数値は、カラムのサイズ（ｃｍ）を表わしている。
【００２４】
一方、低透水性土壌層Ａ４を設けない以外は前述のＡ１と同様の構成のカラムを、対照カラムＡ２として用意した。
【００２５】
水道水に硝酸カリウムを加えた溶液Ａ８をカラムＡ１およびＡ２に供給して、出口における溶液の硝酸態窒素濃度の変化を調べた。
【００２６】
２０ｍｇ／Ｌ硝酸カリウム溶液を０．０５ｍｌ／日で供給した場合の出口の硝酸態窒素濃度を、図６のグラフに示す。図示するように、対照カラムＡ２では窒素除去効果が得られなかったのに対して、低透水性土壌層を設けたカラムＡ１では、出口の窒素濃度が実験開始後１０日程度で１〜５ｍｇ／Ｌ程度と著しく減少している。
【００２７】
このように、低透水性土壌層を設けた本発明にかかる硝酸態窒素の除去方法の効果が確認された。
【００２８】
なお、敷地が大きく浸透水がそのごく一部を浸透する場合、低透水性層が一様にぬれないことが想定される。このような場合は、例えば図７に示されるように深さ隔壁１５を設置することができる。これにより、側方からの酸素供給を可能にすることができる。隔壁１５の深さは、設置する位置により変ってくるが、概ね１〜２ｍ程度となる。
【００２９】
【発明の効果】
以上詳述したように、本発明によれば、畑や土壌表層数十センチを好気性に保つ必要のある排水土壌浸透処理場に適用することができ、構造物を設けることなく、効率よく簡便に脱窒を行なうことが可能な、土壌浸透水からの硝酸態窒素の除去方法が提供される。
【００３０】
本発明を用いることによって、土壌浸透水からの硝酸態窒素の除去、特に排水の土壌浸透処理場や畑からの浸透水から窒素を効率よく除去することが可能となり、その工業的価値は絶大である。
【図面の簡単な説明】
【図１】本発明の一実施例にかかる方法の概念を説明する図。
【図２】水分飽和度と地表からの深さとの関係を説明する図。
【図３】粘土質土壌の割合と飽和透水係数との関係を説明するグラフ図。
【図４】本発明の他の例における概念を説明する図。
【図５】実験装置の概略を説明する図。
【図６】カラム出口における硝酸態窒素濃度の経時変化を説明するグラフ図。
【図７】本発明の他の例における概念を説明する図。
【符号の説明】
１１…土壌
１２…低透水性土壌層
１３…電子供与体混入層
１４…下層
１５…隔壁
２１…バッファ層
２２…低透水性層
Ａ１…低透水性土壌層を設けたカラム
Ａ２…対照カラム
Ａ３…土壌層
Ａ４…低透水性土壌層
Ａ５…電子供与体混入層
Ａ６…礫層
Ａ７…ＦＤＲ式土壌水分計
Ａ８…硝酸カリウム溶液[0001]
BACKGROUND OF THE INVENTION
The present invention relates to environmental protection and water treatment, and more particularly to a method for removing nitrate nitrogen from soil permeated water.
[0002]
[Prior art]
In recent years, contamination of groundwater by nitrate nitrogen has occurred around the world. This is because denitrification does not occur because the soil is kept aerobic in soil infiltrated with nitrate nitrogen, such as farmland (excluding paddy fields) and drainage soil infiltration treatment plants.
[0003]
As a method for removing nitrogen from soil permeated water, methods described in JP 2000-296394 A and JP 2000-288563 A are known. In either case, an anaerobic part is generated in the soil by installing an impermeable structure in the soil and forming water in the interior to some extent.
[0004]
A so-called multi-stage soil layer method has also been developed, in which organic layers are embedded in soil (1993, T. Wakatsuki, H. Esumi, S. Omura, High performance and N & P removable on-site domestic waste water treatment system by multi- soil-layering method (In G. Ho and K. Mathew ed., Water Science and Technology, Volume 27, No. 1, Appropriate Waste Management Technologies), Pergamon Press, Oxford, pp 220 (31-40)). In this method, organic substances such as jute bags are placed in multiple stages, and installation takes time. In addition, there is a possibility that organic substances may be decomposed aerobically to cause loss, and aeration is necessary to prevent excessive anaerobic conditions from continuing.
[0005]
Further, nitrogen removal from drained soil permeated water includes those which are expected to be absorbed by plants as described in JP-A-5-104085. In general, nitrogen removal by plant absorption is not only less efficient than denitrification, but it cannot be expected to absorb in winter.
[0006]
In addition, as a method for removing nitrogen from soil permeated water, JP-A-9-47779 discloses a method of permeating water into a wetland and removing nitrogen by the action of soil and plants. This method is a technique that uses soil in flooded conditions such as wetlands, fallow fields, or paddy fields, and it can be applied to drainage soil infiltration treatment plants that need to maintain aerobic tens of centimeters of soil and soil surface. Can not.
[0007]
[Problems to be solved by the invention]
INDUSTRIAL APPLICABILITY The present invention can be applied to a drainage soil infiltration treatment plant that needs to keep an aerobic field and several tens of centimeters of soil surface, and can perform denitrification efficiently and simply without providing a structure. An object of the present invention is to provide a method for removing nitrate nitrogen from soil seepage water.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is a method for removing nitrate nitrogen from soil permeated water containing nitrate nitrogen , wherein the electron donor is mixed with an electron donor on a lower layer in the soil. A step of providing a body-mixed layer in direct contact, a step of providing a low-permeability soil layer in direct contact only on the electron donor-mixed layer, and Passing the soil permeated water in the depth direction of the permeable soil layer, suppressing the supply of oxygen to the soil permeated water, and the soil permeated water in which the oxygen supply is suppressed toward the lower layer, The step of reducing the concentration of nitrate nitrogen by passing through the electron donor layer in the depth direction and contacting the electron donor to perform denitrification, and the soil infiltration with reduced nitrate nitrogen water, by including the step of infiltrating the lower layer To provide a method for the butterflies.
[0009]
Unlike the conventional nitrogen removal method, the method for removing nitrate nitrogen according to the present invention utilizes the property that the soil moisture content increases as the amount of soil inundation increases. Made it possible to get.
[0010]
In particular, since the physical properties of the soil (water permeability, water retention, and gas diffusion) are utilized, in the method for removing nitrate nitrogen according to the present invention, oxygen is supplied in a place where water penetrates the soil. It is possible to suppress nitrogen and promote nitrogen removal by denitrification. Moreover, when water does not permeate into the soil, the soil recovers aerobic and can prevent harm caused by soil anaerobic.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0012]
FIG. 1 shows a conceptual diagram of an example of a method for removing nitrate nitrogen according to the present invention. As shown in the figure, a low-permeability soil layer 12 is installed in the soil 11, and sulfur, which is a substance serving as an electron donor for denitrification, is mixed below the low-permeability soil layer 12. Layer 13 is provided. When water containing nitrate nitrogen penetrates into the low-permeability soil layer 12, the water content in the low-permeability soil layer 12 increases and oxygen supply from the ground surface is suppressed. When nitrate nitrogen-containing water in which oxygen supply is suppressed further penetrates into the electron donor mixed layer 13, an oxygen-free condition is achieved here, and nitrogen is removed by the action of denitrifying bacteria. As a result, the nitrate nitrogen concentration of water that permeates the lower layer 14 is lower than that of water that permeates the layer 11.
[0013]
The low water permeability soil layer 12 can be provided, for example, at a depth of about 0 to 200 cm from the ground surface with a layer thickness of about 0.5 to 50 cm. The water saturation in the low water permeability soil layer in this case is shown in the graph of FIG. As shown in the graph of FIG. 2, the water saturation in the low water permeability soil layer 12 is about 0.9, which indicates that the water permeability is lower than the upper and lower layers. In addition, it is preferable that the water | moisture-content saturation in the low water-permeable soil layer 12 will be the soil effective water | moisture content saturation substantially 1 in the state which the water has osmose | permeated the soil. When the effective water saturation becomes low, it becomes difficult to sufficiently suppress the oxygen supply.
[0014]
In such a low water permeability soil layer 12, it is preferable to accommodate a soil whose permeability coefficient is substantially equal to the amount of osmotic water. The saturated hydraulic conductivity can be adjusted by mixing sand with viscous soil. The graph of FIG. 3 shows the relationship between the proportion of clayey soil in the low water permeability soil and the saturated hydraulic conductivity. For example, when no clay soil is contained, the saturated hydraulic conductivity is about 1, and the saturated hydraulic conductivity is reduced to about 0.01 by setting the clay soil to 100%. Based on these relationships, a low water permeability soil can be appropriately prepared. In addition, even when the diameters of the clay soil to be mixed are 10 mm and 50 mm, as shown in FIG. 3, there is no significant difference in the saturated hydraulic conductivity.
[0015]
The low water permeability soil layer 12 can also be divided into two layers of a low water permeability layer 22 and a buffer layer 21 as shown in FIG. The buffer layer 21 contains soil having a saturated hydraulic conductivity that is one digit higher than that of the low water permeability layer 22. By this method, even when the amount of osmotic water is larger than the saturated hydraulic conductivity of the low-permeability layer soil, it is possible to avoid overflow and to prevent the lower layer of the soil layer 11 from becoming saturated. The thickness of the buffer layer 21 is preferably about 3 to 10 times the thickness of the low water permeable layer 22.
[0016]
When the saturated hydraulic conductivity of the buffer layer 21 is sufficiently high, specifically, when the saturated hydraulic conductivity of the low-permeable layer 22 is about 10 times or more, the amount of osmotic water equal to the saturated hydraulic conductivity of the low-permeable soil layer Therefore, it is possible to cope with the amount of permeated water up to about a / b times the saturated hydraulic conductivity. Here, a represents the buffer layer thickness, and b represents the low water permeability soil layer thickness.
[0017]
The electron donor mixed layer 13 provided below the low water permeability soil layer 12 contains, for example, sulfur as an electron donor substance. In this case, it is preferable to mix a neutralizing agent such as calcium carbonate for neutralization. The sulfur content is preferably about 5% by mass with respect to the entire soil contained. When it is about 10%, there is a concern of generating nitrous oxide, which is a warming gas. On the other hand, when the input amount is reduced, the service life or the period until sulfur supply is shortened.
[0018]
In addition to sulfur and calcium carbonate, rice straw, sawdust, biodegradable plastics and the like can also be used as electron donor materials.
[0019]
The thickness of the electron donor mixed layer 13 can be appropriately determined according to the amount of permeated water to be treated, the concentration of nitrate nitrogen in the permeated water, the expected service life, and the like.
[0020]
Although not shown, an electron donor substance such as sulfur and calcium carbonate may be mixed in the low water permeability soil layer 12. In this case, it is possible to perform both suppression of oxygen supply to the soil seepage water and denitrification from the soil seepage water in a single layer. Even when mixed in the low water permeability soil layer, the content of electron donor substances such as sulfur and calcium carbonate is preferably about 0 to 10% by mass for the same reason as described above, and about 5%. More preferably.
[0021]
Next, the present invention will be described in more detail with reference to specific examples.
[0022]
A schematic diagram showing the configuration of the apparatus used in the experiment is shown in FIG. In the column A1 for performing the method of the present invention, a low-permeability soil layer A4 and an electron donor-mixed layer A5 are sequentially provided below the sample soil layer A3 (collected from the field of Saitama Agricultural Experiment Station). Specifically, the layer A4, saturated hydraulic conductivity accommodate soil 1Md -1 soil and 0.01Md -1 saturated hydraulic conductivity 0.1Md -1 which was prepared by mixing the soil, the layer A5 In this case, a mixture of sulfur and calcium carbonate in A3 soil so as to be 5% by mass was accommodated. Below the layer A5, an A3 soil layer similar to the above was disposed, and a gravel layer A6 was provided at the bottom of the column. Furthermore, FRD type soil moisture meter A7 was installed in each soil layer.
[0023]
The numerical values in FIG. 5 represent the column size (cm).
[0024]
On the other hand, a column having the same configuration as A1 described above was prepared as the control column A2 except that the low water permeability soil layer A4 was not provided.
[0025]
A solution A8 obtained by adding potassium nitrate to tap water was supplied to the columns A1 and A2, and changes in the nitrate nitrogen concentration of the solution at the outlet were examined.
[0026]
The graph of FIG. 6 shows the nitrate nitrogen concentration at the outlet when the 20 mg / L potassium nitrate solution was supplied at 0.05 ml / day. As shown in the figure, in the control column A2, the nitrogen removal effect was not obtained, whereas in the column A1 provided with the low water permeability soil layer, the nitrogen concentration at the outlet was about 1 to 5 mg / day after about 10 days from the start of the experiment. Remarkably reduced to about L.
[0027]
Thus, the effect of the removal method of nitrate nitrogen concerning this invention which provided the low-permeability soil layer was confirmed.
[0028]
In addition, when a site is large and permeated water permeates a small part thereof, it is assumed that the low water permeability layer is not uniformly wetted. In such a case, for example, as shown in FIG. 7, a depth partition 15 can be installed. Thereby, oxygen supply from the side can be enabled. The depth of the partition wall 15 varies depending on the installation position, but is approximately 1 to 2 m.
[0029]
【The invention's effect】
As described above in detail, according to the present invention, it can be applied to a drainage soil infiltration treatment plant that needs to maintain aerobic fields and several tens of centimeters of soil surface, and can be efficiently and easily performed without providing a structure. A method for removing nitrate nitrogen from soil infiltrated water that can be denitrified is provided.
[0030]
By using the present invention, it is possible to remove nitrate nitrogen from soil infiltrated water, in particular, nitrogen efficiently from the infiltrated water from soil infiltration treatment plants and fields of drainage, and its industrial value is tremendous. is there.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the concept of a method according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the relationship between moisture saturation and depth from the ground surface.
FIG. 3 is a graph illustrating the relationship between the clay soil ratio and the saturated hydraulic conductivity.
FIG. 4 is a diagram illustrating a concept in another example of the present invention.
FIG. 5 is a diagram illustrating an outline of an experimental apparatus.
FIG. 6 is a graph for explaining the temporal change of nitrate nitrogen concentration at the column outlet.
FIG. 7 is a diagram for explaining a concept in another example of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Soil 12 ... Low water permeability soil layer 13 ... Electron donor mixed layer 14 ... Lower layer 15 ... Partition 21 ... Buffer layer 22 ... Low water permeability layer A1 ... Column A2 provided with low water permeability soil layer ... Control column A3 ... Soil layer A4 ... low water permeability soil layer A5 ... electron donor mixed layer A6 ... gravel layer A7 ... FDR soil moisture meter A8 ... potassium nitrate solution

Claims (13)

硝酸態窒素を含有する土壌浸透水から硝酸態窒素を除去する方法であって、
土壌中の下層の上に、電子供与体が混入された電子供与体混入層を直接接して設ける工程と、
前記電子供与体混入層の上のみに選択的に、低透水性土壌層を直接接して設ける工程と、
前記電子供与体混入層に向けて、前記低透水性土壌層の深さ方向に前記土壌浸透水を通過させ、前記土壌浸透水への酸素の供給を抑制する工程と、
前記酸素供給が抑制された土壌浸透水を、前記下層に向けて前記電子供与体層の深さ方向に通過させて前記電子供与体に接触させて脱窒を行なうことにより、前記硝酸態窒素の濃度を低減する工程と、
前記硝酸態窒素が低減された前記土壌浸透水を、前記下層に浸透させる工程と
を具備することを特徴とする方法。A method for removing nitrate nitrogen from soil seepage water containing nitrate nitrogen,
A step of directly contacting an electron donor mixed layer mixed with an electron donor on a lower layer in the soil;
Selectively providing only a low water-permeable soil layer on the electron donor-mixed layer; and
Passing the soil permeated water in the depth direction of the low water permeability soil layer toward the electron donor mixed layer, and suppressing the supply of oxygen to the soil permeated water;
By passing the soil permeated water in which the oxygen supply is suppressed toward the lower layer in the depth direction of the electron donor layer and bringing it into contact with the electron donor to perform denitrification , Reducing the concentration ; and
A step of infiltrating the lower layer of the permeated water with reduced nitrate nitrogen into the lower layer . 前記低透水性土壌層上に、前記低透水性土壌層より一桁以上高い飽和透水係数を有するバッファ層を設ける工程をさらに具備し、前記土壌浸透水は、前記低透水性土壌層に浸透する前に前記バッファ層に浸透することを特徴とする請求項１に記載の土壌浸透水からの硝酸態窒素の除去方法。The method further comprises a step of providing a buffer layer having a saturated hydraulic conductivity that is an order of magnitude higher than that of the low-permeability soil layer on the low-permeability soil layer, and the soil permeated water penetrates into the low-permeability soil layer. The method for removing nitrate nitrogen from soil infiltrated water according to claim 1 , wherein the buffer layer penetrates before . 前記電子供与体混入層における前記電子供与体の含有量は、質量で１０％以下であることを特徴とする請求項２に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil permeated water according to claim 2, wherein the content of the electron donor in the electron donor mixed layer is 10% or less by mass. 前記低透水性土壌層は、粘土質土壌と砂との混合物を含有することを特徴とする請求項１ないし３のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil permeated water according to any one of claims 1 to 3, wherein the low-permeability soil layer contains a mixture of clayey soil and sand . 前記電子供与体は、硫黄を含むことを特徴とする請求項１ないし４のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil infiltrated water according to any one of claims 1 to 4, wherein the electron donor contains sulfur . 前記電子供与体混入層は、炭酸カルシウムをさらに含有することを特徴とする請求項５に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil infiltrated water according to claim 5, wherein the electron donor mixed layer further contains calcium carbonate. 前記低透水性土壌層の膜厚は、０．５〜５０ｃｍであることを特徴とする請求項１ないし６のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil infiltrated water according to any one of claims 1 to 6, wherein the low water-permeable soil layer has a thickness of 0.5 to 50 cm. 前記低透水性土壌層は、地表から０〜２００ｃｍの深さに設けられることを特徴とする請求項１ないし７のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil permeated water according to any one of claims 1 to 7, wherein the low water permeability soil layer is provided at a depth of 0 to 200 cm from the ground surface. 前記低透水性土壌層における水分飽和度は、０．９以上であることを特徴とする請求項１ないし８のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil seepage water according to any one of claims 1 to 8, wherein the water saturation in the low water permeability soil layer is 0.9 or more. 前記低透水性土壌層に収容される土壌は、その飽和透水係数が浸透水量に等しいことを特徴とする請求項１ないし９のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。10. The removal of nitrate nitrogen from soil permeated water according to any one of claims 1 to 9, wherein the soil contained in the low water permeable soil layer has a saturated hydraulic conductivity equal to the amount of permeated water. Method. 前記低透水性土壌層における飽和透水係数は、０．１ｍｄThe saturated hydraulic conductivity in the low water permeability soil layer is 0.1 md. -1-1 以下であることを特徴とする請求項１ないし１０のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil infiltrated water according to any one of claims 1 to 10, wherein: 前記バッファ層の厚さは、前記低透水性土壌層の厚さの３〜１０倍であることを特徴とする請求項２ないし１１のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。The nitrate nitrogen from soil permeated water according to any one of claims 2 to 11, wherein the buffer layer has a thickness of 3 to 10 times the thickness of the low-permeability soil layer. Removal method. 前記電子供与体の含有量は、質量で５％以上であることを特徴とする請求項３ないし１２のいずれか１項に記載の土壌浸透水からの硝酸態窒素の除去方法。The method for removing nitrate nitrogen from soil infiltrated water according to any one of claims 3 to 12, wherein the content of the electron donor is 5% or more by mass.
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