JP4026811B2 - Disposal method of contaminated bottom sediment - Google Patents

Disposal method of contaminated bottom sediment Download PDF

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JP4026811B2
JP4026811B2 JP2002204607A JP2002204607A JP4026811B2 JP 4026811 B2 JP4026811 B2 JP 4026811B2 JP 2002204607 A JP2002204607 A JP 2002204607A JP 2002204607 A JP2002204607 A JP 2002204607A JP 4026811 B2 JP4026811 B2 JP 4026811B2
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sediment
contaminated
water
density
area
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JP2004044268A (en
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昌宏 田中
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Kajima Corp
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Kajima Corp
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【0001】
【発明の属する技術分野】
本発明は水底の汚染底質処分方法に関し、とくにダイオキシン類等の汚染物質で汚染された水底の底質を封じ込め又は浚渫して処分する方法に関する。
【0002】
【従来の技術】
近年、廃棄物焼却施設等から排出されるダイオキシン類等の汚染物質による土壌の汚染が大きな社会問題となっており、陸上の汚染土壌については遮断・封じ込めや浄化による土壌保全対策が進められている。他方、発生源から大気中に放出された汚染物質は河川等に到達し、主に粒子状物質に付着・吸着して海域や湖沼域に移行することが知られている。現実に東京湾等の閉鎖性水域では、底質中にダイオキシン等の汚染物質が含まれている場所が多数存在していることが報告されている。これら水底の汚染された底質は環境中への二次的な汚染発生源となる可能性があるため、水底の底質環境についても適切な保全対策が求められる。従来、水底の汚染された底質は、浚渫して安定化処理等を施したのち処分する方法が一般的である。
【0003】
【発明が解決しようとする課題】
しかし、従来の汚染底質を浚渫する方法は、浚渫時に底泥を巻き上げて汚染物質を拡散するおそれがある。環境を保全する観点からは、汚染物質の拡散を最小限に抑える必要がある。また、底質中の汚染物質は粒子状物質に付着・吸着する形で存在することが知られており、粒度が大きい粒子よりも比較的粒径が小さな微細粒子(以下、細粒分ということがある。)に大部分が付着・吸着していると考えられている。従来の汚染底質を浚渫する方法は、巻き上がり易く沈澱し難い細粒分の回収が難しく、単位重量当たりの汚染物質含有量が高い細粒分を効率的に除去することが難しい問題点もある。水底の底質環境を保全するためには、細粒分を効率的に処分できる技術が必要である。
【0004】
そこで本発明の目的は、底質中の細粒分を効率的に処分する水底の汚染底質処分方法を提供することにある。
【0005】
【課題を解決するための手段】
図1の実施例を参照するに、本発明の水底の汚染底質処分方法は、水底1の底質が汚染された汚染域5に隣接して該汚染域5外の窪地6へ向け下降する溝7を穿ち、汚染域5内の底層水2の密度を域外より高めつつ(図2(b)及び(c)参照)該汚染域5内の底質を撹乱し、溝7へ潜入する高密度底層水2の密度流Lにより撹乱で巻き上げた底質粒子3を溝7へ導いて窪地6に集め、汚染底質粒子3を窪地6に封じ込め又は窪地6から浚渫してなるものである。
【0006】
好ましくは、汚染域5内の底質へ冷却水及び/又は冷却剤を送入して底層水2を冷却することにより、汚染域5内の底層水2の密度を高める。底質汚染域5が海底にある場合は、汚染域5内の底質へ塩分濃縮海水を送入することにより汚染域5内の底層水2の密度を高めてもよい。
【0007】
【発明の実施の形態】
図1は、水底の底質の汚染物質分布を適当な計測・分析方法で求め、汚染物質が低濃度で広範囲に分布している汚染域5に本発明を適用した実施例を示す。図示例では底質の汚染域5を斜線で示す。実際の閉鎖性水域には、このように低濃度の底質汚染域5が多数存在すると推定される。本発明は、後述するように底質中の汚染物質を一箇所に集めて処分することができるので、広範囲に分散した低濃度の汚染底質を処分する際にとくに有効である。但し、本発明の適用対象は図示例に限定されず、例えば汚染濃度が高い及び/又は汚染範囲が狭い汚染域5に本発明を適用することも可能である。以下、図1を参照して本発明の処分方法を説明する。
【0008】
先ず、汚染域5に隣接して、汚染域5の外側の既存又は人工の窪地6へ向け下降する溝7を穿つ。水底1の窪地6は自然に形成されたものを利用できるが、汚染域5の近傍に適当な窪地6がない場合は、溝7の低端部を掘削して窪地6としてもよい。溝7は図示例のように汚染域5の外側に沿って設けることが望ましいが、汚染域5の汚染物質濃度が低濃度であって溝7の穿設時に巻き上がる汚染底質の拡散が大きな問題とならない場合は、例えば汚染域5の内側から外側の窪地6へ向けて溝7を設けてもよい。汚染物質に多少の巻き上げが発生した場合でも、広い汚染域5から汚染物質を集めて処分する本発明では全体的に見れば水底の底質環境の保全への寄与が期待できる。
【0009】
次いで、溝7に隣接する汚染域5の底質と接する底層水2の密度を域外より高めながら、その汚染域5の底質を撹乱する。自然の海洋や湖沼では、鉛直方向の深度zに応じて密度ρが徐々に増大する密度分布が形成されているが、深度z方向に密度ρが急激に変化する密度躍層(pycnoline)と呼ばれる層構造の存在が知られている。水中の密度躍層は力学的に安定しており、その上層と下層とは容易に混合しない。本発明は、汚染域5内の底層水2の密度を域外よりも高めることにより、汚染域5上にいわば人工的な密度躍層を形成する(図2(B)参照)。密度躍層を形成しながら汚染域5内の底質を撹乱することにより、撹乱時に巻き上がる底質からの汚染底質粒子3の上方への拡散を最小限に抑え、汚染底質粒子3を底層水2中にいわば閉じ込めておくことができる。
【0010】
汚染域5内の底層水2の密度は、例えば底層水2を冷却することにより高めることができる。高密度底層水2を冷却により形成する方法の一例を図3に示す。同図では、汚染域5の水面4上の船舶10に汲み上げ装置12と水冷却装置13とを搭載し、汚染域5の底質を巻き上げない水深位置から汲み上げ装置12に接続した汲み上げ管11により水を汲み上げる。汚染域5の底層の水温を測定し、汲み上げた水を冷却装置13で前記測定した水温より低温に冷却し、冷却した水を送入管14経由で汚染域5の底質へ送入する。送入管14は、断熱性の高い鉛直管等とすることが望ましい。
【0011】
図3において、冷却装置13から送入された周囲の水より重い冷却水は、底質上で広がりながら徐々に蓄積して高密度底層水2となり、密度躍層(この場合は、水温躍層(thermocline))を形成する。冷却水の送入流量は、送入方法にもよるが、必要部分のみを冷却・撹乱するために必要な最小限の流量とするのが理想的である。冷却水の送入に代えて又は加えて、氷やドライアイス等の冷却剤を送入管14により汚染域5の底質上に投下して底層水2を冷却してもよい。この場合は、冷却剤の溶解により汚染域5の底層水2が徐々に冷却されて高密度底層水2となり、密度躍層を形成する。
【0012】
底質の汚染域5が海底にある場合は、冷却水又は冷却剤に代えて又は加えて、汚染域5の底質へ塩分濃縮海水を送入して底層水2の密度を高めてもよい。例えば図3の船舶10上に汲み上げ装置12と塩濃度調整装置15とを搭載し、汚染域5の底層水2の塩濃度を測定する。汲み上げ装置12で汲み上げた海水の塩濃度を前記測定した塩濃度より高くなるように塩濃度調整装置15で調整し、高塩濃度に調製した海水を送入管14により汚染域5の底質へ送入する。周囲の海水より重い塩分濃縮海水は底質上で広がりながら徐々に蓄積して高密度底層水2となり、密度躍層(この場合は、塩分躍層(halocline又はsalinocline))を形成する。
【0013】
例えば、冷却水や冷却剤を底質へ向けて圧入することにより、底質そのものを冷却して底質と接する底層水2の密度を高めながら、図中の矢印Mで示すように底質中の汚染底質粒子3を巻き上げることができる。また、塩分濃縮海水を底質へ向けて圧入することにより、底層水2の密度を高めながら汚染底質粒子3を巻き上げることも可能である。但し、汚染底質3の巻き上げ方法は冷却水や塩分濃縮海水の圧入に限定されず、例えば図3の船舶10から水底の汚染域5の底質まで適当な攪拌器(図示せず)を吊り下げ、その攪拌器で汚染域5の底質を撹乱して汚染底質粒子3を巻き上げてもよい。巻き上げられた汚染底質粒子3のうち粒度が大きいものは比較的早期に沈降するが、細粒分は沈降速度が遅く、前述したように底層水2中に閉じ込められた状態で長時間浮遊する。
【0014】
他方、汚染域5内に形成された高密度底層水2は、周囲の密度の低い水の下方へ潜り込む密度流(図1の矢印L参照)となって移動する。一般に密度差のある軽い水と重い水とが接触すると、安定な構造になろうとするため、重い水が軽い水の下へ潜り込み且つ軽い水が重い水の上へ乗り上がる密度流(重力流)が生じる。本発明では、図2(C)に示すように溝7内に比し汚染域5内の底層水2の密度を高くするので、汚染域5の底層水2は溝7の底へ沈降する密度流Lとなって移動し、逆に溝7内の軽い水は底層水2の上へ乗り上がる密度流Uとなる。溝7の底へ沈降した底層水2の密度流Lは、窪地6へ向けて下降する溝7に沿って更に窪地6まで沈降する。
【0015】
撹乱により底層水2中に巻き上げられた汚染底質粒子3は、図示例に示す底層水2の密度流Lにより汚染域5の端縁から溝7へ落とされ、更に溝7に沿って沈降する密度流Lによって窪地6まで運ばれる。すなわち本発明は、汚染域5内の底層水2の密度を高めることにより、上述の如く密度躍層を形成して汚染底質粒子3の拡散を抑えるだけでなく、密度流を形成して汚染底質粒子3を窪地6まで輸送する駆動力を得ることができる。こうして溝7を汚染域5内の汚染底質粒子3を運ぶ通路とし、窪地6を汚染底質粒子3の集積場所とすることができる。窪地6に集めた汚染底質粒子3は、窪地6を蓋材で被覆して封じ込めるか、又は窪地6から船上又は陸上に浚渫して処分することができる。
【0016】
本発明によれば、水底汚染域の底層水の密度を高めて密度躍層を形成しながら汚染域の底質を撹乱するので、底質粒子及びそれに付着・吸着した汚染物質の拡散を最小限に抑えることができる。また、撹乱により巻き上げた汚染底質粒子を高密度底層水の密度流により窪地へ導くことができるので、新たな輸送エネルギーを要さずに広範囲に分散した汚染物質を経済的に一箇所に集積することができる。更に、底質中の粒径の大きい底質粒子は集積過程で沈澱するが、底層水に浮遊する細粒分は窪地まで運ばれるので、本発明ではとくに底質中の細粒分のみを選択的に集積することが可能となる。ダイオキシン等の汚染物質の大部分は底質中の細粒分に付着・吸着していると考えられており、本発明によれば、このような細粒分に付着・吸着した汚染物質を効率的且つ経済的に集めて処分することが可能である。
【0017】
こうして本発明の目的である「底質中の細粒分を効率的に処分する水底の汚染底質処分方法」の提供を達成できる。
【0018】
なお、水底1に複数の汚染域5がある場合でも、本発明によれば、汚染域5の各々に隣接する溝7をそれぞれ窪地6へ向けて設けることにより、複数の汚染域5に分散している汚染物質を一箇所の窪地6へ集積することも可能である。こうすることにより水底に分散した汚染底質の一層効率的な処分が期待できる。
【0019】
【実施例】
図1のように、比較的広い汚染域5に形成した高密度底層水2は、溝7へ向かう向きだけでなく様々な向きに潜入して移動し得る。高密度底層水2を溝7へ誘導するため、例えば汚染域5の底層水2の密度を、溝7に隣接する端縁側から汚染域内方へ向け順次高めていくことができる。先ず溝7の近傍で底層水2の密度を高めて溝7へ沈降する密度流を形成すれば、その後に溝7から離れた隣接部位に形成した高密度底層水2を溝7へ向けて誘導することができる。必要に応じ、汚染域5の両端縁に隣接させて又は汚染域5の周囲を囲むように溝7を穿ち、汚染域5から両端縁又は周囲に向けて移動する密度流の全てが潜入するように溝7を配置してもよい。
【0020】
図4は、窪地6に汚染底質粒子3を集めたのち、窪地6を蓋材17で被覆して封じ込める一実施例を示す。例えば水底に大量に存在するダイオキシン類で汚染された底質を全て浚渫して処分するのではなく、汚染濃度が低い場合(例えば3000pg/g乾重以下の場合)は汚染底質を低コストで封じ込めて現地処分することが望ましい場合がある。本発明は、汚染底質粒子3を拡散させず効率的に窪地6へ集め、集めた汚染底質粒子3を覆砂や汚染物質の漏洩が防止できる適当な蓋材17で封じ込めることができるので、例えば、ダイオキシン類等の汚染物質で低濃度に汚染された広範囲に亘る底質の現地処分方法として有効利用が期待できる。汚染底質粒子3を現地処分する場合は、窪地6の底面にも漏洩防止被覆等を設けることが望ましい。
【0021】
汚染物質が嫌気性微生物で分解可能である場合は、窪地6に封じ込めた汚染底質粒子3に嫌気性微生物を添加し、集めた汚染物質粒子3を現地で浄化処理することも期待できる。また、窪地6に集めた汚染底質粒子3を例えば船上又は陸上に浚渫して浄化し、浄化後の底質粒子を水底に戻してもよい。本発明は汚染底質粒子3を拡散させず窪地6へ集めることができるので、浚渫する際にも汚染底質の効率的な回収が期待できる。
【0022】
【発明の効果】
以上説明したように、本発明による水底の汚染底質処分方法は、水底の底質汚染域に隣接して該汚染域外の既存又は人工の窪地へ向け下降する溝を穿ち、汚染域内の底層水の密度を域外より高めつつ該汚染域内の底質を撹乱し、溝へ潜入する高密度底層水の密度流により前記撹乱で巻き上げた底質を溝へ導いて窪地に集めるので、次の顕著な効果を奏する。
【0023】
(イ)汚染域内の底層水の密度を高めて密度躍層を形成しながら汚染域の底質を撹乱するので、汚染域からの汚染物質の拡散を最小限に抑えることができる。
(ロ)撹乱により底層水中に巻き上げた汚染物質を高密度底層水の密度流により運搬するので、広範囲に分散した汚染物質の経済的な集積が可能である。
(ハ)底質中の粒径の大きい底質粒子は集積過程で沈澱するので、単位重量当たりの汚染物質含有量が高い細粒分のみを選択的に集積することが可能である。
(ニ)広範囲に亘る低濃度の汚染底質を狭い窪地に集めて封じ込めることが可能であり、低コストの現地処分方法を提供することができる。
【図面の簡単な説明】
【図1】は、本発明の一実施例の説明図である。
【図2】は、本発明における高密度底層水の作用の説明図である。
【図3】は、底質汚染域の底層水の密度を高める方法の一例の説明図である。
【図4】は、窪地に集めた汚染底質粒子の処分方法の一例の説明図である。
【符号の説明】
1…水底 2…高密度底層水
3…汚染底質粒子 4…水面
5…汚染域 6…窪地
7…溝 10…作業船
11…汲み上げ管 12…汲み上げ装置
13…冷却装置 14…送入管
15…塩濃度調整装置 17…蓋材
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for disposing of polluted bottom sediments, and more particularly to a method for containing or clogging bottom sediment contaminated with pollutants such as dioxins.
[0002]
[Prior art]
In recent years, soil contamination by dioxins and other pollutants discharged from waste incineration facilities has become a major social problem, and on land contaminated soil, soil conservation measures are being promoted by blocking, containment and purification. . On the other hand, it is known that pollutants released from the source to the atmosphere reach rivers, etc., and adhere to and adsorb mainly to particulate matter and migrate to the sea and lakes. In fact, in closed waters such as Tokyo Bay, it has been reported that there are many places where pollutants such as dioxin are contained in the sediment. Since these bottom polluted sediments may become secondary sources of pollution into the environment, appropriate conservation measures are also required for the bottom sediment environment. Conventionally, it has been common practice to dispose of contaminated bottom sediment after subjecting it to stabilization treatment.
[0003]
[Problems to be solved by the invention]
However, the conventional method of dripping contaminated sediment may roll up the bottom mud and spread the pollutant during dredging. From the viewpoint of environmental conservation, it is necessary to minimize the diffusion of pollutants. Also, pollutants in the sediment are known to be attached to and adsorbed to particulate matter, and fine particles with a relatively small particle size (hereinafter referred to as fine particles) than particles with a large particle size. Most of them are attached and adsorbed. The conventional method of dripping contaminated bottom sediment is difficult to recover fine particles that are easy to roll up and difficult to settle, and it is difficult to efficiently remove fine particles with high contaminant content per unit weight. is there. In order to preserve the bottom sediment environment of the bottom of the water, technology that can dispose of fine particles efficiently is necessary.
[0004]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for disposing of polluted bottom sediment in a water bottom that efficiently disposes fine particles in bottom sediment.
[0005]
[Means for Solving the Problems]
Referring to the embodiment of FIG. 1, the contaminated bottom sediment disposal method of the present invention descends toward a depression 6 outside the contaminated area 5 adjacent to the contaminated area 5 where the bottom sediment of the bottom 1 is contaminated. The groove 7 is pierced while the density of the bottom layer water 2 in the contaminated area 5 is increased from outside the area (see FIGS. 2B and 2C). The sediment particles 3 wound up by disturbance by the density flow L of the density bottom layer water 2 are guided to the grooves 7 and collected in the depressions 6, and the contaminated sediment particles 3 are contained in the depressions 6 or trapped from the depressions 6.
[0006]
Preferably, the density of the bottom layer water 2 in the contaminated area 5 is increased by feeding the cooling water and / or coolant to the bottom sediment in the contaminated area 5 to cool the bottom layer water 2. When the bottom polluted area 5 is on the seabed, the density of the bottom water 2 in the polluted area 5 may be increased by sending salt-enriched seawater to the bottom sediment in the polluted area 5.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment in which the present invention is applied to a polluted area 5 where the pollutant distribution in the bottom sediment is obtained by an appropriate measurement / analysis method and the pollutant is distributed at a low concentration over a wide range. In the illustrated example, the contaminated area 5 of the bottom sediment is indicated by hatching. In an actual closed water area, it is estimated that there are many low-concentration bottom polluted areas 5 in this way. As described later, the present invention can collect and dispose of pollutants in the bottom sediment in one place, and is particularly effective when disposing of low-concentration polluted bottom sediment dispersed over a wide area. However, the application target of the present invention is not limited to the illustrated example. For example, the present invention can be applied to a contaminated area 5 having a high contamination concentration and / or a narrow contamination range. Hereinafter, the disposal method of the present invention will be described with reference to FIG.
[0008]
First, adjacent to the contaminated area 5, a groove 7 descending toward an existing or artificial depression 6 outside the contaminated area 5 is drilled. As the depression 6 in the bottom 1, a naturally formed one can be used. However, when there is no suitable depression 6 near the contaminated area 5, the lower end of the groove 7 may be excavated to form the depression 6. The groove 7 is preferably provided along the outside of the contaminated area 5 as shown in the figure, but the pollutant concentration in the contaminated area 5 is low and the diffusion of the contaminated sediment that is rolled up when the groove 7 is drilled is large. If not a problem, for example, the groove 7 may be provided from the inside of the contaminated area 5 to the outer depression 6. Even if the pollutant is slightly wound up, the present invention that collects and disposes of the pollutant from the wide contaminated area 5 can be expected to contribute to the conservation of the bottom sediment environment of the water bottom as a whole.
[0009]
Next, the bottom sediment in the contaminated area 5 is disturbed while increasing the density of the bottom layer water 2 in contact with the bottom sediment in the contaminated area 5 adjacent to the groove 7 from outside the area. In natural oceans and lakes, a density distribution is formed in which the density ρ gradually increases according to the vertical depth z, which is called a pycnoline where the density ρ changes rapidly in the depth z direction. The existence of a layer structure is known. The density stratum in water is mechanically stable and its upper and lower layers do not mix easily. In the present invention, an artificial density jump layer is formed on the contaminated area 5 by increasing the density of the bottom layer water 2 in the contaminated area 5 more than outside (see FIG. 2B). By disturbing the bottom sediment in the contaminated area 5 while forming the density stratum, the upward diffusion of the contaminated sediment particles 3 from the sediment that is rolled up during the disturbance is minimized, and the contaminated sediment particles 3 are It can be confined in the bottom water 2.
[0010]
The density of the bottom layer water 2 in the contaminated area 5 can be increased, for example, by cooling the bottom layer water 2. An example of a method of forming the high density bottom layer water 2 by cooling is shown in FIG. In the figure, a pumping device 12 and a water cooling device 13 are mounted on a ship 10 on the water surface 4 in the contaminated area 5, and a pumping pipe 11 connected to the pumping apparatus 12 from a water depth position where the bottom sediment of the contaminated area 5 is not rolled up. Pump up water. The water temperature of the bottom layer of the contaminated area 5 is measured, the pumped water is cooled to a temperature lower than the measured water temperature by the cooling device 13, and the cooled water is sent to the bottom sediment of the contaminated area 5 through the inlet pipe 14. The feed pipe 14 is preferably a vertical pipe with high heat insulation.
[0011]
In FIG. 3, the cooling water heavier than the surrounding water fed from the cooling device 13 gradually accumulates while spreading on the bottom sediment and becomes the high-density bottom water 2, and the density climatic layer (in this case, the water temperature climatic layer). (Thermocline)). Although the cooling water feeding flow rate depends on the feeding method, it is ideal that the cooling water feeding flow rate is a minimum flow rate necessary for cooling and disturbing only the necessary portion. Instead of or in addition to the cooling water feeding, a cooling agent such as ice or dry ice may be dropped onto the bottom sediment of the contaminated area 5 through the feeding pipe 14 to cool the bottom water 2. In this case, the bottom layer water 2 in the contaminated area 5 is gradually cooled by the dissolution of the coolant to become the high density bottom layer water 2 to form a density jump layer.
[0012]
When the bottom polluted area 5 is on the seabed, the density of the bottom water 2 may be increased by sending salt-enriched seawater to the bottom sediment of the polluted area 5 instead of or in addition to the cooling water or the coolant. . For example, the pumping device 12 and the salt concentration adjusting device 15 are mounted on the ship 10 shown in FIG. 3, and the salt concentration of the bottom water 2 in the contaminated area 5 is measured. The salt concentration of the seawater pumped by the pumping device 12 is adjusted by the salt concentration adjusting device 15 so as to be higher than the measured salt concentration, and the seawater prepared to a high salt concentration is sent to the bottom sediment of the contaminated area 5 by the inlet pipe 14. Send in. The salt-enriched seawater heavier than the surrounding seawater gradually accumulates while spreading on the bottom sediment and becomes the high-density bottom water 2, forming a density jump layer (in this case, a salt jump layer (halocline or salinocline)).
[0013]
For example, by injecting cooling water or a coolant into the bottom sediment, the bottom sediment itself is cooled to increase the density of the bottom layer water 2 in contact with the bottom sediment, while the bottom sediment in the bottom sediment as indicated by an arrow M in the figure. The contaminated sediment particles 3 can be rolled up. Moreover, it is also possible to roll up the polluted sediment particles 3 while increasing the density of the bottom water 2 by pressing the salt-enriched seawater toward the sediment. However, the method of rolling up the polluted sediment 3 is not limited to the injection of cooling water or salt-enriched seawater. For example, a suitable stirrer (not shown) is suspended from the ship 10 in FIG. The bottom sediment in the contaminated area 5 may be disturbed with the stirrer, and the contaminated sediment particles 3 may be wound up. Of the polluted bottom sediment particles 3 that have been rolled up, those having a large particle size settle relatively early, but the fine particles have a slow sedimentation speed and float for a long time in a state of being confined in the bottom water 2 as described above. .
[0014]
On the other hand, the high-density bottom layer water 2 formed in the contaminated area 5 moves as a density flow (see arrow L in FIG. 1) that sinks below the surrounding low-density water. In general, when light water with different density and heavy water come into contact with each other, the density flow (gravity flow) in which heavy water enters under light water and light water rides over heavy water in order to achieve a stable structure. Occurs. In the present invention, as shown in FIG. 2C, the density of the bottom water 2 in the contaminated area 5 is higher than that in the groove 7, so that the density of the bottom water 2 in the contaminated area 5 sinks to the bottom of the groove 7. On the contrary, the light water in the groove 7 moves as a flow L, and becomes a density flow U that climbs onto the bottom water 2. The density flow L of the bottom water 2 that has settled to the bottom of the groove 7 further sinks to the depression 6 along the groove 7 that descends toward the depression 6.
[0015]
The contaminated sediment particles 3 wound up in the bottom layer water 2 by the disturbance are dropped from the edge of the contaminated area 5 to the groove 7 by the density flow L of the bottom layer water 2 shown in the illustrated example, and further settled along the groove 7. It is carried to the depression 6 by the density flow L. That is, according to the present invention, by increasing the density of the bottom water 2 in the contaminated area 5, not only does the formation of the density climbing layer as described above suppress the diffusion of the polluted bottom sediment particles 3, but also the density flow is formed to cause the contamination. A driving force for transporting the sediment particles 3 to the depression 6 can be obtained. In this way, the groove 7 can be used as a passage for carrying the contaminated sediment particles 3 in the contaminated area 5, and the depression 6 can be used as an accumulation place of the contaminated sediment particles 3. The contaminated sediment particles 3 collected in the depressions 6 can be disposed by covering the depressions 6 with a cover material or enclosing the depressions 6 on the ship or on land.
[0016]
According to the present invention, the bottom water in the polluted area is disturbed while increasing the density of the bottom water in the bottom polluted area to form a density jump layer. Can be suppressed. In addition, polluted sediment particles rolled up by disturbance can be guided to the depression by the density flow of high-density bottom water, so that pollutants dispersed over a wide area can be economically accumulated in one place without requiring new transport energy. can do. In addition, sediment with large particle size in the sediment is precipitated during the accumulation process, but the fine particles floating in the bottom water are transported to the depression, so in the present invention, only the fine particles in the sediment are selected. Can be integrated. Most of the pollutants such as dioxin are thought to adhere to and adsorb to fine particles in the sediment. According to the present invention, contaminants adhering to and adsorbed to such fine particles are efficiently treated. Can be collected and disposed of economically and economically.
[0017]
Thus, the object of the present invention can be provided as “a method for disposal of polluted bottom sediment in water bottom which efficiently disposes fine particles in bottom sediment”.
[0018]
Even in the case where there are a plurality of contaminated areas 5 on the bottom 1, according to the present invention, the grooves 7 adjacent to each of the contaminated areas 5 are respectively provided toward the depressions 6 to disperse the plurality of contaminated areas 5. It is also possible to accumulate the pollutants present in one depression 6. By doing so, it is possible to expect more efficient disposal of the polluted bottom sediment dispersed in the water bottom.
[0019]
【Example】
As shown in FIG. 1, the high-density bottom water 2 formed in the relatively large contaminated area 5 can infiltrate and move in various directions as well as in the direction toward the groove 7. Since the high-density bottom layer water 2 is guided to the groove 7, for example, the density of the bottom layer water 2 in the contaminated area 5 can be sequentially increased from the edge side adjacent to the groove 7 toward the inside of the contaminated area. First, if density of the bottom layer water 2 is increased in the vicinity of the groove 7 to form a density flow that settles into the groove 7, then the high density bottom layer water 2 formed in an adjacent part away from the groove 7 is guided toward the groove 7. can do. If necessary, a groove 7 is formed adjacent to or surrounding the both edges of the contaminated area 5 so as to infiltrate all of the density flow moving from the contaminated area 5 toward the both edges or the periphery. A groove 7 may be arranged in the groove.
[0020]
FIG. 4 shows an embodiment in which the contaminated sediment particles 3 are collected in the depressions 6 and then the depressions 6 are covered with a lid material 17 and contained. For example, instead of dripping and disposing of all sediments contaminated with a large amount of dioxins present in the bottom of the water, if the concentration of contamination is low (for example, below 3000 pg / g dry weight), the contaminated sediment is low-cost. It may be desirable to contain and dispose of on site. In the present invention, the contaminated sediment particles 3 can be efficiently collected in the depressions 6 without being diffused, and the collected contaminated sediment particles 3 can be enclosed with an appropriate cover material 17 that can prevent leakage of sand and contaminants. For example, it can be expected to be effectively used as an on-site disposal method for a wide range of sediments contaminated at low concentrations with contaminants such as dioxins. When the contaminated sediment particles 3 are disposed of locally, it is desirable to provide a leak-proof coating or the like on the bottom surface of the depression 6.
[0021]
If the pollutant can be decomposed by anaerobic microorganisms, it can be expected that the anaerobic microorganisms are added to the contaminated sediment particles 3 contained in the depression 6 and the collected contaminant particles 3 are purified on site. Further, the polluted sediment particles 3 collected in the depression 6 may be purified on a ship or on land, for example, and the purified sediment particles may be returned to the water bottom. In the present invention, the contaminated sediment particles 3 can be collected in the depressions 6 without being diffused, so that efficient collection of the contaminated sediment can be expected even when dredging.
[0022]
【The invention's effect】
As described above, the method for disposing contaminated bottom sediment according to the present invention includes a groove that descends toward an existing or man-made depression outside the contaminated area adjacent to the bottom polluted area of the bottom and The bottom sediment in the contaminated area is disturbed while increasing the density of the soil from outside the area, and the bottom sediment rolled up by the disturbance by the density flow of high-density bottom water that infiltrates into the groove is led to the groove and collected in the depression. There is an effect.
[0023]
(B) Since the bottom sediment in the contaminated area is disturbed while increasing the density of the bottom water in the contaminated area to form a density stratum, it is possible to minimize the diffusion of pollutants from the contaminated area.
(B) Since pollutants wound up in the bottom water by disturbance are conveyed by the density flow of the high-density bottom water, it is possible to economically accumulate the pollutants dispersed in a wide range.
(C) Since the bottom sediment particles having a large particle size in the sediment are precipitated in the accumulation process, it is possible to selectively accumulate only fine particles having a high contaminant content per unit weight.
(D) It is possible to collect and contain low-concentration contaminated sediments in a wide area in a narrow depression, and provide a low-cost on-site disposal method.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of the present invention.
FIG. 2 is an explanatory view of the action of high-density bottom layer water in the present invention.
FIG. 3 is an explanatory diagram showing an example of a method for increasing the density of bottom layer water in a bottom polluted area.
FIG. 4 is an explanatory diagram of an example of a disposal method for contaminated sediment particles collected in a depression.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Water bottom 2 ... Dense bottom water 3 ... Contaminated sediment particle 4 ... Water surface 5 ... Contaminated area 6 ... Recess 7 ... Groove 10 ... Work ship
11 ... pumping pipe 12 ... pumping device
13 ... Cooling device 14 ... Inlet pipe
15 ... Salt concentration adjusting device 17 ... Cover material

Claims (10)

水底の底質が汚染された汚染域に隣接して該汚染域外の窪地へ向け下降する溝を穿ち、汚染域内の底層水の密度を域外より高めつつ該汚染域内の底質を撹乱し、溝へ潜入する高密度底層水の密度流により前記撹乱で巻き上げた底質粒子を溝へ導いて窪地に集め、汚染底質粒子を窪地に封じ込め又は窪地から浚渫してなる水底の汚染底質処分方法。Drilling a groove that descends toward the depression outside the contaminated area adjacent to the contaminated area where the bottom sediment is contaminated, while disturbing the sediment within the contaminated area while increasing the density of the bottom water in the contaminated area from outside the area, The bottom sediment particles rolled up by the above disturbance by the density flow of the high-density bottom water that infiltrates into the groove are collected in the depression, and the contaminated bottom sediment is contained in the depression or suspended from the depression. . 請求項1の処分方法において、前記汚染域内の底層水の密度を該底層水の冷却により高めてなる水底の汚染底質処分方法。2. The disposal method according to claim 1, wherein the density of bottom layer water in the contaminated area is increased by cooling the bottom layer water. 請求項2の処分方法において、前記汚染域内の底質への冷却水及び/又は冷却剤の送入により底層水を冷却してなる水底の汚染底質処分方法。The disposal method according to claim 2, wherein the bottom layer water is cooled by feeding cooling water and / or coolant to the bottom sediment in the contaminated area. 請求項3の処分方法において、前記汚染域内の底質を冷却水及び/又は冷却剤の圧入により撹拌してなる水底の汚染底質処分方法。4. The disposal method according to claim 3, wherein the bottom sediment in the contaminated area is agitated by injection of cooling water and / or coolant. 請求項1の処分方法において、前記底質汚染域を海底とし、前記汚染域内の底層水の密度を該汚染域内の底質への塩分濃縮海水の送入により高めてなる水底の汚染底質処分方法。The disposal method according to claim 1, wherein the bottom polluted area is a sea bottom, and the density of bottom water in the polluted area is increased by feeding salt-enriched seawater into the bottom sediment in the polluted area. Method. 請求項の処分方法において、前記汚染域内の底質を前記塩分濃縮海水の圧入により撹乱してなる水底の汚染底質処分方法。6. The disposal method according to claim 5 , wherein the bottom sediment in the contaminated area is disturbed by the injection of the salt-enriched seawater. 請求項1、2、3又は5の何れかの処分方法において、前記汚染域内の底質を攪拌器により撹乱してなる水底の汚染底質処分方法。In any of the disposal method of claim 1, 2, 3 or 5, underwater contaminated sediment disposal formed by disrupting the agitator sediment of the contaminated region. 請求項1から7の何れかの処分方法において、前記汚染域内の底層水の密度を前記溝に隣接する端縁側から汚染域内方へ向け順次高めてなる水底の汚染底質処分方法。The disposal method according to any one of claims 1 to 7 , wherein the density of bottom water in the contaminated area is sequentially increased from the edge side adjacent to the groove toward the inside of the contaminated area. 請求項1から8の何れかの処分方法において、前記窪地に集めた汚染底質粒子を覆砂又は蓋材により封じ込めてなる水底の汚染底質処分方法。9. The disposal method according to claim 1 , wherein the contaminated sediment particles collected in the depression are contained by covering sand or a cover material. 請求項1から8の何れかの処分方法において、前記窪地に集めた汚染底質粒子を窪地から浚渫して浄化し、浄化後の底質粒子を水底に戻してなる水底の汚染底質処分方法。9. The disposal method according to any one of claims 1 to 8 , wherein the contaminated sediment particles collected in the depression are removed from the depression and purified, and the purified sediment particles are returned to the bottom. .
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