JP3760494B2

JP3760494B2 - Soil purification method

Info

Publication number: JP3760494B2
Application number: JP35204895A
Authority: JP
Inventors: 幸生福島; 陽一郎小野; 明雄田中
Original assignee: 日立プラント建設株式会社
Priority date: 1995-12-27
Filing date: 1995-12-27
Publication date: 2006-03-29
Anticipated expiration: 2015-12-27
Also published as: JPH09174034A

Description

【０００１】
【発明の属する技術分野】
本発明は揮発性の有害物質で汚染された土壌の浄化方法に係り、特に汚染された土壌内に抽出井戸を設けて汚染物質を除去する方法に関する。
【０００２】
【従来の技術】
ドライクリ−ニング店などの敷地に含まれる有機塩素系溶剤などの、揮発性有害物質が地下水に溶解し地下汚染の原因となっている。この有害物質で汚染された土壌は例えば図３に示すように表土Ａ、ロ−ム層Ｂ、粘土層Ｃ，れき層Ｄで構成されている。除去対象となる有害物質は表土Ａやロ−ム層Ｂに多く存在しているが、一部は粘土層Ｃ内にも拡散している。粘土層Ｃに浸透した有害物質は帯水層であるれき層Ｄ内の地下水に溶解し拡散する。
【０００３】
従来、この汚染された土壌から有害物質を除去する方法は、仕切板１０をれき層Ｄに達する深さまで埋め込み汚染された地下水の拡散を防ぎ、次いで仕切板１０の内側の地下水を揚水井戸１１に備えてある揚水ポンプ１２で汲み揚げ曝気槽１４に送る。ここで地下水をエアレ−ションし有害物質を気化させる。気化した有害物質は排気管１８を通り処理槽３０に送られ活性炭に吸着される。一方曝気槽１４で浄化された処理水は送水ポンプ１６で地上に放流される。
更に、粘土層Ｃ及びロ−ム層Ｂに存在する有害物質は抽出井戸２１から真空ポンプ２３により吸引され、処理槽３０に送られ活性炭に吸着される。揚水井戸１１及び抽出井戸２１の構造は下端部に多数の小径の穴が設けられており、この穴を介して地下水を揚水し、また、有害物質を真空抽出する。
【０００４】
しかし、土壌内で液状のまま存在している有害物質や、土壌に吸着している有害物質を気化させ抽出するのは困難で、長期間の真空抽出が必要である。特に粘土層などの透気性が悪い土壌に含まれる有害物質の除去は難しく、真空抽出に３年以上要することもある。このため土壌を掘削して地上に取り出し、洗浄等の処理をすることもあるが、多大な費用が必要となり限界がある。
【０００５】
【発明が解決しようとする課題】
本発明は、前記従来技術の欠点を解消し、土壌内で液状のまま存在している有害物質や、土壌に吸着している有害物質を短期間で気化させ除去できる土壌の浄化方法を提供するにある。
【０００６】
【課題を解決するための手段】
本発明は前記課題を解決するために、土壌を加熱することによって有害物質の気化を促進させることが有効であることに着目し、その具体的手段として、帯水層中の地下水を汲み揚げる揚水井戸の他に圧入井戸を設けて、揚水井戸から汲み揚げた前記地下水を浄化した後、この処理水を加熱し前記圧入井戸を介し再度土壌の帯水層に圧入するとともに、加熱した処理水を圧入する圧入井戸の深さを、前記地下水を汲み揚げる揚水井戸の深さよりも浅くするように構成したものである。
【０００７】
【発明の実施の形態】
次に、実施例に基づいて本発明を更に具体的に説明する。図１は本発明の実施例を示す系統図である。本実施例が図３の従来方法と違うところは、帯水層中の地下水を揚水ポンプ１２で揚水し曝気槽１４で浄化処理した後、この処理水を熱交換器１５で４０℃〜７０℃に加熱し、送水ポンプ１６により圧入井戸１７から再度土壌の帯水層へ圧入する点にある。圧入井戸１７はれき層Ｄの上部に開放端が位置し、この開放端には多数の小径の穴が設けられている。この穴から加熱された処理水が押し出されるが、処理水の温度が地下水よりも高く密度が小さいため帯水層であるれき層Ｄの最上部に拡散する。この加熱した処理水の拡散によって、上部の粘土層Ｃは加熱され徐々に温度が上昇する。このため、従来除去が困難とされていた粘土層Ｃに含まれる有害物質は気化し易くなり、短期間で真空抽出ができる。
【０００８】
また、圧入井戸の深さを揚水井戸の深さよりも浅くすることによって、帯水層であるれき層Ｄは底部から低温の地下水を揚水井戸で吸入し、また、上部から加熱された処理水が混入することにより、温度差による密度層を形成する。このため、有害物質を比較的高濃度に含む低温の地下水を、加熱した処理水との混合が少ない状態で揚水することができ、地上での浄化処理の効率が向上する。
【０００９】
図２は本発明による浄化方法と、浄化処理した処理水を地上に放流する従来の方法とを比較したものである。本発明による方法では粘土層Ｃ内に含まれる有害物質であるトリクレンの総除去量が多いだけでなく、除去速度が低下しにくい。これは処理水の加熱によって土壌に浸透したトリクレンの気化が促進されるだけでなく、土壌に吸着されているトリクレンや、土壌粒子間に捕捉されているトリクレンも、水分と共に気化させ除去できるためである。したがって、短期間で土壌を浄化でき、また、浄化後の土壌中の有害物質の濃度も低い。
【００１０】
【発明の効果】
以上、本発明の方法によれば、地下水を揚水し浄化した後、この処理水を加熱し、予め設けた圧入井戸を介し再度土壌の帯水層に圧入するとともに、加熱した処理水を圧入する圧入井戸の深さを、前記地下水を汲み揚げる揚水井戸の深さよりも浅くすることにより、帯水層の上部に位置する土壌内の有害物質の気化を促進させることができ、短期間に土壌中の有害物質を除去できる。
【００１１】
【図面の簡単な説明】
【図１】本発明の実施例を示す系統図
【図２】有害物質の除去に対する本発明と従来方法との比較
【図３】従来方法の系統図
【符号の説明】
１０・・・仕切板
１１・・・揚水井戸
１４・・・曝気槽
１５・・・熱交換器
１７・・・圧入井戸
２１・・・抽出井戸
２３・・・真空ポンプ
３０・・・処理槽[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying soil contaminated with volatile harmful substances, and more particularly, to a method for removing contaminants by providing an extraction well in the contaminated soil.
[0002]
[Prior art]
Volatile toxic substances such as organic chlorinated solvents contained in sites such as dry cleaning stores dissolve in groundwater and cause underground pollution. For example, as shown in FIG. 3, the soil contaminated with this harmful substance is composed of a top soil A, a loam layer B, a clay layer C, and a gravel layer D. Although many harmful substances to be removed exist in the topsoil A and the loam layer B, some of them also diffuse in the clay layer C. The harmful substances that have permeated the clay layer C dissolve and diffuse in the groundwater in the gravel layer D, which is an aquifer.
[0003]
Conventionally, the method of removing harmful substances from this contaminated soil prevents the diffusion of contaminated groundwater by embedding the partition plate 10 to a depth reaching the gravel layer D, and then uses the groundwater inside the partition plate 10 to the pumping well 11. The water is pumped by the provided pump 12 and sent to the aeration tank 14. Here, groundwater is aerated to vaporize harmful substances. The vaporized harmful substance passes through the exhaust pipe 18 and is sent to the treatment tank 30 and is adsorbed by the activated carbon. On the other hand, the treated water purified in the aeration tank 14 is discharged to the ground by a water pump 16.
Furthermore, harmful substances present in the clay layer C and the loam layer B are sucked from the extraction well 21 by the vacuum pump 23, sent to the treatment tank 30, and adsorbed on the activated carbon. The structure of the pumping well 11 and the extraction well 21 is provided with a large number of small-diameter holes at the lower end portion, through which groundwater is pumped and harmful substances are vacuum extracted.
[0004]
However, it is difficult to vaporize and extract harmful substances that exist in a liquid state in the soil and harmful substances that are adsorbed on the soil, and vacuum extraction is required for a long period of time. In particular, it is difficult to remove harmful substances contained in soil with poor air permeability such as clay layers, and vacuum extraction may take 3 years or more. For this reason, soil may be excavated and taken out to the ground, and processing such as washing may be performed, but there is a limit because it requires a large amount of cost.
[0005]
[Problems to be solved by the invention]
The present invention provides a soil purification method that eliminates the disadvantages of the prior art and can vaporize and remove harmful substances present in liquid form in the soil and harmful substances adsorbed on the soil in a short period of time. It is in.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention pays attention to the fact that it is effective to promote the vaporization of harmful substances by heating the soil, and as a specific means, pumping up the groundwater in the aquifer In addition to the well, a press-in well is provided to purify the groundwater pumped from the pumping well, and then the treated water is heated and again injected into the soil aquifer through the press-in well, and the heated treated water is The depth of the press-fitting well to be press-fitted is configured to be shallower than the depth of the pumped well for pumping up the ground water .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described more specifically based on examples. FIG. 1 is a system diagram showing an embodiment of the present invention. This embodiment is different from the conventional method of FIG. 3 in that groundwater in the aquifer is pumped by a pump 12 and purified by an aeration tank 14, and then this treated water is heated at 40 ° C. to 70 ° C. by a heat exchanger 15. It is in the point which press-fits into the aquifer of soil again from the press-in well 17 with the water pump 16. The open well 17 has an open end located above the debris layer D, and a number of small-diameter holes are provided at the open end. Although the treated water heated from this hole is pushed out, the temperature of the treated water is higher than that of the groundwater and its density is small, so that it diffuses to the top of the gravel layer D that is an aquifer. Due to the diffusion of the heated treated water, the upper clay layer C is heated and the temperature gradually rises. For this reason, harmful substances contained in the clay layer C, which has conventionally been difficult to remove, are easily vaporized and can be vacuum extracted in a short period of time.
[0008]
In addition, by making the depth of the injection well shallower than the depth of the pumping well, the gravel layer D, which is an aquifer, draws low-temperature groundwater from the bottom through the pumping well, and the treated water heated from the top By mixing, a density layer due to a temperature difference is formed. For this reason, low-temperature groundwater containing a relatively high concentration of harmful substances can be pumped with little mixing with heated treated water, and the efficiency of purification treatment on the ground is improved.
[0009]
FIG. 2 shows a comparison between the purification method according to the present invention and a conventional method for discharging the treated water after purification treatment to the ground. In the method according to the present invention, not only the total removal amount of trichlene, which is a harmful substance contained in the clay layer C, is large, but also the removal rate is difficult to decrease. This is because heating of the treated water not only promotes the vaporization of trichrene that has penetrated into the soil, but also allows trichrene adsorbed on the soil and trichlene trapped between soil particles to be vaporized and removed together with moisture. is there. Therefore, soil can be purified in a short period of time, and the concentration of harmful substances in the soil after purification is low.
[0010]
【The invention's effect】
As described above, according to the method of the present invention, after pumping up and purifying the groundwater, the treated water is heated and again injected into the aquifer of the soil through a pre-installed injection well , and the heated treated water is injected. By making the depth of the injection well shallower than the depth of the pumping well for pumping up the groundwater, it is possible to promote the vaporization of harmful substances in the soil located above the aquifer, Can remove harmful substances.
[0011]
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of the present invention. FIG. 2 is a comparison between the present invention and a conventional method for removing harmful substances. FIG. 3 is a system diagram of the conventional method.
DESCRIPTION OF SYMBOLS 10 ... Partition plate 11 ... Pumping well 14 ... Aeration tank 15 ... Heat exchanger 17 ... Press-in well 21 ... Extraction well 23 ... Vacuum pump 30 ... Processing tank

Claims

A predetermined partition of soil consisting of an upper layer contaminated with volatile harmful substances and an aquifer below it is surrounded by a partition plate, and the harmful substances in the upper layer are extracted in the form of gas with a vacuum pump inside Establish an extraction well and a pumping well for pumping up groundwater in the aquifer. After purifying the gas extracted from these wells and the pumped-up groundwater on the ground, heat the treated water and install a pre-installed well. In the soil purification method, which is pressed again into the soil aquifer,
A method for purifying soil, characterized in that a depth of a press-fitting well into which the heated treated water is injected is shallower than a depth of a pumping well from which the groundwater is pumped.