JP2005058805A

JP2005058805A - Method and system for purifying solid

Info

Publication number: JP2005058805A
Application number: JP2003206940A
Authority: JP
Inventors: Akira Oshitani; 明押谷; Koichi Hiraishi; 浩一平石; Tokio Kamoshita; 時男鴨下; Yuji Kawamura; 裕二河村; Takeshi Sakurai; 健櫻井
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 2003-08-08
Filing date: 2003-08-08
Publication date: 2005-03-10
Anticipated expiration: 2023-08-08
Also published as: JP4470408B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for purifying soil excellent in washing effect and a system for the method. <P>SOLUTION: In the method for purifying a polluted area, an irrigation trench and a pumping trench are installed in the soil, washing water is made to flow in the polluted area existing between the irrigation trench and the pumping trench by discharging the washing water from the irrigation trench into the soil, and the washing water which flowed in the polluted area is pumped up from the pumping trench. An oxidizing agent adding means is installed in the irrigation trench, and the oxidizing agent is added. Preferably, the washing water whose concentration of the oxidizing agent is adjusted within a prescribed range is made to flow in the polluted area. More preferably, the pumped-up washing water whose salt concentration exceeds a reference value is subjected to ion-exchange or electrodialysis to reduce the salt concentration and made contact with an adsorbent to adsorb/remove heavy metals. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、土壌中の汚染域に洗浄水を流して土壌を浄化する方法において、汚染域を効果的に洗浄する土壌浄化方法に関する。
【０００２】
【従来の技術】
汚染土壌の浄化方法として従来から各種の処理方法が知られている。例えば、（イ）汚染土壌中に設けた削孔を通じて洗浄水を土中に噴射し、この噴射圧によって掘削した汚染土壌を水の還流によって地上に排出し、浄化処理する方法（特開２００１−１６２２６２）、（ロ）汚染域を囲むように複数の注水井と揚水井とを設け、注水井を通じて洗浄水を汚染土壌中に注水し、汚染域を経由した洗浄水を揚水井によって地上に汲み上げて浄化処理し、これを再び注水井を通じて土中に戻す浄化方法（特開平１０−２７７５３１号）、（ハ）揚水井戸を通じて汲上げた地下水を加熱し、注水井戸を通じて加熱地下水を汚染域に送り込み、土壌中の有害物質の気化を促進させる浄化方法（特開平９−１７４０３４号）、（ニ）汚染域の下流側に設けた揚水井戸を通じて汚染地下水を汲み上げ、地上で浄化処理した水を上流側の注水井戸を通じて土中に戻し、この浄化水が汚染域を流れることよって汚染域を洗浄し、再び揚水して浄化処理するサイクルを繰り返す浄化方法（特開平８−３２３３３８号）などが知られている。
【０００３】
さらに、（ホ）汚染域に複数本の散水井戸を掘削し、この井戸にウオータジェット装置を挿入し、乳化材を含む清浄水を散水井戸から土壌中に噴射して汚染土を粉砕しながら散水して土壌を浄化する方法（特許第２７５５０８３号）が知られており、また（ヘ）地下水面より深く止水壁を設け、止水壁で囲まれた領域に注水孔と揚水孔を掘削し、注水孔から水を導入して地下水位を上昇させて汚染域を洗浄すると共に注水孔から揚水孔に向かう地下水流を発生させ、汚染物質を含む地下水を揚水孔から汲み上げて汚染物質を除去した後に注水孔を通じて再び地下水を土中に戻す浄化方法（特許第３１９１１３２号）が知られている。
【０００４】
しかし、汚染域を水洗処理する従来の上記土壌浄化方法は、何れも汚染域に多数の注水井ないし揚水井を設け、これらの井戸を通じて浄化水を注揚水する処理方法であるため、汚染域全体に洗浄水が流れるようにするためには多数の注水井や揚水井を必要とする。しかも、汚染域に対して注水場所が点状であるため、井戸を多数設けても井戸から流出される洗浄水が汚染域に均一に拡散するのが難しく、汚染域を通過する洗浄水ないし地下水の流束密度が一定とならず、洗浄終了までに要する時間が、最低流束密度の汚染域に時間に律速されると云う問題がある。
【０００５】
さらに、上記（ホ）のように地表面から洗浄水を土中に浸透させる方法では、汚染部位にまで水が拡散して浸透する時間が処理時間の律速となり、処理効率を高めるために揚水井戸からの汲み上げ水量を多くすると、地下水位が揚水井に向かって勾配を有するようになるため、洗浄水の流束が揚水井に向かって偏り、揚水井から離れた地点では未洗浄部分が残るという問題を生じる。また、上記（ヘ）の方法では、洗浄水の流束は個々の注水井から個々の揚水井に向かって流れるが、その向きと流速は井戸の位置関係によって定まるので均一ではなく、そのため洗浄部位と洗浄速度が流束密度の低い部分の洗浄速度によって律速されるという問題がある。
【０００６】
【発明が解決しようとする課題】
本発明は土壌の汚染域に洗浄水を流して浄化する処理方法において、従来方法の上記問題を解決したものであり、浄化処理する土壌にトレンチを施工し、このトレンチの壁面を通じて洗浄水を放水することによって汚染域を含む広い領域に対して効果的に洗浄水を流し、かつ酸化剤添加手段ないし洗浄水の電解手段を設けて洗浄効果を高めると共に、好ましくは、汲み上げた洗浄水に含まれる汚染物質を除去する手段を二段に設けて汚染物質を確実に除去し、洗浄水を循環使用する土壌浄化方法および土壌浄化システムを提供するものである。
【０００７】
【課題を解決する手段】
本発明は以下の土壌浄化方法に関する。
（１）土壌中に注水トレンチと揚水トレンチを設け、注水トレンチから洗浄水を土壌中に放水して注水トレンチと揚水トレンチの間の存在する汚染域に洗浄水を流し、汚染域を流れた洗浄水を揚水トレンチから汲み上げて汚染域を洗浄する浄化方法において、注水トレンチに酸化剤の添加手段を設け、酸化剤を添加した洗浄水を汚染域に流すことを特徴とする土壌浄化方法。
（２）揚水トレンチから汲み上げた洗浄水を注水トレンチに戻す循環路を設け、揚水トレンチから汲み上げた洗浄水に含まれる汚染物質を除去した後に、この洗浄水に含まれる残留酸化剤濃度を測定して酸化剤を添加し、所定濃度の酸化剤を含む洗浄水を汚染域に流す上記（１）の土壌浄化方法。
（３）上記（１）または（２）の方法において、酸化剤の添加手段に代えて洗浄水の電解手段を設け、あるいは酸化剤添加手段および残留酸化剤濃度測定手段に代えて洗浄水の電解手段と残留塩素濃度測定手段を設け、塩素濃度を所定範囲に制御した洗浄水を汚染域に流す土壌浄化方法。
（４）土壌中に注水トレンチと揚水トレンチを設け、注水トレンチから洗浄水を土壌中に放水して注水トレンチと揚水トレンチの間の存在する汚染域に洗浄水を流し、汚染域を流れた洗浄水を揚水トレンチから汲み上げて汚染域を洗浄する浄化方法において、汲み上げた洗浄水に含まれる汚染物質を除去する手段を二段に設け、塩分濃度が基準値を超える洗浄水をイオン交換膜ないし電気透析手段に導いて塩分濃度を低減する一方、洗浄水を吸着剤に接触させて洗浄水に含まれる重金属を吸着除去することを特徴とする土壌浄化方法。
【０００８】
さらに、本発明は以下の土壌浄化システムに関する。
（５）土壌中に相対向して設けた注水トレンチと揚水トレンチ、注水トレンチに洗浄水を供給する手段、揚水トレンチから洗浄水を汲み上げる手段、汲み上げた洗浄水に含まれる汚染物質を除去する手段、浄化した洗浄水を注水トレンチに導入する循環路、浄化した洗浄水に含まれる残留酸化剤濃度を測定する手段、浄化した洗浄水に酸化剤を添加する手段とを備えたことを特徴とする土壌浄化システム。
（６）上記（５）の浄化システムにおいて、残留酸化剤濃度の測定手段および酸化剤添加手段に代えて、洗浄水の電解手段および残留塩素濃度測定手段を有する土壌浄化システム。
（７）上記（５）または６の浄化システムにおいて、汚染物質の除去手段として、揚水トレンチから汲み上げた洗浄水のイオン交換または電気透析を行う手段、および該洗浄水に含まれる重金属を吸着する手段を有する土壌浄化システム。
【０００９】
本発明の土壌浄化方法は、注水トレンチの壁面から洗浄水が放水されるので、従来の注水井戸を用いた場合と異なり、放水面が広く、汚染域に対して洗浄水を均一に流すことができる。さらに、注水トレンチに酸化剤の添加手段を設け、好ましくは残留酸化剤濃度を測定する手段を設け、所定濃度の酸化剤を含む洗浄水を汚染域に流すことによって洗浄効果を高めることができる。あるいは、酸化剤添加手段および残留酸化剤濃度測定手段に代えて、洗浄水の電解手段と残留塩素濃度測定手段を設け、塩素濃度を所定範囲に制御した洗浄水を汚染域に流すことによって洗浄効果を高めることができる。
【００１０】
さらに、揚水トレンチを通じて汲み上げた洗浄水に含まれる汚染物質を除去する手段として、洗浄水のイオン交換または電気透析を行う手段と共に該洗浄水に含まれる重金属の吸着手段を併用することによって、汲み上げた洗浄水に含まれる汚染物質を確実に除去することができ、この洗浄水を循環使用することによって浄化効果をさらに高めると共に、排水処理の負担を軽減し、土壌浄化を低コストで行うことができる。
【００１１】
【発明の実施の形態】
以下、本発明の土壌浄化方法ないし土壌浄化システムについて、図面に示す構成例を参照して具体的に説明する。図１は本発明に係る土壌浄化システムを示す模式的な縦断面図、図２はその模式平面図、図３は汚染域との位置関係を示す模式縦断面図、図４は本発明の土壌浄化システムの汚染物質除去手段、酸化剤添加手段、洗浄水循環路を示す模式構成図である。
【００１２】
図示する本発明の土壌浄化システムは、汚染域Ａを囲むように遮水壁１０を設け、遮水壁１０で囲まれた領域の上流側に注水トレンチ１１を設けると共に下流側に揚水トレンチ１２が設けられている。注水トレンチ１１と揚水トレンチ１２は両側の遮水壁１０に沿って細長く形成されており、汚染域Ａをはさんで相対向して設置されている。各トレンチ１１、１２は地下の難透水層２０に達する深さに掘削されており、トレンチ１１、１２の外周は遮水壁１０によって囲まれている。また、各トレンチ１１、１２の内壁の上側部分は遮水壁１０によって形成されており、その下側部分は透水性壁面によって形成されている。
【００１３】
具体的には、例えば、注水トレンチ１１の内壁の上側部分は遮水性のコンクリート壁などによって形成されており、注水トレンチ１１の下側部分には砕石や砂利などの透水材料が充填され、この透水材料が内壁下部の壁面を形成している。なお、施工場所を遮水壁１０によって囲めば洗浄水が施工域外に拡散するのを防止できるので、汚染域の洗浄効果が向上するが、施工場所の条件によっては遮水壁１０を一部だけに設けても良く、あるいは設けなくても良い。
【００１４】
一方、揚水トレンチ１２の上側部分は遮水性のコンクリート壁などによって形成されており、内壁下部は多数の通孔を有する透水性のコンクリート壁によって形成されている。また、揚水トレンチ１２は汚染域Ａを通過した洗浄水を汲み上げる揚水ポンプ１５が接続している。
【００１５】
注水トレンチ１１および揚水トレンチ１２は鋼矢板で挟んだ構造もしくは鋼管杭を連結した構造でも良い。トレンチ部分の洗浄水が容易に移動できる構造であって、外周部分が遮水性壁面によって形成されており、所定の深度に通水用の孔ないしストレーナーを施工できる構造であれば良い。この外周遮水壁によって洗浄を行う汚染域の地下水とその周囲の地下水との混合を抑止する。難透水層（粘土層等）まで、あるいは洗浄対象深度より十分深い深度まで外周遮水壁を打ち込むのが好ましい。また、内壁上部の遮水壁は洗浄を行う深度より上側への漏水を防止し、かつ洗浄水の注水側水頭圧を維持するために、地上部から土中の洗浄域に入り込む程度の深度まで打ち込むのが好ましい。この、内壁上部の遮水壁の高さを調整することによって、汚染域に対して集中的に洗浄水が流れるように制御することができる。
【００１６】
注水トレンチ１１には洗浄水の注水管路１６が接続しており、注水バルブ１７が装着されている。一方、揚水トレンチ１２には汲み上げた洗浄水を処理設備に導く揚水管路１８が接続している。注水トレンチ１１には洗浄水が管路１６を通じて導入される。洗浄水は管路１６を通じて注水トレンチ１１に供給され、下部透水性内壁面から土中に放水され、注水トレンチ１１と揚水トレンチ１２の間に位置する汚染域Ａを流れてポンプ１５によって揚水トレンチ１２から地上に揚水され、管路１８を通じて処理設備に送られ、ここで洗浄水に含まれる汚染物質が除去される。
【００１７】
本発明の土壌浄化システムには地下を流れる洗浄水の水位（以下、地下水位と云う）を測定する手段を設けるのが好ましい。図１および図２に示す構成例では地下水位の傾斜を測定できるように、上流側と下流側に水位測定孔３１、３２が設けられており、この水位測定孔３１、３２に水位センサーが設置されている。なお、水位測定孔を設けずに、注水トレンチ１１と揚水トレンチ１２に水位測定センサーを設けても良い。この水位測定手段によって地下水位をモニタリングして土壌浄化を行う。
【００１８】
さらに、図示する構成例では、水位測定センターと注水バルブ１７および揚水ポンプ１５を結ぶ水位制御ユニット３３が形成されている。この制御系３３は水位センサーの情報に基づいて注水バルブ１７および揚水ポンプ１５の運転を制御し、地下水位が汚染域Ａよりも上側になり、汚染域Ａが水没するように地下水位を自動制御する。具体的には、例えば地下水位が基準水位より低い場合には注水バルブ１７を開いて注水を行い、あるいは揚水ポンプ１５を停止する。一方、地下水位が基準水位より高い場合には注水バルブ１７を閉じ、または揚水ポンプ１５を稼動させる。
【００１９】
図４に示す土壌洗浄システムには、汚染物質を除去した洗浄水に酸化剤を添加する手段、汲み上げた洗浄水に含まれている汚染物質を除去する手段、この洗浄水を注水トレンチに戻す循環路が設けられている。この循環路には適宜の箇所に送液ポンプ３５が設けられている。
【００２０】
図示するように、注水トレンチ１１は管路１６を通じて調整槽２６に接続している。この調整槽２６には洗浄水が導入されており、さらに洗浄水の残留酸化剤濃度を測定する手段２７と、酸化剤を供給する手段２８が設けられている。残留酸化剤濃度の測定値は酸化剤の供給手段２８に伝達され、この値に応じた量の酸化剤が調整槽２７の洗浄水に添加され、洗浄水の酸化剤濃度が一定範囲に保たれる。酸化剤としては、例えば次亜塩素酸ソーダ（ＮａＯＣｌ）などを用いることができる。酸化剤の濃度は土壌の汚染程度に応じて調整される。酸化剤の濃度が調整された洗浄水は調整槽２６から注水管路１６およびバルブ１７を通じて注水トレンチ１１に供給される。
【００２１】
酸化剤の添加に代えて洗浄水の電気分解手段を設けてもよい。この電気分解手段は注水トレンチ１１の上端に設置してもよく、あるいは土壌中の汚染域Ａに設置してもよい。洗浄水の電気分解によって次亜塩素酸ソーダが生成される。電気分解の条件は、例えば、電流密度１〜１００Ａ／ｍ^２、電圧１．５〜１０Ｖが適当である。
【００２２】
次亜塩素酸ソーダは最終的に塩化ナトリウムと酸素に分解する（２ＮａＯＣｌ→２ＮａＣｌ＋Ｏ_２）が、次亜塩素酸イオン（ＯＣｌ⁻）が存在している間は強い酸化力を示す。この酸化力を利用してＣｄＳ、ＰｂＳなどの硫化物や、Ｓｅ、Ａｓなどの不溶性重金属化合物の汚染物質をイオン化して可溶性に変える。前述したように次亜塩素酸ソーダの濃度はその残留イオン濃度によって調整する。なお、注水トレンチ１１に供給する洗浄水の次亜塩素酸イオン濃度は概ね０．４〜４０ｍｇ／ｌが適当である。
【００２３】
酸化剤を含む洗浄水は注水トレンチ１１の壁面から土壌中に放水され、汚染域を通過して揚水トレンチ１２に流れる。なお、注水トレンチ１１から放水される洗浄水を加圧してもよく、また脈動を与えて放水しても良い。汚染域を流れて揚水トレンチ１２に達した洗浄水は揚水トレンチ１２に設けた管路１８を通じて汲み上げられる。
【００２４】
揚水トレンチ１２から延びた揚水管路１８はバルブ１９を介して受水槽２０と処理槽２１に接続している。受水槽２０には洗浄水に含まれる残留塩分濃度を測定する手段２２が設けられており、この測定値が上記バルブ１９に伝達されて管路１８の接続が受水槽２０または処理槽２１の何れかに切り替えられる。
【００２５】
残留塩分濃度が基準より高い洗浄水はバルブ１９を通じて処理槽２１に導入される。この処理槽２１にはイオン交換膜または電気透析手段が設けられており、イオン交換または電気透析によって洗浄水から残留塩分を分離して洗浄水を浄化する。処理槽２１から流出した洗浄水は管路２３を通じて受水槽２０に導入される。一方、残留塩分濃度が基準より低い洗浄水はバルブ１９の通路を切り替えて直接に受水槽２０に導入される。分離した塩分は処理槽２１から外部に排出される。
【００２６】
上記残留塩分濃度の基準は処理条件に応じて設定される。例えば、２．０ｗｔ％程度である。一般に汲み上げた洗浄水の残留塩分濃度がこれより高いと、洗浄後の土壌中の塩分濃度が高くなる。なお、残留塩分濃度の上限基準２．０ｗｔ％のとき、この９０％を超える濃度、すなわち残留塩分濃度が１．８ｗｔ％以上になった場合は塩分の分離を行うとよい。
【００２７】
一方、洗浄水に含まれるＣｄやＰｂなどの重金属はイオン交換や電気透析では除去できない。そこで、受水槽２０の洗浄水を吸着槽２４に導き、ここで重金属を吸着剤に吸着させて除去する。図５に示すように、吸着槽２４は内部を二つに仕切り、下流側の部分に吸着剤２５を充填し、上流側の室内に流入した洗浄水が吸着剤２５を通過してオバーフローするように形成するとよい。この構造によれば洗浄水と吸着剤との接触時間が長くなり、また吸着剤の入替えも容易である。吸着剤２５としては、ＣｄやＰｂなどの陽イオン系金属に対してはリン酸カルシウム（リン灰石）などが用いられ、ＡｓやＳｅなどの陰イオン系金属に対してはシュベルトマナイトなどの粘土鉱物を用いるとよい。
【００２８】
リン灰石は平均粒径５〜３０ｍｍ程度に粉砕したものを用いるとよい。これより粗いと表面積が小さくなり、また微細過ぎると槽外への流失量が多くなるので好ましくない。また、シュベルトマナイトなどの粘土鉱物は粒径２０〜３０ｍｍの砕石と共に吸着槽２４に充填するとよい。なお、吸着槽２４の内部にリン灰石充填部と粘土鉱物充填部を形成して洗浄水が両充填部を連続して流れるようにし、陽イオン系重金属と陰イオン系重金属の両方を吸着除去してもよい。
【００２９】
吸着槽２４で浄化された洗浄水は貯槽２５を経て調整槽２６に送られる。先に述べたように、この調整槽２７で洗浄水の酸化剤濃度が一定範囲に調整された後に管路１６およびバルブ１７を通じて注水トレンチ１１に供給され、汚染域の洗浄に繰り返し使用される。
【００３０】
【実施例】
以下、本発明を実施例によって具体的に示す。
〔実施例１〕
底部に通液孔を有する処理容器を用い、容器底部に定性濾紙を敷き、その上に硫化カドミウム（ＣｄＳ）２００ｍｇ／ｋｇを含有する試験土壌４００ｇを充填し、次亜塩素酸ソーダを含む洗浄水を容器上部から流し入れて土壌を洗浄した。この結果を表１に示した。なお、洗浄水量は１５０ｍｌ／ｍｉｎ、単位面積当たりの水量は２．６３ｃｍ^３／ｃｍ^２・分であり、残留塩素濃度と溶出Ｃｄ濃度は容器底部から流出した洗浄水に含まれる塩素濃度とＣｄ濃度であり、残留Ｃｄ濃度は土壌に残留するＣｄ濃度である。洗浄水量が１０００ｍ^３／ｍ^２までの洗浄効果は低いが、洗浄水量が１００００ｍ^３／ｍ^２以上になると、土壌中の硫化カドミウムが殆ど溶出除去され、最終的に土壌中の残留Ｃｄ濃度を０．１ｍｇ／ｋｇに低減することができる。
【００３１】
【表１】

【００３２】
〔実施例２〕
図４の土壌浄化システムによって土壌中の重金属汚染域を洗浄した。処理条件と効果を表２に示した。
【００３３】
【表２】

【００３４】
【発明の効果】
本発明の土壌浄化方法では、注水トレンチの壁面から洗浄水が放水されるので放水面が広く、汚染域に対して洗浄水を均一に流すことができ、さらに水位測定孔を設け、測定水位に基づいて注水量ないし揚水量を制御して土壌中の汚染域を流れる洗浄水の水位を適正に保つことによって洗浄効果が向上する。また、洗浄水の酸化剤濃度を所定範囲に調整することによって洗浄効果をさらに向上することができる。さらに、揚水トレンチを通じて汲み上げた洗浄水に含まれる汚染物質を二段階に処理して除去することによって洗浄水の浄化効果を高め、洗浄水を繰り返し使用することができる。
【図面の簡単な説明】
【図１】本発明に係る土壌浄化システムを示す模式的な縦断面図
【図２】図１の土壌浄化システムの模式平面図
【図３】図１の土壌浄化システムの模式縦断面図
【図４】本発明の土壌浄化システムの汚染物質除去手段、酸化剤添加手段、洗浄水循環路を示す模式構成図
【図５】処理槽の模式断面図
【符号の説明】１０−遮水壁、１１−注水トレンチ、１２−揚水トレンチ、１３−透水層、１５−揚水ポンプ、１６−注水管路、１７−注水バルブ、１８−揚水管路、２０−難透水層、３１、３２−水位測定孔、３３−水位コントロールユニット、[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a soil purification method for effectively washing a contaminated area in a method for purifying soil by flowing wash water into the contaminated area in soil.
[0002]
[Prior art]
Conventionally, various treatment methods are known as methods for purifying contaminated soil. For example, (a) a method of injecting cleaning water into the soil through a hole provided in the contaminated soil and discharging the contaminated soil excavated by this injection pressure to the ground by water recirculation (Japanese Patent Laid-Open No. 2001-2001). 162262), (b) A plurality of water injection wells and pumping wells are provided so as to surround the contaminated area, and the wash water is poured into the contaminated soil through the water injection well, and the wash water passing through the contaminated area is pumped to the ground by the pumping well. Purification method to return to the soil through the injection well (JP-A-10-277531), (c) Groundwater pumped up through the pumping well is heated, and the heated groundwater is sent to the contaminated area through the injection well , A purification method for promoting the vaporization of harmful substances in soil (Japanese Patent Laid-Open No. 9-174034), (d) water that has been contaminated by pumping up contaminated groundwater through a pumping well provided downstream of the contaminated area There is known a purification method (Japanese Patent Laid-Open No. 8-323338) that returns to the soil through an upstream water injection well, and the purified water flows through the contaminated area to wash the contaminated area and repeat the cycle of pumping and purifying again. It has been.
[0003]
(E) Drilling multiple water wells in the contaminated area, inserting a water jet device into this well, spraying clean water containing emulsifying material into the soil from the water well, and sprinkling the contaminated soil In addition, a method for purifying soil (Japanese Patent No. 2755083) is known, and (f) a water blocking wall is provided deeper than the groundwater surface, and a water injection hole and a water pumping hole are excavated in an area surrounded by the water blocking wall. Introducing water from the water injection hole to raise the groundwater level to clean the contaminated area and to generate a groundwater flow from the water injection hole to the pumping hole, pumping the groundwater containing the pollutant from the water pumping hole to remove the pollutant A purification method (Japanese Patent No. 3191132) for returning groundwater to the soil again through a water injection hole later is known.
[0004]
However, the conventional soil purification methods for washing the contaminated area with water are all treatment methods in which a large number of injection wells or pumping wells are provided in the contaminated area and the purified water is pumped through these wells. A large number of water injection wells and pumping wells are required to allow the washing water to flow through. In addition, since the water injection location is dotted with respect to the contaminated area, it is difficult for the wash water flowing out from the well to spread evenly in the contaminated area even if many wells are provided. However, there is a problem that the time required for the end of cleaning is limited by time in the contaminated area having the lowest flux density.
[0005]
Furthermore, in the method of infiltrating washing water from the ground surface into the soil as in (e) above, the time for the water to diffuse and penetrate to the contaminated site becomes the rate limiting treatment time, and the pumping well is used to increase the treatment efficiency. If the amount of water pumped up from the ground becomes higher, the groundwater level will have a gradient toward the pumping well, so the washing water flux will be biased toward the pumping well, and unwashed parts will remain at points away from the pumping well. Cause problems. In the method (f) above, the washing water flux flows from the individual injection wells to the individual pumping wells, but the direction and flow rate are determined by the positional relationship of the wells and are not uniform. In addition, there is a problem that the cleaning speed is limited by the cleaning speed of the portion having a low flux density.
[0006]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the conventional method in a treatment method in which washing water is poured into a contaminated area of the soil, and a trench is constructed in the soil to be treated, and the washing water is discharged through the wall of the trench. In this way, the washing water is effectively allowed to flow over a wide area including the contaminated area, and an oxidant addition means or a washing water electrolysis means is provided to enhance the washing effect, and preferably, the washing water is included in the pumped washing water. The present invention provides a soil purification method and a soil purification system in which means for removing contaminants are provided in two stages to reliably remove the contaminants and to circulate and use wash water.
[0007]
[Means for solving the problems]
The present invention relates to the following soil purification method.
(1) A water injection trench and a water pumping trench are provided in the soil, the cleaning water is discharged from the water injection trench into the soil, the cleaning water is poured into the contaminated area between the water pouring trench and the water pumping trench, and the cleaning is performed through the contaminated area. In the purification method of pumping up water from the pumping trench and cleaning the contaminated area, an oxidant addition means is provided in the water injection trench, and the cleaning water to which the oxidizing agent is added is caused to flow to the contaminated area.
(2) A circulation path is provided to return the cleaning water pumped up from the pumping trench to the water injection trench, and after removing contaminants contained in the cleaning water pumped up from the pumping trench, the residual oxidant concentration in the cleaning water is measured. The soil purification method according to (1) above, wherein an oxidant is added and washing water containing a predetermined concentration of oxidant is passed through the contaminated area.
(3) In the above method (1) or (2), an electrolyzing means for washing water is provided instead of the means for adding the oxidizing agent, or electrolysis of the washing water is substituted for the oxidizing agent adding means and the residual oxidant concentration measuring means. A soil remediation method in which cleaning water is provided to the contaminated area by providing means and residual chlorine concentration measuring means and controlling the chlorine concentration within a predetermined range.
(4) A water injection trench and a water pumping trench are provided in the soil, the cleaning water is discharged from the water injection trench into the soil, the cleaning water is poured into the contaminated area existing between the water pouring trench and the water pumping trench, and the cleaning flows through the contaminated area. In the purification method that pumps water from the pumping trench and cleans the contaminated area, there are two stages to remove the pollutants contained in the pumped cleaning water, and the cleaning water whose salinity exceeds the standard value is supplied to the ion-exchange membrane or electricity. A soil purification method characterized by reducing the salinity concentration by introducing to a dialysis means, and bringing the washing water into contact with the adsorbent to adsorb and remove heavy metals contained in the washing water.
[0008]
Furthermore, this invention relates to the following soil purification systems.
(5) Water injection trench and pumping trench provided opposite to each other in the soil, means for supplying cleaning water to the water injection trench, means for pumping cleaning water from the pumping trench, means for removing contaminants contained in the pumped cleaning water A circulation path for introducing the purified cleaning water into the water injection trench, means for measuring the residual oxidant concentration contained in the purified cleaning water, and means for adding an oxidant to the purified cleaning water. Soil purification system.
(6) In the purification system of (5), a soil purification system having electrolysis means for washing water and residual chlorine concentration measurement means instead of the measurement means for residual oxidant concentration and the oxidant addition means.
(7) In the purification system according to (5) or (6), as means for removing contaminants, means for performing ion exchange or electrodialysis of wash water pumped from a pumping trench, and means for adsorbing heavy metals contained in the wash water Having soil purification system.
[0009]
In the soil purification method of the present invention, since the wash water is discharged from the wall surface of the water injection trench, unlike the case of using a conventional water injection well, the water discharge surface is wide and the wash water can be flowed uniformly over the contaminated area. it can. Further, an oxidant addition means is provided in the water injection trench, preferably a means for measuring the residual oxidant concentration, and the cleaning effect can be enhanced by flowing cleaning water containing a predetermined concentration of oxidant into the contaminated area. Alternatively, instead of the oxidant addition means and the residual oxidant concentration measurement means, a cleaning water electrolysis means and a residual chlorine concentration measurement means are provided, and the cleaning effect is achieved by flowing the cleaning water whose chlorine concentration is controlled within a predetermined range to the contaminated area. Can be increased.
[0010]
Furthermore, as a means for removing contaminants contained in the wash water pumped up through the pumping trench, pumping was performed by using a means for adsorbing heavy metals contained in the wash water together with a means for performing ion exchange or electrodialysis of the wash water. Contaminants contained in the wash water can be reliably removed, and by using this wash water in a circulating manner, the purification effect can be further enhanced, the burden of waste water treatment can be reduced, and soil purification can be performed at low cost. .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a soil purification method or a soil purification system of the present invention will be specifically described with reference to a configuration example shown in the drawings. 1 is a schematic longitudinal sectional view showing a soil purification system according to the present invention, FIG. 2 is a schematic plan view thereof, FIG. 3 is a schematic longitudinal sectional view showing a positional relationship with a contaminated area, and FIG. 4 is a soil according to the present invention. It is a schematic block diagram which shows the contaminant removal means of a purification system, an oxidizing agent addition means, and a washing water circulation path.
[0012]
In the illustrated soil purification system of the present invention, a water shielding wall 10 is provided so as to surround a contaminated area A, a water injection trench 11 is provided on the upstream side of a region surrounded by the water shielding wall 10, and a pumping trench 12 is provided on the downstream side. Is provided. The water injection trench 11 and the pumping trench 12 are formed to be elongated along the impermeable walls 10 on both sides, and are placed opposite to each other across the contaminated area A. Each of the trenches 11 and 12 is excavated to a depth reaching the underground water-impermeable layer 20, and the outer peripheries of the trenches 11 and 12 are surrounded by the water-impervious wall 10. Moreover, the upper part of the inner wall of each trench 11 and 12 is formed of the water-impervious wall 10, and the lower part is formed of the water-permeable wall surface.
[0013]
Specifically, for example, the upper portion of the inner wall of the water injection trench 11 is formed of a water-impervious concrete wall, and the lower portion of the water injection trench 11 is filled with a water-permeable material such as crushed stone or gravel. The material forms the lower wall surface of the inner wall. In addition, since the washing water can be prevented from diffusing outside the construction area if the construction place is enclosed by the impermeable wall 10, the cleaning effect of the contaminated area is improved. However, depending on the conditions of the construction place, only a part of the impermeable wall 10 is provided. May or may not be provided.
[0014]
On the other hand, the upper part of the pumping trench 12 is formed by a water-impervious concrete wall or the like, and the lower part of the inner wall is formed by a water-permeable concrete wall having a large number of through holes. Further, the pumping trench 12 is connected to a pumping pump 15 that pumps the cleaning water that has passed through the contaminated area A.
[0015]
The water injection trench 11 and the pumping trench 12 may have a structure sandwiched between steel sheet piles or a structure in which steel pipe piles are connected. Any structure can be used as long as the cleaning water in the trench portion can easily move, the outer peripheral portion is formed by a water-impervious wall surface, and a hole or strainer for passing water can be constructed at a predetermined depth. Mixing of the groundwater in the contaminated area to be cleaned and the surrounding groundwater is suppressed by this outer peripheral impermeable wall. It is preferable to drive the outer impermeable wall up to a hardly water permeable layer (such as a clay layer) or a depth sufficiently deeper than the depth to be cleaned. In addition, the water-impervious wall at the top of the inner wall prevents water leaking upward from the depth at which cleaning is performed, and maintains a water head pressure on the injection side of the cleaning water up to a depth enough to enter the cleaning area in the soil. It is preferable to drive in. By adjusting the height of the water-impervious wall at the upper part of the inner wall, it is possible to control the washing water to flow intensively with respect to the contaminated area.
[0016]
A water injection conduit 16 for cleaning water is connected to the water injection trench 11 and a water injection valve 17 is attached. On the other hand, a pumping pipe 18 is connected to the pumping trench 12 to guide the cleaning water pumped up to the treatment facility. Wash water is introduced into the water injection trench 11 through the pipe line 16. The washing water is supplied to the water injection trench 11 through the pipe line 16, discharged into the soil from the lower permeable inner wall surface, flows through the contaminated area A located between the water injection trench 11 and the pumping trench 12, and is pumped by the pump 15. The water is pumped to the ground and sent to the treatment facility through the pipe 18 where the contaminants contained in the wash water are removed.
[0017]
The soil purification system of the present invention is preferably provided with a means for measuring the water level of the wash water flowing in the underground (hereinafter referred to as the groundwater level). In the configuration example shown in FIGS. 1 and 2, water level measurement holes 31 and 32 are provided on the upstream side and the downstream side so that the inclination of the groundwater level can be measured, and a water level sensor is installed in the water level measurement holes 31 and 32. Has been. In addition, you may provide a water level measurement sensor in the water injection trench 11 and the pumping trench 12 without providing a water level measurement hole. Soil purification is performed by monitoring the groundwater level with this water level measuring means.
[0018]
Further, in the illustrated configuration example, a water level control unit 33 that connects the water level measurement center to the water injection valve 17 and the pumping pump 15 is formed. The control system 33 controls the operation of the water injection valve 17 and the pump 15 based on the information of the water level sensor, and automatically controls the groundwater level so that the groundwater level is above the contaminated area A and the contaminated area A is submerged. To do. Specifically, for example, when the groundwater level is lower than the reference water level, the water injection valve 17 is opened to perform water injection, or the pumping pump 15 is stopped. On the other hand, when the groundwater level is higher than the reference water level, the water injection valve 17 is closed or the pumping pump 15 is operated.
[0019]
The soil cleaning system shown in FIG. 4 includes means for adding an oxidizing agent to cleaning water from which contaminants have been removed, means for removing contaminants contained in the pumped cleaning water, and circulation for returning the cleaning water to the water injection trench. There is a road. The circulation path is provided with a liquid feed pump 35 at an appropriate location.
[0020]
As shown in the drawing, the water injection trench 11 is connected to the adjustment tank 26 through the pipe line 16. Wash water is introduced into the adjustment tank 26, and means 27 for measuring the residual oxidant concentration of the wash water and means 28 for supplying the oxidant are provided. The measured value of the residual oxidant concentration is transmitted to the oxidant supply means 28, and an amount of oxidant corresponding to this value is added to the wash water in the adjustment tank 27, so that the wash water oxidant concentration is kept within a certain range. It is. As the oxidizing agent, for example, sodium hypochlorite (NaOCl) can be used. The concentration of the oxidizing agent is adjusted according to the degree of soil contamination. The cleaning water whose oxidant concentration is adjusted is supplied from the adjustment tank 26 to the water injection trench 11 through the water injection pipe 16 and the valve 17.
[0021]
Instead of adding an oxidizing agent, electrolysis means for washing water may be provided. This electrolysis means may be installed at the upper end of the water injection trench 11 or may be installed in a contaminated area A in the soil. Sodium hypochlorite is produced by electrolysis of the wash water. Suitable conditions for the electrolysis are, for example, a current density of 1 to 100 A / m ² and a voltage of 1.5 to 10 V.
[0022]
Sodium hypochlorite eventually decomposes into sodium chloride and oxygen (2NaOCl → 2NaCl + O ₂ ), but exhibits strong oxidizing power while hypochlorite ions (OCl ⁻ ) are present. Using this oxidizing power, sulfides such as CdS and PbS and contaminants of insoluble heavy metal compounds such as Se and As are ionized to be soluble. As described above, the concentration of sodium hypochlorite is adjusted by the residual ion concentration. The concentration of hypochlorite ions in the cleaning water supplied to the water injection trench 11 is generally about 0.4 to 40 mg / l.
[0023]
The cleaning water containing the oxidizing agent is discharged into the soil from the wall surface of the water injection trench 11, passes through the contaminated area, and flows into the pumping trench 12. In addition, you may pressurize the wash water discharged from the water injection trench 11, and you may give a pulsation and may discharge water. The cleaning water that has flowed through the contaminated area and reached the pumping trench 12 is pumped up through a pipe line 18 provided in the pumping trench 12.
[0024]
A pumping pipe line 18 extending from the pumping trench 12 is connected to a water receiving tank 20 and a processing tank 21 through a valve 19. The water receiving tank 20 is provided with means 22 for measuring the residual salt concentration contained in the washing water, and this measured value is transmitted to the valve 19 so that the pipe 18 is connected to either the water receiving tank 20 or the processing tank 21. It can be switched to.
[0025]
Washing water having a residual salinity concentration higher than the reference is introduced into the treatment tank 21 through the valve 19. The treatment tank 21 is provided with an ion exchange membrane or electrodialysis means, and purifies the washing water by separating residual salt from the washing water by ion exchange or electrodialysis. The washing water that has flowed out of the treatment tank 21 is introduced into the water receiving tank 20 through the conduit 23. On the other hand, the wash water having a residual salinity concentration lower than the reference is directly introduced into the water receiving tank 20 by switching the passage of the valve 19. The separated salt is discharged from the treatment tank 21 to the outside.
[0026]
The reference for the residual salinity concentration is set according to the processing conditions. For example, it is about 2.0 wt%. Generally, if the residual salinity of the wash water pumped up is higher than this, the salinity in the soil after washing becomes high. In addition, when the upper limit standard of the residual salinity concentration is 2.0 wt%, if the concentration exceeds 90%, that is, the residual salinity concentration becomes 1.8 wt% or more, the salinity may be separated.
[0027]
On the other hand, heavy metals such as Cd and Pb contained in washing water cannot be removed by ion exchange or electrodialysis. Therefore, the washing water of the water receiving tank 20 is guided to the adsorption tank 24 where heavy metals are adsorbed on the adsorbent and removed. As shown in FIG. 5, the adsorption tank 24 is divided into two parts, the adsorbent 25 is filled in the downstream portion, and the washing water flowing into the upstream chamber passes through the adsorbent 25 and overflows. It is good to form. According to this structure, the contact time between the washing water and the adsorbent becomes long, and the adsorbent can be easily replaced. As the adsorbent 25, calcium phosphate (apatite) is used for cationic metals such as Cd and Pb, and clay minerals such as Schwertmannite for anionic metals such as As and Se. Should be used.
[0028]
The apatite may be pulverized to an average particle size of about 5 to 30 mm. If it is coarser than this, the surface area becomes small, and if it is too fine, the amount of loss to the outside of the tank increases, which is not preferable. Moreover, it is good to fill the adsorption tank 24 with clay minerals, such as a Schwermannite, with a crushed stone with a particle size of 20-30 mm. In addition, an apatite filling portion and a clay mineral filling portion are formed inside the adsorption tank 24 so that washing water flows continuously through both filling portions, and both cationic heavy metals and anionic heavy metals are removed by adsorption. May be.
[0029]
The washing water purified in the adsorption tank 24 is sent to the adjustment tank 26 through the storage tank 25. As described above, the oxidant concentration of the cleaning water is adjusted to a certain range in the adjusting tank 27 and then supplied to the water injection trench 11 through the pipe line 16 and the valve 17 and repeatedly used for cleaning the contaminated area.
[0030]
【Example】
Hereinafter, the present invention will be specifically described by way of examples.
[Example 1]
Using a processing container having a liquid passage hole at the bottom, qualitative filter paper is laid on the bottom of the container, 400 g of test soil containing 200 mg / kg of cadmium sulfide (CdS) is filled thereon, and washing water containing sodium hypochlorite Was poured from the top of the container to wash the soil. The results are shown in Table 1. The amount of washing water is 150 ml / min, the amount of water per unit area is 2.63 cm ³ / cm ² · min, and the residual chlorine concentration and elution Cd concentration are the chlorine concentration and Cd concentration contained in the washing water flowing out from the bottom of the container. The residual Cd concentration is the Cd concentration remaining in the soil. Although the cleaning effect is low up to 1000 m ³ / m ² , the cadmium sulfide in the soil is almost completely eluted and removed, and finally the residual Cd concentration in the soil is reduced to 0 when the cleaning water amount is 10,000 m ³ / m ² or more. It can be reduced to 1 mg / kg.
[0031]
[Table 1]

[0032]
[Example 2]
The heavy metal contaminated area in the soil was washed by the soil purification system of FIG. Treatment conditions and effects are shown in Table 2.
[0033]
[Table 2]

[0034]
【The invention's effect】
In the soil purification method of the present invention, the wash water is discharged from the wall surface of the water injection trench, so that the water discharge surface is wide and the wash water can be made to flow uniformly over the contaminated area. The cleaning effect is improved by controlling the amount of water injected or pumped based on this and maintaining the water level of the cleaning water flowing through the contaminated area in the soil appropriately. Further, the cleaning effect can be further improved by adjusting the oxidizing agent concentration of the cleaning water to a predetermined range. Furthermore, the cleaning water can be reused by increasing the purification effect of the cleaning water by removing the contaminants contained in the cleaning water pumped up through the pumping trench in two stages.
[Brief description of the drawings]
1 is a schematic longitudinal sectional view showing a soil purification system according to the present invention. FIG. 2 is a schematic plan view of the soil purification system in FIG. 1. FIG. 3 is a schematic longitudinal sectional view of the soil purification system in FIG. 4] Schematic configuration diagram showing the contaminant removal means, oxidant addition means, and washing water circulation path of the soil purification system of the present invention. [FIG. 5] Schematic cross-sectional view of the treatment tank. [Explanation of symbols] 10- Impermeable wall, 11- Water injection trench, 12-pumping trench, 13-water permeable layer, 15-pumping pump, 16-poured water pipe, 17-poured water valve, 18-pumped water pipe, 20-hardly permeable layer, 31, 32-water level measurement hole, 33 -Water level control unit,

Claims

A water injection trench and a water pumping trench are provided in the soil, the cleaning water is discharged from the water injection trench into the soil, the cleaning water flows into the contaminated area between the water pouring trench and the pumping trench, and the cleaning water flowing through the contaminated area is pumped up. A soil purification method for cleaning a contaminated area by pumping up from a trench, characterized in that means for adding an oxidizing agent is provided in a water injection trench, and the cleaning water to which the oxidizing agent is added flows into the contaminated area.

A circulation path is provided to return the cleaning water pumped up from the pumping trench to the water injection trench, and after removing contaminants contained in the cleaning water pumped up from the pumping trench, the residual oxidizing agent concentration in the cleaning water is measured to determine the oxidizing agent. The soil remediation method according to claim 1, wherein washing water containing an oxidizing agent at a predetermined concentration is added to the contaminated area.

3. The method according to claim 1, wherein electrolysis means for washing water is provided instead of means for adding oxidant, or electrolysis means for washing water and residual chlorine concentration measurement instead of means for adding oxidant and means for measuring residual oxidant concentration. A soil remediation method in which cleaning water is supplied to a contaminated area by providing means and controlling the chlorine concentration within a predetermined range.

A water injection trench and a water pumping trench are provided in the soil, the cleaning water is discharged from the water injection trench into the soil, the cleaning water flows into the contaminated area between the water pouring trench and the pumping trench, and the cleaning water flowing through the contaminated area is pumped up. In the purification method that pumps up the trench and cleans the contaminated area, there are two stages to remove the pollutants contained in the pumped wash water, and the wash water whose salinity exceeds the standard value is applied to the ion exchange membrane or electrodialysis means. A soil remediation method characterized in that, while guiding and reducing the salinity, the washing water is brought into contact with the adsorbent to adsorb and remove heavy metals contained in the washing water.

Water injection trench and pumping trench provided opposite to each other in the soil, means for supplying cleaning water to the water injection trench, means for pumping cleaning water from the pumping trench, means for removing contaminants contained in the pumped cleaning water, and purification A soil purification system comprising: a circulation path for introducing cleaning water into the water injection trench; means for measuring a residual oxidant concentration contained in the cleaned cleaning water; and means for adding an oxidant to the cleaned cleaning water. .

6. The soil purification system according to claim 5, wherein instead of means for measuring residual oxidant concentration and means for adding oxidant, means for electrolyzing washing water and means for measuring residual chlorine concentration.

The purification system according to claim 5 or 6, comprising means for performing ion exchange or electrodialysis of washing water pumped up from a pumping trench and means for adsorbing heavy metals contained in the washing water as means for removing contaminants. system.