JP2004181314A

JP2004181314A - Method for decontaminating contaminated soil by microorganism

Info

Publication number: JP2004181314A
Application number: JP2002349557A
Authority: JP
Inventors: Yoji Ishikawa; 洋二石川; Hiroyuki Chino; 裕之千野; Mizuyo Yomoto; 瑞世四本
Original assignee: Obayashi Corp
Current assignee: Obayashi Corp
Priority date: 2002-12-02
Filing date: 2002-12-02
Publication date: 2004-07-02

Abstract

<P>PROBLEM TO BE SOLVED: To decompose a contaminated substance within contaminated soil by a microorganism in a short period of time. <P>SOLUTION: In the method for decontaminating the contaminated soil by the microorganism, the contaminated soil spread in a contaminated soil region 1 is first dug and the dug contaminated soil 2 is defined as the first contaminated soil. Next, the first contaminated substance, for example, oil, included in the contaminated soil 1 is subjected microorganism decomposition by decomposition bacteria 3 which are the microorganisms existing in the contaminated soil (step 101). Subsequently, the contaminated soil 1 progressed in the decomposition up to about desired degree is defined as treated soil 4 (step 102). Subsequently, the treated soil 4 is preserved while a nutrient salt and moisture are suitably added thereto under maintenance of an aerobic environment in order to maintain the decomposition activity and the amount of microbial cells of the decomposition bacteria 3 in the treated soil (step 103). Next, the treated soil 4 is added to the contaminated soil 12 as the second contaminated soil produced by digging the contaminated soil region 11 existing in a place different from the contaminated soil region 1. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、汚染土に含まれた汚染物質を微生物によって分解する微生物による汚染土の浄化方法に関する。
【０００２】
【従来の技術】
工場跡地の土壌内には、トリクロロエチレンなどの有機塩素系化合物や、重油やガソリンなどの石油系炭化水素が含まれていることがあり、このような土壌をそのまま放置すると、上述した有機塩素系化合物等の汚染物質が地下水等を介して環境に拡散するおそれがある。そのため、かかる汚染土壌に対しては所定の浄化処理を行わねばならない。
【０００３】
一方、微生物の活性を利用して環境中の汚染物質を分解無害化する技術、すなわちバイオレメディエーションの研究が進んできており、従来から原油による海洋汚染などの浄化に適用されてきたが、最近では汚染土壌へも適用されるようになってきた。
【０００４】
バイオレメディエーションとは、細菌やかびなどの微生物の分解能力を利用して汚染物質を分解し、無害化する方法であり、汚染物質が含まれた土壌などを微生物の活動に最適な水分・栄養・通気などの環境に調整して微生物の活性を向上させることにより、自然状態よりも効率よく汚染物質の分解を行うことができる。
【０００５】
バイオレメディエーションを用いて汚染土壌中の汚染物質を浄化するにあたっては、まず、汚染土壌を掘削して掘削汚染土を仮用地に移動し、次いで、仮用地にて掘削汚染土内の汚染物質を微生物で分解する。そして、汚染物質が分解処理された後は、処理済み土を元の位置に埋め戻すといった手順が一般的である。
【０００６】
【特許文献１】
特開２０００−２５４６３５号公報
【０００７】
【発明が解決しようとする課題】
しかしながら、掘削された汚染土に分解菌を添加して該汚染土内の汚染物質を分解するには、添加した分解菌の増殖を待たねばならないため、汚染物質の分解には時間がかかるという問題を生じていた。
【０００８】
かかる問題は、汚染土の土量が多かったり、仮用地の広さや土量の関係で処理工期をいくつかに分けなければならない場合、さらに深刻となる。
【０００９】
本発明は、上述した事情を考慮してなされたもので、汚染土内の汚染物質を短期間に微生物分解可能な微生物による汚染土の浄化方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
上記目的を達成するため、本発明に係る微生物による汚染土の浄化方法は請求項１に記載したように、第１の汚染土に含まれる第１の汚染物質を該第１の汚染土内の微生物で分解して処理済み土とし、次いで、前記微生物によって分解が可能な第２の汚染物質を含む第２の汚染土に前記処理済み土の少なくとも一部を添加するものである。
【００１１】
また、本発明に係る微生物による汚染土の浄化方法は、前記第２の汚染物質を前記第１の汚染物質と同一としたものである。
【００１２】
また、本発明に係る微生物による汚染土の浄化方法は請求項３に記載したように、所定の汚染物質が含まれた汚染土を所定の土量ずつに分けて複数の処理対象土とし、該複数の処理対象土のうち、任意に選択された処理対象土に含まれる前記汚染物質を該処理対象土内の微生物で分解して処理済み土とし、前記複数の処理対象土のうち、微生物分解処理が行われていない未処理土に前記処理済み土の少なくとも一部を添加することによって該未処理土に含まれる前記汚染物質を微生物分解して処理済み土とし、前記処理対象土がすべて処理済み土となるまで、前記処理済み土を前記未処理土に添加する工程を繰り返し行うものである。
【００１３】
また、本発明に係る微生物による汚染土の浄化方法は請求項４に記載したように、地盤内に拡がる汚染土壌領域を掘削するとともに掘削された汚染土を処理対象土とし、該処理対象土に含まれる汚染物質を該処理対象土内の微生物で分解して処理済み土とし、前記汚染土壌領域からあらたに汚染土として掘削された処理対象土に前記処理済み土の少なくとも一部を添加することによって該処理対象土に含まれる前記汚染物質を微生物分解して処理済み土とし、前記汚染土壌領域から掘削された処理対象土がすべて処理済み土となるまで、前記処理済み土を前記処理対象土に添加する工程を繰り返し行うものである。
【００１４】
請求項１の発明に係る微生物による汚染土の浄化方法においては、まず、第１の汚染土に含まれる第１の汚染物質を該第１の汚染土内の微生物で分解し、分解が所望の程度まで進行した第１の汚染土を処理済み土とする。
【００１５】
分解処理中は、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで微生物の活性や増殖の促進を図るのが望ましい。
【００１６】
対象となる第１の汚染物質としては、油をはじめ、好気性環境下で微生物分解可能なものを全て含むものとする。
【００１７】
第１の汚染土内の微生物は、土中菌として元々存在する場合をはじめ、別途添加する場合も含む。
【００１８】
すなわち、第１の汚染物質が自然界に存在する原油等であれば、第１の汚染土中に生息する頻度の高い微生物、例えばシュードモナス属の菌体をそのまま利用することができる。
【００１９】
一方、第１の汚染土内で元々生息している土中菌を分解菌として利用することができない場合、すなわち、第１の汚染物質を分解できる微生物の菌体数が第１の汚染土内にあまり存在しない場合には、他の環境で生息している微生物から対象となる第１の汚染物質を分解できる微生物をスクリーニングにより単離して育種し、これを第１の汚染土に添加するようにしてもよい。
【００２０】
次に、第２の汚染土に上述した処理済み土の少なくとも一部を添加する。第２の汚染土に処理済み土を添加する場合には、該処理済み土を第２の汚染土内に均一に分散させるべく、適宜攪拌混合を行うのが望ましい。
【００２１】
ここで、第２の汚染土に含まれる第２の汚染物質は、好気性環境下で微生物分解可能でかつ第１の汚染土に含まれる第１の汚染物質の分解に用いた微生物で分解できるのであれば、第１の汚染物質と異なってもかまわないが、これらの汚染物質が同一であれば、下記の作用効果を確実に期待できるため、本発明は、第２の汚染物質が第１の汚染物質と同一である場合により適した方法であると言える。
【００２２】
このように第１の汚染土内の微生物で該第１の汚染土に含まれる第１の汚染物質を微生物分解させると、微生物としての分解菌は、第１の汚染物質を分解していく過程において、他の土中菌よりも菌体数が増え、第１の汚染土内では優占種となる。
【００２３】
したがって、第１の汚染物質の分解が所望の程度まで進行した第１の汚染土を処理済み土とし、該処理済み土の少なくとも一部を第２の汚染物質を含む第２の汚染土に添加するようにすれば、該添加の段階において、処理済み土内の分解菌の活性が既に十分に高くなっており、あるいは多量の分解酵素が生成されているため、かかる処理済み土が添加された第２の汚染土内では、第２の汚染物質の微生物分解が添加直後から速やかに進行する。
【００２４】
そのため、第２の汚染土内の微生物を用いる場合に比べ、該微生物の増殖や分解活性の向上あるいは分解酵素の生成を待つ必要がない分だけ、より短時間で微生物分解を終了させることが可能となる。
【００２５】
なお、第２の汚染土内には微生物の分解対象となる第２の汚染物質が含まれているため、処理済み土が添加された第２の汚染土内において微生物が増殖し、あるいは分解活性が向上することは言うまでもない。
【００２６】
請求項３に係る発明においては、まず、所定の汚染物質が含まれた汚染土を所定の土量ずつに分け、これらを複数の処理対象土とする。
【００２７】
次に、これら複数の処理対象土のうち、任意に選択された処理対象土に含まれる汚染物質を該処理対象土内の微生物で分解し、分解が所望の程度まで進行した処理対象土を処理済み土とする。
【００２８】
分解処理中は、請求項１に係る発明と同様、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで微生物の活性や増殖の促進を図るのが望ましい。
【００２９】
対象となる汚染物質としては、上述した第１の汚染物質と同様であるので、ここでは説明を省略するとともに、処理済み土とするための微生物に関しても、土中菌として元々存在する場合をはじめ、別途添加する場合も含まれることは請求項１と同様であり、その説明については省略する。
【００３０】
次に、上述した複数の処理対象土のうち、微生物分解処理が行われていない未処理土に上述した処理済み土の少なくとも一部を添加する。かかる未処理土に処理済み土を添加する場合には、該処理済み土を未処理土内に均一に分散させるべく、適宜攪拌混合を行うのが望ましい。
【００３１】
次に、処理対象土がすべて処理済み土となるまで、上述した未処理土への処理済み土の添加工程を繰り返し行う。
【００３２】
このように最初に任意に選択された処理対象土に含まれる汚染物質を該処理対象土内の微生物で分解させると、微生物としての分解菌は、汚染物質を分解していく過程において、他の土中菌よりも菌体数が増え、処理対象土内では優占種となる。
【００３３】
したがって、汚染物質の分解が所望の程度まで進行した処理対象土を処理済み土とし、該処理済み土の少なくとも一部を未処理土に添加するようにすれば、該添加の段階において、処理済み土内の分解菌の活性が既に十分に高くなっており、あるいは多量の分解酵素が生成されているため、かかる処理済み土が添加された未処理土内では、汚染物質の微生物分解が添加直後から速やかに進行する。
【００３４】
そのため、未処理土内の微生物を用いる場合に比べ、該微生物の増殖や分解活性の向上あるいは分解酵素の生成を待つ必要がない分だけ、より短時間で微生物分解を終了させることが可能となる。
【００３５】
なお、未処理土内には微生物の分解対象となる汚染物質が含まれているため、処理済み土が添加された未処理土内において微生物が増殖し、あるいは分解活性が向上することは言うまでもない。
【００３６】
ここで、未処理土への処理済み土の添加工程において、複数の未処理土に対する処理済み土の添加の時期は任意であり、同時に添加してもよいし、時間をずらしながら添加するようにしてもよい。
【００３７】
前者の場合には、微生物分解の工期を全体として短縮することが可能となり、後者の場合には、攪拌、通気、栄養塩の添加、水分補給といった添加後の養生を順次行えばよいため、微生物分解に必要な養生設備を簡素化することが可能となる。
【００３８】
また、未処理土への処理済み土の添加工程を繰り返し行うにつれて、未処理土がひとつずつ減少し、処理済み土が一つずつ増加することになるが、かかる複数の処理済み土のうち、いずれを未処理土に添加するかは任意であり、微生物処理が終了した直後の処理済み土を使用するのが望ましいが、最初に微生物処理された処理済み土を継続して養生しておき、これを使用するようにしてもかまわない。
【００３９】
汚染土が発生する場所と微生物分解処理を行う場所については、特に限定されるものではなく、汚染土が掘削される汚染土壌領域に隣接して微生物分解処理を行うようにしてもよいし、汚染土壌領域から離れた場所まで汚染土を運搬し、しかる後、微生物分解処理を行うようにしてもよい。
【００４０】
請求項４に係る発明においては、まず、地盤内に拡がる汚染土壌領域を掘削するとともに掘削された汚染土を処理対象土とする。
【００４１】
次に、処理対象土に含まれる汚染物質を該処理対象土内の微生物で分解し、分解が所望の程度まで進行した処理対象土を処理済み土とする。
【００４２】
分解処理中は、請求項１に係る発明と同様、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで微生物の活性や増殖の促進を図るのが望ましい。
【００４３】
対象となる汚染物質としては、上述した第１の汚染物質と同様であるので、ここでは説明を省略するとともに、処理済み土とするための微生物に関しても、土中菌として元々存在する場合をはじめ、別途添加する場合も含まれることは請求項１と同様であり、その説明については省略する。
【００４４】
次に、汚染土壌領域からあらたに汚染土として掘削された処理対象土に、上述した処理済み土の少なくとも一部を添加する。かかる処理対象土に処理済み土を添加する場合には、該処理済み土を他の処理対象土内に均一に分散させるべく、適宜攪拌混合を行うのが望ましい。
【００４５】
このような処理済み土を処理対象土に添加する工程については、汚染土壌領域から掘削された処理対象土がすべて処理済み土となるまで繰り返し行う。
【００４６】
このようにすると、微生物としての分解菌は、汚染物質を分解していく過程において、他の土中菌よりも菌体数が増え、処理対象土内では優占種となる。
【００４７】
したがって、汚染物質の分解が所望の程度まで進行した処理対象土を処理済み土とし、該処理済み土の少なくとも一部を、汚染土壌領域からあらたに汚染土として掘削された処理対象土に添加するようにすれば、該添加の段階において、処理済み土内の分解菌の活性が既に十分に高くなっており、あるいは多量の分解酵素が生成されているため、かかる処理済み土が添加された処理対象土内では、汚染物質の微生物分解が添加直後から速やかに進行する。
【００４８】
そのため、処理対象土内の微生物を用いる場合に比べ、該微生物の増殖や分解活性の向上あるいは分解酵素の生成を待つ必要がない分だけ、より短時間で微生物分解を終了させることが可能となる。
【００４９】
なお、処理対象土内には微生物の分解対象となる汚染物質が含まれているため、処理済み土が添加された処理対象土内において微生物が増殖し、あるいは分解活性が向上することは言うまでもない。
【００５０】
【発明の実施の形態】
以下、本発明に係る微生物による汚染土の浄化方法の実施の形態について、添付図面を参照して説明する。なお、従来技術と実質的に同一の部品等については同一の符号を付してその説明を省略する。
【００５１】
（第１実施形態）
【００５２】
図１は、本実施形態に係る微生物による汚染土の浄化方法の手順を示したフローチャートである。同図に示すように、本実施形態に係る微生物による汚染土の浄化方法において、まず、図２（ａ）に示すように汚染土壌領域１に拡がる汚染土壌を掘削し、掘削された汚染土２を第１の汚染土とする（ステップ１０１）。
【００５３】
汚染土２は、同図に示すように汚染土壌領域１に隣接する地表に設けられた仮用地に仮置きすればよい。
【００５４】
次に、図２（ｂ）に示すように汚染土２に含まれる第１の汚染物質、例えば油を該汚染土２の土中菌である分解菌３で微生物分解し、次いで、分解が所望の程度まで進行した汚染土２を処理済み土４とする（ステップ１０２）。
【００５５】
分解処理中は、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで分解菌３の活性や増殖の促進を図るのが望ましい。
【００５６】
次に、処理済み土４内の分解菌３の分解活性や菌体量を維持すべく、好気性環境を保ちながら、栄養塩や水分を適宜添加しつつ、該処理済み土４を保存する（ステップ１０３）。なお、かかる工程は、次工程までの経過時間により、これを省略することができる。
【００５７】
次に、処理済み土４を、図３に示すように汚染土壌領域１とは異なる場所に存在する汚染土壌領域１１を掘削して生じた第２の汚染土としての汚染土１２に添加する（ステップ１０４）。
【００５８】
処理済み土４の添加量は、汚染土１２の重量に対し、例えば８重量％〜１０重量％程度とすることが考えられる。８重量％未満では、後述する作用を得ることが困難であり、１０重量％以上では、処理済み土４及び汚染土１２の総重量が大きくなり、攪拌その他の養生工程が大規模になるからである。
【００５９】
汚染土１２に処理済み土４を添加する場合には、該処理済み土を汚染土１２内に均一に分散させるべく、適宜攪拌混合を行うのが望ましい。なお、分解処理中はやはり、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで分解菌３の活性や菌体数の維持あるいは増加を図るのが望ましい。
【００６０】
汚染土１２内に含まれる第２の汚染物質は、分解菌３によって分解が可能な物質であればどのような物質でもよく、必ずしも第１の汚染物質と同一である必要はない。
【００６１】
このように汚染土２内の分解菌３によって該汚染土に含まれる第１の汚染物質を微生物分解させると、分解菌３は、第１の汚染物質を分解していく過程において、他の土中菌よりも菌体数が増え、汚染土２内では優占種となる。
【００６２】
したがって、第１の汚染物質の分解が所望の程度まで進行した汚染土２を処理済み土４とし、該処理済み土の一部を第２の汚染物質を含む汚染土１２に添加するようにすれば、該添加の段階において、処理済み土４内の分解菌の活性が既に十分に高くなっており、あるいは多量の分解酵素が生成されているため、かかる処理済み土４が添加された汚染土１２内では、第２の汚染物質の微生物分解が添加直後から速やかに進行する。
【００６３】
以上説明したように、本実施形態に係る微生物による汚染土の浄化方法によれば、第２の汚染物質を分解可能な分解菌３は、処理済み土４内において優占種となり、分解活性が十分に高く、あるいは多量の分解酵素が生成された状態となっているため、かかる処理済み土４を汚染土１２に添加すれば、第２の汚染物質の微生物分解が添加直後から速やかに進行する。
【００６４】
そのため、汚染土１２内の微生物を用いる場合に比べ、該微生物の増殖や分解活性の向上あるいは分解酵素の生成を待つ必要がない分だけ、より短時間で微生物分解を終了させることが可能となる。
【００６５】
なお、汚染土１２に含まれる第２の汚染物質は、好気性環境下で微生物分解可能でかつ汚染土２に含まれる第１の汚染物質の分解に用いた分解菌３で分解できるのであれば、第１の汚染物質と異なってもかまわないが、これらの汚染物質が同一であれば、上述した作用効果をより確実に期待することができる。言い換えれば、本実施形態に係る微生物による汚染土の浄化方法は、第２の汚染物質が第１の汚染物質と同一である場合により適した方法であると言える。
【００６６】
次に、本実施形態に係る微生物による汚染土の浄化方法の作用効果を室内試験で確認したので、実験概要及びその結果について以下に述べる。
【００６７】
まず、第１の汚染物質をＣ重油とするとともに該Ｃ重油で汚染された汚染土を第１の汚染土とし、これを油分解菌で分解処理したものを処理済み土として用意した。かかる処理済み土は、油分濃度が１，２００ｍｇ／ｋｇ・ｄｒｙ（ソクステック抽出装置で計測した値）であった。また、第２の汚染物質も第１の汚染物質と同様、Ｃ重油とするとともに該Ｃ重油で汚染された汚染土を第２の汚染土として用意した。かかる第２の汚染土は、油分濃度が３，９００ｍｇ／ｋｇ・ｄｒｙ（ソクステック抽出装置で計測した値）であった。なお、処理済み土及び第２の汚染土は、２ｍｍの篩にかけて土粒子の粒径を均一にした。
【００６８】
次に、栄養塩であるハイポネックス（商品名）を、油汚染土の炭素量（Ｔ―Ｃ）と窒素量（Ｔ―Ｎ）との比（Ｃ／Ｎ比）が約２０になるよう、１０ｇあたり０．１ｇの割合で汚染土に添加するとともに、十分な量の蒸留水を添加し、かかる状態で一ヶ月間、微生物分解を行った。
【００６９】
ここで、処理済み土の添加量については、５重量％、８重量％とした。また、分解処理中においては、１週間に一度の割合で第２の汚染土を十分に攪拌するとともに、減少した水分を補充し、エアコンプレッサーで通気を行った。
【００７０】
なお、油分解時には二酸化炭素が発生するため、これを検出する試薬として、水酸化ナトリウムも１週間に一度の割合で第２の汚染土に添加した。
【００７１】
計測方法としては、１週間に一度の割合で水酸化ナトリウムに吸収された炭酸ガスをＴＯＣ計で計測するとともに、一ヶ月に一度の割合でノルマルヘキサン抽出による油分含有量をソクステック装置で計測した。
【００７２】
処理済み土を添加した時点からの経過日数と炭酸ガス発生量との関係を示したものを表１及び図４に示す。
【００７３】
【表１】

【００７４】
これらの図表でわかるように、試験開始時（処理済み土の添加時）から１週間経過した時点では、処理済み土の添加の有無による炭酸ガス発生量に違いは見られなかったが、２週間後には、処理済み土を添加しない場合に比べ、８重量％の処理済み土を加えたものは、炭酸ガス発生量が約１０％多くなり、処理済み土の添加によって油分解速度の上昇傾向が確認された。
【００７５】
処理済み土を添加してから一ヶ月経過した時点での油分含有量を図５に示す。
【００７６】
同図でわかるように、試験開始一ヶ月後、処理済み土を添加しない場合には、油分含有量が３，９００ｍｇ／ｋｇ・ｄｒｙと分解処理が全く進行していないのに対し、８重量％の処理済み土を加えたものは、油分含有量が３，２００ｍｇ／ｋｇ・ｄｒｙに減少していることがわかる。これは、比率にして約８０％低減したことに相当し、処理済み土の添加によって初期段階における油分解速度が促進されていることが確認された。
【００７７】
すなわち、上述した炭酸ガスの発生量の結果と併せ考えれば、処理済み土を８重量％添加すれば、微生物分解処理の速度を約２０％促進することが可能であり、例えば処理済み土を添加しない場合に９０日間の処理日数が必要な場合であれば、該処理日数を７２日に短縮することが可能となる。
【００７８】
（第２実施形態）
【００７９】
次に、第２実施形態について説明する。なお、第１実施形態と実質的に同一の部品等については同一の符号を付してその説明を省略する。
【００８０】
図６は、本実施形態に係る微生物による汚染土の浄化方法の手順を示したフローチャートである。同図に示すように、本実施形態に係る微生物による汚染土の浄化方法において、まず、図７（ａ）に示すように汚染土壌領域２１に拡がる汚染土壌を掘削し、掘削された汚染土を所定の土量ずつ、例えば５つに分け、これらを複数の処理対象土２２ａ〜２２ｅとする（ステップ１１１）。
【００８１】
処理対象土２２ａ〜２２ｅは、同図に示すように汚染土壌領域２１近傍の地表に設けられた仮用地に畝状に仮置きすればよい。
【００８２】
次に、これら複数の処理対象土２２ａ〜２２ｅのうち、図７（ｂ）に示すように任意に選択された処理対象土としての処理対象土２２ａに含まれる汚染物質、例えば油を該処理対象土に存在する分解菌３で微生物分解し、次いで、分解が所望の程度まで進行した処理対象土２２ａを処理済み土２４ａとする（ステップ１１２）。
【００８３】
分解処理中は、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで分解菌３の活性や増殖の促進を図るのが望ましい。
【００８４】
次に、処理済み土２４ａを、図８（ａ）に示すように微生物分解処理が行われていない未処理土としての処理対象土２２ｂに添加する（ステップ１１４）。
【００８５】
処理済み土２４ａの添加量は、第１実施形態と同様、処理対象土２２ｂの重量に対し、例えば８重量％〜１０重量％程度とすることが考えられる。
【００８６】
処理対象土２２ｂに処理済み土２４ａを添加する場合には、該処理済み土を処理対象土２２ｂ内に均一に分散させるべく、適宜攪拌混合を行うのが望ましい。なお、分解処理中はやはり、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで分解菌３の活性や菌体数の維持あるいは増加を図るのが望ましい。
【００８７】
このように最初に任意に選択された処理対象土２２ａ内の分解菌３を用いて該処理対象土に含まれる汚染物質を微生物分解させると、分解菌３は、汚染物質を分解していく過程において、他の土中菌よりも菌体数が増え、処理対象土２２ａ内では優占種となる。
【００８８】
したがって、汚染物質の分解が所望の程度まで進行した処理対象土２２ａを処理済み土２４ａとし、該処理済み土の一部を処理対象土２２ｂに添加するようにすれば、該添加の段階において、処理済み土２４ａ内の分解菌の活性が既に十分に高くなっており、あるいは多量の分解酵素が生成されているため、かかる処理済み土２４ａが添加された処理対象土２２ｂ内では、汚染物質の微生物分解が添加直後から速やかに進行し、短期間に処理済み土２４ｂとなる。
【００８９】
次に、処理済み土２４ｂを処理対象土２２ｃに添加し（ステップ１１５）、該処理対象土２２ｃを処理済み土２４ｃとする。以下、処理対象土２２ａ〜２２ｅがすべて処理済み土２４ａ〜２４ｅとなるまで、上述した処理済み土を未処理土に添加する工程を繰り返し行う（ステップ１１６、１１７）。
【００９０】
次に、処理済み土２４ａ〜２４ｅを図８（ｂ）に示すように掘削領域２５に埋め戻す（ステップ１１８）。
【００９１】
以上説明したように、本実施形態に係る微生物による汚染土の浄化方法によれば、汚染物質を分解可能な分解菌３は処理済み土２４ａ〜２４ｄ内において優占種となり、分解活性が十分に高く、あるいは多量の分解酵素が生成された状態となっているため、かかる処理済み土４を処理対象土２２ｂ〜２２ｅに添加すれば、汚染物質の微生物分解が添加直後から速やかに進行する。
【００９２】
そのため、処理対象土２２ａ〜２２ｅ内の微生物を用いる場合に比べ、該微生物の増殖や分解活性の向上あるいは分解酵素の生成を待つ必要がない分だけ、より短時間で微生物分解を終了させることが可能となる。
【００９３】
本実施形態では、地盤内に拡がる汚染土壌領域２１を掘削し、次いで、掘削された汚染土を所定の土量ずつに分け、これらを複数の処理対象土２２ａ〜２２ｅとして汚染土壌領域２１に隣接する地表に設けられた仮用地に畝状に仮置きするようにしたが、汚染土壌領域２１と微生物分解処理を行う場所とが離れていてもかまわない。
【００９４】
例えば、微生物分解処理を行うプラントを所定の地域に設置しておき、汚染土壌領域から掘削された汚染土を運搬して該プラントに搬入し、次いで、該汚染土を複数の処理対象土に分割して上述した微生物分割処理を行うようにしてもよい。
【００９５】
また、本実施形態では、処理対象土２２ａ内の汚染物質が微生物分解されてなる処理済み土２４ａの一部を処理対象土２２ｂに添加し、次いで、該処理済み土の一部を処理対象土２２ｃに添加する、すなわち、微生物分解処理するごとに生じる処理済み土を、次の処理対象土に順次添加するようにしたが、これに代えて、処理対象土２２ａ内の汚染物質が微生物分解されてなる処理済み土２４ａの一部を処理対象土２２ｂ〜２２ｅにそれぞれ添加するようにしてもかまわない。
【００９６】
（第３実施形態）
【００９７】
次に、第３実施形態について説明する。なお、上述した各実施形態と実質的に同一の部品等については同一の符号を付してその説明を省略する。
【００９８】
図９は、本実施形態に係る微生物による汚染土の浄化方法の手順を示したフローチャートである。同図に示すように、本実施形態に係る微生物による汚染土の浄化方法において、まず、図１０（ａ）に示すように、地盤内に拡がる汚染土壌領域３１を掘削するとともに、掘削された汚染土を処理対象土３２ａとする（ステップ１２１）。
【００９９】
処理対象土３２ａは、順次行われる掘削作業の支障とならぬ程度に汚染土壌領域３１から離隔した位置にて畝状に仮置きすればよい。
【０１００】
次に、処理対象土３２ａに含まれる汚染物質、例えば油を該処理対象土に存在する微生物である分解菌３で微生物分解し、次いで、分解が所望の程度まで進行した処理対象土３２ａを処理済み土３４ａとする（ステップ１２２）。
【０１０１】
分解処理中は、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで分解菌３の活性や増殖の促進を図るのが望ましい。
【０１０２】
次に、図１０（ｂ）に示すように、汚染土壌領域３１からあらたに汚染土として掘削された処理対象土３２ｂに、上述した処理済み土３４ａの少なくとも一部を添加する（ステップ１２４）。
【０１０３】
処理済み土３４ａの添加量は、第１実施形態と同様、処理対象土３２ｂの重量に対し、例えば８重量％〜１０重量％程度とすることが考えられる。
【０１０４】
処理対象土３２ｂに処理済み土３４ａを添加する場合には、該処理済み土を処理対象土３２ｂ内に均一に分散させるべく、適宜攪拌混合を行うのが望ましい。なお、分解処理中はやはり、必要に応じて通気を行うとともに、栄養塩や水分を適宜添加することで分解菌３の活性や菌体数の維持あるいは増加を図るのが望ましい。
【０１０５】
このようにすると、分解菌３は、汚染物質を分解していく過程において、他の土中菌よりも菌体数が増え、処理対象土２２ａ内では優占種となる。
【０１０６】
したがって、汚染物質の分解が所望の程度まで進行した処理対象土３２ａを処理済み土３４ａとし、該処理済み土の一部を処理対象土３２ｂに添加するようにすれば、該添加の段階において、処理済み土３４ａ内の分解菌の活性が既に十分に高くなっており、あるいは多量の分解酵素が生成されているため、かかる処理済み土３４ａが添加された処理対象土３２ｂ内では、汚染物質の微生物分解が添加直後から速やかに進行し、短期間に処理済み土３４ｂとなる。
【０１０７】
次に、図１０（ｃ）に示すように、汚染土壌領域３１からあらたに汚染土として掘削された処理対象土３２ｃに、上述した処理済み土３４ｂの少なくとも一部を添加する（ステップ１２５）。
【０１０８】
以下、このような処理済み土を処理対象土に添加する工程については、汚染土壌領域３１から掘削された処理対象土がすべて処理済み土となるまで繰り返し行う。
【０１０９】
以上説明したように、本実施形態に係る微生物による汚染土の浄化方法によれば、汚染物質を分解可能な分解菌３は処理済み土３４ａ、３４ｂ・・・内において優占種となり、分解活性が十分に高く、あるいは多量の分解酵素が生成された状態となっているため、かかる処理済み土３４ａ、３４ｂ・・・を処理対象土３２ｂ、３２ｃ・・・に添加すれば、汚染物質の微生物分解が添加直後から速やかに進行する。
【０１１０】
そのため、処理対象土３２ａ、３２ｂ、３２ｃ・・・内の微生物を用いる場合に比べ、該微生物の増殖や分解活性の向上あるいは分解酵素の生成を待つ必要がない分だけ、より短時間で微生物分解を終了させることが可能となる。
【０１１１】
【発明の効果】
以上述べたように、本発明に係る微生物による汚染土の浄化方法によれば、汚染物質を分解可能な微生物は処理済み土内において優占種となり、分解活性が十分に高く、あるいは多量の分解酵素が生成された状態となっているため、かかる処理済み土を第２の汚染土や処理対象土に添加すれば、汚染物質の微生物分解が添加直後から速やかに進行する。
【０１１２】
そのため、微生物を第２の汚染土や処理対象土に直接添加する場合に比べ、微生物の増殖や分解活性の向上あるいは分解酵素の生成を待つ必要がない分だけ、より短時間で微生物分解を終了させることが可能となる。
【０１１３】
【図面の簡単な説明】
【図１】第１実施形態に係る微生物による汚染土の浄化方法の手順を示したフローチャート。
【図２】第１実施形態に係る微生物による汚染土の浄化方法を用いて汚染土を処理する様子を示した作業図。
【図３】引き続き第１実施形態に係る微生物による汚染土の浄化方法を用いて汚染土を処理する様子を示した作業図。
【図４】第１実施形態に係る微生物による汚染土の浄化方法の作用を室内試験によって確認した結果を示したグラフ。
【図５】同じく第１実施形態に係る微生物による汚染土の浄化方法の作用を室内試験によって確認した結果を示したグラフ。
【図６】第２実施形態に係る微生物による汚染土の浄化方法の手順を示したフローチャート。
【図７】第２実施形態に係る微生物による汚染土の浄化方法を用いて汚染土を処理する様子を示した作業図。
【図８】引き続き第２実施形態に係る微生物による汚染土の浄化方法を用いて汚染土を処理する様子を示した作業図。
【図９】第３実施形態に係る微生物による汚染土の浄化方法の手順を示したフローチャート。
【図１０】第３実施形態に係る微生物による汚染土の浄化方法を用いて汚染土を処理する様子を示した作業図。
【符号の説明】
２第１の汚染土
３分解菌（微生物）
４処理済み土
１２第２の汚染土
２２ａ〜２２ｅ処理対象土
２４ａ〜２４ｅ処理済み土
３２ａ〜３２ｃ処理対象土
３４ａ〜３４ｃ処理済み土[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for purifying contaminated soil with microorganisms that decomposes pollutants contained in the contaminated soil with microorganisms.
[0002]
[Prior art]
Organochlorine compounds such as trichloroethylene and petroleum hydrocarbons such as heavy oil and gasoline may be contained in the soil of the former factory site. And other contaminants may diffuse into the environment through groundwater and the like. Therefore, a predetermined purification treatment must be performed on such contaminated soil.
[0003]
On the other hand, research on bioremediation, a technique for decomposing and detoxifying pollutants in the environment using the activity of microorganisms, has been progressing, and it has been applied to the purification of marine pollution by crude oil. It has also been applied to contaminated soils.
[0004]
Bioremediation is a method of decomposing and detoxifying contaminants by utilizing the decomposing ability of microorganisms such as bacteria and fungi. By adjusting the environment such as ventilation to improve the activity of microorganisms, it is possible to decompose pollutants more efficiently than in the natural state.
[0005]
When purifying contaminants in contaminated soil using bioremediation, first, the contaminated soil is excavated, the excavated contaminated soil is moved to a temporary site, and then the contaminants in the excavated contaminated soil are removed from the temporary site using microorganisms. Decompose with. After the contaminants are decomposed, a general procedure is to bury the treated soil in its original position.
[0006]
[Patent Document 1]
JP 2000-254635 A
[0007]
[Problems to be solved by the invention]
However, in order to add decomposing bacteria to the excavated contaminated soil to decompose pollutants in the contaminated soil, it is necessary to wait for the growth of the added decomposing bacteria, so that it takes time to decompose the pollutants. Was occurring.
[0008]
Such a problem becomes more serious when the amount of contaminated soil is large or when the treatment period has to be divided into several depending on the size of the temporary site and the amount of soil.
[0009]
The present invention has been made in consideration of the above-described circumstances, and has as its object to provide a method for purifying contaminated soil using microorganisms capable of biodegrading contaminants in contaminated soil in a short period of time.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the method for purifying contaminated soil by microorganisms according to the present invention includes, as described in claim 1, the first contaminant contained in the first contaminated soil contained in the first contaminated soil. A microorganism is decomposed into treated soil, and then at least a part of the treated soil is added to a second contaminated soil containing a second contaminant degradable by the microorganism.
[0011]
In the method for purifying contaminated soil by microorganisms according to the present invention, the second contaminant is the same as the first contaminant.
[0012]
Further, in the method for purifying contaminated soil by microorganisms according to the present invention, as described in claim 3, the contaminated soil containing a predetermined contaminant is divided into a predetermined amount of soil to obtain a plurality of soils to be treated. Among the plurality of soils to be treated, the contaminants contained in the arbitrarily selected soil to be treated are decomposed by microorganisms in the soil to be treated to a treated soil, and the biodegradation among the soils to be treated is By adding at least a portion of the treated soil to untreated soil that has not been treated, the contaminants contained in the untreated soil are microbially decomposed into treated soil, and all of the treated soil is treated. The step of adding the treated soil to the untreated soil is repeatedly performed until the soil becomes finished soil.
[0013]
In addition, the method for purifying contaminated soil by microorganisms according to the present invention excavates a contaminated soil area extending in the ground and treats the excavated contaminated soil as a soil to be treated, as described in claim 4. Degrading the contained contaminants with microorganisms in the soil to be treated into treated soil, and adding at least a part of the treated soil to the treated soil newly excavated as contaminated soil from the contaminated soil region. The microorganisms decompose the contaminants contained in the soil to be treated into treated soil, and treat the treated soil until all of the treated soil excavated from the contaminated soil region becomes treated soil. Is repeatedly performed.
[0014]
In the method for purifying contaminated soil by microorganisms according to the first aspect of the present invention, first, the first contaminant contained in the first contaminated soil is decomposed by the microorganisms in the first contaminated soil, and the decomposition is desired. The first contaminated soil that has progressed to the extent is treated soil.
[0015]
During the decomposition treatment, it is desirable to perform aeration as needed and to promote the activity and growth of microorganisms by appropriately adding nutrients and water.
[0016]
The first contaminants to be used include all substances that can be degraded by microorganisms in an aerobic environment, such as oil.
[0017]
The microorganisms in the first contaminated soil include those originally added as soil bacteria and those added separately.
[0018]
That is, if the first contaminant is crude oil or the like existing in the natural world, a microorganism that frequently inhabits the first contaminated soil, for example, a bacterium of the genus Pseudomonas can be used as it is.
[0019]
On the other hand, when soil bacteria originally inhabiting in the first contaminated soil cannot be used as decomposing bacteria, that is, the number of microorganisms capable of decomposing the first contaminant is increased in the first contaminated soil. In the case where the microorganisms do not exist in a large amount, microorganisms capable of decomposing the first contaminant of interest from microorganisms living in other environments are isolated and bred by screening, and added to the first contaminated soil. It may be.
[0020]
Next, at least a part of the treated soil described above is added to the second contaminated soil. When the treated soil is added to the second contaminated soil, it is desirable to appropriately mix and stir the treated soil so as to uniformly disperse the treated soil in the second contaminated soil.
[0021]
Here, the second contaminant contained in the second contaminated soil is microbial decomposable in an aerobic environment and can be decomposed by the microorganism used for decomposing the first contaminant contained in the first contaminated soil. In this case, the first contaminant may be different from the first contaminant. However, if these contaminants are the same, the following effects can be reliably obtained. This is a more suitable method when the contaminants are the same.
[0022]
As described above, when microorganisms in the first contaminated soil cause the first contaminant contained in the first contaminated soil to undergo microbial degradation, the decomposing bacteria as microorganisms degrade the first contaminant. In the above, the number of cells increases more than other soil bacteria, and it becomes a dominant species in the first contaminated soil.
[0023]
Therefore, the first contaminated soil in which the decomposition of the first contaminant has progressed to a desired degree is treated soil, and at least a part of the treated soil is added to the second contaminated soil containing the second contaminant. In this case, the activity of the decomposing bacteria in the treated soil has already been sufficiently increased, or a large amount of the degrading enzyme has been generated, so that the treated soil was added. In the second contaminated soil, the microbial decomposition of the second contaminant proceeds promptly immediately after the addition.
[0024]
Therefore, as compared with the case of using microorganisms in the second contaminated soil, it is possible to terminate the microbial decomposition in a shorter time because there is no need to wait for the growth of the microorganisms, improvement of the decomposition activity or generation of the degrading enzyme. It becomes.
[0025]
Since the second contaminated soil contains the second contaminant to be decomposed by microorganisms, the microorganisms proliferate in the second contaminated soil to which the treated soil is added, or the degrading activity is increased. Needless to say, this is improved.
[0026]
In the invention according to claim 3, first, contaminated soil containing a predetermined pollutant is divided into predetermined soil amounts, and these are set as a plurality of soils to be treated.
[0027]
Next, of the plurality of soils to be treated, the contaminants contained in the arbitrarily selected soil to be treated are decomposed by microorganisms in the soil to be treated, and the soil to be treated which has been decomposed to a desired degree is treated. Soiled soil.
[0028]
During the decomposition treatment, similarly to the first aspect of the present invention, it is desirable that aeration is performed as necessary and that the activity and growth of microorganisms are promoted by appropriately adding nutrients and water.
[0029]
The contaminants to be treated are the same as the above-mentioned first contaminants, and thus the description thereof is omitted here. Regarding the microorganisms used as the treated soil, there are cases where the microorganisms originally exist as soil bacteria. It is the same as in claim 1 that the case where it is separately added is included, and the description thereof is omitted.
[0030]
Next, at least a part of the treated soil described above is added to the untreated soil that has not been subjected to the microbial decomposition treatment among the plurality of treatment target soils described above. When the treated soil is added to the untreated soil, it is desirable to perform appropriate stirring and mixing in order to uniformly disperse the treated soil in the untreated soil.
[0031]
Next, the above-described process of adding the treated soil to the untreated soil is repeatedly performed until all the soil to be treated becomes the treated soil.
[0032]
When the contaminants contained in the soil to be treated arbitrarily selected first are decomposed by the microorganisms in the soil to be treated, the decomposing bacteria as microorganisms cause other substances in the process of decomposing the contaminants. The number of cells increases more than soil bacteria, and it becomes a dominant species in the soil to be treated.
[0033]
Therefore, if the soil to be treated in which the decomposition of the contaminants has progressed to a desired degree is treated soil, and at least a part of the treated soil is added to the untreated soil, at the stage of the addition, Since the activity of degrading bacteria in the soil is already sufficiently high or a large amount of degrading enzyme has been generated, in untreated soil to which such treated soil has been added, microbial degradation of pollutants immediately after addition Proceed quickly from.
[0034]
Therefore, compared to the case of using microorganisms in untreated soil, it is possible to terminate microbial degradation in a shorter time, because there is no need to wait for the growth of the microorganisms, improvement of the degradation activity or generation of the degrading enzyme. .
[0035]
In addition, since the untreated soil contains pollutants to be decomposed by microorganisms, it is needless to say that the microorganisms grow in the untreated soil to which the treated soil is added, or the decomposition activity is improved. .
[0036]
Here, in the process of adding the treated soil to the untreated soil, the timing of addition of the treated soil to a plurality of untreated soils is arbitrary, and they may be added at the same time, or may be added at staggered times. You may.
[0037]
In the former case, it is possible to shorten the period of the microbial decomposition as a whole, and in the latter case, the curing after addition such as stirring, aeration, addition of nutrients, and water replenishment can be performed sequentially, so that the microorganism It is possible to simplify the curing equipment required for decomposition.
[0038]
In addition, as the process of adding the treated soil to the untreated soil is repeated, the untreated soil decreases one by one, and the treated soil increases one by one. Which one to add to the untreated soil is optional, it is desirable to use the treated soil immediately after the microbial treatment is completed, but the treated soil that has been first microbial treated is continuously cured, This may be used.
[0039]
The place where the contaminated soil is generated and the place where the microbial decomposition treatment is performed are not particularly limited, and the microbial decomposition treatment may be performed adjacent to the contaminated soil area where the contaminated soil is excavated. The contaminated soil may be transported to a location distant from the soil area, and then subjected to a microbial decomposition treatment.
[0040]
In the invention according to claim 4, first, a contaminated soil region extending in the ground is excavated, and the excavated contaminated soil is set as a processing target soil.
[0041]
Next, contaminants contained in the soil to be treated are decomposed by microorganisms in the soil to be treated, and the soil to be treated that has been decomposed to a desired degree is treated soil.
[0042]
During the decomposition treatment, similarly to the first aspect of the present invention, it is desirable that aeration is performed as necessary and that the activity and growth of microorganisms are promoted by appropriately adding nutrients and water.
[0043]
The contaminants to be treated are the same as the above-mentioned first contaminants, and thus the description thereof is omitted here. Regarding the microorganisms used as the treated soil, there are cases where the microorganisms originally exist as soil bacteria. It is the same as in claim 1 that the case where it is separately added is included, and the description thereof is omitted.
[0044]
Next, at least a part of the treated soil described above is added to the soil to be treated newly excavated as the contaminated soil from the contaminated soil region. When the treated soil is added to the soil to be treated, it is desirable to appropriately mix and mix the treated soil to uniformly disperse the treated soil in the other soil to be treated.
[0045]
The process of adding the treated soil to the soil to be treated is repeatedly performed until all the soil to be treated excavated from the contaminated soil region becomes the treated soil.
[0046]
In this way, in the process of decomposing contaminants, the number of decomposing bacteria as microorganisms increases compared to other soil bacteria, and becomes a dominant species in the soil to be treated.
[0047]
Therefore, the soil to be treated in which the decomposition of the contaminants has progressed to a desired degree is regarded as treated soil, and at least a part of the treated soil is added to the treated soil newly excavated as contaminated soil from the contaminated soil region. By doing so, the activity of the decomposing bacteria in the treated soil is already sufficiently high or a large amount of degrading enzyme is generated at the stage of the addition. In the target soil, the microbial decomposition of the pollutant proceeds promptly immediately after the addition.
[0048]
Therefore, as compared with the case of using microorganisms in the soil to be treated, there is no need to wait for the growth of the microorganisms, the improvement of the decomposition activity, or the generation of the degrading enzyme, so that the microbial decomposition can be completed in a shorter time. .
[0049]
Since the soil to be treated contains a pollutant to be decomposed by microorganisms, it goes without saying that the microorganisms proliferate in the soil to be treated to which the treated soil is added, or the decomposition activity is improved. .
[0050]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for purifying contaminated soil by microorganisms according to the present invention will be described with reference to the accompanying drawings. In addition, the same reference numerals are given to components and the like that are substantially the same as those in the related art, and description thereof is omitted.
[0051]
(1st Embodiment)
[0052]
FIG. 1 is a flowchart showing a procedure of a method for purifying contaminated soil by microorganisms according to the present embodiment. As shown in the figure, in the method of purifying contaminated soil by microorganisms according to the present embodiment, first, as shown in FIG. Is the first contaminated soil (step 101).
[0053]
The contaminated soil 2 may be temporarily placed on a temporary site provided on the ground surface adjacent to the contaminated soil area 1 as shown in FIG.
[0054]
Next, as shown in FIG. 2B, a first contaminant, for example, oil contained in the contaminated soil 2 is microbial-degraded by a decomposing bacterium 3 which is a soil bacterium of the contaminated soil 2, and then the decomposition is desired. The contaminated soil 2 that has progressed to the extent described above is treated soil 4 (step 102).
[0055]
During the decomposition treatment, it is desirable to promote ventilation and activity of the decomposing bacterium 3 by appropriately adding nutrients and water while performing ventilation as needed.
[0056]
Next, in order to maintain the decomposition activity of the decomposing bacteria 3 and the amount of cells in the treated soil 4, the treated soil 4 is preserved while appropriately adding nutrients and water while maintaining an aerobic environment ( Step 103). This step can be omitted depending on the elapsed time until the next step.
[0057]
Next, the treated soil 4 is added to the contaminated soil 12 as a second contaminated soil generated by excavating the contaminated soil area 11 existing in a different place from the contaminated soil area 1 as shown in FIG. 3 ( Step 104).
[0058]
It is conceivable that the added amount of the treated soil 4 is, for example, about 8% by weight to 10% by weight based on the weight of the contaminated soil 12. If the amount is less than 8% by weight, it is difficult to obtain the effects described below. If the amount is more than 10% by weight, the total weight of the treated soil 4 and the contaminated soil 12 increases, and the stirring and other curing processes become large. is there.
[0059]
When the treated soil 4 is added to the contaminated soil 12, it is desirable to perform appropriate stirring and mixing in order to uniformly disperse the treated soil 4 in the contaminated soil 12. During the decomposition treatment, it is desirable to maintain the aeration or the number of cells of the decomposing bacteria 3 by appropriately adding nutrients and water while performing ventilation as needed.
[0060]
The second contaminant contained in the contaminated soil 12 may be any substance as long as it can be decomposed by the decomposing bacteria 3, and need not necessarily be the same as the first contaminant.
[0061]
As described above, when the first contaminant contained in the contaminated soil is microbially decomposed by the decomposing bacteria 3 in the contaminated soil 2, the decomposing bacteria 3 may cause other soil in the process of decomposing the first contaminant. The number of cells increases compared to the medium bacteria, and it becomes a dominant species in the contaminated soil 2.
[0062]
Therefore, the contaminated soil 2 in which the decomposition of the first contaminant has progressed to a desired degree is regarded as a treated soil 4, and a part of the treated soil is added to the contaminated soil 12 containing the second contaminant. For example, at the stage of the addition, the activity of the decomposing bacteria in the treated soil 4 is already sufficiently high, or a large amount of the degrading enzyme has been generated. Within 12, the microbial degradation of the second contaminant proceeds rapidly immediately after addition.
[0063]
As described above, according to the method for purifying contaminated soil by microorganisms according to the present embodiment, the decomposing bacteria 3 capable of decomposing the second contaminant become the dominant species in the treated soil 4 and have a decomposing activity. Since the treated soil 4 is added to the contaminated soil 12 because the decomposition enzyme is generated in a sufficiently high or large amount, the microbial decomposition of the second contaminant proceeds promptly immediately after the addition. .
[0064]
Therefore, compared with the case of using the microorganisms in the contaminated soil 12, it is possible to finish the microbial decomposition in a shorter time because there is no need to wait for the growth of the microorganisms, the improvement of the decomposition activity, or the generation of the degrading enzyme. .
[0065]
The second contaminant contained in the contaminated soil 12 can be decomposed by microorganisms in an aerobic environment and can be decomposed by the decomposing bacteria 3 used for decomposing the first contaminant contained in the contaminated soil 2. The first contaminant may be different, but if these contaminants are the same, the above-described effects can be more reliably expected. In other words, the method for purifying contaminated soil by microorganisms according to the present embodiment can be said to be a more suitable method when the second contaminant is the same as the first contaminant.
[0066]
Next, the effects of the method for purifying contaminated soil by microorganisms according to the present embodiment were confirmed by a laboratory test, and the outline of the experiment and the results will be described below.
[0067]
First, the first contaminant was C heavy oil, and the contaminated soil contaminated with the C heavy oil was first contaminated soil, which was decomposed with oil-decomposing bacteria to prepare a treated soil. This treated soil had an oil concentration of 1,200 mg / kg · dry (a value measured by a Soxtec extractor). Similarly to the first pollutant, the second pollutant was C heavy oil, and the contaminated soil contaminated with the C heavy oil was prepared as the second contaminated soil. The second contaminated soil had an oil concentration of 3,900 mg / kg · dry (a value measured by a Soxtec extraction device). The treated soil and the second contaminated soil were sieved through a 2 mm sieve to make the particle size of the soil particles uniform.
[0068]
Next, 10 g of Hyponex (trade name), which is a nutrient salt, was added so that the ratio (C / N ratio) between the amount of carbon (TC) and the amount of nitrogen (TN) of the oil-contaminated soil was about 20. 0.1 g of the solution was added to the contaminated soil at the same time, and a sufficient amount of distilled water was added.
[0069]
Here, the added amount of the treated soil was 5% by weight and 8% by weight. In addition, during the decomposition treatment, the second contaminated soil was sufficiently stirred once a week, the reduced water was replenished, and ventilation was performed with an air compressor.
[0070]
Since carbon dioxide is generated during oil cracking, sodium hydroxide was also added to the second contaminated soil once a week as a reagent for detecting carbon dioxide.
[0071]
As a measuring method, the carbon dioxide gas absorbed in the sodium hydroxide was measured once a week with a TOC meter, and the oil content by normal hexane extraction was measured once a month with a Soxtec device.
[0072]
Table 1 and FIG. 4 show the relationship between the number of days elapsed since the addition of the treated soil and the amount of generated carbon dioxide.
[0073]
[Table 1]

[0074]
As can be seen from these charts, at one week after the start of the test (at the time of addition of the treated soil), there was no difference in the amount of carbon dioxide generated by the presence or absence of the treated soil, but two weeks. Later, compared with the case where the treated soil was not added, when the treated soil of 8 wt% was added, the amount of carbon dioxide gas generated increased by about 10%, and the oil decomposition rate tended to increase due to the addition of the treated soil. confirmed.
[0075]
FIG. 5 shows the oil content one month after the addition of the treated soil.
[0076]
As can be seen from the figure, one month after the start of the test, when the treated soil was not added, the oil content was 3,900 mg / kg · dry and the decomposition treatment had not progressed at all, whereas the oil content was 8% by weight. It can be seen that the oil content of the soil to which the treated soil was added was reduced to 3,200 mg / kg · dry. This corresponds to a reduction of about 80% in proportion, and it was confirmed that the addition of the treated soil accelerated the oil decomposition rate in the initial stage.
[0077]
That is, considering the above-mentioned results of the amount of generated carbon dioxide gas, adding 8% by weight of the treated soil can accelerate the speed of the microbial decomposition treatment by about 20%. Otherwise, if 90 days are required, the number of processing days can be reduced to 72 days.
[0078]
(2nd Embodiment)
[0079]
Next, a second embodiment will be described. In addition, the same reference numerals are given to components and the like that are substantially the same as those in the first embodiment, and description thereof is omitted.
[0080]
FIG. 6 is a flowchart showing the procedure of the method for purifying contaminated soil by microorganisms according to the present embodiment. As shown in the figure, in the method for purifying contaminated soil by microorganisms according to the present embodiment, first, as shown in FIG. 7A, contaminated soil spreading to the contaminated soil region 21 is excavated, and the excavated contaminated soil is removed. A predetermined soil amount is divided into, for example, five, and these are set as a plurality of processing target soils 22a to 22e (step 111).
[0081]
The processing target soils 22a to 22e may be temporarily placed in a ridge shape on a temporary site provided on the ground surface near the contaminated soil region 21 as shown in FIG.
[0082]
Next, as shown in FIG. 7B, of the plurality of soils to be treated 22a to 22e, contaminants, for example, oil contained in the soil to be treated 22a, which is arbitrarily selected as the soil to be treated, are removed. Microbial degradation is performed by the degrading bacteria 3 present in the soil, and then the soil 22a to be treated, which has been decomposed to a desired degree, is treated as a treated soil 24a (step 112).
[0083]
During the decomposition treatment, it is desirable to promote ventilation and activity of the decomposing bacterium 3 by appropriately adding nutrients and water while performing ventilation as needed.
[0084]
Next, as shown in FIG. 8A, the treated soil 24a is added to the untreated soil 22b, which has not been subjected to the microbial decomposition treatment (step 114).
[0085]
As in the first embodiment, the amount of the treated soil 24a may be, for example, about 8% to 10% by weight based on the weight of the processing target soil 22b.
[0086]
When adding the treated soil 24a to the treatment target soil 22b, it is desirable to perform appropriate stirring and mixing in order to uniformly disperse the treated soil 24a in the treatment target soil 22b. During the decomposition treatment, it is desirable to maintain the aeration or the number of cells of the decomposing bacteria 3 by appropriately adding nutrients and water while performing ventilation as needed.
[0087]
When the contaminants contained in the soil to be treated are microbial-decomposed using the decomposers 3 in the soil 22a to be treated initially arbitrarily selected, the decomposers 3 degrade the contaminants. In the above, the number of cells increases more than other soil bacteria, and becomes a dominant species in the processing target soil 22a.
[0088]
Therefore, if the treatment target soil 22a in which the decomposition of the contaminant has progressed to a desired degree is regarded as the treated soil 24a and a part of the treated soil is added to the treatment target soil 22b, in the addition stage, Since the activity of the decomposing bacteria in the treated soil 24a is already sufficiently high or a large amount of the decomposing enzyme has been generated, in the treatment target soil 22b to which the treated soil 24a is added, pollutants are not removed. The microbial degradation proceeds promptly immediately after the addition, and becomes the treated soil 24b in a short time.
[0089]
Next, the treated soil 24b is added to the treated soil 22c (step 115), and the treated soil 22c is set as the treated soil 24c. Hereinafter, the above-described process of adding the treated soil to the untreated soil is repeatedly performed until all of the treated soils 22a to 22e become the treated soils 24a to 24e (steps 116 and 117).
[0090]
Next, the processed soils 24a to 24e are backfilled in the excavation area 25 as shown in FIG. 8B (step 118).
[0091]
As described above, according to the method for purifying contaminated soil by microorganisms according to the present embodiment, the degrading bacteria 3 capable of decomposing pollutants become dominant species in the treated soils 24a to 24d, and the degrading activity is sufficiently high. Since a high or a large amount of a decomposing enzyme is generated, if the treated soil 4 is added to the soils 22b to 22e to be treated, the microbial decomposition of the pollutant proceeds promptly immediately after the addition.
[0092]
Therefore, compared with the case of using the microorganisms in the soils 22a to 22e to be treated, the microbial degradation can be completed in a shorter time because there is no need to wait for the growth of the microorganisms, the improvement of the decomposition activity, or the generation of the degrading enzyme. It becomes possible.
[0093]
In the present embodiment, the contaminated soil area 21 that spreads in the ground is excavated, and then the excavated contaminated soil is divided into a predetermined amount of soil, and these are divided into a plurality of processing target soils 22a to 22e. Although the ridges are temporarily placed on a temporary site provided on the ground surface to be contaminated, the contaminated soil area 21 may be separated from the place where the microbial decomposition treatment is performed.
[0094]
For example, a plant that performs microbial decomposition treatment is installed in a predetermined area, and contaminated soil excavated from a contaminated soil area is transported and carried into the plant, and then the contaminated soil is divided into a plurality of soils to be treated. Then, the above-described microorganism division processing may be performed.
[0095]
In the present embodiment, a part of the treated soil 24a obtained by microbial decomposition of the contaminants in the treated soil 22a is added to the treated soil 22b, and then a part of the treated soil 22a is removed. 22c, that is, the treated soil that is generated each time the microorganism is decomposed is added sequentially to the next soil to be treated. Instead, the contaminants in the soil 22a to be treated are degraded by microorganisms. A part of the processed soil 24a may be added to each of the processing target soils 22b to 22e.
[0096]
(Third embodiment)
[0097]
Next, a third embodiment will be described. Note that the same reference numerals are given to components and the like that are substantially the same as those in the above-described embodiments, and description thereof will be omitted.
[0098]
FIG. 9 is a flowchart illustrating a procedure of the method for purifying contaminated soil by microorganisms according to the present embodiment. As shown in the figure, in the method of purifying contaminated soil by microorganisms according to the present embodiment, first, as shown in FIG. 10A, a contaminated soil area 31 extending in the ground is excavated, and The soil is set as the processing target soil 32a (step 121).
[0099]
The processing target soil 32a may be temporarily placed in a ridge shape at a position separated from the contaminated soil region 31 so as not to hinder the excavation work to be performed sequentially.
[0100]
Next, the contaminants, for example, oil contained in the soil to be treated 32a are microbial-degraded by the decomposing bacteria 3 which are microorganisms present in the soil to be treated, and then the soil 32a having been decomposed to a desired degree is treated. The finished soil 34a is set (step 122).
[0101]
During the decomposition treatment, it is desirable to promote ventilation and activity of the decomposing bacterium 3 by appropriately adding nutrients and water while performing ventilation as needed.
[0102]
Next, as shown in FIG. 10B, at least a part of the above-described treated soil 34a is added to the treatment target soil 32b newly excavated as the contaminated soil from the contaminated soil region 31 (step 124).
[0103]
Similar to the first embodiment, the amount of the treated soil 34a may be, for example, about 8% by weight to 10% by weight based on the weight of the processing target soil 32b.
[0104]
When the treated soil 34a is added to the treated soil 32b, it is desirable to perform appropriate stirring and mixing in order to uniformly disperse the treated soil in the treated soil 32b. During the decomposition treatment, it is desirable to maintain the aeration or the number of cells of the decomposing bacteria 3 by appropriately adding nutrients and water while performing ventilation as needed.
[0105]
In this manner, in the process of decomposing contaminants, the number of the decomposing bacteria 3 increases in comparison with other soil bacteria, and becomes a dominant species in the treatment target soil 22a.
[0106]
Therefore, if the target soil 32a in which the decomposition of the contaminants has progressed to a desired degree is set as the processed soil 34a, and a part of the processed soil is added to the target soil 32b, at the stage of the addition, Since the activity of the decomposing bacteria in the treated soil 34a is already sufficiently high or a large amount of the decomposing enzyme has been generated, in the treatment target soil 32b to which the treated soil 34a is added, pollutants are not removed. The biodegradation proceeds promptly immediately after the addition, and becomes the treated soil 34b in a short time.
[0107]
Next, as shown in FIG. 10C, at least a part of the above-described treated soil 34b is added to the treatment target soil 32c newly excavated as the contaminated soil from the contaminated soil region 31 (step 125).
[0108]
Hereinafter, the step of adding the treated soil to the treated soil is repeatedly performed until all the treated soil excavated from the contaminated soil region 31 becomes the treated soil.
[0109]
As described above, according to the method for purifying contaminated soil by microorganisms according to the present embodiment, the decomposing bacteria 3 capable of decomposing pollutants become dominant species in the treated

soils

34a, 34b,. Is sufficiently high or a large amount of degrading enzyme is generated, so that if the treated

soils

34a, 34b... Are added to the soils 32b, 32c. Decomposition proceeds promptly immediately after addition.
[0110]
Therefore, as compared with the case of using microorganisms in the

soils

32a, 32b, 32c,. Can be terminated.
[0111]
【The invention's effect】
As described above, according to the method for purifying contaminated soil by microorganisms according to the present invention, microorganisms capable of decomposing contaminants become dominant species in the treated soil and have sufficiently high decomposition activity or a large amount of decomposition. Since the enzyme has been generated, if the treated soil is added to the second contaminated soil or the soil to be treated, the microbial decomposition of the contaminant proceeds promptly immediately after the addition.
[0112]
Therefore, compared to the case where microorganisms are directly added to the second contaminated soil or the soil to be treated, the microbial degradation can be completed in a shorter time because there is no need to wait for the growth of microorganisms, improvement of decomposition activity, or generation of degrading enzymes. It is possible to do.
[0113]
[Brief description of the drawings]
FIG. 1 is a flowchart showing a procedure of a method for purifying contaminated soil by microorganisms according to a first embodiment.
FIG. 2 is a work diagram showing a state of treating contaminated soil using the method for purifying contaminated soil by microorganisms according to the first embodiment.
FIG. 3 is a work diagram showing a state where the contaminated soil is treated using the method for purifying contaminated soil by microorganisms according to the first embodiment.
FIG. 4 is a graph showing the result of confirming the operation of the method for purifying contaminated soil by microorganisms according to the first embodiment by a laboratory test.
FIG. 5 is a graph showing the result of confirming the operation of the method of purifying contaminated soil by microorganisms according to the first embodiment by a laboratory test.
FIG. 6 is a flowchart showing a procedure of a method for purifying contaminated soil by microorganisms according to the second embodiment.
FIG. 7 is a work diagram showing a state of treating contaminated soil using the method for purifying contaminated soil by microorganisms according to the second embodiment.
FIG. 8 is a work diagram showing a state in which contaminated soil is treated using the method for purifying contaminated soil by microorganisms according to the second embodiment.
FIG. 9 is a flowchart showing a procedure of a method for purifying contaminated soil by microorganisms according to the third embodiment.
FIG. 10 is a work diagram showing a state of treating contaminated soil using the method for purifying contaminated soil by microorganisms according to the third embodiment.
[Explanation of symbols]
2 First contaminated soil
3 decomposing bacteria (microorganisms)
4 treated soil
12 Second contaminated soil
22a-22e Soil to be treated
24a-24e treated soil
32a-32c Processing target soil
34a-34c treated soil

Claims

A first contaminant contained in the first contaminated soil is decomposed by microorganisms in the first contaminated soil into a treated soil, and then a second contaminant containing a second contaminant decomposable by the microorganisms A method for purifying contaminated soil with microorganisms, comprising adding at least a part of the treated soil to the contaminated soil.

The method for purifying contaminated soil with microorganisms according to claim 1, wherein the second contaminant is the same as the first contaminant.

The contaminated soil containing the predetermined contaminant is divided into a plurality of soils to be treated by a predetermined soil amount, and among the plurality of soils to be treated, the contaminant contained in the arbitrarily selected treatment soil is selected. The treated soil is decomposed by microorganisms in the treated soil to obtain a treated soil, and at least a part of the treated soil is added to the untreated soil that has not been subjected to the microbial decomposition treatment among the plurality of treated soils. Repeating the step of adding the treated soil to the untreated soil until the contaminants contained in the untreated soil are microbially decomposed into treated soil and the treated soil is all treated soil. A method for purifying contaminated soil with microorganisms, characterized in that:

Excavating a contaminated soil area extending into the ground, treating the excavated contaminated soil as a soil to be treated, decomposing contaminants contained in the soil to be treated with microorganisms in the soil to be treated into treated soil, By adding at least a part of the treated soil to the treated soil newly excavated as a contaminated soil from a soil area, the contaminants contained in the treated soil are microbially decomposed into treated soil, and the contaminated soil is removed. A method for purifying contaminated soil with microorganisms, comprising repeating the step of adding the treated soil to the treated soil until all of the treated soil excavated from the soil area becomes treated soil.