JP2004066193A - Contaminated soil cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably and efficiently remove oil, aromatic hydrocarbon and cyanogen from contaminated soil. <P>SOLUTION: A method of removing a contaminant in the contaminated soil by making the soil a slurry is characterized by performing the steps of adding to the soil at least one solution selected from the group of seawater and activated sludge treatment water of ammonia water produced from a coke plant or a solution made by adding fresh water to the above solution to make the soil slurry and supplying oxygen to the soil slurry and stirring the resulting slurry to keep the oxidation-reduction potential of the soil slurry (reference of silver/silver chloride composite electrode) at ≥0 mV and <+200 mV under a control of controlling the pH of the soil slurry at ≥6.0 and <9.0 so that the contaminant in the soil slurry is desorbed into water and is microbially decomposed, and the above steps are successively executed in a soil slurry reaction vessel. <P>COPYRIGHT: (C)2004,JPO

Description

【００５１】
最初に、本発明プロセスの土壌スラリーを調整する方法について説明する。
【００５２】
土壌スラリー反応槽で、汚染土壌１に水２を添加して土壌をスラリー化する。ただし、汚染土壌の粒度や性状が広範囲で不均一な場合には、土壌スラリー反応槽９でスラリー操作を行わず、この前段に、スラリー調整槽３を設けて、汚染土壌を均一化した後、土壌スラリー反応槽９に投入してもよい。
【００５３】
汚染土壌１に添加する水としては、海水が容易に得られる場合は、海水を用いることが望ましい。また、海水に淡水を混合して用いてもよく、海水が流入している汽水域の河川水を用いてもよい。淡水と海水をより厳密に混合する場合には、土壌間隙水の電気伝導度を測定し、電気伝導度がほぼ同様の値となるように、淡水と海水を混合する。例えば、汚染土壌が海域に近くなればなるほど土壌間隙水の電気伝導度は上昇し、海水の添加量を増大させることになる。土壌間隙水の硫酸イオン濃度や塩素イオン濃度を測定し、ほぼ同様の値となるように、淡水と海水を混合してもかまわない。
【００５４】
海水の使用に対しては、微生物に対する浸透圧の影響から否定的な意見が多いが、あえて、本発明者らが積極的に海水を用いるのは、以下の理由によるものである。
【００５５】
１）　微生物処理に必要な微量栄養源を含有している。特に、沿岸域、汽水域であれば窒素、リンの濃度も高い場合がある。
【００５６】
２）　ｐＨ緩衝能がある。
【００５７】
３）　ｐＨが８〜８．５と比較的高い。
【００５８】
４）　安価で大量入手可能である。
【００５９】
５）　水温がほぼ一定である。
【００６０】
６）　汚染土壌中の間隙水は河川等の淡水に比べ、イオン濃度、言い換えれば電気伝導度が高い場合が多く、この状況に応じた微生物が生息している。海水混合によってこの状況を作り出せる。
【００６１】
７）　海水中にＰＡＨｓ分解細菌、シアン分解菌の存在の報告事例が多い。
【００６２】
また、製鉄所のコークス工場から発生する安水の活性汚泥処理水を汚染土壌に添加する水として用いてもかまわない。これは、製鉄所のコークス工場における安水の活性汚泥処理は、安水に海水を１５０〜３００容積％添加し、活性汚泥処理を行っているためである。また、安水の活性汚泥処理水は、水温も約３０〜３８℃で一定しているため、冬場の微生物活性の低下する時期には最適である。さらに、微生物の栄養源である窒素、リンなども大量に含有しているため、汚染土壌をスラリー化して用いる水として望ましい。
【００６３】
このほかに、脱水機１２から発生する脱離液１４や、土壌スラリー反応槽９での沈降操作によって発生する上澄液１３に対して後述の処理を行った処理水を補給水として用いてもかまわない。海水が容易に得られなければ淡水を用いてもよいが、淡水単独の場合は、微生物処理に必要な微量栄養源を添加する必要があることから、海水を添加することが望ましい。
【００６４】
前記汚染土壌１と水２との混合比は、土壌の含水率を測定後決定するが、土壌スラリー濃度が１０質量％以上５０質量％未満であることが好ましい。５０質量％以上では、攪拌動力が過大となり攪拌を維持することが難しく、一方、１０質量％未満では、水使用量が増大してしまい経済的でない。
【００６５】
次に、土壌スラリー反応槽９における脱離操作により、土壌粒子から分離された汚染物質は、土壌スラリ−反応槽９の微生物および／または汚染物質で馴養した微生物を用いて分解処理される。この工程における処理を詳細に説明する。
【００６６】
土壌粒子から分離された汚染物質は、汚染土壌中に生息していた微生物および／または汚染物質で馴養した微生物を用いて分解処理される。通常、汚染土壌中に存在する微生物は、汚染物質、例えば芳香族炭化水素で既に馴養されていることが多く、これを土壌スラリー反応槽９で増殖させて用いればよい。微生物と汚染物質の反応速度をさらに上げる必要がある場合は、汚染物質である芳香族炭化水素で馴養された微生物を添加すればよい。この場合、芳香族炭化水素で馴養された微生物であれば特に種類は問わないが、製鉄所のコークス工場から発生する安水の活性汚泥が望ましい。安水の活性汚泥は、安水に含まれる多種類の芳香族炭化水素で十分に馴養されており、また、海水にも馴養されているため、反応槽での芳香族炭化水素の分解を加速することができる。安水の活性汚泥の添加量は、土壌に対して１質量％以上添加すればよく、１質量％未満では添加効果は顕著に現れない。添加量の上限は特にはないが、経済性を考えると５０質量％以下が望ましい。
【００６７】
土壌スラリー反応槽９は、ブロアー８によって連続的に空気で曝気する。土壌スラリーの沈降を防止するために、最低限度の空気量および／または攪拌は必要である。水中攪拌機や超音波攪拌をブロアー８と併用しても良く、水中攪拌の強化によって、汚染物の土壌付着防止や気固液の接触頻度が増加し、汚染物の分解速度が向上する。超音波周波数は、汚濁物質の種類によって異なるが、２０〜２００ｋＨｚ程度が望ましい。
【００６８】
土壌スラリー反応槽９における汚染物質の分解を促進するためには、土壌スラリー反応槽９の酸化還元電位（ＯＲＰ）が０ｍＶ（銀／塩化銀複合電極基準、以下同じ）以上に維持されるように、ブロアー８および／または攪拌機の回転数を制御し、空気を供給することが望ましい。汚染物質の分解反応は、好気的雰囲気で促進されるため、溶存酸素の維持は反応促進に絶対必要であり、ＯＲＰ値としては０ｍＶ以上が好ましい。ＯＲＰ値の上限値は特に限定はないが、＋２００ｍＶ未満が好ましい。
【００６９】
土壌スラリー反応槽９のｐＨは、微生物の生育に適した６．０以上９．０未満に維持されることが望ましい。油分の土壌粒子からの洗浄効果のみを考えると、ｐＨは高い方が望ましいことは公知であるが、ｐＨが９．０以上では油分の洗浄効果は増大しても、微生物の活性が急激に低下するので、ｐＨは９．０未満であることが必要である。また、ｐＨが６．０未満では洗浄効果が小さく、また微生物の活性もやはり衰えるため、ｐＨは６．０以上であることが望ましい。
【００７０】
このように、スラリー反応槽９のｐＨは、洗浄促進効果と微生物による分解促進効果の両面から決定すべきであり、より好ましくは、ｐＨは７．０以上９．０未満である。ｐＨ調整剤としては、希硫酸や水酸化ナトリウムの水溶液を用いて調整すればよい。海水を用いたスラリーであれば、ｐＨ緩衝作用があるため、薬品費も削減できる利点がある。
【００７１】
さらに、汚染土壌中にシアンが存在する場合には、鉄系凝集剤４をスラリー反応槽９に添加し、鉄シアン錯塩（２価の鉄イオンの場合はフェロシアン（［Ｆｅ（ＣＮ）_６］^４−）、３価の鉄イオンの場合はフェリシアン（［Ｆｅ（ＣＮ）_６］^３−））を形成させることにより、微生物反応阻害物質であるシアンイオン（ＣＮ⁻）を無害化することが極めて重要である。なお、土壌スラリー反応槽９の前段にスラリー調整槽３を設ける場合には、鉄系凝集剤４をスラリー調整槽３に投入してもよい。
【００７２】
本発明に用いる鉄系凝集剤としては、塩化第一鉄、塩化第二鉄、硫酸第一鉄、硫酸第二鉄、ポリ硫酸第二鉄などが好ましい。鉄系凝集剤の添加量は、シアンイオンの濃度にもよるが、通常、鉄とシアンの理論モル比の２倍以上３倍未満添加すればよい。シアンイオンの毒性は、シアンと鉄が安定なキレート結合をすることにより各段に弱くなる。汚染土壌に鉄分がかなり含まれる場合は、既に鉄シアン錯体を形成しているため、鉄系凝集剤の添加が不要の場合もある。汚染土壌中の微生物は、フェロシアンまたはフェリシアンであれば、分解することができるものもあり、分解過程で発生するＮＨ_４−Ｎを窒素源、ＨＣＯＯ⁻を有機炭素源として増殖できる。この場合もｐＨは６．０以上９．０未満であることが望ましく、特にｐＨが６．０未満の酸性域では、シアンガスが発生する可能性があるため極めて危険であり、一方、ｐＨが９．０以上ではシアン分解細菌の活性が低下してしまう。製鉄所のコークス工場から発生する安水の活性汚泥は、シアン分解細菌を大量に含有しているため、これを添加してもかまわない。
【００７３】
次に、本発明プロセスの土壌スラリーの搬出工程における処理について説明する。
【００７４】
汚染土壌が粘土やシルトを多く含む場合には、スラリー中の固液分離が困難となる。このような場合には、土壌スラリー反応槽での固液分離を行わずに、土壌スラリーを直接、脱水機１２にかけることが望ましい。すなわち、前記土壌スラリーを土壌と上澄液に分離する工程を前記土壌スラリー反応槽で行うことを省略する。
【００７５】
一方、汚染土壌がレキ主体の場合には、沈降性が優れているため、固液分離を行えば土壌と上澄液に容易に沈降分離し、沈降した土壌は、脱水機にかけずにそのまま再利用できる場合がある。沈降した土壌の含水率が高い場合には、沈降した土壌をさらに脱水機１２にかけて土壌の含水率を下げた後に土壌を再利用してもよい。なお、土壌スラリー反応槽９と脱水機１２の能力差によっては、中継槽を設ける必要がある場合もあるが、それは全体の処理計画の中で勘案すればよい。このように処理された土壌は、通常、元の位置に埋め戻される。
【００７６】
脱水機１２は、通常のタイプ、例えばフィルタープレスタイプの脱水機を使用できる。
【００７７】
最後に、本発明プロセスの、土壌スラリー反応槽９から発生した上澄液１３、または、脱水機１２から発生した脱離液１４の処理方法について説明する。
【００７８】
微生物で処理された土壌スラリーは、上述のように、脱水機１２にかけられ、脱離液１４が発生する。土壌スラリー反応槽９での沈降操作によって、上澄液１３が発生する場合もある。脱離液１４および上澄液１３には、未分解の油分や細かく砕かれた土壌粒子が含まれ、ＣＯＤ（化学的酸素要求量）やＢＯＤ（生化学的酸素要求量）が高いことがあるが、新たに活性汚泥などの生物学的排水処理設備を設けることはコストがかかるため、極力、スラリー反応槽９で水中ＣＯＤやＢＯＤ成分の分解も進めることが好ましい。しかし、生物難分解のＣＯＤ成分が残存し、廃水基準を遵守できない場合には、オゾン、過酸化水素、紫外線、光触媒等を用いて酸化分解処理をすればよい。前記処理により、大量のＯＨラジカルが発生し、難分解性ＣＯＤ成分の分解を促進できる。さらに、活性炭吸着装置を酸化分解処理設備の後段に設置してもかまわない。
【００７９】
上記操作により生成した最終処理水は、土壌スラリー反応槽９において補給水として再利用する、あるいは放流する。
【００８０】
【実施例】
以下、本発明の実施例を説明する。なお、本発明は本実施例に限定されるものではない。
（実施例）
汚染土壌として、油分、ベンゼン、コールタールの主成分であるナフタレン、フェナンスレンなどの多環芳香族炭化水素（ＰＡＨｓ）およびシアンで、高濃度に汚染された土壌（高濃度汚染土系）、および前者よりも低濃度で汚染された土壌（低濃度汚染土系）を用いた。表２に、実施例で用いた汚染土壌の油分濃度を示す。表３には、実施例で用いた高濃度汚染土壌のＰＡＨｓ濃度を示す。
【００８１】
表２に示すように、高濃度汚染土壌では油分を１２０００ｍｇ／ｋｇ−乾燥質量（ノルマルヘキサン〜ソックスレー抽出重量法で測定）、低濃度汚染土壌では油分を１６００ｍｇ／ｋｇ−乾燥質量程度含んでいた。
【００８２】
また、表３に示すように、ナフタレン及びフェナンスレンなど１６種類のＰＡＨｓの和であるＴｏｔａｌ−ＰＡＨｓ（Ｔ−ＰＡＨｓ）も、高濃度汚染地帯で１３８ｍｇ／ｋｇ−乾燥質量（溶媒抽出−ＧＣＭＳ（ガスクロマトグラフ質量分析計）法で測定）含んでいた。また、ベンゼン、シアンも溶出試験で、それぞれ１〜２ｍｇ／Ｌ、０．１〜０．２ｍｇ／Ｌ程度検出され、土壌環境基準をオーバーしていた。
【００８３】
作業の手順を図２に従って説明する。
【００８４】
まず、スラリー反応槽３において、汚染土壌１に、土壌容量の１倍量の海水と淡水の混合水２（海水：淡水＝１：１（容量比））を添加し、攪拌機によって攪拌し、スラリー化した。前記混合水２の混合割合は、汚染土壌間隙水の硫酸イオン濃度が、１２００ｍｇ／Ｌ程度であり、河川等の淡水（１０〜２０ｍｇ／Ｌ程度）よりも著しく高い値を示し、海水（２３００ｍｇ／Ｌ）の５０％近い値を示したため、このような混合割合とした。なお、汚染土壌の含水率は、３０質量％であるため、スラリー中の土壌（乾燥質量）の割合は３５質量％である。
【００８５】
土壌スラリーには、鉄系凝集剤４として、塩化第一鉄を鉄として０．０５ｍＭ添加し、土壌中のシアンイオンをフェリシアンとし、シアンの微生物阻害性を除去した。
【００８６】
次に、前記土壌スラリーを土壌スラリー反応槽９に移した。土壌スラリー反応槽９の水理学的滞留時間（ＨＲＴ）は４０日とし、適宜、スラリー反応槽９の汚染物質除去率の評価を行った。反応槽９には、ＯＲＰセンサー７とブロアー８を設置し、反応槽９の酸化還元電位（ＯＲＰ）（銀／塩化銀複合電極基準、以下同じ）が０ｍＶ以上＋１００ｍＶ未満に維持されるようにブロアー８の回転数を制御して、空気曝気量の制御を行った。また、空気流量が仮に停止した際の土壌スラリーの堆積を防止するため、スラリー反応槽９には水中攪拌機を設置し、常時攪拌を行った。反応槽９のｐＨは、水酸化ナトリウム水溶液および硫酸水溶液を用いて、７．０以上〜９．０未満に維持し、リンや窒素は特に添加しなかった。
【００８７】
表２に、土壌スラリーのスラリー反応槽９での滞留時間が７〜４０日の油分除去率を示す。高濃度汚染系の初期油分濃度は１２０００ｍｇ／ｋｇであったが、滞留時間の増加につれて減少し、２０日後で２２００ｍｇ／ｋｇ−乾燥質量（除去率８３％）、３０日後で４５０ｍｇ／ｋｇ−乾燥質量（除去率９６％）、４０日後では２００ｍｇ／ｋｇ−乾燥質量（除去率９８％）まで減少し、土壌から異臭もほとんど消失した。低濃度汚染系でも同様の傾向が見られ、初期油分濃度は１６００ｍｇ／ｋｇ−乾燥質量であったが、２０日後には２００ｍｇ／ｋｇ−乾燥質量（除去率８８％）、４０日後には１００ｍｇ／ｋｇ−乾燥質量（除去率９４％）まで減少した。
【００８８】
【表２】

【００８９】
表３に、土壌スラリーの滞留時間が４０日後におけるＰＡＨｓ濃度を示す。Ｔ−ＰＡＨｓは、１３８ｍｇ／ｋｇ−乾燥質量から１５ｍｇ／ｋｇ−乾燥質量まで除去された。ＰＡＨｓの中で二環、三環化合物はほぼ完全に除去されていたが、四環化合物フルオラテン、ピレンが残存する傾向が認められた。
【００９０】
【表３】

【００９１】
さらに、土壌からのベンゼン溶出濃度は、当初１．３ｍｇ／Ｌであったが、２日後の測定で既に土壌環準の０．０１ｍｇ／Ｌを下回っていた。土壌からのシアン溶出濃度は、２日後の測定で既に検出限界以下であった。
【００９２】
汚染土壌は粘土・シルト成分が多く、沈降分離が困難なため、前記土壌スラリー反応槽９から排出された土壌スラリーを、直接、遠心脱水機１２に通水し脱水した後、埋め戻した。
【００９３】
土壌スラリー反応槽９での沈降操作は行わなかったため、本実施例では、図２の上澄液１３は発生しなかった。
【００９４】
脱水機１２から発生する脱離液は、ＣＯＤが４０ｍｇ／Ｌ程度、ＢＯＤが２０ｍｇ／Ｌ以下で、かなり浄化が進んでいたが、水処理操作によってＣＯＤを廃水基準（２０ｍｇ／Ｌ）以下まで処理する必要があった。そこで、オゾン酸化装置２０を設置し、難分解性ＣＯＤ成分の分解促進を図った結果、最終処理水のＣＯＤを２０ｍｇ／Ｌ以下とすることができた。
【００９５】
このように、バッチ式のスラリー法を用いることにより、従来法と比較し、格段に設備数を減少させ、かつ、同等の処理性能を得ることが可能となった。
【００９６】
【発明の効果】
本発明により、小規模汚染地域においても、油分、芳香族炭化水素、シアン等の汚染物質を含有する土壌を、微生物を用いて浄化処理することが可能となり、容易・簡便かつ効率的で、さらに安価に、汚染物質の高い除去率による除去が可能となる。
【図面の簡単な説明】
【図１】土壌中の油分、芳香族系化合物、シアンを除去する従来のプロセスフローである。
【図２】土壌中の油分、芳香族系化合物、シアンを除去する本発明のプロセスフローである。
【符号の説明】
１…汚染土壌
２…海水と淡水の混合水及び／又は最終処理水
３…スラリー調整槽
４…鉄系凝集剤
５…ｐＨセンサー
６…酸及び／又はアルカリ添加装置
７…ＯＲＰセンサー
８…ブロアー
９…土壌スラリー反応槽
１０…スラリー貯留槽
１１…固液分離槽
１２…脱水機
１３…上澄液
１４…脱離液
１５…処理土壌
１６…活性汚泥処理槽
１７…ＯＲＰセンサー
１８…ブロアー
１９…活性汚泥
２０…オゾン酸化槽
２１…最終処理水
２２…余剰汚泥[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for purifying soil contaminated with an oil component, aromatic hydrocarbons such as naphthalene contained in the oil component, and cyanide.
[0002]
[Prior art]
Contaminated with monocyclic aromatic hydrocarbons (Monoaromatic Hydrocarbons) such as benzene, toluene, xylene and polycyclic aromatic hydrocarbons (Polycyclic Aromatic Hydrocarbons, hereinafter referred to as PAHs) such as naphthalene and phenanthrene, which are the main components of coal tar. There are many reports on soil, mainly in the United States. These soil pollutions are caused by the soil being contaminated with petroleum products such as gasoline and coal products such as coal tar, and are mainly found on former factory sites. These substances are environmentally unfriendly and must be removed if soil or groundwater is contaminated.
[0003]
The method for purifying soil contaminated with such an oil component or an aromatic hydrocarbon which is a main component of the oil component is roughly classified into the following methods.
[0004]
(1) Cleaning method
(2) Heating (volatilization / desorption) treatment method, thermal decomposition method, melting method
(3) Adsorption method
(4) Chemical decomposition method
(5) Biodegradation method
The washing method is a method of dispersing or dissolving oil and aromatic hydrocarbons contained and adsorbed in soil in water, and does not decompose aromatic hydrocarbons. Rather than processing, it is positioned as a preprocessing operation.
[0005]
The heat treatment method has a high effect of volatilizing aromatic hydrocarbons in the soil, but aromatic hydrocarbons volatilized from the soil by heating cannot be released to the atmosphere as they are, and eventually trap and decompose. , Need to be harmless. Furthermore, they are hardly used because of the high processing cost, the high equipment cost, the significant change in soil properties due to heating, and the generation of odor.
[0006]
The method of adsorbing aromatic organic substances using activated carbon or the like is used in combination with the washing method. Activated carbon has an adsorbing effect on aromatic hydrocarbons, but has the disadvantage of requiring enormous costs for regeneration.
[0007]
In addition, the chemical decomposition method of aromatic hydrocarbons using a chemical such as potassium permanganate usually requires an excessive amount of chemicals to be added, so that the treatment cost is increased and, in addition, secondary contamination by residual chemicals is required. there is a possibility.
[0008]
The biodegradation method has advantages such as low possibility of secondary pollution, energy saving, low cost, application to a wide range of soil, and no change in the properties of the soil itself. The biodegradation method using microorganisms is commonly called bioremediation.
[0009]
Among the above main methods, bioremediation is becoming common, mainly in Europe and the United States.
[0010]
Bioremediation applies the principle of organic matter decomposition by microorganisms to the treatment of soil and groundwater contaminated with harmful chemicals.It essentially consists of a biochemical wastewater treatment process and bioremediation of toxic chemicals in soil. There is no significant difference in the mediation process. The target harmful chemicals are oils such as petroleum, monocyclic aromatic hydrocarbons (benzene, etc.), and polycyclic aromatic compounds (naphthalene, etc.). And removed from soil and water.
[0011]
The bioremediation process mainly includes three methods: a land farming method, a slurry method, and a combined method of a bioremediation process and a cleaning method.
[0012]
The land farming method (including the land pile method) is widely used in the United States and the like as a countermeasure for pollutants near the soil surface. Management targets include oily sludge and petroleum refinery waste, and treatment of surface soils contaminated with hydrocarbons and pesticides. Although it takes time for purification, there are advantages such as low treatment cost and easy reuse of soil. The method is designed to use the soil to be treated itself as a microbial species and utilize aerobic microorganisms to optimize the degradation of contaminants. The following measures are required to promote aerobic microbial degradation.
[0013]
1) Supply of air (ventilation by tillage machines, securing soil porosity by adding bulking agent)
2) Addition of nutrients (fertilizer, etc.)
3) Drying prevention (periodic water addition)
4) Soil pH adjustment (maintained neutral by adding lime etc.)
Furthermore, in order to improve the decomposition rate of a specific substance, there is a case where a specific microorganism is inoculated from the outside, and there are also reports of use of sewage sludge, cow dung, compost, and the like.
[0014]
As the treatment equipment, a bed for disposing of excavated contaminated soil, a leachate treatment facility from the bed, a reuse facility, and, in some cases, a cover facility are required.
[0015]
The slurry method is a method in which water is added to soil to form a slurry (slurry reactor or slurry lagoon) for microbial decomposition of contaminants, and is applied in the United States and the like. Although the processing cost is higher than the land farming method, the processing speed and the contaminant removal performance are excellent. The microbial reaction tank in the slurry method is an open tank, a closed tank, or a lagoon, and requires the following equipment.
[0016]
1) Slurry adjustment tank
2) Microbial reaction tank (reactor or lagoon)
3) Concentration tank (settling pond)
4) Dehydrator
5) Treatment equipment for wastewater generated from dehydrators, etc.
In the reaction tank, etc., operations such as air supply (air supply by a blower), prevention of slurry precipitation (stirring with a stirrer), pH adjustment (neutral), addition of nutrients, promotion of solid-liquid separation are required. It is. Furthermore, in order to improve the decomposition rate of a specific substance, a specific microorganism may be inoculated from outside. In addition, wastewater generated from a concentration tank or a dehydrator needs to be treated until the wastewater standard can be complied with.
[0017]
The combined use of the bioremediation process and the washing method involves washing the soil, dissolving most of the contaminants in the wash water, and then treating the contaminants in the wash water with microorganisms. Is required. The challenge is how to efficiently dissolve most of the contaminants in the wash water.
[0018]
For example, there is a report in the Netherlands that cleans soil and cleans water. This is because the pollutants are removed from the soil and groundwater at the site of the asphalt manufacturing plant that has been contaminated with monocyclic aromatic hydrocarbons such as benzene, toluene and xylene, and polycyclic aromatic hydrocarbons (PAHs) such as naphthalene and phenanthrene. Microbial degradation was studied for removal (Environ Technology, Vol. 10, No. 2, 185-189, 1989). Here, after washing the soil and dissolving the contaminants in the washing water, the water washed from the soil is circulated in the biological reaction tank for treatment. As a result, the benzene concentration in the washing water was 2.5 mg / L at the beginning, but was removed 94% by mass after 37 days and 100% by mass after 92 days. The PAHs concentration in the washing water was 4.4 mg / L at the beginning, but 99% by mass after 37 days and 100% by mass after 92 days. However, in terms of the removal rate from soil, benzene in the soil decreased by 95% by mass or more after 140 days, but PAHs was strongly adsorbed on the soil and the removal rate was about 40% by mass. Removal of PAHs is quite difficult.
[0019]
As described above, methods for treating monocyclic aromatic hydrocarbons such as oil and benzene and polycyclic aromatic hydrocarbons (PAHs) such as naphthalene and phenanthrene using a biodegradation method (bioremediation) have been widely developed. It is getting.
[0020]
On the other hand, many cases of soil contamination by cyanide have been reported. Cyanide is contained in wastewater from plating industry, metal refining industry, petroleum industry (acrylonitrile production), coke gas industry, and the like. Cyanide is highly toxic, and its main purpose is to remove and contain it.Due to chemical or biodegradation methods, there are cases of thermal decomposition and oxidation by chemicals such as hydrogen peroxide. Is considered difficult to apply.
[0021]
[Problems to be solved by the invention]
The following problems remain in the conventional bioremediation process.
[0022]
1) The purification period is long.
[0023]
2) Poor removal rate of PAHs.
[0024]
3) Application is difficult when a substance (especially cyanide) that inhibits microorganisms is contained.
[0025]
First, the reason why it takes a long time to purify contaminated soil is that the growth of microorganisms having a function of decomposing specific pollutants has not progressed, and the concentration of the microorganisms is extremely low. For example, in the decomposition of aromatic hydrocarbons, activated sludge in municipal sewage treatment plants and food industry wastewater treatment plants has a low concentration of microorganisms having a decomposition function. If activated sludge having a high concentration of microorganisms having a function of decomposing hydrocarbons, for example, activated sludge of chemical plant wastewater or coke plant wastewater (amsible water) can be maintained at a high concentration, the possibility of shortening the treatment period is increased.
[0026]
In addition, not only the concentration of the microorganisms, but also the environmental conditions under which these microorganisms can sufficiently function must be established. For example, environmental conditions include pollutant load, pH, DO (dissolved oxygen), temperature, moisture, trace nutrients, the presence or absence of toxic substances, the contact efficiency between microorganisms, air and pollutants, and the like. Therefore, it is possible for the first time to maintain a high concentration of microorganisms and to shorten the period required for decomposition. For example, if the contaminants are at an appropriate load, the removal of the contaminants is mainly by microbial degradation, but if the load of the contaminants is too high, the contaminants are more likely to diffuse into the air than the microbial decomposition, or More likely to remain in water.
[0027]
Furthermore, among contaminants, PAHs generally have a lower removal rate than monocyclic aromatic hydrocarbons such as benzene. This is because PAHs have a higher adsorptivity to soil than benzene or the like, and have a greater effect of not being able to be separated from soil, rather than a lower degradability of PAHs by microorganisms. Therefore, for PAHs, it is necessary to first efficiently separate contaminants from soil, and then it is necessary to promote the application of bacteria that degrade PAHs.
[0028]
When contaminated soil contains a substance such as cyanide that has an effect on microorganisms, the microorganism inhibition of cyanide is known, and the bioremediation process cannot be applied as it is, and it is necessary to perform a treatment to detoxify cyanide in advance. .
[0029]
As described above, among the bioremediation processes, the slurry method is excellent in processing speed and contaminant removal performance. However, this method is suitable for a large-scale contaminated area such as a factory site, but is not suitable for a gas station. There is a problem that costs increase in small-scale contaminated areas such as ruins.
[0030]
Therefore, the present invention solves the above-mentioned problems, and can reduce the cost even if the soil containing a high concentration of oil and PAHs particularly contains cyan, and even if the target area is small. It is another object of the present invention to provide a method for purifying contaminated soil that can obtain a high removal rate of oil and PAHs.
[0031]
[Means for Solving the Problems]
The present inventors have proposed a method for purifying contaminated soil in Japanese Patent Application No. 2002-130548. The purification method is a method of biochemically purifying oils derived from petroleum products such as coal tar, gasoline and heavy oil, particularly PAHs such as benzene, and soil highly contaminated with cyanide. Is a method of continuously purifying through a process using a soil slurry adjusting tank, a soil slurry reaction tank or a lagoon, a solid-liquid separation tank, an activated sludge treatment tank, and the like. FIG. 1 shows a process flow of a continuous purification method of contaminated soil by a slurry method proposed by the present inventors in Japanese Patent Application No. 2002-130548.
[0032]
However, this method is suitable for large-scale contaminated areas such as factory sites, but has the problem of increasing costs in small-scale contaminated areas such as gas station sites, and the process is complicated due to multiple steps. There is a problem that is. Therefore, the present inventors have studied a method for purifying contaminated soil which can be more easily performed, particularly as a measure for a small-scale contaminated area.
[0033]
Conventionally, a step of adding water to the contaminated soil to form a soil slurry, a step of desorbing the contaminants in the soil slurry into water and providing microbial decomposition of the contaminants by giving oxygen supply and stirring, A step of discharging the soil slurry as it is, or a step of separating the soil slurry into a soil and a supernatant and separately discharging (solid-liquid separation tank), and further performing a microbial treatment of generated wastewater separately in each tank. I was However, the present inventors have conducted various studies and found that the oxidation-reduction potential of the soil slurry in the microbial decomposition step was 0 mV or more (based on a silver / silver chloride composite electrode) and the pH was 6.0 or more and less than 9.0. It has been newly found that the above-mentioned control can be sufficiently carried out in batches sequentially in the same soil slurry reaction tank without performing the above operations separately.
[0034]
The process of the present invention has fewer components and simplification, and can easily and quickly respond to oil treatment of small-scale contaminated soil, for example, a gas station site, as compared with the conventional continuous treatment method. .
[0035]
The present invention has been made based on the above findings, and the gist thereof is as follows.
[0036]
(1) A method for removing contaminants in contaminated soil by converting the contaminated soil into a soil slurry, wherein the contaminated soil is treated with at least one selected from the group consisting of seawater and activated sludge-treated treated water produced from a coke plant. Or a step of adding a solution obtained by mixing fresh water to the solution to form a soil slurry, and controlling the pH of the soil slurry to not less than 6.0 and less than 9.0, and adjusting the soil slurry according to the pH control value. By supplying oxygen and stirring to the soil slurry so that the oxidation-reduction potential (based on a silver / silver chloride composite electrode) of 0 mV or more and less than +200 mV, contaminants in the soil slurry are removed into water. Separating the contaminants and decomposing the contaminants by microorganisms in the same soil slurry reactor in sequence.
[0037]
(2) A method for removing contaminants in contaminated soil by converting the contaminated soil into a soil slurry, wherein the contaminated soil is at least one selected from the group consisting of seawater and activated sludge-treated wastewater generated from a coke plant. Or a step of adding a solution obtained by mixing fresh water to the solution to form a soil slurry in a slurry adjusting tank, and then controlling the pH of the soil slurry to 6.0 or more and less than 9.0, By applying oxygen supply and stirring to the soil slurry so that the oxidation-reduction potential (based on the silver / silver chloride composite electrode) of the soil slurry is maintained at 0 mV or more and less than +200 mV according to the pH control value, A method for purifying contaminated soil, comprising the steps of desorbing contaminants in water and decomposing the contaminants by microorganisms in a soil slurry reactor.
[0038]
(3) The step (1) or (2), wherein, after the step of microbial decomposition of the contaminants, the step of separating the soil slurry into soil and supernatant is performed in the same soil slurry reaction tank. The method for purifying contaminated soil according to the above.
[0039]
(4) The purification of contaminated soil according to any one of (1) to (3), wherein a dehydrator is provided at a stage subsequent to the soil slurry reaction tank, and a dehydrator performs dehydration of the soil slurry. Method.
[0040]
(5) The method for purifying contaminated soil according to any one of (1) to (4), wherein the soil slurry concentration is 10% by mass or more and less than 50% by mass.
[0041]
(6) To the contaminated soil, add one or more solutions selected from activated sludge treated water of seawater and a low-temperature activated sludge generated from a coke plant, or a solution obtained by mixing fresh water with the solution to form a soil slurry. The method for purifying contaminated soil according to any one of (1) to (5), wherein an iron-based coagulant is added to the soil slurry in the step.
[0042]
(7) One or two of ozone, ultraviolet light, hydrogen peroxide, a photocatalyst, and activated carbon are applied to the supernatant generated from the soil slurry reaction tank and / or the wastewater generated by the dewatering of the soil slurry by the dehydrator. The method for purifying contaminated soil according to any one of the above (1) to (6), wherein a treatment using at least a seed is performed.
[0043]
(8) The contaminant in the contaminated soil contains any one or more of coal tar, gasoline, and oil derived from heavy oil, wherein (1) to (7). Method of cleaning contaminated soil.
[0044]
(9) The method for purifying contaminated soil according to (8), wherein the contaminant contains cyan.
[0045]
(10) The contaminated soil according to (9), wherein the contaminant includes a monocyclic aromatic hydrocarbon mainly composed of benzene and / or a polycyclic aromatic hydrocarbon mainly composed of naphthalene. Purification method.
[0046]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 2 shows an example of the purification method by the slurry method of the present invention, but the present invention is not limited to this.
[0047]
The process of the present invention is basically a process of treating contaminants using contaminated soil as a soil slurry.However, a point that is significantly different from the conventionally reported soil slurry process is that water is added to contaminated soil. A soil slurry, the step of desorbing the contaminants in the soil slurry by giving oxygen supply and agitation into water and decomposing the contaminants by microorganisms, or discharging the soil slurry as it is, or The step of separating the slurry into a soil and a supernatant and discharging the slurry separately is to sequentially perform the batch in the same soil slurry reaction tank.
[0048]
As can be seen from FIG. 2, the process of the present invention has a very small number of components and is extremely simple. Can respond easily and quickly.
[0049]
The process of the present invention will be described in detail below. The process of the present invention is carried out in the same soil slurry reaction tank, as shown in Table 1, by dividing the time for each step.
[0050]
[Table 1]

[0051]
First, a method for preparing a soil slurry in the process of the present invention will be described.
[0052]
In a soil slurry reactor, water 2 is added to contaminated soil 1 to slurry the soil. However, when the particle size and properties of the contaminated soil are wide and non-uniform, the slurry operation is not performed in the soil slurry reaction tank 9 and the slurry adjusting tank 3 is provided at the preceding stage to homogenize the contaminated soil. It may be charged into the soil slurry reaction tank 9.
[0053]
As seawater to be easily added to the contaminated soil 1, seawater is desirably used. Alternatively, freshwater may be mixed with seawater, or river water in a brackish water region into which seawater flows may be used. When mixing fresh water and seawater more strictly, the electric conductivity of soil pore water is measured, and the freshwater and seawater are mixed so that the electric conductivity becomes almost the same value. For example, the closer the contaminated soil is to the sea area, the higher the electrical conductivity of the soil pore water will be and the more seawater will be added. Sulfate ion concentration and chloride ion concentration of soil pore water are measured, and fresh water and seawater may be mixed so that the values are almost the same.
[0054]
Although there are many negative opinions regarding the use of seawater due to the effect of osmotic pressure on microorganisms, the reason why the present inventors actively use seawater is as follows.
[0055]
1) Contains micronutrients necessary for microbial treatment. Especially in coastal and brackish water areas, nitrogen and phosphorus concentrations may be high.
[0056]
2) It has a pH buffering capacity.
[0057]
3) The pH is relatively high at 8 to 8.5.
[0058]
4) Inexpensive and available in large quantities.
[0059]
5) Water temperature is almost constant.
[0060]
6) Pore water in contaminated soil often has higher ion concentration, in other words, higher electrical conductivity, than fresh water such as rivers, and microorganisms according to this situation inhabit. Sea water mixing can create this situation.
[0061]
7) There are many reports of the presence of PAHs-degrading bacteria and cyanolytic bacteria in seawater.
[0062]
In addition, activated sludge treated water generated from a coke plant at a steel mill may be used as water to be added to contaminated soil. This is because the activated sludge treatment in the coke plant of the ironworks is performed by adding 150 to 300% by volume of seawater to the treated water. In addition, since the temperature of the activated sludge treated water of constant water is constant at about 30 to 38 ° C., it is most suitable in winter when the microbial activity decreases. Furthermore, since it contains a large amount of nitrogen, phosphorus, and the like, which are nutrient sources of microorganisms, it is desirable to use contaminated soil as slurry water.
[0063]
In addition, treated water obtained by subjecting the desorbed liquid 14 generated from the dehydrator 12 or the supernatant 13 generated by the sedimentation operation in the soil slurry reaction tank 9 to a treatment described below may be used as makeup water. I don't care. If seawater is not easily obtained, freshwater may be used. However, in the case of freshwater alone, it is desirable to add seawater since it is necessary to add a trace nutrient necessary for microbial treatment.
[0064]
The mixing ratio between the contaminated soil 1 and the water 2 is determined after measuring the water content of the soil, and it is preferable that the soil slurry concentration is 10% by mass or more and less than 50% by mass. If it is 50% by mass or more, the stirring power becomes excessively large and it is difficult to maintain the stirring. On the other hand, if it is less than 10% by mass, the amount of water used increases and it is not economical.
[0065]
Next, the contaminants separated from the soil particles by the desorption operation in the soil slurry reaction tank 9 are decomposed using microorganisms in the soil slurry reaction tank 9 and / or microorganisms acclimated to the contaminants. The processing in this step will be described in detail.
[0066]
The contaminants separated from the soil particles are decomposed using microorganisms that have inhabited the contaminated soil and / or microorganisms that have become accustomed to the contaminants. Usually, the microorganisms present in the contaminated soil are often already acclimated with contaminants, for example, aromatic hydrocarbons, and may be used after being propagated in the soil slurry reaction tank 9. When it is necessary to further increase the reaction rate between the microorganism and the contaminant, a microorganism acclimated to the contaminant aromatic hydrocarbon may be added. In this case, any type of microorganism can be used as long as it is microorganisms acclimated with aromatic hydrocarbons, but activated sludge generated from a coke plant of a steel mill is preferably used. Activated sludge of Ansui is well acclimated to various kinds of aromatic hydrocarbons contained in Ansui and accelerating the decomposition of aromatic hydrocarbons in a reaction tank because it is acclimated to seawater. can do. The amount of the activated sludge added to the water may be 1% by mass or more based on the soil, and if it is less than 1% by mass, the effect of addition is not remarkably exhibited. Although there is no particular upper limit for the amount of addition, it is preferably 50% by mass or less in view of economy.
[0067]
The soil slurry reaction tank 9 is continuously aerated with air by a blower 8. A minimum amount of air and / or agitation is required to prevent sedimentation of the soil slurry. An underwater stirrer or ultrasonic stirring may be used in combination with the blower 8, and by strengthening the underwater stirring, the frequency of contact of the contaminants with the soil and gas-solid contact increases, and the decomposition rate of the contaminants increases. The ultrasonic frequency varies depending on the type of the pollutant, but is preferably about 20 to 200 kHz.
[0068]
In order to promote the decomposition of pollutants in the soil slurry reaction tank 9, the oxidation-reduction potential (ORP) of the soil slurry reaction tank 9 is maintained at 0 mV or more (based on a silver / silver chloride composite electrode, the same applies hereinafter). It is desirable to control the rotation speed of the blower 8 and / or the stirrer and supply air. Since the decomposition reaction of pollutants is promoted in an aerobic atmosphere, maintaining dissolved oxygen is absolutely necessary for promoting the reaction, and the ORP value is preferably 0 mV or more. The upper limit of the ORP value is not particularly limited, but is preferably less than +200 mV.
[0069]
The pH of the soil slurry reaction tank 9 is desirably maintained at 6.0 or more and less than 9.0 suitable for the growth of microorganisms. It is known that the higher the pH, the better, considering only the cleaning effect of the oil from soil particles. However, when the pH is 9.0 or higher, the activity of the microorganisms rapidly decreases even if the cleaning effect of the oil increases. Therefore, the pH needs to be less than 9.0. When the pH is less than 6.0, the washing effect is small, and the activity of the microorganism is also deteriorated. Therefore, the pH is desirably 6.0 or more.
[0070]
As described above, the pH of the slurry reaction tank 9 should be determined from both the cleaning promotion effect and the decomposition promotion effect by microorganisms. More preferably, the pH is 7.0 or more and less than 9.0. The pH adjuster may be adjusted using an aqueous solution of dilute sulfuric acid or sodium hydroxide. A slurry using seawater has an advantage that the chemical buffer can be reduced since it has a pH buffering action.
[0071]
Further, when cyanide is present in the contaminated soil, an iron-based flocculant 4 is added to the slurry reaction tank 9 and iron cyanide complex salt (in the case of divalent iron ion, ferrocyan ([Fe (CN) ₆ ] ^4- ) In the case of trivalent iron ions, ferricyan ([Fe (CN) ₆ ] ^3- )) To form a cyanide ion (CN ⁻ ) Is extremely important. In the case where the slurry adjusting tank 3 is provided before the soil slurry reaction tank 9, the iron-based flocculant 4 may be introduced into the slurry adjusting tank 3.
[0072]
As the iron-based flocculant used in the present invention, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, ferric polysulfate and the like are preferable. The amount of the iron-based coagulant depends on the concentration of cyan ions, but it is usually sufficient to add the iron to cyan in a molar ratio of 2 times or more and less than 3 times. The toxicity of cyanide ion is weakened by the stable chelate bond between cyanide and iron. If the contaminated soil contains a considerable amount of iron, it may not be necessary to add an iron-based flocculant because the iron cyanide complex has already been formed. Some microorganisms in contaminated soil can be decomposed as long as they are ferrocyan or ferricyan. ₄ -N as a nitrogen source, HCOO ⁻ Can be grown as a source of organic carbon. In this case as well, the pH is desirably 6.0 or more and less than 9.0. Particularly, in an acidic region where the pH is less than 6.0, cyanide gas may be generated, which is extremely dangerous. If it is greater than 0.0, the activity of cyanolytic bacteria will be reduced. The activated water sludge generated from the coke plant of the steel mill contains a large amount of cyanolytic bacteria, and may be added.
[0073]
Next, the processing in the step of carrying out the soil slurry in the process of the present invention will be described.
[0074]
When the contaminated soil contains a large amount of clay or silt, solid-liquid separation in the slurry becomes difficult. In such a case, it is desirable to apply the soil slurry directly to the dehydrator 12 without performing solid-liquid separation in the soil slurry reaction tank. That is, the step of separating the soil slurry into the soil and the supernatant is omitted in the soil slurry reaction tank.
[0075]
On the other hand, if the contaminated soil is mainly rek, sedimentation is excellent, so if solid-liquid separation is performed, sedimentation can be easily separated into soil and supernatant, and the sedimented soil can be re-used without being dewatered. May be available. When the water content of the settled soil is high, the settled soil may be further subjected to a dehydrator 12 to reduce the water content of the soil, and then the soil may be reused. Depending on the capacity difference between the soil slurry reaction tank 9 and the dehydrator 12, it may be necessary to provide a relay tank, which may be considered in the overall treatment plan. The soil thus treated is usually backfilled.
[0076]
The dehydrator 12 can be a conventional type, for example, a filter press type dehydrator.
[0077]
Lastly, a method of treating the supernatant 13 generated from the soil slurry reaction tank 9 or the desorbed liquid 14 generated from the dehydrator 12 in the process of the present invention will be described.
[0078]
The soil slurry treated with the microorganism is applied to the dehydrator 12 as described above, and a desorbed liquid 14 is generated. The settling operation in the soil slurry reaction tank 9 may generate the supernatant 13. The desorbed liquid 14 and the supernatant 13 contain undecomposed oil and finely crushed soil particles, and may have high COD (chemical oxygen demand) and BOD (biochemical oxygen demand). However, since it is costly to newly provide a biological wastewater treatment facility such as activated sludge, it is preferable to promote the decomposition of COD and BOD components in water in the slurry reaction tank 9 as much as possible. However, when COD components that are hardly biodegradable remain and the wastewater standards cannot be observed, oxidative decomposition treatment may be performed using ozone, hydrogen peroxide, ultraviolet light, a photocatalyst, or the like. The treatment generates a large amount of OH radicals and can promote the decomposition of the hardly decomposable COD component. Further, the activated carbon adsorption device may be installed at a stage subsequent to the oxidative decomposition treatment equipment.
[0079]
The final treated water generated by the above operation is reused or discharged as makeup water in the soil slurry reaction tank 9.
[0080]
【Example】
Hereinafter, examples of the present invention will be described. Note that the present invention is not limited to the present embodiment.
(Example)
The soil contaminated with polycyclic aromatic hydrocarbons (PAHs) such as naphthalene and phenanthrene, which are the main components of oil, benzene, and coal tar, and cyanide (highly contaminated soil), and the former Soil contaminated at a lower concentration (low-contamination soil system) was used. Table 2 shows the oil concentration of the contaminated soil used in the examples. Table 3 shows the PAHs concentration of the highly contaminated soil used in the examples.
[0081]
As shown in Table 2, the high-contamination soil contained about 12,000 mg / kg-dry mass of oil (measured by normal hexane to Soxhlet extraction weight method), and the low-contamination soil contained about 1600 mg / kg-dry mass of oil.
[0082]
Further, as shown in Table 3, Total-PAHs (T-PAHs), which is the sum of 16 types of PAHs such as naphthalene and phenanthrene, was also 138 mg / kg-dry mass (solvent extraction-GCMS (gas chromatograph) in the highly contaminated area. Mass spectrometry) method. In addition, benzene and cyan were also detected in the dissolution test at about 1-2 mg / L and about 0.1-0.2 mg / L, respectively, which exceeded the soil environmental standards.
[0083]
The operation procedure will be described with reference to FIG.
[0084]
First, in the slurry reaction tank 3, mixed water 2 (seawater: freshwater = 1: 1 (volume ratio)) of seawater and freshwater having a volume of 1 times the soil volume is added to the contaminated soil 1, and the mixture is stirred by a stirrer. It has become. The mixing ratio of the mixed water 2 is such that the concentration of sulfate ions in the contaminated soil pore water is about 1200 mg / L, which is significantly higher than fresh water (about 10 to 20 mg / L) such as rivers, and seawater (2300 mg / L). Since L) showed a value close to 50%, such a mixing ratio was used. Since the water content of the contaminated soil is 30% by mass, the ratio of the soil (dry mass) in the slurry is 35% by mass.
[0085]
To the soil slurry, as the iron-based coagulant 4, 0.05 mM ferrous chloride was added as iron, and cyanic ions in the soil were changed to ferricyan to remove the microbial inhibitory effect of cyanide.
[0086]
Next, the soil slurry was transferred to the soil slurry reaction tank 9. The hydraulic residence time (HRT) of the soil slurry reaction tank 9 was 40 days, and the pollutant removal rate of the slurry reaction tank 9 was evaluated as appropriate. An ORP sensor 7 and a blower 8 are installed in the reaction tank 9, and the blower is set so that the oxidation-reduction potential (ORP) of the reaction tank 9 (based on a silver / silver chloride composite electrode, the same applies hereinafter) is maintained at 0 mV or more and less than +100 mV. The number of rotations of 8 was controlled to control the amount of air aeration. In order to prevent the accumulation of soil slurry when the air flow was temporarily stopped, an underwater stirrer was installed in the slurry reaction tank 9 to constantly stir. The pH of the reaction tank 9 was maintained at 7.0 or more to less than 9.0 using an aqueous solution of sodium hydroxide and an aqueous solution of sulfuric acid, and phosphorus and nitrogen were not particularly added.
[0087]
Table 2 shows the oil removal rate of the soil slurry in the slurry reaction tank 9 for a retention time of 7 to 40 days. The initial oil concentration of the highly contaminated system was 12000 mg / kg, but decreased as the residence time increased. After 20 days, 2200 mg / kg-dry mass (removal rate 83%) and after 30 days 450 mg / kg-dry mass (Removal rate: 96%), and after 40 days, it was reduced to 200 mg / kg-dry mass (removal rate: 98%), and the off-flavor was almost completely eliminated from the soil. A similar tendency was observed in the low-concentration contaminated system, and the initial oil concentration was 1600 mg / kg-dry mass, but 200 mg / kg-dry mass (removal rate 88%) after 20 days, and 100 mg / kg after 40 days. kg-dry mass (removal rate 94%).
[0088]
[Table 2]

[0089]
Table 3 shows the PAHs concentration after a residence time of the soil slurry of 40 days. T-PAHs were removed from 138 mg / kg-dry mass to 15 mg / kg-dry mass. Bicyclic and tricyclic compounds were almost completely removed from the PAHs, but the tetracyclic compounds fluoratin and pyrene tended to remain.
[0090]
[Table 3]

[0091]
Furthermore, the concentration of benzene eluted from the soil was 1.3 mg / L at first, but was already lower than the soil standard of 0.01 mg / L by the measurement 2 days later. The concentration of cyanide eluted from the soil was already below the detection limit by the measurement two days later.
[0092]
Since the contaminated soil has a large amount of clay and silt components and is difficult to settle and separate, the soil slurry discharged from the soil slurry reaction tank 9 was directly passed through the centrifugal dewatering machine 12, dewatered, and then backfilled.
[0093]
Since the sedimentation operation in the soil slurry reaction tank 9 was not performed, the supernatant 13 in FIG. 2 was not generated in this example.
[0094]
The desorbed liquid generated from the dehydrator 12 had a COD of about 40 mg / L and a BOD of 20 mg / L or less, and purification was considerably advanced. However, COD was treated to a wastewater standard (20 mg / L) or less by a water treatment operation. I needed to. Then, the ozone oxidation apparatus 20 was installed to promote the decomposition of the hardly decomposable COD component, and as a result, the COD of the final treated water could be reduced to 20 mg / L or less.
[0095]
As described above, by using the batch-type slurry method, it becomes possible to significantly reduce the number of facilities and obtain the same processing performance as compared with the conventional method.
[0096]
【The invention's effect】
According to the present invention, even in a small-scale contaminated area, oil, aromatic hydrocarbons, soil containing contaminants such as cyanide can be purified using microorganisms, and it is easy, simple, and efficient. It is possible to remove contaminants at a high removal rate at a low cost.
[Brief description of the drawings]
FIG. 1 is a conventional process flow for removing oil, aromatic compounds and cyanide in soil.
FIG. 2 is a process flow of the present invention for removing oil, aromatic compounds and cyanide in soil.
[Explanation of symbols]
1: Contaminated soil
2: Seawater and freshwater mixed water and / or final treated water
3 ... Slurry adjustment tank
4: Iron-based flocculant
5 ... pH sensor
6. Acid and / or alkali addition device
7 ORP sensor
8. Blower
9 ... Soil slurry reactor
10 ... Slurry storage tank
11 ... solid-liquid separation tank
12 ... dehydrator
13 ... Supernatant
14 Desorption liquid
15 ... treated soil
16 ... Activated sludge treatment tank
17… ORP sensor
18 ... Blower
19 ... Activated sludge
20 ... Ozone oxidation tank
21: Final treated water
22 ... Excess sludge

Claims (10)

A method of turning contaminated soil into a soil slurry to remove contaminants in the soil, comprising:
For the contaminated soil, a step of adding one or more solutions selected from activated sludge treated water of seawater and a low-temperature activated sludge generated from a coke plant, or a solution obtained by mixing fresh water with the solution to form a soil slurry,
While controlling the pH of the soil slurry to 6.0 or more and less than 9.0, the oxidation-reduction potential (based on a silver / silver chloride composite electrode) of the soil slurry is maintained at 0 mV or more and less than +200 mV according to the pH control value. As described above, by supplying oxygen to the soil slurry and stirring the soil slurry, the contaminants in the soil slurry are desorbed into water, and the contaminants are microbially decomposed.
Are sequentially performed in the same soil slurry reaction tank. A method of turning contaminated soil into a soil slurry to remove contaminants in the soil, comprising:
Slurry adjustment is performed by adding one or more solutions selected from activated sludge treated water from seawater and a coke plant to a contaminated soil, or a solution obtained by mixing fresh water with the solution to form a soil slurry. After performing the reaction in the tank, the oxidation-reduction potential (based on the silver / silver chloride composite electrode) of the soil slurry was adjusted to 0 mV according to the pH control value while controlling the pH of the soil slurry to 6.0 or more and less than 9.0. By providing oxygen supply and stirring of the soil slurry so as to be maintained at +200 mV or less, the process of desorbing contaminants in the soil slurry into water and decomposing the contaminants by microorganisms is performed by a soil slurry reaction. A method for purifying contaminated soil, which is performed in a tank. The contaminated soil according to claim 1 or 2, wherein the step of separating the soil slurry into soil and a supernatant liquid is performed in the same soil slurry reactor after the step of microbial decomposition of the contaminants. Purification method. The method for purifying contaminated soil according to any one of claims 1 to 3, wherein a dehydrator is provided at a stage subsequent to the soil slurry reaction tank, and the soil slurry is dehydrated by the dehydrator. The method for purifying contaminated soil according to any one of claims 1 to 4, wherein the soil slurry concentration is 10% by mass or more and less than 50% by mass. For the contaminated soil, in a step of adding one or more solutions selected from activated sludge treated water of seawater and aqua generated from a coke plant, or a solution obtained by mixing fresh water with the solution to form a soil slurry, The method for purifying contaminated soil according to any one of claims 1 to 5, wherein an iron-based coagulant is added to the soil slurry. One or two or more of ozone, ultraviolet light, hydrogen peroxide, a photocatalyst, and activated carbon are added to the supernatant generated from the soil slurry reaction tank and / or the wastewater generated by the dewatering treatment of the soil slurry by the dehydrator. The method for purifying contaminated soil according to any one of claims 1 to 6, wherein the used treatment is performed. The purification of the contaminated soil according to any one of claims 1 to 7, wherein the contaminants in the contaminated soil contain at least one of coal tar, gasoline, and oil derived from heavy oil. Method. The method according to claim 8, wherein the contaminants include cyan. The method for purifying contaminated soil according to claim 9, wherein the contaminants include a monocyclic aromatic hydrocarbon mainly composed of benzene and / or a polycyclic aromatic hydrocarbon mainly composed of naphthalene.

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