JP3748000B2 - Remediation method for oil-contaminated soil - Google Patents
Remediation method for oil-contaminated soil Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、石油系炭化水素等による油汚染土壌からの汚染油分の分離除去方法に関し、特に、バイオレメディエーションと土壌洗浄法との段階的な組合せによる汚染油分の分離除去方法に関する。
【0002】
【従来の技術】
石油系炭化水素等による油汚染土壌の代表的な修復方法としては、微生物による油分の分解を図る土壌修復法即ちバイオレメディエーションおよび水等との混合状態において疎水性油分の浮遊分離を図る土壌洗浄法があり、それぞれ幾つかの技術が提案されあるいは実施されている。
【0003】
例えば、油汚染土壌に油分解能を有する微生物を散布して、土壌粒子の表面に付着した油分を分解・除去する微生物による洗浄方法(特開平7−102298号公報)、また、油汚染土壌に対し硝酸アンモニウム等窒素源おびリン源の水溶液を添加混合して土壌中の微生物を活性化し、土壌中の石油等油分を分解させる石油汚染土壌の修復方法(特開平9−276831号公報)、油で汚染された砂を分級し、篩下分として大部分の油分を回収すると共に、篩上分について浮遊選別手段により油分を浮上分離させて回収する含油砂からの油の回収法(特公昭57−57070号公報)、難水溶性有機物等油分で汚染された土壌をスラリー状にし、酸化剤と共にアルカリ剤を加えた後、気泡を供給して油分を浮上分離させる土壌浄化法(特開平9−299924号公報)等が提案されている。また、土壌洗浄法とバイオレメディエーションを組み合わせた方法(特開平10−211486号公報)等も提案されている。
【0004】
【発明が解決しようとする課題】
しかしながら、バイオレメディエーションは、前記のように、汚染土壌中の微生物を活性化させ、また、高分解能を有する微生物を散布して菌数を増加させる等により、土壌中の油分を分解させる方法であって、低コスト且つ低エネルギー消費で、副生成物の恐れもなく二次処理が不要で、且つまた、常温常圧で実施できて操業上また安全上有利であり、現位置処理が比較的容易である等の多くの利点があるが、処理速度が遅く、油分の濃度や油分の組成(芳香族炭化水素や重質成分のアスファルテンあるいはレジン等については微生物分解が困難)によっては微生物による分解は困難であり、さらには、野外処理の場合、気温や降水等の影響を受けやすい等の問題があった。
【0005】
一方、石油系炭化水素等油分で汚染された土壌を水等との混合状態において気泡の吹き込み等により、油の疎水的性質を利用して浮遊泡沫と共に浮上分離させる土壌洗浄法に関しては、処理そのものは比較的、効率よく行われるが、土壌粗粒子の表面の凹凸に入り込んだ油分については分離が困難であって、結局、油分の分離回収は泡沫浮上分離装置で処理できる粒度の土壌粒子に付着した油分と土壌粒子表面から洗い落とされた油分に限られるという問題があった。
また、土壌洗浄法とバイオレメディエーションを組み合わせた特開平10−211486号公報に記載されている方法(気泡連行法)は、第一に難水溶性有機物を浮上分離させる工程と、第二に残存汚染物を含む沈砂をバイオレメディエーションで処理する工程の2工程からなる。
この方法は物理選別的な手法と微生物の洗浄能力を活用した手法の組み合わせであるが、土壌中油分の分離にアルカリ剤の添加を必要とする。そのため、アルカリ剤の使用によるコストの発生や、pH8以上で微生物の死滅の恐れがある、等の問題点がある。
【0006】
上記の問題に鑑み、本発明は、処理にあまり時間をかけることなく、土壌を汚染する油分の組成に係わらず、且つ、油分が高濃度の土壌であっても適用が可能で、また、土壌粒子の表面に強く吸着した油分、粗粒子の表面凹凸に入り込んだ油分についても分離除去が可能な石油等による汚染土壌の浄化方法の提供を目的とするものである。
【0007】
【課題を解決するための手段】
上記の目的を達成するために、本発明は、第1に、微生物を含む油汚染土壌に水を加えてスラリー化して分級し、分別された−2mmの粒度区分の土壌粒子に対してアトリッションを行い、気泡の吹き込みにより油分を分離する土壌洗浄処理を施した後、得られた洗浄土壌に栄養源を添加し、該栄養源の補給と酸素と水の供給により前記微生物を活性化して油分解を促進させるバイオレメディエーションを施すことを特徴とする、石油系油汚染土壌の修復方法を、第2に、前記油汚染土壌に前記土壌洗浄処理を施した後に前記バイオレメディエーションによる油分解処理を施し、次いで、得られた処理土壌に再度前記土壌洗浄処理を施すことを特徴とする、前記第1記載の石油系油汚染土壌の修復方法を、第3に、微生物を含む油汚染土壌に、栄養源の補給と酸素と水の供給を行い、前記微生物を活性化して油分解を促進させるバイオレメディエーションによる油分解処理を施した後、得られた処理土壌に水を加えてスラリー化して分級し、分別された−2mmの粒度区分の土壌粒子に対してアトリッションを行い、気泡の吹き込みにより油を分離する土壌洗浄処理を施すことを特徴とする、石油系油汚染土壌の修復方法を提供する。
【0008】
【発明の実施の形態】
石油系油汚染土壌に対して、初めに、前記の土壌洗浄処理を実施して、泡沫浮上分離手段により油分の70〜90%を泡沫と共に浮上分離させて回収する。洗浄処理後に土壌中に残存している油分については、さらに、バイオレメディエーション処理の一つであるバイオパイル処理を実施することにより微生物を利用した油分の分解処理を行った後、好ましくはさらに、再度洗浄処理を行うことによって、油汚染土壌の十分な清浄化が可能である。あるいはまた、比較的低濃度の油分で汚染された土壌に対しては、初めに、前記のバイオレメディエーションを施した後、前記の土壌洗浄処理を施すことによって土壌の修復化が可能である。
【0009】
本発明を処理工程の概要を示した図1によって説明する。
油汚染土壌にスラリー濃度(w/w)が10〜40%になるように水を加えて解砕し、洗浄を兼ねてスラリー化する。スラリー化処理の後、篩分装置により土壌を+2mm (2mm 径以上)、−2mm (2mm 径以下)の粒子区分に分級する(土壌洗浄工程)。
【0010】
分級後、−2mm 粒子区分の土壌についてアトリッションを行った後、泡沫浮上分離装置を使用し、気泡を吹き込んで浮上分離処理を実施し、油分を付着した浮物(フロス)即ち浮遊泡沫と沈物(シンク)即ち沈殿粒子とに分離する(浮上分離工程)。この浮上分離工程で、浮遊泡沫と共に除かれる油分は、通常、元土(油汚染土壌)に含まれていた油分の80%以上を占めており、油分が低濃度に低減した沈殿粒子が得られる。
【0011】
前記浮上分離工程で得られた沈殿粒子を、前記土壌洗浄工程の分級操作で区分された+2mm 粒子の土壌と混合し、脱水装置により含水率が20%程度になるまで脱水して洗浄土壌を得、処理水は排水する(脱水工程)。
【0012】
次にバイオレメディエーション処理の一つであるバイオパイル処理を施す。すなわち、前記脱水工程で水分を調整された洗浄土壌に対して、窒素およびリン酸またカリウム等の無機塩類による栄養塩水溶液とさらに通気性および保水性を改善するための副資材(例えば大鋸屑等)を適宜の水と共に混合する。ここで混合する栄養塩類は、洗浄土壌中の油分濃度に応じて窒素およびリン酸またカリウムの添加比率を変えて添加する。さらに洗浄土壌の性質によっては、土壌pHの安定や栄養塩類の流出防止等の目的で副資材として土質改良剤(例えばゼオライト等)を加えて混合する。このように、洗浄土壌に必要な添加物を加えて混合した混合土壌を用い、積み上げて山状堆積物(パイル)を造成すると共に、通気および散水を行うための塩化ビニル等樹脂製パイプを埋設してバイオパイルとする(バイオパイル造成工程)。
【0013】
前記バイオパイル中の土壌微生物は、供給された栄養塩を資化しながら、土壌中の油分を分解して土壌を修復する(バイオパイル処理工程)。通気は混合土壌間隙ガス中の酸素濃度を 6〜21%程度となるように制御管理する。パイル内温度は18〜24℃程度となるように管理する。混合土壌の水分は、通気により減少するので、適度に散水を行い、含水率(水分重量÷湿土壌重量×100%)を15〜20%程度になるように管理する。場合によっては水分の蒸発防止および保温のためにビニルシート等でパイル表面を覆う。また、バイオパイルの処理管理にあたっては、パイル中の酸素濃度測定結果から酸素消費速度を推定して栄養塩類の追加を適宜行う。無機栄養塩類の追加は水溶性の肥料等を用いて水に溶解させて散水時に供給することで容易に行うことができる。バイオパイル処理においてこれらの栄養塩を供給するためには徐放性の園芸用肥料などを併用することも好ましい手段である。
【0014】
なお、土壌は本来的にその土地に自生する油分分解能を有する微生物を含むので、バイオパイル処理においては、特に新たな微生物の供給を必要としないが、必要があれば、微生物含有土壌をバイオパイル造成工程において添加してもよい。
【0015】
このようなバイオパイル処理において、処理開始から2〜3か月間で酸素消費速度が遅くなり、微生物による油分分解活性が低下した兆候が現れる。油分組成にもよるが、この時点での油分濃度は元土の油分濃度に比べて約50%程度に低減する。3か月以上の運転により油分をさらに低減させることができる。
【0016】
以上のように、土壌洗浄法により高濃度の油分や微生物によって分解し難い油分を低減し、引き続くバイオパイル処理即ちバイオレメディエーションにより残存油分の分解処理を行うことにより実質的に油汚染土壌の修復が図れるが、特に、このバイオパイル処理において油分分解能を有する微生物は界面活性剤(バイオサーファクタント)を分泌し、この界面活性剤が土壌粒子の微細孔等に付着した油分を分離させるので、汚染油の組成等によりバイオパイルによる微生物分解処理を実施した後も未分解の油分または難分解性の油分が残存する場合について、さらに、再度、前記土壌洗浄法を繰り返すことにより、効率的に残存油分を分離除去させることが可能であり、土壌の十分な修復が図られる。
【0017】
この二次的な土壌洗浄法は、図2の工程図に示したように、前記バイオパイル処理に先立つ土壌洗浄法と同一である。
即ち、バイオパイル処理からの処理土壌をスラリー化して分級する二次土壌洗浄工程と、−2mm 粒子をアトリッションの後、浮上分離処理して沈殿粒子と含油浮上泡沫を得る二次浮上分離工程と、該二次浮上分離工程の沈殿粒子と前記二次土壌洗浄工程からの+2mm 粒子とを混合して脱水する脱水工程とからなる二次土壌洗浄法により修復土壌を得ることができる。
【0018】
なお、比較的に低濃度の石油系油汚染土壌に対しては、土壌洗浄工程を経ることなく、対象となる石油系油汚染土壌から、石や植物残渣などの異物を取り除いてバイオパイルを造成し、このバイオパイルによる生物分解処理を実施した後、残存している未分解の油分または難分解性の油分について、土壌洗浄処理を実施して泡沫浮上により残存油分を分離除去することも可能である。この場合、前記のように、バイオパイル処理において微生物による界面活性剤が有利に活用できる利点がある。また、このような土壌の場合、ランドファーミングなどのより自然条件に近い状況でのバイオレメディエーションが適用可能である。
【0019】
【実施例】
〔実施例1〕
油分濃度40,000mg/kg の土壌をスラリー濃度(w/w) で20%となるように、水でリパルプして分級し、+2mm 、−2mm の土壌粒子に分別した(土壌洗浄工程)。−2mm の粒度区分の土壌粒子に対してアトリッションを行い、沈殿粒子と油分の付着した微細な浮遊粒子を含んだ液層に分かれるようにし、この浮遊粒子を続く泡沫浮上分離装置により、油分と共に浮遊泡沫(フロス)として分離・除去した(浮上分離工程)。次いで、泡沫浮上分離装置で分離された沈殿粒子に前記+2mm 粒子を合わせて脱水し、油分濃度10,000mg/kg の洗浄土壌を得た(脱水工程)。
【0020】
さらに、得られた洗浄土壌に栄養塩類(油分:窒素:燐=100 :22:5 )を徐放性添加剤の形態で添加し、また、保水および通気改良材として大鋸屑を土壌乾重量に対して10%、そして、土質改良材としてゼオライトを 2%となるように加えて混合した。この混合土壌を用いて、3 〜 6 m3のバイオパイルを造成した(バイオパイル造成工程)。バイオパイルの散水および通気用のパイプをパイル内のガス中酸素濃度をモニタリングし、酸素消費速度が200mg O2 /kg-soil/min以上となるよう通気流量の調整ならびに水溶性栄養塩類の添加を行った(バイオパイル処理)。約2か月間のバイオパイル処理後、パイル土壌の油分濃度は、3,000mg/kgとなった。
【0021】
〔実施例2〕
実施例1のバイオパイル処理土壌を再度土壌洗浄法により処理した。即ち、油分濃度3,000mg/kgのバイオパイル処理土壌を水でリパルプしてスラリー濃度20%(w/w)のスラリーとし、アトリッション後、二次浮上分離工程に供し、泡沫浮上分離した結果、含油浮上泡沫によって油分の分離がさらに進み、脱水後、油分濃度1,500mg/kgの修復土壌を得ることができた。
【0022】
〔実施例3〕
油分濃度25,000mg/kg の汚染土壌を篩い分けして石や植物残渣等の異物を除去し、副資材として大鋸屑を乾土重量当たり10%となるように添加した。また、栄養塩として油分:窒素:リン= 1,000:11.5:5 となるように徐放性の固形肥料を加えて混合した。前記の実施例1の場合と同様に、通気および散水性の塩化ビニル製パイプを埋設したパイルを造成した。パイルは温室内に設置し、気温を18〜24℃に管理して処理を実施した。通気流量は、パイル内の酸素濃度が 5〜15%(酸素消費速度 500〜200mg O2 /kg-soil/min. )となるように制御した。処理実施中は、パイルをビニルシートで覆った状態で運転し、パイル土壌の含水率を18%程度に保つことができた。約3か月間の運転期間中に栄養塩の補給を1回実施した(水溶性リン酸塩の供給)。土壌の油分濃度は30日目で約17,000mg/kg へ、60日目で約14,000mg/kg へと減少し、3か月間の処理後には12,000mg/kg まで減少した。このバイオパイル処理土壌を用いて土壌洗浄法による残存油分の分離・除去を実施した。バイオパイル処理土壌は、パルプ濃度 17 %で解砕して、泡沫浮上分離装置で処理した。
【0023】
得られた結果を表1に示した。浮物(フロス)は全土壌の重量分布で13.8%であり、油分濃度85,300mg/kg にまで濃縮されて回収された。残土壌(重量分布86.2%)は、油分濃度1,066mg/kgとなり、低濃度の洗浄土壌として回収された。
【0024】
【表1】
【0025】
【発明の効果】
以上のように、本発明によれば、バイオレメディエーション処理において、微生物は、油分を分解させると共に、油分の分解過程で界面活性剤(バイオサーファクタント)を生成し、土壌粒子の微細孔に付着した難分解性の油分を遊離させる等有効に作用するので、高濃度の油分や微生物に難分解性の油分を効率的に分離できるが、油分の付着条件に左右されることの多い土壌洗浄法と併用することにより、汚染油の濃度や組成に係わらず相乗的な油分の分離効果が得られるものである。
【0026】
即ち、土壌洗浄処理の後バイオレメディエーションによる油分解処理を行うことにより、高濃度の汚染油についても洗浄処理で効率的に除去し、その洗浄土壌に付着残存する油分をバイオレメディエーションにより効果的に除去分離する油汚染土壌の修復方法を提供できるという効果を奏する。また、前記のように土壌洗浄後バイオレメディエーション処理し、引き続き再土壌洗浄を施すことにより、油分の濃度および組成に係わらず、さらに効率的に且つ十分に油分の分離除去を可能とする油汚染土壌の修復方法を提供できるという効果を奏する。比較的に低濃度の油汚染土壌に対しては、バイオレメディエーション処理の後、土壌洗浄を施すことにより、効率的に従って経済的に油分の分離除去が可能になる油汚染土壌の修復方法の提供が可能になるという効果を奏する。
【図面の簡単な説明】
【図1】本発明の油汚染土壌の修復方法を示す工程図である。
【図2】図1の修復方法に連続する再土壌洗浄法を示す工程図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for separating and removing contaminated oil from oil-contaminated soil by petroleum hydrocarbons, and more particularly to a method for separating and removing contaminated oil by a stepwise combination of bioremediation and soil washing.
[0002]
[Prior art]
Typical methods for remediation of oil-contaminated soil with petroleum hydrocarbons include soil remediation methods that attempt to break down oil by microorganisms, that is, bioremediation and soil washing methods that perform floating separation of hydrophobic oils in a mixed state with water, etc. There are several technologies proposed or implemented.
[0003]
For example, a microorganism washing method (Japanese Patent Laid-Open No. 7-102298) that disperses oil-degrading microorganisms on oil-contaminated soil and decomposes / removes the oil adhering to the surface of the soil particles. A method for repairing oil-contaminated soil (JP 9-276831 A), which activates microorganisms in the soil by adding an aqueous solution of nitrogen and phosphorus sources such as ammonium nitrate to activate the microorganisms in the soil and decomposes oil and other oils in the soil. The collected sand is classified, and most of the oil is recovered as the under-sieving portion, and the oil is recovered from the oil-containing sand by separating the oil from the floating portion by floating selection means (Japanese Patent Publication No. 57-57070). No.), a soil purification method in which soil contaminated with oil such as poorly water-soluble organic matter is made into a slurry, an alkali agent is added together with an oxidizing agent, and then bubbles are supplied to float and separate the oil. -299924 JP) have been proposed. In addition, a method combining a soil washing method and bioremediation (Japanese Patent Laid-Open No. 10-21486) has been proposed.
[0004]
[Problems to be solved by the invention]
However, as described above, bioremediation is a method of degrading oil in soil by activating microorganisms in contaminated soil or increasing the number of bacteria by spraying high-resolution microorganisms. Low cost, low energy consumption, no risk of by-products, no secondary treatment is required, and it can be carried out at room temperature and normal pressure. However, depending on the oil concentration and oil composition (aromatic hydrocarbons and heavy components such as asphaltenes and resins are difficult to microbially decompose), microbial degradation may not be possible. Furthermore, in the case of outdoor treatment, there are problems such as being easily affected by temperature and precipitation.
[0005]
On the other hand, regarding the soil cleaning method, where soil contaminated with oil such as petroleum hydrocarbons is floated and separated together with floating foam using the hydrophobic properties of oil by blowing bubbles in a mixed state with water etc., the treatment itself Is relatively efficient, but it is difficult to separate the oil that has entered the surface irregularities of the coarse soil particles, and eventually the oil separation and recovery adheres to the soil particles of a particle size that can be processed by the foam flotation device. There was a problem that it was limited to the oil that was washed off from the soil and the surface of the soil particles.
In addition, the method (bubble entrainment method) described in Japanese Patent Application Laid-Open No. 10-212486, which combines the soil washing method and bioremediation, includes firstly a step of levitating and separating a hardly water-soluble organic substance, and secondly residual contamination. It consists of two steps, a process of treating sediment containing sand with bioremediation.
This method is a combination of a physical sorting method and a method utilizing the ability of washing microorganisms, but it requires the addition of an alkaline agent to separate the oil in the soil. Therefore, there are problems such as generation of cost due to the use of an alkaline agent, and risk of killing microorganisms at pH 8 or higher.
[0006]
In view of the above problems, the present invention can be applied to a soil having a high concentration of oil, regardless of the composition of the oil that contaminates the soil, without taking much time for the treatment. An object of the present invention is to provide a method for purifying contaminated soil with petroleum or the like that can separate and remove oil that is strongly adsorbed on the surface of particles and oil that has entered the surface irregularities of coarse particles.
[0007]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, first, the present invention first adds water to an oil-contaminated soil containing microorganisms to form a slurry by slurrying and classifying the classified soil particles having a particle size of -2 mm. performed, after performing soil washing process for separating the oil by blowing of air bubbles, the nutrients added to the cleaning soil obtained, by activating the microorganisms by supplying replenishing the oxygen and water of the nutrient source oil breakdown A method for repairing petroleum-based oil-contaminated soil, characterized in that bioremediation is performed to promote oil, and secondly, after subjecting the oil-contaminated soil to the soil washing treatment, subjecting the oil-resolving treatment to the bioremediation, Next, the method for repairing petroleum-based oil-contaminated soil according to the first aspect is characterized in that the obtained soil is again subjected to the soil washing treatment. Third, the oil-contaminated soil containing microorganisms Performs the supply of replenishing oxygen and water nutrients, the microorganism to activate the after performing oil degradation process by bioremediation that promote oil degradation, the treated soil obtained by adding water classification Mr slurried The present invention provides a method for repairing petroleum-based oil-contaminated soil, characterized in that attrition is performed on the sorted soil particles having a particle size classification of -2 mm, and soil washing treatment is performed to separate oil by blowing bubbles.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
First, the soil washing treatment is performed on the petroleum-based oil-contaminated soil, and 70 to 90% of the oil content is floated and separated together with the foam by the foam floating separation means and recovered. For the oil remaining in the soil after the washing treatment, further, after performing the oil decomposition treatment using microorganisms by carrying out a biopile treatment, which is one of the bioremediation treatments, preferably again, By performing the washing treatment, the oil-contaminated soil can be sufficiently cleaned. Alternatively, for soil contaminated with a relatively low concentration of oil, the soil can be repaired by first performing the bioremediation and then performing the soil washing treatment.
[0009]
The present invention will be described with reference to FIG.
Water is added to the oil-contaminated soil so that the slurry concentration (w / w) becomes 10 to 40%, and the mixture is crushed and slurried. After slurrying, the soil is classified into + 2mm (2mm diameter or more) and -2mm (2mm diameter or less) particle classification using a sieving machine (soil washing process).
[0010]
After classification, after attributing to the soil of -2mm particle class, using a foam floating separator, blowing up bubbles and carrying out the floating separation process, the floating substance (floss) with oil attached, that is, floating foam and sediment (Sink), that is, separated into precipitated particles (floating separation step). In this floating separation process, the oil removed together with the floating foam usually occupies 80% or more of the oil contained in the base soil (oil-contaminated soil), and precipitated particles with a reduced oil content can be obtained. .
[0011]
The precipitated particles obtained in the floating separation step are mixed with +2 mm particle soil classified by the classification operation in the soil washing step, and dewatered by a dehydrator until the water content becomes about 20% to obtain washed soil. The treated water is drained (dehydration process).
[0012]
Next, the biopile process which is one of the bioremediation processes is performed. That is, with respect to the washed soil whose moisture has been adjusted in the dehydration step, an aqueous nutrient salt solution containing inorganic salts such as nitrogen, phosphoric acid and potassium, and auxiliary materials for further improving air permeability and water retention (for example, large sawdust) Is mixed with appropriate water. The nutrient salts to be mixed here are added by changing the addition ratio of nitrogen, phosphoric acid or potassium according to the oil concentration in the washed soil. Furthermore, depending on the properties of the washed soil, a soil condition improver (for example, zeolite) is added and mixed as an auxiliary material for the purpose of stabilizing soil pH and preventing the outflow of nutrients. In this way, using the mixed soil mixed with the necessary additives to the washed soil, pile up to form mountain piles (pile), and bury resin pipes such as vinyl chloride for aeration and watering To make a biopile (biopile creation process).
[0013]
The soil microorganisms in the biopile repair the soil by decomposing oil in the soil while assimilating the supplied nutrients (biopile treatment step). Aeration is controlled and controlled so that the oxygen concentration in the mixed soil interstitial gas is about 6 to 21%. The pile temperature is controlled to be about 18-24 ° C. Since the water content of the mixed soil decreases due to aeration, the water content (water weight / wet soil weight × 100%) is controlled so as to be about 15 to 20%. In some cases, the pile surface is covered with a vinyl sheet or the like in order to prevent moisture evaporation and keep warm. In biopile treatment management, the oxygen consumption rate is estimated from the oxygen concentration measurement results in the pile, and nutrients are added as appropriate. The addition of inorganic nutrient salts can be easily performed by dissolving in water using a water-soluble fertilizer or the like and supplying it during watering. In order to supply these nutrient salts in the biopile treatment, it is also preferable to use a combination of sustained-release horticultural fertilizers and the like.
[0014]
In addition, since soil inherently contains microorganisms with oil-degrading ability that naturally grow on the land, biopile treatment does not require the supply of new microorganisms. You may add in a creation process.
[0015]
In such a biopile process, the oxygen consumption rate becomes slow in 2 to 3 months from the start of the process, and there is an indication that the oil decomposition activity by microorganisms has decreased. Although depending on the oil composition, the oil concentration at this point is reduced to about 50% compared to the oil concentration of the main soil. The oil content can be further reduced by operation for 3 months or more.
[0016]
As described above, the soil washing method reduces oil content that is difficult to decompose by high-concentration oil and microorganisms, and the residual oil content is decomposed by subsequent biopile treatment, that is, bioremediation, so that oil-contaminated soil can be substantially restored. In particular, microorganisms with oil-degrading ability in this biopile treatment secrete surfactants (biosurfactants), and this surfactant separates oils adhering to the micropores of soil particles. When undegraded oil or persistent oil remains after biodegradation by biopile depending on the composition, etc., the remaining oil is efficiently separated by repeating the soil washing method again. It can be removed, and sufficient restoration of the soil is achieved.
[0017]
This secondary soil cleaning method is the same as the soil cleaning method prior to the biopile treatment, as shown in the process diagram of FIG.
That is, a secondary soil washing step in which the treated soil from the biopile treatment is slurried and classified, a secondary floating separation step in which −2 mm particles are subjected to floating separation treatment after attrition, to obtain precipitated particles and oil-impregnated floating foam, The repaired soil can be obtained by a secondary soil washing method comprising a dewatering step of mixing and dewatering the precipitated particles of the secondary flotation separation step and +2 mm particles from the secondary soil washing step.
[0018]
For relatively low-concentration petroleum-based oil-contaminated soil, a biopile is created by removing foreign substances such as stones and plant residues from the target oil-based oil-contaminated soil without going through a soil washing process. However, after the biodegradation treatment with this biopile, the remaining undegraded oil or the hardly degradable oil can be subjected to soil washing treatment to separate and remove the remaining oil by foam floating. is there. In this case, as described above, there is an advantage that the surfactant by the microorganism can be advantageously used in the biopile treatment. In addition, in the case of such soil, bioremediation under conditions closer to natural conditions such as land farming can be applied.
[0019]
【Example】
[Example 1]
The soil with an oil concentration of 40,000 mg / kg was repulped with water so as to have a slurry concentration (w / w) of 20%, and classified into +2 mm and −2 mm soil particles (soil washing step). -Attribution to soil particles with a particle size of -2mm is divided into a liquid layer containing fine suspended particles with precipitated particles and oil, and these suspended particles are floated along with the oil by a subsequent foam floating separator. Separated and removed as foam (floss) (floating separation step). Next, the +2 mm particles were combined with the precipitated particles separated by the foam floating separator, and dehydrated to obtain washed soil having an oil concentration of 10,000 mg / kg (dehydration step).
[0020]
Furthermore, nutrient salts (oil: nitrogen: phosphorus = 100: 22: 5) are added to the obtained washed soil in the form of sustained release additives, and large sawdust is added to the dry weight of the soil as a water retention and ventilation improver. 10% and, as a soil conditioner, 2% zeolite was added and mixed. Using this mixed soil, a biopile of 3 to 6 m 3 was created (biopile creation process). Sprinkle and vent pipes for biopile, monitor oxygen concentration in the gas in the pile, adjust the aeration flow rate and add water-soluble nutrients so that the oxygen consumption rate is 200 mg O 2 / kg-soil / min or more Performed (biopile treatment). After about 2 months of biopile treatment, the oil concentration in the pile soil was 3,000 mg / kg.
[0021]
[Example 2]
The biopile-treated soil of Example 1 was treated again by the soil washing method. That is, biopile-treated soil with an oil concentration of 3,000 mg / kg is repulped with water to form a slurry with a slurry concentration of 20% (w / w). After attrition, the slurry is subjected to a secondary levitation separation process, resulting in foam levitation separation. Oil separation further progressed by floating foam, and after dehydration, it was possible to obtain repaired soil with an oil concentration of 1,500 mg / kg.
[0022]
Example 3
The contaminated soil with an oil concentration of 25,000 mg / kg was sieved to remove foreign substances such as stones and plant residues, and large sawdust was added as a secondary material to 10% per dry soil weight. Further, as a nutrient salt, a sustained-release solid fertilizer was added and mixed so that oil content: nitrogen: phosphorus = 1,000: 11.5: 5. As in the case of Example 1 above, a pile in which a ventilated and water-dispersed vinyl chloride pipe was embedded was created. The pile was installed in a greenhouse and the temperature was controlled at 18-24 ° C. for processing. The aeration flow rate was controlled so that the oxygen concentration in the pile would be 5-15% (oxygen consumption rate 500-200 mg O2 / kg-soil / min.). During the treatment, the pile was covered with a vinyl sheet, and the moisture content of the pile soil was kept at about 18%. Nutrient supplementation was carried out once during the operation period of about 3 months (supply of water-soluble phosphate). The oil concentration in the soil decreased to about 17,000 mg / kg on the 30th day, to about 14,000 mg / kg on the 60th day, and decreased to 12,000 mg / kg after 3 months of treatment. Using this biopile treated soil, the residual oil was separated and removed by the soil washing method. The biopile-treated soil was crushed at a pulp concentration of 17% and treated with a foam floating separator.
[0023]
The obtained results are shown in Table 1. The float (floss) was 13.8% in the weight distribution of the whole soil, and it was recovered after being concentrated to an oil concentration of 85,300 mg / kg. The residual soil (weight distribution: 86.2%) had an oil concentration of 1,066 mg / kg and was recovered as low-concentration washed soil.
[0024]
[Table 1]
[0025]
【The invention's effect】
As described above, according to the present invention, in the bioremediation treatment, microorganisms decompose oil and produce a surfactant (biosurfactant) during the oil decomposition process, which is difficult to adhere to the micropores of soil particles. Since it works effectively, such as liberating degradable oil, it can efficiently separate high-concentration oil and difficult-to-decompose oil from microorganisms. By doing so, a synergistic oil separation effect can be obtained regardless of the concentration and composition of the contaminated oil.
[0026]
In other words, by performing oil decomposition treatment by bioremediation after soil washing treatment, highly concentrated contaminated oil is efficiently removed by washing treatment, and oil remaining on the washed soil is effectively removed by bioremediation. There exists an effect that the repair method of the oil-contaminated soil to isolate | separate can be provided. In addition, oil-contaminated soil that can be separated and removed more efficiently and sufficiently regardless of the concentration and composition of the oil, by performing bioremediation treatment after soil washing as described above, followed by re-soil washing. There is an effect that a repair method can be provided. For relatively low-concentration oil-contaminated soil, by providing soil washing after bioremediation treatment, it is possible to provide a method for repairing oil-contaminated soil that enables efficient and economical separation and removal of oil. There is an effect that it becomes possible.
[Brief description of the drawings]
FIG. 1 is a process diagram illustrating a method for repairing oil-contaminated soil according to the present invention.
FIG. 2 is a process diagram showing a re-soil washing method continued from the repair method of FIG. 1;
Claims (3)
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JP34742798A JP3748000B2 (en) | 1998-12-07 | 1998-12-07 | Remediation method for oil-contaminated soil |
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JP4852717B2 (en) * | 2001-09-28 | 2012-01-11 | Dowaエコシステム株式会社 | Purification method for contaminated soil |
JP4640673B2 (en) * | 2005-10-06 | 2011-03-02 | 清水建設株式会社 | Purification method for highly concentrated oil-contaminated soil |
CN106906810B (en) * | 2017-02-27 | 2019-08-30 | 中国石油大学(华东) | A kind of removing treatment process of marine oil spill |
JP6439072B1 (en) * | 2018-10-01 | 2018-12-19 | 株式会社*** | Excavation method for contaminated soil layer |
CN114939596A (en) * | 2022-04-20 | 2022-08-26 | 中国石油化工股份有限公司 | Method for determining relationship between crude oil content of crude oil contaminated soil and particle size of soil aggregate and grading pretreatment method for crude oil contaminated soil |
CN116213448B (en) | 2022-07-19 | 2024-05-28 | 成都理工大学 | Soil groundwater evaluation method for repairing hydrocarbon pollution |
CN115228919B (en) * | 2022-08-12 | 2023-05-09 | 中铁三局集团有限公司 | Green restoration method for organic contaminated soil |
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