JP3880712B2 - Treatment method of dredged mud - Google Patents
Treatment method of dredged mud Download PDFInfo
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- JP3880712B2 JP3880712B2 JP32073497A JP32073497A JP3880712B2 JP 3880712 B2 JP3880712 B2 JP 3880712B2 JP 32073497 A JP32073497 A JP 32073497A JP 32073497 A JP32073497 A JP 32073497A JP 3880712 B2 JP3880712 B2 JP 3880712B2
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- Prior art keywords
- mud
- dredged
- added
- oxidation
- bottom mud
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Description
【0001】
【発明の属する技術分野】
本発明は、湖沼、河川、ダム、港湾等の浚渫工事の際に発生する底泥の処理方法に関する。
【0002】
【従来の技術】
湖沼、河川、ダム、港湾等の浚渫工事の際に発生する底泥のうち、含水比が150%を超える高含水底泥を脱水処理するにあたっては、無薬注、高圧フィルタープレスによる方法、はじめに無機凝集剤またはカチオン系高分子凝集剤を加え、次にノニオンまたはアニオン系の高分子凝集剤を加えてフロックをつくり、機械脱水する方法、はじめにノニオンまたはアニオン系の高分子凝集剤を加え、次に無機凝集剤またはカチオン系高分子凝集剤を加えてフロックをつくり、機械脱水する方法などが知られている。
【0003】
このうち、はじめにノニオンまたはアニオン系の高分子凝集剤を加え、次に無機凝集剤またはカチオン系高分子凝集剤を加えてフロックをつくり機械脱水する方法は、作られたフロックの強度が大きいことから脱水機に対する適応性が高く、有望な処理方法として着目されている。しかし、無機凝集剤とカチオン系高分子凝集剤を比較した場合、カチオン系高分子凝集剤の魚毒性が非常に高いことから、安全性の高い無機凝集剤を使う方が望ましいと考えられる。
【0004】
しかし、この場合に用いられる無機凝集剤は、ポリ塩化アルミニウム、硫酸アルミニウムなどの酸性物質であり、所要量の無機塩を加えると、底泥のpHにかかわらず脱水後の分離液のpHが7.0以下になる。pHが7.0以下になると浚渫底泥の中に含まれる鉄の水に溶けだす割合が増加し、結局、それが分離水に入って放流されるから、二次汚染問題としてクローズアップされることになる。
【0005】
数字をあげて説明する。浚渫底泥は一般に還元状態にあり、鉄は二価鉄の状態で存在する。pHと二価の可溶性鉄イオン濃度の関係は、次のようになる。
すなわち、pH7で4500mg/lもの鉄イオンが溶け出す可能性がある。実際、なんらの対策を行わずに浚渫底泥をノニオンまたはアニオン系の高分子凝集剤と無機凝集剤で処理した場合、分離水は、数時間後、赤色を帯びてくる。これは、浚渫底泥から溶け出した二価の鉄が、時間の経過とともに空気で酸化され三価の水酸化鉄になって析出するためである。
【0006】
【発明が解決しようとする課題】
本発明は、はじめにノニオンまたはアニオン系の高分子凝集剤を加え、次に無機凝集剤を加えてフロックをつくり機械脱水する浚渫底泥の処理方法において、分離水に溶け出す鉄イオン量等を極力低減する方法を提供することにある。
【0007】
【課題を解決するための手段】
本発明は、含水比150%以上の浚渫底泥にノニオンまたはアニオン系の高分子凝集剤を加えて混合し、続いて、無機凝集剤を加えて混合してフロックをつくり、しかるのちに自然脱水または機械脱水で水を抜く浚渫底泥の処理方法において、前処置として、浚渫底泥を酸化工程に送って酸化してから凝集反応に供することを特徴とする浚渫底泥の処理方法に関する。
【0008】
【発明の実施の形態】
本発明において、浚渫底泥を酸化工程に送って酸化する目的は、例えば、浚渫底泥に含まれる二価の鉄を三価の鉄に変えることである。三価の水酸化鉄は、二価の水酸化鉄よりはるかに溶解度積が小さく、次に示すように、pHが低下しても、殆ど水に溶け出さない。
すなわち、pHが7になっても、3×10-2mg/リットル 程度の溶解度でゼロに近いから、分離水が赤く変色することがなくなる。
【0009】
本発明における酸化の方法としては、攪拌、曝気、酸化剤添加のいずれか、または、それらの組み合わせを用いることができる。
攪拌または曝気の目的は、空気と浚渫底泥を接触させ、空気の力で二価の鉄を三価にすることにあり、攪拌機やポンプによる単純な攪拌のほか、より積極的に空気と底泥を接触させる方法、例えば、底泥を滝のように流すとか、噴水のように空気中に吹き上げるとかいった方法が考えられる。さらに、空気圧縮機または送風機で得られた空気と底泥を接触させる方法として、空気をノズルから浚渫底泥中に吹き出す方法、配管中で空気と底泥を混合し、ラインミキサー、スタッテクミキサーなどで混合する方法、段塔で空気と底泥を接触させる方法をとってもよい。
【0010】
つぎに、酸化剤を使って二価の鉄を三価にする方法を説明する。酸化剤としては、酸素、オゾン、過酸化水素、次亜塩素酸ナトリウムなどが使用できるが、次亜塩素酸ナトリウムは、残留塩素やトリハロメタンによる二次公害を引き起こす可能性があり、出来るだけ避けた方がよい。酸素、オゾンは気体であり、圧縮空気と類似した方法で底泥と接触させることが出来、過酸化水素は液体であるから、底泥に必要量加えて攪拌混合すればよい。
【0011】
攪拌や曝気に要する時間、酸化剤の必要量は、底泥中に含まれる還元物質の量で異なる。目的とする二価鉄の量がさほど多くなくても、鉄イオンの酸化より優先的に酸化される物質が多く含まれていれば、攪拌や曝気に要する時間がふえたり、酸化剤の必要量が増したりする。よって、攪拌や曝気に要する時間、酸化剤の必要量は、予備実験によりこれを決める。
【0012】
本発明において、浚渫底泥を酸化工程に送って酸化することにより、溶出を抑制することができるのは、鉄に限定されない。すなわち、酸化状態により溶解度積が異なるものであって、酸化数の大きい方が小さい溶解度積を有するもの(溶解しずらいもの)は本発明の対象となる。
例えば、一価と二価との溶解度積、または二価と三価との溶解度積等が大きく異なる金属類であれば、本発明の適用の対象となる。すなわち、コバルト、クロム、ニッケルの溶出も抑制することができるから、コバルト、クロム、ニッケルの溶出抑制を主たる目的とする場合にも利用できる。
【0013】
酸化工程に送り酸化した浚渫底泥を、その後、通常の浚渫底泥の処理方法を用いて処理する。すなわち、浚渫底泥にノニオンまたはアニオン系の高分子凝集剤を加えて攪拌混合機で攪拌混合し、続いて、無機凝集剤を加えて攪拌混合機で攪拌混合してフロックをつくり、しかるのちに自然脱水または機械脱水で水を抜く。
本発明の対象となる底泥は、固液分離が可能な液状物であって、含水比がおよそ150%以上のものが好ましい。
ここで、含水比とは、110℃の炉乾燥によって失われる土中水の質量の土の炉乾燥重量に対する比を百分率で表した値であり、JIS A 1203(含水比試験方法)によって測定される値である。
【0014】
【実施例】
(実施例)、(比較例)
湖沼底から採取したヘドロ(比重1.08、含水率88.2%)を8個のビーカーに各500ミリリットルとり、表1の第2列に示す方法で酸化を試みた。ただし、1個はブランク試験として静置のままとした。次にポリアクリルアミド系高分子凝集剤の0.2wt%水溶液300ミリリットルを加え、3分間攪拌し、反応させた。続いて、両者にポリ塩化アルミニウム水溶液(Al2O310%)を2.5ミリリットル加え、1分間凝集反応させ、加圧脱水した。ポリアクリルアミド系高分子凝集剤は、東亜合成社製(アロンフロックA140−T)を使用した。分離液をビーカーにとり、開放状態で室内に三日間放置した。ブランクの静置したビーカーは赤い沈殿が多数発生し、全体としてオレンジ色に見えた。各分離液の色調を表1の第3列に、鉄イオン濃度を表1の第4列に示す。
【0015】
【発明の効果】
含水比150%以上の浚渫底泥にノニオンまたはアニオン系の高分子凝集剤を加えて攪拌混合機で攪拌混合し、続いて、無機凝集剤を加えて攪拌混合機で攪拌混合してフロックをつくり、しかるのちに自然脱水または機械脱水で水を抜く浚渫底泥の処理方法において、前処理として、浚渫底泥を酸化工程に送って酸化してから凝集反応に供することにより、処理に伴って分離水に溶出してくる鉄イオンの量を極端に減らすことができ、分離水を放流するときに問題となる二次公害の防止におおいに役立つ。この技術は、鉄イオンの溶出を抑制することを目的とするが、結果として、二価と三価の溶解度積が大きく異なる金属類、すなわち、コバルト、クロム、ニッケルの溶出も抑制することになるから、コバルト、クロム、ニッケルの溶出抑制を主たる目的とする場合にも利用できることは言うまでもない。
【表1】
オゾン発生器は、濁川理化工業社製のNG−N−O3 型を使用した。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating bottom mud generated during dredging work such as lakes, rivers, dams, and harbors.
[0002]
[Prior art]
When dewatering high-moisture bottom mud with a water content of over 150% of dredging mud generated during dredging work in lakes, rivers, dams, harbors, etc. Add inorganic flocculant or cationic polymer flocculant, then add nonionic or anionic polymer flocculant to create floc, mechanical dehydration, first add nonionic or anionic polymer flocculant, then A method is known in which an inorganic flocculant or a cationic polymer flocculant is added to the floc and mechanically dehydrated.
[0003]
Of these, the method of adding a nonionic or anionic polymer flocculant first and then adding an inorganic flocculant or a cationic polymer flocculant to make a floc and mechanically dehydrating is because the strength of the produced floc is high It is attracting attention as a promising treatment method with high adaptability to dehydrators. However, when comparing an inorganic flocculant and a cationic polymer flocculant, it is considered desirable to use a highly safe inorganic flocculant because the fish toxicity of the cationic polymer flocculant is very high.
[0004]
However, the inorganic flocculant used in this case is an acidic substance such as polyaluminum chloride or aluminum sulfate. When a required amount of inorganic salt is added, the pH of the separated liquid after dehydration is 7 regardless of the pH of the bottom mud. 0.0 or less. When the pH falls below 7.0, the rate of dissolution in iron water contained in dredged mud increases, and eventually it is discharged into separated water, which is closed up as a secondary contamination problem. It will be.
[0005]
Explain with numbers. Dredged mud is generally in a reduced state, and iron exists in the form of divalent iron. The relationship between pH and divalent soluble iron ion concentration is as follows.
That is, as much as 4500 mg / l of iron ions may dissolve at pH 7. Actually, when dredging mud is treated with nonionic or anionic polymer flocculant and inorganic flocculant without taking any measures, the separated water turns red after several hours. This is because the divalent iron melted out from the dredged mud is oxidized with air and deposited as trivalent iron hydroxide over time.
[0006]
[Problems to be solved by the invention]
The present invention first adds a nonionic or anionic polymer flocculant, then adds an inorganic flocculant to create a floc and mechanically dehydrates the dredged bottom mud treatment method to reduce the amount of iron ions dissolved in the separated water as much as possible. It is to provide a method of reducing.
[0007]
[Means for Solving the Problems]
In the present invention, nonionic or anionic polymer flocculant is added and mixed with dredged bottom mud having a water content of 150% or more, and then an inorganic flocculant is added and mixed to form a floc. or in the processing method of dredging mud removing the water in the machine dewatering, as a pre-treatment, to treatment methods dredging mud, characterized in that subjected to agglutination dredging sediment after oxidation sent to the oxidation process.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the purpose of oxidizing the dredged bottom mud to the oxidation step is, for example, to change the divalent iron contained in the dredged bottom mud to trivalent iron. Trivalent iron hydroxide has a much lower solubility product than divalent iron hydroxide, and hardly dissolves in water even when the pH is lowered, as shown below.
That is, even when the pH reaches 7, the solubility of 3 × 10 −2 mg / liter is close to zero, so that the separated water does not turn red.
[0009]
As the oxidation method in the present invention, any one of stirring, aeration, addition of an oxidizing agent, or a combination thereof can be used.
The purpose of agitation or aeration is to bring air and dredged mud into contact with each other to make the divalent iron trivalent by the force of the air. A method of contacting mud, for example, a method of flowing bottom mud like a waterfall or blowing it up into the air like a fountain can be considered. Furthermore, as a method of bringing the air obtained from the air compressor or blower into contact with the bottom mud, a method of blowing air from the nozzle into the bottom mud, mixing the air and the bottom mud in the pipe, a line mixer, a static mixer For example, a method of mixing by air or a method of bringing air and bottom mud into contact with a plate tower may be used.
[0010]
Next, a method for making divalent iron trivalent using an oxidizing agent will be described. Oxygen, ozone, hydrogen peroxide, sodium hypochlorite, etc. can be used as oxidizing agents, but sodium hypochlorite may cause secondary pollution due to residual chlorine and trihalomethane, and was avoided as much as possible. Better. Oxygen and ozone are gases, and can be brought into contact with the bottom mud by a method similar to compressed air. Since hydrogen peroxide is a liquid, it may be added to the bottom mud and stirred and mixed.
[0011]
The time required for stirring and aeration, and the required amount of oxidizer vary depending on the amount of reducing substances contained in the bottom mud. Even if the target amount of divalent iron is not so large, if there are many substances that are preferentially oxidized over the oxidation of iron ions, the amount of time required for stirring and aeration can be adjusted, and the required amount of oxidizer Or increase. Therefore, the time required for stirring and aeration and the necessary amount of oxidant are determined by preliminary experiments.
[0012]
In the present invention, it is not limited to iron that elution can be suppressed by sending the bottom mud to the oxidation step and oxidizing it. In other words, those having different solubility products depending on the oxidation state and having a smaller oxidation product with a higher oxidation number (difficult to dissolve) are objects of the present invention.
For example, the present invention can be applied to any metal having a significantly different solubility product between monovalent and divalent, or a solubility product between divalent and trivalent. That is, since elution of cobalt, chromium, and nickel can also be suppressed, it can be used for the main purpose of suppressing elution of cobalt, chromium, and nickel.
[0013]
The dredged bottom mud sent to the oxidation process is then treated using a normal dredged bottom mud treatment method. In other words, nonionic or anionic polymer flocculant is added to dredged bottom mud and stirred and mixed with a stirrer / mixer, then inorganic flocculant is added and stirred and mixed with a stirrer / mixer to create a flock, and then Drain water with natural or mechanical dehydration.
The bottom mud that is the subject of the present invention is a liquid that can be separated into solid and liquid, and preferably has a water content of about 150% or more.
Here, the water content ratio is a value representing the ratio of the mass of soil water lost by oven drying at 110 ° C. to the oven dry weight of the soil as a percentage, measured by JIS A 1203 (water content ratio test method). Value.
[0014]
【Example】
(Example), (Comparative example)
500 ml of sludge (specific gravity 1.08, water content 88.2%) collected from the bottom of the lake was placed in 8 beakers, and oxidation was attempted by the method shown in the second column of Table 1. However, one was left stationary as a blank test. Next, 300 ml of a 0.2 wt% aqueous solution of polyacrylamide-based polymer flocculant was added and stirred for 3 minutes to react. Subsequently, 2.5 ml of a polyaluminum chloride aqueous solution (Al 2 O 3 10%) was added to both, and the mixture was subjected to an agglomeration reaction for 1 minute, followed by pressure dehydration. As the polyacrylamide polymer flocculant, Toa Gosei Co., Ltd. (Aron Flock A140-T) was used. The separated liquid was taken in a beaker and left in the room in an open state for 3 days. A large number of red precipitates appeared in the blank beaker, and the whole looked orange. The color tone of each separation liquid is shown in the third column of Table 1, and the iron ion concentration is shown in the fourth column of Table 1.
[0015]
【The invention's effect】
Add nonionic or anionic polymer flocculant to dredged bottom mud with a water content of 150% or more, stir and mix with a stirrer, then add inorganic flocculant and stir and mix with stirrer to create floc Then, in the processing method of dredged bottom mud, which drains water by natural dehydration or mechanical dehydration, as a pretreatment, the dredged bottom mud is sent to the oxidation process and oxidized, and then subjected to agglomeration reaction, so that it is separated along with the treatment. The amount of iron ions leached into water can be extremely reduced, and it is extremely useful for preventing secondary pollution that becomes a problem when the separated water is discharged. This technique aims to suppress the elution of iron ions, but as a result, it also suppresses the elution of metals having greatly different divalent and trivalent solubility products, that is, cobalt, chromium and nickel. Therefore, it goes without saying that the present invention can also be used for the main purpose of suppressing the elution of cobalt, chromium and nickel.
[Table 1]
As the ozone generator, NG-N-O 3 type manufactured by Nuragawa Rika Kogyo Co., Ltd. was used.
Claims (4)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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JP32073497A JP3880712B2 (en) | 1997-11-21 | 1997-11-21 | Treatment method of dredged mud |
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JP32073497A JP3880712B2 (en) | 1997-11-21 | 1997-11-21 | Treatment method of dredged mud |
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JPH11156397A JPH11156397A (en) | 1999-06-15 |
JP3880712B2 true JP3880712B2 (en) | 2007-02-14 |
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US7264734B2 (en) * | 2002-01-03 | 2007-09-04 | Agl Resources | Method for treating dredged material |
GB0601000D0 (en) | 2006-01-18 | 2006-03-01 | Ciba Sc Holding Ag | Concentration of suspensions |
AR094422A1 (en) | 2011-10-25 | 2015-08-05 | Basf Se | SUSPENSION CONCENTRATION |
EA201590227A1 (en) | 2012-07-31 | 2015-07-30 | Басф Се | CONCENTRATION OF SUSPENSIONS |
CN113526840A (en) * | 2020-04-22 | 2021-10-22 | 水木金谷环境科技有限公司 | Method for treating polluted bottom mud by organic acid chelated ferrous iron catalytic oxidation technology |
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