JP3962284B2 - Waste water treatment apparatus and waste water treatment method - Google Patents

Waste water treatment apparatus and waste water treatment method Download PDF

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JP3962284B2
JP3962284B2 JP2002159466A JP2002159466A JP3962284B2 JP 3962284 B2 JP3962284 B2 JP 3962284B2 JP 2002159466 A JP2002159466 A JP 2002159466A JP 2002159466 A JP2002159466 A JP 2002159466A JP 3962284 B2 JP3962284 B2 JP 3962284B2
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sludge
aeration
tank
aeration tank
waste water
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JP2004000835A (en
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正憲 若山
次郎 碓井
渉 藤井
実 岡田
直也 田中丸
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Japan Sewage Works Agency
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Japan Sewage Works Agency
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Priority to PCT/JP2003/006686 priority patent/WO2003101896A1/en
Priority to KR20047019099A priority patent/KR100651092B1/en
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00—Biological treatment of water, waste water, or sewage
    • C02F3/02—Aerobic processes
    • C02F3/12—Activated sludge processes
    • C02F3/1236—Particular type of activated sludge installations
    • C02F3/1268—Membrane bioreactor systems
    • C02F3/1273—Submerged membrane bioreactors
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00—Biological treatment of water, waste water, or sewage
    • C02F3/02—Aerobic processes
    • C02F3/12—Activated sludge processes
    • C02F3/20—Activated sludge processes using diffusers
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00—Biological treatment of water, waste water, or sewage
    • C02F3/30—Aerobic and anaerobic processes
    • C02F3/308—Biological phosphorus removal
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2201/00—Apparatus for treatment of water, waste water or sewage
    • C02F2201/002—Construction details of the apparatus
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/04—Oxidation reduction potential [ORP]
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/22—O2
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00—Technologies for wastewater treatment
    • Y02W10/10—Biological treatment of water, waste water, or sewage

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  • Life Sciences & Earth Sciences (AREA)
  • Biodiversity & Conservation Biology (AREA)
  • Water Supply & Treatment (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Microbiology (AREA)
  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Molecular Biology (AREA)
  • Purification Treatments By Anaerobic Or Anaerobic And Aerobic Bacteria Or Animals (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、有機物を含む排水を効率的に処理する装置及び処理方法に関する。
【０００２】
【従来の技術】
排水の処理方法における脱リン方法としては、嫌気槽と曝気槽、沈殿槽を配し、沈殿槽の汚泥を嫌気槽に返送するいわゆるＡＯ法が挙げられる。この方法は、活性汚泥に嫌気状態と好気状態を連続して繰り返すことにより、リン蓄積細菌が細胞内にリン酸をポリリン酸として蓄積することを利用している。しかし、この方法は脱リンは可能であるが、脱窒は行えなかった。
排水の処理方法における脱窒方法として、無酸素槽と曝気槽の汚泥を循環させ、曝気槽においてアンモニア性窒素を硝酸性窒素に酸化し、無酸素槽で、硝酸性窒素を還元し、窒素ガスとして系外に排出する活性汚泥循環変法が従来から広く行われている。しかしこの方法は、窒素は効率よく除去できるものの、リンの除去は十分には行えなかった。これは、好気槽からの循環水の溶存酸素及び硝酸性窒素、亜硝酸性窒素により、無酸素槽の嫌気度が十分上がらず、リン蓄積細菌からのリン放出が十分に起こらないためである。
このため、脱窒とリン除去を同時に行う必要がある場合、活性汚泥循環変法の無酸素槽または曝気槽内に無機凝集剤を添加し、リン酸イオンを不溶化させ、余剰汚泥とともに系外に取り除く方法や、活性汚泥循環変法の無酸素槽の前に、（完全）嫌気槽を配し生物的に脱窒と脱リンを行ういわゆるＡ2 Ｏ法が用いられてきた。
【０００３】
【発明が解決しようとする課題】
しかし、凝集剤を添加する方法は、凝集剤のコストがかかる上に、余剰汚泥の発生量が増加することから、余剰汚泥の処理費用までもが増加するという問題があった。また、Ａ2 Ｏ法は、活性汚泥循環変法と比較して、（完全）嫌気槽を余分に設けなければならず、加えて広い装置設置面積も必要となるという問題があった。
【０００４】
【課題を解決するための手段】
本発明は、このような課題を解決するためになされたものであり、無酸素槽と、曝気槽の２つの処理槽のみで、窒素及びリンを凝集剤を使用せずに除去できる排水処理装置及び処理方法を提供することを目的とする。
【０００５】
すなわち本発明の第一の発明の要旨は、無酸素槽と曝気槽との間で汚泥を循環させて排水を生物学的に処理する排水処理装置であって、曝気部分において汚泥を上昇させ、曝気されていない部分で汚泥を下降させる曝気装置と、前記曝気装置の上部に浸漬されて配置され、処理水を系外に取り出す膜分離装置とを前記曝気槽内に具備し、前記曝気槽から前記無酸素槽へ循環液である汚泥を送液する際、前記曝気槽内に配された前記曝気装置より下部から循環液である汚泥を取り出すように構成した排水処理装置にある。
また、本発明は循環液（汚泥）を取り出す位置が曝気槽中に配された最も低い位置にある曝気装置から２０ｃｍ以上離れていることを特徴とする上記排水処理装置にある。
【０００６】
本発明の第二の発明の要旨は、上記排水処理装置を用いた排水処理方法であって、曝気槽からの汚泥が無酸素槽に入る部位での溶存酸素濃度（以下、ＤＯと記載する。）を、０．２ｍｇ／Ｌ以下および／または曝気槽より汚泥を取り出す部位のＤＯを０．５ｍｇ／Ｌ以下とすることを特徴とする排水の処理方法にある。
さらに、第二の発明は、曝気槽からの循環液の無酸素槽出口でのＤＯを０．２ｍｇ／Ｌ以下および／または、曝気槽よりの循環液取り出し口のＤＯを０．５ｍｇ／Ｌ以下とすると共に曝気槽汚泥の酸素利用速度（ｒr ）を１５ｍｇ／Ｌ・時以上に維持する上記排水処理方法にある。
【０００７】
また、第二の発明は、曝気槽の汚泥濃度（以下、ＭＬＳＳまたはＭＬＳＳ濃度と記載する。）を５０００ｍｇ／Ｌ以上に維持すること、曝気槽のＤＯを１〜３ｍｇ／Ｌの範囲に維持すること、曝気槽から無酸素槽へ循環させる際、最も低い曝気装置の位置よりも下から、より好ましくは２０ｃｍ以上離れた下から循環液（汚泥）を取り出すこと、無酸素槽のＯＲＰを−１５０ｍＶ（銀−塩化銀基準）以下に維持すること、無酸素槽の溶解性リン酸イオン態リン濃度を１０ｍｇ／Ｌ以上に維持することを特徴とする上記排水の処理方法にある。
【０００８】
【発明の実施の形態】
以下、本発明を詳細に説明するが、本発明はこれらに限定解釈されるものではない。
添付の図１は、本発明の実施態様の一例を示す模式図である。図１において符号１は無酸素槽、符号２は曝気槽を示しており、排水（原水）は矢印ａから無酸素槽１に入り、次いでオーバーフロー（矢印ｄ）により曝気槽２内に入り、同槽２内の曝気装置３より下方の部位６において管９よりポンプ４による吸引流ｂとして送液され無酸素槽１に排出部５より入り（矢印ｃ）盾還される。
【０００９】
排水原水ａは、無酸素槽１及び曝気槽２において、活性汚泥により生物学的に浄化される。窒素の除去は、無酸素槽１及び曝気槽２との間で汚泥を循環させることにより、いわゆる硝化脱窒反応によって行われる。ＢＯＤは、主として曝気槽２内に配置された曝気装置３の空気排出部より排出される空気により好気的に酸化され分解される。
【００１０】
本発明においてリンの除去は、汚泥中の微生物（リン蓄積細菌）の作用によりポリリン酸として微生物体内に取り込まれることにより行われる。リンは好気状態において微生物に取り込まれ、また、嫌気状態において、微生物が体内に蓄えたリンを放出する。リン蓄積細菌は、嫌気状態、好気状態に繰り返し曝されると、嫌気状態で放出したリンの量より多くのリンを好気状態で吸収する。
【００１１】
無酸素槽１及び曝気槽２の間での汚泥の循環は、ポンプ４を用いて一方の槽から他方の槽へ送液し、他方の槽からオーバーフローによって流入させる。この際、どちらの槽からポンプを用いて送液するかは必ずしも限定するものではないが、曝気槽２から無酸素槽１へ送液すると、送液量が少なくて済みエネルギーコスト的に好ましい。
【００１２】
本発明では、曝気槽２からの循環液が無酸素槽１に入る部位５におけるＤＯを０．２ｍｇ／Ｌ以下および／または曝気槽２より循環液を取り出す部位６のＤＯを０．５ｍｇ／Ｌ以下とすることにより、無酸素槽１への溶存酸素の流入を抑制することができ、無酸素槽１内の嫌気度が十分維持されることにより、リンの放出が促進される。
無酸素槽１内に溶存酸素、硝酸イオン、亜硝酸イオンが実質的に存在しないと、有機物が嫌気的に分解され、このとき菌に蓄積されたポリリン酸がリン酸として菌体外に放出される。
【００１３】
本発明において曝気槽２からの循環液（汚泥）が無酸素槽１に入る部位５におけるＤＯ濃度は０．２ｍｇ／Ｌ以下とする必要があり、０．１ｍｇ／Ｌ以下とするとリンの除去性がより安定するため好ましい。さらに０．０５ｍｇ／Ｌ以下とするとより好ましい。
曝気槽２からの循環液（汚泥）が無酸素槽１に入る部位５におけるＤＯ濃度を低減させるためには、曝気槽２から汚泥を取出す部位６から、無酸素槽１に入る部位５までの配管９の長さを長くする等により配管中でＤＯを消費させること、配管中に脱気手段を設けること等も可能であり、必ずしも限定はされないが、曝気槽２中でＤＯ濃度が低くなる部位を設け、ここから循環液を取り出すと、簡便な装置構成で無酸素槽１に入る部位５でのＤＯを低減することができる。
【００１４】
無酸素槽１に入る部位５におけるＤＯ濃度を０．２ｍｇ／Ｌ以下とするには、曝気槽２より循環液（汚泥）を取り出す部位６のＤＯ濃度は０．５ｍｇ／Ｌ以下とすればよいことが実験的に確かめられた。曝気槽２より循環液（汚泥）を取り出す部位６のＤＯ濃度は０．３ｍｇ／Ｌ以下とするとリンの除去性がより安定するため好ましい。さらに０．２ｍｇ／Ｌ以下とするとより好ましい。
なお、ＤＯ濃度の測定は、隔膜電極法による通常のＤＯ計を用いて測定することができる。
【００１５】
曝気槽２から循環液（汚泥）を取り出す部位６のＤＯ濃度を０．５ｍｇ／Ｌ以下とするためには、曝気槽２から無酸素槽１へ汚泥を取り出す際、汚泥の滞留部から取り出すことが好ましい。汚泥の滞留部とは、曝気による汚泥の流動の影響を受けにくい部位を指し、曝気装置３と、曝気槽２の底との間に空間を設けてやると、曝気装置３の下の部分に存在する汚泥は良く撹拌されないため、滞留部となる。
【００１６】
したがって、図１に示すように曝気装置３の位置よりも下の位置から汚泥を取り出すことにより、曝気槽２より循環液（汚泥）を取り出す部位６のＤＯ濃度を０．５ｍｇ／Ｌ以下とすることができる。なお、曝気装置３が曝気槽２内に複数設けられている場合は、汚泥を取り出す部位は最も低い位置にある曝気装置３の下に設ける。また、曝気装置３から取り出す部位６までの距離は２０ｃｍ以上離すことが好ましく、３０ｃｍ以上離すことがさらに好ましい。
また、曝気槽２より循環液（汚泥）の取り出しは、別の態様として図３に示すように、曝気槽２内部に仕切７板を設け、汚泥が良く撹拌されない部位６を設け、ここから汚泥を取り出すようにしてもよい。
【００１７】
曝気槽２内における汚泥の流動は、主として曝気装置３による曝気部分において空気の吹き出し口からの気泡の上昇に伴って汚泥も上昇し、曝気されていない部分においては汚泥が下降し、全体が撹拌される。この際、曝気槽内の汚泥の酸素利用速度（ｒr ）を高く維持すると、曝気されていない部分で酸素が急速に消費されることから、曝気槽２中でＤＯが低くなる部位を形成しやすくなる。具体的なｒr としては、１５ｍｇ／Ｌ・時以上に維持することが必要であり、２５ｍｇ／Ｌ・時以上に維持すると、リンの除去性がより安定するため好ましい。
【００１８】
曝気槽汚泥のｒr を１５ｍｇ／Ｌ以上に維持するには、曝気強度の調整（図のブロワーＢの送気量の調整）、ＭＬＳＳ濃度の調整等によって行うことができる。
なお、曝気槽汚泥のｒr とは、曝気槽２の曝気されている部分から取った汚泥のｒr をいい、測定方法は下水道試験方法（１９９７年、社団法人日本下水道協会）に従って求めることができる。
【００１９】
無酸素槽１および曝気槽２内のＭＬＳＳ濃度は、ＳＲＴ（固形物滞留時間）によって制御することができるが、より安定して脱リンを行うためには、高濃度で維持することが好ましい。これは、ＭＬＳＳ濃度が高いと曝気されていない部分で酸素が急速に消費されることから、曝気槽２中でＤＯが低くなる部位を形成しやすくなるためである。また、高濃度ＭＬＳＳ下では単位容量当たりの脱窒細菌数が多いので脱窒速度が速く、無酸素槽内で溶存酸素、結合酸素のない嫌気状態となる場所が生じる。具体的なＭＬＳＳ濃度は、５０００ｍｇ／Ｌ以上を維持することが好ましく、８０００ｍｇ／Ｌ以上を維持することが更に好ましい。なお、あまりＭＬＳＳ濃度を上げすぎると、汚泥流動性の低下により酸素の溶解効率が極端に低下するため、上限としては２００００ｍｇ／Ｌ迄とすることが好ましい。
なお、ＭＬＳＳ濃度の測定は下水道試験方法（１９９７年、社団法人日本下水道協会）に従い測定することができる。
【００２０】
曝気槽２内の曝気部におけるＤＯ濃度は、ＢＯＤ分解処理及び硝化処理に必要な濃度以上に維持する必要があり、１ｍｇ／Ｌ以上に維持することが好ましい。ただし、あまり高濃度にするとリン除去性能を低下させるため、３ｍｇ／Ｌ以下に維持することが好ましい。曝気部におけるＤＯ濃度は、曝気量を調整することや、曝気装置３の溶解効率を変化させること等によって調整することが可能である。
【００２１】
リン酸蓄積細菌が無酸素槽１においてリンを多く放出すると、曝気槽２においてより多くリンを取り込むことができる。従って無酸素槽１の溶解性リン酸イオン態リン濃度が高い状態で処理を行うと、リンの除去性能を高くすることができる。無酸素槽１の溶解性リン酸イオン態リン濃度は、１０ｍｇ／Ｌ以上に保つことが好ましく、１５ｍｇ／Ｌ以上に保つことがより好ましい。
【００２２】
また、無酸素槽１においてリンを多く放出させるためには、無酸素槽１のＯＲＰを低く保つことも有効である。無酸素槽１のＯＲＰは、−１５０ｍＶ（銀−塩化銀基準）以下に維持することが好ましく、−２００ｍＶ以下に維持するとより好ましい。
なお、ＯＲＰ（酸化還元電位）は、物質が他の物質を酸化し易いか、還元し易いかの指標となり、＋の数字大きい程酸化し易く、−の数字大きい程還元し易いことを表す。この測定は、参照電極に飽和塩化銀電極を用いた金属電極法等により行う。
【００２３】
本発明の排水処理方法で曝気槽２で処理された汚泥の一部は、固液分離され、必要に応じて消毒された後放流される。固液分離手段は特に限定されず、従来の沈殿分離方法を用いることもできるが、図１に示すように曝気槽２内に膜分離装置８を浸漬させて濾過を行うと固形分が実質的に含まれない、水質の高い処理水を得ることができるため好ましい。また、膜分離装置を用いて固液分離を行うと、容易にＭＬＳＳ濃度を高く維持することができ、リン除去の効率を高めることができる。膜分離装置８としては特に限定されず、平膜、中空糸膜、管状セラミック膜、回転円盤膜等、公知のものを用いることができる。膜分離された処理水は矢印ｅによって系外に排出される。
【００２４】
本発明の処理方法において、無酸素槽１または曝気槽２、あるいはその両方に微生物固定化担体を添加することも可能である。これにより実質のＭＬＳＳ濃度が上昇するとともに、曝気槽２においては、増殖速度の遅い硝化菌が担体に固定されることによって、槽内の硝化速度が速くなり、短時間で窒素除去処理が行えるようになる。使用する担体は、特に限定はされず、ポリオレフィン製の中空発泡体、ウレタンフォーム製の担体等を用いることができる。
なお、担体を添加する場合、各槽からの汚泥取出し口、オーバーフロー口等には、担体が流出しないようにスクリーン、メッシュ等を設けると良い。また、滞留部への沈降等を回避するため担体の比重は１以下であるものが好ましい。
【００２５】
また、降雨時運転中に雨水が排水（原水）中に混入し、排水濃度が低下したときのように、処理水のリンの濃度が一時的に高くなることもあるが、その場合ポリ塩化アルミニウム等の凝集剤を原水、無酸素槽、または曝気槽に添加して、処理水のリン濃度を低減させても良い。
【００２６】
【実施例】
以下、実施例を挙げて本発明をさらに詳細に説明する。
［実施例１］
図１に示す装置を用いて、都市下水を原水とする排水の処理を約４５０日間実施した。槽のサイズ等は以下のように構成した。
（１）無酸素槽及び曝気槽の汚泥容量（サイズ）
６．７５ｍ3 （Ｌ１５０ｃｍ×Ｗ１００ｃｍ×Ｈ６００ｃｍ、水深４５０ｃｍ）
（２）曝気装置：曝気槽底面より６０ｃｍの高さに設置
（３）曝気槽よりの循環液（汚泥）取り出し口：曝気槽底面より２０ｃｍの高さに設置
（４）処理水量：５４ｍ3 ／日
（５）曝気槽から無酸素槽への汚泥取り出し量：６．７５ｍ3 ／日（循還量）
（６）余剰汚泥引き抜き量：０．４８〜０．９６ｍ3 ／日
（７）曝気量：４０〜７０Ｎｍ3 ／ｈｒ
さらに、曝気槽の曝気装置の上部５０ｃｍの位置に、中空糸膜を用いた膜分離装置（膜面積１２６ｍ2 ）（三菱レイヨン（株）製、ポリエチレン中空糸膜使用、製品名ＥＸ５４０Ｖ）を設置し、濾液を処理水として取り出した。
【００２７】
処理期間中の原水及び汚泥の性状を表１に示す。
【表１】

Figure 0003962284
【００２８】
なお、表１における評価項目の各測定方法は、下水道試験方法（１９９７年、社団法人日本下水道協会）に従い、以下のように行った。
（１）ＢＯＤ
ＢＯＤは、硝化抑制試薬を加えずに測定した。
（２）ＣＯＤ
ＣＯＤは、過マンガン酸カリウム消費量から求めるいわゆるマンガン法により測定した。
（３）全窒素
全窒素は、総和法により測定した。
（４）全リン
全リンは、完全分解定量法により測定した。
（５）ＤＯ
ＤＯは、溶存酸素計（横河電機製 溶存酸素センサー（型番：ＤＯ３０Ｇ）と溶存酸素変換器（型番：ＤＯ４０２Ｇ））を用いて測定した。
（６）ＯＲＰ（銀−塩化銀基準）
ＯＲＰは、ＯＲＰ計（横河電機（株）製 ＯＲＰセンサー（型番：ＯＲ８ＥＦＧ）とＯＲＰ変換器（型番：ＯＲ４００Ｇ））を用いて測定した。電極は、飽和塩化銀電極を用い、直読の値を用いた。
（７）溶解性リン酸イオン態リン濃度
溶解性リン酸イオン態リン濃度は、無酸素槽汚泥試料を乾燥濾紙５種Ｂにて濾過後、濾液をモリブデン青（アスコルビン酸還元）吸光光度法を用いて測定した。
（８）固形分含量及びＭＬＳＳ
ＭＬＳＳは、遠心分離法を用いて測定した。すなわち、汚泥試料適量を沈殿管に採り、３０００〜４０００ｒｐｍで２〜３分遠心分離を行い、上澄液を捨て、沈殿管に水を加え、攪拌し、再び同様に遠心分離を行い、上澄液を捨て、この沈殿物を蒸発皿に洗い入れ、１０５〜１１０℃で２時間乾燥し、質量を測定し、以下の計算式によって算出した。
汚泥濃度（ＭＬＳＳ）＝汚泥の乾燥質量（ｍｇ）／試料量（Ｌ）
（９）酸素利用速度（ｒr ）
曝気槽の曝気部から汚泥１Ｌを細口瓶に採り、１０〜２０分間静置した後、上澄液をサイホンで細口の瓶に入れた。ＭＬＳＳが高い場合は、静置による沈降がほとんどないため、遠心法により汚泥と上澄液とに分離した。ついで細口瓶の上澄液をＤＯが約５ｍｇ／Ｌ以上になるように散気装置を用いて、５〜１０分間激しく曝気した後、上記の沈殿した汚泥とよく攪拌し、この混合溶液を三角フラスコに満たし、空気が入らないようにＤＯ計（セントラル化学（株）製 ＵＣ１０１）のセンサー部を挿入し、酸素濃度の減少を記録した。記録された減少曲線の内、初期の直線部分を用い、以下の式により、酸素利用速度を求めた。
酸素利用速度（ｒr ）（ｍｇ／Ｌ・ 時）＝酸素減少量（ｍｇ／Ｌ）／経過時間（時間）
【００２９】
処理期間中の処理水水質の範囲を表２に示す。
【表２】
Figure 0003962284
表２に示すように、処理期間中、各水質項目の何れも良好な除去性能を達成でき、中でもリンに関しては、凝集剤の添加を行っていないにも拘らず、期間中の平均除去率として約９６％という、極めて高い除去率を達成できた。
【００３０】
【発明の効果】
以上、詳細に説明したように、本発明によれば、無酸素槽と曝気槽の２槽のみによって、窒素、ＢＯＤの除去を行うことに加えて、リンの除去も行うことができる。さらに、凝集剤を添加しないため、余剰汚泥の発生量を低く抑えることができる。
【図面の簡単な説明】
【図１】本発明の実施態様の一例を示す模式図である。
【図２】本発明の別の実施態様を示す模式図である。
【図３】本発明の別の実施態様を示す模式図である。
【符号の説明】
１ 無酸素槽
２ 曝気槽
３ 曝気装置
４ ポンプ
５ 循環液が無酸素槽に入る部位
６ 循環液を取り出す部位
７ 仕切板
８ 膜分離装置
９ 配管
ａ 原水流
ｂ 循環（汚泥）液の取出
ｃ 循環液（汚泥）流
ｄ オーバーフロー
ｅ 処理水放出流[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and a processing method for efficiently treating wastewater containing organic matter.
[0002]
[Prior art]
As a dephosphorization method in the wastewater treatment method, there is a so-called AO method in which an anaerobic tank, an aeration tank, and a sedimentation tank are arranged, and sludge in the sedimentation tank is returned to the anaerobic tank. This method utilizes the fact that phosphorus accumulating bacteria accumulate phosphoric acid as polyphosphoric acid in cells by continuously repeating anaerobic and aerobic conditions on activated sludge. However, this method can dephosphorize, but cannot denitrify.
As a denitrification method in the wastewater treatment method, the sludge in the anaerobic tank and the aeration tank is circulated, ammonia nitrogen is oxidized to nitrate nitrogen in the aeration tank, nitrate nitrogen is reduced in the anoxic tank, nitrogen gas Conventionally, the activated sludge circulation modified method discharged out of the system has been widely used. However, although this method can remove nitrogen efficiently, phosphorus cannot be removed sufficiently. This is because dissolved oxygen, nitrate nitrogen, and nitrite nitrogen from the aerobic tank does not sufficiently increase the anaerobic degree of the oxygen-free tank, and phosphorus release from phosphorus-accumulating bacteria does not occur sufficiently. .
For this reason, when it is necessary to perform denitrification and phosphorus removal at the same time, an inorganic flocculant is added to the anoxic tank or aeration tank of the modified activated sludge circulation method to insolubilize phosphate ions, and the excess sludge is removed from the system. A so-called A 2 O method has been used in which a (complete) anaerobic tank is placed in front of an oxygen-free tank for the method of removing and changing the activated sludge circulation method to perform denitrification and dephosphorization biologically.
[0003]
[Problems to be solved by the invention]
However, the method of adding a flocculant has a problem that the cost of the flocculant is increased and the amount of surplus sludge generated increases, so that the treatment cost of surplus sludge increases. In addition, the A 2 O method has a problem that an (complete) anaerobic tank has to be provided in addition to the activated sludge circulation modified method, and in addition, a large apparatus installation area is required.
[0004]
[Means for Solving the Problems]
The present invention has been made to solve such a problem, and is a wastewater treatment apparatus capable of removing nitrogen and phosphorus without using a flocculant in only two treatment tanks, an oxygen-free tank and an aeration tank. And a processing method.
[0005]
That the gist of the first invention of the present invention, there is provided a wastewater treatment apparatus that processes biologically drainage by circulating the sludge between the anoxic tank and the aeration tank, raising the sludge in the aeration section An aeration apparatus for lowering sludge in a portion that has not been aerated, and a membrane separation apparatus that is immersed in an upper part of the aeration apparatus and takes out treated water out of the system. when feeding a sludge which is circulating fluid to the anoxic tank from the bath, in waste water treatment device configured to take out the sludge which is circulating fluid from the lower portion than the disposed in the aeration tank in the aeration device.
Further, the present invention resides in the above-described waste water treatment apparatus, wherein the position where the circulating liquid (sludge) is taken out is 20 cm or more away from the lowest aeration apparatus disposed in the aeration tank.
[0006]
The gist of the second invention of the present invention is a wastewater treatment method using the above wastewater treatment apparatus, wherein the dissolved oxygen concentration (hereinafter referred to as DO) at the site where sludge from the aeration tank enters the anoxic tank. ) Is 0.2 mg / L or less and / or the DO at the site where sludge is taken out from the aeration tank is 0.5 mg / L or less.
Furthermore, in the second invention, the DO at the outlet of the anaerobic tank of the circulating fluid from the aeration tank is 0.2 mg / L or less and / or the DO at the outlet of the circulating fluid from the aeration tank is 0.5 mg / L or less. And the wastewater treatment method for maintaining the oxygen utilization rate (r r ) of the aeration tank sludge at 15 mg / L · hour or more.
[0007]
Moreover, 2nd invention maintains the sludge density | concentration (henceforth MLSS or MLSS density | concentration) of an aeration tank to 5000 mg / L or more, and maintains DO of an aeration tank in the range of 1-3 mg / L. When circulating from the aeration tank to the anaerobic tank, the circulating fluid (sludge) is taken out from below the position of the lowest aeration apparatus, more preferably 20 cm or more away, and the ORP of the anaerobic tank is -150 mV (Silver-silver chloride standard) The above-mentioned waste water treatment method is characterized in that the concentration of soluble phosphate ion-type phosphorus in an oxygen-free tank is maintained at 10 mg / L or more.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail, but the present invention is not construed as being limited thereto.
FIG. 1 attached herewith is a schematic diagram showing an example of an embodiment of the present invention. In FIG. 1, reference numeral 1 indicates an anaerobic tank, and reference numeral 2 indicates an aeration tank. Drainage (raw water) enters the anaerobic tank 1 from the arrow a, and then enters the aeration tank 2 by an overflow (arrow d). In a portion 6 below the aeration device 3 in the tank 2, the liquid is sent as a suction flow b by the pump 4 from the pipe 9 and enters the anoxic tank 1 from the discharge part 5 (arrow c) and shielded.
[0009]
The raw waste water a is biologically purified by activated sludge in the anoxic tank 1 and the aeration tank 2. The removal of nitrogen is performed by a so-called nitrification denitrification reaction by circulating sludge between the anoxic tank 1 and the aeration tank 2. BOD is aerobically oxidized and decomposed by the air discharged mainly from the air discharge unit of the aeration apparatus 3 disposed in the aeration tank 2.
[0010]
In the present invention, the removal of phosphorus is carried out by being incorporated into the microorganism as polyphosphoric acid by the action of microorganisms (phosphorus-accumulating bacteria) in the sludge. Phosphorus is taken up by microorganisms in the aerobic state, and in the anaerobic state, the microorganisms release phosphorus stored in the body. When repeatedly exposed to anaerobic and aerobic conditions, phosphorus-accumulating bacteria absorb more phosphorus in the aerobic state than the amount of phosphorus released in the anaerobic state.
[0011]
The sludge is circulated between the anaerobic tank 1 and the aeration tank 2 by using the pump 4 to send the liquid from one tank to the other tank and to flow in from the other tank by overflow. At this time, the tank from which the liquid is fed using the pump is not necessarily limited. However, if the liquid is fed from the aeration tank 2 to the oxygen-free tank 1, the amount of liquid fed is small, which is preferable in terms of energy cost.
[0012]
In the present invention, the DO in the portion 5 where the circulating fluid from the aeration tank 2 enters the anoxic tank 1 is 0.2 mg / L or less and / or the DO in the portion 6 where the circulating fluid is taken out from the aeration tank 2 is 0.5 mg / L. By making it below, it is possible to suppress the inflow of dissolved oxygen into the oxygen-free tank 1, and by sufficiently maintaining the anaerobic degree in the oxygen-free tank 1, the release of phosphorus is promoted.
If dissolved oxygen, nitrate ions, and nitrite ions are not substantially present in the anaerobic tank 1, the organic matter is decomposed anaerobically, and the polyphosphate accumulated in the bacteria is released to the outside of the cells as phosphoric acid. The
[0013]
In the present invention, the DO concentration in the portion 5 where the circulating fluid (sludge) from the aeration tank 2 enters the anoxic tank 1 needs to be 0.2 mg / L or less. Is preferable because it is more stable. Further, 0.05 mg / L or less is more preferable.
In order to reduce the DO concentration in the part 5 where the circulating fluid (sludge) from the aeration tank 2 enters the anaerobic tank 1, the part 6 from which the sludge is removed from the aeration tank 2 to the part 5 that enters the anoxic tank 1. It is possible to consume DO in the pipe by increasing the length of the pipe 9, etc., and to provide a deaeration means in the pipe. Although not necessarily limited, the DO concentration in the aeration tank 2 decreases. If a site | part is provided and circulating fluid is taken out from here, DO in the site | part 5 which enters the anoxic tank 1 can be reduced with a simple apparatus structure.
[0014]
In order to set the DO concentration in the part 5 entering the anoxic tank 1 to 0.2 mg / L or less, the DO concentration in the part 6 for extracting the circulating fluid (sludge) from the aeration tank 2 may be set to 0.5 mg / L or less. It was confirmed experimentally. It is preferable that the DO concentration in the portion 6 for taking out the circulating fluid (sludge) from the aeration tank 2 is 0.3 mg / L or less because phosphorus removal is more stable. Furthermore, it is more preferable when it is 0.2 mg / L or less.
In addition, the measurement of DO density | concentration can be measured using the normal DO meter by the diaphragm electrode method.
[0015]
In order to set the DO concentration of the portion 6 where the circulating fluid (sludge) is extracted from the aeration tank 2 to 0.5 mg / L or less, when removing the sludge from the aeration tank 2 to the oxygen-free tank 1, the DO2 should be extracted from the sludge retention part. Is preferred. The sludge retention part refers to a part that is not easily affected by the flow of sludge due to aeration. If a space is provided between the aeration apparatus 3 and the bottom of the aeration tank 2, the sludge stays in the lower part of the aeration apparatus 3. Since the existing sludge is not well stirred, it becomes a staying part.
[0016]
Therefore, as shown in FIG. 1, the DO concentration of the portion 6 for extracting the circulating fluid (sludge) from the aeration tank 2 is set to 0.5 mg / L or less by removing the sludge from a position below the position of the aeration device 3. be able to. In addition, when the aeration apparatus 3 is provided with two or more in the aeration tank 2, the site | part which takes out sludge is provided under the aeration apparatus 3 in the lowest position. Further, the distance from the aeration apparatus 3 to the part 6 to be taken out is preferably 20 cm or more, and more preferably 30 cm or more.
Further, as shown in FIG. 3, as another embodiment, the circulating liquid (sludge) is taken out from the aeration tank 2, and a partition 7 plate is provided inside the aeration tank 2, and a portion 6 where the sludge is not well stirred is provided. You may make it take out.
[0017]
The flow of sludge in the aeration tank 2 is mainly due to the rise of air bubbles from the air outlet in the aeration part by the aeration apparatus 3, and the sludge descends in the part that is not aerated, and the whole is stirred. Is done. At this time, if the oxygen utilization rate (r r ) of the sludge in the aeration tank is kept high, oxygen is rapidly consumed in the non-aerated part, so that a portion where the DO becomes low in the aeration tank 2 is formed. It becomes easy. The specific r r needs to be maintained at 15 mg / L · hour or more, and is preferably maintained at 25 mg / L · hour or more because phosphorus removal is more stable.
[0018]
The r r aeration tank sludge maintained above 15 mg / L, the (adjustment of feed amount of the blower B in the figure) the adjustment of the aeration intensity can be performed by adjustment of the MLSS concentration.
It is to be noted that the r r of the aeration tank sludge, refers to r r of sludge taken from the portion that is aerated in the aeration tank 2, measurement method sewer test method (1997, Japan Sewage Works Association) be determined in accordance with it can.
[0019]
The MLSS concentration in the anaerobic tank 1 and the aeration tank 2 can be controlled by SRT (solid matter residence time), but is preferably maintained at a high concentration in order to perform dephosphorization more stably. This is because when the MLSS concentration is high, oxygen is rapidly consumed in a portion that has not been aerated, and therefore, it is easy to form a portion where the DO becomes low in the aeration tank 2. In addition, since the number of denitrifying bacteria per unit volume is large under high concentration MLSS, the denitrification rate is fast, and a place where anaerobic state without dissolved oxygen and bound oxygen is generated in the anoxic tank. The specific MLSS concentration is preferably maintained at 5000 mg / L or more, and more preferably maintained at 8000 mg / L or more. If the MLSS concentration is increased too much, the dissolution efficiency of oxygen is extremely reduced due to a decrease in sludge fluidity, so the upper limit is preferably set to 20000 mg / L.
The MLSS concentration can be measured according to a sewer test method (1997, Japan Sewerage Association).
[0020]
The DO concentration in the aeration section in the aeration tank 2 needs to be maintained at a concentration higher than that required for the BOD decomposition treatment and nitrification treatment, and is preferably maintained at 1 mg / L or more. However, if the concentration is too high, the phosphorus removal performance is deteriorated, so it is preferable to maintain it at 3 mg / L or less. The DO concentration in the aeration unit can be adjusted by adjusting the amount of aeration or changing the dissolution efficiency of the aeration apparatus 3.
[0021]
When phosphate-accumulating bacteria release more phosphorus in the anoxic tank 1, more phosphorus can be taken up in the aeration tank 2. Therefore, if the treatment is performed in a state where the concentration of soluble phosphate ion phosphorus in the oxygen-free tank 1 is high, the phosphorus removal performance can be enhanced. The concentration of soluble phosphate ion phosphorus in the anaerobic tank 1 is preferably maintained at 10 mg / L or more, and more preferably maintained at 15 mg / L or more.
[0022]
In order to release a large amount of phosphorus in the oxygen-free tank 1, it is also effective to keep the ORP of the oxygen-free tank 1 low. The ORP of the anaerobic tank 1 is preferably maintained at −150 mV (silver-silver chloride standard) or less, more preferably −200 mV or less.
Note that ORP (oxidation-reduction potential) is an indicator of whether a substance is easy to oxidize or reduce another substance, and the greater the + number, the easier it is to oxidize, and the greater the-number, the easier it is to reduce. This measurement is performed by a metal electrode method using a saturated silver chloride electrode as a reference electrode.
[0023]
Part of the sludge treated in the aeration tank 2 by the wastewater treatment method of the present invention is separated into solid and liquid, and after being disinfected as necessary, it is discharged. The solid-liquid separation means is not particularly limited, and a conventional precipitation separation method can be used. However, when the membrane separation device 8 is immersed in the aeration tank 2 and filtration is performed as shown in FIG. It is preferable because treated water with high water quality that is not contained in the water can be obtained. Further, when solid-liquid separation is performed using a membrane separator, the MLSS concentration can be easily maintained high, and the efficiency of phosphorus removal can be increased. The membrane separation device 8 is not particularly limited, and a known device such as a flat membrane, a hollow fiber membrane, a tubular ceramic membrane, and a rotating disk membrane can be used. The treated water separated from the membrane is discharged out of the system by an arrow e.
[0024]
In the treatment method of the present invention, it is also possible to add a microorganism-immobilized carrier to the anoxic tank 1, the aeration tank 2, or both. As a result, the actual MLSS concentration is increased, and in the aeration tank 2, nitrifying bacteria having a slow growth rate are fixed to the carrier, so that the nitrification speed in the tank is increased and the nitrogen removal treatment can be performed in a short time. become. The carrier to be used is not particularly limited, and a hollow foam made of polyolefin, a carrier made of urethane foam, or the like can be used.
In addition, when adding a support | carrier, it is good to provide a screen, a mesh, etc. in the sludge extraction port, overflow port, etc. from each tank so that a support | carrier may not flow out. Further, the carrier preferably has a specific gravity of 1 or less in order to avoid sedimentation in the staying portion.
[0025]
In addition, the concentration of phosphorus in the treated water may temporarily increase as in the case of rainwater mixed into the wastewater (raw water) during operation during rainfall and the concentration of the wastewater decreases. A flocculant such as raw water may be added to raw water, an oxygen-free tank, or an aeration tank to reduce the phosphorus concentration of the treated water.
[0026]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[Example 1]
Using the apparatus shown in FIG. 1, wastewater treatment using municipal sewage as raw water was carried out for about 450 days. The tank size was configured as follows.
(1) Sludge capacity (size) of oxygen-free tank and aeration tank
6.75m 3 (L150cm × W100cm × H600cm, water depth 450cm)
(2) Aeration device: installed at a height of 60 cm from the bottom of the aeration tank (3) Circulating fluid (sludge) outlet from the aeration tank: installed at a height of 20 cm from the bottom of the aeration tank (4) Amount of treated water: 54 m 3 / Day (5) Amount of sludge taken out from the aeration tank to the oxygen-free tank: 6.75 m 3 / day (recirculation amount)
(6) Excess sludge extraction amount: 0.48 to 0.96 m 3 / day (7) Aeration amount: 40 to 70 Nm 3 / hr
Furthermore, a membrane separation device (membrane area 126 m 2 ) using a hollow fiber membrane (manufactured by Mitsubishi Rayon Co., Ltd., using a polyethylene hollow fiber membrane, product name EX540V) is installed at a position 50 cm above the aeration device of the aeration tank. The filtrate was taken out as treated water.
[0027]
Table 1 shows the properties of raw water and sludge during the treatment period.
[Table 1]
Figure 0003962284
[0028]
In addition, each measuring method of the evaluation item in Table 1 was performed as follows according to a sewer test method (1997, Japan Sewerage Association).
(1) BOD
BOD was measured without adding a nitrification inhibitor.
(2) COD
COD was measured by a so-called manganese method determined from potassium permanganate consumption.
(3) Total nitrogen Total nitrogen was measured by the summation method.
(4) Total phosphorus Total phosphorus was measured by a complete decomposition quantitative method.
(5) DO
The DO was measured by using a dissolved oxygen meter (a dissolved oxygen sensor (model number: DO30G) and a dissolved oxygen converter (model number: DO402G) manufactured by Yokogawa Electric Corporation).
(6) ORP (silver-silver chloride standard)
The ORP was measured using an ORP meter (ORP sensor (model number: OR8EFG) and ORP converter (model number: OR400G) manufactured by Yokogawa Electric Corporation). As the electrode, a saturated silver chloride electrode was used, and a value read directly was used.
(7) Soluble Phosphate Ionic Phosphorus Concentration The soluble phosphate ion phosphorous concentration was determined by filtering the oxygen-free tank sludge sample with 5 kinds of dry filter paper B, and then using the molybdenum blue (ascorbic acid reduction) spectrophotometric method for the filtrate. And measured.
(8) Solid content and MLSS
MLSS was measured using a centrifugation method. That is, an appropriate amount of sludge sample is taken in a sedimentation tube, centrifuged at 3000 to 4000 rpm for 2 to 3 minutes, the supernatant is discarded, water is added to the sedimentation tube, stirred, and centrifuged again in the same manner. The liquid was discarded, the precipitate was washed in an evaporating dish, dried at 105 to 110 ° C. for 2 hours, measured for mass, and calculated according to the following formula.
Sludge concentration (MLSS) = Dry mass of sludge (mg) / Sample amount (L)
(9) Oxygen utilization rate (r r )
1 L of sludge was collected from the aeration section of the aeration tank into a narrow mouth bottle and allowed to stand for 10 to 20 minutes, and then the supernatant was siphoned into the narrow mouth bottle. When MLSS was high, there was almost no sedimentation due to standing, so that the sludge and supernatant were separated by centrifugation. Next, the supernatant of the narrow-bottle bottle was vigorously aerated for 5 to 10 minutes using an air diffuser so that the DO was about 5 mg / L or more, and then stirred well with the precipitated sludge. A sensor unit of a DO meter (UC101 manufactured by Central Chemical Co., Ltd.) was inserted so that the flask was filled and air did not enter, and the decrease in oxygen concentration was recorded. The oxygen utilization rate was calculated | required by the following formula | equation using the initial linear part among the recorded decreasing curves.
Oxygen utilization rate (r r ) (mg / L · hr) = oxygen reduction (mg / L) / elapsed time (hours)
[0029]
Table 2 shows the range of treated water quality during the treatment period.
[Table 2]
Figure 0003962284
As shown in Table 2, during the treatment period, each of the water quality items can achieve good removal performance, and in particular, regarding phosphorus, as an average removal rate during the period, although no flocculant is added. An extremely high removal rate of about 96% was achieved.
[0030]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to remove phosphorus and nitrogen in addition to removing nitrogen and BOD by only two tanks, an oxygen-free tank and an aeration tank. Furthermore, since no flocculant is added, the amount of excess sludge generated can be kept low.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention.
FIG. 2 is a schematic view showing another embodiment of the present invention.
FIG. 3 is a schematic view showing another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Anoxic tank 2 Aeration tank 3 Aeration apparatus 4 Pump 5 Part where the circulating fluid enters the anoxic tank 6 Part where the circulating liquid is taken out 7 Partition plate 8 Membrane separator 9 Piping a Raw water flow b Circulation (sludge) liquid extraction c Circulation Liquid (sludge) flow d overflow e treated water discharge flow

Claims (11)

無酸素槽と曝気槽との間で汚泥を循環させて排水を生物学的に処理する排水処理装置であって、
曝気部分において汚泥を上昇させ、曝気されていない部分で汚泥を下降させる曝気装置と、前記曝気装置の上部に浸漬されて配置され、処理水を系外に取り出す膜分離装置とを前記曝気槽内に具備し、
前記曝気槽から前記無酸素槽へ循環液である汚泥を送液する際、前記曝気槽内に配された前記曝気装置より下部から循環液である汚泥を取り出すように構成した排水処理装置。A wastewater treatment apparatus that processes biologically drainage by circulating the sludge between the anoxic tank and the aeration tank,
An aeration apparatus that raises sludge in the aeration part and lowers sludge in an unaerated part, and a membrane separation apparatus that is immersed in the upper part of the aeration apparatus and extracts treated water out of the system are disposed in the aeration tank. And
When feeding a sludge which is circulating fluid to the anoxic tank from the aeration tank, the waste water treatment apparatus configured to retrieve the sludge is circulating fluid from the lower portion than the disposed in the aeration tank in the aeration device. 前記曝気槽から循環液である汚泥を取り出す位置が、最も低い位置にある前記曝気装置から２０ｃｍ以上下方に離れている請求項１記載の排水処理装置。Position to take out the sludge which is circulating fluid from the aeration tank, the waste water treatment apparatus according to claim 1 wherein the downward apart than 20cm from the aeration device in the lowest position. 請求項１記載の排水処理装置を用いた排水処理方法であって、前記曝気槽から送液される汚泥が無酸素槽に入る部位での溶存酸素濃度（ＤＯ）を、０．２ｍｇ／Ｌ以下とし、および／または前記曝気槽より汚泥を取り出す部位の溶存酸素濃度（ＤＯ）を０．５ｍｇ／Ｌ以下とする排水処理方法。 A wastewater treatment method using the wastewater treatment apparatus according to claim 1 , wherein a dissolved oxygen concentration (DO) at a site where sludge fed from the aeration tank enters the anoxic tank is 0.2 mg / L or less. and then, and / or the waste water treatment method of the dissolved oxygen concentration of the portion taken out sludge from the aeration tank (DO) or less 0.5 mg / L. 前記曝気槽内の汚泥の酸素利用速度（ｒr ）を１５ｍｇ／Ｌ・時以上に維持することを特徴とする請求項３記載の排水処理方法。The wastewater treatment method according to claim 3, wherein the oxygen utilization rate (r r ) of sludge in the aeration tank is maintained at 15 mg / L · hour or more. 前記曝気槽内の汚泥の酸素利用速度（ｒr ）を２５ｍｇ／Ｌ・時以上に維持することを特徴とする請求項３記載の排水処理方法。The wastewater treatment method according to claim 3, wherein the oxygen utilization rate (r r ) of the sludge in the aeration tank is maintained at 25 mg / L · hour or more. 前記曝気槽内の汚泥濃度（ＭＬＳＳ濃度）を５０００ｍｇ／Ｌ以上に維持することを特徴とする請求項３〜５の何れかに記載の排水処理方法。The wastewater treatment method according to any one of claims 3 to 5, wherein a sludge concentration (MLSS concentration) in the aeration tank is maintained at 5000 mg / L or more. 前記曝気槽の溶存酸素濃度（ＤＯ）を１〜３ｍｇ／Ｌの範囲に維持することを特徴とする請求項３〜６の何れかに記載の排水処理方法。The dissolved oxygen concentration (DO) of the said aeration tank is maintained in the range of 1-3 mg / L, The waste water treatment method in any one of Claims 3-6 characterized by the above-mentioned. 前記無酸素槽の溶解性リン酸イオン態リン濃度を１０ｍｇ／Ｌ以上に維持することを特徴とする請求項３〜７の何れかに記載の排水処理方法。The wastewater treatment method according to any one of claims 3 to 7, wherein the concentration of soluble phosphate ion phosphorus in the anaerobic tank is maintained at 10 mg / L or more . 前記無酸素槽のＯＲＰを−１５０ｍＶ（銀−塩化銀基準）以下に維持することを特徴とする請求項３〜８の何れかに記載の排水処理方法。The wastewater treatment method according to any one of claims 3 to 8 , wherein the ORP of the anaerobic tank is maintained at -150 mV (silver-silver chloride standard) or less . 前記曝気装置と、曝気槽の底との間から循環液である汚泥を取り出すことを特徴とする請求項１記載の排水処理装置。The waste water treatment apparatus according to claim 1, wherein sludge as circulating liquid is taken out between the aeration apparatus and the bottom of the aeration tank. 前記曝気装置が前記曝気槽内に複数設けられており、最も低い曝気装置の下から循環液である汚泥を取り出すことを特徴とする請求項１記載の排水処理装置。The waste water treatment apparatus according to claim 1, wherein a plurality of the aeration apparatuses are provided in the aeration tank, and sludge as a circulating liquid is taken out from under the lowest aeration apparatus.
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