JP3677783B2

JP3677783B2 - Nitrification method

Info

Publication number: JP3677783B2
Application number: JP12730593A
Authority: JP
Inventors: 雅秀柴田; 美由紀諏佐
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 1993-05-28
Filing date: 1993-05-28
Publication date: 2005-08-03
Anticipated expiration: 2020-08-03
Also published as: JPH06335698A

Description

【０００１】
【産業上の利用分野】
本発明は、有機性排液中の窒素化合物を生物学的に硝化する硝化方法に関し、有機性排液の生物学的硝化脱窒法に利用可能な硝化方法に関するものである。
【０００２】
【従来の技術】
アンモニア性または有機性窒素化合物を含む排液を処理する方法として、生物学的硝化脱窒処理法がある。この方法は活性汚泥により排液中のＣＯＤ、ＢＯＤ成分を分解するとともに、有機性窒素化合物をアンモニア性窒素とし、このアンモニア性窒素を硝化細菌により亜硝酸性または硝酸性窒素に硝化（酸化）した後、脱窒細菌により脱窒（還元）する方法である。この処理法では、脱窒槽を前段に設け、硝化液と分離汚泥を脱窒槽に返送して原水と混合して、脱窒を行うと同時にＢＯＤ成分を分解する方法も行われている。
【０００３】
このような生物学的硝化脱窒法は実績も多く、し尿処理分野などで広く採用されている。しかし、従来の生物学的硝化脱窒法における硝化方法では、硝化槽内の硝化細菌の保持量を多くすることが困難であるため、硝化槽の滞留時間を長くとる必要があり、このため硝化槽が大きくなるという問題点がある。
【０００４】
このような問題点を改善する方法として、硝化槽にスポンジなどの担体を投入し、担体表面に硝化細菌を付着させて硝化細菌の保持量を多くし、これにより硝化槽全体としての硝化速度（ＮＨ₄−Ｎ除去速度）を向上させる方法が知られている。
【０００５】
図２は前段に脱窒槽を設置し、硝化槽に担体を投入した従来の硝化方法を採用した生物学的硝化脱窒法を示すフロー図である。図において、１は脱窒槽、２は硝化槽、３は最終脱窒槽、４は最終好気処理槽、５は固液分離槽であり、硝化槽２で硝化を行うようになっている。
【０００６】
図２のフローに従って原水を処理するには、まず脱窒槽１に窒素化合物およびＢＯＤ成分を含む原水を原水管６から導入するとともに、返送汚泥を汚泥返送管７から導入し、また硝化槽２で硝化を受けた硝化液を循環液管８から導入し、撹拌器１０により脱窒細菌を含む活性汚泥と混合し、嫌気状態を維持して脱窒を行う。このような脱窒工程では循環液中の硝酸または亜硝酸イオンを窒素に還元する脱窒細菌が優勢となり、原水中の窒素成分が除去されるとともに、ＢＯＤ成分も除去される。
【０００７】
脱窒槽１内の脱窒液は一部ずつ連絡管９から取出して、硝化槽２に導入し、浮遊汚泥と担体１４とを共存させて硝化を行う。硝化は、空気管１２から空気を送って散気装置１３から散気して好気性条件とし、添加した担体１４が浮遊する状態で行い、ここでもＢＯＤを除去するとともに原水中の窒素成分を硝酸イオンまたは亜硝酸イオンにまで硝化する。担体１４の流出はスクリーン１５により防止される。
【０００８】
硝化槽２において硝化を行った硝化液の一部は連絡管１１から最終脱窒槽３に導入し、水素供与体としてメタノール等の有機物を有機物供給管１８から供給して、脱窒槽１の場合と同様にして最終的な脱窒を行う。
最終脱窒槽３の最終脱窒液は最終好気処理槽４において、空気管２１から空気を送って最終散気装置２２から散気して再曝気することにより、残留する有機物を除去する。
【０００９】
最終好気処理槽４内の最終好気処理液は一部ずつ連絡管２０から取出して、固液分離槽５に導入して固液分離し、分離液と分離汚泥とに分離する。分離液は処理水として処理水管２３から排出する。分離汚泥は汚泥管２４から取出し、その一部は返送汚泥として汚泥返送管７から脱窒槽１に返送する。残部は余剰汚泥として汚泥排出管２５から系外に排出する。
【００１０】
このような生物学的硝化脱窒法に採用されている上記従来の硝化方法は、既設の硝化槽（曝気槽）に担体を投入するだけで簡単に実施できるので、装置の改造コストがほとんどかからず、汎用性の高い方法である。
担体を使用する硝化方法において硝化速度を上昇させるためには、担体表面にできるだけ多くの硝化細菌を付着させることが必要である。
【００１１】
しかしこのような従来の硝化方法では、担体表面には硝化細菌のほかに他栄養性細菌も付着するので、両細菌により付着場所の競合が生じる。このため排液中のＢＯＤ濃度が高い場合には、ＢＯＤ分解菌も担体に付着するため硝化細菌だけを多く付着させることが困難となり、担体の硝化活性を高くすることができず、硝化速度はそれほど上昇しないという問題点がある。
【００１２】
一方、特開昭５７−７５１９２号には、第１段の曝気槽でＢＯＤ成分の大部分を除去したのち、第２段の硝化槽で担体の存在下に硝化を行う方法が提案されている。しかしこの方法では、担体を投入した硝化槽において、残留するＢＯＤ成分を除去するとともに硝化を行っているため、前記と同様の問題点があるほか、第１段の曝気槽と第２段の硝化槽の間に汚泥分離槽を設置するため、装置が大型化し、操作も複雑になるなどの問題点がある。
【００１３】
【発明が解決しようとする課題】
本発明の目的は、上記問題点を解決するため、ＢＯＤ濃度が高い排液を処理する場合でも、簡単な装置と操作により効率よくＢＯＤ成分を除去して、担体の硝化活性を高め、これにより高窒素負荷の場合でも硝化速度を速くすることが可能な硝化方法を提案することである。
【００１４】
【課題を解決するための手段】
本発明は、窒素化合物を含む有機性排液を、返送汚泥とともに硝化槽内で曝気し、硝化槽には硝化細菌を付着させる担体を投入して硝化細菌による硝化を行う硝化方法において、
担体を投入した硝化槽の前段に、曝気槽および硝化槽の合計容量の５〜２０容量％の曝気槽を設け、
有機性排液を前段の曝気槽で曝気し、浮遊汚泥にＢＯＤ成分を吸着させて実質的に除去したのち、
汚泥を分離することなく後段の硝化槽に導入し、担体の存在下に曝気を行って硝化を行うことを特徴とする硝化方法である。
【００１５】
担体を投入した硝化槽の前段に曝気槽を設けるには、それぞれ独立した別の槽により各槽を形成することもできるが、１つの好気槽を有機性排液が流れる方向に複数に区画して前段の曝気槽と後段の硝化槽を形成し、後段の硝化槽に担体を投入し、この投入した担体が前段の曝気槽に流入しないようにするのが好ましい。
【００１６】
１つの好気槽を区画するには板状のものや金網などが使用できる。１つの好気槽が区画された各槽間では、前段の槽から後段の槽へ汚泥を分離することなく液が流れるように、両槽間に流路を設けておく必要がある。硝化槽は前段の曝気槽と区画されれば効果が得られるが、さらに２つ以上設けてもよい。
【００１７】
本発明の方法では、後段の硝化槽に担体を投入し、前段の曝気槽には担体は投入してもしなくてもよい。そして前段の曝気槽において、酸素含有ガスまたは空気を曝気し、浮遊汚泥にＢＯＤ成分を吸着させて実質的に除去する。この場合ＢＯＤ濃度が１０ｍｇ／ｌ以下、特に６ｍｇ／ｌ以下になるのが好ましい。このようにＢＯＤ成分が実質的に除去された液を、汚泥を分離することなくそのまま後段の硝化槽に導入し、後段の硝化槽において酸素含有ガスまたは空気を用いて曝気し、浮遊汚泥に吸着されたＢＯＤ成分を酸化分解するとともに、担体を浮遊させた状態で硝化細菌を選択的に付着させて硝化する。
【００１８】
曝気槽と硝化槽は汚泥の生物相が異なるため、一般的には特開昭５７−７５１９２号のように、中間で汚泥を分離する必要があるとされているが、本発明のように前段の曝気槽でＢＯＤ成分を実質的に除去すると、中間で汚泥を分離することなくそのまま後段の硝化槽に流入させても、後段の硝化槽におけるＢＯＤ分解細菌の増殖が抑制され、浮遊汚泥は吸着したＢＯＤ成分を酸化分解し、担体には硝化細菌が選択的に付着し、硝化細菌の保持量が多くなって硝化速度が上昇する。
【００１９】
前段の曝気槽容量と、担体を投入する後段の硝化槽容量との比率は、前段の曝気槽でのＢＯＤ成分の除去速度および後段の硝化槽での硝化速度を考慮して、曝気槽および硝化槽全体として硝化速度が速くなるように設定する。通常吸着によるＢＯＤ成分の除去速度は硝化速度に比べて非常に速いので、前段の曝気槽の容量は小さくても、後段の硝化槽における硝化速度は速くなる。従って、前段の曝気槽および後段の硝化槽の合計容量に対する前段の曝気槽の比率は、後段の硝化槽に投入する担体の量などにより変動するが、５〜２０容量％とする。
【００２０】
１つの好気槽を区画した場合、担体が前段の曝気槽（ＢＯＤ除去部）に流入すると、硝化細菌以外のＢＯＤ分解細菌が流入した担体に付着するので、好気槽全体としての硝化細菌の保持量が減少し、硝化速度（ＮＨ₄−Ｎ除去速度）が低下する。従って、後段の硝化槽に投入した担体が前段の曝気槽に流入しない状態で処理する必要がある。担体の曝気槽への流入防止は、前段の曝気槽から後段の硝化槽へ液が溢流するようにすればよく、また前段の曝気槽に流入する水量（圧）、または後段の硝化槽から流出する水量（圧）を調節する方法、槽を金網で仕切る方法、あるいは流路に金網を設けるなどの方法により行うことができる。
【００２１】
硝化細菌を付着させる担体としては、スポンジが好ましいが、ポリマーからなる多孔質体など硝化細菌が付着するものなら制限なく使用できる。担体の投入量は、後段の硝化槽の場合槽の容量に対して５〜４０容量％、好ましくは１０〜３０容量％とするのが望ましい。
【００２２】
担体としては比表面積が大きいものが好ましい。担体の大きさは、浮遊汚泥との分離性を考慮すれば２〜２０ｍｍのものが好ましい。形状は特に限定されず、例えば球状、立方体状のものなどが使用できる。また担体の素材も特に限定されず、例えばポリウレタンなどがあげられる。
【００２３】
本発明の硝化方法は、有機性排液の生物学的窒素除去法（硝化脱窒法）における硝化方法として好適に採用することができ、これにより高窒素負荷の条件においても効率よく窒素を除去することができる。
【００２４】
【実施例】
以下、本発明の実施例を図面により説明する。
図１は本発明の硝化方法を採用した有機性排液の生物学的硝化脱窒法を示すフロー図であり、１つの好気槽を前段の曝気槽と後段の硝化槽に区画した場合の実施例である。図において、図２と同一符号は同一または相当部分を示す。
【００２５】
脱窒槽１には原水管６、汚泥返送管７、循環液管８および連絡管９が接続し、撹拌器１０で緩やかに攪拌し、嫌気状態を維持して脱窒を行うようになっている。
【００２６】
好気槽３０内には原水の流れる方向に対して直交して区画板３１が設けられ、前段の曝気槽３２と後段の硝化槽２とに区画されており、後段の硝化槽２にはスポンジからなる担体１４が投入され、後段の硝化槽２の出口には担体１４流失防止用のスクリーン１５が設けられている。前段の曝気槽３２には脱窒槽１からの連絡管９、後段の硝化槽２には最終脱窒槽３への連絡管１１が接続している。そして空気管１２から前段の曝気槽３２および後段の硝化槽２に空気を送り、前段の散気装置３４および後段の散気装置３５から散気して、前段の曝気槽３２ではＢＯＤ成分の除去、後段の硝化槽２では硝化を行うようになっている。区画板３１と好気槽３０の壁面または底面には流路３６が設けられており、この流路３６から前段の曝気槽３２の液は後段の硝化槽２へ流れ込むようになっている。流路３６には金網（図示せず）が設けられ、担体１４が前段の曝気槽３２に逆流しないようになっている。
【００２７】
最終脱窒槽３には連絡管１１、１７および有機物供給管１８が接続し、攪拌器１９により緩やかに攪拌して嫌気状態を保つようになっている。
最終好気処理槽４には連絡管１７、２０が接続し、空気管２１から空気を送り、最終散気装置２２から散気して、好気処理を行うようになっている。
【００２８】
固液分離槽５には連絡管２０、処理水管２３および汚泥管２４が接続し、沈降分離により固液分離するようになっている。汚泥管２４は汚泥返送管７および汚泥排出管２５に分岐し、分離汚泥の一部は汚泥返送管７を通して脱窒槽１に返送されるようになっている。
【００２９】
図１のフローに従って原水を処理するには、まず脱窒槽１に窒素化合物およびＢＯＤ成分を含む原水を原水管６から導入するとともに、返送汚泥を汚泥返送管７から導入し、また後段の硝化槽２で硝化を受けた硝化液を循環液管８から導入し、撹拌器１０により脱窒細菌を含む活性汚泥と混合し、嫌気状態を維持して脱窒を行う。硝化液の循環量は原水量に対して通常１００〜５００容量％とする。このような脱窒工程では循環液中の硝酸または亜硝酸イオンを窒素に還元する脱窒細菌が優勢となり、原水中の窒素成分が除去されるとともに、ＢＯＤ成分も除去される。
【００３０】
脱窒槽１内の脱窒液は一部ずつ連絡管９から取出して、前段の曝気槽３２に導入し、空気管１２から空気を送って前段の散気装置３４から散気して好気性条件とし、浮遊汚泥によりＢＯＤ成分を実質的に除去し、ＢＯＤ濃度を１０ｍｇ／ｌ以下にする。この場合、窒素化合物の一部を硝化してもよい。前段の曝気槽３２内の混合液は、一部ずつ汚泥を分離することなくそのまま流路３６から後段の硝化槽２に流入する。後段の硝化槽２では、前段の曝気槽３２でＢＯＤ成分を除去した液に空気管１２から空気を送って後段の散気装置３５から散気して好気性条件とし、投入した担体１４が浮遊する状態で硝化細菌により硝化を行い、原水中の窒素成分を硝酸イオンまたは亜硝酸イオンにまで硝化する。ここでは通常のＢＯＤ除去のための曝気よりも過剰に曝気して、硝化細菌を優勢にする。
【００３１】
好気槽３０では、区画板３１の下部の流路３６に金網を張って、後段の硝化槽２中の担体１４が前段の曝気槽３２に流入しないようにしている。
このように好気槽３０を区画し、前段の曝気槽３２でＢＯＤ成分を除去した後、後段の硝化槽２で硝化することにより、硝化細菌が担体１４に安定して多量に保持され、高い硝化活性が維持される。
【００３２】
好気槽３０の条件は、ｐＨが６〜９、好ましくは７〜８．５、温度が０〜４０℃、好ましくは１５〜３５℃とするのが望ましい。
【００３３】
後段の硝化槽２において硝化を行った硝化液の一部は連絡管１１から最終脱窒槽３に導入し、水素供与体としてメタノール等の有機物を有機物供給管１８から供給して、脱窒槽１の場合と同様にして最終的な脱窒を行う。最終脱窒槽３の最終脱窒液は最終好気処理槽４において再曝気することにより、残留する有機物を除去する。
【００３４】
最終好気処理槽４内の最終好気処理液は一部ずつ連絡管２０から取出して、固液分離槽５に導入して固液分離し、分離液と分離汚泥とに分離する。分離液は処理水として処理水管２３から排出する。分離汚泥は汚泥管２４から取出し、その一部は返送汚泥として汚泥返送管７から脱窒槽１に返送する。残部は余剰汚泥として汚泥排出管２５から系外に排出する。
なお図１の方法では、最終脱窒槽３および最終好気処理槽４は省略することができる。
【００３５】
次に試験例について説明する。
試験例１
最終脱窒槽３および最終好気処理槽４を省略した以外は図１の方法に従って、有機性排液の生物学的硝化脱窒を次のようにして行い、好気槽３０におけるＮＨ₄−Ｎ除去速度を判定した。
【００３６】
原水としては合成排水（窒素源：ＮＨ₄Ｃｌ、ＢＯＤ源：グルコース、酢酸）を用いた。処理条件は表１に示すように、好気槽３０容量全体に対する前段の曝気槽３２の比率を０（対照）、５、１０、１５または２０容量％とし、それ以外は同一条件で各試験を行った。担体１４としては３ｍｍ角のポリウレタン製のスポンジを用い、後段の硝化槽２の容量に対して２０容量％となるように添加した。ｐＨは好気槽３０のｐＨを７．５にコントロールした。循環液量は原水量の３倍とした。返送汚泥量は原水量に対して３０％とした。
試験は窒素除去可能な最大能力を調べるために、過大の窒素負荷をかけて、処理水のＮＨ₄−Ｎ水質を知ることで全体の硝化能力を知ることができるようにして行った。運転条件および結果を表１に示す。
【００３７】
【表１】

【００３８】
表１から、前段の曝気槽の比率を５容量％、１０容量％と増加するに従ってＮＨ₄−Ｎ除去速度は速くなり、１０容量％で最も高いＮＨ₄−Ｎ除去速度を示し、その後は徐々に減少することがわかる。
【００３９】
【発明の効果】
以上の通り、本発明の硝化方法によれば、担体を投入する硝化槽の前段に、曝気槽および硝化槽の合計容量の５〜２０容量％の曝気槽を設け、有機性排液を前段の曝気槽で曝気し、浮遊汚泥にＢＯＤ成分を吸着させて実質的に除去したのち、汚泥を分離することなく後段の硝化槽に導入して、担体の存在下に曝気を行って硝化を行うようにしたので、ＢＯＤ濃度が高い排液を処理する場合でも効率よくＢＯＤ成分を除去して、担体の硝化活性を高めることができ、これにより高窒素負荷の場合でも硝化速度を速くして処理時間を短縮できるとともに、中間の汚泥分離を省略して、装置を小型化し、操作も簡略化することができる。
【図面の簡単な説明】
【図１】本発明の硝化方法を採用した生物学的硝化脱窒法を示すフロー図である。
【図２】従来の硝化方法を採用した生物学的硝化脱窒法を示すフロー図である。
【符号の説明】
１脱窒槽
２硝化槽
３最終脱窒槽
４最終好気処理槽
５固液分離槽
６原水管
７汚泥返送管
８循環液管
９、１１、１７、２０連絡管
１０、１９攪拌器
１２、２１空気管
１３散気装置
１４担体
１５スクリーン
１８有機物供給管
２２最終散気装置
２３処理水管
２４汚泥管
２５汚泥排出管
３０好気槽
３１区画板
３２曝気槽
３４前段の散気装置
３５後段の散気装置
３６流路[0001]
[Industrial application fields]
The present invention relates to a nitrification method for biologically nitrifying nitrogen compounds in organic effluents, and relates to a nitrification method that can be used in a biological nitrification denitrification method for organic effluents.
[0002]
[Prior art]
There is a biological nitrification denitrification method as a method for treating a drainage liquid containing ammoniacal or organic nitrogen compounds. This method decomposes COD and BOD components in the effluent with activated sludge, converts the organic nitrogen compound to ammonia nitrogen, and nitrifies (oxidizes) the ammonia nitrogen to nitrite or nitrate nitrogen by nitrifying bacteria. Then, it is a method of denitrifying (reducing) with denitrifying bacteria. In this treatment method, a denitrification tank is provided in the previous stage, and the nitrification liquid and the separated sludge are returned to the denitrification tank and mixed with raw water to perform denitrification and simultaneously decompose the BOD component.
[0003]
Such a biological nitrification denitrification method has many achievements and is widely adopted in the field of human waste treatment. However, in the nitrification method in the conventional biological nitrification denitrification method, it is difficult to increase the amount of nitrifying bacteria retained in the nitrification tank, so it is necessary to increase the residence time of the nitrification tank. There is a problem that becomes larger.
[0004]
As a method for solving such problems, a carrier such as a sponge is put into a nitrification tank, and nitrifying bacteria are attached to the surface of the carrier to increase the amount of nitrifying bacteria retained. A method for improving (NH ₄ —N removal rate) is known.
[0005]
FIG. 2 is a flow chart showing a biological nitrification denitrification method employing a conventional nitrification method in which a denitrification tank is installed in the previous stage and a carrier is introduced into the nitrification tank. In the figure, 1 is a denitrification tank, 2 is a nitrification tank, 3 is a final denitrification tank, 4 is a final aerobic treatment tank, 5 is a solid-liquid separation tank, and nitrification is performed in the nitrification tank 2.
[0006]
In order to treat the raw water according to the flow of FIG. 2, first, raw water containing nitrogen compounds and BOD components is introduced into the denitrification tank 1 from the raw water pipe 6, and return sludge is introduced from the sludge return pipe 7. The nitrifying liquid that has undergone nitrification is introduced from the circulating liquid pipe 8 and mixed with the activated sludge containing denitrifying bacteria by the agitator 10, and denitrification is performed while maintaining the anaerobic state. In such a denitrification step, denitrifying bacteria that reduce nitric acid or nitrite ions in the circulating fluid to nitrogen are dominant, and the nitrogen component in the raw water is removed and the BOD component is also removed.
[0007]
A part of the denitrification liquid in the denitrification tank 1 is taken out from the connecting pipe 9 and introduced into the nitrification tank 2, and nitrification is carried out in the presence of the suspended sludge and the carrier 14. Nitrification is performed in a state where aerobic conditions are obtained by sending air from the air pipe 12 and diffused from the air diffuser 13, and the added carrier 14 is in a floating state. Here again, BOD is removed and nitrogen components in the raw water are mixed with nitric acid. Nitrates to ions or nitrite ions. Outflow of the carrier 14 is prevented by the screen 15.
[0008]
A part of the nitrification liquid nitrified in the nitrification tank 2 is introduced into the final denitrification tank 3 from the communication pipe 11, and an organic substance such as methanol is supplied from the organic substance supply pipe 18 as a hydrogen donor. The final denitrification is performed in the same manner.
In the final aerobic treatment tank 4, the final denitrification liquid in the final denitrification tank 3 sends air from the air pipe 21, diffuses from the final air diffuser 22, and is re-aerated to remove residual organic substances.
[0009]
The final aerobic treatment liquid in the final aerobic treatment tank 4 is taken out from the connecting pipe 20 one by one, introduced into the solid-liquid separation tank 5 and separated into solid and liquid, and separated into separated liquid and separated sludge. The separation liquid is discharged from the treated water pipe 23 as treated water. The separated sludge is taken out from the sludge pipe 24 and a part thereof is returned to the denitrification tank 1 from the sludge return pipe 7 as return sludge. The remainder is discharged out of the system from the sludge discharge pipe 25 as excess sludge.
[0010]
The conventional nitrification method employed in such biological nitrification / denitrification method can be implemented simply by putting the carrier into the existing nitrification tank (aeration tank), so the cost of remodeling the equipment is almost negligible. It is a highly versatile method.
In order to increase the nitrification rate in a nitrification method using a carrier, it is necessary to attach as many nitrifying bacteria as possible to the surface of the carrier.
[0011]
However, in such a conventional nitrification method, other vegetative bacteria in addition to nitrifying bacteria adhere to the surface of the carrier, and competition between the attachment sites is caused by both bacteria. For this reason, when the BOD concentration in the effluent is high, BOD-degrading bacteria also adhere to the carrier, making it difficult to attach only a large amount of nitrifying bacteria, making it impossible to increase the nitrification activity of the carrier, and the nitrification rate is There is a problem that it does not rise so much.
[0012]
On the other hand, JP-A-57-75192 proposes a method in which most of the BOD component is removed in the first stage aeration tank and then nitrification is performed in the presence of the carrier in the second stage nitrification tank. . However, in this method, since the remaining BOD component is removed and nitrification is performed in the nitrification tank into which the carrier is charged, there are the same problems as described above, and the first stage aeration tank and the second stage nitrification. Since the sludge separation tank is installed between the tanks, there is a problem that the apparatus becomes large and the operation becomes complicated.
[0013]
[Problems to be solved by the invention]
The purpose of the present invention is to solve the above-mentioned problems, even in the case of treating a drainage liquid having a high BOD concentration, the BOD component is efficiently removed by a simple apparatus and operation, and the nitrification activity of the carrier is thereby increased. The purpose is to propose a nitrification method capable of increasing the nitrification rate even in the case of a high nitrogen load.
[0014]
[Means for Solving the Problems]
The present invention relates to a nitrification method in which an organic effluent containing a nitrogen compound is aerated in a nitrification tank together with return sludge, and a nitrification tank is charged with a carrier for adhering nitrifying bacteria to perform nitrification by nitrifying bacteria.
An aeration tank of 5 to 20% by volume of the total capacity of the aeration tank and the nitrification tank is provided in the front stage of the nitrification tank into which the carrier is charged,
After the organic drainage is aerated in the preceding aeration tank and the BOD component is adsorbed to the suspended sludge and substantially removed,
In this nitrification method, sludge is introduced into a nitrification tank at a subsequent stage without separation, and aeration is performed in the presence of a carrier to perform nitrification.
[0015]
In order to provide an aeration tank in the previous stage of the nitrification tank into which the carrier is introduced, each tank can be formed by separate independent tanks, but one aerobic tank is partitioned into a plurality of directions in which the organic drainage flows. Thus, it is preferable to form a first-stage aeration tank and a second-stage nitrification tank, and load the carrier into the second-stage nitrification tank so that the loaded carrier does not flow into the first-stage aeration tank.
[0016]
In order to partition one aerobic tank, a plate-shaped object or a wire mesh can be used. Between each tank in which one aerobic tank is partitioned, it is necessary to provide a flow path between both tanks so that the liquid flows without separating the sludge from the preceding tank to the subsequent tank. The effect can be obtained if the nitrification tank is separated from the preceding aeration tank, but two or more nitrification tanks may be provided.
[0017]
In the method of the present invention, the carrier may be charged into the latter nitrification tank, and the carrier may or may not be charged into the preceding aeration tank. Then, in the preceding aeration tank, oxygen-containing gas or air is aerated, and the BOD component is adsorbed to the suspended sludge and substantially removed. In this case, the BOD concentration is preferably 10 mg / l or less, particularly 6 mg / l or less. In this way, the liquid from which the BOD component has been substantially removed is introduced into the latter nitrification tank as it is without separating the sludge, and is aerated with oxygen-containing gas or air in the latter nitrification tank and adsorbed on the floating sludge. The BOD component is oxidized and decomposed , and nitrifying bacteria are selectively attached in a state where the carrier is suspended to nitrify.
[0018]
Since the aeration tank and the nitrification tank have different sludge biota, it is generally said that it is necessary to separate the sludge in the middle as disclosed in JP-A-57-75192. When the BOD component is substantially removed in the aeration tank, the growth of BOD-degrading bacteria in the latter nitrification tank is suppressed even if it flows directly into the latter nitrification tank without separating the sludge in the middle, and the suspended sludge is adsorbed. The BOD component is oxidized and decomposed, and nitrifying bacteria selectively adhere to the carrier, and the amount of nitrifying bacteria retained increases and the nitrification rate increases.
[0019]
The ratio of the aeration tank capacity in the previous stage and the nitrification tank capacity in the subsequent stage where the carrier is introduced is determined by considering the removal rate of the BOD component in the previous aeration tank and the nitrification speed in the subsequent nitrification tank. It is set so that the nitrification speed of the entire tank is increased. Since the removal rate of the BOD component by normal adsorption is much faster than the nitrification rate, the nitrification rate in the subsequent nitrification tank is increased even if the capacity of the previous aeration tank is small. Accordingly, the ratio of the preceding aeration tank to the total capacity of the preceding aeration tank and the subsequent nitrification tank varies depending on the amount of carrier introduced into the subsequent nitrification tank, but is 5 to 20% by volume.
[0020]
When one aerobic tank is partitioned, if the carrier flows into the preceding aeration tank (BOD removal section), BOD-degrading bacteria other than nitrifying bacteria adhere to the inflowed carrier, so that the nitrifying bacteria as a whole aerobic tank The retention amount decreases, and the nitrification rate (NH ₄ —N removal rate) decreases. Therefore, it is necessary to perform the treatment in a state in which the carrier charged into the subsequent nitrification tank does not flow into the previous aeration tank. In order to prevent the carrier from entering the aeration tank, the liquid should overflow from the preceding aeration tank to the subsequent nitrification tank, and the amount of water (pressure) flowing into the previous aeration tank or from the subsequent nitrification tank It can be performed by a method of adjusting the amount (pressure) of flowing water, a method of partitioning the tank with a wire mesh, or a method of providing a wire mesh in the flow path.
[0021]
As a carrier to which nitrifying bacteria are attached, a sponge is preferable, but any nitrifying bacteria such as a porous body made of a polymer can be used without limitation. In the case of a nitrification tank in the latter stage, the amount of the carrier introduced is 5 to 40% by volume, preferably 10 to 30% by volume, with respect to the tank capacity.
[0022]
A carrier having a large specific surface area is preferable. The size of the carrier is preferably 2 to 20 mm in consideration of separability from suspended sludge. The shape is not particularly limited, and for example, a spherical shape or a cubic shape can be used. The material of the carrier is not particularly limited, and examples thereof include polyurethane.
[0023]
The nitrification method of the present invention can be suitably employed as a nitrification method in a biological nitrogen removal method (nitrification denitrification method) of organic effluent, thereby efficiently removing nitrogen even under high nitrogen load conditions. be able to.
[0024]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a flow chart showing a biological nitrification denitrification method for organic drainage employing the nitrification method of the present invention, and is performed when one aerobic tank is divided into a front aeration tank and a rear nitrification tank. It is an example. In the figure, the same reference numerals as those in FIG. 2 denote the same or corresponding parts.
[0025]
A raw water pipe 6, a sludge return pipe 7, a circulating liquid pipe 8 and a connecting pipe 9 are connected to the denitrification tank 1, and are gently stirred by a stirrer 10 to maintain an anaerobic state for denitrification. .
[0026]
A partition plate 31 is provided in the aerobic tank 30 so as to be orthogonal to the flow direction of the raw water, and is divided into a front aeration tank 32 and a rear nitrification tank 2. The carrier 14 made of the above is introduced, and a screen 15 for preventing the carrier 14 from being lost is provided at the outlet of the nitrification tank 2 in the subsequent stage. A communication pipe 9 from the denitrification tank 1 is connected to the aeration tank 32 in the front stage, and a communication pipe 11 to the final denitrification tank 3 is connected to the nitrification tank 2 in the rear stage. Then, air is sent from the air pipe 12 to the preceding aeration tank 32 and the subsequent nitrification tank 2 and diffused from the preceding aeration apparatus 34 and the subsequent aeration apparatus 35, and the BOD component is removed in the preceding aeration tank 32. In the latter nitrification tank 2, nitrification is performed. A flow path 36 is provided on the wall surface or bottom surface of the partition plate 31 and the aerobic tank 30, and the liquid in the front aeration tank 32 flows from the flow path 36 into the nitrification tank 2 in the subsequent stage. A wire net (not shown) is provided in the flow path 36 so that the carrier 14 does not flow backward to the aeration tank 32 in the preceding stage.
[0027]
Connecting

pipes

11 and 17 and an organic substance supply pipe 18 are connected to the final denitrification tank 3 and are gently stirred by a stirrer 19 to maintain an anaerobic state.
Connecting

pipes

17 and 20 are connected to the final aerobic treatment tank 4, and air is sent from the air pipe 21 and diffused from the final air diffuser 22 to perform the aerobic treatment.
[0028]
The solid-liquid separation tank 5 is connected to a communication pipe 20, a treated water pipe 23, and a sludge pipe 24 so that solid-liquid separation is performed by sedimentation separation. The sludge pipe 24 branches to the sludge return pipe 7 and the sludge discharge pipe 25, and a part of the separated sludge is returned to the denitrification tank 1 through the sludge return pipe 7.
[0029]
In order to treat the raw water according to the flow of FIG. 1, first, raw water containing a nitrogen compound and a BOD component is introduced into the denitrification tank 1 from the raw water pipe 6, and the return sludge is introduced from the sludge return pipe 7. The nitrification liquid that has undergone nitrification in 2 is introduced from the circulating liquid pipe 8 and mixed with the activated sludge containing denitrifying bacteria by the agitator 10 to perform denitrification while maintaining an anaerobic state. The circulation amount of the nitrification liquid is usually 100 to 500% by volume with respect to the raw water amount. In such a denitrification step, denitrifying bacteria that reduce nitric acid or nitrite ions in the circulating fluid to nitrogen are dominant, and the nitrogen component in the raw water is removed and the BOD component is also removed.
[0030]
The denitrification liquid in the denitrification tank 1 is taken out from the connecting pipe 9 part by part, introduced into the aeration tank 32 in the preceding stage, sent from the air pipe 12 and diffused from the aeration device 34 in the previous stage to aerobic conditions The BOD component is substantially removed by floating sludge, and the BOD concentration is 10 mg / l or less. In this case, a part of the nitrogen compound may be nitrified. The liquid mixture in the upstream aeration tank 32 flows from the flow path 36 into the subsequent nitrification tank 2 without separating the sludge part by part. In the latter stage nitrification tank 2, air is sent from the air pipe 12 to the liquid from which the BOD component has been removed in the previous stage aeration tank 32 and diffused from the subsequent stage diffuser 35 to obtain an aerobic condition. In this state, nitrification is performed by nitrifying bacteria, and the nitrogen component in the raw water is nitrified to nitrate ions or nitrite ions. Here, aeration in excess of the aeration for normal BOD removal makes the nitrifying bacteria dominant.
[0031]
In the aerobic tank 30, a wire net is stretched in the flow path 36 below the partition plate 31 so that the carrier 14 in the nitrification tank 2 in the subsequent stage does not flow into the aeration tank 32 in the preceding stage.
In this way, the aerobic tank 30 is partitioned, the BOD component is removed in the preceding aeration tank 32, and then nitrified in the subsequent nitrification tank 2, whereby the nitrifying bacteria are stably retained in the carrier 14 in a large amount, and high Nitrification activity is maintained.
[0032]
The conditions of the aerobic tank 30 are pH 6-9, preferably 7-8.5, temperature 0-40 ° C, preferably 15-35 ° C.
[0033]
A part of the nitrification liquid nitrified in the latter nitrification tank 2 is introduced into the final denitrification tank 3 from the communication pipe 11, and an organic substance such as methanol is supplied from the organic substance supply pipe 18 as a hydrogen donor. Final denitrification is performed as in the case. The final denitrification liquid in the final denitrification tank 3 is re-aerated in the final aerobic treatment tank 4 to remove remaining organic substances.
[0034]
The final aerobic treatment liquid in the final aerobic treatment tank 4 is taken out from the connecting pipe 20 one by one, introduced into the solid-liquid separation tank 5 and separated into solid and liquid, and separated into separated liquid and separated sludge. The separation liquid is discharged from the treated water pipe 23 as treated water. The separated sludge is taken out from the sludge pipe 24 and a part thereof is returned to the denitrification tank 1 from the sludge return pipe 7 as return sludge. The remainder is discharged out of the system from the sludge discharge pipe 25 as excess sludge.
In the method of FIG. 1, the final denitrification tank 3 and the final aerobic treatment tank 4 can be omitted.
[0035]
Next, test examples will be described.
Test example 1
According to the method of Figure 1 but omitting the final denitrification tank 3 and final aerobic treatment tank 4, a biological nitrification and denitrification of organic waste liquid was as follows, NH ₄ -N in aerobic tank 30 The removal rate was determined.
[0036]
As raw water, synthetic waste water (nitrogen source: NH ₄ Cl, BOD source: glucose, acetic acid) was used. As shown in Table 1, the treatment conditions were set such that the ratio of the previous aeration tank 32 with respect to the entire volume of the aerobic tank 30 was 0 (control), 5, 10, 15 or 20% by volume. went. A 3 mm square polyurethane sponge was used as the carrier 14 and added so as to be 20% by volume with respect to the volume of the nitrification tank 2 in the subsequent stage. The pH of the aerobic tank 30 was controlled at 7.5. The amount of circulating fluid was 3 times the amount of raw water. The amount of returned sludge was 30% of the amount of raw water.
In order to investigate the maximum capacity capable of removing nitrogen, the test was carried out by applying an excessive nitrogen load and knowing the NH ₄ -N water quality of the treated water so that the overall nitrification ability can be known. The operating conditions and results are shown in Table 1.
[0037]
[Table 1]

[0038]
From Table 1, the NH ₄ —N removal rate increases as the ratio of the previous aeration tank increases to 5% by volume and 10% by volume, and the highest NH ₄ —N removal rate is shown at 10% by volume. It can be seen that the number decreases.
[0039]
【The invention's effect】
As described above, according to the nitrification method of the present invention, an aeration tank of 5 to 20% by volume of the total capacity of the aeration tank and the nitrification tank is provided in the previous stage of the nitrification tank into which the carrier is introduced, and the organic waste liquid is supplied in the previous stage. Aeration is performed in an aeration tank, and BOD components are adsorbed to the suspended sludge and substantially removed. Then, the sludge is introduced into a subsequent nitrification tank without separation, and aeration is performed in the presence of a carrier to perform nitrification. As a result, it is possible to efficiently remove the BOD component and increase the nitrification activity of the carrier even when processing the drainage with a high BOD concentration, thereby increasing the nitrification rate even in the case of a high nitrogen load and the processing time. The intermediate sludge separation can be omitted, the apparatus can be downsized, and the operation can be simplified.
[Brief description of the drawings]
FIG. 1 is a flow diagram showing a biological nitrification denitrification method employing the nitrification method of the present invention.
FIG. 2 is a flow diagram showing a biological nitrification denitrification method employing a conventional nitrification method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Denitrification tank 2 Nitrification tank 3 Final denitrification tank 4 Final aerobic treatment tank 5 Solid-liquid separation tank 6 Raw water pipe 7 Sludge return pipe 8 Circulating

liquid pipe

9, 11, 17, 20 Connecting

pipe

10, 19

Stirrer

12, 21 Air Pipe 13 Air diffuser 14 Carrier 15 Screen 18 Organic substance supply pipe 22 Final air diffuser 23 Treated water pipe 24 Sludge pipe 25 Sludge discharge pipe 30 Aerobic tank 31 Partition plate 32 Aeration tank 34 Air diffuser 35 in the previous stage Air diffuser in the subsequent stage 36 flow path

Claims

In the nitrification method in which organic waste liquid containing nitrogen compounds is aerated in the nitrification tank together with the return sludge, and the nitrification tank is charged with a carrier for adhering nitrifying bacteria to perform nitrification by nitrifying bacteria.
An aeration tank of 5 to 20% by volume of the total capacity of the aeration tank and the nitrification tank is provided in the front stage of the nitrification tank into which the carrier is charged,
After the organic drainage is aerated in the preceding aeration tank and the BOD component is adsorbed to the suspended sludge and substantially removed,
A nitrification method comprising introducing sludge into a subsequent nitrification tank without separation and performing aeration in the presence of a carrier to perform nitrification.