JP3814835B2

JP3814835B2 - Biological nitrification denitrification equipment

Info

Publication number: JP3814835B2
Application number: JP02980795A
Authority: JP
Inventors: 敦渡辺
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 1995-02-17
Filing date: 1995-02-17
Publication date: 2006-08-30
Anticipated expiration: 2021-08-30
Also published as: JPH08224594A

Description

【０００１】
【産業上の利用分野】
本発明は、被処理液中の窒素化合物を生物学的に硝化脱窒する生物学的硝化脱窒装置に関し、さらに詳細には窒素化合物含有排液の生物学的硝化脱窒法に利用可能な生物学的硝化脱窒装置に関する。
【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の存在下に好気性処理して排液中の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、その後硝化細菌が増殖した活性汚泥の存在下に曝気してアンモニア性窒素（ＮＨ₄−Ｎ）を硝化細菌により亜硝酸性または硝酸性窒素（以下、これらをまとめてＮＯ_x−Ｎという場合がある）に硝化（酸化）した後、脱窒細菌が増殖した活性汚泥の存在下に嫌気状態に維持することにより、亜硝酸性または硝酸性窒素を窒素ガスに還元して脱窒する方法である。このような生物学的硝化脱窒処理法では、脱窒の際に硝酸または亜硝酸を酸素源とする硝酸呼吸が行われるため、水素供与体が必要である。この水素供与体としては排液中の有機物が利用され、排液中の窒素に対して有機物が２．５〜３倍必要であるとされている。従ってこれ以上の有機物が排液中に存在している場合には新たに水素供与体を添加する必要はないが、これより少ない場合はメタノール、エタノール等の易分解性の有機物を水素供与体として添加して処理が行われる。
【０００３】
ところで生物学的硝化脱窒処理法の一つに循環法と呼ばれる方法がある。この方法は硝化槽の前段に脱窒槽を備え、脱窒槽および硝化槽で処理した硝化処理液を前段の脱窒槽に循環（返送）して脱窒する方法である。このような循環法による窒素除去率は、被処理液に対する硝化処理液の循環比（被処理液の流量に対する循環液の流量）により決定され、循環比が大きくなるほど窒素除去率は大きくなる。つまり、窒素除去率は窒素除去率＝循環比／（１＋循環比）の式で表わされ、循環比が２の場合、すなわち被処理液に対して２倍の硝化処理液を循環する場合で約６７％、循環比４の場合で８０％、循環比９の場合で９０％の窒素除去率となる。
【０００４】
【発明が解決しようとする課題】
しかし硝化処理液は溶存酸素で飽和状態となっているため、循環比が大きくなるに伴って硝化処理液中の溶存酸素が多量に脱窒槽に持込まれることになり、これにより脱窒槽の嫌気度が保てなくなって脱窒が不完全となる。これを防止するためには過剰の水素供与体を脱窒槽に添加して溶存酸素を除去することができるが、この方法は脱窒に必要な水素供与体に加えて溶存酸素除去のために水素供与体が消費されるので、水素供与体の添加量が多くなる。さらに循環比が大きくなり、また溶存酸素の除去量が多くなるに従って、有機物の除去量も増加するため、排液中の窒素に対して有機物が２．５〜３倍以上存在しているような場合でも水素供与体を添加することが必要になる。
【０００５】
従来の処理法では、水素供与体は一定量で添加されており、しかも予想される被処理液中の窒素濃度の変動の内、最も高濃度の場合にも目標水質が得られるように循環比を設定しているので、通常過剰の水素供与体が添加されることになり、水素供与体が無駄に消費される。別の添加方法として、脱窒槽の酸化還元電位を検出して水素供与体の添加量を制御する場合もあるが、この場合も循環比を制御することは行われていない。このため被処理液の水質が変動して処理液の水質が目標水質より十分よい場合でも、循環比が一定であるため、硝化処理液の循環により持込まれる溶存酸素を除去するために水素供与体が添加されることになり、やはり水素供与体が無駄に消費される。
【０００６】
本発明の目的は、被処理液の窒素濃度の変動に応じて循環水量を調整するとともに、水素供与体の添加量を自動的に調整し、これにより水素供与体の過剰添加を防止して、低コストで硝化脱窒を行うことが可能な生物学的硝化脱窒装置を提供することである。
【０００７】
【課題を解決するための手段】
本発明は、被処理液および硝化槽から循環される硝化処理液を受入れて生物学的に脱窒を行う脱窒槽と、
この脱窒槽で脱窒した脱窒処理液を受入れて生物学的に硝化を行う硝化槽と、
この硝化槽で硝化した硝化処理液の窒素濃度を検出する窒素濃度検出装置と、
循環液中の溶存酸素濃度を検出する溶存酸素濃度検出装置と、
被処理液および循環液の流量を測定する流量計と、
窒素濃度検出装置で検出した硝化処理液の窒素濃度（Ｃｏｕｔ）、現在の循環比（ｒ０）および目標水質（Ｃｅ）に基づいて、被処理液の窒素濃度（Ｃｉｎ）を下式〔１〕で演算し、目標とする硝化処理液の窒素濃度を得るための被処理液に対する硝化処理液の循環比（ｒ）を下式〔２〕で演算して循環比制御信号を出力し、かつ前記循環比に応じて被処理液に添加する水素供与体の添加量を、下式〔３〕で求められる溶存酸素を除去するために必要な量（Ｅ _１）と、下式〔４〕で求められる脱窒反応に必要な量（Ｅ _２）との合計量から被処理水中に含まれている水素供与体の量を減じた量として演算して添加量制御信号を出力する制御装置と、
この制御装置から送信される循環比制御信号に応じて、その循環比が得られるように、硝化処理液の循環液量を調整する循環液量調整装置と、
前記制御装置から送信される添加量制御信号に応じて、その添加量が添加できるように、水素供与体を被処理液に注入する薬剤注入装置と
を備え、被処理液の窒素濃度を検出して制御する手段を備えていないことを特徴とする生物学的硝化脱窒装置である。
Ｃｉｎ＝Ｃｏｕｔ×（１＋ｒ０） …〔１〕
ｒ＝（Ｃｉｎ／Ｃｅ）−１ …〔２〕
Ｅ _１＝溶存酸素量×Ｋ _１ ×循環液流量 …〔３〕
Ｅ _２＝被処理液中の窒素濃度×Ｋ _２ ×被処理液流量 …〔４〕
（式中、Ｋ _１は溶存酸素単位量除去に必要な有機物量を表わす係数、Ｋ _２は２．５〜３の係数である。）
【０００８】
本発明の装置において処理の対象となる被処理液は、アンモニア性または有機性窒素化合物を含有する液であり、このほか有機物、亜硝酸性または硝酸性窒素、その他の不純物を含んでいてもよい。
【０００９】
本発明の装置を構成する脱窒槽は、脱窒細菌を含む生物汚泥と被処理液とを嫌気性下に接触させて脱窒を行う装置であり、固定床式または流動床式等の生物ろ過式のもの、あるいは浮遊式で用いられる完全混合型のものなど任意のものが使用できる。
【００１０】
本発明の装置を構成する硝化槽は、脱窒槽で脱窒した脱窒処理液と硝化細菌を含む生物汚泥とを好気性下に接触させて硝化を行う装置であり、固定床式または流動床式等の生物ろ過式のもの、あるいは浮遊式で用いられる完全混合型のものなど任意のものが使用できる。
脱窒槽と硝化槽とは別々に設けることもできるし、両者を１個の槽内に設けることもできる。後者の例としては、例えば充填層に生物汚泥を付着させた生物ろ過装置の中間に散気装置を設け、上部を好気状態に保ち、上向流で通液すると、下部を脱窒槽、上部を硝化槽として一体化することができる。
【００１１】
本発明の装置を構成する窒素濃度検出装置は硝化処理液の窒素濃度を検出し、その窒素濃度信号を制御装置に送信する装置である。検出する窒素濃度は全窒素濃度でも、硝酸性窒素濃度でもよく、目標水質に応じて選択することができる。
【００１２】
本発明の装置を構成する制御装置は、前記窒素濃度検出装置から出力される窒素濃度信号を入力し、この信号から目標水質が得られるように硝化処理液の循環比を演算し、この循環比制御信号を循環液量調整装置に出力して循環液量を調整するように構成する。
【００１３】
循環比は次のようにして求めることができる。処理液（硝化処理液）の窒素濃度（Ｃｏｕｔ）と現在の循環比（ｒ０）とから被処理液中の窒素濃度（Ｃｉｎ）を下式〔１〕から推定し、目標とする窒素濃度（Ｃｅ）を得るための適正な循環比（ｒ）を下式〔２〕で計算する。
Ｃｉｎ＝Ｃｏｕｔ×（１＋ｒ０） …〔１〕
ｒ＝（Ｃｉｎ／Ｃｅ）−１ …〔２〕
上記数式〔１〕、〔２〕から分るように、処理液の窒素濃度（Ｃｏｕｔ）が上昇すると循環液量を多くし、低下すると循環液量を少なくするように制御される。
【００１４】
また制御装置は、上記循環比の変動に応じて被処理液に添加する水素供与体の添加量を演算し、この添加量制御信号を薬剤注入装置に出力して水素供与体（薬剤）の添加量を調整するように構成する。循環比が変動すると脱窒槽に導入される硝化処理液（循環液）の液量もそれに応じて変動するので、脱窒槽に持込まれる溶存酸素の量が変動する。このため循環比が大きくなる（循環液量が多くなる）と脱窒槽に持込まれる溶存酸素の量が多くなり、脱窒に必要な嫌気性が保てなくなる。従って制御装置では、循環比の変動に応じて変動する必要最低限の水素供与体の添加量を求める。
【００１５】
水素供与体の添加量は、溶存酸素を除去するために必要な量（Ｅ_１）と脱窒反応に必要な量（Ｅ_２）との合計量から、被処理液中に含まれている水素供与体（有機物）の量を減じた量として求める。Ｅ_１、Ｅ_２は次の数式により求める。
Ｅ_１＝溶存酸素量×Ｋ_１×循環液流量 …〔３〕
Ｅ_２＝被処理液中の窒素濃度×Ｋ_２×被処理液流量 …〔４〕
【００１６】
上記数式〔３〕、〔４〕において、溶存酸素量は処理液中の濃度を溶存酸素濃度検出装置により検出して求めることもできるし、飽和濃度などの定数を用いてもよい。Ｋ₁は溶存酸素単位量除去に必要な有機物量を表わす係数であり、通常０．８７である。Ｋ₂は係数であり、通常２．５〜３である。
また被処理液中の水素供与体（有機物）は予め測定した値を用いるか、有機物の濃度測定装置を設置して測定して求めてもよい。
【００１７】
本発明の装置を構成する循環液量調整装置は、前記制御装置から送信される循環比制御信号に応じて循環液の流量を調整する装置であり、ポンプ、流量調整弁などが採用できる。
本発明の装置を構成する薬剤注入装置は、前記制御装置から送信される添加量制御信号に応じて水素供与体（薬剤）の添加量を調整する装置であり、ポンプなどが採用できる。なお水素供与体としては、メタノール、エタノールなどの易分解性有機物が使用できる。
【００１８】
【作用】
本発明の生物学的硝化脱窒装置では、窒素濃度検出装置で検出される処理液（硝化処理液）中の窒素濃度に応じて制御装置により循環比が決定され、循環液量調整装置により循環液量が自動的に増減されるので、被処理液中の窒素濃度が変動しても常に安定した処理液水質を得ることができる。
【００１９】
そして循環液量の増減に応じて、制御装置により必要最低限の水素供与体の添加量が決定され、薬剤注入装置により添加量が自動的に増減されるので、循環液量（循環比）が変動しても常に適切な量の水素供与体を添加することが可能になる。これにより水素供与体の過剰添加は防止され、低コストでの運転が可能になる。
【００２０】
【実施例】
次に本発明の実施例を図面により説明する。
図１は実施例の生物学的硝化脱窒装置を示す系統図であり、硝化槽および脱窒槽が一体化した場合の例を示している。図１において、１は脱窒硝化槽、２は脱窒部、３は硝化部、４は制御装置、５は窒素濃度検出装置、６は溶存酸素濃度検出装置、７は薬剤貯槽、８、９は流量計である。
【００２１】
脱窒硝化槽１の内部には空気供給路１１に接続する散気装置１２が設けられ、散気装置１２の下部に脱窒細菌を含む生物ろ過層１３、上部に硝化細菌を含む生物ろ過層１４が形成され、それぞれ脱窒部２および硝化部３を構成している。生物ろ過層１３、１４としては造粒化汚泥を充填したもの、あるいは充填層に生物汚泥を付着させたものなど、任意のものが採用できる。また生物ろ過層１３、１４は固定床のほかに、脱窒部２と硝化部３との間に仕切を設けて流動床とすることもできる。脱窒硝化槽１の下部には被処理液ポンプ２１を有する被処理液路２２が連絡し、薬注ポンプ２３を有する薬注路２４が被処理液路２２に連絡している。脱窒硝化槽１の上部には処理液路２５および排ガス路２６が連絡している。処理液路２５は循環路２７が分岐して被処理液路２２に接続している。循環路２７の中間には循環ポンプ２８が設けられている。
【００２２】
窒素濃度検出装置５は硝化処理液（循環液）中の窒素濃度が検出できるように構成されている。溶存酸素濃度検出装置６は循環液中の溶存酸素濃度が検出できるように構成されている。流量計８、９はそれぞれ被処理液および循環液の流量が測定できるように構成されている。
【００２３】
制御装置４は窒素濃度検出装置５で検出した硝化処理液（循環液）中の窒素濃度信号、溶存酸素濃度検出装置６で検出した循環液中の溶存酸素濃度信号、流量計８、９で測定した被処理液および循環液の流量信号を入力し、目標水質が得られる必要循環比を演算し、循環ポンプ２８に循環比制御信号を出力するように構成されている。そして上記必要循環比および溶存酸素濃度信号に基づいて、脱窒部２に水素供与体となる薬剤を添加する際の必要薬注量を演算し、薬注ポンプ２３に添加量制御信号を出力するように構成されている。
【００２４】
図１の装置により硝化脱窒を行うには、まず被処理液ポンプ２１を駆動するとともに循環ポンプ２８を駆動し、被処理液路２２を通して供給される被処理液と循環路２７を通して循環される循環液とを混合する。さらに薬注ポンプ２３を駆動し、薬剤貯槽７から薬注路２４を通して水素供与体を混合し、この混合液を脱窒硝化槽１下部から脱窒部２に導入する。被処理液の流量は流量計９で連続的または間欠的に検出し、この流量信号を制御装置４に送信する。脱窒部２では混合液を生物ろ過層１３中を上向流で通液し、脱窒細菌の作用により混合液中の亜硝酸または硝酸性窒素を窒素ガスに生物学的に脱窒する。
【００２５】
脱窒処理液は硝化部３に導入して硝化する。硝化部３では空気供給路１１から供給する空気を散気装置１２から散気した状態で、脱窒処理液を生物ろ過層１４中を上向流で通液し、硝化細菌の作用により脱窒処理液中のアンモニア性窒素を亜硝酸または硝酸性窒素に生物学的に硝化する。脱窒処理液中に有機性窒素化合物が含有されている場合は、この有機性窒素化合物は生物ろ過層１４中の微生物の作用によりアンモニア性窒素に分解され、さらに硝化細菌の作用により亜硝酸または硝酸性窒素に硝化される。
【００２６】
硝化処理液の一部は循環路２７から循環ポンプ２８により循環液として循環し、残部は処理液として処理液路２５から取出す。排ガスは排ガス路２６から排出する。処理液（硝化処理液）中の窒素濃度は窒素濃度検出装置５により連続的または間欠的に検出し、この窒素濃度信号を制御装置４に送信する。また循環液中の溶存酸素濃度を溶存酸素濃度検出装置６により連続的または間欠的に検出し、この溶存酸素濃度信号を制御装置４に送信する。さらに循環液の流量を流量計８で連続的または間欠的に検出し、この流量信号を制御装置４に送信する。
【００２７】
制御装置４では、窒素濃度信号および被処理液の流量信号から目標水質を得るための循環比を演算し、その循環液量が得られるように、循環ポンプ２８に対して循環比制御信号を出力し、循環液量を調整する。これにより、被処理液中の窒素化合物の含有量などが変動する場合でも常に安定して目標水質を得ることができる。
【００２８】
また制御装置４では、溶存酸素濃度信号および循環液の流量信号に基づいて水素供与体の添加量を演算し、その添加量が添加できるように、薬注ポンプ２３に対して添加量制御信号を出力し、水素供与体の添加量を調整する。これにより、循環液量、被処理液中の窒素濃度や有機物含有量などが変動しても、変動に応じて常に適切な量の水素供与体が添加できるので、水素供与体の無駄な添加が防止できる。
【００２９】
なお図１の生物学的硝化脱窒装置では、被処理液の流量が一定している場合、流量計９は省略することができる。
また図１の生物学的硝化脱窒装置では脱窒槽と硝化槽が一体化した脱窒硝化槽１を用いているが、脱窒槽と硝化槽とを別々に設けることもできる。この場合被処理液と生物汚泥とを混合して脱窒または硝化する完全混合型の浮遊法による槽を採用することもできる。
【００３０】
さらに薬注路２４は被処理液路２２に接続する代わりに脱窒硝化槽１に直接接続させて、被処理液と循環液との混合液に薬剤を添加するように構成することもできる。
【００３１】
試験例１
図１の装置により塗装排液の硝化脱窒を行った。運転は、まず全窒素濃度１００ｍｇ／ｌ、ＢＯＤ濃度１５０ｍｇ／ｌ、ＳＳ４５ｍｇ／ｌの排水を、下記条件で処理した。このときの水素供与体としてのメタノールの添加量は１００ｍｌ／ｌ−被処理液、処理液の全窒素濃度は９ｍｇ／ｌであった。
脱窒硝化槽：
直径；４００ｍｍ
有効高さ；３，０００ｍｍ
硝化部長；２，０００ｍｍ
脱窒部長；１，０００ｍｍ
負荷：
硝化負荷；０．７ｋｇ−Ｎ／ｍ³・ｄ
脱窒負荷；１．４ｋｇ−Ｎ／ｍ³・ｄ
被処理液流量：１．８ｍ³／ｄ
循環比：９倍
処理液の全窒素濃度の目標水質：１０ｍｇ／ｌ
【００３２】
次に被処理液の全窒素濃度を６５ｍｇ／ｌ（ＢＯＤ濃度は１５０ｍｇ／ｌで一定）に低下させて運転した。このとき水素供与体の添加量は１２ｍｇ／ｌ−被処理液と約１２％に低下した。また処理液の全窒素濃度は８ｍｇ／ｌ、循環比は７倍であった。
【００３３】
【発明の効果】
本発明の生物学的硝化脱窒装置は、硝化処理液の窒素濃度を検出する窒素濃度検出装置と、循環液中の溶存酸素濃度を検出する溶存酸素濃度検出装置と、被処理液および循環液の流量を測定する流量計と、窒素濃度検出装置で検出した硝化処理液の窒素濃度、現在の循環比および目標水質に基づいて、被処理液の窒素濃度を演算し、目標とする硝化処理液の窒素濃度を得るための被処理液に対する硝化処理液の循環比を演算して循環比制御信号を出力し、かつ前記循環比に応じて被処理液に添加する水素供与体の添加量を、溶存酸素を除去するために必要な量と、脱窒反応に必要な量との合計量から被処理水中に含まれている水素供与体の量を減じた量として演算して添加量制御信号を出力する制御装置と、この制御装置から送信される循環比制御信号に応じて、その循環比が得られるように、硝化処理液の循環液量を調整する循環液量調整装置と、前記制御装置から送信される添加量制御信号に応じて、その添加量が添加できるように、水素供与体を被処理液に注入する薬剤注入装置とを備えているので、被処理液の窒素濃度が変動しても、その変動に応じて添加する水素供与体の量を自動的に調整でき、これにより水素供与体の過剰な添加を防止して低コストで硝化脱窒を行うことができる。
【図面の簡単な説明】
【図１】実施例の生物学的硝化脱窒装置を示す系統図である。
【符号の説明】
１脱窒硝化槽
２脱窒部
３硝化部
４制御装置
５窒素濃度検出装置
６溶存酸素濃度検出装置
７薬剤貯槽
８、９流量計
１１空気供給路
１２散気装置
１３、１４生物ろ過層
２１被処理液ポンプ
２２被処理液路
２３薬注ポンプ
２４薬注路
２５処理液路
２６排ガス路
２７循環路
２８循環ポンプ[0001]
[Industrial application fields]
The present invention relates to a biological nitrification denitrification apparatus for biologically nitrifying and denitrifying nitrogen compounds in a liquid to be treated, and more specifically, a biological substance that can be used in a biological nitrification and denitrification method of a nitrogen compound-containing effluent. The present invention relates to a chemical nitrification denitrification device.
[0002]
[Prior art]
There is a biological nitrification denitrification method as a method for treating a drainage liquid containing ammoniacal or organic nitrogen compounds. In this method, aerobic treatment is performed in the presence of activated sludge to decompose COD and BOD components in the effluent, and the organic nitrogen compound is changed to ammonia nitrogen, and then aerated in the presence of activated sludge on which nitrifying bacteria have grown. After nitrifying (oxidizing) ammoniacal nitrogen (NH ₄ -N) to nitrite or nitrate nitrogen (hereinafter, these may be collectively referred to as NO _x -N) by nitrifying bacteria, denitrifying bacteria This is a method of denitrifying by reducing nitrite or nitrate nitrogen to nitrogen gas by maintaining it in an anaerobic state in the presence of activated activated sludge. In such a biological nitrification denitrification treatment method, nitric acid respiration using nitric acid or nitrous acid as an oxygen source is performed at the time of denitrification, so a hydrogen donor is necessary. As this hydrogen donor, organic matter in the drainage is used, and it is said that the organic matter is required 2.5 to 3 times the nitrogen in the drainage. Therefore, it is not necessary to add a new hydrogen donor when more organic substances are present in the effluent, but when the amount is less than this, easily decomposable organic substances such as methanol and ethanol are used as the hydrogen donor. Addition is performed.
[0003]
By the way, there is a method called a circulation method as one of biological nitrification denitrification treatment methods. In this method, a denitrification tank is provided in the previous stage of the nitrification tank, and the nitrification treatment liquid treated in the denitrification tank and the nitrification tank is circulated (returned) to the previous denitrification tank for denitrification. The nitrogen removal rate by such a circulation method is determined by the circulation ratio of the nitrification treatment liquid to the liquid to be treated (the flow rate of the circulation liquid with respect to the flow rate of the liquid to be treated), and the nitrogen removal rate increases as the circulation ratio increases. In other words, the nitrogen removal rate is expressed by the formula nitrogen removal rate = circulation ratio / (1 + circulation ratio), and when the circulation ratio is 2, that is, when the nitrification liquid is circulated twice as much as the liquid to be treated. The nitrogen removal rate is about 67%, 80% when the circulation ratio is 4, and 90% when the circulation ratio is 9.
[0004]
[Problems to be solved by the invention]
However, since the nitrification liquid is saturated with dissolved oxygen, as the circulation ratio increases, a large amount of dissolved oxygen in the nitrification liquid is brought into the denitrification tank. Can no longer be maintained and denitrification is incomplete. To prevent this, excess hydrogen donor can be added to the denitrification tank to remove dissolved oxygen, but this method adds hydrogen to remove the dissolved oxygen in addition to the hydrogen donor required for denitrification. Since the donor is consumed, the amount of hydrogen donor added is increased. Furthermore, as the circulation ratio increases and the removal amount of dissolved oxygen increases, the removal amount of organic matter also increases, so that the organic matter is present 2.5 to 3 times or more with respect to nitrogen in the effluent. Even if it is necessary to add a hydrogen donor.
[0005]
In the conventional treatment method, the hydrogen donor is added in a fixed amount, and the circulation ratio is set so that the target water quality can be obtained even at the highest concentration among the expected fluctuations in the nitrogen concentration in the liquid to be treated. Therefore, usually an excess of hydrogen donor is added, and the hydrogen donor is wasted. As another addition method, the redox potential in the denitrification tank may be detected to control the addition amount of the hydrogen donor, but in this case as well, the circulation ratio is not controlled. For this reason, even if the water quality of the liquid to be treated fluctuates and the water quality of the treatment liquid is sufficiently better than the target water quality, the circulation ratio is constant, so the hydrogen donor is used to remove dissolved oxygen brought in by circulation of the nitrification liquid. As a result, hydrogen donors are wasted.
[0006]
The purpose of the present invention is to adjust the amount of circulating water according to the variation in the nitrogen concentration of the liquid to be treated, and automatically adjust the amount of hydrogen donor added, thereby preventing excessive addition of the hydrogen donor, A biological nitrification denitrification apparatus capable of performing nitrification denitrification at low cost is provided.
[0007]
[Means for Solving the Problems]
The present invention includes a denitrification tank that receives a nitrification treatment liquid circulated from a liquid to be treated and a nitrification tank and performs biological denitrification;
A nitrification tank that receives the denitrification solution denitrified in this denitrification tank and biologically nitrifies,
A nitrogen concentration detection device for detecting the nitrogen concentration of the nitrification solution nitrified in the nitrification tank;
A dissolved oxygen concentration detection device for detecting the dissolved oxygen concentration in the circulating fluid;
A flow meter for measuring the flow rate of the liquid to be treated and the circulating fluid;
Nitrogen concentration in the nitrified liquid detected by the nitrogen concentration detection device (Cout), the current circulation ratio (r0) and based on the target quality (Ce), the following formula the nitrogen concentration of the liquid to be treated (Cin) [1] To calculate the circulation ratio (r) of the nitrification liquid to the liquid to be treated for obtaining the target nitrogen concentration of the nitrification liquid by the following equation [2] , and output the circulation ratio control signal; The amount of hydrogen donor added to the liquid to be treated according to the circulation ratio is determined by the amount (E ₁ ) required to remove dissolved oxygen determined by the following equation [3] and by the following equation [4]. A controller that calculates the amount obtained by subtracting the amount of hydrogen donor contained in the water to be treated from the total amount required for the denitrification reaction (E ₂ ) and outputs an addition amount control signal;
In accordance with the circulation ratio control signal transmitted from this control device, a circulating fluid amount adjusting device that adjusts the circulating fluid amount of the nitrification liquid so as to obtain the circulation ratio;
A chemical injection device for injecting a hydrogen donor into the liquid to be treated so that the amount of addition can be added in response to an addition amount control signal transmitted from the control device, and detecting the nitrogen concentration of the liquid to be treated. The biological nitrification denitrification apparatus is characterized in that it does not have a control means .
Cin = Cout × (1 + r0) (1)
r = (Cin / Ce) −1 (2)
E ₁ = dissolved oxygen amount × K ₁ × circulating fluid flow rate [3]
E ₂ = nitrogen concentration in the liquid to be processed × K ₂ × flow rate of the liquid to be processed ... [4]
(In the formula, K ₁ is a coefficient representing the amount of organic substances necessary for removing the dissolved oxygen unit amount, and K ₂ is a coefficient of 2.5 to _3. )
[0008]
The liquid to be treated in the apparatus of the present invention is a liquid containing ammoniacal or organic nitrogen compounds, and may further contain organic substances, nitrite or nitrate nitrogen, and other impurities. .
[0009]
The denitrification tank constituting the apparatus of the present invention is an apparatus for performing denitrification by contacting biological sludge containing denitrifying bacteria and the liquid to be treated under anaerobic conditions, and biological filtration such as fixed bed type or fluidized bed type. Arbitrary ones such as those of the formula or those of the complete mixing type used in the floating type can be used.
[0010]
The nitrification tank constituting the apparatus of the present invention is an apparatus that performs nitrification by contacting the denitrification treatment liquid denitrified in the denitrification tank and the biological sludge containing nitrifying bacteria under aerobic conditions, and is a fixed bed type or fluidized bed. Arbitrary things such as a biological filtration type such as a formula, or a completely mixed type used in a floating type can be used.
The denitrification tank and the nitrification tank can be provided separately, or both can be provided in one tank. As an example of the latter, for example, an air diffuser is provided in the middle of a biological filtration device in which biological sludge is adhered to the packed bed, and the upper part is kept in an aerobic state. Can be integrated as a nitrification tank.
[0011]
The nitrogen concentration detection device constituting the device of the present invention is a device that detects the nitrogen concentration of the nitrification solution and transmits the nitrogen concentration signal to the control device. The nitrogen concentration to be detected may be the total nitrogen concentration or the nitrate nitrogen concentration, and can be selected according to the target water quality.
[0012]
The control device constituting the device of the present invention receives the nitrogen concentration signal output from the nitrogen concentration detection device, calculates the circulation ratio of the nitrification solution so as to obtain the target water quality from this signal, and the circulation ratio. A control signal is output to the circulating fluid amount adjusting device to adjust the circulating fluid amount.
[0013]
The circulation ratio can be obtained as follows. The nitrogen concentration (Cin) in the liquid to be treated is estimated from the following equation [1] from the nitrogen concentration (Cout) of the treatment liquid (nitrification liquid) and the current circulation ratio (r0), and the target nitrogen concentration (Ce) ) proper circulation ratio for obtaining a (r) calculated by the following formula (2).
Cin = Cout × (1 + r0) (1)
r = (Cin / Ce) −1 (2)
As can be seen from the above formulas [1] and [2], the amount of circulating fluid is controlled to increase when the nitrogen concentration (Cout) of the processing solution increases, and the amount of circulating fluid is decreased when it decreases.
[0014]
In addition, the control device calculates the amount of hydrogen donor added to the liquid to be treated according to the change in the circulation ratio, and outputs this addition amount control signal to the drug injection device to add the hydrogen donor (drug). Configure to adjust the amount. When the circulation ratio varies, the amount of the nitrification treatment liquid (circulation solution) introduced into the denitrification tank also varies accordingly, so the amount of dissolved oxygen brought into the denitrification tank varies. For this reason, when the circulation ratio increases (the amount of circulating fluid increases), the amount of dissolved oxygen brought into the denitrification tank increases and the anaerobic property necessary for denitrification cannot be maintained. Therefore, the control device obtains the minimum necessary amount of hydrogen donor that varies depending on the circulation ratio.
[0015]
The amount of hydrogen donor added is determined from the total amount of the amount necessary for removing dissolved oxygen (E ₁ ) and the amount necessary for the denitrification reaction (E ₂ ), and the amount of hydrogen contained in the liquid to be treated. Calculated as the reduced amount of donor (organic). _E _1, E ₂ is Ru determined by the following formula.
E ₁ = dissolved oxygen amount × K ₁ × circulating fluid flow rate [3]
E ₂ = nitrogen concentration in the liquid to be processed × K ₂ × flow rate of the liquid to be processed ... [4]
[0016]
In the above formulas [3] and [4], the dissolved oxygen amount can be obtained by detecting the concentration in the processing solution with a dissolved oxygen concentration detector, or a constant such as a saturated concentration may be used. K ₁ is a coefficient representing the amount of organic matter necessary for removing the dissolved oxygen unit amount, and is usually 0.87. K ₂ is a coefficient, which is usually 2.5-3.
The hydrogen donor (organic substance) in the liquid to be treated may be obtained by using a value measured in advance or by installing an organic substance concentration measuring device.
[0017]
The circulating fluid amount adjusting device constituting the device of the present invention is a device that adjusts the flow rate of the circulating fluid in accordance with the circulating ratio control signal transmitted from the control device, and can employ a pump, a flow rate adjusting valve, and the like.
The drug injection device constituting the device of the present invention is a device that adjusts the addition amount of the hydrogen donor (drug) in accordance with the addition amount control signal transmitted from the control device, and can employ a pump or the like. As the hydrogen donor, easily decomposable organic substances such as methanol and ethanol can be used.
[0018]
[Action]
In the biological nitrification denitrification apparatus of the present invention, the circulation ratio is determined by the control device according to the nitrogen concentration in the treatment liquid (nitrification treatment liquid) detected by the nitrogen concentration detection device, and the circulation ratio is circulated by the circulation liquid amount adjustment device. Since the amount of the liquid is automatically increased or decreased, a stable treatment liquid water quality can always be obtained even if the nitrogen concentration in the liquid to be treated fluctuates.
[0019]
Then, according to the increase / decrease of the circulating fluid volume, the minimum amount of hydrogen donor added is determined by the control device, and the added amount is automatically increased / decreased by the chemical injection device, so that the circulating fluid volume (circulation ratio) is Even if it fluctuates, it is always possible to add an appropriate amount of hydrogen donor. This prevents excessive addition of the hydrogen donor and enables operation at a low cost.
[0020]
【Example】
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a system diagram showing a biological nitrification denitrification apparatus of an embodiment, and shows an example in which a nitrification tank and a denitrification tank are integrated. In FIG. 1, 1 is a denitrification nitrification tank, 2 is a denitrification section, 3 is a nitrification section, 4 is a control device, 5 is a nitrogen concentration detection device, 6 is a dissolved oxygen concentration detection device, 7 is a chemical reservoir, and 8 and 9 Is a flow meter.
[0021]
Inside the denitrification nitrification tank 1, an air diffuser 12 connected to the air supply path 11 is provided, a biological filtration layer 13 containing denitrifying bacteria at the lower part of the air diffuser 12, and a biological filtration layer containing nitrifying bacteria at the upper part. 14 are formed, constituting the denitrification part 2 and the nitrification part 3, respectively. As the biological filtration layers 13 and 14, arbitrary ones such as those filled with granulated sludge, or those obtained by attaching biological sludge to the packed bed can be adopted. In addition to the fixed bed, the biofiltration layers 13 and 14 may be a fluidized bed by providing a partition between the denitrification unit 2 and the nitrification unit 3. A treatment liquid passage 22 having a treatment liquid pump 21 communicates with a lower portion of the denitrification nitrification tank 1, and a chemical injection passage 24 having a chemical injection pump 23 communicates with the treatment liquid passage 22. A processing liquid passage 25 and an exhaust gas passage 26 communicate with the upper part of the denitrification nitrification tank 1. In the processing liquid path 25, the circulation path 27 is branched and connected to the processing liquid path 22. A circulation pump 28 is provided in the middle of the circulation path 27.
[0022]
The nitrogen concentration detection device 5 is configured to detect the nitrogen concentration in the nitrification treatment liquid (circulating liquid). The dissolved oxygen concentration detection device 6 is configured to detect the dissolved oxygen concentration in the circulating fluid. The flow meters 8 and 9 are configured to measure the flow rates of the liquid to be treated and the circulating liquid, respectively.
[0023]
The control device 4 measures the nitrogen concentration signal in the nitrification solution (circulating fluid) detected by the nitrogen concentration detector 5, the dissolved oxygen concentration signal in the circulating fluid detected by the dissolved oxygen concentration detector 6, and measured by the flow meters 8 and 9. The flow rate signals of the liquid to be treated and the circulating fluid are input, the necessary circulation ratio for obtaining the target water quality is calculated, and the circulation ratio control signal is output to the circulation pump 28. Based on the required circulation ratio and the dissolved oxygen concentration signal, the required chemical injection amount for adding the chemical agent serving as a hydrogen donor to the denitrification unit 2 is calculated, and the additional control signal is output to the chemical injection pump 23. It is configured as follows.
[0024]
In order to perform nitrification denitrification by the apparatus of FIG. 1, first, the liquid pump 21 to be processed and the circulation pump 28 are driven, and the liquid to be processed supplied through the liquid path 22 to be processed and the circulation path 27 are circulated. Mix with the circulating fluid. Further, the chemical injection pump 23 is driven to mix the hydrogen donor from the chemical storage tank 7 through the chemical injection path 24, and this mixed liquid is introduced into the denitrification section 2 from the lower part of the denitrification nitrification tank 1. The flow rate of the liquid to be treated is detected continuously or intermittently by the flow meter 9, and this flow rate signal is transmitted to the control device 4. In the denitrification unit 2, the mixed solution is passed through the biological filtration layer 13 in an upward flow, and nitrous acid or nitrate nitrogen in the mixed solution is biologically denitrified into nitrogen gas by the action of denitrifying bacteria.
[0025]
The denitrification treatment liquid is introduced into the nitrification unit 3 for nitrification. In the nitrification unit 3, the denitrification solution is passed through the biological filtration layer 14 in an upward flow while the air supplied from the air supply passage 11 is diffused from the diffuser 12, and denitrification is performed by the action of nitrifying bacteria. Biologically nitrifies ammoniacal nitrogen in the processing solution to nitrite or nitrate nitrogen. When an organic nitrogen compound is contained in the denitrification treatment liquid, the organic nitrogen compound is decomposed into ammonia nitrogen by the action of microorganisms in the biological filtration layer 14, and further, nitrous acid or nitrous acid is added by the action of nitrifying bacteria. Nitrified to nitrate nitrogen.
[0026]
A part of the nitrification treatment liquid is circulated as a circulation liquid from the circulation path 27 by the circulation pump 28, and the remaining part is taken out from the treatment liquid path 25 as a treatment liquid. The exhaust gas is discharged from the exhaust gas passage 26. The nitrogen concentration in the treatment liquid (nitrification treatment liquid) is detected continuously or intermittently by the nitrogen concentration detection device 5, and this nitrogen concentration signal is transmitted to the control device 4. Further, the dissolved oxygen concentration in the circulating fluid is detected continuously or intermittently by the dissolved oxygen concentration detecting device 6, and this dissolved oxygen concentration signal is transmitted to the control device 4. Further, the flow rate of the circulating fluid is detected continuously or intermittently by the flow meter 8, and this flow rate signal is transmitted to the control device 4.
[0027]
The control device 4 calculates a circulation ratio for obtaining the target water quality from the nitrogen concentration signal and the flow rate signal of the liquid to be treated, and outputs a circulation ratio control signal to the circulation pump 28 so as to obtain the amount of the circulating fluid. And adjust the amount of circulating fluid. Thereby, even when the content of the nitrogen compound in the liquid to be treated fluctuates, the target water quality can always be obtained stably.
[0028]
Further, the control device 4 calculates the addition amount of the hydrogen donor based on the dissolved oxygen concentration signal and the flow rate signal of the circulating fluid, and sends an addition amount control signal to the chemical injection pump 23 so that the addition amount can be added. Output and adjust the amount of hydrogen donor added. As a result, even if the amount of the circulating fluid, the nitrogen concentration in the liquid to be treated, the organic matter content, etc. fluctuate, an appropriate amount of hydrogen donor can always be added in accordance with the fluctuation. Can be prevented.
[0029]
In the biological nitrification denitrification apparatus of FIG. 1, the flow meter 9 can be omitted when the flow rate of the liquid to be treated is constant.
Moreover, although the denitrification nitrification tank 1 in which the denitrification tank and the nitrification tank are integrated is used in the biological nitrification denitrification apparatus of FIG. 1, the denitrification tank and the nitrification tank can be provided separately. In this case, it is possible to employ a tank by a fully mixed type floating method in which the liquid to be treated and biological sludge are mixed to denitrify or nitrify.
[0030]
Dosing passage 24 is further allowed to connect directly to a de-窒硝of tank 1 instead of connecting to the liquid to be treated path 22 may be configured to add an agent to the mixture of the circulating fluid and the liquid to be treated .
[0031]
Test example 1
The apparatus shown in FIG. 1 was used to nitrify and denitrify the paint effluent. In operation, first, wastewater having a total nitrogen concentration of 100 mg / l, a BOD concentration of 150 mg / l, and SS of 45 mg / l was treated under the following conditions. At this time, the amount of methanol added as a hydrogen donor was 100 ml / l-treated liquid, and the total nitrogen concentration of the treated liquid was 9 mg / l.
Denitrification nitrification tank:
Diameter: 400mm
Effective height: 3,000mm
Nitrification head: 2,000mm
Denitrification manager: 1,000mm
load:
Nitrification load: 0.7kg-N / m ³ · d
Denitrification load: 1.4 kg-N / m ³ · d
Processed liquid flow rate: 1.8 m ³ / d
Circulation ratio: 9 times the total nitrogen concentration of the treatment liquid Target water quality: 10 mg / l
[0032]
Next, the total nitrogen concentration of the liquid to be treated was lowered to 65 mg / l (the BOD concentration was constant at 150 mg / l), and the operation was performed. At this time, the amount of hydrogen donor added was reduced to about 12% with 12 mg / l-treated liquid. The total nitrogen concentration of the treatment liquid was 8 mg / l, and the circulation ratio was 7 times.
[0033]
【The invention's effect】
The biological nitrification denitrification device of the present invention includes a nitrogen concentration detection device that detects the nitrogen concentration of a nitrification solution, a dissolved oxygen concentration detection device that detects a dissolved oxygen concentration in the circulating fluid, a liquid to be treated, and a circulating fluid. a flow meter for measuring the flow rate, the nitrogen concentration of the nitrified liquid detected by the nitrogen concentration detection apparatus, based on the current circulation ratio and the target quality, calculates the nitrogen concentration of the liquid to be treated, nitrification process of a target Calculate the circulation ratio of the nitrification liquid to the liquid to be treated to obtain the nitrogen concentration of the liquid, output a circulation ratio control signal, and add the amount of hydrogen donor added to the liquid to be treated according to the circulation ratio , the amount required to remove the dissolved oxygen, calculates and amount control signal as an amount obtained by subtracting the amount of hydrogen donor contained in the treatment water from the total amount of the amount necessary for denitrification Output from the control device and the circulation transmitted from the control device A circulating fluid amount adjusting device that adjusts the circulating fluid amount of the nitrification solution so as to obtain the circulation ratio according to the control signal, and the addition amount according to the addition amount control signal transmitted from the control device. Since a chemical injection device for injecting a hydrogen donor into the liquid to be treated is provided, even if the nitrogen concentration of the liquid to be treated fluctuates, the amount of the hydrogen donor to be added according to the fluctuation Thus, nitrification denitrification can be performed at a low cost by preventing excessive addition of a hydrogen donor.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a biological nitrification denitrification apparatus of an example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Denitrification nitrification tank 2 Denitrification part 3 Nitrification part 4 Control apparatus 5 Nitrogen concentration detection apparatus 6 Dissolved oxygen concentration detection apparatus 7 Drug storage tank 8, 9 Flowmeter 11 Air supply path 12 Aeration apparatus 13, 14 Biofiltration layer 21 Cover Process liquid pump 22 Processed liquid path 23 Chemical injection pump 24 Chemical injection path 25 Process liquid path 26 Exhaust gas path 27 Circulation path 28 Circulation pump

Claims

A denitrification tank that receives the nitrification liquid circulated from the liquid to be treated and the nitrification tank and performs biological denitrification;
A nitrification tank that receives the denitrification solution denitrified in this denitrification tank and biologically nitrifies,
A nitrogen concentration detection device for detecting the nitrogen concentration of the nitrification solution nitrified in the nitrification tank;
A dissolved oxygen concentration detection device for detecting the dissolved oxygen concentration in the circulating fluid;
A flow meter for measuring the flow rate of the liquid to be treated and the circulating fluid;
Nitrogen concentration in the nitrified liquid detected by the nitrogen concentration detection device (Cout), the current circulation ratio (r0) and based on the target quality (Ce), the following formula the nitrogen concentration of the liquid to be treated (Cin) [1] To calculate the circulation ratio (r) of the nitrification liquid to the liquid to be treated for obtaining the target nitrogen concentration of the nitrification liquid by the following equation [2] , and output the circulation ratio control signal; The amount of hydrogen donor added to the liquid to be treated according to the circulation ratio is determined by the amount (E ₁ ) required to remove dissolved oxygen determined by the following equation [3] and by the following equation [4]. A controller that calculates the amount obtained by subtracting the amount of hydrogen donor contained in the water to be treated from the total amount required for the denitrification reaction (E ₂ ) and outputs an addition amount control signal;
In accordance with the circulation ratio control signal transmitted from this control device, a circulating fluid amount adjusting device that adjusts the circulating fluid amount of the nitrification liquid so as to obtain the circulation ratio;
A chemical injection device for injecting a hydrogen donor into the liquid to be treated so that the amount of addition can be added in response to an addition amount control signal transmitted from the control device, and detecting the nitrogen concentration of the liquid to be treated. The biological nitrification denitrification apparatus characterized by not having the means to control .
Cin = Cout × (1 + r0) (1)
r = (Cin / Ce) −1 (2)
E ₁ = dissolved oxygen amount × K ₁ × circulating fluid flow rate [3]
E ₂ = nitrogen concentration in the liquid to be processed × K ₂ × flow rate of the liquid to be processed (4)
(In the formula, K ₁ is a coefficient representing the amount of organic substances necessary for removing the dissolved oxygen unit amount, and K ₂ is a coefficient of 2.5 to _3. )