JP4882175B2 - Nitrification method - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、アンモニア性窒素を含む原水をアンモニア酸化細菌の存在下に曝気して硝化する方法に係り、特に、硝化槽内のｐＨ調整を効果的に行って、安定かつ効率的な亜硝酸型硝化を行う硝化処理方法に関する。
【０００２】
【従来の技術】
排液中に含まれるアンモニア性窒素は河川、湖沼及び海洋などにおける富栄養化の原因物質の一つであり、排液処理工程で効率的に除去する必要がある。一般に、排水中のアンモニア性窒素は、アンモニア性窒素をアンモニア酸化細菌により亜硝酸性窒素に酸化し、更にこの亜硝酸性窒素を亜硝酸酸化細菌により硝酸性窒素に酸化する硝化工程と、これらの亜硝酸性窒素及び硝酸性窒素を従属栄養性細菌である脱窒菌により、有機物を電子供与体として利用して窒素ガスにまで分解する脱窒工程との２段階の生物反応を経て窒素ガスにまで分解される。
【０００３】
このような硝化脱窒処理では、アンモニア性窒素を酸化するために必要な曝気動力が運転コストのうちの大部分を占めている。
【０００４】
また、従来の硝化脱窒法では、曝気のためのコストのみならず、脱窒工程において電子供与体としてメタノールなどの有機物を多量に必要とし、発生汚泥量も多いという欠点がある。
【０００５】
曝気のためのコストを低滅する方法として、硝酸性窒素を生成させず、亜硝酸性窒素を生成させ、亜硝酸性窒素を脱窒する方法が考えられる。
【０００６】
近年、アンモニア性窒素を電子供与体とし、亜硝酸性窒素を電子受容体とする独立栄養性微生物を利用し、アンモニア性窒素と亜硝酸性窒素とを反応させて脱窒する方法が提案された。この方法であれば、有機物の添加は不要であるため、従属栄養性の脱窒菌を利用する方法と比べて、コストを低減することができる。また、独立栄養性の微生物は収率が低く、汚泥の発生量が従属栄養性微生物と比較すると著しく少ないので、余剰汚泥の発生量を抑えることができる。更に、従来の硝化脱窒法で観察されるＮ２Ｏの発生がなく、環境に対する負荷を低減できるといった特長もある。
【０００７】
この独立栄養性脱窒微生物を利用する生物脱窒プロセスは、Strous, M, et al., Appl. Microbiol. Biotechnol., 50, p.589-596 (1998) に報告されており、以下のような反応でアンモニア性窒素と亜硝酸性窒素が反応して窒素ガスに分解されると考えられており、アンモニア性窒素と亜硝酸性窒素とは、アンモニア性窒素：亜硝酸性窒素＝０．４３：０．５７（モル比）＝１：１．３（重量比）で反応する。
【０００８】
【化１】
従って、この独立栄養性脱窒微生物を用いて脱窒処理を行う場合、原水のアンモニア性窒素と亜硝酸性窒素の割合はモル比でアンモニア性窒素１に対して亜硝酸性窒素０．５〜２、特に１〜１．５（即ち、アンモニア性窒素：亜硝酸性窒素＝２：１〜１：２好ましくは１：１〜１：１．５）とするのが好ましい。このためアンモニア性窒素を含む原水を処理する場合には、この原水の一部について亜硝酸型硝化を行い、アンモニア性窒素を含む原水と亜硝酸性窒素を含む硝化液とを混合して原水とするか、或いは原水中のアンモニア性窒素の一部について亜硝酸化を行った液を原水とすることが好ましい。この場合においても、アンモニア性窒素の亜硝酸型硝化を行うことが必要となる。
【００１０】
従来、硝化工程において、アンモニア性窒素の酸化を亜硝酸性窒素で止め、硝酸性窒素を生成させない亜硝酸型硝化を行うための制御方法としては、
(1)高濃度のアンモニア性窒素や亜硝酸性窒素を硝化槽に添加することによって、アンモニア性窒素や亜硝酸性窒素の毒性で亜硝酸性窒素の硝酸性窒素への酸化を停止する方法
(2) 低溶存酸素（ＤＯ）濃度で運転するか、水温を３０℃以上に調整する方法
(3) 硝化汚泥のＳＲＴ（汚泥滞留時間）を短くすることで、亜硝酸性窒素を酸化する微生物を系内から排除する方法
などが提案されているが、いずれも十分な方法とは言えず、生成した亜硝酸性窒素が硝酸性窒素にまで酸化されてしまうことがあった。
【００１１】
ところで、アンモニア性窒素を亜硝酸性窒素に酸化する反応では、アルカリ性のアンモニア性窒素が酸性の亜硝酸性窒素に酸化されるため、硝化槽内のｐＨは低下しやすい。そして、ｐＨが５以下まで低下すると、アンモニア酸化細菌の活性が著しく低下する。この場合は、アンモニア性窒素の酸化速度は中性域の場合の酸化速度より低下してしまう。これを防ぐために、水酸化ナトリウムなどの比較的高価なアルカリ薬品を外部から添加してｐＨ調整する必要がある。
【００１２】
なお、一般的な有機性排水中に含まれるタンパク質等の有機性窒素の分解で、アンモニア性窒素が生成する際には、アルカリ性のアンモニア性窒素の生成でｐＨが上昇する。アンモニア性窒素から亜硝酸性窒素又は硝酸性窒素が生成する際はｐＨは低下するが、亜硝酸性窒素から硝酸への酸化工程では新たな酸は生成しないため、ｐＨの低下は起こらない。
【００１３】
【発明が解決しようとする課題】
従来においては、硝化工程において安定的に亜硝酸性窒素を生成させる亜硝酸型硝化を行うことが困難であり、亜硝酸型硝化を行うための有効な硝化処理方法の開発が望まれている。
【００１４】
また、従来においては、アンモニア性窒素から亜硝酸性窒素が生成した際に低下したｐＨを調整するために、ＮａＯＨ等の比較的高価なアルカリ薬品を必要とするため、薬品コスト、薬液の調整、薬液タンク薬品管理等の費用、作業が必要となるという問題もあった。
【００１５】
本発明は上記従来の問題点を解決し、アンモニア性窒素を含有する原水をアンモニア酸化細菌の存在下に曝気して硝化する硝化槽に導入して硝化する方法において、亜硝酸型硝化を安定に行うことができ、しかも、ｐＨ調整のための高価な薬品を必要とすることがない、或いはその使用量を大幅に低減することができる硝化処理方法を提供することを目的とする。
【００１６】
【課題を解決するための手段】
本発明の硝化処理方法は、アンモニア性窒素を含む原水をアンモニア酸化細菌の存在下に曝気する硝化槽に供給して硝化処理する方法において、硝化槽に供給する原水をｐＨ調整剤としてその供給量を調節すると共に、必要に応じ他のｐＨ調整剤を添加することにより、硝化槽内のｐＨを６〜８に制御して硝化を行う硝化処理方法であって、原水をｐＨ調整剤として利用し、硝化槽内のｐＨを６〜８とするために原水の供給量を調節し、原水だけではｐＨ調整し得ない場合に他のｐＨ調整剤を補助的に用い、硝化槽内のｐＨが低い場合には原水の供給量を増やし、硝化槽内のｐＨが高い場合には原水の供給量を減らし、これにより硝化槽内のｐＨが６〜８に回復した場合には原水の供給量を元の供給量に戻すことを特徴とする。
【００１７】
本発明の硝化処理方法では、アンモニア性窒素を含むアルカリ性の原水を硝化槽内のｐＨ制御に用い、原水だけではｐＨ調整し得ない場合にｐＨ調整剤を補助的に用いる。このため、ｐＨ調整のためのアルカリ薬品が不要となるか、或いはその必要量を大幅に低減することができる。
【００１８】
また、このように原水をｐＨ調整剤として利用し、硝化槽内のｐＨを６〜８とするために、原水の供給量を調節し、硝化槽内のｐＨが低い場合には原水の供給量を増やし、これにより硝化槽内のｐＨが好適範囲に回復した場合には原水の供給量を元の供給量に戻すことにより、良好な亜硝酸型硝化を行うことが可能となる。
【００１９】
これは次のような理由による。
【００２０】
即ち、アンモニア性窒素をアンモニア酸化細菌で酸化する場合、反応系内の無機窒素部分の大部分がアンモニア性窒素と亜硝酸性窒素となるように、かつ、アンモニア性窒素と亜硝酸性窒素とをバランスよく共存させるように処理を行うことにより、アンモニア性窒素と亜硝酸性窒素の両方の毒性が期待でき、これにより、亜硝酸性窒素を硝酸性窒素に酸化する亜硝酸性細菌の活性が低下し、亜硝酸性窒素から硝酸性窒素への酸化は防止され、亜硝酸性型硝化を安定に行うことができるようになる。
【００２１】
本発明では、硝化槽内の亜硝酸性窒素が増え硝化槽のｐＨが低下した場合に、原水供給量を増やすため、硝化槽内へのアンモニア性窒素導入量が増え、これにより硝化槽内のアンモニア性窒素濃度と亜硝酸性窒素濃度とがバランス良く共存するようになる。逆に、硝化槽のｐＨが高く、硝化槽内の亜硝酸性窒素量がアンモニア性窒素量よりも少ない場合に原水供給量を減らすことで、硝化槽内へのアンモニア性窒素導入量が減り、これにより硝化槽内のアンモニア性窒素濃度と亜硝酸性窒素濃度とがバランス良く共存するようになる。
【００２２】
アンモニア性窒素及び亜硝酸性窒素による毒性を発揮させて安定な亜硝酸型硝化を維持するためには、硝化液中のアンモニア性窒素：亜硝酸性窒素＝２：１〜１：２（重量濃度比）であり、アンモニア性窒素と亜硝酸性窒素の合計濃度が１００〜１０，０００ｍｇ−Ｎ／Ｌとなるように処理を行うのが好ましく、このためには、硝化処理の開始時に硝化槽内のアンモニア性窒素濃度と亜硝酸性窒素の少なくとも一方が、５００ｍｇ−Ｎ／Ｌ以上となるように、硝化槽にアンモニア性窒素及び／又は亜硝酸性窒素を添加することが好ましい。
【００２３】
更に、次の(1)〜(2)の条件を採用することにより、より一層高い亜硝酸型硝化活性を維持することができ好ましい。
(1) 硝化槽内のＤＯ濃度を０．５〜４ｍｇ／Ｌとする。
(2) 硝化槽内の水温を１０〜４０℃に調節する。
【００２４】
なお、アンモニア性窒素濃度：亜硝酸性窒素濃度＝２：１〜１：２好ましくは１：１〜１：１．５の硝化液であれば、前述の独立栄養性微生物による脱窒処理の原水として効率的に脱窒処理することができる。
【００２５】
【発明の実施の形態】
以下に図面を参照して本発明の実施の形態を詳細に説明する。
【００２６】
図１は本発明の硝化処理方法の実施に好適な硝化装置を示す概略的な構成図である。
【００２７】
原水（アンモニア性窒素含有水）は、原水ポンプＰにより硝化槽（曝気槽）１に導入され、曝気下、硝化汚泥と接触して硝化処理され、硝化液が処理水として排出される。
【００２８】
この硝化槽１にはｐＨセンサ２が設けられ、硝化槽１内液のｐＨが測定される。測定されたｐＨ値は制御器３に入力され、このｐＨ値に基いて制御器３から原水ポンプＰの制御信号が出力され、原水の流入量が調節される。
【００２９】
即ち、硝化槽１内のｐＨが予め設定した値よりも低いときには、原水の流入量を増加して、槽内ｐＨを上げる。アルカリ性の原水流入量を増加させることにより、槽内ｐＨを上げることができる。逆に、硝化槽内のｐＨが予め設定した値よりも高いときには、原水の流入量を減らして槽内ｐＨを下げる。アルカリ性の原水流入量を減らすことにより、槽内ｐＨを下げることができる。
【００３０】
この原水流入量の制御は、ＰＩＤ制御で行っても良く、また、原水ポンプのｏｎ−ｏｆｆ操作であっても良い。
【００３１】
このように原水をｐＨ調整剤としてその供給量を調節することにより、前述の如く、硝化槽内のアンモニア性窒素濃度と亜硝酸性窒素の割合をバランスさせることが可能となり、良好な亜硝酸型硝化を行うことができる。
【００３２】
なお、原水の流入量の制御のみでは、硝化槽内のｐＨを調整し得ない場合には、ＮａＯＨ等のアルカリを補給しても良い。この場合には、更に薬注配管を設け、制御器３により、原水ポンプＰと共に薬注ポンプの制御を行えば良い。
【００３３】
本発明において、安定な亜硝酸型硝化を行うためには、硝化処理の開始時に硝化槽１内のアンモニア性窒素濃度と亜硝酸性窒素の少なくとも一方が、５００ｍｇ／Ｌ以上となるように、好ましくは８００〜１，５００ｍｇ／Ｌとなるように、より好ましくはアンモニア性窒素９００〜１，０００ｍｇ／Ｌ、亜硝酸性窒素９００〜１，０００ｍｇ／Ｌとなるように、硝化槽１にアンモニア性窒素及び／又は亜硝酸性窒素を添加することが好ましい。このような濃度でアンモニア性窒素及び／又は亜硝酸性窒素を存在させることにより、それぞれが亜硝酸酸化細菌に与える毒性の効果で良好な亜硝酸型硝化を行えるようになる。
【００３４】
また、本発明において、安定な亜硝酸型硝化を行うために、硝化槽から流出する硝化液のアンモニア性窒素濃度と亜硝酸性窒素濃度との比は２：１〜１：２、特に１：１．２〜１：１．３となるようにするのが好ましく、このためには、硝化槽１内のｐＨを６〜８、好ましくは６．０〜６．５となるように制御する。
【００３５】
更に、本発明では、安定な亜硝酸型硝化を行うために、この硝化槽１内のＤＯ濃度を０．５〜４ｍｇ／Ｌとなるように硝化槽１の曝気量を調節することが好ましい。この曝気量の調節は、例えば、硝化槽１内にＤＯ計を設け、このＤＯ計の測定結果に基いて、硝化槽１の散気部に空気を供給するブロワの風量を制御することにより行うことができる。硝化槽１内のＤＯ濃度が４ｍｇ／Ｌを超えるとＤＯが過剰となって、硝化反応が硝酸型となり、硝酸性窒素が生成するようになるため好ましくない。０．５ｍｇ／Ｌ未満では硝化に必要な酸素量が不足する。
【００３６】
更に、安定な亜硝酸型硝化のために、硝化槽１内の水温は１０〜４０℃とするのが好ましい。水温が４０℃を超えると硝化反応が硝酸型となり易く、１０℃未満では硝化活性が劣るものとなる。
【００３７】
なお、ＳＲＴについては、汚泥濃度が高くなって高負荷の処理ができるため、ＳＲＴが長い運転の方が好ましい。ただし、汚泥濃度が高くなると、同時に亜硝酸性窒素を硝酸性窒素に酸化する微生物の濃度も増えるため、予期せぬ硝酸化が起こる可能性がある。また、汚泥濃度が高くなると、硝化槽の酸素不足や硝化槽の後段に沈殿槽が設けられる場合には、この沈殿池の固液分離障害が起きる。これらの障害を防ぐには、汚泥を定期的に引き抜き、硝化速度（アンモニア消費速度）を適切に調整することが好ましい。
【００３８】
例えば、ＳＲＴ＝１ｄａｙという短い滞留時間であっても運転は可能であるが、この場合には汚泥濃度が低くなるため、運転可能な負荷は低い。このような運転は、原水から多量のＳＳが流入して槽内の汚泥濃度が上昇することに対処するものであり、一般的にはＳＲＴ＝１０〜１００ｄａｙ程度とするのが好ましい。
【００３９】
本発明で用いる硝化槽の型式には特に制限はない。固定床、流動床、グラニュール法、担体添加法等の生物膜式の硝化槽であれば、後段の固液分離のための沈殿槽を省略することができる。汚泥懸濁式の硝化槽であれば、硝化槽の流出水を沈殿槽で固液分離して分離汚泥を硝化槽に返送することで系内に汚泥を保持することができる。
【００４０】
【実施例】
以下に比較例及び実施例を挙げて本発明をより具体的に説明する。
【００４１】
比較例１
硝化汚泥３，０００ｍｇ−ＳＳ／Ｌを保持する曝気槽に、アンモニア性窒素濃度７〜７００ｍＭ（約１００〜１０，０００ｍｇ−Ｎ／Ｌ）を含む下水嫌気消化脱離液（ｐＨ７．０）をＨＲＴ＝２ｄａｙの条件で通水した。このとき、表１に示すような異なる実験条件のもとで、処理水のアンモニア性窒素、亜硝酸性窒素、硝酸性窒素の各濃度及び硝化活性を維持するＮａＯＨ添加量について調べた。
【００４２】
なお、いずれの場合も、立ち上げ時には、曝気槽にアンモニア性窒素と亜硝酸性窒素を合計で１，０００ｍｇ−Ｎ／Ｌ（アンモニア性窒素５００ｍｇ−Ｎ／Ｌ，亜硝酸性窒素５００ｍｇ−Ｎ／Ｌ）添加した。
【００４３】
この結果、いずれの場合も、運転当初は処理水中の窒素成分は、亜硝酸性窒素が大部分となり、亜硝酸型の運転ができたが、経時後には、表１に示す通りとなり、汚泥の引き抜きを行わなかった場合には、硝酸型硝化となった。
【００４４】
なお、ＮａＯＨ添加量はいずれの場合も原水中のアンモニア性窒素量の２倍当量であった。
【００４５】
【表１】
実施例１
原水の少なくとも一部をｐＨ調整用のアルカリ源として使用すること以外は、比較例１と同じ条件で運転を行った。ここでは、ｐＨが設定値以下に低下した場合には、原水量を増加させることでアルカリ源を補給し、ｐＨが設定値に戻った場合には元の原水量に戻した。
【００４７】
処理水の窒素成分とアルカリ添加量を調べ、結果を表２に示した。
【００４８】
【表２】
表２の通り、汚泥の引き抜きの有無にかかわらず、亜硝酸型硝化を安定に行うことができた。また、ＮａＯＨの添加は不要であった。
【００５０】
なお、得られた処理水は、アンモニア性窒素濃度：亜硝酸性窒素濃度＝１：１〜１：１．３でアンモニア性窒素濃度５００〜１，５００ｍｇ−Ｎ／Ｌ、亜硝酸性窒素濃度５００〜２，０００ｍｇ−Ｎ／Ｌのものであり、この処理水は、前述の独立栄養性微生物による脱窒処理で効率的に脱窒処理することができた。
【００５１】
実施例２
実施例１のＮｏ．１の条件において、得られる処理水中のアンモニア性窒素濃度と亜硝酸性窒素濃度との比に対するｐＨの影響を調べるべく、ｐＨを６〜９の範囲で種々変更したこと以外は同様にして処理を行い、得られた処理水のアンモニア性窒素及び亜硝酸性窒素の濃度割合とｐＨとの関係を図２に示した。
【００５２】
図２より明らかなように、ｐＨを低く設定すると亜硝酸性窒素の割合が増加し、逆にｐＨを高く設定するとアンモニア性窒素の割合が増加する。従って、亜硝酸型硝化を維持すると共に、処理水を更に前述の独立栄養性微生物により脱窒処理するために、アンモニア性窒素濃度：亜硝酸性窒素濃度＝２：１〜１：２の処理水を得るためには、硝化槽のｐＨを６〜８、好ましくは６．５〜７．５の範囲で精度良く制御することが必要であることがわかる。
【００５３】
【発明の効果】
以上詳述した通り、本発明の硝化処理方法によれば、原水をｐＨ調整剤として利用することにより、薬品としてのｐＨ調整剤を必要とすることなく、或いはその必要添加量を大幅に低減した上で、長期にわたり安定した亜硝酸型硝化を行うことができる。
【図面の簡単な説明】
【図１】 本発明の硝化処理方法の実施に好適な硝化装置を示す概略的な構成図である。
【図２】 実施例２における処理水のアンモニア性窒素濃度及び亜硝酸性窒素濃度の割合とｐＨとの関係示すグラフである。
【符号の説明】
１ 硝化槽（曝気槽）
２ ｐＨセンサ
３ 制御器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for aeration of raw water containing ammoniacal nitrogen in the presence of ammonia-oxidizing bacteria to nitrify, and in particular, by effectively adjusting the pH in the nitrification tank, a stable and efficient nitrite type The present invention relates to a nitrification treatment method for performing nitrification.
[0002]
[Prior art]
Ammonia nitrogen contained in the effluent is one of the causative substances of eutrophication in rivers, lakes and oceans, and it is necessary to remove it efficiently in the effluent treatment process. In general, ammonia nitrogen in wastewater is oxidized by ammonia oxidizing bacteria to nitrite nitrogen, and nitrifying nitrogen is oxidized to nitrate nitrogen by nitrite oxidizing bacteria. Nitrite nitrogen and nitrate nitrogen are denitrified bacteria, which are heterotrophic bacteria, and are converted into nitrogen gas through a two-stage biological reaction with a denitrification process that decomposes organic matter into nitrogen gas using an electron donor. Disassembled.
[0003]
In such nitrification denitrification treatment, aeration power necessary for oxidizing ammonia nitrogen occupies most of the operating cost.
[0004]
Further, the conventional nitrification denitrification method has not only a cost for aeration, but also has a drawback that a large amount of organic matter such as methanol is required as an electron donor in the denitrification step, and a large amount of sludge is generated.
[0005]
As a method of reducing the cost for aeration, a method of generating nitrite nitrogen without generating nitrate nitrogen and denitrifying nitrite nitrogen can be considered.
[0006]
Recently, a method for denitrification by reacting ammonia nitrogen and nitrite nitrogen using an autotrophic microorganism using ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor has been proposed. . If this method is used, it is not necessary to add an organic substance, so that the cost can be reduced as compared with a method using heterotrophic denitrifying bacteria. Moreover, since the yield of autotrophic microorganisms is low and the amount of sludge generated is significantly less than that of heterotrophic microorganisms, the amount of surplus sludge generated can be suppressed. Furthermore, there is also a feature that there is no generation of N 2 O observed by the conventional nitrification denitrification method, and the burden on the environment can be reduced.
[0007]
A biodenitrification process using this autotrophic denitrification microorganism has been reported in Strous, M, et al., Appl. Microbiol. Biotechnol., 50, p.589-596 (1998). It is considered that ammonia nitrogen and nitrite nitrogen react to be decomposed into nitrogen gas by a simple reaction. Ammonia nitrogen and nitrite nitrogen are ammonia nitrogen: nitrite nitrogen = 0.43. : 0.57 (molar ratio) = 1: 1.3 (weight ratio).
[0008]
[Chemical 1]
Therefore, when performing denitrification treatment using this autotrophic denitrifying microorganism, the ratio of ammonia nitrogen and nitrite nitrogen in the raw water is 0.5 to 0.5 nitrite nitrogen relative to ammonia nitrogen 1 in molar ratio. 2, especially 1 to 1.5 (that is, ammonia nitrogen: nitrite nitrogen = 2: 1 to 1: 2, preferably 1: 1 to 1: 1.5). For this reason, when treating raw water containing ammonia nitrogen, nitrite-type nitrification is performed on a part of this raw water, and raw water containing ammonia nitrogen and nitrification liquid containing nitrite nitrogen are mixed to produce raw water and Alternatively, it is preferable that the raw water is a liquid obtained by performing nitritation on a part of the ammoniacal nitrogen in the raw water. Even in this case, it is necessary to perform nitrite-type nitrification of ammoniacal nitrogen.
[0010]
Conventionally, in the nitrification process, the control method for performing the nitrite type nitrification without stopping the oxidation of ammonia nitrogen with nitrite nitrogen and generating no nitrate nitrogen,
(1) Method of stopping oxidation of nitrite nitrogen to nitrate nitrogen due to toxicity of ammonia nitrogen or nitrite nitrogen by adding high concentration ammonia nitrogen or nitrite nitrogen to nitrification tank
(2) Method of operating at low dissolved oxygen (DO) concentration or adjusting the water temperature to 30 ° C or higher
(3) Proposals have been made to eliminate microorganisms that oxidize nitrite nitrogen from the system by shortening the SRT (sludge retention time) of nitrified sludge, but none of them are sufficient. In some cases, the produced nitrite nitrogen is oxidized to nitrate nitrogen.
[0011]
By the way, in the reaction of oxidizing ammonia nitrogen to nitrite nitrogen, alkaline ammonia nitrogen is oxidized to acidic nitrite nitrogen, so that the pH in the nitrification tank tends to decrease. And when pH falls to 5 or less, the activity of ammonia oxidation bacteria will fall remarkably. In this case, the oxidation rate of ammonia nitrogen is lower than the oxidation rate in the neutral range. In order to prevent this, it is necessary to adjust the pH by adding a relatively expensive alkaline chemical such as sodium hydroxide from the outside.
[0012]
In addition, when ammonia nitrogen is produced | generated by decomposition | disassembly of organic nitrogen, such as protein contained in a general organic waste water, pH raises by production | generation of alkaline ammonia nitrogen. When nitrite nitrogen or nitrate nitrogen is produced from ammonia nitrogen, the pH is lowered, but no new acid is produced in the oxidation process from nitrite nitrogen to nitric acid, and therefore no pH drop occurs.
[0013]
[Problems to be solved by the invention]
Conventionally, it is difficult to perform nitrite type nitrification that stably generates nitrite nitrogen in the nitrification step, and development of an effective nitrification method for performing nitrite type nitrification is desired.
[0014]
In addition, conventionally, in order to adjust the pH lowered when nitrite nitrogen is generated from ammonia nitrogen, relatively expensive alkaline chemicals such as NaOH are required. There was also a problem that the cost and work of chemical tank chemical management etc. was required.
[0015]
The present invention solves the above-mentioned conventional problems and stabilizes nitrite-type nitrification in a method of nitrifying by introducing raw water containing ammonia nitrogen into a nitrification tank that is aerated and nitrified in the presence of ammonia-oxidizing bacteria. It is an object of the present invention to provide a nitrification method that can be carried out and that does not require expensive chemicals for pH adjustment or that can greatly reduce the amount of use.
[0016]
[Means for Solving the Problems]
The nitrification treatment method of the present invention is a method for supplying raw water containing ammoniacal nitrogen to a nitrification tank that is aerated in the presence of ammonia-oxidizing bacteria and performing nitrification treatment. And a nitrification treatment method in which the pH in the nitrification tank is controlled to 6-8 by adding another pH adjuster as necessary, and raw water is used as a pH adjuster. When the raw water supply amount is adjusted to adjust the pH in the nitrification tank to 6 to 8, and the pH cannot be adjusted only with the raw water, another pH adjuster is used as an auxiliary, and the pH in the nitrification tank is low. If the pH in the nitrification tank is high, the supply amount of the raw water is decreased. If the pH in the nitrification tank is restored to 6-8, the supply amount of the raw water is restored. It is characterized by returning to the supply amount .
[0017]
In the nitrification treatment method of the present invention, alkaline raw water containing ammonia nitrogen is used for pH control in the nitrification tank, and a pH adjuster is supplementarily used when the pH cannot be adjusted only with the raw water. Therefore, if the alkali chemicals for the pH adjustment is not necessary, or can be greatly reduced the required amount.
[0018]
Moreover, in this way utilizing the raw water as a pH adjusting agent, in order to 6-8 pH nitrification tank, by adjusting the supply amount of the raw water, the supply of raw water when the pH of the nitrifying tank is low When the amount is increased and the pH in the nitrification tank is restored to a suitable range, the nitrite type nitrification can be performed by returning the supply amount of the raw water to the original supply amount.
[0019]
This is due to the following reason.
[0020]
That is, when ammoniacal nitrogen is oxidized by ammonia-oxidizing bacteria, the majority of the inorganic nitrogen in the reaction system is ammonia nitrogen and nitrite nitrogen, and ammonia nitrogen and nitrite nitrogen are combined. By treating in a balanced manner, the toxicity of both ammonia nitrogen and nitrite nitrogen can be expected, which reduces the activity of nitrite bacteria that oxidize nitrite nitrogen to nitrate nitrogen. In addition, oxidation from nitrite nitrogen to nitrate nitrogen is prevented, and nitrite type nitrification can be performed stably.
[0021]
In the present invention, when the nitrite nitrogen in the nitrification tank is increased and the pH of the nitrification tank is lowered, the amount of ammonia nitrogen introduced into the nitrification tank is increased in order to increase the supply amount of raw water. Ammonia nitrogen concentration and nitrite nitrogen concentration coexist in a well-balanced manner. Conversely, when the pH of the nitrification tank is high and the amount of nitrite nitrogen in the nitrification tank is less than the amount of ammonia nitrogen, the amount of ammonia nitrogen introduced into the nitrification tank is reduced by reducing the raw water supply amount, As a result, the ammonia nitrogen concentration and the nitrite nitrogen concentration in the nitrification tank coexist in a well-balanced manner.
[0022]
In order to maintain the stability of nitrite-type nitrification by exhibiting toxicity due to ammonia nitrogen and nitrite nitrogen, ammonia nitrogen in the nitrification solution: nitrite nitrogen = 2: 1 to 1: 2 (weight concentration It is preferable to perform the treatment so that the total concentration of ammonia nitrogen and nitrite nitrogen is 100 to 10,000 mg-N / L. For this purpose, the treatment is performed in the nitrification tank at the start of the nitrification treatment. It is preferable to add ammonia nitrogen and / or nitrite nitrogen to the nitrification tank so that at least one of the ammonia nitrogen concentration and nitrite nitrogen is 500 mg-N / L or more.
[0023]
Furthermore, by adopting the following conditions (1) to (2) , it is preferable that a higher nitrite type nitrification activity can be maintained .
(1) The DO concentration in the nitrification tank is 0.5-4 mg / L.
(2) Adjust the water temperature in the nitrification tank to 10-40 ° C.
[0024]
In addition, if it is a nitrification solution of ammonia nitrogen concentration: nitrite nitrogen concentration = 2: 1 to 1: 2, preferably 1: 1 to 1: 1.5, raw water for denitrification treatment by the above-mentioned autotrophic microorganisms As an efficient denitrification treatment.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0026]
FIG. 1 is a schematic configuration diagram showing a nitrification apparatus suitable for carrying out the nitrification method of the present invention.
[0027]
The raw water (ammonia nitrogen-containing water) is introduced into the nitrification tank (aeration tank) 1 by the raw water pump P, nitrified by contact with the nitrification sludge under aeration, and the nitrification liquid is discharged as treated water.
[0028]
The nitrification tank 1 is provided with a pH sensor 2, and the pH of the liquid in the nitrification tank 1 is measured. The measured pH value is input to the controller 3, and the control signal of the raw water pump P is output from the controller 3 based on this pH value, and the inflow amount of the raw water is adjusted.
[0029]
That is, when the pH in the nitrification tank 1 is lower than a preset value, the inflow amount of raw water is increased to raise the pH in the tank. By increasing the amount of alkaline raw water inflow, the pH in the tank can be increased. Conversely, when the pH in the nitrification tank is higher than a preset value, the inflow of raw water is reduced to lower the pH in the tank. By reducing the amount of alkaline raw water inflow, the pH in the tank can be lowered.
[0030]
The control of the raw water inflow amount may be performed by PID control, or may be an on-off operation of the raw water pump.
[0031]
By adjusting the supply amount of raw water as a pH adjuster in this way, as described above, it becomes possible to balance the ammonia nitrogen concentration and the ratio of nitrite nitrogen in the nitrification tank, and a good nitrite type Nitrification can be performed.
[0032]
In addition, when the pH in the nitrification tank cannot be adjusted only by controlling the inflow amount of raw water, alkali such as NaOH may be replenished. In this case, a chemical injection pipe may be further provided, and the controller 3 may control the chemical injection pump together with the raw water pump P by the controller 3.
[0033]
In the present invention, in order to perform stable nitrite type nitrification, it is preferable that at least one of ammonia nitrogen concentration and nitrite nitrogen in the nitrification tank 1 is 500 mg / L or more at the start of nitrification treatment. Is 800-1500 mg / L, more preferably ammonia nitrogen 900-1000 mg / L and nitrite nitrogen 900-1000 mg / L in the nitrification tank 1 with ammonia nitrogen. And / or nitrite nitrogen is preferably added. The presence of ammonia nitrogen and / or nitrite nitrogen at such a concentration makes it possible to perform good nitrite type nitrification due to the toxic effect of each on nitrite oxidizing bacteria.
[0034]
In the present invention, in order to perform stable nitrite type nitrification, the ratio of the ammonia nitrogen concentration and the nitrite nitrogen concentration of the nitrification liquid flowing out from the nitrification tank is 2: 1 to 1: 2, particularly 1: 1.2 to 1: as is preferred to be 1.3, for this purpose, the pH of the nitrification tank 1 6-8, that controls so preferably a 6.0 to 6.5 .
[0035]
Furthermore, in the present invention, in order to perform stable nitrite type nitrification, it is preferable to adjust the amount of aeration in the nitrification tank 1 so that the DO concentration in the nitrification tank 1 is 0.5 to 4 mg / L. The adjustment of the aeration amount is performed, for example, by providing a DO meter in the nitrification tank 1 and controlling the air volume of a blower that supplies air to the air diffuser of the nitrification tank 1 based on the measurement result of the DO meter. be able to. If the DO concentration in the nitrification tank 1 exceeds 4 mg / L, DO becomes excessive, the nitrification reaction becomes nitric acid type, and nitrate nitrogen is generated, which is not preferable. If it is less than 0.5 mg / L, the amount of oxygen necessary for nitrification is insufficient.
[0036]
Furthermore, the water temperature in the nitrification tank 1 is preferably 10 to 40 ° C. for stable nitrite type nitrification. If the water temperature exceeds 40 ° C., the nitrification reaction tends to be nitric acid type, and if it is less than 10 ° C., the nitrification activity is poor.
[0037]
In addition, about SRT, since a sludge density | concentration becomes high and a high load process can be performed, the operation | movement with long SRT is preferable. However, as the sludge concentration increases, the concentration of microorganisms that oxidize nitrite nitrogen to nitrate nitrogen also increases, which may lead to unexpected nitrification. In addition, when the sludge concentration becomes high, when the oxygen deficiency of the nitrification tank is insufficient or a precipitation tank is provided at the subsequent stage of the nitrification tank, a solid-liquid separation failure of the precipitation tank occurs. In order to prevent these obstacles, it is preferable to periodically extract sludge and adjust the nitrification rate (ammonia consumption rate) appropriately.
[0038]
For example, operation is possible even with a short residence time of SRT = 1 day, but in this case, the sludge concentration is low, so the operable load is low. Such an operation is to cope with a large amount of SS flowing from the raw water to increase the sludge concentration in the tank, and it is generally preferable to set SRT to about 10 to 100 days.
[0039]
There is no particular limitation on the type of nitrification tank used in the present invention. In the case of a biofilm type nitrification tank such as a fixed bed, fluidized bed, granule method, and carrier addition method, a subsequent precipitation tank for solid-liquid separation can be omitted. If it is a sludge suspension type nitrification tank, sludge can be held in the system by separating the effluent from the nitrification tank into a solid-liquid separation in a sedimentation tank and returning the separated sludge to the nitrification tank.
[0040]
【Example】
Hereinafter, the present invention will be described more specifically with reference to comparative examples and examples.
[0041]
Comparative Example 1
A sewage anaerobic digestion desorption liquid (pH 7.0) containing ammonia nitrogen concentration of 7 to 700 mM (about 100 to 10,000 mg-N / L) in an aeration tank holding nitrified sludge of 3,000 mg-SS / L is HRT. Water was passed under the condition of = 2 day. At this time, the concentrations of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the treated water and the amount of NaOH added to maintain the nitrification activity were examined under different experimental conditions as shown in Table 1.
[0042]
In either case, at the time of start-up, ammonia nitrogen and nitrite nitrogen are combined into the aeration tank in a total of 1,000 mg-N / L (ammonia nitrogen 500 mg-N / L, nitrite nitrogen 500 mg-N / L). L) Added.
[0043]
As a result, in all cases, the nitrogen component in the treated water was mostly nitrite nitrogen at the beginning of operation, and nitrite type operation was possible. When the drawing was not performed, nitric acid type nitrification was achieved.
[0044]
In each case, the amount of NaOH added was twice the equivalent of the amount of ammoniacal nitrogen in the raw water.
[0045]
[Table 1]
Example 1
The operation was performed under the same conditions as in Comparative Example 1 except that at least part of the raw water was used as an alkali source for pH adjustment. Here, when pH fell below the set value, the alkali source was replenished by increasing the amount of raw water, and when the pH returned to the set value, it was returned to the original amount of raw water.
[0047]
The nitrogen content of the treated water and the amount of alkali added were examined, and the results are shown in Table 2.
[0048]
[Table 2]
As shown in Table 2, nitrite type nitrification could be performed stably regardless of whether sludge was drawn or not. Moreover, addition of NaOH was unnecessary.
[0050]
The obtained treated water had ammonia nitrogen concentration: nitrite nitrogen concentration = 1: 1 to 1: 1.3, ammonia nitrogen concentration 500 to 1,500 mg-N / L, and nitrite nitrogen concentration 500. The treated water could be efficiently denitrified by the denitrification treatment by the above-mentioned autotrophic microorganisms.
[0051]
Example 2
No. of Example 1 In order to investigate the effect of pH on the ratio of ammonia nitrogen concentration and nitrite nitrogen concentration in the treated water obtained under the condition 1, the treatment was performed in the same manner except that the pH was variously changed in the range of 6-9. The relationship between the concentration ratio of ammonia nitrogen and nitrite nitrogen and the pH of the treated water obtained and the pH is shown in FIG.
[0052]
As is clear from FIG. 2, when the pH is set low, the proportion of nitrite nitrogen increases, and conversely, when the pH is set high, the proportion of ammoniacal nitrogen increases. Therefore, in order to maintain the nitrite type nitrification and further denitrify the treated water by the aforementioned autotrophic microorganisms, the treated water of ammonia nitrogen concentration: nitrite nitrogen concentration = 2: 1 to 1: 2 is used. It can be seen that it is necessary to accurately control the pH of the nitrification tank in the range of 6 to 8, preferably 6.5 to 7.5 in order to obtain the above.
[0053]
【Effect of the invention】
As described in detail above, according to the nitrification method of the present invention, by using raw water as a pH adjuster, the required addition amount is greatly reduced without requiring a pH adjuster as a chemical. Above, stable nitrite type nitrification can be performed over a long period of time.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a nitrification apparatus suitable for carrying out the nitrification method of the present invention.
2 is a graph showing the relationship between the ratio of ammonia nitrogen concentration and nitrite nitrogen concentration of treated water and pH in Example 2. FIG.
[Explanation of symbols]
1 Nitrification tank (aeration tank)
2 pH sensor 3 Controller
Claims (5)
硝化槽に供給する原水をｐＨ調整剤としてその供給量を調節すると共に、必要に応じ他のｐＨ調整剤を添加することにより、硝化槽内のｐＨを６〜８に制御して硝化を行う硝化処理方法であって、
原水をｐＨ調整剤として利用し、硝化槽内のｐＨを６〜８とするために原水の供給量を調節し、原水だけではｐＨ調整し得ない場合に他のｐＨ調整剤を補助的に用い、硝化槽内のｐＨが低い場合には原水の供給量を増やし、硝化槽内のｐＨが高い場合には原水の供給量を減らし、これにより硝化槽内のｐＨが６〜８に回復した場合には原水の供給量を元の供給量に戻すことを特徴とする硝化処理方法。In a method for supplying raw water containing ammonia nitrogen to a nitrification tank that is aerated in the presence of ammonia-oxidizing bacteria and performing nitrification treatment,
Nitrification performing raw water supplied to the nitrification tank while adjusting the supply quantity as a pH adjusting agent, by adding other pH adjusting agent if necessary, nitrification by controlling the pH of the nitrification tank 6-8 A processing method,
Use raw water as a pH adjuster, adjust the supply amount of raw water to adjust the pH in the nitrification tank to 6-8, and use other pH adjusters when the pH cannot be adjusted with raw water alone When the pH in the nitrification tank is low, the supply amount of raw water is increased, and when the pH in the nitrification tank is high, the supply amount of raw water is decreased, and thereby the pH in the nitrification tank is restored to 6-8. A nitrification method characterized in that the supply amount of raw water is returned to the original supply amount .
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| JP4735256B2 (en) * | 2003-02-21 | 2011-07-27 | 栗田工業株式会社 | Ammonia nitrogen-containing water treatment method |
| JP2005131452A (en) * | 2003-10-28 | 2005-05-26 | Kobelco Eco-Solutions Co Ltd | Nitrification method for ammonia nitrogen-containing wastewater |
| JP4910266B2 (en) * | 2004-03-01 | 2012-04-04 | 栗田工業株式会社 | Nitrification method and treatment method of ammonia-containing nitrogen water |
| JP2006289277A (en) * | 2005-04-12 | 2006-10-26 | Tsukishima Kikai Co Ltd | Nitrate forming nitrification/denitrification method, method for nitrifying/denitrifying ammonia nitrogen-containing liquid and nitrate forming nitrification/denitrification equipment |
| JP4788645B2 (en) * | 2007-04-25 | 2011-10-05 | 株式会社日立プラントテクノロジー | Method of using nitrite type nitrification carrier, wastewater treatment method and wastewater treatment apparatus |
| JP4837706B2 (en) * | 2008-06-27 | 2011-12-14 | 水ｉｎｇ株式会社 | Ammonia nitrogen removal equipment |
| JP5592677B2 (en) * | 2010-03-12 | 2014-09-17 | 新日鐵住金株式会社 | Biological nitrogen treatment method of ammonia containing wastewater |
| WO2011134011A1 (en) * | 2010-04-28 | 2011-11-03 | The University Of Queensland | Production of nitrite |
| JP5516892B2 (en) * | 2010-12-17 | 2014-06-11 | 栗田工業株式会社 | Water treatment method and ultrapure water production method |
| JP5516874B2 (en) * | 2010-04-30 | 2014-06-11 | 栗田工業株式会社 | Water treatment method and ultrapure water production method |
| JP6046373B2 (en) * | 2012-04-24 | 2016-12-14 | パナソニック株式会社 | Nitrogen-containing wastewater treatment equipment |
| JP6883992B2 (en) * | 2017-01-17 | 2021-06-09 | 三菱ケミカルアクア・ソリューションズ株式会社 | Wastewater treatment method and wastewater treatment equipment |
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| JP2019181377A (en) * | 2018-04-11 | 2019-10-24 | 株式会社日立製作所 | Nitrogen treatment method |
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| JPS6323795A (en) * | 1986-07-16 | 1988-02-01 | Ebara Infilco Co Ltd | Biological nitrification of ammonia-containing aqueous solution |
| JPH0773714B2 (en) * | 1989-01-30 | 1995-08-09 | 栗田工業株式会社 | Wastewater nitrification method |
| JP3937664B2 (en) * | 1999-10-12 | 2007-06-27 | 栗田工業株式会社 | Biological nitrogen removal method and apparatus |
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| CN107032498A (en) * | 2017-06-23 | 2017-08-11 | 长春工程学院 | The method that batch enters enhanced water SBR technique deep denitrifications |
| CN107032498B (en) * | 2017-06-23 | 2019-02-19 | 长春工程学院 | The method that SBR technique deep denitrification is strengthened in batch water inlet |
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