JP3937664B2 - Biological nitrogen removal method and apparatus - Google Patents

Description

【００６８】
このようにして１００日程度通水を継続すると、アンモニア性窒素および亜硝酸性窒素が除去されるようになり、独立栄養性脱窒菌の増殖が確認された。約１年半通水を継続した結果、アンモニア性窒素除去速度と亜硝酸性窒素除去速度とを合計したリアクターの全窒素除去速度が１〜２ｋｇ−Ｎ／ｍ³・ｄａｙ以上となる程度の独立栄養性脱窒菌が集積した。菌が集積するに従って、アンモニア性窒素除去速度および亜硝酸性窒素除去速度がどちらも増加してくるので、基質不足にならないように負荷を増加させた。培地中の炭酸塩のモル濃度は、培地中のアンモニア性窒素のモル数の０．０５倍以上のモル数とした。
【００６９】
参考例１および２
１）硝化細菌脱窒−硝化プロセスによって生物学的窒素除去を行っている下水道処理場の脱窒硝化汚泥（汚泥は脱窒工程と硝化工程を循環しているため、脱窒菌と硝化菌の両者を含んでいる）を硝化装置の植種汚泥として使用した。
【００７０】
２）独立栄養性脱窒菌の集積
独立栄養性脱窒菌を集積するために、発泡スチロール製の球形ろ材（平均粒径３．５ｍｍ）を充填したカラムを用いた。このカラムは直径１５０ｍｍ、高さ１５００ｍｍの塩化ビニル製であり、見かけの充填容量が２０ Ｌになるようにろ材を充填して用いた。またカラムの上部のストレーナーによってろ材の流出を防止した。このようなカラムを２組用意（以下、カラムＡ、カラムＢという）した。
【００７１】
上記カラムＡに、有機源としてメタノールを用いて脱窒を行っている排水処理プラントの脱窒汚泥を種汚泥（試験例１においてこの汚泥中に独立栄養性脱窒菌が存在することを確認している）として添加した後、カラム下部からアンモニア性窒素１００ｍｇ−Ｎ／Ｌおよび亜硝酸性窒素１００ｍｇ−Ｎ／Ｌを含む前記表１の無機培地（３０℃、ｐＨ７）を上向流で通水し、処理水中のアンモニア性窒素濃度および亜硝酸性窒素濃度の低下を確認しながら、流速を上げることによって窒素負荷を増加させた。このようにして約１年半通水した結果、独立栄養性脱窒菌が集積し、アンモニア性窒素および亜硝酸性窒素を合計した全窒素除去速度は約２ｋｇ−Ｎ／ｍ³−リアクター／ｄａｙとなった。
【００７２】
前記カラムＢには、亜硝酸窒素の代わりに硝酸性窒素１００ｍｇ−Ｎ／Ｌを含む（アンモニア性窒素との合計では２００ｍｇ−Ｎ／Ｌを含む）前記表１の無機培地（３０℃、ｐＨ７）をカラムＡと同じように通水した。このようにして約１年運転したが、処理水のアンモニア性窒素濃度、硝酸性窒素濃度はどちらも９０ｍｇ−Ｎ／Ｌより低下することはなく、両者ともほとんど分解されなかった。過去に報告されている通り（von de Graaf, A. A., et al., Microbiology, 143(1997),p2415-2421）、アンモニア性窒素および硝酸性窒素を分解する独立栄養性脱窒菌を集積することは困難であると言える。
【００７３】
確認のため、独立栄養性脱窒菌が集積したカラムＡ（全窒素除去速度は約２ｋｇ−Ｎ／ｍ³−リアクター／ｄａｙ）について、基質をアンモニア性窒素１００ｍｇ−Ｎ／Ｌおよび硝酸性窒素１００ｍｇ−Ｎ／Ｌを含む表１の前記無機培地に変更し、全窒素負荷０．０５ｋｇ−Ｎ／ｍ³−リアクター／ｄａｙで１５日間運転したが、両基質ともほとんど分解されなかった。
【００７４】
３）装置
図１に示した装置を１組、および図２に示した装置を１組用意した。ただし、参考例１では、図１の装置において、浮遊式の脱窒槽２の代わりに生物ろ過式の脱窒装置を用い、バイパス原水路１１は連絡路４に接続し、連絡路４中で亜硝酸化液と原水とが混合されるように構成した。また参考例２では、図２の装置において、活性炭塔２１としてカラム直径８０ｍｍ、高さ５００ｍｍの塩化ビニル製のカラムに平均粒径１ｍｍの粒状活性炭を充填した活性炭塔を用いた。
【００７５】
参考例１および２のいずれの参考例も亜硝酸化槽１としては、２ Ｌの処理槽に対してスポンジ１０担体を見かけ容積３０％の量で添加した曝気槽を使用した。スポンジ１０は空気を曝気することにより流動させた。試験に先立ち、前記１）の脱窒亜硝酸化汚泥を５００ｍｌ添加した。
【００７６】
参考例１および２のいずれの参考例も脱窒装置としては、発泡スチロール製の球形ろ材（平均粒径３．５ｍｍ）を充填した生物ろ過カラムを用いた。このカラムは直径８０ｍｍ、高さ５００ｍｍの塩化ビニル製であり、見かけの充填容量が２ Ｌになるようにろ材を充填し、カラム下部から液を上向流で通水し、カラムの上部のストレーナーによってろ材の流出を防いだ。ただし、ろ材は新品を使用せず、前記２）で独立栄養性脱窒菌を集積したカラムＡ中から独立栄養性脱窒菌が付着しているろ材を抜き取り、各カラムに２ Ｌずつ充填した。
【００７７】
４）亜硝酸化＋独立栄養性脱窒による窒素の連続分解試験
表２に示した組成のアンモニア性窒素含有合成排水の窒素除去について検討した。この合成排水は窒素としてアンモニア性窒素を２０００ｍｇ−Ｎ／Ｌ含んでいる。
【００７８】
【表２】

【００７９】
試験は次のようにして行った。すなわち、スポンジ担体に亜硝酸化汚泥が付着し、亜硝酸化槽のアンモニア性窒素の除去速度が上昇するまでは、独立栄養性脱窒装置を設置せず、亜硝酸化槽のみの運転を行った。また亜硝酸化槽における反応を亜硝酸型とするため、当初原水に５００ｍｇ−Ｎ／Ｌの亜硝酸性窒素を添加し、亜硝酸酸化細菌の生育を抑えた。原水への亜硝酸性窒素の添加は２０日まで継続し、それ以降は行わなかった。
【００８０】
亜硝酸化槽の初期ＨＲＴは５０ｈとしたが、処理水のアンモニア性窒素濃度の低下を確認しながら、徐々にＨＲＴを短縮し、負荷を増加させた。その結果、約６０日後には、ＨＲＴ＝２４ｈ、窒素負荷２ｋｇ−Ｎ／ｍ³・ｄａｙで、処理水のアンモニア性窒素濃度は５ｍｇ−Ｎ／Ｌ以下になった。それ以降、試験終了まで亜硝酸化槽はこの負荷で運転したが、窒素処理能に変化はなく、処理水のアンモニア性窒素濃度は安定していた。亜硝酸化反応は当初から亜硝酸型で推移し、試験終了まで処理水から５ｍｇ−Ｎ／Ｌ以上の硝酸性窒素が検出されることはなかった。亜硝酸化槽は、参考例１および２のいずれも上記方法で運転し、得られた結果もほぼ同じであった。
【００８１】
亜硝酸化槽の亜硝酸化能が安定した６０日目以降、溶存酸素除去槽＋独立栄養性脱窒装置への亜硝酸化液の通液を開始するとともに、亜硝酸化槽をバイパスさせた原水を溶存酸素除去装置へ導入した。このときバイパス流量は全処理水流量の４３％（原水導入比＝０．４３）とした。なお参考例１には、溶存酸素除去装置がないため、亜硝酸化槽をバイパスさせた原水は直接独立栄養性脱窒装置に流入させた。脱窒装置では温度３０℃、ｐＨ７で脱窒を行った。６０日目（溶存酸素除去装置＋独立栄養性脱窒装置への通液を開始した日）以降の参考例１および２の水質測定結果を表３および表４に示す。
【００８２】
【表３】

【００８３】
【表４】

【００８４】
表３および表４の値は６０〜１５０日の平均値であるが、この期間中各濃度の経時変化はほとんど見られず、値は安定していた。参考例１および２における亜硝酸化槽の処理能力はほぼ等しく、脱窒装置に流入する被処理液中のアンモニア性窒素、亜硝酸性窒素および硝酸性窒素は参考例１および２でほぼ等しかった。脱窒装置に流入する被処理液中の溶存酸素濃度は、溶存酸素除去装置を設置していない参考例１では約２．２ｍｇ／Ｌであった。溶存酸素除去装置を設置した参考例２の溶存酸素濃度は０．０５ｍｇ／Ｌ未満であり、溶存酸素は効率的に除去されていることが確認された。なお、脱窒装置出口の溶存酸素濃度は参考例１および２とも０．０５ｍｇ／Ｌ未満であった。参考例１においても脱窒装置出口の溶存酸素濃度が０．０５ｍｇ／Ｌ未満になったのは、脱窒装置内でＢＯＤやアンモニアが酸化され酸素が消費されたためと考えられる。しかし、参考例１の処理水水質は溶存酸素除去装置を設けた参考例２に比べて低く、これは溶存酸素の影響により脱窒能が低下したためと推測される。
【００８５】
溶存酸素除去装置を設置した参考例２では、脱窒装置において効果的にアンモニア性窒素および亜硝酸性窒素が分解されており、実験期間中いずれの値も５ｍｇ−Ｎ／Ｌを超えることはなかった。
【００８６】
以上の結果から、溶存酸素により独立栄養性脱窒菌の脱窒能は低下するが、この場合は脱窒装置の前段に溶存酸素除去装置を設置し、脱窒装置への溶存酸素の流入を抑えることが、独立栄養性脱窒菌の脱窒能を高く維持することに有効であることが確認できた。
【００８７】
参考例３
参考例１の装置を用い、ただし亜硝酸化槽処理液に溶存酸素が残存しないように曝気量を少なくするとともに亜硝酸化槽の容積を１．５倍とし、前記表２に示した組成のアンモニア性窒素含有合成排水の窒素除去について検討した。結果を表５に示す。
【００８８】
【表５】

【００８９】
表５の結果より、参考例１に比べて亜硝酸化槽の容量を大きくするとともに、曝気量を少なくして溶存酸素濃度を低くすることにより、脱窒装置出口のアンモニア性窒素および亜硝酸性窒素濃度が低くなることがわかる。
【００９０】
実施例１および２
溶存酸素除去装置の代わりにＢＯＤ除去装置を用いて試験した。実施例１および２のいずれの実施例も亜硝酸化槽および脱窒装置としては、参考例１および２と同じ装置を用いた。
【００９１】
図３に示した装置を２組用意した。ただし、実施例１では、図３の装置において、ＢＯＤ除去装置として、スポンジ３８を見かけ容積３０％添加した容積２Ｌの浮遊式嫌気性処理装置（従属栄養性脱窒槽３０）用い、窒素ガスを曝気してスポンジを流動させた。従属栄養性脱窒槽３０の後段には膜分離装置４０を設けた。また実施例２では、図３の装置において、ＢＯＤ除去装置として、発泡スチロール製の球形ろ材（平均粒径３．５ｍｍ）を充填した生物ろ過カラム（従属栄養性脱窒装置）を用いた。このカラムは直径８０ｍｍ、高さ５００ｍｍの塩化ビニル製であり、見かけの充填容量が２ Ｌになるようにろ材を充填し、カラム下部から液を上向流で通水し、カラムの上部のストレーナーによってろ材の流出を防いだ。各ＢＯＤ除去装置には、試験に先立ち、脱窒亜硝酸化汚泥を３００ｍｌ添加した。また、いずれの装置でもバイパス原水路１１は連絡路３２に接続し、連絡路３２中で亜硝酸化液と原水とが混合されるように構成した。
【００９２】
上記装置を用いて、表６に示した組成のアンモニア性窒素含有合成排水の窒素除去について、以下の通り検討した。１〜５９日目までは参考例１および２と同じ方法で通水した。亜硝酸化槽の亜硝酸化能が安定した６０日目以降、ＢＯＤ除去装置＋独立栄養性脱窒装置への亜硝酸化液の通液を開始するとともに、亜硝酸化槽をバイパスさせた原水をＢＯＤ除去装置へ流入させた。このときバイパス流量は全処理水流量の４３％（原水導入比＝０．４３）とした。６０日目（ＢＯＤ除去装置＋独立栄養性脱窒装置への亜硝酸化液の通液を開始した日）以降の実施例１および２の各処理槽の水質測定結果（６０〜１５０日の平均値）を表７および表８に示す。なお、実施例１については１５０日目以降、ＢＯＤ除去装置の後段に孔径０．１μｍの精密ろ過膜を有する膜分離装置を設置し、ＢＯＤ除去装置の脱ＢＯＤ処理液を膜を通過させた後、独立栄養性脱窒装置に流入するようにし、濃縮液は亜硝酸化槽に戻した。膜を設置した以降の実施例１の処理水質（１５０〜２４０日の平均値）を表９に示す。
【００９３】
【表６】

【００９４】
【表７】

【００９５】
【表８】

【００９６】
【表９】

【００９７】
実施例１および２の各亜硝酸化槽の処理水質は亜硝酸型で安定しおり、硝化液のアンモニア性窒素および硝酸性窒素の濃度は５ｍｇ−Ｎ／Ｌ以下であった。このため、亜硝酸化液とバイパスした原水とを混合した時のアンモニア性窒素と亜硝酸性窒素の濃度比は、バイパス流量と亜硝酸化槽流量との比（４３：５７）にほぼ等しかった。また亜硝酸化槽ではＢＯＤもほぼ完全に分解されていた。
【００９８】
実施例１および２のＢＯＤ除去装置においては、バイパス原水路から導入された原水に含まれていたＢＯＤは完全に分解されており、同時に亜硝酸性窒素も減少していた。
【００９９】
参考例４
参考例１と同じ装置を用いて、前記表６に示した組成のアンモニア性窒素含有排水の窒素除去について、参考例１と同じ方法で検討した。結果を表１０に示す。
【０１００】
【表１０】

【０１０１】
最終処理水中のアンモニア性窒素および亜硝酸性窒素の濃度は実施例１、２および参考例４で大きく異なった。参考例４の処理水濃度が最も高く、アンモニア性窒素濃度が２３２ｍｇ−Ｎ／Ｌ、亜硝酸性窒素濃度が２８２ｍｇ−Ｎ／Ｌであった。次に処理濃度が高かったのは精密ろ過膜を設置する前の実施例１であり、アンモニア性窒素濃度が６２ｍｇ−Ｎ／Ｌ、亜硝酸性窒素濃度が４８ｍｇ−Ｎ／Ｌであった。実施例１では精密ろ過膜を設置した後、最終処理水のアンモニア性窒素および亜硝酸性窒素は大幅に減少し、アンモニア性窒素濃度が２．７ｍｇ−Ｎ／Ｌ、亜硝酸性窒素濃度が２．１ｍｇ−Ｎ／Ｌであった。実施例２の最終処理水の水質が最もよく、精密ろ過膜設置後の実施例２と同程度であり、アンモニア性窒素濃度が２．８ｍｇ−Ｎ／Ｌ、亜硝酸性窒素濃度が１．１ｍｇ−Ｎ／Ｌであった。
【０１０２】
以上の結果から、ＢＯＤ成分により独立栄養性脱窒菌の脱窒能が低下する場合は、脱窒装置の前段にＢＯＤ除去装置を設置し、脱窒装置へのＢＯＤ成分の流入を抑えることが、独立栄養性脱窒菌の脱窒能を高く維持することに有効であることが確認できた。またＢＯＤ除去装置を生物ろ過式とするか、または後段に膜を設置し、菌体ＳＳの流入を防止することによって、脱窒装置の脱窒処理能がさらに向上することが確認できた。
【０１０３】
また、今回の試験ではバイパスした原水に含まれるＢＯＤを利用した従属栄養性の脱窒菌による亜硝酸性窒素の減少を考慮し、式〔１〕に従ってパイパスする流量の比を決めたため（定数ａは１．３、ｂは３．０として計算）、脱窒装置でアンモニア性窒素と亜硝酸性窒素が効果的に反応し、ＢＯＤと菌体ＳＳを前段で除いた場合、処理水中のアンモニア性窒素濃度および亜硝酸性窒素濃度とともに３ｍｇ−Ｎ／Ｌ以下にすることができた。
なお、いずれの実施例でも脱窒装置で硝酸性窒素が増加するのは、独立栄養性脱窒菌が亜硝酸性窒素の一部を硝酸性窒素に変換するためであると推測される。
【図面の簡単な説明】
【図１】 図１は第１参考例の生物学的窒素除去装置を示す系統図である。
【図２】 図２は第２参考例の生物学的窒素除去装置を示す系統図である。
【図３】 図３は本発明の実施例の生物学的窒素除去装置を示す系統図である。
【符号の説明】
１ 亜硝酸化槽
２ 脱窒槽
３ 固液分離装置
４、５、２６、２７、３１、３２、４１ 連絡路
６ 原水路
７ａ、１４、２８、３３、４６ ｐＨ調整剤供給路
７ｂ 薬剤供給路
８ 空気供給路
９、３６ 散気装置
１０、３８ スポンジ
１１ バイパス原水路
１２ 返送汚泥路
１３、３４ 排ガス路
１５、３７ 撹拌器
１６ 処理水路
１７ 汚泥取出路
１８、４５ 余剰汚泥路
２１ 活性炭塔
２２ 活性炭層
２４ 脱窒装置
２５ 生物層
３０ 従属栄養性脱窒槽
３５ 窒素供給路
４０ 濃縮装置
４２ 濃縮液取出路
４３ 分離膜
４４ 濃縮液循環路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biological nitrogen removing method and apparatus for biologically purifying waste water containing ammoniacal nitrogen.
[0002]
[Prior art]
Ammonia nitrogen contained in wastewater is one of the causative substances of eutrophication in rivers, lakes and oceans, and it is desired to be removed efficiently in the wastewater treatment process. In general, ammonia nitrogen in wastewater is decomposed into nitrogen gas by a two-stage biological reaction of nitrification and denitrification. Specifically, in the nitrification process, ammonia nitrogen is oxidized to nitrite nitrogen by an ammonia oxidizing bacterium that is an autotrophic bacterium under aerobic conditions, and this nitrite nitrogen is a nitrite oxidizing bacterium that is an autotrophic bacterium. Is oxidized to nitrate nitrogen. Next, in the denitrification step, these nitrite nitrogen and nitrate nitrogen are decomposed into nitrogen gas under the anaerobic condition by denitrifying bacteria, which are heterotrophic bacteria, using organic substances as electron donors.
[0003]
Such conventional biological nitrogen removal requires a large amount of oxygen in the nitrification process that oxidizes ammonia nitrogen to nitrite nitrogen and nitrate nitrogen, and utilizes denitrifying bacteria that are heterotrophic bacteria. In the denitrification step, it is necessary to add a large amount of an organic substance such as methanol as an electron donor, which increases the running cost.
[0004]
By the way, in recent years, a new nitrogen treatment technology using an autotrophic microorganism group that can generate nitrogen gas by reacting ammonia nitrogen as an electron donor and nitrate nitrogen as an electron acceptor under anaerobic conditions. Is being developed (for example, Japanese translations of PCT publication No. 3-501099). In this method, nitrate nitrogen is added to raw water containing ammonia nitrogen and brought into contact with the microorganism group, thereby reacting ammonia nitrogen and nitrate nitrogen to remove them as nitrogen gas. In Japanese Patent Laid-Open No. 8-192185, raw water containing ammonia nitrogen is partially nitrified in a nitrification tank to leave a part of ammonia nitrogen, and the rest is oxidized to nitrite nitrogen and nitrate nitrogen. Is removed by reacting ammoniacal nitrogen with nitrite nitrogen and nitrate nitrogen.
However, it is difficult to collect such a microorganism using nitrate nitrogen as an electron acceptor from a normal wastewater treatment system. Moreover, in order to oxidize nitrite nitrogen to nitrate nitrogen, there is a problem that a large amount of oxygen is required and the processing cost is increased.
[0005]
On the other hand, as a microbial group similar to such a microbial group, a treatment technique using a microbial group using nitrite nitrogen as an electron acceptor is known (FEMS Microbiology Letters, 16 (1995), p177-184 and Wat. Res., 31 (1997), p1955-1962). In this method, ammonia nitrogen and nitrite nitrogen are caused to react with each other by bringing them into contact with the above-mentioned microorganism group so as to be removed as nitrogen gas. Here, an example in which nitrite is added as nitrite nitrogen is shown, but a method of partially nitrifying ammonia nitrogen is also suggested. However, if the raw water containing ammonia nitrogen is partially nitrified, it is difficult to keep the ratio of residual ammonia nitrogen and oxidized nitrite nitrogen constant. In addition, nitrification produces nitrate nitrogen as well as nitrite nitrogen, but this nitrate nitrogen is not assimilated by the above-mentioned microorganism group, and there is a problem that the treatment efficiency is lowered.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to propose a biological nitrogen removal method that can easily obtain high treated water quality at low cost.
Another object of the present invention is to provide a biological nitrogen removing apparatus that can easily obtain high treated water quality at low cost.
[0007]
[Means for Solving the Problems]
  The present invention provides the following biological nitrogen removal method and apparatus.
  (1) A nitritation step in which raw water containing ammonia nitrogen is brought into contact with ammonia oxidizing bacteria under aerobic conditions to oxidize ammonia nitrogen to nitrite nitrogen;
  Introducing nitritation liquid treated in the nitritation process and raw water containing ammonia nitrogen,Denitrification by contacting with heterotrophic denitrifying bacteria under anaerobic conditions and removing BOD and dissolved oxygenRemoval step, and
  Introducing the de-BOD treatment solution treated in the BOD removal step,Denitrification process in which denitrification is performed by contact with autotrophic denitrifying bacteria under anaerobic conditions
  A biological nitrogen removal method comprising:
  (2)  A nitrification device that introduces raw water containing ammonia nitrogen, contacts ammonia-oxidizing bacteria under aerobic conditions, and oxidizes ammonia nitrogen to nitrite nitrogen,
  Introducing a nitrating solution treated with a nitrifying device and raw water containing ammonia nitrogen, contacting with heterotrophic denitrifying bacteria under anaerobic conditions, denitrifying, and removing BOD and dissolved oxygen Removal device, and
  A biological nitrogen removal apparatus having a denitrification apparatus that introduces a de-BOD treatment solution treated with a BOD removal apparatus and makes contact with autotrophic denitrification bacteria under anaerobic conditions to perform denitrification.
  (3)  Control the amount of nitrite and raw water introduced into the BOD removal device so as to satisfy the following formula [1]Above (2)The device described.
r = b.N / (a.b.N + b.N + B) [1]
(In the formula [1], r is the raw water introduction ratio indicated by the amount of raw water introduced into the BOD removal device relative to the sum of the amount of nitrite introduced into the BOD removal device and the amount of raw water introduced into the BOD removal device. , N is the ammonia nitrogen concentration (mg-N / L) of the raw water, B is the BOD concentration (mg / L) of the raw water, a is the ammonia nitrogen concentration (mg-N / L) reacting in the denitrification device It is a constant indicating the ratio (nitrite nitrogen concentration / ammonia nitrogen concentration) to the nitrate nitrogen concentration (mg-N / L), and the number 0.5 to 2, b is nitrite nitrogen in the BOD removal apparatus (It is a constant indicating the BOD concentration (mg / L) consumed when 1 mg-N / L is denitrified, and is a number of 1.5 to 7.)
  (4)  A solid-liquid separation device was installed between the BOD removal device and the denitrification device.(2) or (3) aboveThe device described.
  (5)  Return the sludge separated by the solid-liquid separator to the BOD removal device or nitritation deviceAbove (4)The device described.
[0008]
In the present invention, “denitrification” means denitrification by autotrophic denitrifying bacteria unless otherwise specified.
The raw water to be treated in the present invention is raw water containing ammonia nitrogen, and may contain organic matter, nitrite nitrogen, other impurities, and the like. The raw water containing the organic nitrogen compound may be used for the present invention as it is, but may be used for the present invention after converting the organic nitrogen compound to ammonia nitrogen by anaerobic treatment or aerobic treatment. The raw water containing nitrate nitrogen can be subjected to the present invention after being reduced to nitrite nitrogen by a method such as bringing nitrate nitrogen into contact with a reduction catalyst. Examples of raw water to be treated in the present invention include human waste, sewage, food wastewater, fertilizer factory wastewater and the like.
[0009]
  In the biological nitrogen removal method of the present invention, the raw water containing ammonia nitrogen is brought into contact with ammonia oxidizing bacteria under aerobic conditions in the nitritation step to oxidize ammonia nitrogen to nitrite nitrogen,BOD removalIntroducing nitrite and ammonia water containing ammonia nitrogen in the processWhile performing denitrification, with BODRemove the dissolved oxygen and in the denitrification processRemove BOD treatment solutionDenitrification is carried out in contact with autotrophic denitrifying bacteria under anaerobic conditions.
[0010]
In the nitritation process, almost all ammonia nitrogen in the raw water is oxidized to nitrite nitrogen, and oxidation is performed so that ammonia nitrogen is not substantially left and nitrate nitrogen is not substantially formed. . In order to prevent the ammonia nitrogen from remaining, the oxygen supply amount and the residence time required for oxidizing the ammonia nitrogen are set. In order to prevent the formation of nitrate nitrogen, nitritation may be performed in an environment that inhibits the growth of nitrite-oxidizing bacteria.
[0011]
As such an environment, nitritation may be carried out under conditions of pH 5-9, preferably 6-8, and nitrite ion concentration of 50-10000 mg-N / L, preferably 200-3000 mg-N / L. When nitrate ions are insufficient, they can be added from the outside. When the nitrite ion exceeds the above range, the activity of the ammonia-oxidizing bacteria decreases, so that nitritation can be performed with a reduced load. Thus, in the present invention, it is not necessary to oxidize ammoniacal nitrogen to nitrate nitrogen, so that the required amount of oxygen is smaller than that of the conventional method in which nitrification is performed.
[0012]
In the denitrification step, denitrification is performed by setting the ratio of ammonia nitrogen to nitrite nitrogen to 1: 0.5 to 2, preferably 1: 1 to 1.5. In the present invention, almost all of the ammonia nitrogen in the raw water is converted to nitrite nitrogen in the nitritation step. Therefore, the above ratio can be obtained only by controlling the mixing ratio of the raw water containing ammonia nitrogen and the nitrite. Can be controlled, and control is easy. Further, since nitrate nitrogen is not generated, denitrification reaction is not inhibited in the denitrification step, and denitrification can be performed efficiently.
[0013]
  In the denitrification step, the reaction is performed under anaerobic conditions, and the denitrification reaction proceeds efficiently by setting the dissolved oxygen concentration to 2.5 mg / L or less, preferably 0.2 mg / L or less. In order to obtain such a dissolved oxygen concentration, there is a method of removing excess dissolved oxygen in the raw water and the nitrite solution itself. Activated carbon treatment as a method for removing dissolved oxygenHowever, in the present invention, instead of or in addition to these,See belowRemove by BOD removal device in BOD removal processThe method can be adopted.
[0014]
Since the denitrification step is a treatment with autotrophic denitrifying bacteria, denitrification can be efficiently performed by setting the BOD concentration to 50 mg / L or less, preferably 20 mg / L or less. Since BOD is decomposed in the nitritation process, when the BOD in the raw water is in the above range, it can be introduced into the denitrification process as it is. When the BOD concentration in the raw water exceeds the above range, the BOD can be removed by aerobic treatment or conventional heterotrophic denitrification treatment and introduced into the denitrification step of the present invention.
[0015]
The nitritation apparatus constituting the biological nitrogen removal apparatus of the present invention introduces raw water containing ammonia nitrogen and makes it contact with ammonia oxidizing bacteria under aerobic conditions to oxidize ammonia nitrogen to nitrite nitrogen. Any device such as a biological filtration type, a floating type, and an aeration type can be used. It is also possible to add a floating carrier such as a sponge in the apparatus so as to maintain a high amount of microorganisms.
[0016]
The nitritation apparatus is controlled so that the activity of ammonia-oxidizing bacteria is high and the activity of nitrite-oxidizing bacteria is low, and suppresses the production of nitric acid. That is, the nitrite-type nitric acid is controlled to proceed. For example, the treatment liquid in the apparatus has a pH of 5 to 9, preferably 6 to 8, a nitrite ion concentration of 50 to 10000 mg-N / L, preferably 200 to 3000 mg-N / L, and a temperature of 10 to 40 ° C. , Preferably 20 to 35 ° C., nitrogen load is 0.1 to 3 kg-N / m^Three-Day, preferably 0.2-1 kg-N / m^Three-Control to be day. In addition, the concentration of dissolved oxygen in the liquid to be treated in the apparatus can be lowered, or a substance that inhibits the growth of nitrite oxidizing bacteria such as sulfides can be added to control the nitritation to proceed.
[0017]
  The denitrification apparatus constituting the biological nitrogen removal apparatus of the present invention,Remove the BOD treatment solution treated in the BOD removal processIt is an apparatus that introduces and denitrifies by contacting with autotrophic denitrifying bacteria under anaerobic conditions, and any of biological filtration type, floating type, etc. can be used. The denitrification apparatus is controlled so that the denitrification ability of the autotrophic denitrifying bacteria is high. For example, the temperature of the liquid to be treated in the apparatus is 10 to 40 ° C, preferably 20 to 35 ° C, and the pH is 5 to 9, preferably 6-8, dissolved oxygen concentration 0-2.5 mg / L, preferably 0-0.2 mg / L, BOD concentration 0-50 mg / L, preferably 0-20 mg / L, nitrogen load 0.1 ~ 5kg-N / m^Three-Day, preferably 0.2-2 kg-N / m^Three-It is controlled by day.
[0018]
The mixed liquid of nitrite and raw water introduced into the denitrification apparatus usually has a molar ratio of nitrite nitrogen and ammonia nitrogen (nitrite nitrogen / ammonia nitrogen) of 0.5 to 2, preferably 1 to 1.5, the dissolved oxygen concentration is controlled to 0 to 2.5 mg / L, preferably 0 to 0.2 mg / L, and the BOD concentration is controlled to 0 to 50 mg / L, preferably 0 to 20 mg / L.
[0019]
The raw water introduced into the denitrification apparatus may be the same raw water as that used for nitritation in the nitritation apparatus, that is, raw water of the same treatment system, or may be raw water of another treatment system. . The introduction ratio between the nitrite and the raw water can be controlled so that the ratio of nitrite nitrogen to ammonia nitrogen (nitrite nitrogen / ammonia nitrogen) falls within the above range.
[0020]
  The activity of autotrophic denitrifying bacteria is inhibited by dissolved oxygen and BOD, and the denitrifying ability decreases as these concentrations increase. Therefore, the concentration of the liquid to be treated in the denitrifying apparatus is controlled within the above range. Is preferred. When the dissolved oxygen concentration and the BOD concentration of the liquid to be treated in the apparatus do not fall within the above ranges by simply introducing the mixed liquid of nitrite and raw water or introducing them separately into the denitrification apparatusBecause there is thisDissolved oxygen removal device to remove them and / orInstead of thisBOD removal device,Install between the nitritation unit and the denitrification unit toAnd BRemove OD. These can also be combined.
[0022]
In the biological nitrogen removing apparatus of the present invention, the dissolved oxygen removing apparatus provided when removing the dissolved oxygen from the nitrating liquid and raw water includes a nitrating liquid treated with the nitrifying apparatus, and ammonia nitrogen. It is a device that introduces raw water containing and removes dissolved oxygen from these mixed solutions. As such a dissolved oxygen removing apparatus, an apparatus capable of removing dissolved oxygen without adversely affecting the denitrification by the subsequent autotrophic denitrifying bacteria can be used without limitation. For example, the following apparatus can be mentioned.
[0023]
1) A vacuum type deaerator that lowers the solubility of oxygen by lowering the pressure of the gas in contact with the liquid to be treated and removes dissolved oxygen from the liquid to be treated.
2) A degassing membrane device that includes a gas separation membrane that allows oxygen to permeate and does not allow water to permeate, and decompresses the side opposite to the liquid to send dissolved oxygen in the liquid to be treated to the pressure reducing side.
3) A deoxygenation resin tower in which hydrogen gas as a reducing agent is injected and dissolved in a liquid to be treated, and then passed through a deoxygenation resin packed layer to deoxygenate by the catalytic action of the deoxidation resin.
4) An activated carbon tower for passing a liquid to be treated through an activated carbon packed bed to convert dissolved oxygen into carbon dioxide and remove it.
5) An oxygen-free gas aeration apparatus that removes dissolved oxygen by aeration of oxygen-free gas such as nitrogen gas, methane gas, argon gas, helium gas, carbon dioxide gas or a mixed gas thereof. As the nitrogen gas, nitrogen gas generated by a subsequent denitrification apparatus can also be used. Moreover, when an anaerobic fermentation apparatus is provided in the front | former stage or back | latter stage of the biological nitrogen removal apparatus of this invention, the methane gas and carbon dioxide gas which generate | occur | produced from there, and these mixed gas can also be utilized.
6) An oxygen scavenger addition device for reducing dissolved oxygen concentration by adding sodium sulfite, metabisulfite, succinic acid, hydrazine or the like as a reducing agent to the liquid to be treated.
[0024]
In the dissolved oxygen removing device, it is desirable to remove the dissolved oxygen so that the dissolved oxygen concentration of the deoxygenated treatment solution is 0 to 2.5 mg / L, preferably 0 to 0.2 mg / L as described above.
The raw water introduced into the dissolved oxygen removing apparatus may be the raw water of the same treatment system or the raw water of another treatment system, similarly to the raw water introduced into the denitrification apparatus. The deoxygenation treatment liquid from which dissolved oxygen has been removed is introduced into a subsequent denitrification apparatus for denitrification treatment.
[0025]
  In the biological nitrogen removal apparatus of the present invention,Remove BOD and dissolved oxygen from nitrite and raw waterFor the BOD removal processThe BOD removal device provided is a device that biologically removes BOD by introducing a nitritation solution treated with a nitritation device and raw water containing ammoniacal nitrogen, a biological filtration method, a floating method, Any fluid bed type can be used. It is also possible to add a floating carrier such as a sponge in the apparatus so as to maintain a high retention amount of microorganisms. In the BOD removal apparatus, it is desirable to remove the BOD so that the BOD concentration of the de-BOD treatment solution is 0 to 50 mg / L, preferably 0 to 20 mg / L as described above.
[0026]
  When BOD is removed biologically with the BOD removal device, sludge is generated, but when this sludge flows into the denitrification device at the subsequent stage, various BOD components are generated by self-decomposition. It is preferable to install a solid-liquid separation device such as a membrane separation device or a filtration tower to separate sludge and prevent inflow into the denitrification device. In this case, it is preferable to use a biological filtration type BOD removal device because BOD decomposition and sludge trapping can be performed simultaneously in one device. When concentrating sludge using a sedimentation tank, membrane separator, etc., the separated sludge can be returned to the previous nitritation device or BOD removal device to increase the sludge concentration in each device and increase the treatment capacity. it can. BOD removal device is an anaerobic treatment device, especially a denitrification type BOD removal device that performs denitrification by contacting with heterotrophic denitrifying bacteria under anaerobic conditionsBy adopting, BOD removal and dissolved oxygen removal can be performed simultaneously in one apparatus.
[0027]
  Raw water to be introduced into BOD removal equipmentIs the sameThe raw water of the same treatment system may be used, or the raw water of another treatment system may be used. The de-BOD treatment liquid from which BOD has been removed is introduced into the denitrification device at the subsequent stage and denitrified.The
[0028]
In the anaerobic BOD removal device, it is preferable to control the amount of nitrite and raw water introduced into the BOD removal device so as to satisfy the above formula [1]. By controlling the raw water introduction ratio r so that the formula [1] is satisfied, ammonia nitrogen and nitrite nitrogen are effectively reacted in the denitrification apparatus, thereby reducing the total nitrogen concentration in the final treated water. Thus, high treated water quality can be obtained.
[0029]
The formula [1] will be described in detail.
r is the raw water introduction ratio indicated by the amount of raw water introduced into the BOD removal device relative to the sum of the amount of nitrite introduced into the BOD removal device and the amount of raw water introduced into the BOD removal device, and N is the ammonia of the raw water Nitrogen concentration (mg-N / L), B is the BOD concentration (mg / L) of raw water, a is the ammonia nitrogen concentration (mg-N / L) and nitrite nitrogen concentration (mg mg-N / L) is a constant indicating the ratio (nitrite nitrogen concentration / ammonia nitrogen concentration), and the number of 0.5 to 2 is expressed as 1 mg-N / nitrogen nitrogen in the BOD removal apparatus. It is a constant indicating the BOD concentration (mg / L) consumed when L is denitrified, and is a number between 1.5 and 7.
[0030]
In this case, the BOD concentration flowing into the BOD removal device is represented by B · r (mg / L). Moreover, it is nitrite nitrogen produced | generated with a nitritation apparatus, Comprising: The nitrite nitrogen density | concentration which flows into a BOD removal apparatus is shown by N * (1-r) (mg-N / L). Further, since a part of nitrous acid is consumed by denitrification that occurs in the BOD removal apparatus, the concentration of nitrous acid nitrogen flowing into the denitrification apparatus is N · (1-r) −B · r · 1 / b (mg− N / L). Moreover, it is ammonia nitrogen derived from raw | natural water, Comprising: The ammonia nitrogen concentration which flows in into a denitrification apparatus is shown by N * r (mg-N / L).
[0031]
Therefore, when ammonia nitrogen and nitrite nitrogen react effectively in the denitrification device and the total nitrogen concentration in the treated water is minimized, the following equation [2] is established, When the equation [2] is solved with respect to the raw water introduction ratio r, the above equation [1] is obtained.
[Equation 3]
a = {N · (1-r) −B · r · 1 / b} / (N · r) (2)
[0032]
In the BOD removal apparatus, it is more preferable to control the amount of nitrite introduced into the BOD removal apparatus and the amount of raw water so as to satisfy the following formula (1 ').
[Expression 4]
r = b'.N / (a'.b'.N + b'.N + B) ... [1 ']
(In the formula [1 ′], r, N and B are the same as in the formula [1]. A ′ is a constant having the same meaning as a in the formula [1], and is a number from 1 to 1.5; b is a constant having the same meaning as b in the formula [1], and is a number from 2 to 5.
[0033]
In Formula [1], the removal rate of ammonia nitrogen in the nitrifier is 100%, and BOD decomposition by aerobic heterotrophic bacteria using dissolved oxygen remaining in the nitrite treatment solution is performed. Ignoring. If necessary, equation [1] may be corrected in consideration of these.
[0034]
[Action]
In the nitritation apparatus, raw water containing ammonia nitrogen is introduced and contacted with ammonia oxidizing bacteria under aerobic conditions by aeration to perform nitritation, thereby converting ammonia nitrogen into nitrite nitrogen. Here, almost all of the ammonia nitrogen in the raw water is oxidized to nitrite nitrogen, and nitritation is performed under conditions where nitrite nitrogen is not oxidized to nitrate nitrogen. In this nitritation apparatus, it is not necessary to leave ammonia nitrogen in the raw water, and it is sufficient to oxidize substantially all of it to nitrite nitrogen, so that control is easy. Further, since it is not necessary to oxidize ammoniacal nitrogen to nitrate nitrogen, the amount of oxygen supplied can be reduced, and the running cost can be reduced.
[0035]
  Dissolved oxygen removerWhen providingThe nitritation liquid treated with the nitrification apparatus and the raw water containing ammonia nitrogen are mixed, and dissolved oxygen in the mixed liquid is removed. Since the denitrification ability of the autotrophic denitrifying bacteria is lowered by dissolved oxygen, when the dissolved oxygen concentration of the liquid to be denitrified exceeds 2.5 mg / L, preferably 0.2 mg / L, for example, a denitrification device When the dissolved oxygen concentration of the mixture of nitrite introduced into the raw water and raw water exceeds 2.5 mg / L, preferably exceeds 0.2 mg / L, and the BOD concentration of this mixture is low, A dissolved oxygen removal device is provided in front of the filtration-type denitrification device, and the dissolved oxygen concentration in the deoxygenated liquid is reduced to 2.5 mg / L, preferably 0.2 mg / L or less.Can. Even when a floating denitrification tank is used instead of the biological filtration type denitrification apparatus, a dissolved oxygen removal apparatus is provided so that the dissolved oxygen concentration in the deoxygenation treatment liquid is 2.5 mg / L, preferably 0.2 mg / L. Lower than LCan. In this case, since the deoxygenated liquid is diluted with the liquid in the tank of the denitrification tank, the dissolved oxygen concentration of the diluted liquid in the tank (processed liquid) is lower than that of the deoxygenated liquid.
[0036]
  In addition, even if the dissolved oxygen concentration of the to-be-denitrified solution mixed with the nitrite and raw water introduced into the denitrification device is within the above range, or even if more dissolved oxygen is contained, the denitrification device Even when ammonia and BOD are oxidized inside, dissolved oxygen is consumed and anaerobic conditions are maintained.BODIf the removal device is provided, the entire denitrification device can be efficiently used for the autotrophic denitrification reaction, so that a high treated water quality can be obtained. in this way,BODBy providing the removal device, the denitrification device is maintained in an anaerobic state, denitrification in the denitrification device is performed more efficiently, and high treated water quality is obtained.
[0037]
  In the BOD removal device, the nitritation solution treated with the nitritation device and the raw water containing ammonia nitrogen are mixed, and the BOD in this mixture solution is mixed.And dissolved oxygenIs removed. Since the denitrification ability of the autotrophic denitrifying bacteria is reduced by BOD, when the BOD concentration of the liquid to be denitrified exceeds 50 mg / L, for example, the BOD removal device is placed before the biological filtration type denitrification device. It is preferable to reduce the BOD concentration in the de-BOD treatment solution to 50 mg / L or less, preferably 20 mg / L or less, and then introduce this de-BOD treatment solution into the subsequent denitrification apparatus. Even when a floating denitrification tank is used instead of a biological filtration denitrification device, a BOD removal device is provided to reduce the BOD concentration in the de-BOD treatment solution to 50 mg / L or less, preferably 20 mg / L or less. After that, it is preferable to introduce the de-BOD treatment liquid into a subsequent denitrification apparatus. In this case, since the de-BOD treatment liquid is diluted with the liquid in the tank of the denitrification tank, the BOD concentration of the diluted liquid in the tank (treatment liquid) is lower than that of the de-BOD treatment liquid.
[0038]
  Thus, by providing the BOD removal device, the denitrification ability of the autotrophic denitrification bacteria in the denitrification device is prevented from being lowered, denitrification in the denitrification device is performed more efficiently, and high treated water quality is obtained. It is done. When the BOD concentration of the denitrification solution is 50 mg / L or less, preferably 20 mg / L or less, the BOD removal device can be omitted. Adopting denitrification type BOD removal device by heterotrophic denitrifying bacteria as BOD removal deviceBy, BOD is decomposed and removed by denitrification reaction using nitrite nitrogen contained in nitrite as an electron acceptor.ButSince dissolved oxygen in the nitrite is consumed with BOD decomposition by aerobic heterotrophic bacteria, it is convenient for maintaining the anaerobic property of the subsequent denitrification apparatus.
[0039]
When a denitrification-type BOD removal device using heterotrophic denitrifying bacteria is adopted as the BOD removal device, when the nitrite and raw water are mixed in the BOD removal device, this mixed solution is usually derived from the raw water. Due to the presence of BOD, some nitrite nitrogen is consumed by heterotrophic denitrifying bacteria. For this reason, unreacted ammonia nitrogen may remain in the final treated water unless the raw water introduction ratio is determined in consideration of the decrease in nitrite nitrogen, so that the above formula [1] is satisfied. By determining the raw water introduction ratio r, such water quality deterioration can be easily prevented.
[0040]
  With denitrification equipmentIs aFrom a mixture of nitrate solution and raw waterBOD and dissolved oxygenThe de-BOD treatment liquid from which the water has been removed is introduced, and denitrification is carried out by contacting with autotrophic denitrifying bacteria under anaerobic conditions. Since the autotrophic denitrifying bacteria can be denitrified by reacting nitrite nitrogen and ammonia nitrogen without adding organic substances, treatment at low cost is possible.
[0041]
The autotrophic denitrifying bacterium used in the present invention can be obtained by the following method. Add denitrification sludge such as wastewater treatment plant, sewage treatment or human waste treatment as seeding source to floating sludge type (SRT 15d or more) or biofilm type reactor, temperature 10-40 ° C, pH 5-9, BOD concentration Under anaerobic conditions (dissolved oxygen concentration of 0.2 mg / L or less) at 20 mg / L or less, an inorganic medium containing ammonia nitrogen, nitrite nitrogen and inorganic carbonate is passed through. At that time, the loads of ammonia nitrogen and nitrite nitrogen to the reactor are adjusted so that the concentration of both in the treated water is 1 to 200 mg-N / L. If water is continued for about 30 to 360 days in this way, ammonia nitrogen and nitrite nitrogen will be removed, and autotrophic denitrifying bacteria will accumulate in the reactor. Furthermore, if water flow is continued, for example, if water is passed for 1 to 2 years, the total nitrogen removal rate of the reactor, which is the sum of the ammonia nitrogen removal rate and the nitrite nitrogen removal rate, is 1 to 2 kg-N / m.^Three-Autotrophic denitrifying bacteria that accumulate to a day or more accumulate. As the fungus accumulates, both the ammoniacal nitrogen removal rate and the nitrite nitrogen removal rate increase, so the load is increased so as not to run out of substrate. As the inorganic medium, those containing metal salts to the extent that medium is added when cultivating ordinary microorganisms are used, and when using tap water or factory effluent containing a part of these, it is necessary to add them separately. Absent. The molar concentration of carbonate in the medium is set to 0.05 or more times the number of moles of ammonia nitrogen in the medium.
[0042]
  The biological nitrogen removing apparatus of the present invention comprises a nitrifying apparatus and a denitrifying apparatus using autotrophic denitrifying bacteria, and the raw water containing ammonia nitrogen is converted into almost all of the ammonia nitrogen in the nitrifying apparatus. After converting toBODAside from this, raw water containing ammonia nitrogen is bypassed through the nitritation unit.BODIntroduced into removal equipmentTo denitrify and remove BOD and dissolved oxygenAndIntroducing the de-BOD treatment liquid into the denitrification equipmentDenitrification treatment. For this reason, the nitritation apparatus may be controlled so as to convert almost the entire amount of ammonia nitrogen into nitrite nitrogen, and the control of the nitritation apparatus becomes simple. Moreover, the ratio of ammonia nitrogen and nitrite nitrogen in the denitrification device can be easily adjusted to an appropriate range simply by controlling the introduction ratio of raw water into each device, and high treatment efficiency can be obtained. . Note that the raw water introduced into the denitrification apparatus by bypassing the nitritation apparatus may be a raw water obtained by branching a part of the raw water introduced into the nitritation apparatus at the front stage of the nitritation apparatus. The raw water supplied from a system different from the raw water introduced into the nitrification apparatus may be used.thisThus, raw water containing ammonia nitrogen can be easily treated at a low cost and with a high quality of treated water.
[0043]
【The invention's effect】
  The biological nitrogen removal method of the present invention includes a nitritation step for oxidizing ammonia nitrogen to nitrite nitrogen, a nitrite treated in the nitritation step, and raw water containing ammonia nitrogen,And BOD that removes BOD and dissolved oxygen while contacting with heterotrophic denitrifying bacteria under anaerobic conditionsRemoval step, andIntroduce the de-BOD treatment liquid processed in the BOD removal processSince there is a denitrification process in which denitrification is performed in contact with autotrophic denitrifying bacteria under anaerobic conditions, control for nitritation in the nitritation process, as well as ammonia nitrogen and nitrous acid introduced in the denitrification process The ratio of oxygen to nitrogen can be easily adjusted, and there is no need for nitrification.Preventing the denitrification of autotrophic denitrifiers by BOD and dissolved oxygen,Raw water containing ammonia nitrogen can be biologically treated at low cost and easily with high treated water quality.
[0044]
  The biological nitrogen removing apparatus according to claim 2 of the present invention comprises a nitritation apparatus that oxidizes ammonia nitrogen to nitrite nitrogen, a nitrite treated by the nitritation apparatus, and ammonia nitrogen. Including raw waterIntroduced and contacted with heterotrophic denitrifying bacteria under anaerobic conditions to denitrify, remove BOD and dissolved oxygen, and remove BOD treatment liquid treated in BOD removal processSince it is equipped with a denitrification device that is introduced and brought into contact with autotrophic denitrifying bacteria under anaerobic conditions, control for nitritation in the nitritation process and ammonia nitrogen introduced in the denitrification process And the ratio of nitrogen to nitrite nitrogen becomes easy, and since there is no need for nitrification, the amount of oxygen supply may be small,With BODPreventing the decline in the denitrification ability of autotrophic denitrifying bacteria due to dissolved oxygen, it is possible to biologically treat raw water containing ammonia nitrogen at a low cost and easily with high treated water quality.The
[0045]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the present invention will be described with reference to the drawings. Figure 1First reference exampleIt is a systematic diagram which shows the biological nitrogen removal apparatus of No. 1, and is an apparatus used suitably for the process of raw | natural water with a low BOD density | concentration, for example, 50 mg / L or less. In FIG. 1, 1 is a nitritation tank, 2 is a floating autotrophic denitrification tank, 3 is a solid-liquid separator, and these are connected via communication paths 4 and 5.
[0046]
A raw water channel 6, a pH adjusting agent supply channel 7a, a drug supply channel 7b and a communication channel 4 are connected to the nitritation tank 1, and an air diffuser 9 communicating from an air supply channel 8 is provided inside the tank. . Further, a sponge 10 for supporting biological sludge is added in the tank.
The denitrification tank 2 is connected to a bypass raw water path 11 branched from the raw water path 6, a return sludge path 12, an exhaust gas path 13, a pH adjuster supply path 14, and communication paths 4 and 5, and a stirrer 15 is provided inside the tank. It has been.
The solid-liquid separator 3 is connected to a communication path 5, a treatment water path 16 and a sludge extraction path 17, and the sludge extraction path 17 branches into a return sludge path 12 and an excess sludge path 18.
[0047]
In order to remove biological nitrogen with the apparatus of FIG. 1, a part of the raw water is introduced into the nitritation tank 1 from the raw water channel 6, mixed with biological sludge containing ammonia oxidizing bacteria in the tank, and the aeration apparatus. 9 is aerated and ammonia nitrogen is oxidized to nitrite nitrogen by ammonia oxidizing bacteria. Although the dissolved oxygen concentration in the liquid in the tank is increased by aeration, if no means for removing dissolved oxygen is provided at the subsequent stage as shown in FIG. 1, the amount of air to be aerated is reduced so that the dissolved oxygen concentration is as low as possible. Aerate. In this case, since the nitritation efficiency is lowered, in order to make the processing amount of the entire treatment system equal to the case where the dissolved oxygen removing device is provided, the residence time is increased by increasing the capacity of the nitritation tank 1 or the like. Lengthen.
[0048]
The nitritation tank 1 has a pH of 5 to 9, preferably 6 to 8, a nitrite ion concentration of 50 to 10,000 mg-N / L, preferably 200 to 3000 mg-N / L, and a temperature of the liquid mixture in the tank. 10 to 40 ° C., preferably 20 to 35 ° C., nitrogen load is 0.1 to 3 kg-N / m^Three-Day, preferably 0.2-1 kg-N / m^Three-The nitritation is advanced by controlling to become day.
[0049]
The pH of the liquid in the nitritation tank 1 is within the above range by adding a pH adjuster such as an alkali such as sodium carbonate or sodium hydroxide; an acid such as hydrochloric acid or nitric acid from the pH adjuster supply path 7a. Can be controlled. In the nitritation tank 1, the pH decreases with the oxidation of ammonia. Therefore, alkali is usually added to adjust the pH. Further, by maintaining the nitrite ion concentration within the above range, nitrification is prevented and ammonia nitrogen is oxidized to nitrite nitrogen. When the nitrite ion concentration is lower than the above range, for example, nitrite such as sodium nitrite can be controlled within the above range by adding from the drug supply path 7b. Nitrite may be added during the period from the start of treatment until nitritation is fixed, and when nitritation is fixed, the concentration of nitrite in the tank is usually in the above range. Addition can be omitted. When the nitrite ion concentration exceeds the above range, the treatment is performed with the ammonia nitrogen load lowered. In addition, although the detection apparatus of pH and nitrite ion concentration is provided in the nitritation tank 1, illustration is abbreviate | omitted.
[0050]
The nitrite in the nitrification tank 1 is introduced from the communication channel 4 to the denitrification tank 2, and another part of the raw water is introduced from the bypass raw water channel 11, and the organism containing the autotrophic denitrifying bacteria in the tank is introduced. Mixing with sludge, denitrification is performed while gently stirring with an agitator 15 under anaerobic conditions. The dissolved oxygen concentration of the liquid in the denitrification tank 2 is maintained at 2.5 mg / L or less, preferably 0.2 mg / L or less by adjusting the amount of aeration in the nitritation tank 1. In the above denitrification using autotrophic denitrifying bacteria, it is not necessary to add an electron donor, which is necessary in the conventional method of performing denitrification using heterotrophic denitrifying bacteria. When denitrification is performed in this manner, ammonia nitrogen derived from the raw water reacts with nitrite nitrogen derived from the nitrite to produce nitrogen gas by autotrophic denitrifying bacteria. The generated nitrogen gas is discharged out of the system from the exhaust gas passage 13.
[0051]
The denitrification tank 2 is maintained under conditions that increase the denitrification ability of the autotrophic denitrifying bacteria. For example, the temperature of the liquid in the tank is 10 to 40 ° C, preferably 20 to 35 ° C, and the pH is 5 to 9, preferably 6 to 6. 8. The dissolved oxygen concentration is 0 to 2.5 mg / L, preferably 0 to 0.2 mg / L, the BOD concentration is 0 to 50 mg / L, preferably 0 to 20 mg / L, and the nitrogen load is 0.1 to 5 kg- N / m^Three-Day, preferably 0.2-2 kg-N / m^Three-It is controlled by day.
[0052]
The pH of the liquid in the denitrification tank 2 is controlled within the above range by adding an acid such as hydrochloric acid and nitric acid; and a pH adjusting agent such as alkali such as sodium carbonate and sodium hydroxide from the pH adjusting agent supply path 14 as necessary. However, in the case of a denitrification reaction by autotrophic denitrifying bacteria using ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor, the pH adjustment can be omitted because the pH fluctuation is small. . The ratio of nitrite nitrogen / ammonia nitrogen is controlled within the above range by adjusting the amount of raw water introduced from the bypass raw water channel 11.
[0053]
The denitrification liquid is introduced from the communication path 5 into the solid-liquid separation device 3 and separated into solid and liquid. The separation liquid is discharged out of the system from the treatment water channel 16 as treated water, and the separated sludge is taken out from the sludge extraction channel 17 and returned from the return sludge channel 12 to the denitrification tank 2. When surplus sludge is generated, it is discharged out of the system from the surplus sludge path 18.
[0054]
In the apparatus of FIG. 1, the sponge 10 is added to the nitritation tank 1, but it may not be added. If the sponge 10 is not added, the concentration of biological sludge in the nitritation tank 1 may be reduced, which may hinder the treatment. Therefore, a solid-liquid separation device is provided at the subsequent stage of the nitritation tank 1, and this solid-liquid separation is performed. The sludge separated by the apparatus is preferably returned to the nitritation tank 1. Further, as the denitrification tank 2, a biological filtration type denitrification tower or the like can be adopted instead of the floating denitrification tank. In this case, the subsequent solid-liquid separation device 3 can be omitted. Although the returned sludge is returned to the denitrification tank 2, it can also be returned to the nitritation tank 1. When the BOD concentration of raw water is high, this raw water is introduced into the nitritation tank 1 for treatment, and raw water of another treatment system having a low BOD concentration is introduced into the denitrification tank 2, and the BOD concentration in the denitrification tank 2 is introduced. Is preferably maintained at 50 mg / L or less, preferably 20 mg / L or less.
[0055]
In such biological nitrogen removal, it is not necessary to oxidize ammonia nitrogen to nitric acid in the nitritation tank 1, so the amount of air supplied from the air diffuser 9 may be small, and therefore aeration. It is possible to reduce the energy required for. Moreover, since it is not necessary to add organic substances, such as methanol used as an electron donor, to the denitrification tank 2, the cost of the additive can be reduced. Furthermore, ammonia nitrogen and nitrite nitrogen can be reacted without excess and deficiency simply by controlling the amount of raw water introduced from the bypass raw water channel 11 into the denitrification tank 2, and high treatment water quality can be obtained. Easy to control. Thus, in the apparatus of FIG. 1, raw water containing ammoniacal nitrogen can be treated at low cost, easily and with high treated water quality.
[0056]
  FIG. 2 includes an activated carbon tower 21 as a dissolved oxygen removing device.Second reference exampleIt is a systematic diagram which shows the biological nitrogen removal apparatus of FIG. When the activated carbon tower 21 is used as a dissolved oxygen removing device, dissolved oxygen is removed by activated carbon and BOD is also removed by microorganisms adhering to the activated carbon. Therefore, it can be used for the treatment of raw water containing BOD. It is an apparatus suitably used for the treatment of raw water exceeding 50 mg / L, and it is an apparatus for treating raw water while preventing a decrease in the activity of autotrophic denitrifying bacteria due to dissolved oxygen and BOD.
[0057]
In FIG. 2, reference numeral 21 denotes an activated carbon tower. A communication path 26 connected from the nitritation tank 1 is connected to the lower part, a communication path 27 connected to the denitrification device 24 is connected to the upper part, and the inside is filled with activated carbon. The activated carbon layer 22 is formed, and the mixture of the nitrite and raw water is passed in an upward flow to remove dissolved oxygen. Reference numeral 24 denotes a biofiltration type denitrification apparatus, which is connected to the lower part of a communication path 27 connected from the activated carbon tower 21, to the upper part of the treatment water path 16 and the exhaust gas path 13, and contains autotrophic denitrification bacteria inside the apparatus. A biological layer 25 is formed, and the deoxygenation liquid is passed in an upward flow for denitrification. The bypass raw water channel 11 is connected to the communication channel 26, and the nitrite solution and the raw water are mixed in the communication channel 26. A pH adjuster supply path 28 is connected to the communication path 27 so that the pH adjuster is mixed with the deoxygenated liquid. Other configurations are the same as those of the apparatus shown in FIG.
[0058]
In the apparatus of FIG. 2, the activated carbon tower 21 is provided as a dissolved oxygen removing apparatus at the subsequent stage of the nitritation tank 1, so it is not necessary to reduce the amount of aeration in the nitritation tank 1, and the total amount of ammonia nitrogen is sublimated. Nitrated by aeration so that it is oxidized to nitrate nitrogen. This nitritation solution and raw water are mixed in the communication path 26, and this mixed solution is passed upward through the activated carbon layer 22 to remove dissolved oxygen. In the activated carbon tower 21, dissolved oxygen is removed to a concentration at which the activity of the autotrophic denitrifying bacteria in the denitrifying device 24 is maintained high. For example, the dissolved oxygen is removed so that the dissolved oxygen concentration of the deoxygenation treatment solution introduced from the communication path 27 to the denitrification apparatus 24 is reduced to 0 to 2.5 mg / L, preferably 0 to 0.2 mg / L. To do. In the activated carbon tower 21, BOD is also removed by microorganisms attached to the activated carbon.
The deoxygenated treatment liquid from which dissolved oxygen has been removed is taken out from the communication path 27, added with a pH adjuster from the pH adjuster supply path 28 if necessary, and then introduced into the denitrification device 24, and passed through the biological layer 25 in an upward flow. To denitrify. Other operations are the same as those in FIG.
[0059]
In the apparatus of FIG. 2, since the mixed oxygen nitrite and raw water is introduced into the activated carbon tower 21 to remove dissolved oxygen before denitrification, autotrophic properties by dissolved oxygen in the denitrification apparatus 24 are removed. It is possible to prevent the denitrification ability of the denitrifying bacteria from being lowered, and to perform treatment at a low cost, easily and with a high quality of treated water.
Instead of the activated carbon tower 21, a vacuum type deaeration device, a deaeration membrane device provided with a gas separation membrane, a deoxygenated resin tower, an oxygen-free gas aeration device, an oxygen scavenger addition device, or the like can be used. When these dissolved oxygen removing apparatuses are used, BOD is not removed, so it is preferable to treat raw water having a low BOD concentration, for example, 50 mg / L or less.
[0060]
  FIG. 3 shows a biological nitrogen removal apparatus equipped with a denitrification tank (hereinafter referred to as a heterotrophic denitrification tank) using heterotrophic denitrifying bacteria as a BOD removal apparatus.Example ofIt is a systematic diagram and is a device used for processing raw water having a high BOD concentration, for example, exceeding 50 mg / L. In FIG. 3, 30 is a heterotrophic denitrification tank, which is connected to communication paths 31 and 32, a pH adjuster supply path 33 and an exhaust gas path 34, and a diffuser 36 and agitator that communicate from a nitrogen supply path 35 inside. A vessel 37 is provided, and is configured to perform denitrification and decomposition of BOD components by denitrification of biological sludge containing heterotrophic denitrifying bacteria under anaerobic conditions. 38 is a sponge. A concentrating device 40 is connected to the communication paths 32 and 41 and the concentrated liquid take-out path 42, and a separation membrane 43 is provided inside the apparatus. The communication path 32 is provided with a pump P1. The concentrate extraction path 42 branches into a concentrate circulation path 44 and an excess sludge path 45, and the concentrate circulation path 44 communicates with the nitritation tank 1 so that the concentrated sludge is circulated through the nitritation tank 1. . A pH adjusting agent supply path 46 is connected to the communication path 41 so that the pH adjusting agent is mixed with the de-BOD processing solution. Other configurations are the same as those of the apparatus shown in FIG.
[0061]
In the apparatus of FIG. 3, raw water is introduced into the heterotrophic denitrification tank 30 from the nitrite and the bypass raw water channel 11, mixed with biological sludge containing heterotrophic denitrification bacteria in the tank, and nitrogen gas is subjected to anaerobic conditions. Is diffused from the diffuser 36 and denitrification is performed while the sponge 38 is suspended. The generated nitrogen gas is discharged from the exhaust gas passage 34, but can also be used as nitrogen gas diffused from the diffuser 36. The nitrogen supply path 35, the air diffuser 36, and the exhaust gas path 34 can be omitted.
[0062]
The amount of raw water introduced from the bypass raw water channel 11 to the heterotrophic denitrification tank 30 is preferably a water amount satisfying the above formula [1]. In the heterotrophic denitrification tank 30, the BOD component contained in the raw water introduced from the bypass raw water channel 11 is used as an electron donor by the heterotrophic denitrifying bacterium, and the nitrite contained in the nitrite solution Nitrogen is denitrified and the BOD component is removed.
In the heterotrophic denitrification tank 30, BOD is removed to a concentration at which the activity of the autotrophic denitrifying bacteria in the denitrification apparatus 24 is maintained high. For example, the BOD is removed so that the BOD concentration in the de-BOD treatment solution introduced into the denitrification device 24 from the communication path 41 is 50 mg / L or less, preferably 0 to 20 mg / L.
[0063]
Moreover, in the heterotrophic denitrification tank 30, since dissolved oxygen in the liquid in the tank is consumed by aerobic microorganisms in the tank, dissolved oxygen is also removed. Even if no special deoxygenation operation is performed, dissolved oxygen is usually removed to 0.05 mg / L or less. The de-BOD treatment liquid from which the BOD component and dissolved oxygen have been removed in this way is the pump P₁Is pressurized and introduced into the concentrating device 40 for membrane separation. The concentrated sludge is circulated from the concentrated sludge circulation path 44 to the nitritation tank 1. The separation liquid is taken out from the communication path 41, added with a pH adjuster from the pH adjuster supply path 46 if necessary, introduced into the denitrification device 24, and denitrified as in the case of FIG. When surplus sludge is generated, it is discharged from the surplus sludge passage 45 outside the system. Nitrogen gas discharged from the exhaust gas passage 13 may be used as nitrogen gas diffused from the diffuser 36. Other operations are the same as those in FIG. 1 or FIG.
[0064]
In the apparatus of FIG. 3, BOD and dissolved oxygen are removed in the heterotrophic denitrification tank 30 before denitrification by the autotrophic denitrifier in the denitrifier 24, so that the BOD and dissolved oxygen in the denitrifier 24 The autotrophic denitrifying bacteria can be prevented from lowering the denitrifying ability, and can be treated at a low cost, easily and with a high quality of treated water.
Instead of the floating heterotrophic denitrification tank 30, a biofiltration heterotrophic denitrification tank or the like may be used.
[0065]
【Example】
Next, examples of the present invention will be described.
[0066]
Test example 1
It was confirmed as follows that autotrophic denitrifying bacteria can be induced spontaneously.
Add 1/100 of the denitrification sludge of the wastewater treatment plant as a seeding source to the biofilm reactor, temperature 30 ° C, pH 7, BOD concentration 20 mg / L or less, anaerobic condition (dissolved oxygen concentration 0.2 mg / L or less) was passed through the medium of Table 1 containing 2000 mg-N / L of ammonia nitrogen and 2000 mg-N / L of nitrite nitrogen. At that time, the loads of ammonia nitrogen and nitrite nitrogen to the reactor were adjusted so that the concentration of both in the treated water was 1 to 200 mg-N / L.
[0067]
[Table 1]

[0068]
In this way, when water was continued for about 100 days, ammonia nitrogen and nitrite nitrogen were removed, and growth of autotrophic denitrifying bacteria was confirmed. As a result of continuing the water flow for about one and a half years, the total nitrogen removal rate of the reactor, which is the sum of the ammonia nitrogen removal rate and the nitrite nitrogen removal rate, is 1-2 kg-N / m.^Three-Autotrophic denitrifying bacteria accumulated to a day or more accumulated. As the bacteria accumulated, both the ammonia nitrogen removal rate and the nitrite nitrogen removal rate increased, so the load was increased so as not to run out of substrate. The molar concentration of the carbonate in the medium was set to 0.05 or more times the number of moles of ammoniacal nitrogen in the medium.
[0069]
Reference Example 1 and2
  1) Nitrification bacteria Denitrification-Denitrification nitrification sludge in sewerage treatment plants that are removing biological nitrogen by the nitrification process (Sludge circulates between the denitrification process and the nitrification process. Was used as seeding sludge for nitrification equipment.
[0070]
2) Accumulation of autotrophic denitrifying bacteria
In order to accumulate autotrophic denitrifying bacteria, a column filled with a spherical filter medium (average particle size 3.5 mm) made of polystyrene foam was used. This column was made of vinyl chloride having a diameter of 150 mm and a height of 1500 mm, and was used with a filter medium packed so that the apparent packing capacity was 20 L. The strainer at the top of the column prevented the filter medium from flowing out. Two sets of such columns were prepared (hereinafter referred to as column A and column B).
[0071]
In column A above, denitrified sludge from a wastewater treatment plant that is denitrifying using methanol as the organic source is seed sludge (in Test Example 1, it is confirmed that autotrophic denitrifying bacteria exist in this sludge. After that, the inorganic medium (30 ° C., pH 7) of Table 1 containing 100 mg-N / L of ammonia nitrogen and 100 mg-N / L of nitrite nitrogen was passed from the bottom of the column in an upward flow. The nitrogen load was increased by increasing the flow rate while confirming the decrease in ammonia nitrogen concentration and nitrite nitrogen concentration in the treated water. As a result of passing water for about one and a half years in this way, autotrophic denitrifying bacteria accumulate, and the total nitrogen removal rate of ammonia nitrogen and nitrite nitrogen is about 2 kg-N / m.^Three-Reactor / day.
[0072]
The column B contains 100 mg-N / L of nitrate nitrogen instead of nitrogen nitrite (including 200 mg-N / L in total with ammonia nitrogen) The inorganic medium of Table 1 (30 ° C., pH 7) Was passed in the same manner as column A. The operation was continued for about one year in this manner, but neither the ammonia nitrogen concentration nor the nitrate nitrogen concentration of the treated water decreased below 90 mg-N / L, and both were hardly decomposed. As previously reported (von de Graaf, AA, et al., Microbiology, 143 (1997), p2415-2421), accumulating autotrophic denitrifying bacteria that degrade ammoniacal nitrogen and nitrate nitrogen It can be said that it is difficult.
[0073]
For confirmation, column A with autotrophic denitrifying bacteria accumulated (total nitrogen removal rate is about 2 kg-N / m^Three-For the reactor / day), the substrate was changed to the inorganic medium of Table 1 containing 100 mg-N / L ammoniacal nitrogen and 100 mg-N / L nitrate nitrogen, total nitrogen load 0.05 kg-N / m^Three-Reactor / day was run for 15 days, but both substrates were hardly degraded.
[0074]
  3) Equipment
  One set of the apparatus shown in FIG. 1 and one set of the apparatus shown in FIG. 2 were prepared. However, in Reference Example 1, a biological filtration type denitrification device is used instead of the floating type denitrification tank 2 in the apparatus of FIG. 1, the bypass raw water channel 11 is connected to the communication channel 4, and The nitrate solution and raw water were mixed. AlsoReference example 2In the apparatus shown in FIG. 2, an activated carbon tower in which granular activated carbon having an average particle diameter of 1 mm is packed in a column made of vinyl chloride having a column diameter of 80 mm and a height of 500 mm is used as the activated carbon tower 21.
[0075]
  Reference Example 1 and2Any ofReference exampleAs the nitritation tank 1, an aeration tank in which a sponge 10 carrier was added in an apparent volume of 30% to a 2 L treatment tank was used. The sponge 10 was made to flow by aeration of air. Prior to the test, 500 ml of the denitrified nitrite sludge of 1) was added.
[0076]
  Reference Example 1 and2Any ofReference exampleAs the denitrification apparatus, a biological filtration column packed with a spherical filter medium (average particle size 3.5 mm) made of polystyrene foam was used. This column is made of vinyl chloride with a diameter of 80 mm and a height of 500 mm. The column is packed with a filter medium so that the apparent packing volume is 2 L, and the liquid is passed upward from the bottom of the column. This prevented the filter medium from leaking. However, a new filter medium was not used, and the filter medium on which autotrophic denitrifying bacteria adhered was extracted from column A in which autotrophic denitrifying bacteria were accumulated in 2) above, and 2 L was packed in each column.
[0077]
4) Continuous decomposition test of nitrogen by nitritation + autotrophic denitrification
The nitrogen removal of the ammoniacal nitrogen-containing synthetic wastewater having the composition shown in Table 2 was examined. This synthetic wastewater contains 2000 mg-N / L of ammonia nitrogen as nitrogen.
[0078]
[Table 2]

[0079]
The test was conducted as follows. That is, until the nitrite sludge adheres to the sponge carrier and the removal rate of ammonia nitrogen in the nitrite tank increases, the autotrophic denitrifier is not installed and only the nitrite tank is operated. It was. In addition, in order to make the reaction in the nitritation tank nitrite type, 500 mg-N / L of nitrite nitrogen was initially added to the raw water to suppress the growth of nitrite oxidizing bacteria. The addition of nitrite nitrogen to the raw water continued until the 20th and was not performed thereafter.
[0080]
  Although the initial HRT of the nitritation tank was 50 h, the HRT was gradually shortened and the load was increased while confirming the decrease in the ammonia nitrogen concentration of the treated water. As a result, after about 60 days, HRT = 24 h, nitrogen load 2 kg-N / m^Three-The ammonia nitrogen concentration of treated water became 5 mg-N / L or less at day. Since then, the nitritation tank was operated at this load until the end of the test, but there was no change in the nitrogen treatment capacity and the ammonia nitrogen concentration in the treated water was stable. The nitritation reaction changed from the beginning to the nitrite type, and nitrate nitrogen of 5 mg-N / L or more was not detected from the treated water until the end of the test. The nitritation tank was used in Reference Example 1 and2Both were operated by the above method, and the obtained results were almost the same.
[0081]
  After the 60th day when the nitritation capacity of the nitrification tank was stabilized, the nitritation liquid started to pass through the dissolved oxygen removal tank + autotrophic denitrification equipment, and the nitritation tank was bypassed. Raw water was introduced into the dissolved oxygen remover. At this time, the bypass flow rate was 43% of the total treated water flow rate (raw water introduction ratio = 0.43). In additionReference example 1Since there was no dissolved oxygen removal device, the raw water bypassing the nitritation tank was directly flowed into the autotrophic denitrification device. In the denitrification apparatus, denitrification was performed at a temperature of 30 ° C. and a pH of 7. Reference Example 1 on and after the 60th day (the day when the solution was passed through the dissolved oxygen removing device + autotrophic denitrification device) and2Table 3 and Table 4 show the water quality measurement results.
[0082]
[Table 3]

[0083]
[Table 4]

[0084]
  The values in Tables 3 and 4 are average values for 60 to 150 days, but almost no change in each concentration with time was observed during this period, and the values were stable. Reference Example 1 and2The treatment capacities of the nitritation tanks are almost equal, and ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the liquid to be treated flowing into the denitrification apparatus are the same as in Reference Example 1 and2It was almost equal. The dissolved oxygen concentration in the liquid to be treated flowing into the denitrification apparatus was about 2.2 mg / L in Reference Example 1 in which no dissolved oxygen removal apparatus was installed. Installed dissolved oxygen removal deviceReference example 2The dissolved oxygen concentration was less than 0.05 mg / L, and it was confirmed that the dissolved oxygen was efficiently removed. It should be noted that the dissolved oxygen concentration at the denitrification device outlet is the same as in Reference Example 1 and2Both were less than 0.05 mg / L.referenceIn Example 1 as well, the reason why the dissolved oxygen concentration at the outlet of the denitrification apparatus was less than 0.05 mg / L is considered that oxygen was consumed by oxidizing BOD and ammonia in the denitrification apparatus. However, reference examples1The quality of treated water was equipped with a device for removing dissolved oxygen.Reference example 2It is estimated that the denitrification ability was lowered due to the influence of dissolved oxygen.
[0085]
  Installed dissolved oxygen removal devicereferenceExample2In the denitrification apparatus, ammonia nitrogen and nitrite nitrogen were effectively decomposed, and neither value exceeded 5 mg-N / L during the experiment.
[0086]
From the above results, the denitrification ability of autotrophic denitrifying bacteria is reduced by dissolved oxygen, but in this case, a dissolved oxygen removal device is installed in front of the denitrification device to suppress the inflow of dissolved oxygen to the denitrification device. This was confirmed to be effective in maintaining the high denitrification ability of the autotrophic denitrifying bacteria.
[0087]
Reference example 3
  Using the apparatus of Reference Example 1, except that the amount of aeration was reduced so that no dissolved oxygen remained in the nitritation tank treatment liquid, and the volume of the nitritation tank was 1.5 times, and the composition shown in Table 2 above was used. Nitrogen removal from ammonia-based nitrogen-containing synthetic wastewater was investigated. The results are shown in Table 5.
[0088]
[Table 5]

[0089]
  From the results in Table 5,referenceCompared to Example 1, while increasing the capacity of the nitritation tank and reducing the aeration amount to lower the dissolved oxygen concentration, the concentrations of ammonia nitrogen and nitrite nitrogen at the denitrifier outlet can be lowered. Recognize.
[0090]
Example1and2
  The test was conducted using a BOD removal device instead of the dissolved oxygen removal device. Example1and2In any of the Examples, as the nitritation tank and the denitrification apparatus, Reference Example 1 and2The same equipment was used.
[0091]
  Two sets of the apparatus shown in FIG. 3 were prepared. However, the example1Then, in the apparatus of FIG. 3, a floating anaerobic treatment apparatus (heterotrophic denitrification tank 30) having a volume of 2 L to which an apparent volume of 30% was added as a BOD removal apparatus was used, and the sponge was flowed by aeration of nitrogen gas. I let you. A membrane separation device 40 was provided at the subsequent stage of the heterotrophic denitrification tank 30. Examples2In the apparatus of FIG. 3, a biofiltration column (heterotrophic denitrification apparatus) filled with a spherical filter medium made of polystyrene foam (average particle size: 3.5 mm) was used as the BOD removal apparatus. This column is made of vinyl chloride with a diameter of 80 mm and a height of 500 mm. The column is packed with a filter medium so that the apparent packing volume is 2 L, and the liquid is passed upward from the bottom of the column. This prevented the filter medium from leaking. Prior to the test, 300 ml of denitrified nitrite sludge was added to each BOD removal apparatus. In any apparatus, the bypass raw water channel 11 is connected to the communication channel 32 so that the nitrite and the raw water are mixed in the communication channel 32.
[0092]
  Using the above apparatus, the nitrogen removal of the ammoniacal nitrogen-containing synthetic wastewater having the composition shown in Table 6 was examined as follows. From day 1 to day 59referenceWater was passed in the same manner as in Examples 1 and 2. Starting from the 60th day when the nitritation capacity of the nitrification tank was stabilized, the nitritation liquid started to pass through the BOD removal device + autotrophic denitrification device, and the raw water bypassed the nitrification tank Was allowed to flow into the BOD remover. At this time, the bypass flow rate was 43% of the total treated water flow rate (raw water introduction ratio = 0.43). Examples after the 60th day (the day when the nitrite was passed through the BOD removal device + autotrophic denitrification device)1and2Table 7 and Table 8 show the water quality measurement results (average values for 60 to 150 days) of each treatment tank. Examples1After 150 days, a membrane separation device having a microfiltration membrane with a pore size of 0.1 μm was installed at the subsequent stage of the BOD removal device, the BOD removal solution of the BOD removal device was passed through the membrane, The concentrated solution was returned to the nitritation tank. Examples after installing the membrane1Table 9 shows the treated water quality (average value of 150 to 240 days).
[0093]
[Table 6]

[0094]
[Table 7]

[0095]
[Table 8]

[0096]
[Table 9]

[0097]
  Example1and2The treated water quality of each of the nitrification tanks was stable in the nitrite type, and the concentrations of ammonia nitrogen and nitrate nitrogen in the nitrification solution were 5 mg-N / L or less. For this reason, the concentration ratio of ammonia nitrogen and nitrite nitrogen when mixing the nitrite and the raw water bypassed was almost equal to the ratio of the bypass flow rate to the nitrite flow rate (43:57). . Also, BOD was almost completely decomposed in the nitritation tank.
[0098]
  Example1and2In the BOD removal apparatus, the BOD contained in the raw water introduced from the bypass raw water channel was completely decomposed, and at the same time, nitrite nitrogen was reduced.
[0099]
Reference example4
  Using the same apparatus as in Reference Example 1, nitrogen removal from the ammoniacal nitrogen-containing wastewater having the composition shown in Table 6 was examined in the same manner as in Reference Example 1. The results are shown in Table 10.
[0100]
[Table 10]

[0101]
  Concentrations of ammonia nitrogen and nitrite nitrogen in the final treated water are examples1,2And reference examples4It was very different. Reference example4The ammonia water concentration was 232 mg-N / L and the nitrite nitrogen concentration was 282 mg-N / L. Next, the treatment concentration was the highest before the installation of the microfiltration membrane.1The ammonia nitrogen concentration was 62 mg-N / L, and the nitrite nitrogen concentration was 48 mg-N / L. Example1After installing the microfiltration membrane, the ammoniacal nitrogen and nitrite nitrogen in the final treated water are greatly reduced, the ammoniacal nitrogen concentration is 2.7 mg-N / L, and the nitrite nitrogen concentration is 2.1 mg- N / L. Example2The quality of the final treated water is the best, and the example after installation of the microfiltration membrane2The ammonia nitrogen concentration was 2.8 mg-N / L, and the nitrite nitrogen concentration was 1.1 mg-N / L.
[0102]
From the above results, when the denitrification ability of the autotrophic denitrifying bacteria is reduced by the BOD component, a BOD removal device is installed in the front stage of the denitrification device to suppress the inflow of the BOD component to the denitrification device. It was confirmed that it is effective for maintaining the high denitrification ability of autotrophic denitrifying bacteria. In addition, it was confirmed that the denitrification ability of the denitrification apparatus was further improved by adopting a BOD removal apparatus as a biological filtration type or installing a membrane in the subsequent stage to prevent the inflow of the bacterial cell SS.
[0103]
In this test, the ratio of flow rate to bypass was determined according to the formula [1] in consideration of the decrease of nitrite nitrogen due to heterotrophic denitrifying bacteria using BOD contained in the bypassed raw water (constant a is 1.3 and b are calculated as 3.0), when ammonia nitrogen and nitrite nitrogen react effectively in the denitrification device, and BOD and microbial cell SS are removed in the previous stage, ammonia nitrogen in the treated water The concentration and the concentration of nitrite nitrogen could be reduced to 3 mg-N / L or less.
In any of the examples, it is assumed that nitrate nitrogen increases in the denitrification apparatus because autotrophic denitrification bacteria convert part of nitrite nitrogen to nitrate nitrogen.
[Brief description of the drawings]
[FIG. 1] FIG.First reference exampleIt is a systematic diagram which shows the biological nitrogen removal apparatus of FIG.
[FIG. 2] FIG.Second reference exampleIt is a systematic diagram which shows the biological nitrogen removal apparatus of FIG.
FIG. 3 is an illustration of the present invention.ExampleIt is a systematic diagram which shows the biological nitrogen removal apparatus of FIG.
[Explanation of symbols]
1 Nitrite tank
2 Denitrification tank
3 Solid-liquid separator
4, 5, 26, 27, 31, 32, 41
6 Raw waterway
7a, 14, 28, 33, 46 pH adjuster supply path
7b Drug supply channel
8 Air supply path
9, 36 Air diffuser
10, 38 sponge
11 Bypass raw waterway
12 Return sludge path
13, 34 Exhaust gas passage
15, 37 Stirrer
16 treatment channel
17 Sludge outlet
18, 45 Surplus sludge path
21 Activated carbon tower
22 Activated carbon layer
24 Denitrification equipment
25 Biological layer
30 Heterotrophic denitrification tank
35 Nitrogen supply channel
40 Concentrator
42 Concentrated liquid outlet
43 Separation membrane
44 Concentrate circuit

Claims (5)

A nitritation process in which raw water containing ammonia nitrogen is contacted with ammonia oxidizing bacteria under aerobic conditions to oxidize ammonia nitrogen to nitrite nitrogen,
Introducing a nitrating solution treated in the nitrifying step and raw water containing ammonia nitrogen, and contacting with heterotrophic denitrifying bacteria under anaerobic conditions to perform denitrification and to remove BOD and dissolved oxygen Removal step, and
The biological nitrogen removal method which has the denitrification process which introduce | transduces the de-BOD processing liquid processed with the BOD removal apparatus, contacts with an autotrophic denitrifying bacterium on anaerobic conditions, and denitrifies. A nitrification device that introduces raw water containing ammonia nitrogen, contacts ammonia-oxidizing bacteria under aerobic conditions, and oxidizes ammonia nitrogen to nitrite nitrogen,
Introducing a nitrating solution treated with a nitrifying device and raw water containing ammonia nitrogen, contacting with heterotrophic denitrifying bacteria under anaerobic conditions, denitrifying, and removing BOD and dissolved oxygen A biological nitrogen removal apparatus having a removal apparatus and a denitrification apparatus that introduces a de-BOD treatment solution treated by the BOD removal apparatus and makes contact with autotrophic denitrifying bacteria under anaerobic conditions to perform denitrification. The apparatus according to claim 2, wherein the amount of nitrite introduced into the BOD removal device and the amount of raw water are controlled so as to satisfy the following formula [1].
r = b.N / (a.b.N + b.N + B) [1]
(In the formula [1], r is the raw water introduction ratio indicated by the amount of raw water introduced into the BOD removal device relative to the sum of the amount of nitrite introduced into the BOD removal device and the amount of raw water introduced into the BOD removal device. , N is the ammonia nitrogen concentration (mg-N / L) of the raw water, B is the BOD concentration (mg / L) of the raw water, a is the ammonia nitrogen concentration (mg-N / L) reacting in the denitrification device It is a constant indicating the ratio (nitrite nitrogen concentration / ammonia nitrogen concentration) to the nitrate nitrogen concentration (mg-N / L), and the number 0.5 to 2, b is nitrite nitrogen in the BOD removal apparatus (It is a constant indicating the BOD concentration (mg / L) consumed when 1 mg-N / L is denitrified, and is a number of 1.5 to 7.) The apparatus according to claim 2 or 3, wherein a solid-liquid separation device is provided between the BOD removal device and the denitrification device. The apparatus of Claim 4 which returns the sludge isolate | separated with the solid-liquid separator to a BOD removal apparatus or a nitritation apparatus.

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