JP3918349B2 - Biological treatment method and apparatus for nitrous oxide gas - Google Patents

Biological treatment method and apparatus for nitrous oxide gas Download PDF

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JP3918349B2
JP3918349B2 JP5742099A JP5742099A JP3918349B2 JP 3918349 B2 JP3918349 B2 JP 3918349B2 JP 5742099 A JP5742099 A JP 5742099A JP 5742099 A JP5742099 A JP 5742099A JP 3918349 B2 JP3918349 B2 JP 3918349B2
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gas
nitrous oxide
oxide gas
tank
oxygen
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JP2000246055A (en
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美幸 高嶋
立夫 角野
信子 橋本
一彦 能登
多佳子 小笠原
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Hitachi Plant Technologies Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

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Description

【０００１】
【発明の属する技術分野】
本発明は、亜酸化窒素ガスの生物学的処理方法及び装置に係り、特に、硝化槽での硝化処理で発生する亜酸化窒素ガスを効率良く生物学的に処理するための亜酸化窒素ガスの生物学的処理方法及び装置に関する。
【０００２】
【従来の技術】
有機性又は無機性の廃水中の窒素成分を生物学的に処理する廃水処理装置では、窒素成分の硝化処理における反応副産物として亜酸化窒素ガスが発生することが知られている。しかし、発生した亜酸化窒素ガスの除去処理は行われておらず、大気中に放出しているのが実情である。
【０００３】
ところで、亜酸化窒素ガスは、二酸化炭素ガスの数百倍の温室効果を有しており、世界的な地球温暖化防止の高まりにともない、二酸化炭素ガスやメタンガスとともに排出削減対象物質となっている。
亜酸化窒素ガスを生物学的に処理する従来の装置としては、特開平６─１９０２４１号公報にみられるように、亜酸化窒素ガスを含有するガスを、吸着工程で吸着剤に亜酸化窒素ガスを吸着させた後、該吸着剤又は該吸着剤から脱着した亜酸化窒素ガス、又は亜酸化窒素ガスを吸収させた吸収液を嫌気性条件下にある生物学的な亜酸化窒素ガスの分解工程で分解するものである。
【０００４】
【発明が解決しようとする課題】
しかしながら、従来の亜酸化窒素ガスの生物学的処理装置は、運転しずらいという欠点がある。
更に、従来の亜酸化窒素ガスの生物学的処理方法は、吸着という物理的手段と微生物という生物学的手段のように、性質の全く異なる２つの手段を組み合わせているので、運転操作が複雑になると共に運転管理の面でも煩雑になるという欠点がある。このような背景から、生物学的な処理のみで亜酸化窒素ガスを分解除去する方法が要望されている。
【０００５】
本発明は、このような事情に鑑みてなされたもので、亜酸化窒素ガスの分解性能を向上させることができると共に、装置構成のシンプル化を図ることができる亜酸化窒素ガスの生物学的処理方法及び装置を提供することを目的とする。
【０００６】
【発明を解決するための手段】
本発明は、前記目的を達成するために、亜酸化窒素ガスを含有する含有ガスを、嫌気性の生物反応槽に導入して微生物による還元処理を行う前に、前記含有ガスに混在する酸素を予め除去しておくことを特徴とする。
また、本発明は、前記目的を達成するために、亜酸化窒素ガスを含有する含有ガスから混在する酸素を除去する酸素除去装置と、前記酸素除去装置で酸素を予め除去した脱酸素ガスを導入して、該脱酸素ガス中の亜酸化窒素ガスを嫌気性条件下で微生物により還元処理を行う嫌気性の生物反応槽と、を備えたことを特徴とする。
【０００７】
本発明によれば、亜酸化窒素ガスを含有する含有ガスを、嫌気性の生物反応槽に導入して還元処理する前に、生物学的処理を阻害する直接物質である酸素を除去したので、嫌気性の生物反応槽において亜酸化窒素ガスを効率的に除去することができる。
【０００９】
更にまた、本発明は、前記目的を達成するために、アンモニア性窒素を含有する廃水を複数の硝化槽で多段式に硝化処理する際に各硝化槽で発生する亜酸化窒素ガスを含有する含有ガスのうち、少なくとも１段目の硝化槽で発生する前記含有ガスを請求項２の生物学的処理装置に導く含有ガス送気経路を設けたことを特徴とする。
【００１０】
本発明は、多段式硝化処理の場合、複数の硝化槽で発生する亜酸化窒素ガスの含有ガスのうち、１段目の硝化槽で全体の約７０％発生することに着目して成されたもので、本発明によれば、少なくとも１段目の硝化槽で発生する含有ガスを請求項２の生物学的処理装置に導く含有ガス送気経路を設けたので、少ない設備改造で亜酸化窒素ガスを効率的に処理することができる。
【００１１】
【発明の実施の形態】
以下、添付図面により本発明の亜酸化窒素ガスの生物学的処理方法及び装置の好ましい実施の形態について詳説する。
図１は、本発明の亜酸化窒素ガスの生物学的処理装置の第１の実施の形態であり、本発明を活性汚泥循環変法式の廃水処理装置に組み込んだ構成図である。
【００１２】
図１に示すように、アンモニア性窒素を含有する有機性廃水又は無機性廃水の原水は、嫌気性の脱窒槽１０に流入してから好気性の硝化槽１２に送られ、硝化槽１２で処理された処理水の一部が循環路１４を介して脱窒槽１０に戻されると共に、残りが固液分離槽１６に送られる。固液分離槽１６では、処理水に同伴される活性汚泥を固液分離し、汚泥返送経路１８を介して脱窒槽１０に返送して脱窒槽１０内の生物量を維持する。また、一部の汚泥は余剰汚泥として排出管２０を介して装置外に排出される。
【００１３】
そして、硝化槽１２では、散気装置２２によりブロア３０から供給されたエアが散気され、好気性条件下で活性汚泥中の好気性微生物である硝化菌により廃水中のアンモニア性窒素が亜硝酸性窒素や硝酸性窒素に硝化処理される。また、脱窒槽１０で処理しきれなかった廃水中の有機物が水と二酸化炭素に分解される。硝化槽１２から液が循環される脱窒槽１０では、硝化槽１２で生成された亜硝酸性窒素や硝酸性窒素が、廃水中の有機物或いはメタノール等の電子供与体を還元剤として、嫌気性微生物である脱窒菌により脱窒処理されて窒素ガスに還元する。これにより廃水中のアンモニア性窒素が除去される。この廃水の流れにおいて、硝化槽１２での硝化処理の反応副産物として亜酸化窒素ガスが生成する。
【００１４】
硝化槽１２で発生した亜酸化窒素ガスの含有ガスを、脱窒槽１０の廃水中に直接導入して活性汚泥中の脱窒菌により生物学的に還元処理すると、含有ガス中に多く混在する酸素が嫌気性微生物である脱窒菌の還元反応を阻害する。そこで、本発明では、硝化槽１２で発生した亜酸化窒素ガスを酸素除去装置２４に送気し、含有ガスに混在する酸素を予め除去した脱酸素ガスを脱窒槽１０の廃水中に導入するようにした。
【００１５】
酸素除去装置２４としては、分子ふるい活性炭、ガス分離膜を用いた装置を使用することが好ましい。
図２（ａ）は、分子ふるい活性炭を用いた酸素除去装置２４の一例を示したもので、分子ふるい活性炭の吸着塔を２基並列に設けて２基で交互運転を行う場合である。この酸素除去装置２４は、酸素（Ｏ2 ）の分子径（３．９×２．８Å）が、亜酸化窒素ガス（Ｎ2 Ｏ）の分子径（５．６７×３．０Å）よりも小さく、小さいものほど速く吸着することを利用したものである。図２（ｂ）に、酸素除去装置２４の吸着塔Ｉ側を運転する際のバルブ切替要領を示した。
【００１６】
酸素除去装置２４は、均圧→加圧（吸着）→減圧（脱着）を１サイクル（通常２分）とする酸素除去サイクルを繰り返す。これにより、亜酸化窒素ガスの含有ガスから酸素を除いた脱酸素ガスと、酸素を富有に含む酸素富有ガスとに分離される。この結果、脱酸素ガス中の酸素濃度を０．５％以下にすることができる。また、図示しないが、ガス分離膜を用いた酸素除去装置では、ガス分離膜として分子径の小さな酸素の透過速度が大きく、分子径の大きな亜酸化窒素ガスの透過速度が小さなシリコーン系ポリマー膜を用いることができる。しかし、酸素と亜酸化窒素ガスとの膜分離ができるものであればシリコーン系ポリマー膜に限定するものではない。
【００１７】
図３は、本発明の第１の実施の形態の効果を説明するものであり、脱窒槽１０の活性汚泥による亜酸化窒素ガスの分解性能を示したものである。尚、脱窒槽１０の廃水中の活性汚泥濃度は１０００ｍｇ／Ｌ、分解開始前の亜酸化窒素ガス濃度は５ｍｇ／Ｌの場合である。
曲線Ａは、硝化槽１２で発生する亜酸化窒素ガスの含有ガスを分子ふるい活性炭を用いた酸素除去装置２４で酸素を除去してから脱窒槽１０に導入した場合の脱窒槽１０における亜酸化窒素ガスの分解性能を示したものである。
【００１８】
曲線Ｂは、硝化槽１２で発生した前記含有ガスを酸素除去装置２４を通さずに脱窒槽１０に直接導入した場合の脱窒槽１０での分解性能を示したものである。尚、曲線Ｃと曲線Ｄについては、本発明の第２の実施の形態の効果で説明する。図３の曲線Ａから分かるように、酸素除去装置２４を通した場合には、約１時間１５分程度で５ｍｇ／Ｌ濃度の亜酸化窒素ガスがほぼ０ｍｇ／Ｌになったのに対し、酸素除去装置２４を通さない場合には、４時間経過しても４ｍｇ／Ｌ程度までしか低下しなかった。このように、本発明の亜酸化窒素ガスの生物学的処理装置によれば、亜酸化窒素ガスを含有する含有ガスを、嫌気性の脱窒槽１０に導入して還元処理する前に、脱窒菌の還元処理を阻害する酸素を除去したので、亜酸化窒素ガスを短時間で効率的に除去することができる。
【００１９】
この場合、従来技術のように、含有ガスから亜酸化窒素ガスのみを取り出して脱窒槽１０に導入することも考えられる。しかしながら、硝化槽１２で発生する含有ガスの中には亜酸化窒素ガス以外にも、廃水中への散気により廃水中から揮散されるアンモニアガスがある。従って、従来技術のように含有ガスから亜酸化窒素ガスのみを取り出して脱窒槽に導入すると、分離された他方のガス側（亜酸化窒素ガスが除去されたガス側）にアンモニアガスが混入することになり好ましくない。
【００２０】
これに対し、本発明の場合には、酸素除去装置２４で酸素が除去された脱酸素ガス側に、前記揮散されたアンモニアガスが含有されるので、揮散されたアンモニアガスは再び生物学的な処理系統に戻されることになる。
また、亜酸化窒素ガスや酸素等が混在する含有ガス中の酸素濃度を測定することは、含有ガス中の亜酸化窒素ガスを測定することよりも容易である。従って、亜酸化窒素ガスを濃縮する装置を運転管理するよりも酸素を除去する装置を運転管理する方が容易である。即ち、酸素除去装置２４の入口と脱酸素ガス側の出口のうちの少なくとも入口側に酸素濃度測定手段を設けて、除去すべき酸素量を把握することにより、脱酸素ガス中の酸素レベルが高くならないような酸素除去装置２４の運転を容易かつ確実に行うことができる。
【００２１】
図４は、分子ふるい活性炭を用いた酸素除去装置２４で含有ガスの酸素除去処理を行った場合の酸素富有ガスの発生量と酸素濃度を、前述した１サイクル（１２０秒）の経時変化として表したものである。この結果、酸素富有ガスの酸素濃度は平均２４％（１９％〜５７％）であり、エア中の酸素濃度２１％よりも大きくなった。
【００２２】
図５は、図４の知見に基づいて成された本発明の第１の実施の形態の変形例であり、酸素除去装置２４で得られた酸素富有ガスを硝化槽１２の散気装置２２に供給するための配管２６と送気ファン２８を設けたものである。硝化槽１２では、常時、ブロア３０からエアを散気装置２２に送気して硝化槽１２内を好気性にしているが、酸素除去装置２４で得られる酸素濃度の高い酸素富有ガスを利用することにより、エアよりも廃水中の酸素効率が良くなる。これにより、廃水中の有機物の分解除去率を向上させることができる。また、酸素除去装置２４から発生する酸素富有ガスの発生量が多い場合には、ブロア３０を設置しないか、設置しても小さなブロア能力のもので足りるので、装置コストの低減になる。
【００２３】
図６は、亜酸化窒素ガスの生物学的処理装置の第２の実施の形態であり、第１の実施の形態と同じ装置及び部材には同符号を付して説明する。脱窒槽１０、硝化槽１２、固液分離槽１６、硝化槽１２から脱窒槽１０への循環路１４については、第１の実施の形態と同様である。そして、第２の実施の形態では、脱窒槽１０の前段に微好気性の生物反応槽である微好気槽３２を設け、硝化槽１２で発生する亜酸化窒素ガスの含有ガスを、ガス経路３４を介して微好気槽３２に直接導入するようにした。また、固液分離槽１６からの汚泥返送経路１８を微好気槽３２に繋いで微好気槽３２での生物量を維持するようにした。また、微好気槽３２内に低部に配設した微好気用散気装置３６には、ブロア３０からのエアが流量調整バルブ３８で制御され、微好気槽の溶存酸素濃度が０．１〜３ｐｐｍになるように散気されるようにした。
【００２４】
図３の曲線Ｃは、硝化槽１２で発生する亜酸化窒素ガスの含有ガスを、微好気槽３２に直接導入した場合の微好気槽３２における亜酸化窒素ガスの分解性能を示したものである。曲線Ｃから分かるように、含有ガスを微好気槽３２に直接導入した場合には、５ｍｇ／Ｌ濃度の亜酸化窒素ガスを０．５ｍｇ／Ｌまで低下するのに２．５時間を要した。この結果は、第１の実施の形態のように酸素除去装置２４を通した場合よりも亜酸化窒素ガスの低減に時間がかかる。しかし、亜酸化窒素ガスを含む含有ガスを嫌気性の脱窒槽１０に直接導入する場合に比べて格段に分解性能が良かった。この理由は、脱窒槽１０中の微生物は、嫌気性状態に慣らされているために、含有ガスに同伴される酸素が脱窒槽１０に混入すると、微生物の活性が極端に低下するものと考察される。これに対し、微好気槽３２の微生物は、溶存酸素濃度が、微好気性状態に慣らされているために、含有ガスに同伴される酸素が微好気槽３２に混入しても酸素に対する耐性があるものと考察される。また、微好気槽３２における亜酸化窒素ガスの窒素ガスへの還元反応を調べたところ、活性汚泥がブロック化したブロック内部、活性汚泥を厚膜状にした生物膜の内部のように、微好気槽３２内でも嫌気性に近い条件に生息する脱窒菌が反応を支配することが分かった。
【００２５】
図３の曲線Ｄは、上記知見に基づいて成されたもので、脱窒菌を高分子ゲルに包括固定化した微生物担体を投入した脱窒槽１０に、硝化槽１２で発生した亜酸化窒素ガスの含有ガスを直接導入した場合である。図３の曲線Ｄから分かるように、酸素除去装置２４を通した場合よりも亜酸化窒素ガスの分解性能がやや劣るものの、活性汚泥のみの微好気槽３２の場合よりも分解性能を向上させることができた。この理由としては、微生物担体の内部が嫌気性に近い状態になるために、亜酸化窒素ガスの分解を促進するものと考察される。
【００２６】
上記の如く構成した第２の実施の形態によれば、生物学的な処理を行う微好気槽のみで亜酸化窒素ガスを処理でき、物理的手段を必要としないので、装置構成を極めてシンプル化することができる。また、生物学的手段のみの運転でよいので、装置の運転操作や運転管理が容易になる。また、一般的な廃水処理方法である活性汚泥循環変法式の廃水処理装置の前段に微好気槽３２を配設するだけでよいので、増設コストも安価ですむ。また、微好気槽３２の後段に循環嫌気性の脱窒槽が配設される構成になるので、微好気槽で残存した亜酸化窒素ガスを脱窒槽で確実に除去することができる。尚、図６では、微好気槽３２での亜酸化窒素ガスの処理負荷を考慮して、硝化槽１２で処理した液を循環路１４で脱窒槽１０に循環させるようにしたが、微好気槽３２に循環させてもよい。
【００２７】
また、図示しなかったが、硝化槽１２から微好気槽３２に送気される含有ガス中の酸素濃度を計測する酸素測定装置を設けると共に、微好気槽３２内の廃水中のＤＯ濃度を測定するＤＯ濃度計を設けるとよい。これにより、含有ガスに同伴される酸素量を見込んで微好気用散気装置３６からの散気量を制御することができるので、微好気槽３２の脱窒菌の活性が低下することがないと共に、散気量の削減にも寄与する。
【００２８】
図７及び図８は、本発明の亜酸化窒素ガスの生物学的処理装置の第３の実施の形態であり、第１及び第２の実施の形態と同じ装置及び部材には同符号を付して説明する。
本発明の第３の実施の形態は、アンモニア性窒素含有の廃水を多段式に硝化処理する場合、複数の硝化槽１２で発生する亜酸化窒素ガスの含有ガスのうち、１段目の硝化槽１２Ａで全体の約７０％の亜酸化窒素ガスが発生することに着目して成されたものである。そして、複数の硝化槽１２で発生する亜酸化窒素ガスの含有ガスのうち、少なくとも１段目の硝化槽１２Ａで発生する含有ガスを、亜酸化窒素ガスの生物学的処理装置に導いて還元処理するようにした。
【００２９】
図７は、第１硝化槽１２Ａ、第２硝化槽１２Ｂ、第３硝化槽１２Ｃの３槽から成る多段式の硝化処理装置のうち、第１硝化槽１２Ａに蓋４０をして、ヘッドスペース４２に溜まった亜酸化窒素ガスの含有ガスを、送気ファン４４により含有ガス送気経路４６を介して亜酸化窒素ガスの生物学的処理装置に送気するようにようにしたものである。これにより、亜酸化窒素ガスの大気放出を低減できると共に、１槽のみの設備改造で亜酸化窒素ガスを効率的に処理することができる。
【００３０】
また、図８は、前記３槽１２Ａ、１２Ｂ、１２Ｃの硝化槽１２の全てに蓋４０をして、各硝化槽１２Ａ、１２Ｂ、１２Ｃで発生する亜酸化窒素ガスの含有ガスを、送気ファン４４により含有ガス送気経路４６を介して亜酸化窒素ガスの生物学的処理装置に送気するようにしたものである。
第３の実施の形態における亜酸化窒素ガスの生物学的処理装置は、酸素除去装置２４と脱窒槽１０を組み合わせたもの、微好気槽３２のみのもの、或いは微好気槽３２と脱窒槽１０を組み合わせたものを使用するとよい。
【００３１】
尚、本発明の実施の形態では、本発明の亜酸化窒素ガスの生物学的処理装置を、硝化槽から発生する亜酸化窒素ガスを処理する例で説明したが、これに限定されるものではなく、例えば、ゴミ処理場で発生する亜酸化窒素ガスを処理する場合にも適用することができる。また、亜酸化窒素ガス（Ｎ2 Ｏ）にＮＯが混在する場合にも本発明を適用することができる。
【００３２】
【発明の効果】
以上説明したように、本発明の亜酸化窒素ガスの生物学的処理方法及び装置によれば、亜酸化窒素ガスの分解性能を向上させることができると共に、装置構成のシンプル化を図ることができる。
また、アンモニア性窒素を含有する廃水を多段式硝化処理の場合に発生する亜酸化窒素ガスを効率的に処理することができる。
【図面の簡単な説明】
【図１】本発明の亜酸化窒素ガスの生物学的処理装置の第１の実施の形態を説明する構成図
【図２】酸素除去装置を説明する説明図
【図３】亜酸化窒素ガスの含有ガスを、脱窒槽に直接導入した場合、酸素除去装置を通してから脱窒槽に導入した場合、微好気槽に直接導入した場合、微好気槽に脱窒菌の包括固定化担体を投入した場合におけるそれぞれの亜酸化窒素ガスの分解性能を説明する説明図
【図４】酸素除去装置で得られる酸素富有ガスの発生量と酸素濃度を説明する説明図
【図５】本発明の亜酸化窒素ガスの生物学的処理装置の第１の実施の形態の変形例を説明する構成図
【図６】第２の実施の形態の変形例を説明する構成図
【図７】本発明の亜酸化窒素ガスの生物学的処理装置の第３の実施の形態を説明する構成図
【図８】本発明の第３の実施の形態の変形例を説明する構成図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biological treatment method and apparatus for nitrous oxide gas, and more particularly, to a nitrous oxide gas for efficiently biologically treating nitrous oxide gas generated by nitrification in a nitrification tank. The present invention relates to a biological treatment method and apparatus.
[0002]
[Prior art]
In a wastewater treatment apparatus that biologically treats nitrogen components in organic or inorganic wastewater, it is known that nitrous oxide gas is generated as a reaction byproduct in the nitrification treatment of nitrogen components. However, the process of removing the generated nitrous oxide gas has not been performed, and the actual situation is that it is released into the atmosphere.
[0003]
By the way, nitrous oxide gas has a greenhouse effect several hundred times that of carbon dioxide gas, and it has become an emission reduction target substance together with carbon dioxide gas and methane gas as global warming prevention increases. .
As a conventional apparatus for biologically treating nitrous oxide gas, as disclosed in JP-A-6-190241, a gas containing nitrous oxide gas is used as an adsorbent in the adsorption step. A process of decomposing biological nitrous oxide gas under anaerobic conditions after adsorbing sorbent, nitrous oxide gas desorbed from the adsorbent, or an absorption liquid absorbing nitrous oxide gas It will be disassembled.
[0004]
[Problems to be solved by the invention]
However, the conventional biological treatment apparatus for nitrous oxide gas has a drawback that it is difficult to operate.
Furthermore, the conventional biological treatment method of nitrous oxide gas combines two completely different means, such as physical means of adsorption and biological means of microorganisms, so that the operation is complicated. In addition, there is a drawback that the operation management becomes complicated. From such a background, a method for decomposing and removing nitrous oxide gas only by biological treatment is desired.
[0005]
The present invention has been made in view of such circumstances, and it is possible to improve the decomposition performance of nitrous oxide gas and to simplify the configuration of the apparatus, and to biological treatment of nitrous oxide gas It is an object to provide a method and apparatus.
[0006]
[Means for Solving the Invention]
In order to achieve the above object, the present invention introduces oxygen contained in the contained gas before introducing the contained gas containing nitrous oxide gas into an anaerobic biological reaction tank and performing a reduction treatment with microorganisms. It is characterized by being removed in advance.
In order to achieve the above object, the present invention introduces an oxygen removing device that removes mixed oxygen from a gas containing nitrous oxide gas, and a deoxygenated gas from which oxygen has been removed beforehand by the oxygen removing device. And an anaerobic biological reaction tank in which the nitrous oxide gas in the deoxygenated gas is reduced by microorganisms under anaerobic conditions.
[0007]
According to the present invention, before introducing the gas containing nitrous oxide gas into the anaerobic bioreactor and carrying out the reduction treatment, oxygen, which is a direct substance that inhibits biological treatment, is removed. Nitrous oxide gas can be efficiently removed in an anaerobic biological reaction tank .
[0009]
Furthermore, in order to achieve the above-mentioned object, the present invention contains nitrous oxide gas generated in each nitrification tank when wastewater containing ammonia nitrogen is nitrified in multiple stages in a plurality of nitrification tanks. Among the gases, a contained gas supply path for guiding the contained gas generated in at least the first stage nitrification tank to the biological treatment apparatus according to claim 2 is provided.
[0010]
In the case of multi-stage nitrification treatment, the present invention has been made paying attention to the fact that about 70% of the total amount of nitrous oxide gas generated in a plurality of nitrification tanks is generated in the first nitrification tank. Therefore, according to the present invention, since the contained gas air supply path for introducing the contained gas generated in at least the first stage nitrification tank to the biological treatment apparatus according to claim 2 is provided, nitrous oxide can be obtained with a small number of equipment modifications. Gas can be processed efficiently.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a biological treatment method and apparatus for nitrous oxide gas according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a first embodiment of a biological treatment apparatus for nitrous oxide gas according to the present invention, and is a configuration diagram in which the present invention is incorporated into an activated sludge circulation modified type wastewater treatment apparatus.
[0012]
As shown in FIG. 1, organic wastewater or inorganic wastewater containing ammonia nitrogen is fed into an anaerobic denitrification tank 10 and then sent to an aerobic nitrification tank 12 for treatment in the nitrification tank 12. A part of the treated water is returned to the denitrification tank 10 via the circulation path 14 and the rest is sent to the solid-liquid separation tank 16. In the solid-liquid separation tank 16, the activated sludge accompanying the treated water is solid-liquid separated and returned to the denitrification tank 10 via the sludge return path 18 to maintain the biomass in the denitrification tank 10. A part of the sludge is discharged outside the apparatus through the discharge pipe 20 as surplus sludge.
[0013]
In the nitrification tank 12, the air supplied from the blower 30 is diffused by the air diffuser 22, and ammonia nitrogen in the wastewater is converted to nitrous acid by nitrifying bacteria which are aerobic microorganisms in the activated sludge under aerobic conditions. Nitrified to basic nitrogen and nitrate nitrogen. Moreover, the organic matter in the wastewater that could not be treated in the denitrification tank 10 is decomposed into water and carbon dioxide. In the denitrification tank 10 in which the liquid is circulated from the nitrification tank 12, the nitrite nitrogen and nitrate nitrogen generated in the nitrification tank 12 are anaerobic microorganisms using an organic donor in waste water or an electron donor such as methanol as a reducing agent. It is denitrified by denitrifying bacteria and reduced to nitrogen gas. As a result, ammoniacal nitrogen in the wastewater is removed. In this wastewater flow, nitrous oxide gas is generated as a reaction byproduct of the nitrification treatment in the nitrification tank 12.
[0014]
When the gas containing the nitrous oxide gas generated in the nitrification tank 12 is directly introduced into the waste water of the denitrification tank 10 and biologically reduced by denitrifying bacteria in the activated sludge, a large amount of oxygen present in the contained gas is present. It inhibits the reduction reaction of anaerobic microorganisms, denitrifying bacteria. Therefore, in the present invention, the nitrous oxide gas generated in the nitrification tank 12 is sent to the oxygen removing device 24, and the deoxygenated gas from which oxygen contained in the contained gas has been removed in advance is introduced into the waste water of the denitrifying tank 10. I made it.
[0015]
As the oxygen removing device 24, it is preferable to use a device using a molecular sieve activated carbon and a gas separation membrane.
FIG. 2 (a) shows an example of an oxygen removing device 24 using molecular sieve activated carbon, and shows a case where two adsorption towers of molecular sieve activated carbon are provided in parallel and the two are operated alternately. In this oxygen removing device 24, the molecular diameter of oxygen (O 2 ) (3.9 × 2.8Å) is smaller than the molecular diameter of nitrous oxide gas (N 2 O) (5.67 × 3.0Å). The smaller one uses faster adsorption. FIG. 2B shows a valve switching procedure when operating the adsorption tower I side of the oxygen removing device 24.
[0016]
The oxygen removing device 24 repeats an oxygen removing cycle in which the pressure equalization → pressurization (adsorption) → depressurization (desorption) is one cycle (usually 2 minutes). Thereby, it isolate | separates into the deoxygenation gas which remove | excluded oxygen from the gas containing nitrous oxide gas, and the oxygen rich gas which contains oxygen richly. As a result, the oxygen concentration in the deoxygenated gas can be reduced to 0.5% or less. In addition, although not shown, an oxygen removal apparatus using a gas separation membrane uses a silicone polymer membrane that has a large permeation rate of oxygen having a small molecular diameter and a small permeation rate of nitrous oxide gas having a large molecular size. Can be used. However, the present invention is not limited to the silicone polymer membrane as long as membrane separation between oxygen and nitrous oxide gas can be performed.
[0017]
FIG. 3 explains the effect of the first embodiment of the present invention, and shows the decomposition performance of nitrous oxide gas by the activated sludge in the denitrification tank 10. The activated sludge concentration in the waste water of the denitrification tank 10 is 1000 mg / L, and the nitrous oxide gas concentration before the start of decomposition is 5 mg / L.
Curve A shows the nitrous oxide in the denitrification tank 10 when the gas containing the nitrous oxide gas generated in the nitrification tank 12 is introduced into the denitrification tank 10 after removing oxygen with an oxygen removing device 24 using molecular sieve activated carbon. This shows the gas decomposition performance.
[0018]
Curve B shows the decomposition performance in the denitrification tank 10 when the contained gas generated in the nitrification tank 12 is directly introduced into the denitrification tank 10 without passing through the oxygen removing device 24. Note that the curves C and D will be described using the effects of the second embodiment of the present invention. As can be seen from the curve A in FIG. 3, when the oxygen removing device 24 is passed, the nitrous oxide gas having a concentration of 5 mg / L became almost 0 mg / L in about 1 hour and 15 minutes, whereas oxygen When the removal device 24 was not passed, it decreased only to about 4 mg / L even after 4 hours. Thus, according to the biological treatment apparatus for nitrous oxide gas of the present invention, the denitrifying bacterium is introduced before the containing gas containing nitrous oxide gas is introduced into the anaerobic denitrification tank 10 for reduction treatment. Since the oxygen that obstructs the reduction treatment is removed, the nitrous oxide gas can be efficiently removed in a short time.
[0019]
In this case, it is also conceivable to extract only the nitrous oxide gas from the contained gas and introduce it into the denitrification tank 10 as in the prior art. However, the contained gas generated in the nitrification tank 12 includes ammonia gas that is volatilized from the wastewater by aeration into the wastewater, in addition to the nitrous oxide gas. Therefore, when only the nitrous oxide gas is taken out from the contained gas and introduced into the denitrification tank as in the prior art, ammonia gas is mixed into the other separated gas side (the gas side from which the nitrous oxide gas has been removed). It is not preferable.
[0020]
On the other hand, in the case of the present invention, the volatilized ammonia gas is contained in the deoxygenated gas side from which oxygen has been removed by the oxygen removing device 24, so that the volatilized ammonia gas is biological again. It will be returned to the processing system.
Moreover, it is easier to measure the oxygen concentration in the contained gas containing nitrous oxide gas, oxygen, etc. than to measure the nitrous oxide gas in the contained gas. Accordingly, it is easier to manage the operation of the device for removing oxygen than to manage the device for concentrating nitrous oxide gas. That is, by providing an oxygen concentration measuring means on at least the inlet side of the inlet of the oxygen removing device 24 and the outlet of the deoxygenated gas, and grasping the amount of oxygen to be removed, the oxygen level in the deoxygenated gas is increased. It is possible to easily and reliably operate the oxygen removing device 24 that does not become necessary.
[0021]
FIG. 4 is a graph showing the amount of oxygen-rich gas generated and the oxygen concentration when the oxygen removal treatment of the contained gas is performed by the oxygen removal device 24 using molecular sieve activated carbon as the time-dependent change of one cycle (120 seconds) described above. It is a thing. As a result, the oxygen concentration of the oxygen-rich gas was 24% (19% to 57%) on average, which was higher than the oxygen concentration in air of 21%.
[0022]
FIG. 5 is a modified example of the first embodiment of the present invention based on the knowledge of FIG. 4, and oxygen-rich gas obtained by the oxygen removing device 24 is transferred to the aeration device 22 of the nitrification tank 12. A pipe 26 and an air supply fan 28 for supply are provided. In the nitrification tank 12, air is always sent from the blower 30 to the aeration device 22 to make the inside of the nitrification tank 12 aerobic, but an oxygen-rich gas having a high oxygen concentration obtained by the oxygen removal device 24 is used. As a result, the oxygen efficiency in the wastewater is better than that of air. Thereby, the decomposition removal rate of the organic substance in wastewater can be improved. In addition, when the amount of oxygen-rich gas generated from the oxygen removing device 24 is large, the blower 30 is not installed, or even if it is installed, a device having a small blower capacity is sufficient, so that the device cost is reduced.
[0023]
FIG. 6 shows a second embodiment of the biological treatment apparatus for nitrous oxide gas, and the same apparatus and members as those in the first embodiment are denoted by the same reference numerals. The denitrification tank 10, the nitrification tank 12, the solid-liquid separation tank 16, and the circulation path 14 from the nitrification tank 12 to the denitrification tank 10 are the same as those in the first embodiment. And in 2nd Embodiment, the microaerobic tank 32 which is a microaerobic biological reaction tank is provided in the front | former stage of the denitrification tank 10, and the gas containing the nitrous oxide gas which generate | occur | produces in the nitrification tank 12 is gas path | route. It was introduced directly into the microaerobic tank 32 via 34. In addition, the sludge return path 18 from the solid-liquid separation tank 16 is connected to the microaerobic tank 32 to maintain the biomass in the microaerobic tank 32. Further, in the microaerobic diffuser 36 disposed in the lower part in the microaerobic tank 32, the air from the blower 30 is controlled by the flow rate adjusting valve 38, and the dissolved oxygen concentration in the microaerobic tank is 0. It was made to diffuse so that it might become 1-3 ppm.
[0024]
A curve C in FIG. 3 shows the decomposition performance of the nitrous oxide gas in the microaerobic tank 32 when the gas containing the nitrous oxide gas generated in the nitrification tank 12 is directly introduced into the microaerobic tank 32. It is. As can be seen from curve C, when the contained gas was directly introduced into the microaerobic tank 32, it took 2.5 hours to reduce the nitrous oxide gas having a concentration of 5 mg / L to 0.5 mg / L. . As a result, it takes more time to reduce the nitrous oxide gas than when the oxygen removing device 24 is passed as in the first embodiment. However, the decomposition performance was much better than when the containing gas containing nitrous oxide gas was directly introduced into the anaerobic denitrification tank 10. This is because the microorganisms in the denitrification tank 10 are accustomed to an anaerobic state, and therefore the activity of the microorganisms is considered to be extremely reduced when oxygen accompanying the contained gas is mixed into the denitrification tank 10. The On the other hand, since the dissolved oxygen concentration of the microorganisms in the microaerobic tank 32 is accustomed to the microaerobic state, even if oxygen accompanying the contained gas is mixed into the microaerobic tank 32, the microbes are not sensitive to oxygen. Considered resistant. Further, when the reduction reaction of nitrous oxide gas to nitrogen gas in the microaerobic tank 32 was examined, it was found that the inside of the block where activated sludge was blocked and the inside of the biofilm where activated sludge was formed into a thick film were fine. It was found that even in the aerobic tank 32, denitrifying bacteria that inhabit conditions close to anaerobic control the reaction.
[0025]
A curve D in FIG. 3 is formed based on the above knowledge, and the nitrous oxide gas generated in the nitrification tank 12 is introduced into the denitrification tank 10 in which a microbial carrier in which denitrifying bacteria are comprehensively immobilized in a polymer gel is charged. This is a case where the contained gas is directly introduced. As can be seen from the curve D in FIG. 3, the decomposition performance of the nitrous oxide gas is slightly inferior to the case of passing through the oxygen removing device 24, but the decomposition performance is improved as compared with the case of the microaerobic tank 32 using only activated sludge. I was able to. The reason for this is considered that the decomposition of nitrous oxide gas is promoted because the inside of the microbial carrier is in an anaerobic state.
[0026]
According to the second embodiment configured as described above, the nitrous oxide gas can be processed only in the microaerobic tank for performing biological processing, and no physical means is required. It can be simplified. In addition, since only the biological means need be operated, the operation and management of the apparatus are facilitated. Further, since the microaerobic tank 32 only needs to be disposed in front of the activated sludge circulation modified type wastewater treatment apparatus, which is a general wastewater treatment method, the expansion cost can be reduced. In addition, since the circulation anaerobic denitrification tank is arranged at the subsequent stage of the microaerobic tank 32, the nitrous oxide gas remaining in the microaerobic tank can be reliably removed in the denitrification tank. In FIG. 6, the liquid treated in the nitrification tank 12 is circulated to the denitrification tank 10 through the circulation path 14 in consideration of the treatment load of the nitrous oxide gas in the microaerobic tank 32. It may be circulated in the air tank 32.
[0027]
Although not shown, an oxygen measuring device for measuring the oxygen concentration in the contained gas sent from the nitrification tank 12 to the microaerobic tank 32 is provided and the DO concentration in the wastewater in the microaerobic tank 32 is provided. It is recommended to provide a DO densitometer that measures the above. Thereby, since the amount of air diffused from the microaerobic air diffuser 36 can be controlled in anticipation of the amount of oxygen accompanying the contained gas, the activity of denitrifying bacteria in the microaerobic tank 32 may be reduced. It also contributes to a reduction in the amount of air diffused.
[0028]
7 and 8 show a third embodiment of the biological treatment apparatus for nitrous oxide gas according to the present invention. The same apparatus and members as those in the first and second embodiments are denoted by the same reference numerals. To explain.
In the third embodiment of the present invention, when ammoniacal nitrogen-containing wastewater is subjected to nitrification in a multistage manner, the first-stage nitrification tank among the nitrous oxide gas-containing gases generated in the plurality of nitrification tanks 12 It is made by paying attention to the fact that about 70% of the total nitrous oxide gas is generated at 12A. Of the nitrous oxide gas contained in the plurality of nitrification tanks 12, the contained gas produced in at least the first nitrification tank 12 </ b> A is introduced into a biological treatment apparatus for nitrous oxide gas for reduction treatment. I tried to do it.
[0029]
FIG. 7 shows a headspace 42 in which a first nitrification tank 12A is covered with a lid 40 in a multi-stage nitrification treatment apparatus comprising three tanks of a first nitrification tank 12A, a second nitrification tank 12B, and a third nitrification tank 12C. The nitrous oxide gas-containing gas accumulated in the gas is supplied to the biological treatment apparatus of nitrous oxide gas via the gas-containing air supply path 46 by the air supply fan 44. As a result, the emission of nitrous oxide gas into the atmosphere can be reduced, and the nitrous oxide gas can be efficiently processed by remodeling only one tank.
[0030]
Further, FIG. 8 shows that the nitrification tanks 12 of the three tanks 12A, 12B, and 12C are covered with a lid 40, and the gas containing the nitrous oxide gas generated in each of the nitrification tanks 12A, 12B, and 12C is supplied to the air supply fan. 44 is supplied to the biological treatment apparatus of nitrous oxide gas via the contained gas supply passage 46.
The biological treatment apparatus for nitrous oxide gas in the third embodiment is a combination of the oxygen removing device 24 and the denitrification tank 10, only the microaerobic tank 32, or the microaerobic tank 32 and the denitrification tank. A combination of 10 may be used.
[0031]
In the embodiment of the present invention, the biological treatment apparatus for nitrous oxide gas according to the present invention has been described with an example of treating nitrous oxide gas generated from a nitrification tank. However, the present invention is not limited to this. For example, the present invention can also be applied to processing nitrous oxide gas generated in a garbage disposal site. Further, the present invention can also be applied when NO is mixed in nitrous oxide gas (N 2 O).
[0032]
【The invention's effect】
As described above, according to the biological treatment method and apparatus for nitrous oxide gas of the present invention, it is possible to improve the decomposition performance of nitrous oxide gas and to simplify the apparatus configuration. .
Further, nitrous oxide gas generated in the case of multistage nitrification treatment of wastewater containing ammonia nitrogen can be efficiently treated.
[Brief description of the drawings]
FIG. 1 is a configuration diagram for explaining a first embodiment of a biological treatment apparatus for nitrous oxide gas according to the present invention. FIG. 2 is an explanatory diagram for explaining an oxygen removal apparatus. When the contained gas is introduced directly into the denitrification tank, introduced into the denitrification tank through the oxygen removal device, introduced directly into the microaerobic tank, or when the denitrifying entrapping immobilization support is introduced into the microaerobic tank FIG. 4 is a diagram for explaining the decomposition performance of each nitrous oxide gas in FIG. 4. FIG. 5 is a diagram for explaining the amount of oxygen-rich gas generated and oxygen concentration obtained by the oxygen removing device. FIG. The block diagram explaining the modification of 1st Embodiment of the biological treatment apparatus of FIG. 6 [FIG. 6 ] The block diagram explaining the modification of 2nd Embodiment. FIG. 7 The nitrous oxide gas of this invention FIG. 8 is a configuration diagram for explaining a third embodiment of the biological treatment apparatus of the present invention. Configuration diagram for explaining a modified example of the third embodiment

Claims (3)

亜酸化窒素ガスを含有する含有ガスを、嫌気性の生物反応槽に導入して微生物による還元処理を行う前に、前記含有ガスに混在する酸素を予め除去しておくことを特徴とする亜酸化窒素ガスの生物学的処理方法。  Prior to introducing a gas containing nitrous oxide gas into an anaerobic biological reaction tank and performing reduction treatment with microorganisms, oxygen contained in the gas contained is removed in advance. Biological treatment method of nitrogen gas. 亜酸化窒素ガスを含有する含有ガスから混在する酸素を除去する酸素除去装置と、
前記酸素除去装置で酸素を予め除去した脱酸素ガスを導入して、該脱酸素ガス中の亜酸化窒素ガスを嫌気性条件下で微生物により還元処理を行う嫌気性の生物反応槽と、
を備えたことを特徴とする亜酸化窒素ガスの生物学的処理装置。An oxygen removing device that removes mixed oxygen from a gas containing nitrous oxide gas;
An anaerobic bioreactor that introduces deoxygenated gas from which oxygen has been removed in advance by the oxygen removing device, and performs nitrous oxide gas reduction in the deoxygenated gas by microorganisms under anaerobic conditions;
An apparatus for biological treatment of nitrous oxide gas, comprising: アンモニア性窒素を含有する廃水を複数の硝化槽で多段式に硝化処理する際に各硝化槽で発生する亜酸化窒素ガスを含有する含有ガスのうち、少なくとも１段目の硝化槽で発生する前記含有ガスを請求項２の生物学的処理装置に導く含有ガス送気経路を設けたことを特徴とする亜酸化窒素ガスの生物学的処理装置。Of the containing gas containing nitrous oxide gas generated in each nitrification tank when wastewater containing ammonia nitrogen is nitrified in multiple stages in a plurality of nitrification tanks, it is generated in at least the first nitrification tank A biological treatment apparatus for nitrous oxide gas, comprising a gas delivery path for introducing a contained gas to the biological treatment apparatus according to claim 2 .
JP5742099A 1999-03-04 1999-03-04 Biological treatment method and apparatus for nitrous oxide gas Expired - Fee Related JP3918349B2 (en)

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