JP3591031B2

JP3591031B2 - Biological nitrogen removal method of septic tank sludge

Info

Publication number: JP3591031B2
Application number: JP4332195A
Authority: JP
Inventors: 謙介松井; 英斉安井
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 1995-03-02
Filing date: 1995-03-02
Publication date: 2004-11-17
Anticipated expiration: 2019-11-17
Also published as: JPH08238498A

Description

【０００１】
【産業上の利用分野】
本発明は浄化槽汚泥から窒素を生物学的硝化脱窒処理により除去するようにした浄化槽汚泥の生物学的窒素除去方法に関する。
【０００２】
【従来の技術】
家庭等において発生する生活排水を処理する浄化槽では、腐敗槽において排水の固液分離および嫌気性処理を中心とした処理を行い、酸化槽において脱離液の好気性処理を行って放流している。このような浄化槽では主として易生物分解性のＢＯＤが除去され、ＳＳ性物質を中心とする浄化槽汚泥が発生する。この浄化槽汚泥は未処理の汚水と生物処理されつくした汚泥とが混在しているため、汚水と汚泥の両方の性格をもっており、従来はし尿処理場において、し尿とともに活性汚泥処理により処理されている。
【０００３】
浄化槽汚泥は多量のアンモニア性窒素および有機性窒素を含んでいるので、上記活性汚泥処理としては、アンモニア性または有機性窒素化合物を除去するために、生物学的硝化脱窒処理法が採用されている。この方法は活性汚泥の存在下に好気性処理して被処理液中のＣＯＤ、ＢＯＤ成分を分解するとともに、有機性窒素化合物をアンモニア性窒素とし、その後硝化細菌が増殖した活性汚泥の存在下に曝気してアンモニア性窒素を硝化細菌により亜硝酸性または硝酸性窒素に硝化（酸化）した後、脱窒細菌が増殖した活性汚泥の存在下に嫌気状態に維持することにより亜硝酸性また硝酸性窒素を窒素ガスに還元して脱窒する方法である。この方法には被処理液を、循環する硝化処理液と混合して脱窒した後、硝化処理を行う方法も含まれる。
【０００４】
このような生物学的硝化脱窒処理法では、脱窒の際に脱窒細菌の硝酸呼吸に水素の供与体が必要となる。水素供与体としては被処理液中の易生物分解性の有機物が利用され、被処理液中の窒素に対して易生物分解性の有機物が３倍以上存在している場合は新たに水素供与体を添加する必要はないが、これより少ない場合はメタノール、エタノール等の易生物分解性の有機物を水素供与体として添加する必要がある。
【０００５】
図２は従来の浄化槽汚泥を処理するための生物学的硝化脱窒処理法を示すフローシートである。従来の方法では、まず浄化槽汚泥１は貯留槽２で一時貯留したのち第一脱窒槽３に導入するとともに、循環液４および返送汚泥５と混合し、嫌気性を維持した状態で脱窒する。この脱窒処理液は硝化槽６に導入し、空気を吹込み曝気して、残留するＢＯＤの酸化および硝化を行う。硝化処理液の一部は循環液４として第一脱窒槽３に循環し、他の一部は最終脱窒槽７に導入し、メタノールなどの水素供与体８を添加し、嫌気性を維持した状態で脱窒する。この脱窒処理液は再曝気槽９に導入して再曝気し、残留ＢＯＤを除去する。再曝気処理液は固液分離装置１０に導入して固液分離し、分離液は処理液１１として排出し、分離汚泥１２は一部を返送汚泥５として第一脱窒槽３に返送し、残部は余剰汚泥１３として排出している。
【０００６】
しかし、上記のような方法により浄化槽汚泥を生物学的に硝化脱窒する場合には次のような問題点がある。
（１）浄化槽汚泥を活性汚泥処理しても分解除去される有機物量は全有機物含量の１０〜２０％にすぎず、ＳＳ性物質（有機物の含有量は約８０％）の８０％以上は未分解のまま残留する。このため活性汚泥処理により多量の余剰汚泥が生じ、通常ＢＯＤ負荷に対して１５０％以上、例えば除去ＢＯＤ３５００ｍｇ／ｌに対して余剰汚泥生成量は６０００ｍｇ／ｌにも達し、この多量の汚泥の処理、処分が大きな問題となる。
（２）浄化槽汚泥中には、量的には十分な量のＢＯＤが存在しているにもかかわらず易生物分解性のＢＯＤが少ないため、高い窒素除去率を安定して確保することが困難になる場合がある。このため最終脱窒槽を設けて、メタノールのような薬品を水素供与体として添加する必要がある。従って、薬品のコストのほか最終脱窒槽の設備コストがかかり、処理コストが高くなるとともに、余剰汚泥が増加する。また脱窒工程に被処理液または他の排液を導入して、そのＢＯＤ成分を利用することもできるが、そのままの状態で処理液を排出すると処理液にアンモニウムイオンがそのまま残留するため、最終脱窒槽には窒素を含まない有機物を系外から添加する必要がある。
【０００７】
ところで、特公昭５９−４８６７７号には、余剰汚泥を熱アルカリで分解し、その可溶化液を脱窒工程に導入して水素供与体として用いる方法が記載されている。
しかしながらこの方法によれば、熱アルカリで分解して可溶化する際、汚泥中の糖と蛋白が縮合反応を起こすことによって難生物分解性の有機物が生成し、処理液の色度、ＣＯＤ_Ｍｎが上昇する等の問題点がある。またこの方法は好気性処理による硝化と嫌気性処理による脱窒とからなる従来の生物学的硝化脱窒処理法に適用する方法であり、硝化槽と脱窒槽とを別々に設ける必要があるため、装置および操作が煩雑になるという問題点もある。
【０００８】
また特開昭５９−１０５８９７号には、生物処理汚泥をオゾン処理したのち嫌気性処理する汚泥の処理方法が記載されている。しかしこの公報には、オゾン処理した汚泥を硝化脱窒することは記載されていない。
【０００９】
一方、特開平５−３１７８８０号には、有機酸の存在下に溶存酸素濃度が０．５ｍｇ／ｌ以下の好気性状態を維持して曝気することにより、硝化と脱窒を同時に行う方法が記載されている。しかしこの方法では有機酸の存在が必要とされ、浄化槽汚泥をオゾン処理したのち硝化と脱窒を同時に行うことは記載されていない。
【００１０】
【発明が解決しようとする課題】
本発明の目的は、脱窒のための有機物の添加量を削減することができ、余剰汚泥の生成量を減少させることができる浄化槽汚泥の生物学的窒素除去方法を提案することである。
【００１１】
【課題を解決するための手段】
本発明は、浄化槽汚泥を後工程の硝化脱窒処理で生じる汚泥と混合してオゾン処理したのち曝気処理し、生物学的に硝化および脱窒を行うことを特徴とする浄化槽汚泥の生物学的窒素除去方法である。
【００１２】
本発明の処理対象とする浄化槽汚泥は、家庭、事務所等において発生する生活排水その他の汚水を処理する浄化槽から発生する汚泥であって、アンモニア性または有機性窒素化合物を含有する汚泥であり、有機物、硝酸性または亜硝酸性窒素、その他の不純物を含んでいてもよい。上記の浄化槽としては、腐敗槽において排水の固液分離および嫌気性処理を中心とした処理を行い、好気性処理を行うものが一般的であるが、他の形式のものであってもよい。
【００１３】
オゾン処理は浄化槽汚泥とオゾンとを、１０〜４０℃、例えば常温で接触させることにより行うことができる。接触方法としては、オゾン処理槽に浄化槽汚泥を導入してオゾンを吹込む方法などが採用できる。オゾン処理は、浄化槽汚泥を後工程の硝化脱窒処理で生じる汚泥と混合してオゾン処理する。オゾンとしてはオゾンガスの他、オゾン含有空気、オゾン化空気などが使用できる。
【００１４】
オゾン処理においては、オゾンを浄化槽汚泥に対して２〜１０重量％の範囲内で反応させるのが好ましい。こうしてオゾン処理されたオゾン処理汚泥はＢＯＤ化して生物分解性が向上する。特に、対汚泥あたりのオゾン注入率が０．０２ｍｇ−Ｏ_３／ｍｇ−ＳＳ以上の場合、浄化槽汚泥の細胞壁の糖鎖長が小さくなって生物分解性が非常に向上する。
【００１５】
オゾン処理に際しては浄化槽汚泥をｐＨ５以下に調整してオゾン処理すると、オゾン使用量を減少させることができる。その場合、オゾン処理後に再度ｐＨ調整し、硝化脱窒工程に導入して硝化脱窒することにより、硝化脱窒工程における微生物の活性を高く維持することが可能である。
【００１６】
オゾン処理した浄化槽汚泥（オゾン処理汚泥）を硝化脱窒するための硝化脱窒工程としては、従来法で説明したような硝化工程と脱窒工程とが分離した方法（図２のように脱窒槽を先に配置する場合を含む）によってもよいが、硝化脱窒槽に導入して好気的に曝気し、生物学的に硝化と脱窒とを同時に行う方法が好ましい。脱窒は還元反応であるため通常嫌気性を維持した状態で行われるが、後者の同時処理では溶存酸素濃度０．５ｍｇ／ｌ以下、または酸化還元電位（ＯＲＰ）が＋５０〜−２００ｍＶの条件で曝気することにより、硝化と脱窒とを１つの硝化脱窒槽内で同時に行うことができる。
【００１７】
この場合、オゾン処理によって脱窒細菌に資化されやすい成分が生成するため、有機酸を添加しなくてもよい。またオゾン処理により易生物分解性のＢＯＤが多量に生成して汚泥中の窒素に対する易生物分解性ＢＯＤの比が非常に大きくなっているので、水素供与体（薬品）の添加は必要ないか、あるいは添加量は少なくなる。
一方、オゾン処理により生成したＢＯＤが硝化脱窒処理により無機化されるため、排出される余剰汚泥量は減少する。余剰汚泥はそのまま排出することなく、一部または全部を浄化槽汚泥と混合してオゾン処理することができ、この場合余剰汚泥の減容化効果は大きくなる。
【００１８】
【実施例】
以下、本発明を図面の実施例により説明する。
図１は実施例の浄化槽汚泥の生物学的窒素除去方法を示すフローシートである。図１において、１は浄化槽汚泥、２は貯留槽、２４はオゾン処理槽、２７は硝化脱窒槽、２１は固液分離装置である。
図１のフローによる方法では、まず浄化槽汚泥１は貯留槽２に導入して一時貯留する。また固液分離装置２１で分離した分離汚泥２２の一部（余剰汚泥）を被オゾン処理汚泥２３として貯留槽２に導入し、浄化槽汚泥１と混合して貯留する。貯留槽２内の混合汚泥はオゾン処理槽２４に導入し、オゾン供給路２５から供給するオゾンと接触させてオゾン処理する。排オゾンガスは排オゾン路２６から排出する。オゾン処理により、汚泥が酸化分解されて脱窒細菌が水素供与体として利用可能なＢＯＤ成分が生成する。この場合オゾン処理汚泥に有機酸などを添加することなくそのまま好気性処理を行っても、硝化と脱窒とが同時に進行するような、脱窒細菌が資化しやすい成分が生成する。
【００１９】
オゾン処理汚泥は硝化脱窒槽２７に導入し、返送汚泥２８と混合した状態で、空気を前記条件となるように散気装置２９から散気して曝気する。これにより、硝化と脱窒とが同時に行われ、窒素が除去される。またＢＯＤ成分も無機化されて除去されるので、余剰汚泥の生成量が少なくなる。この場合、オゾン処理により、生物分解されやすいＢＯＤが多量に生成しているので、水素供与体となる薬品は添加する必要はない。なおオゾン処理しない浄化槽汚泥を同様に好気性処理しても硝化と脱窒の進行は不十分なものとなる。
【００２０】
硝化脱窒処理汚泥は固液分離装置２１に導入して固液分離し、分離液は処理液１１として排出する。分離汚泥２２は一部を返送汚泥２８として硝化脱窒槽２７に返送し、残部を被オゾン処理汚泥２３として貯留槽２に返送する。なお残部の分離汚泥２２は必ずしもすべてを被オゾン処理汚泥２３として貯留槽２に返送する必要はなく、一部を省略することもできる。この場合、分離汚泥２２は余剰汚泥３０として排出する。
【００２１】
上記のように浄化槽汚泥をオゾン処理することにより、易生物分解性のＢＯＤが多量に生成し、このＢＯＤが脱窒の際の水素供与体として利用されるので、系外からの硝化脱窒槽２７への水素供与体（薬品）の添加は必要なくなるか、あるいは添加量が少なくなる。また、従来の硝化脱窒処理法と同程度の処理液水質を得ることができるとともに、オゾン処理により生成したＢＯＤが硝化脱窒処理により無機化されるため、排出される余剰汚泥量は減少する。さらに硝化と脱窒とを同時に行うことが可能であり、一段の好気性処理による簡単な操作で、効率よく窒素を除去することができる。この場合、特開平５−３１７８８０号に記載されているような有機酸の添加は必要ない。
【００２２】
なお図１では、硝化と脱窒とを同時に行っているが、硝化と脱窒とを別の槽で行うこともできる。この場合、硝化槽の後段に脱窒槽を設けて硝化脱窒を行うこともできるし、図２のように硝化槽の前段に脱窒槽を設けて硝化処理液を脱窒槽に循環して硝化脱窒を行うこともできる。
【００２３】
実施例１
図１のフローにより浄化槽汚泥の硝化脱窒処理を行った。硝化脱窒槽の容量は処理量の５日分とした。試験に用いた浄化槽汚泥は、下記平均性状を有する前処理後の浄化槽汚泥である。
ＢＯＤ：３，３５０ｍｇ／ｌ
総窒素：７３０ｍｇ／ｌ
ＳＳ：７，７００ｍｇ／ｌ
【００２４】
このような浄化槽汚泥と同量（１００％）の固液分離汚泥（被オゾン処理汚泥）を貯留槽に返送し、この混合汚泥にオゾンを約５５０ｍｇ／ｌ（約０．７ｍｇ−Ｏ₃／ｌ−ＳＳ）吹込んでオゾン処理した。このオゾン処理汚泥のＢＯＤは１０，７００ｍｇ／ｌに増大した。
このようなオゾン処理汚泥を硝化脱窒槽に連続的に導入し、ＭＬＳＳ濃度を８，２００ｍｇ／ｌとし、水素供与体を添加しないで、槽内の溶存酸素濃度を０．５ｍｇ／ｌ前後に保って曝気した。その結果、硝化率はほぼ１００％、脱窒率は約９９％の反応が同時に進行し、固液分離後の処理液の無機性窒素は１０ｍｇ／ｌ以下になった。また余剰汚泥の生成量は２，６００ｍｇ／ｌとなり、後述の比較例２に比べて約６０％の減量化が達成された。
【００２５】
比較例１
実施例１と同様にして、だだし固液分離汚泥を貯留槽に返送しないで、また硝化脱窒の条件を変更して硝化脱窒処理を行った。すなわち、実施例１で用いた浄化槽汚泥と同様の浄化槽汚泥にオゾン含有ガスをオゾンとして約５５０ｍｇ／ｌ吹込んでオゾン処理した。このオゾン処理汚泥のＢＯＤは１１，４００ｍｇ／ｌに増大した。
このようなオゾン処理汚泥を硝化脱窒槽に連続的に導入し、ＭＬＳＳ濃度を８，３００ｍｇ／ｌとし、水素供与体を添加しないで、槽内の溶存酸素濃度を０．５ｍｇ／ｌ前後に保って曝気した。その結果、硝化率はほぼ１００％、脱窒率は約９９％の反応が同時に進行し、固液分離後の処理液の無機性窒素は１０ｍｇ／ｌ以下になった。また余剰汚泥の生成量は４，２００ｍｇ／ｌとなり、比較例２に比べて約３５％の減量化が達成された。
【００２６】
比較例２
図２のフローにより、実施例１で用いた浄化槽汚泥と同様の浄化槽汚泥の硝化脱窒処理を行った。第一脱窒槽、硝化槽、最終脱窒槽、再曝気槽の合計容量は処理量の７日分とした。第一脱窒槽での窒素除去率は約７０％で、最終脱窒槽にメタノールを約４００ｍｇ／ｌ添加することで、固液分離後の処理液の無機性窒素は１０ｍｇ／ｌ以下になった。また余剰汚泥の生成量は６，５００ｍｇ／ｌであった。
【００２７】
【発明の効果】
以上の通り、本発明では浄化槽汚泥を後工程の硝化脱窒処理で生じる汚泥と混合してオゾン処理したのち曝気処理し、生物学的に硝化および脱窒を行うようにしたので、水素供与体となる有機物を添加しなくても硝化脱窒が可能となり、しかも余剰汚泥の生成量を減少させて、浄化槽汚泥から窒素を効率よく除去できる。また硝化と脱窒とを同時に行うことが可能であり、一段の好気性処理による簡単な操作で、効率よく窒素を除去することができる。
【図面の簡単な説明】
【図１】実施例の浄化槽汚泥の生物学的窒素除去方法のフローシートである。
【図２】従来の浄化槽汚泥の生物学的窒素除去方法のフローシートである。
【符号の説明】
１浄化槽汚泥
２貯留槽
３第一脱窒槽
４循環液
５、２８返送汚泥
６硝化槽
７最終脱窒槽
８水素供与体
９再曝気槽
１０、２１固液分離装置
１１処理液
１２、２２分離汚泥
１３、３０余剰汚泥
２３被オゾン処理汚泥
２４オゾン処理槽
２５オゾン供給路
２６排オゾン路
２７硝化脱窒槽
２９散気装置[0001]
[Industrial applications]
TECHNICAL FIELD The present invention relates to a biological nitrogen removal method for septic tank sludge, wherein nitrogen is removed from septic tank sludge by biological nitrification and denitrification treatment.
[0002]
[Prior art]
In a septic tank that treats domestic wastewater generated at home, etc., a treatment centering on solid-liquid separation and anaerobic treatment of the wastewater is performed in a septic tank, and an aerobic treatment of the desorbed liquid is performed and discharged in an oxidation tank. . In such a septic tank, easily biodegradable BOD is mainly removed, and septic tank sludge mainly containing SS substances is generated. This septic tank sludge is a mixture of untreated sewage and sludge that has been biologically treated, so it has the characteristics of both sewage and sludge.Conventionally, it is treated by activated sludge together with night soil at a night soil treatment plant. .
[0003]
Septic tank sludge contains a large amount of ammonia nitrogen and organic nitrogen. As the activated sludge treatment, a biological nitrification and denitrification treatment method is used to remove ammonia or organic nitrogen compounds. I have. In this method, COD and BOD components in the liquid to be treated are decomposed by aerobic treatment in the presence of activated sludge, and the organic nitrogen compound is converted to ammonia nitrogen. After aerating and nitrifying (oxidizing) ammoniacal nitrogen to nitrite or nitrate nitrogen by nitrifying bacteria, it is maintained in an anaerobic state in the presence of activated sludge in which denitrifying bacteria are grown, so that nitrite or nitrate is maintained. In this method, nitrogen is reduced to nitrogen gas for denitrification. This method also includes a method in which the liquid to be treated is mixed with a circulating nitrification treatment liquid, denitrified, and then subjected to nitrification treatment.
[0004]
In such a biological nitrification and denitrification treatment method, a hydrogen donor is required for nitrate respiration of denitrifying bacteria during denitrification. As the hydrogen donor, an easily biodegradable organic substance in the liquid to be treated is used. If the amount of the organic substance that is readily biodegradable with respect to nitrogen in the liquid to be treated is three times or more, a new hydrogen donor is used. Need not be added, but if less than this, it is necessary to add a readily biodegradable organic substance such as methanol or ethanol as a hydrogen donor.
[0005]
FIG. 2 is a flow sheet showing a conventional biological nitrification and denitrification treatment method for treating septic tank sludge. In the conventional method, first, the septic tank sludge 1 is temporarily stored in the storage tank 2 and then introduced into the first denitrification tank 3, mixed with the circulating liquid 4 and the returned sludge 5, and denitrified while maintaining anaerobic. The denitrification treatment liquid is introduced into the nitrification tank 6, and air is blown and aerated to oxidize and nitrify the remaining BOD. A part of the nitrification treatment liquid is circulated as the circulating liquid 4 to the first denitrification tank 3, and the other part is introduced into the final denitrification tank 7, and a hydrogen donor 8 such as methanol is added to maintain the anaerobic state. To denitrify. This denitrification treatment liquid is introduced into the re-aeration tank 9 and re-aerated to remove residual BOD. The re-aeration treatment liquid is introduced into a solid-liquid separation device 10 to be separated into a solid and a liquid. The separated liquid is discharged as a treatment liquid 11, and a part of the separated sludge 12 is returned to the first denitrification tank 3 as return sludge 5, and the remaining part is removed. Are discharged as surplus sludge 13.
[0006]
However, when the septic tank sludge is biologically nitrified and denitrified by the above-mentioned method, there are the following problems.
(1) Even if the septic tank is treated with activated sludge, the amount of organic matter decomposed and removed is only 10 to 20% of the total organic matter content, and 80% or more of the SS substance (the organic matter content is about 80%) is not yet available. It remains as decomposed. For this reason, a large amount of excess sludge is generated by the activated sludge treatment, and the amount of excess sludge reaches 150% or more with respect to the normal BOD load, for example, 6000 mg / l with respect to 3500 mg / l of removed BOD. , Disposal is a big problem.
(2) Although a sufficient amount of BOD is present in the septic tank sludge, the amount of easily biodegradable BOD is small, so it is difficult to stably secure a high nitrogen removal rate. In some cases. Therefore, it is necessary to provide a final denitrification tank and add a chemical such as methanol as a hydrogen donor. Accordingly, equipment costs for the final denitrification tank in addition to the cost of chemicals are required, so that the treatment cost is increased and excess sludge is increased. In addition, the BOD component can be used by introducing the liquid to be treated or another drainage liquid to the denitrification step. However, if the processing liquid is discharged as it is, ammonium ions remain in the processing liquid as it is. It is necessary to add nitrogen-free organic matter to the denitrification tank from outside the system.
[0007]
By the way, Japanese Patent Publication No. S59-48677 describes a method in which excess sludge is decomposed with a hot alkali, and a solubilized liquid is introduced into a denitrification step and used as a hydrogen donor.
However, according to this method, when decomposed with hot alkali and solubilized, sugar and protein in the sludge undergo a condensation reaction to produce a hardly biodegradable organic substance, and the chromaticity and COD _{Mn of the} treatment liquid are reduced. There are problems such as rising. Further, this method is a method applied to a conventional biological nitrification denitrification treatment method consisting of nitrification by aerobic treatment and denitrification by anaerobic treatment, and it is necessary to separately provide a nitrification tank and a denitrification tank. Also, there is a problem that the device and the operation are complicated.
[0008]
JP-A-59-105897 discloses a method for treating sludge by subjecting biologically treated sludge to ozone treatment and then anaerobic treatment. However, this publication does not describe nitrifying and denitrifying ozone-treated sludge.
[0009]
On the other hand, JP-A-5-317880 describes a method of simultaneously performing nitrification and denitrification by aerating while maintaining an aerobic state with a dissolved oxygen concentration of 0.5 mg / l or less in the presence of an organic acid. Have been. However, this method requires the presence of an organic acid, and does not disclose performing nitrification and denitrification simultaneously after treating the septic tank sludge with ozone.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to propose a method for removing biological nitrogen from septic tank sludge, which can reduce the amount of organic matter added for denitrification and reduce the amount of excess sludge generated.
[0011]
[Means for Solving the Problems]
The present invention provides a biological treatment of a septic tank sludge, which comprises mixing the septic tank sludge with the sludge generated in the nitrification denitrification treatment in the subsequent step, performing ozone treatment, and then performing aeration treatment, and biologically performing nitrification and denitrification. This is a nitrogen removal method.
[0012]
Septic tank sludge to be treated according to the present invention is sludge generated from a septic tank for treating domestic wastewater and other sewage generated in homes, offices, and the like, and is a sludge containing an ammoniacal or organic nitrogen compound. It may contain organic matter, nitrate or nitrite nitrogen, and other impurities. As the above-mentioned septic tank, a septic tank that performs a treatment centering on solid-liquid separation and anaerobic treatment of wastewater and performs an aerobic treatment in general is used, but another type may be used.
[0013]
The ozone treatment can be performed by bringing septic tank sludge into contact with ozone at 10 to 40 ° C., for example, at room temperature. As a contacting method, a method of introducing septic tank sludge into the ozone treatment tank and blowing ozone into the tank can be employed. Ozone treatment, ozone treatment is mixed with sludge that occurs in nitrification denitrification treatment of post-process the septic tank sludge. As ozone, ozone-containing air, ozonized air and the like can be used in addition to ozone gas.
[0014]
In the ozone treatment, it is preferable to react ozone with the septic tank sludge within a range of 2 to 10% by weight. The ozone-treated sludge thus treated with ozone is converted to BOD to improve biodegradability. In particular, the ozone injection rate per pair sludge For more _{0.02mg-O 3 / mg-SS} , biodegradable smaller sugar chain length of the cell wall of septic tank sludge is greatly improved.
[0015]
At the time of ozone treatment, if the septic tank sludge is adjusted to pH 5 or less and ozonated, the amount of ozone used can be reduced. In that case, the pH of the microorganism is adjusted again after the ozone treatment, and the microorganism is introduced into the nitrification and denitrification step to perform the nitrification and denitrification, so that the activity of the microorganisms in the nitrification and denitrification step can be kept high.
[0016]
The nitrification and denitrification step for nitrifying and denitrifying the ozone-treated septic tank sludge (ozone-treated sludge) is a method in which the nitrification step and the denitrification step are separated as described in the conventional method (as shown in FIG. 2). Is included, but a method of introducing into a nitrification-denitrification tank, aerobically aerating, and performing biological nitrification and denitrification simultaneously is preferable. Since denitrification is a reduction reaction, it is usually performed in a state where anaerobic is maintained. However, in the latter simultaneous treatment, the dissolved oxygen concentration is 0.5 mg / l or less, or the oxidation-reduction potential (ORP) is +50 to -200 mV. By aeration, nitrification and denitrification can be performed simultaneously in one nitrification denitrification tank.
[0017]
In this case, the ozone treatment produces a component that is easily assimilated by the denitrifying bacteria, so that it is not necessary to add an organic acid. Also, since a large amount of biodegradable BOD is generated by the ozone treatment and the ratio of biodegradable BOD to nitrogen in sludge is very large, it is necessary to add a hydrogen donor (chemical). Alternatively, the amount of addition decreases.
On the other hand, since the BOD generated by the ozone treatment is mineralized by the nitrification and denitrification treatment, the amount of excess sludge discharged decreases. The excess sludge can be ozone-treated by mixing a part or the whole thereof with the septic tank sludge without discharging the sludge as it is, and in this case, the effect of reducing the volume of the excess sludge is increased.
[0018]
【Example】
Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 is a flow sheet showing a method for removing biological nitrogen from septic tank sludge according to an embodiment. In FIG. 1, 1 is a septic tank sludge, 2 is a storage tank, 24 is an ozone treatment tank, 27 is a nitrification denitrification tank, and 21 is a solid-liquid separation device.
In the method based on the flow shown in FIG. 1, first, the septic tank sludge 1 is introduced into the storage tank 2 and temporarily stored therein. A part (excess sludge) of the separated sludge 22 separated by the solid-liquid separation device 21 is introduced into the storage tank 2 as the ozone-treated sludge 23, and is mixed with the septic tank sludge 1 and stored. The mixed sludge in the storage tank 2 is introduced into an ozone treatment tank 24, and is contacted with ozone supplied from an ozone supply path 25 to ozone treatment. The discharged ozone gas is discharged from a discharged ozone passage 26. By the ozone treatment, the sludge is oxidized and decomposed to produce a BOD component that can be used by the denitrifying bacteria as a hydrogen donor. In this case, even if the aerobic treatment is performed without adding an organic acid or the like to the ozone-treated sludge, a component that is easily assimilated by the denitrifying bacteria, such that nitrification and denitrification proceed simultaneously, is generated.
[0019]
The ozone-treated sludge is introduced into the nitrification denitrification tank 27, and is mixed with the returned sludge 28, and air is diffused from the diffuser 29 so as to satisfy the above-mentioned conditions, and is aerated. Thereby, nitrification and denitrification are performed simultaneously, and nitrogen is removed. In addition, since the BOD component is also mineralized and removed, the amount of excess sludge generated is reduced. In this case, since a large amount of biodegradable BOD is generated by the ozone treatment, it is not necessary to add a chemical serving as a hydrogen donor. Even if the septic tank sludge not subjected to the ozone treatment is similarly aerobic-treated, the progress of nitrification and denitrification becomes insufficient.
[0020]
The nitrification-denitrification-treated sludge is introduced into a solid-liquid separator 21 for solid-liquid separation, and the separated liquid is discharged as a processing liquid 11. Separating the sludge 22 is returned as return sludge 28 part nitrification denitrification tank 27, it is returned to the storage tank 2 the remaining part as an object to be ozonated sludge 23. It is not necessary to return all of the remaining separated sludge 22 to the storage tank 2 as the ozone-treated sludge 23, and a part of the sludge can be omitted. In this case, the separated sludge 22 is discharged as surplus sludge 30.
[0021]
By subjecting the septic tank sludge to ozone treatment as described above, a large amount of readily biodegradable BOD is generated, and this BOD is used as a hydrogen donor during denitrification. Addition of a hydrogen donor (chemical) to the gas is not necessary or the amount of the hydrogen donor is small. In addition, it is possible to obtain the same treatment liquid water quality as the conventional nitrification and denitrification treatment method, and since the BOD generated by the ozone treatment is mineralized by the nitrification and denitrification treatment, the amount of excess sludge discharged decreases. . Further, nitrification and denitrification can be performed simultaneously, and nitrogen can be efficiently removed by a simple operation using a single aerobic treatment. In this case, there is no need to add an organic acid as described in JP-A-5-317880.
[0022]
Although nitrification and denitrification are performed simultaneously in FIG. 1, nitrification and denitrification can be performed in different tanks. In this case, nitrification and denitrification can be performed by providing a denitrification tank after the nitrification tank, or by providing a denitrification tank before the nitrification tank and circulating the nitrification treatment solution to the denitrification tank as shown in FIG. Nitriding can also be performed.
[0023]
Example 1
The nitrification denitrification treatment of the septic tank sludge was performed according to the flow of FIG. The capacity of the nitrification denitrification tank was set to 5 days of the processing amount. The septic tank sludge used in the test is a septic tank sludge after pretreatment having the following average properties.
BOD: 3,350mg / l
Total nitrogen: 730mg / l
SS: 7,700mg / l
[0024]
The same amount (100%) of solid-liquid separated sludge (ozone-treated sludge) as that of the septic tank is returned to the storage tank, and ozone is added to the mixed sludge at about 550 mg / l (about 0.7 mg-O ₃ / l). -SS) Ozone treatment was performed by blowing. The BOD of this ozonated sludge increased to 10,700 mg / l.
Such ozone-treated sludge is continuously introduced into the nitrification denitrification tank, the MLSS concentration is set to 8,200 mg / l, and the dissolved oxygen concentration in the tank is maintained at about 0.5 mg / l without adding a hydrogen donor. And aerated. As a result, the nitrification rate was almost 100%, and the denitrification rate was about 99%. The reaction proceeded at the same time, and the inorganic nitrogen in the treatment liquid after solid-liquid separation became 10 mg / l or less. In addition, the amount of excess sludge generated was 2,600 mg / l, and a reduction of about 60% was achieved as compared with Comparative Example 2 described later.
[0025]
Comparative Example 1
In the same manner as in Example 1, the nitrification denitrification treatment was performed without returning the solid-liquid separated sludge to the storage tank and changing the nitrification denitrification conditions. That is, about 550 mg / l of ozone-containing gas was injected as ozone into the septic tank sludge similar to the septic tank sludge used in Example 1 to perform ozone treatment. The BOD of this ozonated sludge increased to 11,400 mg / l.
Such ozone-treated sludge is continuously introduced into a nitrification denitrification tank, the MLSS concentration is adjusted to 8,300 mg / l, and the dissolved oxygen concentration in the tank is maintained at about 0.5 mg / l without adding a hydrogen donor. And aerated. As a result, the nitrification rate was almost 100%, and the denitrification rate was about 99%. The reaction proceeded at the same time, and the inorganic nitrogen in the treatment liquid after solid-liquid separation became 10 mg / l or less. In addition, the amount of excess sludge generated was 4,200 mg / l, and a reduction of about 35% as compared with Comparative Example 2 was achieved.
[0026]
Comparative Example 2
According to the flow of FIG. 2, nitrification and denitrification treatment of the septic tank sludge similar to the septic tank sludge used in Example 1 was performed. The total capacity of the first denitrification tank, nitrification tank, final denitrification tank, and re-aeration tank was set to 7 days of the processing amount. The nitrogen removal rate in the first denitrification tank was about 70%. By adding about 400 mg / l of methanol to the final denitrification tank, the inorganic nitrogen in the treatment liquid after solid-liquid separation was reduced to 10 mg / l or less. The amount of excess sludge generated was 6,500 mg / l.
[0027]
【The invention's effect】
As described above, in the present invention, the septic tank sludge is mixed with the sludge generated in the nitrification and denitrification treatment in the subsequent step, followed by ozone treatment and aeration treatment, so that biological nitrification and denitrification are performed. Nitrification and denitrification can be performed without adding an organic substance, and the amount of excess sludge generated can be reduced, and nitrogen can be efficiently removed from septic tank sludge. In addition, nitrification and denitrification can be performed simultaneously, and nitrogen can be efficiently removed by a simple operation using a single aerobic treatment.
[Brief description of the drawings]
FIG. 1 is a flow sheet of a biological nitrogen removal method for septic tank sludge according to an embodiment.
FIG. 2 is a flow sheet of a conventional method for removing biological nitrogen from septic tank sludge.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Septic tank sludge 2 Storage tank 3 First denitrification tank 4 Circulating fluid 5, 28 Returned sludge 6 Nitrification tank 7 Final denitrification tank 8 Hydrogen donor 9 Reaeration tank 10, 21 Solid-liquid separation device 11 Treatment liquid 12, 22 Separated sludge 13 , 30 Excess sludge 23 Ozonated sludge 24 Ozone treatment tank 25 Ozone supply passage 26 Waste ozone passage 27 Nitrification denitrification tank 29 Air diffuser

Claims

A biological nitrogen removal method for septic tank sludge, comprising mixing septic tank sludge with sludge generated by nitrification and denitrification treatment in a subsequent step, performing ozone treatment, aeration treatment, and biological nitrification and denitrification.