JP2004089956A

JP2004089956A - Nitrogen and phosphorus removing method

Info

Publication number: JP2004089956A
Application number: JP2002258521A
Authority: JP
Inventors: Kazuhiko Noto; 能登　一彦; Tetsuya Otsubo; 大坪　徹也; Kiyokazu Takemura; 武村　清和
Original assignee: Hitachi Plant Technologies Ltd
Current assignee: Hitachi Plant Technologies Ltd
Priority date: 2002-09-04
Filing date: 2002-09-04
Publication date: 2004-03-25

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitrogen and phosphorus removing method constituted so as to draw out treated water using a separation membrane while putting its advantages to practical use, having simple constitution and easy in operation control. <P>SOLUTION: Raw water containing nitrogen, phosphorus and organic matter supplied from a pipeline 24 is passed through an anaerobic tank 12 and an aerobic tank 14 in this order in the presence of activated sludge and separated into treated water and a sludge mixed liquid by the separation membrane 28 immersed in the aerobic tank 14. The total amount other than an excess sludge component of the separated sludge mixed liquid is returned to an oxygen-free tank 10 and stagnated in this oxygen free tank 10, to which a hydrogen donor is added, for a predetermined time before supplied to the anaerobic tank 12. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は窒素とリンと有機物とを含む原水からの窒素・リン除去方法に係り、特に分離膜を用いて処理水を抜き出すようにした窒素・リン除去方法に関する。
【０００２】
【従来の技術】
窒素とリンと有機物とを含む原水を生物学的に処理して、原水中の有機物のみならず、窒素とリンとを同時に除去する方法が知られている。この方法は例えば特許文献１に記載されているように、原水を嫌気槽、無酸素槽、好気槽及び沈殿槽の順に通水し、沈殿槽で分離した汚泥混合液を最前段の嫌気槽に返送し、かつ、好気槽の処理液を無酸素槽に循環させることを基本としている。
この方法によれば、嫌気槽では嫌気条件下で原水中の有機物が活性汚泥に取り込まれると同時に、活性汚泥中のリンが放出される。無酸素槽では有機物の存在下で硝酸性窒素が脱窒菌の作用により還元されて窒素ガスとなる脱窒処理が進行する。したがって、この無酸素槽を脱窒槽と別称する場合もある。好気槽では硝化菌による原水中のアンモニア態窒素の硝化と、活性汚泥中へのリンの取り込みが行われる。好気槽での硝化反応により生成した硝酸性窒素を脱窒処理するために好気槽の処理液を前段の無酸素槽に循環させる。沈殿槽では好気槽の処理液を沈殿処理し、上澄水である処理水と沈殿物である汚泥混合液とに分離する。沈殿した汚泥混合液の一部を余剰汚泥として系外に排出するとともに、残部の大部分の汚泥混合液を最前段の嫌気槽に返送する。
また、特許文献２には、上記の方法をさらに発展させ、好気槽（曝気槽）内に浸漬した分離膜によって処理水を分離する方法が開示されている。この方法によれば沈殿槽を省略することができる。また、好気槽で分離した高濃度の汚泥混合液を嫌気槽、無酸素槽（脱窒槽）及び好気槽に循環させることができるので、各槽での反応速度が大きくなり、結果として装置全体の小容量化を図ることができるという利点がある。
【０００３】
【特許文献１】
特開平６−２９６９９１号公報
【特許文献２】
特開２００１−３１４８９０号公報
【０００４】
【発明が解決しようとする課題】
しかしながら、上記の各方法はいずれも窒素とリンと有機物とを含む原水を嫌気槽、無酸素槽、好気槽の順に通水するという旧来の方法を踏襲するものである。特に特許文献２に記載された方法は、好気槽内に浸漬した分離膜によって処理水を抜き出すという新たな手法を採用しているにもかかわらず、上記旧来の方法を踏襲しているため装置構成がやや複雑であった。すなわち、好気槽で分離した汚泥混合液は硝酸性窒素と溶存酸素を含むので、この汚泥混合液を最前段の嫌気槽に直接に送っても槽内を嫌気状態にすることが困難であり、活性汚泥からリンの放出させることができない。このため、汚泥混合液を無酸素槽に返送して脱窒処理をした後に、無酸素槽内の混合液の一部を前段の嫌気槽に循環させるという複雑な構成を採用している。
本発明の目的は上記従来技術の問題点を改善し、分離膜を用いて処理水を抜き出すようにした窒素・リン除去方法の利点を生かしつつ、構成が簡単で、かつ運転管理が容易な窒素・リン除去方法を提供することにある。
【０００５】
【課題を解決するための手段】
上記の課題を解決するために、本発明に係る窒素・リン除去方法は、窒素とリンと有機物とを含む原水を活性汚泥の存在下で嫌気槽、好気槽の順に通水し、前記好気槽では内部に浸漬した分離膜により処理水と汚泥混合液とに分離し、分離した前記汚泥混合液の余剰汚泥分以外の全量を水素供与体が添加される無酸素槽で所定時間滞留させた後に前記嫌気槽に供給することを特徴とする。
このような構成によれば、嫌気槽では活性汚泥からのリン放出が活発に進行する。好気槽では残存する有機物の酸化分解と、活性汚泥のリン取り込みによる脱リン反応と、硝化反応と、膜分離による処理水の抜き出しが併行して進行する。無酸素槽では好気槽で分離した汚泥混合液中の硝酸性窒素が脱窒反応によって除去される。無酸素槽から嫌気槽に供給される汚泥混合液には溶存酸素や硝酸性窒素が実質的に存在しないので、嫌気槽では嫌気状態を容易に維持できる。したがって、分離膜を用いて処理水を抜き出すようにした窒素・リン除去方法の利点を生かしつつ、構成が簡単で、かつ運転管理が容易な窒素・リン除去方法を実現することができる。
【０００６】
また、本発明に係る窒素・リン除去方法は、窒素とリンと有機物とを含む原水の一部を活性汚泥の存在下で嫌気槽、第１好気槽の順に通水し、次いで前記原水の残部と前記第１好気槽で処理を受けた被処理水とを第１無酸素槽、第２好気槽の順に通水し、前記第２好気槽では内部に浸漬した分離膜により処理水と汚泥混合液とに分離し、分離した前記汚泥混合液の余剰汚泥分以外の全量を水素供与体が添加される第２無酸素槽で所定時間滞留させた後に前記嫌気槽に供給することを特徴とする。
【０００７】
また、本発明に係る窒素・リン除去方法は、前記水素供与体として有機酸、メタノール又は前記原水の一部のいずれかを用いることを特徴とする。
【０００８】
【発明の実施の形態】
図１は本発明の第１の実施形態を実現するための装置系統図である。本装置は、主に無酸素槽１０、嫌気槽１２、好気槽１４とによって構成される。無酸素槽１０には撹拌機１６が配備され、好気槽１４から管路１８を介して返送されてきた汚泥混合液が無酸素状態に置かれる。なお、本発明においては「無酸素状態」とは液中に溶存する遊離酸素が実質的に零に近いが、脱窒反応の際に脱窒菌の呼吸作用に必要な酸素源としての硝酸性窒素が供給されている状態を意味する。また、無酸素槽１０には有機酸、メタノールなどの水素供与体の供給管路２０が接続している。
【０００９】
嫌気槽１２には撹拌機２２が配備され、内部の被処理水が嫌気状態に置かれる。なお、本発明においては「嫌気状態」とは液中に溶存する遊離酸素が実質的に零であり、かつ、硝酸性窒素も実質的に存在しない状態を意味する。また、嫌気槽１２には原水の供給管路２４と無酸素槽１０からの汚泥混合液の供給管路２６が接続している。
【００１０】
好気槽１４には嫌気槽１２からの被処理水が流入するとともに、内部に分離膜２８が浸漬されており、被処理水を処理水と槽内に残留する汚泥混合液とに分離する。分離膜２８の下部にはブロワ３０で昇圧した空気が散気手段３２から散気され、内部の被処理水（汚泥混合液）が好気状態に置かれる。なお、本発明においては「好気状態」とは活性汚泥中の硝化菌などの好気性菌が活発に呼吸するための遊離酸素が液中に十分に溶存している状態を意味する。分離膜２８の二次側には管路３４が接続し、この管路３４に設けた吸引ポンプ３６によって分離膜２８を透過した処理水が系外へ排出される。また、好気槽１４には汚泥混合液を抜き出す管路１８が接続している。管路１８にはポンプ４０が配置され、管路１８の他端は無酸素槽１０に接続している。また、管路１８からは余剰汚泥を排出するための管路４２が分岐している。
【００１１】
上記の構成において、嫌気槽１２には管路２４からアンモニア態窒素とリンと有機物とを含む原水が連続的に流入し、また、管路２６から無酸素槽１０からの汚泥混合液が自然流下によって連続的に流入する。流入した原水と汚泥混合液とは撹拌機２２によって撹拌、混合され嫌気状態に置かれる。この嫌気状態では流入した原水中の有機物が活性汚泥に取り込まれるとともに、活性汚泥は体内に過剰蓄積していたリンを体外に放出する。すなわち、この嫌気槽１２は主としてリンの放出槽としての機能を果たす。次いで、この活性汚泥から放出されたリンと原水中のアンモニア態窒素とリンとを含む被処理水は嫌気槽１２を溢流し、好気槽１４に流入する。
【００１２】
好気槽１４では被処理水は散気手段３２からの散気によって好気状態に置かれており、以下に説明するように主に４つの処理が同時に進行する。第１に被処理水中に残存する有機物が活性汚泥により酸化分解される。第２に被処理水中のリンが活性汚泥に取り込まれて除去され、活性汚泥は体内にリンを過剰に蓄積する。第３に被処理水中のアンモニア態窒素が活性汚泥中の硝化菌の作用によって硝化され、硝酸性窒素となる。第４に上記の処理を受けた被処理水が分離膜２８によって膜分離される。膜透過水は処理水として分離膜２８の二次側に接続された管路３４を介して系外に排出される。
【００１３】
処理水が分離されることにより、濃縮された好気槽１４内の被処理水は汚泥混合液として管路１８から抜き出される。ポンプ４０によって抜き出された汚泥混合液は余剰汚泥として系外へ排出される分以外の全量が管路１８を介して無酸素槽１０に返送される。抜き出された汚泥混合液の一部は管路４２から余剰汚泥として系外へ排出される。この汚泥混合液は体内にリンを過剰に蓄積した活性汚泥と硝酸性窒素と溶存酸素を含む。
【００１４】
無酸素槽１０では、管路１８から流入した汚泥混合液と、管路２０から添加された水素供与体が撹拌機１６によって撹拌混合され、無酸素状態に置かれて所定時間滞留する。この状態では活性汚泥中に存在する脱窒菌が添加された水素供与体を栄養源として活発に呼吸する。その結果、汚泥混合液中の溶存酸素を直ちに消費するとともに、硝酸性窒素を電子受容体とした硝酸呼吸である脱窒反応が進行する。この結果、硝酸性窒素は還元されて窒素ガスとなり、大気に放散される。すなわち、無酸素槽１０は主として脱窒槽としての機能を果たす。
【００１５】
系内に循環させる活性汚泥の濃度は８，０００〜１５，０００ｍｇ／Ｌの範囲に維持することが好ましい。活性汚泥の濃度は前記管路４２から系外に排出する余剰汚泥の量を調節することによって、容易にコントロールすることができる。また、系内に循環させる汚泥混合液の量、すなわち好気槽１４から管路１８を介して無酸素槽１０に返送する汚泥混合液の循環率は、原水の流入量に対して２〜４倍の範囲に維持することが好ましい。２倍未満では無酸素槽１０での脱窒処理率が相対的に低下し、好気槽１４から排出される処理水中の硝酸性窒素の濃度が相対的に高くなる。また、４倍を越えると運転動力が増大するとともに、各槽での被処理水、汚泥混合液の滞留時間が減少して処理が不十分となる可能性がある。したがって、原水中の窒素濃度が低い時や原水流入量が多い時には、上記の範囲で汚泥混合液の循環率を小さく選定し、原水中の窒素濃度が高い時や原水流入量が少ない時には、上記の範囲で汚泥液の循環率を大きく選定すればよい。
【００１６】
なお、本実施の形態では好気槽１４から排出される処理水に硝酸性窒素が含まれる。したがって、必要に応じて処理水中の硝酸性窒素を脱窒処理するための脱窒槽を別途、設けるようにしてもよい。また、本実施の形態では無酸素槽１０に添加する水素供与体として有機酸、メタノールなどを用いた。しかしながら、原水中の有機物濃度が高い場合には、原水の全量を嫌気槽１２に供給せずに、一部を無酸素槽１０に分注し、原水中の有機物を水素供与体として利用するようにしてもよい。
【００１７】
上述のとおり、本実施の形態によればアンモニア態窒素とリンと有機物とを含む原水が、きわめて自然に、円滑な生物学的な硝化脱窒処理と脱リン処理を受けて浄化される。かつ、好気槽で膜分離した高濃度の汚泥混合液を無酸素槽、嫌気槽及び好気槽に循環させることができるので、各槽での反応速度が大きくなり、結果として装置全体の小容量化を図ることができる。このため、原水を嫌気槽、無酸素槽、好気槽の順に通水するという旧来の方法を踏襲する場合に比べて、構成が簡単で、かつ運転管理が容易な窒素・リン除去方法を実現することができる。
【００１８】
図２は本発明の第２の実施形態を実現するための装置系統図である。本装置は、主に嫌気槽５０、第１好気槽５２、第１無酸素槽５４、第２好気槽５６、第２無酸素槽５８とによって構成される。
第２無酸素槽５８には撹拌機６０が配備され、第２好気槽５６から管路６２を介して返送されてきた汚泥混合液が無酸素状態に置かれる。また、第２無酸素槽５８には有機酸、メタノールなどの水素供与体の供給管路６４が接続している。
嫌気槽５０には撹拌機６６が配備され、内部の被処理水が嫌気状態に置かれる。また、嫌気槽５０には原水の供給管路６８と第２無酸素槽５８からの汚泥混合液の供給管路７０が接続している。
第１好気槽５２には嫌気槽５０からの被処理水が流入するとともに、ブロワ７２で昇圧した空気が散気手段７４から散気され、内部の被処理水が好気状態に置かれる。
第１無酸素槽５４には管路７６から原水が、第１好気槽５２から被処理水が流入するとともに、撹拌機７７が配備され、内部の被処理水が無酸素状態に置かれる。
第２好気槽５６には第１無酸素槽５４からの被処理水が流入するとともに、内部に分離膜７４が浸漬されており、被処理水を処理水と槽内に残留する汚泥混合液とに分離する。分離膜７４の下部にはブロワ７２で昇圧した空気が散気手段７６から散気され、内部の被処理水（汚泥混合液）が好気状態に置かれる。分離膜７４の二次側には管路７８が接続し、この管路７８に設けた吸引ポンプ８０によって分離膜７４を透過した処理水が系外へ排出される。また、第２好気槽５６には汚泥混合液を抜き出す管路６２が接続している。管路６２にはポンプ８２が配置され、管路６２の他端は第２無酸素槽５８に接続している。また、管路６２からは余剰汚泥を排出するための管路８４が分岐している。そして、第２好気槽５６から抜き出された汚泥混合液は、余剰汚泥分以外の全量がポンプ８２によって第２無酸素槽５８に返送される。
【００１９】
この第２実施形態と前記第１実施形態とを対比すると、本実施形態における第２無酸素槽５８、嫌気槽５０及び第２好気槽５６が、図１に示した第１実施形態の無酸素槽１０、嫌気槽１２及び好気槽１４と対応しており、同一の作用と機能を果たす。本実施形態では嫌気槽５０と第２好気槽５６との間に、更に第１好気槽５２と第１無酸素槽５４が追設され、原水は嫌気槽５０と第１無酸素槽５４とに分注される。この構成は、いわゆる「ステップ流入式硝化脱窒処理」の考え方を取り入れたものであり、第１好気槽５２では一次的な硝化反応、第１無酸素槽５４では一次的な脱窒反応が複合して進行する。このため、第２好気槽５６での二次的な硝化反応と第２無酸素槽５８での二次的な脱窒反応の負荷がそれぞれ低減する。この結果、本実施形態によれば、前記第１実施形態で説明した作用効果にプラスして、更に全体的な処理の安定化、汚泥混合液の循環率の低減化、処理水の硝酸性窒素濃度の低減化を達成できる。
【００２０】
また、「ステップ流入式硝化脱窒処理」を更に進め、第２実施形態に対して、第１無酸素槽５４と第２好気槽５６との間に、更に第３の好気槽と第３の無酸素槽を追設し、原水を第３の無酸素槽にも分注するように構成すれば、より一層，木目の細かい処理が可能となる。本発明は、このような実施の形態をも含む。
【００２１】
【発明の効果】
本発明によれば、分離膜を用いて処理水を抜き出すようにした窒素・リン除去方法の利点を生かしつつ、構成が簡単で、かつ運転管理が容易な窒素・リン除去方法を実現することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施形態を実現するための装置系統図である。
【図２】本発明の第２の実施形態を実現するための装置系統図である。
【符号の説明】
１０……無酸素槽
１２……嫌気槽
１５……好気槽
１８……（汚泥混合液の）返送管路
２０……（水素供与体の）供給管路
２４……（原水の）供給管路
２８……分離膜
３４……（処理水の）排出管路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for removing nitrogen / phosphorus from raw water containing nitrogen, phosphorus, and organic matter, and more particularly to a method for removing nitrogen / phosphorus using a separation membrane to extract treated water.
[0002]
[Prior art]
There is known a method of biologically treating raw water containing nitrogen, phosphorus, and organic substances to simultaneously remove not only organic substances in the raw water but also nitrogen and phosphorus. In this method, for example, as described in Patent Document 1, raw water is passed through an anaerobic tank, an anoxic tank, an aerobic tank, and a sedimentation tank in this order, and the sludge mixture separated in the sedimentation tank is placed in the first anaerobic tank. And the treatment liquid in the aerobic tank is circulated to the oxygen-free tank.
According to this method, in the anaerobic tank, the organic matter in the raw water is taken into the activated sludge under anaerobic conditions, and simultaneously, the phosphorus in the activated sludge is released. In the anoxic tank, nitrate nitrogen is reduced by the action of denitrifying bacteria in the presence of organic substances, and the denitrification process in which nitrogen gas is produced proceeds. Therefore, this anoxic tank is sometimes referred to as a denitrification tank. In the aerobic tank, nitrification of ammonia nitrogen in raw water by nitrifying bacteria and uptake of phosphorus into activated sludge are performed. In order to denitrify the nitrate nitrogen generated by the nitrification reaction in the aerobic tank, the treatment liquid in the aerobic tank is circulated to the preceding anoxic tank. In the sedimentation tank, the treatment liquid in the aerobic tank is subjected to sedimentation treatment and separated into treated water as supernatant water and sludge mixed liquid as sediment. A part of the settled sludge mixture is discharged out of the system as surplus sludge, and most of the remaining sludge mixture is returned to the forefront anaerobic tank.
Patent Literature 2 discloses a method in which the above-mentioned method is further developed and the treated water is separated by a separation membrane immersed in an aerobic tank (aeration tank). According to this method, the sedimentation tank can be omitted. In addition, since the high-concentration sludge mixture separated in the aerobic tank can be circulated to the anaerobic tank, the anoxic tank (denitrification tank) and the aerobic tank, the reaction speed in each tank increases, and as a result, the apparatus There is an advantage that the overall capacity can be reduced.
[0003]
[Patent Document 1]
JP-A-6-296991 [Patent Document 2]
JP 2001-314890 A
[Problems to be solved by the invention]
However, each of the above methods follows the conventional method of passing raw water containing nitrogen, phosphorus, and organic matter in the order of an anaerobic tank, an anoxic tank, and an aerobic tank. In particular, the method described in Patent Literature 2 follows the above-mentioned conventional method despite the adoption of a new method of extracting treated water by a separation membrane immersed in an aerobic tank. The configuration was somewhat complicated. That is, since the sludge mixture separated in the aerobic tank contains nitrate nitrogen and dissolved oxygen, it is difficult to make the inside of the tank anaerobic even if this sludge mixture is directly sent to the anaerobic tank in the first stage. , Cannot release phosphorus from activated sludge. For this reason, a complicated configuration is adopted in which the sludge mixture is returned to the anoxic tank for denitrification treatment, and then a part of the mixture in the anoxic tank is circulated to the preceding anaerobic tank.
SUMMARY OF THE INVENTION An object of the present invention is to improve the problems of the prior art described above and to take advantage of the nitrogen / phosphorus removal method in which treated water is extracted using a separation membrane, while using a simple configuration and easy operation management.・ To provide a method for removing phosphorus.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the method for removing nitrogen and phosphorus according to the present invention comprises passing raw water containing nitrogen, phosphorus, and organic matter in the order of an anaerobic tank and an aerobic tank in the presence of activated sludge. In the gas tank, the treated water and the sludge mixed liquid are separated by the separation membrane immersed inside, and the entire amount of the separated sludge mixed liquid except for the excess sludge is retained in the oxygen-free tank to which the hydrogen donor is added for a predetermined time. After that, it is supplied to the anaerobic tank.
According to such a configuration, the release of phosphorus from the activated sludge actively proceeds in the anaerobic tank. In the aerobic tank, the oxidative decomposition of the remaining organic matter, the dephosphorization reaction by taking in activated sludge with phosphorus, the nitrification reaction, and the withdrawal of treated water by membrane separation proceed in parallel. In the anoxic tank, nitrate nitrogen in the sludge mixture separated in the aerobic tank is removed by a denitrification reaction. Since substantially no dissolved oxygen or nitrate nitrogen is present in the sludge mixture supplied from the anoxic tank to the anaerobic tank, the anaerobic tank can easily maintain the anaerobic state. Therefore, it is possible to realize a nitrogen / phosphorus removal method with a simple configuration and easy operation management, while taking advantage of the nitrogen / phosphorus removal method in which treated water is extracted using a separation membrane.
[0006]
Further, in the method for removing nitrogen and phosphorus according to the present invention, a part of raw water containing nitrogen, phosphorus and organic matter is passed in the order of an anaerobic tank and a first aerobic tank in the presence of activated sludge, and then the raw water The remainder and the water to be treated which have been treated in the first aerobic tank are passed through in the order of a first anoxic tank and a second aerobic tank, and the second aerobic tank is treated by a separation membrane immersed therein. Separation into water and sludge mixture, and the entire amount of the separated sludge mixture other than the excess sludge is retained in the second oxygen-free tank to which the hydrogen donor is added for a predetermined time and then supplied to the anaerobic tank. It is characterized by.
[0007]
Further, the method for removing nitrogen and phosphorus according to the present invention is characterized in that any one of an organic acid, methanol, or a part of the raw water is used as the hydrogen donor.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is an apparatus system diagram for realizing the first embodiment of the present invention. The present apparatus mainly includes an anoxic tank 10, an anaerobic tank 12, and an aerobic tank 14. A stirrer 16 is provided in the oxygen-free tank 10, and the sludge mixture returned from the aerobic tank 14 via the pipe 18 is placed in an oxygen-free state. In the present invention, “anoxic state” means that free oxygen dissolved in a liquid is substantially close to zero, but nitrate nitrogen as an oxygen source necessary for respiration of denitrifying bacteria during a denitrification reaction. Is supplied. A supply line 20 for a hydrogen donor such as an organic acid or methanol is connected to the oxygen-free tank 10.
[0009]
The stirrer 22 is provided in the anaerobic tank 12, and the to-be-processed water inside is put in an anaerobic state. In the present invention, the “anaerobic state” means a state in which free oxygen dissolved in the liquid is substantially zero and nitrate nitrogen is substantially absent. The anaerobic tank 12 is connected to a supply pipe 24 for raw water and a supply pipe 26 for the sludge mixture from the anoxic tank 10.
[0010]
The water to be treated from the anaerobic tank 12 flows into the aerobic tank 14, and a separation membrane 28 is immersed therein to separate the water to be treated into the treated water and the sludge mixture remaining in the tank. The air pressurized by the blower 30 is diffused below the separation membrane 28 from the diffuser 32, and the water to be treated (sludge mixture) is placed in an aerobic state. In the present invention, the "aerobic state" means a state in which free oxygen for aerobic bacteria such as nitrifying bacteria in activated sludge to breathe actively is sufficiently dissolved in the liquid. A pipe 34 is connected to the secondary side of the separation membrane 28, and the treated water that has passed through the separation membrane 28 is discharged out of the system by a suction pump 36 provided in the pipe 34. The aerobic tank 14 is connected to a pipe 18 for extracting the sludge mixture. A pump 40 is disposed in the pipe 18, and the other end of the pipe 18 is connected to the oxygen-free tank 10. A pipe 42 for discharging excess sludge branches off from the pipe 18.
[0011]
In the above configuration, raw water containing ammonia nitrogen, phosphorus and organic matter continuously flows into the anaerobic tank 12 from the pipe 24, and the sludge mixture from the anoxic tank 10 flows down naturally from the pipe 26. To continuously flow. The inflowing raw water and the sludge mixture are stirred and mixed by the stirrer 22 and placed in an anaerobic state. In this anaerobic state, the organic matter in the raw water that has flowed in is taken up by the activated sludge, and the activated sludge releases phosphorus that has excessively accumulated in the body to the outside. That is, the anaerobic tank 12 mainly functions as a phosphorus releasing tank. Next, the water to be treated containing the phosphorus released from the activated sludge, the ammonia nitrogen in the raw water, and the phosphorus overflows the anaerobic tank 12 and flows into the aerobic tank 14.
[0012]
In the aerobic tank 14, the water to be treated is placed in an aerobic state by the aeration from the aeration means 32, and four processes mainly proceed simultaneously as described below. First, organic matter remaining in the water to be treated is oxidatively decomposed by activated sludge. Second, phosphorus in the water to be treated is taken in and removed by the activated sludge, and the activated sludge excessively accumulates phosphorus in the body. Third, the ammonia nitrogen in the water to be treated is nitrified by the action of nitrifying bacteria in the activated sludge, and becomes nitrate nitrogen. Fourth, the water to be treated that has undergone the above treatment is membrane-separated by the separation membrane 28. The membrane permeated water is discharged out of the system as treated water via a pipe 34 connected to the secondary side of the separation membrane 28.
[0013]
By separating the treated water, the treated water in the concentrated aerobic tank 14 is extracted from the pipe 18 as a sludge mixture. The entire amount of the sludge mixed liquid extracted by the pump 40 except for the amount discharged as excess sludge to the outside of the system is returned to the oxygen-free tank 10 via the pipe 18. Part of the extracted sludge mixture is discharged out of the system as excess sludge from the pipe 42. This sludge mixture contains activated sludge that has excessively accumulated phosphorus in the body, nitrate nitrogen, and dissolved oxygen.
[0014]
In the anoxic tank 10, the mixed sludge flowing from the pipe 18 and the hydrogen donor added from the pipe 20 are agitated and mixed by the stirrer 16, placed in an anoxic state and retained for a predetermined time. In this state, active respiration is performed using the hydrogen donor to which the denitrifying bacteria present in the activated sludge is added as a nutrient source. As a result, the dissolved oxygen in the sludge mixture is immediately consumed, and a denitrification reaction, which is nitrate respiration using nitrate nitrogen as an electron acceptor, proceeds. As a result, the nitrate nitrogen is reduced to nitrogen gas and released to the atmosphere. That is, the oxygen-free tank 10 mainly functions as a denitrification tank.
[0015]
It is preferable to maintain the concentration of the activated sludge circulated in the system in the range of 8,000 to 15,000 mg / L. The concentration of the activated sludge can be easily controlled by adjusting the amount of excess sludge discharged from the pipe 42 to the outside of the system. The amount of the sludge mixture circulated in the system, that is, the circulation rate of the sludge mixture returned from the aerobic tank 14 to the anoxic tank 10 via the pipe 18 is 2 to 4 times the flow rate of the raw water. It is preferable to maintain it in the range of twice. If it is less than twice, the denitrification rate in the oxygen-free tank 10 is relatively reduced, and the concentration of nitrate nitrogen in the treated water discharged from the aerobic tank 14 is relatively high. If it exceeds four times, the operating power increases and the residence time of the water to be treated and the sludge mixture in each tank decreases, which may result in insufficient treatment. Therefore, when the nitrogen concentration in the raw water is low or the raw water inflow is large, the circulation rate of the sludge mixture is selected to be small in the above range, and when the nitrogen concentration in the raw water is high or the raw water inflow is small, The sludge liquid circulation rate may be selected to be large within the range described above.
[0016]
In the present embodiment, the treated water discharged from the aerobic tank 14 contains nitrate nitrogen. Therefore, if necessary, a denitrification tank for denitrifying nitrate nitrogen in the treated water may be separately provided. In the present embodiment, an organic acid, methanol, or the like is used as a hydrogen donor added to the oxygen-free tank 10. However, when the concentration of the organic matter in the raw water is high, the whole amount of the raw water is not supplied to the anaerobic tank 12, but a part of the raw water is dispensed to the oxygen-free tank 10, and the organic matter in the raw water is used as a hydrogen donor. It may be.
[0017]
As described above, according to the present embodiment, raw water containing ammonia nitrogen, phosphorus, and organic matter is very naturally purified by undergoing smooth biological nitrification and denitrification and dephosphorization. In addition, since a high-concentration sludge mixture separated by membrane in an aerobic tank can be circulated to an anoxic tank, an anaerobic tank, and an aerobic tank, the reaction speed in each tank increases, and as a result, the size of the entire apparatus becomes small. The capacity can be increased. Therefore, compared to the conventional method of passing raw water through an anaerobic tank, an anoxic tank, and an aerobic tank in order, a nitrogen / phosphorus removal method with a simpler configuration and easier operation management is realized. can do.
[0018]
FIG. 2 is an apparatus system diagram for realizing the second embodiment of the present invention. The present apparatus mainly includes an anaerobic tank 50, a first aerobic tank 52, a first anoxic tank 54, a second aerobic tank 56, and a second anoxic tank 58.
A stirrer 60 is provided in the second anoxic tank 58, and the sludge mixture returned from the second aerobic tank 56 via the pipe 62 is placed in an anoxic state. Further, a supply line 64 for a hydrogen donor such as an organic acid or methanol is connected to the second oxygen-free tank 58.
A stirrer 66 is provided in the anaerobic tank 50, and the water to be treated inside is placed in an anaerobic state. The anaerobic tank 50 is connected to a supply pipe 68 for raw water and a supply pipe 70 for the sludge mixture from the second oxygen-free tank 58.
The to-be-processed water from the anaerobic tank 50 flows into the first aerobic tank 52, and the air pressurized by the blower 72 is diffused from the diffusing means 74, so that the to-be-processed water inside is placed in an aerobic state.
Raw water flows into the first oxygen-free tank 54 from a pipe 76, and water to be treated flows from the first aerobic tank 52. A stirrer 77 is provided, and the water to be treated is placed in an oxygen-free state.
The to-be-processed water from the first anoxic tank 54 flows into the second aerobic tank 56, and the separation membrane 74 is immersed therein, so that the to-be-processed water is mixed with the treated water and the sludge mixed liquid remaining in the tank. And separated into The air pressurized by the blower 72 is diffused below the separation membrane 74 from the diffuser 76, and the water to be treated (sludge mixture) is placed in an aerobic state. A pipe 78 is connected to the secondary side of the separation membrane 74, and the treated water that has passed through the separation membrane 74 is discharged out of the system by a suction pump 80 provided in the pipe 78. The second aerobic tank 56 is connected to a conduit 62 for extracting the sludge mixture. A pump 82 is disposed in the pipe 62, and the other end of the pipe 62 is connected to the second oxygen-free tank 58. A pipeline 84 for discharging excess sludge is branched from the pipeline 62. Then, the entire amount of the sludge mixture extracted from the second aerobic tank 56 except for the excess sludge is returned to the second oxygen-free tank 58 by the pump 82.
[0019]
When the second embodiment is compared with the first embodiment, the second anoxic tank 58, the anaerobic tank 50, and the second aerobic tank 56 in the present embodiment are different from the first embodiment shown in FIG. It corresponds to the oxygen tank 10, the anaerobic tank 12, and the aerobic tank 14, and has the same function and function. In the present embodiment, a first aerobic tank 52 and a first anoxic tank 54 are additionally provided between the anaerobic tank 50 and the second aerobic tank 56, and raw water is supplied from the anaerobic tank 50 and the first anoxic tank 54. And is dispensed to. This configuration adopts the concept of a so-called “step-flow type nitrification and denitrification treatment”. In the first aerobic tank 52, a primary nitrification reaction is performed, and in the first anoxic tank 54, a primary denitrification reaction is performed. Progress in combination. For this reason, the loads of the secondary nitrification reaction in the second aerobic tank 56 and the secondary denitrification reaction in the second anoxic tank 58 are reduced. As a result, according to the present embodiment, in addition to the functions and effects described in the first embodiment, the overall treatment is further stabilized, the circulation rate of the sludge mixture is reduced, and the nitrate nitrogen of the treated water is reduced. A reduction in concentration can be achieved.
[0020]
Further, the “step-flow nitrification and denitrification treatment” is further advanced, and a third aerobic tank and a third aerobic tank are further disposed between the first anoxic tank 54 and the second aerobic tank 56 with respect to the second embodiment. If the third anoxic tank is additionally provided and the raw water is also dispensed to the third anoxic tank, finer grain treatment can be achieved. The present invention includes such an embodiment.
[0021]
【The invention's effect】
Advantageous Effects of Invention According to the present invention, it is possible to realize a nitrogen / phosphorus removal method that is simple in configuration and easy in operation management while taking advantage of a nitrogen / phosphorus removal method in which treated water is extracted using a separation membrane. it can.
[Brief description of the drawings]
FIG. 1 is an apparatus system diagram for realizing a first embodiment of the present invention.
FIG. 2 is an apparatus system diagram for realizing a second embodiment of the present invention.
[Explanation of symbols]
10 anoxic tank 12 anaerobic tank 15 aerobic tank 18 return line 20 (for sludge mixture) supply line 24 (for hydrogen donor) supply line (raw water) Line 28 Separation membrane 34 Discharge line of (processed water)

Claims

窒素とリンと有機物とを含む原水を活性汚泥の存在下で嫌気槽、好気槽の順に通水し、前記好気槽では内部に浸漬した分離膜により処理水と汚泥混合液とに分離し、分離した前記汚泥混合液の余剰汚泥分以外の全量を水素供与体が添加される無酸素槽で所定時間滞留させた後に前記嫌気槽に供給することを特徴とする窒素・リン除去方法。Raw water containing nitrogen, phosphorus and organic matter is passed in the order of an anaerobic tank and an aerobic tank in the presence of activated sludge, and separated into treated water and a sludge mixed solution by a separation membrane immersed in the aerobic tank in the aerobic tank. A nitrogen / phosphorus removal method, wherein the total amount of the separated sludge mixed liquid other than the excess sludge is retained in an oxygen-free tank to which a hydrogen donor is added for a predetermined time and then supplied to the anaerobic tank.

窒素とリンと有機物とを含む原水の一部を活性汚泥の存在下で嫌気槽、第１好気槽の順に通水し、次いで前記原水の残部と前記第１好気槽で処理を受けた被処理水とを第１無酸素槽、第２好気槽の順に通水し、前記第２好気槽では内部に浸漬した分離膜により処理水と汚泥混合液とに分離し、分離した前記汚泥混合液の余剰汚泥分以外の全量を水素供与体が添加される第２無酸素槽で所定時間滞留させた後に前記嫌気槽に供給することを特徴とする窒素・リン除去方法。Part of the raw water containing nitrogen, phosphorus and organic matter was passed in the order of an anaerobic tank and a first aerobic tank in the presence of activated sludge, and then treated in the remaining part of the raw water and the first aerobic tank. The water to be treated is passed in the order of a first oxygen-free tank and a second aerobic tank. In the second aerobic tank, the treated water and the sludge mixture are separated by a separation membrane immersed therein, and separated. A nitrogen / phosphorus removal method, characterized in that a total amount of the sludge mixture other than the excess sludge is retained in a second anoxic tank to which a hydrogen donor is added for a predetermined time and then supplied to the anaerobic tank.

前記水素供与体として有機酸、メタノール又は前記原水の一部のいずれかを用いることを特徴とする請求項１又は請求項２に記載の窒素・リン除去方法。3. The method for removing nitrogen and phosphorus according to claim 1, wherein any one of an organic acid, methanol, and a part of the raw water is used as the hydrogen donor.