JP3844347B2

JP3844347B2 - Method and apparatus for removing and recovering phosphorus from organic wastewater

Info

Publication number: JP3844347B2
Application number: JP2002333701A
Authority: JP
Inventors: 隆生萩野; 裕一府中; 栄小三田
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2002-11-18
Filing date: 2002-11-18
Publication date: 2006-11-08
Anticipated expiration: 2022-11-18
Also published as: JP2004167307A

Description

【０００１】
【発明の属する技術分野】
本発明は、下水処理場や各種廃水処理施設等において有機性汚水を処理するシステムに係わり、更に詳しくは、これらの有機性汚水処理システムで発生する有機性汚泥に対して濃縮、嫌気性消化、脱水などの処理を行った時に分離され、水処理系に返流される返流水を水処理システム全体のバランスを考慮した条件で返流させることにより、該水処理システムから排出される放流水中のリン濃度の軽減を安定的に図る技術に関するものである。
【０００２】
【従来の技術】
有機性汚水を処理する処理場では多量の有機性汚泥が発生する。この汚泥は減量化処理としての濃縮、消化、脱水などの工程を経て処理される場合が多く、これらのプロセスにおいて汚泥から分離される分離水は通常水処理系に返流される。なお、この場合の減量化処理としては、主として濃縮、脱水、乾燥等の汚泥のＳＳ量は減少させないが、全体の容積を減少させる処理を指す場合と、ＳＳ量を減少させる嫌気性消化処理、オゾン処理、熱処理、超音波処理等を指す場合がある。この返流水中にはＢＯＤ、アンモニア性窒素、溶解性リン等が高濃度に含まれており、これら返流水中の高濃度の処理対象物質が、水処理系の処理水質を悪化させる場合が少なからずある。このＢＯＤ、窒素、リンの３物質の内、特にリンは近年水質規制項目としての取り締まりが強化されつつある物質の一つである。
【０００３】
従来、下水処理場等で行われている代表的な脱リン処理方式としては、生物学的処理法としての嫌気好気法や、物理化学的処理法としての凝集沈殿法等が挙げられる。嫌気好気法では、流入水質の変化や季節変動等の外部環境の変化により処理性能が安定しない等の問題があり、凝集沈殿方式では、凝集剤として添加するＰＡＣ、ポリ鉄、及び高分子凝集剤等の薬品代コストが、処理場全体のランニングコストを過大にする等の問題があった。
これまで、汚泥処理プロセスより発生する返流水からリンを回収する方法としては、該返流水からリン及び一部のアンモニア性窒素をリン酸マグネシウムアンモニウム粒子として回収した後、残留するアンモニア性窒素を生物学的に硝化し、その処理水に生汚泥を加えて、水処理系と関係しないＢＯＤを使って脱窒を行う汚泥処理系返流水の処理方法が提案されている（特許文献１）。
【０００４】
【特許文献１】
特開平１１−１０４６９３号公報
【０００５】
【発明が解決しようとする課題】
特に、嫌気好気法では、嫌気槽において活性汚泥微生物が過剰に摂取したリン酸を菌体外に放出する際に、溶解性ＢＯＤを菌体内に取り込む必要があるが、嫌気槽に流入する溶解性ＢＯＤは、時々刻々と変化する流入原水と返流水の水質に依存するためにコントロールすることが困難である。そのため、リン酸放出に必要十分な溶解性ＢＯＤが得られず、好気槽での活性汚泥によるリン酸摂取能力を十分に発揮させることが困難となり、最終的には放流水中のリン酸濃度が目標放流水質を上回るケースも多く発生していた。
【０００６】
そこで、上述した生物学的リン除去を採用する水処理システムにおける従来の問題点を解消できるよう、比較的容易にリン処理効率を向上させる技術を開発する必要がある。従来法としての生物学的リン除去システムの課題であった、「流入水質の変化や季節変動等の外部環境の変化によるリン除去処理性能の不安定性」が、大きく改善することが求められる。
【０００７】
また、返流水中の有機物量は、嫌気好気法などのリン除去システムの処理性能に影響を及ぼす以外に、硝化脱窒法等の窒素除去システムの処理性能にも大きく影響を及ぼす。例えば、嫌気−無酸素−好気法を採用する水処理施設の場合は、返流水中の有機物量が脱窒、脱リンの両方の処理性能に影響を及ぼすため、システムに流入する有機物量を安定供給することは、良好なリン・窒素同時除去を実現するための重要な課題の一つであった。
【０００８】
【課題を解決するための手段】
本発明は、上述した従来技術の課題を解決するものである。要するに、本発明は、汚泥減量化工程により分離された溶解性有機物や溶解性リンを多く含む返流水から、有機物はなるべく除去せずにリンを除去又は回収し、リン除去又は回収後の返流水及びリン酸マグネシウムアンモニウム粒子回収後の汚泥由来の返流水のうちの少なくとも１つを一時的に貯留する槽を設け、該返流水貯留槽から実際に水処理系に返流させる量をコントロールすることにより、水処理系での嫌気好気法によるリン除去効率を向上させることを基本的な構成とする。
【０００９】
すなわち、本発明は、下記の手段により上記の課題を解決した。
（１）有機性汚水を処理して生物学的にリンを除去する工程、及び生成汚泥を減量化する工程を含み、それに加えて、該汚泥減量化工程の減量化汚泥から分離した返流水からリンを除去又は回収する工程と、有機性汚水の処理工程で発生する汚泥の嫌気性消化工程において発生するリン酸マグネシウムアンモニウム粒子を回収する工程のうちの少なくとも１工程を含む有機性汚水の処理システムにおいて、リン除去又は回収後の返流水及びリン酸マグネシウムアンモニウム粒子回収後の汚泥から分離した返流水のうちの少なくとも１つを生物学的リン除去工程又はその前段に返流させる途中に該返流水を貯留する槽を設け、該返流水貯留槽から生物学的リン除去工程又はその前段に流入させる該返流水の有機物量を制御することを特徴とする有機性汚水の処理方法。
【００１０】
（２）汚泥の減量化工程として濃縮処理、嫌気性発酵処理、脱水処理、オゾン処理、超音波処理、熱処理のうちの少なくとも１つの処理を含むことを特徴とする前記（１）に記載の有機性汚水の処理方法。
（３）前記返流水貯留槽に、水処理系プロセスの最初沈殿池において沈降分離した最初沈殿池汚泥、汚泥処理系プロセスにおいて生成した濃縮汚泥、嫌気性消化汚泥、脱水ケーキのうちの少なくとも１つの一部又は全部を導入することを特徴とする前記（１）又は（２）に記載の有機性汚水の処理方法。
（４）前記返流水貯留槽から生物学的リン除去工程又はその前段に流入する貯留槽流出水の有機物量を制御する方法として、該返流水貯留槽流出水中の有機物量と、処理場流入水由来の有機物量を計量することによって、生物学的リン除去工程に流入する有機物量を把握し、得られた該データを生物学的リン除去工程を最適に制御するための説明変数とすることを特徴とする前記（１）〜（３）のいずれか１項に記載の有機性汚水の処理方法。
【００１１】
（５）該返流水貯留槽流出水中のリン負荷量と、処理場流入水由来のリン負荷量を計量することによって、生物学的リン除去工程に流入するリン負荷量を把握し、得られた該データを生物学的リン除去工程を最適に制御するための説明変数とすることにより、前記返流水貯留槽から生物学的リン除去工程又はその前段に流入する貯留槽流出水についてそのリン負荷量を制御することを特徴とする前記（１）〜（３）のいずれか１項に記載の有機性汚水の処理方法。
（６）有機性汚水を処理して生物学的にリンを除去する嫌気好気生成物反応槽、及び生成汚泥を減量化する装置を有し、さらに該汚泥減量化装置の減量化処理汚泥を固液分離装置で分離した返流水からリンを除去又は回収する脱リン反応槽と、汚泥の嫌気性消化槽において発生するリン酸マグネシウムアンモニウム粒子を回収する装置のうちの少なくとも１つを含む有機性汚水の処理装置において、リン除去又は回収後の返流水、及びリン酸マグネシウムアンモニウム粒子の回収後の汚泥を固液分離装置で分離した返流水のうちの少なくとも１つを生物学的リン除去装置又はその前段のいずれかの箇所に返流させる途中に配置した一時的に貯留可能であって、該返流水の有機物量を制御する手段を備えた返流水貯留槽、及び該返流水貯留槽に本システム内で発生する汚泥のうち少なくとも１つを導入する配管と、該返流水が該返流水貯留槽を経由せずに水処理系ラインに返流するためのバイパス管のうちの少なくとも１つの配管を設けたことを特徴とする有機性排水の処理装置。
【００１２】
本発明の骨子とするところは、上記課題を解決するために、汚泥減量化工程により分離された溶解性有機物や溶解性リンを多く含む返流水から、有機物は除去せずにリンを除去又は回収したリン除去又は回収後の返流水、及び汚泥の嫌気性消化工程に関連してリン酸マグネシウムアンモニウム粒子を回収した後の返流水のうちの少なくとも１つを一時的に貯留する槽を設け、該返流水貯留槽から生物学的リン除去工程に流入させる有機物量を制御する方法である。この返流水貯留槽を設けることにより、該返流水貯留槽では、水処理系の脱リンプロセスにおいて必要とされる水素供与体としての有機物、特に易分解性の溶解性ＢＯＤ成分が多量に貯留される環境にあるので、水処理系の脱リンプロセスの必要に応じて返流水貯留槽流出水の生物処理系に返流させる量を調節することで、前記脱リンプロセスの最適化を行うことができる。すなわち、返流水中のリンが少なく、かつ溶解性ＢＯＤ成分が多い点が、水処理系の生物学的リン除去プロセスの処理効率を大幅に高める効果を生じる。
【００１３】
【発明の実施の形態】
以下、本発明の実施の形態とその作用等について図面に基づいて詳細に説明する。なお、本発明は以下の実施形態に何ら限定されるものではない。
【００１４】
図１に示すフローは、水処理系が嫌気好気法を採用し、汚泥処理系が濃縮、嫌気性消化、脱水の各工程からなるフローを採用している。流入汚水１は最初沈殿池１６にて固形物の一部を沈殿分離し、最初沈殿池流出水２は生物反応槽１７の嫌気槽１７ａに送られる。嫌気槽１７ａでは、活性汚泥微生物が菌体内のポリリン酸をリン酸として放出し、代わりに水素供与体としての溶解性ＢＯＤ成分を菌体内に取り込む。この時、嫌気槽１７ａ内に溶解性ＢＯＤが十分に存在しないとリン酸の放出が不十分となり、後段の好気槽１７ｂにおける活性汚泥のリン酸摂取量が減少し、結果的には最終沈殿池１８からの処理水４に残留するリン酸濃度を高めることになる。すなわち、嫌気槽１７ａに流入する有機物量、とりわけ溶解性ＢＯＤ成分は、水処理系におけるリン除去性能に影響を及ぼす重要な因子の一つであると言える。
【００１５】
もちろん、嫌気槽１７ａ内の水温、ｐＨ、ＯＲＰ等も重要で因子であるが、本発明者らがこれまでに得た知見の範囲では、リン放出量を左右する最大の因子が溶解性ＢＯＤ成分であるケースが特に多かった。それにもかかわらず、従来法では嫌気槽１７ａに流入する溶解性ＢＯＤ成分の量をコントロールする手段としては、初沈汚泥５の直接投入などに限定されており、流入水質の日変動、気象変動、及び季節変動に対応したきめの細かい溶解性ＢＯＤの制御は困難であった。
しかし、本発明法では返流水貯留槽３２に貯留された溶解性ＢＯＤが豊富で、リン濃度が低い返流水１３を、水処理系の水質変動に応じて最初沈殿池１６や嫌気槽１７ａに返流するので、安定したリン除去処理に必要なきめの細かい溶解性ＢＯＤ負荷量の制御が可能となる。本発明プロセスの要となる返流水貯留槽３２と、該槽から流出する返流水貯留槽流出水１３について以下に詳細に説明する。
【００１６】
返流水貯留槽３２に流入する液体は、基本的には汚泥処理系由来の分離水である。汚泥処理系の汚泥濃縮装置２１で分離された濃縮汚泥脱離液１０、及び脱水装置２３で分離された脱水ろ液１１は、ともに脱リン反応槽３１に導入される。脱リン反応槽３１は、液体から溶解性のリンを除去又は回収するために設けられた反応槽であり、ＰＡＣやポリ鉄等の凝集剤の添加により、リン酸をリン酸アルミニウムやリン酸鉄等の不溶性の塩として固液分離する方法、又はアルカリ剤とマグネシウム源やカルシウム源を供給することによりリン酸マグネシウムアンモニウム（以下「ＭＡＰ」ともいう）やリン酸カルシウムを析出させることにより、リンを分離回収する方法等が挙げられる。流入汚水水質、及び水処理系や汚泥処理系の方式によっては、その適性に合ったリン除去・回収方法を選択する必要があり、必要に応じてこれらのリン除去・回収方式を組み合わせて用いても良い。
【００１７】
仮に図１に示した処理フローを例にして脱リン方式の選定を行う。脱水装置２３の前段に嫌気性消化反応槽２２があることから、脱水ろ液１１中には多量のリン酸、アンモニアイオン、及びＭアルカリ成分等が含まれる。これらの成分を有効利用したリン除去・回収方法としては、ＭＡＰ法が挙げられる。マグネシウム源と必要に応じてアルカリ剤をこの脱水ろ液１１、又は脱水ろ液１１と濃縮汚泥脱離液１０の混合液に対して添加し、晶析造粒することにより、液体中のリン酸及びアンモニアイオンの一部はＭＡＰとして回収することができる。ＭＡＰ晶析反応では、槽内のｐＨを７．３〜８．２程度の従来までのＭＡＰ晶析法の設定ｐＨよりやや低めに設定することにより、析出したＭＡＰ粒子がほとんど有機性ＳＳ成分を含まない、純度の高いＭＡＰ粒子に造粒することも可能である。要するに、脱リン反応槽３１においてＭＡＰを回収した後の脱リン槽流出液１３中の有機物量が、脱リン反応槽３１流入水中の有機物量とほぼ同量存在するようにすることが可能となる。
【００１８】
脱リン槽流出液１２は、返流水貯留槽３２において数時間〜数日間の滞留時間を経た後、返流水貯留槽流出水１３として最初沈殿池１１及び／又は嫌気槽１７ａに返流される。返流水貯留槽３２は、槽内を混合撹拌する機能や沈殿物を回収する機能を持たせる場合もある。返流水貯留槽３２で一時的に貯留された返流水は、流入汚水１の日変動、気象変動、季節変動に合わせて水処理系に返流させる。例えば、雨が降った場合は、返流水貯留槽流出水１３を水処理系に比較的多く返流することで、流入水量が急激に増加するファーストフラッシュの前や、雨で希釈された流入汚水１が流入する場合に、嫌気槽１２ａに溶解性ＢＯＤ成分を随時補給しリン酸放出速度を高めることができる。
【００１９】
また、本発明法では、初沈汚泥５の一部を返流水貯留槽３２に導入することを可能にしているため、状況に応じて初沈汚泥５を返流水貯留槽３２に導入し、該槽にて汚泥の酸発酵を促進させ、より多くの溶解性ＢＯＤ成分を生成させることも可能である。
一般的に下水の初沈汚泥を単独で酸発酵する場合、溶液中のアルカリ成分の消耗により約３日程度で有機酸濃度が極大となる場合が多いが、本発明の１つのフローである図１のフローの場合、返流水貯留槽３２に流入する水は、嫌気性消化汚泥の脱水ろ液由来である点と、脱リン反応槽３１においてアルカリ剤を添加されている点からMアルカリ成分を多く含み、返流水貯留槽３２に導入された初沈汚泥５の酸発酵を大幅に促進させることが可能になる。
【００２０】
また、導入した初沈汚泥５の返流水貯留槽３２での滞留時間を調節するために、バイパス管３３を通じて脱リン槽流出液１２の一部を返流水貯留槽３２に導入せずに、直接水処理系に返流させる場合もある。バイパス管３３は、初沈汚泥５を返流水貯留槽３２に導入しない場合においても適宜使用することにより、返流水貯留槽３２内での実質的滞留時間をコントロールすることができる。
【００２１】
また、酸発酵により生成した有機酸等が、メタン発酵菌や硫酸還元菌により消費されることを防止するために、返流水貯留槽３２内を曝気可能な構造としたり、該槽３２内の有機酸生成環境をＯＲＰで監視及び制御したりすることも有効である。また、返流水貯留槽３２を加温することにより、有機酸生成反応を促進させることが可能であるので、処理場内に廃熱が残っている場合等は、この加温処理と熱源とし、熱源量に応じて３０〜５５℃程度まで返流水貯留槽３２を加温する方法は有効である。このような方式により、初沈汚泥５の該槽３２での滞留時間を７日以上に設定した場合においても、該槽３２内での遊離有機酸や遊離アンモニアの濃度レベルは、有機酸生成反応に阻害に及ぼすレベルにはほとんど到達しないことを、本発明者らの実験データにより確認している。
【００２２】
また、リン除去ではなくリン回収に重きを置いたプロセスを設計する場合は、特開２０００−２３１６３３や特開２００２−１１６３５７等に開示した有機性排水からのリン回収方法を、本発明法に組み入れることにより、水処理系における排水からの高効率リン除去と、汚泥処理系における高効率リン回収を同時に行うことが可能になる。すなわち、必要に応じてマグネシウム源を嫌気性消化反応槽２２に供給することで該槽２２におけるＭＡＰ晶析反応を促進し、消化汚泥中に発生し
たＭＡＰ粒子を、液体サイクロンや振動ふるい等のＭＡＰ分離装置により分離及び回収し、ＭＡＰ粒子が取り除かれた汚泥の一部を該槽２２に返送するとともに、残りの汚泥を汚泥脱水装置２３により脱水する方式を採用することにより、従来法では脱水ケーキ中に多量に混在していたＭＡＰの大部分を、ＭＡＰ粒子という形態で回収することが可能になる。また、このＭＡＰ粒子は粒径が３００μｍ以上で、沈降性が良く固液分離性に優れている場合が多く、後段の脱リン反応槽３１内で流動させる種結晶とすることにより、該槽３１でのリン回収を効率良く行える。この方式によるリン回収を行うことにより、脱リン反応槽３１を省略しても、水処理系における生物学的リン除去性能を十分に発揮できる場合もある。
【００２３】
以上、説明したように返流水貯留槽３２では、水処理系の脱リンプロセスにおいて必要とされる水素供与体としての有機物、特に易分解性の溶解性ＢＯＤ成分が多量に貯留される環境にあるので、水処理系の必要に応じて返流水貯留槽流出水１３を調節することで、該脱リンプロセスの最適化を行うことができる。該脱リンプロセスをより正確に制御する必要がある場合には、流入汚水及び返流水貯留槽流出水中の有機物量やリン濃度を常時または適宜計測し、該脱リンプロセスに流入するトータルの有機物負荷量やリン負荷量を把握し、それらのデータに基づいて返流水貯留槽流出水１３の流量や初沈汚泥５の返流水貯留槽３２導入量を制御することにより、より効率的な脱リンプロセスの運転が可能になる。
【００２４】
また、上述してきた「脱リンシステム効率化のための返流水中の有機物量制御」に関する技術は、当然のことながら水処理系の脱窒システムにおいても適応することは可能である。すなわち、脱窒プロセスにおいても返流水中の溶解性ＢＯＤ成分の量は、脱窒プロセスに不可欠な水素供与体として、プロセスの性能に大きく影響する因子となる。そのため、生物学的脱リンと生物学的脱窒を組み合わせた方式を採用する水処理系に対して返流水が発生し、それを返流するシステムを採用する場合には、脱窒と脱リンを両方考慮した上で、返流水貯留槽流出水１３の流量や、初沈汚泥５の返流水貯留槽３２導入量を制御することも有効である。
【００２５】
【実施例】
本発明を実施例により具体的に説明する。なお、本発明は以下の実施例によりなんら制限されるものではない。
【００２６】
実施例１
先に解説した図１に示すフローを採用したＡ処理場での本発明法実験プラントの運転条件について説明する。なお、本実施例の発明効果を評価しやすくするために、対照系としてＡ処理場での本発明法実験プラントと同規模の対照系プラント（１）、（２）（図２及び図３参照）を併設し、３系列ともに３ヶ月の運転を行った。
【００２７】
３系列は、図１に示すように、水処理系は嫌気好気法を、汚泥処理系では嫌気性消化法を採用している。水処理系で発生した初沈汚泥５の一部と余剰汚泥６は、滞留時間約２時間の汚泥混合槽（図示せず）にて混合された後、遠心濃縮機２１において３０〜４０ｇ／リットル程度に濃縮される。汚泥濃縮装置である遠心濃縮機２１で分離された濃縮汚泥脱離液１０は、本発明法系列と対照系（２）では脱リン反応槽としてのＭＡＰ反応槽３１に導入され、対照系（１）では最初沈殿池１６に返流させる。濃縮汚泥７は全系列とも嫌気性消化槽２２に導入される。全系列とも嫌気性消化は中温３５℃で滞留時間は３０日とし、消化汚泥８は、スクリュープレス型の脱水機２３により脱水され脱水ケーキ９は系外に排出する。
【００２８】
脱水ろ液１１は、本発明法系列と対照系（２）ではＭＡＰ反応槽３１に導入し、対照系（１）では最初沈殿池１６に返流される。ＭＡＰ反応槽３１は滞留時間：７０分、添加マグネシウム源：水酸化マグネシウムとし、必要に応じて水酸化ナトリウム溶液を添加しｐＨを７．７に維持した。ＭＡＰ反応槽３１にて晶析したＭＡＰ粒子は回収し、ＭＡＰ反応槽流出水１２は本発明法系列では返流水貯留槽２３に導入し、対照系（２）では最初沈殿池１１に返送した。返流水貯留槽２３は、槽内を混合撹拌するゾーンと静置するゾーンに分割されており、両ゾーンの延べ平均滞留時間は７２時間とした。該槽２３には必要に応じて水処理系から初沈汚泥５の一部を導入し、ＭＡＰ反応槽流出水１２の一部をバイパス管３３によりバイパスさせることにより、初沈汚泥５の返流水貯留槽２３での滞留時間を最大１８０時間までコントロールすることを可能にした。本発明法系列の返流水貯留槽流出水１３は、全量最初沈殿池１１に返送した。
【００２９】
以下に、本実施例の運転結果について説明する。本発明法実験プラント、対照系プラント（１）及び（２）に対する３ヶ月間の運転結果を第１表に示す。
【００３０】
【表１】

【００３１】
返流水の水質としては、本発明法と対照系（２）は溶解性リンの約８０％をＭＡＰとして回収しているので、平均Ｔ−Ｐがそれぞれ３５ｍｇ／リットル、２７ｍｇ／リットルであるのに対して、対照系（１）では１４４ｍｇ／リットルである。また、平均溶解性ＢＯＤは、本発明法が１３５０ｍｇ／リットルであるのに対して、対照系（１）、（２）はそれぞれ５７０ｍｇ／リットル、３５０ｍｇ／リットルと、本発明法の半分以下であった。放流水中の平均Ｔ−Ｐ濃度は、対照系（１）：０．８３ｍｇ／リットル、対照系（２）：０．５７ｍｇ／リットルに対して本発明法０．２７ｍｇ／リットルと本発明法では大幅にリン濃度低減が可能であった。
【００３２】
本発明法の返流水中のリンが少なく、かつ溶解性ＢＯＤ成分が多い点が、水処理系の生物学的リン除去プロセスの処理効率を大幅に高める要因となったと考えられる。とりわけ、本発明法と対照系（２）とを比較した場合、本発明法では、実験開始後４５日前後と８３日前後において大雨が降った際に、初沈汚泥から返送汚泥貯留槽に導入する量を増加させる等の処置を行ったことが、非常に効果的であったと考えられる。
【００３３】
【発明の効果】
本発明によれば、以下の優れた効果が得られる。
（１）従来の生物学的リン除去システムでは、下水の場合、放流水のリン濃度を定常的に０．５ｍｇ／リットル以下にすることは困難であったが、本発明では可能になった。
（２）処理水リン濃度が減少できるとともに、リン回収が可能であり、環境負荷低減と資源回収とが両立する。
（３）既存の水処理システムに対して、リンの晶析装置と貯留槽を新たに設けるだけで、リン回収と効率的な生物学的リン除去を行えるため、従来プロセスを大幅に変更することなく、複雑なプロセスや運転管理を行う必要もなく、リン除去性能が大幅に向上する。
【図面の簡単な説明】
【図１】本発明の一実施例のフローチャートである。
【図２】比較例としての対照系（１）のフローチャートである。
【図３】比較例としての対照系（２）のフローチャートである。
【符号の説明】
１流入汚水
２最初沈殿池流出水
３生物反応槽流出水
４処理水
５沈殿汚泥
６余剰汚泥（返送汚泥）
７濃縮汚泥
８消化汚泥
９脱水ケーキ
１０濃縮汚泥脱離液
１１脱水ろ液
１２脱リン槽流出水
１３返流水貯留槽流出水
１６最初沈殿池
１７生物反応槽
１７ａ嫌気槽
１７ｂ好気槽
１８最終沈殿池
２１遠心濃縮機（汚泥濃縮装置）
２２嫌気性消化反応槽
２３汚泥脱水装置
３１脱リン反応槽
３２返流水貯留槽
３３バイパス管[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a system for treating organic sewage in a sewage treatment plant or various wastewater treatment facilities, and more specifically, concentrates anaerobic digestion on organic sludge generated in these organic sewage treatment systems, By returning the return water that is separated when the treatment such as dehydration is performed and returned to the water treatment system in a condition that considers the balance of the entire water treatment system, the amount of the discharged water discharged from the water treatment system is reduced. The present invention relates to a technique for stably reducing the phosphorus concentration.
[0002]
[Prior art]
A large amount of organic sludge is generated at treatment plants that treat organic sewage. In many cases, this sludge is processed through steps such as concentration, digestion, and dehydration as a reduction treatment, and the separated water separated from the sludge in these processes is usually returned to the water treatment system. In this case, as the weight reduction process, the SS amount of sludge such as concentration, dehydration, and drying is not mainly reduced, but the case of referring to the process of reducing the overall volume and the anaerobic digestion process of reducing the SS amount, It may refer to ozone treatment, heat treatment, ultrasonic treatment, and the like. This return water contains a high concentration of BOD, ammonia nitrogen, soluble phosphorus, etc., and there are few cases where the high concentration target substances in the return water deteriorate the treated water quality of the water treatment system. There is. Among the three substances BOD, nitrogen, and phosphorus, phosphorus is one of the substances whose control as a water quality control item is being strengthened in recent years.
[0003]
Conventionally, as a typical dephosphorization treatment method performed in a sewage treatment plant or the like, an anaerobic aerobic method as a biological treatment method, an agglomeration precipitation method as a physicochemical treatment method, or the like can be given. In the anaerobic aerobic method, there is a problem that the processing performance is not stable due to changes in the inflowing water quality and changes in the external environment such as seasonal fluctuations. There was a problem that the cost of chemicals such as chemicals made the running cost of the entire treatment plant excessive.
Until now, as a method of recovering phosphorus from the return water generated from the sludge treatment process, after recovering phosphorus and a part of ammonia nitrogen from the return water as magnesium ammonium phosphate particles, A treatment method for sludge treatment system return water has been proposed in which nitrification is carried out scientifically, raw sludge is added to the treated water, and denitrification is performed using BOD not related to the water treatment system (Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-104693
[Problems to be solved by the invention]
In particular, in the anaerobic aerobic method, it is necessary to take in soluble BOD into the microbial cells when releasing the phosphoric acid ingested excessively by the activated sludge microorganisms in the anaerobic tubs. The sex BOD is difficult to control because it depends on the quality of the incoming raw water and the return water which change from moment to moment. Therefore, it is difficult to obtain a sufficient soluble BOD necessary for releasing phosphoric acid, making it difficult to fully exert the phosphate intake ability by activated sludge in the aerobic tank. Finally, the phosphoric acid concentration in the discharged water is Many cases exceeded the target effluent quality.
[0006]
Therefore, it is necessary to develop a technique for improving the phosphorus treatment efficiency relatively easily so that the conventional problems in the water treatment system employing the biological phosphorus removal described above can be solved. The problem of the conventional biological phosphorus removal system, “instability of phosphorus removal treatment performance due to changes in the external environment such as changes in influent water quality and seasonal fluctuations” is required to be greatly improved.
[0007]
Further, the amount of organic matter in the return water greatly affects the processing performance of a nitrogen removal system such as a nitrification denitrification method in addition to affecting the processing performance of a phosphorus removal system such as an anaerobic aerobic method. For example, in the case of a water treatment facility that uses the anaerobic-anoxic-aerobic method, the amount of organic matter in the return water affects both denitrification and dephosphorization treatment performance, so the amount of organic matter that flows into the system is reduced. The stable supply was one of the important issues for realizing good simultaneous removal of phosphorus and nitrogen.
[0008]
[Means for Solving the Problems]
The present invention solves the above-described problems of the prior art. In short, the present invention removes or recovers phosphorus without removing organic matter as much as possible from the return water containing a large amount of soluble organic matter and soluble phosphorus separated by the sludge reduction process, and returns water after removing or recovering phosphorus. And a tank for temporarily storing at least one of the return water derived from the sludge after the recovery of the magnesium ammonium phosphate particles, and controlling the amount of the returned water actually returned to the water treatment system. Thus, the basic configuration is to improve the phosphorus removal efficiency by the anaerobic aerobic method in the water treatment system.
[0009]
That is, the present invention has solved the above problems by the following means.
(1) It includes a process of biologically removing organic phosphorus by biologically removing phosphorus, and a process of reducing generated sludge. In addition, from the return water separated from the reduced sludge in the sludge reduction process Organic wastewater treatment system comprising at least one of a step of removing or recovering phosphorus and a step of recovering magnesium ammonium phosphate particles generated in the anaerobic digestion step of sludge generated in the treatment step of organic wastewater In this case, at least one of the return water after removal or recovery of phosphorus and the return water separated from the sludge after recovery of magnesium ammonium phosphate particles is returned to the biological phosphorus removal step or in the process of returning it to the preceding stage. And a biological phosphorus removal step from the return water storage tank or the amount of organic matter in the return water flowing into the preceding stage is controlled. Processing method of the machine of sewage.
[0010]
(2) The organic as described in (1) above, which includes at least one of concentration treatment, anaerobic fermentation treatment, dehydration treatment, ozone treatment, ultrasonic treatment, and heat treatment as a sludge reduction step Of wastewater.
(3) At least one of the first settling basin sludge settled and separated in the first settling basin of the water treatment system process, the concentrated sludge generated in the sludge treatment system process, the anaerobic digested sludge, and the dewatered cake in the return water storage tank. Part or all of the organic sewage treatment method according to (1) or (2), wherein a part or the whole is introduced.
(4) As a method for controlling the amount of organic matter in the effluent of the storage tank flowing into the biological phosphorus removal step or the preceding stage from the return water storage tank, the amount of organic matter in the return water storage tank effluent and the treatment plant inflow water By measuring the amount of organic matter derived, the amount of organic matter flowing into the biological phosphorus removal process is grasped, and the obtained data is used as an explanatory variable for optimally controlling the biological phosphorus removal process. The organic sewage treatment method according to any one of (1) to (3), which is characterized in that it is characterized.
[0011]
(5) By measuring the phosphorus load in the effluent of the return water storage tank and the phosphorus load derived from the treatment plant inflow water, the phosphorus load flowing into the biological phosphorus removal process was grasped and obtained. By using the data as an explanatory variable for optimally controlling the biological phosphorus removal process, the phosphorus load on the biological phosphorus removal process from the return water storage tank or the storage tank effluent flowing into the preceding stage The method for treating organic sewage according to any one of (1) to (3), wherein the organic sewage is controlled.
(6) An anaerobic and aerobic product reaction tank that biologically removes phosphorus by treating organic sewage, and a device for reducing the amount of generated sludge. Organic containing at least one of a dephosphorization reaction tank for removing or recovering phosphorus from the return water separated by the solid-liquid separator and an apparatus for recovering magnesium ammonium phosphate particles generated in an anaerobic digester of sludge In the sewage treatment apparatus, at least one of the return water after phosphorus removal or recovery and the return water obtained by separating the sludge after recovery of magnesium ammonium phosphate particles with a solid-liquid separator is a biological phosphorus removal apparatus or In the return water storage tank provided with a means for controlling the amount of organic matter in the return water, which can be temporarily stored in the middle of returning to any part of the previous stage, and in the return water storage tank Piping for introducing at least one of sludge generated in the system and at least one piping for returning the returned water to the water treatment system line without going through the returned water storage tank An organic wastewater treatment apparatus characterized by comprising:
[0012]
The main point of the present invention is to remove or recover phosphorus without removing organic matter from the return water containing a large amount of soluble organic matter and soluble phosphorus separated by the sludge reduction process in order to solve the above problems. A tank for temporarily storing at least one of the returned water after removing or recovering the recovered phosphorus and the returned water after recovering the magnesium ammonium phosphate particles in connection with the anaerobic digestion process of sludge, This is a method for controlling the amount of organic matter that flows from the return water storage tank into the biological phosphorus removal step. By providing this return water storage tank, the return water storage tank stores a large amount of organic matter, particularly a readily degradable soluble BOD component, as a hydrogen donor required in the dephosphorization process of the water treatment system. Therefore, the dephosphorization process can be optimized by adjusting the amount of the return water storage tank effluent to be returned to the biological treatment system as necessary for the dephosphorization process of the water treatment system. it can. That is, the fact that there is little phosphorus in the return water and there are many soluble BOD components has the effect of greatly increasing the treatment efficiency of the biological phosphorus removal process of the water treatment system.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention and the operation thereof will be described in detail below with reference to the drawings. In addition, this invention is not limited to the following embodiment at all.
[0014]
In the flow shown in FIG. 1, the water treatment system employs an anaerobic aerobic method, and the sludge treatment system employs a flow comprising steps of concentration, anaerobic digestion, and dehydration. The inflowing sewage 1 precipitates and separates a part of the solids in the first settling tank 16, and the first settling tank outflow water 2 is sent to the anaerobic tank 17 a of the biological reaction tank 17. In the anaerobic tank 17a, activated sludge microorganisms release polyphosphoric acid in the microbial cells as phosphoric acid, and instead take in a soluble BOD component as a hydrogen donor. At this time, if there is not enough soluble BOD in the anaerobic tank 17a, the release of phosphoric acid becomes insufficient, and the amount of phosphoric acid intake of activated sludge in the aerobic tank 17b in the subsequent stage decreases, resulting in the final precipitation. The concentration of phosphoric acid remaining in the treated water 4 from the pond 18 will be increased. That is, it can be said that the amount of organic substances flowing into the anaerobic tank 17a, particularly the soluble BOD component, is one of the important factors affecting the phosphorus removal performance in the water treatment system.
[0015]
Of course, the water temperature, pH, ORP, etc. in the anaerobic tank 17a are also important factors, but within the scope of knowledge obtained so far by the present inventors, the largest factor governing the amount of released phosphorus is the soluble BOD component. There were particularly many cases. Nevertheless, in the conventional method, the means for controlling the amount of the soluble BOD component flowing into the anaerobic tank 17a is limited to the direct input of the first settling sludge 5 and the like. In addition, it was difficult to control finely soluble BOD corresponding to seasonal variations.
However, in the method of the present invention, the return water 13 having a high amount of soluble BOD stored in the return water storage tank 32 and having a low phosphorus concentration is returned to the first settling tank 16 and the anaerobic tank 17a according to the water quality fluctuation of the water treatment system. Therefore, it is possible to control the finely soluble BOD loading necessary for stable phosphorus removal treatment. The return water storage tank 32 and the return water storage tank outflow water 13 flowing out from the tank will be described below in detail.
[0016]
The liquid flowing into the return water storage tank 32 is basically separated water derived from the sludge treatment system. The concentrated sludge desorbed liquid 10 separated by the sludge concentration system 21 of the sludge treatment system and the dehydrated filtrate 11 separated by the dehydrator 23 are both introduced into the dephosphorization reaction tank 31. The dephosphorization reaction tank 31 is a reaction tank provided for removing or recovering soluble phosphorus from a liquid. By adding a flocculant such as PAC or polyiron, phosphoric acid is converted into aluminum phosphate or iron phosphate. Separating and recovering phosphorus by solid-liquid separation as an insoluble salt such as, or by precipitating magnesium ammonium phosphate (hereinafter also referred to as “MAP”) or calcium phosphate by supplying an alkali agent and a magnesium source or calcium source And the like. Depending on the quality of the influent sewage and the water treatment system and sludge treatment system, it is necessary to select a phosphorus removal / recovery method that suits the suitability, and if necessary, use a combination of these phosphorus removal / recovery methods. Also good.
[0017]
The dephosphorization method is selected by taking the processing flow shown in FIG. 1 as an example. Since there is an anaerobic digestion reaction tank 22 in front of the dehydrator 23, the dehydrated filtrate 11 contains a large amount of phosphoric acid, ammonia ions, M alkali components, and the like. An example of a phosphorus removal / recovery method that effectively uses these components is the MAP method. Phosphoric acid in the liquid is obtained by adding a magnesium source and, if necessary, an alkaline agent to the dehydrated filtrate 11 or a mixture of the dehydrated filtrate 11 and the concentrated sludge desorbed liquid 10 and crystallization and granulation. And some of the ammonia ions can be recovered as MAP. In the MAP crystallization reaction, the pH in the tank is set slightly lower than the conventional MAP crystallization method pH of about 7.3 to 8.2, so that the precipitated MAP particles are almost free of organic SS components. It is also possible to granulate into high-purity MAP particles not contained. In short, the amount of organic matter in the dephosphorization tank effluent 13 after MAP is recovered in the dephosphorization reaction tank 31 can be made to be substantially the same as the amount of organic matter in the inflow water of the dephosphorization reaction tank 31. .
[0018]
The dephosphorization tank effluent 12 is returned to the first settling tank 11 and / or the anaerobic tank 17a as the return water storage tank effluent 13 after a residence time of several hours to several days in the return water storage tank 32. The return water storage tank 32 may have a function of mixing and stirring the inside of the tank and a function of collecting precipitates. The return water temporarily stored in the return water storage tank 32 is returned to the water treatment system in accordance with the daily fluctuation, weather fluctuation, and seasonal fluctuation of the incoming sewage 1. For example, when it rains, by returning a relatively large amount of the return water storage tank effluent 13 to the water treatment system, inflow sewage diluted before rain or before the first flush when the inflow water amount increases rapidly. When 1 flows in, a soluble BOD component can be replenished to the anaerobic tank 12a at any time to increase the phosphate release rate.
[0019]
Further, in the method of the present invention, since it is possible to introduce a part of the initial settling sludge 5 into the return water storage tank 32, the initial settling sludge 5 is introduced into the return water storage tank 32 depending on the situation, It is also possible to promote acid fermentation of sludge in the tank and produce more soluble BOD components.
In general, when acid fermentation is performed on the primary sedimentation sludge alone, the organic acid concentration often reaches a maximum in about 3 days due to consumption of alkaline components in the solution, but this is one flow of the present invention. In the case of the flow 1, the water flowing into the return water storage tank 32 is derived from the dehydrated filtrate of the anaerobic digested sludge and the M alkaline component is added from the point that the alkaline agent is added in the dephosphorization reaction tank 31. It is possible to greatly promote the acid fermentation of the first settling sludge 5 introduced into the return water storage tank 32.
[0020]
Further, in order to adjust the residence time of the introduced initial settling sludge 5 in the return water storage tank 32, a part of the dephosphorization tank effluent 12 is not directly introduced into the return water storage tank 32 through the bypass pipe 33. It may be returned to the water treatment system. The bypass pipe 33 can control the substantial residence time in the return water storage tank 32 by using it appropriately even when the initial settling sludge 5 is not introduced into the return water storage tank 32.
[0021]
Moreover, in order to prevent the organic acid etc. which were produced | generated by acid fermentation from being consumed by methane fermentation bacteria and a sulfate reduction bacterium, the inside of the return water storage tank 32 can be aerated, or the organic in the tank 32 can be aerated. It is also effective to monitor and control the acid generation environment by ORP. Moreover, since it is possible to accelerate | stimulate organic-acid production | generation reaction by heating the return water storage tank 32, when waste heat remains in a processing place etc., this heating process and a heat source are used, and a heat source A method of heating the return water storage tank 32 to about 30 to 55 ° C. according to the amount is effective. Even when the residence time of the initial settling sludge 5 in the tank 32 is set to 7 days or longer by such a method, the concentration level of the free organic acid and free ammonia in the tank 32 is the organic acid generation reaction. It has been confirmed by the experimental data of the present inventors that the level of inhibition is hardly reached.
[0022]
In addition, when designing a process that emphasizes phosphorus recovery rather than phosphorus removal, the method for recovering phosphorus from organic waste water disclosed in JP 2000-231633 A, JP 2002-116357 A, etc. is incorporated into the method of the present invention. This makes it possible to simultaneously perform high-efficiency phosphorus removal from waste water in the water treatment system and high-efficiency phosphorus recovery in the sludge treatment system. That is, by supplying a magnesium source to the anaerobic digestion reaction tank 22 as needed, the MAP crystallization reaction in the tank 22 is promoted, and the MAP particles generated in the digested sludge are converted into MAP such as a liquid cyclone or a vibrating sieve. In the conventional method, a dehydrated cake is removed by adopting a method in which a part of sludge separated and recovered by a separator and removed from MAP particles is returned to the tank 22 and the remaining sludge is dehydrated by a sludge dewaterer 23. Most of the MAP mixed in a large amount can be recovered in the form of MAP particles. In addition, the MAP particles have a particle size of 300 μm or more, often have good sedimentation properties and excellent solid-liquid separation properties. By using seed crystals that flow in the subsequent dephosphorization reaction tank 31, the tank 31 Can efficiently recover phosphorus. By performing phosphorus recovery by this method, even if the dephosphorization reaction tank 31 is omitted, the biological phosphorus removal performance in the water treatment system may be sufficiently exhibited.
[0023]
As described above, the return water storage tank 32 is in an environment in which a large amount of organic matter, particularly a readily degradable soluble BOD component, required as a hydrogen donor in the dephosphorization process of the water treatment system is stored. Therefore, the dephosphorization process can be optimized by adjusting the return water storage tank outflow water 13 as required by the water treatment system. When it is necessary to control the dephosphorization process more accurately, the organic matter amount and phosphorus concentration in the influent sewage and return water storage tank effluent are constantly or appropriately measured, and the total organic matter load flowing into the dephosphorization process is measured. More efficient dephosphorization process by grasping the amount and phosphorus load, and controlling the flow rate of the return water storage tank effluent 13 and the introduction amount of the return water storage tank 32 of the first settling sludge 5 based on these data Can be operated.
[0024]
In addition, the above-described technique relating to “control of the amount of organic matter in the return water for improving the efficiency of the dephosphorization system” can naturally be applied to a denitrification system of a water treatment system. That is, even in the denitrification process, the amount of the soluble BOD component in the return water is a factor that greatly affects the performance of the process as a hydrogen donor essential for the denitrification process. For this reason, when water is returned to a water treatment system that employs a combination of biological dephosphorization and biological denitrification, and a system that returns the water is used, denitrification and dephosphorization are required. It is also effective to control the flow rate of the return water storage tank outflow water 13 and the amount of the return water storage tank 32 introduced into the first settling sludge 5 in consideration of both.
[0025]
【Example】
The present invention will be specifically described with reference to examples. In addition, this invention is not restrict | limited at all by the following examples.
[0026]
Example 1
The operating conditions of the experimental plant according to the present invention in the treatment plant A adopting the flow shown in FIG. 1 described above will be described. In addition, in order to make it easy to evaluate the invention effect of the present embodiment, the control system plants (1) and (2) of the same scale as the experimental plant of the present invention in the A treatment plant as the control system (see FIGS. 2 and 3). ) And the three trains were operated for 3 months.
[0027]
As shown in FIG. 1, the three systems employ an anaerobic aerobic method for the water treatment system and an anaerobic digestion method for the sludge treatment system. A part of the first settling sludge 5 generated in the water treatment system and the excess sludge 6 are mixed in a sludge mixing tank (not shown) having a residence time of about 2 hours, and then 30 to 40 g / liter in the centrifugal concentrator 21. Concentrated to a degree. The concentrated sludge detachment liquid 10 separated by the centrifugal concentrator 21 as a sludge concentrator is introduced into the MAP reaction tank 31 as a dephosphorization reaction tank in the method series of the present invention and the control system (2), and the control system (1 ) First return to the settling basin 16. The concentrated sludge 7 is introduced into the anaerobic digester 22 in all series. In all series, the anaerobic digestion has an intermediate temperature of 35 ° C. and a residence time of 30 days. The digested sludge 8 is dehydrated by the screw press type dehydrator 23 and the dehydrated cake 9 is discharged out of the system.
[0028]
The dehydrated filtrate 11 is introduced into the MAP reaction tank 31 in the method series of the present invention and the control system (2), and is first returned to the settling tank 16 in the control system (1). The MAP reaction tank 31 had a residence time of 70 minutes, an added magnesium source: magnesium hydroxide, and a sodium hydroxide solution was added as necessary to maintain the pH at 7.7. The MAP particles crystallized in the MAP reaction tank 31 were collected, and the MAP reaction tank effluent 12 was introduced into the return water storage tank 23 in the method of the present invention, and was first returned to the settling tank 11 in the control system (2). The return water storage tank 23 is divided into a zone for mixing and stirring the inside of the tank and a zone for standing, and the total average residence time of both zones is 72 hours. If necessary, a part of the first settling sludge 5 is introduced into the tank 23 from the water treatment system, and a part of the MAP reaction tank effluent 12 is bypassed by the bypass pipe 33, thereby returning the return water of the first settling sludge 5. The residence time in the storage tank 23 can be controlled up to a maximum of 180 hours. The total amount of the return water storage tank effluent 13 of the method series of the present invention was returned to the first sedimentation tank 11.
[0029]
Below, the driving | running result of a present Example is demonstrated. Table 1 shows the operation results for three months for the experimental plant of the present invention and the control plant (1) and (2).
[0030]
[Table 1]

[0031]
As for the quality of the return water, the method of the present invention and the control system (2) collect about 80% of the soluble phosphorus as MAP, so the average TP is 35 mg / liter and 27 mg / liter respectively. In contrast, in the control system (1), it is 144 mg / liter. The average solubility BOD was 1350 mg / liter for the method of the present invention, whereas the control systems (1) and (2) were 570 mg / liter and 350 mg / liter, respectively, which were less than half of the method of the present invention. It was. The average TP concentration in the effluent water is 0.27 mg / liter of the present invention compared to the control system (1): 0.83 mg / liter and the control system (2): 0.57 mg / liter. In addition, the phosphorus concentration could be reduced.
[0032]
The fact that the amount of phosphorus in the return water and the amount of soluble BOD component in the method of the present invention is large is considered to be a factor for greatly increasing the treatment efficiency of the biological phosphorus removal process of the water treatment system. In particular, when the method of the present invention is compared with the control system (2), the method of the present invention introduces the first settling sludge into the return sludge storage tank when heavy rain falls around 45 days and 83 days after the start of the experiment. It was thought that it was very effective to take measures such as increasing the amount to be used.
[0033]
【The invention's effect】
According to the present invention, the following excellent effects can be obtained.
(1) In the conventional biological phosphorus removal system, in the case of sewage, it has been difficult to steadily reduce the phosphorus concentration of the effluent water to 0.5 mg / liter or less, but this is possible in the present invention.
(2) The concentration of phosphorus in the treated water can be reduced, and phosphorus can be recovered, and both environmental load reduction and resource recovery are compatible.
(3) Compared to existing water treatment system, it is possible to recover phosphorus and efficiently remove biological phosphorus by simply installing a new phosphorus crystallizer and storage tank. In addition, there is no need to perform complicated processes and operation management, and the phosphorus removal performance is greatly improved.
[Brief description of the drawings]
FIG. 1 is a flowchart of an embodiment of the present invention.
FIG. 2 is a flowchart of a control system (1) as a comparative example.
FIG. 3 is a flowchart of a control system (2) as a comparative example.
[Explanation of symbols]
1 Influent sewage 2 First sedimentation basin effluent 3 Biological reactor effluent 4 Treated water 5 Precipitated sludge 6 Surplus sludge (returned sludge)
7 Concentrated sludge 8 Digested sludge 9 Dehydrated cake 10 Concentrated sludge desorption liquid 11 Dehydrated filtrate 12 Dephosphorization tank effluent 13 Return water storage tank effluent 16 First sedimentation tank 17 Biological reaction tank 17a Anaerobic tank 17b Aerobic tank 18 Final sedimentation Pond 21 Centrifugal Concentrator (Sludge Concentrator)
22 Anaerobic digestion reaction tank 23 Sludge dewatering device 31 Dephosphorization reaction tank 32 Return water storage tank 33 Bypass pipe

Claims

It includes a step of biologically removing phosphorus by treating organic sludge and a step of reducing the amount of produced sludge. In addition, it removes phosphorus from the return water separated from the reduced sludge in the sludge reduction step. Or in an organic sewage treatment system comprising at least one of a step of collecting and a step of collecting magnesium ammonium phosphate particles generated in an anaerobic digestion step of sludge generated in the treatment step of organic sewage, At least one of the return water after the removal or recovery and the return water separated from the sludge after the recovery of the magnesium ammonium phosphate particles is stored in the biological phosphorus removal step or in the process of returning it to the preceding stage. Organicity characterized by providing a tank and controlling the amount of organic matter in the return water to be introduced from the return water storage tank into the biological phosphorus removal step or the preceding stage Processing method of the water.

The treatment of organic sewage according to claim 1, comprising at least one of concentration treatment, anaerobic fermentation treatment, dehydration treatment, ozone treatment, ultrasonic treatment, and heat treatment as a sludge reduction step. Method.

A part of at least one of the first sedimentation basin sludge settled and separated in the first sedimentation basin of the water treatment system process, the concentrated sludge generated in the sludge treatment system process, the anaerobic digested sludge, and the dewatered cake in the return water storage tank or The method for treating organic sewage according to claim 1 or 2, wherein the whole is introduced.

As a method of controlling the amount of organic matter in the effluent of the storage tank flowing into the biological phosphorus removal step or the preceding stage from the return water storage tank, the amount of organic matter in the effluent of the return water storage tank and the organic matter derived from the treatment plant inflow water By measuring the amount, the amount of organic matter flowing into the biological phosphorus removal process is grasped, and the obtained data is used as an explanatory variable for optimal control of the biological phosphorus removal process. The processing method of the organic waste water of any one of Claims 1-3.

By measuring the phosphorus load in the return water storage tank effluent and the phosphorus load derived from the treatment plant inflow water, the phosphorus load flowing into the biological phosphorus removal process is ascertained, and the obtained data is By using an explanatory variable for optimal control of the biological phosphorus removal process, the phosphorus load amount is controlled for the biological phosphorus removal process from the return water storage tank or the storage tank effluent flowing into the preceding stage. The method for treating organic sewage according to any one of claims 1 to 3, wherein:

It has an anaerobic and aerobic product reaction tank that biologically removes phosphorus by treating organic sewage, and a device that reduces the generated sludge, and further reduces the sludge reduced sludge by solid-liquid separation. Treatment of organic sewage including at least one of a dephosphorization reaction tank for removing or recovering phosphorus from the return water separated by the apparatus, and an apparatus for recovering magnesium ammonium phosphate particles generated in the anaerobic digester of sludge In the apparatus, at least one of the return water after removal or recovery of phosphorus and the return water obtained by separating the sludge after recovery of magnesium ammonium phosphate particles by a solid-liquid separator is used as a biological phosphorus removal apparatus or a preceding stage. The return water storage tank, which is temporarily stored in the middle of returning to any location and can be temporarily stored, has a means for controlling the amount of organic matter in the return water, and the return water storage tank. Piping for introducing at least one of the sludge generated in the system, and at least one piping for returning the return water to the water treatment system line without going through the return water storage tank An organic wastewater treatment apparatus characterized by comprising: