JP2004025051A

JP2004025051A - Organic wastewater treatment method and organic wastewater treatment apparatus

Info

Publication number: JP2004025051A
Application number: JP2002186042A
Authority: JP
Inventors: Yasuhiko Nagamori; 永森　泰彦; Kyotaro Iyasu; 居安　巨太郎; Seiichiro Sano; 佐野　誠一郎; Koji Akimoto; 秋本　弘司
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2002-06-26
Filing date: 2002-06-26
Publication date: 2004-01-29

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic waste water treatment method and an organic waste water treatment apparatus which can generate more biogas by anaerobic methane fermentation, can reduce the nitrogen concentration in an organic wastewater to an effluent standard, and stably and can efficiently perform these operations. <P>SOLUTION: The concentration of organic substances in a water to be treated is judged. If the concentration of the organic substances is equal to or higher than a set concentration, the water to be treated is subjected to the anaerobic methane fermentation to efficiently generate a large volume of the biogas. If the concentration of the organic substances is below the set concentration, the water to be treated is subjected, together with a digestive liquid, to aerobic treatment, thereby obtaining the organic substances required for denitrification. As a result, the concentration of nitrogen in the treated water can be stably and efficiently reduced to the effluent standard by the aerobic treatment. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、被処理水を嫌気性メタン発酵処理し、処理後の消化液を活性汚泥法に基づく好気性処理する有機性廃水処理方法及び有機性廃水処理装置に関する。
【０００２】
【従来の技術】
畜産産業や食品産業等から排出される有機性廃水の処理方法として、嫌気性メタン発酵処理が知られて入る。嫌気性メタン発酵処理とは、嫌気性微生物の代謝反応を利用して液状又は固形状の有機物を分解し、メタンを主成分とするバイオガスを生成する反応である。嫌気性メタン発酵処理は、好気性処理と比較して曝気が不要なため運転動力費用が安価である。また、生成したメタンは各種発電設備の燃料として使用でき、電気を生産することができる。
【０００３】
しかし、嫌気性メタン発酵処理のみでは有機性廃水を、河川などに放流できる水質までに浄化することができない。このため、嫌気性メタン発酵処理後の消化液を、排水処理設備において活性汚泥法に基づく好気性排水処理を行ない、放流基準を満足する水質まで浄化した後、河川に放流している。この嫌気性メタン発酵と活性汚泥法に基づく好気性処理との組合わせによる有機性廃水処理プロセスは、すべてを好気性廃水処理で処理するよりも安価であり、例えば、特開２００１−３２１７９２により提案されている。
【０００４】
また、嫌気性メタン発酵と発電設備と好気性廃水処理とを組合わせたバイオガス発電システムは、比較的安価に有機性廃水を放流基準に適合する水質まで浄化し、温室効果ガスの一つであるメタンの大気放出を行なわず、利用価値の高い電気を生産するため、環境問題とエネルギー問題との両面で利点がある。
【０００５】
このようなバイオガス発電システムに適用される嫌気性メタン発酵処理と活性汚泥法に基づく好気性排水処理とによる有機性廃水処理プロセスでは、まず、畜産産業や食品産業等から排出された有機性廃水を、スクリーンにより夾雑物を除去して原水受入槽に受入れ、原水貯留槽に移送する。
【０００６】
原水貯留槽に貯留された有機物廃水は、計画的に所定量がメタン発酵槽に移送される。メタン発酵槽では嫌気性メタン発酵反応に基づき有機性廃水中の有機物がバイオガスへと変換される。このようにして生成されたバイオガスは脱硫器で硫化物を除去され、発電設備に送られ、発電に供される。
【０００７】
メタン発酵後に、メタン発酵槽から排出された消化液は消化液貯留槽に貯留される。消化液貯留槽に貯留された消化液は、計画的に所定量が排水処理槽に移送され、この排水処理槽にて攪拌曝気され、活性汚泥法による好気性処理により浄化される。
【０００８】
好気性処理後の処理水は凝集沈殿槽にて凝集沈澱処理された後、上澄水は放流水路を経て河川へと放流される。凝集沈殿槽から河川へ放流されるまでの間に、塩素による消毒や高度処理などが施されることもある。
【０００９】
好気性処理における凝集沈殿で発生した余剰汚泥は汚泥貯留槽に引き抜かれる。汚泥貯留槽に貯留された余剰汚泥は、脱水装置により計画的に所要量が脱水され、脱水汚泥は汚泥処理設備に移送される。
【００１０】
このような有機性廃水処理プロセスをバイオガス発電システムに適用した場合、メタン発酵槽で生成されるバイオガスは発電のエネルギーになるため、多くのバイオガスを生成することが望まれる。そのためには有機性廃水中の有機物を多くバイオガスに変換する必要がある。
【００１１】
しかし、畜産産業や食品産業から放出される有機性廃水の有機物濃度は一定ではなく、時間変動が激しい。嫌気性メタン発酵における最適有機物負荷は、メタン発酵槽の仕様により異なるが、有機物負荷が増加すると有機酸の過剰生成をきたし、メタン発酵菌の増殖を阻害して異常状態になる。逆に負荷が低すぎてもメタン発酵が阻害される。すなわち、有機性廃棄物の有機物濃度が大きく変動すると、結果として生成されるバイオガス量が低下する。
【００１２】
また、有機性廃水処理プロセスでは、有機性排水を放流基準を満足する水質まで浄化することが求められている。放流基準は従来からのｐＨ，ＢＯＤ，ＣＯＤ，ＳＳに加えて、窒素、リンについても基準が設けられつつある。
【００１３】
窒素除去については、生物学的窒素除去法として、硝化・脱窒法がある。硝化・脱窒法は、好気性雰囲気において、まず、硝化菌によりアンモニア性窒素を亜硝酸性窒素に酸化し（式１）、続いて硝酸性窒素に酸化する（式２）。
【化１】

この後、無酸素雰囲気において脱窒菌によって硝酸性窒素を窒素ガスへと還元する（式３）。これにより廃水中の窒素を除去する。脱窒反応によって生成した酸素は、有機物の酸化に用いられる（式４）。
【化２】

上記（式３）（式４）の反応を進行させるためにはある程度の有機物量が必要であるといわれている。例えば、硝酸性窒素１ｇを還元するには２．８６ｇのＢＯＤに相当する有機物量が必要であるといわれている。
【００１４】
ところが、有機性プロセスでは、嫌気性メタン発酵処理において多くのバイオガスを得ようとすると、有機性廃水中の多くの有機物を除去することとなる。このため脱窒反応に必要な有機物が不足し、放流基準を満足するまでに有機性廃水中の窒素を除去できなくなる。
【００１５】
【発明が解決しようとする課題】
このように、従来の有機性廃水処理システムでは、有機物濃度が大きく変動する場合にメタン発酵処理に阻害要因が生じ、バイオガス発生量が低下する。また、有機性廃水中の窒素を、放流基準を満足するまで除去できないという問題があった。
【００１６】
本発明の目的は、嫌気性メタン発酵により多くのバイオガスを生成でき、かつ有機性廃水中の窒素濃度を放流基準まで低減でき、しかも、これらを安定的に効率よく行なうことができる有機性廃水処理方法及び有機性廃水処理装置を提供することにある。
【００１７】
【課題を解決するための手段】
本発明による有機性廃水処理方法は、被処理水を嫌気性メタン発酵処理し、処理後の消化液を活性汚泥法に基づく好気性処理する方法であって、前記被処理水の有機物濃度が、設定濃度以上であれば嫌気性メタン発酵処理を行い、前記設定濃度に達しない場合は前記消化液と共に好気性処理することを特徴とする。
【００１８】
本発明による有機性廃水処理装置は、嫌気性メタン発酵処理を行なうメタン発酵槽と、活性汚泥法に基づく好気性処理を行なう排水処理槽とを組合わせたもので、被処理水を貯留する原水貯留槽と、前記メタン発酵槽によって処理され、排水処理槽に供給される消化液を一旦貯留する消化液貯留槽と、前記原水貯留槽に貯留された被処理水を、前記メタン発酵槽に供給する第１の供給路及び前記消化液貯留槽に供給する第２の供給路と、前記原水貯留槽に貯留された被処理水の有機物濃度が設定濃度以上かを判別し、設定濃度以上であれば第１の供給路により被処理水をメタン発酵槽に供給させ、設定濃度に達していない場合は第２の供給路によって消化液貯留槽に供給させる制御装置とを備えたことを特徴とする。
【００１９】
本発明では、制御装置は、被処理水の受入時刻と有機物濃度との関係を予め把握しており、有機物濃度が設定濃度以上になる時刻に受入れた被処理水は第１の供給路によりメタン発酵槽に供給させ、それ以外の時刻に受入れた被処理水は第２の供給路により消化液処理槽に供給させる。
【００２０】
また、本発明では、制御装置は、被処理水の単位時間当たりの受入量と有機物濃度との関係を予め把握しており、単位時間当たりの受入量が設定量以上のときの被処理水は第１の供給路によりメタン発酵槽に供給させ、それ以外の被処理水は第２の供給路により消化液処理槽に供給させる。
【００２１】
また、本発明では、制御装置は、被処理水のアンモニアイオン濃度を測定するアンモニア計を有し、測定されたアンモニア濃度に基づいて有機物濃度を演算する。
【００２２】
さらに、本発明では、制御装置は、被処理水の導電率を測定する導電率計を有し、測定された導電率に基づいて有機物濃度を演算する。
【００２３】
これらの発明では、被処理水の有機物濃度を判断し、これが設定濃度以上であれば嫌気性メタン発酵処理を行い、効率的に多くのバイオガスを発生させる。また、設定濃度に達しない場合は、消化液と共に好気性処理することにより、脱窒に必要な有機物を確保するので、好気性処理により処理水の窒素濃度を放流基準まで安定的に効率よく低減することができる。
【００２４】
【発明の実施の形態】
以下、本発明による有機性廃水処理方法及び有機性廃水処理装置の一実施の形態を図面を参照して説明する。
【００２５】
図１はこの実施の形態の全体構成を示している。図１において、図示しない畜産産業や食品産業等から排出された有機性廃水は、スクリーン１１により夾雑物が除去され、原水受入槽１２に受入られ、ポンプ１３によりスクリーン１４を介して、原水貯留槽１５に移送される。
【００２６】
原水貯留槽１５に貯留された有機性廃水（被処理水）は、ポンプ１６を有する第１の供給路１７によって、計画的に所定量がメタン発酵槽１８に移送される。メタン発酵槽１８では嫌気性メタン発酵反応に基づき有機性廃水中の有機物がバイオガスへと変換される。このようにして生成されたバイオガスは脱硫器１９で硫化物を除去され、燃料電池等の発電設備に送られ、発電に供される。
【００２７】
メタン発酵後に、メタン発酵槽１８から排出された消化液は消化液貯留槽２０に貯留される。この消化液貯留槽２０には、原水貯留槽１５に貯留された有機性廃水が、ポンプ２１を有する第２の供給路２２によって供給される。有機性廃水が消化液貯留槽２０に供給される理由は後述する。
【００２８】
消化液貯留槽２０に貯留された消化液は、ポンプ２３を有する供給路２４により、計画的に所定量が排水処理槽２５に移送され、排水処理槽２５にて攪拌曝気され、活性汚泥法による好気性処理により浄化される。ここでは、排水処理槽２５として回分式のものを用いており、ブロア２６を有する曝気管２７による攪拌曝気と沈降分離とを異なる時刻毎に繰り返す。
【００２９】
好気性処理後の処理水は凝集沈殿槽２８に移送され、ここでポンプ２９により凝集剤タンク３０から供給される凝集剤が加えられ、凝集沈澱処理された後、上澄水は放流水路３１を経て河川へと放流される。凝集沈殿槽２８から河川へ放流されるまでの間に、塩素による消毒や高度処理などが施されることもある。
【００３０】
好気性処理により、排水処理槽２５や凝集沈殿槽２８で発生した余剰汚泥は、ポンプ３２，３３で汚泥貯留槽３４に引き抜かれる。汚泥貯留槽３４に貯留された余剰汚泥は、ポンプ３５によって脱水装置３６に移送され、脱水装置３６で計画的に所要量が脱水される。
【００３１】
脱水装置３６で生じた脱水汚泥はポンプ３７によって汚泥処理設備に移送され、脱離液はポンプ３８によって消化液貯留槽２０に移送される。
【００３２】
本発明では、原水貯留槽１５に貯留された被処理水を、メタン発酵槽に供給する第１の供給路１７及び消化液貯留槽２０に供給する第２の供給路２２を持っており、これらによる被処理水の供給は、制御装置４０によって制御される。
【００３３】
制御装置４０は、原水貯留槽１５に貯留された被処理水の有機物濃度が設定濃度以上かを判別し、設定濃度以上であれば、第１の供給路１７により被処理水をメタン発酵槽１８に供給させる。一方、設定濃度に達していない場合は、第２の供給路２２により被処理水を消化液貯留槽２０に供給させる。
【００３４】
上記設定濃度とは、メタン発酵槽１８の仕様によって定まるもので、嫌気性メタン発酵処理の最適有機物負荷を満足する有機物濃度を指す。
【００３５】
上記構成において、制御装置４０は、原水貯留槽１５内の被処理水の有機物濃度を判断し、有機物濃度が設定濃度異常であればポンプ１６を動作させ、被処理水を第１の供給路１７によってメタン発酵槽１８に送水する。これに対し、設定濃度に達していなければ、ポンプ２１を動作させ、第２の供給路２２によって被処理水を消化液貯留槽２０に送水する。
【００３６】
この動作により、メタン発酵槽１８の有機物負荷を低減させる要因であった低濃度の廃水がメタン発酵槽１８に投入されなくなる。このため、メタン発酵槽１８における有機物負荷が最適範囲に保持され、低有機物負荷によるメタン発酵の阻害が発生せず、嫌気性メタン発酵処理を安定的に効率よく実施できる。その結果、多くのバイオガスが生成され有機物除去率が向上する。
【００３７】
また、メタン発酵槽１８に流入する有機性廃水量が、消化液貯留槽２５に送水した水量分だけ減少するので、メタン発酵槽１８の容積を小さくすることができる。この結果、建設費用と運転動力費用が低減され、投資費用に対する生産効率が向上する。
【００３８】
さらに、設定濃度に達しない被処理水を消化液貯留槽２０に送水しているので、嫌気性メタン発酵で有機物が除去されていない廃水が消化液貯留槽２０に供給されることになる。このため、メタン発酵槽１８から排出された消化液の有機物濃度が過剰に低くても、第２の供給路２２によって有機物が除去されていない比較的低濃度の廃水（被処理水）が直接供給されるため、後段の排水処理槽１８での好気性排水処理において、窒素除去に必要な有機物量を確保できる。この結果、好気性排水処理における窒素除去性能が向上し、窒素濃度を放流基準まで低下させることができる。
【００３９】
上記内容をシミュレーション結果に基づき定量的に説明する。ここでは、有機物濃度が設定濃度以上の被処理水７５ｍ^３、設定濃度に達しない被処理水が２５ｍ^３である有機性廃水にてシミュレーションを行なった。図６に上記実施の形態による結果を、図７に従来方法による結果を示す。
【００４０】
図６及び図７において、設定濃度以上の廃水の平均ＢＯＤ（生物学的酸素要求量）は２５０００ｇ／ｍ^３、設定濃度に達しない廃水の平均ＢＯＤは５０００ｇ／ｍ^３とする。同じく、Ｔ−Ｎ（前窒素）は前者が３７５０ｇ／ｍ^３、後者が７５０ｇ／ｍ^３とする。また、原水貯留槽１５に流入する有機性廃水は合計で１００ｍ^３、その平均ＢＯＤは２００００ｇ／ｍ^３、平均Ｔ−Ｎは３０００ｇ／ｍ^３であった。
【００４１】
図６で示す上記実施の形態では、ＢＯＤ：２５０００ｇ／ｍ^３、Ｔ−Ｎ：３７５０ｇ／ｍ^３の被処理水７５ｍ^３はメタン発酵槽１８に流入し、嫌気性メタン発酵処理される。処理後のメタン発酵槽から排水された消化液のＢＯＤは４７５０ｇ／ｍ^３、Ｔ−Ｎは１８７５ｇ／ｍ^３となり、ＢＯＤ除去率は８１％、Ｔ−Ｎ除去率は５０％となる。
【００４２】
一方、ＢＯＤ：５０００ｇ／ｍ^３、Ｔ−Ｎ：７５０ｇ／ｍ^３の被処理水２５ｍ^３は消化液貯留槽２０に流入し、メタン発酵槽１８から排出された消化液（ＢＯＤ：４７５０ｇ／ｍ^３、Ｔ−Ｎ：１８７５ｇ／ｍ^３、水量７５ｍ^３）と混合され、ＢＯＤ：４８１３ｇ／ｍ^３、Ｔ−Ｎ：１５９４ｇ／ｍ^３、水量１００ｍ^３の被処理水になる。このように消化液貯留槽２０で混合された被処理水が排水処理槽２５供給にされ、好気性処理される。
【００４３】
これらの結果、バイオガス転換ＢＯＤ量は次式から１５１９ｋｇとなる。
【００４４】
７５ｍ^３×２５０００ｇ／ｍ^３×８１％＝１５１９ｋｇ
また、ＢＯＤ／Ｔ−Ｎ比は、好気性処理において窒素除去に必要な値２．８６を超えて３．０２となった。
【００４５】
これに対し従来方法では、図７で示すように、平均ＢＯＤ：２００００ｇ／ｍ^３、平均Ｔ−Ｎ：３０００ｇ／ｍ^３の有機性廃水１００ｍ^３がそのまま、メタン発酵槽１８に流入する。処理後にメタン発酵槽１８から排水された消化液のＢＯＤは５０００ｇ／ｍ^３、Ｔ−Ｎは１８００ｇ／ｍ^３となり、ＢＯＤ除去率は７５％、Ｔ−Ｎ除去率は４０％となる。そして、この消化液がそのまま排水処理槽２５供給され、好気性処理される。
【００４６】
これらの結果、バイオガス転換ＢＯＤ量は１５００ｋｇとなり、ＢＯＤ／Ｔ−Ｎ比は、窒素除去に必要な値２．８６に達せず２．７８となった。
【００４７】
このように、上記一実施の形態によれば、従来例に比べて、多くのバイオガス転換ＢＯＤ量が得られ、かつ好気性処理における窒素除去に必要なＢＯＤ／Ｔ−Ｎ比を充分にクリアする。したがって、嫌気性メタン発酵により多くのバイオガスを生成でき、かつ有機性廃水中の窒素濃度を放流基準まで低減できる。
【００４８】
次に、図２で示す実施の形態を説明する。この実施の形態では、制御装置４０において、被処理水の有機物濃度を判断するための手法として被処理水の受入時刻と有機物濃度との関係を利用している。すなわち、畜産産業や食品産業から排出され、原水受入槽１２に受け入れられる原水の有機物濃度は時刻によって大きく変動するが、この特性を逆に利用し、予め有機物濃度と時刻との関係を把握しておく。
【００４９】
そして、時刻―有機物濃度設定表４１をテーブルとして作成し、有機物濃度が設定濃度以上になる時刻に受入れた被処理水は、メタン発酵槽送水量演算手段４２の指令により第１の供給路１７を通してメタン発酵槽１８に送水する。また、それ以外の時刻に受入れた被処理水は、消化液貯留槽送水量演算手段４３の指令により、第２の供給路２２を通して消化液処理槽２０に送水する。
【００５０】
次に、図３で示す実施の形態を説明する。この実施の形態では、制御装置４０において、被処理水の有機物濃度を判断するための手法として被処理水の受入水量と有機物濃度との関係を利用している。すなわち、畜産産業や食品産業から排出され、原水受入槽１２に受け入れられる原水は、時刻によって水量が大きく変動する。通常、受入水量が多いときは有機物濃度が高いことが知られている。特に水量が大きく立ち上がるときは有機物濃度も高くなる。したがって、この水量の変化と有機物濃度との関係を予め把握し、水量―有機物濃度換算手段４４設けておく。
【００５１】
また、水量を検出するために、原水受入槽１２に水位計４５を設けると共に、ポンプ１３の運転量検出器１３ａを設ける。制御装置４０には、これらの検出値を入力とする水量検出手段４６を設ける。
【００５２】
水量検出手段４６は、ポンプ１３の運転量と、原水受入槽１２の水位変化から、受入水量を算出する。この算出された水量を用いて、水量―有機物濃度換算手段４４により原水（被処理水）の濃度を推定し、その結果により第１の供給路１７または第２の供給路２２を動作させ、被処理水をメタン発酵槽１８または消化液貯留槽２０に送水する。
【００５３】
すなわち、この場合、制御装置４０は、被処理水の単位時間当たりの受入量と有機物濃度との関係を予め把握しており、単位時間当たりの受入量が設定量以上のときの被処理水は第１の供給路１７によりメタン発酵槽１８に供給させ、それ以外の被処理水は第２の供給路２２により消化液処理槽２０に供給させている。
【００５４】
次に、図４で示す実施の形態を説明する。この実施の形態では、制御装置４０に有機物濃度演算手段４７を設け、原水受入槽１２に設けたアンモニア計４８の測定値に従って有機物濃度を算出する。すなわち、原水受入槽１２に設けたアンモニア計４８は、被処理水のアンモニアイオン濃度を測定するので、測定されたアンモニアイオン濃度に基づいて有機物濃度を演算する。その結果、被処理水の有機物濃度が設定濃度であれば第１の供給路１７を通して被処理水をメタン発酵槽１８に供給させ、設定濃度に達していない場合は第２の供給路２２を通して消化液貯留槽２０に供給させる。
【００５５】
次に、図５で示す実施の形態を説明する。この実施の形態では、図４で示したアンモニア計４９に代って、被処理水の導電率を測定する導電率計４９を設けている。アンモニアイオン濃度と導電率との間の相関性が高いことから、導電率計４９の測定値により、制御装置４０に設けた有機物濃度演算手段４７ａによって、被処理水の有機物濃度を算出することができる。
【００５６】
【発明の効果】
本発明によれば、嫌気性メタン発酵により多くのバイオガスを生成でき、かつ好気性処理により有機性廃水中の窒素濃度を放流基準まで低減でき、しかも、これらを安定的に効率よく行なうことができる。
【図面の簡単な説明】
【図１】
本発明による有機性廃水処理装置の一実施の形態を示すシステム構成図である
。
【図２】
本発明における有機性濃度判断手法の一例を説明するシステム構成図である。
【図３】本発明における有機性濃度判断手法の他の例を説明するシステム構成図であ
る。
【図４】
本発明における有機性濃度判断手法のさらに他の例を説明するシステム構成図
である。
【図５】
図４におけるアンモニア計を導電率計に置き換えた例である。
【図６】
本発明の効果を説明する図表である。
【図７】
従来例を説明する図表である。
【符号の説明】
１５　　原水貯留槽
１７　第１の供給路
１８　　メタン発酵槽
２０　　消化液貯留槽
２２　　第２の供給路
２５　　排水処理槽
４０　　制御装置
４１　　時刻―有機物濃度設定表
４４　　水量―有機物濃度換算手段
４７　　有機物濃度演算手段
４８　　アンモニア計
４９　　導電率計[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to an organic wastewater treatment method and an organic wastewater treatment apparatus for subjecting water to be treated to anaerobic methane fermentation treatment and subjecting digested liquid after treatment to aerobic treatment based on the activated sludge method.
[0002]
[Prior art]
Anaerobic methane fermentation treatment is known as a method for treating organic wastewater discharged from the livestock industry, the food industry, and the like. The anaerobic methane fermentation treatment is a reaction in which a liquid or solid organic substance is decomposed by utilizing a metabolic reaction of an anaerobic microorganism to generate a biogas containing methane as a main component. The anaerobic methane fermentation treatment does not require aeration as compared with the aerobic treatment, so the operating power cost is low. In addition, the generated methane can be used as fuel for various power generation facilities, and can produce electricity.
[0003]
However, anaerobic methane fermentation alone cannot purify organic wastewater to a level that can be discharged to rivers and the like. For this reason, the digested liquid after the anaerobic methane fermentation treatment is subjected to aerobic wastewater treatment based on the activated sludge method in a wastewater treatment facility, purified to a water quality satisfying a discharge standard, and then discharged to a river. The organic wastewater treatment process by the combination of the anaerobic methane fermentation and the aerobic treatment based on the activated sludge method is cheaper than treating all with the aerobic wastewater treatment, and is proposed, for example, in Japanese Patent Application Laid-Open No. 2001-321792. Have been.
[0004]
In addition, biogas power generation systems that combine anaerobic methane fermentation, power generation equipment, and aerobic wastewater treatment purify organic wastewater to water quality that meets discharge standards at a relatively low price, and use it as one of greenhouse gases. It produces high-value electricity without the emission of certain methane to the atmosphere, which has both environmental and energy benefits.
[0005]
In the organic wastewater treatment process by the anaerobic methane fermentation treatment applied to such a biogas power generation system and the aerobic wastewater treatment based on the activated sludge method, first, the organic wastewater discharged from the livestock industry, the food industry, etc. Is removed into a raw water receiving tank after removing impurities by a screen, and is transferred to a raw water storage tank.
[0006]
A predetermined amount of the organic wastewater stored in the raw water storage tank is systematically transferred to the methane fermentation tank. In the methane fermentation tank, organic matter in organic wastewater is converted into biogas based on an anaerobic methane fermentation reaction. The biogas generated in this manner is subjected to desulfurization to remove sulfides, sent to a power generation facility, and used for power generation.
[0007]
After methane fermentation, the digestive juice discharged from the methane fermenter is stored in the digestive juice storage tank. A predetermined amount of the digested fluid stored in the digested fluid storage tank is systematically transferred to a wastewater treatment tank, agitated and aerated in the wastewater treatment tank, and purified by aerobic treatment using an activated sludge method.
[0008]
The treated water after the aerobic treatment is subjected to coagulation sedimentation treatment in the coagulation sedimentation tank, and then the supernatant water is discharged to the river via the discharge water channel. Before being discharged from the coagulation sedimentation tank into the river, disinfection with chlorine and advanced treatment may be performed.
[0009]
Excess sludge generated by coagulation and sedimentation in the aerobic treatment is drawn into the sludge storage tank. Excess sludge stored in the sludge storage tank is dewatered in a required amount by a dewatering device in a planned manner, and the dewatered sludge is transferred to a sludge treatment facility.
[0010]
When such an organic wastewater treatment process is applied to a biogas power generation system, the biogas generated in the methane fermentation tank becomes energy for power generation, and thus it is desired to generate a large amount of biogas. For that purpose, it is necessary to convert a large amount of organic matter in organic wastewater into biogas.
[0011]
However, the organic matter concentration of the organic wastewater discharged from the livestock industry and the food industry is not constant and fluctuates with time. The optimum organic matter load in anaerobic methane fermentation differs depending on the specifications of the methane fermentation tank. However, when the organic matter load increases, organic acids are excessively generated, and the growth of methane fermentation bacteria is inhibited, resulting in an abnormal state. Conversely, methane fermentation is inhibited even if the load is too low. That is, when the organic matter concentration of the organic waste greatly changes, the amount of biogas generated as a result decreases.
[0012]
Further, in the organic wastewater treatment process, it is required to purify the organic wastewater to a water quality satisfying a discharge standard. Regarding the discharge standard, standards are being established for nitrogen and phosphorus in addition to the conventional pH, BOD, COD and SS.
[0013]
Regarding nitrogen removal, there is a nitrification / denitrification method as a biological nitrogen removal method. In the nitrification / denitrification method, in an aerobic atmosphere, nitrifying bacteria first oxidize ammonia nitrogen to nitrite nitrogen (formula 1), and then oxidize to nitrate nitrogen (formula 2).
Embedded image

Thereafter, nitrate nitrogen is reduced to nitrogen gas by denitrifying bacteria in an oxygen-free atmosphere (Equation 3). This removes the nitrogen in the wastewater. The oxygen generated by the denitrification reaction is used for oxidizing organic substances (Equation 4).
Embedded image

It is said that a certain amount of organic substances is required to advance the reactions of (Equation 3) and (Equation 4). For example, it is said that reducing 1 g of nitrate nitrogen requires an organic matter equivalent to 2.86 g of BOD.
[0014]
However, in the organic process, in order to obtain a large amount of biogas in the anaerobic methane fermentation treatment, a large amount of organic matter in the organic wastewater is removed. For this reason, the amount of organic substances required for the denitrification reaction is insufficient, and it becomes impossible to remove nitrogen in the organic wastewater until the discharge standard is satisfied.
[0015]
[Problems to be solved by the invention]
As described above, in the conventional organic wastewater treatment system, when the organic matter concentration largely fluctuates, an inhibiting factor occurs in the methane fermentation treatment, and the biogas generation amount decreases. In addition, there is a problem that nitrogen in organic wastewater cannot be removed until the discharge standard is satisfied.
[0016]
SUMMARY OF THE INVENTION An object of the present invention is to provide an organic wastewater capable of producing a large amount of biogas by anaerobic methane fermentation, reducing the nitrogen concentration in the organic wastewater to a discharge standard, and performing these stably and efficiently. It is an object of the present invention to provide a treatment method and an organic wastewater treatment device.
[0017]
[Means for Solving the Problems]
The organic wastewater treatment method according to the present invention is a method for subjecting treated water to anaerobic methane fermentation treatment and subjecting the digested liquid after treatment to aerobic treatment based on the activated sludge method, wherein the concentration of organic matter in the treated water is: An anaerobic methane fermentation treatment is performed when the concentration is equal to or higher than the set concentration, and an aerobic treatment is performed together with the digestive juice when the concentration does not reach the set concentration.
[0018]
The organic wastewater treatment apparatus according to the present invention is a combination of a methane fermentation tank for performing anaerobic methane fermentation treatment and a wastewater treatment tank for performing aerobic treatment based on the activated sludge method, and the raw water for storing the water to be treated. A storage tank, a digestion liquid storage tank for temporarily storing digestion liquid that is processed by the methane fermentation tank and supplied to a wastewater treatment tank, and a treatment water stored in the raw water storage tank is supplied to the methane fermentation tank. Determining whether the concentration of organic matter in the water to be treated stored in the raw water storage tank is equal to or higher than a predetermined concentration, and determining whether the concentration of organic matter in the raw water storage tank is equal to or higher than a predetermined concentration. For example, a control device for supplying the water to be treated to the methane fermentation tank through the first supply path and supplying the water to the digestion liquid storage tank through the second supply path when the concentration has not reached the set concentration. .
[0019]
In the present invention, the control device grasps in advance the relationship between the reception time of the water to be treated and the organic matter concentration, and the water to be treated received at the time when the organic matter concentration becomes equal to or higher than the set concentration is supplied to the first supply passage through methane. The water to be treated is supplied to the fermentation tank, and the water to be treated received at other times is supplied to the digestion liquid treatment tank through the second supply path.
[0020]
Further, in the present invention, the control device grasps in advance the relationship between the amount of received water per unit time and the organic matter concentration, and the amount of water to be treated when the amount of received water per unit time is equal to or more than the set amount is determined. The first supply path is supplied to the methane fermentation tank, and the other water to be treated is supplied to the digestion liquid treatment tank through the second supply path.
[0021]
Further, in the present invention, the control device has an ammonia meter for measuring the ammonia ion concentration of the water to be treated, and calculates the organic matter concentration based on the measured ammonia concentration.
[0022]
Further, in the present invention, the control device has a conductivity meter for measuring the conductivity of the water to be treated, and calculates the organic matter concentration based on the measured conductivity.
[0023]
In these inventions, the organic matter concentration of the water to be treated is determined, and if the concentration is equal to or higher than the set concentration, anaerobic methane fermentation treatment is performed to efficiently generate a large amount of biogas. In addition, when the concentration does not reach the set concentration, aerobic treatment with digestive juice is performed to secure the organic matter necessary for denitrification, so the nitrogen concentration of treated water can be stably and efficiently reduced to the discharge standard by aerobic treatment. can do.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an organic wastewater treatment method and an organic wastewater treatment apparatus according to the present invention will be described with reference to the drawings.
[0025]
FIG. 1 shows the overall configuration of this embodiment. In FIG. 1, organic wastewater discharged from a livestock industry, a food industry, or the like (not shown) is cleaned of impurities by a screen 11, received in a raw water receiving tank 12, and fed to a raw water storage tank via a screen 14 by a pump 13. Transferred to No. 15.
[0026]
A predetermined amount of organic wastewater (water to be treated) stored in the raw water storage tank 15 is systematically transferred to the methane fermentation tank 18 by the first supply path 17 having the pump 16. In the methane fermentation tank 18, organic matter in the organic wastewater is converted into biogas based on the anaerobic methane fermentation reaction. The biogas generated in this manner is subjected to removal of sulfide in a desulfurizer 19, sent to a power generation facility such as a fuel cell, and used for power generation.
[0027]
After the methane fermentation, the digestive juice discharged from the methane fermenter 18 is stored in the digestive juice storage tank 20. The organic wastewater stored in the raw water storage tank 15 is supplied to the digestion fluid storage tank 20 by a second supply path 22 having a pump 21. The reason why the organic wastewater is supplied to the digestive juice storage tank 20 will be described later.
[0028]
A predetermined amount of the digested liquid stored in the digested liquid storage tank 20 is systematically transferred to a wastewater treatment tank 25 by a supply path 24 having a pump 23, and is agitated and aerated in the wastewater treatment tank 25 by the activated sludge method. Purified by aerobic treatment. Here, a batch-type wastewater treatment tank 25 is used, and agitation and sedimentation and sedimentation by an aeration tube 27 having a blower 26 are repeated at different times.
[0029]
The treated water after the aerobic treatment is transferred to the coagulation sedimentation tank 28, where the coagulant supplied from the coagulant tank 30 is added by the pump 29, and after the coagulation sedimentation treatment, the supernatant water passes through the discharge channel 31. Released into the river. Before being discharged from the coagulation sedimentation tank 28 to the river, disinfection with chlorine or advanced treatment may be performed.
[0030]
Excess sludge generated in the wastewater treatment tank 25 and the coagulation sedimentation tank 28 by the aerobic treatment is drawn out to the sludge storage tank 34 by the

pumps

32 and 33. Excess sludge stored in the sludge storage tank 34 is transferred to a dewatering device 36 by a pump 35, and a required amount is dewatered by the dewatering device 36 systematically.
[0031]
The dewatered sludge generated by the dehydrator 36 is transferred to a sludge treatment facility by a pump 37, and the desorbed liquid is transferred to the digestion solution storage tank 20 by a pump 38.
[0032]
The present invention has a first supply path 17 for supplying the water to be treated stored in the raw water storage tank 15 to the methane fermentation tank and a second supply path 22 for supplying the digested liquid storage tank 20 to the methane fermentation tank. Is controlled by the control device 40.
[0033]
The control device 40 determines whether or not the concentration of the organic matter in the water to be treated stored in the raw water storage tank 15 is equal to or higher than the set concentration. If the concentration is equal to or higher than the set concentration, the first supply passage 17 converts the water to be treated into the methane fermentation tank 18. To be supplied. On the other hand, when the concentration has not reached the set concentration, the water to be treated is supplied to the digestive juice storage tank 20 through the second supply path 22.
[0034]
The above-mentioned set concentration is determined by the specifications of the methane fermentation tank 18 and refers to an organic matter concentration that satisfies the optimum organic matter load of the anaerobic methane fermentation treatment.
[0035]
In the above configuration, the control device 40 determines the organic matter concentration of the water to be treated in the raw water storage tank 15, and if the organic matter concentration is abnormal at the set concentration, operates the pump 16 to supply the water to the first supply path 17. To the methane fermenter 18. On the other hand, if the concentration has not reached the set concentration, the pump 21 is operated, and the water to be treated is sent to the digestion solution storage tank 20 through the second supply path 22.
[0036]
By this operation, low-concentration wastewater, which is a factor for reducing the organic matter load of the methane fermentation tank 18, is not supplied to the methane fermentation tank 18. For this reason, the organic matter load in the methane fermentation tank 18 is kept in the optimum range, the methane fermentation is not inhibited by the low organic matter load, and the anaerobic methane fermentation treatment can be stably and efficiently performed. As a result, a large amount of biogas is generated, and the organic matter removal rate is improved.
[0037]
Further, since the amount of organic wastewater flowing into the methane fermentation tank 18 is reduced by the amount of water sent to the digestion liquid storage tank 25, the volume of the methane fermentation tank 18 can be reduced. As a result, construction costs and operating power costs are reduced, and production efficiency relative to investment costs is improved.
[0038]
Further, since the water to be treated that does not reach the set concentration is sent to the digestive juice storage tank 20, wastewater from which organic substances have not been removed by anaerobic methane fermentation is supplied to the digestive juice storage tank 20. For this reason, even if the organic matter concentration of the digested liquid discharged from the methane fermentation tank 18 is excessively low, relatively low-concentration wastewater (water to be treated) from which organic matter has not been removed by the second supply path 22 is directly supplied. Therefore, in the aerobic wastewater treatment in the wastewater treatment tank 18 at the subsequent stage, the amount of organic substances necessary for nitrogen removal can be secured. As a result, the nitrogen removal performance in the aerobic wastewater treatment is improved, and the nitrogen concentration can be reduced to the discharge standard.
[0039]
The above contents will be described quantitatively based on simulation results. Here, the simulation was performed using 75 m ^{3 of} the water to be treated whose organic matter concentration is equal to or higher than the set concentration, and 25 m ³ of the water to be treated that does not reach the set concentration. FIG. 6 shows the result according to the above embodiment, and FIG. 7 shows the result according to the conventional method.
[0040]
6 and 7, the average BOD of more than nominal concentration of the waste water (biological oxygen demand) of 25 000 g / ^{m 3,} the average BOD of waste water does not reach the set concentration and 5000 g / ^{m 3.} Similarly, T-N (pre nitrogen) the former is 3750 g / ^{m 3,} the latter is to 750 g / ^{m 3.} Further, organic wastewater is 100 m ³ in total flowing into the raw water reservoir 15, the average BOD is 20000 g / ^{m 3,} the average T-N was 3000 g / ^{m 3.}
[0041]
In the embodiment shown in FIG. 6, 75 m ³ of water to be treated having a BOD of 25000 g / m ³ and a TN of 3750 g / m ³ flows into the methane fermentation tank 18 and is subjected to anaerobic methane fermentation. The digested liquid discharged from the methane fermentation tank after the treatment has a BOD of 4750 g / m ³ , a TN of 1875 g / m ³ , a BOD removal rate of 81%, and a TN removal rate of 50%.
[0042]
On the other hand, 25 m ³ of the water to be treated having a BOD of 5000 g / m ³ and a TN of 750 g / m ³ flow into the digestion liquid storage tank 20 and the digestion liquid discharged from the methane fermentation tank 18 (BOD: 4750 g / m ^3). , TN: 1875 g / m ³ , water amount 75 m ³ ) to be treated water having BOD: 4813 g / m ³ , TN: 1594 g / m ³ , and water amount 100 m ³ . The water to be treated mixed in the digestion fluid storage tank 20 in this way is supplied to the wastewater treatment tank 25 and is subjected to aerobic treatment.
[0043]
As a result, the biogas conversion BOD amount is 1519 kg from the following equation.
[0044]
75m ³ × 25000g / m ³ × 81% = 1519kg
In addition, the BOD / TN ratio exceeded the value required for nitrogen removal in the aerobic treatment, 2.86, to 3.02.
[0045]
In contrast conventional method, as shown in Figure 7, the average BOD: 20000g / ^{m 3,} the average T-N: organic wastewater 100 m ³ of 3000 g / ^{m 3} are directly flows into the methane fermenter 18. The digested liquid discharged from the methane fermentation tank 18 after the treatment has a BOD of 5000 g / m ³ , a TN of 1800 g / m ³ , a BOD removal rate of 75%, and a TN removal rate of 40%. Then, this digested liquid is supplied to the wastewater treatment tank 25 as it is, and is subjected to aerobic treatment.
[0046]
As a result, the biogas conversion BOD amount was 1500 kg, and the BOD / TN ratio was 2.78, not reaching the value required for nitrogen removal of 2.86.
[0047]
As described above, according to the embodiment, a larger amount of biogas conversion BOD can be obtained than in the conventional example, and the BOD / TN ratio required for nitrogen removal in the aerobic treatment can be sufficiently cleared. I do. Therefore, a large amount of biogas can be generated by anaerobic methane fermentation, and the nitrogen concentration in the organic wastewater can be reduced to the discharge standard.
[0048]
Next, the embodiment shown in FIG. 2 will be described. In this embodiment, the control device 40 uses the relationship between the reception time of the water to be treated and the organic matter concentration as a method for determining the organic matter concentration of the water to be treated. That is, the organic matter concentration of raw water discharged from the livestock industry and the food industry and received by the raw water receiving tank 12 greatly fluctuates depending on time, but this characteristic is used in reverse to grasp the relationship between the organic matter concentration and time in advance. deep.
[0049]
Then, a time-organic matter concentration setting table 41 is created as a table, and the water to be treated received at the time when the organic matter concentration becomes equal to or higher than the set concentration passes through the first supply path 17 according to a command from the methane fermentation tank water supply amount calculating means 42. Water is supplied to the methane fermentation tank 18. In addition, the water to be treated received at other times is sent to the digestion solution treatment tank 20 through the second supply path 22 according to a command from the digestion solution storage tank water supply amount calculation means 43.
[0050]
Next, the embodiment shown in FIG. 3 will be described. In this embodiment, the control device 40 uses the relationship between the amount of water to be treated and the concentration of organic matter as a method for determining the concentration of organic matter in the water to be treated. That is, the amount of raw water discharged from the livestock industry and the food industry and received in the raw water receiving tank 12 varies greatly depending on the time. It is generally known that when the amount of received water is large, the concentration of organic substances is high. In particular, when the amount of water rises significantly, the organic matter concentration also increases. Therefore, the relationship between the change in the water amount and the organic matter concentration is grasped in advance, and a water amount-organic matter concentration conversion means 44 is provided.
[0051]
Further, in order to detect the amount of water, a water level gauge 45 is provided in the raw water receiving tank 12, and an operation amount detector 13a of the pump 13 is provided. The control device 40 is provided with a water amount detecting means 46 to which these detected values are input.
[0052]
The water amount detection means 46 calculates the amount of received water from the amount of operation of the pump 13 and the change in the water level of the raw water receiving tank 12. Using the calculated amount of water, the concentration of the raw water (water to be treated) is estimated by the water amount-organic matter concentration conversion means 44, and the first supply path 17 or the second supply path 22 is operated based on the result, and The treated water is sent to the methane fermentation tank 18 or the digestion liquid storage tank 20.
[0053]
That is, in this case, the control device 40 knows in advance the relationship between the amount of water to be treated per unit time and the organic matter concentration, and the amount of water to be treated when the amount of water per unit time is equal to or greater than the set amount is The first supply path 17 supplies the methane fermentation tank 18, and the other water to be treated is supplied to the digestion liquid treatment tank 20 through the second supply path 22.
[0054]
Next, the embodiment shown in FIG. 4 will be described. In this embodiment, an organic matter concentration calculating means 47 is provided in the control device 40, and the organic matter concentration is calculated according to the measurement value of the ammonia meter 48 provided in the raw water receiving tank 12. That is, since the ammonia meter 48 provided in the raw water receiving tank 12 measures the ammonia ion concentration of the water to be treated, the ammonia concentration is calculated based on the measured ammonia ion concentration. As a result, if the organic matter concentration of the water to be treated is the set concentration, the water to be treated is supplied to the methane fermentation tank 18 through the first supply path 17, and if the organic substance concentration has not reached the set concentration, the water is digested through the second supply path 22. The liquid is supplied to the liquid storage tank 20.
[0055]
Next, an embodiment shown in FIG. 5 will be described. In this embodiment, a conductivity meter 49 for measuring the conductivity of the water to be treated is provided instead of the ammonia meter 49 shown in FIG. Since the correlation between the ammonium ion concentration and the conductivity is high, the organic matter concentration of the water to be treated can be calculated by the organic matter concentration calculating means 47a provided in the control device 40 based on the measurement value of the conductivity meter 49. it can.
[0056]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, many biogas can be produced | generated by anaerobic methane fermentation, and nitrogen concentration in organic wastewater can be reduced to a discharge | release standard by aerobic treatment, and these can be performed stably and efficiently. it can.
[Brief description of the drawings]
FIG.
1 is a system configuration diagram showing an embodiment of an organic wastewater treatment device according to the present invention.
FIG. 2
FIG. 1 is a system configuration diagram illustrating an example of an organic concentration determination method according to the present invention.
FIG. 3 is a system configuration diagram illustrating another example of an organic concentration determination method according to the present invention.
FIG. 4
FIG. 9 is a system configuration diagram illustrating still another example of the organic concentration determination method according to the present invention.
FIG. 5
This is an example in which the ammonia meter in FIG. 4 is replaced with a conductivity meter.
FIG. 6
5 is a table illustrating an effect of the present invention.
FIG. 7
9 is a chart illustrating a conventional example.
[Explanation of symbols]
15 Raw water storage tank 17 First supply path 18 Methane fermentation tank 20 Digested liquid storage tank 22 Second supply path 25 Wastewater treatment tank 40 Controller 41 Time-organic matter concentration setting table 44 Water volume-organic matter concentration conversion means 47 Organic matter concentration calculation Means 48 Ammonia meter 49 Conductivity meter

Claims

An organic effluent treatment method for subjecting treated water to anaerobic methane fermentation treatment and subjecting digested juice after treatment to aerobic treatment based on the activated sludge method,
An organic wastewater treatment method, wherein an anaerobic methane fermentation treatment is performed if the concentration of organic matter in the water to be treated is equal to or higher than a set concentration, and an aerobic treatment is performed together with the digested liquid when the concentration does not reach the set concentration.

An organic wastewater treatment device combining a methane fermentation tank for performing anaerobic methane fermentation treatment and a wastewater treatment tank for performing aerobic treatment based on the activated sludge method,
A raw water storage tank for storing the water to be treated,
Digestion fluid storage tank that stores the digestion fluid that is processed by the methane fermentation tank and supplied to the wastewater treatment tank,
A first supply path for supplying the water to be treated stored in the raw water storage tank to the methane fermentation tank and a second supply path for supplying the digested liquid storage tank to the methane fermentation tank;
It is determined whether or not the organic matter concentration of the water to be treated stored in the raw water storage tank is equal to or higher than a set concentration. If not, a control device for supplying to the digestive juice storage tank by the second supply path,
An organic wastewater treatment apparatus comprising:

The controller grasps in advance the relationship between the reception time of the water to be treated and the organic matter concentration, and supplies the water to be treated received at the time when the organic matter concentration becomes equal to or higher than the set concentration to the methane fermentation tank through the first supply path. 3. The organic wastewater treatment apparatus according to claim 2, wherein the water to be treated received at other times is supplied to the digestion solution treatment tank through the second supply path.

The control device knows in advance the relationship between the amount of water to be treated per unit time and the organic matter concentration, and the water to be treated when the amount of water per unit time is equal to or greater than the set amount is supplied to the first supply path. The organic wastewater treatment apparatus according to claim 2, wherein the methane fermentation tank is supplied, and the other water to be treated is supplied to the digestion liquid treatment tank through a second supply path.

The organic wastewater treatment apparatus according to claim 2, wherein the control device includes an ammonia meter that measures an ammonia ion concentration of the water to be treated, and calculates an organic matter concentration based on the measured ammonia concentration.

The organic wastewater treatment apparatus according to claim 2, wherein the control device has a conductivity meter that measures the conductivity of the water to be treated, and calculates the organic matter concentration based on the measured conductivity.