JP3611292B2

JP3611292B2 - Wastewater treatment method

Info

Publication number: JP3611292B2
Application number: JP36806899A
Authority: JP
Inventors: 展行鵜飼; 清菅田
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 1999-12-24
Filing date: 1999-12-24
Publication date: 2005-01-19
Anticipated expiration: 2019-12-24
Also published as: JP2001179285A

Description

【０００１】
【発明の属する技術分野】
本発明は、下水汚泥等や工場排水、し尿処理施設等の有機性排水を活性汚泥法や生物膜法等の好気性生物処理、又はメタン発酵法等の嫌気性生物処理を施して該排水に含有するＢＯＤ、ＣＯＤ又はＳＳ等の汚濁物質を除去し、場合によってはメタンガスを回収することもできる排水処理方法において、特に前記生物処理により生じる余剰汚泥を減容化することのでき、またメタンガスの転換効率の高い排水処理方法に関する。
【０００２】
【従来の技術】
従来より、下水汚泥や工場排水等のＢＯＤ、ＣＯＤ又はＳＳ等を含有する有機性排水（少量の無機物を含んでいてもよい）は、一般に生物処理によって処理されている。
しかし、活性汚泥法やメタン発酵法などの生物処理により生じる余剰汚泥は、難濾過性で沈降分離などによる濃縮が非常に困難で、また汚泥自身の圧縮性が著しく大きいためその処理は非常に困難であるため、汚泥の濾過性、脱水性の改善、または余剰汚泥の減容化のために、熱処理、薬品添加、オゾン処理など、様々な処理が施されている。
【０００３】
特開平８−１１８３号公報では、前記余剰汚泥の減容化を可能とした有機性排液の処理システムを提案している。
かかる処理システムを図７に基づき簡単に説明すると、活性汚泥処理系５１の曝気槽５２に被処理液５６、返送汚泥５７及び加熱処理汚泥６２を導入し、曝気槽５２内の活性汚泥と混合して好気性生物処理を行なう。混合液５８は固液分離部５３で処理水と汚泥とを分離し、該分離汚泥５９の一部は返送汚泥としてオゾン処理槽５４に導入し、オゾン処理を行なう。オゾン処理汚泥６１は加熱処理槽５５に導入し、５０〜１００℃で加熱処理を行い、加熱処理汚泥６２は曝気槽５２に返送して好気性生物処理を行なう。
【０００４】
前記従来技術のように、前記分離汚泥５９をオゾン処理した後、５０〜１００℃で加熱処理することにより、オゾン単独での処理に比べてオゾン使用量を少なくすることができる。また、加熱処理を施した汚泥を生物処理することにより、オゾン処理及び加熱処理した汚泥中の有機物が容易に生物分解されて除去され、系全体から排出される汚泥の量が低減する。
【０００５】
また、前記余剰汚泥を生物処理槽に返送せず、メタン発酵することによりメタンガスに転換して有用回収する方法も広く用いられており、これは、固液分離装置で処理水と分離された余剰汚泥を混合槽にて略１日程度貯溜した後、該余剰汚泥をメタン発酵槽に導入してメタン発酵させ、メタンガスを回収するシステムである。
【０００６】
【発明が解決しようとする課題】
しかしながら、前記従来技術においては、余剰汚泥をオゾン処理した後加熱処理することで該余剰汚泥の生分解性が向上し、オゾン単独での処理よりオゾン使用量の低減が期待できるものの、固液分離による余剰汚泥の濃縮のみでは該余剰汚泥の含水率が高く、該余剰汚泥を可溶化処理するために要するオゾン添加コスト、加熱コストは依然として高い。
また、難生物分解物質の十分な可溶化効果が得られないため、生物処理装置から排出する余剰汚泥中に該難生物分解物質が常に残存している可能性がある。
【０００７】
また、メタン発酵槽を設けた場合においても、余剰汚泥の可溶化が十分でないため、該余剰汚泥の分解が困難で、メタンガスの回収率が低く、かつ前記メタン発酵槽から排出する余剰汚泥量も多いため汚泥処理費用が嵩む。
本発明は、かかる従来技術の課題に鑑み、難生物分解物質を高効率で分解可能で、かつオゾン添加コスト、加熱コスト等のランニングコストが低減でき、またメタン発酵槽を設けた場合においては余剰汚泥のメタンガス転換率が高く、汚泥処理費用を低減することが可能な排水処理方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明はかかる課題を解決するために、生物処理槽にて有機性排水に生物処理を施す生物処理ステップと、該生物処理槽から排出した余剰汚泥と処理水とを固液分離装置にて分離する固液分離ステップと、脱水機にて前記余剰汚泥を脱水するステップと、ｐＨ８〜１２のアルカリ条件下で前記脱水機により脱水された余剰汚泥をオゾン処理装置にてオゾン処理を施すオゾン処理ステップと、略６０〜８０℃の温度域で溶菌酵素生産微生物の存在下に恒温生物処理装置にて前記オゾン処理後の余剰汚泥に含まれる有機物を低分子化する恒温生物処理ステップと、該有機物を低分子化された余剰汚泥をメタン発酵槽にて嫌気性生物処理を施すメタン発酵ステップとからなることを特徴とし、好ましくは、前記恒温生物処理ステップが、略６０〜８０℃の温度域で生ゴミと混合し溶菌酵素生産微生物の存在下に前記オゾン処理後の余剰汚泥に含まれる有機物を低分子化する恒温生物処理ステップであることを要旨とする。
【０００９】
かかる発明によれば、前記ｐＨ８〜１２のアルカリ条件下で前記脱水機により脱水された余剰汚泥をオゾン処理装置にてオゾン処理を施すオゾン処理ステップとの前段のステップに余剰汚泥の脱水を行なう前記脱水ステップを設けることで該余剰汚泥量の低減ができ、可溶化処理におけるオゾン添加量、加熱に要する熱量の低減が可能となるため、オゾン添加コスト、加熱コスト等のランニングコストの低減が図れる。
そして請求項１記載の発明は、前記恒温生物処理を略６０〜８０℃の温度域にて行うことにより、前記余剰汚泥中の溶菌酵素生産微生物が優占的に増殖し、該溶菌酵素生産微生物の働きにより有機物が低分子化され、前記生物処理における分解が促進され、該生物処理から排出される余剰汚泥量が低減する。
さらに、ｐＨ８〜１２のアルカリ条件下でオゾン処理を行うことにより、高効率で以ってオゾン処理を行うことができ、オゾン添加コストが低減できる。
【００１０】
さらに、特にオゾン処理ステップをヒドロキシラジカル等の非常に酸化力の強いラジカルの発生し易いｐＨ８〜１２（好ましくはｐＨ８〜１０）のアルカリ状態に保持することにより、効率良くオゾン処理を施すことができ、オゾン添加コストを低減できる。
【００１１】
かかる発明によれば、前記生物処理装置から排出する余剰汚泥を、ｐＨ８〜１２（好ましくはｐＨ８〜１０）に維持されたオゾン処理ステップと恒温生物処理ステップにより、該余剰汚泥中に含まれる有機物を低分子化し、これにより前記メタン発酵槽におけるメタンガス転換率が向上し、かつ該メタン発酵槽で生じる余剰汚泥量も大幅に減少するため、汚泥処理費用の削減が可能となる。
【００１２】
また、前記オゾン処理ステップの前段に余剰汚泥の脱水を行なう前記脱水機を設けることで、オゾン添加量を低減することができ、かつ難生物分解物質の十分な可溶化効果が得られる。
さらに、請求項２若しくは３記載のように前記メタン発酵ステップの後段にメタン発酵槽から排出する余剰汚泥を脱水するステップを設け、該脱水ステップで脱水した余剰汚泥の少なくとも一部を前記オゾン処理ステップに返送することで、メタンガスへの転換がさらに困難な該メタン発酵槽の余剰汚泥を処理することができ、該メタン発酵槽から排出する余剰汚泥量を限りなくゼロに近づけることができる。
【００１３】
かかる発明によれば、前記生物処理装置から排出する余剰汚泥を、ｐＨ８〜１２（好ましくはｐＨ８〜１０）に維持されたオゾン処理ステップとその後段の恒温生物処理ステップにより、該余剰汚泥中に含まれる有機物を低分子化し、これにより前記メタン発酵槽におけるメタンガス転換率が向上し、かつ該メタン発酵槽で生じる余剰汚泥量も大幅に減少するため、汚泥処理費用の削減が可能となる。
【００１４】
【発明の実施の形態】
以下、本発明を図に示した実施例を用いて詳細に説明する。但し、この実施例に記載されている構成部品の寸法、材質、形状、その相対配置などは特に特定的な記載がない限り、この発明の範囲をそれのみに限定する趣旨ではなく、単なる説明例にすぎない。
図１は本発明の参考例に係る排水処理方法の概略構成図で、図２、３はそれぞれ図１に対応する別の参考例に係る排水処理方法の概略構成図である。
【００１５】
まず本発明の理解を容易にする為の参考例を図１乃至図３を参照して説明する。
図１において、１は活性汚泥処理またはメタン発酵等を施す生物処理槽、２は固液分離装置、３ａは濃縮装置、４は恒温生物処理装置、５はオゾン処理装置である。
本発明における排水は、下水汚泥、工場排水またはし尿処理設備等における有機物を含有する排水であれば何でもよく、該有機性排水１０は前記生物処理槽１内に存在する微生物によって活性汚泥処理又はメタン発酵等の生物処理を施された後、固液分離装置２にて余剰汚泥１２と処理水１１とに分離され、該処理水１１は系外へ排出される。
【００１６】
前記余剰汚泥１２の一部は前記生物処理槽１に返送され、他の余剰汚泥は濃縮装置３ａに導入され、濃縮された余剰汚泥１４は恒温生物処理装置４にて生物処理される。
温度域が略６０〜８０℃に保持された前記恒温生物処理装置４内では汚泥中の溶菌酵素生産微生物の増殖が活性化されるため、前記余剰汚泥中の生分解性物質は該溶菌酵素生産微生物により低分子化が促進され、該恒温生物処理装置４内で処理できない難分解性物質が残存する汚泥は次段のオゾン処理装置５にて可溶化処理される。
【００１７】
該オゾン処理装置５はアルカリ６を添加して余剰汚泥をアルカリ性、好ましくはｐＨ８〜１０に保持し、非常に酸化力の強いラジカルであるヒドロキシラジカルが発生し易い状態にして該余剰汚泥に残存する難分解性物質を分解処理するが、前記恒温生物処理装置により難分解性物質を除く殆どの有機物が低分子化しているため、該オゾン処理装置５に使用されるオゾン添加量は従来より少なくてすむ。
前記オゾン処理装置５にて分解処理された余剰汚泥は返送汚泥１５として前記生物処理槽１に返送され再び生物処理を施されるが、前記オゾン処理装置５、恒温生物処理装置４にて低分子化した余剰汚泥は容易に分解可能であるため、効率良く生物処理を行うことができ、かつ該生物処理により生じる余剰汚泥量は減少する。
【００１８】
図２、図３は図１に示す参考例に対応する排水処理システムを示したもので、図２は図１の参考例と同様に前記生物処理槽１にて生物処理を施され、固液分離された余剰汚泥を濃縮装置３ａにて濃縮し、含水率の低減した該余剰汚泥を恒温生物処理装置４で低分子化した後、該恒温生物処理装置４から排出する余剰汚泥を固液分離装置６に導入して、余剰汚泥を処理水１２と分離することによりさらに含水率を低減し、アルカリ２１を添加したオゾン処理装置５にて分解処理した後該処理水１６と余剰返送汚泥１５とを前記生物処理槽１に返送する。
これにより、第１実施例よりオゾン処理する余剰汚泥量が低減するため、オゾン添加量が低減され、オゾン添加コストの削減が図れる。
【００１９】
また、図３は前記参考例の可溶化処理手段において、前記濃縮装置３ａから排出される余剰汚泥１４をアルカリ２１を添加したオゾン処理装置５にて分解処理した後、後段に設けられたの恒温処理生物装置４にて低分子化し、該恒温処理生物処理装置の余剰汚泥１５を前記生物処理槽１に返送したものである。
【００２０】
尚、これらの参考例における恒温生物処理装置４内の最適な温度域を求めるために行なった実験結果を図８（ａ）、（ｂ）に示す。図８（ａ）は汚泥中の溶菌酵素生産微生物の活性変化を示す反応時間−ＴＯＣグラフである。
該グラフにおいて、温度が略６０℃〜８０℃前後まで急激にＴＯＣ濃度が増加し、８０℃〜９５℃では顕著な効果が見られなくなる。これは、６０〜８０℃では溶菌酵素生産微生物以外の微生物の働きが盛んであるが、８０℃以上を越えると溶菌酵素生産微生物が死亡する等、失活するためと考えられる。
【００２１】
図８（ｂ）は汚泥中の溶菌酵素生産微生物の活性変化を示す汚泥温度−ＴＯＣ可溶化率を表わし、このグラフにより明らかなように、従来技術のように汚泥温度を５０℃まで上昇しただけでは、ＴＯＣ可溶化率は常温（略２５℃）に較べて殆ど効果は見られない。
また、一方汚泥温度を最高温度１００℃まで上昇させると、８０℃と大差はないが、加熱コストは８０℃で２６０円／ｔであるにもかかわらず、１００℃における加熱コストは３４０円／ｔと大幅に割高になる。
【００２２】
さらに、図９には汚泥の処理温度及び溶存オゾン濃度の変化に伴う可溶化効果を示す反応時間−ＴＯＣ可溶化率のグラフを示す。これにより明らかなように、常温（２０℃）、ｐＨ８、かつ溶存オゾン濃度０ｍｇ／ｇ（Ｏ_３／ＳＳ）のＴＯＣ可溶化率が滞留時間２４時間で僅かな増加しか見られないのに対して、温度８０℃、ｐＨ９かつ溶存オゾン濃度５０ｍｇ／ｇの条件では略５５％の可溶化率と、非常に高い値を示す。
これにより、可溶化手段にはオゾン処理と恒温生物処理とを併用することによる効果が非常に大きいことがわかる。
【００２３】
次に、本発明のメタン発酵槽を備えた排水処理システムの実施例を図４乃至図６を用いて以下に説明する。
[実施例Ａ]
まず、図４に示す排水処理システムの全体構成図を用いて実施例Ａの構成を説明する。
し尿、浄化槽汚泥等の有機性排水を生物処理槽１にて生物学的脱窒素処理等の生物処理を施した後、固液分離装置２にて処理水と分離した余剰汚泥を脱水機３ｂで脱水し、該脱水した余剰汚泥をｐＨ８〜１０のアルカリ状態のオゾン処理槽５にて該余剰汚泥中の有機物を酸化分解処理する。該酸化分解処理した余剰汚泥を略６０〜８０℃に保持された恒温生物処理装置４にて生ゴミ２２と混合し、溶菌酵素生産微生物によりさらに低分子化した後メタン発酵槽７に導入し、メタン発酵させる。
【００２４】
該メタン発酵で発生するメタンガス１７は回収してリサイクルし、処理水１８は系外へ排出するとともに、前記メタン発酵槽７から排出する余剰汚泥１９は脱水機３ｃにより脱水した後、後処理工程へ送給、若しくは廃棄する。
これにより、従来技術におけるメタン発酵槽を設けた排水処理方法での汚泥分解率が略２０〜３０％であったのに対し、本実施例では略５０％前後まで向上することが確認された。
【００２５】
ここで、図１０に可溶化処理した汚泥のメタン発酵槽内における反応時間−汚泥分解率のグラフを示す。該グラフにより余剰汚泥のメタン発酵処理状況を説明すると、常温（２０℃）で溶存オゾン濃度０ｍｇ／ｇ（Ｏ_３／ＳＳ）の場合、該メタン発酵槽内で１５日間（２４０時間）発酵させたときの汚泥分解率は略１０％と非常に低い値を示す。
また、余剰汚泥を加熱して温度６０℃とし、溶存オゾン濃度が０ｍｇ／ｇの条件としたときは、１５日間の発酵で汚泥分解率は略２５％となり、常温における反応より汚泥分解率は向上するが、汚泥分解の促進は十分とは言えない。
【００２６】
そこで、前記余剰汚泥にオゾンを添加して溶存オゾン濃度を略５０ｍｇ／ｇ、かつ温度を８０℃とすると汚泥分解率は略５５％と非常に高い値を示す。これは、メタンガスを高効率で回収するためには、余剰汚泥を略６０〜８０℃まで加熱するのみではなく、オゾンを添加することにより、さらに該余剰汚泥の低分子化が促進されることがわかる。
【００２７】
前記実施例Ａにより生成するメタンガス発生量と汚泥処理費用を例示的に求めると、し尿１０ｋｌ／日、浄化槽汚泥７０ｋｌ／日、生ゴミ１．３ｔ／日を処理する場合、
し尿汚泥からのメタンガス発生量（分解率略６０％）：３．３Ｎｍ^３／ｋｌ
浄化槽汚泥からのメタンガス発生量（分解率略６０％）：３．７Ｎｍ^３／ｋｌ
生ゴミからのメタンガス発生量（分解率略７０％）：７８Ｎｍ^３／ｔ
となる。（なお、分解率とは余剰汚泥の分解率をいう。）
したがって、１日当たりの全体のメタン発生量：３９３Ｎｍ^３／日
また、発電量に換算すると１日当たり１，１７１Ｋｗｈ／日となる。
【００２８】
また、汚泥処理費用は前記条件の場合、
メタン発酵槽からの汚泥発生量：２．４ｔ／日
処理費用が２万円／ｔとすると、全体の処理費用：４８千円／日となり、従来に比較して発電量の増大とともに、処理費用が低減していることが理解できる。
【００２９】
[実施例Ｂ]
図５に本発明の実施例Ｂの全体構成図を示す。
かかる実施例は、図４に示した実施例Ａに、前記メタン発酵槽７から排出する余剰汚泥を脱水機３ｃにより脱水した後、該余剰汚泥の少なくとも一部を返送汚泥２０として前記オゾン処理装置５に返送する返送路を加えたもので、これにより、メタンガス発生量が大幅に向上し、かつ該余剰汚泥の発生量がゼロに限りなく近く、効率の良い排水処理方法が実現する。
そして実証実験の結果、本実施例の余剰汚泥の汚泥分解率は略６０％前後まで向上することが見込まれることが確認された。
【００３０】
前記実施例Ｂにより生成するメタンガス発生量と汚泥処理費用を求めると、
実施例Ａと同様な条件を設定し、し尿１０ｋｌ／日、浄化槽汚泥７０ｋｌ／日、生ゴミ１．３ｔ／日を処理する場合、
し尿汚泥からのメタンガス発生量（分解率略８０％）：４．４２Ｎｍ^３／ｋｌ
浄化槽汚泥からのメタンガス発生量（分解率略８０％）：４．９８Ｎｍ^３／ｋｌ
生ゴミからのメタンガス発生量（分解率略７０％）：７８Ｎｍ^３／ｔ
したがって、１日当たりの全体のメタン発生量：４９４．２Ｎｍ^３／日
また、発電量に換算すると１日当たり１，４７３Ｋｗｈ／日となる。
【００３１】
また、汚泥処理費用は前記条件の場合、メタン発酵槽からの汚泥発生量：１．２ｔ／日、全体の処理費用：２４千円／日となる。
【００３２】
[比較例]
図６に現在使用されている排水処理方法の全体構成図を示す。
かかる排水処理方法は、生物処理槽１にて生化学的窒素除去処理等の生物処理を施された有機性排水１０は固液分離装置２により処理水１１と余剰汚泥とに分離され、該余剰汚泥は脱水機３ｂにより脱水された後混合槽８に導かれ、該混合槽にて生ゴミ２２と混合して略１日程度滞留させた後、メタン発酵槽７に送給され、該メタン発酵槽７にて略２週間ほど発酵され、処理水１８と余剰汚泥１９とメタンガス１７とに分離されて後工程に送られる。
【００３３】
比較例により生成するメタンガス発生量と汚泥処理費用を求めると、
実施例Ａと同様な条件を設定し、し尿１０ｋｌ／日、浄化槽汚泥７０ｋｌ／日、生ゴミ１．３ｔ／日を処理する場合、
し尿汚泥からのメタンガス発生量（分解率略８０％）：１．６６Ｎｍ^３／ｋｌ
浄化槽汚泥からのメタンガス発生量（分解率略８０％）：２．１８Ｎｍ^３／ｋｌ
生ゴミからのメタンガス発生量（分解率略７０％）：７８Ｎｍ^３／ｔ
したがって、１日当たりの全体のメタン発生量：２７０．０Ｎｍ^３／日
また、発電量に換算すると１日当たり８０４Ｋｗｈ／日となる。
【００３４】
また、汚泥処理費用は前記条件の場合、メタン発酵槽からの汚泥発生量：４．３ｔ／日、全体の処理費用：８６千円／日となる。
【００３５】
以上の実施例より実施例Ａにおける排水処理方法では比較例に比べて発電量で３６７Ｋｗｈ／日の増加、処理費用で３８千円／日の削減となり、また、実施例Ｂでは比較例に比べて発電量で６６９Ｋｗｈ／日の増加、処理費用で６２千円の削減となる。
実施例Ａでは、し尿処理装置等の生物処理槽から排出する余剰汚泥を可溶化処理することにより、メタンガスへの転換効率が向上するとともに、メタン発酵槽からの余剰汚泥が低減し、汚泥処理費用も低減することとなる。
また、実施例Ｂでは、メタンガスへの転換がさらに困難であるメタン発酵槽の余剰汚泥を可溶化手段に返送して、該メタン発酵槽にて再処理を施すことにより、メタンガス発生量が大幅に向上し、さらには該余剰汚泥の発生が限りなくゼロに近い排水処理方法を提供することが可能となる。
【００３６】
【発明の効果】
以上記載のごとく、オゾン処理ステップの前段に脱水機にて前記余剰汚泥を脱水するステップを設けることにより、可溶化処理装置において処理する汚泥量が減少し、オゾン添加コストや加熱コストの低減ができる。
また、オゾン処理ステップをｐＨ８〜１２（好ましくはｐＨ８〜１０）のアルカリ状態、かつ恒温生物処理装置を略６０〜８０℃に維持することにより、高効率で以って可溶化処理を行うことができる。
【００３７】
また、かかる発明によれば、オゾン処理ステップと、恒温生物処理ステップを設けることにより、メタン発生量が増加し、さらに、メタン発酵槽で生じる余剰汚泥を該可溶化手段に返送して再処理することにより、メタン発生量が大幅に増加するとともに、前記余剰汚泥の発生が限りなくゼロに近い排水処理方法を提供することが可能となる。
【図面の簡単な説明】
【図１】本発明の排水処理方法にかかる参考例を示す概略構成図である。
【図２】図１に対応する別の参考例を示す概略構成図である。
【図３】図１に対応する別の参考例を示す概略構成図である。
【図４】本発明のメタン発酵槽を具えた排水処理方法の実施例Ａを示す全体構成図である。
【図５】図４に対応する排水処理方法の実施例Ｂを示す全体構成図である。
【図６】図４に対応する排水処理方法の比較例を示す全体構成図である。
【図７】従来技術を示す排水処理方法の概略構成図である。
【図８】汚泥中の溶菌酵素生産微生物の活性変化を示す反応時間−ＴＯＣグラフ（ａ）、反応温度−ＴＯＣ可溶化率のグラフ（ｂ）である。
【図９】汚泥の処理温度及び溶存オゾン濃度の変化に伴う可溶化効果を示す反応時間−ＴＯＣ可溶化率のグラフである。
【図１０】可溶化処理した汚泥のメタン発酵処理槽内における反応時間-汚泥分解率を示すグラフである。
【符号の説明】
１生物処理槽
２固液分離装置
３ａ濃縮装置
３ｂ，３ｃ脱水機
４恒温生物処理装置
５オゾン処理装置
６固液分離装置
７メタン発酵槽
１３返送汚泥
１７メタンガス
２１アルカリ[0001]
BACKGROUND OF THE INVENTION
In the present invention, organic wastewater such as sewage sludge, factory wastewater, and human waste treatment facilities is subjected to anaerobic biological treatment such as activated sludge method and biofilm method, or anaerobic biological treatment such as methane fermentation method. In the wastewater treatment method that can remove pollutants such as BOD, COD or SS, and possibly collect methane gas, it is possible to reduce the volume of excess sludge generated by the biological treatment, The present invention relates to a wastewater treatment method with high conversion efficiency.
[0002]
[Prior art]
Conventionally, organic wastewater containing BOD, COD, SS, or the like such as sewage sludge or factory wastewater (which may contain a small amount of inorganic matter) is generally treated by biological treatment.
However, surplus sludge produced by biological treatment such as activated sludge method and methane fermentation method is very difficult to concentrate by sedimentation separation, etc. due to the difficulty of filtering, and the sludge itself is extremely compressible. Therefore, various treatments such as heat treatment, chemical addition, and ozone treatment are applied to improve the filterability and dewaterability of sludge or reduce the volume of excess sludge.
[0003]
Japanese Patent Application Laid-Open No. 8-1183 proposes an organic wastewater treatment system capable of reducing the volume of the excess sludge.
This processing system will be briefly described with reference to FIG. 7. The liquid to be treated 56, the return sludge 57 and the heat treatment sludge 62 are introduced into the aeration tank 52 of the activated sludge treatment system 51 and mixed with the activated sludge in the aeration tank 52. Aerobic biological treatment. The mixed liquid 58 separates the treated water and sludge at the solid-liquid separator 53, and a part of the separated sludge 59 is introduced into the ozone treatment tank 54 as return sludge and subjected to ozone treatment. The ozone-treated sludge 61 is introduced into the heat treatment tank 55 and heat-treated at 50 to 100 ° C., and the heat-treated sludge 62 is returned to the aeration tank 52 for aerobic biological treatment.
[0004]
Like the said prior art, after carrying out the ozone treatment of the said separation sludge 59, the ozone usage-amount can be decreased compared with the process only by ozone by heat-processing at 50-100 degreeC. In addition, by biologically treating the heat-treated sludge, organic substances in the sludge that has been subjected to ozone treatment and heat treatment are easily biodegraded and removed, and the amount of sludge discharged from the entire system is reduced.
[0005]
In addition, a method in which the surplus sludge is not returned to the biological treatment tank but is converted to methane gas by methane fermentation and usefully recovered is widely used. This is the surplus separated from the treated water by the solid-liquid separator. In this system, after sludge is stored in a mixing tank for about one day, the surplus sludge is introduced into a methane fermentation tank and subjected to methane fermentation to recover methane gas.
[0006]
[Problems to be solved by the invention]
However, in the prior art, the surplus sludge is treated with ozone and then heat-treated to improve the biodegradability of the surplus sludge. Concentration of surplus sludge by only the high water content of the surplus sludge, the ozone addition cost and heating cost required to solubilize the surplus sludge are still high.
In addition, since a sufficient solubilizing effect of the hardly biodegradable substance cannot be obtained, the hardly biodegradable substance may always remain in the excess sludge discharged from the biological treatment apparatus.
[0007]
In addition, even when a methane fermentation tank is provided, because the solubilization of excess sludge is not sufficient, it is difficult to decompose the excess sludge, the methane gas recovery rate is low, and the amount of excess sludge discharged from the methane fermentation tank is also low. Because there are many, sludge treatment costs increase.
In view of the problems of the prior art, the present invention is capable of decomposing a hardly biodegradable substance with high efficiency, reducing running costs such as ozone addition cost and heating cost, and surplus when a methane fermentation tank is provided. An object of the present invention is to provide a wastewater treatment method capable of reducing the sludge treatment cost with a high sludge methane gas conversion rate.
[0008]
[Means for Solving the Problems]
In order to solve such a problem, the present invention separates a biological treatment step in which biological wastewater is subjected to biological treatment in a biological treatment tank, and excess sludge and treated water discharged from the biological treatment tank by a solid-liquid separator. A solid-liquid separation step, a step of dehydrating the excess sludge with a dehydrator, and an ozone treatment step of subjecting the excess sludge dehydrated with the dehydrator under alkaline conditions of pH 8 to 12 to ozone treatment with an ozone treatment device And a constant temperature biological treatment step for reducing the molecular weight of organic matter contained in the excess sludge after the ozone treatment in a constant temperature biological treatment device in the presence of a lytic enzyme-producing microorganism in a temperature range of about 60 to 80 ° C., and It is characterized by comprising a methane fermentation step for subjecting excess sludge reduced in molecular weight to an anaerobic biological treatment in a methane fermentation tank. Preferably, the isothermal biological treatment step is approximately 60-8. And summarized in that the ℃ mixed with raw garbage in a temperature range of organic materials contained in the excess sludge after the ozone treatment in the presence of a lytic enzyme producing microorganism is a thermostatic biological treatment step of a low molecular weight.
[0009]
According to this invention, the excess sludge is dehydrated in a step preceding the ozone treatment step in which the excess sludge dehydrated by the dehydrator under the alkaline condition of pH 8 to 12 is subjected to ozone treatment by an ozone treatment apparatus. By providing a dehydration step, the amount of surplus sludge can be reduced, and the amount of ozone added in the solubilization treatment and the amount of heat required for heating can be reduced. Therefore, the running costs such as the ozone addition cost and the heating cost can be reduced.
In the invention described in claim 1, by performing the constant temperature biological treatment in a temperature range of approximately 60 to 80 ° C., the lytic enzyme-producing microorganism in the excess sludge proliferates preferentially, and the lytic enzyme-producing microorganism As a result, the organic substance is reduced in molecular weight, the decomposition in the biological treatment is promoted, and the amount of excess sludge discharged from the biological treatment is reduced.
Furthermore, by performing ozone treatment under alkaline conditions of pH 8-12, ozone treatment can be performed with high efficiency, and the ozone addition cost can be reduced.
[0010]
Furthermore, in particular, the ozone treatment step can be efficiently performed by maintaining an alkaline state of pH 8 to 12 (preferably pH 8 to 10) in which radicals having very strong oxidizing power such as hydroxy radicals are easily generated. The ozone addition cost can be reduced.
[0011]
According to this invention, the excess sludge discharged from the biological treatment apparatus is subjected to an organic treatment contained in the excess sludge by an ozone treatment step and a constant temperature biological treatment step maintained at pH 8 to 12 (preferably pH 8 to 10). Since the methane gas conversion rate in the methane fermentation tank is improved and the amount of excess sludge generated in the methane fermentation tank is greatly reduced, the sludge treatment cost can be reduced.
[0012]
In addition, by providing the dehydrator for dehydrating excess sludge before the ozone treatment step, the amount of ozone added can be reduced, and a sufficient solubilizing effect of the hardly biodegradable substance can be obtained.
Furthermore, the step which dehydrates the excess sludge discharged | emitted from a methane fermenter in the back | latter stage of the said methane fermentation step as described in Claim 2 or 3 is provided, The ozone treatment step removes at least one part of the excess sludge dehydrated by this dehydration step. The excess sludge of the methane fermentation tank, which is more difficult to convert to methane gas, can be processed by returning to the methane gas, and the amount of excess sludge discharged from the methane fermentation tank can be made as close to zero as possible.
[0013]
According to this invention, the excess sludge discharged from the biological treatment apparatus is included in the excess sludge by the ozone treatment step maintained at pH 8 to 12 (preferably pH 8 to 10) and the constant-temperature biological treatment step subsequent thereto. As a result, the methane gas conversion rate in the methane fermentation tank is improved, and the amount of excess sludge generated in the methane fermentation tank is greatly reduced, so that the sludge treatment cost can be reduced.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.
FIG. 1 is a schematic configuration diagram of a wastewater treatment method according to a reference example of the present invention. FIGS. 2 and 3 are schematic configuration diagrams of a wastewater treatment method according to another reference example corresponding to FIG.
[0015]
First, a reference example for facilitating understanding of the present invention will be described with reference to FIGS.
In FIG. 1, 1 is a biological treatment tank for performing activated sludge treatment or methane fermentation, 2 is a solid-liquid separator, 3a is a concentrating device, 4 is a constant temperature biological treatment device, and 5 is an ozone treatment device.
The wastewater in the present invention may be any wastewater containing organic matter in sewage sludge, factory wastewater or human waste treatment equipment, and the organic wastewater 10 is treated with activated sludge or methane by microorganisms present in the biological treatment tank 1. After being subjected to biological treatment such as fermentation, it is separated into excess sludge 12 and treated water 11 by the solid-liquid separator 2, and the treated water 11 is discharged out of the system.
[0016]
A part of the surplus sludge 12 is returned to the biological treatment tank 1, the other surplus sludge is introduced into the concentrating device 3 a, and the concentrated surplus sludge 14 is biologically treated in the constant temperature biological treatment device 4.
Since the growth of the lytic enzyme-producing microorganisms in the sludge is activated in the constant temperature biological treatment apparatus 4 in which the temperature range is maintained at about 60 to 80 ° C., the biodegradable substance in the excess sludge is produced by the lytic enzyme production. The sludge in which the low molecular weight is promoted by microorganisms and the hardly decomposable substance that cannot be treated in the constant temperature biological treatment apparatus 4 remains is solubilized in the ozone treatment apparatus 5 in the next stage.
[0017]
The ozone treatment apparatus 5 adds the alkali 6 to keep the excess sludge alkaline, preferably pH 8 to 10, and makes it easy to generate hydroxy radicals, which are radicals having very strong oxidizing power, and remains in the excess sludge. Although the degradable substance is decomposed, most of the organic substances excluding the hardly degradable substance are reduced in molecular weight by the constant temperature biological treatment apparatus. Therefore, the amount of ozone added to the ozone treatment apparatus 5 is less than the conventional amount. I'm sorry.
The surplus sludge decomposed in the ozone treatment device 5 is returned to the biological treatment tank 1 as a return sludge 15 and subjected to biological treatment again. However, the low-molecular-weight in the ozone treatment device 5 and the constant temperature biological treatment device 4. Since the surplus sludge that has been converted can be easily decomposed, biological treatment can be performed efficiently, and the amount of excess sludge generated by the biological treatment is reduced.
[0018]
2 and 3 show a wastewater treatment system corresponding to the reference example shown in FIG. 1, and FIG. 2 shows that the biological treatment is performed in the biological treatment tank 1 in the same manner as the reference example of FIG. The separated excess sludge is concentrated by the concentrating device 3a, the excess sludge having a reduced water content is reduced in molecular weight by the constant temperature biological treatment device 4, and then the excess sludge discharged from the constant temperature biological treatment device 4 is solid-liquid separated. Introducing into the apparatus 6, the excess water sludge is separated from the treated water 12 to further reduce the water content, and after being decomposed in the ozone treatment apparatus 5 to which the alkali 21 is added, the treated water 16 and the excess return sludge 15 Is returned to the biological treatment tank 1.
Thereby, since the surplus sludge amount to be ozone-treated is reduced from the first embodiment, the ozone addition amount is reduced, and the ozone addition cost can be reduced.
[0019]
FIG. 3 shows the constant temperature provided in the subsequent stage after the surplus sludge 14 discharged from the concentrator 3a is decomposed by the ozone treatment device 5 to which the alkali 21 is added in the solubilization means of the reference example. The molecular weight is reduced by the treatment biological device 4 and the surplus sludge 15 of the constant temperature treatment biological treatment device is returned to the biological treatment tank 1.
[0020]
In addition, the experimental result performed in order to obtain | require the optimal temperature range in the thermostat biological treatment apparatus 4 in these reference examples is shown to Fig.8 (a), (b). FIG. 8A is a reaction time-TOC graph showing a change in the activity of the lytic enzyme-producing microorganism in the sludge.
In the graph, the TOC concentration rapidly increases until the temperature is about 60 ° C. to about 80 ° C., and no remarkable effect is observed at 80 ° C. to 95 ° C. This is probably because microorganisms other than the lytic enzyme-producing microorganism are active at 60 to 80 ° C., but when the temperature exceeds 80 ° C. or higher, the lytic enzyme-producing microorganism is deactivated.
[0021]
FIG. 8 (b) shows the sludge temperature-TOC solubilization rate indicating the activity change of the lytic enzyme-producing microorganisms in the sludge. As is apparent from this graph, the sludge temperature was only raised to 50 ° C. as in the prior art. Then, the TOC solubilization rate shows almost no effect as compared with normal temperature (approximately 25 ° C.).
On the other hand, when the sludge temperature is raised to the maximum temperature of 100 ° C., there is no great difference from 80 ° C., but the heating cost at 80 ° C. is 260 yen / t, but the heating cost at 100 ° C. is 340 yen / t. And it becomes very expensive.
[0022]
Further, FIG. 9 shows a graph of the reaction time-TOC solubilization rate showing the solubilization effect accompanying the change of the sludge treatment temperature and the dissolved ozone concentration. As is clear from this, the TOC solubilization rate at room temperature (20 ° C.), pH 8, and dissolved ozone concentration 0 mg / g (O ₃ / SS) is only slightly increased with a residence time of 24 hours. Under the conditions of a temperature of 80 ° C., a pH of 9 and a dissolved ozone concentration of 50 mg / g, a solubilization rate of about 55% and a very high value are shown.
Thereby, it turns out that the effect by using together ozone treatment and a constant temperature biological treatment for a solubilization means is very large.
[0023]
Next, an embodiment of a wastewater treatment system equipped with the methane fermentation tank of the present invention will be described below with reference to FIGS.
[Example A]
First, the configuration of Example A will be described with reference to the overall configuration diagram of the wastewater treatment system shown in FIG.
Organic wastewater such as human waste and septic tank sludge is subjected to biological treatment such as biological denitrification treatment in the biological treatment tank 1, and then the excess sludge separated from the treated water in the solid-liquid separator 2 is removed by the dehydrator 3b. The dehydrated excess sludge is subjected to oxidative decomposition treatment of the organic matter in the excess sludge in an alkaline ozone treatment tank 5 having a pH of 8 to 10. The oxidatively decomposed surplus sludge is mixed with the garbage 22 in the constant temperature biological treatment device 4 maintained at about 60 to 80 ° C., further reduced in molecular weight by the lytic enzyme-producing microorganism, and then introduced into the methane fermentation tank 7. Make methane fermentation.
[0024]
The methane gas 17 generated in the methane fermentation is recovered and recycled, and the treated water 18 is discharged out of the system, and the excess sludge 19 discharged from the methane fermentation tank 7 is dehydrated by the dehydrator 3c, and then the post-treatment process is performed. Send or discard.
Thereby, it was confirmed that the sludge decomposition rate in the wastewater treatment method provided with the methane fermentation tank in the prior art was about 20 to 30%, but in this example, it was improved to about 50%.
[0025]
Here, the graph of the reaction time-sludge decomposition rate in the methane fermentation tank of the sludge solubilized in FIG. 10 is shown. Explaining the state of methane fermentation treatment of excess sludge with the graph, when the dissolved ozone concentration was 0 mg / g (O ₃ / SS) at room temperature (20 ° C.), the fermentation was carried out for 15 days (240 hours) in the methane fermentation tank. The sludge decomposition rate at that time shows a very low value of approximately 10%.
In addition, when the excess sludge is heated to a temperature of 60 ° C. and the dissolved ozone concentration is set to 0 mg / g, the sludge decomposition rate is approximately 25% after 15 days of fermentation, and the sludge decomposition rate is improved over the reaction at room temperature. However, the promotion of sludge decomposition is not sufficient.
[0026]
Therefore, when ozone is added to the surplus sludge so that the dissolved ozone concentration is about 50 mg / g and the temperature is 80 ° C., the sludge decomposition rate is as high as about 55%. This is because, in order to recover methane gas with high efficiency, not only heating the excess sludge to about 60-80 ° C. but also adding ozone may further promote the reduction of the molecular weight of the excess sludge. Understand.
[0027]
When the amount of methane gas generated and sludge treatment cost generated according to Example A is exemplarily determined, human waste 10 kl / day, septic tank sludge 70 kl / day, and garbage 1.3 t / day are treated.
Methane gas generation from human waste sludge (decomposition rate approximately 60%): 3.3 Nm ³ / kl
Methane gas generation from septic tank sludge (decomposition rate approximately 60%): 3.7 Nm ³ / kl
Amount of methane gas generated from garbage (decomposition rate approximately 70%): 78 Nm ³ / t
It becomes. (The decomposition rate means the decomposition rate of excess sludge.)
Therefore, the total amount of methane generated per day: 393 Nm ³ / day, or 1,171 Kwh / day per day when converted into the amount of power generation.
[0028]
In addition, the sludge treatment cost is
Sludge generation amount from methane fermenter: 2.4t / day If processing cost is 20,000 yen / t, the total processing cost is 48,000 yen / day. It can be understood that is reduced.
[0029]
[Example B]
FIG. 5 shows an overall configuration diagram of the embodiment B of the present invention.
This embodiment is the same as the embodiment A shown in FIG. 4 except that the excess sludge discharged from the methane fermentation tank 7 is dehydrated by the dehydrator 3c, and then at least a part of the excess sludge is returned to the sludge 20 as the ozone treatment apparatus. In this way, a return path for returning is added, so that the amount of methane gas generated is greatly improved, and the amount of surplus sludge generated is almost zero and an efficient wastewater treatment method is realized.
As a result of the verification experiment, it was confirmed that the sludge decomposition rate of the excess sludge of this example is expected to improve to about 60%.
[0030]
When determining the amount of methane gas generated and sludge treatment cost generated by Example B,
When the same conditions as in Example A are set and 10 kl / day of human waste, 70 kl / day of septic tank sludge, and 1.3 t / day of raw garbage are treated,
Methane gas generation from human waste sludge (decomposition rate approximately 80%): 4.42 Nm ³ / kl
Methane gas generation from septic tank sludge (decomposition rate approximately 80%): 4.98 Nm ³ / kl
Amount of methane gas generated from garbage (decomposition rate approximately 70%): 78 Nm ³ / t
Therefore, the total amount of methane generated per day: 494.2 Nm ³ / day, or 1,473 Kwh / day per day when converted into power generation.
[0031]
In the case of the above conditions, the sludge treatment cost is sludge generation amount from the methane fermentation tank: 1.2 t / day, and the total treatment cost: 24,000 yen / day.
[0032]
[Comparative example]
FIG. 6 shows an overall configuration diagram of a currently used wastewater treatment method.
In this wastewater treatment method, the organic wastewater 10 that has been subjected to biological treatment such as biochemical nitrogen removal treatment in the biological treatment tank 1 is separated into treated water 11 and surplus sludge by the solid-liquid separation device 2, and the surplus The sludge is dehydrated by the dehydrator 3b and then guided to the mixing tank 8, mixed with the garbage 22 in the mixing tank and retained for about one day, and then fed to the methane fermentation tank 7, where the methane fermentation is performed. It is fermented in the tank 7 for about two weeks, separated into treated water 18, excess sludge 19 and methane gas 17 and sent to a subsequent process.
[0033]
When calculating the amount of methane gas generated and the sludge treatment cost generated by the comparative example,
When the same conditions as in Example A are set and 10 kl / day of human waste, 70 kl / day of septic tank sludge, and 1.3 t / day of raw garbage are treated,
Methane gas generation from human waste sludge (decomposition rate approximately 80%): 1.66 Nm ³ / kl
Methane gas generation amount from septic tank sludge (decomposition rate approximately 80%): 2.18 Nm ³ / kl
Amount of methane gas generated from garbage (decomposition rate approximately 70%): 78 Nm ³ / t
Therefore, the total amount of methane generated per day: 270.0 Nm ³ / day, or 804 Kwh / day per day when converted into power generation.
[0034]
In the case of the above conditions, the sludge treatment cost is sludge generation amount from the methane fermentation tank: 4.3 t / day, and the total treatment cost: 86,000 yen / day.
[0035]
From the above examples, in the wastewater treatment method in Example A, the power generation amount is increased by 367 Kwh / day and the processing cost is reduced by 38,000 yen / day compared to the comparative example, and in Example B, compared with the comparative example. The amount of power generation will increase by 669 Kwh / day, and the processing cost will be reduced by 62,000 yen.
In Example A, the surplus sludge discharged from the biological treatment tank such as the human waste treatment apparatus is solubilized to improve the conversion efficiency to methane gas, reduce the excess sludge from the methane fermentation tank, and reduce the sludge treatment cost. Will also be reduced.
Moreover, in Example B, the surplus sludge of the methane fermentation tank, which is more difficult to convert to methane gas, is returned to the solubilization means and reprocessed in the methane fermentation tank, so that the amount of methane gas generated is greatly increased. Further, it is possible to provide a wastewater treatment method in which the generation of the excess sludge is almost zero.
[0036]
【The invention's effect】
As described above, by providing the step of dehydrating the excess sludge with a dehydrator before the ozone treatment step, the amount of sludge to be treated in the solubilization treatment device is reduced, and the ozone addition cost and the heating cost can be reduced. .
Further, the solubilization treatment can be performed with high efficiency by maintaining the ozone treatment step in an alkaline state of pH 8 to 12 (preferably pH 8 to 10) and a constant temperature biological treatment apparatus at about 60 to 80 ° C. it can.
[0037]
Also, according to the invention, the ozone treatment step, by providing a thermostatic biological treatment step, methane emissions will increase further, reprocessing the excess sludge produced in the methane fermentation tank and return to the solubilization means By doing so, it is possible to provide a wastewater treatment method in which the amount of methane generated is greatly increased and the generation of the excess sludge is almost zero.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a reference example according to the wastewater treatment method of the present invention.
FIG. 2 is a schematic configuration diagram showing another reference example corresponding to FIG. 1;
FIG. 3 is a schematic configuration diagram showing another reference example corresponding to FIG. 1;
FIG. 4 is an overall configuration diagram showing Example A of a wastewater treatment method provided with a methane fermentation tank of the present invention.
FIG. 5 is an overall configuration diagram showing Example B of the waste water treatment method corresponding to FIG. 4;
6 is an overall configuration diagram showing a comparative example of a wastewater treatment method corresponding to FIG. 4;
FIG. 7 is a schematic configuration diagram of a wastewater treatment method showing a conventional technique.
FIG. 8 is a reaction time-TOC graph (a) and a reaction temperature-TOC solubilization rate graph (b) showing changes in the activity of a lytic enzyme-producing microorganism in sludge.
FIG. 9 is a graph of reaction time-TOC solubilization rate showing the solubilization effect associated with changes in the sludge treatment temperature and dissolved ozone concentration.
FIG. 10 is a graph showing reaction time-sludge decomposition rate in a methane fermentation treatment tank of sludge solubilized.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Biological treatment tank 2 Solid-liquid separation apparatus 3a Concentration apparatus 3b, 3c Dehydrator 4 Constant temperature biological treatment apparatus 5 Ozone treatment apparatus 6 Solid-liquid separation apparatus 7 Methane fermentation tank 13 Return sludge 17 Methane gas 21 Alkali

Claims

In a biological treatment step that performs biological treatment on organic wastewater in a biological treatment tank, a solid-liquid separation step that separates excess sludge and treated water discharged from the biological treatment tank with a solid-liquid separation device, and a dehydrator A step of dehydrating the excess sludge, an ozone treatment step of performing ozone treatment on the excess sludge dehydrated by the dehydrator under an alkaline condition of pH 8 to 12 in an ozone treatment device, and a temperature range of approximately 60 to 80 ° C. A constant temperature biological treatment step for reducing the molecular weight of organic matter contained in the excess sludge after the ozone treatment in a constant temperature biological treatment apparatus in the presence of a lytic enzyme-producing microorganism; Do and a methane fermentation step for subjecting the anaerobic biological treatment by Ri,
The constant temperature biological treatment step is a constant temperature biological treatment step in which the organic matter contained in the excess sludge after the ozone treatment is reduced in the presence of lytic enzyme-producing microorganisms in the presence of lytic enzyme producing microorganisms in a temperature range of about 60-80 ° C. waste water treatment method characterized in that there.

Claim 1, characterized in that return provided the step of dewatering the surplus sludge is discharged from the methane fermentation tank in the subsequent stage of the methane fermentation step, at least part of the excess sludge dehydrated in the dehydration step in the ozone treatment step The described waste water treatment method.

In a biological treatment step that performs biological treatment on organic wastewater in a biological treatment tank, a solid-liquid separation step that separates excess sludge and treated water discharged from the biological treatment tank with a solid-liquid separation device, and a dehydrator A step of dehydrating the excess sludge, an ozone treatment step of performing ozone treatment on the excess sludge dehydrated by the dehydrator under an alkaline condition of pH 8 to 12 in an ozone treatment device, and a temperature range of approximately 60 to 80 ° C. A constant temperature biological treatment step for reducing the molecular weight of organic matter contained in the excess sludge after the ozone treatment in a constant temperature biological treatment apparatus in the presence of a lytic enzyme-producing microorganism; Methane fermentation step that performs anaerobic biological treatment at
A wastewater treatment method characterized in that a step of dewatering excess sludge discharged from the methane fermentation tank is provided after the methane fermentation step, and at least a part of the excess sludge dehydrated in the dewatering step is returned to the ozone treatment step. .