JP3884638B2

JP3884638B2 - Method and apparatus for disinfecting sewage in rainy weather in combined sewers

Info

Publication number: JP3884638B2
Application number: JP2001321804A
Authority: JP
Inventors: 弘鳥海; 弘高須; 忠志名川; 純雄安斎; 純夫小峯; 准一稲村; 和広長谷川; 秀潔吉田
Original assignee: Ebara Corp; Tokyo Metropolitan Government
Current assignee: Ebara Corp; Tokyo Metropolitan Government
Priority date: 2001-10-19
Filing date: 2001-10-19
Publication date: 2007-02-21
Anticipated expiration: 2021-10-19
Also published as: JP2003121431A

Description

【０００１】
【発明の属する技術分野】
本発明は、合流式下水道において、雨水を含む下水（以下、雨天時下水という）を消毒剤により消毒処理する方法及び装置に関し、更に詳細には、雨天時下水の大腸菌群数と濁度とを指標として消毒剤注入率を求め、雨天時下水を消毒剤により消毒処理する方法及び装置に関する。
【０００２】
【従来の技術】
合流式下水道は、一般に、図１に示すように、一般家庭、事務所、公共施設などの汚水排出源１から排出される汚水や雨水源２から排出される雨水を集めて流す下水道管渠３、集めた下水を処理場まで送るための中継基地となるポンプ所５、送られてきた下水を浄化して河川や海などの放流水域に放流する下水処理場６などにより構成されている。
【０００３】
前記合流式下水道では、通常、下水処理場６に送られた下水は、砂などを除去するための沈砂池処理、活性汚泥処理、次いで消毒処理などを経て、放流水域に放流される。
【０００４】
しかし、集中豪雨などで浄化処理能力を超える大量の雨天時下水が下水処理場６に流れ込んできた場合に、その超過分は一次処理（沈砂池処理）の状態で放流される（７ａ）。また、雨水吐き室４、ポンプ所５においても、雨天時下水の流量が計画流量を超えたときに超過分は未処理で河川や海域に放流される（７ｂ及び７ｃ）。このように処理予定量を上回る雨天時下水を含み、一次処理又は未処理で放流水域に放流されるものを雨天時越流水という。
【０００５】
これらの雨天時越流水の放流は、浸水被害などを未然に防ぐために行われている。一方、雨天時越流水は、雨水によって希釈されているとはいえ汚水を含むので、未処理の汚水が河川や海域に放流されることになり、水質汚濁学的見地からは大腸菌群を指標とした消毒処理が必要である。
【０００６】
このような浄化処理能力を超える場合の消毒処理方法として、累積降雨量と降雨強度とを指標として消毒剤の注入量を決定し、ポンプ所放流水を消毒する消毒処理方法が提案されている。
【０００７】
しかしこの方法には、雨天時下水の水質、例えば消毒剤を消費する有機物及び／又は無機物が消毒効果に及ぼす影響を消毒剤の注入量に反映できないという問題があった。
【０００８】
下水処理場で処理された放流水とは異なり、雨天時下水の水質は、降雨の状況により瞬時に大きく変動するものである。すなわち、降雨初期など雨水の含有比率が低く、汚水濃度が高く且つ還元性の有機物濃度及び／又は無機物濃度が高い場合と、雨水による希釈が進んで汚水濃度が低下し且つ還元性の有機物濃度及び／又は無機物濃度が低下した場合では、酸化能力を有する消毒剤の必要量が異なる。このため消毒剤注入率の管理が難しく、過剰注入や過小注入になりやすい、という問題があった。すなわち、消毒剤過剰注入の場合には、放流水中に活性な消毒剤成分が残存したまま放流水域に放流されることになり、河川や海域の生物に悪影響を及ぼすおそれが大きく、消毒剤の経済的損失も大きい。一方、消毒剤過少注入の場合には、消毒剤量が不足し、十分な消毒効果が得られない、という問題がある。
【０００９】
これまで、消毒剤の過剰注入や過小注入を防ぎ、最適量を注入し効率的に消毒するためには、雨天時下水の化学的酸素要求量（ＣＯＤ）、塩素必要量、ヨウ素消費量、有機物濃度などを測定し、これらを還元性の有機物濃度及び／又は無機物濃度の指標として、消毒剤注入率を決定する必要があった。しかし、還元性の有機物濃度及び／又は無機物濃度の指標となるＣＯＤ、塩素必要量、ヨウ素必要量、有機物濃度の測定は煩雑であり、瞬時にモニタすることは難しい。したがって、降雨の状況により瞬時に大きく変動する雨天時下水水質に対応して、過剰注入や過小注入とならない最適な消毒剤注入率を決定するために、還元性の有機物濃度及び／又は無機物濃度の指標となるＣＯＤや塩素必要量、ヨウ素消費量、有機物濃度などを測定する方法を用いることは実用的ではなかった。例えば、下水処理場からの処理水の消毒において、処理水の有機物濃度測定値を指標として塩素注入率を演算し、消毒する消毒処理方法が提案されているが、降雨の状況により瞬時に大きく変動する雨天時下水の消毒には適用することができなかった。
【００１０】
【本発明が解決しようとする課題】
したがって、本発明の目的は、降雨状況により変動する雨天時下水の消毒処理において、過剰注入又は過小注入とならないような最適な消毒剤注入率を簡易且つ瞬時に決定し、雨天時越流水として放流水域に放流される雨天時下水の消毒処理を効果的に行う方法及び装置を提供することにある。
【００１１】
【課題を解決するための手段】
本発明者らは、上記課題を解決すべく、種々の条件での雨天時下水の水質を分析した結果、雨天時下水の濁度と、還元性の有機物濃度及び／又は無機物濃度の指標となるＣＯＤとの間には、高い相関関係があることを知見した。更に、本発明者らは、還元性の有機物及び／又は無機物での消毒剤の消費量が同じであっても、消毒対象である大腸菌群などが多い場合と少ない場合とでは消毒剤の必要量が異なることをも知見した。これらの知見に基づいて、下水の濁度と大腸菌群数とを指標として最適な消毒剤注入率を求めることにより、前記目的を達成しうることを見出し、本発明を完成するに至った。
【００１２】
すなわち、本発明は、合流式下水道の雨天時下水を消毒剤により消毒するに際し、雨天時下水の大腸菌群数と濁度とを指標として消毒剤注入率を決めることを特徴とする消毒処理方法を提供するものである。
【００１３】
前記雨天時下水とは、汚水排出源からの汚水と雨水とが合流して得られる混合下水を意味する。
前記消毒剤としては、通常、放流下水の消毒に用いることができるものであれば特に制限なく用いることができるが、本発明においては、酸化能力を有する消毒剤が特に好ましく用いられる。
【００１４】
酸化能力を有する消毒剤としては、次亜塩素酸ソーダ、塩素、さらし粉などの塩素系消毒剤や、ＢＣＤＭＨ（１−ブロモ−３−クロロ−５，５−ジメチルヒダントイン）等の臭素系消毒剤などが挙げられるが、これらに制限されない。
【００１５】
雨天時下水の大腸菌群数と濁度とは、雨天時下水を適宜サンプリングして得られた下水サンプルについて測定するが、特に、ポンプ所流入下水、下水処理場流入下水又は雨水吐き室流入下水をサンプリングして得られた下水サンプルについて大腸菌群数と濁度とを測定することが好ましい。なお、ポンプ所流入下水、下水処理場流入下水及び雨水吐き室流入下水については、後述する。
【００１６】
雨天時下水中の大腸菌群数は、酵素抗原抗体反応や蛍光酵素発色反応などを応用した大腸菌群数測定器等（例えば、明電舎（株）製のＵＰＤ−７７００Ｅなど）の、当該技術において公知の手法を用いて測定することができる。
【００１７】
濁度は、排水などの濁り具合を評価するための数値であり、一般に市販されている濁度計（例えば電気化学計器（株）製のＳＳＴ−５など）を用いて、極めて容易に測定することができる。濁度は、瞬時に測定可能であるばかりか、非常に簡易な方法で測定できる。このため、濁度を測定することにより前記消毒剤の消費量を瞬時に推定することが可能となる。
【００１８】
雨天時下水への消毒剤の最適注入率は、例えば、以下の方法によって求めることができる。すなわち、種々の下水を試水として用いる机上消毒試験によって、試水の大腸菌群数の範囲ごとに、（ア）試水の濁度と、（イ）処理目標とする消毒効果（例えば大腸菌群数を水質汚濁防止法の放流規制値である３０００CFU/mL以下にする)を、目標とする残留ハロゲン濃度で達成するために必要な消毒剤の注入率との関係を求めておき、この関係を用いて、実際の施設において測定された雨天時下水の大腸菌群数及び濁度から求められる消毒剤の最適注入率を求め、求められた注入率で雨天時下水に消毒剤を投入することによって、その条件下での最適の消毒を行うことができる。
【００１９】
なお、雨天時下水中の大腸菌群数は上述したような測定法によって測定することもできるが、この代わりに、下水排除施設に所定量以上の雨天時下水が流入開始してから流入が終了するまでの時間を複数の時間帯に分割し、それぞれの時間帯ごとに降雨量と濁度とを測定し、得られた降雨量と濁度とを指標として下水中の大腸菌群数を推定することもできる。すなわち、ポンプ所、下水処理場、雨水吐き室などの下水排除施設に所定流量以上の雨天時下水が流入開始してからの経過時間範囲毎に、降雨量と濁度とを測定し、測定された降雨量と濁度とを必須の指標として推定的に算出することができる。これにより、大腸菌群数を実際に測定する場合に比して簡易且つ瞬時に推定できる。
【００２０】
更に具体的に説明すると、ポンプ所、下水処理場、雨水吐き室等の施設に、所定流量以上の雨天時下水が流入開始してから、経過時間０〜Ｘ分、Ｘ＋１〜Ｙ分（Ｘ，Ｙは、いずれも整数を示し、Ｙ＞Ｘである）の各範囲において、濁度と降雨量とを測定する。次いで得られたデータを独立変数として、下記式（１）に代入することにより大腸菌群数を推定できる。
【００２１】
【式１】
Ｃ＝ａ×Ｒ＋ｂ×Ｔ＋ｃ…（１）
〔式中、Ｃは大腸菌群数(CFU/mL)を示し、Ｒは、所定時間あたりの降雨量(mm)を示し、Ｔは、濁度（度）を示す。また、ａ，ｂ，ｃは、それぞれ定数である。〕
前記式（１）において、定数ａ，ｂ，ｃは、それぞれ所定流量以上の雨天時下水が流入を開始してからの経過時間やポンプ所、雨水吐き室、処理場などの対象となる雨天時下水排除施設、流域環境により異なる。定数ａ，ｂ，ｃは、例えば、対象となる雨天時下水排除施設において、種々の気象条件下での雨天時下水について、降雨量、雨天時下水の大腸菌群数及び濁度を測定し、測定された数値を変数として重回帰分析することによって求めることができる。なお、この手法において、流入開始から流入終了までの時間を複数の時間帯に分割しないで、降雨量と濁度を測定しただけでは、重回帰分析の決定係数が低く、信頼性のある結果が得られない。
【００２２】
また、降雨量及び濁度の他に、電気伝導率、ＳＳ(懸濁物質）、ＳＳの粒度、ｐＨ、アンモニア性窒素濃度などの水質項目を変数に加えて大腸菌群数を推定しても良い。
【００２３】
このようにして大腸菌群数が推定できる論拠については、詳細は不明であるが、下水排除施設に流入する大腸菌群数が、以下のような挙動をとることに関係していると考えられる。
【００２４】
すなわち、下水道管渠内に堆積している大腸菌群を含有する汚濁物は、下水流量が所定流量に達すると流動しやすくなり、雨天時下水排除施設に本格的に流入し始める。大腸菌群は、下水道管渠内に堆積している汚濁物中に多量に含有されているので、下水流量が所定流量に達して、下水道管渠内に堆積している汚濁物が本格的に流動を開始した直後は、雨天時下水排除施設への大腸菌群の流入量が多い。しかし、時間の経過と共に、下水道管渠内の堆積物量は減少し、同じ下水流量であっても、雨水の含有割合が高くなり汚濁物の含有割合が減少するので、大腸菌群の流入量は減少すると考えられる。また、下水の濁度は、汚濁物含有割合が高いほど高く、汚濁物含有割合が低くなるほど低下する。すなわち、下水の濁度が高いほど、汚濁物含有割合が高く、大腸菌群数も高いと考えられる。一方、降雨量は、路面や家屋の屋根などに堆積している大腸菌群を含有する土壌の流入量及び雨天時下水の汚水と雨水との含有比率すなわち汚水の希釈割合に影響を与えると考えられる。
【００２５】
なお、本発明において、雨天時下水の大腸菌群数を降雨量と濁度とから推定する場合には、下水排除施設に所定量以上の雨天時下水が流入開始してから流入が終了するまでの時間を複数の時間帯に分割し、それぞれの時間帯ごとに降雨量を測定するが、ここでいう所定量とは、例えば、雨天時下水排除施設で雨天時越流水の放流が始まるときの雨天時下水の流入量としても良いし、或いはその他任意に設定された流入量を設定しても良い。
【００２６】
また、本発明は、上記に説明した本発明に係る技術思想に基づいて雨天時下水を消毒処理する装置も提供する。即ち、本発明の他の態様は、雨天時下水を消毒剤により消毒する消毒槽と；該消毒槽で消毒した下水を放流水域に放流する下水放流手段と；を備え、更に、該消毒槽に導入される下水の濁度及び大腸菌群数を測定する測定手段と；該測定手段によって測定された下水の濁度及び大腸菌群数を指標として下水に加える消毒剤の添加率を制御する制御手段と；を備えることを特徴とする雨天時下水の消毒処理装置に関する。更に本発明の更なる態様は、雨天時下水を消毒剤により消毒する消毒槽と；該消毒槽で消毒した下水を放流水域に放流する下水放流手段と；を備え、更に、該消毒槽に導入される下水の濁度を測定する濁度測定手段と；降雨量を測定する降雨量測定手段と；該濁度測定手段によって測定された下水の濁度と、該降雨量測定手段によって測定された下水排除施設に所定量以上の雨天時下水が流入開始してからの経過時間範囲毎における降雨量と下水の濁度とを指標として推定された大腸菌群数とを指標として下水に加える消毒剤の添加率を制御する制御手段と；を備えることを特徴とする雨天時下水の消毒処理装置に関する。
【００２７】
前記消毒槽は、沈砂地としても作用するようになされていることが好ましい。
【００２８】
【発明の実施の形態】
以下、図面を参照しながら、本発明の雨天時下水消毒処理装置の好ましい一実施形態について説明する。
【００２９】
本発明の消毒処理方法を実施するための装置の一具体例を図２に示す。
図２に示す装置10は、雨天時下水19を消毒剤により消毒する消毒槽11と、該消毒槽11で消毒した下水を放流水域17に放流する下水放流手段13及び通常の活性汚泥処理や消毒処理などの処理工程に移送する移送手段14と、該消毒槽11に導入される下水の濁度を測定する濁度測定手段18と、を具備する。
【００３０】
図２に示す処理装置は、大腸菌群数の測定装置を設けずに、濁度計で測定された雨天時下水の濁度と、降雨量計（図示せず）によって測定された降雨量とから大腸菌群数を推定するものであるが、雨天時下水中の大腸菌群数を直接測定する大腸菌群数測定装置を設置することも可能である。
【００３１】
図２に示す処理装置10は、図１における下水道管渠３、雨水吐き室４、ポンプ所５及び下水処理場６のいずれかに設けることができる。
具体的には、本実施形態において、雨水排除施設がポンプ所の場合を例にとると、消毒槽としては、１次処理のために下水が導入される沈砂池11を用いることができ、沈砂池11には消毒剤を貯留する消毒剤貯留槽15が設けられている。また、下水放流手段としては、沈砂池11にポンプ井12を介して連結された雨水ポンプ13が設けられており、移送手段14としてはポンプ井12を介して連結された槽排水ポンプ14が設けられている。そして濁度測定手段18としては、沈砂池11に雨天時下水を供給する下水管渠に濁度計18が設けられている。
【００３２】
次に、図２に示す装置をポンプ所に設置した場合を例にとり、本発明の雨天時下水の消毒処理方法について具体的に説明する。
本発明の雨天時下水の消毒処理方法は、合流式下水道の雨天時下水を消毒剤により消毒するに際し、雨天時下水のサンプルの大腸菌群数と濁度とを指標として消毒剤注入率を決めることを特徴とする。
【００３３】
本発明の消毒処理方法を図２の装置を用いて実施するには、先ず、上記に説明した方法によって、予め雨天時下水の濁度及び大腸菌群数と消毒剤最適注入率との関係を求めておくと共に、消毒処理を行う下水排除施設において、降雨量及び雨天時下水の濁度と大腸菌群数との関係を求めておく。
【００３４】
雨天時下水の消毒処理にあたっては、１次処理を施すべく沈砂池11に雨天時下水を供給する際に、下水の濁度を濁度計18により測定する。また、これとは別に降雨量を外部の降雨計（図示せず）により測定する。そして、これらの測定値を予め机上で作成しておいた回帰式に代入して消毒剤注入率を決定し、消毒剤貯留槽15から消毒剤注入点16において所定量の消毒剤を沈砂池11中の下水に混入する。
【００３５】
そして、消毒剤と雨天時下水とを撹拌して十分に接触させることにより所定時間消毒処理を行った後、二次処理可能な量の下水は槽排水ポンプ14などの移送手段を通じて下水処理場に移送し、下水処理場の許容量を超える場合にはポンプ井12を切り替えて雨水ポンプ13などの下水放流手段により放流水域17に放流する。
【００３６】
このように実施される本発明の合流式下水道雨天時下水の消毒処理方法によれば、消毒剤を過剰に注入したり、過少に注入することなく、最適な消毒剤注入率で十分に消毒することが可能である。
【００３７】
【実施例】
以下本発明を実施例及び比較例により更に具体的に説明するが本発明はこれらに限定されるものではない。
【００３８】
試験例１：雨天時下水の濁度及び大腸菌群数と、消毒剤注入率との関係
雨天時下水を試水として、消毒剤としてＢＣＤＭＨ（1-ブロモ-3-クロロ-5,5-ジメチルヒダントイン）を用い、消毒剤注入率を変えて、雨天時下水の濁度及び大腸菌群数と、消毒後の大腸菌群数及び残留ハロゲン濃度との関係を机上で試験した。
【００３９】
この試験は、消毒後に残留ハロゲンを検出させることなく、大腸菌群数を水質汚濁防止法の放流基準である３×１０³(CFU/mL)以下に処理することを消毒目標とし、処理目標を達成するのに必要な消毒剤注入率を雨天時下水の濁度及び大腸菌群数の範囲毎に明らかにするために実施したものである。
【００４０】
具体的には、各試験条件ごとに、ガラスビーカーに試水５００mLをとり、大腸菌群数と濁度を測定した後に、攪拌羽根にて周速度０．５m/秒で攪拌しながら、表１に示す所定量のＢＣＤＭＨを添加した。添加後、攪拌を継続しながら、１分経過後採水し、大腸菌群数と残留ハロゲン濃度とを測定した。なお、試水の濁度は散乱光測定法により、大腸菌群数はデソキシコール酸塩培地法により、残留ハロゲン濃度はオルトトリジン法により測定した。残留ハロゲン濃度は、残留する消毒剤の活性成分量の指標となる。このように試験を行い、雨天時下水の濁度及び大腸菌群数の範囲、消毒剤注入率、消毒後の大腸菌群数及び消毒後の残留ハロゲン濃度を求めた。その結果を表１に示す。
【００４１】
【表１】

【００４２】
表１に示す結果から、雨天時下水の濁度、大腸菌群数及び消毒剤注入率の関係について、一例を挙げて説明する。
雨天時下水の濁度Ｔが２５＜Ｔ≦５０(度)、試水の大腸菌群数Ｃが１０⁴＜Ｃ≦１０⁵(CFU/mL)のときの各消毒剤注入率における消毒効果を比較すると、消毒剤注入率が３〜５mg/Lの場合（試験条件５）には、残留ハロゲンを検出させることなく、大腸菌群数を３×１０³(CFU/mL)以下に消毒できたことがわかる。しかし、消毒剤注入率が６〜８mg/Lの場合（試験条件１７）には、大腸菌群数は３．０×１０³(CFU/mL)以下に消毒できるものの、残留ハロゲンが検出された（０．１〜０．２mg/L as Cl）。また、消毒剤注入率が１〜２mg/Lの場合（試験条件２９）には、残留ハロゲンは検出されなかったが、大腸菌群数を３×１０³(CFU/mL)以下に消毒できなかった。
【００４３】
これらの結果から、雨天時下水の濁度Ｔ及び大腸菌群数Ｃの範囲が、それぞれ、２５＜Ｔ≦５０(度)、１０⁴＜Ｃ≦１０⁵(CFU/mL)の条件下においては、残留ハロゲンを検出させることなく、大腸菌群数が3×10³(CFU/mL)以下になるように消毒するための最適消毒剤注入率は、３〜５mg/Lであると求められる。
【００４４】
表１から、試験条件１〜１２では、残留ハロゲンを検出させることなく、大腸菌群数を目標値の３×１０³(CFU/mL)以下に消毒でき、雨天時下水の濁度と大腸菌群数ごとに、最適な消毒剤注入率の範囲を得た。しかし、試験条件１３〜２４では、大腸菌群数を３×１０³(CFU/mL)以下に消毒できたが、残留ハロゲンが検出され（過剰注入）、試験条件２５〜３６では、残留ハロゲンは検出されなかったが、大腸菌群数を３×１０³(CFU/mL)以下に消毒できなかった（過小注入）。
【００４５】
これらの結果から、雨天時下水の濁度Ｔ及び大腸菌群数Ｃの範囲毎に、残留ハロゲンを検出させることなく、大腸菌群数を３×１０³(CFU/mL)以下とするための最適消毒剤注入率を表２にまとめた。
【００４６】
【表２】

【００４７】
試験例２：降雨量及び雨天時下水の濁度と、大腸菌群数との関係
実際に稼動しているポンプ所において、種々の気象条件下での雨天時下水について、流入下水の大腸菌群数、濁度、及び降雨量を測定した。大腸菌群数及び濁度の測定は、試験例１と同様に行い、降雨量の測定は、転倒ます式によって計測した。雨天時下水の流入量が、放流するために設置されている雨水ポンプが稼動する流量（本実施例においては８０m³/min）に達し、雨水ポンプが可動し始めてからの経過時間Ｐが、Ｐ＜３０(分)、３０(分)≦Ｐの各範囲において、流入下水の大腸菌群数を従属変数とし、降雨量と、流入下水の濁度を独立変数として、重回帰分析したところ、決定係数（Ｒ²）０．５以上の相関で回帰式が得られた。その結果を表３及び表４に示す。また、雨水ポンプが稼動し始めてからの経過時間Ｐが０（分）＜Ｐにおいて、流入下水の大腸菌群数を従属変数とし、降雨量と、流入下水の濁度を独立変数として、重回帰分析したところ、決定係数（Ｒ²）は０．３５以下であった。この結果を表５に示す。
【００４８】
【表３】

【００４９】
【表４】

【００５０】
【表５】

【００５１】
実施例及び比較例
試験例２と同じポンプ所において、流入する雨天時下水を以下の方法で消毒処理した。
【００５２】
図２に示す装置を用い、消毒処理は、雨水ポンプ13が稼動して、雨天時越流水が放流水域に放流される条件で行った。消毒剤としては、ＢＣＤＭＨを用いた。雨天時下水サンプルの濁度は、ポンプ所に流入する箇所で、濁度計18（電気化学計器（株）製のＳＳＴ−５）で測定して、実測値を得た。大腸菌群数は、雨水ポンプ稼動開始からの経過時間ＰがＰ＜３０（分）の場合は表３に示した回帰式から推定し、雨水ポンプ稼動開始からの経過時間ＰがＰ≧３０（分）の場合は表４に示した回帰式から推定した。
【００５３】
所定量の消毒剤を沈砂池11入り口の消毒剤注入点16で注入した。消毒剤が注入された雨天時下水の一部は、雨水ポンプ13により放流水域17に放流した。この放流された消毒処理後の下水を採取し、消毒処理後の下水サンプル中の大腸菌群数をデソキシコレート寒天培地法によって測定した。また、消毒処理後の下水の残留ハロゲン濃度をポーラログラフ法により測定した。なお、消毒処理前の流入雨天時下水中の大腸菌群数についても、上記と同様のデソキシコレート寒天培地法によって測定し、実測値を得た。
【００５４】
表６に雨水ポンプ稼動開始からの経過時間ＰがＰ＜３０（分）の時の、降雨量、流入雨天時下水の濁度、表３の回帰式から求めた流入雨天時下水サンプル中の推定大腸菌群数、デソキシコレート寒天培地法によって求めた流入雨天時下水サンプル中の大腸菌群数の実測値、流入雨天時下水の濁度Ｔ及び大腸菌群数Ｃから決定した設定注入率（表２から求めた）、実際の注入率、消毒後の大腸菌群数と残留ハロゲン濃度を示す。
【００５５】
同様に、表７に雨水ポンプ稼動開始からの経過時間ＰがＰ≧３０（分）のときの、降雨量、流入雨天時下水の濁度、表４の回帰式から求めた流入雨天時下水サンプル中の推定大腸菌群数、デソキシコレート寒天培地法によって求めた流入雨天時下水大腸菌群数、流入雨天時下水の濁度Ｔ及び大腸菌群数Ｃから決定した設定注入率（表２から求めた）、実際の注入率と、消毒後の大腸菌群数と残留ハロゲン濃度を示す。
【００５６】
【表６】

【００５７】
【表７】

【００５８】
表６及び７に示す結果から、実施例１〜３、５〜８では、設定注入率の範囲内で消毒剤を注入したところ、消毒後下水からは、残留ハロゲンが検出されず、大腸菌群数を３×１０³(CFU/mL)以下に消毒できたことがわかる。一方、比較例１〜４及び比較例６〜７では、実際の注入率が設定注入率より低く、消毒後下水の大腸菌群数が３×１０³(CFU/mL)を越えており、充分に消毒できなかったことがわかる。比較例５及び比較例８〜１０では、実際の注入率が設定注入率より高く、処理後下水の大腸菌群数を３×１０³(CFU/mL)以下に消毒することはできたものの、残留ハロゲンが検出されたことがわかる。
【００５９】
【発明の効果】
以上詳述したように、本発明の消毒処理方法によれば、水質が瞬時に大きく変動する雨天時下水の消毒処理において、雨天時下水中の汚水濃度が高く、汚染指標細菌である大腸菌群数や酸化性消毒剤を消費する還元性の有機物濃度及び／又は無機物濃度が高い場合でも、あるいは低い場合でも、雨天時下水中の大腸菌群数及び濁度を指標として、最適な消毒剤注入率を求めることができ、消毒剤の過剰注入又は過少注入などを防止できる。この結果、過剰に注入した場合に懸念される消毒剤の活性成分が残留したまま河川や海域に放流されることに起因する生態系への悪影響や、過少注入による不十分な消毒効果などの問題を起こすことなく、雨天時下水を消毒処理することができ、しかも、消毒剤を過剰に注入することがなくなるので経済的である。更には、本発明の更なる態様においては、下水中の大腸菌群数を、下水の濁度と、降雨量から推定することができ、より簡便に最適の消毒剤注入率を求めることができる。
【図面の簡単な説明】
【図１】図１は、本発明の消毒処理方法を適用することのできる合流式下水道の構成の一例を示す概略図である。
【図２】図２は、本発明の雨天時下水の消毒処理装置の要部を概略的に示す模式図である。
【符号の説明】
1：汚水排出源
2：雨水源
3：下水道管渠
4：雨水吐き室
5：ポンプ所
6：下水処理場
7：放流水域
10：雨天時下水消毒処理装置
11：消毒槽（沈砂池）
12：ポンプ井
13：雨水ポンプ
14：槽排水ポンプ
15：消毒剤貯留槽
16：消毒剤注入点
17：放流水域
18：濁度計
19：雨天時下水[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for disinfecting sewage containing rainwater (hereinafter referred to as sewage in rainy weather) with a disinfectant in a combined sewer, and more specifically, the coliform count and turbidity of sewage in rainy weather. The present invention relates to a method and apparatus for obtaining a disinfectant injection rate as an index and disinfecting sewage in rainy weather with a disinfectant.
[0002]
[Prior art]
As shown in FIG. 1, a combined sewer generally has a sewer pipe 3 that collects and flows sewage discharged from a sewage discharge source 1 such as a general household, an office, or a public facility or rainwater discharged from a rainwater source 2. The pump station 5 serves as a relay base for sending the collected sewage to the treatment plant, and the sewage treatment plant 6 purifies the sent sewage and discharges it into a discharge water area such as a river or the sea.
[0003]
In the combined sewer system, the sewage sent to the sewage treatment plant 6 is usually discharged into a discharge water area through a sand basin treatment for removing sand and the like, an activated sludge treatment, and then a disinfection treatment.
[0004]
However, when a large amount of rainy sewage that exceeds the purification capacity due to heavy rain flows into the sewage treatment plant 6, the excess is discharged in the state of primary treatment (sedimentation basin treatment) (7a). In the rainwater discharge chamber 4 and the pump station 5, when the flow rate of sewage in rainy weather exceeds the planned flow rate, the excess amount is untreated and discharged into rivers and sea areas (7b and 7c). In this way, rainwater that overflows in the amount that is expected to be treated and that is discharged into the discharge water area in the primary treatment or untreated is called rainwater overflow.
[0005]
These overflowing rainwater discharges are carried out to prevent inundation damage. On the other hand, rainwater overflowing water contains sewage even though it is diluted with rainwater, so untreated sewage is discharged into rivers and seas, and from the perspective of water pollution, the coliform group is used as an indicator. Disinfection is necessary.
[0006]
As a sterilization treatment method in the case where the purification treatment capacity is exceeded, a sterilization treatment method has been proposed in which the injection amount of the disinfectant is determined using the accumulated rainfall amount and the rainfall intensity as an index, and the pump station discharge water is disinfected.
[0007]
However, this method has a problem in that the influence of the quality of sewage in rainy weather, for example, organic substances and / or inorganic substances that consume the disinfectant, on the disinfecting effect cannot be reflected in the injection amount of the disinfectant.
[0008]
Unlike effluent treated at a sewage treatment plant, the quality of sewage during rainy weather varies greatly depending on the rainfall conditions. That is, when the content of rainwater is low, such as at the beginning of the rain, when the sewage concentration is high and the reducing organic substance concentration and / or the inorganic substance concentration is high, dilution with rainwater proceeds and the sewage concentration decreases and the reducing organic substance concentration and When the mineral concentration is reduced, the required amount of the disinfectant having oxidation ability is different. For this reason, there has been a problem that it is difficult to manage the disinfectant injection rate, and it is easy to over-inject or under-inject. In other words, in the case of excessive disinfection of the disinfectant, the active disinfectant component remains in the discharge water and is discharged into the discharge water area, which is likely to adversely affect the organisms in the river and sea area. The loss is also large. On the other hand, in the case of an excessive injection of the disinfectant, there is a problem that the disinfectant amount is insufficient and a sufficient disinfecting effect cannot be obtained.
[0009]
So far, chemical oxygen demand (COD), chlorine requirement, iodine consumption, organic matter in sewage in rainy weather can be effectively prevented by injecting the optimal amount by disinfecting the over and under injection of disinfectant. It was necessary to measure the concentration and the like and determine the injection rate of the disinfectant using these as indicators of the reducing organic substance concentration and / or the inorganic substance concentration. However, the measurement of COD, chlorine requirement, iodine requirement, and organic matter concentration, which are indicators of reducing organic substance concentration and / or inorganic substance concentration, is complicated and difficult to monitor instantaneously. Therefore, in order to determine the optimal disinfectant injection rate that does not result in over-injection or under-injection, corresponding to the quality of sewage in the rainy season, which varies greatly depending on rainfall conditions, the concentration of reducing organic matter and / or inorganic matter It has been impractical to use a method for measuring COD, chlorine requirement, iodine consumption, organic substance concentration, and the like as indicators. For example, when disinfecting treated water from a sewage treatment plant, a disinfection method has been proposed in which the chlorine injection rate is calculated using the measured organic concentration of treated water as an index, and disinfection has been proposed. It could not be applied to disinfect sewage in rainy weather.
[0010]
[Problems to be solved by the present invention]
Accordingly, an object of the present invention is to easily and instantaneously determine an optimal disinfectant injection rate that does not cause over-injection or under-injection in the disinfection treatment of rainy sewage that varies depending on rainfall conditions, and discharges it as overflowing water in rainy weather. It is an object of the present invention to provide a method and apparatus for effectively disinfecting sewage in rainy weather discharged into a water area.
[0011]
[Means for Solving the Problems]
As a result of analyzing the quality of sewage in rainy conditions under various conditions in order to solve the above problems, the present inventors are an index of the turbidity of sewage in rainy weather and the concentration of reducing organic substances and / or inorganic substances. It has been found that there is a high correlation with COD. Furthermore, the present inventors have shown that the amount of disinfectant required when the amount of the disinfectant used in the reducing organic substance and / or inorganic substance is the same, depending on whether the coliform group to be disinfected is large or small. It was also found that they are different. Based on these findings, the inventors have found that the above-mentioned object can be achieved by obtaining an optimal disinfectant injection rate by using turbidity of sewage and the number of coliforms as indicators, and have completed the present invention.
[0012]
That is, the present invention provides a disinfecting treatment method characterized in that when disinfecting rainwater sewage in a combined sewer with a disinfectant, the disinfectant injection rate is determined using the number of coliforms and turbidity of rainwater sewage as indicators. It is to provide.
[0013]
The rainy sewage means mixed sewage obtained by combining sewage and rainwater from a sewage discharge source.
As the disinfectant, any disinfectant that can be used for disinfecting discharged sewage can be used without particular limitation. In the present invention, a disinfectant having an oxidizing ability is particularly preferably used.
[0014]
Examples of the disinfectant having oxidation ability include chlorine-based disinfectants such as sodium hypochlorite, chlorine, and bleaching powder, and bromine-based disinfectants such as BCDMH (1-bromo-3-chloro-5,5-dimethylhydantoin). However, it is not limited to these.
[0015]
The coliform count and turbidity of sewage in rainy weather are measured on sewage samples obtained by appropriately sampling sewage in rainy weather, and in particular, sewage flowing into pump stations, sewage treatment plant sewage, or stormwater discharge chamber sewage. It is preferable to measure the number of coliforms and the turbidity of the sewage sample obtained by sampling. In addition, pump station inflow sewage, sewage treatment plant inflow sewage, and rainwater discharge chamber inflow sewage will be described later.
[0016]
The number of Escherichia coli in sewage during rainy weather is known in the art, such as an E. coli group counter using enzyme antigen-antibody reaction or fluorescent enzyme color reaction (for example, UPD-7700E manufactured by Meidensha Co., Ltd.). It can be measured using a technique.
[0017]
Turbidity is a numerical value for evaluating the degree of turbidity such as drainage, and is measured very easily using a commercially available turbidimeter (for example, SST-5 manufactured by Electrochemical Instruments Co., Ltd.). be able to. Turbidity can be measured not only instantaneously but also by a very simple method. For this reason, it becomes possible to estimate the consumption of the said disinfectant instantaneously by measuring the turbidity.
[0018]
The optimum injection rate of the disinfectant into the sewage during rainy weather can be determined by the following method, for example. That is, according to the desktop disinfection test using various sewage as the test water, (a) turbidity of the test water and (b) the target disinfection effect (for example, the number of coliforms) Is determined to be 3000 CFU / mL or less, which is the discharge regulation value of the Water Pollution Control Act), and the relationship with the injection rate of the disinfectant necessary to achieve the target residual halogen concentration is used. The optimal injection rate of the disinfectant determined from the number of coliforms and turbidity of rainwater sewage measured in an actual facility is obtained, and the disinfectant is injected into the rainwater sewage at the determined injection rate. Optimal disinfection under conditions can be performed.
[0019]
In addition, the number of coliforms in sewage during rainy weather can be measured by the above-described measurement method. Instead, the inflow ends after a predetermined amount or more of rainy sewage starts flowing into the sewage drainage facility. Time is divided into multiple time zones, the rainfall and turbidity are measured for each time zone, and the number of coliforms in the sewage is estimated using the obtained rainfall and turbidity as an index. You can also. In other words, rainfall and turbidity are measured and measured for each elapsed time since the start of inflow of rainwater at a predetermined flow rate or higher into a sewage drainage facility such as a pump station, a sewage treatment plant, or a rainwater spout chamber. It is possible to estimate the amount of rainfall and turbidity as essential indicators. Thereby, it can estimate simply and instantaneously compared with the case where the number of coliforms is actually measured.
[0020]
More specifically, the lapse of time 0 to X minutes, X + 1 to Y minutes (X, 1 minute) since the start of inflow of rainwater at a predetermined flow rate or higher into facilities such as a pump station, a sewage treatment plant, and a rainwater discharge chamber. Y is an integer, and Y> X, and turbidity and rainfall are measured. Next, the number of coliforms can be estimated by substituting the obtained data as an independent variable into the following equation (1).
[0021]
[Formula 1]
C = a * R + b * T + c (1)
[In the formula, C represents the number of coliforms (CFU / mL), R represents the rainfall per mm (mm), and T represents turbidity (degree). Further, a, b, and c are constants. ]
In the above formula (1), the constants a, b, and c are the time elapsed since the start of inflow of sewage at a predetermined flow rate or higher, and the rainy weather subject to pump stations, rainwater discharge chambers, treatment plants, etc. Varies by sewage drainage facility and basin environment. Constants a, b, and c are measured, for example, by measuring the amount of rainfall, the number of coliforms and the turbidity of sewage in rainy weather, in rainy weather sewage under various weather conditions in the target rainy sewage drainage facility. The obtained numerical value can be obtained as a variable by performing multiple regression analysis. In this method, the measurement coefficient of the multiple regression analysis is low and reliable results are obtained only by measuring rainfall and turbidity without dividing the time from the start of inflow to the end of inflow into multiple time zones. I can't get it.
[0022]
In addition to rainfall and turbidity, the number of coliforms may be estimated by adding water quality items such as electrical conductivity, SS (suspended matter), SS particle size, pH, and ammonia nitrogen concentration to the variables. .
[0023]
The reason why the number of coliforms can be estimated in this way is not known in detail, but it is thought that the number of coliforms flowing into the sewage drainage facility is related to the following behavior.
[0024]
That is, the pollutant containing coliforms accumulated in the sewer pipes becomes easy to flow when the sewage flow rate reaches a predetermined flow rate, and starts to flow into the sewage drainage facility in the rain. Coliform bacteria are contained in a large amount in the contaminants accumulated in the sewer pipes, so that the sewage flow rate reaches the predetermined flow rate and the contaminants accumulated in the sewer pipes flow in earnest. Immediately after starting, there is a large inflow of coliform bacteria to the sewage drainage facility in rainy weather. However, with the passage of time, the amount of sediment in the sewer pipes decreases, and even at the same sewage flow rate, the content of rainwater increases and the content of contaminants decreases, so the inflow of coliforms decreases. It is thought that. Moreover, the turbidity of sewage is higher as the pollutant content is higher, and decreases as the pollutant content is lower. That is, it is considered that the higher the turbidity of sewage, the higher the content of contaminants and the higher the number of coliforms. Rainfall, on the other hand, is thought to affect the inflow of soil containing coliform bacteria that accumulates on the road surface, the roof of houses, etc., and the content ratio of sewage and rainwater in rainy weather, that is, the dilution ratio of sewage. .
[0025]
In the present invention, when estimating the number of coliforms of sewage in rainy weather from rainfall and turbidity, from the start of inflow of a predetermined amount or more of rainy sewage to the sewage drainage facility until the inflow ends. Divide the time into multiple time zones and measure the amount of rainfall for each time zone. The predetermined amount here is, for example, rainy weather when rainwater overflow discharge starts at a rainwater drainage facility. It is good also as the inflow amount of hourly sewage, or you may set the inflow amount set arbitrarily arbitrarily.
[0026]
The present invention also provides an apparatus for disinfecting sewage during rainy weather based on the technical idea according to the present invention described above. That is, another aspect of the present invention comprises: a disinfection tank that disinfects sewage in rainy weather with a disinfectant; and sewage discharge means that discharges sewage disinfected in the disinfection tank to a discharge water area, and further, the disinfection tank includes Measuring means for measuring the turbidity of the introduced sewage and the number of coliforms; and control means for controlling the rate of addition of the disinfectant added to the sewage using the turbidity of the sewage and the number of coliforms measured by the measuring means as indicators. A disinfecting apparatus for sewage in rainy weather. Furthermore, a further aspect of the present invention comprises: a disinfection tank for disinfecting sewage in rainy weather with a disinfectant; and sewage discharge means for discharging the sewage disinfected in the disinfection tank to a discharge water area, and further introduced into the disinfection tank A turbidity measuring means for measuring the turbidity of the sewage to be measured; a rainfall measuring means for measuring the rainfall; a turbidity of the sewage measured by the turbidity measuring means, and a measurement by the rainfall measuring means A disinfectant that is added to sewage as an indicator of the number of coliforms estimated using the amount of rainfall and the turbidity of sewage as an index for each elapsed time since the start of inflow of sewage in a rainy day into a sewage drainage facility. A control means for controlling the addition rate; and a disinfecting treatment apparatus for sewage in rainy weather.
[0027]
The disinfecting tank is preferably configured to act as a sand sink.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of a rainwater sewage disinfection apparatus according to the present invention will be described with reference to the drawings.
[0029]
A specific example of an apparatus for carrying out the disinfection method of the present invention is shown in FIG.
The apparatus 10 shown in FIG. 2 includes a disinfection tank 11 for disinfecting sewage 19 in the rain with a disinfectant, a sewage discharge means 13 for discharging the sewage disinfected in the disinfection tank 11 to a discharge water area 17, and normal activated sludge treatment and disinfection. Transfer means 14 for transferring to a processing step such as processing, and turbidity measuring means 18 for measuring the turbidity of sewage introduced into the disinfection tank 11 are provided.
[0030]
The treatment apparatus shown in FIG. 2 is based on the turbidity of rainwater measured by a turbidimeter and the rainfall measured by a rain gauge (not shown) without providing a measuring device for the number of coliforms. Although estimating the number of coliforms, it is also possible to install an apparatus for measuring the number of coliforms that directly measures the number of coliforms in sewage during rainy weather.
[0031]
The treatment apparatus 10 shown in FIG. 2 can be provided in any one of the sewer pipe 3, the rain discharge chamber 4, the pump station 5, and the sewage treatment plant 6 in FIG.
Specifically, in this embodiment, taking the case where the rainwater drainage facility is a pump station as an example, a sand basin 11 into which sewage is introduced for the primary treatment can be used as the disinfection tank. The pond 11 is provided with a disinfectant storage tank 15 for storing the disinfectant. Further, as a sewage discharge means, a rainwater pump 13 connected to the sand basin 11 via a pump well 12 is provided, and as a transfer means 14, a tank drain pump 14 connected via the pump well 12 is provided. It has been. As the turbidity measuring means 18, a turbidimeter 18 is provided in a sewer pipe for supplying sewage in the rain to the sand basin 11.
[0032]
Next, taking the case where the apparatus shown in FIG. 2 is installed at a pump station as an example, the method for disinfecting sewage in rainy weather according to the present invention will be specifically described.
The method for disinfecting sewage in rainy weather according to the present invention, when disinfecting rainy sewage in a combined sewer with a disinfectant, determines the injection rate of the disinfectant using the number of coliforms and turbidity of the sample in the rainy sewage as an index It is characterized by.
[0033]
In order to implement the disinfection method of the present invention using the apparatus of FIG. 2, first, the relationship between the turbidity of sewage in rainy weather and the number of coliforms and the optimum disinfectant injection rate is obtained in advance by the method described above. At the same time, in a sewage drainage facility that performs disinfection, the relationship between the amount of rainfall and the turbidity of sewage in rainy weather and the number of coliforms is obtained.
[0034]
In the sewage disinfection treatment in rainy weather, the turbidity of the sewage is measured by a turbidimeter 18 when the rainwater sewage is supplied to the sand basin 11 to perform the primary treatment. Separately, the rainfall is measured by an external rain gauge (not shown). Then, these measured values are substituted into a regression equation prepared in advance on a desk to determine the disinfectant injection rate, and a predetermined amount of disinfectant from the disinfectant storage tank 15 at the disinfectant injection point 16 is added to the sand basin 11 Mix in sewage.
[0035]
After the disinfectant and sewage in rainy weather are agitated and sufficiently brought into contact with each other for a predetermined time, the amount of sewage that can be secondarily treated is transferred to a sewage treatment plant through a transfer means such as a tank drainage pump 14. When it is transferred and exceeds the allowable capacity of the sewage treatment plant, the pump well 12 is switched and discharged to the discharge water area 17 by the sewage discharge means such as the rainwater pump 13.
[0036]
According to the combined sewage rainwater sewage disinfection method of the present invention thus performed, the disinfectant can be sufficiently disinfected at an optimal disinfectant injection rate without excessively or injecting a disinfectant excessively. It is possible.
[0037]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
[0038]
Test Example 1: Relationship between turbidity of sewage in rainy weather and number of coliforms and injection rate of disinfectant
Using rainwater sewage as test water, BCDMH (1-bromo-3-chloro-5,5-dimethylhydantoin) as disinfectant, changing disinfectant injection rate, The relationship between the number of coliforms after disinfection and the residual halogen concentration was examined on a desk.
[0039]
In this test, without detecting residual halogen after disinfection, the number of coliforms was determined as 3 × 10 which is the release standard of the Water Pollution Control Law. ^Three (CFU / mL) Disinfection target to be treated below, and implemented to clarify the disinfectant injection rate required to achieve the treatment target for each range of rainwater turbidity and coliform group count Is.
[0040]
Specifically, for each test condition, take 500 mL of test water in a glass beaker, measure the number of coliforms and turbidity, and then stir with a stirring blade at a peripheral speed of 0.5 m / sec. The indicated amount of BCDMH was added. After the addition, water was collected after 1 minute while stirring was continued, and the number of coliforms and the residual halogen concentration were measured. The turbidity of the test water was measured by the scattered light measurement method, the number of coliforms was measured by the desoxycholate medium method, and the residual halogen concentration was measured by the orthotolidine method. Residual halogen concentration is an indicator of the amount of active ingredient in the remaining disinfectant. In this way, the turbidity of sewage in rainy weather and the range of the number of coliforms, the disinfectant injection rate, the number of coliforms after disinfection, and the residual halogen concentration after disinfection were determined. The results are shown in Table 1.
[0041]
[Table 1]

[0042]
From the results shown in Table 1, the relationship between the turbidity of sewage during rainy weather, the number of coliforms, and the disinfectant injection rate will be described with an example.
The turbidity T of sewage in rainy weather is 25 <T ≦ 50 (degrees), and the coliform count C of the sample water is 10 ^Four <C ≦ 10 ^Five Comparing the disinfection effect at each disinfectant injection rate at (CFU / mL), when the disinfectant injection rate is 3 to 5 mg / L (test condition 5), the coliform group is not detected without detecting residual halogen. Number 3 × 10 ^Three It can be seen that (CFU / mL) or less could be disinfected. However, when the disinfectant injection rate is 6 to 8 mg / L (test condition 17), the number of coliforms is 3.0 × 10 ^Three Although it could be disinfected below (CFU / mL), residual halogen was detected (0.1-0.2 mg / L as Cl). When the disinfectant injection rate was 1 to 2 mg / L (test condition 29), no residual halogen was detected, but the number of coliforms was 3 × 10. ^Three Disinfection below (CFU / mL) was not possible.
[0043]
From these results, the ranges of turbidity T and coliform count C of sewage in rainy weather are 25 <T ≦ 50 (degrees), 10 ^Four <C ≦ 10 ^Five Under the conditions of (CFU / mL), the number of coliforms is 3 × 10 without detecting residual halogen. ^Three The optimal disinfectant injection rate for disinfection to be (CFU / mL) or less is required to be 3-5 mg / L.
[0044]
From Table 1, in test conditions 1 to 12, the number of coliforms was set to a target value of 3 × 10 without detecting residual halogen. ^Three It was possible to disinfect (CFU / mL) or less, and the optimal range of disinfectant injection rates was obtained for each turbidity of sewage in rainy weather and the number of coliforms. However, in test conditions 13 to 24, the number of coliforms was 3 × 10 ^Three (CFU / mL) could be disinfected, but residual halogen was detected (excess injection). Under test conditions 25 to 36, no residual halogen was detected, but the number of coliforms was 3 × 10. ^Three (CFU / mL) could not be disinfected below (under-injection).
[0045]
From these results, for each range of turbidity T and coliform group number C in sewage in rainy weather, the number of coliform groups was 3 × 10 without detecting residual halogen. ^Three Table 2 summarizes the optimal disinfectant injection rate to achieve (CFU / mL) or less.
[0046]
[Table 2]

[0047]
Test example 2: Relationship between rainfall and turbidity of sewage in rainy weather and number of coliforms
At the actual pumping station, the number of coliforms, turbidity, and rainfall of influent sewage were measured for sewage under rainy conditions. The number of coliforms and the turbidity were measured in the same manner as in Test Example 1, and the rainfall was measured by the falling formula. The inflow amount of sewage during rainy weather is the flow rate at which a rainwater pump installed to discharge (80m in this embodiment) ^Three / min), and the elapsed time P from the start of the rainwater pump operation is P <30 (minutes), 30 (minutes) ≦ P, the amount of coliforms of the influent sewage is the dependent variable, and the amount of rainfall As a result of multiple regression analysis using the turbidity of the influent sewage as an independent variable, the coefficient of determination (R ² ) A regression equation was obtained with a correlation of 0.5 or more. The results are shown in Tables 3 and 4. In addition, when the elapsed time P from the start of operation of the rainwater pump is 0 (min) <P, the number of coliforms of influent sewage is a dependent variable, and the rainfall and turbidity of influent sewage are independent variables. The coefficient of determination (R ² ) Was 0.35 or less. The results are shown in Table 5.
[0048]
[Table 3]

[0049]
[Table 4]

[0050]
[Table 5]

[0051]
Examples and Comparative Examples
In the same pump station as in Test Example 2, the inflowing sewage was sterilized by the following method.
[0052]
The disinfection treatment was performed using the apparatus shown in FIG. 2 under the condition that the rainwater pump 13 was operated and the overflow water was discharged into the discharge water area. BCDMH was used as a disinfectant. The turbidity of the sewage sample in rainy weather was measured with a turbidimeter 18 (SST-5 manufactured by Electrochemical Instrument Co., Ltd.) at the location flowing into the pump station. The number of coliforms is estimated from the regression equation shown in Table 3 when the elapsed time P from the start of rainwater pump operation is P <30 (minutes), and the elapsed time P from the start of rainwater pump operation is P ≧ 30 (minutes). ) Was estimated from the regression equation shown in Table 4.
[0053]
A predetermined amount of disinfectant was injected at the disinfectant injection point 16 at the entrance of the sand basin 11. A part of the sewage in rainy weather injected with the disinfectant was discharged into the discharge water area 17 by the rainwater pump 13. The discharged sewage after the sterilization treatment was collected, and the number of coliforms in the sewage sample after the sterilization treatment was measured by a desoxycholate agar medium method. In addition, the residual halogen concentration of sewage after disinfection was measured by a polarographic method. In addition, the number of coliform bacteria in the sewage during inflow rain before the disinfection treatment was also measured by the same desoxycholate agar medium method as described above, and an actual measurement value was obtained.
[0054]
Table 6 shows the amount of rainfall, the turbidity of inflowing sewage when the elapsed time P from the start of the rainwater pump operation is P <30 (min), and the estimation in the inflowing sewage sample obtained from the regression equation in Table 3. E. coli group number, measured value of E. coli group in sewage sample during inflow rain, determined by desoxycholate agar medium method, turbidity T of sewage in inflow rain, and set injection rate determined from E. coli group number C (determined from Table 2) ) Shows the actual injection rate, the number of coliforms after disinfection, and the residual halogen concentration.
[0055]
Similarly, Table 7 shows the amount of rainfall, the turbidity of sewage during inflowing rain, and the sewage sample during the inflowing rainy weather obtained from the regression equation in Table 4 when the elapsed time P from the start of the rainwater pump operation is P ≧ 30 (minutes). Estimated number of coliforms in the sewage, sewage coliforms in the inflowing rain determined by the desoxycholate agar method, turbidity T of the sewage in the inflowing rain and set injection rate determined from the number C of the coliforms (determined from Table 2) Injection rate, the number of coliforms after disinfection, and the residual halogen concentration.
[0056]
[Table 6]

[0057]
[Table 7]

[0058]
From the results shown in Tables 6 and 7, in Examples 1 to 3 and 5 to 8, when the disinfectant was injected within the range of the set injection rate, no residual halogen was detected from the sewage after disinfection, and the number of coliforms 3 × 10 ^Three It can be seen that (CFU / mL) or less could be disinfected. On the other hand, in Comparative Examples 1-4 and Comparative Examples 6-7, the actual injection rate is lower than the set injection rate, and the number of coliforms of sewage after disinfection is 3 × 10. ^Three (CFU / mL) is exceeded, and it can be seen that disinfection was not possible. In Comparative Example 5 and Comparative Examples 8 to 10, the actual injection rate is higher than the set injection rate, and the number of coliforms in the treated sewage is 3 × 10. ^Three Although it was possible to disinfect (CFU / mL) or less, it can be seen that residual halogen was detected.
[0059]
【The invention's effect】
As described above in detail, according to the disinfecting treatment method of the present invention, in the disinfection treatment of rainy sewage whose water quality fluctuates instantaneously, the concentration of sewage in rainy sewage is high, and the number of coliform bacteria that are pollution indicator bacteria Even if the concentration of reducing organic substances and / or inorganic substances that consume oxidative disinfectants is high or low, the optimal disinfectant injection rate should be determined using the number of coliforms and turbidity in sewage during rainy days as indicators. And can prevent over-injection or under-injection of the disinfectant. As a result, problems such as adverse effects on ecosystems caused by the release of active ingredients of disinfectants that are concerned about excess injection into rivers and sea areas, and inadequate disinfection effects due to under injection It is economical because it is possible to disinfect sewage during rainy weather without causing excessive injection of a disinfectant. Furthermore, in a further aspect of the present invention, the number of coliforms in the sewage can be estimated from the turbidity of the sewage and the amount of rainfall, and the optimum disinfectant injection rate can be determined more easily.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of the configuration of a combined sewer system to which the disinfection method of the present invention can be applied.
FIG. 2 is a schematic view schematically showing a main part of a sewage disinfection treatment apparatus according to the present invention.
[Explanation of symbols]
1: Wastewater discharge source
2: Rainwater source
3: Sewer pipe
4: Rainwater spout chamber
5: Pump station
6: Sewage treatment plant
7: Effluent area
10: Sewage disinfection treatment device in case of rain
11: Disinfection tank (sedimentation pond)
12: Pump well
13: Rainwater pump
14: Tank drain pump
15: Disinfectant storage tank
16: Disinfectant injection point
17: Effluent area
18: Turbidimeter
19: Sewage in rainy weather

Claims

A method of disinfecting sewage in the rainwater of a combined sewer with a disinfectant,
Divide the time from the start of inflow of rainwater at a predetermined amount or more into the sewage drainage facility until the end of inflow into multiple time zones, and calculate the amount of rainfall and the turbidity of sewage in rainy weather for each time zone. A disinfection method characterized by measuring the amount of rainfall and turbidity obtained and estimating the number of coliforms in sewage during rainy weather to determine a disinfectant injection rate.

The number of coliforms and turbidity of the sewage in the rainy weather are obtained from the rainy sewage obtained by sampling the sewage flowing into the pump station, the sewage treatment plant sewage, or the rainwater discharge chamber sewage. Disinfection treatment method.

The disinfectant is BCDMH The method according to claim 1 or 2, which is (1-bromo-3-chloro-5,5-dimethylhydantoin).

Regression formula (1) obtained by performing multiple regression analysis based on rainfall, colombia count and turbidity measured for rainy sewage under various weather conditions at the target rainwater drainage facility:
C = a * R + b * T + c
[In the formula, C represents the number of coliforms ( CFU / mL ), R represents rainfall per mm ( mm ), and T represents turbidity (degree). a, b, and c are constants.]
The number of coliform bacteria in the sewage in rainy weather is estimated from the rainfall and turbidity measured values in the rainy sewage during disinfection. Method.

A disinfection tank for disinfecting sewage in rainy weather with a disinfectant;
Sewage discharge means for discharging sewage sterilized in the disinfection tank to a discharge water area,
A turbidity measuring means for measuring the turbidity of sewage introduced into the disinfection tank;
Rainfall measurement means for measuring rainfall;
The turbidity of the sewage measured by the turbidity measuring means, the rainfall amount for each elapsed time range after the start of inflow of a predetermined amount or more of rainy water into the sewage drainage facility measured by the rainfall measuring means, Control means for controlling the addition rate of a disinfectant added to sewage using as an index the number of coliforms estimated using turbidity of sewage as an index;
An apparatus for disinfecting sewage during rainy weather.

The sterilization apparatus for sewage in rainy weather according to claim 5, wherein the sterilization tank also functions as a sand sink.