JP3691650B2

JP3691650B2 - Water treatment method and control device

Info

Publication number: JP3691650B2
Application number: JP34104397A
Authority: JP
Inventors: 昭二渡辺; 茂植木; 直樹原; 文智木村; 義昭田代; 義行大沢; 三郎安藤
Original assignee: Hitachi Ltd; Tokyo Metropolitan Government
Current assignee: Hitachi Ltd; Tokyo Metropolitan Government
Priority date: 1997-12-11
Filing date: 1997-12-11
Publication date: 2005-09-07
Anticipated expiration: 2017-12-11
Also published as: JPH11169866A

Description

【０００１】
【発明の属する技術分野】
本発明は、都市下水や産業排水あるいは水道原水中のリンを、物理化学凝集または生物学的処理と物理化学凝集の併用で除去する水処理システムに関し、特に、物理化学凝集剤を適正に調節し、処理水中のリン濃度を目標値に管理する水処理制御プロセスにおける凝集剤注入率演算方法及び装置に関する。
【０００２】
【従来の技術】
水中の溶解性リンは湖沼や河川を汚濁する富栄養化物質の一因となることが知られている。下水処理場においては流入する下水中のリンを除去するために、活性汚泥プロセスの一施設である曝気槽を好気領域と嫌気領域より組み合わせた微生物反応槽を使用している。
【０００３】
微生物反応槽の方式には嫌気‐無酸素‐好気法（Ａ₂Ｏ法）、嫌気‐好気法（ＡＯ法）などがあり、少なくとも嫌気槽を前段に、好気槽を後段に配置している。この配置によって活性汚泥のリン過剰摂取機能を利用し、活性汚泥は嫌気槽でリンを吐き出し、好気槽で吐き出した以上のリンを摂取することで、流入水中のリンを生物学的に除去する。しかし、活性汚泥のリン過剰摂取機能は流入水の水質状態やプラント操作条件、あるいは活性汚泥（複合微生物の総称）の管理状態によって変化し、吐出不良や摂取不良などを生じて処理水のリン濃度を増加させることがある。
【０００４】
このため、下水処理場では金属塩などの凝集剤を注入し、物理化学的に除去する方法を併用している。凝集剤は注入量が不足するとリン除去が不十分となり、処理水中のリン濃度を高める。一方、過剰注入は運転コストや汚泥発生量の増加、さらに微生物の活性にも悪影響を与える。したがって、凝集剤の注入量はリン目標値に対して必要最小限にする必要がある。
【０００５】
下水処理場において、物理化学凝集によりリンを除去する場合、アルミニウム系や鉄系の金属塩、あるいは消石灰が凝集剤として用いられる。液中でのリンはオルトリン酸や縮合リン酸の形態で存在し、凝集剤の注入により難溶性の塩を形成する。また、凝集剤は重炭酸塩と反応し、水酸化物のフロックを形成してさらにリンを吸着除去する。アルミニウム系の凝集剤を用いた場合の反応は、（カ１）及び（カ２）式により表わされる。
【０００６】
【化１】

【０００７】
（カ１）式から、液中のリンを難溶性塩にするには理論的に１モル比のアルミニウムを注入すればよいが、（カ２）式のように他の物質にも消費されるのでモル比を１より大きくする必要がある（引用例１：村田恒雄編著；「下水の高度処理技術」、理工図書、平成４年５月）。
【０００８】
リンの除去を目的とした凝集剤注入量制御方法として、現在の処理水のリン濃度Ｐｉと一定時間ｂ前の処理水のリン濃度Ｐｏから変化率ｄ（＝（Ｐｉ−Ｐｏ）/ｂ）を求め、この変化率で将来も推移するとしてｃ時間後の処理水のリン濃度変化△Ｐｃ（＝ｄ・ｃ）予測し、目標値との偏差で注入量を設定する提案がある（引用例２：特開平３−８９９９３号）。あるいは、処理水のリン濃度に対して凝集剤をモル比換算で一定に制御し、リン含有フロックを砂ろ過で分離する方式（引用例３：特開昭６３−２４２３９２号）、脱水ろ液のリン濃度に当量換算係数を乗じて凝集剤注入量を設定する方式（引用例４：特開平７−８８４９７号）などの提案がある。
【０００９】
【発明が解決しようとする課題】
上記した引用例２〜４の凝集剤注入量制御は、（カ１）式及び（カ２）式に基づいて、モル比あるいはアルミニウムとリンの濃度比を予め設定し、凝集剤を制御する比率一定制御方式を採用している。
【００１０】
例えば、引用例２でその試験結果（第１表）によれば、流入水のリン濃度に対してアルミニウム注入率がほぼ比例関係とみられ、モル比換算で約１．３と推算できる。しかし、引用例２の図示からも明らかなように、下水処理場などの流入水中のりん濃度は人間の生活周期によって大きく変化する。従って、将来のリン濃度も過去と同じ変化率で推移するとした予測方法では、凝集剤量の適切な制御は困難となる。事実、本発明者らの試験結果によれば、アルミニウムとリンの濃度比を一定とする引用例のような凝集剤制御方式では、処理水のリン濃度を目標値以下に維持することができなかった。
【００１１】
さらに、引用例２では流入水リン濃度に比例して凝集剤量を制御しているが、嫌気槽と好気槽からなる微生物反応槽のように、流入水のリン濃度より反応槽のリン濃度が変化し、増えることさえあるような処理プロセスには適用できない。
【００１２】
本発明の目的は従来技術の状況に鑑み、被処理水あるいは処理水のリン濃度に応じて処理水のリン濃度を目標値に以下に維持する、水処理プロセスにおける凝集剤注入率演算方法及び装置を提供することにある。
【００１３】
【課題を解決するための手段】
本発明は、水中の溶解性リンを化学凝集あるいは生物処理と化学凝集作用により除去する水処理プロセスにおいて、水中のリン濃度と凝集剤注入濃度の対数比率特性に基づいて凝集剤注入量を演算することを特徴とする。
【００１４】
実施態様的に表現すれば、化学凝集剤注入前の被処理水（以下、被処理水）から計測したリン濃度（Ｐｉ）と予め設定されている化学凝集処理水（以下、処理水）のリン濃度の目標値（Ｐｍ）の対数比率（ｌｏｇＰｉ/Ｐｍ）に基づいて凝集剤注入量を演算することを特徴とする。
【００１５】
または、前記処理水から計測したリン濃度（Ｐｏ）と目標値との対数比率（ｌｏｇＰｏ/Ｐｍ）に基づく。あるいは、被処理水、処理水の各々のリン濃度と目標値との対数比率の和（ｌｏｇＰｉ/Ｐｍ＋ｌｏｇＰｏ/Ｐｍ＝ｌｏｇ(ＰｉＰｏ/Ｐｍ²)）に基づくことを特徴とする。
【００１６】
本発明の方法に好適な水処理プロセスは少なくとも好気槽と沈殿池を有し、好気槽の流出部（出口または近傍）に凝集剤の注入量を調節する注入設備を具備し、凝集剤注入位置より上流の被処理水および／または沈殿池の流出部（出口または近傍）の処理水のリン濃度を計測する手段と、凝集剤注入位置の流量を計測する手段と、計測したリン濃度と予め前記処理水に対し設定されているリン濃度目標値との対数比率、及び前記流量の計測値に基づいて凝集剤注入量を演算する手段とを設け、前記処理水のリン濃度が前記目標値以下となるように前記凝集剤注入量を演算して前記凝集剤注入設備を制御することを特徴とする。
【００１７】
この本発明は、「凝集剤の注入前／後の被処理水または処理水のリン濃度は、凝集剤注入濃度（初期値は注入量＝０）に応じて所定時間後に対数関係に減少する」という、前記対数比率特性の実験的知見に基づいてなされたものである。以下、本発明の動作メカニズムを説明する。
【００１８】
図２（ａ）は、活性汚泥の存在する好気槽の混合液にアルミニウム系凝集剤（PAC：ポリ塩化アルミニウム）を注入し、３０分後における処理水中の溶解性リン濃度とアルミニウム注入濃度の測定値を示したもので、縦軸のリン濃度は対数値で表わされている。注入濃度が０におけるリン濃度Ｐをパラメータとすれば、図２（ｂ）に示すように、注入濃度Ｒに対する対数値表示のリン濃度Ｐは比例関係で減少している。従って、被処理水のリン濃度計測値Ｐｉ及び処理水のリン濃度目標値Ｐｍを基に、必要凝集剤濃度Ｒｍは（１）式によって求めることができる。
【００１９】
【数１】
Ｒｍ＝ｋ1・（ｌｏｇＰi−ｌｏｇＰm）＝ｋ1・ｌｏｇ(Ｐi/Ｐm) …（１）
ただし、ｋ１：係数（勾配tanθの逆数）である。（１）式で対数比率が０以下のときは、被処理水のリン濃度計測値が目標値Ｐｍ以下となっているので凝集剤の注入は不要となる。
【００２０】
ところで、（１）式は図２（ｂ）のＡ点とＢ点の加算値と見ることができるので、処理水のリン濃度計測値Ｐｏを用いて変換すると、凝集剤注入濃度不足分（補正値）△Ｒｍを求める（２）式を誘導できる。
【００２１】
【数２】

すなわち、処理水中のリン濃度の計測値と目標値の対数比率に応じて凝集剤注入濃度の補正値△Ｒｍを決定できる。リン濃度の計測精度は反応槽の混合液より処理水の方が高いので、（１）式による場合に比べて応答性は劣るが制御精度を向上できる。なお、（２）式で対数比率が０以下のときは補正不要であり、凝集剤注入量は現在値に維持される。
【００２２】
さらに、被処理水のリン濃度Ｐｉと処理水のリン濃度Ｐｏの両計測値を用いると、精度と応答性を共に向上できる制御が可能になる。図２（ｃ）に示すように、被処理水のリン濃度Ｐｉで目標値Ｐｍとなるように、係数ｋ１の直線関係に従い凝集剤注入濃度をＣ点（Ｒｍ’）に設定する。一方、この時の処理水のリン濃度ＰｏがＡ点であれば、目標値Ｐｍは係数ｋ２に従うＢ点となるので、△Ｒｍ分の補正が必要になる。従って、必要凝集剤注入濃度Ｒｍは両計測値Ｐｉ，Ｐｏから（３）式によって表わされる。
【００２３】
【数３】

このように、本発明の水処理プロセスは処理水または被処理水中のリン濃度の実測値と処理水での目標値との対数比率に基づいて凝集剤量を制御することで、最小限の凝集剤量で処理水中のリン濃度を目標値以下に維持することができ、低コストの運転管理を実現できる。なお、（１）〜（３）式で、対数値からの偏差と比率からの対数値とは同値であり、本発明で述べる対数比率の定義には両者を含む。
【００２４】
【発明の実施の形態】
以下、本発明の複数の実施例を図面に従って詳細に説明する。なお、各図を通して同等の構成要素には同一の符号を付してある。
【００２５】
〔実施例１〕
図１は、嫌気‐好気法（ＡＯ法）による下水処理設備の構成図で、処理水のリン濃度を目標値以下に管理する凝集剤制御装置を設けている。実施例１の下水処理設備は嫌気槽１Ａと好気槽１Ｃからなる生物反応槽１、最終沈殿池２、水中撹拌機３、送風機５、汚泥返送設備６、汚泥排出設備７、凝集剤タンク８、凝集剤注入設備９から構成されている。
【００２６】
家庭や工場から排出された下水は最初沈殿池(図示なし）で粗大な狭雑物が除去され、生物反応槽１に流入する。流入下水１１の導かれる嫌気槽１Ａには、最終沈殿池２から汚泥返送設備６を介して活性汚泥と呼ばれ微生物群である返送汚泥１２が供給され、流入下水１１と返送汚泥１２が水中撹拌機３で撹拌混合される。嫌気状態下の嫌気槽１Ａにおいて、活性汚泥は細胞内に蓄積していたポリリン酸を加水分解してオルトリン酸（ＰＯ₄−Ｐ）として液中に放出する。また、活性汚泥はリン放出時に有機物を吸着し、細胞内に蓄積する。このため、嫌気槽１Ａではリン濃度が増加し、有機物が減少する。
【００２７】
嫌気槽１Ａの混合液は隔壁１９を介して好気槽１Ｃに導かれる。好気槽１Ｃの底部には散気管４が設置されており、送風機５からの空気を散気し、混合液を撹拌するとともに活性汚泥の酸素源を供給する。好気槽１Ｃにおいて、活性汚泥は吸着した有機物を酸素存在下のもと水と炭酸ガスに分解する。また、アンモニア性窒素を硝酸性あるいは亜硝酸性窒素に酸化する。さらに、液中のオルトリン酸をポリリン酸として細胞内に摂取する。この摂取量は、通常、嫌気槽１Ａで放出した以上の過剰摂取となるため、プロセス全体ではリンが減少して、除去されたことになる。
【００２８】
好気槽１Ｃの流出水は最終沈殿池２に導かれ、混合液中の活性汚泥が重力沈降する。上澄み液は処理水１４として塩素殺菌後に河川や海洋に放流される。一方、沈殿した高濃度の活性汚泥は、その大部分が汚泥返送設備６により返送汚泥１２として生物反応槽１に返送され、増殖分に相当する一部を余剰汚泥として汚泥排出設備７を介して系外に排出する。余剰汚泥には生物反応槽１で除去されたリンも含まれている。
【００２９】
このように生物学的にリンを除去するプロセスでは、嫌気槽１Ａでの嫌気状態を維持してリンを良好に放出させる必要がある。リン放出が不十分な場合、好気槽１Ｃでのリンの摂取も悪く、過剰摂取をしなくなる。リン放出・摂取状態の悪化は、プロセス全体でのリン除去率の低下を招き、処理水１４のリン濃度が流入下水１１より高くなることもある。
【００３０】
リン放出・摂取状態が悪化した場合、生物処理による急激な回復は困難なので、速やかなリン除去のために金属塩などの凝集剤を注入する化学凝集処理を併用する。このため、本実施例の下水処理設備は凝集剤タンク８と凝集剤注入設備９を配設し、撹拌混合の必要がない好気槽１Ｃの流出部に、計算機３０により演算制御される必要量の凝集剤１７を注入する。
【００３１】
以下、計算機３０によって実現される凝集剤注入制御装置の構成と動作について説明する。好気槽１Ｃに採水設備２０を設置し、リン濃度計２１に送水する。リン濃度計２１では、送水された好気槽混合液の活性汚泥を分離し、液中の溶解性リン濃度を計測し、計算機３０に入力される。採水設備２０の設置位置は少なくとも凝集剤１７の注入位置より上流側とし、凝集剤注入前（本例では好気槽の混合液）の被処理水のリン濃度を測定する。流量計２２及び流量計２３で計測された流入下水流量Ｑｉと返送汚泥流量Ｑｒも計算機３０に入力される。
【００３２】
これらの入力値に基づいて、計算機３０は凝集剤注入量を演算し、凝集剤注入設備９を制御する。注入濃度演算部３１は、目標値入力部３２に設定されている処理水のリン濃度目標値Ｐｍと好気槽１Ｃの混合液のリン濃度Ｐｉから、金属塩注入濃度Ｒｍを上記した（１）式より計算する。係数ｋ１は、金属塩がＰＡＣの場合、５〜２０の範囲で設定される。
【００３３】
注入量演算部３３は、注入濃度Ｒｍと流入下水流量Ｑｉ及び返送汚泥流量Ｑｒから、金属塩注入量Ｍを（４）式より計算する。
【００３４】
【数４】
Ｍ＝Ｒｍ・（Ｑｉ＋Ｑｒ） …（４）
凝集剤に含有する金属塩濃度Ｃｍは使用する凝集剤や溶解条件により異なる。凝集剤量演算部３４は、必要とする金属塩注入量Ｍが含まれる凝集剤量Ｇを（５）式より計算する。
【００３５】
【数５】
Ｇ＝Ｍ／Ｃｍ …（５）
凝集剤量制御部３６は凝集剤注入設備９を調節し、好気槽１Ｃへ注入する凝集剤量Ｇとなるように制御する。この例の注入設備９は注入ポンプであり、制御部３６は流量計２５の測定値が凝集剤量Ｇの流量レートになるようにポンプ回転数を設定する。
【００３６】
なお、（１）式の対数項で、比率Ｐi／Ｐm≦１あるいはＰi／（Ｐm＋ΔＰ）≦１となれば、処理水のリン濃度は目標値を満足していると判定し、凝集剤の注入を停止する。この間欠操作により、余分な凝集剤の注入を抑制して運転コストを低減し、かつ活性汚泥への悪影響を回避する。
【００３７】
ここで、ΔＰはリン放出・摂取が正常時の採水設備２０から処理水１４の間で低下する溶解性リン濃度で、プロセスの固有値として設定でき、予め目標値に含んでもよい。また、間欠制御の停止または再開時のリン濃度には、通常、目標値に対する許容誤差が含まれる。
【００３８】
さらに、計算機３０の機能として表示部３８を設け、凝集剤の注入可否や注入量の計算結果、処理水リン濃度が目標値まで低下していないプロセス状態などを表示し、必要に応じアラームを発生する。
【００３９】
〔実施例２〕
図３は、嫌気‐好気法による下水処理設備の構成図で、処理水リン濃度の計測値を用いる凝集剤制御装置を設けている。図１の構成との相違は、処理水１４を対象に採水設備２０とリン濃度計２１を設置し、計算機３０に処理水のリン濃度計測値Ｐｏを入力する点と、凝集剤量の演算方式にある。
【００４０】
注入濃度演算部３１は、処理水のリン濃度計測値Ｐｏとリン濃度目標値Ｐｍから、金属塩注入濃度補正値ΔＲｍを上記の（２）式により計算する。注入量演算部３３は金属塩注入量補正値ΔＭを（６）式より、凝集剤補正量演算部３５は凝集剤補正量ΔＧを（７）式より計算する。
【００４１】
【数６】
ΔＭ＝ΔＲｍ・（Ｑｉ＋Ｑｒ） …（６）
ΔＧ＝ΔＭ／Ｃｍ …（７）
凝集剤量演算部３４は現在の凝集剤量Ｇと補正量ΔＧの差分から操作量Ｇ’を計算し、現在の凝集剤量Ｇに対応する流量計２５の信号値との偏差で凝集剤注入設備９を調節して好気槽１Ｃへの凝集剤を制御する。
【００４２】
実施例２の方式は実施例１に比べ、沈殿池２の滞留時間に相当する制御遅れを生じる。しかし、採水設備２０よりサンプリングされる処理水には活性汚泥が殆ど含まれないので正確な計測情報が得られ、また、計測前の分離操作が不要になる。
【００４３】
〔実施例３〕
図４は、嫌気‐好気法による下水処理設備の構成図で、被処理水と処理水の両方のリン濃度を用いる凝集剤制御装置を設けている。実施例３は図１と図３を合わせた構成で、採水設備２０及び２０Ａを好気槽１Ｃと処理水１４を対象に設置し、採水液切換設備２７で切り替えながらサンプリングした混合液または処理水をリン濃度計２１に送水する。リン濃度計２１に採水液切換機構を内蔵したり、対象水毎にリン濃度計を設ける構成としてもよい。
【００４４】
リン濃度計２１から交互に出力された好気槽１Ｃのリン濃度Ｐｉと処理水のリン濃度Ｐｏ、及び処理水の目標値Ｐｍに基づき、注入濃度演算部３１で金属塩注入濃度Ｒｍを上記の（３）式より計算する。その後は実施例１の場合と同様にして凝集剤注入量Ｇを決定し、凝集剤量制御部３６より凝集剤注入設備９を調節して好気槽１Ｃへの凝集剤を制御する。
【００４５】
本実施例によれば、好気槽１Ｃの混合液リン濃度の誤差が処理水の計測値で補正でき、かつ、沈殿池２による制御遅れを伴わないので、処理水リン濃度を高速に目標値まで低下できる。
【００４６】
〔実施例４〕
図５は、嫌気‐無酸素‐好気法（Ａ₂Ｏ法）による下水処理設備の構成図で、混合液リン濃度を用いる凝集剤制御装置を設けている。本下水処理設備は生物反応槽１を嫌気槽１Ａ‐無酸素槽１Ｂ‐好気槽１Ｃの３室に分け、好気槽１Ｃに設置した送水設備１０で好気槽混合液を第２室目の無酸素槽１Ｂに循環液１８として環流する。無酸素槽１Ｂでは、好気槽１Ｃで生成された硝酸性あるいは亜硝酸性窒素を窒素ガスに還元する脱窒機能を有する。
【００４７】
実施例４における凝集剤注入制御方式は、注入量演算部３３を除いて実施例１と同じになる。注入量演算部３３は好気槽１Ｃの凝集剤注入位置での混合液流量に、流量計２４による循環液流量Ｑｊも加算して、金属塩注入量Ｍを（８）式より計算する。
【００４８】
【数７】
Ｍ＝Ｒｍ・（Ｑｉ＋Ｑｒ＋Ｑｊ） …（８）
実施例４の変形例として、被処理水に変えて処理水のリン濃度を用いる場合は、金属塩注入量補正値ΔＭを求める（６）式に循環液流量Ｑｊを加える以外は、実施例２と同じになる。あるいは、被処理水と処理水の両方のリン濃度を用いる場合は、（３）式で求めた金属塩注入濃度Ｒｍを基に、（８）式で金属塩注入量Ｍを求める以外は、実施例３と同じになる。
【００４９】
以上のように、本発明の実施例１〜４は、ＡＯ法またはＡ₂Ｏ法を対象としたが、標準活性汚泥法や硝化液循環法（活性汚泥循環変法）、嫌気‐好気‐嫌気‐好気法（ＡＯＡＯ法）にも適用可能である。標準活性汚泥法やＡＯＡＯ法では流入下水量と返送汚泥量、硝化液循環法ではさらに循環液流量を加えて金属塩注入量Ｍを演算する。また、本実施例では生物学的処理の下水処理設備を例に説明したが、被処理水の溶解性リンを凝集剤により直接物理化学処理する水処理法にも適用できる。
【００５０】
図６は、実施例４のプラントでアルミニウム注入量を連続注入した試験結果の一例である。本試験は好気槽１Ｃのアルミニウム注入濃度の計測値Ｐｉと処理水リン濃度の目標値Ｐｏに基づく（１）式による制御結果で、処理水中の溶解性リン濃度は測定値である。アルミニウム注入濃度と処理水中の溶解性リン濃度との関係は、図２に示した実験結果とよく一致している。図中の□印は流入下水量を基準とした注入濃度、○印は流入下水量に返送汚泥量と循環液流量を加算して求めた注入濃度である。注入濃度は循環液も考慮することにより、凝集剤注入制御精度を向上できる。
【００５１】
図７は、図６と同じ設備で測定した別の試験結果の一例で、図６の場合と同様に、好気槽１Ｃのアルミニウム注入濃度Ｐｉに基づく制御結果である。グラフの縦軸に処理水中の溶解性リン濃度（Ｔ‐Ｐ）の対数値、横軸にアルミニウム注入濃度を示している。図中、黒丸の測定値は、好気槽１Ｃで活性汚泥の存在する混合液のリン濃度に基づき、また、白丸の測定値は、好気槽１Ｃで活性汚泥のない上澄液のリン濃度に基づいて、それぞれ凝集剤量を制御した結果である。
【００５２】
本実施例の制御方式によれば、処理水リン濃度と凝集剤注入濃度の関係は、被処理水リン濃度が混合液でも上澄液でも、ほぼ同等の対数比率特性となることが認められた。
【００５３】
従って、本発明の対数比率特性に基づく凝集剤制御方式は、嫌気槽と好気槽を備える水処理プロセスに止まらず、好気槽のみの水処理プロセス、さらには活性汚泥の存在しない排水に直接、凝集剤を注入する水処理方式に適用して、リン除去の効果がある。
【００５４】
【発明の効果】
本発明によれば、被処理水および／または処理水のリン濃度と凝集剤注入濃度の対数比率特性に基づいて凝集剤注入量を制御するので、生物学的処理のリン除去能が変化しても、処理水のリン濃度を目標値に維持する凝集剤注入量を正確に、かつ高速に制御することができ、良質の処理水を提供できる効果がある。
【００５５】
また、リン目標値を維持する上での必要最小の凝集剤量に制御できるので、水処理装置の運転コストを低減し、凝集剤注入による活性汚泥の処理阻害を抑制できる。
【図面の簡単な説明】
【図１】本発明の実施例１による凝集剤制御装置を含む下水処理設備の構成図。
【図２】アルミニウム注入濃度に対する溶解性リン濃度の変化を示す試験結果と対数比率特性を示す説明図。
【図３】実施例２による凝集剤制御装置を含む下水処理設備の構成図。
【図４】実施例３による凝集剤制御装置を含む下水処理設備の構成図。
【図５】実施例４による凝集剤制御装置を含む下水処理設備の構成図。
【図６】実施例４による検証試験結果の一例を示すグラフ。
【図７】実施例４による検証試験結果の他の例を示すグラフ。
【符号の説明】
１…生物反応槽、１Ａ…嫌気槽、１Ｂ…無酸素槽、１Ｃ…好気槽、２…沈殿池、５…送風機、６…汚泥返送設備、７…汚泥排出設備、８…凝集剤タンク、９…凝集剤注入設備、１０…循環設備、２０…採水設備、２１…リン濃度計、２２，２３，２４，２５…流量計、３０…計算機、３１…注入濃度演算部、３２…目標値入力部、３３…注入量演算部、３４…凝集剤量演算部、３５…凝集剤補正量演算部、３６…凝集剤量制御部、３８…表示部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a water treatment system that removes phosphorus in municipal sewage, industrial wastewater, or raw water from water by physicochemical flocculation or a combination of biological treatment and physicochemical flocculation, and in particular, appropriately adjusts the physicochemical flocculant. The present invention also relates to a method and an apparatus for calculating a coagulant injection rate in a water treatment control process for managing a phosphorus concentration in treated water to a target value.
[0002]
[Prior art]
It is known that soluble phosphorus in water contributes to eutrophication substances that pollute lakes and rivers. In the sewage treatment plant, in order to remove phosphorus in the inflowing sewage, an aeration tank, which is one facility of the activated sludge process, is combined with an aerobic region and an anaerobic region.
[0003]
There are anaerobic-anoxic-aerobic method (A ₂ O method), anaerobic-aerobic method (AO method), etc. as a method of microbial reaction tank. ing. This arrangement makes use of activated sludge's excessive phosphorus intake function. Activated sludge exhales phosphorus in an anaerobic tank and ingests more phosphorus than exhaled in an aerobic tank to biologically remove phosphorus in the influent water. . However, the phosphorus intake function of activated sludge varies depending on the quality of the influent water, the plant operating conditions, or the activated sludge (general name for complex microorganisms), resulting in poor discharge and poor intake. May increase.
[0004]
For this reason, in sewage treatment plants, a method of injecting a coagulant such as a metal salt and removing it physically is used in combination. When the injection amount of the flocculant is insufficient, phosphorus removal is insufficient and the concentration of phosphorus in the treated water is increased. On the other hand, excessive injection has an adverse effect on the operating cost, the amount of sludge generation, and the activity of microorganisms. Therefore, it is necessary to minimize the injection amount of the flocculant with respect to the phosphorus target value.
[0005]
In the case of removing phosphorus by physicochemical coagulation at a sewage treatment plant, an aluminum-based or iron-based metal salt or slaked lime is used as a coagulant. Phosphorus in the liquid exists in the form of orthophosphoric acid or condensed phosphoric acid, and forms a hardly soluble salt by injecting the flocculant. In addition, the flocculant reacts with the bicarbonate to form a hydroxide floc and further adsorb and remove phosphorus. The reaction in the case of using an aluminum-based flocculant is expressed by the formulas (f1) and (f2).
[0006]
[Chemical 1]

[0007]
From formula (1), it is theoretically necessary to inject aluminum in a molar ratio to make the phosphorus in the solution a sparingly soluble salt, but it is also consumed by other substances as in formula (2). Therefore, it is necessary to make the molar ratio larger than 1 (cited example 1: edited by Tsuneo Murata; “Advanced Sewage Treatment Technology”, Rikosho, May 1992).
[0008]
As a method for controlling the injection amount of the flocculant for the purpose of removing phosphorus, the change rate d (= (Pi−Po) / b) is calculated from the current phosphorus concentration Pi of the treated water and the phosphorous concentration Po of the treated water before a certain time b. There is a proposal to predict the phosphorus concentration change ΔPc (= d · c) of the treated water after c hours and set the injection amount by deviation from the target value, assuming that the rate of change will continue in the future. : JP-A-3-89993). Alternatively, the coagulant is controlled to a fixed molar ratio relative to the phosphorus concentration of the treated water, and the phosphorus-containing floc is separated by sand filtration (Cited Example 3: Japanese Patent Laid-Open No. 63-242392). There are proposals such as a method of multiplying the phosphorus concentration by an equivalent conversion factor to set the amount of flocculant injected (Cited Example 4: Japanese Patent Laid-Open No. 7-88497).
[0009]
[Problems to be solved by the invention]
The control of the amount of the flocculant injected in the above cited examples 2 to 4 is a ratio for controlling the flocculant by presetting the molar ratio or the concentration ratio of aluminum and phosphorus based on the formulas (1) and (2). A constant control method is adopted.
[0010]
For example, according to the test result (Table 1) in Cited Example 2, the aluminum injection rate is considered to be substantially proportional to the phosphorus concentration of the influent water, and can be estimated to be about 1.3 in terms of molar ratio. However, as is clear from the illustration of Cited Example 2, the phosphorus concentration in the inflow water such as the sewage treatment plant varies greatly depending on the life cycle of the human. Therefore, it is difficult to appropriately control the amount of the flocculant with the prediction method in which the future phosphorus concentration also changes at the same rate of change as in the past. In fact, according to the test results of the present inventors, in the coagulant control method as in the cited example in which the concentration ratio of aluminum and phosphorus is constant, the phosphorus concentration of the treated water cannot be maintained below the target value. It was.
[0011]
Further, in Citation 2, the amount of the flocculant is controlled in proportion to the inflow water phosphorus concentration, but the phosphorus concentration in the reaction tank is higher than the inflow water phosphorus concentration, as in a microbial reaction tank composed of an anaerobic tank and an aerobic tank. It cannot be applied to a processing process in which changes and even increases.
[0012]
In view of the state of the prior art, the object of the present invention is to maintain the phosphorus concentration of treated water at a target value or less according to the phosphorus concentration of treated water or treated water, and a method and apparatus for calculating the coagulant injection rate in a water treatment process Is to provide.
[0013]
[Means for Solving the Problems]
The present invention calculates a flocculant injection amount based on a logarithmic ratio characteristic of phosphorus concentration in water and flocculant injection concentration in a water treatment process in which soluble phosphorus in water is removed by chemical flocculation or biological treatment and chemical flocculation. It is characterized by that.
[0014]
In terms of an embodiment, the phosphorus concentration (Pi) measured from the water to be treated before the chemical flocculant injection (hereinafter referred to as water to be treated) and the phosphorus in the chemical agglomerated water (hereinafter referred to as treated water) set in advance. The flocculant injection amount is calculated based on the logarithmic ratio (logPi / Pm) of the concentration target value (Pm).
[0015]
Or based on the logarithmic ratio (logPo / Pm) of the phosphorus concentration (Po) measured from the treated water and the target value. Alternatively, characterized in that based on the sum of the logarithmic ratio of the phosphorus concentration and the target value of each of the water to be treated, the treated water (logPi / Pm + logPo / Pm = log (PiPo / Pm 2)).
[0016]
A water treatment process suitable for the method of the present invention has at least an aerobic tank and a sedimentation basin, and has an injection facility for adjusting the injection amount of the flocculant at the outflow part (exit or in the vicinity) of the aerobic tank. Means for measuring the phosphorus concentration of the treated water upstream of the injection position and / or the treated water at the outflow part (exit or near) of the settling basin, means for measuring the flow rate at the flocculant injection position, and the measured phosphorus concentration A logarithmic ratio with a phosphorus concentration target value set in advance for the treated water, and a means for calculating a flocculant injection amount based on the measured value of the flow rate, and the phosphorus concentration of the treated water is the target value The flocculant injection amount is controlled by calculating the flocculant injection amount so as to be as follows.
[0017]
According to the present invention, “the concentration of water to be treated or treated before / after the injection of the flocculant decreases logarithmically after a predetermined time according to the flocculant injection concentration (the initial value is the injection amount = 0)”. This is based on the experimental knowledge of the log ratio characteristic. The operation mechanism of the present invention will be described below.
[0018]
Fig. 2 (a) shows the concentration of soluble phosphorus and aluminum injection concentration in the treated water after 30 minutes of injecting aluminum flocculant (PAC: polyaluminum chloride) into the mixture in the aerobic tank containing activated sludge. The measured values are shown, and the phosphorus concentration on the vertical axis is represented by a logarithmic value. If the phosphorus concentration P at an injection concentration of 0 is used as a parameter, the logarithmically expressed phosphorus concentration P with respect to the injection concentration R decreases in a proportional relationship as shown in FIG. Therefore, the required coagulant concentration Rm can be obtained from the formula (1) based on the measured phosphorus concentration value Pi of the water to be treated and the target phosphorus concentration Pm of the treated water.
[0019]
[Expression 1]
Rm = k1. (LogPi-logPm) = k1.log (Pi / Pm) (1)
However, k1: coefficient (reciprocal of gradient tanθ). When the logarithmic ratio is 0 or less in the equation (1), the phosphorus concentration measurement value of the water to be treated is equal to or less than the target value Pm, so that the injection of the flocculant becomes unnecessary.
[0020]
By the way, since the equation (1) can be regarded as an addition value of the points A and B in FIG. 2B, if the conversion is performed using the measured phosphorus concentration value Po of the treated water, the insufficient concentration of the flocculant injection (correction) Value) Equation (2) for obtaining ΔRm can be derived.
[0021]
[Expression 2]

That is, the correction value ΔRm of the flocculant injection concentration can be determined according to the logarithmic ratio between the measured value of the phosphorus concentration in the treated water and the target value. Since the measurement accuracy of the phosphorus concentration is higher in the treated water than in the mixed solution in the reaction tank, the control accuracy can be improved although the responsiveness is inferior to that in the case of the formula (1). Note that when the logarithmic ratio is equal to or less than 0 in the equation (2), no correction is necessary, and the amount of the flocculant injected is maintained at the current value.
[0022]
Furthermore, if both measured values of the phosphorus concentration Pi of the water to be treated and the phosphorus concentration Po of the treated water are used, it is possible to perform control that can improve both accuracy and responsiveness. As shown in FIG. 2 (c), the flocculant injection concentration is set to the point C (Rm ′) according to the linear relationship of the coefficient k1, so that the phosphorus concentration Pi of the treated water becomes the target value Pm. On the other hand, if the phosphorus concentration Po of the treated water at this time is the point A, the target value Pm is the point B according to the coefficient k2, and thus correction for ΔRm is necessary. Therefore, the required flocculant injection concentration Rm is expressed by the equation (3) from both measured values Pi and Po.
[0023]
[Equation 3]

Thus, the water treatment process of the present invention controls the amount of flocculant based on the logarithmic ratio between the measured value of the phosphorus concentration in the treated water or the treated water and the target value in the treated water, thereby minimizing the aggregation. The phosphorus concentration in the treated water can be maintained below the target value with the agent amount, and low-cost operation management can be realized. In the equations (1) to (3), the deviation from the logarithmic value and the logarithmic value from the ratio are the same value, and the definition of the logarithmic ratio described in the present invention includes both.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a plurality of embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the equivalent component throughout each figure.
[0025]
[Example 1]
FIG. 1 is a configuration diagram of a sewage treatment facility using an anaerobic-aerobic method (AO method), and is provided with a flocculant control device that manages the phosphorus concentration of treated water below a target value. The sewage treatment facility of Example 1 includes an anaerobic tank 1A and an aerobic tank 1C, a biological reaction tank 1, a final sedimentation tank 2, an underwater agitator 3, a blower 5, a sludge return facility 6, a sludge discharge facility 7, and a flocculant tank 8 The flocculant injection equipment 9 is constituted.
[0026]
The sewage discharged from the home or factory is first removed from the coarse sediment in the sedimentation basin (not shown) and flows into the biological reaction tank 1. Returning sludge 12, which is called activated sludge and is a microorganism group, is supplied from the final sedimentation basin 2 to the anaerobic tank 1A through which the inflowing sewage 11 is guided through the sludge return equipment 6, and the inflowing sewage 11 and the return sludge 12 are stirred in water. Stir and mix in machine 3. In the anaerobic tank 1A under the anaerobic condition, the activated sludge hydrolyzes the polyphosphoric acid accumulated in the cells and releases it into the liquid as orthophosphoric acid (PO ₄ -P). Activated sludge adsorbs organic substances when phosphorus is released and accumulates in cells. For this reason, in the anaerobic tank 1A, the phosphorus concentration increases and the organic matter decreases.
[0027]
The mixed solution in the anaerobic tank 1A is guided to the aerobic tank 1C through the partition wall 19. An air diffuser 4 is installed at the bottom of the aerobic tank 1C, and air from the blower 5 is diffused to stir the mixed solution and supply an oxygen source of activated sludge. In the aerobic tank 1C, activated sludge decomposes the adsorbed organic matter into water and carbon dioxide in the presence of oxygen. It also oxidizes ammonia nitrogen to nitrate or nitrite nitrogen. Furthermore, the orthophosphoric acid in the liquid is taken into the cells as polyphosphoric acid. Since this intake amount is usually an excessive intake amount more than that released in the anaerobic tank 1A, phosphorus is reduced and removed in the entire process.
[0028]
The outflow water from the aerobic tank 1C is guided to the final sedimentation basin 2, and the activated sludge in the mixed solution is gravity settled. The supernatant liquid is discharged as treated water 14 into the river or ocean after chlorination. On the other hand, most of the precipitated high-concentration activated sludge is returned to the biological reaction tank 1 as the return sludge 12 by the sludge return equipment 6, and a part corresponding to the breeding portion is used as surplus sludge via the sludge discharge equipment 7. Discharge out of the system. The excess sludge also contains phosphorus removed in the biological reaction tank 1.
[0029]
Thus, in the process of biologically removing phosphorus, it is necessary to maintain the anaerobic state in the anaerobic tank 1A and to release phosphorus satisfactorily. When the phosphorus release is insufficient, the intake of phosphorus in the aerobic tank 1C is also bad and the excessive intake is not performed. The deterioration of the phosphorus release / intake state leads to a decrease in the phosphorus removal rate in the entire process, and the phosphorus concentration of the treated water 14 may be higher than the inflow sewage 11.
[0030]
When the phosphorus release / intake state deteriorates, rapid recovery by biological treatment is difficult, so chemical coagulation treatment in which a coagulant such as a metal salt is injected is used in combination for rapid phosphorus removal. For this reason, the sewage treatment facility of this embodiment is provided with the flocculant tank 8 and the flocculant injection facility 9, and the necessary amount that is calculated and controlled by the computer 30 at the outflow portion of the aerobic tank 1C that does not require stirring and mixing. The flocculant 17 is injected.
[0031]
Hereinafter, the configuration and operation of the flocculant injection control device realized by the computer 30 will be described. A water sampling facility 20 is installed in the aerobic tank 1C, and water is supplied to the phosphorus concentration meter 21. In the phosphorus concentration meter 21, the activated sludge of the aerobic tank mixed liquid fed is separated, and the soluble phosphorus concentration in the liquid is measured and input to the calculator 30. The installation position of the water sampling facility 20 is at least upstream from the injection position of the flocculant 17, and the phosphorus concentration of the water to be treated is measured before the flocculant injection (in this example, the liquid mixture in the aerobic tank). The inflow sewage flow rate Qi and return sludge flow rate Qr measured by the flow meter 22 and the flow meter 23 are also input to the computer 30.
[0032]
Based on these input values, the calculator 30 calculates the coagulant injection amount and controls the coagulant injection equipment 9. The injection concentration calculation unit 31 described above the metal salt injection concentration Rm from the phosphorus concentration target value Pm of the treated water set in the target value input unit 32 and the phosphorus concentration Pi of the mixed solution of the aerobic tank 1C (1). Calculate from the formula. The coefficient k1 is set in the range of 5 to 20 when the metal salt is PAC.
[0033]
The injection amount calculation unit 33 calculates the metal salt injection amount M from the equation (4) from the injection concentration Rm, the inflow sewage flow rate Qi, and the return sludge flow rate Qr.
[0034]
[Expression 4]
M = Rm · (Qi + Qr) (4)
The metal salt concentration Cm contained in the flocculant varies depending on the flocculant used and the dissolution conditions. The flocculant amount calculator 34 calculates the flocculant amount G including the required metal salt injection amount M from the equation (5).
[0035]
[Equation 5]
G = M / Cm (5)
The flocculant amount control unit 36 adjusts the flocculant injection equipment 9 to control the flocculant amount G to be injected into the aerobic tank 1C. The injection equipment 9 in this example is an injection pump, and the control unit 36 sets the pump rotation speed so that the measurement value of the flow meter 25 becomes the flow rate of the coagulant amount G.
[0036]
If the ratio Pi / Pm ≦ 1 or Pi / (Pm + ΔP) ≦ 1 in the logarithmic term of the formula (1), it is determined that the phosphorus concentration of the treated water satisfies the target value, and the flocculant is injected. To stop. By this intermittent operation, injection of excess flocculant is suppressed, operation cost is reduced, and adverse effects on activated sludge are avoided.
[0037]
Here, ΔP is a soluble phosphorus concentration that decreases between the water collection facility 20 and the treated water 14 when phosphorus release / intake is normal, and can be set as an eigenvalue of the process, and may be included in the target value in advance. In addition, the phosphorus concentration at the time of stopping or resuming intermittent control usually includes an allowable error with respect to the target value.
[0038]
Furthermore, a display unit 38 is provided as a function of the computer 30 to display whether or not the coagulant can be injected, the calculation result of the injection amount, the process state in which the treated water phosphorus concentration has not decreased to the target value, and an alarm is generated if necessary. To do.
[0039]
[Example 2]
FIG. 3 is a configuration diagram of a sewage treatment facility using an anaerobic-aerobic method, and a flocculant control device using a measured value of the treated water phosphorus concentration is provided. 1 is different from the configuration of FIG. 1 in that a water sampling facility 20 and a phosphorus concentration meter 21 are installed for the treated water 14 and the phosphorus concentration measurement value Po is input to the computer 30 and the calculation of the amount of coagulant. Is in the scheme.
[0040]
The injection concentration calculation unit 31 calculates the metal salt injection concentration correction value ΔRm by the above equation (2) from the phosphorus concentration measurement value Po and the phosphorus concentration target value Pm of the treated water. The injection amount calculator 33 calculates the metal salt injection amount correction value ΔM from the equation (6), and the coagulant correction amount calculator 35 calculates the coagulant correction amount ΔG from the equation (7).
[0041]
[Formula 6]
ΔM = ΔRm · (Qi + Qr) (6)
ΔG = ΔM / Cm (7)
The flocculant amount calculation unit 34 calculates the operation amount G ′ from the difference between the current flocculant amount G and the correction amount ΔG, and injects the flocculant with the deviation from the signal value of the flow meter 25 corresponding to the current flocculant amount G. The equipment 9 is adjusted to control the flocculant to the aerobic tank 1C.
[0042]
The method of the second embodiment causes a control delay corresponding to the residence time of the settling basin 2 as compared with the first embodiment. However, since the activated sludge is hardly contained in the treated water sampled from the water sampling facility 20, accurate measurement information can be obtained, and a separation operation before measurement is not necessary.
[0043]
Example 3
FIG. 4 is a configuration diagram of a sewage treatment facility using an anaerobic-aerobic method, and is provided with a flocculant control device that uses the phosphorus concentrations of both the treated water and the treated water. Example 3 is a configuration in which FIGS. 1 and 3 are combined, and the sampled

water

20 and 20A are installed in the aerobic tank 1C and the treated water 14 and sampled while switching with the sampled liquid switching equipment 27 or The treated water is sent to the phosphorus concentration meter 21. The phosphorus concentration meter 21 may have a built-in sampling liquid switching mechanism, or a phosphorus concentration meter may be provided for each target water.
[0044]
Based on the phosphorus concentration Pi of the aerobic tank 1C, which is alternately output from the phosphorus concentration meter 21, the phosphorus concentration Po of the treatment water, and the target value Pm of the treatment water, the injection concentration calculation unit 31 calculates the metal salt injection concentration Rm as described above. Calculate from equation (3). Thereafter, the coagulant injection amount G is determined in the same manner as in Example 1, and the coagulant injection device 9 is adjusted by the coagulant amount control unit 36 to control the coagulant into the aerobic tank 1C.
[0045]
According to the present embodiment, the error of the mixed solution phosphorus concentration in the aerobic tank 1C can be corrected by the measured value of the treated water, and the control delay by the settling basin 2 is not accompanied. Can be reduced.
[0046]
Example 4
FIG. 5 is a configuration diagram of a sewage treatment facility using an anaerobic-anoxic-aerobic method (A ₂ O method), and is provided with a flocculant control device using a mixed solution phosphorus concentration. In this sewage treatment facility, the biological reaction tank 1 is divided into three chambers, an anaerobic tank 1A, an anaerobic tank 1B, and an aerobic tank 1C, and the aerobic tank mixed solution in the aerobic tank 1C in the second chamber. Is recirculated as a circulating liquid 18 to the anoxic tank 1B. The oxygen-free tank 1B has a denitrification function for reducing nitrate or nitrite nitrogen generated in the aerobic tank 1C to nitrogen gas.
[0047]
The flocculant injection control method in the fourth embodiment is the same as that in the first embodiment except for the injection amount calculation unit 33. The injection amount calculator 33 adds the circulating fluid flow rate Qj from the flow meter 24 to the mixed solution flow rate at the coagulant injection position of the aerobic tank 1C, and calculates the metal salt injection amount M from the equation (8).
[0048]
[Expression 7]
M = Rm · (Qi + Qr + Qj) (8)
As a modified example of the fourth embodiment, when using the phosphorous concentration of the treated water instead of the treated water, the second embodiment except that the circulating fluid flow rate Qj is added to the equation (6) for obtaining the metal salt injection amount correction value ΔM. Will be the same. Or when using the phosphorus concentration of both to-be-processed water and treated water, it implements except calculating | requiring the metal salt injection amount M by (8) Formula based on the metal salt injection density | concentration Rm calculated | required by (3) Formula. Same as Example 3.
[0049]
As described above, Examples 1 to 4 of the present invention are directed to the AO method or the A ₂ O method. However, the standard activated sludge method, the nitrification liquid circulation method (activated sludge circulation modified method), anaerobic-aerobic- It can also be applied to the anaerobic-aerobic method (AOAO method). In the standard activated sludge method and AOAO method, the inflowing sewage amount and return sludge amount are added, and in the nitrification solution circulation method, the circulating fluid flow rate is further added to calculate the metal salt injection amount M. In this embodiment, the sewage treatment facility for biological treatment has been described as an example. However, the present invention can also be applied to a water treatment method in which soluble phosphorus in water to be treated is directly subjected to physical chemical treatment with a flocculant.
[0050]
FIG. 6 is an example of a test result obtained by continuously injecting an aluminum injection amount in the plant of Example 4. This test is a control result by the formula (1) based on the measured value Pi of the aluminum injection concentration in the aerobic tank 1C and the target value Po of the treated water phosphorus concentration, and the soluble phosphorus concentration in the treated water is a measured value. The relationship between the aluminum injection concentration and the soluble phosphorus concentration in the treated water is in good agreement with the experimental results shown in FIG. In the figure, □ indicates the injection concentration based on the inflow sewage amount, and ○ indicates the injection concentration obtained by adding the return sludge amount and the circulating fluid flow rate to the inflow sewage amount. The injection concentration can also improve the flocculant injection control accuracy by considering the circulating fluid.
[0051]
FIG. 7 is an example of another test result measured with the same equipment as in FIG. 6, and is a control result based on the aluminum injection concentration Pi of the aerobic tank 1C, as in FIG. The vertical axis of the graph shows the logarithmic value of the soluble phosphorus concentration (TP) in the treated water, and the horizontal axis shows the aluminum injection concentration. In the figure, the measured value of the black circle is based on the phosphorus concentration of the mixed liquid in which the activated sludge is present in the aerobic tank 1C, and the measured value of the white circle is the phosphorus concentration of the supernatant in the aerobic tank 1C without the activated sludge. This is the result of controlling the amount of the flocculant based on each.
[0052]
According to the control method of the present example, it was recognized that the relationship between the treated water phosphorus concentration and the flocculant injection concentration has substantially the same log ratio characteristics regardless of whether the treated water phosphorus concentration is a mixed solution or a supernatant. .
[0053]
Therefore, the flocculant control method based on the log ratio characteristic of the present invention is not limited to a water treatment process including an anaerobic tank and an aerobic tank, but directly to a water treatment process including only an aerobic tank, and further to wastewater that does not include activated sludge. Applying to a water treatment method in which a flocculant is injected, there is an effect of removing phosphorus.
[0054]
【The invention's effect】
According to the present invention, since the flocculant injection amount is controlled based on the logarithmic ratio characteristic of the phosphorus concentration of the treated water and / or the treated water and the flocculant injection concentration, the phosphorus removal ability of biological treatment is changed. However, the amount of the flocculant injected for maintaining the phosphorus concentration of the treated water at the target value can be controlled accurately and at high speed, and it is possible to provide high-quality treated water.
[0055]
Moreover, since it can control to the minimum amount of coagulant | flocculant required in maintaining phosphorus target value, the operating cost of a water treatment apparatus can be reduced and the process inhibition of the activated sludge by coagulant | flocculant injection | pouring can be suppressed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a sewage treatment facility including a flocculant control device according to Embodiment 1 of the present invention.
FIG. 2 is an explanatory view showing logarithmic ratio characteristics and test results showing changes in soluble phosphorus concentration with respect to aluminum injection concentration.
FIG. 3 is a configuration diagram of a sewage treatment facility including a flocculant control device according to a second embodiment.
4 is a configuration diagram of a sewage treatment facility including a flocculant control device according to Embodiment 3. FIG.
FIG. 5 is a configuration diagram of a sewage treatment facility including a flocculant control device according to a fourth embodiment.
6 is a graph showing an example of a verification test result according to Example 4. FIG.
7 is a graph showing another example of the verification test result according to Example 4. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Biological reaction tank, 1A ... Anaerobic tank, 1B ... Anoxic tank, 1C ... Aerobic tank, 2 ... Sedimentation basin, 5 ... Blower, 6 ... Sludge return equipment, 7 ... Sludge discharge equipment, 8 ... Coagulant tank, DESCRIPTION OF SYMBOLS 9 ... Coagulant injection equipment, 10 ... Circulation equipment, 20 ... Water sampling equipment, 21 ... Phosphor concentration meter, 22, 23, 24, 25 ... Flow meter, 30 ... Computer, 31 ... Injection concentration calculating part, 32 ... Target value Input unit 33... Injection amount calculation unit 34... Flocculant amount calculation unit 35... Flocculant correction amount calculation unit 36 36 flocculant amount control unit 38.

Claims

In a water treatment method for removing soluble phosphorus in water by chemical flocculation or biological treatment and chemical flocculation,
A water treatment method characterized by controlling an injection amount of a flocculant based on a logarithmic ratio characteristic of a concentration of soluble phosphorus in water and an injection concentration of an aluminum-based chemical flocculant (hereinafter referred to as a flocculant).

In Claim 1, the phosphorus concentration (Pi) measured from the to-be-processed water (henceforth, to-be-treated water) before injection | pouring of the said coagulant | flocculant, and the phosphorus density | concentration of the preset chemical-aggregation treated water (henceforth, treated water) The treatment based on the logarithmic ratio of the target value (Pm) of the water, or the sum of the logarithmic ratio of the target value (Pm) to each of the phosphorus concentration (Pi) measured from the treated water and the phosphorus concentration (Po) measured from the treated water The flocculant injection concentration in water is calculated, and the flocculant injection amount necessary to maintain the target value is controlled by the product of the injection concentration and the flow rate of water to be treated measured from the injection position of the flocculant. A water treatment method characterized.

In Claim 1, based on the logarithmic ratio of the phosphorus concentration (Po) measured from the chemical coagulation treated water (hereinafter, treated water) and the target value (Pm) of the phosphorus concentration of the treated water set in advance, the treated water The correction value of the aluminum-based flocculant injection concentration is calculated, and the current flocculant injection amount is corrected by the product of the correction value and the flow rate of water to be treated measured from the injection position of the flocculant. Water treatment method .

At least aerobic tank and settling tank, the aerobic tank or settling tank to the flocculant injection equipment coagulant biological water treatment facility comprising an injection equipment aluminum-based coagulant for phosphorus removal In the control device for controlling the injection amount ,
Set for in advance the treated water and the phosphorus concentration measured by the upstream means for measuring the phosphorus concentration of treated water means and / or the sedimentation tank outlet to measure the phosphorus concentration of treated water from the injection position of the flocculant A means for calculating a flocculant injection amount based on a logarithmic ratio with a target value of phosphorus concentration and a measured value of a flow rate measured by a means for measuring a flow rate of a flocculant injection position ;
A control apparatus that controls the flocculant injection facility so that the phosphorus concentration of the treated water is equal to or less than the target value.

Anaerobic tank from the upstream, the aerobic tank, comprising a sedimentation tank, said aerobic tank comprises a coagulant injection equipment of an aluminum system for phosphorus removal in biological water treatment facility of the coagulant injection equipment coagulant In the control device for controlling the injection amount ,
The means for measuring the phosphorus concentration of the water to be treated upstream from the position where the flocculant is injected and / or the means for measuring the phosphorus concentration of the treated water at the outlet of the settling basin are used in advance with one or both of the measured phosphorus concentrations. Coagulant injection based on the logarithmic ratio of the phosphorus concentration target value set for the treated water and the flow rate of the coagulant injection position by the sum of the inflow water flow rate to the anaerobic tank and the return sludge flow rate to the anaerobic tank A means for calculating the quantity,
A control apparatus that controls the flocculant injection facility so that the phosphorus concentration of the treated water is equal to or less than the target value.

According to claim 5, mixture from the previous SL aerobic tank, wherein the anaerobic tank in case you refluxing the anoxic tank which is provided between the aerobic tank, the flow rate of the previous SL coagulant injection position A control device characterized in that the flocculant injection amount is calculated by adding the recirculation flow rate measured by the means for measuring the recirculation flow rate.