JP3883358B2 - Filtration separation method and apparatus for sewage treatment - Google Patents
Filtration separation method and apparatus for sewage treatment Download PDFInfo
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- JP3883358B2 JP3883358B2 JP2000086540A JP2000086540A JP3883358B2 JP 3883358 B2 JP3883358 B2 JP 3883358B2 JP 2000086540 A JP2000086540 A JP 2000086540A JP 2000086540 A JP2000086540 A JP 2000086540A JP 3883358 B2 JP3883358 B2 JP 3883358B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、汚水の処理に関するもので、活性汚泥の固液分離や余剰汚泥の濃縮等に関するものであり、有機性工業廃水や生活排水などに用いることができる汚水のろ過分離方法及び装置に関する。
【０００２】
【従来の技術】
従来、活性汚泥による水処理では、処理水を得るためには処理後に活性汚泥の固液分離を行わなければならない。通常では、活性汚泥を沈殿池に導入させ、重力沈降によって、汚泥を沈降させ、上澄液を処理水として沈殿池から流出させる方法が用いられる。この場合、活性汚泥を沈降させるため十分な沈降面積及び滞留時間を有する沈殿池が必要であり、処理装置の大型化と設置容積の増大要因となっている。また、活性汚泥がバルキング等、沈降性の悪化した場合、沈殿池より汚泥が流出し、処理水の水質悪化を招く。
近年、沈殿池に代わって膜分離による活性汚泥の固液分離を行う手法も用いられている。この場合、固液分離用膜として、一般的に精密ろ過膜や限外ろ過膜が用いられる。
【０００３】
最近、沈殿池に代わる活性汚泥の固液分離法として、曝気槽に間隔保持用の通水性多孔質材を間に介在させて重ね合わせた不織布等の通水性シートの周囲を密閉して形成した袋状のろ過体を浸漬させ、低い水頭圧でろ過水を得る方法が知られている。この場合、ろ過体表面に形成された汚泥のダイナミックろ過層による分離で清澄なろ過水が得られる。
また、安定したダイナミックろ過層の形成手法として、ろ過体表面の活性汚泥流速を平均０．０５ｍ／ｓ〜０．４ｍ／ｓ、好ましくは０．１５〜０．２５ｍ／ｓに制御する活性汚泥濾過方法が知られているが、本公報で、ろ過体表面流速０．２ｍ／ｓ時、ろ過Ｆｌｕｘは約２ｍ／ｄでろ過継続時間２．５ｈ以上となっている。
【０００４】
【発明が解決しようとする課題】
しかし、本発明者らは、ろ過体のろ過Ｆｌｕｘと表面流速との関係を詳細に実験した結果、ろ過体表面の流速を０．０５〜０．４ｍ／ｓ、特に好ましいとされる０．１５〜０．２５ｍ／ｓとした場合、ろ過体表面の汚泥流動が激しく、汚泥の均一なダイナミックろ過層の形成が困難であり、有効なろ過面積も得られない。また、微細な汚泥フロックによるろ過体表面の閉塞が早く、空洗や水洗による効果が少ないという欠点があることがわかった。
本発明は、上記の問題点を解決するもので、通水性ろ過体を用いて汚水等をろ過するに当たり、均一なダイナミックろ過層の形成が容易であり、高いろ過Ｆｌｕｘが得られる汚水処理のろ過分離方法及びその装置を提供することを目的としている。
【０００５】
【課題を解決するための手段】
本発明者らの研究によれば、生物反応槽における曝気による空気泡の形成や破裂、空気泡の激しい上昇運動などの影響がないところでは、ろ過体の洗浄直後においては、ろ過体の表面流速は汚泥沈降速度以上〜０．０５ｍ／ｓ未満のほうが安定したダイナミックろ過層が５分以内と極めて短時間で形成され、ろ過Ｆｌｕｘは５ｍ／ｄ以上を４時間以上継続できるという知見が得られた。さらに表面流速が汚泥沈降速度〜０．０５ｍ／ｓ未満の条件では、ろ過体表面に形成されたダイナミックろ過層が空洗のみで容易に剥離できることが確認できた。これらの研究の結果を基にして本発明を完成した。
【０００６】
すなわち、本発明は、下記の手段により前記の課題を解決した。
（１）生物反応槽に仕切板を介し通水性ろ過体を浸漬し、ダイナミックろ過層を形成させるろ過によりろ過水を得る汚水処理のろ過分離方法において、活性汚泥混合液を通水性ろ過体に対して、通常運転時の通水性ろ過体表面の平均流速が汚泥沈降速度以上〜０．０５ｍ／ｓ未満となるように流通させることを特徴とする汚水処理のろ過分離方法。
（２）前記通水性ろ過体でダイナミックろ過層を形成させるろ過によりろ過水を得るに際し、通水性ろ過体が浸漬されていない曝気部における曝気風量を変動させ、前記通水性ろ過体表面の流速を制御することを特徴とする前記（１）記載の汚水処理のろ過分離方法。
（３）生物反応槽に仕切板を介し通水性ろ過体を浸漬し、ダイナミックろ過層を形成させるろ過によりろ過水を得る汚水処理のろ過分離装置であって、活性汚泥混合液を通水性ろ過体に対して、通常運転時の通水性ろ過体表面の平均流速が汚泥沈降速度以上〜０．０５ｍ／ｓ未満となるように流通させることを特徴とする汚水処理のろ過分離装置。
【０００７】
【発明の実施の形態】
本発明において、ダイナミックろ過層で高いろ過Ｆｌｕｘが得られるよう、通水性ろ過体表面の平均流速が汚泥沈降速度以上〜０．０５ｍ／ｓ未満となるようにするには、曝気されている生物反応槽内に通水性ろ過体をそのまま配置したのでは、生物反応を進行させるに必要な曝気量により液が強く攪乱されているので、その条件を得ることが困難である。
そのため、生物反応槽内を仕切板を設けて曝気部とは区画されたろ過部とし、そこに通水性ろ過体を配置することにより、通水性ろ過体表面の平均流速が前記した条件内にあるように制御することができる。なお、槽は、全体を処理槽とし、曝気部を生物反応槽、ろ過部をろ過槽と呼んでもよい。
その際、仕切板の大きさや配置箇所を適宜設定して、仕切板の上下部で曝気部と連通させ、生物反応槽内の液が循環するようにする。その仕切板の配置は、曝気部における曝気による激しい水の運動が伝わらないように、仕切板の上端と液面との距離及び仕切板の下端と底板との距離を小さくすることが好ましい。かつ通水性ろ過体の大きさ配置位置等を含めて、通水性ろ過体表面の平均流速が汚泥沈降速度以上〜０．０５ｍ／ｓ未満となるように設定することができる。
その他、通水性ろ過体表面の平均流速が汚泥沈降速度以上〜０．０５ｍ／ｓ未満となるように、種々の補助部材を用いることができる。
【０００８】
通水性ろ過体としては、不織布、ろ布、金属網等のいずれを用いても同様な効果が得られる。また、ろ過体形状としては、平面型、円筒型、中空型のいずれを用いることも可能であり、複数個を束ねてモジュールろ過体として用いることが可能である。
本発明を実施するに当たっては、曝気部で曝気している関係で、上昇する空気泡とともに水が上昇するので、曝気部の上方では上昇した水が仕切板の上端を越えてろ過部に入る流れを形成することになる。このためろ過部では活性汚泥混合液が下方に流れる流れを形成するのが普通である。その場合、その流れは仕切板からの距離で大きく異なる。
そこで、ろ過部に設置した通水性ろ過体について、その表面の平均流速が前記の範囲にあるようにするには、ろ過部の上部に前記混合液の流れを平均化するための整流装置を設けることが好ましい。
本発明のろ過分離手段としては、水頭圧を利用するのが好ましい。
【０００９】
この場合、前記ろ過部では、その上部に整流装置を設置し、活性汚泥混合液を整流装置上部に導入しているため、ろ過部内において活性汚泥混合液の流れ方向が一定であり、整流装置の下部に設置されているろ過体に汚泥のダイナミックろ過層が均一に形成される。また、ろ過体表面に沿って汚泥沈降速度以上〜０．０５ｍ／ｓ 未満で活性汚泥混合液を一定方向で流れるため、ろ過体表面に流れる汚泥濃度がほぼ均一であり、ダイナミックろ過層の形成が容易となる。また、ろ過体下部に洗浄装置を設置しておき、定期的にろ過を停止し、洗浄すれば、ろ過体表面に形成された汚泥層を容易に剥離することができる。この洗浄方法は空洗及び水洗の一方または両方を用いてもよい。
ここでは、ろ過により、通水性ろ過体の下部周囲に活性汚泥が濃厚化された液が形成されるので、その濃縮活性汚泥を外部に排出させる。また、通水性ろ過体の表面に活性汚泥が堆積してろ過速度が低下して、空気逆洗したときにも、通水性ろ過体の下部周囲に濃縮活性汚泥が溜まるので、これを排出する。
【００１０】
本発明によれば、生物反応槽において、曝気風量を変動させれば、仕切板反対側（ろ過部）に浸漬したろ過体表面の流速を変動させることが可能であり、ろ過水量及び汚泥性状に対応し、均一なダイナミックろ過層を形成させることが可能である。さらに安定したろ過水質も得ることができる。
洗浄直後からろ過体表面にダイナミックろ過層形成までのろ過初期においては、曝気風量が少なく、ろ過体表面の流速が遅いと、生物反応槽内の汚泥凝集性がよく、ろ過体表面に良好なダイナミックろ過層が短時間内に容易に形成できる。その結果、ダイナミックろ過層が均一であり、ろ過面積が有効に利用できる。
ダイナミックろ過層形成直後からろ過体表面洗浄までの定常ろ過期間中において、ろ過体表面の流速を速くすれば、ダイナミックろ過層に汚泥の付着が少なくなり、ろ過圧上昇によるろ過水量の低下が少ない。この結果、ろ過体表面への空洗頻度が少なくなる。さらにダイナミックろ過層に汚泥が過剰に付着した場合でも、空洗時少ない風量で瞬間的にろ過体表面の汚泥層を容易に剥離することができ、再びろ過初期のろ過水量が得られる。
【００１１】
また、本発明においては、通水性ろ過体表面のダイナミックろ過層が厚くなって、ろ過抵抗が大きくなった場合には、空気洗浄によりろ過層を剥離させるために、通水性ろ過体の下方に空気を入れるための散気装置を配置することが好ましい。状況によりろ過中に前記散気装置から空気を送るようにすることもできる。
【００１２】
図１は、団地下水に対する本発明による処理法の一例をフローシートで示した。
図１に示す如く、流入原水１が生物反応槽５に流入し、生物反応槽供給ブロワー２によって空気を供給し、活性汚泥による好気処理を行う。曝気により上昇する生物反応槽混合液が仕切板６の上方から仕切板６によって形成されたろ過槽７に下向流入し、不織布ろ過体８の表面を下向流しながら、不織布ろ過体８よりろ過し、取水管９を通って、処理水１０が得られる。なお、不織布ろ過体の洗浄は空洗ブロワー１１より一定時間間隔で底部より曝気し、上向流式で表面洗浄を行う。この間ろ過を停止する。また、余剰汚泥は定期的に排泥管１２より系外に排出される。ここで、洗浄直後からダイナミックろ過層形成までの初期ろ過時、ダイナミックろ過層形成直後から洗浄までの定常ろ過時は生物反応槽供給ブロワー２の出力を電磁流量計４よりそれぞれ、所定の曝気風量となるようにブロワー制御装置３より制御される。このように一定時間間隔で洗浄を行い、ブロワー２の出力を調整する。
【００１３】
【実施例】
以下に本発明を実施例により具体的に説明するが、本発明はこの実施例のみに限定されるものではない。
【００１４】
実施例１
図１のフローシートに示す団地下水に対する本発明による処理法を行った。
ここで、洗浄直後からダイナミックろ過層形成までの初期ろ過時、ダイナミックろ過層形成直後から洗浄までの定常ろ過時は生物反応槽供給ブロワー２の出力を電磁流量計４よりそれぞれ、所定の曝気風量となるようにブロワー制御装置３より制御される。このように一定時間間隔で洗浄を行い、ブロワー２の出力を調整し、約２ヶ月の長期ろ過を行った。
第１表に生物反応槽の処理条件を示す。第２表にろ過体の処理条件を示す。
【００１５】
【表１】
第１表に示すように曝気槽への原水流入量が１０ｍ3 ／ｄであり、曝気風量が約０．０２ｍ3 ／ｍ2 ／ｍｉｎと０．１ｍ3 ／ｍ2 ／ｍｉｎとした。なお、ここでの曝気風量は曝気槽断面積当たりの風量とした。ろ過体定常ろ過時は曝気風量をおよそ０．１ｍ3 ／ｍ2 ／ｍｉｎと一定とした。ろ過体洗浄直後からダイナミックろ過層形成までの初期ろ過時は、曝気風量をおよそ０．０２ｍ 3／ｍ2 ／ｍｉｎとした。なお、曝気槽ＭＬＳＳが約２５００ｍｇ／リットルであり、汚泥の凝集性が良好でフロックが大きかった。また、槽全体のＢＯＤ負荷が約０．１５ｋｇ／ｋｇ・ｄとなった。
なお、本実施例は本発明の一例に過ぎない。流入原水ＢＯＤが生物反応槽において、完全分解除去されるＢＯＤ負荷とするのが本発明の効果を一層高められる。ろ過体が浸漬設置されるろ過槽を除いた生物反応槽のＢＯＤ負荷を０．３ｋｇ／ｋｇ／ｄ以下とするのが好ましい。この場合、ろ過槽に流入する活性汚泥混合液中、原水のＢＯＤがまったく残留しないことから、ろ過体表面での生物膜生成がなく、長期問において安定したろ過水量の確保ができる。
本実験では、団地下水を原水とした活性汚泥を用いた。
【００１７】
【表２】
第２表にろ過体の処理条件を示す。本実施例では、有効ろ過面積０．５ｍ2 の平面形不織布ろ過体４枚をろ過体モジュールとして用いた。ろ過体は、厚さ０．４ｍｍ，目開き約２０〜３０μｍのポリエステル製の不織布を用いた。目付量は６０ｇ／ｍ2 であった。ろ過時の平均水頭圧は約１０ｃｍである。洗浄直後からダイナミックろ過層形成までの間、ここでは、ろ過水濁度が１０度以下までの間を初期ろ過時とした。この間はろ過体表面の平均流速が０．０１ｍ／ｓとなるように生物反応槽の曝気風量を約０．０２ｍ 3／ｍ2 ／ｍｉｎで調整を行った。
なお、初期ろ過時のろ過体表面流速が汚泥沈降速度以上、０．０５ｍ／ｓ未満であれば、良好なダイナミックろ過層が形成される。通常、活性汚泥の沈降速度は最大で約０．００２ｍ／ｓであり、初期ろ過時では、ろ過体表面流速が０．００２ｍ／ｓ〜０．０１ｍ／ｓとすれば、比較的短時間内に良好なダイナミックろ過層が形成できる。
本実験では、表面流速ができるだけ均一となるようにし、具体的な方法としては、散気装置から空気が均一に供給できるようにし、旋回流れの流れを均一にした。仕切板と散気装置の距離及び仕切板とろ過体の距離をほぼ同じにした。
【００１９】
定常ろ過時、ここではダイナミックろ過層形成直後からろ過体洗浄までの間、ろ過体表面の平均流速を約０．０３ｍ／ｓとなるように生物反応槽の曝気風量を約０．１ｍ3 ／ｍ2 ／ｍｉｎとした。また、空洗時のろ過体表面平均流速が０．５ｍ／ｓとなるように空洗風量を設定した。なお、空洗時はろ過を停止した。初期ろ過時間、定常ろ過時間及び空洗（停止）時間間隔をそれぞれ、５分、１２時間と３分とした。このように約２ヶ月連続処理した時の原水及び処理水の平均値を第３表に示す。
【００２０】
【表３】
第３表に示すように、原水のｐＨが７．１、濁度１５０度、ＳＳ８６ｍg ／リットル であるのに対し、処理水では、ｐＨ７．６、濁度４．１度、ＳＳ５．０ｍg ／リットル となり、不織布ろ過体モジュールによって得られたろ過水が清澄であると認められた。
また、ＣＯＤとＳ−ＣＯＤ、ＢＯＤとＳ−ＢＯＤについて、原水では、それぞれ、７５ｍg ／リットルと４２ｍg ／リットル、１１０ｍg ／リットルと６５ｍg ／リットルであるのに対し、処理水では、それぞれ１３．５ｍg ／リットルと１１．０ｍg ／リットル、５．８ｍg ／リットルと５ｍg ／リットル以下であり、処理水質としても良好であると認められた。
【００２２】
図２に本実施例におけるろ過Ｆｌｕｘの時間経過を示す。初期ろ過から約５時間経過してもろ過Ｆｌｕｘの低下が少なく、約５ｍ／ｄ以上を維持でき、安定した処理が得られた。
図３にろ過水の濁度経過を示す。初期ろ過５分後にろ過水濁度が１０度以下となり、その後約５度であり、大きな変動が見られず、汚泥のダイナミックろ過層が短時間内に形成し、安定した処理ができたと認められた。
【００２３】
比較例１
実施例１と同一な処理フローにおいて、同一なろ過体モジュールを用い、表面流速を０．２ｍ／ｓとした場合のろ過Ｆｌｕｘとろ過水濁度の経過をそれぞれ、図４、図５に示す。
表面流速０．２ｍ／ｓでは、ろ過Ｆｌｕｘが初期の約７ｍ／ｄであるのに対し、３０分後に約１ｍ／ｄ以下に低下し、ろ過体表面に良好なダイナミックろ過層が形成されず、汚泥が付着し、ろ過Ｆｌｕｘが低下したものと認められる。
ろ過水濁度は図５に示すように初期ろ過開始時の濁度が約３４度と実施例より若干高かったが、その後は約１０度以下となり、実施例１と同程度であった。
【００２４】
【発明の効果】
本発明によれば、生物反応槽と仕切板を介して設けた通水性ろ過体における表面の平均流速が汚泥沈降速度以上〜０．０５ｍ／ｓ未満となるようにすることにより、ろ過水量及び汚泥性状に対応し、均一なダイナミックろ過層を形成させることが可能であり、ろ過Ｆｌｕｘを高く維持してろ過を行うことができる。さらに安定したろ過水質も得ることができる。
また、生物反応槽において、曝気風量を変動させれば、仕切板反対側に浸漬したろ過体表面の流速を変動させることが可能であり、ろ過水量及び汚泥性状に対応し、均一なダイナミックろ過層を形成させることが可能である。さらに安定したろ過水質も得ることができる。
【００２５】
ろ過体表面にダイナミックろ過層形成までの初期ろ過において、曝気風量が少なく、ろ過体表面の流速が遅いと、生物反応槽内の汚泥凝集性がよく、ろ過体表面に良好なダイナミックろ過層が短時間内に容易に形成できる。また、ダイナミックろ過層が均一であり、ろ過面積が有効に利用できる。ダイナミックろ過層が一旦形成されるとろ過期間中にろ過体表面の流速を速くすれば、ダイナミックろ過層に汚泥の付着が少なくなり、ろ過圧上昇によるろ過水量の低下が少ない。この結果、ろ過体表面への空洗頻度が少なくなる。さらにダイナミックろ過層に汚泥が過剰に付着した場合、少ない風量による空洗で、容易にろ過体表面の汚泥層を剥離することができ、再びろ過初期のろ過水量が得られる。
【図面の簡単な説明】
【図１】本発明の処理方法の１例のフローシートを示す。
【図２】実施例１におけるろ過Ｆｌｕｘの時間経過のグラフを示す。
【図３】実施例１におけるろ過水の濁度の時間経過のグラフを示す。
【図４】比較例１におけるろ過Ｆｌｕｘの時間経過のグラフを示す。
【図５】比較例１におけるろ過水の濁度の時間経過のグラフを示す。
【符号の説明】
１ 流入原水
２ 生物反応槽供給ブロワー
３ ブロワー制御装置
４ 電磁流量計
５ 生物反応槽
６ 仕切板
７ ろ過槽
８ ろ過体
９ 取水管
１０ 処理水
１１ 空洗ブロワー
１２ 排泥管
１３ 散気管
１４ 散気管[0001]
BACKGROUND OF THE INVENTION
The present invention relates to treatment of sewage, and relates to solid-liquid separation of activated sludge, concentration of surplus sludge, and the like, and relates to a filtration and separation method and apparatus for sewage that can be used for organic industrial wastewater and domestic wastewater.
[0002]
[Prior art]
Conventionally, in water treatment with activated sludge, in order to obtain treated water, solid-liquid separation of activated sludge has to be performed after treatment. Normally, a method is used in which activated sludge is introduced into a sedimentation basin, the sludge is sedimented by gravity sedimentation, and the supernatant is discharged from the sedimentation basin as treated water. In this case, a sedimentation basin having a sufficient sedimentation area and residence time is required to settle the activated sludge, which is a factor for increasing the size of the processing apparatus and increasing the installation volume. Moreover, when activated sludge deteriorates sedimentation property, such as a bulking, sludge flows out from a sedimentation basin and causes the quality of treated water to deteriorate.
In recent years, a method of performing solid-liquid separation of activated sludge by membrane separation instead of a sedimentation basin has been used. In this case, a microfiltration membrane or an ultrafiltration membrane is generally used as the solid-liquid separation membrane.
[0003]
Recently, as a solid-liquid separation method of activated sludge as an alternative to a sedimentation basin, it was formed by sealing the periphery of a water-permeable sheet such as a non-woven fabric laminated with a water-permeable porous material for maintaining a gap in the aeration tank. There is known a method of immersing a bag-shaped filter body to obtain filtered water at a low head pressure. In this case, clear filtered water can be obtained by separating the sludge formed on the surface of the filter body by the dynamic filtration layer.
Further, as a method for forming a stable dynamic filtration layer, activated sludge filtration for controlling the activated sludge flow rate on the surface of the filter body to an average of 0.05 m / s to 0.4 m / s, preferably 0.15 to 0.25 m / s. Although the method is known, in this publication, when the filter surface flow velocity is 0.2 m / s, the filtration flux is about 2 m / d and the filtration duration is 2.5 h or more.
[0004]
[Problems to be solved by the invention]
However, as a result of detailed experiments on the relationship between the filtration flux of the filter body and the surface flow velocity, the present inventors have determined that the flow velocity on the surface of the filter body is 0.05 to 0.4 m / s, particularly preferably 0.15. When it is set to ˜0.25 m / s, the sludge flow on the surface of the filter body is intense, it is difficult to form a uniform dynamic filtration layer of sludge, and an effective filtration area cannot be obtained. In addition, it was found that the filter body surface was quickly blocked by fine sludge flocs, and that the effect of washing and rinsing was small.
The present invention solves the above-mentioned problems, and when filtering sewage using a water-permeable filter, it is easy to form a uniform dynamic filtration layer, and filtration of sewage treatment to obtain a high filtration flux. It is an object to provide a separation method and apparatus.
[0005]
[Means for Solving the Problems]
According to the studies by the present inventors, in the place where there is no influence of the formation and rupture of air bubbles due to aeration in the biological reaction tank, the air bubbles are vigorously lifted, the surface flow velocity of the filter immediately after washing the filter. Was found that a stable dynamic filtration layer was formed in a very short time of less than 5 minutes when the sludge sedimentation speed was above -0.05 m / s, and the filtration flux was able to continue at 5 m / d or more for 4 hours or more. . Furthermore, it was confirmed that the dynamic filtration layer formed on the surface of the filter body can be easily peeled off only by air washing under the condition that the surface flow velocity is less than 0.05 m / s. The present invention was completed based on the results of these studies.
[0006]
That is, this invention solved the said subject by the following means.
(1) In a filtration and separation method for sewage treatment, in which a water-permeable filter is immersed in a biological reaction tank through a partition plate to obtain filtrate by filtration that forms a dynamic filtration layer, the activated sludge mixture is passed through the water-filter. The filtration separation method for sewage treatment is characterized in that it is circulated so that the average flow velocity on the surface of the water-permeable filter during normal operation is not less than the sludge sedimentation rate and less than 0.05 m / s.
(2) When obtaining filtered water by filtration that forms a dynamic filtration layer with the water-permeable filter body, the aeration air volume in the aeration section where the water-permeable filter body is not immersed is varied, and the flow rate on the surface of the water-permeable filter body is changed. The method for filtering and separating sewage treatment as described in (1) above, wherein the method is controlled.
(3) A sewage treatment filtration separation apparatus for obtaining filtered water by filtration by immersing a permeable filter in a biological reaction tank through a partition plate to form a dynamic filtration layer, wherein the activated sludge mixed liquid is permeable to water. On the other hand, the sewage treatment filtration and separation device is characterized in that it is circulated so that the average flow velocity on the surface of the water-permeable filter during normal operation is not less than the sludge sedimentation rate and less than 0.05 m / s.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, in order to obtain a high filtration flux in the dynamic filtration layer, the biological reaction being aerated is performed so that the average flow velocity on the surface of the water-permeable filter body is not less than the sludge settling velocity and less than 0.05 m / s. If the water-permeable filter body is placed in the tank as it is, the liquid is strongly disturbed by the amount of aeration necessary for advancing the biological reaction, so it is difficult to obtain the conditions.
Therefore, a partition plate is provided in the biological reaction tank to form a filtration unit partitioned from the aeration unit, and by arranging the water-permeable filter therein, the average flow velocity on the surface of the water-permeable filter is within the above-described conditions. Can be controlled. The tank may be a treatment tank as a whole, the aeration part may be called a biological reaction tank, and the filtration part may be called a filtration tank.
At that time, the size and location of the partition plate are appropriately set, and the upper and lower portions of the partition plate are communicated with the aeration unit so that the liquid in the biological reaction tank circulates. As for the arrangement of the partition plate, it is preferable to reduce the distance between the upper end of the partition plate and the liquid surface and the distance between the lower end of the partition plate and the bottom plate so that intense water movement due to aeration in the aeration unit is not transmitted. And including the magnitude | size arrangement position of a water-permeable filter body, etc., it can set so that the average flow velocity of a water-permeable filter surface may become more than sludge sedimentation speed | velocity-less than 0.05 m / s.
In addition, various auxiliary members can be used so that the average flow speed on the surface of the water-permeable filter body is not less than the sludge settling speed and less than 0.05 m / s.
[0008]
The same effect can be obtained by using any of nonwoven fabric, filter cloth, metal net, etc. as the water-permeable filter. Moreover, as a filter body shape, any of a plane type, a cylindrical type, and a hollow type can be used, and a plurality of filter bodies can be bundled and used as a module filter body.
In carrying out the present invention, since the water rises with the rising air bubbles in the relationship of aeration in the aeration section, the flow of the rising water passes over the upper end of the partition plate and enters the filtration section above the aeration section. Will be formed. For this reason, it is common to form a flow in which the activated sludge mixed liquid flows downward in the filtration section. In that case, the flow differs greatly depending on the distance from the partition plate.
Therefore, in order to ensure that the average flow velocity of the surface of the water-permeable filter installed in the filtration unit is in the above range, a rectifier for averaging the flow of the mixed liquid is provided at the upper part of the filtration unit. It is preferable.
As the filtration and separation means of the present invention, it is preferable to use water head pressure.
[0009]
In this case, since the rectifier is installed in the upper part of the filtration unit and the activated sludge mixed liquid is introduced into the upper part of the rectifier, the flow direction of the activated sludge mixed liquid is constant in the filtration unit. A sludge dynamic filtration layer is uniformly formed on the filter body installed at the bottom. Moreover, since the activated sludge mixed liquid flows in a certain direction at a sludge settling speed of not less than 0.05 m / s along the filter body surface, the concentration of sludge flowing on the filter body surface is almost uniform, and a dynamic filtration layer is formed. It becomes easy. Moreover, if the washing | cleaning apparatus is installed in the filter lower part, filtration will be stopped regularly and it will wash | clean, the sludge layer formed in the filter body surface can be peeled easily. This washing method may use one or both of air washing and water washing.
Here, since the liquid in which activated sludge is concentrated is formed around the lower part of the water-permeable filter body by filtration, the concentrated activated sludge is discharged to the outside. Moreover, when activated sludge accumulates on the surface of the water-permeable filter and the filtration rate decreases and air backwashing is performed, the concentrated activated sludge accumulates around the lower part of the water-permeable filter, and is discharged.
[0010]
According to the present invention, in the biological reaction tank, if the aeration air volume is changed, the flow velocity of the surface of the filter body immersed on the opposite side of the partition plate (filter part) can be changed, and the amount of filtered water and sludge properties can be changed. Correspondingly, it is possible to form a uniform dynamic filtration layer. Furthermore, stable filtered water quality can be obtained.
In the initial stage of filtration from immediately after washing to the formation of a dynamic filtration layer on the filter surface, if the aeration air volume is small and the flow rate on the filter surface is slow, the sludge coagulation in the biological reaction tank is good, and the filter surface has good dynamics. A filtration layer can be easily formed within a short time. As a result, the dynamic filtration layer is uniform and the filtration area can be used effectively.
If the flow rate on the surface of the filter body is increased during the steady filtration period immediately after the formation of the dynamic filtration layer to the washing of the filter surface, sludge adheres to the dynamic filtration layer, and the amount of filtered water decreases due to an increase in filtration pressure. As a result, the frequency of air washing on the filter body surface is reduced. Furthermore, even when sludge adheres excessively to the dynamic filtration layer, the sludge layer on the surface of the filter body can be easily peeled off instantaneously with a small air volume during air washing, and the amount of filtered water at the initial stage of filtration can be obtained again.
[0011]
Further, in the present invention, when the dynamic filtration layer on the surface of the water-permeable filter becomes thick and the filtration resistance increases, the air is placed below the water-permeable filter in order to peel off the filter layer by air washing. It is preferable to arrange an air diffuser for putting in. Depending on the situation, air can be sent from the diffuser during filtration.
[0012]
FIG. 1 is a flow sheet showing an example of a treatment method according to the present invention for a group groundwater.
As shown in FIG. 1, the inflow
[0013]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to only these examples.
[0014]
Example 1
The treatment method according to the present invention was applied to the groundwater shown in the flow sheet of FIG.
Here, at the time of initial filtration from immediately after washing to dynamic filtration layer formation, and at the time of steady filtration from immediately after dynamic filtration layer formation to washing, the output of the biological reaction
Table 1 shows the processing conditions of the biological reaction tank. Table 2 shows the processing conditions of the filter body.
[0015]
[Table 1]
As shown in Table 1, the amount of raw water flowing into the aeration tank was 10 m 3 / d, and the amount of aeration air was about 0.02 m 3 / m 2 / min and 0.1 m 3 / m 2 / min. In addition, the aeration air volume here was made into the air volume per aeration tank cross-sectional area. During steady filtration of the filter body, the amount of aeration was kept constant at about 0.1 m 3 / m 2 / min. During the initial filtration from immediately after washing the filter body to the formation of the dynamic filtration layer, the amount of aeration air was set to approximately 0.02 m 3 / m 2 / min. The aeration tank MLSS was about 2500 mg / liter, the cohesiveness of sludge was good, and the floc was large. Further, the BOD load of the entire tank was about 0.15 kg / kg · d.
This embodiment is only an example of the present invention. The effect of the present invention can be further enhanced by setting the BOD load so that the inflow raw water BOD is completely decomposed and removed in the biological reactor. It is preferable that the BOD load of the biological reaction tank excluding the filter tank in which the filter body is immersed is set to 0.3 kg / kg / d or less. In this case, since BOD of raw water does not remain at all in the activated sludge mixed liquid flowing into the filtration tank, there is no biofilm formation on the surface of the filter body, and a stable amount of filtered water can be ensured for a long period of time.
In this experiment, activated sludge was used as the raw water.
[0017]
[Table 2]
Table 2 shows the processing conditions of the filter body. In this example, four flat nonwoven fabric filters with an effective filtration area of 0.5 m 2 were used as filter modules. As the filter body, a non-woven fabric made of polyester having a thickness of 0.4 mm and an opening of about 20 to 30 μm was used. The basis weight was 60 g / m 2 . The average head pressure during filtration is about 10 cm. From the time immediately after washing to the formation of the dynamic filtration layer, here, the time between the filtration water turbidity and 10 degrees or less was defined as the initial filtration. During this period, the amount of aeration air in the biological reaction tank was adjusted at about 0.02 m 3 / m 2 / min so that the average flow velocity on the filter body surface was 0.01 m / s.
In addition, a favorable dynamic filtration layer will be formed if the filter body surface flow velocity at the time of initial filtration is more than sludge sedimentation speed and less than 0.05 m / s. Usually, the sedimentation rate of activated sludge is about 0.002 m / s at the maximum, and at the time of initial filtration, if the filter surface flow rate is 0.002 m / s to 0.01 m / s, within a relatively short time. A good dynamic filtration layer can be formed.
In this experiment, the surface flow velocity was made as uniform as possible. As a specific method, air was supplied uniformly from the diffuser, and the flow of the swirling flow was made uniform. The distance between the partition plate and the air diffuser and the distance between the partition plate and the filter body were made substantially the same.
[0019]
At the time of steady filtration, between the time immediately after the formation of the dynamic filtration layer and the washing of the filter body, the aeration air volume in the biological reaction tank is about 0.1 m 3 / m so that the average flow velocity on the surface of the filter body is about 0.03 m / s. 2 / min. Moreover, the air washing air volume was set so that the filter body average flow velocity at the time of air washing might be 0.5 m / s. In addition, the filtration was stopped at the time of air washing. The initial filtration time, steady filtration time, and air washing (stop) time interval were 5 minutes, 12 hours, and 3 minutes, respectively. Table 3 shows the average values of the raw water and the treated water when treated continuously for about 2 months.
[0020]
[Table 3]
As shown in Table 3, the pH of raw water is 7.1, turbidity is 150 degrees, and SS is 86 mg / liter, whereas in treated water, pH is 7.6, turbidity is 4.1 degrees, and SS is 5.0 mg / liter. It was recognized that the filtrate water obtained by the nonwoven fabric filter module was clear.
Regarding COD and S-COD, and BOD and S-BOD, the raw water is 75 mg / liter and 42 mg / liter, and the 110 mg / liter and 65 mg / liter, respectively, while the treated water is 13.5 mg / liter. The liters were 11.0 mg / liter and 5.8 mg / liter and 5 mg / liter or less.
[0022]
FIG. 2 shows the time lapse of the filtration flux in this example. Even after about 5 hours have passed since the initial filtration, the decrease in the filtration flux was small and it was possible to maintain about 5 m / d or more, and a stable treatment was obtained.
FIG. 3 shows the turbidity course of filtered water. After 5 minutes of initial filtration, the turbidity of the filtered water became 10 degrees or less, and after that it was about 5 degrees, no significant fluctuation was observed, and a sludge dynamic filtration layer was formed within a short time, and it was recognized that stable treatment was achieved. It was.
[0023]
Comparative Example 1
In the same processing flow as in Example 1, the same filter module is used, and the flow of filtered flux and filtered water turbidity when the surface flow velocity is 0.2 m / s are shown in FIGS. 4 and 5, respectively.
At a surface flow velocity of 0.2 m / s, the filtration flux is about 7 m / d at the initial stage, but after about 30 minutes it drops to about 1 m / d or less, and a good dynamic filtration layer is not formed on the surface of the filter body. It is recognized that the sludge adhered and the filtration flux decreased.
As shown in FIG. 5, the turbidity of the filtered water was about 34 degrees at the start of initial filtration, which was slightly higher than that of the example.
[0024]
【The invention's effect】
According to the present invention, the amount of filtered water and sludge are adjusted such that the average flow velocity on the surface of the water-permeable filter provided via the biological reaction tank and the partition plate is not less than the sludge sedimentation rate to less than 0.05 m / s. It is possible to form a uniform dynamic filtration layer corresponding to the properties, and filtration can be performed while maintaining the filtration flux high. Furthermore, stable filtered water quality can be obtained.
Moreover, in the biological reaction tank, if the aeration air volume is changed, the flow velocity of the filter body immersed on the opposite side of the partition plate can be changed, corresponding to the amount of filtered water and sludge properties, and a uniform dynamic filtration layer. Can be formed. Furthermore, stable filtered water quality can be obtained.
[0025]
In the initial filtration until the dynamic filtration layer is formed on the filter surface, if the aeration air volume is small and the flow rate on the filter surface is slow, the sludge coagulation in the biological reaction tank is good and the good dynamic filtration layer is short on the filter surface. Can be easily formed in time. Moreover, the dynamic filtration layer is uniform and the filtration area can be used effectively. Once the dynamic filtration layer is formed, if the flow rate on the surface of the filter body is increased during the filtration period, sludge adheres to the dynamic filtration layer, and the amount of filtered water decreases due to an increase in filtration pressure. As a result, the frequency of air washing on the filter body surface is reduced. Furthermore, when sludge adheres excessively to the dynamic filtration layer, the sludge layer on the surface of the filter body can be easily peeled off by air washing with a small air volume, and the amount of filtered water at the initial stage of filtration can be obtained again.
[Brief description of the drawings]
FIG. 1 shows a flow sheet of an example of the processing method of the present invention.
FIG. 2 is a graph showing the passage of time of filtered flux in Example 1.
FIG. 3 shows a graph of the time lapse of turbidity of filtered water in Example 1.
4 shows a graph of the time course of filtered flux in Comparative Example 1. FIG.
5 shows a graph of the time lapse of turbidity of filtered water in Comparative Example 1. FIG.
[Explanation of symbols]
DESCRIPTION OF
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