JP2004344745A

JP2004344745A - Diffuser and diffusion method

Info

Publication number: JP2004344745A
Application number: JP2003143505A
Authority: JP
Inventors: Takeshi Oda; 剛織田; Akira Ishiyama; 明石山; Shozo Watanabe; 昌造渡辺
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2003-05-21
Filing date: 2003-05-21
Publication date: 2004-12-09
Anticipated expiration: 2023-05-21
Also published as: JP4069012B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffuser and a diffusion method where coarse bubbles can be generated by a simple means without requiring excessive equipment cost and the increase in the consumption of electric power, and a separation membrane and a simple substance separation screen can effectively be cleaned. <P>SOLUTION: A tube 3 made of a material having a specific gravity higher than that of water, and in which one end is a closed end 5 and the other end is an open end 4, and has a rotary axis 7 orthogonal to the tube axis and also along the horizontal direction, more on the closed end 5 side than the centroid of the tube, is installed sideways so that the open end 4 is located at the lower part of a separation membrane or a carrier separation screen. Then, the lower part of the open end 4 is provided with an air feed nozzle 6 as an air feeding means for feeding air into the tube 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、汚水処理を行う生物処理槽において、膜分離法を用いる場合には膜面に付着する汚泥ケーキの洗浄手段、担体法を用いる場合には担体と処理水を分離する担体分離スクリーンに付着する夾雑物の洗浄手段に関する。
【０００２】
【従来の技術】
これまでは、生物処理槽において汚水処理された処理水は、沈殿池にて汚泥と上澄水とに重力沈降分離されるのが普通であったが、沈降分離に長時間を要するために滞留時間の大きい沈殿槽を必要とする問題があった。そこで最近では、生物処理槽中に分離膜を浸漬し、処理水を濾過しつつ直接取り出すようにした膜分離法が開発されている。そして、分離膜の表面には汚泥などが堆積して短時間で閉塞に至るため、分離膜の直下に曝気装置または散気装置を配置し、浮上気泡により膜表面の洗浄を行うのが普通である。膜表面の洗浄効果をあげるためには、膜表面の液流速はできるだけ大きくすることが好ましく、同一風量であれば気泡径は大きいほうがよい。そこで、気泡径の大きい粗大気泡を発生させる曝気装置または散気装置として以下のようなものが開示されている。
【０００３】
例えば、活性汚泥処理を行う反応槽の上部に分離膜を設置し、反応層の下部に微細気泡を発生する曝気装置を設置するとともに、これらの分離膜と曝気装置との間に、傾斜板や粒子充填層を設けて微細気泡を合一させて肥大化気泡としたうえ、分離膜に向けて浮上させる方法が提案されており、その実施例において、肥大化気泡の好ましい粒径は５ｍｍと開示されている（特許文献１参照）。
【０００４】
また、分離膜の下方に２段に散気装置を設け、その下段側の散気装置からは微細気泡を散気し、上段側の散気装置からは粗大気泡を散気する方法が提案されており、上段側の散気装置として、吹き出し口で０．８〜２０ｍｍの散気孔を有するものが開示されている（特許文献２参照）。
【０００５】
さらに、上記と同様の、膜分離装置の下方に２段に散気装置を設け、その下段側の散気装置からは微細気泡を散気し、上段側の散気装置からは粗大気泡を散気する方法において、上段側の散気装置として、孔径約５〜１０ｍｍの散気管を複数個有する散気管を並列に複数本設けた構成のものが開示されている（特許文献３参照）。
【０００６】
また、最近の新しい生物処理法として、生物処理槽中に微生物を担持させた担体を投入して窒素やりん等の富栄養化成分を除去する担体法が開発されている。この担体法では、処理槽中に担体を滞留させておくために、処理槽から処理水を排水するための流出口に担体を分離するスクリーン（担体分離スクリーン）を設けている。そして、担体分離スクリーンの表面には、担体とともに汚泥などが付着して閉塞しやすいため、本出願人は、担体分離スクリーンの前面側に対向してモータ駆動の循環ベルトからなる移動壁装置を設けて強制流動を与えることにより担体分離スクリーンの洗浄効果を高める方法を開示した（特許文献４参照）。
【０００７】
しかしながら、上記従来技術には以下のような改善の余地がある。すなわち、その後の調査により、担体法において、汚水中に含まれる繊維質等の狭雑物が単体分離スクリーンの表面に絡み付くように付着するため、上記特許文献４に開示したような強制流動を与える手段によってはこのような繊維質等の狭雑物を担体分離スクリーンの表面から剥がすことに労力を要することがわかった。また、膜分離法においても、上記特許文献１〜３に開示されたような程度の気泡径（最大２０ｍｍ程度）では、このような繊維質等の狭雑物を分離膜から除去することは困難であることがわかった。本発明者らの調査によれば、このような繊維質等の狭雑物を分離膜や担体分離スクリーンから剥離させるためには気泡径は１００ｍｍ以上にする必要があることを見出した。
【０００８】
ここで、上記特許文献１に開示された微細気泡を合一させる方法で１００ｍｍ径の粗大気泡を作ろうとすると、特許文献１の図２および図３の方法の場合には、傾斜板でできた上部隙間を１００ｍｍ程度にする必要があるが、そうするとほとんどの微細気泡は合一する前にこの大きな隙間をすり抜けてしまい、所望の径の粗大気泡は得られない。また、同文献の図４の場合にも粒子隙間を１００ｍｍ程度にする必要があり、同様に微細気泡が合一する前にこの大きな隙間をすり抜けてしまい、所望の径の粗大気泡は得られない。
【０００９】
また、特許文献２および３の方法のように散気管に設けた散気孔から気泡を発生させる方法で１００ｍｍ径の粗大気泡を作るには散気孔の径を１００ｍｍ程度とすれば可能であるが、この場合には散気管に大量の空気を連続的に供給し続ける必要があり、ブロワ能力の増強のために余分の設備コストがかかることや電力消費量が過大となる問題があり、この方法は実際上適用できない。
【００１０】
【特許文献１】
特開２００３−５３３６８号公報
【特許文献２】
特開２００１−２１２５８７号公報
【特許文献３】
特開２００２−２２４６８５号公報
【特許文献４】
特開２００２−８６１７７号公報
【００１１】
【発明が解決しようとする課題】
そこで、本発明はかかる問題点に鑑みてなされたものであって、その目的は、過大な設備コストや電力消費量の上昇をともなうことなく、簡易な手段により粗大気泡を発生させることができ、分離膜や単体分離スクリーンを効果的に洗浄することができる散気装置および散気方法を提供することを目的とする。
【００１２】
【課題を解決するための手段】
請求項１に記載の発明は、汚水処理を行う生物処理槽内に配置された分離膜または担体分離スクリーンを洗浄する散気装置であって、少なくとも一端が開放端であり、この開放端が前記分離膜または担体分離スクリーンの下方に位置するように略水平に設置された管と、この管内へ空気を供給する空気供給手段とを備えたことを特徴とする散気装置である。
【００１３】
請求項２に記載の発明は、汚水処理を行う生物処理槽内に配置された分離膜または担体分離スクリーンを洗浄する散気装置であって、比重が水よりも大きい材料で作られ、一端が閉止端で多端が開放端であり、この開放端が前記分離膜または担体分離スクリーンの下方に位置するように横向きに設置された管であって、この管の重心よりも前記閉止端側に、管軸に直交し且つ水平方向に沿う回転軸を有する管と、この管内へ空気を供給する空気供給手段とを備えたことを特徴とする散気装置である。
【００１４】
請求項３に記載の発明は、汚水処理を行う生物処理槽内に配置された分離膜または担体分離スクリーンを洗浄する散気装置であって、一端が閉止端で他端が開放端であり、この開放端が前記分離膜または担体分離スクリーンの下方に位置するように横向きに設置された管と、この管内へ空気を供給する空気供給手段と、前記開放端を前記閉止端より周期的に高くしたり低くしたりするように前記管を傾動させる傾動手段とを設けたことを特徴とする散気装置である。
【００１５】
請求項４に記載の発明は、請求項１〜３のいずれか１項に記載の散気装置を用いて、前記開放端から間欠的に粗大気泡を発生させることにより、前記分離膜または前記担体分離スクリーンを洗浄する散気方法である。
【００１６】
【発明の実施の形態】
本発明を担体法による汚水処理を行う生物処理槽に適用した場合について図を参照しつつ説明する。なお、本発明は膜分離法による汚水処理を行う生物処理槽にも当然に適用できるものである。
【００１７】
［実施形態１］
図１に示すように、担体法による汚水処理を行う生物処理槽（以下、単に「処理槽」ともいう。）１の端部に担体分離スクリーン（以下、単に「スクリーン」ともいう。）２が設けられている。そして、一端が開放端４である管３を、この開放端４がスクリーン２の下方に位置するように水平に設置する。この管３には空気供給手段として空気供給枝管６を設けておく。
【００１８】
空気供給枝管６から水平に設置された管３内へ空気を供給していくと、図２に示すように、空気供給枝管６との接続部から管３内の上部に空気が溜まり始める（（ａ）→（ｂ））。管３内上部に溜まった空気には表面張力が作用するので、この空気溜まりＡ’は分散して存在することはなく、さらに空気の供給を継続していくと徐々に広がりながらも連続した気泡であり続ける（（ｂ）→（ｃ））。この空気溜まりＡ’の先端が管３の開放端４に達した時にこの開放端４から気泡Ｃが放出されるが、このとき表面張力により管３内に存在する空気Ａ’の多くを引き連れて一気に管３から放出され、径の大きな粗大気泡Ｃが発生することになる（（ｄ））。そして、この粗大気泡Ｃが発生した後は（ａ）の状態に戻り、再度空気Ａ’が所定量溜まるまで気泡Ｃが放出されることがなく、粗大気泡Ｃが間欠的に発生することになる。
【００１９】
粗大気泡Ｃ発生の時にどれだけの量の空気を引き連れて一度に放出するかは、管３内面の粗さや液（処理水）Ｂとの濡れ性に依存する。管３内面が滑らかで濡れやすい表面処理が施されている方が、一度に多量の空気が塊となって浮上しやすく、気泡Ｃの径が大きくなる。
【００２０】
管３の内径や空気供給枝管６から開放端４までの長さも、管３内上部に保持できる空気溜まりＡ’の量に影響し、粗大気泡Ｃの径にも影響するため、適宜調整することが望ましい。なお、管３の内径は、少なくとも粗大気泡Ｃの径よりも大きくすることが好ましい。
【００２１】
管３の設置は必ずしも厳密に水平とする必要はなく、略水平としてもよい。ここに、略水平とは、空気Ａ’が管３内上部に所定量溜まり、かつ粗大気泡Ｃ発生の時に引き連れて一度に放出する空気Ａ’量を確保して粗大気泡Ｃの径を維持できる程度に、開放端４の高さ位置を空気供給枝管６との接続部の高さ位置より少しだけ低く設置する場合を含むことを意味する。また管３は、必ずしも直管とする必要はなく、図１に示すように曲がり部が存在するものを用いてもよい。また、設置する管３の本数は、図１では４本としたがこれに限られるものではなく、スクリーン２の幅等に応じて適宜変更し得るものである。
【００２２】
空気Ａの供給量は、上記従来の複数の散気孔を設けた散気管による場合と同程度の量とすればよい。これにより、従来のように気泡の発生頻度を増加させることなく、却って気泡の発生頻度を低減しつつ、上昇速度の大きい粗大気泡Ｃをほぼ一定周期で間欠的にスクリーン２表面に沿って上昇させることができるため、スクリーン２表面に付着した繊維質等の狭雑物を効果的に除去することができる。
【００２３】
すなわち、気泡の形状を球形と仮定すると、定常速度にて水中を上昇する気泡に作用する流体抵抗と浮力との釣り合いから以下の数１が得られる。
【００２４】
【数１】

【００２５】
ここで、π：円周率、Ｄ：気泡直径、ρ：液密度、ｇ：重力加速度、Ｃ_Ｄ：抵抗係数、Ｖ：気泡上昇速度である。
【００２６】
数１を変形することにより、以下の数２が得られる。
【００２７】
【数２】

【００２８】
抵抗係数Ｃ_Ｄは図７に示すようにレイノルズ数Ｒｅの関数であるが、レイノルズ数Ｒｅは気泡直径Ｄと気泡上昇速度Ｖに正比例して増加するものであるため、一般にレイノルズ数Ｒｅが増加すると、すなわち気泡直径や気泡上昇速度が増加すると、抵抗係数Ｃ_Ｄは低下する。したがって、数２より気泡径が大きくなると気泡の上昇速度も増加することがわかる。
【００２９】
ここで、従来の散気孔により粗大気泡を発生させようとして散気孔径を大きくすると、過大な散気量の増加を招くことになる。例えば、散気孔から放出される気泡の頻度は一定であると仮定して、気泡径を２倍にすると、気泡の体積は８倍になるので８倍の散気量が必要になる。実際には、気泡径が大きくなるにしたがって散気孔に気泡が付着し続けようとして作用する表面張力が気泡に作用する浮力に負けてしまうために、単純に散気孔を大きくしただけでは、気泡の粗大化は困難になってくる。つまり、例えば１００ｍｍ径の散気孔を設けても１００ｍｍ径まで気泡が成長する以前に１０ｍｍ径程度の気泡になって順次放出されてしまう。あくまでも散気孔を大きくして気泡の粗大化を行おうとすれば、さらに大量の空気を供給することにより可能であるが、気泡の放出頻度が気泡の粗大化とともに増加することとなり、過大な散気量を必要とすることになってしまう。
【００３０】
これに対し、本発明によれば、散気量の増加を必要とせずに粗大気泡を発生することが可能となるものである。
【００３１】
なお、空気供給枝管６は、図１では管３の上部に接続しているがこれに限られるものではなく、管３の下部や側面部、閉止端５端面に接続してもよい。
【００３２】
管３の開放端４と反対側の端５の処理は、図３のように管３の上半分を閉止し、下半分を開放とすれば、気泡Ｃが開放端４から放出される時に開放端４側に向かって気泡Ｃとともに同一方向の液Ｂの流れが生じるので、管３内に存在していた空気溜まりＡ’を一度に全部噴出させるのに効果的である。これに対し、図２のように反対側の端５を完全に閉止端とすると、気泡Ｃが開放端４から放出されたときそれに伴う体積の欠損分を補うために液Ｄが開放端４から管３内に流入するため、液Ｄと空気（気泡）Ｃとの間に作用する剪断力により開放端４から放出される空気（気泡）Ｃの流速が低下し、管３内に一部の空気Ａ’が取り残される可能性が高くなる。
【００３３】
［実施形態２］
上記実施形態１では、管３を水平に設置していることから単位長さ当たりの管３内に保持できる空気Ａ’の量が少ないため、所定量の空気Ａ’を管３内に溜めるには相当の長さの管３を設置する必要がある。処理槽１内のスペースの制約等よりこのような長い管３を設置できない場合には以下の実施形態を採用することが推奨される。
【００３４】
図４に示すように、比重が水よりも大きい材料で作られ、一端が閉止端５で他端が開放端４であり、管の重心よりも閉止端５側に、管軸に直交し且つ水平方向に沿う回転軸７を有する管３を、開放端４がスクリーン２の下方に位置するように横向きに設置する。そして、この管３内へ空気Ａを供給する空気供給手段として、開放端４の下方に空気供給ノズル６を設け、開放端４をその下部を切り欠いてその上部がノズル６の上方を覆うような形状に形成しておく。これにより、ノズル６から放出された気泡が開放端４の上部で捕捉されて管３内に入り閉止端５側に空気溜まりＡ’を形成し始める（（ａ）→（ｂ））。さらに、ノズル６からの空気の供給を続けると空気溜まりＡ’は開放端４側へと拡大していき（（ｂ）→（ｃ））、ついにはその浮力により回転軸７を回転中心として開放端４側を上方へ押し上げる。すると、空気溜まりＡ’が開放端４から一気に放出されて粗大気泡Ｃとなる（（ｄ））。粗大気泡Ｃが発生した後は空気溜まりＡ’による浮力がなくなるので（ａ）の状態に戻る。
【００３５】
したがって、上記実施形態１と同様に、間欠的に粗大気泡Ｃがスクリーン３表面に沿って上昇することとなり、スクリーン３表面が効果的に洗浄されることとなる。
【００３６】
管３の材料は水より比重の大きいものであれば特に限定されるものではなく、例えば従来の散気管に用いられるステンレス鋼管、塩化ビニル管等を用いればよい。また回転軸７の位置は、管３の重心に近づけすぎると空気溜まりＡ’の量が少ないうちに開放端４側が浮力により上昇しやすくなるため気泡Ｃの径が小さくなり、逆に管３の重心から遠ざけすぎると開放端４側が持ち上がらなくなり所望の気泡Ｃ径が得られなくなるので、所望の気泡Ｃ径が得られるように適宜調整することが好ましい。
【００３７】
また空気供給手段として、ノズル６の代わりに閉止端５側に空気供給枝管を設けてもよい。この場合、閉止端５側の昇降を阻害しないように空気供給枝管には伸縮自在のフレキ管を接続して用いることが望ましい。
【００３８】
［実施形態３］
上記実施形態２では、管３の全重量、回転軸７の位置、ノズル６からの空気供給量等によって空気溜まりＡ’の量が変化し、発生する気泡Ｃの径も変化するため、所望の気泡Ｃ径を一定時間ごとに確実に発生させることは容易ではない。そこで、以下の実施形態が推奨される。
【００３９】
図５に示すように、一端が閉止端５で他端が開放端４である管３を、開放端４がスクリーン２の下方に位置するように横向きに設置する。本実施形態では回転軸７の代わりに、閉止端５側に支点９を設けておく。そして、この管３内へ空気Ａを供給する空気供給手段として、上記実施形態２と同様、開放端４の下方に空気供給ノズル６を設け、開放端４をその下部を切り欠いてその上部がノズル６の上方を覆うような形状に形成しておく。さらに、開放端４を閉止端５より周期的に高くしたり低くしたりするように管３を傾動させる傾動手段８を設ける。傾動手段８としては、例えば処理槽１上部に固定したアクチュエータ８ａとこのアクチュエータ８ａに接続された吊下げ金具８ｂとから構成されたものとし、吊下げ金具８ｂは管３の開放端４側に接続しておく。そして、アクチュエータ８ａを周期的に駆動させることによって吊下げ金具８ｂを介して開放端４側を上下させることにより、支点９を中心として管３を傾動させて開放端４を閉止端５より周期的に高くしたり低くしたりできる。したがって、ノズル６からの空気供給量とアクチュエータ８ａの駆動周期とを適宜調整することにより、所望の径の気泡Ｃを一定時間ごとに確実に発生させることが容易にできる。
【００４０】
また、本実施形態の場合も上記実施形態２と同様、管３を比重が水よりも大きい材料で製作することが好ましく、管３内の空気溜まりＡ’による浮力と管３の自重とがほぼつり合う状態でアクチュエータ８ａを作動させるようにすると、非常に小さな動力源で作動させることが可能となる。
【００４１】
なお、本実施形態では傾動手段８を開放端４側に設け、支点９を閉止端５側に設けたが、これとは逆に傾動手段８を閉止端５側に設け、支点９を開放端４側に設けてもよい。
【００４２】
また上記実施形態２と同様、空気供給手段として、ノズル６の代わりに閉止端５側に空気供給枝管を設け、これに伸縮自在のフレキ管を接続したものを用いてもよい。
【００４３】
【実施例】
担体分離スクリーン２を粗大気泡を用いて洗浄する方法について、従来の複数の散気孔を設けた散気管による方法（比較例１，２）と本発明の上記実施形態１の方法（実施例）とを比較した。比較は、流体力学に基づくシミュレーション計算モデルを用いて各方法により発生させた気泡の軌跡を計算し、この気泡がスクリーン２表面を通過する領域を洗浄領域１０とし、この洗浄領域１０の広さを比較することにより行った（図６参照）。
【００４４】
ここに、スクリーン２は高さ６２００ｍｍ、幅４０００ｍｍでスクリーンの開き目は２．０ｍｍとした。
【００４５】
（比較例１）
計算条件としては、スクリーン２の下方にスクリーン２幅に沿って直管の散気管を水平に設置し、この散気管には１０ｍｍ径の散気孔を４０ｍｍピッチで１００個設け、散気管に２ｍ^３／ｍｉｎの空気を供給するとした。シミュレーション計算の結果、図６（ａ）に示すように、本比較例１では、気泡径が小さいため、スクリーン２を透過する処理水の流れに乗って気泡もスクリーン裏面へ直ちに透過してしまい、気泡によるスクリーン２の洗浄領域１０はスクリーン２の下部の狭い範囲に限定され、洗浄効果が小さいことがわかる。
【００４６】
（比較例２）
計算条件としては、上記比較例１と同じ１０ｍｍ径の散気孔を４０ｍｍピッチで１００個設けた散気管をスクリーン２の下方にスクリーン２幅に沿って上下２段に設置し、各散気管には比較例１と同じ２ｍ^３／ｍｉｎで空気を供給するとした。シミュレーション計算の結果、図６（ｂ）に示すように、気泡によるスクリーン２の洗浄領域１０は比較例１よりわずかに増加しているが、散気量を比較例１の２倍にしていることを考慮するとその洗浄効果の改善の度合いは小さい。
【００４７】
（実施例）
計算条件としては、一端が開放端で他端が閉止端である５００ｍｍ径の管を合計４本、各管の開放端がスクリーン２の下方でスクリーン２幅に沿って等間隔に位置するように水平に設置し、散気量は管４本合計で比較例１と同じ２ｍ^３／ｍｉｎとし、管１本当たり平均１０秒に１度１００ｍｍ径の粗大気泡を放出させるとした。シミュレーション計算の結果、図６（ｃ）に示すように、気泡によるスクリーン２の洗浄領域１０が比較例１，２に比べ大幅に増加していることがわかる。
【００４８】
【発明の効果】
以上より、本発明によれば、過大な設備コストや電力消費量の上昇をともなうことなく、簡易な手段により粗大気泡を発生させることができ、分離膜や単体分離スクリーンを効果的に洗浄することができる散気装置および散気方法を提供できるようになった。
【図面の簡単な説明】
【図１】実施形態１の散気装置を模式的に示す斜視図である。
【図２】実施形態１の散気装置の作動状況を模式的に示す垂直断面図である。
【図３】実施形態１の散気装置における気泡発生時の様子を模式的に示す垂直断面図である。
【図４】実施形態２の散気装置の作動状況を模式的に示す垂直断面図である。
【図５】実施形態３の散気装置の作動状況を模式的に示す垂直断面図である。
【図６】気泡による単体分離スクリーンの洗浄領域を示す斜視図である。
【図７】レイノルズ数と抵抗係数との関係を示すグラフ図である。
【符号の説明】
１…生物処理槽
２…担体分離スクリーン
３…管
４…開放端
５…閉止端
６…空気供給手段（空気供給枝管、ノズル）
７…回転軸
８…傾動手段（アクチュエータ）
８ａ…アクチュエータ
８ｂ…吊下げ金具
９…支点
１０…洗浄領域
Ａ…空気
Ａ’…空気溜まり
Ｂ…液
Ｃ…粗大気泡
Ｄ…液[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides, in a biological treatment tank for performing sewage treatment, a washing means for sludge cake attached to a membrane surface when using a membrane separation method, and a carrier separation screen for separating carrier and treated water when using a carrier method. The present invention relates to a washing means for removing contaminants.
[0002]
[Prior art]
Until now, sewage treated water in biological treatment tanks was usually settled by gravity sedimentation into sludge and supernatant water in a sedimentation basin. There is a problem that a large sedimentation tank is required. Therefore, recently, a membrane separation method has been developed in which a separation membrane is immersed in a biological treatment tank and treated water is directly removed while being filtered. Since sludge and the like accumulate on the surface of the separation membrane and blockage in a short time, an aeration device or a diffuser is placed immediately below the separation membrane, and the membrane surface is usually washed with floating bubbles. is there. In order to enhance the cleaning effect on the membrane surface, it is preferable to increase the liquid flow velocity on the membrane surface as much as possible. If the air volume is the same, the larger the bubble diameter, the better. Therefore, the following is disclosed as an aerator or a diffuser for generating coarse bubbles having a large bubble diameter.
[0003]
For example, a separation membrane is installed at the upper part of the reaction tank for performing the activated sludge treatment, and an aerator for generating fine bubbles is installed at the lower part of the reaction layer, and an inclined plate or the like is provided between these separation membranes and the aeration apparatus. A method has been proposed in which a particle-packed layer is provided to combine microbubbles to form enlarged bubbles, and then float toward a separation membrane. In this embodiment, the preferred particle size of the enlarged bubbles is 5 mm. (See Patent Document 1).
[0004]
Also, a method has been proposed in which a diffuser is provided in two stages below the separation membrane, and fine bubbles are diffused from the lower diffuser, and coarse bubbles are diffused from the upper diffuser. As the upper-stage diffuser, there is disclosed a diffuser having a diffuser of 0.8 to 20 mm at an outlet (see Patent Document 2).
[0005]
Further, similar to the above, a diffuser is provided in two stages below the membrane separation device, and fine bubbles are diffused from the lower diffuser, and coarse bubbles are diffused from the upper diffuser. Japanese Patent Application Laid-Open No. H11-163,086 discloses a method of disposing a plurality of diffuser tubes having a plurality of diffuser tubes having a hole diameter of about 5 to 10 mm as an upper diffuser.
[0006]
Further, as a recent new biological treatment method, a carrier method for removing a eutrophic component such as nitrogen and phosphorus by introducing a carrier carrying microorganisms into a biological treatment tank has been developed. In this carrier method, a screen (carrier separation screen) for separating carriers is provided at an outlet for draining treated water from the treatment tank in order to keep the carriers in the treatment tank. And, on the surface of the carrier separation screen, sludge and the like adhere together with the carrier, so that it is likely to be clogged. Therefore, the present applicant has provided a moving wall device comprising a motor driven circulation belt facing the front side of the carrier separation screen. A method for enhancing the washing effect of the carrier separation screen by applying forced flow to the carrier separation screen has been disclosed (see Patent Document 4).
[0007]
However, the above-mentioned prior art has room for improvement as described below. That is, according to the subsequent investigation, in the carrier method, since the contaminants such as fibrous substances contained in the sewage adhere to the surface of the single separation screen so as to be entangled with each other, a forced flow as disclosed in Patent Document 4 is given. It has been found that, depending on the means, labor is required to peel off such fibrous substances or the like from the surface of the carrier separation screen. Also, in the membrane separation method, it is difficult to remove such fibrous and other contaminants from the separation membrane with a bubble diameter (up to about 20 mm) as disclosed in Patent Documents 1 to 3 described above. It turned out to be. According to the investigation by the present inventors, it has been found that the bubble diameter needs to be 100 mm or more in order to separate such a foreign matter such as fibrous material from the separation membrane or the carrier separation screen.
[0008]
Here, when trying to form a coarse bubble having a diameter of 100 mm by the method of coalescing the fine bubbles disclosed in Patent Document 1, in the case of the method of FIGS. The upper gap needs to be about 100 mm. However, in this case, most of the fine bubbles pass through the large gap before coalescing, and a coarse bubble having a desired diameter cannot be obtained. Also, in the case of FIG. 4 of the same document, it is necessary to make the particle gap about 100 mm, and similarly, the fine bubbles pass through this large gap before they coalesce, so that a coarse bubble having a desired diameter cannot be obtained. .
[0009]
Further, it is possible to make a large bubble having a diameter of 100 mm by a method of generating bubbles from a diffuser hole provided in a diffuser tube as in the methods of

Patent Documents

2 and 3, if the diameter of the diffuser hole is set to about 100 mm. In this case, it is necessary to continuously supply a large amount of air to the air diffuser, and there is a problem that extra equipment cost is required to increase the blower capacity and power consumption is excessive. Not practically applicable.
[0010]
[Patent Document 1]
JP 2003-53368 A [Patent Document 2]
Japanese Patent Application Laid-Open No. 2001-212587 [Patent Document 3]
Japanese Patent Application Laid-Open No. 2002-224885 [Patent Document 4]
JP 2002-86177 A
[Problems to be solved by the invention]
Therefore, the present invention has been made in view of such a problem, and its object is to generate coarse bubbles by simple means without accompanying excessive equipment cost or increase in power consumption, It is an object of the present invention to provide an air diffusing device and an air diffusing method capable of effectively cleaning a separation membrane and a single separation screen.
[0012]
[Means for Solving the Problems]
The invention according to claim 1 is an aeration device for cleaning a separation membrane or a carrier separation screen disposed in a biological treatment tank for performing sewage treatment, wherein at least one end is an open end, and the open end is the open end. An air diffuser, comprising: a tube installed substantially horizontally so as to be located below a separation membrane or a carrier separation screen; and air supply means for supplying air into the tube.
[0013]
The invention according to claim 2 is an air diffuser for cleaning a separation membrane or a carrier separation screen disposed in a biological treatment tank that performs sewage treatment, and is made of a material having a specific gravity larger than that of water. A closed end is a multi-ended open end, a tube which is disposed laterally so that the open end is located below the separation membrane or the carrier separation screen, and which is closer to the closed end than the center of gravity of the tube, An air diffuser, comprising: a pipe having a rotation axis orthogonal to a pipe axis and extending along a horizontal direction; and air supply means for supplying air into the pipe.
[0014]
The invention according to claim 3 is a diffuser for cleaning a separation membrane or a carrier separation screen disposed in a biological treatment tank that performs sewage treatment, one end being a closed end and the other end being an open end, A tube installed horizontally so that this open end is located below the separation membrane or the carrier separation screen, air supply means for supplying air into the tube, and the open end being periodically raised from the closed end. And a tilting means for tilting the pipe so as to lower or lower the pipe.
[0015]
According to a fourth aspect of the present invention, the separation membrane or the carrier is generated by using the air diffuser according to any one of the first to third aspects to generate large bubbles intermittently from the open end. This is an aeration method for cleaning the separation screen.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
A case where the present invention is applied to a biological treatment tank that performs sewage treatment by a carrier method will be described with reference to the drawings. The present invention is naturally applicable to a biological treatment tank for performing sewage treatment by a membrane separation method.
[0017]
[Embodiment 1]
As shown in FIG. 1, a carrier separation screen (hereinafter, also simply referred to as “screen”) 2 is provided at an end of a biological treatment tank (hereinafter, simply referred to as “treatment tank”) 1 for performing sewage treatment by a carrier method. Is provided. Then, the tube 3 whose one end is the open end 4 is installed horizontally so that the open end 4 is located below the screen 2. The pipe 3 is provided with an air supply branch pipe 6 as an air supply means.
[0018]
When air is supplied from the air supply branch pipe 6 into the horizontally installed pipe 3, as shown in FIG. 2, the air starts to accumulate in the upper part of the pipe 3 from the connection with the air supply branch pipe 6. ((A) → (b)). Since the surface tension acts on the air accumulated in the upper part of the pipe 3, the air accumulation A 'does not exist in a dispersed manner. ((B) → (c)). When the tip of the air reservoir A 'reaches the open end 4 of the tube 3, air bubbles C are released from the open end 4. At this time, most of the air A' existing in the tube 3 is drawn by surface tension. The large bubbles C which are discharged from the tube 3 at a stretch and have a large diameter are generated ((d)). Then, after the generation of the coarse bubbles C, the state returns to the state (a), and the bubbles C are not released until the predetermined amount of the air A 'is accumulated again, and the coarse bubbles C are generated intermittently. .
[0019]
The amount of air that is drawn and released at once when the coarse bubbles C are generated depends on the roughness of the inner surface of the tube 3 and the wettability with the liquid (treatment water) B. When the inner surface of the tube 3 is subjected to a surface treatment that is smooth and easy to get wet, a large amount of air is lumped at a time and easily floats, and the diameter of the bubble C increases.
[0020]
The inner diameter of the pipe 3 and the length from the air supply branch pipe 6 to the open end 4 also affect the amount of the air pool A 'that can be held in the upper part of the pipe 3 and the diameter of the coarse bubble C. It is desirable. It is preferable that the inner diameter of the tube 3 be larger than at least the diameter of the coarse bubble C.
[0021]
The installation of the pipe 3 does not necessarily have to be strictly horizontal, but may be substantially horizontal. Here, “substantially horizontal” means that a predetermined amount of air A ′ is accumulated in the upper part of the pipe 3 and the amount of air A ′ released at a time when the coarse bubbles C are generated can be secured to maintain the diameter of the coarse bubbles C. This means that the height of the open end 4 is set slightly lower than the height of the connection with the air supply branch 6. The pipe 3 does not necessarily have to be a straight pipe, but may be a pipe having a bent portion as shown in FIG. The number of tubes 3 to be installed is four in FIG. 1, but is not limited to this, and can be changed as appropriate according to the width of the screen 2 and the like.
[0022]
The supply amount of the air A may be approximately the same as that of the conventional air diffuser provided with a plurality of air diffusion holes. As a result, the large bubbles C having a large rising speed are intermittently raised along the surface of the screen 2 at a substantially constant period without increasing the frequency of occurrence of the bubbles as in the related art, but rather reducing the frequency of occurrence of the bubbles. Therefore, it is possible to effectively remove impurities such as fibers attached to the surface of the screen 2.
[0023]
That is, assuming that the shape of the bubble is spherical, the following equation 1 is obtained from the balance between the fluid resistance acting on the bubble rising in the water at a steady speed and the buoyancy.
[0024]
(Equation 1)

[0025]
Here, π: pi, D: bubble diameter, ρ: liquid density, g: gravitational acceleration, _CD : resistance coefficient, and V: bubble rising speed.
[0026]
By transforming Equation 1, the following Equation 2 is obtained.
[0027]
(Equation 2)

[0028]
The resistance coefficient C _D is a function of the Reynolds number Re as shown in FIG. 7, for the Reynolds number Re is to increase in direct proportion to the cell diameter D and bubble rising velocity V, the general Reynolds number Re is increased , that is, cell diameter and bubble rising speed increases, the drag coefficient C _D is reduced. Therefore, it can be seen from Equation 2 that as the bubble diameter increases, the rising speed of the bubbles also increases.
[0029]
Here, if the diameter of the diffused holes is increased in order to generate coarse bubbles by the conventional diffused holes, an excessive increase in the amount of diffused air is caused. For example, assuming that the frequency of the air bubbles released from the air diffusion holes is constant, if the air bubble diameter is doubled, the volume of the air bubbles becomes eight times, so that the air diffusion amount is required eight times. In fact, as the bubble diameter increases, the surface tension acting to keep the air bubbles adhered to the air diffusion holes loses the buoyancy acting on the air bubbles. Coarsening becomes difficult. That is, even if a diffuser hole having a diameter of, for example, 100 mm is provided, the bubbles will be sequentially released as bubbles having a diameter of about 10 mm before the bubbles grow to a diameter of 100 mm. If it is necessary to increase the size of the air diffusion holes to make the bubbles coarser, it is possible to supply a larger amount of air.However, the frequency of release of the bubbles increases with the coarseness of the air bubbles, resulting in excessive air diffusion. You will need an amount.
[0030]
On the other hand, according to the present invention, it is possible to generate coarse bubbles without increasing the amount of diffused air.
[0031]
The air supply branch pipe 6 is connected to the upper part of the pipe 3 in FIG. 1, but is not limited to this. The air supply branch pipe 6 may be connected to the lower part, the side part, or the end face of the closed end 5.
[0032]
The processing of the end 5 opposite to the open end 4 of the tube 3 is performed by closing the upper half of the tube 3 and opening the lower half as shown in FIG. Since the liquid B flows in the same direction along with the bubbles C toward the end 4, it is effective to eject all the air pools A ′ existing in the pipe 3 at a time. On the other hand, when the opposite end 5 is completely closed as shown in FIG. 2, the liquid D flows from the open end 4 in order to compensate for the volume loss associated with the release of bubbles C from the open end 4. Due to the flow into the pipe 3, the flow rate of the air (bubbles) C discharged from the open end 4 is reduced by the shearing force acting between the liquid D and the air (bubbles) C, and some of the air flows into the pipe 3. The possibility that the air A 'is left behind increases.
[0033]
[Embodiment 2]
In the first embodiment, since the pipe 3 is installed horizontally, the amount of air A ′ that can be held in the pipe 3 per unit length is small, so that a predetermined amount of air A ′ is stored in the pipe 3. Requires the installation of a tube 3 of considerable length. When such a long pipe 3 cannot be installed due to space restrictions in the processing tank 1, it is recommended to adopt the following embodiment.
[0034]
As shown in FIG. 4, the specific gravity is made of a material larger than water, one end is a closed end 5 and the other end is an open end 4, closer to the closed end 5 side than the center of gravity of the pipe, orthogonal to the pipe axis and The tube 3 having the axis of rotation 7 along the horizontal direction is placed sideways so that the open end 4 is located below the screen 2. As an air supply means for supplying air A into the pipe 3, an air supply nozzle 6 is provided below the open end 4, and the open end 4 is cut off at the lower part and the upper part covers the upper part of the nozzle 6. It is formed in a suitable shape. As a result, bubbles released from the nozzle 6 are caught at the upper part of the open end 4 and enter the pipe 3 to start forming an air pool A ′ on the closed end 5 side ((a) → (b)). Further, when the supply of air from the nozzle 6 is continued, the air pool A 'expands toward the open end 4 ((b) → (c)), and finally the air pool A' is opened around the rotating shaft 7 due to its buoyancy. Push up the end 4 side. Then, the air pool A 'is released at a stretch from the open end 4 and becomes a coarse bubble C ((d)). After the generation of the coarse bubbles C, the buoyancy due to the air pool A 'disappears, so that the state returns to the state of FIG.
[0035]
Therefore, as in the first embodiment, the coarse bubbles C intermittently rise along the surface of the screen 3, and the surface of the screen 3 is effectively cleaned.
[0036]
The material of the tube 3 is not particularly limited as long as it has a specific gravity greater than that of water. For example, a stainless steel tube, a vinyl chloride tube, or the like used for a conventional diffuser tube may be used. If the position of the rotary shaft 7 is too close to the center of gravity of the tube 3, the diameter of the bubble C becomes small because the open end 4 side easily rises due to buoyancy while the amount of the air reservoir A ′ is small. If the distance from the center of gravity is too great, the open end 4 will not lift and the desired bubble C diameter will not be obtained. Therefore, it is preferable to appropriately adjust the bubble C diameter to obtain the desired bubble C diameter.
[0037]
As the air supply means, an air supply branch pipe may be provided on the closed end 5 side instead of the nozzle 6. In this case, it is desirable to connect and use an extendable flexible pipe to the air supply branch pipe so as not to hinder the vertical movement of the closed end 5 side.
[0038]
[Embodiment 3]
In the second embodiment, the amount of the air pool A ′ changes according to the total weight of the tube 3, the position of the rotating shaft 7, the amount of air supplied from the nozzle 6, and the like, and the diameter of the generated bubbles C also changes. It is not easy to reliably generate the bubble C diameter at regular intervals. Therefore, the following embodiment is recommended.
[0039]
As shown in FIG. 5, the tube 3 having one end closed and the other end open 4 is placed sideways so that the open end 4 is located below the screen 2. In the present embodiment, a fulcrum 9 is provided on the closed end 5 side instead of the rotating shaft 7. As an air supply means for supplying air A into the pipe 3, an air supply nozzle 6 is provided below the open end 4 as in the second embodiment, and the open end 4 is cut off at the lower part and the upper part is cut off. It is formed in a shape that covers the upper part of the nozzle 6. Further, a tilting means 8 is provided for tilting the pipe 3 so that the open end 4 is periodically raised or lowered from the closed end 5. The tilting means 8 is composed of, for example, an actuator 8a fixed on the upper part of the processing tank 1 and a hanging metal 8b connected to the actuator 8a. The hanging metal 8b is connected to the open end 4 of the pipe 3. Keep it. Then, by periodically driving the actuator 8a to move the open end 4 side up and down via the hanging bracket 8b, the pipe 3 is tilted about the fulcrum 9 to periodically open the open end 4 from the closed end 5. Can be higher or lower. Therefore, by appropriately adjusting the amount of air supplied from the nozzle 6 and the drive cycle of the actuator 8a, it is possible to easily generate bubbles C having a desired diameter at regular intervals.
[0040]
Also in the case of the present embodiment, it is preferable that the tube 3 be made of a material having a specific gravity larger than that of water, as in the case of the second embodiment. If the actuator 8a is operated in a balanced state, it can be operated with a very small power source.
[0041]
In this embodiment, the tilting means 8 is provided on the open end 4 side, and the fulcrum 9 is provided on the closed end 5 side. Conversely, the tilting means 8 is provided on the closed end 5 side, and the fulcrum 9 is provided on the open end side. It may be provided on the fourth side.
[0042]
Further, as in the second embodiment, the air supply means may be one in which an air supply branch pipe is provided on the closed end 5 side instead of the nozzle 6 and a flexible pipe is connected to the air supply branch pipe.
[0043]
【Example】
The method of cleaning the carrier separation screen 2 by using coarse bubbles includes a conventional method using a diffuser tube having a plurality of diffuser holes (Comparative Examples 1 and 2) and a method (Example) of the first embodiment of the present invention. Were compared. For comparison, the trajectory of bubbles generated by each method is calculated using a simulation calculation model based on fluid mechanics, a region where the bubbles pass through the surface of the screen 2 is defined as a cleaning region 10, and the width of the cleaning region 10 is determined. This was performed by comparison (see FIG. 6).
[0044]
Here, the screen 2 had a height of 6200 mm, a width of 4000 mm and an opening of the screen of 2.0 mm.
[0045]
(Comparative Example 1)
The calculation conditions are as follows: a straight diffuser pipe is installed horizontally below the screen 2 along the width of the

screen

2, 100 diffuser holes having a diameter of 10 mm are provided at a pitch of 40 mm in the diffuser pipe, and 2 m ³ / Min air was supplied. As a result of the simulation calculation, as shown in FIG. 6A, in Comparative Example 1, since the bubble diameter is small, the bubbles immediately pass through the flow of the treated water passing through the screen 2 to the back surface of the screen. It can be seen that the cleaning area 10 of the screen 2 by air bubbles is limited to a narrow area below the screen 2 and the cleaning effect is small.
[0046]
(Comparative Example 2)
As the calculation conditions, the same diffuser tube as that of Comparative Example 1 having 100 diffuser holes having a diameter of 10 mm and having a pitch of 40 mm was installed below the screen 2 in two vertical stages along the width of the screen 2. It was assumed that air was supplied at 2 m ³ / min, the same as in Comparative Example 1. As a result of the simulation calculation, as shown in FIG. 6B, the cleaning area 10 of the screen 2 by air bubbles is slightly increased as compared with Comparative Example 1, but the amount of diffused air is twice that of Comparative Example 1. In consideration of the above, the degree of improvement of the cleaning effect is small.
[0047]
(Example)
The calculation conditions are as follows: a total of four tubes of 500 mm diameter, one end being an open end and the other end being a closed end, such that the open ends of each tube are positioned at equal intervals below the screen 2 along the width of the screen 2. The tube was set horizontally, and the amount of air diffused was 2 m ³ / min, the same as in Comparative Example 1, for the total of four tubes, and large bubbles with a diameter of 100 mm were released once every 10 seconds per tube. As a result of the simulation calculation, as shown in FIG. 6C, it can be seen that the cleaning area 10 of the screen 2 by air bubbles is significantly increased as compared with Comparative Examples 1 and 2.
[0048]
【The invention's effect】
As described above, according to the present invention, coarse bubbles can be generated by simple means without excessively increasing equipment cost and power consumption, and the separation membrane and the separation screen can be effectively cleaned. It has become possible to provide an air diffusion device and an air diffusion method which can perform the air diffusion.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing an air diffuser according to a first embodiment.
FIG. 2 is a vertical sectional view schematically showing an operation state of the air diffuser according to the first embodiment.
FIG. 3 is a vertical sectional view schematically showing a state when air bubbles are generated in the air diffuser of the first embodiment.
FIG. 4 is a vertical sectional view schematically showing an operation state of an air diffuser according to a second embodiment.
FIG. 5 is a vertical sectional view schematically showing an operation state of an air diffuser according to a third embodiment.
FIG. 6 is a perspective view showing a cleaning area of the unitary separation screen with bubbles.
FIG. 7 is a graph showing a relationship between Reynolds number and resistance coefficient.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Biological treatment tank 2 ... Carrier separation screen 3 ... Tube 4 ... Open end 5 ... Closed end 6 ... Air supply means (air supply branch pipe, nozzle)
7 ... rotating shaft 8 ... tilting means (actuator)
8a ... Actuator 8b ... Hanging bracket 9 ... Support point 10 ... Cleaning area A ... Air A '... Air pool B ... Liquid C ... Large bubbles D ... Liquid

Claims

A diffuser for cleaning a separation membrane or a carrier separation screen disposed in a biological treatment tank that performs sewage treatment,
At least one end is an open end, a tube installed substantially horizontally such that the open end is located below the separation membrane or the carrier separation screen,
Air supply means for supplying air into the pipe;
An air diffuser, comprising:

A diffuser for cleaning a separation membrane or a carrier separation screen disposed in a biological treatment tank that performs sewage treatment,
A tube made of a material having a specific gravity greater than that of water, one end of which is a closed end and the other end of which is an open end, and the open end is a tube which is placed sideways so as to be located below the separation membrane or the carrier separation screen. A pipe having a rotation axis perpendicular to the pipe axis and extending along the horizontal direction on the closed end side of the center of gravity of the pipe;
Air supply means for supplying air into the pipe;
An air diffuser, comprising:

A diffuser for cleaning a separation membrane or a carrier separation screen disposed in a biological treatment tank that performs sewage treatment,
One end is a closed end and the other end is an open end, and a tube installed sideways so that the open end is located below the separation membrane or the carrier separation screen,
Air supply means for supplying air into the pipe;
Tilting means for tilting the pipe so that the open end is periodically raised or lowered from the closed end,
An air diffuser, comprising:

An air diffusion method for washing the separation membrane or the carrier separation screen by intermittently generating large bubbles from the open end using the air diffusion device according to any one of claims 1 to 3.