JP3807542B2

JP3807542B2 - Filtration sand washing method

Info

Publication number: JP3807542B2
Application number: JP2001138429A
Authority: JP
Inventors: 安弘齋藤
Original assignee: Nihon Genryo Co Ltd
Current assignee: Nihon Genryo Co Ltd
Priority date: 2000-11-06
Filing date: 2001-05-09
Publication date: 2006-08-09
Anticipated expiration: 2021-05-09
Also published as: WO2002036239A1; JP2002136810A

Description

【０００１】
【発明の属する技術分野】
本発明は、水の浄化を行う濾過池の濾過砂を洗浄する方法に関し、詳しくは急速濾過池の濾過砂の一部を取り出して洗浄を行う洗浄方法に関するものである。
【０００２】
【従来の技術】
浄水場における浄水処理は、河川、湖沼から引き込んだ原水に薬品を注入して原水中の浮遊物を沈殿しやすい大きさの塊にして沈殿させ、上澄みを濾過池に送り、ここでさらに微細な浮遊物を砂（濾過砂）の層を通して取り除き、濾過した水を塩素で消毒することにより行われている。急速濾過池では、一般に24〜72時間おきに定期的に濾過材の洗浄が行われる。洗浄には、ノズルから噴射される砂層表面を叩くように洗浄する表面洗浄と、下部圧力室から浄水を濾過池内に圧入して砂を浮上させ、砂と砂とをもみ合わせて汚れを落とす逆流洗浄がある。
【０００３】
この浄水処理に使用される濾過砂は、このような表面洗浄、逆流洗浄を定期的に行っていても、長年繰り返し使用していると表面に汚れ（汚泥等の濁質）が付着してくる。濁質の付着により濾過砂の粒径肥大が進むと、逆流洗浄の効果が低下したり、付着物質の剥離や原水中の懸濁物質が捕捉できずリークなどが起きるようになる。逆流洗浄の回数を増やすなどしてこれに対応しているが、逆流洗浄を長年繰り返しているとその水圧により濾過砂を支持している砂利層にも影響が出て、本来水平に敷き詰められているはずの砂利層が部分的に厚くなったり薄くなったりしてしまう現象である不陸が生じたりする。この不陸ができると砂利層の厚い部分では砂層が薄くなり、その部分では濾過が不十分になり、本来発揮される濾過機能が低下して濾過池が正常に働かず安全な水の供給ができなくなってくる。また、砂利層の薄い部分では、砂を支持する砂利層が薄いために集水装置に砂が落ち込み、濾過池を停止せざるを得なくなる。
【０００４】
正常な濾過機能を復帰させるためには、濾過池の運転を一端停止して濾過材を搬出し、搬出した濾過材を洗浄・篩い分けし、濾過池内部を点検修理した後、洗浄した濾過材を再び濾過池へ敷き直すという更生工事を行う必要がある。しかしこの更生工事には莫大なコストを要し、また工事の期間は濾過池の運転を停止する必要があり、更生工事にかかる期間はそのまま浄水効率の低下につながるため、更生工事の周期はなるべく長くしたいという浄水場側の要望がある。
【０００５】
一方、更生工事で敷き直す濾過砂には、新しい砂が用いられる場合もあるが、採取した砂そのままで濾過砂として再利用できるのはわずか１〜２割程度と少なく、濾過材には厳しい条件となり、また新しい砂を使用する場合にはコストの増大にもつながるため、濾過砂は洗浄などによって再生されている。本発明者らはすでに、揉み洗い工法という画期的な方法で、洗浄濁度30度以下という新砂に近い状態にまで砂の再生を可能とする砂洗浄装置を提案している（特開平10−109051号,特開平11−57526号）。この装置により、更生工事の際に濾過池へ敷き直す濾過砂に新砂を用いなくても、新砂を用いた濾過池と同様の浄化機能を実現することが可能となっている。
【０００６】
【発明が解決しようとする課題】
しかし、近年の都市排水、工業排水、農業排水等による河川、湖、海の水質汚染、あるいは大気汚染物質の窒素酸化物や硫黄酸化物が溶け込んで降る酸性雨等により水道用原水は急速に悪化している。このような原水の悪化により、濾過砂の状態は表１に示すように汚濁が進み、かつては通常の運転において７〜10年の長期間にわたり使用可能であった濾過池も、更生工事のペースを早めなければならなくなっている。
【０００７】
【表１】

一方、濾過池で行われる濾過砂のメンテナンスはもっぱら不陸測定や粒径調査などの更生工事の時期を判断するために行われるものであり、更生工事によって本来の浄化機能を取り戻した砂の機能を維持するためのメンテナンスは、表面洗浄、逆流洗浄による定期的な濾過砂の洗浄工程のみに限られている。
【０００８】
また、1996年に制定されたクリプトスポリジウム暫定対策を受けて濾過池出口の濁度を0.1 度以下に維持するという厚生省の指針に対応するため、浄水場では上記のような表面洗浄、逆流洗浄の頻度を上げて対応しているが、その間は浄水ができず取得できる水量は減るため浄化効率は悪くなっている。また洗浄のたびに細砂が流出し、さらに逆流洗浄の頻度が増えると不陸の形成を早めることにもなり、結果として更生工事の時期を早める結果となる場合もあり、従来の表面洗浄、逆流洗浄という洗浄工程のみで対応するには限界があると考えられる。
【０００９】
また、汚れを除去した濾過砂を、急速濾過池に戻すまでの間、貯留しておく貯留槽を設置する敷地がない場合がある。
【００１０】
本発明は上記事情に鑑みなされたものであり、汚れを除去した濾過砂を貯留する貯留槽を設置できない場合であっても、濾過池の運転を休止することなく、砂の浄化機能を表面洗浄、逆流洗浄という通常の洗浄方法以外の方法で再生させて、濾過池の更生工事の周期を飛躍的に延長することを可能とする濾過砂洗浄方法を提供することを目的とするものである。
【００１１】
【課題を解決するための手段】
本発明の濾過砂洗浄方法は、濾過砂により水の浄化を行う急速濾過池の逆流洗浄時に該急速濾過池から所定量の濾過砂を吸い取り、該吸い取った濾過砂を砂洗浄装置に供給し、該砂洗浄装置によって前記濾過砂の汚れを除去し、汚れを除去した前記濾過砂を前記逆流洗浄時における逆流洗浄が終了する前に前記急速濾過池に戻し、前記濾過砂の吸取り、洗浄、戻しの工程を繰り返して前記急速濾過池内の濾過砂を洗浄することを特徴とするものである。
【００１２】
「濾過砂の吸取り」を急速濾過池の逆流洗浄時に行うのは、濾過砂は通常の状態では水を濾過している状態であり、この状態で濾過砂の吸取りを行うと濾過砂の層に層厚の薄い部分ができてしまい濁質がリークする可能性があるためである。濾過砂の吸取りは逆流洗浄と同時に表面洗浄が行われている時であっても差し支えない。また、「濾過砂の戻し」も急速濾過池の逆流洗浄時に行うのは、逆流洗浄時は、下部圧力室から浄水を濾過池内に圧入して砂が浮上している状態であるので、この状態で濾過砂を戻せば、逆流洗浄が終わったときには濾過砂が平らな層を形成することができるからである。なお、濾過砂の戻しも、濾過砂の吸取りと同様に逆流洗浄と同時に表面洗浄が行われている時であっても差し支えない。「所定量」とは、濾過池の水の浄化に影響を与えない程度の濾過砂の量を意味する。
【００１３】
また、「濾過砂の吸取り」は、急速濾過池の砂利層の表面に不陸を形成しない大きさの吸引力で行わせることが好ましい。急速濾過池の濾過砂層は60cm前後であるが、あまりに強い吸引力で濾過砂を吸い取ったり、あるいは砂利層との境界近くで濾過砂を吸い取る場合には、濾過砂を支持している砂利層が部分的に薄くなったり厚くなったりするので、砂利層の表面に不陸を形成しない程度の吸引力で濾過砂を吸い取ることが好ましい。濾過砂の吸取りは、濾過層構成やその吸取りの吸引力にもよるが濾過砂層の表面から濾過砂の層の15〜70％の深さ、さらには40〜60％の深さが好ましい。また、不陸防止ネットが使用されている場合には、100 ％の深さ、すなわち砂利層のすぐ上からの吸引であっても差し支えない。
【００１４】
砂洗浄装置によって濾過砂の汚れを除去した後、汚れを除去した前記濾過砂は、該濾過砂を吸い取った前記逆流洗浄時における逆流洗浄が終了する前に戻すが、この場合、前記濾過砂の吸取り、洗浄、戻しの工程を前記逆流洗浄時に連続して行ってもよい。
【００１５】
「砂洗浄装置」としては、特開平10-109051 号に開示されているような装置、すなわち砂とともに洗浄水を貯留する洗浄槽と、該洗浄槽内でほぼ鉛直な軸の回りに回転するスクリューコンベアと、該スクリューコンベアを、前記洗浄水の水面下にある前記スクリューコンベアの下部において該スクリューコンベアの回転により前記砂と前記洗浄水を上昇させるとともに該洗浄水を介在させた前記砂同士の接触により該砂の汚れを除去し、前記洗浄水の水面上にある前記スクリューコンベアの上部において前記砂を前記スクリューコンベア上で流動させて、汚泥を含む水をわずかに含む前記砂同士の接触によって該砂の汚れを除去するような速度で回転させる手段と、上昇させた該砂を前記スクリューコンベアの下部まで下降させ、再び該スクリューコンベアで上昇させる循環手段とからなる装置を使用することが好ましい。
【００１６】
【発明の効果】
従来表面洗浄、逆流洗浄という洗浄方法のみに頼っていた濾過砂の洗浄を、本発明の濾過砂洗浄方法は、濾過砂により水の浄化を行う急速濾過池の逆流洗浄時に急速濾過池から所定量の濾過砂を吸い取り、吸い取った濾過砂を砂洗浄装置に供給し、砂洗浄装置によって供給された濾過砂の汚れを除去し、汚れを除去した濾過砂を、濾過砂を吸い取った際の逆流洗浄が終了する前に上記急速濾過池に戻し、濾過砂の吸取り、洗浄、戻しの工程を繰り返して急速濾過池内の濾過砂を洗浄することとしたので、濾過池の運転を休止することなく効果的に濾過砂の洗浄を行うことができ、濾過池の更生工事の周期を飛躍的に延長することができる。
【００１７】
より具体的には、たとえば濾過砂の吸取り、洗浄、戻しを繰り返すことによって急速濾過池内のほぼ全濾過砂を自動的に洗浄すれば、濾過池の水浄化機能を再生させることが可能となる。また、濾過砂の汚れが除去されていれば濾過抵抗を減らすことが可能となるので設計通りの圧力で逆流洗浄を行えばよく、従って濾過砂の流出を減らすことが可能となり、また不陸の形成を遅らせることが可能となるので、この点からも濾過池の更生工事の周期を飛躍的に延長することができる。
【００１８】
また、汚れを除去した濾過砂を、濾過砂を吸い取った際の逆流洗浄が終了する前に急速濾過池に戻すため、洗浄した濾過砂を貯留しておく貯留槽を設ける必要がなく、貯留槽にかかる費用を節約することが可能となり、また、急速濾過池の周囲に貯留槽を設置する土地の余裕がない場合であっても、本発明の方法により濾過砂を洗浄することができる。
【００１９】
また、逆流洗浄が行われている時間内に、汚砂の吸取りと浄砂の戻しを行うことにより、短時間で汚砂の洗浄を行うことが可能となり、濾過砂の吸取り、洗浄、戻しの工程を逆流洗浄時に連続して行うことにより、さらに短時間で汚砂の洗浄を行うことができる。
【００２０】
また、本発明の濾過砂洗浄方法に、砂とともに洗浄水を貯留する洗浄槽と、この洗浄槽内でほぼ鉛直な軸の回りに回転するスクリューコンベアと、このスクリューコンベアを、洗浄水の水面下にあるスクリューコンベアの下部においてスクリューコンベアの回転により砂と洗浄水を上昇させるとともに、洗浄水を介在させた砂同士の接触により砂の汚れを除去し、洗浄水の水面上にあるスクリューコンベアの上部において砂をスクリューコンベア上で流動させて、汚泥を含む水をわずかに含む砂同士の接触によって砂の汚れを除去するような速度で回転させる手段と、上昇させた砂をスクリューコンベアの下部まで下降させ、再びスクリューコンベアで上昇させる循環手段とからなる砂洗浄装置を使用すれば、砂を砕くことなく砂同士が揉み合って汚れを落とすことが可能となるので、濾過砂の水浄化機能を新砂に近い状態に再生することができ、濾過池の更生工事の周期をさらに飛躍的に延長することができる。
【００２１】
【発明の実施の形態】
本発明の濾過砂洗浄方法に用いられるシステムとしては、たとえば図１に示すような、急速濾過池１と、急速濾過池１から汚れが付着した濾過砂を吸い取るポンプ２と、汚れが付着した濾過砂５を洗浄する砂洗浄装置３と、砂洗浄装置３から急速濾過池１へ汚れを除去した砂を戻す経路７とを備えてなるものを用いることができる。本発明の濾過砂洗浄方法では、洗浄した砂を貯留しておく貯留槽（洗浄砂ストック槽）を備えていない濾過砂洗浄システムを用いることができるので、洗浄砂ストック槽にかかる費用を節約することが可能となり、また、急速濾過池の周囲に洗浄砂ストック槽を設置する土地の余裕がない場合などにより好ましい態様となる。
【００２２】
図１に示す濾過砂洗浄システムの処理の例としては、例えば図２に示すように、濾過池１の表面洗浄、逆流洗浄が行われている時間（例：15分〜25分）内に約１m³の汚れた濾過砂を濾過池１からポンプ２で吸引し、ポンプ２で吸引した濾過砂を砂洗浄装置３に送り、砂洗浄装置３で短い時間（約10分程度）内の洗浄を行い、濾過池１の表面洗浄、逆流洗浄が終了する前に洗浄後の濾過砂（浄砂）を濾過池１に戻すという工程により行うことができる。このように一つの表面洗浄、逆流洗浄が行われている時間内に、汚砂の吸取りと浄砂の戻しを行うことにより、短時間で汚砂の洗浄を行うことが可能となる。
【００２３】
あるいは、図３に示すように、濾過池１の表面洗浄、逆流洗浄が行われている時間（例：７分〜10分）内に汚れた濾過砂を濾過池１からポンプ２で連続して吸引し、ポンプ２で吸引した濾過砂を砂洗浄装置３に連続して送り、砂洗浄装置３で連続洗浄を行い、濾過池１の表面洗浄、逆流洗浄が終了する前に浄砂を濾過池１に連続して戻すという工程により処理を行うこともできる。このように表面洗浄、逆流洗浄が行われている時間内に連続して処理を行えば、短時間でより多くの汚砂の洗浄を行うことができる。
【００２４】
急速濾過池１は、図４に示すように濾過層として濾過砂層12と、濾過砂層12を支える13〜16の砂利層を備えている。濾過砂層12は、一般的に有効径 0.6mm、均等係数 1.5以下の砂からなる。砂利層は粒径の異なる４層からなり、支持層として濾過砂12が集水装置（図示していないが、浄化された水が集水される装置が急速濾過池１のさらに下部に設けられている）に入ることを防いでいる。砂利層13〜16は、逆流洗浄を均等に行うため、球形に近く硬質で清浄、均質なものが選定され、その粒径としては一般的に用いられるもの、すなわち砂利層13には有効径2.0 〜3.5mm、砂利層14には3.5〜7.0mm、砂利層15には7.0〜13.0mm、砂利層16には13.0〜20.0mmと、細粒を上層に粗粒を下層に順次不陸のないように敷き詰められている。濾過砂層12の上には原水の濁質を凝集剤によって凝集、沈殿させて前処理された水が導入されている。また濾過砂層12の上方には、表面洗浄の際に濾過砂層を表面から叩くように洗浄する表洗水をノズルから噴射する表洗管22と、表面洗浄、逆流洗浄の際の洗浄排水を排出するトラフ21が設けられている。
【００２５】
次に原水の一般的な浄化処理工程を簡単に説明する。河川、湖などから凝集沈殿池に引き込まれた原水の濁質をポリ塩化アルミニウムなどの凝集剤によって凝集、沈殿させた後、上澄みは塩素を添加された後、急速濾過池１の濾過砂層12の上に送水される。この濾過砂層12によって凝集沈殿池では除去できなかった微細な浮遊物が取り除かれる。濾過した水は急速濾過池１の下部に設けられている集水装置に集水される。集水された水はさらに塩素で消毒されて配水池に貯水される。濾過速度は通常 120〜150m／日である。一般にはこの濾過速度で定時的にあるいは損失水頭が1.5mに達すると、浄水のための濾過は中止され急速濾過池の下部圧力室から洗浄水を圧入して濾過砂を浮上させ、砂と砂とをもみ合わせて洗浄が行われる。表面洗浄は逆流洗浄時または逆洗サイクルのある時間に合わせて、濾過砂12の表面に表洗管22から洗浄水を噴射させて行われる。表面洗浄、逆流洗浄後の洗浄排水11はトラフ21から排出される。洗浄が終了すると再び、前処理された原水が送水されて濾過が再開される。この浄水、洗浄の工程は通常自動化されており、急速濾過法で浄水処理を行う浄水場の原水の状態により、表面洗浄、逆流洗浄を行うタイミングがあらかじめ設定されていたり、あるいは損失水頭が一定値以上になると自動的に表面洗浄、逆流洗浄が行われるように設定されている。
【００２６】
表２に示すように濾過砂の選定標準（日本水道協会規格JWWA A 103-1988 ）は、洗浄濁度は30度以下、塩酸可溶率は3.5％以下、有効径0.45〜0.70mm、均等係数1.7 以下と定められている。上記のような一般的な表面洗浄、逆流洗浄を定期的に行っていても、新砂から10年もたつと、７年おきに更生工事を行っても表２の原汚砂に示すように洗浄濁度1480度、塩酸可溶率9.7％、有効径0.533mm、均等係数1.485 と濾過砂に濁質が付着し、相当に汚れてくる。
【００２７】
【表２】

このように、濁質が付着した濾過砂を使用し続けると濁質による目詰まり現象が起こり、急激な損失水頭の上昇により逆流洗浄の回数が増加し、その逆流洗浄の水圧により砂利層にも影響が出て不陸の形成を早める。不陸の形成により砂利層が厚い部分では砂層が薄くなり、その部分での濾過が不十分となり、また汚泥物質や濾過砂から剥離した吸着物質により、ブレークスルーが起こって濾過水に悪影響を及ぼすようになる。このような状態になると、更生工事が必要となってくる。また、砂利層が薄い部分では、砂を支持する砂利層が薄いので集水装置に砂が落ち込み、濾過池を停止せざるを得なくなる。
【００２８】
本発明の濾過砂洗浄方法によれば、濾過砂により水の浄化を行う急速濾過池の逆流洗浄時に急速濾過池から所定量の濾過砂を吸い取り、吸い取った濾過砂を砂洗浄装置に供給し、砂洗浄装置によって供給された濾過砂の汚れを除去し、汚れを除去した濾過砂を、濾過砂を吸い取った際の逆流洗浄が終了する前に上記急速濾過池に戻し、濾過砂の吸取り、洗浄、戻しの工程を繰り返して急速濾過池内の濾過砂を洗浄することとしたので、濾過池の運転を休止することなく、短時間で効果的に濾過砂の洗浄を行うことができ、濾過池の更生工事の周期を飛躍的に延長することができる。
【００２９】
また、汚れを除去した濾過砂を、濾過砂を吸い取った際の逆流洗浄が終了する前に急速濾過池に戻すため、洗浄した濾過砂を貯留しておく貯留槽を設ける必要がなく、貯留槽にかかる費用を節約することが可能となり、また、急速濾過池の周囲に貯留槽を設置する土地の余裕がない場合であっても濾過砂を洗浄することができる。
【図面の簡単な説明】
【図１】本発明の濾過砂洗浄方法に用いることができるシステム例を示す概略図
【図２】本発明の濾過砂洗浄方法の一の実施の形態を示す工程図
【図３】本発明の濾過砂洗浄方法の他の実施の形態を示す工程図
【図４】図１に示す急速濾過池のＡ−Ａ線断面図
【符号の説明】
１急速濾過池
２ポンプ
３砂洗浄装置
５濾過砂[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cleaning the filter sand of a filter basin for purifying water, and more particularly to a cleaning method for taking out and cleaning a part of the filter sand of a rapid filter pond.
[0002]
[Prior art]
Water treatment at the water treatment plant is performed by injecting chemicals into the raw water drawn from rivers and lakes to settle the suspended matter in the raw water into large-sized sediments, and sending the supernatant to the filtration pond. This is done by removing suspended matter through a layer of sand (filtered sand) and disinfecting the filtered water with chlorine. In the rapid filtration basin, the filter medium is generally periodically cleaned every 24 to 72 hours. For cleaning, surface cleaning is performed so that the surface of the sand layer sprayed from the nozzle is struck, and backflow is performed by pressing the clean water from the lower pressure chamber into the filter basin to float the sand and intermingling the sand with the sand. There is cleaning.
[0003]
Even if the filtration sand used for this water purification treatment is regularly subjected to such surface cleaning and backwashing, if it is used repeatedly for many years, dirt (turbidity such as sludge) will adhere to the surface. . When the particle size of the filtered sand increases due to the adhering of turbidity, the effect of backwashing is reduced, or the adhering substances are peeled off or the suspended substances in the raw water cannot be captured, causing leaks. This has been dealt with by increasing the number of backwashing, etc., but if backwashing is repeated for many years, the water pressure will also affect the gravel layer that supports the filtered sand, and it will essentially be laid horizontally. Unevenness, which is a phenomenon that the gravel layer that should have been partially thickened or thinned, occurs. When this unevenness occurs, the sand layer becomes thin in the thick gravel layer, and the filtration becomes insufficient in that part, and the filtration function that is originally exhibited declines, so that the filtration pond does not work properly and safe water supply is possible. It becomes impossible. Moreover, in the thin part of a gravel layer, since the gravel layer which supports sand is thin, sand falls in a water collecting apparatus and must stop a filtration pond.
[0004]
In order to restore the normal filtration function, stop the operation of the filter basin, carry out the filter media, wash and screen the filter media that has been carried out, inspect and repair the inside of the filter basin, and then wash the filter media It is necessary to carry out rehabilitation work by re-laying in the filtration pond. However, this rehabilitation work requires enormous costs, and it is necessary to stop the operation of the filtration basin during the construction period, and the period of rehabilitation work leads to a decrease in water purification efficiency. There is a request from the water purification plant side to make it longer.
[0005]
On the other hand, new sand may be used for filtered sand to be laid again in rehabilitation work, but only about 10 to 20% of the collected sand can be reused as filtered sand. In addition, when new sand is used, the cost increases, so the filtered sand is regenerated by washing or the like. The present inventors have already proposed a sand cleaning apparatus that can regenerate sand to a state close to new sand having a cleaning turbidity of 30 degrees or less by an epoch-making method called a scum washing method (Japanese Patent Laid-open No. Hei 10) No.-109051, JP-A-11-57526). With this device, it is possible to achieve the same purification function as a filtration pond using fresh sand without using fresh sand as filtration sand to be relaid on the filtration pond during rehabilitation work.
[0006]
[Problems to be solved by the invention]
However, raw water for water supply deteriorates rapidly due to water pollution of rivers, lakes, and seas due to recent urban wastewater, industrial wastewater, agricultural wastewater, etc., or acid rain that falls due to the dissolution of nitrogen and sulfur oxides of air pollutants. is doing. Due to the deterioration of the raw water, the state of the filter sand is becoming more polluted as shown in Table 1, and the filter pond, which was once usable for a long period of 7 to 10 years in normal operation, is also the pace of rehabilitation work. Has to be accelerated.
[0007]
[Table 1]

On the other hand, the maintenance of the filtration sand in the filter basin is performed exclusively to determine the timing of rehabilitation work such as unevenness measurement and particle size survey, and the function of sand that has regained its original purification function by rehabilitation work. The maintenance for maintaining the pressure is limited only to the regular filtration sand washing process by surface washing and backwashing.
[0008]
In addition, following the provisional measures for Cryptosporidium enacted in 1996, the water purification plant has the above-mentioned surface cleaning and backflow cleaning in order to comply with the guidelines of the Ministry of Health and Welfare to maintain the turbidity of the filter basin outlet below 0.1 degree Although the frequency is increased, it is not possible to purify the water during that time, and the amount of water that can be obtained is reduced, so the purification efficiency is deteriorated. In addition, fine sand flows out each time it is washed, and if the frequency of backwashing increases, it will also accelerate the formation of unevenness, which may result in earlier timing of rehabilitation work. There seems to be a limit to dealing with only the washing process called back-flow washing.
[0009]
Moreover, there may be no site which installs the storage tank which stores the filter sand which removed the dirt until it returns to the rapid filtration pond.
[0010]
The present invention has been made in view of the above circumstances, and even if it is not possible to install a storage tank for storing the filtered sand from which dirt has been removed, the sand purification function can be cleaned without stopping the operation of the filtering pond. An object of the present invention is to provide a filtration sand washing method that can be regenerated by a method other than the normal washing method called back-flow washing to dramatically extend the period of rehabilitation work for the filtration pond.
[0011]
[Means for Solving the Problems]
The filtration sand washing method of the present invention sucks a predetermined amount of filtered sand from the rapid filtration pond at the time of backflow washing of the rapid filtration pond that purifies water with the filtered sand, and supplies the sucked filtered sand to the sand washing device. The filter sand is removed by the sand cleaning device, and the filtered sand is returned to the rapid filtration basin before the backwashing in the backwashing is completed, and the filter sand is sucked, washed and returned. The above-mentioned process is repeated to wash the sand in the rapid filtration basin.
[0012]
The “filter sand absorption” is performed at the time of backwashing of the rapid filtration basin because the filter sand normally filters water, and if the filter sand is sucked in this state, the filter sand layer is filtered. This is because a thin portion may be formed, and turbidity may leak. The filtering sand can be sucked even when the surface cleaning is performed simultaneously with the back-flow cleaning. In addition, “return of filtered sand” is also performed during the backwashing of the rapid filtration basin, because during the backwashing, clean water is pressed into the filtration basin from the lower pressure chamber and the sand is floating. If the filtration sand is returned, the filtration sand can form a flat layer when the backwashing is completed. The filter sand may be returned even when the surface cleaning is performed at the same time as the backflow cleaning in the same manner as the filter sand suction. The “predetermined amount” means an amount of filter sand that does not affect the purification of water in the filter pond.
[0013]
Moreover, it is preferable that the “filter sand absorption” is performed with a suction force that does not form unevenness on the surface of the gravel layer of the rapid filtration pond. The filtration sand layer of the rapid filtration pond is around 60cm, but if the filtration sand is sucked up with a too strong suction force or if the filtration sand is sucked up near the boundary with the gravel layer, the gravel layer supporting the filtration sand Since it is partially thinned or thickened, it is preferable to suck the filtered sand with a suction force that does not form unevenness on the surface of the gravel layer. The suction of the filtration sand is preferably 15 to 70% deep, more preferably 40 to 60% of the filtration sand layer from the surface of the filtration sand layer depending on the filtration layer structure and the suction force of the suction. In addition, when a non-land prevention net is used, it may be 100% deep, that is, suction from just above the gravel layer.
[0014]
After the filter sand is removed by the sand cleaning device, the filter sand from which the dirt has been removed is returned before the backwashing in the backwashing in which the filter sand has been sucked up is completed. The steps of sucking, washing, and returning may be performed continuously during the backwashing.
[0015]
As the “sand cleaning apparatus”, an apparatus as disclosed in JP-A-10-109051, that is, a cleaning tank for storing cleaning water together with sand, and a screw that rotates around a substantially vertical axis in the cleaning tank. Contact between the conveyor and the screw conveyor, wherein the sand and the cleaning water are raised by rotation of the screw conveyor at the bottom of the screw conveyor below the surface of the cleaning water and the cleaning water is interposed between the sand and the cleaning water. The sand is removed by the above, and the sand is caused to flow on the screw conveyor at the upper portion of the screw conveyor on the surface of the washing water, and the sand is slightly contacted with the sand by contacting the sand. Means for rotating at a speed so as to remove dirt on the sand, and lowering the raised sand to the lower part of the screw conveyor, and again the screw -It is preferable to use an apparatus comprising a circulating means for raising by a conveyor.
[0016]
【The invention's effect】
The filtration sand cleaning method according to the present invention, which has conventionally relied only on cleaning methods such as surface cleaning and backflow cleaning, is a predetermined amount from the rapid filtration basin during the backwashing of the rapid filtration basin in which the water is purified by the filtration sand. The filtered sand is sucked up, and the sucked filtered sand is supplied to the sand cleaning device. The filter sand supplied by the sand cleaning device is removed, and the filtered sand from which the soil has been removed is backwashed when the filtered sand is sucked up. It is effective without stopping the operation of the filtration basin because the filtration sand in the rapid filtration basin is washed by repeating the steps of sucking, washing and returning the filtration sand. The filter sand can be washed and the period of rehabilitation work for the filter pond can be greatly extended.
[0017]
More specifically, the water purification function of the filtration basin can be regenerated by automatically washing almost all the filtration sand in the rapid filtration basin by, for example, repeatedly sucking, washing and returning the filtration sand. In addition, if the dirt of the filter sand is removed, it is possible to reduce the filtration resistance. Therefore, it is only necessary to perform backwashing at the designed pressure, and therefore it is possible to reduce the outflow of the filter sand, Since it is possible to delay the formation, the cycle of rehabilitation work for the filtration pond can be dramatically extended from this point.
[0018]
Moreover, since the filtered sand from which the dirt has been removed is returned to the rapid filtration pond before the backwashing when the filtered sand is sucked off, there is no need to provide a storage tank for storing the cleaned filtered sand. The filtration sand can be washed by the method of the present invention even when there is no room for installing a storage tank around the rapid filtration pond.
[0019]
In addition, it is possible to clean up the sand in a short time by sucking up the sand and returning the sand after the backwashing is performed. By carrying out the process continuously during backwashing, the dirty sand can be washed in a shorter time.
[0020]
Further, in the filtration sand cleaning method of the present invention, a cleaning tank for storing cleaning water together with sand, a screw conveyor that rotates about a substantially vertical axis in the cleaning tank, and the screw conveyor are disposed below the surface of the cleaning water. At the bottom of the screw conveyor, the sand and washing water are raised by the rotation of the screw conveyor, and the dirt of the sand is removed by contact between the sands with the washing water interposed therebetween. The sand is made to flow on the screw conveyor in order to rotate the sand at a speed that removes the dirt of the sand by contact with the sand containing a little water containing sludge, and the raised sand is lowered to the lower part of the screw conveyor. If you use a sand cleaning device that consists of a circulating means that lifts it again with a screw conveyor, the sand will stagnate without breaking the sand. Since it is possible to remove the dirt I, can play water purification function of the filtration sand a state close to the new sand, can be further dramatically extend the rehabilitation period of construction of the filtration reservoir.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
As a system used for the filtration sand washing | cleaning method of this invention, as shown in FIG. 1, for example, the rapid filtration pond 1, the pump 2 which absorbs the filtration sand which adhered dirt from the rapid filtration pond 1, and the filtration which dirt adhered What comprises the sand washing | cleaning apparatus 3 which wash | cleans the sand 5, and the path | route 7 which returns the sand which removed the dirt from the sand washing apparatus 3 to the rapid filtration pond 1 can be used. In the filtration sand washing | cleaning method of this invention, since the filtration sand washing | cleaning system which is not equipped with the storage tank (washing sand stock tank) which stores washed sand can be used, the cost concerning a washing sand stock tank is saved. Moreover, it becomes a more preferable aspect when there is no room for land to install a washing sand stock tank around the rapid filtration pond.
[0022]
As an example of the processing of the filtration sand washing system shown in FIG. 1, for example, as shown in FIG. 2, the surface washing and backwashing of the filtration pond 1 are performed within a time period (eg, 15 to 25 minutes). 1 m ³ of dirty filter sand is sucked from the filter pond 1 by the pump 2, and the filter sand sucked by the pump 2 is sent to the sand cleaning device 3, and the sand cleaning device 3 performs cleaning within a short time (about 10 minutes). It can be performed by a process of returning the filtered sand (cleaned sand) after washing to the filter basin 1 before the surface cleaning and backwashing of the filter pond 1 are completed. Thus, it is possible to clean the dirty sand in a short time by absorbing the dirty sand and returning the clean sand within the time during which one surface cleaning and backflow cleaning are performed.
[0023]
Alternatively, as shown in FIG. 3, the filter sand soiled within the time during which the surface cleaning and backwashing of the filtration basin 1 are performed (for example, 7 minutes to 10 minutes) is continuously performed from the filtration basin 1 by the pump 2. The filtered sand sucked by the pump 2 is continuously sent to the sand washing device 3 and continuously washed by the sand washing device 3, and the clean sand is filtered before the surface washing and backwashing of the filtering pond 1 are completed. Processing can also be performed by a process of continuously returning to 1. Thus, if it processes continuously within the time when surface washing | cleaning and backflow washing | cleaning are performed, more dirty sand can be wash | cleaned in a short time.
[0024]
As shown in FIG. 4, the rapid filtration pond 1 includes a filtration sand layer 12 as a filtration layer and 13 to 16 gravel layers that support the filtration sand layer 12. The filter sand layer 12 is generally made of sand having an effective diameter of 0.6 mm and a uniformity coefficient of 1.5 or less. The gravel layer is composed of four layers having different particle sizes, and the filter sand 12 is provided as a support layer in a water collecting device (not shown, but a device for collecting purified water is provided in the lower part of the rapid filtration pond 1. To prevent entry). For the gravel layers 13-16, in order to perform backwashing evenly, a sphere-like hard, clean, and homogeneous one is selected, and its particle size is generally used, that is, the gravel layer 13 has an effective diameter of 2.0. ~ 3.5mm, gravel layer 14 3.5-7.0mm, gravel layer 15 7.0-13.0mm, gravel layer 16 13.0-20.0mm It is laid down like this. On the filtered sand layer 12, water pretreated by coagulating and precipitating the turbidity of raw water with a flocculant is introduced. Also, above the filter sand layer 12, a surface wash pipe 22 for spraying the surface wash water from the nozzle to wash the filter sand layer from the surface when cleaning the surface, and the washing waste water at the time of surface washing and backflow washing are discharged. A trough 21 is provided.
[0025]
Next, a general purification process of raw water will be briefly described. After turbidity of the raw water drawn into the coagulation sedimentation pond from rivers, lakes, etc. is coagulated and precipitated with a coagulant such as polyaluminum chloride, the supernatant is added with chlorine and then the sand of the filtration sand layer 12 of the rapid filtration pond 1 Water is sent to the top. The filtered sand layer 12 removes fine suspended matters that could not be removed in the coagulating sedimentation basin. The filtered water is collected in a water collecting device provided at the lower part of the rapid filtration pond 1. The collected water is further sterilized with chlorine and stored in the reservoir. The filtration rate is usually 120 to 150 m / day. In general, at this filtration speed or when the head loss reaches 1.5 m, filtration for clean water is stopped, and wash water is injected from the lower pressure chamber of the rapid filtration basin to float the filtered sand. Washing is performed by combining the two. The surface cleaning is performed by spraying cleaning water from the surface cleaning pipe 22 onto the surface of the filter sand 12 at the time of backwashing or at a certain time of the backwashing cycle. The washing waste water 11 after the surface washing and back washing is discharged from the trough 21. When the washing is finished, the pretreated raw water is sent again and the filtration is resumed. This water purification and washing process is usually automated, and the timing for surface washing and backwashing is set in advance or the head loss is a constant value depending on the state of the raw water at the water purification plant that performs water treatment by rapid filtration. It is set to automatically perform surface cleaning and back-flow cleaning when the above is reached.
[0026]
As shown in Table 2, the selection standard for filtration sand (Japan Water Works Association Standard JWWA A 103-1988) is that the washing turbidity is 30 degrees or less, the hydrochloric acid solubility is 3.5% or less, the effective diameter is 0.45 to 0.70 mm, and the uniformity coefficient 1.7 It is stipulated as follows. Even if regular surface washing and backwashing as described above are performed regularly, even after 10 years from fresh sand, rehabilitation work every 7 years is performed as shown in Table 2 Turbidity is 1480 degrees, hydrochloric acid solubility is 9.7%, effective diameter is 0.533mm, uniformity coefficient is 1.485, and turbidity adheres to the filter sand, resulting in considerable contamination.
[0027]
[Table 2]

In this way, clogging due to turbidity occurs when the filter sand with turbidity adhered is used, the number of backwashing increases due to a sudden rise in head loss, and the pressure of backwashing also increases the gravel layer. Impacts and accelerates the formation of unevenness. The sand layer becomes thin in the thick gravel layer due to the formation of unevenness, and the filtration in that part becomes insufficient, and the sludge material and the adsorbed material peeled off from the filtered sand cause breakthrough and adversely affect the filtered water It becomes like this. When this happens, rehabilitation work is required. Moreover, in the part where the gravel layer is thin, since the gravel layer supporting the sand is thin, the sand falls into the water collecting device, and the filtration pond must be stopped.
[0028]
According to the filtration sand washing method of the present invention, a predetermined amount of filtered sand is sucked from the rapid filtration pond when backwashing the rapid filtration pond that purifies water with the filtered sand, and the sucked filtered sand is supplied to the sand washing device. Remove the dirt of the filter sand supplied by the sand cleaning device, and return the filter sand after removing the dirt to the rapid filter basin before the backwashing when the filter sand is sucked up. Because the filtration sand in the rapid filtration basin is washed by repeating the returning process, the filtration sand can be washed effectively in a short time without stopping the operation of the filtration pond. The period of rehabilitation work can be dramatically extended.
[0029]
Moreover, since the filtered sand from which the dirt has been removed is returned to the rapid filtration pond before the backwashing when the filtered sand is sucked off, there is no need to provide a storage tank for storing the cleaned filtered sand. It is possible to save the cost, and even when there is no room for installing a storage tank around the rapid filtration pond, the filtration sand can be washed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a system that can be used in the filtration sand cleaning method of the present invention. FIG. 2 is a process diagram showing an embodiment of the filtration sand cleaning method of the present invention. Process drawing which shows other embodiment of the filtration sand washing | cleaning method. [FIG. 4] AA sectional view taken on the line AA of the quick filtration pond shown in FIG.
1 Quick filtration pond 2 Pump 3 Sand cleaning device 5 Filter sand

Claims

A predetermined amount of filtered sand is sucked from the rapid filtration basin at the time of backwashing of the rapid filtration pond in which water is purified by the filtered sand, and the sucked filtered sand is supplied to the sand cleaning device. Remove the dirt, and return the filtered sand from which the dirt has been removed to the rapid filtration basin before the backwashing in the backwashing is completed, and repeat the steps of sucking, washing and returning the filtered sand. The filtration sand washing | cleaning method characterized by wash | cleaning the filtration sand of.

As the sand cleaning device, a cleaning tank that stores cleaning water together with sand, a screw conveyor that rotates about a substantially vertical axis in the cleaning tank, and the screw conveyor that is below the surface of the cleaning water. In the lower part of the conveyor, the sand and the washing water are raised by rotation of the screw conveyor and the sand is removed by contact between the sands with the washing water interposed therebetween. The sand is caused to flow on the screw conveyor at the top of the screw conveyor, and is rotated with a means for rotating the sand at a speed so as to remove the dirt of the sand by contact between the sands slightly including water containing sludge. A device comprising circulating means for lowering the sand to the lower part of the screw conveyor and raising it again by the screw conveyor is used. Filtration sand cleaning method of claim 1, wherein a.

The filtration sand washing method according to claim 1 or 2, wherein the steps of sucking, washing, and returning the filtration sand are continuously performed during the backwashing.