JP3919893B2

JP3919893B2 - Cleaning method

Info

Publication number: JP3919893B2
Application number: JP25091697A
Authority: JP
Inventors: 弘伸西尾; 博行知福
Original assignee: Kobelco Eco Solutions Co Ltd
Current assignee: Shinko Pantec Co Ltd
Priority date: 1997-09-16
Filing date: 1997-09-16
Publication date: 2007-05-30
Anticipated expiration: 2017-09-16
Also published as: JPH1190190A

Description

【０００１】
【発明の属する技術分野】
本発明は、河川水、湖沼水などを原水として、その濁度及び色度を膜によって除去する際に用いられ、膜モジュールで構成される濾過ブロックの洗浄を効率的に行える濾過装置及びこの装置における濾過ブロックの洗浄方法に関し、さらに詳細には、被処理液を濾過するにつれて濾過ブロックに滞留する無機物・有機物などの付着物を除去するための洗浄において、システムを停止して行われる大規模な薬液洗浄の必要回数を低減することができる装置及び方法に関する。
【０００２】
【従来の技術】
上記のごとき被処理液の膜処理は、主として除濁の目的で行われるが、濁度以外にも、例えば、濾過前にアルミニウム塩を添加するなどの技術により、着色物質も除去できる。その運用上の最大の問題点は膜の閉塞であるが、その程度は使用環境により異なる。数度から数十度の濁質濃度を有する原水にアルミニウム塩を注入して膜濾過した場合、後述する小規模洗浄を行っていれば、膜は数ヶ月に一度の大規模の薬品洗浄を行うだけで適切な濾過効率を維持できる。しかし、低濁度で、且つ色度が高い原水にアルミニウム塩を添加した後に膜濾過を行うと、除去すべき固形成分は、濁質分含量が少なく、粘着性の高い水酸化アルミニウム等を大量に含むものとなり、かかる粘着性物質が膜に強固に付着すると膜の閉塞が起こりやすくなるため、大規模な薬品洗浄の実施を要する間隔は数週間から１ヶ月と短くなってしまう。
【０００３】
すなわち、前記原水を浄水処理あるいは用水処理する場合は、通常、フミン酸などに起因する茶褐色の着色を除去するためにポリ塩化アルミニウム（ＰＡＣ）または硫酸アルミニウムなどを注入してフミン酸を吸着する処理が行われることが多いが、低濁度で且つ色度の高い原水に対してこの処理を行うと、前記のごとく主に水酸化アルミニウムなどからなる粘着性物質が発生する。従来は、このようなアルミニウム塩を添加した後凝集させ、沈殿、砂濾過による分離が一般的に実施されてきたが、最近では、例えばポリプロピレン製の中空糸などで構成される膜モジュールブロックを含む濾過装置で濾過する技術が実用化されている。しかし、かかる濾過装置において濾過を継続すると、膜面上に前記の粘着性を有する水酸化アルミニウムなどを主成分とする固形物や粘着物が付着、蓄積して膜を閉塞させてしまう。膜が閉塞すれば、濾過速度の低下、濾過圧力の上昇が生じ、安定な濾過処理ができなくなる。そこで、このような膜への付着物を除去するために小規模洗浄を短い間隔で実施するわけであるが、それでも定期的にシステムを停止して大規模な薬液洗浄を行う必要が生じるのである。
【０００４】
この薬液洗浄作業は、原水タンクに水酸化ナトリウム水溶液や硫酸などの洗浄用の薬液を投入し、ｐＨを調整した後、原水タンクと膜モジュールブロックの間で薬液を数時間以上にわたり循環させる作業であり、通常、薬液循環後の水洗も加えて数日にわたって行われるので、労力及び時間の浪費につながっていた。また、この際に排出される強塩基性の水酸化ナトリウム、あるいは強酸性の硫酸廃液等の処理が必要となり、この処理作業にも手間を要するものであった。
【０００５】
小規模洗浄（物理洗浄）は、１日に２４〜４８回程度、膜の付着物が蓄積されないうちにこまめに除去することで、大規模な薬液洗浄を行わねばならない時期の間隔を延ばすべく行われている。この小規模洗浄は、概して、逆洗工程と、続く洗浄工程とに分けられる。逆洗工程では、まず、濾過ブロックの膜モジュールの一次側（被処理水流入側）からの原水の供給を停止し、続いて加圧して逆洗をする。加圧は膜の二次側（被処理水流出側）より透過水などの液体で行うのが一般的である。さらに、簡単な設備の増加で、加圧のための液体中に薬液を混入させて、加圧と同時に薬液洗浄を行う、すなわち物理化学洗浄の方法も実施されている。その後の洗浄工程では、原水を一次側より膜モジュールブロックに供給して水洗し、一次側のドレンから排出するというものである。このような小規模洗浄を、例えば、３０分〜１時間に１回の頻度で行うことにより、薬液を用いた大規模洗浄の必要回数は低減されたが、さらに大規模洗浄の必要回数を低減できる方法が望まれていた。
【０００６】
【発明が解決しようとする課題】
しかし最近、膜の二次側から加圧して一次側に空気を通す空気逆洗を行う方法が実用化された。この方法は、濾過ブロックを一旦閉鎖系にした状態で加圧し、一挙に開放することにより圧縮された空気が膨張する際の力を利用することもできることから、従来の液体洗浄による方法に比して総合的にはるかに優れた逆洗効果を生じる。
【０００７】
ところが、空気逆洗による方式でもやはり、粘着物質の除去が効率的に行われうるとは言い難く、かなり頻繁な大規模洗浄の実施が必要となるものであった。
【０００８】
本発明はかかる現状に鑑みてなされたものであり、空気逆洗式濾過装置を用いる低濁度且つ高色度の原水の濾過において、膜モジュールなどで構成される濾過ブロックに滞留する無機物・有機物などの付着物を除去するために、薬液を一度に大量に用いて大規模に洗浄する必要回数を低減することができる装置及び方法を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明は、濾過装置における、前記の目的を達成するために鋭意研究を重ねた結果成し遂げられたものであって、上述の空気逆洗において、薬液を二次側から供給することができないことに起因する欠点を克服し、一次側より薬液を効果的に供給し、効率よく洗浄する方法を提供する。すなわち、前記空気逆洗を応用した物理洗浄と薬液による化学洗浄の双方が並行して行われることによって、優れた洗浄効果が発揮される物理化学洗浄を行うことを特徴とするものである。
【００１０】
すなわち、本発明は、濾過装置において、（ａ）被処理液を被処理液タンクから膜モジュールを含む濾過ブロックの一次側に送るための被処理液供給手段、（ｂ）前記被処理液タンクから濾過ブロックまでの流路を形成する送液経路、（ｃ）洗浄用薬液を、薬液タンクから送液するための薬液供給手段、（ｄ）濾過ブロックから排水するためのドレン、及び（ｅ）濾過ブロックの二次側から膜モジュールの空気逆洗を行うための空気逆洗手段を含む濾過装置であって、前記薬液供給手段によって、洗浄用薬液が前記送液経路における被処理液供給手段の下流に送液されること、ならびに前記空気逆洗手段による膜モジュールの物理洗浄中に、前記洗浄用薬液による化学洗浄を並行して行うことができるために、物理化学洗浄が成し遂げられることを特徴とする濾過装置を提供する。
【００１１】
さらに本発明は、上記の濾過装置において濾過ブロックを物理化学洗浄する方法であって、以下の工程、すなわち、（１）逆洗手段１３を用いて濾過ブロック３を加圧しながら排液を行い、（２）逆洗手段１３を用いて濾過ブロック３を加圧する空気逆洗と、被処理液供給手段１１の作動により、送液経路２１を介した濾過ブロック３内へ液体を導入及び排出し、濾過ブロック３から付着物を排出する逆洗洗浄を行い、さらに（３）逆洗手段１３による加圧を停止して、被処理液を濾過ブロック３内に導入及び排出することで濾過ブロック３の洗浄を行う工程を含み、前記工程（２）が終了するまでに、薬液タンク２から薬液供給手段１２によって送液経路２１に薬液を導入し、工程（２）において該薬液が被処理液供給手段１１によって濾過ブロック３に導入され、空気圧及び薬液の双方による物理化学洗浄効果が発揮され、次いで被処理液による洗浄が成し遂げられることを特徴とする洗浄方法を提供するものである。
【００１２】
洗浄用の薬液は、薬液供給手段により薬液タンクから濾過ブロックの一次側に直接送るようにすることも可能ではあるものの、この場合、空気逆洗中に薬液を供給する場合には吐出圧が濾過ブロック内圧を凌がねばならず、また供給時間を短縮するために大型のポンプが必要となる。また、新規に薬液用の送液経路を設ける必要もあるので、配管コストが上がるという不利益も生じる。従って、薬液タンクから、送液経路における被処理液供給手段の下流に至る流路を形成し、前記逆洗洗浄工程が終了するまでに洗浄用薬液を送液経路に導入すると、被処理液供給手段による強力な吐出能力を用いて薬液が濾過ブロックに導入されて化学洗浄が行われるので好ましい。
【００１３】
すなわち、本発明者らは、従来行われていた逆洗工程の物理洗浄中に、酸またはアルカリ水溶液等の薬液を用いる化学洗浄工程を併せて行なって物理化学洗浄を成し遂げるべく、空気逆洗工程に並行するように薬液を濾過ブロック内へ導入し、以下、通常の逆洗及び洗浄工程を経ることによって、小規模洗浄の効果が著しく高められ、大規模洗浄の必要回数を格段に低減することができることを見出し、本発明を完成するに至った。
【００１４】
本発明の薬液を用いる化学洗浄工程では、従来の大規模洗浄の際に採用されていたような大掛かりな薬液供給手段を必要とせずに効率的な薬液供給を行え、また一回当たりの薬液使用量も少量ですむので、洗浄後の廃液処理の問題も軽減される。そして、洗浄工程の時間は、従来の小規模洗浄に比して、薬液を膜モジュールに通液するごくわずかの時間のみが延長されるか、あるいは同じであり、短い所要時間で効果的な洗浄効果が得られる。
【００１５】
【発明の実施の形態】
以下、本発明の実施態様を示した図面１〜６に基づき、本発明の装置及び洗浄方法を詳説する。しかしながら、かかる実施態様に基づき本発明が限定的に解釈されるべきではない。
【００１６】
図１〜６にその概略が示される本発明の濾過装置５１は、本質的に、被処理液タンク１、薬液タンク２、濾過ブロック３及び処理液タンク４を含み、適宜バルブを備えた経路により連結されている。通液のために、ポンプ、あるいは水頭差を利用する被処理液供給手段１１及び薬液供給手段１２が配置され、また空気による逆洗を行うために、コンプレッサーなどを含む逆洗手段１３が配置されている。逆洗手段１３は、一般的には、上流側からコンプレッサー、逆止弁、エアタンク、電磁弁の順に配管されることが多い。濾過ブロック３の一次側３１にドレン２５ａ、及び二次側３２にドレン２５ｂが設けられており、これを介して廃液タンクなどに洗浄後の液などが排液される。各図中、バルブの開閉状態を明らかにするため、開放バルブを明色で、閉止バルブを濃色で示した。
【００１７】
濾過ブロック３は、従来より使用されている、例えば、ポリプロピレンなどで製造された中空糸の膜モジュールブロックであるとよい。膜の孔径は、被処理液の混入物、物性等に応じて適宜選択されるが、一般に０．２μｍ程度である。
【００１８】
その他の構成要素も、従来より当業者に知られている形態及び材質のものを適宜選択して用ることができる。但し、後述するように薬液供給手段１２は、比較的短くなるように形成された経路を通じて、少量の液体を時間に余裕を持って送液するためのものであるから、被処理液供給手段１１よりも小規模なものとすることができる。また、洗浄効率を高めることを目的として、薬液タンク２に加熱手段を設けることも可能である。
【００１９】
被処理液の原水は主として河川水、湖沼水等であり、低濁度であって、色度の高い原水にアルミニウム塩で処理を施した後の、粘着性物質を多量に含有する被処理液も、本発明の濾過装置５１によって好適に濾過することができる。
図１には、本発明の濾過装置５１にて通常の濾過が実施されている際の作動態様が示されており、具体的には、被処理液供給手段１１を運転して被処理液タンク１から送液経路２１を介して中空糸膜の膜モジュールブロックである濾過ブロック一次側３１に被処理液を導入し、濾過後の処理液は、濾過ブロック二次側３２から処理液タンク４に貯留される。
【００２０】
本発明の洗浄方法にかかる小規模洗浄の各工程を示す図２から図６において、まず図２は排液工程を示している。この工程では、被処理液供給手段１１を停止し、送液経路２１を遮断して、さらに濾過ブロック３から処理液タンク４に送出される経路も封じておいて、逆洗手段１３により二次側から加圧することによって、濾過ブロック３内の被処理液をドレン２５ｂより排出し、中空糸膜内の液体を除いておく。
【００２１】
次に、図３から図５までの工程を示す。まず、図３に示される逆洗準備工程が実施される。この工程では、濾過ブロック３のドレン２５ａ及び２５ｂも封じた状態で、すなわち、濾過ブロック３を実質的に閉鎖系にして、逆洗手段１３により濾過ブロック３内に膜モジュールの二次側から加圧する。この際の圧力の上限は、少なくとも濾過膜を空気が通過する際の抵抗を上回る圧力が必要であり、好ましくは濾過ブロックの耐圧性を考慮してなるべく高い値に定められるべきである。
【００２２】
かかる逆洗準備工程に並行して、洗浄用の薬液を貯留した薬液タンク２から、薬液供給手段１２によって送液経路２１に薬液を導入しておく。経路内に円滑に薬液を導入するためには、ドレン２５ｃに至る経路を設けて導入時に開放しておくとよい。薬液供給手段１２は、やはりポンプまたは水頭差を利用でき、比較的短い経路を少量の液体を時間に余裕を持って送液するために適用されるものであるから、被処理液供給手段１１に比して吐出力がかなり小さいもので充分である。従って、このような構成にすることで、設備費用、ランニングコストの大幅な削減が期待できる。図中に示されるように、薬液は送液経路２１において被処理液供給手段１１の下流に導入されるので、後述する逆洗洗浄工程（図５参照）の際に被処理液の供給に先んじて、薬液が希釈されることなく濾過ブロック３にまで一気に供給できる。
【００２３】
薬液は、好ましくは、このように逆洗準備工程に並行して送液経路２１に導入しておくが、逆洗洗浄の工程が終了するまでであれば、例えば、後述する主逆洗工程に並行して行ってもよい。このようにして、薬液供給の時間に余裕を与えるにかかわらず、そのための時間が浪費されることを回避できる。
【００２４】
なお、薬液は送液経路２１においてできるだけ濾過ブロック３に近い位置に導入充満されているほうが、希釈されにくい点でより好ましい。また、希釈されにくくするために配管ラインを工夫し、薬液供給手段１２からの経路が送液経路２１に合流する部位に、薬液導入部として例えばＵ字やＶ字などの下垂部を形成し、薬液を充満しやすくしてもよい。
【００２５】
使用可能な洗浄用薬液としては、硫酸水溶液、水酸化ナトリウム水溶液等、好ましくは１〜４０％（重量／容量）、特に好ましくは１〜５％（重量／容量）の水酸化ナトリウム水溶液が挙げられる。
薬剤の供給量は、洗浄排液のｐＨ及び洗浄後の濾過処理液のｐＨがそれぞれ放流基準と水質基準（いずれも５．８〜８．６）を維持できるような量とする。
【００２６】
次いで、図４に示される主逆洗工程が実施される。すなわち、図３の状態から、上記逆洗準備工程と同様に加圧を行ったままで、濾過ブロック３よりドレン２５ａを一挙に開放して、二次側から空気圧を濾過膜を通して一次側に抜き、さらに剥離物質を空気とともに濾過ブロック３外に噴出させることで空気逆洗する物理洗浄が行われる。この工程は、一次側膜表面に付着した物質を隅々まで剥離させる。この際、前記のごとく圧力が高い程、付着物を充分に除去できる。
【００２７】
続いて、図５に示されるように、薬液及び被処理液を通液しながら、逆洗手段による逆洗を行う逆洗洗浄工程が実施される。この工程では、図４の状態から、さらに送液経路２１を開放し、被処理液供給手段１１を作動して、二次側からの加圧による空気逆洗下に、それに並行して薬液及び被処理液が濾過ブロック３へ一次側から導入される物理化学洗浄が行われる。加圧は、前記主逆洗時と同様に逆洗手段１３にて行われる。この工程では、処理能力が大きい被処理液供給手段１１によって、薬液が高濃度を保ったまま濾過ブロック３にまで一気に供給され、次いで被処理液が供給される間逆洗が充分に行われ、これらの液はすべてドレン２５ａより排出される。この際の圧力も、濾過膜の耐圧性、被処理液供給手段１１の吐出圧等を考慮して、なるべく高い値に定められるべきである。
【００２８】
この場合、図示のごとくに、送液経路２１が濾過ブロック３の底部に接続され、導入された薬液が濾過ブロック３内を上昇してその上方から排出されるように構成されていると、まず高濃度の薬液が濾過ブロック３に底部接続口から、底部接続口より上方に所定高さの層を形成するまで供給された後、続いて被処理液の供給に伴って前記層が全体的に上方に押し上げられるので、薬液が被処理液によって希釈されにくい。また、濾過ブロック内では、収納されている多数の中空糸膜が内部液体の攪乱を防止する働きをするので、薬液の前記層と被処理液の混合が起こりにくくなっている。その結果、濾過膜全体が高濃度の薬液により順次物理化学洗浄され、少ない薬液の使用量で高い洗浄効果が期待できるので、より好ましい。ここで底部は、濾過ブロック３の底面に限定されず、底面からある程度上方の部分も包含する。
【００２９】
なお、薬液タンク２から送液経路２１に至る流路を形成する代わりに、薬液タンク２と濾過ブロック３を直結する流路を設けて、洗浄用薬液を逆洗に並行して濾過ブロック３に直接導入してもよいが、この場合には、薬液供給手段１２には逆洗加圧による圧力を凌ぐために供給処理手段１１と同等の吐出圧を提供できものであることが要求される。
【００３０】
また、本発明の洗浄方法の実施態様において、前記逆洗準備工程及び主逆洗工程を経ることが望ましいが、これを省略することも可能である。逆洗準備工程及び主逆洗工程を実施すれば、物理洗浄の効果がより高くなり、また、前記の通り、これらの工程中に送液経路２１へ薬液を導入しておけば、従来の空気逆洗による洗浄方法と変わらない所要時間で、濾過ブロックに高濃度に薬液が供給でき物理化学洗浄による優れた洗浄効果が達成される。
【００３１】
最後に、図６は洗浄工程であり、被処理液による洗浄が実施される。この工程は、濾過ブロック通液後の液体が処理液タンク４ではなくドレン２５ａから排出されることを除いては、実質的に図１に前記した濾過工程と同様であり、加圧せずに被処理液を通液して膜を一次側より流去し、薬液で洗浄した後の濾過ブロックを充分に洗浄する。この工程は、前記逆洗洗浄工程の加圧を停止した直後から連続して開始しても、または停止後少し時間を経た後に濾過ブロックの内圧が下がってから行なってもよい。
【００３２】
これらの各工程を実施する時間は、濾過装置の規模、濾過ブロックの容量、耐圧性、被処理液供給手段や逆洗手段による処理能力に応じて、適宜に設定すればよい。
【００３３】
従来、以上記載した本発明の洗浄方法において薬液を用いる化学洗浄の工程が含まれない小規模の物理洗浄は、通常、１０〜１００分に１回行われている。この物理洗浄を実施する毎に上記薬液を用いる化学洗浄を含む本発明の洗浄方法を行なってもよいが、原水特性、アルミニウム塩の添加量によっては物理洗浄を２〜４８回行う間に１回の割合で本発明の洗浄方法を実施してもよい。このようにして、濾過ブロックへの物質の付着量を顕著に少ない状態に維持でき、従って、大規模洗浄の必要回数を低減することができる。
【００３４】
また、本発明の別の態様において、濾過ブロックを複数設けて適宜の連結形態とし、洗浄操作を一部の濾過ブロックずつ順に行なって、濾過装置全体を停止することなく洗浄を順に遂行することも可能である。
【００３５】
なお、逆洗による物理洗浄と薬液による化学洗浄とで成し遂げられる物理化学洗浄の効果は、主に双方の洗浄工程が同時進行する時間の長さに依存して変動しうるが、物理洗浄と化学洗浄とを並行して行うタイミングは特に限定されず、いずれかが先に開始あるいは終了してもよい。
【００３６】
【実施例】
浄水場の沈砂池より取水した表流水を原水として、以下の実験を行った。
【００３７】
まず、原水は、夾雑物除去用のプレフィルター（目開：０．２ｍｍ）を通して前処理した後、フミン酸除去を目的として、ポリ塩化アルミニウムを１０ｍｇ／Ｌの濃度となるように添加した。こうして調製した被処理液について、外圧式中空糸型精密濾過膜（ポリプロピレン製、孔径：０．２μｍ、外径／内径＝５５０μｍ／２５０μｍ、膜面積：１５ｍ²）を収めるφ１２０ｍｍ、高さ１７４８ｍｍの膜モジュール２本で構成される濾過ブロックを用いて、前記の溶液の濾過及び小規模洗浄を繰り返し、小規模洗浄時毎に薬液を用いる化学洗浄を行う場合（本発明の方法）と物理洗浄のみを行う場合との、膜の差圧の変化を経時的に測定した。被処理液供給手段は、電磁式ダイヤフラムポンプ（６８０Ｗ）を用い、薬液供給手段には、電磁式ダイヤフラムポンプを用いた。
【００３８】
被処理液の供給量は３１．２ｍ³／日とし、膜面に対する流束は、１．０ｍ³／ｍ²／日とした。物理洗浄は、５７分に１回の頻度で、以下の設定に基づいて行った。なお、加圧力は、逆洗手段部にて測定した。
【００３９】
▲１▼排液：１２０ｋＰａで１０秒間加圧
▲２▼逆洗準備：６００ｋＰａで１０秒間加圧。
【００４０】
▲３▼主逆洗：６００ｋＰａで２秒間加圧。
【００４１】
▲４▼逆洗洗浄：６００ｋＰａで１５秒間加圧、被処理液を、８ｍ³／時にて送液。
【００４２】
▲５▼洗浄：被処理液を、７秒間、８ｍ³／時にて送液。
【００４３】
本発明の方法に従う、薬液を用いる化学洗浄を伴う小規模洗浄を行う場合は、上記▲２▼の逆洗準備の際に２．８％水酸化ナトリウム水溶液を１０秒で３．５mL送液経路に供給し、以下上記と同様の工程を経て、洗浄を成し遂げた。
【００４４】
しかして、濾過後の処理液は、２９．０ｍ³／日、そして洗浄排液は、２．２ｍ³／日採取されるように維持して、１２５日目まで継続した。毎日、水温及び流量を自動記録し、この数値から膜モジュールブロックの膜の差圧を２０℃の場合に換算して求めた。
【００４５】
この結果を図７に示す。通常のポリプロピレン製の膜では、運転圧力を１００〜１５０ｋＰａ以下に抑える必要があり、これ以上圧力が上昇すると膜性能の回復性が悪くなる。従来の物理洗浄の方法によれば（図中、●で示す）、実験開始から２０日を経過した頃から膜差圧が顕著に上昇し始め、２８日目には、膜の回復性が悪くなる１００ｋＰａを越え、大規模洗浄が必要となった。一方、本発明の方法に従って、水酸化ナトリウムを使用した物理化学洗浄を行う毎に実施した場合（図中、○で示す）は、３０日が経過した後も、膜差圧は低値を維持し、さらに１２５日まで継続して初めて１００ｋＰａにまで上昇し、かかる長期間にわたって大規模洗浄の必要が生じないことが判明した。
【００４６】
また、いずれの方法によって得られた処理液も、ｐＨ、濁度、色度等すべての点において上水道用水として申し分のない質を維持していた。全排液のｐＨは、本発明の方法による場合でも８以下であり、そのまま河川に放流しても差し支えのないものであった。
【００４７】
【発明の効果】
以上説明した本発明の濾過装置及びその洗浄方法によって、以下の効果が奏される。
【００４８】
１．濾過装置の小規模洗浄の効果が著しく高められ、大規模洗浄の必要回数を格段に低減することができる。
【００４９】
２．濾過後の処理液は、従来の物理洗浄法のみによって洗浄された濾過装置で濾過した場合と比較して、同等の水質が得られる。
【００５０】
３．効率的な洗浄薬液供給により高濃度の薬液を濾過ブロックに導入できるため、少量の薬液使用量で充分な洗浄効果が提供される。洗浄後の全排液を混合するとｐＨが約８以下となるため廃液の処理の問題もなく、また上水道用水などの処理液の水質も保証される。
【００５１】
４．洗浄工程の時間は、従来の小規模洗浄より長くなったとしても、供給しておいた比較的少量の薬液を膜モジュールに通液するごくわずかの時間のみが加わるだけであり、比較的短い所要時間で効果的な洗浄効果が得られる。
【図面の簡単な説明】
【図１】本発明の一実施態様の濾過装置の概略を示し、濾過作業時の作動様態を表す図である。
【図２】図１の濾過装置において、逆洗を行う前の排液時の作動様態を表す図である。
【図３】図１の濾過装置において、逆洗準備及び薬液供給時の作動様態を表す図である。
【図４】図１の濾過装置において、主逆洗時の作動様態を表す図である。
【図５】図１の濾過装置において、逆洗洗浄時の作動様態を表す図である。
【図６】図１の濾過装置において、被処理液による洗浄時の作動様態を表す図である。
【図７】従来の物理洗浄方法及び本願発明の物理化学洗浄方法を定期的に実施した場合の、濾過ブロック内の膜圧の変化の経時的な推移を表すグラフである。
【符号の説明】
１…被処理液タンク
２…薬液タンク
３…濾過ブロック
４…処理液タンク
１１…被処理液供給手段
１２…薬液供給手段
１３…逆洗手段
２１…送液経路
２５ａ…一次側ドレン
２５ｂ…二次側ドレン
３１…濾過ブロック一次側
３２…濾過ブロック二次側
５１…濾過装置[0001]
BACKGROUND OF THE INVENTION
The present invention is a filtration device that can be used for removing turbidity and chromaticity with a membrane using river water, lake water, or the like as raw water, and can efficiently wash a filtration block composed of membrane modules. In more detail, the cleaning method for the filtration block in FIG. 5 is a large-scale operation performed by stopping the system in the cleaning for removing deposits such as inorganic substances and organic substances staying in the filtration block as the liquid to be treated is filtered. The present invention relates to an apparatus and a method that can reduce the number of times of chemical cleaning.
[0002]
[Prior art]
The film treatment of the liquid to be treated as described above is mainly performed for the purpose of turbidity. In addition to turbidity, for example, a colored substance can be removed by a technique such as adding an aluminum salt before filtration. The biggest problem in operation is the blockage of the membrane, but the extent depends on the usage environment. When aluminum salt is injected into raw water having a turbidity concentration of several to several tens of degrees and membrane filtration is performed, if the membrane is subjected to small-scale cleaning described later, the membrane is subjected to large-scale chemical cleaning once every several months. It is possible to maintain an appropriate filtration efficiency. However, when membrane filtration is performed after adding an aluminum salt to raw water with low turbidity and high chromaticity, the solid component to be removed is low in turbidity content and a large amount of highly sticky aluminum hydroxide, etc. When such a sticky substance adheres firmly to the film, the film is likely to be clogged, so that the interval for performing large-scale chemical cleaning is shortened from several weeks to one month.
[0003]
That is, when the raw water is purified or treated, the treatment is usually performed by injecting polyaluminum chloride (PAC) or aluminum sulfate in order to remove the brown color caused by humic acid, etc., and adsorbing humic acid. However, when this treatment is performed on raw water having low turbidity and high chromaticity, a sticky substance mainly composed of aluminum hydroxide or the like is generated as described above. Conventionally, such an aluminum salt is added and then agglomerated, and precipitation and separation by sand filtration are generally performed. Recently, however, a membrane module block composed of, for example, a hollow fiber made of polypropylene is included. A technique of filtering with a filtering device has been put into practical use. However, if filtration is continued in such a filtration apparatus, solid matter or sticky matter mainly composed of the above-mentioned adhesive aluminum hydroxide or the like adheres to and accumulates on the membrane surface to block the membrane. If the membrane is clogged, the filtration speed is lowered and the filtration pressure is increased, and stable filtration treatment cannot be performed. Therefore, in order to remove such deposits on the film, small-scale cleaning is performed at short intervals. However, it is still necessary to periodically stop the system and perform large-scale chemical cleaning. .
[0004]
In this chemical cleaning operation, a chemical solution for cleaning such as aqueous sodium hydroxide or sulfuric acid is introduced into the raw water tank, the pH is adjusted, and then the chemical solution is circulated for several hours or more between the raw water tank and the membrane module block. In general, it is carried out over several days with water washing after circulating the chemical solution, which leads to waste of labor and time. Further, it is necessary to process strongly basic sodium hydroxide discharged at this time, or strongly acidic sulfuric acid waste liquid, and this processing work is also troublesome.
[0005]
Small-scale cleaning (physical cleaning) is performed about 24 to 48 times a day in order to increase the interval of time when large-scale chemical cleaning must be performed by removing the deposits frequently before the film deposits accumulate. It has been broken. This small-scale washing is generally divided into a back washing process and a subsequent washing process. In the backwashing step, first, the supply of raw water from the primary side (treated water inflow side) of the membrane module of the filtration block is stopped, followed by pressurization and backwashing. The pressurization is generally performed with a liquid such as permeate from the secondary side of the membrane (outflow side of the treated water). Furthermore, with a simple increase in equipment, a chemical solution is mixed in a liquid for pressurization, and chemical cleaning is performed simultaneously with pressurization, that is, a physicochemical cleaning method has been implemented. In the subsequent washing step, raw water is supplied to the membrane module block from the primary side, washed with water, and discharged from the drain on the primary side. By performing such small-scale cleaning, for example, once every 30 minutes to 1 hour, the required number of large-scale cleaning using a chemical solution has been reduced. However, the required number of large-scale cleaning is further reduced. There was a need for a method that could do this.
[0006]
[Problems to be solved by the invention]
Recently, however, a method has been put to practical use in which air backwash is performed by applying pressure from the secondary side of the membrane and passing air through the primary side. This method can utilize the force when the compressed air expands by pressurizing the filter block in a closed system once and then releasing it at once, so compared with the conventional liquid cleaning method. This produces a far better backwashing effect overall.
[0007]
However, even with a method using air backwashing, it is difficult to say that the removal of the adhesive substance can be performed efficiently, and it has been necessary to carry out fairly large-scale cleaning.
[0008]
The present invention has been made in view of the current situation, and in the filtration of raw water with low turbidity and high chromaticity using an air backwash filter, inorganic and organic substances staying in a filtration block composed of a membrane module and the like. An object of the present invention is to provide an apparatus and method that can reduce the number of times that a large amount of chemical solution is used at one time to remove a deposit such as a large-scale cleaning solution.
[0009]
[Means for Solving the Problems]
The present invention has been accomplished as a result of intensive studies in order to achieve the above object in the filtration device, and the chemical solution cannot be supplied from the secondary side in the air backwash described above. Provided is a method for overcoming the disadvantages caused by the above, effectively supplying a chemical solution from the primary side, and efficiently cleaning. That is, a physical chemical cleaning that exhibits an excellent cleaning effect is performed by performing both the physical cleaning applying the air backwashing and the chemical cleaning with the chemical solution in parallel.
[0010]
That is, the present invention provides a filtration apparatus, wherein (a) a liquid to be treated is sent from the liquid tank to be treated to a primary side of a filtration block including a membrane module, and (b) from the liquid tank to be treated. A liquid supply path that forms a flow path to the filtration block; (c) a chemical supply means for supplying the cleaning chemical from the chemical tank; (d) a drain for draining the filtration block; and (e) filtration. A filtration device including air backwashing means for performing air backwashing of the membrane module from the secondary side of the block, wherein the chemical liquid supply means causes the cleaning chemical liquid to be downstream of the liquid supply means in the liquid supply path. And chemical cleaning with the cleaning chemical solution can be performed in parallel during physical cleaning of the membrane module by the air backwashing means, so that physical chemical cleaning is achieved. Providing a filtration device characterized by and.
[0011]
Furthermore, the present invention is a method for physicochemical cleaning of the filtration block in the above-described filtration device, and the following steps are performed, that is, (1) performing drainage while pressurizing the filtration block 3 using the backwashing means 13, (2) Air backwashing that pressurizes the filtration block 3 using the backwashing means 13 and the operation of the liquid supply means 11 to introduce and discharge liquid into the filtration block 3 via the liquid feeding path 21; Perform backwashing to discharge the deposits from the filtration block 3, and (3) stop the pressurization by the backwashing means 13 and introduce and discharge the liquid to be treated into the filtration block 3. Including the step of cleaning, before the step (2) is completed, the chemical solution is introduced from the chemical solution tank 2 into the liquid supply path 21 by the chemical solution supply means 12, and the chemical solution is supplied to the liquid to be treated in the step (2). Filter by 11 Is introduced into the block 3, a physical chemical cleaning effect by both the air pressure and chemical is exhibited, then there is provided a cleaning method characterized in that it is achieved that cleaning with the liquid to be treated.
[0012]
Although it is possible to send the chemical solution for cleaning directly from the chemical solution tank to the primary side of the filtration block by the chemical solution supply means, in this case, when supplying the chemical solution during backwashing with air, the discharge pressure is filtered. The internal pressure of the block must be exceeded, and a large pump is required to shorten the supply time. Further, since it is necessary to newly provide a liquid supply path for the chemical solution, there is a disadvantage that the piping cost increases. Therefore, if a flow path is formed from the chemical tank to the downstream of the liquid supply means to be processed in the liquid supply path, and the cleaning chemical liquid is introduced into the liquid supply path before the backwashing cleaning process is completed, the liquid supply It is preferable because the chemical solution is introduced into the filtration block using the powerful discharge capability of the means and chemical cleaning is performed.
[0013]
That is, the present inventors have performed an air backwashing step in order to achieve a physical chemical cleaning by performing a chemical cleaning step using a chemical solution such as an acid or alkaline aqueous solution during the physical washing of the backwashing step that has been conventionally performed. The chemical solution is introduced into the filtration block in parallel with the filter block, and then the normal backwashing and washing steps are performed to greatly enhance the effect of small-scale washing, and the number of times of large-scale washing is drastically reduced. As a result, the present invention has been completed.
[0014]
In the chemical cleaning process using the chemical solution of the present invention, the chemical solution can be efficiently supplied without the need for a large-scale chemical solution supply means used in the conventional large-scale cleaning, and the chemical solution is used per time. Since the amount is small, the problem of waste liquid treatment after washing is also reduced. The time required for the cleaning process is the same as that of conventional small-scale cleaning, and only a very short time for passing the chemical solution through the membrane module is extended or the same. An effect is obtained.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the apparatus and the cleaning method of the present invention will be described in detail with reference to FIGS. 1 to 6 showing the embodiments of the present invention. However, the present invention should not be construed in a limited manner based on such embodiments.
[0016]
The filtration device 51 of the present invention whose outline is shown in FIGS. 1 to 6 essentially includes a liquid tank 1 to be treated, a chemical liquid tank 2, a filtration block 3, and a treatment liquid tank 4, and is appropriately provided with a path provided with a valve. It is connected. In order to pass the liquid, a treatment liquid supply means 11 and a chemical liquid supply means 12 using a pump or a head difference are arranged, and a backwashing means 13 including a compressor is arranged for backwashing with air. ing. In general, the backwashing means 13 is often arranged in the order of a compressor, a check valve, an air tank, and an electromagnetic valve from the upstream side. A drain 25 a is provided on the primary side 31 of the filtration block 3 and a drain 25 b is provided on the secondary side 32, and the liquid after washing is discharged to a waste liquid tank or the like through this. In each figure, in order to clarify the open / closed state of the valve, the open valve is shown in light color and the closed valve is shown in dark color.
[0017]
The filtration block 3 may be a hollow fiber membrane module block that is conventionally used, for example, made of polypropylene or the like. The pore diameter of the membrane is appropriately selected according to the contaminants, physical properties, etc. of the liquid to be treated, but is generally about 0.2 μm.
[0018]
Other components can be appropriately selected and used in the form and material conventionally known to those skilled in the art. However, as will be described later, the chemical supply means 12 is for sending a small amount of liquid with sufficient time through a path formed so as to be relatively short. Smaller than that. Further, it is possible to provide a heating means in the chemical tank 2 for the purpose of increasing the cleaning efficiency.
[0019]
The raw water of the liquid to be treated is mainly river water, lake water, etc., and the liquid to be treated contains a large amount of sticky substances after the raw water with low turbidity and high chromaticity is treated with aluminum salt. Moreover, it can filter suitably by the filtration apparatus 51 of this invention.
FIG. 1 shows an operation mode when normal filtration is performed by the filtration device 51 of the present invention. Specifically, the liquid supply tank 11 is operated by operating the liquid supply means 11 to be processed. The liquid to be treated is introduced into the primary side 31 of the filtration block which is a membrane module block of the hollow fiber membrane from 1 through the liquid feed path 21, and the treated liquid after filtration is fed from the secondary side 32 of the filtration block to the treatment liquid tank 4. Stored.
[0020]
In FIGS. 2 to 6 showing the steps of small-scale cleaning according to the cleaning method of the present invention, FIG. 2 first shows the draining step. In this step, the liquid supply means 11 to be treated is stopped, the liquid feed path 21 is shut off, and the path sent from the filtration block 3 to the treatment liquid tank 4 is also sealed, and the secondary washing means 13 performs the secondary cleaning. By applying pressure from the side, the liquid to be treated in the filtration block 3 is discharged from the drain 25b, and the liquid in the hollow fiber membrane is removed.
[0021]
Next, the steps from FIG. 3 to FIG. 5 will be described. First, the backwash preparation step shown in FIG. 3 is performed. In this step, the drains 25a and 25b of the filtration block 3 are also sealed, that is, the filtration block 3 is substantially closed, and the backwashing means 13 adds the filtration block 3 from the secondary side of the membrane module. Press. In this case, the upper limit of the pressure needs to be at least a pressure exceeding the resistance when air passes through the filtration membrane, and should preferably be set as high as possible in consideration of the pressure resistance of the filtration block.
[0022]
In parallel with the backwash preparation step, the chemical solution is introduced into the liquid supply path 21 by the chemical solution supply means 12 from the chemical tank 2 in which the cleaning chemical solution is stored. In order to smoothly introduce the chemical into the path, it is preferable to provide a path that reaches the drain 25c and open it during the introduction. The chemical solution supply means 12 can also use a pump or a water head difference, and is applied to send a small amount of liquid with sufficient time through a relatively short path. In comparison, a discharge force that is considerably small is sufficient. Therefore, a drastic reduction in equipment cost and running cost can be expected with such a configuration. As shown in the figure, since the chemical solution is introduced downstream of the liquid supply means 11 in the liquid supply path 21, it is ahead of the supply of the liquid to be processed in the backwashing cleaning process (see FIG. 5) described later. Thus, the chemical solution can be supplied to the filtration block 3 without being diluted.
[0023]
The chemical solution is preferably introduced into the liquid feeding path 21 in parallel with the backwash preparation step as described above. However, until the backwash cleaning step is completed, for example, in the main backwash step described later. You may do it in parallel. In this way, it is possible to avoid wasting the time for supplying the chemical solution, regardless of time.
[0024]
In addition, it is more preferable that the chemical solution is introduced and filled in a position close to the filtration block 3 as much as possible in the liquid supply path 21 in that it is difficult to be diluted. In addition, a piping line is devised to make it difficult to dilute, and a drooping portion such as a U-shape or a V-shape is formed as a chemical solution introduction portion at a site where the route from the chemical solution supply means 12 joins the liquid supply route 21, You may make it easy to fill a chemical | medical solution.
[0025]
Usable cleaning chemicals include sulfuric acid aqueous solution, sodium hydroxide aqueous solution, etc., preferably 1-40% (weight / volume), particularly preferably 1-5% (weight / volume) sodium hydroxide aqueous solution. .
The supply amount of the chemical is set such that the pH of the washing waste liquid and the pH of the filtered liquid after washing can respectively maintain the discharge standard and the water quality standard (both 5.8 to 8.6).
[0026]
Next, the main backwashing step shown in FIG. 4 is performed. That is, from the state of FIG. 3, with the pressure applied in the same manner as the backwash preparation step, the drain 25a is released from the filtration block 3 at once, and the air pressure is drawn from the secondary side through the filtration membrane to the primary side, Further, physical cleaning is performed in which air is back-washed by ejecting the release material together with air to the outside of the filter block 3. In this step, the substance adhering to the surface of the primary side film is peeled to every corner. At this time, as the pressure is higher as described above, the deposits can be sufficiently removed.
[0027]
Subsequently, as shown in FIG. 5, a backwashing cleaning process is performed in which backwashing is performed by backwashing means while passing the chemical solution and the liquid to be processed. In this step, from the state of FIG. 4, the liquid supply path 21 is further opened, the liquid supply means 11 is operated, and the chemical liquid and A physicochemical cleaning is performed in which the liquid to be treated is introduced into the filtration block 3 from the primary side. The pressurization is performed by the backwashing means 13 as in the main backwashing. In this step, the processing solution supply means 11 having a large processing capacity supplies the chemical solution to the filtration block 3 while maintaining a high concentration, and then backwashing is sufficiently performed while the processing solution is supplied. All of these liquids are discharged from the drain 25a. The pressure at this time should also be set as high as possible in consideration of the pressure resistance of the filtration membrane, the discharge pressure of the liquid supply means 11 to be processed, and the like.
[0028]
In this case, as shown in the figure, when the liquid feeding path 21 is connected to the bottom of the filtration block 3 and the introduced chemical liquid is configured to rise in the filtration block 3 and be discharged from above, After the high concentration chemical solution is supplied from the bottom connection port to the filtration block 3 until a layer having a predetermined height is formed above the bottom connection port, the layer is entirely formed along with the supply of the liquid to be processed. Since it is pushed upward, the chemical solution is not easily diluted by the liquid to be treated. Further, in the filtration block, the numerous hollow fiber membranes that are housed function to prevent disturbance of the internal liquid, so that it is difficult for the chemical liquid layer to be mixed with the liquid to be treated. As a result, the entire filtration membrane is sequentially subjected to physicochemical cleaning with a high concentration chemical solution, and a high cleaning effect can be expected with a small amount of chemical solution used, which is more preferable. Here, the bottom portion is not limited to the bottom surface of the filtration block 3, and includes a portion that is somewhat above the bottom surface.
[0029]
Instead of forming a flow path from the chemical liquid tank 2 to the liquid supply path 21, a flow path directly connecting the chemical liquid tank 2 and the filtration block 3 is provided so that the cleaning chemical liquid is supplied to the filtration block 3 in parallel with the backwashing. In this case, the chemical supply means 12 is required to be able to provide a discharge pressure equivalent to that of the supply processing means 11 in order to surpass the pressure due to the backwash pressure.
[0030]
Moreover, in the embodiment of the cleaning method of the present invention, it is desirable to go through the backwash preparation step and the main backwash step, but this can be omitted. If the backwashing preparation process and the main backwashing process are performed, the effect of physical cleaning becomes higher, and as described above, if the chemical solution is introduced into the liquid feeding path 21 during these processes, the conventional air The chemical solution can be supplied to the filtration block at a high concentration in the same time as the cleaning method by backwashing, and an excellent cleaning effect by physicochemical cleaning is achieved.
[0031]
Finally, FIG. 6 shows a cleaning process, in which cleaning with a liquid to be processed is performed. This process is substantially the same as the filtration process described above with reference to FIG. 1 except that the liquid after passing through the filtration block is discharged from the drain 25a instead of the treatment liquid tank 4, without applying pressure. The liquid to be treated is passed through to remove the membrane from the primary side, and the filtration block after washing with the chemical solution is thoroughly washed. This process may be started continuously immediately after the pressurization of the backwashing washing process is stopped, or may be performed after the internal pressure of the filtration block is lowered after a while after the stop.
[0032]
What is necessary is just to set suitably the time which implements each of these processes according to the scale of a filtration apparatus, the capacity | capacitance of a filtration block, pressure | voltage resistance, and the processing capability by a to-be-processed liquid supply means or a backwashing means.
[0033]
Conventionally, small-scale physical cleaning that does not include a chemical cleaning step using a chemical in the cleaning method of the present invention described above is usually performed once every 10 to 100 minutes. Each time this physical cleaning is performed, the cleaning method of the present invention including the chemical cleaning using the above chemical solution may be performed. However, depending on the raw water characteristics and the addition amount of the aluminum salt, the cleaning is performed once every 2 to 48 times. You may implement the washing | cleaning method of this invention in the ratio. In this way, the amount of substance adhering to the filtration block can be maintained in a significantly reduced state, and therefore the number of large-scale washings required can be reduced.
[0034]
In another aspect of the present invention, a plurality of filtration blocks may be provided to form an appropriate connection form, and the washing operation may be performed sequentially for each of the filtration blocks, and the washing may be performed in order without stopping the entire filtration device. Is possible.
[0035]
Note that the effects of physical and chemical cleaning achieved by physical cleaning by backwashing and chemical cleaning by chemical solutions can vary depending mainly on the length of time during which both cleaning steps proceed simultaneously. The timing for performing the cleaning in parallel is not particularly limited, and either may start or end first.
[0036]
【Example】
The following experiment was conducted using the surface water taken from the sand basin of the water treatment plant as raw water.
[0037]
First, the raw water was pretreated through a pre-filter for removing contaminants (opening: 0.2 mm), and then polyaluminum chloride was added to a concentration of 10 mg / L for the purpose of removing humic acid. About the liquid to be treated thus prepared, an external pressure type hollow fiber microfiltration membrane (made of polypropylene, pore diameter: 0.2 μm, outer diameter / inner diameter = 550 μm / 250 μm, membrane area: 15 m ² ) of 120 mm in height and 1748 mm in height Using a filtration block composed of two membrane modules, repeated filtration and small-scale cleaning of the above solution, and chemical cleaning using a chemical solution for each small-scale cleaning (method of the present invention) and physical cleaning only The change in the differential pressure of the film with the case of performing was measured over time. An electromagnetic diaphragm pump (680 W) was used as the liquid supply means to be treated, and an electromagnetic diaphragm pump was used as the chemical liquid supply means.
[0038]
The supply amount of the liquid to be treated was 31.2 m ³ / day, and the flux with respect to the membrane surface was 1.0 m ³ / m ² / day. Physical cleaning was performed once every 57 minutes based on the following settings. The applied pressure was measured at the backwashing unit.
[0039]
(1) Drainage: Pressurization for 10 seconds at 120 kPa (2) Preparation for backwashing: Pressurization for 10 seconds at 600 kPa.
[0040]
(3) Main backwash: Pressurized at 600 kPa for 2 seconds.
[0041]
{Circle around (4)} Backwashing: Pressurized at 600 kPa for 15 seconds, and feed the liquid to be treated at 8 m ³ / hour.
[0042]
(5) Cleaning: The liquid to be treated is fed at 8 m ³ / hour for 7 seconds.
[0043]
When performing small-scale cleaning with chemical cleaning using a chemical solution according to the method of the present invention, a 2.8% sodium hydroxide aqueous solution is supplied in 3.5 seconds in 10 seconds during the back-washing preparation of (2) above. Then, through the same steps as described above, washing was accomplished.
[0044]
Thus, the treated liquid after filtration was maintained at 29.0 m ³ / day, and the washing drainage was maintained at 2.2 m ³ / day and continued until day 125. The water temperature and flow rate were automatically recorded every day, and the membrane pressure difference of the membrane module block was calculated from these values when converted to 20 ° C.
[0045]
The result is shown in FIG. In the case of a normal polypropylene film, the operating pressure needs to be suppressed to 100 to 150 kPa or less, and when the pressure is further increased, the recoverability of the film performance is deteriorated. According to the conventional physical cleaning method (indicated by ● in the figure), the membrane differential pressure starts to increase remarkably from about 20 days after the start of the experiment, and on the 28th day, the membrane recoverability is poor. Over 100 kPa, large-scale cleaning was required. On the other hand, when the physicochemical cleaning using sodium hydroxide is performed according to the method of the present invention (indicated by a circle in the figure), the membrane pressure difference remains low even after 30 days. Furthermore, it was found that the pressure rose to 100 kPa for the first time until 125 days, and that there was no need for large-scale cleaning over such a long period.
[0046]
Moreover, the treatment liquid obtained by any of the methods maintained an excellent quality as water for tap water in all points such as pH, turbidity, and chromaticity. The pH of the total drainage was 8 or less even in the case of the method of the present invention, and it could be safely discharged into the river as it was.
[0047]
【The invention's effect】
The following effects are produced by the filtration device and the cleaning method of the present invention described above.
[0048]
1. The effect of the small-scale cleaning of the filtration device is remarkably enhanced, and the required number of large-scale cleaning can be significantly reduced.
[0049]
2. The treated liquid after the filtration can obtain an equivalent water quality as compared with the case where the treatment liquid is filtered only by a conventional physical washing method.
[0050]
3. Since a chemical solution with a high concentration can be introduced into the filtration block by an efficient supply of the cleaning chemical solution, a sufficient cleaning effect is provided with a small amount of the chemical solution used. When the total waste liquid after washing is mixed, the pH becomes about 8 or less, so there is no problem of waste liquid treatment, and the quality of the treatment liquid such as water for tap water is also guaranteed.
[0051]
4). Even if the cleaning process takes longer time than the conventional small-scale cleaning, only a very short time is required for passing a relatively small amount of the supplied chemical solution through the membrane module. An effective cleaning effect can be obtained over time.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of a filtration apparatus according to an embodiment of the present invention and showing an operation state during a filtration operation.
FIG. 2 is a diagram illustrating an operation state at the time of draining before performing backwashing in the filtration device of FIG.
FIG. 3 is a diagram illustrating an operation state during backwash preparation and chemical supply in the filtration device of FIG. 1;
4 is a diagram illustrating an operation state during main backwashing in the filtration device of FIG. 1; FIG.
FIG. 5 is a diagram illustrating an operation state at the time of backwashing cleaning in the filtration device of FIG. 1;
6 is a diagram showing an operation state at the time of cleaning with a liquid to be treated in the filtration device of FIG. 1. FIG.
FIG. 7 is a graph showing the change over time of the change in membrane pressure in the filtration block when the conventional physical cleaning method and the physicochemical cleaning method of the present invention are periodically performed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Liquid tank 2 ... Chemical tank 3 ... Filtration block 4 ... Liquid tank 11 ... Liquid supply means 12 ... Liquid supply means 13 ... Backwash means 21 ... Liquid feed path 25a ... Primary drain 25b ... Secondary Side drain 31 ... Filtration block primary side 32 ... Filtration block secondary side 51 ... Filtration device

Claims

(A) To-be-treated liquid supply means 11 for sending the to-be-treated liquid from the to-be-treated liquid tank 1 to the primary side 31 of the filtration block 3 including the membrane module,
(B) a liquid feeding path 21 that forms a flow path from the liquid tank 1 to be treated to the filtration block 3;
(C) a chemical supply means 12 for feeding the cleaning chemical from the chemical tank 2;
(D) a drain 25 for draining from the filtration block 3, and
(E) A filtration device including air backwashing means 13 for performing air backwashing of the membrane module from the secondary side of the filtration block 3, wherein the chemical supply means 12 supplies the cleaning chemical liquid to the liquid supply path 21. The chemical cleaning with the cleaning chemical solution can be performed in parallel during the physical cleaning of the membrane module by the backwashing means 13 and the downstream of the liquid supply means 11 to be processed in In a filtration apparatus in which chemical cleaning is achieved, a method for physicochemical cleaning of the filtration block 3,
The following steps:
(1) Using the backwashing means 13, the liquid is discharged to the secondary drain 25b while pressurizing the filtration block 3 from the secondary side ,
(2) using the backwash means 13, and the air backwash to pull the primary side under pressure filtered block 3 from the secondary side, by the operation of the treatment liquid supply means 11, filtered through a liquid supply path 21 By introducing liquid from the primary side of the block 3 and discharging it from the primary drain 25a , backwashing is performed to discharge the deposits from the filtration block 3, and (3) pressurization by the backwashing means 13 is stopped. Te, is introduced from the primary liquid to be treated in the filtration block 3, comprising the step of cleaning the filtration block 3 by discharging from the primary side drain 25a,
Before the step (2) is completed, the chemical liquid is introduced from the chemical liquid tank 2 into the liquid supply path 21 by the chemical liquid supply means 12, and the chemical liquid is firstly filtered by the liquid supply means 11 to be processed in the step (2). The cleaning method is characterized in that the physicochemical cleaning effect is exhibited by both air pressure and chemical solution, and then cleaning with the liquid to be treated is achieved.

Between the draining step (1) and the backwashing step (2), the pressure from the secondary side by the backwashing means 13 is released from the primary side, and the deposits and remaining liquid are removed from the filtration block 3. further cleaning method according to claim 1 comprising a Shugyaku washing step of discharging from the primary side drain 25a.