JP4605951B2

JP4605951B2 - Membrane filtration system and operation method thereof

Info

Publication number: JP4605951B2
Application number: JP2001248697A
Authority: JP
Inventors: 周和村田
Original assignee: Organo Corp
Current assignee: Organo Corp
Priority date: 2001-08-20
Filing date: 2001-08-20
Publication date: 2011-01-05
Anticipated expiration: 2021-08-20
Also published as: JP2003053159A

Description

【０００１】
【発明の属する技術分野】
本発明は、精密濾過膜や限外濾過膜などの膜エレメントを有する膜濾過ユニットを処理槽（浸漬槽）内の水中に浸漬し、膜エレメントを透過した濾過処理水を、処理水槽等からなる後工程へと採水するようにした膜濾過システム、およびその運転方法に関する。
【０００２】
【従来の技術】
精密濾過膜や限外濾過膜などの膜エレメントを有する膜濾過ユニットを浸漬槽内の水中に浸漬し、膜エレメントを透過した濾過処理水を採水する膜濾過システムは多数考案されている。例えば特許第３１２４１７４号においては、濾過膜を原水貯留槽へ浸漬し、ポンプ吸引により濾過水を得て、一定時間ごとに処理水槽より加圧ポンプにて膜の逆洗を実施するようにした装置が示されている。同特許には示されていないが、一般に、逆洗によって貯留槽へ逆流した余剰水は、貯留槽底部の抜き出し弁より固形物とともに排出されるようになっている。
【０００３】
【発明が解決しようとする課題】
ところが、特許第３１２４１７４号に示されたような装置には、以下のような問題が残されている。まず、濾過処理水を膜濾過ユニットからポンプで吸引しているので、装置構成が複雑であるとともに運転コストが高いという問題がある。また、ポンプで強制吸引しているため、膜濾過ユニットの膜エレメントの閉塞状態（膜前後の差圧状態）を把握しにくく、最適な逆洗のタイミングを把握しにくいという問題がある。したがって実際には、例えばタイマー設定等により、膜濾過ユニットの状態にかかわらず、一定時間ごとに一定時間の逆洗を実施することになるが、必ずしも逆洗の最適なタイミングとは限らない。逆洗不十分であれば、濾過膜が閉塞し、処理水量の低下を招くおそれがあり、過剰逆洗になれば、結果的に濾過処理運転時間の低減からシステム全体の稼働率の低下を招くおそれがあり、さらに、逆洗用水の使用量が増加したり、逆洗排水の濃度が薄くなるためその処理（例えば、固液分離処理等）の効率が低下するなどの問題を招くおそれがある。
【０００４】
また、特許第３１２４１７４号に示されたような装置では、濾過膜に捕捉された被処理水中の固形物や凝集フロックは、逆洗によって濾過膜より剥離させた後、貯留槽底部に沈積させて貯留槽内の水とともに系外排出する運転を意図している。しかしながら、このような装置の場合、貯留槽内水は被処理水の供給や逆洗水の放出などによって対流しているため、膜面より剥離した固形物が貯留槽底部へ沈降濃縮されることはほとんどない。したがって、継続される濾過運転中に、貯留槽内に残留固形物が徐々に蓄積されていくことになり、被処理水中の固形物濃度が徐々に高まって、濾過膜への負荷が増大していく現象がおこる。結果として、膜の閉塞が早まり、稼働率の低下、回収率の低下、薬品洗浄頻度の増大や膜寿命の短縮を招き、ランニングコストも増大するなどの問題が発生する。
【０００５】
また、仮に被処理水中の固形物が貯留槽内で都合良く沈降濃縮されていたとしても、一般に濾過膜の逆洗は数十分〜１時間程度の頻度で多量の逆洗用水を使用して実施するので、その逆洗排水は希薄なものとなってしまうことが多く、逆洗排水処理設備の規模を大きなものにしなくてはならないことが多い。さらには、逆洗用水として濾過処理水を使用する場合には、その分後工程へと供給可能な濾過処理水量が減るので、水回収率も高いとは言えない。
【０００６】
そこで本発明の課題は、システム全体構成の簡素化、ランニングコストの低減をはかることができるとともに、逆洗実施の最適なタイミングを容易に把握でき、また、貯留槽内で残留固形物濃度が徐々に高まったり、逆洗によって剥離された固形物が濾過膜への再負荷となることを効率よく回避でき、逆洗による効果を最大限発揮できるようにし、その逆洗を少量の用水で実施でき、長期間安定運転を継続できるとともにシステム全体の水回収率の向上をはかることができ、さらに、逆洗排水処理への負荷も小さくできる、浸漬型膜濾過ユニットを用いた膜濾過システムおよびその運転方法を提供することにある。
【０００７】
【課題を解決するための手段】
上記課題を解決するために、本発明に係る膜濾過システムの運転方法は、供給されてきた被処理水を、浸漬槽内の水中に浸漬した膜濾過ユニットで濾過し、濾過処理水を後工程に送給する膜濾過システムの運転方法において、前記膜濾過ユニットによる濾過および濾過処理水の後工程への送給を、浸漬槽と後工程との間の水頭差を利用して行い、かつ、浸漬槽内の水位が予め定められた水位に到達した時点で浸漬槽内水を全量排出し、次いで膜濾過ユニットの逆洗を実施し、浸漬槽内の水位が予め定められた水位に到達するまでの間に、前記浸漬槽内水の全量排出後の逆洗とは別に一回以上の逆洗操作を実施することを特徴とする方法からなる。
【０００８】
この膜濾過システムの運転方法においては、浸漬槽内の水位が予め定められた水位に到達した時点で浸漬槽内水を全量排出し、次いで膜濾過ユニットの逆洗を実施することが望ましい。
【０００９】
また、浸漬槽内の水位が予め定められた水位に到達するまでの間に、一回以上の濾過停止操作を実施することが好ましい。さらに、浸漬槽内の水位が予め定められた水位に到達するまでの間に、上記浸漬槽内水の全量排出後の逆洗とは別に、一回以上の逆洗操作を実施する。この逆洗は、上記浸漬槽内水の全量排出後の逆洗に比べ、短時間行えばよい。
【００１０】
本発明に係る膜濾過システムは、被処理水を受け入れる浸漬槽と、該浸漬槽内の水中に浸漬した膜濾過ユニットと、該膜濾過ユニットによる濾過処理水の後工程への送給ラインとを有する膜濾過システムにおいて、前記浸漬槽内から膜濾過ユニットを介して前記後工程へと至る系を、浸漬槽と後工程との間の水頭差を利用して送水する系に構成するとともに、浸漬槽に、浸漬槽内の水位の上昇度合の検知手段を設け、前記後工程への送給ラインに前記膜濾過ユニットの逆洗ラインが接続され、該逆洗ラインが前記検知手段からの信号に連動して逆洗可能に構成され、前記浸漬槽に浸漬槽内水を全量排出可能な排水ラインが接続されており、浸漬槽内の水位が予め定められた水位に到達した時点で浸漬槽内水を全量排出し、次いで膜濾過ユニットの逆洗を実施し、浸漬槽内の水位が予め定められた水位に到達するまでの間に、前記浸漬槽内水の全量排出後の逆洗とは別に一回以上の逆洗操作を実施することを特徴とするものからなる。
【００１１】
この膜濾過システムにおいては、上記後工程への送給ラインに、膜濾過ユニットの逆洗ラインを接続し、該逆洗ラインを、上記検知手段からの信号に連動運転可能に構成する。また、上記浸漬槽には、浸漬槽内水を全量排出可能な排水ラインが接続されている。
【００１２】
従来までの膜濾過装置では、濾過膜の閉塞をできる限り抑制する目的で数十分〜１時間程度の頻度で逆洗操作を繰り返し、逆洗によって剥離した固形物を浸漬槽内へ蓄積していた。本発明者は、この逆洗工程に注目し、逆洗の頻度よりもむしろ、除去した固形物が濾過膜への再負荷となる方が、濾過膜の閉塞に大きな影響を与えていることを知見した。すなわち、逆洗頻度を多くするよりも、逆洗によって剥離した固形物などを確実に系外に排出した方が、濾過膜の安定運転が可能であることを知見した。さらに本発明者は、濾過膜の濾過負荷がある程度高まった時点で逆洗を実施する方法が、タイマー設定で短時間で逆洗を実施する従来までの方法に対し、洗浄に関しては同様の効果を得つつ、逆洗の頻度を低減して、濾過処理運転の稼働率を向上したり、濾過処理水を逆洗用水として使用する場合にシステム全体の水回収率を大幅に向上できることを知見した。
【００１３】
すなわち、本発明に係る膜濾過システムおよびその運転方法においては、従来システムのようにポンプによる強制吸引によって濾過処理水を得るのではなく、浸漬槽と後工程との間の水頭差を利用して膜濾過ユニットによる濾過および濾過処理水の後工程への送給を行うので、ポンプ運転動力が不要になりシステム全体が簡素になるとともにランニングコストを低減することができることは勿論のこと、強制吸引でないため膜濾過ユニット中の膜エレメントの閉塞状態に応じて浸漬槽の水位が自然上昇し、この水位上昇の程度により膜エレメントの閉塞状態を容易にかつ適切に把握できるようになり、それに応じて、逆洗実施のタイミングを容易に最適なタイミングに設定できるようになる。したがって、必要かつ十分な逆洗の実施が可能になり、逆洗不足、過剰逆洗を回避できる。その結果、まずこの面から、長期間安定運転の継続をはかることができ、濾過処理水の水質向上、逆洗用水量の低減、濾過処理運転のためのシステムの稼働率向上、それらによるシステム全体としての水回収率の向上などをはかることができる。
【００１４】
また、本発明に係るシステムにおいて、膜濾過ユニットの負荷が予め設定された水位（水頭）に達するまでは、浸漬槽内の水を系外排出せず、排出時には浸漬槽内水を一旦すべて排出して逆洗を実施するようにすれば、浸漬槽内に蓄積した固形物などが濾過膜への再負荷となることを回避でき、少量の用水で極めて効果的な逆洗を行うことができる。また、濾過処理水を逆洗用水として使用する場合においても、システム全体の水回収率を向上でき、さらには、逆洗排水の効率的な固形物濃縮も可能となるので、逆洗排水処理系への負荷も低減できる。
【００１５】
また、本発明者は、浸漬型膜濾過システムにおいては、濾過停止時には、濾過膜面に付着していた被処理水中の固形物などが膜面よりわずかに剥離することを知見して検討を重ねた結果、濾過工程中に短時間の濾過停止時間を挿入することで、濾過膜の閉塞が大幅に軽減されることを発見した。したがって、この方法を本発明に係る方法と併用することで、濾過負荷が設定水頭へ到達する時間が延長され、より回収率が向上し、さらには固形物濃度のより高い逆洗排水を得ることができるようになる。
【００１６】
また、本発明者は、浸漬型膜濾過システムにおいては、濾過停止によって、被処理水中の固形物などが膜面よりわずかに剥離したのちに、従来の逆洗工程に比較して短時間の逆洗を行うことで（本発明においては、浸漬槽内水の全量排出後の逆洗とは別に短時間の逆洗を行うことで）、濾過膜の閉塞が大幅に軽減されることを知見した。この時必要な逆洗水量は浸漬槽容量全体に対して微少量でよいので、浸漬槽へ流入した逆洗水量分を系外へ排出する必要はない。したがって、この方法を本発明に係る方法と併用することで、濾過負荷が設定水頭へ到達する時間が延長され、より回収率が向上し、さらには固形物濃度のより高い逆洗排水を得ることができるようになる。
【００１７】
【発明の実施の形態】
以下に、本発明の望ましい実施の形態を、図面を参照して詳細に説明する。図１は、本発明の一実施態様に係る膜濾過システムを示している。図１において、被処理水１（原水）は、浸漬槽２内へ供給され、浸漬槽２内には、膜濾過ユニット３が浸漬されている。膜濾過ユニット３には、膜濾過ユニット３によって濾過された処理水を浸漬槽２外へと導出する処理水ライン４が接続されている。処理水ライン４は、処理水槽５へと延長され、濾過処理水６が処理水槽５に溜められる。この処理水ライン４には、本実施態様では、濾過操作起動時のみに、および逆洗操作時に運転される吸引ポンプ７が設けられている（つまり、吸引ポンプ７は、濾過操作起動時の濾過処理水６の吸引用ポンプと、逆洗操作時に、ライン８、９を介して処理水槽５内の濾過処理水６の一部を逆洗用水として濾過膜ユニット３に供給するためのポンプとを兼ねている。１０、１１、１２、１３は、これら操作を切り替えるためのバルブを示している。
【００１８】
図１に示したシステムにおいては、処理水槽５が本発明で言う後工程に相当している。浸漬槽２と処理水槽５との間には、水頭差が設定されており、濾過処理時には、必ず、浸漬槽２内の水位が、処理水槽５内の水位よりも高くなるように設定されている。この水頭差を利用して、膜濾過ユニット３による濾過および処理水ライン４を介しての濾過処理水の処理水槽５内への送給が行われる。このように水頭差を利用しているため、基本的に濾過処理時には動力は不要である（ただし、後述の如く、本実施態様では、起動時の安定運転化のために、濾過操作起動時のみ、吸引ポンプ７を作動させる）。また、濾過処理中に吸引ポンプ７の制御等も不要であり、システム全体の構成が簡素化されている。
【００１９】
濾過処理の進行とともに膜濾過ユニット３の膜面に被処理水中の固形物等が捕捉され、差圧上昇により浸漬槽２内の水位が上昇するが、この水位の上昇度合と差圧上昇度合とは対応していると考えられるので、逆洗を必要とする差圧上昇度合に至った時点を上昇した水位で検知するために、逆洗実施の判定用およびそのときの浸漬槽２内の水を排出するための水位が、排出・逆洗設定水位１４として浸漬槽２に設定されている。実際の水位がこの設定水位１４に到達した場合、センサー１５によって検知できるようになっている。このセンサー１５による検知と、後述の浸漬槽２内からの排水操作、および逆洗のための吸引ポンプ７の作動および各バルブ１０、１１、１２、１３、１７の動作を連動させることができる。浸漬槽２の底部には、逆洗直前の浸漬槽２内の水、および逆洗水を浸漬槽２内から排出するために、排水ライン１６および開閉バルブ１７が接続されている。
【００２０】
上記のような膜濾過システムにおいては、濾過時には、被処理水１は浸漬槽２内へ導入され、膜濾過ユニット３を介して水頭差を利用して濾過され、得られた濾過処理水６が水頭差により処理水槽５に送給される。吸引ポンプ７は濾過初期に膜濾過ユニット３と処理水ライン４の濾過水流出配管を満水とするために起動し、膜濾過ユニット３と周辺配管が満水となった後は停止する。吸引ポンプ７停止後、膜濾過は水頭差によって継続される。濾過水量は被処理水１の流入量を制御することで、定量に保持される。
【００２１】
浸漬槽２の水位は濾過に伴って濾過膜が閉塞するとともに上昇していく。浸漬槽２には、浸漬槽２内水を排出する水位１４が設定されているので、浸漬槽２内水位が設定水位１４に到達した時点で、排水ライン１６より浸漬槽２内水を全量排出する。設定水位１４への到達によって、濾過膜の閉塞状態が逆洗すべきタイミングに到達したことを精度よく検知でき、最適なタイミングで浸漬槽２内水の全量排出、続いて逆洗が実施される。
【００２２】
浸漬槽２内水を全量排出後、逆洗工程へ移行する。逆洗時には被処理水１の流入は停止しており、吸引ポンプ７によって濾過処理水が濾過時とは逆方向に膜濾過ユニット３へ導入される。逆洗排水は浸漬槽２内へ受けられて、排水ライン１６より排出される。
【００２３】
なお、図１に示すシステムは本発明の実施の形態の一例を示すものであって、本発明はその要旨を越えない限り、何ら図示のものに限定されるものではない。
【００２４】
膜濾過ユニット３のエレメント形状には、中空糸膜、管状膜、平膜などがありいずれの形状のものでも本発明に用いることができる。
【００２５】
濾過膜の素材には、ポリアクリロニトリル、ポリスルフォン、ポリフッ化ビニリデン、ポリプロピレン、ポリエチレン、酢酸セルロース、セラミック、燒結金属など分離膜に用いられているあらゆる素材が使用可能である。
【００２６】
濾過膜の分離孔径はその処理用途によって、様々なものが使用可能であるが、通常は分画分子量数万程度から分離孔径数μｍの分離膜が適用される。
【００２７】
本発明における被処理水は、特に限定されるものではなく、河川水、湖沼水、地下水、工業用水、上水、各種排水に適用可能である。
【００２８】
浸漬槽２内水を全量排出する設定水位１４は、膜濾過ユニット３が浸漬される水位ならば特に限定はないが、好ましくは、濾過膜上端から１０００ｍｍ〜４０００ｍｍの高さで設定する。
【００２９】
水位１４の設定機器（検出機器）はレベルセンサーや圧力計、フロートスイッチなど、浸漬槽水位を検知できるものであれば、いかなる方法、機器も適用可能である。とくに上昇してくる水位を連続的に検出できるものであれば、水位の上昇度合や膜差圧の上昇度合を連続的にモニターできるので、上昇度合の途中経過まで知ることができ、被処理水の性状変化などの観測に利用することも可能となる。
【００３０】
浸漬槽の底部形状は、発明の実施の形態では特別に図示していないが、ホッパー形状として最深部に排水管を設置したり、効率的に排水、排泥可能な形状あるいは機器であれば、何ら限定されるものではない。
【００３１】
膜濾過補助用の吸引手段についても特に制限されるものはなく、発明の実施の形態で示した吸引ポンプ７の他に、サイフォン構造、エゼクターやその他真空発生手段を適用することができる。また、特に膜濾過補助用の吸引手段が必要ない場合には、省略することも可能である。
【００３２】
本発明に係る浸漬型膜濾過システムには凝集剤を使用することもあり、使用する凝集薬品は、ポリ塩化アルミニウム、硫酸ばんど、塩化鉄、硫酸鉄などの無機凝集剤のほかに、アクリルアミド系などの有機高分子凝集剤も適用可能であり、さらには各種凝集補助剤や酸、アルカリなどのｐＨ調整薬品も添加薬品として使用可能である。
【００３３】
本発明に係る浸漬型膜濾過システムにおいては、膜濾過ユニット底部に散気設備を設ける方法もあり、散気設備はブロアと散気管を用いる方法や、空気源としてコンプレッサーやその他の機器、散気には散気板などの微細気泡を発生できる機器などいかなる方法も採用可能である。
【００３４】
【実施例】
以下に、参考例および比較例を挙げて本発明をより具体的に説明する。
本発明の実施の形態で述べた、図１の装置を使用して、河川表流水より上水を得る目的で比較運転を実施した。
【００３５】
膜濾過ユニットには、ポリエチレン製、中空糸ＭＦ膜、分画孔径０．１μｍ、有効膜面積４ｍ²を用いて、濾過流量は４ｍ³／日の定流量運転とした。浸漬槽容量は０．２５ｍ³とした。
【００３６】
参考例１
浸漬槽内排出水位を濾過膜上端より２０００ｍｍで設定し、逆洗を浸漬槽内水全量排出後、流量０．５ｍ^３／ｈで３０秒間行う運転を実施した。
【００３７】
参考例２
浸漬槽内排出水位を濾過膜上端より２０００ｍｍで設定し、濾過工程中に６０分ごとに３０秒間の濾過停止時間を設け、逆洗を浸漬槽内水全量排出後、流量０．５ｍ^３／ｈで３０秒間行う運転を実施した。
【００３８】
比較例１
従来までの運転方法として濾過時間３０分ごとに３０秒間の逆洗を実施し、逆洗ごとに逆洗で使用した水量分を系外排出する方法での運転も実施した。逆洗条件は、参考例と同様の流量０．５ｍ^３／ｈで３０秒間とした。
【００３９】
参考例１、参考例２と比較例１について、濾過吸引圧力（膜差圧）の経時変化を図２に、回収率と排泥濃度を表１に示す。
【００４０】
【表１】

【００４１】
表１より、参考例１、参考例２ともに比較例１より回収率が高く、また、排水中の固形物濃度も参考例１、参考例２の方が高いことが確認され、本発明による浸漬型膜濾過システムが従来システムに比較して回収率、排水処理で有利となることが確認された。また、参考例１と参考例２では、参考例２の方が回収率が高く、排泥濃度も高いことが確認された。
【００４２】
次に図２より、比較例１のシステムでは運転期間約１２０日で膜差圧上昇が顕著で薬品洗浄を実施したのに対し、参考例１の運転では薬品洗浄まで約１８０日の運転が可能であり、参考例２の装置では約２００日の安定運転が可能であることが確認された。本発明によって浸漬型膜濾過システムの安定運転期間を延長できることが確認された。
【００４３】
【発明の効果】
以上説明したように、本発明の膜濾過システムおよびその運転方法によれば、浸漬槽と後工程との間の水頭差を利用して膜濾過ユニットによる濾過および濾過処理水の後工程への送給を行うようにしたので、基本的に、濾過処理時のポンプ運転動力が不要になりシステム全体が簡素になるとともにランニングコストを低減することができる。そして、強制吸引ではないため膜濾過ユニット中の膜エレメントの閉塞状態に応じて浸漬槽の水位が自然上昇し、この自然上昇する水位を膜差圧に対応する状態量として有効に利用できるようになり、上昇度合に応じて、逆洗実施のタイミングを容易に最適なタイミングに設定できるようになる。必要最小限の、かつ適切な逆洗を実施することにより、濾過処理の長期間にわたる安定運転の継続、濾過処理運転のためのシステムの稼働率向上、濾過処理水の水質向上、逆洗用水量の低減、それらによるシステム全体としての水回収率の向上などをはかることができる。
【００４４】
また、膜濾過ユニットの負荷が予め設定された水位（水頭）に達するまでは、浸漬槽内の水を系外排出せず、排出時には浸漬槽内水をすべて排出して逆洗を実施するようにすれば、浸漬槽内に蓄積した固形物などが濾過膜への再負荷となることを回避できて、回収率が向上し、さらには、逆洗排水における効率的な固形物濃縮が可能となる。
【００４５】
また、濾過工程中に濾過停止操作を挿入することで、濾過膜の閉塞が大幅に軽減され、膜濾過への負荷が設定水頭へ到達する時間が延長され、より回収率が向上し、さらには固形物濃度の高い逆洗排水を得ることができる。
【００４６】
また、濾過工程中に短時間の濾過停止時間を行った後、従来の逆洗工程あるいは本発明における全量排出後の逆洗工程に比較して短時間の逆洗を行うことで、濾過膜の閉塞が大幅に軽減されることとなり、濾過負荷が設定水頭へ到達する時間が延長され、より回収率が向上し、さらには固形物濃度の高い逆洗排水を得ることができる。
【００４７】
このように、本発明においては、システムの安定運転期間を延長し、薬品洗浄の低減や膜寿命の延長が可能となり、ランニングコストも削減できるなどの効果が得られる。
【図面の簡単な説明】
【図１】本発明の一実施態様に係る膜濾過システムの機器系統図である。
【図２】参考例、比較例における運転日数と吸引圧力（膜差圧）との関係図である。
【符号の説明】
１被処理水
２浸漬槽
３膜濾過ユニット
４処理水ライン
５処理水槽
６濾過処理水
７吸引ポンプ
８、９逆洗用のライン
１０、１１、１２、１３、１７バルブ
１４排出・逆洗設定水位
１５センサー
１６排水ライン[0001]
BACKGROUND OF THE INVENTION
In the present invention, a membrane filtration unit having a membrane element such as a microfiltration membrane or an ultrafiltration membrane is immersed in water in a treatment tank (immersion tank), and the filtered treated water that has permeated the membrane element comprises the treatment water tank or the like. The present invention relates to a membrane filtration system for collecting water to a subsequent process, and an operation method thereof.
[0002]
[Prior art]
Many membrane filtration systems have been devised in which membrane filtration units having membrane elements such as microfiltration membranes and ultrafiltration membranes are immersed in water in the immersion tank, and filtered water that has permeated through the membrane elements is collected. For example, in Japanese Patent No. 312174, an apparatus in which a filtration membrane is immersed in a raw water storage tank, filtered water is obtained by pump suction, and the membrane is back-washed with a pressure pump from a treated water tank at regular intervals. It is shown. Although not shown in the patent, generally, surplus water that has flowed back to the storage tank by backwashing is discharged together with solid matter from an extraction valve at the bottom of the storage tank.
[0003]
[Problems to be solved by the invention]
However, the following problems remain in the apparatus as shown in Japanese Patent No. 3124174. First, since filtered water is sucked from the membrane filtration unit by a pump, there is a problem that the apparatus configuration is complicated and the operation cost is high. In addition, since the suction is forced by the pump, there is a problem that it is difficult to grasp the closed state (differential pressure state before and after the membrane) of the membrane element of the membrane filtration unit, and it is difficult to grasp the optimal backwash timing. Therefore, in practice, backwashing for a fixed time is performed every fixed time regardless of the state of the membrane filtration unit, for example, by setting a timer or the like, but it is not always the optimal timing for backwashing. If backwashing is insufficient, the filtration membrane may be clogged, resulting in a decrease in the amount of treated water. If excessive backwashing is performed, the operation rate of the entire system will be reduced as a result of the reduction in filtration processing operation time. In addition, there is a risk that the amount of backwash water used will increase, and the concentration of backwash wastewater will decrease, leading to problems such as reduced efficiency of the treatment (for example, solid-liquid separation treatment). .
[0004]
In addition, in an apparatus as shown in Japanese Patent No. 3124174, solids and agglomerated floc trapped in the filtration membrane are separated from the filtration membrane by backwashing and then deposited on the bottom of the storage tank. The operation is intended to be discharged out of the system together with the water in the storage tank. However, in the case of such an apparatus, the water in the storage tank is convected by the supply of treated water, the release of backwash water, etc., so that the solid matter separated from the membrane surface is settled and concentrated at the bottom of the storage tank. There is almost no. Accordingly, during the continuous filtration operation, the residual solids are gradually accumulated in the storage tank, the solids concentration in the water to be treated is gradually increased, and the load on the filtration membrane is increased. A phenomenon occurs. As a result, membrane clogging is accelerated, causing problems such as a reduction in operating rate, a reduction in recovery rate, an increase in chemical cleaning frequency and a reduction in membrane life, and an increase in running cost.
[0005]
In addition, even if the solid matter in the water to be treated is conveniently settled and concentrated in the storage tank, generally the backwashing of the filtration membrane uses a large amount of backwashing water with a frequency of about several tens of minutes to one hour. As it is implemented, the backwash wastewater often becomes dilute, and the backwash wastewater treatment facility must often be scaled up. Furthermore, when filtered water is used as backwash water, the amount of filtered water that can be supplied to the subsequent process is reduced accordingly, so the water recovery rate cannot be said to be high.
[0006]
Therefore, the problems of the present invention are that the overall system configuration can be simplified and the running cost can be reduced, the optimum timing of backwashing can be easily grasped, and the residual solid concentration in the storage tank gradually increases. It is possible to efficiently avoid the solid matter peeled off due to backwashing and re-loading the filtration membrane, and to maximize the effect of backwashing, and backwashing can be performed with a small amount of water. Membrane filtration system using submerged membrane filtration unit and its operation, which can continue stable operation for a long period of time and can improve the water recovery rate of the whole system, and can also reduce the load on backwash wastewater treatment It is to provide a method.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the membrane filtration system operating method according to the present invention is to filter the treated water that has been supplied with a membrane filtration unit that has been immersed in water in a dipping tank. In the operation method of the membrane filtration system to be fed to, the filtration by the membrane filtration unit and the feeding of the filtered water to the subsequent process using the water head difference between the immersion tank and the subsequent process, and When the water level in the immersion tank reaches a predetermined water level, all the water in the immersion tank is discharged, and then the membrane filtration unit is back-washed, and the water level in the immersion tank reaches the predetermined water level. In the meantime, a backwashing operation is performed one or more times separately from the backwashing after discharging the entire amount of water in the immersion bath .
[0008]
In the operation method of the membrane filtration system, it is desirable to discharge the entire amount of water in the immersion tank when the water level in the immersion tank reaches a predetermined water level, and then backwash the membrane filtration unit.
[0009]
In addition, it is preferable to perform one or more filtration stop operations until the water level in the immersion tank reaches a predetermined water level. Furthermore, until the water level in the immersion tank reaches a level predetermined, apart from the backwash after totally drained of the immersion bath water, implement backwash operation more than once. This backwashing may be performed for a short time as compared with backwashing after discharging the entire amount of water in the immersion bath.
[0010]
The membrane filtration system according to the present invention includes an immersion tank that receives the water to be treated, a membrane filtration unit that is immersed in the water in the immersion tank, and a feed line to the subsequent process of the filtered water by the membrane filtration unit. In the membrane filtration system having, the system leading from the inside of the immersion tank to the post-process through the membrane filtration unit is configured to be a system that feeds water using the water head difference between the immersion tank and the post-process, and the immersion The tank is provided with a means for detecting the degree of rise in the water level in the immersion tank, the backwash line of the membrane filtration unit is connected to the feed line to the subsequent process, and the backwash line is used as a signal from the detector. It is configured to be interlocked and backwashable, and is connected to a drain line capable of discharging all the water in the immersion tank to the immersion tank, and when the water level in the immersion tank reaches a predetermined water level, Drain all of the water and then use a membrane filtration unit. In addition to backwashing after draining the entire amount of water in the immersion tank, perform one or more backwash operations until the water level in the immersion tank reaches a predetermined water level. it consists those characterized by that.
[0011]
In this membrane filtration system, the supply line to the back end processing, to connect the backwash line of membrane filtration units, a backwash line, linked operations can configure the signal from said detecting means. In addition, a drainage line capable of discharging all the water in the immersion tank is connected to the immersion tank .
[0012]
In the conventional membrane filtration apparatus, the backwashing operation is repeated at a frequency of several tens of minutes to 1 hour for the purpose of suppressing the clogging of the filtration membrane as much as possible, and the solid matter peeled off by backwashing is accumulated in the immersion tank. It was. The present inventor pays attention to this backwashing process, and rather than the frequency of backwashing, the fact that the removed solid is reloaded on the filtration membrane has a greater influence on the clogging of the filtration membrane. I found out. That is, it was found that the stable operation of the filtration membrane can be achieved by reliably discharging solids and the like separated by backwashing out of the system rather than increasing the frequency of backwashing. Furthermore, the present inventor has the same effect on the washing method as compared with the conventional method in which the back washing is performed in a short time by setting the timer when the filtration load of the filtration membrane is increased to some extent. It was found that the water recovery rate of the entire system can be significantly improved when the frequency of backwashing is reduced and the operation rate of the filtration treatment operation is improved or when the filtered water is used as backwashing water.
[0013]
That is, in the membrane filtration system and the operation method thereof according to the present invention, the filtered water is not obtained by forced suction by a pump as in the conventional system, but the water head difference between the immersion tank and the subsequent process is utilized. Since the filtration by the membrane filtration unit and the supply of the filtered water to the subsequent process are performed, the pump operating power is not required, the entire system is simplified and the running cost can be reduced. Therefore, the water level of the immersion tank rises naturally according to the clogged state of the membrane element in the membrane filtration unit, and the clogged state of the membrane element can be easily and appropriately grasped according to the degree of this water level rise, The timing of backwashing can be easily set to the optimal timing. Accordingly, necessary and sufficient backwashing can be performed, and insufficient backwashing and excessive backwashing can be avoided. As a result, first of all, from this aspect, stable operation can be continued for a long time, improving the quality of filtered water, reducing the amount of backwash water, improving the operating rate of the system for filtering operation, and the entire system As a result, the water recovery rate can be improved.
[0014]
Further, in the system according to the present invention, the water in the immersion tank is not discharged outside the system until the load of the membrane filtration unit reaches a preset water level (water head), and all the water in the immersion tank is once discharged at the time of discharge. If backwashing is performed, it is possible to avoid the solid matter accumulated in the immersion tank from being reloaded on the filtration membrane, and to perform extremely effective backwashing with a small amount of water. . In addition, even when filtered water is used as backwash water, the water recovery rate of the entire system can be improved, and moreover, it is possible to concentrate solids efficiently in backwash wastewater. The load on can also be reduced.
[0015]
In addition, the present inventor has repeatedly studied in the submerged membrane filtration system, knowing that the solid matter in the water to be treated attached to the filtration membrane surface slightly peels off the membrane surface when the filtration is stopped. As a result, it was found that the clogging of the filtration membrane was significantly reduced by inserting a short filtration stop time during the filtration process. Therefore, when this method is used in combination with the method according to the present invention, the time for the filtration load to reach the set head is extended, the recovery rate is further improved, and further backwash drainage with a higher solid matter concentration is obtained. Will be able to.
[0016]
In addition, in the submerged membrane filtration system, the present inventor confirmed that the solid matter in the water to be treated is slightly separated from the membrane surface by stopping the filtration, and then the reverse filtration is performed for a short time compared to the conventional backwashing process. It was found that by performing washing (in the present invention, by performing backwashing for a short time separately from backwashing after discharging the entire amount of water in the immersion tank), the clogging of the filtration membrane is greatly reduced. . Since the amount of backwash water required at this time may be very small with respect to the entire immersion tank capacity, it is not necessary to discharge the amount of backwash water flowing into the immersion tank out of the system. Therefore, when this method is used in combination with the method according to the present invention, the time for the filtration load to reach the set head is extended, the recovery rate is further improved, and further backwash drainage with a higher solid matter concentration is obtained. Will be able to.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a membrane filtration system according to an embodiment of the present invention. In FIG. 1, treated water 1 (raw water) is supplied into an immersion tank 2, and a membrane filtration unit 3 is immersed in the immersion tank 2. A treated water line 4 is connected to the membrane filtration unit 3 for leading the treated water filtered by the membrane filtration unit 3 out of the immersion tank 2. The treated water line 4 is extended to the treated water tank 5, and filtered treated water 6 is stored in the treated water tank 5. In this embodiment, the treated water line 4 is provided with a suction pump 7 that is operated only when the filtration operation is started and when the backwash operation is performed (that is, the suction pump 7 is filtered when the filtration operation is started). A pump for sucking the treated water 6 and a pump for supplying a part of the filtered treated water 6 in the treated water tank 5 as backwash water to the filtration membrane unit 3 through the

lines

8 and 9 during the backwash operation.

Reference numerals

10, 11, 12, and 13 denote valves for switching these operations.
[0018]
In the system shown in FIG. 1, the treated water tank 5 corresponds to the post-process described in the present invention. A water head difference is set between the immersion tank 2 and the treated water tank 5, and the water level in the immersion tank 2 is always set higher than the water level in the treated water tank 5 at the time of filtration treatment. Yes. Utilizing this water head difference, filtration by the membrane filtration unit 3 and supply of the filtered treated water into the treated water tank 5 through the treated water line 4 are performed. Since the head differential is used in this way, basically no power is required during the filtration process (however, as will be described later, in this embodiment, only when the filtration operation is started for stable operation at the time of startup. The suction pump 7 is operated). Further, it is not necessary to control the suction pump 7 during the filtration process, and the configuration of the entire system is simplified.
[0019]
As the filtration process proceeds, solid matter in the water to be treated is trapped on the membrane surface of the membrane filtration unit 3, and the water level in the immersion tank 2 rises due to the increase in the pressure difference. Therefore, in order to detect the point of time when the differential pressure increase that requires backwashing is reached, the water level in the immersion bath 2 is determined for the backwashing determination. The water level for discharging water is set in the immersion tank 2 as the discharge / backwash setting water level 14. When the actual water level reaches the set water level 14, it can be detected by the sensor 15. The detection by the sensor 15 can be linked to the operation of the suction pump 7 and the operation of the

valves

10, 11, 12, 13, and 17 for the drainage operation from the immersion tank 2 to be described later and backwashing. A drain line 16 and an open / close valve 17 are connected to the bottom of the immersion tank 2 in order to discharge the water in the immersion tank 2 immediately before the backwash and the backwash water from the immersion tank 2.
[0020]
In the membrane filtration system as described above, at the time of filtration, the treated water 1 is introduced into the immersion tank 2 and filtered using the water head difference through the membrane filtration unit 3, and the obtained filtered treated water 6 is obtained. It is fed to the treated water tank 5 by the water head difference. The suction pump 7 is started to fill the filtrate outlet pipe of the membrane filtration unit 3 and the treated water line 4 at the initial stage of filtration, and is stopped after the membrane filtration unit 3 and the surrounding pipes are full. After the suction pump 7 is stopped, the membrane filtration is continued by the water head difference. The amount of filtered water is kept constant by controlling the amount of inflow of the treated water 1.
[0021]
The water level in the dipping tank 2 rises as the filtration membrane is blocked with filtration. Since the water level 14 for discharging the water in the immersion tank 2 is set in the immersion tank 2, all the water in the immersion tank 2 is discharged from the drain line 16 when the water level in the immersion tank 2 reaches the set water level 14. To do. By reaching the set water level 14, it can be accurately detected that the filtration membrane has reached the timing to be backwashed, and all the water in the immersion tank 2 is discharged at the optimum timing, followed by backwashing. .
[0022]
After the total amount of water in the immersion tank 2 is discharged, the process proceeds to the back washing process. At the time of backwashing, the inflow of the treated water 1 is stopped, and the filtered water is introduced into the membrane filtration unit 3 by the suction pump 7 in the direction opposite to that at the time of filtration. The backwash waste water is received in the immersion tank 2 and discharged from the drain line 16.
[0023]
The system shown in FIG. 1 shows an example of an embodiment of the present invention, and the present invention is not limited to the illustrated one as long as it does not exceed the gist of the present invention.
[0024]
The element shape of the membrane filtration unit 3 includes a hollow fiber membrane, a tubular membrane, and a flat membrane, and any shape can be used in the present invention.
[0025]
Any material used for the separation membrane such as polyacrylonitrile, polysulfone, polyvinylidene fluoride, polypropylene, polyethylene, cellulose acetate, ceramic, and sintered metal can be used as the material for the filtration membrane.
[0026]
Various separation pore diameters of the filtration membrane can be used depending on the processing application. Usually, a separation membrane having a fractional molecular weight of about tens of thousands to a separation pore diameter of several μm is applied.
[0027]
The treated water in the present invention is not particularly limited, and can be applied to river water, lake water, ground water, industrial water, tap water, and various types of waste water.
[0028]
The set water level 14 for discharging the entire amount of water in the immersion tank 2 is not particularly limited as long as the membrane filtration unit 3 is immersed therein, but is preferably set at a height of 1000 mm to 4000 mm from the upper end of the filtration membrane.
[0029]
As the setting device (detection device) for the water level 14, any method and device can be applied as long as they can detect the immersion tank water level, such as a level sensor, a pressure gauge, and a float switch. In particular, if the rising water level can be detected continuously, the rising level of the water level and the rising pressure of the membrane differential pressure can be monitored continuously, so that it is possible to know until the middle of the rising level. It can also be used to observe changes in the properties of
[0030]
The bottom shape of the immersion tank is not specifically shown in the embodiment of the invention, but if it is a shape or equipment that can efficiently drain and drain mud, install a drain pipe at the deepest part as a hopper shape, It is not limited at all.
[0031]
The suction means for supporting membrane filtration is not particularly limited, and a siphon structure, an ejector, and other vacuum generation means can be applied in addition to the suction pump 7 shown in the embodiment of the invention. In particular, when a suction means for supporting membrane filtration is not necessary, it can be omitted.
[0032]
In the submerged membrane filtration system according to the present invention, a flocculant may be used, and the flocculant used may be an acrylamide type in addition to an inorganic flocculant such as polyaluminum chloride, sulfate, iron chloride, and iron sulfate. Organic polymer flocculants such as these can also be applied, and various coagulant aids and pH adjusting chemicals such as acids and alkalis can be used as additive chemicals.
[0033]
In the submerged membrane filtration system according to the present invention, there is also a method of providing a diffuser facility at the bottom of the membrane filtration unit. The diffuser facility is a method using a blower and a diffuser tube, a compressor or other equipment as an air source, a diffuser Any method such as a device that can generate fine bubbles, such as a diffuser plate, can be used.
[0034]
【Example】
Hereinafter, the present invention will be described more specifically with reference to reference examples and comparative examples.
Using the apparatus of FIG. 1 described in the embodiment of the present invention, a comparative operation was carried out for the purpose of obtaining clean water from river surface water.
[0035]
The membrane filtration unit was made of polyethylene, hollow fiber MF membrane, fractional pore size 0.1 μm, effective membrane area 4 m ² , and the filtration flow rate was constant flow rate operation of 4 m ³ / day. The immersion tank capacity was 0.25 m ³ .
[0036]
Reference example 1
The discharge water level in the immersion tank was set at 2000 mm from the upper end of the filtration membrane, and after the total amount of water in the immersion tank was discharged, an operation was carried out for 30 seconds at a flow rate of 0.5 m ³ / h.
[0037]
Reference example 2
The discharge water level in the immersion tank is set at 2000 mm from the upper end of the filtration membrane, a filtration stop time of 30 seconds is provided every 60 minutes during the filtration process, and the flow rate is 0.5 m ³ / h after discharging all the water in the immersion tank. The operation for 30 seconds was performed.
[0038]
Comparative Example 1
As a conventional operation method, backwashing for 30 seconds was performed every 30 minutes of filtration time, and operation was also performed by discharging the amount of water used in backwashing every time backwashing. The backwash condition was 30 seconds at a flow rate of 0.5 m ³ / h similar to the reference example.
[0039]
With respect to Reference Example 1, Reference Example 2 and Comparative Example 1, the time-dependent change in filtration suction pressure (membrane differential pressure) is shown in FIG.
[0040]
[Table 1]

[0041]
From Table 1, it is confirmed that both Reference Example 1 and Reference Example 2 have a higher recovery rate than Comparative Example 1, and that the solids concentration in the wastewater is higher in Reference Example 1 and Reference Example 2, and the immersion according to the present invention. It was confirmed that the mold membrane filtration system is more advantageous in the recovery rate and wastewater treatment than the conventional system. Moreover, in Reference Example 1 and Reference Example 2, it was confirmed that Reference Example 2 had a higher recovery rate and a higher sludge concentration.
[0042]
Next, as shown in FIG. 2, in the system of Comparative Example 1, the increase in the membrane differential pressure was remarkable in the operation period of about 120 days, and the chemical cleaning was performed. In the operation of Reference Example 1, the operation was possible for about 180 days until the chemical cleaning. Thus, it was confirmed that the apparatus of Reference Example 2 was capable of stable operation for about 200 days. It was confirmed that the stable operation period of the submerged membrane filtration system can be extended by the present invention.
[0043]
【The invention's effect】
As described above, according to the membrane filtration system and the operation method of the present invention, the filtration by the membrane filtration unit and the post-treatment water are sent to the subsequent process using the water head difference between the immersion tank and the subsequent process. Since the supply is performed, basically, the pump driving power during the filtration process is not required, the entire system is simplified, and the running cost can be reduced. And since it is not forced suction, the water level of the immersion tank naturally rises according to the clogged state of the membrane element in the membrane filtration unit, so that this naturally rising water level can be effectively used as a state quantity corresponding to the membrane differential pressure. Accordingly, the timing of backwashing can be easily set to the optimum timing according to the degree of increase. Maintaining stable operation over a long period of filtration processing, improving the system availability for filtration processing operation, improving the quality of filtered water, and amount of backwash water by implementing the minimum necessary and appropriate backwashing And the improvement of the water recovery rate of the entire system can be achieved.
[0044]
Also, until the load on the membrane filtration unit reaches a preset water level (water head), the water in the immersion tank is not discharged out of the system, and all the water in the immersion tank is discharged at the time of discharge to perform backwashing. By doing so, it is possible to avoid the solid matter accumulated in the immersion tank from being reloaded on the filtration membrane, improving the recovery rate, and further enabling efficient solid concentration in the backwash drainage. Become.
[0045]
In addition, by inserting a filtration stop operation during the filtration step, the filtration membrane is greatly blocked, the time for the membrane filtration load to reach the set head is extended, and the recovery rate is further improved. Backwash wastewater with a high solids concentration can be obtained.
[0046]
In addition, after performing a short filtration stop time during the filtration process, by performing a short backwashing compared to the conventional backwashing process or the backwashing process after discharging the entire amount in the present invention, the filtration membrane The blockage is greatly reduced, the time for the filtration load to reach the set head is extended, the recovery rate is further improved, and the backwash drainage with a high solid matter concentration can be obtained.
[0047]
As described above, in the present invention, it is possible to extend the stable operation period of the system, reduce chemical cleaning, extend the membrane life, and reduce the running cost.
[Brief description of the drawings]
FIG. 1 is an equipment system diagram of a membrane filtration system according to an embodiment of the present invention.
FIG. 2 is a diagram showing the relationship between the number of operating days and suction pressure (membrane differential pressure) in a reference example and a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Water to be treated 2 Immersion tank 3 Membrane filtration unit 4 Treatment water line 5 Treatment water tank 6 Filtration water 7

Suction pump

8, 9 Line for back washing 10, 11, 12, 13, 17 Valve 14 Discharge / back washing set water level 15 Sensor 16 Drainage line

Claims

Filtration and filtration by the membrane filtration unit in the operation method of the membrane filtration system in which the treated water that has been supplied is filtered by a membrane filtration unit immersed in the water in the immersion tank, and the filtered water is fed to the subsequent process. The water in the immersion tank is supplied when the treated water is supplied to the subsequent process using the difference in water head between the immersion tank and the subsequent process, and the water level in the immersion tank reaches a predetermined water level. In addition to backwashing the membrane filtration unit, the membrane filtration unit is backwashed until the water level in the immersion tank reaches a predetermined water level. A method for operating a membrane filtration system, comprising performing one or more backwash operations .

Until the water level in the immersion tank reaches a level predetermined to perform the filtering operation of stopping one or more times, membrane filtration system method of operation of Claim 1.

In a membrane filtration system comprising: a soaking tank that receives water to be treated; a membrane filtration unit that is soaked in water in the soaking tank; and a feed line for post-treatment water that is filtered by the membrane filtration unit. a system leading to the rear step through the membrane filtration unit from the inner, together constitute the system of water by using a water head difference between the dipping bath and post-process, the increase in water level in the immersion tank to immersion tank A degree detection means is provided , and a backwash line of the membrane filtration unit is connected to the feed line to the subsequent process, and the backwash line is configured to be backwashable in conjunction with a signal from the detection means, A drainage line capable of discharging all the water in the immersion tank is connected to the immersion tank, and when the water level in the immersion tank reaches a predetermined water level, all the water in the immersion tank is discharged, and then the membrane filtration unit The water level in the immersion tank Before reaching the predetermined water level, membrane filtration system which comprises carrying out the backwashing operation apart of more than once the backwash after totally drained of the immersion bath water.