JP3570030B2

JP3570030B2 - Cleaning method of immersion type membrane separation device

Info

Publication number: JP3570030B2
Application number: JP21171295A
Authority: JP
Inventors: 幹夫北川; 晃士堀; 哲朗深瀬
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 1995-08-21
Filing date: 1995-08-21
Publication date: 2004-09-29
Anticipated expiration: 2015-08-21
Also published as: JPH0957074A

Description

【０００１】
【発明の属する技術分野】
本発明は浸漬型膜分離装置の洗浄方法に係り、特に、好気性生物処理反応槽又は、これに連結された槽内に浸漬設置された膜分離装置の膜を安全かつ効率的に洗浄する方法に関する。
【０００２】
【従来の技術】
近年、合併浄化槽、その他の各種生活系排水処理設備において、排水処理設備のコンパクト化と高度な処理水質を安定して得ることを目的として、活性汚泥処理装置や接触曝気処理装置の曝気槽内に中空糸形状のＭＦ（精密濾過）膜やＵＦ（限外濾過）膜モジュールを浸漬した膜分離機付き好気性生物処理装置が開発されている。
【０００３】
このように曝気槽内に中空糸膜モジュールを浸漬することにより、沈澱槽が不要になるとともに、生物処理反応槽内の生物濃度を高めることができることから、原水の水量変動や水質変動に対しても安定した高度な処理を継続的に行うことが可能となる上に、処理水中に汚泥や原水のＳＳが流出することも皆無となって、運転管理が容易となる。
【０００４】
しかしながら、曝気槽に浸漬した膜モジュールには、膜の表面に原水中の蛋白質や脂質等の種々の汚染物質が付着し、経時により膜の透過性能を大幅に低減させる。そのため、汚染物質の付着により、膜の透過性能が低下した場合には、膜の洗浄を行って透過性能を回復させることが必要となる。
【０００５】
従来、この膜の洗浄手段としては、塩酸やカセイソーダ、又は次亜塩素酸ソーダを含有した洗浄水中に曝気槽から取り出した膜を浸漬するか、或いは、膜を曝気槽に浸漬したままの状態で膜の透過液側（二次側）からこれらの洗浄水を注入して、膜の表面に付着した各種の汚染物質を除去する（特開平３−７７６２９号公報，同４−１３１１８２号公報）薬品洗浄法が一般的である。
【０００６】
【発明が解決しようとする課題】
上記従来の薬品洗浄方法のうち、膜を曝気槽から取り出す方法では、膜の取り出し、洗浄後の膜の浸漬作業を要し、効率的ではない。曝気槽に浸漬したままの状態で膜を洗浄する方法であれば、この膜の取り出し、洗浄後の膜の浸漬作業が不要となり、効率的な洗浄を行えるが、塩酸やカセイソーダ、次亜塩素酸ソーダ等の薬品を用いる従来の洗浄方法では、次のような問題があった。
【０００７】
即ち、膜表面の汚染物質が未分解の蛋白質や脂質が主体である場合には、このような薬品洗浄では十分な洗浄効果を得ることができず、温度を高めた高濃度なカセイソーダや次亜塩素酸ソーダを多量に、かつ頻繁に使用したり、カセイソーダや次亜塩素酸ソーダを用いた後、更に塩酸を使用して洗浄を行うなど、洗浄操作が煩雑であった。しかも、このような洗浄法では洗浄用の薬品が使用時に危険性を伴うものであるため、洗浄作業は高度な技術を持った専門の作業員が十分な管理の元に行う必要があるといった問題もあった。
【０００８】
一方で、今後、蛋白質や脂質を高濃度に含有する生活系排水を、よりコンパクトな装置で高度に処理することが必要となり、そのために、膜モジュールを浸漬した曝気槽の採用は、益々増加することが予測されることから、浸漬膜をより効果的に洗浄することができ、しかも安全性の高い洗浄方法を確立することが望まれている。
【０００９】
本発明は上記従来の問題点を解決し、好気性生物処理反応槽又は、これに連結された槽内に浸漬設置された膜分離装置を高い安全性にて効率的に洗浄する浸漬型膜分離装置の洗浄方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明の浸漬型膜分離装置の洗浄方法は、好気性生物処理反応槽内又は、該生物処理反応槽と連結された槽内に浸漬設置された膜分離装置を洗浄する方法において、蛋白質分解酵素を含む洗浄水及び／又は脂質分解酵素を含む洗浄水を膜の透過液流出側から注入して洗浄を行った後、過酸化水素を含む洗浄水を膜の透過液流出側から注入することを特徴とする。
【００１１】
蛋白質や脂質を高濃度に含んだ生活系排水を、中空糸膜モジュールを組み入れた好気性生物処理装置で処理した場合、汚染物質の付着により透過性能が低下した膜を洗浄するに当っては、膜の表面や内部に付着した未分解の蛋白質や脂質からなる汚染物質を効率的に低分子化させるとともに、膜の表面や内部から低分子化した汚染物質を排除することが必要となる。
【００１２】
本発明においては、膜面に付着した蛋白質や脂質からなる汚染物質を低分子化させる手段として、蛋白質分解酵素や脂質分解酵素を含んだ洗浄水を用い、この酵素含有洗浄水を膜透過液側（二次側）から膜内に流入させ、洗浄水中の酵素が膜の原水側（一次側）に透過する際に、膜内や膜表面に付着している汚染物質を低分子化させることにより、安全かつ効率的な洗浄を行う。
【００１３】
更に、このような酵素による洗浄を行った後、過酸化水素を含有する洗浄水を膜の透過液側（二次側）から注入し、酵素により低分子化された汚染物質を分解し、また、過酸化水素の分解で発生する酸素気泡により低分子化した汚染物質を膜面から剥離排除させることにより、より一層高い洗浄効果を得ることができる。
【００１４】
【発明の実施の形態】
以下、図面を参照して本発明を詳細に説明する。
【００１５】
図１は、本発明の浸漬型膜分離装置の洗浄方法の一実施例を示す系統図であって、中空糸膜浸漬型活性汚泥処理装置の中空糸膜モジュールの洗浄に本発明方法を適用した例を示すものである。
【００１６】
図中、１は曝気槽であり、曝気管２を備え、中部には中空糸膜分離装置３が浸漬されている。４は減圧ポンプ、５，６，７は、各々、蛋白質分解酵素含有洗浄水、脂質分解酵素含有洗浄水、過酸化水素含有洗浄水の貯槽である。５Ａ，６Ａ，７Ａはポンプ、１１〜１５の各符号は配管を示す。
【００１７】
まず、本実施例装置の構成及び運転条件等について説明する。
【００１８】
本実施例において、原水は、厨房排水に代表される生活系排水であり、炭水化物以外に蛋白質や脂質を含むものである。基本的には原水は原水調整槽に貯留した後、この活性汚泥処理装置に導入するが、原水量が少ない場合は原水調整槽を省き、直接導入することも可能である。
【００１９】
曝気槽１は、負荷量５Ｋｇ−ＢＯＤ／ｍ^３・ｄａｙ以上の高負荷量運転も可能であるが、原水変動に伴う処理水質の変動を防止する観点から、また発生汚泥量を低減させる面からも２Ｋｇ−ＢＯＤ／ｍ^３・ｄａｙ以下で運転することが好ましい。
【００２０】
この曝気槽１に浸漬された膜分離装置３は、中空糸膜状のＭＦ膜又はＵＦ膜を用いたものであり、この膜分離装置３からは通水量に見合った膜透過液を排出させる。この透過液の排出手段としては、図示の如く、減圧ポンプ４又は真空ポンプを用いて中空糸膜内部を減圧にして透過液を吸引する方法と、槽全体を加圧状態とし、その槽内の圧力を利用して透過液を流出させる方法とがあるが、構造面や運転操作面からは中空糸膜内部を減圧にして透過液を吸引する方法が適当である。この際、連続的に透過液を吸引する方式とせずに、１０分〜３０分間の一定時間吸引後、数分間の一定時間吸引休止を行う間欠吸引方式を採用することにより、膜表面への汚染物質の付着量を低減することができる。
【００２１】
本実施例の装置において、配管１１より曝気槽１に導入された原水は、曝気管２からの曝気空気で好気的に生物処理され、その後、中空糸膜分離装置３で処理される。中空糸膜の透過液は、減圧ポンプ４による吸引で、配管１２より系外へ排出される。
【００２２】
装置の運転により膜面に汚染物質が付着して膜の透過液量が低減した場合には、原水の導入及び減圧ポンプ４を停止し、本発明方法に従って酵素を含んだ洗浄水を透過液側（二次側）から圧入して膜表面の汚染物質を低分子化ないし溶解させて膜の洗浄を行う。
【００２３】
本発明において、酵素洗浄に用いる蛋白質分解酵素としては、ズブチリシンやプロテアーゼ−Ｎ等が、脂質分解酵素としてはリパーゼ−Ｐやリポザイム等が使用可能である。特に、洗浄する膜分離装置の原水が、活性汚泥処理が行われている一般的な家庭の厨房排水を主体とする場合には、蛋白質分解酵素としてプロテアーゼ−Ｎ（天野製薬（株）製）を０．５〜１０重量％、特に２重量％含む洗浄水を用い、更に、脂質分解酵素としてリパーゼ−Ｐ（天野製薬（株）製）を０．５〜１０重量％、特に５重量％含む洗浄水を用いることが適当である。洗浄水量は膜の汚染状況によるが、洗浄圧力として１〜３Ｋｇ／ｃｍ^２に加圧した洗浄水を膜面積１ｍ^２当たり１〜５Ｌ（リットル）用い、最低３０分間は膜内に洗浄水が滞留するような条件で洗浄を行うことが好ましい。
【００２４】
本発明の実施に当り、特に注意すべき点は、蛋白質分解酵素と脂質分解酵素とを併用する際、両酵素を混合しない点である。即ち、両酵素を混合すると、脂質分解酵素が蛋白質分解酵素により不活性化される可能性があるため、蛋白質分解酵素と脂質分解酵素とを併用する場合には、必ず、蛋白質分解酵素を含む洗浄水で洗浄した後、脂質分解酵素を含む洗浄水で洗浄する。或いは、脂質分解酵素を含む洗浄水で洗浄した後、蛋白質分解酵素を含む洗浄水で洗浄する。
【００２５】
なお、洗浄後の洗浄排液中には、十分に多くの活性を持った酵素が含まれているため、洗浄排液に残留している酵素の活性を、曝気槽内液中の蛋白質や脂質の酵素分解に利用することも可能である。その際、曝気槽が曝気状態で曝気槽内の活性汚泥の活性が高いと、洗浄排液中の残留酵素は活性汚泥により分解されてしまうため、残留酵素の酵素活性を有効に活用するためには、曝気を一次停止して、槽内を緩やかな撹拌状態に置くことが好ましい。曝気を停止することで、活性汚泥の活性は一時的に低下し酵素の分解が防止される。
【００２６】
本発明においては、これらの手段で酵素洗浄した後、２〜３重量％の過酸化水素を含有する洗浄水を、膜の透過液側（二次側）から注入し、酵素により低分子化された汚染物質を分解すると共に、過酸化水素の分解時に発生する酸素気泡により膜面から剥離排除する。
【００２７】
なお、この過酸化水素による洗浄時には、曝気を行うか、又は曝気槽内の撹拌を十分に行い、過酸化水素を含んだ洗浄排液を槽内に速やかに拡散・希釈させる。即ち、洗浄排液中に残留している過酸化水素は、活性汚泥への酸素供給源として有効に使用されるが、過酸化水素濃度が高濃度の時は活性汚泥の活性が阻害される。そのため、この過酸化水素による洗浄に当っては、洗浄排液が曝気槽内混合液で希釈された後の過酸化水素濃度が２０００ｍｇ／Ｌ以下になるように、注入量や注入速度を調整すると共に、十分な混合、撹拌を行う必要がある。
【００２８】
図１に示す装置において、具体的な洗浄操作は次の通りである。
【００２９】
即ち、まず、原水の導入を停止すると共に、曝気及び減圧ポンプ４を停止した後、ポンプ５Ａを作動させて貯槽５内の蛋白質分解酵素含有洗浄水を配管１３を経て膜分離装置３の透過液側より所定の流量で所定時間注入する。
【００３０】
その後ポンプ５Ａを停止すると共に、ポンプ６Ａを作動させて、貯槽６内の脂質分解酵素含有洗浄水を配管１４を経て膜分離装置３の透過液側より、所定の流量で所定時間注入する。
【００３１】
このようにして蛋白質分解酵素による洗浄及び脂質分解酵素による洗浄を行った後は、過酸化水素による洗浄を行う。
【００３２】
即ち、ポンプ６Ａを停止すると共に、ポンプ７Ａを作動させて、貯槽７内の過酸化水素含有洗浄水を配管１５を経て膜分離装置３の透過液側より、所定の流量で所定時間注入する。
【００３３】
この際、前述の如く、洗浄排液中の残留過酸化水素を速やかに槽内に拡散・希釈させるために、曝気を再開するなどして十分な撹拌を行う。
【００３４】
過酸化水素による洗浄後は、ポンプ７Ａを停止して、原水の導入を行うと共に、減圧ポンプ４を作動させて処理を再開する。
【００３５】
なお、図示の装置は、曝気槽内に中空糸膜分離装置を設置したものであるが、本発明は、生物反応槽と連結している別な槽内に膜分離装置を浸漬設置し、生物反応槽と膜設置槽との間でポンプやエアーリフトポンプ等の手段で槽内液を移送する方式を採用した装置の洗浄にも適用可能である。
【００３６】
また、洗浄する膜の形態としても、中空糸膜に限らず、例えば平膜、チューブラー膜等の他の形態の膜であっても良い。
【００３７】
【実施例】
以下に実施例を挙げて本発明をより具体的に説明する。
【００３８】
実施例１，比較例１，２
食堂の厨房から排出されるＳＳ：３００〜２２００ｍｇ／Ｌ、ＢＯＤ：５００〜３３００ｍｇ／Ｌ、Ｎ−ヘキサン可溶性物質（脂質由来）：７０〜１２００ｍｇ／Ｌ、有機体窒素（蛋白質由来）：３０〜５５０ｍｇ／Ｌの排水を原水とする図１に示すような装置において、本発明による洗浄効果を調べた。
【００３９】
曝気槽容量は１０００Ｌで、この曝気槽内に、中空糸ＵＦ膜として、有効表面積４ｍ^２の三菱レイヨン（株）製「ステラポア−Ｌ（分画特性０．１μｍ、膜素材ポリエチレン）」を３組浸漬した（中空糸膜の全有効表面積は１２ｍ^２）。装置への原水通水量は６００Ｌ／ｄａｙ、曝気槽容量当たりの負荷量は０．３〜２．０Ｋｇ−ＢＯＤ／ｍ^３・ｄａｙとした。
【００４０】
曝気槽内の汚泥濃度は１００００ｍｇ／Ｌに調整し、曝気槽内水温は２４〜２８℃とした。曝気は曝気槽底部から行い、曝気槽内液のＤＯ濃度を３ｍｇ／Ｌ以上に保持した。処理水は中空糸ＵＦ膜の透過液流出側から減圧ポンプを用いて、減圧下（圧力−０．０５〜−０．１Ｋｇ／ｃｍ^２）、各中空糸ＵＦ膜当り、２００Ｌ／ｄａｙ（３組で６００Ｌ／ｄａｙ）で引き抜いた。この透過液の引き抜きは、２０分間吸引、２分間休止の間欠方式とした。
【００４１】
以上の条件で連続運転を１ケ月間行い、膜透過液（処理水）水質としては、ＢＯＤ：２０ｍｇ／Ｌ以下、Ｎ−ヘキサン可溶性物質：５ｍｇ／Ｌ以下の高水質を安定に得た。
【００４２】
連続運転１ケ月後に３組の中空糸ＵＦ膜を下記の方法で別々に洗浄した。洗浄前後の最大透過液量を水温２５℃の水道水を用いて測定し、結果を表１に示した。
【００４３】
実施例１：蛋白質分解酵素としてプロテアーゼ−Ｎを水道水に２重量％溶解した蛋白質分解酵素含有洗浄水と、脂質分解酵素としてリパーゼ−Ｐを水道水に５重量％溶解した脂質分解酵素含有洗浄水とを用い、先に蛋白質含有洗浄水を１Ｌ／ｈｒの水量で中空糸ＵＦ膜の透過液流出側から３０分間通水した。次に、同様な方法で脂質分解酵素含有洗浄水を同条件で３０分間通水した。最後に過酸化水素を３重量％含んだ水道水を３０分間通水した。
【００４４】
比較例１：４重量％カセイソーダ水溶液（温度７０℃）を、２Ｌ／ｈｒの水量で膜の透過液流出側から３０分間通水し、その後、５重量％塩酸水溶液を２Ｌ／ｈｒの水量で同様に３０分通水し、最後に透過液のｐＨが中性になるまで、水道水を透過液流出側から通水した。
【００４５】
比較例２：カセイソーダ水溶液の代りに４重量％の次亜塩素酸ソーダ水溶液（温度７０℃）を用いたこと以外は比較例１と同様にして洗浄を行った。
【００４６】
【表１】

【００４７】
表１より、蛋白質分解酵素及び脂質分解酵素と過酸化水素による本発明の洗浄方法によれば、カセイソーダと塩酸、又は、次亜塩素酸ソーダと塩酸を用いる従来の洗浄方法に比べて、１．５〜１．８倍の最大透過液量を得ることができ、洗浄効率が大幅に改善されることが明らかである。
【００４８】
【発明の効果】
以上詳述した通り、本発明の浸漬型膜分離装置の洗浄方法によれば、
▲１▼ 膜の洗浄を効率的に行うことができるため、洗浄頻度を低減できる。
▲２▼ 酵素による洗浄で、取り扱い上危険な薬品を必要としないため、洗浄作業が容易で、専門の作業員による高度な管理も不要となる。
▲３▼ 洗浄排液を生物処理反応槽内に排出することが可能となるため、洗浄排液処理が不要となる。
▲４▼ 洗浄排液中に残留している酵素を生物処理反応槽内液中の蛋白質や脂質の酵素分解に、また、過酸化水素を活性汚泥の酸素供給源として、それぞれ有効に活用できる。
といった効果が奏され、好気性生物処理反応槽又は、これに連結された槽内に浸漬設置された膜分離装置を高い安全性にて効率的に洗浄することができる。
【図面の簡単な説明】
【図１】本発明の一実施例方法を示す系統図である。
【符号の説明】
１曝気槽
２曝気管
３中空糸膜分離装置
４減圧ポンプ
５蛋白質分解酵素含有洗浄水貯槽
６脂質分解酵素含有洗浄水貯槽
７過酸化水素含有洗浄水貯槽[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for cleaning an immersion type membrane separation device, and particularly to a method for safely and efficiently cleaning a membrane of an aerobic biological treatment reaction tank or a membrane separation apparatus immersed and installed in a tank connected thereto. About.
[0002]
[Prior art]
In recent years, in merger septic tanks and other various types of domestic wastewater treatment facilities, the purpose of making wastewater treatment facilities more compact and stably obtaining advanced treated water quality is to install activated sludge treatment equipment and contact aeration treatment equipment in the aeration tanks. An aerobic biological treatment apparatus equipped with a membrane separator in which a hollow fiber-shaped MF (microfiltration) membrane or a UF (ultrafiltration) membrane module is immersed has been developed.
[0003]
By immersing the hollow fiber membrane module in the aeration tank in this way, a precipitation tank is not required, and the concentration of organisms in the biological treatment reaction tank can be increased. In addition, stable and advanced treatment can be continuously performed, and sludge and raw water SS do not flow out into the treated water, thereby facilitating operation management.
[0004]
However, on the membrane module immersed in the aeration tank, various contaminants such as proteins and lipids in the raw water adhere to the surface of the membrane, and the permeation performance of the membrane is significantly reduced with time. Therefore, when the permeability of the membrane is reduced due to the attachment of the contaminant, it is necessary to clean the membrane to restore the permeability.
[0005]
Conventionally, as a means for cleaning this film, the film taken out of the aeration tank is immersed in cleaning water containing hydrochloric acid, caustic soda, or sodium hypochlorite, or in a state where the film is immersed in the aeration tank. These washing waters are injected from the permeated liquid side (secondary side) of the membrane to remove various contaminants adhering to the surface of the membrane (JP-A-3-77629, JP-A-4-131182). Washing methods are common.
[0006]
[Problems to be solved by the invention]
Of the above-mentioned conventional chemical cleaning methods, the method of taking out the film from the aeration tank requires the work of taking out the film and immersing the film after cleaning, which is not efficient. If the method is to wash the membrane while it is immersed in the aeration tank, it is not necessary to take out the membrane and immerse the membrane after washing, and it is possible to carry out efficient washing, but hydrochloric acid, caustic soda, hypochlorous acid, etc. The conventional cleaning method using a chemical such as soda has the following problems.
[0007]
In other words, when the contaminants on the membrane surface are mainly composed of undegraded proteins and lipids, a sufficient cleaning effect cannot be obtained by such chemical cleaning, and high-concentration caustic soda or hypoxia at elevated temperatures is used. The washing operation was complicated, such as using a large amount and frequently of sodium chlorate, or using caustic soda or sodium hypochlorite, and then washing with hydrochloric acid. In addition, such cleaning methods involve the dangers of cleaning chemicals during use, and the problem is that cleaning operations must be carried out by well-managed specialists with sufficient skills. There was also.
[0008]
On the other hand, in the future, it will be necessary to treat domestic wastewater containing proteins and lipids at a high concentration with a more compact device, and the use of aeration tanks immersed with membrane modules will increase more and more. Therefore, it is desired to establish a cleaning method which can more effectively clean the immersion film and has high safety.
[0009]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides an immersion type membrane separation for efficiently and efficiently washing a membrane separation apparatus installed in an aerobic biological treatment reaction tank or a tank connected thereto with high safety. An object of the present invention is to provide a method for cleaning an apparatus.
[0010]
[Means for Solving the Problems]
The method for cleaning an immersion type membrane separation device of the present invention is a method for cleaning a membrane separation device immersed and installed in an aerobic biological treatment reaction tank or a tank connected to the biological treatment reaction tank, the method comprising the steps of: After injecting washing water containing lipolytic enzyme and / or washing water containing lipolytic enzyme from the permeate outflow side of the membrane to perform washing , injecting wash water containing hydrogen peroxide from the permeate outflow side of the membrane. Features.
[0011]
When a domestic wastewater containing a high concentration of proteins and lipids is treated with an aerobic biological treatment device that incorporates a hollow fiber membrane module, in cleaning the membrane whose permeation performance has decreased due to the attachment of contaminants, It is necessary to efficiently reduce the molecular weight of undegraded contaminants consisting of undegraded proteins and lipids attached to the surface and inside of the membrane, and to eliminate the low molecular weight contaminants from the surface and inside of the membrane.
[0012]
In the present invention, as a means for reducing the molecular weight of contaminants consisting of proteins and lipids attached to the membrane surface, washing water containing proteolytic enzymes and lipolytic enzymes is used. When the enzyme in the wash water permeates into the raw water side (primary side) of the membrane by flowing into the membrane from the (secondary side), it reduces the contaminants attached to the membrane and on the membrane surface to lower molecules. Perform safe and efficient cleaning.
[0013]
Further, after performing such an enzyme washing, washing water containing hydrogen peroxide is injected from the permeated liquid side (secondary side) of the membrane to decompose contaminants degraded to low molecular weight by the enzyme, and Further, by removing the contaminants degraded by the oxygen bubbles generated by the decomposition of hydrogen peroxide from the film surface, a higher cleaning effect can be obtained.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0015]
FIG. 1 is a system diagram showing an embodiment of a method for cleaning a submerged membrane separation device of the present invention, in which the method of the present invention is applied to cleaning a hollow fiber membrane module of a hollow fiber membrane submerged activated sludge treatment device. This is an example.
[0016]
In the figure, reference numeral 1 denotes an aeration tank provided with an aeration tube 2, and a hollow fiber membrane separation device 3 is immersed in the center. Reference numeral 4 denotes a decompression pump, and

reference numerals

5, 6, and 7 denote storage tanks for proteolytic enzyme-containing wash water, lipolytic enzyme-containing wash water, and hydrogen peroxide-containing wash water, respectively.

Reference numerals

5A, 6A, and 7A indicate pumps, and reference numerals 11 to 15 indicate piping.
[0017]
First, the configuration, operating conditions, and the like of the apparatus of this embodiment will be described.
[0018]
In this embodiment, the raw water is domestic wastewater represented by kitchen wastewater, and contains proteins and lipids in addition to carbohydrates. Basically, raw water is stored in a raw water adjustment tank and then introduced into this activated sludge treatment apparatus. However, when the amount of raw water is small, the raw water adjustment tank can be omitted and directly introduced.
[0019]
The aeration tank 1 can be operated at a high load of 5 kg-BOD / m ³ · day or more, but from the viewpoint of preventing the fluctuation of the treated water quality due to the fluctuation of the raw water, and from the viewpoint of reducing the amount of generated sludge. It is also preferable to operate at 2 kg-BOD / m ³ · day or less.
[0020]
The membrane separator 3 immersed in the aeration tank 1 uses a hollow fiber membrane-like MF membrane or UF membrane, and discharges a membrane permeated liquid corresponding to the flow rate from the membrane separator 3. As a means for discharging the permeated liquid, as shown in the figure, a method in which the inside of the hollow fiber membrane is depressurized by using a decompression pump 4 or a vacuum pump to suction the permeated liquid, There is a method in which the permeate is allowed to flow out using pressure. From the viewpoint of the structure and operation and operation, a method in which the inside of the hollow fiber membrane is depressurized and the permeate is suctioned is appropriate. At this time, the surface of the membrane is contaminated by adopting an intermittent suction system in which suction is stopped for a certain period of time for several minutes after suction for a certain period of time from 10 minutes to 30 minutes instead of a system for continuously sucking the permeate. The amount of substances attached can be reduced.
[0021]
In the apparatus of the present embodiment, the raw water introduced into the aeration tank 1 from the pipe 11 is subjected to aerobic biological treatment with aerated air from the aeration pipe 2, and then treated by the hollow fiber membrane separation device 3. The permeated liquid of the hollow fiber membrane is discharged out of the system from the pipe 12 by suction by the vacuum pump 4.
[0022]
When the operation of the apparatus causes contaminants to adhere to the membrane surface and the permeate volume of the membrane is reduced, the introduction of raw water and the depressurizing pump 4 are stopped, and the washing water containing the enzyme is removed according to the method of the present invention. (Secondary side) to reduce the molecular weight or dissolve contaminants on the membrane surface by press-fitting to wash the membrane.
[0023]
In the present invention, subtilisin and protease-N can be used as the proteolytic enzymes used for enzyme washing, and lipase-P and lipozyme can be used as the lipolytic enzymes. In particular, when the raw water of the membrane separation device to be washed mainly consists of kitchen wastewater of a general home where activated sludge treatment is performed, protease-N (manufactured by Amano Pharmaceutical Co., Ltd.) is used as a protease. Washing water containing 0.5 to 10% by weight, particularly 2% by weight, and further containing 0.5 to 10% by weight, especially 5% by weight of lipase-P (manufactured by Amano Pharmaceutical Co., Ltd.) as a lipolytic enzyme. It is appropriate to use water. The amount of cleaning water depends on the contamination status of the membrane, but the cleaning water pressurized to 1 to ³ kg / cm ² as the cleaning pressure is used in an amount of 1 to ⁵ L (liter) per 1 m ² of the membrane area, and the cleaning water stays in the membrane for at least 30 minutes. It is preferable to perform washing under such conditions.
[0024]
In carrying out the present invention, it should be particularly noted that, when a protease and a lipolytic enzyme are used in combination, the enzymes are not mixed. That is, if both enzymes are mixed, the lipolytic enzyme may be inactivated by the proteolytic enzyme. Therefore, when using the proteolytic enzyme and the lipolytic enzyme in combination, be sure to wash the lipolytic enzyme containing the proteolytic enzyme. After washing with water, the plate is washed with washing water containing a lipolytic enzyme. Alternatively, after washing with washing water containing a lipolytic enzyme, washing is performed with washing water containing a protease.
[0025]
Since the washing wastewater after washing contains an enzyme having a sufficiently large amount of activity, the activity of the enzyme remaining in the washing wastewater is measured by the protein and lipid in the liquid in the aeration tank. It can also be used for enzymatic degradation of. At this time, if the activated sludge in the aeration tank has high activity while the aeration tank is in the aerated state, the residual enzyme in the washing wastewater will be decomposed by the activated sludge. Preferably, the aeration is temporarily stopped and the inside of the tank is kept in a gentle stirring state. By stopping the aeration, the activity of the activated sludge is temporarily reduced, and the decomposition of the enzyme is prevented.
[0026]
In the present invention, after the enzyme is washed by these means, washing water containing 2 to 3% by weight of hydrogen peroxide is injected from the permeated liquid side (secondary side) of the membrane to be depolymerized by the enzyme. while decomposing the contaminants, it peels removed from the membrane surface by the oxygen bubbles generated during the decomposition of hydrogen peroxide.
[0027]
At the time of cleaning with hydrogen peroxide, aeration is performed or the inside of the aeration tank is sufficiently stirred, so that the cleaning wastewater containing hydrogen peroxide is quickly diffused and diluted in the tank. That is, the hydrogen peroxide remaining in the washing wastewater is effectively used as an oxygen supply source to the activated sludge, but when the hydrogen peroxide concentration is high, the activity of the activated sludge is inhibited. Therefore, in this cleaning with hydrogen peroxide, the injection amount and the injection speed are adjusted so that the concentration of hydrogen peroxide after the cleaning effluent is diluted with the mixture in the aeration tank is 2000 mg / L or less. In addition, it is necessary to perform sufficient mixing and stirring.
[0028]
In the apparatus shown in FIG. 1, a specific washing operation is as follows.
[0029]
That is, first, the introduction of raw water is stopped, the aeration and the decompression pump 4 are stopped, and then the pump 5A is operated to remove the protease-containing washing water in the storage tank 5 through the pipe 13 through the permeate of the membrane separation device 3. Inject at a predetermined flow rate from the side for a predetermined time.
[0030]
Thereafter, the pump 5A is stopped, and the pump 6A is operated to inject the lipolytic enzyme-containing washing water in the storage tank 6 from the permeate side of the membrane separation device 3 via the pipe 14 at a predetermined flow rate for a predetermined time.
[0031]
After the washing with the proteolytic enzyme and the washing with the lipolytic enzyme in this manner, washing with hydrogen peroxide is performed.
[0032]
That is, while the pump 6A is stopped, the pump 7A is operated, and the hydrogen peroxide-containing cleaning water in the storage tank 7 is injected through the pipe 15 from the permeate side of the membrane separation device 3 at a predetermined flow rate for a predetermined time.
[0033]
At this time, as described above, in order to quickly diffuse and dilute the residual hydrogen peroxide in the cleaning wastewater into the tank, sufficient agitation is performed by restarting aeration.
[0034]
After the cleaning with hydrogen peroxide, the pump 7A is stopped, the raw water is introduced, and the decompression pump 4 is operated to restart the processing.
[0035]
Although the illustrated device has a hollow fiber membrane separation device installed in an aeration tank, the present invention provides a bioreactor in which a membrane separation device is immersed and installed in another tank connected to a biological reaction tank. The present invention is also applicable to cleaning of an apparatus adopting a method of transferring a liquid in a tank between a reaction tank and a membrane installation tank by means such as a pump or an air lift pump.
[0036]
The form of the membrane to be washed is not limited to the hollow fiber membrane, but may be a membrane of another form such as a flat membrane or a tubular membrane.
[0037]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0038]
Example 1, Comparative Examples 1 and 2
SS discharged from the kitchen of the cafeteria: 300-2200 mg / L, BOD: 500-3300 mg / L, N-hexane soluble substance (derived from lipid): 70-1200 mg / L, organic nitrogen (derived from protein): 30-550 mg The cleaning effect according to the present invention was examined in an apparatus as shown in FIG. 1 using / L wastewater as raw water.
[0039]
The capacity of the aeration tank is 1000 L. In this aeration tank, three sets of “Stellapore-L” (fractionation characteristics: 0.1 μm, polyethylene membrane) manufactured by Mitsubishi Rayon Co., Ltd. having an effective surface area of 4 m ² are formed as hollow fiber UF membranes. It was immersed (the total effective surface area of the hollow fiber membrane was 12 m ² ). Raw water through water to devices 600L / day, load per aeration tank volume was ^{0.3~2.0Kg-BOD / m 3 · day} .
[0040]
The concentration of sludge in the aeration tank was adjusted to 10,000 mg / L, and the temperature of the water in the aeration tank was set to 24-28 ° C. Aeration was performed from the bottom of the aeration tank, and the DO concentration of the liquid in the aeration tank was maintained at 3 mg / L or more. The treated water was decompressed (pressure -0.05 to -0.1 kg / cm ² ) from the permeate outflow side of the hollow fiber UF membrane under reduced pressure (pressure -0.05 to -0.1 kg / cm ² ), and 200 L / day (three sets) per each hollow fiber UF membrane At 600 L / day). This permeate was withdrawn for 20 minutes by an intermittent method with a 2 minute pause.
[0041]
Under the above conditions, continuous operation was performed for one month, and as the water quality of the membrane permeated liquid (treated water), a high water quality of BOD: 20 mg / L or less and N-hexane soluble substance: 5 mg / L or less was stably obtained.
[0042]
One month after continuous operation, three sets of hollow fiber UF membranes were separately washed by the following method. The maximum amount of permeate before and after washing was measured using tap water at a water temperature of 25 ° C., and the results are shown in Table 1.
[0043]
Example 1: Protease-N-containing washing water in which 2% by weight of protease-N was dissolved in tap water as a protease, and lipase-containing washing water in which 5% by weight of lipase-P was dissolved in tap water as a lipolytic enzyme Using the above, the protein-containing washing water was first passed for 30 minutes from the permeate outflow side of the hollow fiber UF membrane at a water amount of 1 L / hr. Next, lipolytic enzyme-containing washing water was passed in the same manner for 30 minutes under the same conditions. Finally, tap water containing 3% by weight of hydrogen peroxide was passed for 30 minutes.
[0044]
Comparative Example 1: A 4% by weight aqueous solution of sodium hydroxide (temperature: 70 ° C.) was passed through the permeate outlet side of the membrane for 30 minutes at a water amount of 2 L / hr, and then a 5% by weight aqueous hydrochloric acid solution was used at 2 L / hr. For 30 minutes, and finally tap water was passed from the permeate outlet side until the pH of the permeate became neutral.
[0045]
Comparative Example 2: Cleaning was performed in the same manner as in Comparative Example 1 except that a 4% by weight aqueous solution of sodium hypochlorite (temperature: 70 ° C.) was used instead of the aqueous solution of sodium hydroxide.
[0046]
[Table 1]

[0047]
As shown in Table 1, according to the cleaning method of the present invention using protease and lipolytic enzyme and hydrogen peroxide, as compared with the conventional cleaning method using caustic soda and hydrochloric acid, or the conventional cleaning method using sodium hypochlorite and hydrochloric acid. It is clear that a maximum permeate volume of 5 to 1.8 times can be obtained, and the cleaning efficiency is greatly improved.
[0048]
【The invention's effect】
As described above in detail, according to the cleaning method of the immersion type membrane separation device of the present invention,
{Circle around (1)} Since the film can be efficiently cleaned, the frequency of cleaning can be reduced.
(2) Since cleaning with enzymes does not require dangerous chemicals in handling, the cleaning operation is easy and sophisticated management by specialized workers is not required.
{Circle around (3)} Since the washing wastewater can be discharged into the biological treatment reaction tank, the washing wastewater treatment becomes unnecessary.
{Circle around (4)} Enzymes remaining in the washing wastewater can be effectively used for enzymatic decomposition of proteins and lipids in the liquid in the biological treatment reaction tank, and hydrogen peroxide can be effectively used as an oxygen supply source for activated sludge.
Thus, the aerobic biological treatment reaction tank or the membrane separation device immersed and installed in the tank connected thereto can be efficiently washed with high safety.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a method according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Aeration tank 2 Aeration tube 3 Hollow fiber membrane separation device 4 Decompression pump 5 Washing water storage tank containing proteolytic enzyme 6 Washing water storage tank containing lipolytic enzyme 7 Washing water storage tank containing hydrogen peroxide

Claims

In a method for cleaning a membrane separation device immersed and installed in an aerobic biological treatment reaction tank or a tank connected to the biological treatment reaction tank, cleaning water containing a protease and / or cleaning containing a lipolytic enzyme A method for cleaning an immersion type membrane separation device, comprising: injecting water from a permeate outflow side of a membrane to perform washing, and then injecting cleaning water containing hydrogen peroxide from a permeate outflow side of the membrane.