JP3894043B2

JP3894043B2 - Operation method of membrane separator

Info

Publication number: JP3894043B2
Application number: JP2002148562A
Authority: JP
Inventors: 義寿伊藤; 卓也常住; 真人大西
Original assignee: Hitachi Plant Technologies Ltd
Current assignee: Hitachi Plant Technologies Ltd
Priority date: 2002-05-23
Filing date: 2002-05-23
Publication date: 2007-03-14
Anticipated expiration: 2022-05-23
Also published as: JP2003340497A

Description

【０００１】
【発明の属する技術分野】
本発明は膜分離装置の運転方法に係り、特に汚泥を膜分離処理して透過液と濃縮汚泥とに分離する膜分離装置の運転方法に関する。
【０００２】
【従来の技術】
廃水処理や浄水処理の分野では、生物学的や物理化学的な処理によって発生した汚泥を膜分離処理して透過液と濃縮汚泥とに分離することが行われている。濃縮のための膜分離装置としては、濃縮汚泥を満たした分離槽内に膜モジュールを浸漬したのものが知られている。この浸漬式の膜分離装置においては、定量の原汚泥を分離槽に連続的に供給しつつ、膜モジュールから吸引する透過液の流量を一定に保持する運転が一般的に行われている。分離槽からオーバーフローして排出される濃縮汚泥の量も原汚泥と透過液の差分として一定となる運転であった。濃縮汚泥の汚泥濃度は原汚泥量と濃縮汚泥量との比である濃縮倍率によって定まる。したがって、上記のような濃縮倍率が一定の運転では原汚泥の汚泥濃度が変動した場合には濃縮汚泥の汚泥濃度も比例して変動する。
【０００３】
【発明が解決しようとする課題】
上述の運転方法によれば量的な観点からは安定な処理が可能であるが、何らかの原因によって原汚泥の汚泥濃度が高くなった時には、濃縮汚泥の汚泥濃度も高くなり、濾過膜の目詰まりなどを誘発して膜分離装置の運転操作上の不具合を招く。また、濃縮汚泥は後段処理として脱水、天日乾燥、焼却などの処理を受けるが、濃縮汚泥の汚泥濃度が変動すると後段処理の負荷や運転が不安定となり、処理性能や効率を低下させるという問題点があった。
【０００４】
このような問題点を解決するために、濃縮汚泥の汚泥濃度を計測し、その計測結果に基づいて濃縮汚泥の汚泥濃度が目標値となるように原汚泥や透過液の流量をフィードバック制御することが考えられる。しかしながら、このような方法はフィードバック制御を実現するための装置構成が複雑で高価になるとともに、原汚泥の汚泥濃度の変動が大きい場合には膜分離装置の負荷も追随して変動することになり、運転の不安定を招く。
本発明の目的は、上記従来技術の問題点を改善し、原汚泥の汚泥濃度の変動が大きい場合でも、複雑なフィードバック制御を行うことなく膜分離装置の負荷を安定に維持し、かつ、最終的に系外に排出する濃縮汚泥の汚泥濃度を目標値に近づけることができる膜分離装置の運転方法を提供することにある。
【０００５】
【課題を解決するための手段】
上記の課題を解決するために、本発明に係る膜分離装置の運転方法は、汚泥供給槽からの供給汚泥を膜分離処理して透過液と濃縮汚泥とに分離する膜分離装置の運転方法であって、膜分離処理を行いつつ膜分離装置から排出される濃縮汚泥の全量を装置外に排出する排出運転と、膜分離処理を行いつつ前記膜分離装置から排出される濃縮汚泥の全量を前記汚泥供給槽に返送する循環運転と、膜分離処理を停止しつつ供給される供給汚泥に相当する量の濃縮汚泥を装置外に排出する押出運転との、いずれかの運転を濃縮汚泥の汚泥濃度に応じて自動的に切り替えることを特徴とする。
【０００６】
また、本発明に係る膜分離装置の運転方法は上記の構成において、前記濃縮汚泥の汚泥濃度を下限値、中間値、上限値の３段階に区分し、前記排出運転の結果、前記濃縮汚泥の汚泥濃度が下降して下限値に達した時には前記循環運転に切り替え、この循環運転の結果、前記濃縮汚泥の汚泥濃度が上昇して中間値に達した時には前記排出運転に切り替え、前記排出運転の結果、濃縮汚泥の汚泥濃度が上限値に達した時には押出運転に切り替え、この押出運転の結果、前記濃縮汚泥の汚泥濃度が下降して前記中間値に達した時には前記排出運転に切り替えることを特徴とする。
また、本発明に係る膜分離装置の運転方法は上記の構成において、前記濃縮汚泥の汚泥濃度を下限値、上限値の２段階に区分し、前記排出運転の結果、前記濃縮汚泥の汚泥濃度が下降して下限値に達した時には前記循環運転を所定時間実行した後に前記排出運転に切り替え、前記排出運転の結果、前記濃縮汚泥の汚泥濃度が上昇して上限値に達した時には前記押出運転を所定時間実行した後に前記排出運転に切り替えることを特徴とする。
なお、本発明において「下限値（中間値、上限値）に達した時」の「達した時」という用語は、「その値に接近した時」「その値に一致した時」「その値を超えた時」のいずれにも理解し得るものとする。
【０００７】
また、本発明に係る膜分離装置の運転方法は上記の構成において、前記膜分離装置は分離槽と、この分離槽内の濃縮汚泥に浸漬された膜モジュールと、濃縮汚泥の液面を一定に保持する濃縮汚泥の排出手段とを具備していることを特徴とする。
【０００８】
【発明の実施の形態】
図１は本発明に係る膜分離装置の運転方法を実施するための装置系統図である。図１において汚泥供給槽１０には管路１２から濃縮対象物である原汚泥が流入する。また、この汚泥供給槽１０には管路１４から後述するように濃縮汚泥が返送される場合がある。汚泥供給槽１０は管路１６によって膜分離装置２０と接続され、汚泥供給槽１０内の汚泥は管路１６の途中に設けた供給ポンプ１８によって、膜分離装置２０に供給される。本発明においては、このような汚泥供給槽１０から膜分離装置２０に供給される汚泥を供給汚泥と定義し、前記原汚泥と区別する。膜分離装置２０は主として分離槽２２と、この分離槽２２内の濃縮汚泥に浸漬された膜モジュール２４とからなる。膜モジュール２４の二次側には管路２６が接続され、この管路２６に設けた吸引ポンプ２８によって、膜モジュール２４の濾過膜を透過した透過液が管路２６から抜き出され、装置外に排出される。また、膜分離によって濃縮された分離槽２２内の濃縮汚泥は、その液面が一定に保持されつつ、オーバーフロー分が管路３０から排出される。
【０００９】
膜モジュール２４の膜材としては有機材料又はセラミック材料で形成された精密濾過膜又は限外濾過膜が用いられる。膜モジュール２４の型式としては浸漬式の中空糸膜、平膜が好ましく、特に円盤状の平膜を回転させるようにした回転平膜式の膜モジュールが汚泥の濃縮用に好都合である。しかしながら、本発明に係る膜分離装置は上記の浸漬式の膜モジュールを用いたものに限らず、例えば管型の膜モジュールを用いたものにも適用可能である。
【００１０】
管路３０から排出された濃縮汚泥は汚泥溜３２を経由したのち、排出ポンプ３４によって管路３６から前記汚泥供給槽１０又は汚泥貯槽３８のいずれか一方に送出される。すなわち、管路３６は循環用の管路１４と排出用の管路４０とに分岐しており、管路１４には切替弁１５が、管路４０には切替弁４２が設けられている。この切替弁１５と切替弁４２の開閉を操作することによって、管路３６からの濃縮汚泥は管路１４を介して汚泥供給槽１０に返送されるか、又は管路４２を介して汚泥貯槽３８に排出される。
切替弁１５と切替弁４２の操作は前記分離槽２２に配設した汚泥濃度計４４の検出信号を取り込む制御器４６によって制御される。また、この制御器４６は汚泥濃度計４４の検出信号に応じて、吸引ポンプ２８の稼動と停止を切り替える信号を出力する機能を備えている。
なお、分離槽２２内の濃縮汚泥の液面を一定に保持する濃縮汚泥の排出手段としては前記したオーバーフローによる方法に限らない。例えば管路３０と排出ポンプ３４とを汚泥溜３２を介さずに直接に接続し、分離槽２２内に設けた液面計の指示値が一定となるように排出ポンプ３４による濃縮汚泥の引き抜き量を制御するようにしてもよい。
【００１１】
上記の構成において、汚泥供給槽１０には管路１２から原汚泥が連続的又は間欠的に流入する。また、後述する循環運転時には汚泥供給槽１０に管路１４から濃縮汚泥が流入する。このように濃縮汚泥が汚泥供給槽１０内に流入する場合には、原汚泥よりは汚泥濃度が比較的高い濃度に調整された供給汚泥が膜分離装置２０に供給される。通常は膜分離装置２０では供給される供給汚泥の流量及び膜モジュール２４から吸引する透過液の流量を一定に保持する運転をする。その結果、分離槽２２をオーバーフローして排出される濃縮汚泥の流量も一定に保持される。なお、分離槽２２内の濃縮汚泥の汚泥濃度は汚泥濃度計４４によって連続的に又は適当な制御間隔で検出され、制御器４６にその検出信号が送信される。
【００１２】
当該膜分離装置２０の運転モードは排出運転、循環運転、押出運転の３種類に区分される。
排出運転は濃縮汚泥の汚泥濃度が目標範囲内の正常な時の運転であり、膜分離処理を行いつつ膜分離装置２０から排出される濃縮汚泥の全量を装置外に排出する。具体的には供給ポンプ１８と吸引ポンプ２８を稼動し、供給汚泥の流量及び膜モジュール２４から吸引する透過液の流量を一定に保持して膜分離処理を行いつつ、切替弁１５を閉、切替弁４２を開として膜分離装置２０から排出される濃縮汚泥を汚泥貯槽３８に排出する。
循環運転は濃縮汚泥の汚泥濃度が比較的低濃度な時の運転であり、膜分離処理を行いつつ膜分離装置２０から排出される濃縮汚泥の全量を汚泥供給槽１０に返送する。具体的には供給ポンプ１８と吸引ポンプ２８を稼動し、供給汚泥の流量及び膜モジュール２４から吸引する透過液の流量を一定に保持して膜分離処理を行いつつ、切替弁１５を開、切替弁４２を閉として膜分離装置２０から排出される濃縮汚泥を汚泥供給槽１０に返送する。この循環運転を行うと汚泥供給槽１０では原汚泥と濃縮汚泥が混合し、供給汚泥の濃縮汚泥が上昇する。その結果、濃縮汚泥の汚泥濃度も上昇する。
押出運転は濃縮汚泥の汚泥濃度が比較的高濃度な時の運転であり、膜分離処理を停止しつつ供給される供給汚泥に相当する量の濃縮汚泥の全量を装置外に排出する。具体的には供給ポンプ１８からの供給汚泥の流量一定に保持するとともに、吸引ポンプ２８を停止して膜分離処理を停止し、切替弁１５を閉、切替弁４２を開として供給汚泥に相当する量の濃縮汚泥を汚泥貯槽３８に排出する。この押出運転を行うと分離槽２２内の濃縮汚泥が逐次、汚泥濃度が低い供給汚泥と置換される。その結果、濃縮汚泥の汚泥濃度が比較的急速に下降する。
【００１３】
上記３種類の運転モードの切り替えは汚泥濃度計４４からの検出信号に応じた制御器４６による前記切替弁１５と切替弁４２の切り替え信号及び吸引ポンプ２８の稼動と停止の切り替え信号によって実行される。図２はその制御手順を示すフローチャートである。排出運転からスタートした場合、濃縮汚泥の汚泥濃度が下限値以上、上限値未満の正常値であれば排出運転を継続し（Ｓ１００）、下限値未満になると循環運転に切り替え（Ｓ１１０）、上限値以上になると押出運転に切り替える（Ｓ１２０）。循環運転をしても汚泥濃度が中間値未満であれば循環運転を継続し（Ｓ１３０）、中間値以上になると排出運転に切り替える（Ｓ１４０）。また、押出運転をしても汚泥濃度が中間値を超える時には押出運転を継続し（Ｓ１５０）、中間値以下になると排出運転に切り替える（Ｓ１６０）。このような運転モードの切り替えによって、原汚泥の汚泥濃度が大幅に変動した場合でも膜分離装置２０から装置外へ排出される濃縮汚泥の汚泥濃度を下限値以上、上限値未満の目標範囲内にほぼ維持することができる。
なお、上記の例は中間値を１点とする場合であるが、本発明はこれに限らない。例えば中間値として中間値▲１▼と中間値▲２▼を設定し、循環運転と排出運転との切り替え制御点として中間値▲１▼を用い、押出運転と排出運転との切り替え制御点として中間値▲２▼を用いるようにしてもよい。
【００１４】
図３は上記の運転モードの切り替え制御を実行した場合に、原汚泥と濃縮汚泥の汚泥濃度の経時変化状況をモデル化して示したものである。（イ）は原汚泥の汚泥濃度の経時変化を示し、例えば標準濃度１.０％に対して、時間帯Ｔ１では０.５％以下、時間帯Ｔ２では１.５％以上に原汚泥の汚泥濃度が変動したと仮定する。（ロ）は原汚泥の濃度変動に伴う濃縮汚泥の汚泥濃度の経時変化を示し、例えば標準濃度４.０％を中間値とし、下限値を３.８％、上限値を４.２％に設定して制御を実行した場合である。汚泥供給槽１０や分離槽２２は相応の容量を有しており、汚泥が一定時間滞留するので、濃縮汚泥の汚泥濃度は原汚泥の濃度変動に対して遅れて、かつ濃度変動をある程度吸収して平均化した状態で変動する。このため、原汚泥の汚泥濃度が標準濃度１.０％を中心に多少変動しても、排出運転Ａを実行すれば濃縮汚泥の汚泥濃度は標準濃度４.０％を中心に比較的安定に推移する。しかしながら、（イ）に示したように原汚泥の汚泥濃度が０.５％以下の時間帯Ｔ１が比較的長時間にわたって継続すると、濃縮汚泥の汚泥濃度は徐々に下降して、終には下限値の３.８％に達する。すると制御器４６は汚泥濃度計４４からの検出信号に応じて切替弁１５を開、切替弁４２を閉とする切り替え信号を出力して、運転モードを循環運転Ｂに切り替える。この循環運転Ｂの結果、濃縮汚泥の汚泥濃度が徐々に上昇し、中間値である標準濃度４.０％に達する。すると制御器４６は汚泥濃度計４４からの検出信号に応じて切替弁１５を閉、切替弁４２を開とする切り替え信号を出力して、運転モードを排出運転Ａに復帰させる。しかしながら、原汚泥の汚泥濃度が０.５％以下の時間帯が継続している場合には排出運転Ａにより、濃縮汚泥の汚泥濃度は再び下降する。したがって、原汚泥の汚泥濃度が０.５％以下の時間帯Ｔ１が継続する期間中はこのような排出運転Ａと循環運転Ｂが交互に繰り返されることになる。
【００１５】
一方、（イ）に示したように原汚泥の汚泥濃度が１.５％以上の時間帯Ｔ２が比較的長時間にわたって継続すると、濃縮汚泥の汚泥濃度は徐々に上昇して、終には上限値を４.２％に達する。すると制御器４６は汚泥濃度計４４からの検出信号に応じて運転モードを排出運転Ａから押出運転Ｃに切り替える。すなわち、切替弁１５を閉、切替弁４２を開とした状態を維持しつつ、供給ポンプ１８からの供給汚泥の流量一定に保持するとともに、吸引ポンプ２８を停止して膜分離処理を停止する。この押出運転Ｃの結果、分離槽２２内の濃縮汚泥が逐次、汚泥濃度が低い供給汚泥と置換され、濃縮汚泥の汚泥濃度が急速に下降して中間値である標準濃度４.０％に達する。すると制御器４６は汚泥濃度計４４からの検出信号に応じて吸引ポンプ２８を再稼動し、運転モードを排出運転Ａに復帰させる。しかしながら、原汚泥の汚泥濃度が１.５％以上の時間帯が継続している場合には排出運転Ａにより、濃縮汚泥の汚泥濃度は再び上昇する。したがって、原汚泥の汚泥濃度が１.５％以上の時間帯Ｔ２が継続する期間中はこのような排出運転Ａと押出運転Ｃが交互に繰り返されることになる。
【００１６】
上述のとおり、本実施の形態によれば原汚泥の汚泥濃度が標準濃度１.０％に対して、０.５％以下や１.５％以上の範囲で大きく変動する場合でも、装置外に排出する濃縮汚泥の汚泥濃度を常に平均約４％（上限４.２％、下限３.８％）の安定した値にすることができる。このため、汚泥濃度の変動に対して原汚泥や透過液の流量制御などの複雑な制御を必要とせず、安定した汚泥の濃縮操作を実施できる。
【００１７】
図４は他の制御手順を示すフローチャートである。排出運転からスタートし、濃縮汚泥の汚泥濃度が下限値以上、上限値未満の正常値であれば排出運転を継続し（Ｓ２００）、下限値未満になると循環運転に切り替え（Ｓ２１０）、上限値以上になると押出運転に切り替える（Ｓ２２０）。循環運転では所定の設定時間Ｔ３が経過するまで運転を継続し（Ｓ２３０）、所定の設定時間Ｔ３を経過すると排出運転に切り替える（Ｓ２４０）。また、押出運転では所定の設定時間Ｔ４が経過するまで運転を継続し（Ｓ２５０）、所定の設定時間Ｔ４を経過すると排出運転に切り替える（Ｓ２６０）。この制御方法によれば、循環運転と押出運転の運転時間をタイマーによって設定するので図２に示した中間値（標準濃度）に基づく制御に比べて、制御の単純化を図ることができる。なお、循環運転と押出運転とでは、濃縮汚泥の汚泥濃度に対する応答性に差がある。したがって、応答が緩慢な循環運転では設定時間Ｔ３を長めとし、応答が敏感な押出運転では設定時間Ｔ４を短めとし、各運転を排出運転に切り替えた際の濃縮汚泥の汚泥濃度が下限値と上限値とのほぼ中間となるように設定することが好ましい。
【００１８】
【発明の効果】
上述のとおり、本発明に係る汚泥の濃縮方法によれば、原汚泥の汚泥濃度の変動が大きい場合でも、複雑なフィードバック制御を行うことなく膜分離装置の負荷を安定に維持し、かつ、最終的に系外に排出する濃縮汚泥の汚泥濃度を一定の目標値に近づけることができる。
【図面の簡単な説明】
【図１】本発明に係る膜分離装置の運転方法を実施するための装置系統図。
【図２】本発明に係る運転方法の実施形態を示すフローチャート。
【図３】本発明に係る運転方法実行した場合に濃縮汚泥などの汚泥濃度の経時変化を例示した説明図。
【図４】本発明に係る運転方法の他の実施形態を示すフローチャート。
【符号の説明】
１０……汚泥供給槽
１５……切替弁
１８……（供給汚泥の）供給ポンプ
２０……膜分離装置
２２……分離槽
２４……膜モジュール
２８……（透過液の）吸引ポンプ
３２……汚泥溜
３４……（濃縮汚泥の）排出ポンプ
３８……汚泥貯槽
４２……切替弁
４２……汚泥濃度計
４６……制御[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for operating a membrane separator, and more particularly, to a method for operating a membrane separator that separates sludge into permeate and concentrated sludge by membrane separation treatment.
[0002]
[Prior art]
In the field of wastewater treatment and water purification treatment, sludge generated by biological or physicochemical treatment is separated into permeate and concentrated sludge by membrane separation treatment. As a membrane separation device for concentration, one in which a membrane module is immersed in a separation tank filled with concentrated sludge is known. In the submerged membrane separation apparatus, an operation is generally performed in which a constant amount of raw sludge is continuously supplied to the separation tank and the flow rate of the permeate sucked from the membrane module is kept constant. The operation was such that the amount of concentrated sludge overflowed from the separation tank was constant as the difference between the raw sludge and the permeate. The sludge concentration of the concentrated sludge is determined by the concentration ratio, which is the ratio of the raw sludge amount and the concentrated sludge amount. Therefore, in the operation where the concentration rate is constant as described above, when the sludge concentration of the raw sludge varies, the sludge concentration of the concentrated sludge also varies in proportion.
[0003]
[Problems to be solved by the invention]
According to the operation method described above, stable treatment is possible from a quantitative point of view, but when the sludge concentration of the raw sludge increases for some reason, the sludge concentration of the concentrated sludge also increases and the filtration membrane is clogged. This causes problems in the operation of the membrane separator. Concentrated sludge is subject to subsequent treatments such as dehydration, sun drying, and incineration, but if the sludge concentration in the concentrated sludge varies, the load and operation of the subsequent treatment will become unstable, reducing the processing performance and efficiency. There was a point.
[0004]
In order to solve such problems, the sludge concentration of the concentrated sludge is measured, and the flow rate of the raw sludge and permeate is feedback controlled so that the sludge concentration of the concentrated sludge becomes the target value based on the measurement result. Can be considered. However, in such a method, the apparatus configuration for realizing feedback control is complicated and expensive, and when the fluctuation of the sludge concentration of the raw sludge is large, the load of the membrane separation apparatus also fluctuates. , Driving instability.
The object of the present invention is to improve the above-mentioned problems of the prior art, stably maintain the load of the membrane separation device without complicated feedback control even when the fluctuation of the sludge concentration of the raw sludge is large, and finally An object of the present invention is to provide a method for operating a membrane separation device that can bring the sludge concentration of concentrated sludge discharged out of the system closer to the target value.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the operation method of the membrane separation apparatus according to the present invention is an operation method of the membrane separation apparatus that separates the supplied sludge from the sludge supply tank into a permeate and concentrated sludge by membrane separation treatment. A discharge operation for discharging the entire amount of the concentrated sludge discharged from the membrane separator while performing the membrane separation treatment, and the total amount of the concentrated sludge discharged from the membrane separator while performing the membrane separation treatment. Concentration sludge concentration is one of the following operations: circulation operation for returning to the sludge supply tank and extrusion operation for discharging the amount of concentrated sludge equivalent to the supply sludge supplied while stopping the membrane separation process. It is characterized by switching automatically according to
[0006]
Moreover, the operation method of the membrane separation apparatus according to the present invention is the above-described configuration, wherein the concentrated sludge concentration is divided into three stages of a lower limit value, an intermediate value, and an upper limit value, and as a result of the discharge operation, When the sludge concentration decreases and reaches the lower limit value, the operation is switched to the circulation operation. As a result of the circulation operation, when the sludge concentration of the concentrated sludge reaches an intermediate value, the operation is switched to the discharge operation. As a result, when the sludge concentration of the concentrated sludge reaches the upper limit value, the operation is switched to the extrusion operation, and as a result of the extrusion operation, when the sludge concentration of the concentrated sludge reaches the intermediate value, the operation is switched to the discharge operation. And
Further, the operation method of the membrane separation apparatus according to the present invention has the above-described configuration, wherein the sludge concentration of the concentrated sludge is divided into two stages of a lower limit value and an upper limit value, and as a result of the discharge operation, the sludge concentration of the concentrated sludge is When the lower limit is reached and the lower limit value is reached, the circulation operation is performed for a predetermined time and then switched to the discharge operation. As a result of the discharge operation, when the sludge concentration of the concentrated sludge reaches the upper limit value, the extrusion operation is performed. It is characterized by switching to the discharge operation after executing for a predetermined time.
In the present invention, the term “when reaching” of “when reaching the lower limit (intermediate value, upper limit)” means “when approaching that value”, “when matching that value”, “ It can be understood at any time when it is exceeded.
[0007]
The operation method of the membrane separation apparatus according to the present invention is the above-described configuration, wherein the membrane separation apparatus has a separation tank, a membrane module immersed in the concentrated sludge in the separation tank, and a liquid level of the concentrated sludge. And a means for discharging the concentrated sludge to be retained.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an apparatus system diagram for carrying out a method of operating a membrane separation apparatus according to the present invention. In FIG. 1, raw sludge that is an object to be concentrated flows into a sludge supply tank 10 from a pipe 12. In addition, concentrated sludge may be returned to the sludge supply tank 10 from the pipeline 14 as will be described later. The sludge supply tank 10 is connected to the membrane separation device 20 by a pipe line 16, and the sludge in the sludge supply tank 10 is supplied to the membrane separation apparatus 20 by a supply pump 18 provided in the middle of the pipe line 16. In the present invention, such sludge supplied from the sludge supply tank 10 to the membrane separation device 20 is defined as supply sludge and is distinguished from the raw sludge. The membrane separation device 20 mainly comprises a separation tank 22 and a membrane module 24 immersed in the concentrated sludge in the separation tank 22. A conduit 26 is connected to the secondary side of the membrane module 24, and a permeate that has permeated through the filtration membrane of the membrane module 24 is extracted from the conduit 26 by a suction pump 28 provided in the conduit 26. To be discharged. The concentrated sludge in the separation tank 22 concentrated by membrane separation is discharged from the conduit 30 while its liquid level is kept constant.
[0009]
As the membrane material of the membrane module 24, a microfiltration membrane or an ultrafiltration membrane formed of an organic material or a ceramic material is used. As a type of the membrane module 24, a submerged hollow fiber membrane or a flat membrane is preferable, and a rotary flat membrane membrane module in which a disk-like flat membrane is rotated is particularly convenient for the concentration of sludge. However, the membrane separation apparatus according to the present invention is not limited to the one using the above-described immersion type membrane module, and is applicable to, for example, one using a tubular membrane module.
[0010]
The concentrated sludge discharged from the pipe line 30 passes through the sludge reservoir 32 and is then sent from the pipe line 36 to either the sludge supply tank 10 or the sludge storage tank 38 by the discharge pump 34. That is, the pipe 36 is branched into a circulation pipe 14 and a discharge pipe 40, and the switching valve 15 is provided in the pipe 14, and the switching valve 42 is provided in the pipe 40. By operating the switching valve 15 and the switching valve 42 to open and close, the concentrated sludge from the pipe line 36 is returned to the sludge supply tank 10 through the pipe line 14, or the sludge storage tank 38 through the pipe line 42. To be discharged.
The operation of the switching valve 15 and the switching valve 42 is controlled by a controller 46 that takes in a detection signal of a sludge concentration meter 44 disposed in the separation tank 22. The controller 46 also has a function of outputting a signal for switching the operation and stop of the suction pump 28 in accordance with the detection signal of the sludge concentration meter 44.
The concentrated sludge discharge means for keeping the liquid level of the concentrated sludge in the separation tank 22 constant is not limited to the above-described overflow method. For example, the conduit 30 and the discharge pump 34 are directly connected without passing through the sludge reservoir 32, and the amount of concentrated sludge drawn by the discharge pump 34 so that the indicated value of the level gauge provided in the separation tank 22 is constant. May be controlled.
[0011]
In the above configuration, the raw sludge flows from the pipe 12 continuously or intermittently into the sludge supply tank 10. Further, during the circulation operation described later, the concentrated sludge flows into the sludge supply tank 10 from the pipeline 14. In this way, when the concentrated sludge flows into the sludge supply tank 10, the supplied sludge having a sludge concentration adjusted to a relatively higher concentration than the original sludge is supplied to the membrane separation device 20. Normally, the membrane separation apparatus 20 operates to keep the supplied sludge flow rate and the permeate flow rate sucked from the membrane module 24 constant. As a result, the flow rate of the concentrated sludge discharged after overflowing the separation tank 22 is also kept constant. The sludge concentration of the concentrated sludge in the separation tank 22 is detected continuously or at an appropriate control interval by the sludge concentration meter 44, and the detection signal is transmitted to the controller 46.
[0012]
The operation mode of the membrane separation device 20 is classified into three types: discharge operation, circulation operation, and extrusion operation.
The discharge operation is an operation when the sludge concentration of the concentrated sludge is normal within the target range, and the entire amount of the concentrated sludge discharged from the membrane separation device 20 is discharged outside the device while performing the membrane separation treatment. Specifically, the supply pump 18 and the suction pump 28 are operated, and the switching valve 15 is closed and switched while performing the membrane separation process while keeping the flow rate of the supplied sludge and the flow rate of the permeate sucked from the membrane module 24 constant. The valve 42 is opened and the concentrated sludge discharged from the membrane separation device 20 is discharged to the sludge storage tank 38.
The circulation operation is an operation when the sludge concentration of the concentrated sludge is relatively low, and the whole amount of the concentrated sludge discharged from the membrane separation device 20 is returned to the sludge supply tank 10 while performing the membrane separation treatment. Specifically, the supply pump 18 and the suction pump 28 are operated, and the switching valve 15 is opened and switched while performing the membrane separation process while keeping the flow rate of the supplied sludge and the flow rate of the permeate sucked from the membrane module 24 constant. The valve 42 is closed and the concentrated sludge discharged from the membrane separator 20 is returned to the sludge supply tank 10. When this circulation operation is performed, the raw sludge and the concentrated sludge are mixed in the sludge supply tank 10, and the concentrated sludge of the supplied sludge rises. As a result, the sludge concentration of the concentrated sludge also increases.
The extrusion operation is an operation when the sludge concentration of the concentrated sludge is relatively high, and the entire amount of the concentrated sludge corresponding to the supplied sludge supplied while the membrane separation process is stopped is discharged out of the apparatus. Specifically, the flow rate of the supplied sludge from the supply pump 18 is kept constant, the suction pump 28 is stopped to stop the membrane separation process, the switching valve 15 is closed, and the switching valve 42 is opened to correspond to the supplied sludge. An amount of concentrated sludge is discharged into the sludge storage tank 38. When this extrusion operation is performed, the concentrated sludge in the separation tank 22 is successively replaced with the supplied sludge having a low sludge concentration. As a result, the sludge concentration of the concentrated sludge decreases relatively rapidly.
[0013]
The switching of the three operation modes is performed by a switching signal for the switching valve 15 and the switching valve 42 and a switching signal for operating and stopping the suction pump 28 by the controller 46 according to the detection signal from the sludge concentration meter 44. . FIG. 2 is a flowchart showing the control procedure. When starting from the discharge operation, if the sludge concentration of the concentrated sludge is a normal value that is not less than the lower limit value and less than the upper limit value, the discharge operation is continued (S100), and if it is less than the lower limit value, the operation is switched to the circulation operation (S110). If it becomes above, it will switch to extrusion operation (S120). Even if the circulation operation is performed, if the sludge concentration is less than the intermediate value, the circulation operation is continued (S130). Further, even if the extrusion operation is performed, the extrusion operation is continued when the sludge concentration exceeds the intermediate value (S150), and when the sludge concentration becomes the intermediate value or less, the operation is switched to the discharge operation (S160). Even if the sludge concentration of the raw sludge varies greatly by such switching of the operation mode, the sludge concentration of the concentrated sludge discharged from the membrane separation device 20 to the outside of the device is within the target range that is not less than the lower limit value and less than the upper limit value. Can be almost maintained.
In the above example, the intermediate value is one point, but the present invention is not limited to this. For example, intermediate value (1) and intermediate value (2) are set as intermediate values, intermediate value (1) is used as a switching control point between circulation operation and discharging operation, and intermediate control point is set as switching operation between extrusion operation and discharging operation. The value {circle over (2)} may be used.
[0014]
FIG. 3 shows a modeled change with time of the sludge concentrations of the raw sludge and the concentrated sludge when the above-described operation mode switching control is executed. (A) shows the change over time in the sludge concentration of the raw sludge. For example, the sludge of the original sludge is 0.5% or less in the time zone T1 and 1.5% or more in the time zone T2 with respect to the standard concentration 1.0%. Assume that the concentration has fluctuated. (B) shows the change over time in the sludge concentration of the concentrated sludge accompanying the change in the concentration of the raw sludge. For example, the standard concentration 4.0% is the intermediate value, the lower limit is 3.8%, and the upper limit is 4.2%. This is a case where control is executed after setting. The sludge supply tank 10 and the separation tank 22 have appropriate capacities, and sludge stays for a certain period of time. Therefore, the sludge concentration of the concentrated sludge is delayed with respect to the concentration fluctuation of the original sludge and absorbs the concentration fluctuation to some extent. Fluctuate in an averaged state. For this reason, even if the sludge concentration of the raw sludge slightly fluctuates around the standard concentration of 1.0%, the sludge concentration of the concentrated sludge becomes relatively stable around the standard concentration of 4.0% if the discharge operation A is executed Transition to. However, as shown in (a), when the time period T1 in which the sludge concentration of the raw sludge is 0.5% or less continues for a relatively long time, the sludge concentration of the concentrated sludge gradually decreases and finally reaches the lower limit. It reaches 3.8% of the value. Then, the controller 46 outputs a switching signal for opening the switching valve 15 and closing the switching valve 42 according to the detection signal from the sludge concentration meter 44, and switches the operation mode to the circulation operation B. As a result of this circulation operation B, the sludge concentration of the concentrated sludge gradually increases and reaches a standard concentration of 4.0%, which is an intermediate value. Then, the controller 46 outputs a switching signal for closing the switching valve 15 and opening the switching valve 42 according to the detection signal from the sludge concentration meter 44, and returns the operation mode to the discharge operation A. However, when the time period in which the sludge concentration of the raw sludge is 0.5% or less continues, the sludge concentration of the concentrated sludge decreases again by the discharge operation A. Accordingly, the discharge operation A and the circulation operation B are alternately repeated during the period in which the time period T1 in which the sludge concentration of the raw sludge is 0.5% or less continues.
[0015]
On the other hand, as shown in (a), when the time period T2 in which the sludge concentration of the raw sludge is 1.5% or more continues for a relatively long time, the sludge concentration of the concentrated sludge gradually increases and finally reaches the upper limit. The value reaches 4.2%. Then, the controller 46 switches the operation mode from the discharge operation A to the extrusion operation C according to the detection signal from the sludge concentration meter 44. That is, while maintaining the state where the switching valve 15 is closed and the switching valve 42 is opened, the flow rate of the supplied sludge from the supply pump 18 is kept constant, and the suction pump 28 is stopped to stop the membrane separation process. As a result of this extrusion operation C, the concentrated sludge in the separation tank 22 is successively replaced with the supplied sludge having a low sludge concentration, and the sludge concentration of the concentrated sludge rapidly decreases to reach the standard concentration of 4.0%. . Then, the controller 46 restarts the suction pump 28 in accordance with the detection signal from the sludge concentration meter 44, and returns the operation mode to the discharge operation A. However, when the time period in which the sludge concentration of the raw sludge is 1.5% or more continues, the sludge concentration of the concentrated sludge increases again by the discharge operation A. Therefore, such discharge operation A and extrusion operation C are alternately repeated during a period in which the time period T2 in which the sludge concentration of the raw sludge is 1.5% or more continues.
[0016]
As described above, according to the present embodiment, even if the sludge concentration of the raw sludge varies greatly within the range of 0.5% or less or 1.5% or more with respect to the standard concentration of 1.0%, it is outside the apparatus. The sludge concentration of the discharged concentrated sludge can always be a stable value of an average of about 4% (upper limit 4.2%, lower limit 3.8%). Therefore, it is possible to carry out stable sludge concentration operation without requiring complicated control such as control of the flow rate of raw sludge or permeate with respect to fluctuations in the sludge concentration.
[0017]
FIG. 4 is a flowchart showing another control procedure. Starting from the discharge operation, if the sludge concentration of the concentrated sludge is a normal value that is not less than the lower limit and less than the upper limit, the discharge operation is continued (S200), and if it is less than the lower limit, the operation is switched to the circulation operation (S210). Then, the operation is switched to the extrusion operation (S220). In the circulating operation, the operation is continued until a predetermined set time T3 elapses (S230), and when the predetermined set time T3 elapses, the operation is switched to the discharge operation (S240). Further, in the extrusion operation, the operation is continued until a predetermined set time T4 elapses (S250), and when the predetermined set time T4 elapses, the operation is switched to the discharge operation (S260). According to this control method, since the operation time of the circulation operation and the extrusion operation is set by the timer, the control can be simplified as compared with the control based on the intermediate value (standard concentration) shown in FIG. Note that there is a difference in the response of the concentrated sludge to the sludge concentration between the circulation operation and the extrusion operation. Therefore, the set time T3 is lengthened in the circulation operation with slow response, the set time T4 is shortened in the extrusion operation with sensitive response, and the sludge concentration of the concentrated sludge when each operation is switched to the discharge operation is the lower limit value and the upper limit value. It is preferable to set so as to be approximately in the middle of the value.
[0018]
【The invention's effect】
As described above, according to the sludge concentration method according to the present invention, the load of the membrane separation device can be stably maintained without complicated feedback control even when the variation of the sludge concentration of the raw sludge is large, and the final In particular, the sludge concentration of the concentrated sludge discharged out of the system can be brought close to a certain target value.
[Brief description of the drawings]
FIG. 1 is an apparatus system diagram for carrying out a method of operating a membrane separation apparatus according to the present invention.
FIG. 2 is a flowchart showing an embodiment of an operation method according to the present invention.
FIG. 3 is an explanatory view exemplifying a change over time in the concentration of sludge such as concentrated sludge when the operation method according to the present invention is executed.
FIG. 4 is a flowchart showing another embodiment of the operation method according to the present invention.
[Explanation of symbols]
10 ... Sludge supply tank 15 ... Switching valve 18 ... (Supply sludge) supply pump 20 ... Membrane separator 22 ... Separation tank 24 ... Membrane module 28 ... (Permeate) suction pump 32 ... Sludge reservoir 34 ... (concentrated sludge) discharge pump 38 ... Sludge storage tank 42 ... Switching valve 42 ... Sludge concentration meter 46 ... Control

Claims

This is a method of operating a membrane separation device that separates the supplied sludge from the sludge supply tank into a permeate and concentrated sludge, and the total amount of concentrated sludge discharged from the membrane separation device while performing the membrane separation treatment. A discharge operation for discharging outside the apparatus, a circulation operation for returning the entire amount of concentrated sludge discharged from the membrane separation apparatus to the sludge supply tank while performing a membrane separation process, and a supply supplied while stopping the membrane separation process A method for operating a membrane separation apparatus, characterized in that either operation is automatically switched according to the sludge concentration of the concentrated sludge, with an extrusion operation for discharging the amount of concentrated sludge corresponding to the sludge to the outside of the apparatus.

The sludge concentration of the concentrated sludge is divided into three stages of a lower limit value, an intermediate value, and an upper limit value, and as a result of the discharge operation, when the sludge concentration of the concentrated sludge reaches a lower limit value, the operation is switched to the circulation operation, As a result of this circulation operation, when the sludge concentration of the concentrated sludge increases and reaches an intermediate value, the operation is switched to the discharge operation. When the sludge concentration of the concentrated sludge reaches the upper limit as a result of the discharge operation, the operation is switched to the extrusion operation. As a result of this extrusion operation, when the sludge concentration of the concentrated sludge decreases and reaches the intermediate value, the operation is switched to the discharge operation.

After the sludge concentration of the concentrated sludge is divided into two stages, a lower limit value and an upper limit value, when the sludge concentration of the concentrated sludge reaches the lower limit value as a result of the discharge operation, the circulation operation is performed for a predetermined time. 2. The operation is switched to the discharge operation, and when the sludge concentration of the concentrated sludge increases and reaches an upper limit as a result of the discharge operation, the extrusion operation is performed for a predetermined time and then the operation is switched to the discharge operation. A method for operating the membrane separation apparatus described in 1.

The membrane separation device includes a separation tank, a membrane module immersed in the concentrated sludge in the separation tank, and a concentrated sludge discharging means for keeping the liquid level of the concentrated sludge constant. The operation method of the membrane separator according to any one of claims 1 to 3.