JP2004216225A

JP2004216225A - Operation method of membrane filtration apparatus

Info

Publication number: JP2004216225A
Application number: JP2003004318A
Authority: JP
Inventors: Motoharu Noguchi; 基治野口; Shinshiro Kanetani; 新志郎金谷
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2003-01-10
Filing date: 2003-01-10
Publication date: 2004-08-05

Abstract

<P>PROBLEM TO BE SOLVED: To prolong a period until the next chemical cleaning of a membrane filtration apparatus by changing the usual operation method of the membrane filtration apparatus and restraining the filtration differential pressure from being increased. <P>SOLUTION: The operation of the membrane filtration apparatus is stopped several times for a specified time during the period until the differential pressure reaches the value predetermined for performing the chemical cleaning. For example, the membrane filtration apparatus is stopped three times, namely, as the first stop for about 15 hours when 170 hours have passed since the membrane filtration apparatus is started, as the second stop for about 15 hours when 290 hours have passed and as the third stop for about 15 hours when 400 hours have passed. When 450 hours have passed (it is shown by an alternate long and short dash line b in Fig.1.), one cycle is completed and the chemical cleaning is performed. Since the differential pressure is lowered by about 5 kPa whenever the membrane filtration apparatus is stopped, the period until the differential pressure reaches 40 kPa and the chemical cleaning is performed can be prolonged from the usual 250 hours to 450 hours (including the downtime of 15 x 3 hours). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、薬洗間隔を長期化できる膜ろ過装置の運転方法の改良に関するものである。
【０００２】
【従来の技術】
従来、膜ろ過装置の運転方法は、一定期間、連続して吸引などによるろ過操作（逆洗および短時間の運転停止のある間欠運転を含む）を行い、ろ過差圧が高くなってろ過作用が低下したところで、薬液洗浄を行い、ろ過差圧を回復させて、ろ過操作を再開するという、薬液洗浄とろ過操作とを繰り返し行うのが通常の運転方法である。（特許文献１を参照のこと）
【０００３】
そして、この薬洗（薬液洗浄）の間隔は、１〜６ヶ月程度であるが、この薬洗自体の所要期間が２〜３日を要するところから、このような薬洗作業は、膜ろ過装置の運転効率を低下させる原因となるうえ、それに要する人手間と薬液など資材費はコストアップの要因にもなるので、薬洗間隔を長くできる運転方法が望まれていた。
【０００４】
【特許文献１】
特開２００２−５２３２１号公報：段落（０００２）、（０００３）、（０００４）
【０００５】
【発明が解決しようとする課題】
本発明は、上記の問題点を解決するためになされたものであり、従来のろ過運転方法を変更することにより、ろ過差圧の上昇を抑制して、前記薬洗の間隔を長期化できる膜ろ過装置の運転方法を提供する。
【０００６】
【課題を解決するための手段】
上記の問題は、膜ろ過装置の運転中に、ろ過差圧が薬品洗浄を行うよう設定した値に到達するまでの期間内に、複数回の休止期間を設けることを特徴とする本発明の膜ろ過装置の運転方法によって、解決することができる。
また、これら本発明の膜ろ過装置の運転方法は、前記休止期間中は、少なくとも１次側の被処理水を満水状態に保持する形態。さらに前記休止期間を０．５日〜４日とする形態、
【０００７】
さらに、上記の問題は、複数の膜ろ過装置を並列に運転するようにした運転方法において、ある膜ろ過装置が前記請求項１、２または３に記載の運転休止するときには、他の膜ろ過装置が所定のろ過運転するように、運転休止とろ過運転とを交互に行うようにしたことを特徴とする本発明の膜ろ過装置の運転方法によって解決することができる。
【０００８】
【発明の実施の形態】
次に、本発明の膜ろ過装置の運転方法に係る実施形態について、図１、２を参照しながら説明する。
（第１発明）
本発明の膜ろ過装置の運転方法は、装置の構成は従前となんら変わるところはなく、その特徴は、膜ろ過装置の運転中に、ろ過差圧が薬品洗浄を行うよう設定した値に到達するまでの期間内に、複数回の休止期間を設ける点にある。
【０００９】
図１に示すある事例によって説明すると、ろ過運転開始後、１７０時間で第１回目の運転休止を約１５時間行った。次いで運転を再開して２９０時間目で同様に第２回目の運転休止を行った。さらに運転を再開して４００時間目で同様に第３回目の運転休止を行い、約４５０時間経過（１点鎖線ｂで示す）して、１サイクルを終了し薬洗操作に移ったことを示している。
【００１０】
この膜ろ過装置では、従前の運転方法では、約２５０時間の連続ろ過運転後（鎖線ａ、ａ’で示す）に薬洗を行うのが通常のパターンであったが、本発明では、ろ過運転を休止するというごく簡単な操作を行うだけで、その都度ろ過差圧が約５ｋＰａ低下した結果、薬洗が必要になる４０ｋＰａに到達するまでの期間が、従前の２５０時間から４５０時間（１５×３時間の休止時間を含む）に長期化することができたのである。
【００１１】
図２は、従前の方法と本発明の方法を模式的に比較した図であり、従前の方法では、差圧は時間とともにほぼ継続してほぼ直線Ａのように上昇し、Ａ１点で薬洗に移行する。一方、本発明では、運転期間Ｂの間に休止期間Ｂ’を設けている。このとき、休止期間Ｂ’を設けたことによるろ過抵抗の減少の結果として、低下したろ過差圧Ｃがその効果が現れたことを示している。これらの結果、薬洗移行のタイミングは、Ｂ１点まで長期化するのである。この場合、短い休止時間に大きなろ過差圧の低下が生じる場合が好ましいが、休止時間と休止中のろ過差圧の低下の程度は、その膜ろ過装置の個別的条件によって異なるものである。
【００１２】
膜ろ過装置を上記のように運転休止することにより、ろ過差圧が低下する理由は以下のように推測される。ろ過運転が進むに従いケーキ層が厚くなり、圧密化するのでろ過水のろ過抵抗が増大するためろ過差圧が逐次増大するが、ろ過運転を休止すると、ろ過水の通過が停止するので圧密化したケーキ層の全体が膨潤して組織が緩むためにろ過差圧が低下すると考えられる。さらに、時間が経過すると膨潤したケーキ層が部分的に剥離して脱落するようになり、さらにろ過抵抗が低下するようになると考えられる。
【００１３】
このように、運転休止中のケーキ層の膨潤現象や剥離現象がろ過差圧低下の原因と考えられるので、本発明の休止期間中は、少なくともケーキが積層される１次側の被処理水を排水状態にするのは好ましくなく、満水状態に保持するのが効果的である。また、この休止期間を膜ろ過装置の仕様、ろ過対象物などによって変動するものの、０．５日〜４日とするのが適当である。過小の場合はろ過差圧の低下効果が少なく、過大であってもそれ以上の効果が得られないからである。また、膜ろ過開始時には、曝気や逆洗などにより膜表面に付着したケーキを剥離するのが効果的である。
【００１４】
（第２発明）
次に、本願第２発明である膜ろ過装置の運転方法を説明すると、それは、複数の膜ろ過装置を並列に運転するようにした運転方法において、ある膜ろ過装置が前記した運転休止するときには、それ以外の膜ろ過装置が所定のろ過運転するように、運転休止とろ過運転とを交互に行うようにした運転方法であって、この方法によって、ろ過装置全体としてろ過運転の中断あるいはろ過能力の変動を抑えて安定な運転を実現することができる。
【００１５】
例えば、２系統のろ過装置を前記のように運転休止とろ過運転とを交互に行うと、一方の休止期間中はろ過能力が１／２に低下するので、休止期間が１２時間を超えるような場合には応用しにくいが、負荷が低下する夜間の運転休止で済むような場合には問題がない。
【００１６】
また、運転サイクルがろ過運転：５日。運転休止：２日というような、休止期間の比重の高いケースの場合でも、表１に例示するように、Ａ〜Ｇ系の７系列でろ過〜休止の交互運転を行えば、ろ過能力の変動を完全に解消することができるようになる。
【００１７】
【表１】

【００１８】
なお、本発明の膜ろ過装置としては、高分子あるいはセラミックス材料からなるＭＦ膜、ＵＦ膜、ＮＦ膜、ＲＯ膜などをモノリス、チューブラ、スパイラル、ハニカムまたは平膜形状に構成し、加圧方式は外圧式、内圧式など多岐にわたる形式に適用可能である。また、被処理水としては特に限定されない。例えば、下水、返流水、工場排水、ごみ浸出水、屎尿、農業廃水、畜産廃水、養殖排水などの排水・廃水処理はもちろんのこと、上水処理も対象とされ得る。
【００１９】
【発明の効果】
本発明の膜ろ過装置の運転方法は、以上説明したように構成されているので、従来のろ過運転方法の途中で運転を一時休止するという簡単な操作を加えることにより、ろ過差圧を低下させ、薬洗が必要となる所定のろ過差圧に到達するタイニングを遅らせることができる。かくして、薬洗の間隔を長期化できるので、ろ過運転を安定して連続して長期にわたり行えるほか、薬洗の手間工数と薬剤費などを節減できるという優れた効果がある。よって本発明は、従来の問題点を解消した膜ろ過装置の運転方法として、実用的価値はきわめて大なるものがある。
【図面の簡単な説明】
【図１】本発明の実施形態を説明するための差圧−経過時間のグラフ。
【図２】本発明の実施形態を説明するための差圧−経過時間の模式的グラフ。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in a method of operating a membrane filtration device that can lengthen a chemical washing interval.
[0002]
[Prior art]
Conventionally, the operation method of a membrane filtration device has been to continuously perform filtration operations (including backwashing and intermittent operation with short-time operation stoppage) for a certain period of time by suction, etc. The normal operation method is to repeat the chemical liquid washing and the filtering operation, in which the chemical liquid is washed, the filtration pressure difference is recovered, and the filtration operation is restarted when the temperature is lowered. (See Patent Document 1)
[0003]
The interval of this chemical washing (chemical liquid washing) is about 1 to 6 months, but since the time required for this chemical washing itself takes 2 to 3 days, such a chemical washing operation is performed by a membrane filtration device. In addition to this, the operation efficiency can be reduced, and the labor required for the operation and the cost of materials such as a chemical solution also increase the cost.
[0004]
[Patent Document 1]
JP-A-2002-52321: paragraphs (0002), (0003), (0004)
[0005]
[Problems to be solved by the invention]
The present invention has been made in order to solve the above problems, and by changing the conventional filtration operation method, it is possible to suppress an increase in filtration differential pressure and to lengthen the interval between the chemical washings. An operation method of a filtration device is provided.
[0006]
[Means for Solving the Problems]
The above problem is that the membrane of the present invention is characterized in that, during the operation of the membrane filtration device, a plurality of suspension periods are provided within a period until the filtration pressure difference reaches a value set to perform chemical cleaning. The problem can be solved by the operation method of the filtration device.
Further, in the method for operating the membrane filtration device of the present invention, at least the water to be treated on the primary side is kept full during the suspension period. Further, a form in which the suspension period is set to 0.5 to 4 days,
[0007]
Further, the above problem is caused by the operation method in which a plurality of membrane filtration devices are operated in parallel, and when one of the membrane filtration devices is shut down according to claim 1, 2 or 3, the other membrane filtration device is stopped. Can be solved by the operation method of the membrane filtration device of the present invention, wherein the operation suspension and the filtration operation are alternately performed so that a predetermined filtration operation is performed.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment according to a method for operating a membrane filtration device of the present invention will be described with reference to FIGS.
(First invention)
The operation method of the membrane filtration device of the present invention, the configuration of the device is not different from the previous one, the feature is that during the operation of the membrane filtration device, the filtration differential pressure reaches a value set to perform chemical cleaning The point is that a plurality of suspension periods are provided within the period up to.
[0009]
Explaining with an example shown in FIG. 1, the first operation stop was performed for about 15 hours at 170 hours after the start of the filtration operation. Next, the operation was restarted, and the second operation suspension was similarly performed at 290 hours. Further, the operation was restarted, and the third operation was similarly stopped at the 400th hour. About 450 hours passed (indicated by the dashed line b), indicating that one cycle was completed and the washing operation was started. ing.
[0010]
In this membrane filtration device, in the conventional operation method, the chemical cleaning is normally performed after continuous filtration operation for about 250 hours (indicated by chain lines a and a ′). By simply performing a very simple operation of suspending the filtration, the filtration pressure difference is reduced by about 5 kPa each time, and as a result, the period required to reach 40 kPa at which chemical washing is required is increased from the previous 250 hours to 450 hours (15 × 15). (Including 3 hours of downtime).
[0011]
FIG. 2 is a diagram schematically comparing the conventional method and the method of the present invention. In the conventional method, the differential pressure almost continuously increases with time and almost rises as a straight line A, and the chemical washing is performed at the point A1. Move to On the other hand, in the present invention, a pause period B ′ is provided between the operation periods B. At this time, as a result of the decrease in the filtration resistance due to the provision of the pause period B ′, the decreased filtration differential pressure C indicates that the effect has appeared. As a result, the timing of the transfer to the chemical washing is prolonged to the point B1. In this case, it is preferable that a large decrease in the filtration pressure difference occurs during a short pause time, but the pause time and the degree of the decrease in the filtration pressure difference during the suspension time vary depending on individual conditions of the membrane filtration device.
[0012]
The reason why the filtration differential pressure is reduced by suspending the operation of the membrane filtration device as described above is assumed as follows. As the filtration operation progresses, the cake layer becomes thicker and becomes more compact, so that the filtration resistance of the filtrate increases, so that the filtration differential pressure increases sequentially. It is considered that the filtration differential pressure decreases because the entire cake layer swells to loosen the tissue. Further, it is considered that the swollen cake layer partially peels and falls off with the elapse of time, and the filtration resistance further decreases.
[0013]
As described above, since the swelling phenomenon and the peeling phenomenon of the cake layer during the suspension of the operation are considered to be the cause of the decrease in the filtration pressure difference, during the suspension period of the present invention, at least the water to be treated on the primary side where the cake is laminated is removed. It is not preferable to make the drainage state, and it is effective to keep the state full. Further, the period of this suspension varies depending on the specifications of the membrane filtration device, the object to be filtered, and the like, but is preferably 0.5 days to 4 days. If the amount is too small, the effect of lowering the filtration pressure difference is small, and if it is too large, no further effect can be obtained. At the start of membrane filtration, it is effective to remove the cake attached to the membrane surface by aeration or backwashing.
[0014]
(Second invention)
Next, the operation method of the membrane filtration device according to the second invention of the present application will be described. In the operation method in which a plurality of membrane filtration devices are operated in parallel, when a certain membrane filtration device suspends the operation described above, An operation method in which the operation suspension and the filtration operation are alternately performed so that the other membrane filtration devices perform a predetermined filtration operation. By this method, the filtration operation is interrupted or the filtration capacity of the entire filtration device is reduced. A stable operation can be realized by suppressing the fluctuation.
[0015]
For example, when the operation suspension and the filtration operation are alternately performed on the two filtration devices as described above, the filtration capacity is reduced to 中 during one suspension period, so that the suspension period exceeds 12 hours. In this case, it is difficult to apply, but there is no problem when the operation is stopped at night when the load is reduced.
[0016]
The operation cycle is filtration operation: 5 days. Shutdown: Even in a case where the specific gravity of the shutdown period is high, such as 2 days, as shown in Table 1, if the filtration-stop operation is performed alternately in the 7 series of A to G systems, the fluctuation of the filtration capacity will occur. Can be completely eliminated.
[0017]
[Table 1]

[0018]
In addition, as the membrane filtration device of the present invention, a MF membrane, a UF membrane, an NF membrane, an RO membrane, or the like made of a polymer or a ceramic material is formed in a monolithic, tubular, spiral, honeycomb, or flat membrane shape. It can be applied to various types such as external pressure type and internal pressure type. The water to be treated is not particularly limited. For example, not only wastewater and wastewater treatment such as sewage, return water, industrial wastewater, leachate leachate, human waste, agricultural wastewater, livestock wastewater, and culture wastewater, but also water treatment can be targeted.
[0019]
【The invention's effect】
Since the operation method of the membrane filtration device of the present invention is configured as described above, the filtration differential pressure is reduced by adding a simple operation of temporarily suspending the operation in the middle of the conventional filtration operation method. In addition, it is possible to delay the timing at which a predetermined filtration pressure difference requiring chemical washing is reached. In this way, since the washing interval can be lengthened, there is an excellent effect that the filtration operation can be performed stably and continuously for a long period of time, and the labor and time required for washing can be reduced and the cost of chemicals can be reduced. Therefore, the present invention has an extremely large practical value as a method of operating a membrane filtration device that solves the conventional problems.
[Brief description of the drawings]
FIG. 1 is a graph of differential pressure-elapsed time for explaining an embodiment of the present invention.
FIG. 2 is a schematic graph of differential pressure-elapsed time for explaining an embodiment of the present invention.

Claims

A method for operating a membrane filtration device, comprising providing a plurality of suspension periods during a period in which the filtration differential pressure reaches a value set to perform chemical cleaning during operation of the membrane filtration device.

The operation method of the membrane filtration device according to claim 1, wherein during the suspension period, at least the water to be treated on the primary side is maintained in a full state.

The method for operating a membrane filtration device according to claim 1 or 2, wherein the suspension period is 0.5 days to 4 days.

In an operating method in which a plurality of membrane filtration devices are operated in parallel, when one of the membrane filtration devices is shut down according to claim 1, 2, or 3, the other membrane filtration device performs a predetermined filtration operation. And a method of operating the membrane filtration device, wherein the operation suspension and the filtration operation are alternately performed.