JP5024158B2

JP5024158B2 - Membrane filtration method

Info

Publication number: JP5024158B2
Application number: JP2008089939A
Authority: JP
Inventors: 亮太高木; 有北出; 智宏前田
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2008-03-31
Filing date: 2008-03-31
Publication date: 2012-09-12
Anticipated expiration: 2028-03-31
Also published as: JP2009240903A

Description

本発明は、塩分を含有する原水をろ過膜モジュールで処理して膜ろ過水を得る膜ろ過方法において、膜ろ過水や淡水を効率的に用いて効果的な逆洗を行う逆洗方法に関するものである。 TECHNICAL FIELD The present invention relates to a backwashing method for performing effective backwashing by efficiently using membrane filtered water or fresh water in a membrane filtration method for obtaining membrane filtered water by treating raw water containing salt with a membrane filter module. It is.

海水・かん水からの淡水の生成には、たとえば逆浸透膜モジュールを備えた膜分離装置が用いられる。この種の膜分離装置は、基本的には図１に示すように、原水（海水・かん水）から濁質成分除去等のための前処理を施した後、高圧ポンプ１１によって所定の圧力（例えば６．０ＭＰａ程度）に高めて逆浸透膜モジュール１３に供給し、逆浸透作用により透過した透過水と濃縮水とを得るように構成される。 For the production of fresh water from seawater / brine, for example, a membrane separation device equipped with a reverse osmosis membrane module is used. As shown in FIG. 1, this type of membrane separation apparatus basically performs a pretreatment for removing turbid components from raw water (seawater / brine) and then a predetermined pressure (for example, And is supplied to the reverse osmosis membrane module 13 to obtain permeated water and concentrated water permeated by the reverse osmosis action.

前処理としては、例えば、砂ろ過、活性炭ろ過、膜ろ過などが挙げられ、特に膜ろ過が好ましく用いられる。しかし、この種の膜ろ過装置は、膜ろ過を継続していくと、原水に含まれる濁質や有機物、無機物等の除去対象物が膜面に蓄積し、膜の目詰まりが生じてくる。膜が目詰まりするとろ過膜モジュールの膜ろ過抵抗が上昇し、やがて膜ろ過を継続することができなくなる。そこで膜ろ過を継続するため、膜の洗浄を行う必要がある。膜の洗浄には膜ろ過水を膜の２次側（膜ろ過水側）から１次側（原水側）へ逆流させる逆流洗浄（以下、逆洗と称する）や、気体を膜の１次側に供給して膜の汚れを取る空気洗浄や、薬剤含有水を一定時間膜と接触させて洗浄する薬液洗浄がある。これらの洗浄を有効に行うことが膜ろ過を安定して継続実施するために非常に重要である。 Examples of the pretreatment include sand filtration, activated carbon filtration, and membrane filtration, and membrane filtration is particularly preferably used. However, when this type of membrane filtration device continues the membrane filtration, removal objects such as turbidity, organic matter, and inorganic matter contained in the raw water accumulate on the membrane surface, resulting in clogging of the membrane. When the membrane is clogged, the membrane filtration resistance of the filtration membrane module increases, and it becomes impossible to continue membrane filtration. Therefore, in order to continue membrane filtration, it is necessary to wash the membrane. For membrane cleaning, reverse flow cleaning (hereinafter referred to as backwashing) in which membrane filtered water flows backward from the secondary side (membrane filtered water side) of the membrane to the primary side (raw water side), or gas on the primary side of the membrane There are air cleaning to remove the dirt of the membrane by supplying to the membrane, and chemical cleaning to wash the drug-containing water in contact with the membrane for a certain period of time. It is very important to perform these washings effectively in order to carry out the membrane filtration stably and continuously.

膜の目詰まりの程度は、原水の水質に依存するが、一般的に最も問題となるのが有機物による目詰まりである。この有機物の目詰まりの解消のためには次亜塩素酸ナトリウム等の酸化剤を含む水で逆洗することが有効であり、逆洗に使用する洗浄水としては、膜ろ過水が一般的に使われている。 The degree of clogging of the membrane depends on the quality of the raw water, but generally the most problematic is clogging with organic matter. In order to eliminate this clogging of organic matter, it is effective to backwash with water containing an oxidizing agent such as sodium hypochlorite. As the washing water used for backwashing, membrane filtered water is generally used. It is used.

そこで、特許文献１では、海水・かん水などの塩分を含有する原水を膜ろ過して得られた膜ろ過水を、逆浸透膜モジュールで逆浸透処理して透過水を得る膜分離方法において、膜ろ過水に次亜塩素酸ナトリウムといった酸化剤を添加した水を用いてろ過膜モジュールを逆洗する方法や、透過水を用いてろ過膜モジュールを逆洗する方法が開示されている。しかしながら、この方法のように膜ろ過水に次亜塩素酸ナトリウムを添加すると、膜ろ過水に含まれる高濃度のカルシウム等と反応してカルシウムスケール等が発生し、次亜塩素酸ナトリウム添加配管が詰まったり、ろ過膜モジュールが詰まったりする問題が生じ易い。また、透過水に酸化剤を添加しないで逆洗を行なう場合には、十分な洗浄効果が得られない問題があった。 Therefore, in Patent Document 1, in a membrane separation method in which membrane filtrate obtained by membrane filtration of raw water containing salt such as seawater and brine is subjected to reverse osmosis treatment with a reverse osmosis membrane module to obtain permeated water, There are disclosed a method of backwashing a filtration membrane module using water in which an oxidizing agent such as sodium hypochlorite is added to filtered water, and a method of backwashing a filtration membrane module using permeated water. However, when sodium hypochlorite is added to the membrane filtrate as in this method, it reacts with high-concentration calcium contained in the membrane filtrate to generate calcium scale and the like, and the sodium hypochlorite addition pipe is Problems such as clogging and filtration membrane module clogging are likely to occur. Further, when backwashing is performed without adding an oxidizing agent to the permeated water, there is a problem that a sufficient cleaning effect cannot be obtained.

一方、特許文献２では、塩分を含有する原水を膜ろ過して得られた膜ろ過水を、第１の逆浸透膜モジュールで逆浸透処理し、さらに第２の逆浸透膜モジュールで逆浸透処理して透過水を得る膜分離方法において、第２の逆浸透膜モジュールで得られた濃縮水に、酸化剤を添加してろ過膜モジュールの逆洗を行う方法が開示されている。しかしながら、この方法では逆浸透膜モジュールを２段に設置した設備でしか適用できない。逆浸透膜モジュールを１段しか設置していない設備では濃縮水の塩分濃度が高すぎるために、濃縮水で逆洗しても効果が却って得られない。また、膜ろ過水を逆洗に用いないで、第２の逆浸透膜モジュールで得られた濃縮水を用いてろ過膜モジュールの逆洗を行っているが、第２の逆浸透膜モジュールの濃縮水は、第1の逆浸透膜モジュールの供給水として還流させるのが一般的であり、その場合に比べて、得られる透過水の回収率が低くなる問題があった。また、第２の逆浸透膜モジュールの濃縮水に含まれる塩分濃度は、原水に比べると減じられているとはいえ、十分には低くないため、期待した洗浄効果が得られない問題もあった。 On the other hand, in Patent Document 2, membrane filtration water obtained by membrane filtration of raw water containing salt is subjected to reverse osmosis treatment with a first reverse osmosis membrane module, and further reverse osmosis treatment with a second reverse osmosis membrane module. In the membrane separation method for obtaining permeated water, a method is disclosed in which an oxidant is added to the concentrated water obtained by the second reverse osmosis membrane module to backwash the filtration membrane module. However, this method can be applied only to equipment in which reverse osmosis membrane modules are installed in two stages. In facilities where only one stage of reverse osmosis membrane module is installed, the salinity of the concentrated water is too high, so the effect cannot be obtained even if backwashing with concentrated water. In addition, the membrane filtration water is not used for backwashing, and the filtration membrane module is backwashed using the concentrated water obtained by the second reverse osmosis membrane module, but the second reverse osmosis membrane module is concentrated. The water is generally refluxed as the supply water for the first reverse osmosis membrane module, and there is a problem that the recovery rate of the permeated water obtained is lower than that. Moreover, although the salt concentration contained in the concentrated water of the 2nd reverse osmosis membrane module is reduced compared with raw | natural water, since it was not low enough, there also existed a problem that the expected cleaning effect was not acquired. .

特開２００６−２７２１３６号公報JP 2006-272136 A 特開２００６−２７２１３５号公報JP 2006-272135 A

本発明は、上記した従来技術の問題点を解決し、ろ過膜モジュールに蓄積した濁質や有機物、無機物等の目詰まり原因物質を、膜ろ過水や淡水を効率的に用いて効果的に洗浄除去するための膜ろ過方法を提供することを目的とする。 The present invention solves the above-mentioned problems of the prior art, and effectively cleans clogging cause substances such as turbidity, organic matter, and inorganic matter accumulated in the filtration membrane module using membrane filtration water and fresh water efficiently. It aims at providing the membrane filtration method for removing.

上記目的を達成するための本発明の膜ろ過方法は、次の構成を特徴とするものである。
（１）塩濃度が１，０００ｍｇ／Ｌ以上の原水をろ過膜モジュールで処理して膜ろ過水を得る膜ろ過方法において、膜ろ過工程の間にろ過膜モジュールの逆洗を行う逆洗工程を有し、該逆洗工程として、酸化剤を含有させていない、前記膜ろ過水を逆浸透処理した塩濃度が５００ｍｇ／Ｌ未満の逆浸透膜透過水を逆洗水に用いて前記ろ過膜モジュールを逆洗し、前記ろ過膜モジュールの原水側の水を排出することを行い、引き続いて、酸化剤を５０ｍｇ／Ｌ以上の濃度で含有させた前記逆浸透膜透過水を逆洗水に用いた酸化剤含有淡水逆洗工程を行い、引き続いて、前記酸化剤を含有する前記逆浸透膜透過水を前記ろ過膜モジュール内で保持させた状態を３〜１２０分間維持することを行い、かつ、該酸化剤含有淡水逆洗工程の実施頻度を３時間〜１０日間に１回とすることを特徴とする膜ろ過方法。
Membrane filtration method of the present invention for achieving the above object is characterized in the following configuration.
(1) In the membrane filtration method by salt concentration processes the above raw water 1,000 mg / L in the filtration membrane module obtaining a membrane filtration water backwash step of performing backwash of the filtration membrane module during the membrane filtration step In the backwashing step , the filtration membrane is obtained by using reverse osmosis membrane permeated water having a salt concentration of less than 500 mg / L as a backwash water. the module backwashing, the make possible to discharge the water in the raw water side of the filtration membrane module, subsequently, the reverse osmosis membrane permeated water an acid agent was contained at a concentration of at least 50 mg / L in the backwash water as was carried out oxidant containing fresh water backwash engineering using performs that subsequently, maintaining the 3 to 120 minutes while being held the reverse osmosis membrane permeated water containing an oxidizing agent in the filtration membrane module, And the frequency of the oxidant-containing fresh water backwashing step is 3 Membrane filtration method characterized in that a once during ~ 10 days.

本発明の膜ろ過方法によると、ろ過膜モジュールに蓄積した濁質や有機物、無機物等の目詰まり原因物質を、膜ろ過水や淡水を効率的に用いて効果的に洗浄除去することが可能となる。 According to the membrane filtration method of the present invention, clogging-causing substances such as turbidity, organic matter, and inorganic matter accumulated in the filtration membrane module can be effectively washed and removed using membrane filtration water and fresh water efficiently. Become.

図２、図３は、それぞれ、本発明の膜ろ過方法の好ましい一実施様態を示す工程概略図である。各々の図において同一符号は同一または同等の構成要素を示す。 FIG. 2 and FIG. 3 are process schematic diagrams respectively showing a preferred embodiment of the membrane filtration method of the present invention. In each drawing, the same reference numerals indicate the same or equivalent components.

図２や図３において、取水された海水・かん水などの塩分を含有する原水は、適宜前処理を施された後、ろ過ポンプ１でもって原水配管２を介してろ過膜モジュール３へと供給され、膜ろ過された膜ろ過水が得られる。膜ろ過水は、ろ過水配管４を介してろ過水槽５に貯留される。本発明では膜ろ過水を得る工程を、膜ろ過工程と称する。ろ過水槽５に貯留された膜ろ過水は、高圧ポンプ１１によって逆浸透膜供給配管１２を介して逆浸透膜モジュール１３へと供給され、逆浸透処理された透過水と、濃縮水が得られる。透過水は透過水配管１４を介して取り出され、濃縮水は濃縮水配管１５を介して系外に排出される。本発明では逆浸透処理をして透過水を得る工程を、逆浸透処理工程と称する。また、図２では系外から供給される淡水が淡水配管１６を介して淡水水槽１７に貯留される。図３では、逆浸透膜モジュール１３で処理された透過水が淡水として供給され淡水水槽１７に貯留される。 In FIG. 2 and FIG. 3, the raw water containing salt such as seawater / brine collected is appropriately pretreated and then supplied to the filtration membrane module 3 via the raw water pipe 2 by the filtration pump 1. A membrane-filtered water obtained by membrane filtration is obtained. The membrane filtrate is stored in the filtrate tank 5 via the filtrate pipe 4. In the present invention, the step of obtaining membrane filtrate is referred to as a membrane filtration step. The membrane filtrate stored in the filtrate tank 5 is supplied to the reverse osmosis membrane module 13 via the reverse osmosis membrane supply pipe 12 by the high-pressure pump 11, and the permeated water subjected to the reverse osmosis treatment and the concentrated water are obtained. The permeated water is taken out through the permeated water pipe 14, and the concentrated water is discharged out of the system through the concentrated water pipe 15. In the present invention, the process of obtaining the permeate by performing the reverse osmosis process is referred to as a reverse osmosis process. In FIG. 2, fresh water supplied from outside the system is stored in a fresh water tank 17 through a fresh water pipe 16. In FIG. 3, the permeated water treated by the reverse osmosis membrane module 13 is supplied as fresh water and stored in the fresh water tank 17.

ろ過膜モジュール３の膜面に蓄積した濁質や有機物、無機物を洗浄除去するため、所定時間膜ろ過を行った後、ろ過ポンプ１を停止して、当該ろ過膜モジュール３の逆洗が行われる。ろ過水槽５に貯留された膜ろ過水等を逆洗水とする場合は、膜ろ過水を逆洗ポンプ２１によって逆洗水配管２２を介してろ過膜モジュール３に供給し、膜の２次側（膜ろ過水側）から膜の１次側（原水側）へ逆流させて行われる。本発明では逆洗に用いられる洗浄水を逆洗水と称する。逆洗水は、ろ過膜モジュール３の原水側に流れ出た後、逆洗水排水配管２６および／またはドレン排水配管２７を介してろ過モジュール３の系外へ排出される。膜ろ過水を用いて逆洗を行う工程を、本発明では通常逆洗工程と称する。所定の時間経過後、逆洗ポンプ２１を停止して、再び膜ろ過が行われる。 In order to wash away turbidity, organic matter, and inorganic matter accumulated on the membrane surface of the filtration membrane module 3, after performing membrane filtration for a predetermined time, the filtration pump 1 is stopped and the filtration membrane module 3 is backwashed. . When the membrane filtrate stored in the filtrate tank 5 is used as the backwash water, the membrane filtrate is supplied to the filtration membrane module 3 via the backwash water pipe 22 by the backwash pump 21 and the secondary side of the membrane. It is carried out by flowing back from the membrane filtration water side to the primary side of the membrane (raw water side). In the present invention, the washing water used for backwashing is referred to as backwashing water. The backwash water flows out to the raw water side of the filtration membrane module 3 and is then discharged out of the filtration module 3 via the backwash water drain pipe 26 and / or the drain drain pipe 27. In the present invention, the step of performing backwashing using membrane filtrate is usually referred to as a backwashing step. After a predetermined time has elapsed, the backwash pump 21 is stopped and membrane filtration is performed again.

また、淡水を逆洗水として用いる場合には、淡水水槽１７に貯留された淡水を、淡水逆洗ポンプ３１によって淡水逆洗配管３２を介してろ過膜モジュール３に供給し、膜の２次側（膜ろ過水側）から膜の１次側（原水側）へ逆流させて行われる。この時に、酸化剤貯槽２３に貯留された酸化剤薬液を、酸化剤注入ポンプ２４によって酸化剤注入配管２５を介して淡水逆洗配管３２に注入した場合、酸化剤含有淡水が逆洗水として供給される。逆洗水は、ろ過膜モジュール３の原水側に流れ出た後、逆洗水排水配管２６および／またはドレン排水配管２７を介してろ過モジュール３の系外へ排出される。所定の時間経過後、淡水逆洗ポンプ３１、酸化剤注入ポンプ２４を停止して、再び膜ろ過が行われる。本発明では、酸化剤を含有させた淡水を逆洗水に用いて逆洗を行う工程を、酸化剤含有淡水逆洗工程と称する。 In addition, when fresh water is used as backwash water, fresh water stored in the fresh water tank 17 is supplied to the filtration membrane module 3 by the fresh water back wash pump 31 via the fresh water back wash pipe 32, and the secondary side of the membrane. It is carried out by flowing back from the membrane filtration water side to the primary side of the membrane (raw water side). At this time, when the oxidant chemical stored in the oxidant storage tank 23 is injected into the fresh water backwash pipe 32 by the oxidant injection pump 24 through the oxidant injection pipe 25, the oxidant-containing fresh water is supplied as backwash water. Is done. The backwash water flows out to the raw water side of the filtration membrane module 3 and is then discharged out of the filtration module 3 via the backwash water drain pipe 26 and / or the drain drain pipe 27. After a predetermined time has elapsed, the fresh water backwash pump 31 and the oxidant injection pump 24 are stopped, and membrane filtration is performed again. In the present invention, the step of backwashing using fresh water containing an oxidizing agent as backwashing water is referred to as an oxidizing agent-containing freshwater backwashing step.

ここで、淡水とは、イオン類を相当量除去した水で飲用水品質を有するものをいい、例えば蒸発残留物濃度（塩濃度）が５００ｍｇ／Ｌ未満、塩化物イオン濃度が２００ｍｇ／Ｌ未満である水であり、飲料水、蒸留水、逆浸透処理された透過水等を使用できるが、透過水を使用すると、図３に示すように透過水返送配管１８を介して淡水水槽１７へ容易に導入することができるので好ましい。 Here, fresh water refers to water from which a considerable amount of ions have been removed and having drinking water quality. For example, the evaporation residue concentration (salt concentration) is less than 500 mg / L, and the chloride ion concentration is less than 200 mg / L. Although it is a certain water, drinking water, distilled water, reverse osmosis treated permeated water or the like can be used. However, if permeated water is used, it is easily transferred to the fresh water aquarium 17 via the permeated water return pipe 18 as shown in FIG. Since it can introduce | transduce, it is preferable.

ところで、海水・かん水などの塩分を高濃度に含有する原水では、原水中に含まれる濁質や有機物、無機物等が塩析により析出、沈殿し易くなっており、これらがろ過膜モジュールの膜面に蓄積し、膜の目詰まりが起こり易くなっている。本発明者の検討によると、原水の塩分濃度と膜の目詰まりの起こり易さの関係は、５００ｍｇ／Ｌ未満であった場合に比べて、１，０００ｍｇ／Ｌ以上になると目詰まりが起こり易くなり始め、１０，０００ｍｇ／Ｌを超えると目詰まりがより起こり易くなり、３０，０００ｍｇ／Ｌを超えると目詰まりがさらに起こり易くなることが分かっている。 By the way, in raw water containing a high concentration of salt, such as seawater and brine, turbidity, organic matter, inorganic matter, etc. contained in the raw water are likely to precipitate and precipitate by salting out, and these are the membrane surfaces of the filtration membrane module. The film tends to clog. According to the study of the present inventor, when the relationship between the salinity of raw water and the likelihood of membrane clogging is less than 500 mg / L, clogging is likely to occur at 1,000 mg / L or more. It has been found that clogging is more likely to occur when exceeding 10,000 mg / L, and clogging is more likely to occur when exceeding 30,000 mg / L.

また、海水・かん水を原水とした場合、得られた膜ろ過水は、原水に含まれる濁質や有機物、無機物等の除去対象物が除去されているものの、塩分が含有されたままである。したがって、塩析により析出、沈殿して膜面に蓄積して、膜の目詰まりを発生させた濁質や有機物、無機物等の除去対象物は、膜ろ過水を逆洗水に用いて逆洗した場合、物理的作用によって膜面から剥離させ除去させることが必要である。一方、淡水を逆洗水に用いて逆洗した場合、原水中に含まれる塩濃度による塩析現象によって析出、沈殿した濁質や有機物、無機物等の除去対象物は、低い塩濃度の淡水中では溶解し易く、物理的作用によって膜面から剥離させる効果と、淡水中に溶解させて除去させる効果とによる除去効果が発揮される。このため、淡水を逆洗水に用いて逆洗した方が、洗浄除去の効果が高いので好ましい。 Moreover, when seawater / brine is used as raw water, the obtained membrane filtered water is free from turbidity, organic matter, inorganic matter, and other removal objects contained in the raw water, but still contains salt. Therefore, the object to be removed, such as turbidity, organic matter, and inorganic matter, which has been deposited and precipitated by salting out and accumulated on the membrane surface, causing membrane clogging, is backwashed using membrane filtered water as backwash water. In this case, it is necessary to remove the film from the film surface by physical action. On the other hand, when backwashing is performed using fresh water as backwash water, objects to be removed such as turbidity, organic matter, and inorganic matter that have precipitated and precipitated due to the salting out phenomenon due to the salt concentration contained in the raw water are not suitable for fresh water with low salt concentration. Then, it is easy to dissolve, and the removal effect by the effect of peeling from the film surface by a physical action and the effect of dissolving and removing in fresh water are exhibited. For this reason, it is preferable to use fresh water for backwashing water because it has a high cleaning effect.

このとき、原水と淡水の塩濃度差が大きいほど、膜ろ過工程において塩析によって膜面に析出、沈殿した濁質や有機物、無機物等が、淡水を逆洗水に用いた逆洗によって溶解して除去し易くなる。ここで、淡水は、蒸発残留物濃度が５００ｍｇ／Ｌ未満であることから、原水と淡水の塩濃度差を有意にするためには、原水の塩濃度は少なくとも１，０００ｍｇ／Ｌ以上であることが好ましく、さらには１０，０００ｍｇ／Ｌ以上、より好ましくは３０，０００ｍｇ／Ｌ以上であることが、原水と淡水との塩濃度差が十分に大きくなるので好ましい。 At this time, the greater the difference in salt concentration between the raw water and fresh water, the more turbidity, organic matter, inorganic matter, etc., precipitated and precipitated on the membrane surface by salting out in the membrane filtration step, dissolved by backwashing using freshwater as backwash water. It becomes easy to remove. Here, since fresh water has an evaporation residue concentration of less than 500 mg / L, the salt concentration of raw water should be at least 1,000 mg / L or more in order to make the salt concentration difference between raw water and fresh water significant. Is more preferably 10,000 mg / L or more, and more preferably 30,000 mg / L or more because the difference in salt concentration between the raw water and fresh water is sufficiently large.

淡水を用いて逆洗を行うためには、予め淡水を準備する必要があり、膜ろ過工程の間に頻繁に行われる毎回逆洗に淡水を使用する場合、本発明による膜ろ過法のランニングコストが高くなるというデメリットが生じる。特に、海水・かん水から淡水である透過水を生成するための前処理として本発明による膜ろ過法を用いる場合では、生成された透過水のうちの多くを逆洗水として消費することになり、透過水の回収率を下げてしまうデメリットが生じる。従って、淡水による逆洗は、逆洗効果は高いものの頻繁に行うことが難しい。 In order to perform backwashing using fresh water, it is necessary to prepare fresh water in advance, and when fresh water is used for backwashing frequently performed during the membrane filtration step, the running cost of the membrane filtration method according to the present invention There is a demerit that becomes higher. In particular, in the case of using the membrane filtration method according to the present invention as a pretreatment for generating permeated water that is fresh water from seawater and brine, most of the generated permeated water will be consumed as backwash water, There is a demerit that lowers the permeate recovery rate. Therefore, backwashing with fresh water is difficult to perform frequently, although the backwashing effect is high.

ここで、回収率とは、供給された水量に対する処理水流量の割合であり、例えば、膜ろ過工程にあっては、前処理を施された原水量に対する、逆洗水として使用された分を差し引いた膜ろ過水量の割合である。逆浸透処理工程にあっては、逆浸透膜モジュール１３に供給された膜ろ過水量に対する、逆洗水として使用された分を差し引いた透過水量の割合である。また、図２に示されるような膜ろ過工程と逆浸透処理工程を組合せた海水淡水化システムにおいてはろ過膜モジュール３に供給された原水量に対する透過水量（逆洗水としての使用分を除く。）の割合である。 Here, the recovery rate is the ratio of the treated water flow rate to the supplied water amount. For example, in the membrane filtration step, the amount used as backwash water with respect to the pretreated raw water amount. It is the ratio of the amount of membrane filtration water subtracted. In the reverse osmosis treatment step, it is the ratio of the amount of permeated water obtained by subtracting the amount used as backwash water to the amount of membrane filtrate supplied to the reverse osmosis membrane module 13. Moreover, in the seawater desalination system combining the membrane filtration step and the reverse osmosis treatment step as shown in FIG. 2, the permeated water amount relative to the raw water amount supplied to the filtration membrane module 3 (excluding the portion used as backwash water). ).

さらに、逆洗水に酸化剤を含有させると、酸化剤による膜の洗浄効果を高めることができるので好ましい。酸化剤としては、次亜塩素酸ナトリウム、二酸化塩素、過酸化水素、クロラミン等が使用できるが、使用し易さと、コスト、洗浄効果の観点から次亜塩素酸ナトリウムが好ましい。通常、ろ過膜モジュールの逆洗は、膜ろ過を続ける途中に定期的に行われ、その頻度は、１５分〜１２０分に１回程度である。通常は、膜ろ過水を逆洗水に用いて１５分〜１２０分に１回程度の頻度で逆洗を行い、膜に蓄積した濁質や有機物、無機物等の膜の目詰まり原因物質を洗浄除去する。膜ろ過水を逆洗水に用いた場合、淡水あるいは酸化剤含有淡水を逆洗水に用いた場合よりも洗浄効果が小さいために、洗浄除去しきれなかった濁質や有機物、無機物等の膜の目詰まり原因物質が徐々に蓄積されていく。そこで、3時間に1回〜１０日間に１回程度の頻度で、酸化剤含有淡水を逆洗水に用いた逆洗（酸化剤含有淡水逆洗工程）を行い、これによって得られる高い洗浄効果によって、蓄積した濁質や有機物、無機物等の膜の目詰まり原因物質を洗浄除去する。このように、通常逆洗工程と酸化剤含有淡水逆洗とを組合わせて実施することにより、膜の目詰まり原因物質を効果的に除去できると同時に、ろ過膜モジュールの逆洗に使用する淡水量を最小限に抑えることができる。淡水の使用量を減らすことによって、海水淡水化システムにおける回収率を高く維持することができるようになる。 Furthermore, it is preferable to include an oxidizing agent in the backwash water because the cleaning effect of the film by the oxidizing agent can be enhanced. As the oxidizing agent, sodium hypochlorite, chlorine dioxide, hydrogen peroxide, chloramine and the like can be used, but sodium hypochlorite is preferable from the viewpoint of ease of use, cost, and cleaning effect. Usually, the backwashing of the filtration membrane module is periodically performed while continuing the membrane filtration, and the frequency thereof is about once every 15 to 120 minutes. Normally, membrane filtration water is used as backwash water, and backwashing is performed about once every 15 to 120 minutes to clean the substances causing clogging of the membrane such as turbidity, organic matter, and inorganic matter accumulated in the membrane. Remove. When membrane filtered water is used for backwashing water, the cleaning effect is smaller than when using freshwater or fresh water containing an oxidizer for backwashing water. Substances that cause clogging are gradually accumulated. Therefore, the backwashing using the oxidant-containing fresh water as the backwash water (the oxidant-containing freshwater backwash process) is performed once every 3 hours or about once every 10 days. In this way, accumulated substances such as turbidity, organic matter, and inorganic matter are washed and removed. As described above, the normal backwashing step and the oxidant-containing freshwater backwashing are carried out in combination to effectively remove the substances causing the clogging of the membrane, and at the same time, the freshwater used for the backwashing of the filtration membrane module. The amount can be minimized. By reducing the amount of fresh water used, the recovery rate in the seawater desalination system can be maintained high.

また、酸化剤含有淡水を用いた逆洗の頻度を増やすと、逆洗水に含有させる酸化剤のコストと、逆洗水を含む洗浄廃水中の酸化剤を中和するための薬液のコストが高くなる。逆に、その頻度が少なすぎると、ろ過膜モジュールの洗浄が効果的に行われない。これらを勘案すると、酸化剤を含有させた淡水を用いた逆洗は、３時間に１回〜１０日間に１回程度の頻度で実施する。６時間に１回〜３日間に１回の頻度で実施することが好ましい。 Moreover, if the frequency of backwashing using oxidant-containing fresh water is increased, the cost of the oxidant contained in the backwash water and the cost of the chemical solution for neutralizing the oxidant in the washing wastewater containing backwash water are reduced. Get higher. Conversely, if the frequency is too low, the filtration membrane module is not effectively cleaned. Taking these into consideration, backwashing using fresh water containing an oxidizing agent is carried out at a frequency of about once every 3 hours to about once every 10 days. It is preferable to carry out the method once every 6 hours to once every 3 days.

酸化剤含有淡水を用いた逆洗を行う時には、その酸化剤含有淡水による逆洗に引き続き、ろ過膜モジュール内に酸化剤含有淡水を保持させた状態を維持する薬液保持工程を設けることが好ましい。薬液保持工程を設けることにより、ろ過膜モジュールの膜と酸化剤との接触時間を長く取ることができ、膜の洗浄効果をさらに高めることが可能となる。 When backwashing using oxidant-containing fresh water, it is preferable to provide a chemical solution holding step for maintaining the state in which the oxidant-containing fresh water is held in the filtration membrane module following the backwashing with the oxidant-containing fresh water. By providing the chemical solution holding step, the contact time between the membrane of the filtration membrane module and the oxidizing agent can be increased, and the membrane cleaning effect can be further enhanced.

薬液保持工程は、次のような具体的方法で実施すればよい。淡水水槽１７に貯留された淡水を、淡水逆洗ポンプ３１によって淡水逆洗配管３２を介してろ過膜モジュール３へと供給する途中で、酸化剤貯槽２３に貯留された酸化剤薬液を、酸化剤注入ポンプ２４によって酸化剤注入配管２５を介して注入して、淡水に酸化剤を添加し、この酸化剤含有淡水を、ろ過膜モジュール３内の膜の２次側（膜ろ過水側）から膜の１次側（原水側）へ逆流させて薬液逆洗工程を行なうと、ろ過膜モジュール３の膜の1次側の水は、ドレン排水配管２７を介してろ過膜モジュール外へと排出され、酸化剤含有淡水が、ろ過膜モジュール３の膜の２次側のみを満たした状態となる。この状態で、淡水逆洗ポンプ３１、酸化剤注入ポンプ２４を停止すると、ろ過膜モジュール３の膜と酸化剤とが接触した状態を保つことができる。 What is necessary is just to implement a chemical | medical solution holding process with the following concrete methods. While supplying the fresh water stored in the fresh water tank 17 to the filtration membrane module 3 through the fresh water back washing pipe 32 by the fresh water back washing pump 31, the oxidizing chemical stored in the oxidizing agent storage tank 23 is used as the oxidizing agent. It is injected through an oxidant injection pipe 25 by an injection pump 24, an oxidant is added to fresh water, and this oxidant-containing fresh water is fed from the secondary side (membrane filtered water side) of the membrane in the filtration membrane module 3 to the membrane. When the chemical liquid back washing process is performed by flowing back to the primary side (raw water side), water on the primary side of the membrane of the filtration membrane module 3 is discharged out of the filtration membrane module via the drain drain pipe 27, The oxidant-containing fresh water is in a state where only the secondary side of the membrane of the filtration membrane module 3 is filled. When the fresh water backwash pump 31 and the oxidant injection pump 24 are stopped in this state, the state in which the membrane of the filtration membrane module 3 and the oxidant are in contact can be maintained.

薬液保持工程を行うための別の具体的な実施方法としては、淡水水槽１７に貯留された淡水に、淡水逆洗配管３２の途中で酸化剤薬液を添加することにより酸化剤含有淡水とし、これをろ過膜モジュール３内に供給し、膜の２次側（膜ろ過水側）から膜の１次側（原水側）へ逆流させて薬液逆洗を行う時に、ドレン排水配管２７を閉め切っておき、ろ過膜モジュール３の膜の２次側と膜の１次側の両方が酸化剤含有淡水で満たされた状態とする。この状態で、淡水逆洗ポンプ３１、酸化剤注入ポンプ２４を停止すると、ろ過膜モジュール３の膜と酸化剤が接触した状態を保つことができる。 As another specific implementation method for performing the chemical solution holding step, the oxidant containing fresh water is obtained by adding the oxidant chemical solution to the fresh water stored in the fresh water tank 17 in the middle of the fresh water backwash pipe 32. Is supplied into the filtration membrane module 3, and when draining the chemical solution backflow from the membrane secondary side (membrane filtered water side) back to the membrane primary side (raw water side), the drain drain pipe 27 is closed. Both the secondary side of the membrane of the filtration membrane module 3 and the primary side of the membrane are filled with oxidant-containing fresh water. If the fresh water backwash pump 31 and the oxidant injection pump 24 are stopped in this state, the state where the membrane of the filtration membrane module 3 and the oxidant are in contact can be maintained.

この薬液保持工程の時間は３〜１２０分程度であることが好ましく、さらには１０〜３０分程度がより好ましい。薬液保持工程の時間が短か過ぎると、膜と酸化剤の接触時間が不十分となって高い洗浄効果が得られなくなり、逆に、薬液保持工程の時間が長過ぎると、装置の停止時間が長くなって稼働率が低下するからである。 The time for this chemical solution holding step is preferably about 3 to 120 minutes, and more preferably about 10 to 30 minutes. If the time of the chemical solution holding process is too short, the contact time between the membrane and the oxidant is insufficient, and a high cleaning effect cannot be obtained. Conversely, if the time of the chemical solution holding process is too long, the stop time of the apparatus is This is because the operating rate decreases as the length increases.

また、薬液保持工程を設ける場合は、薬液保持工程中に膜に蓄積した濁質や有機物、無機物等と酸化剤との反応が進んで、酸化剤が消費されていくために、酸化剤濃度が低すぎると薬液保持工程中に酸化剤がすべて消費し尽くされてしまい十分な洗浄効果が得られない場合がある。 In addition, when a chemical solution holding step is provided, the reaction between the turbidity, organic matter, inorganic matter, etc. accumulated in the film during the chemical solution holding step and the oxidizing agent proceeds and the oxidizing agent is consumed. If it is too low, all of the oxidizing agent is consumed during the chemical solution holding step, and a sufficient cleaning effect may not be obtained.

逆洗水に含有させる酸化剤の濃度は、通常、０．１ｍｇ／Ｌから１０，０００ｍｇ／Ｌの範囲であるが、本発明では５０ｍｇ／Ｌ以上にする。また、薬液保持工程を設けた場合に十分な洗浄効果を得るためには、酸化剤の消費減少分を考慮して濃度を高めにすることが好ましい。このようなことから２００ｍｇ／Ｌ以上にすることが好ましい。また、１，０００ｍｇ／Ｌよりも濃度を高めると、逆洗水に含有させる酸化剤のコストと、逆洗水を含む洗浄廃水中の酸化剤を中和するための薬液のコストが高くなり不経済であることから、高くても１，０００ｍｇ／Ｌ以下であることが好ましい。 The concentration of the oxidizing agent contained in the backwash water is usually in the range of 0.1 mg / L to 10,000 mg / L, but is 50 mg / L or more in the present invention. In order to obtain a sufficient cleaning effect when the chemical solution holding step is provided, it is preferable to increase the concentration in consideration of a decrease in consumption of the oxidizing agent. For these reasons, it is preferable to set it to 200 mg / L or more. Further, if the concentration is higher than 1,000 mg / L, the cost of the oxidizing agent contained in the backwashing water and the cost of the chemical solution for neutralizing the oxidizing agent in the washing wastewater containing the backwashing water are increased. In view of economy, it is preferably 1,000 mg / L or less at the highest.

また、酸化剤含有淡水逆洗工程を行うにあたって、酸化剤を含有させない淡水を逆洗水に用いて逆洗を行ってから、酸化剤を含有させた淡水を逆洗水に用いて逆洗を行うことが好ましい。膜ろ過工程においては、塩分を含有した原水をろ過しているために、膜の１次側および膜の２次側は塩分を含有した原水あるいは膜ろ過水で満たされている。この状態で、酸化剤含有淡水を逆洗水に用いて逆洗を開始しても、ろ過膜モジュールの膜の１次側および膜の２次側に残留した塩分を含有した原水あるいは膜ろ過水と混合することによって、逆洗水として供給した酸化剤含有淡水の塩濃度が高くなってしまうために、高い洗浄効果が得られ難いためである。 In addition, when performing the oxidant-containing fresh water backwashing step, the backwashing is performed using fresh water not containing the oxidant as the backwash water, and then backwashing is performed using the fresh water containing the oxidant as the backwash water. Preferably it is done. In the membrane filtration step, since raw water containing salt is filtered, the primary side of the membrane and the secondary side of the membrane are filled with raw water or membrane filtered water containing salt. In this state, even if oxidant-containing fresh water is used as backwash water and backwashing is started, raw water or membrane filtrate containing salt remaining on the primary side of the membrane of the filtration membrane module and the secondary side of the membrane This is because the salt concentration of the oxidant-containing fresh water supplied as the backwash water becomes high by mixing with the water, and it is difficult to obtain a high cleaning effect.

そこで、あらかじめ、酸化剤を含有させない淡水を逆洗水に用いて逆洗を行うことによって、ろ過膜モジュール内に残留している原水および膜ろ過水を淡水に置換し、続いて、酸化剤含有淡水を逆洗水に用いて逆洗を行うと、高い洗浄効果が得ることができる。また、外圧型のろ過膜モジュールを使用する場合、膜の１次側は、膜の２次側よりも容量が大きいので、膜の１次側の原水を淡水に置換するためには多量の淡水が必要となる。そこで、酸化剤を含有させない淡水を逆洗水に用いて逆洗を行う前に、酸化剤を含有させない淡水を逆洗水に用いて逆洗を行っている途中に、または、酸化剤を含有させない淡水を逆洗水に用いて逆洗を行った後に、ドレン排水配管から膜の１次側の水を排出することが、膜の１次側の原水を淡水に置換するための淡水必要量を少なくできるので好ましい。 Therefore, the raw water remaining in the filtration membrane module and the membrane filtrate water are replaced with fresh water by performing backwashing using fresh water that does not contain an oxidizer as the backwash water in advance, and subsequently containing the oxidizer. When backwashing is performed using fresh water as backwashing water, a high cleaning effect can be obtained. When an external pressure type filtration membrane module is used, since the primary side of the membrane has a larger capacity than the secondary side of the membrane, a large amount of fresh water is required to replace the raw water on the primary side of the membrane with fresh water. Is required. Therefore, before performing the backwash using the fresh water not containing the oxidizer for the backwash water, the fresh water not containing the oxidizer is used for the backwash water during the backwash, or the oxidizer is contained. The amount of fresh water required to replace the raw water on the primary side of the membrane with fresh water is to discharge the water on the primary side of the membrane from the drain drain pipe after back washing using unwashed fresh water as backwash water Can be reduced, which is preferable.

さらに、酸化剤含有淡水を逆洗水に用いて逆洗をする前に、酸化剤を含有させない淡水を逆洗水に用いて逆洗を行ない、ろ過膜モジュールの膜に蓄積した濁質や有機物、無機物等を予め除去しておくと、酸化剤含有淡水を用いて逆洗した際に、除去された分の濁質や有機物、無機物等と反応するはずだった酸化剤の消費量を低減できるために、高い洗浄効果を得ることができ、酸化剤のコストを低減できるので好ましい。 Furthermore, before backwashing using oxidant-containing fresh water for backwashing water, backwashing is performed using freshwater not containing oxidant for backwashing water, and turbidity and organic matter accumulated in the membrane of the filtration membrane module. If inorganic substances are removed in advance, it is possible to reduce the consumption of oxidant that should react with turbidity, organic matter, inorganic substances, etc. when removed by using oxidant-containing fresh water. Therefore, it is preferable because a high cleaning effect can be obtained and the cost of the oxidizing agent can be reduced.

ここで、取水された海水・かん水などの塩分含有原水が、ろ過膜モジュール３によって膜ろ過される前に施される前処理としては、例えば、凝集、沈殿、砂ろ過、加圧浮上、活性炭ろ過、生物処理、ｐＨ調整、殺菌剤添加、酸化等が採用できるが、適宜選択すればよい。 Here, examples of the pretreatment to be performed before the salt-containing raw water such as seawater / brine taken is subjected to membrane filtration by the filtration membrane module 3 include aggregation, precipitation, sand filtration, pressurized flotation, and activated carbon filtration. Biological treatment, pH adjustment, addition of bactericide, oxidation, etc. can be employed, but may be selected as appropriate.

ここでろ過膜モジュール３としては、外圧式でも内圧式であっても差し支えはないが、前処理の簡便さの観点から外圧式である方が好ましい。また膜ろ過方式としては全量ろ過型モジュールでもクロスフローろ過型モジュールであっても差し支えはないが、エネルギー消費量が少ないという点から全量ろ過型モジュールである方が好ましい。さらに加圧型モジュールであっても浸漬型モジュールであっても差し支えはないが、高流速運転が可能であるという点から加圧型モジュールである方が好ましい。 Here, the filtration membrane module 3 may be an external pressure type or an internal pressure type, but is preferably an external pressure type from the viewpoint of simplicity of pretreatment. The membrane filtration method may be a total filtration module or a cross flow filtration module, but a full filtration module is preferred from the viewpoint of low energy consumption. Further, it may be a pressurization type module or an immersion type module, but the pressurization type module is preferred from the viewpoint that a high flow rate operation is possible.

また、ろ過膜モジュール３の形態としては、中空糸型、平膜型、スパイラル型、またはチューブラー型を用いることができるが、コスト低減の点から中空糸型が好ましい。 Moreover, as a form of the filtration membrane module 3, a hollow fiber type, a flat membrane type, a spiral type, or a tubular type can be used, but the hollow fiber type is preferable from the viewpoint of cost reduction.

ここで、ろ過膜モジュール３を構成する膜としては、多孔質の膜であれば特に限定しないが、セラミック等の無機素材、ポリエチレン、ポリプロピレン、ポリアクリロニトリル、エチレン−テトラフルオロエチレン共重合体、ポリクロロトリフルオロエチレン、ポリテトラフルオロエチレン、ポリビニルフルオライド、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体、クロロトリフルオロエチレン−エチレン共重合体、ポリフッ化ビニリデン、ポリスルホン、酢酸セルロース、ポリビニルアルコール、ポリエーテルスルホン、塩化ビニールからなる群から選ばれる少なくとも１種類からなる膜であることが好ましい。さらに膜強度や耐薬品性の点からはポリフッ化ビニリデン（ＰＶＤＦ）製の膜がより好ましい。また、親水性が高く耐汚れ性が強いという点からはポリアクリロニトリル製の膜がより好ましい。膜表面の細孔径については特に限定されず、精密ろ過膜であっても限外ろ過膜であってもかまわないが、０．００１μｍ〜１０μｍの範囲内で便宜選択することができる。 Here, the membrane constituting the filtration membrane module 3 is not particularly limited as long as it is a porous membrane, but it is not limited to inorganic materials such as ceramics, polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychloro Trifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, A membrane made of at least one selected from the group consisting of polysulfone, cellulose acetate, polyvinyl alcohol, polyethersulfone and vinyl chloride is preferred. Furthermore, from the viewpoint of film strength and chemical resistance, a film made of polyvinylidene fluoride (PVDF) is more preferable. In addition, a film made of polyacrylonitrile is more preferable from the viewpoint of high hydrophilicity and strong stain resistance. The pore diameter on the membrane surface is not particularly limited and may be a microfiltration membrane or an ultrafiltration membrane, but can be conveniently selected within a range of 0.001 μm to 10 μm.

また、中空糸型のろ過膜モジュールを使用する場合、中空糸膜の外径は特に限定されないが、洗浄時における中空糸膜の振動性が高く、洗浄性に優れるため２５０μｍ〜２０００μｍの範囲内であることが好ましい。 Moreover, when using a hollow fiber type filtration membrane module, the outer diameter of the hollow fiber membrane is not particularly limited, but the vibration property of the hollow fiber membrane at the time of washing is high and the washing property is excellent, so that it is within the range of 250 μm to 2000 μm. Preferably there is.

ここで膜ろ過工程におけるろ過流量の制御方法としては、定流量ろ過であっても定圧ろ過であっても差し支えはないが、ろ過水の生産水量の制御のし易さの点から定流量ろ過である方が好ましい。 Here, as a control method of the filtration flow rate in the membrane filtration step, there is no problem whether it is constant flow filtration or constant pressure filtration, but constant flow filtration is used from the viewpoint of easy control of the production amount of filtrate water. Some are preferred.

逆浸透膜モジュール１３を構成する逆浸透膜については、例えば、素材としては、ポリアミド系、ポリピペラジンアミド系、ポリエステルアミド系、あるいは水溶性のビニルポリマーを架橋したものなどを使用することができ、その膜構造としては、膜の少なくとも片面に緻密層を持ち、緻密層から膜内部あるいはもう片面の膜に向けて徐々に大きな孔径の微細孔を有するもの（非対称膜）や、このような非対称膜の緻密層の上に別の素材で形成された非常に薄い分離機能層を有するもの（複合膜）などを使用することができる。しかしながら、低圧運転時における高造水量のためには複合膜であることが好ましく、中でも、透過水量、耐薬品性等の点からポリアミド系複合膜が、さらにはピペラジンポリアミド系複合膜が好ましい。 For the reverse osmosis membrane constituting the reverse osmosis membrane module 13, for example, as a material, polyamide-based, polypiperazine amide-based, polyester amide-based, or a water-soluble vinyl polymer crosslinked can be used, The membrane structure has a dense layer on at least one side of the membrane, and has fine pores with gradually increasing pore diameters from the dense layer to the inside of the membrane or the membrane on the other side (asymmetric membrane), or such an asymmetric membrane. A material having a very thin separation functional layer (composite film) formed of another material on the dense layer can be used. However, a composite membrane is preferred for high water production during low-pressure operation, and among them, polyamide composite membranes and piperazine polyamide composite membranes are more preferable from the viewpoints of the amount of permeated water and chemical resistance.

また、逆浸透膜モジュール１３は、平膜状の膜を集水管の周囲に巻囲したスパイラル型エレメントや、プレート型支持板の両面に平膜を張ったものをスペーサーを介して一定の間隔で積層してモジュール化したプレート・アンド・フレーム型エレメント、さらには、管状膜を用いたチューブラー型エレメント、中空糸膜を束ねてケースに収納した中空糸膜エレメントを、耐圧容器に単数もしくは複数個直列に接続して収容して構成される。エレメントの形態としては、いずれの形態であってもよいが、操作性や互換性の観点からはスパイラル型エレメントを使用するのが好ましい。なお、エレメント本数は、膜性能に応じて任意に設定することができる。スパイラル型エレメントを用いた場合、１つのモジュールに装填するエレメントの本数は、直列に１本から８本程度に配列することが好ましい。また、逆浸透膜モジュール１３を複数本並列に配置しても構わない。 The reverse osmosis membrane module 13 is a spiral type element in which a flat membrane membrane is wound around a water collecting pipe, or a plate type support plate with flat membranes stretched on both sides at regular intervals via spacers. One or more plate-and-frame elements stacked and modularized, tubular elements using tubular membranes, and hollow fiber membrane elements bundled with hollow fiber membranes and housed in a case It is constructed by connecting in series. The element may be in any form, but it is preferable to use a spiral element from the viewpoint of operability and compatibility. The number of elements can be arbitrarily set according to the membrane performance. When spiral type elements are used, the number of elements to be loaded in one module is preferably arranged in a series of about 1 to 8 elements. A plurality of reverse osmosis membrane modules 13 may be arranged in parallel.

＜実施例１＞
外圧式PＶＤＦ中空糸精密ろ過膜モジュールＨＦＳ−２０２０（東レ（株）製）を１本、ろ過膜モジュール３として用い、スパイラル型逆浸透膜エレメントＳＵ−８１０（東レ（株）製）を６本装填した逆浸透膜モジュール１３を使用して、図４に示したフローにて以下の条件で実験を行った。 <Example 1>
One external pressure type PVDF hollow fiber microfiltration membrane module HFS-2020 (manufactured by Toray Industries, Inc.) is used as the filtration membrane module 3, and six spiral reverse osmosis membrane elements SU-810 (manufactured by Toray Industries, Inc.) are loaded. Using the reverse osmosis membrane module 13, the experiment was conducted under the following conditions in the flow shown in FIG.

海水を原水とし、ろ過流束２．０ｍ^３／（ｍ^２・ｄ）、全量ろ過方式かつ定流量ろ過方式で、膜ろ過工程を３０分間行った後、続いて、膜ろ過水を逆洗水に用いた通常逆洗工程を３０秒間行い、空気洗浄を行い、ろ過膜モジュール内の原水側の水を全量排出し、ろ過膜モジュール内の原水側を原水で満たす順序で洗浄を行い、再び膜ろ過工程に戻る操作を繰り返した。さらに、１日に１回の頻度で、通常逆洗工程を行う代わりに、逆浸透膜透過水を用いた酸化剤含有淡水逆洗工程を１２０秒間行い、薬液保持工程を２０分間行い、酸化剤を含有しない逆浸透膜透過水を逆洗水に用いた淡水逆洗工程（薬剤リンス工程）を１２０秒間行い、ろ過膜モジュール内の原水側の水を全量排出し、ろ過膜モジュール内の原水側を原水で満水とする順序で酸化剤含有淡水による逆洗を行い、膜ろ過工程に戻る操作を行った。 Seawater is used as raw water, and the membrane filtration process is performed for 30 minutes using a filtration flux of 2.0 m ³ / (m ² · d), a total filtration method and a constant flow filtration method, and then the membrane filtration water is backwashed. The normal backwashing process used for 30 seconds is performed, air cleaning is performed, the raw water side in the filtration membrane module is completely discharged, the raw water side in the filtration membrane module is filled with raw water, and the membrane is washed again. The operation of returning to the filtration step was repeated. Furthermore, instead of performing the normal backwashing process once a day, the oxidizing agent-containing fresh water backwashing process using reverse osmosis membrane permeated water is performed for 120 seconds, the chemical solution holding process is performed for 20 minutes, and the oxidizing agent A fresh water backwash process (drug rinsing process) using reverse osmosis membrane permeated water that does not contain water for 120 seconds, discharges all of the water on the raw water side in the filtration membrane module, and the raw water side in the filtration membrane module Were backwashed with oxidant-containing fresh water in the order of filling the raw water with water, and the operation to return to the membrane filtration step was performed.

酸化剤含有淡水逆洗工程においては、酸化剤濃度が３００ｍｇ／Ｌとなるように次亜塩素酸ナトリウム水溶液（１２％）を注入した。また、逆浸透処理工程では、逆浸透膜供給水に対する逆浸透膜透過水の割合を４５％にして実験を行った。 In the oxidizing agent-containing fresh water backwashing step, an aqueous sodium hypochlorite solution (12%) was injected so that the oxidizing agent concentration was 300 mg / L. In the reverse osmosis treatment step, the experiment was conducted with the ratio of the reverse osmosis membrane permeated water to the reverse osmosis membrane feed water being 45%.

運転初期の膜差圧は２５℃温度補正差圧で２０ｋＰａであり、１ヶ月間運転を行った後の膜差圧は２５℃温度補正差圧で４０ｋＰａであった。また、原水量に対する、逆洗水として使用された分を差し引いた透過水量の割合は４１．６％であった。なお、実験期間中の原水である海水の平均塩濃度は３４，０００ｍｇ／Ｌ、通常逆洗に用いた膜ろ過水の平均塩濃度は３４，０００ｍｇ／Ｌ、酸化剤含有淡水逆洗に用いた逆浸透膜透過水の平均塩濃度は２００ｍｇ／Ｌであった。 The film differential pressure at the initial stage of operation was 20 kPa at 25 ° C. temperature corrected differential pressure, and the film differential pressure after one month operation was 40 kPa at 25 ° C. temperature corrected differential pressure. Moreover, the ratio of the amount of permeate which subtracted the part used as backwash water with respect to the amount of raw water was 41.6%. In addition, the average salt concentration of seawater, which is the raw water during the experiment period, was 34,000 mg / L, the average salt concentration of membrane filtration water normally used for backwashing was 34,000 mg / L, and used for backwashing with fresh water containing oxidizing agent. The average salt concentration of reverse osmosis membrane permeated water was 200 mg / L.

＜比較例１＞
膜ろ過方法を図１のフローに変更し、酸化剤含有水による逆洗を以下の条件に変更した以外は、実施例１と同様に実験を行った。
１日に１回の頻度で行った酸化剤含有水による逆洗では、酸化剤を含有させた膜ろ過水を逆洗水に用いた酸化剤含有ろ過水逆洗工程を１２０秒間行い、薬液保持工程を２０分間行い、酸化剤を含有しない膜ろ過水を逆洗水に用いた通常逆洗工程（薬剤リンス工程）を１２０秒間行い、ろ過膜モジュール内の原水側の水を全量排出し、ろ過膜モジュール内の原水側を原水で満水とする順序で行い、膜ろ過工程に戻る操作を行った。 <Comparative Example 1>
Experiments were conducted in the same manner as in Example 1 except that the membrane filtration method was changed to the flow of FIG. 1 and the backwashing with the oxidizing agent-containing water was changed to the following conditions.
In backwashing with oxidant-containing water performed once a day, the oxidant-containing filtered water backwashing process using membrane filtered water containing oxidant as backwash water is performed for 120 seconds, and the chemical solution is retained. The process is performed for 20 minutes, a normal backwashing process (medicine rinsing process) using membrane filtered water containing no oxidizing agent for backwashing water is performed for 120 seconds, and the raw water side of the filtration membrane module is completely discharged and filtered. The raw water side in the membrane module was filled with raw water in order, and the operation to return to the membrane filtration step was performed.

酸化剤含有ろ過水逆洗工程においては、酸化剤濃度が３００ｍｇ／Ｌとなるように次亜塩素酸ナトリウム水溶液（１２％）を注入した。また、逆浸透処理工程では、逆浸透膜供給水に対する逆浸透膜透過水の割合を４５％にして実験を行った。 In the oxidizing agent-containing filtered water backwashing step, an aqueous sodium hypochlorite solution (12%) was injected so that the oxidizing agent concentration was 300 mg / L. In the reverse osmosis treatment step, the experiment was conducted with the ratio of the reverse osmosis membrane permeated water to the reverse osmosis membrane feed water being 45%.

運転初期の膜差圧は２５℃温度補正差圧で２０ｋＰａであり、１ヶ月間運転を行った後の膜差圧は２５℃温度補正差圧で６０ｋＰａと洗浄効果が不十分であった。また、原水量に対する、逆洗水として使用された分を差し引いた透過水量の割合は４１．８％であった。なお、実験期間中の原水である海水の平均塩濃度、逆洗水に使用した膜ろ過水の平均塩濃度は実施例１の場合と同じであった。 The membrane differential pressure at the initial stage of operation was 20 kPa at 25 ° C. temperature correction differential pressure, and the membrane differential pressure after one month operation was 60 kPa at 25 ° C. temperature correction differential pressure, and the cleaning effect was insufficient. Moreover, the ratio of the amount of permeate which subtracted the part used as backwash water with respect to the amount of raw water was 41.8%. In addition, the average salt concentration of seawater which is raw water during the experiment period and the average salt concentration of membrane filtration water used for backwash water were the same as those in Example 1.

＜比較例２＞
膜ろ過方法を図６のフローに変更し、膜ろ過工程と膜ろ過工程との間に行う通常逆洗工程を、以下の条件に変更した以外は、実施例１と同様に実験を行った。
膜ろ過工程を３０分間行った後、続いて、逆浸透膜透過水を逆洗水に用いた逆洗工程を３０秒間行い、空気洗浄を行い、ろ過膜モジュール内の原水側の水を全量排出し、ろ過膜モジュール内の原水側を原水で満たす順序で洗浄を行い、再び膜ろ過工程に戻る操作を繰り返した。 <Comparative example 2>
Experiments were conducted in the same manner as in Example 1 except that the membrane filtration method was changed to the flow of FIG. 6 and the normal backwashing step performed between the membrane filtration step and the membrane filtration step was changed to the following conditions.
After performing the membrane filtration process for 30 minutes, subsequently, the backwash process using reverse osmosis membrane permeated water as backwash water is performed for 30 seconds, air washing is performed, and the water on the raw water side in the filtration membrane module is completely discharged. Then, washing was performed in the order of filling the raw water side in the filtration membrane module with the raw water, and the operation of returning to the membrane filtration step was repeated.

運転初期の膜差圧は２５℃温度補正差圧で２０ｋＰａであり、１ヶ月間運転を行った後の膜差圧は２５℃温度補正差圧で３７ｋＰａであった。また、原水量に対する、逆洗水として使用された分を差し引いた透過水量の割合は４０．６％と低下した。なお、実験期間中の原水である海水の平均塩濃度、逆洗水に使用した逆浸透膜透過水の平均塩濃度は実施例１の場合と同じであった。 The membrane differential pressure at the initial stage of operation was 20 kPa at 25 ° C. temperature correction differential pressure, and the membrane differential pressure after one month operation was 37 kPa at 25 ° C. temperature correction differential pressure. Moreover, the ratio of the amount of permeated water which subtracted the part used as backwash water with respect to the amount of raw water fell with 40.6%. In addition, the average salt concentration of the seawater which is the raw water during the experiment period and the average salt concentration of the reverse osmosis membrane permeated water used for the backwash water were the same as those in Example 1.

＜実施例２＞
浸漬型PＶＤＦ中空糸限外ろ過膜モジュールＣＦＵ−１０１５Ｖ（東レ（株）製）を１本、ろ過膜モジュール３として用い、スパイラル型逆浸透膜エレメントＳＵ−８１０（東レ（株）製）を６本装填した逆浸透膜モジュール１３を使用して、図５に示したフローにて以下の条件で実験を行った。 <Example 2>
One immersion type PVDF hollow fiber ultrafiltration membrane module CFU-1015V (manufactured by Toray Industries, Inc.) is used as the filtration membrane module 3, and six spiral reverse osmosis membrane elements SU-810 (manufactured by Toray Industries, Inc.) are used. Using the loaded reverse osmosis membrane module 13, the experiment was performed under the following conditions in the flow shown in FIG.

海水を原水とし、ろ過流束１．７ｍ^３／（ｍ^２・ｄ）、全量ろ過方式かつ定流量ろ過方式で、膜ろ過工程を３０分間行った後、続いて、膜ろ過水を逆洗水に用いた通常逆洗工程を３０秒間行い、空気洗浄を行い、ろ過膜モジュール内の原水側の水を全量排出し、ろ過膜モジュール内の原水側を原水で満水とする順序で洗浄を行い、再び膜ろ過工程に戻る操作を繰り返した。さらに、１日に１回の頻度で、通常逆洗工程を行う代わりに、逆浸透膜透過水を用いた酸化剤含有淡水逆洗工程を１２０秒間行い、薬液保持工程を２０分間行い、酸化剤を含有しない逆浸透膜透過水を逆洗水に用いた淡水逆洗工程（薬剤リンス工程）を１２０秒間行い、ろ過膜モジュール内の原水側の水を全量排出し、ろ過膜モジュール内の原水側を原水で満水とする順序で酸化剤含有淡水による逆洗を行い、膜ろ過工程に戻る操作を行った。 Seawater is used as raw water, and the membrane filtration process is performed for 30 minutes using a filtration flux of 1.7 m ³ / (m ² · d), a total filtration method and a constant flow filtration method, and then the membrane filtration water is backwashed. The normal backwashing process used for 30 seconds is performed, air cleaning is performed, the raw water side in the filtration membrane module is discharged in its entirety, and the raw water side in the filtration membrane module is fully filled with raw water for cleaning. The operation of returning to the membrane filtration step was repeated. Furthermore, instead of performing the normal backwashing process once a day, the oxidizing agent-containing fresh water backwashing process using reverse osmosis membrane permeated water is performed for 120 seconds, the chemical solution holding process is performed for 20 minutes, and the oxidizing agent A fresh water backwash process (drug rinsing process) using reverse osmosis membrane permeated water that does not contain water for 120 seconds, discharges all of the water on the raw water side in the filtration membrane module, and the raw water side in the filtration membrane module Were backwashed with oxidant-containing fresh water in the order of filling the raw water with water, and the operation to return to the membrane filtration step was performed.

運転初期の膜差圧は２５℃温度補正差圧で１８ｋＰａであり、１ヶ月間運転を行った後の膜差圧は２５℃温度補正差圧で３５ｋＰａであった。また、原水量に対する、逆洗水として使用された分を差し引いた透過水量の割合は４２．９％であった。なお、実験期間中の原水である海水の平均塩濃度、通常逆洗に用いた膜ろ過水の平均塩濃度、酸化剤含有逆洗に用いた逆浸透膜透過水の平均塩濃度は、実施例１の場合と同じであった。 The film differential pressure at the initial stage of operation was 18 kPa at 25 ° C. temperature correction differential pressure, and the film differential pressure after one month operation was 35 kPa at 25 ° C. temperature correction differential pressure. Moreover, the ratio of the amount of permeate which subtracted the part used as backwash water with respect to the amount of raw water was 42.9%. The average salt concentration of seawater, which is the raw water during the experimental period, the average salt concentration of membrane filtration water used for normal backwashing, and the average salt concentration of reverse osmosis membrane permeated water used for oxidant-containing backwashing are shown in Examples. It was the same as the case of 1.

以上の実施例及び比較例より、本発明法の膜ろ過方法によると、酸化剤を含有させた淡水を逆洗水に用いた逆洗を時々行うことにより、膜差圧の上昇を抑制でき、さらに、通常逆洗では膜ろ過水を逆洗水に用いることにより、水の回収率を高く維持できる。 From the above examples and comparative examples, according to the membrane filtration method of the present invention, by performing backwashing using fresh water containing oxidant in backwashing water from time to time, it is possible to suppress an increase in membrane differential pressure, Furthermore, in normal backwashing, the rate of water recovery can be maintained high by using membrane filtrate for backwashing water.

従来の一般的な膜ろ過方法の一実施態様を示す工程フロー図である。It is a process flow figure showing one embodiment of the conventional general membrane filtration method. 本発明法に係る膜ろ過方法の一実施態様を示す工程フロー図である。It is a process flow figure showing one embodiment of a membrane filtration method concerning the present invention method. 本発明法に係る膜ろ過方法の別の一実施態様を示す工程フロー図である。It is a process flow figure showing another embodiment of a membrane filtration method concerning the present invention method. 実施例１に係る膜ろ過方法の実施態様を示す工程フロー図である。It is a process flow figure showing an embodiment of a membrane filtration method concerning Example 1. 実施例２に係る膜ろ過方法の実施態様を示す工程フロー図である。It is a process flow figure showing an embodiment of a membrane filtration method concerning Example 2. 比較例２に係る膜ろ過方法の実施態様を示す工程フロー図である。It is a process flow figure showing an embodiment of a membrane filtration method concerning comparative example 2.

符号の説明Explanation of symbols

１：ろ過ポンプ
２：原水配管
３：ろ過膜モジュール
４：ろ過水配管
５：ろ過水槽
６：浸漬槽
７：原水供給ポンプ
１１：高圧ポンプ
１２：逆浸透膜供給配管
１３：逆浸透膜モジュール
１４：透過水配管
１５：濃縮水配管
１６：淡水配管
１７：淡水水槽
１８：透過水返送配管
２１：逆洗ポンプ
２２：逆洗水配管
２３：酸化剤貯槽
２４：酸化剤注入ポンプ
２５：酸化剤注入配管
２６：逆洗水排水配管
２７：ドレン排水配管
３１：淡水逆洗ポンプ
３２：淡水逆洗配管
３３：膜ろ過水逆洗弁
３４：淡水逆洗弁 1: Filtration pump 2: Raw water pipe 3: Filtration membrane module 4: Filtration water pipe 5: Filtration water tank 6: Immersion tank 7: Raw water supply pump 11: High pressure pump 12: Reverse osmosis membrane supply pipe 13: Reverse osmosis membrane module 14: Permeated water pipe 15: Concentrated water pipe 16: Fresh water pipe 17: Fresh water tank 18: Permeated water return pipe 21: Backwash pump 22: Backwash water pipe 23: Oxidant storage tank 24: Oxidant injection pump 25: Oxidant injection pipe 26: Backwash water drain pipe 27: Drain drain pipe 31: Fresh water back wash pump 32: Fresh water back wash pipe 33: Membrane filtrate backwash valve 34: Fresh water backwash valve

Claims

塩濃度が１，０００ｍｇ／Ｌ以上の原水をろ過膜モジュールで処理して膜ろ過水を得る膜ろ過方法において、膜ろ過工程の間にろ過膜モジュールの逆洗を行う逆洗工程を有し、該逆洗工程として、酸化剤を含有させていない、前記膜ろ過水を逆浸透処理した塩濃度が５００ｍｇ／Ｌ未満の逆浸透膜透過水を逆洗水に用いて前記ろ過膜モジュールを逆洗し、前記ろ過膜モジュールの原水側の水を排出することを行い、引き続いて、酸化剤を５０ｍｇ／Ｌ以上の濃度で含有させた前記逆浸透膜透過水を逆洗水に用いた酸化剤含有淡水逆洗工程を行い、引き続いて、前記酸化剤を含有する前記逆浸透膜透過水を前記ろ過膜モジュール内で保持させた状態を３〜１２０分間維持することを行い、かつ、該酸化剤含有淡水逆洗工程の実施頻度を３時間〜１０日間に１回とすることを特徴とする膜ろ過方法。 In membrane filtration method by salt concentration processes the above raw water 1,000 mg / L in the filtration membrane module obtaining a membrane filtration water has a backwash step of performing backwash of the filtration membrane module during the membrane filtration step In the backwashing step , the membrane filter water is reversely osmosis treated using reverse osmosis membrane permeated water having a salt concentration of less than 500 mg / L, which contains no oxidant, washing, and the filtration membrane subjected to discharge water of the raw water side of the module, subsequently, using the reverse osmosis membrane permeated water an acid agent was contained at a concentration of at least 50 mg / L in the backwash water oxidation agent performed as containing fresh water backwash Engineering, subsequently, performed in that the reverse osmosis membrane permeated water containing the oxidizing agent to maintain the filter membrane state of being held in the module 3 to 120 minutes, and the The frequency of the oxidant-containing fresh water backwash process is 3 hours ~ Membrane filtration method characterized in that a one to zero days.