JP3641854B2 - Reverse osmosis membrane separation method and reverse osmosis membrane separation device - Google Patents
Reverse osmosis membrane separation method and reverse osmosis membrane separation device Download PDFInfo
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Description
【０００１】
【産業上の利用分野】
本発明は、逆浸透膜による脱塩、分離方法に関するものであり、特に、海水の淡水化や、かん水の淡水化、および廃水の再利用等に関するものである。
【０００２】
【従来の技術】
膜による分離技術は、海水及びカン水の淡水化、医療、工業用純水、超純水の製造、工業廃水処理など幅広い分野に利用されている。これらの膜による分離において、微生物による分離装置の汚染は、被処理液中の微粒子、ＴＯＣ（全有機炭素）を増加させ、得られる透過水の水質を悪化することや、膜面上で微生物が繁殖したり、あるいは微生物およびその代謝物などからなる有機性物質が膜面に付着したりして、膜の透過性、分離性を低下させるなどの問題を生じる。そのため膜分離装置の殺菌は膜分離を行なう上で重要な技術である。膜分離装置の殺菌法は種々提案されており、一般的には殺菌剤を常時、あるいは間欠的に供給液に添加する方法がとられている。
【０００３】
殺菌剤としては、古くから塩素系の殺菌剤が用いられてきたが、最近では、用いる膜に合せて、クロラミン類、過酸化水素、過酢酸、亜硫酸水素ナトリウムなどの塩素に代る新しい殺菌方法が提案されている。しかし、その価格および操作の容易さから塩素系殺菌剤が用いられているのが現状である。逆浸透膜はその素材の特徴から塩素などの酸化性物質によって化学的に劣化を生じる。最近では耐酸化剤性の比較的高い膜素材が開発されているがその耐久性も充分なものであるとはいえない。
【０００４】
このため、一般的には塩素系などの殺菌剤を用いて供給液の殺菌を行ない、逆浸透膜に供給する前に還元剤を用い、遊離塩素を還元した後に、分離操作を行うようにしている。ここで還元剤としては、亜硫酸ナトリウム、亜硫酸水素ナトリウムが広く用いられている。
【０００５】
逆浸透膜装置を安全に運転するため、酸化剤（殺菌剤）が膜装置に流入しないように、膜装置の供給水において残留塩素等の酸化剤濃度あるいはこれに相当する値である酸化還元電位（ＯＲＰ）を測定して、酸化剤の有無を検出し、運転管理を行うのが通常であった。
【０００６】
【発明が解決しようとする課題】
従来の装置で問題なく運転されるプラントもあるが、近年の海水淡水化等の装置においては、酸化剤の存在を逆浸透膜の供給水中で検出監視し、その検出器が正常に作動しているにもかかわらず、酸化剤によって膜の性能劣化が生じるという問題のあることが解り、これまでの方法では必ずしも充分でないことが明らかになってきた。この現象は、ポリアミド系の逆浸透膜や、これよりも耐酸化剤性が高いといわれている酢酸セルロース系の膜においても起きていることが明らかとなってきた。
【０００７】
【課題を解決するための手段】
課題解決のため、本発明は下記の構成を有する。
【０００８】
すなわち、「逆浸透膜を用いて被処理水を透過液と濃縮液とに分離する方法であって、濃縮液中の酸化剤濃度あるいは還元剤濃度を測定することを特徴とする逆浸透膜分離方法」および「被処理液を昇圧するポンプと、昇圧された被処理液を透過液と濃縮液とに分離する逆浸透膜と、濃縮液の酸化剤濃度あるいは還元剤濃度の測定装置とを設けたことを特徴とする逆浸透膜分離装置」に関するものである。
【０００９】
本発明において、逆浸透分離とは、逆浸透膜分離装置を用いて造水、濃縮、分離などの目的で被処理液を透過液と濃縮液に分離することをいう。また、逆浸透膜分離装置とは造水、濃縮、分離などの目的で被処理液を加圧下で逆浸透膜モジュールに供給し、透過液と濃縮液に分離するための装置をいい、通常は逆浸透膜エレメント、圧力容器、加圧ポンプなどで構成される。該逆浸透膜装置に供給される被分離液は通常、殺菌剤、凝集剤、さらに還元剤、ｐＨ調整剤などの薬液添加と、砂濾過、活性炭濾過、保安フィルターなどの前処理が行なわれる。例えば、海水の脱塩の場合には、海水を取込んだ後、沈殿池で粒子などを分離し、またここで殺菌剤を添加して殺菌を行なう。さらに、塩化鉄などの凝集剤を添加して砂濾過を行なう。ろ液は貯槽に貯められ、硫酸などでｐＨを調整した後、高圧ポンプに送られる。この送液中に亜硫酸水素ナトリウムなどの還元剤を添加して殺菌剤を消去し、保安フィルターを通過した後、高圧ポンプで昇圧されて逆浸透膜モジュールに供給される。ただし、これらの前処理は、用いる供給液の種類、用途に応じて適宜取捨選択される。
【００１０】
ここで逆浸透膜とは、被分離混合液中の一部の成分、例えば溶媒を透過させ他の成分を透過させない半透性を有する膜である。その素材には酢酸セルロース系ポリマー、ポリアミド、ポリエステル、ポリイミド、ビニルポリマーなどの高分子素材がよく使用されている。またその膜構造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方の面に向けて徐々に大きな孔径の微細孔を有する非対称膜、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活性層を有する複合膜がある。膜形態には中空糸、平膜がある。しかし、本発明の方法は、逆浸透膜の素材、膜構造や膜形態によらず利用することができ、いづれも効果がある。代表的な逆浸透膜としては、例えば酢酸セルロース系やポリアミド系の非対称膜およびポリアミド系、ポリ尿素系の活性層を有する複合膜などがあげられる。これらのなかでも、酢酸セルロース系の非対称膜、ポリアミド系の複合膜に本発明の方法が有効であり、さらに芳香族系のポリアミド複合膜では効果が大きい。
【００１１】
酢酸セルロース系の膜としては、酢酸セルロース、二酢酸セルロース、三酢酸セルロース、プロピオン酸セルロース、酪酸セルロース等のセルロースの有機
酸エステルの単独もしくはこれらの混合物並びに混合エステルを用いたものが挙げられる。ポリアミド系の膜としては脂肪族、芳香族のポリアミドで線状ポリマー、架橋ポリマーが挙げられる。
【００１２】
逆浸透膜モジュールとは上記逆浸透膜を実際に使用するために形態化したものであり、平膜の場合はスパイラル、チューブラー、プレート・アンド・フレームのモジュールに組み込んで、また中空糸の場合は束ねた上でモジュールに組み込んで使用することができるが、本発明はこれらの逆浸透膜モジュールの形態に左右されるものではない。
【００１３】
一般的に、逆浸透膜装置の前処理の段階で添加される殺菌剤は、供給液中あるいは前処理装置中での菌類、微生物の繁殖、付着などを防ぐために添加されるもので、塩素系殺菌剤、過酸化水素類、過酢酸類、クロラミン類などが使用できる。一般的には、殺菌力の点から酸化性物質が、さらに、価格、殺菌力、取り扱いの容易さなどから、塩素系の殺菌剤を使用することが多い。
【００１４】
殺菌剤の濃度は、用いる供給水の水質にもよるが、一般的に供給液に添加した後の残留有効濃度で０．１〜１０ｍｇ／Ｌ程度であり、塩素系殺菌剤においては、あとの還元剤の添加量を減らすためと、殺菌に必要な有効濃度を考え、還元剤添加の直前濃度で、残留塩素濃度として０．１〜１ｍｇ／Ｌ程度である。残留塩素とは、遊離塩素と結合塩素の合計をいい、残留塩素の濃度測定はＪＩＳ−Ｋ０１０１に記載されているオルトトリジン法などによって簡単に行なうことができる。
【００１５】
逆浸透膜は酸化力のある殺菌剤、特に塩素系の殺菌剤が直接接触すると膜性能が低下する。特にポリアミド系やポリ尿素系の複合膜は、酢酸セルロース系の非対称膜に比較して耐塩素性が劣り、酢酸セルロース系の非対称膜においてもそのｐＨなど条件によっては大きな性能低下が起こりうる。そこで、実際のプラントの多くでは塩素系殺菌剤の使用時には逆浸透膜に直接塩素が接触するのを防ぐために、被処理液を逆浸透膜モジュールに供給する前に還元剤を添加して残存する殺菌剤を連続的にあるいは一定時間還元することが必要となる。また、クロラミン類など膜性能への影響のない、あるいは少ない殺菌剤の使用時においても運転の安定化、トラブル時の対策のために、還元剤を添加することが好ましい。
【００１６】
還元剤としては、水溶性で、還元性が大きく、逆浸透膜への影響のないものを使用することができる。さらに価格が安価である、取り扱いが容易であるなどの点から、亜硫酸ナトリウム、亜硫酸水素ナトリウムなどが好ましい。用いる還元剤の濃度は供給液中に残存している殺菌剤を全て消去するのに充分な量が必要である。また、還元剤は供給液中に溶存している酸素とも反応するので、残存殺菌剤と溶存酸素の量、温度やｐＨなどを考慮して、殺菌剤添加量の１〜１０倍当量を添加することが好ましい。さらに、殺菌剤を完全に消去することと還元剤の使用量を低減することを考慮すると殺菌剤の１．１〜５倍当量の還元剤が好ましい。通常、還元剤は殺菌剤よりも過剰に加えられるので逆浸透膜装置の供給液には未反応の還元剤あるいはその反応生成物が混在している。
【００１７】
還元剤として、亜硫酸ナトリウム、亜硫酸水素ナトリウムを用いる場合でも、標準的な海水のように、銅の濃度が２μｇ／Ｌ以下の場合には、酸化性物質の生成は実質的に問題とならないレベルであるが、この濃度を超える場合には、温度、ｐＨ、全溶解性物質の濃度、反応時間、溶存酸素濃度の条件によっても異なるが、多くの場合、酸化性物質が生成される可能性があり、この場合、逆浸透膜の性能が低下する。
【００１８】
本発明者らは、逆浸透膜装置の運転に際して、殺菌剤である塩素などの酸化性物質を還元剤で完全に消去し、且つ逆浸透膜装置の供給水中に酸化剤が検出されていないにもかかわらず、膜性能が低下する問題についてその原因究明と対策について、鋭意検討した結果、銅、コバルトなどのイオンが存在している場合には、これら重金属は膜の種類によらずそのほとんどが膜を透過しないため、濃縮水でその濃度が次第に高くなること（給水中の銅が濃縮されること）と、あるいは逆浸透膜の膜面に付着ないしは沈着した給水中からの供給物である物質からの溶出があることとから、例え逆浸透膜の供給水中に酸化剤が無くとも、逆浸透膜の中を供給水が通過する間に、その膜面でこの重金属が触媒となって還元剤が反応して酸化性物質が生成されることが問題の原因であることを見いだすことに成功した。
【００１９】
このため、逆浸透膜を用いる淡水化装置においては、その逆浸透膜の濃縮水中の酸化剤の存在有無を監視することより、酸化剤が生成される初期の段階で検出可能となり、逆浸透膜の性能劣化を最小限に押さえることができるようになり、非常に効果のあることを見出し、本発明に到達したものである。
【００２０】
濃縮水中の酸化剤の検出方法は、特に規定されるものではないが、通常は酸化還元電位（ＯＲＰ）、または残留塩素の計測する方法が挙げられ、これらの値が大きいほど酸化剤が多く存在していると判定できる。また、逆に還元剤の存在量が少なければ、酸化剤が多いことが推定できるので、還元剤を検出する方法も有効であり、例えば、残存ＳＢＳ（重亜硫酸ナトリウム）濃度を計測することが挙げられ、ＳＢＳが少ないほど還元剤が少なく、即ち酸化剤が多いと判定できる。
【００２１】
また、逆浸透膜の濃縮水中の酸化剤濃度あるいは還元剤濃度の検出データに基づき、警報を出したり、装置の運転を停止し、膜の酸洗浄を実施するなどの、装置全体の運転を制御できるようにすることもできる。前記警報や各種の制御が発動されるべき検出データのレベルは、装置や膜の種類、あるいは水温などの環境条件などに応じて適宜設定されるものであるが、一例を挙げるならば、酸化還元電位（ｐＨ７．０に換算した値）としては、３００ｍＶ以上、好ましくは２５０ｍＶ以上、残留塩素としては、オルトトリジン法で発色（肉眼で０．１ｐｐｍ、装置判定で０．０１ｐｐｍ）が認められる場合、ＳＢＳ量としては０．１ｐｐｍ以下、好ましくは１ｐｐｍ以下、より好ましくは２ｐｐｍ以下のとき、膜の酸洗浄を実施するなどの制御を発動すればよい。これらのパラメータ計測やそのための測定装置を単独で用いても良いし、いくつか複数を組み合わせて用いても良い。また測定手段としては、テレメータ方式の自動測定装置でもよいし、ハンディタイプの測定装置や判定試験器で随時測定しても良いし、その他人の手で試験反応を実施する方法でも良い。
【００２２】
また、供給水側でも測定することを併せることにより、逆浸透膜中での酸化剤の存在の有無をより正確に判断することが出来るのでより好ましい。
【００２３】
なお、洗浄方法としては、前記銅化合物が除去できるものであるのならば特に限定されるものではないが、例えば該銅化合物を溶解できる水溶液、好ましくは酸性水溶液を用いた酸洗浄が挙げられる。酸洗浄としては特に限定されるものではないが、銅化合物の溶解性を考慮するとｐＨ３以下が好ましく、ｐＨ２以下がより好ましい。しかし、あまりｐＨが低すぎると逆浸透膜素材や装置や配管の金属材料などを侵す恐れがあるので材料に応じて適宜ｐＨの下限値を設定すべきである。酸洗浄としては例えば、有機酸または無機酸の水溶液、あるいはそれに塩基性物質を加えて、ｐＨ乃至は緩衝性を調製した溶液を膜の供給水側に流通、循環、乃至は静置させることにより、行われる。
【００２４】
【実施例】
実施例１
図１の装置で、海水を、圧力５６ｋｇ／ｃｍ2 、温度２５℃、回収率４０％、透過水量１２ｍ3 ／ｄａｙ、ｐＨ６．７、前処理水中の残留塩素濃度０．５ｍｇ／Ｌ、逆浸透膜供給水中の脱塩素剤ＳＢＳ（ＮａＨＳＯ3 ）４ｍｇ／Ｌの条件で、逆浸透膜（東レ株式会社製ＳＵー８１０×４本）を用いて、逆浸透分離処理をした。
【００２５】
上記条件でしばらく運転したところ、濃縮水のＯＲＰが顕著に上昇する現象を捕らえることが出来た（図２実線）。
【００２６】
比較例１
実施例の処理装置において、給水のＯＲＰを測定した。実施例１のＯＲＰ（濃縮水の酸化還元電位）が顕著に上昇する現象が起きたとき、給水のＯＲＰには、何等変化を検出することは出来なかった（図２点線）。
【００２７】
実施例２
実施例１においてＯＲＰ（濃縮水の酸化還元電位）に顕著な上昇が生じ３００ｍＶに達した時点で装置を停止し、膜の酸洗浄を実施した。即ち、２％クエン酸水溶液をアンモニアでｐＨを２．５に調製した酸性水溶液を２０Ｌ／ｍｉｎの流速で３０分間膜の供給水側に流した。流すのを停止し、３時間半放置した。次に放置した水溶液を３０分間循環させた。以上の酸洗浄処理をしたのち、運転を再開したところ、濃縮水のＯＲＰは低下し、この洗浄前後で、膜の性能はほとんど変化せず、膜の性能を維持することが出来た（図２）。
【００２８】
【発明の効果】
逆浸透膜の濃縮水中の酸化剤の有無を検出することにより、逆浸透膜装置の性能低下を早期に把握できるので、性能の維持安定化ができるようになり、膜の使用期間を延長でき、装置の運転費用の低減化が図れる。
【図面の簡単な説明】
【図１】 逆浸透膜分離装置のフローと酸化剤の検出位置
【図２】 濃縮水及び給水でのＯＲＰ値と膜性能（除去率）[0001]
[Industrial application fields]
The present invention is desalted by reverse osmosis membrane, it is related to the separation method, in particular, desalination or desalination of brine, and to a recycling such waste water.
[0002]
[Prior art]
Membrane separation technology is used in a wide range of fields such as desalination of seawater and can water, medical treatment, industrial pure water, ultrapure water production, and industrial wastewater treatment. In the separation by these membranes, contamination of the separation device by microorganisms increases the fine particles in the liquid to be treated, TOC (total organic carbon), deteriorates the quality of the permeated water obtained, and microorganisms on the membrane surface. Proliferation or organic substances composed of microorganisms and their metabolites adhere to the membrane surface, causing problems such as reducing the permeability and separation of the membrane. Therefore, sterilization of the membrane separation apparatus is an important technique for performing membrane separation. Various sterilization methods for membrane separators have been proposed, and generally a method in which a sterilizing agent is added to the supply liquid constantly or intermittently is employed.
[0003]
The disinfectant has been chlorine disinfectant is used for a long time, and recently, in accordance with the film used, chloramines, hydrogen peroxide, peracetic acid, a new sterilization alternative to chlorine such as sodium bisulfite Has been proposed. However, chlorinated fungicides are currently used because of their price and ease of operation. Reverse osmosis membranes are chemically degraded by oxidizing substances such as chlorine due to the characteristics of the material. Recently, a film material having a relatively high oxidation resistance has been developed, but its durability is not sufficient.
[0004]
For this reason, in general, the supply liquid is sterilized using a chlorine-based sterilizing agent, and the reducing agent is used before being supplied to the reverse osmosis membrane. After reducing free chlorine, the separation operation is performed. Yes. Here, sodium sulfite and sodium hydrogen sulfite are widely used as the reducing agent.
[0005]
In order to operate the reverse osmosis membrane device safely, an oxidation-reduction potential which is a concentration of an oxidant such as residual chlorine in the water supplied to the membrane device or a value corresponding thereto so that an oxidant (bactericidal agent) does not flow into the membrane device. It was usual to measure (ORP), detect the presence or absence of an oxidizing agent, and perform operation management.
[0006]
[Problems to be solved by the invention]
Some plants operate without problems with conventional devices, but in recent devices such as seawater desalination, the presence of an oxidant is detected and monitored in the reverse osmosis membrane feed water, and the detector operates normally. Nevertheless, it has been found that there is a problem that the performance of the film is deteriorated by the oxidizing agent, and it has become clear that the conventional methods are not necessarily sufficient. It has been clarified that this phenomenon occurs also in polyamide-based reverse osmosis membranes and cellulose acetate-based membranes, which are said to have higher oxidation resistance.
[0007]
[Means for Solving the Problems]
In order to solve the problem, the present invention has the following configuration.
[0008]
That is, "using a reverse osmosis membrane to a process for separating the water to be treated and the permeate and the concentrate, reverse osmosis, characterized in that measuring the oxidant concentration or reducing agent concentration in the concentrated solution Membrane separation method ”and“ a pump for boosting the liquid to be treated, a reverse osmosis membrane for separating the pressure-treated liquid into a permeate and a concentrated liquid, and an apparatus for measuring the oxidizing agent concentration or reducing agent concentration of the concentrated liquid, The present invention relates to a reverse osmosis membrane separation device characterized in that
[0009]
In the present invention, reverse osmosis separation means that a liquid to be treated is separated into a permeate and a concentrate for the purpose of water production, concentration, separation, etc. using a reverse osmosis membrane separation device. The reverse osmosis membrane separation device is a device for supplying the liquid to be treated to the reverse osmosis membrane module under pressure for the purpose of fresh water, concentration, separation, etc., and separating it into permeate and concentrate. Consists of reverse osmosis membrane element, pressure vessel, pressurizing pump and the like. The liquid to be separated supplied to the reverse osmosis membrane device is usually subjected to pretreatment such as addition of chemicals such as bactericides, flocculants, reducing agents, pH adjusters, sand filtration, activated carbon filtration, and safety filters. For example, in the case of desalination of seawater, after taking in seawater, particles and the like are separated in a sedimentation basin, and a bactericidal agent is added here to perform sterilization. Furthermore, sand filtration is performed by adding a flocculant such as iron chloride. The filtrate is stored in a storage tank, adjusted to pH with sulfuric acid, etc., and then sent to a high pressure pump. A reducing agent such as sodium bisulfite is added to the solution to eliminate the bactericidal agent, and after passing through a safety filter, the pressure is increased by a high-pressure pump and supplied to the reverse osmosis membrane module. However, these pretreatments are appropriately selected according to the type and application of the supply liquid to be used.
[0010]
Here, the reverse osmosis membrane is a membrane having a semi-permeability that allows a part of components in the mixed liquid to be separated, for example, a solvent to permeate and does not permeate other components. As the material, polymer materials such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer are often used. Also, the membrane structure has a dense layer on at least one side of the membrane, an asymmetric membrane having fine pores gradually increasing from the dense layer to the inside of the membrane or the other side, and another layer on the dense layer of the asymmetric membrane. There are composite membranes with a very thin active layer formed of a material. The membrane form includes hollow fiber and flat membrane. However, the method of the present invention can be used regardless of the reverse osmosis membrane material, membrane structure, and membrane form, and both are effective. Typical reverse osmosis membranes include, for example, cellulose acetate-based and polyamide-based asymmetric membranes and composite membranes having polyamide-based and polyurea-based active layers. Among these, the method of the present invention is effective for cellulose acetate-based asymmetric membranes and polyamide-based composite membranes. Furthermore, aromatic polyamide composite membranes are highly effective.
[0011]
Examples of the cellulose acetate film include cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, and other organic acid esters of cellulose alone or a mixture thereof and those using mixed esters. Examples of the polyamide-based film include aliphatic and aromatic polyamides, linear polymers, and crosslinked polymers.
[0012]
The reverse osmosis membrane module is formed for actual use of the above reverse osmosis membrane. In the case of a flat membrane, it is incorporated into a spiral, tubular, plate and frame module, or in the case of a hollow fiber. Can be used after being bundled into a module, but the present invention does not depend on the form of these reverse osmosis membrane modules.
[0013]
In general, the bactericidal agent added at the pretreatment stage of the reverse osmosis membrane device is added to prevent the growth of fungi and microorganisms in the supply liquid or in the pretreatment device. Bactericides, hydrogen peroxides, peracetic acids, chloramines, etc. can be used. In general, an oxidizing substance is often used from the viewpoint of bactericidal power, and a chlorine-based bactericidal agent is often used because of its cost, bactericidal power, ease of handling, and the like.
[0014]
The concentration of the disinfectant depends on the quality of the feed water used, but is generally about 0.1 to 10 mg / L of residual effective concentration after being added to the supply solution. Considering the effective concentration necessary for sterilization in order to reduce the amount of reducing agent added, the concentration immediately before the reducing agent addition is about 0.1 to 1 mg / L as the residual chlorine concentration. Residual chlorine means the sum of free chlorine and combined chlorine, and the concentration of residual chlorine can be easily measured by the orthotolidine method described in JIS-K0101.
[0015]
When a reverse osmosis membrane is in direct contact with an oxidizing disinfectant, particularly a chlorine-based disinfectant, the membrane performance deteriorates. Particularly, polyamide-based and polyurea-based composite membranes are inferior in chlorine resistance compared to cellulose acetate-based asymmetric membranes, and even cellulose acetate-based asymmetric membranes can have a significant performance deterioration depending on conditions such as pH. Therefore, in many actual plants, in order to prevent chlorine from coming into direct contact with the reverse osmosis membrane when using a chlorine-based disinfectant, a reducing agent is added and left before supplying the liquid to be treated to the reverse osmosis membrane module. It is necessary to reduce the disinfectant continuously or for a certain period of time. Further, it is preferable to add a reducing agent in order to stabilize operation and take measures against troubles even when using a bactericidal agent such as chloramines which does not affect the membrane performance or has a small amount.
[0016]
As the reducing agent, a water-soluble and highly reducing agent that does not affect the reverse osmosis membrane can be used. Further, sodium sulfite, sodium hydrogen sulfite and the like are preferable from the viewpoints of low price and easy handling. The concentration of the reducing agent used should be sufficient to erase all the germicide remaining in the feed solution. In addition, since the reducing agent also reacts with oxygen dissolved in the supply liquid, 1 to 10 times the equivalent amount of the sterilizing agent is added in consideration of the amount of residual sterilizing agent and dissolved oxygen, temperature, pH, and the like. It is preferable. Furthermore, in consideration of completely eliminating the bactericidal agent and reducing the amount of the reducing agent used, a reducing agent equivalent to 1.1 to 5 times the bactericidal agent is preferable. Usually, the reducing agent is added in excess of the sterilizing agent, so that the unreacted reducing agent or its reaction product is mixed in the supply liquid of the reverse osmosis membrane apparatus.
[0017]
Even when sodium sulfite or sodium hydrogen sulfite is used as the reducing agent, as with standard seawater, when the copper concentration is 2 μg / L or less, the generation of the oxidizing substance is at a level that does not substantially cause a problem. However, if this concentration is exceeded, depending on the conditions of temperature, pH, concentration of all soluble substances, reaction time, dissolved oxygen concentration, in many cases, oxidizing substances may be generated. In this case, the performance of the reverse osmosis membrane is reduced.
[0018]
In the operation of the reverse osmosis membrane device, the present inventors completely erased an oxidizing substance such as chlorine as a bactericide with a reducing agent, and no oxidant is detected in the water supplied to the reverse osmosis membrane device. Nevertheless, as a result of diligent investigation on the cause and countermeasures for the problem of film performance degradation, when heavy ions such as copper and cobalt exist, most of these heavy metals are not related to the type of film. Substances that are supplied from the feed water that does not permeate the membrane, and whose concentration gradually increases with concentrated water (concentration of copper in the feed water), or that adheres to or deposits on the membrane surface of the reverse osmosis membrane Therefore, even if there is no oxidizing agent in the feed water of the reverse osmosis membrane, the heavy metal acts as a catalyst on the membrane surface while the feed water passes through the reverse osmosis membrane. Reacts to produce oxidizing substances It is successful in finding that it is the cause of the problem.
[0019]
For this reason, in a desalination apparatus using a reverse osmosis membrane, by monitoring the presence or absence of an oxidant in the concentrated water of the reverse osmosis membrane, it becomes possible to detect at an early stage when the oxidant is generated. As a result, the present invention has been found to be extremely effective.
[0020]
The method for detecting the oxidant in the concentrated water is not particularly defined, but usually there is a method for measuring the oxidation-reduction potential (ORP) or residual chlorine. The larger these values, the more oxidant is present. Can be determined. On the other hand, if the amount of the reducing agent is small, it can be estimated that the oxidizing agent is large. Therefore, a method for detecting the reducing agent is also effective, for example, measuring the residual SBS (sodium bisulfite) concentration. It can be determined that the smaller the SBS, the less the reducing agent, that is, the more the oxidizing agent.
[0021]
In addition, based on the detected data of the oxidant concentration or reducing agent concentration in the concentrated water of the reverse osmosis membrane, control the operation of the entire device, such as issuing an alarm, stopping the device operation, and performing acid cleaning of the membrane. It can also be made possible. The level of the detection data on which the alarm and various controls should be activated is appropriately set according to the environmental conditions such as the type of the device, the membrane, or the water temperature. When the potential (value converted to pH 7.0) is 300 mV or higher, preferably 250 mV or higher, and the residual chlorine is colored by the orthotolidine method (0.1 ppm by the naked eye, 0.01 ppm by device judgment), SBS When the amount is 0.1 ppm or less, preferably 1 ppm or less, more preferably 2 ppm or less, control such as acid cleaning of the film may be activated. These parameter measurements and measurement devices therefor may be used alone or in combination of several. As a measuring means, a telemeter type automatic measuring device may be used, a handy type measuring device or a judgment tester may be used as needed, or a method in which a test reaction is carried out by other human hands may be used.
[0022]
Moreover, it is more preferable to combine the measurement on the supply water side because the presence or absence of the oxidizing agent in the reverse osmosis membrane can be determined more accurately.
[0023]
The washing method is not particularly limited as long as it can remove the copper compound, and examples thereof include an aqueous solution that can dissolve the copper compound, preferably an acid washing using an acidic aqueous solution. Although it does not specifically limit as acid washing, Considering the solubility of a copper compound, pH 3 or less is preferable and pH 2 or less is more preferable. However, if the pH is too low, the reverse osmosis membrane material, the metal material of the apparatus or piping, etc. may be affected, so the lower limit of pH should be set appropriately according to the material. As acid cleaning, for example, an aqueous solution of an organic acid or an inorganic acid, or a basic substance is added to the solution to adjust the pH or buffering property, and the solution is circulated, circulated, or allowed to stand on the supply water side of the membrane. Done.
[0024]
【Example】
Example 1
In the apparatus of FIG. 1, seawater is pressure 56 kg / cm 2 , temperature 25 ° C., recovery rate 40%, permeated water amount 12 m 3 / day, pH 6.7, residual chlorine concentration in pretreated water 0.5 mg / L, reverse osmosis. Reverse osmosis separation treatment was performed using a reverse osmosis membrane (SU-810 × 4 manufactured by Toray Industries, Inc.) under the condition of a dechlorinating agent SBS (NaHSO 3 ) 4 mg / L in the membrane feed water.
[0025]
When operated for a while under the above conditions, it was possible to capture the phenomenon that the ORP of the concentrated water rose significantly (solid line in FIG. 2).
[0026]
Comparative Example 1
In the processing apparatus of the example, the ORP of water supply was measured. When a phenomenon in which the ORP (concentrated water oxidation-reduction potential) of Example 1 significantly increased occurred, no change was detected in the ORP of the water supply (dotted line in FIG. 2).
[0027]
Example 2
Stop device when significant increase was reached 300mV occur ORP (oxidation-reduction potential of the retentate) in Example 1 was carried out acid washing of the membrane. That is, an acidic aqueous solution prepared by adjusting the pH of a 2% aqueous citric acid solution to 2.5 with ammonia was allowed to flow to the feed water side of the membrane at a flow rate of 20 L / min for 30 minutes. The flow was stopped and left for 3 and a half hours. The standing aqueous solution was then circulated for 30 minutes. When the operation was resumed after the above acid cleaning treatment, the ORP of the concentrated water decreased, and the membrane performance was hardly changed before and after the washing, and the membrane performance could be maintained (FIG. 2). ).
[0028]
【The invention's effect】
More presence or absence of oxidizing agent in the concentrate water in the reverse osmosis membrane in a detection child, it is possible to grasp the performance deterioration of the reverse osmosis unit at an early stage, will be able to maintain stabilization of the performance, extend the life of the film It is possible to reduce the operating cost of the apparatus.
[Brief description of the drawings]
[Fig. 1] Flow of reverse osmosis membrane separator and detection position of oxidant [Fig. 2] ORP value and membrane performance (removal rate) in concentrated water and feed water
Claims (11)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21917995A JP3641854B2 (en) | 1995-08-28 | 1995-08-28 | Reverse osmosis membrane separation method and reverse osmosis membrane separation device |
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| Application Number | Priority Date | Filing Date | Title |
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| JP21917995A JP3641854B2 (en) | 1995-08-28 | 1995-08-28 | Reverse osmosis membrane separation method and reverse osmosis membrane separation device |
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| Publication Number | Publication Date |
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| JPH0957076A JPH0957076A (en) | 1997-03-04 |
| JP3641854B2 true JP3641854B2 (en) | 2005-04-27 |
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| JP21917995A Expired - Fee Related JP3641854B2 (en) | 1995-08-28 | 1995-08-28 | Reverse osmosis membrane separation method and reverse osmosis membrane separation device |
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| JP2011110531A (en) | 2009-11-30 | 2011-06-09 | Mitsubishi Heavy Ind Ltd | Desalination apparatus and desalination method |
| JP5807634B2 (en) * | 2010-03-31 | 2015-11-10 | 栗田工業株式会社 | Reverse osmosis membrane treatment method |
| JP5634250B2 (en) * | 2010-12-18 | 2014-12-03 | 三菱重工業株式会社 | Membrane monitoring method |
| JP5669651B2 (en) * | 2011-03-31 | 2015-02-12 | 三菱重工業株式会社 | Desalination apparatus and desalination method |
| JP5908185B2 (en) * | 2013-12-10 | 2016-04-26 | 学校法人 中央大学 | Organic film modification method, modified organic film, and reformer |
| JP5928504B2 (en) * | 2014-02-19 | 2016-06-01 | 三浦工業株式会社 | Water treatment method and water treatment system |
| JP5888354B2 (en) * | 2014-02-19 | 2016-03-22 | 三浦工業株式会社 | Water treatment method and water treatment system |
| JP5888355B2 (en) * | 2014-02-19 | 2016-03-22 | 三浦工業株式会社 | Water treatment method and water treatment system |
| MY188356A (en) | 2014-12-25 | 2021-12-02 | Organo Corp | Method for controlling slime on separation membrane |
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