JP2004097911A - Treatment method for highly concentrated solution using reverse osmosis membrane - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、高濃度溶液の逆浸透処理に関する発明であり、特に海水の淡水化を目的とする分離方法に関するものである。
【０００２】
【従来の技術】
逆浸透法は、海水及びかん水の淡水化、半導体工業及び医薬品工業用の純水、超純水の製造、都市排水処理等の幅広い分野で利用されている。蒸発法、電気透析法と比較して省エネルギーの点で有利であり、広く普及が進んでいる。
特に、中空糸型逆浸透膜は、単位容積当たりの膜面積を大きくできるため、膜分離操作に適した形状であり、例えば、逆浸透膜による海水淡水化分野では広く用いられている
【０００３】
逆浸透法で処理された水は飲料水にも使用されているが、安全意識の高まりともに、水質基準の遵守が求められている。水質基準値を達成するため、逆浸透膜処理した透過水を一旦集めて、再度逆浸透膜で処理する２段法が検討されている。
【０００４】
米国特許公報４，５７４，０４９には、１段目の逆浸透膜処理された透過水の全量が２段目の逆浸透膜で処理され、２段目の逆浸透膜の濃縮水が１段目の供給水に戻す処理方法が開示されている。しかしながら、この方法では、１段目の逆浸透膜処理された透過水の全量が２段目で処理されるので、消費エネルギーが大きくなること、また、原水の水質によっては透過水の水質が必要以上になる場合があり、好ましくない。
【０００５】
一方、ニューメンブレンテクノロジーシンポジウム２００２の予稿集には、海水淡水化でのホウ素除去を目的として、１段目の逆浸透膜の濃縮側の透過水のみを２段目の逆浸透膜モジュールへ供給する２段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内部での濃縮側透過水と供給側透過水の区分が明確ではなく、供給側透過水と濃縮側透過水の濃度が制御ができず、２段目の逆浸透モジュールへの供給水を制御するのが困難であるという問題がある。また、この方法では濃縮側透過水の全量が２段目で処理されるため、２段目モジュールで処理された透過水の水質の制御が難しいという問題がある。
【０００６】
【発明が解決しようとする課題】
単純に１段目の逆浸透膜モジュールの透過水を一旦集めて、２段目の逆浸透膜モジュールに供給すると、必要以上に２段目逆浸透膜モジュールの規模が大きくなるという問題がある。また、１段目のモジュールの透過水の１部を２段目のモジュールへ供給する場合、２段目のモジュールへの供給水の水質が制御できないという問題がある。本発明は、このような点に鑑みなされたもので、逆浸透膜モジュールで処理した透過水を部分的に再度逆浸透膜で処理する膜処理方法において、後段の逆浸透膜部の規模を低減でき、効率的な処理が可能で生産水の水質の制御も容易である逆浸透膜処理方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明者等は、鋭意検討した結果、１段目の逆浸透膜モジュールとして逆浸透膜エレメント２つが直列配置されている逆浸透膜モジュールを用い、濃縮側の逆浸透膜エレメントの透過水の一部ないし全量、あるいはそれに供給側の逆浸透膜エレメントの透過水の一部を混合した透過水を２段目の逆浸透膜モジュールへ供給して２段の逆浸透処理することによって本発明を完成するに至った。すなわち本発明は、
（１）高濃度原水を２段の逆浸透モジュールで処理し、高濃度の濃縮水と低濃度の透過水とに分離する処理方法において、１段目の逆浸透膜モジュールとしては１本の逆浸透膜モジュールが２本の逆浸透膜エレメントから構成され、供給側の逆浸透膜エレメントに高濃度原水が供給され、濃縮側の逆浸透膜エレメントに供給側の逆浸透膜エレメントの濃縮水が供給されるように直列に配置され、各逆浸透膜エレメントの透過水が個別に取り出せる構造の逆浸透膜モジュールを用い、２段目の逆浸透膜モジュールで１段目の濃縮側の逆浸透膜エレメントの透過水の５０％から１００％を逆浸透処理することを特徴する高濃度溶液の処理方法。
（２）供給側の逆浸透膜エレメントの透過水と濃縮側の逆浸透膜エレメントの透過水を１：９９から５０：５０の割合で混合して２段目の逆浸透膜モジュールで逆浸透処理することを特徴する（１）の高濃度溶液の処理方法。
（３）高濃度原水が海水であることを特徴とする（１）、（２）の高濃度溶液の処理方法。
（４）高濃度原水に殺菌処理として間欠的に塩素を注入することを特徴とする（１）〜（３）の高濃度溶液の処理方法。
である。
【０００８】
【発明の実施の形態】
本発明における高濃度原水および高濃度溶液とは、逆浸透処理が可能な溶質が溶解した液体であり、濃度はその浸透圧から逆浸透処理が可能な範囲であるものである。例えば、海水などがあげられる。回収率によっても異なるが、海水の場合は、逆浸透圧が５．４ＭＰａから９ＭＰａで淡水化処理が可能である。
【０００９】
本発明における逆浸透膜とは、数十ダルトンの分子量の分離特性を有する領域の分離膜であり、具体的には、０．５ＭＰａ以上の操作圧力で、食塩を９０％以上、除去可能であるものである。海水淡水化に使用される中空糸型逆浸透膜は、操作圧力が大きく、また、食塩の除去率は９９％以上が一般的である。
【００１０】
本発明における高濃度原水を２段の逆浸透モジュールで処理し、高濃度の濃縮水と低濃度の透過水とに分離する処理方法とは、原水を１段目の逆浸透膜モジュールで処理して得た透過水を、再度、逆浸透膜モジュールで処理する方法である。１段目の逆浸透膜モジュールと２段目の逆浸透膜モジュールの間には昇圧操作が必要となる。本発明においては、高濃度原水を１段目の逆浸透モジュールで処理して得た透過水の一部分を２段目の逆浸透膜モジュールで処理する。２段目の逆浸透膜モジュールで処理しない１段目のモジュールの透過水は、２段目のモジュールの透過水と合流させて生産水として取り出される。
【００１１】
本発明における１段目の逆浸透膜モジュールとしては、１本の逆浸透膜モジュールが２本の逆浸透膜エレメントから構成され、供給側の逆浸透膜エレメントに高濃度原水が供給され、濃縮側の逆浸透膜エレメントに濃縮水が供給されるように直列に配置され、各逆浸透膜エレメントの透過水が個別に取り出せる構造の逆浸透モジュールを用いる。逆浸透膜モジュール内で逆浸透膜エレメントが直列に配置されているとは、高濃度原水を１つ目の逆浸透膜エレメント（供給側）で逆浸透処理した濃縮水が２つ目の逆浸透膜エレメント（濃縮側）で逆浸透処理するように配置することであり、具体的な例としては、図３や図４に示した構造であり、供給側の逆浸透膜エレメントの濃縮側と濃縮側の逆浸透膜エレメントの供給側がモジュール内で連通している状態である。
【００１２】
１段目の逆浸透膜モジュールとして上記の構造のモジュールを用いると、１段目の逆浸透膜モジュール内部での供給側透過水と濃縮側透過水とが区分され、各透過水の濃度が安定するので、２段目の逆浸透モジュールへの供給する量を制御することで２段目モジュールで処理された透過水の水質を制御することが容易となる。
【００１３】
２段目の逆浸透膜モジュールは、１段目のモジュールと同一の特性でも異なる特性でもかまわない。
また、２段目のモジュールでの除去性能を向上させるために１段目のモジュールと２段目のモジュールの間で添加剤を注入してもかまわない。例えば、海水淡水化の場合は、ホウ素の除去率は一般的には食塩の除去率に比べて高くないが、アルカリを添加してｐＨを９以上にすると、ホウ素の除去率は大幅に増加させることができるため、アルカリを添加することが考えられる。また、１段目の逆浸透膜モジュールに耐塩素性モジュールを使用し塩素殺菌処理した後、還元剤を注入してから２段目で耐塩素性のないモジュールを使用することが可能である。
【００１４】
本発明において、２段目の逆浸透膜モジュールで処理する１段目のモジュールの透過水の量は、１段目の逆浸透膜モジュールの透過水の水質によって決まる。１段目の逆浸透膜モジュールの透過水の水質が不十分である場合、例えばホウ素の濃度が基準値より高い場合は、１段目の逆浸透膜モジュールの濃縮側の逆浸透膜エレメントの透過水を２段目の逆浸透膜モジュールへ多く供給して逆浸透処理する。２段法全体の透過水の水質が基準値に対して余裕がある場合は、例えばホウ素の濃度が基準値より十分低い場合は、１段目の逆浸透膜モジュールの濃縮側の逆浸透膜エレメントの透過水の一部を２段目の逆浸透膜モジュールへ供給して逆浸透処理すれば良い。逆に、不十分であれば、１段目の逆浸透膜モジュールの濃縮側の逆浸透膜エレメントの透過水全量に更に供給側の逆浸透膜エレメントの透過水の一部を加えた混合液を２段目の逆浸透膜モジュールで逆浸透処理することができる。
【００１５】
２段目の逆浸透膜モジュールで処理する１段目の逆浸透膜モジュールの濃縮側の逆浸透膜エレメントの透過水の割合は、５０％〜１００％が好ましく、より好ましくは７０％〜１００％である。この割合が少なすぎると２段法の効果が小さくなるので好ましくない。
【００１６】
一方、１段目の逆浸透膜モジュールの供給側の逆浸透膜エレメントの透過水の一部を濃縮側の逆浸透膜エレメントの透過水に加えた混合液を２段目の逆浸透膜モジュールで処理する場合は、供給側の逆浸透膜エレメントの透過水と濃縮側の逆浸透膜エレメントの透過水の割合を１：９９から５０：５０の割合にするのが好ましく、より好ましくは１：９９から３０：７０である。供給側の逆浸透膜エレメントの透過水の割合が大きすぎると２段目の処理の負荷が大きくなりすぎて好ましくない。
【００１７】
本発明における逆浸透膜の素材としては、酢酸セルロース系高分子、ポリアミド系高分子、ポリスルホン系高分子が挙げられる。１段目と２段目の逆浸透膜の素材は同一でも異なっていても良い。
【００１８】
酢酸セルロース系高分子としては酢酸セルロース、三酢酸セルロース、両者の混合物が例として挙げられる。性能及びその安定性の点から三酢酸セルロースが特に好ましい。また、酢酸セルロース系高分子は耐塩素性に優れるため、供給水に殺菌剤として塩素系殺菌剤を添加することが可能である。耐塩素性を有するとは、水道水程度（約１ｐｐｍ）の残留塩素の存在下での１年程度の連続使用が可能であることを意味する。
【００１９】
ポリアミド系高分子としては、線状ポリアミド高分子、架橋ポリアミド高分子等が例として挙げられる。耐塩素性を有するポリアミド系逆浸透膜としては、例えば東洋紡績（株）製のＨＳシリーズが挙げられる。
ポリスルホン系高分子としては、ポリスルホン、ポリエーテルスルホン等が挙げられる。
【００２０】
高濃度原水に塩素系殺菌剤を添加する場合は、２段目の逆浸透膜モジュールも耐塩素性のモジュールを使用することが好ましく、１段目の逆浸透膜モジュールの供給原水に塩素系殺菌剤を添加し、その塩素系殺菌剤が１段目のモジュールの透過水中に残留しても、その透過水を還元処理することなく２段目逆浸透膜モジュールへ供給できる点で好ましい。
【００２１】
殺菌剤として塩素系殺菌剤を添加する場合は、間欠的に注入する方法が、副生成物の発生量が少ない点や薬品使用量が少なくてすむ点で好ましい。
【００２２】
本発明の実施の形態の一例を図１に基づいて説明する。
図１は、１段目の逆浸透膜モジュールとして、２つの逆浸透膜エレメントを直列に配置した逆浸透膜モジュール１を用い、濃縮側の逆浸透膜エレメントの透過水のみを２段目の逆浸透膜モジュールへ供給して分離操作を行う場合を示している。高圧ポンプ５により昇圧された高濃度原水７は１段目の供給側の逆浸透膜エレメントに供給され、その濃縮水はモジュール内で連続的に濃縮側の逆浸透膜エレメント３に供給される。濃縮側の逆浸透膜エレメント３の濃縮水１０は排出され、透過水９は昇圧ポンプ６によりで昇圧され、２段目の逆浸透膜モジュール４へ供給され濃縮水１２は排出され、透過水１１は供給側の逆浸透膜エレメントの透過水８と合流し生産水１３として得られる。
【００２３】
更に本発明の実施の形態の一例を図２に基づいて説明する。
図２は、１段目の供給側の逆浸透膜エレメント２の透過水８と１段目の濃縮側の逆浸透膜エレメント３の透過水９とが流量調整バルブ１４，１５、１６で連通しており、２段目逆浸透膜モジュール４への供給する各逆浸透膜エレメントの透過水の流量を制御でき、生産水の水質を変更することができる。例えば、流量調整バルブ１４、１５を開け、流量調整バルブ１６を絞れば、供給側の逆浸透膜エレメント２の透過水８の混合割合が増加し、逆に、流量調整バルブ１４、１６を開け、流量調整バルブ１５を絞れば、濃縮側の逆浸透膜エレメント３の透過水の流量を減少させることが可能である。
【００２４】
【実施例】
以下に、実施例を挙げて本発明を説明するが、本発明はこれらの実施例により何ら制限されるものではない。なお、実施例は、海水淡水化用の逆浸透膜の場合を示す。
【００２５】
（実施例１）
図１に示すような、２つの逆浸透膜エレメントが直列配置した逆浸透膜モジュールと１つの逆浸透膜エレメントからなる逆浸透膜モジュールからなる２段の逆浸透モジュールによって海水を処理した。１段目の逆浸透膜モジュールとして三酢酸セルロース製の中空糸型逆浸透膜エレメントが圧力容器内に２本装着した中空糸型逆浸透膜モジュールを用い、２段目の逆浸透膜モジュールとして耐塩素性ポリアミド製の中空糸型逆浸透膜モジュールを用いた。但し、２段目のモジュールの供給水には水酸化ナトリウムを添加し、ｐＨを９に調整した。運転条件は以下の通りであった。高濃度原水の温度２５℃、全溶解塩濃度（ＴＤＳ濃度）３．５％、ホウ素濃度４．５ｍｇ／ｌ、１段目の操作圧力７０ｋｇ／ｃｍ２、２段目の操作圧力１５ｋｇ／ｃｍ２、１段目の回収率５３％、２段目の回収率８５％で運転した。２段処理後に得られた生産水の水質はＴＤＳ濃度１４３ｍｇ／ｌ、ホウ素濃度１．２３ｍｇ／ｌであった。また、２段目の昇圧ポンプの消費電力は０．１８ｋＷｈ／ｍ３であった。結果を表１に示した。
【００２６】
（実施例２）
逆浸透膜モジュールの配置が図２であること以外、実施例１と同様に海水を処理した。但し、２段目逆浸透膜モジュールへの供給水が濃縮側の逆浸透膜エレメントの透過水の８０％とし、２段目の処理用の逆浸透膜モジュールの処理量が実施例１と同じ程度となるように、中空糸本数を８０％にした。得られた２段処理としての生産水の水質はＴＤＳ濃度１６６ｍｇ／ｌ、ホウ素濃度１．３９ｍｇ／ｌであった。また、２段目の昇圧ポンプの消費電力は０．１４ｋＷｈ／ｍ３であった。結果を表１に示した。
【００２７】
（実施例３）
逆浸透膜モジュールの配置が図２であり、２段目逆浸透膜モジュールへの供給水が濃縮側の逆浸透膜エレメントの透過水の１００％と供給側の逆浸透膜エレメントの２５％の混合水（供給側の逆浸透膜エレメントの透過水と濃縮側の逆浸透膜エレメントの透過水の割合が１８：８２の混合水）であること以外、実施例２と同様に海水を処理した。但し、２段目の処理用の逆浸透膜モジュールの処理量が実施例１と同じ程度となるように、中空糸本数を１５０％にした。得られた２段処理としての生産水の水質はＴＤＳ濃度１１６ｍｇ／ｌ、ホウ素濃度１．０４ｍｇ／ｌであった。また、２段目の昇圧ポンプの消費電力は０．２７ｋＷｈ／ｍ３であった。結果を表１に示した。
【００２８】
（比較例１）
図２のモジュール配置で、１段目の供給側の逆浸透膜エレメントの透過水と濃縮側の逆浸透膜エレメントの透過水がすべて２段目の逆浸透膜モジュールの供給水となるような、完全な２段法で実施例３と同様に海水を処理した。但し、２段目の処理用の逆浸透膜モジュール当たりの処理量が実施例１と同じ程度となるように、逆浸透膜モジュール本数を約３倍にした。得られた２段処理としての生産水の水質はＴＤＳ濃度２５ｍｇ／ｌ、ホウ素濃度０．４ｍｇ／ｌであった。また、２段目の昇圧ポンプの消費電力は０．５９ｋＷｈ／ｍ３であった。生産水質の濃度は非常に低いが、ＴＤＳ濃度が低すぎる傾向があることと、２段目の昇圧ポンプの消費電力が非常に大きく、過剰な処理の運転であると考えられる。結果を表１に示した。
【００２９】
（比較例２）
図２のモジュール配置で、２段目の逆浸透膜モジュールへの供給を断ち、完全な１段法で海水を処理した。生産水の水質はＴＤＳ濃度１８８ｍｇ／ｌ、ホウ素濃度１．５ｍｇ／ｌであり、水質基準値を満たさないものであった。
【００３０】
【表１】
【発明の効果】
本発明によれば１段目の逆浸透膜モジュールで処理した透過水を部分的に再度逆浸透膜処理する２段の逆浸透膜処理方法において、２段目の逆浸透膜モジュールの規模および消費電力を低減する方法を提供することができる。また、２段目の逆浸透膜モジュールへの供給水の量を変更することによって、容易に生産水の水質を制御することができ、システム全体の最適化が容易である。
【図面の簡単な説明】
【図１】本発明の処理方法の一例で、１段目の逆浸透膜モジュール内の濃縮側の逆浸透膜エレメントの透過水のみ２段目の逆浸透膜モジュールに供給される場合の簡単な構成図である。
【図２】本発明の処理方法の一例で、１段目の逆浸透膜モジュール内の濃縮側の逆浸透膜エレメントの透過水と供給側の逆浸透膜エレメントの透過水の混合水が２段目の逆浸透膜モジュールに供給される場合の簡単な構成図である。
【図３】本発明における１段目の逆浸透膜モジュールの構造の一例である。
【図４】本発明における１段目の逆浸透膜モジュールの構造の一例である。
【符号の説明】
１：１段目の逆浸透膜モジュール
２：１段目の逆浸透膜モジュール内の供給側の逆浸透膜エレメント
３：１段目の逆浸透膜モジュール内の濃縮側の逆浸透膜エレメント
４：２段目の逆浸透膜モジュール
５：高圧ポンプ
６：昇圧ポンプ
７：供給水（高濃度原水）
８：供給側の逆浸透膜エレメントの透過水
９：濃縮側の逆浸透膜エレメントの透過水
１０：１段目の逆浸透膜モジュールの濃縮水
１１：２段目の逆浸透膜モジュールの透過水
１２：２段目の逆浸透膜モジュールの濃縮水
１３：生産水
１４、１５，１６：流量調整バルブ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reverse osmosis treatment of a high-concentration solution, and more particularly to a separation method for desalination of seawater.
[0002]
[Prior art]
The reverse osmosis method is used in a wide range of fields such as desalination of seawater and brackish water, production of pure water and ultrapure water for the semiconductor industry and the pharmaceutical industry, and municipal wastewater treatment. Compared to the evaporation method and the electrodialysis method, they are advantageous in energy saving and are widely used.
In particular, the hollow fiber type reverse osmosis membrane has a shape suitable for a membrane separation operation because the membrane area per unit volume can be increased, and is widely used, for example, in the field of seawater desalination using a reverse osmosis membrane.
Although water treated by the reverse osmosis method is used for drinking water, compliance with water quality standards is required with increasing safety awareness. In order to achieve the water quality standard value, a two-stage method of once collecting permeated water treated with a reverse osmosis membrane and treating it again with a reverse osmosis membrane is being studied.
[0004]
In U.S. Pat. No. 4,574,049, the total amount of permeated water that has been treated with the first-stage reverse osmosis membrane is treated by the second-stage reverse osmosis membrane, and the concentrated water of the second-stage reverse osmosis membrane is subjected to the first stage. A treatment method for returning to the supply water of the eye is disclosed. However, in this method, the entire amount of permeated water that has been subjected to the reverse osmosis membrane treatment in the first stage is treated in the second stage, so that energy consumption increases, and the quality of the permeated water is required depending on the quality of the raw water. In some cases, this is not preferable.
[0005]
On the other hand, in the proceedings of the New Membrane Technology Symposium 2002, only the permeated water on the concentration side of the first-stage reverse osmosis membrane is supplied to the second-stage reverse osmosis membrane module for the purpose of removing boron in seawater desalination. A two-stage method is disclosed. However, in this method, the distinction between the concentrated permeated water and the supplied permeated water inside the reverse osmosis membrane module is not clear, and the concentrations of the supplied permeated water and the concentrated permeated water cannot be controlled. There is a problem that it is difficult to control the water supply to the infiltration module. Further, in this method, since the entire amount of the concentrated-side permeated water is treated in the second stage, there is a problem that it is difficult to control the quality of the permeated water treated in the second-stage module.
[0006]
[Problems to be solved by the invention]
If the permeated water of the first-stage reverse osmosis membrane module is simply collected and supplied to the second-stage reverse osmosis membrane module, there is a problem that the size of the second-stage reverse osmosis membrane module becomes unnecessarily large. Further, when a part of the permeated water of the first-stage module is supplied to the second-stage module, there is a problem that the quality of the water supplied to the second-stage module cannot be controlled. The present invention has been made in view of such a point, and in a membrane treatment method in which permeated water treated by a reverse osmosis membrane module is partially treated again with a reverse osmosis membrane, the size of a subsequent reverse osmosis membrane section is reduced. It is an object of the present invention to provide a reverse osmosis membrane treatment method capable of performing efficient treatment and easily controlling the quality of production water.
[0007]
[Means for Solving the Problems]
As a result of extensive studies, the present inventors have used a reverse osmosis membrane module in which two reverse osmosis membrane elements are arranged in series as the first-stage reverse osmosis membrane module, and used one of the permeated water of the reverse osmosis membrane element on the concentration side. The present invention is completed by supplying permeated water mixed with a part or all of the permeated water or a part of permeated water of the reverse osmosis membrane element on the supply side to the second-stage reverse osmosis membrane module and performing two-stage reverse osmosis treatment. I came to. That is, the present invention
(1) In a treatment method in which high-concentration raw water is treated by a two-stage reverse osmosis module and separated into high-concentration concentrated water and low-concentration permeated water, one reverse-osmosis membrane module is used as the first-stage reverse osmosis membrane module. The osmosis membrane module is composed of two reverse osmosis membrane elements, high concentration raw water is supplied to the supply side reverse osmosis membrane element, and concentrated water of the supply side reverse osmosis membrane element is supplied to the concentration side reverse osmosis membrane element The reverse osmosis membrane module is arranged in series so that the permeated water of each reverse osmosis membrane element can be individually taken out. A reverse osmosis treatment of 50% to 100% of the permeated water.
(2) The permeated water of the reverse osmosis membrane element on the supply side and the permeated water of the reverse osmosis membrane element on the concentration side are mixed at a ratio of 1:99 to 50:50 and subjected to reverse osmosis treatment in the second reverse osmosis membrane module. (1) The method for treating a highly concentrated solution according to (1).
(3) The method for treating a high-concentration solution according to (1) or (2), wherein the high-concentration raw water is seawater.
(4) The method for treating a high concentration solution according to (1) to (3), wherein chlorine is intermittently injected into the high concentration raw water as a sterilization treatment.
It is.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The high-concentration raw water and the high-concentration solution in the present invention are liquids in which a solute that can be subjected to reverse osmosis treatment is dissolved. For example, seawater and the like can be mentioned. Although it depends on the recovery rate, seawater can be desalinated at a reverse osmotic pressure of 5.4 MPa to 9 MPa.
[0009]
The reverse osmosis membrane in the present invention is a separation membrane in a region having a separation characteristic of a molecular weight of several tens of daltons, and specifically, can remove 90% or more of salt at an operation pressure of 0.5 MPa or more. Things. A hollow fiber type reverse osmosis membrane used for seawater desalination has a large operating pressure, and the salt removal rate is generally 99% or more.
[0010]
In the present invention, the processing method of treating high-concentration raw water with a two-stage reverse osmosis module and separating it into high-concentration concentrated water and low-concentration permeated water is as follows. This is a method of treating the permeated water thus obtained again with a reverse osmosis membrane module. A pressurizing operation is required between the first-stage reverse osmosis membrane module and the second-stage reverse osmosis membrane module. In the present invention, a part of the permeated water obtained by treating the high-concentration raw water with the first-stage reverse osmosis module is treated with the second-stage reverse osmosis membrane module. The permeated water of the first-stage module that is not treated by the second-stage reverse osmosis membrane module is combined with the permeated water of the second-stage module and taken out as product water.
[0011]
As the first-stage reverse osmosis membrane module in the present invention, one reverse osmosis membrane module is composed of two reverse osmosis membrane elements, high-concentration raw water is supplied to the reverse osmosis membrane element on the supply side, and The reverse osmosis module is arranged in series so that the concentrated water is supplied to the reverse osmosis membrane elements, and the permeate of each reverse osmosis membrane element can be individually taken out. The arrangement of the reverse osmosis membrane elements in series in the reverse osmosis membrane module means that concentrated water obtained by subjecting high-concentration raw water to reverse osmosis treatment by the first reverse osmosis membrane element (supply side) is subjected to the second reverse osmosis. The arrangement is such that reverse osmosis treatment is performed on the membrane element (concentration side). As a specific example, the structure shown in FIGS. 3 and 4 is used. The supply side of the reverse osmosis membrane element is in communication with the inside of the module.
[0012]
When a module having the above structure is used as the first-stage reverse osmosis membrane module, the permeate on the supply side and the permeate on the concentrate side are separated inside the first-stage reverse osmosis membrane module, and the concentration of each permeate is stable. Therefore, by controlling the amount supplied to the second-stage reverse osmosis module, it becomes easy to control the quality of the permeated water treated in the second-stage module.
[0013]
The second-stage reverse osmosis membrane module may have the same or different characteristics as the first-stage module.
Further, an additive may be injected between the first-stage module and the second-stage module in order to improve the removal performance of the second-stage module. For example, in the case of seawater desalination, the removal rate of boron is generally not higher than the removal rate of salt, but when an alkali is added to increase the pH to 9 or more, the removal rate of boron is greatly increased. Therefore, it is conceivable to add an alkali. In addition, it is possible to use a chlorine-resistant module for the first-stage reverse osmosis membrane module, perform chlorine sterilization treatment, and then inject a reducing agent, and then use a second-stage module having no chlorine resistance.
[0014]
In the present invention, the amount of permeated water of the first-stage reverse osmosis membrane module treated by the second-stage reverse osmosis membrane module is determined by the quality of the permeated water of the first-stage reverse osmosis membrane module. When the quality of the permeated water of the first-stage reverse osmosis membrane module is insufficient, for example, when the concentration of boron is higher than a reference value, the permeation of the reverse osmosis membrane element on the concentration side of the first-stage reverse osmosis membrane module is performed. A large amount of water is supplied to the second-stage reverse osmosis membrane module to perform reverse osmosis treatment. When the water quality of the permeated water in the entire two-stage method has a margin with respect to the reference value, for example, when the concentration of boron is sufficiently lower than the reference value, the reverse osmosis membrane element on the concentration side of the first-stage reverse osmosis membrane module May be supplied to the second-stage reverse osmosis membrane module for reverse osmosis treatment. Conversely, if insufficient, a mixed solution obtained by further adding a part of the permeated water of the supply-side reverse osmosis membrane element to the total amount of the permeated water of the reverse osmosis membrane element on the concentration side of the first-stage reverse osmosis membrane module is used. Reverse osmosis treatment can be performed by the second-stage reverse osmosis membrane module.
[0015]
The percentage of permeated water of the reverse osmosis membrane element on the concentration side of the first-stage reverse osmosis membrane module to be treated by the second-stage reverse osmosis membrane module is preferably 50% to 100%, more preferably 70% to 100%. It is. If the ratio is too small, the effect of the two-stage method is undesirably reduced.
[0016]
On the other hand, a mixture obtained by adding a part of the permeated water of the reverse osmosis membrane element on the supply side of the first-stage reverse osmosis membrane module to the permeated water of the reverse osmosis membrane element on the concentration side is used in the second-stage reverse osmosis membrane module. In the case of treatment, the ratio of the permeated water of the reverse osmosis membrane element on the supply side and the permeated water of the reverse osmosis membrane element on the concentration side is preferably 1:99 to 50:50, more preferably 1:99. From 30:70. If the ratio of the permeated water in the reverse osmosis membrane element on the supply side is too large, the load of the treatment in the second stage becomes too large, which is not preferable.
[0017]
Examples of the material of the reverse osmosis membrane in the present invention include a cellulose acetate polymer, a polyamide polymer, and a polysulfone polymer. The materials of the first and second reverse osmosis membranes may be the same or different.
[0018]
Examples of the cellulose acetate-based polymer include cellulose acetate, cellulose triacetate, and a mixture of both. Cellulose triacetate is particularly preferred in view of performance and its stability. Moreover, since the cellulose acetate polymer has excellent chlorine resistance, it is possible to add a chlorine-based disinfectant as a disinfectant to the supply water. Having chlorine resistance means that it can be used continuously for about one year in the presence of residual chlorine of the order of tap water (about 1 ppm).
[0019]
Examples of the polyamide polymer include a linear polyamide polymer and a crosslinked polyamide polymer. Examples of the polyamide-based reverse osmosis membrane having chlorine resistance include the HS series manufactured by Toyobo Co., Ltd.
Examples of the polysulfone-based polymer include polysulfone and polyether sulfone.
[0020]
When a chlorine-based disinfectant is added to high-concentration raw water, it is preferable to use a chlorine-resistant module for the second-stage reverse osmosis membrane module, and to use chlorine-based sterilization for the raw water supplied to the first-stage reverse osmosis membrane module. Even if an agent is added and the chlorine-based disinfectant remains in the permeated water of the first-stage module, it is preferable because the permeated water can be supplied to the second-stage reverse osmosis membrane module without reduction treatment.
[0021]
When a chlorine-based disinfectant is added as a disinfectant, an intermittent injection method is preferred in that the amount of by-products generated is small and the amount of chemicals used is small.
[0022]
An example of an embodiment of the present invention will be described with reference to FIG.
FIG. 1 shows a reverse
[0023]
Further, an example of the embodiment of the present invention will be described with reference to FIG.
FIG. 2 shows that the permeated
[0024]
【Example】
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. In addition, an Example shows the case of the reverse osmosis membrane for seawater desalination.
[0025]
(Example 1)
As shown in FIG. 1, seawater was treated by a two-stage reverse osmosis module including a reverse osmosis membrane module in which two reverse osmosis membrane elements were arranged in series and a reverse osmosis membrane module including one reverse osmosis membrane element. A hollow fiber type reverse osmosis membrane module in which two hollow fiber type reverse osmosis membrane elements made of cellulose triacetate are mounted in a pressure vessel as a first-stage reverse osmosis membrane module is used. A hollow fiber type reverse osmosis membrane module made of chlorinated polyamide was used. However, the pH was adjusted to 9 by adding sodium hydroxide to the supply water of the second stage module. The operating conditions were as follows. High-concentration raw water temperature 25 ° C., total dissolved salt concentration (TDS concentration) 3.5%, boron concentration 4.5 mg / l, first stage operating pressure 70 kg / cm 2 , second
[0026]
(Example 2)
Seawater was treated in the same manner as in Example 1 except that the arrangement of the reverse osmosis membrane module was as shown in FIG. However, the supply water to the second-stage reverse osmosis membrane module is assumed to be 80% of the permeated water of the reverse osmosis membrane element on the concentration side, and the throughput of the second-stage reverse osmosis membrane module is about the same as in Example 1. So that the number of hollow fibers is 80%. The water quality of the obtained production water as a two-stage treatment was a TDS concentration of 166 mg / l and a boron concentration of 1.39 mg / l. The power consumption of the second-stage booster pump was 0.14 kWh / m 3 . The results are shown in Table 1.
[0027]
(Example 3)
The arrangement of the reverse osmosis membrane module is shown in FIG. 2, and the supply water to the second-stage reverse osmosis membrane module is a mixture of 100% of the permeated water of the reverse osmosis membrane element on the concentration side and 25% of the reverse osmosis membrane element on the supply side. Seawater was treated in the same manner as in Example 2, except that water (mixed water having a ratio of 18:82 permeated water of the reverse osmosis membrane element on the supply side and permeated water of the reverse osmosis membrane element on the concentration side) was used. However, the number of hollow fibers was set to 150% so that the throughput of the reverse osmosis membrane module for the second stage treatment was about the same as in Example 1. The water quality of the obtained production water as a two-stage treatment was a TDS concentration of 116 mg / l and a boron concentration of 1.04 mg / l. The power consumption of the second-stage booster pump was 0.27 kWh / m 3 . The results are shown in Table 1.
[0028]
(Comparative Example 1)
In the module arrangement of FIG. 2, the permeated water of the reverse osmosis membrane element on the supply side of the first stage and the permeated water of the reverse osmosis membrane element on the concentration side are all supplied water of the reverse osmosis membrane module of the second stage. Seawater was treated as in Example 3 in a complete two-stage process. However, the number of reverse osmosis membrane modules was approximately tripled so that the processing amount per reverse osmosis membrane module for the second stage treatment was about the same as in Example 1. The water quality of the obtained production water as a two-stage treatment was a TDS concentration of 25 mg / l and a boron concentration of 0.4 mg / l. The power consumption of the second-stage booster pump was 0.59 kWh / m 3 . Although the concentration of the produced water quality is very low, the TDS concentration tends to be too low, and the power consumption of the second stage booster pump is very large, which is considered to be an operation of excessive treatment. The results are shown in Table 1.
[0029]
(Comparative Example 2)
In the module arrangement of FIG. 2, the supply to the second reverse osmosis membrane module was cut off, and seawater was treated by a complete one-stage method. The water quality of the produced water was 188 mg / l in TDS concentration and 1.5 mg / l in boron concentration, and did not satisfy the water quality standard value.
[0030]
[Table 1]
【The invention's effect】
According to the present invention, in the two-stage reverse osmosis membrane treatment method for partially re-permeating the permeated water treated by the first-stage reverse osmosis membrane module, the size and consumption of the second-stage reverse osmosis membrane module A method for reducing power can be provided. Further, by changing the amount of water supplied to the second-stage reverse osmosis membrane module, the quality of the produced water can be easily controlled, and the optimization of the entire system is easy.
[Brief description of the drawings]
FIG. 1 shows an example of a processing method according to the present invention, in which only permeated water of a reverse osmosis membrane element on the concentration side in a first osmosis membrane module is supplied to a second osmosis membrane module. It is a block diagram.
FIG. 2 shows an example of the treatment method of the present invention, in which the mixed water of the permeated water of the reverse osmosis membrane element on the concentration side and the permeated water of the reverse osmosis membrane element on the supply side in the first-stage reverse osmosis membrane module has two stages. It is a simple block diagram when supplied to the reverse osmosis membrane module of the eye.
FIG. 3 is an example of the structure of a first-stage reverse osmosis membrane module according to the present invention.
FIG. 4 is an example of the structure of a first-stage reverse osmosis membrane module according to the present invention.
[Explanation of symbols]
1: Reverse osmosis membrane module of the first stage 2: Reverse osmosis membrane element on the supply side in the first stage reverse osmosis membrane module 3: Reverse osmosis membrane element on the concentration side in the first stage reverse osmosis membrane module 4: Second-stage reverse osmosis membrane module 5: high-pressure pump 6: boost pump 7: supply water (high-concentration raw water)
8: permeated water of the reverse osmosis membrane element on the supply side 9: permeated water of the reverse osmosis membrane element on the concentration side 10: concentrated water of the first-stage reverse osmosis membrane module 11: permeated water of the second-stage reverse osmosis membrane module 12: Concentrated water of the reverse osmosis membrane module of the second stage 13: Produced
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| KR101402345B1 (en) | 2012-12-26 | 2014-07-01 | 주식회사 포스코 | System making fresh water from sea water using reverse osmosis |
| US9309138B2 (en) | 2009-08-21 | 2016-04-12 | Toray Industries, Inc. | Fresh water production method |
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| CN115520934A (en) * | 2021-06-25 | 2022-12-27 | 中国石油化工股份有限公司 | Membrane separation recovery system and method |
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2002
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| JPH10296058A (en) * | 1997-04-24 | 1998-11-10 | Toyobo Co Ltd | Hollow fiber type permselective membrane module |
| JPH1110146A (en) * | 1997-06-18 | 1999-01-19 | Nitto Denko Corp | Reverse osmosis membrane separation apparatus |
| JPH11253761A (en) * | 1998-01-09 | 1999-09-21 | Nitto Denko Corp | Solution separation device |
| JP2001047045A (en) * | 1999-08-17 | 2001-02-20 | Japan Organo Co Ltd | Reverse osmosis membrane type desalination apparatus |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011021420A1 (en) | 2009-08-21 | 2011-02-24 | 東レ株式会社 | Fresh water generator |
| US9309138B2 (en) | 2009-08-21 | 2016-04-12 | Toray Industries, Inc. | Fresh water production method |
| JP2014036932A (en) * | 2012-08-17 | 2014-02-27 | Ube Ind Ltd | Gas separation membrane module and method for replacing hollow fiber element |
| KR101402345B1 (en) | 2012-12-26 | 2014-07-01 | 주식회사 포스코 | System making fresh water from sea water using reverse osmosis |
| US11492275B2 (en) | 2019-11-15 | 2022-11-08 | Kabushiki Kaisha Toshiba | Water treatment device and water treatment method |
| CN115520934A (en) * | 2021-06-25 | 2022-12-27 | 中国石油化工股份有限公司 | Membrane separation recovery system and method |
| RU2817723C1 (en) * | 2023-01-18 | 2024-04-19 | Федеральное государственное казенное военное образовательное учреждение высшего образования "Военный учебно-научный центр Военно-Морского Флота "Военно-морская академия им. Адмирала Флота Советского Союза Н.Г. Кузнецова" | Method for preparation of permeate of first stage of reverse osmosis seawater desalination plant |
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| JP4332774B2 (en) | 2009-09-16 |
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