JP2004130233A

JP2004130233A - Treatment method for high-concentration solution with reverse osmosis membrane

Info

Publication number: JP2004130233A
Application number: JP2002297819A
Authority: JP
Inventors: Toshitaka Tanaka; 田中　利孝; Atsuo Kumano; 熊野　淳夫; Shinya Fujiwara; 藤原　信也
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 2002-10-10
Filing date: 2002-10-10
Publication date: 2004-04-30
Anticipated expiration: 2022-10-10
Also published as: JP4304573B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method wherein a portion of permeating water treated with a reverse osmosis membrane is treated again with a reverse osmosis membrane and whereby the size of a reverse osmosis membrane module and an electric power consumption in the second step can be reduced. <P>SOLUTION: The reverse osmosis membrane module section in the first step of this treatment method comprises two reverse osmosis membrane modules, the first and second modules, set in a series. A portion or the total of high-concentration permeating water from the second module or a mixture of the total of this high-concentration permeating water and a portion of permeating water from the first module is supplied to the reverse osmosis membrane module of the second step. Thus, a two-step reverse osmosis treatment is carried out. <P>COPYRIGHT: (C)2004,JPO

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、特に海水の淡水化など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、中空糸膜逆浸透膜は、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ともに、水質基準の遵守が求められている。そのため、逆浸透膜の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】
従来、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を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質が必要過度となる場合があり、好ましくない。
【０００５】
一方、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、１段目の逆浸透膜モジュールからの透過水で供給側透過水と濃縮側透過水の取り出し部は区分されているものの、逆浸透膜モジュール内部で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は制御ができず、２段目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、濃縮側透過水の全量が２段目で処理されるため、２段目の透過水が必要過度の水質となったり、逆に水質が不足したりすることに対し、対応できないという問題がある。
【０００６】
【特許文献１】
米国特許第４，５７４０４９号明細書（第３欄３４行−第４欄４行、図１）
【０００７】
【非特許文献１】
ニューメンブレンテクノロジーシンポジウム２００２予稿集（第６−１−１頁−第６−１−１０頁）
【０００８】
【発明が解決しようとする課題】
単純に１段目逆浸透膜の透過水を一旦集めて、２段目逆浸透膜に供給すると、必要以上に２段目逆浸透膜の規模が大きくなるという問題がある。また、１段目の透過水の一部を２段目へ供給する場合、２段目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てなされたもので、逆浸透膜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、後段の逆浸透膜部分の規模を低減し、効率的な処理が可能な処理方法を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明者らは、上記課題を克服すべく鋭意検討を重ねた結果、本発明に到達した。すなわち、本願発明は下記の構成を有するものである。
（１）高濃度原水を２段の逆浸透膜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であって、１段目の逆浸透膜モジュールで分離された低濃度の透過水が２段目の逆浸透膜モジュールに供給されるように配設され、１段目の逆浸透膜モジュールの透過水の１０％から１００％を２段目の逆浸透膜モジュールで処理することを特徴とする高濃度溶液の処理方法。
（２）１段目の逆浸透膜モジュールにおいて逆浸透膜モジュールが２連に配置され、１連目逆浸透膜モジュールに高濃度原水が供給され、２連目逆浸透膜モジュールに１連目モジュールの濃縮水が供給される構成をもつ（１）記載の高濃度溶液の処理方法。
（３）１段目の逆浸透膜モジュールの２連目の逆浸透膜モジュールの透過水と１連目の逆浸透膜モジュールの透過水を１００：０から４０：６０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）、（２）いずれか記載の高濃度溶液の処理方法。
（４）中空糸型逆浸透膜が酢酸セルロース系高分子からなることを特徴とする（１）〜（３）いずれか記載の高濃度溶液の処理方法。
（５）２段目の逆浸透膜モジュールがポリアミド系素材の逆浸透膜からなることを特徴とする（１）〜（４）いずれか記載の高濃度溶液の処理方法。
（６）高濃度原水が海水であることを特徴とする（１）〜（５）いずれか記載の高濃度溶液の処理方法。
（７）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）〜（６）いずれか記載の高濃度溶液の処理方法。
【００１０】
本発明における高濃度原水とは、逆浸透処理が可能な溶質の溶解液体であり、濃度はその浸透圧から逆浸透処理が可能な範囲にあるものである。例えば、海水などがあげられ、回収率によっても異なるが、逆浸透膜では、５．４ＭＰａから９ＭＰａで淡水化処理が可能である。
【００１１】
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。
【００１２】
本発明における２段の逆浸透処理とは、原水を一度、逆浸透処理した透過水を再度、逆浸透処理する処理方法であり、１段目逆浸透膜モジュールと２段目逆浸透膜モジュールの間には昇圧操作が必要となる。本発明の場合は、部分的な２段処理のため、２段目の処理がなされない１段目の透過水は、２段目の処理水と合流して生産水として取り出される。なお、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は同一の特性でも異なる特性でもかまわない。２段目の逆浸透膜モジュールの除去率が１段目の逆浸透膜モジュールの除去率より高いほうが好ましい。また、２段目での除去性能を向上させるためや、２段目の膜特性を考慮して、１段目と２段目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以上にあげると、ホウ素の除去率は大幅に増加するため、アルカリを添加する場合がある。また、１段目の逆浸透膜モジュールが耐塩素性を有し、供給水、透過水に残留塩素が存在する場合、還元剤を注入する場合がある。アルカリの例としては、水酸化ナトリウム、水酸化カルシウムなどがあげられ、水酸化ナトリウムが最も好ましい。また、還元剤の例としては、亜硫酸水素ナトリウム、亜硫酸水素ナトリウム、チオ硫酸ナトリウムなどがあげられ、亜硫酸水素ナトリウムが最も好ましい。
【００１３】
本発明において、逆浸透膜モジュールが２連に配置されるとは、原水を一度、逆浸透処理した濃縮水を再度、逆浸透処理する処理方法であり、１連目の逆浸透膜モジュールと２連目の逆浸透膜モジュールの間には昇圧操作は不要である。
【００１４】
本発明において、２段目の逆浸透膜モジュールで処理される１段目の透過水の一部は、１段目だけでは透過水の水質が不十分である２連目逆浸透膜モジュールの透過水が主となる。しかしながら、２段法全体の透過水の水質から判断して、余裕がある場合は、２連目逆浸透膜モジュールの透過水の一部で良いが、逆に、不十分であれば、２連目逆浸透膜モジュールの透過水全量に、１連目逆浸透膜モジュールの透過水の一部を加えた混合液となる。２連目逆浸透膜モジュールの透過水の一部で良い場合は、その割合は２０％〜１００％が好ましく、より好ましくは５０％〜１００％である。さらに好ましくは７０％〜１００％である。この範囲内にあれば、２段法の効果が顕著となり好ましい。一方、１連目逆浸透膜モジュールの透過水の一部を加えた混合液の場合は、その混合割合は１％〜５０％が好ましく、より好ましくは１％〜３０％である。さらに、１〜３０％であれば、２段目の処理の負荷を低く抑えることができ２段法のシステムが有効に作用する点で好ましい。
また、１段目の逆浸透膜モジュール内の供給水流量が大きくなり、膜表面の更新が促進されるような、２本の逆浸透膜モジュールが２連に直列に配置されている場合は、高回収率運転時等にはより好ましい。さらに、２段目の逆浸透膜モジュールに供給され、逆浸透処理される１段目の逆浸透膜モジュールの透過水は、１段目の逆浸透膜モジュールのなかでも透過水の濃度が高い２連目の逆浸透膜モジュールの透過水を主とするのが好ましい。１連目の逆浸透膜モジュールの透過水量が２連目の逆浸透膜モジュールの透過水量より多いことを考慮して、１連目の逆浸透膜モジュールの透過水と２連目の逆浸透膜モジュールの透過水の割合は、０：１００から６０：４０の割合が好ましい。
【００１５】
本発明における酢酸セルロース系高分子とは、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あげられる。性能面、性能の安定性等から三酢酸セルロースが好ましい。また、これらの素材は耐塩素性に優れるため、供給水に殺菌剤として塩素を添加が可能である。間欠的に注入するほうが、消毒物副生製物の発生量や薬品使用量が小さくなり好ましい。
【００１６】
本発明におけるポリアミド系素材とは、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あげられ、除去性能が優れているものであれば、いずれでもかまわない。また、耐塩素性を有するものとそうでないものがあるが、運転管理上、耐塩素性を有しているものが好ましい。
【００１７】
本発明における耐塩素性を有するとは、水道水程度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。耐塩素性を有するポリアミド系逆浸透膜の例としては、東洋紡績（株）製のＨＳ（Ｒ）シリーズなどがあげられる。この２段目の逆浸透膜モジュールが耐塩素性を有すると、１段目の逆浸透膜モジュールへの供給水に塩素を用いて、透過水中に残留しても、そのまま、２段目逆浸透膜モジュールの処理が可能となるため、操作性、還元剤の薬品使用量の点から好ましい。
【００１８】
【発明の実施の形態】
本発明の実施の形態１を図１に基づいて説明する。図１は、一例として１段目の逆浸透膜として、２つの中空糸型逆浸透膜モジュールを２連に配置し、２連目の逆浸透膜モジュールの透過水のみを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４により昇圧された供給水６は１段目１連目の逆浸透膜モジュールに供給され、濃縮水８は２連目の逆浸透膜モジュール２に供給される。２連目の逆浸透膜モジュール２の濃縮水１０は排出され、透過水９は昇圧ポンプ５によりで昇圧され、２段目の逆浸透膜モジュール３へ供給され濃縮水１２は排出され、透過水１１は１連目の透過水７と合流し生産水１３として得られる。
【００１９】
図２は図１と類似しており、１段目の１連目逆浸透膜モジュール１の透過水７と１段目２連目逆浸透膜モジュール２の透過水９とが連通しており、流量調整バルブ１４，１５、１６で１連目、２連目の各逆浸透膜モジュールの透過水の割合を制御可能で２段目逆浸透膜モジュール２への供給水の流量、水質を変更可能である。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、１連目逆浸透膜モジュール１の透過水７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、２連目逆浸透膜モジュール２透過水の流量を減少させることが可能である。
【００２０】
【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。
【００２１】
（実施例１）
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本装着され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、図１に示すような、１段目が２連の２段のモジュール配置で海水を処理した。但し、２段目への供給水へＮａＯＨを添加し、ｐＨを９に設定した。運転条件は以下の通りであった。原水の温度２５℃、ＴＤＳ濃度３．５％、ホウ素濃度４．５ｍｇ／Ｌ、１段目の操作圧力７０ｋｇ／ｃｍ^２、２段目の操作圧力１５ｋｇ／ｃｍ^２、１段目の回収率５３％、２段目の回収率８５％。得られた２段処理としての生産水の水質はＴＤＳ１４３ｍｇ／Ｌ、ホウ素１．２３ｍｇ／ｌであった。また、２段目の昇圧ポンプの消費電力は０．１８ｋｗ／ｍ^３であった。１、２段目の水質等は表１にまとめて示した。
【００２２】
（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２連目逆浸透膜モジュールの透過水の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、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ＴＤＳ１６６ｍｇ／Ｌ、ホウ素１．３９ｍｇ／ｌであった。また、２段目の昇圧ポンプの消費電力は０．１４ｋｗ／ｍ^３であった。１、２段目の水質等は表１にまとめて示した。
【００２３】
（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２連目逆浸透膜モジュールの透過水の１００％と１連目逆浸透膜モジュールの２５％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、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ＴＤＳ１１６ｍｇ／Ｌ、ホウ素１．０４ｍｇ／ｌであった。また、２段目の昇圧ポンプの消費電力は０．２７ｋｗ／ｍ^３であった。１、２段目の水質等は表１にまとめて示した。
【００２４】
（比較例１）
図２のモジュール配置で、１段目の１連目逆浸透膜モジュールの透過水、２連目の逆浸透膜モジュールの透過水がすべて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ＴＤＳ２５ｍｇ／Ｌ、ホウ素０．４ｍｇ／ｌであった。また、２段目の昇圧ポンプの消費電力は０．５９ｋｗ／ｍ^３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。１、２段目の水質等は表１にまとめて示した。
【００２５】
【表１】

【００２６】
【発明の効果】
逆浸透膜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、２段目の逆浸透膜モジュール部分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を変更して、全体のシステムの最適化が可能である。
【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２連目逆浸透膜モジュールの透過水のみ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を示す。
【図２】本発明の処理方法の一例で、１段目の２連目逆浸透膜モジュールの透過水と１連目の逆浸透膜モジュール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を示す。
【符号の説明】
１：１段目の１連目の逆浸透膜モジュール
２：１段目の２連目の逆浸透膜モジュール
３：２段目の逆浸透膜モジュール
４：高圧ポンプ
５：昇圧ポンプ
６：供給水
７：１連目の逆浸透膜モジュールの透過水
８：１連目の逆浸透膜モジュールの濃縮水
９：２連目の逆浸透膜モジュールの透過水
１０：２連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 and the like.
[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 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.
[0003]
Water treated by the reverse osmosis method is also used for drinking water, but as safety awareness increases, compliance with water quality standards is required. Therefore, a two-stage method of once collecting permeated water of the reverse osmosis membrane and treating it again with the reverse osmosis membrane is being studied.
[0004]
Conventionally, there is a processing method in which the entire amount of permeated water subjected to the first-stage reverse osmosis membrane treatment is treated by the second-stage reverse osmosis membrane, and the concentrated water of the second-stage reverse osmosis membrane is returned to the first-stage supply water. It has been disclosed. However, in this method, since the entire amount of the first stage is treated in the second stage, energy consumption is increased, and the quality of the permeated water may be excessively necessary depending on the quality of the raw water, which is not preferable.
[0005]
On the other hand, for the purpose of removing boron in seawater desalination, a two-stage method is disclosed in which only permeated water on the concentration side of a first-stage reverse osmosis membrane is supplied to a second-stage reverse osmosis membrane module. However, the permeated water from the first-stage reverse osmosis membrane module separates the supply side permeated water and the concentrated side permeated water withdrawal sections, but the division inside the reverse osmosis membrane module is not clear, There is a problem that the concentration of water and the permeate on the concentration side cannot be controlled, and it is difficult to control the supply water to the second stage. In addition, since the entire amount of the permeated water on the concentration side is treated in the second stage, there is a problem that the second stage permeated water cannot cope with an excessively required water quality or conversely a shortage of the water quality. is there.
[0006]
[Patent Document 1]
U.S. Pat. No. 4,574,049 (column 3, line 34-column 4, line 4, FIG. 1)
[0007]
[Non-patent document 1]
Proceedings of New Membrane Technology Symposium 2002 (pages 6-1-1 to 6-1-10)
[0008]
[Problems to be solved by the invention]
If the permeated water of the first-stage reverse osmosis membrane is simply collected and supplied to the second-stage reverse osmosis membrane, there is a problem that the size of the second-stage reverse osmosis membrane becomes unnecessarily large. Further, when a part of the permeated water in the first stage is supplied to the second stage, there is a problem that the quality of the water supplied to the second stage 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 with a reverse osmosis membrane is partially treated again with a reverse osmosis membrane, the scale of a subsequent reverse osmosis membrane portion is reduced. It is another object of the present invention to provide a processing method capable of performing efficient processing.
[0009]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to overcome the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention has the following configuration.
(1) A high-concentration raw water is treated by a two-stage reverse osmosis membrane module, and is separated into a high-concentration concentrated water and a low-concentration permeated water. Is disposed so as to supply the low-concentration permeated water to the second-stage reverse osmosis membrane module. A method for treating a high-concentration solution, wherein the treatment is performed by a module.
(2) In the first-stage reverse osmosis membrane module, the reverse osmosis membrane modules are arranged in two rows, high-concentration raw water is supplied to the first reverse osmosis membrane module, and the first module is provided to the second reverse osmosis membrane module. (1) The method for treating a highly concentrated solution according to (1), wherein the concentrated water is supplied.
(3) The permeated water of the second reverse osmosis membrane module of the first reverse osmosis membrane module and the permeated water of the first reverse osmosis membrane module are mixed at a ratio of 100: 0 to 40:60, The method for treating a high-concentration solution according to any one of (1) and (2), wherein the reverse osmosis treatment is performed by a second-stage reverse osmosis membrane module.
(4) The method for treating a high-concentration solution according to any one of (1) to (3), wherein the hollow fiber type reverse osmosis membrane is made of a cellulose acetate polymer.
(5) The method for treating a high-concentration solution according to any one of (1) to (4), wherein the second-stage reverse osmosis membrane module is formed of a reverse osmosis membrane made of a polyamide material.
(6) The method for treating a high-concentration solution according to any one of (1) to (5), wherein the high-concentration raw water is seawater.
(7) The method for treating a high concentration solution according to any one of (1) to (6), wherein chlorine is intermittently injected into the high concentration raw water as a sterilization treatment.
[0010]
The high-concentration raw water according to the present invention is a dissolved liquid of a solute that can be subjected to reverse osmosis treatment, and has a concentration within a range in which reverse osmosis treatment is possible based on its osmotic pressure. For example, seawater and the like can be mentioned, and depending on the recovery rate, the reverse osmosis membrane can be desalinated at 5.4 MPa to 9 MPa.
[0011]
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.
[0012]
The two-stage reverse osmosis treatment in the present invention is a treatment method in which raw water is subjected once to reverse osmosis treatment of permeated water subjected to reverse osmosis treatment. During that time, a boost operation is required. In the case of the present invention, because of the partial two-stage treatment, the first-stage permeated water that is not subjected to the second-stage treatment is combined with the second-stage treated water and taken out as product water. The first-stage reverse osmosis membrane module and the second-stage reverse osmosis membrane module may have the same characteristics or different characteristics. The removal rate of the second-stage reverse osmosis membrane module is preferably higher than the removal rate of the first-stage reverse osmosis membrane module. In addition, an additive may be injected between the first and second stages in order to improve the removal performance in the second stage or in consideration of the film characteristics of the second stage. 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 the pH is increased to 9 or more by adding an alkali, the removal rate of boron is greatly increased. For this purpose, an alkali may be added. When the first-stage reverse osmosis membrane module has chlorine resistance and there is residual chlorine in the supply water and the permeated water, a reducing agent may be injected. Examples of the alkali include sodium hydroxide and calcium hydroxide, with sodium hydroxide being most preferred. Examples of the reducing agent include sodium bisulfite, sodium bisulfite, sodium thiosulfate and the like, and sodium bisulfite is most preferred.
[0013]
In the present invention, the phrase “the reverse osmosis membrane modules are arranged in two rows” refers to a treatment method in which raw water is once subjected to reverse osmosis treatment of concentrated water that has been subjected to reverse osmosis treatment. No pressurizing operation is required between consecutive reverse osmosis membrane modules.
[0014]
In the present invention, a part of the permeated water of the first stage treated in the second reverse osmosis membrane module is transmitted through the second reverse osmosis membrane module in which the quality of the permeated water is insufficient only in the first stage. Water is the main. However, judging from the quality of the permeated water of the entire two-stage method, if there is a margin, part of the permeated water of the second reverse osmosis membrane module may be used. A mixed liquid is obtained by adding a part of the permeated water of the first reverse osmosis membrane module to the total amount of permeated water of the first reverse osmosis membrane module. When a part of the permeated water of the second reverse osmosis membrane module is sufficient, the ratio is preferably 20% to 100%, more preferably 50% to 100%. More preferably, it is 70% to 100%. Within this range, the effect of the two-stage method is remarkable, which is preferable. On the other hand, in the case of a mixed solution to which a part of the permeated water of the first reverse osmosis membrane module is added, the mixing ratio is preferably 1% to 50%, more preferably 1% to 30%. Further, if it is 1 to 30%, the load of the second stage processing can be suppressed low, and the system of the two-stage method is effective in that it is preferable.
In addition, when the two reverse osmosis membrane modules are arranged in series in two rows such that the supply water flow rate in the first-stage reverse osmosis membrane module is increased and the renewal of the membrane surface is promoted, It is more preferable when operating at a high recovery rate. Further, the permeated water of the first-stage reverse osmosis membrane module supplied to the second-stage reverse osmosis membrane module and subjected to the reverse osmosis treatment has a high concentration of permeated water among the first-stage reverse osmosis membrane modules. It is preferable to mainly use the permeated water of the continuous reverse osmosis membrane module. Considering that the amount of permeated water of the first reverse osmosis membrane module is larger than that of the second reverse osmosis membrane module, the permeated water of the first reverse osmosis membrane module and the second reverse osmosis membrane are used. The ratio of the permeated water of the module is preferably from 0: 100 to 60:40.
[0015]
Examples of the cellulose acetate polymer in the present invention include cellulose acetate, cellulose triacetate, and a mixture of both. Cellulose triacetate is preferred from the viewpoint of performance and stability of performance. Further, since these materials have excellent chlorine resistance, it is possible to add chlorine as a disinfectant to the supplied water. It is preferable to inject intermittently because the amount of disinfectant by-products generated and the amount of chemicals used are reduced.
[0016]
Examples of the polyamide-based material in the present invention include a linear polyamide polymer, a crosslinked polyamide polymer, and the like, and any material having excellent removal performance may be used. Further, there are those having chlorine resistance and those having no chlorine resistance, but those having chlorine resistance are preferable in terms of operation management.
[0017]
Having chlorine resistance in the present invention means that it can be used continuously for about one year in the presence of residual chlorine such as tap water. Examples of the polyamide-based reverse osmosis membrane having chlorine resistance include the HS (R) series manufactured by Toyobo Co., Ltd. If the second-stage reverse osmosis membrane module has chlorine resistance, the second-stage reverse osmosis will remain as it is even if chlorine is used as the supply water to the first-stage reverse osmosis membrane module and remains in the permeated water. Since the membrane module can be processed, it is preferable in terms of operability and the amount of chemicals used in the reducing agent.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 shows an example in which two hollow fiber type reverse osmosis membrane modules are arranged in duplicate as a first-stage reverse osmosis membrane, and only permeated water of the second reverse osmosis membrane module is subjected to second-stage reverse osmosis. It shows a case where the separation operation is performed by supplying to a membrane module. The supply water 6 pressurized by the high-pressure pump 4 is supplied to the first-stage first-stage reverse osmosis membrane module, and the concentrated water 8 is supplied to the second-stage reverse-osmosis membrane module 2. The concentrated water 10 of the second reverse osmosis membrane module 2 is discharged, and the permeated water 9 is pressurized by the pressurizing pump 5 and supplied to the second stage reverse osmosis membrane module 3 and the concentrated water 12 is discharged and the permeated water is discharged. 11 is combined with the first permeated water 7 and obtained as product water 13.
[0019]
FIG. 2 is similar to FIG. 1, wherein the permeated water 7 of the first-stage reverse osmosis membrane module 1 and the permeated water 9 of the first-stage second reverse osmosis membrane module 2 communicate with each other. The flow

rate control valves

14, 15, and 16 can control the percentage of permeated water in each of the first and second reverse osmosis membrane modules, and can change the flow rate and water quality of the supply water to the second-stage reverse osmosis membrane module 2. It is. For example, if the flow control valves 14 and 15 are opened and the flow control valve 16 is throttled, the mixing ratio of the permeated water 7 of the first reverse osmosis membrane module 1 increases, and conversely, the

flow control valves

14 and 16 are opened. If the flow control valve 15 is throttled, the flow rate of permeated water in the second reverse osmosis membrane module 2 can be reduced.
[0020]
【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.
[0021]
(Example 1)
As a first-stage reverse osmosis membrane module, a hollow-fiber reverse osmosis membrane module in which two hollow fiber-type reverse osmosis membrane elements made of cellulose triacetate are installed in a pressure vessel is used. Using a hollow fiber type reverse osmosis membrane module made of chlorine-resistant polyamide, seawater was treated in a two-stage module arrangement in which the first stage was a double stage as shown in FIG. However, the pH was set to 9 by adding NaOH to the water supplied to the second stage. The operating conditions were as follows. Raw water temperature 25 ° C., TDS concentration 3.5%, boron concentration 4.5 mg / L, first stage operating pressure 70 kg / cm ² , second stage operating pressure 15 kg / cm ² , first stage recovery 53 %, Second-stage recovery rate 85%. The water quality of the resulting production water as a two-stage treatment was 143 mg / L for TDS and 1.23 mg / L for boron. The power consumption of the second-stage booster pump was 0.18 kw / m ³ . Table 1 summarizes the water quality and the like of the first and second stages.
[0022]
(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 second-stage reverse osmosis membrane module, and the throughput of the second-stage reverse osmosis membrane module is about the same as that of the first embodiment. The number was reduced to 80% so that The quality of the obtained product water as a two-stage treatment was 166 mg / L for TDS and 1.39 mg / L for boron. The power consumption of the second-stage booster pump was 0.14 kw / m ³ . Table 1 summarizes the water quality and the like of the first and second stages.
[0023]
(Example 3)
The arrangement of the reverse osmosis membrane module is shown in FIG. 2, and the water supplied to the second reverse osmosis membrane module is a mixture of 100% of the permeated water of the second reverse osmosis membrane module and 25% of the first reverse osmosis membrane module. Except for being water, seawater was treated in the same manner as in Example 2. However, the number of reverse osmosis membrane modules for processing in the second stage was set to 150% so that the throughput was about the same as in Example 1. The water quality of the obtained production water as a two-stage treatment was 116 mg / L for TDS and 1.04 mg / l for boron. The power consumption of the second-stage booster pump was 0.27 kw / m ³ . Table 1 summarizes the water quality and the like of the first and second stages.
[0024]
(Comparative Example 1)
In the module arrangement of FIG. 2, the permeated water of the first-stage reverse osmosis membrane module in the first stage is such that all the permeated water of the second reverse osmosis membrane module becomes the supply water for the second-stage reverse osmosis membrane module The 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 TDS 25 mg / L and boron 0.4 mg / L. The power consumption of the second-stage booster pump was 0.59 kw / 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. Table 1 summarizes the water quality and the like of the first and second stages.
[0025]
[Table 1]

[0026]
【The invention's effect】
In the membrane treatment method for partially treating the permeated water treated with the reverse osmosis membrane again with the reverse osmosis membrane, it is possible to provide a method for reducing the scale and power consumption of the second-stage reverse osmosis membrane module. Further, it is possible to optimize the entire system by changing the supply water to the second-stage reverse osmosis membrane module.
[Brief description of the drawings]
FIG. 1 shows a simple configuration diagram in a case where only permeated water of a first-stage second reverse osmosis membrane module is supplied to a second-stage reverse osmosis membrane module in an example of the treatment method of the present invention.
FIG. 2 shows an example of a treatment method according to the present invention, in which a mixture of permeated water of a first-stage second reverse osmosis membrane module and permeated water of a first-stage reverse osmosis membrane module is used in a second-stage reverse osmosis membrane. FIG. 4 shows a simple configuration diagram when supplied to a module.
[Explanation of symbols]
1: First-stage first-stage reverse osmosis membrane module 2: First-stage second-stage reverse osmosis membrane module 3: Second-stage reverse osmosis membrane module 4: High-pressure pump 5: Boost pump 6: Supply water 7: Permeated water of the first reverse osmosis membrane module 8: Concentrated water of the first reverse osmosis membrane module 9: Permeated water of the second reverse osmosis membrane module 10: Permeate of the second reverse osmosis membrane module Concentrated water 11: Permeated water of the second-stage reverse osmosis membrane module 12: Concentrated water of the second-stage reverse osmosis membrane module 13: Production water 14, 15, 16: Flow control valve

Claims

This is a method of treating high-concentration raw water with a two-stage reverse osmosis membrane module and separating it into high-concentration water and low-concentration permeate water. Is disposed so as to be supplied to the second-stage reverse osmosis membrane module, and 10% to 100% of the permeated water of the first-stage reverse osmosis membrane module is treated by the second-stage reverse osmosis membrane module. A method for treating a highly concentrated solution.

In the first-stage reverse osmosis membrane module, the reverse osmosis membrane modules are arranged in duplicate, the high concentration raw water is supplied to the first reverse osmosis membrane module, and the concentrated water of the first module is supplied to the second reverse osmosis membrane module. 2. The method for treating a high-concentration solution according to claim 1, wherein the high-concentration solution is supplied.

The permeated water of the second reverse osmosis membrane module of the first reverse osmosis membrane module and the permeated water of the first reverse osmosis membrane module are mixed at a ratio of 100: 0 to 40:60, and the second stage is used. 3. The method for treating a high-concentration solution according to claim 1, wherein the reverse osmosis treatment is performed by the reverse osmosis membrane module.

The method for treating a high-concentration solution according to any one of claims 1 to 3, wherein the hollow fiber type reverse osmosis membrane is made of a cellulose acetate polymer.

The method for treating a high-concentration solution according to any one of claims 1 to 4, wherein the second-stage reverse osmosis membrane module comprises a reverse osmosis membrane made of a polyamide material.

The method for treating a high-concentration solution according to any one of claims 1 to 5, wherein the high-concentration raw water is seawater.

The method for treating a high-concentration solution according to any one of claims 1 to 6, wherein chlorine is intermittently injected into the high-concentration raw water as a sterilization treatment.