JP3938821B2

JP3938821B2 - Electrodialyzer and desalting method and apparatus using the same

Info

Publication number: JP3938821B2
Application number: JP18608799A
Authority: JP
Inventors: 二朗佐藤; 康平三木; 勇井上; 政信大方; 英一西川
Original assignee: Sumitomo Heavy Industries Ltd
Current assignee: Sumitomo Heavy Industries Ltd
Priority date: 1999-06-30
Filing date: 1999-06-30
Publication date: 2007-06-27
Anticipated expiration: 2019-06-30
Also published as: JP2001009459A

Description

【０００１】
【発明の属する技術分野】
本発明は、電気透析装置並びにこれを用いた脱塩処理方法及び装置に関するものである。
【０００２】
【従来の技術】
埋立地浸出水には、カルシウムイオン等の塩類が多く含有されており、カルシウムイオン濃度やｐＨの値によっては、浸出水の処理工程中で配管の閉塞などのスケールトラブルが起こることが知られている。そこで、浸出水中のカルシウムイオン濃度を低減すべく浸出水に対して脱塩処理が行われ、その脱塩処理の一手段として、電気透析装置等が知られている。
【０００３】
図１０は、従来からある電気透析装置の内部構造の一例を示す概略図である。図１０に示す電気透析装置１００は、電気透析槽１０１を有しており、その内部に陰極１０２と陽極１０３とを備えている。槽１０１内には、陰極１０２と陽極１０３との間に陰極１０２から陽極１０３に向けてイオン交換膜がＣ，Ａ，Ｃ，Ａ，Ｃ，Ｃの順に並設されている。ここで、「Ｃ」は陽イオン交換膜を、「Ａ」は陰イオン交換膜を表す記号である。これらのイオン交換膜によって、陰極１０２を含む陰極室１０４、及び陽極１０３を含む陽極室１０５が形成され、陰極室１０４と陽極室１０５との間には、脱塩室１０６と濃縮室１０７とが交互に形成される。陰極室１０４と陽極室１０５には、硫酸ナトリウム水溶液や硝酸ナトリウム水溶液といった水溶液が注入される。そこで、脱塩室１０６及び濃縮室１０７にそれぞれ塩含有水を導入し、陽極１０３と陰極１０２との間に電圧を印加すると、ある脱塩室１０６を通過する塩含有水中のカルシウムイオン等の陽イオンが陽イオン交換膜Ｃを通して濃縮室１０７中に導入され、脱塩処理水中での塩濃度の低減が図られ且つ濃縮液中での濃縮が進む。
【０００４】
【発明が解決しようとする課題】
しかしながら、前述した従来の電気透析装置１００では、電気透析の性能が時間とともに低下し、安定した脱塩処理が行われない場合があった。
【０００５】
そこで、本発明は、塩含有水の安定した脱塩処理を可能とする電気透析装置並びにこれを用いた脱塩処理方法及び装置を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明者らは、上述した従来の電気透析装置の問題点について検討した結果、従来の電気透析装置では、電気透析によって、陰極室１０４へのカルシウムイオンの流入が防止されず、陰極の近くに配置されたイオン交換膜にカルシウムスケールが析出してそれが膜に付着したり膜を閉塞させたりし、そのため、陽極及び陰極間の抵抗が増加して、塩含有水の脱塩処理が不安定となることを見出した。
【０００７】
そこで、請求項１に係る発明は、カルシウムイオンを含有する塩含有水を電気透析槽内で脱塩処理する電気透析装置において、電気透析槽内に配置される陰極及び陽極と、陰極及び陽極間に並設され、複数の室を形成する複数のイオン交換膜とを備え、複数の室のうち陰極を含む室内には陰極酸性溶液が導入され、陽極を含む室内には陽極酸性溶液が導入されるようになっており、陰極に最も近いイオン交換膜が陰イオン交換膜であることを特徴とする。
【０００８】
この構成によれば、陰極を含む室と、陽極を含む室との間の室内にカルシウムを含む塩含有水を導入し、陽極と陰極との間に電圧を印加すると、塩含有水が濃縮され且つ脱塩処理される。このとき、塩含有水から陰極を含む室内の陰極酸性溶液へのカルシウムイオン等の陽イオンの移動が防止され、スケールによる陰イオン交換膜の閉塞等が防止される。
【０００９】
また、請求項５に係る発明は、カルシウムイオンを含む塩含有水の脱塩処理方法において、塩含有水を酸性にｐＨ調整するｐＨ調整工程と、ｐＨ調整された塩含有水を逆浸透によって濃縮し且つ透過させる逆浸透工程と、逆浸透工程の逆浸透によって得られる濃縮水を、上記の電気透析装置で脱塩処理する電気透析工程とを含むことを特徴とする。
【００１０】
この場合、ｐＨ調整によって塩含有水中に存在する炭酸イオンの生成が抑えられ、これにより炭酸イオンとカルシウムイオンとの結合によるカルシウムスケールの析出が抑制される。そして、この塩含有水が逆浸透膜装置で濃縮され且つ脱塩処理され、これによって得られる濃縮水が電気透析装置で濃縮され且つ脱塩処理される。このとき、電気透析装置でもカルシウムスケールの析出が十分に防止され、また、これまで達成困難であった高濃度までの濃縮が可能となる。
【００１１】
また請求項６に係る発明は、カルシウムイオンを含む塩含有水の脱塩処理装置において、塩含有水を酸性にｐＨ調整するｐＨ調整槽と、ｐＨ調整された塩含有水を逆浸透によって濃縮し且つ透過させる逆浸透膜装置と、逆浸透膜装置における逆浸透によって得られる濃縮水を濃縮し且つ脱塩処理する上記の電気透析装置とを備えることを特徴とする。この装置によれば、請求項５に係る発明の方法を有効に実施することができる。
【００１２】
また、請求項７に係る発明は、カルシウムイオンを含む塩含有水の脱塩処理方法において、塩含有水を酸性にｐＨ調整するｐＨ調整工程と、ｐＨ調整された塩含有水を上記の電気透析装置で濃縮し且つ脱塩処理する電気透析工程と、電気透析工程で得られる脱塩液を逆浸透によって濃縮し且つ透過させる逆浸透工程とを含むことを特徴とする。
【００１３】
更に、請求項８に係る発明は、カルシウムイオンを含む塩含有水の脱塩処理装置において、塩含有水を酸性にｐＨ調整するｐＨ調整槽と、ｐＨ調整された塩含有水を濃縮し且つ脱塩処理する上記の電気透析装置と、電気透析装置で得られる脱塩液を逆浸透によって濃縮し且つ透過させる逆浸透膜装置とを備えることを特徴とする。この場合、請求項７に係る発明の方法を有効に実施することができる。
【００１４】
また、請求項９に係る発明は、カルシウムイオンを含む塩含有水の脱塩処理方法において、塩含有水中の塩濃度が所定値以下の場合に、塩含有水をｐＨ調整した後、逆浸透によって濃縮し且つ透過させ、そのうちの濃縮された濃縮水を上記の電気透析装置で濃縮し且つ脱塩処理する第１工程と、塩含有水中の塩濃度が所定値を超える場合に、電気透析装置で得られる脱塩液を濃縮し且つ脱塩処理する第２工程と、電気透析装置で脱塩された塩含有水をｐＨ調整工程のｐＨ調整に使用する第３工程とを含むことを特徴とする。
【００１５】
この場合、塩含有水中の塩濃度が所定値以下の場合に、第１工程の後に第３工程を行うと、逆浸透及び電気透析で処理すべき水量が少なくて済む。一方、塩含有水中の塩濃度が所定値を超える場合には、第２工程の後に第３工程を行うと、逆浸透及び電気透析で処理すべき水量が少なくて済む。従って、塩含有水中の塩濃度の変動に応じて上記のように処理の手順を変更すると、逆浸透及び電気透析処理に要する負担を常に小さくすることができる。
【００１６】
更に、請求項１０に係る発明は、カルシウムイオンを含む塩含有水の脱塩処理装置において、塩含有水を酸性にｐＨ調整するｐＨ調整槽と、ｐＨ調整槽でｐＨ調整された塩含有水を逆浸透によって濃縮し且つ透過させる逆浸透膜装置と、逆浸透膜装置における逆浸透によって得られる濃縮水を濃縮し且つ脱塩処理する上記の電気透析装置と、逆浸透膜装置に塩含有水を導入する第１流入ラインと、第１流入ラインに設けられる第１の弁と、第１流入ラインから分岐して電気透析装置に塩含有水を流入させる第２流入ラインと、第２流入ラインに設けられる第２の弁と、電気透析装置で得られる脱塩液をｐＨ調整槽又はその上流側に流入させる返送手段とを備えることを特徴とする。この装置によれば、請求項９に係る発明の方法を有効に実施できる。
【００１７】
【発明の実施の形態】
以下、図面と共に本発明の脱塩処理装置の実施形態について詳細に説明する。
【００１８】
図１は、本発明の脱塩処理装置の第１実施形態を示すフローシートである。図１に示すように、脱塩処理装置１０は、カルシウムイオンを含む塩含有水を酸性にｐＨ調整するｐＨ調整槽１を備える。ここで、カルシウムイオンを含む塩含有水としては、例えば埋立地における浸出水などが挙げられる。以下、浸出水を例にして脱塩処理装置１０について説明する。
【００１９】
流入ライン（第１流入ライン）Ｌ０を通してｐＨ調整槽１に流入される浸出水中の塩濃度は、一定値でかつその値が約３０，０００ｍｇ／ｌ以下であることが好ましい。塩濃度が３０，０００ｍｇ／ｌを超える浸出水を脱塩処理装置１０によって処理する場合、脱塩処理装置１０で処理すべき塩含有水の量が多くなり、脱塩処理装置１０にかかる負担が大きくなり、ひいてはランニングコストが増加する傾向があるからである。ｐＨ調整槽１は、浸出水を酸性に保持することで下流の逆浸透膜装置２で浸出水中の炭酸イオンの生成を防止するものである。ｐＨ調整槽１は、ラインＬ１を介して逆浸透膜装置２に接続され、逆浸透膜装置２は、浸出水を逆浸透膜２ａによって濃縮水と透過水とに膜分離する。ここで、透過水は系外へ排出され、濃縮水はラインＬ２を通して電気透析装置３へ導入される。なお、ラインＬ１には、逆浸透膜装置２でのカルシウムスケールの析出を一層防止する点から、ｐＨ調整槽１と逆浸透膜装置２との間に、浸出水に散気空気を供給する曝気槽（脱炭酸槽）４が設置されることが好ましい。
【００２０】
電気透析装置３は、逆浸透膜装置２で得られた濃縮水を濃縮液と脱塩液とに分離するものであり、電気透析装置３からは、濃縮液を系外へ排出するラインＬ３が延びている。なお、脱塩液中の塩濃度低下による電気透析装置３内の電気抵抗の上昇を防止する点からは、脱塩液をｐＨ調整槽１に返送する返送ラインＬ４が電気透析装置３から延びていることが好ましい。返送ライン４には、ポンプ５が取り付けられている。
【００２１】
ここで、電気透析装置３の構成について図２、図３を用いて説明する。
【００２２】
図２に示すように、電気透析装置３は、逆浸透膜装置２から導入される濃縮水を濃縮液として貯留する濃縮液槽６と、濃縮水を脱塩液として貯留する脱塩液槽７とを備えている。また、図３に示すように、電気透析装置３は電気透析槽８を備えており、電気透析槽８内には、平板状の陰極１４と、平板状の陽極１８が配置され、陰極１４と陽極１８との間には、複数枚のイオン交換膜が並設されている。ここで、陰極１４に最も近いイオン交換膜は、陰イオン交換膜Ａになっており、他のイオン交換膜はそれぞれ、陰極１４から陽極１８に向けて順次陰イオン交換膜Ａ、陽イオン交換膜Ｃ、陰イオン交換膜Ａ、陽イオン交換膜Ｃ、陽イオン交換膜Ｃとなっている。これらイオン交換膜によって、陰極１４を含む陰極室９、陽極１８を含む陽極室１１が形成され、陽極室１１と陰極室９との間には、脱塩室２１と濃縮室２２とが交互に形成され、最も陰極室９に近い側には脱塩室２１が形成されている。ここで、陰極室９内には、万一カルシウムイオンの漏洩によりスケールの形成があったとしても陰極１４までスケールが達しないように、陰イオン交換膜Ａが少なくとも一つ配置されることが好ましい。
【００２３】
なお、脱塩室２１には、脱塩液槽７からラインＬ１７を通して脱塩液が導入され、濃縮室２２には、濃縮液槽６からラインＬ１８を通して濃縮液が導入され、脱塩液はラインＬ１９を通して脱塩液槽７に戻され、濃縮液はラインＬ２０を通して濃縮液槽６に戻されるようになっている（図２参照）。また、脱塩液槽７にはラインＬ４が接続され、脱塩液がラインＬ４を通してｐＨ調整槽１に返送され使用されるようになっており、濃縮液槽６にはラインＬ３が接続され、濃縮液がラインＬ３を通して系外へ排出されるようになっている。
【００２４】
図３に示すように、陰極室９には、陰極１４が浸漬されるように陰極酸性溶液１３が注入され、陰極酸性溶液１３は、酸と陰極溶液とからなり、酸としては、例えば塩酸、硫酸、硝酸等が用いられ、陰極溶液としては、例えば塩化ナトリウム水溶液、硫酸ナトリウム水溶液、硝酸ナトリウム水溶液等が用いられる。このうち、扱いが容易で且つ安価であることから、塩化ナトリウム溶液を用いることが好ましく、更には、塩素という成分が共通であることから、塩酸を含む塩化ナトリウム溶液がより好ましい。
【００２５】
陰極酸性溶液１３のｐＨは通常は１．５〜２．５に保持されている。陰極室９には、図２に示すように、ポンプ１６を備えたラインＬ５を介して電極液槽１５が接続されている。陰極酸性溶液１３を上記範囲のｐＨに調整するために、ポンプ１６によりｐＨの低い同種の酸性溶液が陰極酸性溶液１３に補充されるようになっている。なお、電極液槽１５には、陰極酸性溶液１３中の酸と同種の酸を供給する酸供給源がラインＬ１３を介して接続されている。電極液槽１５は、余剰酸性溶液の有効利用の点から、ラインＬ６を通してｐＨ調整槽１又はその上流側のラインＬ０に接続されることが好ましい。また、陰極室９は、ｐＨの高くなった陰極酸性溶液１３を電極液槽１５に戻すようラインＬ７を介して電極液槽１５に接続されている。
【００２６】
陽極室１１には、図３に示すように、陽極１８が浸漬されるように陽極酸性溶液１７が注入されている。陽極酸性溶液１７は、塩素ガスの発生防止及び塩化カルシウムスケールの析出防止の点から、塩素イオン非含有溶液からなることが好ましい。塩素イオン非含有溶液は、塩素イオンを含まない酸のみでもよく塩素イオンを含まない酸と陽極溶液とからなっていてもよい。塩素イオンを含まない酸としては、例えば硫酸、硝酸などが挙げられ、陽極溶液としては、硫酸ナトリウム水溶液、硝酸ナトリウム水溶液などが挙げられる。このうち、硫酸のみを用いても十分に陽極溶液としての用をなす。陽極酸性溶液１７のｐＨは、通常は０．５〜２．５に保持されている。陽極室１１は、ポンプ２０を備えたラインＬ８を介して電極液槽１９に接続されている。陽極酸性溶液１７のｐＨを上記範囲内に調整するよう陽極酸性溶液１７中の酸と同種のｐＨの低い酸を供給する酸供給源がラインＬ１４を介して接続されている。電極液槽１９は、余剰の酸性溶液の有効利用の観点から、ラインＬ９を介してラインＬ６に接続されることが好ましい。陽極室１１には、ｐＨの高くなった陽極酸性溶液１７を電極液槽１９に戻すようラインＬ１０を介して電極液槽１９に接続されている。
【００２７】
次に、前述した構成の脱塩処理装置１０を用いた脱塩処理方法について説明する。
【００２８】
図１に示すように、浸出水をラインＬ０を通してｐＨ調整槽１に導入し、ｐＨ調整槽１で酸性にｐＨ調整し、好ましくは５以下のｐＨに調整する（ｐＨ調整工程）。ｐＨ調整することで炭酸イオンが生成しにくくなるので、後段の逆浸透膜装置２におけるカルシウムスケールの析出が防止される。ｐＨ調整された浸出水をラインＬ１を通して曝気槽４に導入する。曝気槽４では、炭酸イオンが二酸化炭素として放出されるので、逆浸透膜装置２におけるカルシウムスケールが一層防止されることとなる。その後、浸出水を逆浸透膜装置２に導入する。逆浸透膜装置２では、逆浸透膜２ａによって浸出水を濃縮し且つ透過させ、透過水は系外へ排出し、濃縮水はラインＬ２を通して電気透析装置３に導入する（逆浸透工程）。
【００２９】
図２に示すように、電気透析装置３では、濃縮液槽６に濃縮水を濃縮液として導入し、脱塩液槽７には濃縮水を脱塩液として導入し、濃縮液槽６中の濃縮液を電気透析槽８の濃縮室２２に導入し、脱塩液槽７中の脱塩液を電気透析槽８の脱塩室２１に導入する。このとき、図３に示すように、陰極１４と陽極１８との間に電圧を印加すると、脱塩液中の陽イオンは陰極１４へ、陰イオンは陽極１８へ向かい、濃縮及び脱塩処理が行われる。すなわち、脱塩室２１中の脱塩液は脱塩処理され、濃縮室２２中の濃縮液は濃縮される（電気透析工程）。
【００３０】
このとき、陰極室９と脱塩室２１との間に配置される陰イオン交換膜Ａにより、脱塩液から陰極室９中の陰極酸性溶液１３へのカルシウム等の陽イオンの移動が防止される。このため、カルシウム等の陽イオンと陰極室９内の塩素イオン等の陰イオンとの結合によるカルシウムスケールの析出が防止され、カルシウムスケールの陰イオン交換膜Ａの膜面への付着や膜閉塞が防止される。以上のことから、陽極１８及び陰極１４間の電気抵抗の増加が防止される。従って、脱塩液の安定した脱塩処理が可能となる。
【００３１】
なお、電気透析工程においては、陰極室９及び陽極室１１内のカルシウムスケールの析出を一層抑制する観点から、電極液槽１５，１９における酸性溶液のｐＨは４以下に保持されることが好ましい。また、電極液槽１５，１９の酸性溶液を有効利用する観点からは、電極液槽１５，１９の酸性溶液をラインＬ６を通してｐＨ調整槽１又はその上流側のラインＬ０に返送することが好ましい（図１、図２参照）。
【００３２】
そして、図２に示すように、濃縮液は濃縮液槽６に戻され、その後、ラインＬ３を通して系外へ排出される。一方、脱塩液は、脱塩液槽７に戻された後、ラインＬ４を通してポンプ５によりｐＨ調整槽１に返送される（図１参照）。このとき、返送される脱塩液は酸性となっているので、ｐＨ調整槽１で供給する酸の量を低減することができ、酸の有効利用を図ることができる。なお、脱塩液槽７の脱塩液はｐＨ調整槽１に限らず、その上流側に返送されてもよい。
【００３３】
次に、本発明の脱塩処理装置の第２実施形態について説明する。
【００３４】
図４は、第２実施形態の脱塩処理装置３０を示す概略図であり、第１実施形態と同一又は同等の構成要素については同一の符号が付されている。図４に示すように、脱塩処理装置３０は、電気透析装置３を上流側に、逆浸透膜装置２を下流側に配置し、電気透析装置３で得られる脱塩液をラインＬ１５を通して逆浸透膜装置２に導入し、逆浸透膜装置２で得られる濃縮水を返送ラインＬ１６を通してポンプによりｐＨ調整槽１に返送する点で第１実施形態の脱塩処理装置１０と異なる。
【００３５】
この場合、脱塩処理装置３０を用いた脱塩処理は、ｐＨ調整された浸出水を電気透析装置３で濃縮及び脱塩処理し（電気透析工程）、電気透析装置３で得られる脱塩液を逆浸透膜装置２で逆浸透によって濃縮及び透過させ（逆浸透工程）、逆浸透工程で得られた濃縮水をｐＨ調整槽１に返送する（返送工程）点以外は、第１実施形態の脱塩処理方法と同様にして行われる。この場合、ｐＨ調整槽１に流入される浸出水中の塩濃度が３０，０００ｍｇ／ｌを超える場合に、逆浸透膜装置２及び電気透析装置３で処理すべき浸出水の量が少なくて済み、逆浸透膜装置２及び電気透析装置３で要する負担が小さくなる傾向がある。従って、装置全体としてのランニングコストを低減することができる。
【００３６】
次に、本発明の脱塩処理装置の第３実施形態について説明する。
【００３７】
図５は、第３実施形態の脱塩処理装置４０を示す概略図であり、第１実施形態と同一又は同等の構成要素については同一の符号が付されている。図５に示すように、脱塩処理装置４０は、流入ラインＬ０の途中から分岐する流入ライン（第２流入ライン）Ｌ１２がラインＬ２に接続され、流入ラインＬ０には弁Ｖ１が取り付けられ、流入ラインＬ１２には上流側から弁Ｖ２（第２の弁）、曝気槽（第２の脱炭酸槽）４１が順次取り付けられている点で第１実施形態の脱塩処理装置１０と異なる。
【００３８】
この場合、脱塩処理は以下のようにして行う。即ち、浸出水中の塩濃度が３０，０００ｍｇ／ｌ以下の場合には、弁Ｖ２を閉じ、弁Ｖ１を開き、浸出水をｐＨ調整槽１に導入する。そして、ｐＨ調整された浸出水を曝気槽４に通し、逆浸透膜装置２に導入する。逆浸透膜装置２は、浸出水を濃縮及び透過させ、逆浸透で得られる濃縮水は、ラインＬ２を通して電気透析装置３に送られ、電気透析装置３で濃縮され且つ脱塩処理される（第１工程）。電気透析装置３で得られる脱塩液は、返送ラインＬ４を通してポンプ５によりｐＨ調整槽１に返送される（第３工程）。
【００３９】
一方、浸出水中の塩濃度が３０，０００ｍｇ／ｌを超える場合には、弁Ｖ１を閉じ、弁Ｖ２を開いて浸出水を流入ラインＬ１２に導入し、浸出水を曝気槽４１で曝気した後、ラインＬ２を通して電気透析装置３に導入する。そして、電気透析装置３で浸出水を濃縮し且つ脱塩処理する（第２工程）。電気透析装置３で得られる脱塩液は、返送ラインＬ４を通してポンプ５によりｐＨ調整槽１に返送する（第３工程）。その後、脱塩液を曝気槽４に通し、逆浸透膜装置２に導入する。逆浸透膜装置２では、脱塩液は濃縮及び透過され、そのうちの濃縮水が電気透析装置３に導入される。
【００４０】
このような脱塩処理方法によれば、浸出水中の塩濃度が３０，０００ｍｇ／ｌ以下の場合に、逆浸透膜装置２で処理した後、電気透析装置３で処理し、一方、浸出水中の塩濃度が３０，０００ｍｇ／ｌを超える場合に、浸出水を電気透析装置３で処理した後、逆浸透膜装置２で処理すると、逆浸透膜装置２及び電気透析装置３で処理すべき浸出水の量が常に少なくてなる。従って、浸出水中の塩濃度の変動に応じて上記のように処理の手順を変更すると、逆浸透膜装置２及び電気透析装置３でかかる負担を常に小さくすることができ、ひいてはランニングコストを低減することができる。
【００４１】
以下、実施例により本発明の内容を具体的に説明する。
【００４２】
【実施例】
（実施例１）
電気透析装置として、陽極に最も近いイオン交換膜を陽イオン交換膜（旭硝子社製セレミオンＣＭＶ）、陰極に最も近いイオン交換膜を陰イオン交換膜（旭硝子社製セレミオンＡＳＶ）とし、これらイオン交換膜間に陽極室側から陰極室側に向けて陽イオン交換膜、陰イオン交換膜を交互に配置し、脱塩室を１１室、濃縮室を１０室形成したものを用いた。陰極室には、陰極酸性溶液として、塩酸酸性の３％食塩水溶液を注入し、陰極酸性溶液は、塩酸添加した同種の酸性溶液を注入することでｐＨ２以下に調整した。一方、陽極室には、陽極酸性溶液として、３％硫酸水溶液を注入し、陽極酸性溶液は、硫酸添加した同種の酸性溶液を陽極室に注入することでｐＨ１．０前後に調整した。
【００４３】
そして、脱塩室及び濃縮室のそれぞれに約３．４％の塩含有水を導入しながら、陰極と陽極との間に電圧を印加して電気透析を行い、濃縮液塩濃度及び脱塩液塩濃度のそれぞれの経時変化、及び陰極と陽極との間に流れる電流値の経時変化を調べた。その結果を図６、図７に示す。図６及び図７に示すように、濃縮液塩濃度は１７％であり、このように塩濃度が高いにもかかわらず、電流値は７日間にわたって安定していた。
【００４４】
（比較例１）
陽極酸性溶液、陰極酸性溶液として、硝酸酸性の３％硝酸ナトリウム水溶液を用い、陰極に最も近い陰イオン交換膜に代えて陽イオン交換膜を用い、更に両極酸性溶液のｐＨを２．５以下に保持するようにした以外は実施例１と同様の電気透析槽を用いた。なお、両極酸性溶液のｐＨ調整は、単一の電極液槽内の硝酸を添加した同種の酸性溶液を陽極室及び陰極室にそれぞれ注入することで行った。
【００４５】
この電気透析装置を用いて実施例１と同様にして濃縮液塩濃度及び脱塩液塩濃度のそれぞれの経時変化、及び陰極と陽極との間に流れる電流値の経時変化を調べた。その結果を図８、図９に示す。図８及び図９に示すように、濃縮液塩濃度は１０％であり、電流値は時間の経過とともに徐々に低下した。このとき、陰極酸性溶液の白濁が観察され、陰極室において流動抵抗が発生した。この電気透析装置を分解したところ、陰極室の陰イオン交換膜の膜面全体及び濃縮室内に白色スケールが生じていた。陽極室の一部でも同様のことが起こっていた。この白色スケールを分析した結果、その主成分は水酸化カルシウムであることが分かった。この結果、この方法で長期安定運転を望むことには無理があることが分かった。
【００４６】
【発明の効果】
以上述べたように本発明の電気透析装置によれば、カルシウムを含む塩含有水が脱塩処理されるとき、塩含有水から陰極を含む室内の陰極酸性溶液へのカルシウムイオン等の陽イオンの移動が防止され、スケールによる陰イオン交換膜の閉塞等が防止され、また、濃縮される塩含有水中の塩の高濃度化が実現される。従って、陽極及び陰極間の電気抵抗の増加が防止され、塩含有水の安定した処理が可能となる。更に、この電気透析装置を適用した脱塩処理方法及び装置によると、電気透析や逆浸透で処理すべき塩含有水の量が少なくて済むので、ランニングコストを低減することができる。
【図面の簡単な説明】
【図１】本発明の脱塩処理装置の一実施形態を示すフローシートである。
【図２】本発明の電気透析装置の一実施形態を示すフローシートである。
【図３】図２の電気透析装置の電気透析槽の内部構成を示す断面図である。
【図４】本発明の脱塩処理装置の別の実施形態を示すフローシートである。
【図５】本発明の脱塩処理装置の更に別の実施形態を示すフローシートである。
【図６】実施例１における電気透析による濃縮液塩濃度及び脱塩液塩濃度の経時変化を示すグラフである。
【図７】実施例１における電気透析による電流値の経時変化を示すグラフである。
【図８】比較例１における電気透析による濃縮液塩濃度及び脱塩液塩濃度の経時変化を示すグラフである。
【図９】比較例１における電気透析による電流値の経時変化を示すグラフである。
【図１０】従来の電気透析槽の内部構成を示す断面図である。
【符号の説明】
１…ｐＨ調整槽、２…逆浸透膜装置、３…電気透析装置、４…曝気槽（脱炭酸槽、第１の脱炭酸槽）５…ポンプ（返送手段）、９…陰極室（陰極を含む室）、１１…陽極室（陽極を含む室）、１２…処理水室、１３…陰極酸性溶液、１４…陰極、１７…陽極酸性溶液、１８…陽極、Ａ…陰イオン交換膜、４１…曝気槽（第２の脱炭酸槽）、Ｌ０…流入ライン（第１流入ライン）、Ｌ４，Ｌ１６…返送ライン（返送手段）、Ｌ１２…流入ライン（第２流入ライン）、Ｖ１…弁（第１の弁）、Ｖ２…弁（第２の弁）。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrodialysis apparatus and a desalination treatment method and apparatus using the same.
[0002]
[Prior art]
Landfill leachate contains a lot of salts such as calcium ions, and depending on the calcium ion concentration and pH value, it is known that scale troubles such as piping clogging may occur during the leachate treatment process. Yes. Therefore, desalting treatment is performed on the leachate to reduce the calcium ion concentration in the leachate, and an electrodialysis apparatus or the like is known as one means of the desalting treatment.
[0003]
FIG. 10 is a schematic view showing an example of the internal structure of a conventional electrodialysis apparatus. An electrodialysis apparatus 100 shown in FIG. 10 includes an electrodialysis tank 101 and includes a cathode 102 and an anode 103 therein. In the tank 101, ion exchange membranes are arranged in the order of C, A, C, A, C, C from the cathode 102 to the anode 103 between the cathode 102 and the anode 103. Here, “C” is a symbol representing a cation exchange membrane, and “A” is a symbol representing an anion exchange membrane. By these ion exchange membranes, a cathode chamber 104 including the cathode 102 and an anode chamber 105 including the anode 103 are formed. Between the cathode chamber 104 and the anode chamber 105, a desalting chamber 106 and a concentration chamber 107 are formed. It is formed alternately. An aqueous solution such as an aqueous sodium sulfate solution or an aqueous sodium nitrate solution is injected into the cathode chamber 104 and the anode chamber 105. Therefore, when salt-containing water is introduced into each of the desalting chamber 106 and the concentration chamber 107 and a voltage is applied between the anode 103 and the cathode 102, positive ions such as calcium ions in the salt-containing water passing through the certain desalting chamber 106 are obtained. Ions are introduced into the concentration chamber 107 through the cation exchange membrane C, the salt concentration in the desalted water is reduced, and the concentration in the concentrate proceeds.
[0004]
[Problems to be solved by the invention]
However, in the conventional electrodialysis apparatus 100 described above, the performance of electrodialysis decreases with time, and stable desalting treatment may not be performed.
[0005]
Then, an object of this invention is to provide the electrodialysis apparatus which enables the stable desalination process of salt-containing water, and the desalination process method and apparatus using the same.
[0006]
[Means for Solving the Problems]
As a result of examining the problems of the above-described conventional electrodialysis apparatus, the present inventors have found that in the conventional electrodialysis apparatus, the inflow of calcium ions into the cathode chamber 104 is not prevented by electrodialysis, and is close to the cathode. Calcium scale is deposited on the ion exchange membrane, which adheres to the membrane or clogs the membrane, which increases the resistance between the anode and the cathode, which makes the desalting treatment of salt-containing water unstable. I found out that
[0007]
Accordingly, the invention according to claim 1 is an electrodialysis apparatus for desalinating salt-containing water containing calcium ions in an electrodialysis tank, and a cathode and an anode disposed in the electrodialysis tank, and between the cathode and the anode. And a plurality of ion exchange membranes forming a plurality of chambers, wherein a cathode acidic solution is introduced into a chamber including a cathode among the plurality of chambers, and an anodic acidic solution is introduced into a chamber including the anode. The ion exchange membrane closest to the cathode is an anion exchange membrane.
[0008]
According to this configuration, when salt-containing water containing calcium is introduced into a chamber between the chamber containing the cathode and the chamber containing the anode, and a voltage is applied between the anode and the cathode, the salt-containing water is concentrated. And it is desalted. At this time, the movement of cations such as calcium ions from the salt-containing water to the indoor cathodic acidic solution including the cathode is prevented, and the anion exchange membrane is blocked by the scale.
[0009]
Further, the invention according to claim 5 is a method for desalinating salt-containing water containing calcium ions, a pH adjusting step for adjusting the pH of the salt-containing water to an acid, and concentrating the pH-adjusted salt-containing water by reverse osmosis. And a reverse osmosis step for allowing permeation, and an electrodialysis step for desalting the concentrated water obtained by reverse osmosis in the reverse osmosis step using the electrodialysis apparatus.
[0010]
In this case, the production of carbonate ions present in the salt-containing water is suppressed by adjusting the pH, thereby suppressing the precipitation of calcium scale due to the binding of carbonate ions and calcium ions. Then, the salt-containing water is concentrated and desalted by the reverse osmosis membrane device, and the concentrated water thus obtained is concentrated and desalted by the electrodialyzer. At this time, precipitation of calcium scale is sufficiently prevented even with an electrodialysis apparatus, and concentration to a high concentration, which has been difficult to achieve so far, is possible.
[0011]
The invention according to claim 6 is the desalination apparatus for salt-containing water containing calcium ions, wherein the pH-adjusting tank for adjusting the pH of the salt-containing water to an acidic pH and the salt-containing water whose pH has been adjusted are concentrated by reverse osmosis. And a reverse osmosis membrane device for permeation, and the electrodialysis device for concentrating and desalting the concentrated water obtained by reverse osmosis in the reverse osmosis membrane device. According to this apparatus, the method of the invention according to claim 5 can be effectively implemented.
[0012]
The invention according to claim 7 is a method of desalinating salt-containing water containing calcium ions, wherein a pH adjustment step for adjusting the pH of the salt-containing water to an acidic pH, and the pH-adjusted salt-containing water is electrodialyzed as described above. It comprises an electrodialysis step of concentrating and desalting with an apparatus, and a reverse osmosis step of concentrating and permeating the desalted solution obtained in the electrodialysis step by reverse osmosis.
[0013]
Furthermore, the invention according to claim 8 is a demineralization apparatus for salt-containing water containing calcium ions, wherein the pH-adjusting tank for adjusting the pH of the salt-containing water to an acidic pH, the salt-containing water whose pH has been adjusted is concentrated and removed. The electrodialysis apparatus for salt treatment and a reverse osmosis membrane apparatus for concentrating and permeating the desalted solution obtained by the electrodialysis apparatus by reverse osmosis are characterized by the following. In this case, the method according to the seventh aspect can be effectively carried out.
[0014]
Further, the invention according to claim 9 is a method for desalinating salt-containing water containing calcium ions, when the salt concentration in the salt-containing water is not more than a predetermined value, after adjusting the pH of the salt-containing water, by reverse osmosis. A first step of concentrating and permeating, concentrating the concentrated water in the electrodialyzer and desalinating, and when the salt concentration in the salt-containing water exceeds a predetermined value, A second step of concentrating and desalting the obtained desalted solution, and a third step of using the salt-containing water desalted by the electrodialyzer for pH adjustment in the pH adjustment step. .
[0015]
In this case, when the salt concentration in the salt-containing water is equal to or lower than the predetermined value, if the third step is performed after the first step, the amount of water to be processed by reverse osmosis and electrodialysis can be reduced. On the other hand, when the salt concentration in the salt-containing water exceeds a predetermined value, if the third step is performed after the second step, the amount of water to be processed by reverse osmosis and electrodialysis can be reduced. Therefore, if the procedure of the treatment is changed as described above according to the change in the salt concentration in the salt-containing water, the burden required for reverse osmosis and electrodialysis treatment can always be reduced.
[0016]
Furthermore, the invention according to claim 10 is the desalination apparatus for salt-containing water containing calcium ions, wherein the pH-adjusting tank for adjusting the pH of the salt-containing water to be acidic, and the salt-containing water whose pH is adjusted in the pH-adjusting tank A reverse osmosis membrane device that concentrates and permeates by reverse osmosis, the electrodialysis device that concentrates and desalinates the concentrated water obtained by reverse osmosis in the reverse osmosis membrane device, and salt-containing water in the reverse osmosis membrane device. A first inflow line to be introduced, a first valve provided in the first inflow line, a second inflow line branching from the first inflow line and allowing salt-containing water to flow into the electrodialyzer, and a second inflow line It is characterized by comprising a second valve provided and a return means for allowing the desalted liquid obtained by the electrodialyzer to flow into the pH adjusting tank or its upstream side. According to this apparatus, the method according to the ninth aspect of the invention can be effectively implemented.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the desalination apparatus of the present invention will be described in detail with reference to the drawings.
[0018]
FIG. 1 is a flow sheet showing a first embodiment of a desalting apparatus of the present invention. As shown in FIG. 1, the desalting apparatus 10 includes a pH adjusting tank 1 that adjusts the pH of salt-containing water containing calcium ions to an acidic pH. Here, examples of the salt-containing water containing calcium ions include leachate in a landfill. Hereinafter, the desalting apparatus 10 will be described using leachate as an example.
[0019]
It is preferable that the salt concentration in the leachate flowing into the pH adjusting tank 1 through the inflow line (first inflow line) L0 is a constant value and the value is about 30,000 mg / l or less. When leachate having a salt concentration exceeding 30,000 mg / l is processed by the desalting apparatus 10, the amount of salt-containing water to be processed by the desalting apparatus 10 is increased, and the load on the desalting apparatus 10 is increased. This is because the running cost tends to increase as a result. The pH adjusting tank 1 prevents the production of carbonate ions in the leachate in the downstream reverse osmosis membrane device 2 by keeping the leachate acidic. The pH adjustment tank 1 is connected to the reverse osmosis membrane device 2 via the line L1, and the reverse osmosis membrane device 2 separates the leachate into concentrated water and permeated water by the reverse osmosis membrane 2a. Here, the permeated water is discharged out of the system, and the concentrated water is introduced into the electrodialysis apparatus 3 through the line L2. In addition, in the line L1, the aeration which supplies diffused air to leachate between the pH adjustment tank 1 and the reverse osmosis membrane apparatus 2 from the point which prevents the calcium scale precipitation in the reverse osmosis membrane apparatus 2 further. A tank (decarbonation tank) 4 is preferably installed.
[0020]
The electrodialyzer 3 separates the concentrated water obtained by the reverse osmosis membrane device 2 into a concentrated solution and a desalted solution. From the electrodialyzer 3, a line L3 for discharging the concentrated solution out of the system is provided. It extends. In order to prevent an increase in electrical resistance in the electrodialysis apparatus 3 due to a decrease in salt concentration in the desalted solution, a return line L4 for returning the desalted solution to the pH adjusting tank 1 extends from the electrodialyzer 3. Preferably it is. A pump 5 is attached to the return line 4.
[0021]
Here, the configuration of the electrodialysis apparatus 3 will be described with reference to FIGS.
[0022]
As shown in FIG. 2, the electrodialysis apparatus 3 includes a concentrated liquid tank 6 that stores concentrated water introduced from the reverse osmosis membrane apparatus 2 as a concentrated liquid, and a desalted liquid tank 7 that stores concentrated water as a desalted liquid. And. As shown in FIG. 3, the electrodialysis apparatus 3 includes an electrodialysis tank 8, and a flat cathode 14 and a flat anode 18 are disposed in the electrodialysis tank 8. A plurality of ion exchange membranes are arranged in parallel with the anode 18. Here, the ion exchange membrane closest to the cathode 14 is an anion exchange membrane A, and the other ion exchange membranes are sequentially anion exchange membrane A and cation exchange membrane from the cathode 14 toward the anode 18, respectively. C, anion exchange membrane A, cation exchange membrane C, and cation exchange membrane C. By these ion exchange membranes, a cathode chamber 9 including a cathode 14 and an anode chamber 11 including an anode 18 are formed. Between the anode chamber 11 and the cathode chamber 9, a desalting chamber 21 and a concentration chamber 22 are alternately arranged. A desalting chamber 21 is formed on the side closest to the cathode chamber 9. Here, it is preferable that at least one anion exchange membrane A is disposed in the cathode chamber 9 so that the scale does not reach the cathode 14 even if a scale is formed due to leakage of calcium ions. .
[0023]
A desalinating solution is introduced into the desalting chamber 21 through the line L17 from the desalting solution tank 7, and a concentrated solution is introduced into the concentrating chamber 22 through the line L18 from the concentrated solution tank 6. The concentrated solution is returned to the desalted solution tank 7 through L19, and the concentrated solution is returned to the concentrated solution tank 6 through the line L20 (see FIG. 2). Further, a line L4 is connected to the desalting solution tank 7, and the desalting solution is returned to the pH adjusting tank 1 through the line L4 for use, and a line L3 is connected to the concentrated solution tank 6, The concentrated liquid is discharged out of the system through the line L3.
[0024]
As shown in FIG. 3, a cathodic acidic solution 13 is injected into the cathode chamber 9 so that the cathode 14 is immersed. The cathodic acidic solution 13 is composed of an acid and a cathodic solution. Examples of the acid include hydrochloric acid, Sulfuric acid, nitric acid or the like is used, and as the cathode solution, for example, a sodium chloride aqueous solution, a sodium sulfate aqueous solution, a sodium nitrate aqueous solution, or the like is used. Among these, a sodium chloride solution is preferably used because it is easy to handle and inexpensive, and a sodium chloride solution containing hydrochloric acid is more preferable because a component called chlorine is common.
[0025]
The pH of the cathodic acidic solution 13 is normally maintained at 1.5 to 2.5. As shown in FIG. 2, an electrode solution tank 15 is connected to the cathode chamber 9 via a line L5 provided with a pump 16. In order to adjust the cathodic acid solution 13 to a pH in the above range, the pump 16 replenishes the cathodic acid solution 13 with the same acidic solution having a low pH. Note that an acid supply source that supplies the same kind of acid as the acid in the cathodic acid solution 13 is connected to the electrode bath 15 via a line L13. The electrode solution tank 15 is preferably connected to the pH adjusting tank 1 or the upstream line L0 through the line L6 from the viewpoint of effective use of the surplus acidic solution. The cathode chamber 9 is connected to the electrode solution tank 15 via a line L7 so as to return the cathodic acid solution 13 having a high pH to the electrode solution tank 15.
[0026]
As shown in FIG. 3, an anodic acidic solution 17 is injected into the anode chamber 11 so that the anode 18 is immersed therein. The anodic acidic solution 17 is preferably composed of a chlorine ion-free solution from the viewpoint of preventing generation of chlorine gas and preventing precipitation of calcium chloride scale. The chlorine ion-free solution may be composed of only an acid not containing chlorine ions or an acid containing no chlorine ions and an anodic solution. Examples of the acid not containing chlorine ions include sulfuric acid and nitric acid, and examples of the anodic solution include an aqueous sodium sulfate solution and an aqueous sodium nitrate solution. Of these, even if only sulfuric acid is used, it can be used as an anodic solution. The pH of the anodic acidic solution 17 is normally maintained at 0.5 to 2.5. The anode chamber 11 is connected to the electrode liquid tank 19 through a line L8 provided with a pump 20. An acid supply source that supplies an acid having a low pH of the same type as the acid in the anodic acid solution 17 is connected via a line L14 so as to adjust the pH of the anodic acid solution 17 within the above range. The electrode bath 19 is preferably connected to the line L6 via the line L9 from the viewpoint of effective use of the surplus acidic solution. The anode chamber 11 is connected to the electrode solution tank 19 through a line L10 so that the anodic acid solution 17 having a high pH is returned to the electrode solution tank 19.
[0027]
Next, a desalting treatment method using the desalting treatment apparatus 10 having the above-described configuration will be described.
[0028]
As shown in FIG. 1, leachate is introduced into the pH adjusting tank 1 through the line L0, and the pH is adjusted to acidic in the pH adjusting tank 1, and preferably adjusted to a pH of 5 or less (pH adjusting step). Since it becomes difficult to produce carbonate ions by adjusting the pH, precipitation of calcium scale in the reverse osmosis membrane device 2 in the subsequent stage is prevented. The pH adjusted leachate is introduced into the aeration tank 4 through the line L1. In the aeration tank 4, since carbonate ions are released as carbon dioxide, the calcium scale in the reverse osmosis membrane device 2 is further prevented. Thereafter, leachate is introduced into the reverse osmosis membrane device 2. In the reverse osmosis membrane device 2, the leachate is concentrated and permeated by the reverse osmosis membrane 2a, the permeate is discharged out of the system, and the concentrated water is introduced into the electrodialysis device 3 through the line L2 (reverse osmosis step).
[0029]
As shown in FIG. 2, in the electrodialysis apparatus 3, the concentrated water is introduced into the concentrated liquid tank 6 as a concentrated liquid, and the concentrated water is introduced into the desalted liquid tank 7 as a desalted liquid. The concentrated solution is introduced into the concentration chamber 22 of the electrodialysis tank 8, and the desalted solution in the desalted solution tank 7 is introduced into the desalting chamber 21 of the electrodialysis tank 8. At this time, as shown in FIG. 3, when a voltage is applied between the cathode 14 and the anode 18, the cation in the desalting solution goes to the cathode 14, and the anion goes to the anode 18. Done. That is, the desalting solution in the desalting chamber 21 is desalted, and the concentrated solution in the concentration chamber 22 is concentrated (electrodialysis step).
[0030]
At this time, the anion exchange membrane A disposed between the cathode chamber 9 and the desalting chamber 21 prevents the movement of cations such as calcium from the desalting solution to the cathodic acidic solution 13 in the cathode chamber 9. The For this reason, precipitation of calcium scale due to the combination of cations such as calcium and anions such as chlorine ions in the cathode chamber 9 is prevented, and adhesion and membrane clogging of the calcium scale anion exchange membrane A are prevented. Is prevented. From the above, an increase in electrical resistance between the anode 18 and the cathode 14 is prevented. Therefore, a stable desalting treatment of the desalting solution becomes possible.
[0031]
In the electrodialysis step, the pH of the acidic solution in the electrode baths 15 and 19 is preferably maintained at 4 or less from the viewpoint of further suppressing calcium scale deposition in the cathode chamber 9 and the anode chamber 11. Further, from the viewpoint of effectively using the acidic solution in the electrode liquid tanks 15 and 19, it is preferable to return the acidic solution in the electrode liquid tanks 15 and 19 to the pH adjusting tank 1 or the upstream line L0 through the line L6 ( (See FIGS. 1 and 2).
[0032]
And as shown in FIG. 2, a concentrate is returned to the concentrate tank 6, and is discharged | emitted out of the system through the line L3 after that. On the other hand, the desalted liquid is returned to the desalted liquid tank 7 and then returned to the pH adjusting tank 1 by the pump 5 through the line L4 (see FIG. 1). At this time, since the desalted liquid to be returned is acidic, the amount of acid supplied in the pH adjusting tank 1 can be reduced, and the acid can be effectively used. The desalting solution in the desalting solution tank 7 is not limited to the pH adjusting tank 1 and may be returned to the upstream side thereof.
[0033]
Next, a second embodiment of the desalting apparatus of the present invention will be described.
[0034]
FIG. 4 is a schematic view showing a desalting apparatus 30 according to the second embodiment, and the same or equivalent components as those in the first embodiment are denoted by the same reference numerals. As shown in FIG. 4, the desalting apparatus 30 has the electrodialysis apparatus 3 on the upstream side and the reverse osmosis membrane apparatus 2 on the downstream side, and reverses the desalted solution obtained by the electrodialysis apparatus 3 through a line L15. It differs from the desalination processing apparatus 10 of 1st Embodiment by the point which introduce | transduces into the osmosis membrane apparatus 2, and returns the concentrated water obtained with the reverse osmosis membrane apparatus 2 to the pH adjustment tank 1 with a pump through the return line L16.
[0035]
In this case, the desalination treatment using the desalination treatment device 30 is performed by concentrating and desalting the pH-adjusted leachate with the electrodialysis device 3 (electrodialysis step), and obtaining a desalting solution obtained by the electrodialysis device 3 Except that the concentrated water obtained in the reverse osmosis step is returned to the pH adjustment tank 1 (return step) (return osmosis step). This is performed in the same manner as the desalting treatment method. In this case, when the salt concentration in the leachate flowing into the pH adjustment tank 1 exceeds 30,000 mg / l, the amount of leachate to be treated by the reverse osmosis membrane device 2 and the electrodialysis device 3 can be reduced. The burden required for the reverse osmosis membrane device 2 and the electrodialysis device 3 tends to be reduced. Therefore, the running cost as the whole apparatus can be reduced.
[0036]
Next, a third embodiment of the desalting apparatus of the present invention will be described.
[0037]
FIG. 5 is a schematic view showing a desalting apparatus 40 according to the third embodiment, and the same or equivalent components as those of the first embodiment are denoted by the same reference numerals. As shown in FIG. 5, in the desalination treatment apparatus 40, an inflow line (second inflow line) L12 branched from the middle of the inflow line L0 is connected to the line L2, and a valve V1 is attached to the inflow line L0. The line L12 is different from the demineralization apparatus 10 of the first embodiment in that a valve V2 (second valve) and an aeration tank (second decarboxylation tank) 41 are sequentially attached from the upstream side.
[0038]
In this case, the desalting treatment is performed as follows. That is, when the salt concentration in the leachate is 30,000 mg / l or less, the valve V2 is closed, the valve V1 is opened, and the leachate is introduced into the pH adjustment tank 1. Then, the pH adjusted leachate is passed through the aeration tank 4 and introduced into the reverse osmosis membrane device 2. The reverse osmosis membrane device 2 concentrates and permeates the leachate, and the concentrated water obtained by reverse osmosis is sent to the electrodialysis device 3 through the line L2, and is concentrated and desalted by the electrodialysis device 3 (first desalting process). 1 step). The desalted solution obtained by the electrodialyzer 3 is returned to the pH adjustment tank 1 by the pump 5 through the return line L4 (third step).
[0039]
On the other hand, when the salt concentration in the leachate exceeds 30,000 mg / l, the valve V1 is closed, the valve V2 is opened, the leachate is introduced into the inflow line L12, and the leachate is aerated in the aeration tank 41. It introduces into the electrodialyzer 3 through the line L2. Then, the leachate is concentrated and desalted by the electrodialyzer 3 (second step). The desalted solution obtained by the electrodialyzer 3 is returned to the pH adjustment tank 1 by the pump 5 through the return line L4 (third step). Thereafter, the desalted solution is passed through the aeration tank 4 and introduced into the reverse osmosis membrane device 2. In the reverse osmosis membrane device 2, the desalted solution is concentrated and permeated, and the concentrated water is introduced into the electrodialysis device 3.
[0040]
According to such a desalting treatment method, when the salt concentration in the leachate is 30,000 mg / l or less, it is treated by the reverse osmosis membrane device 2 and then by the electrodialysis device 3, while the salt concentration in the leachate is When the salt concentration exceeds 30,000 mg / l, leachate is treated with the electrodialysis device 3 and then treated with the reverse osmosis membrane device 2, and the leachate to be treated with the reverse osmosis membrane device 2 and the electrodialysis device 3. The amount of always decreases. Therefore, if the processing procedure is changed as described above according to the change in the salt concentration in the leachate, the burden on the reverse osmosis membrane device 2 and the electrodialysis device 3 can always be reduced, thereby reducing the running cost. be able to.
[0041]
Hereinafter, the contents of the present invention will be specifically described with reference to examples.
[0042]
【Example】
Example 1
As an electrodialysis apparatus, the ion exchange membrane closest to the anode is a cation exchange membrane (Celemion CMV manufactured by Asahi Glass Co., Ltd.), and the ion exchange membrane closest to the cathode is an anion exchange membrane (Celemion ASV manufactured by Asahi Glass Co., Ltd.). In the meantime, a cation exchange membrane and an anion exchange membrane were alternately arranged from the anode chamber side to the cathode chamber side, and 11 demineralization chambers and 10 concentration chambers were formed. Into the cathode chamber, a 3% aqueous solution of hydrochloric acid as a cathodic acid solution was poured, and the cathodic acid solution was adjusted to pH 2 or less by pouring the same kind of acidic solution added with hydrochloric acid. On the other hand, a 3% sulfuric acid aqueous solution was injected into the anode chamber as an anodic acid solution, and the anodic acid solution was adjusted to about pH 1.0 by injecting the same kind of acid solution with sulfuric acid added into the anode chamber.
[0043]
Then, while introducing about 3.4% of salt-containing water into each of the desalting chamber and the concentrating chamber, a voltage is applied between the cathode and the anode to perform electrodialysis, and the concentrated salt concentration and desalting solution The change with time of each salt concentration and the change with time of the current value flowing between the cathode and the anode were examined. The results are shown in FIGS. As shown in FIGS. 6 and 7, the concentrated solution salt concentration was 17%, and the current value was stable over 7 days despite the high salt concentration.
[0044]
(Comparative Example 1)
As the anodic acid solution and the cathodic acid solution, a 3% sodium nitrate aqueous solution that is nitric acid is used, a cation exchange membrane is used in place of the anion exchange membrane closest to the cathode, and the pH of the bipolar acidic solution is further reduced to 2.5 or less. The same electrodialysis tank as in Example 1 was used, except that it was held. In addition, pH adjustment of the bipolar acidic solution was performed by inject | pouring the acidic solution of the same kind which added the nitric acid in a single electrode liquid tank into the anode chamber and the cathode chamber, respectively.
[0045]
Using this electrodialyzer, the time-dependent changes in the concentrated solution salt concentration and the desalted solution salt concentration and the time-dependent change in the current value flowing between the cathode and the anode were examined in the same manner as in Example 1. The results are shown in FIGS. As shown in FIGS. 8 and 9, the concentration of the concentrated liquid salt was 10%, and the current value gradually decreased over time. At this time, white turbidity of the cathodic acid solution was observed, and flow resistance was generated in the cathode chamber. When this electrodialyzer was disassembled, white scale was generated in the entire anion exchange membrane surface of the cathode chamber and in the concentration chamber. The same thing happened in part of the anode chamber. As a result of analyzing the white scale, it was found that the main component was calcium hydroxide. As a result, it has been found that it is impossible to desire long-term stable operation by this method.
[0046]
【The invention's effect】
As described above, according to the electrodialysis apparatus of the present invention, when the salt-containing water containing calcium is desalted, cations such as calcium ions from the salt-containing water to the cathodic acidic solution in the room including the cathode are removed. The migration is prevented, the anion exchange membrane is not blocked by the scale, and the concentration of the salt in the salt-containing water to be concentrated is increased. Therefore, an increase in electrical resistance between the anode and the cathode is prevented, and stable treatment of salt-containing water is possible. Furthermore, according to the desalination treatment method and apparatus to which this electrodialysis apparatus is applied, the amount of salt-containing water to be treated by electrodialysis or reverse osmosis is small, so that the running cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing an embodiment of a desalting apparatus of the present invention.
FIG. 2 is a flow sheet showing an embodiment of the electrodialysis apparatus of the present invention.
3 is a cross-sectional view showing an internal configuration of an electrodialysis tank of the electrodialysis apparatus of FIG.
FIG. 4 is a flow sheet showing another embodiment of the desalting apparatus of the present invention.
FIG. 5 is a flow sheet showing still another embodiment of the desalting apparatus of the present invention.
6 is a graph showing changes over time in concentrated salt concentration and desalted salt concentration by electrodialysis in Example 1. FIG.
7 is a graph showing the change over time of the current value by electrodialysis in Example 1. FIG.
8 is a graph showing changes over time in concentrated salt concentration and desalted salt concentration by electrodialysis in Comparative Example 1. FIG.
9 is a graph showing a change with time of a current value by electrodialysis in Comparative Example 1. FIG.
FIG. 10 is a cross-sectional view showing the internal configuration of a conventional electrodialysis tank.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... pH adjustment tank, 2 ... Reverse osmosis membrane apparatus, 3 ... Electrodialysis apparatus, 4 ... Aeration tank (decarbonation tank, 1st decarboxylation tank) 5 ... Pump (returning means), 9 ... Cathode chamber (cathode) 11) anode chamber (chamber containing anode), 12 ... treated water chamber, 13 ... cathodic acid solution, 14 ... cathode, 17 ... anodic acid solution, 18 ... anode, A ... anion exchange membrane, 41 ... Aeration tank (second decarboxylation tank), L0 ... inflow line (first inflow line), L4, L16 ... return line (return means), L12 ... inflow line (second inflow line), V1 ... valve (first Valve), V2... Valve (second valve).

Claims

In an electrodialysis apparatus for desalinating salt-containing water containing calcium ions in an electrodialysis tank,
A cathode and an anode disposed in the electrodialysis tank;
A plurality of ion exchange membranes arranged in parallel between the cathode and the anode and forming a plurality of chambers;
A cathode acidic solution is introduced into the chamber including the cathode among the plurality of chambers, and an anodic acidic solution is introduced into the chamber including the anode.
The electrodialysis apparatus, wherein the ion exchange membrane closest to the cathode is an anion exchange membrane.

The electrodialysis apparatus according to claim 1, wherein the anodic acid solution is a chloride ion-free solution.

The electrodialyzer according to claim 1 or 2, wherein the cathodic acidic solution is an acidic solution containing a calcium-free electrolyte.

Of the plurality of ion exchange membranes, the one closest to the anion exchange membrane is an anion exchange membrane, and the cathodic acid solution is introduced into a chamber formed by the anion exchange membranes adjacent to each other. The electrodialysis apparatus according to any one of claims 1 to 3, wherein the electrodialysis apparatus is characterized.

In the method for desalinating salt-containing water containing calcium ions,
A pH adjusting step for adjusting the pH of the salt-containing water to an acid;
a reverse osmosis step of concentrating and permeating the pH-adjusted salt-containing water by reverse osmosis;
An electrodialysis step of desalinating the concentrated water obtained by reverse osmosis in the reverse osmosis step with the electrodialysis apparatus according to any one of claims 1 to 4,
A desalinization treatment method comprising:

In a desalination apparatus for salt-containing water containing calcium ions,
A pH adjusting tank for adjusting the pH of the salt-containing water to an acid;
a reverse osmosis membrane device for concentrating and permeating the salt-containing water adjusted in pH by reverse osmosis;
The electrodialysis apparatus according to any one of claims 1 to 4, wherein the concentrated water obtained by reverse osmosis in the reverse osmosis membrane apparatus is desalted.
A desalinization treatment apparatus comprising:

In the method for desalinating salt-containing water containing calcium ions,
A pH adjusting step for adjusting the pH of the salt-containing water to an acid;
an electrodialysis step of desalting the salt-adjusted water adjusted in pH with the electrodialysis apparatus according to any one of claims 1 to 4;
A reverse osmosis step of concentrating and permeating the desalted solution obtained in the electrodialysis step by reverse osmosis;
A desalinization treatment method comprising:

In a desalination apparatus for salt-containing water containing calcium ions,
A pH adjusting tank for adjusting the pH of the salt-containing water to an acid;
The electrodialysis apparatus according to any one of claims 1 to 4, wherein the salt-containing water whose pH has been adjusted is concentrated and desalted.
A reverse osmosis membrane device for concentrating and permeating the desalted solution obtained by the electrodialyzer by reverse osmosis;
A desalinization treatment apparatus comprising:

In the salt-containing water desalination treatment method including calcium ions, when the salt concentration in the salt-containing water is a predetermined value or less, after adjusting the pH of the salt-containing water, it is concentrated and permeated by reverse osmosis, of which A first step of concentrating the concentrated water with the electrodialysis apparatus according to any one of claims 1 to 4 and desalting;
A second step of concentrating and desalting the salt-containing water with the electrodialyzer when the salt concentration in the salt-containing water exceeds a predetermined value;
A third step of using a desalted solution obtained by the electrodialyzer for pH adjustment in the pH adjustment step;
A desalinization treatment method comprising:

In a desalination apparatus for salt-containing water containing calcium ions,
A pH adjusting tank for adjusting the pH of the salt-containing water to an acid;
A reverse osmosis membrane device for concentrating and permeating the salt-containing water whose pH is adjusted in the pH adjustment tank by reverse osmosis;
The electrodialyzer according to any one of claims 1 to 4, wherein the concentrated water obtained by the reverse osmosis membrane device is concentrated and desalted.
A first inflow line for introducing the salt-containing water into the reverse osmosis membrane device;
A first valve provided in the first inflow line;
A second inflow line that branches from the first inflow line and allows the salt-containing water to flow into the electrodialyzer;
A second valve provided in the second inflow line;
A return means for allowing the desalted solution obtained by the electrodialyzer to flow into the pH adjusting tank or its upstream side;
A desalinization treatment apparatus comprising: