JP3800450B2 - Method and apparatus for treating organic wastewater containing high concentrations of salts - Google Patents
Method and apparatus for treating organic wastewater containing high concentrations of salts Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、高濃度の塩類を含有する有機性廃水からその塩類を脱塩し、有機物を除去する処理方法及び処理装置に関するものであり、特にし尿やごみ浸出水などような塩類濃度の高い有機性廃水の高度処理、脱塩処理、塩類物質の濃縮回収、処理水の回収・再利用などに用いることができる。
【０００２】
【従来の技術】
し尿や浸出水などの塩類濃度が高い有機性廃水は、一般に、カルシウムイオンなどの塩類や有機物などの汚濁物質を高濃度に含んでいる。しばしば、生化学的酸素要求量（ＢＯＤ）や化学的酸素要求量（ＣＯＤ）が高く、多くの懸濁固体（ＳＳ）を含み、さらにコロイド物質などに原因する色度を有している。そのため、通常これらを何らかの用途に直接再利用したり河川などに直接放流したりすることはできない。
このような有機性廃水の処理方法としては、従来では、有機汚濁物の除去を主体とした処理方法が用いられている。主な処理方法としては、例えば、ＢＯＤ除去を目的とした生物処理、色度、ＣＯＤ及びＳＳなどの除去を目的とした凝集沈殿処理、ＳＳなど濁質の除去を目的とした砂ろ過や精密ろ過膜（ＭＦ膜）処理がある。さらに、高度処理方法として一般的にオゾンや活性炭を用いる方法などがある。
【０００３】
【発明が解決しようとする課題】
前記した有機性廃水の処理方法においては、それらの処理を組み合わせることにより、ＢＯＤ、ＣＯＤなどの有機性成分を十分に除去することができるような技術水準に達している。しかし、有機性廃水は一般に有機物の他にも様々な塩類を含んでおり、場合によってはかなりの高い濃度の塩類を含有する場合がある。このような廃水を処理して河川などに放水する場合には、放流水域の水質保護、あるいは農業用水への影響も考慮しなければならず、近来、有機汚濁成分だけでなく特にそのような塩類も廃水中から一緒に除去する必要性が高まってきている。従来の有機性廃水の浄化方法は、いずれも主にその中の有機汚濁成分を除去することを目的としているため、塩類を除去する効果がなく、その処理水の塩類濃度は流入原水とほぼ同程度となっている。
【０００４】
塩類を含む水相中から塩類を除去する処理方法はそれ自体では良く知られている技術であって、例えば逆浸透法、電気透析法、蒸発法などを挙げることができる。
逆浸透法は、半透膜（ＲＯ膜）で仕切られた室中の塩類水に浸透圧以上の機械的圧力を加えて、半透膜を通して水を室外に出すことにより脱塩した水を得るという方法である。この方法の場合、効率は塩類水の塩類濃度に左右されるという欠点がある。塩類水の濃度が高い場合には脱塩水の回収率は低い。例えば、３．５ｗｔ％ＮａＣｌ水溶液を脱塩処理する場合、処理圧力を６０ｋｇｆ／ｃｍ2 としても、水回収率は高くても３５〜４０％である。水の回収率を５０％以上にするには操作圧力を７０ｋｇｆ／ｃｍ2 以上にしなければならない。しかし、このような高圧では、処理コストの増加となるだけではなく、逆浸透処理装置の寿命などを考えるとその限界がある。
さらに、塩類水が高い濃度でカルシウムイオンを含んでいると半透膜表面にカルシウムスケールが析出する危険性がある。塩類濃度が比較的低くても、半透膜表面でのカルシウムスケールの析出により透過水量の低下で処理水の高い回収率での処理が困難となる。
【０００５】
電気透析法では、基本的に水の回収率を高く得ることができる。しかし、電気透析される被処理水がカルシウムイオンを高い濃度で含んでいる場合にはカルシウムスケールが装置内に析出する。特に、電気透析法では、陽極からの水素イオン及び陰極からの水酸イオンの移動に伴うｐＨ変化などによりカルシウムスケールが生成しやすい。カルシウムスケールが析出すれば水を高い回収率を得ることはできない点は、逆浸透法の場合と同様である。しかも、この方法ではＣＯＤなどの有機物を除去することができないため、良質の処理水を得るためには活性炭処理法などの他の処理法による有機物の除去が必要となる。
また、蒸発法は、系の相変化を伴う方法であるため、必要エネルギーが大きく、処理コストを非常に増大させるという問題点がある。さらに、廃水が揮発性の有機物や窒素−アンモニウム塩化合物（ＮＨ4 −Ｎ）などを含んでいればそれらも処理水中に混入することがあり、良質な処理水は得にくいという問題点もある。
【０００６】
本発明は、塩類を高い濃度で含む有機性廃水を処理して、再利用したり河川などに直接放流することができる程にまで効率よく浄化する際に、有機性成分を十分除去できるだけではなく、塩類を十分に除去することができ、かつその処理に際してカルシウムスケールの析出などの処理効果を低下させるという問題を起こさないで、浄化を行い、塩濃度の低い処理水を高い効率で得ることができる処理方法及び処理装置を提供することを目的とするものである。
【０００７】
【課題を解決するための手段】
即ち本発明の目的は下記の構成によって達成される。
（１）高濃度の塩類を含有した有機性廃水の処理方法であって、前記有機性廃水に前処理として、生物処理、凝集沈殿処理、砂ろ過処理、精密ろ過膜処理のいずれか、又は２以上の組合せからなる処理を行い、次いで逆浸透膜により脱塩処理して、逆浸透濃縮水と逆浸透処理水とに分離し、前記逆浸透処理水を回収し、前記逆浸透濃縮水をカルシウムを除去するための軟化処理を行った後、電気透析処理を施して電気透析濃縮水と電気透析脱塩水とに分離し、前記電気透析脱塩水を再び逆浸透処理の供給側に戻すことを特徴とする高濃度の塩類を含有する有機性廃水の処理方法。
（２）前記軟化処理は、処理水中のカルシウム濃度を１００ｍｇ／リットル以下にすることを特徴とする前記（１）記載の高濃度の塩類を含有する有機性廃水の処理方法。
【０００８】
（３）前記電気透析処理は脱塩率が９８％以上で、電気透析脱塩水の蒸発残留物が１０００ｍｇ／リットル以下となるように行うことを特徴とする前記（１）又は（２）記載の高濃度の塩類を含有する有機性廃水の処理方法。
（４）前記電気透析処理後の電気透析濃縮水は蒸発残留物が１３ｗｔ％以上となることを特徴とする前記（１）〜（３）のいずれか１項記載の高濃度の塩類を含有する有機性廃水の処理方法。
（５）高濃度の塩類を含有する有機性廃水の処理装置であって、前記有機性廃水を供給する生物処理装置、凝集沈殿処理装置、砂ろ過処理装置、精密ろ過膜処理装置のいずれか、又は２以上の組合せからなる前処理装置、前記前処理装置からの処理水を供給し、脱塩処理により逆浸透濃縮水と逆浸透処理水とに分離する逆浸透膜を用いる逆浸透処理装置、前記逆浸透濃縮水を供給し、カルシウムを除去するための軟化処理を行う軟化処理装置、前記軟化処理装置からの軟化処理水を供給し、電気透析処理により電気透析濃縮水と電気透析脱塩水とに分離する電気透析処理装置、前記電気透析処理装置からの電気透析脱塩水を逆浸透処理装置の供給側に戻す配管、及び前記逆浸透処理装置から逆浸透処理水を回収する配管を有することを特徴とする高濃度の塩類を含有する有機性廃水の処理装置。
【０００９】
【発明の実施の形態】
次に、本発明の実施の形態を図面により説明する。
図１は、本発明にかかる廃水の処理方法を行う処理装置の一実施態様を示す概略図である。
図１に示す有機性廃水の処理装置は、図示外の有機物の除去処理装置から延びる被処理水流入管１の出口を逆浸透処理供給槽２内に開口させている。逆浸透処理供給槽２から逆浸透処理供給配管３が逆浸透処理装置４に連結している。この逆浸透処理装置４からは逆浸透処理水配管５と逆浸透濃縮水配管６とが別々に延びており、逆浸透濃縮水配管６から逆浸透濃縮水が軟化処理装置７へ導いている。逆浸透処理水は逆浸透処理水管５から系外に回収される。前記軟化処理装置７は軟化処理した処理水を導く軟化処理水配管９を電気透析処理供給槽１０に通じており、また生成した泥状物を排出する排泥管８を有する。この電気透析処理供給槽１０からは電気透析処理供給配管１１が電気透析処理装置１２につながっている。
この電気透析処理装置１２から電気透析濃縮水を送る電気透析濃縮水配管１４が蒸発乾燥処理装置１５に接続され、また電気透析脱塩水を送る電気透析脱塩水配管１３が前記逆浸透処理供給槽２に接続されている。
【００１０】
本発明では、その処理の対象とする有機性廃水としては、有機性成分としてはそれほど高くないものでも処理できるものであって、有機性成分が電気透析処理にまで入ると悪影響を及ぼすので、それを逆浸透処理において除去することができる。また、その有機性廃水中の塩類濃度については、かならずしも著しく高い濃度のものを対象とするものではなく、前記したように放流するには支障となる程度に高い濃度のもの、乃至はそれよりも高い濃度のものを対象とするに適しているものである。
本発明の有機性廃水の処理方法は、このような装置を使用して例えば次のようにして実施するとよい。
有機性廃水は、まず前処理として、生物処理、凝集沈殿処理、砂ろ過処理または精密ろ過膜（ＭＦ膜）処理のいずれか、又は２つ以上の処理を組合せの処理を行うが、有機性物質の濃度を低下させる上で生物処理を組み合わせた処理を行うことが好ましい。この前処理を行った廃水を被処理水流入管１を通じて逆浸透処理供給槽２にいったん貯蔵する。前記した生物処理方法としては、具体的には標準的な活性汚泥法の他に、生物学的硝化脱窒素法なども挙げることができる。これらの方法を利用すればＢＯＤも低下する。凝集精密ろ過（凝集ＭＦ膜ろ過）方法としては、具体的には凝集剤、例えば無機凝集剤を添加して凝集させたものを精密ろ過膜でろ過する、という方法を挙げることができる。このような方法を使用すると、特にＳＳなどの濁質を廃水中から除去することができる。凝集沈殿処理方法は、凝集剤を添加した後、沈殿槽で凝集物を沈殿させる方法である。色度やＳＳなどを除去し、ＣＯＤも下げることができる。砂ろ過方法は、ＳＳなど濁質を除去することができる。
【００１１】
このようにして主として有機物の除去を行う前処理が終わった廃水は、逆浸透処理供給槽２から逆浸透処理供給配管３を通じて逆浸透処理装置４に導入し、ここで逆浸透処理（「ＲＯ処理」ともいう）を行う。逆浸透処理では、半透膜（「ＲＯ膜」ともいう）で仕切られた前記廃水に５Ｍｐａ以上の機械的な圧力を加え廃水中の水をＲＯ膜を通すことにより、逆浸透濃縮水（「ＲＯ濃縮水」ともいう）と逆浸透処理水とに分離し、逆浸透処理水は逆浸透処理水配管５を通じて回収する。
なお、有機物の除去処理操作の中で十分除去できなかった有機物は更にこの半透膜でろ過することとなり、回収する脱塩水中に汚濁有機物成分が流れ込むことはほとんどない。
【００１２】
前記逆浸透濃縮水は、逆浸透濃縮水配管６を通って軟化処理装置７に導入する。軟化処理は、例えば、石灰ソーダ軟化法やイオン交換硬水軟化法によって、水中のカルシウムやマグネシウムの硬水成分（難溶性塩形成成分）をナトリウムのような易溶性塩形成成分に置換するなどのような方法で行うことができる。
このような軟化処理においては、逆浸透濃縮水中のカルシウム濃度を１００ｍｇ／リットル以下にすることが好ましい。カルシウム濃度が１００ｍｇ／リットル以下にすることにより、電気透析処理装置１２でカルシウムスケールが発生することを効果的に防止することができるので、好ましい。軟化処理に伴って生じるスラッジは排泥管８を通して系外に排出する。
【００１３】
カルシウムイオンを除去した高濃度塩類を含む軟化処理水は、軟化処理水配管９を通じて電気透析処理供給槽１０にいったん貯蔵し、さらに電気透析処理供給配管１１を通じて電気透析処理装置１２に導入する。その導入と電気透析処理は回分式に行うことが好ましい。電気透析処理（「ＥＤ処理」ともいう）は、多数の電気透析膜を配列し、交互に形成した濃縮室と希釈室に、或いはそれらの中の希釈室のみに前記の軟化処理水を供給して通電して、濃縮室に高濃度の電気透析濃縮水を得、希釈室に電気透析脱塩水を得るものである。
【００１４】
電気透析脱塩水は電気透析脱塩水配管１３を通して逆浸透処理供給槽２に還流する。還流水に有機物が残存していても逆浸透処理装置４でろ過するため、これが逆浸透処理水中に漏洩することが防止される。電気透析濃縮水は蒸発乾燥処理装置１５に導いて蒸発乾燥して、水分と塩類とに分離し、塩類を単離する。
この方法では、カルシウムを含有する被処理水に対し、逆浸透膜を用いて脱塩処理して、カルシウムスケールが析出しない範囲の水回収率で、被処理水の塩分及び有機物を同時に除去するようにすることにより、良質の処理水（逆浸透処理水）を得る。
さらに、カルシウム濃度が高くなった逆浸透濃縮水に対して、カルシウムの除去を目的とした軟化処理を行い、カルシウム濃度が十分に低減された軟化処理水を電気透析処理、好ましくは回分式に電気透析処理することにより、高脱塩率、高水回収率で処理してもカルシウムスケールの析出がなく、塩類濃度の低い電気透析脱塩水及び塩類濃度の高い電気透析濃縮水を得ることができる。
【００１５】
通常、電気透析処理において、回分式に行うと、連続式よりも脱塩率及び処理効率が高く、塩類濃度が高い（蒸発残留物成分濃度で１３ｗｔ％以上（１３０００ｍｇ／リットル以上））の塩類濃縮水が得られ、かつ脱塩水と濃縮水との塩類濃度比は１５０以上とすることができる。蒸発残留物とは、水分を蒸発させれば固形成分として蒸発缶中に残留する成分をいう。この濃度での変化を判り易く表現すると、濃縮水から分離した脱塩水においては、９８ｗｔ％以上の塩類が減少し、塩類濃度は１０００ｍｇ／リットル以下に低下したことになる。
【００１６】
上記した実施の形態では電気透析処理で生じた低濃度の電気透析脱塩水を逆浸透処理供給槽２に還流される。このように戻すことにより電気透析処理で除去できなかったＣＯＤなどの有機物を逆浸透処理で除去できる。
また、この電気透析脱塩水の塩類濃度、特にカルシウムイオン濃度は逆浸透処理供給槽２からの被処理水よりもそれらの濃度が低いものである。したがって、その逆浸透処理は通常の廃水より塩類濃度の低い状態で行うことができる。逆浸透処理ではその透過流束（透過水量）は基本的に被処理水の塩類濃度増加に伴う浸透圧の増加があると減少する関係にあるが、このように脱塩水の還流により被処理水の塩類濃度が低くなるため、逆浸透処理の透過流束の低下はなく、このため逆浸透処理コストの増加も少なく、高い水回収率で良質な逆浸透脱塩水を得ることができる。
さらに、被処理水にカルシウムイオンが混在していてもその濃度は低く、これが逆浸透膜の表面などにスケールとして析出するトラブルはほとんど生じない。
【００１７】
電気透析処理は、逆浸透処理で大量の逆浸透脱塩水を除去した後で行うことから、電気透析処理を受ける全体の容量は縮小しており、高濃度に濃縮した塩類濃縮水を効率よく得ることができる。しかも、電気透析処理に先立って予め軟化処理を行い、カルシウム溶解濃度を下げている。したがって、電気透析処理装置１２内でカルシウムイオンがスケールとして析出してこれがトラブルを起こすということもほとんどない。
電気透析処理に続いて塩類濃縮水には蒸発乾燥処理を行い、ここで塩類を単離する。蒸発乾燥処理は電気透析処理で更に容積が縮小した高濃度の塩類濃縮水をその対象とする。したがって、相変化をともなって大量のエネルギーを要する処理であっても効率よく行うことができ、塩類成分を固形成分として容易に単離することができる。
【００１８】
【実施例】
以下、本発明の実施例を説明するが、本発明はこれらに限定されることはない。
（実施例）
し尿について生物処理、凝集沈殿処理及び精密ろ過膜処理の各処理を行って出てきた被処理水を、図１に示す処理装置を用いて処理を行った。なお、逆浸透処理での操作圧力は５〜６ＭＰａの高圧条件であり、軟化処理装置７からは軟化処理後のスラッジを排泥管８から排出する。
有機物の除去処理後の処理対象の被処理水、逆浸透処理して得た処理水（「ＲＯ処理水」という）、軟化処理して得た処理水（「軟化処理水」）、電気透析処理して得た濃縮水（「ＥＤ濃縮水」）、それぞれについて水質を測定した。測定結果は第１表に示す。
【００１９】
【表１】
カルシウムスケールの析出の有無は、化学分析と各装置の処理性能を基に判断した。
以上の結果から次のことが分かった。
被処理水、すなわち前処理を行った廃水の色度が１５０度、ＣＯＤが５０ｍｇ／リットル、カルシウム濃度が６０ｍｇ／リットル、蒸発残留物成分濃度が５６００ｍｇ／リットルであるのに対し、逆浸透処理して得た処理水すなわちＲＯ処理水は色度が４度、ＣＯＤが５．０ｍｇ／リットル、蒸発残留物成分濃度が３８０ｍｇ／リットルとなり、良好な水質の処理水が得られた。
【００２１】
また、逆浸透処理して得たＲＯ濃縮水を軟化処理をすることことにより、カルシウム濃度が処理前の６００ｍｇ／リットルから６５ｍｇ／リットル程度に低減した結果、軟化処理水に対して電気透析処理による塩類濃縮を行っても、ＥＤ濃縮水のカルシウム濃度は１８０ｍｇ／リットルであり、カルシウムスケールの生成はまったく認められなかった。
ＥＤ濃縮水は電気伝導率を約１３００００μＳ／ｃｍ、蒸発残留物を１６５０００ｍｇ／リットルにすることができた。電気透析脱塩水を逆浸透処理に返送していることから、被処理水量に対する処理水量の割合を示す水回収率は９６．８％となり、濃縮水の水量は被処理水量に対して約３０分の１以下に減少することができた。
【００２２】
（比較例１）
実施例と同様の被処理水に対し、逆浸透処理のみを行った。すなわち、前処理を行い、軟化処理、電気透析処理を省略した他は実施例と同様にした。
前処理した対象の廃水（被処理水）、逆浸透処理によって得たＲＯ処理水、ＲＯ濃縮水についてそれぞれ水質を測定した。測定結果を第２表に示す。
【００２３】
【表２】
第２表の結果から次のことが分かった。
前処理を行った被処理水に逆浸透処理を単独で行った場合、被処理水量に対するＲＯ処理水量（処理水量）割合を示す水回収率が９０．９％に止どまり、９６．８％を示した実施例より５．９％少なくなった。さらに、逆浸透処理によって得たＲＯ濃縮水の蒸発残留物成分濃度が５８０００ｍｇ／リットルしかなく、実施例の電気透析濃縮水（ＥＤ濃縮水）に比べて約３分の１程度に止どまった。
すなわち、濃縮水量は前記のおよそ３倍に増加し、これを蒸発乾燥処理に用いた場合、前記より処理コストの増大となる。また、ＲＯ濃縮水中のカルシウム濃度は６１０ｍｇ／リットルとなり、それ以上の濃縮を行うとカルシウムスケールの析出という危険性が考えられる。
【００２５】
（比較例２）
実施例と同様な有機物の除去の前処理を行った被処理水に対し、電気透析処理のみを行い、逆浸透処理や軟化処理を省略した。被処理水、電気透析処理によって得たＥＤ脱塩水、電気透析処理によって得たＥＤ濃縮水についてそれぞれ水質を測定した。測定結果を第３表に示す。
【００２６】
【表３】
第３表に示すように、被処理水に対し、電気透析の単独処理を行って逆浸透処理や軟化処理を行わないと、電気透析処理によって得た電気透析濃縮水のカルシウム濃度が１８００ｍｇ／リットルに増加し、カルシウムスケールの発生が顕著であると認められた。第３表には示していないが、実施例に比べると電気透析処理の回分処理回数の増加に伴い、処理効率が顕著に低下した。これはカルシウムスケールの生成による影響である。
処理水の水質では、電気透析処理の前後の色度およびＣＯＤについては変化がなかった。また、被処理水、電気透析脱塩水（ＥＤ脱塩水）、ＥＤ濃縮水いずれも色度１５０度、ＣＯＤ５０ｍｇ／リットルであり、有機物の除去は全くなかった。このため、実施例と同程度の処理水を得るには更に他の処理方法で有機物を除去する必要があり、例えば、活性炭吸着処理を用いた場合、設備の増加や活性炭交換が必要なことから、処理コストの増加要因となる。
【００２８】
【発明の効果】
本発明は、高濃度の塩類を含有する有機性廃水である被処理水に対し、逆浸透処理を行うことにより、良質な脱塩水（処理水）が得られる一方、逆浸透濃縮水についてカルシウム除去の軟化処理を行うことにより、カルシウム濃度を１００ｍｇ／リットル以下に低減させた後、その軟化処理水をさらに電気透析処理を行っても、その処理においてカルシウムスケールの生成がまったくなく、きわめて高い濃縮率及び脱塩率で電気透析処理を行うことができる。特に、電気透析処理を回分式に行うときには、脱塩率が高く、塩類濃度の低い電気透析脱塩水（蒸発残留物１０００ｍｇ／リットル以下）と、塩類濃度の高い電気透析濃縮水（蒸発残留物１３００００ｍｇ／リットル以上）を得ることができる。
さらに、ＣＯＤ、色度などの有機物を含有する電気透析脱塩水を逆浸透処理に返送して再度逆浸透処理を行うことにより、ＣＯＤ、色度などの有機物が除去される。この結果、電気透析濃縮水量は、被処理水量の約３０分の１以下に減量でき、蒸発乾燥処理での必要エネルギーは逆浸透濃縮水について蒸発乾燥処理を行う場合よりも、少なくなるという利点がある。
【図面の簡単な説明】
【図１】本発明の一実施例を行う廃水の処理装置の概略図
【符号の説明】
１ 被処理水流入管
２ 逆浸透処理供給槽
３ 逆浸透処理供給配管
４ 逆浸透処理装置
５ 逆浸透処理水配管
６ 逆浸透濃縮水配管
７ 軟化処理装置
８ 排泥管
９ 軟化処理水配管
１０ 電気透析処理供給槽
１１ 電気透析処理供給配管
１２ 電気透析処理装置
１３ 電気透析脱塩水配管
１４ 電気透析濃縮水配管
１５ 蒸発乾燥処理装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a treatment method and a treatment apparatus for removing salt from organic wastewater containing high-concentration salt, and particularly organic matter having a high salt concentration such as human waste and waste leachate. It can be used for advanced treatment, desalination treatment, concentration recovery of salt substances, and recovery / reuse of treated water.
[0002]
[Prior art]
Organic wastewater with a high salt concentration such as human waste and leachate generally contains a high concentration of pollutants such as salts such as calcium ions and organic matter. Often, the biochemical oxygen demand (BOD) or chemical oxygen demand (COD) is high, contains many suspended solids (SS), and has chromaticity caused by colloidal materials. For this reason, they cannot usually be reused directly for some purpose or discharged directly into rivers.
As such a method for treating organic wastewater, conventionally, a treatment method mainly using removal of organic pollutants has been used. The main treatment methods include, for example, biological treatment for the purpose of removing BOD, coagulation sedimentation treatment for the purpose of removing chromaticity, COD and SS, sand filtration and microfiltration for the purpose of removing turbidity such as SS. There is a membrane (MF membrane) treatment. Furthermore, there is a method using ozone or activated carbon in general as an advanced treatment method.
[0003]
[Problems to be solved by the invention]
The organic wastewater treatment method described above has reached a technical level that allows organic components such as BOD and COD to be sufficiently removed by combining these treatments. However, organic wastewater generally contains various salts in addition to organic substances, and in some cases may contain a considerably high concentration of salts. When treating such wastewater and discharging it to rivers, etc., it is necessary to consider the protection of the water quality of the discharge water area and the effect on agricultural water. Recently, in addition to organic pollutants, especially such salts There is a growing need to remove them from wastewater together. All of the conventional methods for purifying organic wastewater are mainly intended to remove the organic pollutant components therein, so there is no effect of removing salts, and the salt concentration of the treated water is almost the same as the inflowing raw water. It is about.
[0004]
A treatment method for removing salts from an aqueous phase containing salts is a technique well known per se, and examples thereof include a reverse osmosis method, an electrodialysis method, and an evaporation method.
The reverse osmosis method obtains desalted water by applying mechanical pressure higher than osmotic pressure to salt water in a chamber partitioned by a semipermeable membrane (RO membrane), and letting the water out through the semipermeable membrane. It is a method. This method has the disadvantage that the efficiency depends on the salt concentration of the salt water. When the concentration of saline water is high, the recovery rate of demineralized water is low. For example, when desalting a 3.5 wt% NaCl aqueous solution, even if the treatment pressure is 60 kgf / cm 2 , the water recovery rate is 35 to 40% at the highest. In order to increase the water recovery rate to 50% or more, the operating pressure must be 70 kgf / cm 2 or more. However, such a high pressure not only increases the processing cost, but also has a limit when considering the lifetime of the reverse osmosis processing apparatus.
Furthermore, if the salt water contains calcium ions at a high concentration, there is a risk that calcium scale is deposited on the surface of the semipermeable membrane. Even if the salt concentration is relatively low, it becomes difficult to treat the treated water at a high recovery rate due to a decrease in the amount of permeated water due to precipitation of calcium scale on the surface of the semipermeable membrane.
[0005]
In electrodialysis, basically a high water recovery rate can be obtained. However, when the water to be electrodialyzed contains calcium ions at a high concentration, calcium scale is deposited in the apparatus. In particular, in the electrodialysis method, a calcium scale is easily generated due to a change in pH accompanying the movement of hydrogen ions from the anode and hydroxide ions from the cathode. Similar to the reverse osmosis method, if the calcium scale is precipitated, a high water recovery rate cannot be obtained. Moreover, since organic substances such as COD cannot be removed by this method, it is necessary to remove organic substances by other treatment methods such as an activated carbon treatment method in order to obtain high-quality treated water.
Further, since the evaporation method is a method involving phase change of the system, there is a problem that the required energy is large and the processing cost is greatly increased. Furthermore, if the wastewater contains volatile organic substances, nitrogen-ammonium salt compound (NH 4 -N), etc., they may be mixed in the treated water, and there is a problem that it is difficult to obtain good quality treated water.
[0006]
The present invention is not only capable of sufficiently removing organic components when treating organic wastewater containing salt at a high concentration and purifying it efficiently so that it can be reused or discharged directly into a river. It is possible to sufficiently remove salts and to purify and obtain treated water with low salt concentration with high efficiency without causing the problem of reducing the treatment effect such as precipitation of calcium scale during the treatment. An object of the present invention is to provide a processing method and a processing apparatus that can be used.
[0007]
[Means for Solving the Problems]
That is, the object of the present invention is achieved by the following configuration.
(1) A method for treating organic wastewater containing high-concentration salts, wherein the organic wastewater is pretreated as biological treatment, coagulation sedimentation treatment, sand filtration treatment, microfiltration membrane treatment, or 2 A treatment comprising the above combination is performed, followed by desalting with a reverse osmosis membrane, separating into reverse osmosis concentrated water and reverse osmosis treated water, collecting the reverse osmosis treated water, and converting the reverse osmosis concentrated water to calcium After performing a softening treatment for removing water, electrodialysis treatment is performed to separate electrodialysis concentrated water and electrodialysis demineralized water, and the electrodialysis demineralized water is returned to the reverse osmosis treatment supply side again. A method for treating organic wastewater containing high-concentration salts.
(2) The method for treating organic wastewater containing high-concentration salts as described in (1) above, wherein the softening treatment is performed by setting the calcium concentration in the treated water to 100 mg / liter or less.
[0008]
(3) The electrodialysis treatment is performed such that the desalination rate is 98% or more and the evaporation residue of electrodialysis desalted water is 1000 mg / liter or less. A method for treating organic wastewater containing high concentrations of salts.
(4) The electrodialyzed concentrated water after the electrodialysis treatment contains high-concentration salts according to any one of (1) to (3), wherein an evaporation residue is 13 wt% or more. Organic wastewater treatment method.
(5) An organic wastewater treatment apparatus containing high-concentration salts, which is one of a biological treatment apparatus, a coagulation sedimentation treatment apparatus, a sand filtration treatment apparatus, and a microfiltration membrane treatment apparatus that supplies the organic wastewater. Or a reverse osmosis treatment apparatus using a reverse osmosis membrane that supplies a pretreatment device composed of a combination of two or more, supplies treated water from the pretreatment device, and separates into reverse osmosis concentrated water and reverse osmosis treated water by desalination treatment A softening treatment device that supplies the reverse osmosis concentrated water and performs a softening treatment for removing calcium; a softening treatment water from the softening treatment device is supplied; and electrodialysis concentrated water and electrodialysis desalted water by electrodialysis treatment An electrodialysis treatment apparatus that separates the electrodialysis treatment water from the electrodialysis treatment apparatus into a reverse osmosis treatment apparatus supply side, and a pipe that collects the reverse osmosis treatment water from the reverse osmosis treatment apparatus. Features and Processor of organic waste water containing high concentrations of salts that.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing an embodiment of a treatment apparatus for performing the wastewater treatment method according to the present invention.
The organic wastewater treatment apparatus shown in FIG. 1 has an outlet of a treated water inflow pipe 1 extending from an organic matter removal treatment apparatus (not shown) opened in a reverse osmosis treatment supply tank 2. A reverse osmosis treatment supply pipe 3 is connected to a reverse osmosis treatment supply device 4 from the reverse osmosis treatment supply tank 2. A reverse osmosis treatment water pipe 5 and a reverse osmosis concentrate water pipe 6 extend separately from the reverse osmosis treatment device 4, and the reverse osmosis concentrate water pipe 6 leads the reverse osmosis concentrate water to the softening treatment device 7. The reverse osmosis treated water is recovered from the reverse osmosis treated water pipe 5 outside the system. The softening treatment apparatus 7 has a softened treated water pipe 9 for guiding the treated water subjected to the softened treatment, connected to an electrodialysis treatment supply tank 10 and has a mud discharge pipe 8 for discharging generated mud. An electrodialysis treatment supply pipe 11 is connected to the electrodialysis treatment device 12 from the electrodialysis treatment supply tank 10.
An electrodialysis concentrated water pipe 14 for sending electrodialyzed concentrated water from the electrodialyzer 12 is connected to the evaporating and drying treatment apparatus 15, and an electrodialysis desalted water pipe 13 for sending electrodialyzed desalted water is the reverse osmosis treatment supply tank 2. It is connected to the.
[0010]
In the present invention, the organic wastewater to be treated can be treated even if it is not so high as an organic component, and when the organic component enters the electrodialysis treatment, it has an adverse effect. Can be removed in a reverse osmosis process. Moreover, the salt concentration in the organic wastewater is not necessarily intended to have a significantly high concentration, and as described above, the salt concentration is high enough to hinder the release, or higher than that. It is suitable for targeting high concentrations.
The organic wastewater treatment method of the present invention may be carried out, for example, as follows using such an apparatus.
Organic wastewater is first treated as a biological treatment, coagulation sedimentation treatment, sand filtration treatment or microfiltration membrane (MF membrane) treatment, or a combination of two or more treatments. In order to reduce the concentration of, it is preferable to perform a treatment that combines biological treatment. The pretreated waste water is temporarily stored in the reverse osmosis treatment supply tank 2 through the treated water inflow pipe 1. Specific examples of the biological treatment method described above include a biological nitrification denitrification method in addition to a standard activated sludge method. If these methods are utilized, BOD will also fall. A specific example of the coagulation microfiltration (aggregation MF membrane filtration) method is a method of adding a coagulant, for example, an inorganic coagulant and coagulating it with a microfiltration membrane. When such a method is used, particularly turbidity such as SS can be removed from waste water. The coagulation sedimentation treatment method is a method in which an aggregate is added in a sedimentation tank after adding a coagulant. Chromaticity and SS can be removed and COD can be lowered. The sand filtration method can remove turbidity such as SS.
[0011]
The wastewater that has been pretreated mainly for removing organic substances in this way is introduced from the reverse osmosis treatment supply tank 2 through the reverse osmosis treatment supply pipe 3 into the reverse osmosis treatment device 4, where the reverse osmosis treatment (“RO treatment”) is performed. ”). In reverse osmosis treatment, reverse osmosis concentrated water ("" is obtained by applying mechanical pressure of 5 Mpa or more to the waste water partitioned by a semipermeable membrane (also referred to as "RO membrane") and passing the waste water through the RO membrane. The reverse osmosis treated water is also collected through the reverse osmosis treated water pipe 5.
The organic matter that has not been sufficiently removed during the organic matter removal treatment operation is further filtered through this semipermeable membrane, and the contaminated organic matter component hardly flows into the recovered desalted water.
[0012]
The reverse osmosis concentrated water is introduced into the softening treatment device 7 through the reverse osmosis concentrated water pipe 6. The softening treatment includes, for example, substituting calcium or magnesium hard water components (slightly soluble salt forming components) in water with easily soluble salt forming components such as sodium by lime soda softening method or ion exchange hard water softening method. Can be done by the method.
In such a softening treatment, the calcium concentration in the reverse osmosis concentrated water is preferably 100 mg / liter or less. By making the calcium concentration 100 mg / liter or less, it is possible to effectively prevent the calcium scale from being generated in the electrodialysis treatment apparatus 12, which is preferable. Sludge generated by the softening treatment is discharged out of the system through the sludge pipe 8.
[0013]
Softened treated water containing high-concentration salts from which calcium ions have been removed is temporarily stored in the electrodialysis treatment supply tank 10 through the softened treatment water pipe 9 and further introduced into the electrodialysis treatment apparatus 12 through the electrodialysis treatment supply pipe 11. The introduction and electrodialysis treatment are preferably carried out batchwise. In electrodialysis (also referred to as “ED treatment”), a number of electrodialysis membranes are arranged, and the above-mentioned softened water is supplied to the concentration chamber and dilution chamber formed alternately, or only to the dilution chamber in them. Then, a high concentration electrodialyzed concentrated water is obtained in the concentrating chamber, and electrodialyzed demineralized water is obtained in the diluting chamber.
[0014]
The electrodialysis demineralized water returns to the reverse osmosis treatment supply tank 2 through the electrodialysis demineralized water pipe 13. Even if organic matter remains in the reflux water, it is filtered by the reverse osmosis treatment device 4, so that it is prevented from leaking into the reverse osmosis treatment water. The electrodialyzed concentrated water is guided to the evaporating and drying treatment device 15 and evaporated to dryness to separate into water and salts, and the salts are isolated.
In this method, to-be-treated water containing calcium is desalted using a reverse osmosis membrane, so that the salinity and organic matter of the to-be-treated water are simultaneously removed with a water recovery rate within a range where calcium scale does not precipitate. By doing so, high-quality treated water (reverse osmosis treated water) is obtained.
Further, the reverse osmosis concentrated water having a high calcium concentration is subjected to softening treatment for the purpose of removing calcium, and the softened water having a sufficiently reduced calcium concentration is electrodialyzed, preferably batchwise. By dialysis treatment, electrodialysis demineralized water having a low salt concentration and electrodialyzed concentrated water having a high salt concentration can be obtained without causing calcium scale precipitation even when treated at a high desalination rate and a high water recovery rate.
[0015]
Usually, when the batch is used in electrodialysis, the salt concentration is higher in desalination rate and processing efficiency than in the continuous method, and the salt concentration is high (evaporation residue component concentration is 13 wt% or more (13000 mg / liter or more)). Water is obtained, and the salt concentration ratio of demineralized water and concentrated water can be 150 or more. The evaporation residue means a component that remains in the evaporation can as a solid component when moisture is evaporated. Expressing the change in concentration in an easy-to-understand manner, in salt water separated from concentrated water, 98 wt% or more of salts decreased and the salt concentration decreased to 1000 mg / liter or less.
[0016]
In the above-described embodiment, low-concentration electrodialysis demineralized water generated in the electrodialysis treatment is returned to the reverse osmosis treatment supply tank 2. By returning in this way, organic substances such as COD that could not be removed by electrodialysis treatment can be removed by reverse osmosis treatment.
Further, the salt concentration of this electrodialyzed demineralized water, particularly the calcium ion concentration, is lower than that of the water to be treated from the reverse osmosis treatment supply tank 2. Therefore, the reverse osmosis treatment can be performed in a state where the salt concentration is lower than that of normal waste water. In reverse osmosis treatment, the permeation flux (permeated water amount) basically decreases as the osmotic pressure increases with increasing salt concentration in the water to be treated. Therefore, there is no decrease in the permeation flux of the reverse osmosis treatment, and therefore there is little increase in the reverse osmosis treatment cost, and high-quality reverse osmosis demineralized water can be obtained with a high water recovery rate.
Furthermore, even if calcium ions are mixed in the water to be treated, the concentration thereof is low, and there is almost no trouble that this precipitates as a scale on the surface of the reverse osmosis membrane.
[0017]
Since the electrodialysis treatment is performed after removing a large amount of reverse osmosis demineralized water by reverse osmosis treatment, the overall volume subjected to electrodialysis treatment is reduced, and salt concentrated water concentrated to a high concentration can be obtained efficiently. be able to. In addition, prior to the electrodialysis treatment, a softening treatment is performed in advance to lower the calcium dissolution concentration. Therefore, calcium ions are hardly deposited as scales in the electrodialysis treatment apparatus 12 and this hardly causes trouble.
Following the electrodialysis treatment, the salt concentrate is subjected to an evaporative drying treatment, where the salts are isolated. The evaporative drying treatment targets high-concentration salt concentrated water whose volume is further reduced by electrodialysis treatment. Therefore, even a process that requires a large amount of energy with a phase change can be performed efficiently, and the salt component can be easily isolated as a solid component.
[0018]
【Example】
Examples of the present invention will be described below, but the present invention is not limited thereto.
(Example)
The treated water that was produced by performing biological treatment, coagulation sedimentation treatment, and microfiltration membrane treatment on human waste was treated using the treatment apparatus shown in FIG. The operating pressure in the reverse osmosis treatment is a high pressure condition of 5 to 6 MPa, and the sludge after the softening treatment is discharged from the mud pipe 8 from the softening treatment device 7.
Water to be treated after removal of organic matter, treated water obtained by reverse osmosis treatment (referred to as “RO treated water”), treated water obtained by softening treatment (“softened treated water”), electrodialysis treatment The water quality of each of the concentrated water ("ED concentrated water") thus obtained was measured. The measurement results are shown in Table 1.
[0019]
[Table 1]
Presence or absence of calcium scale deposition was judged based on chemical analysis and the processing performance of each device.
The following was found from the above results.
Reverse osmosis treatment is applied to the water to be treated, that is, the chromaticity of pretreated wastewater is 150 degrees, the COD is 50 mg / liter, the calcium concentration is 60 mg / liter, and the evaporation residue component concentration is 5600 mg / liter. The treated water thus obtained, that is, the RO treated water, had a chromaticity of 4 degrees, a COD of 5.0 mg / liter, and an evaporation residue component concentration of 380 mg / liter, and thus treated water with good water quality was obtained.
[0021]
Also, by softening the RO concentrated water obtained by reverse osmosis treatment, the calcium concentration was reduced from about 600 mg / liter before treatment to about 65 mg / liter. As a result, the softened water was electrodialyzed. Even when the salt concentration was performed, the calcium concentration of the ED concentrated water was 180 mg / liter, and no generation of calcium scale was observed.
The ED concentrated water was able to have an electric conductivity of about 130,000 μS / cm and an evaporation residue of 165000 mg / liter. Since the electrodialysis desalted water is returned to the reverse osmosis treatment, the water recovery rate indicating the ratio of the treated water amount to the treated water amount is 96.8%, and the concentrated water amount is about 30 minutes relative to the treated water amount. Can be reduced to 1 or less.
[0022]
(Comparative Example 1)
Only the reverse osmosis process was performed with respect to the to-be-processed water similar to an Example. That is, the same procedure as in Example was performed except that pretreatment was performed and softening treatment and electrodialysis treatment were omitted.
Water quality was measured for pretreated target wastewater (treated water), RO treated water obtained by reverse osmosis treatment, and RO concentrated water. The measurement results are shown in Table 2.
[0023]
[Table 2]
The following was found from the results in Table 2.
When reverse osmosis treatment is performed on the pretreated water alone, the water recovery rate indicating the ratio of the RO treated water amount (treated water amount) to the treated water amount is only 90.9%, and 96.8% 5.9% less than the example shown. Furthermore, the concentration of the evaporation residue component of the RO concentrated water obtained by the reverse osmosis treatment is only 58000 mg / liter, which is about one third of that of the electrodialyzed concentrated water (ED concentrated water) of the example. .
That is, the amount of concentrated water increases approximately three times the above, and when this is used for the evaporative drying process, the processing cost is further increased. In addition, the calcium concentration in the RO concentrated water is 610 mg / liter, and if the concentration is further increased, there is a risk of precipitation of calcium scale.
[0025]
(Comparative Example 2)
Only the electrodialysis treatment was performed on the water to be treated which had been subjected to the same pretreatment for removing organic substances as in the examples, and the reverse osmosis treatment and the softening treatment were omitted. Water quality was measured for each of the water to be treated, ED desalted water obtained by electrodialysis treatment, and ED concentrated water obtained by electrodialysis treatment. The measurement results are shown in Table 3.
[0026]
[Table 3]
As shown in Table 3, the calcium concentration of the electrodialyzed concentrated water obtained by electrodialysis treatment is 1800 mg / liter unless the reverse osmosis treatment or softening treatment is performed on the water to be treated. It was recognized that the occurrence of calcium scale was remarkable. Although not shown in Table 3, the treatment efficiency was significantly reduced as the number of batch treatments of the electrodialysis treatment was increased as compared with the Example. This is the effect of calcium scale generation.
In the quality of the treated water, there was no change in chromaticity and COD before and after the electrodialysis treatment. The treated water, electrodialysis demineralized water (ED demineralized water), and ED concentrated water all had a chromaticity of 150 degrees and COD of 50 mg / liter, and no organic substances were removed. For this reason, it is necessary to further remove organic matter by other treatment methods in order to obtain treated water of the same level as in the examples. For example, when activated carbon adsorption treatment is used, it is necessary to increase equipment or replace activated carbon. This increases the processing cost.
[0028]
【The invention's effect】
In the present invention, high-quality demineralized water (treated water) is obtained by performing reverse osmosis treatment on treated water that is organic wastewater containing high-concentration salts, while calcium removal is performed on reverse osmosis concentrated water. After reducing the calcium concentration to 100 mg / liter or less by performing the softening treatment, even if the softened water is further subjected to electrodialysis treatment, there is no generation of calcium scale in the treatment, and the concentration rate is extremely high. The electrodialysis treatment can be performed at a desalting rate. In particular, when the electrodialysis treatment is performed batchwise, the electrodialysis desalted water (evaporation residue 1000 mg / liter or less) having a high salt rejection and a low salt concentration and the electrodialysis concentrated water (evaporation residue 130000 mg having a high salt concentration). / Liter or more).
Furthermore, organic substances such as COD and chromaticity are removed by returning electrodialysis desalted water containing organic substances such as COD and chromaticity to the reverse osmosis treatment and performing the reverse osmosis treatment again. As a result, the amount of the electrodialyzed concentrated water can be reduced to about 1/30 or less of the amount of water to be treated, and the energy required for the evaporative drying process is less than that when the evaporative drying process is performed on the reverse osmosis concentrated water. is there.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a wastewater treatment apparatus according to an embodiment of the present invention.
1 treated water inflow pipe 2 reverse osmosis treatment supply tank 3 reverse osmosis treatment supply pipe 4 reverse osmosis treatment apparatus 5 reverse osmosis treatment water pipe 6 reverse osmosis concentrated water pipe 7 softening treatment apparatus 8 drainage pipe 9 softened treatment water pipe 10 electrodialysis Treatment supply tank 11 Electrodialysis treatment supply pipe 12 Electrodialysis treatment apparatus 13 Electrodialysis desalted water pipe 14 Electrodialysis concentrated water pipe 15 Evaporation drying treatment apparatus
Claims (5)
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| JP07818297A JP3800450B2 (en) | 1997-03-28 | 1997-03-28 | Method and apparatus for treating organic wastewater containing high concentrations of salts |
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| JP07818297A JP3800450B2 (en) | 1997-03-28 | 1997-03-28 | Method and apparatus for treating organic wastewater containing high concentrations of salts |
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- 1997-03-28 JP JP07818297A patent/JP3800450B2/en not_active Expired - Lifetime
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| CN105130066A (en) * | 2015-08-19 | 2015-12-09 | 杭州上拓环境科技有限公司 | Combined processing method for salts and COD generated during production of cellulose ether |
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| JPH10272495A (en) | 1998-10-13 |
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