JP3721871B2 - Production method of ultra pure water - Google Patents

Production method of ultra pure water Download PDF

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JP3721871B2
JP3721871B2 JP21556299A JP21556299A JP3721871B2 JP 3721871 B2 JP3721871 B2 JP 3721871B2 JP 21556299 A JP21556299 A JP 21556299A JP 21556299 A JP21556299 A JP 21556299A JP 3721871 B2 JP3721871 B2 JP 3721871B2
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water
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biological reaction
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reaction tank
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JP2001038390A (en
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聡 山田
桂 北辻
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Kurita Water Industries Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

【０００１】
【発明の属する技術分野】
本発明は超純水の製造方法に係り、特に、半導体製造工程からの排出水等の被処理水を、膜処理装置及びイオン交換樹脂を内蔵したイオン交換塔を備える超純水処理手段と、微生物のエネルギー源及び栄養源の存在下に生物処理する生物反応槽及び該生物反応槽からの処理水が導入される菌体分離器を備える生物処理手段とで処理して超純水を製造する方法において、生物反応槽において有機物とアンモニア態窒素を効率的に除去して高純度の超純水を製造する方法に関する。
【０００２】
【従来の技術】
従来の超純水製造システムは、図１に示す如く、膜式処理（精密濾過（ＭＦ）膜、限外濾過（ＵＦ）膜、逆浸透（ＲＯ）膜等）、イオン交換樹脂塔、紫外線酸化装置、脱気装置等を組み合わせた一次純水系１及び二次純水系２と、排水回収系３とで構成されている。被処理水のうち、工水、市水等は一次純水系１及び二次純水系２で処理されて超純水としてユースポイント（半導体洗浄工程等）４に送給され、ユースポイント４からの排出水（使用済み超純水。以下「回収水」と称す場合がある。）は、排水回収系３で処理された後、工水や市水と共に、一次純水系１及び二次純水系２で処理されてユースポイント４に送給される。
【０００３】
この排水回収系３としては、微生物のエネルギー源及び栄養源の存在下に生物処理する生物反応槽と、この生物反応槽からの処理水が導入される菌体分離器とを有する生物処理手段を適用したものが提案されている（特許第２１３０３８４号）。
【０００４】
図２はこの特許第２１３０３８４号公報に記載されるシステムの実施例であって、工水や市水は、前処理システム（凝集槽１１及び二槽濾過器１２からなる。）５、一次純水系（ＲＯ膜分離装置１３、脱気塔１４及びイオン交換装置１５からなる。）１及び二次純水系（紫外線（ＵＶ）殺菌装置１６、混床式イオン交換装置１７及びＵＦ膜分離装置１８からなる。）２で順次処理されて超純水としてユースポイント４に送給される。このユースポイント４からの回収水は、排水回収系３において、まず活性炭吸着塔１９において活性炭吸着処理され、イオン交換塔２０で処理されて脱塩された後、ＵＶ酸化装置２１で有機物の酸化分解が行われ、更に生物反応槽２２で生物処理された後、菌体分離器２３で菌体分離され、その後、工水、市水等の前処理水と共に一次純水系１及び二次純水系２で処理される。
【０００５】
生物反応槽２２は、生物固定手段、例えば材質がセラミックからなるハニカムチューブ等の固定床、又は活性炭やスポンジ或いはセラミックの粒状物等の流動床を内蔵したものであり、微生物のエネルギー源及び栄養源の存在下に微生物が十分に繁殖（増殖）するに必要な時間以上反応が行われる。なお、通常、純水中には溶存酸素（ＤＯ）が数ｐｐｍ存在するので、この反応は好気的に進行するが、ＤＯが少ないときには、純酸素等で曝気し、好気的条件を与えることが必要である。この反応により、微生物は活性化し、水中のＴＯＣ成分を資化する。生物反応槽２２内の水に、微生物の増殖に十分な量のリン及び窒素が含まれている場合には、生物反応槽２２内の水に含まれるＴＯＣ成分が殆ど完全に無くなるまでこの生物反応が継続する。
【０００６】
生物反応槽２２におけるかかる反応により、有機炭素はＣＯ2或いは菌体となる。菌体は後続の菌体分離器２３において、マイクロフィルター等で捕捉され分離される。マイクロフィルターとしてはメンブレンフィルター、セラミックからなる多孔質濾過等が利用できる。また、菌体分離器２３としてはＵＦ膜分離装置であっても良い。菌体が分離された水はＴＯＣが極めて低濃度にまで低減されている。
【０００７】
なお、ＵＶ酸化装置２１からの水のリン又は窒素濃度がＴＯＣ濃度に対して著しく低い場合には、生物反応槽２２における生物処理速度が非常に遅くなる。このような場合には、生物が増殖し、有機性炭素を資化できるように、生物反応槽２２の入口部において微量のリン又は窒素を添加しても良い。
【０００８】
なお、この生物反応槽２２及び菌体分離器２３からなる生物処理手段は、一次純水系１と二次純水系２との間に設けた構成としても良い。
【０００９】
従来においては、このように、回収水中に数ｐｐｍ程度含まれる微量の有機成分を排水回収系３の生物処理手段で除去し、更に一次純水系１及び二次純水系２で純度を高めて再利用している。
【００１０】
しかし、回収水中には、半導体の洗浄工程で使用されるアンモニアが数ｐｐｍ含まれているが、従来の排水回収系３の生物処理手段ではアンモニアの除去については考慮されておらず、また、排水回収系３に更にアンモニア除去のための手段が組み込まれていることも殆どない。一方で、アンモニアは分子量が小さいために後段のＲＯ膜での除去率が悪く、このためＲＯ膜分離装置の後段のイオン交換樹脂塔に流入してここで捕捉されることになる。そして、この結果、イオン交換樹脂の負荷となり、その再生頻度を高める原因となっている。
【００１１】
ＲＯ膜での除去効率の面からは、アンモニアを硝化して得られる硝酸又は亜硝酸の方が、アンモニアに比べて有利である。即ち、硝酸や亜硝酸はアンモニアに比べて分子量が大きいため、ＲＯ膜で効率的に除去することができることから、後段のイオン交換樹脂の負荷を軽減することができる。従って、排水回収系の生物処理手段で、回収水中の微量有機物の除去と共に、アンモニアの硝化を行うことができれば、アンモニアを硝酸又は亜硝酸に変えてこれをＲＯ膜で除去し、イオン交換樹脂の負荷を軽減することができる。
【００１２】
生物処理手段におけるアンモニアの硝化法については、特開平９−１８７７８５号公報に、酸素を加圧溶解した加圧水を生物反応槽に供給する方法が記載されている。この方法は、生物反応槽のＤＯを高くすることにより、アンモニアの亜硝酸、更には硝酸への酸化を促進してアンモニア除去率を高めるものである。しかし、この方法では、加圧水の製造及び供給のための装置を設ける必要があり、装置が複雑になり、メンテナンス、設備コスト等の面で不利である。
【００１３】
【発明が解決しようとする課題】
本発明は、上記従来の問題点を解決し、生物反応槽において、有機物を除去すると共に、アンモニアを硝化し、後段のＲＯ膜で効率的に除去することにより、イオン交換樹脂の負荷を軽減し、その再生頻度を低減する超純水の製造方法を提供することを目的とする。
【００１４】
【課題を解決するための手段】
本発明の超純水の製造方法は、半導体製造工程からの排出水、工水、市水又は井水よりなる、アンモニア態窒素を含む被処理水を、膜処理装置及びイオン交換樹脂を内蔵したイオン交換塔を備える超純水処理手段と、微生物のエネルギー源及び栄養源の存在下に生物処理する生物反応槽及び該生物反応槽からの処理水が導入される菌体分離器を備える生物処理手段とで処理して超純水を製造する方法において、該生物反応槽における生物処理をｐＨ８以上で、かつ、生物処理した水のＤＯが２ｐｐｍ以上となるように酸素を供給して行い、得られたＮＨ ４ −Ｎ濃度が１ｐｐｍ以下の生物処理した水を逆浸透膜濾過し、逆浸透膜濾過した水を前記イオン交換塔で処理することを特徴とする。
【００１５】
本発明に従って、生物反応槽のｐＨを８以上として運転することにより、アンモニア態窒素の亜硝酸への酸化を促進することができるため、生物反応槽のＤＯを高める特別な装置を設けることなく、生物反応槽において有機物とアンモニアを効率よく分解除去することができる。
【００１６】
本発明において、生物反応槽のｐＨを８以上とすることにより、アンモニアを亜硝酸に酸化する作用機構は次のように考えられる。
【００１７】
即ち、水中のアンモニア態窒素にはイオン化したアンモニウムイオン（ＮＨ4 +）とイオン化していない未解離のアンモニア（ＮＨ3）とがあり、これらはＮＨ4 +＋Ｈ2Ｏ⇔ＮＨ3＋Ｈ3Ｏ+の平衡関係にあるため、ｐＨを高くすると、水中のアンモニア態窒素はイオン化していないＮＨ3の存在比が多くなる。
【００１８】
一方で、微生物の細胞膜はイオン化したＮＨ4 +より、イオン化していないＮＨ3を通過させ易く、このためｐＨを８以上とすることによりアンモニア態窒素（ＮＨ3）が微生物の細胞内に取り込まれ易くなり、分解が促進され、アンモニアが亜硝酸に酸化され易くなる。このｐＨ８以上の条件では有機物の生物分解も十分に行われるため、このようにｐＨ調整することにより生物反応槽における有機物の分解が阻害されることはない。
【００１９】
なお、ｐＨを８以上とすることはアンモニアから亜硝酸への反応を促進するが、必ずしも亜硝酸から硝酸への反応を促進するとは限らない。しかし、亜硝酸も硝酸と同様にＲＯ膜での除去率が優れているため、亜硝酸を硝酸にまで酸化させる必要はなく、アンモニアを亜硝酸に酸化するだけでシステム全体としてのアンモニア除去率を高めることができる。
【００２０】
【発明の実施の形態】
以下に本発明の実施の形態を詳細に説明する。
【００２１】
本発明の方法において、処理対象となる被処理水はＴＯＣ２０ｐｐｍ以下、ＮＨ4−Ｎ（アンモニア態窒素）２０ｐｐｍ以下程度の水であって、主に半導体製造工程からの排出水（洗浄工程排出水）が挙げられるが、その他、工水、市水、井水、或いはこれらの混合水であっても良い。
【００２２】
本発明の方法は、半導体製造工程からの排出水、工水、市水又は井水或いはこれらの混合水を、膜処理装置及びイオン交換樹脂を内蔵したイオン交換塔を備える超純水処理手段と、微生物のエネルギー源及び栄養源の存在下に生物処理する生物反応槽及び該生物反応槽からの処理水が導入される菌体分離器を備える生物処理手段とで処理する超純水製造システムにおいて、生物反応槽における生物処理をｐＨ８以上で行うこと以外は、従来と同様に実施することができる。
【００２３】
より具体的には、図２に示すような超純水製造システムの生物反応槽２２においてｐＨ８以上で処理を行う。
【００２４】
生物反応槽のｐＨ調整には、水酸化ナトリウム、水酸化カリウム、塩酸や硫酸などの公知のｐＨ調整剤を用いれば良く、ｐＨ調整を行う場所に特に制限はない。例えば、ｐＨ調整剤を生物反応槽に直接添加する他、その導入側の配管にｐＨ調整剤を添加しても良い。
【００２５】
生物反応槽の調整ｐＨが８未満では、アンモニアの亜硝酸への酸化が十分に促進されないが、このｐＨが過度に高過ぎると後段の装置の負荷が増大するため、生物反応槽の調整ｐＨは８〜９程度とするのが好ましい。
【００２６】
この生物反応槽は好気的生物処理を行うために、必要に応じて曝気などの手段で酸素を供給する。この酸素供給量は、生物反応槽の出口水のＤＯが２ｐｐｍ以上となる量とする。なお、生物反応槽への酸素の供給手段としては空気や純酸素などの曝気の他、加圧下で酸素を溶解させるなどしてＤＯを高めた水を供給しても良いが、通常は曝気により必要な酸素が供給される。
【００２７】
生物反応槽の型式には特に制限はなく、活性炭やスポンジ担体或いはセラミック担体に貧栄養細菌（オリゴトロフィックバクテリア）を担持した固定床又は流動床式で良い。
【００２８】
この生物反応槽の処理温度は２５〜３５℃、特に３０〜３５℃であることが、有機物の分解効率及びアンモニアの亜硝酸への酸化効率の面で好ましい。
【００２９】
通常の場合、ｐＨ８以上の生物処理により、回収水中のアンモニア態窒素はそのほぼ全量を亜硝酸に酸化することができ、また、回収水中の有機物は９０％以上分解できる。
【００３０】
【実施例】
以下に実施例及び比較例を挙げて本発明をより具体的に説明する。
【００３１】
実施例１，２、比較例１，２
脱塩水にＴＯＣ（酢酸）：３ｐｐｍ，ＮＨ4−Ｎ：５ｐｐｍ，ＫＨ2ＰＯ4：０．３ｐｐｍを添加した模擬排水（導電率１００μＳ／ｃｍ）を原水として生物反応槽に通水して表１に示す条件で処理し、生物処理水をＵＦ膜分離装置（菌体分離器）及びＲＯ膜分離装置に順次通水した。なお、生物反応槽における曝気は生物反応槽の出口水のＤＯが３ｐｐｍとなるように行った。
【００３２】
その結果、ＵＦ膜処理水及びＲＯ膜処理水の水質は表１に示す通りであった。
【００３３】
【表１】

Figure 0003721871
【００３４】
なお、実施例１及び比較例１のＵＦ膜処理水のＮＯ2−Ｎ＋ＮＯ3−Ｎ及びＴＯＣの経日変化とＲＯ膜処理水の導電率の経日変化は図３（ａ）〜（ｃ）に示す通りであった。
【００３５】
実施例及び比較例の結果から、生物反応槽のｐＨを８以上とすることにより、生物反応槽内でのＴＯＣ除去には何ら悪影響を及ぼすことなく、ＴＯＣの除去と共にアンモニア態窒素の亜硝酸態窒素（ないしは硝酸態窒素）への酸化を行うことができ、この生物反応槽で生成した亜硝酸態窒素（ないしは硝酸態窒素）をＲＯ膜で効率的に除去できることが明らかである。
【００３６】
【発明の効果】
以上詳述した通り、本発明の超純水の製造方法によれば、半導体製造工程からの排出水等の被処理水を、膜処理装置及びイオン交換樹脂を内蔵したイオン交換塔を備える超純水処理手段と、微生物のエネルギー源及び栄養源の存在下に生物処理する生物反応槽及び該生物反応槽からの処理水が導入される菌体分離器を備える生物処理手段とで処理して超純水を製造する方法において、生物反応槽において、有機物の分解除去と共に、アンモニアの亜硝酸への酸化を行うことができ、この生物反応槽で生成した亜硝酸をＲＯ膜分離装置で効率的に除去して高水質の処理水を得ることができる。このため、ＲＯ膜処理水の水質が大幅に向上するため、ＲＯ膜分離装置の後段のイオン交換樹脂塔への負荷を軽減することができ、イオン交換樹脂の交換頻度を低減して、システム全体の運転効率を高めることができる。
【図面の簡単な説明】
【図１】一般的な超純水製造システムを示す系統図である。
【図２】特許第２１３０３８４号公報に記載されるシステムの系統図である。
【図３】実施例１及び比較例１のＵＦ膜処理水のＮＯ2−Ｎ＋ＮＯ3−Ｎ及びＴＯＣの経日変化とＲＯ膜処理水の導電率の経日変化を示すグラフである。
【符号の説明】
１ 一次純水系
２ 二次純水系
３ 排水回収系
４ ユースポイント
５ 前処理系
１３ ＲＯ膜分離装置
１５ イオン交換装置
２２ 生物反応槽
２３ 菌体分離器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing ultrapure water, in particular, ultrapure water treatment means comprising an ion exchange tower incorporating a membrane treatment device and an ion exchange resin for water to be treated such as discharged water from a semiconductor production process, Ultrapure water is produced by treatment with a biological reaction vessel for biological treatment in the presence of an energy source and nutrient source of microorganisms and a biological treatment means having a cell separator into which treated water from the biological reaction vessel is introduced. The method relates to a method for producing high purity ultrapure water by efficiently removing organic substances and ammonia nitrogen in a biological reaction tank.
[0002]
[Prior art]
As shown in FIG. 1, the conventional ultrapure water production system has membrane treatment (microfiltration (MF) membrane, ultrafiltration (UF) membrane, reverse osmosis (RO) membrane, etc.), ion exchange resin tower, ultraviolet oxidation. A primary pure water system 1 and a secondary pure water system 2 combined with a device, a deaeration device, and the like, and a waste water recovery system 3 are configured. Among treated water, industrial water, city water, etc. are treated with primary pure water system 1 and secondary pure water system 2 and sent to use point (semiconductor cleaning process, etc.) 4 as ultra pure water. Discharged water (used ultrapure water; hereinafter sometimes referred to as “recovered water”) is treated by the wastewater recovery system 3, and then, together with the industrial water and city water, the primary pure water system 1 and the secondary pure water system 2. Is processed and sent to the use point 4.
[0003]
The waste water recovery system 3 includes a biological treatment means having a biological reaction tank for biological treatment in the presence of microbial energy sources and nutrient sources, and a cell separator into which treated water from the biological reaction tank is introduced. An application is proposed (Japanese Patent No. 2130384).
[0004]
FIG. 2 shows an embodiment of the system described in this Japanese Patent No. 2130384, and the industrial water and city water are pretreatment system (consisting of a coagulation tank 11 and a double tank filter 12) 5, a primary pure water system. (Consisting of RO membrane separator 13, degassing tower 14 and ion exchanger 15) 1 and secondary pure water system (comprising ultraviolet (UV) sterilizer 16, mixed bed ion exchanger 17 and UF membrane separator 18) .) Sequentially processed in 2 and supplied to the use point 4 as ultrapure water. The recovered water from the use point 4 is first subjected to activated carbon adsorption treatment in the activated carbon adsorption tower 19 in the waste water collection system 3, treated in the ion exchange tower 20 and desalted, and then oxidatively decomposed organic matter in the UV oxidizer 21. And further biologically treated in the biological reaction tank 22 and then separated in the bacterial cell separator 23, and then the primary pure water system 1 and the secondary pure water system 2 together with pretreated water such as industrial water and city water. Is processed.
[0005]
The biological reaction tank 22 contains a biological fixing means, for example, a fixed bed such as a honeycomb tube made of a ceramic material, or a fluidized bed such as activated carbon, sponge or ceramic particles, and is a source of microorganism energy and nutrients. The reaction is carried out for more than the time necessary for the microorganisms to fully propagate (grow) in the presence of. In addition, since several ppm of dissolved oxygen (DO) is usually present in pure water, this reaction proceeds aerobically. However, when DO is low, aeration is performed with pure oxygen to give aerobic conditions. It is necessary. By this reaction, microorganisms are activated and assimilate TOC components in water. If the water in the biological reaction tank 22 contains sufficient amounts of phosphorus and nitrogen for the growth of microorganisms, the biological reaction is carried out until the TOC component contained in the water in the biological reaction tank 22 is almost completely eliminated. Will continue.
[0006]
By this reaction in the biological reaction tank 22, the organic carbon becomes CO 2 or bacterial cells. The cells are captured and separated by a microfilter or the like in the subsequent cell separator 23. As the microfilter, a membrane filter, a porous filter made of ceramic, or the like can be used. Further, the microbial cell separator 23 may be a UF membrane separator. The water from which the cells are separated has a TOC reduced to a very low concentration.
[0007]
In addition, when the phosphorus or nitrogen density | concentration of the water from the UV oxidation apparatus 21 is remarkably low with respect to the TOC density | concentration, the biological treatment speed in the biological reaction tank 22 will become very slow. In such a case, a trace amount of phosphorus or nitrogen may be added at the inlet of the biological reaction tank 22 so that the organism can grow and assimilate organic carbon.
[0008]
In addition, the biological treatment means including the biological reaction tank 22 and the cell separator 23 may be provided between the primary pure water system 1 and the secondary pure water system 2.
[0009]
Conventionally, in this way, a trace amount of organic components contained in the recovered water of about several ppm is removed by the biological treatment means of the wastewater recovery system 3, and the purity is further increased by the primary pure water system 1 and the secondary pure water system 2. We are using.
[0010]
However, the recovered water contains several ppm of ammonia used in the semiconductor cleaning process, but the biological treatment means of the conventional wastewater recovery system 3 does not consider the removal of ammonia, and the wastewater There is almost no further means for removing ammonia in the recovery system 3. On the other hand, since ammonia has a low molecular weight, the removal rate at the downstream RO membrane is poor, and therefore, it flows into the ion exchange resin tower at the downstream stage of the RO membrane separation apparatus and is captured here. And as a result, it becomes a load of an ion exchange resin and becomes the cause which raises the regeneration frequency.
[0011]
From the viewpoint of the removal efficiency of the RO membrane, nitric acid or nitrous acid obtained by nitrifying ammonia is more advantageous than ammonia. That is, since nitric acid and nitrous acid have a molecular weight larger than that of ammonia and can be efficiently removed by the RO membrane, the load on the ion exchange resin in the subsequent stage can be reduced. Therefore, if the biological treatment means of the wastewater recovery system can remove the trace amount of organic matter in the recovered water and nitrify ammonia, the ammonia is converted into nitric acid or nitrous acid, and this is removed by the RO membrane. The load can be reduced.
[0012]
As for the nitrification method of ammonia in the biological treatment means, JP-A-9-187785 describes a method of supplying pressurized water in which oxygen is dissolved under pressure to the biological reaction tank. In this method, by increasing the DO of the biological reaction tank, the oxidation of ammonia to nitrous acid and further to nitric acid is promoted to increase the ammonia removal rate. However, in this method, it is necessary to provide an apparatus for producing and supplying pressurized water, which complicates the apparatus and is disadvantageous in terms of maintenance, equipment costs, and the like.
[0013]
[Problems to be solved by the invention]
The present invention solves the above-mentioned conventional problems, reduces organic substances in a biological reaction tank, nitrifies ammonia, and efficiently removes it with a subsequent RO membrane, thereby reducing the load on the ion exchange resin. An object of the present invention is to provide a method for producing ultrapure water that reduces the frequency of regeneration.
[0014]
[Means for Solving the Problems]
The method for producing ultrapure water of the present invention comprises water to be treated comprising ammonia nitrogen , waste water from a semiconductor production process, industrial water, city water or well water, and a membrane treatment device and an ion exchange resin. Biological treatment comprising ultrapure water treatment means comprising an ion exchange tower, a biological reaction tank for biological treatment in the presence of a microorganism energy source and nutrient source, and a cell separator into which treated water from the biological reaction tank is introduced In the method of producing ultrapure water by treatment with means, the biological treatment in the biological reaction tank is carried out by supplying oxygen so that the biological treatment water has a pH of 8 or more and the DO of the biologically treated water is 2 ppm or more. The biologically treated water having an NH 4 —N concentration of 1 ppm or less is subjected to reverse osmosis membrane filtration, and the water subjected to reverse osmosis membrane filtration is treated in the ion exchange tower .
[0015]
According to the present invention, by operating the biological reaction tank at a pH of 8 or more, the oxidation of ammonia nitrogen to nitrous acid can be promoted, so without providing a special device for increasing the DO of the biological reaction tank, Organic matter and ammonia can be efficiently decomposed and removed in the biological reaction tank.
[0016]
In the present invention, the mechanism of action of oxidizing ammonia into nitrous acid by setting the pH of the biological reaction tank to 8 or more is considered as follows.
[0017]
That is, ammonia nitrogen in water includes ionized ammonium ions (NH 4 + ) and non-ionized undissociated ammonia (NH 3 ), which are NH 4 + + H 2 O⇔NH 3 + H 3 O +. Therefore, when the pH is increased, the abundance ratio of NH 3 which is not ionized in ammonia nitrogen in water increases.
[0018]
On the other hand, the cell membrane of microorganisms is easier to pass non-ionized NH 3 than ionized NH 4 +. Therefore, ammonia nitrogen (NH 3 ) is taken into the cells of microorganisms by setting the pH to 8 or more. Facilitates decomposition and facilitates oxidation of ammonia to nitrous acid. Since the biodegradation of the organic matter is sufficiently performed under the condition of pH 8 or higher, the degradation of the organic matter in the biological reaction tank is not inhibited by adjusting the pH in this way.
[0019]
Note that setting the pH to 8 or more promotes the reaction from ammonia to nitrous acid, but does not necessarily promote the reaction from nitrous acid to nitric acid. However, nitrous acid has an excellent removal rate at the RO membrane, as is nitric acid. Therefore, it is not necessary to oxidize nitrous acid to nitric acid. Can be increased.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0021]
In the method of the present invention, the water to be treated is water having a TOC of 20 ppm or less and NH 4 —N (ammonia nitrogen) of 20 ppm or less, mainly discharged from the semiconductor manufacturing process (cleaning process discharged water). In addition, industrial water, city water, well water, or a mixed water thereof may be used.
[0022]
The method of the present invention comprises an ultrapure water treatment means comprising an ion exchange tower containing a membrane treatment device and an ion exchange resin, and water discharged from a semiconductor manufacturing process, industrial water, city water or well water or a mixed water thereof. In an ultrapure water production system for treatment with a biological reaction vessel for biological treatment in the presence of an energy source and nutrient source of microorganisms and a biological treatment means having a cell separator into which treated water from the biological reaction vessel is introduced The biological treatment in the biological reaction tank can be carried out in the same manner as before except that the biological treatment is performed at pH 8 or higher.
[0023]
More specifically, the treatment is performed at a pH of 8 or higher in the biological reaction tank 22 of the ultrapure water production system as shown in FIG.
[0024]
For pH adjustment of the biological reaction tank, a known pH adjusting agent such as sodium hydroxide, potassium hydroxide, hydrochloric acid or sulfuric acid may be used, and there is no particular limitation on the place where pH adjustment is performed. For example, in addition to adding the pH adjusting agent directly to the biological reaction tank, the pH adjusting agent may be added to the pipe on the introduction side.
[0025]
If the adjusted pH of the biological reaction tank is less than 8, the oxidation of ammonia to nitrous acid is not sufficiently promoted. However, if this pH is too high, the load on the subsequent apparatus increases. It is preferably about 8-9.
[0026]
In order to perform aerobic biological treatment, this biological reaction tank supplies oxygen by means such as aeration as necessary. The oxygen supply amount is set to an amount that DO of outlet water of the bioreactor is greater than or equal to 2 ppm. In addition, as a means for supplying oxygen to the biological reaction tank, in addition to aeration such as air or pure oxygen, water in which DO is increased by dissolving oxygen under pressure may be supplied. Necessary oxygen is supplied.
[0027]
There is no particular limitation on the type of the biological reaction tank, and it may be a fixed bed or fluidized bed type in which an oligotrophic bacterium is supported on activated carbon, a sponge carrier or a ceramic carrier.
[0028]
The treatment temperature of this biological reaction tank is preferably 25 to 35 ° C., particularly 30 to 35 ° C., from the viewpoint of the decomposition efficiency of organic matter and the oxidation efficiency of ammonia to nitrous acid.
[0029]
In general, the biological treatment at pH 8 or higher can oxidize almost all the ammonia nitrogen in the recovered water to nitrous acid, and the organic matter in the recovered water can be decomposed by 90% or more.
[0030]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0031]
Examples 1 and 2 and Comparative Examples 1 and 2
Simulated wastewater (conductivity 100 μS / cm) in which TOC (acetic acid): 3 ppm, NH 4 —N: 5 ppm, KH 2 PO 4 : 0.3 ppm was added to demineralized water as raw water was passed through the biological reaction tank. The biologically treated water was sequentially passed through a UF membrane separator (bacterial cell separator) and an RO membrane separator. In addition, the aeration in a biological reaction tank was performed so that DO of the outlet water of a biological reaction tank might be 3 ppm.
[0032]
As a result, the quality of UF membrane treated water and RO membrane treated water was as shown in Table 1.
[0033]
[Table 1]
Figure 0003721871
[0034]
In Examples 1 and lapse of days changes in lapse of days changes and conductivity of the RO membrane treated water NO 2 -N + NO 3 -N and TOC of UF membrane treated water of Comparative Example 1 FIG. 3 (a) ~ (c) It was as shown in.
[0035]
From the results of Examples and Comparative Examples, by setting the pH of the biological reaction tank to 8 or more, the nitrous acid state of ammonia nitrogen was removed together with the removal of TOC without any adverse effect on the TOC removal in the biological reaction tank. It is clear that oxidation to nitrogen (or nitrate nitrogen) can be performed, and nitrite nitrogen (or nitrate nitrogen) generated in this biological reaction tank can be efficiently removed by the RO membrane.
[0036]
【The invention's effect】
As described above in detail, according to the method for producing ultrapure water of the present invention, the water to be treated such as the discharged water from the semiconductor production process is treated with ultrapure water that includes a membrane treatment apparatus and an ion exchange tower that incorporates an ion exchange resin. It is treated with a water treatment means, a biological reaction tank for biological treatment in the presence of a microorganism energy source and a nutrient source, and a biological treatment means having a cell separator into which treated water from the biological reaction tank is introduced. In a method for producing pure water, in a biological reaction tank, organic substances can be decomposed and removed, and ammonia can be oxidized to nitrous acid. The nitrous acid generated in this biological reaction tank can be efficiently removed by an RO membrane separator. By removing it, high quality treated water can be obtained. For this reason, since the water quality of RO membrane treated water is greatly improved, it is possible to reduce the load on the ion exchange resin tower at the latter stage of the RO membrane separation apparatus, and the exchange frequency of the ion exchange resin is reduced. Can improve the driving efficiency.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a general ultrapure water production system.
FIG. 2 is a system diagram of a system described in Japanese Patent No. 2130384.
FIG. 3 is a graph showing changes over time in NO 2 —N + NO 3 —N and TOC of UF membrane treated water of Example 1 and Comparative Example 1 and changes in conductivity of RO membrane treated water.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Primary pure water system 2 Secondary pure water system 3 Waste water collection system 4 Use point 5 Pretreatment system 13 RO membrane separation apparatus 15 Ion exchange apparatus 22 Biological reaction tank 23 Cell separator

Claims (1)

半導体製造工程からの排出水、工水、市水又は井水よりなる、アンモニア態窒素を含む被処理水を、膜処理装置及びイオン交換樹脂を内蔵したイオン交換塔を備える超純水処理手段と、微生物のエネルギー源及び栄養源の存在下に生物処理する生物反応槽及び該生物反応槽からの処理水が導入される菌体分離器を備える生物処理手段とで処理して超純水を製造する方法において、
該生物反応槽における生物処理をｐＨ８以上で、かつ、生物処理した水のＤＯが２ｐｐｍ以上となるように酸素を供給して行い、得られたＮＨ ４ −Ｎ濃度が１ｐｐｍ以下の生物処理した水を逆浸透膜濾過し、逆浸透膜濾過した水を前記イオン交換塔で処理することを特徴とする超純水の製造方法。Ultrapure water treatment means comprising an ion exchange tower containing a membrane treatment device and an ion exchange resin, treated water containing ammonia nitrogen, which is drained water from a semiconductor manufacturing process, industrial water, city water or well water To produce ultrapure water by treatment with a biological reaction vessel for biological treatment in the presence of an energy source and nutrient source of microorganisms and a biological treatment means equipped with a cell separator into which treated water from the biological reaction vessel is introduced In the way to
Biological treatment in the biological reaction tank is carried out by supplying oxygen so that the biological treatment water has a pH of 8 or more and DO of the biological treatment water is 2 ppm or more, and the resulting NH 4 -N concentration is 1 ppm or less. Is subjected to reverse osmosis membrane filtration, and the water subjected to reverse osmosis membrane filtration is treated in the ion exchange tower .
JP21556299A 1999-07-29 1999-07-29 Production method of ultra pure water Expired - Fee Related JP3721871B2 (en)

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