JP4879818B2 - Pretreatment method for seawater desalination using reverse osmosis membrane - Google Patents
Pretreatment method for seawater desalination using reverse osmosis membrane Download PDFInfo
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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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- Y02A20/124—Water desalination
- Y02A20/131—Reverse-osmosis
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Description
本発明は、逆浸透膜を用いた海水淡水化処理の前処理方法に関し、特に、供給水中に含まれる溶解性有機物の除去に有効な逆浸透膜を用いた海水淡水化処理の前処理方法に関するものである。 The present invention relates to a pretreatment method for seawater desalination using a reverse osmosis membrane, and particularly relates to a pretreatment method for seawater desalination using a reverse osmosis membrane that is effective for removing soluble organic substances contained in feed water. Is.
従来、逆浸透膜を用いた海水淡水化施設の前処理では、様々な薬品の注入と濾過を組み合わせることにより、ＲＯ膜（逆浸透膜）にダメージを与えないような水を作り出して逆浸透膜施設に供給するようにしている。
このような逆浸透膜処理の前処理方法は、従来は凝集沈澱と砂濾過を使ったものが主流であったが、特に中東での海水の水質悪化が著しく、現在では凝集剤と膜濾過を組み合わせたものが主流になりつつある。
Conventionally , in the pretreatment of seawater desalination facilities using reverse osmosis membranes, reverse osmosis membranes are created by combining various chemical injections and filtration to produce water that does not damage RO membranes (reverse osmosis membranes). Supply to facilities.
Conventionally, the pretreatment method for reverse osmosis membrane treatment used mainly coagulation sedimentation and sand filtration, but the quality of seawater deteriorated particularly in the Middle East. At present, coagulant and membrane filtration are used. The combination is becoming mainstream.
しかし、この凝集処理と膜濾過の組み合わせは、ＦＩ値（ＳＤＩ値）を下げることには寄与するが、そのままでは供給水中に溶解したフミン質のような有機物を完全には除去することができず、これら漏出した溶解性有機物質がＲＯ膜のバイオファウリングの原因となることが判っている。 However, this combination of flocculation and membrane filtration contributes to lowering the FI value (SDI value), but as it is, organic substances such as humic substances dissolved in the feed water cannot be completely removed. These leaked soluble organic substances have been found to cause biofouling of RO membranes.
フミン質の内、フミン酸は、供給水のｐＨを下げて酸性にすれば析出する。
しかし、ｐＨを６程度以下にすると、凝集剤である塩化第二鉄の鉄分がイオン化して凝集剤として作用しなくなるため、凝集させることは難しい。
フミン質の内、フルボ酸はｐＨ調整だけでは不溶化せず、殆ど凝集効果は期待できない。未凝集の溶解性有機物の一部は前処理の濾過膜を潜り抜けてＲＯ膜に到達することになる。これら漏出したフミン質がＲＯ膜のバイオファウリングの原因となると考えられる。
Of the humic substances, humic acid precipitates when the pH of the feed water is lowered to make it acidic.
However, if the pH is about 6 or less, the iron content of ferric chloride, which is an aggregating agent, is ionized and does not act as an aggregating agent.
Of the humic substances, fulvic acid is not insolubilized only by pH adjustment, and almost no aggregation effect can be expected. A part of the unaggregated soluble organic substance penetrates through the pretreatment filter membrane and reaches the RO membrane. These leaked humic substances are thought to cause biofouling of the RO membrane.
本発明は、上記従来の逆浸透膜処理の前処理方法が有する問題点に鑑み、供給水中の溶解性有機物質を安価に低減し、ＲＯ膜への負荷を減らしてバイオファウリングの発生を抑制するようにした逆浸透膜を用いた海水淡水化処理の前処理方法を提供することを目的とする。 In view of the problems of the conventional reverse osmosis membrane pretreatment method, the present invention reduces the amount of soluble organic substances in the feed water at a low cost, reduces the load on the RO membrane, and suppresses the occurrence of biofouling. An object of the present invention is to provide a pretreatment method for seawater desalination using a reverse osmosis membrane.
上記目的を達成するため、本発明の逆浸透膜を用いた海水淡水化処理の前処理方法は、取水した海水に凝集剤を混合するとともに、この凝集剤を混合した海水を逆浸透膜施設の前段で膜濾過する逆浸透膜を用いた海水淡水化処理の前処理方法において、凝集剤の投入前に酸化剤を投入して溶解性有機物質の凝集前酸化を行うに当たり、酸化剤として次亜塩素酸ナトリウムを用い、該次亜塩素酸ナトリウムの添加量をＣＯＤ ＯＨ と残留有効塩素が共に最小となるように調整するとともに、セラミックＭＦ膜又はセラミックＵＦ膜からなる膜モジュールで膜濾過されなかった戻り水を冷却した後、再度膜モジュールに循環させるようにしたことを特徴とする。 To achieve the above object, the pretreatment method of reverse osmosis desalination process using the present invention is to mix the flocculant into the water intake and sea water, reverse osmosis membrane sea water mixed with the coagulant In the pretreatment method of seawater desalination using a reverse osmosis membrane that performs membrane filtration at the front stage of the facility, an oxidant is added before the flocculant is added to oxidize the soluble organic substance as an oxidant. Using sodium hypochlorite, the amount of sodium hypochlorite added is adjusted so that both COD OH and residual effective chlorine are minimized, and membrane filtration is performed with a membrane module comprising a ceramic MF membrane or a ceramic UF membrane. The return water that has not been cooled is cooled and then circulated through the membrane module again .
本発明の逆浸透膜を用いた海水淡水化処理の前処理方法によれば、溶解性有機物を酸化し改質することにより凝集し易くし、この凝集した溶解性有機物を濾過することにより供給水中の溶解性有機物質を安価に低減することができ、これにより、ＲＯ膜への負荷を減らしてバイオファウリングの発生を抑制することができる。 According to the pretreatment method of seawater desalination using the reverse osmosis membrane of the present invention , the soluble organic matter is easily aggregated by oxidizing and reforming, and the aggregated soluble organic matter is filtered to supply water. It is possible to reduce the soluble organic substance at low cost, thereby reducing the load on the RO membrane and suppressing the occurrence of biofouling.
そして、酸化剤として次亜塩素酸ナトリウムを用い、この次亜塩素酸ナトリウムの添加量をブレークポイントとなるよう調整することにより、比較的安価な薬品でしかも短い接触時間にて凝集前酸化を実施することができる。 And by using sodium hypochlorite as the oxidant and adjusting the amount of sodium hypochlorite added to be a breakpoint, pre-aggregation oxidation is performed with a relatively inexpensive chemical and in a short contact time. can do.
以下、本発明の逆浸透膜を用いた海水淡水化処理の前処理方法の実施の形態を、図面に基づいて説明する。 Hereinafter, an embodiment of a pretreatment method for seawater desalination using the reverse osmosis membrane of the present invention will be described with reference to the drawings.
図１に、本発明の逆浸透膜を用いた海水淡水化処理の前処理方法の一実施例を示す。 In FIG. 1, one Example of the pre-processing method of the seawater desalination process using the reverse osmosis membrane of this invention is shown.
この逆浸透膜を用いた海水淡水化処理の前処理方法は、取水した海水に凝集剤を混合するとともに、この凝集剤を混合した海水を逆浸透膜施設の前段で膜濾過する逆浸透膜を用いた海水淡水化処理の前処理方法において、凝集剤を投入する前に酸化剤を投入し、凝集前酸化を行うことにより溶解性有機物質の改質を行う。
酸化剤によって溶解性有機物質の分子は小さくなるが、改質効果によって凝集し易くすることができる。
Pretreatment method of seawater desalination process using the reverse osmosis membrane is configured to mix the flocculant into the water intake and sea water, reverse osmosis membrane filtration of the sea water mixed with the coagulant in the preceding stage of reverse osmosis membrane facility In a pretreatment method for seawater desalination using a membrane , an oxidizing agent is added before the flocculant is charged, and the soluble organic substance is modified by performing the pre-flocculation oxidation.
The molecules of the soluble organic substance are reduced by the oxidizing agent, but can be easily aggregated by the modification effect.
酸化剤として用いることのできる物質として、本実施例では次亜塩素酸ナトリウムを用いた例を示す。
次亜塩素酸ナトリウムの添加量は、図２に示すように、ＣＯＤＯＨと残留有効塩素の両者が、共に最小となるブレークポイント付近で平衡に達する量を算出して決定する。
また、次亜塩素酸ナトリウム添加時の反応時間は、図３に示すように２分程度、安全を見て５分程度取ることが好ましい。
このとき、ｐＨを６程度以下にすると凝集剤である塩化第二鉄の鉄分がイオン化して凝集剤として作用しなくなるため、凝集剤添加前の供給水のｐＨを約６〜８の範囲で調整する。
In this example, sodium hypochlorite is used as a substance that can be used as an oxidizing agent.
As shown in FIG. 2, the amount of sodium hypochlorite added is determined by calculating the amount at which COD OH and residual effective chlorine both reach equilibrium near the minimum break point.
Further, the reaction time when adding sodium hypochlorite is preferably about 2 minutes as shown in FIG. 3 and about 5 minutes for safety.
At this time, if the pH is reduced to about 6 or less, the iron content of ferric chloride, which is a coagulant, is ionized and does not act as a coagulant. To do.
一方、凝集剤の塩化第二鉄の量は、図４に示すように、５ｍｇ−Ｆｅ／Ｌ程度が妥当である。
以上の組み合わせを行い、凝集したものをＭＦ膜やＵＦ膜にて膜濾過し、濾過後の水をＲＯ膜への供給水とする。
また、濾過膜としては、化学的及び物理的に安定したセラミックＭＦ膜もしくはセラミックＵＦ膜を用いるのが望ましい。
On the other hand, the amount of ferric chloride as the flocculant is appropriate to be about 5 mg-Fe / L as shown in FIG.
The above combination is performed, and the aggregated material is subjected to membrane filtration with an MF membrane or UF membrane, and the filtered water is used as the supply water to the RO membrane.
As the filter membrane, to use chemically and physically stable ceramic MF membrane or ceramic UF membrane is desirable.
したがって、本実施例では下記のような処理過程を採用した。
１．上流側の混合攪拌槽１にて、酸化剤として次亜塩素酸ナトリウムを適量添加するとともに、急速攪拌を行い、ブレークポイント付近の濃度となるように調整する。
この場合、攪拌後、５分程度接触時間が取れるように混合攪拌槽１の容積を決定する。２．次亜塩素酸ナトリウムによる酸化処理後、下流側の混合攪拌槽２にて、凝集剤の塩化第二鉄を５ｍｇ−Ｆｅ／Ｌ程度投入し、急速攪拌する。
この場合、攪拌後、１分程度接触時間が取れるように混合攪拌槽２の容積を決定する。３．ＭＦ膜又はＵＦ膜を用いた膜モジュール３にて濾過を行い、濾過後の水をＲＯ膜に供給する。
Therefore, in this embodiment, the following process is adopted.
1. In the upstream mixing and stirring tank 1, an appropriate amount of sodium hypochlorite is added as an oxidizing agent, and rapid stirring is performed to adjust the concentration to be near the breakpoint.
In this case, the volume of the mixing and stirring tank 1 is determined so that a contact time of about 5 minutes can be obtained after stirring. 2. After the oxidation treatment with sodium hypochlorite, about 5 mg-Fe / L of the coagulant ferric chloride is charged in the mixing and stirring
In this case, the volume of the mixing and stirring
かくして、本実施例の逆浸透膜を用いた海水淡水化処理の前処理方法によれば、取水した海水に凝集剤を混合するとともに、この凝集剤を混合した海水を逆浸透膜施設の前段で膜濾過する逆浸透膜を用いた海水淡水化処理の前処理方法において、凝集剤の投入前に酸化剤を投入して溶解性有機物質の凝集前酸化を行うことから、溶解性有機物を酸化し改質することにより凝集し易くし、この凝集した溶解性有機物を濾過することにより供給水中の溶解性有機物質を安価に低減することができ、これにより、ＲＯ膜への負荷を減らしてバイオファウリングの発生を抑制することができる。
また、酸化剤として次亜塩素酸ナトリウムを用い、この次亜塩素酸ナトリウムの添加量をブレークポイント付近となるよう調整することにより、比較的安価な薬品でしかも短い接触時間にて凝集前酸化を実施することができる。
Thus, according to the pretreatment method of seawater desalination treatment using a reverse osmosis membrane of the present embodiment, the inventors mixed the coagulant intake with sea water, the reverse osmosis membrane facility sea water mixed with the coagulant In the pretreatment method of seawater desalination using a reverse osmosis membrane that performs membrane filtration in the previous stage, the oxidant is added before the flocculant is added to oxidize the soluble organic substance. Oxidizing and reforming makes it easy to agglomerate, and filtering this agglomerated soluble organic matter can reduce the soluble organic substance in the feed water at a low cost, thereby reducing the load on the RO membrane. Generation of biofouling can be suppressed.
In addition, by using sodium hypochlorite as the oxidant and adjusting the amount of sodium hypochlorite to be close to the breakpoint, it is possible to oxidize before aggregation with a relatively inexpensive chemical and in a short contact time. Can be implemented.
以上、本発明の逆浸透膜を用いた海水淡水化処理の前処理方法について、その実施例に基づいて説明したが、本発明は上記実施例に記載した構成に限定されるものではなく、その趣旨を逸脱しない範囲において適宜その構成を変更することができる。 As mentioned above, although the pretreatment method of the seawater desalination process using the reverse osmosis membrane of the present invention was explained based on the example, the present invention is not limited to the configuration described in the above example, The configuration can be changed as appropriate without departing from the spirit of the invention.
本発明の逆浸透膜を用いた海水淡水化処理の前処理方法は、溶解性有機物を酸化して凝集濾過することにより、供給水中の溶解性有機物質を安価に低減し、ＲＯ膜への負荷を減らしてバイオファウリングの発生を抑制するという特性を有していることから、ＲＯ膜を使用する海水淡水化施設に好適に適用することができる。 The pretreatment method for seawater desalination using the reverse osmosis membrane of the present invention reduces the soluble organic substances in the supply water at low cost by oxidizing the soluble organic matter and performing coagulation filtration, and the load on the RO membrane from that has a characteristic of suppressing generation of biofouling reduced, it can be suitably applied to a seawater desalination facility using the RO membrane.
１ 上流側の混合攪拌槽
２ 下流側の混合攪拌槽
３ 膜モジュール
DESCRIPTION OF SYMBOLS 1 Upstream mixing
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