JP4528643B2 - How to reuse acid backwash wastewater - Google Patents
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- JP4528643B2 JP4528643B2 JP2005026094A JP2005026094A JP4528643B2 JP 4528643 B2 JP4528643 B2 JP 4528643B2 JP 2005026094 A JP2005026094 A JP 2005026094A JP 2005026094 A JP2005026094 A JP 2005026094A JP 4528643 B2 JP4528643 B2 JP 4528643B2
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Description
本発明は、膜を酸逆洗した際に発生する酸逆洗排水の再利用方法に関するものである。 The present invention relates to a method for reusing acid backwash wastewater generated when a membrane is backwashed with acid.
河川水や湖沼水などを水源とする上水製造プロセスにおいては、膜ろ過が普及している。膜としては例えば細孔径が0.1μmのろ過面を備えたセラミック膜が用いられ、原水には予めポリ塩化アルミニウム(PAC),ポリシリカ鉄(PSI)等の無機系の凝集剤が添加・混合されたうえ膜に送られ、膜ろ過される。PACはアルミニウム系の凝集剤であり、PSIは鉄系の凝集剤である。 Membrane filtration is widely used in the water production process using river water, lake water, or the like as a water source. For example, a ceramic membrane having a filtration surface with a pore size of 0.1 μm is used as the membrane, and an inorganic flocculant such as polyaluminum chloride (PAC) or polysilica iron (PSI) is previously added and mixed in the raw water. In addition, it is sent to the membrane and filtered. PAC is an aluminum-based flocculant, and PSI is an iron-based flocculant.
しかし運転を継続すると膜面には次第にSS等が堆積し、膜ろ過損失が増加してくる。そこで定期的にろ過水による逆洗を行っているが、単なる逆洗によっては除去できない堆積物を除去するため、従来から特許文献1,2に示すような希釈薬液を用いた逆洗が行われている。
However, if the operation is continued, SS and the like gradually accumulate on the membrane surface, and membrane filtration loss increases. Therefore, backwashing with filtered water is periodically performed, but in order to remove deposits that cannot be removed by simple backwashing, backwashing using a diluting chemical solution as shown in
特許文献1には、塩素を用いた膜の逆洗法が開示されている。また特許文献2には、酸とアルカリを膜に交互に注入する逆洗法が開示されている。しかし何れの文献にも逆洗排水の再利用に関する詳細な説明はなく、逆洗時に発生する逆洗排水は適切な処理を行ったうえで放流されているのが普通である。
本発明は上記した従来の問題点を解決して、逆洗時に発生する逆洗排水の成分に注目し、その再利用を図ることによって膜ろ過装置のランニングコストを低減させる手段を提供することを目的とするものである。 The present invention provides a means for solving the above-mentioned conventional problems, paying attention to the components of backwash wastewater generated during backwashing, and reducing the running cost of the membrane filtration device by reusing it. It is the purpose.
本発明者は、上水製造プロセスにおいて多用されているPAC,PSI等の無機系の凝集剤の主成分である金属が、酸逆洗排水中にどのように存在するかを調査した結果、酸逆洗排水中ではその大部分が液中に溶解しており、そのまま放流されていることを確認した。ここで酸逆洗とは特開2002-52321に公開されている方法等によって逆洗を行うものである。しかし酸逆洗排水を中性に戻すことにより液中に溶解した鉄またはアルミニウムが凝集剤としての機能を発揮することを見出した。
本発明は上記の知見に基づいてなされたものであって、無機系の凝集剤が添加された原水を膜ろ過する膜を酸逆洗した際に発生する酸逆洗排水をpH6〜8に調整し、鉄またはアルミニウムを沈降分離した上澄水を原水に返送することを特徴とするものである。
The present invention was made based on the above findings, the Sangyaku washing wastewater generated a film raw water free machine-based coagulant is added to membrane filtration upon Sangyakuarai to pH6~8 The supernatant water that has been adjusted and separated by sedimentation of iron or aluminum is returned to the raw water.
本発明によれば、酸逆洗排水をpH6〜8に調整し、無機系の凝集剤の主成分である鉄またはアルミニウムの一部を沈殿させたうえ、上澄水を原水に返送する。これにより従来は単に放流されていた酸逆洗排水を再び原水の一部として利用することができ、水資源の有効活用を図ることができる。
According to the present invention, the acid backwash waste water is adjusted to pH 6 to 8, and a part of iron or aluminum as the main component of the inorganic flocculant is precipitated, and the supernatant water is returned to the raw water. As a result, the acid backwash wastewater that has been simply discharged in the past can be used again as a part of the raw water, and water resources can be effectively utilized.
以下に図面を参照しつつ、本発明の好ましい実施形態を説明する。
図1は本発明の参考形態を模式的に示す図面である。この参考形態は本発明を上水製造プロセスに適用した例を示すもので、河川水や湖沼水などを水源とする原水は図示しない着水槽から凝集混和槽1に導入され、鉄系またはアルミニウム系等の無機系の凝集剤が添加されてフロック形成が行われる。アルミニウム系の凝集剤としてはPACや硫酸バンドが代表的なものであり、鉄系の凝集剤としては塩化第二鉄やPSIが代表的なものである。なお、凝集混和槽1に硫酸などの酸を凝集助剤として添加し、pHを7前後に調整して凝集効果を高める場合もある。
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a drawing schematically showing a reference embodiment of the present invention. This reference embodiment shows an example in which the present invention is applied to a clean water production process. Raw water using river water, lake water, or the like as a water source is introduced into an agglomeration mixing tank 1 from a landing tank (not shown), and is iron-based or aluminum-based. Inorganic flocculants such as these are added to form flocks. PAC and sulfuric acid band are typical as aluminum-based flocculants, and ferric chloride and PSI are typical as iron-based flocculants. In some cases, an acid such as sulfuric acid is added to the flocculation mixing tank 1 as a flocculation aid, and the pH is adjusted to around 7 to increase the flocculation effect.
凝集混和槽1を出た原水は膜2により膜ろ過される。この実施形態では膜2として、細孔径が0.1μmのろ過面を備えたセラミック膜が用いられているが、膜2はこれに限定されるものではなく、高分子膜であっても差し支えない。膜ろ過水は上水池に貯留され、塩素を添加されたうえで水道水として供給される。
The raw water leaving the coagulation mixing tank 1 is membrane filtered by the
膜2は定期的に逆洗されるが、通常の逆洗では除去しきれない堆積物を膜面から溶出させるために、酸を含んだ水を用いて酸逆洗が行われる。その際に生じる酸逆洗排水は逆洗排水槽3に貯留され、重力沈降分離が行われる。しかし酸逆洗排水はpHが例えば4程度の酸性水であり、多くの金属成分は液中に溶解しているために沈降性が悪いのが普通である。例えば、凝集剤としてPACを用いた系において逆洗排水槽3の上澄水を分析すると、28.5mg/Lのアルミニウムが含有されていたが、そのうち25.6mg/Lは溶解性である。そして上澄水の濁度は6.4と高い。
Although the
本発明ではこのような逆洗排水槽3の上澄水を、返送水路4を通じて凝集混和槽1に返送し、原水中に戻す。前記したように凝集混和槽1ではpHは中性域となるため、酸逆洗排水中に含まれている溶解性のアルミニウムや鉄は、凝集剤としての機能を発揮する。表1に、実験的に酸逆洗排水をpH調整し沈降分離した上澄水のアルミニウムの含有率の変化を示す。pH6〜8の中性域にpH調整することによって大部分が非溶解性となり、沈降分離されることが分る。
In the present invention, the supernatant water of the
本参考形態では、溶解性のアルミニウムや鉄を含んだままの酸性の上澄水を凝集混和槽1に戻す。これらのアルミニウムや鉄は原水と混和されpHが中性域になることにより凝集効果を発揮するため、後述の実施例に示すように凝集剤の添加量を減少させることができる。また酸性の酸逆洗水が凝集混和槽1に返送されるので、凝集助剤としての酸添加量も削減することができる。しかし返送水量比が小さすぎると本発明の効果を得ることができず、返送水量比が大きすぎると原水の濁度が上昇することとなる。実験によれば返送水量比(返送水量/原水量の比)は1/10よりも少なくすることが好ましく、最も好ましいのは1/50〜1/200程度である。
In this reference embodiment , acidic supernatant water containing soluble aluminum and iron is returned to the coagulation mixing tank 1. Since these aluminum and iron are mixed with raw water and the pH is in a neutral range to exert a coagulation effect, the amount of coagulant added can be reduced as shown in the examples described later. Moreover, since acidic acid backwash water is returned to the coagulation-mixing tank 1, the amount of acid added as the coagulant aid can also be reduced. However, if the returned water amount ratio is too small, the effects of the present invention cannot be obtained, and if the returned water amount ratio is too large, the turbidity of the raw water will increase. According to experiments, the ratio of the amount of returned water (ratio of the amount of returned water / raw water) is preferably less than 1/10, and most preferably about 1/50 to 1/200.
また本発明では、酸逆洗排水をpH6〜8に調整し、鉄またはアルミニウムを沈降分離した上澄水を原水に返送する。逆洗排水をpH:6〜8に調整したうえ沈降分離した上澄水質は原水並であるため、これを原水1に返送することで逆洗排水の放流量を減少させるとともに、水資源としての有効利用を図ることができる。 Moreover, in this invention , the acid backwash waste_water | drain is adjusted to pH 6-8, and the supernatant water which settled and separated iron or aluminum is returned to raw | natural water. Since the quality of the supernatant water settled and separated by adjusting the pH of the backwash wastewater to 6 to 8 is the same as that of the raw water, it is returned to the raw water 1 to reduce the discharge amount of the backwash wastewater and as a water resource. Effective use can be achieved.
図1に示した構造の上水製造プロセスの実験装置を製作し、濁度0.9、TOC(トータルオーガニックカーボン)1.1mg/L、全アルミニウム0.02mg/L、溶解性アルミニウム0.01mg/Lの原水を用い本発明の効果を確認した。使用した凝集剤はPACであり、その添加量を変化させながら実験した。使用した膜は出願人会社製のセラミック膜である。 An experimental apparatus for the water production process of the structure shown in FIG. 1 was manufactured, and turbidity 0.9, TOC (total organic carbon) 1.1 mg / L, total aluminum 0.02 mg / L, soluble aluminum 0.01 mg The effect of the present invention was confirmed using / L raw water. The flocculant used was PAC, and experiments were performed while changing the amount of addition. The film used is a ceramic film manufactured by the applicant company.
図2はその結果を示すグラフであり、丸印で示す従来法では原水へのPACの添加量が15mg/Lではフロック形成が不十分でセラミック膜におけるろ過性が悪く、25mg/Lまで増加させるとろ過性が良化する。これに対して四角印で示す本発明方法(返送水量比1/100)では、PACの添加量が10mg/Lでも良好なろ過性を達成することができた。 FIG. 2 is a graph showing the results. In the conventional method indicated by circles, when the amount of PAC added to the raw water is 15 mg / L, the floc formation is insufficient and the filterability in the ceramic membrane is poor, and it is increased to 25 mg / L. And filterability improves. On the other hand, in the method of the present invention indicated by the square mark (returned water amount ratio 1/100), good filterability could be achieved even when the amount of PAC added was 10 mg / L.
また図3のグラフに示すように、従来法によっても本発明法によっても原水中の有機物の60%以上を除去することができたが、本発明法による場合の方がPACの添加量が少なくてよいことが確認された。これらの実施例の実験結果から、本発明によれば従来よりも少ないPACの添加量で、良好なろ過性とろ過水質とを達成できることが確認できた。 Further, as shown in the graph of FIG. 3, 60% or more of the organic matter in the raw water could be removed by the conventional method and the method of the present invention. It was confirmed that From the experimental results of these examples, it was confirmed that according to the present invention, good filterability and filtered water quality can be achieved with a smaller amount of PAC than conventional.
1 凝集混和槽
2 膜
3 逆洗排水槽
4 返送水路
1 Coagulation /
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JP2001129308A (en) * | 1999-11-01 | 2001-05-15 | Ebara Corp | Flocculation and precipitation facility and flocculation and precipitation method |
JP2002177963A (en) * | 2000-12-13 | 2002-06-25 | Yuji Sekine | Water cleaning treatment system and water cleaning method |
JP2003112198A (en) * | 2001-10-02 | 2003-04-15 | Ebara Corp | Method and apparatus for removing cod component in water |
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JP3735883B2 (en) * | 1995-03-08 | 2006-01-18 | 栗田工業株式会社 | Membrane separation apparatus and membrane module cleaning method |
JPH08323350A (en) * | 1995-06-02 | 1996-12-10 | Kurita Water Ind Ltd | Membrane treating device for oil-containing waste water |
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JP2001129308A (en) * | 1999-11-01 | 2001-05-15 | Ebara Corp | Flocculation and precipitation facility and flocculation and precipitation method |
JP2002177963A (en) * | 2000-12-13 | 2002-06-25 | Yuji Sekine | Water cleaning treatment system and water cleaning method |
JP2003112198A (en) * | 2001-10-02 | 2003-04-15 | Ebara Corp | Method and apparatus for removing cod component in water |
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