JP4111880B2

JP4111880B2 - Aggregation precipitation apparatus and control method thereof

Info

Publication number: JP4111880B2
Application number: JP2003187200A
Authority: JP
Inventors: 友明宮ノ下; 裕一郎鳥羽; 孝雄長谷川; 康浩江原
Original assignee: Organo Corp; Suido Kiko Kaisha Ltd
Current assignee: Organo Corp; Suido Kiko Kaisha Ltd
Priority date: 2003-06-30
Filing date: 2003-06-30
Publication date: 2008-07-02
Anticipated expiration: 2023-06-30
Also published as: JP2005021742A

Description

【０００１】
【発明の属する技術分野】
本発明は、浄水処理、工業用水処理、下水処理、排水処理等において、凝集剤と沈降促進材とを用いて凝集沈澱処理による水処理を行う凝集沈澱装置およびその制御方法に関する。
【０００２】
【従来の技術】
原水中の懸濁物質を無機凝集剤と高分子凝集剤と沈降促進材（例えば、粒状物、とくに砂）の添加によりフロック状に凝集させる凝集槽と、凝集槽から導入される被処理水中の凝集物を沈澱させ処理水と沈澱物とに分離する沈澱槽と、沈澱槽から沈澱物を引き抜き、引き抜かれた沈澱物を汚泥と沈降促進材とに分離して分離された沈降促進材を凝集槽に戻す引き抜き分離ラインとを備えた沈降促進材添加凝集沈澱装置（たとえば、特許文献１）において、高分子凝集剤として活性ケイ酸や鉄シリカ凝集剤（例えば、水道機工（株）製のＰＳＩ）等の無機高分子凝集剤を用いることがある。
【０００３】
上記ＰＳＩの製造法は、特許文献２、特許文献３、特許文献４に記載されているように、市販の水ガラス（ケイ酸ソーダ）を水で希釈し、そこに硫酸（塩酸、硝酸でも可）を加えてｐＨ４程度に調整し、緩やかに撹拌を行うことによって重合ケイ酸（：ポリシリカ）を生成し、更にそこに塩化第二鉄を加えるというものである。通常製造されているＳｉＯ₂含有率２．２％程度のＰＳＩであれば、常温で１ヶ月以上品質は安定している。
【０００４】
【特許文献１】
特開２０００−３３４２０９号公報
【特許文献２】
特許第１７８４３７３号公報
【特許文献３】
特許第２７３２０６７号公報
【特許文献４】
特開２００１−７０７０８号公報
【０００５】
【発明が解決しようとする課題】
ところが、上記のような無機高分子凝集剤を使用する場合、沈降促進材の濃度が高すぎると、フロック形成時に沈降促進材が十分に取り込まれない上、フロックを破砕してしまうことが分かった。沈降促進材の濃度が低いと、フロックの密度が高くならないため、沈澱槽にて十分に固液分離されない。また、フロックが破砕されると、沈澱槽で処理水と沈澱物とを分離する際に、目標とする分離性能が得られない。従って、とくに無機高分子凝集剤を使用する場合には、従来よりも厳密に沈降促進材の濃度を制御する必要がある。
【０００６】
ところで、無機高分子凝集剤の分子量は、重合条件（ｐＨ、温度、Ｎａ、Ｋなどの塩濃度、時間）によって決まる。ｐＨや温度、時間は製造装置の制御により概ね一定であるが、気温や湿度、装置の設置条件などによりいくらかは変動する。またＮａ、Ｋなどの塩濃度は、原料の品質などにより多少ばらつきがある。従って無機高分子凝集剤の分子量は常に一定とは限らない。また、意図的に重合条件を変化させて、無機高分子凝集剤の分子量を変化させる場合もある。
【０００７】
参考として、有機高分子凝集剤の場合、分子量８００万〜１，６００万（オルフロック）で、凝集槽における最適沈降促進材濃度は０．５〜２．０％である。これに対し無機高分子凝集剤の場合、分子量数十万〜百万（ＰＳＩでは４５万〜５５万）で、凝集槽における最適沈降促進材濃度は０．２〜０．５％であり、相当狭い最適範囲となっている。有機高分子凝集剤の場合、最適範囲は広いものの、とくにアクリルアミドモノマーの問題が残されており、水道用途での使用には未だ躊躇しているのが現状である。
【０００８】
従って、無機高分子凝集剤を使用することが望まれる場合が多い。水面積負荷が１〜５ｍ／ｈの通常の凝集沈澱処理であれば、無機高分子凝集剤の分子量のばらつきが±１０％程度あっても処理にほとんど影響を与えないが、水面積負荷２０〜５０ｍ／ｈと通常の凝集沈澱処理の１０倍以上となる沈降促進材添加凝集沈澱処理においては、処理水水質、特に濁度に対して影響が出てくる。
【０００９】
そこで本発明の課題は、とくに沈降促進材添加凝集沈澱処理において、処理の良否への影響度が高い無機高分子凝集剤の分子量に応じて、沈降促進材の濃度を最適に制御可能とし、安定して優れた処理性能を発揮できるようにすることにある。
【００１０】
【課題を解決するための手段】
上記課題を解決するために、本発明に係る凝集沈澱装置の制御方法は、原水中の懸濁物質を無機凝集剤と無機高分子凝集剤と沈降促進材の添加により凝集させる凝集槽と、凝集槽から導入される被処理水中の凝集物を沈澱させ処理水と沈澱物とに分離する沈澱槽と、沈澱槽から沈澱物を引き抜き、引き抜かれた沈澱物を汚泥と沈降促進材とに分離して分離された沈降促進材を凝集槽に戻す引き抜き分離ラインとを備えた沈降促進材添加凝集沈澱装置における制御方法であって、前記無機高分子凝集剤の分子量を測定し、その分子量に応じて凝集槽内の沈降促進材の濃度を制御することを特徴とする方法からなる。
【００１１】
この制御方法においては、上記無機高分子凝集剤の分子量を、該無機高分子凝集剤の注入前の粘度の測定により、測定することができる。すなわち、後述の如く、実際に行われる無機高分子凝集剤の注入量の範囲においては、該無機高分子凝集剤の分子量と粘度とが、実質的に比例関係、あるいは実質的に１：１の対応関係にあることが確認されており、粘度計などを用いて粘度を測定することにより、実質的に無機高分子凝集剤の分子量を測定することができる。
【００１２】
また、この制御方法においては、原水の濁度に応じて上記無機高分子凝集剤の注入率を制御することが好ましい。原水の濁度が高ければ、注入すべき最適な無機高分子凝集剤の注入率も高くなる。また、この無機高分子凝集剤の注入率に応じて凝集槽内の沈降促進材の濃度を制御することが好ましい。つまり、原水の濁度が高く、無機高分子凝集剤の注入率が高くなれば、それだけ分離すべき原水中の懸濁物質も多いわけであるから、より多量に凝集フロックを形成して沈澱分離に供する必要があるので、これに対応して沈降促進材の濃度を制御することが好ましい。この無機高分子凝集剤は、無機凝集剤と別々に注入することもできるし、無機凝集剤と無機高分子凝集剤を予め混合した凝集剤を注入することもできる。前述のＰＳＩは、このように予め混合した形態の凝集剤の一種である。このように予め混合した凝集剤であっても、無機凝集剤自体には殆ど粘度がないので、混合した凝集剤の粘度を測定すれば、その測定値は実質的に無機高分子凝集剤の粘度とみなすことができ、その粘度に対応した無機高分子凝集剤の分子量を測定することができる。
【００１３】
本発明に係る凝集沈澱装置は、上記のような制御を実施可能な構成を備えたもので、原水中の懸濁物質を無機凝集剤と無機高分子凝集剤と沈降促進材の添加により凝集させる凝集槽と、凝集槽から導入される被処理水中の凝集物を沈澱させ処理水と沈澱物とに分離する沈澱槽と、沈澱槽から沈澱物を引き抜き、引き抜かれた沈澱物を汚泥と沈降促進材とに分離して分離された沈降促進材を凝集槽に戻す引き抜き分離ラインとを備えた沈降促進材添加凝集沈澱装置であって、前記無機高分子凝集剤の分子量を測定し、その分子量に応じて凝集槽内の沈降促進材の濃度を制御する手段を有することを特徴とするものからなる。
【００１４】
上記のような本発明に係る凝集沈澱装置およびその制御方法においては、無機高分子凝集剤の分子量を、粘度測定等を介して測定し、その分子量に対応した最適な凝集槽内沈降促進材の濃度に制御される。前述の如く、無機高分子凝集剤の分子量に対応する沈降促進材の最適な濃度範囲は比較的狭い範囲に限定されるが、本発明に係る制御により、確実に目標とする濃度範囲内に納められることになる。したがって、沈降促進材を取り込むことによる凝集フロックの形成が良好に行われるとともに、沈降促進材の濃度が高すぎる場合のフロック破砕も適切に防止されることになり、目標とする凝集沈澱処理性能、ひいては優れた処理水水質が得られるとともに、その性能が安定して維持されることになる。
【００１５】
【発明の実施の形態】
以下に、本発明の望ましい実施の形態を、図面を参照して説明する。
図１は、本発明の一実施態様に係る凝集沈澱装置１を示している。凝集沈澱装置１は、原水供給ライン２を介して供給される原水３を受け入れる凝集槽４と、凝集槽４から導入される被処理水中の凝集物を沈澱させ処理水６と沈澱物７とに分離する沈澱槽５とを有している。凝集槽４には、その入口に一体に形成された注入部８にて、無機凝集剤と無機高分子凝集剤が注入され、本実施態様では、これらが混合された無機・高分子混合凝集剤９（たとえば、前述のＰＳＩ）の形態でポンプ１０により注入されるようになっている。この凝集剤９の注入ライン１１には、バイパス部を介して無機高分子凝集剤の粘度を測定する粘度計１２が設けられている。混合凝集剤９であっても、無機凝集剤にはほとんど粘度がないので、混合凝集剤９の粘度測定は、実質的に無機高分子凝集剤の粘度測定となる。
【００１６】
凝集槽４には攪拌機１３が設けられており、槽内が攪拌機１３により攪拌されつつ、原水中の懸濁物質が、上記無機・高分子混合凝集剤９の添加と、沈降促進材回収・供給装置１４からの沈降促進材１５の添加により、フロック状に凝集される。沈降促進材１５は、粒状物、とくに本実施態様では、粒径が所定の範囲に調整された砂からなる。この沈降促進材１５の添加量は、沈澱槽５から引き抜きポンプ１６、引き抜き分離ライン１７を介して送られてきた沈澱物７を砂・汚泥分離サイクロン１８で分離した沈降促進材１５（砂）を凝集槽４内へ添加するものと、必要に応じて貯留タンク１９から添加されるものからなる。貯留タンク１９は、サイクロン１８からの分離・回収沈降促進材１５のうち凝集槽４内へ添加しない余剰の沈降促進材１５を貯留するものである。余剰の沈降促進材１５の貯留タンク１９への供給は、コントロール弁２０によって制御され、貯留タンク１９から凝集槽４への添加は、コントロール弁２１によって制御される。なお、貯留タンク１９は新たな沈降促進材１５の補充タンクとしても併用される。砂・汚泥分離サイクロン１８で分離された汚泥は、汚泥排水管２２を介して排出される。なお、沈澱槽５には、傾斜板２３が設けられており、処理水６と沈澱物７との分離効率が高められているとともに、処理水６側への汚泥の流出が抑えられている。
【００１７】
凝集槽４には、固形分濃度計２４が付設されており、実質的に凝集槽４内における沈降促進材１５の濃度を測定できるようになっている。固形分濃度計２４からの測定信号は、制御装置としての演算器２５に送られる。演算器２５からは、コントロール弁２０、２１に作動信号が送られ、それによって貯留タンク１９から凝集槽４内への沈降促進材１５の添加量が制御されるとともに、サイクロン１８から凝集槽４内への沈降促進材１５の添加量およびサイクロン１８から貯留タンク１９への沈降促進材１５の分岐供給量が制御され、この制御を介して凝集槽４内における沈降促進材１５の濃度が制御される。この沈降促進材１５の濃度制御には、粘度計１２からの無機高分子凝集剤の粘度測定信号が用いられ、無機高分子凝集剤の粘度に応じた沈降促進材１５の濃度に制御される。
【００１８】
なお、上記実施態様では、無機・高分子混合凝集剤９を凝集槽４内、とくにその入口部の注入部８に注入するようにしたが、図１に２点鎖線で示すように、原水供給ライン２にラインミキサー２６を配置してその直前に注入するようにすることもできる。また、ラインミキサー２６に代えて攪拌機を備えた混和槽を設置してもよい。
【００１９】
このように構成された凝集沈澱装置１においては、無機高分子凝集剤の分子量が、凝集槽４へ注入前の無機・高分子混合凝集剤９の粘度測定を通して、測定され、測定された無機高分子凝集剤の分子量に応じて、凝集槽４内の沈降促進材１５の濃度が、予め把握された最適な濃度に制御される。また、この制御は、導入される原水３の濁度に応じて無機・高分子混合凝集剤９（とくに無機高分子凝集剤）の注入率を適宜変更制御し、さらに、無機・高分子混合凝集剤９（とくに無機高分子凝集剤）の注入率に応じて凝集槽４内の沈降促進材１５の濃度を制御することにより、より最適な沈降促進材濃度に制御できる。沈降促進材１５の最適濃度範囲は比較的狭いものの、上記のような制御により確実に目標とする範囲内への制御が可能となる。しかも、この制御を連続的に行うことにより、常時最適な条件で良好な凝集沈澱処理を継続することができ、安定して優れた処理水水質を得ることができる。
【００２０】
【実施例】
図１に示した装置を用いて、本発明に係る凝集沈澱装置およびその制御方法による効果を確認した。
ダム水を原水とする浄水処理において、急速砂ろ過の前処理として、本発明による凝集沈澱処理を行った。図１に示した装置を用いたが、その装置仕様、運転条件は以下の通りである。
【００２１】
・処理水量：7.0m³/h（線速度LV＝30m/h）
・原水濁度：カオリンを用いて100度±10度に調整した
・凝集沈澱装置：凝集槽；0.44m³
沈澱槽；0.50m³（表面積0.25m²、0.5m×0.5m）
汚泥循環量；0.5m³/h
・凝集剤：ポリシリカ鉄凝集剤（ＰＳＩ）
Fe₂O₃含有率1.0%、SiO₂含有率2.2%、分子量45万〜55万daltonの無機高分子凝集剤を含む。
注入率40mg/L（無機凝集剤と無機高分子凝集剤の混合物の合計）で一定とした。
（ＰＳＩは、市販の水ガラス（ケイ酸ソーダ）をSi濃度3.0%となるように市水で希釈し、そこに希硫酸を加えてpH4.0 ±0.2 に調整し、温度を30〜40℃に保ちながら１時間緩やかに撹拌を行うことによって重合ケイ酸（＝ポリシリカ）を生成し、更にそこにFeCl₃濃度38%の塩化第二鉄をSiとFeのモル比、Si：Fe＝３：１となるように加えことにより得られる無機凝集剤と無機高分子凝集剤の混合物である。そのＰＳＩを貯槽に移し、通水実験に用いた。）
【００２２】
・粘度計：ＰＳＩの粘度を測定、回転式粘度計（サンプルにローターを浸し、ローターをモータで回転させ一定速度にした時に発生するトルク（力）をバネのねじれ（トルクセンサー）で測定し粘度を求めもの。ここでは、ブックフィールド社製ＣＡＰ１０００を用いた。粘度計の指示値は電気的信号により取り出すことが可能であり、その信号を演算器に送信し制御を行った。ところで、粘度計には超音波式、落球式、振動式など様々な測定方式があり、１〜100 mPa・sの範囲を測定でき、指示値を電気信号で取り出せるものであればどのようなものを用いてもよい。例えば、西華産業製超音波粘度計ＦＵＶ−１などがある。）
・固形分濃度計；超音波式、超音波工業社製固形分濃度計を用いた。空気中、液体中あるいは固体中を伝わる超音波の伝播速度を測定し、演算処理し濃度として表すものである。
【００２３】
粘度計により得られたＰＳＩの粘度と限外膜分離法により得られたＰＳＩ中の無機高分子凝集剤の平均分子量との関係を調べたところ、分子量は粘度の0.3乗に比例して変化することが分かった。ただし、温度、濃度が一定条件の場合である。従って、温度補正、濃度補正を行う必要があるが、本実施例の場合、24℃±１℃の恒温ジャケット内に粘度計を設置しているので、温度補正は行っていない。また濃度補正は、Fe₂O₃含有率1.0%、SiO₂含有率2.2%で一定としているため必要ない。
【００２４】
粘度計の指示値をもって分子量の変化と捉え、凝集槽内の沈降促進材濃度を変化させた。ＰＳＩ中の無機高分子凝集剤の平均分子量と最適な沈降促進材濃度との関係は、事前の実験により確認しておいた。その関係を表１に示す。
【００２５】
【表１】

【００２６】
上記において、粘度計指示値13.0未満ないし30.5以上となった場合は、異常と見なし運転停止とする。この凝集槽内での最適沈降促進材濃度を決定するために行った予備実験においては、原水濁度が一定の条件で、平均分子量45万、47万、49万、51万、53万、55万について、凝集槽内での沈降促進材濃度を変化させ、沈澱処理水濁度が最小となる時の沈降促進材濃度を最適促進材濃度とした。例えば、原水濁度はカオリンを用いて100度±10度とし、ＰＳＩ中の無機高分子凝集剤の平均分子量が51万でＰＳＩ注入率40mg/Lとした場合、凝集槽での最適沈降促進材濃度を0.30〜0.40%まで0.01%ずつ変化させたところ、0.32〜0.38%の時が最も沈澱処理水濁度が低くなった。
【００２７】
ところで、表１はＰＳＩ注入率を40mg/Lで一定とした場合のものである。当然、ＰＳＩ注入率が変化すると凝集槽での最適沈降促進材濃度も変化する。原水濁度はカオリンを用いて10度、50度、100度、ＰＳＩ中の無機高分子凝集剤の平均分子量が51万のものを用いて通水実験を行った。ＰＳＩの最適注入率は、沈降促進材を添加しない状態でビーカー試験を実施し、最適値を求めておいた。その最適ＰＳＩ注入率において沈降促進材濃度を変化させ、沈澱処理水濁度が最小となる時の促進材濃度を最適沈降促進材濃度とした。その結果を表２に示す。
【００２８】
【表２】

【００２９】
前述の表１の関係を用いて、粘度計によるＰＳＩの粘度＝ＰＳＩ中の無機高分子凝集剤の平均分子量の測定とそれに応じた凝集槽での固形分濃度（固形物濃度）を演算器を用いた自動制御により沈降促進材を増減させて変化させた場合（本発明に係る制御を行った場合）と、制御を行わず凝集槽での固形分濃度を0.5%で一定とした場合の比較データを図２に示す。
【００３０】
図２に示す結果から明らかなように、本発明に係る制御を行った場合には、無機高分子凝集剤の分子量（無機高分子凝集剤の粘度〔粘度計の指示地〕）が変動する場合にあっても、安定して優れた処理水水質（処理水濁度）を得ることができ、無機高分子凝集剤の分子量に応じて凝集槽における沈降促進材濃度を最適な範囲内に制御することが極めて有効な手法であることが確認された。
【００３１】
なお、図１のフローでは、無機凝集剤と無機高分子凝集剤の混合物の粘度を測定したが、無機高分子凝集剤単独、たとえばＰＳＩについて言えば、塩化第二鉄を混合する前の重合ケイ酸の粘度を測定して、凝集槽内の沈降促進材の濃度を制御することもできる。
【００３２】
【発明の効果】
以上説明したように、本発明に係る凝集沈澱装置およびその制御方法によれば、高分子凝集剤として特に無機高分子凝集剤を用いる場合に、フロック形成を確実に行えるようになり、それにより沈澱処理水質を安定させることが可能となった。本発明はとくに、無機高分子凝集剤は分子量が小さいことから沈降促進材の濃度の影響を受けやすいので、無機高分子凝集剤を使用する凝集沈澱処理に有効な手段となる。
【図面の簡単な説明】
【図１】本発明の一実施態様に係る凝集沈澱装置の概略構成図である。
【図２】本発明に係る制御を行った場合と行わなかった場合との比較試験の結果を示す特性図である。
【符号の説明】
１凝集沈澱装置
２原水供給ライン
３原水
４凝集槽
５沈澱槽
６処理水
７沈澱物
８注入部
９無機・高分子混合凝集剤（無機凝集剤と無機高分子凝集剤の混合物）
１０ポンプ
１１凝集剤注入ライン
１２粘度計
１３攪拌機
１４沈降促進材回収・供給装置
１５沈降促進材
１６引き抜きポンプ
１７引き抜き分離ライン
１８砂・汚泥分離サイクロン
１９貯留タンク
２０、２１コントロール弁
２２汚泥排水管
２３傾斜板
２４固形分濃度計
２５制御装置としての演算器
２６ラインミキサー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a coagulating sedimentation apparatus for performing water treatment by coagulating sedimentation treatment using a coagulant and a settling accelerator in water purification treatment, industrial water treatment, sewage treatment, wastewater treatment, and the like, and a control method therefor.
[0002]
[Prior art]
A coagulation tank that aggregates suspended substances in the raw water into a floc form by adding an inorganic coagulant, a polymer coagulant, and a settling accelerator (for example, particulates, particularly sand), and a treated water introduced from the coagulation tank A sedimentation tank that precipitates agglomerates and separates them into treated water and sediments, withdraws the sediments from the sedimentation tank, separates the extracted sediments into sludge and sedimentation accelerators, and aggregates the separated sedimentation accelerators In a sedimentation accelerator-added coagulating sedimentation apparatus (for example, Patent Document 1) equipped with a drawing separation line that returns to the tank, activated silicic acid or iron silica coagulant (for example, PSI manufactured by Seiko Kiko Co., Ltd.) Inorganic polymer flocculants such as) may be used.
[0003]
As described in Patent Document 2, Patent Document 3, and Patent Document 4, the production method of the PSI is obtained by diluting a commercially available water glass (sodium silicate) with water and adding sulfuric acid (hydrochloric acid or nitric acid to it). ) To adjust the pH to about 4 and gently stirring to produce polymerized silicic acid (: polysilica), and then ferric chloride is added thereto. In the case of PSI having a SiO ₂ content of about 2.2% that is normally manufactured, the quality is stable for one month or more at room temperature.
[0004]
[Patent Document 1]
JP 2000-334209 A [Patent Document 2]
Japanese Patent No. 1784373 [Patent Document 3]
Japanese Patent No. 2732067 [Patent Document 4]
Japanese Patent Laid-Open No. 2001-70708
[Problems to be solved by the invention]
However, when the inorganic polymer flocculant as described above is used, it has been found that if the concentration of the sedimentation promoting material is too high, the sedimentation promoting material is not sufficiently taken in at the time of floc formation and the floc is crushed. . If the concentration of the settling accelerator is low, the floc density does not increase, so that solid-liquid separation is not sufficiently achieved in the precipitation tank. Further, when the floc is crushed, the target separation performance cannot be obtained when separating the treated water and the precipitate in the precipitation tank. Therefore, particularly when an inorganic polymer flocculant is used, it is necessary to control the concentration of the settling accelerator more strictly than in the past.
[0006]
By the way, the molecular weight of the inorganic polymer flocculant is determined by the polymerization conditions (pH, temperature, salt concentration of Na, K, etc., time). The pH, temperature, and time are generally constant by controlling the manufacturing apparatus, but somewhat vary depending on the temperature, humidity, and installation conditions of the apparatus. The salt concentration of Na, K, etc. varies somewhat depending on the quality of the raw materials. Therefore, the molecular weight of the inorganic polymer flocculant is not always constant. In some cases, the molecular weight of the inorganic polymer flocculant is changed by intentionally changing the polymerization conditions.
[0007]
For reference, in the case of an organic polymer flocculant, the molecular weight is 8 million to 16 million (Olflock), and the optimum concentration accelerator is 0.5 to 2.0% in the coagulation tank. On the other hand, in the case of an inorganic polymer flocculant, the molecular weight is several hundreds of thousands to millions (450,000 to 550,000 in PSI), and the optimum settling accelerator concentration in the flocculation tank is 0.2 to 0.5%. It is a narrow optimum range. In the case of organic polymer flocculants, although the optimum range is wide, the problem of acrylamide monomer in particular remains, and the current situation is that it is still unsuitable for use in water supply applications.
[0008]
Therefore, it is often desirable to use an inorganic polymer flocculant. In the case of a normal coagulation precipitation treatment with a water area load of 1 to 5 m / h, even if the molecular weight variation of the inorganic polymer flocculant is about ± 10%, the treatment is hardly affected. In the sedimentation accelerator-added coagulation sedimentation process, which is 50 m / h, which is 10 times or more of the normal coagulation sedimentation process, the water quality of the treated water, particularly the turbidity, is affected.
[0009]
Therefore, the object of the present invention is to make it possible to optimally control the concentration of the settling accelerator in accordance with the molecular weight of the inorganic polymer flocculant having a high influence on the quality of the process, particularly in the settling accelerator added aggregation settling process. In order to achieve excellent processing performance.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, a control method for a coagulating sedimentation apparatus according to the present invention includes a coagulation tank that coagulates suspended substances in raw water by adding an inorganic coagulant, an inorganic polymer coagulant, and a settling accelerator, A sedimentation tank that precipitates agglomerates in the water to be treated introduced from the tank and separates it into treated water and precipitates, withdraws the sediment from the sedimentation tank, and separates the extracted sediment into sludge and sedimentation accelerator. A sedimentation accelerator-added coagulation sedimentation apparatus comprising a drawing separation line for returning the separated sedimentation accelerator to the coagulation tank, and measuring the molecular weight of the inorganic polymer flocculant, and depending on the molecular weight It consists of the method characterized by controlling the density | concentration of the sedimentation promoter in a coagulation tank.
[0011]
In this control method, the molecular weight of the inorganic polymer flocculant can be measured by measuring the viscosity before injection of the inorganic polymer flocculant. That is, as will be described later, in the range of the injection amount of the inorganic polymer flocculant that is actually performed, the molecular weight and the viscosity of the inorganic polymer flocculant are substantially proportional or substantially 1: 1. It has been confirmed that there is a correspondence relationship, and the molecular weight of the inorganic polymer flocculant can be substantially measured by measuring the viscosity using a viscometer or the like.
[0012]
Moreover, in this control method, it is preferable to control the injection rate of the inorganic polymer flocculant according to the turbidity of raw water. If the turbidity of the raw water is high, the injection rate of the optimum inorganic polymer flocculant to be injected also increases. Further, it is preferable to control the concentration of the settling accelerator in the coagulation tank according to the injection rate of the inorganic polymer flocculant. In other words, the higher the turbidity of the raw water and the higher the injection rate of the inorganic polymer flocculant, the more suspended substances in the raw water that should be separated. Therefore, it is preferable to control the concentration of the sedimentation promoting material correspondingly. The inorganic polymer flocculant can be injected separately from the inorganic flocculant, or a flocculant obtained by mixing the inorganic flocculant and the inorganic polymer flocculant in advance can be injected. The aforementioned PSI is a kind of aggregating agent in such a premixed form. Even if the flocculant is mixed in advance as described above, the inorganic flocculant itself has almost no viscosity. Therefore, if the viscosity of the mixed flocculant is measured, the measured value is substantially the viscosity of the inorganic polymer flocculant. And the molecular weight of the inorganic polymer flocculant corresponding to the viscosity can be measured.
[0013]
The coagulation / sedimentation apparatus according to the present invention has a configuration capable of performing the control as described above, and aggregates suspended substances in raw water by adding an inorganic coagulant, an inorganic polymer coagulant, and a settling accelerator. A coagulation tank, a sedimentation tank that precipitates the aggregate in the water to be treated introduced from the coagulation tank and separates it into treated water and sediment, and pulls the sediment from the sedimentation tank, and the extracted sediment is promoted to sludge and sedimentation. A sedimentation accelerator-added coagulating sedimentation apparatus comprising a drawing separation line for returning the sedimentation promoting material separated and separated into a coagulation tank to the molecular weight of the inorganic polymer flocculant Accordingly, it comprises means for controlling the concentration of the sedimentation promoting material in the coagulation tank.
[0014]
In the coagulation precipitation apparatus and the control method thereof according to the present invention as described above, the molecular weight of the inorganic polymer flocculant is measured through viscosity measurement or the like, and the optimum settling accelerator in the coagulation tank corresponding to the molecular weight is measured. Controlled by concentration. As described above, the optimum concentration range of the sedimentation accelerator corresponding to the molecular weight of the inorganic polymer flocculant is limited to a relatively narrow range, but the control according to the present invention ensures that the concentration is within the target concentration range. Will be. Therefore, the formation of agglomerated flocs by incorporating the sedimentation promoting material is performed well, and floc crushing when the concentration of the sedimentation promoting material is too high will be appropriately prevented, and the targeted agglomeration sedimentation processing performance, As a result, excellent quality of treated water is obtained and its performance is stably maintained.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a coagulating sedimentation apparatus 1 according to an embodiment of the present invention. The coagulating sedimentation apparatus 1 is a coagulating tank 4 that receives raw water 3 supplied via the raw water supply line 2, and coagulates in the water to be treated introduced from the coagulating tank 4 to precipitate the treated water 6 and the precipitate 7. And a settling tank 5 for separation. An inorganic flocculant and an inorganic polymer flocculant are injected into the agglomeration tank 4 at an injection portion 8 integrally formed at the inlet, and in this embodiment, an inorganic / polymer mixed flocculant mixed with these. Injected by the pump 10 in the form of 9 (for example, the aforementioned PSI). The injection line 11 for the flocculant 9 is provided with a viscometer 12 for measuring the viscosity of the inorganic polymer flocculant via a bypass portion. Even with the mixed flocculant 9, since the inorganic flocculant has almost no viscosity, the viscosity measurement of the mixed flocculant 9 is substantially the viscosity measurement of the inorganic polymer flocculant.
[0016]
The agglomeration tank 4 is provided with a stirrer 13. While the inside of the agitation tank 13 is agitated by the agitator 13, suspended substances in the raw water are added to the inorganic / polymer mixed flocculant 9 and the settling accelerator is recovered and supplied. By the addition of the sedimentation promoting material 15 from the device 14, the flocs are aggregated. The settling accelerator 15 is made of granular material, particularly sand whose particle size is adjusted to a predetermined range in this embodiment. The amount of the sedimentation promoting material 15 added is the sedimentation promoting material 15 (sand) obtained by separating the sediment 7 sent from the sedimentation tank 5 through the drawing pump 16 and the drawing separation line 17 by the sand / sludge separation cyclone 18. It consists of what is added into the aggregation tank 4 and what is added from the storage tank 19 as needed. The storage tank 19 stores the excess sedimentation promoting material 15 that is not added to the aggregation tank 4 among the separation / recovery sedimentation promoting material 15 from the cyclone 18. The supply of the surplus sedimentation promoting material 15 to the storage tank 19 is controlled by the control valve 20, and the addition from the storage tank 19 to the aggregation tank 4 is controlled by the control valve 21. The storage tank 19 is also used as a replenishment tank for the new settling accelerator 15. The sludge separated by the sand / sludge separation cyclone 18 is discharged through the sludge drain pipe 22. In addition, the sedimentation tank 5 is provided with an inclined plate 23, and the separation efficiency between the treated water 6 and the precipitate 7 is enhanced, and the outflow of sludge to the treated water 6 side is suppressed.
[0017]
The coagulation tank 4 is provided with a solid content concentration meter 24 so that the concentration of the settling accelerator 15 in the coagulation tank 4 can be substantially measured. A measurement signal from the solid content concentration meter 24 is sent to a calculator 25 as a control device. An operation signal is sent from the computing unit 25 to the

control valves

20 and 21, thereby controlling the amount of the sedimentation promoting material 15 added from the storage tank 19 into the coagulation tank 4 and from the cyclone 18 to the coagulation tank 4. The amount of settling accelerator 15 added to the water and the branch supply amount of the settling accelerator 15 from the cyclone 18 to the storage tank 19 are controlled, and the concentration of the settling accelerator 15 in the coagulation tank 4 is controlled via this control. . For controlling the concentration of the sedimentation accelerator 15, the viscosity measurement signal of the inorganic polymer flocculant from the viscometer 12 is used, and the concentration of the sedimentation accelerator 15 is controlled according to the viscosity of the inorganic polymer flocculant.
[0018]
In the above embodiment, the inorganic / polymer mixed coagulant 9 is injected into the coagulation tank 4, particularly into the injection part 8 at the inlet, but as shown by a two-dot chain line in FIG. It is also possible to arrange the line mixer 26 in the line 2 and to inject immediately before that. Moreover, it may replace with the line mixer 26 and you may install the mixing tank provided with the stirrer.
[0019]
In the coagulation / precipitation apparatus 1 configured as described above, the molecular weight of the inorganic polymer flocculant is measured through the viscosity measurement of the inorganic / polymer mixed flocculant 9 before being injected into the coagulation tank 4, and the measured inorganic high In accordance with the molecular weight of the molecular flocculant, the concentration of the sedimentation promoting material 15 in the aggregation tank 4 is controlled to an optimum concentration grasped in advance. In addition, this control appropriately changes and controls the injection rate of the inorganic / polymer mixed flocculant 9 (particularly, the inorganic polymer flocculant) according to the turbidity of the raw water 3 to be introduced. By controlling the concentration of the settling accelerator 15 in the coagulation tank 4 according to the injection rate of the agent 9 (particularly inorganic polymer flocculant), it is possible to control the concentration of the settling accelerator more optimally. Although the optimum concentration range of the sedimentation promoting material 15 is relatively narrow, the control within the target range can be reliably performed by the control as described above. In addition, by continuously performing this control, it is possible to continue a good coagulation precipitation treatment under optimum conditions at all times, and to obtain a stable and excellent treated water quality.
[0020]
【Example】
Using the apparatus shown in FIG. 1, the effects of the coagulation precipitation apparatus according to the present invention and the control method thereof were confirmed.
In the water purification treatment using dam water as raw water, the coagulation sedimentation treatment according to the present invention was performed as a pretreatment for rapid sand filtration. Although the apparatus shown in FIG. 1 was used, the apparatus specifications and operating conditions are as follows.
[0021]
・ Processed water volume: 7.0m ³ / h (Line speed LV = 30m / h)
-Raw water turbidity: adjusted to 100 +/- 10 degrees using kaolin-Coagulation precipitation apparatus: Coagulation tank; 0.44 m ³
Precipitation tank: 0.50m ³ (surface area 0.25m ² , 0.5m × 0.5m)
Sludge circulation rate: 0.5m ³ / h
-Flocculant: Polysilica iron flocculant (PSI)
Contains inorganic polymer flocculant with Fe ₂ O ₃ content of 1.0%, SiO ₂ content of 2.2% and molecular weight of 450,000-550,000 daltons.
The injection rate was fixed at 40 mg / L (total of the mixture of inorganic flocculant and inorganic polymer flocculant).
(PSI is a commercially available water glass (sodium silicate) diluted with city water so that the Si concentration is 3.0%, adjusted to pH 4.0 ± 0.2 by adding dilute sulfuric acid, and the temperature is 30-40 ° C. The polymerized silicic acid (= polysilica) is produced by gently stirring for 1 hour while maintaining the same, and further, ferric chloride with a concentration of FeCl _{3 of} 38% is added to the molar ratio of Si and Fe, and Si: Fe = 3: (It is a mixture of an inorganic flocculant and an inorganic polymer flocculant obtained by adding so that it becomes 1. The PSI was transferred to a storage tank and used for water flow experiments.)
[0022]
・ Viscometer: Measures viscosity of PSI, rotary viscometer (measures the torque (force) generated when a rotor is immersed in a sample and the rotor is rotated at a constant speed by a spring twist (torque sensor)) Here, CAP1000 manufactured by Bookfield Co., Ltd. was used, and the indication value of the viscometer could be taken out by an electrical signal, and the signal was transmitted to the calculator for control. There are various measurement methods such as ultrasonic, falling ball, and vibration methods, and any method can be used as long as it can measure the range of 1 to 100 mPa · s and can take the indicated value as an electrical signal. (For example, there is an ultrasonic viscometer FUV-1 manufactured by Seika Sangyo Co., Ltd.)
Solid content concentration meter: An ultrasonic type, a solid content concentration meter manufactured by Ultrasonic Industry Co., Ltd. was used. It measures the propagation speed of ultrasonic waves traveling in air, liquid, or solid, computes it, and expresses it as concentration.
[0023]
When the relationship between the viscosity of the PSI obtained by the viscometer and the average molecular weight of the inorganic polymer flocculant in the PSI obtained by the ultrafiltration method was examined, the molecular weight changed in proportion to the 0.3th power of the viscosity. I understood that. However, this is the case where the temperature and concentration are constant. Accordingly, it is necessary to perform temperature correction and density correction. However, in this embodiment, since the viscometer is installed in a constant temperature jacket of 24 ° C. ± 1 ° C., temperature correction is not performed. Further, the concentration correction is not necessary because the Fe ₂ O ₃ content is 1.0% and the SiO ₂ content is 2.2%.
[0024]
The indicated value of the viscometer was regarded as a change in molecular weight, and the concentration of sedimentation accelerator in the coagulation tank was changed. The relationship between the average molecular weight of the inorganic polymer flocculant in PSI and the optimum sedimentation accelerator concentration has been confirmed by prior experiments. The relationship is shown in Table 1.
[0025]
[Table 1]

[0026]
In the above, if the viscometer indication value is less than 13.0 or more than 30.5, it is regarded as abnormal and the operation is stopped. In preliminary experiments conducted to determine the optimum sedimentation accelerator concentration in this coagulation tank, the average molecular weights were 450,000, 470,000, 490,000, 510,000, 530,000, 55 under the condition of the raw water turbidity being constant. As a matter of course, the concentration of the sedimentation accelerator in the coagulation tank was changed, and the concentration of the sedimentation accelerator when the sedimentation water turbidity was minimized was determined as the optimum promoter concentration. For example, when the raw water turbidity is 100 ° ± 10 ° using kaolin, the average molecular weight of the inorganic polymer flocculant in PSI is 510,000, and the PSI injection rate is 40 mg / L, the optimum settling accelerator in the coagulation tank When the concentration was changed by 0.01% from 0.30 to 0.40%, the precipitation-treated water turbidity was lowest when the concentration was 0.32 to 0.38%.
[0027]
Table 1 shows the case where the PSI injection rate is constant at 40 mg / L. Naturally, when the PSI injection rate changes, the optimum settling accelerator concentration in the coagulation tank also changes. The raw water turbidity was 10 °, 50 °, 100 ° using kaolin, and a water flow experiment was conducted using an inorganic polymer flocculant having an average molecular weight of 510,000 in PSI. The optimum injection rate of PSI was determined by conducting a beaker test without adding a settling accelerator, and obtaining an optimum value. The concentration of the sedimentation accelerator was changed at the optimum PSI injection rate, and the concentration of the accelerator when the sedimentation water turbidity was minimized was taken as the optimum sedimentation accelerator concentration. The results are shown in Table 2.
[0028]
[Table 2]

[0029]
Using the relationship shown in Table 1 above, the viscosity of PSI by a viscometer = measurement of the average molecular weight of the inorganic polymer flocculant in PSI and the solid content concentration (solid matter concentration) in the coagulation tank corresponding to the calculator Comparison between the case where the sedimentation accelerator is changed by increasing / decreasing the automatic control used (when the control according to the present invention is performed) and the case where the solid content concentration in the coagulation tank is kept constant at 0.5% without control. The data is shown in FIG.
[0030]
As is apparent from the results shown in FIG. 2, when the control according to the present invention is performed, the molecular weight of the inorganic polymer flocculant (viscosity of the inorganic polymer flocculant [indicator of viscometer]) varies. Even in this case, stable and excellent treated water quality (treated water turbidity) can be obtained, and the concentration of the settling accelerator in the coagulation tank is controlled within the optimum range according to the molecular weight of the inorganic polymer flocculant. Was confirmed to be a very effective method.
[0031]
In the flow of FIG. 1, the viscosity of the mixture of the inorganic flocculant and the inorganic polymer flocculant was measured. For the inorganic polymer flocculant alone, for example, PSI, the polymerization silica before mixing ferric chloride was used. By measuring the viscosity of the acid, the concentration of the settling accelerator in the coagulation tank can be controlled.
[0032]
【The invention's effect】
As described above, according to the coagulation / sedimentation apparatus and the control method thereof according to the present invention, when an inorganic polymer coagulant is used as the polymer coagulant, floc formation can be reliably performed. It became possible to stabilize treated water quality. In particular, the present invention is an effective means for coagulation-precipitation treatment using an inorganic polymer flocculant because the inorganic polymer flocculant is easily affected by the concentration of the settling accelerator since the molecular weight is small.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a coagulation precipitation apparatus according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the results of a comparative test between when the control according to the present invention is performed and when it is not performed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Coagulation precipitation apparatus 2 Raw water supply line 3 Raw water 4 Coagulation tank 5 Precipitation tank 6 Treated water 7 Precipitate 8 Injection part 9 Inorganic / polymer mixed coagulant (mixture of inorganic coagulant and inorganic polymer coagulant)
DESCRIPTION OF SYMBOLS 10 Pump 11 Coagulant injection line 12 Viscometer 13 Stirrer 14 Settling promotion material collection | recovery / supply apparatus 15 Settling promotion material 16 Drawing pump 17 Drawing separation line 18 Sand and sludge separation cyclone 19

Storage tank

20, 21 Control valve 22 Sludge drain pipe 23 Inclined plate 24 Solid concentration meter 25 Calculator 26 as control device Line mixer

Claims

A flocculation tank for flocculating suspended matter in raw water by adding an inorganic flocculant, an inorganic polymer flocculant, and a settling accelerator; and agglomerates in the water to be treated introduced from the flocculation tank; A settling tank equipped with a settling tank that separates the settling precipitate into a coagulating tank, withdrawing the settling precipitate from the settling tank, separating the pulled set precipitate into sludge and settling promoting material, and returning the separated settling promoting material to the coagulating tank. A control method in an accelerator-added coagulating sedimentation apparatus, comprising measuring the molecular weight of the inorganic polymer coagulant and controlling the concentration of the sedimentation accelerator in the coagulation tank according to the molecular weight. Control method of the device.

The control method of the coagulation precipitation apparatus of Claim 1 which measures the molecular weight of the said inorganic polymer flocculent by the measurement of the viscosity before injection | pouring of this inorganic polymer flocculant.

The control method of the coagulation precipitation apparatus of Claim 1 or 2 which controls the injection rate of the said inorganic polymer flocculant according to the turbidity of raw | natural water.

The control method of the coagulation sedimentation apparatus in any one of Claims 1-3 which controls the density | concentration of the sedimentation promoter in the coagulation tank according to the injection rate of the inorganic polymer coagulant.

The control method of the coagulation precipitation apparatus in any one of Claims 1-4 which inject | pour the coagulant which mixed the said inorganic coagulant and the inorganic polymer coagulant previously.

A flocculation tank for flocculating suspended matter in raw water by adding an inorganic flocculant, an inorganic polymer flocculant, and a settling accelerator; and agglomerates in the water to be treated introduced from the flocculation tank; A settling tank equipped with a settling tank that separates the settling precipitate into a coagulating tank, withdrawing the settling precipitate from the settling tank, separating the pulled set precipitate into sludge and settling promoting material, and returning the separated settling promoting material to the coagulating tank. An accelerator-added coagulating sedimentation apparatus comprising a means for measuring the molecular weight of the inorganic polymer coagulant and controlling the concentration of the sedimentation accelerator in the coagulation tank according to the molecular weight. .