JP3866054B2 - Aggregation precipitation apparatus and control method thereof - Google Patents

Description

【００１０】
表１におけるようなサイクロン上流側に排出される汚泥の濃度が上昇すること自体は別段問題なく、むしろ好ましいことであるが、サイクロン１１５は、一般にその分離性能が、入口圧の変動、それに伴うサイクロン上下流側の流量バランスや、サイクロンに供給される被分離処理流体、被分離処理流体中の分離されるべき成分（上記凝集沈澱装置の場合には、とくに汚泥成分）の濃度に大きく左右され、通常、ある条件に対応して設計すると、極端に大きな変化には対応できず、大きな変化が生じると、分離性能が大幅に低下する。したがって、サイクロン１１５は、その設計仕様の対応させて、極力定流量で運転し、かつ、被分離処理流体中の汚泥濃度の大きな変動を抑制することが好ましい。
【００１１】
しかし、表１に示したようにサイクロン１１５に送られる引抜汚泥の濃度が大きく変化する条件では、単に図２に示したような系で定流量で汚泥の引抜きを行うと、サイクロン１１５に送られる引抜汚泥の濃度の変化の度合いが大きくなりすぎ、それによってサイクロン１１５の分離性能が大幅に低下するおそれがある。サイクロン１１５の分離性能が大幅に低下すると、循環再使用されるべき砂が大量に流出してしまい、凝集沈澱処理系全体として安定した運転ができなくなり、処理水質の悪化や、回収率の低下を招くことにもなる。また、砂との分離が不十分な分離汚泥が、サイクロン１１５から後段の汚泥濃縮等の処理工程に送られてしまうので、後段の処理設備での効率の悪化を招くことにもなる。
【００１２】
また、上記問題とは別に、次のような問題もある。すなわち、凝集沈澱装置全体が小型の場合、通常サイクロンも小型のものとなるが、サイクロンの入口孔や下流側孔の径が小さくなると、送られてくる汚泥の濃度が高くなった場合、分離されるべき成分あるいは分離された成分によって、これらの部分が閉塞されやすくなる。閉塞されると、運転不可になるか、分離性能が極端に低下する。したがって、サイクロンとしては、このような閉塞の問題が生じない、比較的大型のものを使用したいが、装置全体が比較的小型であるにもかかわらず単にサイクロンに比較的大型のものを採用すると、そのサイクロンの設計流量（サイクロンに送られるべき被処理流体の流量）も大きくなるので、沈澱槽からの抜出量が多くなりすぎ、その分処理水の回収率が低下することになる。
【００１３】
そこで本発明の課題は、上記のような問題に鑑み、原水の性状等が変化した場合にも、とくに原水の濁度が高くなった場合にも、サイクロンの分離効率の低下を抑え、凝集沈澱処理系全体として安定して所望の性能を発揮することが可能な、凝集沈澱装置およびその制御方法を提供することにある。
【００１４】
【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は、原水中の懸濁物質を粒状物と凝集剤の添加によりフロックとして凝集させる凝集槽と、凝集槽からの導入水中のフロックを沈降させ処理水とスラリーとに分離する沈澱槽と、沈澱槽からスラリーを抜き出す汚泥引抜ポンプと、抜き出したスラリーを汚泥と粒状物とに分離し、分離した粒状物を凝集槽に戻すサイクロンとを備えた凝集沈澱装置において、サイクロンの上部出口からのラインを汚泥排出ラインと汚泥循環ラインとに分岐し、分岐した汚泥循環ラインを汚泥引抜ポンプの吸い込み側に接続したことを特徴とするものからなる。
【００１５】
この凝集沈澱装置においては、上記汚泥循環ラインに流量コントロール弁が設けられていることが好ましい。
【００１６】
また、本発明に係る凝集沈澱装置の制御方法は、上記のような凝集沈澱装置を制御する方法であって、原水の濁質負荷または／および原水中への無機凝集剤の添加量に応じて、汚泥循環ラインの流量を制御することを特徴とする方法からなる。
【００１７】
この方法においては、原水の濁度を検知し、検知した値に応じて、汚泥循環ラインの流量を制御することができる。また、検知した原水の濁度から添加すべき無機凝集剤量を求め、濁度と無機凝集剤量に応じて、汚泥循環ラインの流量を制御することもできる。
【００１８】
こ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、サイクロンの上部出口からのラインが汚泥排出ラインと汚泥循環ラインとに分岐され、分岐した汚泥循環ラインが汚泥引抜ポンプの吸い込み側へと接続されているので、サイクロンへの供給流量を実質的に一定に保ちながら、汚泥循環ラインを介して返送循環される流量分、沈澱槽からの引抜スラリー量を低減することができる。つまり、サイクロンへの供給流量を実質的に一定に保ちながら、サイクロンへ供給される時間当たりの汚泥量を低減することができる。したがって、原水の濁度が上がった場合には、上記汚泥循環ラインにおける流量を増やし、沈澱槽からの引抜スラリー量を低減することにより、サイクロンでの処理流量を定流量に保ちながら、サイクロンで分離処理される被処理流体中の濁質成分濃度の大幅な上昇を抑えることが可能になり、所望のサイクロンの分離性能が安定して発揮されることになる。その結果、凝集沈澱系全体の処理が安定して円滑に行われ、良好な処理水質が維持されるとともに回収率の悪化が防止される。
【００１９】
また、サイクロンの入口流量は、実質的に常時最適な設計流量に保つことができるので、流量に依存するサイクロンの分離性能も常時安定して良好な性能に保たれる。したがって、サイクロン上流側から排出され、後段の汚泥処理設備に送られる排出汚泥の性状の大きな変動も抑えられることになり、後段での処理も安定する。
【００２０】
さらに、汚泥循環ラインによる循環汚泥は再びサイクロンへと供給されることになるので、サイクロンの入口流量は比較的大きなものとすることができ、装置全体が比較的小型の場合にあっても、サイクロンのサイズとしては比較的大きなものを採用することが可能になる。その結果、サイクロン部での閉塞等の不都合の発生も確実に防止される。
【００２１】
【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。図１において、凝集沈澱装置１は、予備凝集槽２と、凝集槽３と、それに隣接配置された沈澱槽４を備えている。予備凝集槽２には、原水導入ライン５を介して原水６が導入され、無機凝集剤７が添加されて、モータ８で駆動される攪拌機９によって攪拌される。原水導入ライン５には、本実施態様では、原水６の濁度を検知する濁度計１０が設けられており、検知した値によって後述の汚泥引抜分離系における汚泥循環ラインの流量を制御できるようになっている。
【００２２】
予備凝集槽２からの原水は、凝集槽３に導入されるが、そのときに高分子凝集剤１１がライン注入されるようになっている。凝集槽３内には、粒状物としての砂１２が添加され、モータ１３によって駆動される攪拌機１４による攪拌により、原水の懸濁物質が、無機凝集剤７、高分子凝集剤１１、砂１２を含むフロック１５として凝集される。この凝集においては、無機凝集剤７が懸濁物質を凝集させて微細なフロックを生成させ、それに高分子凝集剤１１が絡まってより大きなフロックに成長させ、成長したフロックには比重の大きい粒状物としての砂１２が含有され、全体として比較的大きな、比重の大きい沈澱しやすいフロックに成長する。
【００２３】
成長した凝集フロック１５を含む被処理水は、越流ぜき１６を介して沈澱槽４へと導入される。沈澱槽４では、導入水中のフロックが下方に沈澱され、沈澱されたフロックは上方の処理水１７に対して分離される。沈澱槽４内の上部には、複数の傾斜板１８が並設されており、処理水１７とともにフロックが流出するのを抑制している。
【００２４】
沈澱槽４の底部には、沈澱されたフロックを含むスラリーを抜き出すための引抜ライン１９が接続されており、引抜ライン１９には、抜き出したスラリーをサイクロン２０に送る汚泥引抜ポンプ２１が設けられている。サイクロン２０では、送られてきたスラリーを遠心分離により、サイクロン上流側ライン２２に排出される汚泥２３と、サイクロン下流側ライン２４へと導出される砂１２とに分離し、分離された砂１２は、再び凝集槽３内に戻されて循環使用される。このサイクロン上流側ライン２２は、汚泥２３を後段の汚泥処理設備（たとえば、汚泥貯槽や脱水機、図示略）へと送る汚泥排出ライン２５と、汚泥循環ライン２６とに分岐され、分岐された汚泥循環ライン２６は、汚泥引抜ポンプ２１の吸い込み側に接続されている。
【００２５】
この汚泥循環ライン２６には、流量計２７および流量コントロール弁２８が設けられており、前述の濁度計１０によって検知された原水６の濁度信号に応じて、循環される汚泥の流量が制御されるようになっている。また、この制御に加え、無機凝集剤７の添加量にも応じて、汚泥循環流量の制御を行うようにしてもよい。たとえば、上記濁度計１０で検知した濁度に応じて無機凝集剤７の添加すべき量を計算し、その濁度と無機凝集剤７の添加量に応じて汚泥循環ライン２６における汚泥循環流量を制御することもできる。
【００２６】
上記のように構成された凝集沈澱装置１は、次のように運転、制御される。予備凝集槽２へと導入されてくる原水６の濁質負荷として濁度が濁度計１０で検知され、この検知濁度に応じて、汚泥循環ライン２６における循環汚泥流量が、流量計２７で確認されつつ、流量コントロール弁２８によって制御される。すなわち、原水６の濁質負荷が増加した場合、その増加の度合いに応じて、汚泥循環ライン２６における循環汚泥流量が増大されるように制御される。汚泥引抜ポンプ２１の流量は実質的に定流量とされているから、汚泥引抜ポンプ２１の吸い込み側に循環汚泥が返送されることにより、その返送分、沈澱槽４からの抜き出し流量が低減されることになる。
【００２７】
したがって、サイクロン２０への供給スラリー量は、汚泥引抜ポンプ２１の吐出流量の一定流量に保たれつつ、沈澱槽４からの抜き出し流量が低減されることになる。その結果、原水６の濁質負荷が増加しても、サイクロン２０へ供給される濁質成分の大きな増加は抑えられることになり、濁質成分の大きな増加によるサイクロン２０の分離性能の低下が抑えられる。しかも、サイクロン２０への供給流量は実質的に一定流量に保たれるから、流量的にも、サイクロン２０は設計通りの望ましい分離性能を発揮することが可能になる。したがって、良好なサイクロン２０の分離性能が維持され、分離されるべき砂１２が安定して良好に分離されて凝集槽３へと戻され、排出されるべき汚泥２３が安定して良好に分離されてその一部が後段の汚泥処理設備へと送られる。安定した分離処理が円滑に行われるため、凝集沈澱装置１全体としての運転が安定し、良好な処理水質が維持されるとともに、回収率の悪化も防止される。また、後段の汚泥処理設備でも、安定した処理が可能になる。
【００２８】
また、汚泥循環ライン２６による循環汚泥は再びサイクロン２０へと供給されることになるので、サイクロン２０の入口流量は当初から比較的大きなものとすることが可能となり、装置全体が比較的小型の場合にあっても、サイクロン２０のサイズとしては比較的大きなものを採用することが可能になる。その結果、サイクロン２０部分、つまり、その入口部や下流側への出口部での閉塞等の不都合の発生も確実に防止される。さらに、引抜ライン１９中を送られるスラリーの濁質成分の濃度が極端に高くなることが抑えられ、かつ、汚泥引抜ポンプ２１からサイクロン２０までのラインの流量は比較的大流量に保たれるから、引抜ライン１９中での閉塞等の不都合の発生も確実に防止されることになる。
【００２９】
なお、本発明に係る凝集沈澱装置およびその制御方法は、河川水等のみでなく、本発明に係る装置が適用できるもの（たとえば、生物処理水や重金属のアルカリ凝集沈澱等）なら何でも適用可能である。
【００３０】
また、本発明において使用する無機凝集剤や高分子凝集剤の種類はとくに限定されず、無機凝集剤としては、たとえばポリ塩化アルミニウム（ＰＡＣ）、塩化第二鉄、硫酸第二鉄を使用できる。高分子凝集剤としては、たとえばノニオン性、アニオン性あるいは両性の高分子凝集剤を用いることができる。アニオン性の高分子凝集剤としては、たとえば、アクリル酸またはその塩の重合物、アクリル酸またはその塩とアクリルアミドとの共重合物、アクリルアミドと２−アクリルアミド−２メチルプロパンスルホン酸塩の共重合物、アクリル酸またはその塩とアクリルアミドと２−アクリルアミド−２−メチルプロパンスルホン酸塩の３元共重合物、ポリアクリルアミドの部分加水分解物などが挙げられるが、特にこれらに限定されるものではない。ノニオン性の高分子凝集剤としては、代表的なものとしてポリアクリルアミドが挙げられるが、特にこれに限定されるものではない。両性の高分子凝集剤としては、たとえば、ジメチルアミノエチル（メタ）アクリレートの３級塩および４級塩（塩化メチル塩等）等の少なくとも１種のカチオン性単量体と、アクリル酸およびその塩（ナトリウム、カルシウム等の塩類）、２−アクリルアミド−２−メチルプロパンスルホン酸塩（ナトリウム、カルシウム等の塩類）等の少なくとも１種のアニオン性単量体の共重合物、あるいは、上記の少なくとも１種のカチオン性単量体および上記の少なくとも１種のアニオン性単量体とアクリルアミド等の少なくとも１種のノニオン性単量体との三元もしくは四元以上の共重合物等が挙げられるが、特にこれらに限定されるものではない。高分子凝集剤の分子量の範囲は特に限定されないが、５００万〜２０００万の範囲が好ましい。これらの高分子凝集剤は、単独で又は混合物として用いることができる。
【００３１】
【発明の効果】
以上説明したように、本発明の凝集沈澱装置およびその制御方法によれば、サイクロン上流側ラインを分岐して分岐した汚泥循環ラインを汚泥引抜ポンプの吸い込み側に接続し、汚泥引抜ポンプからサイクロンへの供給流量は一定に保ちながら沈澱槽からの抜き出しスラリー量を、原水の濁度に応じて低減できるようにしたので、サイクロンの良好な分離性能を安定して維持することが可能になり、装置全体としての安定した円滑な運転が可能になる。したがって、原水の濁度が増加した場合にあっても、処理水質の低下、回収率の低下を防止でき、後段の汚泥処理工程の安定した運転も維持できる。
【００３２】
さらに、装置全体が比較的小型のものである場合にあっても、サイクロンとしては比較的大型のものを採用することが可能になり、サイクロン部および引抜ラインでの閉塞等の不都合の発生も防止できる。
【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全体構成図である。
【図２】従来の凝集沈澱装置の全体構成図である。
【符号の説明】
１ 凝集沈澱装置
２ 予備凝集槽
３ 凝集槽
４ 沈澱槽
５ 原水導入ライン
６ 原水
７ 無機凝集剤
９ 攪拌機
１０ 濁度計
１１ 高分子凝集剤
１２ 粒状物としての砂
１４ 攪拌機
１５ 凝集フロック
１６ 越流ぜき
１７ 処理水
１８ 傾斜板
１９ 汚泥引抜ライン
２０ サイクロン
２１ 汚泥引抜ポンプ
２２ サイクロン上流側ライン
２３ 汚泥
２４ サイクロン下流側ライン
２５ 汚泥排出ライン
２６ 汚泥循環ライン
２７ 流量計
２８ 流量コントロール弁[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a coagulating sedimentation apparatus and a control method for separating suspended solids in raw water into sludge and treated water by adding a granular material and a coagulant and coagulating sediment, and in particular, a slurry extracted from a sedimentation tank by a cyclone. The present invention relates to a coagulating sedimentation apparatus and a control method therefor, which can be operated optimally as an entire apparatus while maintaining desired cyclone separation performance according to the properties of raw water and the like when separating into sludge and particulate matter.
[0002]
[Prior art]
An apparatus for separating and removing substances suspended in raw water (hereinafter sometimes referred to as SS [Suspended Solid]) by precipitation is known. As a conventional coagulating sedimentation apparatus for removing SS in raw water, an apparatus that simply adds a coagulant to raw water to precipitate the aggregate, pulls the aggregate as sludge, and derives treated water from the top is well known. In such a general coagulation precipitation apparatus, it takes a long time to precipitate the coagulum, and a very large sedimentation tank is required. Therefore, the coagulation precipitation can be performed more efficiently. A device has been proposed.
[0003]
For example, as a coagulation precipitation apparatus for removing SS in raw water, flocs are formed in raw water by adding granular material (sand) having a particle size of about 10 to 200 μm and a polymer flocculant to SS in raw water. There is known an apparatus comprising a coagulation tank, a precipitation tank that separates floc flowing out from the coagulation tank from treated water, and a cyclone that separates slurry extracted from the precipitation tank into sand and sludge.
[0004]
This type of coagulating sedimentation apparatus is configured as shown in FIG. 2, for example. An inorganic flocculant 103 is added to the raw water 102 introduced into the preliminary flocculation tank 101 and stirred with a stirrer 104. A polymer flocculant 105 is added to the raw water and introduced into the flocculation tank 106, and stirred with a stirrer 107. The floc 109 is formed together with the particulate matter (sand) 108, the treated water is introduced into the sedimentation tank 110, the sludge is settled and separated, and the treated water 112 is obtained from above through the inclined plate 111. Slurry is extracted from the lower part of the precipitation tank 110 by a sludge extraction pump 113 and sent to a cyclone 115 as a separator via a line 114. The cyclone 115 is centrifuged into sludge and sand, and the separated sludge 117 is discharged from the upper outlet side 116 (referred to herein as the “cyclone upstream side”) and sent to the subsequent sludge treatment step. At the same time, the separated sand 108 is returned to the agglomeration tank 106 from the lower outlet side 118 (referred to herein as “the cyclone downstream side”).
[0005]
[Problems to be solved by the invention]
The conventional coagulation sedimentation apparatus as shown in FIG. 2 can be applied to coagulation sedimentation treatment of water containing turbidity such as river water and drainage and SS.
[0006]
By the way, the raw water turbidity concentration of river water has a large difference between the normal time and the rainy time, and the normal turbidity is several degrees to several tens of degrees. is there. In general, the higher the turbidity, the more the inorganic flocculant such as PAC (polyaluminum chloride) needs to be increased.
[0007]
When such an increase in the turbidity load of raw water or an increase in the amount of inorganic flocculant occurs, the concentration of sludge slurry that settles in the precipitation tank 110 increases, and the concentration of sludge that is extracted and sent to the cyclone 115 increases. Therefore, the concentration of sludge discharged to the upstream side of the cyclone also increases.
[0008]
For example, as shown in Table 1, even when the raw water flow rate and the amount of sludge withdrawn from the settling tank 110 are the same, if the turbidity of the raw water changes (normal time [10 degrees], rain [100 degrees], flooding Time [1000 degrees]), the PAC addition amount is increased accordingly, and both the extracted sludge concentration and the cyclone upstream concentration are increased.
[0009]
[Table 1]

[0010]
Although the increase in the concentration of sludge discharged upstream of the cyclone as shown in Table 1 is not a problem in itself and is rather preferable, the cyclone 115 generally has a separation performance that varies with the fluctuation of the inlet pressure and the cyclone associated therewith. The flow rate balance on the upstream and downstream sides, the separation fluid to be supplied to the cyclone, and the concentration of the components to be separated in the separation fluid (especially sludge components in the case of the above-mentioned coagulating sedimentation device) Normally, when designing for a certain condition, an extremely large change cannot be handled, and when a large change occurs, the separation performance is greatly reduced. Therefore, the cyclone 115 is preferably operated at a constant flow rate as much as possible in accordance with the design specifications, and it is preferable to suppress a large fluctuation in the sludge concentration in the separation target fluid.
[0011]
However, as shown in Table 1, under the condition that the concentration of the extracted sludge sent to the cyclone 115 changes greatly, if the sludge is simply extracted at a constant flow rate in the system as shown in FIG. 2, it is sent to the cyclone 115. There is a possibility that the degree of change in the concentration of the drawn sludge becomes too large, and thereby the separation performance of the cyclone 115 is significantly lowered. If the separation performance of the cyclone 115 is greatly reduced, a large amount of sand to be recycled and reused, and stable operation cannot be performed as the entire coagulation sedimentation treatment system, resulting in deterioration of the treated water quality and reduction in the recovery rate. It will also invite you. Further, since the separated sludge that is insufficiently separated from the sand is sent from the cyclone 115 to a treatment process such as the subsequent sludge concentration, the efficiency of the subsequent treatment equipment is also deteriorated.
[0012]
In addition to the above problems, there are the following problems. In other words, when the entire coagulation sedimentation apparatus is small, the cyclone is usually small, but if the diameter of the cyclone inlet hole or the downstream hole becomes small, it will be separated if the concentration of the sludge sent increases. These parts are likely to be blocked by the component to be separated or separated. If it is blocked, the operation becomes impossible or the separation performance is extremely lowered. Therefore, as a cyclone, it is desirable to use a relatively large one that does not cause such a blocking problem. However, when the entire device is relatively small, simply adopting a relatively large cyclone, Since the design flow rate of the cyclone (the flow rate of the fluid to be processed to be sent to the cyclone) also increases, the amount of extraction from the sedimentation tank becomes excessive, and the recovery rate of the treated water is reduced accordingly.
[0013]
Therefore, in view of the above-described problems, the object of the present invention is to suppress a decrease in cyclone separation efficiency even when the properties of raw water are changed, particularly when the turbidity of raw water is increased, and aggregation precipitation is suppressed. It is an object of the present invention to provide an agglomeration precipitation apparatus and its control method capable of stably exhibiting desired performance as a whole treatment system.
[0014]
[Means for Solving the Problems]
In order to solve the above problems, the coagulation sedimentation apparatus according to the present invention comprises a coagulation tank that aggregates suspended substances in raw water as flocs by adding particulate matter and a coagulant, and settles flocs in water introduced from the coagulation tank. A sedimentation tank for separating the treated water and the slurry, a sludge extraction pump for extracting the slurry from the precipitation tank, and a cyclone for separating the extracted slurry into sludge and particulates and returning the separated particulates to the agglomeration tank In the coagulating sedimentation apparatus, the line from the upper outlet of the cyclone is branched into a sludge discharge line and a sludge circulation line, and the branched sludge circulation line is connected to the suction side of the sludge extraction pump.
[0015]
In this coagulating sedimentation apparatus, it is preferable that a flow rate control valve is provided in the sludge circulation line.
[0016]
Moreover, the control method of the coagulation sedimentation apparatus according to the present invention is a method for controlling the coagulation precipitation apparatus as described above, depending on the turbidity load of raw water or / and the amount of inorganic coagulant added to the raw water. And a method characterized by controlling the flow rate of the sludge circulation line.
[0017]
In this method, the turbidity of the raw water is detected, and the flow rate of the sludge circulation line can be controlled according to the detected value. Further, the amount of the inorganic flocculant to be added can be obtained from the detected turbidity of the raw water, and the flow rate of the sludge circulation line can be controlled according to the turbidity and the amount of the inorganic flocculant.
[0018]
In such a coagulation sedimentation apparatus and control method thereof according to the present invention, a line from the upper outlet of the cyclone is branched into a sludge discharge line and a sludge circulation line, and the branched sludge circulation line is directed to the suction side of the sludge extraction pump. Therefore, the amount of slurry withdrawn from the settling tank can be reduced by the amount of the flow returned and circulated through the sludge circulation line while keeping the supply flow rate to the cyclone substantially constant. That is, the amount of sludge per hour supplied to the cyclone can be reduced while keeping the supply flow rate to the cyclone substantially constant. Therefore, when the turbidity of raw water increases, the flow rate in the sludge circulation line is increased, and the amount of slurry withdrawn from the sedimentation tank is reduced, so that the treatment flow rate in the cyclone is kept constant and the cyclone is separated. A significant increase in the concentration of turbid components in the fluid to be treated can be suppressed, and the desired cyclone separation performance can be stably exhibited. As a result, the treatment of the entire coagulating sedimentation system is performed stably and smoothly, maintaining good treated water quality and preventing the recovery rate from deteriorating.
[0019]
In addition, since the inlet flow rate of the cyclone can be maintained at the optimum design flow rate at all times, the cyclone separation performance depending on the flow rate is always kept stable and good. Therefore, large fluctuations in the properties of the discharged sludge discharged from the upstream side of the cyclone and sent to the subsequent sludge treatment facility can be suppressed, and the subsequent treatment is also stabilized.
[0020]
Furthermore, since the circulating sludge from the sludge circulation line is supplied again to the cyclone, the inlet flow rate of the cyclone can be made relatively large, and even if the entire device is relatively small, the cyclone It is possible to adopt a relatively large size. As a result, the occurrence of inconvenience such as blockage in the cyclone portion is reliably prevented.
[0021]
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. In FIG. 1, the coagulation precipitation apparatus 1 is provided with the preliminary coagulation tank 2, the coagulation tank 3, and the precipitation tank 4 arrange | positioned adjacent to it. Raw water 6 is introduced into the preliminary coagulation tank 2 through the raw water introduction line 5, an inorganic flocculant 7 is added, and the mixture is stirred by a stirrer 9 driven by a motor 8. In this embodiment, the raw water introduction line 5 is provided with a turbidimeter 10 for detecting the turbidity of the raw water 6 so that the flow rate of the sludge circulation line in the sludge extraction / separation system described later can be controlled by the detected value. It has become.
[0022]
The raw water from the preliminary coagulation tank 2 is introduced into the coagulation tank 3, and at that time, the polymer flocculant 11 is line-injected. In the agglomeration tank 3, sand 12 as a granular material is added, and the suspended material of raw water becomes the inorganic flocculant 7, the polymer flocculant 11, and the sand 12 by stirring with a stirrer 14 driven by a motor 13. Aggregates as containing flock 15. In this agglomeration, the inorganic flocculant 7 agglomerates suspended substances to form fine flocs, and the polymer flocculant 11 is entangled with them to grow into larger flocs. The grown flocs have a large specific gravity. As a whole, it grows into flocs that are relatively large and have a large specific gravity and are likely to settle.
[0023]
The water to be treated containing the grown flocs 15 is introduced into the sedimentation tank 4 via the overflow basin 16. In the settling tank 4, flocs in the introduced water are precipitated downward, and the precipitated flocs are separated from the upper treated water 17. A plurality of inclined plates 18 are juxtaposed in the upper portion of the settling tank 4 to prevent the floc from flowing out together with the treated water 17.
[0024]
At the bottom of the settling tank 4 is connected a drawing line 19 for extracting the slurry containing the precipitated floc, and the drawing line 19 is provided with a sludge extraction pump 21 for sending the extracted slurry to the cyclone 20. Yes. In the cyclone 20, the sent slurry is separated by centrifugation into sludge 23 discharged to the cyclone upstream line 22 and sand 12 led out to the cyclone downstream line 24. Then, it is returned to the agglomeration tank 3 again for circulation. The upstream cyclone line 22 is branched into a sludge discharge line 25 for sending the sludge 23 to a subsequent sludge treatment facility (for example, a sludge storage tank or a dehydrator, not shown) and a sludge circulation line 26. The circulation line 26 is connected to the suction side of the sludge extraction pump 21.
[0025]
The sludge circulation line 26 is provided with a flow meter 27 and a flow control valve 28, and the flow rate of the circulated sludge is controlled according to the turbidity signal of the raw water 6 detected by the turbidimeter 10 described above. It has come to be. In addition to this control, the sludge circulation flow rate may be controlled according to the amount of the inorganic flocculant 7 added. For example, the amount of the inorganic flocculant 7 to be added is calculated according to the turbidity detected by the turbidimeter 10, and the sludge circulation flow rate in the sludge circulation line 26 according to the turbidity and the amount of inorganic flocculant 7 added. Can also be controlled.
[0026]
The coagulation sedimentation apparatus 1 configured as described above is operated and controlled as follows. Turbidity is detected by the turbidimeter 10 as a turbidity load of the raw water 6 introduced into the preliminary flocculation tank 2, and according to this detected turbidity, the circulating sludge flow rate in the sludge circulation line 26 is detected by the flowmeter 27. It is controlled by the flow control valve 28 while being confirmed. That is, when the turbid load of the raw water 6 increases, control is performed so that the circulating sludge flow rate in the sludge circulation line 26 is increased according to the degree of increase. Since the flow rate of the sludge extraction pump 21 is substantially constant, when the circulating sludge is returned to the suction side of the sludge extraction pump 21, the return flow rate and the extraction flow rate from the settling tank 4 are reduced. It will be.
[0027]
Accordingly, the amount of slurry supplied to the cyclone 20 is maintained at a constant flow rate of the discharge flow rate of the sludge extraction pump 21, while the flow rate of extraction from the sedimentation tank 4 is reduced. As a result, even if the turbidity load of the raw water 6 increases, a large increase in the turbid component supplied to the cyclone 20 is suppressed, and a decrease in the separation performance of the cyclone 20 due to a large increase in the turbid component is suppressed. It is done. In addition, since the supply flow rate to the cyclone 20 is maintained at a substantially constant flow rate, the cyclone 20 can exhibit a desired separation performance as designed even in terms of flow rate. Therefore, good separation performance of the cyclone 20 is maintained, the sand 12 to be separated is stably separated and returned to the agglomeration tank 3, and the sludge 23 to be discharged is stably and satisfactorily separated. Part of it is sent to the sludge treatment facility at the later stage. Since the stable separation process is smoothly performed, the operation of the coagulation sedimentation apparatus 1 as a whole is stabilized, the quality of the treated water is maintained, and the recovery rate is prevented from being deteriorated. In addition, stable treatment is possible even at a subsequent sludge treatment facility.
[0028]
In addition, since the circulating sludge from the sludge circulation line 26 is supplied again to the cyclone 20, the inlet flow rate of the cyclone 20 can be made relatively large from the beginning, and the entire apparatus is relatively small. Even in this case, a relatively large size of the cyclone 20 can be adopted. As a result, the occurrence of inconveniences such as blockage at the cyclone 20 portion, that is, the inlet portion and the outlet portion to the downstream side can be reliably prevented. Furthermore, the concentration of turbid components in the slurry sent through the drawing line 19 is suppressed from becoming extremely high, and the flow rate of the line from the sludge drawing pump 21 to the cyclone 20 is kept at a relatively high flow rate. In addition, occurrence of inconvenience such as blockage in the drawing line 19 is reliably prevented.
[0029]
It should be noted that the coagulation sedimentation apparatus and the control method thereof according to the present invention are applicable not only to river water and the like but to any apparatus to which the apparatus according to the present invention can be applied (for example, biologically treated water or alkali coagulation sedimentation of heavy metals). is there.
[0030]
Moreover, the kind of the inorganic flocculant and the polymer flocculant used in the present invention is not particularly limited, and examples of the inorganic flocculant include polyaluminum chloride (PAC), ferric chloride, and ferric sulfate. As the polymer flocculant, for example, nonionic, anionic or amphoteric polymer flocculants can be used. Examples of the anionic polymer flocculant include a polymer of acrylic acid or a salt thereof, a copolymer of acrylic acid or a salt thereof and acrylamide, and a copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonate. , A terpolymer of acrylic acid or a salt thereof, acrylamide and 2-acrylamido-2-methylpropanesulfonate, a partial hydrolyzate of polyacrylamide, and the like, but is not particularly limited thereto. A typical example of the nonionic polymer flocculant includes polyacrylamide, but is not particularly limited thereto. Examples of amphoteric polymer flocculants include at least one cationic monomer such as dimethylaminoethyl (meth) acrylate tertiary salt and quaternary salt (such as methyl chloride salt), acrylic acid and salts thereof. (Salts such as sodium and calcium), copolymers of at least one anionic monomer such as 2-acrylamido-2-methylpropanesulfonate (salts such as sodium and calcium), or at least one of the above Examples of the cationic monomer and terpolymer or quaternary copolymer of at least one anionic monomer and at least one nonionic monomer such as acrylamide, In particular, it is not limited to these. The molecular weight range of the polymer flocculant is not particularly limited, but a range of 5 million to 20 million is preferable. These polymer flocculants can be used alone or as a mixture.
[0031]
【The invention's effect】
As described above, according to the coagulation sedimentation apparatus and the control method thereof of the present invention, the sludge circulation line branched from the cyclone upstream line is connected to the suction side of the sludge extraction pump, and the sludge extraction pump is transferred to the cyclone. The amount of slurry extracted from the sedimentation tank can be reduced according to the turbidity of the raw water while keeping the supply flow rate constant, so that it is possible to stably maintain good cyclone separation performance. As a whole, stable and smooth operation is possible. Therefore, even when the turbidity of the raw water is increased, it is possible to prevent the quality of the treated water from being lowered and the recovery rate from being lowered, and the stable operation of the subsequent sludge treatment process can be maintained.
[0032]
In addition, even when the entire device is relatively small, it is possible to adopt a relatively large cyclone and prevent inconveniences such as blockages in the cyclone section and the extraction line. it can.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a coagulation precipitation apparatus according to an embodiment of the present invention.
FIG. 2 is an overall configuration diagram of a conventional coagulation precipitation apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Coagulation sedimentation apparatus 2 Preliminary coagulation tank 3 Coagulation tank 4 Precipitation tank 5 Raw water introduction line 6 Raw water 7 Inorganic flocculant 9 Stirrer 10 Turbidimeter 11 Polymer flocculant 12 Sand as granular material 14 Stirrer 15 Aggregation floc 16 Overflow 17 treated water 18 inclined plate 19 sludge extraction line 20 cyclone 21 sludge extraction pump 22 cyclone upstream line 23 sludge 24 cyclone downstream line 25 sludge discharge line 26 sludge circulation line 27 flow meter 28 flow control valve

Claims (5)

A flocculation tank that aggregates suspended substances in raw water as flocs by adding particulate matter and a flocculant, a precipitation tank that settles flocs in water introduced from the flocculation tank and separates them into treated water and slurry, and a slurry from the precipitation tank In a coagulation sedimentation device equipped with a sludge extraction pump that extracts the sludge and a cyclone that separates the extracted slurry into sludge and particulate matter and returns the separated particulate matter to the coagulation tank, the line from the upper outlet of the cyclone is the sludge discharge line And a sludge circulation line, and the branched sludge circulation line is connected to the suction side of the sludge extraction pump. The coagulation sedimentation apparatus according to claim 1, wherein a flow rate control valve is provided in the sludge circulation line. It is a control method of the coagulation sedimentation apparatus of Claim 1 or 2, Comprising: Controlling the flow volume of a sludge circulation line according to the suspended load of raw | natural water or / and the addition amount of the inorganic flocculant to raw | natural water. A control method for a coagulating sedimentation apparatus. The method for controlling a coagulation sedimentation apparatus according to claim 3, wherein the turbidity of the raw water is detected and the flow rate of the sludge circulation line is controlled according to the detected value. The amount of the inorganic flocculant to be added is determined from the detected turbidity of the raw water, and the flow rate of the sludge circulation line is controlled according to the turbidity and the amount of the inorganic flocculant. Control method of the device.

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