JP4464035B2

JP4464035B2 - Treatment method of sludge return water

Info

Publication number: JP4464035B2
Application number: JP2002261404A
Authority: JP
Inventors: 裕士加納; 健理千種
Original assignee: Unitika Ltd
Current assignee: Unitika Ltd
Priority date: 2002-09-06
Filing date: 2002-09-06
Publication date: 2010-05-19
Anticipated expiration: 2022-09-06
Also published as: JP2004097903A

Description

【０００１】
【発明の属する技術分野】
本発明は、下水処理場から発生する初沈汚泥や消化汚泥等の汚泥を濃縮処理または脱水処理する際に発生する汚泥処理系の返流水の処理方法に関するものである。
【０００２】
【従来の技術】
従来の下水処理においては、下水処理場から発生する多量の有機性汚泥は、濃縮、消化、脱水等の各工程を経て処理されるが、これらの各処理工程中に発生する分離水いわゆる汚泥返流水は、通常最初沈殿池等の水処理系に返送される。汚泥返流水中にはＣＯＤ、アンモニア性窒素、リン酸態リン等の成分が高濃度に含有しており、このため、汚泥返流水にともなう負荷が、水処理系の負荷量を増大させ、処理水質の低下を招く原因となっている。
【０００３】
汚泥返流水の処理として、リン酸態リンの除去に関しては、造粒脱リン法がすでに実用化されている（例えば、特許文献１参照。）。この造粒脱リン法は、アンモニア性窒素を多量に含有したし尿、産業排水などからリンを効率よく除去する技術であり、水中のリンをマグネシウムの添加によってリン酸マグネシウムアンモニウム粒子として結晶化させ、固液分離するものである。
【０００４】
また、アンモニア性窒素の処理は、生物学的方法でアンモニア性窒素を硝酸性窒素に硝化した後、脱窒のＢＯＤ源として最初沈殿池で沈降分離された生汚泥を用い、硝酸性窒素を窒素ガスに変換して液中から除去する生物学的脱窒方法が知られている（例えば、特許文献２〜４参照。）。
【０００５】
【特許文献１】
特公平７−１２４７７号公報
【特許文献２】
特開平１１−１０４６９３号公報
【特許文献３】
特開２００１−２０５３００号公報
【特許文献４】
特開２００２−０６６５９１号公報
【０００６】
【発明が解決しようとする課題】
しかしながら、上記した方法により汚泥返流水から、効率的にアンモニア性窒素及びリン酸態リンを除去することが可能であるが、特に閉鎖性水域への水質改善を目的とした水質規制の強化にともない、ＣＯＤ成分についても効率的に除去することが望まれている。
また、生汚泥から生じる汚泥濃縮分離液と、余剰汚泥を消化して得られる消化汚泥から生じる脱水ろ液とを混合し、好気的にＣＯＤ酸化、硝化処理を行っても、ＣＯＤ処理ではＣＯＤ_Cr値が減少するに従って、ＣＯＤ_Mn値が増加するといった傾向を示し、分解の難しい分子量の大きな成分が、小さく寸断され中間代謝物として残る形となった。
【０００７】
本発明は、汚泥返流水に含有するＣＯＤ、アンモニア性窒素等を除去して蓄積を防止し、水処理系への負荷の増大や処理水質の低下を抑制するための処理方法を提供することを目的とするものである。
【０００８】
【課題を解決するための手段】
本発明者らは、上記目的を達成すべく鋭意研究した結果、生汚泥から生ずる汚泥濃縮分離液と余剰汚泥を消化して得られる脱水ろ液とを別個に処理することにより有機物および窒素を高い除去率で除去できることを見出し、本発明に到達した。
【０００９】
すなわち、本発明は、水処理系で発生した汚泥を処理する汚泥処理系から前記水処理系へ返送される汚泥返流水中の有機物及び窒素を生物学的に処理するに際し、前記水処理系の最初沈殿池で分離された生汚泥から生ずる汚泥濃縮分離液が流入する処理槽（以下、汚泥濃縮分離液処理槽という。）と、前記水処理系の最終沈殿池で分離された余剰汚泥を消化して得られる脱水ろ液が流入する処理槽（以下、脱水ろ液処理槽という。）とを別個に設け、前記の汚泥濃縮分離液処理槽においては、前記の脱水ろ液処理槽から流出する処理水の一部が導入されて脱窒工程による処理が行われ、汚泥濃縮分離液処理槽から流出する処理水と、前記の脱水ろ液処理槽から流出する処理水の残部とを汚泥返流水として前記水処理系へ返流することを特徴とする汚泥返流水の処理方法を要旨とするものである。
本発明においては、好ましくは、汚泥濃縮分離液処理槽から流出する処理水の全量を脱水ろ液処理槽へ導入するものである。
また本発明においては、汚泥濃縮分離液処理槽および／または脱水ろ液処理槽における処理工程ではSRTが１０日以上になる生物処理が好ましく、また生物付着担体を用いる処理、膜処理が行われることが好ましい。
【００１０】
【発明の実施の形態】
以下、本発明について詳細に説明する。
図１に示した水処理系および汚泥処理系を備えた下水処理場での処理フローの一例を参照しながら説明する。流入下水は、水処理系の最初沈殿池１で夾雑物など比重の重いものを沈殿除去された後、生物反応槽２に導入されて有機物、窒素、リンなどが除去され、最終沈殿池３にて活性汚泥を沈殿分離した後に処理水として放流される。
【００１１】
一方、最初沈殿池１で沈殿した生汚泥１１や、最終沈殿池３にて沈殿した余剰汚泥１２は、汚泥処理系に導入し処理される。ここで発生した生汚泥１１は、重力濃縮槽５に導かれて濃縮生汚泥１５とされ、一方、余剰汚泥１２は加圧浮上濃縮槽４などの機械濃縮槽で濃縮され濃縮余剰汚泥１４とされる。そして、濃縮生汚泥１５と濃縮余剰汚泥１４の全量または一部が消化槽６に導かれ嫌気性消化されて減容化される。消化槽６から排出される消化汚泥１６は、脱水機７に導かれ脱水汚泥８と脱水ろ液１８とに分離される。
【００１２】
汚泥処理系で処理され発生する汚泥濃縮分離液１７、加圧浮上分離水１３および脱水ろ液１８は、汚泥返流水として最終的には最初沈殿池１などの水処理系へ返送されることになる。これら水処理系へ返送されるもののうち汚泥濃縮分離液１７には、ＣＯＤ、ＢＯＤ成分の有機物が高濃度に含まれ、一方、脱水ろ液１８には、嫌気性消化などの汚泥処理によって汚泥からアンモニア性窒素やリン酸態リンが移行している。そのため、これら汚泥返流水を最初沈殿池１などの水処理系へ返送する前に何らかの処理を行うことが必要となる。
【００１３】
本発明は、汚泥濃縮分離液１７を処理するための汚泥濃縮分離液処理槽１０と、脱水ろ液１８を処理するための脱水ろ液処理槽９とを別個に設けて処理することに特徴を有するものである。
【００１４】
汚泥濃縮分離液処理槽１０では、通常、汚泥濃縮分離液１７を好気状態で汚泥滞留時間（SRT）が１０日以上の生物処理方法により、主にＣＯＤ成分等の有機物の除去が行われる。
一方、脱水ろ液処理槽９では、通常、脱水ろ液１８を好気状態で生物処理を実施し、アンモニア性窒素の硝化及びＣＯＤ成分の処理を行う。また、脱水ろ液１８を脱水ろ液処理槽９に流入する前に、造粒脱リン法により、リンと一部のアンモニア性窒素を回収することもできる。
それぞれの処理水１９，２０は、返流水として最初沈殿池１の前に返送されることになる。
【００１５】
通常、ＣＯＤ処理、硝化処理は好気条件で行われるが、硝化工程でのアルカリ度の消費を補うためには、アルカリ剤の注入が必要となり、ランニングコストがかかる。もう1つアルカリ度を上げる方法として、脱窒工程を取り入れ、生物反応によって生じるアルカリ度を用いる手段が考えられる。脱窒反応は、酸化態窒素を電子受容体として、有機物を酸化させるものであり、好気酸化と同程度の分解が期待できる。脱窒反応の導入は水槽を複数に分けるという煩わしさもあるが、ＣＯＤの分解と窒素除去およびアルカリ度の補給と多くのメリットがある。
【００１６】
図２および図３は、上記のことを考慮に入れた本発明の他の実施形態を示す処理フロー図である。図２に示した汚泥返流水の処理方法においては、汚泥濃縮分離液処理槽１０及び脱水ろ液処理槽９で、各々別個に流入する汚泥濃縮分離液１７及び脱水ろ液１８を処理するのであるが、汚泥濃縮分離液処理槽１０では無酸素条件下で脱窒工程による処理が行われ、さらに脱水ろ液処理槽９で処理されたものの一部を汚泥濃縮分離液処理槽１０に導入する方法である。脱水ろ液処理槽９から汚泥濃縮分離液処理槽１０へ導入する処理水２１の量としては、汚泥濃縮分離液１７のCOD負荷量、および脱水ろ液の窒素負荷量にも関係するが、脱水ろ液１８の水量に対し１０〜５０％程度が好ましいが、それに限定されるものではない。
この方法によれば、汚泥濃縮分離液１７の持つＢＯＤ、ＣＯＤ成分を単に好気分解するのではなく、それらの有効利用を考え、脱水ろ液１８の窒素除去に用いることができる。
【００１７】
また、図３に示す汚泥処理系では、図２に示した処理方法に加え、さらに汚泥濃縮分離液処理槽１０で処理されたものの全量を脱水ろ液処理槽９に戻すことを行う方法である。すなわち、汚泥濃縮分離液処理槽１０と脱水ろ液処理槽９との間を循環する流路を設けて処理を行う方法である。
この方法によれば、脱水ろ液１８の硝化の際に必要となるアルカリ度を、汚泥濃縮分離液１７による脱窒反応によって補給することができるようになると共に、脱窒工程で除去しきれなかったＣＯＤを脱水ろ液処理槽９で仕上げ処理を行うことができる。
【００１８】
本発明における担体として、公知の各種の担体を使用することができるが、ゲル状担体、プラスチック担体および繊維担体から選ばれた1種類の担体、あるいはこれらの担体の2種類以上を組み合わせた担体を使用することができる。担体の充填率は、処理効率と担体の流動性の点から、槽容積の５％以上、４０％以下であることが好ましく、さらには、１０％以上、３０％以下であることがより好ましい。
【００１９】
以下、参考例、実施例により、本発明を詳細に説明する。
参考例１
図１に示したフローに従って処理を行った。担体は、大きさ８ｍｍ、見かけ比重１．０５、空隙率８５％のポリエステル製繊維担体を用いた。
汚泥濃縮分離液処理槽１０として、２Ｌのメスシリンダーに担体を２０％充填し、汚泥濃縮分離液１７を１Ｌ／日で供給した。また、脱水ろ液処理槽９として１０Ｌの容器に担体を２０％充填し、脱水ろ液１８を１０Ｌ／日で供給した。各水槽の底部に散気装置を設け空気で曝気して、好気条件とした。
汚泥濃縮分離液処理槽１０での処理前後の水質を表１に、また、脱水ろ液処理槽９での処理前後の水質を表２に示した。
【００２０】
【表１】

【００２１】
【表２】

【００２２】
各原水および処理水を水量平均した結果を表３に示す。
【表３】

【００２３】
汚泥濃縮分離液１７、脱水ろ液１８共に好気処理を行う本実施例では、汚泥濃縮分離液１７のＣＯＤ処理は、ＣＯＤ_Mnにおいて８０％以上の除去率が得られた。また、脱水ろ液１８の硝化、ＣＯＤ処理については、ほぼ１００％の硝化率と、７０％のＣＯＤ_Mn除去率となった。
【００２４】
実施例１
図２に示したフローに従って処理を行った。担体は参考例１と同じ大きさ８ｍｍ、見かけ比重１．０５、空隙率８５％のポリエステル製繊維担体を用いた。
汚泥濃縮分離液１７のＣＯＤ処理に脱水ろ液からの硝化液２１を導入した脱窒反応とし、２Ｌのメスシリンダーに担体を２０％充填し、汚泥濃縮分離液１７を１Ｌ／日、脱水ろ液の硝化液２１を３Ｌ／日で供給した。また、脱水ろ液処理槽９として１０Ｌの容器に担体を２０％充填し、脱水ろ液１８を１０Ｌ／日で供給した。各水槽の底部に散気装置を設け、汚泥濃縮分離液処理槽１０は窒素ガスで、また脱水ろ液処理槽９は空気で曝気を行った。
汚泥濃縮分離液処理槽１０での処理前後の水質を表４に、また、脱水ろ液処理槽９での処理前後の水質を表５に示した。汚泥濃縮分離液１７、脱水ろ液１８の性状は実施例１と同様であり、ここでの汚泥濃縮分離液処理槽１０への原水は、汚泥濃縮分離液１７と硝化後の脱水ろ液２１の水量平均となる。
【００２５】
【表４】

【００２６】
【表５】

【００２７】
各原水および処理水を水量平均した結果を表６に示す。
【表６】

【００２８】
脱窒工程（汚泥濃縮分離液処理槽１０）で２５０ｍｇ／Ｌあった酸化態窒素（NO2−N＋NO3−N）が処理水ではほとんどゼロとなった。それに伴いＣＯＤも６０％以上除去された。処理水に酸化態窒素がなくなり、ＣＯＤ処理が進まなくなって、参考例１よりＣＯＤ除去率が若干低下する結果となった。脱水ろ液処理槽９の硝化、ＣＯＤ処理は参考例１表２と同程度を維持した。
【００２９】
実施例２
図３に示したフローに従って処理を行った。担体は参考例１、実施例１と同じ大きさ８ｍｍ、見かけ比重１．０５、空隙率８５％のポリエステル製繊維担体を用いた。
実施例１と同様に、汚泥濃縮分離液１７のＣＯＤ処理に、脱水ろ液からの硝化液２１を導入した脱窒反応とし、２Ｌのメスシリンダーに担体を２０％充填し、汚泥濃縮分離液を１Ｌ／日、脱水ろ液の硝化液２１を３Ｌ／日で供給した。また、脱水ろ液１８の硝化、ＣＯＤ処理は、脱水ろ液処理槽９として１０Ｌの容器に担体を２０％充填し、脱水ろ液１８を１０Ｌ／日で供給し、さらに、汚泥濃縮分離液処理槽１０からの上記汚泥濃縮分離液処理水２０を脱水ろ液処理槽９に全量返送させた。
汚泥濃縮分離液処理槽１０での処理前後の水質を表７に、また、脱水ろ液処理槽９での処理前後の水質を表８に示した。汚泥濃縮分離液１７、脱水ろ液１８の性状は参考例１と同様であり、ここでの汚泥濃縮分離液処理槽１０への原水は、汚泥濃縮分離液１７と硝化後の脱水ろ液２１の水量平均となる。また、汚泥濃縮分離液処理槽１０の処理水２０を全量脱水ろ液処理槽９に返送したため、脱水ろ液処理槽９の原水も脱水ろ液１８と汚泥濃縮分離液処理水２０の水量平均となる。
【００３０】
【表７】

【００３１】
【表８】

【００３２】
各原水および処理水を水量平均した結果を表９に示す。
【表９】

【００３３】
実施例２は、実施例１で参考例１より若干悪くなったＣＯＤ処理性能を、脱窒工程の処理水２０を硝化槽（脱水ろ液処理水槽）９に持ち込むことで精度を上げるシステムである。その結果、脱水ろ液１８と汚泥濃縮分離液１７の水量平均である処理水がＣＯＤ_Ｃｒで３１３ｍｇ／Ｌであったものが、９５ｍｇ／Ｌまで、ＣＯＤ_Ｍｎで６７ｍｇ／Ｌであったものが、１７ｍｇ／Ｌまで低下した。
【００３４】
比較例１
図４に示したフローに従い、汚泥濃縮分離液１７と脱水ろ液１８を混合し、単一槽２２で好気的にＣＯＤ処理、硝化を行った。汚泥濃縮分離液１．７Ｌ／日、脱水ろ液８．３Ｌ／日で、１０Ｌの反応槽２２に供給した。反応槽２２には担体を２０％充填し、空気を底部から散気した。
その結果を表１０に示す。
【００３５】
【表１０】

【００３６】
ＣＯＤ_Crは若干処理されたが、ＣＯＤ_Mnが逆に増加するなどの結果となった。より分解の難しい高分子の物質が、細かく寸断された結果、ＣＯＤ_Mnでも測定できる中間代謝物として残ってしまったためであると考えられる。
【００３７】
【発明の効果】
本発明によれば、汚泥濃縮分離液のＣＯＤ処理に脱水ろ液の硝化液の脱窒反応を利用することで、窒素除去を兼ねたＣＯＤ処理が可能となった。さらに、汚泥濃縮分離液処理水を全量脱水ろ液処理槽へ流入させることにより、再度好気処理することで、ＣＯＤ処理性能を下水の放流水並に低減することが可能となった。処理水に残留するNOx-Nは、水処理系の最初沈殿池へ戻すことで、最初沈殿池や水処理系の脱窒槽にて速やかに脱窒される。
【図面の簡単な説明】
【図１】本発明における処理工程のフローを示す概略図である。
【図２】本発明における処理工程の他のフローを示す概略図である。
【図３】本発明における処理工程の他のフローを示す概略図である。
【図４】従来の技術における処理工程のフローを示す概略図である。
【符号の説明】
１最初沈殿池
２生物反応槽
３最終沈殿池
４加圧浮上濃縮槽
５重力濃縮槽
６消化槽
７脱水機
８脱水汚泥
９脱水ろ液処理槽
１０汚泥濃縮分離液処理槽
１１生汚泥
１２余剰汚泥
１３加圧浮上分離水
１４濃縮余剰汚泥
１５濃縮生汚泥
１６消化汚泥
１７汚泥濃縮分離液
１８脱水ろ液
１９、２１脱水ろ液処理水
２０汚泥濃縮分離液処理水
２１循環水
２２処理槽[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for treating return water of a sludge treatment system that is generated when a sludge such as initially settled sludge or digested sludge generated from a sewage treatment plant is concentrated or dehydrated.
[0002]
[Prior art]
In conventional sewage treatment, a large amount of organic sludge generated from a sewage treatment plant is processed through steps such as concentration, digestion, and dehydration. The running water is usually returned to a water treatment system such as a settling basin. The sludge return water contains high concentrations of components such as COD, ammonia nitrogen, and phosphorous phosphorus. Therefore, the load associated with the sludge return water increases the load of the water treatment system. This is a cause of water quality degradation.
[0003]
As the treatment of sludge return water, a granulation dephosphorization method has already been put to practical use with respect to the removal of phosphate phosphorus (see, for example, Patent Document 1). This granulation dephosphorization method is a technology that efficiently removes phosphorus from human waste, industrial wastewater, etc., containing a large amount of ammonia nitrogen, and crystallizes magnesium in the water as magnesium ammonium phosphate particles by adding magnesium, Solid-liquid separation.
[0004]
In addition, ammonia nitrogen is treated with biological sludge after nitrifying ammonia nitrogen into nitrate nitrogen, and then using raw sludge that has been settled and separated in the first sedimentation basin as a BOD source for denitrification. There is known a biological denitrification method in which it is converted into gas and removed from the liquid (for example, see Patent Documents 2 to 4).
[0005]
[Patent Document 1]
Japanese Patent Publication No. 7-12477 [Patent Document 2]
JP 11-104693 A [Patent Document 3]
JP 2001-205300 A [Patent Document 4]
Japanese Patent Laid-Open No. 2002-066591
[Problems to be solved by the invention]
However, ammonia nitrogen and phosphate phosphorus can be efficiently removed from the sludge return water by the above-mentioned method, but with the strengthening of water quality regulations especially for the purpose of improving water quality in closed water areas Further, it is desired to efficiently remove the COD component.
Moreover, even if COD oxidation and nitrification treatment are carried out aerobically by COD oxidation and nitrification treatment, COD treatment is COD by mixing sludge concentrated separation liquid produced from raw sludge and dehydrated filtrate produced from digested sludge obtained by digesting excess sludge. _{As the Cr} value decreased, the COD _Mn value tended to increase, and the components with large molecular weight that were difficult to decompose were cut into small pieces and remained as intermediate metabolites.
[0007]
The present invention provides a treatment method for preventing accumulation by removing COD, ammonia nitrogen, and the like contained in sludge return water, and suppressing an increase in load on the water treatment system and a decrease in the quality of treated water. It is the purpose.
[0008]
[Means for Solving the Problems]
As a result of diligent research to achieve the above object, the present inventors have increased the amount of organic matter and nitrogen by separately treating the sludge concentrated and separated liquid produced from raw sludge and the dehydrated filtrate obtained by digesting excess sludge. The inventors have found that it can be removed at a removal rate, and have reached the present invention.
[0009]
That is, the present invention, when biologically treating the organic matter and nitrogen in the sludge return water returned to the water treatment system from the sludge treatment system for treating the sludge generated in the water treatment system, Digesting the treatment tank into which the sludge concentrated separation liquid generated from the raw sludge separated in the first sedimentation basin flows (hereinafter referred to as the sludge concentration separation liquid treatment tank) and the excess sludge separated in the final sedimentation basin of the water treatment system A treatment tank into which the dehydrated filtrate obtained in this way flows (hereinafter referred to as a dehydrated filtrate treatment tank) is provided separately, and the sludge concentrated separation liquid treatment tank flows out of the dehydrated filtrate treatment tank. A part of the treated water is introduced and the treatment by the denitrification process is performed, and the treated water flowing out from the sludge concentrated separation liquid treatment tank and the remaining treated water flowing out from the dehydrated filtrate treatment tank are sludge return water and characterized in that return flow to the water treatment system as That the sludge return the flowing water treatment method in which the subject matter.
In the present invention, preferably, it is intended to introduce the entire amount of the treated water flowing out of the sludge concentration and separation liquid treatment vessel to dewatering filtrate treatment vessel.
In the present invention, in the treatment step in the sludge concentration / separation liquid treatment tank and / or the dehydrated filtrate treatment tank, biological treatment with an SRT of 10 days or more is preferable, and treatment using a bioadhesive carrier and membrane treatment are performed. Is preferred.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
It demonstrates referring an example of the processing flow in the sewage treatment plant provided with the water treatment system and sludge treatment system shown in FIG. The inflowing sewage is settled and removed in the first sedimentation basin 1 of the water treatment system, and then introduced into the biological reaction tank 2 to remove organic matter, nitrogen, phosphorus, etc. The activated sludge is separated by sedimentation and discharged as treated water.
[0011]
On the other hand, raw sludge 11 precipitated in the first sedimentation basin 1 and surplus sludge 12 precipitated in the final sedimentation basin 3 are introduced into the sludge treatment system and processed. The raw sludge 11 generated here is guided to the gravity concentration tank 5 to be the concentrated raw sludge 15, while the excess sludge 12 is concentrated in a mechanical concentration tank such as the pressurized flotation concentration tank 4 to be the concentrated excess sludge 14. The Then, all or part of the concentrated raw sludge 15 and the concentrated excess sludge 14 is guided to the digestion tank 6 and anaerobically digested to reduce the volume. The digested sludge 16 discharged from the digester 6 is guided to the dehydrator 7 and separated into the dehydrated sludge 8 and the dehydrated filtrate 18.
[0012]
The sludge concentrated separation liquid 17, the pressurized flotation separation water 13 and the dehydrated filtrate 18 generated and processed in the sludge treatment system are finally returned to the water treatment system such as the first sedimentation basin 1 as sludge return water. Become. Among those returned to the water treatment system, the sludge concentrated separation liquid 17 contains high concentrations of organic substances such as COD and BOD components, while the dehydrated filtrate 18 is separated from sludge by sludge treatment such as anaerobic digestion. Ammonia nitrogen and phosphate phosphorus have migrated. Therefore, it is necessary to perform some kind of treatment before returning the sludge return water to the water treatment system such as the settling basin 1 first.
[0013]
The present invention is characterized in that the sludge concentrated separation liquid treatment tank 10 for treating the sludge concentrated separation liquid 17 and the dehydrated filtrate treatment tank 9 for treating the dehydrated filtrate 18 are separately provided and treated. It is what you have.
[0014]
In the sludge concentrated separation liquid treatment tank 10, organic substances such as COD components are mainly removed by a biological treatment method in which the sludge concentrated separation liquid 17 is in an aerobic state and the sludge residence time (SRT) is 10 days or longer.
On the other hand, in the dehydrated filtrate treatment tank 9, biological treatment is usually performed with the dehydrated filtrate 18 in an aerobic state, and nitrification of ammonia nitrogen and treatment of COD components are performed. Further, before the dehydrated filtrate 18 flows into the dehydrated filtrate treatment tank 9, phosphorus and some ammonia nitrogen can be recovered by granulation dephosphorization.
Each treated

water

19 and 20 is returned before the first settling basin 1 as return water.
[0015]
Normally, COD treatment and nitrification treatment are carried out under aerobic conditions. However, in order to compensate for the consumption of alkalinity in the nitrification step, it is necessary to inject an alkaline agent, which increases running costs. As another method for increasing the alkalinity, a method using a denitrification step and using the alkalinity generated by a biological reaction can be considered. The denitrification reaction uses oxidized nitrogen as an electron acceptor to oxidize organic matter, and can be expected to be decomposed to the same extent as aerobic oxidation. Although the introduction of the denitrification reaction is troublesome in that the water tank is divided into a plurality of tanks, there are many merits such as COD decomposition, nitrogen removal, and alkalinity replenishment.
[0016]
2 and 3 are process flow diagrams illustrating another embodiment of the present invention that takes the above into consideration. In the method of treating sludge return water shown in FIG. 2, the sludge concentrated separation liquid treatment tank 10 and the dehydrated filtrate treatment tank 9 treat the sludge concentrated separation liquid 17 and the dehydrated filtrate 18 that flow in separately, respectively. However, in the sludge concentration / separation liquid treatment tank 10, the treatment by the denitrification process is performed under anoxic conditions, and a part of the treatment in the dehydrated filtrate treatment tank 9 is introduced into the sludge concentration / separation liquid treatment tank 10. It is. The amount of the treated water 21 introduced from the dehydrated filtrate treatment tank 9 to the sludge concentrated / separated liquid treatment tank 10 is related to the COD load of the sludge concentrated / separated liquid 17 and the nitrogen load of the dehydrated filtrate. Although about 10 to 50% is preferable with respect to the amount of water of the filtrate 18, it is not limited thereto.
According to this method, the BOD and COD components of the sludge concentrated separation liquid 17 are not simply aerobically decomposed but can be used for removing nitrogen from the dehydrated filtrate 18 in view of their effective utilization.
[0017]
Further, in the sludge treatment system shown in FIG. 3, in addition to the treatment method shown in FIG. 2, the whole amount of the sludge concentrated / separated liquid treatment tank 10 is returned to the dehydrated filtrate treatment tank 9. . That is, this is a method of performing treatment by providing a flow path that circulates between the sludge concentrated separation liquid treatment tank 10 and the dehydrated filtrate treatment tank 9.
According to this method, the alkalinity required for nitrification of the dehydrated filtrate 18 can be replenished by the denitrification reaction by the sludge concentrated separation liquid 17 and cannot be completely removed in the denitrification step. The COD can be finished in the dehydrated filtrate treatment tank 9.
[0018]
As the carrier in the present invention, various known carriers can be used. One type of carrier selected from a gel carrier, a plastic carrier and a fiber carrier, or a carrier obtained by combining two or more of these carriers. Can be used. The filling rate of the carrier is preferably 5% or more and 40% or less of the tank volume, and more preferably 10% or more and 30% or less from the viewpoint of processing efficiency and carrier fluidity.
[0019]
Hereinafter, the present invention will be described in detail with reference examples and examples.
Reference example 1
Processing was performed according to the flow shown in FIG. As the carrier, a polyester fiber carrier having a size of 8 mm, an apparent specific gravity of 1.05, and a porosity of 85% was used.
As the sludge concentrated separation liquid treatment tank 10, a 2 L graduated cylinder was filled with 20% of the carrier, and the sludge concentrated separation liquid 17 was supplied at 1 L / day. Further, 20% of the carrier was filled in a 10 L container as the dehydrated filtrate treatment tank 9, and the dehydrated filtrate 18 was supplied at 10 L / day. An aeration device was provided at the bottom of each water tank and aerated with air to achieve aerobic conditions.
Table 1 shows the water quality before and after the treatment in the sludge concentrated separation liquid treatment tank 10, and Table 2 shows the water quality before and after the treatment in the dehydrated filtrate treatment tank 9.
[0020]
[Table 1]

[0021]
[Table 2]

[0022]
Table 3 shows the result of averaging the amount of each raw water and treated water.
[Table 3]

[0023]
In this example in which both the sludge concentrated separation liquid 17 and the dehydrated filtrate 18 are subjected to aerobic treatment, the COD treatment of the sludge concentrated separation liquid 17 obtained a removal rate of 80% or more in COD _Mn . Further, regarding the nitrification and COD treatment of the dehydrated filtrate 18, the nitrification rate was almost 100% and the COD _Mn removal rate was 70%.
[0024]
Example 1
Processing was performed according to the flow shown in FIG. The carrier used was a polyester fiber carrier having the same size of 8 mm as in Reference Example 1 , an apparent specific gravity of 1.05, and a porosity of 85%.
A denitrification reaction in which the nitrification liquid 21 from the dehydrated filtrate is introduced into the COD treatment of the sludge concentrated separated liquid 17 is filled with 20% of a carrier in a 2 L graduated cylinder, and the sludge concentrated separated liquid 17 is 1 L / day, the dehydrated filtrate. Was supplied at a rate of 3 L / day. Further, 20% of the carrier was filled in a 10 L container as the dehydrated filtrate treatment tank 9, and the dehydrated filtrate 18 was supplied at 10 L / day. An air diffuser was provided at the bottom of each water tank, the sludge concentrated separation liquid treatment tank 10 was aerated with nitrogen gas, and the dehydrated filtrate treatment tank 9 was aerated with air.
Table 4 shows the water quality before and after the treatment in the sludge concentrated separation liquid treatment tank 10, and Table 5 shows the water quality before and after the treatment in the dehydrated filtrate treatment tank 9. The properties of the sludge concentrated separation liquid 17 and the dehydrated filtrate 18 are the same as in Example 1. The raw water to the sludge concentrated separation liquid treatment tank 10 here is the sludge concentrated separation liquid 17 and the dehydrated filtrate 21 after nitrification. Average amount of water.
[0025]
[Table 4]

[0026]
[Table 5]

[0027]
Table 6 shows the results obtained by averaging the amount of each raw water and treated water.
[Table 6]

[0028]
Oxidized nitrogen (NO2-N + NO3-N) that was 250 mg / L in the denitrification step (sludge-concentrated separation liquid treatment tank 10) became almost zero in the treated water. Along with this, COD was also removed by 60% or more. Oxidized nitrogen disappeared in the treated water, and COD treatment did not progress, resulting in a slightly lower COD removal rate than in Reference Example 1 . The nitrification and COD treatment of the dehydrated filtrate treatment tank 9 was maintained at the same level as in Reference Example 1 Table 2.
[0029]
Example 2
Processing was performed according to the flow shown in FIG. As the carrier, a polyester fiber carrier having the same size as Reference Example 1 and Example 8 of 8 mm, an apparent specific gravity of 1.05, and a porosity of 85% was used.
In the same manner as in Example 1 , the COD treatment of the sludge concentrated separation liquid 17 was carried out by a denitrification reaction in which the nitrification liquid 21 from the dehydrated filtrate was introduced, and a 2 L graduated cylinder was filled with 20% of the carrier. 1 L / day, dehydrated filtrate nitrification solution 21 was supplied at 3 L / day. Further, the nitrification and COD treatment of the dehydrated filtrate 18 is carried out by filling a 10 L container as a dehydrated filtrate treatment tank 9 with 20% of the carrier, supplying the dehydrated filtrate 18 at 10 L / day, and further treating the sludge concentrated separation liquid. The entire amount of the sludge concentrated separation liquid treated water 20 from the tank 10 was returned to the dehydrated filtrate treatment tank 9.
Table 7 shows the water quality before and after the treatment in the sludge concentrated separation liquid treatment tank 10, and Table 8 shows the water quality before and after the treatment in the dehydrated filtrate treatment tank 9. The properties of the sludge concentrated separation liquid 17 and the dehydrated filtrate 18 are the same as in Reference Example 1. The raw water to the sludge concentrated separation liquid treatment tank 10 here is the sludge concentrated separation liquid 17 and the dehydrated filtrate 21 after nitrification. Average amount of water. In addition, since the entire amount of the treated water 20 in the sludge concentrated separation liquid treatment tank 10 is returned to the dehydrated filtrate treatment tank 9, the raw water in the dehydrated filtrate treatment tank 9 is also the average amount of water of the dehydrated filtrate 18 and the sludge concentrated separation liquid treated water 20. Become.
[0030]
[Table 7]

[0031]
[Table 8]

[0032]
Table 9 shows the result of averaging the amount of each raw water and treated water.
[Table 9]

[0033]
Example 2 is a system to improve the accuracy by bringing the COD performance became slightly worse than Example 1 in Example 1, the treated water 20 in the denitrification to the nitrification reactor (dehydration filtrate treatment water tank) 9 . As a result, the treated water, which is the average amount of water of the dehydrated filtrate 18 and the sludge concentrated separation liquid 17, was 313 mg / L in COD _Cr , up to 95 mg / L, and that in COD _Mn was 67 mg / L. It decreased to 17 mg / L.
[0034]
Comparative Example 1
According to the flow shown in FIG. 4, the sludge concentrated separation liquid 17 and the dehydrated filtrate 18 were mixed, and COD treatment and nitrification were performed aerobically in a single tank 22. The sludge concentrated separation liquid 1.7 L / day and the dehydrated filtrate 8.3 L / day were supplied to the 10 L reaction tank 22. The reaction tank 22 was filled with 20% carrier and air was diffused from the bottom.
The results are shown in Table 10.
[0035]
[Table 10]

[0036]
Although COD _Cr was slightly treated, COD _Mn increased on the contrary. This is probably because a more difficult-to-decompose polymer substance remained as an intermediate metabolite that can be measured by COD _Mn as a result of being shredded finely.
[0037]
【The invention's effect】
According to the present invention, COD treatment that also serves as nitrogen removal can be performed by utilizing the denitrification reaction of the nitrating solution of the dehydrated filtrate for the COD treatment of the sludge concentrated separation liquid. Furthermore, the COD treatment performance can be reduced to the same level as the sewage effluent by performing the aerobic treatment again by flowing the sludge concentrated separation liquid treated water into the dehydrated filtrate treatment tank. NOx-N remaining in the treated water is quickly denitrified in the first sedimentation basin or water treatment system denitrification tank by returning it to the first sedimentation basin of the water treatment system.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a flow of processing steps in the present invention.
FIG. 2 is a schematic view showing another flow of processing steps in the present invention.
FIG. 3 is a schematic view showing another flow of processing steps in the present invention.
FIG. 4 is a schematic diagram showing a flow of processing steps in the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 First sedimentation tank 2 Biological reaction tank 3 Final sedimentation tank 4 Pressurization flotation concentration tank 5 Gravity concentration tank 6 Digestion tank 7 Dehydrator 8 Dehydrated sludge 9 Dehydrated filtrate treatment tank 10 Sludge concentration separation liquid treatment tank 11 Raw sludge 12 Surplus sludge 13 Pressurized floating separated water 14 Concentrated surplus sludge 15 Concentrated raw sludge 16 Digested sludge 17 Sludge concentrated separated liquid 18

Dehydrated filtrate

19, 21 Dehydrated filtrate treated water 20 Sludge concentrated separated liquid treated water 21 Circulating water 22 Treatment tank

Claims

When biologically treating organic matter and nitrogen in the sludge return water returned to the water treatment system from the sludge treatment system that treats sludge generated in the water treatment system, it is separated in the first sedimentation basin of the water treatment system. A treatment tank into which the sludge concentrated separation liquid generated from the raw sludge flows and a treatment tank into which the dehydrated filtrate obtained by digesting excess sludge separated in the final sedimentation basin of the water treatment system flows , In the treatment tank into which the sludge concentrated separation liquid flows, a part of the treated water flowing out from the treatment tank into which the dehydrated filtrate flows in is introduced and processed by the denitrification process, and the sludge concentrated separation liquid flows in. Sludge return water, wherein the treated water flowing out from the treatment tank and the remainder of the treated water flowing out from the treatment tank into which the dehydrated filtrate flows are returned to the water treatment system as sludge return water. Processing method.

In the treatment tank into which the sludge concentrate / separate flows, a part of the treated water flowing out from the treatment tank into which the dehydrated filtrate flows is introduced, the treatment by the denitrification process is performed, and the treatment in which the sludge concentrate / separate flows in The entire amount of treated water flowing out from the tank is introduced into the treatment tank into which the dehydrated filtrate flows, and the remainder of the treated water flowing out from the treatment tank into which the dehydrated filtrate flows is returned to the water treatment system as sludge return water. The method for treating sludge return water according to claim 1.

The method for treating sludge return water according to claim 1 or 2, wherein the bioadhesive carrier is used in a treatment step in the treatment tank into which the sludge concentrated separation liquid flows and / or the treatment tank into which the dehydrated filtrate flows.