JPS61146395A - Method for denitrifying biologically waste water - Google Patents

Abstract

PURPOSE:To nitrate and denitrify efficiently by removing previously dissolved oxygen in a nitrating liq., untreated waste water, and return sludge in the first denitrification vessel, and then carrying out denitrification when a nitrating liq. circulation system adopted by the Ludsack method, etc., is used. CONSTITUTION:In the biological treatment of waste water by a nitrating liq. circulation system, >=2 denitrification vessel 1 and 1' which are substantially sealed hermetically are provided. Waste water 2, return sludge 3, and a circulating liq. 4 from a nitration vessel 5 are introduced into the first denitrification vessel 1, and dissolved oxygen in the mixture is consumed by activated sludge under strong agitation. A part of nitric nitrogen and nitrous nitrogen are simultaneously denitrified. The remaining nitric and nitrous nitrogen are completely denitrified in the second denitrification vessel 1'. BOD components in the denitrified liq. are oxidized and decomposed in the nitration vessel 5, and ammoniacal nitrogen and org. nitrogen are simultaneously oxidized to nitric nitrogen and nitrous nitrogen. Consequently, the denitrification efficiency can be remarkably increased and hence the content of BOD and total nitrogen in waste water can be reduced.

Description

【発明の詳細な説明】 産業上の利用分野 本発明は活性汚泥を用いる廃水の処理法、就中、硝化液
循環方式を採用した廃水処理法の改良に関する。DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for treating wastewater using activated sludge, particularly to an improvement in a method for treating wastewater using a nitrified liquid circulation system.

従来技術および問題点 活性汚泥処理法は廃水、例えば、工場廃水、都市下水、
畜産廃水等の浄化に広く採用されている。Prior art and problems The activated sludge treatment method is used to treat wastewater, such as industrial wastewater, municipal sewage,
It is widely used to purify livestock wastewater, etc.

活性汚泥処理法の最も基本的形態は、廃水中のＢＯＤ成
分と窒素成分とを、それぞれ別の汚泥を用いて、個別に
処理する方法である。この方法はＢＯＤ成分の酸化、窒
素成分の硝化および硝化された成分の還元による脱窒工
程を含みそれぞれ別の処理槽中で最適条件のもとで処理
し得るため、その点では最も好ましいものであるが、装
置を個別に設ける必要があるため設備が膨大となり広い
敷地面積を必要とする。加えて硝化工程での中和剤、脱
窒工程での水素供与体を必要とし、必らずしも一般的に
採用し得るものではない。The most basic form of the activated sludge treatment method is a method in which BOD components and nitrogen components in wastewater are treated separately using different sludges. This method includes denitrification steps by oxidizing BOD components, nitrifying nitrogen components, and reducing nitrified components, and can be treated under optimal conditions in separate treatment tanks, so it is the most preferable from that point of view. However, since each device needs to be installed individually, the equipment becomes enormous and requires a large site area. In addition, it requires a neutralizing agent in the nitrification process and a hydrogen donor in the denitrification process, which cannot necessarily be generally adopted.

上記の方法を改良するものとしてルドザック（Ｌｕｄｚ
ａｃｋ　）法として知られる方法がある。この方法は有
機炭素源を分解する好気性菌、硝化菌および脱窒菌の混
存する単相の汚泥を用い、これを、脱窒槽と硝化槽に入
れ、廃水は、脱窒槽と硝化槽を循環させながら処理する
。硝化槽では空気曝気を行なっている。この方法では装
置の設置面積を小さくでき、中和剤や水素供与体を必要
としないため経済的であるが、硝化工程の効率が悪くそ
のため曝気槽を大きくしなければならない欠点がある。As an improvement on the above method, Ludz
There is a method known as the ack method. This method uses single-phase sludge containing aerobic bacteria that decompose organic carbon sources, nitrifying bacteria, and denitrifying bacteria, which is placed in a denitrifying tank and a nitrifying tank, and the wastewater is circulated between the denitrifying tank and nitrifying tank. Process while doing so. Air aeration is performed in the nitrification tank. This method is economical because the installation area of the device can be reduced and no neutralizing agent or hydrogen donor is required, but it has the disadvantage that the nitrification process is inefficient and therefore requires a larger aeration tank.

この欠点を改良するため、硝化槽の空気曝気に代えて、
酸素曝気を行なう方法がある（特開昭５７−１０３９１
号公報）。この方法はルビザック法に比べ硝化効率を高
くすることができ、従って装置の小型化が図れるが、硝
化工程で多量の溶存酸素が液中に含まれることとなり、
これを脱窒槽に送ると、脱窒槽での嫌気性レベルを高め
ることができないため、脱窒反応を遅らせることとなる
。In order to improve this drawback, instead of air aeration in the nitrification tank,
There is a method of oxygen aeration (Japanese Patent Application Laid-Open No. 57-10391)
Publication No.). This method can increase the nitrification efficiency compared to the Rubizac method, and the equipment can therefore be made more compact, but a large amount of dissolved oxygen is included in the liquid during the nitrification process.
If this is sent to the denitrification tank, the anaerobic level in the denitrification tank cannot be increased, so the denitrification reaction will be delayed.

以上の如く、従来の活性汚泥による廃水処理技術では、
硝化と脱窒を経済的かつ効率的に行なう上で更に改良す
べき点があった。As mentioned above, with conventional wastewater treatment technology using activated sludge,
There were points that needed to be further improved in order to perform nitrification and denitrification economically and efficiently.

問題点を　決するための手段 本発明はルビザック法等に採用されている硝化液循環方
式を用いるに当り、硝化液、原廃水、返送汚泥中の溶存
酸素を予め第１の脱窒槽内で除いた後、脱窒処理する方
法であり、これによって硝化および脱室反応を効率よく
行なうことを可能にする。Means for Solving Problems The present invention uses a nitrification solution circulation method adopted in the Rubizac method, etc., by removing dissolved oxygen in the nitrification solution, raw wastewater, and returned sludge in advance in the first denitrification tank. This method is followed by denitrification treatment, which enables efficient nitrification and dechambering reactions.

即ち、本発明は第１図に示すごとく硝化液循環方式によ
る廃水の生物学的処理方法において、２以上の実質上密
閉した脱窒槽（１）、（１゛）を設は第１の脱窒槽に廃
水（２）、返送汚泥（３）および硝化槽からの循環液（
４）を導入し、強撹拌下これらに溶存する酸素を活性汚
泥により消費すると共に硝酸性窒素および亜硝酸性窒素
の一部を脱窒し、次いで第２以降の脱窒槽（１°）で硝
酸性窒素および亜硝酸性窒素を実質上完全に脱窒し、脱
窒液を更に硝化槽でＢＯＤ成分を酸化分解すると共にア
ンモニア態窒素および有機態窒素を硝酸性窒素および亜
硝酸性窒素に酸化することを特徴とする廃水の生物学的
脱窒方法に関する。That is, the present invention provides a biological treatment method for wastewater using a nitrifying solution circulation system as shown in FIG. wastewater (2), return sludge (3) and circulating liquid from the nitrification tank (
4) is introduced, the oxygen dissolved in these is consumed by activated sludge under strong stirring, and a part of nitrate nitrogen and nitrite nitrogen is denitrified, and then nitric acid is BOD components are oxidized and decomposed in the denitrification tank, and ammonia nitrogen and organic nitrogen are oxidized to nitrate nitrogen and nitrite nitrogen. This invention relates to a biological denitrification method for wastewater characterized by the following.

本発明において硝化液循環方式とは第１図に示すごとく
廃水をまず脱窒槽に送り、硝酸性窒素や亜硝酸性窒素の
ごとき酸化型窒素を窒素ガスにして脱窒し、この処理液
を更に硝化槽（５）に導入して、原液中のＢＯＤ成分を
空気または酸素曝気により酸化すると共に廃液中のアン
モニア態窒素や有機態窒素を酸化型窒素に代え（硝化）
、硝化槽から流出する硝化液（硝化槽流出水（６））の
一部を脱窒槽（１）へ循環（４）し、残りを固液分離装
置（７）で処理し、汚泥（３）を脱室槽に送って再使用
し、分離した処理水（８）を排水する方法である。硝化
槽流出水（６）中の酸化型窒素含量が多い場合は、循環
液（４）の竜を多くするか、固液分離装置（７）での処
理前に別の脱窒槽を設けてもよい。また汚泥の量が過剰
となった場合は過剰分を系外に排出する。In the present invention, the nitrification liquid circulation system is as shown in Figure 1. Wastewater is first sent to a denitrification tank, where oxidized nitrogen such as nitrate nitrogen and nitrite nitrogen is converted into nitrogen gas, denitrified, and this treated liquid is further Introduced into the nitrification tank (5), the BOD components in the stock solution are oxidized by air or oxygen aeration, and the ammonia nitrogen and organic nitrogen in the waste solution are replaced with oxidized nitrogen (nitrification).
A part of the nitrification liquid flowing out from the nitrification tank (nitrification tank effluent (6)) is circulated (4) to the denitrification tank (1), and the rest is treated with the solid-liquid separator (7), and the sludge (3) is recycled. In this method, the treated water (8) is sent to a derooming tank for reuse, and the separated treated water (8) is drained. If the oxidized nitrogen content in the nitrification tank effluent (6) is high, increase the amount of nitrogen in the circulating fluid (4) or install another denitrification tank before treatment with the solid-liquid separator (7). good. In addition, if the amount of sludge becomes excessive, the excess amount is discharged outside the system.

本発明において脱窒槽は少なくとも２個設ける。In the present invention, at least two denitrification tanks are provided.

脱窒槽は２個以上、パイプで連結されていてもよいが、
第１図に示すごとく貫通孔を有する隔壁で仕切られてい
てもよい、脱窒槽は実質上密閉型であって、外部の空気
から遮断されている。脱窒槽で発生する窒素ガスは適当
な手段、例えばダクト（図示されていない）で外部へ放
出してもよい。また混合液に溶解または分散した状態で
硝化槽へ送ってもよい。Two or more denitrification tanks may be connected by pipes, but
The denitrification tank, which may be partitioned by partition walls having through holes as shown in FIG. 1, is substantially closed and isolated from outside air. The nitrogen gas generated in the denitrification tank may be discharged to the outside by suitable means, such as a duct (not shown). Alternatively, it may be sent to the nitrification tank in a state of being dissolved or dispersed in the mixed liquid.

第１の脱窒槽（１）には、廃水（２）と、酸化型窒素を
含む硝化槽からの循環液（４）および返送汚泥（３）が
送り込まれる。The first denitrification tank (1) is fed with wastewater (2), circulating fluid (4) containing oxidized nitrogen from the nitrification tank, and return sludge (3).

廃水（２）中には溶存酸素、ＢＯＤ成分、アンモニア態
窒素、有機態窒素等が含まれており、場合によっては酸
化型窒素が含まれているときもある。The wastewater (2) contains dissolved oxygen, BOD components, ammonia nitrogen, organic nitrogen, etc., and may also contain oxidized nitrogen in some cases.

循環液（４）中には、活性汚泥、溶存酸素、アンモニア
態窒素や有機態窒素の酸化によって生ずる酸化型窒素、
例えば硝酸性窒素、亜硝酸性窒素等が含まれている。活
性汚泥中には有機性炭素化合物を好気的に分解する菌、
硝化菌および脱窒菌が含まれている。The circulating fluid (4) contains activated sludge, dissolved oxygen, oxidized nitrogen produced by the oxidation of ammonia nitrogen and organic nitrogen,
For example, nitrate nitrogen, nitrite nitrogen, etc. are included. Activated sludge contains bacteria that aerobically decompose organic carbon compounds.
Contains nitrifying and denitrifying bacteria.

脱窒菌は通性嫌気性菌であるため廃液（２）や循環液（
４）を−個の脱窒槽（１）で処理すると、脱窒槽に存在
する溶存酸素を優先的に消費するため、脱窒反応が抑制
され、脱窒を効率的に行なうことができない。この現象
は、硝化工程で酸素曝気を行なったとき顕著である。さ
らに後述するごとく、酸素の導入を最終硝化槽で行なう
向流法では脱窒槽に導入される循環液（４）中の溶存酸
素濃度が高くなりこの現象は著しい。Denitrifying bacteria are facultative anaerobic bacteria, so they are used in waste liquid (2) and circulating liquid (
When 4) is treated in − number of denitrification tanks (1), the dissolved oxygen present in the denitrification tank is preferentially consumed, so the denitrification reaction is suppressed and denitrification cannot be carried out efficiently. This phenomenon is remarkable when oxygen aeration is performed during the nitrification process. Furthermore, as will be described later, in the countercurrent method in which oxygen is introduced in the final nitrification tank, the concentration of dissolved oxygen in the circulating fluid (4) introduced into the denitrification tank becomes high, and this phenomenon is remarkable.

本発明では、少なくとも２個の脱窒槽を設け、その最初
の脱窒槽で一部の酸化型窒素の脱窒と同時に溶存酸素を
完全に消費させる。第１の脱窒槽にはＢＯＤ成分やアン
モニア態窒素等を含む廃液が導入されるため、これを強
撹拌下で活性汚泥と接触させることにより、ＢＯＤ成分
およびアンモニア態窒素、有機態窒素等の一部を酸化し
、溶存酸素を実質上完全に消費することができる。この
撹拌は同時に、活性汚泥中の微生物を細分化し、その結
果廃液との接触面積が広くなるため、活性汚泥への廃水
中の各種成分の吸着を促進し、ＢＯＤ成分の酸化並びに
脱窒および硝化効率を一層向上させることに寄与する。In the present invention, at least two denitrification tanks are provided, and the first denitrification tank completely consumes dissolved oxygen while denitrifying some of the oxidized nitrogen. Since waste liquid containing BOD components, ammonia nitrogen, etc. is introduced into the first denitrification tank, by bringing it into contact with activated sludge under strong stirring, BOD components, ammonia nitrogen, organic nitrogen, etc. are removed. oxidation and virtually complete consumption of dissolved oxygen. At the same time, this stirring fragments the microorganisms in the activated sludge, resulting in a wider contact area with the wastewater, which promotes the adsorption of various components in the wastewater to the activated sludge, oxidation of BOD components, and denitrification and nitrification. This contributes to further improving efficiency.

撹拌は、通常撹拌機による機械撹拌、水中ポンプなどの
液循環撹拌で行なわれるが、窒素、アルゴン等の酸素を
含まないガスを吹き込むことによる気体吹込み撹拌など
の種々の方法によって行なうことができる。Stirring is usually performed by mechanical stirring using a stirrer or liquid circulation stirring using a submersible pump, but it can also be performed by various methods such as gas injection stirring by blowing in oxygen-free gas such as nitrogen or argon. .

また、その撹拌強度は、活性汚泥のフロックが可及的微
少となる程廃水処理の効率を向上することができるが、
そこに生存する微生物（細菌、原生動物、後生動物など
）の細胞が破壊され、死滅する程のものであってはなら
ない。従って、撹拌強度は、流体の瞬時の平均速度勾配
であるＧ値（１／５ｅｅ）： ａ＝ｐワ７７ ［式中二Ｐ二流体容積（Ｖ）中で消費された動力（ｋｇ
　＠ｚ／　５ｅｃ） μ：流体の粘度（ｋｙ・ｓｅｃ／ｍ”　）Ｖ：撹拌槽の
容積（１’）　］ で示した場合、Ｇ＝　１５０（１／５ｅｃ）以上好まし
くはＧ＝２００（１／５ｅｃ）以上で、しかも上記微生
物の細胞が破壊されない撹拌の強さがとられる　　　　
゛べきである。In addition, the stirring intensity can improve the efficiency of wastewater treatment as the activated sludge flocs become as small as possible.
It must not be so severe that the cells of microorganisms (bacteria, protozoa, metazoa, etc.) living there will be destroyed or killed. Therefore, the stirring intensity is the G value (1/5ee), which is the instantaneous average velocity gradient of the fluid:
@z/5ec) μ: Viscosity of fluid (ky・sec/m") V: Volume of stirring tank (1') /5ec) or more, and the strength of stirring is such that the cells of the microorganisms mentioned above are not destroyed.
゛Should.

この第１脱窒槽での液の滞留時間は硝化液の循環量、溶
存酸素濃度、廃水の性状等によって多少の変動があるが
、流入廃水を基準として、１時間以内であり、好ましく
は４０分以内になるようにするのが良い。この第１脱窒
槽の液の滞留時間を長くとり過ぎると後段での処理槽中
で活性汚泥のブロック化が充分に行なわれない場合があ
り、沈降槽での汚泥と水との分離に障害をきたし、処理
水中に微細な活性汚泥が流出するという問題が生じるこ
とがある。The residence time of the liquid in this first denitrification tank varies somewhat depending on the amount of circulation of the nitrification liquid, the dissolved oxygen concentration, the properties of the wastewater, etc., but it is within one hour, preferably 40 minutes, based on the inflow wastewater. It is best to keep it within the range. If the residence time of the liquid in the first denitrification tank is too long, the activated sludge may not be sufficiently blocked in the subsequent treatment tank, which may impede the separation of sludge and water in the settling tank. Therefore, a problem may arise in which fine activated sludge flows out into the treated water.

第１脱窒槽で処理された廃液は第２脱窒槽（ｌｏ）に導
かれる。溶存酸素は第１脱窒槽で実質上完全に消費され
ており、かつ汚泥は細分化されているため脱窒は非常に
効果的に行なわれる。The waste liquid treated in the first denitrification tank is led to the second denitrification tank (lo). Dissolved oxygen is substantially completely consumed in the first denitrification tank, and the sludge is fragmented, so denitrification is very effective.

必要ならば第３、第４の脱窒槽を設けてもよく、脱窒処
理液中の酸化型窒素が実質上完全に無くなる条件で、硝
化槽に導入する。第１脱窒槽の効果により、第２脱窒槽
及びそれ以降の脱窒槽では嫌気のレベルは高く、それを
示す酸化還元電位（ＯＲＰ）は通常−５０ｍＶ、好まし
くは一１００１Ｖよりも低い値に維持される。If necessary, third and fourth denitrification tanks may be provided, and the denitrification treatment liquid is introduced into the nitrification tank under conditions such that oxidized nitrogen in the denitrification treatment liquid is substantially completely eliminated. Due to the effect of the first denitrification tank, the anaerobic level is high in the second denitrification tank and subsequent denitrification tanks, and the oxidation-reduction potential (ORP) indicating this is maintained at a value lower than -50 mV, preferably -1001V. Ru.

第２脱窒槽及びそれ以降の脱窒槽での撹拌は、活性汚泥
が沈降しない程の低速でよい。The stirring in the second denitrification tank and the subsequent denitrification tanks may be performed at a low speed that does not cause the activated sludge to settle.

第２脱窒槽以降の緩やかな撹拌は、最終工程での汚泥の
沈降分離を容易にするために非常に効果がある。Gentle stirring after the second denitrification tank is very effective in facilitating sedimentation and separation of sludge in the final step.

脱窒槽内の混合液は、酸素と接触させない様な条件で処
理させる必要がある。酸素と液が触れれば液中に酸素が
溶は込み脱窒反応が遅延するため処理効率が悪くなる。The mixed liquid in the denitrification tank must be treated under conditions that prevent it from coming into contact with oxygen. If oxygen and the liquid come into contact, oxygen will dissolve into the liquid and the denitrification reaction will be delayed, resulting in poor processing efficiency.

従って、通常脱窒槽は密閉槽で行なう。Therefore, denitrification is usually carried out in a closed tank.

脱窒槽全体での滞留時間は、廃水中の窒素濃度、硝化液
の循環量、酸化型窒素濃度、溶存酸素濃度及び活性汚泥
濃度等によって変わるが、最も一般的な下水の場合では
、流入廃水基準で１．５〜５時間、好ましくは２．５〜
４時間である。The residence time in the entire denitrification tank varies depending on the nitrogen concentration in the wastewater, the circulation amount of nitrification solution, the oxidized nitrogen concentration, the dissolved oxygen concentration, the activated sludge concentration, etc., but in the case of the most common sewage, it is based on the inflow wastewater standard. for 1.5 to 5 hours, preferably 2.5 to 5 hours.
It is 4 hours.

脱窒槽に導入する循環液、返送汚泥の量は、流入廃液に
対して循環液の量で１〜５倍の範囲に設定される。また
返送汚泥量は０．３〜２倍の範囲で設定される。The amount of circulating fluid and returned sludge introduced into the denitrification tank is set in a range of 1 to 5 times the amount of circulating fluid relative to the inflow waste fluid. Further, the amount of returned sludge is set in a range of 0.3 to 2 times.

硝化槽におけるＢＯＤ成分の酸化およびアンモニア態窒
素、有機性窒素の酸化型窒素への酸化は第１図に示すご
とく空気曝気によって通常行なわれる（（９）は空気曝
気用ニアコンプレッサーを示す）。The oxidation of BOD components and the oxidation of ammonia nitrogen and organic nitrogen into oxidized nitrogen in the nitrification tank are normally carried out by air aeration as shown in FIG. 1 ((9) shows a near compressor for air aeration).

しかし、高濃度酸素含有ガスにより曝気することは処理
設備をコンパクト化することができるのでより好適な方
法である。However, aerating with a highly concentrated oxygen-containing gas is a more suitable method because the processing equipment can be made more compact.

第２図に示す方法は、硝化槽（５）を密閉型の曝気槽に
し、高濃度酸素含有ガス（１０）を槽へ供給し、表面曝
気型の曝気装置（１２）により処理を行なった例である
。曝気は表面曝気以外にガス循環曝気等通常用いられる
曝気手段を用いることができる。The method shown in Figure 2 is an example in which the nitrification tank (5) is made into a closed aeration tank, a high concentration oxygen-containing gas (10) is supplied to the tank, and the treatment is performed using a surface aeration type aeration device (12). It is. For aeration, other than surface aeration, commonly used aeration means such as gas circulation aeration can be used.

高濃度酸素含有ガスを用いる方法では第２図に示したよ
うな単槽の硝化槽では、酸素の利用効率が悪いので通常
は、２段以上の多段の槽にして処理する場合がある。２
段以上にした場合液とガスの流れは並流の場合と向流の
場合が考えられる。In a method using a highly concentrated oxygen-containing gas, a single nitrification tank as shown in FIG. 2 has poor oxygen utilization efficiency, so the process is usually carried out in two or more multi-stage tanks. 2
When the number of stages or more is used, the flow of liquid and gas may be parallel flow or countercurrent flow.

酸素曝気は酸素の導入と硝化槽内液の流れを並流させて
行なってもよいが、この場合はＢＯＤ成分の分解によっ
て生じた炭酸ガスが酸素と共に常に硝化槽内液の流れと
並行して移動するため、ガス中の炭酸ガス濃度が増加し
硝化槽内液中に炭酸ガスが多量に溶解し、その結果硝化
槽内液のｐＨが低下する。アンモニア態窒素ならびに有
機態窒素の硝化に最適なｐＨは７．０〜８．６であり、
従ってこの様な方法では、ｐＨ調整に多くのアルカリを
必要とする。従って、酸素の導入を、２段の硝化槽につ
いて例示した第３図に示すごとく、硝化槽内液の流れと
向流させて曝気するのが好ましい。Oxygen aeration may be carried out by introducing oxygen and the flow of the nitrification tank liquid in parallel, but in this case, the carbon dioxide gas generated by the decomposition of BOD components is always flowing in parallel with the flow of the nitrification tank liquid together with oxygen. Due to the movement, the concentration of carbon dioxide in the gas increases and a large amount of carbon dioxide gas dissolves in the liquid in the nitrification tank, resulting in a decrease in the pH of the liquid in the nitrification tank. The optimum pH for nitrification of ammonia nitrogen and organic nitrogen is 7.0 to 8.6,
Therefore, such a method requires a large amount of alkali for pH adjustment. Therefore, it is preferable to introduce oxygen countercurrently to the flow of the liquid in the nitrification tank for aeration, as shown in FIG. 3, which is an example of a two-stage nitrification tank.

この方法では炭酸ガスの発生が最も多い硝化槽の前段の
部分から排ガスを排出（１１）させるので硝化槽の気相
部への炭酸ガスの蓄積が少なくなり、ｐＨ８整に要する
アルカリが不要であるかまたは必要であったとしてもそ
の量が少なくてすむ。この方法では、循環液（４）中の
溶存酸素濃度が高くなるが、本発明方法のごとく第１脱
窒槽中で溶存酸素を消費させる方法を採用することによ
り、溶存酸素による弊害を避けることができる。In this method, exhaust gas is discharged from the front stage of the nitrification tank where the most carbon dioxide gas is generated (11), so the accumulation of carbon dioxide gas in the gas phase of the nitrification tank is reduced, and the alkali required to adjust the pH to 8 is not required. Or, even if it is necessary, the amount is small. In this method, the concentration of dissolved oxygen in the circulating fluid (4) increases, but by adopting a method of consuming dissolved oxygen in the first denitrification tank as in the method of the present invention, it is possible to avoid the harmful effects of dissolved oxygen. can.

酸素導入を硝化槽内液の流れと向流させる方法において
、導入酸素は、濃度５０容量％、より好ましくは７０容
量％以上とする。５０容量％より少ないと酸素曝気によ
る著るしい効果は期待できない。７０容量％以上とする
ことにより、硝化槽の容積を空気曝気に比べ１／２〜１
／３にすることができる。In the method of introducing oxygen countercurrently to the flow of the liquid in the nitrification tank, the introduced oxygen has a concentration of 50% by volume, more preferably 70% by volume or more. If the amount is less than 50% by volume, no significant effect of oxygen aeration can be expected. By setting the volume to 70% or more, the volume of the nitrification tank can be reduced to 1/2 to 1/2 compared to air aeration.
/3.

第１硝化槽から排出される酸素濃度は、２５容量％、よ
り好ましくは３０容量％以上とするのがよい。The oxygen concentration discharged from the first nitrification tank is preferably 25% by volume, more preferably 30% by volume or more.

硝化槽内の汚泥濃度（ＭＬＳＳ）は３０００ｍ９／Ｌ以
上、より好ましくは５０００ｘｇ／４以上である。The sludge concentration (MLSS) in the nitrification tank is 3000 m9/L or more, more preferably 5000xg/4 or more.

また、硝化槽内液中の溶存酸素濃度は硝化槽での硝化反
応の重要な操作因子であり、２段に分割した硝化槽では
、脱窒槽からの混合液が流入する第１の硝化槽での溶存
酸素農度カ月所／克以上好ましくは２　ｍ９／　１１以
上に、後段の第２の硝化槽での溶存酸素濃度が２ｏ／１
以上、好ましくは４皮９／克〜１Ｏｘ９／Ｊｌになるよ
うにする。また３段以上の場合は第１の硝化槽の溶存酸
素濃度がｌｊ！９／克以上、好ましくは２ｍｇ／４以上
に、第２以降の硝化槽での溶存酸素濃度が２巧／克以上
、好ましくは４〜ｘｂ への酸素の供給は、第２図に示す様な表面曝気方法によ
るもの、第３図に示す様なガス循環曝気によるものなど
、通常の曝気手段を選択して用いればよい。In addition, the dissolved oxygen concentration in the liquid in the nitrification tank is an important operating factor for the nitrification reaction in the nitrification tank, and in a nitrification tank divided into two stages, the first nitrification tank receives the mixed liquid from the denitrification tank. The dissolved oxygen concentration in the second nitrification tank is preferably 2 m9/11 or more, and the dissolved oxygen concentration in the second nitrification tank is 2 o/1.
Above, it is preferably set to 4 skins 9/K to 1 Ox 9/Jl. In addition, in the case of three or more stages, the dissolved oxygen concentration in the first nitrification tank is lj! Oxygen is supplied to a concentration of 9/x or more, preferably 2 mg/4 or more, and the dissolved oxygen concentration in the second and subsequent nitrification tanks is 2 mg/x or more, preferably 4 to xb, as shown in Figure 2. Any conventional aeration means may be selected and used, such as a surface aeration method or a gas circulation aeration method as shown in FIG.

硝化槽での滞留時間は、処理する廃水のＢＯＤあるいは
窒素濃度によって違うが、最も一般的な下水の場合では
、廃水（２）流入廃液基準で２〜５゜５時間、より好ま
しくは３〜４．５時間となる。The residence time in the nitrification tank varies depending on the BOD or nitrogen concentration of the wastewater to be treated, but in the case of the most common sewage, it is 2 to 5 hours, more preferably 3 to 4 hours, based on the wastewater (2) inflow waste liquid. .5 hours.

以下実施例を挙げて本発明を説明する。The present invention will be explained below with reference to Examples.

実施例１ 都市下水（ＢＯＤ　１５０ｐｐｍ　、総窒素３５　ｐｐ
ｍ　）を第３図に示すごとき装置で活性汚泥処理した。Example 1 Urban sewage (BOD 150 ppm, total nitrogen 35 ppm)
m) was subjected to activated sludge treatment using an apparatus as shown in Fig. 3.

第１脱窒槽（１）の容積は１４０児、第２脱窒槽（１°
）の容積は５４０ｉ、、第１硝化槽（５）は３９０児、
第２硝化槽（５°）は３９０ｉ、であった。The capacity of the first denitrification tank (1) is 140 children, and the capacity of the second denitrification tank (1°
) has a capacity of 540 i, the first nitrification tank (5) has a capacity of 390 i,
The second nitrification tank (5°) was 390i.

処理条件は以下の通りであった。The processing conditions were as follows.

水温　　　　　　　２５℃ 汚泥濃度　　　　　５，０００Ｒ９／克返送汚泥濃度　
　１０，０００ｘ９／克都市下水流量　　　　　　５ｍ
３／日 返送汚泥量　　　　　　　５ｍ３／日 循環水量　　　　　　　１５ｊｌ’／日酸素　炭酸ガス 第１脱窒槽の撹拌機の回転数：　　　７２０　ｒｐｎ＋
〃　　　の　　　　Ｇ　　　値：１．２００／ｓｅｃ第
２脱窒槽の撹拌機の回転数＋　　　１００ｒｐＩＩｌ〃
　　　の　　　　Ｇ　　　値：　　　　　８０／ｓｅａ
処理操作中ＮａＯＨ４８％水溶液を用い、硝化槽内液の
ｌ）Ｈを７．０に維持した。ＮａＯＨは１８゜２ｇ／ｌ
１３下水を要した。Water temperature: 25℃ Sludge concentration: 5,000R9/K Returned sludge concentration
10,000x9/city sewage flow rate 5m
3/day return sludge volume 5m3/day circulating water volume 15jl'/day Oxygen Carbon dioxide Number of revolutions of the stirrer in the first denitrification tank: 720 rpn+
G value: 1.200/sec Second denitrification tank stirrer rotation speed + 100rpIIl
G value: 80/sea
During the treatment operation, a 48% NaOH aqueous solution was used to maintain the l)H of the solution in the nitrification tank at 7.0. NaOH is 18°2g/l
13 sewage was required.

以上の操作中、第１脱窒槽内のｐＨは７．０、ＯＲＰは
−１０ｍＶおよび第２脱窒槽内のｐＨは７．６、ＯＲＰ
は一２１０１１ｖであった。循環液の溶存酸素濃度は８
　ｍ９／　ｌであったが第２脱窒槽中の溶存酸素濃度は
Ｏｙ、９／　１に減少し、第２脱窒槽で処理された液中
の硝酸性窒素および亜硝酸窒素の濃度は検出限界以下で
あった。また最終排水中のＢＯＤは１４．Ｏｏ／ｉ、、
総窒素濃度は７．３所／！であった。During the above operations, the pH in the first denitrification tank is 7.0, ORP is -10 mV, and the pH in the second denitrification tank is 7.6, ORP
was -21011v. Dissolved oxygen concentration in circulating fluid is 8
m9/l, but the dissolved oxygen concentration in the second denitrification tank decreased to Oy, 9/1, and the concentrations of nitrate nitrogen and nitrite nitrogen in the liquid treated in the second denitrification tank were below the detection limit. Met. Also, the BOD in the final waste water is 14. Oo/i,,
Total nitrogen concentration is 7.3 places/! Met.

比較例１ 第１脱窒槽と第２脱窒槽の隔壁を外し、第１脱窒槽の撹
拌機を１０　Ｏｒｐｍで回転する以外、実施例１と同様
の条件で都市下水を処理した。Comparative Example 1 Urban sewage was treated under the same conditions as in Example 1, except that the partition between the first denitrification tank and the second denitrification tank was removed and the agitator of the first denitrification tank was rotated at 10 Orpm.

得られた結果を以下に示す。The results obtained are shown below.

脱窒槽内ＯＲＰ　　　　　　　　　−４５ａｔＶ脱窒槽
で処理された液中の 硝酸性および亜硝酸性窒素濃度２．０Ｒｆｔ／Ｉ。ORP in denitrification tank - Nitrate and nitrite nitrogen concentration in the liquid treated in the 45atV denitrification tank: 2.0 Rft/I.

最終排水中のＢＯＤ　　　　　　１８．Ｏｚｙ／克〃　
　総窒素　　　　１３．０ｉｙ／克発明の効果 本発明方法を用いることにより脱窒効率が著るしく高く
なり、その結果廃水中のＢＯＤや総窒素含量を低くする
ことかできる。従って廃水処理時間を短縮することが可
能となる。また、硝化工程における酸素の導入を処理液
と向流させた際、循環液中の溶存酸素濃度が上昇し、脱
窒が抑制されると云う問題が解消でき、その結果、上記
方法におけるｐＨ８整剤の節減と云う目的の達成が容易
となる。BOD in final drainage 18. Ozy/Katsu
Total nitrogen: 13.0 iy/k Effects of the invention By using the method of the present invention, denitrification efficiency is significantly increased, and as a result, BOD and total nitrogen content in wastewater can be lowered. Therefore, it becomes possible to shorten the wastewater treatment time. Furthermore, when introducing oxygen in the nitrification process in a countercurrent flow to the treatment liquid, the problem that the dissolved oxygen concentration in the circulating liquid increases and denitrification is suppressed can be solved, and as a result, the pH 8 adjustment in the above method This makes it easier to achieve the goal of reducing the amount of chemicals used.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図および第３図は、本発明の廃水の生物学的処理装
置の概要を示す図、第２図は硝化槽の別の態様を示す図
である。 （Ｄ第１脱窒槽、　　　　（１°）第２脱窒槽、（２）
廃　　水、　　　　　（３）返送汚泥、（４）硝化槽か
らの循環液、（５）硝化槽、（５°）第１硝化槽、　　
　　（５”）第２硝化槽、（６）硝化槽流出水、　　　
（７）固液分離装置、（８）処理水、 （９）ニアコンプレッサーあるいはブロワ、（１０）高
濃度酸素含有ガス、（１１）排ガス、（１２）表面曝気
装置。 手続補正書。、。 昭和６０年２月５日 １、事件の表示 昭和５９年特許願第　２；６９３９０　　　　　号２、
発明の名称 廃水の生物学的脱窒方法 ３、補正をする者 代表者大西正文 ４、代理人 ５、補正命令の日付　（自発） ７、補正の内容 （１）明細書第９頁第４行、「ブロック」とあるを「フ
ロック」に訂正する。 （２）同第１４頁下から第６行、ｒ（５）Ｊとあるをｒ
（５’）Ｊに訂正する。 （３）同第１４頁下から第５行、「（５′）」とあるを
ｒ（５”）Ｊに訂正する。 以上FIGS. 1 and 3 are diagrams showing an outline of the wastewater biological treatment apparatus of the present invention, and FIG. 2 is a diagram showing another embodiment of the nitrification tank. (D 1st denitrification tank, (1°) 2nd denitrification tank, (2)
Wastewater, (3) Returned sludge, (4) Circulating liquid from the nitrification tank, (5) Nitrification tank, (5°) First nitrification tank,
(5”) Second nitrification tank, (6) Nitrification tank effluent,
(7) Solid-liquid separator, (8) Treated water, (9) Near compressor or blower, (10) Highly concentrated oxygen-containing gas, (11) Exhaust gas, (12) Surface aeration device. Procedural amendment. ,. February 5, 1985 1, Case Indication 1988 Patent Application No. 2; 69390 No. 2,
Title of the invention: Biological denitrification method for wastewater 3. Person making the amendment Representative: Masafumi Onishi 4. Agent 5. Date of amendment order (voluntary) 7. Contents of the amendment (1) Specification, page 9, line 4 , correct the word "block" to "flock". (2) Page 14, line 6 from the bottom, r(5) J and r
(5') Correct to J. (3) On page 14, line 5 from the bottom, correct “(5′)” to r(5”)J.

Claims (1)

【特許請求の範囲】[Claims] １、硝化液循環方式による廃水の生物学的処理方法にお
いて、２以上の実質上密閉した脱窒槽（１）および（１
′）を設け、第１の脱窒槽に廃水（２）、返送汚泥（３
）および硝化槽からの循環液（４）を導入し、強撹拌下
、これらに溶存する酸素を活性汚泥により消費すると共
に硝酸性窒素および亜硝酸性窒素の一部を脱窒し、次い
で第２以降の脱窒槽（１′）で硝酸性窒素および亜硝酸
性窒素を実質上完全に脱窒し、脱窒液を更に硝化槽でＢ
ＯＤ成分を酸化分解すると共にアンモニア態窒素および
有機態窒素を硝酸性窒素および亜硝酸性窒素に酸化する
ことを特徴とする廃水の生物学的脱窒方法。1. In a biological treatment method for wastewater using a nitrification liquid circulation method, two or more substantially sealed denitrification tanks (1) and (1) are used.
'), and wastewater (2) and return sludge (3) are installed in the first denitrification tank.
) and the circulating liquid (4) from the nitrification tank are introduced, and under strong stirring, the oxygen dissolved in these is consumed by activated sludge, and a part of the nitrate nitrogen and nitrite nitrogen is denitrified, and then the second In the subsequent denitrification tank (1'), nitrate nitrogen and nitrite nitrogen are virtually completely denitrified, and the denitrification liquid is further transferred to B in the nitrification tank.
A biological denitrification method for wastewater, which comprises oxidizing and decomposing OD components and oxidizing ammonia nitrogen and organic nitrogen into nitrate nitrogen and nitrite nitrogen.