JP3707626B2

JP3707626B2 - Method and apparatus for removing nitrogen from organic wastewater

Info

Publication number: JP3707626B2
Application number: JP31213795A
Authority: JP
Inventors: 克之片岡
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 1995-11-30
Filing date: 1995-11-30
Publication date: 2005-10-19
Anticipated expiration: 2015-11-30
Also published as: JPH09150189A

Description

【０００１】
【発明の属する技術分野】
本発明は下水などのアンモニア含有汚水を高度に浄化する技術に関し、特に窒素成分を従来技術よりも安定して除去可能な新規窒素除去技術に関する。また生物処理にともなって発生する余剰汚泥の発生量を従来よりも減少することが可能な新技術に関する。
【０００２】
【従来の技術】
下水などの汚水の窒素を除去する方法としてもっとも代表的な技術は、硝化液循環型生物学的硝化脱窒素法である。この技術は有機性汚水を生物学的脱窒素部（嫌気槽）に供給し、その脱窒素液を硝化部（好気槽）に供給してアンモニアを硝化し、硝化液の一部を脱窒素部に循環し他部を沈殿槽に供給し活性汚泥を分離し処理水を得るものである。硝化部に硝化菌を固定化したゲル担体を投入する技術も最近実用化されている。
【０００３】
この方法は下水を処理する場合窒素除去率８０％程度が得られ、処理水にはアンモニアはほとんど残らず硝酸性窒素が残留する。
【０００４】
【発明が解決しようとする課題】
しかしこの方法では原水のＢＯＤ／Ｎ比が３以下の場合脱窒素のための有機炭素源が不足し窒素除去率が著しく悪化する問題点があった。
また余剰汚泥発生量が除去ＢＯＤ量の３０〜４０％程度と多く、汚泥処理の設備費、運転費が非常に多額であった。汚泥脱水ケーキ、汚泥焼却灰の処分コストも多額であった。
【０００５】
従って、本発明の目的は、生物学的窒素除去法及び装置の欠点を解決できる新技術を確立し、原水のＢＯＤ／Ｎ比が小さい場合においてもメタノールなどの高価な有機炭素源を使わずに安定した窒素除去率を得ることが可能で、汚泥発生量も著しく少なくできる新システムを提供することである。
【０００６】
【課題を解決するための手段】
即ち、本発明の目的は、以下の構成（１）〜（２）によって達成することができる。
（１）有機性汚水を硝化液循環型の生物学的硝化脱窒素法で処理する方法において、硝化槽から硝化スラリを脱窒素槽に循環する経路を少なくとも２系統に分け、その一方の経路内にオゾンガスを注入し汚泥と接触させて汚泥をオゾンの酸化作用により可溶化しオゾン気泡共存汚泥としたのち、前記脱窒素槽水面下に前記オゾン気泡共存汚泥を流出させることを特徴とする有機性汚水の窒素除去方法。
（２）有機性汚水を硝化液循環型の生物学的硝化脱窒素法で処理する装置において、硝化槽から硝化スラリを脱窒素槽に循環する経路を少なくとも２系統に分け、その一方の経路内にオゾンガスを注入し汚泥と接触させて汚泥をオゾンの酸化作用により可溶化しオゾン気泡共存汚泥としたのち、前記脱窒素槽水面下に前記オゾン気泡共存汚泥を流出させることを特徴とする有機性汚水の窒素除去装置。
【０００７】
本発明は、硝化槽から脱窒素槽に循環する硝化スラリ３を２系統に分岐し、一方の経路内にオゾンを注入して汚泥をオゾンの酸化作用により可溶化（オゾン気泡共存汚泥）し、糖類などの可溶性、コロイド性ＢＯＤ成分を汚泥から溶出させ脱窒素部に供給する。その結果、脱窒素菌がこれらのＢＯＤを利用して原水のＢＯＤ／Ｎ比が小さい場合も充分な脱窒素反応が進むことを見いだした。更に、汚泥がオゾンにより可溶化するので、余剰汚泥の発生が極めて少なくなる。
【０００８】
本発明のポイントの一つは活性汚泥からオゾンによって可溶性有機物（ＢＯＤ）を生産しこれを生物学的脱窒素反応の脱窒素菌の有機炭素源として有効利用するという新規思想にある。
【０００９】
従来の生物学的脱窒素法は、既述の如く、原水に含まれるＢＯＤ成分のみを脱窒素のための有機炭素源とせざるを得ないため、原水中のＢＯＤ／Ｎ比が３以下の場合、ＮＯ_x−Ｎの窒素ガスへの還元反応が充分進まず、処理水にＮＯ_x−Ｎが残留してしまう。更に、従来の方法では、除去ＢＯＤ成分の３０〜４０％が余剰汚泥の固形物になり汚泥処理が大きな負担になっている。
【００１０】
【発明の実施の形態】
有機性汚水とは、都市排水（下水あるいはし尿）および有機性産業排水等である。
硝化液循環型の生物学的硝化脱窒素法とは、少なくとも各１槽の嫌気性の脱窒素槽および好気性の硝化槽を有する生物処理工程と、少なくとも１槽の沈殿槽を有する固液分離工程とからなり、さらに硝化槽内の硝化スラリの一部を脱窒素槽へ循環するものである。
【００１１】
硝化スラリの脱窒素槽への循環は、少なくとも２系統の経路により循環されていて、少なくとも１つの経路中にオゾンを注入して汚泥をオゾンの酸化作用により可溶化しオゾン気泡共存汚泥とし脱窒素槽内に循環される。脱窒素槽内への循環位置は、特に限定されないが、脱窒素槽の底部に循環されるのが好ましい。また、分割された経路は、脱窒素槽に別々に接続されても、再び統一されて接続されていてもよい。脱窒素槽内の嫌気性細菌（脱窒素菌）の活性が低下しないようにオゾンの注入量が調節されていれば、分割された経路は統一されて脱窒素槽に接続されているのが好ましい。
【００１２】
硝化槽は、好気性細菌の働きを活発にするために、空気が槽の底部から注入されている。
沈殿槽は、沈殿槽内に蓄積する沈殿汚泥を脱窒素槽ヘ返送する経路を設けている。また、仮に沈殿汚泥を取り除く必要が生じた場合のために、余剰汚泥を系外に排出する経路が設けられている。
【００１３】
更に、図１を用い本発明の好ましい一実施の形態を説明する。
下水などの原水１（有機性汚水）は、脱窒素槽４に導入され嫌気性細菌により処理されたのち、硝化槽２へ流過し好気性細菌で処理され、さらに沈殿槽６へ流過して固液分離され処理水５として排出される。脱窒素槽４で処理されさらに硝化槽２で処理された原水１の一部は、硝化槽２内の硝化スラリ３とともに、硝化槽２から２系統に分岐された経路３−１及び経路３−２を経由して脱窒素槽４の底部に循環される。ここで、硝化スラリ３の循環する経路３−１には、オゾンが注入され、硝化スラリ３中の生物汚泥を酸化し可溶化しＢＯＤ成分を生成させる。分割された経路３−１と経路３−２は、再び統一され脱窒素槽４に接続される。
【００１４】
脱窒素槽４には脱窒素菌を含む活性汚泥が高濃度に存在している。硝化槽２に後続する沈殿槽６から沈殿汚泥の大部分（返送汚泥８）が、脱窒素槽４に返送される。硝化槽２には、好気性細菌を活性化するため、硝化槽２内の底部から空気が散気されている。
経路３−１と経路３−２の流量は、各経路に設けられているバルブにより調整される。
【００１５】
経路３−１内へのオゾン７注入量は、過剰であるとオゾン添加コストがいたずらにアップするので避けなければならず、汚泥の種類等によって調整される。オゾン適正注入量は汚泥の種類によっても変化するが、概略汚泥ＳＳ重量あたり２〜２０％、好ましくは１０〜１５％である。
オゾン７は、活性汚泥を構成する微生物細胞の菌体外高分子（ムコ多糖類など）、細胞壁を強力に酸化分解して低分子化し、微生物細胞から可溶性有機物（ＢＯＤ成分）を溶出させる作用がある。溶出したＢＯＤ成分（可溶化汚泥１０）は、オゾンによって炭酸ガスと水にまでは酸化されないので脱窒素菌のための有機炭素源として利用できる。可溶化汚泥１０は、脱窒素槽４および硝化槽２において微生物に資化され炭酸ガス、水に分解するので余剰汚泥がほとんど発生しない。
【００１６】
オゾン７を汚泥に接触させると、汚泥から強い発泡作用を持つ蛋白質泥が溶出し汚泥が激しく発泡し、開放系のオゾン酸化槽では発泡汚泥が槽外に溢れ出すことが認められた。従って、経路３−１内のオゾン酸化部は、密閉流路とし排オゾンガスおよび泡が大気中に流出しないようにし、残留オゾン気泡を脱窒素槽４の底部に供給する。こうすることによって発泡汚泥が槽外に溢れるトラブルが無くなり、更に残留オゾンが脱窒素槽４内で水面に上昇する過程で、活性汚泥に接触し吸収されるので排オゾンガスの処理設備が不要になる利点がある。
【００１７】
本発明は、活性汚泥からオゾンによって可溶性有機物（ＢＯＤ成分）を生産しこれを生物学的脱窒素反応の脱窒素菌の有機炭素源として有効利用するものである。その結果、脱窒素槽４内の脱窒素菌は、原水１中のＢＯＤ成分が不足する場合でも汚泥から可溶化したＢＯＤ成分を利用して、硝化槽２から循環される硝化スラリ３中のＮＯ_x−Ｎを速やかに窒素ガスに還元して脱窒素する。
【００１８】
脱窒素部４から流出する活性汚泥スラリは、硝化槽２において原水中のアンモニアを生物学的に硝化したのち沈殿槽６に導かれ活性汚泥が沈殿分離され硝酸性窒素、アンモニア性窒素の両者が高度に除去された処理水５となる。
本発明の方法によって余剰汚泥発生量は顕著に減少し、系外に排出すべき余剰汚泥量はほとんど無くなる。つまり、経路３−１においてオゾン酸化してから脱窒素槽４に返送する汚泥量を、硝化槽２内の活性汚泥濃度が一定範囲に納まるようにその流量を制御すれば余剰汚泥の発生量がほぼゼロとなる。また、汚泥の可溶化によって脱窒素槽に効率良く有機炭素源を供給できる。
【００１９】
【実施例】
図１の工程にしたがって下水（平均水質を表１に示す）を対象に本発明の実証試験を行った。
【００２０】
【表１】

【００２１】
表２に試験条件を示す。
【００２２】
【表２】

【００２３】
実験の結果、運転開始後２か月後に処理が安定してからの処理水質は下水のＢＯＤ／Ｎ比が小さいにも関わらず表３処理水水質のように高度に窒素が除去されており、Ｔ−Ｎ除去率７５％以上が安定して得られた。また脱窒素槽から流出する排ガスのオゾン濃度は０．１ｐｐｍ以下であった。オゾン注入部における発泡トラブルはなかった。
【００２４】
【表３】

【００２５】
運転開始後１年間に渡り、汚泥を余剰汚泥として系外に排出する必要が無かった。
【００２６】
【発明の効果】
１．生物学的硝化脱窒素技術とオゾンによる汚泥可溶化技術を新規な態様で結合
したので原水のＢＯＤが不足する場合でも安定した脱窒素が行なわれる。
２．余剰活性汚泥がほとんど発生しない。
３．オゾン酸化部での汚泥発泡トラブルがない。
４．排オゾンの処理設備（活性炭によるオゾン分解塔など）が不要である。
【図面の簡単な説明】
【図１】本発明の一実施の形態である有機性汚水の窒素除去方法のフローチャートである。
【符号の説明】
１原水
２硝化槽
３硝化スラリ
３−１、３−２経路
４脱窒素槽
５処理水
７オゾン
８返送汚泥
９余剰汚泥
１０可溶化汚泥
１１空気[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for highly purifying ammonia-containing sewage such as sewage, and more particularly to a novel nitrogen removal technique that can remove nitrogen components more stably than in the prior art. The present invention also relates to a new technology capable of reducing the amount of surplus sludge generated with biological treatment as compared with the conventional technology.
[0002]
[Prior art]
The most representative technique for removing nitrogen from sewage and other sewage is a nitrification liquid circulation type biological nitrification denitrification method. This technology supplies organic sewage to a biological denitrification section (anaerobic tank), supplies the denitrification liquid to a nitrification section (aerobic tank), nitrifies ammonia, and denitrifies part of the nitrification liquid It circulates in the part and supplies the other part to the settling tank to separate the activated sludge and obtain treated water. A technique for introducing a gel carrier in which nitrifying bacteria are immobilized in a nitrification part has also been put into practical use recently.
[0003]
In this method, when sewage is treated, a nitrogen removal rate of about 80% is obtained, and almost no ammonia remains in the treated water, and nitrate nitrogen remains.
[0004]
[Problems to be solved by the invention]
However, in this method, when the BOD / N ratio of the raw water is 3 or less, there is a problem that the organic carbon source for denitrification is insufficient and the nitrogen removal rate is remarkably deteriorated.
Further, the amount of surplus sludge generated was as large as about 30 to 40% of the removed BOD amount, and the equipment cost and operation cost for the sludge treatment were very large. The disposal costs for sludge dewatering cake and sludge incineration ash were also large.
[0005]
Therefore, the object of the present invention is to establish a new technology capable of solving the disadvantages of biological nitrogen removal method and apparatus, without using an expensive organic carbon source such as methanol even when the BOD / N ratio of raw water is small. To provide a new system that can obtain a stable nitrogen removal rate and can significantly reduce the amount of sludge generated.
[0006]
[Means for Solving the Problems]
That is, the object of the present invention can be achieved by the following configurations (1) to (2).
(1) In the method of treating organic sewage by the nitrification liquid circulation type biological nitrification denitrification method, the route for circulating the nitrification slurry from the nitrification tank to the denitrification tank is divided into at least two systems, Organic gas is characterized by injecting ozone gas into the sludge and bringing it into contact with sludge to solubilize the sludge by the oxidation of ozone into ozone bubble coexisting sludge, and then let the ozone bubble coexisting sludge flow out under the surface of the denitrification tank How to remove nitrogen from sewage.
(2) In an apparatus for treating organic sewage using a nitrification liquid circulation type biological nitrification denitrification method, the route for circulating the nitrification slurry from the nitrification tank to the denitrification tank is divided into at least two systems, Organic gas is characterized by injecting ozone gas into the sludge and bringing it into contact with sludge to solubilize the sludge by the oxidation of ozone into ozone bubble coexisting sludge, and then let the ozone bubble coexisting sludge flow out under the surface of the denitrification tank Sewage nitrogen removal equipment.
[0007]
The present invention branches the nitrification slurry 3 circulating from the nitrification tank to the denitrification tank into two systems, injects ozone into one path, solubilizes the sludge by the oxidizing action of ozone (ozone coexisting sludge), Soluble and colloidal BOD components such as saccharides are eluted from the sludge and supplied to the denitrification section. As a result, it was found that denitrifying bacteria proceed sufficiently even when the BOD / N ratio of raw water is small using these BODs. Furthermore, since sludge is solubilized by ozone, the generation of excess sludge is extremely reduced.
[0008]
One of the points of the present invention lies in a novel idea that soluble organic matter (BOD) is produced from activated sludge by ozone and effectively used as an organic carbon source for denitrifying bacteria in biological denitrification.
[0009]
In the conventional biological denitrification method, as described above, only the BOD component contained in the raw water must be used as an organic carbon source for denitrification, and therefore the BOD / N ratio in the raw water is 3 or less. Further, the reduction reaction of NO _x -N to nitrogen gas does not proceed sufficiently, and NO _x -N remains in the treated water. Further, in the conventional method, 30 to 40% of the removed BOD component becomes a solid matter of excess sludge, and the sludge treatment is a heavy burden.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Organic sewage includes municipal wastewater (sewage or human waste) and organic industrial wastewater.
Biological nitrification denitrification method with nitrification liquid circulation is a solid-liquid separation having at least one anaerobic denitrification tank and an aerobic nitrification tank, and at least one precipitation tank. And a part of the nitrification slurry in the nitrification tank is circulated to the denitrification tank.
[0011]
Circulation of the nitrification slurry to the denitrification tank is circulated through at least two routes. Ozone is injected into at least one route to solubilize the sludge by the oxidizing action of ozone to make ozone bubble coexistent sludge. It is circulated in the tank. The position of circulation into the denitrification tank is not particularly limited, but it is preferably circulated to the bottom of the denitrification tank. Moreover, the divided | segmented path | route may be separately connected to a denitrification tank, or may be unified and connected again. If the injection amount of ozone is adjusted so that the activity of anaerobic bacteria (denitrifying bacteria) in the denitrification tank is not lowered, it is preferable that the divided paths are unified and connected to the denitrification tank. .
[0012]
In the nitrification tank, air is injected from the bottom of the tank in order to activate the action of aerobic bacteria.
The settling tank is provided with a path for returning the precipitated sludge accumulated in the settling tank to the denitrification tank. Further, in the case where it is necessary to remove the precipitated sludge, a route for discharging the excess sludge out of the system is provided.
[0013]
Furthermore, a preferred embodiment of the present invention will be described with reference to FIG.
Raw water 1 (organic sewage) such as sewage is introduced into the denitrification tank 4 and treated with anaerobic bacteria, then flows to the nitrification tank 2 and is treated with aerobic bacteria, and further flows to the sedimentation tank 6. Then, it is separated into solid and liquid and discharged as treated water 5. Part of the raw water 1 treated in the denitrification tank 4 and further treated in the nitrification tank 2 together with the nitrification slurry 3 in the nitrification tank 2 is divided into a path 3-1 and a path 3- 2 is circulated to the bottom of the denitrification tank 4. Here, ozone is injected into the path 3-1 through which the nitrified slurry 3 circulates, and the biological sludge in the nitrified slurry 3 is oxidized and solubilized to generate a BOD component. The divided paths 3-1 and 3-2 are unified again and connected to the denitrification tank 4.
[0014]
In the denitrification tank 4, activated sludge containing denitrifying bacteria is present at a high concentration. Most of the precipitated sludge (return sludge 8) is returned to the denitrification tank 4 from the settling tank 6 following the nitrification tank 2. In the nitrification tank 2, air is diffused from the bottom of the nitrification tank 2 in order to activate aerobic bacteria.
The flow rates of the paths 3-1 and 3-2 are adjusted by valves provided in the respective paths.
[0015]
If the amount of ozone 7 injected into the path 3-1 is excessive, the ozone addition cost will increase unnecessarily, so it must be avoided, and is adjusted according to the type of sludge and the like. The appropriate ozone injection amount varies depending on the type of sludge, but is generally 2 to 20%, preferably 10 to 15% per sludge SS weight.
Ozone 7 has an action of eluting soluble organic matter (BOD component) from microbial cells by oxidatively decomposing exocellular polymers (mucopolysaccharides, etc.) of microbial cells that constitute activated sludge and cell walls. is there. Since the eluted BOD component (solubilized sludge 10) is not oxidized to carbon dioxide and water by ozone, it can be used as an organic carbon source for denitrifying bacteria. The solubilized sludge 10 is assimilated by microorganisms in the denitrification tank 4 and the nitrification tank 2 and decomposes into carbon dioxide gas and water, so that surplus sludge is hardly generated.
[0016]
When ozone 7 was brought into contact with the sludge, protein mud having a strong foaming action was eluted from the sludge and the sludge was vigorously foamed, and it was confirmed that the foamed sludge overflowed outside the tank in the open ozone oxidation tank. Therefore, the ozone oxidation part in the path 3-1 is a closed channel so that the exhaust ozone gas and bubbles do not flow out into the atmosphere, and the residual ozone bubbles are supplied to the bottom of the denitrification tank 4. By doing so, there is no trouble that the foamed sludge overflows outside the tank, and further, residual ozone rises to the surface of the water in the denitrification tank 4 and is absorbed by contact with the activated sludge, so the waste ozone gas treatment facility is not required. There are advantages.
[0017]
This invention produces | generates a soluble organic substance (BOD component) from activated sludge with ozone, and uses this effectively as an organic carbon source of the denitrifying bacterium of biological denitrification reaction. As a result, denitrifying bacteria in the denitrification tank 4 can be used for NO in the nitrification slurry 3 circulated from the nitrification tank 2 using the BOD component solubilized from the sludge even when the BOD component in the raw water 1 is insufficient. _x- N is quickly reduced to nitrogen gas and denitrified.
[0018]
The activated sludge slurry flowing out from the denitrification unit 4 is biologically nitrified in the nitrification tank 2 and then led to the precipitation tank 6 where the activated sludge is precipitated and separated, and both nitrate nitrogen and ammonia nitrogen are removed. The treated water 5 is removed to a high degree.
By the method of the present invention, the amount of excess sludge generated is remarkably reduced, and the amount of excess sludge to be discharged out of the system is almost eliminated. That is, if the flow rate is controlled so that the activated sludge concentration in the nitrification tank 2 falls within a certain range, the amount of excess sludge generated will be increased if the amount of sludge returned to the denitrification tank 4 after ozone oxidation in the path 3-1. Nearly zero. Moreover, an organic carbon source can be efficiently supplied to a denitrification tank by solubilization of sludge.
[0019]
【Example】
The demonstration test of the present invention was conducted on sewage (average water quality is shown in Table 1) according to the process of FIG.
[0020]
[Table 1]

[0021]
Table 2 shows the test conditions.
[0022]
[Table 2]

[0023]
As a result of the experiment, the treated water quality after the stabilization of the treatment two months after the start of operation is highly nitrogen-removed as shown in Table 3 treated water quality even though the BOD / N ratio of the sewage is small. A TN removal rate of 75% or more was stably obtained. The ozone concentration of the exhaust gas flowing out from the denitrification tank was 0.1 ppm or less. There was no foaming trouble in the ozone injection part.
[0024]
[Table 3]

[0025]
There was no need to discharge the sludge out of the system as surplus sludge for one year after the start of operation.
[0026]
【The invention's effect】
1. Since biological nitrification denitrification technology and sludge solubilization technology using ozone are combined in a novel manner, stable denitrification is performed even when the BOD of raw water is insufficient.
2. Surplus activated sludge is hardly generated.
3. There is no sludge foaming trouble in the ozone oxidation part.
4). There is no need for waste ozone treatment equipment (such as activated carbon ozonolysis tower).
[Brief description of the drawings]
FIG. 1 is a flowchart of a nitrogen removal method for organic wastewater according to an embodiment of the present invention.
[Explanation of symbols]
1 Raw Water 2 Nitrification Tank 3 Nitrification Slurry 3-1, 3-2 Path 4 Denitrification Tank 5 Treated Water 7 Ozone 8 Return Sludge 9 Surplus Sludge 10 Solubilized Sludge 11 Air

Claims

In the method of treating organic sewage by the nitrification liquid circulation type biological nitrification denitrification method, the route for circulating the nitrification slurry from the nitrification tank to the denitrification tank is divided into at least two systems, and ozone gas is contained in one of the routes. Nitrogen of organic sewage, which is injected and brought into contact with sludge to solubilize the sludge by the oxidation of ozone into ozone bubble coexistent sludge, and then discharge the ozone bubble coexistent sludge below the denitrification tank water surface Removal method.

In an apparatus for treating organic sewage by the nitrification liquid circulation type biological nitrification denitrification method, the route for circulating the nitrification slurry from the nitrification tank to the denitrification tank is divided into at least two systems, and ozone gas is introduced into one of the paths. Nitrogen of organic sewage, which is injected and brought into contact with sludge to solubilize the sludge by the oxidation of ozone into ozone bubble coexistent sludge, and then discharge the ozone bubble coexistent sludge below the denitrification tank water surface Removal device.