JP2004148144A - Method for treating sewage - Google Patents

Method for treating sewage Download PDF

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Publication number
JP2004148144A
JP2004148144A JP2002313563A JP2002313563A JP2004148144A JP 2004148144 A JP2004148144 A JP 2004148144A JP 2002313563 A JP2002313563 A JP 2002313563A JP 2002313563 A JP2002313563 A JP 2002313563A JP 2004148144 A JP2004148144 A JP 2004148144A
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Japan
Prior art keywords
membrane
biological reaction
reaction tank
tank
amount
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JP2002313563A
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Japanese (ja)
Inventor
Seiji Izumi
清司 和泉
Yutaka Yamada
山田  豊
Taichi Kamisaka
太一 上坂
Kazuhisa Nishimori
一久 西森
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Kubota Corp
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Kubota Corp
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02WCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00Technologies for wastewater treatment
    • Y02W10/10Biological treatment of water, waste water, or sewage

Abstract

<P>PROBLEM TO BE SOLVED: To restrain lowering of the pH of a membrane-permeated water and to prevent the production of scale when nitrogen-containing organic sewage is treated by a membrane separation type activated sludge treatment method. <P>SOLUTION: When the nitrogen-containing organic water to be treated is treated by the membrane separation type activated sludge treatment method, the amount of excess sludge to be withdrawn from a biological reaction tank 4 is controlled so that SRT is within five days, the SRT being defined as a value which is obtained by dividing the amount of the total activated sludge amount in the biological reaction tank 4 by the excess sludge withdrawn from the biological reaction tank 4, and MLSS (mixed liquid conc.) in the biological reaction tank 4 is kept within the prescribed concentration by taking out the membrane-permeated water of the prescribed amount through a tank immersion type membrane separation unit 5 immersed in the biological reaction tank 4. <P>COPYRIGHT: (C)2004,JPO

Description

【0001】
【発明の属する技術分野】
本発明は汚水の処理方法に関し、窒素を含有する有機性汚水を処理する技術に係るものである。
【0002】
【従来の技術】
従来、膜分離活性汚泥処理(MBR)は処理水質が安定し、維持管理も容易なことから広く普及している。膜分離活性汚泥処理は高濃度MLSSで運転可能なことから汚泥の滞留時間(SRT)が長くとれるため硝化細菌を槽内に容易に保持できる。SRTは生物反応槽内の汚泥量を余剰汚泥量で除した値で通常は日数表示しており、硝化菌は増殖が遅くて水温に依存するが通常5〜7日程度のSRTが必要といわれている。
【0003】
膜分離活性汚泥処理は確実に汚水中の窒素を硝化できるので、脱窒槽と組み合わせることにより窒素除去が可能なプロセスとなっている。膜分離活性汚泥処理した膜透過水は非常に高品質であるために水資源として再利用される例も多く、さらに逆浸透膜(RO)などの高度処理を施して利用する場合もある。
【0004】
膜分離活性汚泥処理(MBR)は生物反応槽の内部に槽浸漬型膜分離装置を浸漬して行うものであり、槽浸漬型膜分離装置は鉛直方向に沿って配置する複数の平膜カートリッジを平行に充填した膜充填部を有し、膜充填部の下方に散気装置を内蔵した散気装置部を配置している。
【0005】
槽浸漬型膜分離装置では散気装置から散気する空気のエアリフト作用により固気液混相の上昇流が発生し、上昇流が膜充填部の平膜カートリッジ間の流路を膜面に沿って通過する間にろ過を行い、上昇流の掃流効果によって膜面を洗浄している。このことをクロスフローろ過という。この上昇流によって生物反応槽の反応槽混合液が槽内で循環し、反応槽混合液を散気装置から散気する空気で曝気して被処理水の有機性汚水を生物学的処理する。
【0006】
この種の浸漬型膜分離装置としては例えば特許文献1又は2に開示する技術がある。
【0007】
【特許文献1】特開平8−80497号公報
【0008】
【特許文献2】特開平11−267687号公報
【0009】
【発明が解決しようとする課題】
ところで、膜分離活性汚泥処理では硝化菌が野生しており、被処理水である有機性汚水中に窒素があれば曝気によって供給される酸素の存在下で必ず硝化が起こる。このため、膜分離活性汚泥処理で脱窒槽を設けない場合には硝化のみが行われるので膜透過液のpHが下がり過ぎ、pH調整のためにアルカリ剤の添加が必要となることがある。このpH低下を防止するためには供給する酸素量を制限する必要があるが、クロスフローろ過において膜面を洗浄する上昇流の掃流効果を維持するためには散気装置から散気する空気量は一定量以下にはできない制約がある。
【0010】
また、被処理水としてCaを含有する廃水を処理する場合は、pH調整を行うことによりCaCOのスケール生成を防止することができるが、被処理水中の窒素の硝化量をコントロールすることはできない。このため、スケール生成を防止するために系外から酸を添加することを余儀なくされていた。
【0011】
さらに、逆浸透膜では膜面上のスライムの生成を防ぐために滅菌剤として塩素などを添加しているが、逆浸透膜の塩素耐性が小さいので膜の寿命が短くなる問題があり、その対策として逆浸透膜を浸漬する被処理水中にアンモニアを添加し、塩素とアンモニアを反応させて結合塩素(クロラミン)とすることで酸化力を低減し、逆浸透膜の耐久性を延ばしている。
【0012】
本発明は膜分離活性汚泥処理において窒素を含有する有機性汚水を処理するのに際して、pHの低下を抑制し、スケールの発生を防止することができる汚水の処理方法を提供することを目的とする。
【0013】
【課題を解決するための手段】
上記課題を解決するために、請求項1に記載の本発明の汚水の処理方法は、窒素を含有した有機性の被処理水を膜分離活性汚泥処理するのに際して、生物反応槽内の全活性汚泥量を生物反応槽から引き抜く余剰汚泥量で除した値で定義するSRTが5日以下となるように引き抜く余剰汚泥量を制御し、生物反応槽内に浸漬した槽浸漬型膜分離装置を通して所定量の膜透過水を取り出すことで生物反応槽内のMLSSを所定濃度に維持するものである。
【0014】
上記した構成において、被処理水中の窒素をどの程度硝化するかはSRTをコントロールすることで調整可能であり、硝化菌は増殖が遅くて水温に依存するが通常5〜7日程度のSRTが必要といわれているので、膜分離活性汚泥処理においてSRTを5日以下の極端に短くした運転(例えばSRT=3日)を行うことにより、増殖速度の遅い硝化細菌はウォッシュアウトされて系内に多量に存在できなくなるので、酸素供給が十分な環境であっても被処理水中の窒素の完全硝化が出来なくなり、pHの低下を防止できる。
【0015】
一方、SRTの小さい運転をする場合あっても、被処理水を十分に生物学的処理するためには生物反応槽内のMLSSを所定濃度に維持する必要があり、そのためにHRT(水の滞留時間)を小さくする必要がある。HRTが大きくなるとMLSS濃度は薄くなり、MLSS濃度が適値でないとBOD除去率が低下し、酸素消費量も低下し、消費しきれない酸素が無駄となる。
【0016】
このため、槽浸漬型膜分離装置の膜透過水量を増加させる。このSRTとHRTの関係は以下のものである。
SRT=V×MLSS/(Q×ss)=HRT×MLSS/ss
V:生物反応槽容量(m)、MLSS:反応槽混合液濃度(mg/L)
ss:汚泥発生量(mg/L)、Q:被処理水量(m/d)
請求項2に記載の本発明の汚水の処理方法は、槽浸漬型膜分離装置の膜透過水を逆浸透膜でろ過するのに際して、生物反応槽のSRTを制御して膜透過水中に残存するNH−NとNOx−Nの濃度を制御してpH調整し、逆浸透膜におけるスケール発生を防止するものである。
【0017】
上記した構成により、生物反応槽では被処理水中のNH−NおよびBOD酸化菌の異化代謝によって有機性窒素から転換されるNH−Nを硝化菌によりNO−N、もしくはNO−Nに酸化する。このため、被処理水がCaを含有する場合には、SRTの制御により膜透過水中のNH−NとNOx−Nの濃度を制御してpH調整することによってCaCOのスケール生成を防止し、逆浸透膜の耐久性を延ばす。
【0018】
請求項3に記載の本発明の汚水の処理方法は、膜充填密度10%以上に膜を充填した槽浸漬型膜分離装置を使用するものである。
上記した構成により、槽浸漬型膜分離装置の膜透過水量を増加させる場合に、膜を高密度に充填することで対応する。膜充填密度は槽浸漬型膜分離装置に装着する膜が占有する容積を生物反応槽の槽容積で除した値で定義するものである。
【0019】
請求項4に記載の本発明の汚水の処理方法は、膜を上下方向に多段に配置した槽浸漬型膜分離装置を使用するものである。
上記した構成により、槽浸漬型膜分離装置において膜を平面方向に増設すると占有する床面積が増加し、散気装置の増設も必要となるが、上昇流の流れ方向において膜面積を増加させることで単位床面積当たりで上昇流が接触する膜面積が増加し、散気装置の増設を伴うことなく膜透過水量を増加させることができる。
【0020】
【発明の実施の形態】
以下、本発明の実施の形態を図面に基づいて説明する。図1において、被処理水1は窒素およびCaを含有する有機性汚水であり、前処理手段2においてSS除去等の処理を施して後に流量調整槽3に一旦貯留し、その後に所定量ずつ被処理水1を生物反応槽4へ投入し、生物反応槽4で膜分離活性汚泥処理する。
【0021】
膜分離活性汚泥処理(MBR)は生物反応槽4の内部に槽浸漬型膜分離装置5を浸漬して行う。槽浸漬型膜分離装置5は膜充填部6に鉛直方向に配置する複数の平膜カートリッジ7を平行に充填しており、各平膜カートリッジ7を膜充填部6の内部に形成した膜収納部の夫々に収納している。平膜カートリッジ7は濾板の表裏面に有機平膜からなる濾過膜を配置したもので、槽内の自然水頭を利用して重力濾過して濾過膜を透過した膜透過水を取り出すものであり、例えば高さ1m、幅0.5m、厚さ14mmもしくは8mmの形状をなしている。
【0022】
膜充填部6には平膜カートリッジ7を膜充填密度10%以上に充填する。この膜充填密度は槽浸漬型膜分離装置5に装着する平膜カートリッジ7が占有する容積を生物反応槽4の槽容積で除した値で定義する。また、平膜カートリッジ7は上下方向に多段に配置することが好ましく、槽水深に応じて2段もしくは3段に配置する。膜充填部6の下方には散気装置8を内蔵した散気装置部9を配置している。
【0023】
この槽浸漬型膜分離装置5では散気装置8から散気する空気のエアリフト作用により固気液混相の上昇流が発生し、上昇流が膜充填部6の平膜カートリッジ7の間の流路を膜面に沿って通過する間にろ過を行い、上昇流の掃流効果によって膜面を洗浄するクロスフローろ過を行う。この上昇流によって生物反応槽4の反応槽混合液が槽内で循環し、反応槽混合液を散気装置8から散気する空気で曝気して被処理水の有機性汚水を生物学的処理する。
【0024】
槽浸漬型膜分離装置5の膜透過水は滅菌槽10へ導き、生物反応槽4の余剰汚泥はポンプ11で槽外へ取り出す。生物反応槽4での膜分離活性汚泥処理において被処理水中の窒素をどの程度硝化するかはSRTをコントロールすることで調整可能であり、硝化菌は増殖が遅くて水温に依存するが通常5〜7日程度のSRTが必要といわれているので、SRTが5日以下となるように引き抜く余剰汚泥量を制御する。SRTは生物反応槽4の内部の全活性汚泥量を生物反応槽4から引き抜く余剰汚泥量で除した値で定義する。
【0025】
このように、膜分離活性汚泥処理においてSRTを5日以下の極端に短くした運転(例えばSRT=3日)を行うことにより、増殖速度の遅い硝化細菌はウォッシュアウトされて系内に多量に存在できなくなるので、酸素供給が十分な環境であっても被処理水中の窒素の完全硝化が出来なくなり、pHの低下を防止できる。例えば、SRTを5日に制御することで、被処理水中のNH4−N40mg/Lが20mg/Lに低下したのみであり、100%の完全硝化とならず、pHの低下もほとんどなく、6.7程度であった。SRTが15日の場合は、硝化が100%生じ、pHは5.3まで低下した。
【0026】
一方、SRTの小さい運転をする場合であっても、被処理水を十分に生物学的処理するためには生物反応槽4のMLSSを所定濃度に維持する必要があり、HRT(水の滞留時間)を小さくする必要がある。
【0027】
このため、平膜カートリッジ7を膜充填密度10%以上に充填し、平膜カートリッジ7を上下に多段に配置することで、槽浸漬型膜分離装置5を通して取り出す膜透過水量の増加を図り、生物反応槽4のMLSSを所定濃度に維持するのに必要な所定量を確保する。槽浸漬型膜分離装置5において平膜カートリッジ7を平面方向に増設すると占有する床面積が増加し、散気装置8の増設も必要となるが、上昇流の流れ方向において膜面積を増加させることで単位床面積当たりで上昇流が接触する膜面積が増加し、散気装置8の増設を伴うことなく膜透過水量を増加させることができる。
【0028】
滅菌槽10の滅菌した処理水は放流し、あるいは一部を逆浸透膜の濾過装置12でろ過して再利用する。ところで、生物反応槽4では被処理水中のNH−NおよびBOD酸化菌の異化代謝によって有機性窒素から転換されるNH−Nを硝化菌によりNO−N、もしくはNO−Nに酸化する。このため、前段の生物反応槽4のSRTを制御することで逆浸透膜の濾過装置12へ導く滅菌槽10の処理水中に残存するNH−NとNOx−Nの濃度を制御してpH調整し、逆浸透膜におけるCaCOのスケール生成を防止し、逆浸透膜の耐久性を延ばす。
【0029】
【発明の効果】
以上のように本発明によれば、膜分離活性汚泥処理においてSRTを5日以下とする運転を行って増殖速度の遅い硝化細菌をウォッシュアウトすることで、酸素供給が十分な環境下においても被処理水中の窒素の硝化を抑制してpHの低下を防止できる。また、SRTの制御により膜透過水中のNH−NとNOx−Nの濃度を制御してpH調整することによってCaCOのスケール生成を防止して逆浸透膜の耐久性を延ばすことができる。
【図面の簡単な説明】
【図1】本発明の実施の形態における汚水の処理方法を示すフローシート図である。
【符号の説明】
1 被処理水
2 前処理手段
3 流量調整槽
4 生物反応槽
5 槽浸漬型膜分離装置
6 膜充填部
7 平膜カートリッジ
8 散気装置
9 散気装置部
10 滅菌槽
11 ポンプ
12 逆浸透膜の濾過装置
[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for treating sewage, and relates to a technique for treating organic sewage containing nitrogen.
[0002]
[Prior art]
BACKGROUND ART Conventionally, membrane separation activated sludge treatment (MBR) has been widely used because its treated water quality is stable and its maintenance is easy. Since the membrane separation activated sludge treatment can be operated at a high concentration of MLSS, the residence time (SRT) of the sludge can be long, so that the nitrifying bacteria can be easily held in the tank. SRT is usually a value obtained by dividing the amount of sludge in a biological reaction tank by the amount of excess sludge, and is usually indicated in days. Nitrifying bacteria are slow in growth and depend on the water temperature, but it is said that an SRT of about 5 to 7 days is usually required. ing.
[0003]
Since the membrane separation activated sludge treatment can surely nitrify nitrogen in wastewater, it is a process capable of removing nitrogen by combining with a denitrification tank. Since the permeated water treated with the membrane separation activated sludge is very high in quality, it is often reused as a water resource, and in some cases, is subjected to advanced treatment such as reverse osmosis membrane (RO).
[0004]
The membrane separation activated sludge treatment (MBR) is performed by immersing a tank immersion type membrane separation device inside a biological reaction tank, and the tank immersion type membrane separation device includes a plurality of flat membrane cartridges arranged along a vertical direction. An air diffuser unit having a film filling unit filled in parallel and having a built-in air diffuser is disposed below the film filling unit.
[0005]
In the tank immersion type membrane separation device, an upward flow of the solid-gas-liquid mixed phase is generated by the air lift action of the air diffused from the air diffuser, and the upward flow flows along the flow path between the flat membrane cartridges of the membrane filling part along the membrane surface. Filtration is performed during the passage, and the membrane surface is cleaned by the sweeping effect of the upward flow. This is called cross-flow filtration. Due to the upward flow, the reaction mixture in the biological reaction tank is circulated in the tank, and the reaction mixture is aerated with air diffused from an air diffuser to biologically treat the organic wastewater of the water to be treated.
[0006]
As this type of immersion type membrane separation device, for example, there is a technology disclosed in Patent Document 1 or 2.
[0007]
[Patent Document 1] Japanese Patent Application Laid-Open No. 8-80497
[Patent Document 2] Japanese Patent Application Laid-Open No. 11-267687
[Problems to be solved by the invention]
By the way, nitrifying bacteria are wild in the membrane separation activated sludge treatment, and if there is nitrogen in the organic wastewater to be treated, nitrification always occurs in the presence of oxygen supplied by aeration. For this reason, when no denitrification tank is provided in the membrane separation activated sludge treatment, only nitrification is performed, so that the pH of the membrane permeate is too low, and an alkali agent may need to be added for pH adjustment. In order to prevent this pH drop, it is necessary to limit the amount of oxygen to be supplied. However, in order to maintain the sweeping effect of the upward flow for cleaning the membrane surface in cross-flow filtration, air diffused from the air diffuser is required. There is a restriction that the amount cannot be less than a certain amount.
[0010]
Further, when treating wastewater containing Ca as the water to be treated, pH adjustment can prevent the generation of scale of CaCO 3 , but cannot control the nitrification amount of nitrogen in the water to be treated. . For this reason, it has been necessary to add an acid from outside the system in order to prevent scale formation.
[0011]
Furthermore, in reverse osmosis membranes, chlorine and the like are added as a sterilizing agent to prevent the generation of slime on the membrane surface.However, since the chlorine resistance of the reverse osmosis membrane is small, the life of the membrane is shortened. Ammonia is added to the water to be treated in which the reverse osmosis membrane is immersed, and chlorine and ammonia are reacted to form bound chlorine (chloramine), thereby reducing the oxidizing power and extending the durability of the reverse osmosis membrane.
[0012]
An object of the present invention is to provide a method for treating sewage that can suppress a decrease in pH and prevent generation of scale when treating organic sewage containing nitrogen in the membrane separation activated sludge treatment. .
[0013]
[Means for Solving the Problems]
In order to solve the above problem, the method for treating sewage according to the present invention according to claim 1 is a method for treating a nitrogen-containing organic water to be treated by membrane separation activated sludge. The amount of excess sludge withdrawn is controlled so that the SRT defined by the amount of sludge divided by the amount of excess sludge withdrawn from the biological reaction tank is 5 days or less. The MLSS in the biological reaction tank is maintained at a predetermined concentration by taking out a fixed amount of membrane permeated water.
[0014]
In the above-described configuration, the amount of nitrification of nitrogen in the water to be treated can be adjusted by controlling the SRT. Nitrifying bacteria grow slowly and depend on the water temperature, but usually require an SRT of about 5 to 7 days. Therefore, by performing an operation with an extremely short SRT of 5 days or less (eg, SRT = 3 days) in the membrane separation activated sludge treatment, nitrifying bacteria having a slow growth rate are washed out and a large amount of nitrifying bacteria is introduced into the system. Therefore, even in an environment where the oxygen supply is sufficient, complete nitrification of nitrogen in the water to be treated cannot be performed, and a decrease in pH can be prevented.
[0015]
On the other hand, even in the case of operation with a small SRT, it is necessary to maintain the MLSS in the biological reaction tank at a predetermined concentration in order to sufficiently treat the water to be treated biologically. Time) must be reduced. As the HRT increases, the MLSS concentration decreases. If the MLSS concentration is not an appropriate value, the BOD removal rate decreases, the oxygen consumption decreases, and oxygen that cannot be consumed is wasted.
[0016]
For this reason, the amount of permeated water in the tank immersion type membrane separation device is increased. The relationship between SRT and HRT is as follows.
SRT = V × MLSS / (Q × ss) = HRT × MLSS / ss
V: Biological reaction tank capacity (m 3 ), MLSS: Reaction tank mixture concentration (mg / L)
ss: sludge generation amount (mg / L), Q: treated water amount (m 3 / d)
In the method for treating sewage according to the second aspect of the present invention, the SRT of the biological reaction tank is controlled to remain in the permeated water by controlling the SRT of the biological reaction tank when filtering the permeated water of the tank immersion type membrane separation device with the reverse osmosis membrane. The pH is controlled by controlling the concentrations of NH 4 —N and NOx—N to prevent the generation of scale in the reverse osmosis membrane.
[0017]
With the configuration described above, the biological reactor NO 2 -N and NH 3 -N by nitrifying bacteria that is converted from the organic nitrogen by catabolism of NH 3 -N and BOD-oxidizing bacteria in the water to be treated, or NO 3 -N Oxidizes to Therefore, when the water to be treated contains Ca, the generation of CaCO 3 scale is prevented by controlling the concentration of NH 4 —N and NOx—N in the membrane permeated water by controlling the SRT and adjusting the pH. Extend the durability of the reverse osmosis membrane.
[0018]
The sewage treatment method according to the present invention described in claim 3 uses a tank immersion type membrane separation apparatus in which a membrane is packed to a membrane packing density of 10% or more.
With the above-described configuration, when the amount of water permeated through the membrane of the tank immersion type membrane separation device is increased, the membrane is densely filled to cope with the increase. The membrane packing density is defined as a value obtained by dividing the volume occupied by the membrane mounted on the tank immersion type membrane separation device by the tank volume of the biological reaction tank.
[0019]
The sewage treatment method of the present invention described in claim 4 uses a tank immersion type membrane separation apparatus in which membranes are arranged in multiple stages in the vertical direction.
According to the above-described configuration, in the tank immersion type membrane separation device, when the membrane is added in the plane direction, the occupied floor area increases, and an additional air diffuser is required. However, the membrane area is increased in the upward flow direction. As a result, the area of the membrane contacted by the ascending flow per unit floor area increases, and the amount of water permeated through the membrane can be increased without adding an air diffuser.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, treated water 1 is an organic wastewater containing nitrogen and Ca. The treated water 1 is subjected to a treatment such as removal of SS in a pretreatment means 2, temporarily stored in a flow control tank 3, and thereafter treated by a predetermined amount. The treated water 1 is introduced into the biological reaction tank 4, and is subjected to membrane separation activated sludge treatment in the biological reaction tank 4.
[0021]
The membrane separation activated sludge treatment (MBR) is performed by immersing a tank immersion type membrane separation device 5 inside the biological reaction tank 4. The tank immersion type membrane separation device 5 has a plurality of flat membrane cartridges 7 arranged in a vertical direction in a membrane filling section 6 in parallel, and each flat membrane cartridge 7 is formed in a membrane storage section formed inside the membrane filling section 6. Are stored in each of them. The flat membrane cartridge 7 has a filtration membrane composed of an organic flat membrane disposed on the front and back surfaces of a filter plate, and is used for gravity filtration using a natural head in a tank to take out the permeated water that has passed through the filtration membrane. For example, the shape is 1 m in height, 0.5 m in width, and 14 mm or 8 mm in thickness.
[0022]
The membrane filling section 6 is filled with a flat membrane cartridge 7 at a membrane packing density of 10% or more. The membrane packing density is defined as a value obtained by dividing the volume occupied by the flat membrane cartridge 7 mounted on the immersion type membrane separation device 5 by the volume of the biological reaction tank 4. Further, the flat membrane cartridges 7 are preferably arranged in multiple stages in the vertical direction, and are arranged in two or three stages according to the tank water depth. An air diffuser unit 9 having a built-in air diffuser 8 is disposed below the film filling unit 6.
[0023]
In this tank immersion type membrane separation device 5, an upward flow of the solid-gas-liquid mixed phase is generated by the air lift function of the air diffused from the air diffuser 8, and the upward flow is generated between the flat membrane cartridges 7 of the membrane filling unit 6. Is passed along the membrane surface, and cross-flow filtration is performed to wash the membrane surface by the sweeping effect of the upward flow. Due to the upward flow, the reaction mixture in the biological reaction tank 4 is circulated in the tank, and the reaction mixture is aerated with air diffused from the diffuser 8 to biologically treat the organic sewage of the water to be treated. I do.
[0024]
The permeated water of the tank immersion type membrane separation device 5 is guided to a sterilization tank 10, and excess sludge of the biological reaction tank 4 is taken out of the tank by a pump 11. The degree of nitrification of the nitrogen in the water to be treated in the membrane separation activated sludge treatment in the biological reaction tank 4 can be adjusted by controlling the SRT. Nitrifying bacteria grow slowly and depend on the water temperature. Since it is said that an SRT of about 7 days is required, the amount of excess sludge to be drawn out is controlled so that the SRT is 5 days or less. The SRT is defined as a value obtained by dividing the total amount of activated sludge inside the biological reaction tank 4 by the amount of excess sludge withdrawn from the biological reaction tank 4.
[0025]
As described above, by performing the operation in which the SRT is extremely shortened to 5 days or less (eg, SRT = 3 days) in the membrane separation activated sludge treatment, nitrifying bacteria having a low growth rate are washed out and are present in a large amount in the system. Therefore, even in an environment where the oxygen supply is sufficient, complete nitrification of nitrogen in the water to be treated cannot be performed, and a decrease in pH can be prevented. For example, by controlling the SRT on the 5th, NH4 4 -N40 mg / L in the water to be treated was only reduced to 20 mg / L, complete nitrification was not 100%, and there was almost no decrease in pH. Was about 0.7. When the SRT was 15 days, nitrification occurred 100% and the pH dropped to 5.3.
[0026]
On the other hand, even when the operation is performed with a small SRT, the MLSS in the biological reaction tank 4 needs to be maintained at a predetermined concentration in order to sufficiently treat the water to be treated biologically. ) Needs to be smaller.
[0027]
For this reason, by filling the flat membrane cartridge 7 with a membrane packing density of 10% or more and arranging the flat membrane cartridges 7 vertically in multiple stages, the amount of membrane permeated water taken out through the tank immersion type membrane separation device 5 is increased, and biological A predetermined amount required to maintain the MLSS in the reaction tank 4 at a predetermined concentration is secured. When the flat membrane cartridge 7 is expanded in the planar direction in the tank immersion type membrane separation device 5, the occupied floor area increases, and the air diffusion device 8 also needs to be expanded. However, it is necessary to increase the membrane area in the upward flow direction. As a result, the membrane area with which the ascending flow comes into contact per unit floor area increases, and the amount of water permeated through the membrane can be increased without adding the air diffuser 8.
[0028]
The sterilized treated water in the sterilization tank 10 is discharged, or a part of the treated water is filtered through a reverse osmosis membrane filtration device 12 and reused. Incidentally, oxidation of NH 3 -N are converted from the organic nitrogen NO 2 -N by nitrifying bacteria, or the NO 3 -N by catabolism of NH 3 -N and BOD-oxidizing bacteria in the water to be treated in the bioreactor 4 I do. For this reason, by controlling the SRT of the biological reaction tank 4 in the preceding stage, the concentration of NH 4 —N and NOx—N remaining in the treated water of the sterilization tank 10 guided to the reverse osmosis membrane filtration device 12 is controlled to adjust the pH. In addition, the formation of CaCO 3 scale in the reverse osmosis membrane is prevented, and the durability of the reverse osmosis membrane is extended.
[0029]
【The invention's effect】
As described above, according to the present invention, by performing the operation of setting the SRT to 5 days or less in the membrane separation activated sludge treatment to wash out nitrifying bacteria having a low growth rate, the treatment can be performed even in an environment where the oxygen supply is sufficient. Nitrification of nitrogen in the treated water can be suppressed to prevent a decrease in pH. Further, by controlling the concentration of NH 4 —N and NOx—N in the membrane permeated water by controlling the SRT and adjusting the pH, it is possible to prevent the generation of scale of CaCO 3 and extend the durability of the reverse osmosis membrane.
[Brief description of the drawings]
FIG. 1 is a flow sheet diagram showing a method for treating wastewater according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 To-be-processed water 2 Pre-processing means 3 Flow control tank 4 Biological reaction tank 5 Tank immersion type membrane separation device 6 Membrane filling part 7 Flat membrane cartridge 8 Air diffuser 9 Air diffuser part 10 Sterilization tank 11 Pump 12 Reverse osmosis membrane Filtration device

Claims (4)

窒素を含有した有機性の被処理水を膜分離活性汚泥処理するのに際して、生物反応槽内の全活性汚泥量を生物反応槽から引き抜く余剰汚泥量で除した値で定義するSRTが5日以下となるように引き抜く余剰汚泥量を制御し、生物反応槽内に浸漬した槽浸漬型膜分離装置を通して所定量の膜透過水を取り出すことで生物反応槽内のMLSSを所定濃度に維持することを特徴とする汚水の処理方法。SRT defined as a value obtained by dividing the total amount of activated sludge in the biological reaction tank by the amount of excess sludge withdrawn from the biological reaction tank when treating organic treated water containing nitrogen with membrane separation activated sludge is 5 days or less. By controlling the amount of excess sludge to be drawn out so as to obtain a predetermined amount of membrane permeated water through a tank immersion type membrane separator immersed in the biological reaction tank, the MLSS in the biological reaction tank is maintained at a predetermined concentration. A method for treating wastewater. 槽浸漬型膜分離装置の膜透過水を逆浸透膜でろ過するのに際して、生物反応槽のSRTを制御して膜透過水中に残存するNH−NとNOx−Nの濃度を制御してpH調整し、逆浸透膜におけるスケール発生を防止することを特徴とする請求項1に記載の汚水の処理方法。When filtering the permeated water of the tank immersion type membrane separation device with a reverse osmosis membrane, controlling the SRT of the biological reaction tank and controlling the concentrations of NH 4 —N and NOx—N remaining in the permeated water to control the pH. The method for treating sewage according to claim 1, wherein the method is adjusted to prevent scale generation in the reverse osmosis membrane. 膜充填密度10%以上に膜を充填した槽浸漬型膜分離装置を使用することを特徴とする請求項1又は2に記載の汚水の処理方法。The method for treating sewage according to claim 1 or 2, wherein a tank immersion type membrane separation device filled with a membrane having a membrane packing density of 10% or more is used. 膜を上下方向に多段に配置した槽浸漬型膜分離装置を使用することを特徴とする請求項3に記載の汚水の処理方法。The method for treating sewage according to claim 3, wherein a tank immersion type membrane separation device in which membranes are arranged in multiple stages in a vertical direction is used.
JP2002313563A 2002-10-29 2002-10-29 Method for treating sewage Pending JP2004148144A (en)

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Cited By (9)

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JP2006015236A (en) * 2004-07-01 2006-01-19 Toray Ind Inc Apparatus and method for preparing regenerated water
JP2008188498A (en) * 2007-02-01 2008-08-21 Kobelco Eco-Solutions Co Ltd Treatment method and treatment equipment for water to be treated
CN101811804A (en) * 2010-04-21 2010-08-25 上海方合正环境工程科技发展有限公司 Domestic sewage bioreaction treatment and recycling system
CN101880080A (en) * 2010-07-02 2010-11-10 哈尔滨工程大学 Airlift multi-stage loop membrane bioreactor with worm bed
JP2011088151A (en) * 2011-02-09 2011-05-06 Toray Ind Inc Apparatus and method for preparing regenerated water
JP2011177607A (en) * 2010-02-26 2011-09-15 Toray Ind Inc Oil-containing waste water treatment method
CN102757157A (en) * 2012-08-01 2012-10-31 南宁佳迪斯电气科技有限责任公司 Sewage treatment system used in medical field
JP2014000538A (en) * 2012-06-20 2014-01-09 Meidensha Corp Method for controlling active sludge concentration
CN103922465A (en) * 2014-03-28 2014-07-16 黄骏 Immobilized activated sludge plate

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006015236A (en) * 2004-07-01 2006-01-19 Toray Ind Inc Apparatus and method for preparing regenerated water
JP2008188498A (en) * 2007-02-01 2008-08-21 Kobelco Eco-Solutions Co Ltd Treatment method and treatment equipment for water to be treated
JP4536740B2 (en) * 2007-02-01 2010-09-01 株式会社神鋼環境ソリューション Treatment method and treatment equipment for treated water
JP2011177607A (en) * 2010-02-26 2011-09-15 Toray Ind Inc Oil-containing waste water treatment method
CN101811804A (en) * 2010-04-21 2010-08-25 上海方合正环境工程科技发展有限公司 Domestic sewage bioreaction treatment and recycling system
CN101880080A (en) * 2010-07-02 2010-11-10 哈尔滨工程大学 Airlift multi-stage loop membrane bioreactor with worm bed
JP2011088151A (en) * 2011-02-09 2011-05-06 Toray Ind Inc Apparatus and method for preparing regenerated water
JP2014000538A (en) * 2012-06-20 2014-01-09 Meidensha Corp Method for controlling active sludge concentration
CN102757157A (en) * 2012-08-01 2012-10-31 南宁佳迪斯电气科技有限责任公司 Sewage treatment system used in medical field
CN103922465A (en) * 2014-03-28 2014-07-16 黄骏 Immobilized activated sludge plate

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