【発明の詳細な説明】[Detailed description of the invention]
産業上の利用分野
本発明は好気性微生物による汚水浄化処理、例
えば排水や下水の活性汚泥処理を効率よく行い得
る散気式曝気槽に関するものである。
先行技術と問題点
有機性物質を含む汚水を好気性微生物による生
物学的作用で処理する通常の活性汚泥法において
は、曝気槽で処理した汚水を沈澱槽に移流させ
て、上澄液と汚泥とに分離し、この分離汚泥を曝
気槽に返送する必要がある。而るに、曝気槽、沈
澱槽のそれぞれにおける処理水の滞留時間を長時
間に設定する必要があり、装置の大型化を免れ得
ない。更に、処理水を再利用するには、活性単
過や膜装置を付加する必要があり、設備費と運転
費の大巾の増大を避け得ず、その再利用は至難で
ある。
かかる不利を解消する方法として、上記沈澱槽
の代りに逆浸透装置や限外過装置を設置し、汚
泥の分離に要する付帯設備の設置積を小さくする
と共に曝気槽を高汚泥濃度下で使用可能ならしめ
る曝気槽容積を大巾に小さくすることが提案され
ている。
しかしながら、この方法では、高濃度の汚泥を
含む液を膜装置で処理するので、濃度分極作用や
膜面汚損による透過水量の低下が避けられない。
かかる不利を解消するには、膜面での流速を大き
く保ち、液圧を高くする必要があるが、膜装置に
大容量のポンプ及び配管、弁及び制御盤を必要と
する。而して膜面流路を速くするためには、ポン
プの動力費の飛躍的高騰を招き、処理費用が増大
し、必ずしも設備費の低減を確保し得ない。
発明の目的
本発明の目的は膜装置を利用するにもかかわら
ず、曝気槽内の散気流の利用により、濃度分極や
膜汚損を防止して、膜装置に付属する設備の簡略
化を可能ならしめ、設備費や運転費を低減できる
散気式曝気槽を提供することにある。
発明の構成
本発明の散気式曝気槽は、散気装置を有し、膜
面に沿い鉛直方向通路を有する膜装置を前記散気
装置の直上に配設し、該膜装置の膜体透過側を負
圧とするための手段を設けたことを特徴とする構
成である。
実施例
以下、図面により本発明を説明する。
第１図において、１は散気型曝化槽であり、底
面近傍に散気装置、例えば散気管２（多孔パイ
プ）を設けてある。この散気管２に送気管２１に
より空気または酸素含有気体を圧送し、散気管か
ら気泡を散出させ、その散気流（気・液混合液）
によつて処理液を循環させると共に液中の活性汚
泥により酸素の存在下、液を好気性菌の作用によ
り分解処理していく。
３は膜装置であり、上記散気管２の直上に配設
してある。この膜装置は、散気管２からの気・液
混合流を通過させる鉛直方向通路３１，３１…を
有しており、この通路において気・液混合流が膜
面に接触し、膜面上での活性汚泥の濃度分極、膜
面の活性汚泥による汚損を防止できる。４は膜装
置３の透過水側を減圧し、移送するための真空引
きポンプであり、これにより透過水を膜装置３か
ら取出すことができる。
上記膜装置３には、内径約10mm以上の管状膜を
複数本並べた、いわゆるパラレル型流路の膜モジ
ユール、あるいは任意の巾の平膜型（例えば、ス
パイラル型、プリーツ型）あるいは平板型の膜エ
レメントを上記鉛直通路を確保するように組立て
た膜モジユールを使用できる。かかる膜モジユー
ルの鉛直方向の長さは曝気槽の深さによつて異る
が、通常は曝気槽の深さから0.3ｍを減じた長さ
であり、一般に0.5ｍ以上である。これらは数箇
に分割した型式で使用することもできる。
上記スパイラル型等の平膜型の膜エレメントに
おいては、上記した鉛直通路中に流路スペーサを
設けないことが望ましい。何れの膜エレメントに
おいても、鉛直通路の厚みは10mm以上とすること
が望ましい。しかし、その厚みを余り大きくする
と、設置できる膜面積が減少するので好ましくな
い。
第２図Ａは本発明において使用する膜装置の一
例を示し、不織布等の多孔支持管３２上に膜３３
を設けた管状膜３０を数本、外筒３４内に納め
（第２図Ｂ参照）、両端をエンドプレート３５，３
５または注型樹脂によつて封止した構成であり上
記の気・液混合流は管状膜内を流動し、透過水は
外筒内より透過水取出口を経て取出される。膜に
は、精密過膜、半透膜、特に限外過膜あるい
は食塩除去率の低い、いわゆるルーズ逆浸透膜を
用いる。
第３図Ａは本発明において使用する膜装置の別
例を示し、一対の透過水集水管３５，３５に第３
図Ｂにも示すように平板型膜（平膜３３，３３間
に透過水路用スペーサ３６を介在させたもの）を
連通し、これをユニツトとしてホルダーにより一
定の間隔で並設してある。この膜エレメントの場
合、ユニツト間に散気管を配設することができ
る。
本発明においては、第４図に示すように膜装置
３の系統と散気管２の系統とをセツトしておき、
洗浄槽５（例えば、次亜塩素酸ソーダ、界面活性
剤を薬剤槽）でこれらを同時に定期的に洗浄する
こともできる。第４図において、６はバルブ、４
は減圧ポンプである。
本発明の散気式曝気槽においては、膜面上での
濃度分極作用、膜汚損を防止できるから、曝気槽
内の汚泥濃度を高濃度になし得（6000〜
10000ppm）、処理すべき有機性物質の生物学的反
応滞留時間を短時間になし得る（１〜２時間）の
で、曝気槽の容量を大巾に縮小できる（従来の1/
２〜1/6）。処理水中の有機性物質（BOD）は活性
汚泥により高度に除去されるから、透過水中には
実質上SS、大腸菌、ビールスが検出されず、従
つて、透過水をいわゆる三次処理を行うことなく
工業用水、雑用水等として再利用できる。
膜装置を曝気槽の系外に設ける従来例において
は、膜面上に濃度分極を生じさせない膜面流速を
得るには、膜装置の運転に高エネルギーを必要と
するが（膜面流速を得るためのエネルギーが膜エ
レメント運転の全エネルギーの70〜80％を占め
る）、本発明の散気式曝気槽では、膜装置の透過
側を負圧とすることによつて膜分離に必要な膜間
差圧を確保しており、曝気槽内液圧を実質上大気
圧にできるから、散気装置から曝気槽内の液中に
空気を高流量を放出し得、曝気空気量を通常の場
合に較べ、曝気容積当たり２〜６倍と高くするだ
けで膜面での処理液流速を１〜1.5ｍ／秒にでき、
膜装置運転のための上記高エネルギーを必要とし
ない。
実施例
有効容積４m3の曝気槽内に、内径12mmφ、長さ
1.25ｍ管状限外過膜648本（膜総面積29m2）か
らなる膜装置を設置し、ソルセルブ、アセトンな
どの有機生物質を多量に含有する工場排水を、曝
気槽内の活性汚泥濃度を約8000ppmに維持しつ
つ、毎時2.5m3で処理したところ、原水に対する
処理水の水質は次の通りであつた。
INDUSTRIAL APPLICATION FIELD The present invention relates to a diffused aeration tank that can efficiently perform sewage purification treatment using aerobic microorganisms, such as activated sludge treatment of wastewater and sewage. Prior art and problems In the normal activated sludge method, which treats wastewater containing organic substances by the biological action of aerobic microorganisms, wastewater treated in an aeration tank is advected to a settling tank, and supernatant liquid and sludge are It is necessary to separate the sludge and return the separated sludge to the aeration tank. However, it is necessary to set the residence time of treated water in each of the aeration tank and the settling tank for a long time, which inevitably increases the size of the apparatus. Furthermore, in order to reuse the treated water, it is necessary to add an activated filter or a membrane device, which inevitably increases equipment costs and operating costs, making it extremely difficult to reuse it. As a method to eliminate this disadvantage, a reverse osmosis device or an ultrafiltration device is installed in place of the above-mentioned settling tank, which reduces the installation area of the ancillary equipment required for sludge separation, and allows the aeration tank to be used under high sludge concentrations. It has been proposed to significantly reduce the volume of the aeration tank used for leveling. However, in this method, since a liquid containing highly concentrated sludge is treated with a membrane device, a decrease in the amount of permeated water due to concentration polarization and membrane surface fouling is unavoidable.
In order to eliminate this disadvantage, it is necessary to maintain a high flow rate at the membrane surface and increase the liquid pressure, but this requires a large-capacity pump, piping, valves, and control panel for the membrane device. In order to increase the speed of the membrane flow path, the power cost of the pump increases dramatically, the processing cost increases, and it is not necessarily possible to reduce the equipment cost. Purpose of the Invention The purpose of the present invention is to prevent concentration polarization and membrane fouling by using the aeration flow in the aeration tank, and to simplify the equipment attached to the membrane device, even though a membrane device is used. The purpose of the present invention is to provide a diffused aeration tank that can reduce equipment costs and operating costs. Structure of the Invention The aeration tank of the present invention has an aeration device, and a membrane device having a vertical passage along the membrane surface is disposed directly above the aeration device, and the membrane device permeates through the membrane of the membrane device. This configuration is characterized by providing means for creating a negative pressure on the side. EXAMPLES The present invention will be explained below with reference to the drawings. In FIG. 1, reference numeral 1 denotes an aeration type aeration tank, and an aeration device, for example, an aeration pipe 2 (porous pipe) is provided near the bottom of the tank. Air or oxygen-containing gas is force-fed to the diffuser pipe 2 through the air supply pipe 21, air bubbles are dispersed from the diffuser pipe, and the diffused flow (gas/liquid mixture)
The treatment liquid is circulated by the activated sludge in the liquid, and in the presence of oxygen, the liquid is decomposed by the action of aerobic bacteria. Reference numeral 3 denotes a membrane device, which is disposed directly above the aeration pipe 2. This membrane device has vertical passages 31, 31... through which the gas/liquid mixed flow from the aeration pipe 2 passes, and in these passages, the gas/liquid mixed flow contacts the membrane surface, and the gas/liquid mixed flow contacts the membrane surface. It is possible to prevent concentration polarization of activated sludge and fouling of the membrane surface by activated sludge. Reference numeral 4 denotes a vacuum pump for reducing the pressure on the permeated water side of the membrane device 3 and transferring it, so that the permeated water can be taken out from the membrane device 3. The membrane device 3 may include a so-called parallel channel membrane module in which a plurality of tubular membranes each having an inner diameter of approximately 10 mm or more are lined up, or a flat membrane type (such as a spiral type or a pleated type) or a flat plate type with an arbitrary width. A membrane module in which membrane elements are assembled to ensure the above-mentioned vertical passage can be used. The vertical length of such a membrane module varies depending on the depth of the aeration tank, but is usually the depth of the aeration tank minus 0.3 m, and is generally 0.5 m or more. These can also be used in several divided formats. In a flat membrane type membrane element such as the spiral type described above, it is desirable that no flow path spacer is provided in the above-mentioned vertical passage. In any membrane element, it is desirable that the thickness of the vertical passage be 10 mm or more. However, if the thickness is too large, the area of the membrane that can be installed will be reduced, which is not preferable. FIG. 2A shows an example of a membrane device used in the present invention, in which a membrane 33 is placed on a porous support tube 32 made of non-woven fabric or the like.
Several tubular membranes 30 provided with
5 or sealed with casting resin, the above-mentioned gas/liquid mixed flow flows in the tubular membrane, and permeated water is taken out from the outer cylinder through the permeated water outlet. As the membrane, a precision membrane, a semipermeable membrane, especially an ultrafiltration membrane, or a so-called loose reverse osmosis membrane with a low salt removal rate is used. FIG. 3A shows another example of the membrane device used in the present invention, in which a pair of permeated water collection pipes 35, 35 have a third
As shown in FIG. B, flat membranes (with a permeation channel spacer 36 interposed between the flat membranes 33) are communicated and arranged side by side at regular intervals by a holder as a unit. In the case of this membrane element, diffuser pipes can be arranged between the units. In the present invention, as shown in FIG. 4, the system of the membrane device 3 and the system of the air diffuser 2 are set,
These can also be periodically cleaned at the same time in a cleaning tank 5 (for example, a chemical tank containing sodium hypochlorite and a surfactant). In Fig. 4, 6 is a valve;
is a vacuum pump. In the diffused aeration tank of the present invention, the concentration polarization effect on the membrane surface and membrane fouling can be prevented, so the sludge concentration in the aeration tank can be made high (6000 ~
10,000 ppm), the biological reaction residence time of the organic substances to be treated can be shortened (1 to 2 hours), so the capacity of the aeration tank can be greatly reduced (1/2 of the conventional one).
2-1/6). Since organic substances (BOD) in the treated water are highly removed by activated sludge, virtually no SS, E. coli, or viruses are detected in the permeated water. Therefore, the permeated water can be used industrially without so-called tertiary treatment. It can be reused as drinking water, miscellaneous water, etc. In the conventional example where the membrane device is installed outside the aeration tank system, high energy is required to operate the membrane device in order to obtain a membrane surface flow velocity that does not cause concentration polarization on the membrane surface. (The energy required for membrane element operation accounts for 70 to 80% of the total energy for membrane element operation). In the diffused aeration tank of the present invention, the permeation side of the membrane device is under negative pressure to reduce the gap between the membranes necessary for membrane separation. Since a differential pressure is ensured and the liquid pressure in the aeration tank can be brought to substantially atmospheric pressure, a high flow rate of air can be released from the aeration device into the liquid in the aeration tank, reducing the amount of aeration air to the normal level. In comparison, by simply increasing the aeration volume by 2 to 6 times, the flow rate of the treated liquid at the membrane surface can be increased to 1 to 1.5 m/sec.
The above-mentioned high energy for membrane device operation is not required. Example: In an aeration tank with an effective volume of 4 m3 , an inner diameter of 12 mmφ and a length of
A membrane device consisting of 648 1.25m tubular ultrafiltration membranes (total membrane area 29m 2 ) was installed to reduce the activated sludge concentration in the aeration tank from industrial wastewater containing large amounts of organic substances such as Solserv and acetone. When treated at a rate of 2.5 m 3 per hour while maintaining the concentration at 8000 ppm, the quality of the treated water relative to the raw water was as follows.
【表】
また、膜の透過特性は安定であり、運転後１ケ
月後での透過水量は120／m2・ｈ・atmであつ
た。
発明の効果
本発明の散気式曝気槽は上述した通りの構成で
あり、膜装置の膜間差圧を透過側を負圧とするこ
とにより確保しているから、曝気槽内液圧をほぼ
大気圧にでき、従つて、散気装置からの空気流速
を速くし得、膜面に接触する液の流速を高速にで
き、膜面上での濃度分極、膜汚染をよく防止でき
る。而して、曝気槽外に膜装置を設置せる従来例
に較べて、装置全体の小型化または設置面積の縮
小化、運転動力費の低減化、ひいては設備の簡略
化を図ることができる。
例えば、例えば、チユーブラ膜モジユールで活
性汚泥を含む液を膜分離するには、処理水１m3当
たり２〜4KwHの電力を必要とするが、本発明
においては、処理水を吸引する動力として１m3当
たり0.03〜0.05KwHの電力を必要とするに過ぎ
ない。[Table] Furthermore, the permeation characteristics of the membrane were stable, and the amount of permeated water after one month of operation was 120/m 2 ·h ·atm. Effects of the Invention The diffused aeration tank of the present invention has the above-mentioned configuration, and the pressure difference between the membranes of the membrane device is ensured by making the permeate side negative pressure. Atmospheric pressure can be achieved, therefore, the air flow rate from the diffuser can be increased, the flow rate of the liquid in contact with the membrane surface can be increased, and concentration polarization on the membrane surface and membrane contamination can be effectively prevented. Therefore, compared to conventional examples in which a membrane device is installed outside the aeration tank, it is possible to downsize the entire device, reduce the installation area, reduce operating power costs, and simplify the equipment. For example, in order to membrane-separate a liquid containing activated sludge using a tubular membrane module, 2 to 4 KwH of electricity is required per 1 m 3 of treated water, but in the present invention, 1 m 3 is used as the power to suck the treated water. It only requires 0.03~0.05KwH of power per unit.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は本発明に係る膜処理装置を示す説明
図、第２図Ａは本発明において使用する膜装置を
示す説明図、第２図Ｂは第２図Ａにおけるｂ−ｂ
断面説明図、第３図Ａは本発明において使用する
膜装置の別例を示す説明図、第３図Ｂは第３図Ａ
におけるｂ−ｂ断面説明図、第４図は本発明の別
実施例を示す説明図である。
図において、１は曝気槽、２は散気装置、３は
膜装置、４は減圧ポンプである。
FIG. 1 is an explanatory diagram showing a membrane processing apparatus according to the present invention, FIG. 2 A is an explanatory diagram showing a membrane apparatus used in the present invention, and FIG. 2 B is a line bb in FIG. 2 A.
A cross-sectional explanatory diagram, FIG. 3A is an explanatory diagram showing another example of the membrane device used in the present invention, and FIG. 3B is a diagram illustrating FIG. 3A.
FIG. 4 is an explanatory diagram showing another embodiment of the present invention. In the figure, 1 is an aeration tank, 2 is an aeration device, 3 is a membrane device, and 4 is a pressure reducing pump.