【考案の詳細な説明】[Detailed explanation of the idea]
（産業上の利用分野）
本考案は活性汚泥処理で使用する曝気装置のう
ち、槽水深５〜８ｍの曝気槽に好適で高い酸素移
動効率を有する曝気装置に関するものである。
（従来の技術）
従来第７図にその一例を示すように、槽水深ｈ
が５〜８ｍの曝気槽１１では槽１１の中段部の片
側で底部から0.5〜２ｍの位置に散気装置１２を
設置して曝気することで、旋回流を生じさせると
ともに酸素を溶解させ、汚泥濃度を均一に保つて
きた。
上述した旋回流方式の曝気槽では、散気装置よ
り発生した気泡は旋回流に乗つて上昇するため、
清水中の気泡の上昇速度より大きな速度で上昇し
水面に達する。このため、気泡の液中での滞溜時
間すなわち気液接触時間が短く、その結果酸素移
動効率があまり高くならない欠点があつた。
近年、第８図にその一例を示すように、水深ｈ
が５ｍ程度の曝気槽１１においては、上記旋回流
方式の欠点を補う方式として槽１１の底盤全面に
散気装置１２を配置する全面曝気装置が採用され
ている。この装置では、上昇流と下降流が明確に
区別されず旋回流がほとんど生じないため、気泡
の液中での滞溜時間が長くなる。また、散気装置
を槽全面に配置したことで気泡の分散性が向上す
る。このような理由から、全面曝気装置は旋回流
式散気装置に比べ、約20％の酸素移動効率アツプ
が可能となり、省エネ化を達成している。
（発明が解決しようとする問題点）
しかしながら、槽水深５〜８ｍの曝気槽におい
て上述した底面全体に散気装置を設置した全面曝
気装置を採用すると、以下のような欠点が生じ
る。
(1) プロワ吐出圧が大きくなり、大吐出圧ブロワ
もしくはコンプレツサが新たに必要となるた
め、既存の処理場の曝気槽の改修または増設す
る場合に、既存のブロワを転用することができ
ない場合が多い。
(2) 散気装置から水面までの散気水深が６ｍ以上
になると、空気中の窒素ガスも多量に水中に溶
解し、沈殿池において析出した窒素ガスが活性
汚泥ブロツクに付着するため、汚泥の浮上現象
が生じ、処理水の水質が悪化してしまう。従つ
て、この浮上現象を抑えるには、曝気槽の後段
に、散気水深を浅くして曝気槽内を攪拌して付
着した窒素ガスを取除くポストエアレーシヨン
等のための設備が必要となる。
(3) 全面曝気装置は旋回流がほとんど生じないた
め、散気装置表面にスライム（微生物膜）が形
成されて、気泡の粗大化を招き、その結果、酸
素移動効率の低下をもたらす場合が多い。
また、上記(1)，(2)の問題点は、散気水深を浅く
することで解決できるが、槽中段に散気装置を全
面配置すると、散気装置の上層と下層の液の交換
作用が悪化し、槽底部では嫌気状態になるととも
に、最低でも10cm／ｓ程度の流速が必要な槽底面
付近の流れが遅くなり汚泥の堆積が生じる欠点が
あつた。
本考案の目的は上述した不具合を解消して、特
に槽水深５〜８ｍの曝気槽において、従来の旋回
流方式より酸素移動効率が高く、槽内の汚泥濃
度、溶存酸素濃度を均一に保ち、槽底部での汚泥
堆積を防止し得るとともに、既存ブロワの利用が
可能で汚泥の浮上現象が生じない中段散気式曝気
装置を提供しようとするものである。
（問題点を解決するための手段）
本考案の中段散気式曝気装置は、槽水深５〜８
ｍでバツフル板の設置していない曝気槽におい
て、曝気槽の底盤から0.5〜２ｍの位置に、設置
幅比（散気装置設置幅／槽幅）が0.5〜0.8となる
よう散気装置を槽壁片側から水平方向に設けたこ
とを特徴とするものである。
なお、本考案で中段散気式曝気槽とは、槽水深
５〜８ｍ程度の曝気槽で、散気装置が槽底盤より
0.5〜２ｍ程度離れた位置に設置された曝気槽の
ことをいう。
また、本考案における散気装置は、従来から公
知のものを使用でき、例えば、最大気孔径の細か
いセラミツク製または樹脂製の多孔質散気板また
は散気筒を使用することができる。
（作用）
上述した構成において、散気装置の曝気槽の底
盤からの距離とともに設置幅比を規定することの
相乗効果により、底面への汚泥の沈積防止、酸素
溶解度の向上および窒素ガスの混入防止を達成で
きる。
なお、曝気槽の底盤から0.5〜２ｍの中段位置
に散気装置を設けるのは、槽水深５〜８ｍの曝気
槽において散気装置から水面までの距離である散
気水深を4.5〜6.0ｍと規定するためである。すな
わち、散気水深が4.5ｍ未満であると気泡と水の
接触時間が短かくなり酸素移動効率が低下すると
ともに、エアリフト効果が小さくなり槽底部の底
面流速が小さくなり汚泥の堆積が生じるためであ
る。また、散気水深が6.0ｍを超えると空気中の
窒素ガスが溶解して、沈殿池で析出した窒素ガス
による汚泥の浮上現象が生じるためである。
また、散気装置の曝気槽に対する設置幅比を
0.5〜0.8と規定したのは、中段散気の場合の平均
底面流速と酸素移動効率との関係を示す後述する
第４図および第５図からわかるように、平均底面
流速が10cm／ｓ以下とならずまた酸素移動効率も
良好な範囲を規定したためである。なお、設置幅
比は0.65〜0.75であると好ましい。
（実施例）
第１図は本考案の中段散気式曝気装置の一実施
例を示す横断面図である。本実施例では、曝気槽
１の槽水深Ｈを５〜８ｍの中間槽とするととも
に、散気装置２を散気水深ｈが4.5〜6.0ｍすなわ
ち曝気槽１の底盤３から0.5〜2.0ｍの位置に設け
ている。また、散気装置２は、槽幅をＷ、散気装
置設置幅をｗとしたときの設置幅比ｗ／Ｗが0.5
〜0.8となるよう片側の槽壁４から設置している。
さらに、散気装置２は曝気槽１の縦断面方向にも
一定の間隔で全面にわたつて設けられ、底面全体
に対する発泡面積は２〜８％となつている。散気
装置２としては、例えば300×100×30mmのセラミ
ツクスの多孔板よりなる散気板をステンレス製の
ホルダーで一体としたのを好適に使用することが
できる。
以下、実際の例について説明する。
実施例
槽有効水深10ｍ×槽幅10ｍ×長さ５ｍの鋼板製
実験タンクを仕切板で槽内を分割して、槽形状を
有効水深6.3ｍ×槽幅５ｍ×長さ５ｍ（槽容積
157.5m3）とし、清水実験を行つた。第２図ａ〜
ｃは実験に使用した槽内の散気装置を示してお
り、第２図ａに示す設置幅比ｗ／Ｗ＝1.0の場合、
第２図ｂに示すｗ／Ｗ＝0.7の場合、第２図ｃに
示すｗ／Ｗ＝0.5の場合について実験を行つた。
実験に用いた散気装置に使用する散気板として
は、第１表に示すように最大気孔径の異なる２種
類のものを準備し、底面全体で７枚用ホルダーを
７個合わせて49枚の散気板を使用した。そのた
め、設置密度は4.4％であつた。
(Field of Industrial Application) The present invention relates to an aeration device used in activated sludge treatment, which is suitable for an aeration tank with a water depth of 5 to 8 m and has high oxygen transfer efficiency. (Prior art) As shown in Fig. 7, conventional technology
In the aeration tank 11 with a length of 5 to 8 m, an aeration device 12 is installed at a position of 0.5 to 2 m from the bottom on one side of the middle part of the tank 11 to generate a swirling flow and dissolve oxygen, dissolving the sludge. The concentration was kept uniform. In the above-mentioned swirling flow type aeration tank, the bubbles generated from the aeration device rise along with the swirling flow, so
It rises at a higher speed than the rising speed of air bubbles in fresh water and reaches the water surface. Therefore, the residence time of the bubbles in the liquid, that is, the gas-liquid contact time is short, and as a result, the oxygen transfer efficiency is not very high. In recent years, as shown in Figure 8, water depth h
In the aeration tank 11 with a length of about 5 m, a full-surface aeration system in which an aeration device 12 is arranged over the entire bottom of the tank 11 is adopted as a method to compensate for the drawbacks of the swirling flow system. In this device, upward flow and downward flow are not clearly distinguished and almost no swirling flow occurs, so the residence time of bubbles in the liquid becomes long. Furthermore, dispersion of air bubbles is improved by arranging the air diffuser over the entire surface of the tank. For these reasons, full-surface aeration equipment is able to increase oxygen transfer efficiency by approximately 20% compared to swirling air diffusers, achieving energy savings. (Problems to be Solved by the Invention) However, if the above-mentioned full-surface aeration device in which the air diffuser is installed on the entire bottom surface of an aeration tank with a water depth of 5 to 8 m is employed, the following drawbacks occur. (1) As the blower discharge pressure increases and a new high-pressure blower or compressor is required, it may not be possible to repurpose the existing blower when renovating or expanding the aeration tank of an existing treatment plant. many. (2) When the depth of the aeration water from the aeration device to the water surface is 6 m or more, a large amount of nitrogen gas in the air dissolves in the water, and the nitrogen gas precipitated in the settling tank adheres to the activated sludge blocks, causing sludge deterioration. A floating phenomenon occurs and the quality of the treated water deteriorates. Therefore, in order to suppress this flotation phenomenon, it is necessary to install post-aeration equipment downstream of the aeration tank to reduce the depth of the aeration water and stir the inside of the aeration tank to remove the attached nitrogen gas. Become. (3) Full-surface aeration equipment generates almost no swirling flow, which often causes slime (microbial film) to form on the diffuser surface, causing bubbles to become coarser, resulting in a decrease in oxygen transfer efficiency. . In addition, the above problems (1) and (2) can be solved by making the depth of the aeration water shallow, but if the aeration device is placed all over the middle of the tank, the exchange effect between the liquid in the upper and lower layers of the aeration device will increase. The problem was that the tank bottom became anaerobic, and the flow near the bottom of the tank, which required a flow rate of at least 10 cm/s, slowed down, causing sludge to accumulate. The purpose of this invention is to eliminate the above-mentioned problems, and to achieve higher oxygen transfer efficiency than the conventional swirl flow system, especially in an aeration tank with a tank water depth of 5 to 8 m, and to maintain a uniform sludge concentration and dissolved oxygen concentration in the tank. The object of the present invention is to provide a middle-stage diffused aeration system that can prevent sludge from accumulating at the bottom of a tank, can use an existing blower, and does not cause sludge floating. (Means for solving the problem) The intermediate stage aeration system of the present invention has a tank water depth of 5 to 8.
In an aeration tank where a full plate is not installed, install an aeration device at a position of 0.5 to 2 m from the bottom of the aeration tank so that the installation width ratio (diffuser installation width / tank width) is 0.5 to 0.8. It is characterized by being installed horizontally from one side of the wall. In addition, in this invention, a middle-stage diffused type aeration tank is an aeration tank with a tank water depth of approximately 5 to 8 m, and the diffuser is located from the bottom of the tank.
This refers to an aeration tank installed approximately 0.5 to 2 meters away. Further, the diffuser in the present invention may be a conventionally known one, such as a porous diffuser plate or a diffuser tube made of ceramic or resin with a small maximum pore diameter. (Function) In the above configuration, the synergistic effect of specifying the installation width ratio as well as the distance from the bottom of the aeration tank of the aeration device prevents sludge from settling on the bottom, improves oxygen solubility, and prevents nitrogen gas from entering. can be achieved. In addition, installing the aeration device at the middle position of 0.5 to 2 m from the bottom of the aeration tank means that in an aeration tank with a tank water depth of 5 to 8 m, the aeration water depth, which is the distance from the aeration device to the water surface, is 4.5 to 6.0 m. This is to stipulate. In other words, if the aeration water depth is less than 4.5 m, the contact time between air bubbles and water will be shortened, reducing oxygen transfer efficiency, and the air lift effect will be reduced, resulting in lower flow velocity at the bottom of the tank and sludge accumulation. be. In addition, if the aeration water depth exceeds 6.0 m, nitrogen gas in the air will dissolve, causing sludge to float due to the nitrogen gas precipitated in the settling tank. In addition, the installation width ratio of the air diffuser to the aeration tank should be
The reason for specifying 0.5 to 0.8 is that the average bottom flow velocity is 10 cm/s or less, as shown in Figures 4 and 5 below, which show the relationship between the average bottom flow velocity and oxygen transfer efficiency in the case of middle-stage aeration. This is because the oxygen transfer efficiency was also within a good range. Note that the installation width ratio is preferably 0.65 to 0.75. (Embodiment) FIG. 1 is a cross-sectional view showing an embodiment of the middle stage aeration device of the present invention. In this embodiment, the aeration tank 1 is an intermediate tank with a water depth H of 5 to 8 m, and the aeration device 2 is installed at a depth h of 4.5 to 6.0 m, that is, 0.5 to 2.0 m from the bottom plate 3 of the aeration tank 1. It is located at the location. In addition, the air diffuser 2 has an installation width ratio w/W of 0.5 when the tank width is W and the air diffuser installation width is w.
It is installed from tank wall 4 on one side so that the angle is ~0.8.
Further, the aeration device 2 is provided over the entire surface of the aeration tank 1 at regular intervals in the longitudinal cross-sectional direction, and the foaming area relative to the entire bottom surface is 2 to 8%. As the air diffuser 2, for example, a diffuser plate made of a perforated ceramic plate of 300 x 100 x 30 mm and integrated with a stainless steel holder can be suitably used. An actual example will be explained below. Example A steel plate experimental tank with an effective water depth of 10 m x a tank width of 10 m x a length of 5 m was divided by partition plates, and the tank shape was changed to an effective water depth of 6.3 m x a tank width of 5 m x a length of 5 m (tank volume
157.5m 3 ), and a fresh water experiment was conducted. Figure 2 a~
c shows the air diffuser in the tank used in the experiment, and when the installation width ratio w/W = 1.0 shown in Figure 2 a,
Experiments were conducted for the case of w/W=0.7 shown in FIG. 2b and the case of w/W=0.5 shown in FIG. 2c.
As shown in Table 1, two types of air diffusers with different maximum pore diameters were prepared for the air diffuser used in the air diffuser used in the experiment, and a total of 7 7-sheet holders totaled 49 sheets on the entire bottom surface. A diffuser plate was used. Therefore, the installation density was 4.4%.
【表】
清水実験は、槽内攪拌混合特性調査として、電
磁誘導型流向流速計を槽内に設けて、空気吹込率
Gs／Ｖと槽底面流速Vbとの関係を求めるととも
に、酸素供給性能調査として、ｗ／Ｗ＝0.7の場
合において亜硫酸ソーダ法によりKLaを求め、比
較基準の20℃のKLa(20)に換算し、以下の(1)の式に
代入して酸素移動効率ηを算出し、この酸素移動
効率ηと空気吹込率Gs／Ｖとの関係を求めた。
η＝Cs(20)・KLa(20)・10-8／δ・（Gs／Ｖ）×100〔
％〕…(1)
ここで、Cs20：20℃、散気水深ｈｍにおける清
水中の酸素飽和濃度（mg／）、δ：空気１m3中
の酸素量（20℃、１気圧ではδ＝0.277Kg−O2／
m3）、Gs／Ｖ：空気吹込率（m3／m3・hrただし、
Gsは吹込空気量m3／hr、Ｖは槽容積m3）である。
結果を第３図および第４図に示す。第３図に示
す空気吹込率と槽底面流速との関係から、散気装
置を槽中段に設置した場合、平均底面流速Vbは
ｗ／Ｗ＝1.0のとき空気吹込率Gs／Ｖ＝0.380〜
0.952m3／m3・hrで2.5〜5.0cm／sec.と10cm／sec.
以下であつた。ｗ／Ｗ＝0.7のときGs／Ｖ＝0.450
〜0.952m3／m3・hrで11.6〜18.4cm／sec.、ｗ／Ｗ
＝0.5のときGs／Ｖ＝0.594〜0.952m3／m3・hrで
12.6〜16.2cm／sec.と共に、汚泥堆積防止の限界
平均底面流速といわれる10cm／sec.以上の値を確
保することができた。
また、第４図に示す酸素移動効率と空気吹込率
との関係から、ｗ／Ｗ＝0.7の場合、従来の旋回
流式散気装置に比べて、酸素移動効率ηは最大気
孔径400μｍの散気板で13〜15％程度、最大気孔
径260μｍの散気板で30％程度アツプ、換言すれ
ば、約13〜23％のブロワ消費電力の削減が可能と
なることがわかつた。さらに、散気板の最大気孔
径を400μｍ、空気吹込率Gs／Ｖ＝0.6m3／m3・hr
の条件下での、設置幅比ｗ／Ｗと平均底面流速
Vbとの関係および設置幅比ｗ／Ｗと酸素移動効
率ηとの関係を、それぞれ第５図および第６図に
示す。
（考案の効果）
以上詳細に説明したところから明らかなよう
に、本考案の中段散気式曝気装置によれば、散気
装置の曝気槽の底盤からの距離とともに設置幅比
を規定することの相乗効果により、底面への汚泥
の沈積防止、酸素溶解度の向上および窒素ガスの
混入防止を達成できる。その結果従来の旋回流式
散気装置に比べて13〜30％程度の酸素移動効率の
アツプ、換言すれば約13〜23％のブロワ消費電力
の削減が可能となつた。
曝気槽での電力消費量は下水処理場全体の消費
量の40〜50％を占めることを考慮にいれると、本
考案の中段散気式曝気装置を用いる意義は大き
い。[Table] In the fresh water experiment, an electromagnetic induction current meter was installed in the tank to investigate the stirring and mixing characteristics in the tank, and the air blowing rate was measured.
In addition to determining the relationship between G s /V and the flow velocity V b at the bottom of the tank, K La was determined by the sodium sulfite method in the case of w/W = 0.7 as an oxygen supply performance investigation, and K La (20 ) and substituted into the following equation (1) to calculate the oxygen transfer efficiency η, and the relationship between the oxygen transfer efficiency η and the air blowing rate G s /V was determined. η＝C s(20)・K La(20)・10 -8 /δ・(G s /V)×100 [
%]...(1) Where, C s20 : Oxygen saturation concentration (mg/) in fresh water at 20°C and aeration water depth hm, δ: Amount of oxygen in 1 m3 of air (δ = 0.277 at 20°C and 1 atm) Kg−O 2 /
m 3 ), G s /V: Air blowing rate (m 3 /m 3・hr However,
G s is the amount of blown air (m 3 /hr), and V is the tank volume (m 3 ). The results are shown in FIGS. 3 and 4. From the relationship between the air blowing rate and the tank bottom flow velocity shown in Figure 3, when the air diffuser is installed in the middle of the tank, the average bottom flow velocity V b is when w/W = 1.0, the air blowing rate G s /V = 0.380 ~
0.952m3 / m3・hr 2.5~5.0cm/sec. and 10cm/sec.
It was below. When w/W=0.7, G s /V=0.450
~ 0.952m3 / m3・hr 11.6~18.4cm/sec., w/W
= 0.5, G s /V = 0.594 to 0.952m 3 /m 3・hr
Together with 12.6 to 16.2 cm/sec., we were able to secure a value of 10 cm/sec. or higher, which is said to be the critical average bottom flow velocity for preventing sludge accumulation. Also, from the relationship between oxygen transfer efficiency and air blowing rate shown in Figure 4, when w/W = 0.7, the oxygen transfer efficiency η is lower than that of the conventional swirling flow diffuser with a maximum pore diameter of 400 μm. It has been found that it is possible to reduce blower power consumption by about 13 to 15% with an air plate, and by about 30% with a diffuser plate with a maximum pore diameter of 260 μm.In other words, it is possible to reduce blower power consumption by about 13 to 23%. Furthermore, the maximum pore diameter of the diffuser plate was set to 400 μm, and the air blowing rate G s /V = 0.6 m 3 /m 3・hr
Installation width ratio w/W and average bottom flow velocity under the conditions of
The relationship between V b and the installation width ratio w/W and the oxygen transfer efficiency η are shown in FIGS. 5 and 6, respectively. (Effects of the invention) As is clear from the detailed explanation above, according to the middle stage aeration system of the present invention, it is possible to specify the installation width ratio as well as the distance from the bottom of the aeration tank of the aeration system. The synergistic effect can prevent sludge from settling on the bottom, improve oxygen solubility, and prevent nitrogen gas from entering. As a result, it has become possible to increase oxygen transfer efficiency by approximately 13 to 30% compared to conventional swirl flow diffusers, or in other words, to reduce blower power consumption by approximately 13 to 23%. Considering that the electricity consumption in the aeration tank accounts for 40 to 50% of the consumption of the entire sewage treatment plant, the significance of using the middle-stage diffuser type aeration device of the present invention is significant.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は本考案の中段散気式曝気装置の一実施
例を示す横断面図、第２図ａ〜ｃは、それぞれ実
験に使用した散気装置の槽内の設置状況を示す説
明図、第３図は本考案の曝気装置における空気吹
込率と槽底面流速との関係を示すグラフ、第４図
は同じく空気吹込率と酸素移動効率との関係を示
すグラフ、第５図は同じく散気板の設置幅比と平
均底面流速との関係を示すグラフ、第６図は同じ
く散気板の設置幅比と酸素移動効率との関係を示
すグラフ、第７図および第８図は従来の曝気槽の
一例を示す横断面図である。
１……曝気槽、２……散気装置、３……底盤、
４……槽壁。
FIG. 1 is a cross-sectional view showing one embodiment of the middle-stage diffuser type aeration device of the present invention, and FIGS. 2 a to c are explanatory diagrams showing the installation situation in the tank of the aeration device used in the experiment, respectively. Figure 3 is a graph showing the relationship between air blowing rate and tank bottom flow velocity in the aeration device of the present invention, Figure 4 is a graph showing the relationship between air blowing rate and oxygen transfer efficiency, and Figure 5 is also a graph showing the relationship between air blowing rate and oxygen transfer efficiency. A graph showing the relationship between the installation width ratio of the plate and the average bottom flow velocity, Figure 6 is a graph showing the relationship between the installation width ratio of the diffuser plate and the oxygen transfer efficiency, and Figures 7 and 8 are for conventional aeration. It is a cross-sectional view showing an example of a tank. 1...Aeration tank, 2...Aeration device, 3...Bottom plate,
4...tank wall.