JP4199976B2 - Immersion membrane separator - Google Patents

Description

【００３６】
式（１）において、ｉは第１（ｉ＝１）から第１０（ｉ＝１０）の計測点を表し、ｊは５Ｐａ刻みで段階的に評価する剪断応力レベルτ_jを定めるためのレベル値を表す。すなわち、ｊ＝１〜１３での評価する剪断応力レベルτ_jは、τ_j＝５ｊ−６５である（ｊ＝１のときはτ₁＝−６０Ｐａ、ｊ＝１３のときはτ₁₃＝０Ｐａ）。また、ｊ＝１４〜２６での評価する剪断応力レベルτ_jは、τ_j＝５ｊ−７０である（ｊ＝１４のときはτ₁₄＝０Ｐａ、ｊ＝２６のときはτ₂₆＝６０Ｐａ）。したがって、α_3,17は、第３計測点における剪断応力レベルτ₁₇：１５Ｐａ以上となる時間比率を表している。また、β_3,17は、第３計測点における剪断応力レベルτ₁₇：１５Ｐａ以上となる頻度を表している。
【００３７】
また、α_ave,jは式（２）で表され、評価しようとする所定の剪断応力レベルτ_j（レベル値ｊ）の場合における第１から第１０の各計測点での時間比率の平均値である。β_ave,jは式（３）で表され、前記剪断応力レベルτ_j（レベル値ｊ）の場合における第１から第１０の各計測点での頻度の平均値である。
【００３８】
【数２】

【００３９】
【数３】

【００４０】
式（１）の気泡分布指針値γは、２６段階の各剪断応力レベルτ_jにおける平均値からの変位量を表している。つまり、式（１）の右辺の第１項は時間比率α_i,jについての平均値α_ave,jからの変位量の大小を表しており、第２項は頻度β_i,jについての平均値β_ave,jからの変位量の大小を表しています。式（１）の係数「０．５」は重み付けの値であり、気泡分布指針値γは時間比率と頻度をそれぞれ５０％ずつ等しく重み付けをして扱っている。よって、もし全ての計測点で時間比率α_i,j＝α_ave,j、かつ、頻度β_i,j＝β_ave,jであれば、すなわち、時間比率α_i,jと頻度β_i,jが、それぞれ、１０箇所全ての計測点で平均値と一致していれば、気泡分布指針値γはゼロとなり、それぞれが平均値から離れるにしたがって、気泡分布指針値γは大きくなる。したがって、気泡分布指針値γの大小によって粗大気泡散気管６₁〜６₅による粗大気泡の分布状態を評価することができ、平板状膜モジュール幅方向において粗大気泡が不均一分布するような粗大気泡の上昇流の発生を抑制すると、気泡分布指針値γはその値が小さくなることになる。
【００４１】
表１に散気量についての実験条件を示す。ケース１とケース２とは粗大気泡の散気量については同一であり、ケース１とケース２との違いは、ケース１では散気ケース５外部のメンブレン式微細気泡散気板８_R，８_Lによる微細気泡の散気を行い（散気板８_Cは設置せず）、一方、ケース２では平板状膜モジュール幅方向中央部の下方に位置するメンブレン式微細気泡散気板８_Cによる微細気泡の散気を行った点にある（散気板８_R，８_Lは設置せず）。この表１に示す条件で、前記第１〜第６の管配置それぞれにて浸漬型膜分離装置１を運転し、そのときの上段膜ユニット３Ａの平板状膜モジュール４の膜面４ａに作用する剪断応力を計測し、得られた計測値から、前記気泡分布指針値γを求めた。結果を表２、表３に示す。
【００４２】
【表１】

【００４３】
【表２】

【００４４】
【表３】

【００４５】
表２、表３からわかるように、前記第１〜第５の管配置とした本発明による浸漬型膜分離装置１によれば、第１〜第５のいずれの管配置の場合にも従来例である第６の管配置としたものに比較して気泡分布指針値γを小さくすることができており、目視観察によっても、引き上げられた平板状膜モジュール４の膜面４ａでの汚泥の付着もなかった。特に、ケース１、ケース２にともに第１、第２及び第４の管配置において良好な結果が得られた。このように、一方の端部領域用粗大気泡散気管６₁，６₂による散気量Ｖ_R（＝２００ＮＬ／ｍｉｎ）と他方の端部領域用粗大気泡散気管６₄，６₅による散気量Ｖ_L（＝２００ＮＬ／ｍｉｎ）が、それぞれ、中央部領域用粗大気泡散気管６₃による散気量Ｖ_C（＝１００ＮＬ／ｍｉｎ）の本例では２倍となるように、散気を行うことにより、幅寸法が１０００ｍｍ程度の幅広の平板状膜モジュール４を備えたものでも、平板状膜モジュール幅方向において粗大気泡が中央部領域付近に集まってきて不均一分布するような粗大気泡の上昇流の発生を抑制することができ、これにより平板状膜モジュール４の膜面全体にわたって膜面洗浄効果を得ることができた。
【００４６】
ここで、表２に示す前記ケース１の場合に比べて、表３に示す、平板状膜モジュール幅方向中央部の下方にメンブレン式微細気泡散気板８_Cを配置した前記ケース２の場合には、気泡分布指針値γが大きくなっており、粗大気泡が不均一分布するような上昇流の発生を抑制する効果が小さくなっている。この原因は、前記ケース２の場合、中央部にあるメンブレン式微細気泡散気板８_Cからの微細気泡により、粗大気泡散気管６₁，６₂，６₄，６₅からの粗大気泡が記ケース１の場合に比べて平板状膜モジュール幅方向中央部に寄ってくるためと考えられる。したがって、好気性微生物に対する酸素供給に効果的である微細気泡散気装置については、前記ケース１の場合のように、散気ケース５の外部に配置することが好ましい。
【００４７】
図７は、ケース１での第１の管配置（本発明例）の場合における時間比率α_i,j（ｉ＝１〜１０，ｊ＝１〜２６）を示す図である。図７において横軸は剪断応力、縦軸は時間比率、奥行き軸は計測位置（第１〜第１０の計測点）をそれぞれ示す。図８は、ケース１での第１の管配置（本発明例）の場合における頻度β_i,j（ｉ＝１〜１０，ｊ＝１〜２６）を示す図である。図８において横軸は剪断応力、縦軸は頻度、奥行き軸は計測位置（第１〜第１０の計測点）をそれぞれ示す。また、図９は、図８における剪断応力レベルが１５Ｐａでの頻度β_i,17（ｉ＝１〜１０）を示す図である。
【００４８】
ケース１の場合、表２に示すように、第１の管配置、第２の管配置及び第４の管配置としたものでは、従来例である第６の管配置としたものに比較して気泡分布指針値γの値を半分以下に小さくすることができた。このことは、前記図７〜図９に示されるように、各計測点での、例えば剪断応力レベルが１５Ｐａでの頻度β_i,17（ｉ＝１〜１０）と時間比率α_i,17（ｉ＝１〜１０）が、ほぼ一定で変動が小さいことからも裏付けられた。
【００４９】
図１０は、ケース１での第６の管配置（従来例）の場合における時間比率α_i,j（ｉ＝１〜１０，ｊ＝１〜２６）を示す図である。同じく、図１１は、ケース１での第６の管配置（従来例）の場合における頻度β_i,j（ｉ＝１〜１０，ｊ＝１〜２６）を示す図である。また、図１２は、図１１における剪断応力レベルが１５Ｐａでの頻度β_i,17（ｉ＝１〜１０）を示す図である。
【００５０】
これに対して、第６の管配置（従来例）のものでは、気泡分布指針値γの値は０．０５４であり（表２参照）、目視観察によっても、引き上げられた平板状膜モジュールの幅方向における両側端部の膜面への汚泥の付着、また中央部にも膜面への汚泥の付着が発生していることが観察された。このことは、前記図１０〜図１２に示されるように、各計測点での、例えば剪断応力レベルが１５Ｐａでの頻度β_i,17（ｉ＝１〜１０）と時間比率α_i,17（ｉ＝１〜１０）が、ほぼ一定でなく変動が大きいことからも裏付けられた。
【００５１】
【発明の効果】
以上述べたように、本発明による浸漬型膜分離装置は、一方と他方の端部領域用粗大気泡散気装置による各散気量Ｖ_R，Ｖ_Lが、それぞれ、中央部領域用粗大気泡散気装置による散気量Ｖ_Cの２倍以上となるように、散気を行うよう構成されている。これにより、本発明による浸漬型膜分離装置によれば、幅寸法が１０００ｍｍ程度の幅広の平板状膜モジュールを備えたものでも、平板状膜モジュール幅方向において粗大気泡が中央部領域付近に集まってきて不均一分布するような粗大気泡の上昇流の発生を抑制することができるので、平板状膜モジュールの膜面全体にわたって膜面洗浄効果を得ることができ、平板状膜モジュールの幅方向における端部領域などに汚泥ケーキ層が堆積することを防止することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態による浸漬型膜分離装置の構成を示す一部破断斜視図である。
【図２】５本の粗大気泡散気管の配置位置を説明するための図である。
【図３】平板状膜モジュールの膜面に作用する剪断応力を説明するための図である。
【図４】上段膜ユニットの平板状膜モジュールの膜面に作用する剪断応力を計測する剪断応力計の設置位置を示す図である。
【図５】時間比率を説明するための図である。
【図６】頻度を説明するための図である。
【図７】ケース１での第１の管配置（本発明例）の場合における時間比率α_i,j（ｉ＝１〜１０，ｊ＝１〜２６）を示す図である。
【図８】ケース１での第１の管配置（本発明例）の場合における頻度β_i,j（ｉ＝１〜１０，ｊ＝１〜２６）を示す図である。
【図９】図８における剪断応力レベルが１５Ｐａでの頻度β_i,17（ｉ＝１〜１０）を示す図である。
【図１０】ケース１での第６の管配置（従来例）の場合における時間比率α_i,j（ｉ＝１〜１０，ｊ＝１〜２６）を示す図である。
【図１１】ケース１での第６の管配置（従来例）の場合における頻度β_i,j（ｉ＝１〜１０，ｊ＝１〜２６）を示す図である。
【図１２】図１１における剪断応力レベルが１５Ｐａでの頻度β_i,17（ｉ＝１〜１０）を示す図である。
【図１３】従来の浸漬型膜分離装置の構成を説明するための一部破断斜視図である。
【図１４】図１３に示す従来の浸漬型膜分離装置を備えた活性汚泥処理設備の構成を示す図である。
【図１５】従来の浸漬型膜分離装置における５本の粗大気泡散気管の配置位置を説明するための図である。
【図１６】上昇するに従って徐々に平板状膜モジュールの幅方向における中央部領域付近に集まってくるような粗大気泡の上昇流の様子を説明するための図である。
【符号の説明】
１…浸漬型膜分離装置 ２…膜ケース ３Ａ…上段膜ユニット ３Ｂ…下段膜ユニット ４…平板状膜モジュール ４ａ…膜面 ５…散気ケース ６₁〜６₅…粗大気泡散気管 ７_R，７_L…補助用粗大気泡散気管 ８_R，８_L，８_C…メンブレン式微細気泡散気板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a submerged membrane separation apparatus used for membrane separation activated sludge treatment such as sewage and organic sewage.
[0002]
[Prior art]
The submerged membrane separation device is used in small domestic wastewater small treatment facilities such as small merged treatment septic tanks and large-scale sewage treatment facilities in cities. A flat membrane module, and an air diffuser that is disposed below the flat membrane module and diffuses air. For example, Japanese Patent Application Laid-Open No. 7-275668 discloses an immersion type membrane separation apparatus that is supposed to be used in a small merged treatment septic tank. This immersion type membrane separation apparatus is a diffuser as two air diffusers. A trachea is provided.
[0003]
On the other hand, in a submerged membrane separation apparatus used in a large-scale activated sludge treatment facility such as a city sewage treatment facility, as shown in FIG. 13, a plurality of flat membrane modules 53 having a width of about 1000 mm are wide. Usually, the coarse bubble diffusing tube 55 as five coarse bubble diffusers₁~ 55_FiveAnd are provided. FIG. 13 is a partially broken perspective view for explaining the configuration of a conventional submerged membrane separator, and FIG. 14 is a diagram showing the configuration of an activated sludge treatment facility equipped with the conventional submerged membrane separator shown in FIG. is there.
[0004]
As shown in FIG. 13, this conventional submerged membrane separation apparatus 51 has a plurality of flat membrane modules 53 arranged in a box-shaped membrane case 52 that is open at the top and bottom, with membrane surfaces 53a vertically perpendicular to each other. Arranged in parallel in the depth direction at appropriate intervals so as to be parallel, and further inside the box-shaped air diffuser case 54 opened at the top and bottom and the left and right side surfaces as five coarse bubble diffusers Coarse bubble diffuser 55₁~ 55_FiveAnd five coarse bubble diffusers 55 below a plurality of flat membrane modules 53 arranged in parallel.₁~ 55_FiveThe membrane case 52 and the diffuser case 54 are stacked so as to be separated from each other vertically. Coarse bubble diffuser 55₁~ 55_FiveEach of these is supplied with a predetermined amount of air for air diffusion through a supply pipe 58 from a blower 57 as an air source installed outside the reaction tank 56.
[0005]
Coarse bubble diffuser 55₁~ 55_FiveAs shown in FIG. 13, each of the flat membrane modules 53 is arranged below the plurality of flat membrane modules 4 and extends in a direction (depth direction) perpendicular to the flat membrane module width direction. They are arranged orthogonally below them. Coarse bubble diffuser 55₁~ 55_FiveIn the lower part of the outer peripheral surface, a large number of diffused holes having a hole diameter of 5 to 15 mmφ are provided along the longitudinal direction of the diffuser tube. These coarse bubble diffusers 55₁~ 55_FiveThe purpose of aeration by the coarse bubble diffusion tube 55₁~ 55_FiveThe membrane surface 53a is cleaned by using shear stress acting on the membrane surface 53a of the flat membrane module 53 by the gas-liquid two-phase upward flow generated by the coarse bubbles from the membrane, and the membrane surface 53a is sludged. It is to prevent the cake layer from being deposited and to supply oxygen for aerobic treatment of aerobic microorganisms in the liquid to be treated. In this case, the coarse bubbles are effective in cleaning the membrane surface of the flat membrane module 53 because the rising speed is higher and the shear stress is larger than the fine bubbles.
[0006]
In the conventional submerged membrane separation apparatus 1, the coarse bubble diffuser 55₁~ 55_FiveAs shown in FIG. 15, it is arranged below the flat membrane module 53 having a width of about 1000 mm. That is, the coarse bubble diffusing tube 55 for the flat membrane module 53 is used.₁~ 55_FiveAs for the arrangement of the five coarse bubble diffusers 55 of No. 1 to No. 5₁~ 55_FiveNo. 3 coarse bubble diffusing tubes 55 in the middle, having an equal interval of 200 mm from each other_ThreeAre arranged below the center of the width of the flat membrane module 53. Each coarse bubble diffuser 55₁~ 55_FiveAnd the flat membrane module 53 in the vertical direction are constant. Also, five coarse bubble diffusing tubes 55₁~ 55_FiveAre supplied with the same amount of air, and these coarse bubble diffusing tubes 55.₁~ 55_FiveThe amount of air diffused from each of these is set to be the same.
[0007]
As shown in FIG. 14, the submerged membrane separation apparatus 1 configured in this way is immersed in the water to be treated (mixed liquid of activated sludge and raw water) in the reaction tank 56, and has a flat plate shape. The membrane module 53 is connected via a collecting pipe 59 to a treated water extraction pipe 61 in which a suction pump 60 is interposed in the middle of the pipe. In the activated sludge treatment facility provided with the submerged membrane separation device 51, the coarse bubble diffusing tube 55 is used.₁~ 55_FiveThe water to be treated is separated into solid and liquid by the flat membrane module 53 and filtered, and the membrane permeated water that has permeated through the flat membrane module 53 is treated with the suction pump 60 as the treated water. Membrane separation activated sludge treatment that is taken out to the outside is performed.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-275668 (FIG. 2)
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-224585 (FIG. 1)
[0009]
[Problems to be solved by the invention]
However, in the conventional submerged membrane separation apparatus 1 described above, the five coarse bubble diffusing tubes 55 are used.₁~ 55_FiveIs not appropriate, the membrane surface cleaning effect cannot be obtained over the entire membrane surface of the wide flat membrane module 53 having a width of about 1000 mm, and the end of the flat membrane module 53 in the width direction with the passage of operating time. There is a problem that a sludge cake layer accumulates in the area.
[0010]
  To explain this, buoyancy acts on the bubbles and tries to rise faster than the surrounding liquid. Therefore, as shown in FIG.55 ₁ ~ 55 ₅ Ascending coarse bubbles rise from the earlier to the earlier direction, and gradually gather near the central region in the width direction of the flat membrane module 53 as it rises. Once such an upward flow (plume) of coarse bubbles gathering in the central region of the flat membrane module width direction is generated, the flow is not uniform in the flat membrane module width direction.
[0011]
For this reason, since the membrane surface is not cleaned at a site where coarse bubbles do not pass, sludge accumulated on the membrane surface is not removed. As a result, the gas-liquid two-phase upward flow between the membranes slows down, making it difficult for the bubbles to spread further. It becomes a strongly sticky solid called a layer. In this way, regarding the distribution of coarse bubbles in the width direction of the flat membrane module, there is no self-healing function in the case of non-uniformity, and it is triggered by the local membrane surface clogging once. Membrane surface cleaning is difficult to perform.
[0012]
This invention is made | formed in view of such a situation, The objective of this invention is suppressing generation | occurrence | production of the upward flow of a coarse bubble in which a coarse bubble is unevenly distributed in a flat membrane module width direction. Accordingly, an object of the present invention is to provide a submerged membrane separation apparatus which can obtain a membrane surface cleaning effect over the entire membrane surface of a flat membrane module.
[0013]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention takes the following technical means. Invention of Claim 1 is immersed in the to-be-processed water in a reaction tank, The flat membrane module which filters the said to-be-processed water, The aeration apparatus which is arrange | positioned under this flat membrane module and performs aeration In the submerged membrane separation apparatus, the air diffuser is disposed below one end region in the width direction of the flat membrane module having a quarter of the effective width of the flat membrane module., Composed of multiple coarse bubble diffusersA coarse bubble diffusing device for one end region and the other flat membrane module width direction end region having a quarter of the effective width of the flat membrane module are disposed below., Composed of multiple coarse bubble diffusersA coarse bubble diffuser for the other end region;It is arranged below the center position in the width direction of the flat membrane module and is composed of one coarse bubble diffusing tube.A coarse bubble diffuser for the central region,Each of the coarse bubble diffusing tubes extends in a direction perpendicular to the flat membrane module width direction, and the one piece constituting the coarse bubble diffuser for the central region in the flat membrane module width direction. The plurality of coarse bubble diffusing tubes constituting the one end region coarse bubble diffusing device and the other end region coarse bubble diffusing device are equidistant from the coarse bubble diffusing tube. Each of the coarse bubble diffusing tubes of the book, and each of the coarse bubble diffusing tubes is arranged at an equal distance from the flat membrane module in the vertical direction of the reaction tank,Air is diffused from the one end region coarse bubble diffuser, the other end region coarse bubble diffuser, and the central region coarse bubble diffuser, and both the end region coarse Immersion type characterized in that each air diffused by the bubble diffuser is diffused so that the amount of air diffused by the coarse bubble diffuser for the central region is twice or more. It is a membrane separator.
[0014]
According to a second aspect of the present invention, the submerged membrane separation apparatus according to the first aspect further includes a fine bubble diffusing device.
[0015]
According to a third aspect of the present invention, there is provided the submerged membrane separation apparatus according to the second aspect, wherein the fine bubble diffusing device includes both the large-area bubble diffuser for the end region and the coarse-bubble diffuser for the central region. It is arrange | positioned outside the diffuser case which accommodates an apparatus, It is characterized by the above-mentioned.
[0016]
According to the submerged membrane separation apparatus according to the first to third aspects of the present invention, each of the three air bubble diffusers for each region causes each air diffuser by the one and the other end region coarse bubble diffuser. Amount V_R, V_LHowever, the amount of air diffused by the coarse bubble diffuser for the central region is V, respectively._CTherefore, even if a wide flat membrane module having a width of about 1000 mm is provided, coarse bubbles are centered in the flat membrane module width direction. As a result, it is possible to suppress the generation of an upward flow of coarse bubbles that are gathered in the vicinity of the partial area and are unevenly distributed, so that a membrane surface cleaning effect can be obtained over the entire membrane surface of the flat membrane module. It is possible to prevent the sludge cake layer from being deposited on the end region in the width direction of the membrane module.
[0017]
In this case, the amount of air diffused from one end region coarse bubble diffuser V_RAnd the amount of air diffused from the coarse bubble diffuser for the other end region_LIs preferably the same amount of air diffused. Also, the amount of air diffused by the coarse bubble diffuser for the central region V_CVentilation amount V_R, V_LThe upper limit value of is not generally determined by the size of the flat membrane module, but the amount of air diffused V_C3 times is appropriate.
[0018]
Moreover, in the submerged membrane separation apparatus according to the present invention, it is desirable that the diffuser has a fine bubble diffuser. The fine bubble diffusing device has a large number of diffusing holes having a pore diameter of 1 to 5 mmφ, and has higher oxygen dissolution efficiency than the coarse bubble diffusing device, and is effective in supplying oxygen to aerobic microorganisms. Therefore, when oxygen supply by the coarse bubble diffusing device is insufficient, it is desirable to provide a fine bubble diffusing device. In this case, the fine bubble diffuser is arranged on the bottom of the reaction tank outside the diffuser case that houses the coarse bubble diffuser (outside the membrane case) so that the fine bubbles do not merge with the coarse bubbles. Is good. In addition, a downward flow that descends outside the case from the opening at the upper end of the membrane case is formed outside the diffuser case (outside the membrane case).
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a partially broken perspective view showing a configuration of a submerged membrane separation apparatus according to an embodiment of the present invention.
[0020]
As shown in FIG. 1, the submerged membrane separation apparatus 1 includes an upper membrane unit 3A and a lower membrane unit 3B arranged in two upper and lower rows at a predetermined interval in a box-like membrane case 2 that is open at the top and bottom. The coarse bubble diffusing tube 6 as five coarse bubble diffusing devices is disposed inside a box-like diffuser case 5 that is open at the top and bottom and left and right side lower portions.₁~ 6_FiveAnd the coarse bubble diffuser 6 below the lower membrane unit 3B.₁~ 6_FiveThe membrane case 2 and the diffuser case 5 are stacked so as to be separated from each other vertically.
[0021]
Each of the upper membrane unit 3A and the lower membrane unit 3B is formed by arranging a plurality of flat membrane modules 4 in parallel in the depth direction at appropriate intervals so that the membrane surfaces 4a are vertical in the vertical direction and parallel to each other. It is. The flat membrane module 4 of the upper membrane unit 3A and the flat membrane module 4 of the lower membrane unit 3B are arranged so that their positions in the depth direction coincide with each other.
[0022]
The five coarse bubble diffusers 6₁~ 6_FiveIs arranged below the flat membrane module 4 of the lower membrane unit 3B and extends in a direction (depth direction) perpendicular to the width direction of the flat membrane module, and each flat membrane module 4 is below them. It arrange | positions so that it may orthogonally cross. These coarse bubble diffusers 6₁~ 6_FiveIn the lower part of the outer peripheral surface, a large number of diffused holes having a hole diameter of 5 to 15 mmφ are provided along the longitudinal direction of the diffuser tube. Coarse bubble diffuser 6₁~ 6_FiveThe detailed arrangement position will be described later. Coarse bubble diffuser 6₁~ 6_FiveAnd the flat membrane module 4 of the lower membrane unit 3B are constant in the vertical direction.
[0023]
Further, one auxiliary coarse bubble diffusing tube 7 extending in the depth direction of the flat membrane module 4 is disposed at one end of the flat membrane module width direction between the upper membrane unit 3A and the lower membrane unit 3B._RIs arranged. Similarly, one auxiliary coarse bubble diffusing tube 7 is provided at the other end in the width direction of the flat membrane module._LIs arranged.
[0024]
Further, on the bottom surface of the reaction tank outside the diffuser case 5 (outside the membrane case 2), a membrane-type fine bubble diffuser plate 8 having a flat plate shape as a fine bubble diffuser on both sides of the diffuser case 5 is provided._R, 8_LAre arranged respectively. Further, a coarse bubble diffusing tube 6 is provided on the bottom of the reaction tank in the diffusing case 5.₁~ 6_FiveOne membrane type fine bubble diffuser plate 8 so as to be located below and below the central portion of the flat membrane module width direction._CIs arranged. Membrane type fine bubble diffuser 8_R, 8_L, 8_CAre provided with a large number of diffused holes having a hole diameter of 1 mmφ.
[0025]
Using the submerged membrane separation apparatus 1 configured as described above, a coarse bubble diffusing tube 6 is used.₁~ 6_FiveExperiments were conducted to investigate the distribution of coarse bubbles. In this experiment, the submerged membrane separation apparatus 1 is installed in an experimental reaction tank having a water depth of about 5 m, which is the same as the actual depth, and the coarse bubble diffuser 6₁~ 6_FiveThe arrangement position in the width direction of the flat membrane module is changed to first to sixth pipe arrangements described later (the sixth pipe arrangement is a conventional example), and the submerged membrane separation apparatus 1 is operated with each of these pipe arrangements. And carried out. The shear stress acting on the membrane surface 4a of the flat membrane module 4 of the upper membrane unit 3A during these operations is measured with a shear stress meter, and the measurement results and sludge on the membrane surface 4a of the flat membrane module 4 are measured. Based on the observation result of the adhesion state, the coarse bubble diffuser 6₁~ 6_FiveThe distribution of coarse bubbles was evaluated.
[0026]
FIG. 2 is a view for explaining the arrangement positions of five coarse bubble diffusing tubes.
[0027]
As shown in FIG. 2, the flat membrane module 4 of the lower membrane unit 3 </ b> B is divided into four equal parts in the width direction, and has one flat membrane module width direction end having a quarter of the effective width of the flat membrane module 4. Partial area L_RAnd the other flat membrane module width direction end region L having 1/4 of the effective width of the flat membrane module 4_LAnd these end regions L_R, L_LCentral area L in the width direction of the remaining flat membrane module excluding_CIs stipulated. In this case, the effective width of the flat membrane module 4 is 1000 mm, and the width direction central region L_CIs 500 mm and the one width direction end region L located on the right side thereof is 500 mm._RThe length of the other width direction end region L located on the left side is 250 mm_LThe length of is 250 mm.
[0028]
Coarse bubble diffuser 6₁~ 6_FiveAre the first, second, third, fourth, fifth coarse bubble diffusers in order from the right in FIG. 2 and arranged as shown in FIG. 2 in the experiment. In this case, the coarse bubble diffuser 6₁~ 6_FiveSince the distribution of coarse bubbles is a bilaterally symmetrical phenomenon, the center of the flat membrane module width direction is the origin, the right side is positive and the left side is negative. The first to fifth tube arrangements are the examples of the present invention, and the sixth tube arrangement is the conventional example.
[0029]
In the first to fifth tube arrangements of the present invention example, the first coarse bubble diffusing tube 6₁And No. 2 coarse bubble diffuser 6₂And said one flat membrane module width direction end region L_RThe coarse bubble diffusing device for one end part region arranged below is constituted. No. 5 coarse bubble diffuser 6_FiveAnd No. 4 coarse bubble diffuser 6_FourAnd the other flat membrane module width direction end region L_LThe coarse bubble diffusing device for the other end region arranged below is constituted. No. 3 coarse bubble diffuser 6_ThreeIs the flat membrane module width direction central region L_CThe coarse bubble diffusing device for the central region disposed below is configured. In the third tube arrangement and the fifth tube arrangement, the end region L_RAnd the central region L_CNo. 2 coarse bubble diffuser 6 on the boundary with₂Constitutes the one end region coarse bubble diffusing device because of its effect, and similarly, the end region L_LAnd the central region L_CNo. 4 coarse bubble diffuser 6 on the boundary with_FourIs configured as the above-described coarse bubble diffusing device for the other end region because of its function and effect.
[0030]
FIG. 3 is a diagram for explaining shear stress acting on the membrane surface of the flat membrane module, and FIG. 4 is an installation position of a shear stress meter for measuring the shear stress acting on the membrane surface of the flat membrane module of the upper membrane unit. FIG.
[0031]
As shown in FIG. 3, when there is an upward flow between the membrane surfaces 4a of the opposed flat membrane modules 4, the velocity is large at the center of the membrane and the velocity is zero at the membrane surface. The shear stress τ is a stress acting in the tangential direction of the film surface 4a, and is proportional to the gradient of the upward flow speed in the direction perpendicular to the film surface, and is expressed by τ = μ × (× v / ∂x). Here, v: velocity, μ: viscosity coefficient, x: displacement in the direction perpendicular to the film surface. As shown in FIG. 4, such shear stress is measured at first to ten ten measurement points in the width direction of the flat membrane module 4 of the upper membrane unit 3A. From the measurement result of such shear stress, the coarse bubble diffuser 6₁~ 6_FiveTherefore, the distribution state of coarse bubbles can be evaluated.
[0032]
In order to evaluate the distribution state of the coarse bubbles, two evaluation guidelines were introduced. One of them is the time ratio α. FIG. 5 is a diagram for explaining the time ratio, where the horizontal axis indicates time, and the vertical axis indicates the shear stress acting on the membrane surface of the flat membrane module 4. The time ratio α is a predetermined shear stress level τ as shown in FIG._jThis is the percentage of time experiencing the above (below the predetermined shear stress level in the case of negative shear stress). The predetermined shear stress level τ_jIn this example, as will be described later, 26 levels are set in positive and negative directions in increments of 5 Pa. The large value of the time ratio α means that a predetermined shear stress level τ at the measurement point._jIt represents that the time during which the above shear stress is applied is long.
[0033]
Another evaluation guideline is the frequency β. FIG. 6 is a diagram for explaining the frequency. The horizontal axis indicates time, and the vertical axis indicates the shear stress acting on the membrane surface of the flat membrane module 4. The frequency β indicates that the shear stress is 1 minute (t₁= Shear stress level τ per 60 s)_jIncreased above (in the case of negative shear stress, shear stress level τ_jIs the number of times to descend). In the case of FIG. 6, the shear stress is the set shear stress level τ_j7 times and frequency β = (60 / t₁) × 7 = 7 times / min. As shown in FIG. 6, since the shear stress acting on the film surface fluctuates, a certain shear stress level τ_jIf the shear stress that exceeds is acting while fluctuating like a blood flow pulse, and sludge adhering to the membrane surface is removed by such fluctuation, the frequency β representing the number of fluctuations becomes important. .
[0034]
Then, the bubble distribution guide value γ is obtained by the formula (1) in which the time ratio α and the frequency β are introduced, and the distribution state of the coarse bubbles by the coarse bubble diffusing tubes 61 to 65 is quantitatively evaluated.
[0035]
[Expression 1]

[0036]
In Expression (1), i represents the first (i = 1) to 10th (i = 10) measurement points, and j is the shear stress level τ evaluated stepwise in increments of 5 Pa._jRepresents a level value for determining That is, the shear stress level τ to be evaluated at j = 1 to 13_jIs τ_j= 5j−65 (when j = 1, τ₁= -60 Pa, j = 13 when τ₁₃= 0 Pa). Further, the shear stress level τ to be evaluated at j = 14 to 26_jIs τ_j= 5j−70 (when j = 14, τ₁₄= 0 when = 0 Pa and j = 26₂₆= 60 Pa). Therefore, α_3,17Is the shear stress level τ at the third measurement point₁₇: Represents a time ratio of 15 Pa or more. Β_3,17Is the shear stress level τ at the third measurement point₁₇: Represents the frequency of 15 Pa or more.
[0037]
Α_{ave, j}Is expressed by equation (2), and a predetermined shear stress level τ to be evaluated_jIt is an average value of time ratios at the first to tenth measurement points in the case of (level value j). β_{ave, j}Is expressed by equation (3) and the shear stress level τ_jThe average value of the frequencies at the first to tenth measurement points in the case of (level value j).
[0038]
[Expression 2]

[0039]
[Equation 3]

[0040]
The bubble distribution guide value γ in the equation (1) is expressed by each of 26 shear stress levels τ._jThe amount of displacement from the average value at. That is, the first term on the right side of Equation (1) is the time ratio α._{i, j}Mean value for α_{ave, j}Represents the amount of displacement from, and the second term is the frequency β_{i, j}Mean value for β_{ave, j}Indicates the amount of displacement from. The coefficient “0.5” in the equation (1) is a weighting value, and the bubble distribution guide value γ is handled by equally weighting the time ratio and the frequency by 50%. Therefore, if all measurement points have time ratio α_{i, j}= Α_{ave, j}And frequency β_{i, j}= Β_{ave, j}That is, the time ratio α_{i, j}And frequency β_{i, j}However, if the average value coincides with the average value at all ten measurement points, the bubble distribution guide value γ becomes zero, and the bubble distribution guide value γ increases as the distance from the average value increases. Accordingly, the coarse bubble diffusing tube 6 depends on the size of the bubble distribution guide value γ.₁~ 6_FiveThe bubble distribution guideline value γ is smaller when the generation of coarse bubbles that cause uneven distribution of coarse bubbles in the width direction of the flat membrane module is suppressed. Will be.
[0041]
Table 1 shows the experimental conditions for the amount of diffused air. Case 1 and case 2 are the same in terms of the amount of diffused air bubbles, and the difference between case 1 and case 2 is that in case 1, membrane type fine bubble diffuser plate 8 outside diffuser case 5 is used._R, 8_LAeration of fine bubbles by (air diffuser plate 8_COn the other hand, in the case 2, in the case 2, the membrane type fine bubble diffusing plate 8 located below the central part in the width direction of the flat membrane module_CIt is in the point where fine air bubbles were diffused by (air diffuser plate 8_R, 8_LIs not installed). Under the conditions shown in Table 1, the submerged membrane separator 1 is operated in each of the first to sixth tube arrangements, and acts on the membrane surface 4a of the flat membrane module 4 of the upper membrane unit 3A at that time. Shear stress was measured, and the bubble distribution guide value γ was determined from the obtained measurement value. The results are shown in Tables 2 and 3.
[0042]
[Table 1]

[0043]
[Table 2]

[0044]
[Table 3]

[0045]
As can be seen from Tables 2 and 3, the submerged membrane separation apparatus 1 according to the present invention having the first to fifth tube arrangements is a conventional example in any of the first to fifth tube arrangements. The bubble distribution guideline value γ can be made smaller than that of the sixth pipe arrangement, and sludge adheres to the membrane surface 4a of the raised flat membrane module 4 by visual observation. There was not. In particular, good results were obtained in the first, second and fourth tube arrangements for both Case 1 and Case 2. Thus, the coarse bubble diffuser 6 for one end region₁, 6₂Aeration amount due to V_R(= 200 NL / min) and coarse bubble diffuser 6 for the other end region_Four, 6_FiveAeration amount due to V_L(= 200 NL / min), respectively, a coarse bubble diffuser 6 for the central region_ThreeAeration amount due to V_C(= 100 NL / min) In this example, even if the flat plate membrane module 4 having a wide width of about 1000 mm is provided by aeration so as to be doubled, in the flat membrane module width direction It is possible to suppress the generation of an upward flow of coarse bubbles where the coarse bubbles gather near the central region and are unevenly distributed, thereby obtaining a membrane surface cleaning effect over the entire membrane surface of the flat membrane module 4. I was able to.
[0046]
Here, as compared with the case 1 shown in Table 2, the membrane-type microbubble diffuser 8 shown in Table 3 below the central portion of the flat membrane module width direction is shown in Table 3._CIn the case 2 in which the bubble is disposed, the bubble distribution guide value γ is large, and the effect of suppressing the generation of the upward flow in which coarse bubbles are unevenly distributed is small. In the case 2, this is caused by the membrane type fine bubble diffuser plate 8 at the center._CCoarse bubble diffusing tube 6 due to fine bubbles from₁, 6₂, 6_Four, 6_FiveIt is considered that the coarse bubbles from the end are closer to the central portion in the width direction of the flat membrane module than in the case 1. Therefore, it is preferable to arrange the fine bubble diffuser effective for supplying oxygen to the aerobic microorganisms outside the diffuser case 5 as in the case 1.
[0047]
FIG. 7 shows the time ratio α in the case of the first tube arrangement (case of the present invention) in Case 1._{i, j}It is a figure which shows (i = 1-10, j = 1-26). In FIG. 7, the horizontal axis represents shear stress, the vertical axis represents time ratio, and the depth axis represents measurement positions (first to tenth measurement points). FIG. 8 shows the frequency β in the case of the first tube arrangement (case of the present invention) in Case 1._{i, j}It is a figure which shows (i = 1-10, j = 1-26). In FIG. 8, the horizontal axis represents shear stress, the vertical axis represents frequency, and the depth axis represents measurement positions (first to tenth measurement points). FIG. 9 shows the frequency β when the shear stress level in FIG._{i, 17}It is a figure which shows (i = 1-10).
[0048]
In case 1, as shown in Table 2, the first pipe arrangement, the second pipe arrangement, and the fourth pipe arrangement are compared with the conventional pipe arrangement of the sixth pipe arrangement. The bubble distribution guideline value γ could be reduced to less than half. As shown in FIGS. 7 to 9, this is the frequency β at each measurement point, for example, when the shear stress level is 15 Pa._{i, 17}(I = 1 to 10) and time ratio α_{i, 17}(I = 1 to 10) is supported by the fact that the fluctuation is almost constant and the fluctuation is small.
[0049]
FIG. 10 shows the time ratio α in the case of the sixth pipe arrangement (conventional example) in case 1._{i, j}It is a figure which shows (i = 1-10, j = 1-26). Similarly, FIG. 11 shows the frequency β in the case of the sixth pipe arrangement (conventional example) in case 1._{i, j}It is a figure which shows (i = 1-10, j = 1-26). FIG. 12 shows the frequency β when the shear stress level in FIG._{i, 17}It is a figure which shows (i = 1-10).
[0050]
On the other hand, in the case of the sixth tube arrangement (conventional example), the value of the bubble distribution guide value γ is 0.054 (see Table 2). It was observed that sludge adheres to the film surface at both ends in the width direction, and that sludge adheres to the film surface at the center. As shown in FIGS. 10 to 12, this is the frequency β at each measurement point, for example, when the shear stress level is 15 Pa._{i, 17}(I = 1 to 10) and time ratio α_{i, 17}(I = 1 to 10) was supported by the fact that the fluctuation was not substantially constant but was large.
[0051]
【The invention's effect】
As described above, the submerged membrane separation device according to the present invention has each of the diffused air amounts V by the coarse bubble diffuser for one and the other end region._R, V_LHowever, the amount of air diffused by the coarse bubble diffuser for the central region is V, respectively._CIt is configured to perform aeration so as to be twice or more. As a result, according to the submerged membrane separation apparatus according to the present invention, even if a flat membrane module having a width of about 1000 mm is provided, coarse bubbles gather near the central region in the flat membrane module width direction. Therefore, it is possible to suppress the generation of the upward flow of coarse bubbles that are unevenly distributed, so that the membrane surface cleaning effect can be obtained over the entire membrane surface of the flat membrane module, and the edge in the width direction of the flat membrane module can be obtained. It is possible to prevent the sludge cake layer from accumulating in the partial area.
[Brief description of the drawings]
FIG. 1 is a partially broken perspective view showing a configuration of a submerged membrane separation apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the arrangement positions of five coarse bubble diffusing tubes.
FIG. 3 is a diagram for explaining shear stress acting on the membrane surface of a flat membrane module.
FIG. 4 is a diagram showing an installation position of a shear stress meter that measures a shear stress acting on a membrane surface of a flat membrane module of an upper membrane unit.
FIG. 5 is a diagram for explaining a time ratio.
FIG. 6 is a diagram for explaining a frequency.
FIG. 7 shows the time ratio α in the case of the first pipe arrangement in the case 1 (example of the present invention)._{i, j}It is a figure which shows (i = 1-10, j = 1-26).
FIG. 8 shows the frequency β in the case of the first pipe arrangement (example of the present invention) in Case 1_{i, j}It is a figure which shows (i = 1-10, j = 1-26).
FIG. 9 shows the frequency β when the shear stress level is 15 Pa in FIG._{i, 17}It is a figure which shows (i = 1-10).
FIG. 10 shows a time ratio α in the case of the sixth tube arrangement (conventional example) in case 1;_{i, j}It is a figure which shows (i = 1-10, j = 1-26).
FIG. 11 shows the frequency β in the case of the sixth pipe arrangement (conventional example) in case 1_{i, j}It is a figure which shows (i = 1-10, j = 1-26).
12 shows frequency β when the shear stress level in FIG. 11 is 15 Pa. FIG._{i, 17}It is a figure which shows (i = 1-10).
FIG. 13 is a partially broken perspective view for explaining the configuration of a conventional submerged membrane separation apparatus.
14 is a diagram showing the configuration of an activated sludge treatment facility equipped with the conventional submerged membrane separation apparatus shown in FIG.
FIG. 15 is a view for explaining the arrangement positions of five coarse bubble diffusing tubes in a conventional submerged membrane separation apparatus.
FIG. 16 is a view for explaining the state of the rising flow of coarse bubbles that gradually gather near the central region in the width direction of the flat membrane module as it rises.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Submerged membrane separator 2 ... Membrane case 3A ... Upper membrane unit 3B ... Lower membrane unit 4 ... Flat membrane module 4a ... Membrane surface 5 ... Air diffuser case 6₁~ 6_Five... Coarse bubble diffuser 7_R, 7_L... Auxiliary coarse bubble diffuser 8_R, 8_L, 8_C... Membrane type fine bubble diffuser

Claims (3)

Submerged membrane separation comprising a flat membrane module that is immersed in the water to be treated in the reaction tank and filters the water to be treated, and an air diffuser that is disposed below the flat membrane module and diffuses air. In the device
The air diffuser is disposed under one flat membrane module width direction end region having a quarter of the effective width of the flat membrane module , and is constituted by a plurality of coarse bubble diffusers . A coarse bubble diffuser for the end region;
Coarse bubbles for the other end region, which are arranged below the other end region in the width direction of the other flat membrane module and have a plurality of coarse bubble diffusing tubes, which have a quarter of the effective width of the flat membrane module. An air diffuser;
A coarse bubble diffusing device for a central region , which is arranged below the center position in the width direction of the flat membrane module and is composed of one coarse bubble diffusing tube ;
Each of the coarse bubble diffusing tubes extends in a direction perpendicular to the width direction of the flat membrane module,
The plurality of constituents constituting the one end region coarse bubble diffuser at an equal distance from the one coarse bubble diffuser constituting the central region coarse bubble diffuser in the width direction of the flat membrane module A plurality of coarse bubble diffusing tubes and the plural large bubble diffusing tubes constituting the other end region coarse bubble diffusing device are respectively disposed in the vertical direction of the reaction tank from the flat membrane module. Each of the coarse bubble diffusing tubes is arranged at an equal distance,
Air is diffused from the one end region coarse bubble diffuser, the other end region coarse bubble diffuser, and the central region coarse bubble diffuser, and both the end region coarse Immersion type characterized in that each air diffused by the bubble diffuser is diffused so that the amount of air diffused by the coarse bubble diffuser for the central region is twice or more. Membrane separator.   The submerged membrane separation device according to claim 1, wherein the air diffuser further includes a fine bubble diffuser.   The fine bubble diffusing device is disposed outside a diffusing case that accommodates both of the end region large bubble diffusing devices and the central region large bubble diffusing device. Item 3. A submerged membrane separation apparatus according to Item 2.

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