JPH07185270A - Immersion membrane device - Google Patents

Abstract

PURPOSE:To effectively peel the gel layer and cake layer bonded to a membrane surface, in an immersion membrane apparatus wherein a membrane unit is immersed in the liquid of a treatment tank and the filtered treated water transmitted through a membrane is obtained, by providing the apparatus with a coarse air bubble diffusing device and a fine air bubble diffusing device under the membrane unit within the treatment tank. CONSTITUTION:The immersion membrane apparatus wherein a membrane unit 11 is immersed in the liquid of a treatment tank 10 and the filtered treated water transmitted through a membrane is obtained, is provided with a coarse air bubble diffusing device 14 and a fine air bubble diffusing device 15 under the membrane unit 11 within the treatment tank 10. By this constitution, the gel layer and cake layer bonded to a membrane surface are effectively peeled by the min. energy of air bubbles and an effective membrane area contributing to filtering is largely taken and, therefore, the filtered flux transmitted through the membrane surface is always held to the best state and filtering can be performed by low energy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated body in which a plurality of flat membranes are laminated, a laminated body in which a plurality of membrane elements having hollow fiber membranes in a planar shape or a blind shape are laminated, and a plurality of tubular membranes. The present invention relates to a submerged membrane device that uses those connected in parallel as a membrane unit.

[0002]

2. Description of the Related Art Immersion membrane devices for immersing the above-mentioned membrane unit in the liquid of a treatment tank and sucking the inside of the membrane unit to obtain filtered treated water that has permeated the membrane have been conventionally known. When the immersion membrane device is operated to perform membrane filtration, as the filtration progresses, a high concentration concentration polarization layer such as a polymer dissolved substance near the membrane surface,
Alternatively, a non-filter substance such as a gel layer becomes gelled, and a cake layer made of non-filter substances such as fine particles, biological flocs, and metal hydroxide adheres to the membrane surface. The growth rate of the filtration resistance of the cake layer is much slower than that of the gel layer, but it forms a thick adhesion layer. These gel layers and cake layers cause filtration resistance, which lowers filtration efficiency. Therefore, after performing the membrane filtration for a certain period of time, or every time the membrane filtration operation reaches a certain filtration pressure, the operation is stopped, and bubbles are bubbled from the bottom of the membrane unit to float between the membranes and upward water flow. After removing the gel layer and the cake layer from the membrane surface, back washing is performed to recover the filtration performance. Aeration may be performed not only before backwashing but also after backwashing.

[0003]

However, conventionally, it takes a very long time to remove and remove the gel layer and the cake layer from the film surface by air diffusion. Therefore, the power cost for driving the air diffuser is also very high.

[0004]

Therefore, the present invention is an immersion membrane device in which a membrane unit is immersed in a liquid in a treatment tank to obtain filtered treated water that has permeated the membrane. A diffuser for coarse bubbles and a diffuser for fine bubbles are provided.

[0005]

In the illustrated embodiment, 10 is a treatment tank, in which the membrane unit 11 is immersed in the liquid of the treatment tank, and a suction pipe 13 connected to a pump 12 sucks the inside of the membrane unit to perform treatment. The undiluted solution in the tank that permeates the membrane unit 11 is sampled as filtered water. The membrane unit is, as described above, a laminate of a plurality of flat membranes, or a hollow fiber membrane in a planar shape,
Or a laminate of a plurality of blind-shaped membrane elements,
Alternatively, a plurality of tubular membranes are connected in parallel.

In order to effectively separate the above-mentioned concentration polarization layer or gel layer, which causes filtration resistance as the filtration progresses, and the cake layer from the film surface by the bubbles, the relationship between the size of the bubbles and the effect thereof is described. The research revealed the following: First, in order to suppress the concentration polarization layer or the gel layer, it is effective to apply a large flow velocity along the film surface to the liquid in the processing tank, and it is more effective to use micro bubbles having a diameter of 3 mm or less. This is because the hold-up (the ratio of the gas in the bubble mixing portion) of the micro bubbles is larger and the air lift circulation flow rate is increased. To obtain the same effect with the coarse bubbles, the air diffusion amount must be significantly increased. The energy consumption will be high.

Further, in order to peel off the cake layer adhering to the film surface, it is effective to make coarse bubbles having a diameter of 10 mm or more collide with the film surface. This is because the peeling of the cake layer is caused by the shearing force at the interface of the bubbles, so that only the bubbles having a certain size contribute to the peeling. Conversely, it means that even if minute air bubbles are diffused and the film surface is collided, the cake layer is not separated. In short, when only fine bubbles are diffused, it is effective in suppressing the concentration polarization layer,
Since the cake layer cannot be peeled off, the filtration resistance increases with time, and the filtration flow rate passing through the membrane surface decreases. or,
When only coarse bubbles are diffused, a large amount of diffused air is required to give the flow velocity on the membrane surface, resulting in a large energy loss.

Therefore, in the filtration tank, below the membrane unit 11, an air diffuser 14 for large air bubbles having a large air diffusion hole for causing air bubbles to act on the entire lower surface of the membrane unit, and a micro air bubble having a small air diffusion hole are provided. An air diffuser for use is provided, and in this embodiment, a common blower 16 is used to supply air.

Therefore, when the membrane filtration is performed for a certain period of time, or when a certain filtration pressure is reached during the operation of the membrane filtration, the operation is stopped, and both the air diffusers 14 and 15 are continuously operated at the same time before and after backwashing. Alternatively, the air diffuser 15 for micro bubbles is operated intermittently, or the air diffuser 14 for coarse bubbles is operated intermittently, or both air diffusers 14, 15 are intermittently operated. However, both air diffusers are operated by, for example, shortening the air diffusing time of the coarse air bubble diffusing device (including prolonging the air dwell interruption interval) to remove the coarse air bubbles and the fine air bubbles. It acts on the membrane surface of the unit. It should be noted that, in the embodiment, due to the aeration, the explanation has been given on the condition that it is carried out before and after the backwashing which is carried out after the operation of the membrane is stopped.

[0010]

As a result, the gel layer and cake layer adhering to the membrane surface are effectively separated from the membrane surface with the minimum energy, and the effective membrane area that contributes to filtration can be increased, so that the filtration that permeates the membrane surface is performed. It is possible to keep the flux in the best condition at all times and perform the filtration with low energy.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

[Explanation of symbols]

 10 Treatment Tank 11 Membrane Unit 12 Pump 13 Suction Tube 14 Diffuser for Coarse Bubbles 15 Diffuser for Micro Bubbles 16 Blower

Claims (1)

[Claims] 1. An immersion membrane apparatus for immersing a membrane unit in a liquid in a treatment tank to obtain filtered treated water that has permeated the membrane, comprising: a diffuser for coarse bubbles and a fine bubble below the membrane unit in the treatment tank. An immersion membrane device, which is provided with an air diffuser.