JP3341427B2 - Immersion membrane equipment - Google Patents

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 hollow fiber membranes are formed in a planar or interdigital shape, and a plurality of tubular membranes. The present invention relates to an immersion membrane device using parallel-connected membrane units.

[0002]

2. Description of the Related Art An immersion membrane apparatus in which the above-mentioned membrane unit is immersed in a liquid in a treatment tank, and the inside of the membrane unit is suctioned to obtain filtered water permeated through the membrane is conventionally known. When the membrane filtration is performed by operating this immersion membrane device, a concentration-polarized layer having a high concentration of a polymer-dissolved substance or the like near the membrane surface as the filtration proceeds,
Alternatively, a non-filtration substance such as a gel layer formed from a gel thereof is present, and a cake layer made of a non-filtration substance such as fine particles, biological flocs, and metal hydroxides 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 forms a thick adhesion layer. These gel layers and cake layers cause filtration resistance and reduce filtration efficiency. Therefore, after performing the membrane filtration for a certain period of time, or whenever the filtration pressure becomes constant during the membrane filtration operation, the operation is stopped, and the bubbles are applied to the membrane unit from below and float between the membranes, and the upward water flow. After the gel layer and the cake layer are peeled off 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]

Conventionally, however, it takes a very long time to separate and remove the gel layer and the cake layer from the film surface by aeration. Therefore, the power cost for driving the air diffuser is very high.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a submerged membrane apparatus in which a membrane unit is immersed in a liquid in a treatment tank to obtain filtered water permeated through the membrane. A diffuser for large bubbles with a diameter of 10 mm or more and a diameter
An air diffuser for fine bubbles of 3 mm or less is provided.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the illustrated embodiment, reference numeral 10 denotes a processing tank, in which a membrane unit 11 is immersed in the liquid in the processing tank, and a suction pipe 13 connected to a pump 12 sucks the inside of the membrane unit to process. The undiluted solution in the tank that has passed through the membrane unit 11 is sampled as filtered water. The membrane unit is formed by stacking a plurality of flat membranes or hollow fiber membranes as described above,
Alternatively, a plurality of laminated bodies of interleaved membrane elements,
Alternatively, a plurality of tubular membranes are connected in parallel.

[0006] In order to effectively separate the above-mentioned concentration-polarized layer or gel layer, which causes filtration resistance as the filtration proceeds, and the cake layer from the membrane surface with the bubbles, the relationship between the size of the bubbles and the effect thereof is described. The study revealed the following: First, to suppress the concentration polarization layer or the gel layer, it is effective to apply a large flow velocity along the membrane surface to the liquid in the treatment tank, and the effect is more enhanced by microbubbles having a diameter of 3 mm or less. This is because the hold-up (the proportion of gas in the bubble mixing section) of the microbubbles becomes larger and the circulation flow rate of the air lift increases. Need to be increased, and energy consumption will be large.

In order to peel off the cake layer adhering to the film surface, it is effective to cause large bubbles having a diameter of 10 mm or more to collide with the film surface. This is because the peeling of the cake layer is caused by the shearing force at the interface between the bubbles, and the cake layer does not contribute to the peeling unless the bubbles are somewhat large. In other words, the cake layer does not peel off even if small bubbles are scattered and collided with the film surface. In short, when only microbubbles 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 permeating the membrane surface decreases. or,
When only coarse bubbles are diffused, a large amount of gas diffusion is required to give a film surface flow velocity, resulting in a large energy loss.

For this reason, in the filtration tank, below the membrane unit 11, a diffuser 14 for large bubbles having a large diameter of 10 mm or more, which has a large diffuser hole for allowing bubbles to act on the entire lower surface of the membrane unit, Is provided with an air diffuser for small air bubbles having a diameter of 3 mm or less . In this embodiment, air is supplied by a common blower 16.

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 before and after the backwashing, the two air diffusers 14 and 15 are simultaneously and continuously operated. , Or intermittently, or only the microbubble diffuser 15 having a diameter of 3 mm or less is continuously operated, and has a diameter of 10 mm.
The diffuser 14 for coarse bubbles having a diameter of not less than 1 mm is operated intermittently, or both diffusers 14 and 15 are operated intermittently. of driving both air diffuser in so on the included) to be prolonged interruption interval, the more coarse bubble diameter 10 mm, straight
A microbubble having a diameter of 3 mm or less acts on the membrane surface of the membrane unit, and a large bubble having a diameter of 10 mm or more adheres to the membrane surface.
The gel layer adhered to the film surface was effectively peeled off with a diameter of 3 mm.
mm effectively peeling in the following micro-bubbles. In the embodiment, the air diffusion is described as being performed before and after the backwashing performed after the operation of the membrane is stopped. However, the invention is not limited to this and may be performed constantly during the operation of the membrane.

[0010]

EFFECT OF THE INVENTION] This minimum gel layer adheres to <br/> film surface with an energy of at microbubbles under 3mm diameter than,
The cake layer is effectively separated from the membrane surface by coarse bubbles with a diameter of 10 mm or more , and the effective membrane area contributing to filtration can be increased, so that the filtration flux passing through the membrane surface is always kept in the best condition, Filtration can be performed with energy.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Processing tank 11 Membrane unit 12 Pump 13 Suction pipe 14 Air diffuser for coarse bubbles 15 Air diffuser for fine bubbles 16 Blower

Claims (1)

(57) [Claims] 1. An immersion membrane apparatus for immersing a membrane unit in a liquid in a processing tank to obtain filtered water permeated through the membrane, wherein a diffuser for coarse bubbles having a diameter of 10 mm or more is provided below the membrane unit in the processing tank. And an air diffusion device for fine bubbles having a diameter of 3 mm or less .