JP3117607B2 - Wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater,
In particular, domestic wastewater treatment such as merger treatment septic tanks, sewage treatment,
The present invention relates to a method for treating sewage performed in industrial wastewater treatment using activated sludge treatment.

[0002]

2. Description of the Related Art In a sewage treatment plant, for example, sewage and night soil are treated by an activated sludge treatment method, and activated sludge separated from an activated sludge mixture is taken out as treated water and subjected to a treatment such as disinfection. Has been released. In separating activated sludge from the activated sludge mixture, a membrane separation device as shown in FIG. 3 is used.

[0003] The membrane separation apparatus 1 is provided with a treatment water 3 in a treatment tank 2.
A plurality of plate-shaped membrane cartridges 5 arranged in the vertical direction are provided in parallel in the inside of a box-shaped casing 4 having an open top and bottom.

In the membrane cartridge 5, a permeated water flow path is formed by a filter plate or a spacer on the permeation side of the filtration membrane, and the permeated water flow path is connected to a self-priming pump 7 outside the tank via a water collecting pipe 6. Then, the activated sludge in the water to be treated is trapped by the filtration membrane by suctioning with the self-priming pump 7 to make the inside of the permeated water channel negative pressure, and the permeated water 8 permeating through the filtration membrane and flowing into the permeated water channel is treated. It is designed to be taken out of the tank 2.
A pressure gauge 9 is provided at a suction part of the self-priming pump 7.

[0005] A diffuser 11 connected to a blower 10 outside the tank is disposed below the membrane cartridge 5. The diffuser 11 is generated by bubbles of aerated air supplied through the diffuser 11 and an air lift action of the aerated air. The membrane surface of the membrane cartridge 5 is cleaned by the upward flow.

[0006]

The immersion type membrane separation device is
A pressure difference (transmembrane pressure difference) is provided between the front and back of the filtration membrane using a self-priming pump or the like, and filtration is performed using this pressure difference as a driving force to overcome cake resistance due to deposits attached to the membrane surface. is there. This driving force usually corresponds to a head difference of 0.5 to 4 m.

However, in the above-mentioned conventional suction filtration method, the distance from the upper portion of the filtration membrane to the surface of the water to be treated 3 is usually 50 cm or less, and a suction force as a driving force for compensating for the shortage of the head difference is applied. Usually, one suction port is provided for one membrane cartridge 5. Therefore, the negative pressure concentrates near the suction port, and there is a problem that not only the negative pressure supplied by the self-priming pump 7 is not effectively used, but also the entire surface of the filtration membrane is not used. In addition, in the vicinity of the suction port, the filtration membrane adheres to the filter plate due to the suction, and as a result, the filtration resistance increases. Therefore, it is necessary to periodically stop the suction. For this reason, intermittent suction is usually performed in which the suction pump 7 is operated for 8 minutes and stopped for 2 minutes, which is not efficient.

[0008] On the other hand, a filtration method using only the head as a driving force is also known. However, when the same head is used, even if a large permeation flux is obtained in the initial stage of the filtration membrane, the permeation flux is gradually reduced. The decline is inevitable. In order to keep the permeation flux constant, it is necessary to gradually increase the water head from the start of operation.However, such operation causes the amount of water to be treated in the tank, such as when the treated water tank is an aeration tank. However, there is a problem that inconvenience such as a change in processing capability occurs as a result.

The present invention solves the above-mentioned problems, and provides a method for treating wastewater that can effectively use the suction pressure of a pump and a membrane surface to efficiently filter and suppress an increase in filtered water head. It is the purpose.

[0010]

In order to solve the above problems, a method for treating sewage according to the present invention is characterized in that water to be treated is filtered by a filtration membrane of an immersion type membrane separation device provided in a treatment tank. In the method for treating sewage in which the permeated water flowing into the permeate side of the wastewater is taken out by the suction pressure of a self-priming pump provided outside the treatment tank, the distance from the upper part of the filtration membrane to the surface of the water to be treated is set to an appropriate distance. The suction pressure of the self-priming pump is set to a pressure equal to or lower than the filtration head generated at a distance from the upper part of the filtration membrane to the surface of the water to be treated. Is performed.

In the method for treating sewage of the present invention, when the water to be treated is an activated sludge mixture, the suction pressure of the self-priming pump is generated at a distance from the top of the filtration membrane to the surface of the water to be treated. As the pressure less than the sum of the filtered head and the head generated at the distance from the surface of the water to be treated to the self-priming pump,
It is characterized in that constant flow filtration is performed with a constant permeation flux while the permeate side of the filtration membrane is at a positive pressure.

Further, in the method for treating sewage of the present invention, the suction pressure of the self-priming pump is increased by a distance between the upper part of the filtration membrane and the surface of the water to be treated. 4 of the sum with the head generated at the distance to the self-priming pump
It is characterized in that the pressure is set to about 3 / min.

[0013]

According to the above construction, the head of the water to be treated existing above the filtration membrane is used as the driving force, and the permeated water is sucked up by the self-priming pump so as to maintain the permeate side at a positive pressure, thereby performing filtration. As a result, the filtration pressure is evenly applied to the entire membrane surface, and the filtration can be efficiently performed by effectively utilizing the suction pressure of the pump and the membrane surface. In addition, as a result of applying the filtration pressure evenly over the entire membrane surface, local deposition of the membrane surface deposits is prevented, thereby enabling continuous operation, increasing the filtration efficiency, and increasing the filtration head too much. A constant flux can be obtained without filtration.

When the water to be treated is a mixed liquid of activated sludge, the head of filtration is increased, and the pressure is adjusted in consideration of the head generated at the distance from the surface of the water to be treated to the self-priming pump. By the suction, a driving force for filtering the thick water to be treated can be obtained.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a treatment tank and a membrane separation apparatus in which the wastewater treatment method of the present invention is performed. The illustrated treatment tank and the membrane separation apparatus have the same configuration as the conventional one described with reference to FIG. Therefore, the same reference numerals are given to the same members, and the description is omitted. However, the average pore size of 0.2 μm
Using a microfiltration membrane of about 1 μm, a constant flow valve 12 was installed on the discharge side of the self-priming pump 7. In addition, Ph shown in the figure is a water head generated from the water surface to the self-priming pump 7.

In the treatment tank 2 and the membrane separation apparatus 1 having the above-mentioned structures, the activated sludge mixture having a concentration of about 1 to 2% was filtered as the water 3 to be treated. The results are shown in the graph of FIG. The graph shows changes in the permeation flux (m ³ / m ² · day) and the suction pressure (mH ₂ O) with the number of elapsed days.

When the distance from the upper part of the filtration membrane to the surface of the water 3 to be treated 3 is 2 m (that is, the filtration head = 2 m), filtration is performed at a constant flux, and the filtration membrane is gradually clogged and sucked. Although the pressure increased, continuous filtration was possible for one year or more until the suction pressure reached 3 m (filtration head 2 m + Ph1 m). (Shown as constant flow rate filtration and continuous suction in the graph.) Under the same conditions as above, continuous filtration was performed while controlling the rotation speed of the self-priming pump 7 by inverter and controlling the suction pressure to be equal to or lower than the filtration head. In this case, continuous filtration for one year or more was possible. (In the graph, it was shown as constant pressure filtration and continuous suction.) Under the same conditions as above, filtration was performed intermittently according to a conventional filtration method so as to obtain a constant permeation flux. The rise was great. (In the graph, it is shown as constant flow filtration and intermittent suction.) In the constant flow filtration and constant pressure filtration of the present invention,
The head of the water to be treated present above the filtration membrane is used as the driving force,
Since the permeated water is sucked up and filtered by a self-priming pump so that the permeate side is maintained at a positive pressure, the sediment formed on the membrane surface is harder and more dense than the conventional method of forced suction filtration. And the membrane was easy to clean.

[0018]

As described above, according to the present invention, filtration is performed by using the head of the water to be treated present above the filtration membrane of the membrane separation device as a driving force, and the permeate side is maintained at a positive pressure at this time. Since the permeated water was sucked up by a self-priming pump,
The filtration pressure can be evenly applied to the entire surface of the membrane. As a result, not only the suction pressure of the pump and the membrane surface can be effectively used to efficiently filter, but also the deposition on the membrane surface can be reduced. And, as a result of being able to reduce the film surface sediment, continuous operation of the membrane separation device becomes possible, and a constant permeate flux can be obtained without increasing the water head so much that the amount of water to be treated in the tank changes. Can reduce the influence on the processing effect. Cleaning of the membrane is also facilitated.

When the water to be treated is a mixed liquid of activated sludge, the head of filtration is increased and the suction pressure is adjusted in consideration of the head generated at the distance from the surface of the water to be treated to the self-priming pump. By setting the input pressure, a large driving force can be obtained, and the thick water to be treated can be filtered.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a treatment tank and a membrane separation device in which a wastewater treatment method of the present invention is performed.

FIG. 2 is a graph showing the results of the present invention and a conventional method for treating wastewater as changes in permeation flux and suction pressure.

FIG. 3 is an explanatory view showing a treatment tank and a membrane separation device in which a conventional wastewater treatment method is performed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Membrane separation apparatus 2 Processing tank 3 Water to be treated 7 Self-priming pump

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 35/027

Claims (3)

(57) [Claims] 1. A self-priming pump in which water to be treated is filtered by a filtration membrane of a submerged membrane separation device provided in a treatment tank, and permeated water flowing into a permeation side of the filtration membrane is provided outside the treatment tank. In the method of treating sewage which is taken out by suction pressure,
The distance from the upper part of the filtration membrane to the surface of the water to be treated is an appropriate distance, and the suction pressure of the self-priming pump is equal to or less than the filtration head generated by the distance from the upper part of the filtration membrane to the surface of the water to be treated. A method for treating sewage, comprising performing filtration in a state where the pressure on the permeate side of a filtration membrane is set to a positive pressure. 2. When the water to be treated is an activated sludge mixture,
The suction pressure of the self-priming pump, the filtration head generated at the distance from the top of the filtration membrane to the surface of the water to be treated, and the head generated at the distance from the surface of the water to be treated to the self-priming pump 2. The method for treating sewage according to claim 1, wherein a constant flow rate filtration is performed with a constant permeation flux in a state where the permeation side of the filtration membrane is set to a positive pressure at a pressure equal to or less than the sum. 3. The suction pressure of the self-priming pump is adjusted to a distance between the upper surface of the filtration membrane to the surface of the water to be treated and the distance from the surface of the water to be treated to the self-priming pump. 3. The method for treating sewage according to claim 2, wherein the pressure is set to about three-fourths of the sum of the water head and the generated water.