JP2009119427A - Method of treating muddy water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of treating muddy water capable of cleaning up to an extent enabling discharge to rivers and the like by treating a muddy water generated at a tunnel worksite and the like. <P>SOLUTION: The method of treating muddy water containing a suspensoid including clay comprises flocculation-treating the muddy water with a flocculant, and thereafter filtration-treating the muddy water with a filtrating membrane immersed in the muddy water. The muddy water generated at a worksite is stored in a tank, flocculation-treated in the tank, and thereafter filtered out with the filtering membrane immersed in the tank. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a muddy water treatment method suitable for construction sites where clay-mixed muddy water is produced, such as in tunnels, dam works or road works.

  The turbid water generated at the construction site contains a large amount of mud and sand and cannot be discharged into a river or the like as it is, and is conventionally discharged after a coagulation treatment. However, the composition of the turbid water generated at the construction site varies greatly, so when applying the flocculation method, it is difficult to control the amount of flocculant input, and it is also greatly affected by the stirring conditions, etc., so stable turbid water Processing was difficult.

  For the treatment of muddy water (tunnel muddy water) generated in tunnel construction, a method by coagulation sedimentation is generally used. However, since the composition of tunnel turbid water is large, it is difficult to control the amount of flocculant added in the coagulation sedimentation method, and treated water containing aluminum flocculant and polymer flocculant is discharged into the river. There is a problem of adversely affecting the environment.

  Civil works, especially highway construction, are often done in mountainous areas, and such places are upstream of rivers and close to the water source, so the water quality is good and there are many types of river fish. Therefore, from the viewpoint of maintaining the river ecosystem, there is a high demand for the quality of the discharged water, and water supply with a turbidity of 10 mg / L or 1 mg / L against the general discharge standard (turbidity of 50 mg / L). There is an increasing demand for advanced water treatment. However, the conventional simple coagulation sedimentation treatment cannot meet the above-described requirements.

  The present inventors have proposed a dynamic filtration method using a membrane separation method as a method replacing the coagulation precipitation method (see Patent Document 1). This invention filters turbid water using a non-woven membrane, forms a dynamic layer by depositing particle components in turbid water on the membrane, and filters turbid water using the dynamic layer as a filter. . According to this invention, turbid water with a low clay content can be treated well, but the turbid water with a high clay content is clogged because the clay content cannot pass through the membrane or the clay content adheres to the membrane, The clogged clay is not peeled off from the membrane even by back pressure cleaning, and the clogging cannot be eliminated. The reason why such a problem occurs is estimated as follows.

  In the case of dynamically filtering turbid water containing a large amount of clay, the clay passes through the mesh of the membrane at the initial stage when filtration is started, and the filtered water does not become clean treated water. This is because the size of the clay particles is about 5 to 10 μm, which is much smaller than the mesh of the nonwoven fabric film, and the clay particles easily pass through the film. And if the filtration process is continued for a long time, clay particles begin to adhere around the fibers constituting the nonwoven fabric film, and it gradually gets thicker as time passes without peeling off due to the clay-specific adhesiveness. Is considered to grow to such an extent that the mesh of the nonwoven fabric film is blocked.

If the mesh of the nonwoven fabric membrane becomes blocked in this way, the subsequent filtration treatment cannot be performed. Therefore, the membrane surface is usually washed by back pressure washing at this point or before such a state. Remove the clay adhering to the surface. However, in the case of turbid water containing a large amount of clay, the clay adhering to the membrane cannot be removed even by this washing because the clay has strong adhesive strength, and the filtration ability cannot be recovered. For this reason, when a method of dynamically filtering turbid water containing a large amount of clay with a nonwoven membrane is applied, the filtered water is turbid at the initial stage, and after a certain amount of time has passed, clean filtered water is used. From this stage, clogging occurs in a short time, and as a result, it is considered that almost no filtration treatment is possible.
JP 2001-104953 A

  This invention makes it a subject to provide the processing method of the muddy water which can process the muddy water containing the clay produced in a tunnel, a dam construction site, etc., and can treat the treated water at a high degree.

The invention of claim 1 is a method for treating turbid water containing a suspended solid containing clay, and the turbid water is agglomerated with a flocculant and then filtered with a filtration membrane immersed in the muddy water after treatment. Provide a method for treating turbid water.
According to a second aspect of the present invention, turbid water generated at a work site is stored in a tank, and after aggregating in the tank, the turbid water is filtered through a filter membrane immersed in the tank. Provide a method.

  The clay as used in the present invention includes kaolinite, halloysite, pyrophyllite, sericite, montmorillonite, chlorite, illite, vermiculite and other known clay minerals.

  By applying the muddy water treatment method of the present invention, muddy water generated at a tunnel construction site or the like can be treated and purified to such an extent that it can be discharged into a river or the like.

  With reference to FIG. 1, the muddy water treatment method of the present invention will be described. FIG. 1 is a conceptual diagram showing a processing flow.

  Turbid water (raw water) containing clay generated by tunnels and dam construction is collected in the raw water tank 1 from the line 21 after removing large stones, sand, mud and the like. A liquid feed pump is immersed in the raw water tank 1.

  Next, the liquid feed pump in the raw water tank 1 is operated, and the raw water is sent to the coagulation and membrane separation tank 2 through the line 22. The raw water tank 1 may be omitted and turbid water (raw water) may be directly supplied to the coagulation and membrane separation tank 2.

  The coagulation and membrane separation tank 2 is divided into a coagulation tank 3 and a membrane separation tank 4 by a partition wall 13 inside. It is preferable that the volume of the agglomeration tank 3 and the membrane separation tank 4 is approximately the same, or the membrane separation tank 4 is larger. The boundary between the bottom surface of the coagulation and membrane separation tank 2 and the side surface on the coagulation tank 3 side can be an inclined surface 2a as shown in the figure.

  Both sides of the partition wall 13 are fixed to the opposing wall surfaces of the aggregation and membrane separation tank 2, the lower surface 13a is separated from the bottom surface of the aggregation and membrane separation tank 2, and the upper surface 13b is closer to the water surface when full. Is also set to be located below. For this reason, the agglomeration tank 3 and the membrane separation tank 4 are in communication with each other on the upper surface (upper end) 13b side and lower surface (lower end) 13a side of the partition wall 13 so that the liquid can flow.

  The agglomeration tank 3 is provided with a flocculant addition device 11 for adding a predetermined amount of a flocculant, and a stirrer 12 for agitating the inside of the tank, and a pH adjusting device (not shown) is also provided if necessary. Can do. Further, a swirling flow can be generated by using a submersible pump or an air diffuser instead of the stirrer. When using a submersible pump, it is preferable to install it under the membrane.

  The membrane separation module 15 is immersed in the membrane separation tank 4 in a suspended or fixed state. As the membrane separation module 15, for example, a known hollow fiber membrane module (external pressure type or internal pressure type, preferably external pressure type) can be used. An air diffuser for cleaning the membrane surface from the outside can be installed on the bottom surface of the tank immediately below the membrane separation module 15 as necessary. The coagulation and membrane separation tank 2 is connected to the permeate tank 5 by a permeate line 23 equipped with a pump.

  In the aggregating tank 3, a required amount of aggregating agent is added by the aggregating agent adding device 11 while stirring the inside of the tank by the agitator 12. At this time, if necessary, the pH can be adjusted to 9 to 10 by adding a pH adjusting agent with a pH adjusting device. The flocculant adding device 11 and the pH adjusting device may be omitted and added artificially.

  As the flocculant, for example, an adsorbent, a coagulant, a polymer flocculant and the like can be used. As adsorbents, oil adsorbents such as diatomaceous earth, montmorillonite and activated clay; as coagulants, inorganic compounds such as aluminum sulfate; as polymer flocculants, anionic, cationic and nonionic polymer flocculants are used. Can be mentioned. The polymer flocculant can be an anionic and cationic combination, an anionic and nonionic combination, or an anionic, cationic and nonionic combination.

  Moreover, a calcium type flocculant can also be used as a flocculant. The calcium-based flocculant preferably has a calcium content of 5% by mass or more, more preferably 10% by mass or more, and examples thereof include calcium sulfate and calcium chloride.

  In the membrane separation tank 4, filtration is performed by the membrane separation module 15. At the time of filtration by the membrane separation module 15, since the membrane surface is washed from the outside, it can be diffused by an air diffuser. In addition, the back pressure cleaning line 24 can perform back pressure cleaning with a cleaning liquid containing a chemical solution at an appropriate interval. The back pressure washing line 24 may be omitted, the membrane in the membrane separation tank 4 may be taken out and replaced with another membrane, and the taken out membrane may be washed separately.

  At the time of filtration in the membrane separation tank 4, the water to be treated in the aggregation tank 3 and the membrane separation tank 4 passes under the lower surface 13 a of the partition wall 13 because the inside of the aggregation tank 3 is stirred by the stirrer 12. It circulates over the upper surface 13b. For this reason, the to-be-processed water in the membrane separation tank 4 becomes a uniform state without uneven distribution of flocs, the membrane surface of the separation membrane module 15 is hardly blocked, and the filtration performance by the separation membrane module 15 is stabilized.

  The permeate filtered in the membrane separation tank 4 is sent to the permeate tank 5 through the permeate line 23 and stored. The permeated water in the permeated water tank 5 is treated with activated carbon as necessary, and then discharged to a river or the like as appropriate, and is also used as back pressure washing water for the membrane separation module 15. Note that the permeated water tank 5 may be omitted and discharged from the permeated water line 23 to a river or the like.

  Flock (sludge) collected near the bottom of the agglomeration and membrane separation tank 2 is extracted from the sludge extraction line 25 and sent to the sludge storage tank 6. In the sludge storage tank 6, the sludge is dehydrated, the water is returned to the raw water tank 1, and the sludge is discarded.

Example 1
Raw water obtained by adding 400 liters of water to 30 kg of turbid water containing clay generated at the tunnel construction site and stirring and mixing for 10 minutes (turbidity 300 by the scattered light measurement method described in the Japan Water Works Association water test method) Placed in agglomeration and membrane separation tank. Thereafter, a flocculant (trade name Memfloc P001, manufactured by Daisen Membrane Systems Co., Ltd.) was added to a concentration of 100 ppm (mass basis).

Thereafter, the agglomeration treatment was performed while stirring with a stirrer provided in the agglomeration tank. After 10 minutes from the start of stirring, suction filtration was started by the separation membrane module immersed in the membrane separation tank. As the separation membrane module, a module in which 8 units of 2.2 m ² of a casing-free immersion type membrane element filled with a polyethersulfone hollow fiber membrane was immersed was used. The transmembrane pressure difference was 0.01 MPa at the start of filtration, and was the same value after 5 hours of filtration. The turbidity after membrane separation was 1 or less.

The conceptual diagram of the processing flow of the waste water treatment method of this invention.

Explanation of symbols

1 Raw water tank (drainage tank)
2 Coagulation and membrane separation tank 3 Coagulation tank 4 Membrane separation tank 5 Permeate tank 6 Sludge storage tank 11 Coagulant addition device 12 Stirrer 13 Partition wall 15 Membrane separation module

Claims (2)

  A method for treating turbid water containing a suspended matter containing clay, wherein the turbid water is agglomerated with a flocculant and then filtered with a filter membrane immersed in the muddy water after treatment.   The turbid water treatment method according to claim 1, wherein muddy water generated at a work site is stored in a tank, subjected to a coagulation treatment in the tank, and then filtered through a filter membrane immersed in the tank.

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