JP4359025B2 - Muddy water treatment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a muddy water treatment method and a muddy water treatment apparatus suitable for construction sites where turbid water mixed with clay is generated, such as in tunnels and dam construction.
[0002]
[Prior art and problems to be solved by the invention]
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.
[0003]
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.
[0004]
On the other hand, the present inventors have proposed a dynamic filtration method using a membrane separation method as a method instead of the coagulation sedimentation method (see Japanese Patent Application Laid-Open No. 2001-104953). 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.
[0005]
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.
[0006]
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.
[0007]
This invention makes it a subject to provide the processing method of the muddy water containing the clay produced in a tunnel, a dam construction site, etc.
[0008]
[Means for Solving the Problems]
The present invention is a method for treating turbid water containing a suspension containing clay as a means for solving the above problems, and after turbid water is agglomerated with a flocculant mainly composed of an inorganic component containing calcium, Provided is a method for treating muddy water by membrane filtration.
[0009]
Further, the present invention is a turbid water treatment apparatus applicable to the above-described turbid water treatment method as a means for solving the above-mentioned other problems. A sedimentation treatment unit for sedimentation of turbid water, and a supernatant after sedimentation as needed. Neutralization treatment unit for neutralization treatment, flocculation treatment unit with flocculant addition means and stirring means that can detect the turbidity of turbid water and adjust the addition amount of flocculant, filtration treatment part, permeate is concentrated A concentration processing unit, and a water storage unit for storing permeate, wherein each of the processing units is connected by a connection line in at least the order, and the liquid separated from the concentrated solution in the concentration processing unit is settled An apparatus for treating turbid water in which a concentration processing unit, a sedimentation processing unit, a neutralization processing unit, or a coagulation processing unit are connected by a connection line so as to be returned to the unit, the neutralization processing unit, or the coagulation processing unit.
[0010]
The clay referred to in the present invention includes kaolinite, halloysite, pyrophyllite, sericite, montmorillonite, chlorite, illite, vermiculite, and other known clay minerals.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, one embodiment of the muddy water treatment method according to the present invention will be described in the case where the muddy water treatment apparatus shown in FIG. 1 is applied. FIG. 1 is a conceptual diagram of a muddy water treatment apparatus according to the present invention. The turbid water treatment apparatus shown in FIG. 1 can be changed by modifications usually made by those skilled in the art.
[0012]
Turbid water (raw water) containing clay generated by tunnels, dam construction, etc. is supplied to the sedimentation tank 1 to settle large stones, sand, mud, etc., and then the first supernatant is fed to the feed line 30. To the muddy water tank (first supernatant tank) 2. The muddy water tank 2 is provided with a liquid feed pump 10. This muddy water tank 2 can also be omitted.
[0013]
Next, the first supernatant in the turbid water tank 2 is sent to the flocculation treatment tank 3 through the liquid feed line 31, but if necessary, a neutralization treatment tank is provided between the turbid water tank 2 and the flocculation treatment tank 3. In addition, the neutralization treatment can be performed in the aggregation treatment tank 3.
[0014]
The muddy water containing clay contains hydrates of polyvalent oxides such as alkaline earth oxides, SiO ₂ , Al ₂ O ₃ , TiO ₂ , P ₂ O ₅ , ZnO and water. When the filter treatment unit 4 is brought into contact with the filter body as it is, the hydrate adheres to the surface of the filter body and lowers the permeation flux. If it is left as it is, it causes a further decrease in permeation flux and cannot be removed by back pressure washing. For this reason, it is desirable to neutralize prior to the treatment with the filter body. The neutralization treatment method is not particularly limited, but it is preferable to neutralize by contacting turbid water and a weak acid, preferably carbon dioxide gas. For example, from the bottom of the aggregation treatment tank 3 (or neutralization treatment tank). A method of neutralizing by aeration with carbon dioxide gas can be applied.
[0015]
The agglomeration treatment tank 3 is provided with a flocculant addition means that can detect the suspended solid (SS) concentration of muddy water and adjust the addition amount of the flocculant, and a stirring means 15.
[0016]
The flocculant is mainly composed of an inorganic flocculant containing calcium, and considering the flocculating effect of turbid water containing clay and the subsequent membrane filterability based on the experimental results, the calcium content is 5% by mass. Those contained above are preferred, those containing 8% by mass or more are more preferred, and those containing 10% by mass or more are more preferred.
[0017]
The flocculant is preferably a mixture of an inorganic flocculant containing calcium and an organic flocculant. In the case of a mixture, only one flocculant charging device is required, and the equipment cost is reduced. Also, by using both coagulants together, the function of lowering the viscosity of the inorganic coagulant and the function of forming a moderately sized floc of the organic coagulant can be combined to perform subsequent dynamic filtration. Water to be treated can be obtained in a state suitable for the above. Moreover, it is preferable that content of the inorganic type coagulant containing calcium is 5 mass% or more in a mixture. Examples of inorganic flocculants containing calcium include calcium sulfate and calcium chloride.
[0018]
Examples of other inorganic flocculants include polyaluminum chloride, polyiron chloride, ferric sulfate, aluminum sulfate, bentonite, and silica. Examples of organic flocculants include polyacrylic acid ester-based, polymethacrylic acid ester-based, polyacrylamide-based, polyamine-based, polydicyandiamide-based cationic polymer flocculants, polyacrylic acid soda-based, polyacrylamide-based anions, etc. And a low molecular organic flocculant such as an amine-based polymer flocculant, a polyacrylamide-based nonionic polymer flocculant, and an amine-based flocculant.
[0019]
When the flocculant contains 5% by mass or more of calcium, the amount of the flocculant is 0.2 to 2.0% by mass with respect to the amount of suspended matter (SS) in muddy water. The amount is preferably, more preferably 0.4 to 2.0% by mass, and still more preferably 0.4 to 1.0% by mass.
[0020]
The amount of the flocculant added can be determined according to the amount of clay by measuring in advance the amount of clay at the construction site or the like that is the source of turbid water suspension. At this time, the rough addition amount of the flocculant may be adjusted according to the amount of clay measured in advance, and the addition amount may be finely adjusted in the actual processing.
[0021]
When adding the flocculant, it is desirable that the flocculant and the first supernatant be sufficiently brought into contact with each other and gently stirred by the stirring means 15 so that flocs can be easily formed.
[0022]
Next, the liquid to be processed after being subjected to the coagulation treatment in the coagulation treatment tank 3 is sent to the filtration processing unit 4 through the liquid feed line 32. The filtration processing unit 4 is of an immersion type in which a filter body is immersed in a treatment tank in which the liquid to be treated is stored and is subjected to filtration treatment. A filtration body is installed outside the treatment tank to filter the treatment liquid in the treatment tank. It may be an external type that circulates in the body.
[0023]
In the filtration processing unit 4, for example, a filtration device 20 having a structure as shown in FIG. 2 can be used. FIG. 2 is a front view including a partial cross section (a main body portion is shown in cross section).
[0024]
The filtration device 20 has a required number of filtration elements 22 immersed in a treatment tank 21, and an air bubbling air diffuser 23 connected to the pump 11 is attached to the bottom. An overflow line 24 is connected to the liquid supply line 37.
[0025]
The filter element 22 has a bag shape in which a filter body is pasted on both surfaces of a frame body having a required number of water collecting pipes of 1 or more (if necessary, a spacing member is provided between two filter bodies. In FIG. 1, one water collecting pipe is a permeate nozzle 25. Each permeate nozzle 25 in the plurality of filtration elements 22 is connected to a permeate line 33.
[0026]
Any filter body may be used, but a filter body having holes and gaps with a uniform diameter is preferable, and a lattice-shaped net is preferably used. In the case of a non-uniform pore film, in order to ensure the quality of the treated water, it is necessary to select the pore diameter based on the vicinity of the maximum pore diameter of the membrane, and the average pore diameter becomes smaller than necessary. For this reason, the fine particles of the undiluted solution get stuck in the pores of the membrane, and clogging is likely to occur. On the other hand, in the case of a uniform pore membrane, the pores for maintaining the quality of the treated water are selected with an average pore diameter. Furthermore, since the pore diameter is uniform, there are few small pores themselves, and the pore size of the membrane is small. There will be less clogging.
[0027]
The uniform hole diameter does not mean that the diameters of all the holes are completely uniform, and an error due to manufacturing or material (for example, ± There is no problem even if there is an error of several percent).
[0028]
The filter body preferably has an average pore diameter of 10 to 100 μm, more preferably 10 to 50 μm, and has the following three requirements: (a) average pore diameter, (b) open area ratio, and (c) thickness. The net provided is more preferable.
The average pore size of (a) is a pore size distribution defined by the following formula: (ML) / M × 100 (L is the minimum pore size, M is the average pore size) within ± 20%, preferably ± 15% Is within.
The porosity of (b) is preferably 20 to 60%, more preferably 25 to 50%.
The thickness of (c) is preferably 25 to 150 μm, more preferably 30 to 100 μm.
[0029]
Furthermore, the net having the requirements (a) to (c) preferably has a requirement (d) that the wire diameter is preferably 20 to 80 μm, more preferably 30 to 70 μm.
[0030]
Depending on the composition of the turbid water, the filter body is preferably resistant to sodium hypochlorite, and the filter body having a size of 2 × 10 cm is placed in a sodium hypochlorite aqueous solution having an effective chlorine concentration of 1 mass% for one month. It is preferable that when dipped, the reduction rate with respect to the initial tensile strength is less than 30%.
[0031]
The filter body is preferably made of metal fibers or plastic fibers. Examples of the metal fiber include iron, silver, copper, copper alloy, titanium, stainless steel, and metal made by plating silver or copper on a base metal, but copper or stainless steel is preferable. Plastic fibers include polyester, polystyrene, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, poly (meth) acrylic acid ester, viscose rayon, cellulose acetate, polyethylene, polypropylene, and other polyolefins, polyethers, polyether esters And copolymers, blends or cross-linked products of these, and polyvinylidene chloride, polyester, polyethylene and polypropylene are preferred, and polyester and polyethylene are more preferred.
[0032]
In the filtration processing unit 4, it is desirable to perform dynamic filtration with a low transmembrane pressure difference, the transmembrane differential pressure can be kept low, and energy can be saved, so that it is preferably 0.5 to 50 cm, more preferably 1 It is desirable to perform dynamic filtration using a water head difference of 10 cm (Δh in FIG. 2).
[0033]
The permeate filtered by the filtration unit 4 is sent to the water storage tank 5 through the permeate line 33 at a flow rate smaller than the supply flow rate of the raw water, stored, and discharged to a river or the like. At this time, the permeate can be filtered again or settled according to the SS concentration in the permeate.
[0034]
When such a filtration treatment is continued, an excessive cake layer made of SS is formed on the surface of the filtration element 22 of the filtration treatment unit 4 (the surface of the filter body), resulting in clogging of the holes. If left as it is, the permeation flux will be significantly reduced. For this reason, it is desirable to adjust the thickness of the cake layer by performing back pressure washing of the filtration element 22 accompanied by air bubbling after stopping the inflow of muddy water at an appropriate operation interval.
[0035]
The back pressure washing method of the filtration element 22 is not particularly limited, and a method in which the permeate in the water storage tank 5 is supplied by the back wash pump 13 and is press-fitted into the filter element 22 from the permeate line 33, and a filtration process. A method of air bubbling from the bottom surface of the processing tank 21 of the unit 4 by the air diffusion tube 23, or a method of combining them can be applied. A chemical solution such as sodium hypochlorite can be added to the back pressure wash water from the chemical solution tank 8 as necessary.
[0036]
The cleaning liquid used for the reverse pressure cleaning is sent to the concentration processing unit 6 through the liquid supply line 34 together with the concentrated liquid. In the concentration processing unit 6, sedimentation is performed, and the supernatant (second supernatant) is returned to the aggregating treatment tank 3 through the liquid feeding line 37 by operating the pump 12. At this time, the second supernatant can be returned to the sedimentation tank 1 or the muddy water tank 2.
[0037]
After the sludge staying in the concentration processing unit 6 is sent to the sludge storage tank 7 through the liquid feed line 36, the pump 14 is operated and sent to the filter press machine for dehydration, and the residual liquid is the sedimentation tank 1 and the muddy water tank. 2 or return to the coagulation treatment tank 3. When the amount of sludge is excessive, the sludge is extracted from the sludge extraction line 35 as appropriate.
[0038]
In the method for treating turbid water of the present invention, the permeation flux is preferably set to 3 m / day or more, more preferably 5 to 15 m / day, so that (Depending on the method) can be reduced to 90% or more, more preferably 95% or more.
[0039]
It is presumed that the processing mechanism in the processing method of the present invention is as follows. By the agglomeration treatment, the clay content in the muddy water is agglomerated, and due to the caking action of the calcium component, it becomes a lump (floc) having a certain size and caking degree, and the stickiness like clay particles is reduced. This lump is not significantly smaller than the membrane mesh used in the filtration process and is not significantly larger. Therefore, with filtration, a dynamic layer is quickly formed on the membrane surface, and muddy water is efficiently filtered by this dynamic layer. The dynamic layer is in a state in which lumps obtained by consolidation of clay components are stacked, and sufficient voids are formed between the lumps through which filtered water can pass.
[0040]
After a certain period of time, the dynamic layer is thickly deposited on the film surface and the filtration rate is reduced. At this time, the dynamic layer deposited on the film surface is subjected to back pressure cleaning as described above. Will peel off easily. This is because the dynamic layer is formed of lumps obtained by uniting clay, so that the adhesive force is small and the lumps are formed, and the contact area between the particles is also small.
[0041]
Since it is a processing mechanism as described above, it is possible to stably exhibit high filtration ability even for turbid water containing clay.
[0042]
The method and apparatus for treating muddy water of the present invention are suitable for treating muddy water containing clay generated at construction sites such as tunnels and dams, but can also be applied to muddy water not containing clay.
[0043]
Further, the processing apparatus of the present invention uses a single filtration apparatus shown in FIG. 2 or a combination of the filtration apparatus and another apparatus as shown in FIG. 1, and these apparatuses are used in construction sites of tunnels and dams. It can be configured to be carried by car.
[0044]
【Example】
Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.
[0045]
Example 1
The muddy water was treated using the treatment apparatus shown in FIGS. First, in the sedimentation treatment tank 1, turbid water containing clay discharged from the tunnel construction site was settled, and then the first supernatant (SS concentration was about 5000 mg / L, pH 10.5) was sent to the turbid water tank 2. .
[0046]
Next, muddy water (first supernatant) was sent from the muddy water tank 2 to the coagulation treatment tank 3 to perform neutralization and coagulation treatment. Neutralization was performed by aeration of carbon dioxide gas at 5 liter / min for about 10 minutes from the bottom of the aggregation treatment tank 3. The agglomeration treatment was performed by adding an inorganic flocculant (calcium content: 11% by mass) (Papyrus 001, manufactured by MC Mining Co., Ltd.) to 50 mg / L and stirring with a stirrer 15 for about 2 minutes.
[0047]
Next, the liquid after the aggregation treatment (SS concentration is about 5000 mg / L, pH 7.5) was sent to the filtration treatment unit 4 and subjected to dynamic filtration. In the filtration processing unit 4, the water head difference Δh shown in FIG. 2 was 5 cm ( 0.5 kPa), and continuous dynamic filtration was performed, and the permeate was sent to the water storage tank 5 and stored. In addition, as a filter element, a filter body composed of two twill weave stainless nets (average pore diameter 43 μm, pore diameter distribution within ± 5%, wire diameter 34 μm, aperture ratio 30%, thickness 70 μm) was attached to both sides of the frame body. A bag (effective filtration area 0.01 m ² ) was used. After filtration for 30 minutes, backwashing and air bubbling were performed for 0.5 minutes, and this operation cycle was repeated.
[0048]
The SS concentration of the permeate at the initial stage of operation was 10 mg / L on average, and the average treatment capacity was 5.1 m ³ / m ² · day per effective filtration area of the filter body. The SS concentration of the permeate after 5 hours of operation is 10 mg / L on average, and the average treatment capacity is 5.0 m ³ / m ² · day per effective filtration area of the filter, which is the difference from the filtration performance from the initial operation. There was no.
[0049]
Example 2
Muddy water was treated in the same manner as in Example 1. However, the first supernatant had an SS concentration of about 700 mg / L and a pH of 11.3, and the amount of flocculant added was 7 mg / L. The SS concentration of the permeate at the beginning of the operation was 5 mg / L on average and the average treatment capacity was 9.4 m ³ / m ² · day per effective filtration area, and there was no change even after 5 hours.
[0050]
Comparative Example 1
Muddy water was treated in the same manner as in Example 1 except that polyaluminum chloride (manufactured by Taiki Pharmaceutical Co., Ltd.) was used as a flocculant. The SS concentration of the permeate at the beginning of the operation was an average of 45 mg / L and the average processing capacity was 4.8 m ³ / m ² · day per effective filtration area, but after 5 hours, the SS concentration of the permeate was an average of 25 mg. / L, the average treatment capacity was 1.3 m ³ / m ² · day per effective filtration area, and the filtration performance was greatly reduced.
[0051]
Comparative Example 2
Muddy water was treated in exactly the same manner as in Example 2 except that ferric chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was used as the flocculant. The SS concentration of the permeate at the beginning of operation averaged 31 mg / L, and the average processing capacity was 7.8 m ³ / m ² · day per effective filtration area, but after 5 hours, the SS concentration of the permeate averaged 19 mg. / L, the average treatment capacity was 1.9 m ³ / m ² · day per effective filtration area, and the filtration performance was greatly reduced.
[0052]
As is clear from the comparison with the above Examples and Comparative Examples, by applying the treatment method of the present invention, when the tunnel turbid water containing a large amount of clay content is treated, the clay content is removed by filtration with a membrane, Furthermore, since the neutralization process is used together, it can suppress that a clay component adheres to the film | membrane surface at the time of filtration. For this reason, the SS concentration in the processing liquid is low, and the change with time of the average processing capacity can be reduced.
[0053]
【The invention's effect】
By applying the turbid water treatment method of the present invention, when processing tunnel turbid water containing a large amount of clay, etc., the SS concentration in the treatment liquid can be reduced and the change in the average treatment capacity over time can be reduced. Even when water is discharged into rivers, water quality is not contaminated.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a treatment apparatus used in a muddy water treatment method.
FIG. 2 is a conceptual diagram of a filtration device included in the processing device.

Claims (6)

The turbid water containing the suspension containing clay is agglomerated with an inorganic flocculant containing 5% by mass or more of calcium, and the flocs containing flocs after the agglomeration are sent to the filtration unit as they are and subjected to dynamic filtration. It is a treatment method of turbid water that performs membrane filtration treatment,
The agglomeration treatment is performed by adding an amount of 0.2 to 2.0% by mass of the inorganic flocculant with respect to the suspended mass in the muddy water,
A method for treating turbid water, wherein the dynamic filtration is performed such that a transmembrane differential pressure is a water head difference of 1 to 10 cm.   The turbid water treatment method according to claim 1, wherein the turbid water and carbon dioxide gas are brought into contact with each other and neutralized, and then a flocculation treatment is performed with a flocculant.   The method for treating turbid water according to claim 1 or 2, wherein the filtration treatment is performed by a filter body having pores having a uniform diameter.   The concentrated water after the filtration treatment is settled to settle the suspended matter, further concentrated, the precipitated sludge is solidified, and the supernatant is mixed with the turbid water before the flocculation treatment. The method for treating muddy water according to 1.   The method for treating turbid water according to any one of claims 1 to 4, wherein the permeate after the filtration treatment is subjected to sedimentation treatment or filtration treatment again.   It is a turbid water processing apparatus applicable to the turbid water processing method of any one of Claims 1-5, and the neutralization process is performed for the sedimentation processing part which settles turbid water, and the supernatant liquid after sedimentation treatment as needed. A neutralization treatment unit, a coagulant addition unit capable of detecting the turbidity of turbid water and adjusting the addition amount of the coagulant and a coagulation treatment unit equipped with a stirring unit, a filtration treatment unit, a concentration treatment unit for concentrating the permeate, A water storage section for storing the permeate, wherein each of the processing sections is connected by a connection line in at least the order, and the liquid separated from the concentrated liquid in the concentration processing section is settled and neutralized. A turbid water treatment apparatus in which a concentration processing unit, a sedimentation processing unit, a neutralization processing unit, or a coagulation processing unit are connected by a connection line so that they can be returned to the unit or the coagulation processing unit.

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