JP4207479B2 - How to treat dredged mud - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating dredged mud for the purpose of improving the water quality of seas, lakes or rivers.
[0002]
[Prior art]
Seas, lakes, and rivers are attracting attention as spaces for multipurpose use, including living and leisure. On the other hand, in closed waters, eutrophication and hypoxia with organic substances have progressed, and such water pollution There is an urgent need for countermeasures.
[0003]
Water pollution caused by organic matter is caused by excessive inflow load from the land area, and is gradually being improved by reducing industrial wastewater and using organic detergents. It accumulates on the sea floor without being decomposed to form a sludge layer called sediment, from which nutrient salts such as nitrogen and phosphorus are eluted into the water and cause water pollution.
[0004]
Therefore, it is important to reduce the elution of nutrient salts from the sediment by taking measures such as removing mud with high organic matter content by dredging.
[0005]
Here, when dredging mud deposited on the bottom of the water, a large amount of excess water is sucked up together with the mud, and the water content becomes extremely high. Therefore, it is necessary to separate and remove the excess water from the mud by sun drying, dewatering with a drain material, mechanical dewatering with a pressure dewatering device such as a filter press.
[0006]
[Problems to be solved by the invention]
However, even when mechanical dehydration is performed, a large sedimentation basin is required to separate a large amount of surplus water contained in dredged mud. Considering the recent land conditions, it was extremely difficult to secure such a large site, and the problem was that it was difficult to install facilities due to the foul odor scattered around.
[0007]
In addition, there has been a problem that it is difficult to secure a place for disposal of a large amount of dehydrated cake produced in the final process of mechanical dehydration.
[0008]
The present invention has been made in consideration of the above-mentioned circumstances, and the progress of water pollution by treating dredged mud without the need to secure a site for dewatering dredged mud and a site for disposing dewatered cake. An object of the present invention is to provide a method for treating dredged mud that can effectively prevent dewatering cake generated at that time.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the dredged mud treatment method according to the present invention dredged mud deposited on the bottom of the water, then separated the dredged mud, and then separated the earth and sand. This is a method for treating dredged mud, in which a cloth formwork is laid on the bottom of a coastal area such as a sea or a lake, and the primary dewatered cake generated by the centrifugation is filled in the cloth formwork. Then, after coagulating and sedimenting the over mud produced by the centrifugation, the coagulated sediment is subjected to pressure dehydration, and the secondary dehydrated cake produced by the pressure dehydration is filled with the primary dehydrated cake. It is laid on the frame and leveled .
[0012]
In the dredged mud processing method according to the present invention, first, mud deposited on the bottom of the sea, lakes and the like is dredged with a grab dredger or the like.
[0013]
Next, the dredged mud is separated into sediment using a sediment separator or the like.
[0014]
Next, the mud thus separated is centrifuged, and the underside is used as a primary dewatered cake. For example, a screw decanter can be used for the centrifugation.
[0015]
On the other hand, cloth formwork will be laid on the bottom of coastal areas such as seas and lakes.
[0016]
Next, the primary dehydrated cake generated by centrifugation is filled into a cloth mold. At this time, a solidifying agent is added to the primary dehydrated cake as necessary.
[0017]
In this way, the primary dewatered cake is filled in the cloth formwork laid on the coastal water bottom, eliminating the need for final disposal, and the primary dewatering in the cloth formwork laid on the coastal water bottom. The product formed by filling the cake can be effectively used for various purposes. For example, it is possible to create a tidal flat on the coastal water bottom by filling a primary dehydrated cake in a cloth formwork.
[0018]
Here, after the over mud produced by centrifugation is coagulated and settled, the coagulated sediment is subjected to pressure dehydration, and the secondary dewatered cake generated by the pressure dewatering is filled with a primary dewatered cake. If it is spread on the top, it will be possible to effectively use even the soil particles remaining in the centrifuge over mud water on the cloth formwork. As a result, most of the soil particles in the dredged mud are effective.
[0019]
In addition, since the primary dewatered cake is in a state in which the soil particles are difficult to separate from each other due to the effect of centrifugation, there is no risk of being dispersed in water through the gaps in the cloth formwork, and for the secondary dehydrated cake, Dispersion in water is suppressed by the effect of pressure dehydration and does not become muddy again.
[0020]
Since nutrient salts such as phosphorus and nitrogen are confined in the primary dehydrated cake and the secondary dehydrated cake in this way and do not elute into the water, it is not necessary to newly secure a disposal place for the dehydrated cake. Water pollution such as eutrophication and hypoxia of water is prevented, and an excellent natural environment can be created because, for example, tidal flats can be created at the bottom of coastal areas using primary and secondary dehydrated cakes. It is also possible to do.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a dredged mud disposal method according to the present invention will be described with reference to the accompanying drawings. Note that components that are substantially the same as those of the prior art are assigned the same reference numerals, and descriptions thereof are omitted.
[0022]
FIGS. 1 and 2 are flowcharts showing a procedure for performing the dredged mud processing method according to the present embodiment, and FIGS. 3 and 4 are conceptual diagrams showing equipment for performing a series of processing. As can be seen from these figures, in the treatment method according to the present embodiment, first, as shown in FIG. 3 (a), mud soil 2 deposited on the bottom of the water area 1 such as the sea, lake, river, etc. Hesitate (FIG. 1, step 101). For dredging, the grab dredger shown in the figure may be used, but a pump type high concentration dredger capable of dredging with high concentration and stability may be used. By employing such a high-concentration dredger, the amount of surplus water contained in dredged mud can be reduced as much as possible.
[0023]
Next, the dredged mud 2 is put into the raw water tank 5 installed on land as shown in FIG. 3 (b) and temporarily stored (step 102). In addition, before transferring the dredged mud to the raw water tank 5, it may be screened in advance to selectively remove earth and sand having a relatively large particle size.
[0024]
Next, the mud sent from the raw water tank 5 is separated by the earth / sand separator 6 and the over mud is primarily stored in the storage tank 7 (step 103).
[0025]
Next, as shown in FIG. 3 (c), the over mud water in the storage tank 7 is driven into the screw decanter 8 and classified, and the underflow is used as the primary dewatered cake 14 (step 104).
[0026]
On the other hand, the flocculant stored in the flocculant tank 9 is added to the over mud water of the screw decanter 8, and the flocculant is stirred in the pipe by the line mixer 10, and then the flocculant settling tank 12 such as a slurry tank is passed through the mud pipe 11. The mud is agglomerated and settled in the tank (step 105).
[0027]
As the flocculant, for example, about 10 to 150 kg of aluminum-based flocculant such as aluminum sulfate called sulfate band and polyaluminum chloride called PAC and calcium-based flocculant such as slaked lime are added.
[0028]
In addition, you may add a pH adjuster, a deodorizing agent, the additive which prevents the elution of a harmful metal ion, etc. as needed. For example, if weakly acidic hydrogen sulfide that causes odor is contained, add cement or slaked lime to make the pH neutral or alkaline, or add hydrogen peroxide to oxidize sulfur. Deodorization can be performed with. If it is desired to suppress elution of iron, manganese, etc., the pH may be neutral or alkaline with cement, lime, or the like.
[0029]
Next, the mud settled in the coagulation sedimentation tank 12 is drawn out, transferred to a mechanical dehydration processing device 13 such as a filter press or a roll press, and dehydrated under pressure, and the underside is used as a secondary dehydrated cake 15 (step) 106).
[0030]
The filtrate from the mechanical dehydration apparatus 13 is discharged to a river or the like as appropriate after performing necessary treatments such as pH adjustment.
[0031]
On the other hand, as shown in FIG. 4 (a), a cloth form 22 is laid on the bottom 21 of the coastal area such as the sea or lake (step 107).
[0032]
The cloth formwork 22 is a commercially available concrete used for slope protection or revetment in which, for example, tubular cloth fabrics are connected in a grid pattern, and fresh concrete or fresh mortar is poured into the hollow interior. A mat can be used. Specifically, a product commercially available from Taiyo Kogyo Co., Ltd. under the trade name of Tacom, or a product commercially available from Asahi Kasei Geotech Co., Ltd. under the trade name of Fabry Foam (registered trademark) can be used.
[0033]
Next, as shown in FIG. 4 (b), the primary dewatered cake 14 is filled into the cloth form 22 via a mud pump (not shown), and a mat-like composition 23 is formed on the coastal water bottom 21 (step). 108). In filling the primary dewatered cake 14, a solidifying agent such as cement is appropriately added as necessary.
[0034]
Next, as shown in FIG. 4 (c), a secondary dewatered cake 15 is spread on the mat-like composition 23 and further covered with sand as necessary to create a tidal flat 24 ( Step 109). The thickness of the secondary dewatered cake 15 and the sand cover or the thickness of the cloth formwork is appropriately determined in consideration of the high tide level (HWL) and the low tide level (LWL).
[0035]
Here, since the primary dehydrated cake 14 is in a state in which the soil particles are difficult to separate from each other due to the effect of centrifugal separation, there is no possibility that the primary dehydrated cake 14 will be dispersed in water through the gaps in the cloth form 22, and the secondary dehydrated cake. About 15, the dispersion | distribution in water is suppressed by the effect of pressure dehydration, and it does not become muddy again.
[0036]
As described above, according to the dredged mud processing method according to the present embodiment, the dredged mud 2 is separated into the earth and sand, and then the separated mud is centrifuged with the screw decanter 8, while the sea, the lake A cloth form 22 is laid on the water bottom 21 of the coastal area, etc., and the primary dehydrated cake 14 generated by centrifugation is filled in the cloth form, and the secondary dehydrated cake 15 generated by pressure dehydration is filled with the cloth form. As shown in FIG. 4 (c), the tidal flat 24 shown in FIG. 4 (c) can be formed on the coastal bottom 21 using the primary dehydrated cake 14 and the secondary dehydrated cake 15. Various aquatic organisms such as birds and fish and shellfish gathered in the tidal flat can interact with each other to form an excellent natural environment.
[0037]
In addition, according to the dredged mud processing method according to the present embodiment, the primary dewatered cake 14 and the secondary dewatered cake 15 obtained by dewatering the dredged mud can be effectively used for creating the tidal flat 24, The final disposal site for dehydrated cake is no longer required.
[0038]
In addition, nutrient salts such as phosphorus and nitrogen contained in the dredged mud are confined in the primary dehydrated cake 14 and the secondary dehydrated cake 15 and do not elute in water. Therefore, it is also possible to prevent the progress of water pollution such as eutrophication and hypoxia of the water area without newly securing a disposal place for the primary dehydrated cake 14 and the secondary dehydrated cake 15.
[0039]
In addition, according to the dredged mud processing method according to the present embodiment, the underflow from the screw decanter 8, that is, the primary dewatered cake 14 is filled in the cloth mold 22, so that the screw is relatively soft and difficult to handle. While preventing the dewatered cake from decanter from diffusing into the water, it is possible to maintain its shape for a long period of time, and to prevent the situation where the shape of the tidal flat changes due to the water flow.
[0040]
In this embodiment, the secondary dehydrated cake 15 is spread on the composition 23 in which the primary dehydrated cake 14 is filled in the cloth form 22, but in some cases, the secondary dehydrated cake 15 is spread. The leveling may be omitted, and in this case, whether or not to cover the cloth formwork is optional.
[0041]
Further, in this embodiment, the primary dewatered cake 14 is filled in the cloth form 22 to create the tidal flat 24 on the coastal bottom 21. What kind of composition is created on the coastal bottom. Is optional. For example, the present invention may be applied to the case of creating a normal beach.
[0042]
Although not particularly mentioned in the present embodiment, when the over mud of the sediment separator 6 is primarily stored in the storage tank 7, a coagulant similar to that described above is added as necessary to perform coagulation sedimentation. It may be.
[0043]
In the present embodiment, the underside of the screw decanter 8 is used as the primary dewatered cake 14, and the coagulation sedimentation treatment is performed in the coagulation sedimentation tank 12 on the over mud of the screw decane (steps 104 to 105). The mud settled in the agglomeration settling tank is pulled out and dehydrated under pressure by the mechanical dehydration processing device 13 to form a secondary dewatered cake 15 (step 106), which is included in the over mud water in the storage tank 7. If substantially all of the soil particles can be separated by the screw decanter 8, the primary dewatered cake 14 which is the underside of the soil particles is filled in the cloth mold 22 and mated on the coastal bottom 21 as described above. On the other hand, since the secondary dehydrated cake 15 is not generated, the step of spreading this on the mat-like product 23 is omitted. It may also be in.
[0044]
In this configuration, the screw decanter 8 functions as a dehydrator, and the coagulant tank 9, the line mixer 10, the mud pipe 11, the coagulation sedimentation tank 12, and the mechanical dehydration apparatus 13 are not required. Further, the over water of the screw decanter 8 may be discharged into a river or the like as appropriate after performing necessary treatment such as pH adjustment.
[0045]
【The invention's effect】
As described above, according to the dredged mud disposal method according to the present invention, it becomes possible to create a tidal flat or other constructed material on the coastal bottom using the primary dewatered cake or the secondary dewatered cake. The primary dehydrated cake and the secondary dehydrated cake obtained by dehydration can be used effectively, and the final disposal site for the dehydrated cake is not required.
[0046]
[Brief description of the drawings]
FIG. 1 is a flowchart showing a procedure of a method for treating dredged mud according to the present embodiment.
FIG. 2 is a flowchart showing the procedure of the dredged clay treatment method according to the present embodiment.
FIG. 3 is a work diagram showing a state in which the method for treating dredged mud according to the present embodiment is being carried out.
FIG. 4 is a work diagram showing a state in which the dredged clay treatment method according to the present embodiment is being carried out.
[Explanation of symbols]
14 Primary dehydrated cake 15 Secondary dehydrated cake 22 Fabric formwork

Claims (1)

The mud deposited on the bottom of the water is dredged, then the dredged mud is separated into sediments, and then the separated mud is centrifuged, while a cloth formwork is laid on the bottom of the coastal area of the sea, lake, etc. A method for treating dredged mud that fills a cloth formwork with the primary dewatered cake generated by the centrifugation ,
After coagulating and sedimenting the over mud produced by the centrifugal separation, the coagulated sediment is subjected to pressure dehydration, and the secondary dewatered cake produced by the pressure dewatering is added to the cloth formwork filled with the primary dewatered cake. A method for treating dredged mud, characterized by spreading on the top .

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