JP4178557B2 - How to treat dredged mud - Google Patents

Description

  The present invention relates to a method for treating mud soil dredged from the bottom of a sea, lake, or river.

    When water pollution of the sea, lakes, or rivers is progressing, it is extremely important from the viewpoint of maintaining the ecosystem to prevent such water pollution from progressing and restore a good environment.

  The cause of water pollution is the inflow of organic substances from the outside and the elution of nutrients from the bottom mud. Therefore, it is effective to remove and remove the bottom mud to improve the water quality of the lake. Is.

  However, dredged mud has a high water content and a huge amount, and as it is, it is difficult to secure a disposal site and reuse it. Therefore, it is essential to reduce the volume and increase the strength of the dredged mud.

  Conventionally, coagulant is added to dredged mud to pre-agglomerate the soil particles, and then the volume is reduced by dewatering with a filter press or the like, and the strength of the treated soil is increased by adding a solidifying material together with the coagulant. I was trying to improve.

JP-A-9-155395

  However, in order to reduce the volume of dredged mud soil with a high water content to a certain ratio and improve its strength, a large amount of aggregating agent and solidifying material are required, resulting in high material costs, filter presses, etc. When a dehydrator is used, the overall equipment cost increases, and a problem arises that a large installation space must be secured.

  Therefore, the present applicant has developed a new treatment method for dredged mud soil, and succeeded in reducing the equipment scale of the dewatering equipment and saving the use amount of the coagulant and the solidifying material.

  However, since this treatment method is to dehydrate the entire amount of the screw decanter overflow, there is a limit to reducing the volume to be dehydrated, and the concentration is low because of the overflow, There was a problem that the dehydration efficiency was poor.

  The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a method for treating dredged mud that can greatly reduce the scale of a dewatering facility and improve the dewatering efficiency.

  In order to achieve the above-mentioned object, the apparatus according to the present invention drowns the bottom mud of the sea, rivers, lakes and the like as described in claim 1 and removes foreign matters such as reki from the drowned bottom mud. Thereafter, dewatering and classifying with a sediment separator comprising a vibrating sieve and a cyclone, the cyclone over fraction of the sediment separator is classified with a screw decanter, and the overflowed fraction by the classification with the screw decanter is placed in a concentration tank, The sediment is separated and settled in the concentration tank, and the concentrated mud in the concentration tank settled by the sedimentation is dehydrated.

  In the method for treating dredged mud according to the present invention, dredged mud with a high water content is classified by centrifugation in advance, but instead of dewatering the entire amount overflowed in the classified treatment, the overflow is settled and separated. Thereafter, the concentrated mud settled by the sedimentation is dehydrated by a predetermined method.

  In this way, the amount to be dewatered can be reduced to 1/2 to 1/10 compared to the dredged soil treatment method (Japanese Patent Laid-Open No. 9-155395) previously developed by the applicant. Is done. In addition, since the specific gravity of the concentrated mud to be dewatered is larger than the above-described overflow, the dewatering efficiency is improved.

  As the dehydration method, a pressure dehydration method such as a filter press may be employed, or a centrifugal separation method such as a screw decanter may be employed. Incidentally, according to the latter method, the facility scale can be further reduced.

  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.

  FIG. 1 is a flow chart showing the flow of the dredged clay treatment method according to the present embodiment, and FIGS. 2 and 3 are equipment configuration diagrams. As can be seen from these drawings, in the dredged mud processing method according to the present embodiment, first, the bottom mud 1 such as the sea, a river, or a lake is dredged by the dredger 2 (FIG. 1, step 101). The dredged bottom mud 1 is stored in the raw water tank 4 after removing foreign matter such as scum with a screen 3.

  Next, the mud soil stored in the raw water tank 4 is subjected to a dewatering and classifying process by the earth and sand separator 5 including a vibrating sieve and a cyclone (step 102).

  Next, after the cyclone over portion of the earth and sand separator 5 is temporarily stored in the drainage raw water tank 21, it is classified by the screw decanter 6 that is a centrifugal separator (step 103). The under portion generated in the classification process is discharged as a cake.

  Next, the portion overflowed by the classification process by the screw decanter 6 is put into the concentration tank 7 and settled and separated in the concentration tank (step 104). About the supernatant water of the concentration tank 7, it adjusts pH with the pH adjustment tank 14 mentioned later as needed, and discharges it to the original water area after an appropriate time.

  Next, the concentrated mud 8 in the concentration tank 7 settled by the settling separation is temporarily stored in the slurry tank 22, and after adding a flocculant if necessary, the dewatering process is performed by the filter press 9 as a dehydrator (step 105). ). The under portion generated by the dehydration process is discharged as a cake.

  In addition, about the part overflowed by the dehydration process, after having once stored in the filtrate tank 10, the inorganic flocculant accommodated in the inorganic flocculant tank 11 and the polymer flocculant stored in the polymer dissolution storage tank 12 are added. In addition, the supernatant is flocculated and settled by the square thickener 13, and the supernatant is neutralized and discharged by the pH adjusting tank 14, and the flocculated sediment is returned to the concentration tank 7 (step 106).

  Here, as an inorganic flocculant, polyaluminum chloride called a sulfate band or PAC is used, and as a polymer flocculant, it can be appropriately selected from commercially available products manufactured from water-soluble polyacrylamide.

  As described above, according to the dredged clay treatment method according to the present embodiment, the entire portion that has overflowed in the classification by the screw decanter 6 is not dewatered, but the overflow is settled and separated in the concentration tank 7. After that, since the concentrated mud 8 settled by the settling and separation was dewatered, the amount of dewatering required for the filter press 9 was determined by the dredging mud soil processing method (special Compared to Kaihei 9-155395), the volume can be reduced to 1/2 to 1/10, and the target to be dehydrated is concentrated mud 8, so the overflow from the screw decanter The specific gravity of the object to be dehydrated, that is, the concentrated mud 8, can be increased as compared with the case of directly dewatering the water, and the dewatering efficiency in the filter press 9 is dramatically improved.

  Therefore, the scale of the filter press 9 as a dehydrator can be greatly reduced, and accordingly, the initial cost of equipment and the installation space can be reduced.

  Next, since the experiment which confirms the effect of the treatment method of dredged mud according to this embodiment was performed, the outline thereof will be described below.

  In the experiment, dredged mud soil having a specific gravity of 2.6 was used, and the dredged mud was treated by the above-described procedure. The results are shown in Table 1.

In the table, ρ _SI indicates the specific gravity on the supply side of the screw decanter, ρ _{SOF also} indicates the specific gravity on the overflow side, C ₁ indicates the volume ratio of the concentrated mud to the overflow from the screw decanter, and C ₂ Indicates the volume ratio of the concentrated mud to the supply to the screw decanter. The specific gravity of the concentrated mud was about 1.16, not depending on the specific gravity on the screw decanter supply side.

From the above results, the volume ratio C ₂ (concentrated mud volume / volume supplied to the screw decanter), that is, the volume reduction rate before the dehydration treatment was 10.5 to 33.3% (1/10 to 10%). It can be seen that 1/3). Further, it can be seen that the specific gravity 1.16 before the dehydration treatment exceeds the specific gravity ρ _SOF on the overflow side.

  In the present embodiment, the portion overflowed in the classification process by the screw decanter 6 is put into the concentration tank 7 as it is for sedimentation separation, but an inorganic flocculant (PAC) or slaked lime is added to the overflow portion of the screw decanter 6. You may make it aim at promotion of sedimentation separation.

The flowchart which showed the flow of the processing method of dredged mud according to this embodiment. The equipment block diagram for enforcing the disposal method of dredged mud according to this embodiment. The equipment block diagram for enforcing the dredged mud processing method which similarly concerns on this embodiment.

Explanation of symbols

1 Bottom mud 6 Screw decanter (equipment for classification by centrifugation)
7 Concentration tank (equipment for sedimentation)
8 Concentrated mud 9 Filter press (Dehydration equipment)

Claims (1)

After dredging the bottom mud of the sea, rivers, lakes, etc., and removing foreign matter such as leki from the dredged bottom mud, it is subjected to dewatering classification with a sediment separator consisting of a vibrating sieve and a cyclone. The cyclone over fraction is classified with a screw decanter, the portion overflowed by the classification with the screw decanter is put into a concentration tank, settled and separated in the concentration tank, and the concentrated mud in the concentration tank settled by sedimentation separation is dehydrated. A method for treating dredged mud soil.

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