JP2001212600A - Method for treating dredged sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the scale of a dewatering apparatus and to improve the dewatering efficiency of the apparatus. SOLUTION: In a method for treating dredged sludge, the bottom sludge 1 of seas, rivers, lakes, marshes, etc., is dredged by a dredger 2 (Fig. 1 step 101). Next, sludge stored in a raw water tank 4 is dewatered/sorted by an earth-sand separator 5 comprising a vibrating screen and a cyclone (step 2). Next, the cyclone-over portion of the sludge in the separator 5, after being stored temporarily in a drainage raw water tank 21, is sorted by a screw decanter 6, which is a centrifugal separator (step 103). Next, the overflow portion of the sludge in the sorting by the screw decanter is precipitated/separated in a concentration tank 7 (step 104). Next, the concentrated sludge 8 in the tank 7, which has been precipitated by the precipitation/separation, after being stored temporarily in a slurry tank 22, is dewatered by a filter press 9, which is a dewaterer (step 105).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art When water pollution of the sea, lakes, or rivers is progressing, it is extremely important from the viewpoint of maintaining an ecosystem to prevent the progress of water pollution and restore a favorable environment.

[0003] The cause of the progress of water pollution is the inflow of organic matter from the outside and the elution of nutrients from the bottom mud. Therefore, in order to improve the water quality of lakes and marshes, the bottom mud is removed by dredging. Is effective.

[0004] However, the dredged mud has a high water content and an enormous amount, and it is difficult to secure a disposal site and reuse it as it is. Therefore, it is essential to reduce the volume and increase the strength of the dredged mud.

Conventionally, a flocculant is added to a dredged mud to coagulate soil particles in advance, and then dewatering is performed by a filter press or the like to reduce the volume, and a treatment is performed by adding a solidifying material together with the flocculant. Improving the strength of the soil.

[0006]

However, in order to reduce the volume of the dredged mud having a high water content to a certain ratio and to improve its strength, a large amount of a coagulant and a solidifying material are required, and the material cost is high. If a dewatering device such as a filter press is used, the overall equipment cost increases and a wide installation space must be secured.

Accordingly, the present applicant has developed a new method for treating dredged mud (see Japanese Patent Application Laid-Open No. 9-155395) to reduce the scale of dewatering equipment and to save the amount of coagulant and solidified material used. I succeeded in planning.

[0008] However, such a treatment method involves dehydrating the entire amount of the overflow of the screw decanter. Therefore, there is a limit to reducing the volume to be dehydrated, and the concentration of the overflow due to the overflow is limited. And the dewatering efficiency is low.

The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a method for treating dredged mud which can greatly reduce the scale of a dewatering facility and improve the dewatering efficiency. I do.

[0010]

In order to achieve the above object, a method for treating dredged mud according to the present invention is to dredge bottom mud such as seas, rivers, lakes and marshes and to draw the dredged mud. The sludge thus obtained is classified by centrifugation, the portion overflowed by the classification is sedimented and separated, and then the concentrated mud settled by the sedimentation is dehydrated by a predetermined method.

In the method for treating dredged mud according to the present invention, the dredged mud having a high water content is classified in advance by centrifugal separation. After sedimentation and separation, the concentrated mud sedimented by the sedimentation is dehydrated by a predetermined method.

Thus, the amount to be dehydrated is:
A method of treating dredged mud previously developed by the present applicant (Japanese Unexamined Patent Application Publication No.
-155395), the volume is reduced to 1/2 to 1/10. In addition, the specific gravity of the concentrated mud to be dehydrated is larger than the above-mentioned overflow, so that the dewatering efficiency is also improved.

The dewatering method may be a pressure dehydration method such as a filter press, or a centrifugal separation method such as a screw decanter. Incidentally, according to the latter method, it is possible to further reduce the equipment scale.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for treating dredged mud according to the present invention will be described below with reference to the accompanying drawings. It is to be noted that the same reference numerals are given to components and the like that are substantially the same as those in the conventional technology, and description thereof will be omitted.

FIG. 1 is a flow chart showing the flow of a method for treating dredged mud according to the present embodiment, and FIGS.
FIG. As you can see in these figures,
In the method for treating dredged mud according to the present embodiment, first, bottom mud 1 such as the sea, a river, a lake or the like is dredged by a dredger 2 (FIG. 1, step 101). The dredged bottom mud 1 is stored in a raw water tank 4 after removing foreign matters such as recreation by a screen 3.

Next, the mud stored in the raw water tank 4 is subjected to dewatering and classification by a sediment separating apparatus 5 comprising a vibrating sieve and a cyclone (step 102).

Next, after the cyclone excess of the earth and sand separation device 5 is temporarily stored in the raw water tank 21, the classification process is performed by the screw decanter 6, which is a centrifugal separator (step 103). The under part generated in the classification process is discharged as cake.

Next, the portion which has overflowed in 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, a pH adjustment tank
The pH is adjusted with, and then discharged into the original water area.

Next, the concentrated mud 8 in the concentration tank 7 settled by the sedimentation separation is once stored in the slurry tank 22, and a coagulant is added as required, and then dewatered by a filter press 9 which is a dehydrator. (Step 105). The under part generated in the dehydration treatment is discharged as cake.

The portion overflowed during the dehydration treatment is once stored in the drainage tank 10 and then stored in the inorganic coagulant tank 11 and the polymer coagulant stored in the polymer dissolution storage tank 12. Is added to cause coagulation and sedimentation in the square thickener 13, and the supernatant is neutralized in the pH adjustment tank 14 and discharged, and the coagulation and sediment is returned to the concentration tank 7 (step 106).

Here, as the inorganic coagulant, a sulfate band or polyaluminum chloride called PAC is used.
The polymer flocculant can be appropriately selected from commercial products produced from water-soluble polyacrylamide.

As described above, according to the method for treating dredged mud according to the present embodiment, not the entire amount of the overflow caused by the classification by the screw decanter 6 is dehydrated, but the overflow is stored in the concentration tank 7. Then, the concentrated mud 8 settled by the sedimentation is subjected to dehydration treatment. Therefore, the amount of dehydration treatment required by the filter press 9 is reduced by the dredging mud treatment previously developed by the present applicant. Method (Japanese Patent Laid-Open No. 9-155395)
It is possible to reduce the volume to 〜 1/10, and since the object to be dewatered is the concentrated mud 8, the object to be dewatered compared to the case where the overflow from the screw decanter is directly dewatered, That is, it is possible to increase the specific gravity of the concentrated mud 8, and the filter press 9
The efficiency of dehydration in the system is dramatically improved.

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

Next, an experiment was conducted to confirm the operation and effect of the method for treating dredged mud according to the present embodiment, and the outline thereof will be described below.

In the experiment, dredged mud having a specific gravity of soil particles of 2.6 was used, and the dredged mud was treated according to the above-described procedure. Table 1 shows the results.

[0026]

[Table 1]

In the table, ρ _SI indicates the specific gravity at the supply side of the screw decanter, ρ _SOF indicates the specific gravity at the overflow side, and C ₁ indicates the volume ratio of the concentrated mud to the overflow from the screw decanter. , C
₂ shows the volume ratio of the concentrated mud to the amount supplied to the screw decanter, respectively. The specific gravity of the concentrated mud does not depend on the specific gravity on the supply side of the screw decanter, but is about 1.16.
It became.

From the above results, the volume ratio C ₂ (volume of concentrated mud / volume supplied to the screw decanter), that is, the volume reduction rate before the dehydration treatment is 10.5 to 33.3% (1
/ 10 to 1/3). The specific gravity 1.16 before the dehydration treatment is the specific gravity ρ on the overflow side.
It turns out that it is higher than _SOF .

In the present embodiment, the portion overflowed in the classification treatment by the screw decanter 6 is directly placed in the concentration tank 7 for sedimentation and separation. However, an inorganic flocculant (PAC) or slaked lime is added to the overflow of the screw decanter 6. It may be added to promote sedimentation and separation.

[0030]

As described above, according to the method for treating dredged mud according to the present invention, it is possible to greatly reduce the amount of dewatering treatment in the step of performing dehydration treatment, and at the same time, to carry out dehydration treatment. Since the object to be concentrated is concentrated mud, the specific gravity of the substance to be dehydrated, that is, the concentrated mud, can be increased as compared with the case where the overflow component after the centrifugation step is directly dehydrated. The efficiency is dramatically improved.

[0031]

[Brief description of the drawings]

FIG. 1 is a flowchart showing a flow of a method for treating dredged mud according to the present embodiment.

FIG. 2 is an equipment configuration diagram for carrying out a method for treating dredged mud according to the present embodiment.

FIG. 3 is an equipment configuration diagram for implementing the dredging mud treatment method according to the embodiment.

[Explanation of symbols]

1 bottom mud 6 screw decanter (equipment for classifying by centrifugation) 7 thickening tank (equipment for sedimentation) 8 thickened mud 9 filter press (equipment for dewatering)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Mitsuteru Sumita 4-640 Shimoseito, Kiyose-shi, Tokyo F-term in Obayashi Corporation Research Laboratory Co., Ltd. 4D059 AA09 BE16 BE31 BE38 BE39 BE49 BE55 BE56 BK30 CA24 CA25 DA05 DA16 DA17 DB24

Claims (1)

[Claims] 1. Dredging of sediment in the sea, river, lake, marsh, etc., classification of the dredged mud by centrifugal separation, sedimentation and separation of the overflowed part by the classification, and sedimentation by sedimentation A method for treating dredged mud, wherein the concentrated mud is dewatered by a predetermined method.