JP2000288600A - Dehydration method of dredged bottom mud - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply and economically dehydrate medium- small-scale dredged bottom mud for a short time and to reutilize treated matter by dehydrating treated matter obtained by adding crushed old paper and a water-soluble polymeric substance to dredged bottom mud. SOLUTION: Crushed old paper and a water-soluble polymeric substance are together added to and mixed with dredged bottom mud or crushed old paper is added to and mixed with the dredged bottom mud and, if necessary, a divalent or trivalent metal salt is added to and mixed with the resulting mixture and the water-soluble polymeric substance is further added to and mixed with this mixture to dehydrate the bottom mud. Herein, dredged bottom mud has a sand and gravel removed corrected water content ratio of 250-500% and the content of clay occupied in an anhydrous solid is 20% or more and/or the ignition loss of the solid is 20% or more. Crushed old paper to be used is obtained by cutting old newspaper or an old magazine into a size of 20 mm2 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for dewatering dredged sediment with a high concentration obtained from relatively small and medium-sized lakes, rivers, and harbors while minimizing environmental impact. Regarding the processing method.

[0002]

2. Description of the Related Art Conventionally, as a method of treating bottom mud (hedro) obtained from lakes, marshes, rivers, ports, etc., dredged bottom mud is dredged with a dredger, and dredged bottom mud is placed in a pound surrounded by a dike, a sheet pile or the like. And drain the sediment under the sun by dripping the bottom sediment with a pump, and add a flocculant to this dredged bottom mud to flocculate. To reduce the volume by using a dehydrator. For small and medium-sized dredging, the above-mentioned solar drying method is often used. However, it takes a long time (1
Years or more), there is no place to make pounds, and even if it is sun-dried and de-fluidized, treated soil with sufficient strength cannot be obtained, making it difficult to reuse.

[0003] Further, it is preferable that the dredged bottom mud is originally coagulated and dewatered without being diluted. However, when the coagulant is added at a high concentration, there is a problem that the bottom mud becomes gel-like and cannot be dehydrated. In recent years, a dredging method capable of dredging at a much higher concentration than the conventional pump dredging (for example, a large-diameter negative pressure suction type high concentration dredging system) has been developed. As a result, without drying or dehydration, attempts have been made to solidify the whole amount with cement or a cement-based solidifying agent, but solidification by cement does not reduce at all, and there is concern about environmental pollution due to high alkali. There are problems such as things.

[0004]

SUMMARY OF THE INVENTION The present invention provides a dredged bottom that can easily and economically dewater small and medium-sized dredged bottom mud in the shortest possible time and recycle the processed material. An object of the present invention is to provide a method for dehydrating mud.

[0005]

In order to achieve the above object, a method for dewatering a dredged bottom mud according to the present invention comprises the steps of:
It is characterized in that crushed waste paper and a water-soluble polymer substance are added and mixed, and the resulting treated product is dehydrated. Further, the present invention is characterized in that a crushed waste paper is added to and mixed with the dredged bottom mud, and then a treated material obtained by adding and mixing a water-soluble polymer substance is dewatered. Further, the present invention provides a method for adding and mixing crushed waste paper to dredged bottom mud, then adding and mixing a divalent or trivalent metal salt, and further adding and mixing a water-soluble polymer substance. The obtained processed product is dehydrated.

[0006] The dredged bottom mud has a gravel removal corrected moisture content of not less than 250% and not more than 500%, and has a clay content in the anhydrous solid of not less than 20% and / or an ignition loss of not less than 20%. Can be targeted. Here, the gravel is a material in which the size of the particles contained in the dredged bottom mud is 75 microns or more, and the corrected water content excluding the gravel content is defined as the normal water content ((100−gravity content (% )) / 100). In addition, clay has a particle size of 5 microns or less contained in the dredged bottom mud. The size of the crushed waste paper is preferably 20 mm or less. The amount of the crushed waste paper added can be from (((gravel content removal corrected water content ratio) × 25) / (gravel content removal corrected water content ratio +40)) kg / ((gravel content removal corrected water content) per m ^{3 of} dredged bottom mud. Ratio x 100) / (gravity removal corrected water content ratio +40)) kg would be appropriate.

[0007] The water-soluble polymer substance is selected from the group consisting of gums or derivatives thereof, starch or derivatives thereof, sodium alginate, cellulose derivatives, and water-soluble synthetic polymer substances containing a carboxyl group. Species or a combination of two or more can be used.
The amount of the water-soluble polymer substance added is 1 m
³ , in the case of natural, 1.0-20 kg,
In the case of a semi-synthetic system, 1.0 to 15 kg can be used, and in the case of a synthetic system, 0.2 to 5.0 kg can be used.

[0008]

Embodiments of the present invention will be described below. The method for dehydrating a dredged bottom mud according to the present invention comprises the steps of: adding and mixing the crushed waste paper and the water-soluble polymer substance to the dredged bottom mud; or adding and mixing the crushed waste paper, and then mixing A divalent or trivalent metal salt is added and mixed according to, and a water-soluble polymer substance is further added and mixed.
It is performed by dehydration.

In the treatment method of the present invention, first, a crushed waste paper is added to the dredged bottom mud. The target sediment here is a high concentration of dredged sediment obtained from relatively small and medium-sized lakes, rivers, ports and the like. Its soil composition is, for example,
Sand 10%, Silt 40%, Viscosity 50%
It is such that the loss on ignition, which is rich in very fine soil particles and indicates the amount of organic matter, can reach 10 to 30%. In addition, the water content of the above-mentioned dredged bottom mud is 250 to 500% in terms of the corrected water content excluding gravel, and the clay content in the anhydrous solid is 20% or more and / or the ignition loss is 20% or more. It is preferred that Here, the gravel exclusion corrected water content ratio is a value obtained by dividing the normal water content ratio by ((100−grass content ratio (%)) / 100). Gravel (particle size of 75 microns or more) has almost no water absorption, so even if the normal water content is the same, depending on the level of the proportion of gravel in the dredged bottom mud, The free water in the sediment, that is, the substantial water content, varies greatly. For this reason, in the present invention, the above-mentioned gravel-grain exclusion corrected water content ratio is used as the water content ratio for the dredged bottom mud excluding the gravel content.

[0010] The dredged bottom mud having a water content ratio of less than 250%, excluding debris, has no or very little separated water even when dewatered, and has no merit in the dewatering step. on the other hand,
For dredged bottom mud having a water content of more than 500%, a general method of flocculation and separation, that is, a method of adding flocculant to make floc, and applying it to a dehydrator such as a filter press or belt press to dewater, is economical. There is no advantage to using waste paper. In addition, clay (grain size is 5
Containing less than 20% clay content in anhydrous solids, the content of which is less than 20% can be dehydrated only with divalent or trivalent metal salts and water-soluble polymer substances. There is no merit of using.

As used paper used in the present invention, for example, used paper having excellent water absorption, such as used newspapers, used magazines, used cardboards, used telephone books, and the like are used. Crushed waste paper has recently attracted attention as a litter for livestock, and has an excellent effect not found in other absorbent materials. That is, waste paper is crushed into dredged bottom mud having a gravel removal exclusion corrected water content of 250 to 500% and a clay content in the anhydrous solid of 20% or more and / or a loss on ignition of 20% or more. When the substance is added and mixed, water absorption proceeds within 1 to 3 minutes, and the fluidity of the dredged sludge is significantly reduced. On the other hand, other absorbents, for example, a water-absorbing polymer widely used in sanitary articles have a water-absorbing power, but a slip phenomenon between the polymers remains after water absorption, and the effect of improving the treated product is weak. Although natural minerals have an excellent water absorbency of bentonite, powdery products absorb sticky water when they absorb water, and crushed products are expensive and do not meet the purpose of the present invention. Good effects cannot be obtained even with cotton, straw, husk, sawdust, wood chips and the like.

The crushed waste paper is, for example, an old newspaper, old magazine, or the like cut into a square of 20 mm or less, and more preferably a square of 5 mm or more and 10 m or less.
Those cut to m squares or less are preferred. Crushed waste paper larger than 20 mm square is difficult to handle and is not preferred. In addition, it is not practical to make waste paper having a size of less than 5 mm square because of excessive cost. Amount of crushed waste paper, dredging mud 1 m ³ per ((gravel portion removal correction water content ratio × 25) / (gravel portion removal correction water content ratio +40))
It is preferably in the range of kg to ((gravity excluded exclusion corrected water content × 100) / (gravel exclusion corrected water content + 40)) kg.
With this amount of addition, the increase in dredged sludge after treatment is small.

Next, a divalent or trivalent metal salt is added and mixed as required. The case where a divalent or trivalent metal salt needs to be added is a case where the dredged bottom mud contains a large amount of organic matter and is in a strong reducing atmosphere. In the case of such dredged bottom mud, even if the used paper crushed material and the water-soluble polymer are added and mixed, they cannot be hydrophobized and cannot be dewatered. Therefore, by adding a crushed waste paper, adding a divalent or trivalent metal salt, and further adding a water-soluble polymer substance to be described later, hydrophobicity is removed and dehydration becomes possible. In addition, when the organic matter is small, but the clay content in the dredged bottom mud is very large, the amount of waste paper can be reduced by adding a divalent or trivalent metal salt, which is more economical. Processing may be possible.

The divalent or trivalent metal salt used in the present invention is preferably a divalent or trivalent water-soluble metal salt. 2
Trivalent or trivalent water-soluble metal salts include sodium sulfate, PA
C (polyaluminum chloride), calcium chloride, ferrous chloride, ferric chloride and the like. In addition, a divalent or trivalent metal salt can be used as long as it has a certain degree of solubility, even if it is not water-soluble like gypsum (calcium sulfate). The amount of the divalent or trivalent metal salt to be added is not particularly limited, but is preferably 0.3 to 10 kg in terms of anhydride per 1 m ^{3 of} dredged bottom mud. Here, in the case of a water-insoluble substance such as gypsum, it is converted into an anhydride of a water-soluble portion calculated based on the water solubility of the substance.

In the present invention, a water-soluble polymer substance is further added and stirred. By stirring for several minutes, the dredged bottom mud completely loses its fluidity and becomes an aggregated treated material. As the water-soluble polymer substance, gums or derivatives thereof, starch or derivatives thereof, sodium alginate, cellulose derivatives, at least one selected from the group consisting of water-soluble synthetic polymer substances containing a carboxyl group, or It is a combination of two or more. Examples of the water-soluble synthetic polymer material containing a carboxyl group include, for example, sodium polyacrylate or a derivative thereof, a copolymer of acrylic acid or a salt thereof and acrylamide, a partially hydrolyzed product of an acrylamide polymer, maleic acid or a mixture thereof. Copolymers of salts and vinyl acetate, copolymers of itaconic acid or its salts and acrylamide, and the like.

The amount of the water-soluble polymer substance to be added is 1.0 to 20 in the case of a natural system per 1 m ^{3 of} dredged bottom mud.
kg, preferably 2.0 to 10 kg. In the case of a semi-synthetic system, 1.0 to 15 kg, preferably 2.0 to 15 kg
10 kg. In the case of a synthetic system, 0.2 to 5.
0 kg, preferably 0.5 to 3.0 kg. Examples of the natural water-soluble polymer include gums or derivatives thereof, starch or derivatives thereof, and sodium alginate. The semi-synthetic water-soluble polymer includes, for example, CMC and other cellulose derivatives. Further, the synthetic water-soluble polymer, for example,
Water-soluble synthetic polymer substances containing a carboxyl group.

In the present invention, finally, the aggregated dredged soil is dewatered. As a dehydration method used in the present invention, any method can be adopted as long as it is a method of dehydrating a solid containing water, and is not particularly limited. Dehydration methods can be broadly divided into those using mechanical dehydrators,
Some are based on the in-situ dewatering method. As the mechanical dehydrator, the type in which the aggregated dredged soil has low fluidity and is spread thinly on the surface of the filter cloth such as a filter press or a belt press and pressurized is not preferable. It is preferable to use a dehydrator that squeezes and dehydrates a solid substance having a high water content. As the in-situ dewatering method, it is preferable to use a vacuum dewatering method applying a well-point method conventionally used as a soft ground improvement method. As a typical example of the vacuum dewatering method, there is the Arpass CVC method (Maruyama Kogyo Co., Ltd., Japanese Patent Application Laid-Open No. 9-151448).

The present invention relates to small and medium-sized rivers, lakes, marshes, dams,
It provides an optimal treatment method for dredging in harbors and the like. As a representative example, a method will be described in which a medium-sized lake or marsh is dredged using a clamshell, and the resulting high-concentration bottom mud is improved by a batch-type mixer and dewatered by a screw press.

The bottom mud removed by the clamshell is generally sent to a pit on the ground after dust is removed by a vibrating sieve. 1-3m bottom mud by hose pump from pit
^It is sent to the batch type paddle mixer of No. ³ and the required amount of waste paper is first added and mixed. When the bottom mud contains a large amount of organic substances, the above-mentioned divalent or trivalent metal salt is added and mixed in an amount of about 0.3 to 10 kg / m ^{3 in} terms of pure content. Further, a required amount of a water-soluble polymer powder is added, and the mixture is stirred well.
Finally, the aggregated dredged soil is dewatered by a screw press. Thereby, the dredged bottom mud can be improved into a reusable treated product.

In the present invention, the high-concentration dredged soil is mixed with a water-absorbing material consisting of crushed waste paper in a first stage, and a divalent or trivalent metal salt is added and mixed as required in a second stage. 3 steps (2nd step if divalent or trivalent metal salt is not used)
The water-soluble polymer substance is added and mixed. Dehydration cannot be performed only by adding and mixing the water absorbing material in the first stage. Also,
The dehydration cannot be performed only by adding and mixing the water-soluble polymer substance of the third step (the second step in the case where the divalent or trivalent metal salt is not used) or only the metal salt of the second step. In the combination of the divalent or trivalent metal salt of the second stage and the water-soluble polymer substance of the third stage (the second stage when the divalent or trivalent metal salt is not used), the clay content is approximately 20%. % Of dredged soil can be treated. By adding and mixing waste paper and two water-soluble polymer substances, or waste paper and two or three-valent metal salts and three water-soluble polymer substances, the dredged soil with a clay content of about 20% or more is dehydrated. It is possible and the dewatered cake can be reused.

A major feature of the present invention is that high-concentration bottom mud can be dewatered with a simple apparatus at low cost. Conventional dehydration treatments have been performed on relatively low-concentration bottom mud, and high-concentration sediments have not been very successful. However, in the present invention, most of the water from the high-concentration bottom mud is absorbed by the waste paper, and as a result, the water content of the bottom mud is greatly reduced, thereby making the soil particles hydrophobic by the water-soluble polymer substance. Is being planned. For example, 75 g of water is present in 100 g of bottom mud having a water content of 300%. When 6 g of waste paper is added to this, the waste paper has a water absorption capacity 10 times that of the weight ratio.
Absorb g of water. Therefore, the residual water content of the bottom mud is 15 g, and apparently the water content of the bottom mud is reduced to 60%. Depends on soil quality, but water content is generally 10
Regardless of the amount of the water-soluble polymer substance added to the bottom mud exceeding 0%, it is only dissolved in the water in the bottom mud to form a paste, and does not become hydrophobic. However, the surface becomes hydrophobic when the water content falls below 100%, and the appearance becomes dry, and dehydration occurs when a force is applied.

According to the present invention, when the water-soluble polymer substance is added to the bottom mud by utilizing the water absorption of the waste paper, the apparent water content ratio of the dredged bottom mud is reduced to the extent that it can be made hydrophobic. It has special features. In the past, wastewater and sludge treatment used waste paper as a dewatering aid to improve the dehydration of aggregates.However, the apparent moisture content of high-concentration sludge was reduced, and water-soluble polymer substances were used. There have been no reports of any use cases aimed at making the bottom mud hydrophobic.
Conventionally, high-concentration bottom mud has been diluted and reduced in concentration, and then coagulated with a coagulant, followed by dehydration.However, by diluting, the processing amount increases, and as a result, a large-scale processing apparatus must be provided. Did not get. For example, a water content of 300%
Assuming that the processing is carried out by diluting to 00%, the processing amount is approximately tripled. ADVANTAGE OF THE INVENTION According to this invention, dehydration is attained with a compact apparatus, and it becomes possible to employ | adopt the dehydration method also for small and medium rivers and lakes.

Smell becomes a problem in the treatment of sludge, but used paper has an action of adsorbing bad smells, which leads to a reduction in bad smell problems. The dehydrated cake is neutral and granular, rich in air permeability and water permeability, and becomes an optimum vegetation soil if nutrients are added as necessary. Normally, waste paper is subjected to delignification treatment and contains easily decomposable carbohydrates, so that it is easily composted. Organic matter in sludge also has a positive effect on composting. It is also worth mentioning that it is inexpensive, abundant, and contributes to the expansion of the use of waste paper that has become too small recently. Further, in the present invention, a method in which a waste paper crushed material, a divalent or trivalent metal ion, and a water-soluble polymer, if necessary, are added in advance by mixing or mixing at the site, or simultaneously added is also used. Improvements can be made, but the improvement effect is slightly reduced.

[0024]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 Sediment of lake water dredging with a water content of 346% (water content ratio excluding sand and gravel correction 368%, clay content 43.2%, loss on ignition 27%)
Take 60 liters into a batch type twin-screw paddle mixer (manufactured by Taiheiyo Kiko), add 3.0 to 4.2 kg of crushed waste paper (size 10 mm or less, trade name: Anshin-kun) manufactured by Japan Creativel Co., Ltd., and add 1 minute. Mixed. Next, 0.5 liter of a polyaluminum chloride aqueous solution (Al ₂ O ₃ 10%) was added and mixed for 1 minute. Subsequently, Toa Gosei Co., Ltd.'s acrylamide and acrylic acid copolymer (Part No. T-14)
0.06 kg) was added and mixed for another 1 minute. The treated product was finely agglomerated. This was subjected to a screw press dehydrator (SHX-200) manufactured by Fukoku Kogyo, and subjected to 2 rpm
And dehydrated. Table 1 shows the water content and strength of the processed product (dehydrated cake) and the properties of the separated water.

Example 2 Lake dredged bottom mud with a water content of 286% (water content ratio excluding gravel content: 304%, clay content: 28.9%, ignition loss: 19%) 6
1. Take 0 liters into a batch-type 2-axis paddle mixer (manufactured by Taiheiyo Kiko), and use Japan Creative Corporation's waste paper crushed product (size 10 mm or less, trade name Anshin-kun).
4-3.6 kg was added and mixed for 1 minute. Next, Toa Gosei's acrylamide and acrylic acid copolymer (Part No. T-
140) was added and mixed for an additional minute. The treated product was finely agglomerated. This was subjected to a screw press dehydrator (SHX-200) manufactured by Fukoku Kogyo to obtain 2
Dehydrated at rpm. Table 1 shows the water content and strength of the processed product (dehydrated cake) and the properties of the separated water.

Comparative Example 1 60 liters of lake water dredging bottom mud having a water content of 346% (corrected water content excluding gravel content: 368%, clay content: 43.2%) was placed in a batch type twin-screw paddle mixer (manufactured by Taiheiyo Kiko). ,
Japan Creative's waste paper crushed product (size 1
6 mm (0 mm or less, trade name: Anshin) was added and mixed for 1 minute. Although the obtained treated product apparently lost fluidity, even when dewatered in the same manner as in the examples, the separated liquid was muddy and no dehydrated cake was obtained.

COMPARATIVE EXAMPLE 2 60 liters of lake water dredging bottom mud having a water content of 346% (corrected water content excluding gravel content: 368%, clay content: 43.2%) was placed in a batch type twin-screw paddle mixer (manufactured by Taiheiyo Kiko). ,
0.06 to 0.18 kg of acrylamide / acrylic acid copolymer (product number T-140) from Toa Gosei Co., Ltd. was added and mixed for 1 minute. The obtained processed product became sticky and could not be dehydrated at all.

[0028]

[Table 1]

As shown in Table 1, in both Examples 1 and 2, the properties before dehydration were agglomerated and were in a favorable state. The water content ratio was reduced to 70 to 87% in Example 1 and to 84 to 97% in Example 2, and the cone index was not penetrable. The capacity of the dewatered cake was reduced by about 45% in Example 1 and about 40% in Example 2 as compared with the capacity of the original bottom mud. In both Example 1 and Example 2, the turbidity of the separated water was slight,
Was also neutral. On the other hand, Comparative Example 1, in which only used paper was added,
In Comparative Example 2 to which only the water-soluble polymer was added, and no water-soluble polymer was added, none of the samples became dehydrated.

[0030]

As described above, according to the treatment method of the present invention, it is possible to dewater the dredged bottom mud without adversely affecting the environment, and to obtain an aggregated hydrophobic cake. According to the present invention, waste paper and water-soluble polymer, by using a small amount of inorganic metal salt as needed, it is possible to perform dehydration treatment without dilution, the apparatus can be simplified,
Can be easily constructed.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shuichi Ogura 1-7-5 Hatagaya, Shibuya-ku, Tokyo F-term (reference) 4D059 AA09 BE26 BE55 BE56 BE60 BE61 BJ03 BJ07 CC01 DA07 DA16 DA17 DA24 DB08 DB11 DB14 DB16 DB19 DB20 DB24 DB29 DB34 EB01 EB11

Claims (8)

[Claims] 1. A method for dehydrating a dredged bottom mud, comprising adding and mixing a crushed waste paper and a water-soluble polymer substance to the dredged bottom mud, and dehydrating the resulting treated product. 2. A dredged bottom mud characterized in that a crushed waste paper is added to and mixed with the dredged bottom mud, and then a treated product obtained by adding and mixing a water-soluble polymer substance is dewatered. Dehydration treatment method. 3. A dredged bottom mud is obtained by adding and mixing crushed waste paper, then adding and mixing a divalent or trivalent metal salt, and further adding and mixing a water-soluble polymer substance. A method of dehydrating a dredged bottom mud, comprising dehydrating a treated material. 4. The dredged bottom mud has a gravel removal corrected moisture content of not less than 250% and not more than 500%, and has a clay content in the anhydrous solid of not less than 20% and / or an ignition loss of not more than 20%. % Or more. 5. The method according to claim 1, wherein the size of the crushed waste paper is 20 mm or less. 6. The amount of the crushed waste paper added per 1 m ^{3 of} dredged bottom mud is ((gravure removal corrected water content ratio × 25) /
((Grass and Grains Removal Corrected Moisture Content +40)) kg to (((Grases and Grains Removal Corrected Moisture Content Ratio x 100))
40)) in the range of 1 kg.
The method for dehydrating a dredged bottom mud according to any one of claims 5 to 5. 7. The water-soluble polymer substance is selected from the group consisting of gums or derivatives thereof, starch or derivatives thereof, sodium alginate, cellulose derivatives, and water-soluble synthetic polymer substances containing a carboxyl group. 2. The method according to claim 1, wherein the at least one kind comprises at least one kind.
7. The method for dehydrating a dredged bottom mud according to any one of claims 6 to 6. 8. The amount of the water-soluble polymer substance added is 1.0 to 2 in the case of a natural type with respect to 1 m ^{3 of} dredged bottom mud.
0 kg, 1.0-15 kg in case of semi-synthetic system,
The method according to any one of claims 1 to 7, wherein the weight is 0.2 to 5.0 kg in the case of a synthetic system.