JPH11235600A - Method for reforming bottom mud - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method for reforming bottom mud without need for a large disposal area, without causing such a trouble as the disposal of separated water and by which the anaerobic state of the water bottom is changed into an aerobic state to restore the water bottom, and the elution of nutrient salts into the upper water from bottom mud is prevented. SOLUTION: The bottom mud 2 drawn up from the lakes, marshes, sea, etc., or the bottom mud 2 increased in SS concn. by a high molecular weight flocculant 6 in a solid-liq. separating means is admixed with water galss 4 and acid 5 and gelled, and the gell 11 is deposited on the water bottom. The drawn up bottom mud 2 is preferably admixed with an aluminous or ferrous inorg. flocculant 9 and temporarily flocculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reforming bottom mud, and more particularly, to a method for reforming bottom mud deposited on the bottom of a closed water area.

[0002]

2. Description of the Related Art Water flows in lakes, marshes, seas, rivers, etc. are poor.
There are not a few water bottoms where sludge is deposited.
In such closed water bodies, organic substances often consume oxygen by anaerobic decomposition, and nutrients (phosphorus, nitrogen) are also eluted and eutrophication occurs. For example, in waters where fish such as hamachi are cultivated, food left over by the cultivated fish sediments on the bottom of the water. When these settle, they rapidly become sediment. The water that flows into the water area, by purifying it in advance, can prevent the influx of nutrients from the outside, but putrefactive substances containing nitrogen and phosphorus accumulate in the sediment, and eventually elute If it comes, the occurrence of blue-green algae and red tide is inevitable. In addition, a large amount of fallen leaves are deposited on dam lakes (for example, Kurobe Dam), which rot and become muddy on the bottom of the lake.

Conventionally, as a countermeasure for preventing the occurrence of blue water and red tide, a method of dredging and removing septic bottom mud and removing it from the system has been the mainstream. For example, rotting mud is dredged and landfilled on land. After dewatering the dredged mud, it is caked and landfilled on land. Alternatively, a method has been adopted in which the bottom mud layer is covered with a large amount of sand (sand covering) to prevent the elution of nutrients from the putrefactive bottom mud into the water area.

[0004]

However, methods for treating and disposing of such bottom mud have many difficulties. Landfill requires a large landfill site. However, there is a problem that it is extremely difficult to secure such a vast landfill on land. Although studies have been conducted to reuse the dredged bottom mud as soil improvement material, cultivation soil, and civil engineering material without landfill disposal, the actual problem has been stalled because sufficient demand has not been realized. I have. In addition, there is a problem that a large amount of sand is required for covering sand in a wide area of water and the cost is high.

[0005] In order to solve such problems, the present invention does not require a vast disposal site, does not cause a difficult problem of disposal of separated water, and reduces the bottom of the anaerobic water area. It is an object of the present invention to provide a new method of reforming bottom sediment that can be changed to an aerobic state to revive the environment of the water bottom and suppress elution of nutrients from the bottom mud into the upper water.

[0006]

In order to solve the above problems, the present invention employs the following means. (1) Water glass and an acid are added to the bottom mud pumped from a lake, a marsh, the sea, or the like or the bottom mud whose SS concentration is increased by solid-liquid separation means to cause gelation. A method for reforming bottom mud, comprising depositing on the water bottom. (2) The method for modifying bottom mud as described in (1) above, wherein an aluminum-based or iron-based inorganic coagulant is added to the collected bottom mud.

[0007] Even if the collected bottom mud is separated into solid and liquid, if it is returned to the bottom without adding water glass and acid, the bottom is again atomized and the water bottom returns to its original state. However, if anaerobic bottom mud fine particles can be converted into strong coarse particles such as sand by an extremely simple operation, their particle properties,
The physicochemical and biological conditions are fundamentally improved and the elution of nutrients can be suppressed. The environment at the bottom of the water changes from an anaerobic state to an aerobic environment in which coarse particles are deposited.

[0008]

Embodiments of the present invention will be described below, but the present invention is not limited thereto. FIG. 1 is a schematic diagram showing an example of the flow of the method for reforming bottom mud according to the present invention. FIG.
The present invention will be described with reference to FIG. The bottom mud 2 deposited on the water bottom 1 of the sea, river, lake, etc. is pumped up and introduced into the gelling tank 3. A water glass 4 and an acid 5 are added to the gelling tank 3 into which the solid content has been introduced, and the mixture is stirred so that the acid-alkali property becomes substantially neutral. This causes the silica of the water glass 4 to undergo a polymerization reaction and instantaneously gel. The reason why the bottom mud is gelled is that the silicic acid in the water glass 4 is polymerized to form a three-dimensional structure.

The addition amount of the water glass 4 is determined by adding the water glass 4 to silicic acid (Si
2-5% (w / v, volume of bottom mud) in terms of weight in terms of O ₂ )
Is appropriate. If the added amount of the water glass 4 is too small, gelation does not occur or the gel strength becomes too weak, which is not preferable. On the other hand, if it is too much, it is not preferable because it leads to meaningless cost increase. The acid 5 is added until the mixture of bottom mud and water glass reaches a neutral region, preferably at a pH of about 5-8. This may increase the gelation rate.

[0010] Pumped bottom mud SS (insoluble solid component)
The concentration is higher as the amount of inorganic matter in the bottom mud is larger, and lower as the amount of organic matter is larger. Usually, it is about 3 to 15% by weight. If the SS concentration of the collected bottom mud is as low as less than about 5 wt%,
It is preferable to add the polymer flocculant 6 to coagulate the bottom mud, separate it into floc and water with, for example, a screen 7 having a mesh size of about 2 mm, increase the solid content of the bottom mud, and introduce it into the gelling tank 3. If the bottom mud SS concentration is low, it is preferable to gel the floc once aggregated with water glass since the required amount of water glass is reduced. Examples of the polymer flocculant 6 include a polyacrylamide polymer flocculant.

When the polymer flocculant 6 is added, if the inorganic flocculant 9 is added first and then the polymer flocculant 6 is added, a floc is formed, which makes solid-liquid separation easier. As the inorganic coagulant 9 to be added to the bottom mud, for example, an aluminum-based or iron-based inorganic coagulant is preferable. Examples of the aluminum-based coagulant include aluminum sulfate and polyaluminum chloride. Examples of the iron-based coagulant include ferric chloride and ferric polysulfate. When the inorganic coagulant 9 is used in combination with the polymer coagulant 6, the phosphate ions may be chemically insolubilized and the phosphate ions in the sediment may be more firmly fixed. In this case, the present inventors have found that phosphate ions are not eluted from the gel particles at all.

The gelled bottom mud is preferably crushed by a crusher 10.
Crushed to a particle size of 5 to 20 mm to obtain pebble-like particles composed of the coarse-particle gel 11, which is again deposited on the water bottom. If the coarse particulate gel 11 is used, it can be quickly settled even if it returns to the original water bottom. Even though it contains anaerobic sediment fines, it has been transformed into a tightly confined state within the gel. Almost no eutrophication-causing substances such as phosphorus and nitrogen elute even when deposited on the water bottom. Further, the granular gelled material can be used as it is for covering unmodified bottom mud with sand.

[0013] As a method of concentrating the collected bottom mud,
Instead of using a polymer flocculant and screening together,
Solid-liquid separation means such as a centrifuge can also be applied. In this case, it is not necessary to form a large floc, and there is also an effect that the addition of the polymer flocculant can be omitted.

[0014]

EXAMPLES Examples will be described below, but the present invention is not limited to these examples. [Example 1] Sediment was pumped up from Lake K in Ibaraki Prefecture with an airlift pump, and the water quality was measured. The SS concentration was 52 g / liter, the oxidation-reduction potential was -330 mV, the odor was very anaerobic and putrefaction odor was observed, the SS particle size was several to several tens of microliters, and the phosphate ion concentration was 2.4 mg / liter. When a polyacrylamide polymer flocculant was added to the pumped bottom mud at 1 wt% per SS and stirred, large flocs were quickly formed.
Then, when a wedge wire screen having a mesh size of 2 mm was used, flocs and water could be easily separated. The SS concentration of the obtained screened sediment was about 9%. pH
Was 8.1.

Water glass was added to the thus obtained sediment separated mud so as to have a concentration of 4% as SiO ₂ , and sulfuric acid was further added to adjust the pH to 6, and after 2 minutes, the whole sediment became firm. It gelled. When this gel was crushed by a rotary blade crusher, a coarse particulate gel having a particle size of about 10 mm was obtained. The gel particles thus obtained were deposited in a thickness of 30 cm on the bottom of a column at a depth of 2 m filled with tap water and allowed to stand for 10 months. Ten months later, one of the gel deposits
Water was sampled from the top of 0 cm, and the phosphorus concentration in that portion was analyzed.
At a concentration of 0.11 mg / liter, it was found that very little phosphorus was eluted from the gel particles. The redox potential of the gel deposit was also aerobic with +12 mV. Initially, it was found that the bottom mud that had a rotten odor and a hydrogen sulfide odor changed to odorless as a result of this treatment.

[0016]

According to the present invention, since the bottom mud is gelled and settled on the water bottom, a vast disposal site is not required, and the bottom of the anaerobic water area is changed to an aerobic state. It revives the environment on the bottom of the water and can also suppress the elution of nutrients from the bottom mud into the upper water. The operation is very simple and can be performed at low cost. The effect is great if the anaerobic bottom mud fine particles are converted into coarse particles having high strength such as sand.
Since the bottom mud fine particles themselves are converted into particles such as sand using the bottom mud itself, it can also be used for covering unmodified bottom mud. The anaerobic bottom mud on the water bottom can be maintained in an aerobic state for a long time, and the elution of nutrients can be suppressed. Sand for covering sand, which has been required in the past, becomes unnecessary.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a method for reforming bottom mud according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Water bottom 2 Bottom mud 3 Gelation tank 4 Water glass 5 Acid 6 Polymer coagulant 7 Screen 8 Separation water 9 Inorganic coagulant 10 Crusher 11 Coarse-particle gel

Claims (2)

[Claims] 1. A method of adding water glass and an acid to a bottom mud pumped from a lake, a sea or the like, or a bottom mud having an increased SS concentration by solid-liquid separation means, to form a gel. A method of improving bottom sediment, comprising depositing a compound on a water bottom. 2. The method according to claim 1, wherein an aluminum-based or iron-based inorganic coagulant is added to the collected bottom mud.