JPH09206800A - Treatment of water-area bottom mud - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obviate the need for the land disposal place for dredged bottom mud by adding powdery zeolite, cement, inorg. flocculant and high molecular flocculant to the bottom mud from the water area such as lake and sea, forming the pellet in an agitating and granulating tank and depositing the pellet on the water bottom. SOLUTION: The anaerobic bottom mud 1 also called HEDORO depositing on the bottom of a lake, etc., is pumped up into an agitating and granulating tank 6, and powdery zeolite 2, cement 3 or aluminous inorg. flocculant 4 and high molecular flocculant 5 are added. An appropriate revolving flow is then given, hence the contents of the tank 6 consisting essentially of the bottom mud 1 are flocculated to form a high-strength globular pellet 7, and the pellet is thrown into the water, deposited and accumulated on the water bottom. Consequently, dissolved oxygen is easily diffused into the void between the packed pellets 7, the pellet 7 surface is kept aerobic, the org. bottom mud is decomposed by the methane fermentation in the pellet, and gaseous methane and carbon dioxide are formed.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the prevention of eutrophication in water bodies such as lakes, marshes, seas and rivers, and more particularly to the treatment of sediment in said water bodies.

[0002]

2. Description of the Related Art The problem of eutrophication of water bodies such as lakes, marshes, seas, and rivers is becoming more and more apparent. The mud deposited on the bottom of the water area, that is, the organic matter contained in the bottom mud anaerobically decomposes and consumes oxygen, so that nutrient salts containing phosphorus, nitrogen and the like are eluted from the bottom mud. Therefore, even if the inflow load to water bodies such as lakes, seas, and rivers is reduced by measures such as wastewater treatment and change of flow paths, in these water bodies, the enrichment of nutrient salts containing phosphorus, nitrogen, etc. from bottom mud Due to the nutritional phenomenon, blue water and red tide are generated, and the water area is polluted.
A similar problem has occurred in fishponds. In addition, a large amount of leaves accumulate on dam lakes of rivers, causing leaves to rot,
In many cases, the bottom of the dam lake has become sludge, and it is extremely difficult to reduce the weight of this sludge and dispose of it.

Conventionally, as a measure against eutrophication in the above-mentioned water area, a method in which the polluted bottom mud is dredged and removed to the outside of the system has been the mainstream. That is, the conventional method for treating bottom mud is to dispose of the dredged bottom mud on land. After dewatering the dredged bottom mud, the dewatered cake is landfilled for disposal. Such disposal methods were adopted. However, these conventional techniques have the following problems. A large area of land is required for landfill disposal, but securing land disposal is extremely difficult. In addition, studies are being made on the reuse of dredged bottom mud for soil improvement materials, cultivation soil, and civil engineering materials, but the demand has not been apparent and has continued to increase. When the dredged bottom mud is dewatered, a large amount of separated water is generated. However, since the separated water contains phosphorus and nitrogen which cause eutrophication, treatment of the separated water is a major problem. recently,
As measures for eutrophication of water bodies, in addition to dredging removal of polluted bottom mud, phosphorus and nitrogen elution measures such as sand cover are being considered.

[0004]

Since oxygen transport from the upper layer water is extremely small in the bottom mud, anaerobic acid fermentation of organic substances, sulfate reduction, and iron reduction actively proceed in the bottom mud.
As a result, ammoniacal nitrogen or phosphorus is solubilized and becomes an elution source. Further, the sulfide generated by the sulfate reduction promotes release of phosphate ions from iron phosphate. further,
The acid fermentation of the organic matter causes a decrease in the pH of the interstitial water and promotes the solubilization of phosphorus compounds. Based on such a background, the present invention fundamentally improves the physicochemical and biological environment of the bottom mud of the anaerobic water area, revives the bottom environment, and the bottom of nutrient salts. It is to provide a new technology capable of suppressing elution from mud to upper water. Another object of the present invention is to provide a novel method for utilizing bottom mud, and to provide a method for treating bottom mud that does not require landfill disposal sites on land and does not generate dehydrated separated water.

[0005]

The above-mentioned object of the present invention can be achieved by the method for treating aquatic bottom mud of the present invention. That is, (1) powdered zeolite, cement, an inorganic coagulant and a polymer coagulant are added to bottom mud from a body of water such as a lake, sea, or river, and a pellet is formed in a stirring granulation tank, and the pellet is placed on the bottom of the water. It is a method of treating bottom mud in water bodies, which is characterized by sedimentation.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A processing flow of a method for treating water bottom mud of the present invention is shown in FIG. 1, and the present invention will be described below with reference to FIG. In FIG. 1, an anaerobic bottom mud 1, also called sludge, deposited at the bottom of lakes, seas, and rivers is pumped up into a stirring granulation tank 6, and powdered zeolite 2, cement 3, iron or aluminum system is used. After adding the inorganic coagulant 4 and the polymer coagulant 5 in (1), when an appropriate swirling flow is applied, the contents mainly composed of the bottom mud 1 in the stirring granulation tank 6 are agglomerated, and spherical pellets having high strength 7 is generated. When these pellets 7 are put into water, they settle down rapidly and settle and accumulate on the bottom of the water. The amount of the powdered zeolite, cement, inorganic coagulant and polymer coagulant added is appropriately determined depending on the properties of the bottom mud, but the preferable range of addition is as shown in Table 1 below.

[0007]

[Table 1]

The operation of the pellets settled and deposited on the water bottom will be described below. When they are deposited on the water bottom, dissolved oxygen is likely to diffuse into the filling voids between the pellets, and the pellet surface is likely to be maintained aerobically. Recently, in order to prevent the nutrient salts from leaching from the sludge layer, so-called cover sand is sprayed on the sludge layer. However, when the pellets of the present invention are deposited on the sludge layer, the same as the cover sand is obtained. The effect of is also exhibited. The sedimented organic bottom mud is anaerobic. Therefore, when pellets containing methane bacteria that are naturally present in the bottom mud are deposited on the water bottom, the organic bottom mud is produced by the methane fermentation action of the methane bacteria immobilized inside the pellets. Is decomposed, methane gas,
Generates carbon dioxide. In the conventional water area where the sludge layer is accumulated, methane fermentation occurs after the acid fermentation of the organic matter progresses, so that the pH of the sludge layer is biased to the acidic side due to the advanced acid fermentation. Since the methane bacterium has high activity in the neutral region, the activity of the methane bacterium stops when the pH of the sludge layer is biased to the acidic side. However, in the present invention, since the alkaline cement particles are confined inside the pellets, the pH is not excessively lowered by the acid fermentation, and the methane acid fermentation effectively proceeds. The above is the action of the pellets settled and deposited on the water bottom.

Among the additives added with the above-mentioned bottom mud, the cement not only keeps the inside of the pellet alkaline but also has the function of solidifying the pellet. The pellets at the time of flowing out from the agitation granulation tank have such strength that they can be broken by picking them with fingers, but when left in water, they are solidified by the action of cement and the strength is remarkably increased. The term "pellet" as used in the present invention means, unlike flocs, a dense, slightly spherical, granulated substance that can be picked up from water by pinching with tweezers. On the other hand, the flock cannot be picked up by tweezers, but is a fluffy cotton-like thing.

Inside the pellets, in addition to the cement added to the bottom mud, powdered zeolite, an inorganic coagulant and a polymer coagulant are enclosed. Among these additives, powdered zeolite adsorbs and removes ammonia. In addition, an inorganic coagulant such as iron hydroxide or aluminum hydroxide removes phosphorus and has the effect of increasing the strength of pellets.
(Phosphorus does not elute from the inside of the pellet because it binds to calcium, iron or aluminum and becomes insoluble.)

As the cement, Portland cement may be used, but an early-strength cement such as alumina cement or jet cement is more preferable because it solidifies the pellet in a short time. As the inorganic coagulant, aluminum sulfate,
Materials known in the field of water treatment such as polyaluminum chloride, ferric chloride, and ferric polysulfate may be applied. As the polymer flocculant, various known commercially available polymers can be applied. Polymers effective in forming the pellets of the present invention have a molecular weight of 10
Polymers of the polyacrylamide type of more than 1,000,000 are suitable. When a cationic polymer and an anionic polymer are used in combination, a pellet having higher strength can be formed. As the stirring and granulating tank, an apparatus already developed by the applicant of the present invention and a product name of Volte Peretta can be preferably used. Details of this agitated underwater granulation apparatus are described in, for example, Reference: Hedro 2
No. 3, pp. 58-64, published in 1982 by the Japan Sediment Purification Association.

[0012]

EXAMPLE A verification test of the treatment of the marine sediment of the present invention was conducted according to the treatment flow of FIG. Example 1 2 wt% of powdered zeolite and 5 wt% of early-strength cement were added to bottom mud (mud content 8%, phosphorus ion 10.5 mg / liter, ammonia 8.1 mg / liter) collected from Lake K, Ibaraki Prefecture. In addition, 1000 mg / liter of polyaluminum chloride (PAC) as an inorganic coagulant and 250 m of anionic polyacrylamide as a polymer coagulant
As a result of adding g / l and supplying to a stirring granulation tank (liquid retention time 6 minutes), pellets (bottom particle diameter 2 to 4 m) in which bottom mud SS, zeolite, cement and aluminum hydroxide are integrated
m) was formed. 30 cm of this pellet in the column
It was deposited, filled with tap water for 2 m, and left for 1 year. One year later, water was sampled from a position 10 cm above the bottom mud layer and analyzed for phosphorus and ammonia. As a result, the phosphorus concentration was 1.1 mg /
The liter and the ammonia concentration were 1.8 mg / liter. Also, the height of the pellet decreased by 3 cm after one year. Collect air bubbles rising to the surface of the column regularly,
Qualitative analysis with a detector tube revealed methane and carbon dioxide. The pH of the pore water in the pellet packed bed is 6.7,
It was suitable for the activity of methane bacteria.

[0013]

According to the method for treating bottom mud of the present invention, (i) the dredged bottom mud is prepared by adding powdered zeolite, cement, iron- or aluminum-based inorganic coagulant and polymer coagulant having various functions. Since it is made into pellets and returned to the bottom of the water area again, the land disposal site of the dredged bottom mud is unnecessary. (Ii) In the pellets returned to the bottom of the water area, the organic matter in the bottom mud is decomposed and reduced by methane fermentation. (Iii) The pellets returned to the bottom of the water body can suppress the elution of phosphorus and ammonium from the bottom mud. (Iii) Since it is not necessary to dehydrate the dredged bottom mud, de-separated water does not occur and the separated water treatment is unnecessary.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a flow of a treatment facility for sludge in a water area according to the present invention.

[Explanation of symbols]

 1 Bottom Mud 2 Powder Zeolite 3 Cement 4 Inorganic Flocculant 5 Polymer Flocculant 6 Stirring Granulator 7 Pellets

Claims (1)

[Claims] 1. A powder mud, cement, an inorganic coagulant and a polymer coagulant are added to bottom mud from water bodies such as lakes, seas and rivers to form pellets in a stirring granulation tank, and the pellets are placed on the bottom of the water. A method for treating bottom sediment in a water area, characterized by depositing.