JPS6322876B2 - - Google Patents

Description

[Detailed description of the invention]

In recent years, eutrophication in stagnant water bodies such as lakes, oceans, and rivers has become a serious social problem. The main causes of eutrophication are thought to be nutrient salts or organic matter, but phosphorus is said to be the limiting factor for eutrophication. As measures to prevent eutrophication, it is important to remove nutrients and organic matter that flow into water bodies, and it is also important to prevent the elution of nutrients accumulated in the bottom sludge in water bodies and to remove this eluted phosphorus. This is one of the countermeasures. Countermeasures against nutrient salts in the bottom sludge include dredging the bottom sludge, coating the bottom sludge, and inactivating the nutrient salts with chemicals, but dredging the bottom sludge requires a large amount of cost to remove the bottom sludge. At the same time, the treatment and disposal of the removed bottom sludge has become a difficult problem. Pharmaceutical inactivation of nutrients is mainly due to Al
There is a method of directly adding salt to water bodies, but problems arise due to the large amount of chemicals used and the impact of these chemicals on the ecosystem. Bottom sludge is coated with fly ash, sand, plastic sheets, etc., but sand and plastic sheets have little effect on preventing the elution of nutrients, while fly ash is effective in preventing the elution of phosphorus. However, over a long period of time, air bubbles generated from the bottom sludge destroy the flyash layer, causing leaching of nutrients and organic matter. Furthermore, since fly ash has a slow sedimentation rate, it takes a long time to form a layer that covers the bottom sludge, which conversely becomes a factor in the pollution of water bodies. Furthermore, even if the phosphorus removal ability of this flyash decreases, it is difficult to recover and regenerate it.
There is no other way than to add it again. The present invention solves the above-mentioned problems and relates to a method for extremely efficiently preventing the elution of phosphorus from the bottom sludge and removing the eluted phosphorus. That is, in order to remove phosphorus eluted from bottom sludge of lakes and marshes, or to prevent phosphorus elution, the present invention provides granular materials having phosphorus adsorption ability on the bottom sludge and/or in the liquid phase above the bottom sludge. This is a method for removing phosphorus from a liquid, which is characterized by the presence of a network or porous structure filled with phosphorus. Next, embodiments of the present invention will be described based on the drawings. FIG. 1 shows a case where a rectangular parallelepiped network structure 3 filled with phosphate rock 2 is installed on bottom sludge 1 of a lake where eutrophication is progressing. After filling the rectangular parallelepiped network structure 3 with phosphate rock 2, the structure is usually installed on the bottom sludge using a crane or the like. FIG. 2 shows an example in which a porous structure 3' with holes formed on the surface is used as the structure, and a third porous structure 3' is used as the structure.
The figure shows an example in which a spherical net structure is used. The devices shown in FIGS. 1, 2, and 3 can also mainly prevent phosphorus elution from the bottom sludge. When installing on the bottom sludge 1 as shown in Figures 1, 2, and 3, it can be installed evenly on the bottom sludge of a water body in a short time. Furthermore, since the phosphate rock is contained in a net-like or porous structure, the packed layer will not be disturbed by gas generated from the bottom sludge even after long-term use. Figure 4 shows the inside of the spherical network structure shown in Figure 3.
This is an example in which an adsorbent having the ability to adsorb phosphorus is housed in the sludge and an air phase 4 is provided, and the phosphorus is suspended in a water body to remove phosphorus eluted from the bottom sludge. Normally, an air pumping tube or the like is used to supply DO to the deep water layer of a body of water, but if a sphere like the one shown in Figure 4 is circulated in the air pumping tube, the DO
It is possible to simultaneously supply phosphorus and remove phosphorus. FIG. 5 shows a cylindrical network structure in which a phosphorus adsorbent is placed, and FIG. 6 shows the internal structure of the structure shown in FIG. 5 in which an air phase is further provided. The structures shown in Figures 1-5 are easily retrievable and can be refilled if their phosphorus removal capacity decreases. Furthermore, the phosphorus removal ability can be restored by immersing the recovered structure in acid or alkali. Further, if the above-mentioned structure is used as a sea wall or a tetrapod, it can contribute to preventing eutrophication in the bay, and this is one of the preferred application examples. Regarding granular materials having phosphorus adsorption ability, natural phosphate rock and Kanuma soil are good for the ecosystem, and bone charcoal, slag, and light burnt magnesia are excellent in terms of phosphorus removal ability. As the slag, any of converter furnace, blast furnace, and granulated slag may be used. Slag containing a large amount of CaO has the effect of precipitating phosphorus in the form of calcium phosphate, so that phosphorus inactivation is also possible. The particle size of the granules is preferably finer, and is practically about 0.4 to 0.6 mm, and the mesh size and each pore size of the network and porous structure should be such that the granules do not flow out. It is necessary to do so. Examples of the present invention are shown below. Example 1 A cylindrical transparent acrylic column with a diameter of 100 mm and a height of 800 mm was filled with bottom sludge from Hiroshima Bay to a thickness of 300 mm.
A cylindrical network structure (60 meshes) filled with 0.4 mm to 0.6 mm phosphate rock to a thickness of 200 mm was placed on top of the structure, and the supernatant water was placed in an anaerobic state to determine the phosphorus elution rate. The same bottom sludge is filled, and the phosphorus elution rate is determined when bone coal (0.4 to 0.6 mm) is added instead of phosphate rock to the net structure, and when converter slag (0.4 to 0.6 mm) is added to the net structure. A comparison was made with the case where no structure was installed. Table 1 shows the processing results. As can be seen from the results in Table 1, all of the examples had the effect of preventing phosphorus elution, and converter slag was especially effective.

[Table] Example 2 In Example 1, a comparison was made between the case where phosphate rock was placed in the network structure and the case where phosphate rock was directly filled. The results are shown in Table-2.

【table】

[Table] As shown in Table 2, when the phosphate rock of the comparative example was directly filled, the turbidity of the supernatant water increased at the time of filling, and after 30 days, the filled layer was disturbed by the gas generated from the bottom sludge, and the The turbidity and phosphorus elution rate in the clear fluid increased. On the other hand, in the example, the turbidity of the supernatant water at the time of filling was low, and the filled layer was not disturbed by the gas generated from the bottom sludge. Example 3 Two acrylic cylindrical columns measuring 100 mm × 1600 mmH were filled with Nakaumi bottom sludge to a thickness of 300 mm.
The top water of Nakaumi's bottom sludge was poured into the tank to a thickness of 130 mm to create an anaerobic condition. In one column, a spherical mesh structure (the mesh is made of stainless steel with a diameter of 40 mm and 60 mesh holes) is filled with bone charcoal of 0.4 to 0.6 mm, and a ping pong ball is placed inside.
The phosphorus concentration of the supernatant water was measured.

[Table] * When no spherical network structure is added As shown in Table 3, the present invention has a high phosphorus removal efficiency.

[Brief explanation of the drawing]

FIGS. 1, 2, 3 and 5 are schematic views of a network or porous structure filled with granules having phosphorus adsorption ability used in the present invention, and FIGS. 5A and 5B are schematic diagrams illustrating an example in which an air phase is further provided in the structures shown in FIGS. 3 and 5, respectively. 1... Bottom sludge, 2... Granular material having phosphorus adsorption ability, 3... Network structure, 3'... Structure provided with small holes,
4...Air phase.

Claims (1)

[Claims] 1. Removal of phosphorus eluted from bottom sludge of lakes, marshes, etc.
Alternatively, in order to prevent the elution of phosphorus, a network or porous structure filled with granular materials having phosphorus adsorption ability is present on the bottom sludge and/or in the liquid phase above the bottom sludge. How to remove phosphorus. 2. The method for removing phosphorus from a liquid according to claim 1, wherein the particulate material having phosphorus adsorption ability is phosphate rock, Kanuma soil, bone charcoal, slag, or lightly burnt magnesia.