JPH0220315B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention is a dephosphorization method for wastewater that can easily and efficiently remove phosphoric acid or phosphates (hereinafter simply referred to as phosphorus) contained in wastewater such as livestock urine wastewater and household wastewater. Regarding materials. <Prior art> Phosphorus contained in wastewater such as livestock urine wastewater and miscellaneous household wastewater causes eutrophication that induces "blue water" and red tide in lakes and inland seas. Therefore, coagulation-sedimentation methods and crystallization methods have been conventionally used to remove phosphorus from wastewater. As shown in Figure 8(a), an example of the treatment process of the coagulation-sedimentation method is to increase the pH of wastewater by adding slaked lime, cement, slag, or crushed concrete to wastewater containing phosphorus and stirring. In this method, phosphorus is precipitated and removed in the form of calcium hydroxyapatite produced by the reaction of phosphoric acid and calcium, but the treated water after this first precipitation has a pH
Neutralization and calcium removal are required due to the high pH and large amount of lime content.Usually, primary carbonation and removal of calcium carbonate precipitates at pH 9.3 to 10.0, where the solubility of calcium carbonate is the lowest, are required. Post-treatment steps of secondary carbonation and filtration of calcium carbonate are required. An example of the crystallization process is shown in Figure 8(b).
As shown in , the Ca ²⁺ concentration of phosphorus-containing wastewater and
After delicately controlling the OH ^- concentration (PH),
Phosphorus is removed in the form of calcium hydroxyapatite by passing water through a contact material layer containing "crystal seeds" similar to calcium phosphate or calcium hydroxyapatite, but the above-mentioned Ca ²⁺ concentration and OH ^- concentration As a pretreatment process to delicately control the pH, normally, if the wastewater contains carbonic substances, it is decarboxylated with sulfuric acid, and then the pH is adjusted using slaked lime or gypsum.
A method is used in which Ca ²⁺ is adjusted and CaCO ₃ and insoluble matter in the treated solution are precipitated and removed. <Problems to be Solved by the Invention> In the above-mentioned coagulation-sedimentation method, a large amount of chemicals (slaked lime) are used, which inevitably increases the amount of sludge generated, and requires the complicated post-processing described above. Become. On the other hand, as mentioned above, the crystallization method requires complicated pretreatment to delicately control the Ca ²⁺ concentration and pH, and also requires a special contact material that serves as a crystal seed for crystallizing calcium hydroxyapatite. Become. As described above, all of the conventional dephosphorization methods have complicated processes and have many problems in terms of equipment, operation management, cost, etc. In view of these circumstances, an object of the present invention is to provide a dephosphorizing material for wastewater containing phosphorus that can efficiently remove phosphorus through simple and easy treatment without requiring complicated treatment steps. <Means for Solving the Problems> As a result of various studies to achieve the above object, the present inventors have found that certain constituents of calcium silicate hydrate obtained by a specific method are relatively It has a high degree of crystallinity, and when placed in water, the PH is lower than that of conventional dephosphorization materials, and it was discovered that this result is deeply related to the disappearance and disappearance of phosphate ions in the liquid phase, and the present invention was completed. . The present invention consists of a calcium silicate hydrate obtained by hydrothermally reacting a raw material obtained by adding a foaming agent to an aqueous slurry whose main raw materials are a silicic raw material and a calcareous raw material under high temperature and high pressure. Adopts a structure that is a dephosphorizing material for wastewater. The configuration of the present invention will be explained in detail below. To explain more specifically, the porous treated material used in the present invention is prepared by adding a foaming agent such as aluminum powder to a slurry whose main raw materials are silicate raw materials and calcareous raw materials, and then hydrothermal reaction treatment is performed under high temperature and high pressure. A molded product obtained by molding, or a crushed product obtained by crushing this molded product with a porosity of 50 to 90%, or a slurry whose main raw materials are silicic raw materials and calcareous raw materials are mixed with water at high temperature and high pressure. It is a granulated or molded product obtained by granulating or molding a powder obtained by heat reaction treatment with air bubbles in it, and has a porosity of 50 to 90%. Here, calcium silicate hydrate is prepared by combining a silicate raw material and a calcareous raw material at a predetermined CaO/SiO ₂ molar ratio (0.5~
2.0) and is obtained by curing at high temperature and high pressure under the required pressure and temperature in an autoclave according to a conventional method. Silica raw materials include silica stone, silica sand, cristobalite, amorphous silica, diatomaceous earth, Powder such as ferrosilicon dust, white clay,
Examples of calcareous raw materials include powders such as quicklime, slaked lime, and cement. The calcium silicate hydrate thus obtained is one or more selected from the group consisting of tobermorite, xonotlite, CSH gel, phosiyaite, gyalolite, heleprandite, and the like. Among these, tobermorite, zonolite, and CSH gel are particularly preferred because they have a high PH buffering ability and a large specific surface area of 20 to 400 m ² /g. The porous treated material used in the present invention has a porosity of 50 to 90%, but when this porosity is obtained during the production of calcium silicate hydrate, it is created by slurrying a silicic material and a calcareous material. After adding a foaming agent such as a metal foaming agent such as aluminum powder or a foaming agent such as an AE agent, a hydrothermal reaction treatment may be performed at high temperature and high pressure. Here, the metal foaming agent generates gas through a chemical reaction, and its usage ratio varies depending on the amount of air bubbles and water entrained in the slurry, but can be derived from the chemical reaction equation. Specific examples of foaming agents include resin soaps, saponins, synthetic surfactants, hydrolyzed proteins, and polymeric surfactants, which mainly introduce air bubbles physically through surfactant action. There are cases where foam is generated simply by mixing with the raw material and stirring, and cases where stable foam is created using a special stirring tank or foaming device, and this foam is measured by volume and mixed with the raw material. be. When using such a foaming agent, it is necessary to determine the amount to be added after investigating the stability of the foam. In addition, when calcium silicate hydrate without voids is obtained, if each is a molded product, it may be pulverized and then air bubbles may be introduced during the granulation or molding process to adjust the porosity. In other words, an aqueous solution of a polymer resin sizing agent such as an acrylic resin emulsion is added to powdered calcium silicate hydrate, a foaming agent is added if necessary, the mixture is kneaded, and the resulting mixture is granulated using a pan pelletizer. It can be molded into a mold. As the drying method here, either natural drying or heat drying may be employed. Also,
Here, as the powdered calcium silicate hydrate, a powder obtained by crushing a molded product with voids as described above may be used. In addition, when making a porous treated material with high porosity,
It is better to use formwork molding. In the dephosphorization method using the dephosphorization material according to the present invention, a column or a packed bed is filled with the above-mentioned porous treatment material to form a packed bed, and wastewater containing phosphorus is directly passed through the packed bed. It is done by doing. The porous treatment material supplies Ca ²⁺ necessary for crystallization of calcium hydroxyapatite from the surface of the calcium silicate hydrate that forms it, and also lowers the pH of wastewater due to the PH buffering ability of the treatment material. In addition, even if the value fluctuates, a stable state of pH 8 to 9 is always created, so phosphate ions in the wastewater react with Ca ²⁺ and crystallize on the surface of the treated material in the form of calcium hydroxyapatite. be done.
At this time, the voids in the porous treatment material act to disturb the flow of wastewater in one direction and to moderate the flow velocity on the surface of the treatment material, so that phosphate ions and
Precipitation or growth of calcium hydroxyapatite with Ca ²⁺ is promoted. Although the porous treatment material used in the present invention does not contain "crystal seeds" similar to calcium phosphate or calcium hydroxyapatite, it has an adsorption ability, so it adsorbs the generated calcium hydroxyapatite at the initial stage of water flow. After that, the surface takes on a structure suitable for nucleation of calcium hydroxyapatite, and nucleation of calcium hydroxyapatite is formed in the microscopic voids and pores. When porous treated material after wastewater treatment is observed using a scanning electron microscope (SEM), many calcium hydroxyapatite crystals are present on the inner surface of the pores. As is clear from this, the porosity of the porous treated material has a large effect on the dephosphorization effect. As described later, when we tested the relationship between the porosity of the treated material and the phosphorus removal rate, we found that the porosity was 50~50.
It has been found that a phosphorus removal rate of 90%, preferably 60 to 80%, is high. If the porosity of the porous treated material is less than 50%, the specific surface area is small, so the phosphorus removal rate is low, and if it exceeds 90%, the phosphorus removal rate decreases due to floating during water flow, and the strength decreases significantly. The durability of the removal effect also deteriorates, which is not preferable. Further, the size of the porous treatment material used in the present invention also has a large effect on the phosphorus removal performance. If the diameter of the treated material is smaller than 0.5 mm, it will be easily clogged by SS and crystallized crystals, so it cannot be used for a long time.On the other hand, if the diameter is too large, the phosphorus removal rate will decrease due to the reduction of the contact area. Both are undesirable. Therefore, the treated material preferably has a size of 0.5 to 10 mm. As shown in FIG. 1, the dephosphorization method according to the present invention allows wastewater containing phosphorus to be processed using conventional crystallization methods.
Water can be directly passed through the packed bed of porous treatment material without performing any pre-treatment such as pH adjustment. In addition, the treated water has a neutral pH of 8 to 9 and does not contain sludge, so there is no need for post-treatment. Further, according to the present invention, dephosphorization is possible even if the phosphate concentration in wastewater is high. However, it is necessary to adjust the flow rate of wastewater depending on the concentration of phosphate.
For example, if the phosphate concentration is 500mg/, then 1t/
In the case of 50mg ^/ day, it is possible to process up to about 6t/day/ ^m3 . Note that the phosphorus removal rate at this time is 90% or more. Production examples and test examples are shown below. (Manufacturing example of porous treated material) (1) CSH gel treatment agent 4 parts by weight of silica powder, 2 parts by weight of quicklime powder, 1 part by weight of slaked lime powder, and 3 parts by weight of ordinary Portland cement (CaO/SiO ₂ molar ratio = 1.5) 7 parts by weight of water was added to a mixture prepared by adding 0.008 parts by weight of metallic aluminum powder to form a slurry.
Next, this slurry was poured into a mold, left to stand for 4 hours, and then removed from the mold in an autoclave at 150°C.
Hydrothermal treatment was carried out under 5 atm for 10 hours. This molded product was crushed using a crusher and sieved to a particle size of 2.5 to 5 mm to obtain a porous treated material. The porosity of this treated material was 72%. (2) Tobermorite treated material: 5 parts by weight of silica powder, 2 parts by weight of quicklime powder, and 3 parts by weight of ordinary Portland cement (CaO/
_SiO2 molar ratio = 0.8) to metallic aluminum powder
A slurry was prepared by adding 7 parts by weight of water to the mixture obtained by adding 0.008 parts by weight. This slurry was poured into a mold, left to stand for 4 hours, and then removed from the mold, which was then hydrothermally treated in an autoclave at 180°C under 10 atm for 10 hours. The obtained molded product was crushed using a crusher and sieved to a particle size of 2.5 to 5 mm to obtain a porous treated material. The porosity of this material was 75%. (3) Zonotlite treated material Silica stone powder and slaked lime powder are mixed at a CaO/SiO ₂ molar ratio of 1.0, dispersed in water 10 times the weight of the solid component to form an aqueous slurry, and then autoclaved. 210℃ inside, 20
Hydrothermal treatment was carried out for 10 hours while stirring under atmospheric pressure. Acrylic resin emulsion (solid content 10
%) was added 4 times by weight, kneaded, and then granulated.
It was dried and solidified at 110°C and sieved to a particle size of 2.5 to 5 mm to obtain a porous treated material. The porosity of this material was 73%. (4) Tobermorite-treated materials with various porosity In the production method shown in (2) above, various tobermorite-treated materials can be obtained by changing the addition ratio of metal aluminum powder and water as shown in Table 1. Ta.

[Table] (5) Zonotlite-treated materials with various porosity Air bubbles relative to the volume of the kneaded material
The same procedure was performed except that 80% and 160% were added, respectively, to obtain treated materials having the porosity shown in Table 2. When the amount of foam added was 160%, after kneading, the mixture was poured into a mold having a depression of 3 to 5 mm in diameter and dried and solidified together with the mold.

[Table] The product with no added amount of foam was manufactured in (3). Test Example 1 As shown in Figure 2, various porous treated materials were prepared using an experimental device that allows the test liquid to be treated to flow through an acrylic column with an inner diameter of 30 mm and a length of 400 mm filled with porous treated materials. We investigated the performance of A-1, A-2, and A-3 were filled with 150 ml of each treatment material produced in Production Examples (1) to (3) above.
and fill these columns with the various types of raw water shown in Table 3.
Water was passed through at a flow rate of 300ml/hr, and the treated water for the first week was
PH and phosphate ion concentration were measured. The results are also shown in Table 3. In addition, as a test solution, monopotassium phosphate (KH ₂ PO ₄ ) was added to pure water to give a phosphorus concentration of 5 mg/
The calcium ion concentration was adjusted to a range of 0 to 100 mg/by using an aqueous solution of calcium chloride (CaCl ₂ 2H ₂ O), and the pH was adjusted to a range of 5 to 10 using an aqueous solution of sodium hydroxide (NaOH). A modified version was used. For comparison, phosphate rock with a particle size of 2.5 to 5 mm from Angaur Island in the South Pacific was placed in the same column as above.
The column was filled with 150 ml (referred to as column B-1), and the same operation was performed. The results are also shown in Table 3. Furthermore, Figure 3 shows the influence of the PH of the test solution on the phosphorus removal rate (Ca ²⁺ concentration 60 mg/constant), and Figure 4 shows the influence of the calcium ion concentration on the phosphorus removal rate (pH 9 of the test solution constant). Shown below.

【table】

[Table] As shown in the above results, according to the present invention, the PH of the treated water is maintained at approximately 9 to 10 even if the PH of the test solution changes, and the phosphorus removal rate is always over 80%. However, in the comparative example, the phosphorus removal rate did not reach 80% unless the pH of the test solution was 8.5 or higher. Further, in the present invention, a phosphorus removal rate of 80% or more can be obtained even when the Ca ²⁺ concentration in the test solution is 0, but in the comparative example, the phosphorus removal effect does not occur unless the Ca ²⁺ concentration is about 60 mg/. In addition, in the present invention, the phosphorus removal rate is further improved when Ca ²⁺ is present in the test solution, and when the Ca ²⁺ concentration is 40 mg/or more, phosphorus removal is improved when tobermorite-treated material is used (A-2). The rate is almost
It becomes 100%. Test Example 2 Using the same experimental equipment as Test Example 1, using the various treatment materials shown in Production Examples (4) and (5), a phosphorus concentration of 5 mg/,
A test solution with a pH of 7 and no addition of calcium ions was treated to test the difference in phosphorus removal rate depending on the porosity of the treated material. Note that other conditions were the same as in Test Example 1. The results are shown in Table 4 and Figure 5.

[Table] As shown in Table 4 and FIG. 5, the phosphorus removal rate is high when the porosity of the treated material is 50 to 90%. Note that when the porosity exceeds 90%, the phosphorus removal rate decreases due to the floating phenomenon during water flow, and at the same time, the strength decreases significantly. From this result, the pore structure of the treated material is
It was found that it is extremely important for increasing the contact opportunities between the treated material and phosphate ions and for the crystal growth of calcium hydroxyapatite that crystallizes in the pores and voids, contributing greatly to the phosphorus removal effect. did. Test Example 3 Using the same experimental equipment as Test Example 1, the particle size of the tobermorite-treated material of Production Example (2) was adjusted to 0.6 to 1.2, 1.2 to 2.5,
A test solution with a phosphorus concentration of 5 mg/, pH 7, and no calcium ion added was treated with five types of treatment materials adjusted to 2.5-5, 5-10, and 10-15 mm, and the phosphorus removal rate was determined by the difference in particle size of the treatment materials. Tested for changes. Note that other conditions were the same as in Test Example 1. The results are shown in FIG. As shown in FIG. 6, as the particle size of the treated material increased, the phosphorus removal rate decreased. In addition, if the particle size was less than 0.5 mm, clogging occurred due to enlargement of the treated material due to SS and crystallization, and it could not be used for a long period of time. Test Example 4 Using the same experimental equipment as in Test Example 1, a test solution with the phosphorus concentration shown in Table 5 was applied to the tobermorite-treated material of Production Example (2) at 1800 ml/day (12 t/day m ³ ) and 900 ml/day.
day (6t/day・m ³ ), 300ml/day (2t/day・m ³ ), 150
ml/day (1t/day・m ³ ), 75ml/day (0.5t/day・m ³ )
The effect of the phosphorus concentration of the test solution and the flow rate on the phosphorus removal rate was tested. Note that other conditions are the same as in Test Example 1. The results are also shown in Table 5.

[Table] As shown in Table 5, according to the present invention, phosphorus can be removed with high efficiency even when the phosphorus concentration is as high as 500 mg/by reducing the flow rate. <Example> Particle size 5 to 8 produced in the same manner as in Production Example (2) above
Treated material whose main constituent is tobermorite of mm.
100 samples were filled into a 400 x 400 x 800 mm dephosphorization tank. Pig house wastewater (solid-liquid mixture of pig manure and pig house washing water) is fed into this dephosphorization tank with an upward flow of 120
Water was passed at a flow rate (flow rate) of /day (1.2t/day・m ³ ). The phosphorus concentrations of the pigsty wastewater and treated water were measured over a period of about seven months, and the results are shown in Figure 7. As shown in the figure, the phosphorus concentration in the treated water was 3 ppm or less, unaffected by the phosphorus concentration in the pigsty wastewater. As described above, according to the present invention, a stable phosphorus removal effect can be obtained over a long period of time. Comparative Example 2 3 parts by weight of calcium carbonate powder (CaO 54%) and 1 part by weight of silica powder (SiO ₂ 95%) were mixed and heated in an electric furnace.
It was baked at 1450°C for 2 hours. After pulverizing this with a vibration mill, 3 parts by weight of water was added to 1 part by weight of the obtained powder, and hydration was carried out for 1 hour to obtain a calcium silicate hydrate. This was filtered and dried in a drier at 110°C to obtain an absolutely dry product. Four times by weight of acrylic resin emulsion (solid content 10%) was added to this mixture, and after kneading, the mixture was granulated, dried and solidified at 110°C, and sieved to a particle size of 2.5 to 5 mm to obtain a porous treated material. Using this, we tried a wastewater treatment experiment similar to the example, and found that the phosphorus concentration in the treated water was 2 to 5 ppm, but the PH
The value was as high as 11.2, which was considerably higher than 8.7 in Example. <Effects of the Invention> As specifically explained above along with test examples and examples, according to the present invention, phosphorus can be efficiently removed through simple and easy treatment without the need for complicated processes, and maintenance and management is possible. is also easy. Therefore, not only industrial wastewater and sewage, but also livestock sewage, domestic wastewater, etc.
Small and medium scale dephosphorization treatment, which has been considered difficult until now, can be easily and economically performed. In addition, when the dephosphorization material according to the present invention is used for a long period of time, it is more economical because it can be reused as a raw material for silicate calcareous fertilizer, phosphoric acid fertilizer, or phosphorus.

[Brief explanation of drawings]

Figures 1 to 7 relate to the present invention, Figure 1 is a process diagram of the method of the present invention, Figure 2 is an explanatory diagram of the experimental equipment used in the test example, and Figure 3 is the phosphorus removal rate in Test Example 1. Figure 4 is a graph showing the relationship between the phosphorus removal rate and the calcium ion concentration of the test liquid in Test Example 1, and Figure 5 is the graph showing the relationship between the phosphorus removal rate and the test liquid pH in Test Example 2. A graph showing the relationship with the porosity of the material, FIG. 6 is a graph showing the relationship between the phosphorus removal rate and the particle size of the treated material in Test Example 3, and FIG. 7 is a graph showing the results of the example.
FIG. 8a is a process diagram of a coagulation precipitation method according to the prior art, and FIG. 8b is a process diagram of a crystallization method according to the prior art.

Claims (1)

[Scope of Claims] 1. Calcium silicate hydrate obtained by hydrothermally reacting a raw material obtained by adding a foaming agent to an aqueous slurry whose main raw materials are silicic raw materials and calcareous raw materials under high temperature and high pressure. A wastewater dephosphorization material consisting of. 2. The wastewater dephosphorization material according to claim 1, wherein the calcium silicate hydrate is one or more selected from the group of tobermorite, xonotlite, phosiyaite, gyalolite, and hillebrandite. 3. The wastewater dephosphorization material according to claim 1 or 2, wherein the calcium silicate hydrate is a granulated or molded product with a porosity of 50 to 90%.