JPS605282A - Treatment of phosphate ion-containing water - Google Patents

Abstract

PURPOSE:To stably remove a phosphate ion to a low concn. over a long period of time by omitting a decarbonization process, by a method wherein Ca-salt is added to phosphate ion-containing water and, after pH-adjustment, the treated water is brought into contact with a phosphate removing agent in the coexistence of an Mg-ion. CONSTITUTION:Ca-salt such as CaCl2 is added to phosphate ion-containing water such as sewerage, excretion sewage or factory waste water. This treated water is adjusted to a pH of 8.5 or more and brought into contact with a phosphate removing agent such as granular MgO in the coexistence of about 50mg/l of an Mg-ion. By the coexistence of the Mg-ion, the good removal effect of the phosphate ion is obtained within a short retention time without receiving the influence of carbonate in water.

Description

Detailed Description of the Invention The present invention treats water containing phosphate ions, such as tap water, sewage, human waste water, industrial water, factory wastewater, boiler water, etc.
The present invention relates to a method for removing phosphate ions.

The above various wastewaters discharged into natural water systems contain inorganic phosphates such as orthophosphates and condensed phosphates, as well as organic phosphates, and these phosphate ions are released into rivers, lakes, marshes, etc. It causes eutrophication of closed water bodies such as inner bays.

These phosphate ions are present in water at a concentration of 0.01 to 0.02
The mere presence of /It (as P) is said to cause eutrophication. Therefore, there is a need for the development of a highly reliable treatment method that can efficiently remove phosphate ions to extremely low concentrations.

Crystallization is attracting attention as an advanced treatment method for water containing phosphate ions. In this crystallization method, a soluble calcium salt is added to the wastewater, the pH is adjusted to 7 or more, and then the water is passed through a tower filled with phosphate rock, and the phosphate ions in the water are precipitated on the surface of the phosphate rock as calcium phosphate. This is a method to remove phosphate ions.

This method is effective because the quality of the treated water is stable and it does not generate sludge, but because it is interfered with by the carbonic acid components in the liquid, desorption is required to remove the carbonic acid components before crystallization. The disadvantage is that a carbonation process must be installed. The decarboxylation process is a process of volatilizing carbonic acid components as carbon dioxide gas, and since the pH value must be adjusted to 3 to 5, a large amount of acid is required.

JP-A-57-71693 discloses a method for avoiding interference with carbonic acid components, b71!
A method is disclosed in which purified phosphate ion-containing water is brought into contact with magnesium hydroxide or magnesium oxide in the presence of calcium ions from a neutral salt of Li. It is also stated that when the pH exceeds 8, calcium carbonate is generated, effective calcium ions are consumed, and the phosphate ion removal efficiency is reduced. However, since the dissolved carbon of hydroxycalcium apatite decreases as the pH value increases, the removal efficiency of phosphate ions cannot be said to be satisfactory under the pH conditions described in the above publication. For example, in Example 2 of the above publication, water is passed at a rate of 20 cc/min, and 19
After 2 hours, the phosphate ion removal rate had already decreased to 90%.

The purpose of the present invention is to provide a method that can remove phosphate ions stably over a very long period of time by omitting the decarboxylation step, and can remove phosphate ions at low concentrations. In a method for removing jl phosphate ions by adding a calcium salt to and then contacting with a phosphorus removal material,
It is characterized in that the pH of water is adjusted to 8.5 dino, and the water is brought into contact with a phosphorus removing material in the coexistence of magnesium ions.

Calcium salts include neutral calcium salts such as calcium chloride, calcium sulfate, and calcium nitrate.
When magnesium oxide is used as the di-Q phosphorus removing material, mu ions may be supplied from the magnesium oxide.

Ca"-Mg'"co;- system with MIF" (7) Ca
In order to examine the effect on CO3 production, M-alkalinity was set at 100 ■/l! Sample a synthetic solution of (as CaCO3) and 50% calcium chloride // (as Ca)
Add, adjust pH to 10, add magnesium salt,
After stirring for 1 hour, experiments were conducted to measure the amount of precipitated calcium carbonate and the amount of remaining calcium while varying the amount of magnesium added. The results are shown in Figure 1. From this result, M
It can be seen that as the g'm degree increases, the amount of calcium carbonate precipitated decreases. On the other hand, if Mg ions are present in the process of reacting phosphoric acid and calcium to crystallize hydroxyapatite on the surface of the crystallization material, a compound containing Mg will be produced as an intermediate product of the above reaction, inhibiting the production of hydroxyapatite. There is a risk of However, as a result of various studies, the concentration of magnesium ions was reduced to 50 mg/
11; It has been found that the coexistence of calcium carbonate under J (as h) can prevent the precipitation of calcium carbonate without inhibiting the formation of hydroxyapatite7. Since the crystallization reaction is carried out under alkaline conditions, the method of the present invention does not precipitate calcium carbonate and does not require a decarboxylation step, even though the environment is such that calcium carbonate is likely to precipitate.

Furthermore, since magnesium ions and calcium ions remain in the treated water and it is alkaline, it is possible to reduce the amount of chemicals added for inflow water conditioning by circulating and mixing a portion of the treated water with the raw water. can.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

Example 1 Phosphate ions were charged into a column having a diameter of 27 mm and a height of 1 m, each filled with phosphate rock and granular magnesium oxide.
Calcium chloride in secondary sewage treatment water containing 5-2.5 mg/ρ is 20-30 mg/7! Add p
A sample with H adjusted to 8.5 was passed through water and compared. The results are shown in FIG.

Secondary sewage treatment water contains M-alkalinity (CaC03
) component is included at 100 to 200 mg/1,
In a phosphate rock packed tower, it is affected by M-alkalinity, and about 5
The quality of the treated water gradually deteriorated after water was drained for 0 hours. On the other hand, in a granular magnesium oxide-packed tower, 10 to 25 μ/e of magnesium ions are always present in the liquid due to the elution of magnesium oxide, so it is not affected by the M-alkalinity component. Even when observed over time, stable and good treated water was obtained.

When using phosphate rock as a crystallizing material, if the inflow water is adjusted to pH 3 to 5 in advance and the carbonate component is removed by aeration, then the above operation is performed, resulting in a result similar to that obtained when magnesium oxide is used. is obtained.

In this way, when magnesium ions coexist, there is no effect of carbonic acid components in water, and even without a decarboxylation process,
Better results can be obtained than when decarboxylation is performed using phosphate rock.

Example 2 Particle size Q, 5 to 1.01 in a column with a diameter of 27 mm and a height of 1 m.
of granular magnesium oxide, and water was passed through the same sample as in Example 1 and a sample to which 25.50 and ]00 mg/a of magnesium salt was added at 5V2h. Concentration (■/ρ
) are shown in the table below.

From this table, it can be seen that as the amount of magnesium added increases, the quality of treated water tends to deteriorate, but low concentrations have a significant effect. Especially when granular magnesium oxide is used as a phosphorus removal material, the limit concentration is 10 to 25 ■/β of magnesium as eluted bone from the removal material, so 25 ■/β of magnesium is added to this eluted bone! Added 35
~50■/ρ. No difference in treatment effect was observed depending on the type of magnesium salt.

Example 3 A column with a diameter of 27 cm and a height of 1 m was filled with granular magnesium oxide having a particle size of 0.5 to 1.0 m, and the same sample as in Example 1 was passed through it at 5V2h', and the resulting treated water was A phosphate ion removal experiment was conducted by circulating 50% of the phosphate ion to the inflow water. The results are shown in Figure 3.

In addition, the pH of the circulating water is 10.0 to 10.5, the magnesium concentration is 25 to 30 mg/(1, and the phosphate ion concentration is 0.
．． It was 2 to 0.3 ■/β.

In this way, the treated water containing magnesium is
By using E, Magneji Ram was able to suppress the interference of carbonic acid components, and stable treated water quality was obtained.

In this case, since the pH of the treated water is 10-10;5,
By circulating the treated water, the pH of the inflow water can be shifted to the alkaline side, or calcium ions remain in the treated water, so there is also an advantage in this respect that the amount of chemicals for adjusting the inflow water can be reduced.

Example 4 A column with a diameter of 200 inches and a height of 350 mva was filled with granular magnesium oxide having a particle size of 0.5 to 1.0 fins, and calcium chloride was added to the filtrate of secondary sewage treatment water by 20 to 10 g of calcium chloride.
30■/7! (as Ca) and ρ1 (8.5
The sample adjusted to
Water was passed for 0 hours. The results are shown in Figure 4. Under these conditions, magnesium is 10-25 E/7! ? '4 has been issued,
Stable and good treated water quality was obtained without decarboxylation.

4 As shown in Figure 1, magnesium or IO~25m
In the range of g/#, the amount that prevents the precipitation of calcium carbonate is 20 to 30 ■/l, and the M-alkalinity is 100
■/a, calcium carbonate is 70-80trv
z/l! Although it is calculated that the carbonate component will precipitate, actual measurements in this example showed that the amount of decrease in the carbonate component in the crystallization tower was 5 to 10% in the inflow water.

This is because the residence time in the crystallization tower is about 20 minutes, so in addition to the coexistence effect of magnesium, the short residence time also makes it impossible to reach equilibrium, which prevents the precipitation of calcium carbonate. You can also think that. Even with such a short residence time, hydroxyapatite can be efficiently crystallized according to the present invention.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the amount of magnesium added and the amount of calcium carbonate precipitated, Figure 2 is a graph showing changes over time in the quality of water treated by the method of the present invention and the conventional method, and Figure 3 is Example 3. FIG. 4 is a graph showing the results of Example 4.

Claims (4)

[Claims] (1) In the method of adding calcium salt to phosphate ion-containing water and then bringing it into contact with a phosphorus removal material to remove phosphate ions, the pH of the water is adjusted to 8.5 or higher, and the water is added in the presence of magnesium ions. A method for treating water containing phosphate ions, the method comprising bringing the water into contact with a phosphorus removing material. (2) Magnesium ions are eluted from the removal material using granular magnesium oxide as the removal material and/
Or the method according to claim 1, wherein a soluble magnesium salt is added. (3) The method according to claim 1 or 2, in which magnesium ions of 50+n+r/ρ or less are allowed to coexist. (4) The method according to any one of claims 1 to 3, wherein a part of the treated water is recycled and mixed with raw water for treatment.