JPS5913913B2 - How to treat water containing phosphates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating water containing phosphate to remove phosphate.

In recent years, the progress of eutrophication in closed water bodies such as lakes, marshes, and inner bays has been remarkable and has become a problem.

Phosphate present in water has been highlighted as a cause of eutrophication, and its removal has been raised as an urgent issue.

Phosphates, which cause eutrophication, are contained in tap water, sewage, industrial water, factory wastewater, boiler water, etc.; It exists in the form of phosphate.

As a method for removing such phosphates, a method has been proposed in which water containing phosphates is brought into contact with crystal species containing calcium phosphate, such as phosphate rock, in the presence of calcium ions (DissertationAbstrac.
ts International*Vol, 3(L
No. 12, Part I, page 5878-B, etc.).

This method removes phosphate ions that are separated in water by converting them into calcium phosphate such as hydroxyapatite and crystallizing them into crystal seeds. , processing efficiency will also be significantly improved.

However, in this method, especially when used for organic wastewater, slime adheres to the surface of the crystal seeds, reducing the activity and reducing the removal rate.

Furthermore, when using a natural ore such as phosphate rock as a crystal seed, the removal ability of the phosphate rock itself not only varies widely depending on the place of production (also, even in the same place of origin, the removal ability differs depending on its properties.

Additionally, organic matter contained in the ore causes a decrease in activity.

This invention prevents such a decrease in the activity of crystal seeds, and even when using crystal seeds with particularly low removal ability, it can efficiently (
An object of the present invention is to provide a method for treating phosphate-containing water that can remove phosphates.

This invention is a method for treating water containing phosphate, which is characterized by bringing water containing phosphate into contact with crystal seeds containing calcium phosphate in the presence of a chlorine agent.

The reaction that occurs when water containing phosphate is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions varies depending on the reaction conditions, but is usually expressed by the following formula.

5Ca2++70H−+, 3H2pQ4−→Ca5(O
H)(PO4)3+6HzO-" (S) As can be seen from equation (1), in order to increase the removal rate of phosphate, it is necessary to advance the reaction to the right, and at the same time to clean the surface of the crystal seeds. Keep the activity high (need to be maintained).

For this purpose, in the present invention, water containing phosphate is brought into contact with the crystal seeds in the presence of a chlorine agent.

The chlorine agent is an agent that generates free chlorine in water, and examples of examples of agents that can be used include chlorine gas, chlorine water, sodium hypochlorite, saran powder, and high-grade saran powder.

There is no particular limit to the amount of chlorine added, but as a rough guide, it is added continuously or intermittently so that 0.5 to 5 ppm of residual chlorine is detected.

However, if ammonia is present, chlorine is consumed in the production of chloramines, so this must be taken into consideration.

When water containing phosphates to which a chlorine agent has been added is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions, the calcium phosphate produced by the above formula (1) precipitates on the surface of the crystal seeds and crystallizes. grows and phosphoric acid in the water is removed.

In this case, the presence of the chlorine agent decomposes organic matter adhering to the crystal surface, prevents the formation of slime, and allows precipitation of calcium phosphate while keeping the crystal seed surface clean.

Calcium ions and hydroxide ions to be present in water do not need to be added from the outside if they are present in the raw water from the beginning, but if they are not present in the raw water or are insufficient, they are added from the outside.

The amount added should be in excess of the reaction equivalent, but if too much is added, fine precipitates may precipitate in places other than the crystal seeds, and impurities such as calcium carbonate may be generated, so these should not be generated. should be within the range.

That is, the amounts of calcium ions and hydroxide ions are (0
The conditions are such that hydroxyapatite is produced at a concentration higher than the solubility of hydroxyapatite produced in the formula and lower than supersolubility, that is, a concentration in the metastable range.

Here, supersolubility is the concentration at which crystals begin to precipitate when no crystal seeds are present in the reaction system.

In other words, at a concentration higher than the supersolubility, new crystals precipitate in places where crystal seeds do not exist, forming fine precipitates, and P
Although bed clogging occurs, in the metastable region lower than supersolubility, new crystals are precipitated on top of the crystal seeds and the crystals grow, but no precipitate is formed.

In addition, crystals do not precipitate in systems lower than the solubility.

The amount of hydroxyapatite produced is controlled by the phosphate ion concentration, calcium ion concentration, and pH of the reaction system.

The amount of calcium ions and pH value that bring the amount of produced hydroxyapatite within the metastable range can be determined experimentally by changing these values for each reaction system.

The approximate range is when phosphate ion is 50 ppm or less, calcium ion is 10 to 100 p100p.
p is about 6 to 12, but varies depending on each condition.

The chlorine agent may be added to the raw water or directly to the crystal seed bed.

In the former case, it may be added before addition of calcium ions or the like.

As crystal seeds containing calcium phosphate, calcium phosphate such as hydroxyapatite (Ca5(OH)(PO,i) 31, fluoroapatite [Ca5(F)(PO4)3) or tricalcium phosphate CCa3(PO4)2,1 is used. Natural phosphate rock contains these calcium phosphates as a main component and is suitable as a crystal seed.

Further, crystal seeds such as calcium phosphate precipitated on the surface of a p-material such as sand can also be used.

The crystal seed is preferably one whose main component is calcium phosphate of the same type as the calcium phosphate produced by the reaction.

For example, in a system that produces evaporative hydroxyapatite, if a crystal seed containing hydroxyapatite as the main component is used, new crystals will grow on top of the original crystals, and phosphates will be removed efficiently. rate goes up.

The method of contacting the water containing phosphate with the crystal seeds containing calcium phosphate may be a fixed bed method or a fluidized bed method.

When removing turbidity at the same time, a fixed bed type is recommended (if turbidity removal is not required, a fluidized bed type may be used).

The smaller the size of the crystal seeds, the larger the surface area, which makes it easier for new crystals to precipitate, but if the size of the seeds is too small, it will be difficult to contact or separate the crystal seeds from water.

Further, if the particle size is too large, the specific surface area based on the unit filling amount will be small, so particles of about 9 to 300 mesh are usually used.

Among these, the larger ones are suitable for fixed beds, and the smaller ones are suitable for fluidized beds.

In the case of a fixed bed, crystal seeds having a particle size of 9 to 35 meshes are packed, and water is passed upwardly or downwardly at a flow rate of SVI to 5 (1/hr) to precipitate calcium phosphate crystals.

When water is processed in a downward flow, it is desirable to pre-treat the raw water to remove impurities in order to avoid adhesion of impurities to the surface of the crystal seeds and to avoid wasteful consumption of chlorine agent. .

If the crystal seed surface becomes contaminated or clogged during water flow, periodically perform backwashing using upward flow to expand and clean the crystal seed bed and peel off impurities attached to the surface. This is desirable.

Example 1 To artificial wastewater containing 10 ppm of phosphate ions and 1100 ppm of 1M alkali, an aqueous calcium chloride solution was added to give a concentration of 40 ppm as calcium, and the pH was further adjusted to 9 with an aqueous sodium hydroxide solution, and 16 to 32 meshes were added as crystal seeds containing calcium phosphate. A cylindrical cylinder with an inner diameter of 30 mm was filled with 450 ounces of phosphate rock from Florida having a particle size of 30 mm, and water was continuously passed through the cylinder in an upward flow at a flow rate of 5 V2 hr'.

The phosphate ion concentration of the treated water gradually increased from the 6th day after the start of water flow, and on the 144th day, the phosphate ion concentration of the treated water reached 3.
It was 0 ppm.

Therefore, on the 155th day, when lppm of the following sodium chlorate was added as C62 to the raw water using a cylinder filled with phosphate rock, and the water was passed through the same process, the phosphate ion concentration of the treated water decreased rapidly, and after that the concentration of phosphate ions decreased below lppm. I was able to process it stably.

Example 2 Phosphate ions at about 10-18 ppm, C0DIO~
Calcium chloride aqueous solution was added to the secondary treated sewage water containing 20 ppm, SS 10-30 ppm so that the calcium ion concentration was approximately 40 ppm, and the pH was further adjusted to 9 with sodium hydroxide aqueous solution, and the pH was adjusted to 16-32 ppm.
5V2hr in a cylinder with an inner diameter of 30rrrIn filled with 450r/11 phosphate rock from Florida with a mesh size.
' (LVI, 3 m/hr). Water was passed in an upward flow.

Backwashing was performed once a day for 15 minutes at a LV of 30 m/hr.

The average phosphate ion concentration of the treated water was 2 ppm.

Next, when sodium hypochlorite (Ct2) was added to the raw water in a cylinder filled with phosphate rock at an amount of 1 ppm and the water was passed through the same process, the phosphate ion concentration of the treated water gradually decreased, making it possible to stably treat the water below 1 ppm. did it.

A comparison of the treatment results is shown in Table 1. As described above, according to the present invention, the phosphate removal rate is higher and the phosphate ion concentration of the treated water is lower than when no chlorine agent is added.

In particular, in the case of raw water containing organic matter, it is possible to prevent the formation of slime on the surface of crystal seeds, prevent the activity of crystal seeds from decreasing due to organic contamination, and when using natural ores such as phosphate rock as crystal seeds, it is possible to prevent slime from forming on the surface of crystal seeds. It oxidizes and decomposes the organic matter contained in the organic matter and increases the activity of crystal planes, increasing the phosphate removal effect.

In addition, when filling crystal seed particles and using it as a fixed bed,
Blocking of crystal seeds due to slime etc. can be prevented, and stable treatment effects can be maintained.

Claims (1)

[Scope of Claims] 1. A method for treating water containing phosphate, which comprises bringing water containing phosphate into contact with crystal seeds containing calcium phosphate in the presence of a chlorine agent. 2. The method for treating water containing phosphates according to claim 1, wherein the chlorine agent is chlorine gas, chlorine water, sodium hypochlorite, saran powder, or high-grade saran powder. 3. The method for treating water containing phosphate according to claim 1 or 2, wherein the crystal seeds containing calcium phosphate contain hydroxyapatite, fluoroapatite, or tricalcium phosphate. 4. The method for treating water containing phosphate according to claim 1 or 2, wherein the crystal seed containing calcium phosphate is phosphate rock.