JPS59123592A - Treatment of water containing phosphate - Google Patents

Abstract

PURPOSE:To maintain high dephosphorizing efficiency and to effectively treat the reactivated waste liquor by reactivating degraded crystal seeds contg. calcium phosphate used for removing phosphate with an acidic soln., separating solids from the liquid after adding an alkaline agent to the waste liquor, and adding the separated liquid to the original water to crystallize. CONSTITUTION:In the water contg. phosphate adjusted to >=6pH wherein Ca<2+> is present, calcium phosphate is brought into contact with crystal seeds, and the phosphorous in the liquid is removed by crystallization on the surface of the seeds according to the equation. The crystal seeds with degraded activity and dephosphorizing efficiency after repetition of the crystallization are brought into contact with an acidic soln. such as hydrochloric or acetic acid of <=6pH, and the dephosphorizing efficiency is recovered. Meanwhile, an alkaline agent such as slaked lime is added to the waste liquor resulting from the reactivation to regulate the liquor to >=9pH, and the phosphorous in the waste liquor is precipitated and separated as calcium phosphate from the liquid. Then the separated liquid is added to the original water to crystallize.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing phosphate from water containing phosphate by crystallization.

As a method for treating phosphate-containing water to remove phosphates, a method has been proposed in which phosphate-containing water is brought into contact with crystalline species containing calcium phosphate, such as phosphate rock, in the presence of calcium ions. There is. This method removes phosphate ions contained in water by converting them into calcium phosphate such as hydroxyapatite and crystallizing them on the surface of crystal seeds. The processing efficiency is also significantly improved.

However, with this method, if magnesium ions or organic matter are present in the raw water, the surface of the crystal seeds will gradually become inactive.
There is a problem that dephosphorization performance deteriorates.

This invention is intended to solve these problems, and improves the dephosphorization performance by reactivating the crystal seeds whose performance has deteriorated with acid, and by treating the reactivation waste liquid and returning it to raw water. It is an object of the present invention to provide a method for treating water containing phosphate, which can maintain a high concentration of phosphate and efficiently treat reactivation waste liquid.

This invention uses water containing phosphate in the presence of calcium ions and under conditions of pH 6 or higher.

In the method of crystallization by contacting crystal seeds containing calcium phosphate, the crystal seeds whose performance has deteriorated are reactivated by contacting them with an acidic solution, and an alkaline agent is added to the red activated waste liquid to separate solid and liquid, and one separated liquid is added to raw water. This is a method for treating water containing phosphate, which is characterized by adding phosphate to crystallization.

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.

5Ca 2”+58PO4”-+40H-→Ca5(O
)II (PO4+!, +RO ■(20.(1) As can be seen from equation (1), in order to increase the removal rate of phosphate, it is necessary to advance the 5 reactions to the right, and at the same time, the crystal seeds It is necessary to keep the surface clean and maintain high activity.For this reason, in the present invention, crystal seeds containing calcium phosphate treated with an acidic solution are brought into contact with water containing phosphate.

As crystal seeds containing calcium phosphate, crystal seeds containing calcium phosphate such as hydroxyapatite [Ca5 (OHI (PO413)), fluoroapatite (cas (pupo4+s)) or tricalcium phosphate [Ca3 (PO4)2] can be used, and natural Phosphate stone or bone char has calcium phosphate as the main component and is suitable as a crystal seed.Also, a crystal seed in which calcium phosphate is precipitated on the surface of P material such as sand can also be used.As a crystal seed, reaction It is desirable that the main component is calcium phosphate of the same type as the calcium phosphate produced by hydroxyapatite.For example, in a system that produces hydroxyapatite, the use of hydroxyapatite will facilitate the precipitation of new crystals and efficiently remove phosphates. carried out, increasing the removal rate.

The raw water that is subjected to crystallization by contacting with crystal seeds containing calcium phosphate as described above is water containing phosphate, and is water that contains sewage,
Examples include secondary treated water such as human waste and industrial wastewater. In the present invention, even if these raw waters contain magnesium, organic substances, etc., crystallization can be performed without pre-treating the raw water.

The crystallization conditions are the same as those of the conventional method, and when brought into contact with a crystal seed containing calcium phosphate in the presence of calcium ions and under conditions of [lH6 or more], the calcium phosphate produced by the above formula (1) is crystallized. Crystals precipitate on the seed surface and grow, removing phosphate ions from the water.

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 hydroxyl ions are set to be higher than the solubility of the hydroxyapatite produced in equation (1), but lower than the supersolubility, that is, the conditions are such that hydroxyapatite is produced at 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 tRW higher than supersolubility, new crystals precipitate where crystal seeds do not exist, forming fine precipitates and clogging the guard bed, but in the metastable region lower than supersolubility, new crystals precipitate where crystal seeds do not exist. New crystals are precipitated 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 the 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'm97Z or less, calcium ion is 10-100m
y/A and PH are approximately 6 to 12, but vary depending on each condition.

Below, the present invention will be explained with reference to the drawings. The drawing is a system diagram showing one embodiment of the present invention. In the drawings, reference numeral 1
2 is a calcium agent tank, and 2 is an alkali agent tank, from which a calcium agent and/or an alkali agent are added to the raw water in the raw water pipe 3. In order to remove the precipitation of calcium carbonate, calcium phosphate, etc. that is generated by these additions and the turbidity originally contained in the raw water, P such as sand is added.
E-filtration is performed using the filter tank 4 filled with the material 4a. The filtered water is introduced into the crystallization tank 6 from the connecting pipe 5, and the filled crystal seeds 6a
Crystallization is carried out by contacting with.

The method of contacting the raw water containing phosphate with the crystal seeds containing calcium phosphate may be a fixed bed type or a fluidized bed type. The smaller the size of the crystal seeds, the larger the surface area and the easier it is for new crystals to precipitate.5 However, if the size of the crystal seeds is too small, it is difficult to contact or separate the crystal seeds from water. Also, if the particle size is too large, the specific surface area per unit packed particle will be small, so it is usually 9 to 300.
Use something similar to mesh. The larger ones are suitable for fixed beds, and the smaller ones are suitable for fluidized beds. In the case of a fixed bed, it is packed with crystal seeds with a particle size of 9 to 5 mesh, and the flow rate is
Water is passed in an upward flow or a downward flow at V1 to 5 hr to precipitate calcium phosphate crystals.

The crystallization tank 6 in the drawing is of a fixed bed type, and crystallization is performed using upwardly flowing water.

By crystallization in the crystallization tank 6, phosphorus in the liquid is crystallized on the surface of the crystal seed according to equation (1) and removed. The treated water, which has a low phosphorus concentration due to crystallization, is discharged from the treated water pipe 7.

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

Water flow conditions during backwashing include a flow rate of 20 to 80 m/hr.
The cleaning time is approximately 5 to 60 minutes. Even when the V5 filter tank 4 becomes clogged, backwashing can be performed using upward flow in the same manner.

If the above crystallization operation is continued, the raw water may contain impurities such as magnesium ions and organic substances.
The activity of the crystal seeds 6a may decrease and the dephosphorization performance may decrease. The crystal seeds 6a whose performance has deteriorated are reactivated by contacting with the acidic bath liquid injected from the chemical injection pipe 8, and the dephosphorization performance is restored once again.

Use an acidic solution with a pH of 6 or less.

Aqueous solutions of inorganic or organic acids can be used.

Examples of inorganic acids are hydrochloric acid, 5-sulfuric acid, nitric acid, carbonic acid, hydrofluoric acid,
Examples of organic acids such as sulfamic acid include acetic acid, oxalic acid, and citric acid. Sulfuric acid, nitric acid, sulfamino acid, acetic acid and citric acid are preferred.

The acid concentration varies depending on the degree of contamination, the frequency of acid treatment, etc., but is usually 10005 to 5 mol/'A8[.

The acidic bath solution treatment can be carried out by simply bringing the crystal seeds into contact with an acidic solution. Any method can be used, for example, water passage through a packed bed or immersion method, but it is preferable to use a method that corresponds to the crystallization method. For example, if crystallization is performed using a packed bed water flow method, activation can be performed using the same packed bed water flow method as in the previous year.Especially in the case of reactivation, it is more efficient to treat with an acidic solution during backwashing. It is true. Although the treatment time depends on the acid concentration, it is about several minutes to several hours; if the stirring is too long, the amount of phosphorus eluted will increase, which is not desirable. In the drawing, an acidic solution is passed through the filled crystal seeds 6a in a downward flow and circulated through five circulation cycles 9 to maintain a long contact time.

When a crystal seed is treated with an acidic solution, the surface of the crystal seed and a part of the inside of the seed crystal are dissolved into cracks, the impurity layer is removed, and the active surface inside is stained and new active points are created. It occurs. This activates the crystal seeds and maintains a high phosphorus removal rate.

Such treatment of the crystal seeds with a brittle solution can be carried out every time the activity of the crystal seeds decreases, thereby making it possible to maintain a highly active state.

The reactivated crystal seed 6a is subjected to crystallization as before, but the pH of the treated water after reactivation decreases from the alkaline side to neutral (11111, reaching pH 869, below). , it can be discharged without neutralization treatment.

The waste liquid generated by reactivation has impurities on the surface of the crystal seeds and calcium phosphate dissolved or dispersed in an acid solution, and requires treatment because it contains a large amount of acid and phosphorus. It includes minutes, so
The present invention makes effective use of this to perform efficient processing.

That is, the reactivated waste liquid is taken out from the waste liquid pipe 1D to the reaction tank 11, and an alkaline agent is injected from the alkaline agent tank 12 to raise the pH to 9.5 pf (9.5%) to precipitate phosphorus in the waste liquid as calcium phosphate.

Solid-liquid separation is performed in a solid-liquid separation tank 16. Since the waste liquid is in the form of calcium phosphate dissolved in acid, calcium phosphate is generated again by injecting an alkaline agent, but if an alkali agent containing calcium, such as slaked lime, is used, precipitation separation can be improved. In addition, impurities in the waste liquid are also transferred to the settled sludge side.

The separated liquid in the solid-liquid separation tank 16 has a P+i of 9 or more and contains a large amount of calcium ions, and especially if an alkali agent containing calcium such as slaked lime is used, a large amount of residual calcium ions will be present. can be used as a source of calcium ions and hydroxide ions. For this purpose, the separated liquid is injected into the raw water pipe B through the return pipe 14 and reacted with the raw water.

It may be returned to the calcium agent tank 1 or the alkaline agent tank 2. The separated solid content in the solid-liquid separation tank 16 is discharged from the drain pipe 15 and is used as fertilizer or as crystal seed μ.
It can also be used as

In the above description, the operation means such as crystallization, reactivation, waste liquid treatment, etc. are not limited to those described above, and can be changed as desired.

As explained above, according to the present invention.

The structure is configured to reactivate the crystal seeds whose performance has deteriorated with an acidic solution, and to process the reactivation waste liquid and return it to raw water, so it is possible to maintain a high level of activity of the crystal seeds, and to reduce the reactivation waste liquid. can be efficiently treated, and efficient crystallization can be performed by effectively utilizing calcium ions and hydroxide ions in the waste liquid.

Example 15Qmg of phosphate rock with a particle size of 05 to 1 Ovrm, which was used as a crystal seed for about 1 year to remove phosphorus from secondary treated sewage water by the crystallization dephosphorization method, was mixed with an inner diameter of 50mm and a length of 5oomm.
was filled into an acrylic resin column to form a crystallization tank. And phosphorus concentration 2 m9/A, calcium concentration 20 m
97B, alkalinity 10'Omg/, e raw water,
Calcium chloride was added as calcium at 151%'/f, and a slaked lime aqueous solution of o, 5f/A was added to adjust the pH'.
The amount of calcium ion supplied is approximately 45 m9/i when adjusted to 8.8 to 90 l,? After filtering in a filter tank, 500ml
Crystallization was performed by flowing water upward into the crystallization tank at a flow rate of /hr.

The average value of the phosphorus concentration in the treated water during continuous water flow treatment for one month was 0.49 m97Z.

Next, 750 ml of a 0.5 M acetic acid aqueous solution was circulated through the crystallization tank for 7 hours to reactivate the crystal seeds.

The waste liquid produced by this has a soluble phosphorus concentration of 315 m9
/A, calcium ion concentration 6560m9/! , PH4
,65. Slaked lime 85] was added to this waste liquid, and 1
After the reaction was stirred for an hour, the reaction product was allowed to stand still for about 1 hour and separated by sedimentation (-7. The separated liquid had a phosphorus concentration of 01m9/
I! , hereafter, calcium ioff 6 degrees 7850mty/,
5 pH was 11.2.

Subsequently, this separated liquid was added to the raw water at a rate of 2.5 me/A, and then a slaked lime aqueous solution of 05)/f was added to adjust the pl-13.3 to 90, and crystallization was carried out in the same manner as above. As a result, the average value of phosphorus patterning degree in the treated water during continuous water flow treatment for one month was 011 rQ/go or less.

In the above results, the decrease in the average phosphorus concentration in the treated water indicates performance recovery due to reactivation.

The calcium supply solution due to the addition of slaked lime after reactivation is approximately 1 omg7i, which accounts for approximately 2 of the amount of calcium supply required for reactivation (the amount of calcium chloride and slaked lime added).
The amount of 0m91A could be covered by the reactivation waste liquid.

[Brief explanation of drawings]

The drawing is a system diagram showing one embodiment of the present invention, in which 1 is a calcium agent tank, 2.12 is an alkali agent tank, 4 is a filtration tank, 6 is a crystallization tank, 11 is a reaction tank, and 16 is a solid-liquid separation tank. It's a tank. Agent Patent Attorney Sei Yanagihara

Claims (5)

[Claims] (1) In the method of crystallizing water containing phosphate by contacting it with crystal seeds containing calcium phosphate in the presence of calcium ions and under conditions of P) 16 or more, the crystal seeds with degraded performance are removed. Reactivate by contacting with acidic solution,
A method for treating water containing phosphates, which comprises adding an alkaline agent to a reactivated antiliquid to separate solid and liquid, and adding one separated liquid to raw water for crystallization. (2) A method for treating water containing phosphate according to claim 1, wherein filtration is performed before crystallization. (3) The method for treating water containing phosphates according to claim 1 or 2, wherein the alkaline agent contains calcium. (4) The phosphate salt according to any one of claims 1 to 3, wherein the acidic solution is an aqueous solution of an acid selected from hydrochloric acid, sulfuric acid, nitric acid, sunoshi-famic acid, acetic acid, and citric acid. water treatment methods including; (5) The method for treating water containing phosphate according to any one of claims 1 to 4, wherein the calcium phosphate is hydroxyapatite, fluoroapatite, or tricalcium phosphate.