JPS632237B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for activating a crystallizing material for water treatment for crystallizing and removing phosphate ions in water as hydroxyapatite in a crystallizing material made of bone char. .

[Technical development of inventions and their problems]

Generally, organic phosphorus compounds or inorganic phosphates exist in various states in human excreta or detergents, but these are often discharged into wastewater, and moreover, during normal wastewater treatment processes, However, most of the phosphate ions remain in the water as inorganic phosphate ions without being sufficiently removed. These phosphate ions cause eutrophication of environmental water bodies, contaminate water quality, and cause pollution, so tertiary treatment (advanced treatment) is required to remove these phosphate ions. Ru.

Conventionally, a coagulation precipitation method using metal salts or slaked lime is well known as a method for removing phosphate ions. This method involves reacting phosphate ions in water with metal ions or slaked lime to generate poorly soluble salts, which are separated by precipitation, but this method requires a large amount of added chemicals and also generates a large amount of sludge. This method requires a large amount of processing cost.

In order to eliminate these drawbacks of the conventional method and efficiently remove phosphate ions from water with simple operations, a so-called crystallization dephosphorization method that utilizes the crystallization phenomenon of hydroxyapatite has been developed. In this method, by adding a small amount of calcium ions (Ca ²⁺ ) to the water to be treated, phosphate ions (PO ₄ ^3- ) dissolved in the water are converted into hydroxyapatite (Ca ₅
(PO ₄ ) ₃ OH) is precipitated as microcrystals, and the colloidal water containing hydroxyapatite, which is difficult to separate by mere sedimentation, is brought into immediate contact with a crystallizing material made of bone char or phosphate minerals. The purpose is to crystallize the hydroxyapatite microcrystals into hydroxyapatite crystals widely distributed in the crystallization material, and sequentially remove phosphate ions. By this method, phosphate ions can be efficiently removed by adding a small amount of chemicals without generating a large amount of sludge.

Generally, in this method, the selection of the crystallization material is an important factor, and the performance of the crystallization material determines the processing results of this method. In other words, the crystallization materials that are usually considered include bone char and phosphate minerals whose main component is apatite, but the performance of these materials depends on their composition and
It varies depending on the composition, the surface condition of the crystallization material, the degree of crystal activation, etc., and depending on the type of crystallization material, the phosphorus removal performance may be poor, the performance may not last for a long time, or the phosphorus removal performance may be There are some types of water that require some kind of pretreatment on the water to be treated.

When bone char is used as a crystallization material, the surface of the crystallization material contains organic substances and some inorganic substances as impurities. In particular, carbon, which contains about 10%, participates in the adsorption of organic substances, causing crystallization. There was a problem that the performance as a material deteriorated.

[Purpose of the invention]

In view of the above-mentioned problems, the present invention eliminates impurities on the surface of the crystallization material by bringing the crystallization material made of bone char, which crystallizes the hydroxyapatite dispersed in the water to be treated, into contact with an aqueous solution of an alkaline agent having a hydroxyl group. The purpose is to wash away the crystallization material and supplement the hydroxyl ions, which are the constituents of hydroxyapatite, to activate the crystallization material.

[Summary of the invention]

The present invention adds calcium ions to treated water containing phosphate ions to generate hydroxyapatite, and removes phosphate ions in the water by crystallizing this hydroxyapatite in a crystallization material made of bone char whose main component is apatite. In the water treatment method,
This method attempts to clean the crystallization material and replenish the crystallization material with hydroxyl ions by bringing the crystallization material into contact with an alkaline agent having a hydroxyl group.

[Structure and operation of the invention]

The crystallizing material is a granular material made of bone charcoal mainly composed of apatite, and the alkaline aqueous solution used is an aqueous solution of an alkaline agent having a hydroxyl group, such as sodium hydroxide or calcium hydroxide, adjusted to a pH of 10 or higher. Methods for bringing the crystallization material into contact with the alkaline aqueous solution include immersing the crystallization material in the alkaline aqueous solution or passing the alkaline aqueous solution through a crystallization material layer packed in a column. The amount of the alkaline aqueous solution to be used is equal to or greater than the volume of the crystallization material in order to sufficiently contact and react with the crystallization material. The crystallized material after the alkali treatment is thoroughly washed with water or with treated water or treated water for dephosphorization treatment. However, in the case of mild alkali treatment, cleaning can be omitted.

By bringing the crystallization material made of bone char into contact with the alkaline aqueous solution as described above, impurities made of organic substances and some inorganic substances contained in the bone char are washed away, hydroxyapatite crystals are exposed, and the crystallization material is exposed. surface is activated. Furthermore, the hydroxyl ions in the alkaline aqueous solution supplement the hydroxyl groups, which are the constituent molecules of hydroxyapatite, to the crystallization material, and the crystallization material becomes in a state of excess hydroxyl ions, promoting crystal growth of hydroxyapatite.

The activation treatment of the crystallization material may be performed either before it is used as a crystallization material for dephosphorization or during use for dephosphorization.

〔Effect of the invention〕

According to the present invention, calcium ions are added to treated water containing phosphate ions to generate hydroxyapatite, and the hydroxyapatite is crystallized using a crystallization material made of bone char to remove phosphate ions from the water. In the treatment method, the crystallization material is
By bringing it into contact with an aqueous solution of an alkaline agent having hydroxyl groups, the surface of the crystallizing material made of bone char is washed with the alkaline agent, impurities such as organic matter are removed and activated, and hydroxyl ions are replenished. Since the crystallization reaction is promoted, the crystallization action can be effectively continued for a long period of time. Therefore, phosphate ions in water can be efficiently and stably removed continuously for a long period of time.

[Embodiments of the invention]

Example 1 Two cylindrical columns with a diameter of 5 cm and a height of 150 cm are prepared, and each column is filled with bone char 2 having a particle size of 0.5 to 1.0 mm to form columns No. 1 and No. 2.

Regarding column No. 2, a saturated calcium hydroxide solution was passed in an amount equivalent to twice the amount of bone char packed, and then washed with water to activate the packed bone char.

Next, secondary treated sewage water was used as the water to be treated (raw water) in each column, and calcium hydroxide was added to it to adjust the pH to 8-9, which was then continuously fed to the superficial velocity (SV) 2/- bone char.・Water was passed through the water at various times, and the amount of PO ₄ ^3- ions in each treated water was measured.

As a result, P conversion was approximately 1.52 to 2.02 mg/
The amount of PO ₄ ^3- ions in the treated water in each column after 50 days of flowing the water containing PO ₄ ^3- ions was 0.42 mg/in terms of P for column No. 1 and 0.16 mg/in for column No. 2.
(The amount of PO ₄ ^3- ions in the water to be treated on that day was 1.88 mg/in terms of P), and the effect of the activation treatment using calcium hydroxide was clear.

Example 2 Particle size 0.5~ in a cylindrical tank with a diameter of 30 cm and a height of 300 cm
Approximately 100 pieces of 1.0 bone char are filled, and secondary treated sewage water adjusted to pH 8-9 with calcium hydroxide is passed through this as water to be treated at a superficial velocity of 2/- bone char/hour to remove phosphate ions in the water. There is a device to remove it.

After passing water for a certain period of time, 1% sodium hydroxide solution 100%
The bone char was activated by passing a solution through it and then washing it with water.

The measurement results of the amount of PO ₄ ^3- ions in the treated water before and after the activation treatment are shown in the figure.

In other words, the treated water PO ₄ ^3- ion before activation is P
Converted to 0.4 to 0.5 mg/, whereas after activation treatment by the method of the present invention, the treated water
PO ₄ ^3- ion (in terms of P) decreased to 0.1 to 0.2 mg/, and the effect of the activation treatment was clear.

[Brief explanation of the drawing]

The figure is a chart showing the relationship between the phosphate ion concentration in treated water dephosphorized by the method of Example-2 and the number of days of water flow.

Claims (1)

[Claims] 1 Add calcium ions to treated water containing phosphate ions to generate hydroxyapatite,
A water treatment method in which phosphate ions in water are removed by crystallizing this hydroxyapatite in a crystallization material made of bone char, characterized in that the crystallization material is brought into contact with an aqueous solution of an alkaline agent having a hydroxyl group. Method for activating crystallization material for processing.