JPS6238291A - Dephosphorization treatment - Google Patents

Abstract

PURPOSE:To enhance dephosphorization effect, by adjusting pH of waste water before using cement pretreated with a phosphate ion as a dephosphorizing precipitation material. CONSTITUTION:A waste water supply line 1, an alkali supply line 2 and a calcium supply line 3 are connected to a pH adjustment tank 4 having a stirrer and waste water after pH adjustment is sent to a dephosphorizing precipitation tank 6 by a pump 5 to perform dephosphorization treatment. Treated water is discharged from a treated water line 7. Cement treated with a phosphate ion is preliminarily charged in the dephosphorizing precipitation tank 6 as a dephosphorizing precipitation agent. By this method, the dephosphorization treatment of waste water containing a phosphorus compound can be efficiently performed in an extremely economical manner.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for removing phosphorus contained in water, and particularly to a dephosphorization treatment method using cement pretreated with phosphate ion-containing wastewater as a dephosphorization crystallization material. .

Conventional technology In recent years, phosphorus components along with nitrogen components have attracted particular attention as substances that cause eutrophication of lakes, marshes, inner bays, etc. It is required that phosphoric acid contained in water be removed before discharge.

Traditionally, the most common method for removing phosphorus components in υ1 water is the coagulation-sedimentation method (physicochemical treatment method), which uses sulfuric acid, polyaluminum chloride (PAC), etc. alone or in combination as a dephosphorizing agent. It has been adopted as
In addition, pilot-scale research is being conducted on a crystallization dephosphorization method that uses natural phosphate rock as a crystallization material and uses slaked lime to precipitate phosphorus contained in wastewater as hydroxyapatite on the surface of the phosphate rock. Furthermore, a method (Japanese Patent Publication No. 59-1113) is known in which a mixed film phosphor of alkali-treated slag and a magnesia-based adsorbent is used as a dephosphorizing agent.

Problems that Ming is trying to solve However, in the above coagulation-sedimentation method, the salt concentration in the treated water increases due to the addition of a dephosphorizing agent, and the concentration and dewatering properties of the settled sludge produced during the treatment process are poor. There are undesirable problems such as the high cost of sludge treatment and the difficulty in returning green areas to such sludge.

In addition, in the crystallization dephosphorization method using phosphate rock, the phosphate rock that can be used is limited to specific brands (for example, phosphate rock imported from Jordan) and is very expensive, so large quantities of phosphate rock are required. Not only is it not suitable for wastewater treatment, but from a system perspective, the presence of carbonate ions (bicarbonate ions and carbonate ions) in wastewater significantly reduces dephosphorization performance.
In order to maintain stable dephosphorization performance, the wastewater to be treated must be decarboxylated prior to dephosphorization.

Furthermore, a method of using alkali-treated slag and a magnesia-based adsorbent together as a dephosphorizing agent (Japanese Patent Publication No. 59-1113) provides excellent dephosphorization when brought into contact with wastewater using a general-purpose solid-liquid contact device. Although it shows good performance, magnesia is very expensive and there is a problem that wastewater treatment costs are high.

Means for Solving the Problems As a result of extensive research in order to solve the above problems, the present invention has been developed by using cement pretreated with a phosphate ion-containing aqueous solution and/or phosphate ion-containing wastewater. It was discovered that an excellent dephosphorization effect can be obtained, and the present invention was completed.

That is, in removing phosphorus compounds contained in wastewater, the present invention uses an aqueous solution containing phosphate ions and/or cement pretreated with phosphate ion-containing wastewater to be treated as a dephosphorization crystallization material. This is a phosphorus treatment method.

The wastewater to which the dephosphorization treatment of the present invention is applied may be any type of wastewater as long as it contains phosphorus compounds and requires removal of these phosphorus compounds, such as industrial wastewater, plating wastewater, etc. , sewage, domestic wastewater, etc.
Further, these wastewaters may contain pollutants such as ammonia and COD substances.

When dephosphorization is carried out by the method of the present invention using cement pretreated with an aqueous solution containing phosphate ions and/or wastewater to be treated, the pH of the wastewater is adjusted to 1) H using a pH adjuster.
The pH is adjusted to 8-11, more preferably within the range of 9 to 10.5.

By adjusting l)H within such a range, the excellent dephosphorization effect intended by the method of the present invention can be achieved. As the pH adjuster used for this purpose, for example, a caustic alkali such as caustic soda, soda carbonate, slaked lime, magnesia, dolomite, cement, etc. can be used.

Furthermore, during escaping phosphorus, it is thought that the following reaction proceeds, so calcium ions (Ca 2+ ions) are required.

5Ca'" + 38" PO43-+ 40H-
→ Cas (OH) (PO4)
3 + 382 0 If enough calcium ions exist in the wastewater to be treated to proceed with such a reaction, it is not necessary to add new calcium ions, but if there is a shortage, chloride It is necessary to increase the concentration of calcium ions in wastewater by adding calcium, cement, slaked lime, calcium nitrate, etc.

Examples of phosphorus compounds that can be removed by the dephosphorization treatment method of the present invention include phosphorus M salts such as or]-phosphates, metaphosphates, and polyphosphates.

Further, there is no particular restriction on the phosphorus concentration in the wastewater, and the present invention can be applied to wastewater having a phosphorus concentration ranging from several ppm in sewage treatment water to several 11,000 ppm in plating wastewater, or even higher.

The cement used in the dephosphorization treatment method according to the present invention is a general term for Portland cement, blast furnace cement, alumina cement, etc. Among these, bometland cement is preferred. Portland cement is obtained by blending raw materials such as iron oxide raw materials, clay, and limestone in appropriate proportions and pulverizing the resulting clinker by firing it in a dry rotary kiln. A cement clinker containing gypsum wax may be used as a setting retarder, or a cement clinker containing no gypsum may be used.

Its shape may be either granular or powdery.

In actual use, it is necessary to pre-treat it by bringing it into sufficient contact with the phosphate ion-containing aqueous solution and/or the phosphate ion-containing wastewater to be treated. This pretreatment is carried out while controlling the pH of the liquid side, and is continued until the pH falls within the range of 7 to 10. The phosphate ions used in cement pretreatment may be any of orthophosphate ions, metaphosphate ions, and polyphosphate ions. Further, there is no particular restriction on the concentration of phosphate ions.

Therefore, it is possible to pre-treat cement using phosphate ions in the wastewater to be treated, and it is also possible to pre-treat cement using wastewater enriched with phosphate ions. . For example, when carrying out the dephosphorization treatment method according to the present invention using a fixed bed method, first, cement clinker of an appropriate particle size is filled in the fixed bed, and wastewater to be treated or wastewater enriched with phosphate ions is poured into this and fixed. A pretreatment method in which this operation is continued until p(-1) of the waste water (treated water) after passing through the bed falls within the range of 8 to 10 can also be applied.

There are no particular restrictions on the temperature at which cement is pretreated, but it is usually carried out in the range of room temperature to 120°C. Pretreatment at a high temperature has the advantage of shortening treatment time.

As a system that can be applied when treating wastewater containing phosphorus compounds by the dephosphorization treatment method of the present invention, (1) A stirring mixing tank (mixer) and a separation tank (settler) are combined using pretreated powdered cement. Two methods are proposed: a well-known mixer/settler system, and a general-purpose fixed bed system filled with pretreated granular cement clinker.

Next, a case where carbon dioxide ions coexist in the wastewater to be treated will be explained.

In the normal crystallization dephosphorization method using phosphate rock, the dephosphorization performance is significantly affected by the coexisting carbon dioxide ions.
Prior to dephosphorization, the wastewater is made acidic and carbon dioxide gas is stripped using air. This complicates equipment operation. On the other hand, the dephosphorization treatment method according to the present invention has the feature that even if carbonate ions are contained in the wastewater, the dephosphorization treatment can be performed directly without performing any carbon dioxide gas stripping in advance. There is.

An example of a flow sheet for implementing the present invention will be described with reference to the drawings. A waste water supply line 1, an alkali supply line 2, and a calcium supply line 3 are connected to a pH adjustment tank 4 having a stirrer, and the pH is adjusted. The adjusted wastewater is sent to a dephosphorization crystallization tank 6 by a pump 5, and is subjected to dephosphorization treatment.
The treated water is discharged from the treated water line 7.

Hereinafter, the method of the present invention will be specifically explained based on Examples.

1. Preparation of phosphate ion-treated cement clinker (dephosphorization crystallization material) Powdered cement having the composition shown in Table 1, particle size 3200c1/
+I+ ) 1 part (weight) of phosphate ion (P
20 parts (by weight) of a 2 wt % aqueous solution of O43-) was added thereto, and the mixture was stirred at room temperature for 10 hours, and then allowed to stand overnight. supernatant p
When H was measured, it was 8.2. . Separate the precipitate by filtration, wash thoroughly with water, and add 1.4 parts of phosphate ion-treated cement (
(on a dry weight basis) was obtained. This was used in the experiment of Example 1.

Also, granular Portland cement clinker (particle size 2~
3 mm) was treated at 100° C. for 5 hours under the same conditions as above and left to stand day and night. When the pH of the supernatant liquid at that time was measured, it was 9.0, and 1.4 parts (dry weight basis) of phosphate ion-treated granular Portland cement clinker was obtained. This was used as a dephosphorization crystallization material in Example 2.

Table 1 (Typical cement composition percentage) Example 1 Orthophosphoric acid, calcium chloride, and sodium bicarbonate were dissolved in water to give a phosphorus concentration of 4.5 mLJ/f;t (as P) and a calcium concentration of 24 IIQ/i (as Ca). ), a synthetic wastewater containing 120 mg/12 (as HC03) of bicarbonate ions was prepared. Portland cement or hydrochloric acid was added as a pH adjuster to adjust the pH to various values of pl-1.

The above-mentioned powdered cement treated with phosphate ions was added as a crystallizing agent to these pH-adjusted synthetic wastewaters, and after stirring for 60 minutes, the phosphorus concentration in the supernatant liquid, pH 1 and lucium ion concentration in the supernatant liquid were determined. It was measured. The results are shown in Table 2.

Table 2 (Effect of adding seed crystals and phosphate ion pre-treated cement clinker through crystallization dephosphorization reaction)
As is clear from these results, it can be seen that the powdered cement treated with phosphate ions works extremely effectively as a dephosphorization crystallizer.

Example 2 The above phosphate ion-treated granular Portland cement clinker was packed into a glass column with an inner diameter of 30 InI11 to a height of 600 InI1 m. The same synthetic wastewater as described in Example 1 was pretreated and directly adjusted to various pH values with caustic soda without carbon dioxide stripping.

Each 1) H-adjusted synthetic wastewater is transferred to the above column with a liquid hourly velocity of 1
．． 5 in an upward flow mode for 5 hours, and the phosphorus concentration was measured every hour. In order to investigate whether a crystallization dephosphorization reaction was occurring, the phosphorus concentration was also measured when the treated water was filtered after passing through the column. The results are also shown in Table 3.

Table 3 (Results of dephosphorization experiments using column water flow) As is clear from these results, even if carbonate ions coexist in the wastewater, the crystallization dephosphorization reaction progresses on the cement clinker surface treated with phosphate ions. I understand that.

Go to 11 11 As explained above, according to the dephosphorization treatment method of the present invention, by using cement treated with phosphate ions as a dephosphorization crystallization material, the crystallization dephosphorization reaction progresses, and phosphorus compounds containing The dephosphorization treatment of wastewater can be carried out efficiently and extremely economically.

[Brief explanation of the drawing]

The drawing is a flow sheet for carrying out one method of the present invention. 1... Drainage supply line, 2... Alkali supply line, 3... Calcium ion supply line, 4... pH adjustment tank, 5... Water pump, 6... Dephosphorization crystallization layer, 7
...Treatment water line.

Claims (3)

[Claims] (1) In removing phosphorus compounds contained in wastewater,
A dephosphorization treatment method characterized by using cement pretreated with phosphate ions as a dephosphorization crystallization material. (2) Prior to dephosphorization treatment, the pH value of wastewater is 8~8.
11, preferably in the range of 9 to 10.5. (3) The dephosphorization treatment method according to claim (1) or (2), wherein the wastewater to be treated or the wastewater enriched with phosphate ions is treated when pre-treating cement with phosphate ions. .