JP2002205080A - Dephosphorization method and dephosphorization equipment for orthophosphoric acid-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain treated water of a low phosphorus concentration and high water quality by surely removing the phosphorus in raw water which is drastic in the fluctuation of water quality, such as a calcium concentration, calcium ion concentration and M-alkalinity. SOLUTION: This dephosphorization method comprises measuring the pH and calcium ion concentration in the treated water and adding pH control agents and calcium ions to the raw water in such a manner that the respective measured values attain prescribed values. This dephosphorization equipment reacts the raw water and the calcium ions in reaction chambers 2 and 3 and subjects insoluble matter to a separation of solid from the liquid in a settling tank. The equipment has an arithmetic controller which is inputted with the output signal of pH measuring means 6 for the treated water and the output signal of calcium concentration measuring means 7, computes the pH and calcium concentration to give the prescribed value of the orthophosphoric acid concentration of the treated water from the relation between the pH and the dissolution product of calcium phosphate and outputs the control signal to control the amounts of the pH control agents and the amounts of the calcium ions to be added respectively to pH control agent adding means P3 and calcium adding means P2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing water containing orthophosphoric acid by adding calcium ions to raw water containing orthophosphate ions to form an insolubilized product of calcium phosphate and separating it to obtain treated water. The present invention relates to a phosphorus method and a dephosphorization apparatus, and in particular, by adjusting the addition amount of a pH adjuster and calcium ions based on the pH and calcium ion concentration of treated water, to adjust the phosphorus concentration, calcium ion concentration, M-alkaliness, etc. The present invention relates to a dephosphorization method and a dephosphorization device for reliably removing phosphorus in raw water in which water quality fluctuates greatly and stably obtaining high-quality treated water having a low phosphorus concentration.

[0002]

2. Description of the Related Art As a method for removing phosphorus from raw water containing orthophosphate ions, such as sludge dewatered filtrate and digestion desorbed liquid generated in anaerobic and aerobic treatment processes such as sewage, human waste, and wastewater, calcium is added to raw water. There is a method of removing ions by adding ions to generate an insoluble calcium phosphate at a pH of alkaline and separating it. As a calcium ion source used in this method, there are calcium hydroxide (Ca (OH) ₂ ), calcium chloride (CaCl ₂ ), etc. Among them, when Ca (OH) ₂ is used,
An alkaline agent for adjusting pH can be used also.
When CaCl ₂ is used, the pH is adjusted by separately adding an alkali such as sodium hydroxide (NaOH).
In addition, the reaction mode includes a precipitation method in which a calcium compound and an alkali agent are added to the raw water in the reaction tank to cause a reaction, and the insolubilized product is separated in the precipitation tank, and a seed is introduced by introducing the raw water into the crystallization tank. There is a crystallization method in which calcium phosphate is precipitated on the surface of the crystal.

Conventionally, in such a dephosphorization method, chemical injection control is performed based on a measured value of pH, and chemical injection control is performed on raw water so that the pH is constant.
However, in the chemical injection control based on the pH value, the contained phosphorus cannot be reliably insolubilized as calcium phosphate and removed from the raw water in which the phosphorus concentration and the calcium ion concentration fluctuate, and the phosphorus concentration of the treated water is reduced. There is a drawback that it fluctuates greatly depending on the phosphorus concentration of the raw water.

[0004] In carrying out the dephosphorization treatment by adding calcium ions to the phosphorus-containing water, Japanese Patent Application Laid-Open No.
No. 76278 discloses that the concentration of residual calcium ions in a reaction solution obtained by the reaction is measured and calculated from the amount of calcium ions added and the amount of residual calcium ions.
The concentration of soluble phosphorus (PO ₄ -P) in raw water (the amount of phosphorus that reacts with the amount of consumed calcium ions to produce calcium phosphate) is calculated, and from the calculated phosphorus concentration in raw water, it is necessary to treat this. A method is described in which the amount of calcium ions is determined and a drug is injected based on the result.

[0005]

However, Japanese Patent Application Laid-Open No.
In the method described in Japanese Patent No. 76278, the phosphorus concentration of the raw water cannot be reliably grasped, and therefore, there are cases where the phosphorus removal treatment cannot be performed stably. That is, when PO ₄ -P ions in phosphorus-containing water such as sewage treatment water are reacted with calcium ions to insolubilize them, calcium ions are converted into calcium carbonate (CaCO 2) by reaction with M-alkali in raw water or carbon dioxide in air. _{Since 3} ) is precipitated, the PO ₄ —P concentration in the raw water cannot be accurately determined from the amount of added calcium ions and the amount of residual calcium ions. In particular, in the case of wastewater treatment in which the water quality fluctuates greatly, such as M-alkaliness, or in a dephosphorization treatment system operated in an open system, the amount of calcium ions consumed by factors other than PO ₄ -P ions is large, and Since the fluctuation is severe, it is not appropriate to determine the PO ₄ —P ion amount based on the difference between the added calcium ion amount and the residual calcium ion amount.

[0006] The present invention solves the above-mentioned conventional problems, and adds calcium ions to raw water containing orthophosphate ions to form calcium phosphate insolubilized products. Dephosphorization of orthophosphoric acid-containing water that can reliably remove the phosphorus in raw water with severe water quality fluctuations such as calcium ion concentration, M-alkalinity, etc., and stably obtain high-quality treated water with low phosphorus concentration It is an object to provide a method and a dephosphorization device.

[0007]

According to the method for dephosphorizing orthophosphoric acid-containing water of the present invention, calcium phosphate is added to raw water containing orthophosphate ions to separate calcium phosphate insolubilized product and treated water. In the method of dephosphorizing the orthophosphoric acid-containing water, the pH and the calcium ion concentration of the treated water are measured, and p-water is added to the raw water so that each measured value becomes a predetermined value.
It is characterized by adding an H regulator and calcium ions.

[0008] The dephosphorization apparatus of the present invention comprises a reaction tank for reacting orthophosphate ions and calcium ions to produce calcium phosphate insolubilized material, and a raw water supply means for supplying raw water containing orthophosphate ions to the reaction tank. A calcium addition means for adding calcium ions to the reaction tank, a pH adjustment agent addition means for adding a pH adjuster to the reaction tank, and a reaction solution containing calcium phosphate insolubilized product in the reaction tank, sludge and treated water. A solid-liquid separation unit for separating solid-liquid into a mixture, a pH measurement unit for measuring the pH of the treated water, a calcium concentration measurement unit for measuring a calcium ion concentration of the treated water,
The output signal of the H measuring means and the output signal of the calcium concentration measuring means are inputted, and a predetermined value of the concentration of normal phosphoric acid in the treated water is given from the relationship between pH and the solubility product of calcium phosphate.
An arithmetic and control unit for calculating H and calcium concentrations, and outputting a control signal for controlling the amount of the pH adjuster and the amount of calcium ion added to the pH adjuster adding means and the calcium adding means, respectively. .

That is, the present inventors have conducted intensive studies on a chemical injection control method for reliably removing phosphorus in raw water without being affected by fluctuations in the quality of raw water. there are inherent solubility product, it from the ion concentration remaining in the treated water and the pH of the treated water, it is possible to determine the solubility of phosphorus (PO 4 _-P) concentration in the treated water obtained, therefore, the processing determined whether the target value to what extent the PO 4 _-P concentration of water, so that the pH and the residual calcium ion concentration in the treated water is the PO 4 _-P concentration is achieved by performing the dosing control, The present inventors have found that stable and reliable dephosphorization can be performed, and have achieved the present invention.

[0010] For example, calcium ion and alkali
Dephosphorization to add calcium chloride to precipitate calcium phosphate
Process water pH, PO₄-P concentration and calci
Figure 3 shows the relationship between the measured ion concentration and
The result as shown in FIG. In FIG. 3 (a)
From the measured values, the pH of the treated water and the calcium phosphate
(Ca₃(PO₄)₂) (Log ([Ca
²⁺]³[PO₄ ^3-] ²)) And figure out
3 (b), measured against the theoretical value of the solubility product
The solubility product calculated from the values is about 10 times.
You can see that That is, 10 times the theoretical value of the solubility product
The pH of the treated water and the concentration of residual calcium ions in the treated water
Stipulates that the treated water PO₄-Determine the P concentration
Can be. In other words, 10 times the theoretical value of the solubility product
On the other hand, the target PO₄-By substituting the P concentration
PH of treated water and calcium ions remaining in treated water
The concentration can be determined.
Controlling chemical dosing to achieve lucium ion concentration
More target PO₄-Stably and reliably obtain treated water with P concentration
It becomes possible.

[0011]

Embodiments of the present invention will be described below in detail.

In the present invention, a dephosphorization treatment is performed by adding a calcium compound and, if necessary, a pH adjuster such as an alkali agent to raw water containing soluble PO ₄ -P to precipitate an insolubilized product of calcium phosphate. In this case, the pH of the treated water and the calcium ion concentration are measured, and the amounts of the calcium compound and the pH adjuster are controlled so that the measured values become predetermined values.

That is, as described above, in such a dephosphorization treatment, the solubility product of calcium phosphate in the treated water obtained from the actually measured value is a predetermined value with respect to the pH of the treated water, and the solubility product is a theoretical value. About 10 times. Therefore, by substituting the target PO ₄ -P concentration into the solubility product corresponding to the measured pH value (this value is about 10 times the theoretical value), the PO ₄ -P concentration can be obtained. Since the calcium ion concentration of the treated water can be calculated, the amount of the calcium compound added may be controlled so that the calcium ion concentration of the treated water becomes the calculated calcium ion concentration.

According to a preferred embodiment of the present invention, the amount of a pH adjuster such as an alkali agent is controlled so that the pH of the treated water is constant, based on the value measured by the pH measuring means of the treated water. From the solubility product corresponding to this pH value, a calcium ion concentration for obtaining the target treated water PO ₄ -P concentration is calculated, and the measured value of the calcium ion concentration measuring means is the calcium ion concentration. A method of controlling the amount of the calcium compound to be added is exemplified.

In the present invention, since the pH and the calcium ion concentration are individually controlled as described above, neutral CaCl ₂ is used as the calcium compound rather than using alkaline Ca (OH) _2. Preferably, an alkali agent such as NaOH is added for pH adjustment.

The raw water to be treated by the method for dephosphorizing orthophosphoric acid-containing water and the dephosphorization apparatus of the present invention includes sewage treated water and wastewater generated by sewage sludge intensive treatment. For the precipitation method in which such raw water is reacted by adding a calcium compound and an alkali agent as necessary in a reaction tank, and the insolubilized substance is separated in a precipitation tank, the raw water is introduced into a crystallizing tank to form seed crystals. The present invention can be effectively applied to a crystallization method in which calcium phosphate is precipitated on the surface.

[0017]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 A synthetic wastewater was treated by the apparatus shown in FIG.

[0019] First of all, synthetic drainage _(PO 4 -P: 10mg /
L, Ca: 39 mg / L, M-alkali: 88 mg /
L) is introduced into the raw water tank 1, where the orthophosphate (monosodium dihydrogen phosphate: NaH ₂ PO ₄ ) is introduced.
Adding an aqueous solution, by varying the operating time and rotational speed of the infusion pump _{P 1} at this time, the _PO 4 -P concentration of the raw water was varied in the range of 10 to 50 mg / L.

After injecting the aqueous solution of CaCl ₂ into the synthetic waste water, the first reaction tank 2 and the third reaction tank 3 having a stirring device are provided.
After that, the mixture was sequentially fed to the reaction vessel and reacted, and then subjected to solid-liquid separation in the precipitation tank 4. In the first reaction tank 2, NaO was used as an alkaline agent.
An aqueous H solution was added to adjust the pH. A part of the separated sludge in the settling tank 4 was returned to the first reaction tank 2, and the remaining part was discharged out of the system. The separated liquid was taken out of the system via the treatment water tank 5.

In the present embodiment, a pH meter 6
And a Ca ion sensor 7, and the measured value of the pH meter 6 is 9.
As becomes 0 and controls the operation of the infusion pump _{P 3} of NaOH solution, the measured value of Ca ion sensor 7 3
Was controlled operation of CaCl ₂ aqueous infusion pump _{P 2} so that 5 to 40 mg / L.

At this time, the addition amount of the CaCl ₂ aqueous solution is 2
It varied in the range of 5-95 mg-Ca2 ⁺ / L.

[0023] of the _PO 4 -P concentration of the raw water and treated water PO ₄ -
The time course of the P concentration is as shown in FIG.
Despite the fluctuation of the _4- P concentration, the PO ₄ -P concentration of the treated water could be stably maintained at about 5 mg / L.

[0024] In Comparative Example 1 Example 1, without providing the Ca ion sensor, only the control by the pH meter, the addition of CaCl ₂ aqueous solution, 50
The treatment was carried out in the same manner as in Example 1 except that it was kept constant at 55 mg-Ca ²⁺ / L. As a result, PO _{4 of} raw water
The PO ₄ -P concentration of the treated water is shown in FIG.
As shown in the figure, it fluctuated greatly, and stable processing could not be performed.

[0025]

As described above in detail, according to the method and apparatus for dephosphorizing orthophosphoric acid-containing water of the present invention, calcium phosphate is added to raw water containing orthophosphate ions to remove calcium phosphate insolubilized product. In producing and separating water to obtain treated water, phosphorus concentration, calcium ion concentration,
It is possible to reliably remove the phosphorus in the raw water whose water quality fluctuates greatly, such as M-alkalinity, and stably obtain high-quality treated water having a low phosphorus concentration.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a dephosphorization device used in Example 1.

FIG. 2 is a graph showing the results of Example 1 and Comparative Example 1.

FIG. 3 (a) is a graph showing the relationship between the pH of treated water and the calcium ion concentration and PO ₄ -P concentration,
(B) is a graph showing the relationship between the pH of the treated water and the solubility product.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water tank 2 1st reaction tank 3 2nd reaction tank 4 Sedimentation tank 5 Treatment water tank 6 pH meter 7 Ca ion sensor

Claims (2)

[Claims] 1. A method for dephosphorizing orthophosphoric acid-containing water, wherein calcium phosphate is added to raw water containing orthophosphate ions to separate calcium phosphate insolubilized water and treated water, wherein the pH of the treated water and the calcium ion A method for dephosphorizing orthophosphoric acid-containing water, comprising measuring a concentration and adding a pH adjuster and calcium ions to the raw water so that each measured value becomes a predetermined value. 2. A reaction tank for reacting orthophosphate ions with calcium ions to produce calcium phosphate insolubilized material, raw water supply means for supplying raw water containing orthophosphate ions to the reaction tank, Calcium addition means for adding calcium ions, pH adjustment agent addition means for adding a pH adjuster to the reaction tank, solid-liquid separation of the reaction solution containing the calcium phosphate insolubilized substance of the reaction tank into sludge and treated water. Liquid separating means; pH measuring means for measuring the pH of the treated water; calcium concentration measuring means for measuring the calcium ion concentration of the treated water; and an output signal of the pH measuring means and an output signal of the calcium concentration measuring means. From the relationship between the pH and the solubility product of calcium phosphate, the pH and calcium concentration that give a predetermined value of the orthophosphoric acid concentration of the treated water are calculated, Dephosphorization device being characterized in that an arithmetic control unit for outputting a control signal for controlling the amount of calcium ions added amount of each pH adjusting agent to Seizai adding means and calcium addition means.