JPH09206760A - Method for dephosphorylating waste water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out an efficient dephosphorylating reaction by detecting a variation of a pH of a waste water in a reactor to control a pour of an alkali ion and also increasing and decreasing the pour of a magnesium ion in accordance with its pour. SOLUTION: The waste water containing an ammonium ion and a phosphate ion is flowed into a pH adjusting means 2 and its pH is measured with a pH indicating controller 13. Then an alkali soln. is supplied by actuating an injection pump 12a at an alkali injection line 12 so that an alkali component in the waste water flowed into a dephosphorylating reactor 1 may be almost constant. The waste water after adjusting the pH is sent to the dephosphorylating reactor 1 with a pump 6a and flowed into a tank body 1a by upward stream, and the alkali soln. and a magnesium soln. are continuously injected respectively from each injecting means 3 and 4 in a fixed injection ratio, and the phosphate ion and the ammonium ion are converted to magnesium ammonium phosphate and the phosphate is crystallized on a surface of MAP particles previously formed in the waste water.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to efficient removal of harmful substances such as phosphate ions and high-concentration ammonium ions, which are the causative substances that cause eutrophication in lakes and closed sea areas, from wastewater. The present invention relates to a dephosphorization method and its apparatus.

[0002]

2. Description of the Related Art Conventionally, high concentration ammonium ion (NH
₄ ^+), from the waste water containing the phosphate ions (HPO ₄ ^2-), the removal of these ions, JP 4-1412
A dephosphorization method and a dephosphorization apparatus for embodying the method have been proposed as disclosed in Japanese Patent Application No. 93, Japanese Patent Application No. 7-57455 and the like.

For example, in the dephosphorization apparatus as shown in Japanese Patent Application No. 7-57455, the waste water is introduced from the inlet b at the bottom of the reaction vessel a, and the waste water in the reaction vessel a becomes insufficient. While injecting magnesium ions (Mg ²⁺ ), an alkaline solution such as NaOH is injected to adjust the pH, and while blowing air into it, Mg ²⁺ + NH ₄ ⁺ + H
_{^{PO 4 2- + OH - + 6H}} 2 O → MgNH 4 PO 4 · 6H
_The reaction of ₂ O + H ₂ O occurs, and NH in the wastewater
_The dephosphorization treatment is carried out by producing and insolubilizing ₄ ⁺ and HPO ₄ ^2- as MgNH ₄ PO ₄ .6H ₂ O (magnesium ammonium phosphate). And
The MgNH ₄ PO ₄ produced by this reaction is precipitated on the surface of the previously produced MgNH ₄ PO ₄ particles and granulated, and the treated water from which the MgNH ₄ PO ₄ has been removed is further treated in the container a. It goes up inside and is discharged from the outflow line f through the gas recovery section c, the sedimentation section d, and the overflow weir e.

[0004]

By the way, in such a conventional dephosphorization apparatus, magnesium ion (Mg ²⁺ )
When injecting water into wastewater, the average value of phosphate ion (HPO ₄ ²⁻ ) contained in the wastewater is predicted empirically or by sampling, and an equimolar amount of magnesium ion to magnesium chloride (MgC
(1 ₂ ) solution or magnesium hydroxide (Mg (OH) ₂ ) solution.

However, in the method of quantitatively injecting the magnesium solution in this way, when the phosphate ion concentration in the wastewater increases or decreases due to the change in the quality of the inflowing wastewater, that is, the phosphate concentration in the inflowing wastewater is magnesium. If it exceeds the injection amount of the solution, the phosphate ions that could not be reacted due to lack of magnesium solution flow out with the treated water and the quality of the treated water deteriorates. When the acid concentration is lower than the injection amount of the magnesium solution, the magnesium solution becomes excessive and wasted, resulting in a high running cost.

Therefore, the present invention has been devised to effectively solve such a problem, and its purpose is to maintain an appropriate amount according to the amount of phosphate ion in wastewater, even if the concentration of phosphate ion increases or decreases. It is intended to provide a novel dephosphorization method and a dephosphorization apparatus in wastewater, by which magnesium ions can be injected to perform an efficient dephosphorization reaction.

[0007]

In order to solve the above-mentioned problems, according to the present invention, waste water containing phosphate ions (HPO ₄ ²⁻ ) and ammonium ions (NH ₄ ⁺ ) is continuously poured into a reaction vessel. While continuously injecting magnesium ions (Mg ²⁺ ) and alkali ions (OH ⁻ ) into the wastewater, the phosphate ions and ammonium ions are added to the magnesium ammonium phosphate (MgNH ₄ PO ₄ ·.
6H ₂ O) in the dephosphorization method of waste water that is produced and insolubilized in the reaction vessel, the pH value of the waste water in the reaction vessel is constantly detected, and the pH value is always maintained within a predetermined range. As described above, the injection amount of the alkali ions is increased or decreased, and the injection amount of the magnesium ions is increased or decreased according to the injection amount of the alkali ions.

[0008] As a result, even if the concentration of phosphate ions in the waste water flowing into the reaction vessel fluctuates, an appropriate amount of magnesium ions are always injected, and the phosphate ions that could not be completely reacted together with the treated water. It is possible to prevent waste and the like due to excessive outflow of magnesium ions.

That is, as described above, if the concentration of phosphate ion in the waste water flowing into the reaction vessel is always constant, the magnesium ion consumed when magnesium ammonium phosphate is produced in the reaction vessel is also constant. Therefore, if a preset amount of magnesium ion is injected into the reaction vessel in an equimolar amount to this, an efficient dephosphorization reaction can be performed, but the concentration of this phosphate ion fluctuates. In such a case, the amount of magnesium ions to be implanted will be excessive or deficient with such a method of quantitative supply. Therefore, magnesium ions corresponding to the phosphate ion concentration may be injected into the reaction vessel, but it is difficult to directly measure the phosphate ion concentration, and much time and labor are required. Therefore, the present inventor has noticed that the pH value of the wastewater changes due to the change of the consumption amount of the alkali ions in the wastewater according to the concentration of the phosphate ion,
By increasing or decreasing the implantation amount of magnesium ions in accordance with the increase or decrease of the implantation amount of alkali ions so that the value is always maintained at a predetermined value, an efficient reaction is performed.

As a device for concretely implementing this method, a pH adjusting means for injecting an arbitrary amount of an alkaline solution into the waste water to adjust it to a predetermined pH, and a pH adjusting means for adjusting the pH to a predetermined pH. The prepared wastewater is continuously poured into the wastewater, and alkali ions and magnesium ions are injected into the wastewater to remove phosphate ions and ammonium ions from the wastewater.
A pH detector that constantly detects H, an alkaline agent injecting unit that increases or decreases the amount of the alkali ions injected according to the pH value of the waste liquid detected by the pH detector, and And a magnesium agent injection means for increasing or decreasing the amount of magnesium ion injection.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a preferred embodiment of the present invention will be described.

FIG. 1 shows an embodiment of the dephosphorization apparatus for wastewater according to the present invention. As shown in the figure, this dephosphorization apparatus comprises a pH adjusting means 2 shown on the left side of the figure, a dephosphorization reaction container 1 shown at the substantially central part of the figure, an alkaline agent injection means 3 and a magnesium agent injection means 4 shown on the right side of the figure. It is mainly composed of and.

First, the pH adjusting means 2 is equipped with a stirrer 5 such as a mixer in a tank 2a for introducing waste water containing ammonium ions (NH ₄ ⁺ ) and phosphate ions (PO ₄ ^2- ), and a supply line. Is connected to the bottom introduction port 1b side of the dephosphorization reaction container 1 via 6, and the waste water flowing into the tank 2a is stirred by a stirrer 5,
Dephosphorization reaction vessel 1 from supply line 6 by pump 6a
It is designed to flow in.

Next, the dephosphorization reaction container 1 is provided with a gas recovery section 7 and a separating means 8 in a vertical tank body 1a, and a gas-liquid separator 9 is provided above the tank body 1a. An air trap 10 is provided, and the wastewater sent from the supply line 6 is sent from the bottom introduction port 1b of the tank 1a in an upward flow and at the same time sent from the alkaline agent injection means 3 and the magnesium agent injection means 4. Depending on the solution that comes in, the phosphate ions contained in the wastewater are deposited and separated as particulate magnesium ammonium phosphate (MgNH ₄ PO ₄ .6H ₂ O, hereinafter referred to as MAP particles), and treated. It is designed to drain water from its upper end.

The alkaline agent injecting means 3 has two alkaline agent injecting lines 11, 1 in an alkaline tank 3a which stores an alkaline solution such as sodium hydroxide (NaOH).
2 is connected, and the alkaline solution in the alkaline tank 3a is supplied to the dephosphorization reaction vessel 1 by a metering pump 11a provided on one alkaline agent injection line 11 side.
Side, and the other alkaline agent injection line 12
A variable flow rate pump 12a provided on the side can also supply an arbitrary amount of the alkaline solution in the alkaline tank 3a into the tank 2a of the pH adjusting means 2 respectively. These metering pumps 11a and 12a
Is a pH indicator controller 1 for constantly detecting the pH in the pH adjusting means 2 and the dephosphorization reaction container 1, as indicated by the dotted line in the figure.
3 and 14 are respectively connected to inject the alkaline solution so that the pH value of the wastewater detected by the pH indicator controllers 13 and 14 falls within a predetermined value.

On the other hand, the magnesium agent injecting means 4 includes magnesium chloride (M 2) containing magnesium ions (Mg ²⁺ ).
A magnesium tank 4a for storing a magnesium solution such as gCl ₂ ) or magnesium hydroxide (Mg (OH) ₂ ).
Is connected to the magnesium agent injection line 15 having one end connected to the bottom side of the dephosphorization reaction vessel 1.
A variable flow rate pump 15a provided in the magnesium agent injection line 15 can supply an arbitrary amount of magnesium solution in the tank 4a into the dephosphorization reaction container 1 from the bottom thereof.

Further, the pump 11a of the alkali agent injection line 11 and the pump 15 of the magnesium agent injection line 15
On the discharge side of a, the flow rate instruction integrating flow meter 11b,
A flow rate indicator adjusting integrator 15b is provided to measure the flow rate of the solution flowing through the lines 11 and 15 and to control the pumps 11a and 15a to adjust the discharge amount per unit time. Has become.

Next, an embodiment of the dephosphorization method of the present invention using the dephosphorization apparatus thus constructed will be described.

As shown in the figure, first, the waste water containing ammonium ions (NH ₄ ⁺ ) and phosphate ions (PO ₄ ²⁻ ) is poured into the tank 2a of the pH adjusting means 2, where it is stirred by the stirrer 5. While the temperature is being measured, the pH is measured by the pH indicator controller 13. At this time, the injection pump 12a of the alkaline agent injection line 12 is operated so that the alkaline component of the waste water flowing into the lower portion of the dephosphorization reaction vessel 1 through the supply line 6 becomes substantially constant, and the alkali ion-containing alkali from the tank 3a is discharged. Supply a solution (NaOH). Since the waste water in the pH adjusting means 2 lacks magnesium ions, such a pH adjustment does not cause a reaction such as precipitation of the phosphate ions.

Next, the waste water adjusted to a predetermined pH in this way flows through the line 6 by the pump 6a into the tank 1a from the inlet 1b at the bottom of the dephosphorization reaction vessel 1, and inside the tank 1a. Flows upward. An alkaline solution and a magnesium solution are continuously injected into the tank 1a from the alkaline agent injecting means 3 and the magnesium agent injecting means 4, respectively, at a constant injection amount ratio, and at the same time, by an air supply means 16 such as a blower. Since the air is forcibly sent, the waste water in the tank body 1a is stirred and fluidized by this, and phosphate ions (HPO ₄ ²⁻ ) in the waste water are generated.
And ammonium ion (NH ₄ ⁺⁾ is, magnesium ions of the magnesium solution (Mg ²⁺⁾ and alkali ions in the alkali solution (OH ^-) and reacted with the magnesium ammonium phosphate equimolar (MgNH ₄ PO ₄ · 6
H ₂ O) and crystallizes on the surface of the MAP particles that were previously generated in the wastewater (Mg ²⁺ + NH ₄ ⁺ + HPO ₄ ^{2−
_{+ OH - + 6H 2 O →}} MgNH 4 PO 4 · 6H 2 O + H
₂ O). After that, the air sent by the air supply means 16 is recovered by the solid-liquid separation means 7 located in the central portion of the tank body 1a, and the wastewater is collected in the rising pipe 17 by the air lift effect together with the MAP particles to the gas-liquid separator 9 side. After transporting to
Here, it is separated from the wastewater, passes through the air trap 10, is treated by a deodorizing facility, etc., and is then released into the atmosphere. On the other hand, the wastewater and the MAP particles separated by the gas-liquid separator 9 descend in the downcomer 18 and are returned to the tank 1a again. Then, the wastewater separated by the solid-liquid separation means 7 further flows in the tank body 1a in an upward flow, then overflows from the overflow weir 16 at the upper end thereof and is drained as treated water. The MAP particles separated in 7 return to the inside of the tank body 1a and flow again to contribute to the crystallization of magnesium ammonium phosphate that is sequentially generated.

By the way, during this reaction, the tank 1a
If the phosphate ion concentration in the waste water flowing into the inside is constant, maintaining a constant injection ratio between the magnesium solution and the alkaline solution will always lead to a good reaction. When the concentration of the phosphate ions changes and the concentration of the phosphate ions changes, the consumption amount of the alkali ions changes in association with this, and the pH value of the wastewater changes accordingly. When the pH value fluctuates, the p value provided in the tank 1a
The H indicator controller 14 detects this, and controls the pump 11a of the alkaline agent injection line 11 to inject the alkaline solution to return the pH in the tank 1a to a predetermined value.

Usually, the injection amount of the alkali solution per unit time is the flow rate instruction integrating flowmeter 11b provided in the alkali agent injection line 11, and the injection amount of the magnesium solution per unit time is the magnesium agent injection line 15. The injection rate ratio optimal for the reaction is calculated by monitoring the flow rate adjusting accumulators 15b provided, respectively.
As described above, when the injection amount ratio of the alkaline solution and the magnesium solution is out of the optimum injection amount ratio range, the discharge amount of the magnesium agent injection pump 15a is changed by the pump controller 19 attached to the flow rate instruction adjusting integrator 15b. Then, the injection amount of the magnesium solution is increased / decreased, and the injection amount ratio is returned to the range of the constant injection amount ratio in the normal reaction.
For example, if the phosphate ion concentration in the wastewater increases, the tank body 1a
When a large amount of alkali ions are consumed at the same time as magnesium ions injected into the inside of the tank 1a and become insufficient, the pH in the tank 1a is reduced accordingly. Therefore, the amount of alkali solution injected to restore the pH value to a predetermined value. Will increase. Then, since the injection amount ratio of the alkali solution and the magnesium solution changes from the normal state, the injection amount of the magnesium solution is increased to restore the injection amount ratio to the normal injection amount ratio. On the contrary, when the phosphate ion concentration in the waste water decreases, the injection amount of the magnesium solution is reduced in order to return the injection amount ratio of both to the normal level by the same action.

The flow chart of this control method is shown in FIG. That is, the injection amount of the alkali solution per unit time is constantly monitored by the flow rate indicating integration flow meter 11b, and the injection amount of the magnesium solution per unit time is constantly monitored by the flow rate instruction adjusting integrator 15b, and this flow rate ratio is initially set. If it is within the range, the phosphate ion concentration in the wastewater and the amount of magnesium ions to be injected are equimolar, and it is determined that an appropriate amount of magnesium ions has been injected, and the flow rate ratio should be maintained. The flow rate control of the magnesium agent injection pump 15a is stopped. However, when this flow rate ratio is out of the set range and exceeds the set range, it is determined that the magnesium phosphate concentration in the wastewater rises and the injection amount of magnesium ions is insufficient, so that the magnesium agent from the pump 15b is removed. Increase injection volume. On the other hand, when this flow rate ratio falls below the set range, it is determined that the magnesium phosphate concentration in the wastewater has decreased and the magnesium ion injection amount has become excessive, and the injection amount of the magnesium agent from the pump 15b is decreased. . Then, when the flow rate control of the magnesium agent is performed and the flow rate ratio falls within the set range, the control is stopped and the flow rate ratio is constantly monitored.

As a result, even if the phosphate ion concentration in the wastewater changes, it becomes possible to constantly inject the optimum amount of magnesium ions in accordance with the phosphoric acid concentration into the wastewater. It is possible to prevent the inconvenience caused by the excess or deficiency of the injection amount of. In the present embodiment, the case where the tank 2a and the stirring means 5 are provided as the pH adjusting means 2 provided on the upstream side of the reaction container 1 has been described, but such a tank 2a and the stirring means 5 are omitted. The pH indicator controller 6a may be directly provided in the wastewater supply line 6 and the configuration may be simplified so that the alkaline agent injection line 12 is connected.

[0025]

Next, specific examples of the present invention will be described.

Using the dephosphorization apparatus configured as shown in FIG. 1, the injection amount of magnesium agent (MgCl ₂ .6H ₂ O) was kept constant and the phosphate ion concentration was changed as shown in Table 1. The injection amount ratio of the consumed NaOH / magnesium solution and the phosphate-phosphorus removal rate were monitored, and the results are shown in Table 1. In Table 1, RUN 1 is a steady state, RUN 2 is an insufficient amount of magnesium agent injection due to an increase in phosphate ion concentration, RUN 3 is an optimal operation state due to an increase in magnesium agent injection amount, and RUN 4 is due to a decrease in phosphate ion concentration again. Excessive magnesium injection amount, RUN 5 shows the return to the steady state by re-decrease of magnesium injection amount.

[0027]

[Table 1]

As a result, as is clear from Table 1, in the RUN 1, 3, and 5 in which an appropriate amount of magnesium agent was injected, the ratio of the amount of consumed NaOH / magnesium solution injected was high, even when the inflowing phosphate concentration was different. However, the injection amount of magnesium agent is too short or RUN 2,
In No. 3, it can be seen that the injection amount ratio of the consumed NaOH / magnesium solution fluctuates greatly. Therefore, consumed NaOH
Amount and injection amount of magnesium solution are measured per unit time, and these ratios are monitored.If this ratio is different from the steady state, for example, the discharge amount of the magnesium agent injection pump is automatically increased or decreased to set the above ratio. Only by adjusting to the value, the optimum injection amount of the magnesium agent can always be obtained, and the processing performance can be stabilized and the consumption amount of the magnesium agent can be suppressed.

[0029]

In summary, according to the present invention, since the optimum amount of magnesium ions can be always supplied to efficiently perform the removal reaction according to the increase or decrease of the phosphate ion concentration in the waste water, the phosphoric acid It is possible to prevent inconvenience due to the outflow of ions and to suppress an increase in running cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a flowchart showing injection control of a magnesium agent.

FIG. 3 is an explanatory diagram showing one form of a conventional dephosphorization apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction container 1a Tank body 2 pH adjusting means 3 Alkaline agent injecting means 4 Magnesium agent injecting means 6a, 15a Flow rate variable pump 11b Flow rate instruction | integration flowmeter 15b Flow rate instruction adjustment integrator 13,14 pH instruction controller

Claims (2)

[Claims] 1. A waste water containing a phosphate ion (HPO ₄ ²⁻ ) and an ammonium ion (NH ₄ ⁺ ) is continuously poured into a reaction vessel, and a magnesium ion (Mg ²⁺ ) and an alkali ion are introduced into the waste water. While continuously injecting (OH ⁻ ), the above-mentioned phosphate ions and ammonium ions are added to magnesium ammonium phosphate (MgNH ₄ PO ₄ ·.
6H ₂ O) in the dephosphorization method of waste water that is produced and insolubilized in the reaction vessel, the pH value of the waste water in the reaction vessel is constantly detected, and the pH value is always maintained within a predetermined range. As described above, the method for dephosphorizing waste water is characterized in that the injection amount of the alkali ions is controlled and the injection amount of the magnesium ions is increased or decreased according to the injection amount of the alkali ions. 2. A pH adjusting means for injecting an arbitrary amount of an alkaline solution into waste water containing phosphate ions (HPO ₄ ²⁻ ) and ammonium ions (NH ₄ ⁺ ) to adjust it to a predetermined pH, and this pH adjustment. And a reaction container for continuously injecting waste water adjusted to a predetermined pH by means and for injecting alkali ions and magnesium ions into the waste water to remove phosphate ions and ammonium ions from the waste water, PH indicator controller for constantly detecting the pH of the waste liquid, alkaline agent injecting means for injecting the alkali ion according to the pH value of the waste liquid detected by the pH indicator controller, and the amount of the alkali ion injected And a magnesium agent injection means for increasing or decreasing the injection amount of the magnesium ions.