JPH11314092A - Treatment of phosphate ion-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phosphate ion-containing waste water treatment method capable of keeping phosphate ion removing efficiency high over a long period of time. SOLUTION: In a waste water treatment method for electrochemically eluting iron ions and/or aluminum ions in waste water containing phosphate ions by using an electrode containing iron and/or aluminum to flocculate and sediment phosphate ions in a form of an insoluble salt with iron and/or aluminum, a current is controlled so that the molar ratio of the eluted metal to the concn. of phosphorus flowing in the electrolytic cell arranged to a waste water treatment apparatus becomes 1-4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating domestic wastewater containing phosphate ions, such as wastewater, particularly domestic wastewater or collective housing wastewater.

[0002]

It is well known that one of the causes of eutrophication of rivers and lakes is the presence of phosphorus compounds. In addition, although this phosphorus compound is present in a large amount in household wastewater, it is difficult to purify it, and at present, no effective countermeasure can be taken.

Various treatment apparatuses for phosphorus compounds have been proposed. For household wastewater, an electrolytic elution method of iron is known (JP-A-3-89998, C02F 3/1).
2). This technology reacts phosphate ions in wastewater with iron ions to form water-insoluble salts such as FePO ₄ and Fe (O
H) _x (PO ₄ ) This is a technique in which coagulation and precipitation are performed as _x (PO ₄ ) _y to remove iron ions in the wastewater by energizing an iron electrode installed in an electrolytic cell.

[0004]

However, in the conventional method, no consideration was given to the relationship between the concentration of phosphate ions and the amount of metal eluted. The wastewater was not purified.

[0005] In view of the above circumstances, an object of the present invention is to provide a method for treating phosphate ion-containing wastewater that can maintain phosphate ion removal efficiency for a long period of time with high efficiency.

[0006]

According to the method for treating phosphate ion-containing wastewater of the present invention, iron ions and / or aluminum ions are converted into wastewater containing phosphate ions by using an electrode containing iron and / or aluminum. A method for treating wastewater in which phosphate ions are chemically eluted and coagulated and precipitated in the form of insoluble salts with iron and / or aluminum, wherein the amount of the dissolved metal depends on the concentration of phosphorus flowing into an electrolytic cell installed in a wastewater treatment device. It is characterized in that the current is controlled so that the molar ratio becomes 1 to 4.

In the method for treating phosphate ion-containing waste water according to the present invention, iron ions and / or aluminum ions are electrochemically eluted into waste water containing phosphate ions using an electrode containing iron and / or aluminum. A method for treating wastewater in which phosphate ions are coagulated and precipitated in the form of an insoluble salt with iron and / or aluminum, wherein a molar ratio of a dissolved metal to a phosphorus concentration flowing into an electrolytic cell installed in a circulation path of a wastewater treatment device is provided. Is characterized in that the current is controlled so as to be 1 to 4.

The method for treating phosphate ion-containing waste water according to the present invention is characterized in that iron ions or aluminum ions are electrochemically eluted into phosphate ion-containing waste water by using an electrode containing iron or aluminum to form phosphate ions. A method for treating wastewater that is coagulated and precipitated in the form of an insoluble salt with iron or aluminum, wherein the molar ratio of the eluted metal to the phosphorus concentration flowing into the electrolytic cell installed in the wastewater treatment device is set to 1 to 4, When the electrode contains iron, the elution concentration is 1 to 60
When the electrode contains aluminum, the current is controlled so that the elution concentration is 0.5 to 30 mg / liter.

Further, in the method for treating a phosphate ion-containing waste water of the present invention, the iron ion or the aluminum ion is electrochemically eluted into the phosphate ion-containing waste water by using an electrode containing iron or aluminum to remove the phosphate ion. This is a method for treating wastewater which is coagulated and precipitated in the form of an insoluble salt with iron or aluminum, wherein the molar ratio of the dissolved metal to the phosphorus concentration flowing into the electrolytic cell installed in the circulation path of the wastewater treatment device is 1 to 4. Therefore, when the electrode contains iron, the elution concentration is controlled to 1.5 to 40 mg / l, or when the electrode includes aluminum, the current is controlled to be 1 to 20 mg / l. Features.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for treating wastewater containing phosphate ions according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an explanatory view showing a wastewater treatment apparatus according to an embodiment of the present invention, FIG. 2 is a partially cutaway perspective view showing an electrolytic cell in FIG. 1, and FIG. 3 is an explanatory view showing an electrode unit.

The present invention is used, for example, in a wastewater treatment device such as a combined septic tank. As shown in FIG. 1, such a wastewater treatment apparatus includes a first anaerobic filter bed tank A and a second anaerobic filter bed tank B.
, A biological filtration tank C, a treatment water tank D, and a disinfecting tank E. The wastewater flowing into the first anaerobic filter bed tank A is treated in each tank, and then discharged from the disinfecting tank E. ing.
The electrolytic cell 1 is installed in a circulation path L for returning the treated water pumped from the treated water tank D by the air pump F to the first anaerobic filter bed tank A.

The electrolytic cell 1 is, as shown in FIGS.
A wastewater treatment chamber 4 having a wastewater inlet 2 and a wastewater outlet 3, electrodes 5, 6 arranged so as to be at least partially immersed in the wastewater in the treatment chamber 4, and electrodes 5, 6. A controller 8 having a power supply 7 for supplying electricity, a polarity reversing circuit for switching the polarity of the electrodes 5 and 6 at predetermined time intervals, and a current control circuit for controlling a current supplied to the electrodes 5 and 6; An air aeration device 9 for supplying air into the wastewater in the wastewater treatment chamber 4 is provided.

The electrodes 5, 6 can be made from iron and / or aluminum ion sources such as iron, iron alloys, aluminum, aluminum alloys or iron-aluminum alloys.

As shown in FIGS. 2 and 3, the electrodes 5 and 6 are provided in the electrolytic cell 1 as an electrode unit 12 which is housed in a partition case 10 at a predetermined interval with a handle 11 therebetween. Four sets are assembled by the partition bar 13. A terminal 14 is fixed to the electrodes 5 and 6 by screwing or soldering, and a lead wire 15 drawn from the terminal 14 is connected to a connector 16. The partition case 10 has a drainage inlet 1.
0a and an outlet 10b are formed, and an air inlet 10c is formed.

The air aerator 9 includes a porous diffuser pipe 17 or a diffuser plate installed at the center of the bottom of the wastewater treatment chamber 4.
The air diffuser 17 includes an air pump (not shown) for sucking compressed air into the air diffuser 17. The air diffuser 17 and the air pump are connected by a pipe 18.

In the present embodiment, the diffuser pipe 17 is provided at the center of the bottom of the wastewater treatment chamber 4. However, the present invention is not particularly limited to this. A position where water-insoluble salts, which are reaction products of phosphate ions in the wastewater and iron ions (aluminum ions) eluted from the electrode together with the outflow, can be easily selected and installed. In addition, the convection of the drainage can be easily generated by moving the air diffuser vertically in the wastewater in the processing chamber. In the present embodiment, the reactivity between iron ions and phosphate ions can be improved by stirring the wastewater.

As a method for eluting iron (aluminum) electrolytically, a conventionally known method can be employed, and energization of the electrode may be continuous, intermittent, or pulsed. However, the amount of electricity varies depending on the concentration of phosphoric acid and other ions, the flow rate of waste water, and the like, but the molar ratio of the concentration of iron ions and / or aluminum ions in the waste water / the concentration of phosphorus (hereinafter, abbreviated as “Fe / P”). ) Is adjusted to be 1.0 to 4.0, preferably 1.5 to 2.0. That is, phosphorus in the wastewater exists as phosphate ions, and reacts the phosphate ions with iron ions to produce and precipitate FePO ₄ or Fe (OH) _x (PO ₄ ) y. _In the case of ₄ , a molar ratio of Fe to P of 1 is sufficient, but considering the reaction efficiency, a high phosphorus removal efficiency of 70 to 80% or more cannot be obtained unless the molar ratio is 1 or more. On the other hand, when the molar ratio is 4 or more, the phosphorus removal rate becomes 99% or more (that is, the efficiency reaches the limit).
This is because excess iron is discharged to the outflow side, which may increase running costs and lead to environmental pollution.

Therefore, in the present embodiment, the controller controls the current supplied to the iron electrode so that the Fe / P becomes 1 to 4 depending on the concentration of the inflowing phosphorus.
The required amount of iron ions to be eluted is controlled by Faraday's law. Thereby, the phosphorus removal efficiency can be stably maintained at 70 to 80% or more.

Here, when controlling the elution amount of iron by electric current, the electric current value is proportional to the phosphorus amount flowing into the combined septic tank.

The amount of phosphorus inflow is 1.2 g per person per day in domestic wastewater, and the amount of wastewater per person per day is 2 g.
Since it is said to be 00 liters, the inflowing phosphorus concentration is statistically expressed as a numerical value. From this, the calculated inflowing phosphorus concentration is 6 mg / liter. However, in practice it is a little lower, about 5 mg / l.

This phosphorus removal technique by the electrolytic elution of iron requires that the amount of inflowing phosphorus or the concentration of inflowing phosphorus be known, and the following parameters are necessary for determining the amount of inflowing phosphorus or the concentration of inflowing phosphorus. .

1. 1. Number of users of the combined septic tank or how many people use the combined septic tank Measurement of Inflowing Phosphorus Concentration The flow rate (number of users × 200 liters × circulation ratio) passing through the electrolytic cell is determined based on the number of users.

For the inflowing phosphorus concentration, the phosphorus concentration may be measured in advance. Alternatively, a statistical value of 6 mg / liter may be used. However, when the inflow state changes, the phosphorus concentration may be 0.5 mg / liter when the phosphorus concentration is low, and may be as high as 8 mg / liter when the phosphorus concentration is high. Therefore, when importance is attached to the stability of the phosphorus removal amount, the inflowing phosphorus concentration may be set to a higher value of 6.5 to 7 mg / liter.

In the present invention, the treatment of iron (aluminum) in the phosphate ion-containing wastewater by the electrolytic elution method is as follows:
It utilizes a reaction (reaction A) in which iron ions (aluminum ions) eluted from the electrode react with phosphate ions in wastewater to form a salt between water-insoluble phosphoric acid and iron (aluminum). Hydroxide ions are present in the wastewater, and the eluted iron ions (aluminum ions) also react with hydroxide ions (reaction B). Since reaction B is faster than reaction A, it is necessary to increase the amount of current to increase the elution amount of iron ions (aluminum ions) in order to capture phosphate ions.

However, when calcium ions or magnesium ions are present in the waste water, those ions react with hydroxide ions (reaction D). This reaction D
Has a higher priority than the reaction B between the iron ion (aluminum ion) and the hydroxide ion, the reaction B is suppressed, and the iron ion (aluminum ion) is effectively used for the reaction A with the phosphate ion. Furthermore, calcium ions and magnesium ions also react with phosphate ions to form water-insoluble salts, which contributes to phosphate ion removal.

For this reason, in the present invention, calcium ion or magnesium ion is added to suppress the reaction B between iron ion (aluminum ion) and hydroxide ion, and to reduce the reaction A between iron ion (aluminum ion) and phosphate ion.
Can be performed efficiently. As a result, the amount of electricity can be reduced, power can be saved, and the elution amount of iron and aluminum can be reduced.

As described above, the wastewater treatment apparatus of the present invention can be used particularly advantageously for general household wastewater. Therefore, it may be used alone, but it may be combined with other purification systems, for example, activated sludge method, membrane separation method, anaerobic / aerobic circulation method, etc., to form a comprehensive wastewater purification system for homes and apartment houses. it can. It can also be used for large-scale processing systems (human waste processing plants).

Next, the present invention will be described based on examples, but the present invention is not limited to only these examples.

Example 1 In the iron electrolytic elution wastewater treatment apparatus shown in FIG. 1, a high-purity iron plate was used as four pairs of electrodes immersed in wastewater. The polarity reversal time was controlled to 6 hours so that electrolysis of the electrode was performed at both electrodes.

Then, domestic wastewater containing a phosphorus concentration of 3 to 5 mg / liter is introduced at 1200 liter / day from the inlet, and the circulation flow rate in the treatment apparatus is set to 6000 liter / day. The concentration of phosphorus in the treated water when it is biologically treated in each treatment tank and flows into the electrolytic tank is 1 to 3 mg / liter. At this time, if Fe / P is set to 2, the elution amount of iron will be (1 to 3/31) × 2 × 55.847 =
It becomes 3.6-10.8 mg / liter.

(Phosphorus concentration / phosphorus atomic weight) × (molar ratio) × (iron atomic weight) (1)

Therefore, the amount of iron eluted between 3.6 and 10.
Since the circulation rate is 8 mg / liter and the circulation amount is 6000 liter / day, the electrolytic current value for securing 21.6 to 64.8 g of iron elution per day is calculated according to the following equation (2).
6-64.8 / 55.847) × 2 × 96500 / (24 × 60 × 60) = 0.86
~ 2.6A.

(Eluted amount per day / atomic iron weight) × (gram equivalent) × (charge amount) / (seconds per day) (2)

For this reason, the immersion surface area of the electrode for setting the current value to 0.86 to 2.6 A is determined by setting the current density to 0.5
When mA / cm ^2, become 1720~5200cm ^2. Therefore, the immersion surface area of the electrode is set to 1720 to 520.
The electrolytic current value was controlled to 0.86 to 2.6 A so that the Fe / P became 2 at 0 cm ² .

Then, by electrolysis of the electrode, the eluted iron ions react with phosphate ions to form water-insoluble salts. The produced salt is stirred by the air (2 liter / min) generated from the air diffuser together with the inflow water, and flows out to the outflow side. Therefore, there was little accumulation of water-insoluble salts.

Then, the waste water collected at the outlet was discharged with a pore size of 0.4.
The filtrate filtered with a 5 μm filter is passed through JIS K01.
As a result of examination according to the total phosphorus analysis method (46.3) specified in No. 02, it was found that the phosphorus removal efficiency was 70 to 80% or more.

Next, another embodiment of the present invention will be described. In the present embodiment, the phosphorus concentration is 0.5 to 8 mg.
The controller controls the current supplied to the electrodes so that Fe / P becomes 1 to 4 per liter, and controls the required amount of iron or aluminum to be eluted according to Faraday's law. According to the following formula (3), the elution amount is about 1 to 60 mg / liter (0.
5/31 × 1 × 55.847 to 8/31 × 4 × 55.8
47 mg / liter). When the electrode contains aluminum, about 0.5 to 30 mg / liter (0.5 / 31 × 1 × 27 to 8/31 × 4 × 27)
mg / liter).

(Phosphorus concentration / phosphorus atomic weight) × (molar ratio) × (iron or aluminum atomic weight) (3)

On the other hand, when the wastewater is biologically treated by the circulation type treatment apparatus according to the present embodiment, the concentration of phosphorus flowing into the electrolytic cell is reduced to 1 to 5 mg / liter by the biological treatment. The calculation is about 1.5 to 40 mg / liter when the electrode contains iron, and about 1 to 20 mg / liter when the electrode contains aluminum.

Thus, the phosphorus removal efficiency is 70-80%.
The above can be stably maintained.

Next, the present invention will be described based on examples, but the present invention is not limited to only these examples.

Example 2 In the same manner as in Example 1 described above, in the iron electrolytic elution wastewater treatment apparatus shown in FIG. 1, a high-purity iron plate was used as the four pairs of electrodes immersed in the wastewater. The polarity reversal time was controlled to 6 hours so that electrolysis of the electrode was performed at both electrodes.

Then, domestic wastewater containing a phosphorus concentration of 3 to 5 mg / liter is introduced at 1200 liter / day from the inflow port, and the circulation flow rate in the treatment apparatus is set to 6000 liter / day. The concentration of phosphorus in the treated water when it is biologically treated in each treatment tank and flows into the electrolytic tank is 1 to 3 mg / liter. At this time, if Fe / P is set to 1 to 4, the elution amount of iron becomes (1 to 3/31) ×
(1-4) x 55.847 = 11.8-21.6 mg /
Liters.

Therefore, the amount of iron eluted is 1.8 to 21.
Since the circulation amount is 6 mg / l and the circulation amount is 6000 l / day, the iron elution amount per day is 10.8 to 129.6 g.
The electrolytic current value for securing is (10.8 to 64.8 / 55.847) × 2 × 9650 according to the following equation (4).
0 / (24 × 60 × 60) = 0.43 to 5.18A.

(Amount of elution per day / atomic weight of iron) × (gram equivalent) × (amount of charge) / (number of seconds per day) (4)

For this reason, the current value is set to 0.43 to 5.18 A.
The inundation surface area of the electrode for setting the current density to 0.
If it 5mA / cm ^2, becomes 860~10360cm ^2. Therefore, the flooded surface area of the electrode is 860-1036.
The electrolytic current value was controlled to 0.43 to 5.18 A so that the Fe / P became 1 to 4 at 0 cm ² .

Then, by the electrolysis of the electrode, the eluted iron ions react with the phosphate ions to form water-insoluble salts. The produced salt is stirred by the air (2 liter / min) generated from the air diffuser together with the inflow water, and flows out to the outflow side. Therefore, there was little accumulation of water-insoluble salts.

Then, the waste water collected at the outlet was discharged with a pore size of 0.4.
The filtrate filtered with a 5 μm filter is passed through JIS K01.
As a result of examination according to the total phosphorus analysis method (46.3) specified in No. 02, it was found that the phosphorus removal efficiency was 70 to 80% or more.

In the above embodiment, the electrolytic cell installed in the circulation path of the wastewater treatment apparatus has been described.
In the present invention, the present invention is not limited to this. For example, the present invention can be applied to those installed in a small-scale septic tank such as a batch tank of a batch type wastewater treatment apparatus.

[0051]

As described above, according to the present invention,
Highly efficient phosphorus removal performance can be maintained for a long time.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a wastewater treatment device according to an embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view showing the electrolytic cell in FIG.

FIG. 3 is an explanatory view showing an electrode unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyzer 2 Inflow port 3 Outflow port 4 Processing chamber 5, 6 Electrode 7 Power supply 8 Controller 9 Air aerator 10 Partition case 11 Handle 12 Electrode unit 13 Partition rod 14 Terminal 15 Lead wire 16 Connector 17 Air diffuser 18 Pipe

Claims (4)

[Claims] An iron and / or aluminum electrode is used to electrochemically elute iron and / or aluminum ions into waste water containing phosphate ions to make phosphate ions insoluble in iron and / or aluminum. A method for treating wastewater that is coagulated and settled in the form of a salt, wherein the phosphate ion controls the current so that the molar ratio of the eluted metal to the phosphorus concentration flowing into the electrolytic cell installed in the wastewater treatment apparatus is 1 to 4. How to treat contained wastewater. 2. An iron and / or aluminum electrode is used to electrochemically elute iron and / or aluminum ions into waste water containing phosphate ions to make phosphate ions insoluble in iron and / or aluminum. This is a method for treating wastewater that is coagulated and settled in the form of salt, wherein the current is controlled such that the molar ratio of the dissolved metal to the phosphorus concentration flowing into the electrolytic cell installed in the circulation path of the wastewater treatment device is 1 to 4. A method for treating wastewater containing phosphate ions. 3. An iron- or aluminum-containing electrode is used to electrochemically elute iron or aluminum ions into wastewater containing phosphate ions to aggregate and precipitate phosphate ions in the form of an insoluble salt with iron or aluminum. Wastewater treatment method, wherein the molar ratio of the dissolved metal to the phosphorus concentration flowing into the electrolytic cell installed in the wastewater treatment device is 1 to
The current is controlled so that the elution concentration is 1 to 60 mg / l when the electrode contains iron, or the elution concentration is 0.5 to 30 mg / l when the electrode contains aluminum. Of wastewater containing phosphate ions. 4. An iron or aluminum electrode is used to electrochemically elute iron or aluminum ions into waste water containing phosphate ions to aggregate and precipitate phosphate ions in the form of an insoluble salt with iron or aluminum. A method for treating wastewater, wherein the electrode contains iron so that the molar ratio of the dissolved metal to the phosphorus concentration flowing into the electrolytic cell installed in the circulation path of the wastewater treatment device is 1 to 4,
When the elution concentration is 1.5 to 40 mg / liter or when the electrode contains aluminum, the elution concentration is 1 to 20 m
A method for treating phosphate ion-containing wastewater in which the current is controlled so as to be g / liter.