JP3438508B2 - Advanced water treatment method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an advanced water treatment method for filtering raw water to which a flocculant and powdered activated carbon have been added by a membrane separator, and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, in advanced water treatment equipment, when removing suspending substances, colloidal substances, dissolved organic substances, etc. in raw water, a flocculant and powdered activated carbon are added to raw water to perform flocculation and precipitation treatment. A method of performing a membrane separation treatment after performing the above is adopted. FIG. 4 shows an example of a conventional advanced water treatment device. First, raw water is supplied to a reaction tank 101 through a pipe 111, a coagulant is supplied through a pipe 112, and a powdered activated carbon is supplied through a pipe 113.
Is supplied to the reaction tank 101 from the reactor and stirred by the stirrer 102 together with the suspending substance, colloidal substance, dissolved organic substance and the like in the raw water to cause an agglutination reaction. The coagulated water to be treated is supplied from the pipe 114 to the separation tank 103 and subjected to solid-liquid separation treatment. The supernatant water obtained in the separation tank 103 passes through the pipe 115 and the pipe 11 by the power of the pump P.
After passing through 6, the film is supplied to the membrane separation device 104 and subjected to membrane separation treatment. The permeated water of the membrane separation device 104 is discharged out of the system as treated water through the pipe 117. On the other hand, in the case of the cross-flow filtration method, the concentrated water is passed through the pipe 118 and the reaction tank 10
It is cycled to 1.

[0003]

In the conventional advanced water treatment equipment, flocs containing aluminum hydroxide, which is an aluminum compound used as a flocculant, are produced in the flocculation-precipitation treatment which is the pretreatment of the membrane separation device. Further, since a small amount of flocs containing aluminum hydroxide also exists in the supernatant water after the solid-liquid separation, this is the membrane separation device 104.
The separation membrane 105 has a drawback that it adheres to the membrane surface and causes clogging in a relatively short period of time. Therefore, in order to eliminate the clogging, it is necessary to frequently carry out chemical cleaning with an acid or an alkali, which causes a problem that the cost and labor for the chemical cleaning operation and the cost increase.

Oxygen is consumed by the organic substances adsorbed on the powdered activated carbon to anaerobically oxidize the inside of the reaction tank, resulting in elution of manganese from raw water (for example, river water, dam water, groundwater, etc.) and decay of organic substances. There was a problem that an offensive odor was generated.

The present invention has been made in view of the above problems, and can prevent clogging of the membrane separation device, reduce the number of times of chemical cleaning, and make the reaction site aerobic to generate a foul odor. It is an object of the present invention to provide an advanced water treatment method and apparatus capable of preventing the above.

[0006]

The present invention has achieved the above object, and the invention of claim 1 uses a membrane separation device.
In the advanced water treatment method, the raw water is supplied to the front stage of the membrane separation device, the reaction tank to which the flocculant and the powdered activated carbon are added, and the suspension water of the reaction tank are introduced, and the S
A separation tank for precipitating S content is provided on the separation tank.
The advanced water treatment method is characterized in that clear water is caused to flow into the membrane separation device, and sludge (precipitated SS content) obtained from the separation tank is returned to the reaction tank. In the present invention, the sludge (precipitated SS content) obtained from the separation tank at the subsequent stage is returned to the reaction tank for adding the flocculant and the powdered activated carbon to the raw water, so that the suspending substance and the powdered activated carbon etc. in the sludge are returned. Since the SS content of is high in concentration, the generation of flocs containing aluminum hydroxide is promoted, and the treatment time with powdered activated carbon can be extended, so that the adsorption treatment effect with powdered activated carbon is increased. You can

Further, the invention of claim 2 is the advanced water treatment method according to claim 1, characterized in that the liquid in the reaction tank is aerated using an aerator or an air diffuser. Is. In this invention, by aerating the reaction tank using an aerator or an air diffuser,
It is possible to prevent the inside of the reaction tank from becoming anaerobic.

Further, the invention of claim 3 is characterized in that, in the advanced water treatment method of claim 1, the aggregating agent is an aluminum compound such as aluminum sulfate or polyaluminum chloride. In this invention, since the concentration of SS of the water to be treated introduced into the separation tank can be increased, the coprecipitation action becomes large, and the supernatant water supplied to the membrane separation device contains aluminum hydroxide. The concentration of the suspended solids is reduced, clogging of the membrane separation device is prevented, and the chemical cleaning interval can be lengthened.

The invention of claim 4 uses a membrane separation device.
In the advanced water treatment device, a reaction tank to which raw water to which a coagulant and powdered activated carbon are added and a suspension water of the reaction tank are introduced before the membrane separation device,
A separation tank for precipitating the components is provided, and the concentrated water on the inflow side of the membrane separation device into which the supernatant water of the separation tank flows is returned to the reaction tank, and sludge obtained from the separation tank
The (precipitated SS content) is returned to the reaction tank. In this invention, sludge (sludge) obtained from the separation tank at the latter stage is added to the reaction tank for adding the flocculant and the powdered activated carbon to the raw water.
By returning the SS content) , the sludge contains a high concentration of SS content such as suspending substances and powdered activated carbon,
This is a high-performance water treatment device that can promote the generation of flocs containing aluminum hydroxide and can extend the treatment time with powdered activated carbon, so that the adsorption treatment effect with powdered activated carbon can be enhanced.

The invention of claim 5 is the advanced water treatment apparatus according to claim 4, further comprising an aerator or an air diffuser for aerating the liquid in the reaction tank. . The present invention is an advanced water treatment device that can prevent the inside of the reaction tank from becoming anaerobic by aerating the reaction tank using an aerator or an air diffuser.

Further, the invention of claim 6 is the advanced water treatment apparatus according to claim 4, wherein the coagulant is an aluminum compound such as aluminum sulfate or polyaluminum chloride. The advanced water treatment device described. In this invention, since the concentration of SS of the water to be treated introduced into the separation tank can be increased,
The coprecipitation effect becomes large, and the concentration of suspending solids containing aluminum hydroxide in the supernatant water supplied to the membrane separation device becomes small, clogging of the membrane separation device is prevented, and the interval of chemical cleaning is increased. It is an advanced water treatment device that can be extended.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the advanced water treatment method and apparatus of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a system diagram showing an embodiment of the advanced water treatment device according to the present invention. In the figure, the advanced water treatment device comprises a reaction tank 1, a separation tank 4, and a membrane separation device 5. Raw water (for example, river water, dam water, ground water, etc.) is supplied to the reaction tank 1 from a pipe 11, a coagulant is supplied from a coagulant supply device 7, and a powder activated carbon is supplied from a powder activated carbon supply device 8. It In the reaction tank 1,
An aerator or an air diffuser 3 is provided, and the liquid in the reaction tank 1 is agitated by the agitator 2 while being aerated by the air diffuser 3, and the coagulated treated water in the reaction tank 1 is separated through the pipe 14 into a separation tank. Sent to 4.

In the separation tank 4, the SS component of the treated water that has been subjected to the coagulation treatment is separated and precipitated. The sludge in the separation tank 4 is pump P1
It is returned to the reaction tank 1 from the pipe 15 provided with. Excess sludge is discharged from the system through the pipe 16 through the valve V. The supernatant water of the separation tank 4 is supplied from the pump P2 via the pipe 18 to the membrane separation device 5 via the pipe 19.

The membrane separation device 5 is provided with a separation membrane 6 made of a microfiltration membrane, the side where the supernatant water of the separation tank 4 flows in is defined as an inflow side 5a, and the side where the treated water permeating the separation membrane 6 flows out is permeated. The side 5b. The pipe 2 is provided on the permeate side 5b of the membrane separation device 5.
0 is provided, and a pipe 21 for returning the concentrated water is provided on the inflow side 5a.

Next, a treatment method of the advanced water treatment device will be described with reference to FIG. First, raw water is supplied to the reaction tank 1 through a pipe 11, and a flocculant and powdered activated carbon are supplied through pipes 12 and 13, respectively, and the liquid in the reaction tank 1 is stirred by a stirrer 2 to cause a coagulation reaction and to be dispersed. Aeration is performed by the air device 3. The coagulated water to be treated is supplied from the pipe 14 to the separation tank 4 and subjected to solid-liquid separation treatment.
The sludge settled in the separation tank 4 is withdrawn from the pipe 15 provided with the pump P1 and returned to the reaction tank 1 via the pipe 17. At this time, by opening and closing the valve V,
Excess sludge is discharged from the pipe 16 to the outside of the system. Further, the supernatant water obtained in the separation tank 4 is supplied from the pipe 18 to the membrane separation device 5 through the pipe 19 by the power of the pump P2 and subjected to the membrane separation treatment. The permeated water of the membrane separation device 5 is discharged out of the system as treated water through the pipe 20. On the other hand, in the case of the cross flow filtration method, the concentrated water on the inflow side 5a is pipe 2
1 to the reaction tank 1.

As the coagulant, an aluminum compound such as aluminum sulfate or polyaluminum chloride (PAC) is used, and the addition amount thereof is 5 with respect to the raw water.
It is preferably about 100 mg / l. As the powdered activated carbon, either coal-based or coconut husk charcoal-based is used, and the addition amount is 10 to 40 m with respect to the raw water.
It is preferably about g / l. Since the activated carbon powder is circulated and used at the injection position of the activated carbon powder, the reaction tank 1
However, it may be at a position after the separation tank 4 and at a position before the membrane separation device 5.

As the separation membrane used in the membrane separation device 5, a membrane such as an ultrafiltration membrane may be used in addition to the microfiltration membrane. Further, from the viewpoints of effective use of powdered activated carbon, coprecipitation effect and improvement of water recovery rate, the physical cleaning wastewater of the membrane separation device 5 may be returned to the reaction tank 1, or the physical separation device 5 may be actively subjected to physical cleaning. By combining the above, it is possible to provide a more effective advanced water treatment method.

In order to describe the present invention more specifically, examples will be described below. The present invention is not limited to the following examples.

Example 1 In accordance with the advanced water treatment method shown in FIG. 1, raw water is introduced into the reaction tank 1, polyaluminum chloride (PAC) is used as a coagulant, and powdered activated carbon is added at the following ratio. . Further, 50% of the sludge in the separation tank 4 was returned to the reaction tank 1 and reacted by stirring. The mixed liquid obtained by the reaction was introduced into the separation tank 4 for solid-liquid separation. Further, the supernatant water of the separation tank 4 was supplied to the membrane separation device 5 having the following specifications for membrane separation treatment.

Reaction tank PAC addition amount: 10 mg / l Powdered activated carbon addition amount: 20 mg / l Aeration amount: 50 l / min

Decomposition tank Liquid retention time: 2 hours

Membrane Separation Device Membrane type: Microfiltration membrane Membrane material: Polypropylene membrane shape: Hollow fiber nominal pore size: 0.2 μm Filtration method: External pressure type total filtration membrane permeation flux: 1.5 m / day Backwash interval: 30 minutes Filtration / 3 minutes backwash

The result of the water flow experiment under the above conditions is
As shown in FIG. 2, the horizontal axis represents the water passage time and the vertical axis represents the transmembrane pressure difference. The transmembrane pressure difference represents the pressure obtained by subtracting the membrane outlet pressure from the membrane inlet pressure in the microfiltration membrane of the membrane separation device 5. The transmembrane pressure changes with the passage of water flow time. As shown in FIG. 2, in Example 1, the results shown by ● in the figure were obtained. On the other hand, Comparative Example 1 was the same as Example 1 except that the sludge in the separation tank 4 was not returned to the reaction tank 1 and that the reaction tank 1 was not aerated using the advanced water treatment apparatus of FIG. The same process was performed. as a result,
In Comparative Example 1, the results shown by ◯ in FIG. 2 were obtained.

As is clear from FIG. 2, Example 1 shows that the change in transmembrane pressure difference is smaller and more stable than Comparative Example 1. In the advanced water treatment method of the present invention, it was proved that stable water flow was possible without an increase in transmembrane pressure difference of the microfiltration membrane device being observed. In addition, during the experiment for about one month, the reaction tank 1 did not detect any coloring that is considered to be caused by the elution of manganese or a bad odor resulting from the decomposition of organic matter.

(Embodiment 2) Next, other experimental results will be described under the conditions according to Embodiment 2. With the advanced water treatment device of FIG. 1, raw water is introduced into the reaction tank 1, aluminum sulfate and powdered activated carbon are added at the following ratios, and 40% of sludge in the separation tank 4 and concentrated water of the membrane separation device 5 are added. Was returned to the reaction tank 1 through the pipe 21 and stirred by the stirrer 2 to cause a reaction. The mixed solution obtained by the reaction was introduced into the separation tank 4 and further supplied to the membrane separation device 5 having the following specifications for membrane separation treatment.

Reaction tank Aluminum sulfate addition amount: 10 mg / l Powdered activated carbon addition amount: 20 mg / l Concentrated water circulation amount: 0.2 times amount of raw water Aeration amount: 50 l / min

Separation tank Liquid retention time: 3 hours

Membrane separation device Membrane type: Ultrafiltration membrane Membrane material: Polyacrylonitrile membrane shape: Hollow fiber fractionated molecular weight: 13,000 Filtration method: External pressure type cross flow filtration membrane permeation flux: 0.7 m / day Backwash Interval: 20 minutes filtration / 20 seconds backwash

Example 2 and Comparative Example 2 under the above experimental conditions
In contrast, the results shown in FIG. 3 were obtained. FIG. 3 shows the average filtration pressure with respect to the water passage time. The results of Example 2 are shown by ● in FIG. Here, the average filtration pressure represents a pressure obtained by subtracting the membrane outlet pressure from the average of the membrane inlet pressure and the circulating water pressure when an extraocular filtration membrane is used in the membrane separation device 5.

Comparative Example 2 to Example 2 is the same as Example 2 except that the sludge in the separation tank 4 was not returned to the reaction tank 1 in the advanced water treatment and that the reaction tank 1 was not aerated. The same process was performed. Comparative example 2 has a circle in FIG.
The results shown in are obtained.

As is clear from the results shown in FIG.
By using the above advanced water treatment method, the average filtration pressure of the ultrafiltration membrane device of the separation membrane 6 of the membrane separation device 5 was not increased, and stable water flow was possible. During the experiment for about 1 month, no odor or the like caused by the elution of manganese, which is considered to be due to the elution of manganese, or the odor derived from the decomposition of organic matter was not detected. In Example 2, it was demonstrated that the separation membrane 6 was not clogged and stable operation was possible for a long period of time.

[0032]

As described above, according to the present invention, by returning the sludge obtained from the subsequent separation tank to the reaction tank for adding the flocculant and the powdered activated carbon to the raw water, the membrane separation apparatus can be used. Has an advantage that it is possible to stably and continuously pass water without a sudden increase in the effective transmembrane pressure or the average filtration pressure.

Further, since the interval of chemical cleaning in the membrane separation device becomes long, there is an advantage that the cost and labor for the chemical cleaning operation can be reduced. Further, the reaction vessel is aerobically leached by manganese elution. It has the effect of preventing the generation of a bad odor due to coloring and the decay of organic substances.

Further, by returning the sludge obtained from the separation tank at the latter stage into the reaction tank for adding the flocculant and the powdered activated carbon to the raw water, the sludge contains SS components such as suspending substances and powdered activated carbon. Since it is contained in a high concentration, the formation of flocs containing aluminum hydroxide is promoted, and since the treatment time with powdered activated carbon can be extended, the adsorption treatment effect with powdered activated carbon is maximized. There is an advantage that the water treatment cost can be reduced.

The SS of the water to be treated introduced into the separation tank
Since the concentration of the component is high, the coprecipitation effect is large, and the concentration of the suspended solids containing aluminum hydroxide is small in the supernatant water supplied to the membrane separation device. It prevents clogging and is effective in extending the interval between chemical cleanings.

Further, by aerating the reaction tank by using an aerator or an air diffuser, it is possible to prevent the inside of the reaction tank from becoming anaerobic, so that it is possible to prevent an offensive odor.

[Brief description of drawings]

FIG. 1 is a system diagram schematically showing an embodiment of an advanced water treatment device according to the present invention.

FIG. 2 is a diagram showing a comparison of operation results between Example 1 and Comparative Example 1.

FIG. 3 is a diagram showing a comparison of operation results between Example 2 and Comparative Example 2.

FIG. 4 is a system diagram of an advanced water treatment device in the prior art.

[Explanation of symbols]

1 reaction tank 2 stirrer 3 Air diffuser 4 separation tanks 5 Membrane separation device 6 Separation membrane 7 Flocculant supply device 8 Powdered activated carbon feeder 11-21 piping P1, P2 pump V valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ identification code FI C02F 9/00 504 C02F 9/00 504B (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 61/00-65 / 10 C02F 1/44 C02F 1/28 C02F 9/00

Claims (6)

(57) [Claims] 1. An advanced water treatment method using a membrane separator.
Then, in the preceding stage of the membrane separation device, a reaction tank to which raw water is supplied, a flocculant and powdered activated carbon are added, and a suspension water of the reaction tank is introduced, and a separation tank for precipitating the SS content thereof is provided. , The supernatant water of the separation tank is introduced into the membrane separation device.
And the sludge (precipitated SS content) obtained from the separation tank is returned to the reaction tank. 2. The advanced water treatment method according to claim 1, wherein the liquid in the reaction tank is aerated using an aerator or an air diffuser. 3. The advanced water treatment method according to claim 1, wherein the aggregating agent is an aluminum compound such as aluminum sulfate or polyaluminum chloride. 4. An advanced water treatment apparatus using a membrane separator, wherein a raw water is supplied to a preceding stage of the membrane separator, a reaction tank to which a flocculant and powdered activated carbon are added, and a suspension water in the reaction tank. A sludge that is introduced and is provided with a separation tank for precipitating the SS content is returned to the reaction tank, and the concentrated water on the inflow side of the membrane separation device into which the supernatant water of the separation tank flows is returned to the reaction tank. An advanced water treatment device, wherein (precipitated SS content) is returned to the reaction tank. 5. The advanced water treatment device according to claim 4, further comprising an aerator or an air diffuser for aerating the liquid in the reaction tank. 6. The advanced water treatment device according to claim 4, wherein the aggregating agent is an aluminum compound such as aluminum sulfate or polyaluminum chloride.