JP3381556B2 - Water purification method and device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for water purification, and more particularly to a method and a device for water purification using a membrane separation device for treating backwash wastewater of a sand filter in a treatment system.

[0002]

2. Description of the Related Art Conventional water purification facilities are coagulation sedimentation facilities,
It consists of sand filtration equipment and other chemical injection equipment, and produces wastewater such as sand washing wastewater, settled sludge, and sand filtration washing wastewater. Of these, the water purification capacity of the water purification equipment is 10,000m
Wastewater from sedimentation equipment and filtration equipment of ³ / d or more is subject to the wastewater regulation under the Water Pollution Control Law in consideration of the environment. These wastewaters are processed by sun drying or mechanical dehydration, and the dehydrated cakes are disposed of in landfills or embankments. On the other hand, in recent years, as a new water purification system for simple water supply, a system using a membrane has been developed in the Ministry of Health and Welfare large-scale project "MAC21 plan", and an actual device is also in operation. A system has also been developed in which the cleaning wastewater discharged from the membrane water purification system is treated with a membrane.

[0003]

However, since it is difficult to secure a landfill disposal site for a cake obtained by dehydrating the wastewater generated in a water purification plant, it is required to reduce its volume.
Further, since the wastewater generated in the water purification plant becomes 5 to 10% of the amount of raw water received by the water purification plant, it is required to improve the water recovery rate by reprocessing these and collecting them as purified water. . The sand filtration equipment is operated while periodically cleaning the air, backwashing the water, and cleaning the water surface to remove the suspended components because the suspended components that have been input cause clogging. . Usually, backwashing with sand filtration is performed for 5 to 20 minutes,
The SS content in the backwash drainage reaches its maximum a few minutes after the start of backwash, and then gradually decreases. In addition, after the backwashing, the sand filtration water immediately after the restart of filtration tends to be slightly turbid, which causes an increase in the chlorine injection amount in the subsequent chlorine disinfection step. The present invention solves the above-mentioned problems of the prior art, and provides a water purification method and a device capable of efficiently treating backwash wastewater of a sand filtration device and realizing a reduction in wastewater volume and a high water recovery rate. With the goal.

[0004]

According to the present invention, a backwash drainage of a sand filter is provided with two membrane separators, and the backwash drainage is treated by one of the membrane separators according to its SS concentration. This has achieved the above-mentioned subject. That is, the water purification treatment method of the present invention is a water purification treatment method in which sand filtration and the treatment of backwash drainage of a sand filtration device are performed, and the backwash drainage of the sand filtration device of two membrane separation devices according to its SS concentration. The feature is that one of them is processed. Further, the water purification apparatus of the present invention is a water purification apparatus comprising a sand filtration apparatus and a backwash wastewater treatment apparatus of the sand filtration apparatus, in which the backwash wastewater treatment apparatus can be operated by switching from two membrane separation apparatuses. It is characterized by

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION When carrying out the water purification method of the present invention, coagulated water that has undergone the coagulating sedimentation step is usually used as the water to be treated, but the water is not limited to this. In the water purification method and device of the present invention, two membrane separation devices capable of switching operation are used, but a membrane separation device composed of a hollow fiber module or a fixed flat membrane module and a membrane separation device composed of a rotating flat membrane module. 2 series of membrane separation device consisting of and, the backwash wastewater of the sand filtration device is treated with the membrane separation device consisting of the rotating flat membrane module until the SS concentration decreases to a predetermined value, and the SS concentration becomes lower than the predetermined value. Then, it is preferable to treat with a membrane separation device consisting of a hollow fiber type module or a fixed flat membrane type module. Further, it is preferable to treat the sand-filtered water immediately after the sand filtration is restarted with a membrane separation device including a hollow fiber type module or a fixed flat membrane module.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the water purification method and the processing apparatus according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a system diagram of a water purification device of the present invention. The water purification apparatus of the present invention shown in FIG. 1 comprises a sand filter 1, a membrane separator 2 and a membrane separator 3. The water to be treated is supplied to the sand filter 1 through the valve 4, the suspended matter in the water is removed, and the sand filtered water is discharged from the lower part to the outside of the system through the valve 5. Air and water for backwashing can be supplied to the sand filter 1. Backwashing of the sand filter is performed regularly, and the drainage is discharged from the top of the device. The discharge line is branched into two and is connected to the membrane separation device 2 and the membrane separation device 3 via valves 7 and 6, so that either one can be operated. In addition, in the membrane separation device 2, the sand filtered water immediately after the sand filtration is restarted after the back washing is completed is opened by the valve 8
Is supplied via. Air used for cleaning the membrane surface and backwash water can be supplied to the membrane separation device 2. Physical cleaning of the membrane separation device 2 is regularly performed, and the cleaning wastewater is supplied to the membrane separation device 3 via the valve 9. The permeated water of the membrane separation device 2 and the membrane separation device 3 becomes treated water of this system. Further, the concentrated sludge is discharged from the membrane separation device 3 to the outside of the system.

FIG. 2 shows a change with time of the SS concentration in the backwash drainage discharged from the sand filter 1. S in backwash drainage
After the S concentration reached its maximum 2-3 minutes after the start of backwashing,
The concentration gradually decreases, and the difference in concentration becomes several hundred mg / l. Therefore, in the present invention, the backwash drainage from the start of backwash until the SS concentration decreases to a predetermined value is treated with a membrane separator suitable for high concentration separation, that is, a membrane separator composed of a rotary flat membrane module, and SS The low-concentration backwashing wastewater having a lower concentration is preferably treated by the other membrane separation device, that is, a membrane separation device composed of a hollow fiber type or a fixed flat membrane type module. Therefore, in the apparatus shown in FIG. 1, each membrane separation device is optimized by constructing the membrane separation device 2 from a hollow fiber type or fixed flat membrane module and the membrane separation device 3 from a rotating flat membrane module. It is possible to operate while maintaining a stable membrane permeation flux under various operating conditions.

FIG. 3 shows the time-dependent change in the SS concentration in the sand-filtered water immediately after restarting the sand filtration after the backwashing of the sand filter.
The sand filter layer expands by backwashing, and the expanded filter sand gradually settles back to its original state after backwashing. There is a tendency to leak some water and the sand filtration water will become slightly turbid. Therefore, it is preferable to treat the sand-filtered water immediately after the sand filtration is restarted with the membrane separation device 2 including the hollow fiber type or the fixed flat membrane type module to recover the treated water. This can be expected to stabilize the quality of sand filtered water and improve the water recovery rate of the entire system.

When the method of the present invention is carried out by using the water purification apparatus shown in FIG. 1, the valves are opened and closed as shown in Table 1.

[0010]

[Table 1]

That is, at the time of normal sand filtration, the valve 4 on the feed line for the treated water and the valve 5 on the line for discharging the sand filtration water are opened. Next, from the start of backwashing until the SS concentration decreases to the set value, the valve 6 is opened so that the backwash drainage is supplied to the membrane separation device 3. When the SS concentration falls below the set value, the valve 7 is opened so that the backwash drainage is supplied to the membrane separation device 2. Immediately after the backwashing is finished and immediately after the sand filtration is restarted, the valve 4 of the feed line for the treated water and the valve 8 for feeding the sand filtered water to the membrane separation device 2 are opened. When the quality of sand filtered water becomes stable, the valve 8 is closed and the valve 5 is opened. By repeating such opening and closing of the valve, stable operation of each membrane separation device becomes possible.

The switching between the valve 6 and the valve 7 is
It is desirable to perform it when the SS concentration in the backwash wastewater has dropped to about 200 mg / l, but it can be changed as appropriate depending on the operating conditions of the sand filtration device. Moreover, the timing of switching between the valve 8 and the valve 5 is SS in sand filtration water.
It is desirable to set the time when the concentration has dropped to 1 mg / l.

Next, the effect of dividing the membrane separation device into two series having different performances in the present invention will be described. FIG. 4 shows the tendency of the relationship between the sludge concentration in the membrane module and the flux (unit time, amount of membrane permeated water per unit membrane area) for each of the hollow fiber module and the rotary flat membrane module. As is clear from this figure, the hollow fiber module can obtain a high flux in the low sludge concentration range, but the flux decreases with an increase in the sludge concentration, and when it exceeds 10000 mg / l, the filtration operation becomes difficult. Become. On the other hand, when the rotating flat sheet membrane module is used, the flux becomes lower in the low concentration range compared to the hollow fiber type module, but the flux does not decrease so much even if the sludge concentration increases, and the sludge concentration is 10000 mg / l. Even if it becomes the above, filtration operation is possible and the arrival concentration of concentrated sludge can be expected to be 3 to 5 times that of the hollow fiber type module. For example,
When the sludge concentration of 10000 mg / l, the flux in the case of using a hollow-fiber module is 0.1 to 0.2M ³
/ M was ² · d, but in the case of using a rotary flat membrane module flux was 1.0m ³ / m ² · d.
When the sludge concentration rises, the use of the rotary flat membrane module also leads to a reduction in the volume of sludge generated from the treatment system. As described above, by dividing the membrane separation device into two series, the concentration characteristics of the two modules can be effectively utilized, which makes it possible to extend the chemical cleaning interval of each membrane module and extend the life of the membrane. .

[0014]

According to the present invention, the backwash drainage discharged from the sand filter is treated by one of the two series of membrane separators according to its SS concentration, so that each membrane separator is optimal. It becomes possible to operate while maintaining a stable flux under the operating conditions, and the water recovery rate can be significantly improved. In particular, the backwash drainage from the start of backwash until the SS concentration drops to a predetermined value is treated with a membrane separation device consisting of a rotary flat membrane module, and the backwash drainage with a low SS concentration is a hollow fiber. By performing the treatment with the membrane separation device including the mold or the fixed flat membrane type module, it is possible to select the optimum membrane separation device according to the water quality of the backwash drainage and perform the efficient treatment. Further, by treating the membrane cleaning wastewater generated from the membrane separation device composed of the hollow fiber type or fixed flat membrane type module with the rotary flat membrane module, the water recovery rate can be further improved, and the wastewater and sludge generated from the treatment system can be improved. Volume reduction can also be achieved. Furthermore, by treating the sand filtered water immediately after resuming sand filtration with a membrane separation device consisting of a hollow fiber type or fixed flat membrane type module, it is possible to stabilize the quality of sand filtered water and improve the water recovery rate of the entire system. You can

[Brief description of drawings]

FIG. 1 is a system diagram of a water purification device of the present invention.

FIG. 2 is a graph showing changes over time in SS concentration in backwash drainage discharged from a sand filter.

[Fig. 3] S in the sand filtration water immediately after the sand filtration of the sand filtration device is restarted
It is a graph which shows a time-dependent change of S concentration.

FIG. 4 is a graph showing the relationship between the sludge concentration in the membrane module and the flux of each membrane module.

[Explanation of symbols]

1 sand filter 2 membrane separator 3 Membrane separation device 4 valves 5 valves 6 valves 7 valves 8 valves 9 valves

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI B01D 29/08 540A 29/38 510B 520A (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 24/00 B01D 29 / 66

Claims (8)

(57) [Claims] 1. A water purification treatment method for sand filtration and treatment of backwash drainage of a sand filter, wherein the backwash drainage of the sand filter is treated by one of two membrane separators depending on its SS concentration. A method for purifying water comprising: 2. The backwash wastewater of the sand filter is treated with a membrane separation device composed of a rotating flat sheet membrane module until the SS concentration decreases to a predetermined value, and when the SS concentration becomes lower than a predetermined value, a hollow fiber type module. Alternatively, the water purification method according to claim 1, wherein the treatment is performed by a membrane separation device including a fixed flat membrane module. 3. The water purification treatment method according to claim 1, wherein one of the membrane separation devices is composed of a hollow fiber type module or a fixed flat membrane module, and sand filtration water immediately after restarting sand filtration is treated by the membrane separation device. 4. The water purification method according to claim 1, wherein the cleaning wastewater of the membrane separation device including a hollow fiber type module or a fixed flat membrane module is treated with a membrane separation device including a rotating flat membrane module. 5. A water purification treatment device comprising a sand filtration device and a backwash wastewater treatment device of the sand filtration device, wherein the backwash wastewater treatment device comprises two membrane separation devices capable of switching operation. Water purification device to do. 6. The water purification apparatus according to claim 5, wherein the membrane separation device is a membrane separation device including a hollow fiber type module or a fixed flat membrane type module and a rotating flat membrane module. 7. The water purification treatment according to claim 5, wherein a pipe for passing the treated water of the sand filter to one of the membrane separators is provided, and the membrane separator is composed of a hollow fiber type module or a fixed flat membrane type module. apparatus. 8. The water purification apparatus according to claim 5, further comprising a pipe for supplying the cleaning wastewater of the membrane separation device including the hollow fiber type module or the fixed flat membrane type module to the membrane separation device including the rotating flat membrane module.