JP3223568B2 - Water treatment equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment apparatus using a membrane separation device. More specifically, the present invention relates to an improved water treatment apparatus that increases the recovery rate of water and reduces overall operating power costs.

[0002]

2. Description of the Related Art As is well known, a membrane separation apparatus supplies raw water under pressure to one side (primary chamber) of a separation membrane provided in a pressure-resistant container, and transmits permeated water of the membrane to the other side (primary chamber). (Secondary room).

[0003] This membrane separation apparatus is a membrane filtration (hereinafter sometimes referred to as dead-end filtration) type membrane separation in which the entire amount of raw water supplied to a primary chamber in the vessel is permeated through a membrane and treated. An apparatus and a parallel flow filter (hereinafter referred to as a cross flow) in which raw water is circulated and supplied to the primary chamber, and a part of the raw water passing through the primary chamber is permeated through the membrane and taken out from the secondary chamber. ) Type membrane separation device.

Hereinafter, the respective advantages and disadvantages of the cross flow type membrane separation apparatus and the dead end type membrane separation apparatus will be described.

[0005] In a cross-flow type membrane separation apparatus, even if there is turbidity fluctuation, membrane filtration can be continued without lowering the filtration rate to a level that cannot be used. For this reason, UF (ultrafiltration) membranes and MF (microfiltration) membranes are used instead of flocculation, precipitation, and filtration in pretreatment for RO (reverse osmosis) membrane separation of river water, industrial water, and clean water. Filtration can be performed to simplify the pretreatment process.

However, in a cross-flow type membrane separation apparatus, it is necessary to circulate a larger amount of raw water than the amount to be filtered in order to always give a constant flow rate to the membrane surface. Therefore, the operating power cost per filtered water is inevitably increased. In order to reduce the driving power without lowering the filtration speed, the raw water flow path may be narrowed to lower the circulation flow rate of the raw water, but if the raw water flow path is narrowed, the raw water flow path is easily clogged by SS in the raw water. It is not suitable for practical use.

On the other hand, in the case of a dead end type membrane separation device, only the amount of raw water to be filtered needs to be pumped into the membrane separation device, and the operating power can be reduced.

However, in this dead-end type membrane separation apparatus, the filtration rate decreases with time because cake-like products accumulate on the membrane surface, and even if cakes accumulate, a sufficient amount of filtered water is removed. There is a problem that a large film area is required to obtain.

[0009] In the dead-end type membrane separation device, a device for backwashing operation (backwash pump, automatic valve, etc.) is provided to recover the filtration rate, and cake-like products accumulated on the membrane surface are removed. Perform a backwash operation.

[0010] Along with this backwashing, washing wastewater containing a cake-like product at a high concentration (backwashing wastewater) is generated. As this backwash water, permeated water is usually used.

If the washing wastewater is returned to the raw water tank again in order to maintain a high water recovery rate, the concentration of the turbid substance in the raw water increases, and the load of the turbid substance on the membrane surface increases. The filtration rate of the membrane is reduced.

If the washing wastewater is discharged out of the system, the load of the turbidity on the membrane surface can be kept constant without increasing the turbidity concentration of the raw water, so that the filtration speed of the membrane is kept constant. be able to. However, if the backwash wastewater is not reused as described above, the water recovery rate is reduced accordingly. In particular, when the turbid concentration of the raw water is high and the filtration rate tends to decrease remarkably, it is necessary to frequently perform membrane cleaning, and as a result, the amount of cleaning water discharged is increased, and the recovery rate of service water is considerably reduced.

[0013]

As described above, the cross
The flow type membrane separation apparatus has a problem that power cost is increased. In a dead-end type membrane separation device, back washing of the membrane is required, and the operation is complicated,
There is a problem that the water recovery rate tends to decrease.

An object of the present invention is to solve such a problem and to provide a water treatment apparatus having a low power cost and a high water recovery rate.

[0015]

The water treatment apparatus of the present invention comprises:
It comprises a first membrane separation device for filtering the whole amount of raw water, and a second membrane separation device for performing parallel flow filtration of the washing wastewater of the first membrane separation device.

[0016]

In the water treatment apparatus of the present invention, raw water is subjected to membrane separation treatment by a first membrane separation apparatus (dead end type membrane separation apparatus), and the permeated water is obtained as treated water. Since the first membrane separation device is of a dead end type, the power cost for operation is low.

In order to remove cake-like substances accumulated on the membrane surface of the first membrane separation device, the first membrane separation device is backwashed periodically or as needed using permeated water or raw water. This backwashing wastewater (washing wastewater) is treated by the second membrane separation device. Since the second membrane separation apparatus is a cross-flow type membrane separation apparatus, it can stably treat even washing wastewater containing a high concentration of turbidity without blocking the membrane surface.
In addition, since the washing wastewater is the backwash wastewater of the first membrane separation device, the amount thereof is small in quantity, and the power cost is small when the cross-flow treatment is performed as a whole of the water treatment device. .

[0018]

FIG. 1 is a system diagram of an apparatus according to an embodiment. Raw water is
Dead end type 1st pump from raw water receiving tank 1 by pump 2
Into the raw water chamber (primary chamber) 3 a of the membrane separation device 3. The water that has passed through the separation membrane 3b is taken out through the pressurized water tank 4 for back washing and the take-out line 5 as membrane permeated water.

When the cake-like substance accumulated in the separation membrane 3b is backwashed and removed, the pump 2 is stopped, the valve 5a of the extraction line 5 is closed, and the valve 6a of the air line 6 connected to the pressurized water tank 4 is closed. Open. Thereby, the permeated water in the pressurized water tank 4 is sent to the permeated water chamber (secondary chamber) 3c of the membrane separation device 3 under pressure, and the backwashing of the separation membrane 3b is performed. The backwash drainage is sent to the intermediate water tank 8 via the wash drainage line 7.

The valve 7a of the washing and draining line 7 is
As a matter of course, it is opened only when the backwash drainage is discharged, and is closed during the operation of the membrane separation device 3.

The washing wastewater in the intermediate water tank 8 is pumped by a pump 9 into a primary chamber 1 of a cross-flow type second membrane separation apparatus 10.
0a, and then returned to the intermediate water tank 8 via the circulation line 11. At this time, the valve 11a of the circulation line 11 is open. The permeated water of the separation membrane 10b in the second membrane separation device 10 is recovered from the secondary chamber 10c to the pressurized water tank via the extraction line 13 as the permeated water.

When the turbidity concentration in the intermediate water tank 8 becomes equal to or higher than a predetermined concentration, the valve 11a is closed, and the valve 14a of the concentrated drainage line 14 branched from the circulation line 11 is opened. The concentrated water is discharged out of the system. In addition, this valve 1
Reference numeral 4a is closed at times other than the discharge.

To perform backwashing of the separation membrane 10b, the valve 13a of the extraction line 13 is closed, the valve 15a of the air line 15 is opened, and permeated water is sent to the permeated water chamber 10c by air pressure.

This water treatment apparatus has the following excellent features.

For example, 50 to 90% of the amount of raw water to be treated
Can be treated by filtration by the first membrane separation device 3,
Only the raw water to be filtered needs to be sent by the pump 2, and the operating power can be reduced.

Further, since the washing wastewater of the first membrane separation device 3 is discharged to the intermediate water tank 8, the concentration of the turbid substance in the raw water does not increase. Therefore, the load of the turbid substance on the membrane surface of the separation membrane 3b can be kept constant, and the filtration rate of the membrane can be kept high and constant.

Even when the turbidity of the raw water is extremely high, the filtration speed of the first membrane separation device 3 can be maintained by shortening the washing interval. In addition, blockage of the film 3b can be prevented.

Since the washing wastewater of the first membrane separation device 3 containing a large amount of peeled cake layer adhered to the membrane surface is concentrated in the second membrane separation device 10, the water recovery rate of the whole water treatment device is also improved. It will be expensive.

In the second membrane separation device 10 of the cross flow filtration type, the growth of the cake layer is suppressed due to the strong shearing force generated on the membrane surface of the raw water flow path. Therefore, even raw water containing a large amount of turbid matter can be filtered without blocking the raw water flow path.

The filtration amount of the second membrane separation device 10 is as small as about 10 to 50% of the whole, and the operating power cost related to the cross-flow filtration is negligible as a whole of the water treatment device. is there.

In the present invention, the form of the membrane module is
Any of hollow fibers and flat membranes may be used, and any of external pressure and internal pressure may be used. It is preferable to use a material that can be easily physically cleaned to remove the cake layer on the film surface. The membrane module may be of the same type for both the first and second membrane separation devices 3 and 10, or may have different shapes depending on the filtration method. The separation membrane may be any as long as it can remove turbid matter, and RO (reverse osmosis), UF (ultrafiltration), MF (microfiltration), or the like is adopted according to the target treated water quality.

[0032]

As described above, according to the water treatment apparatus of the present invention, the operating power can be reduced and the water recovery rate can be increased without lowering the filtration speed.

[Brief description of the drawings]

FIG. 1 is a system diagram of an embodiment apparatus.

[Explanation of symbols]

 Reference Signs List 1 Raw water receiving tank 3 First membrane separation device 4 Pressurized water tank 8 Intermediate water tank 10 Second membrane separation device 12 Pressurized water tank

Claims (1)

(57) [Claims] 1. A water treatment apparatus comprising: a first membrane separation device for filtering a whole amount of raw water; and a second membrane separation device for performing a parallel flow filtration of a washing wastewater of the first membrane separation device.