JP4825932B2 - Water treatment method - Google Patents

Description

The present invention relates to a water treatment method, and more particularly to a water treatment method in which water to be treated is separated by a reverse osmosis membrane unit having a reverse osmosis membrane (RO membrane).

  As such a water treatment method, in order to prevent clogging of the membrane, the water to be treated and a chemical containing a chlorine component are mixed, and the free residual chlorine concentration obtained by the mixing is in the range of 0.1 to 1 mg / L. A method of performing membrane separation with a reverse osmosis membrane unit using free residual chlorine-containing treated water as the treated water is known (for example, Patent Document 1).

JP 2005-152688 A

  However, such a method cannot sufficiently suppress clogging of the reverse osmosis membrane (RO membrane).

  On the other hand, simply trying to sufficiently suppress clogging of the reverse osmosis membrane (RO membrane) by increasing the free residual chlorine concentration of the treated water containing free residual chlorine, the free residual chlorine containing water There is a possibility that the reverse osmosis membrane (RO membrane) may deteriorate due to the free residual chlorine of the treated water.

In view of the above problems, the present invention provides a water treatment method in which a reverse osmosis membrane (RO membrane) is hardly deteriorated while suppressing clogging of the reverse osmosis membrane (RO membrane) using a chemical containing a chlorine component. This is the issue.

The present invention is a water treatment method for membrane separation of water to be treated by a reverse osmosis membrane unit having an osmosis membrane,
Measure the differential pressure on the non-permeate side of the reverse osmosis membrane unit with a differential pressure measuring device,
When the measured value measured by the differential pressure measuring device is less than the reference value, the free residual chlorine-containing treated water whose free residual chlorine concentration is in the range of 0.20 mg / L or more and less than 1.2 mg / L When the measured value measured by the differential pressure measuring device is equal to or higher than a reference value, the free residual chlorine concentration is in the range of 1.2 to 2 mg / L. It is characterized in that membrane treatment is carried out by the reverse osmosis membrane unit using free residual chlorine-containing treated water as treated water .
According to such a water treatment method, when the measured value is less than the reference value, the free residual chlorine-containing treated water having a low free residual chlorine concentration (0.20 mg / L or more and less than 1.2 mg / L) ) Can be obtained, and purified water as permeate can be obtained by suppressing the deterioration of the reverse osmosis membrane (RO membrane) while suppressing clogging of the membrane. Further, when the measured value is equal to or higher than the reference value, the membrane water is separated by membrane separation of free residual chlorine-containing treated water (1.2 to 2 mg / L) having a higher free residual chlorine concentration. Clogging can be further suppressed. In addition, when the water to be treated is membrane-separated with a constant flux, if the differential pressure starts to rise, the difference may be caused even if the reverse osmosis membrane (RO membrane) is washed with a chemical such as alkali other than free residual chlorine. Although the pressure continues to rise, according to such a water treatment method, even if the differential pressure rises somewhat, the differential pressure can be lowered.

Further, the present invention is a water treatment method for membrane separation of water to be treated by a reverse osmosis membrane unit having a reverse osmosis membrane,
Measure the differential pressure on the non-permeate side of the reverse osmosis membrane unit with a differential pressure measuring device,
When the measured value measured by the differential pressure measuring device is below the reference value, the free residual chlorine-containing treated water whose free residual chlorine concentration is in the range of 0.20 mg / L or more and less than 1.2 mg / L When the measured value measured by the differential pressure measuring device exceeds the reference value, the free residual chlorine concentration is within the range of 1.2 to 2 mg / L. The water treatment method is characterized in that membrane treatment is performed by the reverse osmosis membrane unit using the water to be treated containing free residual chlorine as the water to be treated.

  As described above, according to the present invention, the reverse osmosis membrane (RO membrane) is hardly deteriorated while the clogging of the reverse osmosis membrane (RO membrane) is suppressed using a chemical containing a chlorine component.

Schematic of a water treatment apparatus. The figure which shows the time-dependent change of the free residual chlorine concentration of the 2nd free residual chlorine containing to-be-processed water, and the differential pressure | voltage of the non-permeation | transmission side of a reverse osmosis membrane unit. The figure which shows the time-dependent change of the salt rejection of the reverse osmosis membrane of a reverse osmosis membrane unit.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

First, the water treatment apparatus used in the water treatment method of this embodiment will be described.
As shown in FIG. 1, the water treatment device 1 is divided Nigomaku unit 21 treated water A to obtain a first permeate and a first retentate C is membrane separation is provided,該除Nigomaku unit 21 And a reverse osmosis membrane unit 31 that separates the first permeate from the membrane and obtains the second permeate and the second concentrated water D. A reverse osmosis membrane treatment unit 3 for membrane separation of the first permeated water by the membrane unit 31 is provided. Moreover, the water treatment apparatus 1 is transferred to a processing unit 2 treated water A is clarification, first permeate is transferred to the reverse osmosis membrane treatment unit 3, the first concentrated water C is first concentrated water reservoir The second permeated water is transferred to the purified water storage tank (not shown) as the purified water B, and the second concentrated water D is transferred to the second concentrated water storage tank (not shown). It is comprised so that it may be.
In the present specification, turbidity is filtration that is rougher than reverse osmosis membrane filtration, that is, before filtration through a reverse osmosis membrane (RO membrane) and separated by a reverse osmosis membrane (RO membrane). It means removing coarser impurities (for example, solid substances).

Moreover, the said water treatment apparatus 1 is equipped with the chlorine-type aqueous solution storage part 4 which stores the chlorine-type aqueous solution of the chemical | medical agent containing chlorine components, such as sodium hypochlorite. Moreover, the water treatment apparatus 1 is chlorine aqueous solution of the salt Motokei solution reservoir 4 is transferred to the clarification process unit 2, the transfer chlorine aqueous solution of the salt Motokei solution reservoir 4 to the reverse osmosis membrane treatment unit 3 It is comprised so that it may be.

  The turbidity treatment unit 2 includes a mixing unit 22 that mixes the water to be treated A and a chlorine-based aqueous solution to obtain first free residual chlorine-containing water to be treated. The treated water A is transferred to the turbidity membrane unit 21 and separated from the membrane.

  Moreover, the said turbidity treatment part 2 adjusts the mixing ratio of the to-be-processed water A and chlorine system aqueous solution, and adjusts the free residual chlorine concentration of the 1st free residual chlorine containing to-be-processed water obtained. An adjustment mechanism (not shown) is provided.

The treated water A mixed with the chlorinated aqueous solution in the mixing unit 22 is not particularly limited, for example. Examples of the treated A include human waste water, sewage, and factory waste water (food factories, chemicals). Examples include supernatant water obtained by biological treatment and precipitation separation of organic wastewater such as wastewater from factories such as factories, electronic industry factories, and pulp factories, river water, and lake water.
The to-be-treated water A has turbidity, and the turbidity in the to-be-treated water A is, for example, 0.1 degree or more, more specifically 0.1 to 50 degrees. In this specification, turbidity means a value measured by a laser scattering method.

The turbidity unit 21 has an ultrafiltration membrane and / or a microfiltration membrane.
The turbidity unit 21 is of a spiral type. The spiral membrane unit has a structure in which a flat membrane filter membrane is overlapped with a net-like spacer for maintaining strength.

  The reverse osmosis membrane treatment unit 3 includes a first permeate storage unit 32 that stores a first permeate containing free residual chlorine, and the first permeate as the second free residual chlorine-containing treated water is treated water. It is configured to be transferred to the reverse osmosis membrane unit 31 as A and to be membrane-separated. In addition, in order to adjust the free residual chlorine density | concentration of 1st permeated water, it is comprised so that a chlorine-type aqueous solution can be added to the 1st permeated water storage part 32. FIG.

  Further, the reverse osmosis membrane treatment unit 3 regulates the free residual chlorine concentration of the first permeated water as the second free residual chlorine-containing treated water by adjusting the mixing ratio of the first permeated water and the chlorine-based aqueous solution. A second mixing ratio adjusting mechanism (not shown) is provided.

The reverse osmosis membrane treatment unit 3 includes a differential pressure measurement device (not shown) that measures the differential pressure (flow path pressure loss) on the non-permeation side of the reverse osmosis membrane unit 31.
The differential pressure on the non-permeate side (flow path pressure loss) is obtained without passing through the reverse osmosis membrane from the pressure value of the supply water supplied to the reverse osmosis membrane of the reverse osmosis membrane unit 31. It means a value obtained by subtracting the value of the concentrated water pressure, and more specifically, from the value of the feed water pressure at the feed water inlet of the membrane module of the reverse osmosis membrane unit 31, the concentrated water of the membrane module. It means a value obtained by subtracting the pressure of concentrated water at the outlet.

  Further, the reverse osmosis membrane treatment unit 3 has a free residual chlorine concentration of 0.20 mg / L or more when the measured value measured by the differential pressure measuring device (not shown) is less than a reference value. A second free residual chlorine-containing treated water that is less than 2 mg / L, preferably greater than 0.25 mg / L and less than 1.2 mg / L, more preferably in the range of 0.3 to 1.0 mg / L. In the case where water A is continuously separated by the reverse osmosis membrane unit 31 and the measured value measured by the differential pressure measuring device (not shown) is equal to or higher than a reference value, The second free residual chlorine-containing treated water having a free residual chlorine concentration in the range of 1.2 to 2 mg / L, preferably 1.4 to 1.8 mg / L is continuously treated as the treated water A by the reverse osmosis. Configured to be separated by the membrane unit 31 That.

  In addition, the reverse osmosis membrane device 3 contains the second free residual chlorine content by the second mixing ratio adjusting mechanism (not shown) based on the measured value obtained by the differential pressure measuring device (not shown). It is comprised so that the free residual chlorine density | concentration of the 1st permeated water which is to-be-processed water may be adjusted.

  The reference value per reverse osmosis membrane unit is preferably 0.01 to 0.1 MPa, more preferably 0.02 to 0.09 MPa.

The reverse osmosis membrane unit 31 has a reverse osmosis membrane (RO membrane) and is of a hollow fiber type.
The reverse osmosis membrane (RO membrane) is composed of cellulose acetate.

Although the said water treatment apparatus is comprised as mentioned above, the water treatment method of this embodiment is demonstrated next.

  The water treatment method of this embodiment is measured by the differential pressure measuring device (not shown), and when the measured value measured by the differential pressure measuring device (not shown) is less than a reference value, the water treatment method is free. The second free residual chlorine-containing treated water having a residual chlorine concentration in the range of 0.20 mg / L or more and less than 1.2 mg / L is separated into membranes by the reverse osmosis membrane unit 31 as treated water A, and the differential pressure When the measured value measured by the measuring device (not shown) is equal to or higher than the reference value, the second free residual chlorine-containing treated water whose free residual chlorine concentration is in the range of 1.2 to 2 mg / L. In this method, the water to be treated A is separated by the reverse osmosis membrane unit 31.

In addition, although the said water treatment apparatus and the water treatment method of this embodiment had the said structure, the said water treatment apparatus and the water treatment method of this invention are not limited to the said structure, A design change is possible suitably. It is.
For example, the water treatment system, the reverse osmosis membrane treatment unit 3, if the measured value measured by the differential pressure measuring device (not shown) is less than the reference value, the free residual chlorine concentration 0. The second free residual chlorine-containing treated water in the range of 20 mg / L or more and less than 1.2 mg / L is continuously separated by the reverse osmosis membrane unit 31 as treated water A. In the case where the measured value measured by the differential pressure measuring device (not shown) is equal to or higher than the reference value, the free residual chlorine content is within the range of 1.2 to 2 mg / L of free residual chlorine. becomes configured to the water to be treated is continuously membrane separation by the reverse osmosis membrane unit 31 as treated water A, water treatment apparatus, said reverse osmosis membrane treatment unit 3, the differential pressure measuring device The measured value measured by (not shown) is below the reference value In the case where the concentration of free residual chlorine is within the range of 0.20 mg / L or more and less than 1.2 mg / L, the second free residual chlorine-containing treated water is continuously treated as the treated water A. When the measured value measured by the differential pressure measuring device (not shown) exceeds a reference value, the free residual chlorine concentration is 1.2 to 2 mg / L. The second free residual chlorine-containing treated water that falls within the range may be continuously separated by the reverse osmosis membrane unit 31 as the treated water A.

  Next, the present invention will be described more specifically with reference to test examples.

The supernatant water (turbidity: fluctuates between 0.1 and 50 degrees) obtained by biological treatment of sewage and subsequent precipitation separation is mixed with a chlorinated aqueous solution (sodium hypochlorite aqueous solution). Free treated chlorine-containing water was obtained. And this 1st free residual chlorine containing treated water is membrane-separated with the spiral-type turbidity membrane unit (brand name: RS50-S8, Nitto Denko Co., Ltd.) which has an ultrafiltration membrane (UF membrane), The 1st permeated water was obtained as the 2nd free residual chlorine containing treated water. The second free residual chlorine-containing treated water is subjected to membrane separation with a hollow fiber type reverse osmosis membrane unit (trade name: HB10255FI, manufactured by Toyobo Co., Ltd.) having a cellulose triacetate reverse osmosis membrane (RO membrane). Thus, second permeated water was obtained. The differential pressure on the non-permeation side of the reverse osmosis membrane unit during membrane separation was measured with a pressure data logger (trade name: DAQSTATION DX120, manufactured by Yokogawa Electric Corporation) as a differential pressure measuring device. The results are shown in FIG.
In addition, as shown in FIG. 2, when the measured value measured by the differential pressure measuring device is less than the reference value (0.06 MPa), the second free residual chlorine-containing treated water is used as the free residual chlorine concentration. Was within the range of 0.20 mg / L or more and less than 1.2 mg / L, and membrane separation was performed by the reverse osmosis membrane unit as water to be treated. Further, when the measured value measured by the differential pressure measuring device is equal to or higher than a reference value, the second free residual chlorine-containing water to be treated has a free residual chlorine concentration within a range of 1.2 to 2 mg / L. Then, membrane separation was performed by the reverse osmosis membrane unit as water to be treated.
Moreover, in order to calculate the salt rejection of the reverse osmosis membrane (RO membrane) of the reverse osmosis membrane unit, the electrical conductivities of the second free residual chlorine-containing treated water and the second permeated water were measured. The electrical conductivity was measured according to the electrode method. The results are shown in FIG.
The salt rejection of the reverse osmosis membrane (RO membrane) of the reverse osmosis membrane unit is a value calculated by the following equation.
Salt rejection (%) = (1−Cp / Cf) × 100
Cf: electric conductivity of the second free residual chlorine-containing treated water, Cp: electric conductivity of the second permeated water

As shown in FIG. 2, the differential pressure was 0.1 MPa or less, indicating that almost no blockage of the reverse osmosis membrane (RO membrane) occurred. Further, when the differential pressure becomes 0.06 MPa or more, the differential pressure increases by making the free residual chlorine concentration within the range of more than 0.25 mg / L and less than 1.2 mg / L. It was suggested that it can be lowered even at the beginning.
Moreover, as shown in FIG. 3, the salt rejection was 97% or more, suggesting that the reverse osmosis membrane (RO membrane) was not deteriorated by free residual chlorine.

  1: water treatment device, 2: turbidity treatment unit, 3: reverse osmosis membrane treatment unit, 4: chlorinated aqueous solution storage unit, 21: turbidity membrane unit, 22: mixing unit, 31: reverse osmosis membrane unit, 32: First permeated water storage unit, A: treated water, B: purified water, C: first concentrated water, D: second concentrated water

Claims (5)

A water treatment method for membrane separation of water to be treated by a reverse osmosis membrane unit having a reverse osmosis membrane,
Measure the differential pressure on the non-permeate side of the reverse osmosis membrane unit with a differential pressure measuring device,
When the measured value measured by the differential pressure measuring device is less than the reference value, the free residual chlorine-containing treated water whose free residual chlorine concentration is in the range of 0.20 mg / L or more and less than 1.2 mg / L When the measured value measured by the differential pressure measuring device is equal to or higher than a reference value, the free residual chlorine concentration is in the range of 1.2 to 2 mg / L. A water treatment method characterized in that membrane treatment is carried out by the reverse osmosis membrane unit using free residual chlorine-containing treated water as treated water. Wherein when the measured value is less than the reference value, the inverse free residual chlorine concentration of free residual chlorine contained water to be treated is in the range of less than greater 1.2 mg / L than 0.25 mg / L as water to be treated water treatment method according to claim 1, wherein you membrane separation by osmotic membrane unit. A water treatment method for membrane separation of water to be treated by a reverse osmosis membrane unit having a reverse osmosis membrane,
Measure the differential pressure on the non-permeate side of the reverse osmosis membrane unit with a differential pressure measuring device,
When the measured value measured by the differential pressure measuring device is below the reference value, the free residual chlorine-containing treated water whose free residual chlorine concentration is in the range of 0.20 mg / L or more and less than 1.2 mg / L When the measured value measured by the differential pressure measuring device exceeds the reference value, the free residual chlorine concentration is within the range of 1.2 to 2 mg / L. A water treatment method characterized in that membrane treatment is carried out by the reverse osmosis membrane unit using the treated water containing free residual chlorine as the treated water. When the measured value is equal to or lower than the reference value, the free residual chlorine-containing treated water whose free residual chlorine concentration is in the range of more than 0.25 mg / L and less than 1.2 mg / L is treated as the reverse water. water treatment method according to claim 3, wherein you membrane separation by osmotic membrane unit. Water treatment according to claim 1 wherein the reverse osmosis membrane has been configured with cellulose acetate
Way .

Images