JP5999087B2 - Water treatment apparatus and water treatment method - Google Patents

Description

  The present invention relates to a water treatment apparatus using a semipermeable membrane unit for treating seawater, river water, groundwater, wastewater treated water to obtain fresh water, and more specifically, enables low cost and stable operation. The present invention relates to a water treatment apparatus and a water treatment method.

  With the worsening of the water environment that has become increasingly serious in recent years, water treatment technology has become more important than ever, and separation membrane utilization technology has been applied very widely. In order to obtain drinking water, industrial water, agricultural water, etc., the purification of river water, lake water, etc. is the main, but the Middle East region where water resources are extremely small and heat resources from oil are extremely abundant. However, seawater desalination has been promoted mainly by the evaporation method. However, there is a growing need for seawater desalination even in areas where heat sources other than the Middle East are abundant, especially since 1990, a desalination process using semipermeable membranes (especially reverse osmosis membranes) with low power requirements has been adopted. Many plants have been built and put into practical use in the Mediterranean and Mediterranean areas. In reverse osmosis membrane equipment, concentrated seawater having pressure energy is discharged, so that pressure recovery is generally performed by an energy recovery unit, which further reduces the required power. Recently, in addition to the improvement in reliability and cost reduction due to technological advancement of reverse osmosis, a significant improvement in energy recovery technology has led to the establishment of many reverse osmosis seawater desalination plants in the Middle East.

  The desalination process itself using reverse osmosis membranes has been continuously developed and improved. Reverse osmosis membranes apply pressure against the osmotic pressure caused by the difference in membrane surface concentration, which is the name of the membrane, to obtain fresh water, but the effective pressure for membrane separation depends on the osmotic pressure based on the supply water concentration. The pressure has been subtracted. For this reason, as described in Patent Document 1 and Non-Patent Document 1, as a desalination process using a reverse osmosis membrane, the operating pressure is increased on the way and the fresh water is efficiently used against the concentrated high osmotic pressure in the latter stage. The separation size is larger than that of a reverse osmosis membrane as shown in Non-Patent Document 2, and the permeate is treated twice using a nanofiltration membrane that is usually unsuitable for seawater desalination. As exemplified in Patent Document 3, energy efficiency is improved by using river water and seawater together, or sewage and low pressure are added to seawater as described in Patent Document 2, Non-Patent Document 4, and Non-Patent Document 5. A process has been proposed in which reverse osmosis membrane concentrated water is mixed with seawater to lower the osmotic pressure. In particular, the process described in Non-Patent Document 4 and Non-Patent Document 5 in which the concentrated water of the low pressure reverse osmosis membrane is mixed to lower the osmotic pressure greatly reduces the required energy compared to the conventional seawater desalination process. It is highly expected because it can.

  For example, FIG. 3 shows a schematic flow diagram of a conventional water treatment apparatus that reduces the osmotic pressure of seawater by mixing concentrated water of a low pressure reverse osmosis membrane. This water treatment apparatus treats waste water a and seawater d containing organic substances with a pretreatment unit x, a low-pressure reverse osmosis membrane unit y, and a reverse osmosis membrane unit z, thereby obtaining fresh water so as to reduce required energy. Device.

  In FIG. 3, the waste water a containing organic matter passes through the first treated water tank 2, is taken in by the water intake pump 3, is supplied to the pretreatment unit x, and is then subjected to low pressure reverse via the pressure pump 6. The permeated water c1 and the concentrated water c2 are divided by the osmotic membrane unit y. The permeated water c1 is stored in the first production water tank 10, and the concentrated water c2 is sent to the mixing tank 17 of the seawater d treatment line. The seawater d passes through the second treated water tank 14 and is taken by the water intake pump 15, treated by the pretreatment unit 16, then sent to the mixing tank 17, and mixed with the concentrated water c <b> 2. The mixed water f thus obtained has a low salt concentration and a reduced osmotic pressure. By supplying and processing this mixed water f to the reverse osmosis membrane unit z by the pressure pump 18, the required energy is reduced as compared with the conventional seawater desalination process, and the separated water e1 and the concentrated water e2 are separated. Can do.

  However, the concentrated water of the low-pressure reverse osmosis membrane is concentrated water, and therefore contains a large amount of impurities, especially organic matter. When mixed with seawater and treated with a high-pressure reverse osmosis membrane, the reverse osmosis membrane is fouled. It has the problem of being easy. In particular, as a low-pressure reverse osmosis membrane for reusing sewage treated water used in the process of Non-Patent Document 4, the adhesion of microorganisms is improved by improving the hydrophilicity of the membrane surface, controlling the call, and improving the smoothness. Products that are resistant to suppressed organic contamination (for example, TML series manufactured by Toray Industries, Inc., Non-Patent Document 6) are sold and used. In contrast, high-pressure reverse osmosis membranes used for seawater-based water treatment have been developed with the main target of reducing required energy, and have fouling that tends to negatively affect the water permeability and blocking performance of the membrane. Reduction techniques are difficult to apply and usually no such measures are taken. Therefore, when low-pressure reverse osmosis membrane concentrated water derived from sewage treated water is supplied to the high-pressure reverse osmosis membrane, it has a problem that it is easy to promote the growth of organisms and easily causes biofouling of the high-pressure reverse osmosis membrane. Yes. Furthermore, when the low pressure reverse osmosis membrane installed on the upstream side of the water treatment apparatus shown in FIG. 3 causes biofouling, the fouling substance will be mixed into the high pressure reverse osmosis membrane on the downstream side, There is a risk that not only the low pressure reverse osmosis membrane but also the high pressure reverse osmosis membrane may deteriorate in performance. In order to prevent these, frequent washing of the low-pressure reverse osmosis membrane and the high-pressure reverse osmosis membrane and the introduction of a bactericidal agent are required, and as shown in Patent Document 3, a contrivance for cost reduction by reusing the cleaning liquid has been proposed. , Essentially leading to increased operating costs.

Japanese Unexamined Patent Publication No. 8-108048 Japanese Unexamined Patent Publication No. 2003-285058 Japanese Unexamined Patent Publication No. 2011-104504

Hiroyuki Yamamura et al., “Development of energy-saving low-cost reverse osmosis membrane seawater desalination technology”, Membrane, 23 (5), p245-250 (1998) R. C. Cheng et. Al., "A Novel Approach to Seawater Desalination Using Dual Dual-Staged Nanofiltration Process," AWWA Annual Conference (2005.6) J. S. S. Chin et. Al., "Increasing Water Resources through Desalination in Singapore: Planning for a Sustainable Future," Proc. IDA World Congress, Dubai, 2009. Yuki Sekine et al., “Start of water supply for production water in integrated seawater and sewage reuse system (Water Plaza)”, 14th Water Environment Symposium (2011). P. Glueckstern, "Design and operation of medium- and small-size desalination plants in remote areas, New perspective for improved reliability, durability and lower costs," Desalination 122 (1999) 123-140. Takeharu Inoue et al., “Low fouling reverse osmosis membrane for sewage”, Membrane, 27 (4), p209-212 (2002)

  An object of the present invention is a water treatment apparatus and a water treatment method for obtaining treated water from a plurality of types of water to be treated, and is a low-cost, stable water treatment apparatus, particularly for fresh water production using a semipermeable membrane. It is providing the water treatment apparatus and water treatment method of this.

In order to solve the above problems, the water treatment apparatus of the present invention has any one of the following configurations (1) to (5).
(1) A pretreatment unit X for pretreating the water to be treated A, a membrane separation unit Y for separating a part B1 of the treated water B of the pretreatment unit X into a permeated water C1 and a concentrated water C2, and the treated water And having a membrane separation unit Z for separating mixed water F obtained by mixing at least a part B2 of B with treated water D different from treated water A into permeated water E1 and concentrated water E2, and at least the concentrated water C2 A water treatment apparatus comprising a line for refluxing one part to the pretreatment unit X.
(2) The water treatment apparatus according to (1), wherein the pretreatment unit X is a unit capable of performing treatment combining biological treatment and solid-liquid separation.
(3) The water treatment apparatus according to (1) or (2), wherein a chemical treatment unit is provided on a line refluxed from the concentrated water C2 to the pretreatment unit X.
(4) The water treatment apparatus according to any one of (1) to (3), wherein at least one of the membrane separation unit Y and the membrane separation unit Z is a semipermeable membrane unit.
(5) The water treatment apparatus according to any one of (1) to (4), wherein the maximum operating pressure of the membrane separation unit Z is higher than the maximum operating pressure of the membrane separation unit Y.

Moreover, the water treatment method of this invention takes the structure in any one of following (6)-(10).
(6) A part B1 of the treated water B obtained by treating the treated water A with the pretreatment unit X is separated into the permeated water C1 and the concentrated water C2 by the membrane separation unit Y, and at least one of the remaining treated water B After mixing the part B2 with the treated water D different from the treated water A, the obtained mixed water F is separated into the permeated water E1 and the concentrated water E2 by the membrane separation unit Z, and the concentrated water C2 is pretreated. A water treatment method characterized by refluxing to X.
(7) The organic matter concentration of the treated water A is higher than the organic matter concentration of the treated water D, and the salinity concentration of the treated water D is higher than the salinity concentration of the treated water A (6 ) Water treatment method.
(8) The water according to (6) or (7), wherein the main component of the treated water A is sewage wastewater or treated water thereof, and the main component of the treated water D is seawater. Processing method.
(9) The flow rate of the treated water B2 and the treated water D is controlled so that the operating pressure fluctuation of the membrane separation membrane unit Z is reduced. Water treatment method.
(10) The water treatment according to (9), wherein the flow rates of the treated water B2 and the treated water D are controlled based on at least one of the temperature and the concentration of the treated water B2 and the treated water D. Method.

  According to the water treatment apparatus of the present invention, when obtaining treated water from a plurality of types of treated water A and D, the drainage load on the environment is reduced, the contamination of the separation membrane is reduced, the frequency of washing and the introduction of a bactericide Cost is reduced and stable operation is possible. In particular, when the water to be treated D is seawater and the membrane separation unit Z is a water treatment device for producing fresh water using a semipermeable membrane unit, the separation of the separation membrane in the membrane separation unit Z, the frequency of cleaning, and the cost of the disinfectant are reduced. Reduction and stable operation are possible, and it becomes easy to maintain high energy recovery efficiency when the energy recovery unit is arranged.

  According to the water treatment method of the present invention, the treatment water is discharged from a plurality of types of treated waters A and D while reducing the drainage load on the environment, reducing the contamination of the separation membrane, and reducing the cleaning frequency and the cost of the sterilizing agent. The obtained driving can be performed stably.

FIG. 1 is a schematic flow diagram illustrating an embodiment of the water treatment apparatus of the present invention. FIG. 2 is a schematic flow diagram illustrating another embodiment of the water treatment device of the present invention. FIG. 3 is a schematic flow diagram illustrating a conventional water treatment apparatus.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to these.

  FIG. 1 is a schematic flow diagram showing an example of a fresh water production apparatus as an embodiment of the water treatment apparatus of the present invention. The water treatment apparatus of the present invention necessarily includes a pretreatment unit X, a membrane separation unit Y, and a membrane separation unit Z. The membrane separation unit Y and the membrane separation unit Z are preferably semipermeable membrane units. By this water treatment apparatus, two different kinds of treated water A and treated water D are treated with water.

  The pretreatment unit X pretreats the treated water A and discharges the treated water B. The pretreatment unit X is preferably a unit capable of performing a treatment combining biological treatment and solid-liquid separation. The membrane separation unit Y processes part B1 of the treated water B and separates it into permeated water C1 and concentrated water C2. Among these, the line which recirculates at least 1 part of the concentrated water C2 to the pretreatment unit X is provided.

  The water treatment apparatus of the present invention can have a mixing tank 17 that mixes at least a part B2 of the treated water D and the treated water B. The mixed water F thus obtained is processed by the membrane separation unit Z and separated into permeated water E1 and concentrated water E2. When seawater is treated as the water to be treated D, the membrane separation unit Z may have a maximum operation pressure higher than the maximum operation pressure of the membrane separation unit Y. At this time, the energy recovery unit 20 can be provided to recover the pressure energy of the concentrated water E2.

  FIG. 2 is a schematic flow diagram illustrating another embodiment of the water treatment apparatus of the present invention. In the schematic flow chart shown in FIG. 2, as an example of the pretreatment unit X, a membrane separation activated sludge tank in which the membrane separation unit 24 is immersed in the biological treatment tank 23 and suction-separated is applied. Further, a chemical treatment unit 22 different from the pretreatment unit X is provided in a line for refluxing the concentrated water C2 to the pretreatment unit X. This chemical treatment unit 22 is preferable because impurities contained in the concentrated water C2 can be removed. In particular, the reflux water composed of the concentrated water C2 contains many impurities that could not be removed by the pretreatment unit X. For this reason, it is preferable that the chemical processing unit 22 is a pretreatment means for assisting the treatment in the pretreatment unit X. For example, a unit that adsorbs organic matter or accelerates decomposition is suitable. In particular, considering the sustainability of the equipment, it is preferable that the chemical treatment unit can decompose organic substances. By providing the chemical processing unit 22, the efficiency of decomposing / removing organic substances in the preprocessing unit X can be increased. When the pretreatment unit X is a membrane separation activated sludge tank, examples of the suitable chemical treatment unit 22 include accelerated oxidation means for adding ozone or hydrogen peroxide.

  In the water treatment method of the present invention, as shown in FIG. 1, the water to be treated A is taken by the water intake pump 3 through the first water to be treated tank 2 and supplied / treated to the pretreatment unit X. The treated water B treated by the pretreatment unit X is fed by the supply pump 5 and divided into treated water B1 and treated water B2. The separated treated water B1 is supplied and processed to the membrane separation unit Y via the pressurizing pump 6, and is divided into permeated water C1 and concentrated water C2. Among these, the permeated water C 1 is stored in the first production water tank 10, and the concentrated water C 2 is returned to the pretreatment unit X through the reflux line 9. If there is no problem even if the amount of reflux of the concentrated water C2 is small, at least a part of the concentrated water C2 can be discharged from the drain line 8 as it is. In addition, when a plurality of pretreatment units are configured in series or in parallel as the pretreatment unit X, the concentrated water C2 is disposed in the middle of the pretreatment unit X arranged in series or in a part of the pretreatment unit X arranged in parallel. It can also be refluxed.

  Further, at least a part of the remaining portion branched from the treated water B and the treated water B1 is sent to the mixing tank 17 by the water supply line 12 as treated water B2. Here, when it is desired to reduce the flow rate of the treated water B2, it is also possible to discharge a part of it from the drainage line 11 to the outside of the system.

  The treated water D passes through the second treated water tank 14 and is taken by the water intake pump 15 and, if necessary, treated by the pretreatment unit 16 and then sent to the mixing tank 17 to be treated with the treated water B2. Mixed. The mixed water F of the treated water B2 and the treated water D is supplied and treated to the membrane separation unit Z by the pressurizing pump 18, and is separated into the permeated water E1 and the concentrated water E2.

  Here, the treated water A and the treated water D are not limited, but the treated water A is more polluted than the treated water D, specifically, the treated water A. It is preferable that the concentration of organic substances and suspended substances in water A is higher than that of water D to be treated. Further, the pretreatment unit X that treats the water to be treated A is not limited. The pretreatment performed by the pretreatment unit X can be appropriately selected from chemical treatment such as coagulation sedimentation and pressurized flotation, physical solid-liquid separation treatment such as sand filtration and membrane filtration, biological treatment, or a combination thereof. . Considering the load on the subsequent membrane separation unit Y, the pretreatment unit X is preferably a combined unit including biological treatment and solid-liquid separation for reducing the organic substance concentration and the suspension concentration.

  As the biological treatment method here, the activated sludge method is representative, and the activated sludge method is to decompose and remove organic substances in wastewater and pollutants such as nitrogen and phosphorus by microorganisms such as activated sludge. . Activated sludge is generally used for wastewater treatment and the like, and sludge extracted from other wastewater treatment facilities is usually used as seed sludge. In the activated sludge method, the sludge concentration is about 2,000 mg / L to 5,000 mg / L, and the residence time of the water to be treated A is usually 1 hour to 24 hours. Further, in the membrane separation activated sludge method to be described later, the sludge concentration is about 2,000 mg / L to 20,000 mg / L, and the residence time of the liquid A to be treated is usually 1 hour to 24 hours. In any case, it is preferable to select an optimum one according to the properties of the water to be treated A. In addition, it is also preferable to install a device for adding a flocculant and add the flocculant to the water to be treated A containing activated sludge, in that phosphorus and soluble organic matter can be reduced from the membrane separation activated sludge treatment liquid. .

  In this way, it is possible to obtain a clear treated water by solid-liquid separation of the biologically treated intermediate treated water. The conventional simplest method is a gravity sedimentation process, which is preferable in that it requires little energy. However, there is a problem that a large area is required for settling the solid components, and depending on the water quality, poor settling occurs and the treated water quality deteriorates. Therefore, in recent years, a process with excellent solid-liquid separation performance, specifically, as shown in FIG. 2, an activated sludge method is performed, and the biologically treated intermediate treated water is treated with a microfiltration membrane or ultrafiltration. A so-called membrane separation activated sludge method in which solid-liquid separation treatment is performed by a separation membrane unit 24 such as a membrane is suitable.

  The microfiltration membrane and ultrafiltration membrane here are often called without a clear definition, but in IUPAC, the microfiltration membrane can remove particles of 0.1 μm or more, and the pressure is reduced. It is defined as a separation membrane as a driving force. The ultrafiltration membrane is generally described as a membrane having pores of 0.001 to 0.1 μm. For microfiltration / ultrafiltration membrane separation of biologically treated water, pressure filtration that supplies water to the membrane separation unit with a pressure pump, or immersion that separates the membrane separation unit into the biological treatment tank and performs suction filtration separation Although various methods such as a filtration method can be applied, it is preferable to apply the immersion filtration method, which is easy to operate stably and has a relatively low energy cost, from the viewpoint of treating water containing high-concentration activated sludge. The membrane applied here is not limited to a hollow fiber membrane or a flat membrane, but a flat membrane is preferable from the viewpoint that the unit structure is simple and suitable for high concentration treatment.

  The membrane separation unit Y at the subsequent stage is not particularly limited as long as the treated water of the pretreatment unit X can be further purified, but a semi-filtration membrane such as a nanofiltration membrane or a reverse osmosis membrane that can separate even smaller molecules than a microfiltration membrane or an ultrafiltration membrane. It is preferable to apply a semipermeable membrane unit such as a permeable membrane unit or an ultrafiltration membrane such as a charged ultrafiltration membrane whose separation performance is enhanced by increasing the surface charge.

  Here, when a microfiltration membrane or an ultrafiltration membrane is applied to the pretreatment unit X, suspended substances in the treated water B can be removed almost 100%, but it is difficult to make the organic substance concentration zero. is there. For this reason, the concentrated water C2 discharged by the membrane separation unit Y has a higher organic substance concentration than the treated water B. Therefore, if the concentrated water C2 satisfies the discharge standard to the environment, it is of course possible to discharge it from the drainage line 8 to the outside of the system. However, when the concentrated water C2 does not satisfy the discharge standard to the environment, the concentrated water C2 is refluxed before the pretreatment unit X and treated again by the pretreatment unit X. As a result, not only the drainage line 8 but also the treated water B of the pretreatment unit Y is discharged from the drainage line 11, for example, to reduce the organic matter concentration of the treated water and improve the drainage load to the environment. be able to. Furthermore, as described above, the chemical treatment unit 22 having treatment means different from the pretreatment unit X may be arranged in the reflux line 9 for refluxing the concentrated water C2 to the pretreatment unit X to apply various treatment processes. preferable.

  On the other hand, the water to be treated D is mixed and diluted with the treated water B2 and sent to the membrane separation unit Z as mixed water F. The membrane separation unit Z is preferably a semipermeable membrane unit. As the liquid D to be treated, it is preferable that the osmotic pressure is higher than the water A to be treated, that is, the concentration of dissolved components such as salinity is high. By selecting such treated water D, it is diluted by mixing with treated water B2, and the osmotic pressure of mixed water F is reduced compared with the osmotic pressure of treated liquid D. It is possible to achieve a reduction in operating pressure when using a semipermeable membrane.

  In such a case, the operating pressure of the membrane separation unit Z is usually higher than that of the membrane separation unit Y, depending on the water permeability of the membrane and the operating conditions. That is, it is preferable to design the membrane separation unit Z so that the maximum operating pressure can be higher than the membrane separation unit Y, such as a pressure pump and pressure resistance of piping. Furthermore, as the material, since the membrane separation unit Z is exposed to a higher salt concentration, it is preferable that the corrosion durability is also high. More specifically, high-grade stainless steel having higher corrosion durability than the membrane separation unit Y, and more specifically, as the peripheral member of the membrane separation unit Y, standard materials such as SUS304L and SAF2304 are used. Those having corrosion resistance or those having slightly enhanced corrosion resistance such as SUS316, SUS317, etc., and the membrane separation unit Z peripheral member are SUS316L, SUS317L, SAF2507, SUS836L, SUS890L with further enhanced corrosion resistance. It is preferable to use high-grade stainless steel such as SUS329J3L and SUS329J4L.

  From the above, in the water treatment method of the present invention, the organic matter concentration of the treated water A is made higher than the organic matter concentration of the treated water D, and the salinity concentration of the treated water D is higher than the salt concentration of the treated water A. It is preferable to do. Thus, by selecting the water to be treated A and D, the merit of the water treatment method of the present invention can be maximized.

  Examples of the water to be treated A include river water, lake water, ground water, sewage, industrial waste water, or treated water thereof. Moreover, as a thing suitable as the to-be-processed water D, highly concentrated brine, brackish water, seawater, or those treated water can be mentioned. In particular, from the viewpoint of organic matter concentration, if the wastewater or its treated water is treated water A and seawater or its treated water is treated water D, the effect of the present invention is great.

  Therefore, the membrane separation unit Y and the membrane separation unit Z are not particularly limited, although the nanofiltration membrane and the reverse osmosis membrane are preferable as described above, and the membrane shape is not particularly limited such as a flat membrane or a hollow fiber membrane. However, as the membrane separation unit Y, it is preferable to apply a separation membrane having excellent fouling resistance due to organic substances, specifically, a fouling resistance like the Toray reverse osmosis membrane TML series. In addition, as the membrane separation unit Z, a reverse osmosis membrane using seawater can be generally applied. If the operation pressure is kept low by mixing, a relatively low pressure reverse osmosis membrane for brine can be applied. Is possible.

  By the way, in the water treatment method of the present invention, when the solute concentration of the treated water D is high in accordance with seawater or the like, the operating pressure of the membrane separation unit Z varies depending on the temperature and solute concentration of the treated water D. Cheap. The fact that the operating pressure fluctuates requires a wide range of output control of the pressurizing pump, leading to an increase in equipment cost due to an increase in the size of the pressurizing pump and the provision of a control function. Therefore, in applying the present invention, it is preferable to reduce the fluctuation of the temperature and concentration of the mixed water F and the osmotic pressure based thereon by adjusting the mixing ratio of the treated water B2 and the treated water D. Thereby, the operating pressure fluctuation of the membrane separation unit Z can be suppressed. Specifically, for example, when seawater is used as the treated water D, the operating pressure increases when the concentration increases or the water temperature decreases, so the osmotic pressure is decreased by increasing the ratio of the treated water B2 (= the effective pressure is increased). ), It is preferable to suppress fluctuations in the operating pressure. At this time, it is preferable to keep the total flow rates of the treated water B2 and the treated water D constant because the permeation flux (treated flow rate per membrane area) of the membrane separation unit Z is the same.

  In addition, when the water to be treated A and the water to be treated D are sewage wastewater, it is necessary to treat the entire inflow amount. For this reason, if there is room in the water tanks 2 and 14 to be treated, it is easy to adjust the flow rates of the treated water B2 and the treated water D, but it is often difficult to adjust the flow rates of the treated water B2 and the treated water D. Accordingly, the flow rates of the treated water B1 and B2 and the mixed flow rate of the treated water D, including being discharged out of the system through the drainage lines 8 and 11, so that the membrane separation unit Y and the membrane separation unit Z are properly operated. It is also preferable to control.

  As a result, the fluctuation in output of the pressurizing pump 18 can be suppressed to a small level, so that it is not necessary to provide the pressurizing pump 18 with an output control function, that is, an expensive inverter or a control valve that leads to energy loss. Since these facilities can be minimized, the effect on energy is great.

  An energy recovery unit 20 can be disposed in the pipe through which the concentrated water C2 discharged from the membrane separation unit Z is sent, and pressure energy can be recovered. The energy recovery unit 20 is not particularly limited, and can be applied to conventional units such as reverse pumps and Pelton turbines, high efficiency units such as turbochargers and pressure exchange types. Moreover, if the fluctuation | variation of the operation pressure of the membrane separation unit Z can be suppressed as mentioned above, it will become easy to maintain these energy recovery efficiencies. In particular, since the reverse pump and the Pelton turbine cannot maintain high efficiency against pressure and flow fluctuations, suppressing the fluctuation in the operating pressure of the membrane separation unit Z is very effective in terms of energy recovery. .

  The present invention relates to a water treatment apparatus for obtaining treated water from a plurality of types of treated water, and more particularly to an apparatus for obtaining fresh water from treated water such as sewage having a high organic matter concentration and seawater having a high salt concentration. Yes, by mixing part of the water to be treated such as sewage with high organic matter concentration with seawater, and returning the concentrated water generated by sewage treatment and reuse, the drainage load to the environment is small and the separation membrane It is possible to provide a water treatment apparatus capable of stable operation, in particular, a water treatment apparatus for fresh water production to which a semipermeable membrane is applied, with less contamination and low cleaning frequency and cost of a bactericide.

2 First treated water tank 3 Intake pump 5 Supply pump 6 Pressure pump 8 Drain line 9 Reflux line 10 First production water tank 11 Drain line 12 Water supply line 14 Second treated water tank 15 Intake pump 16 2 pretreatment units 17 mixing tank 18 pressure pump 20 energy recovery unit 21 second production water tank 22 chemical treatment unit 23 biological treatment tank 24 membrane separation unit

Claims (10)

  A pretreatment unit X for pretreatment of the water to be treated A, a membrane separation unit Y for separating a part B1 of the treated water B of the pretreatment unit X into a permeated water C1 and a concentrated water C2, and the remainder of the treated water B And a membrane separation unit Z that separates the mixed water F obtained by mixing at least a portion B2 of the treated water D with the treated water D different from the treated water A into the permeated water E1 and the concentrated water E2, and at least a part of the concentrated water C2 A water treatment apparatus comprising a line that returns to the pretreatment unit X.   The water treatment apparatus according to claim 1, wherein the pretreatment unit X is a unit capable of performing a treatment combining biological treatment and solid-liquid separation.   3. The water treatment apparatus according to claim 1, further comprising a chemical treatment unit on a line refluxed from the concentrated water C <b> 2 to the pretreatment unit X. 4.   The water treatment apparatus according to claim 1, wherein at least one of the membrane separation unit Y and the membrane separation unit Z is a semipermeable membrane unit.   The water treatment device according to any one of claims 1 to 4, wherein the maximum operating pressure of the membrane separation unit Z is higher than the maximum operating pressure of the membrane separation unit Y.   A part B1 of the treated water B obtained by treating the treated water A with the pretreatment unit X is separated into the permeated water C1 and the concentrated water C2 by the membrane separation unit Y, and at least a remaining part B2 of the treated water B is separated. After being mixed with the water to be treated D different from the water to be treated A, the obtained mixed water F is separated into the permeated water E1 and the concentrated water E2 by the membrane separation unit Z, and the concentrated water C2 is returned to the pretreatment unit X. A water treatment method characterized by:   The organic matter concentration of the to-be-treated water A is higher than the organic matter concentration of the to-be-treated water D, and the salinity concentration of the to-be-treated water D is higher than the salinity concentration of the to-be-treated water A. Water treatment method.   The water treatment method according to claim 6 or 7, wherein the main component of the treated water A is sewage wastewater or treated water thereof, and the main component of the treated water D is seawater.   The water treatment method according to any one of claims 6 to 8, wherein the flow rates of the treated water B2 and the water to be treated D are controlled so that the operating pressure fluctuation of the membrane separation membrane unit Z is reduced.   The water treatment method according to claim 9, wherein the flow rates of the treated water B2 and the treated water D are controlled based on at least one of the temperature and the concentration of the treated water B2 and the treated water D.

Images