JP5550205B2 - Flat membrane filtration device and flat membrane filtration method - Google Patents

Description

  The present invention relates to a flat membrane filtration device and a flat membrane filtration method, and more particularly to a flat membrane filtration device and a flat membrane filtration method that can increase the operating pressure of membrane treatment using an ultrafiltration membrane or a microfiltration membrane.

  Recently, membrane separation technology has been used as a solid-liquid separation method for biological treatment of wastewater containing organic matter, nitrogen, phosphorus, etc., which causes pollution in the ocean and rivers, due to reduced installation space and ease of maintenance. It has come to be used.

  Conventionally, reverse osmosis membranes (RO membranes), ultrafiltration membranes (UF membranes), and microfiltration membranes (MF membranes) are known as membranes used for general membrane treatment. Each membrane is selected according to the diameter of the solid content to be separated.

However, ultrafiltration membranes and microfiltration membranes are used as membranes used as solid-liquid separation means for biological treatment. A reverse osmosis membrane requires a high pressure of 10 kg / cm ² or more as a filtration pressure, and there is no example of selective use because of excessive energy costs.

  Examples of ultrafiltration membranes and microfiltration membranes include flat membranes, tubular membranes, spiral membranes, and hollow fiber membranes, and submerged membranes that are used by immersing these membranes in sludge are also known.

  The present invention relates to a membrane treatment technique using a flat membrane type ultrafiltration membrane or a microfiltration membrane, and solves a technical problem peculiar to the flat membrane.

  As described in Patent Documents 1, 2, 3, etc., the flat membrane module structure that is the subject of the present invention has flat membranes stretched on both sides of the membrane plate, and a gap (groove) is provided between the membrane and the plate. The module units of the membrane-attached plate are arranged side by side on the same axis so that the stock solution is passed between the flat membranes.

  As a conventional technique of flat membrane treatment, as a basic technique, a membrane device described in Patent Document 4 is known. In that literature, obstruction by flat membrane treatment is (1) occlusion inside the membrane, There are three types of clogging: (2) clogging at the membrane surface gel layer and (3) clogging of the intermembrane flow path. So-called clogging has completely different types of clogging, and each requires different measures. There is something to say.

  Patent Document 4 discloses solving means for the above three types of blockage, and describes that the blockage inside the membrane of (1) can be solved by the structure of the membrane itself, and the membrane surface of (2) It is described that the blockage in the gel layer can be solved by making the shape of the support for membrane attachment corrugated (see Patent Document 5), etc., and the blockage of the intermembrane flow path in (3) is dealt with by open frame cleaning. However, in order to reduce the number of times of open-frame cleaning, a technique for solving the problem by widening the interval between adjacent films is disclosed.

  Here, the open frame cleaning refers to disassembling the packing or frame (frame) in the membrane module, exposing the membrane surface, and cleaning with a sponge or the like.

  The gel (layer) generated on the membrane surface is generated when the polymer substance dissolved in the membrane raw water is concentrated and precipitated on the membrane surface. The gel (layer) is generated whenever the molecular weight of the substance dissolved in the raw water is larger than the fractional molecular weight of the membrane (in the case of an ultrafiltration membrane). Therefore, occlusion by the gel (layer) means clogging of the membrane pores on the membrane surface. On the other hand, the clogging of the intermembrane flow path means that fine particles (insoluble substances), slurry and the like contained in the raw membrane water block the intermembrane flow path and the raw water does not contact the membrane surface. In other words, the clogging at the membrane surface gel layer is clogging of the membrane pores at the membrane surface, and the clogging of the intermembrane flow path mechanically clogs the gap between the membranes with fine particles or slurry. The state is fundamentally different.

  However, since the clogging at the membrane surface gel layer and the clogging of the intermembrane flow path have an interaction, conventionally, as a technique for solving the clogging of both, Patent Document 6 discloses the lower end of the intermembrane flow path. A film device having a fine bubble discharge part in the part is disclosed. Not only does the flow of the stock solution occur due to the fine bubbles released from the discharge part, but also the fine bubbles come into contact with or rub against the membrane surface alone or together with the stock solution, preventing the growth of the gel layer on the membrane surface and high permeation filtration. The blockage of the intermembrane flow path is prevented while maintaining the amount.

  In order to establish the flat membrane as a practical device, the present applicant has made extensive studies and proposed improved flat membrane filtration devices in Patent Document 7 and Patent Document 8. Patent Document 7 is a technique using a suction pump, not a circulation pump, as a power for taking out filtrate by providing a circulation tank and a circulation pump in the circulation line. Patent Document 8 provides a circulation tank and a circulation pump in the circulation line, This is a technology that uses the head pressure of the head tank as the power for taking out the filtrate. Both Patent Documents 7 and 8 specify a low flow rate of 0.5 to 1.9 m / sec for the stock solution in the intermembrane flow path. doing. These techniques have the effect of reducing the number of open frame cleanings, eliminating the hassle of disassembly cleaning, and reducing operating power costs.

In addition, in the patent document 9, the present applicant proposed a technique for adding to the take-out energy of the filtrate in addition to the head pressure of the circulating cleaning tank by a valve for narrowing the overflow liquid amount from the circulating cleaning tank. ing.
Japanese Patent Publication No.52-10113 Japanese Patent Publication No.53-3756 Japanese Patent Publication No.57-7524 Japanese Patent No. 2538789 JP 55-86510 A Japanese Patent No. 3160609 JP-A-11-300188 JP 2000-5574 JP 2001-179056 A

  The feature of the technique described in Patent Document 9 is a configuration in which a circulation washing tank is disposed in a circulation line by a circulation pump, and an air phase is present in the circulation washing tank above the overflow surface of the circulation liquid. The reason for this configuration is that it is meaningful in itself, and the upper part of the overflow surface is made into an air phase (hereinafter also simply referred to as “gas phase”), and the dynamic pressure is once released to static pressure. This is because it is necessary to use the head pressure of the liquid column of the circulating cleaning tank for the membrane cleaning, and it is necessary to secure a predetermined transmembrane flow rate.

  However, there has been a problem that even if the discharge amount of the overflow liquid discharge pipe is narrowed down and the pressure is increased in addition to the head pressure, the film cleaning pressure does not increase.

  As a result of intensive studies to investigate the cause, the following was found.

  First, in the presence of the gas phase, the compression force squeezed by the squeezing valve is almost consumed for air compression, and does not contribute to the increase in pressure required for membrane cleaning, and a sufficient intermembrane flow velocity is obtained. Not found out. Further, it has been found that the pressure by the stock solution pump is also consumed for the gas phase compression, and there is a disadvantage that the power cost is high.

  Secondly, it has been found that when a gas phase is present, a large amount of fine bubbles are generated in the circulating liquid and the bubbles cause cavitation of the circulation pump when the gas is narrowed by a narrowing valve.

  Then, the 1st subject of this invention is providing the flat membrane filtration apparatus and flat membrane filtration method which can aim at the increase in permeated water amount, can reduce running cost, and can reduce the frequency of open-frame washing | cleaning.

  The second problem of the present invention is to solve the problem of the above-mentioned Patent Document 9, and it is not necessary to narrow down with a narrowing valve, and the pressure of the raw liquid pump that supplies the raw liquid to the circulation line can be efficiently reduced as it is. An object of the present invention is to provide a flat membrane filtration apparatus and a flat membrane filtration method that can be used as washing pressure.

  Furthermore, the other subject of this invention becomes clear by the following description.

  The above problems are solved by the following inventions.

(Claim 1)
A flat membrane device in which membrane-attached plates are arranged in parallel in the vertical direction and fixed with a membrane filter made of a flat membrane-like ultrafiltration membrane or a microfiltration membrane on both sides of the membrane support member;
A liquid-sealed circulation pipe connecting the stock solution inlet and the stock solution outlet of the flat membrane device;
A circulation pump provided in the middle of the circulation pipe;
A cleaning tank that is provided separately from the circulation pipe and stores a cleaning liquid for cleaning the filtration membrane;
A cleaning pipe for supplying the cleaning liquid from the cleaning tank to the circulation pipe to enable cleaning of the filtration membrane;
A raw liquid pump for supplying the raw liquid to the circulation pipe, and applying the pressure of the raw liquid pump to the film outlet which is the raw liquid outlet of the flat membrane device without depending on the pressure of the circulating pump. A flat membrane filtration device characterized by having a configuration for increasing the operating pressure of the device.

(Claim 2)
It is a flat membrane filtration method filtered using the flat membrane filtration apparatus of Claim 1, Comprising: When increasing the outlet pressure of a flat membrane apparatus, it does not depend on the pressure of the said circulation pump, The pressure of the said undiluted | stock solution pump A flat membrane filtration method characterized by adding the amount to increase .

(Claim 3)
It is a flat membrane filtration method filtered using the flat membrane filtration apparatus of Claim 1, Comprising: When increasing the outlet pressure of a flat membrane apparatus, it does not depend on the pressure of the said circulation pump, The pressure of the said undiluted | stock solution pump A flat membrane filtration method characterized by adding water and increasing water and performing water washing at regular intervals.

(Claim 4)
A flat membrane filtration method for filtering using the flat membrane filtration device according to claim 1, wherein the outlet pressure of the flat membrane device is increased and water washing is performed at regular intervals. 3. The flat membrane filtration method according to 3.

  According to the present invention, the amount of permeated water can be increased. The amount of permeated water per unit area is increased by about 15% compared to the conventional pressurization type (described later) and about 30-40% compared with the circulation type (including the pressurization circulation type described later). Since the required membrane area is reduced by increasing the amount of permeated water per unit area, the number of membrane modules can be reduced even when a large amount of permeated water is required. That is, the installation area is reduced.

  Further, according to the present invention, the running cost can be reduced. The running cost per unit permeated water amount can be reduced by about 50% compared to the conventional pressure type, and about 20-30% compared with the circulation type.

  Furthermore, according to the present invention, all the circulation pipes (lines) are liquid-sealed (the gas phase portion is eliminated), so that the open frame cleaning frequency is once / 1.5 months to once / 3.5 compared with the circulation type. Decreases with months.

  Furthermore, this effect is further improved by introducing a batch-type water washing system in which water washing is performed at regular intervals and all circulation lines are liquid-sealed. In addition, by incorporating a separate chemical tank in the module into the membrane circulation line, the number of pumps to be transferred from the chemical tank to the membrane module can be reduced, and excessive cleaning chemical liquid can be prepared (because the chemical tank is large. It was reduced)

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  A preferred embodiment of the flat membrane device used in the present invention will be described with reference to FIG.

  The flat membrane device 1 constitutes a side frame that can be opened by frame plates 101 and 102 erected at predetermined intervals, and a plurality of partition plates 103 are provided in parallel between the frame plates 101 and 102. The frame plates 101 and 102 are divided into a plurality (seven in the illustrated example) of blocks S1,... S7.

  The partition plate 103 is formed with a liquid circulation port 104 in the upper part or the lower part, and adjacent blocks are connected to each other by the circulation port 104. The partition plate 103 may be configured such that the flow ports 104 are alternately arranged on the upper and lower sides of the adjacent partition plates 103 so that the liquid flow in the adjacent blocks is alternately formed upward and downward. preferable. In each block S of the flat membrane device 1 partitioned by the partition plate 103, a plurality of membrane-attached plates 105 are arranged in parallel.

  The membrane-attached plate 105 includes a membrane support member 108 having openings 106 and 107 formed in the vicinity of upper and lower ends, and flat membranes (filtration membranes) 109 fixed on both side surfaces thereof. It is fixed to the membrane support member 108 by seal rings 110 and 111 fitted in the upper and lower openings 106 and 107, respectively.

  The membrane support member 108 is formed of a plate material, and the surface thereof is formed in an uneven shape having a corrugated cross section. The flat membrane 109 forms a drainage portion 112 for the filtrate that has permeated through the flat membrane 109 while securing a slight gap between the flat membrane 109 and the membrane supporting member 108 on both side surfaces of the membrane supporting member 108.

  Reference numeral 113 denotes a filtrate discharge groove provided at the lower end of the membrane support member 108, which is connected to the header pipe 6 (see FIG. 2) and can be taken out through the header pipe.

  Packing is performed along the outer edge of the film-coated plate 105 between the multiple film-coated plates 105, between the film-coated plate 105 and the frame plates 101, 102, and between the film-coated plate 105 and the partition plate 103. 114 is provided to prevent external leakage of the liquid. Accordingly, the flat membrane device 1 is formed in a watertight manner by the frame plates 101 and 102 and the packing 114 constituting the side frame. At the same time, the packing 114 has an intermembrane flow in which an undiluted solution or a concentrated solution flows between adjacent plates 105 with membranes, between the plate with membranes 105 and the frame plates 101 and 102, and between the plate with membranes 105 and the partition plate 103. A path 115 is formed. Therefore, the distance between the intermembrane flow paths 115 is regulated by the packing 114, and the distance between the intermembrane flow paths 115 can be adjusted by adjusting the thickness of the packing 114. The distance between the intermembrane flow paths 115 is preferably 1.5 mm or more, and more preferably 3.0 mm or more from the viewpoint of preventing the blockage of the flow paths. The upper limit is preferably 8.0 mm or less, and more preferably 6.0 mm or less, for the volume efficiency of the flat membrane device 1. Further, the packing 114 also functions to fix the outer edge of the flat membrane 109 on both side surfaces of the membrane support member 108 in the membrane-equipped plate 105.

  It should be noted that the number of blocks S in the flat membrane device 1 (number of partition plates 103 + 1) and the number of membrane-attached plates 105 provided in each block S are such as flux, throughput, capacity of the circulation pump 3 described later, and the like. It is decided as appropriate considering various conditions.

  In the flat membrane device 1, a stock solution inlet 117 for introducing a stock solution into one frame plate 102 is formed, and a stock solution outlet 116 for flowing out the stock solution (concentrated solution) is formed in the other frame plate 101. Yes.

  The flat membrane device 1 shown in FIG. 1 is characterized in that it has a structure that allows open-frame cleaning, and disassembles the packing and frame (frame) in the membrane module to expose the surface of the flat membrane 109. And cleaning with a sponge or the like (open frame cleaning).

  Next, based on FIG. 2, the flat membrane filtration apparatus of this invention is demonstrated.

  In FIG. 2, reference numeral 2 denotes a circulation pipe, one end of which is connected to the stock solution inlet 117, and the other end is connected to the stock solution outlet 116.

  The circulation pipe 2 sends the stock solution (circulation fluid) discharged from the inside of the flat membrane device 1 to the outside via the stock solution outlet 116 to the stock solution inlet 117 via the outside of the flat membrane device 1 and then flattened again. It is configured to return to the inside of the membrane device 1.

  The circulation pipe 2 is liquid-sealed and has a configuration in which no air phase is present inside. Here, the liquid seal means that there is no air phase as shown in Patent Document 9, and the pressure applied to the circulation pipe 2 is the same at any part inside the pipe (the so-called Pascal principle works). It means such a configuration.

  A circulation pump 3 is provided in the middle of the circulation pipe 2. Since the circulation pump 3 only needs to secure a flow rate and a stroke required for the membrane module, it can contribute to low power and cost reduction. The form of the pump is arbitrary, but space can be saved by using a line pump. Since the circulation pump 3 does not have an air phase as in Patent Document 9 and is liquid-sealed in the middle of the circulation pipe 2, it does not cause cavitation.

  A cleaning tank 4 is provided separately from the circulation pipe 2. In this invention, it differs clearly from the structure which provides a washing tank in circulation piping like patent document 9. FIG. A cleaning pipe 40 is connected to a cleaning tank 4 provided separately from the circulation pipe 2, and a valve 41 is provided in the cleaning pipe 40. As the cleaning liquid, it is preferable to use treated water from the viewpoint of cost reduction, but tap water, industrial water, or the like may be used, or a cleaning liquid containing a surfactant or a detergent may be used.

  By providing the cleaning tank 4 separately from the circulation pipe 2, there is an effect that the liquid sealing of the circulation pipe 2 can be realized completely.

  Reference numeral 5 denotes a stock pump for supplying the stock solution to the circulation pipe 2, and the pressure required for cleaning between the membranes can be easily replenished by the pressure of the stock solution pump 5. In the circulating cleaning tank system having an air phase as in Patent Document 9, even if an attempt is made to pressurize with a stock solution pump, the supply pressure is taken to compress the air, and the inside of the circulating pipe including the flat membrane device is pressurized with low power. It was impossible. On the other hand, since the present invention realizes the closing with the liquid-sealed circulation pipe 2, not only the circulation pipe 2 but also anywhere in the circulation system connects and pressurizes the discharge part of the stock solution pump 5. be able to. For this reason, the installation position of the stock solution pump 5 becomes free, and there is an effect that the apparatus design becomes easy. In the conventional pressurization type membrane treatment method, only the stock solution pump is used without using the circulation pump, and the treatment pressure is increased by increasing the pressure of the stock solution pump. However, in this method, the inlet pressure of the membrane device is only increased. In addition, it is impossible to increase the outlet pressure for processing. This is because the flow rate and pressure of the pump are operating conditions at one point on the performance curve of the pump itself, and it is impossible to change the membrane discharge pressure other than replacing the pump.

  Further, the present invention realizes the closing that can apply the principle of Pascal, so that the operation pressure of the entire apparatus can be increased only by pressurizing a part of the circulation system.

  In FIG. 2, 6 is a header pipe for taking out the processing liquid, and 60 is a processing liquid pipe.

  The flat membrane used in the present invention may be either an ultrafiltration membrane or a microfiltration membrane.

  In the present invention, as the raw solution, for example, sludge in a biological treatment tank, sludge transferred from the reaction tank or concentrated sludge thereof, human waste before biological treatment, agglutination reaction liquid by adding a flocculant or reaction liquid thereof Concentrated sludge separated by a sedimentation tank and its supernatant. The present invention can also be applied to reuse of wastewater, recovery of valuable materials, use of rainwater, various separation and concentration, various separation and concentration purification, and the like. Therefore, various stock solutions are included in the stock solution of the present invention as long as the object is achieved.

  In the above-described embodiment, the case where a plate material having irregularities on the surface is used as the membrane support member 108 is not limited to this, and the membrane support member may be a porous plate material, or the membrane support member May be a plate made of synthetic fiber.

  Next, the features of the closed flat membrane filtration device according to the present invention will be further described.

  In the flat membrane type membrane filtration device, (1) increase of permeated water per unit area, (2) reduction of running cost, and (3) reduction of open frame cleaning frequency by introduction of batch type water cleaning system are important issues. is there.

  First, looking at the increase in the amount of permeate per unit area, from the applicant's experiment and operation data, the operation influencing factors of the flat membrane filtration device are: a. Operating pressure, b. Membrane spacing, c. Processing solution density, viscosity, temperature, d. It has been found that the membrane surface flow rate. When the above is analyzed from the permeated water amount, the above factors, and the π theorem of dimensional analysis, the following relationship is obtained. The following formula quoted “Application of membrane bioreactor to water treatment” (by Yoshihiko Kanayama) described in Chemical Equipment (August 1987).

F / u = K × (d × u × ρ / μ) ^(x) × (P / (u ² × ρ)) ^(y) ---------- KANAYAMA formula

  Here, F: permeation flux, K: constant, u: membrane surface flow velocity, d: pipe diameter (or equivalent pipe diameter), ρ: fluid density, μ: fluid viscosity, P: average operating pressure.

Among the above equations, the constant K and the multipliers x and y on the right side are numerical values determined by the flat membrane filtration device and the operating conditions. The constant K is a numerical value unique to a flat membrane filter if the physical properties of the fluid are constant. The multipliers x and y are calculated based on the operating conditions and the physical properties of the fluid. From the data, K value, x value, y value are K value: 1 × 10 ⁻⁸ to 1 × 10 ⁻⁶ , x value: 0.2 to 0.8 (intermediate value: 0.5), y value: 0 .1 to 0.7 (intermediate value: 0.4). Therefore, the above value can be used as a control factor.

  Next, regarding the operation factor for securing the permeation flux, the permeation flux in the flat membrane filtration apparatus according to the present invention is proportional to the multiplier of (1 + x-2y) with respect to the flow velocity, and the pressure is determined from the above KANAYAMA equation. Is proportional to the multiplier of y.

  That is, the multiplier range of the flow velocity is −0.2 to 1.6, and the multiplier range of the pressure is 0.1 to 0.7.

  Conventionally, in order to secure permeate flux water, the removal of gel material generated on the membrane surface, suppression of generation, and prevention of clogging of the membrane have been made first, so attention has been paid to the membrane surface flow velocity. However, as can be seen from the above equation and the multiplier range, the multiplier of the flow velocity may be negative, so increasing the flow velocity does not necessarily increase the permeation flux. In order to increase the permeation flux, it was found important to focus on increasing the operating pressure, which is another control factor.

  Next, the permeation flux and the operating pressure will be described with reference to FIG. FIG. 3 is a graph showing the relationship between pressure on the horizontal axis and permeation flux on the vertical axis.

  As described above, the permeation flux is proportional to the power of 0.1 to 0.7. The amount of permeated water as the membrane device is the total (integrated) of the area under the curve in the graph of FIG.

  In the graph of FIG. 3, a hatched portion A and a hatched portion B having a constant pressure loss ΔP are shown, and in order to increase the amount of permeated water, it is better to operate on the shaded portion A side, that is, operate on the high pressure side. The amount of permeate will increase. In other words, if the membrane area is the same, the amount of permeate increases as the operating pressure increases.

  In the conventional pressurization type shown in FIG. 4A, this increase in operating pressure is impossible. In this pressurization type system, the stock solution is sent from the stock solution tank 10 to the flat membrane device 1 by the stock solution pump 11 and filtered, the filtrate is taken out to the outside, and the unfiltered stock solution is returned to the stock solution tank 10 again as a concentrated solution.

In this pressurization type filtration system, when the flat membrane device 1 of the present invention (membrane area is about 38 m ² ) is used, the power of the stock pump 11 is 37 kw, and the filtrate is 60 L / m ² · hr. Is obtained.

  In this system, since the outlet of the flat membrane device 1 is open, the operating pressure cannot be increased. This is because even if the capacity (pressure and flow rate) of the stock solution pump 11 is increased, only the flow rate is increased.

  Therefore, to increase the operating pressure, it is conceivable to increase the pressure on the flat membrane device outlet side. Conventionally, as a method of increasing the flat membrane device outlet pressure, a device having a narrowing mechanism at the membrane outlet (example: A pressure circulation type (Patent Document 9, FIG. 4B) in which a valve is installed has been proposed by the present applicant.

  As shown in FIG. 4B, the stock solution is sent from the stock solution tank 10 to the circulation tank 13 by the stock solution pump 12. The stock solution is sent from the circulation tank 13 to the flat membrane device 1 and filtered. The unfiltered stock solution is returned again to the circulation tank 13 as a concentrate. The circulation tank 13 is open to the atmosphere, and the overflow liquid is returned to the stock solution tank 10. 14 is a throttle valve.

In this circulation type filtration system, when the flat membrane device 1 of the present invention (membrane area is about 38 m ² ) is used, the power of the stock solution pump 12 is 3.7 kw and the power of the circulation pump is 15 kw. 55 L / m ² · hr is obtained.

  However, as described above, this system has a drawback that it is difficult to adjust the operation pressure due to the presence of the air phase 15.

  On the other hand, in the present invention as shown in FIG. 4C, it has become easy to pressurize the membrane outlet by realizing the closing to which the Pascal principle can be applied.

  In order to increase the membrane outlet pressure, in the present invention, the operating pressure of the flat membrane filtration device can be increased by using the pressure (discharge pressure) of the stock solution pump 5 as a pressurizing device. That is, by constantly applying the pressure (discharge pressure) of the stock solution pump 5 to the membrane outlet, the operation pressure of the flat membrane filtration device is increased.

  Next, the running cost reduction will be mentioned. The electricity cost that occupies a large part of the operating cost is the power cost of the pump around the membrane. Conventionally, there are two roles of the pumps around the membrane device: supply from the stock solution tank to the membrane device, removal and suppression of gel substances generated on the membrane surface, and circulation for preventing clogging of the membrane. Power can be reduced by installing a pump for each role.

  That is, the stock solution pump transfers a liquid amount several times the required permeated water amount, and the circulation pump circulates a liquid amount several tens of times the required permeated water amount.

  In order to increase the membrane outlet pressure, the power when the increased pressure depends on the circulation pump and the power when the pressure depends on the stock pump is compared, and the case where the pressure depends on the stock pump as in the present invention is about 10%. The power cost is reduced by about twice. The increased power kw is calculated from the product of the flow rate Q and the pressure P (kw∝Q × P). Accordingly, since the added pressure of the stock solution pump and the circulation pump is the same, the difference in power is determined by the difference in flow rate. As described above, if the flow rate of the circulation pump is 10, the flow rate of the stock solution pump is about 1, so the difference in power that increases is about 10 times.

  That is, when applying a pressure that adds the required membrane outlet pressure to the circulation pump, and when adding a pressure that adds the required membrane outlet pressure to the stock pump, the power cost differs by the amount of the transferred liquid. As such (the difference of about 10 times), the method of the present invention allows a significant power reduction.

  In order to efficiently transmit the pressure of the stock solution pump to the membrane outlet, it is important to eliminate the gas phase portion (air zone) in the circulation pipe 2. As described above, if the gas phase portion exists, the gas phase (air) plays the same role as the buffer material, so that it is difficult to transmit all the pressure of the stock solution pump.

  Next, mention will be made of the reduction in the frequency of open frame cleaning due to the introduction of a batch water cleaning system. Conventionally, the membrane apparatus has been cleaned by three methods: water cleaning, chemical cleaning, and open frame cleaning. In order to remove the gel material, concentrate, and solid matter between the membranes, the membrane device should be washed with water first, and if that is not satisfactory, the chemical solution cleaning and the open frame cleaning are performed in this order. Yes. Water cleaning and chemical cleaning have been handled by installing a separate cleaning device (or chemical cleaning device). The guideline for cleaning has been to confirm the pressure loss of the membrane device and the decrease in the amount of permeated water. At that time, concentrate and solid matter between the membranes have already accumulated on the membrane surface, and water cleaning and chemical cleaning It was difficult to deal with. Therefore, it was necessary to perform open frame cleaning each time.

  In the present invention, since the circulation piping (line) is liquid-sealed, all the membrane circulation lines are liquid-sealed (the gas phase portion is eliminated), so that water washing due to air mixing during water washing is incomplete. Improvement (decrease in apparent washing water volume due to aeration) was achieved.

  In the present invention, in order to reduce the frequency of open frame cleaning, batch-type water cleaning in which water cleaning is performed at regular intervals is preferable. Since the generation of gel material due to concentration, which is the initial stage of film clogging, can be suppressed, the time spent for the accumulation of the concentrate on the film surface and the solid matter between the films becomes longer. Increase in pressure loss and decrease in the amount of permeated water are prolonged. Therefore, the open frame cleaning frequency is reduced from once / 1.5 months to once / 3.5 months compared with the circulation type.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
Using the flat membrane filtration apparatus shown in FIG. 2 (closed type in FIG. 4C), a flat membrane treatment test was conducted using biological treatment (high load denitrification treatment) sludge.

  For comparison, the following types of tests were also conducted.

Comparison 1: Pressurization method shown in FIG. 4 (A) Comparison 2: Air diffusion method described in Patent Document 6 (Patent No. 3160609) Comparison 3: Circulation method without throttle valve 15 in FIG. 4 (B) Comparison 4 : Pressurized circulation system shown in FIG.

  Membrane device specifications (membrane area, number of membranes, membrane configuration) of each membrane filtration device, pump power (raw liquid pump, circulation pump, suction pump), power of air blower, total equipment power, operating power, permeated water, flux Table 1 shows the power per processing amount, the shortest open frame cleaning frequency, the integrated permeate flow rate, the design flux x open frame cleaning period, the operation data flux x the open frame cleaning period, the flux comparison, and the power comparison per processing amount. .

  From Table 1, the closed flat membrane filtration device of the present invention has a permeated water amount per unit area increased by about 15% compared to the conventional pressurization type (Comparative 1), and the circulation type (pressurization circulation type described later) It can be seen that there is an increase of about 30 to 40% in comparison with Comparative Examples 3 and 4).

  In addition, the closed flat membrane filtration device of the present invention has a power (running cost) per throughput (unit permeate amount) that is about 50% lower than the conventional pressure type and about 20-30% lower than the circulation type. You can see that

  Furthermore, according to the present invention, all the circulation pipes (lines) are liquid-sealed (the gas phase portion is eliminated), so that the operation data flux × the open frame cleaning period is very high at 352800, which is higher than that of comparisons 1 to 4. It can be seen that a high flux can be maintained without performing frame cleaning for a long time.

Example 2
In Example 1, in order to demonstrate that the closed flat membrane filtration apparatus of the present invention can reduce the number of open frame cleanings, the relationship between the number of operating days and the operating flux was examined in each method. The open frame cleaning was performed at a time when the predetermined operation flux could not be maintained. The result is shown in FIG. In FIG. 5, the open frame cleaning time is indicated by a circle.

  As is apparent from the results shown in FIG. 5, according to the present invention, it is understood that the open frame cleaning frequency is reduced from once / 1.5 months to once / 3.5 months as compared with the circulation type.

Basic configuration diagram showing a flat membrane device Explanatory drawing which shows the flat membrane filtration apparatus of this invention Graph showing the relationship between permeation flux and operating pressure Diagram for comparing the conventional apparatus and the present invention apparatus Graph showing the relationship between operating days and operating flux

Explanation of symbols

1: Flat membrane device 101, 102: Frame plate 103: Partition plate 104: Distribution port 105: Plate with membrane 106, 107: Opening 108: Membrane support member 109: Flat membrane (filtration membrane)
110, 111: Seal ring 112: Filtrate discharge part 113: Filtrate discharge groove 114: Packing 115: Intermembrane flow path 116: Stock solution outlet
117: Stock solution inlet 2: Circulation piping 3: Circulation pump 4: Cleaning tank 40: Piping 41: Valve 5: Stock solution pump 6: Header tube 60: Treatment solution piping

Claims (3)

A flat membrane device in which membrane-attached plates are arranged in parallel in the vertical direction and fixed with a membrane filter made of a flat membrane-like ultrafiltration membrane or a microfiltration membrane on both sides of the membrane support member;
A liquid-sealed circulation pipe connecting the stock solution inlet and the stock solution outlet of the flat membrane device;
A circulation pump provided in the middle of the circulation pipe;
A cleaning tank that is provided separately from the circulation pipe and stores a cleaning liquid for cleaning the filtration membrane;
A cleaning pipe for supplying the cleaning liquid from the cleaning tank to the circulation pipe and allowing the filtration membrane to be cleaned;
A raw liquid pump for supplying the raw liquid to the circulation pipe, and applying the pressure of the raw liquid pump to the film outlet which is the raw liquid outlet of the flat membrane device without depending on the pressure of the circulating pump. A flat membrane filtration device characterized by having a configuration for increasing the operating pressure of the device. It is a flat membrane filtration method filtered using the flat membrane filtration apparatus of Claim 1, Comprising: When increasing the outlet pressure of a flat membrane apparatus, it does not depend on the pressure of the said circulation pump, The pressure of the said undiluted | stock solution pump A flat membrane filtration method characterized by adding the amount to increase . It is a flat membrane filtration method filtered using the flat membrane filtration apparatus of Claim 1, Comprising: When increasing the outlet pressure of a flat membrane apparatus, it does not depend on the pressure of the said circulation pump, The pressure of the said undiluted | stock solution pump A flat membrane filtration method characterized by adding water and increasing water and performing water washing at regular intervals.

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