TW202112434A - System and method for feeding immersed membrane units - Google Patents

Abstract

In an immersed membrane system, the influent flows into an open membrane tank. The membrane tank can have multiple horizontally spaced immersed membrane units. The immersed membrane units may have flat sheet membrane elements within a membrane case. One or more ducts are provided in the tank for directing the flow of influent to the immersed membrane units. In some examples, the influent is divided into sub-streams that are fed through baffles to a corresponding immersed membrane unit, optionally in generally equal amounts, optionally in a single pass flow pattern. In a process of operating a membrane tank, the influent flow is directed across the bottom of the membrane tank and divided into multiple portions. Each of the multiple portions is fed directly to the bottom of a corresponding immersed membrane unit located in the tank. The influent may be mixed liquor in a membrane bioreactor (MBR).

Description

System and method for feeding submerged film unit

The present invention relates to submerged membrane filters and methods of operating them.

Films are usually in the form of flat plates, tubes or hollow fibers. In an immersion film unit, multiple film elements are assembled together into modules or cassettes and immersed in an open tank. The permeate is drawn from the module by suction generated by gravity or an osmotic pump connected to an inner surface of the membrane. Typical applications include filtering surface water to produce drinking water, treating wastewater in a membrane bioreactor (MBR) or treating secondary effluent in a tertiary filtration application. In these applications, membranes usually have pores in the microfiltration or ultrafiltration range.

Some examples of submerged hollow fiber membrane units are described in US Patent 5,639,373. In these hollow fiber membrane units, the hollow fiber membrane extends between the upper potting head and the lower potting head. In other examples, there is only one potting head and/or the film extends horizontally. Some examples of submerged flat sheet membrane units are described in US Patent 6,287,467. In the flat film unit, a flat film pair is assembled together over a frame or spacer to form an element. Many of these components are placed in parallel in a box. The cassette may have a membrane shell, alternatively referred to as a shield, which forms a vertically oriented tube around the element. A set of aerators can be attached to the cassette. In some cases, a diffuser shell below the cassette contains a set of aerators in a vertically oriented tube. The aerator generates bubbles that wash the surface of the film and also generates an air lift that circulates water upward through the film. A similar structure is equipped with a flat ceramic film. In U.S. Publication No. US 2017/0095773, it is described that one of the corrugated film panels assembled without inner frames or spacers replaces the flat immersed film unit, which is incorporated herein by reference.

In membrane filtration systems, one or more submerged membrane units are usually placed in an open (ie, with a water-free surface) membrane tank. In a membrane bioreactor (MBR), the membrane filtration system can function as a secondary clarifier in the same activated sludge process. In this case, the water is treated in a treatment tank upstream of the film tank to produce a mixed liquid that flows to the film tank. The permeate is drawn through the membrane unit, thereby leaving the activated sludge in the membrane tank. The activated sludge is drawn from the membrane tank and divided into waste activated sludge (WAS) and return activated sludge (RAS). RAS returns to the treatment tank and becomes part of the activated sludge. The flow rate (Q) of the influent (raw wastewater) is roughly balanced by the sum of the permeate flow rate and the WAS flow rate. The RAS flow rate is usually in the range of 2Q to 5Q.

This summary of the invention is intended to introduce the reader to the invention and the detailed description below, rather than to limit or define the invention.

In an immersed membrane system, an influent flows into an open membrane tank, the permeate is removed through the membrane, and a concentrate flows out of the membrane tank. The inventors have observed that although air bubbles are used to flush each membrane unit equally, the fouling rate can vary between membrane units in different parts of a tank. For example, in a system in which the membrane units are distributed along a narrow groove in a line, and the grooves are fed from one end with influent, the most downstream membrane unit fouls the most. This can be caused at least in part by a solid (or other dirt) concentration gradient that develops along the length of the tank. However, the membrane units are usually all connected to the common permeate and backwash pipes and operate using the same permeation and cleaning protocol. Therefore, any upstream membrane unit is operated inefficiently or the downstream membrane unit is excessively fouled. However, this configuration is used in many submerged membrane equipment (including membrane bioreactors (MBR)), especially because it facilitates the creation of large systems with multiple parallel membrane tanks. Therefore, there has been a large mounting base for immersed film systems with narrow grooves.

This specification describes an open film tank with one or more submerged film units. Each membrane unit may have one or more cassettes or other structures containing filter membranes. Optionally, the film units are spaced along the length of the groove. Optionally, the immersion membrane unit may have flat membrane elements that can be positioned in a membrane shell. An entrance is provided at one end of the tank (near the bottom of the tank as the case may be). Provided for connecting the inlet to one or more ducts of one or more immersed membrane units. In some examples, a conduit has multiple openings each connected to a different membrane unit. Optionally, the openings have different sizes that can be selected to help equalize the flow of the mixed liquid to different membrane units. Optionally, the duct may have a horizontally extending baffle under a membrane unit. In some cases, the membrane tank is part of a membrane bioreactor.

This manual also describes a procedure for operating an immersed membrane filtration system (for example, an open membrane tank of an MBR). In the procedure, an inflow into a film tank is directed to the bottom of one or more submerged film units. Optionally, the mixed liquid stream can be divided into multiple parts. In some cases, the flow rate of each of the multiple parts is within 10% of the average flow rate of one of the multiple parts. Optionally, the inflow is directed further upwards through a submerged membrane unit. In some cases, a direct current or vertical plug flow regime through one of the membrane units can be provided. The influent can be, for example, a mixed liquid as in an MBR or a secondary effluent as in a tertiary filtration.

The film tanks and procedures described herein result in the inflow being usually fed directly to one or more submerged film units. This helps prevent the inflow (for example, the inflow being fed to a downstream membrane unit) from being pre-concentrated by other membrane units. Optionally, the system can also be configured so that the flow rate of the inflow through the various submerged membrane units is substantially equal. Providing the influent to different immersion membrane units at substantially equal flow rates depending on the situation at its original concentration can lead to higher productivity and/or easier operation of the system as a whole. In addition, the inflow is forced upward through the membrane unit. The influx flowing upward through a membrane unit can help force adjacent membranes to separate from each other, inhibit the dehydration or retention of sludge in the membrane unit and/or disperse fresh inflow throughout the membrane unit. In this way, the influent stream to a submerged membrane tank can be used to help prevent fouling or sludge adhesion in the membrane unit and/or reduce the frequency of membrane cleaning. In the case of an MBR, some of the energy involved in recirculating RAS can be recovered in the form of liquid velocity or pulses.

Figure 1 shows a membrane bioreactor (MBR) 100 using an activated sludge process. Waste water 102 (for example, industrial wastewater or urban sewage) is collected and travels through a coarse screen 104 and, as appropriate, a fine screen 106. The fine screen 106 may have, for example, an opening of 2 mm to 5 mm and may be positioned further downstream in the MBR 100 than the position shown in FIG. 1. The screened wastewater 102 flows through a primary treatment unit 108 (such as a purifier or rotating belt filter). The primary treatment unit 108 generates primary sludge 110 and primary effluent 112.

The primary effluent 112 flows to one or more treatment tanks 114. In some instances, there is an aerobic treatment tank 114. In other examples, there may be a series of two or more treatment tanks 114 containing aerobic, anoxic and/or anaerobic treatment zones. The microorganisms in the treatment tank 114 digest the primary effluent 112 and produce a mixed liquid 116. The mixed liquid 116 is delivered to a film tank 70. In the example shown, the mixed liquid 116 is pumped to the film tank 70. In other examples, the mixed liquid flows to the film tank 70 by gravity.

The film tank 70 includes one or more ducts 80 and one or more film units 120. One or more ducts 80 extend from an inlet 86 of the film tank 70 to the bottom of the film unit 120. A conduit 80 provides for the mixed liquid 116 to flow through it in the membrane tank 70 to reach one of the plenum chambers of the one or more membrane units 120. The mixed liquid 116 then flows upward through the membrane unit 120 and into the membrane tank 70 outside the membrane unit 120. A permeate pump 122 draws the permeate 124 from the mixed liquid 116 when the mixed liquid 116 travels through the membrane unit 120. Therefore, the mixed liquid 116 is concentrated in the membrane unit and leaves the membrane unit as activated sludge 126. The activated sludge 126 is drawn from the membrane tank 70 by pumping or gravity, for example, and is divided into waste activated sludge (WAS) 128 and return (or recovery) activated sludge (RAS) 130.

In FIG. 1, the film groove 70 is part of an MBR 100. The flow rate of wastewater 102 to an MBR 100 is conventionally called Q. The flow rate of the RAS 130 can be, for example, in the range of 1Q to 5Q. The flow rate of the mixed liquid 116 can be, for example, 2Q to 6Q. Therefore, a large amount of energy is applied to the recirculating RAS in an MBR 100. This may cause the mixed liquid 116 to flow into the film tank 70 at a large flow rate and/or energy content. However, in some cases, the membrane tank 70 may be another filtration system (such as a surface water or groundwater filtration system designed to produce drinking water or industrial process water, or a filtration system designed to polish (polish) that has been processed by another process. Wastewater is part of a three-stage filtration system).

The film groove 70 is shown in the side view in FIG. 2 and the end view in FIG. 3. The film groove 70 may have a length that is 2 times or more or 4 times or more of the width of the film groove 70. The distance between the wall of the film groove 70 and the front, side, and back of the film unit 120 may be closer than in the illustrated example.

In the example shown, a duct 80 is partially formed by the bottom of the film groove 70. The side wall 82 extends upward from the bottom of the film groove 70 to the bottom of the film unit 120. The duct 80 extends along the length of the groove 70 below the membrane unit 120. The downstream end of the duct 80 is closed by an end wall 84. The top of the duct 80 is formed by a plate 88. The plate 88 is not continuous, thereby providing a gap 89 that is substantially equal to the horizontal dimension of the film unit 120 in length and width.

The duct 80 has a baffle 90 as appropriate. In the example shown, the baffle 90 extends downward from the plate 88 so that the water flowing through the baffle 90 can be dispersed throughout the entire area of the gap 89 before entering the membrane unit 120. A gap 89 may have an area that is at least 80% of the horizontal cross-sectional area of a thin film unit 120 above it. The baffle 90 also extends horizontally under the bottom of a cassette 90 at least halfway (the whole way as appropriate). The horizontal extension of the baffle 90 defines an opening 92. Optionally, the openings 92 have different sizes with respect to each other to facilitate a selected division of the total influent mixed liquid flow provided to the membrane unit 120. The horizontal extension of a baffle 90 substantially all (ie, 80% or more or 90% or more) or all above the bottom of a membrane unit 120 but shifted down to the top of the duct 80 tends to generate inflow The flow is selected and distributed in the membrane unit 120 within a wider range of influent flow rates. Without intending to be bound by theory, this may be partly because the area of the opening 92 is small relative to the gap 89 (ie, 50% or less) or because the opening 92 faces the inflow stream upstream of the gap 89.

In the example shown, the height of an opening 92 associated with a first (upstream) baffle 90 is defined by the vertical distance between the first baffle 90 and the plate 88. The height of an opening 92 associated with a middle baffle 90 is defined by the vertical distance between the middle baffle 90 and the first baffle 90. A baffle 90 for the most downstream membrane unit 120 is provided by the part of the bottom plate of the tank 70 and the end 84 of the duct 80. An opening 92 for the most downstream membrane unit 120 is defined between the middle baffle 90 and the bottom of the groove 70. Alternatively, a separate duct 80 may be provided for each membrane unit 120, but it is expected that this will require additional materials and manufacturing and may increase the overall head loss of the duct(s) 80. In the example shown, the portion of the duct 80 between the opening 92 and the gap 89 provides a path for the mixed liquid to flow from the duct 80 into the bottom of the membrane unit 120.

The membrane unit 120 optionally includes a membrane shell (alternatively referred to as a shield), which provides a structure including a vertically extending conduit of the membrane itself. The film shell may be a separate structure or may be integrally formed with other parts of the film unit 120. The membrane unit 120 optionally includes an aerator 132 that generates bubbles when air from a blower 134 is provided. In some cases, the aerator 132 is integrated with the membrane unit 120 and, for example, is positioned in the membrane housing. In other cases, the aerator may be placed under the membrane unit 120, and optionally in a shield or aerator housing that connects the duct 80 and a membrane unit 120 to a vertically extending duct. If the membrane is in a membrane shell, the membrane is preferably configured to provide vertical channels for liquid to flow upward through the membrane and through the membrane unit. For example, the film may be a flat plate film or a flat ceramic film.

In some instances, the connection between the conduit 80 and the mixed liquid inlet 86 and the connection between the conduit 80 and the bottom of the membrane unit 120 are generally liquid-tight. Except for the connection to the inlet 86 and the membrane unit 120, the duct 80 is usually a closed plenum. If used, the membrane and the aerator shell are usually closed tubes. In this way, the inflow to the film tank 70 is usually provided directly to the film unit 120. There is substantially no mixing of the previously concentrated influent in the membrane tank 70 and the influent fed to the membrane unit through the conduit 80. However, due to these large-scale civil engineering works, perfect liquid-tight connection or perfect closure of ducts or membrane shells is not expected. For example, the connection between the metal flange of a curved plate of a duct 80 and the concrete wall or bottom plate of a membrane tank 70 or the frame of a box 50 can leak to a certain extent, and the duct 80 itself can be perfectly liquid-tight without use. It is made of multiple pieces connected together. However, the use of an open membrane tank 70 and a submerged membrane unit 120 allows a more economical construction of a large system with respect to a completely sealed system.

Although in the conventionally operated as an open membrane tank 70 of a stirred tank reactor, in the examples of FIGS. 2 and 3, the membrane unit 120 can be operated in a flow pattern that is more like a direct current cross flow. Preferably, at least 90% or at least 95% of the inflow into the membrane tank 70 is guided through the conduit 80 to the membrane unit 120, and contrary to the inflow from the inlet 86 to the membrane tank 70, flows upward through the membrane unit 120 The inflow of no more than 10% or no more than 5% is the inflow from the film groove 70 outside the duct 80. As appropriate, the conduit 80 and its connections to and from it are sufficiently closed and sealed so that the total suspended solids (TSS) concentration of the inflow at the bottom of the membrane unit 120 is no more than 5% or no higher than the TSS concentration of the inflow. More than 3%. In this way, the concentration of the influents reaching the membrane unit 120 in different parts of the membrane tank 70 is also substantially equalized. The duct 80 also helps to provide a substantially uniform distribution of one of the membrane units 120 flowing into different parts of the membrane tank 70. In an example where the membrane unit 120 includes a membrane shell (and if the aerator 132 is below the membrane unit, the aerator shell), the concentration of water leaving the membrane unit 120 is also substantially equalized. For example, in the MBR 100 shown in Figure 1, the total suspended solids (TSS) concentration of the water (concentrate) at the top of the membrane unit 120 is less than the TSS concentration of the activated sludge 126 in the entire membrane tank 120. More than 5%. In the case where the solid content of the mixed liquid 116 and the activated sludge 126 is higher than the MBR 100, reducing the solid concentration difference between the membrane units 120 can reduce the cleaning frequency of the membrane and increase the average throughput of the membrane unit 120. the amount.

The influent (ie, the mixed liquid 116) flows upward from the conduit 80 through the membrane shell of the membrane unit 120 at an average velocity largely determined by the flow rate of the inflow and the open horizontal cross-sectional area of the membrane shell of the membrane unit. The ability to achieve a significant influent concentration in one pass through a membrane unit 120 (which helps avoid excessive RAS recirculation rates or 6Q or more) is largely determined by the membrane unit 120 relative to its equivalent level. The filling density of the cross-sectional area (occupied area) is judged. The high occupied area in a thin film in a flat form (ie, flat plate or flat ceramic) can be achieved by close spacing and/or stacking of multiple plates. For example, the net vertical space (ie, face-to-face separation) between the films can be 5 mm or less, 3 mm or less, or 2 mm or less. The thin film unit 120 can be made using 2 or 3 or more modules stacked vertically.

In an experiment using four film units 120 in one MBR (each film unit 120 is in the form of a cassette 50 as shown in FIG. 11, in which there is a face-to-face spacing of 1.5 mm between the film plates), one of 2.78Q The RAS recirculation rate produces an average (upward) liquid velocity in the cassette 50 of 0.023 m/s. Increasing the RAS recirculation rate to 5Q and 5.6Q produced average (upward) liquid velocities of 0.035 and 0.046 m/s, respectively. Consider the horizontal area of the clear space in the box (that is, the cumulative area of multiple 1.5 mm wide vertical extension gaps between the individual films) and the flow rate of the inflow to the bottom of each box, but without adjusting the amount provided to the box In the case of bubbles, calculate the average liquid velocity. When operating at a speed of 0.023 m/s, there is a 20% difference between the maximum and minimum mixed liquid suspended solids (MLSS) concentrations in the water collected at the top of the four boxes (ie, approximately from the average -10% change), and two of the four cassettes have a higher fouling rate than one of the other two cassettes. When operating at 0.046 m/s, there is only one 10% difference between the maximum and minimum mixed liquid suspended solids (MLSS) concentrations in the water collected at the top of the four cassettes (ie, from the average value of about 5 % Change), and all four cassettes have a similarly low fouling rate. Operation at a speed of 0.035 m/s also produces sustainable operation with similarly low fouling rates in all four cassettes. Without intending to be limited by theory, the relatively poor results at the lowest speed can be attributed to the low speed itself, and at low RAS recovery rates in this particular catheter (which have different opening sizes but are not used as shown in Figure 2 and Figure 2). 3 shows the unequal distribution of the total inflow between the four boxes occurring in a baffle design), or a combination of the two.

Depending on the circumstances, the average liquid velocity in a membrane unit is 0.025 m/s or more or 0.03 m/s or more. In the case of modifying one or more parameters (for example, RAS recirculation rate), higher average liquid velocities of up to 0.05 m/s, up to 0.7 m/s, or up to 0.1 m/s can be achieved. These speeds are much lower than those commonly used in cross-flow filtration in conventional sealing systems (ie, plate and frame systems, inward/outward hollow fiber systems, or tubular membrane systems), which generally clean inflow in the filter The material time is usually about 0.2 m/s or more, and 1.0 m/s or more when filtering mixed liquids. Without intending to be bound by theory, due to the much lower speed involved, in the systems and procedures described in this article, the shear force of the liquid flowing above the membrane surface is in the fluid shear system typical of cross-flow filtration systems The same meaning of the material can be invalid. However, providing fresh mixed liquid at substantially uniform fluid velocity through multiple cassettes seems to advantageously provide consistent conditions in the cassettes, thereby avoiding the cleaning of a system that is determined by fouling one or more cassettes faster than the other cassettes. And operating agreement. In addition, the forced flow of the liquid can provide one or more effects, for example, forcing the film to separate or forcing the initial accumulation of solids from between the films, which is not related to shear force but uses the energy of the flowing inflow to help avoid undesirable effects. The flow initiated by one of the bubbles of the liquid passing through the cassette (ie, air lift) provides a way for fouling or sludge adhesion.

Figures 4 to 11 illustrate an example of a cassette 50, or various parts thereof. The cassette 50 can be used alone or in a group of multiple cassettes 50 to provide a film unit 120.

Fig. 4 shows an example of a film plate 10 (alternatively referred to as an element). The film plate 10 is composed of two substrate plates 12 that are formed and joined together to provide an internal channel 14. A porous separation layer 16 is coated on the outside of the base plate 12. The separation layer 16 can be manufactured by casting a thin film on the base plate 12 to form a coating and then curing the coating in a quenching bath. This procedure is based on the non-solvent-initiated phase separation (NIPS) method to produce pores usually in the ultrafiltration or microfiltration range. A center plate 18 between the two substrate plates 12 is optional but can be added as needed to provide a more rigid film plate 10. In other examples, the element can be made of two flat films attached together in the manner of Kubota or Microdyn Nadir elements over a frame or spacer, for example. In other examples, the elements may be made of plate-form ceramics.

FIG. 5 shows a thin film module 20. The module 20 has one or more film plates 10. The edge of the membrane plate 10 that opens to the internal channel 14 (ie, the edge shown in FIG. 1) is potted in a header 22 (alternatively referred to as a potting head or permeate collector). When in use, the header 22 is oriented generally vertically and the internal channel 14 is generally horizontal. For example, the suction force applied to the permeate port 24 of the header 22 by a pump or a siphon causes the permeate 26 to be generated in the internal channel 14 and flow through the header 22. Depending on the circumstances, the permeate can be drawn from one or both ends of the membrane sheet 10. A module 20 usually has a plurality of parallel film plates 10. Adjacent film plates 10 are separated by vertical gaps having substantially equal widths (for example, between 1.5 mm wide and 4 mm wide). In one example, a module 20 is about 1900 mm wide, about 800 mm high, and about 60 mm thick, and contains 16 film plates 10 spaced substantially equally across its thickness. In this example, the header 22 and the outer membrane plate 10 form a membrane shell. In other examples, a module may be surrounded by a single film shell.

When used in a membrane bioreactor (MBR) or a filtration device, bubbles 28 provided from below the module 20 help the filtered liquid 30 to flow upward through the module 20, including through the gap between adjacent membrane plates 10.

FIG. 6 shows a schematic diagram of a module 20 that has been cut to further illustrate the flow of liquid 30 through the module 20. The undulating shape of the film plate 10 generates turbulence in the liquid 30 when the liquid 30 rises. The membrane plate 10 can vibrate when the liquid 30 and bubbles 28 move between them. In addition to assisting liquid flow, the bubbles 28 can also provide some direct flushing of the membrane plate 10.

FIG. 7 shows a stack 32 of one of the three modules 20. The modules 20 are vertically stacked on top of each other. The permeate port 24 of the lower module is fitted in the socket (not visible) in the header 22 of the upper module. The socket in the lowermost module 20 is plugged. The permeate port 24 of the highest module can be connected to a permeate extraction tube and used to extract permeate from all three modules 20. The stack 32 can also be manufactured using two, four, or other numbers of modules 20. Since the header 22 adjacent to the module is vertically aligned and continuous, the feed liquid can flow vertically through the entire stack 32 without being obstructed by the header 22.

FIG. 8 shows a block 40 containing a plurality of modules 20 in a frame 42. The modules 20 are arranged side by side in the frame 42. A module 20 can be slid into or out of the frame 42 vertically. When in the frame 42, in the example shown, the header 22 of the module 20 fits into the corresponding groove provided by the plastic molding 44 attached to the frame 42. The frame 42 is preferably made of stainless steel, but other materials can also be used. The side plate 45 covers the side of the frame parallel to the module 20. The headers 22 each include a plurality of modules 20 and the adjacent headers 22 touch each other or close to each other, for example, are separated from each other by less than 10 mm or separated from each other by less than 5 mm. The side plate 45 and the header 22 thereby form an integrated membrane shell defining a vertically extending fluid passage through the block 40.

Figure 9 shows an enlarged view of the top of a block 40. A flange 46 at the top of the block 40 and a similar flange on the bottom of the block 40 (not shown in Figure 9) can be used to support an upper or lower block 40 and allow a stack of blocks 40 are fastened together. The permeate port 24 of the module 20 protrudes above the flange 46 to allow permeate connection between the modules 20 in a stack as described in FIG. 4.

FIG. 10 shows an enlarged view of a horizontal section of a portion of the block 40. The header 22 contains a permeate chamber 23 defined by the header 22, the edge of the membrane plate 10, and the potting resin 27 between the membrane plate 10. The permeate chamber 23 is in fluid communication with the permeate port 24 and the socket. In order to hold a module 20 in the frame 42, a bolt 48 travels through the frame 42 and is screwed into a nut 25 attached to the header 22, or molded integrally with the plastic molded header 22, as shown .

FIG. 11 shows that three blocks 40 stacked up and down perpendicular to each other constitute a cassette 50. Depending on the situation, a cassette 50 is made to have one, two, four, or another number of blocks 40. The permeate port 24 of the upper block 40 is optionally connected to a permeate header box tube 54 through a connector tube 52, as shown. The frames 42 of the blocks 40 are connected to each other by pillars 58 which, in the example shown, are threaded rods with nuts on their equal ends. The pillar 58 also attaches the upper block 40 to a cassette frame 56 which can be used to suspend the cassette 50 in a slot. The air supply pipe 60 brings air to the bottom of the box to feed it to a group of aerators (not visible) below the lowermost block 40. The molded part 44 and the side plate 45 vertically adjacent to the block 40 form a continuous vertically extending channel for fluid to flow through the cassette 50. Thereby, the cassette 50 as a whole has an integrated film shell. Alternatively, a separate film shell can be provided.

The cassette 50 can be lowered into a film groove 70 or lifted from the film groove 70 by a crane or hoist attached to the cassette frame 56. The box frame 56 can rest on the flange of the film groove 70. In the example shown, the cassette 50 has 84 modules 20. The filling density by volume is 450 to 500 m ² /m ³ . The packing density based on the occupied area is about 850 m ² /m ³ . In one example, each module 20 is about 7 to 10 cm wide. The modules 20 can be vertically stacked in a cassette 50 from one of 1 to 5 modules 20 high. Each stack of the modules 20 in the cassette 50 has an aerator with a width of about 3 to 6 cm below the lowermost module 20 in the stack.

Additional information describing suitable film boards, modules, blocks and cassettes can be found in the following public case: Method of Operating Membrane Filter published by Fibracast Ltd. on April 6, 2017, US Publication No. US 2017/0095773 ; International Publication No. WO 2013/056373 of Coating Device and Process for Coating Formed Sheet Membrane Element published by Fibracast Ltd. on April 25, 2013; and Formed published by Fibracast Ltd. on October 27, 2011 International Publication No. WO 2011/130853 of Sheet Membrane Element and Filtration System, these cases are incorporated herein by reference.

Figures 12 and 13 show two views of another catheter 80. In this example, the duct 80 guides the inflow to two membrane units 120 each having a cassette 50. A baffle 90 is made of a horizontal plate connected to a vertical plate 96 positioned below a plate 88. The area of the opening 92 of an upstream baffle is defined by the width of the duct 80 multiplied by the displacement of the horizontal plate 94 below the top of the duct 80. The area of the opening 92 of a downstream baffle is defined by the width of the duct 80 multiplied by the displacement of the horizontal plate 94 above the bottom plate of the film groove 70.

FIG. 14 shows another duct 80 extending under the three membrane units 120. The first film unit 120 has three cassettes 50. The second and third film units 120 each have two cassettes 50.

The use of computational fluid dynamics modeling as used in an MBR is intended to be another example of using a conduit with a row of 5 membrane elements of equal size extending downstream away from an inlet. The duct 80 is generally constructed as shown in FIGS. 12 and 13 but has more baffles 90 and openings 92. The area of each middle opening 92 is defined in area by the width of the duct 80 multiplied by the displacement of the horizontal plate 94 of the current baffle under the horizontal plate 94 of an upstream baffle 90.

Table 1 shows the average speed of the mixed liquid passing through the openings in the above modeled example with equal opening sizes. As indicated in Table 1, with the same opening size, the speed of the mixed liquid passing through the different openings is similar but different from each other. Table 1 Opening size (m ² ) Average speed through opening (m/s) 0.38 0.3 0.38 0.28 0.38 0.25 0.38 0.2 0.38 0.22

Table 2 shows the average velocity of the mixed liquid through the openings in the above modeled example with adjusted (unequal) opening sizes. As indicated in Table 2, the speed at which the fluid passes through the opening can be substantially equalized by adjusting the baffle and/or opening. Further adjustment can substantially equalize the average liquid velocity through the membrane unit. Optionally, the speed of the liquid flowing through each membrane unit can be within 10% of an average speed through all membrane units at a selected influent flow rate (for example, an average or peak design flow rate). Generally speaking, an equal speed can be expected, because a membrane unit with a speed that is significantly lower than the average will be exposed to the more concentrated mixed liquid at the top of the membrane unit and/or will be less effectively cleaned by the moving liquid . Table 2 Adjusted opening size (m ² ) Average speed through opening (m/s) 0.34 0.25 0.38 0.25 0.42 0.26 0.38 0.26 0.37 0.27

An experimental MBR has a separate film tank with one of two cassettes, as shown in Figure 11. The slot is significantly larger than the cassette. The return rate of activated sludge (RAS) is 4Q. The film tank was initially operated without the use of a catheter. The film tank is then operated using a catheter 80 as shown in FIGS. 12 and 13. Without increasing the transmembrane pressure (TMP) (which is 2 psi when operating with and without a catheter), when the catheter is added, the permeate output is more than doubled.

10: Membrane board 12: Substrate board 14: internal channel 16: Porous separation layer 18: Center plate 20: Thin film module 22: header 23: Permeate Chamber 24: Permeate Port 25: Nut 26: Permeate 27: potting resin 28: bubbles 30: liquid 32: Stack 40: block 42: Frame 44: Plastic molded parts 45: side panel 46: flange 48: Bolt 50: box 52: connector tube 54: Permeate header box tube 56: box frame 58: Pillar 60: Air supply pipe 70: film tank 80: Catheter 82: side wall 84: end wall 86: Mixed liquid inlet 88: Board 89: gap 90: bezel 92: opening 94: horizontal board 96: vertical plate 100: Membrane Bioreactor (MBR) 102: Wastewater 104: Coarse Sieve 106: fine sieve 108: Primary processing unit 110: Primary sludge 112: Primary effluent 114: processing tank 116: mixed liquid 120: film unit 122: Permeate Pump 124: Penetration 126: Activated sludge 128: Waste activated sludge (WAS) 130: Return activated sludge (RAS) 132: Aerator 134: Blower

Figure 1 is a schematic diagram of a thin film bioreactor.

Figure 2 is a schematic side view of a membrane tank of the membrane bioreactor of Figure 1 with one side removed to show a catheter.

Fig. 3 is a schematic end view of the film groove of Fig. 2 with the front part of the groove removed.

Figure 4 shows an edge view of a film plate.

FIG. 5 shows an elevation view of a thin film module, which includes a thin film plate as shown in FIG. 4.

Figure 6 is a schematic perspective view of one of the split modules, which shows the flow direction of the feed liquid and the permeate.

Figure 7 shows an elevation view of the three modules of Figure 5 stacked together.

FIG. 8 is an isometric view of a block containing the modules of FIG. 5. FIG.

FIG. 9 is an enlarged view of part of the block of FIG. 8. FIG.

Fig. 10 is an enlarged view of a section of the block of Fig. 8;

Figure 11 is an isometric view of one of the three blocks of Figure 8 stacked together.

Figure 12 is an isometric view of another catheter.

Figure 13 is an isometric view of one of the parts of the two cassettes in Figure 11 on the top of the catheter of Figure 12.

Figure 14 is an isometric partial cross-sectional view of one of the seven cassettes in Figure 11 on the top of another conduit installed in a slot.

70: film tank

80: Catheter

86: Mixed liquid inlet

100: Membrane Bioreactor (MBR)

102: Wastewater

104: Coarse Sieve

106: fine sieve

108: Primary processing unit

110: Primary sludge

112: Primary effluent

114: processing tank

116: mixed liquid

120: film unit

122: Permeate Pump

126: Activated sludge

128: Waste activated sludge (WAS)

130: Return activated sludge (RAS)

Claims (16)

A method of operating an immersion film system includes the following steps: Provide a film tank with a plurality of immersed film units; Feed the inflow to the film tank; Divide the inflow into multiple parts; and Lead one of the parts of the inflow to the bottom of each of the plurality of submerged film units. The method of claim 1, wherein the submerged membrane system uses a flow rate of at least 1Q or at least 2Q to operate a part of a membrane bioreactor. Such as the method of claim 1 or 2, which further comprises directing the parts of the inflow upward through the plurality of film units. The method of claim 1 or 2, wherein the film groove is elongated and/or the film units are spaced along the length of the film groove. Such as the method of claim 1 or 2, wherein at least 90% of the influent fed to the film tank flows directly to the bottoms of the submerged film units. The method of claim 1 or 2, wherein the flow rate of each of the plurality of parts is within 10% of the average flow rate of one of the plurality of parts. The method of claim 1 or 2, which includes flowing the influent through a conduit, where each of the plurality of parts exits the conduit through a separate opening as the case may be. The method of claim 1 or 2, wherein the inflow material flows through the membrane units in a single pass. Such as the method of claim 1 or 2, wherein the upward speed in the film units is 0.025 m/s or more. A membrane filtration system, which includes: A film groove; A plurality of immersed film units, which are separated in the film tank; and, One or more conduits, or the like, extend from an inlet to the film tank to a plurality of openings corresponding to the plurality of immersion film units. Such as the system of claim 10, wherein each of the plurality of thin film units has one or more cassettes of flat plate or flat ceramic thin film elements in a thin film shell, thereby generating a vertically oriented flow path through one of the cassettes. Such as the system of claim 10 or 11, wherein the common length of the film units is at least twice their width. For example, the system of claim 10 or 11 includes a duct having baffles that extend horizontally below at least part of a membrane unit above the baffle. Such as the system of claim 13, wherein the baffles are vertically displaced below the top of the duct. Such as the system of claim 10 or 11, wherein the openings have unequal sizes. Such as the system of claim 10 or 11, wherein the size of the openings is less than 50% of the occupied area of the thin film units.

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