Floating apparatus for membrane biofilm reactor and process for water treatment

Abstract

The device has multiple gas delivery membranes. The device floats on water with the membranes submerged in water. To treat the water, gas is supplied to the membranes and delivered to the water or to a biofilm supported on the membranes. The gas is also used to supply mixing or membrane refining bubbles to the water. The mixing or refining bubbles can be supplied by circulating aeration or other gas supply systems, which optionally provide gas at variable pressure to membranes in parallel with or in succession to the aerator. Condensates can be removed from the membranes, and exhaust gases from the membranes can optionally be monitored through one or more dedicated pipes.

Description

Technology Field

[0001] This specification relates to membrane biofilm devices and reactors, and processes for water treatment using membrane-supported biofilms. Background Technology

[0002] In membrane biofilm reactors (MBfRs) for water or wastewater treatment, membranes are used to support the growth of biofilms on the membrane walls and to transport gases to the biofilms through the membrane walls. Membrane biofilm reactors were reviewed by Martin and Nerenberg in "The membrane biofilm reactor (MBfR) for water and wastewater treatment: Principles, applications, and recent developments" (Bioresour. Technol. 2012). Membrane-aerated biofilm reactors (MABRs) are a subset of MBfRs in which oxygen-containing gases are used. MABRs were reviewed by Syron and Casey in "Membrane-Aerated Biofilms for High Rate Biotreatment: Performance Appraisal, Engineering Principles, Scale-up, and Development Requirements" (Environmental Science and Technology, 42(6): 1833-1844, 2008).

[0003] MBfR technology has existed at the laboratory scale for many years, but it has not been widely commercialized or scaled up. ZeeLung, developed by GE Water & Process Technologies TMMABRs use cords, and each cord contains multiple microhollow membranes. The cords are ZeeWeed of hollow fiber ultrafiltration membranes. TM It is packaged into modules and cassettes in a manner similar to packaging into modules and cassettes. Codes are embedded in upper and lower headers to form modules. The modules are mounted in a frame to form a cassette. The cassette can be mounted on the floor of a process tank. An MBfR unit of this type is described in International Publication No. WO 2014 / 130043 A1, published on August 28, 2014, which is incorporated herein by reference.

[0004] This application describes a process in which a membrane-supported biofilm unit is maintained at a generally constant immersion depth in the water being treated. The unit may be mechanically lifted or lowered, but in a preferred embodiment, the unit floats in the water. The unit may move horizontally when it is raised or lowered, or when it is not. Optionally, the unit may be mounted so that it can be moved between various positions in the tank in a plan view, for example, depending on loading conditions, biofilm maturity or health, or seasonal changes.

[0005] An exemplary floating unit has a frame and one or more floats. The frame supports modules or other structures having membranes. The floats may be fixed to the frame before the frame is placed in the tank. Alternatively, the floats may first be provided as part of a raft placed in the tank, and the frames are added later. The frame extends downward from the floats so that, preferably, the membranes are completely submerged. The floats are widened above the waterline to increase their righting moment. The frame may be part of a cassette as described in International Publication No. WO 2014 / 130043 A1.

[0006] Various processes for supplying gas to the unit are also described. Process gas for use by the biofilm can be supplied continuously at a pressure exceeding the static head pressure of the water at the lowest immersion depth. Alternatively, the process gas can be supplied at a lower pressure but with intermittent increases in pressure sufficient to allow the gas to also flow into the aerator. Non-process gases, such as those for mixing tanks or refining membranes, can be supplied periodically, for example, by a valve, by an accumulator, or by a pulsing aerator. In one embodiment, a set of valves is configured to provide sequentially higher flow rates to a series of aerators.

[0007] The unit may be attached to one or more conduits to remove water or exhaust gases from the unit. The removed water may be monitored, for example, to check for leaks in the unit by comparing the amount of water removed over a period of time with the condensate expected during that period. The exhaust gases may be analyzed, for example, to determine the amount of oxygen within them. This may be used to measure or monitor the oxygen delivery rate to the unit.

[0008] Maintaining the unit at a generally constant immersion depth enables the desired process gas pressure relative to the hydrostatic pressure without the need to monitor and compensate for changes in the water depth of the tank. For example, the process gas pressure can be maintained above the hydrostatic head by a fixed amount to minimize or prevent water or gas entry into the membranes. In other processes, a single gas feed is attached to the membranes and aerators, preferably in parallel. By varying the applied gas pressure, process air alone, process air and bubbles from the aerator for mixing, or process gas and bubbles from the aerator for refining can be provided. Non-process air can be provided intermittently or sequentially between multiple units within a tank or group of other units by a circulating aeration system valve unit. A pressure reducing bypass around the valve unit may be provided to allow each unit to continuously receive process air or process air and mixed air at a lower rate.

[0009] In hybrid MABR applications for municipal wastewater treatment, membrane-supported fixed-membrane biomass and suspended biomass are complementary. Fixed-membrane biomass is at least partially aerobic, whereas suspended biomass is at least partially anoxic or anaerobic. Floating membrane units as described herein can be added to existing process tanks of a wastewater treatment plant. For example, one or more units may be optionally added to the tank along with suspended biomass to reduce aeration energy consumption, increase capacity, or reduce nitrogen concentration in the wastewater.

[0010] Rigid anchoring of cassettes is standard for filtration membranes. However, MBfR units are more likely to be installed in existing plants. The ideal location for a unit for a treatment process may have limited mounting points due to existing equipment or structures. In some cases, it may be desirable to add units without shutting down the plant. Additionally, it may be desirable to change the position of the unit to adapt to conditions that change over time. These factors can make it advantageous to provide floating units. Floating units also locate membranes at a generally fixed and predetermined immersion depth, regardless of the tank design or the water level within the tank. In some processes, a constant immersion depth generally assists the operation of the membranes or aerators that are part of the unit. Providing floating units with their own aerators also helps by eliminating the need to adapt the unit to mixing or aeration equipment already present in the plant when reinforcing the unit in a tank. Brief explanation of the drawing

[0011] Figure 1a is a side view of a membrane-supported biofilm module.

[0012] FIG. 1b is a drawing of a cassette containing modules such as those in FIG. 1a, having modules shown in end views.

[0013] FIG. 2a is a top view of a floating membrane-supported biofilm unit having two cassettes of FIG. 1b.

[0014] Fig. 2b is a side view of the unit of Fig. 2a.

[0015] FIG. 2c is a schematic isometric view of a larger membrane-supported biofilm unit composed of the two units of FIG. 2a attached together.

[0016] Figure 3 is a schematic plan view of a membrane biofilm reactor (MBfR) having three larger units of Figure 2c deployed in a tank.

[0017] FIG. 4 illustrates a first example of piping connections for a membrane-supported biofilm unit and an aerator.

[0018] Figure 5 is a graph showing airflow and pressure losses through a membrane-supported biofilm unit.

[0019] Figure 6 illustrates a liquid removal and exhaust monitoring system for use with a membrane-supported biofilm unit.

[0020] FIG. 7 illustrates a second example of piping connections for a membrane-supported biofilm unit and an aerator.

[0021] Figure 8 is a graph showing the supply air flow rate and supply air pressure for the example of Figure 7. Specific details for implementing the invention

[0022] Gas-permeable membranes suitable for supporting the growth of biofilms on their surfaces can be provided in various forms, including flat sheets and hollow fibers. One preferred structure is a "cord" as described in International Publication No. WO 2014 / 130043. The cord consists of multiple filaments. Some of the filaments are hollow fiber gas transfer membranes. Other filaments are reinforcing filaments or are provided to space the gas transfer membranes.

[0023] FIG. 1a illustrates a module (10) having a plurality of cords (12) embedded in an upper header (14) and a lower header (15). The ends of the gas delivery membranes within the cords (12) are open to the cavities within each header (14, 15) and communicate with ports (22) on each header. In use, the ports (22) of the upper header (14) are typically attached to a gas supply line. The ports (22) of the lower header (15) are typically used to exhaust gas from the module (10). The two headers are vertically aligned and kept separated by a frame. For the sake of simplicity in the drawing, only a few cords (12) are shown, but the module (10) may have tens, hundreds, or thousands of cords (12).

[0024] Referring to FIG. 1b, a plurality of modules (10) may be combined to form a cassette (16). In the illustrated example, the modules (10) are connected to a frame (18). The frame also holds a set of aerators (20) below the modules (10). The aerators (20) consist of pipes that extend through the frame (18) and have air outlets along their length. Since the pipes are shown in end view, the air outlets are not visible in the drawing. Typically, the upper headers (14) are connected to a common air supply header pipe, the lower headers (15) are connected to a common exhaust manifold pipe, and the aerators (20) are connected to a third common pipe. These common pipes are attached to the frame (18) so that the cassette (16) has three connection points for all modules (10), or otherwise are integrated into the cassette (16).

[0025] FIGS. 2A and 2B illustrate a top view and a side view of a floating membrane-supported biofilm unit (30). This unit (30) has two cassettes (16) attached to two floats (32) by their own frames (18). The cassettes (16) extend downward from the floats (32) so that, preferably, the cords will be below the expected waterline (34). In this example, the cassette frames (18) are attached to the floats (32) to form an integral assembly. The unit (30) can be placed in a water tank, for example, by a crane. Alternatively, the floats (32) can be assembled into a raft adapted to accommodate the cassettes (16). The raft can be placed in the water first, and then the cassettes can be lowered into the raft. The cassettes (16) of the unit (30) are ZeeLung available from GE Water & Process Technologies TM They could be cassettes. These cassettes are 1,745 mm wide, 2,112 mm long, and 2,540 mm high. Each cassette contains approximately 750 km of membrane cords, which is about 3,500 m 2 It can support the biofilm surface area. In a MABR (membrane aerated bioreactor), the cassette is 8-15 Nm 3 Atmospheric air can be supplied at a flow rate of / h, and about 40-50 kg O2 / d can be delivered directly (i.e., without bubbles) to the attached biofilm. These cassettes (16) will also be used as a basis for calculations or detailed examples in the following additional description.

[0026] In the illustrated unit (30), each float (32) is a hollow tube having two sealed ends defining a sealed cavity. The floats (32) are made of stainless steel. The floats (32) are located on the sides of the cassettes (16). The unit (30) is approximately 5 m long and 2.6 m wide. The floats (32) have an outer diameter of 400 mm and each provide a buoyancy of about 2,900 N. The required buoyancy is determined based on the weight of the cassette (16), but the buoyancy of the hollow fiber membranes, headers (14, 15), and other hollow parts of the cassettes (16) is taken into account. Dynamic forces exerted by bubbles rising from the aerators (20) must also be taken into account. In other alternatives, the floats (30) may have other shapes, materials, or structures for floating. The floats (30) may be placed at different positions relative to the cassettes (30). There may be different numbers of cassettes (16) or floats.

[0027] The center of gravity of the cassettes (16) is below the expected waterline (34). The floats (32) are preferably widened above the expected waterline (34). In the illustrated example, the expected waterline (34) is below the horizontal centerline of the cylindrical floats (32). In this way, the righting moment of the unit (30) is increased, making the unit (30) more stable when subjected to non-centered loads such as wind, blocked aerators, or fluctuations in airflow between aerators (20).

[0028] FIG. 2c illustrates a larger unit (40) manufactured by attaching two units (30) end to end. Alternatively, cassettes (16) or units (30) may be attached together in other configurations. Although other sizes are possible, membrane-supported biofilm units preferably have 1 to 8 cassettes (16), more preferably 2 to 4 cassettes (16). In the following description, references to any of unit (40), unit (30), cassette (16), or module (10) may be applied to other configurations (unit (40), unit (30), cassette (16), or module (10)) described above and, if necessary, to other membrane-supported biofilm devices modified by attaching floats (32), for example, unless otherwise stated or obvious from the details of the reference.

[0029] FIG. 3 illustrates a reactor (50) having three larger units (40) floating in a tank (52). In use, water to be treated, such as a mixture or wastewater, flows through the tank (52). The water in the tank (52) has a free surface. The tank (52) is typically an open tank having a free surface at atmospheric pressure. Optionally, the free surface may be slightly pressurized, for example, by keeping biogas under a cover over the anaerobic tank. The floats (32) can preferably be placed in the tank (52) without the cassettes (16) after attaching the floats (32) together and typically by a crane to form a stable raft adapted to receive the cassettes (16) from above. The cassettes (16) are then lowered into the raft. Alternatively, the floats (32) can be attached to the cassettes (16) on land, and the completed unit (40) can be placed in the tank (52). The units (40) can be removed as a complete unit (40) or by first lifting the cassettes (16) from the floats (32). The units (40) are preferably added to the tank (52) and removed from the tank (52) while the tank (52) has enough water to float at least the unit (40). Alternatively, the frames (18) can be designed to support the cassettes (16) on the ground at least temporarily, in which case the unit (40) can be installed or removed while the tank (52) is empty.

[0030] After being lowered into the tank (52) by cranes, each unit (40) is attached to tethers (54) to position the unit (40) in the tank (52). The other ends of the tethers (54) are attached to the sides of the tank (52), for example, as illustrated, or to the ground or deck around the tank (52). The tethers (54) allow the units (40) to rise and fall in the tank (52) as the water level rises and falls in the tank (52). In this way, the immersion depths of the cords (12) and aerators (20) are generally kept constant. Alternatively, the units (40) can be mechanically raised or lowered in response to changes in water level, but floating units (40) provide this adjustment simply and automatically. Keeping the cords (12) and aerators (20) at a constant and predetermined immersion depth helps to enable some of the processes described further below. However, the processes described herein can also be used with modules (10) fixed in place in the tank (52) or adapted for such use.

[0031] As the units (40) rise and fall, it is undesirable but acceptable for them to move horizontally to some extent. The simplest tether (54) is a rigid cable provided with a slightly excessive length. In other alternatives, the tether (54) includes a taut but elastic member. For example, the tether (54) may have a section of rubber, a coil spring, or other elastic material. In other alternatives, devices used to attach boats or other marine structures to docks or piles may be adapted. For example, the tether (54) may include a curved whip or pole, a vertical rod sliding within a ring, or a spring-deflected lever. Since gas distribution to the cords (12) and aerators (20) is improved when the unit (40) is horizontal, it is desirable to use tethers (54) that tend to stabilize or level the unit (40).

[0032] To facilitate connecting one or more hoses (56) to the units (40), temporary passages may be created at appropriate locations across the walls of the tank (52). The hoses (56) are preferably flexible to move with the unit (40). The hoses (56) may be connected to rigid pipes reaching the ground or walls of the tank (52). Since the hoses (56) primarily transport gases, they typically do not need to be floated and supported on the surface of the water within the tank (52). One hose (56) may be connected to each unit (40) of FIG. 3 and may be used to supply oxygen to the unit (40) that does not collect exhaust gases or operates in a dead end process. Alternatively, each unit (40) may have one or more other hoses (56) to supply mixed / refined gas separately from the process gas, to collect exhaust gas for monitoring, or to remove condensate or other liquids.

[0033] When the unit (40) is used, for example, for water treatment in a MABR, the membranes are typically provided with a gas for delivery to the biofilm supported on the membranes and a gas for generating bubbles outside the membranes. The first gas may be called "process gas" and is pumped into the gas delivery membranes. Optionally, the process gas not delivered to the biofilm may be removed from inside the membranes. The gas used to generate bubbles may be called non-process gas, mixed gas, refining gas, or mixed / refining gas. This gas is preferably supplied to an aerator (20) located below or near the bottom of the module (10). The process gas contains components such as oxygen that support biochemical reactions in the biofilm. The non-process gas may contain the same components for convenience, but this is not essential. In a MABR, air may be used for the process gas and the non-process gas. Optionally, module exhaust gas may be used as the non-process gas. Non-process gas can be used to mix water around the module (10) to facilitate the delivery of aqueous reactants to the biofilm. Non-process gas can also be used when provided at a higher rate than is typically used for mixing to control the thickness of the biofilm or to periodically refine the membranes to remove excess biofilm.

[0034] The floating unit (40) can be used in various membrane biofilm reactors. Depending on the type of gas supplied thereto, the unit (40) can be used, in particular, for the aerobic treatment of wastewater. In this case, the process gas is an oxygen-containing gas such as air. In other examples, the unit (40) can be used for full or partial anaerobic biochemical reactions where the process gas is hydrogen, carbon monoxide, synthesis gas, or methane. For example, a hydrogen-containing process gas can be used to denitrify groundwater or to produce methane. A synthesis gas or a methane-containing process gas can be used to produce ethanol. In this specification, references to "air" may be used for convenience, but should be understood to include other gases where appropriate.

[0035] As another alternative, the floating unit (40) may be used without process air to support the fixed biofilm. In this case, the cords (12) may be provided without hollow fiber membranes, or hollow fiber membranes may be used without supplying air to support the anoxic or anaerobic biofilm. For example, the floating unit (40) may be added to the tank of a conventional activated sludge plant to provide an integrated fixed-film activated sludge (IFAS) reactor.

[0036] The floating unit (40) can be used in an essentially fixed membrane reactor, such as a MABR, where most of the active biomass in the tank (52) is fixed on the surface of the cords (12). Alternatively, the floating unit (40) can be used in a hybrid configuration where biologically active suspended growth (plankton biomass) is also present in the tank. One application for a hybrid configuration is to add the floating unit (40) to the tank (52) in an existing activated sludge plant to enhance nitrogen removal.

[0037] FIG. 4 illustrates a module (10) connected to various hoses (56). For the sake of simplicity, a single module (10) is shown, but the numerical parameters in the following description pertain to a floating unit (40) having four cassettes (16). One hose (56) is used to deliver a generally continuous flow of process air to the membranes within the module (10). This air enters through the upper header (15), flows down into the lumens of the hollow fiber membranes of the cord (12), is collected in the lower header (14), and is preferably exhausted through a hose (56) extending backward over the surface of the water. The flow of process gas from the top to the bottom helps to deliver any condensate or leaked water (which can be removed as described further below) to the lower header (14). The flow rate of process air for the 4-cassette unit (40) is 30-60 Nm 3 It is / h, and the target value is 40-50 Nm 3 It is / h. This can generally be handled with a 25mm (1 inch) hose.

[0038] In this example, process air is supplied at a pressure that is the sum of all pressure losses between the blower and the discharge point. This consists of i) membrane losses, ii) discharge pressure, and iii) conduit losses. The relationship between air flow and membrane losses for two sample cassettes (16) having smaller and larger hollow fibers is shown in FIG. 5. 11 Nm 3 / h / cassette (i.e., 44 Nm for a 4-cassette unit (40)) 3 At a target flow rate of / h), the pressure loss through the cassette (16) is about 25 kPa for small diameter hollow fibers.

[0039] The exhaust discharge pressure is a design choice. Increased exhaust discharge pressure can be provided by using an orifice within the exhaust discharge hose (56). Increased pressure provides additional driving force for gas penetration and can also ensure that the pressure inside the membranes is higher than the water static pressure outside the membranes at the lowest submersion depth of the membranes. This prevents water from entering the membranes in the event of a leak. For example, with the lowest part of the membrane submerged 2.4 m below the water surface, the static head pressure is approximately 25 kPa. The exhaust discharge pressure, optionally reduced by pressure loss in the exhaust hose (56), can be higher than this static head pressure. The composition of the exhaust air is a function of transport conditions at the membrane surface and the activity of the biofilm. Generally, the flow rate of the exhaust gas is 80-95% of the supply flow rate, and the exhaust gas is low in oxygen.

[0040] In the example of the 4-cassette unit (40), the hose (56) sizes can be selected to limit conduit losses to about 5 kPa. Process air is supplied at a total pressure of 55 kPa (25 + 25 + 5), which is within the operating range of conventional centrifugal or positive displacement blowers used in biological wastewater treatment.

[0041] Referring again to FIG. 4, the second hose (56) delivers mixing / refining air to the aerator (20). The air flow required for mixing is 60-100 Nm 3 It is the range of the / h / cassette, and the desirable value is approximately 80 Nm 3 It is a / h / cassette. Multiple cassettes (16) within the plant may be divided into mixing groups. Each mixing group may have, for example, 4 to 24 cassettes (16). Each mixing group is equipped with one or more automatic valves (60). Preferably, the mixed air is provided at a constant rate but directed to the mixing groups in a periodic or sequential manner. For example, each mixing group may receive the mixed air for 10 to 40 seconds, typically 20 seconds, every 1 to 5 minutes.

[0042] In one example, the plant has 24 units (40) (a total of 96 cassettes) each having 4 cassettes (16). Each unit (40) has an automatic valve (60). The units (40) are divided into 6 mixing groups, each mixing group having 4 units (40) and 4 automatic valves (60) that open and close simultaneously. Each mixing group receives mixed air in turn for 20 seconds out of a total cycle time of 120 seconds. While the cassette (16) receives mixed air, the mixed air flow rate is 80 Nm 3 It is a / h / cassette. The total mixed air flow rate is 80 Nm 3 / h / cassette x 96 / 6 or 1,280 Nm 3 / h is.

[0043] In another example, the plant has 24 units (40) (a total of 96 cassettes) each having 4 cassettes (16). There is one automatic valve (60) for every 3 units (40) or a total of 8 automatic valves (60). The units (40) are divided into 8 mixing groups, each mixing group having 3 units (40) and 1 automatic valve (60). Each mixing group receives mixed air in turn for 20 seconds out of a total cycle time of 160 seconds. While the cassettes are receiving mixed air, the mixed air flow rate is 80 Nm 3 It is a / h / cassette. The total mixed air flow rate is 80 Nm 3 / h / cassette x 96 / 8 or 960 Nm 3 / h is.

[0044] The air flow rate required for refining is 160 to 320 Nm 3 It is the range of the / h / cassette, and the desirable value is approximately 240 Nm 3 It is a / h / cassette. The frequency for refining can be, for example, 1 to 14 times per week, and a preferred value is about 7 times per week. If the number of automatic valves in the system is greater than the number of mixing groups, the flow rate used for mixing can be used for refining. In the first example above, if only two automatic valves (60) are opened simultaneously (rather than four), the refining flow rate is 1280 / 2 / 4 or 160 Nm 3 It is a / h / cassette. When only one valve is open, the refining flow rate is 1280 / 1 / 4 or 320 Nm 3 It is a / h / cassette. In the second example, since there is only one automatic valve per mixing group, to achieve the desired refining flow rate, the blower is increased or an additional blower is turned on. To accommodate the refining flow rate, the non-process air hose (56) for the four cassette units (40) can have a diameter of about 100 mm (4 inches).

[0045] Another hose (56) may be used for one or more auxiliary functions, such as removing liquid from the module (10), monitoring gases exhausted from the module (10), or both. This auxiliary function hose (56) may be a small tube, for example, about 5 mm for the 4-cassette unit (40). In the example shown in FIG. 4, the auxiliary hose (56) is connected at a low point where liquid from inside the modules (10) is collected, preferably at or below the bottom of the lower headers (14). The liquid may include condensate or leaks, or both. The auxiliary hose (56) may be attached to another hose (56), for example, the process air hose (56), and extend from the unit (40) to the edge of the tank (52). The end of the auxiliary hose (56) is connected to the monitoring station (70) shown in FIG. 6. The monitoring station (70) can be located on a deck or the ground near the tank (52) and connected to auxiliary hoses (56) from a number of units (40).

[0046] At the monitoring station (70), each auxiliary hose (56) is equipped with a valve (72), for example, an on / off isolation valve. The valve (72) allows the liquid to be individually removed or exhausted from each unit (40). For example, each unit can be processed sequentially once per hour or once per day. The monitoring station (70) has a vacuum pump (74), a liquid reservoir (76) on a load cell (78), and a liquid discharge line (80).

[0047] When monitoring or testing the unit (40), the associated isolation valve (72) is opened (as illustrated with respect to the upper auxiliary hose (56) in FIG. 6), while the other isolation valves (72) remain closed. Liquid is pumped from the unit (40) using a vacuum pump (74) and collected in a condensate reservoir (76). Once the mass of the removed liquid stabilizes (indicating that substantially all liquid has been removed from the unit (40)), the mass is recorded using a load cell (78) and the condensate is discharged through the discharge line (80). Alternatively, the removed liquid may be measured by a level sensor or by other methods. At the same time or approximately simultaneously, the exhaust gas is monitored using one or more instruments (82) to determine the concentration of one or more gases, such as oxygen or carbon dioxide, which provide an indication of biological vitality. When a test for one unit (40) is completed, its associated isolation valve (72) is closed and the process can be repeated for another unit (40). Typically, all units (40) are tested sequentially.

[0048] Liquid may be collected in the unit (40) due to water vapor condensate from the process air or leaks. The liquid is removed to allow for the continuous operation of the unit (40). Measuring the amount of liquid collected can be used, for example, to inspect for leaks in the unit. An estimated amount of condensate can be calculated from data such as the relative humidity of the process air, the flow rate of the process air, and the temperature of the water in the tank (52). Comparing the amount of collected liquid to this estimate provides an indication of whether leaks exist and their severity. Alternatively, the amount of liquid removed over time is monitored, optionally adjusted for seasonal or other factors, and can be used as a baseline. Significant deviations from the baseline indicate leaks.

[0049] Exhaust gas monitoring can be used, for example, to determine the oxygen delivery rate of the unit (40). Using appropriate calculations, for example, the difference in oxygen concentration between the input process air and the exhaust air and the process air flow rate, the rate of oxygen delivered through the unit (40) can be estimated. This rate provides an indication of the health of the biofilm and the rate of reaction in the biofilm. Although all exhaust air can be collected, it is more convenient to have an exhaust hose (56) extending from the sub-header (14) over the water around the module (10) without extending to the sides of the tank (52). Most of the exhaust air is simply released through a restriction that, optionally, causes the process air to be at a higher pressure while in the module (10). Only a small amount of exhaust gas is required for exhaust gas monitoring, and this small amount can be drawn out through an auxiliary hose (56) to reduce the length of the required large-diameter hose (56).

[0050] FIG. 7 illustrates an alternative arrangement of hoses (56) for a module. In this arrangement, each module (10) has only two hoses (56) extending between the side of the tank (52) and the module (10). One hose (56) delivers both process air and non-process air to the module (56). Examples of sizes and flow rates given below are for a 4-cassette unit (40). The above discussion regarding FIG. 4 also applies to this alternative arrangement to the extent that it does not contradict the description below.

[0051] As illustrated in FIG. 7, the process air and the mixed / refined air share the same hose (56) between the side of the tank (52) and the unit (40). At or near the unit (40), the hose (56) is split into two branches. One branch of the hose (56) extends to the aerators (20) below the modules (10). The other branch of the hose (56) extends to the upper header (15) to provide process air to the modules (10). The point of splitting into this branch is preferably above the water surface to prevent wastewater from accidentally entering the process air when the hoses (56) are depressurized.

[0052] Air supplied through the hose (56) flows to the modules (10) (processed air) only or to both the modules (10) and the aerators (20), depending on the flow rate and pressure losses as illustrated in FIG. 8. The process air flow rate is generally linear and proportional to the air supply pressure, as indicated by the ratio of the Hagen-Poisseulle relationship (solid line) for laminar flow. The mixing / refining air flow is zero until the supply pressure exceeds the immersion of the aeration grid (2.4 m or 24 kPa in FIG. 7 and 8), after which it increases rapidly with almost no pressure drop (dashed line in FIG. 8). Thus, it is possible to use all the supplied air as process air by supplying air at a pressure that does not exceed the static hydrostatic pressure at the depth of immersion of the aeration grid (point A in FIG. 8). In this arrangement, it is desirable not to have an orifice or other limiting that creates significant back pressure in the exhaust discharge hose (56). Based on FIG. 5, with no significant back pressure and in relation to an operating pressure of 25 kPa, the flow rate to each cassette (16) is 10 Nm for small diameter hollow fibers. 3 It is / h, and for large-diameter hollow fibers, it is 18 Nm 3 It will be / h, which is the 8 to 15 Nm described above. 3It is within the desirable range of the / h / cassette. For example, at point B in FIG. 8, increasing the applied pressure provides mixing of air from the aerator (20). For example, at point C in FIG. 8, further increasing the applied pressure provides purification of air from the aerator (20).

[0053] The mixing and refining air flow rates and frequencies may be similar to those described in relation to FIG. 4. The mixing and refining flows are obtained by operating the automatic valve (60) shown in FIG. 7. However, a bypass line (88) around the automatic valve (60) provides a continuous flow of process air to the module (10). The bypass line (80) is preferably equipped with a pressure reducer (86), for example, a needle valve that can be adjusted so that air flows through membranes but not into the aerator (20) when the automatic valve (60) is closed. The automatic valve (60) is generally operated as described in relation to FIG. 4 to sequentially provide mixing and refining air to a number of units (40). An auxiliary hose (56) is connected to a monitoring station (70) as described above and is used to remove liquid and monitor exhaust gases in the same processes.

[0054] Floating units (40) can be installed in an existing tank (52) without stopping the operation of the plant or emptying the tank (52). Existing aeration diffusers and piping or other equipment within the tank (52) usually do not need to be removed or relocated. Tethers (54) can be arranged to locate the unit (40) in a desired part of the tank (52), for example, to improve mixing or biological conversion efficiency. If treatment goals evolve over time, the unit (40) can be moved by reconfiguring or relocating its tethers (54). Optionally, the tank may have a set of available tether attachment points to allow the unit (40) to be relocated repeatedly, for example, seasonally. Floating units (40) are generally self-leveling, which helps to evenly distribute process and non-process air between the modules. The aerators (20) are always below the same hydrostatic head despite changes in the water level in the tank (52), so that the desired mixing and refining air flow rates can be accurately achieved by controlling the applied gas pressure. Floating units (40) can be added, for example, to a suspended growth tank of a wastewater treatment plant. The suspended growth can be maintained under aerobic, anoxic, or anaerobic conditions. In some situations, the addition of one or more floating units (40) can provide one or more benefits, such as reducing energy consumption, accommodating higher feed flow rates or contaminant loadings, increasing nitrification capacity, increasing or implementing total nitrogen removal, or implementing biological phosphorus removal.

[0055] This written description discloses the invention using examples and also enables a person skilled in the art to practice the invention, including manufacturing and using any devices or systems and performing any included methods. The patentable scope of this disclosure is defined by the claims and may include other examples conceived by those skilled in the art. The numerical parameters given above are intended as non-limiting examples and may be increased or decreased, for example, by 50% of the end points of a range or a single value.

Claims

Claim 1 delete Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 delete Claim 10 delete Claim 11 delete Claim 12 delete Claim 13 delete Claim 14 delete Claim 15 delete Claim 16 delete Claim 17 delete Claim 18 delete Claim 19 delete Claim 20 delete Claim 21 delete Claim 22 delete Claim 23 delete Claim 24 delete Claim 25 delete Claim 26 delete Claim 27 delete Claim 28 delete Claim 29 delete Claim 30 delete Claim 31 delete Claim 32 delete Claim 33 delete Claim 34 delete Claim 35 A process for treating water comprising: (a) a step of immersing a gas transfer membrane in said water; (b) a step of supplying gas to said gas transfer membrane; (c) a step of exhausting gas from said gas transfer membrane; and (d) a step of monitoring the oxygen concentration of the exhaust gas to determine the health or condition of a biofilm attached to said gas transfer membrane. Claim 36 A process for treating water according to claim 35, comprising the step of determining the amount of oxygen in an exhaust case. Claim 37 A process for treating water according to claim 36, comprising the step of determining the oxygen transfer rate to the gas transfer membrane. Claim 38 A process for treating water, comprising, in any one of claims 35 to 37, further a step of introducing bubbles into the water. Claim 39 In claim 38, the above bubbles are introduced at alternating rates between mixing and refining in a process for treating water. Claim 40 A process for treating water, comprising, in any one of claims 35 to 37, a step of removing liquid from the gas transfer membrane. Claim 41 A process for treating water according to claim 40, further comprising the step of monitoring the amount of liquid to determine whether leakage may occur in the gas transfer membrane, for example, indicated by an unexpected increase in the amount of liquid or a surplus of liquid exceeding the expected amount as condensate. Claim 42 In any one of claims 35 to 37, the gas transfer membrane is a process for treating water, which is added to water in a tank previously used as part of an activated sludge reactor or other wastewater treatment plant. Claim 43 A process for treating water, comprising further the step of moving the gas transfer membrane between two or more positions in a plan view of the tank in any one of claims 35 to 37.

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