Device and method for supporting a phototrophic biofilm

Abstract

This specification describes a module for supplying light to phototrophic organisms in water. Optionally, the module also has gas transfer membranes. In some examples, the module supports a phototrophic biofilm. In some examples, the module is inserted into a tank, which may be a process tank of a wastewater treatment system having a suspended biomass. The specification also describes a hybrid wastewater treatment system including phototrophic organisms and non-phototrophic organisms.

Description

DEVICE AND METHOD FOR SUPPORTING A PHOTOTROPHIC BIOFILMRELATED APPLICATION

[0001] This application claims the benefit of, and priority from, US Provisional Application No. 63 / 562,799, filed on March 8, 2024, which is incorporated by reference.FIELD

[0002] This specification relates to wastewater treatment, to phototrophic biofilm reactors, and to methods of growing phototrophic organisms.BACKGROUND

[0003] The paper, Novel waveguide reactor design for enhancing algal biofilm growth, S.N. Genin et al., Algal Research 12 (2015) 529-538, describes an algal film photobioreactor having a light emitting waveguide capable of distributing a bright light source over a larger surface area. The waveguides are placed in water in a parallel plate airlift reactor. Carbon dioxide bubbles and a nutrient media were added to the water. Algal biofilms were cultured on the waveguides.SUMMARY OF THE INVENTION

[0004] This specification describes a module for supplying light to phototrophic organisms in water. In some examples, the module supports a phototrophic biofilm. In some examples, the module is inserted into a tank, which may be a process tank of a wastewater treatment system.

[0005] The module has a plurality of light emitting filaments extending from at least one header. In some examples, one or more light emitting filaments are combined with one or more hollow fiber gas transfer membranes to form a light emitting cord, and multiple light emitting cords extend from the header. A light source is connected to the header.Optionally, a gas source may also be connected to the header. In some examples, the module has a second header and the light emitting filaments extend between the two headers. Optionally, a light source may be connected to each header. Optionally, a gas source may be connected to one header and gas may be exhausted from the other header.

[0006] A module may be made by potting a plurality of light emitting filaments, a plurality of light emitting cords and / or a plurality of gas transfer fibers or gas transfer cords. The potted filaments, fibers or cords are connected to a header enclosure to form a header. The filaments, fibers or cords are generally independent of each other except in the header. Multiple modules may be attached to a common frame to form a cassette. Different types of filaments, fibers or cords may be mixed within a module, between different modules of a cassette, or between different cassettes located in the same tank or the same wastewater treatment system.

[0007] In a wastewater treatment system, a process unit for growing phototrophic organisms is integrated with an activated sludge system or a system having one or more process units having non-phototrophic organisms. The non-phototrophic organisms may include heterotrophic denitrifiers. In some examples, the process unit for growing phototrophic organisms is provided by one or more modules or cassettes submerged in a tank of water and connected to a light delivery system. Optionally, one or more modules or cassettes may be connected to a gas delivery system. Optionally, none, some or all of the modules or cassettes that are connected to the light delivery system may also be connected to the gas delivery system. In some examples, the system includes a separate diffuser for introducing carbon dioxide into a process tank. In some examples, the system includes a gravimetric selector.

[0008] A process of treating wastewater comprises steps of growing phototrophic organisms and growing non-phototrophic organisms. The phototrophic organisms convert carbon dioxide to organic molecules. The non-phototrophic organisms may include heterotrophic denitrifiers. The non-phototrophic organisms may consume some of the phototrophic organisms. In some examples, the process includes feeding water to a tank and supplying light, and optionally a gas, to the filaments or cords of a module or cassette. In some examples, a biofilm of phototrophic organisms is cultured on the filaments or cords. Excess biofilm may be removed, for example, by introducing scouring bubbles into the tank. Optionally, photogranules derived from the detached biofilm may be retained by a solid liquid separation system, optionally including a gravimetric selector.

[0009] Another process of treating wastewater comprises feeding water to a tank and supplying light, and optionally a gas, to the water in the tank to grow phototrophic organisms.Photogranules derived from the phototrophic organisms are retained by a solid liquid separation system, optionally including a gravimetric selector.BRIEF DESCRIPTION OF THE FIGURES

[0010] Figure 1 shows an example of a light diffusing cord.

[0011] Figure 2 is a schematic drawing of a machine for making a cord.

[0012] Figures 3 to 5 are schematic drawings of steps in a process for making a module comprising a plurality of cords.

[0013] Figure 6 is a schematic drawing of a module comprising a plurality of cords.

[0014] Figure 7 is a schematic drawing of a reactor comprising the module of Figure6.

[0015] Figure 8 is a schematic drawing of an activated sludge plant including the module of Figure 6.

[0016] Figure 9 is a schematic drawing of an activated sludge plant including a gravimetric selector.DETAILED DESCRIPTION

[0017] Figure 1 shows a cord 10. The cord includes one or more light emitting filaments. In some examples, the light emitting filament is a side glow fiber optic cable, alternatively referred to as a side emitting fiber, a side light cable, or by other similar names. Side glow fiber optic cables are typically clear and emit the color of light that is input to them. Side glow fiber optic cable is readily available as monofilaments having a diameter of 0.5-12 mm, or more commonly 1-12 mm. Diameters in the range of 1-3 mm are preferred for their flexibility and high surface area to volume ratio. Side glow fiber optic cables are also available as multi-strand cables having a set of twisted filaments inside of a clear jacket. The individual filaments have a diameter in the range of 0.5 to 1.0 mm and are flexible enough to be wrapped around other filaments. In applications as described herein, a monofilament or set of filaments is optionally removed from the multi-strand cable jacket or obtained from a supplier before being incorporated into the multi-strand cable jacket. It is expected that smaller diameter light emitting filaments are already commercially available, can be produced by adapting current production methods, or may become available in the future.

[0018] A cord 10 may include two or more of a) a core 12, b) one or more warp filaments 14 and c) one or more wrap filaments 16. In the example of Figure 1, all three of these elements are present although the core 12 is not visible behind the warp filaments 14. The core 12 may be, for example, a mono-filament or a yarn, for example a twisted or braided yarn. Warp filaments 14 extend generally in parallel with the core 12 but are not mechanically intertwined with the core 12. Wrap filaments 16 spiral around the warp filaments 14 and / or the core 12. Some or all of the filaments in the core 12, warp 14 or wrap 16 may be hollow gas transfer filaments. Some or all of the filaments in the core 12, warp 14 or wrap 16 may be light emitting filaments.

[0019] In the example of Figure 1 , the core 12 includes one or more light emitting filaments. The core 12 may have a diameter of 0.5 to 6 mm, optionally a diameter in the range of 0.5 mm to 2.0 mm. The warp filaments 14 are gas transfer membranes. For example, the warp filaments 14 may be melt spun hollow fibers having an outside diameter of 100 micrometers or less. In some examples, the hollow fiber gas transfer membranes are dense walled (i.e. non-porous) and made, for example, of polymethyl pentene (Poly (4- methylpentene-1) or PMP), In other examples, the hollow fiber gas transfer membranes may be semi-porous (i.e. with pores of less than about 40 Angstroms that do not admit bulk water) or hydrophobic and porous. The wrap filaments 16 may be a multi-filament yarn or a monofilament. A multi-filament yarn may comprise filaments that are twisted or otherwise united or filaments that are merely collected together in a bundle or tow. A wrap 16 can be wrapped around a core 12 in a clockwise spiral or a counterclockwise spiral. In the example shown, the cord 10 has a multifilament tow wrap 16 in each direction.

[0020] In the example of Figure 1 , the warp filaments 14 cover some of the surface area of the light emitting core 12. However, light diffuses outwards through gaps between the individual warp filaments 14 and possibly through the warp filaments 14 themselves. A biofilm of phototrophic organisms grows on the cord 10, for example in gaps between the warp filaments 14 and the core 12, in gaps between different warp filaments 14, and to some extent on the outside of the warp filaments 14. Optionally, fewer warp filaments 14 may be provided than what is shown in Figure 1 such that more of the surface area of the light emitting core 12 is exposed.

[0021] In another example a light emitting monofilament, or multiple light emitting filaments twisted, wrapped or braided together, are used separately, i.e. without being incorporated into a cord 10. A biofilm of phototrophic organisms grows on exposed surfaces of the light emitting monofilament or filaments.

[0022] In another example, multiple light emitting filaments are twisted or braided together to form a core 12, or provided as warps 14 or wraps 16 along a core 12. Optionally, one or more non-light emitting wraps 16 may be added to inhibit separation of the underlying filaments from each other.

[0023] In another example, the core 12 is provided by a hollow fiber gas transfer membrane. The gas transfer membrane may have a diameter in the range of 0.5 to 2 mm. The gas transfer membrane may be made of silicone, for example PDMS, or a thermoplastic. One or more light emitting filaments are provided as either a warp 14 or wrap 16. If the light emitting filaments are provided as a warp 14, one or more wraps 16 may be added to inhibit separation of the light emitting filaments from the core 12.

[0024] In another example, a hollow fiber monofilament gas transfer membrane or an assembly including one or more gas transfer membranes such as a cord 10, is used separately from, but in the same reactor as, a light emitting monofilament or an assembly including one or more light emitting membranes such as a cord 10.

[0025] In another example, a cord 10 has one or more light emitting filaments as a core 12, hollow fiber gas transfer membranes as a warp 14 and additional light emitting filaments in one or more wraps 16. In another example, a cord 10 has one or more light emitting filaments in a core 12, hollow fiber gas transfer membranes as a warp 14, and one or more multifilament tow or yarn wraps 16 that include neither gas transfer nor light emitting filaments. The wraps 16 may be made of a transparent or translucent polymer such as polyester. Optionally, in either example described in this paragraph, the core 12 may have a 0.5 to 2.5 mm light emitting monofilament or multiple light emitting filaments twisted, wrapped or braided together.

[0026] Other examples of structures having one or more light emitting filaments, one or more gas transfer membranes, or both, may be used. Typically, these structures, including the examples described above, have an outside diameter of 0.5 to 6 mm or 0.5 to 5 mm. The outside diameter of the structure, e.g. a cord 10, may be measured as the smallesthole that the cord 10 will pass through. Anomalies, defects or non-repeating bumps are ignored in these measurements.

[0027] Light emitting filaments may be made, for example, from poly(methyl methacrylate) (PMMA). The full IUPAC name is poly(methyl 2-methylpropenoate). PMMA is a non-crystaline vitreous material sometimes called acrylic or acrylic glass. PMMA transmits light with wavelengths in a range of about 300-2,800 nm. PMMA also scatters a portion of transmitted light from the sides of a filament. PMMA side glow fiber optic filaments are commercially available from several sources and used, for example, for architectural illumination. Light scattering from the sides of PMMA filaments can be increased by various methods such as scratching or sanding the surfaces of the filaments or stretching the filaments. The inventors have also believe that light scattering may be increased by curving a PMMA filament, as occurs for example when one PMMA filament is wrapped around another filament.

[0028] Figure 2 shows a machine 20 for making a cord 10. The machine 20 is built on frame 22 that supports the different components and aligns them. A core 12 and one or more warps 14 are supplied to the machine 20 from a creel 24. The creel 24 has stationary bobbin holders, guides and tensioning devices, as found in other textile equipment. The warps 14 pass through a distributor 28. The distributor 28 may have a central opening and one or more eyelets around the central opening. The core 12 and warps 14 are unwound from a bobbin on the creel 24, positioned to the top of the distributor 28 through a roller and fed vertically down through the distributor 28. A take up winder (not shown) pulls the cord 10 downwards through the machine 20 and onto a bobbin. In other examples, there is a core 12 but no warps 14. In other examples, there are warps 14 but no core 12.

[0029] Optionally, one or more spindles 30, or other yarn wrapping devices, are located below the distributor 28. Each spindle 30 is loaded with a yarn and wraps the yarn around the one or more warps 14 or core 12 as they pass through the spindle 30. Due to the downward movement of the core 12, each wrapped yarn forms a spiral wrap 16. The machine 20 may also have alignment guides (not shown) to keep the core 12 aligned with the central axis of the spindles 30 and to reduce vibration of the core 12.

[0030] An example of a suitable spindle 30 is a Temco™ spindle model MSE150 by Oerlikon Textile. Each spindle 30 has an electrical motor and a hollow core and holds abobbin of wrap yarn 16. The spindle 30 is positioned so that its central axis coincides with the core 12. In the machine 20 of Figure 2, there are two spindles 30, one rotating clockwise and the other rotating counterclockwise. The spindles 30 can rotate at an adjustable speed of up to 25,000 rpm to provide a controllable pitch. Alternatively, a rotating creel may be used in place of the spindle 30. In a rotating creel, bobbins are mounted on a wheel that rotates in one direction around the core 12 without being in contact with it. Each bobbin is preferably equipped with tension control.

[0031] A plurality of cords 10 (or, or in combination with, other filaments or fibers), for example 100 or more, may be made into a module generally in the manner of making an immersed hollow fiber membrane filtration module. At least one end of each of the cords 10 is potted in a block of a potting material such as thermoplastic or thermosetting resin which is sealed to a pan (i.e. a header enclosure) to form a header. The ends of any gas transfer membranes and / or light emitting filaments are made open to the inside of the header, for example by cutting them open after potting. The other ends of the cords 10 may be potted in another header with the ends of the gas transfer membranes and light emitting filaments open or closed, closed individually, or looped back and potted in the first header.

[0032] An optional port in the header allows a gas to be fed to the lumens of the gas transfer membranes 14. The gas may be fed to the gas transfer membranes 14 in a dead end manner or with exhaust through a second header.

[0033] A light source in one header, or in communication with the inside of the header for example by way of one or more fiber optic cables, provides light to the light emitting filaments. Optionally, a light source may also be provided in communication with a second header such that the light emitting filaments receive light from both ends. The light source may include a lamp, for example an LED lamp. Alternatively or additionally, the light source may include a solar collector. A lamp may be selected to produce light at wavelengths suitable for growing selected phototrophic organisms. Sunlight is optionally filtered to produce light at wavelengths suitable for growing selected phototrophic organisms. Light may be provided continuously or in a cycle of, for example, 12 hours per day to emulate a daily sunlight cycle.

[0034] As one example, the cords 10 (or, or in combination with, other filaments or fibers) may be assembled into modules and cassettes according to the configuration ofZeeWeed 500™ immersed membrane filtration units sold by Veolia. Sheets of cords 10 are prepared with the cords 10 generally evenly spaced in the sheet. Multiple sheets are stacked on top of each other to form a bundle with adjacent sheets spaced apart from each other. The bundle is potted. After the potting material cures, it is cut to expose the open ends of the cords 10 and sealed to a header pan. Several such modules may be attached to a common frame with their ports manifolded together to form a cassette. Various useful techniques that may be used or adapted for making a module are described in US Patent 7,169,295, US Patent 7,300,571 , 7303676, US Publication 2003 / 01737006 A1 and International Publication Number WO 02 / 094421 , all of which are incorporated by reference. Alternatively, other known techniques for making a hollow fiber membrane module may be used.

[0035] Referring to Figure 3, multiple cords 10 (or, or in combination with, other filaments or fibers), or an undulating cord 10, are laid out on a flat jig or drum to provide a set of generally parallel segments of cord 10 in a sheet 38. The segments of cord 10 may be kept evenly spaced from each other in the sheet 38, for example by a woven filament 40 or a strip of hot melt adhesive 42. When segments of cord 10 are used, the ends of the cords 10 may be sealed, for example by melting them with an iron or heated cutter along a sealing line 44. Multiple sheets 38 may be stacked on top of each other, preferably with the ends of adjacent sheets 38 separated by spacers. The end of the set of sheets 38 are placed in a potting mold 46 and filled with a potting resin 48 flowing either by gravity or by way of centrifugal force. The potting resin 48 may be, for example, a polyurethane resin formulated to penetrate into and seal around the various filaments of the cord 10.

[0036] Referring to Figure 4, the set of sheets 38 is removed from the potting mold 46 after the potting resin 48 is cured. To expose open ends of any gas transfer membranes and light emitting filaments, the potting resin 48 is cut through along cutting line 50. The other end of the set of sheets 38 may be potted in the same manner. Optionally, one or both of the blocks of potting resin 48 may be cut to expose open ends of any gas transfer membranes and light emitting filaments.

[0037] Referring to Figure 5, a header 60 is formed by sealing the block of potting resin 48 to a header pan 52. The header pan 52 may be made of molded plastic. Optionally, the header pan 52 has an outlet 54 for letting gasses into or out of the header 60. Optionally,the header pan 52 has an optical cable 55, for example a fiber optic cable, for bringing light into or out of the header 60. A distal end of the optical header 55 may be connected to a source of light or to another header 60.

[0038] The block of potting resin 48 may be held in the header pan 52 by an adhesive or a gasket 56 between the perimeter of the potting resin 48 and the header pan 52. Optionally, a second potting material 58 may be pored over the potting resin 48. The second potting material may further seal the cords 10 or the potting resin 48 to the header pan 52, or may cushion the cords 10 where they exit from the header 60. A similar header 60 may be made at the other end of the set of sheets 38. In other examples, the block of potting resin 48 is cured in the header pan 52 directly (rather than in a separate mold) according to methods know in the art of making hollow fiber membrane modules.

[0039] Referring to Figure 6, a module 66 has two headers 60 with cords 10 extending between them. The headers 60 are preferably vertically aligned and held apart by a frame 62. The length of the cords 10 between opposing faces of the headers 60 may be slightly greater than the distance between the opposed faces of the headers 60. In this case, the cords 10 have some slack and can sway. The cords 10 are preferably not connected to each other between the headers 60. Although one cord 10 may contact another as it sways, the movement of a cord 10 is generally independent of other cords 10. Multiple modules 60 may be held in a common frame 62. The frame 62 may also hold an aerator 68 near the bottom of a module 66.

[0040] When used for wastewater treatment, the cords 10 (or, or in combination with, other filaments or fibers) are immersed in a process tank of a bioreactor. A gas, for example air, carbon dioxide, hydrogen, or another gas, is fed through the lumen of any gas transfer membranes. Light is provided through any light emitting filaments. A biofilm may develop on the outside surface of the cords 10 or other filaments or fibers. Alternatively or additionally, a cord 10 or other filament or fiber may supply light and / or a gas for use by suspended organisms, or organisms in a biofilm of other cords 10, filaments or fibers.

[0041] Modules of the cords 10 may be deployed in a bioreactor by immersing them in a process tank of a wastewater treatment system. Cassette frames may be used to facilitate deploying multiple modules with the cords 10 oriented vertically into open tanks. Gas sparging by way of bubbles produced below or near the bottom of the modules can beprovided at a low rate to renew the liquid around the cords 10. Gas sparging at a higher rate may be used to help control biofilm thickness either by the direct action of bubbles, bubble wakes or bubble pressure effects on the biofilm, or by causing cords 10 mounted with slack between the headers to sway in the water to produce turbulence or contact between cords 10. Optionally, gas exhausted from any gas transfer membranes may be recycled for use in gas sparging or to blend with process gas.

[0042] Referring to Figure 7, a module 66 is immersed in a tank 70. The tank 70 is filled with water to be treated from an inlet 72. Treated water is removed through an outlet 74. Optionally, water may recirculate from the outlet 74 to the inlet 72 to provide a flow of water through the module 66, mix the tank 70, or to maintain desired conditions in the tank 70. Optionally, the outlet 74 may be connected directly or indirectly to a solid-liquid separation device and some of a solids rich fraction of the effluent from outlet 74 may be recirculated, directly or indirectly, to the inlet 72. The tank 70 may be part of a series of tanks in a wastewater treatment plant.

[0043] Carbon dioxide, hydrogen, air enriched with carbon dioxide and / or hydrogen, or another gas, is optionally blown into, or drawn out of, the module 66 by a first gas blower 76. In the example shown, the gas is blown into a first header 60, travels through the cords 10, and is exhausted from a second header 60. Optionally, the exhaust gas is recirculated to the first header by way of a second gas blower 80.

[0044] Wastewater treatment plants tend to off gas carbon dioxide present in the influent wastewater or created by the metabolism of microorganisms that metabolize organic carbon (i.e. BOD) in the water. The partial pressure of carbon dioxide in water may be higher than the partial pressure of carbon dioxide in air. The flow of a gas through a dense walled membrane is proportional to the permeability coefficient of the gas in the membrane material and the partial pressure differential across the membrane. Accordingly, to transfer carbon dioxide to the water through a gas transfer membrane, it may be necessary to use a carbon dioxide enriched gas or increase the absolute pressure of the gas in the lumens of the gas transfer membranes. Recirculating the gas through the second gas blower 80 allows for the pressure in the recirculation loop to be at greater than atmospheric pressure.

[0045] In most dense walled membranes, the permeability coefficient for carbon dioxide is 3 to 5 times the permeability coefficient for oxygen. By controlling theconcentration of influent gas, the lumen pressure, the recycle rate, and partial pressures in the water, carbon dioxide and oxygen can be delivered through the gas transfer membrane at various absolute or relative rates. These absolute and / or relative rates, optionally in combination with other factors such a pH, nutrient supply, mechanical stress (e.g. through scouring bubbles) or biological stress (e.g. through periodic alterations of gas or nutrient supply) may be used to preferentially culture a desired type of phototrophic organism.

[0046] Optionally, for example at night or when light is not supplied to the phototrophic organisms, the gas transfer membranes can be used to withdraw and collect carbon dioxide from the water. The collected gas may be stored and re-used as a supply of carbon dioxide enriched gas when light is supplied to the phototrophic organisms.

[0047] A throttle valve 78 may be used to vent waste gas from the recirculation loop so that new gas may be added through first gas blower 76. Alternatively or additionally, aerator valve 79 may be used, continuously or intermittently, to supply gas to an aerator 68 below the module 66. Bubbles from the aerator 68 may be used for mixing the tank 70 or controlling the thickness of the biofilm on the cords 10. Optionally, the aerator 68 may comprise a supply pipe 82 and a transducer 84. The transducer 84 collects gas ejected from the supply pipe in a pocket below a shell 86. Large bursts of bubbles are released periodically. The flow of bubbles from the aerator 68 may be controlled to prevent the growth of excess biofilm on the cords 10. Optionally, a light sensor near the cords 10 may be used to measure light diffusion resistance which may be used as in indicator of whether the biofilm thickness is within a desired range.

[0048] Light is provided to any light emitting filaments of the module 66 from a light source 57. The light source 57 is connected by light cables 55 to the headers 60. Light emitted in the headers 60 enters the ends of any light emitting filaments. Alternatively, light may be provided by lamps, such as LED lamps, in the headers 60 of the modules as shown in Figure 8. Light is released into the water and / or an attached biofilm from the sides of the light emitting filaments.

[0049] Light may be provided from artificial sources, from collected sunlight or both. Light may be provided during daylight hours, during artificially extended daylight hours, or continuously. The intensity and duration of light, optionally in combination with the supply of gas and / or one or more nutrients, may be controlled to provide a selected rate of carbondioxide assimilation in the phototrophic biofilm. The desired rate of carbon dioxide assimilation may be related, for example, to supplying organic carbon by way of the phototrophic biomass to other organisms, such as heterotrophic denitrifiers, in the wastewater system as a whole.

[0050] In some examples, a module 66 has cords 10 that include both light emitting filaments and gas transfer filaments. In some examples, a module 66 has light emitting filaments, either as monofilaments or in cords, that are separated from gas transfer membranes. The gas transfer membranes may be in hollow fiber membrane monofilaments or in cords. In some examples, the gas transfer membranes may be in separate sheets from the light emitting filaments. On other examples, that gas transfer membranes and the light emitting filaments are alternated within each sheet.

[0051] In other examples one module 66 has gas transfer membranes but no light emitting filaments and another module 66 in the same cassette has light emitting filaments but no gas transfer membranes. In other examples, one cassette in wastewater treatment system has gas transfer membranes but no light emitting filaments and another cassette in the wastewater treatment system has light emitting filaments but no gas transfer membranes.

[0052] As noted above, conventional wastewater treatment plants tend to produce excess carbon dioxide, which escapes to the atmosphere as an off gas from the surface of the process tanks. Culturing phototrophic organisms in the wastewater treatment system allows for some of the excess carbon dioxide to be converted to organic carbon, which reduces greenhouse gas emissions from the wastewater treatment plant. The organic carbon is embedded in phototrophic organisms released when excess biofilm is removed from the module 66. This excess phototrophic biomass may be removed from the system, for example by solid liquid separation of an effluent. Carbon in the removed biomass may be, for example, sequestered (for example by pyrolysis, hydrothermal carbonization, hydrothermal gasification, drying or application to soil) and / or converted into methane and carbon dioxide by way of an anaerobic digester. Many phototrophic organisms also incorporate soluble nitrogen and phosphorous into organic molecules, and removal of excess phototrophic biomass helps to directly reduce the nitrogen and phosphorous concentrations in wastewater treatment plant effluent. Alternatively, some of the excess phototrophic biomass may be retained in the wastewater treatment system as a source of carbon for othermicroorganisms. Since nitrogen removal to low levels often requires the addition of organic carbon to a wastewater treatment plant, providing organic carbon by way of phototrophic biomass can reduce or eliminate the need to add a supplemental carbon source to the wastewater treatment plant. Optionally, carbon dioxide can be added through the module 66, or by way of separate carbon dioxide spargers, to increase the generation of organic carbon in the form of phototrophic biomass for use by heterotrophic denitrifiers in the wastewater system, to sequester carbon dioxide, to produce biomass for conversion to methane or a fertilizer, or to enhance the ability of the phototrophic organisms to remove nitrogen and phosphorous directly from the wastewater.

[0053] As shown in Figure 7, the module 66 occupies roughly one third to one half of the volume of the tank 70. However, modules 66 may occupy more or less, for example 5- 95%, of the volume of a tank 77 or of the total volume of tanks in a wastewater treatment system.

[0054] Referring to Figure 8, a module 66 has light emitting filaments, optionally as monofilaments or in cords, and optionally with gas transfer membranes, optionally in cords with the light emitting filaments or in separate cords or monofilaments. Multiple modules 66 are attached to a common frame to form a cassette 80. One or more cassettes 80 are inserted into one or more tanks of an activated sludge plant 82. The sludge plant includes an aerobic tank 88 and a secondary separation device 90. The secondary separation device may be, for example, a clarifier as in the example shown or a membrane filtration module. Optionally, the activates sludge plant 82 may include additional tanks, for example an anaerobic tank 84 and / or an anoxic tank 86. Other types and arrangements of tanks may also be used. Zones withing a tank may be used to replace multiple tanks. In the example shown, the cassette 80 is placed in an aerobic tank 88. In other examples, the cassette 80 may be placed in a different tank. The cassette 80 provides enhanced carbon capture and redirection for the activated sludge plant 82. The cassette 80 may include aerators to scour excess biofilm from the modules 66. Optionally, the aerators are pulsing aerators, for example LEAP™ aerators available from Veolia Water Treatment Solutions.

[0055] The secondary separation device (for example a clarifier, membrane filer, dissolved air floatation unit, etc,) produces an effluent and an activated sludge. A portion of the activated sludge is returned (Returned Activated Sludge, RAS) to the mainline processtanks. Another portion of the activated sludge is waste (Waste Activated Sludge, WAS). The WAS may be sent to an anaerobic digester, optionally after being mixed with primary sludge and / or thickened. Optionally, thickening filtrate and / or a liquid fraction of anaerobic digester sludge (e.g. dewatering centrate) may also be returned to the mainline process tanks. Some of the organic carbon in the phototrophic biomass may be converted to methane in the anaerobic digester for reuse as a fuel. Some of the organic carbon in the phototrophic biomass may be converted to carbon dioxide in the anaerobic digester, and some or all of the carbon dioxide produced in an anerobic digester (from digestion of the phototrophic biomass or other solids) may be used to grow more phototrophic biomass, optionally after purifying the anaerobic digester gas. Some of the organic carbon in the phototrophic biomass may be present in anaerobic digester sludge (or sludge that was not subjected to anaerobic digestion) which may be, for example, dried or pyrolyzed for long term disposal or sequestration, and / or applied to land for use as a soil amendment or to sequester carbon in the soil.

[0056] Figure 9 shows another activated sludge plant 82. In this example, a portion of activated sludge 96 that is designated as waste activated sludge 94 is sent to a gravimetric selector 92. The gravimetric selector 92 may be, for example, a hydrocyclone. The gravimetric selector 92 removes a dense fraction 98 of solids in the waste activated sludge 94 and returns this dense fraction 98 to the main line of the activated sludge plant 82, for example to the anaerobic tank 84. The dense fraction 98 may include photogranules, which are solid aggregates that include phototrophic organisms, which may include phototrophic organisms that were previously shed from a biofilm on the light emitting filaments. The phototrophic organisms in the photogranules may be dormant, but preserve a source of carbon in the activated sludge plant 82 that can be used by other organisms such as hetrotrophic denitrifiers.

[0057] A portion of waste sludge that bypasses the gravimetric selector 92, and a liquid fraction effluent from the gravimetric selector 92, may be further processed, for example by thickening and dewatering, hydrolysis, anaerobic digestion and / or pyrolysis, hydrothermal carbonization, hydrothermal gasification or drying. Organic carbon in the waste sludge is thereby converted to methane and / or stored in a solid form for sequestration and / or reuse, for example as a soil amendment.

[0058] Although Figures 8 and 9 show the use of modules 66 in combination with a wastewater treatment system, phototrophic organisms may alternatively be grown in other forms of suspended growth or biofilm reactors. Suspended growth bioreactors include, for example, photobioreactors (e.g. of the type having phototrophic organisms growing in transparent bags or tubes) and raceway ponds. Biofilm reactors include, for example, reactors with rotating wheels and belts. While these types of reactors may be used, the modules 66 are preferred since they are consistent with the form of tanks typically used in wastewater treatment plants and are efficient in the use of materials. However, many of the systems and methods described herein, for example converting excess or added carbon dioxide to organic carbon for use by heterotrophic dentrifiers, may be applied with other means of growing phototrophic organisms.

[0059] In some examples, sloughing of phototrophic biofilm allows for a transfer of the biofilm to the bulk liquid within a wastewater treatment plant. The may enable the synergetic use of organic carbon stored in the phototrophic biofilm (e.g. purple bacteria) to further remove nitrates (from 10-15 mgN / L to < 3-7 mgN / L preferably but not limited to such as from <25 mgN / L to <10-15 mgN / L) by heterotrophic denitrifiers contained in the bulk liquid. There may also be a synergetic use of dissolved oxygen produced by the phototrophic biofilm (e.g. cyanobacteria) to supply oxygen for enhancing autotrophic nitrification (from 5 mgN / L to < 1 mgN / L preferably but not limited to such as from <100 mgN / L to <5 mgN / L) by nitrifiers contained in the bulk liquid or for increasing dissolved oxygen concentration in the bulk-liquid of the bioreactor. In some examples, DO concentration may be increased from 0 to 9 mgO2 / L or up to saturation, preferably to completely replace or partially or fully offset the oxygen supply from a fine bubble diffusion system typically provided at the bottom of an aeration tank. In some examples, 0 to 0.5 mgO2 / L may be provided by a conventional fine bubble diffuser and 0.5 to 9 mgO2 / L may be provided by the photobiofilm, preferably 0.5 to 4 mgO2 / L.

[0060] The solids retention time (SRT) of photoorganisms in the biological reactor, contained initially in the photobiofilm sloughs colonizing the bulk-liquid, may be increased by allowing the formation and augmentation of photogranules in the bulk-liquid mixed liquor. The mixed liquor may contain a consortium of photoflocs (from 10 to 200 microns particlessizes) and photogranules (from 200 to 1000 microns size particles). The SRT of a photo flocgranule consortium may be increased by 2 to 10X, to an SRT of between 1 to 100 days.

[0061] The volatile solids (VS) content of the waste activated sludge sent to a sludge line may be increased from 50-75% to 76-90% resulting in further carbon capture and production as biogas, for example from an increase from 0.8-0.9 Nm3biogas / kgVS removed to 0.91 to 1.5 Nm3biogas / kgVS removed.

[0062] In some examples, there is a synergetic use and assimilation of CO2 produced by bulk-liquid micro-organisms such as heterotrophs by a photobiofilm grown on the module 66 or another biofilm device.

[0063] In some examples, there is a synergetic use of CO2 produced by anaerobic digestion (20 to 30% v / v), which may be purified (e.g. condensate water removal and / or >90% v / vCO2 content), and input to the gas transfer membranes of module 66. Carbon dioxide produced by anaerobic digestion may be assimilated in a photobiofilm or by the growth of phototrophic organisms directly. This results in a further carbon sink by means of supplemental transformation from CO2 to organic carbon growth of phototrophic organisms (e.g. cyanobacteria or purple bacteria) in the wastewater treatment plant.

[0064] The use of light emitting filaments helps overcome light diffusion resistance through the free surface of water to allow the growth of an oxygenic photoheterotroph biofilm in a deep tank. The biofilm may in turn be used to produce photogranules. The light emitting filaments provide a medium that serves as a support and light source in a biological reactor flowsheet, optionally used in a wastewater treatment plant or lagoon.

[0065] Oxygenic phototrophic organisms, which may be present in a photoheterotroph biofilm or photogranules, include but are not limited to the growth of microbial inventories such as cyanobacteria, red and purple bacteria, eukaryotic algae, purple sulfur bacteria, various genera of cyanobacteria, and cryoconite phototrophic granules.

[0066] The use of light emitting filaments allows the precise control of lux (light emission energy). The control of lux, optionally combined with controlling the 02 and / or CO2 partial pressure on the inner side of gas transfer membranes and / or the scouring energy on the outer side of gas transfer membrane, may be used to preferentially help select and grow selected biofilm-based photoheterotroph organisms. Lux and gas (Air / 02 and CO2) controlstrategies are optionally used to help out-compete detrimental growth such as algae (detrimental to scouring / mixing and light diffusion efficiencies) to favor the growth of biofilmbased inventories such as cyanobacteria, red and purple bacteria.

[0067] When combined with selective sludge wasting, light emitting filaments allow for the growth and bioaccumulation of photogranules in the bulk water in addition to a phototroph biofilm attached on the filaments. Photoheterotroph biofilm and photogranules allow capturing and boosting more carbon for growth, redirection and recovery.

[0068] In some examples, an apparatus may have a biofilm supporting module. The module has light emitting filaments, optionally bundled around a core fiber. Multiple filaments may be potted together in headers at both ends of the filaments. The light emitting filaments may be arranged in sheets within the modules. Multiple modules may be arranged in a cassette format. A module may have top and bottom headers containing (optionally on top of a gas transfer system) a set of light emitting diodes (LEDs) to supply light from bottom to top and / or top to bottom along the light emitting filaments to diffuse lux to a biofilm grown and temporarily fixed on the outer surface of the light emitting filaments. Optionally, a module may have a mix of light emitting filaments and gas transfer fibers (from 5% gas-95% FO, to 95% gas-5% FO). The mix of light emitting filaments and gas transfer fibers may done at the cord, module or cassette level of a system.

[0069] A gas supply and control system may selectively supply air (oxygen) and / or CO2 to the gas transfer membranes. In some examples, during the night, air (oxygen) is diffused through the gas transfer fibers and / or a fine bubbles diffusion system is used to supply oxygen to photoheterotrophic organisms for respiration. During the day, CO2 from the bulk (free culture biomass) is used as a carbon source for assimilation by the phototroph biofilm to grow while oxygen is generated by photosynthesis enhanced by artificial (optionally including artificial concentration of natural sunlight) lux diffusion. In some examples, during the day, optionally, CO2 gas recovered from an anaerobic digester biogas system (30% v / v) or another source of carbon dioxide is optionally purified and optionally enriched (e.g. to >90% v / v carbon dioxide) and supplied through the gas transfer membranes. Optionally, at night air (oxygen) may be diffused through the gas transfer membranes to support the growth of the phototrophic organisms. Growth of the phototrophic organisms provides a readily assimilable carbon source, enhances carbon capture. A gas recycle system may be used tocontrol the level of CO2 and 02 provided to the biofilm to levels favorable for preferential growth and / or to out-compete detrimental photoheterotrophic inventories (e.g. cyanobacteria may be preferred over eukaryotic algae). A scouring system using or reusing air, oxygen or C02 in gas phase provides coarse bubbling, turbulences and sheering effect to control the biofilm layer.

[0070] Optionally, a system or method also includes the use of phototrophic biofilm sloughed from the light emitting filaments to enrich the bulk (i.e. suspended) biomass and optionally to generate photogranules. The system and method may provide a hybrid biofilmflocs and granules bioreactor. The use of selective wasting by means of a gravimetric selector retains and accumulates photogranules in the system. The combination of a growing biofilm on light emitting filaments and selecting and retaining phogranules enables synergistic effects on particles size settling properties (to enhance separators design and performances such as settlers, filters, membranes, clough, flotation) as well as on synergetic effect on organic treatment and capture (carbon, GHG...).

[0071] A combination of free culture (i.e. suspended) biomass known in wastewater treatment with algae or other phototrophic organisms provides a hybrid treatment solution. The combination of free bulk biomass and phototrophic organisms allows wastewater treatment with carbon capture and recovery.

[0072] The conventional growth of phototrophic organisms is limited by light diffusion resistance for the use of photoheterotrophic organisms (e.g. algae) conventionally imposing the implementation within long and shallow tanks (oxidation ditches or carrousels) with high light exposure such as equatorial regions (Maghreb, Middle East, Central Americas, SEA...). Current solutions are tied to greenfield markets and sunny regions. Such solutions cannot be implemented in deep tanks (4, 5, 6, 8 or 10 m) which are widely practiced in wastewater treatment solutions. Moreover, conventional bioreactors with a depth of 0.8 to 1 m can be of 50 to 200 m long, making this configuration extremely high footprint consuming. This remains an extensive footprint solution. Those limits allow application of such solution only to new greenfield construction in desert and remote areas. Those limits prevent the use of conventional algae growing systems to provide a combination of suspended biomass and phototrophic organism in existing brownfield wastewater infrastructure.

[0073] In some examples, the system and methods described herein may have one or more uses or advantages such as: a) overcome light diffusion resistance and debottleneck light diffusion resistance encountered with deep tank applications like conventional activated sludge (CAS) or sequencing batch reactor (SBR), b) favor augmentations of valuable photoheterotroph inventories, c) use of means such as lux and gas (Air / 02 and CO2) control strategies to help out-compete detrimental growth such as algae (detrimental to scouring / mixing and light diffusion efficiencies) to favor the growth of biofilm-based inventories such as cyanobacteria, red and purple bacteria, d) grow carbon capture for redirection with organic biofilm / photogranules from CO2 assimilation (CO2 supplied from biogas reuse or other source and / or available from the bulk mixed liquor bacteria used for WW treatment), e) enhance carbon sink from sludge line into phototrophic biomass reusable into biogas or biopolymer / biodiesel, f) boost biogas / biomethane production / recovery of biosolids line, f) reduce greenhouse gas (GHG) emissions of wastewater treatment plants (WWTPs), g) control mixing requirements for cyanobacteria / algae / photogranules, h) use existing fine bubble aeration to provide oxygen for CO2 fixation, i) allow growth and extraction of bio-based polymers, j) solves extensive-footprint issues required for existing solutions due to swallow reactor (1 m depth CAS carrousel, SBR), k) opens brownfield market, I) enhances carbon / energy recovery, m) expands market outside sunny regions by solving light diffusion resistance.

[0074] Examples

[0075] In laboratory experiments, bundles of 1 to 50 side emitting fibers (SEF) made of uncoated PMMA were connected directly to LED lamps, or connected indirectly to LED lamps through an end-emitting sheathed fiber optic cable by way of 3D printed adapters.

[0076] Samples of 0.5 mm SEF were observed qualitatively in untreated, sanded, kinked, stretched and braided forms. Kinking and stretching produced a moderate increase in light transmission and an increase in algae colonization relative to untreated fibers. Sanding produced the highest light emission and colonization. Braiding 3 fibers together also produced a moderate increase in light transmission but a large increase in algae colonization, particularly in crevices of the braid.

[0077] In a comparative study, a 6 Watt red LED (19,000 Lux) was used to provide light to 30 cm PMMA filaments of various diameters and configurations. The intensity oflight emitted at the side of the filaments was measured 15 cm from the light source. Results are presented in Table 1 below. In the looped configuration, both ends of the filament receive light, which may also be considered to represent a module with light provided from upper and lower headers. As indicated in Table 1, the output light intensity increased with filament diameter, but light intensity / cross sectional area decreased with filament diameter. Thus a set of multiple relatively small filaments may be more effective than a larger monofilament having outside diameter equal to the aggregate outside diameter of the smaller filaments. As also indicated in Table 1, winding a filament increases the output light intensity, which might be a result of one or more of: bending of the wrapped fiber increasing its output per unit length; or, an increase in wrap filament length per unit of cord length. The looped configuration more than doubled the output light intensity under the conditions of this test suggesting a benefit to providing light from both ends of a cord. The results in Table 1 are comparative and, since the light meter was not adapted to the surfaces of the cord, the measured Lux and PAR might understate the absolute values.Table 1

[0078] A portion of the looped and wrapped device was inserted into a flask containing water. The water was inoculated with a mother solution containing multiple strains of microalgae collected from the secondary effluent of a wastewater treatment plant. A biofilm including microalgae formed on the immersed portion.

[0079] In another example, a light emitting cord was made with 9 m of a 1 .5 mm diameter PMMA filament used as a wrap around 1.5 m of a 2.5 mm PMMA filament core.The 1 .5 mm diameter filament made about 1000 turns around the 2.5 mm fiber, resulting in a pitch of about 1.5 mm. Light was emitted at over 10 PAR from the cord, which is predicted to be sufficient for an algae biofilm to form on the cord when immersed in wastewater and supplied with carbon dioxide either bubbled into the wastewater or supplied from gas transfer membranes near, or added to, the cord.

[0080] This written description uses examples to disclose the invention and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art.

Claims

CLAIMS:We claim:1 . A module for supplying light to phototrophic organisms in water comprising a plurality of light emitting filaments extending from at least one header.

2. The module of claim 1 wherein the light emitting filaments are potted in the header.

3. The module of claim 1 or 2 wherein the light emitting filaments are combined with one or more hollow fiber gas transfer membranes.

4. The module of claim 3 wherein the light emitting filaments and the hollow fiber gas transfer membranes are combined in a cord.

5. The module of any of claims 1 to 4 having a light source within or connected to the header.

6. The module of any of claims 1 to 5 having a gas source connected to the header.

7. A process comprising supporting a phototrophic biofilm on a module of any of claims 1 to 6 for example wherein the module is inserted into a tank, which may be a process tank of a wastewater treatment system.

8. The process of claim 7 further comprising growing a suspended biomass in the tank.

9. The process of claim 8 wherein the suspended biomass includes phototrophic organisms.

10. A wastewater treatment system having a module according to any of claims 1 to 6 immersed into a tank of water to be treated.

11. The system of claim 10 further comprising a secondary separation device to retain a suspended biomass in the system.

12. The system of claim 11 further comprising a gravimetric selector.

13. A device comprising, one or more light emitting filaments and one or more hollow fiber gas transfer membranes.

14. The device of claim 13 further comprising one or more inert or structural filaments.

15. The device of claim 13 or 14 wherein one or more of the filaments are wrapped in a spiral around other filaments.

16. A wastewater treatment process comprising growing a phototrophic biofilm and growing a suspended biomass of non-phototrophic organisms.

17. The process of claim 16 further comprising selecting and retaining granules comprising phototrophic organisms.

18. The process of claim 16 or 17 further comprising supplying light to the photrotrophic biofilm from a light emitting media immersed in a tank.

19. The process of any of claims 16 to 18 further comprising supplying externally sourced carbon dioxide to the phototrophic biofilm.

20. The process of claim 19 wherein the externally sourced carbon dioxide is derived at least in part from anaerobic digester gas, optionally after purification, concentration or gas separation steps.

21. The process of any of claims 16 to 20 wherein the non-phototrophic organisms include heterotrophic denitrifiers.

22. A wastewater treatment system comprising a phototrophic organism process tank, a non-phototrophic organism process tank, and a solid liquid separation device, configured to provide a sequential mainline process and recirculation of sludge to the mainline process.

23. The system of claim 22 further comprising a gravimetric selector.

24. The system of claim 22 or 23 wherein the phototrophic organism process tank comprises a light emitting medium immersed in a tank.

25. The system of claim 24 wherein the tank is at least 1 m deep, at least 2 m deep, or at least 3 m deep.

26. A light emitting device comprising a) a plurality of side glow fiber optic cables and / or b) a side glow fiber optic cable wrapped around another filament.

27. The light emitting device of claim 26 comprising two or more side glow fiber optic cables twisted, wrapped or braided together.

28. The light emitting device of claim 26 or 27 wherein the side glow fiber optic cables comprise PMMA filaments.

29. The light emitting device of any of claims 26 to 28 wherein the PMMA filaments have a diameter in the range of 0.5 to 12 mm.

30. The light emitting device of any of claims 26 to 29 further comprising hollow fiber gas transfer membranes.

31. The light emitting device of any of claims 26 to 30 having an outer diameter in the range of 0.5 to 12 mm.

32. A wastewater treatment process comprising immersing the device of any of claims 26 to 31 in wastewater, supplying light to the side glow fiber optic cables and supplying carbon dioxide to the wastewater.

33. The process of claim 32 wherein the carbon dioxide is supplied through a gas transfer membrane.

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