Untitled record

ES 2 394 886 T3

DESCRIPTION

Supported Biofilm Procedure

Field of the invention

The present invention relates to a gas transfer apparatus and method, for example for supporting a biological film in a liquid, as in a water or wastewater treatment method or apparatus.

Background of the invention

Currently, most wastewater treatment plants use an activated sediment process based on biological oxidation of organic contaminants in a suspended growth medium. Oxygen is obtained from the air using bubble type aerators. The efficiency of these systems is poor, which results in very high energy use. The tank size is large as the oxygen demand loads are low. The result is a high cost in capital and operations.

A second type of established biological oxidation procedure uses biological films that have been grown on a solid medium. For example, the wastewater can be circulated over the top of the reactor and filtered. Air is supplied from the bottom. The oxygen transfer rate is limited by the surface area of ​​the biofilm and operating costs are high by the requirements of pumping wastewater.

Development work has recently been done with a membrane-supported bioreactor concept. For example, US Patent Nos. 4,181,604 and 4,746,435 describe a process for treating wastewater by supplying oxygen from one side of a gas-permeable membrane to growing microorganisms on the other side of the membrane. Hollow fibers with porous walls were used as the membrane. In US Pat. 5,116,506, a gas-permeable membrane divides a reactor vessel into a compartment for liquids and a compartment for gases. A biological film grows on the gas permeable membrane on the liquid side of the membrane. Oxygen and alternating gases pass through the membrane to the growing bacteria on the liquid side of the membrane.

Kazuaki Yamagiwa et al .: Simultaneous organic carbon removal and nitrification by biofilm formed on oxygen enrichment membrane, Journal of Chemical Engineering of Japan, Society of Chemical Engineers, Tokyo, JP, vol. 27, no. 5, 1 October 1994, pages 638-643, discloses a support for biofilm consisting of a hollow silicone fiber and a fibrous support. The fibrous support is in the form of superfine polyester fibers woven around the hollow fiber. Biofilm holder is used to treat wastewater in a reactor.

US 5,126,050 discloses an apparatus for the removal of organic compounds from water, sewage or used granular activated carbon. The process comprises introducing the liquid to be treated through the upper part of the reactor where it passes over gas-permeable membrane beds that eliminate contaminants. The gas is supplied to the membrane that provides the necessary electron donors and acceptors to support the growth of suitable microorganisms. The microorganisms that have grown on the surface of the membrane beds and their growth can be controlled. These microorganisms capture electron donors and acceptors from the supplied gas and use contaminants in the liquid to be treated as a carbon source, so that the liquid is decontaminated.

Brindle K et al .: Nitrification and oxygen utilization in a membrane aeration bioreactor, Journal of Membrane Science, Elsevier Scientific Company, Amsterdam, NL, vol. 144, no. 1-2, 10 June 1998, pages 197-209, discloses a laboratory scale membrane aeration bioreactor. The bioreactor comprises porous hollow polyethylene fibers vertically suspended in a tubular reactor containing wastewater to be treated. The fibers are bundled into a bundle and oxygen is supplied at the base of the bundle.

Summary of the invention

The invention is set forth in the appended claims.

To the extent that any of the aspects and embodiments of the treatment methods described below are outside the scope of the claims thereof, such aspects and embodiments are included by way of background to aid in understanding the invention as claimed.

It is an object of the present invention to improve over the prior art. It is another object of the present invention to provide suitable processes and apparatus for treating water, for example industrial and municipal wastewater, using membrane supported bioreactor technology. It is another object of the present invention to provide a hollow fiber gas transfer membrane and module that is, for example, suitable for supporting a biofilm. These aspects and others are fulfilled in the invention described and claimed herein. The following summary will introduce the reader to various aspects of the invention, but are not intended to define the invention, which may reside in a combination or sub-combination of various elements or steps found in the following summary or other parts of this document.

ES 2 394 886 T3

The invention provides a process for treating wastewater with a reasonably high gas transfer rate and adequate surface area, for oxygen transfer, biofilm support, or both, to allow a supported biofilm reactor to provide a advantage over operating costs over other procedures used in the art. The membrane and module can have an oxygen transfer efficiency (ETO) of more than 50% or in the range of 50% to 70% or more. The module can be made of non-porous or dense walled hollow fiber membranes to provide a large surface area while avoiding the tendency of porous fibers to wet out over time, resulting in a drastic decrease in their speeds. oxygen transfer.

The hollow fiber is made of polymethylpentene (PMP), which has a high selectivity and diffusion coefficient for oxygen. Specifically, PMP has a gas permeability of approximately 70,000 cc / m²24 h.Bar in the form of a dense, non-humidifying wall. Although this is significantly lower than silicone, which has extremely high gas permeability, PMP can be melt spun to form a hollow fiber. The fiber can have an outer diameter of 500 microns or less or 100 microns or less. Using such a small diameter fiber helps reduce module costs, as fine fiber textile technology can be used to create modules. A very large surface area can be provided to achieve a high ETO. The non-porous wall avoids humidification problems as described above.

A biofilm is grown on the gas-permeable hollow fibers, for example PMP dense-walled hollow fibers. The oxygen carrier gas is introduced into the lumen of the fiber. Aerobic reactions take place near the surface of the fiber, where the highest oxygen levels exist. These reactions include conversion of organic carbon compounds to carbon dioxide and water, and of ammonia to nitrates. The surface of the biofilm is maintained under anoxic conditions such that conversion of nitrates to nitrogen can take place. The result is the simultaneous reduction of organic carbon, ammonia and total nitrogen.

The process of the invention can be used to carry out other biological reactions on the surface of the fabric. An example is the biological reduction of compounds such as nitrates in water using hydrogen gas supplied in the light of the hollow fiber.

Air or enriched air can be used to supply oxygen. The selection of enriched air and the level of oxygen present in that air can be determined by the strength of the wastewater.

The process of the invention can be used to digest the primary and / or secondary sludge.

The fibers have a small outer diameter (ie, 30-100 pm, and a substantial hollow area, for example 30% or 40% or more, so that they have a thin wall. The fibers may be woven, knitted, embroidered or otherwise forming a fabric. The use of fine hollow fibers allows the wall thickness of the fiber to be low, for example 20 pm or less, which is several times less than what would be necessary to make a film be manageable. Fine fibers can, by themselves, be difficult to handle individually but can be combined to form units, such as strands or cables to handle, which can include forming textile sheets. The fabric, having a large number of hollow fibers, provides sufficient surface area for oxygen transfer capacity so that air can be used as the feed gas without limiting the growth of biofilm or other biological kinetics and with a loss. acceptable pressure due to air flow through the module.

Continuous plug flow or multistage batch or stirred tank reactors can be used to perform the biological reactions at the highest possible substrate concentrations for a given feed. This maximizes the mass transfer of organic carbon and ammonia compounds in the biofilm, eliminating these procedures as potential limitations on reaction rates. In multi-stage reactors, module designs with smaller surface areas can be used for ratios of oxygen transfer to biofilm surface area in downstream stages. The total surface area for oxygen transfer, for example per unit tank volume or feed flow rate, may increase or decrease in the downstream reactor, as the lower ratio may be the result of an increase in the area of biofilm surface rather than a decrease in surface area for oxygen transfer.

The process of the invention can be used in a supported batch biofilm reactor (MSBBR). The reactor includes one or more membrane modules into which an oxygen-containing gas is introduced and supports a layer of biofilm. The modules are located inside a tank that is cyclically filled and drained to provide a batch treatment procedure. In one embodiment, the modules are made of a hollow fiber cloth and are used to reduce COD (Chemical Oxygen Demand), ammonia, total nitrogen, and suspended solids in an industrial wastewater plant to concentrations suitable for their use. discharge into a municipal sewer system or for direct discharge into a receiving stream. In another embodiment, the modules are used to reduce DOC, ammonia, total nitrogen, and suspended solids in a municipal wastewater stream for direct discharge to a receiving stream. In another embodiment, the modules are used to reduce DOC, ammonia, total nitrogen, and solids.

ES 2 394 886 T3 suspended in a septic tank to reduce the size of the septic field or to use simpler and lower cost disposal techniques or for direct discharge to a receiving stream.

The method of the invention can be used to control the growth or thickness of a growing biofilm layer on the modules. Some procedure (s) involve applying one or more substances to the biofilm from the side of the tank while the tank is draining of the feed. These substances can include gases, such as ozone or chlorine, or liquids, such as heated water or basic or acidic solutions. During the application of the control substance, the conditions in the biofilm can be cycled from aerobic to anaerobic by turning the oxygen supply into the module over and over again. Biofilm can also be starved prior to control substance application by removing feed water, replacing feed water with clean water, or substituting feed feed water at a load of 0.1 kg DOC per kg MLSS a day or less. After application of the control substance, mechanical control procedures of the biofilms with the weakened biofilm can also be used.

Air entrainment can be provided on the outside of the fibers as a means of controlling the thickness of the biofilm to an optimal level. Air can be used as a means of controlling the thickness of the biofilm to a desired level. Acid, base, oxidant or enzyme treatment or an anaerobic treatment can be used periodically before air entrainment to weaken the biofilm and improve air efficiency by completely or partially removing the biofilm. Other biofilm control procedures include in situ digestion, periodic ozonation followed by digestion, periodic acid or base treatment followed by digestion, periodic enzyme treatment followed by digestion and use of a higher life form such as worms, to digest biofilm periodically. To speed up biological digestion reactions, the air supplied inside the module can be preheated to raise the temperature of the bioreactor.

To facilitate the construction of modules with minimal reduction in the effective surface area of ​​the fibers, the fibers can be processed or used as cables over a significant portion, for example one half or more, of their length. The modules can be manufactured directly from the cables without first manufacturing a fabric. The cables can also form open fabrics to facilitate molding, for example along the edges of the fabric, while leaving significant portions of the fibers as cables, for example a portion between the edges of the fabric. Modules made of cables can be molded at both ends or molded at one end only, leaving the other end unmolded with the fiber ends open to allow exhaust gases to escape. A single head module can have less costs than a double head module. A single head module can be inserted in a vertical configuration with the head at the bottom and the fibers floating up. This module can be aerated from the outside of the module to remove accumulations of trash and solids. The feed can also be screened through, for example, a 0.5mm sieve, to reduce waste in the feed before it enters the reactor. When the cable module is used in a downstream stage of a multi-stage reactor, the upstream stage can also reduce the amount of trash fed into the cable module reactor.

Reactors for treating wastewater of different strength may be provided with modules having different proportions of the surface area for the transfer of gas to the surface area of ​​the bonded biofilm. The surface area for gas transfer is the area of ​​the external surface of the module that is in contact with the supported biofilm. The surface area of ​​the biofilm is the area of ​​the outer surface of the biofilm that is in contact with the wastewater. In some cases, the surface area of ​​the biofilm depends on the thickness of the biofilm which, for calculations or for comparing modules, can be the actual thickness or the time average of the thicknesses of a biofilm in a reactor or a nominal or design thickness or average thickness, for example 250 microns. A reactor for treating wastewater with a COD of more than 1,000 mg / l may have a modulus with a ratio of the surface area for gas transfer to the surface area of ​​a fixed biological film of more than 1, more than 1, 6 or between 1.6 and 10. A reactor for treating wastewater with a cOd of more than 1,000 mg / l can have a modulus with a ratio of the surface area for gas transfer to the surface area of ​​a fixed biological film of less than 2.5 or between 0 , 2 and 2.5. The COD of the wastewater to be treated decreases through each reactor and the ratio of the surface area for gas transfer to the surface area of ​​the fixed biological film for the modules in a downstream reactor is less than for the modules in an upstream reactor.

Other aspects of the invention are described in the claims or in the following figures or description.

Brief description of the figures

Embodiments of the invention, as well as background and related matters, will now be described with reference to the following figures.

Figure 1 is a photograph of a group of hollow fibers.

Figure 1a is a cross section of a hollow fiber.

Figure 1b shows a group of hollow fibers and inert fibers collected in one unit.

ES 2 394 886 T3

Figures 2a to 2d and 2e show groove arrangements and a spinneret for the melt spun fibers.

Figures 3a and 3b show a plan view and cross section of a woven fabric respectively.

Figure 3c shows stages during the weaving of a fabric.

Figure 3d shows a warp knitted fabric.

Figure 4a shows a hollow fiber sheet with a central portion of the sheet having the cable sheets. Figure 4b shows details of a part of the sheet of Figure 4a.

Figure 5 is a cross section of a loose cable module.

Figure 6 shows a top view of a module having fiber sheets.

Figure 7 is a partial section, in elevation view, of the module of Figure 6.

Figure 8 is a cross section of another part of the module of Figure 6 in plan view.

Figure 9 is an elevation view of a module according to Figures 6 and 7.

Figures 10a, 10b and 10c are elevational, plan and partial sectional views of another module having fiber sheets.

Figures 11 and 12 are plan and elevation views of a tank having hollow fiber sheet module cassettes.

Figure 13 is a drawing of the details of a tensioning mechanism in the apparatus of Figures 11 and 12.

Figure 14 is an elevation view of the mechanism of Figure 13.

Figures 15 and 16 are schematic elevation drawings of the reactors.

Figures 17 and 18 are schematic drawings of other reactors.

Figure 19a is a laboratory scale batch reactor using a cable module.

Figure 19b is a photograph of a biofilm on a strand of fibers growing in the reactor of Figure 19a taken through a microscope.

Figure 20 is a schematic elevation drawing of a septic tank modified to use a supported biofilm module.

Figures 21 to 31 are the results of tests performed with various modules or sample reactors.

Description of the achievements

1.0 Module elements

1.1 Fiber

Figures 1 and 1a show a poly (4-methylpentene-1) (PMP) fiber 10 which is hollow inside but not porous and with dense walls. In a group of fibers 10, the fibers 10 can have various diameters and can be fine fibers having outside diameters of less than 500 microns or less than 100 microns, for example between 30 and 100 microns, or between 50 and 60 microns. The hollow fibers 10 shown are non-porous or dense-walled and water does not flow through the fiber walls by advective flow. However, oxygen or other gases can pass through or travel through the fiber walls by, for example, molecular diffusion or dissolution-diffusion.

Hollow fiber 10 can be prepared by melt spinning, which is alternatively referred to as melt extrusion. In melt spinning, a polymeric granulate, for example PMP, is introduced into the hopper of an extruder. The polymeric granulate is heated and melted in the extruder and is continuously extruded into a rotating head with a pressure of several tens of bars. The rotating head consists of a heated built-in filter and a swath. The row is essentially a steel plate with thin arc-shaped grooves in circular arrangements. Examples of suitable groove arrangements for forming a hollow fiber are shown in Figures 2a to 2d. As shown in Figure 2e, the spinneret can have multiple groups of grooves so that many fibers, 8 in the spinneret shown, can be extruded simultaneously. The molten polymer is extruded through the die, exits through the slots, and is sealed into a hollow fiber in a cooling zone. The voids produced by the segment dividers allow air to enter the fiber to prevent collapse before the fiber sections condense to form the ring. In the cooling zone, the polymeric fiber formed is solidified and cooled by a controlled cross-air flow and at the end

ES 2 394 886 T3 is collected on a tensioning winder. Suitable fibers 10 can also be formed by other melt spinning processes. For example, in conduit in hole spinning the polymer melts and stretches through an annular spinneret while passing a gas to the lumen of the extruded fibers through another hole in the spinneret to prevent fiber collapse. . Procedures other than melt spinning can also be used.

Referring to Figure 1a, in the illustrated embodiment a melt spinning process is used to make fibers 10 with an outer diameter 12 of 100 µm or less. The hollow area (or lumen area 14) of the fiber may be more than 10% or more than 30% or 40% of the cross-sectional area of ​​the fiber. The hollow area is typically less than 60% or 50% of the cross-sectional area of ​​the fiber. For example, a polymethylpentene fiber can be manufactured having an outer diameter of 12 or between about 50 to 60 pm and an inner diameter 16 of 30 pm or greater, resulting in a wall thickness 18 of 10 pm. or less and a gas permeability of more than 30,000 cc'mm / m^2,24h. Bar or more.

In the embodiment illustrated in Figure 1, the textile PMP fiber 10 has an outer diameter 12 of 45 microns and an inner diameter 16 of 15 to 30 microns. Fiber 10 was melt extruded using PMP MX-001 or MX-002, produced by Mitsui Petrochemical of Japan and sold under the name TPC, as a crude polymer through a segmented die as described above. This fiber 10 is used in the embodiments and examples described herein, although other fibers 10 may also be used.

1.2 Fiber aggregates (eg cables)

Referring to Figure 1b, the hollow fibers 10 can be combined into fiber units 19 for handling. The fiber units 19 can be individual fibers 10, cables 20, for example 1 to 200 or 16 to 96 fibers 10 each, either braided or unbraided (Figure 1b), strands, threads, tubular braids, flat or in cables, or other units 19 to manipulate. Cables 20 are manufactured by rewinding fibers from multiple receiver coils in combination onto a second coil. Stronger inert fibers 22, such as PE or PP yarns, can be included in a cable 20 or other unit 19. Fibers 10 can be wound for use in units 19. Coiled fibers 10 can be formed by winding onto a coil with various stresses.

1.3 Sheet structures

The fibers 10 and / or fiber units 19 may be provided in the form of sheets 26. In Figure 3^to and 3b, the fibers 10 are woven as fiber units 19 into a basic two-dimensional structure or fabric sheet 26. In the illustrated embodiment, the units 19 traverse the sheet, ie perpendicular to the direction in which the sheet 26 advances toward off a loom. Inert fibers 22 traverse the length of sheet 26 to provide support for the fiber units 19. Figure 3c illustrates the steps involved in a weaving process. The fiber units 19 are transported in a shuttle through 2 groups of inert fibers 22 which are alternately raised or lowered after each passage of the shuttle. Other weaving or fabric making processes can also be used. The type of unit 19, the beam size of unit 19, the spacing between units 19, and the percentage of fibers in each direction can be tailored to meet the mechanical or biochemical requirements of each unique application.

In more detail, the fiber units 19 provide a support surface for the growth of a biological film 30. The number of hollow fiber units 19 and the number of fibers 10 per unit 19 can be adjusted to provide a desired surface area for O2 transfer compared to the surface area of ​​the biofilm 30 or the planar surface area of ​​the fabric sheet 26. The planar surface area of ​​sheet 26 is simply the length of the sheet times its width times two (since the sheet has two sides). The surface area of ​​biofilm 30 is the total area of ​​that of biofilm 30 exposed to the liquid in the reactor, which, in general, may be the same as the planar area of ​​sheet 26 for a substantially sheet configuration. two-dimensional.

The surface area for O2 transfer is the total area of ​​the hollow fibers 10 in the sheet exposed to the biofilm. This is approximately equal to the product of the effective diameter and the length of the fiber 10, multiplied by the number of fibers 10 in the sheet 26. The effective diameter for diffusion is a logarithmic mean of the fiber diameters to account for the effect of the wall thickness. Inert fibers 22 traversing hollow fibers 10 in sheet 26 and fiber contact 10 may interfere with oxygen transfer in some embodiments, for example a tightly woven fabric, but the interference is usually small and is ignored in the surface area for oxygen transfer calculations.

Although the surface area of ​​the biofilm 30 is generally the same as the planar area of ​​the sheet, it may be slightly larger for very rough or open fabrics or fabrics having more dispersed 19 fiber units. Varying the roughness of the fabric can also be used to affect the thickness of the biofilm 30 or the ease with which the biofilm 30 can be reduced or controlled. High ratios of O2 transfer surface area and biofilm area (AS O2 / AS biofilm) can be obtained in the range of, for example, 6 to 10 or more. However, to treat feed water with a high concentration of DOC, for example 300 mg / l of DOC or more, lower ratios of AS O2 / AS biofilm are sufficient, for example between 1.6 and 10, and can prefer to reduce module costs. A ratio of AS O2 / AS biofilm in the range of about 2 to 8 or about 4 to 6 can provide

ES 2 394 886 T3 satisfactory results in many treatment applications.

The surface area of ​​the biofilm 30 can also be larger than the planar area of ​​the sheet 26 by providing a loose arrangement of the fibers 10 and controlling the thickness of the biofilm 30 to a layer thin enough for the biofilm to 30 on adjacent parallel fibers do not form a continuous layer. A sheet 26 with a rough or textured surface may also be desired, the height of the surface undulations being in the range of the desired biofilm thickness, as it can facilitate biofilm control. The desired biofilm thickness can be 200 to 1,000 microns.

Provided that oxygen transfer through module 40 does not limit reactions in biofilm 30, the rate of COD reduction in wastewater is approximately proportional to the concentration of COD in wastewater. However, for oxygen transfer not to be a limiting factor, more oxygen is required to flow through module 40 to support biomass of the same surface area as DOOC concentrations in the wastewater increase. More oxygen can be provided by increasing the size or speed of operation of a blower. However large pressure drops, for example 69 kPa or more, can occur due to resistance to oxygen flow through the fiber lumens 14. The pressure drop can be kept below 69 kPa or at the range of 41 to 62 kPa, choosing a type of fabric and a series of fibers that produce a sufficient total light area for an external surface area of ​​the given biofilm.

Likewise, the inventors have found that biofilms growing in wastewater with high concentrations of DOC, for example 1,000 mg / L of DOC or more or 2,000 mg / L of DOC or more, are more resilient and tend to grow up to a Undesirable thickness of a few mm or more, faster than biofilms growing in wastewater with lower concentrations of DOC. Therefore, biofilms grown in wastewater with high concentrations of DOC require more vigorous biofilm control procedures.

The various problems discussed above make it preferable to use the fabrics in wastewater with high COD concentrations that have more fibers and, optionally, more surface roughness, for the same overall planar area of ​​a sheet or outer surface area of supported biofilm than for fabrics used to treat wastewater with lower COD concentrations. This can be achieved by choosing the procedure used to create the fabric and choosing the fabric unit or yarn count or fabric tightness. Multi-stage reactors can also be used. In a multi-stage reactor, an upstream reactor treats the feed to its highest COD concentration and is provided with modules having dense fabrics with a high number of fibers. A downstream reactor receives partially treated wastewater with a lower COD and is provided with modules that have a less dense fabric with fewer fibers for the same external surface area of ​​the biofilm or sheet. Less dense fabric is cheaper as it has fewer fibers and can have a larger biofilm area for a sheet of the same planar surface area.

Fabric sheets 26 can also be made by other methods such as braiding, embroidering, or knitting, such as warp knitting. Warp knitting is desirable, for example, when using units 19 or small cables or even individual strands of fine fiber 10. If desired, fabric sheets 26 can be embossed, as in pattern knitting, to provide areas with fewer fibers or holes to enhance flow through the sheets 26.

In warp knitting, fabric sheet 26, as shown in Figure 3d, contains interlocking loops of "knitted stitches". The column of stitches formed on a needle makes a fringe. Fringes in the length ("warp") direction of the fabric can be formed by relatively inexpensive basic yarns, eg PET, PP etc. as inert fibers 22. Inert fibers 22 can withstand stress and wear from processing and use. The fabric sheet 26 is generally strong and stiff in the warp (length) direction and elastic in the weft (transverse) direction. The weft is a system of perpendicular threads that is placed through the fringes and fixed with points (loops) of the fibers of the warp 22. The weft is not part of the fabric formation (loop), so the fiber units 19 of the weft can be processed very smoothly, being subjected to less stress and wear than the warp. Accordingly, the preparation of the sheet 26 with units 19 as the weft can minimize the risk of damaging the fibers 10 during the manufacture of the sheet 26. Typically the weft is a parallel layer or band of yarns that are displaced diagonally with respect to the fringes (warp) during knitting. The width of the cloth sheet can be about 2-3 m.

In the embodiment of Figures 4a and 4b, the sheets 26 are formed with an open fabric by weaving cables 20 through the shuttle of a loom and crossing the cables 20 with an inert fiber 22 only along the edges of the fabric. 26. The fabric shown has a width of approximately 1.3 m, that is, it has active fibers 10 of approximately 1.3 m in length and has inert fibers 22 woven perpendicular to the cables 20 in a strip of approximately 2 cm along the lengths of the fabric. edges. As shown in Figure 4b, the fibers 10 in each cable 20 spread out beyond the strips so that the cables 20 remain unrestricted and partially open between the strips. The resulting roll of 1.3 m wide fabric is cut into sections approximately 20-200 cm or 30-60 cm wide to make individual sheets 26. In Figure 4b, the number of fibers 10 in each cable

ES 2 394 886 T3 is small for clarity, but cables 20 can each have, for example, between 1 and 200, for example 16, or 96 fibers 10.

1.4 Modules

1.4.1 Loose cable module

In accordance with the present invention, multiple fiber units 19, including fibers 10, cables 20, or sheets 26, can be grouped together to form membrane modules 40. Figure 5 shows a module 40 which may be referred to as a cable or cable module. loose cable, with fibers 10 arranged and molded into fiber cables 20. The cables 20 are made of a loose collection of a plurality of fibers 10, for example between 1 and 200 or 16 to 96 fibers 10. The fibers 10 can be lightly braided or they can be left unbraided. The fibers 10 can be wound, crimped, or crimped to provide a three-dimensional structure to each molded row. Winding can be achieved by rewinding the fibers 10 onto a spool by varying the tension of the fibers. The individual fibers 10 remain separable from each other in the cable 20. Said cable 20, when covered by a thin biological film, for example of a thickness less than 1 mm, can provide a ratio of the gas transfer area through the fiber walls and the external surface area of ​​the film. biological (AS oxygen / AS biological film) of less than 2.5, less than 1 or between 0.1 or 0.2 and 1. If required, inert fibers 22 can be added to the cable as reinforcement. Each cable 20 is molded into a resin plug 32 so that its ends 34 are open on one face of the resin 32. The resin plug 32 is glued to the inside of the plastic head housing 35 which has a port 36 which forms a header 44 that connects the port 36 with the open ends 34 of the fibers 10 through a cavity 37. There are two heads 44, one associated with each end of the fibers 10, although modules 40 can also be manufactured with only one inlet head 44. With two heads 44, air or other gases can enter a head 44, flow through from the fibers 10 and exiting from the second head 44. The cables are molded in a resin 32, such as polyurethane, and the molded ends are cut to expose the light from the fiber. Alternatively, a fugitive molding material can be used to block the fiber ends, as described in US Patent 6,592,759, or other molding procedures. In Figure 5, both the number of cables 20 and the number of fibers 10 per cable 20 are small for the sake of clarity in the drawing and in practice can be much larger.

1.4.2 Reed module

A module 40 of a bundle or stack of sheets 26 can also be constructed. The sheets 26 may have perpendicular inert fibers across the entire width of the sheet 26, as in Figure 3a, or only through a portion. of the width of sheet 26, for example at the ends as in Figure 4. The raw material for sheets 26 can be rolled into a roll of cloth. For example, when sheets 26 are prepared by weaving, the material is wound onto a roll at the end of a loom as the material is produced. The fiber units 19 can be extended through the roll, while the inert fibers are wound around the roll. With the fibers oriented in this way, individual sheets 26 can be cut from the roll by removing a length of material from the roll and cutting it with a hot knife or thermal cutter. The thermal cutter melts through the fiber units 19 and the inert fibers and joins them together to protect the edge of the fabric from disintegration or fraying. Since the thermal cutter fuses a strip of fibers on both sides of the cut line, for example a 5mm wide strip, the fibers remaining on the roll are fused together in a similar way to produce a stable edge. After a sheet 26 is cut from the roll, the other two ends of the sheet, that is, the edges of the sheets 26 at right angles to the edges of the thermal cut, are cut to open the lumens of the fiber units 19. To minimize distortion or collapse of the ends of the fibers 10 under shear pressure, the area to be cut is first reinforced, for example, by impregnating it with polyurethane to provide a reinforcing coating around the fibers 10 or units. fiber. Cutting through the fiber units 19 is then done with a sharp cutter, for example a knife edge cutter. The cutter is preferably kept very sharp, eg by changing the blades regularly, to minimize distortion of the ends of the fibers 10. Other cutting machines or tools may also be used in the clothing and textile industries.

The end or ends of single or multiple sheets 26 may be molded into a head to provide one or more ports 36 in communication with the lumens of the fibers 10. To mold one or more sheets 26, the sheets 26 are cut from a roll as has been described above. A plastic spacer strip is fixed, for example with glue or adhesive tape, on one or both sides of the sheet 26, at the end of the sheet 26 parallel but offset from the cutting line of the blade through the fiber units 19. For molding multiple sheets 26, sheets 26 with attached spacer strips are placed on top of each other and fixed, for example with glue or adhesive tape, between adjacent spacer strips or between the spacer strip of one sheet 26 and a second sheet 26 The strips separate adjacent sheets 26, but also form a barrier between a molding material to be applied later and the head cavity containing the fiber ends 10. The ends of sheet 26 or stack of sheets 26 are placed in an elongated cavity of the head that can be made by, for example, injection molding. The separation and sealing of the head walls is maintained with a self-adhesive closed cell neoprene sealant strip attached to each of the long head walls. All openings in the head cavity formed by the spacer strips can be covered with hot melt glue. The final sealing of the head is done by pouring a layer of molding material, for example

ES 2 394 886 T3 a two-component polyurethane compound, on the spacer strips. The layer can be approximately 45mm thick and extend between the interior parts of the head walls. If there are multiple sheets, care must be taken to force or ensure the flow of the molding material, as completely and evenly as possible, between the sheets 26. Once the molding material has set, a seal is formed between the outer portions of the fibers 10 and the walls of the head, but the ends of the fibers 10 remain in communication with a cavity within the head.

Figures 6 to 9 show a module 40 in which a set of parallel sheets 26 are molded with gaps 42 between them in a head 44. Two heads 44 can be used, as shown when an exhaust air outlet is desired. A head 44 can also be used with an exhaust outlet through the opposite open ends of the fibers 10 or with the other ends of the fibers 10 closed for a blind end operation. The gap 42 may have a thickness of between 2mm and 10mm or between 3mm and 15mm. The gap 42 chosen may depend on the water to be treated or the choice of procedure to control the thickness of the biofilm. For example, a stretched sheet 26 module 40 may have a 6mm gap 42 when used with air entrainment to control the thickness of the biofilm. Tension can be provided by mounting the heads 44 to a rigid structure, which may include parts of a tank, with one or both of the heads 44 movable relative to the structure. Alternatively, the heads 44 can be attached to part of a frame separated by an adjustable distance. The sheets of cloth 26 are molded and separated at the heads 44 by various molding materials, such as one or more polyurethane, hot melt glue, adhesive tapes, after plastic or epoxy spacers. The spacing between adjacent sheets 26, or voids 42, provides space for entraining air and substrate flow through module 40. Also, a large sheet of fabric 26 can be rolled or folded to produce a module 40 instead of using individual sheets. The length of module 40 is a compromise between eTo and pressure drop, and can vary from 1 m to 5 m or between 1 m and 3 m.

With reference to Figure 8, to make the module 40 a sheet 26 of fibers 10 is placed on strips 50 (one at each end) of a localized adhesive to pass through the ends of the fibers 10. Other strips 50 of adhesive and spacer tapes 52 are placed on sheet 26, followed by additional strips 50 of adhesive tape and an additional sheet of fabric 26. These steps are repeated as appropriate for the number of sheets 26 desired. The resulting assembly is then sealed in the head housings 35 of a pair of opposing heads 44, so that the lumens 14 of the fibers 10 are in communication with the ports 36 in the heads 44 through the cavities 37. The ends of the fibers 10 are cut prior to molding open, for example as described above. Optionally additional casting glue or resin 41 may be poured into the head housing 35 to further seal the fibers 10 to the head housing 35. Alternatively, the sheets 26 can be glued separately to space the strips at their edges and insert into a head cavity and place additional casting glue or resin 41 around this assembly to glue it to the head housing 35. As another alternative, the first mounting procedure described above can be used.

Figure 9 shows an image of a module 40 assembled as generally described above. The heads 44 are about 2 meters apart. Additional spacers 33 are used midway between the heads to better preserve the spacing of the sheets 26. A stainless steel roll 45 is attached to the edges of the fabric sheet 26 in the right half of the module to address the folding that is occurring. you can see in the left half of the module. Module 40 has an AS oxygen / AS biofilm ratio of approximately 5.

Another embodiment of a module 40 can be seen in Figures 10a to 10c. The module 40 has a single sheet 26 with hollow fiber units 19 and inert fibers 22. The hollow fiber units 19 extend between the heads 44 at either end of the sheet 26. The width 62 of the heads 44 is such that the stacking of multiple adjacent modules 40 with heads 44 of adjacent adjacent modules 40 provides the desired spacing between adjacent sheets 26. The head casings 35 of this module 40 are transparent, allowing the cavity 37 to be seen. To mold the sheet 26, the head casing 35, which is a folded plastic strip, is forced open and a sheet is inserted. 26. The head housing 35 is closed with a spring on the sheet 26. The tubes that function as ports 36 are inserted into the ends of the head housings. The casting resin 31 is placed along the joint between the foil 26 and the head housing 35, between the ports 36 and the head housing 35 and all other openings to seal the cavity 37.

Referring back to Figure 4, another module, which may be referred to as a cable or cable sheet module, can be made from open sheets 26 of cables 20 cut along woven edges to open the fiber ends. 10 and molded with 0 to 10mm spacing between them in one or a pair of opposing heads. Depending on the molding procedure used, which may include molding procedures described above, the fibers 10 can be opened before or after they are inserted into the casting resin. 1 to 100 or 8-20 sheets can be molded in a pair of heads to produce a module. The modules made in this way using the fibers of Figure 1 had AS oxygen / AS biofilm ratios of between 1: 2.5 (0.4) and 1/11 (0.1) with a biofilm thickness of 250 microns.

1.5 Cassettes / Reactors

In general, a plurality of modules can be grouped to form a cassette and one or more modules or one or more

ES 2 394 886 T3 cassettes can be introduced into a tank as part of a reactor. With reference to Figures 11 and 12, the modules 40 of a cassette 110 are mounted in a tank 112 of a pilot reactor to treat 1 cubic meter per day of industrial wastewater having a COD of more than 1,000 mg / l, typically 7,000 mg / l. The feed is treated through a batch or continuous process to reduce its CO concentration to 300 mg / l as required to discharge into the municipal sewer into which it is discharged. Tank 112 has a filling volume of 1.8 m³. Fifteen modules 40 are provided in tank 112, each module 114 containing six sheets 26 of 3.6 m² surface area of ​​a woven fabric of PMP fiber units 19, woven as cables 20, The fibers 10 are 1.8 m long and extend between an input head 116 and an output head 122 of modules 40 The total number of PMP cables per sheet is 1,968 and the fibers per sheet are 94,464, with 48 fibers per cable and a two packages of 50 strands per inch in sheet 26. Also, the polyester yarn is woven perpendicular to the PMP fiber and the total number of yarns per module is 1,912. The air pressure drop across the fiber lumen is in the range of 34 kPa to 69 kPa. The total area of ​​the biofilm is 17 m² and the oxygen transfer area is about 5.1 times the area of ​​the biofilm.

The modules in the illustrated embodiment are mounted in such a way that the tension of the blades 26 extending between the heads 116, 122 can be adjusted. The cassette provides a rigid structure 150 which may include elements of the tank 112 or elements of a cassette subframe adjacent to the modules 40 and one or both of the heads 116, 122 are movable with respect to the rigid structure 150.

In the illustrated embodiment, the rigid frame 150 comprises a pair of side plates 152 that extend along the distal side surfaces of the outer modules 40 of the stack of modules 40. As best seen in Figures 13 and 14, The modules 40 are attached to the side plate 152 by means of a bracket 154 that extends transversely between the side plates 152 at either end of the modules 40. Brackets 154 are provided with notches 156 shaped to receive T-shaped tongues 158 extending from surfaces of heads 116, 122 opposite blades 26. Module 40 can be attached to brackets 154 by sliding the tongues 158 of the heads 116, 122 into the notches 156 of the supports 154. Brackets 154 can be secured to side plate 152 by, for example, a screw 160 passing through an opening 162 that engages plate 152 and braided hole 164 in an edge surface of bracket 154.

Aperture 162 may be slot-shaped so that bracket 154 with attached head 116, 122 can be moved horizontally to increase or decrease the tension of blades 26. An eccentrically mounted cam member 166 may be provided between the head. of screw 160 and plate 152 with an outer diameter surface coupled to a contiguous surface 168 attached to plate 152. The rotation of the cam member 166 can cause the opposing supports 154 to move apart or move closer together, so that the tension of the blades 26 on the modules 40 is adjusted.

The tension adjustment mechanism can be provided at only one end or both ends of the modules 40 and can be modified to provide individual tension adjustment for each module 40 or for subgroups of modules 40. Other methods of testing may also be used. mounting to allow modules 40 to be withdrawn or tensioned.

In another embodiment of the invention, the elements or modules are stacked in a vertical configuration. The flow of the entrainment of air from outside the modules or of water in the tank can be from top to bottom or from bottom to top. This minimizes the capital required for air entrainment and air operations costs.

2.0 Operation / Applications

Fiber units 19 having one or more fibers 10 can be used as membranes to support biofilm in a reactor. In general, oxygen-containing gas flows into at least one of the heads 44 of a module 40. The module 40 can be operated in a blind end mode with no outlet other than through the fibers. Alternatively, the module can be operated in a cross-flow mode, so that the gas enters through one head 44 and flows through the fibers 10, then exits the other head 44. The oxygen content and the gas flow rates can be set to produce oxygen transfer that provides aerobic conditions near the outer surface of the fibers 10, in which the oxygen level is highest. Aerobic reactions occur in this area, including the conversion of organic compounds to carbon dioxide and water, and of ammonia to nitrates. The biofilm can be maintained under anoxic conditions on its outer surface or near the substrate being treated and the conversion of nitrogen to nitrates can take place. Thus, multiple and simultaneous reactions can be performed in the biofilm, including carbon-based reduction of organics, ammonia, and total nitrogen.

An example reactor 80 is shown in Figure 15. Figure 15 provides close plug flow. Reactor 80 has tank 82, feed inlet 84 to tank 82, effluent outlet 86 from tank 82, flow path 88 between feed inlet 84 and effluent outlet 86, and a plurality of units fiber 19 in the form of modules 40 in tank 82. Each module 40 may have one or more sheets 26 extending from one or more heads 44. The plurality of modules 40 can be provided as part of one or more cassettes 110.

The sheets 26 and modules 40 are adapted to fit in the tank 82 and fill a substantial part of its

ES 2 394 886 T3 volume. The sheets 26 can be adapted to provide efficient use of the available space in the tank

82. The sheets 26 are preferably arranged in the tank 82 in a series of rows, one of these rows being shown in Figure 15. The thickness of the sheets 26 can vary from 0.25 to 2 mm and the adjacent sheets 26 are placed in the tank 82 side by side at a distance of 2 to 15 mm to allow the growth of the biological film and the flow of the waste water between the adjacent sheets 26.

Tank 82 is longer than deep and may have a generally horizontal flow path 88 with minimal mixing. This is accomplished by leaving some space near the ends (i.e., near the inlet 84 and outlet 86) of the tank 82 for vertical movement of the water and leaving minimal clearance above, below, and on the sides of the tank 82. . A deflector 90 may also be positioned upstream of the effluent outlet 86 to force the flow path 88 to pass underneath. A sludge outlet 92 is provided to remove excess sludge.

Flow path 88 is generally straight over a substantial portion of tank 82 between feed inlet 84 and effluent outlet 86. Each module 40 is held in tank 82 by its heads 44 attached to a frame (not shown for clarity) that restricts each module 40 at positions in reactor 80, such that the lamellae 26 of each module are generally parallel to flow path 88. Preferably, a plurality of lamellae 26 are spaced serially along flow path 88 so that reactor 80 will have plug flow characteristics. The waste water to be treated can be partially recycled from the effluent outlet 86 to the feed inlet 84. Such recycling can increase the gas transfer rate by increasing the wastewater velocity along flow path 88, but it is preferred that the recycle rate be small so as not to provide nearly more mixed flow characteristics in reactor 80.

The oxygen-containing gas is provided to each module 40 through its inlet conduit 216 connected to an inlet manifold 94 located above the water to be treated. With the inlet manifold 94 located above the water, a leak in any module 40 will not admit water into the manifold or any other module 40. Gas exits each module 40 through its outlet conduit 218 which is connected to a exhaust manifold 95. Although it is not strictly necessary to collect the gases that come out of each module 40, it does provide some advantages. For example, the gas in exhaust manifold 95 can be rich in volatile organic compounds that can create odor or health problems within a building containing reactor 80. Preferably, these gases are then treated or at least removed. outside the building.

Oxygen diffuses or permeates through the fibers 10. The amount of oxygen diffused or permeated in this way can be such that an aerobic biofilm is grown adjacent to the sheets 26, an anoxic biofilm grown adjacent to the aerobic biofilm and the waste water to be treated is kept in an anaerobic state. Such a biofilm provides simultaneous nitrification and denitrification. A source of agitation 98 is operated from time to time to agitate the sheets 26 to release the accumulated biofilm. A suitable source of agitation is a series of large bubble aerators that do not provide sufficient oxygen to the water to be treated to render it non-anaerobic.

Figure 16 shows a second reactor 80 having a tank 82, a feed inlet 84, an effluent outlet 86, a flow path 88, and a plurality of modules 40. Frames (not shown) hold each module 40 in a position whereby the blades 26 of each module 40 are generally parallel to the flow path 88.

The sheets 26 are adapted to fit in the tank 82 and fill a substantial amount of its volume. The sheets 26 can be adapted to provide efficient use of the available space in the tank 182. The thickness of the sheets 26 can vary from 0.25 to 2 mm and they are placed side by side at a distance of 2 to 15 mm to allow biofilm growth and wastewater flow between adjacent sheets 26.

Tank 82 is deeper than long to stimulate a straight and generally vertical flow path 88 over a substantial portion of tank 82 with minimal mixing. This is done by leaving minimal space near the ends and sides of tank 82 but a substantial amount of space near the top and bottom of tank 82. The water to be treated can be partially recycled from the effluent outlet 86 to the feed inlet 84 but it is preferred that the recycling rate is low if a recycle is used.

Oxygen-containing gas is provided to each module 40 through its inlet conduit 216 connected to a manifold 94. The manifold 94 may alternatively be located above the water to be treated so that a leak in any module 40 will not admit water in the manifold 94 or any other module 40. The outlet conduits 218 are connected to an outlet manifold 95 which may alternatively be located above the surface of the water to be treated.

Alternatively, gas flow through module 40 occurs by applying suction to outlet conduits 218. Inlet conduits 216 are placed in fluid communication with the atmosphere. By this method, the gas diffusion rate through the membrane is slightly reduced but the blower outlet can be connected to another apparatus for processing the exhaust gases.

Oxygen diffuses or permeates through membranes 120, preferably such a biofilm

ES 2 394 886 T3 is grown adjacent to the sheets 26, an anoxic biofilm is grown adjacent to the aerobic biofilm, and the wastewater to be treated is kept in an anaerobic state. A stirring source 98 is operated from time to time to stir the sheets 26 to release the accumulated biofilm. A suitable source of agitation is a series of mechanical mixers.

Referring to Figure 17, a reactor 100 has a tank 112 with one or more membrane-supported biofilm module cassettes 110 installed therein. The cassettes can have one or more modules 40, as described above. The module 40 can also be a cable module, a planar element module, or other types of modules using a membrane as a support for a biofilm. Each module 40 has a gas inlet head 116 fed with air or other oxygen-containing gas, through a blower 118. The gas passes from the inlet head 116 into the interior (or lights 14) of one or more fibers 10. The walls of the fibers 10 serve as gas transfer membranes 120. A portion of the gas passes through the membranes 120 while another portion, and possibly some gases captured from the tank 112, flow to an outlet head 122 of the modules 40 and to an exhaust outlet 124. The gases that exit through the exhaust outlet 124 they can be further treated or discharged to the atmosphere.

Feedwater enters reactor 100 through a feed valve 126 and feed pump 128. The feed is charged to a feed charge level 130 above the modules 40. Once a Feed batch opens a drain valve 131 to drain the tank 112 of treated water. The treated water can flow into a municipal sewer, into the environment, be discharged directly into a receiving stream or to another MSBBR (Membrane Supported Biofilm Batch Reactor) stage or to another type of reactor for further processing.

A biofilm 132 grows on the outside of the membranes 120. To control the thickness of the biofilm 132, one or more aerators 134 are provided below the modules 140 and connected to an air entrainment blower 136 through a aeration valve 138. Air entrainment blower 136 can be operated to provide bubbles when tank 112 is full of water. The bubbles travel up the module 140 and physically remove some of the biofilm 132 from the membranes 120. The aerators 134 are also attached to a gas supply 140 through a gas supply valve 142. The gas supply 140 can contain a pressurized gas or gas generator or pump or other device for supplying a gas when tank 112 is empty. Reactor 100 also has a liquid pump 144 operable to charge tank 112 with a liquid other than feed water. The liquid pump 144 may be connected to a reservoir containing the liquid or to a source of clean water that passes through a modifier, such as a chemical injection device or heater. Tank 112 is generally open to atmosphere and contains liquid at generally ambient pressure, but has a lid 146 that can be closed from time to time to provide a closed space.

The main treatment process in reactor 100 involves batch application of feed to biofilm 132. Tank 112 is filled with feed to feed level 130 using feed pump 128. Feed pump 128 is connected to supply. feed through an equalization tank 148 to allow batch operation from a non-batch feed. The feed remains in the tank 112 for a period of time, for example between 12 and 96 hours, while it is treated with the biofilm 32. During the treatment, the lid 46 can remain open, but the water in the tank 112 is , generally, anoxic or anaerobic. However, oxygen, normally as a component of air, is supplied to biofilm 132 through membrane 120 by blower 118 creating an aerobic region on biofilm 132. From time to time during the treatment period it may be opening a recirculation valve 149 and operating feed pump 128 to mix the feed water in tank 112.

After the biofilm 132 has digested the feed to the desired degree, the drain valve 131 opens to drain the tank 112. Drainage can occur in two stages. In the first stage, the suspension of the solids present at the bottom of the tank is drained to remove the settled solids that are then transferred to a sludge handling system. In the second stage, the clear decanted liquid is then drained to the second stage treatment or disinfection system or discharged into a sewer or discharged into a receiving stream.

The supply of oxygen carrier gas can be continued through the filling operations to continue the digestion of the adsorbed material on the biofilm and to ensure that the treatment begins immediately as soon as a portion of the biofilm is immersed in the wastewater. . Similarly, aeration can continue through the drainage operation to continue the treatment as long as a portion of the biofilm is submerged and to digest the organics in the biofilm for a short period of time even when it has not been submerged, in order to maximize the treatment time of each batch.

Referring now to Figure 18, a reactor 400 is shown having similar characteristics to reactor 100 but without the gas supply 140, the gas supply valve 142, or the liquid pump 144.

In a batch procedure, the wastewater concentration decreases towards the end of each period of

ES 2 394 886 T3 processing. The demand for oxygen supplied to the biofilm also decreases and thus the supply of gas to the modules can be reduced. Modules using fibers at least partially in the form of cables allow a very high surface area for oxygen transfer and biofilm growth. Cable modules are particularly useful in treating wastewater having a low COD, for example 1,000 mg / l or less, 500 mg / l or less, or 300 mg / l or less, because they provide large surface areas. The pressure loss through the fine fiber lumens is not limiting to the amount of air supply required to deliver oxygen to a bio-film treating low-COD wastewater. Although they can be useful to treat other wastewater as well, cable modules can be used when the initial feed has low levels of COD or as a second or third stage after other treatment procedures or apparatus that reduce the COD concentration of feedwater. stronger. With municipal wastewater or other feeds, for example feeds having a COD of 1,000 mg / l or more, a two-stage apparatus can be used. In a first stage, the modules of the membrane-supported biological film in the form of a cloth sheet are used as in Figure 9. The outlet of a reactor containing these modules is fed to a reactor containing cable modules with sheets. as in Figure 4 providing a second stage treatment. The inventors have observed that the rapid reduction of the COD of a wastewater with high levels of COD limits the denitrification produced in a membrane-supported biofilm reactor. With a two-stage process, the first stage can be optimized for removal. by COD. The feed to the second stage has a reduced COD and the second stage can be optimized to support nitrifying microorganisms, for example nitrobacter species and nitrosomes, on microorganisms that degrade carbon, to provide better oxidation of the ammonia in the second stage .

In general, when considering DOC, soluble DOC is used since soluble DOC is more easily digested by biofilm 30 and is easily measured. However, particularly for modules 40 with loose cables 20 over some or all of their area, some particles of insoluble COD become trapped in the biofilm. Over time, these particles break down into soluble COD and are digested. Accordingly, the total or total biodegradable COD may also be a relevant parameter in some embodiments.

For feeds that have CODs of 1,000 mg / l or more, a module 40 may have an ASoxygen / ASbiofilm of 1 or more, for example between 1 and 10. For example, modules 40 having sheets 26 woven throughout the length of the fibers 10, in a dense fabric with a high number of fibers for very high loads, are useful. For feeds that have CODs of 1,000 mg / l or more, a module 40 may have an AS_oxí_geno/ACE_pelí_{cell biol}or_gica 0.2 and 2.5. For example, modules 40 having sheets woven through the entire length of the fibers but with less dense weave or sheets 26 with a central open cable area 20 are useful. For feeds that have CODs of 300 mg / l or less, a module 40 may have an ASoxygen / ASbiofilm of 1 or less, for example between 1 and 10. For example, modules 40 with sheets 26 have a central open cable area 20 or modules 40 with loose cables 20 are useful.

Figure 19a shows a laboratory scale reactor having a module 40 manufactured by molding 100 cables 20 each of 96 fibers 10 as shown in Figure 1, into an opposite pair of heads 44. Module 40 was used for treating a feed water in a batch process. In the procedure, module 40 was located in a tank 112 loaded to 4 L of synthetic wastewater. The tank was drained and loaded with fresh feed every 1 to 7 days. Air was applied to the module at 10 ml / min. A biological film 30 of stable thickness grew in module 40 over a period of more than 6 months. Biofilm 30 was essentially endogenous, its growth rate is generally equal to its rate of deterioration, except that a small part of biofilm 30 was released and discharged with part of the tank drains. A section of a cable 20 is shown in Figure 19b. Individual fibers 10 are covered in biofilm 30. In some places, biofilm 30 around a small group of fibers 10 may be fused for a portion of the length of fibers 10. The thickness of biofilm 30 shown is approximately 250 microns.

Referring now to Figure 20 another reactor is shown as suitable, for example for a septic tank, septic tank retrofit or a marine treatment plant. The concrete reactor shown is a septic tank retrofit using a standard 410 septic tank with a 412 inlet and 414 outlet on opposite sides. Tank 410 has two stages that include a primary chamber 416 and a secondary chamber 418. A dividing wall 420 has a submerged orifice 422 that allows flow between chambers 416, 418. One or more modules 424 are placed in secondary chamber 418. Air is supplied to the lower heads of modules 424 through inlet tubes. 426. Exhaust air is vented from the upper heads of modules 424 through exhaust pipes 428. Periodically air entrainment is applied to a sprinkler 430 located below or near the bottom of the modules 424 through the air entrainment tube 432. Each of the modules 424 has 1 to 100 or 8 to 20 sheets as in Figure 4 molded into a pair of heads to produce a 424 module. For example, a single household septic tank might have an 8 to 10 sheet 424 module fed with 1/4 hp air blower and create a pressure drop of approximately 1 to 7 psi or approximately 3 psi. With a typical household feed, an endogenous biofilm generally grows on the surfaces of the individual fiber 19 and cable 20. Biological treatment in the biofilm results in a reduction of suspended solids and chemical oxygen demand of the effluent, allowing the septic tank field to be reduced or eliminated.

ES 2 394 886 T3

A number of bioreactors can be installed in series to provide flow patterns that approach plug flow. This results in higher reaction rates and better oxygen utilization.

Different levels of oxygen can be used in different stages of the bioreactor by introducing oxygen to meet different levels of oxygen demand and achieve high bioreactor loads. Different levels of oxygen can also be used at different times in a single reactor or reactor stage. To increase the oxygen level, the pressure of the gas fed to the fiber lumens or the oxygen content of the feed gas can be increased. In a similar way, to lower the oxygen level, the supplied gas pressure or oxygen content can be lowered. Higher oxygen levels can also be used in upstream stages of multi-stage reactors or in highly loaded reactors. Oxygen levels can also be increased periodically or from time to time to correspond to periods of time when the load on a reactor is temporarily increased, for example to respond to seasonal or daily variations in the strength or amount of wastewater. .

3.0 Biofilm Control

In a membrane supported biofilm reactor it may be advantageous to control the thickness of the biofilm on the membranes. For example, in reactor 100 (Figure 17), although tank 112 is periodically drained, most of the biofilm 132 remains on membranes 120, particularly when the feed has a high level of DOC, for example 300 mg / l. Excess thickness of biofilm 132 of, for example, a thickness of 2mm or more, provides a minimal, if any, increase in the rate of digestion, over a thinner layer, for example a thickness of 1 mm or less. However, keeping the biofilm 132 thin allows the sheets 26 of the modules 40 to be brought closer together, providing more surface area per module volume. This increase in surface area, generally more than deviations from any minor increase in digestion that may or may not be achieved with a thicker biofilm 132.

Accordingly, means are provided to prevent biofilm 32 from becoming unnecessarily thick. The following procedures can be provided individually or in various ways. The frequency and treatment vary with the growth rate of the biofilm 132. For example, a biofilm 132 can grow about 10 microns per day and the module 40 can be manufactured to tolerate a biofilm between 0.2mm and 0. , 8 mm. Biofilm control procedures may be required every 5 to 1 'days. Alternatively, the period between biofilm monitoring procedures may be linked to the amount of DOC that the biofilm has digested since the last monitoring procedure, which, in turn, is related to time and increased biofilm thickness since the last control procedure. For example, control procedures can be performed when the biofilm has digested approximately 20 to 200 grams of CODs per square meter of biofilm since the last control procedure. When control or thickness reduction procedures are performed frequently a stable biofilm layer is maintained for extended periods of time, even when each control period does not have a drastic effect on the biofilm thickness. Control procedures can be applied to the entire biofilm at once or to a portion of the biofilm at a time.

3.1 Mechanical Biofilm Control Procedures

Some procedures for controlling the thickness of the biofilm 132 on the membranes 120 involve mechanically removing part of the biofilm 132. In one of these procedures, still referring to Figure 17, one or more aerators 134 are provided under the modules 114 and connected to a blower 136 through a vent valve 138. With fluid or liquid tank 1124, blower 136 drives it to create bubbles from aerator 134 below modules 40. This can be done, for example, once every day to once a week. Air can also be used to periodically mix the contents of the bioreactor.

Other mechanical procedures include spraying module 40 with water, while tank 112 empties, physically removing biofilm 132 such as with a comb, wire, or brush. The removed biofilm 132 falls to the bottom of tank 112 and can be washed through a drain 131 to further process the residual sludge. These mechanical procedures may be performed less frequently than other procedures and, when performed, may be performed after another procedure has removed the biofilm 132.

The mechanical methods of controlling biofilm are enhanced by providing sheet 26 with a rough or textured surface, with the height of the surface undulations being in the range of the desired biofilm thickness. The desired biofilm thickness can be 200 to 1,000 microns.

3.2 Chemical procedures

In another embodiment, ozone gas, introduced into the lumen of the fiber, is used to oxidize a part of the biofilm to make it digestible. The lights are then supplied with oxygen to allow the biofilm to digest the

ES 2 394 886 T3 oxidized so that the total amounts of solids generated are reduced and to control the thickness of the biofilm. Oxygen can be provided as a separate stage or as part of regular wastewater digestion steps. The reactor can be treated in this way one module or section at a time.

In another procedure, a control substance is applied to the side of the biofilm tank 132. For example, once the tank 112 has been drained, clean water heated to, for example, 35-55 ° C, can be pumped into tank 112 via liquid pump 144. The heated water is held in tank 112 for a period of time (contact period), for example 3-5 hours, sufficient to kill a fraction of the biofilm 132 and dissolve some of the organics that form the film matrix. biological. The biofilm is also starved to some extent as the feed has been removed. Oxygen can continue to be applied to the lights or it can be stopped. Air entrainment can also be provided during this period to enhance biofilm removal, although it may be more economical to carry out this operation without air entrainment, particularly if blower 136 and aerator 134 can be removed from reactor 100 completely. Biofilm 132 is also starved to some extent. After the contact period, the water is drained through a drain valve 131. In an industrial treatment system, the discharge water will have some DOC but the length of the contact period can be chosen in such a way that the discharge is still adequate for discharge into a municipal sewer as most of the dead organisms will remain. on biofilm 32. During a later part of the contact period, the living inner part of biofilm 32 will biodegrade dead organisms. The effect of heated water, or unheated water, can be enhanced with the addition of chemicals such as acids, for example with a pH between 1 and 6 or between 3 and 3, bases, for example with a pH between 8 and 13 or between 9 and 11, or enzymes. The chemicals and their concentration and contact time are chosen to partially dissolve or weaken some organics that are a structural component of the biofilm but to kill only a fraction of the microorganisms leaving the majority in an active biofilm for rapid restart of the biofilm. reactor.

In another procedure, a gaseous control substance is applied to the side of the biofilm tank 132. The gas is applied from the gas supply 140 while the reservoir 112 is drained at the end of a discontinuous cycle. The lid 146 is closed so that the gas remains in the tank 112. The gas can be of various types, for example an acid such as chlorine. As an alternative ozone can be used. The main purpose of ozone is to break down the cell walls of microorganisms in biofilm 132 to make it more biodegradable. The amount of ozone applied would not be sufficient to oxidize more than about 5% of the biofilm directly and to kill only a fraction of the microorganisms present in the biofilm. However, the refractory organic material is converted to organic material which is later reduced by biological oxidation when the tank is reloaded. Ozone is generated in a gaseous phase (air or oxygen) and is easily dispersed in an empty tank 112. The ozone is held in tank 112 for a period of time that allows the biological film 132 to absorb it. The redox conditions in tank 112 can be controlled as it drains to stimulate sludge reduction. Alternate aerobic and anaerobic conditions can be established in biofilm 132 by introducing and suspending feed introduction into inlet head 113 while tank 112 is charged with ozone to enhance the effects of ozone. Dead and partially oxidized organisms remain in biofilm 132 and are later digested in situ so that excess biomass does not have to be removed from tank 112 for further treatment. Denitrification can also be improved by increasing the carbon / nitrogen (C / N) ratio. Ozone can also be used in this procedure with membranes 120 that are sensitive to ozone, since the membranes 120 are protected by biofilm 32.

3.3 Biological procedures

In another procedure, worms or other animals or higher life forms are used in an isolated section of the reactor to digest excess biofilm to reduce the generation of biosolids. Worms etc. they grow in a separate bioreactor. When desired, worms etc. are applied. to the biofilm by filling the tank with a liquid suspension or brine containing the worms etc.

Another biofilm control procedure is endogenous respiration. By this procedure, the feed load applied to the biofilm 132 is maintained such that the rates of deterioration of the biofilm 132 are equal to its growth rate; In practice, the rate of growth may exceed the rate of deterioration by a small amount in a batch process because some of the biofilm 132 may break away from tank 12 when drained. However, endogenous respiration practically only occurs at low loading rates and is therefore more suitable for feedings with low concentrations of POPs, for example 1,000 mg / L of COD or less, or 300 mg / L of COD or less.

Another procedure is periodic food deprivation. In this process, the feed is held in tank 112 for an extended period of time so that the COD concentration drops to levels that are at the end of a typical batch process. Biofilm 132 is not nourished and rapidly deteriorates until the start of the next discontinuous cycle. The biofilm can also be starved by removing the feed and filling the tank with clean water, for example tap or drinking water) or

ES 2 394 886 T3 charging the reactor to less than 0.1 kg CODs per kg MLSS per day.

In another method, the gas supply to inlet header 116 of module 40 is cyclically turned on and off for a period of time. The variable supply of oxygen surprises the biofilm 132 and increases the deterioration. The aerobic and anaerobic areas in the biofilm expand and contract as they consume or be consumed by the other. Alternatively, gases such as ozone or chlorine can be added to the internal head 116 to increase the shock.

With the chemical or biological control of the biofilm a closer separation between the sheets 26 can be used, for example 3-4 mm, since the hydraulic flow of the modules 40 is not required as with air entrainment, agitation or other physical procedures for biofilm removal. Chemical and biological procedures are also useful when the sheets 26 or fibers 10 or units 19 are not arranged so that an entrainment air flow will not reach all parts of the biological film. Biofilm chemical or biological control procedures may also be useful with open sheets 26 or modules with loose or unsupported fibers, fiber units 19, or cables 20 that would be damaged by air entrainment, agitation, or physical procedures. Alternatively, one or more chemical procedures, one or more mechanical procedures, or one or more biological procedures can be combined.

Examples:

Example 1: Reduction of Chemical Oxygen Demand (COD) in a Membrane Supported Bioreactor

A laboratory scale bioreactor was manufactured using a module generally as shown in Figures 6-9 except that only a single sheet of the fibers was used. The length of the sheet was 0.57m and the height 0.45m, providing a total biofilm area of ​​approximately 0.5m² assuming you have both sides of the sheet available for biofilm growth. The ratio of the surface area for the gas transfer and the surface area of ​​the fixed biofilm was between about 5 and 6. The inlet air flow was 25 ml / min at a pressure of 34.5 kPa. The volume of the reactor was 30 l. Synthetic waste water with a COD level of 1,000 mg / l was introduced in a batch mode periodically. The synthetic wastewater consisted of 1.0 g / l of soluble peptone and 0.03 g / l of sodium hydrogen phosphate dissolved in tap water. A series of batch reactions was performed to determine the rate of the reaction and the efficiency of oxygen transfer. Figure 21 presents the results of three discontinuous periods: a three-day period from day 2 to day 5, a three-day period from day 6 to day 9, and a one-day period from day 9 to day 10, It can be seen that a COD reduction of 80-90% was obtained in each of the three-day discontinuous periods. A COD reduction of approximately 40% was achieved in the discontinuous period of one day, which suggests that the speed of the COD reduction is higher, while the wastewater concentration is higher and that the COD reduction stabilizes at as the concentration of DOC in the batch decreases. The oxygen transfer efficiency during this series of tests ranged from 50 to 70%, as measured by the outlet air concentration.

Example 2: Laboratory test with synthetic wastewater

A laboratory scale bioreactor was designed using a single sheet module as described for Example 1. Synthetic wastewater with a COD level of 1,000 mg / L, as described in Example 1, was introduced and treated with the biofilm on the module. The COD removal and oxygen transfer rates and the biofilm thickness were calculated or measured and recorded. For approximately the first 21 days, the reactor (having a loading volume of 30 L) was drained and reloaded with feed after varying discontinuous periods to keep the DOC in the tank generally between 500 and 1,000 mg / L. On day 8 and day 16, in addition to emptying the tank and reloading it with new feed, the module was flushed with a water spray to remove the biofilm. From approximately day 21 to day 30, the biofilm was starved (i.e. the tank was filled with tap water, i.e. clean or potable, while oxygen continued to be supplied to the module) and carryover treatments were carried out. air. At approximately 30 days the tank was emptied and reloaded with feed. Thereafter the tank was emptied and reloaded with residual water daily but no steps were taken to control the biofilm, to let the biofilm thicken and observe the effect and rate of such growth. The test results are presented in Figure 21. It can be seen that the COD removal rate varied between about 19 and 38 grams per square meter per day without being proportionate to the thickness of the biofilm. Oxygen transfer ranged from about 10 to 15% grams per square meter per day, also over a relatively wide range of biofilm thickness, i.e. from about 0.5mm to over 2.3mm, thickness in the which the measuring device reached its maximum thickness.

Example 3: Pilot study with industrial wastewater

A small pilot study was conducted using four modules generally as shown in Figures 6 to 9. Each module has 6 sheets of fibers and a total planar surface area, or biofilm area, of approximately 3.6 m² and a ratio between the surface area for gas transfer and the surface area of ​​the bonded biofilm of between about 5 and 6. The modules were installed in a 300 liter tank. The reactor was initially operated with peptone (approximately 2,000 mg / l) and then added

ES 2 394 886 T3 peptone to the wastewater in a decreasing ratio to accelerate the initial growth of the biofilm on the sheets, but the biofilm is acclimated to the wastewater. After acclimating the biological film, discontinuous operations were carried out, filling the tank with industrial waste water. The wastewater was extracted from multiple sources in proportions chosen to create a feed COD of approximately 3,000 mg / L. "Pure" oxygen was supplied to the modules at a feed pressure of approximately 5 psi. As shown in Figure 23, the COD concentration dropped to less than 1,000 mg / L in approximately 2-3 days. It was also observed that the rates of COD removal decreased with the concentration of COD in the wastewater and with time during each batch.

The COD removal rates were calculated at different time periods during batches corresponding to different COD concentrations in the tank. Batches having initial CODs of 5,000 mg / L and 7,000 mg / L were also tested for the effect of higher initial COD concentrations on the rate of COD removal. The results are presented in Figure 24. As indicated in Figure 24, the removal rate was, in general, higher at higher loads except that, in the analyzed reactor, very high loads did not always produce very high removal rates, suggesting that one or more of air pressure in feed, surface area for air transfer to biofilm surface area, or total modulus area were less than optimal for very high loads.

The same reactor was used for a series of tests performed in continuous operation. In the trials, the input HRT and COD values ​​were varied. The feed gas was "pure" oxygen at a feed pressure of 5 psi. For each assay, the mean entry CODs, exit CODs, and clearance rate, organized by assay HRT, are presented in Figure 25, COD clearance rates generally decreased as HRT increased or as HRT increased. input COD decreased

The efficacy of the biofilm control procedures was also verified in the reactor during the above-mentioned batch tests. Gentle aeration of about 1 scfm / module was applied for 15 seconds every hour, primarily for mixing and a more aggressive air entrainment of about 4 scfm / module was applied for 2-3 minutes every 2-3 days, primarily to remove film biological. The biofilm thickness was successfully maintained in a range of about 0.2mm to less than 0.8mm regardless of the average COD in the reactor, which ranged from about 300mg / l to about 5,500mg / L.

Example 4: Pilot study with municipal wastewater

Another pilot study was conducted using two modules as described in Example 3, each having a surface area of ​​approximately 3.6m², installed in a 85 liter tank. Air was supplied to the modules at a supply pressure of 34 kPa. Peptone was initially added to the sewage to accelerate the initial growth of the biofilm on the sheets as described for example 3. Batch operations were carried out, filling the tank with municipal wastewater, it was passed through a 3 mm sieve, with initial COD averaging approximately 100 to 200 mg / l but, occasionally, up to 700 mg / l. At the end of the batches, the COD concentration had generally decreased to less than 30 mg / l and the COD removal rate had also generally decreased to less than 1 g / m2.²/ d. The levels of COD and CODt with respect to time within a sample period in a batch are presented in Figure 26.

A study was also carried out with a continuous procedure, carrying out different tests in a total period of approximately 60 days. In the trials, HRT ranged from 24 hours to 3 hours and input CODs from 100 mg / L to 200 mg / L. Average removal rates tended to be lower with lower loading rates.

In the continuous process study, the nitrification and denitrification kinetics were also measured. The results of 4 tests are presented in the following Table.

Table 1: Nitrification and denitrification in continuous operation

<td>HRT (h)</td><td>Input COD (mg / l)</td><td>NH3-N inlet (mg / l)</td><td>Output COD (mg / l)</td><td>NH3-N outlet (mg / l)</td><td>NO3-N outlet (mg / l)</td>

<td> 11,5</td><td> 165</td><td> 18,2</td><td> 29</td><td> 3,5</td><td> 3,4</td>

<td> 7,8</td><td> 117</td><td> 19,6</td><td> 25</td><td> 5,4</td><td> 4,4</td>

<td> 4,4</td><td> 105</td><td> 17,7</td><td> 35,9</td><td> 5,6</td><td> 4,3</td>

<td> 3,1</td><td> 84</td><td> 18,7</td><td> 37,6</td><td> 11,6</td><td> 1,3</td>

Biofilm control was also analyzed in the municipal wastewater study. A mean biofilm thickness of 0.2mm was observed with air entrainment, but there appeared to be a thicker biofilm between some individual sheets, indicating that these areas were not receiving full entrainment.

ES 2 394 886 T3 from the air.

Example 5: Laboratory scale study with a cable module with wastewater

A module similar to that shown in Figure 5 was analyzed, having 100 PMP fiber cables, each cable having 96 thick-walled PMP fibers. The total surface area of ​​the fibers in the module was 0.54 m². In the module each cable was individually molded into an upper and lower header. The module was fed with a supply of air at a rate of 10 ml / min in the lower head and exited through the upper head. The module was suspended, with the upper head clamped in a clamp on the surface of the water and the lower head down, in a container loaded to a volume of 4 L. The module was managed in batch mode using a 1,000 mg / l COD synthetic wastewater and also wastewater from a septic tank. At the beginning of each batch processing period, the container was loaded with waste water. Aeration was supplied to the module to support a growing biofilm on the fibers for processing periods ranging from about 1 to 7 days, while no residual water was added or removed from the tank. Shorter discontinuous periods were generally used with wastewater having lower DOC concentrations. At the end of this processing period, the tank was drained. New wastewater was added to start the next processing period. At various times the module was removed to measure the thickness of the biological film on it in a non-destructive way and the COD in the waste water was measured.

The thickness measurements from the synthetic wastewater tests are recorded in Figure 27, which shows the thickness of the biofilm on the fibers over the 180-day period of operation. Initially there was no biofilm but after about 20 to 40 days a biofilm had developed with a thickness generally varying between about 100 and 300 pm. For most of the tests performed no additional procedures were used to control the thickness of the biofilm and, in any event, the thickness of the biofilm remained generally stable and acceptable. Small portions of the biofilm were observed to shed from the module during at least some of the tank drain operations and, on the other hand, endogenous biofilm growth provided control of the biofilm. However, for a period of approximately 15 days, the module was operated in a food deprivation mode. In this mode the tank was charged with tap water and the introduction of air was continued. Biofilm thickness was reduced from about 250 pm to about 100 pm during the deprivation period, indicating that the period was effective in reducing the thickness of the biofilm.

Figures 28 and 29 show the COD removal rate in tests using synthetic wastewater. Figure 28 shows the removal rate as a function of time and Figure 29 shows the removal rate as a function of the COD concentration. Referring first to Figure 28, each vertical line within the figure indicates the start of a new batch processing period. Accordingly, at the times indicated by the vertical lines, new wastewater with a COD of 1,000 mg / l has to be added to the tank. As the batch progresses, the wastewater is treated and the COD concentration is reduced accordingly. As shown in Figure 28, the rate of COD removal tended to decrease with time in each batch processing period, suggesting that the rate of removal is related to the concentration of COD in the wastewater. Also, the removal rate in the batch between day 154 and day 159 was approaching zero, indicating that additional processing time would be of negligible value. In Figure 29, the COD removal rate is plotted directly against the mean COD concentration in the wastewater. As indicated in Figure 29, the relationship between the COD removal rate and the COD concentration in the wastewater is nearly linear, the removal rate being generally proportional to the COD concentration.

For the tests using wastewater from a septic tank, the wastewater was obtained from a second chamber of a septic tank. For one test, the characteristics of the wastewater were as follows:

Total Chemical Oxygen Demand (CODt): 377 mg / l

Soluble COD (CODs): 199 mg / l

Ammonium nitrogen (AN): 55.1 mg / l

Total Suspended Solids (STS): 70 mg / l

The module was operated in batch mode with batch processing periods of approximately 24 hours to simulate actual reaction conditions in a septic tank. Air was supplied during these periods at the rate given above to provide oxygen to the biofilm. After a processing period of 22 hours and 35 minutes, a sample of the treated wastewater was analyzed and the results were as follows:

CODt: 140 mg / l

CODs: 73 mg / l

AN: 24.7 mg / l

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STS: 1 mg / l

A significant improvement in effluent quality was achieved. Specifically, a huge reduction in STS was achieved. By visual observation, a large portion of the removed STS was in the form of colloidal matter.

Figure 30 records the results of another test using septic tank wastewater. The reactor was operated for a two day batch period with a concentration of CODt, CODs and STS and ammonium nitrogen measured at the beginning, middle and end of the batch period. For comparison purposes another sample of the wastewater taken from the same septic tank on the same day was placed in a 500 ml graduated cylinder and monitored as a control. After two days of operation, the reduction of the total COD (CODt) in the reactor approached 75 mg / L with a removal of the excess of 70%. The STS decreased from 34 mg / l to almost negligible after two days of treatment. Ammonia was also reduced during this period. During the same period, the control had less than a 40% reduction in COD and an adequate increase in STS. The batch process and reactor effectively treated septic tank wastewater removing COD but also suspending solids, in part due to the quiescent nature of the process.

Example 6 - Chemical control of the biological film

A biofilm control study was conducted using the single sheet reactor described in Example 1 with a very thick biofilm. At the beginning of the test, the tank was drained and 30 l of sodium hydroxide solution in deionized water at a pH of 9.43 and a temperature of 40 ° C were added to the reactor. After the first 4 hours of soaking, air entrainment was started at 2 scfm and continued for more than 18 hours while the sodium hydroxide solution remained in the tank. Air continued to be supplied to the lights. The thickness of the biofilm decreased slightly (from 4.6mm to 4.3mm) during the first four hour period. After 18 hours of soaking and air entrainment, the thickness of the biofilm was reduced by another 3.2mm.

In another biofilm control study 6 single sheet modules were used, as shown in Figures 10a and 10b. Each sheet was 27 cm long by 20 cm wide and had an available surface area of ​​approximately 0.11 square meters. The sheets were woven with the hollow fibers along the length and open at both ends. The ratio of the air transfer area to the biofilm area was approximately 6 to 1. The modules were introduced into a 20 L reactor (working volume) operated in batch mode at room temperature with discontinuous periods of approximately 3 days. The reactor was fed with synthetic sewage at concentrations of 2,000 to 8,000 mg / l of COD. Air was introduced into the module lumens at approximately 2 psi with a flow rate of approximately 20 ml / min into an inlet head of each sheet. At intervals of 3 to 7 days between batches, the modules were soaked for 4 hours in a NaOH solution in hot water with a pH of 10 to 50 ° C. Air continued to be supplied to the lights. After 4 hours, the reactor was recharged with feed. No air entrainment was provided during the soak periods or during the discontinuous periods. Figure 31 shows the thickness of the biofilm over time, which was maintained between 0.2 and 0.8 mm and averaged approximately 550 microns over a period of 140 days. The results calculated from the batches during this period indicate that during the interval between cleanings the biofilm removed from 66 to 120 grams of DOC per square meter.

Many modifications and variations of the present invention are possible within the teachings of the invention and the invention may be practiced in ways other than those described above. The scope of the invention is defined in the following claims.