Anaerobic reactor with auger in the effluent line

An upflow anaerobic reactor includes an effluent outlet configured to direct effluent out of the reactor and a fluid-filled gas trap configured to prevent loss of biogas from the vessel. An auger assembly is operably coupled to the effluent outlet to prevent clogging of the effluent outlet by solid matter that tends to collect in the effluent outlet. The auger assembly includes at least one helical screw conveyor that rotates so as to remove solid material that collects in the effluent outlet. auger assembly can be operated on a continuous or semi-continuous basis so as to allow for continuous operation of the reactor. The auger assembly can be operated on a continuous or semi-continuous basis so as to allow for continuous operation of the reactor.

CROSS-REFERENCE TO RELATED APPLICATIONS

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to upflow anaerobic reactors that are designed for biodegradation of biodegradable matter and production of biogas therefrom. In particular, the present invention relates to apparatuses and methods for preventing clogging of the effluent line of an upflow anaerobic reactor.

2. The Relevant Technology

A bioreactor is a device that uses bacteria to promote biodegradation or “digestion” of organic waste materials into simple organics and gaseous biogas products. Biogas is typically a mixture of methane, carbon dioxide, hydrogen sulfide, and other volatile organic compounds. If produced in sufficient quantities, the methane gas can be used as a fuel.

A bioreactor can also be used to treat and detoxify organic waste matter and wastewater. Wastewater treatment has always been important, particularly in agricultural production and food processing, which produces wastewater containing high concentrations of organic matter.

Anaerobic digestion is one traditional method of treating wastewater containing high concentrations of organic matter. Anaerobic digestion removes large quantities of organic matter from the waste material and produces biogas as a useful byproduct. Anaerobic digestion is particularly suitable for wastewater containing high concentrations of organics, such as wastewater generated through agricultural production and processing.

Many attempts have been made to decompose organic waste using closed vessels. One type of closed vessel reactor that has shown high decomposition rates is the upflow anaerobic sludge blanket reactor. In this reactor, waste material is introduced into the bottom of the reactor and forced up through the vessel where it passes through a blanket of bacteria, which decompose the organic material and produces biogas that can be collected and used as a fuel.

To achieve high decomposition rates in an upflow bioreactor, the bacterial culture should be well established. Once the bacterial culture is well established, the upflow bioreactor can be operated continuously and a high rate of digestion can be maintained for an extended period of time (e.g., months or even years).

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a bioreactor and operation of a bioreactor for biodegradation of biodegradable matter and collection of a biogas that is a product of the biodegradation. In particular, the present invention relates the operation of upflow anaerobic reactor wherein an influent is introduced via the lower portion of the vessel and an effluent is withdrawn via the upper portion of the vessel. As the influent travels through the reactor from bottom to top, biodegradable materials are broken down by an anaerobic bacterial culture producing large quantities of valuable biogas and treated effluent. Treated effluent, which includes liquid and solid materials (i.e., digested and non-digestible solids that can be sold as valuable compost), is withdrawn form the upper portion of the vessel via an effluent outlet. The effluent outlet includes an auger assembly that prevents clogging of the outlet while allowing liquids and digested solids to pass therethrough.

In one embodiment, the upflow anaerobic reactor includes a vessel having an upper portion and a lower portion that define a volume of the vessel, an effluent outlet coupled to the upper portion of the vessel, an auger assembly operably coupled to the effluent outlet, an inlet coupled to the vessel for introducing biodegradable matter into the lower portion of the vessel, and a gas port coupled to the upper portion of the vessel for collecting biogas produced in the vessel. The effluent outlet includes a column of liquid that forms a fluid-filled gas trap inside the outlet to prevent escape of biogas via the outlet. The fluid-filled gas trap also forms a fluid-air interface where the effluent contacts atmospheric air as it flows out of the reactor.

The solid materials in the effluent (i.e., digested and non-digested solids) are, however, susceptible to collecting at the fluid-air interface. As such, the auger assembly is operably coupled to the effluent outlet and positioned at or through the fluid-air interface in order to prevent clogging of the effluent outlet by solids in the effluent stream. That is, the auger assembly is positioned within the effluent outlet at the fluid-air interface so as to disrupt a solid material in the effluent collecting at the fluid-air interface. The auger assembly can include at least one helical screw conveyor that rotates so as to remove solid material from the fluid-air interface. Solid materials that collect at the fluid-air interface can be removed from the effluent outlet by rotating the auger to either draw solid material up and out of the effluent outlet and/or push solid material in the effluent outlet back into the vessel. The auger assembly can be operated on a continuous or semi-continuous basis so as to allow for continuous operation of the reactor.

In one embodiment, the auger assembly includes at least one screw conveyor A screw conveyor is typically a helical screw having a longitudinal axis that can, when rotated either clockwise or counter-clockwise by a drive assembly, draw solid material up and out of the effluent outlet and/or push solid material in the effluent outlet back into the vessel.

In one embodiment, the screw conveyor includes an outer housing and a sleeve housing that at least partially enclose the screw conveyor. The outer housing and the sleeve housing are inserted into the effluent outlet such that the screw conveyor, the outer housing, and the sleeve housing can readily be coupled to the effluent outlet or uncoupled so that the screw conveyor can be removed for repair or replacement.

In another embodiment, auger assembly includes a screw pump operatively coupled to the effluent outlet. A screw pump is similar to an auger or a screw conveyor with the exception that the housing contains two or more intermeshing helical screws that rotate axially about one another so as to pump fluid and material through the housing and out the effluent outlet. Preferably, at least one of the helical screws of the screw pump pierces or passes through the fluid-air interface such that rotation of the two or more intermeshing helical screws disrupts solids that tend to collect at the fluid-air interface. A screw pump may be advantageous because the mechanical vibration produced by a screw pump is typically low, which may minimize churning and foaming.

In one embodiment, the screw conveyor in an auger assembly or screw pump can be rotated continuously or semi-continuously in order to save energy and prevent unnecessary wear. The interval between rotations of the screw conveyor may depend on the amount of solid matter in the effluent.

In one embodiment, the upflow anaerobic reactor further includes a septum positioned in the upper portion of the vessel. The septum includes a central aperture to create fluid connection between the upper portion and lower portion of the vessel. The septum is positioned in the upper portion of the vessel so as to maintain the bacterial culture below the septum.

In one embodiment, the upflow anaerobic reactor further includes an internal auger device (i.e., a second auger separate and distinct from the auger assembly that is included in the effluent outlet (see, e.g.,FIG. 1)) operatively coupled to the vessel and positioned within the aperture of the septum so as to prevent clogging of the aperture. The internal auger device includes a screw conveyor having sloping fins to move solids from just above the aperture in the septum downward to some distance beyond the bottom of the aperture toward a lower zone in the bioreactor. Alternatively, the internal auger can pull solids up through the hole and above the septum where the solids can be removed from the vessel.

In one embodiment, the upflow anaerobic reactor further includes a pressure sensor for monitoring gas pressure in the vessel. The pressure sensor is preferably coupled to the auger assembly or the screw pump device in the effluent outlet. In one embodiment, a rise in pressure indicates a clog of solid material in the effluent outlet, which actuates the drive assembly and initiates rotation of the screw conveyor so as to clear the clog in the effluent outlet.

In one embodiment, the present invention includes a method for continuous operation of an upflow anaerobic reactor for biodegradation of biodegradable matter and collecting biogas produced therefrom. The method includes steps of (1) providing an upflow anaerobic reactor that includes an effluent outlet having a fluid-filled gas trap and an auger assembly coupled to the effluent outlet, (2) providing a bacterial culture comprising a sludge layer in the lower portion of the vessel for biodegradation of biodegradable material and production of biogas therefrom, (3) operating the upflow anaerobic reactor so as to create an upflow in the vessel by introducing an influent containing biodegradable material into the lower portion of the vessel via the inlet, and withdrawing an effluent from the upper portion of the vessel via the effluent outlet, and (4) rotating the auger assembly so as to disrupt solid material contained in the effluent outlet at the fluid-air interface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a bioreactor and operation of a bioreactor for biodegradation of biodegradable matter and collection of a biogas that is a product of the biodegradation. In particular, the present invention relates the operation of upflow anaerobic reactor wherein an influent is introduced via the lower portion of the vessel and an effluent is withdrawn via the upper portion of the vessel. As the influent travels through the reactor from bottom to top, biodegradable materials are broken down by an anaerobic bacterial culture producing large quantities of valuable biogas. Treated effluent, which includes liquid and solid materials (i.e., digested and non-digestible solids), is withdrawn form the upper portion of the vessel via an effluent outlet. To prevent clogging of the effluent line, the effluent outlet includes an auger assembly configured to disrupt solids that collect at the fluid-air interface while allowing liquids and digested solids to pass therethrough.

FIG. 1illustrates an upflow anaerobic reactor10according to one embodiment of the present invention. Reactor10includes a vessel12in which biodegradable matter (e.g., sewage or wastewater) can be introduced and held for treatment. A septum14is positioned in vessel12to form a lower chamber16(i.e., a lower portion) and an upper chamber18(i.e., an upper portion). An aperture20in septum14provides fluid communication between lower chamber16and upper chamber18. According to one embodiment of the present invention, reactor10includes an internal auger32to facilitate the retention of solids suspended in the effluent passing through aperture20and to prevent the aperture20from becoming plugged. A drive assembly30generates and/or transfers a force for turning internal auger32.

Reactor10is configured for upflow operation. An inlet22is provided in lower chamber16for introducing biodegradable matter. A pump (not shown) is typically coupled to inlet22to provide pressure for introducing the organic material. An effluent outlet24is placed in upper chamber18to allow effluent to exit reactor10. The placement of inlet22in lower chamber16and the placement of outlet24in upper chamber18creates an upflow in reactor10during operation. The upflow in reactor10can be operated continuously or semi-continuously by maintaining a continuous or semi-continuous flow of influent into lower chamber16.

The effluent outlet24is designed to direct liquid and solid effluent out of the vessel while also preventing escape of biogas from the upflow anaerobic reactor10. As such, the effluent outlet24includes a column of liquid that forms a fluid-filled gas trap42inside the outlet24and a fluid-air interface48where the effluent contacts atmospheric air as it flows out of the reactor. Because solid materials in the effluent are susceptible to collecting at the fluid-air interface48and plugging the outlet24, the outlet includes an auger assembly34athat is operably coupled to the effluent outlet24and positioned at or through the fluid-air interface48in order to prevent clogging of the effluent outlet24. Effluent outlet24and auger assembly34aare described in more detail below.

Lower chamber16includes a biomass26. Biomass26is also referred to herein as a sludge layer. Biomass26includes a microbial culture and biodegradable matter. The upflow in reactor10is sufficiently slow that a sludge blanket of bacteria can form in the biomass26of lower chamber16. The biodegradable matter (e.g., animal waste and wastewater) is slowly forced up through the sludge blanket where it is decomposed into smaller organic molecules and biogas. The microbial culture present in biomass26is selected according to the particular organic material that is to be decomposed in reactor10. In an exemplary embodiment, the microbial culture includes anaerobic bacteria.

In one embodiment, the type of microbial culture and type of organic material are selected such that the decomposition of the organic material produces biogas. Upper chamber18can be sealed such that biogas collects within upper chamber18. A gas outlet28allows the biogas to be ported out of reactor10. The biogas can advantageously be used as a fuel. For example, if desired, the biogas can be burned and the heat can be used to maintain an optimal operating temperature in reactor10.

In one embodiment, upper chamber18is sealed for the collection of biogas by configuring the effluent outlet24so that liquid and digested biodegradable matter (i.e., compost) can be withdrawn from the vessel12without allowing biogas to escape. As such, in one embodiment, the effluent outlet24includes a fluid-filled gas trap42.

The fluids within vessel12have a fluid level27that is maintained by effluent outlet24. The fluid level27is set below the top of vessel12such that a gas collection chamber is formed between the bioreactor fluids and the top of vessel12.

Septum14is positioned within vessel12below fluid level. Septum14can be rigid or semi-rigid and can be made from any material compatible with the bioreactor fluids, including but not limited to plastics, metals, and the like. Septum14can be formed from a plurality of panels, or it can be a single, unitary piece of material. Septum14can be secured to the inside of the vessel12in any manner.

In one embodiment, septum14slopes upwardly from the sidewalls of vessel12toward aperture20. Sloping septum14can facilitate the removal of materials that settle out in upper chamber18. A sloped septum can also be advantageous for ensuring that biogas in lower chamber16is directed to aperture20. However, the present invention can also be carried out using a flat septum.

An internal auger32is positioned within aperture20of septum14. Internal auger32can be any device that can be positioned within aperture20and can move solids in a desired direction between or within upper and lower chambers16and18. In an exemplary embodiment, the auger includes a shaft with one or more flanges that are configured to move a material in a direction parallel to the shaft.

In one embodiment, internal auger32creates a force that is opposite the flow of fluids in the bioreactor10. For example, internal auger32can have a flange such that when internal auger32is rotated clockwise, the auger creates a force that is opposite the flow of the bioreactor fluids. During optimal or “normal” operating conditions, internal auger32is rotated in the direction that counters the flow of the bioreactor fluids. This counter-flow force tends to settle out solids suspended in the effluent passing through aperture20. If aperture20becomes clogged, the auger can be rotated in an opposite direction to remove solids to above the septum14where the solids can be more easily removed.

Internal auger32and septum14are provided to help form and maintain biomass26. By retaining the bacteria within the lower chamber16, septum14and internal auger32retain more bacteria, which are available for breaking down the organic material being fed into reactor10. By utilizing the auger and septum, organic materials can be treated much faster and much more efficiently than organic waste being digested in other bioreactors. In addition, use of the septum and auger improves the clarity of effluent exiting the bioreactor.

Essentially any organic material can be decomposed in reactor10so long as a microbial culture is available for degrading the organic material and the organic material can be introduced into the bioreactor in a form that can be mixed with the microbes. Examples of suitable organic materials that can be digested in the bioreactors of the present invention include animal wastes produced from the farming, ranching, and agricultural industries, food processing waste, human waste, and the like.

Referring nowFIG. 2A, a typical effluent outlet24having a fluid-filled gas-trap48is depicted (auger assembly24has been removed for clarity of illustrating the gas-trap48). The effluent outlet24depicted inFIG. 2Ais coupled to the upper portion of the vessel12and is designed to trap biogas produced by biodegradation of biological matter in the reactor10and prevent its escape. This allows the collection of the biogas from the reactor10via a gas port (28inFIG. 1) that is also included in the upper portion of the reactor10.

The effluent outlet24depicted inFIG. 2Aincludes a tube or pipe44that is angled up relative to the side of the vessel12such that the effluent outlet traps a column of liquid. This column of liquid acts as a fluid-filled gas trap42that prevents the escape of gasses through the effluent outlet24. The column of liquid in the effluent outlet24depicted inFIG. 2Arises to a point where it is able to spill over into an effluent line46that is angled down and away from the reactor10such that it carries the effluent away from the reactor10. The height of the column of liquid defines a fluid level27in the vessel12. The portion of the effluent outlet where the column of liquid meets air is referred to as the fluid-air interface48.

While the effluent outlet24depicted inFIG. 2Ais useful for preventing loss of biogas produced in the vessel12, an effluent outlet like the one depicted inFIG. 2Awithout an auger assembly would be prone to clogging by solid material in the effluent that tends to collect at the fluid-air interface48.FIG. 2Billustrates a problem associated with bioreactors that include a fluid-filled gas-trap42but that do not include an auger assembly in the effluent outlet24. A typical clog is represented inFIG. 2Bby mass50that is blocking effluent outlet24. Clogging typically occurs at the fluid-air interface48because of the natural tendency of the solids in the effluent to float on the surface of the liquid. When solids on the surface of the liquid contact the side of the outlet pipe44at the fluid-air interface48they tend to adhere to the pipe44. This creates a cascade effect that leads to the accumulation of more solids at the fluid air interface48, which eventually leads to total blockage of the effluent outlet24. One will of course appreciate that failure to clear clogging in the effluent outlet can be dangerous because of the build-up of pressure caused by the biodegradation of solids in the reactor.

Because of the hazards posed by the formation of clogs in the effluent outlet24, the present invention includes various devices and methods for clearing accumulated solids from the effluent outlet24. Referring again toFIG. 1, a reactor10with an effluent outlet24that includes an auger assembly34ain the effluent outlet24is depicted. The auger assembly34ais inserted into the effluent outlet such that it is positioned at or through the fluid-air interface48in order to prevent clogging of the effluent outlet by solids in the effluent stream. The auger assembly34aincludes a screw conveyor38(i.e., an auger) and a drive assembly40. A screw conveyor38is typically a helical screw having a longitudinal axis that can, when rotated either clockwise or counter-wise, draw solid material up and out of the effluent outlet24and/or push solid material in the effluent outlet back into the vessel12.

Referring now toFIG. 3, the effluent outlet24and the auger assembly34aare shown in greater detail. InFIG. 3it can be seen more clearly that the auger assembly34aincludes a screw38and a drive assembly38. The screw conveyor38further includes a shaft56and a plurality of angled flights58. The auger assembly34aalso includes a drive assembly40that generates and/or transfers a force for turning screw conveyor38via shaft56. For example, the drive assembly40can include an electric drive motor, an explosion-proof housing to isolate any electrical discharge from the explosive gasses in the reactor, and a plurality of bearing surfaces (i.e., axial bearings, thrust bearings, and hybrid axial/thrust bearings) to facilitate rotation of the auger.

In one embodiment, the screw conveyor includes an outer housing52and a sleeve housing54that at least partially enclose the screw conveyor38. The outer housing52and the sleeve housing54are inserted into the effluent outlet24such that the screw conveyor38, the outer housing52, and the sleeve housing54can readily be coupled to the effluent outlet24or uncoupled so that the auger assembly34acan be removed for repair or replacement.

Referring now toFIG. 4, an effluent outlet24having an auger assembly34baccording to one embodiment of the present invention is depicted. The auger assembly34bdepicted inFIG. 4is similar in many respects to the auger assembly34adepicted inFIGS. 1 and 3, except auger assembly34bhas two intermeshing helical screw conveyors60and62that rotate axially about one another so as to pump fluid and material out of the effluent outlet24. An auger assembly having more than one helical screw conveyor is typically referred to as a screw pump. A screw pump may be advantageous because the mechanical vibration produced by a screw pump is typically low, which may minimize churning and foaming.

Auger assembly34bincludes a drive assembly40that drives one screw conveyor, which is referred to as the power screw conveyor60. Because the screw conveyors intermesh with one another, rotation of the power screw conveyor60drives rotation of the second screw conveyor62, which is referred to as the idler. Preferably, at least one of the helical screws of the screw pump pierces or passes through the fluid-air interface48such that rotation of the two intermeshing helical screws60and62disrupts solids that tend to collect at the fluid-air interface.

Referring now toFIG. 5, an effluent outlet24having an auger assembly34caccording to one embodiment of the present invention is depicted. Auger assembly34cdepicted inFIG. 5is similar in many respects to the auger assembly34adepicted inFIGS. 1 and 3, except auger assembly34chas three intermeshing helical screw conveyors64,66, and68that rotate axially about one another so as to pump fluid and material out of the effluent outlet24.

Auger assembly34cincludes a drive assembly40that drives one screw conveyor, which is referred to as the power screw conveyor64. Because the screw conveyors intermesh with one another, rotation of the power screw conveyor64drives rotation of the second and third screw conveyors66and68, which are referred to as the idlers. Preferably, at least one of the helical screws of the screw pump pierces or passes through the fluid-air interface48such that rotation of the three intermeshing helical screws64,66, and68disrupts solids that tend to collect at the fluid-air interface.

In one embodiment, the present invention includes a method for continuous operation of an upflow anaerobic reactor for biodegradation of biodegradable matter and collecting biogas produced therefrom. The method includes steps of (1) providing an upflow anaerobic reactor that includes an effluent outlet having a fluid-filled gas trap and an auger assembly coupled to the effluent outlet, (2) providing a bacterial culture comprising a sludge layer in the lower portion of the vessel for biodegradation of biodegradable material and production of biogas therefrom, (3) operating the upflow anaerobic reactor so as to create an upflow in the vessel by introducing an influent containing biodegradable material into the lower portion of the vessel via the inlet, and withdrawing an effluent from the upper portion of the vessel via the effluent outlet, and (4) rotating the auger assembly so as to disrupt solid material contained in the effluent from the fluid-air interface.

In one embodiment, the screw conveyor can be rotated continuously or semi-continuously in order to save energy and prevent unnecessary wear. The interval between rotations of the screw conveyor may depend on the amount of solid matter in the effluent.

In one embodiment, the upflow anaerobic reactor further includes a pressure sensor for monitoring gas pressure in the vessel. The pressure sensor is preferably coupled to the auger assembly or the screw pump device in the effluent outlet. In one embodiment, a rise in pressure indicates a clog of solid material in the effluent outlet, which actuates the drive assembly and initiates rotation of the screw conveyor so as to clear that

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. In particular, elements of the depicted embodiment may be combined with elements of other depicted embodiments without departing from the spirit or essential characteristics of the present invention. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.