Anaerobic digester

Abstract

The present disclosure relates to an anaerobic digester assembly comprising a horizontally arranged elongated reactor vessel having an elongated bottom member and a resiliently flexible top member covering an operable upper open end of the bottom member, where the resiliently flexible top member is sealed and fixed relative to the bottom member, and further wherein the bottom member defines an organic waste inlet at a first end thereof and a digest outlet at a second end thereof.

Description

Field of the Invention

[0001] The invention relates to a digester, in particular to a single-compartment anaerobic digestion reaction chamber. Background of the Invention

[0003] Households, agriculture and food processing often generate solid and / or liquid waste streams having dissolved or suspended organic solids. Such wastes pose serious environmental disposal problems.

[0004] As is known to all, anaerobic digestion basically has four stages, namely:

[0005] hydrolysis - in which particles are dissolved and substances such as carbohydrates are converted to sugars, fats to fatty acids, and proteins to amino acids;

[0006] Acidogenesis - where simple monomers are converted into volatile fatty acids;

[0007] acetogenesis - where volatile fatty acids are converted to acetic acid, carbon dioxide and hydrogen; and methanogenesis - where products of the foregoing processes, such as acetic acid, are converted to methane, carbon dioxide and water.

[0008] Anaerobic digesters include batch digesters and continuous digesters. Continuous processing is generally preferred because the waste is processed continuously and there is a steady supply of methane. The classic design of an industrial digester is a variation of the single-stage digester, the continuous stirred tank reactor ("CSTR"). In a CSTR digester, all contents are thoroughly mixed. Therefore, the effluent will contain a certain amount of freshly added, undigested waste material and will include some active microorganisms.

[0009] CSTRs are typically used for wastes with moderate solids content, ranging from 2 to 10% dry matter. Two alternative designs that overcome these problems are the "plug flow" digester and the microbial retention digester. In a plug flow digester, the waste passes through the digester in a sequential manner from inlet to outlet.

[0010] The name "plug flow" is often used for designs that are non-agitated and tubular. The solid material tends to move sequentially through the digester, while the liquid portion mixes more quickly. Retention digesters are designed to retain the microorganisms in the digester.

[0011] Some anaerobic digesters are considered two-stage digesters because the hydrolysis and acidification processes are separated from the acetogenesis and methanogenesis processes. This separation generally produces methane gas with lower impurity levels.

[0012] There is no exact classification of current digesters, however certain names are used in the industry including FRP (fiberglass reinforced unsaturated polyester resin) digesters, plastic soft (PS) digesters and plastic hard (PH) digesters. PS digesters are also called bag digesters in some countries because they look like large soft bags. The materials used include soft polyvinyl chloride (PVC), red mud, polymethyl methacrylate, low-density PE, PE and polypropylene (PP). PH digesters are usually hard digesters. In contrast to soft digesters, PH digesters are made of hard PVC, ABS, PE, PP, high-density polyethylene (HDPE) and linear low-density PE.

[0013] In most digesters, temperature is controlled. The methanogenic microorganisms (methanogens) determine the optimal temperature at which the digester operates efficiently. Two common temperature ranges for digesters are the mesophilic temperature range (20°C to 45°C) or the thermophilic temperature range (50°C to 65°C). If the digester operating temperature is sub-optimal or exceeds the optimal temperature range required by the methanogenic microorganisms, methane production is reduced.

[0014] Most, if not all, conventional digesters today are compartmentalized, i.e., they have a digestion section that is divided into compartments in an attempt to separate the biochemical processes (hydrolysis, acid production, acetogenesis, and methanogenesis) in one way or another. This sometimes improves efficiency, but significantly increases digester production costs and the complexity of the machinery required to manufacture the digester.

[0015] Due to its structure, polyester composite never loses its water-repellent properties, reducing replacement or expensive disposal. It offers stronger protection against oils and chemicals than, for example, acrylic fabrics.

[0016] The overall durability of polyester, especially its abrasion resistance, is also unmatched. The monomer vinyl chloride is an organic chloride that combines to form the polymer, polyvinyl chloride (PVC). Although it is flexible and capable of expansion, it cannot withstand UV degradation and heat for long periods of time and may experience cracking due to weathering.

[0017] To compensate for the reduced ability of conventional polyvinyl chloride (PVC) bags to resist the long-term effects of UV radiation, which is the ultimate degradation observed in previous designs after long-term exposure, the present invention incorporates a two-layer approach where the inner bag is PVC and the outer reinforcement bag is composed of a tarp-type polyester coated with a vinyl material.

[0018] Complete prefabricated digesters or materials for their construction are imported mainly from China. Imports seriously increase digester construction costs and delays.

[0019] The present invention therefore focuses on providing an anaerobic digester that takes these current barriers into account and improves upon others to make the production of digesters more economical for the African and more specifically South African environment.

[0020] Furthermore, for most conventional digesters, if scaling occurs, cleaning of the digester is very difficult to perform.

[0021] Purpose of the Invention

[0022] It is an object of the present invention to provide a single compartment anaerobic digestion (AD) reactor and method for treating aqueous organic waste in which at least some of the above-mentioned disadvantages are reduced or eliminated. SUMMARY OF THE INVENTION

[0024] According to a first aspect of the present invention, there is provided an anaerobic digester (AD) assembly, comprising:

[0025] a horizontally arranged elongated reactor vessel having a bottom member and a resiliently flexible top member, wherein the resiliently flexible top member is sealed relative to the bottom member such that the top member covers an operatively upper open end of the bottom member, wherein the bottom member and the top member are arranged to be removably secured to one another,

[0026] Wherein the bottom member defines an organic waste inlet at a first end and a digestate outlet at a second end.

[0027] The digester assembly may include at least one baffle member located within the bottom member and extending at least partially across the bottom member.

[0028] The at least one baffle member may be arranged transversely, in particular perpendicularly, to a longitudinal axis of the base member.

[0029] The at least one baffle member may be disposed on a bottom portion of the bottom member.

[0030] The baffle member may be disposed proximate to the inlet.

[0031] The elongated reactor vessel may have a horizontal longitudinal axis.

[0032] The resiliently flexible top member may be a planar, substantially flat pliable / flexible member.

[0033] The anaerobic digester assembly may include a sealing arrangement for providing and enhancing an airtight seal between the resiliently flexible top member and the bottom member.

[0034] The sealing arrangement may include a first sealing member and a second sealing member, and the resiliently flexible top member may be operably sandwiched between the first sealing member and the second sealing member.

[0035] The anaerobic digester assembly may include securing means for securing the resiliently flexible top member and the bottom member to each other once the resiliently flexible top member has been sandwiched between the first and second sealing members.

[0036] A drain opening may be defined by the bottom member.

[0037] The drain outlet may be arranged close to the waste outlet.

[0038] The bottom member may be inclined relative to the horizontal plane, preferably at an angle of 2 degrees to the horizontal plane. In particular, the bottom of the bottom member may be inclined relative to the horizontal plane from the inlet side to the outlet side at an angle of at least 2 degrees to the horizontal plane.

[0039] The bottom member may have a seat for accommodating the sealing means.

[0040] The base may project laterally outward from the periphery or near the periphery or sides of the bottom member proximate an upper edge of the bottom member.

[0041] The base may be in the form of a flange, in particular an outwardly curved flange.

[0042] The assembly may have an organic waste holding / receiving container in communication with the waste inlet for feeding organic waste into the bottom member.

[0043] The organic waste holding container may be flush with or integrally connected to an end wall of the bottom member defining the inlet.

[0044] All organic waste holding containers may have lids.

[0045] The assembly may include a digestate holding vessel in communication with the outlet.

[0046] The digestate holding vessel may be flush with or integrally connected to an end wall defining the outlet.

[0047] The digestate holding container may have a lid.

[0048] The assembly may also include an attachment arrangement including at least one bracket for allowing a greenhouse cover support structure to be attached and secured thereto, wherein the greenhouse cover support is used to capture heat generated from the digester and enable the temperature in the digester to be increased for efficient digestion.

[0049] The at least one bracket may be disposed at each corner of the bottom member.

[0050] The at least one bracket may be fixed / fastened at each corner of the base member to enable attachment of a removable greenhouse cover.

[0051] The bottom member may be made of a material including a thermoplastic polymer, including but not limited to polypropylene (PP), polyvinyl chloride (PVC) or high-density polyethylene (HDPE), etc., preferably HDPE.

[0052] The resiliently flexible top member may be made from a composite material including polyester and vinyl, and the composite material may have been treated for acid and UV resistance.

[0053] The composite material may be a good thermal conductor arranged to absorb solar energy and transfer it into the base member.

[0054] The first sealing member may be a first gasket, and the second sealing member may be a second gasket.

[0055] The first sealing member may be arranged on the bottom member, in particular accommodated in a base of the bottom member, and the second sealing member may be provided on the elastically flexible top member to ensure airtightness between the top member and the bottom member.

[0056] The first and second washers may be in the form of rubber washers.

[0057] The assembly may further comprise a frame arranged to abut said second sealing member, said second sealing member being provided on said top member.The frame may be a metal frame, in particular a stainless steel frame.

[0058] The fixing means may be arranged to fix the frame, the first sealing member, the top member and the second sealing member to the bottom member.

[0059] The fixing device may include a threaded bolt arranged to pass through aligned openings arranged in sequence of the metal frame, the second sealing member, the top member, the first sealing member and the bottom member, and the fixing device may also include a first nut for fixing the bolt to the frame and a second nut for fixing the bolt to the bottom member. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:

[0061] Figure 1 : shows an exploded view of an anaerobic digester assembly according to the present invention;

[0062] Figure 2 : A perspective view showing a bottom member of a reactor vessel of an anaerobic digester assembly according to the present invention;

[0063] Figure 3 : shows a perspective view of an assembled anaerobic digester according to the present invention;

[0064] Figure 4 : shows a perspective view of an assembled anaerobic digester according to the present invention when in use;

[0065] Figure 5 : A cross-sectional detailed view showing the arrangement of the sealing device, the top member and the bottom member of the anaerobic digester assembly according to the present invention;

[0066] Figure 6 : A bottom view showing the inlet side of the bottom member; and

[0067] Figure 7 : Shows a bottom view of the outlet side of the bottom member.

[0068] DETAILED DESCRIPTION OF THE INVENTION

[0069] refer to Figure 1 An anaerobic digester assembly 10 for anaerobically digesting aqueous organic waste (not shown) is provided. The anaerobic digester comprises a horizontally arranged elongated reactor vessel 12 having a longitudinal axis AA. The anaerobic digester assembly 10 comprises a bottom member 14 and a top member 16.

[0070] The bottom member 14 includes a pair of first and second side walls 14.2 and 14.4, respectively, a pair of first and second end walls 14.6 and 14.8, respectively, and a hemispherical downwardly curved bottom 14.10. The bottom 14.10 can be inclined from the first end wall 14.6 side to the second end wall 14.8 side relative to the horizontal plane. The inclination angle relative to the horizontal plane can be at least about 2 degrees.

[0071] The bottom member 14 defines an upper opening 14.12 which is arranged to be covered, in use, by the top member 16. The bottom member 14 also defines a single hollow space / compartment 14.14 which is arranged to accommodate aqueous organic waste.

[0072] The first end wall 14.6 of the bottom member 14 defines an organic waste inlet 18 and a digestate outlet 20. Figure 2 The bottom member 14 also includes a base 30 that projects laterally outwardly adjacent to the upper edge of each of the side walls 14.2, 14.4 and the end walls 14.6, 14.8. As shown in most of the drawings, the base 30 is rectangular and extends continuously around the upper periphery of the bottom member 14. In this embodiment, as shown in FIG. Figure 5 As shown, the base 30 is in the form of a downwardly bent flange defining a channel 33 and a series of flange openings 30.2 on an outer lip of the flange.

[0073] The bottom member 14 is typically made of a thermoplastic polymer selected from polypropylene, polyvinyl chloride, or high-density polyethylene (HDPE). In this embodiment, the bottom member is made of HDPE. The top member 16 is in the form of a planar member made of a pliable / flexible material. Figure 1 As shown, the top member 16 is rectangular in shape. As described above, the top member 16 is arranged to cover the upper opening 14.12 of the bottom member 14 so as to isolate the hollow portion 14.14 from the external environment, thereby preventing contaminants or foreign matter from being introduced into the reactor vessel 12. A series of spaced top member openings 16.2 are arranged near the outer edge of the rectangular top member 16.

[0074] The top member 16 is made of a polyester and vinyl composite material 16 that has been treated for acid and UV resistance. The anaerobic digester assembly 10 also includes a sealing device 22 for sealing the top member 16 to the bottom member 14, in particular, sealing the top member 16 in the channel 33 of the base 30 of the bottom member 14.

[0075] The sealing device 22 includes a first sealing member 22.2 in the form of a rectangular frame so as to conform to the shape of the base 30 and the channel 33. The sealing device 22 also includes a second sealing member 22.4 of the same shape as the first sealing member 22.2. Each of the first and second sealing members 22.2 and 22.4 defines a series of spaced apart sealing member openings 22.6. It should be understood that the shapes of the first and second sealing devices 22.2 and 22.4, respectively, can be different according to the shape and configuration of the reactor vessel 12. The first sealing member 22.2 and the second sealing member 22.4 are typically rubber gaskets.

[0076] As shown in the attached figure Figure 1 and Figures 3 to 5 As shown, the anaerobic digester assembly 10 also includes a fastening / fixing device 24. The fixing device 24 ( Figure 1 A) For fixing the top member 16 to the bottom member 14, as will be described in more detail below. The fixing means comprises a threaded bolt 24.2, an upper nut 24.4 and a lower nut 24.6.

[0077] like Figure 2As shown, the anaerobic digester assembly 10 also includes a baffle 26 extending inwardly across the base 14.10 of the bottom member 14 and arranged transversely to the longitudinal axis AA of the bottom member 14. The baffle 26 is disposed adjacent to the first end wall 14.6 of the bottom member 14. The baffle 24 is arranged to act as a weir to enhance mixing of organic waste received in the inlet end 18 in the space defined between the baffle 26 and the first end wall 14.6, and further to prevent new organic waste from migrating into the space on the other side of the baffle 26 on the outlet 20 side before the organic waste is completely digested.

[0078] The anaerobic digester assembly 10 also includes a drain 28 defined by the bottom 14.10 of the bottom member 14. The drain 28 is disposed proximate the digestate outlet 20. The drain 28 may be used to discharge digestate or organic waste during periodic maintenance and cleaning of the reactor vessel 12.

[0079] The anaerobic digester assembly 10 also includes an organic waste container 32 that fits flush with the first end wall 14.6 and has an opening that is aligned with and communicates with the inlet 18 on the first end wall 14.6. The organic waste container 32 is equipped with a cover 34. The organic waste receiving container 32 is generally arranged to feed organic waste into the bottom member 14 under gravity, and the organic waste is arranged to stably move within the bottom member 14 and above the baffle 26 under gravity due to the inclined angle of the bottom 14.10 relative to the horizontal plane from the first end wall 14.6 side to the second end wall 14.8 side.

[0080] The anaerobic digester assembly 10 also includes a digestate holding container 36 that fits flush with the second end wall 14.8 and has an opening that is aligned with and communicates with the outlet 20 on the second end wall 14.8. The digestate holding container 36 is equipped with a cover 38. The anaerobic digester assembly 10 also includes an arrangement of attachment means in the form of brackets 40, each bracket being mounted to a respective corner of the bottom member 14. Each bracket 40 is arranged to be attached and secured to a removable greenhouse cover (not shown). The greenhouse cover (not shown) is arranged to capture heat generated from the reactor vessel 12 of the anaerobic digester assembly 10, which heat can be circulated back into the reactor vessel 12, typically via the top member 16, to facilitate further digestion of organic waste.

[0081] The anaerobic digester assembly 10 further comprises an outer frame 15, which is also in the shape of the first and second sealing members 22.2 and 22.4, respectively. The outer frame 15 has an outwardly projecting frame lip 15.1, which is arranged to abut against the lip of the base 30 once secured thereto. The outer frame 15 defines a series of spaced apart outer frame openings 15.2 on the frame lip 15.1.

[0082] In use, such as Figure 5 As more clearly shown in FIG. 1 , the first sealing member 22.2 is received in the channel 33 of the base 30, and the first sealing member opening 22.6 is arranged to align with the flange opening 30.2 of the base 30. The top member 16 is then placed on top of the first sealing member 22.2. When the top member is placed on the first sealing member 22.2, the top member opening 16.2 is arranged to align with the first sealing member opening 22.6, and a major portion of the top member 16 covers the upper opening 14.12 of the bottom member 14, as shown in FIG. Figure 1 As shown. The second sealing member 22.4 is then placed on top of the top member 16 so that the second sealing member opening 22.6 is also aligned with the top member opening 16.2. The outer frame 15 is then placed on top of the second sealing member 22.4, and the outer frame opening 15.2 is arranged to align with the second sealing opening 22.6, and the second sealing opening 22.6 is aligned with the flange opening 30.2. Then, a series of special bolts 24.2 are respectively passed through the channels defined by the sequentially arranged aligned openings 15.2, 22.6, 16.2, 22.6, 30.2 of the outer frame 15, the second sealing member 22.4, the top member 16, the first sealing member 22.2 and the bottom member 14. The upper nut 24.4 is threadedly connected to the upper threaded portion of the bolt 24.2, and the lower nut 24.6 is threadedly connected to the lower threaded portion of the bolt 24.2 to fix the outer frame 15 to the bottom member 14, which causes the top member 16 to be securely sealed between the first and second sealing members 22.2 and 22.4, respectively. During digestion, the top member 16 fixed to the bottom member 14 expands due to the pressure of the expanding gas formed during the digestion of the organic waste, as shown in FIG. Figure 4 shown.

[0083] The anaerobic digester assembly 10 is simple in design, durable, made from low cost materials, compact and portable. The drain port 28 provided in the bottom member 14 also allows for maintenance and cleaning of the reactor vessel 12 when fouling is experienced.

Claims

1. An anaerobic digester assembly comprising: a horizontally arranged elongated reactor vessel having an elongated bottom member and a resiliently flexible top member covering an operatively upper open end of the bottom member, wherein the resiliently flexible top member is sealed and secured relative to the bottom member, and The bottom member defines an organic waste inlet at a first end thereof and a digestate outlet at a second end thereof.

2. The anaerobic digester assembly of claim 1, comprising at least one baffle member located within the bottom member, the baffle member extending at least partially across the bottom member and arranged transverse to the longitudinal axis of the bottom member.

3. The anaerobic digester assembly of claim 2, wherein: The baffle is disposed on the bottom of the bottom member proximate to the inlet of the bottom member.

4. An anaerobic digester assembly according to any one of the preceding claims, wherein: The bottom member defines a drain opening disposed proximate the outlet.

5. An anaerobic digester assembly according to any one of the preceding claims, wherein: The bottom member is arranged inclined relative to a horizontal plane.

6. An anaerobic digester assembly according to claim 5, when claim 5 is dependent on claim 3, wherein: The bottom of the bottom member is arranged at an inclination of at least about 2 degrees relative to a horizontal plane.

7. An anaerobic digester assembly according to any one of the preceding claims, wherein: The bottom member includes a base that protrudes laterally outward from the bottom member.

8. The anaerobic digester assembly of claim 7, wherein: The base defines a channel and has an outer lip defining a plurality of laterally spaced openings.

9. An anaerobic digester assembly according to any one of the preceding claims, comprising sealing means for providing an airtight construction between the top member and the bottom member.

10. An anaerobic digester assembly according to claim 9, when claim 9 is dependent on claim 8, wherein: The sealing device includes an upper first sealing member and a lower second sealing member operable to be received by the channel, wherein a peripheral portion of the top member is sandwiched between the upper first sealing member and the lower second sealing member.

11. The anaerobic digester assembly of claim 10, comprising an outer frame of the first sealing member adjacent the upper portion.

12. The anaerobic digester assembly of claim 11, wherein: The outer frame, the upper first sealing member, and the lower second sealing member each define spaced-apart openings that align with the opening on the outer lip of the base.

13. An anaerobic digester assembly according to any one of claims 8 to 12, comprising securing means for securing the top member to the bottom member.

14. An anaerobic digester assembly according to claim 13, when claim 13 is dependent on claim 12, wherein: The fixing device includes a plurality of bolts, each of which is inserted into a channel defined by each of the aligned openings of the outer frame, the first upper sealing member, the top member, the second lower sealing member and the openings on the outer lip of the base of the bottom member, and wherein the fixing device also includes a plurality of operable upper nuts and operable lower nuts for fixing the plurality of bolts to the outer frame, the first upper sealing member, the top member, the second lower sealing member and the bottom member.

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