WO2013116113A1

WO2013116113A1 - Process and apparatus for producing ethanol from sugar beets

Info

Publication number: WO2013116113A1
Application number: PCT/US2013/023252
Authority: WO
Inventors: Paul S. WHEATON; Wayne Simmons
Original assignee: Wheaton Paul S
Priority date: 2012-01-30
Filing date: 2013-01-25
Publication date: 2013-08-08

Abstract

A process and apparatus for producing ethanol from sugar beets which is energy and water neutral and can be carried out over a wide geographical area. The apparatus for carrying out the process preferably has a modular construction to enable it to be readily scaled-up to produce an ethanol production plant of any desired capacity.

Description

PROCESS AND APPARATUS FOR PRODUCING

ETHANOL FROM SUGAR BEETS

BACKGROUND OF THE INVENTION

[0001] Concerns about depletion of fossil fuel energy sources such as petroleum as well as about the economic and geopolitical ramifications of dependence on imported energy have generated considerable interest in renewable energy sources which can be produced domestically. Foremost among such renewable energy sources is ethanol, which can be used as a fuel per se, but is most often blended with conventional gasoline. Most ethanol produced in the United States is made from corn. The use of corn for ethanol production, however, has some disadvantages. First, production of ethanol from corn has a relatively low net energy yield. That is to say, the total energy input required to grow and process corn into ethanol amounts to a relatively large fraction of the energy yield from the ethanol produced. Second, because corn is basically a food crop, the diversion of corn to ethanol production may adversely affect the availability and cost of corn for food uses.

[0002] In other parts of the world, such as Brazil, ethanol is produced predominantly from sugarcane. The potential use of sugarcane as an ethanol feedstock in the United States is limited, however, by the fact that sugarcane can only be grown in a few areas with a warm climate, and the cost of transporting either the sugarcane feedstock or the produced ethanol to the points of ultimate use can render the overall process uneconomical.

[0003] An alternative feedstock to sugarcane is sugar beets. Sugar beets can be grown successfully in a wide variety of climates ranging from the warm areas of California's imperial valley to the much cooler climate of North Dakota, thus making it possible to locate an ethanol production facility in virtually any part of the country in close proximity to its feedstock source and avoid the prohibitive expense of transporting feedstock materials over long distances. Compared to corn, sugar beets also require less water for their cultivation and produce higher yields of feedstock material per acre thus lessening the burden on land and water resources. Moreover, in contrast to the starch content of corn which must be broken down by thermal and/or enzymatic hydrolysis treatment before it can be fermented to ethanol, the sugars extracted from sugar beets can be fermented directly to ethanol without the need of such treatment. [0004] Sugar beet strains grown for sugar production traditionally have been selected for maximum sucrose yield without regard to their content of other sugars. The use of sugar beets for ethanol production is not subject to such constraints. Instead, ethanol production can make use of so-called "energy beet" strains which produce higher total fermentable sugar yields. This further enhances the efficiency and cost-effectiveness of producing ethanol from sugar beets.

[0005] Various proposals have heretofore been made for producing ethanol from sugar beets, but despite expenditures of considerable money and effort toward this end, there remains a need for a cost-effective, environmentally acceptable and commercially viable process and apparatus for producing ethanol from sugar beets.

SUMMARY OF THE INVENTION

[0006] Accordingly, it is the object of the present invention to provide an improved process and apparatus for producing ethanol from sugar beets.

[0007] Another object of the invention is to provide a process and apparatus for producing ethanol from sugar beets which requires less energy input than prior ethanol production processes.

[0008] A further object of the invention is to provide a process and apparatus for producing ethanol from sugar beets which poses a minimal burden on the environment.

[0009] It is also an object of the invention to provide a process and apparatus for producing ethanol from sugar beets which can be implemented in a wide variety of locations where the ethanol is consumed so as to minimize transportation costs.

[0010] Yet another object of the invention is to provide a process and apparatus for producing ethanol from sugar beets which is net-energy neutral or near net-energy neutral.

[0011] An additional object of the invention is to provide a process and apparatus for producing ethanol from sugar beets which can operate after start-up using only the water content of the beets without additional supplies of water. [0012] A still further object of the invention is to provide a process and apparatus for producing ethanol from sugar beets which is readily scalable to produce modest or large amounts of ethanol to meet existing demand.

[0013] In accordance with a first aspect of the invention, these and other objects are achieved by providing a process for producing ethanol comprising subjecting sugar beets to size reduction and pressing to obtain a sugar-containing juice and a residual beet pulp; pasteurizing the sugar-containing juice; fermenting the pasteurized juice with yeast to obtain an ethanol-containing fermentate; separating the yeast from the fermentate; recovering substantially pure ethanol from the fermentate; anaerobically digesting the residual beet pulp to produce methane, and combusting the methane to obtain energy.

[0014] In accordance with a second aspect of the invention, the objects of the invention are achieved by providing an apparatus for producing ethanol from sugar beets comprising a size reducing apparatus for reducing the sugar beets to small particles; at least one press for pressing sugar-containing juice out of the ground beet particles; a pasteurizer for pasteurizing the sugar-containing juice; a heat exchanger for transferring heat from pasteurized juice discharged from the pasteurizer to incoming juice to be introduced into the pasteurizer; a fermenter for fermenting the pasteurized sugar-containing juice; a still for distilling an ethanol/water azeotrope from fermentate recovered from the fermenter; a membrane separator for separating substantially pure ethanol from the ethanol/water azeotrope from the still, and an anaerobic digester for digesting pulp from said at least one press to produce methane.

[0015] Further advantageous features, aspects and embodiments of the invention will appear from the following more detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention will be described in further detail hereinafter with reference to illustrative embodiments of an ethanol production process schematically illustrated in the accompanying drawing figures, in which:

[0017] Fig. 1 is a schematic diagram of an ethanol production installation in accordance with the present invention; [0018] Fig. 2 is a partial schematic diagram of an alternate arrangement for extracting sucrose from sugar beets;

[0019] Fig. 3 is a side elevation view of an anaerobic digester for converting waste pulp to methane; and

[0020] Fig. 4 is a plan view of the anaerobic digester of Fig. 3. DETAILED DESCRIPTION

[0021] The production of ethanol commences with the cultivation of so-called "energy beets", which have been selected for maximum production of fermentable sugars. The germ plasm for such beets is available from commercial seed vendors such as Syngenta Seeds, Inc. of Longmont, Colorado. After harvesting, the beets preferably are washed in the field utilizing a portable washing apparatus to reduce their tare weight. The portable washer preferably recycles the wash water to minimize water consumption. Tops from the beets may be left in the field as a soil enhancer. The washed and topped beets are then transported to the processing facility.

[0022] At the processing facility, the beets are comminuted or ground to fine particles for further processing. This size reduction may advantageously be achieved with a conventional hammer mill. Other types of size reducing or grinding apparatus might also be used. The resulting particle size should be sufficiently small to maximize release of sugars from the beet pulp, but not so small that it becomes difficult to separate the pulp particles from the sugar- containing juice. Preferably, the particle size will be less than about 15 mm, more preferably less than 10 mm.

[0023] After size reduction, the beet particles are pressed in a screw press to release the sugar-containing juice from the residual pulp. Preferably, the pulp is subjected to one or more additional pressing operations to recover additional sugar-containing juice, which is combined with the juice from the initial pressing stage.

[0024] Pulp from the pressing stage or stages is stored for later use as described hereinafter. It is preferred to store the pulp under anaerobic conditions to prevent deterioration prior to later use. [0025] The pressed juice is then centrifuged to remove any solids. If desired, an optional filtration may be performed prior to centrifugation to reduce the load on the centrifuge. Solids recovered from the centrifuge are a valuable by-product useful as a potting soil.

[0026] The sugar-containing juice is then pasteurized by heating it briefly to a temperature of 85°C. To minimize thermal losses, hot juice being discharged from the pasteurizer is passed through a heat exchanger in heat exchange relation with the incoming juice being supplied to the pasturizer, so that most of its heat is transferred to the incoming juice, and minimal additional energy is required to heat the incoming juice to the pasteurization temperature. The juice leaves the pasteurizer at a temperature which is suitable for the introduction of the yeast, typically approximately 32 to 35°C. As a result, it is not necessary to add heat to the juice in the fermenter, which further improves the energy efficiency of the overall process. Moreover, the introduction of the juice into the fermenter at a temperature of approximately 32° C means that the yeast can be introduced immediately into the fermenter to start fermentation instead of having to delay introduction of the yeast until the juice reaches the proper temperature. Consequently, the process of the invention can complete the fermentation in about 48 hours or less, compared to conventional commercial scale production processes which can take up to 90 hours.

[0027] The pasteurized sugar-containing juice is fermented in the fermenter with yeast to produce ethanol. Suitable yeasts for alcohol production are known to persons skilled in the art, e.g. from the genus Saccharomyces such as Saccharomyces cerevisiae.

[0028] If necessary, a nitrogen source such as urea may also be introduced into the fermenter to provide essential nitrogen for the yeast used to effect fermentation.

[0029] It is important to maintain an aerobic environment in the fermenter to assure that the desired fermentation to ethanol will proceed. For this purpose, oxygen and/or air may optionally also be introduced into the fermenter as needed to assure that an aerobic environment is maintained.

[0030] The fermentable sugar-containing juice introduced into the fermenter typically will have an initial sugar content of approximately 18 to 22 Brix. To improve reaction rates and degree of conversion, the natural sugar content of the juice may be boosted by the addition of supplemental raw sugar and/or molasses feedstock. Advantageously, periodic additions of supplemental feedstock having a sugar content of about 30 Brix may be made to maintain the fermentable sugar level at at least about 5 Brix, preferably about 15 Brix, for at least the first 24 hours, preferably approximately 30 hours, of the fermentation.

[0031] To assure rapid start-up of the fermentation, the yeast may be activated by preconditioning it for three to six hours prior to introduction into the fermenter. Fermentation is continued for a total of 36 to 72 hours, preferably less than 48 hours, or until no more ethanol is being produced.

[0032] Batch fermentations are preferred to facilitate periodic cleaning of the fermenter in order to prevent accumulation of contaminating microorganisms which would compete with the yeast for the sugar feedstock but not produce ethanol. Between batches the fermentation equipment advantageously may be sterilized using a cleaning agent such as a peroxyacetic acid/hydrogen peroxide solution.

[0033] Liquid fermentate from the completed fermentation is then centrifuged to remove yeast solids. A portion of the separated yeast can be recycled though a return line back to be used in the next fermentation. Excess yeast is useful as a fertilizer and/or soil conditioner byproduct.

[0034] Liquid supernatant from the centrifuge is then distilled to separate a 95% ethanol/5% water azeotrope from the fermentation residue or stillage. The 95% ethanol is then subjected to a membrane separation dewatering step to separate essentially pure ethanol from the residual water. Suitable separation membranes are commercially available, for example, from Whitefox Technologies of Calgary, Canada. The use of combined distillation and membrane separation stages facilitates a high degree of energy efficiency and enables ethanol to be produced at a net energy approaching as low as 8000 btu per gallon.

[0035] Stored pulp from the pressing stages is washed with a carefully controlled amount of water to recover any soluble fermentable sugars remaining in the pulp after pressing, and the wash liquid can then be combined with the pressed juices to enhance the overall yield of the process. The washed pulp is then supplied to one or more anaerobic digestion stages, where it is digested to produce a methane-containing fuel gas. Methane-containing gas produced in the anaerobic digester is collected in a suitable gas storage vessel and can then be combusted to drive an electrical generator and/or to produce steam to provide heat for the ethanol production process (e.g., for the distillation) or for other uses. This makes the overall ethanol production process substantially energy self-sufficient.

[0036] In accordance with the invention, the relatively high approximately 75% water content of sugar beets can be used as a source of process water for the ethanol production process, thus further lessening the water demand. By utilizing the natural water content of the sugar beets and recycling the water, the overall process can also become substantially water neutral.

[0037] Residues from the anaerobic digestion contain significant amounts of potassium, nitrogen and phosphorous soil nutrients and can be used as a natural fertilizer by-product and/or as a soil conditioner. The natural fertilizer and soil conditioner by-products of the process can be utilized locally for growing the next crop of sugar beets, thereby reducing or eliminating the requirement for bringing in chemical fertilizers. The overall process is thus extremely energy efficient and results in a minimal environmental burden.

[0038] Apparatus useful to carry out the process of the invention is shown schematically in the accompanying drawing figure.

[0039] Harvested sugar beets 1 are topped in the field and then passed to a washing device 2 where they are freed of soil and debris. Preferably, washing device 2 is a portable apparatus which can be taken to the field so that the beets can be washed before transport. Advantageously, washing device 2 will include a recirculation system 3 for recirculating the wash water to minimize water consumption and the water disposal burden.

[0040] The topped and washed beets are then transported to a size reduction station 4, which may be comprised of a plurality of hammer mills or other suitable comminuting apparatus for reducing the beets to small particles, preferably less than about 15 mm, more preferably less than about 10 mm, in size. The ground beets are then conveyed to a press, such as a screw press, where they are pressed to extract sugar-containing juice. Preferably, the apparatus may comprise one or more additional presses 5' so that the pulp recovered from the initial press may be subjected to additional pressing. Typically the beets will be subjected to at least two or three pressing stages in order to extract as much sugar-containing juice as possible from the beet pulp. [0041] The pressed beet pulp is then conveyed to a storage station 6 where it can be stored, preferably under anaerobic conditions, for later use. As needed for the operation of the anaerobic digester, stored pulp is transferred to a washing station 10 where it is washed with a controlled amount of water to recover any soluble fermentable sugars remaining with the pulp. Washed pulp from washing station 10 is then passed to an anaerobic digester 7, where it is digested to produce combustible methane gas. The methane is collected in a suitable vessel 8 and ultimately may be used to provide energy for the ethanol production process, e.g. by driving a methane fueled electric generator 9 or for producing steam.

[0042] Sugar-containing juice from the press or presses and the washing station is combined and conveyed to a pasteurizer 14. Prior to introduction into pasteurizer 14, the sugar-containing juice may be passed through a centrifuge 12 to remove any residual solids. If desired, an optional filter 11 may be interposed upstream of centrifuge 12 to reduce the solids load on the centrifuge. The sugar-containing juice is also passed through a heat exchanger 13 before being introduced into pasteurizer 14 in heat exchange relation with hot sugar-containing juice being discharged from the pasteurizer to reduce the heat requirement of the pasteurizer and also to cool the pasteurized juice to a temperature which will not inactivate the subsequently added yeast.

[0043] Pasteurized sugar-containing juice is then introduced together with yeast from a yeast source 15 into a fermenter 16, where it is fermented to produce an ethanol-containing liquid. If desired, the yeast source may be provided with a preconditioning tank 17 where the yeast can be pretreated so that it is fully active when introduced into fermenter 16. Fermenter 16 may also be provided with a nitrogen source, such as urea source 18, to assure sufficient essential nitrogen is available to the yeast. In addition, fermenter 16 may be provided with an oxygen or air source 19 for introducing oxygen to assure that a proper aerobic condition for the desired fermentation is maintained in the fermenter. Fermenter 16 may also be connected with a supplemental source 20 of a fermentable feedstock, such as raw sugar or molasses, to maintain optimum fermentation conditions in the fermenter.

[0044] When fermentation is complete, fermenter 16 discharges the fermented liquid fermentate into a centrifuge 21, which separates any solids, primarily yeast, from the ethanol- containing fermentate. If desired, a recirculation line 22 may be provided between centrifuge 21 and yeast source 15, so that some or all of the separated yeast may be recycled. [0045] The ethanol-containing fermentate passes from centrifuge 21 to a still 23, where an ethanol/water azeotrope 24 is distilled from the fermentate. The stillage residue from still 23 is substantially water and is conveyed away through line 25 for use as process water. The ethanol/water azeotrope is conducted to a membrane separator 26, where the ethanol and water are separated to obtain substantially pure ethanol 27. In test runs of the process of the invention it has been found possible to obtain an ethanol product which is 99.2% pure.

[0046] By combining the distillation and membrane separation equipment for energy exchange, the process and apparatus of the invention can achieve a net energy requirement of less than 9,000 btu/gallon. The process and apparatus of the invention are thus considerably more energy efficient than prior art commercial processes for production of ethanol (from corn), which typically require an energy input on the order of 12,000 btu/gallon.

[0047] Fig. 2 shows an alternate arrangement for extracting sucrose and/or other fermentable sugars from sugar beets. In this system, pulp from the size reduction step, which preferably is a hammer mill, is introduced through a feed line 29 into a first tank 30 together with juice from presses 5, 5' and thoroughly mixed. Residence time in mixing tank 30 may vary from about 5 to about 15 minutes, preferably about 8 minutes. The pulp/juice mixture then passes through a connecting line 31 to a macerator 32 and then to a heat exchanger 33 where they are heated to from 65 to 80° C, preferably from 70 to 75° C. The heated pulp mixture from heat exchanger 33 then passes through a connecting line 34 to a second mixing tank 35, where it is further mixed and digested, whereby the cell walls are denatured. The processed pulp thence passes through line 36 back to the presses 5, 5'. Excess sugar- containing juice having a Brix of 14 or more is continuously removed from mixing tank 30 through connecting line 37 and pumped to centrifuge 12 for further processing in accordance with the scheme of Fig. 1.

[0048] This system allows for economical denaturing processing of varying amounts of pulp while simultaneously achieving both a high fermentable sugar extraction rate from the pulp and a high fermentable sugar content (Brix) in the extracted juice in a relatively short period of time. Equipment size is significantly less than in conventional beet pulp processing factories consisting of a countercurrent cosette mixer, an extraction tower and a press and the investment cost is also less. [0049] Fig. 3 is a side view of a preferred anaerobic digestion apparatus 38. Anaerobic digester 38 is comprised of a tank 39 filled with a grate of fixed, plastic film membranes 40. The interior of tank 39 is maintained under anaerobic conditions, and a consortia of bacteria attach to the membranes 40 and grow as a fixed biofilm. A liquid suspension of pressed and washed beet pulp is introduced into tank 39 through inlet 41. The liquid level in tank 39 is such that the fixed, plastic film membranes are fully submersed in the liquid. A series of alternating internal baffles 42, 42' extending transversely across tank 39 form a serpentine pathway through the tank as indicated by arrows 43. The pulp flows along this serpentine pathway through the grate of film membranes 40 and then exits through a discharge outlet 44. As the pulp passes the bacteria-laden membranes, the bacteria convert both soluble and particulate organic matter to methane. A small amount of carbon dioxide may also form. The resulting biogas product can be collected and used as a fuel or as a synthesis gas.

[0050] Immobilization of the bacteria as a biofilm on the plastic-film matrix 40 prevents washout of slower growing cells and provides for retention of the bacterial biomass in the digester independent of the hydraulic retention time of the pulp suspension. And because the bacteria are not washed out with the effluent, a substantial bacterial biomass develops within the digester 38. This leads to a higher anaerobic bacteria content per unit volume compared to conventional suspended growth anaerobic digester designs. Consequently, less time is needed to degrade the pulp, enabling the digester to be operated with short hydraulic retention times in the range of two to five days and still achieve from 60 to 80% solids destruction. This compares very favorably with conventional anaerobic digesters which operate in plug flow or complete mix flow and typically require retention times ranging from 18 to 30 days to achieve 30 to 50% solids destruction. The apparatus of the invention thus enables a more rapid throughput of pulp and yet has a smaller footprint and requires less space than conventional anaerobic digester systems consisting of large rectangular or circular concrete or steel tanks.

[0051] The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.

Claims

CLAIMS What is claimed is:

1. A process for producing ethanol, said process comprising:

- subjecting sugar beets to size reduction and pressing to obtain a sugar-containing juice and a residual beet pulp;

- pasteurizing the sugar-containing juice;

- fermenting the pasteurized juice with yeast to obtain an ethanol-containing

fermentate;

- separating the yeast from the fermentate;

- recovering substantially pure ethanol from the fermentate;

- anaerobically digesting the residual beet pulp to produce methane; and

- combusting the methane to obtain energy.

2. A process according to claim 1, wherein the size reduction of the sugar beets is effected by grinding with a hammer mill.

3. A process according to claim 2, wherein the sugar beets are ground to a particle size of less than about 15 mm, preferably less than about 10 mm.

4. A process according to claim 1, wherein the size reduced sugar beets are subjected to multiple successive pressings, and juices obtained from the respective pressings are combined for subsequent processing.

5. A process according to claim 1, wherein the residual beet pulp is washed with water to recover residual sugars present in the pulp, and sugar-containing wash water from the washing is combined with the sugar-containing juice for subsequent processing.

6. A process according to claim 1, wherein the sugar-containing juice is centrifuged to separate residual solids.

7. A process according to claim 6, wherein the sugar-containing juice is filtered prior to being centrifuged.

8. A process according to claim 1, wherein the sugar-containing juice has a sugar content in the range from about 15 to about 25 Brix.

9. A process according to claim 1, further comprising adding supplemental fermentable sugar to the sugar-containing juice prior to fermentation to increase the sugar content.

10. A process according to claim 1, further comprising adding supplemental fermentable sugar to the sugar-containing juice during fermentation to maintain the sugar content at at least 15 Brix for a period of at least 24 hours.

11. A process according to claim 9 or claim 10, wherein the supplemental fermentable sugar is added in the form of raw sugar or molasses.

12. A process according to claim 10, wherein the sugar content is maintained during fermentation at at least 15 Brix for at least 30 hours.

13. A process according to claim 1, further comprising washing and topping the beets prior to subjecting them to size reduction and pressing.

14. A process according to claim 13, wherein the washing and topping is effected in a field where the beets are grown.

15. A process according to claim 13, wherein water used in the washing is recycled.

16. A process according to claim 1, wherein the pasteurization is effected by heating the sugar-containing juice to a temperature of at least 85°C.

17. A process according to claim 1, wherein pasteurization is effected in a pasteurizer, and hot pasteurized juice being discharged from the pasteurizer is passed in heat exchange relation with cold juice being introduced into the pasteurizer.

18. A process according to claim 1, wherein pasteurized sugar-containing juice is introduced into a fermenter at a temperature of about 32°C to about 35°C.

19. A process according to claim 1, wherein a nitrogen source is introduced in to the fermenter to provide nitrogen for the yeast.

20. A process according to claim 19, wherein said nitrogen source comprises urea.

21. A process according to claim 1, further comprising introducing oxygen into the fermenter to maintain an aerobic environment in the fermenter.

22. A process according to claim 1, wherein the oxygen is introduced by introducing air into the fermenter.

23. A process according to claim 1, wherein the fermentation is carried out for a period of from about 36 to about 72 hours, preferably less than about 48 hours.

24. A process according to claim 1, wherein the yeast is separated from the fermentate by centrifugation.

25. A process according to claim 1, wherein a portion of the separated yeast is recycled to a subsequent fermentation batch.

26. A process according to claim 1, wherein the yeast is preconditioned for a period of from about 3 to about 6 hours prior to introduction of the yeast into the fermenter.

27. A process according to claim 1, wherein substantially pure ethanol is recovered from the fermentate by distilling the fermentate to obtain a water/ethanol azeotrope and then subjecting the water/ethanol azeotrope to membrane treatment to obtain substantially pure ethanol and residual water.

28. A process according to claim 27, wherein the residual water is recycled to the process.

29. A process according to claim 1, wherein the methane is combusted to provide heat for the pasteurization and ethanol recovery steps.

30. A process according to claim 1, wherein the methane is combusted to drive an electric generator to provide electricity for the process.

31. A process according to claim 1, wherein water recovered from the beets is recycled to the process to make the process substantially water neutral.

32. A process according to claim 1, wherein sufficient energy is derived from the methane to make the overall process substantially net energy neutral.

33. A process according to claim 1, wherein pulp from the pressing operation is stored under anaerobic conditions until needed for anaerobic digestion.

34. An apparatus for producing ethanol from sugar beets, said apparatus comprising:

- a size reducing apparatus for reducing the sugar beets to small particles;

- at least one press for pressing sugar-containing juice out of the ground beet particles;

- a pasteurizer for pasteurizing the sugar-containing juice;

- a heat exchanger for transferring heat from pasteurized juice discharged from the pasteurizer to incoming juice to be introduced into the pasteurizer;

- a fermenter for fermenting the pasteurized sugar-containing juice;

- a still for distilling an ethanol/water azeotrope from fermentate recovered from the fermenter;

- a membrane separator for separating substantially pure ethanol from the

ethanol/water azeotrope from the still; and

- an anaerobic digester for digesting pulp from said at least one press to produce

methane.

35. An apparatus according to claim 34, further comprising a methane-fueled electric generator for generating electricity from produced methane.

36. An apparatus according to claim 34, wherein said size reducing apparatus comprises at least one hammer mill.

37. An apparatus according to claim 34, further comprising at least one centrifuge for separating residual solids from the sugar-containing juice prior to pasteurization.