Processes and systems for biological hydrogen and ethanol production from organic material using yeast

Abstract

Processes and systems for biologically producing hydrogen gas and ethanol from organic material, including food waste. During an initial phase of the process, hydrogen is predominantly produced. By selectively altering process parameters, in particular, reducing temperature, increasing pH, and altering composition, the process can be switched to predominantly producing ethanol and possibly also butanol. Such a process includes biologically producing hydrogen gas and ethanol and optionally butanol from organic material by anaerobic fermentation of the organic material with at least one strain of yeast.

Description

PROCESSES AND SYSTEMS FOR BIOLOGICAL HYDROGEN AND ETHANOL PRODUCTION FROM ORGANIC MATERIAL USING YEASTCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to co-pending United States patent application Serial No. 18 / 504,690 fded November 8, 2023, co-pending United States patent application Serial No. 17 / 763,761 fded March 25, 2022, International Patent Application No. PCT / US2020 / 052812 fded September 25, 2020, and U.S. Provisional Application No. 62 / 906,261 fded September 26, 2019. The contents of these prior patent documents are incorporated herein by reference.BACKGROUND OF THE INVENTION

[0002] The present invention generally relates to the biological production of hydrogen and ethanol, and particularly relates to the biological production of hydrogen gas and ethanol and optionally butanol from organic material using yeast.

[0003] Ethanol production from organic matter has long been used as a sustainable process for the production of fuel. More recently, there has been a strong interest in the biological production of hydrogen gas. Hydrogen gas has significant advantages as a clean energy source. Unlike ethanol and other traditional fuels (including fossil fuels), combustion of hydrogen does not produce carbon dioxide or oxides of nitrogen and sulfur. The maj or end products of using hydrogen in a fuel cell or a reciprocating engine are energy (heat, electricity, etc.) and water. Hydrogen also has a higher energy yield (as an example, about 120 kJ / g) than hydrocarbons (as an example, about 44 kJ / g for petroleum).

[0004] There are, however, technical and economic concerns with the production and storage of hydrogen impacting its near-term viability. Conventional chemical processes for hydrogen production are energy intensive and therefore not cost effective. Biologicalhydrogen production processes offer a potentially economic and sustainable alternative for producing hydrogen. The use of microbial organisms is currently attracting increasing interest as a means of producing hydrogen, as indicated in multiple recent publications. Numerous studies have been conducted using microorganisms to generate hydrogen from fermentation of various substrates, nonlimiting examples of which are reported in Kapdan et al., “Bio-hydrogen Production from Waste Materials,” Enzyme Microbial Technology, 38(5):569-582 (2006), and Chen et al., “Using Sucrose as a Substrate in an Anaerobic Hydrogen-producing Reactor,” Adv. Environ Res 7:695-699 (2003). Some studies have used a pure culture of bacteria, such as species of Bacillus, Clostridium, and Enter obacter, while others have used mixed cultures that originated from sludge, animal wastes, sewage, compost, soil, etc. Kummaravel et al., "Influence and Strategies for Enhanced Biohydrogen Production from Food Waste," Renewable and Sustainable Energy Reviews 92: 807-822 (2018), provides a survey of processes to produce hydrogen from food waste. Using organic wastes for bio-production of hydrogen not only has the potential to generate cost effective and renewable energy but also can reduce pollution in the environment.

[0005] Even with the development of biological processes capable of producing hydrogen gas, there remains an ongoing demand for ethanol produced from organic matter as a sustainable process for the production of fuel.BRIEF DESCRIPTION OF THE INVENTION

[0006] The intent of this section of the specification is to briefly indicate the nature and substance of the invention, as opposed to an exhaustive statement of all subject matter and aspects of the invention. Therefore, while this section identifies subject matter recited in the claims, additional subject matter and aspects relating to the invention are set forth in other sections of the specification, particularly the detailed description, as well as any drawings.

[0007] The present invention provides, but is not limited to, processes and systems forbiologically producing hydrogen gas and ethanol and optionally butanol from organic material, including food waste.

[0008] According to a nonlimiting aspect of the invention, a process is provided for biologically producing hydrogen gas and ethanol by anaerobic fermentation of organic material with at least a first yeast strain. The process includes introducing the organic material, water, and at least the first yeast strain to a reactor tank, performing a first anaerobic fermentation of the organic material in the reactor tank at a first elevated temperature of about 32°C to about 42°C, at a first controlled pH of 5.4 to 6.0, at a first pressure above atmospheric pressure but not greater than 6.9 kPa above atmospheric pressure, and at a first oxygen level of less than 0.25%. The first anaerobic fermentation occurs for a first time period to produce the hydrogen gas in a volumetric amount greater than any ethanol produced during the first anaerobic fermentation. The production of the hydrogen gas is monitored during the first anaerobic fermentation to determine an initial hydrogen production peak, and then a temperature of the organic material is reduced to below the first elevated temperature and a pH of the organic material is increased to above the first controlled pH of the organic material to perform a second anaerobic fermentation of the organic material in the reactor tank and produce the ethanol . The second anaerobic fermentation occurs for a second time period to produce the ethanol in a volumetric amount greater than any hydrogen gas produced during the second anaerobic fermentation.

[0009] According to another nonlimiting aspect of the invention, a system is provided for performing a process as described above. The system includes a reactor tank in which the first and second anaerobic fermentations are performed, a source of the first yeast strain, and a means for monitoring the production of the hydrogen gas during the first anaerobic fermentation and determining the initial hydrogen production peak.

[0010] Technical aspects of processes and systems as described above preferably include the ability to use yeast to selectively and successively produce hydrogen andethanol and optionally butanol from organic material.

[0011] Other aspects and advantages of this invention will be appreciated from the following detailed description as well as any drawings.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0012] FIG. 1 schematically represents a system for biologically producing hydrogen gas and ethanol and optionally butanol from organic material by anaerobic fermentation with at least one strain of yeast in accordance with a nonlimiting embodiment of this invention.

[0013] FIG. 2 is a process flow diagram representing a process performed with the system of FIG. 1 to produce hydrogen gas and then ethanol and optionally butanol in sequence from food waste in accordance with a nonlimiting embodiment of this invention.

[0014] FIG. 3 is a graph plotting hydrogen production and carbon dioxide production in volumetric percent (%) and in standard cubic centimeters per minute (SCCM) with two separate additions of yeast and a single addition of Clostridium acetobutylicum.

[0015] FIG. 4 is a graph plotting hydrogen production and carbon dioxide production in volumetric percent (%) and in standard cubic centimeters per minute (SCCM) with a single addition of yeast and a single addition of Clostridium acetobutylicum.

[0016] FIGS. 5A and 5B are graphs plotting (FIG. 5A) hydrogen production and carbon dioxide production in volumetric percent (%) and in standard cubic centimeters per minute (SCCM) and (FIG. 5B) cumulative hydrogen production and carbon dioxide production in standard cubic centimeters (SCC) using a system of the type represented in FIG. 1 in which changes in operating parameters caused the system to shift from primarily hydrogen production to primarily ethanol production.

[0017] FIGS. 6A and 6B are graphs plotting (FIG. 6A) hydrogen production and carbon dioxide production in volumetric percent (%) and in standard cubic centimeters per minute (SCCM) and (FIG. 6B) cumulative hydrogen production and carbon dioxide production in standard cubic centimeters (SCC) using a system of the type represented in FIG. 1 in which changes in operating parameters caused the system to shift from primarily hydrogen production to primarily ethanol production.DETAILED DESCRIPTION OF THE INVENTION

[0018] The intended purpose of the following detailed description of the invention and the phraseology and terminology employed therein is to describe what is shown in the drawings, which include the depiction of and / or relate to one or more nonlimiting embodiments of the invention, and to describe certain but not all aspects of what is depicted in the drawings, including the embodiment(s) depicted in the drawings. The following detailed description also describes certain investigations relating to the embodiment(s) depicted in the drawings, and identifies certain but not all alternatives of the embodiment s) depicted in the drawings. As nonlimiting examples, the invention encompasses additional or alternative embodiments in which one or more features or aspects shown and / or described as part of a particular embodiment could be eliminated, and also encompasses additional or alternative embodiments that combine two or more features or aspects described as part of different embodiments. Therefore, the appended claims, and not the detailed description, are intended to recite what at least provisionally are believed to be aspects of the invention, including certain but not necessarily all of the aspects and alternatives described in the detailed description.

[0019] The following disclosure describes various aspects of processes and systems for biologically producing hydrogen gas and producing ethanol and optionally butanol from organic material by anaerobic fermentation. A nonlimiting example of such a system is schematically represented in FIG. 1. The system represents an approach to producinghydrogen biologically from organic material that employs yeast to increase hydrogen production as compared to processes utilizing only bacteria. The system is further configured to be capable of shifting from primarily hydrogen production to primarily ethanol and possibly also butanol production, without requiring any structural modifications to the system.

[0020] Yeasts particularly suitable for use in systems and processes as described herein include those suitable for use in the commercial production of wine and ethanol, as examples, Saccharomyces cerevisiae and species of the genus Schizosaccharomyces. although other strains of yeast also have shown hydrogen production capability. During investigations leading to the present invention, it was determined that the use of certain yeasts in the system schematically represented in FIG. 1 had the ability to significantly increase hydrogen production as well as reduce processing and operating requirements if the anaerobic fermentation process is performed within certain relatively narrow ranges of processing parameters. Furthermore, the same yeasts were shown to have the ability to switch to the production of ethanol . Minimal preprocessing is required for the organic material and, aside from adhering to certain relatively narrow ranges of processing parameters, the operating conditions during hydrogen and ethanol production are greatly simplified.

[0021] Generally, the nonlimiting embodiment of FIG. 1 represents organic material (feedstock) 10 as being delivered to a receiving hopper 12 where it is initially ground. The organic material 10 is then transferred to a mixing tank 16 where water is introduced and mixed with the ground organic material 10 and additional grinding preferably occurs to form a slurry 14. A pH meter 30a measures the pH of the slurry 14 within the tank 16. The slurry 14 may be heated within the mixing tank 16, as will be discussed below. The slurry 14 is then transferred to a reactor tank 20, as an example, using a screw pump 18. The reactor tank 20 is sealed and maintained at a low pressure, above atmospheric pressure but preferably not greater than about 1.0 psi (about 6.9 kPa) above atmospheric pressure,more preferably in a range of 0.1 to 1.0 psi (about 0.69 to 6.9 kPa) above atmospheric pressure. FIG. 1 further indicates that water (H2O), for example, tap water may also be added directly to the slurry 14 within the reactor tank 20.

[0022] The pressure within the reactor tank 20 is monitored with a pressure transducer 22. At startup, a sparge gas 24 is introduced into the reactor tank 20 to produce anaerobic conditions within the reactor tank 20. The sparge gas 24 is selected to be inert to the anaerobic fermentation process, as a nonlimiting example, nitrogen. The pH within the reactor tank 20 is monitored with a second pH meter 30b and controlled. More particularly, a base 32 or an acid 33, as nonlimiting examples, sodium hydroxide (NaOH) or sulfuric acid (H2SO4), may be added to the reactor tank 20 to achieve a desired initial pH for the slurry 14. As discussed below, in the case that the organic material 10 has undergone some degree of fermentation before being introduced into the system, the slurry 14 is likely to be excessively acidic, with the result that the base 32 may be required at initial startup of the system to reduce the pH of the slurry 14 to an acceptable level for anaerobic fermentation in the reactor tank 20. The temperature of the slurry 14 within the reactor tank 20 is controlled, for example, by a process heater 26, a chiller 27, and a thermostat 28. FIG. 1 represents at least one yeast strain 34 as being separately introduced into the reactor tank 20, though optionally also or instead simultaneously introduced with the slurry 14 and / or water to form what is referred to herein as a mixture 36. The level of the mixture 36 within the reactor tank 20 can be monitored with a level sensor 38. While within the reactor tank 20, the mixture 36 is preferably agitated, for example, with a stirring apparatus 40.

[0023] The system represented in FIG. 1 may be operated in either a batch or continuous mode. Outputs of the pressure transducer 22, thermostat 28, pH meters 30a and 30b, and level sensor 38 can all be supplied to a suitable processor 42 for purposes of controlling the process heater 26 and chiller 27 and the introduction of the organic material 10, water, sparge gas 24, base 32, acid 33, and yeast 34 into the reactor tank 20.

[0024] FIG. 1 represents gaseous products (biogas) 44 of anaerobic fermentation within the reactor tank 20 as drawn from an upper end of the reactor tank 20 through a flow meter 46, which is also preferably monitored with the processor 42. As discussed in more detail below, the system can be controlled so that the gaseous products 44 will primarily contain hydrogen gas or ethanol and optionally also butanol, and the composition of the gaseous products 44 is preferably analyzed and confirmed, for example, using a gas chromatograph (not shown). The gaseous products 44 may undergo compression in a precompressor 47 before being collected in a gas holding tank 48, from where the gaseous products 44 may be transferred 50 to be processed for sale, or utilized by downstream process applications 60, or in some cases vented to atmosphere. FIG. 1 represents an example of processing for sale application as including a gas separator 68 that separates hydrogen gas and carbon dioxide from the gaseous products 44, after which the hydrogen may then be compressed with a compressor 70 and placed in a storage tank 72A for storage or a tanker 72B for transport.

[0025] During the operation of the system in which the gaseous products 44 is primarily hydrogen gas (i.e., hydrogen gas constitutes more than 50% by volume of the gaseous products 44), the remainder (i.e., less than 50% by volume) of the gaseous products 44 may be carbon dioxide. An H2 / CO2 mixture containing about 50% or more of hydrogen gas can be used to produce heat by direct combustion, or directly produce electricity in a reciprocating engine-driven generator, or produce electricity in a fuel cell after additional processing. In FIG. 1, carbon dioxide separated by the gas separator 68 may be collected for use at a carbon dioxide processing facility 74, such as a dry ice and / or carbonation plant.

[0026] FIG. 1 represents residual product 54 as drawn from the reactor tank 20. The residual product 54 may be processed for use in a digester, placed in a landfill, or used as a fertilizer. As previously noted, the system is preferably capable of being controlled to primarily produce ethanol and optionally also butanol, which are not a gaseous product butinstead are liquids within the residual product 54. As such, FIG. 1 represents ethanol and / or butanol 56 as being extracted from the residual product 54. Alternatively or in addition, the residual product 54 (with ethanol and / or butanol 56 entrained therein) may be collected in a tank 58 for later use as a fertilizer and / or as a fuel source for a distributed cogeneration system, such as disclosed in U.S. Patent Application Publication No. 2014 / 0132918.

[0027] FIG. 2 represents a process by which the system of FIG. 1 can be operated in a manner to initially primarily produce hydrogen gas by anaerobic fermentation using combinations of yeast and bacteria, and then subsequently primarily produce ethanol and optionally butanol by anaerobic fermentation using the same combination of yeast and bacteria. Yeasts used by the anaerobic fermentation process, as nonlimiting examples, Saccharomyces cerevisicie and species of the genus Schizosaccharomyces, are well known for use in winemaking, baking, brewing and ethanol production. Notable aspects of the process represented in FIG. 2 involve operating the system at specific conditions that will initially maximize production of hydrogen (as opposed to methane or ethanol), followed by specific conditions that will maximize production of ethanol and optionally butanol. Successive production of hydrogen and ethanol / butanol from the same organic material introduced into the system was shown to be significantly and selectively increased by employing operating conditions that were determined with investigations leading to the present invention. More particularly, temperature and pH were identified as the operating parameters that had the most influence on hydrogen and ethanol / butanol production levels for the tested organic material. Additionally, the initial pH was identified as a parameter that required control if the organic material had undergone a significant degree of fermentation prior to being introduced into the reactor tank 20, such that the organic material would have a pH of less than 6.

[0028] FIG. 2 represents exemplary but not necessarily required steps and parameters carried out with the system of FIG. 1 to initially primarily produce hydrogen gas byanaerobic fermentation using a combination of yeast and bacteria, and then subsequently primarily produce ethanol and likely alsobutanol by anaerobic fermentation using the same combination of yeast and bacteria. In step 102, organic material (e g., food waste) is provided in an amount so as to achieve a final VOLA (volatile material, as defined in EPA Method 1684) content of 19 to 65 grams per liter of water in the reactor tank 20. In step 104, the organic material is ground in the receiving hopper 12 and subsequently in the mixing tank 16 to yield a slurry of the organic material (and any added water). In step 106, the pH of the slurry is determined with the pH meter 30a and, if less than 6, the slurry is heated for a duration sufficient to evaporate the majority of any alcohol (resulting from fermentation and promoting the acidity of the organic material). In step 108, the slurry (and optionally water) is introduced to the reactor tank 20 and the pH is adjusted to a range of 6.0-6.5.

[0029] In step 110, yeast is added to the tank 20 at a rate of 0.13 to 0.63 grams per liter of water. The yeast is identified in step 110 as Saccharomyces cerevisiae, commercially available under the name Lalvin™ K1-V1116, although as previously noted other strains of yeast have shown hydrogen production capability and could be used. In step 112, ferrous sulfate (FeSCH) may be added to the reactor tank 20 to increase the presence of iron ions in the slurry, which has been determined to increase the production of hydrogen by anaerobic fermentation. In step 114, glucose (or dextrose, or another carbohydrate source) may be added to the slurry within the reactor tank 20, which as discussed below was determined to increase the production of hydrogen and ethanol / butanol by anaerobic fermentation. The fermentation process is believed to be enhanced when there is a natural microbial consortium present in the slurry, along with the yeast (step 110) and bacteria (indicated in FIG. 2 as added at step 122). In cases where the organic material was heated before being introduced into the system, the natural microbial consortium within the organic material is generally removed, in which case it is advantageous or necessary to add additional organic material that has not undergone heating so as to introduce a naturalmicrobial consortium to the slurry. Such an addition is indicated as occurring in step 116, as well as agitation of the slurry.

[0030] In step 118 the temperature of the slurry is controlled and the slurry is sparged to create a low pressure (above atmospheric pressure, but not greater than about 1.0 psi (about 6.9 kPa) above atmosphere) anaerobic environment in a temperature range favorable for the production of hydrogen gas. In step 120, the pH is initially adjusted to 5.9 to 6.6, which was determined experimentally to reduce the latency time for the start of hydrogen production. In step 122, bacteria (e.g., Clostridium acetobutylicum) may be added to the reactor tank 20 to achieve or maintain a culture of 0.25 to 1.0 mL of bacteria culture per liter of slurry. In step 124, the pH is controlled to maintain a pH of 5.4 to 6.0, optimally 5.71, which is a pH range favorable for the production of hydrogen gas. Step 126 occurs after a peak in hydrogen gas occurs, at which time additional yeast is added to the reactor tank 20.

[0031] In steps 128 and 130, the process is modified to shift from the primary production of hydrogen gas to the primary production of ethanol and likely also butanol. To do so, glucose (or another carbohydrate source) is added to the slurry within the reactor tank 20 after sufficient time has lapsed from step 126 (step 128), and the temperature and pH of the slurry is reduced and increased, respectively (step 130). In particular, the temperature is reduced to a temperature within a range of about 30°C to about 36°C, optimally 34°C, and the pH is increased to within a range of 5.6 to 6.5, optimally 59.

[0032] The investigations that were conducted and led to the identification of the steps and parameters outlined in FIG. 2 will now be discussed. In the investigations, ethanol production was determined by chemical analysis or by use of a precision hydrometer, and as indicated during operation by observation of carbon dioxide (CO2) concentration in the produced gases.

[0033] FIG. 3 represents hydrogen production data for a test operating in batch modewith a system disclosed in U.S. Patent Application Publication No. 2014 / 0132918. In this test, 246.007 g (dry equivalent) of organic material (equal parts of oatmeal, corn, and mixed vegetables), 8L of tap water, 1.0135 g of yeast (Saccharomyces cerevisiae, Lalvin™ KIVU 16), 0.5 mL of bacteria (Clostridium acetobutylicum), and 0.1109 g FeSCU were combined to form a mixture. On day 1 at 21 : 15 hours, the mixture was placed in a 10 L reactor tank. Head space in reactor tank was 2L. The initial pH was 6.5 and adjusted to 6.2 by adding sulfuric acid, which had been determined to a pH level that reduces the latency time after fermentation is initiated. The mixture in the reactor tank was agitated at 135 RPM with a 4 cm diameter stirring paddle. The reactor tank was maintained at a temperature of 37°C and the pH was maintained at 5.7 by means of a pump fed solution of technical grade sodium hydroxide. An additional 0.5182 g of yeast was added on day 2 at 8:00 hours. Fermentation of the mixture produced hydrogen and carbon dioxide. Gas flow from the reactor tank was measured with a flow meter. Hydrogen was predominantly produced (i.e., greater than 50% of produced gases), the majority (about 90%) of which was produced within 34 hours. Ethanol production was indicated by an increase in carbon dioxide (CO2) concentration in the produced gases, and FIG. 3 evidences that additional production of hydrogen and ethanol occurred during the subsequent 24-48 hours. About 211 mL of hydrogen was produced per gram of volatile solids, and the total hydrogen production during the test was about 52 L.

[0034] FIG. 4 represents the hydrogen production data for a second test operating in batch mode using the same system as the first test (FIG. 3). In this test, 177.601 g of volatile material from organic material (cafeteria food waste collected from Purdue University Food Services), 8L of tap water, 1.0129 g of yeast (Saccharomyces cerevisiae, Lalvin™ KI -VI 116), 6 mL of bacteria (Clostridium acetobutylicum), and 0.0526 g FeSCL were combined to form a mixture. On day 1 at 10:53 hours, the mixture was placed in a 10 L reactor tank 20. Initial pH was 6.06. The reactor tank 20 was maintained at a temperature of 37°C and at a pH of 5.7 by means of a pump fed solution of technical gradesodium hydroxide. No additional yeast was added. Fermentation of the mixture produced hydrogen and carbon dioxide, with carbon dioxide being predominantly produced (i.e., greater than 50% of produced gases) throughout the test, indicating the production of ethanol. About 23 mL of hydrogen was produced per gram of volatile solids, and the total hydrogen production during the test was only about 4 L.

[0035] FIGS. 5A, 5B, 6A, and 6B are graphs plotting hydrogen production and carbon dioxide production using the system of FIG. 1 and the process of FIG. 2 during a third text (FIGS. 5A and 5B) and fourth test (FIGS. 6A and 6B) carried out in batch mode. As with FIGS. 3 and 4, ethanol production was indicated by chemical analysis or by use of a precision hydrometer as well as observation of carbon dioxide (CO2) concentration in the produced gases. In these tests, it was evidenced that the pH and temperature of the system and process could be manipulated to cause the process to switch from predominantly hydrogen production to predominantly ethanol production. Ethanol production was enhanced by additions of yeast and dextrose for this case, but it was concluded that other organic material high in carbohydrates could also be added to enhance production.

[0036] In the test represented by FIGS. 5 A and 5B, 171 .263 g of volatile material from organic material (cafeteria food waste collected from Purdue University Food Services), 240 g of standard food waste (equal parts of oatmeal, corn and mixed vegetables), 8L of tap water, 1.9882 g of yeast (Saccharomyces cerevisiae, Lalvin™ K1-V1116), 6 mL of bacteria (Clostridium acetobutylicum), 0.0489 g FeSCL, and 30 g of dextrose were combined to form a mixture (e.g., the mixture 36 in FIG. 1). On day 1 at 10:51 hours, the mixture 36 was placed in a 10 L reactor tank (e.g., tank 20 in FIG. 1). The initial pH was 6.37. The reactor tank was maintained at a temperature of 37°C (e.g., with the process heater 26, chiller 27, and thermostat 28 of FIG. 1) and at a pH of 5.71 by means of a pump fed solution of technical grade sodium hydroxide. Fermentation of the mixture produced hydrogen and carbon dioxide as product gases, with hydrogen gas initially being the predominant gas produced (i.e., greater than 50% of produced gases). As with previoustests, the production of carbon dioxide was used as the indicator for ethanol production.

[0037] Peak hydrogen production can be seen in FIG. 5A as ending at approximately 13:00 hours on day 2. About one hour later, at approximately 14:00 hours on day 2 (indicated by a vertical dash line), the process was switched from hydrogen production to ethanol production by reducing the temperature in the reactor tank to 34°C and increasing the pH of the mixture to 5.9 with additions of the technical grade sodium hydroxide solution. Also at 14:00 hours on day 2, 0.9920 g of yeast (Saccharomyces cerevisiae, Lalvin™ KI -VI 116) and 400 g of dextrose were added to the mixture in the reactor tank. Though fermentation of the mixture continued to produce hydrogen and carbon dioxide, FIGS. 5 A and 5B show a drastic increase in carbon dioxide production, such that carbon dioxide was predominantly produced (i.e., greater than 50% of produced gases, and at one point exceeding 80% of produced gases) throughout the remainder of the test, indicating the production of ethanol. About 199 mL of hydrogen was produced per gram of volatile solids, and the total hydrogen production during the test was about 34 L. The production of ethanol was verified by laboratory testing using a head space gas chromatographic technique (1.44 v / o) and correlated with results using a precision hydrometer. The coproduction of butanol was concluded to have also likely occurred due to the use of the Clostridium bacterial strain and reports available in the literature.

[0038] In the test represented by FIGS. 6 A and 6B, the pH and temperature of the reactor tank and mixture therein were again manipulated to switch from hydrogen production to ethanol production. In this test 180.768 g of volatile material from organic material (cafeteria food waste collected from Purdue University Food Services), 240 g standard organic material (equal parts of oatmeal, com, and mixed vegetables), 7L of water, 2.0067 g of yeast (Saccharomyces cerevisiae, Lalvin™ K1-V1116), 6 mL of bacteria (Clostridium acetobutylicum), 0.0423 g FeSCU, and 30 g of dextrose were combined to form a mixture. On day 1 at 11 :20 hours, the mixture is placed in the 10 L reactor tank. The initial pH was 6.4. The reactor tank was again maintained at a temperature of 37°Cand at a pH of 5.71. Fermentation of the mixture produced hydrogen and carbon dioxide as product gases, with hydrogen gas initially being the predominant gas produced (i.e., greater than 50% of produced gases). As with previous tests, the production of carbon dioxide was used as the indicator for ethanol production and verified by using a precision hydrometer.

[0039] Peak hydrogen production can be seen in FIG. 5A as ending at approximately 13:00 hours on day 2. About one hour later, at approximately 14:00 hours on day 2 (indicated by a vertical dash line), the process was switched from hydrogen production to ethanol production by reducing the temperature in the reactor tank to 34°C and increasing the pH of the mixture to 5.9 with additions of the technical grade sodium hydroxide solution. Also at 14:00 hours on day 2, 1.150 g of yeast (Saccharomyces cerevisiae, Lalvin™ KI -VI 116) and 1800 g of dextrose were added to the mixture in the reactor tank. Though fermentation of the mixture continued to produce hydrogen and carbon dioxide, FIGS. 6A and 6B show a drastic increase in carbon dioxide production, such that carbon dioxide was predominantly produced (i.e., greater than 50% of produced gases, and at one point exceeding 90% of produced gases) throughout the remainder of the test, indicating the production of ethanol. About 161 mL of hydrogen was produced per gram of volatile solids, and the total hydrogen production during the test was about 29 L. Total ethanol produced was determined by the use of a precision hydrometer as approximately 4 v / o. The co-production of butanol was concluded to have also likely occurred due to the use of the Clostridium bacterial strain and reports available in the literature.

[0040] The investigations described above evidenced that hydrogen can be biologically produced from organic material using a process that employs yeast rather than bacteria alone as the basis for anaerobic fermentation. The investigations further evidenced that ethanol (and presumably butanol) can be biologically produced from organic material using a process that employs yeast rather than bacteria alone as the basis for anaerobic fermentation. The balance of hydrogen to ethanol production levels can be manipulated bycontrolling the pH and temperature of the mixture undergoing fermentation. Furthermore, it was concluded that timing of the pH and temperature change is important. In the investigations, an optimal time was determined to be approximately one hour after the initial maj or peak in hydrogen production, at which time the temperature of the reactor tank is reduced from 37°C to 34°C, and the operating pH is increased from 5.71 to 5.9.

[0041] Also favorable to the switch from predominantly hydrogen production to predominantly ethanol production appeared to be the additions of yeast and a source of sugar (carbohydrate). These process modifications then shift the process from an enhanced hydrogen production mode to a mode that emphasizes ethanol production as indicated by increased CO2 concentration in the produced gases. Depending on the composition and quantity of the newly introduced organic material, there is a greatly reduced hydrogen production level while ethanol production increases. The reactor tank can be operated in the enhanced ethanol production mode for an additional time depending on the desired ethanol production levels. As the CO2 content becomes dominant, the hydrogen collection can be terminated at a time after which the value of gas separation has significantly decreased. At this point the produced gas, which is principally CO2, can be collected separately.

[0042] Negative effects of the production of ethanol and butanol that may occur during the initial production of hydrogen can be reduced by reducing the levels of ethanol and / or butanol in the mixture within the reactor tank. For example, an exchange column can be utilized containing a specially designed polymeric resin, such as Amberlite XAD-7 HP, which has a high selectivity for butanol. It is also possible to reduce the levels of ethanol and / or butanol in the mixture within the reactor tank by using a column with molecular sieve. In such a process, the polymeric resin or molecular sieve is placed in a column and material from the reactor tank 20 is circulated through the column by use of a pump. Periodically the column is back flushed to remove build up of particles from the slurry that have become trapped in the column during the recirculation process, after which thecolumn is returned to operation. At the conclusion of the reactor production run, the column is regenerated and butanol is extracted.

[0043] Based on the above investigations, it was concluded that an acceptable temperature range for initially predominantly producing hydrogen is about 32°C to about 42°C, optimally 37°C, with a controlled pH of 5.4 to 6.0, optimally 5.71 , after which the temperature is reduced to a temperature within a range of about 30°C to about 36°C, optimally 34°C, and the pH is increased to within a range of 5.6 to 6.5, optimally 59 Agitation has been shown to be important for evolution of hydrogen from the solution, as is maintaining a positive pressure that is slightly above atmospheric pressure, preferably not greater than 1.0 psi (6.9 kPa) and more preferably 0.1 to 1.0 psi (0.69 to 6.9 kPa) above atmospheric pressure. Because the process is anaerobic, an inert purge gas is employed as indicated in FIG. 1, and oxygen levels within the reactor tank are preferably initially less than 0.25%.

[0044] As previously noted above, though the foregoing detailed description describes certain aspects of one or more particular embodiments of the invention and investigations associated with the invention, alternatives could be adopted by one skilled in the art. For example, the system and its components could differ in appearance and construction from the embodiments described herein and shown in the drawings, and functions of certain components of the process system could be performed by components of different construction but capable of a similar (though not necessarily equivalent) function, certain process parameters could be modified, and appropriate materials could be substituted for those noted. As such, and again as was previously noted, it should be understood that the invention is not necessarily limited to any particular embodiment described herein or illustrated in the drawings.

Claims

CLAIMS:

1. A process of biologically producing hydrogen gas and ethanol by anaerobic fermentation of organic material with at least a first yeast strain, the process comprising: introducing the organic material, water, and at least the first yeast strain to a reactor tank; performing a first anaerobic fermentation of the organic material in the reactor tank at a first elevated temperature of about 32°C to about 42°C, at a first controlled pH of 5.4 to 6.0, at a first pressure above atmospheric pressure but not greater than 6.9 kPa above atmospheric pressure, and at a first oxygen level of less than 0.25%, the first anaerobic fermentation occurring for a first time period to produce the hydrogen gas in a volumetric amount greater than any ethanol produced during the first anaerobic fermentation; monitoring production of the hydrogen gas during the first anaerobic fermentation to determine an initial hydrogen production peak; and then reducing a temperature of the organic material to below the first elevated temperature and increasing a pH of the organic material to above the first controlled pH of the organic material to perform a second anaerobic fermentation of the organic material in the reactor tank and produce the ethanol, the second anaerobic fermentation occurring for a second time period to produce the ethanol in a volumetric amount greater than any hydrogen gas produced during the second anaerobic fermentation.

2. The process of claim 1, wherein the second anaerobic fermentation is performed at a second elevated temperature of about 30°C to about 36°C, and at a second controlled pH of 5.6 to 6.5.

3. The process of claim 2, wherein the second anaerobic fermentation is performed at a second pressure above atmospheric pressure but not greater than 6.9 kPa above atmospheric pressure and at a second oxygen level of less than 0.25%.

4. The process of claim 1, wherein the organic material is a food waste.

5. The process of claim 4, wherein the food waste is partially decomposed and contains alcohol.

6. The process of claim 5, wherein the food waste has a pH of below 6.0 and the process further comprises heating the food waste to remove at least some of the alcohol before performing the first anaerobic fermentation.

7. The process of claim 4, further comprising adding a carbohydrate waste material to the food waste or to the reactor tank before performing the first anaerobic fermentation, the carbohydrate waste material having a higher sugar content than the food waste.

8. The process of claim 1, further comprising homogenizing and liquifying the organic material prior to introducing the organic material to the reactor tank.

9. The process of claim 1, further comprising controlling an initial pH of the organic material to a range of 6.0 to 6.5 before performing the first anaerobic fermentation.

10. The process of claim 1, wherein the temperature of the organic material is reduced to below the first elevated temperature and the pH of the organic material is increased to above the first controlled pH of the organic material about one hour after the initial hydrogen production peak.

11. The process of claim 1, further comprising agitating the organic material during the first and second anaerobic fermentations.

12. The process of claim 1, wherein the first time period is about 36 hours and the second time period is about 24 to about 48 hours.

13. The process of claim 1, wherein the first time period is about 36 hours and the second time period is about 24 to about 48 hours.

14. The process of claim 1, further comprising monitoring production of carbon dioxide gas during the first anaerobic fermentation to determine a carbon dioxide production peak before performing the second anaerobic fermentation.

15. The process of claim 1, wherein the first yeast strain is a yeast strain used in ethanol and / or wine production.

16. The process of claim 1, wherein the first yeast strain is Saccharomyces cerevisiae and species of the genus Schizosaccharomyces .

17. The process of claim 1, wherein the first and second anaerobic fermentations are performed without intentional additions of bacteria to the organic material.

18. The process of claim 1, wherein the first and second anaerobic fermentations are performed with intentional additions of bacteria to the organic material.

19. The process of claim 1, wherein butanol is also produced during the second anaerobic fermentation.

20. A system for performing the process of claim 1, the system comprising:the reactor tank in which the first and second anaerobic fermentations are performed; a source of the first yeast strain; and means for monitoring the production of the hydrogen gas during the first anaerobic fermentation and determining the initial hydrogen production peak.

Images