Abstract:
A system for the production of methane and other useful products and method of use for generating green natural gas as a fuel or component for use in the manufacturing of specialty chemicals. The system for the production of methane and other useful products and method of use includes a culture of methanogenic archea for converting an input material into an output material, a reactor vessel for housing at least a portion of the culture of methanogenic archea, an input material stream directed into the reactor vessel to facilitate contact between the input material stream and the methanogenic archea, and an output material stream created at least in part by the culture of methanogenic archea.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to application serial number TBD, entitled Methanogenic Reactor filed TBD. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the generation of green natural gas through methanogenic conversion and more particularly pertains to a new system for the production of methane and other useful product and method of use for generating natural gas and cellular biomass from a variety of input material including biomass. 
         [0004]    2. Description of the Prior Art 
         [0005]    The use of methanogens and methanogenic processes is known in the prior art. More specifically, the systems utilizing methanogens to generate natural gas heretofore devised and utilized have generally been either capturing the gaseous output of naturally occurring systems, such as the Volta Experiment on Lake Como in 1778 or anaerobic digestion systems which consist basically of familiar, expected and obvious biological, chemical, and structural configurations, notwithstanding the myriad of designs encompassed by the crowded prior art which have been developed for the fulfillment of countless objectives and requirements. 
         [0006]    The process of Methanogenesis is fairly well known. The following references provide a good working overview of the methanogenic process and are hereby incorporated by reference for all purposes:  Archea: Molecular and Cellular Biology—Chapter  13  Methanogenesis,  James G. Ferry and Kyle A. Kastead, Department of Biochemestry and Molecular Biology, The Pennsylvania State University, Universtiy Park, P A, edited by Ricardo Cavicchiolo, © 2007 ASM Press, Washington, DC; and  Continuous Cultures Limited by a Gaseous Substrate: Development of a Simple, unstructured Mathematical Model and Experimental Verification with Methanobacterium thermoautotrophicum,  N. Schill, W. M. van Gulik, D. Voisard, and U. von Stockar, Institute of Chemical Engineering, Swiss Federal Institute of Technology, Lausanne (EPFL), CH-1015 Lausanne, Switzerland, Biotechnology and Bioengineering, Vol. 51, P6450658 (1996) John Wiley &amp; Sons, Inc. 
         [0007]    Illustrative examples of the types of systems known in the prior art include anaerobic digestion systems and U.S. Pat. Nos. 1,940,944; 2,097,454; 3,640,846; 4,722,741; 5,821,111 and application no. PCT/US07/71138. 
         [0008]    In these respects, the system for the production of methane and other useful product and method of use according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of generating green natural gas and cellular biomass from a variety of source materials including biomass. 
       SUMMARY OF THE INVENTION 
       [0009]    To promote the development of renewable energy sources, the United States government has identified a “billion ton” goal of biomass production per year. At present the largest single component of that supply is corn stover. It is widely accepted that adverse ecological effects of corn production such as the anoxic zone in the Caribbean will encourage biomass production from other sources. Chief among these alternatives will be perennial grasses such as switchgrass and native prairie grasses. Testing currently underway on novel, high yield grasses such as miscanthus points to the prospect of biomass production in lieu of conventional crops on marginal lands. 
         [0010]    Despite these developments on the production side there remain critical issues on the conversion of these biomass sources to useable forms as substitutes for fossil fuels. 
         [0011]    Pelletizing improves the handling characteristics of biomass, but adds enough cost to the resulting fuel cost to largely eliminate any fuel cost advantage. In addition, biomass fuels burn dirty, producing sulfur and nitrogen oxides and hydrogen chloride. Equipment to burn these fuels is expensive and air permitting remains problematic. A clean solution to these limitations would be to convert biomass into pipeline quality biomethane near the point of origin for transmission to existing natural gas customers via existing natural gas pipelines. This same process can also supply biomethane to specialty chemical facilities for the production of green specialty chemicals, including but not limited to “green plastics”. Further, the present invention also generates cellular biomass, which may be utilized as a food or nutrient for livestock and humans 
         [0012]    The two primary routes to biomethane currently recognized are anaerobic digestion and thermochemical conversion. A third process for the conversion of biomass to liquid fuels is being pursued which involves enzymatic breakdown of cellulose and hemicelluloses into fermentable sugars. While these processes are effective on some feedstocks and at some capacities, none of them provide a fully satisfactory route to biomass use. 
         [0013]    To understand why this is so, it is helpful to understand the progression of plant composition during the growing season. The three primary structures in a plant are cellulose, hemicelluloses, and lignin. These compounds are in turn polymers of 6-carbon sugars, 5-carbon sugars, and phenolics respectively. As the plant matures, there is a progressive conversion of cellulose and hemicelluloses to lignin. This is reflected in the decrease of total digestable nutrients and the increase of acid detergent fiber content. 
         [0014]    Anaerobic digestion uses mixed cultures of microbes to break down biomass into fermentable sugars, amino acids, and organic acids. This process is multi-step and is subject to upset by over-production of organic acids which kill the methanogenic organisims. The great benefit of anaerobic digestion is that it is generally recognized as specific, producing methane and carbon dioxide in a readily recoverable form. 
         [0015]    Anaerobic digestion of grasses and corn stover has been extensively studied. Mahert (Mahert, Pia, et al, “Batch and Semi-continuous Biogas Production from Different Grass Species”. December 2005) and others have studied the potential for biomethane production from various grasses. The chief finding of this work is that while biomethane can be produced by this route, the required digester volume per unit of energy produced is uneconomical. In addition, the grasses must be harvested at or before full bloom. Corn stover is substantially limited and in some instances near impervious to anaerobic digestion. 
         [0016]    A further disadvantage of anaerobic digestion of grasses is that when native or prairie grass is cut before October, the yield the following year is half or less of what is expected. This appears to be related to the manner in which nutrients are returned to the root structure after frost. 
         [0017]    Thermochemcial conversion of biomass to biomethane and liquid fuels is a proven technology base on some old coal chemistry. A large scale coal to natural gas plant at Beulah, N. Dak. has been in operation since the late 1980&#39;s. The chief limitation of this technology is that it strongly favors large scale operations, generally over 400 tons per day. 
         [0018]    Enzymatic processes to break down biomass to fermentable sugars remain an elusive and expensive undertaking. Even if successful, however, enzymatic processes are likely to be highly specific to certain species and perhaps even varieties within species due to their high specificity. One of the objectives associated with biomass production is promotion of multiple species cultivation. Highly specific enzyme processes will tend to promote monocultures and leave the ecosystem no richer than a corn/soybean mix. 
         [0019]    As the foregoing shows, there is room for development of a novel process which will address the limitations of all the current options. Such a process will have at least some of the following characteristics:
       1) It will produce a fuel which is directly compatible with existing energy distribution and use equipment;   2) It will use a variety of feed stocks ranging from corn stover to perennial grasses to wood without loss of yield per ton of saleable energy;   3) It will utilize feedstock harvested late in season and preferable after frost;   4) It will be economical at a scale of 200 ton per day or less;   5) It will be modular to allow initial construction and expansion as the biomass supply chain becomes established and more efficient and   6) It will produce cellular biomass that can have useful and economic value.       
 
         [0026]    The present invention provides each of these advantages by using a hybrid process which combines the flexibility and power of gasification with the specificity of anaerobic digestion, and with improved efficiency and higher production rates than anaerobic digestion. The gasification step overcomes biomass species and variety variations producing uniform, readily fermentable feedstock to the reactor. The culture in the reactor is efficient and specific producing only methane, cellular biomass, and water as its co-products. 
         [0027]    The present invention utilizes a wide variety of feedstocks ranging from crop residues, low value co-products from agriculture processing and energy crops such as switchgrass and corn stover, waste wood products, and other similar biomass sources. The raw materials may be processed such as being reduced to a uniform size and moisture content (preferably very low) prior to gasification. The gassification process converts the biomass into an intermediate gas stream known as syngas or synthesis gas. The syngas, after going through a heat recovery process, may be directed through a filtering system and or a water gas shift prior to being directed into the reactor vessel for conversion by the methanogenic culture into methane. 
         [0028]    It is important to note that while the present invention is directed towards providing green natural gas from biomass, the same process can be done with municipal or landfill wastes or nonconventional carbon and hydrogen sources (collectively “landfill waste”). The use of the present invention with landfill wastes as the feed stock would allow the reclamation of hundreds of thousands of acres currently used as landfills. If landfill wastes are utilized as a feedstock, the filtering and cleanup process after gasification can be much more complex than that required for biomass feedstock. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The invention will be better understood and objects of the invention will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
           [0030]      FIG. 1  is a schematic functional block diagram of a new System For The Production Of Methane And Other Useful Products And Method Of Use according to the present invention. 
           [0031]      FIG. 2  is a schematic functional block diagram of an embodiment of the present invention. 
           [0032]      FIG. 3  is a schematic functional block diagram of the agitation system of the present invention. 
           [0033]      FIG. 4  is a schematic functional block diagram of the recirculation system of the present invention. 
           [0034]      FIG. 5  is a schematic functional block diagram of the pH control system of the present invention. 
           [0035]      FIG. 6  is a schematic flow diagram of the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0036]    With reference now to the drawings, and in particular to  FIGS. 1 through 6  thereof, a new System for the production of methane and other useful products and method of use embodying the principles and concepts of the present invention and generally designated by the reference numeral  10  will be described. 
         [0037]    As best illustrated in  FIGS. 1 through 6 , the System for the production of methane and other useful products and method of use  10  generally comprises a culture of methanogenic archea  26  for converting an input material  20 into an output material  70 , a reactor vessel  30  for housing at least a portion of the culture of methanogenic archea  26 , an input material stream  24  directed into the reactor vessel  30  to facilitate contact between the input material stream  24  and the methanogenic archea  26 , and an output material stream  72  created at least in part by the culture of methanogenic archea  26 . 
         [0038]    In at least one embodiment, the present invention includes at least one culture of methanogenic archea  26  (“methanogens”), at least one reactor vessel  30 , at least one input material stream  24 , and at least one output material stream  72 . 
         [0039]    The methanogens convert an input material  20 into an output material, including methane and cellular biomass. Typically, the present invention uses primarily a gas mixture for the input stream and generates at least a gas and excess biological material as the output materials. 
         [0040]    At least one reactor vessel  30  is used for housing at least a portion of the culture of methanogenic archea  26 . The present invention also has at least one embodiment in which multiple reactor vessels  30  are used in parallel. This type of parallel arrangement has the benefits of scaling the total reactor volume as desired by adding additional reactor vessels  30 , providing the ability to continue operations during maintenance procedures, and advantageous vessel sizing. 
         [0041]    The input material stream  24  is directed into the reactor vessel  30  to facilitate contact between the input material stream  24  and the methanogenic archea  26 . While conceptualized as an input material stream  24  the present invention also has at least one embodiment wherein multiple input streams are utilized. As an illustrative example only, one such embodiment may occur when sequestered CO 2  is used along with other input materials. In this example, the sequestered CO 2  could be directed into the reactor vessel  30  separate from the other input materials. Further, the present invention also includes at least one embodiment wherein H 2 , CO, CO 2 , and/or H 2 S are directed into the reactor vessel  30  as separate input streams. 
         [0042]    The output material stream  72  is created at least in part by bringing the methanogens into contact with the input material stream  24 . Preferably, this contact occurs at a molecular scale. The output material stream  72  may also include multiple output material streams  72  such as a gas stream, a solids stream, and a liquids stream. The liquids stream may include particulate matter and dissolved gases. 
         [0043]    In an embodiment each one of the reactor vessels  30  includes at least one input material stream port  31  for operationally coupling the reactor vessel  30  to a source of the input material stream  24 , at least one output material stream port  32  for facilitating removal of the output material stream  72 . 
         [0044]    Preferably each one of the reactor vessel  30   s  also may include an agitation system  40 , a recirculation system, a pH adjustment system  60 , a condenser  54 , an input material stream flow control  34 , atmoshpheric pressure control system  36 , and an Oxidation Reduction Potential control system  38 . The agitation system  40  is at least partially positioned within the reactor vessel  30  and is used for enhancing contact between the input material stream  24  and the culture of methanogenic archea  26  and for reducing foaming within the reactor vessel  30 . In some cases an anti-foaming agent may be added into the reactor to further reduce foaming. The recirculation system  50  is also used to enhance contact between the input material stream  24  and the culture of methanogenic archea  26 . The pH adjustment system  60  facilitates the maintenance of a pH of the methanogenic archea  26  combined with a mixture of the input material stream  24  and the output material stream  72 . Typically if the pH falls below a predetermined level, a buffer solution is added into the reactor vessel  30 , and if the pH increases above a second predetermined level, additional CO2 is introduced into the reactor vessel  30 . The condenser  54  is preferably environmentally coupled to the output material stream  72  port  32 , and allows a gaseous portion of the output material stream  72  to be separated from a non-gaseous portion of the output material stream  72 . In at least one embodiment the condenser  54  is sixed such that the volume of the condenser  54  to the volume of the reactor is between 1:20 and 1:160. The input material stream flow control  34  is used to control the type and rate of material in the input material stream  24  being directed into the reactor vessel  30 . The atmospheric pressure adjustment system facilitates the control and maintenance of atmospheric pressure within the reactor vessel  30 . Typically the pressure utilized within the reactor vessel  30  is between 0.5 and 7 atmospheres. In at least one embodiment at “normal” atmospheric pressure the reactor in operation may maintain between 2 and 7 PSI of back pressure. The oxidation reduction potential adjustment system facilitates the maintenance of an oxidation reduction potential (“ORP”) of the methanogenic archea  26  combined with a mixture of the input material stream  24  and the output material stream  72 . Typically if the ORP falls outside of a desired range a predetermined quantity of H 2  or H 2 S is introduced into the reactor vessel  30 . 
         [0045]    In at least one embodiment, at least a portion of the input material stream  24  is the output of a gasifier  22 . The gasifier  22  type may include steam reforming, air swept, or oxygen swept dependent at least in part on the type of materials to be gasified. The present invention accommodates a wide range of gasifier  22  input materials including corn stover, switch grass, wood waste products, municipal or landfill wastes, and other similar materials. 
         [0046]    The input material stream  24  or streams directed into the reactor vessel  30  may include any of the following combinations:
       1) Carbon Dioxide and Hydrogen;   2) Carbon Monoxide and Hydrogen;   3) Carbon Dioxide and Carbon Monoxide;   4) Carbon Dioxide, Carbon Monoxide, and Hydrogen;   5) Carbon Dioxide, Hydrogen, and Hydrogen Sulfide;   6) Carbon Dioxide, Hydrogen, Hydrogen Sulfide and Nitrogen;   7) Carbon Dioxide, Hydrogen, Hydrogen Sulfide, Nitrogen, and Oxygen;   8) Carbon Dioxide, Hydrogen, Hydrogen Sulfide, Nitrogen, and Oxygen;   9) Carbon Dioxide, Hydrogen, Hydrogen Sulfide, Nitrogen, Carbon Monoxide, and Oxygen;   10) Carbon Dioxide, Hydrogen, Nitrogen, Carbon Monoxide, and Oxygen;   11) Carbon Dioxide, Hydrogen, Carbon Monoxide, and Oxygen;   12) Carbon Dioxide, Hydrogen, Carbon Monoxide, and Nitrogen;   13) Carbon Dioxide, Hydrogen, Carbon Monoxide, and Hydrogen Sulfide;   14) Carbon Dioxide, Hydrogen, Carbon Monoxide, Hydrogen Sulfide, and Oxygen;   15) Carbon Monoxide, Hydrogen, and Hydrogen Sulfide;   16) Carbon Monoxide, Hydrogen, and Nitrogen;   17) Carbon Monoxide, Hydrogen, Hydrogen Sulfide, and Nitrogen;   18) Carbon Monoxide, Hydrogen, Hydrogen Sulfide, Nitrogen, and Oxygen;   19) Carbon Monoxide, Hydrogen, Nitrogen, and Oxygen;   20) Carbon Monoxide, Hydrogen, Hydrogen Sulfide, and Oxygen;   21) Carbon Monoxide, Hydrogen, Nitrogen, and Oxygen;       
 
         [0068]    As may be readily appreciated from reviewing the above listing, the present invention has significant tolerance to variations in the input material stream  24 , and as such gas cleanup prior to introduction into the reactor vessel  30  may be significantly reduced or potentially eliminated. Further, for each of the combinations listed above, the input material stream  24  may be directed into the reactor vessel  30  as a single mixed stream, or as a combination of multiple streams each directed into the reactor vessel  30 . 
         [0069]    For sustained operation, the present invention may also include a growth media solution  65  for promoting the ongoing growth of the culture of methanogenic archea  26 , as well as enhancing the production of methane by the methanogenic archea  26 . 
         [0070]    In an embodiment the growth media solution  65  includes both a macro ingredient solution  66  and a micro ingredient solution  67 . Preferably, the macro ingredient solution  66  comprises KH 2 PO 4 , NH 4 CL, and NaCl. More preferably, the macro ingredient solution  66  comprises 75 to 300 grams of KH 2 PO 4 , 350 to 1600 grams of NH 4 CL, and 30 to 130 grams of NaCl dissolved in 20 to 40 gallons of deionized water. In at least one embodiment, the macro ingredient solution  66  comprises approximately 153.8 grams of KH 2 PO 4 , approximately 725.3 grams of NH 4 CL, and approximately 66.0 grams of NaCl dissolved in approximately 30 gallons of water. 
         [0071]    In a preferred embodiment the micro ingredient solution  67  comprises Na2 nitrilotriacetates, MgCl 2 -6H 2 O, FeSO 4 -7H 2 O, CoCl 2 -6H 2 o, Na 2 MoO 4 -2H 2 O, NiCl 2 -6H 2 o, Na 2 SeO 3 , Na 2 WO 4 -2H 2 O. More preferably the micro ingredient solution  67  comprises 35 to 150 grams per liter of Na 2  nitrilotriacetates, 25 to 100 grams per liter of MgCl 2 -6H 2 O, 6 to 30 grams per liter of FeSO 4 -7H 2 O, 0.07 to 0.30 grams per liter of CoCl 2 -6H 2 O, 0.07 to 0.30 grams per liter of Na 2 MoO 4 -2H 2 O, 0.15 to 0.60 grams per liter of NiCl 2 -6H 2 O, 0.01 to 0.1 grams per liter of Na 2 SeO 3 , 0.40 to 1.7 grams per liter Na 2 WO 4 -2H 2 O. In at least one embodiment, the micro ingredient solution  67  comprises approximately 70.5 grams per liter of Na 2  nitrilotriacetates, approximately 50.8 grams per liter of MgCl 2 -6H 2 O, approximately 13.9 grams per liter of FeSO 4 -7H 2 O, approximately 0.15 grams per liter of CoCl 2 -6H 2 O, approximately 0.15 grams per liter of Na 2 MoO 4 -2H 2 O, approximately 0.30 grams per liter of NiCl 2 -6H 2 O, approximately 0.04 grams per liter of Na 2 SeO 3 , approximately 0.82 grams per liter Na 2 WO 4 -2H 2 O. 
         [0072]    In an embodiment the micro ingredient solution  67  is prepared using deaerated water and maintained in anoxic condition in order to maintain iron ions as iron+3. 
         [0073]    In at least one embodiment, the growth media solution  65  is prepared by first preparing the macro ingredient solution  66  under normal atmospheric conditions and then deaerating the macro ingredient solution  66 . Concurrently, the micro ingredient solution  67  is prepared under anoxic condition. The micro ingredient solution  67  is added to the deaerated macro ingredient solution  66 . 
         [0074]    In a further embodiment the micro ingredient solution  67  is added to the deaerated macro ingredient solution  66  at a ratio between 1 part micro ingredient solution  67  to 100 to 400 parts macro ingredient solution  66 . 
         [0075]    In still a further embodiment the micro ingredient solution  67  is added to the deaerated macro ingredient solution  66  at a ratio of 1 part micro ingredient solution  67  to 250 parts macro ingredient solution  66 . 
         [0076]    In an embodiment the media growth solution is directed into the reactor vessel  30  through at least one media input port. 
         [0077]    Preferably, the media growth solution is maintained under a nitrogen blanket. 
         [0078]    In an embodiment the input material stream  24  comprises at least in part carbon dioxide and a percentage of carbon dioxide is converted into cellular biomass during exposure to the culture of methanogenic archea  26  is less than 20 percent. 
         [0079]    In an embodiment the input material stream  24  comprises at least in part carbon dioxide and a percentage of carbon dioxide is converted into biomass during exposure to the culture of methanogenic archea  26  is between approximately 5 and 15 percent inclusive. 
         [0080]    In an embodiment excess or dead biomass is selectively removed from the reactor through at least one biomass elimination port positioned on a lower portion of the reactor vessel  30 . 
         [0081]    In an embodiment the pH adjustment system  60  further comprises a pH buffer agent  61 . The buffer agent  61  may be sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, ammonium, or ammonia nitrate. Preferably the buffer solution is prepared using deaerated water and maintained under nitrogen until introduction into the reactor vessel  30 . 
         [0082]    In at least one embodiment the buffer agent  61  is prepared as approximately a 1.0 Normal solution. 
         [0083]    In another embodiment the pH buffer agent  61  is prepared as less than a 1.0 Normal solution. 
         [0084]    In still a further embodiment, multiple buffer solutions, selected from the list of buffer solutions provided above are available, and a specific buffer solution or combination of buffer solutions are used based at least in part upon the rate of change of the pH within the reactor vessel  30 . If the pH falls out of a predetermined desirable range, typically 7.6 to 8.6, then buffer solution is added to the reactor vessel  30 . 
         [0085]    In an embodiment the input material stream  24  is routed into the reactor vessel  30  at a rate of 0.5 to 4.0 scfm per 5 cubic feet of reactor vessel  30  volume. 
         [0086]    In an embodiment the input material stream  24  is routed into the reactor vessel  30  at a rate of 1.0 to 2.6 scfm per 5 cubic feet of reactor vessel  30  volume. 
         [0087]    In an embodiment the input material stream  24  is routed into the reactor vessel  30  at a rate of approximately 1.9 to 2.6 scfm per 5 cubic feet of reactor vessel  30  volume. 
         [0088]    In an embodiment the input material stream  24  is routed into the reactor vessel  30  and through a sparger  56  positioned within the reactor vessel  30 . 
         [0089]    In an embodiment the sparger  56  creates bubbles approximately 1 micron to 10 microns in diameter. 
         [0090]    In an embodiment the output material stream  72  is generated at a rate of between 10 and 150 volumes per effective reactor volume per day (“VVD”). As an illustrative example only, let us assume that a 1000 cubic foot reactor is used. Further let us assume that there is a headspace within the reactor that occupies approximately 200 cubic feet. Thus the effective reactor volume is 800 cubic feet. If the output material stream  72  for this illustrative example is produced at 100 VVD, then the resulting output would be 80,000 cubic feet, per day. 
         [0091]    In another embodiment the output material stream  72  is generated at a rate of between 35 and 100 VVD. 
         [0092]    In still another embodiment the output material stream  72  is generated at a rate of between 45 and 70 VVD. 
         [0093]    In at least one embodiment, the input material stream  24 , whether directed into the reactor as a blended gas or as individual gas streams, may include approximately four parts hydrogen to one part carbon dioxide. In the methanogenic reaction which follows, approximately 5 to 15% of the carbon dioxide is converted to cellular biomass through contact with the culture of methanogenic archea and the output material stream  72  comprises approximately 60 to 85% CH4. The output material stream  72  may also include hydrogen. 
         [0094]    In another embodiment, the input material stream  24 , whether directed into the reactor as a blended gas stream or as individual gas streams, may include approximately two parts hydrogen to one part carbon dioxide. In the methanogenic reactor which follows, approximately 5 to 15% of the carbon dioxide is converted to cellular biomass through contact with the culture of methanogenic archea  26 , and the output material stream  72  comprises approximately 50 to 85% CH4. The output material stream  72  may also include carbon dioxide. 
         [0095]    In yet another embodiment, the input material stream  24  whether directed into the reactor as a blended gas or as individual gas streams, or as multiple streams at least one of which comprises a combination of gases, may include between approximately two parts hydrogen, approximately five parts hydrogen and approximately one part carbon dioxide. In the methanogenic reaction which follows, approximately 5 to 15% of the carbon dioxide is converted to cellular biomass through contact with the culture of methanogenic archea  26 . And the output material stream  72  comprises approximately 50 to 85% CH4. The output material stream  72  may also include carbon dioxide and/or hydrogen. 
         [0096]    Depending upon the composition of the input material stream  24  provided, it may be desirous to direct the input material stream  24  through a gas filtering means  58  prior to directing the input material stream  24  into the reactor vessel  30 . Several types of gas filtering means  58  are known, and may be selected at least in part based upon the composition of the input material stream  24 . Examples of such gas filtering means  58  include, but are not limited to: Water Gas Shift Reactors, Pressure Swing Adsorption Reactors, Vacuum Swing Adsorption Reactor, and Membrane Filters. 
         [0097]    Similarly, the output material stream  72  may be directed through a gas filtering means  58 , prior to being stored, compressed, or otherwise utilized. The gas filtering means  58  for the output material stream  72  may be any one of a number of gas filtering means  58 , including but not limited to: Water Gas Shift Reactors, Pressure Swing Adsorption Reactors, Vacuum Swing Adsorption Reactors, and Membrane Filters. 
         [0098]    In at least one embodiment the output stream filtering means includes a methane output and a recycling output. The recycling output may be directed back into the reactor vessel  30 . 
         [0099]    The system may also include a thermal conditioning assembly operationally coupled to the reactor vessel  30 , for helping to maintain an internal temperature for the reactor vessel  30  between 55 and 70 degrees Celsius, and more preferably, between 60 and 65 degrees Celsius. 
         [0100]    The system may also include a second culture of methanogenic archea  28  for converting an input material  20 into an output material. This second culture may be inoculated into the reactor vessel  30 , or may be generated within the reactor vessel  30  during a prolonged operational phase for the system. 
         [0101]    The system may also make use of multiple reactor vessels  30 , with the reactor vessels  30  being connected in parallel between the input material stream  24  and output material stream  72 . Each one of the multiple reactor vessels  30  may enclose an associated culture of methanogenic archea  26 . The cultures of the multiple reactors need not necessarily be the same strain or type of methanogenic archea  26 . 
         [0102]    In at least one embodiment the input material stream  24  is directed into the reactor vessel  30  and the output material stream  72  is released from the reactor vessel  30  in a continuous manner. 
         [0103]    In another embodiment the input material stream  24  is directed into the reactor vessel  30  periodically. 
         [0104]    In still another embodiment the output material stream  72  is released from the reactor vessel  30  periodically. 
         [0105]    The agitation system  40  may include an agitation drive means  41 , and an impeller  44  operationally coupled to the agitation drive means  41 . As an illustrative example of an agitation drive means  41  as contemplated by the present invention a motor electrically coupled to a variable frequency drive to control the speed of the motor may be magnetically coupled to an agitation shaft  43  positioned within the reactor. The impeller  44  is thus operationally coupled to the motor. 
         [0106]    In an embodiment the impeller  44  rotates at between 1100 and 2100 rpm during normal operation of the reactor. More preferable the impeller  44  rotates at between 1500 and 1800 rpm during normal operation. 
         [0107]    In another embodiment the impeller  44  rotates at greater than 110% of the resonance of the reactor vessel  30 . 
         [0108]    It is important to note that the tip speed of the impeller  44  is critical and thus proper sizing is important. In at least one embodiment the tip speed of the impeller  44  is between 5 and 45 mph. 
         [0109]    The recirculation system  50  selectively removes a portion of a combination of the culture of methanogenic archea  26  and the growth media through at least one recirculation outlet port  51  of the reactor vessel  30 . The recirculation system  50  returns the portion of the combination into the reactor through at least one recirculation inlet port  52  of the reactor vessel  30 . 
         [0110]    In an embodiment the selective removal and returning of the portion of the combination is done at a rate of between 5 and 50 percent of the reactor volume per hour. 
         [0111]    In another embodiment the selective removal and returning of the portion of the combination is done at a rate of between 10 and 20 percent of the reactor volume per hour. 
         [0112]    In an embodiment the culture of methanogenic archea  26  comprises methanobacterim thermoautotrophicum or methanothermobacter thermautotrophicus. 
         [0113]    With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. 
         [0114]    Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.