NGVs and Biomethane

Almost a quarter of America’s primary energy consumption is natural gas, and natural gas is primarily composed of methane.  Biogas is a product of the decomposition of organic materials, such as animal or crop wastes.  Biogas composition is typically about 60 percent methane and 30 percent carbon dioxide, with the remaining 10 percent dominated by nitrogen and water vapor.  Biogas can be processed to remove most of these non-methane components, and produce pipeline quality (or better) biomethane.

Biogas is produced at landfills, sewage waste treatment plants, feedlots, and any other place where there is decaying organic material.  The biogas resulting from these activities can be released to the atmosphere, collected and flared, or collected and used as a fuel.  Unfortunately, atmospheric release and flaring are the most common methods of dealing with biogas today.  A 1998 U.S. Department of Energy study estimated that, worldwide, between 25 and 37 quadrillion btus of methane each year is released into the atmosphere (beyond the methane currently captured) due to natural decomposition of organic material.  This is equivalent to between 25 and 38 percent of all of the energy used in the U.S. each year.  Much of the naturally occurring renewable methane is produced in small quantities from disparate sources (e.g., swamp gas), and, therefore, is difficult and expensive to capture.   Fortunately, much of the biogas generated from human activity is produced in larger quantities in discrete locations, where it can be captured.  In the U.S., the DOE study referenced above estimated that the potential biogas production from farm waste, landfills and municipal sewage alone is approximately 3.5 quadrillion btus of methane.  Of that amount, the study estimated that it would be feasible to capture and use over a third of this methane (or about 1.25 quadrillion btus).  This is equivalent to:

• 6 percent of all the natural gas used in the U.S., or
• 25 percent of all the diesel fuel used by all the buses and freight trucks in the U.S.

Landfills
Landfills generate a substantial amount of methane through the anaerobic (oxygen-free) degradation process that occurs naturally within the landfills themselves.  The methane can be a safety hazard if not “drained” properly.  According to the U.S. EPA, there are 380 landfill gas projects in place today.  The U.S. EPA estimates that there are 600-700 additional landfill gas-to-energy projects that could be constructed nationwide. 

Animal Waste
The processing of waste from domesticated animal operations (such as dairies, and pork and poultry production) is an expensive process that presents significant environmental challenges. With the proper financial encouragement, farmers and other operators of these animal facilities could install anaerobic digester systems to convert the waste to usable methane -- with valuable, sanitary fertilizer as a byproduct.  Companies that must cope with large quantities of animal waste can become significant producers of methane through the use of anaerobic digesters.  For example, Smithfield Bioenergy today is producing biogas with a substantial methane component at a Smithfield Foods hog farm in Utah.  That Smithfield facility shows that hog farms and similar operations can be a viable source of methane that can reduce our dependence on imports if the process can be made economically viable.

Sewage
The amount of human sewage that must be processed continues to grow with the population.  The economic costs are large, and the environmental costs are significant.  As with animal waste, sewage can be converted to methane via anaerobic digesters.  In Malmo, Sweden, for example, the city runs part of its fleet of transit buses on methane produced at its local sewage treatment plant

Biomass
While not a major source of fugitive methane, recoverable biomass – including crop waste, plants (such as switch grass) grown especially for energy production and other organic matter – also can be used as a feedstock for the production of methane.  Recent studies have shown that it is more economic and energy efficient to produce biomethane from these sources than to produce liquid fuels such as ethanol