A growing number of new technologies are now being considered worldwide to address municipal solid waste (MSW).  Most require some pre-processing to reduce the size of the MSW feedstock.  These technologies have been employed to address MSW in Europe, Japan and other countries, but none currently are operating on a commercial scale in the United States. The technologies that appear to be of significant interest are:

• Anaerobic Digestion.  Anaerobic digestion occurs when bacteria break down (or "digest") organic materials in the absence of oxygen. This biological process produces a gas, sometimes called biogas, which is principally composed of methane and carbon dioxide. This gas is produced from feedstocks such as sewage sludge, livestock manure, and wet organic materials (including MSW), and can be used to generate energy.   Anaerobic digestion involves putting organic materials, along with various types of bacteria, in an airtight container called a "digester" where the process occurs. Depending on the waste feedstock and the system design, 55 percent to 75 percent of biogas is typically methane.   The solids remaining after the digestion process can be used as compost, although when MSW is used as a feedstock a small percentage of non-organic residuals will still require disposal.  Anaerobic digestion facilities using MSW feedstock currently operate in several European countries and in Israel.
  
  
• Gasification. This is a chemical process that converts carbon-containing material, such as coal, petroleum coke, or MSW into a synthesis gas that can be used for energy production or as a building block for other chemical manufacturing process.  Gasifiers operate at high temperatures (1,400 to 2,500 degrees Fahrenheit) and pressure in an oxygen limited environment. The synthesis gas produced by this process is comprised primarily of carbon monoxide and hydrogen.  This gas can be burned to create electricity or steam or converted into usable products such as hydrogen, ammonia, and other chemicals. Inorganic materials (e.g., metals) are converted to either bottom ash or to a solid, vitreous (glass-like) slag.  Gasification also can produce a concentrated carbon dioxide stream that may have a significant role in carbon sequestration in the future.  Gasification projects using MSW currently operate in several countries, including Japan and Malaysia.  These projects can gasify more than 90 percent of the MSW they accept, leaving 10 percent that must be disposed of.
  
  
• Pyrolosis.  This process involves the thermal decomposition of organic materials into gases, oils and char.  Pyrolysis typically occurs at temperatures in the range of 650 to 1,500 degrees Fahrenheit.  Higher temperatures produce mainly gaseous byproducts, and lower temperatures produce more liquid pyrolysis oils.  In addition to energy production from the resultant gases and oils, ferrous metals contained in the solid residue (i.e. char) can be captured for reuse.  Pyrolosis demonstration projects using MSW feedstock currently are underway in Canada and the U.S. (California).  Pyrolosis is anticipated to use more than 90 percent of the MSW accepted, leaving 10 percent that must be disposed of.