How to Make Methane From Weeds or Grass

For years, scientists have investigated ways to harvest methane gas from digestive byproducts of grass-eating farm animals. Several weed grasses, however, provide raw materials for methane that can be produced in tanks where no dairy cow would ever go. By adding thermochemical pretreatments, biofuel methane production uses anaerobic processes resembling those present in an out-of-control compost pile. Several weed grasses, such as alfalfa, reed canary grass, Bermuda grass and napier grass, make good raw materials, but switchgrass and Miscanthus have proved the richest sources.

50 to 100 acres of switchgrass or Miscanthus
Milling knives or stones
Pressurized hydrolyzer
pH measurement kit
Nitric or sulfuric acid
Digester tank
Starter enzymes
Storage tank

Instructions

- 1
  Harvest switchgrass or other grass stock after it is fully mature to ensure the highest percentage of cellulose, hemicellulose and lignin, the raw materials known as lignocellulose. They provide the sugars and carbon needed for fermentation to create methane, composed of one carbon and four hydrogen atoms. Mill the grass to chop it into fine pieces.
- 2
  Place the milled grass, or biomass, in a steel tank and pressurize with steam up to 460 degrees Fahrenheit for several minutes to begin hydrolysis, the introduction of hydrogen. The higher the moisture content of the biomass, the longer the pretreatment time necessary to make the optimum amount of hemicellulose soluble. Release the pressure and cool the biomass quickly.
- 3
  Measure the pH of the biomass by dipping the litmus paper in the pH kit in the soggy grass. For the grass to ferment properly, the pH should read between 3.0 and 4.0. If the pH is too high, use an acid pretreatment of dilute nitric or sulfuric acid to lower the pH and encourage further hydrolysis.
- 4
  Transfer the cooled biomass to a closed container, called a digester, to ferment. Cool the digester with ice periodically to keep the biomass temperature near 90 degrees Fahrenheit for optimum production. Methanogens, enzymes produced by lignocellulose, work in the acidic environment to produce liquid ethanol and methane gas.
- 5
  Draw finished methane gas out of the tank as it rises out of the biomass through a line on the top of the digester. Store it in tanks for future use.

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