Methane is generally produced by methanogens, a group of over 50 different microorganisms belonging to Euryarchaeota. These microorganisms produce methane by the reduction of either CO2 or acetate, while some have the ability to use methylated compounds such as methanol and methylamine for methane production. Biomethane produced from waste from biodiesel and other biofuel plants can be used to generate energy for their operation. This may dramatically reduce the dependence of the biofuel plant on external energy inputs such as natural gas and coal. However, direct utilization of crude glycerol streams by microbes is not efficient because of high salt levels associated with biodiesel waste streams (glycerol). This problem may be overcome either by diluting the waste stream or by mixing it with other waste streams. Theoretically, 0.43 L methane is produced for every gram of pure glycerol. This yield will obviously go down as the glycerol content of the waste stream decreases. When crude glycerol from swine manure (1.2 g glycerol/g swine manure) was used as the sole carbon source, methane was produced at a yield of 232mL/g glycerol. However, when the glycerol/swine manure ratio was 4.6 or higher, the methane production was negligible, indicating that high glycerol levels are toxic to methanogens mainly due to high salt and methanol levels (Khanal 2008).