Biogas
Anaerobic digestion is much used to make biogas from biodegradable waste because valuable fuel can be produced while destroying disease-causing pathogens and reducing the volume of disposed waste products.  The methane in bio gas burns more cleanly than coal, and produces more energy with less emissions of carbon dioxide.  The harvesting of bio gas is an important role of waste management because methane is a greenhouse gas with a greater global warming potential than carbon dioxide.  The carbon in bio gas was generally recently extracted from the atmosphere by photosynthetic plants, so releasing it back into the atmosphere adds less total atmospheric carbon than the burning of fossil fuels.