Biomass is waste material from plants or animals that is not used for food or feed; it can be waste from farming (like wheat stalks) or horticulture (yard waste), food processing (like corn cobs), animal farming (manure rich in nitrogen and phosphorus), or human waste from sewage plants. It is used in various industrial processes, like energy production or as raw materials for manufacturing chemicals.Burning biomass releases carbon emissions, but has been classed as a renewable energy source in the EU and UN legal frameworks, because plant stocks can be replaced with new growth. It has become popular among coal power stations, which switch from coal to biomass in order to convert to renewable energy generation without wasting existing generating plant and infrastructure. Biomass most often refers to an energy source; biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into: thermal, chemical, and biochemical. Some chemical constituents of plant biomass include lignins, cellulose, and hemicellulose.