Waste-to-Energy (WtE) technologies consist of any waste treatment process that creates energy in the form of electricity or heat from several types of waste: from the semi-solid (e.g. thickened sludge from effluent treatment plants) to liquid (e.g. domestic sewage) waste. The current most known WtE technologies are: Incineration: Direct combustion of municipal solid waste (MSW) and/or refuse-derived fuel between 750 and 1100ºC in the presence of oxygen that produces steam for electricity and/or heat generation in a boiler or steam turbine. It can generate heat or electricity, or combined heat and power. Gasification: Partial oxidation of waste (e.g. wood waste, agricultural residues, sewage sludge, and plastic waste) between 800 and 1200ºC in the presence of a controlled amount of oxygen that produces synthetic gas for further combustion or conversion to chemical feedstock. Pyrolysis: Thermal degradation of waste (e.g. wood waste, agricultural residues, sewage sludge, and plastic waste) between 300 and 1300ºC in the absence of oxygen that produces liquid fuel for further combustion or conversion to chemical feedstock. Anaerobic digestion: Biodegradation of (readily degradable) organic wastes in the absence of oxygen by anaerobic microorganisms. Waste input can be separated organic fraction of MSW, food waste, animal/human excreta, or liquids and sludges. The digestion produces biogas and digestate. Biogas can be used as fuel for power generator. Digestate can be composted for use as a soil conditioner or dewatered and used as a low calorific value refuse-derived fuel.