Energy recovery occurs when the energy that is released from a resource recovery process (i.e., pyrolysis/gasification) is used for another purpose such as to generate steam, fuel or electricity generation. This book examines the energy recovery technologies which use landfill gas to produce energy directly. An overview of a variety of secondary sludge post treatment methods for energy recovery is given, including incineration, gasification, pyrolysis, direct liquefaction, supercritical water oxidation (SCWO) and anaerobic digestion. The several routes that energy recovery can follow from waste are looked at as well, of which the most common is waste direct combustion associated with conventional energy recovery in a steam turbine cycle. Energy recovery in air conditioning systems to promote energy saving and improve environmental quality is also explored in this book.