Energy Recovery from Anaerobic Digestion of Wastewater

Abstract

Anaerobic digestion is an established technology for the treatment of wastewater and its sludge and has been used by humans for centuries. Anaerobic digestion is considered to be a useful tool that can generate renewable energy, and significant research interest has arisen recently. The final product of the anaerobic digestion is biogas: a mixture of methane (55–75 vol%) and carbon dioxide (25–45 vol%) that can be used for heating, upgrading to natural gas quality or cogeneration of electricity and heat. Digestion installations are technologically simple with low energy and space requirements. Anaerobic treatment systems are divided into ‘high-rate’ systems involving biomass retention and ‘low-rate’ systems without biomass retention. High-rate systems are characterized by a relatively short hydraulic retention time but long sludge retention time and can be used to treat many types of wastewater and the sludge. Low-rate systems are generally used to digest slurries and are characterized by a long hydraulic retention time, equal to the sludge retention time. The biogas yield varies with the type and concentration of the feedstock and process conditions. The aim of the chapter is to discuss the basic principles of the anaerobic process, the affecting factors, advantages and disadvantages, various treatment methods and energy recovery in the form of biogas. The energy recovery from the anaerobic digestion would open the doors in the conservation of energy resources and also a sustainable method for management of wastewater and its sludge.