Anaerobic Digestion: Principles, Applications, and Recent Advancements

Due to rapid urbanization and industrialization, a large number of organic wastes are being generated globally, creating serious environmental challenges and the urgent need for effective waste minimization strategies. At the same time, the emerging need for renewable energy has encouraged the development of sustainable resource recovery technologies. Over the last few decades, there has been a growing trend of research interest in the development of effective bioprocesses, which can be used to convert complex waste streams to valuable energy products. Anaerobic digestion (AD) is one of such technologies that has become an established and eco-friendly method of stabilizing waste and bioenergy generation that mitigates the severe environmental and socioeconomic problems. AD is a microbially mediated biological process in which organic substrates are broken down in the absence of oxygen to produce biogas, primarily methane (CH₄) and carbon dioxide (CO₂), along with nutrient-rich digestate. It is an efficient process and reduces waste with benefits including increased energy security and reduced greenhouse gas emissions, and hence it plays an important role in the circular bioeconomy. This chapter discusses the basic concepts of AD and its application in waste treatment, production of renewable energy, and nutrient recovery. It also highlights recent progress, including feedstock pretreatment, high-rate reactor design options such as direct interspecies electron transfer (DIET), biochar amendment, and AI-driven digitalization. The implementation of AD technology will demand a collective input of scientists from various domains to realize expeditious growth.