Anaerobic Digestion for Bioenergy from Agro- Residues and Other Solid Wastes—An Overview of Science, Technology and Sustainability

Abstract

In the quest for a simple technology to realize the goal of ‘sustainable energy for all’, the conversion of non-lignified ‘soft’ non-woody biomass to biogas in modern anaerobic digesters is an important component. Firstly, agro-residues, agro-industrial wastes, terrestrial/aquatic weeds form a major source of sustainably raised bio-resources. Anaerobically converting them to biogas provides a sustainable energy source to a large number of users and simultaneously facilitates nutrient recycling (nutrient-rich compost) permitting nutrient-starved agricultural systems in India to become more sustainable. When processed through biogas plants, over 95% of all plant nutrients within can be recycled making India’s fragile agricultural soils more sustainable while also producing an energy source, biogas. While a lot of science and technology experience exists with regards to animal waste fed biogas plants, understanding of the underlying science, technology and sustainability of anaerobic digestion of agro-residues, weeds and leaf litter (‘non-dung’ soft biomass) for biogas/byproducts is poor. This potential has been inadequately tapped. In this paper, an attempt is made to review the microbiology of anaerobic digestion of various biomass residues, the conversion processes that are being developed/in use and finally to examine methods to make them attractive, provide multiple outputs and services than what was possible through animal dung biogas plants. The micro-organisms responsible, physico-chemical environment process and therefore the technology of digestion of biomass residues are not similar or as simple as that found for animal dung or food wastes. Therefore, novel fermentation concepts and modern digesters being developed for biomass residues are required to make this concept feasible and viable. Many more end-products,  other than compost and biogas, as was done in the past, are required if the digesters have to be economically attractive to use and socially justifiable as well as sustainable in the long run. The sustainability issues that have and will shape this field are discussed. In this paper we show that simultaneous anaerobic digestion of biomass residues to biogas and multiple by-products could be an answer to the search for alternatives to achieve sustainable energy for all in this decade.