Anaerobic digestion of animal waste in biogas plants for energy, manure and sanitation has made a significant impact in quality of rural life wherever it has been deployed. Insufficiency of animal dung resources limits the use of this technology to only an eighth of the overall Indian rural population. Yet the convenience of a biogas plant in rural households has led R&D efforts to extend the use of biogas plants to other nonanimal dung biomass feedstock and rural residues.Fermenting typical biomass residues in conventional slurry-based biogas plants has been far from successful. Most attempts to convert rural biomass residues into ‘flowable’ slurries like animal dung have rarely been successful. Alternative concepts were required. Achieving successful quasi-continuous fermentation of biomass residues has come through a break away from the ‘slurry’ fixation and animal dung digester designs of the past. A better understanding of the underlying processes has greatly helped evolve new fermentation concepts. Success has emerged only through use of multi-stage processes, where key fermentation properties of biomass feedstock have been acknowledged and digesters designed accordingly. Here, a 25-year effort in understanding the processes of biogas and biomass fermentation, developing new techniques and technologies to ferment biomass feedstock and efforts at simplifying the technology to enable sustainability carried out at the Centre for Sustainable Technologies, IISc, Bangalore is described. Finally, integration of the two or three fermentation steps into a single reactor configuration has enabled evolving simple-to-use digester designs for biomass feedstock, namely the plugflow and the solid-state stratified bed digesters
