Research advances in dry anaerobic digestion process of solid organic wastes

The dry anaerobic digestion process is an innovative waste-recycling method to treat high-solid-content bio-wastes. This can be done without dilution with water by microbial consortia in an oxygen-free environment to recover potential renewable energy and nutrient-rich fertilizer for sustainable solid waste management. It generally takes place at solid concentrations higher than 10% and enables a higher volumetric organic loading rate, minimal material handling, lower energy requirements for heating, limited environmental consequences and energetically effective performance. The long retention time, poor startup performance, incomplete mixing and the accumulation of volatile fatty acids (VFAs) are considered as the main disadvantages for the solid-state fermentation process. In order to develop feasible dry anaerobic digestion processes, it is important to review the optimization techniques and suggest possible areas where improvements could be made. These include reactor configuration, mixing, solid retention time, feedstocks, organic loading rate, inoculation, co-digestion, pretreatment, percolation, additives and environmental conditions within the digester such as temperature, pH, buffering capacity and VFAs concentration.