Solid waste digestors: process performance and practice for municipal solid waste digestion

The most common types of anaerobic digesters for solid wastes have been com pared based on biological and technical performance and reliability. Batch systems have the most simple designs and are the least expensive solid wast e digesters. They have high potential for application in developing countri es. Two-stage systems are the most complex and most expensive systems. Thei r greatest advantage lies in the equalisation of the organic loading rate i n the first stage, allowing a more constant feeding rate of the methanogeni c second stage. Two-stage systems with biomass accumulation devices in the second stage display a larger resistance toward toxicants and inhibiting su bstances such as ammonia. However, the large majority of industrial applica tions use one-stage systems and these are evenly split between "dry" system s (wastes are digested as received) and "wet" systems (wastes are slurried to about 12% total solids). Regarding biological performance, this study co mpares the different digester systems in terms of organic loading rates and biogas yields considering differences in input waste composition. As a who le, "dry" designs have proven reliable due to their higher biomass concentr ation, controlled feeding and spatial niches. Moreover, from a technical vi ewpoint the "dry" systems are more robust and flexible than "wet" systems.