Laboratory-, Pilot- and Full-scale Operations of Thermophilic-mesophilic Two-stage System for Anaerobic Digestion of Primary, Secondary Sewage Sludge and Organic Fraction of Municipal Solid Wastes

The thermophilic-mesophilic two-stage anaerobic digestion process has considerable potential for the stabilization of various wastes, especially domestic sewage sludges and municipal solid wastes. This paper summarizes the results from laboratory experiments, pilot-scale and full-scale operations of the thermophilic-mesophilic system for treating primary, secondary sewage sludges, and municipal solid wastes. The collected data of volatile solids destructions and methane productions were analyzed to illustrate the relationships of the system operational parameters, including hydraulic retention time, feed strength and sludge loading rate. In addition, feed sludge characteristics, fecal coliform reduction, odor potential, and other operational problems of the full-scale experiences with this process in the United States were summarized. Odor control, temperature control and feed schedule to ensure sludge disinfection were discussed for designing a thermophilicmesophilic two-stage system. The authors' view of the future development and application of this system was presented at the end.