SHAKEN OR STIRRED: DIGESTER MIXING DESIGN AND OPERATION SUCCESS STORIES

Proper digester mixing benefits digester process operation by providing effective utilization of the digester volume and a healthy digestion environment. A healthy digester promotes higher levels of volatile solids destruction, reducing the volume of solids for disposal and increasing production of digester gas that can be burned as fuel to heat the digesters or produce electricity. Reducing solids deposition also lowers maintenance costs by increasing time between digester cleaning and decreasing the amount of solids to be removed. Review of Digester Mixing Technologies This paper discusses various digester mixing technologies, design factors for implementing mixing systems including energy usage, safety and operation and maintenance considerations. Case Histories This paper presents case histories of several digester mixing designs and upgrades that have been in operation within the last decade. Digester mixing technologies discussed in this paper include both mechanical and gas mixing systems. Case histories covered describe engineering solutions to increase mixing efficiency, increase digester volume, and application of an innovative dynamic mixing system