Mixing Efficiencies in Full-Scale Anaerobic Digesters by Tracer Methods

Abstract

Abstract Tracer analyses of the full-scale anaerobic digestion processes as two water pollution control plants revealed that nonideal mixing conditions existed. In both systems, 75% of the total volume of the gas-mixed primary digesters was inactive, significantly reducing the effective hydraulic retention time in one system to approximately 5 days compared to the theoretical mean of 22 days. In the other primary digester, short-circuiting around the actively mixed zone accounted for 61% of the input flow. The fundamental objectives of digestion cannot be realized under these operating conditions. The results prove that greater attention must be given to reactor mixing in the design and operation of anaerobic digesters.