Flow pattern analysis of a full-scale expanded granular sludge bed-type reactor under different organic loading rates

The hydraulic characteristics of a lab-scale and a full-scale (275 m3) expanded granular sludge bed (EGSB)-type reactor under different organic loading rates varying from 10 kg COD m−3 d−1 to 45 kg COD m−3 d−1 were investigated. A modified combined model composed of two completely mixing regions and a plug flow region was sufficient for simulating the flow pattern of a full-scale EGSB-type reactor. Moreover, the outputs fitted the measured tracer distribution results well. The simplified model structure was in very good agreement with the physical structure of a full-scale EGSB-type reactor. The upflow (liquid + gas) velocity, high concentration of granular sludge, and gas hold-up effect may contribute to the generation of dead spaces (maximum of 19.5%). The bed expansion characteristics indicated that the sludge bed of the EGSB-type reactor performed as a suspended bed, in which the bed expansion was controlled between 20% and 30%, rather than the usually considered expanded bed.