Ten biomass samples from both municipal and industrial pilot and full scale submerged
membrane bioreactors (MBRs) with mixed liquor suspended solids concentrations (MLSS)
ranging from 7.2 to 30.2 g L1 were studied at six air-flow rates (0.7, 1.3, 2.3, 3, 4.4 and
6m3m3h1). Statistical analyses were applied to identify the relative impacts of the
various bulk biomass characteristics on oxygen transfer. Of the biomass characteristics
studied, only solids concentration (correlated with viscosity), the carbohydrate fraction of
the EPS (EPSc) and the chemical oxygen demand (COD) concentration of the SMP (SMPCOD)
were found to affect the oxygen transfer parameters kLa20 (the oxygen transfer coefficient)
and a-factor. The relative influence on kLa20 was MLSS4aeration4EPSc4SMPCOD and on
a-factor was MLSS4SMPCOD4EPSc4aeration. Both kLa20 and a-factor increased with
increasing aeration and EPSc and decreased with increasing MLSS and SMPCOD. MLSS was
found to be the main parameter controlling the oxygen transfer.