Evaluation of kinetic parameters and mass transfer of glucose-fed granules under hypoxic conditions

This study demonstrated that the availability of oxygen influenc the kinetic parameters of sludge granules for the utilization and mass transfer of substrates. Batch experiments revealed that substrate utilization of the coupled sludge granules followed Monod’s kinetic model under hypoxic conditions and at initial substrate concentrations ranging from 1,350 to 4,456 mg/L. The corresponding kinetic coefficients of ks (maximum specific substrate glucose utilization rate), Ks (half saturation coefficient), and Y (growth yield) were 5.6 ∼ 7.8/day, 58 ∼ 64 mg/L, and 0.11 ∼ 0.17 mg of MLSS/mg of COD, respectively. Low dissolved oxygen content suppressed the activity of aerobic enzymes, which resulted in a ks value between those of aerobic granules and anaerobic granules. The maximum oxygen consumption rate (ko = 0.89/day) was relatively higher while the half-saturation constant (Ko = 1.71 mg/L) was significantly lower than those of aerobic granules. These results imply that dissolved oxygen was used more efficiently under hypoxic conditions. Thiele modulus (ϕ) and effectiveness factor (η) analysis revealed that the activity of microorganisms inside the granules was limited by the availability of oxygen. These properties differed from those found in aerobic granules, anaerobic granules, and activated sludge.