The effects of dissolved oxygen concentration on the kinetics and settleability of activated sludge

The objective of this research was to determine whether or not variations in dissolved oxygen concentration above the critical dissolved oxygen concentration affect the kinetic coefficient and settleability of activated sludge. Synthetic substrate loadings of 0.25, 0.50, 0.75 were applied to bench scale activated sludge reactors with average mixed liquor volatile suspended solids concentrations of 2000 mg/1. The substrate removal rate coefficient, oxygen uptake coefficients, yield coefficients, and sludge settling properties were evaluated at dissolved oxygen concentrations of 2, 4, 8, and 10 mg/l.

The kinetic coefficients were different at each dissolved oxygen concentration investigated but the differences could not be correlated with dissolved oxygen concentration variations. Instead, the variations in the coefficients appeared to be distributed in a random manner due to inaccurate test methods and fluctuating environmental conditions. Sludge settling properties as measured by the sludge volume index and the initial settling velocity were independent of dissolved oxygen concentration.

The results of the study indicated dissolved oxygen concentration has no noticeable effect upon the kinetic coefficients and sludge settleability in activated sludge systems operated at loading levels and solids concentrations similar to the ones employed in this study.