Hydrodynamic modeling of clarifiers, as described in the authors’ paper (Vitasovic et al., 1997), has reached a level of sophistication and accuracy where the results are indispensable in clarifier design and evaluation. The authors and writers have long been interested in developing clarifier modeling techniques and using the results to improve clarifier design and performance. The purpose of this discussion is to further the understanding of clarifier model limitations, and to compare the impacts of surface overflow rate and solids loading rate on secondary clarifier effluent suspended solids concentration.