The activated sludge treatment system for treating municipal wastewater presents an interesting application of system dynamics modeling.  This paper presents such a modeling approach to the strategy formulation of the treatment system in order to economically control effluent quality.  First, factorial designs are carried out on the simulation results to identify factors that significantly affect effluent quality.  Thereafter, open-loop control (both constant and time-varying), output feedback control, and output-integrated feedback control strategies have been applied.  Statistical tests of significance indicate that the strategy of output feedback control has the maximum potential, in both summer and winter, to achieve the dual objectives of maintaining effluent quality within acceptable limits and minimizing aerator energy.