3. The System Dynamics model for activated-sludge wastewater treatment plants
In this paper the activated-sludge wastewater treatment process have been modeled as Fig. 1 using a System
Dynamics modeling software, STELLA, based on the model by Das et al. (1997). The model in this paper was
applied to a case study activated-sludge wastewater treatment plant in South Korea in an attempt to determine the
operating rules and policies related to capacity expansion of the treatment plant. The simulations were conducted
for the existing conditions and the anticipated facilities expansion scenarios of a case study treatment plant.
3.1. Analysis of effluent water quality due to changes in activated-sludge return rate
Substrate concentration in aeration tank (SCAT) was considered as the effluent water quality for which the
standard was set as BOD 0.02 kg/m3. For existing conditions, the analyses were performed by varying activatedsludge
return rate from 10% to 100% to observe changes in the effluent water quality and treatment efficiency.
Table 1 shows the simulated effluent water quality due to changes in activated-sludge return rate.