Statistically Based Design of Wastewater Treatment Plants (WWTPs) Using Monte Carlo Simulation of Activated Sludge Model No. 1 (ASM1)

To deal with uncertainties in wastewater treatment plants (WWTPs), high safety factors are commonly adopted in the traditional plant design procedure, which may lead to an over-designed plant. In this paper, the Monte Carlo method is applied in both steady-state and dynamic simulations of the activated sludge model No.1 (ASM1) to quantify the uncertainty of the plant performance. Statistical analysis of the plant effluent indicates that it has a wider distribution, which demonstrates the motivation for using conservative design assumptions in the first place. However, we suggest that a better design approach is proposed based on an acceptable risk of effluent violations. To support this design approach, we will present methodologies for estimating the frequency of occurrence effluent violation based on 7-day and 30-day average effluent permit levels. Armed with this type of information, engineers, regulators and the community can more realistically evaluate the trade-off between risk and cost.