Design of future municipal wastewater treatment plants: A mathematical approach to manage complexity and identify optimal solutions

The increasing number of alternative wastewater treatment (WWT) technologies and stricter effluent requirements imposed by regulations make the early stage decision making for WWTP layout design, which is currently based on expert decisions and previous experiences, much harder. This paper therefore proposes a new approach based on mathematical programming to manage the complexity of the problem and generate/identify novel and optimal WWTP layouts for
municipal/domestic wastewater treatment. Towards this end, after developing a database consisting of primary, secondary and tertiary WWT technologies to build a superstructure, the design problem was formulated as a Mixed Integer Nonlinear Programming problem (MINLP). The tool generates many process alternatives and evaluates them with respect to their optimality. The objective function minimizes the operation cost. The design problem is thus solved to obtain the optimal WWT network and the optimal wastewater and sludge flow through the network. The tool is evaluated on a case study, which was chosen as the Benchmark Simulation Model no.1 (BSM1) and many retrofitting options for obtaining a cost-effective treatment were investigated with the help of the tool. The resulting solutions to the optimization problem are discussed in detail.