A mathematical programming framework for early stage design of wastewater treatment plants

• A mathematical programming based approach for municipal WWTP design is proposed.
• A superstructure based optimization framework is developed for WWT process selection.
• A generic process interval model was developed to represent the treatment alternatives.
• The application of the framework was tested on a carbon/nitrogen removal case study.
• The case study problem was solved for several economic objective functions.

The increasing number of alternative wastewater treatment technologies and stricter effluent requirements make the optimal treatment process selection for wastewater treatment plant design a complicated problem. This task, defined as wastewater treatment process synthesis, is currently based on expert decisions and previous experiences. This paper proposes a new approach based on mathematical programming to manage the complexity of the problem. The approach generates/identifies novel and optimal wastewater treatment process selection, and the interconnection between unit operations to create a process flow diagram. Towards this end, a superstructure approach is used to represent the treatment alternatives for reaction and separation. A generic process interval model is used to describe each alternative in terms of input–output mass balances including conversion and separation factors. Next the design problem is formulated as a Mixed Integer (Non)linear Programming problem – MI(N)LP – and solved. A case study is formulated and solved to highlight the application of the framework.