An optimization based framework for design and retrofit of municipal wastewater treatment plants: Case study on side-stream nitrogen removal technologies

Existing WWTPs need retrofitting due to several d iffe rent reasons such as: change in the wastewater flow and co mposition, change in the effluent limitat ions , as well as changes in the wastewater treatment trends. Specifically, increased nitrogen limitations in the regulations for the WWTP effluents gave rise to development of innovative nitrogen removal technologies mostly used for water strea ms resulting fro m sludge t reatment. In this study we propose a superstructure optimization concept based on mathematica l progra mming to manage the multi - criteria WWTP design /retrofit problem and generate novel and optimal network designs for domestic WWTPs. Alternative treatment te chnologies are represented in a superstructure; each of which is described by a generic model in ter ms of input - output mass balance . The superstructure is coupled with a database containing data for both performance and economics of the alternative technol ogies. The superstructure optimization proble m is formu lated as a Mixed Integer (Non)Linear Progra mming problem and solved in GAMS fo r diffe rent scenarios represented by different objective functions and constraint definitions. Finally, a case study is for mulated to perform a retrofit study addressing the nitrogen removal problem in order to highlight the use of the framework.