A dynamic capacitated facility location and network design problem with capacity expansion for wastewater treatment networks

In our rapidly changing world, especially the increase in population and industrialization activities results in significant increases in wastewater production, which leads to the problem of treatment of the wastewater produced. Therefore, developing effective wastewater treatment networks continues to be vital to ensure environmental sustainability. In this context, wastewater treatment facilities must be located in the most appropriate places to make the best use of limited resources and the network required for wastewater transportation should be designed to meet future needs with the least cost. Although the facility location and network design problems in the literature are related to this issue, they do not cover some specific constraints for wastewater transport and often have a static structure in which time is not taken into consideration. In this thesis, firstly, a dynamic mixed-integer linear programming model for wastewater treatment facility location selection and network design is proposed in which facilities and links are assumed to be capacitated. Later on, a more complicated model which allows the facilities to be expanded in case of need according to time-dependent demand is proposed and defined on a three-dimensional space. Several test experiments are conducted for the proposed models and they are solved with Python modeling library for optimization DOcplex and CPLEX version of 20.1. Moreover, extreme test instances are generated and their results are observed to verify the proposed models.