Multiobjective Optimization in Sewer Network Design to Improve Wastewater Quality

Sewers that constitute the main part of wastewater systems can be used as pretreatment units of wastewater treatment plants. The authors aim to increase the treatment efficiency of sewers by optimization. A hydraulic model is written and validated. A quality calculation section is added to the model according to the Wastewater Aerobic/Anaerobic Transformations in Sewers (WATS) method, and it is calibrated and verified using the data of a real wastewater transition line. An optimization engine is coupled to the proposed model. The new model can simulate the hydraulic and quality parameters of a sewer network and optimize it. Six objective functions and a general one with their decision variables were assessed. A predesigned wastewater collection network was used for the optimization of five scenarios. The results can be used to identify optimization priorities at the network design stage. Results showed that an increase in the removal of organic matter within the sewer can be achieved, but its other performance indices may worsen. Prioritization of objectives according to stakeholder views is required.