Optimal design of municipal wastewater collection networks with long-term performance improvement approach

The purpose of this study is optimal performance based design of municipal wastewater collection networks. Sewer deterioration decreases system performance over time and investigations have shown that diameter, slope, structural condition, length and burial depth are effective factors in hydraulic and structural deterioration. In this research first these factors were used to develop performance indicators based on velocity, depth of flow, burial depth, pipe slope and pipe length. Then, using the Non-dominated Sorting Genetic Algorithm II (NSGA-II) and pipe diameter as decision variable, the optimal design of a case study was performed under different combinations of performance indicators. Part of Kerman's wastewater collection network which includes 20 manholes and 20 pipes and one outlet is considered as case study. The results showed that the pareto points in different combination of factors influencing the overall performance, are very similar and in all scenarios, the designs tend to increase the slope of the pipe, decrease the diameter and increase the depth of burial. It was observed that the performance of the network can be improved about 2 percent in case study and almost without imposing additional costs on the basic design.