Urban wastewater management systems play a pivotal role in safeguarding public health, environmental quality, and sustainable development. Applying multi-criteria decision-making (MCDM) methods in the prioritization of sewer network design alternatives enables the decision-making process to be carried out accurately among a set of potential options. In this study, the criteria weights were determined using the Analytic Hierarchy Process (AHP) based on their mutual interactions, reflecting both natural behavior and human reasoning. The prioritization of the alternatives within the study area was performed using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). The criteria considered for selecting the optimal alternative included technical, socio-economic, environmental, and managerial aspects. Specifically, eight sub-criteria for the technical aspect, four for the socio-economic aspect, three for the environmental aspect, and four for the managerial aspect were evaluated.

Due to significant elevation differences within the study area, the sewer network was designed based on three main zones: Shahriarkala, Alasht, and Galian. From a variety of potential options, four alternatives were selected for the design of Alasht’s sewer collection network. The analysis of sub-criteria indicated that the number of pumping manholes, the length of the pressurized pipeline, the potential for treatment plant expansion, the number of lift stations, implementation and operation costs, and access to equipment, respectively, had the highest weights compared to other sub-criteria. The prioritization results revealed that Alternative 1 received the highest score (0.6925), followed by Alternative 3, Alternative 2, and Alternative 4, in descending order of preference