Wastewater management is a significant challenge, especially for arid and semiarid countries due to the water scarcity crisis. Considering human health, environmental regulations, wastewater treatment plant expenses, and water reusability, this study aims to assist in designing an efficient and economical WWTP.Technical and economic simulation and modeling are important for designing, constructing, and predicting the requirements of wastewater treatment plant designs. Simulation of a project before its implementation, in the first place, reduces additional costs, and from another point of view, a project is examined and researched from different aspects. In this study, three wastewater treatment plants based on conventional activated sludge, contact stabilization, and step aeration were simulated and evaluated technically and economically using the Zargandeh treatment plant data in Tehran. In three scenarios, GPS-X software investigated the effect of raw wastewater variations between their minimum and maximum intervals on effluent quality, and because the range of inlet effluent was different, more precise results were obtained. Then, the economic costs of the project, including implementation, maintenance, and also energy use, were calculated by Capdetwork software, and contact stabilization was found to be more cost-effective.