This study aims to find the most sustainable mature Low-Head (LH) hydropower technology option to generate hydroelectricity at the outlet of wastewater treatment plants by assessing the relevant economic, technical, and environmental criteria. A total of six criteria are assessed: investment cost, payback period, energy generation performance, construction duration, fish-friendliness, and aeration capacity. The fuzzy logic tool estimates satisfaction of each criterion separately and then aggregates them into an Overall Performance Index. The proposed method is applied to an existing wastewater treatment plant (Tatlar WWTP) in Ankara, Turkey. For the assessment, the real-time operational data of the plant and the technical drawings are employed. According to the multi-criteria analysis tool developed in this study to evaluate the LW technologies' the most appropriate hydropower technology for the outlet of Tatlar WWTP is found to be the Archimedean screw, because of its superior environmental and economic performance.