This study proposed a novel practical framework to assess the reliability and resilience of a wastewater treatment plant (WWTP). Such assessment is further extended to enhance the system performance with various scenarios based on fault tree analysis (FTA). Coefficient of reliability (COR) and performance curves of the resilience assessment are determined with respect to discharge standards. The effluent parameter violating the environmental standards is determined, and the causes are traced using an FTA. Monte Carlo simulations (MCs) are performed to validate the FTA results, and a sensitivity analysis is conducted to determine the dominant events that contribute to the failure of the top event. Finally, four operational scenarios are compared by taking into account the social, economic, and environmental costs. The results showed that total nitrogen (TN) concentration exceeded the threshold in the case study. Similar reliability values were obtained by the minimum cut set (21 %) and MCs (17 %) for the TN violations. Thus, four enhanced TN removal reliability scenarios were proposed considering significant impacts of dissolved oxygen, water quality, and hydraulic retention time on the TN removal. Employing supplementary chemicals integrated with scenario 3 was the optimal alternative to operate the WWTP with an econo-socio-environmental cost of 322,600 $/yr. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.