Wastewater treatment systems are essential for the safety of people and the wellness of the environment. Climate change has caused significant changes in precipitation patterns, surface temperatures, snowmelt and run-off events that also change wastewater characteristics. These changes can affect the physical, chemical, and biological processes in wastewater treatment plants (WWTPs) and wastewater treatment performance. This study focused on the impact of variation in wastewater temperature and influent flow on selected biological carbon and nutrient removal systems including conventional activated sludge (AS), Ludzack-Ettinger, modified Ludzack Ettinger (MLE), Phoredox, anaerobic/anoxic/aerobic (A2O), and Modified Bardenpho using a WWTP modelling software. For each treatment process, a wide range of wastewater temperatures and SRT values were assessed and removal efficiencies of total COD, cBOD, total suspended solids (TSS), total ammonia and, total phosphorous were evaluated. The results of this study deliver critical parameters to optimize the WWTPs under the impact of climate change.