Multi-objectiveperformance assessment of operational strategies at wastewater treatment plants(WWTPs) is a challenging task. The holistic perspective applied to evaluationof modern WWTPs, including not only effluent quality but also, resourceefficiency and recovery, global environmental impact and operational cost callsfor assessment methods including both on and off-site effects. In this study amethod combining dynamic process models – including greenhouse gas (GHG)emissions and detailed energy models – and life cycle assessment was developed.The method is applied and calibrated to a large Swedish WWTP. In a performanceassessment study changing the operational strategy to chemically enhanced primarytreatment was performed and evaluated. The results show that the primaryobjectives, to enhance bio-methane production and reduce greenhouse gasemissions were reached. Bio-methane production increased by 14% and the globalwarming potential (GWP) decreased by 28%. However, the LCA revealed that due toincreased consumption of precipitation chemicals and additional carbon sourcedosing (methanol) the abiotic depletion of elements and fossil re-sourcesincreased by 77 and 305%, respectively. The results emphasise the importance ofusing plant-wide mechanistic models and life cycle analysis to capture thedynamics of the plant – e.g. dynamics of GHG emissions – and the potentialglobal environmental impact.