The supernatant resulting from the anaerobic digestion of the sludge generated by a sewage treatment plant (STP) is a small flow in terms of volume but very relevant in terms of N and P loads. Its characteristics make it particularly suitable for technologies such as partial nitritation-anammox (CANON), nitrite shortcut (NSC) and struvite crystallization processes (SCP), and removing nutrients under more favourable conditions than in the main water line. The potential environmental implications of those technologies were assessed using Life Cycle Assessment, both at pilot plant scale and thereafter, integrated in a modelled full STP. Pilot-plant results considered biological N removal technologies as more efficient in environmental terms, distantly followed by SCP. Full-scale modelling, however, highlighted that the differences between technologies were not so relevant once they are integrated in a STP. The addition of these technologies reduced slightly the impacts of the STP in all categories, except for eutrophication, where a substantial reduction was achieved using NSC, SCP and, especially, if CANON and SCP were combined. This study emphasises the need for assessing sewage treatment technologies as part of a WWTP rather than as individual processes and the utility of modelling tools for doing so.