At present the wastewater is discharged at Ringsend, in the southern part of Dublin's Docklands.
The Sandymount and Merrion Residents' Association argues that the new pipeline would discharge effluent into the newly designated marine conservation area between Rockabill and Dalkey Island.
The High Court's approval of residents' challenge to the granting of planning permission for the development was appealed by the State and Dublin City Council, but that appeal was rejected by the Surpreme Court today (10 October).
A similar sewage scheme in North Co Dublin has also faced objections from residents throughout the Fingal area.
RTÉ News has more on the story HERE.