Construction of the sea outfall of the Sa Coma wastewater treatment plant.

The project

The Sa Coma wastewater treatment plant (WWTP) is the main wastewater treatment facility in the town of Sant Llorenç des Cardassar. This plant offers excellent results in water purification and part of the treated water is reused for irrigation and other uses. However, a significant part of the effluent cannot be reused and until now has been discharged through seepage pits.

However, this management system caused water spillage on the adjacent land and a negative impact on the aquifer through salinisation. These problems have made the search for a more sustainable and safer alternative a necessity. After analysing different discharge alternatives, it was concluded that the most responsible option was the construction of a sea outfall.

The planned outfall is a pipeline that will run for the first 735 metres buried under the seabed and then continue on the seabed, stabilised with concrete ballast to resist sea currents and storms. The final section, outside the Posidonia meadow, will have a diffuser system with 12 outlets to dilute the treated water with seawater. This will enable the quality parameters of the discharged water to be lower than those of drinking water, ensuring minimal impact on the marine environment.

Moreover, anti-trawl protection blocks will be placed around the pipeline to prevent damage from illegal trawling, which is prohibited at depths of less than 50 metres. These protection measures will help to preserve the Posidonia meadow, a keystone species for the marine ecosystem.

A monitoring and control plan has also been designed to monitor the evolution of the receiving marine environment throughout the life of the outfall. This plan will include ongoing monitoring by an environmental auditor, who will ensure that all established protective measures are complied with.

The implementation of this project will bring multiple benefits. On the one hand, all legal requirements regarding the discharge of treated water will be met and the protection of the aquifer will be guaranteed, preventing its contamination by infiltration. In addition, it will contribute to the preservation of Posidonia and other protected marine species.