Influence of wastewater treatment level on the seawater quality in the discharge region of Santos Submarine Outfall

This study aimed to evaluate if in the case of the Santos Submarine Outfall (SSO) there was any environmental benefits relative to potential eutrophication if instead of the primary treatment a CEPT, ST-AS or a TT- ASNR was used. The environmental impact of wastewater discharge through the SSO with an average flow of 5,3 m3.s-1 was evaluated using an eutrophication numerical model which solves the two-dimensional vertically integrated hydrodynamic and transport equation. Wastewater mixing conditions in the near field plume was evaluated using the software CORMIX, and the results were coupled to a far-field model considering the conservation of mass flow. The results demonstrate that the use of a secondary treatment with partial ammonia oxidation promotes a reduction of only 30% in the chlorophyll-a, while the use of a CEPT with phosphate removal promotes a better environmental response, resulting in chlorophyll-a concentration reduction of 69%, similar results were obtained when tertiary treatment was considered for nitrogen and phosphorus removals.