Effect of brackish water blending on seawater desalination: carbon footprint and decarbonization potential

In isolated volcanic island territories, the water-energy nexus is critical, particularly as water demand is predominantly met through seawater reverse osmosis (RO) desalination. This process is characterized by its high energy needs that rely heavily on fossil-fuel-based power. This study investigates the decarbonization of RO processes by integrating brackish groundwater (BW) blending into the feed stream. Results demonstrate that increasing the BW fraction enhances the recovery rate and reduces energy consumption, despite a slight increase in chemical requirements. Overall, this strategy significantly lowers the carbon footprint, achieving a reduction of 0.095 kg CO 2 /m 3 prod compared to the baseline scenario. Furthermore, utilizing BW for remineralization simultaneously reduces environmental impact and operating costs. At a 50/50 ratio of brackish water and seawater (BW/SW), the process results in a carbon footprint of 1.183 kg CO 2 /m 3 prod (reduction of 0.222 kg CO₂/m³ prod relative to the baseline) and an operating cost of 0.41 €/m 3 prod . Additionally, by harnessing the hydraulic head of the BW source via a Pelton-turbine-based system, the process can achieve energy self-sufficiency. Under these integrated conditions, a 20/80 BW/SW ratio achieves the lowest environmental impact (0.006 kg CO 2 /m 3 prod ), which represents a 99% decrease relative to the baseline case, while a 40/60 ratio proves to be the most economically advantageous (0.061 €/m 3 prod ).