CS2 is researching the feasibility of the Zero Liquid Discharge concept from a thermal desalination process fed by seawater treated by Nanofiltration (NF) and fuelled by heat collected from solar energy. It will demonstrate a circular economy approach by extracting high value salts and elements from the water during the process.

At the case study site at the Plataforma Solar de Almer?a, a pilot-scale NF plant removes divalent ions from the seawater, which is then fed through a thermal-powered MED system to produce high quality water and brine close to saturation conditions. From the brine, researchers can collect sodium chloride (NaCL) and valuable elements that are combined with NF reject to produce mineral-rich irrigation water. The Zero Liquid Discharge approach means no environmentally damaging brines are released into the sea.

Use of solar thermal energy: The fluctuating nature of solar energy due to factors such as weather conditions could present challenges when it comes to powering the MED unit in such a way as to provide a constant output.

Scaling in the MED unit: The very high temperatures used to operate the MED unit could lead to scaling forming on the heat exchange surfaces, thereby reducing heat transfer.

Managing excess retentate from the NF process: Excess levels can pose a challenge when producing water that is suitable for irrigation purposes.

Quality of water produced by the NF unit: Low rejection factor in divalent ions or high rejection in monovalent ions could compromise the use of the permeate from the NF unit to feed the MED and the use of retentate from the NF for irrigation water.

More than 50% of total energy requirements covered by renewable energy

Reduction in MED energy consumption by >10%

Increase in Recovery Ratio of up to 70% compared to the typical recovery rate of between 30-40% at an MED seawater plant