Influence of supercooling, initial salinity, and post-treatment methods in freeze desalination

Freeze desalination, which produces fresh water by reducing the salinity of seawater, has gained increasing attention due to its low energy consumption and reduced corrosion during the process. While it is an emerging technology, comprehensive studies encompassing key parameters have been lacking. This study examines the effectiveness of indirect freeze desalination by investigating several key parameters including the impact of supercooling, coolant temperature, and initial salinity. This study compares the salinity and ice mass produced with and without supercooling at four different coolant temperatures: −5 °C, −6 °C, −7 °C, and −8 °C. The results show that preventing supercooling significantly improves salt rejection efficiency from 23% to 35% at a coolant temperature of −6 °C. This improvement is attributed to the rapid formation of extensive ice dendritic structures under supercooling conditions, which increases salt entrapment. Several initial salinity levels, ranging from 1.5 to 35 ppt, are examined to assess salt rejection efficiency. The results indicate that salt rejection efficiency increases with an increase in initial salinity, indicating that the desalination process can be more efficient for highly concentrated solutions. Lastly, various post-treatment methods including washing, sweating, crushing, and spraying are compared for their effectiveness in salinity reduction and water production. It is found that spraying ice with freshwater achieves the highest salt rejection efficiency of 94%, but involves additional freshwater consumption and resultant ice mass loss, resulting in a net yield of 17%. The outcome of this research demonstrates the critical impact of supercooling on salinity reduction and highlights the importance of post-treatment processes in determining salinity and water productivity. Insights obtained from this study will bring freeze desalination a step closer to effectively producing fresh water.