Please read the abstract in the section 00front of this document / Thesis (PhD)--University of Pretoria, 2008. / Physics / unrestricted

Owing to the maldistribution of precipitation in the harsh climatic region has resulted in the deficit between freshwater demand and natural supply or water scarcity in these countries. Seawater desalination has emerged as one of the most reliable methods to bridge this gap. However, the thermal desalination (MED and MSF) process faces challenges related to surface scaling phenomena, such as temperature and seawater concentration. Innovative thermodynamic processes and technologies have the potential to overcome these limitations. On one hand, the top brine temperature (TBT) limit can be raised by partially removing the multivalent ions such as SO42-, Mg2+, Ca2+, Cl-, and Na+ dissolved in the seawater. One of the main drawbacks of the current MED processes is their vulnerability to scaling at temperatures above 70°C.. This limitation deprives the technology to be energy efficient and reduces its optimal productivity. However, by implementing an optimized pre-treatment of seawater feed using NF membranes, the efficiency of the process can be significantly improved. In the pilot plant, the experiment was conducted to investigate the efficacy of NF (nanofiltration) as a physical pre-treatment method for partially removing undesirable ions of dissolved salts in Red Sea water, thereby mitigating scaling issues beyond the upper TBT limit in thermal desalination systems. Utilizing the NF-270 membrane, the optimal operating feed pressure of 15 bar was determined to ensure effective ion removal while minimizing operational expenditures (OpEx). The results demonstrated high removal rates, with 97% removal of Sulfate (SO42-), 73% removal of Magnesium (Mg2+), 49% removal of Calcium (Ca2+), 17% removal of Sodium (Na+), and 16% removal of Chloride (Cl-). By employing NF as a pre-treatment method, the concentrations of these ions were significantly reduced, allowing for thermal desalination plants to operate at higher temperatures, with a maximum TBT of 120°C. This, in turn, has the potential to substantially increase water production yield in thermally driven plants by incorporating a greater number of stages in a green new design plant or by exploiting larger temperature differences in existing plants.