Effects of pretreatment parameters on electrodialysis and reverse osmosis combined desalination system / Hamdy Maamoun Abdelghafar Hefny ; Supervised Bahgat E. Elanadouli , Mohamed S. Eldeab

Thesis (Ph.D.) - Cairo University - Faculty of Science - Department of Inorganic Chemistry

Generally, desalination pretreatment process involve inhibition of scale formation (mainly, gypsum) as well as removal of heavy or harmful metals cations (mainly, iron). Nucleation fundamentals of desalination scale (calcium sulfate dihydrate [gypsum]) in a synthetic saline solution of NaCl with high concentration simulating a reverse osmosis desalination system with and without different inhibitors (tri-sodium phosphate, TSP and sodium hexameta-phosphate, SHMP) in two separated models have been studied. Calcium chloride and sodium sulfate were mixed with concentrated sodium chloride solution (40g/L), and the turbidity of the reaction mixture was measured at different time intervals to determine the induction time of precipitated gypsum. Induction time was measured under different high supersaturation ratios ranging from 3.92 to 6.71. The induction time decrease exponentially with increasing the supersaturation ratio. Using crystallization equations that relate induction times with supersaturation ratios, the free energy barrier and critical nuclei radius were calculated with and without addition of different scale inhibitors (TSP and SHMP). The nucleation rates at supersaturation ratio of 4.47 are 0.4x1028 nuclei/cm3.s and 0.5x1028 nuclei/cm3.s with and without TSP addition, respectively. The surface energy increases with TSP compared to the baseline (without TSP). Numbers of molecules required for formation of stable nucleus are calculated to be from 3 to 10 molecules depending on supersaturation ratios and presence of TSP

Issued also as CD