Reverse Osmosis and Seawater Desalination

It has been estimated that the oceans cover about 70% of the earth s area and contain about 80% of the water on or in the earth. Seawater concentration varies from 25,000 mg/E of total dissolved solids up to over 50,000 mg/E in the Arabian Gulf. The average composition of seawater is about 35,000 mg/E with the major ions being shown in Table 4.9. 

The effluent from the roughing filter clearwell is pumped to the pressurized polishing filters which further reduce the SDI to less than 3. There are four operating polishing filters and one standby filter. The filter media is anthracite and green sand. 

Sodium bisulfite is added to the effluent from the polishing filters to remove residual chlorine which would be harmful to the polyamide reverse osmosis membrane. Sulfuric acid is then added to the filter effluent to adjust the pH to about 6.5 and the pretreated water is routed to the primary reverse osmosis system. 

The reverse osmosis system has operated well and the capacity of the plant has been increased to twice that of the initial segment described above. 

---