75 MLD Seawater Desalination Plant.

Feed water pH at 25 deg C - 8.5, Conductivity at 32 deg C - 65000 µs/cm, temperature - 32 deg C, turbidity - 600 NTU, TDS - 42000 ppm, TSS - 2000 ppm, Ca - 500 ppm, Mg - 1500 ppm, Total hardness as CaCO3 - 7500, Na - 13000 ppm, K - 450 ppm, Cl - 24000 ppm, SO4 - 3500 ppm, M Alkalinity - 100 ppm, P Alkalinity - 15 ppm, F - 4 ppm, Oil & Grease - not detected, PO4 - 3 ppm, Fe - 1.6 ppm, TOC - 2 ppm, BOD @ 27 Deg C for 3 days - 10 ppm, COD (ASTM Method) - 50, B - 3 ppm, NO3 - 1 ppm, SiO2 - 25 ppm, NO2 - 0.5 ppm, Colloidal Silica - 1 ppm, Dissolved Oxygen - 6 ppm, H2S - 1 ppm, NH3 - 2 ppm, Sr - 7 ppm, Ba - 0.2 ppm, Total Al - 0.2 ppm, Dissolved Al - 0.01 ppm, Dissolved Mn - not detected, Total Mn - 0.01 ppm, Dissolved Fe - 0.15 ppm, Zn - 0.05 ppm, Cu - 0.1 ppm, Ni - 0.4 ppm, Cd - 0.2/106 ppm, Pb - 15/106 ppm, Hg - 0.05/106 ppm Desired treated water characteristics are TDS - 500 ppm, pH - 7.0 to 7.5, Langelier Index should be higher than 0.1. We are yet to decide between two options: PT-DMF-PSF-RO or PT-DMF-UF-RO. We need to give performance guarantees. Which one of the two options is better?