NARRATIVE OF THE DESALINATION PROCESS*
*per http://www.mcwd.org/!desal.htm

Marina Coast Water District Desalination Project Seawater Intake Well

• Located west of the Marina State Beach parking lot
• Bottom elevation of about- 50 feet MSL (Mean Sea Level)
• 12'' diameter casing, 520 gpm discharge rate
• Seawater Total Dissolved Solids (TDS) = 22,000 mg/L

Pre-Treatment Filtration Anti-Scalant Addition & Cartridge Filtration

• "Threhold treatment" for scalants that can foul up the reverse osmosis membrane
• Represses both calcium cabornate and calcium sulfate crystal formation process
• Inhibits formation of other potential scalants such as oxides or hydroxides of iron, managanese and silica
• Removes turbidity, suspended solids and other materials to prevent scaling of fouling of membrane

Reverse Osmosis Desalination Process

• Pre-treated seawater is forced under pressure through a simipereable membrane for removal of chemical impurities and solids like salt
• Single pass system with profected recovery rate of 67%. Seawater is desalted in one pass of membrane disalination.
• Permeate (Product Water) water quality: Total Dissolved Solids = 280 mg/; ph = 5.7; hardness = 25mg/L; Alkalinity = 2mg/L (corrosive characteristics)

Post Treatment (Lime & Carbon Dioxide Addition; PostChlorination)

• To satbilize corrosive characteristics of premeate (Product Water) produced from the reverse osmosis process
• Addition of hydrated lime to increase calcium hardness and raise ph
• Addition of carbon dioxide to increase alkalinity (carvon dioxide converted to bicarbonate after hydrated lime addition)
• Water quality after post treatment: Total Dissolved Solids = 380mg/L; ph =8.5
• Chlorine is added in the final stage for disinfection

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