Submerged Type Boiling Evaporator (Steam Evaporator)
Boiling Process Evaporator (Low Pr. Evap.)
FWG [Alfa-Laval] (Fresh Water Generator
)
Flash Evaporator
Reverse Osmosis
Osmosis: Natural / Spontaneous Process – Consider a Salt Solution (Salt Water) and Pure Water is Separated by a Semi Permeable Membrane – Pure Water (from Pure Water Side) pass through the Semi Permeable Membrane to Salt Solution Side – Salt Solution is Diluted
Example – Plants absorbing water (from the soil) through its roots
Liquid inside the Roots (strong solution of sugars/mineral salts) – Salt Solution
Skin of the Roots – Semi Permeable Membrane
Water in the Soil (weak solution of mineral salts) – Pure Water
Semi (Selectively or Partially) Permeable Membrane – Only Water Molecules is allowed to pass through the Membrane by Diffusion (Salt Molecules are not allowed to pass through it)
Osmotic Pressure: Pressure required to be applied to Salt Solution to prevent the Pure Water passing through the semi permeable membrane to Salt Solution Side
Reverse Osmosis: Consider Salt Solution (Salt Water) and Pure Water is Separated by a Semi Permeable Membrane – When a Hydrostatic Pressure (greater than the Osmotic Pressure) is applied on the Salt Solution – Pure Water (from Salt Solution Side) pass through the semi permeable membrane to Pure Water Side [direction of flow is opposite to the natural osmosis process]
Reverse Osmosis Plant: Reciprocating (Positive Displacement Pump) is used to pump the S.W at a High Pressure (60 Bar) on one side of the Semi Permeable Membrane (Bunch of Cartridge)
Only F.W (from S.W side) pass through the semi permeable membrane to the F.W side
Salts are left back on the sea water side itself
Treatment of F.W for obtaining Potable Water
F.W is produced at a Low Temp (600C) by FWG (Low Pr. Evap.) & Flash Evap.
F.W produced is not Sterilised/Disinfected & also not Neutralised (Sterilising Temp > 800C) (i.e. it may be infested (contain organism) / Acidic / Flat Taste
Harmful if used for Drinking / Cooking (Culinary)
F.W must be Biologically Pure (Sterilised / Disinfected) & Neutralised (or Slightly Alkaline)
Treatment should be done using Treatment Plants
Potable Water Treatment Plants
It includes Sterilising (Disinfecting) Units & Neutralising Units
(a) Sterilising (Disinfecting) Units
- F.W is Heated to Sterilising Temp ( > 800C)
- Chlorinating/Sterilising is done by adding Chlorine (Gas) to F.W using a Chlorinator
Sodium Hypochlorite (Liquid) or Calcium Chloride (Tablets – Solid Granules)
Chlorine content should be 0.2 ppm
Excess Chlorine (1 ppm) is added to ensure complete Sterilisation
De-Chlorination is done using Carbon Bed Filter (removes the excess chlorine and also removes any taste/odour/colour)
- UV Light – Sterilising is done by passing F.W through Light Rays / Radiation of a Low Pr. Mercury lamps
(Will not prevent re-infection, hence to be used in conjunction with other sterilising methods)
- Ozone – Effective oxidant – equipment is costly and high running cost
- Electrokatadyn Process – Adding Silver Ion (0.08 ppm) – Ag Ions remains suspended for a long term (but chlorine evaporates)
(b) Neutralizing Unit – Acidity will harm human digestive Tract – Passing through Magnesium and Calcium Carbonate will remove CO2 & Acidity and make the F.W Neutral or slightly Alkaline – Adding these hardening salts will also give a better taste to the F.W