DESALINATION PLANT AN OVERVIEW
Desalination is a separation process used to reduce the dissolved salt content of saline water to a usable level.
Involves three liquid feeds
- brackish water or seawater
- low-salinity product water
- brine or reject water
NEED FOR DESALINATION
COMMERCIAL DESALINATION TECHNOLOGIES
Multistage flash distillation
Multi effect distillation
The phenomenon of transport of water across semi-permeable membrane from low salt concentration to high salt concentration is called Osmosis
PRINCIPLE OF REVERSE OSMOSIS
Pressure is applied to saline water to force the pure water molecules through a semi-permeable membrane. The majority of dissolved salts, organic, bacteria and suspended solids are unable to physically pass through the membrane and are discharged form the system in the rejected brine. The pure water is then ready for use without further treatment.
Why Reverse Osmosis ?
Reverse Osmosis : Technical advantages
For the treatment of all types of water: brackish water sea water
Adapted to all sizes of installations and any sources of energy: steam, electricity
Setting up in all geographic zones possible
Aside from the need to dispose of the brine, RO has a negligible environmental impact.
Plant sizing according to the present needs (possibilities to increase production capacity)
Operating cost is proportional to flow variations
Reverse Osmosis: a competitive solution
The membranes are sensitive to abuse.
The feedwater usually needs to be pretreated to remove particulates (in order to prolong membrane life).
Operation of a RO plant requires a high quality standard for materials and equipment.
Brine must be carefully disposed of to avoid deleterious environmental impacts.
There is a risk of bacterial contamination of the membranes; while bacteria are retained in the brine stream, bacterial growth on the membrane itself can introduce tastes and odours into the product water.
Types of Membrane Foulants in SWRO
TYPICAL REJECTION CHARACTERISTICS OF R.O. MEMBRANES
85 - 94%
% may vary based on membrane type water pressure, temperature & TDS
Pre treatment system (PT system)
Sea Water Reverse Osmosis System (SWRO)
Post treatment and treated water storage system
Reverse Osmosis and Mixed Bed Ion Exchangers for DM water system
Chemical Storage and dosing system
SWRO : schematic
INDUSTRIAL MIXED BED DEIONISER
Single column units
Strongly acidic cation and strongly basic anion exchange resin beds
There are four distinct stages in the operation of an industrial mixed-bed deioniser: