Question

Classify desalination technologies according to “Separation method” and “Driving force”. Give examples.

Answer 1

A desalination process essentially separates saline water into two parts - one that has a low concentration of salt (treated water or product water), and the other with a much higher concentration than the original feed water.

The two major types of technologies that are used based on separation method, desalination can be broadly classified as thermal and membrane technologies

Thermal Technology:

Thermal technologies, as the name implies, involve the heating of saline water and collecting the condensed vapor (distillate) to produce pure water. Thermal technologies have rarely been used for brackish water desalination, because of the high costs involved. Examples are Multi-Stage Flash Distillation (MSF), Multi-Effect Distillation (MED), and Vapor Compression Distillation (VCD).

membrane technology:

In this technology water separated using membrane by the application of pressure and electrical potential.

examples are Electrodialyis/Electrodialysis Reversal (ED/EDR), and Reverse Osmosis (RO).

Based on driving forces we have different types of desalination techniques

Membrane separation requires driving forces including pressure (applied and vapor), electric potential, and concentration to overcome natural osmotic pressures and effectively force water through membrane processes.

Examples are,

Reverse osmosis (RO) and Nanofiltration (NF) are the leading pressure driven membrane processes.

Electrodialysis (ED) and Electrodialysis Reversal (EDR) processes are driven by direct current (electric potential).

Forward osmosis (FO) is a relatively new commercial desalting process in which a salt concentration gradient.