In the Multi-Stage Flash (MSF) process seawater is heated and evaporated, after which the steam is condensed to produce desalinated water.
The water vapor being condensed is used as a thermal energy source to heat incoming seawater.
Evaporation and condensation is split into many stages that are repeated several times, thereby increasing overall efficiency.
One of the good features of the MSF process is its ability to produce large amounts of water at a time. Since it uses the low temperature/pressure evaporator as a thermal energy source, while also making desalination possible with waste heat from the power plant, the MSF type is generally employed when building desalination plants in the Middle East.

Some of the feedwater is flash evaporated, but most of the seawater is dispersed over an evaporator tube bundle and boiled.
Steam then condenses to produce fresh water, and this process is continuously repeated. Since the evaporation takes place in a vacuum, the sprayed seawater is able to reach boiling point even at low temperatures.
Since MED uses a progression of stages with ever-dwindling temperatures (at 60~70C), it’s comparatively smaller than MSF in terms of output, but boasts higher heat efficiency and more economical operation.

The ions contained in seawater are larger than water molecules, and this characteristic is exploited through the process of Reverse Osmosis.
This system effectively forces seawater through a semi-permeable membrane in order to filter out the dissolved salts and minerals.
Such a process is applied in both home water filters and large desalination plants.
Although RO carries high electric consumption and maintenance costs, since the semi-permeable membrane has to be replaced periodically, no energy other than electricity is required to heat up the water.

Hybrid is a process of desalination the combines the positive features of MSF and MED.
If adjusted to varying environmental conditions, it’s truly the most economical way to desalinate water.
The largest hybrid desalination plant in the world is the Fujairah Plant (100MIGD = 454,600m3/day) in the United Arab Emirates, which is now being built by Doosan.

Waste water contains various types of chemicals and organics.
The water reuse process is determined each case based on the raw water characteristics and product quality demand.
The system is a combination of physical, biological and chemical treatment in order to eliminate suspended solid and organic matters. Bioreactor is the main process for pollutant removal with activated sludge and clarifier.
The recent advanced process is membrane bioreactor (MBR).
The process combines biological treatment with membrane separation and performs compact process, removing pollutants and separating solid from liquid so as to eliminate sedimentation and filtration process are not necessary.