Desalination

How it Works:

Desalination is the process that removes dissolved minerals from sea water, brakish* water, or treated wastewater. The main technology for doing this is Reverse Osmosis, or RO.

Reverse Osmosis (RO)

In RO, feedwater is pumped at high pressure through a permeable membranes. Basically, it blasts water through membranes. This process separates salt from the water. The feedwater is pretreated to remove particles that would clog the membranes. The quality of water produced depends on the pressure, the amount of salt in the water, and the salt's permeation constant of membranes.

The second stage of RO is distillation, where the water is evaporated, to remove certain minerals.

Energy Requirements

Energy Requirements for desalination are high. For example, an estimated 50 million KWH/yr would be required for full-time operation of the City of Santa Barbara's desalination plant to produce 7,500 AF/YR of water. For every 100 gallons of sea water, 15-50 gallons of freshwater would be produced along with brine water containing dissolved solids.

Other Facts

Of the more than 500 desalination plants operating worldwide, 60% are located in the middle east. The sea has been rising for 1800 years, but the past 100 years, it has rose seven inches opposed to the average two. By 2100, the sea is predicted to rise from 4-36 inches.

*Brackish water is sea water that used to be freshwater, but was contaminated.