Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities and you. In this blog we’ll be discussing the role pressure plays in the desalination efforts in California.
The Pressure for Fresh Water
With water shortages occurring in all regions of the world and especially in California, new sources of water are being explored. In some cases, the new source uses an old approach. Desalination of sea water is getting new attention after being shelved for decades in Santa Barbara. Also, San Diego is building the nation’s largest ocean desalination plant that will be completed in 2016. Pressure is an integral part of turning sea water into drinkable/usable water.
Courtesy Bay Area News Group
A reverse osmosis (RO) process is used to separate the dissolved salts in a saline solution by flowing the liquid through a water-permeable, pressure-driven membrane. The pressure required depends on the type of membrane and the desalination being performed. For example, the desalination plant on Catalina Island uses 900 psi to treat ocean water. Treating underground brackish water only requires 200 to 300 psi.
As shown in the table, there are four categories or classes of pressure-driven membranes for desalination.
|Membrane Type||Pore Size||Transmembrane Pressure||Application|
|Microfiltration (MF)||0.1 – 3 micron||1- 30 psi||Turbidity reduction and bacteria removal|
|Ultrafiltration (UF)||0.01-0.1 micron||1- 30 psi||Same as MF as well as removing viruses and some color, odor and organics|
|Nanofiltration (NF)||< 0.002 micron||75- 150 psi||Natural organic matter (NOM) removal|
|Reverse osmosis (RO)||non-porous||150-500 psi||Removing monovalent salt|
MF/UF membranes are being increasingly employed in the desalination process to shield other membrane types from suspended solids and larger colloidal material that are detrimental to their performance. As part of the control and monitoring process, the differential pressure is sensed across the membrane at each phase.
What do you think/Comments?
Do you have a pressure sensing question? Let me know and I’ll address it in an upcoming blog.
-Han Mai, Senior Marketing Specialist, All Sensors Corporation (firstname.lastname@example.org)