Variable Salinity Desalination
In partnership with the Texas Water Development Board, Brownsville Public Utilities Board, and the Reclamation Oklahoma-Texas Area Office, the Reclamation Desalination Research Team is demonstrating a Flexible Variable Source Water desalination system. Testing at the Southmost Regional Desalination Plant in Brownsville, TX completed on July 24, 2011. The facilities brackish groundwater was pretreated with ultrafiltration (UF) to remove excess iron and then with reverse osmosis (RO) to recover 75% of the feed water as relatively pure water that can be blended with other sources for municipal use. The second half of the test will demonstrate challenging seawater desalination using high turbidity feed water from the Brownsville Ship Channel. Testing at the ship channel will begin August 2, 2011.
The objective of the study is to gather energy use and water quality data and to discover potential operational issues with the flexible system design. The Expeditionary Unit Water Purifier (EUWP) was modified to switch from treating seawater at 50% water recovery using a pressure exchanger to power one third of the system to a two stage brackish water system that can achieve 75%-80% recovery. Variable feed water flexibility is important in the following situations:
- Areas, such as the gulf coast, where different sources of water may be available at different times of the day or year
- Emergency response equipment, such as the EUWP, which may be needed for treating seawater in one mission and brackish water or fresh water in another.
- Irrigation return flow treatment systems, such as needed in the south Central Valley of California, where the salinity of the water depends on the level of irrigation water application.
A flexible design can allow for energy efficiency OR water efficiency depending on which is most important and practical for the feed water quality.
Anna Hoag from Oklahoma-Texas Area Office preparing to verify concentrate flow. From the left flows from UF retentate, RO permeate, and RO concentrate.