With more than more than 2.7 billion acre-feet of brackish groundwater – enough to meet current demands for more than 150 years, according to the Texas Water Development Board – even West Texas isn't technically bone dry. But current desalination techniques are expensive, prompting intense interest in new methods to draw minerals and salt from brackish water.
"You have no choice but to move to worse and worse source waters," said Shankar Chellam, professor of civil and environmental engineering at the University of Houston. "Maybe we don't think very much about our water in Houston, but you go to other areas of Texas and Central Oklahoma, and it's already a crisis."
Chellam recently received a $150,000 grant from the U.S. Bureau of Reclamation to find more efficient, less expensive ways to remove contaminants and salt from brackish surface water. The treatments would also apply to brackish underground aquifers, he said.
The drought has forced many water utilities that rely on surface water to consider desalination for the first time, as evaporation has left the remaining water increasingly salty in the face of extended drought. Chellam said his work is among the first to look at nanofilters to treat brackish surface water.
Chellam's research also will be supported by in-kind contributions from UH, the City of Houston and the Foss Reservoir Master Conservancy District in Oklahoma, which has relied upon a more expensive desalination method for water drawn from the Foss Reservoir, where water quality has worsened during the extended drought. Anna Hoag and Collins Balcombe from the Bureau of Reclamation's Oklahoma-Texas Area Office will provide logistical and technical assistance.
Drought has taken a toll on water supplies around the world, Chellam said, through overutilization of groundwater and, as evaporation and overuse draws down water levels, an increase in the concentration of pollutants. As a result, the relatively clean surface water and groundwater supplies available 50 years ago are virtually nonexistent today.
Chellam's earlier work with nanofiltration membranes focused on improved methods for eliminating contaminants such as viruses, organic matter and inorganic chemicals from surface waters; with this grant he will work on removing salt, as well.
Existing desalination methods are expensive. The most common method is reverse osmosis, considered the best method for removing salt from seawater, but it is so energy-intensive and expensive that only a few countries – including those in the Middle East – routinely use it.
Nanofiltration wouldn't be a good option for desalinating seawater, but Chellam said it could fill a niche, working to desalinate brackish waters, which are less salty than seawater. Nanofiltration requires significantly less pressure than reverse osmosis, dramatically reducing the cost.
Most of the cost savings will come from the reduced energy costs required for nanofiltration, he said, although there may also be some savings from the need for less chemical treatment, as well.
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By Elena Watts