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New Mexico State University

New Mexico State University

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New water purification process saves energy and money

The shortage of fresh water in the nation is becoming an increasingly important challenge that will significantly affect economic development and the daily lives of people.



Shuguang Deng, NMSU assistant professor of chemical engineering, examines solar panels with Prajwal Vikram, chemical engineering graduate student. (NMSU photo by Darren Phillips)


The good news is that New Mexico has large amounts of brackish, or salty, water that can be treated to add to the fresh water supply. New technologies are being invented to deal with this issue; older technologies are being refined. The goal: to desalinate New Mexico's saltwater, thus providing a freshwater supply for residential, agricultural and industrial uses.

Shuguang Deng, an assistant professor of chemical engineering at New Mexico State University, is addressing this issue by combining solar energy and a process called membrane distillation to remove salt from water.

"What we are doing is very important because it has large implications for New Mexico as well as the nation," Deng said. "We need fresh water to meet the demands of our increasing population. By combining the abundance of brackish water and solar energy in this state, New Mexico is an ideal place to test the system. By doing so, we will be able to provide fresh water at the lowest possible cost."

While reverse osmosis is more cost-effective than most current technologies for treating brackish water with low salinity, Deng said it cannot be used to treat water with high salinity because of the extreme high pressure needed to overcome the osmotic pressure.

Another technology, thermal distillation, uses energy to boil water, thus creating water vapor and leaving impurities behind. However, this process requires a lot of energy and is therefore not cost-effective, Deng said.

Deng's process of membrane distillation involves transporting water vapor through a membrane. The membrane is hydrophobic, so it does not let water in its liquid form pass through. On one side of the membrane, the sun heats the water to create water vapor, which passes through the membrane, leaving the salts behind. As condensation occurs at a cooler temperature on the other side of the membrane, the vapor then reverts to its liquid form.

By combining the advantages of membrane process and thermal distillation into the membrane distillation, high-quality fresh water is produced while energy costs are reduced.

The pilot testing of Deng's process was scheduled to take place at the Tularosa Basin National Desalination Research Facility near Alamogordo. Groundwater in that area has a high salinity, ranging from 2,000 to over 10,000 parts per million total dissolved solids. Also, the groundwater has an abundance of sodium chloride, carbonate and sulfates, which makes it challenging to apply the existing desalination technologies of thermal distillation and reverse osmosis.

However, Deng said the research facility is not yet ready to test his membrane distillation process, so the pilot test will take place at NMSU instead. The salinity of NMSU's water - about 1,000 parts per million total dissolved solids - is less brackish than the Tularosa Basin groundwater, but Deng says he will compensate for this by adding enough salt to mimic the Tularosa Basin groundwater.

His current grant will end in May 2006, but he will apply for another one to help fund his work. Sandia National Laboratories has expressed an interest in helping with the new grant, Deng said.

The project is sponsored by the Water Resources Research Institute at NMSU and funded by WERC (NMSU's Consortium for Environmental Education and Technology Development), and Competitive Advantage Consulting Ltd. of Santa Fe. Gov. Richardson's Water Innovation Fund provided the original funding.

NMSU students working on the project include Prajwal Vikram, Amlan Chakraborty and Mahesh Dhanushkodi.


First photo is available at http://ucommphoto.nmsu.edu/newsphoto/deng.jpg.
CUTLINE: Shuguang Deng, NMSU assistant professor of chemical engineering, examines solar panels with Prajwal Vikram, chemical engineering graduate student. (NMSU photo by Darren Phillips)

Bob Nosbisch
March 20, 2006