By: Linda Fresques

Environmental Engineering Associate Professor Pei Xu has been at New Mexico State University for just five years, but she is already earning accolades in the national arena for her research on the development of alternative water supplies. In late February, Xu was named an American Association for the Advancement of Science Alan I. Leshner Leadership Institute Public Engagement Fellow.

Xu is one of 15 food and water security researchers selected for the 2018-2019 honor. The scientists were chosen for demonstrating leadership and excellence in their research careers and an interest in promoting meaningful dialogue between science and society.

“Fresh water is limited and water conservation is not enough to meet our needs, so we must identify alternative sources of water,” said Xu. “Water availability and quality has a significant influence on food and water security for human well-being. With the drought in the Southwest, the Rio Grande struggles to meet the water demands for urban and irrigation uses.”

Xu directs the Environmental Lab for Innovative Technologies Research Group that involves numerous research faculty and graduate students on a quest to create alternative water supplies by modifying and optimizing current technologies in the short-term and creating innovative next-generation technologies in the long-term to remove a broad range of contaminants from water and wastewater for drinking and beneficial uses.

Her work has brought in more than $3 million in research support from the National Science Foundation, the Department of Energy, the Bureau of Reclamation, the New Mexico Environment Department, the New Mexico Water Resources Research Institute, along with industry and water utilities.

Xu’s research group is examining methods for the reuse of municipal wastewater, produced water from the oil and gas industry, and desalination of brackish water sources. The challenges of creating water supplies from these sources are water quality, the intensive energy use of the treatment process, and the management of the resulting waste stream of removed contaminants. Their goal is to develop sustainable, energy-efficient technologies that rely on renewable energy, reduce the cost of producing usable water and can even recover viable resources such as fertilizer, iodine and energy.

In collaboration with Carollo Engineers and Suez Water Technologies, Xu has developed selective ion-exchange membranes for desalination from lab-scale testing to pilot demonstration at the Scottsdale Water Campus in Arizona, where they are developing a supply of reusable wastewater for watering golf courses; and the Kay Bailey Hutchinson Desalination Plant in El Paso, to treat desalination concentrate for irrigation.

“There are 26 golf courses in Scottsdale and each one uses approximately one million gallons of water per day,” Xu said.

The quality of treated wastewater is not suitable for golf course irrigation due to high sodium concentration of the reclaimed water. The city of Scottsdale uses ultrafiltration and reverse osmosis to purify the wastewater, a process that uses high pressure to push the water through a semipermeable membrane. This process is expensive and energy intensive.

Xu conducted bench- and pilot-scale electrodialysis experiments to develop and demonstrate new ion-exchange membranes that selectively remove sodium from water while adjusting salt composition of alternative water for irrigation and thermal plant cooling. To meet the water quality requirements for irrigation, the selective electrodialysis process resulted in a 26 percent cost reduction over reverse osmosis treating reclaimed water.

Xu’s research has further enhanced the effectiveness of ion-selective membranes by coating them with nanoparticles that can kill bacteria on the membrane surface.

“These antifouling membranes are very effective. The membrane selectivity is increased with the coating and they further reduce the energy demand and desalination cost,” Xu said.

A second line of research is devoted to the development of a hybrid algal-membrane system for potable water recovery.

“Creating potable water out of wastewater is a very expensive and tedious process,” explained Xu. “In collaboration with Nagamany Nirmalakhandan, civil engineering professor, we developed an innovative wastewater treatment process. The wastewater is first treated in algal bioreactors to convert organic contaminants and nutrients to algal biomass, followed by membrane processes to separate algae from water. Our idea is to use two membrane filtration processes to produce high-quality potable water while recovering algae for bioenergy production and nutrients that can be used as fertilizers. There is no waste stream left from this process.”

An NMSU student team led by Xu won two prizes at the 27th Annual International Environmental Design Contest this past year with their bench-scale demonstration of this system. The project has the potential to benefit local communities in arid and semi-arid regions of the world by providing a solar driven algal wastewater treatment process that can produce potable quality water and recover resources from wastewater.

A third line of research targets the reuse of produced water – the water trapped in underground formations that is brought to the surface during oil and gas exploration and production. Produced water is by far the largest volume byproduct stream associated with oil and gas exploration and production. The cost of managing produced water is a significant factor in the profitability of oil and gas production.

As the Permian Basin in southeastern New Mexico is the largest producer of oil and natural gas in the nation, the efficient treatment and reuse of this water is critical, as is the protection of the Ogallala Aquifer, which must be sustainable to serve the municipal and irrigation needs in the region.

The physical and chemical properties of produced water vary considerably depending on the geographic location of the field. Xu’s team, supported by funding from the Department of Energy, has developed the Produced Water Treatment Tool Box, a decision-support tool to assist in the characterization of produced water and the evaluation of more than 64 treatment technologies to identify the most effective treatment process for reuse.

“If we can remove contaminants from produced water, we can reuse this water as a new water supply in the region and reduce reliance of the oil and gas industry on fresh water while reducing the cost of oil and gas production.”

Xu’s efforts go beyond research. She is engaged in K-12 activities to enlighten the future generation. Her Leshner fellowship will enable her to expand and sustain public engagement and understanding needed to address growing resource competition.

“It is critical to engage the public on the importance of food, energy and water security issues,” Xu said.

“Eye on Research” is provided by New Mexico State University. This week’s feature was written by Linda Fresques of the College of Engineering. Fresques can be reached at lfresque@nmsu.edu