North Alamo Water Supply Corporation is the state leader in the use of reverse osmosis to produce drinking water and is now pioneering the possible use of nanofiltration in the desalination of groundwater.

Faced with a long ongoing drought, North Alamo Water has tapped into groundwater to supply its customers with a reliable source of safe drinking water. Groundwater in the Rio Grande Valley is often brackish, or salty. Desalination, the process to remove salts and other minerals, is energy intensive, making it more expensive than processing surface water, in our case the Rio Grande. 

With an eye to conserving electricity in the treatment of raw water, General Manager Steven P. Sanchez, turned to engineering firm Freese and Nichols, Inc.

Headquartered in Fort Worth, Freese and Nichols recently evaluated energy-efficient alternatives for brackish groundwater desalination plants and found that nanofiltration could significantly reduce the amount of electricity used by North Alamo Water to treat brackish groundwater. 

The modeling and analyses for North Alamo Water found that replacing reverse osmosis membranes with nanofiltration membranes at two facilities would cut desalination energy use by 52.2 percent at one plant and 49.8 percent at the other. The switch also would provide for a small increase in production and allow the plants to continue meeting water-quality standards.

To test the feasibility of nanomembranes, North Alamo Water is considering a pilot project at a cost of $160,000, Steven P. Sanchez, NAWSC general manager, explained. The results, he said, will be used to determine if nanotechnology will be installed in existing and future water treatment plants.

North Alamo Water operates four brackish groundwater desalination plants (and co-operates a fifth), making it the water operator with the most desalination facilities in Texas. North Alamo Water Supply provides potable water and wastewater utility service for rural residents in eastern Hidalgo, Willacy and northwestern Cameron counties. The service area encompasses 973 square miles in the Rio Grande Regional Planning Area (Region M) and a population of 180,000.

The Freese and Nichols team studied options and concluded that nanofiltration membranes could replace the existing RO elements with minimal infrastructure adjustments while yielding substantial energy-use benefits.

Jason Cocklin is project co-manager with Jorge Arroyo, of treatment, transmission and utilities, for Freese and Nichols in Austin. Cocklin said it is fairly innovative to be looking at nanofiltration for desalination plants.

Traditionally, it’s been reverse osmosis, which has a really tight membrane that allows water molecules through but is relatively impermeable for salt, Cocklin pointed out. Nanofiltration elements have a looser membrane and require less energy in the feedwater stream, he said.

But, he said, the specific circumstances of NAWSC’s operations, along with advancements in membrane technology, make nanofiltration a good fit.

Incremental retrofitting and expansion of well field capacity is projected to increase North Alamo Water’s drought-proof supplies by 33 percent. And with the energy savings, the new membranes are expected to pay for themselves within a few years.

Arroyo said this project offers new ways of viewing the viability of brackish groundwater to supplement drinking water supplies. 

Arroyo said although Texas sits atop of an ocean of brackish groundwater, developing this source into a fresh water supply is often considered too expensive. He explained that the NAWSC study shows an innovative path to lower the energy required to desalinate and thus reduce the cost to produce brackish groundwater desalination supplies.

A successful pilot study to verify performance and provide data for designing a nanofiltration system would change the outlook for tapping into brackish groundwater sources in Texas,” Arroyo pointed out.

The Freese and Nichols team included client representative Ray Longoria, account director, Fort Worth; Also contributing technical expertise to the project were Mike Morrison, Mark Graves, Michael Sherer, and Oliver Haugland, all of Treatment, Transmission & Utilities in Austin; and Dave Buzan, Environmental Science/Coastal, Austin.

The study received funding from the U.S. Bureau of Reclamation, Brownsville Public Utilities Board, and McAllen Public Utility. 

Editor’s Note: The above guest column was penned jointly by Nora N. Garza, customer service outreach coordinator at North Alamo Water Supply Corp, and Jorge A. Arroyo, head of treatment, transmission and utilities for Freese and Nichols in Austin, Texas. Freese and Nichols are evaluating energy-efficient alternatives for brackish groundwater desalination plants.

Editor’s Note: The main image accompanying the above guest column was taken at an early project meeting regarding energy-efficient alternatives for the treatment of groundwater. Second from left is NAWSC General Manager Steven P. Sanchez. From the left are Freese and Nichols representatives Mark Graves, water/wastewater engineering; Ray Longoria Jr., client representative account and director; and Jorge A. Arroyo, co-project manager.