Could desalination prove the ultimate game changer in Texas' hunt for freshwater sources? Desalination plants are becoming more plentiful in Texas. The Kay Bailey Hutchison Desalination Plant in El Paso shows that typically undrinkable brackish water can be employed to quench our thirst. Desalinated water remains costly, however, and promising innovations to reduce its expense and energy requirements remain just that — promising.
The safe disposal of concentrated byproduct adds a substantial cost to desalination.
Some companies and water systems are testing the feasibility of refining the concentrate byproduct for industrially useful materials such as gypsum, hydrochloric acid and pavement additives. If this proves economical, it would remove a considerable challenge to inland desalination.
Several emerging technologies may help make large-scale desalination more economically and environmentally feasible. These include:
Newly developed filters for reverse osmosis feature holes one billionth of a meter wide — small enough to easily trap sodium and chlorine ions when water is forced through them. These new filters, developed by Lockheed Martin, can desalinate water at about half the pressure needed for a traditional filter. This reduction in pressure can lower energy costs by 15 to 20 percent.
Rather than using energy to force water through membranes or filters, forward osmosis relies on the natural phenomenon of osmotic pressure to pull water through a membrane and into a liquid with a higher concentration of solute. Forward osmosis desalination plants are already in place in countries such as Gibraltar and Oman in the Persian Gulf.
Capacitive deionization removes salts and other dissolved minerals by passing saline water between two oppositely charged electrodes. These electrodes separate the sodium and chloride ions comprising salt and pull them through a membrane, leaving only freshwater behind. The process is more energy efficient than reverse osmosis because energy stored in the electrodes can be reused.
Developed in part by UT Austin researchers, electrochemically mediated desalination is one of the newest and potentially most revolutionary breakthroughs in desalination technology. Instead of a membrane, this process relies on a plastic chip containing microchannels about the size of a human hair; a small electrical field separates salt from water traveling along these channels. The process, while still a long way from commercial viability, requires very little energy and is dramatically simpler than existing desalination technologies.
El Paso’s $91 million Kay Bailey Hutchison Desalination Plant can produce up to 27.5 million gallons (about 84 acre-feet) of fresh water daily. The plant, a joint project of the city of El Paso and Fort Bliss, is a critical component of the region’s water supply, converting previously unusable brackish groundwater into fresh water.
The plant uses reverse osmosis to produce potable water from brackish water pumped from the Hueco Bolson. About 83 percent of the water is recovered, with the remainder representing concentrated brine stored in three deep injection wells powered by solar energy.
The plant’s water cost — largely representing the cost of energy — is about 2.1 times higher than ordinary groundwater production, and for that reason it rarely runs at full capacity. On average, the plant produces 3.5 million gallons per day (about 11 acre-feet) at an average production cost of $489 per acre-foot. In 2012, the plant supplied about 4 percent of El Paso’s water.