News and Events
Albuquerque Journal
Monday, December 29, 2008
Brackish Water Is Expensive To Clean
By Sean Olson
Journal Staff Writer
Copyright © 2008 Albuquerque Journal
While desalinating water could become a valuable tool to support a growing New Mexico, residents will have to be ready to bite the bullet when it comes to the huge energy cost associated with the technique.
Experts say that cost comes in two forms: on water bills and in the environment.
"Here we are, trying to reduce energy use, and we're looking at (water) options that use significant amounts of energy," said Santa Fe water policy analyst Consuelo Bokum.
Desalination is a process that cleans brackish water - water that contains strong concentrations of salts and minerals. Sandoval County, SunCal Cos. and others are looking into the possibility of desalination plants to mine and clean the roughly 15 billion acre feet of brackish water under New Mexico's surface.
To clean water found by Sandoval County in the Rio Puerco basin, a desalination plant would use more than 14 times the electricity than the local Water Utility Authority's new river water treatment plant in Albuquerque's North Valley, according to energy-use estimates from the water authority and the U.S. Bureau of Reclamation.
If desalinated water starts making its way into New Mexico's potable water supply, those energy costs will start to pile up, Sandia Labs energy analyst Mike Hightower said.
Hightower estimates that treating water in a desalination plant would cost a little more than twice what traditional treatment of freshwater sources would cost - from $1 to $2 per 1,000 gallons treated to $3 to $5.
"There's nothing preventing (desalination), other than money - the cost of your water bill," University of New Mexico civil engineering professor Kerry Howe said.
On top of that cost is the amount of raw materials needed to create a drinkable water source. Based on the energy use estimates from the water authority and U.S. Reclamation Bureau, it would take about 200 pounds of coal or about 1,900 cubic feet of natural gas to clean 1 million gallons of river water. To clean up the brackish water in the Rio Puerco basin, those numbers jump to well over a ton of coal or more than 27,000 cubic feet of natural gas.
Treatment costs won't be more than 14 times higher because energy isn't the only cost incurred while treating water - the water authority has budgeted about $4 million of its roughly $12 million yearly operating costs for electricity. Electricity is also used to run the entire plant, which includes lights and other energy not used for treatment.
But Hightower's estimates would mean a huge jump in cost for water. The water authority, which distributes water to most of Albuquerque's metro area, pumps on average about 90 million gallons a day. That would be a difference in cost of $270,000 to $450,000 every day using desalination.
Hightower said desalinated water would most likely be used to supplement other water supplies, so the expensive desalinated water would be mixed with cheaper water. This means water bills would increase, but not by the full $2 or $3 per 1,000 gallons.
Bokum said the environmental costs would also be high. She said cutting energy means cutting carbon output and protecting against air pollution and global warming. Since most energy in New Mexico is still supplied by coal and natural gas, she said, it's important people understand desalination would undermine environmental efforts in the state.
"I think a lot of people in this state would not want to use that (energy) load if it's with coal and natural gas," Bokum said.
Bokum said that, before any organizations rush forward to create plants that use that much energy and resources, the public should put in its two cents.
"We should at least talk about these things," she said.
Cost Variables
Alternative energies with less environmental impacts, such as solar or wind power, are possible, but would add to the monetary costs of using desalination, Howe said. Alternative energies aren't widely available in New Mexico and building new plants would come with high capital costs that raise the price of energy, he said.
Bokum said she recently tried to incorporate alternative energy sources into Santa Fe's Buckman Direct Diversion project, but the complexities of trying to find available energy and the costs associated with it made it impossible.
Bokum said as alternative energy technology progresses, however, the option could become more viable.
Energy use - and cost - will vary in every desalination plant, University of New Mexico water resource director Bruce Thomson said. He said it depends on factors that include:
The water's location and depth.
The total dissolved solids, or TDS, in the water - the amount of salts, minerals and other particles.
How the leftover concentrate of salts and minerals is disposed of.
Waste and transport
El Paso's current desalination plant, which has only a fifth of the TDS level that Sandoval County's water has, uses much less energy than a Sandoval County plant would, Thomson said.
Howe said the excess energy use comes from several areas.
The biggest is the way the brackish water is cleaned. The most viable option is reverse osmosis, a process in which the brackish water is pushed through membranes that remove the unwanted salts and minerals, he said.
The higher the TDS level in the water, Howe said, the more energy needed to push the water through the membrane.
Water waste in the treatment process is an issue. While it varies depending on water quality, only about 75 percent of the water pumped into the plant becomes drinkable water, Howe said. The other fourth is turned into the concentrate that has to be re-injected into a well or otherwise disposed of - again, at the expense of more energy, he said.
Also at issue is the distance between water sources and existing developments. John Shomaker, president of water consulting company John Shomaker and Associates, said most of the brackish water supplies are not closely connected with streams, the traditional areas where municipal development has occurred.
If the water is far away from cities where it will be used, transporting the water could also equal big energy costs, Thomson said.
Some experts said the energy costs won't be that much of a problem.
One 2008 study, from the Israeli Institute of Technology, equates the energy use as no different than over-using an air conditioner or driving a gas-guzzling automobile.
Water consultant and former Metropolitan Water District of Southern California CEO Ronald R. Gastelum said the energy use won't be a big problem for desalination in New Mexico, as soon as a market opens for the technique.
"I'm not foreseeing the availability of energy will be an issue or even the cost of energy will be an issue," said Gastelum, who is working as a consultant for SunCal. He added that it will definitely raise the cost of water.