In a desert city, people understand the importance of water security. Learn how a pilot project at El Paso Water Utilities is using direct reuse to increase its drinking water supply.


If everything works as expected with the Advanced Water Purification Pilot Facility in El Paso, Texas, residents will soon be drinking cleaned wastewater. The $5 million test facility opened in August and will operate for about three months to ensure the technology works properly before El Paso Water Utilities begins planning a full-scale facility. The result of ongoing testing during the pilot phase will be sent to the Texas Commission on Environmental Quality, which will have to approve the full-scale facility.

Gilbert Trejo, chief technical officer for El Paso Water Utilities, says the pilot plant at the Roberto Bustamante Wastewater Treatment Plant will treat 140,000 gpd to demonstrate compliance with TCEQ drinking water standards. The agency requires 60 days of compliance testing during which the purified water will go back to the wastewater treatment plant and will not be used for drinking water.

“We’re going to run it for 30 more days in a stressed condition,” Trejo says. “We’ll introduce higher levels of contaminants that we see in our wastewater and others like pharmaceuticals and other emerging contaminants.”

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If everything goes as planned, TCEQ will grant conditional approval for final design of the full-scale, 10 mgd purification plant, which will take about two years to build. The utility’s summer peak demand is 160 mgd, and the lowest daily demand in winter is 60 mgd. El Paso Water Utilities hopes to have the plant online in 2020.

Four-step process
The pilot plant was designed by ARCADIS U.S., part of an international consultant firm. The treated effluent first goes through a microfiltration or ultrafiltration membrane to remove particles and bacteria.

“We’re piloting two types of membrane technology,” Trejo says. “This is one of the processes where we have competing technologies going head to head to make sure they can both meet the water quality requirements we need and so we can have some competition in procuring this equipment at the full-scale level.”

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Next is competition between traditional reverse osmosis and nanofiltration.

“RO removes up to 98 percent of dissolved salts, metals, dissolved organic molecules and other materials. It pretty much removes everything and allows just water molecules to dissolve through the membrane.”

Nanofiltration, on the other hand, lets some of the minerals dissolve across the membrane.

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“Using traditional RO, we have to put some of those minerals back into the water,” Trejo says. “If we don’t have to remove them and can produce water that resembles the water chemistry of the water already in our distribution system that our customers are drinking, that would be most cost-effective to our customer. This is very unique to the concept because across the country, when you hear about direct potable reuse, everyone goes straight to reverse osmosis. We’re saying we don’t think we need to go to that level.”

The third step in the purification process is ultraviolet disinfection with advanced oxidation that introduces hydrogen peroxide just upstream of the UV process.

“When they interact, it creates a highly reactive oxidant,” Trejo explains. “It destroys other complex molecules, the long-chain organic molecules from pharmaceuticals, pesticides and industrial waste. Reverse osmosis and nanofiltration are already proven to remove those, so this is a second barrier.”

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The last barrier is common granular activated carbon to absorb any remaining taste, odor, organic compounds and synthetic organic chemicals, which includes hydrogen peroxide remaining from the UV process. It is also a third barrier to the microconstituent contaminants already treated by the membranes and advanced oxidation.

The pilot facility has one main operator and up to five others maintaining the plant as needed.

Testing along the way
The system includes real-time water-quality monitoring throughout the process.

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“We have analyzers all along the treatment process testing several water quality parameters and constantly recording the data,” Trejo says.

The SCADA system manages the data and shows trend lines as the water makes its way through the system.

“We’ll see any upward trend well in advance, so we can optimize the process before it gets to a maximum allowed level,” he says.

Independent monitoring
The real-time testing will help answer questions about the effectiveness of the technologies being used, which could result in TCEQ approving the steps to be used in the full-scale facility. But there is another body watching the testing that will also make recommendations. El Paso Water Utilities has contracted with a panel of experts from the National Water Research Institute.

“They are independently reviewing all the work,” Trejo says. “These are experts in water treatment, risk assessment, microbiology, regulatory and communications who had a hand in designing the treatment train.”

So even if TCEQ accepts the proposed level of treatment, the NWRI panel might think otherwise. “Because we’re breaking new ground on something that has been controversial in other communities, this panel of experts may recommend keeping four steps. I have a feeling, from our standpoint, that we would keep it at four steps and maybe revisit that after a few years of operation.”

Expensive — but needed — investment
Assuming the $5 million pilot project is successful, El Paso Water Utilities is looking at $100 million for a full-scale advanced water purification plant. Trejo says that might seem like a lot of money, but it’s needed to continue diversification of the water supply.

The utility has water rights to property it owns 100 miles away, but importing that water is even more expensive. Still, it is planning to tap that resource in about 2050 and is looking at purchasing property closer to El Paso for a less expensive supply. It already operates the Kay Bailey Hutchison Desalination Plant, the world’s largest inland desalination plant that cleans brackish groundwater.

The utility has researched the cost of those alternatives and provided a cost structure to the public:

  • Groundwater - $200 per acre foot
  • River water - $300 per acre foot
  • Kay Bailey Hutchison Desalination Plant - $600 per acre foot
  • Advanced Water Purification facility - $1,100 per acre foot
  • Importing groundwater water from utility-owned property 100 miles away - $3,000 per acre foot

“As you diversify your water portfolio, the cost of water gets more expensive,” Trejo says. “That’s one of the educational topics for the community. The days of a cheap water supply are coming to an end, and it’s for the sake of preserving our freshwater supply in our aquifer.”

Communications and Marketing Manager Christina Montoya points out that two years ago, the utility was only able to use river water for six weeks of the year.

“We have water,” she says. “We’re trying to extend the life of our aquifer and other resources by adding another resource into the mix. We’re looking at all of these things working together to help us provide water for the future.”

Public acceptance
Because it has a long history of reclaiming wastewater, Montoya says public acceptance was high from the start. Since 1963, the utility has been using reclaimed water for industrial use and landscape irrigation, and it began using reclaimed water for groundwater replenishment in 1985. Its desalination plant opened in 2007.

For the new plant, Montoya says El Paso Water Utilities began an aggressive speakers bureau and outreach program in June 2014. But first, the utility surveyed the community to get a benchmark of support for putting purified wastewater into the drinking water system.

“We got 84 percent in favor of it,” Montoya says. “When we gave them more information about the process, the number rose to 95 percent. El Paso is probably different than other communities because they know we’ve been doing this for a while and they know we live in a desert and have to look at diversified resources to make sure we have an ample supply of water. We’ve been educating people for decades.”

Public tours of the pilot plant kicked off on Aug. 28 and will be held four times a month.


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