With each issue, Trib+Water brings you an interview with experts on water-related issues. Here is this week's subject:
Anthony Tarquin is a civil engineering professor at the University of Texas at El Paso. Tarquin’s major research interests are in the area of water and wastewater treatment. His most recent projects aim to optimize water treatment operations and desalting projects, in partnership with the city of El Paso. The project will be installed starting this summer. Tarquin earned an industrial engineering bachelors degree, an air pollution masters degree and doctorate in environmental engineering at West Virginia University.
Editor's note: This interview has been edited for length and clarity.
Trib+Water: How does your project reduce the wastewater from desalination treatment?
Anthony Tarquin: A lot of cities are starting to, or have been, using reverse osmosis to take salt out of water, particularly in the Southwest, where you have a lot of brackish water. It has a little more salt in it than we would like. When you try to take the salt out through reverse osmosis, there is always some water left over.
If you start with 10 gallons of water that you want to take the salt out of, you end up with two or three gallons that you have to throw away because all the salt is concentrated there. We started to do research about 10 years ago on how to recover water from that concentrate, the material left over. Because it is still a sizable amount of water — 25 or 30 percent of what you treat — that you have to throw away.
When we first started this research, the reason they had to do that was because of silica. When you get silica in water, if the concentration gets too high, it precipitates out and it coats the membranes to where they can’t pass any water anymore. When we started this research, that was the problem. A lot of this water in the Southwest that comes from sandy types of soils have silica in them and so, in those days, it was you have to stop treating water when the silica concentration reaches a certain value.
And so our research at that time was to try to solve that problem. As it turns out, we were able to come up with a system that does that and at the same time allows you to recover about 80 to 85 percent of that water that you would have normally thrown away.
Trib+Water: How does this process work differently than traditional water desalination?
Tarquin: It is not a lot different. There are two primary differences, one is we have to operate at a higher pressure. As you get more salt in the water, as the water gets more concentrated, you have to apply more pressure to force the water through the membranes. A typical reverse osmosis system might operate at 150 psi, whereas we are going to be operating more in the 500 psi range.
The other thing we do is called the batch treatment process. We treat the water for a little while and then before that silica or something else can precipitate, we throw it out. But if you throw the water out before these constituents have a chance to precipitate, they don’t foul the membranes. That is why we call it a batch treatment process. We can treat for a while, we have to figure out how long that is, then before these substances precipitate, you throw that batch out and start with a new one.
Trib+Water: How did this change from research to solve the silica problem to the project that will be implemented this summer?
Tarquin: They’re related. We started to try to solve the silica problem using a different approach. We were trying to remove the silica. We thought what you had to do was precipitate the silica out and then take that water that has no silica in it, but other salt materials, and then you could treat it with the reverse osmosis system again.
But we accidentally found out when we were doing this batch treatment process that we did have to remove the silica. All we really had to do was control the time that we treat the water before silica presents a problem. The same thing is true for other constituents like calcium sulfate.
Trib+Water: How did that research turn into the field project that will be in place in El Paso?
Tarquin: The city of El Paso has the largest inland desalting plant in the world right now. And, in addition to that, they have smaller systems and individual well sites. This project right now will be at those individual well sites. What they do is that this water that we are talking about that they have to throw away, right now they put that in the sewer system.
That ends up at the wastewater treatment plant, which means they have to handle it and treat it. With our process, if it is successful, it will reduce the amount of water that they put in the sewer system. They will still put what is called super-concentrate in the sewer system but it is going to be a lot less water volume.
Trib+Water: What is the expected impact for the city if it all goes well?
Tarquin: If the first one works, we have enough money for as many as four more. El Paso Water Utilities has 11 well sites. These are relatively small well sites beside that big treatment plant. If the first one works, then we would, to the extent of money available, put it in at two to four more places. That would save quite a bit of water for the city and it would be a cost effective way to do it.
Eventually, if this worked, then we would look at doing it at that big Kay Bailey Hutchison desalting plant here in El Paso. Right now, they just throw that water away by injecting it into the ground. If this project is successful then we would start thinking about if it is possible to treat that large volume of water.