Cities Spin Sewage into Gold

Recycled Water in the Desert Southwest

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This segment is part of the Engineers of the New Millennium: The Global Water Challenge Special Report.

Transcript: Tucson Spins Sewage Into Gold

John Madril: We're looking at a sprinkler right now...This is a Falcon sprinkler, the purple tops meaning that it's actually utilizing reclaimed water.

Lisa Raffensperger: In Tucson, water has always been a common concern.

Wendell Ela: This is the edge of the Santa Cruz River that we're getting on here. So if you look at the original development of Tucson, it marched along and followed the Santa Cruz River, because that was historically the water source before it dried up.

Lisa Raffensperger: Water is a special preoccupation for University of Arizona engineer Wendell Ela. As Tucson continues to grow, its groundwater table gets lower, and Ela sees a time of reckoning.

Wendell Ela: Tucson is one of the places, that many other places will experience in the near future, where it can not sustain its current demand with available water resources.

Lisa Raffensperger: One solution is to use existing water, again. It's called reclaimed water. Tucson already uses it—sewage and storm runoff are treated at the wastewater plant, and then some of the semiclean water is piped back out for irrigation. New housing developments near Tucson are eyeing reclaimed water for use in toilets and fire hydrants. But how do we ensure it's safe to go into homes? Engineers at the University of Arizona have one answer: build a small version of the world in their laboratory…and then mess it up.

Ryan Sinclair: This trigger here seemed to respond, which is good. But although it says "sensor missing," you can see that something happened here, and this turbidity did something but pretty small, so usually the system'll see a little bit but not…not what we expected…you know, not gonna flash E. COLI on the screen or anything like that.

Lisa Raffensperger: In water terms, this is a five-alarm fire: 500 E. coli per minute are flushing through the water mains. But that doesn't scare engineer Ryan Sinclair.

Ryan Sinclair: This one, when this does this, this is pretty good...

Lisa Raffensperger: That's because he put the E. coli there. Sinclair works in the Sensor Lab at the Water Village, a large garage filled with tanks, tubing, and robotic devices. Today, E. coli is what they refer to as the "contaminant du jour.”

Ryan Sinclair: You fill it up in here, and then we can turn that pump on, and that pumps it into this line, here, and this line goes into the sensors.

Lisa Raffensperger: The sensors give immediate feedback on all different measures of water quality, from how cloudy it is to what particular light it absorbs. These sensors are being used in today's water systems. And future reclaimed water systems, going into homes, could use the sensors as well. But first, we have to understand what the sensors mean, says researcher Mark Riley.

Mark Riley: You can have the best sensors in the world, and they all start turning on for some reason. What does that mean? Is it important?

Lisa Raffensperger: This is what researchers are hoping to answer by testing how sensors respond to known contaminants. Ultimately, the team wants to be able to advise cities like Tucson about what sensors would work best for their water system, including for reclaimed water.

Mark Riley: I think a huge hurdle for using reclaimed water is, people have concerns about what's present in that water, is it safe, is it different than the normal drinking water. It's something of an "ick" factor that they need to overcome. And what the sensors would help us do is be able to see if that water is the same quality, if it's just as good as the normal drinking water people would get from their tap.

Lisa Raffensperger: But safety isn't the only hurdle. There's a limit to how much water Tucson can reclaim because of the challenges of distributing that water. It comes back to the traditional way of cleaning water, at a single central plant, says Kevin Lansey, another engineer at the university.

Kevin Lansey: Treating water at one central facility saves on the cost of building the wastewater treatment plant, but to get that water back to users requires construction of major pipelines and pumping costs to move that water back to the users.

Lisa Raffensperger: Lansey's lab is modeling alternative systems for distributing water, because recycling water requires a whole different paradigm—you don't want to get the sewer water as far away from you as possible; you want it nearby. It's called "decentralized treatment."

Kevin Lansey: So, treating the water where it's going to be reused and taking advantage of avoiding the cost of pumping it back uphill is what we're looking for.

Lisa Raffensperger: Tucson's current wastewater treatment is centralized. In an established city, switching over the whole water system isn't really feasible. But Tucson has one small-scale recycling plant: the Randolph Park Water Reclamation Facility, which reclaims enough water to irrigate about 300 acres of grass.

Lisa Raffensperger: Rather than a mammoth complex, the facility is a small building nestled in a park by a pond. Most of its pipes, filters, and machines are underground. And a good deal of its reclaimed water is used close by.

Lisa Raffensperger: This kind of small plant may be ideal for a decentralized system. So the future, in one of Tucson's suburbs, may bring many Randolph Park–size facilities, reclaiming almost all of a city's water. That water would go to toilets and fire hydrants, monitored with real-time sensors. Assistant Manager Tim Mason says the philosophy is spreading in the Tucson area.

Tim Mason: You know, it makes sense, that's the thing. I mean, it's a wasted commodity if you don't. If it just goes onto the ground and just goes away, that's a wasted commodity. So we could use it. So let's do it; let's use it.

Lisa Raffensperger: Advice that areas around Tucson will soon be taking to heart—whether by choice, or by necessity.

Lisa Raffensperger: For Spectrum Radio, I'm Lisa Raffensperger.