Experts on Camera

Dr. Francis de los Reyes: Managing wastewater

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Water sanitation infrastructure in the US is aging and deteriorating, leaving many Americans, particularly those in low-income communities, vulnerable to contaminant exposure from household sewage and industrial and agricultural byproducts. Globally, billions of people don’t have access to safely managed sanitation services.

On Thursday, December 7, 2023, SciLine interviewed: Dr. Francis de los Reyes, a professor of civil, construction, and environmental engineering at North Carolina State University. He discussed topics including: the state of water treatment and sanitation infrastructure in the United States; the global challenge of providing access to safely managed sanitation services; how wastewater is treated and research on new ways to improve the process; new approaches to addressing sustainability, resilience to a changing climate, and equity in sanitation provision; and community-focused approaches for investing in sanitation infrastructure.

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FRANCIS DE LOS REYES: My name is Francis de los Reyes, and I am the Glenn E. and Phyllis J. Futrell Distinguished Professor of Environmental Engineering in the department of civil, construction, and environmental engineering at North Carolina State University. What I study is wastewater treatment and global sanitation. And within wastewater treatment, I look at biological processes—microorganisms for treating and converting our waste to resources and energy—and also looking at wastewater infrastructure globally, so—the sanitation conditions and technologies that can provide access to sustainable sanitation around the world.

Interview with SciLine

What can you tell us about access to water and sanitation in the United States?


FRANCIS DE LOS REYES: The U.S. has one of the most advanced water and wastewater and sanitation infrastructure in the world. If you think about, for example, quantifying it in terms of the sustainable development goals, you will see the number for the U.S well—we have 99% coverage—so we’re well above the target. But the reality is, you know, if you think about the numbers, we still have issues. We have about 2.2 million Americans who don’t have access to clean drinking water in their house, and access to sanitation that actually treats their wastewater.

What are the costs associated with unequal access to sanitation services?


FRANCIS DE LOS REYES: The organization DigDeep did a study and estimated the cost to the U.S. economy of those 2.2 million Americans not being connected or not having services is about $8.6 billion

Can you provide a short overview of water infrastructure in the United States?


FRANCIS DE LOS REYES: About 75% of the U.S. population is connected to centralized treatment systems. So, what this means is that when you open your tap, you get clean drinking water—that clean drinking water is coming from a large reservoir. And that’s treated at the water treatment plant and then transported to your house. And then that wastewater that you generate from your house is collected again through large sewer pipes. And then all of that goes to a centralized wastewater treatment plant. That wastewater treatment plant treats that to a level where it can be discharged into a receiving body of water. So, for 75% of the population, that is what happens. But then you have the 25%—so, you’re talking about 10s of millions of people who rely on small systems—private wells, for example—or on-site systems like septic tanks for their wastewater treatment. And there you see a little bit of a disparity in terms of concerns and issues because, for these private well owners, we know that, again, about 25% of private wells are contaminated. And again, these are contaminants that affect public health. And then about 80 million Americans use septic tanks and cesspools. And again, for them, they’re largely left to their own devices in terms of operation, maintenance and keeping it updated.

What can you tell us about maintenance and upgrades for centralized water infrastructure that are needed throughout the United States?


FRANCIS DE LOS REYES: There is a huge backlog in terms of maintenance needs and upgrading needs. So, the EPA has estimated that over the next two decades, we need about $625 billion of investments just to maintain what we have right there—the pipes and the pumps and the treatment plants I mentioned earlier.

What is the difference between wastewater treatment and wastewater reclamation?


FRANCIS DE LOS REYES: More and more, we think of it not just as treatment but really reclamation and reuse. So, to the extent that we can actually treat it to the level where it can be used for irrigation, for example, then that requires another set of treatment. Basically, it’s very important to make sure the water is disinfected and the pathogen content is very low. You hear more and more about actual water reuse and we divide that into potable use and non-potable use. So, with potable use, what that means is, to the extent it’s actually clean enough to that, it can go back to our drinking water system and can be used as drinking water. And that requires a lot more technology to make that work. You want to have multiple barriers against pathogens, against contaminants. And so you’re really, really getting to the high levels of water quality. And that’s been done in places like Singapore. You’re hearing more and more in the West, you know, San Diego and other cities are testing and thinking about, in the future, having a system where your part of your wastewater is treated for potable reuse. On the non-potable side, it’s a lower level of quality because you’re only going to use it for irrigation, for example, or for power plants or other uses that are not for human consumption.

How can separating wastewater streams improve treatment processes?


FRANCIS DE LOS REYES: There’s a movement in terms of wastewater treatment to separate out these different types of wastewater. And one way of thinking about this is you have yellow water, right, which is urine, you have gray water, which is the water from your sinks. And that’s not as contaminated as the black water, which is basically the water from your toilets. So, by separating these out, you can actually think about “How can I treat them so that I can recover resources of energy?” So, for yellow water, urine has 80% of the nitrogen and 50% of the phosphorus in wastewater. By separating it out, we can think of ways of how we can recover that nitrogen and phosphorus and use that as fertilizer. So, there’s research going on there. On the gray water side, because that’s the water from sinks, they are not contaminated with fecal material—at least not in very high concentrations—they’re cleaner. Then maybe you need less treatment for that to be reused as toilet flushing water, for example. And then on the toilet water side, now that we’ve separated it out, it’s more concentrated. Can we think of ways that we can more efficiently convert this to energy?

What is distributed water infrastructure, and how could it reduce energy costs?


FRANCIS DE LOS REYES: There’s an opportunity to actually have what we call decentralized or distributed water and wastewater infrastructure. So, what that means is, instead of pumping our wastewater hundreds of miles, millions of gallons per day to a centralized facility, maybe keep that water closer to home. And so treat the wastewater of a cluster of houses in a subdivision or two or three subdivisions. Or even at the level of the house, right? Maybe a house of the future of water, where, essentially, the technology for recycling gray water, the technology for treating the black water are all in the house, maybe in your basement or in your garage. And so you’re not pumping the water long distances, you’re not pumping large volumes of water, and you can get energy savings right away.

How can we increase equity in access to water and wastewater infrastructure?


FRANCIS DE LOS REYES: Really think about equity—we need to make sure that these underserved communities are receiving support. And when we think about designing solutions, that we think about these communities in terms again of either connecting them to centralized services or improving the state of these distributed or decentralized systems. The primary reason that most of them are not connected to centralized services is because it may be expensive, like I told you about this, miles and miles of sewer lines or drinking water pipes, and the cost of these pipes and pumping large volumes of water. You know, that’s actually quite high. So, if you think of solutions that are more scale-adaptable, more decentralized, then we can reach more of these underserved communities. So, that’s one way, but we really have to be intentional about this because I think our focus on centralized solutions has left these communities behind. So, if you think about equity, we have to think about who is this system for? Who are we designing for? And even to the level of, how are we thinking about research? How are we thinking about training engineers? You know, for the longest time, we’ve been training environmental engineers to design and operate and maintain these large systems. Today, we need to think about training the next generation of engineers to actually think about, you know, these smaller-scale adaptable solutions.

What advice do you have for reporters covering water infrastructure?