Cover art for Direct Current podcast season 3, episode 4, "This Episode Stinks" depicting headphones and a poop emoji.
U.S. Department of Energy



CLAIRE WITNAH: This is the cafeteria at the National Renewable Energy Laboratory, NREL for short. The lab's sprawling campus in Golden, Colorado, is home to all kinds of cutting-edge energy research. And every day at lunch time, the cafe fills up with hungry scientists, engineers, and program staff.


LISA: It's National Nut Day and we're all here!

WITNAH: National Nut Day?

JAY: You've got the king nut right here! (LAUGHS) You can put that on the podcast.

WITNAH: Yeah. The king of the nuts?

JAY: He's the king of the nuts.

WITNAH: Are you one of the nuts, Jay?

JAY: I'm one of the nuts!


LISA: We're all here, all the nuts are here.

WITNAH: That's Jay and Lisa. They work back in the kitchen, feeding the thousands of customers that walk through the cafe doors every week. The “king of the nuts” is Mark Galinsky. He’s the café manager. I’m here to talk to him about something... well, kind of gross, frankly.

MARK GALINSKY: So basically, every two to three months, we have a company that comes and empties our grease trap, and so commercially — you know, at home you just pour grease and you hope it doesn't go down the trap and then clog your pipes.

WITNAH: As you can probably guess, Mark's a busy guy.

GALINSKY: I flipped all your chicken, is that what I was supposed to do? 8 more minutes?

MAN'S VOICE: I was gonna put it in here as soon as the chicken comes out.

GALINSKY: OK. So we produce so much more grease than a household. It goes into the sewage, into the piping, and then actually as it cools, it rises. So the trap is above the water system. So when that fills up, then they have to empty it otherwise it backs up.

WITNAH: Here's the deal. The NREL Café is actually LEED Platinum certified — one of the highest environmental standards a building can achieve. But beyond its high-efficiency lighting and water-saving innovations, it still has to deal with the same kind of waste as all food service establishments. That includes "brown grease."

PHIL PIENKOS: So brown grease is the materials that are washed down the drain. It's the fats from salad dressing, or from gravy, or what have you — food preparation. Not things like french fryer oil, which is yellow grease, and which actually has a number of organizations that are using it for various products, but this is the stuff that escapes capture and recycle.

WITNAH: That's Phil Pienkos, a strategic project lead here at NREL.

PIENKOS: So if you are a commercial food preparation organization, you probably have a grease trap connected to all of your sinks, so all of the food stuff that gets washed down the drain from the dishwasher or from washing the pots and pans by hand, rather than going into the sewage system, ends up in the grease trap. And it floats to the surface of the grease trap, and periodically the operators of this commercial food preparation company will have their grease traps pumped. The oils will then be transported to be discarded in the landfill.

WITNAH: No one wants this stuff. Mark doesn't want it clogging the cafe's pipes, wastewater treatment plants don't want it overwhelming their systems... And the companies that collect brown grease actually have to pay a fee to get rid of it at the dump. 

WITNAH: Quick content warning here. We're going to get into some pretty gross territory this episode, so if you're squeamish, you might want to skip this one. Case in point — if you let too much brown grease get into the sewer system, it can create a situation like the one that made headlines in London in 2017.


BRITISH REPORTER: (COUGHING, LAUGHTER) Oh man. Every underground labyrinth has its monster, as I'm about to discover. But down here, it's not a minotaur. It's something far, far worse. (SOUND OF WATER RUNNING THROUGH SEWER). Oh God, the stink. Down here lives the "fatberg," a mixture of rancid fat, human excrement, and other unmentionables.


PIENKOS: They call them "fatbergs," and yeah, the sewage pipes can be completely blocked off, causing great expense and challenges for wastewater.

WITNAH: Yeah. Nasty. But, where some people see an inconvenience, Phil saw an opportunity. His focus at NREL is bioenergy — a broad term that covers turning organic matter, such as plants, into a usable source of energy. For years, Phil has worked on creating fuels from algae, the microscopic plants that grow in ponds and lakes and oceans. Crud from kitchen sinks? Not so much.

PIENKOS: Yes, that's true. It is pretty much a side project. I started to explore wet waste to see if there was any way that we could leverage the work that we did for algae into some wet waste streams.

WITNAH: "Wet waste" is the kind of friendly euphemism that bioenergy researchers like to use for, basically, noxious sludge like oils and sewage. 


GALINSKY: When they come here, it actually is at 4:30, 5 o'clock in the morning because it stinks like nothing you've ever smelled before. And when they start emptying that, it can set off some of the alarms in a lot of the other buildings that measure fumes & air quality — they will go off. Which is why they do it so early in the morning, before anyone gets started.

WITNAH: I had no idea. That's nuts!

GALINSKY: It is a stinky process.

WITNAH: Would you mind taking me to go see it?

GALINSKY: Yeah, sure, let's go.


WITNAH: So, when Phil had the idea to investigate brown grease as a potential fuel source, his search led him here, back behind the kitchen of NREL's largest dining establishment.


GALINSKY: Right here is where the grease traps are going to be. 

WITNAH: OK, so we're outside, and right here's where the grease traps are?

GALINSKY: Yeah. Those two sewer caps are the grease traps.

WITNAH: They're not much to look at — just a couple short pipes sticking up out of the ground out behind the cafe.

WITNAH: Phil's team talked to the company that pumps out the traps. They were more than happy to hand over a few 5-gallon buckets of the stomach-turning samples for analysis. Spoiler alert: it doesn't get less disgusting from there.

PIENKOS: We take the material — it has a tendency to separate on its own, and the oil rising to the top, and a lot of the other stuff including water is trapped in that. So you get a sort of a mousse-y layer, "m-o-u-s-s-e" not "moose" — you get a mousse-y layer on the top, but there's so much water and other material in there that it's not really useful.

WITNAH: How do they get from gunk to gas? Well, for starters, they let nature do the dirty work, using a combination of chemistry and biology to convert the unwanted material into useful biofuel components. And Phil's lucky — he doesn't actually have to see or smell the gnarly stuff.

PIENKOS: I have to admit that I have yet to encounter a sample of brown grease. I leave that to my colleagues who actually work in the laboratory. I do not work in the laboratory. They are very careful to work with it in a fume hood, in a chemical fume hood, so that the smell is blown out the roof rather than into the laboratory.

INTERVIEWER: So they're the ones on the front lines.

PIENKOS: They are indeed. But despite the "gnarly" nature of the material, they are all committed to the success of this project.

WITNAH: You might be asking yourself, why on earth would these scientists put themselves through this? Could it really be worth it?

PIENKOS: Overall in the United States, there's enough brown grease generated that could produce somewhere around a billion gallons of biofuel a year. So this is not a small scale.

WITNAH: The impact of this work could be massive. We're talking the equivalent of fuel for more than one million cars and trucks. Removing brown grease could reduce stress on our water infrastructure. And turning it into energy could even let utilities take wastewater treatment facilities "off the grid," to shield them from cyber attacks. 

WITNAH: There are plenty of challenges involved, of course, but if anyone's going to be able to develop this from a promising idea into a viable energy source, it's the energy experts at NREL.


PIENKOS: We've shown that pretty much every molecule that's present in the brown grease can be turned into a biofuel. We're wrapping up that work, this was a one-year project, we've been very successful at it. So it could make for a very rapid handoff from the guys who are doing the small-scale work in the lab to somebody who would be interested in commercializing the technology and actually producing biofuels at thousands, millions, or billions of gallons a year. 

WITNAH: Mark's been in the restaurant business for 34 years. He's keenly aware of the amount of waste food service generates. So the work Phil's team is doing, searching for a new way to turn some of that waste into something useful, speaks to him on a deep level.

GALINSKY: Yeah, if all that grease went into the water system, it would be awful. All that water goes into the sewer system and the grease gets saved and taken away, times, how many restaurants you think are in Denver? All over America.

WITNAH: Thoughts on it being turned into renewable bioenergy?

GALINSKY: I think that'd be fantastic. Everything that we use, that we throw away, could be used. 


MATT DOZIER: Welcome to Direct Current. I'm Matt Dozier.

CORT KREER: And I'm Cort Kreer. That was Claire Witnah you heard earlier, reporting from NREL on the greasy, grimy, gritty side of renewable energy.

DOZIER: And if you thought we were stopping there, think again. Today, we're taking a hard look at the stuff that gets dumped down our sinks, flushed down our toilets, and washed into our waterways.

KREER: Coming up, we've got two more stories about some of the dirtiest jobs we know. Scientists working to turn waste that looks and smells horrible — which no one likes — into energy, which everyone likes!

DOZIER: It's going to get gross... but informative, and hopefully, entertaining.

KREER: Here we go!



CORINNE DRENNAN: My name is Corinne Drennan, and I have a very generic title at work. It's, um, manager. (LAUGHS).

DOZIER: Where do you work?

DRENNAN: I work at Pacific Northwest National Laboratory. So I'm responsible for our bioenergy technologies programs. Those cover a wide swath of technology development and R&D for turning waste and other materials into fuels and chemicals. Our job is to think about what happens after you flush the toilet.

KREER: You could say the average person isn't thinking a whole lot about the potential uses for what's sitting in the hopper, or what happens to it after we flush it away. But for Corinne and her team, this is pretty much all they think about. They're working on a way to convert all that ... material ... into something really, really useful.

DRENNAN: The process that we're using converts the raw sewage, or the sludge that comes from a wastewater treatment plant, into what we call a biocrude. So a biocrude is effectively a liquid-phase storable intermediate that you could further refine in a refinery or using conventional processes outside a refinery, and then use it for transportation fuel. So you would distill it into gasoline, diesel, maybe even jet, and use it in your vehicles.

KREER: Corinne's team at PNNL is transforming poo into power through a process called hydrothermal liquefaction, or HTL. HTL has been around for the better part of a century. It was even used during WWII to make fuels. But what exactly is it? 

DRENNAN: What is hydrothermal liquefaction? Effectively, it's pressure cooking.

KREER: Time to put on your chef's hat, because the worst recipe of all time is as follows:


KREER: Step one. First, you're going to want to gather up your.... ingredients

DRENNAN: Basically we get five-gallon buckets. We try to encourage people to not fill them all the way up and to make them as cold as possible prior to shipping, and hopefully ship on a cool day, maybe in a cooler or an ice chest. So those buckets come to us, and our folks suit up. They wear Tyvek, full on gear, to get in the middle of this.... crap, and get it prepared to go into the reactor systems. 

KREER: Does it look like poop?

DRENNAN: When we get it, it kinda does. There's a lot of toilet paper. There's hair. There's fats, oils, and greases. It's pretty gnarly. I often get photos from a colleague of mine, who likes to remind me that he's up to his elbows in crap for this research. 

DOZIER: That's dedication. 

DRENNAN: It is. It's pure dedication.

KREER: Step two. Make sure your sewage is a good mix of solid and liquid so it can be pumped properly — 20 percent solid to 80 percent liquid ought to do it. Now dump all that in your pressure cooker — in this case, the reactor system.


DRENNAN: We have a couple different reactor systems, we have some that we call bench-scale and those are about the size of a couple of refrigerators side to side. If you look under the insulation and whatnot, it's this serpentine, tubular thing.

DRENNAN: The larger-scale system that we have is a process development unit, and it is out in a high bay, which is like a giant garage. That system comprises three different skids. So if you look at what's in back of a diesel, each one of our three skids is about that size. And it's designed to be transported and deployed so that people can run the system on their material. 


KREER: Step three. Apply about 3,000 PSI of pressure and turn up the heat to about 680 degrees Fahrenheit, or 360 Celsius.

KREER: Step four. Let that pressure and heat cook for about 15 minutes, and voila! 


KREER: What you're left with are three different products: a solid, a liquid, and a gas phase. The liquid phase contains mostly water, but also stuff like acetic acid, the main component of vinegar. There are a few ways you can deal with this leftover liquid. You could send it back to the wastewater treatment facility, or you could do some more chemistry on it to make additional co-products — like pulling the carbon out to make biogas. The other stuff you’re left with — the solids — are inorganics, unreacted carbon, and even some recoverable nutrients like phosphorous.


DRENNAN: The aqueous phase is a yellowish-brownish water. And then the solid phase looks like a cake. Not like a cake you eat, but like a filter cake. (LAUGHS) Technical terms that mean other things, too. It looks like a pressed powder, almost?

KREER: Out of those solids you also get ... crude


KREER: Biocrude, that is. Black gold. Texas.... molasses?

DRENNAN: The biocrude doesn't smell like molasses. But it looks like molasses. And it pours with about that consistency at room temperature as well. 

KREER: To use this biocrude in fuels, you need to remove the oxygen by putting it into a reactor, then flowing it over a catalyst with some hydrogen. What you’re left with then is called a hydrocarbon. Break the hydrocarbon down by distilling it, and you get a blend stock. That blend stock can then be mixed into gasoline or diesel, or however else you want to serve it up. 

KREER: Now, I know what you're thinking -- after all this science is done to it, is it anything like the poo we know and love?

DRENNAN: Not anymore. 


DRENNAN: Not even the smell. 

DOZIER: So it doesn't smell at all coming out the other end?

DRENNAN: Oh, it smells, but it smells different. The biocrude kind of smells like a campfire. The water phase is pretty foul. It doesn't really smell like... biology. It smells like, I keep thinking about sulphur.

KREER: So, once processed, it's a far cry from how it looked sitting in those buckets. But where did the buckets come from? How in the world are they getting their hands on — and in — this much poop?

DRENNAN: Believe it or not, people are not at our door clamoring for us to take their poo. However we have worked with Canadian poo, and poo from the Great Lakes area. So, Detroit poo. Mostly it comes from our partners in wastewater treatment. The Canadian poo came from Metro Vancouver. They are also working on HTL, they're raising funding to build a demonstration there. So they were one of the first to send us their poo. We weren't sure if it was going to represent U.S. poo (LAUGHS), so we did some studies using poo from California, from Detroit. 

KREER: And the results were? (DRUM ROLL)

DRENNAN: Poo is pretty much poo. What we've learned is that it's less of a function of diet and more a function of, what do people put down their drains. When you think about what goes through a wastewater treatment facility, it's not just the toilet. It's your sink, it's your shower, and the other things that we find in those five gallon buckets. 

DOZIER: But in general, though, poo is poo. 

DRENNAN: I think so.

DOZIER: It knows no borders.

DRENNAN: It knows no borders. (LAUGHS)

KREER: So. Does this mean we'll all be filling our gas tanks with high-octane bio-sludge instead of regular unleaded? Not quite yet — we'd need a whole lot more usable waste material to meet that kind of demand. For now, Corinne's team is focusing on bringing this HTL technology to smaller communities to meet more localized energy demands.

DRENNAN: If you look at the municipality of Seattle and the surrounding areas, you could take the sewage from that and power the municipal fleet. So you could essentially have communities that are able to power themselves and that, to me, is huge and is something visible and is something that that community could own.

KREER: Turning excrement — the byproduct of food energy and perhaps the most renewable resource we have — back into energy again... it's a pretty exciting idea. So what's next for biofuels? What new endeavor on the horizon gets Corinne and her team most excited?

DRENNAN: Cow poop. 



DRENNAN: That's the most exciting thing in the future. There's so much more manure than people poo to be had. And also, that's a tremendous liability. We can take the manure and, hopefully, convert it into something useful and not have it be relegated to burial, spreading it on the ground. And there are also bacterial concerns and ick factors and I'm sure people would rather put it in their tank than on their crops. 

KREEER: The creative thinking at work at PNNL is just one example of how the Department of Energy's 17 National Labs use people power to solve big problems. 

DRENNAN: That research is really fascinating because we have such a strong and diverse team. When I think about diversity I think about how different disciplines approach problem solving. So to be able to go talk to a chemist, an entomologist, a mechanical engineer, an economist, an analyst... I can go talk to every one of these characters inside of a couple of hours because they're all right there on campus. 


KREER: And while the implications of this technology are game-changing, Corinne and her team don't always take it too seriously.

DRENNAN: This is not strictly a serious business. There is not a day without a poop joke, and, come on, this kind of humor never dies, you know. In the field that I work in — I've been in bioenergy for gosh, 15, 16 years now — one of the first questions I usually ask an audience when I'm going to talk about the work we do is, "How many of you have played with poo?" Kids love it. We can go into classrooms and talk to kids about what we do. So that's the funnest place to go "Hey, guess what I do with poop?" (LAUGHTER)

KREER: OK, jokes aside, this work is groundbreaking. Not just to address our own skyrocketing energy needs, but to mitigate the damage that excessive waste can do to our planet. It's easy to flush the toilet or pour some crud down the drain and never think about where it goes or what happens to it. That's the nature of our relationship to waste — out of sight, out of mind. Multiply that by several billion people and counting, and the environmental implications become more and more severe. You simply wind up with too much crap and nowhere to put it. That's why sustainability matters.

DRENNAN: This planet is a system. Which means everything is conserved. You can describe it using equations. All we can do is transform things from one thing to another. That's what makes looking at waste, I think, really really important. 



DOZIER: We take you now from the Pacific Northwest to the shores of south Texas to explore waste of another kind. So far, everything we've talked about has focused on waste that goes down our drains. The kind of waste we do our best to capture and treat, so it doesn't cause problems down the line.

DOZIER: But what about things that don't flush neatly out of sight and into our sewer system with the press of a lever? Take pesticides and fertilizers, for example. South Texas is a rich agricultural region, known for growing cotton and sorghum. And when it rains, some of the chemicals sprayed onto those crops get washed into rivers and streams. 

DOZIER: You've probably heard about the problems this can cause. Massive blooms of algae, fed by nitrogen and phosphorous, choke waterways and suffocate fish. In the Gulf of Mexico, a so-called "dead zone" has grown to the size of Delaware as the microscopic plants flourish, then die en masse.

RYAN DAVIS: What causes those fish die-offs is the decomposition of the algae that basically sucks all the oxygen out of the water, and so basically fish are dying because the bacteria that are decomposing the algae require oxygen. That oxygen is removed from the water, so the fish suffocate. So that's one type of harmful algae bloom.

DOZIER: That's Ryan Davis, a biochemist and biophysicist on staff at Sandia National Laboratories. Ryan's been investigating ways to stop these algae blooms, which can cause serious damage to the economy and human health.

DAVIS: The other we occasionally see are things like red tides, toxic cyanobacteria, which bloom in kind of almost random locations when the conditions are right. And I think really understanding how and why that happens is an open field of research, it's very interesting because the economic impacts of these kinds of things are getting worse and worse.

DOZIER: In Florida, a particularly devastating red tide has ravaged coastal areas, driving away tourists and killing marine life like manatees and sea turtles. NOAA estimates these harmful algae blooms have resulted in about $1 billion in losses to coastal communities over the last several years. 

DOZIER: Ryan and his colleagues know a lot about harvesting algae for bioenergy — similar to the work Phil Pienkos does at NREL... when he's not poking around restaurant kitchens. And one thing they know for certain, is once the algae is running wild out in the Gulf of Mexico, it's too late to do anything with it. 

DAVIS: Once the algae is blooming in the open ocean, it's never going got be cost-effective to go and harvest it that way. It's too dilute, we're talking about huge areas, these things are visible from space as just green blobs in the ocean.


DOZIER: So how do you even begin to tackle a problem of this scale? Well, you might start upstream, somewhere along the coast, where polluted runoff starts to mix with seawater.

JACQUELINE MITCHELL: So for my research, we were located in Flower Bluff, a town in Corpus Christi, Texas. We were pumping our water off from the Laguna Madre, which is a hyper-saline water system.

DOZIER: Really salty?

MITCHELL: Yeah. Really salty, yeah. So normal seawater is usually 35 parts per 1,000, and the Laguna Madre can sometimes in the summer get up to 50. 

DOZIER: That's Jackie Mitchell. She recently graduated from Texas A&M University, Corpus Christi, with a master's degree in fisheries and mariculture. The campus has a marine lab down by the water, which is where Jackie spent long hours as a grad student helping Ryan and Sandia Labs with an ambitious algae research project.

DOZIER: So the Laguna Madre is this long, shallow body of really salty water that runs along a 130-mile stretch of the south Texas coastline. It's beautiful, and massively popular as a sport fishing destination.

MITCHELL: It's connected to the different bays within south Texas, so there's kind of a barrier island that separates the Laguna Madre from the ocean, so it gets feed from rivers and certain bays in the area, but then it also has connection to the Gulf of Mexico.

DOZIER: What Jackie, Ryan and the rest of the Sandia team set out to find out is, could there be some way to remove the chemicals that drain into coastal waters like the Laguna before they lead to an algae explosion? The solution, as it turns out, could be wonderfully low-tech.

MITCHELL: So essentially, an algal turf scrubber isn't too complicated. In essence, basically you have some sort of substrate, some sort of surface that you're running seawater over — or any type of water really, freshwater also — that has high nutrient levels like nitrogen or phosphorus.

MITCHELL: As the water runs over the surface, the natural algae in the water takes hold and starts growing and then as the algae grows it can start extracting some of those extra nutrients out of the waterway, and so what you're left with at the end of the system is cleaner water than you started with. 03:51 

DOZIER: That term again, for the less scientifically inclined, is "algae turf scrubber." That's what they're calling the whole setup. As for "substrate..."

MITCHELL: So, substrate is just a fancier word for something for the algae to grow on. So for example, one of my projects, one of the things we used for substrate was just like plastic mesh screening that you'd use on your windows. We also used astroturf, so, common everyday things that algae can get a hold on.

DOZIER: Sandia National Labs research projects regularly employ some of the world's most advanced scientific tools — high-intensity lasers, powerful supercomputers, nanotechnology. This was not one of those projects.


MITCHELL: It was a wooden structure, made out of plywood 2x4s, built slightly on a slope so the water could flow by gravity down to the end. We made three of those, like 50x4 feet platforms, and then within each platform they were divided up into four separate lanes for my different treatments for the experiment. We just used plywood to separate the lanes. And then we had behind the three platforms a head tank where the water from Laguna Madre was pumped into, like a holding tank.

DOZIER: Did you just get the plywood at Home Depot?

MITCHELL: You'd be surprised! I think especially in the media science gets portrayed as the most cutting-edge technology and resources, but Home Depot and Lowes to buy PVC, to buy wood... very common everyday objects is your best friend.

MITCHELL:  My friend came to visit me while I was doing my master's. She's an engineer herself, and we were using tinfoil lasagna trays to carry samples. And she goes, "Huh. So this is what science really looks like." (LAUGHS)

DOZIER: So to recap, Jackie's team basically had a 50-foot slide lined with some kind of material — "substrate" — that they would run lagoon water over. The algae that's naturally floating in the water would attach to the substrate and start to grow, where it could then be harvested for use in biofuel production.

DOZIER: When you say you collect it, what does that look like?

MITCHELL: It looks like a mess. (LAUGHS) We would take 12-inch windshield wipers, like that you would clean off your windshield when you're pumping gas, and just scrape them down the whole lanes, and then use a big feed scooper you'd find at a farm and just picked it up and put it into 5-gallon buckets. It was a sloppy, sludgy mess.

DOZIER: It's a far cry from the stereotype of white-coated scientists shuffling around a spotless laboratory. This was hard, messy work — and not only that, but mostly outdoors. In south Texas. 

MITCHELL: When I was running my system, at one point in the summer there was just a four-foot snake that was hanging out and sunning itself near where I had to work. There were lots of deer around, and havalina, which are these wild hogs that are down in south Texas. As far as the climate goes, it was super hot.

DOZIER: So here they are again with these five-gallon buckets — which seem to be the single most important tool in a bioenergy researcher's toolkit. Anyway. They're filled with algae that looks like — actually, I'll let Ryan describe it.

DAVIS: You have stuff that resembles, sorry for the gross analogy, but it resembles hair that you pull out of the drain, frankly. It's green hair out of the drain. Our students have iron stomachs, I think. I think Corinne's and our stuff probably has a lot of similarities.

DOZIER: So not the most appetizing subject matter, but according to Jackie, it didn't actually have much of an odor... at least when they first scraped it out of the trough. Step 2, however, involved removing as much water from the wet algae as possible, and... I'm sure you can guess where this is going.

MITCHELL: We had these baskets that we lined with felt, and then after we collected the biomass in the five-gallon buckets, we would dump it in these felt-lined baskets and then let gravity drain all the water out. That would take anywhere from three to four hours. So while it would it be sitting outside in the south Texas sun, and it would be drying out, and then we'd have to dump those buckets out and scrape it all out, and that's when it really was in its prime smell.

DOZIER: What did it smell like?

MITCHELL: Like the worst kind of low tide, decaying seaweed stench you can imagine. There were some points that I had to step away from it and like, literally get a breath of fresh air before I would dive back in. From there, we  would dry all the biomass out. You would think that the smell can't get worse, but it does. So now you're drying it out in a 60-degree-celsius oven, and it just smells... putrid is an understatement. It was rough (LAUGHS).

DOZIER: You're out there suffering for your science.

MITCHELL: That's how you know you love it, though. If you're willing to go through all that for it.

DOZIER: So, strenuous and stinky as this work may be, there are two big benefits to using an algae turf scrubber.


DOZIER: First: when the quote-unquote "good" algae settle on the slide, they're effectively cleaning the water by absorbing nitrogen, phosphorous, and other stuff.

DAVIS: So all surface waters have a natural biota, and these include algae that can attach to things and grow. And this is typically what people will observe as just kind of pond scum. This is the green slime that grows. They're scrubbing the excess nutrients, organic contaminants out of the water so they're not available in these larger open waterways for the opportunistic, harmful algae to take up residence. By doing that instead of allowing it to just decompose in the open ocean, we're preventing that secondary problem.

DOZIER: Deploying a large-scale version of the scrubber in a waterway with persistent runoff problems could help stave off the worst of algae disasters in places like Florida. Or, if the installation was big enough — even the Mississippi Delta. The other thing is what you can then do with that algae once you've harvested it. Like the brown grease we covered earlier in this episode, there's big biofuel potential in this "green slime."

DAVIS: We could produce enough algae from these unintentionally released nitrogen, phosphorous, basically just normal fertilizers — to be able to produce over a billion gallons of gasoline equivalent from that biomass. So we have partners at other national labs and universities, and even companies who are considering this using their technologies for biomass conversion.


DOZIER: But that's not all. Ryan said they found other interesting things when they did a chemical analysis of the algae, including high levels of mannitol, a sugar alcohol with medical applications. The slime is also really rich in protein.

DAVIS: I wouldn't recommend anybody to eat this, but what it tells me is that we could process this and use it as a sustainable option for things like aquaculture, basically fish feed, or other kinds of feeding applications.

DOZIER: Remarkably, through all their testing, the Sandia researchers have never seen harmful algae grow on the scrubber — only the benign, naturally occurring kind. Which gives Ryan hope that this technology could make a real impact.

DAVIS: What the world has basically unlimited demand for is energy and protein. And so what I see here is an option to basically produce both, which is exciting, in addition to being able to couple in environmental restoration or remediation. So those things all make me very excited. I haven't seen any red flags that say, "Hey, this is just a dumb idea."


DOZIER: Like all of our stories this week, at its core, this is about a National Lab searching for value in something that everyone else has discarded — and finding it. Ryan calls it "valorizing the biomass," which is a super wonky way of saying, essentially, giving scum some respect.

DAVIS: We call ourselves "scum ranchers," kind of colloquially, and we're a pretty tight-knit community of folks who love scum.

DOZIER: As for Jackie, she's moved on to a new job at another marine lab. But she said her work with Sandia gave her valuable experience, and pushed her to ask big questions through her research. And she's not done with algae yet.

MITCHELL: My fiance actually got me as a graduation gift, when I finished, he made me a shirt that says "algae farmer" on it (LAUGHS). 

DOZIER: You can wear that at the wedding.

MITCHELL: I can, yeah. Right over the dress (LAUGHS). 

DOZIER: As gross as some of this stuff is, you can tell Ryan, Jackie and the other folks at Sandia, PNNL, NREL, and the Energy Department's Bioenergy Technologies Office really have a soft spot for the unwanted, unappreciated byproducts of human life. 

DOZIER: In the world of energy production, they're pulling for the underdog. And that doesn't stink at all.


DOZIER: All right, folks! You did it! You made it through our grossest episode yet. If somehow this deep dive into the underbelly of energy wasn't enough for you, we've got buckets full of bioenergy content waiting for you on our website,

KREER: Don't forget, we really like hearing from you. If you've got a question, want to leave feedback, or just want to say hello, email us at, or tweet @energy. And if you're enjoying the show, share it with a friend and leave us a review on iTunes. It really makes a difference. 

DOZIER: Many thanks to our guests, Phil Pienkos, Mark Galinsky, Corinne Drennan, Ryan Davis, and Jackie Mitchell.

KREER: Thanks as well to Shannon Bates, Kristi Theiss, Jules Bernstein, and the Bioenergy Technologies Office for their help with this episode.

DOZIER: And of course, a huge shout-out to Claire Witnah, for her stellar reporting from NREL.  

KREER: Direct Current is produced by Matt Dozier, Paul Lester, and me, Cort Kreer. I also create original artwork for every episode, which you can find on our website.

DOZIER: Additional support from Ernie Ambrose, Gigi Frias, and Atiq Warraich. We’re a production of the U.S. Department of Energy and published from our nation’s capitol in Washington, D.C.

KREER: Thanks for listening!

Grease. Gunk. Sludge. Where most people see a nasty nuisance, these scientists see powerful potential.

Join us on this episode as we wade into the world of bioenergy and learn about the folks working to turn noxious waste into useful energy. Then read on for more bioenergy stories and background from the Department of Energy and our 17 National Labs!

WARNING: Unless you've got a cast-iron stomach, you might want to hold off until after lunch to listen to this one.

Green Eats

The LEED Platinum-certified NREL Café in Golden, Colorado.

The National Renewable Energy Laboratory Café is LEED Platinum certified, but it's not the only building on NREL's campus to achieve lofty environmental standards. Check out this map of sustainable facilities where lab scientists work, meet, park and eat as they undertake some of the most advance renewable energy projects in the world.

Would you like coffee with that?

Phil Pienkos.
By Dennis Schroeder, NREL.

In addition to exploring the energy potential of kitchen grease, Phil Pienkos has been thinking about what happens to the coffee grounds that go into your morning cup of joe! Read his thoughts on a potential second life for the discarded remnants of America's favorite caffeinated beverage.

Goo for the Gold

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Hydrothermal Liquefaction at Pacific Northwest National Laboratory
Video courtesy of the Department of Energy

It takes millions of years for the earth to turn decaying organic matter into oil. Watch the video above and read up on how Pacific Northwest National Laboratory speeds up that process to create energy from waste and other materials in the (relative) blink of an eye.

The Good, the Bad, and the Algae

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A VICE News profile of Ryan Davis and a Sandia Labs algae research project in California's Salton Sea.

Courtesy of VICE News & HBO.

From the coast of south Texas to one of California's most polluted lakes, researchers with Sandia National Laboratories are testing algae-based energy solutions in a wide range of environments. The 350-square-mile Salton Sea is the site of their most recent test of an "algae turf scrubber" system that could help clean up contamination and produce useful bioenergy.