“People sometimes aren’t interested when you have a cool new technology to show them,” says Laboratory chemical engineer Jim Coons. “But they are always interested if they have a problem and you might have the solution.”
Coons does indeed have a cool new technology—a filtration method he calls UltraSep that uses no filters. It turns out that a lot of industries, from biofuels to craft beer—even the Lab's plutonium facility—have filtration problems that it might be able to solve.
Los Alamos’s plutonium facility supports a variety of applications including nuclear weapons and nuclear-powered heat-sources for spacecraft. As Coons was exploring different applications for UltraSep, he learned about specific bottlenecks in waste-processing at the plutonium facility and he thought UltraSep could help.
A worker could set up a batch of waste to be processed, push a button, and walk away.
Plutonium waste processing requires a worker to repeatedly lift a heavy jug, shake it to mix the contents, pour a small amount of liquid into a membrane-based filtration rig, wait for the liquid to pass through, and then repeat. It can take days or even weeks to process one full jug. These jugs weigh up to 20 pounds and the worker must operate inside a protective glove box, meaning they are lifting the jug while standing with their hands outstretched. In addition to ergonomic concerns, the longer the worker handles the jug of liquid waste, the higher the dose of radiation they receive. Once a preset annual maximum is reached, the worker “doses out,” and can no longer perform that type of work for the rest of the year. So, between the physical demands, the slow pace, the hassle and waste of cleaning the membrane filters, the radiation doses, and subsequent rotation of personnel, there is room for improvement.
Coons explains, “It would be better to set up an automated system. It would involve much less effort and much less personal exposure.” He envisions a push-button operation: The worker could set up a batch of liquid waste to be processed, push the UltraSep button, and walk away.
“It’s like peanut butter,” says chemist Audrey Roman, of the Lab’s plutonium heat-source team, who is working with Coons to bring UltraSep to the plutonium facility. “The sludge that’s left on the membrane filter is the consistency of peanut butter and it’s really hard to clean off. But with UltraSep there would be no membranes, the waste would be captured and stored in the same container.”
Jugs of transuranic waste contain both solids and liquids, which must be chemically and physically separated from each other so that each can be appropriately treated and stored. Dissolved metals must first be undissolved, or precipitated, out of solution. To bring heavy metals like plutonium out of solution, the anion hydroxide (OH-) is added, raising the pH of the solution and binding to the metal atoms, which then precipitate out as solids. Next the mixture must be filtered to remove the precipitated solids, and that’s where UltraSep comes in.
UltraSep uses an ultrasonic standing wave and gravity to continuously separate a flowing solution into its solid and liquid components. The solution enters a vertically-oriented chamber, then silent ultrasonic waves are applied at one side of the chamber. The waves travel through the solution until they reach the other side where they are reflected back off the chamber’s far wall. The returning waves are shifted in orientation compared to the oncoming waves, and their overlap creates alternating positive and negative interference. Although sound waves are traveling in both directions through the solution, the cumulative effect is alternating areas of high and low pressure that don’t travel, resulting in a pattern that appears stationary, thus the term “standing wave.”
Particles in the solution are pushed by the radiative forces of opposing sound waves to regularly spaced positions within the stationary pattern, called nodes. The particles quickly aggregate with other particles at the nodes until a large clump is formed that is heavy enough to be pulled down by gravity to the bottom of the chamber. As particles aggregate and fall to the bottom, the clarified liquid exits the chamber from the top, and fresh suspension enters the chamber through a side channel.
Coons and Los Alamos electrical engineer Eric Raby are working on making the vision of a push-button operation a reality for the heat-source team. This includes the initial pH adjustment step and eventually a final evaporative drying step for the concentrated particles.
“For heat-source work in particular, this could double our production rate,” says Roman. “It would also have a much smaller footprint than current methods, and in our highly specialized facility every square foot comes at a premium.” Both the time and the space that UltraSep would free up could be used for other applications. Once it is successfully implemented for spacecraft heat-sources, Coons is confident it will be picked up by other teams at the Lab who need a solution to their continuous-separations problems.
How it started
UltraSep got its start elsewhere at Los Alamos, far from the plutonium facility, with the Lab’s biofuels team. Microalgae are an ideal candidate in many ways for the development of non-fossil-fuels: they are energy rich, comparatively easy to grow, renewable, and not otherwise needed as food. The removal of waste solids from commodity liquids is called filtering, while the removal of waste liquids from commodity solids is called dewatering, and microalgae that have been grown for biofuels have to be thoroughly dewatered before their energy-dense hydrocarbons are harvested.
“Los Alamos has a very strong program and a long history in acoustics,” says Lab bioscientist Babs Marrone. “We figured out how to use acoustics to separate bioparticles almost ten years before we started looking at algae for fuels. The dewatering step is one of the most expensive steps in the production of microalgae biofuels, so it made sense to try to do it acoustically.”
“For heat-source work in particular, this technology could double our production rate.”
Microalgae cultures need at least 95 percent of their water to be removed and therein lies the rub: unlike plutonium waste applications, biofuel applications are exquisitely energy conscious—there must be more energy coming out than going in, otherwise it’s not sustainable.
It takes the volume of a large backyard swimming pool to grow enough microalgae for one gallon of gasoline-equivalent biofuel. The low concentration of microalgae in this large volume of water creates enormous challenges for dewatering. Los Alamos bioscientists are working on how to grow microalgae in higher concentrations, which will help immensely with the energetics of dewatering. At present, however, filtration is the only technology that can meet the miniscule energy constraints, but it is costly, requires chemical treatments to maintain throughput, and the filters have to be replaced every couple of years.
“Unlike other methods, our technology isn’t expendable,” emphasizes Coons. “There are no filters, no membranes, very little energy goes in, and very little waste comes out.”
To examine how the various particulates under study behave, Coons and Roman paired up with Los Alamos materials scientist Juan Leal and applied mathematician Kim Rasmussen. They discovered that different types of materials precipitate out of solution very differently from one another. For example, metal hydroxide particles interact with water more strongly than do microalgae—essentially absorbing some of the water, so that the particles become larger and dewatering becomes more difficult.
The associated water multiplies the particles' mass and volume many times over, diminishing the efficiency of mechanical removal. With these highly water-associated materials, increasing the particle concentration by a factor of tenfold may be achievable, whereas with less strongly associated materials like microalgae, the team has achieved concentration increases of more than 100-fold.
Using ultrasound for microalgae dewatering has distinct advantages over other methods. It is quieter (silent, in fact) and less dangerous than centrifugation, and it produces much less waste than filtration—no filters, no membranes, no chemicals for cleaning. But it isn’t ready for the big time just yet, because of scaling challenges.
“Scaling from bench-top development to commercial applications is always difficult,” says Marrone. “The separation happens fast, you can watch it, but going from liters at a time to a biofuels-relevant scale has been a challenge.”
The size and shape of containers, for example, can alter how sound waves are reflected and thus affect the system’s performance. On the benchtop separation occurs in small vials, but just how large can a bioreactor, or fermenter, or other type of vessel get?
To help answer this sort of question, Coons and his team collaborated with a private company with expertise in designing chambers for acoustic applications. The collaboration helped with vessel design and also with the energy-in-energy-out challenge. By comparing their own power source to off-the-shelf and commercial power sources, Los Alamos scientists are developing strategies for low-energy deployment of UltraSep for energy-sensitive and other applications.
“We know our efficiencies now,” says Coons. “We know the approach to take, we know which properties matter most, and we’re looking for commercial opportunities to take on those larger volumes.”
How it’s going
The search for large-volume commercial opportunities led, perhaps inevitably, to beer. Unlike nuclear waste processing where both the solid and liquid portions are waste, or biofuels where the solids are the commodity and the liquids are waste, in beer brewing the liquid is the commodity, but sometimes the solids are too. Certain beers are supposed to contain certain solids: Hefeweizen, for example, is famously cloudy, owing to the intentional presence of polyphenols, polysaccharides, protein, and a bit of yeast in the final product.
For the last few years, Coons and his team have been investigating the brewing market in collaboration with five local breweries to evaluate whether UltraSep might have a place in craft beer production. The collaboration was born out of a Department of Energy initiative called Energy I-Corps, which connects national lab researchers with industry mentors to develop pathways for bringing new technologies to market. Through Energy I-Corps, Coons teamed up with Colleen Pastuovic from Los Alamos’ Feynman Center for Innovation. She knew that the craft brewing industry in New Mexico is vibrant and innovative and suggested focusing on that market, so that’s what they did.
Craft beer brewers care a lot about the quality of their beer—above all it must maintain its freshness and taste while on the shelf. A brewer has to decide what to take out and what to leave in to achieve that quality. Before bottling therefore, beer must be clarified to a point where it will have good shelf stability, and things that have been deliberately left in, like yeast, won’t continue to grow and possibly affect flavor.
Over the centuries, beer brewers identified certain organic chemicals, known as finings, that increased the rate of settling for yeast and other particles in beer by increasing the particle size. For example, unflavored gelatin is commonly used by home brewers of lagers and ales because it’s easy to source and does a decent job of taking other particulates with it as it settles. Later, mechanical separation methods were developed but those brought their own set of challenges. For example, the force of the pumps used for filtration can increase dissolved oxygen levels and lead to reduced shelf stability.
Centrifugation is the gold standard for particle removal in large-scale beer production, but it is expensive, very loud, and does too good a job of clarifying. It has no finesse, indiscriminately pulling out all particles, which results in some of them needing to be added back in. Craft brewers generally prefer a lighter touch—they need a technology that is more targeted and tunable—and UltraSep was well received as an attractive alternative.
With funding from the New Mexico Small Business Assistance (NMSBA) program, the team tested UltraSep against a small table-top centrifuge on 12 different beers from the five breweries participating in the proof-of-principle study. As expected, the centrifuge pulled all particles from the beers and UltraSep did not. But UltraSep was able to resolve two populations of particles—large, fast settling particles like yeast, and smaller, slower settling particles like polyphenols and carbohydrates. UltraSep was the most effective on beers with a significant large-particle population to be removed, such as Indian Pale Ales, sours, and seltzers.
The beer study is ongoing. The NMSBA-leveraged project that was born from Energy I-Corps participation got the project started, but there is still a lot that the team plans to do. Because brewers need to control what stays in and what comes out, the scientists are focusing on how UltraSep can best do that.
“The potential to have a new device that brewers can use to dial in a very exact level of separation is incredibly exciting,” says Jeffrey Erway, president of La Cumbre Brewing Company. “We are glad to be included in this study and greatly look forward to seeing what lies ahead for this promising technology.”
"Sometimes it takes an epiphany to realize there’s got to be a better way."
As with biofuels, to be a real contender in the craft beer world, UltraSep needs to be scaled from its current rate of one gallon per hour, up to 50 gallons per minute. In addition to scaling up, the team plans to scale out, which is to include more vessels operating in parallel. “The ability to use fundamental insight to advance technology is woven into the fabric of the Lab,” says Coons. “I’m confident we will get there.”
He’s confident they will get elsewhere as well—ultrasonic continuous separation can be used for many waste streams in which microparticles need to be separated from liquids. From radioactive liquid waste treatment to municipal water treatment, there are many persistent problems that can be overcome with this technology.
“There are challenges that stem from how things were done in the past,” says Coons. “It can be difficult to make improvements because people tend to resist change, even if a process can be made better. Sometimes it takes an epiphany to suddenly realize it doesn’t have to be this way. It’s a wonderful feeling to have an epiphany like that, but it’s even better when there’s a new way, a better way, ready to go.”