Arizona Researchers Study How A Little Plant May Absorb A Lot Of Carbon From Coal-Fired Power Plants
Taking a deep breath when viewing Arizona landscapes may seem unwise with smokestacks on the horizon. But new research from a local partnership is hoping a tiny plant, one known for taking over pools, can absorb carbon dioxide from coal burning power plants, and then maybe use those plants for fuel, food and medicine.
Inside ASU’s Arizona Center for Algae Technology and Innovation (AzCATI), large glass test tubes connected to gas lines bubble and stir. Inside each one, a different strain of algae species swirl in reaction to various levels of carbon dioxide.
AzCATI Professor Thomas Dempster is looking to see which of these species is growing the most.
“Part of our selection process is to isolate each of the strains, bring it back into the laboratory, and expose it to nutrients and carbon dioxide to do growth trials" said Dempster. "We’ll immediately eliminate a number of the isolates that don’t grow well at all. They have no potential for carbon capture.”
These algae strains were taken from nine different water sources at Salt River Project’s (SRP) Coronado Generating Station, a coal-fired power plant just northeast of St. Johns in eastern Arizona. The plant produces more than 6 million tons of CO2 annually and with new EPA carbon regulations, SRP needs to bring that number down which is what brought SRP engineer Sam Villalobos to AzCATI.
“We’re always trying to look at ways to reduce our emissions and control the emissions," Villalobos said. "But really right now, carbon dioxide capture or emissions control is still being developed. So, when we were looking at this, this was one of the technologies that looked like it had potential that we decided to explore.”
Villalobos said he saw algae naturally occurring at the plant's retention and evaporation ponds and thought the tiny plant may help absorb the plant’s CO2 emissions. Of the near 100 species collected and brought to AzCATI, Dempster said 22 have shown promise so far.
“We want to maintain the algae in logarithmic growth phase, so we need fast growing algae that can survive on the flue gas," said Dempster. "Then we’ll do biochemical characterization of the biomass really to see what products are possible from that strain of microalgae. After we generate a large amount of biomass, there may be a second phase where we stress them to drive them towards a product of interest.
Dempster said they stress algae by depriving them of nutrients like nitrates and phosphates and increasing light exposure. By doing so, it changes their metabolism rates and creates products like pigments and lipids for biofuels. So far Dempster said they've exposed the algae to about 12 percent CO2 concentration, which is about the same as Coronado’s flue gas. He pointed to one test tube in particular, sporting a dark shade of green.
“This is currently our most promising and interesting strain," said Dempster. "It grows very fast, does capture a lot of carbon, but it also produced a somewhat unusual omega-3 fatty acid, similar to fish oils. But has a lot of potential health and dietary supplement value.”
So much value that it’s changing the algae industry said Mark Edwards, a retired researcher in the algae industry.
“Economics drives the industry, and that’s why the industry has evolved from biofuels which now are $60 a barrel and a barrel of Omega-3 fatty acids is worth $15,000,” said Edwards.
Edwards said algae’s versatility goes well beyond biofuels and fatty acids for a simple reason.
“We can make almost any bio-product you can imagine," Edwards said. "All land plants evolved from algae about 500 million years ago, so all the compounds we have in our food and fiber systems are available in algae.”
Edwards said the ASU and SRP research may greatly advance algae production. He said for every ton of algae, it absorbs nearly two tons of carbon dioxide, which surprisingly has been hard to access.
“One of the choke points in algae production has been access to a carbon source," said Edwards. "If you take the gas and put it through an algae pond, the algae is going to grab a lot of that carbon, and through photosynthesis, make hydrocarbons out of it which you can then make into food, fuels, fertilizers and even animal feed.”
All of which Edwards said can be done on a much smaller land footprint than other plants used to make similar products. And since ponds already exist at power plants, it would require little to no additional space or water.
Most coal-fired emissions is water vapor. Along with the 12 percent of carbon dioxide, emissions include small amounts of methane, sulfur and nitrous oxides and heavy metals, such as mercury and cadmium. Edwards said that by solidifying the emissions in algae, it would be possible to separate out the heavy metals along with biomass products and even sell those back to other industries.
Edwards pointed out coal plants run non-stop, whereas sunlight for photosynthesis takes place only during the day. But he said productive algae growth needs at least 70 degrees Fahrenheit and lots of sun, making Southwest power plants an ideal location for this research.
Back at AzCATI, outside labs with large 100,000 liters raceway ponds pushing algae in the bright sun. Villalobos said testing at the plant would not require any additional water, unless the operation scales up. He said in a perfect world, at max capacity, they would take the plant’s smokestacks and bend them over into massive algae ponds. But as a pilot project, the infrastructure would look a little different.
“Hooking up a small, 4-inch pipe on the stack somewhere to see if we can even get that flue gas to go over to the algae bed and maybe a couple hundred feet of pipe," said Villalobos. "The pressure behind it should be enough to move it through, and then a small reactor bed with the algae on site to see if that algae can actually survive.”
Villalobos said all water used for cooling stays on site in evaporative retention ponds, so no potential contamination of the water would leave the site. He noted there will be costs, but SRP calls the research an investment.
“Hopefully we can get to a point where if this technology does prove viable, that would be a trade-off that we would be willing to accept," Villalobos said. "And the real goal here is to try to reduce CO2 emissions. If we can get a product that is profitable in the end, that is icing on the cake.”