Algae’s carbon reduction abilities get additional confirmation

When most Americans hear the word “biofuel”, corn is likely the first thing that comes to mind. But algae is another viable alternative — if it can be mass produced.

Algae species like seaweed and pond scum are capable of photosynthesis, and this process can be harnessed by researchers and used for different applications. As a whole, algae have the potential to produce 10 to 100 times more fuel per acre of land compared to other crops but this requires huge water and carbon dioxide (CO₂) inputs. These resources are limited in many US regions, making it hard to sustain production. However, the Midwest — which is abundant in high purity CO₂ thanks to corn ethanol production — is an area where algae generation has the potential to bloom.

Fermenting corn yields concentrated CO₂ along with ethanol. Researchers at the US Department of Energy’s (DOE) Argonne National Laboratory and Pacific Northwest National Laboratory (PNNL) recently published a study detailing the challenges and opportunities associated with leveraging this CO₂ to grow algae in the Midwest.

“This work ultimately shows the potential for growing algae in the Midwest while mitigating emissions from ethanol production. It is a region to consider moving forward for those seeking to commercialise algal carbon capture and utilisation technologies,” Argonne senior scientist Troy Hawkins, a study co-author.

Hawkins and his team’s findings reveal that Midwest conditions can support algae growth and that year-round fuel production can be maintained by using other materials, such as wood residue, to generate fuel in the seasons when algae doesn’t grow well. They also found that cultivating algae in this manner can in turn reduce the greenhouse gas emissions from ethanol production by eliminating the need for ethanol producers to capture the carbon made along the way.

“Warmer regions like the southern states are usually considered better for growing algae, but many locations have limited access to the water and carbon dioxide needed for algae cultivation,” Hawkins said. “One of the questions we tried to answer in this study is whether the benefit of abundant, high-purity CO₂ and freshwater in the Midwest would offset the less favourable growth conditions in the region.”

Benefits of Midwest production

Midwestern states are not generally considered favourable for algae production due to their cold winters. However researchers found that, in warmer months, a Midwest algae pond could cultivate as much algae as southern states but with less water stress. And when concentrated CO₂ from corn ethanol production — versus dilute CO₂ from coal power plants — is used, the process becomes more energy efficient.

“Using the concentrated CO₂ from corn fermentation to grow algae has the potential to reduce the carbon intensity of ethanol while producing additional algal biofuel,” Hawkins said. “This is important, as corn fermentation generates a significant amount of CO₂ — very roughly, one-third of the carbon in corn goes into the ethanol, one-third is left in the distiller’s grain, which is used as animal feed, and one-third goes to the atmosphere.”

Life cycle analysis detailed impact

Researchers arrived at their results after doing a full life cycle analysis of the process for making algae-based biofuel. They relied on Argonne’s Greenhouse gases, Regulated Emissions, and Energy use in Technologies (GREET) model, a one-of-a-kind analytical tool that simulates the energy use and emission outputs of various fuel and vehicle combinations.

“We used GREET to calculate all of the emissions generated in each step of the biofuel production process,” said Argonne energy systems analyst Longwen Ou, study lead author. “This included working through the details of the emissions from the supply chain and from the electricity used for production.”

Argonne and PNNL collaborated on this effort, leveraging modelling capabilities developed at the two laboratories to provide new insights to industry looking to commercialise algae production for biofuels and bioproducts as well as to government agencies involved in setting policies that affect algal biofuel production and decarbonisation measures. PNNL’s Algae Biomass Availability Tool was used to estimate algae productivity.

The study can be read here.