Study addresses sustainability of algae biodiesel

A team of researchers at Kansas State University is studying the environmental and economic sustainability of algae biodiesel production. Results of the environmental portion of the evaluation, titled “Sustainability of algae derived biodiesel: a mass balance approach,” have been published in a peer-reviewed journal. A follow up study will address economic stability.

According to Peter Pfromm, a professor of chemical engineering at KSU, the team used a carbon mass balance to evaluate the environmental sustainability of algae biodiesel production. “The application of mass balance is a very familiar item in chemical engineering, and it’s based on the scientific principal of concentration of mass, so that mass is neither destroyed nor created in a process,” Pfromm said.

Mass balance is addressed in each unit operation. Examples of unit operations include the algae pond, the distillation column, and the biodiesel production process. “These unit operations are then knitted together with mass and energy flows to represent the entire process,” Pfromm continued. “The idea is that mass flows into and out of an operation have to balance…If there are 10 carbon atoms an hour coming in, there must be 10 carbon atoms an hour going out—maybe in a different chemical form of course, but it has to be the same number of carbon atoms.” When the same amount of mass, or in this case, carbon, enters and leaves a system, the unit is balanced. When it does not, the system is unbalanced. One example of an unbalanced system is a natural gas reservoir. Carbon leaves the reservoir, but does not return.

“We are trying to use that principal to [determine] the sustainability of biodiesel from algae, and the operations over the entire life cycle,” Pfromm said, noting that this includes everything from algae production to end use of the resulting biodiesel. “If the atmosphere is a balanced unit operation, the carbon has to come out again of the atmosphere,” he said.

What Pfromm and his team ultimately determined is that algae biodiesel produced using CO₂ sourced from fossil fuels, such as a coal-fired power plant, is not environmentally sustainable in terms of carbon. This is due to the fact that although the CO₂ coming from the coal is recycled and used to produce biodiesel, that carbon is still eventually added to the atmosphere and is not sequestered. Algae biodiesel produced using renewable CO₂, such as that produced at an ethanol plant, however, is nearly environmentally sustainable. “The only nonsustainable [aspect] of the operation is making fertilizer to make the algae, which comes from natural gas.”

In the analysis, it was assumed that biodiesel produced from algae would be used to power algae cultivation and the conversion of algae oil into biodiesel. According to Pfromm, his team concluded that slightly more than 10 percent of the resulting biodiesel would be needed to fuel the process. The rest could be sold commercially.

While environmental sustainability may not be crucial from an economic point of view, Pfromm said many people would expect that algae biodiesel be produced in a sustainable way, so that over the long-term the process could be run without negatively impacting the environment. “We wanted to apply a rational approach to sustainability, based on the bedrock of conservation of mass rather than other concepts that are often applied to sustainability,” which are not as clearly based on scientific principle, he said.

The analysis also addressed the theoretical and realistic limitations of algae oil production. According to Pfromm, the theoretical limitation of algal biomass production—under ideal conditions—ranges from approximately 160 to 200 grams per square meter per day. “There is a clear maximum that we cannot exceed, and that maximum is set by the sun, by the solar radiation, which we cannot change,” Pfromm said. However, the theoretical limit represents ideal conditions, not actually conditions. For the analysis, Pfromm and his team assumed a biomass production rate of 50 grams per square meter per day. Pfromm notes that realistic production rate is supported by a wide range of algae specialists.

To complete the economic analysis, KSU agricultural economics professor Vincent Amanor-Boadu used the data gathered through the technical study to assess the economic feasibility of algae biodiesel production. According to Pfromm, the analysis assumes “no free lunch,” meaning no substantial tax support for the fuel and no access to cheap capital to build a plant. “It’s a fairly straightforward analysis of market-driven [factors] to see if it would fly,” Pfromm said. “The results are that even at 90 grams per square meter per day, it’s doesn’t return a positive economic picture.” That said, economics can change due to rising oil prices and other unforeseen factors.

The team, which also includes KSU resource specialist Richard Nelson, demonstrated that work in the algae industry right now should focus on fundamental biochemistry, biology and genetic engineering, Pfromm said. “The algae organism is the engine under the hood…the work on the engine is probably the most important [right now],” he said, noting that large-scale algae production has already been proven for other industries, such as food additives. To sustainably produce lower-value fuel products, algae strains will need to be optimized. 

Pfromm stresses that the research his team has completed has not been supported by any company or government agency, and that the team has no agenda. He also notes that no members of the research team have active ongoing research in algae cultures or growth.