Algae investigated as source of biodiesel

Council and U of M team up for research project

Algae — that unsightly scum that fouls our lakes and ponds — just might have some redeeming value after all. At the Metropolitan Council’s wastewater treatment plants it could be:

Cultivated and harvested as a source of energy
Used to remove carbon dioxide, phosphorus and nitrogen from wastewater
Used as a carbon offset to meet anticipated greenhouse gas emission requirements.

Some algae are high in oil

Plastic tubing used in the research process

An early step in the research into producing fuel from algae involved pumping water, algae and nutrients through spirals of plastic tubing illuminated with fluorescent light. This process helped researchers to measure algae growth rates.

Researchers at the Council and the University of Minnesota have teamed up to investigate the potential for algae-to-fuel technology. They know that some types of algae consist of up to 40% oil, which can be extracted to produce biodiesel, with the remaining cell mass further processed to produce bio-oils and other energy products.

And with the Council turning more than 250 million gallons of wastewater each day into clean water that is discharged into area rivers, they see a potential supply of water for cultivating large amounts of energy-producing algae.

“The basic concept of producing fuel from algae and growing the algae in our treated wastewater (effluent) is fairly simple, but it will require significant effort to determine if the concept is technically and economically feasible,” said Robert Polta, manager of Research & Development at Metropolitan Council Environmental Services (MCES), the Council division that operates the regional wastewater collection and treatment system.

Helping to offset greenhouse gas emissions

An obvious benefit of developing an algae-to-fuel technology would be harnessing a new local and secure source of renewable energy. Less obvious, though, is that the wastewater treatment process also could stand to gain.

Within the next 10 years federal and state environmental regulations will likely call for increased removal of phosphorus and nitrogen, and control of greenhouse gases in the wastewater treatment process. Algae essentially convert carbon dioxide, nitrogen and phosphorus into cell mass.

This carbon dioxide reduction could help offset the carbon dioxide emissions from the wastewater solids incinerators at two of the Council’s treatment plants — an important factor in future greenhouse gas regulations. And cultivating algae in treated effluent might deliver the required additional phosphorus and nitrogen removal at a lower overall cost than other alternatives, when factors such as energy production and carbon offsets are considered.

Partnership marries research and practical needs

Much more research needs to be done and many questions need answers, and that is where the Council’s work with the U of M comes in. The partnership grew of out of an initial meeting in 2006 involving MCES and the U of M’s Initiative for Renewable Energy and the Environment (IREE).

The two parties were seeking a marriage of the Council’s practical needs with the U of M’s research interest and expertise. Their early discussions and research findings about cultivating algae as a source of fuel proved promising enough to proceed, and the partners each put up $40,000 in 2007 as seed money for laboratory-scale studies.

Partners seek state funding to support studies

The Council recently asked for $990,000 in state funding for a bench-scale study and subsequent pilot-scale process demonstration over the next two years. During the bench-scale study, MCES plans to grow and harvest algae in a wastewater effluent flow of one-half liter per minute (about 180 gallons per day). IREE will determine what kind of algae grows best in the effluent and measure its oil content.

The pilot-scale demonstration would involve an effluent flow of 5 gallons per minute (7,200 gallons per day) that would produce about two pounds of dry algal cell mass per day — enough for IREE to do advanced studies on how much and what kinds of fuel can be produced. This stage of the research is tentatively planned for late 2008 through 2009.

“After operating the pilot plant 24 hours a day for a full year, we hope to have identified all of the technical issues associated with algal growth and harvest, and we anticipate that the university researchers will successfully characterize energy recovery from the algal cell mass,” Polta said. “Together we can then determine the economic feasibility of the concept and proceed with a much larger scale production facility if justified.

“The prospects are intriguing,” Polta said, “but we have many questions to answer and challenges to overcome before we can answer the ultimate question: Is it practical?”