St. Paul Wastewater Plant to Grow Algae for Biomass

John Davis

stpaulsustainabilityOfficials in St. Paul, Minnesota believe a pilot project to grow algae at the city’s wastewater plant will clean the water before it’s pumped back into the Mississippi River and provide biomass for biofuels.

Biomass Magazine reports the process will also take nitrogen and phosphorus out of the water that can be used to make fertilizer:

A team of researchers from the University of Minnesota partnered with the Metropolitan Council for the project, using centrate—liquid waste separated from the solids—to grow several species of algae that can thrive in wastewater. The project started in 2006 on a much smaller scale, using wastewater in labs, and recently moved to Met Council’s treatment plant.

“It’s an opportunity to grow algae on a larger scale in colder climates,” said Todd Reubold, director of communications for the Institute on the Environment. “Rather than flushing all these nutrients, we’re recycling them.”

Heavy research and experimenting went into choosing the strains, and the discovery that centrate is the optimal element. “After screening all kinds of algae, we found types that can grow in concentrated wastewater without any additional nutrients,” said Roger Ruan, professor of bioproducts and biosystems engineering at the university, and director of the Center for Biorefining.

Using a wastewater plant to grow the algae saves a significant amount in capital and energy, said Rod Larkins, associate director of IREE. “You have to fertilize algae, but in our case, the fertilizer is already there,” he said. “You save significant money by not having to add nutrients to the algae.” The necessary high volume of water and heat are available, also.

The project will use an enclosed photobioreactor that allows the algae to grow in a smaller area. Officials believe they could produce daily 1,000 to 4,000 gallons of oil to turn into biodiesel.

Biodiesel, biomass