An algae bloom on the Detroit River.

St. Louis researchers extract wastewater nutrients to grow algae biomass

Algae often gets a bad rap. For example, some types of the photosynthetic organisms cause blooms in waterways that are harmful to humans and animals. But a lot of research is underway for beneficial ways to use algae, including for more environmentally friendly biofuel and fertilizer.

Researchers at Washington University in St. Louis came up with a new way to use nutrients captured from wastewater to grow algae biomass that is a building block for other products.

The problem

Wastewater contains nutrients that algae consume to help them thrive, including nitrogen, phosphorus, and dissolved organic carbon. Many scientists have tried to leverage those nutrients by studying algae grown in wastewater. 

However, the wastewater environment tends to result in contaminated algae, low algae content in the biomass, and high costs. In addition, the useful algae applications that scientists envision in the lab often prove not to be viable in the real world. 

“What you get is messy,” Zhen (Jason) He, professor of energy, environmental and chemical engineering, said in a news release.

“It’s wastewater. Yes, you get algae. You get bacteria also. Anything will grow there. So, algae biomass grown in wastewater has low value, which reduces the overall economic profit.”

The solution

The researchers found a way to extract the nutrients from wastewater and feed them to algae in a separate environment instead of putting algae directly into the wastewater and trying to grow it. This method produces organisms that are more than twice as pure as those grown in conventional wastewater. 

The team developed a microbial electrochemical system. The technologies use bioelectricity to pull the nutrients out of wastewater, transport them to the algae, and then feed them to the algae.

The biomass created from algae that ate the extracted nutrients was more than 90% algae. However, biomass from algae grown in wastewater is only about 30% algae and 70% bacteria.

What’s next

The scientists say their system for recovering nutrient resources for reuse can contribute to the circular economy. The algae biomass could be used to create a variety of products — including fuel, dietary supplements, pigments, and pharmaceuticals — with fewer environmentally harmful results. 

But first, the research team wants to further increase the purity of the biomass to 95% to 98% algae. Then they will investigate which growing conditions certain algae prefer to determine which organisms are most economically viable to produce. 

Once it is further developed, the technology could be used for resource recovery in wastewater systems across the world.

“Municipal wastewater is similar everywhere,” He said. “Wastewater in Europe is the same as wastewater in Los Angeles. And you want to develop something where people in other places can say, ‘That can work here.’”

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