Researchers isolate microalgae strains that capture phosphorus from wastewater for reuse

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Revolving Algal Biofilm System
A close-up of algal biofilm on a RAB system is shown on the left. On the right is a dried algal fertilizer product produced from the system. Photo Credit: Gross-Wen Technologies

Colorado-based National Renewable Energy Laboratory researchers have identified and isolated phosphorus-hyperaccumulating algae that have the potential to capture and reuse phosphorus from wastewater before it can be discharged and cause imbalances such as harmful algal blooms in aquatic ecosystems. 

The Revolving Algal Biofilm (RAB) system by Gross-Wen Technologies is an emerging technology for phosphorus removal from wastewater that maximizes the ability of algae to harness solar energy, and efficiently accumulate and remove the vital nutrient, storing it inside the cell as polyphosphate, a new study says. 

“In the RAB system, phosphorus-laden algae are cultivated in wastewater attached to a revolving belt,” a National Renewable Energy Laboratory (NREL) announcement explained about the project. “The grown algal biomass can then be harvested from the belt and dried for use as agricultural fertilizer or as feedstock for the manufacture of biofuels and bioproducts. This process can help close the phosphorus-cycle loop by recycling and reusing the phosphorus in wastewater, decreasing demand on limited minable phosphorus resources.”

Among 101 microalgae strains identified by NREL researchers, seven possessed high levels of polyphosphate. These seven isolated algal strains possessed at least 50% more polyphosphate by cell dry weight compared to a baseline RAB system algal community, which came in at 5.1% polyphosphate by cell dry weight, the study found. The strains included 82 green algae, 9 diatoms, and 10 cyanobacteria.

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The RAB process can not only help prevent harmful algal blooms in aquatic ecosystems but can also create a closed-looped cycle for phosphorus. In addition to phosphorus recovery, the results from this research may have additional benefits for the recovery and reuse of other valuable resources lost in wastewater, announced NREL researchers.

“The beauty of this research into phosphorus-hyperaccumulating algae is its implication beyond just phosphorus recovery,” announced Jianping Yu, principal investigator at NREL and senior author of the study, in a statement. “Polyphosphate is known to bind to and accumulate metals in algae. So, the strains isolated in this study may be promising for other algal waste-remediation applications, like removing or recovering harmful or valuable metals from industrial processes and wastewater.”

Researchers from NREL, Gross-Wen Technologies, and the Metropolitan Water Reclamation District of Greater Chicago have partnered under a Technology Commercialization Fund grant through the U.S. Department of Energy to further develop the RAB system.

Eric Schaedig, NREL researcher and lead author of the study, said he was curious to know which of the algae species living in the RAB systems were doing the “heaviest lifting” for removing the phosphorus from wastewater.  

“From a biological perspective,” he said, “if we can isolate and enrich RAB systems with these hardworking algal species, it would boost the efficiency of the overall system and help us close the loop on the phosphorus cycle.”

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