by Justin Rickard
Phosphorus in wastewater is a major contributor to harmful algal blooms in water bodies around the globe, with the potential to harm wildlife, livestock, and even humans. To prevent this, wastewater treatment plants often rely on chemical- and energy-intensive techniques to remove phosphorus before it can impact downstream water bodies.
National Renewable Energy Laboratory (NREL) researchers sought to develop new technology for phosphorus removal from wastewater by maximizing the ability of algae to harness solar energy to efficiently accumulate and remove phosphorus from water, storing it inside the cell as polyphosphate.
The Revolving Algal Biofilm (RAB) system by Gross-Wen Technologies is an emerging technology that does just that. In the RAB system, phosphorus-laden algae are cultivated in wastewater attached to a revolving belt. 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.
Now researchers from NREL, Gross-Wen Technologies, and the Metropolitan Water Reclamation District of Greater Chicago have partnered under a Technology Commercialization Fund (TCF) grant through the U.S. Department of Energy (DOE) to further develop the RAB system. TCF grants aim to bring new energy technologies to market by applying DOE funds and national laboratory expertise and infrastructure.
The team of researchers examined the unique properties of phosphorus uptake in the algal strains living in RAB systems. In a new study published in the journal Frontiers in Microbiology, the team detailed how specific algal species outperform the broader population of algae in the system. These findings may offer insight to improve RAB performance while enhancing revenue streams for crop fertilizers or bioenergy feedstocks.
“We were curious to know which of the algae species living in these systems were doing the heaviest lifting in removing the phosphorus from wastewater,” Eric Schaedig, NREL researcher and lead author of the study said. “From a biological perspective, 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.”
Why Optimizing Algal Biofilm Systems Can Boost Efficiency
An interesting behavior of algae is their ability to take up phosphorus at levels that surpass their immediate nutritional needs. This process is called “luxury uptake” and is one of the benefits of using algae to treat wastewater and reclaim nutrients, especially for RAB systems.
In a RAB system, a community of algae adhere as a biofilm to a vertical, revolving belt partially submerged in the wastewater. As they grow, the algae absorb phosphorus and other pollutants from the wastewater while underwater and absorb carbon dioxide and sunlight while above the water. This unique environment supports many algae, and the NREL team sought to isolate and characterize these organisms.
Schaedig said that the process of isolating and characterizing algal strains native to the RAB systems is one way to optimize these systems. Once phosphorus-hyperaccumulating algal strains are isolated and identified in the lab, they can be reintroduced to other RAB systems and prosper, improving phosphorus uptake by the RAB systems.
The researchers isolated nearly 770 algal strains from biofilm samples collected across eight active RAB systems throughout Iowa and Illinois. “Many of these were duplicates of the same algal species, and we pared that number down to 101 unique strains using microscopy,” Schaedig said. Those 101 unique strains were identified using DNA sequencing, and the polyphosphate content of each was determined using advanced screening techniques.
The results were promising. Seven isolated algal strains possessed at least 50% more polyphosphate by cell dry weight (CDW) compared to a baseline RAB system algal community, which came in at 5.1% polyphosphate by CDW. The top phosphorus-hyperaccumulating strain, Craticula molestiformis TCF-8d, accumulated 14.0% polyphosphate by CDW.
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