Growing Coastal Marine Microalgae in Wastewater from a Salmon Farming System

Jenn Hoskins
13th July, 2024

Growing Coastal Marine Microalgae in Wastewater from a Salmon Farming System

Image Source: Natural Science News, 2024

Key Findings

  • The study, conducted at the University of Agder in Norway, tested three microalgal species in aquaculture wastewater (AWW) from an Atlantic salmon RAS facility
  • All three microalgal species grew well in various concentrations of AWW, with the highest growth rates observed at 75% AWW concentration
  • The microalgae achieved nearly complete removal of nitrite, nitrate, and phosphate, and approximately 90% of ammonium was removed when cultivated in 75% AWW
As global demand for seafood increases, sustainable fish farming practices have become critical. Recirculating aquaculture systems (RAS) are increasingly favored for their efficiency and reduced environmental impact. However, managing fish waste remains a significant challenge. A recent study conducted by the University of Agder investigated the growth and nutrient removal capabilities of three microalgal species—Isocrysis galbana, Phaeodactylum tricornutum, and Skeletonema marinoi—in aquaculture wastewater (AWW) from an Atlantic salmon RAS facility in Agder, Norway[1]. The study aimed to determine whether these microalgae could thrive in different concentrations of AWW mixed with cultivation medium and effectively remove nutrients such as nitrate, ammonium, and phosphate. The findings revealed that all three microalgal species exhibited growth in various concentrations of AWW, with average growth rates at 75% AWW concentration being 0.31 ± 0.00 day^-1 for I. galbana, 0.34 ± 0.00 day^-1 for S. marinoi, and 0.25 ± 0.02 day^-1 for P. tricornutum. Notably, these microalgae achieved nearly complete removal of nitrite, nitrate, and phosphate, and approximately 90% of ammonium was removed when cultivated in 75% AWW. The potential of microalgae in aquaculture is not new. Previous studies have highlighted the benefits of using microalgal biomass as a sustainable alternative to fish meal and fish oil in aquaculture feeds[2]. Microalgae are nutrient-rich, providing essential amino acids, valuable lipids, vitamins, and pigments, making them suitable as nutritional supplements in livestock feed formulations. The high digestibility of microalgal biomass reduces production costs, feed waste, and the risk of eutrophication, contributing to a more sustainable aquaculture industry[2]. This recent study aligns with earlier findings on the role of microalgae in wastewater treatment. Mixotrophic microalgae have been recognized for their ability to utilize both organic and inorganic carbon, as well as inorganic nitrogen and phosphorus, in wastewater, thereby reducing the concentration of these substances in water sources[3]. The University of Agder's research demonstrates that microalgae can effectively treat aquaculture wastewater, further validating their role in environmental sustainability. Moreover, the study's focus on Skeletonema marinoi is particularly noteworthy. Previous research has established S. marinoi as a new genetic model for marine diatoms, emphasizing its role in global photosynthetic carbon sequestration and nutrient cycling[4]. The successful growth and nutrient removal capabilities of S. marinoi in AWW underscore its potential for biotechnological applications, including wastewater treatment and sustainable aquaculture. In comparing the nutrient removal efficiencies of different bioreactors, it has been found that algal-bacterial biofilm reactors exhibit significantly higher nutrient removal rates than bacterial biofilm reactors alone[5]. The algal-bacterial biofilm supported twice the nutrient removal efficiency, with phosphorus being effectively removed through assimilation into algal-bacterial biomass. This aligns with the University of Agder's findings, where the tested microalgae species achieved high nutrient removal rates in AWW, suggesting that integrating microalgae into RAS could enhance nutrient management. In summary, the University of Agder's study confirms the viability of using aquaculture wastewater for microalgal cultivation on a laboratory scale, presenting a sustainable route to develop a circular bioeconomy in aquaculture. By leveraging the nutrient removal capabilities of microalgae, this approach addresses the waste management challenges in RAS and contributes to a more sustainable and efficient aquaculture industry.

EnvironmentSustainabilityMarine Biology

References

Main Study

1) Successful growth of coastal marine microalgae in wastewater from a salmon recirculating aquaculture system

Published 12th July, 2024

https://doi.org/10.1007/s10811-024-03310-1

Related Studies

2) An overview of microalgae biomass as a sustainable aquaculture feed ingredient: food security and circular economy.

https://doi.org/10.1080/21655979.2022.2061148

3) Integrating micro-algae into wastewater treatment: A review.

https://doi.org/10.1016/j.scitotenv.2020.142168

4) Skeletonema marinoi as a new genetic model for marine chain-forming diatoms.

https://doi.org/10.1038/s41598-019-41085-5

5) Carbon and nutrient removal from centrates and domestic wastewater using algal-bacterial biofilm bioreactors.

https://doi.org/10.1016/j.biortech.2013.04.008


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