Integrated utilization of microalgae cultured in aquaculture wastewater: wastewater treatment and production of valuable fatty acids and tocopherols

Marika Tossavainen,Martin Romantschuk,Minnamari Edelmann,Reetta Eskola,Anne Ojala,Katariina Lahti,Anna-Maija Lampi,Vieno Piironen,Pasi Korvonen

doi:10.1007/s10811-018-1689-6

Marika Tossavainen, Martin Romantschuk + Show 7 more

Open Access

https://doi.org/10.1007/s10811-018-1689-6

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Abstract

Microalgal cultivation in aquaculture wastewater (AWW) from recirculating aquaculture systems (RAS) is an approach for combined production of valuable algal biomass and AWW treatment. The growth, nutrient uptake, fatty acid (FA) profile, and tocopherol content of mixed algal cultures of Euglena gracilis with Selenastrum grown in AWWs from pikeperch (Sander lucioperca) and catfish (Clarias anguillaris) RAS were studied. The highest algal biomass (1.5 g L−1), lipid (84.9 mg L−1), and tocopherol (877.2 μg L−1) yields were achieved in sludge-amended pike perch AWW. Nutrient removal rates in experiments were 98.9–99.5 and 98.4–99.8% for NH4-N and PO4-P, and 75.4–89.2% and 84.3–95.7% for TN and TP, respectively, whereas the COD was reduced by 45.8–67.6%. Biomass EPA and DHA content met, while ARA and tocopherol content exceeded the requirements for fish feed. Algal cultivation in AWWs is a promising alternative for AWW treatment while providing a replacement for fish oil in feed.

Highlights

Aquaculture is a fast-growing sector in food production, with an average annual growth of 3.2% and in 2014 human consumption of farmed fish outweighed consumption of wildcaught fish for the first time (FAO 2016)
Based on the optimal N/P ratio (Redfield 1958) in algal biomass, nutrient ratios in both aquaculture wastewater (AWW) without sludge amendment were close to algal requirements (N15/P1), whereas the sludge amendment resulted in higher relative amount of P (N12/P1 in sludge-amended pike perch AWW and N11/P1 in sludge-amended catfish AWW)
At the end of cultivation, only E. gracilis was present in pikeperch AWW, and it was the strongly dominating strain in other cultures, where the cell densities of Selenastrum at the end of the cultivation were under reliable counting limits

Summary

Introduction

Aquaculture is a fast-growing sector in food production, with an average annual growth of 3.2% and in 2014 human consumption of farmed fish outweighed consumption of wildcaught fish for the first time (FAO 2016). Due to the increase in fish farming, serious concerns have been raised regarding environmental pollution related to the aquaculture wastewater (AWW) and over-exploitation of wild fish populations used as fish-feed ingredients (Ansari et al 2017). Environmental friendly practices in fish farming and the use of local and low trophic level biomass, e.g., microalgae for feed, may decrease the environmental impacts of fish farming (Martins et al 2010). Use of recirculating aquaculture systems (RASs) decreases the pollution effect of fish farming and the need for fresh water (Martins et al 2010). In RASs, AWW is treated, and a portion of the effluent water is recirculated through the aquaculture system. In comparison to flow-through culturing systems, the water exchange rate in very intensive RASs is reduced from > 50 to < 0.1 m3 kg−1 fish feed (Martins et al 2010). In RASs, treatment of concentrated sludge containing suspended solids and nutrients, especially phosphorus, increase operating costs (Martins et al 2010)

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