Phycoremediation and simultaneous production of protein‐rich algal biomass from aquaculture and agriculture wastewaters

BACKGROUND Microalgae cultivation in wastewaters is a potential remediation technology for converting residual nutrients into valuable biomass for biofuels, fertilizers, animal and aquaculture feeds, and bio‐based chemicals. The objective of this study was to determine the potential for microalgae phycoremediation of aquaculture and agriculture wastewaters for sustainable production of nutrient‐rich algal biomass. RESULTS Thirty‐seven aquaculture and agriculture wastewaters were evaluated as growth media for two freshwater, chlorophytic microalgae strains (Chlorella sorokiniana SMC14M and Scenedesmus sp. AMDD). Although nutrient levels and physicochemical parameters of the wastewaters varied widely, phycoremediation efficiency of nitrogen and phosphorous was high (> 70%) for a large majority of them, with both microalgae strains. Photobioreactor cultivation (300 L) of C. sorokiniana grown on finfish aquaculture wastewater (CA2) and standard growth medium (SGM) exhibited similar biomass production levels and nutritional compositions of moisture (4.9–5.0%), ash (5.9–6.1%), nitrogen (8.6–8.8%), protein (41.0–42.1%), lipid (8.6–8.8%), carbohydrate (38.3–39.3%) and gross energy (22.2–22.3 MJ⋅kg−1) with highly similar fatty acid and amino acid profiles. CONCLUSIONS This study demonstrates that the use of freshwater microalgae to remediate various aquaculture and agriculture wastewaters, while producing valuable nutrient‐rich biomass, is feasible. We have found that a particular finfish aquaculture wastewater (CA2) contains all of the nutrients required for rapid microalgae growth, avoiding the need for expensive commercial fertilizers. The biochemical composition of C. sorokiniana grown on CA2 aquaculture wastewater has good potential for use as a nutrient‐rich ingredient for animal and aquaculture feeds, fertilizers products, biofuels and other applications, resulting in remediated water that could be reused. © 2023 National Research Council Canada. Reproduced with the permission of the Minister of Innovation, Science, and Economic Development.