Photosynthetic bioconversion of hydroponic effluent into biochemical-rich biomass for microalgal biorefineries

Abstract

Here we comparatively assessed eight different microalgae for possible recycling and bioconversion of residual nutrients from hydroponic effluent (HE) into biochemical-rich microalgal biomass. Among the tested strains, S. obliquus sp. 1 could take up nitrate, phosphate and ammonia up to 75.9, 80.8, and 66.7%, respectively. Meanwhile, the nitrate, phosphate and ammonia uptake for other tested microalgae was in the range of 30.6–73.8%, 72.4–72.7%, and 6.6–54.6%, respectively. Further, the highest biomass production, B_x (g L⁻¹), specific growth rate, μ (d⁻¹), and photosynthetic efficiency, PE (mmol per photon m²), were observed for S. obliquus sp. 1 (B_x = 1.42, μ = 0.21, and PE = 22.17) followed by Chlorella sp. (B = 1.35, μ = 0.16, and PE = 16.08) and Chlorella sorokiniana (B = 1.25, μ = 0.15, and PE = 15.99). Moreover, all the tested strains were found to be rich in major biomolecules including carbohydrates (5.76–10.49% TS), lipids (17.78–36.67% TS), and proteins (36.13–50.13% TS). The multivariant correlation analyses revealed that the bioconversion of nutrient-rich HE into biomass was positively correlated with the growth rate, photosynthetic efficiency, and biomolecule accumulation (p < 0.01). Overall, we conclude that S. obliquus sp. 1 may serve as a potential microalga for HE recycling and resource recovery leading towards a wastewater-based circular bioeconomy.