Identification of a microalgae-yeast coculture system for nutrient removal in shrimp culture wastewater

The accumulation of nitrogen and phosphorous has detrimental effects on aquatic animals and negatively influences the economic benefits of aquaculture; thus, the control of water quality is of significance for the development of the aquaculture industry. In this study, a coculture system of Chlorella vulgaris + Rhodosporidium sphaerocarpum exhibited superior nitrogen removal performances compared with those of either the Isochrysis galbana + R. sphaerocarpum or the Tetraselmis helgolandica + R. sphaerocarpum coculture systems. The alginate-immobilized C. vulgaris and suspended R. sphaerocarpum coculture system was advantageous in terms of nutrient removal and the inoculum ratio (IR, dry weight of C. vulgaris to dry weight of R. sphaerocarpum) of 5:1 was determined to yield optimal removal performances of nutrients and the chemical oxygen demand (COD), with which 86.20% of the NH₄⁺ content was removed, and 100.00% removal efficiency of NO₂⁻, NO₃⁻, PO₄³⁻, and COD was detected after 120 h of incubation. The growth of C. vulgaris and R. sphaerocarpum was enhanced and a biomass productivity of 0.22 g L⁻¹ day⁻¹ was obtained. The sustainability of the optimized microalgae-yeast coculture system was confirmed by steady and consistent removal performances in semicontinuous experiments, removing over 80% of NH₄⁺, 100% of NO₃⁻, and over 90% of NO₂⁻, PO₄³⁻, and COD. These results indicated that the optimized microalgae-yeast coculture system developed in our studies might provide a potential method for the biological treatment of aquaculture wastewater.