Removal efficiency of nitrogen and phosphorus in mariculture effluent by an immobilized algae-bacteria system

To explore the removal efficiency of nitrogen and phosphorus in mariculture effluent, Oocystis borgei and Algoriphagus marincola were used to construct an immobilized algae-bacteria system embedded in calcium alginate. Various initial concentrations of ammonia nitrogen (2.5, 10, 30, and 50 mg/L) and carbon (5, 10, 15, and 25 mg/L) with a constant initial phosphorus concentration of 3 mg/L were set to investigate the efficiency of the algae-bacteria system in removing nitrogen and phosphorus from simulated mariculture effluent. The results showed that within a certain range, as the concentration of ammonia nitrogen increased, the removal efficiency of the algae-bacteria system for both nitrogen and phosphate improved, with ammonia nitrogen removal reaching 17.75–20.08 mg/L and phosphate removal rates exceeding 85 % when the ammonia nitrogen concentration was above 30 mg/L. At a carbon concentration of 5 mg/L, the algae-bacteria system had a greater ability to remove nitrogen and phosphorus, with an ammonia nitrogen removal rate of 80.8 % and a phosphate removal rate of 99 %. Compared to the efficiency of single algae or bacteria, the absorption capacity of nitrogen and phosphorus by the algae-bacteria system was significantly enhanced ( P < 0.05). The study showed that the combined use of O. borgei and A. marincola can effectively remove ammonia nitrogen and phosphate in mariculture effluent. This research provides a theoretical basis for the application of immobilized O. borgei and A. marincola in the treatment of industrial mariculture effluent. • An algae-bacteria system with Oocystis borgei and Algoriphagus marincola was built to study nitrogen and phosphorus removal. • Below 50 mg/L nitrogen, the algae-bacteria system beads outperform single algae and bacteria in nitrogen and phosphorus removal. • At 5 mg/L carbon, algae-bacteria beads ouperform single algae/bacteria in nutrient removal but degrade with higher carbon. • Combined immobilized algae and bacteria enhance nitrogen and phosphorus removal more than either alone.