Nutrient removal (nitrogen and phosphorous) in secondary effluent from a wastewater treatment plant by microalgae

Microalgae as a feasible option to remove nutrients (phosphorous and nitrogen) from domestic wastewater treatment plant discharge is demonstrated. Laboratory-scale experiments are described, characterizing nutrient removal of total phosphorous and ammonia by three cultured microalgae strains: Chlorella vulgaris, Spirulina maxima, and mixed cultures of naturally growing algae found in wastewater from the Collingwood Wastewater Treatment Plant in Ontario, Canada containing Synechocystis sp. (dominant), Chlorella sp. (common), and a few cells of Scenedesmus sp. Removal of phosphates strongly positively relates to solution pH. Volatilization of ammonia due to increase in pH is not a dominant contributor to overall removal efficiency. Total phosphorous removal rates reached 95.8% and 90.4% for untreated and autoclaved secondary effluent, respectively. Ammonia removal rates reached 94.6% and 86.2% for untreated and autoclaved secondary effluent, respectively. These results demonstrate that use of microalgae represents a sustainable approach to improve removal efficiencies of nutrients in wastewater treatment.