Nitrate and Phosphate Removal Efficiency of Synechococcus elongatus Under Mixotrophic and Heterotrophic Conditions for Wastewater Treatment

Growing nutrient content of surface waters causes environmental concerns about eutrophication due to the immethodical release of nutrient containing effluent. The potential of microorganisms to decrease nitrogen and phosphorus concentration has drawn increasing attention. The present study is performed to evaluate the nutrient removal potential of cyanobacterium Synechococcus elongatus in different trophic cultivations. For this purpose, 15 experiments were designed by the Box-Behnken method using modified BG-11, including the initial concentrations of phosphorus, nitrogen, and glucose up to 10 mg L-1, 600 mg L-1, and 10 g L-1, respectively. Different trophic conditions were applied by changing carbon sources and light-dark cycles. The maximal removal of phosphorus and nitrogen were obtained in mixotrophic condition with 85.1% and 87.4%, respectively, and the specific growth rate of microalga was 0.99 day(-1). Besides, its nutrient removal efficiency in dairy effluent was about 92% in mixotrophic culture, while the heterotrophic condition was not efficient. Based on the obtained results, mixotrophic cultivation of the cyanobacteria S. elongatus would be useful for application in N-riched and P-riched effluents.