Carbon-negative and high-rate nutrient removal using mixotrophic microalgae.

Abstract Mixotrophic microalgae have demonstrated great potential for wastewater nutrient removal. How autotrophy/heterotrophy shares affect nutrient removal as well as carbon budget has not been understood. In this study, the autotrophy/heterotrophy shares in mixotrophy were quantified, and N removal rate and carbon budget under different mixotrophic autotrophy/heterotrophy shares were modeled. The results showed that mixotrophic N removal rate reached 2.09 mg L−1h−1, which was 53.18% and 37.98% higher than removal rates in autotrophic (0.97 mg L−1h−1) and heterotrophic (1.25 mg L−1h−1) controls. Mixotrophic-autotrophy and mixotrophic-heterotrophy contributed 1.15 mg L−1h−1 and 0.94 mg L−1h−1 in N removal, respectively. Model disclosed that at balanced share of 6:4, more than 2 mg L−1h−1N removal could be achieved, similar to bacterial nitrogen removal rate but with a negative carbon budget of 6.21 mg L−1h−1. Nutrient removal using mixotrophic microalgae would lead to carbon negative sustainable wastewater treatment and resource recycling.