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.
Keywords: Autotrophic/heterotrophic shares; Internal carbon cycling; Mixotrophic microalgae; Negative carbon emissions; Wastewater nutrient removal.
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