Nutrient and tetracycline removal from simulated biogas slurry and biogas upgrading by microalgae cultivation under different carbon nanotubes concentrations

The present study sought to determine the effects of multi-walled carbon nanotubes (MWCNTs) concentrations (0–10 mg L−1) on tetracycline (TC) and biogas slurry nutrient removal by microalga Chlorella vulgaris cultivation. Treatments with 1 mg L−1 MWCNTs yielded the maximum chlorophyll a content, dry weight, and algal density of 143.73 ± 3.11 μg L−1, 0.81 ± 0.008 g L−1, and 5.83×107 cells L−1, respectively, suggesting that 1 mg L−1 MWCNTs could enhance microalgal growth performance and photosynthesis effectively. The highest removal rates of chemical oxygen demand, total phosphorus, total nitrogen, TC, and CO2 under 1 mg L−1 MWCNTs were 90.43 ± 5.15%, 78.12 ± 4.33%, 77.07 ± 4.12%, 89.64 ± 3.08%, and 64.26 ± 0.71%, respectively. These results elucidated that moderate MWCNTs concentrations might promote TC and nutrient removal by enhancing Chlorella vulgaris photosynthesis activity.