Effect of different CO₂ concentrations on biogas upgrading and nutrient removal by microalgae-fungi co-culture

Owing to the high carbon dioxide (CO₂)-fixation efficiency, microalgae-based technology has been widely used for biogas purification. The present study explored the effect of CO₂ concentration on biogas purification by an algal-fungal-bacterial symbiotic system. Two algal-fungal-bacterial symbiotic systems were cultivated to purify four simulated biogas samples with different CO₂ concentrations. The results showed that GR24, a synthetic analog of strigolactone, stimulated the growth of the algal-fungal-bacterial symbiotic system. The optimal CO₂ concentration for the purification of the simulated biogas was 45% (V/V), and the optimal symbiotic system was Chlorella vulgaris-Ganoderma lucidum-endophytic bacteria-GR24. The maximum chemical oxygen demand (COD; 82.61 ± 7.73%), total nitrogen (TN; 81.36 ± 7.97%), total phosphorus (TP; 85.69 ± 8.19), and CO₂ (69.23 ± 6.56%) removal efficiencies were detected with the addition of 10^-9 M GR24 to the C. vulgaris-G. lucidum-endophytic bacterial symbiotic system. These findings confirmed the effect of CO₂ concentration on the purification of biogas by the algal-bacterial symbiotic system. The study provides a theoretical basis for further research on the treatment of wastewater and biogas.