Increasing tetracycline concentrations on the performance and communities of microalgae photo-bioreactors to treat effluent from anaerobic membrane reactors.

This study investigated the impact of different concentrations of tetracycline on the performance of microalgae photo-bioreactors to treat the effluent from anaerobic membrane bioreactors (AnMBR). With carbon dioxide from biogas collected from AnMBR, the removal of nutrient, i.e., nitrogen and phosphorus was not affected at low concentrations of tetracycline (<=150 ug/L), but high concentration of tetracycline at 20 mg/L affected the removal of nutrient. Conversely, the production of microalgal pigments was induced at high concentration of tetracycline. 16S rRNA-based sequencing showed that both Proteobacteria and Bacteroidetes were adversely inhibited, and conversely, Chloroplast were enriched, probably causing the increasing the production of microalgal pigments. Results also showed that both the nitrogen-fixing and phosphate-accumulating organisms were inhibited at high concentration of tetracycline, probably causing the weak performance of microalgae photo-bioreactor to remove nutrient. Additionally, compared to the control, increasing abundance of tetracycline resistance genes associated with efflux pump mechanism was present at high concentrations of tetracycline. The relative abundance of unclassified_Comamonadaceae increased at the high concentration of tetracycline, probably responsible for the increased abundance of tetracycline resistance genes. These findings suggest that microalgae photo-bioreactors can robustly treat nutrient-rich wastewaters with varying concentrations of antibiotics while also generating value-added products.