Enhancing removal performance of ciprofloxacin hydrochloride by Chlorella vulgaris-bacteria consortium: Insights of microbial responses and stoichiometry

The microalgae-bacteria consortia (MBC) system has demonstrated significant potential in enhancing the removal efficiency of antibiotics from wastewater. This study systematically evaluated the treatment of ciprofloxacin hydrochloride (CIP) wastewater using pure microalgae ( Chlorella vulgaris ) (PM), pure bacteria (PB), and the MBC formed by the combination of PM and PB. The MBC system achieved an impressive CIP removal rate of 94.6 ± 0.6 % at an initial concentration of 10 mg/L. As the initial concentration of CIP increased from 10 to 80 mg/L, the biodegradation rate declined from 0.42 to 0.13 d - ¹ , with the half-life of CIP significantly increasing from 1.66 to 5.23 days. The MBC notably enhanced CIP removal efficiency by promoting microbial metabolic activity and increasing the concentration of photosynthetic pigments. The secretion of CIP-degrading enzymes to mitigate intracellular oxidative stress indicates the superior tolerance and degradation capacity of the MBC system towards CIP. Acinetobacter johnsonii was identified as the primary contributor to the CIP biodegradation. The molar yield coefficient (MYC) for the bacteria is nearly 2-times fold of that for C. vulgaris based on the growth-process equations of cells on CIP. Collectively, these findings provide valuable insights into the mechanisms by which MBC outperforms PM or PB in the treatment of CIP-contaminated wastewater, thereby contributing to advancements in sustainable wastewater management practices.