Removal of antibiotics and their impact on growth, nutrient uptake, and biomass productivity in semi-continuous cultivation of Auxenochlorella protothecoides

The prevalence of antibiotics in wastewater poses risks to human and animal health, contributing to antimicrobial resistance. Although various antibiotic removal methods exist, microalgae-based technology presents a cost-effective and eco-friendly alternative; however, limited research on its long-term integration in semi-continuous wastewater treatment trials hinders our understanding of its potential effectiveness.
This investigation explored the antibiotic removal capabilities of the microalga Auxenochlorella protothecoides in photobioreactors with synthetic wastewater under semi-continuous conditions over one month. Additionally, the study assessed the impact of seven commonly used antibiotics (ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole, and trimethoprim) on the microalgal system regarding growth, nutrient removal, and biomass productivity. The microalga effectively removed antibiotics, achieving maximum removal efficiencies ranging from 45.8% to 70.1% over 3–4 days of exposure. Remarkably, antibiotics stimulated algal growth, resulting in an 11.0% increase in biomass. Nutrient removal also improved significantly; ammonium removal rose from 78.0% to 86.4%, and phosphate removal increased from 85.1% to 90.3%. Furthermore, the biomass composition showed notable enhancements, with increases in pigments (12.9%), lipids (20.6%), proteins (45.8%), and carbohydrates (50.6%).
These findings highlight the potential applicability of A. protothecoides as a valuable addition to conventional wastewater treatment plants. The study emphasises the importance of considering antibiotic presence in microalgae-based wastewater treatment technologies, as these compounds can have a stimulatory effect that enhances both growth and nutrient removal efficiency. Overall, this research contributes to the development of more effective strategies for managing antibiotic pollution in wastewater.