Physiological responses and removal pathways of Auxenochlorella protothecoides, Tetradesmus obliquus and Chlamydomonas acidophila to antibiotics commonly found in wastewater

Abstract

The main objective of this study is to investigate the effect of mixtures of seven widely used human antibiotics (ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole and trimethoprim) on the growth, pH, pigment production and antibiotics removal of three microalgal species (Auxenochlorella protothecoides, Tetradesmus obliquus, and Chlamydomonas acidophila). Batch assays were carried out containing media with mixtures of pharmaceuticals at three concentrations: 10, 50 and 100 µg L-1. A decrease in the pH and increased production of chlorophylls and carotenoids, up to 40% for A. protothecoides, were observed in the media with the highest concentration of antibiotics. However, no inhibition has been observed in the growth of the three species. The antibiotics were primarily removed through biosorption by the microalgae biomass, ranging between 21 and 70%. Bioaccumulation and biodegradation were only observed for A. protothecoides – a species never investigated before for the removal of antibiotics – presumably due to a rise in the heterotrophic activity selectively triggered by the concentrations of antibiotics. In the present study, it has been observed that physiological responses and the removal of antibiotics by microalgae are interlinked and depend on the levels and types of exogenous compounds.