Increasing oxytetracycline and enrofloxacin concentrations on the algal growth and sewage purification performance of an algal-bacterial consortia system

Abstract

Oxytetracycline (OTC) and enrofloxacin (EFX) pollution in surface water are very common. Using the algal-bacterial consortia system to remove antibiotics remains to be further studied. In this study, the algal growth and sewage purification performance were studied in an algal-bacterial consortia system with different concentrations of antibiotics. The enzyme activity, malondialdehyde content, chlorophyll-a content, extracellular polysaccharide, and protein content of algae were also tested. It was found that the algal growth was promoted by low-dose antibiotics, 21.83% and 22.11% promotion at 0.1 mg L−1 OTC and EFX, respectively. The nutrients and antibiotics removals of the low-dose groups (OTC <5 mg L−1, EFX <1 mg L−1) were not affected significantly. More than 70% of total organic carbon and total phosphorus, and 97.84–99.76% OTC, 42.68–42.90% EFX were removed in the low-dose groups. However, the algal growth was inhibited, and the nutrients removals performance also declined in the high-concentration groups (10 mg L−1 OTC, 5 mg L−1 EFX). The superoxide dismutase and catalase activity, and malondialdehyde content increased significantly (P < 0.05), indicating the increased activity of reactive oxygen species. In addition, the decreased chlorophyll-a content, thylakoid membrane deformation, starch granules accumulation, and plasmolysis showed that the algal physiological functions were affected. These results showed that the algal-bacterial consortia system was more suitable to treat low-concentration antibiotics and provided basic parameters for the consortia application.