Application of BiVO4–Microalgae Combined Treatment to Remove High Concentration Mixture of Sulfamethazine and Sulfadiazine

Sulfonamides (SAs) are the most common and bio-refractory antibiotics detected in surface water systems, which cause long-term toxic effects on aquatic organisms. This study used the combination of a BiVO4photocatalyst and freshwater micro-green alga (Dictyosphaeriumsp.) to remove sulfadiazine (SD) and sulfamethazine (SM2) at an initial concentration of 5 mg/L (1:1v/v) for 7 days. We set up three gradient concentrations of BiVO4(0.5, 1 and 2 g/L) combined with the same concentration (80 mg/L) ofDictyosphaeriumsp. and then prepared corresponding concentrations of pure BiVO4and pure microalgae as controls. We evaluated the ability of BiVO4andDictyosphaeriumsp. combined technology to remove SAs by observing the removal efficiency of antibiotics and explained the degradation mechanism of antibiotics and the key role of microalgae by studying the changes of reactive oxygen species (ROS) and inorganic ions (nitrogen, sulfur). The results showed that the degradation rate of these two SAs in the 0.5 g/L BiVO4–algae group could reach >96% within 7 d, which was higher than that in the 2 g/L BiVO4group (93%) and the algae group (28%). The increased degradation efficiency of SAs in BiVO4and microalgae systems was mainly due to the increased amount of ROS. Meanwhile, more SAs were degraded to inorganic compounds such as NH4+-N, NO3−-N and SO42−-S under ROS stress. It was found that microalgae can absorb the degradation products of antibiotics such as NH4+-N for their own growth, thereby reducing the toxicity of antibiotic by-products. In addition, BiVO4had no damaging effect on the autofluorescence intensity of the microalgae. Our study provides an efficient and eco-economic approach to remove antibiotics using visible-light irradiation in aquatic environments and provides new insights into the biological removal of other antibiotic contaminants in aquatic environments.Keywords:Dictyosphaeriumsp.;BiVO4;sulfamethazine;sulfadiazine;reactive oxygen species;NH4+-N