Abstract
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 BiVO4 photocatalyst and freshwater micro-green alga (Dictyosphaerium sp.) to remove sulfadiazine (SD) and sulfamethazine (SM2) at an initial concentration of 5 mg/L (1:1 v/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) of Dictyosphaerium sp. and then prepared corresponding concentrations of pure BiVO4 and pure microalgae as controls. We evaluated the ability of BiVO4 and Dictyosphaerium sp. 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 BiVO4 group (93%) and the algae group (28%). The increased degradation efficiency of SAs in BiVO4 and 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, BiVO4 had 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.
Highlights
Licensee MDPI, Basel, Switzerland.Since they were first discovered in 1929, antibiotics have been frequently detected in surface water, ground water, sediments, and even effluent from wastewater treatment plants [1,2]
Because antibiotics can inhibit the growth of bacteria, fungi, and other microorganisms [3], the widespread use of antibiotics in humans and veterinary medicine has had a major impact on the aquatic environment through domestic excretion, hospital waste, and overuse in agriculture and aquaculture [4]
This study provides a cost-effective way to remove antibiotic mixtures using visible light in an aquatic environment, thereby providing theoretical and technical support for the treatment of environmental pollution caused by multi-antibiotics
Summary
Since they were first discovered in 1929, antibiotics have been frequently detected in surface water, ground water, sediments, and even effluent from wastewater treatment plants [1,2]. Because antibiotics can inhibit the growth of bacteria, fungi, and other microorganisms [3], the widespread use of antibiotics in humans and veterinary medicine has had a major impact on the aquatic environment through domestic excretion, hospital waste, and overuse in agriculture and aquaculture [4]. Agents that inhibit dihydrofolic acid synthesis, are a major class of antibiotics detected in the aquatic environment [5]. In light of the non-degradability of SAs and their continuous discharge into surface water, current wastewater treatment plants may not be sufficient to completely remove these compounds [9]. We need to develop more effective methods to remove SAs
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