Abstract
In this study, livestock wastewater treatment plants in South Korea were monitored to determine the characteristics of influent and effluent wastewater, containing four types of veterinary antibiotics (sulfamethazine, sulfathiazole, chlortetracycline, oxytetracycline), and the removal efficiencies of different treatment processes. Chlortetracycline had the highest average influent concentration (483.7 μg/L), followed by sulfamethazine (251.2 μg/L), sulfathiazole (230.8 μg/L) and oxytetracycline (25.7 μg/L), at five livestock wastewater treatment plants. Sulfathiazole had the highest average effluent concentration (28.2 μg/L), followed by sulfamethazine (20.8 μg/L) and chlortetracycline (11.5 μg/L), while no oxytetracycline was detected. For veterinary antibiotics in the wastewater, a removal efficiency of at least 90% was observed with five types of treatment processes, including a bio-ceramic sequencing batch reactor, liquid-phase flotation, membrane bioreactor, bioreactor plus ultrafiltration (BIOSUF) and bio best bacillus systems. Moreover, this study evaluated the removal efficiency via laboratory-scale experiments on the conventional contaminants, such as organic matter, nitrogen, phosphorus and veterinary antibiotics. This was done using the hydraulic retention time (HRT), under three temporal conditions (14 h, 18 h, 27 h), using the anaerobic–anoxic–oxic (A2O) process, in an attempt to assess the combined livestock wastewater treatment process where the livestock wastewater is treated until certain levels of water quality are achieved, and then the effluent is discharged to nearby sewage treatment plants for further treatment. The removal efficiencies of veterinary antibiotics, especially oxytetracycline and chlortetracycline, were 86.5–88.8% and 87.9–90.8%, respectively, exhibiting no significant differences under various HRT conditions. The removal efficiency of sulfamethazine was at least 20% higher at HRT = 27 h than at HRT = 14 h, indicating that sulfamethazine was efficiently removed in the A2O process with increased HRT. This study is expected to promote a comprehensive understanding of the behavior and removal of veterinary antibiotics in the livestock wastewater treatment plants of South Korea.
Highlights
Frequent detection of veterinary antibiotics in aquatic environments, these substances were originally intended for the prevention and treatment of animal diseases, has recently emerged as a major social issue [1]
To calculate the method detection limit (MDL), the reference material was added to the effluent at the minimum detectable concentration level, and the t value at the 99% confidence level was multiplied by the standard deviation of the concentrations detected from seven repetitions of the test
The results showed that MDLs were in the range of 0.010–0.034 μg/L; similar levels of MDLs were found in sulfamethazine and chlortetracycline, while the MDL of sulfathiazole was higher
Summary
Frequent detection of veterinary antibiotics in aquatic environments, these substances were originally intended for the prevention and treatment of animal diseases, has recently emerged as a major social issue [1]. Veterinary antibiotics discharged into the environment have been the cause of Processes 2020, 8, 720; doi:10.3390/pr8060720 www.mdpi.com/journal/processes. Processes 2020, 8, 720 contamination in the aquatic environment from a variety of channels. Examples include inappropriate effluent treatment at manufacturing plants or livestock wastewater treatment plants, the disposal of unused antibiotics into sewers or trash, and drugs metabolized by animals or discharged intact. The long-term presence of such materials in aquatic environments, even in trace quantities of ng/L to μg/L, may have detrimental effects on an ecosystem [2]. Veterinary antibiotics often remain in the environment, and are likely to cause drug tolerance in living organisms. Global discussions are underway on potential countermeasures [3,4,5]
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