Impact of Residual Antibiotics in Livestock Wastewater Effluent on Microbial Activity in a Constructed Wetland

Various types of antibiotics used excessively in the livestock industry are often discharged into aquatic environments without being fully removed. The release of these antibiotics into natural systems causes a variety of issues, including water pollution and ecological toxicity. This study was conducted to elucidate the mechanisms that govern microbial growth by analyzing the behavior of antibiotics and the changes in microbial communities in a constructed wetland (CW) treating effluent from a livestock wastewater treatment plant (LWTP). The main groups of antibiotics detected in the wetland were sulfonamides and tetracyclines. While most antibiotics showed high removal efficiency in the CW, some were found to persist or accumulate in the wetland over a prolonged period. Distinct shifts in microbial community composition were observed between inflow and outflow samples, indicating that the CW functions as an ecological filter that selects for microbial taxa associated with antibiotic persistence and transformation. Bacillus belonging to the phylum Firmicutes was found to play a role in antibiotic removal as it produces various antibiotic-degrading enzymes. Moreover, the phyla Chloroflexi, Gemmatimonadetes, and Acidobacteria appeared to experience no growth inhibition due to antibiotics and were not directly involved in their degradation. The phylum Actinobacteria was found to possess selective degradation abilities. These findings provide insights for improving constructed wetland design by supporting microbial communities, such as Firmicutes (Bacillus) that are associated with enhanced antibiotic removal and compound-specific degradation.