Lime addition significantly attenuates tetracycline resistance genes and class 1 integrons in dewatered sludge by affecting bacterial profiles

Abstract

To verify the hypothesis that adding lime can remove antibiotic resistance genes (ARGs) in excess activated sludge (EAS), in this study, we explored the effects of lime addition at different ratios on the removal of tetracycline resistance genes (TRGs, tetW/tetS/tetZ/tetC/tetX) and class 1 integrons (intI1) in dewatered EAS. The microbial community succession was also analyzed. Drying without lime addition for 7 d significantly reduced the total content of TRGs and intI1 with a removal efficiency of 72.88%, and lime addition further promoted the removal effect and achieved a removal efficiency exceeding 98.54%. A higher L/S ratio did not result in more effective removal of TRGs. The fate of TRGs did not correlate with their resistance mechanism. Lime addition promoted the removal of TRGs by enhancing the decrease in moisture content and changing the microbial community structure. Principal component analysis suggested that the core microbial community was significantly distinct and clustered more by the treatment stage than the method used. Spearman correlation and network analyses indicated that 17 genera belonging to five phyla (Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Nitrospirae) were significantly positively or negatively correlated (|R| > 0.6, p < 0.05) with TRGs and intI1. These findings increase our understanding of the benefits of lime addition treatment for attenuating TRGs and intI1 in EAS. Adding lime to EAS is straightforward and cost-effective and contributes toward preventing the release of TRGs and intI1 into the total environment.