Abstract
The occurrence and removal patterns of 24 antimicrobial agents and antimicrobial resistant determinants namely 6 antibiotic resistance genes (ARGs) and 2 mobile genetic elements (MGEs), and the fecal indicator E. coli were investigated in three full-scale wastewater treatment plants. Their waterlines and biosolids lines (including secondary treatment based on both granular and activated sludge) were sampled monthly throughout one year. Samples were analyzed by means of LC-MS/MS, qPCR and cell enumeration, respectively. The influence of rainfall, temperature, and turbidity on the occurrence and removal of the aforementioned agents was assessed through statistical linear mixed models. Ten of the antimicrobial agents (macrolides, fluoroquinolones, tetracyclines, and sulfonamides) were commonly found in influent in concentrations of 0.1-2 µg L−1, and the predominant ARGs were ermB and sul1 (6.4 and 5.9 log10 mL−1 respectively). Warmer temperatures slightly reduced gene concentrations in influent whilst increasing that of E. coli and produced an uneven effect on the antimicrobial concentrations across plants. Rainfall diluted both E. coli (-0.25 logs, p < 0.001) and antimicrobials but not genes. The wastewater treatment reduced the absolute abundance of both genes (1.86 logs on average) and E. coli (2.31 logs on average). The antimicrobials agents were also partly removed, but 8 of them were still detectable after treatment, and 6 accumulated in the biosolids. ARGs were also found in biosolids with patterns resembling those of influent. No significant differences in the removal of antimicrobials, genes and E. coli were observed when comparing conventional activated sludge with aerobic granular sludge. Irrespective of the type of sludge treatment, the removal of genes was significantly reduced with increasing hydraulic loads caused by rainfall (-0.35 logs per ∆ average daily flow p < 0.01), and slightly decreased with increasing turbidity (-0.02 logs per ∆1 nephelometric turbidy unit p < 0.05) .
Highlights
The occurrence of anthropogenic antibiotic resistance genes (ARGs) in the environment seems to be strongly related to fecal pollution (Karkman et al, 2019)
A one-year sampling campaign of three full-scale WWTPs highlighted that warmer seasonal temperature marginally decreased the concentrations of resistance genes in the influent but increased those of E. coli
Seasonal temperature variation had an impaired effect on concentrations of antimicrobials in the influent
Summary
The occurrence of anthropogenic antibiotic resistance genes (ARGs) in the environment seems to be strongly related to fecal pollution (Karkman et al, 2019). Human fecal bacteria are transported through sewage networks and wastewater treatment plants (WWTPs) to the environment. WWTPs, primarily designed for nutrient removal, have been hypothesized as key vectors in the environmental dissemination of antibiotic resistance (Rizzo et al, 2013). The fate of ARGs in WWTPs has been assessed in recent years, providing a wide range of results. WWTPs reduced the absolute concentration of ARGs (Di Cesare et al, 2016; Rodriguez-Mozaz et al, 2015), while in others, the relative and even absolute abundances of ARGs increased after treatment (Rafraf et al, 2016).
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