Temporal variations of antibiotic resistance genes in influents and effluents of a WWTP in cold regions

Diurnal variation in wastewater flows is a common phenomenon associated to peak water use periods. However, short-term variations of ARGs in WWTPs are not clear due to relatively long sampling intervals or inadequate sampling modes. Therefore, a one-year experimental study was conducted to reveal the time-scale changes in ARG abundance in a WWTP. In particular, sample surveys were carried out to determine the inter-day and intra-day fluctuations in the absolute abundance of several ARGs. Hourly measurements of the ARG absolute abundances revealed three peak concentrations at 9:00–11:00, 17:00–19:00 and 23:00–1:00 due to peak use of toilet in morning and evening. The relative standard deviations (RSDs) in effluent were about three times lower than that in influent due to the mixing and treatment of wastewater treatment process. And the peak effluent discharge was related to the influent fluxes and hydraulic retention time. Seasonality in ARG absolute abundance was found for all target ARGs, with the highest in spring and the lowest in summer. The absolute abundance in spring was one order of magnitude higher than that in summer. In general, the fluctuation of ARG absolute abundance was mainly evident at the intra-day scale, while the variation of the inter-day scale was relatively small. The relative abundance of ARGs showed less temporal variations than that of absolute abundance, indicating that normalization ARGs to 16S rRNA may correct for minor variations in sample processing. Based on the removal rate of ARGs, hydraulic retention time (HRT) was recommended as a guiding principle for sampling strategies. Data from this study are needed for future sampling activities focusing on ARGs and estimating peak concentrations discharged from wastewater sources.