Impacts of backwashing on micropollutant removal and associated microbial assembly processes in sand filters

Highlights

● Backwashing in sand filters with 2-h and 4-h EBCTs was simulated.

● Removal efficiency of five micropollutants recovered within 2 d at 2-h EBCT.

● Active biomass of sand filters recovered within 2 d under two EBCTs.

● Microbial composition gradually recovered to pre-backwashing level at 2-h EBCT.

● Recovered microbes only accounted for 15.55 %–25.69 % in the sand filters at 4-h EBCT.

Abstract

Backwashing is crucial for preventing clogging of sand filters. However, few studies have investigated the effect of backwashing on micropollutant removal and the dynamic changes in the microbial community in sand filters. Here, we used a series of manganese and quartz sand filters under empty bed contact times (EBCTs) of 2 h and 4 h to explore variations in micropollutant degradation and temporal dynamics of the microbial community after backwashing. The results showed that the removal efficiencies of caffeine, sulfamethoxazole, sulfadiazine, trimethoprim, atrazine, and active biomass recovered within 2 d after backwashing in both types of sand filters at 2-h EBCT, but the recovery of sulfadiazine and trimethoprim was not observed at 4-h EBCT. Moreover, the removal efficiency of atenolol increased after backwashing in the manganese sand filters, whereas maintained almost complete removal efficiency in the quartz sand filters at both EBCTs. Pearson correlation analysis indicated that microbial community composition gradually recovered to the pre-backwashing level (R increased from 0.53 to 0.97) at 2-h EBCT, but shifted at 4-h EBCT (R < 0.25) after backwashing. Furthermore, the compositions of the recovered, depleted, and improved groups of microbes were distinguished by applying hierarchical clustering to the differentially abundant amplicon sequence variants. The cumulative relative abundance of recovered microbes at 2-h EBCT was 82.76 % ± 0.43 % and 46.82 % ± 4.34 % in the manganese and quartz sand filters, respectively. In contrast, at 4-h EBCT, the recovered microbes dropped to 15.55 %–25.69 % in both types of sand filters.

Graphical abstract

Keywords

Sand filter / Backwashing / Recovery / Micropollutants / Community composition

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Acknowledgements

This work was supported by the National Key R&D Program of China (No. 2018YFE0204101), the National Natural Science Foundation of China (No. 51778603), and the Alliance of International Science Organizations (ANSO-CR-KP-2020-05). The authors would also like to thank Hongyan Li, Zhiyong Yu, and Yali Cheng from the Laboratory of Environmental Aquatic Chemical Analysis in the Research Center for Eco-Environmental Science, Chinese Academy of Sciences, for technical support.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-023-1634-z and is accessible for authorized users.

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