Rapid sand filter (RSF) is widely used in drinking water treatment plants. Rapid filtration is always considered a physicochemical process, but the effect of the microorganisms that attach to the filter media remain inadequately investigated. In order to understand the composition and functional characteristics of microbial communities in RSFs, influent water, effluent water, and filter materials from eleven RSFs in eight Chinese cities were sampled and analyzed. After filtration, dissolved organic carbon (DOC) showed a slight but significant removal due to the growth of heterotrophic microbes. The activity of ammonia-oxidizing microbes and nitrite-oxidizing microbes promoted a significant decrease in ammonia nitrogen (NH4+-N) and a significant increase in nitrate nitrogen (NO3--N) in water. No significant changes in total nitrogen (TN) were observed, indicating that denitrification and anammox were weak in the RSFs. The composition and function of the microbial communities of RSFs were assessed using metagenomic methods. Genera in the top 10% with respect to relative abundance (14 genera in total) were identified as the dominant genera, including the two ammonia-oxidizing bacteria Nitrospira and Nitrosomonas. Functional gene information for the dominant genera was also extracted for analysis. The dominant genera exhibited higher relative abundances of carbohydrate, nitrogen, sulfur, and xenobiotic metabolic pathways. Aeromonas had the highest relative abundance of carbohydrate metabolic genes, and Bradyrhizobium had the highest relative abundance of nitrogen, sulfur, and xenobiotics metabolic genes, indicating that these two genera play an important role in the transformation of substances in drinking water. Finally, the metabolic potential of the dominant genera on xenobiotics was evaluated, and the results showed that Bradyrhizobium, Sphingomonas, Methyloglobulus, Sphingopyxis, and Klebsiella were the key bacterial genera for the removal of micropollutants in RSFs.
Keywords: dominant microbial community; metagenomics; microbial function; rapid filter for drinking water; xenobiotic.