Nitrifiers have also been found in the biofilms of tropical drinking water (Cruz et al., 2020). Nitrification, which consists of ammonia oxidation and nitrite oxidation, is widely observed in drinking water supply systems (Wagner et al., 2018). However, it is not clear which factor has greater consequences.Īs one of the factors that affects water quality, nitrification is an increasing concern worldwide (Zhang et al., 2009 Tatari et al., 2017 Wang et al., 2017 Albers et al., 2018). The causes of deteriorating tap water quality have previously been explored, as mentioned above. Therefore, water in SWSSs usually contains a physical load (particles), nutrient load (organic and inorganic nutrients), and biological load (cells) (Liu et al., 2017). Long water retention times and low disinfectant concentrations together affect microbial community structures and compositions (Douterelo et al., 2013 Li et al., 2018 Xu et al., 2018). Long stagnation in DWDSs and exogenous microbial invasions from building infrastructures in SWSSs can promote microbial growth (Li et al., 2018 Liu et al., 2018). Traditional purification processes are inefficient in removing all contaminants in drinking water treatment systems (DWTSs), there is still some contaminants left in the effluent (Prest et al., 2016). Despite constant improvements to the water purification process, contaminants (e.g., chlorine-tolerant bacteria and organic and odor compounds) could not be removed completely from the influent and can always be found in SWSSs (Matsui et al., 2015 Zamyadi et al., 2015 Liu et al., 2017 Nescerecka et al., 2018). More attention should be given to controlling incomplete nitrification to improve tap water quality.ĭeterioration of water quality is commonly found in communities in metropolitan cities and in particular, it consists of bacterial and fungal growth (Li et al., 2018 Liu et al., 2017). Incomplete nitrification products were involved in the metabolism of heterotrophic bacteria and promoted the growth of heterotrophic bacteria in the SWSS. In the SWSS, the metabolism of the ammonia oxidation cluster was more vigorous, and ammonia-oxidizing bacteria (AOB) were the dominant nitrifying bacteria. The abundances of ammonia oxidation bacteria, concentration of nitrogen species, and related enzymes demonstrated that ammonia oxidation in the SWSS was more vigorous than that in the DWDS. BATCHPHOTO VIRUS DRIVERStatistical analysis revealed that ammonia oxidation was the dominant driver of increased biomass in the SWSS. It was found that the increased biomass in the SWSS was significantly higher than that in the drinking water distribution system (DWDS). Metagenomic and 16S rRNA gene sequencing were performed to better understand the microbial communities and metabolism. To explore the metabolic mechanism for rapid microbial regrowth in SWSSs, a regrowth potential assessment, flow cytometry, and quantitative PCR were conducted. Deterioration of water quality is commonly found in secondary water supply systems (SWSSs), especially the growth of microbes.
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