Managing Nitrification in Secondary Water Supply Systems: Effects of Chloramine Levels and Material Choice on Nitrifying Guild Dynamics

Nitrification in chloraminated secondary water supply systems remains a significant challenge to maintaining drinking water quality, as it accelerates disinfectant decay and facilitates microbial regrowth. This study investigated the colonization and succession patterns of nitrifying guilds in response to varying chloramine concentrations and commonly used tank and plumbing materials, using continuously operated simulated secondary water supply systems (SWSSs) over a 270-day period. Quantitative PCR analysis of nitrifier marker genes revealed that ammonia-oxidizing bacteria (AOB) were the dominant early colonizers in biofilms whereas Comammox clade A and strict nitrite-oxidizing bacteria (sNOB) became more prevalent as the biofilm matured. Notably, principal coordinate analysis (PCoA) of AOB- and NOB-affiliated operational taxonomic units (OTUs) extracted from 16S rRNA gene sequencing indicated that chloramine and material type exerted a more profound selective pressure on the AOB community than on NOB. Copper surfaces selectively promoted the enrichment of complete ammonia-oxidizing (Comammox) and sNOB, emphasizing the role of material type in shaping nitrifier assembly. Chloramine concentration had a pronounced, dose-dependent effect: Moderate levels supported AOB proliferation, whereas high levels inhibited all nitrifiers. A temporary chlorine burn reduced total bacterial abundance and coincided with a selective increase in Comammox and ammonia-oxidizing archaea (AOA), suggesting differential tolerance among nitrifying taxa. These findings provide insights into the dynamic succession of nitrifying guilds under representative SWSS conditions and underscore the importance of chloramine concentration and material selection in informing integrated nitrification control strategies.