Molecular Characteristics of Dissolved Organic Nitrogen and Its Interaction with Microbial Communities in a Prechlorinated Raw Water Distribution System

Dissolved organic
nitrogen (DON) represents a unique challenge
in prechlorinated raw water distribution systems (PRWDSs) because
of its contribution to the formation of harmful nitrogen-disinfection
byproducts, influence upon biogeochemical processes, and unclear molecular
characteristics. Here, Fourier transform ion cyclotron resonance mass
spectrometry in combination with high-throughput sequencing was applied
to elucidate the molecular changes of DON and biofilm microbial communities
in a PRWDS in Yixing, China. Our study revealed that dynamic characteristics
of DON are significantly correlated with the biofilm. The accumulation
of refractory lignin-like compounds and CnHmOpN1 contributes to the higher recalcitrance molecular characteristics
of DON in the effluent associated with Alphaproteobacteria, Planctomycetes,
and Bacteroidetes. Additionally, with the help of prechlorination,
the biofilm may change the DON characteristics and lead to higher
oxygenation, higher m/z, and lower
saturation during transportation. Despite the promotion of CnHmOpN1 and CnHmOpN3 at the
early stage, we suggest that appropriate concentration of chlorine
can add to the front end of raw water distribution pipes. Prechlorination
may control the nitrification process and stabilize the rapid growth
of diversity and concentration of low molecular weight DON, especially
the refractory CnHmOpN1 in the effluent,
which may help to improve treatment efficiency of drinking water treatment
plants.