Spatial variation of loose deposit characteristics in a 40 km long operational drinking water distribution system
Discoloration problems have occurred in drinking water distribution systems continuously for several years in a rural area of eastern China. Unidirectional flushing was implemented to collect the loose deposits from the flushed water to investigate the variation in their physicochemical and biological characteristics along a 40 km pipeline. X-ray fluorescence was used for elemental analysis of these collected deposits, and Illumina MiSeq sequencing was then used to characterize the bacterial communities of the flushed water. The results showed that Al, Mn and Fe were the main metals in the loose deposits. The mass concentration of Mn in the flushed water decreased with increasing distance from the water treatment plant (WTP), while the mass concentration of Fe varied in an opposite manner. The mass concentration of Al varied, but no discernible trend was observed in the overall pipeline. Compared with normal flow conditions, heavy-metal release occurred during the flushing process, though this problem was not very serious. An analysis of the sequencing data showed that Alphaproteobacteria was predominantly present in the flushed water, followed by Actinobacteria, Cyanobacteria and Betaproteobacteria at the class level. There were obvious variations in the bacterial community in the flushed water at different distances from the WTP. The relative abundances of Hyphomicrobium and Pedomicrobium, which are both potential Mn-oxidizing bacteria, were significantly higher in locations farther away from the WTP, suggesting that the microbial pathway might be predominant in the oxidation of the residual dissolved Mn(II) at the remote end of the pipeline.