Bacterial community structure and microorganism inactivation following water treatment with ferrate(VI) or chlorine

Drinking water disinfection plays a critical role in protecting humans from waterborne pathogens. Ferrate(VI) ((FeO4)-O-VI (2-)) has also been proposed as a disinfectant. This is the first study investigating the bacterial microbiomes of ferrate(VI)-treated water compared to chlorinated water. Tested water was collected after sand filtration and before disinfection from a drinking water treatment plant at Jiaxing, Zhejiang Province, China. A culture-independent method utilizing propidium monoazide was used with quantitative polymerase chain reaction and pyrosequencing of 16S rRNA genes to distinguish between the viable and nonviable bacterial populations. The operational taxonomic units and alpha-diversity indexes of the live bacterial phylotypes in the samples were determined. Viable bacteria remained in all samples following chlorination or ferrate treatment. However, the genera Vibrio, Salmonella, Shigella, Escherichia, Campylobacter, Yersinia, Plesiomonas, Legionella, and Helicobacter, which contain important human pathogens, were not present among the 25 dominant genera seen in these samples. The profiles of the bacteria remaining after treatment with either chlorine or ferrate differed. The ferrate-treated samples showed a reduced percent relative abundance of operational taxonomic units of the class Alphaproteobacteria within the total remaining viable bacteria. The genera Flavobacterium and Duganella were relatively resistant to treatment by either chlorine or ferrate(VI). At the highest doses of chlorine and ferrate(VI), the genus Sphingobium represented a greater percentage of live bacteria in the chlorinated sample than in the ferrate(VI)-treated sample. The results suggest that ferrate(VI) and chlorine could inactivate slightly different sets of bacteria and could have different mechanisms of bacterial inactivation.