Biofilm formation in drinking water distribution systems (DWDS) has many adverse consequences. Knowledge of microbial community structure of DWDS biofilm can aid in the design of an effective control strategy. However, biofilm bacterial community in real DWDS and the impact of drinking water purification strategy remain unclear. The present study investigated the composition and diversity of biofilm bacterial community in real DWDSs transporting waters with different purification strategies (conventional treatment and integrated treatment). High-throughput Illumina MiSeq sequencing analysis illustrated a large shift in the diversity and structure of biofilm bacterial community in real DWDS. Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Nitrospirae, and Cyanobacteria were the major components of biofilm bacterial community. Proteobacteria (mainly Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria) predominated in each DWDS biofilm, but the compositions of the dominant proteobacterial classes and genera and their proportions varied among biofilm samples. Drinking water purification strategy could shape DWDS biofilm bacterial community. Moreover, Pearson's correlation analysis indicated that Actinobacteria was positively correlated with the levels of total alkalinity and dissolved organic carbon in tap water, while Firmicutes had a significant positive correlation with nitrite nitrogen.

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This study investigated the effects of orthophosphate, tripolyphosphate and hexametaphosphate on iron release control under the conditions of different sulphate concentrations in drinking water distribution systems. The results showed that all the three kinds of phosphates had positive effects on controlling the iron release from corrosion scales in distribution systems. Tripolyphosphate was the most effective inhibitor on controlling the release of iron in bulk water, with the addition dosages of 0.50 mg/L and 0.25 mg/L acting better than that of 0.10 mg/L. Hexametaphosphate performed best on controlling color in bulk water, with the addition dosage of 0.10 mg/L achieving the average reduction rate over 40%. Thus, hexametaphosphate was chosen as one kind of preferred inhibitor to iron release, because the discolored water phenomenon in the tap could easily cause the customer complains. Whatever the low (75 mg/L), the middle (150 mg/L) or the high (240 mg/L) concentrations of sulphate, adding different dosages of hexametaphosphate (0.10-0.50 mg/L) all had a significant controlling effect on iron release, with the average reduction rates of the total iron concentration, turbidity and color being 15% to 55%, 35% to 85% and 40% to 92% respectively. While stopping adding hexametaphosphate in bulk water in drinking water distribution systems, under low-sulphate and mid-sulphate conditions, total iron concentration in bulk water slightly increased in first one or two days, and then returned to the low levels after 10 days. However, under high-sulphate conditions, the water quality in drinking water distribution systems deteriorated immediately after stopping hexametaphosphate and could not recover after 10 days.