Effects of flow velocity on biofilm composition and microbial molecular ecological network in reclaimed water distribution systems

The existence of biofilm on the reclaimed water pipeline seriously affects the safety of water distribution. And the flow regimes in the pipeline play a crucial role in the growth of biofilms. In this study, the biofilm composition, surface topography and bacterial community were detected under eight levels of flow velocity in the range of 0.10–1.40 m s−1. The results showed that the dry weight, the concentration of extracellular protein and extracellular polysaccharide in the biofilm reached a dynamic stable period after 640 h. The biofilm composition and surface topography of biofilm were significantly different under the different flow regimes (laminar flow belongs to [0.10, 0.19] m s−1, and turbulent flow belongs to [0.29, 1.40] m s−1). As the flow velocity range increases, the concentration of each component in the biofilm and the parameters of biofilm surface topography increased and then decreased. The flow velocity could be a strong environmental stimulus resulting in the succession of bacterial community in biofilm. As the flow velocity increased from 0.10 m s−1 to 1.40 m s−1, at the phylum level, the average relative abundance of Firmicutes mainly showed a trend of first increasing and then decreasing with the highest abundance value of 71.57% at 0.49 m s−1. The flow velocity increased from 0.10 m s−1 to 0.49 m s−1, a significant increase in microbial diversity could be detected. The increase in flow velocity promoted the proliferation of microorganisms, and the interaction between different microbial components was enhanced. At 0.49 m s−1, the function of the biofilm is complex, and the ability to resist environmental stress is the strongest. This study can effectively improve the cognition depth of biofilms under the influence of flow velocity in the reclaimed water distribution systems, and provide an important theoretical support for the safe distribution of reclaimed water. © 2023 Elsevier Ltd