Effects Of Hydraulic Conditions On Early-stage Biofilm Dynamic In Drinking Water Distribution Systems

Drinking water distribution system is a complex and changing ecological reaction system,where bacteria could attach and self-aggregate(mostly in the presence of biofilm)to adapt to their ever-changing environmental conditions,threatening the safety of drinking water supply.Nowadays,much controversy exists on the effects of hydrodynamic conditions on bacterial aggregation in drinking water distribution systems.However,how bacterial functional responses to hydrodynamic conditions triggers biofilm dynamics remains elusive.The primary goal of this study is to explore the patterns of extracellular polymeric substances(EPS),community structure,surface attachment and early-stage biofilm formation mechanics in response to hydraulic conditions,and to provide mechanistic understanding of biofilm dynamics,thus offering theoretical guidance support and novel ways for preventing bacterial growth in drinking water distribution systems.Firstly,this study investigated the role of flow velocity on bacterial EPS release and early-stage biofilm formation.Results showed that,at low levels of velocity(0.0-1.0 m/s),increasing flow velocity enhanced EPS release and early-stage biofilm formation.However,further increasing flow velocity(>1.0 m/s)inhibited bacterial EPS production and thus early-stage biofilm formation.Significant correlation between bacterial EPS release and Zeta potential,hydrophobic property suggests that hydraulic conditions control bacterial EPS release,and alter surface properties,thus affecting bacterial aggregation onto pipe surfaces.Secondly,the role of flow velocity fluctuations on bacterial EPS release and early-stage biofilm formation was investigated.Results indicated that,compared with the constant hydraulic condition,the fluctuation of flow velocity promoted early-stage biofilm formation and the growth of planktonic bacteria.Increasing the amplitude and frequency of flow velocity fluctuations enhanced the formation of early-stage biofilm on pipes,associating with increased EPS secretion of bacterial.Therefore,flow velocity fluctuation controlled EPS release of planktonic bacteria,and altered surface properties,thus affecting bacterial aggregation onto pipe surfaces.Finally,the effects of flow velocity on bacteria community structures and diversity were investigated.Results indicated that moderate flow velocity(1.0 m/s)yielded more diversity of the biofilm structure.In addition,Pseudomonas Aeruginosa predominated in the biofilm population under various flow velocity conditions and this predominance became more apparent under the moderate flow velocity(1.0 m/s).