Microbial Surface Attachment And Aggregation In Drinking Distribution Water Systems

Drinking water distribution network is a complex and dynamic ecological system, where microorganisms can colonize and aggregate on pipe surfaces as biofilms in response to environmental stimuli, yielding severe water quality issues. While substantial work has been conducted on biofilm formation, the underlying mechanisms behinds environmental stress-driven microbial behaviors and early-stage biofilm development process in drinking water pipelines remain largely unknown. This study aims at investigating the impacts of chlorine and flow velocity on microbial behaviors and surface aggregation, thereby untangling the mechanisms of biofilm formation. It can provide theoretical guidance and novel way for effective prevention of biofilms in drinking water distribution systems.Firstly, this study investigated the role of chlorine stress on microbial surface attachment. The results revealed that at low levels of disinfectant (0.0-1.0 mg/L), presence of chlorine promotes initiation of microbial surface attachment, while higher amounts of disinfectant (>1.0 mg/L) inhibits microbial attachment. The proposed mathematical model further demonstrated that chlorine regulates microbial cell motility and viability, and thus controls initial surface cell attachment.Secondly, the influence of chlorination stresses on microbial surface aggregation was investigated. Presence of chlorine disinfection at low levels promoted microbial EPS excretion (especially extracellular protein); whereas cells confronted with high disinfection stress exhibited an inhibitory response with reduced EPS release. The results revealed that chlorine stress regulated EPS production significantly influenced surface cell aggregation in drinking water pipelines.Finally, the effects of flow velocity on biofilm formation at initial phases on PE pipes were examined. Results showed that the formation of biofilms increased with the flow velocity of water at low levels, and the production of EPS especially extracellular polysaccharides could be stimulated. However, high flow-rate inhibits the formation of biofilm and secretion of EPS. The results demonstrated flow velocity control the secretion of extracellular polysaccharides, and thereby controlling the formation of biofilms.