Control mechanism of Escherichia coli invasion by micro-nano bubbles in drinking water distribution system

Sudden biological contamination in Drinking Water Distribution System (DWDS) significantly threatens the safety of drinking water, with E. coli invasions being particularly hazardous to human health. Traditional disinfection methods (i.e., chlorine, ultraviolet and ozone) provide partial microbial reduction. Micro-nano bubbles (MNBs) offer a promising alternative due to easy preparation, environmental friendliness, and generating ·OH in situ. This study explored the control mechanism of MNBs using different gas sources (i.e., nitrogen, air, oxygen, and ozone) on E. coli invasion in drinking water of the secondary water supply tanks. MNB characteristics, water quality changes, bacterial concentration, and microbial communities were evaluated. Results indicated that E. coli gradually became the dominant bacterium by promoting species interaction and influencing the process of microbial community construction, leading to a 6.25% increase in bacterial counts in water. MNBs generated via a dissolved gas release method exhibited particle sizes ranging from 500 to 800 nm and Zeta of -0.6 to -3.1 mV, and the bubble collapse effect generated a large amount of ·OH (0.11-0.40 mmol/L), which reduced bacterial abundance by 66.53% and microbial community richness, as revealed by decreases in the Chao (10.53%) and ACE (3.75%) indexes. The oxidative stress induced by ·OH inhibited protein transcription and energy production, which damaged DNA repair mechanisms. Thus, the relative abundance of Gammaproteobacteria, including E. coli as the dominant strain, decreased by 47.6%, leading to a balanced microbial community. Additionally, MNBs showed a complete reduction of bacteria, such as Caldisericia and Fusobacteria, thereby improving the drinking water safety and biological stability. This study highlights the potential of MNBs to address sudden exogenous biological pollution in DWDS, providing critical theoretical support to ensure the safety of drinking water quality.