Coupling changes of disinfectant and bacteria induced by the water stagnation and disinfection strategy.

This paper studied stagnation-induced changes of disinfectant and bacteria using an orthogonal test and kinetic analysis, and then proposed a disinfection strategy. Tap water from a drinking water distribution system and ultrafiltrated water were collected and disinfected with four disinfectants (concentrations were set 0.2-1 mg/L as Cl. The study had several findings. First, disinfectants expanded lag phases and shortened generation times of the microbiome. Reduction in culturability, substrate responsiveness, respiratory activity, membrane potential and integrity subsequently occurred with increasing disinfection concentration. Second, the disinfectant decay rate decreased with initial disinfection concentration, and the effective disinfection phase (heterotrophic plate count (HPC) was less than 100 cfu/mL) was longer in water samples with lower organic matter. Moreover, the disinfection process was divided into an effective phase and an invalid phase (HPC>100 cfu/mL). Then a disinfection efficiency model was built and the regulation of disinfection by-products (DBPs) production was studied in chlorinated water samples, which provides a general method for other disinfectant studies. The average trihalomethanes (THMs) production during the effective phase (marked as THM/t) and THMs production during the invalid phase (marked as ΔTHM) were proposed to evaluate the DBPs production. The level of THM/t and ΔTHM were lower in ultrafiltrated water than those in tap water. THM/t were negatively correlated with initial chlorine concentration while ΔTHM were positively correlated with initial chlorine concentration. Finally, for the purpose of raising disinfection efficiency and decreasing DBPs, we propose periodic pulse disinfection.