Effects of initial microbial density on disinfection efficiency in a continuous flow system and validation of disinfection batch kinetics in a continuous flow system.

摘要

This work was designed with two primary objectives. One is to test the hypothesis that initial microbial density has a significant effect on disinfection in a continuous flow system. The other is to validate the disinfection kinetics obtained from the batch studies in a continuous flow system.; Four series of disinfection experiments were conducted at 15°C in phosphate buffer solution using a lab-scale continuously stirred tank reactor (CSTR). These experiments included the inactivation of E. coli in stationary phase using monochloramine (pH 7), the inactivation of E. coli in exponential phase using monochloramine (pH 7), the inactivation of B. subtilis vegetative cells in exponential phase using monochloramine (pH 7), and the inactivation of B. subtilis spores using ozone (pH 8). Prior to these experiments, the reactor was characterized as an ideal CSTR by performing step-input tracer tests.; Statistical analyses of the CSTR disinfection data indicated that the initial microbial density had a significant effect on the inactivation of E. coli in stationary phase using monochloramine in the CSTR system. This result was consistent with the conclusion drawn from batch disinfection data analysis in a previous study. Effects of initial microbial density on disinfection efficiency were not observed in the other three series of experiments, suggesting that this effect might be specific to certain microorganisms in certain growth phases.; The disinfection efficiency in a CSTR was predicted from the mathematical expression obtained from batch inactivation kinetics and the CSTR hydraulic characteristics. The predicted survival ratio was compared with the observed CSTR survival ratio in natural log units. For E. coli in both stationary phase and exponential phase, no significant difference existed between the two sets of data after system correction of the change of E. coli density in the tubing system, indicating that this approach could be used to predict the behavior of E. coli using monochloramine in continuous flow system from batch kinetics. For B. subtilis cells and spores, systematic differences between continuous flow and batch systems precluded the use of batch data for CSTR inactivation estimation.