| The objective of this research was to investigate experimentally the effectiveness of free chlorine, monochloramine and chlorine dioxide on the removal of biofilm in drinking water systems. In particular, biofilm kill at specific disinfectant concentrations was observed as a function of time for each disinfectant over a range of disinfectant doses and dosage periods. The experimental results were used to formulate CT (concentration-time) inactivation values similar to models presently used for the inactivation of suspended cells during primary disinfection. The disinfectants were evaluated on this basis and their effectiveness for biofilm control was compared.; The bench-scale experiment involved an initial 20-day inoculation stage to establish a heterotrophic bacterial biofilm. During this period, dechlorinated, filtered tap water was recirculated through five 125 mL columns, each containing tightly packed 3mm glass beads. The beads acted as media to support biofilm growth. The recirculation columns were similar to those originally designed by Rittmann and co-workers, 1986 for estimating intrinsic biofilm kinetics. Acetate, at a concentration of 250 μg/L, and other nutrients (i.e. nitrate, phosphate) were added to the bulk water to enhance biofilm growth. The columns were operated in upflow mode at a constant rate of 2 L/d.; The results of the experiment showed that, in general, chlorine dioxide was superior to free chlorine and monochloramine for biofilm inactivation at low CT values in the range of 10 mg · min/L < CT < 55 mg · min/L. These results indicate that chlorine dioxide could be considered as a viable alternative to free chlorine or monochloramine. Conversely, at high CT values in the range of 200 mg · min/L < CT < 300 mg · min/L, free chlorine and monochloramine achieved, on average, greater HPC inactivation than chlorine dioxide. (Abstract shortened by UMI.)... |
