Model distribution systems (annular reactors) were operated to investigate the biofilm disinfection efficacies of three disinfectants: free chlorine, monochloramine and combination of free chlorine and silver ion. Biofilm cell number, coverage and structure were examined. At the same dosages, monochloramine showed the poorest biofilm disinfection efficiency compared to free chlorine and combination of free chlorine and silver ion. 40 μg/l of Ag+ showed positive effect to both two dosages of chlorine (0.5 mg/l and 1 mg/l) to disinfect biofilm bacteria. In addition, combinations of free chlorine and silver ion were found to achieve the highest biofilm coverage reduction, while monochloramine showed the least biofilm removal. Biofilm structure could also be affected by different testing agents.

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