Combining chlorination and chloramination processes for the inhibition of biofilm formation in drinking surface water system models

AIMS: The aim of this study was to investigate the inhibition of biofilm formation on stainless steel (SS) and galvanized mild steel (MS) in chlorine (AFC(1)) and chlorine-monochloramine treated waters (AFC(2)M). METHODS AND RESULTS: Disinfection was carried out using 2.5 mg l(-1) free chlorine followed by 1.5 mg l(-1) monochloramine, with non-disinfected water used as control water. Results of the standard spread plate procedure, DAPI epifluorescence microscopy and scanning electron microscopy revealed bacterial colonization of SS and MS exposed to non-disinfected and chlorinated waters between 24 and 720 h, while no bacterial adhesion was detected on SS and MS exposed to AFC(2)M between 48 and 504 h. CONCLUSIONS: The inability of bacteria to grow on SS and MS was observed only when 0.35 mg l(-1) residual monochloramine was maintained throughout the system. SIGNIFICANCE AND IMPACT OF THE STUDY: This demonstrates the inability of chlorine alone to inhibit bacterial growth and suggests a combination of chlorine and monochloramine as a more effective treatment for drinking water, especially for rural communities with very poor source waters in Africa.