Factors Affecting Inactivation Behavior in the Monochloramination Range

The effects of monochloramine application techniques, chlorine-to-ammonia-N (Cl:N) ratios, water matrices, and bacterial origins on fecal coliform bacteria inactivation behavior in the monochloramination range were studied in ammoniacal bacteria suspensions and wastewater samples containing either naturally occurring or reseeded laboratory-cultured fecal coliform bacteria. The time-dependent chlorine residual concentrations and the bacteria counts were measured. The inactivation behavior was strongly affected by the monochloramine application techniques and the initial chlorine and ammonia concentrations and ratios. When dosing free chlorine to the ammoniacal solution, a "two-stage" pattern that coupled initial inactivation by transitory free chlorine and extended inactivation by forming monochloramine was observed at a Cl:N ratio of 3:1, while, at a high initial ammonia concentration (20  mg/L), synergy without initial inactivation was found instead. The difference is explained with calculations of the free-chlorine CT values. The inactivation behavior of laboratory-cultured suspensions differed from that of wastewater effluents, which was primarily attributable to the variations in the water matrix, not to the bacterial origins. Conducting dose-response studies using autoclaved wastewater samples reseeded with fieldisolated, laboratory-cultured bacteria was proposed as the solution.