| This thesis examines a protocol using ozone and monochloramine for disinfection of biofilm bacteria on cement mortar lined pipe used in drinking water distribution systems. An experimental study was carried out in which biofilms were cultivated on cement surfaces in a laboratory biofilm reactor. The biofilms were exposed to ozone, monochloramine and to sequential combinations of ozone followed by monochloramine. An improved procedure for removal and enumeration of biofilm bacteria from the surfaces was developed and tested. Inactivation of biofilm bacteria by ozone was a nonlinear function of the ozone Ct product and was limited to 1.7 log at an ozone Ct of 120 mg x min/L. In contrast, exposure to a monochloramine Ct product of 3,600 mg x min/L resulted in 2.7 log inactivation. Evidence of a synergistic effect when ozone and monochloramine were applied sequentially was inconclusive. The results provide a more rational basis for ozone disinfection of water pipelines in practice and suggested that monochloramine might be an effective disinfectant for biofilm in pipe. |
