AWWA JAW56924

The effect of pH on the inactivation of Nitrosomonas europaeaby chloramines was tested for a range of chloramine concentrations. Cell viability was assessed using the most probable number (MPN) technique and a culture-independent bacterial viability test. For pH 7 to 9, N. europaea inactivation followed Chick-Watson kinetics with n= 1 and k ranging from 2.5 x 10-(03) L/(mgCl2.min) at pH 7 to 2.4 x 10-(04) L/(mgCl2.min) at pH 9 in the bacterial viability-based tests. For the MPN-based tests, k was approximately 1,000-fold higher. Although CT99 values from the MPN-based experiments agreed with CT99 reported elsewhere for ammonia-oxidizing bacteria (AOB), the lower inactivation rates estimated from the bacterial viability tests were more consistent with AOB persistence in distribution systems, suggesting that MPN may overestimate chloramine biocide effectiveness. Finally, the counteracting effect of pH on N. europaea inactivation and chloramine decay indicates that pH control is likely to have a site-specific effect on nitrification. Includes 36 references, tables, figures.