Microbial ecology of nitrification in chloraminated drinking water distribution systems

Although nearly two-thirds of drinking water utilities that use chloramines for secondary disinfection report evidence of nitrification in their distribution systems, little is known about the microbial ecology that gives rise to these nitrification episodes. The research described in this dissertation explored the diversity of nitrifying communities in chloraminated systems and sought to recover ammonia-oxidizing bacteria (AOB) isolates that could be used for phenotypic studies.; Nitrifying communities in samples collected from a pilot-scale and several full-scale chloraminated systems were evaluated using both a 16S rDNA-targeted terminal restriction fragment length polymorphism (T-RFLP) protocol specific for AOB and nitrite-oxidizing bacteria (NOB) and cloning and sequencing of 16S rDNA fragments. The results of the T-RFLP screening indicated the presence of Nitrosomonas in each of the chloraminated systems, with Nitrosospira detected in only some samples and generally at levels just above background. Cloning results showed the AOB communities were dominated by representatives of the Nitrosomonas oligotropha cluster, a group of AOB known to grow at low ammonia concentrations relative to other Nitrosomonas species. The NOB evaluation showed the ubiquotous detection of Nitrospira in each of the systems, with the occasional detection of Nitrobacter. These results indicate the need to focus AOB growth and inactivation studies on Nm. oligotropha, and the ubiquitous detection of NOB suggests some degree of biological reaction as a mechanism for nitrite oxidation in these systems.; The retrieval of AOB representatives from chloraminated systems was attempted using enrichment and isolation techniques. Chemostat reactors seeded with samples from full-scale systems were fed a mineral medium with either a low or high ammonia concentration and aerated to impose either low or high dissolved oxygen conditions. AOB enrichments were only obtained using high dissolved oxygen conditions, with stable ammonia oxidation achieved in two systems with low ammonia feed and intermittent feeding required for two high-ammonia reactors. Cloning and sequencing of PCR products from one of the high-ammonia systems indicated the successful enrichment of Nm. oligotropha. However, isolation efforts recovered a single AOB identified as Nm. europaea , despite the absence of this species in all of the pilot-plant, full-scale, and enrichment clones.