| Today, regulations often mandate removal of ammonium from wastewater discharges, and failure of nitrification cannot be allowed. Fortunately molecular methods are becoming available to detect nitrifiers in environmental samples. Thus, my research focuses on using new molecular tools to identify the specific types of nitrifiers in activated sludge of wastewater treatment plants (WWTPs) in order to understand the microbial structure of these essential, but hard-to-culture microbial communities. I use a polyacrylamide-gel-based DNA oligonucleotide microarray and terminal restriction fragment length polymorphism (T-RFLP) analysis as comparative tools to study nitrifier diversity. I enhance the detection sensitivity of the DNA microarray by hybridizing the pre-amplified RNA so that I am able to detect the dominant nitrifiers, e.g., Nitrosomonas, Nitrobacter, and Nitrospira, in the activated sludge. Using T-RFLP, I can detect various lineages of Nitrosomonas and Nitrosospira, as well Nitrobacter and Nitrospira, in all samples from all 7 water reclamation plants (WRPs) in the Chicago area. This work confirms the coexistence of several nitrifier species, indicating functional redundancy of these microorganisms, a factor that could be vital for the stability of nitrification. I also use a mathematical model to interpret plant-operating data in ways related to my structural analyses. Using the model, I find that most nitrogen coming into all WRPs is nitrified, but I do not find a strong correlation of the effluent NH3-N with temperature and solids retention time, both of which vary widely among the WRPs. Despite the differences in nitrifying community functions determined by modeling analysis, all WRPs harbored Nitrosomonas and Nitrosospira, apparently the backbone of ammonia-oxidizing bacteria in full-scale municipal WRPs. Although nitrite-oxidizing bacteria in the genera Nitrobacter and Nitrospira coexisted in all WRPs, the community structures exhibited diversity among the 7 plants. |
