Ammonia Oxidation Potential and Microbial Diversity in Sediments from Experimental Bench - Scale Oxygen - Activated

by Jennifer Allen, M.S. Washington State University May 2009 Chair: Marc W. Beutel Ammonia pollution, commonly from sewage treatment plants and agricultural activities, can degrade surface waters by causing eutrophication and exhibiting toxicity to aquatic biota. Constructed treatment wetlands can be used to treat a wide array of waste waters, but low oxygen concentrations characteristic of these systems will limit ammonia removal because ammonia must be first oxidized to nitrate before being denitrified to nitrogen gas. My study evaluated the effects of dissolved oxygen enhancement on ammonia oxidation and microbial community diversity in bench-scale wetland mesocosms. Sediments were extracted from oxygenated and non-oxygenated (control) wetland microcosms. Oxygen-activated wetland microcosms underwent side-stream oxygenation with pure oxygen gas and had DO levels > 10 mg/L; DO in controls was typically < 1 mg/L. Potential rates of ammonia oxidation measured in sediments were significantly higher in oxygenated mesocosms (2.6 ± 0.80 mg-N/g-dw•d) versus control mesocosm (0.48 ± 0.20 mg-N/g-dw•d). These rates were higher than those typically measured in agricultural soils (0.0012-1.9 mg-N/g-dw•d) and aquatic sediments (0.0010-1.2 mgN/g-dw•d). Bacterial 16S rDNA libraries were generated using universal PCR primers. Nitrosomonas, a genus of nitrosofying bacteria typically found in nitrifying wastewater treatment plants that are commonly responsible ammonia oxidation, were only observed in the oxygenated systems. Other notable differences in microbial diversity included more species of filamentous cyanobacteria, sulfur-reducing bacteria, and denitrifiers in the low DO control mesocosms. The