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Biogeography, Population Dynamics, and Activity of Ammonia-Oxidizing Archaea and Bacteria in Globally Distributed Wastewater Treatment BioreactorsEPA Grant Number: F07D20719
Title: Biogeography, Population Dynamics, and Activity of Ammonia-Oxidizing Archaea and Bacteria in Globally Distributed Wastewater Treatment Bioreactors
Investigators: Wells, George
Institution: Stanford University
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: January 1, 2007 through January 1, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Environmental Biotechnology , Pollution Prevention/Sustainable Development
Nitrification is a particularly important step in biological wastewater treatment due to its role in removing ammonia from wastewater, thereby protecting the receiving water from the toxicity of ammonia, nitrogenous oxygen demand, and N-stimulated eutrophication. The reliability and cost-effectiveness of nitrifying bioreactors are thus of prime concern from the standpoints of both public health and environmental protection. However, at present nitrification imposes high operational costs on wastewater treatment plants (WWTPs) in the form of increased aeration and extended solids retention times. Furthermore, episodes of nitrification instability or failure leading to high levels of reduced nitrogen in effluent are common in wastewater treatment bioreactors. In many cases, the reasons for these episodes are obscure. Ammonia-oxidation by chemolithoautotrophs is considered the rate-limiting step in nitrification in a variety of environments, including WWTPs. While in theory it should be possible to select for ammonia-oxidizing microbial populations resistant to perturbations that instigate instability events, at this point, engineers lack the scientific foundation necessary to make appropriate operational and design recommendations. The goal of this research is to contribute to such a scientific foundation by elucidating the distribution, activity, and population dynamics of specific groups of ammonia-oxidizing microbes, particularly ammonia-oxidizing archaea, in globally-distributed nitrifying bioreactors. Furthermore, this study aims to correlate variations in ammonia-oxidizing communities in these bioreactors to local geographic, operational, and environmental variables and to systematically investigate the link between dissolved oxygen concentration and ammonia-oxidizing prokaryote community structure in bioreactors.
A three-tiered approach employing both molecular and culture-based methodologies will be used to investigate ammonia-oxidizing microbial communities in bioreactors. First, ammonia-oxidizing bacterial (AOB) and archaeal (AOA) diversity and abundance in 10 globally distributed bioreactors will be assessed over a 1 year time period via quantitative PCR methods, cloning and sequencing of the key functional gene amoA, and the community fingerprinting method Terminal Restriction Fragment Length Polymorphism. The results of these assays will be used as inputs to multivariate statistical analysis methods to link ammonia-oxidizing community structure to environmental or operational variables. Second, the relative activities of AOA and AOB in-situ will be investigated in a targeted sampling period via quantitative reverse transcriptase PCR. Finally, lab-scale activated sludge continuous flow reactors as well as axenic and enrichment batch cultures of AOA and AOB will be used to investigate the specific influence of DO on ammonia-oxidizing community structure.
The proposed course of study is expected to notably increase understanding of the ecology of ammonia-oxidizing microbes, particularly AOA, in engineered settings by:
- assessing the diversity, relative abundance, and relative activities of AOA and AOB in globally distributed bioreactors;
- evaluating the influence of specific operational, environmental, and geographic parameters on the activities and population dynamics of AOA and AOB in bioreactors; and by
- elucidating the specific effect of DO on AOA communities in activated sludge.
On a broader scale, the proposed course of study is anticipated to lead to significant improvements in understanding of bioreactor community ecology and factors affecting stability and adaptation. This understanding will likely provide insights for operating and design strategies that enhance process performance and decrease cost of wastewater treatment systems. Ultimately this will lead to more reliable and robust protection of the environment and human health from nitrogen pollution.