IRFP: Towards Sustainable Wastewater Treatment: Mass Transport Limitations, Microbial Diversity, and Nitrous Oxide Production in Anammox Nutrient Removal Processes

Wells George F, Stanford CA

Investigators

Abstract

The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award supports a twenty four month research fellowship by Dr. George F. Wells to work with Dr. Eberhard Morgenroth and colleagues at Eawag: Swiss Federal Institute of Aquatic Science and Technology. Combined nitritation and anaerobic ammonium oxidation (anammox) in a single reactor is a promising low-energy strategy for removing nitrogen from wastewater, thereby preventing the rash of negative environmental and public health impacts associated with nutrient pollution to natural systems. Combined nitritation/anammox processes rely on the coordinated activities of several groups of microorganisms that grow in close proximity in aggregates, including aerobic ammonia oxidizers and anaerobic ammonia oxidizers (anammox). Although promising, widespread application of these processes is hampered by process instabilities and uncertainty regarding emissions of the potent greenhouse gas nitrous oxide. The major hypothesis of this project is that mass transport limitations impact combined nitritation/anammox process stability and nitrous oxide emissions. To address this hypothesis, ongoing experiments target an improved understanding of how mass transport affects 1) microbial diversity and functional redundancy, 2) nitrous oxide production, and 3) susceptibility to process instabilities of combined nitritation/anammox process variations. Replicate lab-scale bioreactors are operated with two process variations employing different types of microbial aggregates--suspended growth biomass and biofilm carriers. Within each aggregate type, mass transport limitations are characterized using cutting-edge microscopy coupled to microsensor measurements, and differences in microbial community structure are investigated via high-throughput DNA sequencing techniques. In parallel, the production rate and microbial source of nitrous oxide is quantified. Process performance and resilience is then characterized in the face of a simulated process upset, and process stability, nitrous oxide production, and microbial diversity are correlated to microscale aggregate characteristics and mass transport limitations. Results will be integrated into a simple mathematical model and monitoring approach to guide practical design and operation of combined nitritation/anammox systems for sustainable wastewater treatment and environmental protection, and will inform management practices to minimize greenhouse gas production from wastewater treatment systems. This research directly contributes to our knowledge of anammox bacteria, a group of little-understood microorganisms of profound importance to the global biogeochemical nitrogen cycle, by establishing an interdisciplinary collaboration between microbial ecology and process engineering groups. From a practical standpoint, results inform the development and operation of novel biological systems for prevention of nutrient pollution and for sustainable water reuse. Indeed, the proposed work has the potential to dramatically influence municipal and industrial wastewater treatment, as well as nitrogen management in landfill leachate, biomass production for biofuels, and allied agricultural activities associated with nutrient pollution and nitrous oxide production. More broadly, this project provides new insights into the microbial ecology of the global nitrogen cycle, including interactions between anammox, nitrifiers, and denitrifiers. Results also contribute to our understanding of the sources and controls of microbial greenhouse gas production, and shed light on the relationship between microbial diversity and ecosystem function?a critical area of inquiry to the field of microbial ecology.