UC Davis

Enhanced biological phosphorus removal (EBPR) process is an economic and sustainable approach for phosphorus (P) removal from municipal wastewater. A typical EBPR process is composed of an alternating anaerobic-aerobic zone which selectively enriches a group of phosphorus removing bacteria named polyphosphate-accumulating organisms (PAOs). While Candidatus Accumulibacter has been widely recognized as a model PAO in the past, recent studies have identified a diverse group of putative PAOs in activated sludge systems that may also contribute to P removal from wastewater. Among these putative PAOs, Tetrasphaera is the most promising group, and has been identified with high abundance in wastewater treatment plants (WWTPs) worldwide. However, current knowledge about these novel PAOs is limited. To utilize the full benefits of the EBPR process, a thorough understanding of the microbiology and characteristics of these putative PAOs is needed.

This dissertation investigated the diversity and kinetics of putative PAOs in both lab-scale and full-scale wastewater treatment processes with a focus on Tetrasphaera. In Chapter 2, a detailed literature review was conducted to systematically evaluate the identification history of Tetrasphaera genus and summarize our current knowledge about this important PAO. Chapter 3 investigated important biokinetic parameters of Tetrasphaera elongata in lab-scale pure cultures. The specific growth rate determined in this study (1.37-1.42 d-1) appeared to be slightly higher than typical values for other PAOs: 0.12-1.0 d-1. The specific anaerobic carbon uptake rates with glucose, acetate and gluconate were 0.0421, 0.0181 and 0.0159 C-mol·C-mol biomass-1·h-1, respectively. This data suggests that the carbon uptake capacity of Tetrasphaera is dependent on substrate type. In Chapter 4, a field study was conducted to investigate the nutrient removal rates and microbial community structure (e.g., PAOs and the core community) in seven full-scale WWTPs with unintended P removal in the San Francisco Bay Area. The nutrient removal rates in the surveyed facilities appeared to be lower than values seen elsewhere that operate in EBPR mode. A wide variety of PAOs were identified in all seven WWTPs surveyed, even in those facilities with little or no observed P-removal activity. Those facilities surveyed that operate with a pure oxygen aeration configuration was found to significantly impact community diversity, functional gene profile, and the core community structure of activated sludge systems.

Overall, this research systematically evaluated the activity of putative PAOs in both lab-scale and full-scale conditions and the results observed may contribute to the design, modeling, and optimization of EBPR processes.