Influence of Kinetic and Metabolic Selection on 17alpha-ethinylestradiol Biodegradation in Activated Sludge Wastewater Treatment Systems

Abstract

The potent endocrine-disrupting estrogen hormone, 17alpha-ethinylestradiol (EE2), is primarily removed via biodegradation in municipal wastewater treatment plant (WWTP) activated sludge (AS) processes; however, reported EE2 removal efficiencies in AS WWTPs vary widely. A hypothesis of this research was that EE2 biodegradation kinetics vary as a function of AS process and reactor designs, which select for different microbial population compositions. Bench-scale AS reactors treating municipal wastewater and estrogens at ng/L concentrations were operated to simulate kinetic population selection with high initial food-to-biomass ratio feeding conditions (high-F/Mf) or low substrate growth conditions (low-F/Mf), as well as metabolic selection with substrate uptake and growth under aerobic, anaerobic, and anoxic conditions. The latter two metabolic selectors resulted in enhanced biological phosphorus removal and biological nitrogen removal, respectively. A pseudo first-order biodegradation model was used to examine the effects of metabolic and kinetic selective pressures on EE2 biodegradation kinetics. Aerobic low-F/Mf reactors experienced pseudo first-order EE2 biodegradation rate coefficients (kb) that were 1.4 to 2.2 times greater than high-F/Mf aerobic selectors operated in parallel, suggesting that kinetic selection influences EE2 biodegradation activity in AS systems. No significant difference was observed in the EE2 kb of high-F/Mf metabolic bioselectors (aerobic-only, anoxic/aerobic and anaerobic/aerobic). However, metabolic selection reduced the EE2 kb of a low-F/Mf anoxic/aerobic reactor by 40% relative to a low-F/Mf aerobic reactor, demonstrating that the redox state of growth conditions may affect microbial EE2 biodegradation kinetics in AS. The results of this study suggest that operating conditions in which microbial growth occurs aerobically at low substrate concentrations improve EE2 biodegradation kinetics in AS systems, possibly due to the growth of K-strategist heterotrophs capable of more efficient EE2 biodegradation at low ng/L concentrations. Supplementary files to this dissertation include Appendix B, which is a Microsoft Excel file that provides supporting data to the presented research results.