Elucidating the Impact of Low Dissolved Oxygen Wastewater Treatment on Pharmaceutical Fate

More than half of the energy in conventional wastewater treatment is consumed by aeration. To achieve substantial energy savings and comply with increasingly stringent effluent nutrient regulations, wastewater utilities are beginning to control and minimize aeration, thereby operating at a lower dissolved oxygen (DO) concentration. As utilities implement low DO processes, the impact of DO on non-regulated pollutants, such as pharmaceuticals, warrants attention to understand the impact of these technologies on pharmaceutical loads to the environment. This dissertation focuses on the impact of DO on pharmaceutical biotransformation during treatment. Low DO treatment could impact pharmaceutical biotransformation directly by acting as a limiting substrate and slowing the activity of microorganisms involved in biotransformation, and indirectly by selecting for a community that is more (or less) effective at biotransformation. The objective of this work was to evaluate and characterize both direct and indirect impacts of low DO conditions in wastewater treatment bioprocesses on pharmaceutical biotransformation.;To characterize how DO concentration directly impacts pharmaceutical biotransformation rates, oxygen half-saturation constants (KO2) were determined for a suite of compounds that describe the impact of DO on a compound's biotransformation rate. Indirect impacts of DO concentration on pharmaceutical biotransformation rates were demonstrated using bench-scale nitrifying bioreactors operated for over a year under low (~0.3 mg-DO/L) and high (>4 mg-DO/L) DO conditions. Results showed that long-term low DO conditions resulted in a greater biomass concentration in the low DO reactor compared to high DO reactor. The greater biomass concentration in the low DO reactor resulted in a community with lower specific pharmaceutical biotransformation rates but greater net biotransformation rates under non-limiting DO conditions. In addition, the low DO reactor supported the growth of a more diverse microbial community. To follow up on this finding, a direct test of how microbial diversity affects pharmaceutical biotransformation was performed using a dilution-to-extinction approach. The results showed a strong positive association between biodiversity and collective pharmaceutical biotransformation rates. Taken together, these studies demonstrate that that substantial energy savings can be achieved by operating at lower bulk liquid DO concentrations (0.5 - 1 mg/L) without compromising net pharmaceutical biotransformation rates.