Increasing energy costs and climate change necessitate an optimization of energy use at wastewater treatment plants for a sustainable future. Aeration within the biological nutrient removal (BNR) process accounts for a large portion of energy consumption at a wastewater treatment plant. As such, reducing the aeration input is considered a primary solution to reducing the energy required for wastewater treatment. While successful BNR at lower than conventional dissolved oxygen (DO) concentrations has been demonstrated, challenges remain before reduced aeration can be implemented at full-scale. In Chapter 1, we first compared two automated aeration control strategies under low-DO conditions in two pilot-scale treatment systems. We showed that effective, year-round BNR can be achieved with both strategies by increasing the solids retention time. However, both pilot-scale processes experienced poor solids settleability during the winter. While settleability was recovered during warmer temperatures, improving settling quality under low-DO remains a challenged to be resolved. In Chapter 2, we investigated the short- and long-term effect of DO reductions on the production and emission of nitrous oxide, a potent greenhouse gas. We found that while increases in nitrous oxide production and emission immediately followed DO reductions, long-term emissions decreased after prolonged operation under low-DO conditions. Process nuisances and performance deviations (e.g. nitrite accumulation) also corresponded with increased emissions. Finally, in Chapter 3, we used genome-resolved metagenomics and metatranscriptomics to explore the diversity and dynamics of the Candidatus Accumlibacter lineage, key organisms contributing to phosphorus removal from wastewater. We found that Accumulibacter community was highly diverse across time in multiple pilot-scale low-DO systems, supporting evidence that most members of this lineage have a high affinity for oxygen. The information gained in these studies expands on the feasibility and implications of low-DO wastewater treatment at full-scale and adds to our understanding of the microbial community carrying out BNR under these conditions.