Assessment of Full-Scale NO Emission Characteristics and Testing of Control Concepts in an Activated Sludge Wastewater Treatment Plant with Alternating Aerobic and Anoxic Phases.

This work aims to obtain full-scale NO emission characteristics translatable into viable NO control strategies and conduct full-scale testing of the proposed NO control concepts. Data of a long-term monitoring campaign was first used to quantify full-scale NO emission and probe into the seasonal pattern. Then trends between NO production/emission and process variables/conditions during typical operating cycles were revealed to explore the dynamic NO emission behavior. A multivariate statistical analysis was performed to find the dependency of NO emission on relevant process variables. The results show for the first time that relatively low/high NO emission took place in seasons with a decreasing/increasing trend of water temperature, respectively. Aerobic phase contributed to NO production/emission probably mainly through the hydroxylamine pathway. Comparatively, heterotrophic bacteria had a dual role in the anoxic phase and could be responsible for both net NO production and consumption. Incomplete denitrification might contribute mainly to the NO production/emission in the anoxic phase and the accumulation of NO to be significantly emitted in the following cycle due to the competition between different denitrification steps for electron donors. Therefore, properly extending the length of anoxic phase could serve as a potential control means to regulate NO accumulation in the anoxic phase. The full-scale testing not only verified the efficacy of reduced dissolved oxygen set-point in reducing NO emission by 60%, but also confirmed the proposed concepts of control over the aerobic and anoxic phases collectively.