(70g) Wind-Driven Surficial Oxygen Transfer into Treatment Lagoons and Implications on Dinitrogen Emission

When analyzing the complex biochemical and physical processes responsible for ammonia and dinitrogen gas emission in the animal waste treatment lagoons, surficial oxygen transfer plays an important role. This research 1) reviews and analyzes research conducted during the last 5 decades on oxygen and other gas transfer into non-moving, open water bodies, 2) presents the synthesis of a new, unified equation for oxygen mass transfer coefficient, and 3) discusses the potential nitrogen pathways responsible for the dinitrogen gas emissions observed from the treatment lagoons based on the surficial oxygen transfer rate.

Both theoretical and empirically derived oxygen coefficients were evaluated using data derived from investigations in controlled wind tunnels, floating reaeration devices in open waters, and natural open waters. To facilitate the analyses, gas transfer coefficient correlations for other gases were normalized to oxygen, and wind speeds were normalized to 10-m height. Wind was the major turbulence agent facilitating the gas transfer processes. Generally, low wind speed did not significantly influence the transfer coefficients. However, the transfer coefficients increased, even exponentially, with higher wind speeds. Initial attempts to obtain reliable estimates of surficial oxygen transfer rates into treatment lagoons under relevant environmental conditions were not successful, primarily due to large variations among existing transfer coefficients. Instead, we formulated a new unified equation for predicting wind-driven gas transfer coefficients. The new empirical equation is a function of Schmidt number, wind speed, and temperature. With this new equation, the maximum surficial oxygen fluxes into the treatment lagoons were estimated. The stoichiometric amounts of the maximum dinitrogen gas production per unit mass of O2 transferred were calculated based on three most likely biochemical pathways for ammonia removal in the treatment lagoons. These were compared with observed dinitrogen gas emission data.