| The research presented in this study focuses on the activated sludge floc microenvironment believed to be responsible for the simultaneous nitrification and denitrification found to occur in oxidation ditches. The overall objectives of this research were to develop an experimental method to measure intrafloc dissolved oxygen (DO) profiles, to verify if predicted anoxic zones exist within floc, and to model intrafloc dissolved oxygen profiles. A method was developed to measure DO profiles within activated sludge floc particles under controlled bulk solution conditions. Intrafloc DO profiles were obtained for a variety of floc diameters and bulk conditions. The analysis and measurements performed in this research have led to the following observations. The DO profiles of activated sludge floc show that there are anoxic and aerobic zones within the floc particles. Results suggest that floc size and time of floc growth have direct effects on the size of the anoxic zone. Shearing of the floc, or reducing the floc size, is believed to be detrimental to the presence of intraparticle anoxic zones. Based on model results it was found that an increase in chemical oxygen demand concentrations increases the percent volume of the floc that is non-aerobic. Model results show that an increase in the floc diameter increases the percent volume of the floc that is non-aerobic. The model also shows that an increase in the dissolved oxygen concentration decreases the percent volume of the floc that is non-aerobic. It is believed that this will be the groundwork for the design and operation of simultaneous nitrification/denitrification activated sludge processes. Using this research and field data, a better understanding of the nitrification/denitrification processes occurring within an activated sludge reactor, which has no formal anoxic zone, can be reached. |
