Modeling and experimental analyses of membrane-aerated biofilms

Biofilms grown on oxygen filled gas-permeable membranes are unique; the chemical species required for growth diffuse from different sides of the biofilm. Oxygen is delivered directly to the base of the biofilm by the membrane while organic substrates and other soluble nutrients are provided to the upper surface of the biofilm via the water in which the membranes are immersed. This counter-diffusion of nutrients results in a very different growth environment from conventional biofilms that receive both oxygen and other nutrients from the water. As a result, membrane-aerated biofilms offer several unique advantages over conventional biofilms; however, the information necessary to design and operate membrane aerated biofilm reactors is not yet available.; In order to address these knowledge gaps, the primary objectives of this research were (1) to develop a multi-population model that could predict the growth and activity of membrane-aerated biofilms; (2) to characterize the growth and activity of membrane-aerated biofilms that were grown in a laboratory scale reactor via mass balances and microelectrode studies for calibration and verification of the model.; Simulated membrane-aerated biofilm reactor performance was generally in agreement with experimental results. Furthermore, predicted concentration profiles of ammonium, nitrate, pH, and dissolved oxygen in the biofilms were in agreement with profiles measured via microelectrodes. Careful examination of microelectrode profiles suggested that minor discrepancies between simulated and measured performance resulted from dynamic changes in the morphology and structure of cultured membrane-aerated biofilms.; Both experimental results and model simulations demonstrated that the growth and development of membrane-aerated biofilms can increase the rate of oxygen transfer across membranes via biochemical reaction, despite the increased resistance to mass transfer associated with the biofilm structure. Similar to previous studies on conventional biofilms, microelectrode profiles demonstrated that bulk liquid concentrations were not representative of the microenvironments within a membrane-aerated biofilm, and that a model that incorporates both mass transfer and reaction within the biofilm structure is necessary to predict the performance of a membrane-aerated biofilm reactor.